page source_page_order layout_page_order layout_order ref label role_guess included_in_body excluded_risk_level body_decision_reason parser_body_decision_reason production_usage visual_asset_type visual_asset_label visual_asset_caption_preview truncation_marker inside_body_region body_region_id zone column column_index column_count region_id background_rgb background_class is_gray_background has_frame_evidence bbox text_preview cleaned_text_preview text cleaned_text 3 4 3 38 #/texts/39 text body True None body body True p3:body_region:0 body_zone column_1_of_2 1 2 p3:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 89.67, 251.11, 165.13] Owing to the rapid population growth, energy shortage has become one of the most urgent problems to be solved. One promising strategy is to use clean energies which is renewable and environmentally friendly to replace f… Owing to the rapid population growth, energy shortage has become one of the most urgent problems to be solved. One promising strategy is to use clean energies which is renewable and environmentally friendly to replace f… Owing to the rapid population growth, energy shortage has become one of the most urgent problems to be solved. One promising strategy is to use clean energies which is renewable and environmentally friendly to replace fossil fuels [1-3]. Renewable energies like wind and solar are intermittent in nature, and they need to be collected and released using high-efficiency energy storage systems [4]. Lithium ion batteries (LIBs), considering the high energy density and long cycle life, have been widely utilized in electric vehicles (EVs) and consumer electronics like mobile phones and laptop computers [5]. Growing deployment of LIBpowered EVs reduces the emission of CO2, contributing to the mitigation of global warming. Nevertheless, the extensive application of LIBs, especially in the fields of EVs and grid-level energy storage, continues to demand for a higher energy density [6]. The energy density of LIBs largely depends on the electrode materials, especially the cathode materials. In the past decades, layered LiCoO2 Owing to the rapid population growth, energy shortage has become one of the most urgent problems to be solved. One promising strategy is to use clean energies which is renewable and environmentally friendly to replace fossil fuels [1-3]. Renewable energies like wind and solar are intermittent in nature, and they need to be collected and released using high-efficiency energy storage systems [4]. Lithium ion batteries (LIBs), considering the high energy density and long cycle life, have been widely utilized in electric vehicles (EVs) and consumer electronics like mobile phones and laptop computers [5]. Growing deployment of LIBpowered EVs reduces the emission of CO2, contributing to the mitigation of global warming. Nevertheless, the extensive application of LIBs, especially in the fields of EVs and grid-level energy storage, continues to demand for a higher energy density [6]. The energy density of LIBs largely depends on the electrode materials, especially the cathode materials. In the past decades, layered LiCoO2 3 5 5 40 #/texts/40#prov0 text body True None body body False None front_matter column_2_of_2 2 2 p3:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 67.53, 251.09, 185.69] (LCO), spinel LiMn2O4 (LMO), olivine LiFePO4 (LFP), and LiNi x Mn y -Co z O2 (NMC, x + y + z = 1) have been the major cathode materials in LIB market [7-17]. The first-generation cathode material is LCO, which was first… (LCO), spinel LiMn2O4 (LMO), olivine LiFePO4 (LFP), and LiNi x Mn y -Co z O2 (NMC, x + y + z = 1) have been the major cathode materials in LIB market [7-17]. The first-generation cathode material is LCO, which was first… (LCO), spinel LiMn2O4 (LMO), olivine LiFePO4 (LFP), and LiNi x Mn y -Co z O2 (NMC, x + y + z = 1) have been the major cathode materials in LIB market [7-17]. The first-generation cathode material is LCO, which was first introduced in 1980 [18]. LCO has a high theoretical capacity (about 274 mA h g 1 ), although only half of which (140 mA h g 1 ) could be reversibly utilized during practical cycling [7,8]. The second-generation cathode materials include spinel LMO [19], olivine LFP [20], and layered NMC [21]. LMO has been widely utilized in power tools due to the superb cycling stability and low cost, however, its further development is limited due to the low theoretical capacity (148 mA h g 1 ) and even lower practical capacity (110 mA h g 1 ) [9]. LFP cathode has been adopted in EVs in recent years. LFP exhibits a high cycling stability, high rate performance, and superior abuse tolerance due to the unique P-O covalent bond [10]. The low energy density and low tap density restrict LFP cathode from a broader market [11,12]. Compared to LFP cathode, NMC cathode has been applied in EV market more effectively and fruitfully. Ni, Mn, and Co elements work coordina- (LCO), spinel LiMn2O4 (LMO), olivine LiFePO4 (LFP), and LiNi x Mn y -Co z O2 (NMC, x + y + z = 1) have been the major cathode materials in LIB market [7-17]. The first-generation cathode material is LCO, which was first introduced in 1980 [18]. LCO has a high theoretical capacity (about 274 mA h g 1 ), although only half of which (140 mA h g 1 ) could be reversibly utilized during practical cycling [7,8]. The second-generation cathode materials include spinel LMO [19], olivine LFP [20], and layered NMC [21]. LMO has been widely utilized in power tools due to the superb cycling stability and low cost, however, its further development is limited due to the low theoretical capacity (148 mA h g 1 ) and even lower practical capacity (110 mA h g 1 ) [9]. LFP cathode has been adopted in EVs in recent years. LFP exhibits a high cycling stability, high rate performance, and superior abuse tolerance due to the unique P-O covalent bond [10]. The low energy density and low tap density restrict LFP cathode from a broader market [11,12]. Compared to LFP cathode, NMC cathode has been applied in EV market more effectively and fruitfully. Ni, Mn, and Co elements work coordina- 4 1 4 47 #/texts/40#prov1 text body True None body body False None front_matter column_1_of_2 1 2 p4:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 442.89, 251.12, 71.74] tively in NMC cathode: Ni 2+/3+ is responsible for providing capacity, Mn 4+ is for maintaining the structural stability, and Co 3+ could promote the diffusion of Li + ions [13-16]. However, the traditional NMC cathode … tively in NMC cathode: Ni 2+/3+ is responsible for providing capacity, Mn 4+ is for maintaining the structural stability, and Co 3+ could promote the diffusion of Li + ions [13-16]. However, the traditional NMC cathode … tively in NMC cathode: Ni 2+/3+ is responsible for providing capacity, Mn 4+ is for maintaining the structural stability, and Co 3+ could promote the diffusion of Li + ions [13-16]. However, the traditional NMC cathode only offers limited improvements in terms of practical capacity (<200 mA h g 1 ) [17]. The key benchmark for the nextgeneration cathode material is a higher energy density than all current materials. tively in NMC cathode: Ni 2+/3+ is responsible for providing capacity, Mn 4+ is for maintaining the structural stability, and Co 3+ could promote the diffusion of Li + ions [13-16]. However, the traditional NMC cathode only offers limited improvements in terms of practical capacity (<200 mA h g 1 ) [17]. The key benchmark for the nextgeneration cathode material is a higher energy density than all current materials. 4 5 5 48 #/texts/47 text body True None body body False None bottom_margin column_1_of_2 1 2 p4:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 517.7, 251.13, 227.04] Since the report by Dahn et al. in 2001, Li and Mn rich (LMR) layered oxides x Li2MnO3 (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.), have been regarded as the next-generation cathode material due to the high specific capa… Since the report by Dahn et al. in 2001, Li and Mn rich (LMR) layered oxides x Li2MnO3 (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.), have been regarded as the next-generation cathode material due to the high specific capa… Since the report by Dahn et al. in 2001, Li and Mn rich (LMR) layered oxides x Li2MnO3 (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.), have been regarded as the next-generation cathode material due to the high specific capacity (>250 mA h g 1 ) [22,23]. As depicted in the formula, LMR layered oxides contain two components, trigonal LiMO2 and monoclinic Li2MnO3. The Li2MnO3 component could be activated at the first charging above 4.5 V, providing a high capacity coupling with oxygen redox. In addition, manganese is much cheaper and less toxic than cobalt, which makes LMR oxides more economically attractive compared to LCO [24]. Nevertheless, LMR oxides also have a few of drawbacks. (1) The large irreversible capacity loss during the first cycle, which leads to the low initial Coulombic efficiency. (2) Voltage and capacity decay during cycling. (3) Poor rate performance due to the poor electronic conductivity of manganese-based oxide [9,25,26]. In this review, we focus on these challenges for the commercialization of LMR layered oxides and the recent progress to overcome them. In Section 2, the basic crystal structure and the electrochemical behavior of LMR oxides are introduced. In Section 3, the recent progress on overcoming challenges for LMR layered oxides are summarized. In Section 4, promising developments and future directions for LMR oxides are suggested. Since the report by Dahn et al. in 2001, Li and Mn rich (LMR) layered oxides x Li2MnO3 (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.), have been regarded as the next-generation cathode material due to the high specific capacity (>250 mA h g 1 ) [22,23]. As depicted in the formula, LMR layered oxides contain two components, trigonal LiMO2 and monoclinic Li2MnO3. The Li2MnO3 component could be activated at the first charging above 4.5 V, providing a high capacity coupling with oxygen redox. In addition, manganese is much cheaper and less toxic than cobalt, which makes LMR oxides more economically attractive compared to LCO [24]. Nevertheless, LMR oxides also have a few of drawbacks. (1) The large irreversible capacity loss during the first cycle, which leads to the low initial Coulombic efficiency. (2) Voltage and capacity decay during cycling. (3) Poor rate performance due to the poor electronic conductivity of manganese-based oxide [9,25,26]. In this review, we focus on these challenges for the commercialization of LMR layered oxides and the recent progress to overcome them. In Section 2, the basic crystal structure and the electrochemical behavior of LMR oxides are introduced. In Section 3, the recent progress on overcoming challenges for LMR layered oxides are summarized. In Section 4, promising developments and future directions for LMR oxides are suggested. 4 8 8 51 #/texts/50 text body True None body body True p4:body_region:0 body_zone column_2_of_2 2 2 p4:body_zone:column_2_of_2:white [255, 255, 255] white False False [306.6, 487.08, 251.1, 143.43] LMRoxidesaregenerallyconsideredasthecompositeofLi2MnO3 and LiMO2, therefore the formula could be written as x Li2MnO3- (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.). As shown in Fig. 1(a and b) [27], Li2MnO3 belongs to mono… LMRoxidesaregenerallyconsideredasthecompositeofLi2MnO3 and LiMO2, therefore the formula could be written as x Li2MnO3- (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.). As shown in Fig. 1(a and b) [27], Li2MnO3 belongs to mono… LMRoxidesaregenerallyconsideredasthecompositeofLi2MnO3 and LiMO2, therefore the formula could be written as x Li2MnO3- (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.). As shown in Fig. 1(a and b) [27], Li2MnO3 belongs to monoclinic space group C 2/ m, while LiMO2 crystallizes in trigonal space group R -3m[28]. Both of them are constructed by alternately stacking Li layers and transition metal (TM) layers along c axis within the similar cubic close packed oxygen array. The major structural difference of LMR oxides from traditional layeredoxides(LCO,NMC,etc.)istheLi@Mn6 superstructureunit.As shown in Fig. 1(c), a few of peaks could be observed in the range of 20-25 ° of the X-ray diffractogram (XRD) pattern for LMR oxide, and they cannot be observed in the XRD patterns of traditional layered oxides. This special phenomenon originates from the Li@Mn6 superstructure unit shown in Fig. 1(d) [29]. LMRoxidesaregenerallyconsideredasthecompositeofLi2MnO3 and LiMO2, therefore the formula could be written as x Li2MnO3- (1 x )LiMO2 (M = Mn, Ni, Co, Fe, etc.). As shown in Fig. 1(a and b) [27], Li2MnO3 belongs to monoclinic space group C 2/ m, while LiMO2 crystallizes in trigonal space group R -3m[28]. Both of them are constructed by alternately stacking Li layers and transition metal (TM) layers along c axis within the similar cubic close packed oxygen array. The major structural difference of LMR oxides from traditional layeredoxides(LCO,NMC,etc.)istheLi@Mn6 superstructureunit.As shown in Fig. 1(c), a few of peaks could be observed in the range of 20-25 ° of the X-ray diffractogram (XRD) pattern for LMR oxide, and they cannot be observed in the XRD patterns of traditional layered oxides. This special phenomenon originates from the Li@Mn6 superstructure unit shown in Fig. 1(d) [29]. 4 9 9 52 #/texts/51#prov0 text body True None body body True p4:body_region:0 bottom_margin column_2_of_2 2 2 p4:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.6, 633.52, 251.08, 112.02] Although LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the arrangement of these two structures in LMR oxides is still under debate. We list some researches on understanding the structure of LMR oxide… Although LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the arrangement of these two structures in LMR oxides is still under debate. We list some researches on understanding the structure of LMR oxide… Although LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the arrangement of these two structures in LMR oxides is still under debate. We list some researches on understanding the structure of LMR oxides in Table 1. One argument is the composite model, namely, trigonal phase and monoclinic phase co-exist. This model has been proved by many techniques. Qiu et al. proved the co-existence of the two phases in Li1.144Ni0.136Co0.136Mn0.544O2 powder by synchrotron X-ray diffractogram (SXRD) [30]. The composite model was also observed in Li 1.2Mn0.61Ni0.18Mg0.01O2 through high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) [31]. Two Although LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the arrangement of these two structures in LMR oxides is still under debate. We list some researches on understanding the structure of LMR oxides in Table 1. One argument is the composite model, namely, trigonal phase and monoclinic phase co-exist. This model has been proved by many techniques. Qiu et al. proved the co-existence of the two phases in Li1.144Ni0.136Co0.136Mn0.544O2 powder by synchrotron X-ray diffractogram (SXRD) [30]. The composite model was also observed in Li 1.2Mn0.61Ni0.18Mg0.01O2 through high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) [31]. Two 5 1 2 55 #/texts/51#prov1 text body True None body body True p5:body_region:0 front_matter column_1_of_2 1 2 p5:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 67.96, 251.13, 59.69] independent Fe and Mn rich nanodomains in Li1.2Fe0.4Mn0.4O2 were observed by electron energy-loss spectroscopy (EELS) measurements [32]. Besides, the composite model was also supported by Li magic angle spinning (MAS) N… independent Fe and Mn rich nanodomains in Li1.2Fe0.4Mn0.4O2 were observed by electron energy-loss spectroscopy (EELS) measurements [32]. Besides, the composite model was also supported by Li magic angle spinning (MAS) N… independent Fe and Mn rich nanodomains in Li1.2Fe0.4Mn0.4O2 were observed by electron energy-loss spectroscopy (EELS) measurements [32]. Besides, the composite model was also supported by Li magic angle spinning (MAS) NMR, extended X-ray absorption fine structure (EXAFS) spectroscopy, and in situ surface enhanced Raman spectroscopy [33-35]. independent Fe and Mn rich nanodomains in Li1.2Fe0.4Mn0.4O2 were observed by electron energy-loss spectroscopy (EELS) measurements [32]. Besides, the composite model was also supported by Li magic angle spinning (MAS) NMR, extended X-ray absorption fine structure (EXAFS) spectroscopy, and in situ surface enhanced Raman spectroscopy [33-35]. 5 4 3 56 #/texts/55 text body True None body body True p5:body_region:0 front_matter column_1_of_2 1 2 p5:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 130.71, 251.13, 80.61] Another widely accepted model is the solid-solution model, stating that, single solid-solution phase with C 2/ m symmetry exists in LMRoxides[36].Ithasalsobeenprovedthroughmultiplecharacterization techniques. Jarvis et … Another widely accepted model is the solid-solution model, stating that, single solid-solution phase with C 2/ m symmetry exists in LMRoxides[36].Ithasalsobeenprovedthroughmultiplecharacterization techniques. Jarvis et … Another widely accepted model is the solid-solution model, stating that, single solid-solution phase with C 2/ m symmetry exists in LMRoxides[36].Ithasalsobeenprovedthroughmultiplecharacterization techniques. Jarvis et al. observed single-phase ( C 2/ m symmetry) Li1.2Ni0.2Mn0.6O2 with ordered Li + in TM layer by diffraction scanning TEM (D - STEM) [36]. Shunmugasundaram et al. demonstrated the (020), (110), and ( 111) crystallographic planes related with the monoclinic phase in diminished XRD patterns [37]. Another widely accepted model is the solid-solution model, stating that, single solid-solution phase with C 2/ m symmetry exists in LMRoxides[36].Ithasalsobeenprovedthroughmultiplecharacterization techniques. Jarvis et al. observed single-phase ( C 2/ m symmetry) Li1.2Ni0.2Mn0.6O2 with ordered Li + in TM layer by diffraction scanning TEM (D - STEM) [36]. Shunmugasundaram et al. demonstrated the (020), (110), and ( 111) crystallographic planes related with the monoclinic phase in diminished XRD patterns [37]. 5 5 4 57 #/texts/56 text body True None body body True p5:body_region:0 front_matter column_1_of_2 1 2 p5:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 214.39, 251.09, 59.74] In summary, there is no unified conclusion about the crystal structure of LMR oxides (composite or solid-solution) till now. One possible reason is that, the actual crystal structure of LMR oxides varies with the elemen… In summary, there is no unified conclusion about the crystal structure of LMR oxides (composite or solid-solution) till now. One possible reason is that, the actual crystal structure of LMR oxides varies with the elemen… In summary, there is no unified conclusion about the crystal structure of LMR oxides (composite or solid-solution) till now. One possible reason is that, the actual crystal structure of LMR oxides varies with the elemental compositions (especially the content of lithium) and the synthetic conditions (oxygen partial pressure, cooling rate, etc.) [38,39]. In summary, there is no unified conclusion about the crystal structure of LMR oxides (composite or solid-solution) till now. One possible reason is that, the actual crystal structure of LMR oxides varies with the elemental compositions (especially the content of lithium) and the synthetic conditions (oxygen partial pressure, cooling rate, etc.) [38,39]. 5 6 5 58 #/texts/57 text body True None body body True p5:body_region:0 front_matter column_1_of_2 1 2 p5:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 277.15, 251.09, 112.02] In addition, structure defects are easily introduced during the synthetic process, which affects the electrochemical performance of LMR cathodes to a large extent [40]. Zhang et al. found that the quenching process duri… In addition, structure defects are easily introduced during the synthetic process, which affects the electrochemical performance of LMR cathodes to a large extent [40]. Zhang et al. found that the quenching process duri… In addition, structure defects are easily introduced during the synthetic process, which affects the electrochemical performance of LMR cathodes to a large extent [40]. Zhang et al. found that the quenching process during the synthesis of Li2MnO3 would lead to the formation of Mn 3+ defects, which have significant impacts on the electrochemical activation and the cycling stability [41]. Chen et al. used molten-salt method to synthesize LMR oxides, and they noticed that there was a Co- and Ni-rich spinel phase with serious anti-site defects on the particle surface, which may be a previously-neglected factor determining the structural stability [42]. In addition, structure defects are easily introduced during the synthetic process, which affects the electrochemical performance of LMR cathodes to a large extent [40]. Zhang et al. found that the quenching process during the synthesis of Li2MnO3 would lead to the formation of Mn 3+ defects, which have significant impacts on the electrochemical activation and the cycling stability [41]. Chen et al. used molten-salt method to synthesize LMR oxides, and they noticed that there was a Co- and Ni-rich spinel phase with serious anti-site defects on the particle surface, which may be a previously-neglected factor determining the structural stability [42]. 5 8 7 60 #/texts/59 text body True None body body True p5:body_region:0 body_zone column_1_of_2 1 2 p5:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 423.59, 251.12, 300.35] The electrochemical performance of cathode materials is closely related to their structures. Since LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the electrochemical property is a combination of the e… The electrochemical performance of cathode materials is closely related to their structures. Since LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the electrochemical property is a combination of the e… The electrochemical performance of cathode materials is closely related to their structures. Since LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the electrochemical property is a combination of the electrochemical behaviors of LiMO2 and Li2MnO3 to some extent. As shown in Fig. 2(a), the charging profile of Li1.2Ni0.2Mn0.6O2 can be divided into two parts, below 4.5 V and above 4.5 V [35]. It is sloping below 4.5 V, which is similar with that of LiNi0.5Mn0.5O2, indicating the deintercalation of Li + from LiMO2 component and the solid-solution behavior [43,44]. Shimoda et al. proved that this sloping part below 4.5 V was related to TM redox [45]. Above 4.5 V, a long voltage plateau is observed for Li1.2Ni0.2Mn0.6O2, a behavior similar to Li2MnO3, implying the deintercalation of Li + from Li2MnO3 component. This voltage plateau only occurs in the first cycle, and disappears in the following cycles. The CV curves of Li1.2Ni0.2Mn0.6O2 further confirm this phenomenon: a strong oxidation peak occurs around 4.5 V in the first cycle and disappears in the second cycle (Fig. 2b). The long voltage plateau corresponds to the oxygen redox, which could only be found in Li2MnO3 and LMR cathodes [46]. The oxygen redox originates from the special Li-O-Li connection in Li2MnO3 and LMR oxide, as shown in Fig. 2(c). Compared to Mn, the O 2 p states contributes more to the total DOS close to the Fermi level (0 to 2.5 eV). Especially, the states within 0 to 0.9 eV originate from the Li-O-Li configuration, which hints that the Li-O-Li configuration is the origin of the oxygen redox chemistry [47]. It has been proved that both of TM redox and oxygen redox could be found during discharging: Ni, Co, and oxygen redox occur in the voltage range of 4.8-3.5 V and Mn redox occurs in the voltage range of 3.5-2.0 V [45]. The electrochemical performance of cathode materials is closely related to their structures. Since LMR oxides are composed of trigonal LiMO2 and monoclinic Li2MnO3, the electrochemical property is a combination of the electrochemical behaviors of LiMO2 and Li2MnO3 to some extent. As shown in Fig. 2(a), the charging profile of Li1.2Ni0.2Mn0.6O2 can be divided into two parts, below 4.5 V and above 4.5 V [35]. It is sloping below 4.5 V, which is similar with that of LiNi0.5Mn0.5O2, indicating the deintercalation of Li + from LiMO2 component and the solid-solution behavior [43,44]. Shimoda et al. proved that this sloping part below 4.5 V was related to TM redox [45]. Above 4.5 V, a long voltage plateau is observed for Li1.2Ni0.2Mn0.6O2, a behavior similar to Li2MnO3, implying the deintercalation of Li + from Li2MnO3 component. This voltage plateau only occurs in the first cycle, and disappears in the following cycles. The CV curves of Li1.2Ni0.2Mn0.6O2 further confirm this phenomenon: a strong oxidation peak occurs around 4.5 V in the first cycle and disappears in the second cycle (Fig. 2b). The long voltage plateau corresponds to the oxygen redox, which could only be found in Li2MnO3 and LMR cathodes [46]. The oxygen redox originates from the special Li-O-Li connection in Li2MnO3 and LMR oxide, as shown in Fig. 2(c). Compared to Mn, the O 2 p states contributes more to the total DOS close to the Fermi level (0 to 2.5 eV). Especially, the states within 0 to 0.9 eV originate from the Li-O-Li configuration, which hints that the Li-O-Li configuration is the origin of the oxygen redox chemistry [47]. It has been proved that both of TM redox and oxygen redox could be found during discharging: Ni, Co, and oxygen redox occur in the voltage range of 4.8-3.5 V and Mn redox occurs in the voltage range of 3.5-2.0 V [45]. 5 9 8 61 #/texts/60 text body True None body body True p5:body_region:0 bottom_margin column_1_of_2 1 2 p5:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 725.21, 251.13, 30.08] AlthoughLMRoxidescouldprovidehighcapacity(>250mAhg 1 ) and energy density (>900 Wh kg 1 ), they also have a few of disadvantages hindering the commercialization. These include: 1) AlthoughLMRoxidescouldprovidehighcapacity(>250mAhg 1 ) and energy density (>900 Wh kg 1 ), they also have a few of disadvantages hindering the commercialization. These include: 1) AlthoughLMRoxidescouldprovidehighcapacity(>250mAhg 1 ) and energy density (>900 Wh kg 1 ), they also have a few of disadvantages hindering the commercialization. These include: 1) AlthoughLMRoxidescouldprovidehighcapacity(>250mAhg 1 ) and energy density (>900 Wh kg 1 ), they also have a few of disadvantages hindering the commercialization. These include: 1) 5 10 10 63 #/texts/61 text body True None body body True p5:body_region:1 front_matter column_2_of_2 2 2 p5:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.6, 67.95, 251.1, 38.77] lowinitialCoulombicefficiency(<80%);2)severecapacityandvoltage decay during long-term cycling; 3) inferior rate performance compared to that of LCO and NMC cathodes. These challenges are discussed one by one as below. lowinitialCoulombicefficiency(<80%);2)severecapacityandvoltage decay during long-term cycling; 3) inferior rate performance compared to that of LCO and NMC cathodes. These challenges are discussed one by one as below. lowinitialCoulombicefficiency(<80%);2)severecapacityandvoltage decay during long-term cycling; 3) inferior rate performance compared to that of LCO and NMC cathodes. These challenges are discussed one by one as below. lowinitialCoulombicefficiency(<80%);2)severecapacityandvoltage decay during long-term cycling; 3) inferior rate performance compared to that of LCO and NMC cathodes. These challenges are discussed one by one as below. 5 11 11 64 #/texts/62 text body True None body body True p5:body_region:1 front_matter column_2_of_2 2 2 p5:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.6, 107.99, 251.12, 438.1] As shown in Fig. 2(a), about 100 mA h g 1 of irreversible capacity could be observed during the first cycle for Li1.2Ni0.2Mn0.6O2, leading to a low initial Coulombic efficiency of 72.3%, much lower than that of NMC an… As shown in Fig. 2(a), about 100 mA h g 1 of irreversible capacity could be observed during the first cycle for Li1.2Ni0.2Mn0.6O2, leading to a low initial Coulombic efficiency of 72.3%, much lower than that of NMC an… As shown in Fig. 2(a), about 100 mA h g 1 of irreversible capacity could be observed during the first cycle for Li1.2Ni0.2Mn0.6O2, leading to a low initial Coulombic efficiency of 72.3%, much lower than that of NMC and LCO cathodes. The low initial Coulombic efficiency of LMR cathode is largely attributed to the electrode/electrolyte reaction in the first cycle, especially the oxygen loss. When the charge voltage is below 4.6 V, ethylene carbonate (EC), dimethyl carbonate (DMC) and etc. in the solvent would decompose into CO2 and other gases due to the oxidizing O2 2 species at the particle surface. Differential Electrochemical Mass Spectrometry (DEMS) measurements can validate CO2 release from the surface of the active materials, which could also be observed in other layered cathodes [48]. However, while the charging voltage is higher than 4.7 V, lattice O would evolve in the form of O2, leaving vacancies in the structure. These O vacancies lead to the irreversible migration of TM ions to Li sites. Only part of the migrated TM ions can return to their original sites during discharging, which severely decreases the initial Coulombic efficiency of LMR cathode [49]. The form of the oxygen loss has also been debated before. Yin et al. analyzed the evolution of cathode electrolyte interphase (CEI) during the first cycle of the LMR cathode [50]. They found: (1) the reasons of oxygen loss were different for LMR cathodes and Li2MnO3 cathode (caused by electrochemical decomposition and chemical decomposition, respectively); (2) the formation/dissolution of CEI was accompanied with Li + extraction/ insertion; (3) the changes in the valence states of metal ions (Ni, Co, Mn) could accelerate the formation of CEI. Besides, the decomposition of the electrolyte solution at high voltage could not be negligible. The high charging voltage (4.8 V) is normally adopted to obtain high capacity for LMR cathodes by fully utilizing TM redox and oxygen redox. At such a high voltage, the electrolyte normally composed of EC, DMC, and LiPF6, would decompose, which accompanies with the surficial side-reaction and the consumption of Li + , causing the low initial Coulombic efficiency [51]. Except for the high voltage, the highly oxidizing ions O x y , would accelerate the decomposition of LiPF6, which accompanies with the generation of HF and PO x F y z [52]. These decomposition products would erode the electrode-electrolyte interphase, resulting in the dissolution of the transition metal ions. Continuous dissolution of the metal ions from the material further leads to a rugged surface and increased interphase impedance, which would cause rapid degradation of the electrode. As shown in Fig. 2(a), about 100 mA h g 1 of irreversible capacity could be observed during the first cycle for Li1.2Ni0.2Mn0.6O2, leading to a low initial Coulombic efficiency of 72.3%, much lower than that of NMC and LCO cathodes. The low initial Coulombic efficiency of LMR cathode is largely attributed to the electrode/electrolyte reaction in the first cycle, especially the oxygen loss. When the charge voltage is below 4.6 V, ethylene carbonate (EC), dimethyl carbonate (DMC) and etc. in the solvent would decompose into CO2 and other gases due to the oxidizing O2 2 species at the particle surface. Differential Electrochemical Mass Spectrometry (DEMS) measurements can validate CO2 release from the surface of the active materials, which could also be observed in other layered cathodes [48]. However, while the charging voltage is higher than 4.7 V, lattice O would evolve in the form of O2, leaving vacancies in the structure. These O vacancies lead to the irreversible migration of TM ions to Li sites. Only part of the migrated TM ions can return to their original sites during discharging, which severely decreases the initial Coulombic efficiency of LMR cathode [49]. The form of the oxygen loss has also been debated before. Yin et al. analyzed the evolution of cathode electrolyte interphase (CEI) during the first cycle of the LMR cathode [50]. They found: (1) the reasons of oxygen loss were different for LMR cathodes and Li2MnO3 cathode (caused by electrochemical decomposition and chemical decomposition, respectively); (2) the formation/dissolution of CEI was accompanied with Li + extraction/ insertion; (3) the changes in the valence states of metal ions (Ni, Co, Mn) could accelerate the formation of CEI. Besides, the decomposition of the electrolyte solution at high voltage could not be negligible. The high charging voltage (4.8 V) is normally adopted to obtain high capacity for LMR cathodes by fully utilizing TM redox and oxygen redox. At such a high voltage, the electrolyte normally composed of EC, DMC, and LiPF6, would decompose, which accompanies with the surficial side-reaction and the consumption of Li + , causing the low initial Coulombic efficiency [51]. Except for the high voltage, the highly oxidizing ions O x y , would accelerate the decomposition of LiPF6, which accompanies with the generation of HF and PO x F y z [52]. These decomposition products would erode the electrode-electrolyte interphase, resulting in the dissolution of the transition metal ions. Continuous dissolution of the metal ions from the material further leads to a rugged surface and increased interphase impedance, which would cause rapid degradation of the electrode. 5 12 12 65 #/texts/63 text body True None body body True p5:body_region:1 bottom_margin column_2_of_2 2 2 p5:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 549.11, 251.1, 206.18] The fast capacity and voltage decay of the LMR cathodes during long-term cycling is another issue. As shown in Fig. 2(d), only 85% of the initial discharging capacity is maintained after 50 cycles at 0.1 C for Li1.2Ni0.… The fast capacity and voltage decay of the LMR cathodes during long-term cycling is another issue. As shown in Fig. 2(d), only 85% of the initial discharging capacity is maintained after 50 cycles at 0.1 C for Li1.2Ni0.… The fast capacity and voltage decay of the LMR cathodes during long-term cycling is another issue. As shown in Fig. 2(d), only 85% of the initial discharging capacity is maintained after 50 cycles at 0.1 C for Li1.2Ni0.13Co0.13Mn0.54O2. Besides, a severe decay in the discharging voltage could also be observed, as shown in Fig. 2(e) [53]. The decays in both capacity and voltage are largely caused by the structural degradation in the first cycle and the following cycles. Wang et al. proposed a structural degradation model of Li1.2Ni0.1Mn0.525Co0.175O2 [54]. As shown in Fig. 2(f), due to the concurrent oxygen and lithium loss from the lattice of Li2MnO3 component in the first cycle, the layered structure is destroyed, forming a polycrystalline/amorphous matrix. Different from the Li2MnO3 component, the LiMO2 component evolves to a spinel structure at the surface during the first cycle. The formation of a spinel structure was also observed in Li1.2Co0.1Mn0.55Ni0.15O2 during the first charge through selected area electron diffraction (SAED), as shown in Fig. 2(g). The mechanism for the formation of the spinel phase was also proposed. When the voltage is held at 4.5 V, oxygen loss will occur in the form of O2, leading to the reduction of Ni 3+ /Ni 4+ to Ni 2+ due to the charge compensation. Con- The fast capacity and voltage decay of the LMR cathodes during long-term cycling is another issue. As shown in Fig. 2(d), only 85% of the initial discharging capacity is maintained after 50 cycles at 0.1 C for Li1.2Ni0.13Co0.13Mn0.54O2. Besides, a severe decay in the discharging voltage could also be observed, as shown in Fig. 2(e) [53]. The decays in both capacity and voltage are largely caused by the structural degradation in the first cycle and the following cycles. Wang et al. proposed a structural degradation model of Li1.2Ni0.1Mn0.525Co0.175O2 [54]. As shown in Fig. 2(f), due to the concurrent oxygen and lithium loss from the lattice of Li2MnO3 component in the first cycle, the layered structure is destroyed, forming a polycrystalline/amorphous matrix. Different from the Li2MnO3 component, the LiMO2 component evolves to a spinel structure at the surface during the first cycle. The formation of a spinel structure was also observed in Li1.2Co0.1Mn0.55Ni0.15O2 during the first charge through selected area electron diffraction (SAED), as shown in Fig. 2(g). The mechanism for the formation of the spinel phase was also proposed. When the voltage is held at 4.5 V, oxygen loss will occur in the form of O2, leading to the reduction of Ni 3+ /Ni 4+ to Ni 2+ due to the charge compensation. Con- 6 6 6 72 #/texts/70#prov0 text body True None body body True p6:body_region:0 bottom_margin column_1_of_2 1 2 p6:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 629.98, 251.1, 124.06] sidering the similar ionic radii of Ni 2+ and Li + , Ni 2+ migrates to the Li layers preferentially compared to other TM cations. Because oxygen loss occurs at the surface, severe cationic mixing would appear at the sur… sidering the similar ionic radii of Ni 2+ and Li + , Ni 2+ migrates to the Li layers preferentially compared to other TM cations. Because oxygen loss occurs at the surface, severe cationic mixing would appear at the sur… sidering the similar ionic radii of Ni 2+ and Li + , Ni 2+ migrates to the Li layers preferentially compared to other TM cations. Because oxygen loss occurs at the surface, severe cationic mixing would appear at the surface during the first cycle, leading to the formation of a spinel phase, as shown in Fig. 2(h) [55]. The transformation from layered structure to spinel structure in a polycrystalline/amorphous matrix will introduce stress, causing cracks and formation of pores, which are unfavorable for Li + (de)intercalation [55]. During long-term cycling, the structural degradation will propagate from the surface to the bulk, resulting in the continuous decay of capacity and voltage. Kang et al. proposed a transition metal migration model in LMR oxides, and they sidering the similar ionic radii of Ni 2+ and Li + , Ni 2+ migrates to the Li layers preferentially compared to other TM cations. Because oxygen loss occurs at the surface, severe cationic mixing would appear at the surface during the first cycle, leading to the formation of a spinel phase, as shown in Fig. 2(h) [55]. The transformation from layered structure to spinel structure in a polycrystalline/amorphous matrix will introduce stress, causing cracks and formation of pores, which are unfavorable for Li + (de)intercalation [55]. During long-term cycling, the structural degradation will propagate from the surface to the bulk, resulting in the continuous decay of capacity and voltage. Kang et al. proposed a transition metal migration model in LMR oxides, and they 6 7 7 73 #/texts/70#prov1 text body True None body body True p6:body_region:1 bottom_margin column_2_of_2 2 2 p6:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 629.98, 251.1, 124.07] observed that Li + diffusion was much more sluggish during lithiation than during de-lithiation [56]. They thought that, after Li + was extracted from Li layers, TM ions would migrate into Li layers, and they could not … observed that Li + diffusion was much more sluggish during lithiation than during de-lithiation [56]. They thought that, after Li + was extracted from Li layers, TM ions would migrate into Li layers, and they could not … observed that Li + diffusion was much more sluggish during lithiation than during de-lithiation [56]. They thought that, after Li + was extracted from Li layers, TM ions would migrate into Li layers, and they could not migrate back to TM layers easily during discharge. However, as more Li + intercalate at the end of discharge, the tetrahedral lithium occupancy induced by additional lithiation would facilitate the migration of TM ions back to TM layers, leading to recovery of the layered structure. In addition, Tarascon et al. thought that oxygen redox would come along with Mn migration under 4.6 V during charge [57]. After that, O2 was released and a structurally-densified single-phase A' formed within the bulk of the materials, not only at the surface. They also found that the observed that Li + diffusion was much more sluggish during lithiation than during de-lithiation [56]. They thought that, after Li + was extracted from Li layers, TM ions would migrate into Li layers, and they could not migrate back to TM layers easily during discharge. However, as more Li + intercalate at the end of discharge, the tetrahedral lithium occupancy induced by additional lithiation would facilitate the migration of TM ions back to TM layers, leading to recovery of the layered structure. In addition, Tarascon et al. thought that oxygen redox would come along with Mn migration under 4.6 V during charge [57]. After that, O2 was released and a structurally-densified single-phase A' formed within the bulk of the materials, not only at the surface. They also found that the 8 1 2 81 #/texts/70#prov2 text body True None body body True p8:body_region:0 front_matter column_1_of_2 1 2 p8:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 67.96, 251.11, 49.26] capacity loss in the first cycle could be recovered by applying a constant-voltage step during discharge. Li + would occupy the tetrahedral sites to form a new P'' phase under a harsh reductive condition (<1.4 V), and t… capacity loss in the first cycle could be recovered by applying a constant-voltage step during discharge. Li + would occupy the tetrahedral sites to form a new P'' phase under a harsh reductive condition (<1.4 V), and t… capacity loss in the first cycle could be recovered by applying a constant-voltage step during discharge. Li + would occupy the tetrahedral sites to form a new P'' phase under a harsh reductive condition (<1.4 V), and those Mn ions in Li layers triggered by oxygen redox would serve as ''pillars' to stabilize the structure. capacity loss in the first cycle could be recovered by applying a constant-voltage step during discharge. Li + would occupy the tetrahedral sites to form a new P'' phase under a harsh reductive condition (<1.4 V), and those Mn ions in Li layers triggered by oxygen redox would serve as ''pillars' to stabilize the structure. 8 4 3 82 #/texts/79 text body True None body body True p8:body_region:0 front_matter column_1_of_2 1 2 p8:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 120.23, 251.11, 132.99] Another issue for LMR oxides is the unsatisfactory rate performance. This inferior rate performance can be related to the sluggish dynamics of Mn 4+ . It has been reported that Mn 4+ showed slower reaction kinetics in L… Another issue for LMR oxides is the unsatisfactory rate performance. This inferior rate performance can be related to the sluggish dynamics of Mn 4+ . It has been reported that Mn 4+ showed slower reaction kinetics in L… Another issue for LMR oxides is the unsatisfactory rate performance. This inferior rate performance can be related to the sluggish dynamics of Mn 4+ . It has been reported that Mn 4+ showed slower reaction kinetics in LMR oxides compared to Ni 2+ andCo 3+ . Although the Li2MnO3 component has been activated in the first charging process, the reaction kinetics of Mn 4+ is not promoted [25]. On the other hand, the reaction kinetics of Mn 4+ in LiMO2 component is also slow, whichcouldbepromotedbyexchangingMn 4+ byNi 2+ orCo 3+ [58]. In addition, elemental segregation of Ni and Co at the particle surface tends to take place during the synthesis process, and it also inhibits therateperformance.TheseLi + diffusion channelswithinthesurface layer are perpendicular to those in the bulk, leading to a virtual barrier in the diffusion path for Li + at the surface [59]. Another issue for LMR oxides is the unsatisfactory rate performance. This inferior rate performance can be related to the sluggish dynamics of Mn 4+ . It has been reported that Mn 4+ showed slower reaction kinetics in LMR oxides compared to Ni 2+ andCo 3+ . Although the Li2MnO3 component has been activated in the first charging process, the reaction kinetics of Mn 4+ is not promoted [25]. On the other hand, the reaction kinetics of Mn 4+ in LiMO2 component is also slow, whichcouldbepromotedbyexchangingMn 4+ byNi 2+ orCo 3+ [58]. In addition, elemental segregation of Ni and Co at the particle surface tends to take place during the synthesis process, and it also inhibits therateperformance.TheseLi + diffusion channelswithinthesurface layer are perpendicular to those in the bulk, leading to a virtual barrier in the diffusion path for Li + at the surface [59]. 8 6 5 84 #/texts/81 text body True None body body True p8:body_region:0 body_zone column_1_of_2 1 2 p8:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 304.2, 251.09, 70.18] To accelerate the commercialization of LMR cathodes, researchers devoted a lot of efforts to optimize the electrochemical performance through different methods. Fortunately, the three concerns discussed above have been … To accelerate the commercialization of LMR cathodes, researchers devoted a lot of efforts to optimize the electrochemical performance through different methods. Fortunately, the three concerns discussed above have been … To accelerate the commercialization of LMR cathodes, researchers devoted a lot of efforts to optimize the electrochemical performance through different methods. Fortunately, the three concerns discussed above have been resolved to some extent in recent years. In this section, we will elaborate on these effective methods in three categories: morphology design, bulk design, and surface modification. To accelerate the commercialization of LMR cathodes, researchers devoted a lot of efforts to optimize the electrochemical performance through different methods. Fortunately, the three concerns discussed above have been resolved to some extent in recent years. In this section, we will elaborate on these effective methods in three categories: morphology design, bulk design, and surface modification. 8 8 7 86 #/texts/83 text body True None body body True p8:body_region:0 body_zone column_1_of_2 1 2 p8:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 413.16, 251.1, 80.61] Various morphologies, such as 1D nanowires, 1D nanotubes, 2D nanoplates, 3D porous morphology and other hierarchical nano morphologies, have been widely reported in other layered oxides, including LCO and NMC [60,61]. I… Various morphologies, such as 1D nanowires, 1D nanotubes, 2D nanoplates, 3D porous morphology and other hierarchical nano morphologies, have been widely reported in other layered oxides, including LCO and NMC [60,61]. I… Various morphologies, such as 1D nanowires, 1D nanotubes, 2D nanoplates, 3D porous morphology and other hierarchical nano morphologies, have been widely reported in other layered oxides, including LCO and NMC [60,61]. It is also an effective way to optimize the electrochemical performance of LMR oxides, such as mitigating the capacity and voltage degradation during cycling. The detailed electrochemical performance of LMR cathodes with different morphologies reported in recent years are shown in Table 2. Various morphologies, such as 1D nanowires, 1D nanotubes, 2D nanoplates, 3D porous morphology and other hierarchical nano morphologies, have been widely reported in other layered oxides, including LCO and NMC [60,61]. It is also an effective way to optimize the electrochemical performance of LMR oxides, such as mitigating the capacity and voltage degradation during cycling. The detailed electrochemical performance of LMR cathodes with different morphologies reported in recent years are shown in Table 2. 8 9 8 87 #/texts/84#prov0 text body True None body body True p8:body_region:0 bottom_margin column_1_of_2 1 2 p8:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 495.22, 251.12, 260.09] Cathode materials with nano morphology have better Li + diffusion kinetics by shortening the transportation path, thus better rate performance. Deng et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 spinel/layered nanowires … Cathode materials with nano morphology have better Li + diffusion kinetics by shortening the transportation path, thus better rate performance. Deng et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 spinel/layered nanowires … Cathode materials with nano morphology have better Li + diffusion kinetics by shortening the transportation path, thus better rate performance. Deng et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 spinel/layered nanowires with porous structures via a coprecipitation method followed by the controlled calcination steps, as shown in Fig. 3(a) [62]. They found that the content of spinel phase could be easily tuned by changing the heating rate. The nanowires could provide a better connection between the cathode and the electrolyte, which facilitates Li + diffusion and restrains the structural degeneration. Thus, the cathode displays a high capacity of 291 mA h g 1 at 0.1C and an excellent capacity retention of 91.8% after 200 cycles at 1C. As shown in Fig. 3(b), Yang et al. used hydrothermally synthesized b -MnO2 nanorods as a self-template to fabricate x Li2MnO3 (1x )LiMnO2 nanorods with the diameter of 100-200 nm and the length of 400-1000 nm [63]. Increasing the fraction of Li2MnO3 could significantly increase the discharge capacity but lower the cyclic stability, while increasing the fraction of LiMnO2 could enhance the cyclic stability by suppressing the transformation from layered phase to spinel phase. As shown in Fig. 3(c), Xu et al. constructed Li1.2Mn0.52Ni0.2Co0.08O2 oxide with (010)-oriented nanoplates [64]. This novel morphology not only combines the advantages of exposed (010)-planes and the anisotropic Li + transport tunnels for fast Li + (de)intercalation, but also effectively inhibits the volume expansion during the cycling. The cathode exhibits an initial discharge capacity of 303 mA h g 1 with Cathode materials with nano morphology have better Li + diffusion kinetics by shortening the transportation path, thus better rate performance. Deng et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 spinel/layered nanowires with porous structures via a coprecipitation method followed by the controlled calcination steps, as shown in Fig. 3(a) [62]. They found that the content of spinel phase could be easily tuned by changing the heating rate. The nanowires could provide a better connection between the cathode and the electrolyte, which facilitates Li + diffusion and restrains the structural degeneration. Thus, the cathode displays a high capacity of 291 mA h g 1 at 0.1C and an excellent capacity retention of 91.8% after 200 cycles at 1C. As shown in Fig. 3(b), Yang et al. used hydrothermally synthesized b -MnO2 nanorods as a self-template to fabricate x Li2MnO3 (1x )LiMnO2 nanorods with the diameter of 100-200 nm and the length of 400-1000 nm [63]. Increasing the fraction of Li2MnO3 could significantly increase the discharge capacity but lower the cyclic stability, while increasing the fraction of LiMnO2 could enhance the cyclic stability by suppressing the transformation from layered phase to spinel phase. As shown in Fig. 3(c), Xu et al. constructed Li1.2Mn0.52Ni0.2Co0.08O2 oxide with (010)-oriented nanoplates [64]. This novel morphology not only combines the advantages of exposed (010)-planes and the anisotropic Li + transport tunnels for fast Li + (de)intercalation, but also effectively inhibits the volume expansion during the cycling. The cathode exhibits an initial discharge capacity of 303 mA h g 1 with 8 10 10 89 #/texts/84#prov1 text body True None body body True p8:body_region:1 front_matter column_2_of_2 2 2 p8:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 67.95, 251.08, 59.69] a Coulombic efficiency of 93%. After 200 cycles at 1C, it still has an excellent capacity retention of 92%. Similarly, Xu et al. synthesized a hierarchical quasi-spherical Li1.2Ni0.2Mn0.6O2 oxide with active (010)-orien… a Coulombic efficiency of 93%. After 200 cycles at 1C, it still has an excellent capacity retention of 92%. Similarly, Xu et al. synthesized a hierarchical quasi-spherical Li1.2Ni0.2Mn0.6O2 oxide with active (010)-orien… a Coulombic efficiency of 93%. After 200 cycles at 1C, it still has an excellent capacity retention of 92%. Similarly, Xu et al. synthesized a hierarchical quasi-spherical Li1.2Ni0.2Mn0.6O2 oxide with active (010)-oriented surface [65]. Combining the hierarchical structure and active (010)-planes, this material exhibits efficient transports of both Li + ions and electrons. a Coulombic efficiency of 93%. After 200 cycles at 1C, it still has an excellent capacity retention of 92%. Similarly, Xu et al. synthesized a hierarchical quasi-spherical Li1.2Ni0.2Mn0.6O2 oxide with active (010)-oriented surface [65]. Combining the hierarchical structure and active (010)-planes, this material exhibits efficient transports of both Li + ions and electrons. 8 11 11 90 #/texts/85 text body True None body body True p8:body_region:1 front_matter column_2_of_2 2 2 p8:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 130.72, 251.11, 394.46] In addition, a three-dimensional architecture with more free space between primary particles is another way to improve the cycling stability, since the volume expansion can be accommodated during cycling. Zhang et al. b… In addition, a three-dimensional architecture with more free space between primary particles is another way to improve the cycling stability, since the volume expansion can be accommodated during cycling. Zhang et al. b… In addition, a three-dimensional architecture with more free space between primary particles is another way to improve the cycling stability, since the volume expansion can be accommodated during cycling. Zhang et al. built 3D hollow porous bowlshaped Li1.2Ni0.13Co0.13Mn0.54O2 particles by a soft template method, and the detailed synthetic process is shown in Fig. 3(d) [66]. The material with this unique structure exhibited a high capacity of 300.9 mA h g 1 at the current density of 20 mA g 1 . No evident morphological damage could be observed even at a high current density of 400 mA g 1 , enabling its superb rate performance. This 3D hollow bowl-shaped architecture facilitates electrolyte penetration, ensuring sufficient contact between the cathode and electrolyte. The packing density was also increased via excluding the redundant space. Li et al. designed a threedimensional fusiform hierarchical micro/nano Li1.2Ni0.2Mn0.6O2 with preferentially orientated (110) planes through a hydrothermal method (Fig. 3e) [67]. The cathode not only delivered an enhanced rate performance and cycling stability, but also suppressed the voltage decay through the special triangular frame, which could prevent secondary particles from pulverization and ensure the uniform element distribution. The capacity retention achieved 94% after 100 cycles at 0.1C, and no evident voltage decay could be observed. It also delivered a high capacity of 166.8 mA h g 1 at a high rate of 5C. As shown in Fig. 4(a), He et al. used a self-made template to construct a 3D porous Li1.2Ni0.18Co0.08Mn0.54O2 cathode with an in situ modified surface [68]. This 3D porous structure with a surface modified by carbonaceous compounds, not only increased Li + conductivity, but also protected the active material from side reactions with the electrolyte. Thus, the phase transformation from layered to spinel as well as the voltage decay could be suppressed. Li et al. synthesized a 3D reticular Li1.2Ni0.2Mn0.6O2 cathode material using ordered mesoporous silica as the template [69]. The detailed preparation process and morphological evolution could be seen in Fig. 4(b). This oxide exhibited a high capacity of 195.6 mA h g 1 at 1C with the capacity retention of 95.6% after 50 cycles. The unique morphology of the material provides nanoscale Li + pathways, mechanical stability, and easy access for Li + to the center of the particle. In addition, a three-dimensional architecture with more free space between primary particles is another way to improve the cycling stability, since the volume expansion can be accommodated during cycling. Zhang et al. built 3D hollow porous bowlshaped Li1.2Ni0.13Co0.13Mn0.54O2 particles by a soft template method, and the detailed synthetic process is shown in Fig. 3(d) [66]. The material with this unique structure exhibited a high capacity of 300.9 mA h g 1 at the current density of 20 mA g 1 . No evident morphological damage could be observed even at a high current density of 400 mA g 1 , enabling its superb rate performance. This 3D hollow bowl-shaped architecture facilitates electrolyte penetration, ensuring sufficient contact between the cathode and electrolyte. The packing density was also increased via excluding the redundant space. Li et al. designed a threedimensional fusiform hierarchical micro/nano Li1.2Ni0.2Mn0.6O2 with preferentially orientated (110) planes through a hydrothermal method (Fig. 3e) [67]. The cathode not only delivered an enhanced rate performance and cycling stability, but also suppressed the voltage decay through the special triangular frame, which could prevent secondary particles from pulverization and ensure the uniform element distribution. The capacity retention achieved 94% after 100 cycles at 0.1C, and no evident voltage decay could be observed. It also delivered a high capacity of 166.8 mA h g 1 at a high rate of 5C. As shown in Fig. 4(a), He et al. used a self-made template to construct a 3D porous Li1.2Ni0.18Co0.08Mn0.54O2 cathode with an in situ modified surface [68]. This 3D porous structure with a surface modified by carbonaceous compounds, not only increased Li + conductivity, but also protected the active material from side reactions with the electrolyte. Thus, the phase transformation from layered to spinel as well as the voltage decay could be suppressed. Li et al. synthesized a 3D reticular Li1.2Ni0.2Mn0.6O2 cathode material using ordered mesoporous silica as the template [69]. The detailed preparation process and morphological evolution could be seen in Fig. 4(b). This oxide exhibited a high capacity of 195.6 mA h g 1 at 1C with the capacity retention of 95.6% after 50 cycles. The unique morphology of the material provides nanoscale Li + pathways, mechanical stability, and easy access for Li + to the center of the particle. 8 12 12 91 #/texts/86 text body True None body body True p8:body_region:1 body_zone column_2_of_2 2 2 p8:body_zone:column_2_of_2:white [255, 255, 255] white False False [306.6, 528.19, 251.12, 195.75] Design and construction of special morphologies is also a novel and efficient approach to improve the electrochemical performance of electrode materials. As shown in Fig. 4(c), Oh et al. prepared Li1.2Ni0.2Mn0.6O2 in 10… Design and construction of special morphologies is also a novel and efficient approach to improve the electrochemical performance of electrode materials. As shown in Fig. 4(c), Oh et al. prepared Li1.2Ni0.2Mn0.6O2 in 10… Design and construction of special morphologies is also a novel and efficient approach to improve the electrochemical performance of electrode materials. As shown in Fig. 4(c), Oh et al. prepared Li1.2Ni0.2Mn0.6O2 in 10 l m-sized secondary particles, which were composed of submicron flake-shaped primary particles [70]. The cathode exhibited a high capacity of 242 mA h g 1 at 0.1C and displayed a favorable cycling stability with a capacity retention of 93% after 600 cycles at 1C. Similarly, Yu et al. constructed the ball-in-ball hollow Li1.2Ni0.13Co0.13Mn0.54O2 microspheres via the co-precipitation method by tuning the nucleation, growth, and heterogeneity of the crystals [71]. The cathode showed excellent electrochemical performance with a high capacity of 193 mA h g 1 at 3C and a capacity retention of 87.6% after 400 cycles. Zhang et al. fabricated a peanut-like hierarchical micro/nano Li1.2Ni0.18Co0.08Mn0.54O2 via the solvothermal method [72]. This oxide, with better crystallinity and larger specific surface area than the counterparts, delivered a discharge capacity of 229.9 mA g h 1 at 1C and a capacity retention of 94.2% after 100 cycles. Design and construction of special morphologies is also a novel and efficient approach to improve the electrochemical performance of electrode materials. As shown in Fig. 4(c), Oh et al. prepared Li1.2Ni0.2Mn0.6O2 in 10 l m-sized secondary particles, which were composed of submicron flake-shaped primary particles [70]. The cathode exhibited a high capacity of 242 mA h g 1 at 0.1C and displayed a favorable cycling stability with a capacity retention of 93% after 600 cycles at 1C. Similarly, Yu et al. constructed the ball-in-ball hollow Li1.2Ni0.13Co0.13Mn0.54O2 microspheres via the co-precipitation method by tuning the nucleation, growth, and heterogeneity of the crystals [71]. The cathode showed excellent electrochemical performance with a high capacity of 193 mA h g 1 at 3C and a capacity retention of 87.6% after 400 cycles. Zhang et al. fabricated a peanut-like hierarchical micro/nano Li1.2Ni0.18Co0.08Mn0.54O2 via the solvothermal method [72]. This oxide, with better crystallinity and larger specific surface area than the counterparts, delivered a discharge capacity of 229.9 mA g h 1 at 1C and a capacity retention of 94.2% after 100 cycles. 8 13 13 92 #/texts/87 text body True None body body True p8:body_region:1 bottom_margin column_2_of_2 2 2 p8:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.6, 726.95, 251.1, 28.34] In summary, the positive effects of nanoscale morphology design can be summarized as below: (1) shortening Li + diffusion pathway and increasing rate capacity; (2) releasing the strain from In summary, the positive effects of nanoscale morphology design can be summarized as below: (1) shortening Li + diffusion pathway and increasing rate capacity; (2) releasing the strain from In summary, the positive effects of nanoscale morphology design can be summarized as below: (1) shortening Li + diffusion pathway and increasing rate capacity; (2) releasing the strain from In summary, the positive effects of nanoscale morphology design can be summarized as below: (1) shortening Li + diffusion pathway and increasing rate capacity; (2) releasing the strain from 9 4 3 96 #/texts/92 text body True None body body True p9:body_region:0 front_matter column_1_of_2 1 2 p9:front_matter:column_1_of_2:white [250, 250, 250] white False False [37.64, 212.45, 22.48, 5.93] Table 4 Table 4 Table 4 Table 4 9 5 4 97 #/texts/93 text body True None body body True p9:body_region:0 front_matter column_1_of_2 1 2 p9:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 221.01, 317.82, 5.93] The electrochemical performance of LMR cathodes with different element doping reported in recent years. The electrochemical performance of LMR cathodes with different element doping reported in recent years. The electrochemical performance of LMR cathodes with different element doping reported in recent years. The electrochemical performance of LMR cathodes with different element doping reported in recent years. 9 6 5 98 #/texts/94 text body True None body body True p9:body_region:0 front_matter column_1_of_2 1 2 p9:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 380.56, 251.11, 91.09] volume change caused by phase transformation, enhancing the mechanical stability, and contributing to the cycling stability. However, there are also some disadvantages using this strategy, such as complicated preparatio… volume change caused by phase transformation, enhancing the mechanical stability, and contributing to the cycling stability. However, there are also some disadvantages using this strategy, such as complicated preparatio… volume change caused by phase transformation, enhancing the mechanical stability, and contributing to the cycling stability. However, there are also some disadvantages using this strategy, such as complicated preparation, high cost, low tap density and etc., which greatly hinder the practical application in scaling up the cathode materials. In addition, it is difficult to achieve consistent morphology in different batches of materials, while even a slight difference in the morphology might lead to a big difference in the performance. volume change caused by phase transformation, enhancing the mechanical stability, and contributing to the cycling stability. However, there are also some disadvantages using this strategy, such as complicated preparation, high cost, low tap density and etc., which greatly hinder the practical application in scaling up the cathode materials. In addition, it is difficult to achieve consistent morphology in different batches of materials, while even a slight difference in the morphology might lead to a big difference in the performance. 9 8 7 100 #/texts/96 text body True None body body True p9:body_region:0 body_zone column_1_of_2 1 2 p9:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 506.7, 251.07, 28.34] Bulk design is essential to improve the structural stability so as to promote the electrochemical performance of LMR cathode. This section is divided into two parts: structure design and bulk doping. Bulk design is essential to improve the structural stability so as to promote the electrochemical performance of LMR cathode. This section is divided into two parts: structure design and bulk doping. Bulk design is essential to improve the structural stability so as to promote the electrochemical performance of LMR cathode. This section is divided into two parts: structure design and bulk doping. Bulk design is essential to improve the structural stability so as to promote the electrochemical performance of LMR cathode. This section is divided into two parts: structure design and bulk doping. 9 10 9 102 #/texts/98 text body True None body body True p9:body_region:0 body_zone column_1_of_2 1 2 p9:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 559.6, 251.12, 38.82] Structure design is an effective method to enhance the electrochemical performance of LMR cathode, which includes introducing porous structure, structural defects, gradient elemental distribution, and etc. Structure design is an effective method to enhance the electrochemical performance of LMR cathode, which includes introducing porous structure, structural defects, gradient elemental distribution, and etc. Structure design is an effective method to enhance the electrochemical performance of LMR cathode, which includes introducing porous structure, structural defects, gradient elemental distribution, and etc. Structure design is an effective method to enhance the electrochemical performance of LMR cathode, which includes introducing porous structure, structural defects, gradient elemental distribution, and etc. 9 11 10 103 #/texts/99#prov0 text body True None body body True p9:body_region:0 bottom_margin column_1_of_2 1 2 p9:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 601.43, 251.13, 153.86] Firstly, porous structure is an effective strategy to increase the electrolyte/electrode contact area, and buffer the volume expansion due to the phase transformation during cycling. Li et al. designed hierarchical meso… Firstly, porous structure is an effective strategy to increase the electrolyte/electrode contact area, and buffer the volume expansion due to the phase transformation during cycling. Li et al. designed hierarchical meso… Firstly, porous structure is an effective strategy to increase the electrolyte/electrode contact area, and buffer the volume expansion due to the phase transformation during cycling. Li et al. designed hierarchical mesoporous structure in Li1.2Ni0.2Mn0.6O2 through ice-template coprecipitation [73]. As shown in Fig. 5(a and b), the rate performance was promoted notably. For Li1.2Ni0.2Mn0.6O2 cathode synthesized using a traditional method, the reversible capacity at 1C was only about 56% of the capacity at 0.1C. In contrast, the capacity at 1C has been promoted to 67% of that at 0.1C in the hierarchical mesoporous structure. The mesoporous structure increased Li + diffusion channels, facilitating Li + diffusion at a large current density. A similar method was also utilized by Qiu et al, as shown in Fig. 5(c) [74]. They introduced homogeneous three-dimensional (3D) nano-porous structure in Li1.144Ni0.136Co0.136Mn0.544O2, which exhibited a micrometer-sized spherical Firstly, porous structure is an effective strategy to increase the electrolyte/electrode contact area, and buffer the volume expansion due to the phase transformation during cycling. Li et al. designed hierarchical mesoporous structure in Li1.2Ni0.2Mn0.6O2 through ice-template coprecipitation [73]. As shown in Fig. 5(a and b), the rate performance was promoted notably. For Li1.2Ni0.2Mn0.6O2 cathode synthesized using a traditional method, the reversible capacity at 1C was only about 56% of the capacity at 0.1C. In contrast, the capacity at 1C has been promoted to 67% of that at 0.1C in the hierarchical mesoporous structure. The mesoporous structure increased Li + diffusion channels, facilitating Li + diffusion at a large current density. A similar method was also utilized by Qiu et al, as shown in Fig. 5(c) [74]. They introduced homogeneous three-dimensional (3D) nano-porous structure in Li1.144Ni0.136Co0.136Mn0.544O2, which exhibited a micrometer-sized spherical 9 12 12 105 #/texts/99#prov1 text body True None body body True p9:body_region:1 front_matter column_2_of_2 2 2 p9:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 380.56, 251.04, 17.91] morphology. It displayed a better rate performance compared to the sample without a porous structure. morphology. It displayed a better rate performance compared to the sample without a porous structure. morphology. It displayed a better rate performance compared to the sample without a porous structure. morphology. It displayed a better rate performance compared to the sample without a porous structure. 9 13 13 106 #/texts/100 text body True None body body True p9:body_region:1 bottom_margin column_2_of_2 2 2 p9:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 401.48, 251.11, 352.62] Another effective method to improve the electrochemical performance of LMR cathode is introducing structural defects in the lattice. Xia et al. introduced multiple structural defects in Li1.143Ni0.136Co0.136Mn0.544O2 by… Another effective method to improve the electrochemical performance of LMR cathode is introducing structural defects in the lattice. Xia et al. introduced multiple structural defects in Li1.143Ni0.136Co0.136Mn0.544O2 by… Another effective method to improve the electrochemical performance of LMR cathode is introducing structural defects in the lattice. Xia et al. introduced multiple structural defects in Li1.143Ni0.136Co0.136Mn0.544O2 by well-controlled chemical de-lithiation [75]. As shown in Fig. 5(d and e), these structural defects include twins/stacking faults and spinel-like mosaics in the bulk. Due to the fine pre-rearrangement, the obtained oxide has some characteristics of electrochemically induced hybrid compounds, which could make anion redox more stable. Thus, the defect-rich cathode exhibited superior cycling stability compared to pristine cathode, and the voltage decay was also evidently suppressed (Fig. 5f). Liu et al. also successfully introduced stacking faults in Li1.2Ni0.13Co0.13Mn0.54O2 through molten salt method [76]. They could control the concentration of stacking faults through tuning the synthetic temperature and the type of molten salt. When the synthetic temperature was 800 ℃ , the electrochemical performance of Li1.2Ni0.13Co0.13Mn0.54O2 cathode was the best, and the capacity reached 310 mA h g 1 at 0.1C. The optimal capacity could be attributed to an appropriate amount of stacking faults. Li et al. synthesized Li1.2Ni0.2Mn0.6O2 with a small amount of structural defects by combining a fast-evaporating approach and a subsequent high temperature calcination [77]. Due to the structural defects, the oxygen loss during the first cycle was reduced, and Mn migration and the phase transformation from layered to spinel were also suppressed. Zhong et al. introduced surface oxygen defects in Li1.2Ni0.13Co0.13Mn0.54O2 through a facile hydrothermal reaction followed by heat treatment [78]. After the introduction of the oxygen defects, the activity of surface oxygen was reduced, inhibiting the evolution of lattice oxygen in the bulk. Also, surface defects alleviated the lattice microstrain during the delithiation/lithiation process, and enhanced the mechanical property of materials. In addition, the defects induced the formation of spinel structure at the surface, facilitating Li + extraction/insertion so as to promote the rate performance. Another effective method to improve the electrochemical performance of LMR cathode is introducing structural defects in the lattice. Xia et al. introduced multiple structural defects in Li1.143Ni0.136Co0.136Mn0.544O2 by well-controlled chemical de-lithiation [75]. As shown in Fig. 5(d and e), these structural defects include twins/stacking faults and spinel-like mosaics in the bulk. Due to the fine pre-rearrangement, the obtained oxide has some characteristics of electrochemically induced hybrid compounds, which could make anion redox more stable. Thus, the defect-rich cathode exhibited superior cycling stability compared to pristine cathode, and the voltage decay was also evidently suppressed (Fig. 5f). Liu et al. also successfully introduced stacking faults in Li1.2Ni0.13Co0.13Mn0.54O2 through molten salt method [76]. They could control the concentration of stacking faults through tuning the synthetic temperature and the type of molten salt. When the synthetic temperature was 800 ℃ , the electrochemical performance of Li1.2Ni0.13Co0.13Mn0.54O2 cathode was the best, and the capacity reached 310 mA h g 1 at 0.1C. The optimal capacity could be attributed to an appropriate amount of stacking faults. Li et al. synthesized Li1.2Ni0.2Mn0.6O2 with a small amount of structural defects by combining a fast-evaporating approach and a subsequent high temperature calcination [77]. Due to the structural defects, the oxygen loss during the first cycle was reduced, and Mn migration and the phase transformation from layered to spinel were also suppressed. Zhong et al. introduced surface oxygen defects in Li1.2Ni0.13Co0.13Mn0.54O2 through a facile hydrothermal reaction followed by heat treatment [78]. After the introduction of the oxygen defects, the activity of surface oxygen was reduced, inhibiting the evolution of lattice oxygen in the bulk. Also, surface defects alleviated the lattice microstrain during the delithiation/lithiation process, and enhanced the mechanical property of materials. In addition, the defects induced the formation of spinel structure at the surface, facilitating Li + extraction/insertion so as to promote the rate performance. 10 5 5 112 #/texts/106 text body True None body body False None bottom_margin column_1_of_2 1 2 p10:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 705.41, 251.08, 49.26] Besides, gradient cathode materials have become a hot topic in recent years [79]. Ju et al. designed a gradient oxide Li1.2Mn0.44Co0.04Ni0.32O2 (Fig. 5g), in which Ni element increases and Mn element decreases from the … Besides, gradient cathode materials have become a hot topic in recent years [79]. Ju et al. designed a gradient oxide Li1.2Mn0.44Co0.04Ni0.32O2 (Fig. 5g), in which Ni element increases and Mn element decreases from the … Besides, gradient cathode materials have become a hot topic in recent years [79]. Ju et al. designed a gradient oxide Li1.2Mn0.44Co0.04Ni0.32O2 (Fig. 5g), in which Ni element increases and Mn element decreases from the bulk to the surface, which could be proved by Energy dispersive X-ray spectroscopy (EDS) line scan Besides, gradient cathode materials have become a hot topic in recent years [79]. Ju et al. designed a gradient oxide Li1.2Mn0.44Co0.04Ni0.32O2 (Fig. 5g), in which Ni element increases and Mn element decreases from the bulk to the surface, which could be proved by Energy dispersive X-ray spectroscopy (EDS) line scan 10 6 6 113 #/texts/107#prov0 text body True None body body False None bottom_margin column_2_of_2 2 2 p10:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 705.41, 251.09, 49.26] (Fig. 5h-i) [80]. Owing to the gradient distribution of Ni and Mn elements, the Ni/Mn ratio is much higher at the surface. Therefore, TM migration was suppressed and the voltage and capacity decay during long-term cycli… (Fig. 5h-i) [80]. Owing to the gradient distribution of Ni and Mn elements, the Ni/Mn ratio is much higher at the surface. Therefore, TM migration was suppressed and the voltage and capacity decay during long-term cycli… (Fig. 5h-i) [80]. Owing to the gradient distribution of Ni and Mn elements, the Ni/Mn ratio is much higher at the surface. Therefore, TM migration was suppressed and the voltage and capacity decay during long-term cycling decreased. The method has been extended to other LMR oxides [81,82]. Core-shell structural design (Fig. 5h-i) [80]. Owing to the gradient distribution of Ni and Mn elements, the Ni/Mn ratio is much higher at the surface. Therefore, TM migration was suppressed and the voltage and capacity decay during long-term cycling decreased. The method has been extended to other LMR oxides [81,82]. Core-shell structural design 11 1 5 119 #/texts/107#prov1 text body True None body body True p11:body_region:0 page_body column_1_of_2 1 2 p11:page_body:column_1_of_2:white [255, 255, 255] white False False [37.59, 662.95, 251.07, 17.91] is another effective method to improve the electrochemical performance of LMR oxides. We will elaborate on it in Section 3.3. is another effective method to improve the electrochemical performance of LMR oxides. We will elaborate on it in Section 3.3. is another effective method to improve the electrochemical performance of LMR oxides. We will elaborate on it in Section 3.3. is another effective method to improve the electrochemical performance of LMR oxides. We will elaborate on it in Section 3.3. 11 6 6 120 #/texts/113 text body True None body body True p11:body_region:0 bottom_margin column_1_of_2 1 2 p11:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 683.87, 251.12, 70.19] In addition, since O3-type LMR cathodes suffer severe voltage and capacity decay, synthesizing O2-type LMR cathodes is also an effective remedy. Xia et al. prepared an O2-type Li-rich material with a single-layer Li2MnO… In addition, since O3-type LMR cathodes suffer severe voltage and capacity decay, synthesizing O2-type LMR cathodes is also an effective remedy. Xia et al. prepared an O2-type Li-rich material with a single-layer Li2MnO… In addition, since O3-type LMR cathodes suffer severe voltage and capacity decay, synthesizing O2-type LMR cathodes is also an effective remedy. Xia et al. prepared an O2-type Li-rich material with a single-layer Li2MnO3 superstructure via ion exchange [83]. Owing to this novel structure, this oxide could maintain stable oxygen redox reactions and small structural changes during cycling, and delivered an extraordinary reversible capacity of 400 mA h g 1 . In addition, since O3-type LMR cathodes suffer severe voltage and capacity decay, synthesizing O2-type LMR cathodes is also an effective remedy. Xia et al. prepared an O2-type Li-rich material with a single-layer Li2MnO3 superstructure via ion exchange [83]. Owing to this novel structure, this oxide could maintain stable oxygen redox reactions and small structural changes during cycling, and delivered an extraordinary reversible capacity of 400 mA h g 1 . 11 7 7 121 #/texts/114#prov0 text body True None body body False None bottom_margin column_2_of_2 2 2 p11:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 662.95, 251.11, 91.09] In summary, various structure design methods, including introducing porous structure, structural defects, elemental gradient distribution and O2-type structure in LMR cathodes could distinctly promote the electrochemica… In summary, various structure design methods, including introducing porous structure, structural defects, elemental gradient distribution and O2-type structure in LMR cathodes could distinctly promote the electrochemica… In summary, various structure design methods, including introducing porous structure, structural defects, elemental gradient distribution and O2-type structure in LMR cathodes could distinctly promote the electrochemical performance. The detailed electrochemical properties of LMR cathodes with different structure designs reported recently are listed in Table 3. Correspondingly, there are some limitations with them. Porous structure would decrease the tap density of cathode materials, thus the volumetric energy density. Structural defects always require the precise pro- In summary, various structure design methods, including introducing porous structure, structural defects, elemental gradient distribution and O2-type structure in LMR cathodes could distinctly promote the electrochemical performance. The detailed electrochemical properties of LMR cathodes with different structure designs reported recently are listed in Table 3. Correspondingly, there are some limitations with them. Porous structure would decrease the tap density of cathode materials, thus the volumetric energy density. Structural defects always require the precise pro- 12 1 4 126 #/texts/114#prov1 text body True None body body True p12:body_region:0 front_matter column_1_of_2 1 2 p12:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 474.78, 251.13, 38.82] cess control, and bring with the relative low capacity. Elemental gradient design and ion exchange for O2-type structure also demand complicated synthetic devices, thus increasing the difficulty of commercialization and… cess control, and bring with the relative low capacity. Elemental gradient design and ion exchange for O2-type structure also demand complicated synthetic devices, thus increasing the difficulty of commercialization and… cess control, and bring with the relative low capacity. Elemental gradient design and ion exchange for O2-type structure also demand complicated synthetic devices, thus increasing the difficulty of commercialization and the production cost a lot. cess control, and bring with the relative low capacity. Elemental gradient design and ion exchange for O2-type structure also demand complicated synthetic devices, thus increasing the difficulty of commercialization and the production cost a lot. 12 6 6 128 #/texts/120 text body True None body body True p12:body_region:0 body_zone column_1_of_2 1 2 p12:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 538.68, 251.09, 38.82] Bulk doping has been widely reported as a traditional but effective method to improve the electrochemical performance of cathodes in LIBs, and it has also been widely applied in LMR cathodes (Table 4). Bulk doping has been widely reported as a traditional but effective method to improve the electrochemical performance of cathodes in LIBs, and it has also been widely applied in LMR cathodes (Table 4). Bulk doping has been widely reported as a traditional but effective method to improve the electrochemical performance of cathodes in LIBs, and it has also been widely applied in LMR cathodes (Table 4). Bulk doping has been widely reported as a traditional but effective method to improve the electrochemical performance of cathodes in LIBs, and it has also been widely applied in LMR cathodes (Table 4). 12 7 7 129 #/texts/121#prov0 text body True None body body True p12:body_region:0 bottom_margin column_1_of_2 1 2 p12:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 580.52, 251.13, 174.78] Elements in the third period like Na and Mg, have been widely adopted for bulking doping. He et al. successfully introduced Na ions in the lattice of Li1.2Ni0.13Co0.13Mn0.54O2 through a polymer pyrolysis method [84]. Ow… Elements in the third period like Na and Mg, have been widely adopted for bulking doping. He et al. successfully introduced Na ions in the lattice of Li1.2Ni0.13Co0.13Mn0.54O2 through a polymer pyrolysis method [84]. Ow… Elements in the third period like Na and Mg, have been widely adopted for bulking doping. He et al. successfully introduced Na ions in the lattice of Li1.2Ni0.13Co0.13Mn0.54O2 through a polymer pyrolysis method [84]. Owing to the larger radius of Na + , Li slab became thicker while Na + replaced Li + in Li layers. As shown in Fig. 6(a), (003) peak for Li1.17Na0.03[Ni0.13Co0.13Mn0.54]O2 is located at a lower angle compared to that for Li1.2Ni0.13Co0.13Mn0.54O2, implying the increase of Li slab due to Na + substitution. Na doping successfully enhanced the structural stability and Li + diffusivity. Thus, Na-doped cathode exhibited better cycling stability compared to undoped counterpart, and it retained 89% of the capacity after 100 cycles at the current density of 100 mA g 1 (Fig. 6b). He et al. used sodium dodecyl sulfate as a surfactant, and homogenously introduced Na + in the layered lattice of Li1.2Ni0.13Co0.13Mn0.54O2, as shown in Fig. 6(c) [85]. Different from the previous reports [86], the introduction of Na + caused abundant defects in the form of stacking faults in the lattice. These stacking faults Elements in the third period like Na and Mg, have been widely adopted for bulking doping. He et al. successfully introduced Na ions in the lattice of Li1.2Ni0.13Co0.13Mn0.54O2 through a polymer pyrolysis method [84]. Owing to the larger radius of Na + , Li slab became thicker while Na + replaced Li + in Li layers. As shown in Fig. 6(a), (003) peak for Li1.17Na0.03[Ni0.13Co0.13Mn0.54]O2 is located at a lower angle compared to that for Li1.2Ni0.13Co0.13Mn0.54O2, implying the increase of Li slab due to Na + substitution. Na doping successfully enhanced the structural stability and Li + diffusivity. Thus, Na-doped cathode exhibited better cycling stability compared to undoped counterpart, and it retained 89% of the capacity after 100 cycles at the current density of 100 mA g 1 (Fig. 6b). He et al. used sodium dodecyl sulfate as a surfactant, and homogenously introduced Na + in the layered lattice of Li1.2Ni0.13Co0.13Mn0.54O2, as shown in Fig. 6(c) [85]. Different from the previous reports [86], the introduction of Na + caused abundant defects in the form of stacking faults in the lattice. These stacking faults 12 8 8 130 #/texts/121#prov1 text body True None body body True p12:body_region:1 front_matter column_2_of_2 2 2 p12:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 474.78, 251.1, 227.1] enhanced the structural stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode, which displayed better cycling stability. Du et al. performed the similar experiments [87]. Interestingly, Na ions have not been introduced to the … enhanced the structural stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode, which displayed better cycling stability. Du et al. performed the similar experiments [87]. Interestingly, Na ions have not been introduced to the … enhanced the structural stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode, which displayed better cycling stability. Du et al. performed the similar experiments [87]. Interestingly, Na ions have not been introduced to the layered lattice. By contrast, a two-phase composite formed with a new Na0.7MnO2.05 phase. Li + diffused rapidly within the boundaries between these two phases, and composite cathode got superior rate performance (130 mA h g 1 at 5 C). Mg doping can also greatly improve electrochemical performance. Yu et al. synthesized a novel cathode material Li1.4Mg0.1[Mn0.75Ni0.25] O2+ r with uniform Mg doping through coprecipitation and high temperature solid state sintering [88]. They found that, Mg ions were prone to take Li sites (4 h), as shown in Fig. 6(d). The Mg dopant has a distinct effect on promoting Li + diffusivity, which evidently improved the rate performance. As shown in Fig. 6(e), Li1.4Mg0.1[Mn0.75Ni0.25]O2+ r cathode exhibits a discharge capacity of 130 mA h g 1 at 10 C, which is much higher than that of Li1.5[Mn0.75Ni0.25]O2+ r cathode. It has also been reported that, the improved cycling stability of LMR cathode by Mg doping could be explained by the reduced charge transfer resistance and the expansion of the unit cell [89,90]. Besides, TM cations are also selected to improve the performance of LMR cathodes, such as Ti, Fe, Ru, etc. [91-94]. enhanced the structural stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode, which displayed better cycling stability. Du et al. performed the similar experiments [87]. Interestingly, Na ions have not been introduced to the layered lattice. By contrast, a two-phase composite formed with a new Na0.7MnO2.05 phase. Li + diffused rapidly within the boundaries between these two phases, and composite cathode got superior rate performance (130 mA h g 1 at 5 C). Mg doping can also greatly improve electrochemical performance. Yu et al. synthesized a novel cathode material Li1.4Mg0.1[Mn0.75Ni0.25] O2+ r with uniform Mg doping through coprecipitation and high temperature solid state sintering [88]. They found that, Mg ions were prone to take Li sites (4 h), as shown in Fig. 6(d). The Mg dopant has a distinct effect on promoting Li + diffusivity, which evidently improved the rate performance. As shown in Fig. 6(e), Li1.4Mg0.1[Mn0.75Ni0.25]O2+ r cathode exhibits a discharge capacity of 130 mA h g 1 at 10 C, which is much higher than that of Li1.5[Mn0.75Ni0.25]O2+ r cathode. It has also been reported that, the improved cycling stability of LMR cathode by Mg doping could be explained by the reduced charge transfer resistance and the expansion of the unit cell [89,90]. Besides, TM cations are also selected to improve the performance of LMR cathodes, such as Ti, Fe, Ru, etc. [91-94]. 12 9 9 131 #/texts/122#prov0 text body True None body body True p12:body_region:1 bottom_margin column_2_of_2 2 2 p12:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 704.96, 251.06, 49.26] In addition, two or more ions together may play different roles in multiple elemental doping, which make it possible for them to work synergistically to produce better electrochemistry than the single elemental doping, … In addition, two or more ions together may play different roles in multiple elemental doping, which make it possible for them to work synergistically to produce better electrochemistry than the single elemental doping, … In addition, two or more ions together may play different roles in multiple elemental doping, which make it possible for them to work synergistically to produce better electrochemistry than the single elemental doping, namely multi-ion co-doping. Liu et al. doped Na cation and F anion in Li1.2Ni0.2Mn0.6O2 cathode, as shown In addition, two or more ions together may play different roles in multiple elemental doping, which make it possible for them to work synergistically to produce better electrochemistry than the single elemental doping, namely multi-ion co-doping. Liu et al. doped Na cation and F anion in Li1.2Ni0.2Mn0.6O2 cathode, as shown 13 1 5 137 #/texts/122#prov1 text body True None body body True p13:body_region:0 bottom_margin column_1_of_2 1 2 p13:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 611.92, 251.11, 143.37] in Fig. 6(f) [95]. The Na and F dopants worked synergistically in the Li1.2Ni0.2Mn0.6O2 cathode. Na doping partly restricted the forming of spinel structure during cycling, and F doping increased the ionic and electroni… in Fig. 6(f) [95]. The Na and F dopants worked synergistically in the Li1.2Ni0.2Mn0.6O2 cathode. Na doping partly restricted the forming of spinel structure during cycling, and F doping increased the ionic and electroni… in Fig. 6(f) [95]. The Na and F dopants worked synergistically in the Li1.2Ni0.2Mn0.6O2 cathode. Na doping partly restricted the forming of spinel structure during cycling, and F doping increased the ionic and electronic conductivity. Thus, co-doped Li1.12Na0.08Ni0.2Mn0.6O1.95F0.05 exhibited excellent cycling stability and rate performance, much better than the undoped Li1.2Ni0.2Mn0.6O2 and the samples only doped by Na or F element alone (Fig. 6g). Cation co-doping has also been reported by Wynn et al [96]. Co and Mo cations co-doped in Li1.2Ni0.2Mn0.6O2, in which the degradation of capacity and voltage were successfully suppressed during cycling. This could be attributed to the modified distribution of oxygen charge density by Mo doping, which changed the local band structure and impeded the formation of oxygen vacancy, making oxygen redox more reversible. Other co-doping methods for LMR in Fig. 6(f) [95]. The Na and F dopants worked synergistically in the Li1.2Ni0.2Mn0.6O2 cathode. Na doping partly restricted the forming of spinel structure during cycling, and F doping increased the ionic and electronic conductivity. Thus, co-doped Li1.12Na0.08Ni0.2Mn0.6O1.95F0.05 exhibited excellent cycling stability and rate performance, much better than the undoped Li1.2Ni0.2Mn0.6O2 and the samples only doped by Na or F element alone (Fig. 6g). Cation co-doping has also been reported by Wynn et al [96]. Co and Mo cations co-doped in Li1.2Ni0.2Mn0.6O2, in which the degradation of capacity and voltage were successfully suppressed during cycling. This could be attributed to the modified distribution of oxygen charge density by Mo doping, which changed the local band structure and impeded the formation of oxygen vacancy, making oxygen redox more reversible. Other co-doping methods for LMR 13 6 6 138 #/texts/128 text body True None body body True p13:body_region:1 front_matter column_2_of_2 2 2 p13:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 611.92, 251.05, 17.85] cathodes like metal ions and nonmetallic ions co-doping have also been reported recently [97,98]. cathodes like metal ions and nonmetallic ions co-doping have also been reported recently [97,98]. cathodes like metal ions and nonmetallic ions co-doping have also been reported recently [97,98]. cathodes like metal ions and nonmetallic ions co-doping have also been reported recently [97,98]. 13 8 8 140 #/texts/130 text body True None body body True p13:body_region:1 body_zone column_2_of_2 2 2 p13:body_zone:column_2_of_2:white [255, 255, 255] white False False [306.59, 664.19, 251.05, 28.34] Surface modification is another effective way to improve the performance of LMR oxides, which includes surface coating, surface doping, and other special surface treatment. Surface modification is another effective way to improve the performance of LMR oxides, which includes surface coating, surface doping, and other special surface treatment. Surface modification is another effective way to improve the performance of LMR oxides, which includes surface coating, surface doping, and other special surface treatment. Surface modification is another effective way to improve the performance of LMR oxides, which includes surface coating, surface doping, and other special surface treatment. 13 10 10 142 #/texts/132#prov0 text body True None body body True p13:body_region:1 bottom_margin column_2_of_2 2 2 p13:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.59, 716.52, 251.08, 38.77] To reduce the side reactions at the electrode/electrolyte interface, it is straightforward to build an electrochemically-inert protective layer, or a surface coating, on the surface of the cathodes [99-101]. For LMR cat… To reduce the side reactions at the electrode/electrolyte interface, it is straightforward to build an electrochemically-inert protective layer, or a surface coating, on the surface of the cathodes [99-101]. For LMR cat… To reduce the side reactions at the electrode/electrolyte interface, it is straightforward to build an electrochemically-inert protective layer, or a surface coating, on the surface of the cathodes [99-101]. For LMR cathodes, metal oxides, phosphate, fluoride, To reduce the side reactions at the electrode/electrolyte interface, it is straightforward to build an electrochemically-inert protective layer, or a surface coating, on the surface of the cathodes [99-101]. For LMR cathodes, metal oxides, phosphate, fluoride, 14 1 2 145 #/texts/132#prov1 text body True None body body True p14:body_region:0 page_body column_1_of_2 1 2 p14:page_body:column_1_of_2:white [255, 255, 255] white False False [37.59, 67.96, 251.06, 17.85] organic polymer, etc. have been chosen as coating materials, as shown in Table 5. organic polymer, etc. have been chosen as coating materials, as shown in Table 5. organic polymer, etc. have been chosen as coating materials, as shown in Table 5. organic polymer, etc. have been chosen as coating materials, as shown in Table 5. 14 4 3 146 #/texts/136 text body True None body body True p14:body_region:0 page_body column_1_of_2 1 2 p14:page_body:column_1_of_2:white [255, 255, 255] white False False [37.59, 88.88, 251.12, 248.02] Al2O3 has been widely adopted in LMR cathodes as one of the most popular coating materials due to the material availability and various coating routes. Xu et al. coated highly crystalline Al2O3 on Li1.2Ni0.20Co0.08Mn0.5… Al2O3 has been widely adopted in LMR cathodes as one of the most popular coating materials due to the material availability and various coating routes. Xu et al. coated highly crystalline Al2O3 on Li1.2Ni0.20Co0.08Mn0.5… Al2O3 has been widely adopted in LMR cathodes as one of the most popular coating materials due to the material availability and various coating routes. Xu et al. coated highly crystalline Al2O3 on Li1.2Ni0.20Co0.08Mn0.52O2 through the hydrolysis of aluminum isopropoxide [102]. As shown in Fig. 7(a), three different regions formed from the surface to the bulk: the outer surface region for Al2O3 coating layer, the surface region for LiM1x Al x O2/ LiMO2 (M = Ni, Co, Mn) solid solution, and the bulk region for Li1.2Ni0.20Co0.08Mn0.52O2. On one hand, Al2O3 coating layer reduced the contact area between the electrode and electrolyte, which suppressed cation dissolution to a large extent. On the other hand, the formed LiM1x Al x O2/LiMO2 hierarchical structure prohibited the phase transformation at the surface. Nearly no capacity or voltage decay was observed in Al2O3 coated Li1.2Ni0.20Co0.08Mn0.52O2 cathode during long-term cycling (Fig. 7b). Chen et al. successfully coated SnO2 at the surface of Li1.2Ni0.13Co0.13Mn0.54O2 cathode with a uniform thickness of 4-8 nm [103]. The coating layer limited the side reactions between the electrode and electrolyte, producing a thin solid electrolyte interface (SEI) and enhancing the rate performance. In addition, oxygen vacancies were introduced by the SnO2 coating layer, which was beneficial to oxygen migration in the coating layer (Fig. 7c). Thus, the activation of Li2MnO3 in Li1.2Ni0.13Co0.13Mn0.54O2 cathode was promoted during the charging-discharging process, increasing the initial capacity. Al2O3 has been widely adopted in LMR cathodes as one of the most popular coating materials due to the material availability and various coating routes. Xu et al. coated highly crystalline Al2O3 on Li1.2Ni0.20Co0.08Mn0.52O2 through the hydrolysis of aluminum isopropoxide [102]. As shown in Fig. 7(a), three different regions formed from the surface to the bulk: the outer surface region for Al2O3 coating layer, the surface region for LiM1x Al x O2/ LiMO2 (M = Ni, Co, Mn) solid solution, and the bulk region for Li1.2Ni0.20Co0.08Mn0.52O2. On one hand, Al2O3 coating layer reduced the contact area between the electrode and electrolyte, which suppressed cation dissolution to a large extent. On the other hand, the formed LiM1x Al x O2/LiMO2 hierarchical structure prohibited the phase transformation at the surface. Nearly no capacity or voltage decay was observed in Al2O3 coated Li1.2Ni0.20Co0.08Mn0.52O2 cathode during long-term cycling (Fig. 7b). Chen et al. successfully coated SnO2 at the surface of Li1.2Ni0.13Co0.13Mn0.54O2 cathode with a uniform thickness of 4-8 nm [103]. The coating layer limited the side reactions between the electrode and electrolyte, producing a thin solid electrolyte interface (SEI) and enhancing the rate performance. In addition, oxygen vacancies were introduced by the SnO2 coating layer, which was beneficial to oxygen migration in the coating layer (Fig. 7c). Thus, the activation of Li2MnO3 in Li1.2Ni0.13Co0.13Mn0.54O2 cathode was promoted during the charging-discharging process, increasing the initial capacity. 14 5 4 147 #/texts/137#prov0 text body True None body body True p14:body_region:0 page_body column_1_of_2 1 2 p14:page_body:column_1_of_2:white [255, 255, 255] white False False [37.59, 339.91, 251.1, 101.58] Phosphates has also been regarded as effective candidates for surface coating. Xiao et al. coated aluminum phosphate (AlPO4) at the surface of LMR through atomic layer deposition (ALD) method [104]. They found a spinel … Phosphates has also been regarded as effective candidates for surface coating. Xiao et al. coated aluminum phosphate (AlPO4) at the surface of LMR through atomic layer deposition (ALD) method [104]. They found a spinel … Phosphates has also been regarded as effective candidates for surface coating. Xiao et al. coated aluminum phosphate (AlPO4) at the surface of LMR through atomic layer deposition (ALD) method [104]. They found a spinel structure formed at the surface during ALD process, and this spinel layer effectively inhibited the oxygen release during the first charging-discharging, as shown in Fig. 7(d). Therefore, the initial Coulombic efficiency of the LMR cathode was promoted distinctly. When the cathode was coated with 5 ALD cycles of AlPO4, it exhibited the best initial Coulombic efficiency (86.2%), as shown in Fig. 7(e). In addition to the pro- Phosphates has also been regarded as effective candidates for surface coating. Xiao et al. coated aluminum phosphate (AlPO4) at the surface of LMR through atomic layer deposition (ALD) method [104]. They found a spinel structure formed at the surface during ALD process, and this spinel layer effectively inhibited the oxygen release during the first charging-discharging, as shown in Fig. 7(d). Therefore, the initial Coulombic efficiency of the LMR cathode was promoted distinctly. When the cathode was coated with 5 ALD cycles of AlPO4, it exhibited the best initial Coulombic efficiency (86.2%), as shown in Fig. 7(e). In addition to the pro- 14 6 7 150 #/texts/137#prov1 text body True None body body True p14:body_region:1 page_body column_2_of_2 2 2 p14:page_body:column_2_of_2:white [255, 255, 255] white False False [306.59, 67.96, 251.07, 112.02] moted initial Coulombic efficiency, AlPO4 coating was also reported to improve the capacity stability [105,106]. Li3PO4 is another phosphate candidate for surface coating. Lee et al. synthesized Li1.2Ni0.2Mn0.6O2 with a… moted initial Coulombic efficiency, AlPO4 coating was also reported to improve the capacity stability [105,106]. Li3PO4 is another phosphate candidate for surface coating. Lee et al. synthesized Li1.2Ni0.2Mn0.6O2 with a… moted initial Coulombic efficiency, AlPO4 coating was also reported to improve the capacity stability [105,106]. Li3PO4 is another phosphate candidate for surface coating. Lee et al. synthesized Li1.2Ni0.2Mn0.6O2 with a thin Li3PO4 coating layer [107]. The coating was prepared during the synthesis of Li1.2Ni0.2Mn0.6O2, as illustrated in Fig. 8(a). As shown in Fig. 8(b), a thin Li3PO4 coating layer could be observed in TEM image, and it enhanced the rate performance of Li1.2Ni0.2Mn0.6O2. The same coating layer has also been achieved in Li1.2Ni0.13Co0.13Mn0.54O2 by polydopamine template method, which enhanced the cycling and rate performance [108]. moted initial Coulombic efficiency, AlPO4 coating was also reported to improve the capacity stability [105,106]. Li3PO4 is another phosphate candidate for surface coating. Lee et al. synthesized Li1.2Ni0.2Mn0.6O2 with a thin Li3PO4 coating layer [107]. The coating was prepared during the synthesis of Li1.2Ni0.2Mn0.6O2, as illustrated in Fig. 8(a). As shown in Fig. 8(b), a thin Li3PO4 coating layer could be observed in TEM image, and it enhanced the rate performance of Li1.2Ni0.2Mn0.6O2. The same coating layer has also been achieved in Li1.2Ni0.13Co0.13Mn0.54O2 by polydopamine template method, which enhanced the cycling and rate performance [108]. 14 7 8 151 #/texts/138#prov0 text body True None body body True p14:body_region:1 page_body column_2_of_2 2 2 p14:page_body:column_2_of_2:white [255, 255, 255] white False False [306.59, 182.99, 251.11, 258.51] Surface coating using fluorides, organic polymers, layered and spinel oxides etc. for LMR cathodes, have also been widely reported in recent years [109-113]. Zhang et al. successfully coated AlF3 at the surface of Li1.2… Surface coating using fluorides, organic polymers, layered and spinel oxides etc. for LMR cathodes, have also been widely reported in recent years [109-113]. Zhang et al. successfully coated AlF3 at the surface of Li1.2… Surface coating using fluorides, organic polymers, layered and spinel oxides etc. for LMR cathodes, have also been widely reported in recent years [109-113]. Zhang et al. successfully coated AlF3 at the surface of Li1.2Ni0.15Co0.10Mn0.55O2cathode. The AlF3 enhanced the structural stability and restricted the formation of the spinel structure at the surface, effectively suppressing the voltage decay during long-term cycling [111]. Pan et al. constructed a Li x TM3x O4-type spinel shell in Li1.2Ni0.13Co0.13Mn0.54O2 oxide by in situ electrochemical activation [114]. They found that this special spinel coating could slow down the activation of Li2MnO3 and alleviate the oxygen loss and Mn dissolution, suppressing the harmful structural degradation. Zhang et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 with a thin polyimide (PI) layer coated at the surface through polyacrylic acid (PAA) precursor, which improved the cycling stability and rate capability [109]. Multiple-layer coating could combine the function of individual coating layer together. Xu et al. designed a mesoporous Al2O3/polyacene double-shell at the surface of Li1.2Ni0.20Co0.08Mn0.52O2. They found that the best electrochemical performance was achieved when the coating was with 5 wt% of polyacene, and 98% of capacity retention could be obtained at 0.2 C after 100 cycles (Fig. 8c) [115]. Peng's group synthesized a sandwich-like carbon@spinel@layered@spinel@carbon shell at the surface of LMR cathode through a facile template-free method (Fig. 8d) [116]. Owing to the special shell structure, the as-prepared sample Surface coating using fluorides, organic polymers, layered and spinel oxides etc. for LMR cathodes, have also been widely reported in recent years [109-113]. Zhang et al. successfully coated AlF3 at the surface of Li1.2Ni0.15Co0.10Mn0.55O2cathode. The AlF3 enhanced the structural stability and restricted the formation of the spinel structure at the surface, effectively suppressing the voltage decay during long-term cycling [111]. Pan et al. constructed a Li x TM3x O4-type spinel shell in Li1.2Ni0.13Co0.13Mn0.54O2 oxide by in situ electrochemical activation [114]. They found that this special spinel coating could slow down the activation of Li2MnO3 and alleviate the oxygen loss and Mn dissolution, suppressing the harmful structural degradation. Zhang et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 with a thin polyimide (PI) layer coated at the surface through polyacrylic acid (PAA) precursor, which improved the cycling stability and rate capability [109]. Multiple-layer coating could combine the function of individual coating layer together. Xu et al. designed a mesoporous Al2O3/polyacene double-shell at the surface of Li1.2Ni0.20Co0.08Mn0.52O2. They found that the best electrochemical performance was achieved when the coating was with 5 wt% of polyacene, and 98% of capacity retention could be obtained at 0.2 C after 100 cycles (Fig. 8c) [115]. Peng's group synthesized a sandwich-like carbon@spinel@layered@spinel@carbon shell at the surface of LMR cathode through a facile template-free method (Fig. 8d) [116]. Owing to the special shell structure, the as-prepared sample 15 1 2 154 #/texts/138#prov1 text body True None body body True p15:body_region:0 front_matter column_1_of_2 1 2 p15:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 67.96, 251.1, 122.45] delivered a high initial Coulombic efficiency of 89.7% and superb cycling stability, which was demonstrated by a high capacity of 228.3 mA h g 1 after 200 cycles. Chen et al. employed inverse spinel-structured Mg2TiO4… delivered a high initial Coulombic efficiency of 89.7% and superb cycling stability, which was demonstrated by a high capacity of 228.3 mA h g 1 after 200 cycles. Chen et al. employed inverse spinel-structured Mg2TiO4… delivered a high initial Coulombic efficiency of 89.7% and superb cycling stability, which was demonstrated by a high capacity of 228.3 mA h g 1 after 200 cycles. Chen et al. employed inverse spinel-structured Mg2TiO4 coating to suppress oxygen evolution in Li1.2Ni0.13Co0.13Mn0.54O2 oxide [117]. This dielectric coating, through creating a reverse electric field at the surface, effectively restrained the outward migration of oxygen anions. The high oxygen-affinity elements Mg and Ti could also stabilize the surface oxygen via enhancing the energy barrier for the oxygen release. Compared to the unmodified counterpart, the modified electrode showed a superb capacity retention of ~ 81% after 700 cycles at 2C, as shown in Fig. 8(e). delivered a high initial Coulombic efficiency of 89.7% and superb cycling stability, which was demonstrated by a high capacity of 228.3 mA h g 1 after 200 cycles. Chen et al. employed inverse spinel-structured Mg2TiO4 coating to suppress oxygen evolution in Li1.2Ni0.13Co0.13Mn0.54O2 oxide [117]. This dielectric coating, through creating a reverse electric field at the surface, effectively restrained the outward migration of oxygen anions. The high oxygen-affinity elements Mg and Ti could also stabilize the surface oxygen via enhancing the energy barrier for the oxygen release. Compared to the unmodified counterpart, the modified electrode showed a superb capacity retention of ~ 81% after 700 cycles at 2C, as shown in Fig. 8(e). 15 4 3 155 #/texts/143 text body True None body body True p15:body_region:0 front_matter column_1_of_2 1 2 p15:front_matter:column_1_of_2:white [255, 255, 255] white False False [37.59, 193.47, 251.13, 332.49] In addition to these common surface coating, carbon coating or molten salt were also utilized. Carbon coating with a high electric conductivity can improve the electric contact between the particles, thus decreasing the… In addition to these common surface coating, carbon coating or molten salt were also utilized. Carbon coating with a high electric conductivity can improve the electric contact between the particles, thus decreasing the… In addition to these common surface coating, carbon coating or molten salt were also utilized. Carbon coating with a high electric conductivity can improve the electric contact between the particles, thus decreasing the polarization during chargingdischarging. Song et al. wrapped graphene oxide (GO) at the surface of sol-gel synthesized Li1.2Ni0.13Co0.13Mn0.54O2 oxide using a simple chemical approach and subsequent thermal annealing, as shown in Fig. 9(a) [118]. Most interestingly, spinel structure formed at the surface during annealing, which could be observed in HRTEM shown in Fig. 9(b). The modified Li1.2Ni0.13Co0.13Mn0.54O2 cathode displayed a high discharge capacity of 313 mA h g 1 at the current density of 12.5 mA g 1 and 201 mA h g 1 at the current density of 2500 mA g 1 , better than most of the LMR cathodes reported before. The superior rate performance could be attributed to the synergistic effect of the GO coating, the formed spinel structure during annealing, and the recrystallized particles at the surface of the primary particles. Guo et al. used molten MoO2S2 to treat the surface of LMR cathode through a novel chemicaladsorption method, and the detailed process is shown in Fig. 9(c) [119]. A continuous and uniform surface modification layer was obtained since Mo-S and Mo-O bonds in MoO2S2 could flexibly rotate and well connect with TM cations at the surface. Then, the thiomolybdate adsorption layer induced the formation of a spinel structured layer during subsequent annealing, which could provide extra pathways for Li + and electron diffusion (Fig. 9d). Meanwhile, the MoO3 x (SO4) x shell formed after MoO2S2 modification, which could suppress the decomposition of electrolyte and inhibit TM dissolution. Therefore, the modified LMR cathode displayed an increased capacity of 225 mA h g 1 at the current density of 100 mA g 1 , and showed nearly no capacity decay after 100 cycles. Other molten salt modifications have also been reported in recent years, such as Na2S2O8 andLiTaO3 [120,121]. In addition to these common surface coating, carbon coating or molten salt were also utilized. Carbon coating with a high electric conductivity can improve the electric contact between the particles, thus decreasing the polarization during chargingdischarging. Song et al. wrapped graphene oxide (GO) at the surface of sol-gel synthesized Li1.2Ni0.13Co0.13Mn0.54O2 oxide using a simple chemical approach and subsequent thermal annealing, as shown in Fig. 9(a) [118]. Most interestingly, spinel structure formed at the surface during annealing, which could be observed in HRTEM shown in Fig. 9(b). The modified Li1.2Ni0.13Co0.13Mn0.54O2 cathode displayed a high discharge capacity of 313 mA h g 1 at the current density of 12.5 mA g 1 and 201 mA h g 1 at the current density of 2500 mA g 1 , better than most of the LMR cathodes reported before. The superior rate performance could be attributed to the synergistic effect of the GO coating, the formed spinel structure during annealing, and the recrystallized particles at the surface of the primary particles. Guo et al. used molten MoO2S2 to treat the surface of LMR cathode through a novel chemicaladsorption method, and the detailed process is shown in Fig. 9(c) [119]. A continuous and uniform surface modification layer was obtained since Mo-S and Mo-O bonds in MoO2S2 could flexibly rotate and well connect with TM cations at the surface. Then, the thiomolybdate adsorption layer induced the formation of a spinel structured layer during subsequent annealing, which could provide extra pathways for Li + and electron diffusion (Fig. 9d). Meanwhile, the MoO3 x (SO4) x shell formed after MoO2S2 modification, which could suppress the decomposition of electrolyte and inhibit TM dissolution. Therefore, the modified LMR cathode displayed an increased capacity of 225 mA h g 1 at the current density of 100 mA g 1 , and showed nearly no capacity decay after 100 cycles. Other molten salt modifications have also been reported in recent years, such as Na2S2O8 andLiTaO3 [120,121]. 15 5 4 156 #/texts/144 text body True None body body True p15:body_region:0 body_zone column_1_of_2 1 2 p15:body_zone:column_1_of_2:white [255, 255, 255] white False False [37.59, 528.19, 251.13, 164.34] Although surface coating is one effective method to promote the electrochemistry, there are still some concerns during practical operations. (1) The uniformity of the coating. A uniform and thorough coating can effectiv… Although surface coating is one effective method to promote the electrochemistry, there are still some concerns during practical operations. (1) The uniformity of the coating. A uniform and thorough coating can effectiv… Although surface coating is one effective method to promote the electrochemistry, there are still some concerns during practical operations. (1) The uniformity of the coating. A uniform and thorough coating can effectively protect the active materials. Unfortunately, processing routes which can guarantee the uniformity, like ALD, can complicate the synthesis procedures and increase the cost. (2) The thickness of the coating materials. In consideration of the intrinsic inertness, a thick coating may inhibit the electron and Li + transport, and decrease the capacity and rate. (3) The binding force between the coating layer and the active material. The coating layer may fall off due to the volume change of cathode materials during cycling if the binding force is weak. High temperature calcination usually can improve the binding force. In brief, an ideal surface coating is a uniform coating with an optimized thickness and excellent binding force, and it should be implemented through a facile route. Although surface coating is one effective method to promote the electrochemistry, there are still some concerns during practical operations. (1) The uniformity of the coating. A uniform and thorough coating can effectively protect the active materials. Unfortunately, processing routes which can guarantee the uniformity, like ALD, can complicate the synthesis procedures and increase the cost. (2) The thickness of the coating materials. In consideration of the intrinsic inertness, a thick coating may inhibit the electron and Li + transport, and decrease the capacity and rate. (3) The binding force between the coating layer and the active material. The coating layer may fall off due to the volume change of cathode materials during cycling if the binding force is weak. High temperature calcination usually can improve the binding force. In brief, an ideal surface coating is a uniform coating with an optimized thickness and excellent binding force, and it should be implemented through a facile route. 15 7 6 158 #/texts/146#prov0 text body True None body body True p15:body_region:0 bottom_margin column_1_of_2 1 2 p15:bottom_margin:column_1_of_2:white [255, 255, 255] white False False [37.59, 719.87, 251.1, 28.34] Surface doping is an effective way to improve electron and ion conductivity (Table 6). Li et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 through a coprecipitation method and performed Zr surface doping Surface doping is an effective way to improve electron and ion conductivity (Table 6). Li et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 through a coprecipitation method and performed Zr surface doping Surface doping is an effective way to improve electron and ion conductivity (Table 6). Li et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 through a coprecipitation method and performed Zr surface doping Surface doping is an effective way to improve electron and ion conductivity (Table 6). Li et al. synthesized Li1.2Ni0.13Co0.13Mn0.54O2 through a coprecipitation method and performed Zr surface doping 15 8 8 160 #/texts/146#prov1 text body True None body body True p15:body_region:1 front_matter column_2_of_2 2 2 p15:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 67.95, 251.06, 237.53] using a wet chemical method [122]. They found Zr element distributedwithinathicknessof1-2nmfromthesurface,andthislayer appeared in the form of rock-salt structure, as shown in Fig. 10(a). The modified sample exhibited b… using a wet chemical method [122]. They found Zr element distributedwithinathicknessof1-2nmfromthesurface,andthislayer appeared in the form of rock-salt structure, as shown in Fig. 10(a). The modified sample exhibited b… using a wet chemical method [122]. They found Zr element distributedwithinathicknessof1-2nmfromthesurface,andthislayer appeared in the form of rock-salt structure, as shown in Fig. 10(a). The modified sample exhibited better cycling stability compared to un-modified one, and it could retain 83% of the initial capacity after 100 cycles at 1/3C, as shown in Fig. 10(b). The promoted cycling properties could be attributed to the rock-salt structure formed at the surface, which could inhibit the formation of spinel phase during the first cycling. As shown in Fig. 10(c), no spinel structure could be observed in the modified Li1.2Ni0.13Co0.13Mn0.54O2 cathode after 100 cycles. Al doping has been reported as another effective way to promote the performance of LMR cathodes [123]. Nayak et al. doped Li1.2Ni0.16Mn0.56Co0.08O2 (Fig. 10d) with different contents of Al element and found that Li1.2Ni0.16Mn0.51Al0.05Co0.08O2 exhibited the best electrochemical performance [124]. The cooperation of Al element at the surface and in the bulk could be accomplished at this ratio, and it not only decreased the impendence but also stabilized the bulk structure. As shown in Fig. 10(e), the voltage decay was also effectively suppressed during long-term cycling. Furthermore, surface modifications of LMR cathodes using nickel and potassium elements have also been reported in previous studies, all of which exhibited better electrochemical performance compared to the unmodified LMR cathodes [125,126]. using a wet chemical method [122]. They found Zr element distributedwithinathicknessof1-2nmfromthesurface,andthislayer appeared in the form of rock-salt structure, as shown in Fig. 10(a). The modified sample exhibited better cycling stability compared to un-modified one, and it could retain 83% of the initial capacity after 100 cycles at 1/3C, as shown in Fig. 10(b). The promoted cycling properties could be attributed to the rock-salt structure formed at the surface, which could inhibit the formation of spinel phase during the first cycling. As shown in Fig. 10(c), no spinel structure could be observed in the modified Li1.2Ni0.13Co0.13Mn0.54O2 cathode after 100 cycles. Al doping has been reported as another effective way to promote the performance of LMR cathodes [123]. Nayak et al. doped Li1.2Ni0.16Mn0.56Co0.08O2 (Fig. 10d) with different contents of Al element and found that Li1.2Ni0.16Mn0.51Al0.05Co0.08O2 exhibited the best electrochemical performance [124]. The cooperation of Al element at the surface and in the bulk could be accomplished at this ratio, and it not only decreased the impendence but also stabilized the bulk structure. As shown in Fig. 10(e), the voltage decay was also effectively suppressed during long-term cycling. Furthermore, surface modifications of LMR cathodes using nickel and potassium elements have also been reported in previous studies, all of which exhibited better electrochemical performance compared to the unmodified LMR cathodes [125,126]. 15 9 9 161 #/texts/147 text body True None body body True p15:body_region:1 front_matter column_2_of_2 2 2 p15:front_matter:column_2_of_2:white [255, 255, 255] white False False [306.59, 308.56, 251.08, 185.21] In addition to cation doping, anion doping is another route for enhancing LMR cathodes. One of the most widely reported doping elements is fluorine, which has also been widely used to dope others layered cathodes [127,1… In addition to cation doping, anion doping is another route for enhancing LMR cathodes. One of the most widely reported doping elements is fluorine, which has also been widely used to dope others layered cathodes [127,1… In addition to cation doping, anion doping is another route for enhancing LMR cathodes. One of the most widely reported doping elements is fluorine, which has also been widely used to dope others layered cathodes [127,128]. Lin et al. found that, after the surface F doping, the cyclic stability was greatly enhanced, delivering a capacity retention of 93.6% after 100 cycles at 1C [129]. Though surface F doping, Yang et al. demonstrated that the formation of vicious LiF in the SEI layer was suppressed, and thus stabilizing the electrode/electrolyte interface [130]. Breddemann et al. successfully doped F element in Li1.15Ni0.20Co0.11Mn0.55O2 by introducing fluorine gas [131]. They discovered that the rate performance of F-doped LMR cathode was closely related to the F doping content, and it was improved with a low content of F element. This might be attributed to that, the effect of F element only occurred at the surface, and too much F would decrease Li + diffusivity in the bulk. Polyanion doping has also been reported recently, and it could also promote the electrochemical performance of LMR cathode to varied extents [132,133]. In addition to cation doping, anion doping is another route for enhancing LMR cathodes. One of the most widely reported doping elements is fluorine, which has also been widely used to dope others layered cathodes [127,128]. Lin et al. found that, after the surface F doping, the cyclic stability was greatly enhanced, delivering a capacity retention of 93.6% after 100 cycles at 1C [129]. Though surface F doping, Yang et al. demonstrated that the formation of vicious LiF in the SEI layer was suppressed, and thus stabilizing the electrode/electrolyte interface [130]. Breddemann et al. successfully doped F element in Li1.15Ni0.20Co0.11Mn0.55O2 by introducing fluorine gas [131]. They discovered that the rate performance of F-doped LMR cathode was closely related to the F doping content, and it was improved with a low content of F element. This might be attributed to that, the effect of F element only occurred at the surface, and too much F would decrease Li + diffusivity in the bulk. Polyanion doping has also been reported recently, and it could also promote the electrochemical performance of LMR cathode to varied extents [132,133]. 15 11 11 163 #/texts/149 text body True None body body True p15:body_region:1 body_zone column_2_of_2 2 2 p15:body_zone:column_2_of_2:white [255, 255, 255] white False False [306.6, 521.1, 251.08, 206.18] Erickson et al. synthesized a LMR material with ammonia surface modification [134]. Co and Mn reduction in the bulk and the formation of LiOH, Li2CO3, and Li2O at the surface (due to removal of Li-ion from the bulk) cou… Erickson et al. synthesized a LMR material with ammonia surface modification [134]. Co and Mn reduction in the bulk and the formation of LiOH, Li2CO3, and Li2O at the surface (due to removal of Li-ion from the bulk) cou… Erickson et al. synthesized a LMR material with ammonia surface modification [134]. Co and Mn reduction in the bulk and the formation of LiOH, Li2CO3, and Li2O at the surface (due to removal of Li-ion from the bulk) could be observed in the ammonia modified LMR cathode. In addition, the structure rearrangement occurred in the bulk of ammonia modified LMR cathode, and it reduced the coordination number of Co-O and Mn-O bonds, inhibiting the forming of spinel phase. Therefore, the ammonia modified LMR cathode exhibited superior capacity and voltage retention, much better than the un-modified LMR cathode. Similar work has also been reported by Zhang et al., who applied a surface nitridation treatment to Li1.17Ni0.25Mn0.58O2 [135]. The nitridation treatment was accomplished by heating Li1.17Ni0.25Mn0.58O2 at 400 ℃ in the ammonia atmosphere. A trace amount of nitrogen was detected at the surface by XRD, SEM, TEM and X-ray photoelectron spectroscopy (XPS). Owing to the high electrocatalytic activity of nitrogen, the discharge capacity, rate capability, and cycling stability were simultaneously promoted. The modified cathode exhibited a discharge capacity of 255.5 mA h g 1 and nearly no capacity decay was observed after 60 cycles at the current density of 30 mA g 1 . Erickson et al. synthesized a LMR material with ammonia surface modification [134]. Co and Mn reduction in the bulk and the formation of LiOH, Li2CO3, and Li2O at the surface (due to removal of Li-ion from the bulk) could be observed in the ammonia modified LMR cathode. In addition, the structure rearrangement occurred in the bulk of ammonia modified LMR cathode, and it reduced the coordination number of Co-O and Mn-O bonds, inhibiting the forming of spinel phase. Therefore, the ammonia modified LMR cathode exhibited superior capacity and voltage retention, much better than the un-modified LMR cathode. Similar work has also been reported by Zhang et al., who applied a surface nitridation treatment to Li1.17Ni0.25Mn0.58O2 [135]. The nitridation treatment was accomplished by heating Li1.17Ni0.25Mn0.58O2 at 400 ℃ in the ammonia atmosphere. A trace amount of nitrogen was detected at the surface by XRD, SEM, TEM and X-ray photoelectron spectroscopy (XPS). Owing to the high electrocatalytic activity of nitrogen, the discharge capacity, rate capability, and cycling stability were simultaneously promoted. The modified cathode exhibited a discharge capacity of 255.5 mA h g 1 and nearly no capacity decay was observed after 60 cycles at the current density of 30 mA g 1 . 15 12 12 164 #/texts/150#prov0 text body True None body body True p15:body_region:1 bottom_margin column_2_of_2 2 2 p15:bottom_margin:column_2_of_2:white [255, 255, 255] white False False [306.6, 730.3, 251.07, 17.91] In addition, introducing electrolyte additives to form a protective interface for LMR cathodes is also an effective method. Zheng In addition, introducing electrolyte additives to form a protective interface for LMR cathodes is also an effective method. Zheng In addition, introducing electrolyte additives to form a protective interface for LMR cathodes is also an effective method. Zheng In addition, introducing electrolyte additives to form a protective interface for LMR cathodes is also an effective method. Zheng 16 1 3 168 #/texts/150#prov1 text body True None body body True p16:body_region:0 front_matter left_crossing None None p16:front_matter:left_crossing:white [255, 255, 255] white False False [37.59, 67.96, 251.1, 101.53] et al. utilized the phenyl vinyl sulfone (PVS) as a novel electrolyte additive and the cycling stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode was markedly promoted [136]. This could be attributed to the function of PVS … et al. utilized the phenyl vinyl sulfone (PVS) as a novel electrolyte additive and the cycling stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode was markedly promoted [136]. This could be attributed to the function of PVS … et al. utilized the phenyl vinyl sulfone (PVS) as a novel electrolyte additive and the cycling stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode was markedly promoted [136]. This could be attributed to the function of PVS molecule: the aromatic ring enhanced the chemical stability of the interface, and the sulfur enhanced the ionic conductivity. Tan et al. used (C3HF6O)3PO (HFiP) as the electrolyte additive for Li1.2Ni0.16Co0.08Mn0.56O2 cathode [137]. HFiP could decompose at the surface of the LMR cathode around 4.2 V (before the decomposition of the solvents) to form a stable CEI layer, which greatly promoted the cycling performance. et al. utilized the phenyl vinyl sulfone (PVS) as a novel electrolyte additive and the cycling stability of Li1.2Ni0.13Co0.13Mn0.54O2 cathode was markedly promoted [136]. This could be attributed to the function of PVS molecule: the aromatic ring enhanced the chemical stability of the interface, and the sulfur enhanced the ionic conductivity. Tan et al. used (C3HF6O)3PO (HFiP) as the electrolyte additive for Li1.2Ni0.16Co0.08Mn0.56O2 cathode [137]. HFiP could decompose at the surface of the LMR cathode around 4.2 V (before the decomposition of the solvents) to form a stable CEI layer, which greatly promoted the cycling performance. 16 4 7 172 #/texts/154 text body True None body body True p16:body_region:0 front_matter left_crossing None None p16:front_matter:left_crossing:white [255, 255, 255] white False False [37.59, 172.55, 251.12, 80.66] It is possible to achieve multiple purposes in one-pass surface treatment, including elemental doping, surface coating, the formation of surficial spinel phase, and etc. The combination of these modifications may lead t… It is possible to achieve multiple purposes in one-pass surface treatment, including elemental doping, surface coating, the formation of surficial spinel phase, and etc. The combination of these modifications may lead t… It is possible to achieve multiple purposes in one-pass surface treatment, including elemental doping, surface coating, the formation of surficial spinel phase, and etc. The combination of these modifications may lead to better performance than the individual modification mentioned above. However, it is also more difficult to precisely control the effect of each individual medication. Nevertheless, it is normally difficult to ensure a uniform surface after modifications. It is possible to achieve multiple purposes in one-pass surface treatment, including elemental doping, surface coating, the formation of surficial spinel phase, and etc. The combination of these modifications may lead to better performance than the individual modification mentioned above. However, it is also more difficult to precisely control the effect of each individual medication. Nevertheless, it is normally difficult to ensure a uniform surface after modifications. 16 6 20 185 #/texts/156 text body True None body body True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 304.19, 251.1, 91.09] In conclusion, LMR layered oxide as one of the most promising next-generation cathodes, still suffers some disadvantages, including the low initial Coulombic efficiency, poor rate performance, and severe voltage and cap… In conclusion, LMR layered oxide as one of the most promising next-generation cathodes, still suffers some disadvantages, including the low initial Coulombic efficiency, poor rate performance, and severe voltage and cap… In conclusion, LMR layered oxide as one of the most promising next-generation cathodes, still suffers some disadvantages, including the low initial Coulombic efficiency, poor rate performance, and severe voltage and capacity decay. In order to accelerate its commercialization, researchers have developed various effective methods in recent years. We divide these methods into three categories (Fig. 11), and introduce them through various cases in details. Moreover, the issues and limitations for each method are also discussed. In conclusion, LMR layered oxide as one of the most promising next-generation cathodes, still suffers some disadvantages, including the low initial Coulombic efficiency, poor rate performance, and severe voltage and capacity decay. In order to accelerate its commercialization, researchers have developed various effective methods in recent years. We divide these methods into three categories (Fig. 11), and introduce them through various cases in details. Moreover, the issues and limitations for each method are also discussed. 16 7 28 193 #/texts/157 text body True None body body True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 398.3, 251.06, 28.34] Although a large number of research achievements have been reported, there are still some concerns to be considered before successful commercialization. Although a large number of research achievements have been reported, there are still some concerns to be considered before successful commercialization. Although a large number of research achievements have been reported, there are still some concerns to be considered before successful commercialization. Although a large number of research achievements have been reported, there are still some concerns to be considered before successful commercialization. 16 8 31 196 #/texts/158 list_item body True None recovered_body_outside_flow recovered_body_outside_flow True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 429.71, 251.07, 28.34] Although the initial Coulombic efficiency of LMR cathode has been promoted by the modification methods mentioned above, it still cannot meet the requirement for a practical LIB system. Although the initial Coulombic efficiency of LMR cathode has been promoted by the modification methods mentioned above, it still cannot meet the requirement for a practical LIB system. Although the initial Coulombic efficiency of LMR cathode has been promoted by the modification methods mentioned above, it still cannot meet the requirement for a practical LIB system. Although the initial Coulombic efficiency of LMR cathode has been promoted by the modification methods mentioned above, it still cannot meet the requirement for a practical LIB system. 16 9 34 199 #/texts/159 list_item body True None recovered_body_outside_flow recovered_body_outside_flow True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 461.06, 251.09, 38.82] The previously reported modification methods can only promote the electrochemical performance of LMR cathode in one or two aspects, which cannot solve all the problems mentioned above. Thus, better modification methods … The previously reported modification methods can only promote the electrochemical performance of LMR cathode in one or two aspects, which cannot solve all the problems mentioned above. Thus, better modification methods … The previously reported modification methods can only promote the electrochemical performance of LMR cathode in one or two aspects, which cannot solve all the problems mentioned above. Thus, better modification methods still need to be developed. The previously reported modification methods can only promote the electrochemical performance of LMR cathode in one or two aspects, which cannot solve all the problems mentioned above. Thus, better modification methods still need to be developed. 16 10 38 203 #/texts/160 list_item body True None recovered_body_outside_flow recovered_body_outside_flow True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 502.96, 251.08, 28.34] The processing cost should be considered. Most of the modification methods mentioned above are complex and expensive, and they are not ready for extensive application. The processing cost should be considered. Most of the modification methods mentioned above are complex and expensive, and they are not ready for extensive application. The processing cost should be considered. Most of the modification methods mentioned above are complex and expensive, and they are not ready for extensive application. The processing cost should be considered. Most of the modification methods mentioned above are complex and expensive, and they are not ready for extensive application. 16 11 41 206 #/texts/161 list_item body True None recovered_body_outside_flow recovered_body_outside_flow True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 534.31, 251.11, 38.82] It is recommended to improve the performance of LMR cathode from the aspect of the structure unit design, since the electrochemical performance largely depends on the structure units, and little related work is reported. It is recommended to improve the performance of LMR cathode from the aspect of the structure unit design, since the electrochemical performance largely depends on the structure units, and little related work is reported. It is recommended to improve the performance of LMR cathode from the aspect of the structure unit design, since the electrochemical performance largely depends on the structure units, and little related work is reported. It is recommended to improve the performance of LMR cathode from the aspect of the structure unit design, since the electrochemical performance largely depends on the structure units, and little related work is reported. 16 12 45 210 #/texts/162 list_item body True None recovered_body_outside_flow recovered_body_outside_flow True p16:body_region:0 body_zone left_crossing None None p16:body_zone:left_crossing:white [255, 255, 255] white False False [37.59, 576.15, 251.1, 101.58] Compared with LCO, LMR cathode has a low tap density due to the polycrystalline morphology consisting of nanosized primary particles. Therefore, the tap density of LMR cathode should be promoted a lot before the commerc… Compared with LCO, LMR cathode has a low tap density due to the polycrystalline morphology consisting of nanosized primary particles. Therefore, the tap density of LMR cathode should be promoted a lot before the commerc… Compared with LCO, LMR cathode has a low tap density due to the polycrystalline morphology consisting of nanosized primary particles. Therefore, the tap density of LMR cathode should be promoted a lot before the commercialization. One effective method to promote the tap density of the layered materials is to synthesize single crystal layered materials, which has been utilized in LCO and Ni-rich NMC cathode [138,139]. The single-crystal layered cathodes can achieve a larger tap density compared to secondary-particle layered cathodes, because the density of a single crystal particle is close to the theoretical value. Compared with LCO, LMR cathode has a low tap density due to the polycrystalline morphology consisting of nanosized primary particles. Therefore, the tap density of LMR cathode should be promoted a lot before the commercialization. One effective method to promote the tap density of the layered materials is to synthesize single crystal layered materials, which has been utilized in LCO and Ni-rich NMC cathode [138,139]. The single-crystal layered cathodes can achieve a larger tap density compared to secondary-particle layered cathodes, because the density of a single crystal particle is close to the theoretical value.