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      "text": "Anionic and cationic redox chemistries boost ultrahigh specific capacities of Li-rich Mn-based oxides cathodes (LRMO). However, irreversible oxygen evolution and sluggish kinetics result in continuous capacity decay and poor rate performance, restricting the commercial fast-charging cathodes application for lithium ion batteries. Herein, the local electronic structure of LRMO is appropriately modulated to alleviate oxygen release, enhance anionic redox reversibility, and facilitate Li+ diffusion via facile surface defect engineering. Concretely, oxygen vacancies integrated on the surface of LRMO reduce the density of states of O 2p band and trigger much delocalized electrons to distribute around the transition metal, resulting in less oxygen release, enhancing reversible anionic redox and the MnO6 octahedral distortion. Besides, partially reduced Mn and lattice vacancies synchronously stimulate the electrochemical activity and boost the electronic conductivity, Li+ diffusion rate, and fast charge transfer. Therefore, the modified LRMO exhibits enhanced cyclic stability and fast-charging capability: a high discharging capacity of 212.6 mAh·g−1 with 86.98% capacity retention after 100 cycles at 1 C is obtained and to charge to its 80%, SOC is shortened to 9.4 min at 5 C charging rate. This work will draw attention to boosting the fast-charging capability of LRMO via the local electronic structure modulation.",
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      "text": "X. Gao, H. Zhang, S. Li, S. Zhang, J. Guo, Y. Lai, Z. Zhang School of Metallurgy and Environment Hunan Province Key Laboratory of Nonferrous Value-Added Metallurgy Engineering Research Center of the Ministry of Education for Advanced Battery Materials Central South University Changsha, Hunan 410083, P. R. China E-mail: laiyanqingcsu@163.com;zhangzhian@csu.edu.cn H.Zhang Hunan Changyuan LiCo Co.,Ltd Changsha,Hunan 410205,P.R.China C.Guan University of Michigan-Shanghai Jiao Tong University Joint Institute Shanghai Jiao Tong University 800 Dongchuan Road,Shanghai 200240,P.R.China X.Hu School of Materials ScienceandEngineering Central South University Changsha,Hunan 410083,P.R.China",
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      "text": "constructed oxygen vacancy and Li4Mn5O12 on the surface of Li- rich oxide layered cathodes by using a facile oxalic acid assisted delithiation process.[10] The irreversible release of oxygen and voltage decay were obviously alleviated. Therefore, surface defect engineering is a direct and feasible way for tuning the lattice oxy- gen redox and suppressing the irreversible oxygen loss. Neverthe- less, to the best of our knowledge, few study and detailed analyses pay attention to boost the kinetics of reversible anionic redox and fast-charging capability for LRMO materials via surface defect en- gineering. Herein, as shown in Figure 1, a moderate surface defects con- struction strategy with ammonium oxalate thermal treatment is successfully realized for manufacturing oxygen vacancies and spinel-like structure on the surface. The underlying mechanisms of surface defect structure on enhancing the cyclic stability, re- versible oxygen redox, and fast-charging capability are revealed by different characterizations. Oxygen vacancies are able to mod- ulate the local electronic structure via decreasing the density of states of O 2p band and increasing the delocalized electrons to distribute around the transition metal, which is beneficial for pre- cluding the release of oxygen, enhancing reversible oxygen redox and improving the MnO6 octahedral distortion. Moreover, under the synergistic function of oxygen vacancies and partial reduced Mn, the electrochemical activity of Li2MnO3 phase is effectively stimulated with increasing electrical conductivity and fast charge transfer. In addition, the spinel phase possessing 3D Li+ channels embedded in the surface of LRMO can also accelerate the Li+ dif- fusion rate. As a result, the modified material displays improved",
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      "text": "and NHCO-8 samples, respectively. The pristine LRMO without any modification is marked as P0 sample. Figure 2a shows the XRD patterns of P0 and NHCO-5 samples. The narrow and sharp peaks of both the samples demonstrate the good crystallinity. The apparent peaks belonging to the hexagonal 𝛼-NaFeO2 structure with space group R-3m can be observed. Several weak peaks lo- cated at ≈20–25° are assigned to the monoclinic Li2MnO3 phase with space group C2/m, possessing the unique superlattice honeycomb ordering structure[22]. No new phase is found after",
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      "text": "rates of 0.1, 0.2, 0.5, 1, 2, and 5 C, respectively. However, NHCO-5 electrode exhibits superior rate performance with low voltage po- larization. The capacities of NHCO-5 electrode are 292.9, 278.1, 256.7, 240.7, 219.9, and 180.7 mAh·g−1 at rates of 0.1, 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than the values of P0 electrode (Figure 4c). The enhanced rate performance is suit- able for the commercial application of fast-charging lithium ion batteries. As anticipated, the NHCO-5 electrode exhibits excellent cyclic stability due to the enhanced anionic redox and alleviation of oxygen release after surface treatment: high initial reversible discharging capacity of 244.4 and 212.6 mAh·g−1 with capacity retention of 86.98% after 100 cycles at 1 C can still be obtained (Figure 4d). To further examine the fast-charging properties of modified material, both the electrodes were charged at 3 or 5 C and discharged at 1 C for the fast-charging performance assessment. Figure 4e–i; Figure S5c–f, Supporting Information exhibits the relevant electrochemical results. Figure 4e,f; Figure S5c,d,",
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      "text": "and less than P0 (≈11 min), as seen in the Figure 4h. Figure S5f, Supporting Information; Figure 5i show the comparison of the cycling performance of P0 and NHCO-5 electrodes at 3 and 5 C fast-charging rate. P0 and NHCO-5 electrodes have similar initial charging capacity and show little difference on capacity loss as cycled at 3 C fast-charging rate after 100 cycles. Nevertheless, NHCO-5 electrode still can deliver high reversible initial dis- charged capacity of ≈250 mAh·g−1 and obtain a reversible capac- ity of 189.4 mAh·g−1 as cycled at 5 C after 150 cycles. These results have clearly demonstrated that the 5 C fast charging capability of LRMO is enhanced after ammonium oxalate treatment. The sur- face spinel phase provides a 3D lithium-ion channel with fast Li+",
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      "text": "diffusion, and oxygen vacancies can synergistically improve the electronic and ionic conductivity of LRMO.[9b,17c] Therefore, the increasing fast-charging capability is ascribed to the enhanced diffusion kinetic and fast charge transfer after the local electronic structure modulation via surface defect engineering.[24]",
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      "text": "Supporting Information, shows the first and last charge and dis- charge curves at 3 and 5 C charging rate, respectively. There is no obvious difference as charged at 3 C for the two electrodes. How- ever, P0 electrode shows larger voltage polarization as charged at 5 C in comparison with NHCO-5 electrode, indicating surface defect and spinel phase can reduce voltage polarization. The capacity of P0 and NHCO-5 electrodes obtained from constant current charging (CC-Capacity) and constant voltage charging (CV-Capacity) section at 3 and 5 C rate are shown in Figure S5e, Supporting Information; Figure 4 g, respectively. To charge more capacity during the constant current charging state can shorten the total charging time. The charging capacity of P0 and NHCO-5 electrodes driving from CC-Capacity and CV-Capacity show less difference as charged at 3 C. However, higher capacity of NHCO- 5 electrode can be obtained from the CC-Capacity section than P0 electrode at 5 C fast-charging rate. Consequently, the time to charge 80% SOC capacity of NHCO-5 can be shortened to 9.4 min",
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      "text": "shows the EIS Nyquist plots of P0 and NHCO-5 electrodes be- fore electrochemical cycles. All the curves include three regions. A small interrupt in the high frequency represents the Ohmic re- sistance (Rs) of the cell. One semicircle in the middle-high fre- quency represents the charge transfer resistance (Rct). A slop- ing line in the low-frequency regions represents the Warburg impedance (W).[10] The related fitting parameters are listed in Table S2, Supporting Information. The Rct of NHCO-5 is 7.525 Ω smaller than P0 (9.660 Ω), demonstrating a low charge transfer",
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      "text": "As far as mechanisms of the improved rate performance and fast-charging capability are concerned, previous reports have demonstrated that oxygen redox chemistry results in sluggish kinetics with low Li+ diffusion rate and high charge-transfer resistance.[5c,25] Therefore, tuning anionic redox chemistry plays a vital role in raising the electrochemical performance with ex- cellent fast-charging capability. EIS and the GITT were em- ployed to measure the kinetic variation before and after the elec- tronic structure modulation. Figure S6a, Supporting Information",
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      "text": "impedance of NHCO-5 with surface defect construction.[17c] The GITT measurement is also conducted to compare the kinetic per- formance of P0 and NHCO-5 electrodes after five cycles at 0.04 C (Figure S6b, Supporting Information). Figure S6c,d, Support- ing Information, show the calculated DLi + of the charging and discharging process according to the Equation (S2), Supporting Information. The DLi + of the NHCO-5 electrode in “sluggish ki- netic region” (<3.5 V and >4.0 V) is increased in comparison with P0. The average DLi + of NHCO-5 electrode in “sluggish kinetic region” is 8.70 × 10−10 cm2 s−1 and 6.40 × 10−10 cm2 s−1 during charging process and discharging process respectively, which is larger than the values of 5.97 × 10−10 cm2 s−1 and 4.56 × 10−10 cm2",
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      "text": "s−1 for P0 electrode. The improved lithium diffusion rate and fast charge transfer, ascribing to the local electronic structure modu- lation, result in boosting the rate performance and fast-charging capability of LRMO. The O 1s XPS spectra of P0 and NHCO-5 electrodes at charg- ing and discharging state in the first cycle are conducted for ex- ploring the mechanisms of oxygen redox (Figure 5a,b). Three obvious peaks appearing at ≈529.5, ≈531.9, and ≈533.2 eV con- tributing to the lattice oxygen, oxygenated deposited species, and weak electrolyte oxidation, respectively, whether in the charging state of 4.8 V or discharging state 2.0 V, can be found.[26] However, an additional peak at ≈530.5 eV appears in both the XPS spec- tra of P0 and NHCO-5 electrodes at the charging state of 4.8 V, contributing to the preoxo-like O2 n−(n < 2) with a lower elec- tronic density in comparison with lattice oxygen (O2−).[9a] Never- theless, compared with P0 electrode, the larger area ratio of O2 n−",
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      "text": "increasing electrical conductivity, facilitating lithium ion diffu- sion and fast charge transfer, but also suppressing oxygen release and promoting the charge compensation of both cationic and an- ionic redox. To explore the structural evolution of P0 and NHCO-5 elec- trodes after 200 cycles, relevant characterizations were employed to study the changes of crystal structure and morphology. Figure 6a shows the comparison of XRD results for P0 and NHCO-5 electrodes after cycling. The value of I(003)/I(104) for P0 is smaller than NHCO-5, indicating the higher degree of cation mixing due to the irreversible migration of transition metal ions.[17a] In addition, Raman spectroscopy was also used to detect the surface structural evolution after cycling and the corresponding results are displayed in Figure 6b. Two obvious peaks located at around 480 and 605 cm−1 contribute to the vibrations of the layered structure with R-3m spacing group.[33]",
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      "text": "A weak peak at about 430 cm−1 is assigned to the Li2MnO3 phase. The peak II at around 650 cm−1 of both samples is the evidence of the spinel/rock-salt structure due to the shortening of M–O",
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      "text": "bonds.[5b] The smaller area ratio of spinel-like component for NHCO-5 suggests that minor structural transformation occurs from layer to spinel/rock-salt phase. It is mainly ascribed to be the fact that surface defect and spinel-like phase can stabilize the crystal structure via suppressing oxygen release. What is more, the impedance changes of P0 and NHCO-5 electrodes after cycling are also detected, as shown in Figure S8a, Supporting Information. Compared with the EIS spectra of P0 and NHCO-5 electrodes before cycling, additional semicircle belonging to the impedance Rf of cathode–electrolyte interphase (CEI) appears in the middle-high frequency after cycling. According to the equiv- alent circuit, the corresponding fitting parameters are listed in Table S2, Supporting Information. The impedance of CEI film and the charge transfer for NHCO-5 electrode are 8.81 and 36.28 Ω after cycling, respectively, lower than P0 electrode (10.01 and 40.09 Ω), demonstrating better CEI film with low impedance and fast charge transfer for NHCO-5. The contents of Mn and Co elements deposited on the anode after cycling are quantitated by the ICP-MS. The corresponding results are shown in Figure",
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      "text": "The authors acknowledge the financial support of the National Natural Sci- ence Foundation of China (52274309). This work also was supported by the Beamlines MCD–A and MCD–B (Soochow Beamline for Energy Mate- rials) at NSRL.",
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      "text": "In summary, a facile surface defect construction strategy is proved to address the issues of irreversible oxygen release and sluggish kinetic for Li-rich Mn-based oxides cathodes, result- ing in the excellent rate performance and fast-charging capabil- ity with enhanced reversible anionic redox. The modified mate- rial NHCO-5 with appropriate oxygen vacancies and integrated spinel-like phase significantly exhibits outstanding electrochem- ical performance, including a high reversible specific capacity of 297.0 mAh·g−1 with 86.98% capacity retention after 100 cy- cles, high capacity of 180.7 mAh·g−1 at 5 C, and excellent fast- charging capability. Systematical characterization and theoret- ical calculation confirm that the surface defect can modulate the local electronic structure around Mn and O for suppressing oxygen release, irreversible migration of transition metals, and phase transformation. Moreover, the electrochemical activity of Li2MnO3 phase is largely stimulated with the synergistic function of reduced Mn and oxygen vacancies, resulting in both reversible anionic and cationic redox during cycling. The improved elec- trical conductivity, fast charge transfer, and existence of spinel- like phase with 3D Li+ diffusion channels accelerates the kinetics of LRMO, contributing to the enhanced fast-charging capability. Therefore, we believe this work can provide new insight into en- hancing fast-charging capability with reversible anionic redox for LRMO via the strategy of modulating local electronic structure.",
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      "text": "X. Gao, H. Zhang, S. Li, S. Zhang, J. Guo, Y. Lai, Z. Zhang School of Metallurgy and Environment Hunan Province Key Laboratory of Nonferrous Value-Added Metallurgy Engineering Research Center of the Ministry of Education for Advanced Battery Materials Central South University Changsha, Hunan 410083, P. R. China E-mail: laiyanqingcsu@163.com;zhangzhian@csu.edu.cn H.Zhang Hunan Changyuan LiCo Co.,Ltd Changsha,Hunan 410205,P.R.China C.Guan University of Michigan-Shanghai Jiao Tong University Joint Institute Shanghai Jiao Tong University 800 Dongchuan Road,Shanghai 200240,P.R.China X.Hu School of Materials ScienceandEngineering Central South University Changsha,Hunan 410083,P.R.China",
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      "text": "and less than P0 (≈11 min), as seen in the Figure 4h. Figure S5f, Supporting Information; Figure 5i show the comparison of the cycling performance of P0 and NHCO-5 electrodes at 3 and 5 C fast-charging rate. P0 and NHCO-5 electrodes have similar initial charging capacity and show little difference on capacity loss as cycled at 3 C fast-charging rate after 100 cycles. Nevertheless, NHCO-5 electrode still can deliver high reversible initial dis- charged capacity of ≈250 mAh·g−1 and obtain a reversible capac- ity of 189.4 mAh·g−1 as cycled at 5 C after 150 cycles. These results have clearly demonstrated that the 5 C fast charging capability of LRMO is enhanced after ammonium oxalate treatment. The sur- face spinel phase provides a 3D lithium-ion channel with fast Li+",
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      "text": "diffusion, and oxygen vacancies can synergistically improve the electronic and ionic conductivity of LRMO.[9b,17c] Therefore, the increasing fast-charging capability is ascribed to the enhanced diffusion kinetic and fast charge transfer after the local electronic structure modulation via surface defect engineering.[24]",
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      "text": "Supporting Information, shows the first and last charge and dis- charge curves at 3 and 5 C charging rate, respectively. There is no obvious difference as charged at 3 C for the two electrodes. How- ever, P0 electrode shows larger voltage polarization as charged at 5 C in comparison with NHCO-5 electrode, indicating surface defect and spinel phase can reduce voltage polarization. The capacity of P0 and NHCO-5 electrodes obtained from constant current charging (CC-Capacity) and constant voltage charging (CV-Capacity) section at 3 and 5 C rate are shown in Figure S5e, Supporting Information; Figure 4 g, respectively. To charge more capacity during the constant current charging state can shorten the total charging time. The charging capacity of P0 and NHCO-5 electrodes driving from CC-Capacity and CV-Capacity show less difference as charged at 3 C. However, higher capacity of NHCO- 5 electrode can be obtained from the CC-Capacity section than P0 electrode at 5 C fast-charging rate. Consequently, the time to charge 80% SOC capacity of NHCO-5 can be shortened to 9.4 min",
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      "text": "shows the EIS Nyquist plots of P0 and NHCO-5 electrodes be- fore electrochemical cycles. All the curves include three regions. A small interrupt in the high frequency represents the Ohmic re- sistance (Rs) of the cell. One semicircle in the middle-high fre- quency represents the charge transfer resistance (Rct). A slop- ing line in the low-frequency regions represents the Warburg impedance (W).[10] The related fitting parameters are listed in Table S2, Supporting Information. The Rct of NHCO-5 is 7.525 Ω smaller than P0 (9.660 Ω), demonstrating a low charge transfer",
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      "text": "As far as mechanisms of the improved rate performance and fast-charging capability are concerned, previous reports have demonstrated that oxygen redox chemistry results in sluggish kinetics with low Li+ diffusion rate and high charge-transfer resistance.[5c,25] Therefore, tuning anionic redox chemistry plays a vital role in raising the electrochemical performance with ex- cellent fast-charging capability. EIS and the GITT were em- ployed to measure the kinetic variation before and after the elec- tronic structure modulation. Figure S6a, Supporting Information",
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      "text": "impedance of NHCO-5 with surface defect construction.[17c] The GITT measurement is also conducted to compare the kinetic per- formance of P0 and NHCO-5 electrodes after five cycles at 0.04 C (Figure S6b, Supporting Information). Figure S6c,d, Support- ing Information, show the calculated DLi + of the charging and discharging process according to the Equation (S2), Supporting Information. The DLi + of the NHCO-5 electrode in “sluggish ki- netic region” (<3.5 V and >4.0 V) is increased in comparison with P0. The average DLi + of NHCO-5 electrode in “sluggish kinetic region” is 8.70 × 10−10 cm2 s−1 and 6.40 × 10−10 cm2 s−1 during charging process and discharging process respectively, which is larger than the values of 5.97 × 10−10 cm2 s−1 and 4.56 × 10−10 cm2",
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      "text": "s−1 for P0 electrode. The improved lithium diffusion rate and fast charge transfer, ascribing to the local electronic structure modu- lation, result in boosting the rate performance and fast-charging capability of LRMO. The O 1s XPS spectra of P0 and NHCO-5 electrodes at charg- ing and discharging state in the first cycle are conducted for ex- ploring the mechanisms of oxygen redox (Figure 5a,b). Three obvious peaks appearing at ≈529.5, ≈531.9, and ≈533.2 eV con- tributing to the lattice oxygen, oxygenated deposited species, and weak electrolyte oxidation, respectively, whether in the charging state of 4.8 V or discharging state 2.0 V, can be found.[26] However, an additional peak at ≈530.5 eV appears in both the XPS spec- tra of P0 and NHCO-5 electrodes at the charging state of 4.8 V, contributing to the preoxo-like O2 n−(n < 2) with a lower elec- tronic density in comparison with lattice oxygen (O2−).[9a] Never- theless, compared with P0 electrode, the larger area ratio of O2 n−",
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      "text": "increasing electrical conductivity, facilitating lithium ion diffu- sion and fast charge transfer, but also suppressing oxygen release and promoting the charge compensation of both cationic and an- ionic redox. To explore the structural evolution of P0 and NHCO-5 elec- trodes after 200 cycles, relevant characterizations were employed to study the changes of crystal structure and morphology. Figure 6a shows the comparison of XRD results for P0 and NHCO-5 electrodes after cycling. The value of I(003)/I(104) for P0 is smaller than NHCO-5, indicating the higher degree of cation mixing due to the irreversible migration of transition metal ions.[17a] In addition, Raman spectroscopy was also used to detect the surface structural evolution after cycling and the corresponding results are displayed in Figure 6b. Two obvious peaks located at around 480 and 605 cm−1 contribute to the vibrations of the layered structure with R-3m spacing group.[33]",
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      "text": "A weak peak at about 430 cm−1 is assigned to the Li2MnO3 phase. The peak II at around 650 cm−1 of both samples is the evidence of the spinel/rock-salt structure due to the shortening of M–O",
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      "text": "bonds.[5b] The smaller area ratio of spinel-like component for NHCO-5 suggests that minor structural transformation occurs from layer to spinel/rock-salt phase. It is mainly ascribed to be the fact that surface defect and spinel-like phase can stabilize the crystal structure via suppressing oxygen release. What is more, the impedance changes of P0 and NHCO-5 electrodes after cycling are also detected, as shown in Figure S8a, Supporting Information. Compared with the EIS spectra of P0 and NHCO-5 electrodes before cycling, additional semicircle belonging to the impedance Rf of cathode–electrolyte interphase (CEI) appears in the middle-high frequency after cycling. According to the equiv- alent circuit, the corresponding fitting parameters are listed in Table S2, Supporting Information. The impedance of CEI film and the charge transfer for NHCO-5 electrode are 8.81 and 36.28 Ω after cycling, respectively, lower than P0 electrode (10.01 and 40.09 Ω), demonstrating better CEI film with low impedance and fast charge transfer for NHCO-5. The contents of Mn and Co elements deposited on the anode after cycling are quantitated by the ICP-MS. The corresponding results are shown in Figure",
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      "text": "The authors acknowledge the financial support of the National Natural Sci- ence Foundation of China (52274309). This work also was supported by the Beamlines MCD–A and MCD–B (Soochow Beamline for Energy Mate- rials) at NSRL.",
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      "text": "In summary, a facile surface defect construction strategy is proved to address the issues of irreversible oxygen release and sluggish kinetic for Li-rich Mn-based oxides cathodes, result- ing in the excellent rate performance and fast-charging capabil- ity with enhanced reversible anionic redox. The modified mate- rial NHCO-5 with appropriate oxygen vacancies and integrated spinel-like phase significantly exhibits outstanding electrochem- ical performance, including a high reversible specific capacity of 297.0 mAh·g−1 with 86.98% capacity retention after 100 cy- cles, high capacity of 180.7 mAh·g−1 at 5 C, and excellent fast- charging capability. Systematical characterization and theoret- ical calculation confirm that the surface defect can modulate the local electronic structure around Mn and O for suppressing oxygen release, irreversible migration of transition metals, and phase transformation. Moreover, the electrochemical activity of Li2MnO3 phase is largely stimulated with the synergistic function of reduced Mn and oxygen vacancies, resulting in both reversible anionic and cationic redox during cycling. The improved elec- trical conductivity, fast charge transfer, and existence of spinel- like phase with 3D Li+ diffusion channels accelerates the kinetics of LRMO, contributing to the enhanced fast-charging capability. Therefore, we believe this work can provide new insight into en- hancing fast-charging capability with reversible anionic redox for LRMO via the strategy of modulating local electronic structure.",
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      "text": "and less than P0 (≈11 min), as seen in the Figure 4h. Figure S5f, Supporting Information; Figure 5i show the comparison of the cycling performance of P0 and NHCO-5 electrodes at 3 and 5 C fast-charging rate. P0 and NHCO-5 electrodes have similar initial charging capacity and show little difference on capacity loss as cycled at 3 C fast-charging rate after 100 cycles. Nevertheless, NHCO-5 electrode still can deliver high reversible initial dis- charged capacity of ≈250 mAh·g−1 and obtain a reversible capac- ity of 189.4 mAh·g−1 as cycled at 5 C after 150 cycles. These results have clearly demonstrated that the 5 C fast charging capability of LRMO is enhanced after ammonium oxalate treatment. The sur- face spinel phase provides a 3D lithium-ion channel with fast Li+",
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      "text": "diffusion, and oxygen vacancies can synergistically improve the electronic and ionic conductivity of LRMO.[9b,17c] Therefore, the increasing fast-charging capability is ascribed to the enhanced diffusion kinetic and fast charge transfer after the local electronic structure modulation via surface defect engineering.[24]",
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      "text": "shows the EIS Nyquist plots of P0 and NHCO-5 electrodes be- fore electrochemical cycles. All the curves include three regions. A small interrupt in the high frequency represents the Ohmic re- sistance (Rs) of the cell. One semicircle in the middle-high fre- quency represents the charge transfer resistance (Rct). A slop- ing line in the low-frequency regions represents the Warburg impedance (W).[10] The related fitting parameters are listed in Table S2, Supporting Information. The Rct of NHCO-5 is 7.525 Ω smaller than P0 (9.660 Ω), demonstrating a low charge transfer",
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      "text": "As far as mechanisms of the improved rate performance and fast-charging capability are concerned, previous reports have demonstrated that oxygen redox chemistry results in sluggish kinetics with low Li+ diffusion rate and high charge-transfer resistance.[5c,25] Therefore, tuning anionic redox chemistry plays a vital role in raising the electrochemical performance with ex- cellent fast-charging capability. EIS and the GITT were em- ployed to measure the kinetic variation before and after the elec- tronic structure modulation. Figure S6a, Supporting Information",
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      "text": "impedance of NHCO-5 with surface defect construction.[17c] The GITT measurement is also conducted to compare the kinetic per- formance of P0 and NHCO-5 electrodes after five cycles at 0.04 C (Figure S6b, Supporting Information). Figure S6c,d, Support- ing Information, show the calculated DLi + of the charging and discharging process according to the Equation (S2), Supporting Information. The DLi + of the NHCO-5 electrode in “sluggish ki- netic region” (<3.5 V and >4.0 V) is increased in comparison with P0. The average DLi + of NHCO-5 electrode in “sluggish kinetic region” is 8.70 × 10−10 cm2 s−1 and 6.40 × 10−10 cm2 s−1 during charging process and discharging process respectively, which is larger than the values of 5.97 × 10−10 cm2 s−1 and 4.56 × 10−10 cm2",
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      "text": "s−1 for P0 electrode. The improved lithium diffusion rate and fast charge transfer, ascribing to the local electronic structure modu- lation, result in boosting the rate performance and fast-charging capability of LRMO. The O 1s XPS spectra of P0 and NHCO-5 electrodes at charg- ing and discharging state in the first cycle are conducted for ex- ploring the mechanisms of oxygen redox (Figure 5a,b). Three obvious peaks appearing at ≈529.5, ≈531.9, and ≈533.2 eV con- tributing to the lattice oxygen, oxygenated deposited species, and weak electrolyte oxidation, respectively, whether in the charging state of 4.8 V or discharging state 2.0 V, can be found.[26] However, an additional peak at ≈530.5 eV appears in both the XPS spec- tra of P0 and NHCO-5 electrodes at the charging state of 4.8 V, contributing to the preoxo-like O2 n−(n < 2) with a lower elec- tronic density in comparison with lattice oxygen (O2−).[9a] Never- theless, compared with P0 electrode, the larger area ratio of O2 n−",
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      "text": "increasing electrical conductivity, facilitating lithium ion diffu- sion and fast charge transfer, but also suppressing oxygen release and promoting the charge compensation of both cationic and an- ionic redox. To explore the structural evolution of P0 and NHCO-5 elec- trodes after 200 cycles, relevant characterizations were employed to study the changes of crystal structure and morphology. Figure 6a shows the comparison of XRD results for P0 and NHCO-5 electrodes after cycling. The value of I(003)/I(104) for P0 is smaller than NHCO-5, indicating the higher degree of cation mixing due to the irreversible migration of transition metal ions.[17a] In addition, Raman spectroscopy was also used to detect the surface structural evolution after cycling and the corresponding results are displayed in Figure 6b. Two obvious peaks located at around 480 and 605 cm−1 contribute to the vibrations of the layered structure with R-3m spacing group.[33]",
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      "text": "A weak peak at about 430 cm−1 is assigned to the Li2MnO3 phase. The peak II at around 650 cm−1 of both samples is the evidence of the spinel/rock-salt structure due to the shortening of M–O",
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      "text": "bonds.[5b] The smaller area ratio of spinel-like component for NHCO-5 suggests that minor structural transformation occurs from layer to spinel/rock-salt phase. It is mainly ascribed to be the fact that surface defect and spinel-like phase can stabilize the crystal structure via suppressing oxygen release. What is more, the impedance changes of P0 and NHCO-5 electrodes after cycling are also detected, as shown in Figure S8a, Supporting Information. Compared with the EIS spectra of P0 and NHCO-5 electrodes before cycling, additional semicircle belonging to the impedance Rf of cathode–electrolyte interphase (CEI) appears in the middle-high frequency after cycling. According to the equiv- alent circuit, the corresponding fitting parameters are listed in Table S2, Supporting Information. The impedance of CEI film and the charge transfer for NHCO-5 electrode are 8.81 and 36.28 Ω after cycling, respectively, lower than P0 electrode (10.01 and 40.09 Ω), demonstrating better CEI film with low impedance and fast charge transfer for NHCO-5. The contents of Mn and Co elements deposited on the anode after cycling are quantitated by the ICP-MS. The corresponding results are shown in Figure",
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      "text": "In summary, a facile surface defect construction strategy is proved to address the issues of irreversible oxygen release and sluggish kinetic for Li-rich Mn-based oxides cathodes, result- ing in the excellent rate performance and fast-charging capabil- ity with enhanced reversible anionic redox. The modified mate- rial NHCO-5 with appropriate oxygen vacancies and integrated spinel-like phase significantly exhibits outstanding electrochem- ical performance, including a high reversible specific capacity of 297.0 mAh·g−1 with 86.98% capacity retention after 100 cy- cles, high capacity of 180.7 mAh·g−1 at 5 C, and excellent fast- charging capability. Systematical characterization and theoret- ical calculation confirm that the surface defect can modulate the local electronic structure around Mn and O for suppressing oxygen release, irreversible migration of transition metals, and phase transformation. Moreover, the electrochemical activity of Li2MnO3 phase is largely stimulated with the synergistic function of reduced Mn and oxygen vacancies, resulting in both reversible anionic and cationic redox during cycling. The improved elec- trical conductivity, fast charge transfer, and existence of spinel- like phase with 3D Li+ diffusion channels accelerates the kinetics of LRMO, contributing to the enhanced fast-charging capability. Therefore, we believe this work can provide new insight into en- hancing fast-charging capability with reversible anionic redox for LRMO via the strategy of modulating local electronic structure.",
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      "text": "Supporting Information, shows the first and last charge and dis- charge curves at 3 and 5 C charging rate, respectively. There is no obvious difference as charged at 3 C for the two electrodes. How- ever, P0 electrode shows larger voltage polarization as charged at 5 C in comparison with NHCO-5 electrode, indicating surface defect and spinel phase can reduce voltage polarization. The capacity of P0 and NHCO-5 electrodes obtained from constant current charging (CC-Capacity) and constant voltage charging (CV-Capacity) section at 3 and 5 C rate are shown in Figure S5e, Supporting Information; Figure 4 g, respectively. To charge more capacity during the constant current charging state can shorten the total charging time. The charging capacity of P0 and NHCO-5 electrodes driving from CC-Capacity and CV-Capacity show less difference as charged at 3 C. However, higher capacity of NHCO- 5 electrode can be obtained from the CC-Capacity section than P0 electrode at 5 C fast-charging rate. Consequently, the time to charge 80% SOC capacity of NHCO-5 can be shortened to 9.4 min",
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      "text": "The authors acknowledge the financial support of the National Natural Sci- ence Foundation of China (52274309). This work also was supported by the Beamlines MCD–A and MCD–B (Soochow Beamline for Energy Mate- rials) at NSRL.",
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