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      "text": "decades. However, current commercialized LIBs cannot fulfill the demand for high en- ergy density and power density with the rapid development of modern industrial society.[1–4] As the critical component de- termining the energy density of LIBs, ad- vanced cathode materials urgently need to be developed, especially to solve the “range anxiety” in EVs.[5–7] From this per- spective, Lithium and manganese-rich lay- ered oxides (LMRO) with a formula of xLi2MnO3·(1-x)LiTMO2 (TM = Ni, Co, Mn, etc.) are considered one of the most promis- ing cathode materials for the next gener- ation advanced LIBs owing to their high capacity (>250 mAh g−1) and high en- ergy density (>1000 Wh kg−1), far exceed- ing the traditional cathode materials like LiCoO2, LiFePO4 and Ni-rich cathode.[8–14]",
      "category": "front_summary",
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      "text": "Anionic redox chemistry enables extraordinary capacity for Li- and Mn-rich layered oxides (LMROs) cathodes. Unfortunately, irreversible surface oxygen evolution evokes the pernicious phase transition, structural deterioration, and severe electrode-electrolyte interface side reaction with element dissolution, resulting in fast capacity and voltage fading of LMROs during cycling and hindering its commercialization. Herein, a redox couple strategy is proposed by utilizing copper phthalocyanine (CuPc) to address the irreversibility of anionic redox. The Cu-N synergistic effect of CuPc could not only inhibit surface oxygen evolution by reducing the peroxide ion O2 2−back to lattice oxygen O2−, but also enhance the reaction activity and reversibility of anionic redox in bulk to achieve a higher capacity and cycling stability. Moreover, the CuPc strategy suppresses the interface side reaction and induces the forming of a uniform and robust LiF-rich cathode electrolyte, interphase (CEI) to significantly eliminate transition metal dissolution. As a result, the CuPc-enhanced LMRO cathode shows superb cycling performance with a capacity retention of 95.0% after 500 long-term cycles. This study sheds light on the great effect of N-based redox couple to regulate anionic redox behavior and promote the development of high energy density and high stability LMROs cathode.",
      "category": "front_summary",
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      "text": "Based on extensive research, it is consen- sus that the extraordinarily high capac- ity of LMROs originated from the hybrid cationic and anionic redox reaction, and the anionic redox triggered above 4.4 V in- volves reversible oxygen redox occurring in the bulk (O2−→O2 2−) and irreversible oxygen gas release on the surface (O2−→O2).[15–18]",
      "category": "front_summary",
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      "text": "Second, oxygen loss would evoke the continual reduction of tran- sition metal to charge compensation, which activates the cation redox reaction of Co2+/Co3+ and Mn3+/4+, directly leading to the voltage fade.[23] Finally, the interface side reaction deteriorates LMROs as well. The releasing O2 in the form of oxygen radi- cal and O2·singlet will attack organic species, such as ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbon- ate (DEC) and lead to their decomposition and the formation of thick solid cathode-electrolyte interphase (CEI) layer on the sur- face, resulting in inferior Li+ diffusions and poor cyclability.[24,25]",
      "category": "scientific_body",
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      "text": "Moreover, LMROs also suffered from surface structure degrada- tion and transition metal dissolution originating from HF cor- rosion due to the decomposition of LiPF6.[26,27] Therefore, sup- pression of oxygen release and side reaction, and construction of uniform and stable CEI layer are vital to enable the practical application of LMROs material. Various strategies have been employed to solve the draw- backs of LMROs, including surface modification,[28,29] element doping,[30,31] structure design,[32,33] binder readjustment,[34,35]",
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      "text": "and electrolyte optimization.[25,36] Nonetheless, the mentioned strategies still have shortcomings in the complicated method, in- effective protection, and limited improvement of cyclic stability. The redox couple strategy has been proven to be a facile and efficacious approach to inhibit oxygen release and achieve out- standing electrochemical stability via chemically reducing the peroxide ion O2 2−back to stable lattice O2−during the dis- charging process.[37] However, previous research mainly focuses on sulfur elements and lacks discovery of other possible re- dox couples. Phthalocyanine as one type of porphyrin with an 18 𝜋electron aromatic cloud around the macrocycle has a N- redox activity,[38,39] and is widely applied in organic transistors, organic photovoltaics, and organic light-emitting diodes.[40–43]",
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      "text": "Inspired by this, herein, we introduce copper phthalocyanine (CuPc, C32H16CuN8) and other metal phthalocyanine derivatives into LMROs and find that CuPc serves as the best redox cou- ple. Detailed structural and chemical characterizations combined with electrochemical testing confirm that the N element in CuPc can serve as a redox activity center to reduce surface O2 2−to O2−, and a synergistic effect of Cu and N element ensures the reaction reversibility of CuPc, thus suppressing surface oxygen evolution and structural degradation. Moreover, CuPc can induce the for- mation of a uniform and robust LiF-rich CEI on the electrode sur- face suppress the transition metal dissolution, and prevent the cathode against side reactions. As a result, CuPc-enhanced elec- trodes exhibit excellent structural stability and deliver outstand- ing electrochemical performance with higher capacity and volt- age retention.",
      "category": "scientific_body",
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      "text": "Supporting Information) further confirm that the lattice param- eters of LMRO and LMRO@7CuPc electrodes keep well, indi- cating preparation process does not damage the bulk structure. Figure 1a–c shows the high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images of the as-prepared LMRO@7CuPc electrode. The particle has a coat- ing layer with ≈2 nm, while the bulk presents a layered struc- ture with the interplanar spacing of 2.34 Å corresponding to the (012) plane. STEM-energy dispersive spectroscopy (STEM-EDS) in Figure 1d reveals the elements of Mn, Ni, Co, O, and Cu and N of CuPc are uniformly distributed in the particle, confirming that CuPc is coated on the surface of the LMRO particle. The electrochemical performances of CuPc-enhanced elec- trodes in the voltage window of 2.0–4.8 V at 0.1 C and 1 C (1C = 200 mA g−1) are shown in Figure 2, and corresponding data are summarized in Table S2 (Supporting Information). Figure 2a shows the initial charge-discharge profile at 0.1 C. All electrodes display typical redox features of Li-rich cathode with a slope re- gion below 4.4 V associated with Ni2+/3+/4+ and Co3+/4+ cationic redox, and a long plateau ≈4.5 V associated with oxygen redox reaction.[16] Corresponding dQ/dV curves (Figure S3, Support- ing Information) well reflect these redox processes and CuPc en- hanced electrodes show no new redox reaction peak appears, and the peak area is almost uniform at ≈4.5 V during initial cycle, in- dicating that redox couple increases the redox reversibility of lat- tice oxygen during initial cycle, but does not increase the capacity because the introduction of the surface redox couple, the charge- transfer resistance of the electrode is increased since the surface coating layer is insulating. Therefore, the lithiation/delithiation process in Li1.2Ni0.13Co0.13Mn0.54O2 is not changed after the incor- poration of CuPc, and the capacities have come from LMRO it- self. The initial discharge capacities are 272.8, 273.2, 273.4, 278.5 and 267.7 mAh g−1 for LMRO, LMRO@3CuPc, LMRO@5CuPc, LMRO@7CuPc and LMRO@9CuPc electrodes with close initial Coulombic efficiency (ICE) of 75.9%, 75.0%, 75.5%, 78.1% and 72.3%, respectively. That’s because the abundant oxygen-related intermediate species are generated during high-voltage oxidation in lithium-rich layer oxide cathodes. These intermediates include lattice oxygen ions (On −), superoxo (O2 −), peroxo (O2 2−), oxygen vacancies (O-vacancies), O2 dimers, or lost O2, which pose a sig- nificant challenge to the stability of the electrolyte and cathode- electrolyte interface of LMRO. In particular, nucleophilic species such as peroxo and superoxide can preferentially react with cer- tain solvents, altering the way CEI forms, which results in low Coulombic efficiency.[44–46] The capacity of the LMRO electrode shows a variation of first increasing and then decreasing with the increase of CuPc content and 7 wt% CuPc is considered as the optimum content, which is due to the introduction of the surface redox couple, the charge-transfer resistance of the elec- trode is increased since the surface coating layer is insulating. In addition, the charge-transfer resistance is gradually decreased, which is accompanied by the increase of discharge capacity dur- ing the initial cycling. As shown in Figure 2b, after 50 cycles at 0.1 C, the capacity of the LMRO electrode drops to 233.4 mAh g−1",
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      "text": "with a retention of 85.6%. Whereas, LMRO@7CuPc shows more steady cycling and remains at a capacity of 264.6 mAh g−1 with a retention of 91.8% compared to the maximum capacity of the eighth cycle, indicating excellent cycling stability. The long-term cycling performances are also illustrated in Figure 2c–f. It is ob-",
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      "text": "The X-ray diffraction (XRD) patterns shown in Figure S1 (Sup- porting Information) show that a new diffraction peak appears when the amount of CuPc added increases (≥5 wt%), but the LMRO and CuPc-enhanced electrodes display the same diffrac- tion reflection. The Rietveld refinements (Figure S2 and Table S1,",
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      "text": "vious that LMRO electrode shows extremely fast capacity fad- ing from 214.2 to 119.6 mAh g−1, with a poor retention of only 55.8% after 500 cycles, and the discharge curves (Figure 2d) show severe voltage decay with a voltage retention of 73.9%, indicat- ing that LMRO suffers sever spinel phase transition and struc- ture degradation upon cycling. In sharp contrast, CuPc-enhanced electrodes all exhibit significantly improved cycling stability. In particular, LMRO@7CuPc shows the best cycling performance and delivers steady capacity with only a slight decrease from 224.2 to 213.0 mAh g−1 upon 500 cycles with the highest capacity reten- tion of 95.0%. Besides, the voltage decay is also remarkably sup- pressed maintaining 80.3% (Figure 2e), demonstrating the sub- stantially suppressed of irreversible oxygen evolution and struc- tural degradation during the cycle. Controlling oxygen release and regulating the covalency of the TM─O bond in the mate- rial is key to achieving electrochemical stability in LMRO. Cu2+",
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      "text": "doping is considered to be an effective method for stabilizing the structure of close-packed oxygen and improving the local elec- tronic structure, and it can effectively suppress voltage decay in LMRO.[47–49] Benefiting from improved capacity and voltage cy- cling stability, CuPc-enhanced electrodes exhibit higher energy density (Figure 2f). After 500 long-term cycles, LMRO@7CuPc still delivers energy density as high as 615.4 Wh kg−1, nearly twice that of LMRO electrode (327.8 Wh kg−1). Compared with the electrochemical performance of the previously reported LM- ROs (Table S3, Supporting Information), our results clearly ex- hibit the best cycling performance by far. Furthermore, other metal phthalocyanine derivatives are in- vestigated using as redox couple in LMRO as well, including phthalocyanine (Pc), nickel phthalocyanine (NiPc), cooper ph- thalocyanine (CoPc), manganese phthalocyanine (MnPc), iron",
      "category": "scientific_body",
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      "text": "phthalocyanine (FePc) and zinc phthalocyanine (ZnPc). All the additives are added into LMRO and the electrode preparation are same as CuPc enhanced electrodes, and the correspond- ing electrochemical performance data are shown in Figures S4 and S5 and Table S4 (Supporting Information). Interestingly, all the metal phthalocyanine derivatives display the enhance- ment in cycling stability of the LMRO cathode, and the electro- chemical performance at the optimum content of each additive is selected for a more intuitive comparison. All electrodes ex- hibit similar initial charge-discharge profiles, but modified elec- trodes deliver higher capacities and ICE, especially for MnPc- enhanced electrodes with 283.6 mAh g−1 and 81.9%, respectively. The long-term cycling measurement further confirms the pos- itive effect of metal phthalocyanine derivatives on LMRO that each additive-enhanced electrode exhibits higher discharge ca- pacity and improved cycling stability. Among them, CuPc en- hanced electrode shows the highest capacity and the best cycling stability (213.0 mAh g−1 with 95.0% after 500 cycles). Followed by the FePc and MnPc, corresponding electrodes show also high ca- pacity retention of 87.9% and 86.7%, respectively, with a slightly lower capacity unfortunately. Then the CoPc and Pc enhanced electrodes are in the third echelon, delivering a capacity reten- tion of 84.0% and 80.5%. ZnPc and NiPc enhanced electrodes fall behind others, nevertheless, the capacity stability is still bet- ter compared to bare LMRO. In a short summary, the above re- sults clearly confirm the availability and universality of metal ph- thalocyanine derivatives strategy on LMRO, and the modification effect of most phthalocyanine compounds containing metal ions is better than that of phthalocyanine. According to the above discussion of electrochemical perfor- mance, we speculate that there is a synergetic effect on Cu and",
      "category": "scientific_body",
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      "words": 290
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      "text": "and N ensures the high reaction activity of N element to reduce O2 2−of LMRO in time, and the effect of Cu is also maintained in the next cycling (Figure S7, Supporting Information), thus real- izing the high performance of CuPc redox couple. Operando differential electrochemical mass spectrometry (DEMS) was performed to evaluate the gas evolution during the initial cycle. As depicted in Figure 3e, the LMRO electrode dis- plays an obvious O2 and CO2 generation when charging above 4.4 V, which originates from the oxidation of surface O2 2−and electrolyte decomposition, respectively. When charging to 4.8 V, O2 and CO2 have the largest gas flux with 0.656 × 10−2, 0.812 × 10−2 μmol min−1, respectively. In contrast, LMRO@7CuPc ex- hibits significant suppression of gas evolution with the postpone- ment of O2 and CO2 generated voltage and the amount of gas is remarkably lower than that of LMRO (only 0.078 × 10−2 and 0.208 × 10−2 μmol min−1), confirming the elimination of oxygen release enabled by CuPc redox couple. Except for the effect on the LMRO surface, the CuPc strat- egy enhances the oxygen redox in bulk as well. LMRO and LMRO@7CuPc electrodes in different SOC were etched by Ar ion for 20 min to collect the bulk information of O 1s.[54,55] As shown in Figure 3f,g, during the initial cycle, the O2 2−species (peak at 530.5 eV) gradually generate, increase, and then decrease due to the oxygen redox (O2−→O2 2−→O2−), and the intensity of O2 2−is higher in LMRO@7CuPc, indicating more oxygen re- dox. To evaluate oxygen redox activity quantitatively, O2 2−%, de- fined as (O2−/(O2 2−+O2−) by considering the integrated areas, is plotted in Figure S9 (Supporting Information). LMRO shows lower O2 2−% during cycling with a maximum value of 12.41% in 4.8 V, and even 4.45% O2 2−is residual reflecting the partial irre- versible reaction. Whereas, LMRO@7CuPc exhibits higher O2 2−",
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      "text": "ratio with a maximum of 30.84% and full O2 2−is reduced back when discharging to 2.0 V, and the investigation on the second cycle also shows the same pattern (Figure S10, Supporting Infor- mation). The above results verify the enhancement of oxygen re- action activity and reversibility benefitted from the CuPc strategy in LMRO bulk. Therefore, the effect of CuPc redox couple could be briefly summarized as that the irreversible oxygen evolution is the elimination of Cu/N synergetic effect on the surface and the oxygen redox activity and reversibility is greatly improved in the inner bulk region, thus achieving outstanding capacity and cycling stability. To investigate the structural degradation during cycling, XRD patterns of LMRO and LMRO@7CuPc at selected cycles are com- pared and shown in Figure S11 and Table S1 (Supporting In- formation). During the cycling, the diffraction reflections of the LMRO electrode gradually weaken and widen, indicating the de- struction and disordering of the crystal structure. Besides, ac- cording to Rietveld refinement results, the LMRO electrode suf- fers severe phase transition and a large amount of spinel phase is formed which reaches 34.71 wt% after 500 cycles. Oppositely, the LMRO@7CuPc electrode remains a strong reflection dur- ing the cycling process and shows good structure maintenance. Meanwhile, the content of the spinel phase in LMRO@7CuPc shows quite a slow increase, and only 8.24 wt% spinel phase is formed after 500 cycles, indicating the significant suppression of layered spinel phase transition. Moreover, the variation of lat- tice parameter after 500 cycles confirms LMRO@7CuPc shows a much milder unit cell expansion ratio, only half of that of LMRO.",
      "category": "scientific_body",
      "coverage": 0.0,
      "words": 278
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      "text": "The better structure stability is also proven by surface-sensitive Raman spectrometry as shown in Figure S12 (Supporting Infor- mation). For the pristine LMRO electrode, the peak located at 415 cm−1 is ascribed to A1g vibration of monoclinic Li2MnO3 (C2/m structure), and two peaks located at 475 and 592 cm−1",
      "category": "scientific_body",
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      "text": "could be attributed to Eg and A1g vibrations of R-3m structure, respectively.[32,56] After 500 cycles, the A1g peak of C2/m van- ishes due to the damage to the superstructure, and the peaks of R-3m broaden and appear to redshift with a new strong peak of 625 cm−1 related to cubic Fd-3m structure,[56,57] suggesting the degradation of layered structure and sever spinel phase transi- tion, consistent to XRD results, which is because of the oxygen evolution in the charging process, which makes the transition metal become unstable and migrate, causing the transition to the spinel phase.[58,59] In contrast, LMRO@7CuPc exhibits well- preserved Eg and A1g vibration peaks of R-3m as well as A1g vibra- tion of C/2m with tiny cubic Fd-3m peaks, indicating the signifi- cant suppression of structure degradation and oxygen evolution. Furthermore, Atomic-resolution HAADF-STEM is conducted to investigate the structure evolution on the nanoscale. As shown in Figure 4a, the LMRO electrode shows a huge morphology",
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      "text": "pervades the whole particle in LMRO with a thickness of 40 nm, while the Mn3+ reduction layer is remarkably limited to 6 nm in LMRO@7CuPc. Benefiting from the preservation of oxygen lat- tice framework and transition metal valence owning to CuPc re- dox strategy, LMRO@7CuPc exhibits superior structural stability and mitigated voltage decay. Another important effect of CuPc modification is that LMRO@7CuPc forms a more stable, uniform, and robust cathode-electrolyte interface shielding the cathode against elec- trolyte side reactions and suppressing the transition metal dis-",
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      "text": "metal dissolution quantificationally. The dissolution ratios of Ni, Co, and Mn for LMRO electrode are as high as 1.177, 0.831, and 1.937 wt%, respectively, while the corresponding dissolu- tion ratios of TM elements for LMRO@7CuPcelectrode are only 0.079, 0.038, and 0.275 wt%, respectively. It is worth noting that the inhibition effect on the dissolution of Ni and Co ele- ments is more significant, which is conducive to the retention",
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      "text": "of cationic redox reaction thus maintaining electrode capacity. The above results demonstrate that the CuPc strategy can ef- fectively restrain the decomposition of electrolytes and induce the formation of a more uniform and robust LiF-rich CEI, thus improving the surface chemistry stability and suppressing tran- sition metal dissolution, hence realizing steady electrochemical performance.",
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      "text": "operating at a voltage of 40 kV and current of 15 mA with 2𝜃ranging from 10° to 60° at a scan rate of 1° min−1. Rietveld refinements of the XRD data were carried out by a General Structure Analysis System (GSAS) soft- ware package. HAADF-STEM images, STEM-EDS, and EELS spectra were obtained in the JEM-ARM200F microscope, Spectra 300 microscope, and FEI Talos F200x. The Operando differential electrochemical mass spec- trometry (DEMS) was performed in an i-DEMS 100 instrument (Linglu In- struments Co. Lt, Shanghai) with an EI-70 eV ion source and SEM-1100v detector. The cells were assembled in Swagelok-type cells and tested un- der an Ar gas flow of 0.9 mL mi−1n at a current density of 40 mA g−1 at the voltage range of 2.0–4.8 V using LAND CT2001A. XPS measurements were performed using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha) equipped with an Al K𝛼X-ray radiation source (photon energy 1486.6 eV). The collected data were calibrated against the C 1s peak at 284.8 eV. Raman spectrometry was measured in measured on a Renishaw inVia with a 532 nm excitation wavelength. TOF-SIMS analysis was per- formed on PHI nanoTOF II Time-of-Flight SIMS with pulsed 30 keV Bi3 ++",
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      "text": "In summary, we first develop CuPc as a redox couple to LMRO cathode by a facile and effective method and realize outstanding electrochemical performance with improved capacity and voltage stability. The LMRO@7CuPc maintains over 95.0% capacity re- tention and 80.3% voltage retention after 500 cycles at 200 mA g−1. The underlying mechanism of the CuPc redox couple strat- egy is comprehensively researched with various advanced char- acterizations and could be summarized as follows. On the one hand, the N ion in CuPc can reduce the O2 2−back to lattice O2−in time during the charging process to prevent oxygen re- lease, and the oxidized N ion can be reduced back during the discharge process and hence participate in the subsequent re- dox cycle, meanwhile, Cu ion also plays an important role in the above process to improve the reaction reversibility of N ion. The synergistic effect of Cu and N achieves significant suppres- sion of oxygen evolution, thus alleviating structure degradation, spinel phase transition, and transition metal valence reduction. On the other hand, the CuPc strategy inhibits electrolyte decom- position and induces the formation of a uniform and robust LiF- rich CEI, which suppresses side reactions and transition metal dissolution effectively. Furthermore, the comparison between CuPc and other metal phthalocyanine derivatives reveals that dual element redox couple possessing synergistic effect is more desirable for enhancing LMRO performance, and it’s believed that these findings may shed light on subsequent redox couple research.",
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      "text": "ion beam in a high mass resolution mode. All detected secondary ions of interest have a mass range of 2–1850 aum and possess negative polarity over an area of 200 μm × 200 μm. To measure the amount of deposited transition metal, the lithium foil of the cycled cell was dissolved in 10 mL HNO3 and analyzed by ICP-OES (Thermo Fisher iCAP PRO). Electrochemical Measurements: The electrochemical performance was characterized by 2025 coin-type cells. These cells were assembled in an Ar- filled glove box (water and oxygen content < 0.1 ppm) with lithium metal foil as the counter electrode, and Celgard-2400 membrane as a separa- tor. A solution of 1 m LiPF6 in ethylene carbonate (EC), ethyl methyl car- bonate (EMC), and diethyl carbonate (DEC) with a volume ratio of 1:1:1 was used as electrolyte. Galvanostatic charge and discharge tests were performed on a multi-channel battery testing system (NEWARE BST-610, China) at different currents with a potential window of 2.0–4.8 V versus Li/Li+ at 30 °C. The standard sample (LMRO) data used in this paper is consistent with the previous work in order to compare the consistency of data.[75]",
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      "text": "Z.J.W. and C.H.Y. contributed equally to this work. The authors gratefully acknowledge the financial support from the National Key Research and Development Program of China (2022YFB2502000), the National Natural Science Foundation of China (52201277), the key program of the National Natural Science Foundation of China (51831009), the National Outstand- ing Youth Foundation of China (52125104).",
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      "text": "Synthesis of Samples: The Li1.2Ni0.13Co0.13Mn0.54O2 material was syn- thesized by spray pyrolysis followed by high-temperature calcination. Lithium acetate dihydrate (LiAC·2H2O, AR), manganese acetate tetrahy- drate (Mn(AC)2·4H2O, AR), cobalt acetate tetrahydrate (Co(AC)2·4H2O, AR) and nickel acetate tetrahydrate (Ni(AC)2·4H2O, AR) used as the start- ing materials with a molar ratio of Li: Ni: Co: Mn = 1.2:0.13:0.13:0.54 were added into 2 L deionized water in a concentration of 0.3 mol L−1, and 0.8 mol citric acid was added into solution to inhibit the precipitation of metal salts. The mixed solution was stirred for 1 h, and then the spray so- lution was sent to the pulverizer with a high-press gas of 200 °C by a peri- staltic pump to obtain precursor powders. The collected precursor pow- ders were then calcined at 900 °C for 10 h in air to obtain LMRO material. Preparation of Electrodes: LMRO (1.6 g) and conductive additive Super P (TIMCAL) (0.2 g) were mixed via the ball-milling method in a stainless- steel ball mill jar (120 mL) adding tungsten carbide balls (108 g) and ethanol (80 mL) with 400 r min−1 for 6 h. The obtained mixed materials were dried at 80 °C in an air-circulation oven for 12 h. Then the obtained mixed materials and binder sodium carboxymethyl cellulose (CMC), CuPc (Macklin, 𝛽-form, 90%) with a weight ratio of (95-x):5:x (x = 0,3, 5, 7, 9) were mixed with magnetic stirring for 6 h and cast onto an aluminum foil and then dried at 120 °C in a vacuum oven for 20 h. CMC is a better binder for LMRO, which can not only stabilize the electrode structure by prevent- ing the electrode materials from detaching from the current collector but also suppress the voltage fading of the LMRO cathode due to Na+ ions doping. Most importantly, the dissolution of metal elements from the cath- ode materials into the electrolyte is also inhibited.[74] The mass loading of the electrode is 2.20 mg cm−2. The other enhanced electrodes are pre- pared in the same way by adding Pc, MnPc, FePc, CoPc, NiPc, and ZnPc, respectively. Material Structure Characterizations: XRD analysis was performed on a Mini Flex 600 X-ray diffractometer (Rigaku, Japan) with Cu-K𝛼radiation",
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      "text": "Supporting Information) further confirm that the lattice param- eters of LMRO and LMRO@7CuPc electrodes keep well, indi- cating preparation process does not damage the bulk structure. Figure 1a–c shows the high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images of the as-prepared LMRO@7CuPc electrode. The particle has a coat- ing layer with ≈2 nm, while the bulk presents a layered struc- ture with the interplanar spacing of 2.34 Å corresponding to the (012) plane. STEM-energy dispersive spectroscopy (STEM-EDS) in Figure 1d reveals the elements of Mn, Ni, Co, O, and Cu and N of CuPc are uniformly distributed in the particle, confirming that CuPc is coated on the surface of the LMRO particle. The electrochemical performances of CuPc-enhanced elec- trodes in the voltage window of 2.0–4.8 V at 0.1 C and 1 C (1C = 200 mA g−1) are shown in Figure 2, and corresponding data are summarized in Table S2 (Supporting Information). Figure 2a shows the initial charge-discharge profile at 0.1 C. All electrodes display typical redox features of Li-rich cathode with a slope re- gion below 4.4 V associated with Ni2+/3+/4+ and Co3+/4+ cationic redox, and a long plateau ≈4.5 V associated with oxygen redox reaction.[16] Corresponding dQ/dV curves (Figure S3, Support- ing Information) well reflect these redox processes and CuPc en- hanced electrodes show no new redox reaction peak appears, and the peak area is almost uniform at ≈4.5 V during initial cycle, in- dicating that redox couple increases the redox reversibility of lat- tice oxygen during initial cycle, but does not increase the capacity because the introduction of the surface redox couple, the charge- transfer resistance of the electrode is increased since the surface coating layer is insulating. Therefore, the lithiation/delithiation process in Li1.2Ni0.13Co0.13Mn0.54O2 is not changed after the incor- poration of CuPc, and the capacities have come from LMRO it- self. The initial discharge capacities are 272.8, 273.2, 273.4, 278.5 and 267.7 mAh g−1 for LMRO, LMRO@3CuPc, LMRO@5CuPc, LMRO@7CuPc and LMRO@9CuPc electrodes with close initial Coulombic efficiency (ICE) of 75.9%, 75.0%, 75.5%, 78.1% and 72.3%, respectively. That’s because the abundant oxygen-related intermediate species are generated during high-voltage oxidation in lithium-rich layer oxide cathodes. These intermediates include lattice oxygen ions (On −), superoxo (O2 −), peroxo (O2 2−), oxygen vacancies (O-vacancies), O2 dimers, or lost O2, which pose a sig- nificant challenge to the stability of the electrolyte and cathode- electrolyte interface of LMRO. In particular, nucleophilic species such as peroxo and superoxide can preferentially react with cer- tain solvents, altering the way CEI forms, which results in low Coulombic efficiency.[44–46] The capacity of the LMRO electrode shows a variation of first increasing and then decreasing with the increase of CuPc content and 7 wt% CuPc is considered as the optimum content, which is due to the introduction of the surface redox couple, the charge-transfer resistance of the elec- trode is increased since the surface coating layer is insulating. In addition, the charge-transfer resistance is gradually decreased, which is accompanied by the increase of discharge capacity dur- ing the initial cycling. As shown in Figure 2b, after 50 cycles at 0.1 C, the capacity of the LMRO electrode drops to 233.4 mAh g−1",
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      "text": "with a retention of 85.6%. Whereas, LMRO@7CuPc shows more steady cycling and remains at a capacity of 264.6 mAh g−1 with a retention of 91.8% compared to the maximum capacity of the eighth cycle, indicating excellent cycling stability. The long-term cycling performances are also illustrated in Figure 2c–f. It is ob-",
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      "text": "vious that LMRO electrode shows extremely fast capacity fad- ing from 214.2 to 119.6 mAh g−1, with a poor retention of only 55.8% after 500 cycles, and the discharge curves (Figure 2d) show severe voltage decay with a voltage retention of 73.9%, indicat- ing that LMRO suffers sever spinel phase transition and struc- ture degradation upon cycling. In sharp contrast, CuPc-enhanced electrodes all exhibit significantly improved cycling stability. In particular, LMRO@7CuPc shows the best cycling performance and delivers steady capacity with only a slight decrease from 224.2 to 213.0 mAh g−1 upon 500 cycles with the highest capacity reten- tion of 95.0%. Besides, the voltage decay is also remarkably sup- pressed maintaining 80.3% (Figure 2e), demonstrating the sub- stantially suppressed of irreversible oxygen evolution and struc- tural degradation during the cycle. Controlling oxygen release and regulating the covalency of the TM─O bond in the mate- rial is key to achieving electrochemical stability in LMRO. Cu2+",
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      "text": "doping is considered to be an effective method for stabilizing the structure of close-packed oxygen and improving the local elec- tronic structure, and it can effectively suppress voltage decay in LMRO.[47–49] Benefiting from improved capacity and voltage cy- cling stability, CuPc-enhanced electrodes exhibit higher energy density (Figure 2f). After 500 long-term cycles, LMRO@7CuPc still delivers energy density as high as 615.4 Wh kg−1, nearly twice that of LMRO electrode (327.8 Wh kg−1). Compared with the electrochemical performance of the previously reported LM- ROs (Table S3, Supporting Information), our results clearly ex- hibit the best cycling performance by far. Furthermore, other metal phthalocyanine derivatives are in- vestigated using as redox couple in LMRO as well, including phthalocyanine (Pc), nickel phthalocyanine (NiPc), cooper ph- thalocyanine (CoPc), manganese phthalocyanine (MnPc), iron",
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      "text": "phthalocyanine (FePc) and zinc phthalocyanine (ZnPc). All the additives are added into LMRO and the electrode preparation are same as CuPc enhanced electrodes, and the correspond- ing electrochemical performance data are shown in Figures S4 and S5 and Table S4 (Supporting Information). Interestingly, all the metal phthalocyanine derivatives display the enhance- ment in cycling stability of the LMRO cathode, and the electro- chemical performance at the optimum content of each additive is selected for a more intuitive comparison. All electrodes ex- hibit similar initial charge-discharge profiles, but modified elec- trodes deliver higher capacities and ICE, especially for MnPc- enhanced electrodes with 283.6 mAh g−1 and 81.9%, respectively. The long-term cycling measurement further confirms the pos- itive effect of metal phthalocyanine derivatives on LMRO that each additive-enhanced electrode exhibits higher discharge ca- pacity and improved cycling stability. Among them, CuPc en- hanced electrode shows the highest capacity and the best cycling stability (213.0 mAh g−1 with 95.0% after 500 cycles). Followed by the FePc and MnPc, corresponding electrodes show also high ca- pacity retention of 87.9% and 86.7%, respectively, with a slightly lower capacity unfortunately. Then the CoPc and Pc enhanced electrodes are in the third echelon, delivering a capacity reten- tion of 84.0% and 80.5%. ZnPc and NiPc enhanced electrodes fall behind others, nevertheless, the capacity stability is still bet- ter compared to bare LMRO. In a short summary, the above re- sults clearly confirm the availability and universality of metal ph- thalocyanine derivatives strategy on LMRO, and the modification effect of most phthalocyanine compounds containing metal ions is better than that of phthalocyanine. According to the above discussion of electrochemical perfor- mance, we speculate that there is a synergetic effect on Cu and",
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      "text": "and N ensures the high reaction activity of N element to reduce O2 2−of LMRO in time, and the effect of Cu is also maintained in the next cycling (Figure S7, Supporting Information), thus real- izing the high performance of CuPc redox couple. Operando differential electrochemical mass spectrometry (DEMS) was performed to evaluate the gas evolution during the initial cycle. As depicted in Figure 3e, the LMRO electrode dis- plays an obvious O2 and CO2 generation when charging above 4.4 V, which originates from the oxidation of surface O2 2−and electrolyte decomposition, respectively. When charging to 4.8 V, O2 and CO2 have the largest gas flux with 0.656 × 10−2, 0.812 × 10−2 μmol min−1, respectively. In contrast, LMRO@7CuPc ex- hibits significant suppression of gas evolution with the postpone- ment of O2 and CO2 generated voltage and the amount of gas is remarkably lower than that of LMRO (only 0.078 × 10−2 and 0.208 × 10−2 μmol min−1), confirming the elimination of oxygen release enabled by CuPc redox couple. Except for the effect on the LMRO surface, the CuPc strat- egy enhances the oxygen redox in bulk as well. LMRO and LMRO@7CuPc electrodes in different SOC were etched by Ar ion for 20 min to collect the bulk information of O 1s.[54,55] As shown in Figure 3f,g, during the initial cycle, the O2 2−species (peak at 530.5 eV) gradually generate, increase, and then decrease due to the oxygen redox (O2−→O2 2−→O2−), and the intensity of O2 2−is higher in LMRO@7CuPc, indicating more oxygen re- dox. To evaluate oxygen redox activity quantitatively, O2 2−%, de- fined as (O2−/(O2 2−+O2−) by considering the integrated areas, is plotted in Figure S9 (Supporting Information). LMRO shows lower O2 2−% during cycling with a maximum value of 12.41% in 4.8 V, and even 4.45% O2 2−is residual reflecting the partial irre- versible reaction. Whereas, LMRO@7CuPc exhibits higher O2 2−",
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      "text": "ratio with a maximum of 30.84% and full O2 2−is reduced back when discharging to 2.0 V, and the investigation on the second cycle also shows the same pattern (Figure S10, Supporting Infor- mation). The above results verify the enhancement of oxygen re- action activity and reversibility benefitted from the CuPc strategy in LMRO bulk. Therefore, the effect of CuPc redox couple could be briefly summarized as that the irreversible oxygen evolution is the elimination of Cu/N synergetic effect on the surface and the oxygen redox activity and reversibility is greatly improved in the inner bulk region, thus achieving outstanding capacity and cycling stability. To investigate the structural degradation during cycling, XRD patterns of LMRO and LMRO@7CuPc at selected cycles are com- pared and shown in Figure S11 and Table S1 (Supporting In- formation). During the cycling, the diffraction reflections of the LMRO electrode gradually weaken and widen, indicating the de- struction and disordering of the crystal structure. Besides, ac- cording to Rietveld refinement results, the LMRO electrode suf- fers severe phase transition and a large amount of spinel phase is formed which reaches 34.71 wt% after 500 cycles. Oppositely, the LMRO@7CuPc electrode remains a strong reflection dur- ing the cycling process and shows good structure maintenance. Meanwhile, the content of the spinel phase in LMRO@7CuPc shows quite a slow increase, and only 8.24 wt% spinel phase is formed after 500 cycles, indicating the significant suppression of layered spinel phase transition. Moreover, the variation of lat- tice parameter after 500 cycles confirms LMRO@7CuPc shows a much milder unit cell expansion ratio, only half of that of LMRO.",
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      "text": "The better structure stability is also proven by surface-sensitive Raman spectrometry as shown in Figure S12 (Supporting Infor- mation). For the pristine LMRO electrode, the peak located at 415 cm−1 is ascribed to A1g vibration of monoclinic Li2MnO3 (C2/m structure), and two peaks located at 475 and 592 cm−1",
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      "text": "could be attributed to Eg and A1g vibrations of R-3m structure, respectively.[32,56] After 500 cycles, the A1g peak of C2/m van- ishes due to the damage to the superstructure, and the peaks of R-3m broaden and appear to redshift with a new strong peak of 625 cm−1 related to cubic Fd-3m structure,[56,57] suggesting the degradation of layered structure and sever spinel phase transi- tion, consistent to XRD results, which is because of the oxygen evolution in the charging process, which makes the transition metal become unstable and migrate, causing the transition to the spinel phase.[58,59] In contrast, LMRO@7CuPc exhibits well- preserved Eg and A1g vibration peaks of R-3m as well as A1g vibra- tion of C/2m with tiny cubic Fd-3m peaks, indicating the signifi- cant suppression of structure degradation and oxygen evolution. Furthermore, Atomic-resolution HAADF-STEM is conducted to investigate the structure evolution on the nanoscale. As shown in Figure 4a, the LMRO electrode shows a huge morphology",
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      "text": "pervades the whole particle in LMRO with a thickness of 40 nm, while the Mn3+ reduction layer is remarkably limited to 6 nm in LMRO@7CuPc. Benefiting from the preservation of oxygen lat- tice framework and transition metal valence owning to CuPc re- dox strategy, LMRO@7CuPc exhibits superior structural stability and mitigated voltage decay. Another important effect of CuPc modification is that LMRO@7CuPc forms a more stable, uniform, and robust cathode-electrolyte interface shielding the cathode against elec- trolyte side reactions and suppressing the transition metal dis-",
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      "text": "metal dissolution quantificationally. The dissolution ratios of Ni, Co, and Mn for LMRO electrode are as high as 1.177, 0.831, and 1.937 wt%, respectively, while the corresponding dissolu- tion ratios of TM elements for LMRO@7CuPcelectrode are only 0.079, 0.038, and 0.275 wt%, respectively. It is worth noting that the inhibition effect on the dissolution of Ni and Co ele- ments is more significant, which is conducive to the retention",
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      "text": "of cationic redox reaction thus maintaining electrode capacity. The above results demonstrate that the CuPc strategy can ef- fectively restrain the decomposition of electrolytes and induce the formation of a more uniform and robust LiF-rich CEI, thus improving the surface chemistry stability and suppressing tran- sition metal dissolution, hence realizing steady electrochemical performance.",
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      "text": "Z.J.W. and C.H.Y. contributed equally to this work. The authors gratefully acknowledge the financial support from the National Key Research and Development Program of China (2022YFB2502000), the National Natural Science Foundation of China (52201277), the key program of the National Natural Science Foundation of China (51831009), the National Outstand- ing Youth Foundation of China (52125104).",
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      "text": "with a retention of 85.6%. Whereas, LMRO@7CuPc shows more steady cycling and remains at a capacity of 264.6 mAh g−1 with a retention of 91.8% compared to the maximum capacity of the eighth cycle, indicating excellent cycling stability. The long-term cycling performances are also illustrated in Figure 2c–f. It is ob-",
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      "text": "vious that LMRO electrode shows extremely fast capacity fad- ing from 214.2 to 119.6 mAh g−1, with a poor retention of only 55.8% after 500 cycles, and the discharge curves (Figure 2d) show severe voltage decay with a voltage retention of 73.9%, indicat- ing that LMRO suffers sever spinel phase transition and struc- ture degradation upon cycling. In sharp contrast, CuPc-enhanced electrodes all exhibit significantly improved cycling stability. In particular, LMRO@7CuPc shows the best cycling performance and delivers steady capacity with only a slight decrease from 224.2 to 213.0 mAh g−1 upon 500 cycles with the highest capacity reten- tion of 95.0%. Besides, the voltage decay is also remarkably sup- pressed maintaining 80.3% (Figure 2e), demonstrating the sub- stantially suppressed of irreversible oxygen evolution and struc- tural degradation during the cycle. Controlling oxygen release and regulating the covalency of the TM─O bond in the mate- rial is key to achieving electrochemical stability in LMRO. Cu2+",
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      "text": "doping is considered to be an effective method for stabilizing the structure of close-packed oxygen and improving the local elec- tronic structure, and it can effectively suppress voltage decay in LMRO.[47–49] Benefiting from improved capacity and voltage cy- cling stability, CuPc-enhanced electrodes exhibit higher energy density (Figure 2f). After 500 long-term cycles, LMRO@7CuPc still delivers energy density as high as 615.4 Wh kg−1, nearly twice that of LMRO electrode (327.8 Wh kg−1). Compared with the electrochemical performance of the previously reported LM- ROs (Table S3, Supporting Information), our results clearly ex- hibit the best cycling performance by far. Furthermore, other metal phthalocyanine derivatives are in- vestigated using as redox couple in LMRO as well, including phthalocyanine (Pc), nickel phthalocyanine (NiPc), cooper ph- thalocyanine (CoPc), manganese phthalocyanine (MnPc), iron",
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      "text": "phthalocyanine (FePc) and zinc phthalocyanine (ZnPc). All the additives are added into LMRO and the electrode preparation are same as CuPc enhanced electrodes, and the correspond- ing electrochemical performance data are shown in Figures S4 and S5 and Table S4 (Supporting Information). Interestingly, all the metal phthalocyanine derivatives display the enhance- ment in cycling stability of the LMRO cathode, and the electro- chemical performance at the optimum content of each additive is selected for a more intuitive comparison. All electrodes ex- hibit similar initial charge-discharge profiles, but modified elec- trodes deliver higher capacities and ICE, especially for MnPc- enhanced electrodes with 283.6 mAh g−1 and 81.9%, respectively. The long-term cycling measurement further confirms the pos- itive effect of metal phthalocyanine derivatives on LMRO that each additive-enhanced electrode exhibits higher discharge ca- pacity and improved cycling stability. Among them, CuPc en- hanced electrode shows the highest capacity and the best cycling stability (213.0 mAh g−1 with 95.0% after 500 cycles). Followed by the FePc and MnPc, corresponding electrodes show also high ca- pacity retention of 87.9% and 86.7%, respectively, with a slightly lower capacity unfortunately. Then the CoPc and Pc enhanced electrodes are in the third echelon, delivering a capacity reten- tion of 84.0% and 80.5%. ZnPc and NiPc enhanced electrodes fall behind others, nevertheless, the capacity stability is still bet- ter compared to bare LMRO. In a short summary, the above re- sults clearly confirm the availability and universality of metal ph- thalocyanine derivatives strategy on LMRO, and the modification effect of most phthalocyanine compounds containing metal ions is better than that of phthalocyanine. According to the above discussion of electrochemical perfor- mance, we speculate that there is a synergetic effect on Cu and",
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      "text": "and N ensures the high reaction activity of N element to reduce O2 2−of LMRO in time, and the effect of Cu is also maintained in the next cycling (Figure S7, Supporting Information), thus real- izing the high performance of CuPc redox couple. Operando differential electrochemical mass spectrometry (DEMS) was performed to evaluate the gas evolution during the initial cycle. As depicted in Figure 3e, the LMRO electrode dis- plays an obvious O2 and CO2 generation when charging above 4.4 V, which originates from the oxidation of surface O2 2−and electrolyte decomposition, respectively. When charging to 4.8 V, O2 and CO2 have the largest gas flux with 0.656 × 10−2, 0.812 × 10−2 μmol min−1, respectively. In contrast, LMRO@7CuPc ex- hibits significant suppression of gas evolution with the postpone- ment of O2 and CO2 generated voltage and the amount of gas is remarkably lower than that of LMRO (only 0.078 × 10−2 and 0.208 × 10−2 μmol min−1), confirming the elimination of oxygen release enabled by CuPc redox couple. Except for the effect on the LMRO surface, the CuPc strat- egy enhances the oxygen redox in bulk as well. LMRO and LMRO@7CuPc electrodes in different SOC were etched by Ar ion for 20 min to collect the bulk information of O 1s.[54,55] As shown in Figure 3f,g, during the initial cycle, the O2 2−species (peak at 530.5 eV) gradually generate, increase, and then decrease due to the oxygen redox (O2−→O2 2−→O2−), and the intensity of O2 2−is higher in LMRO@7CuPc, indicating more oxygen re- dox. To evaluate oxygen redox activity quantitatively, O2 2−%, de- fined as (O2−/(O2 2−+O2−) by considering the integrated areas, is plotted in Figure S9 (Supporting Information). LMRO shows lower O2 2−% during cycling with a maximum value of 12.41% in 4.8 V, and even 4.45% O2 2−is residual reflecting the partial irre- versible reaction. Whereas, LMRO@7CuPc exhibits higher O2 2−",
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      "text": "ratio with a maximum of 30.84% and full O2 2−is reduced back when discharging to 2.0 V, and the investigation on the second cycle also shows the same pattern (Figure S10, Supporting Infor- mation). The above results verify the enhancement of oxygen re- action activity and reversibility benefitted from the CuPc strategy in LMRO bulk. Therefore, the effect of CuPc redox couple could be briefly summarized as that the irreversible oxygen evolution is the elimination of Cu/N synergetic effect on the surface and the oxygen redox activity and reversibility is greatly improved in the inner bulk region, thus achieving outstanding capacity and cycling stability. To investigate the structural degradation during cycling, XRD patterns of LMRO and LMRO@7CuPc at selected cycles are com- pared and shown in Figure S11 and Table S1 (Supporting In- formation). During the cycling, the diffraction reflections of the LMRO electrode gradually weaken and widen, indicating the de- struction and disordering of the crystal structure. Besides, ac- cording to Rietveld refinement results, the LMRO electrode suf- fers severe phase transition and a large amount of spinel phase is formed which reaches 34.71 wt% after 500 cycles. Oppositely, the LMRO@7CuPc electrode remains a strong reflection dur- ing the cycling process and shows good structure maintenance. Meanwhile, the content of the spinel phase in LMRO@7CuPc shows quite a slow increase, and only 8.24 wt% spinel phase is formed after 500 cycles, indicating the significant suppression of layered spinel phase transition. Moreover, the variation of lat- tice parameter after 500 cycles confirms LMRO@7CuPc shows a much milder unit cell expansion ratio, only half of that of LMRO.",
      "category": "scientific_body",
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      "text": "The better structure stability is also proven by surface-sensitive Raman spectrometry as shown in Figure S12 (Supporting Infor- mation). For the pristine LMRO electrode, the peak located at 415 cm−1 is ascribed to A1g vibration of monoclinic Li2MnO3 (C2/m structure), and two peaks located at 475 and 592 cm−1",
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      "text": "could be attributed to Eg and A1g vibrations of R-3m structure, respectively.[32,56] After 500 cycles, the A1g peak of C2/m van- ishes due to the damage to the superstructure, and the peaks of R-3m broaden and appear to redshift with a new strong peak of 625 cm−1 related to cubic Fd-3m structure,[56,57] suggesting the degradation of layered structure and sever spinel phase transi- tion, consistent to XRD results, which is because of the oxygen evolution in the charging process, which makes the transition metal become unstable and migrate, causing the transition to the spinel phase.[58,59] In contrast, LMRO@7CuPc exhibits well- preserved Eg and A1g vibration peaks of R-3m as well as A1g vibra- tion of C/2m with tiny cubic Fd-3m peaks, indicating the signifi- cant suppression of structure degradation and oxygen evolution. Furthermore, Atomic-resolution HAADF-STEM is conducted to investigate the structure evolution on the nanoscale. As shown in Figure 4a, the LMRO electrode shows a huge morphology",
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      "text": "pervades the whole particle in LMRO with a thickness of 40 nm, while the Mn3+ reduction layer is remarkably limited to 6 nm in LMRO@7CuPc. Benefiting from the preservation of oxygen lat- tice framework and transition metal valence owning to CuPc re- dox strategy, LMRO@7CuPc exhibits superior structural stability and mitigated voltage decay. Another important effect of CuPc modification is that LMRO@7CuPc forms a more stable, uniform, and robust cathode-electrolyte interface shielding the cathode against elec- trolyte side reactions and suppressing the transition metal dis-",
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      "text": "metal dissolution quantificationally. The dissolution ratios of Ni, Co, and Mn for LMRO electrode are as high as 1.177, 0.831, and 1.937 wt%, respectively, while the corresponding dissolu- tion ratios of TM elements for LMRO@7CuPcelectrode are only 0.079, 0.038, and 0.275 wt%, respectively. It is worth noting that the inhibition effect on the dissolution of Ni and Co ele- ments is more significant, which is conducive to the retention",
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      "text": "of cationic redox reaction thus maintaining electrode capacity. The above results demonstrate that the CuPc strategy can ef- fectively restrain the decomposition of electrolytes and induce the formation of a more uniform and robust LiF-rich CEI, thus improving the surface chemistry stability and suppressing tran- sition metal dissolution, hence realizing steady electrochemical performance.",
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      "text": "Supporting Information) further confirm that the lattice param- eters of LMRO and LMRO@7CuPc electrodes keep well, indi- cating preparation process does not damage the bulk structure. Figure 1a–c shows the high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images of the as-prepared LMRO@7CuPc electrode. The particle has a coat- ing layer with ≈2 nm, while the bulk presents a layered struc- ture with the interplanar spacing of 2.34 Å corresponding to the (012) plane. STEM-energy dispersive spectroscopy (STEM-EDS) in Figure 1d reveals the elements of Mn, Ni, Co, O, and Cu and N of CuPc are uniformly distributed in the particle, confirming that CuPc is coated on the surface of the LMRO particle. The electrochemical performances of CuPc-enhanced elec- trodes in the voltage window of 2.0–4.8 V at 0.1 C and 1 C (1C = 200 mA g−1) are shown in Figure 2, and corresponding data are summarized in Table S2 (Supporting Information). Figure 2a shows the initial charge-discharge profile at 0.1 C. All electrodes display typical redox features of Li-rich cathode with a slope re- gion below 4.4 V associated with Ni2+/3+/4+ and Co3+/4+ cationic redox, and a long plateau ≈4.5 V associated with oxygen redox reaction.[16] Corresponding dQ/dV curves (Figure S3, Support- ing Information) well reflect these redox processes and CuPc en- hanced electrodes show no new redox reaction peak appears, and the peak area is almost uniform at ≈4.5 V during initial cycle, in- dicating that redox couple increases the redox reversibility of lat- tice oxygen during initial cycle, but does not increase the capacity because the introduction of the surface redox couple, the charge- transfer resistance of the electrode is increased since the surface coating layer is insulating. Therefore, the lithiation/delithiation process in Li1.2Ni0.13Co0.13Mn0.54O2 is not changed after the incor- poration of CuPc, and the capacities have come from LMRO it- self. The initial discharge capacities are 272.8, 273.2, 273.4, 278.5 and 267.7 mAh g−1 for LMRO, LMRO@3CuPc, LMRO@5CuPc, LMRO@7CuPc and LMRO@9CuPc electrodes with close initial Coulombic efficiency (ICE) of 75.9%, 75.0%, 75.5%, 78.1% and 72.3%, respectively. That’s because the abundant oxygen-related intermediate species are generated during high-voltage oxidation in lithium-rich layer oxide cathodes. These intermediates include lattice oxygen ions (On −), superoxo (O2 −), peroxo (O2 2−), oxygen vacancies (O-vacancies), O2 dimers, or lost O2, which pose a sig- nificant challenge to the stability of the electrolyte and cathode- electrolyte interface of LMRO. In particular, nucleophilic species such as peroxo and superoxide can preferentially react with cer- tain solvents, altering the way CEI forms, which results in low Coulombic efficiency.[44–46] The capacity of the LMRO electrode shows a variation of first increasing and then decreasing with the increase of CuPc content and 7 wt% CuPc is considered as the optimum content, which is due to the introduction of the surface redox couple, the charge-transfer resistance of the elec- trode is increased since the surface coating layer is insulating. In addition, the charge-transfer resistance is gradually decreased, which is accompanied by the increase of discharge capacity dur- ing the initial cycling. As shown in Figure 2b, after 50 cycles at 0.1 C, the capacity of the LMRO electrode drops to 233.4 mAh g−1",
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      "text": "Z.J.W. and C.H.Y. contributed equally to this work. The authors gratefully acknowledge the financial support from the National Key Research and Development Program of China (2022YFB2502000), the National Natural Science Foundation of China (52201277), the key program of the National Natural Science Foundation of China (51831009), the National Outstand- ing Youth Foundation of China (52125104).",
      "category": "back_matter",
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      "words": 58
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}