Layered Transition Metal Research Articles

Thermodynamics-directed bulk/grain-boundary engineering for superior electrochemical durability of Ni-rich cathode

Introducing high-valence Ta element is an essential strategy for addressing the structural deterioration of the Ni-rich LiNi1−x−yCoxMnyO2 (NCM) cathode, but the enlarged Li/Ni cation mixing leads to the inferior rate capability originating from the hindered Li+ migration. Note that the non-magnetic Ti4+ ion can suppress Li/Ni disorder by removing the magnetic frustration in the transition metal layer. However, it is still challenging to directionally design expected Ta/Ti dual-modification, resulting from the complexity of the elemental distribution and the uncertainty of in-situ formed coating compounds by introducing foreign elements. Herein, a LiTaO3 grain boundary (GB) coating and bulk Ti-doping have been successfully achieved in LiNi0.834Co0.11Mn0.056O2 cathode by thermodynamic guidance, in which the structural formation energy and interfacial binding energy are employed to predict the elemental diffusion discrepancy and thermodynamically stable coating compounds. Thanks to the coupling effect of strengthened structural/interfacial stability and improved Li+ diffusion kinetics by simultaneous bulk/GB engineering, the Ta/Ti-NCM cathode exhibits outstanding capacity retention, reaching 91.1% after 400 cycles at 1 C. This elaborate work contributes valuable insights into rational dual-modification engineering from a thermodynamic perspective for maximizing the electrochemical performances of NCM cathodes.

Tailored synthesis and characterization of Zr-doped NaNi1/3Fe1/3Mn1/3O2 cathode materials for advanced energy storage

Utilizing ball milling and spray drying, Zr-doped O3-type NaNi1/3Fe1/3-xMn1/3ZrxO2 (NFM-xZr, x=0, 1 %, 3 %) cathode materials were successfully fabricated, confirmed by XRD and EDS analyses, indicating effective Zr4+ ion integration. Structural adjustments in transition metal and sodium layer spacing were observed, enhancing sodium ion diffusion. The optimal sample, NFM-1 %Zr, exhibited remarkable electrochemical performance, achieving a discharge capacity of 124.4mAhg−1 at 1 C and a retention rate of 87.14 % after 200 cycles. At 5 C, the retention rate remained high at 88.15 % after 200 cycles. Notably, within the voltage range of 2–4.3 V, the capacity retention rate at 1 C increased by 21.94 %. In a full cell configuration (NFM-1 %Zr//HC), a cycling retention rate of 79.78 % was achieved after 200 cycles at 10 C. Ex-situ XRD analysis highlighted the improved cathode material reversibility with Zr incorporation. SEM and EDS revealed that moderate Zr doping inhibited phase transitions and reduced oxygen losses, resulting in excellent electrochemical performance.

Screening Conductive MXenes for Lithium Polysulfide Adsorption

AbstractMXenes are promising passive components that enable lithium‐sulfur batteries (LSBs) by effectively trapping lithium polysulfides (LiPSs) and facilitating surface‐mediated redox reactions. Despite numerous studies highlighting the potential of MXenes in LSBs, there are no systematic studies of MXenes’ composition influence on polysulfide adsorption, which is foundational to their applications in LSB. Here, a comprehensive investigation of LiPS adsorption on seven MXenes with varying chemistries (Ti2CTx, Ti3C2Tx, Ti3CNTx, Mo2TiC2Tx, V2CTx, Nb2CTx, and Nb4C3Tx), utilizing optical and analytical spectroscopic methods is performed. This work reports on the influence of polysulfide concentration, interaction time, and MXenes’ chemistry (transition metal layer, carbide and carbonitride inner layer, surface terminations and structure) on the amount of adsorbed LiPSs and the adsorption mechanism. These findings reveal the formation of insoluble thiosulfate and polythionate complex species on the surfaces of all tested MXenes. Furthermore, the selective adsorption of lithium and sulfur, and the extent of conversion of the adsorbed species on MXenes varied based on their chemistry. For instance, Ti2CTx exhibits a strong tendency to adsorb lithium ions, while Mo2TiC2Tx is effective in trapping sulfur by forming long‐chain polythionates. The latter demonstrates a significant conversion of intermediate polysulfides into low‐order species. This study offers valuable guidance for the informed selection of MXenes in various functional components benefiting the future development of high‐performance LSBs.

Dual-Site Doping in Transition Metal Oxide Cathode Enables High-Voltage Stability of Na-Ion Batteries.

Designing cathode materials that effectively enhancing structural stability under high voltage is paramount for rationally enhancing energy density and safety of Na-ion batteries. This study introduces a novel P2-Na0.73K0.03Ni0.23Li0.1Mn0.67O2 (KLi-NaNMO) cathode through dual-site synergistic doping of K and Li in Na and transition metal (TM) layers. Combining theoretical and experimental studies, this study discovers that Li doping significantly strengthens the orbital overlap of Ni (3d) and O (2p) near the Fermi level, thereby regulates the phase transition and charge compensation processes with synchronized Ni and O redox. The introduction of K further adjusts the ratio of Nae and Naf sites at Na layer with enhanced structural stability and extended lattice space distance, enabling the suppression of TM dissolution, achieving a single-phase transition reaction even at a high voltage of 4.4V, and improving reaction kinetics. Consequently, KLi-NaNMO exhibits a high capacity (105 and 120 mAh g-1 in the voltage of 2-4.2V and 2-4.4V at 0.1 C, respectively) and outstanding cycling performance over 300 cycles under 4.2 and 4.4V. This work provides a dual-site doping strategy to employ synchronized TM and O redox with improved capacity and high structural stability via electronic and crystal structure modulation.

The critical role of titanium cation for the enhanced Na-ion layer spacing of O3 layered oxide cathode materials

O3-NaNi1/3Fe1/3Mn1/3O2 layered cathode material has been widely concerned by the industry for its advantages of simple preparation, low cost and high theoretical specific capacity. However, due to a series of surface side reactions, some transition metal ions are reduced, resulting in structural Jahn-Teller distortion, leading to poor structural stability. Herein, Ti element is introduced into O3-NaNi1/3Fe1/3Mn1/3O2 cathode material, and the effect of Ti doping on the phase structure and electrochemical properties of the material is analyzed in detail. The results show that Ti doping can enlarge the Na layer spacing and decrease the transition metal layer spacing. Thus, the modified material has a smaller Na ion diffusion barrier and a more stable structure. These advantages give a sample with a doping rate of 2.5 wt% a rate capacity of 74.8 mAh g−1 at 10 C, a capacity retention rate of 86.2 % after 100 cycles at 1 C, and an energy density of 320.5 Wh kg−1 for a full cell structure using a hard carbon anode. This strategy provides a valuable reference for cationic doping to improve the properties of O3 layered transition metal oxides.

Construction and catalysis role of a kinetic promoter based on lithium-insertion technology and proton exchange strategy for lithium-sulfur batteries

The high theoretical energy density and specific capacity of lithium-sulfur (Li-S) batteries have garnered considerable attention in the prospective market. However, ongoing research on Li-S batteries appears to have encountered a bottleneck, with unresolved key technical challenges such as the significant shuttle effect and sluggish reaction kinetics. This investigation explores the catalytic efficacy of three catalysts for Li-S batteries and elucidates the correlation between their structure and catalytic impacts. The results suggest that the combined utilization of lithium-insertion technology and a proton exchange approach for δ-MnO2 can optimize its electronic structure, resulting in an optimal catalyst (H/Li inserted δ-MnO2, denoted as HLM) for the sulfur reduction reaction. The replacement of Mn sites in δ-MnO2 with Li atoms can enhance the structural stability of the catalyst, while the introduction of H atoms between transition metal layers contributes to the satisfactory catalytic performance of HLM. Theoretical calculations demonstrate that the bond length of Li2S4 adsorbed by the HLM molecule is elongated, thereby facilitating the dissociation process of Li2S4 and enhancing the reaction kinetics in Li-S batteries. Consequently, the Li-S battery utilizing HLM as a catalyst achieves a high areal specific capacity of 4.2 mAh cm−2 with a sulfur loading of 4.1 mg cm−2 and a low electrolyte/sulfur (E/S) ratio of 8 μL mg−1. This study introduces a methodology for designing effective catalysts that could significantly advance practical developments in Li-S battery technology.

Opportunities of MXenes in Heterogeneous Catalysis: V2C as Aerobic Oxidation Catalyst.

MXenes are two-dimensional nanomaterials having alternating sheets of one atom-thick early transition metal layer and one atom-thick carbide or nitride layer. The external surface contains termination groups, whose nature depends on the etching agent used in the preparation procedure from the MAX phase. The present concept proposes that, due to their composition, the metal-surface termination groups make MXenes particularly suited as heterogeneous catalysts for some reactions. This proposal comes from the consideration that early transition metal atoms bonded to hydroxyl and oxo groups are a general type of active sites in heterogeneous catalysis and that similar catalytic centers can also be present in the MXene structure. After having presented the concept, we have selected V2C Mxene as an example to illustrate its catalytic activity and to show how the catalytic performance varies when the surface groups are modified. As a test reaction, we selected the aerobic oxidation of indane to the corresponding indanol/indanone mixture using molecular oxygen as terminal oxidizing reagent. Two previously reported procedures to modify the surface groups, namely surface dehydroxylation by thermal treatment under diluted hydrogen flow and surface oxidation with ammonium persulfate to convert some surface groups into oxo groups were used, observing in both cases a decrease in the catalytic activity of V2C. Based on this, VIII/IV-OH are proposed as catalytic centers in this aerobic oxidation. Overall, the present concept shows the merits of MXenes in heterogeneous catalysis, based on their chemical composition and the surface functionality.

Anti-siting for stabilizing structure and modulating cationic/anionic redox reactions

The layered Mn-rich oxide cathode materials with oxygen redox activity are highly appealing in sodium-ion (Na-ion) batteries because of their high energy density and low cost. However, the applications of such materials are hindered by issues such as low Mn redox potential and irreversible phase transformation. Rational modulation of the ordering of the transition metal (TM) layer can inhibit the constraints and stabilize the anionic redox reactions. Herein we introduce stable Li/Mn anti-siting in the TM layer of P2-type Na0.6Li0.2Mn0.8O2 as a strategy to create abundant Mn sites and O sites that are inequivalent to the counterpart of each in the lattice, and thus to prompt the diverse Mn and O redox. The self-locking of the anti-siting energetically inhibits the P2-O2 phase transformation and the resultant structural degradations. In addition, such modulation activates more Mn in charge compensation at high potentials. As a result, this regulation increases the reversible capacity from 104.2 mAh g−1 to 153.7 mAh g−1 and enhances the cycling stability of Na0.6Li0.2Mn0.8O2. This anti-siting strategy offers a new solution to designing cathode materials with high structural stability and high energy density.

Destabilization of Oxidized Lattice Oxygen in Layered Oxide Cathode.

Integrating anion-redox capacity with orthodox cation-redox capacity is deemed as a promising solution for high-energy-density battery cathodes surmounting the present technical bottlenecks. However, the evolution of oxidized oxygen species during the electrochemical or chemical process easily jeopardizes the reversibility of oxygen redox and remains poorly understood. Herein, we showcase the gradual conversion of the π-interacting oxygen (localized hole states on O) to the σ-interacting oxygen upon resting at a high voltage for P3-type Na0.6Li0.2Mn0.8O2 with nominally stable ribbon-like superstructure, accompanied by the O-O dimerization and the local structural reorganization. We further pinpoint an abnormal Li+ migration process from the alkali-metal layer to the transition-metal layer for desodiated P3-Na0.6Li0.2Mn0.8O2, thereby leading to a partial reconstruction of the ribbon superstructure. The high-voltage plateau of oxygen-redox cathodes is concluded to be exclusively controlled by the oxygen stabilization mechanism rather than the superstructure ordering. In addition, there exists a kinetic competition between π and σ interaction during the uninterrupted electrochemical process.

Air Corrosion of Layered Cathode Materials for Sodium-Ion Batteries: Cation Mixing and a Practical Suppression Strategy.

Layered oxide cathodes of sodium-ion batteries (SIBs) are considered promising candidates due to their fascinating high capacity, good cyclability, and environmental friendliness. However, the air sensitivity of layered SIB cathodes causes high electrode manufacturing costs and performance deterioration, hampering their practical application. Herein, a commercial O3-type layered Na(Ni1/3Fe1/3Mn1/3)O2 (NNFM) material is adopted to investigate the air corrosive problem and the suppression strategy. We reveal that once the layered material comes in contact with ambient air, cations migrate from transition metal (TM) layers to sodium layers at the near surface, although Na+ and TM ions show quite different ion radii. Experimental results and theoretical calculations show that more Ni/Na disorder occurs in the air-exposed O3-NNFM materials, owing to a lower Ni migration energy barrier. The cation mixing results in detrimental structural distortion, along with the formation of residual alkali species on the surface, leading to high impedance for Na+ diffusion during charge/discharge. To tackle this problem, an ultrathin and uniform hydrophobic molecular layer of perfluorodecyl trimethoxysilane is assembled on the O3-NNFM surface, which significantly suppresses unfavorable chemistry and structure degradation during air storage. The in-depth understanding of the structural degradation mechanism and suppression strategy presented in this work can facilitate high-energy cathode manufacturing from the perspective of future practical implementation and commercialization.

Dual-ion regulation of coordination chemistry for high-voltage stabilized P2-type cathode

P2-Na2/3Ni1/3Mn2/3O2 has shown great potential as cathode material for sodium-ion batteries with its high theoretical capacity and energy density. However, severe structural changes are induced by charging P2-Na2/3Ni1/3Mn2/3O2 above 4.2 V, resulting in rapid capacity decay and poor kinetic capability. In this study, we propose a Zn/Ti synergistic modification strategy to stabilize the P2-type cathode under high voltage. It is found that the P2-O2 phase transition with large volume change is replaced by a milder P2-Z phase transition with the noteworthy improvement in structural stability and Na+ diffusion kinetics, due to the disordered Na+/vacancy and the suppressed of the sliding of transition metal layers, as disclosed by density functional theory calculations and in-situ X-ray diffraction. Concurrently, The phenomenon of Ni and O reductive coupling is inhibited by regulating local O coordination owing to the incorporation of a strong Ti−O covalence bond, leading to the more reversible charge compensation mechanism and the inhibited lattice O evolution, as clearly revealed by ex-situ X-ray absorption spectroscopy and Differential Electrochemical Mass Spectrometry. Consequently, we obtained a stable P2-Na0.67Zn0.05Ni0.28Mn0.52Ti0.15O2 cathode, achieving an average discharge voltage of 3.62 V at 0.1 C and a capacity retention of 80% after 500 cycles at 2 C. This research provides valuable insights into the enhancement of sodium-ion battery cathode materials by utilizing different functional ions in synergy.

Unleashing the impact of Nb-doped, single crystal, cobalt-free P2-type Na0.67Ni0.33Mn0.67O2 on elevating the cycle life of sodium-ion batteries

A synergistic stabilization effect in a Nb-doped P2-type single crystal cobalt-free layered oxide cathode material, offering remarkable cycling stability and high-power performance for Na-ion batteries have unveiled in this study. The introduction of Nb in the transition metal layer not only reduces the electronic band gap but also enhances electronic conductivity and mitigates ionic diffusion energy barriers. The induction of a robust Nb-O bond expedites electron and Na+ transfer, contributing to the stabilization of the host structure is further confirmed through the density functional theory calculations, including electron localization function (ELF) and crystal orbital Hamiltonian population (COHP). To the best of our knowledge, this study is the first to demonstrate a homogeneous distribution of niobium throughout the single crystal, specifically doped at the nickel site within the bulk, without inducing atomic-scale surface reorganization. The presence of single crystals improves various kinetic factors, demonstrating the profound correlation between structural defects and chemical proliferation, thereby reducing the evolution of oxygen gas. The P2-type Nb-doped single crystal cathode (Na0.67Ni0.31Mn0.67Nb0.02O2) exhibits remarkable capacity retention, >95 % after 100 cycles at 0.1 C and >90 % after an extended cycling of 2000 cycles at 1 C. Practical assessments in complete cell setups with a pre-sodiated hard carbon anode further validate the material's viability, showcasing capacity retention of over 93 % after 100 cycles in a coin cell and approximately 89 % in a pouch cell format. This comprehensive study establishes the transformative potential of Nb-doped single crystal cobalt-free P2-type layered oxide cathode materials, marking a significant advancement in sodium-ion battery technology.

Influence of Li Content on the Topological Inhibition of Oxygen Loss in Li-Rich Cathode Materials.

Lithium-rich layer oxide cathodes are promising energy storage materials due to their high energy densities. However, the oxygen loss during cycling limits their practical applications. Here, the essential role of Li content on the topological inhibition of oxygen loss in lithium-rich cathode materials and the relationship between the migration network of oxygen ions and the transition metal (TM) component are revealed. Utilizing first-principles calculations in combination with percolation theory and Monte Carlo simulations, it is found that TM ions can effectively encage the oxidized oxygen species when the TM concentration in TM layer exceeds 5/6, which hinders the formation of a percolating oxygen migration network. This study demonstrates the significance of rational compositional design in lithium-rich cathodes for effectively suppressing irreversible oxygen release and enhancing cathode cycling performance.

Role of Co Content on the Electrode Properties of P3-Type K0.5Mn1-xCoxO2 Potassium Insertion Materials.

Potassium-ion batteries are widely being pursued as potential candidates for stationary (grid) storage, where energy dense K+ insertion cathodes are central to economic and energy efficient operation. To develop robust K-based cathodes, it is key to correlate their underlying electronic states to the final electrochemical performance. Here, we report the synthesis and structure-electrochemical property correlation in P3-type K0.5Mn1-xCoxO2 binary layered oxide cathodes. Spectroscopic analyses revealed a random distribution of Mn and Co in transition metal layers in the oxygen anion framework. In this solid-solution family, Co substitution improved the electronic conductivity and structural stability of P3 phases by minimizing local lattice distortion. Co substitution led to a systematic shift of the Co4+/Co3+ and Mn4+/Mn3+ redox potentials. Galvanostatic cycling showed that the Co substitution reduced the initial capacity while improving the cycling stability. The role of Co on final electrochemical properties of P3-layered oxides has been elucidated as a design tool to develop practical potassium-ion batteries.

Control of Polarity in Kagome‐NiAs Bismuthides

AbstractA 2×2×1 superstructure of the P63/mmc NiAs structure is reported in which kagome nets are stabilized in the octahedral transition metal layers of the compounds Ni0.7Pd0.2Bi, Ni0.6Pt0.4Bi, and Mn0.99Pd0.01Bi. The ordered vacancies that yield the true hexagonal kagome motif lead to filling of trigonal bipyramidal interstitial sites with the transition metal in this family of “kagome‐NiAs” type materials. Further ordering of vacancies within these interstitial layers can be compositionally driven to simultaneously yield kagome‐connected layers and a net polarization along the c axes in Ni0.9Bi and Ni0.79Pd0.08Bi, which adopt Fmm2 symmetry. The polar and non‐polar materials exhibit different electronic transport behaviour, reflecting the tuneability of both structure and properties within the NiAs‐type bismuthide materials family.

Control of Polarity in Kagome-NiAs Bismuthides.

A 2×2×1 superstructure of the P63/mmc NiAs structure is reported in which kagome nets are stabilized in the octahedral transition metal layers of the compounds Ni0.7Pd0.2Bi, Ni0.6Pt0.4Bi, and Mn0.99Pd0.01Bi. The ordered vacancies that yield the true hexagonal kagome motif lead to filling of trigonal bipyramidal interstitial sites with the transition metal in this family of "kagome-NiAs" type materials. Further ordering of vacancies within these interstitial layers can be compositionally driven to simultaneously yield kagome-connected layers and a net polarization along the c axes in Ni0.9Bi and Ni0.79Pd0.08Bi, which adopt Fmm2 symmetry. The polar and non-polar materials exhibit different electronic transport behaviour, reflecting the tuneability of both structure and properties within the NiAs-type bismuthide materials family.

Design of high-entropy P2/O3 hybrid layered oxide cathode material for high-capacity and high-rate sodium-ion batteries

High-entropy layered cathode materials have garnered significant attention due to their exceptional structural stability and capacity retention. However, the complex composition of these materials has posed challenges for performance optimization. Herein, an innovative high-entropy P2/O3 hybrid layered oxide cathode material with impressive reversible capacity and high-rate capabilities is designed according to the configurational entropy adjustment strategy. Specifically, the unique structure of Na0.85Li0.05Ni0.3Fe0.1Mn0.5Ti0.05O2 (LNFMT) exhibits not only enhanced anionic activity but also mitigated migration of transition metals at high voltage. The high-entropy effect facilitates the migration of Li+ to Na layer, forming a pseudo-tetrahedral structure that hinders the movement of Fe3+. Additionally, the robust Ti-O bond ensures the internal cohesion of transition metal layers, enhancing the structural stability during de-/intercalation processes. As a result, the undesirable P2-O2 phase transformation is effectively suppressed in 1.5–4.5 V, leading to a remarkable capacity retention of over 70% after 100 cycles at 0.2 C. Moreover, LNFMT shows a high discharge capacity of 116 mAh/g at 10 C with excellent capacity retention of 94.23% after 150 cycles in 2.0–4.2 V, demonstrating its superior rate capability. This research showcases the significant impact of the high-entropy effect and provides a novel perspective for the design of sodium-ion cathode materials.

Stabilization of Li2MnO3 phase by Mg doping suppressing irreversible oxygen loss and Mn ions migration

Li-rich Mn-based oxide cathode material has attracted people’s attention in that their higher specific capacity, which is attributed to their unique biphasic structure. When the voltage is greater than 4.5V, the Li2MnO3 phase is activated to provide a high specific capacity. But during the cycling process, the Li2MnO3 phase is continuously activated. During this process, O2 will be released and transition metal (TM) ions will migrate, leading to structural phase transition, resulting in voltage decay and capacity loss. In this work, 2wt% Mg-doped Li1.18Mg0.02Mn0.54Co0.13Ni0.13O2 exhibits excellent electrochemical performance. After 100 cycles at 1C, the capacity retention rate is 87.83% By introducing Mg at the position of Li in the TM layer, a more stable Mg-O bond is introduced, in which the inert Mg is not involved in the redox reaction but is fixed in the TM layer. The Li2MnO3 phase is optimized by stabilizing the lattice oxygen to make the Li2MnO3 phase more stable, so as to suppress the irreversible oxygen loss and slow down the structural phase transition. Improved the issue of low initial Coulomb efficiency of materials, the voltage attenuation is alleviated, and the cycle stability is improved.

Strain-modulated Mn-rich layered oxide enables highly stable potassium-ion batteries

Mn-rich layered oxides show great promise as cathode materials for potassium-ion batteries due to their high capacity and cost-effectiveness. However, internal structural strain and irreversible phase transitions caused by Jahn-Teller distortion affect their cycling stability. Here, we present an efficient strategy to concurrently modulate the internal strain and suppress the irreversible phase transition in Mn-rich cathodes by incorporating amounts of zinc (Zn) ions into the transition metal layers. The substituted Zn serves to regulate local chemistry, thereby mitigating octahedral distortion in Mn-O bonds, relieving the strain between layers, and reducing the occurrence of P3-O3 phase transition under high voltages. These findings are supported by EXAFS, in situ X-ray diffraction, advanced transmission electron microscopy, electron tomography, and DFT simulations. The low-strain K0.5Mn0.8Co0.1Zn0.1O2 electrode exhibits a high reversible capacity retention about ∼90 % (105 mAh g−1 at 100 mA g−1), exceptional rate performance in the voltage of 1.5 ∼ 3.9 V, and a substantial capacity retention after 500 cycles. This strain-relieved approach broadens the scope of lattice engineering by addressing internal strain concerns and mitigating the strain associated with potassium (de)intercalation, thereby having potential to advance the development of stable cathodes for PIBs.

Probing the account of phase transition upon electrochemical cycling of the P2-Na0.67Ni0.15Fe0.2Mn0.65O2 layered oxide cathodes for sodium-ion batteries

Layered P2-Na0.67Ni0.15Fe0.2Mn0.65O2 (P2-NFM) cathode material has attracted great attention in sodium-ion batteries due to its high theoretical capacity, low cost, and environmental friendliness. However, P2-NFM exhibits irreversible phase transition and slip of transition metal layers in the high voltage range during charging process, leading to a gradually declined performance of the cathode material. It is therefore necessary to investigate the mechanism of phase transition of P2-NFM as well as the effect of phase transition on its performance. Herein, utilizing ex situ x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, the crystal structure and TM (transition-metal) bonding changes caused by phase transition are elucidated. It is found that P2-NFM is prone to undergo an irreversible P2-O2 phase transition at high voltage, causing changes in lattice parameters and rapid capacity decay. The irreversible phase transition is mainly due to he dynamic transformation of valence states of Fe and Ni in P2-NFM materials at high voltage. It is this process that results in irreversible fluctuations in the bond lengths between these elements and oxygen, consequently instigating interlayer slip within the material. Besides, the charge compensation mechanism of P2-NFM has been elucidated based on the study of its initial charging process. Results show that the charge compensation is mainly contributed by Ni and Fe in the high voltage range, while by a small amount of Mn in the low voltage range. It reveals the essential cause of the adverse phase transition of P2-NFM materials and points out the direction for improving the cycling stability of these layered oxide materials.