Layered Oxide Research Articles

Synergistic Effect of Anchoring Transitional/Interstitial Sites on Boosting Structural and Electrochemical Stability of O3-Type Layered Sodium Oxides.

O3-type layered oxides are considered promising cathode materials for next-generation high-energy-density sodium-ion batteries (SIBs). However, they face challenges, such as low rate capacity and poor cycling stability, which arise from structural deformation, sluggish Na+ diffusion kinetics, and interfacial side reactions. Herein, a synergistic substitution strategy for transitional and interstitial sites was adopted to improve the structure stability and Na+ diffusion kinetics of the O3-type NaNi0.2Fe0.4Mn0.4O2. Simulation results indicate that Co3+/B3+ codoping effectively lowers the Na+ migration energy barrier. In addition, the synergistic effect of Co3+/B3+ codoping provides ultralow lattice strain during repeated Na+ deintercalation/intercalation. In situ characterization verified that the complex phase transformation during charge and discharge was suppressed, thereby significantly improving the structural stability. At 1 and 3 C, the capacity retention of the modified O3-Na(Ni0.2Fe0.4Mn0.4)0.96Co0.04B0.02O2 (NFMCB) improved from 29.6% and 1.7% to 86.7% and 88.6% after 200 cycles, respectively. Even at 10 C, it could still produce 107.2 mAh·g-1. Furthermore, full cells assembled with this material and commercial hard carbon exhibit a high energy density of 316.2 Wh·kg-1 and a capacity retention of 80.8% after 200 cycles at 1 C. It is expected that this strategy will facilitate the commercialization of O3-type layered oxides.

Deciphering the Interfacial Li-Ion Migration Kinetics of Ni-Rich Cathodes in Sulfide-Based All-Solid-State Batteries.

Nickel-rich layered oxide with high reversible capacity and high working potentials is a prevailing cathode for high-energy-density all-solid-state lithium batteries (ASSLBs). However, compared to the liquid battery system, ASSLBs suffer from poor Li-ion migration kinetics, severe side reactions, and undesired formation of space charge layers, which result in restricted capacity release and limited rate capability. In this work, we reveal that the capacity loss lies in the H2-H3 phase transition period, and we propose that the inconsistent interfacial Li-ion migration is the arch-criminal. We introduce Si doping to stabilize the bulk structure and Li4SiO4 fast ionic conductor coating to regulate the interfacial behaviors between the Ni-rich cathode and sulfide-based solid electrolyte Li6PS5Cl. The modified NCM@LSO-2||LPSCl||Li-In ASSLBs deliver a high reversible capacity of 183.5 mA h g-1 at 0.1C, 30.3% higher than the bare NCM811 electrode. Besides, the interfacial regulation strategy enables the operation at a high rate of 5.0C and achieves a high capacity retention ratio of ∼85.8% after 500 cycles at 1.0C. Furthermore, the underlying mechanisms are well investigated through kinetic analyses and theoretical simulations. This work provides an in-depth understanding on the interfacial degradations between Ni-rich cathodes and sulfide-based all-solid-state electrolytes from the view of kinetic limitations and offers potential solutions.

Research Progress on P2/O3-Composite Layer Metal Oxide Cathode Materials for Sodium-Ion Batteries

Abstract The high cost and uneven distribution of lithium resources have prompted searches for alternatives to lithium-ion batteries. Among various alternatives, the sodium layered oxide cathode materials, have shown significant research potential due to their low cost. Layered oxide materials can be categorized into sodium-rich O3 types and sodium-deficient P2 types, which have different structural features. O3 type materials offer high specific capacities but suffer from complex pathways for Na+ de-intercalation, slow Na+ diffusion, and poor air stability. P2 type materials are limited in full cell applications due to their lower practical specific capacities. Therefore, researchers conceived the idea of combining the advantages of both to construct P2/O3 composite structure cathode materials (CSMs), utilizing the synergistic effects of the CSMs to overcome the limitations of single structure material, and successfully synthesized CSMs with appropriate specific capacities. These materials effectively suppress unfavorable phase transitions and enhance Na+ diffusion coefficient, thereby improving electrochemical performance. This paper reviews the recent advancements in CSMs for sodium-ion batteries, highlighting synthesis strategies that incorporate "cationic potential" theory, element substitution, sodium content adjustment, and control of calcination processes to synthesize diverse CSMs.

Using High Valence Nb to Regulate the Superlattice Structure for the Na-Ion Layered Oxide Cathode with Superior Electrochemical Performance

Using High Valence Nb to Regulate the Superlattice Structure for the Na-Ion Layered Oxide Cathode with Superior Electrochemical Performance

Simultaneous Regulating the Surface, Interface, and Bulk via Phosphating Modification for High-Performance Li-Rich Layered Oxides Cathodes.

Li-rich Mn-based layered oxides (LRMOs) are regarded as the leading cathode materials to overcome the bottleneck of higher energy density. Nevertheless, they encounter significant challenges, including voltage decay, poor cycle stability, and inferior rate performance, primarily due to irreversible oxygen release, transition metal dissolution, and sluggish transport kinetics. Moreover, traditionally single modification strategies do not adequately address these issues. Herein, an innovative "all-in-one" modification strategy is developed, simultaneously regulating the surface, interface, and bulk via an in-situ gas-solid interface phosphating reaction to create P-doped Li1.2Mn0.54Ni0.13Co0.13O2@Spinel@Li3PO4. Specifically, Li3PO4 surface coating layer shields particles from electrolyte corrosion and enhances Li+ diffusion; in-situ constructed spinel interfacial layer reduces phase distortion and suppresses the lattice strain; the strong P─O bond derived from P-doping stabilizes the lattice oxygen frame and inhibits the release of O2, thereby improving the reversibility of oxygen redox reaction. As a result, the phosphatized LRMO demonstrates an exceptional capacity retention of 82.1% at 1C after 300 cycles (compared to 50.8% for LRMO), an outstanding rate capability of 170.5 mAh g-1 at 5C (vs 98.9 mAh g-1 for LRMO), along with excellent voltage maintenance and thermostability. Clearly, this "all-in-one" modification strategy offers a novel approach for high-energy-density lithium-ion batteries.

Advanced Balancing of High-Energy Lithium Ion Cells Comprising Lithium-Rich Layered Oxide and a-Si/CuSi Nanowire Using a Cathode Pre-Lithiation Additive

Abstract Advances in lithium-ion battery (LIB) research have strived for high-energy, safe, and sustainable materials. Li-rich Li1.2Ni0.2Mn0.6O2 (LRNM) cathodes have shown great promise with high voltages and excellent specific capacities. Obstacles preventing the viability and commercialization of LRNM are the initial capacity loss of roughly 30% and rapid voltage decay upon cycling. Herein, lithium oxalate (Li2C2O4) is investigated as a pre-lithiation additive to utilize the first-cycle lithium re-intercalation losses of LRNM to compensate the irreversible lithium consumption in graphite and high-capacity a-Si on copper silicide nanowire (a-Si/CuSi NW) anodes. Specifically, the decomposition process of Li2C2O4 as well as the interaction between the electrode components inside the cell are comprehensively examined. This concept allows us to extend the cycle life of graphite||LRNM cells at 1C from less than 500 cycles (142 mAh g-1, 78%) to more than 900 cycles (143 mAh g-1, 82%) before reaching the 80% capacity retention threshold. Finally, LRNM electrodes with a precisely balanced concentration of Li2C2O4 are prepared in order to compensate the high irreversible losses of a-Si/CuSi NW anodes, achieving a capacity retention of almost 50% with a remaining specific capacity of 82 mAh g-1 after 400 cycles in high-energy a-Si/CuSi NW||LRNM lithium-ion cells.

Mitigating Li-Rich Layered Cathode Capacity Loss by Using a Siloxane Electrolyte Additive.

The instability of the electrode-electrolyte interface in high-voltage cathode materials significantly hinders the development of high-energy-density lithium-ion batteries (LIBs). In this study, 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane (DTS) is employed as an electrolyte additive to enhance the cycling stability and capacity retention for Li||LLO (Li-rich layered oxide) batteries operating at 4.8 V. Theoretical calculations show that DTS can preferentially oxidize on the surface of the cathode. The oxidation forms a robust cathode electrolyte interface (CEI) on the LLO surface, significantly mitigating cracking, regeneration, and irreversible phase transitions of the LLO cathode. As anticipated, the Li||LLO batteries with the DTS electrolyte exhibit a capacity retention of 85.4% after 100 cycles at 4.8 V compared to the baseline electrolyte (45.2%). Furthermore, these batteries demonstrate superior capacity retention after 100 cycles at 4.8 V, even with the presence of 1000 ppm of H2O.

Depth‐of‐Discharge Dependent Capacity Decay Induced by the Accumulation of Oxidized Lattice Oxygen in Li‐Rich Layered Oxide Cathode

AbstractMore and more basic practical application scenarios have been gradually ignored/disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths‐of‐discharge (DODs). Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium‐rich layered oxide (LRLO) cathodes present anomalously poor capacity retention at low‐DOD cycling, which is essentially different from typical layered cathodes (e.g. NCM), and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD‐dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen (On−). Upon low‐DOD cycling, the accumulation of On− and the persistent presence of vacancies in the transition metal (TM) layer intensified the in‐plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out‐of‐plane TM migration. As a result, the aggravated structural degradation of LRLO at low‐DOD impeded reversible Li+ intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of On− persistently corroded the electrode‐electrolyte interface, especially negative for pouch‐type full‐cells with the shuttle effect. Once the “double‐edged sword” effect of anionic redox being elucidated under practical condition, corresponding modification strategies/routes would become distinct for accelerating the practical application of LRLO.

Galvanic hydrogenation reaction in metal oxide

Rational reforming of metal oxide has a potential importance to modulate their inherent properties toward appealing characteristics for various applications. Here, we present a detailed fundamental study of the proton migration phenomena between mediums and propose the methodology for controllable metal oxide hydrogenation through galvanic reactions with metallic cation under ambient atmosphere. As a proof of concept for hydrogenation, we study the role of proton adoption on the structural properties of molybdenum trioxide, as a representative, and its impact on redox characteristics in Li-ion battery (LiB) systems using electrochemical experiments and first-principles calculation. The proton adoption contributes to a lattice rearrangement facilitating the faster Li-ion diffusion along the selected layered and mediates the diffusion pathway that promote the enhancements of high-rate performance and cyclic stability. Our work provides physicochemical insights of hydrogenations and underscores the viable approach for improving the redox characteristics of layered oxide materials.

Co-free gradient lithium-rich cathode for high-energy batteries with optimized cyclability

Lithium-rich layered oxides (LLOs) hold the promise for high-energy battery cathodes. However, its application has been hindered by voltage decay associated with irreversible reactions at high voltages despite decades of intensive efforts. Here, we first theoretically studied the molecular orbitals of Mn-based Li-rich configurations. We found that the π-bond ring formed within the LiMn6 structure could participate in stable redox reactions as one unit, but Co could disrupt its symmetry. We thus designed and synthesized Co-free concentration-gradient LLOs (CF-CG-LLOs) materials. The combination of concentration gradient and Co removal leads to exceptional capacity retention without any fading over 100 cycles of the pouch cell. More importantly, it exhibits an extraordinarily low voltage decay of 0.15 mV/cycle, accompanied by a high Coulombic efficiency of 99.86%. This concept and demonstration of CF-CG-LLO cathodes reveal a viable avenue toward low-cost, high-energy-density battery cathodes.

A Collaboration of Interfacial Engineering and Particle Assembly Enables Highly Stable Li‐Rich Layered Cathodes for Li‐ion Batteries

AbstractLithium‐rich layered oxide cathodes (LLO) are renowned for their high specific capacity (>250 mAh g−¹) and have emerged as promising candidates for lithium‐ion batteries. However, significant capacity fades and voltage decay pose challenges to their commercialization, primarily due to the degradation of their original structure. In this study, a simple and rapid approach is presented that combines interfacial engineering and particle assembly to achieve a highly stable LLO cathode. This cathode features a single‐crystal LLO reassembled into a porous microsphere structure, along with a surface coating of polypropylene phosphate amide (PPA) formed through in situ cross‐linking of polyacrylic acid and ammonium polyphosphate, and a deuterogenic spinel interface layer. The dual protective coatings‐PPA and spinel‐effectively inhibit the dissolution of transition metals, delay structural deterioration, and enhance lithium‐ion diffusion. Additionally, the cross‐linked PPA layer strengthens the interconnection among LLO nanoparticles, improving the stability of the assembled microsphere structures while mitigating electrolyte corrosion. Consequently, the LLO@PPA electrode exhibits excellent capacity retention of 84.87% over 500 cycles at 0.5 C and shows significant improvements in rate performance. This work offers an effective modification strategy for developing next‐generation lithium‐rich cathodes with enhanced rate capacity and cycle life.

Sb-anchoring single-crystal engineering enables ultra-high-Ni layered oxides with high-voltage tolerance and long-cycle stability

Ni-rich layered oxides are promising cathodes for Li-ion batteries, but the inherent structural defects result in severe surface/bulk degradation during long cycling, especially at high cutoff voltage. Herein we propose a Sb-anchoring single-crystalline engineering to enhance the microstructural and electrochemical stability of ultra-high-Ni layered oxides, where the surface-enriched Sb doping inhibits Li-Ni mixing, suppressing the undesired layered to mixed/rock-salt phase transformation; the bulk-doped Sb rivets into Ni sites, reinforcing the bulk phase stability; the single-crystal endows enhanced crack resistance and reduced surface area, preventing surface parasitic reactions and the subsequent proliferation of cathode electrolyte interfaces. In-situ XRD reveals an essential correlation between cycle stability and phase reversibility, whereas Sb doping into both surface and bulk structures showcases a continuous anchoring effect, largely enhancing the phase transformation reversibility. DFT calculations prove a high oxidation tolerance, as Ni2+ diffusion barrier is higher than the pure cathode. A representative Li(Ni0.9Co0.05Mn0.05)0.99Sb0.01O2 cathode exhibits a high-voltage up to 4.6V, and a Li(Ni0.9Co0.05Mn0.05)0.99Sb0.01O2//graphite full-cell demonstrates an ultra-high capacity retention of 93.4% after 1000 cycles at 1C in 3.0−4.2V. This simple and efficient cathode engineering will promote the promising application of Ni-rich layered oxides in high-energy Li-ion batteries.

Layered graphene oxide membrane for heavy metal separation via molecular dynamics simulation

Purification of water and industrial wastewater, especially those containing toxic metals, is a critical challenge for developing societies. Nano membranes, including two-dimensional graphene oxide nanomaterials, have recently gained prominence as an alternative to traditional polymer membranes. However, the efficacy of these membranes for the removal of heavy metals has not been extensively studied. In this work, molecular dynamics simulation is used to investigate the performance of graphene oxide membranes, with the oxidation ratio of 20 %, for the removal of mercury and arsenic ions at a concentration of 0.5 M, via reverse osmosis at 200 Mpa pressure. Results demonstrate that graphene oxide membranes are effective for separating heavy metal ions while maintaining good water flow. The mechanism of water molecule passage through the graphene oxide membrane is also investigated by analyzing the structural images of water molecules between the layers, water density diagrams in the nanochannel, and the number of hydrogen bonds at various channel inter-layer distances. In addition, raising the temperature of the aqueous solution from 300 to 340 K increases the water flux and decreases ion rejection. Increasing the concentration of mercury and arsenic ions from 0.5 to 1 M in the feed water leads to decrease in water flux with the least impact on ion rejection. Furthermore, the influence of membrane geometry on its performance is also investigated. By comparing the cross-flow and dead-end geometries, it is found that the cross-flow geometry performs better than the dead-end geometry both in water flux and the removal efficiency of mercury and arsenic ions. The potential of graphene oxide membranes in the treatment of wastewater containing heavy metals is highlighted by these findings, which provide insights into optimizing their design and operational parameters.

Enhancing the electrochemical performance of Ni-rich cathode through an in-situ La-doping and La4NiLiO8-coating synergistic strategy

Ni-rich layered oxides offer numerous advantages such as high discharge capacity, cost-effectiveness, and environmental friendliness, making them the mainstream cathodes for high-energy density lithium-ion batteries. However, their widespread commercialization is hindered by critical challenges in cycling performance, stemming from unstable interface and structure, particularly at elevated charge cut-off voltages. Herein, a dual-modification strategy combining La doping and La4NiLiO8 coating was proposed to synergistically enhance the surface/interface and structure stability of the LiNi0.83Co0.11Mn0.06O2 (referred to as NCM83) cathode. Unlike conventional methods, a well-designed La(OH)3 coating pretreatment was employed on the Ni0.83Co0.11Mn0.06(OH)2 precursor. This pretreatment aimed to facilitate the in-situ formation of La doping and La4NiLiO8 during the lithiation of the coated precursor, while ensuring desired uniformity of the La4NiLiO8 coating and La doping. This dual-modification strategy integrated the advantages of both La doping and La4NiLiO8 coating, demonstrating excellent capability to improve the overall performance of NCM83. The La doping, acting as a pillar, not only strengthened the layered structure of the cathode to mitigate volume changes, but also enhanced Li+ diffusion by broadening the c axis spacing. The La4NiLiO8 coating efficiently protected the cathode from H2O/CO2 attack and electrolyte erosion, while also facilitating Li+ transport owing to its favorable Li-conductive properties. Such a dual-modification strategy significantly enhanced the electrochemical performance of NCM83, as demonstrated by the excellent long-term cyclic stability, rate capability, and thermal stability at a high charge cut-off voltage of 4.5 V. This work highlighted the benefits of integrating elemental doping and surface coating, while offering a promising synthetic protocol for straightforward and effective dual-modification of various cathodes.

Triple modifications of Li-rich manganese-based cathode materials using LiMnPO4 one-step method

Li-rich manganese-based layered oxide (LMR) is one of the most promising cathode materials for lithium batteries owing to its high specific capacity and low cost. Unfortunately, its commercial application is hindered by voltage decay, capacity diminishing, and poor rate performance during cycling. Thus, a facile surface triple modification method for Li1.2Ni0.2Mn0.6O2 has been proposed. This method constructs a protective LiMnPO4 coating layered, a spinel interface, and introduces some oxygen vacancies. The construction of the coating layer and oxygen vacancies alleviates interface side reactions and irreversible loss of O, ultimately suppressing voltage decay and improving cycling performance. The spinel phase constructs a 3D Li+ diffusion pathway, which improves the rate performance. As expected, electrochemical tests indicate that the materials coated by 3 wt% LiMnPO4 exhibit a mitigated voltage attenuation from 2.204 mV to 1.626 mV, an enhanced capacity retention of 85.60 % at 1C after 100 cycles, and a discharge capacity of 171.6 mAh·g−1 at 5C, which is better than that of bare materials (163.9 mAh·g−1 at 5C). This one-step processing method provides a simple and efficient method for modifying LMR materials.

Reversible anion redox in Mn-based layered oxide via Ce-doping for stable Na-ion storage

Reversible anion redox in Mn-based layered oxide via Ce-doping for stable Na-ion storage

Drastically Promoting Rate Capability via Dual-Cations Intercalation of V2O5 Enabling Rapid Zinc-Ion Storage.

Layered vanadium pentoxide (V2O5) has drawn enormous attention as cathode material for aqueous zinc-ion batteries (AZIBs). However, the fragile open-framework and the sluggish Zn2+ migration due to the strong electrostatic interaction between Zn2+ and cathode electrode hinder the development of AZIBs. Here, an effective dual-cations intercalation strategy is employed based on synergistic effect of Mn2+ and Zn2+, which introduces guest species with robust layered construction and weak electrostatic interaction in the V2O5 bulk. Consequently, the (Mn0.13Zn0.03)V2O5 (abbreviated to MZVO) electrode exhibits a high reversible capacity of 463mA h g-1 at 0.1 A g-1, a high cycling stability (94% of capacity retention after 1000 cycles at 10 A g-1) and superior rate performance of 256 mAh g-1 at 20 A g-1. The outstanding performance of MZVO cathode is attributed to the Mn2+-induced fast migration of Zn2+ transfer and Zn2+-induced high structural stability conducted by density functional theory (DFT) calculations. The two-phase reaction mechanism of MZVO during Zn2+ (de)interaction is systematically expounded via operando XRD. This study will provide reference for the design of modified layered metal oxides in the future.

High-Entropy Rock-Salt Surface Layer Stabilizes the Ultrahigh-Ni Single-Crystal Cathode.

Single-crystalline Ni-rich layered oxides are one of the most promising cathode materials for lithium-ion batteries due to their superior structural stability. However, sluggish lithium-ion diffusion kinetics and interfacial issues hinder their practical applications. These issues intensify with increasing Ni content in the ultrahigh-Ni regime (≥90%), significantly threatening the practical viability of the single-crystalline strategy for ultrahigh-Ni layered oxide cathodes. Herein, by developing a high-entropy coating strategy, we successfully constructed an epitaxial lattice-coherent high-entropy rock-salt layer (∼3 nm) via Zr and Al doping on the surface of the single-crystalline cathode LiNi0.92Co0.05Mn0.03O2 through an in situ modification process. The surface high-entropy rock-salt layer with tailored Ni valence and lattice coherence not only greatly improves lithium-ion diffusion kinetics but also suppresses interface parasitic reactions and surface structural degradations. The high-entropy surface layer-stabilized ultrahigh-Ni single-crystalline cathode (SC-Ni92-ZA) demonstrates significantly improved rate and cycling performances (127.5 mAh g-1 at 20C, capacity retention of 74.9% after 500 cycles at 1C) in a half-cell. The SC-Ni92-ZA exhibits a capacity retention of 87.1% after 600 cycles at 1C in a full-cell. This epitaxial lattice-coherent high-entropy coating strategy develops a promising avenue for developing high-capacity, long-life cathode materials.

Depth-of-Discharge Dependent Capacity Decay Induced by the Accumulation of Oxidized Lattice Oxygen in Li-Rich Layered Oxide Cathode.

More and more basic practical application scenarios have been gradually ignored/disregarded, in fundamental research on rechargeable batteries, e.g. assessing cycle life under various depths-of-discharge (DODs). Herein, although benefit from the additional energy density introduced by anionic redox, we critically revealed that lithium-rich layered oxide (LRLO) cathodes present anomalously poor capacity retention at low-DOD cycling, which is essentially different from typical layered cathodes (e.g. NCM), and pose a formidable impediment to the practical application of LRLO. We systemically demonstrated that DOD-dependent capacity decay is induced by the anionic redox and accumulation of oxidized lattice oxygen (On-). Upon low-DOD cycling, the accumulation of On- and the persistent presence of vacancies in the transition metal (TM) layer intensified the in-plane migration of TM, exacerbating the expansion of vacancy clusters, which further facilitated detrimental out-of-plane TM migration. As a result, the aggravated structural degradation of LRLO at low-DOD impeded reversible Li+ intercalation, resulting in rapid capacity decay. Furthermore, prolonged accumulation of On- persistently corroded the electrode-electrolyte interface, especially negative for pouch-type full-cells with the shuttle effect. Once the "double-edged sword" effect of anionic redox being elucidated under practical condition, corresponding modification strategies/routes would become distinct for accelerating the practical application of LRLO.

Na5/6[Ni1/3Mn1/6Fe1/6Ti1/3]O2 as an Optimized O3-Type Layered Oxide Positive Electrode Material for Sodium-Ion Batteries.

Layered oxides, such as NaxMeO2 (Me = transition metal, x = 0-1), are believed to be the most promising positive electrode materials for Na-ion batteries because of their high true density, large capacities, high working potentials, and reversibility. This study identified Na5/6[Ni1/3Mn1/6Fe1/6Ti1/3]O2 as an optimal composition for use as an O3-type positive electrode material in Na-ion batteries on the basis of a comprehensive phase diagram, where the end members of the triangular phase diagram were Na2/3[Ni1/32+Mn2/34+]O2, Na2/3[Ni1/32+Ti2/34+]O2, and the hypothetical composition Na4/3[Ni1/32+Fe2/33+]O2. By investigating the effects of the partial substitution of Mn4+ with Fe3+ and Ti4+ within the Na(2/3+x)[Ni1/3Mn(2/3-x-y)FexTiy]O2 system, we optimized the capacity, working potential, and cycle performance. Substitution with Fe enhanced the discharge capacity due to the increased Na+ content in the initial composition, although it also led to a reduced cycling stability derived from irreversible Fe migration to the Na layers. In contrast, substitution with Ti improved the working potential and cycling stability, although an excessive Ti content caused capacity degradation with cycling. We found that the O3-type Na5/6[Ni1/3Mn1/6Fe1/6Ti1/3]O2 demonstrated an excellent cycle stability with minimal capacity loss over 250 cycles, which was attributed to the suppression of irreversible transition metal migration.