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[Display omitted] The interlayer distances in layered electrode materials, influenced by the chemical composition of the confined interlayer regions, have a significant impact on their electrochemical performance. Chemical preintercalation of inorganic metal ions affects the interlayer spacing, yet expansion is limited by the hydrated ion radii. Herein, we demonstrate that using varying concentrations of decyltrimethylammonium (DTA+) and cetyltrimethylammonium (CTA+) cations in chemical preintercalation synthesis followed by hydrothermal treatment, the interlayer distance of hybrid bilayered vanadium oxides (BVOs) can be tuned between 11.1 Å and 35.6 Å. Our analyses reveal that these variations in interlayer spacing are due to different amounts of structural water and alkylammonium cations confined within the interlayer regions. Increased concentrations of alkylammonium cations not only expand the interlayer spacing but also induce local bending and disordering of the V-O bilayers. Electrochemical cycling of hybrid BVO electrodes in non-aqueous lithium-ion cells show that specific capacities decrease as interlayer regions expand, suggesting that the densely packed alkylammonium cations obstruct intercalation sites and hinder Li+ ion transport. Furthermore, we found that greater layer separation facilitates the dissolution of active material into the electrolyte, resulting in rapid capacity decay during extended cycling. This study emphasizes that layered electrode materials require both spacious interlayer regions as well as high structural and chemical stabilities, providing guidelines for structural engineering of organic–inorganic hybrids. [ABSTRACT FROM AUTHOR]

As a cathode material for potassium-ion batteries (PIBs), manganese-based layered oxides have attracted widespread attention due to their low cost, ease of synthesis, and high performance. However, the Jahn-Teller effect caused by Mn3+ and the irreversible phase transformation of the structure leads to poor cycle stability, limiting the development of layered oxides in PIBs. Herein, we demonstrate the use of phase-transition-free CaTiO3 as rivets in K0.5Mn0.9Ti0.1O2 by a simple solid-state method. As verified by the in situ X-ray diffraction, the CaTiO3 rivets effectively prevent the slippage of the transition metal layer during charge and discharge, inhibiting structural degradation. As a result, the obtained K0.5Mn0.9Ti0.1O2-0.02CaTiO3 shows excellent cycling stability and rate performance, with high capacities of 119.3 and 70.1 mAh·g-1 at 20 and 1000 mA·g-1, respectively. At 200 mA·g-1, the capacity retention remains 94.7% after more than 300 cycles. This work represents a new avenue for designing and optimizing layered cathode materials for PIBs and other batteries. [ABSTRACT FROM AUTHOR]

In recent years, sodium-ion capacitors have attracted attention due to their cost-effectiveness, high power density and similar manufacturing process to lithium-ion capacitors. However, the utilization of oxide electrodes in traditional sodium-ion capacitors restricts their further advancement due to the inherent low operating voltage and electrolyte consumption based on their energy storage mechanism. To address these challenges, we incorporated Zn, Cu, Ti, and other elements into Na0.67Ni0.33Mn0.67O2 to synthesize P2-type Na0.7Ni0.28Mn0.6Zn0.05Cu0.02Ti0.05O2 with a modulated entropy and pillaring Zn. Through the synergistic interplay between the interlayer pillar and the entropy modulation within the layers, the material exhibits exceptional toughness, effectively shielding it from detrimental phase transitions at elevated voltage regimes. As a result, the material showcases outstanding kinetic properties and long-term cycling stability across the voltage range. By integrating these materials with hierarchical porous carbon nanospheres to form a "rocking chair" sodium-ion capacitor, the hybrid full device delivers a high energy density (171 Wh·kg−1) and high power density (5245 W·kg−1), as well as outstanding cycling stability (77% capacity retention after 3000 cycles). This work provides an effective material development route to realize simultaneously high energy and power for next-generation sodium-ion capacitors. [ABSTRACT FROM AUTHOR]

Highlights Vacancy in the transition metal layer of sodium cathode material induces the formation lone-pair electrons in the O 2p orbital. Material delivers more capacity from the oxygen redox validated by density functional calculation. Widened dominance of the OP4 phase without releasing O2 gas.

Highlights: Vacancy in the transition metal layer of sodium cathode material induces the formation lone-pair electrons in the O 2p orbital. Material delivers more capacity from the oxygen redox validated by density functional calculation. Widened dominance of the OP4 phase without releasing O2 gas. This study explores the impact of introducing vacancy in the transition metal layer of rationally designed Na0.6[Ni0.3Ru0.3Mn0.4]O2 (NRM) cathode material. The incorporation of Ru, Ni, and vacancy enhances the structural stability during extensive cycling, increases the operation voltage, and induces a capacity increase while also activating oxygen redox, respectively, in Na0.7[Ni0.2VNi0.1Ru0.3Mn0.4]O2 (V-NRM) compound. Various analytical techniques including transmission electron microscopy, X-ray absorption near edge spectroscopy, operando X-ray diffraction, and operando differential electrochemical mass spectrometry are employed to assess changes in the average oxidation states and structural distortions. The results demonstrate that V-NRM exhibits higher capacity than NRM and maintains a moderate capacity retention of 81% after 100 cycles. Furthermore, the formation of additional lone-pair electrons in the O 2p orbital enables V-NRM to utilize more capacity from the oxygen redox validated by density functional calculation, leading to a widened dominance of the OP4 phase without releasing O2 gas. These findings offer valuable insights for the design of advanced high-capacity cathode materials with improved performance and sustainability in sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Oxygen redox in layered oxide cathodes for Na‐ion batteries is considered a promising approach for improving the energy density. However, oxygen‐redox‐based cathodes suffer from sluggish kinetics and undesirable structural change during charge/discharge, leading to poor electrochemical performances. Herein, introducing vacancies (□) in the transition metal layers enables the enhanced oxygen redox‐based electrochemical performances in the P3‐type Mn‐based layered oxide cathode is demonstrated. The vacancies can play a role of the local distortion buffers, resulting in the enhanced oxygen redox kinetics and the suppressed structural deformation such as P3‐O3(II) phase transition. The oxygen‐redox‐based P3‐type Na0.56[Ni0.1Mn0.81□0.09]O2 exhibits the large discharge capacity of ≈140.95 mAh g−1 at 26 mA g−1 with a high average discharge voltage of ≈3.54 V (vs Na+/Na). Even at 650 mA g−1, its discharge capacity and average operation voltages delivered ≈122.06 mAh g−1 and ≈3.22 V, respectively. Especially, the small gap of average discharge voltage indicates both improves power‐capability and enhanced kinetics of oxygen redox in P3‐type Na0.56[Ni0.1Mn0.81□0.09]O2. Moreover, the vacancy buffer in the transition metal layers results in the stable cycle‐performance of P3‐type Na0.56[Ni0.1Mn0.81□0.09]O2 with the capacity retention of ≈80.80% for 100 cycles, due to the suppressed P3‐O3(II) phase transition. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs), which serve as alternatives or supplements to lithium-ion batteries, have been developed rapidly in recent years. Designing advanced high-performance layered NaxTMO2 cathode materials is beneficial for accelerating the commercialization of SIBs. Herein, the recent research progress on scalable synthesis methods, challenges on the path to commercialization and practical material design strategies for layered NaxTMO2 cathode materials is summarized. Co-precipitation method and solid-phase method are commonly used to synthesize NaxTMO2 on mass production and show their own advantages and disadvantages in terms of manufacturing cost, operative difficulty, sample quality and so on. To overcome drawbacks of layered NaxTMO2 cathode materials and meet the requirements for practical application, a detailed and deep understanding of development trends of layered NaxTMO2 cathode materials is also provided, including high specific energy materials, high-entropy oxides, single crystal materials, wide operation temperature materials and high air stability materials. This work can provide useful guidance in developing practical layered NaxTMO2 cathode materials for commercial SIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] P 2-type layered oxides for rechargeable sodium-ion batteries have drawn a lot of attention because of their excellent electrochemical performance. However, these types of cathodes usually suffer from poor cyclic stability. To overcome this disadvantage, in this work, novel ball-shaped concentration-gradient oxide Na 0.67 Ni 0.17 Co 0.17 Mn 0.66 O 2 with P 2 structure modified by Mn-rich surface is successfully prepared using co-precipitation method. The concentration of Mn increased from the inner core to the surface, endowing the material with an excellent cyclic stability. The cathode exhibits enhanced electrochemical properties than that of the sample synthesized by solid-state method and concentration-constant material. It shows 143.2 mAh/g initial discharge capacity and retains 131 mAh/g between 2 V and 4.5 V after 100 rounds. The significant improvement in the electrochemical properties of the sample benefits from the unique concentration-gradient structure, and the Mn-rich surface that effectively stabilizes the basic P 2 structure. The relatively higher Ni content in the core leads to a slight improvement in the discharge capacity of the sample. This strategy may provide new insights for preparing layered cathodes for sodium-ion batteries with high electrochemical performance. [ABSTRACT FROM AUTHOR]

Owing to their high discharge capacities, P2‐type transition metal layered oxides have attracted attention for use as positive electrode materials in Na‐ion batteries. However, owing to the Na‐deficient compositions of these oxides, additional Na+ must be supplied using a Na‐metal negative electrode to attain a high capacity in a half‐cell configuration. In this study, solid Na2CO3 powder was introduced into the P2−Na2/3Fe1/2Mn1/2O2 composite positive electrode as a sacrificial salt to compensate for the Na deficiency. Na+ was supplied through the electrochemical oxidative decomposition of Na2CO3 during the initial charging process; the decomposition mechanism responsible for this process was investigated in detail. Online electrochemical mass spectrometry confirmed that Na2CO3 was oxidatively decomposed in combination with the decomposition of the ethylene carbonate electrolyte. This reaction produced CO2, wherein the carbon source was derived from both Na2CO3 and the electrolyte. Consequently, Na+ supplementation improved the reversible capacity of the Na‐ion full cell. This study offers practical insights and a mechanistic understanding of the pre‐doping technique for Na‐free negative electrodes. This approach also compensates for the irreversible reductive capacity in a process that can be easily applied to practical sodium‐ and lithium‐ion batteries and capacitors. [ABSTRACT FROM AUTHOR]

Potassium‐ion batteries (PIBs) have attracted increasing interest as promising alternatives to lithium‐ion batteries (LIBs) in large‐scale electrical energy storage systems due to the potential price advantages, abundant availability of potassium resources, and low standard redox potential of potassium. However, the pursuit of suitable cathode materials that exhibit desirable characteristics such as voltage platforms, high capacity, and long cycling stability is of utmost importance. Recently, layered transition‐metal oxides for PIBs offer great potential due to their high theoretical capacity, suitable voltage range, and eco‐friendliness. Nevertheless, the progress of KxMO2 cathodes in PIBs faces obstacles due to the detrimental effects of structural disorder and irreversible phase transitions caused by the Jahn‐Teller effect. This review provides a brief description of the origin and mechanism of the Jahn‐Teller effect, accompanied by the proposed principles to mitigate this phenomenon. In particular, the current status of KxMO2 cathodes for PIBs, is summarized highlighting the challenges posed by the Jahn‐Teller effect. Furthermore, promising strategies, such as composition modulation, synthesis approaches, and surface modification, are proposed to alleviate and suppress the Jahn‐Teller effect. These strategies offer valuable insights into the prospects of innovative cathode materials and provide a foundation for future research in the field of PIBs. [ABSTRACT FROM AUTHOR]

The layered metal oxides are reviewed as the hopeful cathode materials for high-performance sodium-ion batteries (SIBs) due to their large theoretical capacity, favorable two-dimensional (2D) ion diffusion channel, and simple manipuility. However, their cycling stability, rate capability, and thermal stability are still significantly concerned and highlighted before further practical application. The chemical, mechanical and electrochemical stability of the cathode–electrolyte interfaces upon cycling is of great significance. Herein, the unique structural and electrochemical properties of the layered oxide cathode materials for SIB are reviewed. The mechanism of bulk/surface degradation induced by oxygen evolution, phase transition, microcrack, and electrolyte decomposition is thoroughly understood. Furthermore, the interfacial engineering to construct stable interface through various effective methods is fully discussed. The future outlook and challenges for interfacial engineering in this filed are also summarized. This review should shed light on the rational design and construct of robust interface for applications of superior layered oxide cathodes in SIB and may suggest future research directions. [ABSTRACT FROM AUTHOR]

Abstract Layered metal oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical specific capacity and wide Na+ diffusion channels. However, the irreversible phase transitions and cationic/anionic redoxes cause fast capacity decay. Herein, P2-type Na0.67Mg0.1Mn0.8Fe0.1O2 (NMMF-1) cathode material with moderate active Fe3+ doping has been designed for sodium storage. Uneven Mn3+/Mn4+distribution is observed in NMMF-1 and the introduction of Fe3+ is beneficial for reducing the Mn3+ contents both at the surface and in the bulk to alleviate the Jahn–Teller effect. The moderate Fe3+/Fe4+ redox can realize the best tradeoff between capacity and cyclability. Therefore, the NMMF-1 demonstrates a high capacity (174.7 mAh g−1 at 20 mA g−1) and improved cyclability (78.5% over 100 cycles) in a wide-voltage range of 1.5–4.5 V (vs. Na+/Na). In-situ X-ray diffraction reveals a complete solid-solution reaction with a small volume change of 1.7% during charge/discharge processes and the charge compensation is disclosed in detail. This study will provide new insights into designing high-capacity and stable layered oxide cathode materials for SIBs.

Layered metal oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical specific capacity and wide Na+ diffusion channels. However, the irreversible phase transitions and cationic/anionic redoxes cause fast capacity decay. Herein, P2-type Na0.67Mg0.1Mn0.8Fe0.1O2 (NMMF-1) cathode material with moderate active Fe3+ doping has been designed for sodium storage. Uneven Mn3+/Mn4+distribution is observed in NMMF-1 and the introduction of Fe3+ is beneficial for reducing the Mn3+ contents both at the surface and in the bulk to alleviate the Jahn–Teller effect. The moderate Fe3+/Fe4+ redox can realize the best tradeoff between capacity and cyclability. Therefore, the NMMF-1 demonstrates a high capacity (174.7 mAh g−1 at 20 mA g−1) and improved cyclability (78.5% over 100 cycles) in a wide-voltage range of 1.5–4.5 V (vs. Na+/Na). In-situ X-ray diffraction reveals a complete solid-solution reaction with a small volume change of 1.7% during charge/discharge processes and the charge compensation is disclosed in detail. This study will provide new insights into designing high-capacity and stable layered oxide cathode materials for SIBs. [ABSTRACT FROM AUTHOR]

In this work, we applied hot pressing (HP) for the densification of Na2Zn2TeO6 (NZTO) at lower temperature than conventional furnace sintering (FS). Calcined NZTO powder was densified by HP at 700°C for 1 h under uniaxial pressure of 20 and 60 MPa using a graphite mold. By increasing the uniaxial pressure to 60 MPa for HP, high relative density above 90% was obtained. As‐prepared NZTO by HP showed total (bulk + grain‐boundary) ionic conductivity of 0.29 mS cm−1 at room temperature, which is lower than NZTO prepared by FS at 800°C (=0.4 mS cm−1) with lower relative density (<85%). It was found that the contribution of grain‐boundary resistance in as‐prepared NZTO by HP is larger than NZTO by FS. We confirmed that the grain‐boundary resistance was significantly reduced by post‐annealing. Consequently, total conductivity at room temperature was improved to 0.42 and 0.56 mS cm−1 by annealing at 700 and 800°C for 2 h, respectively. X‐ray photoelectron spectroscopy analysis indicated that the residual carbon‐contained secondary phases were reduced by post‐annealing. These secondary phases could be formed by the carbon contamination from a graphite mold used for HP, and their removal by post‐annealing results in the improvement of ionic conduction at grain‐boundary. [ABSTRACT FROM AUTHOR]

A series of Cu-doped layered P2-type Na0.67 Ni0.33-x CuxMn0.67O2 ( x = 0, 0. 05, 0. 10, 0. 15, 0. 20, 0. 25) with regular morphology and smooth surface were synthisized by sol-gel method. The morphology, structure and composition of those materials were characterized using SEM, XRD, EDS and XPS technologies, and their electrochemical properties were investigated by cyclic voltammetry and constant current charge-discharge methods through using them as cathode materials for sodium ion batteries. The optimum doping ratio was obtained. It is found that doping did not change the layered structure and morphology of the materials. Those materials exhibit good cycling stability and multiplicative performance due to the introduction of highly electrochemically active Cu2+ as a substituent and the increase of the surface active sodium storage sites. In the voltage range of 2. 0 V to 4. 3 V and a multiplicity of 0. 1 C, the initial discharge specific capacity of Na0.67Ni0.18Cu Ni0.15Mn Ni0.67O2(with Cu doped ratio of 0. 15) has an initial discharge specific capacity of 126. 74 mAh / g and a capacity retention rate of 79. 10% after 100 cycles, which is 50. 92% higher than that of the undoped material. The enhanced electrochemical properties of the material are attributed to the insertion of Cu2+ into the transition metal layer, and the radius of Cu2+(0. 73 Å) is larger than that of Ni2+(0. 69 Å), which widens the transition metal layer spacing and provides channels for Na+ diffusion, and in turn increases the Na+ diffusion rate. When charged to high voltage, the Na+ vacancy generation during Na+ de/embedding process is inhibited, thus the crystal structure of the material is stabilized, the P2-O2 phase transition is suppressed, and the cycling stability is improved. [ABSTRACT FROM AUTHOR]

In this study, we propose an effective strategy to improve the electrochemical performance of a P2-Na0.67Mn0.75Ni0.25O2 (P2-MNO) cathode material for Na-ion batteries based on MgO surface coating. The MgO coating, with a thickness of ∼20–50 nm, is obtained by means of a facile wet-chemistry approach followed by heat treatment carried out at comparatively low temperatures (400–500 °C) in order to avoid possible Mg doping in the bulk of the P2-MNO. Detailed electrochemical investigations demonstrate improved electrochemical performance of the MgO-coated material (M-P2-MNO) in comparison to pristine bare one at both room and elevated (40 °C) temperatures. Operando differential electrochemical mass spectroscopy (DEMS) demonstrate that the MgO coating is effective in suppressing unwanted gas evolution due to side reactions thus stabilizing the cathode/electrolyte interface.

[Display omitted] Layered transition metal oxides have the greatest potential for commercial application as cathode materials for sodium-ion batteries. However, transition metal oxides inevitably undergo an irreversible oxygen loss process during cycling, which leads to structural changes in the material and ultimately to severe capacity degradation. In this work, using density function theory (DFT) calculations, the Ni-O bond is revealed to be the weakest of the M−O bonds, which may lead to structural failure. Herein, the synergistic surface CeO 2 modification and the trace doping of Ce elements stimulate oxygen redox and improve its reversibility, thus improving the structural stability and electrochemical performance of the material. Theoretical calculations prove that Na 0.67 Mn 0.7 Ni 0.2 Co 0.1 O 2 (MNC) obtains electrons from CeO 2 , avoiding destruction of the Ni-O bond by over-energy released during the charging process and inhibiting oxygen loss. The capacity retention was 77.37% for 200 cycles at 500 mA g−1, compared to 33.84% for the unmodified Na 0.67 Mn 0.7 Ni 0.2 Co 0.1 O 2. Overall, the present work demonstrates that the synergistic effect of surface coating and doping is an effective strategy for realizing tuning oxygen release and high electrochemical performance. [ABSTRACT FROM AUTHOR]

Layered materials exhibit competitively low thermal conductivity along the out-of-plane direction. The solution process is a promising method for preparing stacked structures. However, the thermal stability of the layered materials is poor after processing in solution, thus hindering their applications at high temperatures. One of the solutions to improve the thermal stability of layered structures is to expand the interlayer distance by inserting large-size metal ions. In this work, we studied the thermal properties of Cs+ intercalated layered niobate obtained by the ion-exchanged process. The layered structure of the Cs+ intercalated layered niobate survives after thermal treatment even at 1200 °C. The room temperature thermal conductivity of as prepared stacked Cs–HCa 2 Nb 3 O 10 is as low as 0.11 W m−1 k−1. Upon thermal annealing, the thermal conductivity increases. After annealing at 1200 °C, the value is 0.90 W m−1 k−1. The finding suggests Cs+ intercalated layered niobate is a promising material for high-temperature insulation applications. [ABSTRACT FROM AUTHOR]

Abstract P2‐type Na0.67Ni0.33Mn0.67O2 is a promising cathode for sodium‐ion batteries with features of high specific capacity and air resistance, whereas its cycling stability and rate performance are dissatisfactory suffering from the disastrous P2‐O2 phase transition and Na+/vacancy ordering during sodium‐ion de/intercalation, which makes it an obstruction for future practical applications. Herein, a delicate multicomponent modulation strategy is proposed to tackle these two issues simultaneously, in which Li+ and Ti4+ are introduced to replace the Ni2+ and Mn4+, respectively, whereas the Na+ content is also designed according to the principle of charge balance. Consequently, the designed cathode (Na0.72Ni0.28Li0.05Mn0.57Ti0.10O2) can deliver an enchanting cycling stability of 80% at 1 C after 200 cycles along with a considerable rate performance of 82.7 mAh g−1 at 5 C. In situ X‐ray diffraction measurement demonstrates the destructive P2‐O2 phase transition is suppressed and converted into a P2‐Z phase transition with superior reversibility as well as smooth charge/discharge curves with better Na+/vacancy disordering. In addition, the full cell matched with hard carbon anode delivers an excellent energy density of 263.4 Wh kg−1 at 37.3 W kg−1, exhibiting great practicality. Our work presents a mean to rationally design the component of layered oxide cathode and achieve fabulous performance for sodium ion batteries.

Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn–Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long‐cycle reliability. Here we report a zero‐strain P2‐ Na2/3Li1/6Co1/6Mn2/3O2 cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn3+/Mn4+ redox, mitigating the Jahn–Teller distortion, and minimizing the lattice change. 94.5 % of Na+ in the unit structure can be reversibly cycled with a charge cut‐off voltage of 4.5 V (vs. Na+/Na). Impressively, a solid‐solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. It attains a high discharge capacity of 178 mAh g−1, a high energy density of 534 Wh kg−1, and excellent capacity retention of 95.8 % at 1 C after 250 cycles. [ABSTRACT FROM AUTHOR]

Abstract P2‐type Na0.67Ni0.33Mn0.67O2 is considered as a potential cathode material for sodium‐ion batteries due to the merits of high voltage, low cost, and air stability. However, the unsatisfied cycling stability and rate performance caused by the destructive phase transition and side reactions hinder its practical application. Herein, we present a feasible dual strategy of Mg2+ doping integrated with ZrO2 surface modification for P2‐Na0.67Ni0.33Mn0.67O2, which can well address the issues of phase transition and side reactions benefitting from the enhanced structural and interfacial stabilities. Specifically, it exhibits a decent cycling stability with a capacity retention of 81.5% at 1 C and promising rate performance with a discharge capacity of 76.6 mA h g−1 at 5 C. The in situ X‐ray diffraction measurement confirms that the damaged P2–O2 phase transition is suppressed with better reversibility in high‐voltage region, whereas the side reactions are inhibited due to the protective ZrO2 surface modification. Commendably, the full cell achieves an outstanding operating voltage of 3.57 V and a fabulous energy density of 238.91 W h kg−1 at 36.73 W kg−1, demonstrating great practicability. This work is expected to provide a new insight for designing stable high‐voltage cathode materials and high energy density full cells for sodium ion batteries.

Layered oxides are considered prospective state-of-the-art cathode materials for fast-charging lithium-ion batteries (LIBs) owning to their economic effectiveness, high energy density, and environmentally friendly nature. Nonetheless, layered oxides experience thermal runaway, capacity decay, and voltage decay during fast charging. This article summarizes various modifications recently implemented in the fast charging of LIB cathode materials, including component improvement, morphology control, ion doping, surface coating, and composite structure. The development direction of layered-oxide cathodes is summarized based on research progress. Further, possible strategies and future development directions of layered-oxide cathodes to improve fast-charging performance are proposed. [ABSTRACT FROM AUTHOR]

Realizing reversible reduction-oxidation (redox) reactions of lattice oxygen in batteries is a promising way to improve the energy and power density. However, conventional oxygen absorption spectroscopy fails to distinguish the critical oxygen chemistry in oxide-based battery electrodes. Therefore, high-efficiency full-range mapping of resonant inelastic X-ray scattering (mRIXS) has been developed as a reliable probe of oxygen redox reactions. Here, based on mRIXS results collected from a series of Li1.17Ni0.21Co0.08Mn0.54O2 electrodes at different electrochemical states and its comparison with peroxides, we provide a comprehensive analysis of five components observed in the mRIXS results. While all the five components evolve upon electrochemical cycling, only two of them correspond to the critical states associated with oxygen redox reactions. One is a specific feature at 531.0 eV excitation and 523.7 eV emission energy, the other is a low-energy loss feature. We show that both features evolve with electrochemical cycling of Li1.17Ni0.21Co0.08Mn0.54O2 electrodes, and could be used for characterizing oxidized oxygen states in the lattice of battery electrodes. This work provides an important benchmark for a complete assignment of all mRIXS features collected from battery materials, which sets a general foundation for future studies in characterization, analysis, and theoretical calculation for probing and understanding oxygen redox reactions.

Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migration between layers occurring during oxide cycling was manipulated by oxide morphology. The best cycling stability is observed for Na2/3Ni0.42Al0.08Mn1/2O2 having a column-like morphology of stacked plate-like particles along the common faces. The treatment of the layered oxides with Al2O3 mitigates the Mn dissolution reaction during electrode cycling in the NaPF6-based electrolyte, thus contributing to a high cycling stability. [ABSTRACT FROM AUTHOR]

[Display omitted] Due to the obvious benefits of abundant resources and low cost of sodium, sodium-ion batteries have enormous development potential and a broad market outlook in the field of large-scale energy storage and low-speed electric cars. Layered oxide cathode material is considered as one of the most promising cathode materials for sodium-ion batteries due to its high energy density, rich variety, simple synthesis method and low environmental pollution. However, the layered oxides of sodium-ion batteries suffer from instability in air storage and unstable electrochemical performance during cycling. This review summarizes surface and bulk structural evolution in air exposure and during cycling to reveal the relationship between structure evolution, charge transfer mechanisms and electrochemical performance, which is of great significance for designing advanced electrode materials. The strategies based on the degradation mechanisms for layered oxides cathode materials are also discussed for the future development and industrialized application. We hope that this review will provide a basis for an accurate understanding of the structural evolution of layered oxides and provide some inspiration for the design and development of electrochemical systems with excellent performance. [ABSTRACT FROM AUTHOR]

Structural schematic and cycling performance comparison plots of the W6+-doped Ni-rich layered LiNi 0.83 Co 0.11 Mn 0.06 O 2 cathode powders. [Display omitted] • W6+-doped can provide the stronger W-O bond to effectively stabilize the structure. • NCM-0.5 shows a well-ordered layered structure with dense morphology. • The cells with NCM-0.5 delivers a remarkable capacity retention of 88.5% after 100cycles at 2.0 C and 60 °C. • NCM-0.5 can preserve the integrity of the secondary particles after cycles. WO 3 as tungsten dopant is introduced into lithium nickel cobalt manganese (LiNi 0.83 Co 0.11 Mn 0.06 O 2 , NCM) layered oxide powders to synthesize W6+-doped NCM cathode materials during the lithiation process of the hydroxide precursor. Introducing W6+ into the lattice can lead to the diversities of the crystal structure, surface morphology, and electrochemical performance. The crystal structure confirmed by X-ray diffraction indicates that the W6+-doped oxide powders present a typical R—3m layered structure with larger interplanar distance and cell volume. Also, scanning electron microscope images reveal that the primary particles shrink forming a tighter surface under the effect of W6+, while the specific changes gradually aggravate with increase in the content of W6+ added. The excellent electrochemical stability of W6+-doped samples is observed, as the stable host structure is reinforced by the strong W-O bond. The stable structure does not only inhibit the anisotropic volume change caused by repetitive H2 ⇔ H3 phase transitions, but also sustains the integrated structure to impede the formation of microcracks and the appearance of more side reactions. This research provides an effective route on investigating the potential association between electrochemical performance and structure change for W6+-doped strategy. [ABSTRACT FROM AUTHOR]

The kinetics of interfacial ion insertion govern the uniformity of electrochemical reactions, playing a crucial role in lithium-ion battery performance. In two-dimensional lithium-conducting layered-oxide battery particles, variation in insertion rates across insertion channels remains unclear due to poorly defined crystal orientation at the solid-liquid interface and solid-state-lithium-diffusion length. This ambiguity complicates understanding inhomogeneous lithium-insertion channels activation. A systematic study requires crystallographically predefined interfaces and in situ lithium-concentration mapping. Here, we fabricated a freestanding, (104)-oriented-LiNi 1/3 Mn 1/3 Co 1/3 O 2 single-crystal thin film using dissolution-induced release and performed in situ scanning-transmission-X-ray-microscopy to spatially resolve lithium-insertion at well-defined-interfaces. We observed heterogeneous lithium-concentration evolution due to channel-by-channel insertion rate variation, despite the potential for homogeneous lithium distribution via a solid-solution-phase at equilibrium in NMC111. Increasing current density exacerbates this heterogeneity, highlighting channel-by-channel variation. Our findings provide critical insights into battery electrode utilization and lifetime management, potentially guiding the design of more efficient and durable lithium-ion batteries.

This paper reports on the spin glass-like coexistence of competing magnetic orders in oxygen-deficient V2O5 nanoparticles with a broad size distribution. X-ray photoelectron spectroscopy yields the surface chemical stoichiometry of nearly V2O4.65 due to significant defect density. Temperature-dependent electrical conductivity and thermopower measurements demonstrate a polaronic conduction mechanism with a hopping energy of about 0.112 eV. The V2O5-δ sample exhibits strong field as well as temperature-dependent magnetic behaviour when measured with a SQUID magnetometer, showing positive magnetic susceptibility across the temperature range of 2-350 K. Field-cooled and zero-field-cooled data indicate hysteresis, suggesting glassy behaviour. The formation of small polarons due to oxygen vacancy defects, compensated by V4+ charge defects, results in Magneto-Electronic Phase Separation (MEPS) and various magnetic exchanges, as predicted by first-principle calculations. This is evidenced by the strong hybridisation of V orbitals in the vicinity of vacant oxygen site. An increase in V4+ defects shows an antiferromagnetic (AFM) component. The magnetic diversity in undoped V2O4.9 originates from defect density and their random distribution, leading to MEPS. This involves localised spins in polarons and ferromagnetic (FM) clusters on a paramagnetic (PM) background, while V4+ dimers induce AFM interactions. Electron paramagnetic resonance spectra measured at different temperatures indicate a dominant paramagnetic signal at a g-value of 1.97 due to oxygen defects, with a broad FM resonance-like hump. Both signals diminish with increasing temperature. Neutron diffraction data rules out long-range magnetic ordering, reflecting the composition as V2O4.886. Despite the FM hysteresis, no long-range order is observed in neutron diffraction data, consistent with the polaron cluster-like FM with MEPS nature. This detailed study shall advance the understanding of the diverse magnetic behaviour observed in undoped non-magnetic systems., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

Sodium-ion batteries (SIBs) have emerged as a compelling alternative to lithium-ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta-heuristically assisted NSGA-II algorithm to optimize multi-element doping in electrode materials, aiming to transcend conventional trial-and-error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta-heuristically designed cathode material Na 0.76 Ni 0.20 Mn 0.42 Fe 0.30 Mg 0.04 Ti 0.015 Zr 0.025 O 2 (D-NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5 mAh g -1 and exceptional long-term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques. Remarkably, the irreversible phase transition of P2→OP4 in D-NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P-NFMO) offers profound insights into the long-term electrochemical stability of D-NFMO, highlighting its potential as a high-voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium-ion battery technology., (© 2024 Wiley‐VCH GmbH.)

Flexible thermoelectric materials are presented with potential applications in electronic devices and energy conversion due to their convenient preparation, good flexibility, and various forms. However, as ductility is rarely observed in inorganic semiconductors and ceramic insulators, reports on applications of inorganic oxide materials in flexible thermoelectric materials are sparse. Here, we report a new method for the synthesis of a flexible Na1.4Co2O4 thermoelectric material based on Na1.4Co2O4 bulk materials, which are prepared by a self-flux method and painted on print paper. Seebeck coefficient and power factor of the obtained thermoelectric material are 78–102 μVK-1 and 159–223 μWm−1K−2, respectively, in a temperature range of 303–522 K, which are superior to those values of other conductive polymers and their compounds. More interestingly, the n-type Na1.4Co2O4 flexible material is obtained in the painting process at higher pressure with Seebeck coefficients of −109 to −183 μVK−1 in a temperature range of 303–522 K. The convenient preparation method of these novel flexible thermoelectric materials may be expanded to the synthesis of other flexible thermoelectric materials, which will be the focus of future work.

Elemental doping for substituting lithium or oxygen sites has become a simple and effective technique to improve the electrochemical performance of layered cathode materials. Compared with single-element doping, this work presents an unprecedented contribution to the study of the effect of Na+/F− co-doping on the structure and electrochemical performance of LiNi1/3Mn1/3Co1/3O2. The co-doped Li1-zNazNi1/3Mn1/3Co1/3O2-zFz (z = 0.025) and pristine LiNi1/3Co1/3Mn1/3O2 materials were synthesized via the sol–gel method using EDTA as a chelating agent. Structural analyses, carried out by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, revealed that the Na+ and F− dopants were successfully incorporated into the Li and O sites, respectively. The co-doping resulted in larger Li-slab spacing, a lower degree of cation mixing, and the stabilization of the surface structure, which substantially enhanced the cycling stability and rate capability of the cathode material. The Na/F co-doped LiNi1/3Mn1/3Co1/3O2 electrode delivered an initial specific capacity of 142 mAh g−1 at a 1C rate (178 mAh g−1 at 0.1C), and it maintained 50% of its initial capacity after 1000 charge–discharge cycles at a 1C rate. [ABSTRACT FROM AUTHOR]

The sodium ion layered oxide cathode material NaNi0.4Mn0.4Fe0.2O2 was synthesized by the co-precipitation method， and Al3+was used to effectively control and balance the co-precipitation reaction process. The thermodynamic coupling effect brought by the addition of Al element and its influence on electrochemical performance of cathode materials were investigated. In an environment where Mn2+， Ni2+ and Fe3+ ions coexist， owing to the thermodynamic coupling effect， the superior high supersaturation of Al3+ and the more negative change in the Gibbs free energy(ΔG)can efficiently changes the precipitation driving force between the solution ions， accelerating the precipitation of Ni2+and Mn2+ ions and inhibiting the precipitation of Fe3+ ions. The obtained Na[Ni0.4Mn0.4Fe0.2]0.995Al0.005O2 cathode material has demonstrated excellent electrochemical performance which can be attributed to the high quality precursor(［0.4MnCO3·0.4NiCO3·0.2Fe(OH)3］0.995·0.005Al(OH)3) brought about by the introduction of Al3+. [ABSTRACT FROM AUTHOR]

Layered oxides are considered prospective state-of-the-art cathode materials for fast-charging lithium-ion batteries (LIBs) owning to their economic effectiveness, high energy density, and environmentally friendly nature. Nonetheless, layered oxides experience thermal runaway, capacity decay, and voltage decay during fast charging. This article summarizes various modifications recently implemented in the fast charging of LIB cathode materials, including component improvement, morphology control, ion doping, surface coating, and composite structure. The development direction of layered-oxide cathodes is summarized based on research progress. Further, possible strategies and future development directions of layered-oxide cathodes to improve fast-charging performance are proposed.

Layered sodium ion cathode material is increasingly popular due to the superiority of low-cost and excellent rate performance. However, it usually suffers from poor capacity retention arising from microcracks during multiple-phase transitions. Herein, a Ce-doped O3-type cathode material NaNi 0.5 Mn 0.5 O 2 (NNM) was synthesized by high shear mixer-assisted precipitation of oxalate precursors. Using the characterizations of XRD, XPS, HRTEM, GITT, etc., the results indicate that Ce dopants can adjust the initial phase structure as well as postpone the phase transition in such O3-type material. The optimal NNM-0.06Ce shows a superior initial discharge capacity of 128.3 mAh g−1 and a retention of 85.96% after 100 cycles (1.5–4.0 V, 1 C, 25 °C), as well as superior rate performance of 107 mAh g−1 at 5 C. HAADF-STEM images disclose that the doped Ce atoms are probably located in the sodium layer of the cathode material, moreover, DFT calculations reveal that the Ce dopant is prone to occupy the Na site and cause charge rising of Ni and Mn. In-situ XRD tests indicate that the earlier formed O1 phase induced by Ce dopants can postpone the phase transition and increase the reversibility of the cathode, therefore improving the electrochemical performance of cathode materials. [Display omitted] • Ce-doped NaNi 0.5 Mn 0.5 O 2 was synthesized by high shear mixer-assisted precipitation. • NNM-0.06Ce has a capacity of 128.3 mAh g−1 and a 100th retention of 86% (1.5–4.0 V). • Ce dopant is prone to occupy the Na site, enhancing Na+ diffusion in the O3-type cathode. • NNM-0.06Ce has delayed transition from O3 to P3 phase in charging. [ABSTRACT FROM AUTHOR]

The layered oxide Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 with little lattice oxygen vacancies and abundant surface oxygen vacancies are synthesized. [Display omitted] • Swing-like non-isothermal sintering technique is adopted to stabilize the lattice oxygen. • NH 3 is employed to introduce the surface oxygen vacancies. • The layered oxide with controllable oxygen vacancies is synthesized. • Spinel phase is found in the surface of layered oxide. Li-rich Mn-Based layered oxide is defined as a potential cathode material for its high specific capacity while several significant drawbacks such as inferior cycling stability and voltage decay limit its wide application. In this work, a suite of characterization techniques is employed to comprehensively investigate the crystal structure, surface morphology and chemical state of materials. The results suggest the successful preparation of layered oxide with controllable oxygen vacancies. Specifically, 1) Surface oxygen vacancies can act as a deterrent to irreversible oxygen release, consequently suppressing the voltage decay. 2) Stable lattice oxygen can enhance structural stability during cycling. 3) Swing-like sintering methodology and inducing surface oxygen vacancies technique are connected to synthesize the layered oxide with little lattice oxygen vacancies and abundant surface oxygen vacancies. The as-prepared cathode exhibits a commendable capacity retention of 85 %, and managed to alleviate the voltage attenuation significantly to 3.81 mV/cycle over 150 cycles at 0.5C. This concept of pre-constructing controllable oxygen vacancies provides important groundwork for developing Li-rich cathode with mitigated voltage decay and enhanced cycle life. [ABSTRACT FROM AUTHOR]

Layered sodium transition metal oxides belong to electrode materials for sodium-ion batteries that combine, in a better way, high performance with environmental requirements. However, their cycling stability is still far from desirable. Herein, we demonstrate a rational approach to control the cycling stability of sodium-deficient nickel manganese oxides, Na2/3Ni1/2Mn1/2O2, with two- and three-layer stacking through Al substitution and Al2O3 treatment. Layered Na2/3Ni1/2Mn1/2O2 oxide displays a limited ability to accommodate aluminum in its structure (i.e., up to 8 at. %). The substitution of Ni ions with electrochemically inactive Al3+ ions and keeping the amount of Mn ions in Na2/3Ni1/2−xAlxMn1/2O2 leads to the stabilization of the two-layer stacking and favors the participation of lattice oxygen in the electrochemical reaction in addition to Ni ions. This results in an increase in the specific capacity of the Al-substituted oxides. Furthermore, the kinetics of the cationic migration between layers occurring during oxide cycling was manipulated by oxide morphology. The best cycling stability is observed for Na2/3Ni0.42Al0.08Mn1/2O2 having a column-like morphology of stacked plate-like particles along the common faces. The treatment of the layered oxides with Al2O3 mitigates the Mn dissolution reaction during electrode cycling in the NaPF6-based electrolyte, thus contributing to a high cycling stability.

Layered lithiated oxides are promising materials for next generation Li-ion battery cathode materials; however, instability during cycling results in poor performance over time compared to the high capacities theoretically possible with these materials. Here we report the characterizations of a Li 1.47 Mn 0.57 Al 0.13 Fe 0.095 Co 0.105 Ni 0.095 O 2.49 high-entropy layered oxide (HELO) with the Li 2 MO 3 structure where M = Mn, Al, Fe, Co, and Ni. Using electron microscopy and X-ray spectroscopy, we identify a homogeneous Li 2 MO 3 structure stabilized by the entropic contribution of oxygen vacancies. This defect-driven entropy would not be attainable in the LiMO 2 structure sometimes observed in similar materials as a secondary phase owing to the presence of fewer O sites and a 3+ oxidation state for the metal site; instead, a Li 2-γ MO 3-δ is produced. Beyond Li 2 MO 3 , this defect-driven entropy approach to stabilizing novel compositions and phases can be applied to a wide array of future cathode materials including spinel and rock salt structures.

We investigated the sintering temperature dependency on the properties of Na2Zn2TeO6 (NZTO) solid electrolyte synthesized via a conventional solid‐state reaction method. Sintering temperature of calcined NZTO powder, which was obtained by the calcination of precursor at 850℃, was changed in the range from 650 to 850℃. X‐ray diffraction analysis showed that P2‐type layered NZTO phase was formed in all sintered samples without forming any secondary phases. The relative densities of sintered NZTO samples were approximately 83%−85% for the samples sintered at 700℃ or higher. The all sintered samples showed sodium‐ion conductivity above 10−4 S cm−1 at room temperature and the highest conductivity of 4.0 × 10−4 S cm−1 in the sample sintered at 750℃. The sintering temperature to obtain the highest room temperature conductivity is 100℃ lower than that used in previous works. Such low sintering temperature compared to other Na‐based oxide solid electrolytes could be useful for co‐sintering with electrode active materials for fabrication of all‐solid‐state sodium‐ion battery. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have grasped renewed attentions in recent years owing to the blooming growth of clean energy and corresponding demands of grid‐scale energy storage. Note that, the properties of cathode materials are quite important to the development of SIBs as they largely determine the energy density, cycle life, and cost of a battery. Direct inheriting those Co/Ni based layered cathodes that are successfully utilized in lithium‐ion batteries seems to be impracticable for SIBs in view of the high materials costs. Fortunately, the discovery of the electrochemical activity of Fe3+/Fe4+ redox couple in sodium layered materials has opened a new way to design high capacity/voltage and low‐cost cathodes for SIBs. To date, various Fe‐based layered oxides have been explored, showing encouraging electrochemical performances in SIBs. However, issues and challenges still remain upon the practical utilization of Fe‐based layered cathodes, calling for further targeted and in‐depth investigations. In this review, the developing history, key problems, and current progress of Fe‐based layered cathodes on electrochemical performances and working mechanism are summarized and discussed. In addition, possible research trends and perspectives are proposed. It is believed that Fe‐based layered oxides will be one of the most attractive cathodes for SIBs. [ABSTRACT FROM AUTHOR]

Global interest in the development of sodium-ion batteries (SIBs) continues, largely due to the advantage of the affordable cost of sodium resources (compared to lithium), which could produce cost-effective rechargeable batteries for large-scale applications. However, the discovery of reliable cathodes, tailored amorphous carbon anodes, and compatible electrolytes is required to yield safer, longer lasting SIBs with wide operating temperature. Among various cathodes systems, layered oxide cathodes are of great interest due to 230–245 mAhg−1 theoretical capacity with facile structure forming ability. Among the various phases of NaxCoO2 cathode, the P2 is the most favored, because of low polarization with enhanced structural stability and high theoretical capacity of 183 mAhg−1 for the empirical formula of Na0.74CoO2. Charge/discharge profiles of these systems exhibit plateaus, continuous changes in voltage and voltage drop, which impacts the electrochemical performance. This review discusses recent advancement in NaxCoO2 cathode in terms of the effect of particle morphology, size, crystal structure, electronic structure, cation and anion doping, sacrificial salt, Na deficiency, effect of electrolyte salts and solvents, and thermal safety. We present a comprehensive analysis of the recent developments in NaxCoO2 and its derivative cathode materials and propose various approaches to mitigate the challenges for the near future successful commercialization of SIBs. [ABSTRACT FROM AUTHOR]

Phase transition is common during (de)-intercalating layered sodium oxides, which directly affects the structural stability and electrochemical performance. However, the artificial control of phase transition to achieve advanced sodium-ion batteries is lacking, since the remarkably little is known about the influencing factor relative to the sliding process of transition-metal slabs upon sodium release and uptake of layered oxides. Herein, we for the first time demonstrate the manipulation of oxygen vacancy concentrations in multinary metallic oxides has a significant impact on the reversibility of phase transition, thereby determining the sodium storage performance of cathode materials. Results show that abundant oxygen vacancies intrigue the return of the already slide transition-metal slabs between O3 and P3 phase transition, in contrast to the few oxygen vacancies and resulted irreversibility. Additionally, the abundant oxygen vacancies enhance the electronic and ionic conductivity of the Na0.9Ni0.3Co0.15Mn0.05Ti0.5O2 electrode, delivering the high initial Coulombic efficiency of 97.1%, large reversible capacity of 112.7 mAh·g−1, superior rate capability upon 100 C and splendid cycling performance over 1,000 cycles. Our findings open up new horizons for artificially manipulating the structural evolution and electrochemical process of layered cathodes, and pave a way in designing advanced sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Abstract High‐capacity layered oxide Ni‐rich cathodes are attractive to enhance the driving‐range of electric vehicles because of its preferential costs. Nevertheless, in Ni‐rich cathodes, there are still many issues such as microcracks generation along grain boundaries and interface side reaction between active substance and electrolyte, resulting in the rapidly deterioration of electrochemical property. Herein, improving the performance of Ni‐based cathodes by structural regulation is summarized. The remaining challenges and outlook are discussed as well.

Multifunctional materials that are capable of facilitating multiple electrocatalytic processes are highly desirable. This work reports the observation of bifunctional electrocatalytic properties for water‐splitting in layered oxides, featuring 2‐dimensional layers of octahedrally coordinated transition metals separated by alkaline‐earth or rare‐earth metals. Remarkably, these materials are able to catalyze both half‐reactions of water‐splitting, i. e., oxygen‐evolution reaction (OER) and hydrogen‐evolution reaction (HER). Electrical charge‐transport studies of SrLaFe1‐xCoxO4‐δ in a wide range of temperatures, 25 to 800 °C, indicate semiconducting behavior for all three compounds, where there is a systematic increase in electrical conductivity as a function of temperature. The end member of the series, SrLaCoO4‐δ, exhibits the highest electrical charge transport and best electrocatalytic activity toward both OER and HER. This catalyst also features the highest degree of polyhedral distortion as well as the presence of oxygen‐vacancies. In addition, the transition metals in this material have a favorable electronic configuration for enhanced electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Elemental doping for substituting lithium or oxygen sites has become a simple and effective technique to improve the electrochemical performance of layered cathode materials. Compared with single-element doping, this work presents an unprecedented contribution to the study of the effect of Na+/F− co-doping on the structure and electrochemical performance of LiNi1/3Mn1/3Co1/3O2. The co-doped Li1-zNazNi1/3Mn1/3Co1/3O2-zFz (z = 0.025) and pristine LiNi1/3Co1/3Mn1/3O2 materials were synthesized via the sol–gel method using EDTA as a chelating agent. Structural analyses, carried out by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, revealed that the Na+ and F− dopants were successfully incorporated into the Li and O sites, respectively. The co-doping resulted in larger Li-slab spacing, a lower degree of cation mixing, and the stabilization of the surface structure, which substantially enhanced the cycling stability and rate capability of the cathode material. The Na/F co-doped LiNi1/3Mn1/3Co1/3O2 electrode delivered an initial specific capacity of 142 mAh g−1 at a 1C rate (178 mAh g−1 at 0.1C), and it maintained 50% of its initial capacity after 1000 charge–discharge cycles at a 1C rate.

Layered cathode oxides have been attractive for next-generation high-energy-density rechargeable batteries, only that they are approaching the bottleneck of limited specific capacities based on cation redox reactions. Recently, the utilization of anion redox reaction to participate in charge compensation is an important strategy to increase the upper limit of energy density, but it faces issues such as voltage hysteresis and structure decay. In this review, we discuss the anion redox chemistry and the problems faced by such materials. Subsequently, we reviewed the recent research progress from perspectives of transition metal layer design and stacking fault design, hoping to provide a guide for the design of layered oxide cathodes.

A series of novel KxNa0.6-xMn0.35Fe0.35Co0.3O2 (x = 0, 0.005, 0.01, 0.05, 0.1) materials were successfully synthesized by the solid-state reaction method. The newly prepared cathode materials were examined by means of X-ray diffraction. They were characterized by scanning electron microscopy (SEM-EDS) and inductively coupled plasma mass spectrometry (ICP-OES). Their electrochemical performances for sodium-ion batteries were tested. The effects of varying K+ doping content on the electrochemical battery performance on the prepared cathode materials were investigated. It was found that the potassium-doped K0.01Na0.59Mn0.35Fe0.35Co0.3O2 showed the best electrochemical performance with an initial discharge capacity of 138.0 mAh g−1 among them. The capacity retention after 20 cycles for Na0.6Mn0.35Fe0.35Co0.3O2 (without K+ doping) was 87.6%. After the potassium doped, the capacity retentions for K0.01Na0.59Mn0.35Fe0.35Co0.3O2 and K0.005Na0.595Mn0.35Fe0.35Co0.3O2 compounds were 90.8% and 90.6% respectively. These results proved that the appropriate amount of K+ doping could be a feasible strategy to increase the cycling stability performance of layered cathode for sodium-ion battery. [ABSTRACT FROM AUTHOR]