Sodium-ion batteries (SIBs) are considered as a low-cost complementary or alternative system to prestigious lithium-ion batteries (LIBs) because of their similar working principle to LIBs, cost-effectiveness, and sustainable availability of sodium resources, especially in large-scale energy storage systems (EESs).Among various cathode candidates for SIBs, Na-based layered transition metal oxides have received extensive attention for their relatively large specific capacity, high operating potential, facile synthesis, and environmental benignity.However, there are a series of fatal issues in terms of poor air stability, unstable cathode/electrolyte interphase, and irreversible phase transition that lead to unsatisfactory battery performance from the perspective of preparation to application, outside to inside of layered oxide cathodes, which severely limit their practical application. This work is meant to review these critical problems associated with layered oxide cathodes to understand their fundamental roots and degradation mechanisms, and to provide a comprehensive summary of mainstream modification strategies including chemical substitution, surface modification, structure modulation, and so forth, concentrating on how to improve air stability, reduce interfacial side reaction, and suppress phase transition for realizing high structural reversibility, fast Na + kinetics, and superior comprehensive electrochemical performance. The advantages and

Due to their high capacity and sufficient Na+ storage, O3-NaNi0.5Mn0.5O2 has attracted much attention as a viable cathode material for sodium-ion batteries (SIBs). However, the challenges of complicated irreversible multiphase transitions, poor structural stability, low operating voltage, and an unstable oxygen redox reaction still limit its practical application. Herein, using O3-NaNi0.5Mn0.5–x Sn x O2 cathode materials as the research model, a universal strategy based on bridging microstructure engineering and local electronic structure manipulation is proposed. The strategy can modulate the physical and chemical properties of electrode materials, so as to restrain the unfavorable and irreversible multiphase transformation, improve structural stability, manipulate redox potential, and stabilize the anion redox reaction. The effect of Sn substitution on the intrinsic local electronic structure of the material is articulated by density functional theory calculations. Meanwhile, the universal strategy is also validated by Ti substitution, which could be further extrapolated to other systems and guide the design of cathode materials in the field of SIBs.

The pursuit of high energy density while achieving long cycle life remains a challenge in developing transition metal (TM) oxide cathode materials for sodium‐ion batteries (SIBs). Here, we present a concept of precisely manipulating structural evolution via local coordination chemistry regulation to design high‐performance composite cathode materials. The controllable structural evolution process is realized by tuning magnesium content in Na0.6Mn1−xMgxO2, which is elucidated by a combination of experimental analysis and theoretical calculations. The substitution of Mg into Mn sites not only induces a unique structural evolution from layered–tunnel structure to layered structure but also mitigates the Jahn–Teller distortion of Mn3+. Meanwhile, benefiting from the strong ionic interaction between Mg2+ and O2−, local environments around O2− coordinated with electrochemically inactive Mg2+ are anchored in the TM layer, providing a pinning effect to stabilize crystal structure and smooth electrochemical profile. The layered–tunnel Na0.6Mn0.95Mg0.05O2 cathode material delivers 188.9 mAh g−1 of specific capacity, equivalent to 508.0 Wh kg−1 of energy density at 0.5C, and exhibits 71.3% of capacity retention after 1000 cycles at 5C as well as excellent compatibility with hard carbon anode. This work may provide new insights of manipulating structural evolution in composite cathode materials via local coordination chemistry regulation and inspire more novel design of high‐performance SIB cathode materials.image