Promoting Layered Oxide Cathodes Based on Structural Reconstruction for Sodium-Ion Batteries: Reversible Phase Transition, Stable Interface Regulation, and Multifunctional Intergrowth Structure

Layered transition-metal oxides (NaxTMO2) are one of the most promising cathode materials for sodium-ion batteries due to their high theoretical specific capacities, good conductivity, and environmental friendliness. However, several key scientific issues of NaxTMO2 cathode materials still persist in practical applications: i) complex phase transitions during the charge/discharge process owing to the slip of the transition-metal layer; ii) the tendency for the interface to react with the electrolyte, resulting in structure degradation, and iii) reactions between active materials and H2O as well as CO2 on exposure to air in the environment to form alkaline substances on the surface. To understand electrochemical storage mechanisms and solve these problems, several modification strategies of NaxTMO2 have been reported recently, including bulk doping, concentration gradient structure design, interface regulation, and intergrowth structure construction. This review focuses on reversible phase transitions, stable interface regulation, and multifunctional intergrowth structure of the NaxTMO2 material from the inside to the outside. The future research directions for NaxTMO2 are also analyzed, providing guidance for the development of commercial layered oxides for next-generation energy storage systems. This review focuses on the challenges of NaxTMO2, including irreversible phase transitions, especially at high voltage, interfacial degradation caused by adverse reactions between the electrolyte and the material, and structural breakdown on exposure to air, which can be solved through bulk doping, gradient structure designing, interface coating, interface coating combined with doping synergy, and intergrowth structure designing. image