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

Abstract

Layered transition-metal oxides (Na_xTMO₂) 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 Na_xTMO₂ 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 Na_xTMO₂ 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 Na_xTMO₂ material from the inside to the outside. The future research directions for Na_xTMO₂ are also analyzed, providing guidance for the development of commercial layered oxides for next-generation energy storage systems.