Multi-Scale Interfacial Degradation Mechanisms and Precision Engineering Strategies for Layered Oxide Cathodes in Sodium-Ion Batteries.

Sodium-ion batteries (SIBs), featuring abundant sodium reserves, low cost, and excellent safety, are promising for large-scale energy storage. Layered transition metal oxides (LTMOs) offer high specific capacity and structural tunability but suffer from severe interfacial instability. Repeated Na+ (de)intercalation induces lattice strain and electrode cracking, while reactive oxygen species and unsaturated surface sites accelerate electrolyte decomposition, transition-metal dissolution, and uncontrolled cathode-electrolyte interphase (CEI) growth. Interfacial engineering strategies, including surface coating, gradient doping, surface reconstruction, and electrolyte modification, can suppress side reactions and stabilize both the bulk and interface. This review systematically examines the multiscale degradation mechanisms of layered sodium transition-metal oxide cathodes. Focusing on structural compatibility and ion/electron transport kinetics, it evaluates major interfacial modification strategies and their underlying mechanisms, and summarizes advanced in situ characterization techniques for tracking dynamic interfacial evolution. To overcome poor coating uniformity, limited doping precision, and uncoordinated bulk-interface evolution, we propose a synergistic modification framework integrating multiscale theoretical calculations with advanced in situ characterization. Finally, future research directions and industrial prospects for high-energy, long-life layered oxide cathodes are discussed, offering guidance for the rational design and practical development of high-performance SIBs.