Spinel integrated layered oxide cathodes for sodium-ion batteries: suppressing phase transitions, enhancing air...

Sodium layered transition metal oxides (Na _x TMO₂), as the key cathode material for sodium-ion batteries, are still limited by the core issues such as irreversible phase transitions, air instability, and sluggish kinetics, generally leading to rapid performance degradation. The spinel-type (AB₂O₄) material, with its excellent structural stability and fast ion diffusion channels, provides an effective solution to overcome the challenges faced by Na _x TMO₂ through incorporation. In this study, we systematically review the construction methods of layered/spinel heterostructures and elucidate the core role of the spinel phase in optimizing the properties of Na _x TMO₂ cathodes. Subsequently, we discuss and integrate representative strategies for mitigating irreversible phase transitions, enhancing air stability, and accelerating Na⁺ transport kinetics, including multiphase composites, spinel sublayer coating and spinel coating strategies, etc. Finally, this review summarizes the challenges faced in spinel regulation strategies and provides corresponding research directions, while also looking forward to the development of layered/spinel heterostructures in various fields in the future. We believe that this analysis will inspire more theoretical understanding and practical guidance for the development of Na _x TMO₂ cathodes.