Recent progress of interface modification of layered oxide cathode material for sodium-ion batteries

With the advantages of similar theoretical basis to lithium batteries, relatively low budget and the abundance of sodium resources, sodium ion batteries (SIBs) are recognized as the most competitive alternative to lithium-ion batteries. Among various types of cathodes for SIBs, advantages of high theoretical capacity, nontoxic and facile synthesis are introduced for layered transition metal oxide cathodes and therefore they have attracted huge attention. Nevertheless, layered oxide cathodes suffer from various degradation issues. Among these issues, interface instability including surface residues, phase transitions, loss of active transition metal and oxygen loss takes up the major part of the degradation of layered oxides. These degradation mechanisms usually lead to irreversible structure collapse and cracking generation, which significantly influence the interface stability and electrochemical performance of layered cathodes. This review briefly introduces the background of researches on layered cathodes for SIBs and their basic structure types. Then the origins and effects on layered cathodes of degradation mechanisms are systematically concluded. Finally, we will summarize various interface modification methods including surface engineering, doping modification and electrolyte composition which are aimed to improve interface stability of layered cathodes, perspectives of future research on layered cathodes are mentioned to provide some theoretical proposals.