Metal selenides for high performance sodium ion batteries

In consideration of the abundance of sodium resources, sodium ion batteries (SIBs) have been revisited recently and are considered as a substitution for lithium ion batteries (LIBs). Among all the proposed anodes for SIBs, metal selenides labeled as high theoretical capacity materials have aroused the interest of battery researchers. However, as conversion/alloying based electrode materials, metal selenides suffer from a severe volume change during cycling, thus leading to kinetic problems and poor electrochemical stability, which restrain their further application in SIBs. Therefore, modification strategies such as coupling with carbonaceous material, designing unique structure, selecting an upper cut-off voltage, optimizing the composition of electrolyte, controlling the composition of the material etc. have been adopted to alleviate the volume change issue of metal selenides electrodes. In this article, the research progresses on the metal selenides as electrodes for SIBs are comprehensively reviewed and the difference and necessity of each metal selenide from the perspectives of structure and conductivity are emphasized. The summarization of metal selenides contains the synthesis methods, modification methods for performance improvement, corresponding reaction mechanism and performance in full-cell system. Finally, a conclusion with the challenges and outlook of metal selenides in the field of SIBs is also presented.