Structural engineering of bimetallic selenides for high-energy density sodium-ion half/full batteries

The shortage of high-capacity anode materials with long cycling stability is the main roadblock to the development of sodium-ion batteries (SIBs). The advantages of transition metal selenides are high theoretical capacity, safety and ease of design, which gradually make them potential substitute materials for the anodes of a new generation of SIBs. However, the low intrinsic conductivity of transition metal selenides and the serious powderization during charge and discharge processes restrict their rate performance and cycling stability in SIBs. Herein, bimetallic selenide ZnSe/MoSe₂@NC is fabricated by in situ selenation of a rhombic dodecahedron structured metal-organic framework (MOF) containing Zn/Mo salt. Such a heterojunction and structural regulation effectively promote sodium ion transportation. Furthermore, the porous and hierarchical ZnSe/MoSe₂@NC is capable of adapting to the volume stress generated by sodium ion (de)insertion. Specifically, in SIB half-cell measurement, a comparable capacity of 401.8 mA h g^-1 after 100 cycles at 1 A g^-1 can be achieved by ZnSe/MoSe₂@NC. Additionally, the ZnSe/MoSe₂@NC polyhedron delivers a high capacity of 345.7 mA h g^-1 at 5 A g^-1 (1500 cycles). Electrochemical kinetics analysis is performed in detail. In SIB full battery applications, the cell shows an impressive energy density of 175.1 W h kg^-1. This research broadens the development prospect of transition metal selenides as anodes in SIBs.