Harnessing the volume expansion of metal selenide anode by composition engineering to achieve ultrastable sodium storage

Transition-metal selenides have attracted sustaining interests as promising anodes for sodium-ion batteries (SIBs) due to the suitable electrochemical storage mechanism. However, the intrinsic expansion effect during the electrochemical process restricts their further development, thus their composition engineering aiming at weakening expansion effect is extremely important and urgent. Herein, a versatile strategy combining sol-gel and post-selenization route is proposed for acquiring a series of anion-rich bimetal selenides/sulfoselenides, including a Ni0.75Zn0.25-SSe@C composite with high specific capacity (434.9 mAh g-1 at 0.1 A g-1) and great cyclic stability (271.8 mAh g-1 at 1.0 A g-1 after 300 cycles) as the SIB anode. Particularly, the doping of Zn and S atoms in original anion-rich Ni0.85Se can significantly relieve expansion effect during the long-cycle discharge/charge process, and -the lowered conductivity can be compensated with the surficial carbon coating, resulting in the good performances in SIBs. This new strategy is suitable for the majority of transition metal selenides/sulfoselenides and exhibits an outstanding universality for other multi-component materials even high entropy metal compounds for applications in energy storage and conversion.