Status and prospects of SexSy cathodes for lithium/sodium storage

Abstract

To meet the developing requirements of rechargeable batteries, cathode materials should have light masses, high densities, low costs, low toxicity, small oxidation potentials, and good electronic conductivities. As the cathode active material for lithium storage, sulfur (S) has high theoretical density and cost effectiveness. However, its conductivity is poor. The heavier analogue of S, viz. Se, however, has much larger electronic conductivity and higher density. Combining the advantages of S and Se, a new type of cathode material, namely, Se_xS_y, has attracted much interest in recent years. Though Se_xS_y has good conductivity and high volumetric capacity, the issues of shuttle effects, electrolyte suitability, and volume change during cycling still exist. To alleviate these issues, many groups have made versatile efforts to address Se_xS_y. However, hitherto, there has been no systematic summary of this topic. Convinced by its promising synergetic effect and constructive supplement for S cathodes in rechargeable batteries, we here review the recent progress on Se_xS_y as a cathode material for Li and Na batteries. Their syntheses, structures, electrochemical performances, and the structure–property relationships are referred to. As Se_xS_y is a type of relatively young cathode, the electrolytes for Li–Se_xS_y are also addressed. Finally, the challenges and perspectives for Li/Na–Se_xS_y batteries are given.