Applications of MxSey (M = Fe, Co, Ni) and Their Composites in Electrochemical Energy Storage and Conversion.

Transition-metal selenides (MxSey, M = Fe, Co, Ni) and their composites exhibit good storage capacities for sodium and lithium ions and occupy a unique position in research on sodium-ion and lithium-ion batteries. MxSey and their composites are used as active materials to improve catalytic activity. However, low electrical conductivity, poor cycle stability, and low rate performance severely limit their applications. This review provides a comprehensive introduction to and understanding of the current research progress of MxSey and their composites. Moreover, this review proposes a broader research platform for these materials, including various bioelectrocatalytic performance tests, lithium-sulfur batteries, and fuel cells. The synthesis method and related mechanisms of MxSey and their composites are reviewed, and the effects of material morphologies on their electrochemical performance are discussed. The advantages and disadvantages of MxSey and their composites as well as possible strategies for improving the storage and conversion of electrochemical energy are also summarized.