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

Transition-metal selenides (M x Se y , 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. M x Se y 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 M x Se y 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 M x Se y and their composites are reviewed, and the effects of material morphologies on their electrochemical performance are discussed. The advantages and disadvantages of M x Se y and their composites as well as possible strategies for improving the storage and conversion of electrochemical energy are also summarized.