Ni0.85Se hexagonal nanosheets as an advanced conversion cathode for Mg secondary batteries

Abstract Mg secondary batteries are promising scalable secondary batteries for next-generation energy storage. However, Mg-storage cathode materials are greatly demanded to construct high-performance Mg batteries. Electrochemical conversion reaction provides plenty of cathode options, and strategy for cathode selection and performance optimization is of special significance. In this work, Ni0.85Se with nanostructures of dispersive hexagonal nanosheets (D-Ni0.85Se) and flower-like assembled nanosheets (F-Ni0.85Se) is synthesized and investigated as Mg-storage cathodes. Compared with F-Ni0.85Se, D-Ni0.85Se delivers a higher specific capacity of 168 mAh g‒1 at 50 mA g‒1 as well as better rate performance, owing to its faster Mg2+ diffusion and lower resistance. D-Ni0.85Se also exhibits a superior cycling stability over 500 cycles. An investigation on mechanism indicates an evolution of Ni0.85Se towards NiSe with cycling, and the Mg-storage reaction occurs between NiSe and metallic Ni0. The present work demonstrates that advanced conversion-type Mg battery cathode materials could be constructed by soft selenide anions, and the electrochemical properties could be manipulated by rational material morphology optimization.