First-principles prediction of layered MoO2and MoOSe as promising cathode materials for magnesium ion batteries.

Magnesium ion battery is one of the promising next-generation energy storage systems. Nevertheless, lack of appropriate cathode materials to ensure massive storage and efficient migration of Mg cations is a big obstacle for development of Mg-ion batteries. Herein, by means of first principles calculations, the geometric structure, electronic structure, Mg intercalation behavior and Mg diffusion behavior of the layered MoO2and two MoOSe (MoOSe(I) and MoOSe(V)) were systematically investigated. Layered MoO2shows semiconductor properties, while MoOSe displays metallic characteristics which ensure higher conductivity. The Mg cations tend to intercalate into octahedral sites for both MoO2and MoOSe. The maximum Mg-storage phases of the layered MoO2, MoOSe(I) and MoOSe(V) correspond to Mg0.666MoO2, Mg0.666MoOSe(I) and Mg0.666MoOSe(V), with theoretical specific capacities of 279, 191 and 191 mAh g-1, respectively. The calculated discharge plateaus of MoO2and two MoOSe are all about 1 V, which ensure that the layered MoO2and MoOSe electrodes can act as cathodes for Mg-ion batteries in the early stage. Moreover, comparing with other cathodes, the diffusion barrier of Mg cations and volume expansion during Mg intercalation process are competitive. The results suggest that layered MoO2and MoOSe are the promising cathode materials for Mg-ion batteries.