A two-dimensional VO/VS heterostructure as a promising cathode material for rechargeable Mg batteries: a first principles study.

Rechargeable magnesium batteries (RMBs) are considered as highly promising energy storage systems. However, the lack of cathode materials with fast Mg diffusion kinetics and high energy density severely hinders the development of RMBs. Herein, a two-dimensional (2D) VO/VS heterostructure as a RMB cathode material is proposed by introducing an O-V-O layer in VS to improve the discharge voltage and specific capacity while keeping the fast Mg diffusion kinetics. Based on first principle calculations, the geometric structures, electronic characteristics of the VO/VS heterostructure, and the adsorption properties and diffusion behaviors of Mg in VO/VS are systematically studied. The metallic properties of VO/VS and a relatively low diffusion barrier of Mg (0.6 eV) in VO/VS enable a large potential in delivering high rate performance in actual RMBs. Compared with traditional VS materials (1.25 V), the average discharge platform of VO/VS could be increased to 1.7 V. The theoretical capacities of the layered VS and VO/VS are calculated as 233 and 301 mA h g, respectively. Thus, the VO/VS heterostructure exhibits a high theoretical energy density of 511.7 W h kg, significantly surpassing that of VS (291.3 W h kg). This work provides important guidance for designing high-energy and high-rate 2D heterostructure cathode materials for RMBs and other multivalent ion batteries.