A two-dimensional VO 2 /VS 2 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 2+ diffusion kinetics and high energy density severely hinders the development of RMBs. Herein, a two-dimensional (2D) VO 2 /VS 2 heterostructure as a RMB cathode material is proposed by introducing an O-V-O layer in VS 2 to improve the discharge voltage and specific capacity while keeping the fast Mg 2+ diffusion kinetics. Based on first principle calculations, the geometric structures, electronic characteristics of the VO 2 /VS 2 heterostructure, and the adsorption properties and diffusion behaviors of Mg 2+ in VO 2 /VS 2 are systematically studied. The metallic properties of VO 2 /VS 2 and a relatively low diffusion barrier of Mg 2+ (0.6 eV) in VO 2 /VS 2 enable a large potential in delivering high rate performance in actual RMBs. Compared with traditional VS 2 materials (1.25 V), the average discharge platform of VO 2 /VS 2 could be increased to 1.7 V. The theoretical capacities of the layered VS 2 and VO 2 /VS 2 are calculated as 233 and 301 mA h g -1 , respectively. Thus, the VO 2 /VS 2 heterostructure exhibits a high theoretical energy density of 511.7 W h kg -1 , significantly surpassing that of VS 2 (291.3 W h kg -1 ). This work provides important guidance for designing high-energy and high-rate 2D heterostructure cathode materials for RMBs and other multivalent ion batteries.