A two-dimensional VO₂/VS₂ heterostructure as a promising cathode material for rechargeable Mg batteries: a first principles study

Abstract

Rechargeable magnesium batteries (RMBs) are considered as highly promising energy storage systems. However, the lack of cathode materials with fast Mg²⁺ diffusion kinetics and high energy density severely hinders the development of RMBs. Herein, a two-dimensional (2D) VO₂/VS₂ heterostructure as a RMB cathode material is proposed by introducing an O-V-O layer in VS₂ to improve the discharge voltage and specific capacity while keeping the fast Mg²⁺ diffusion kinetics. Based on first principle calculations, the geometric structures, electronic characteristics of the VO₂/VS₂ heterostructure, and the adsorption properties and diffusion behaviors of Mg²⁺ in VO₂/VS₂ are systematically studied. The metallic properties of VO₂/VS₂ and a relatively low diffusion barrier of Mg²⁺ (0.6 eV) in VO₂/VS₂ enable a large potential in delivering high rate performance in actual RMBs. Compared with traditional VS₂ materials (1.25 V), the average discharge platform of VO₂/VS₂ could be increased to 1.7 V. The theoretical capacities of the layered VS₂ and VO₂/VS₂ are calculated as 233 and 301 mA h g^-1, respectively. Thus, the VO₂/VS₂ heterostructure exhibits a high theoretical energy density of 511.7 W h kg^-1, significantly surpassing that of VS₂ (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.