Cu3VSe4 Cathode for Rechargeable Magnesium Batteries: Favorable Chemical and Electronic Structures Inducing Intercalation and Displacement Reactions

Rechargeable Mg batteries are an advantageous energy-storage technology with low cost and high safety, but the design of high-performance cathode materials is currently the major difficulty. Herein, a new cathode material of Cu₃VSe₄ is fabricated with a comprehensive consideration of the chemical and electronic structures. The intermediate band semiconductor Cu₃VSe₄ has a cubic crystal structure containing interlaced 3D tunnels. The V and Se atoms form chemical bonds with high covalent proportions and facilitate the charge delocalization via the V‒Se bonds. Because of these features, Cu₃VSe₄ provides a high capacity of 251 mAh g^‒1 with co-redox of Cu, V, and Se elements and an outstanding rate performance of 44 mAh g^‒1 at 15 A g^‒1. Prominently, a high mass load of 3.0 mg cm^‒2 is achieved without obvious rate capability decay, which is quite favorable to pair with the high-capacity Mg metal anode in practical application. The mechanism investigation and theoretical computation demonstrate that Cu₃VSe₄ undergoes first a Mg-intercalation and then a displacement reaction, during which the crystal structure is maintained, assisting the reaction reversibility and cycling stability. These findings reveal a rational design principle of rechargeable Mg battery cathodes based on a comprehensive consideration of chemical and electronic structures.