NiAs-type vanadium sulfides: Topological surface and abundant electroactivity as a bi-functional material in Mg/Li batteries

Rechargeable Mg battery (RMB) is a new type of next-generation secondary battery. The unique NiAs-type V3S4 is capable of achieving high electrochemical performance due to its bi-functional effect of electroactive and anchoring ability to the discharge products of polysulfides. Herein, the first-principles calculations were con-ducted to explore the electronic properties, dynamic and absorption behavior of Mg/Li-ions in the bulk and crystal plane of V3S4 to reveal the bi-functional mechanism in Mg/Li batteries. First, the stable surface adsorption and rapid diffusion kinetics of Mg/Li ions render the high-rate capability for V3S4. Second, the Mg/Li polysulfides could effectively anchor on the V3S4 (1 1 1) plane and retain their structural stability during the discharge-charge process for Mg/Li batteries. Even after Li2Sn/MgSn adsorption, the metallic property of V3S4 is still preserved to realize the redox electrochemistry of Li2Sn/MgSn and ameliorates the effect of the insulated low-order poly -sulfides. Meanwhile, the low Gibbs energy differences for Mg and Li polysulfides on V3S4 (111) plane gives the evidence of electrocatalytic property. As bi-functional material, the V3S4 has striking characteristics of low diffusion barrier, benificial adsorption and preeminent electrocatalytic ability of Li/Mg species, which can be leveraged for designing vanadium sulfides as high-conductivity cathode materials for RMBs.