Insight into Janus V2COS as anode material of high-performance alkali metal ion battery: Diffusion barrier, recyclability, specific capacity, and open-circuit voltage

Transition metal carbides, nitrides, and carbonitrides, known as MXenes, exhibit exceptional conductivity, stability, and large specific surface area, rendering them promising candidates for anode materials in rechargeable batteries. Herein, we investigate the electrochemical characteristics of the Janus MXene ${\mathrm{V}}_2\mathrm{COS}$ monolayer, as an anode material of alkali metal ion batteries by using first-principles calculations. The phonon band structure and ab initio molecular dynamics simulations confirm the stability of the Janus ${\mathrm{V}}_2\mathrm{COS}$ monolayer. The mechanical and electrical properties of the Janus ${\mathrm{V}}_2\mathrm{COS}$ monolayer are explored and proved to have good mechanical stability and electrical conductivity. The surface of the Janus ${\mathrm{V}}_2\mathrm{COS}$ monolayer demonstrates the facile adsorption of alkali metal ions and low diffusion barriers. As an anode material, the recyclability of the Janus ${\mathrm{V}}_2\mathrm{COS}$ has been verified in the ion intercalation/deintercalation processes. Furthermore, the theoretical specific capacities and the open-circuit voltages of the Janus ${\mathrm{V}}_2\mathrm{COS}$ monolayer are calculated to be $165.54\mathrm{mA}\mathrm{h}\text{/}\mathrm{g}$ and 2.62 V for Li, $662.18\mathrm{mA}\mathrm{h}\text{/}\mathrm{g}$ and 0.76 V for Na, and $294.43\mathrm{mA}\mathrm{h}\text{/}\mathrm{g}$ and 0.4 V for K, respectively. It presents that the Janus ${\mathrm{V}}_2\mathrm{COS}$ monolayer is a potential anode material of sodium-ion batteries and potassium-ion batteries.