Performance of -S and -O bifunctional V2C MXene monolayer in lithium-ion batteries: A first-principles study

As a potential candidate for lithium-ion batterys (LIBs) electrode materials, V2C, a type of MXene, demonstrates exceptional electrical conductivity, a large specific surface area and easy lithium diffusion. However, the preparation process inevitably leads to the formation of various functional groups on the material's surface, which can significantly influence its electrochemical properties. Four stable symmetrical models V2CO2, V2CO4/S-3(2/3), V2CO2/3S4/3 and V2CS2 with excellent electronic conductivity and thermodynamic stability are selected to investigate the electrochemical performance using first-principles calculations. The results demonstrate that the order of diffusion barriers for Li ion on functionalized V2C MXene is as follows: V2C2O2 (0.15 eV) < V2C2S2 (0.22 eV) < V2CO4/3S2/3 (0.28 eV) < V2CO2/3S4/3 (0.33 eV). The maximum adsorption concentrations of Li ions are observed in V2CO2Li2, V(2)CO(4/3)S(2/3)li(4), V2CO2/3S4/3Li6 and V2CS2Li4 with corresponding theoretical storage capacities 367 mA center dot h/g, 538 mA center dot h/g, 729 mA center dot h/g and 602 mA center dot h/g, respectively. The excellent energy storage capacity of V2CO2/3S4/3, with a low average voltage of 0.29 V, surpasses that of several previously predicted anode materials. This work further elucidates the regulatory mechanism of functional groups on the properties of MXenes and provides a novel strategy for modifying MXenes.