Bi-modified V2C MXene (V2CBi2) monolayer film as an anode for alkali metal-ion (Li/Na) batteries: a first-principles study

Abstract

This study systematically investigates the performance of V₂CBi₂ as an anode for alkali metal-ion (Li/Na/K) batteries using first-principles methods and explores the effect of O-doped V₂CBi₂ on its performance as an anode for ion batteries. We systematically assessed its structural stability, electronic properties, adsorption characteristics, diffusion barriers, open-circuit voltage (OCV), and volumetric capacity. The results show that V₂CBi₂ maintains excellent thermal stability under both room temperature (300 K) and high-temperature (500 K) conditions. In addition, V₂CBi₂ itself exhibits excellent electrical conductivity, and its adsorption energies for Li/Na/K range from −1.55 to −2.05 eV, which is conducive to the formation of stable adsorption configurations. The diffusion barriers of Li/Na/K ions on V₂CBi₂ range from 0.07 to 0.15 eV, and the extremely low diffusion barriers are conducive to improving battery rate performance. The theoretical capacities of V₂CBi₂ for Li, Na, and K ions are 403.11 mAh g⁻¹, 251.94 mAh g⁻¹, and 100.78 mAh g⁻¹, respectively, corresponding to volumetric capacities of 3777.14 mAh cm⁻³, 2356.46 mAh cm⁻³, and 944.31 mAh cm⁻³. The excellent volumetric capacity indicates that V₂CBi₂ can release more energy within the same volume. The OCVs of V₂CBi₂ for Li, Na, and K ions are 0.25 V, 0.48 V, and 2.78 V, respectively. The low volumetric capacity (944.31 mAh cm⁻³ for K) and a high OCV (2.78 V for K) indicate that V₂CBi₂ is unsuitable as an anode for K-ion batteries. Under oxygen-doping conditions, V₂CBi₂ still maintains conductivity, but the diffusion barrier increases significantly. Therefore, oxidation of V₂CBi₂ should be minimized during experimental preparation and use in order to maintain its excellent ion-diffusion properties. In summary, V₂CBi₂ shows significant application promise as an anode material for both Li- and Na-ion batteries and provides an important theoretical foundation for designing advanced cation battery systems.