Unveiling the Potential of Zr ₂ N, Hf ₂ N, and ZrHfN as Anode Materials for Magnesium-Ion Batteries: A DFT Approach

The development of efficient anode materials is crucial for improving the performance of ion storage batteries. MXenes have recently gained significant attention as promising electrode materials for various energy storage applications. In this study, the potential of Zr₂N, Hf₂N, and ZrHfN nanosheets as anodes for magnesium-ion batteries (MIBs) was systematically investigated. The adsorption behavior of magnesium atoms was analyzed, and the most favorable adsorption energies were found to be -2.489, -2.442, and -2.138 eV for Zr₂N, Hf₂N, and ZrHfN, respectively. During the adsorption process, a substantial amount of charge is transferred from the Mg atom to the nanosheets, which significantly influences their electronic properties. Electronic structure analysis reveals that all three MXenes exhibit metallic behavior, as predicted by band structure calculations. The Mg diffusion barriers between adjacent adsorption sites were calculated to be 0.549, 0.119, and 0.065 eV for Zr₂N, Hf₂N, and ZrHfN, respectively, suggesting high charging rates. The average OCVs are 0.55, 0.55, and 0.53 V for Zr₂N, Hf₂N, and ZrHfN nanosheets, respectively. Furthermore, the theoretical capacities were determined to be 861.8, 468, and 606.6 mAhg^-1, highlighting the potential of these MXenes as high-capacity anodes. Among them, Zr₂N and ZrHfN exhibit the high anodic properties, with the high specific capacity and favorable open-circuit voltage. These findings demonstrate that Zr₂N and ZrHfN hold significant promise as anode materials for Mg-ion batteries.