Two-dimensional functionalized MBene Mg2B3T (T = O, H, and F) monolayers as anode materials for high-performance K-ion batteries

Abstract

Two-dimensional metal borides have received attention as high performance battery anode materials. During the practical application, the 2D surface terminalization is an inevitable problem. This study employs first-principles calculations to investigate the termination of the Mg₂B₃ monolayer with O, H, F, and Cl groups. These structures' stabilities are examined through energetic, mechanical, kinetic and thermodynamic stability studies. Electronic property analysis shows that Mg₂B₃T (T = O, H, F, and Cl) monolayers are all metallic. Calculated results reveal that the Mg₂B₃O, Mg₂B₃H, and Mg₂B₃F monolayers exhibit high K ion storage capacities (up to 826 mA h g⁻¹, 980 mA h g⁻¹, and 804 mA h g⁻¹, respectively), with diffusion barriers of 0.338 eV, 0.490 eV, and 0.507 eV, respectively. More importantly, the calculated in-plane lattice constants of the substrate materials exhibit a minimal variation and the observed volume expansion is almost negligible (less than 0.08%) during the entire potassization process, which is much lower than that of the pristine Mg₂B₃ monolayer. This structural stability is attributed to the presence of surface functional groups. These results provide helpful insights into designing and discovering other high-capacity anode materials for batteries.