Exploring the potential of MB4 (M = Cr, Mo, and W) MBenes as high-capacity anode materials for Ca-ion batteries: a DFT approach

Abstract

Two-dimensional MBene monolayers can be used in rechargeable metal-ion batteries because of their layered structure, abundant accommodating sites and high specific surface area. Owing to the abundant resources and cost effectiveness of calcium, calcium ion batteries (CIBs) are a suitable alternative to Li-ion batteries (LIBs). In this study, the performance of MB4 (M = Cr, Mo, and W) monolayer MBenes as an anode material for calcium ion batteries has been predicted via a density functional theory approach. We found that these monolayers have a thermally, mechanically, and dynamically stable structure. Furthermore, the lightweight properties and energetically favorable adsorption of 6 layers of Ca atoms endow CrB4, MoB4 and WB4 with high storage capacities of 3377 mA h g−1, 2311 mA h g−1 and 1416 mA h g−1, as well as comparatively low average open circuit voltage of 0.45 V, 0.47 V and 0.35 V, respectively. This reveals their notable superiority over most 2D anode materials. Likewise, the faster mobility of Ca ions in the MB4 monolayer was proved by low activation barriers values of 0.67 eV, 0.72 eV and 0.79 eV for CrB4, MoB4 and WB4, respectively. Additionally, the metallic nature of the materials remained well maintained after the adsorption of full concentrations of Ca ions. These properties signify that monolayers CrB4, MoB4 and WB4 are promising anode materials for CIBs with commendable rate capacities.