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.