Possible application of 2D-boron sheets as anode material in lithium ion battery: A DFT and AIMD study

Abstract

Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations have been employed to investigate the possibility of 2D boron sheets (BSs) as an anode material in lithium ion batteries (LIBs). Among α, α₁ and η_4/28 metallic BSs, planarity is retained for the α₁ and η_4/28 polymorphs after the formation of the layered structure. The optimum anodic nature of the α₁ and α₁-AA polymorphs has been suggested based on their electronic, structural and Li adsorption/desorption studies. The highly symmetric ‘H’ site is energetically favored for Li adsorption at both 0 and 298 K. Li migration occurs from one ‘H’ site to another via the top of a boron atom, with a 0.66 and 0.39 eV energy barrier at 0 and 298 K respectively. An increase in the lithium concentration, up to a 50% coverage of ‘H’ sites, decreases the diffusion barrier gradually and reaches the saturation point at 0.59 eV (at 0 K). The lithium saturation requires eight lithium atoms per 1.63 nm² surface area of the α₁ sheet, when all ‘H’ sites become occupied. This confers the theoretical estimate of the capacity as 383 mA h g⁻¹, which is higher than that of the conventional graphitic electrode. Finally, the structural stability at the lithium saturation point is confirmed by increasing the number of layers up to four. All of these characteristics suggest the appropriateness of α₁-AA as an anode material for LIBs.