Metallic Be[formula omitted]M (M = Al, Ga) monolayers as potential universal anodes for Li and post-Li ion batteries

Abstract

Developing excellent comprehensive performance anode materials is of vital importance for rechargeable metal ion batteries in the domain of energy conversion and storage. By first-principles calculations, we have appreciated that the highly conductive planar hexacoordinate Be2Al and Be2Ga monolayers can be served as universal anodes for alkali/alkaline metal ion batteries. Due to favorable adsorption energy landscape, the diffusion barriers of Li, Na, K, and Ca atoms on the Be2Al and Be2Ga surfaces are as low as 0.116, 0.075, 0.046, 0.270 eV and 0.044, 0.025, 0.014, 0.217 eV, respectively, indicative of fast rate capabilities. At the same time, the Be2Al and Be2Ga monolayers exhibit the desirable mean open-circuit voltages of 0.049 and 0.104 V for Li+, 0.234 and 0.278 V for Na+, 0.249 and 0.227 V for K+, as well as 0.120 and 0.124 V for Ca2＋, respectively, conducive to achieve high operating voltage at the full-cell level. Arising from stable double-sided multilayer adsorption, the Be2Al (Be2Ga) monolayer can deliver ultrahigh reversible specific capacities up to 2382 (1222), 4764 (1833), 2382 (1222), and 7146 (3665) mA h g−1 for Li, Na, K, and Ca atoms, respectively. All of these advantages along with reliable cycling stability demonstrate that these two 2D materials enjoy great potential as promising anodes for Li, Na, K, and Ca ions batteries.