Enabling enhanced lithium storage capacity of two-dimensional pentagonal BN2 by aluminum doping

Abstract

Researchers studying Li-ion batteries (LIBs) have become very interested in two-dimensional (2D) materials possessing an unusual pentagonal atomic structure. Recently, penta-graphene, penta-B₂C, and penta-BN₂ have been theoretically described. These materials are attractive for use as state-of-the-art anodes in LIBs due to their high storage capacities of 1489, 1594, and 2071 mA h g⁻¹, respectively. Here, we propose enhancing storage capacity by introducing defect doping. For example, one Al atom was incorporated into 2 × 2 penta-BN₂, corresponding to AlB₇N₁₆. The energy calculated for the adsorption of a single Li atom onto the Al-doped material is more favorable than that for the Al-free analog, indicating that doping can strengthen an affinity for Li. The Al-doped penta-BN₂ exhibits metallic conductivity during Li adsorption. In the layer-by-layer Li adsorption, doping a single Al atom into 2 × 2 penta-BN₂ has an 11% higher storage capacity (2297 mA h g⁻¹) than penta-BN₂ despite having a slightly heavier formula weight. The Al-doped penta-BN₂ displays a low open-circuit voltage of 0.48 V. Substituting aluminum for boron enhances the Li adsorption capacity of penta-BN₂, and the computed storage capacity is presently one of the highest published values for pentagonal materials.