Monolayer honeycomb borophene: A promising anode material with a record capacity for lithium-ion and sodium-ion batteries

Two-dimensional (2D) materials are a promising candidate for the anode material of lithium-ion battery (LIB) and sodium-ion battery (NIB) for their unique physical and chemical properties. Recently, a honeycomb borophene (h-borophene) has been fabricated by molecular beam epitaxy (MBE) growth in ultra high vacuum. Here, we adopt the first-principles density functional theory calculations to study the performance of monolayer (ML) h-borophene as an anode material for the LIB and NIB. The binding energies of the ML h-borophene-Li/Na systems are all negative, indicating a steady adsorption process. The diffusion barriers of the Li and Na ions in h-borophene are 0.53 and 0.17 eV, respectively, and the anode overall open-circuit voltages for the LIB and NIB are 0.747 and 0.355 V, respectively. The maximum theoretical storage capacity of h-borophene is 1860 mAh•g-1 for NIB and up to 5268 mAh•g-1 for LIB. The latter is more than 14 times higher than that of commercially used graphite (372 mAh•g-1) and is also the highest theoretical capacity among all the 2D materials for the LIB discovered to date. Our study suggests that h-borophene is a promising anode material for high capacity LIBs and NIBs.