Prediction of Two-dimensional B9 as High-performance Anode Material for Li/Na/K-ion Batteries

Lithium-ion batteries (LIBs) have been widely used as energy storage devices in recent years. Meanwhile, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are new alternatives to LIBs with similar electrochemical properties but with higher capacities, lower costs, and lower toxicity. Nevertheless, a major challenge in the development of LIBs, SIBs, and PIBs is finding anode materials with high energy densities and fast charging-discharging rates. Here, the electronic properties of a novel B-9 monolayer and its potential as a novel anode candidate for LIBs, SIBs, and PIBs have been investigated using first-principles calculations. The B-9 monolayer demonstrates good thermal, dynamic, and mechanical stability, indicating its ability to exist stably at room temperature. Furthermore, the lower adsorption energy of the oxygen molecule on the B-9 monolayer compared to that of beta(12) and chi(3) borophene suggests that the B atom within the B-9 monolayer may possess certain antioxidant properties similar to those of beta(12) and chi(3) borophene. Additionally, its intrinsic metallicity makes it an excellent electrical conductor during LIBs/SIBs/PIBs cycles. In addition, Li, Na, and K have negative adsorption energies, which hinder the formation of dendrites on the B-9 monolayer. Upon the adsorption of Li and Na atoms, a puckered structure is formed on the original B-9-plane structure, which further lowers the diffusion barrier of Li and Na atoms. Remarkably, the B-9 monolayer has very low diffusion barriers of only 0.14/0.04/0.05 eV for Li, Na, and K, respectively, and serves as the anode for LIB, SIB, and PIB with a high theoretical storage capacity of around 2437.62/1029.61/582.01 mA h g(-1), and low open-circuit voltage about 0.37/0.17/0.22 V. The excellent electrochemical performances of B-9 are comparable or superior to other borophene, phosphorene, and other known electrode materials, suggesting that the B-9 monolayer has the potential to be a novel candidate anode material in LIBs/SIBs/PIBs.