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 B9 monolayer and its potential as a novel anode candidate for LIBs, SIBs, and PIBs have been investigated using first-principles calculations. The B9 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 B9 monolayer compared to that of β12 and χ3 borophene suggests that the B atom within the B9 monolayer may possess certain antioxidant properties similar to those of β12 and χ3 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 B9 monolayer. Upon the adsorption of Li and Na atoms, a puckered structure is formed on the original B9-plane structure, which further lowers the diffusion barrier of Li and Na atoms. Remarkably, the B9 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 B9 are comparable or superior to other borophene, phosphorene, and other known electrode materials, suggesting that the B9 monolayer has the potential to be a novel candidate anode material in LIBs/SIBs/PIBs.