Two‐dimensional boron as an impressive lithium‐sulphur battery cathode material

Abstract

β12-borophene is a recently fabricated two-dimensional (2D) allotrope of boron that has many unique electrical, mechanical and chemical properties that make it an excellent candidate as a cathode material in lithium sulphur (Li-S) batteries. Ab initio calculations were performed to determine β12-borophene's applicability as a Li-S battery cathode material. Binding energies of sulphur (S8) and various lithium polysulphides (Li2Sx, x=2,3,4,6,8) on the β12-borophene surface were calculated, along with the diffusion barriers for Li2S6 and Li2S4. Our calculations suggest a moderate adsorption of sulphur and a strong adsorption of all lithium polysulphides, implying β12-borophene would sufficiently inhibit the dissolution of lithium polysulphides into the electrolyte, preventing the “shuttle effect”. Through an exhaustive adsorption site sampling the binding energies were determined to be −1.19eV for S8, −2.98eV for Li2S8, −2.77eV for Li2S6, −3.08eV for Li2S4, −3.48eV for Li2S3, −3.79eV for Li2S2, and −4.57eV for Li2S. The diffusion barriers for Li2S6 and Li2S4 were determined to be moderate, ensuring efficient diffusion, with the lowest diffusion energy barriers being 0.61eV and 0.99eV for Li2S6 and Li2S4, respectively. The strong binding energies and moderate diffusion barriers suggest β12-borophene would be an excellent lithium polysulphide immobilizer in Li-S cathodes.