Metallic BSi3 monolayer as a high rate-capacity anode material for flexible potassium ion batteries: A first-principles study

Potassium ion batteries (PIBs) have attracted great attention as a competitive substitute for lithium ion batteries (LIBs) because of the good safety and low cost; nevertheless, their practical application is severely impeded by the lack of a high-performance anode material. Motivated by the high capacity of silicon and excellent stability of boron, we investigate a 2D B-Si binary compound (h-BSi3 and o-BSi3) as the anode material of PIBs. Our first-principles calculation results demonstrate that BSi3 monolayers have the intrinsic metallicity with high electrical conductivity, which is of great importance for the rapid electronic transport during electrochemical process. Benefitting from the strong affinity of potassium, the h-BSi3 (o-BSi3) anode achieves a high specific capacity of 1268.45 (1190.15) mA h/g and a low averaged open circuit voltage of 0.38 (0.48) V. The potassium diffusion barrier on the h-BSi3 (o-BSi3) anode is as low as 0.02 (0.04) eV. Moreover, a small lattice expansion is observed for the BSi3 anodes without metal dendrite formation at the final potassiated stage, which is beneficial to prolong the cycle life of PIBs. All the unique features suggest that BSi3 monolayers are promising anode candidates for flexible PIBs.