Abstract
K-ion batteries are interesting alternatives to Li-ion batteries because of the earth-abundance of K and the similar chemistry between K and Li. However, a lack of high-performance anode materials is a major obstacle to the development of K-ion batteries. We show that the BC6P monolayer, which is isostructural and isoelectronic to graphene due to charge compensation between the constituent elements, can fill this gap. The capacity is found to be 1410 mAh/g (BC6PK6), i.e., about four times that of graphite. The diffusion barrier is as low as 0.13 eV and the average open-circuit voltage is as low as 0.35 V, ensuring high rate performance and high safety, respectively. Metallic states induced by K adsorption provide electrical conductivity during the battery cycle.