Adsorption of potassium atoms on twin T-graphene and twin-graphene surfaces for K-ion batteries

Abstract

With the development of potassium-ion (K-ion) batteries, the search for two-dimensional materials with potassium storage potential has become a research hotspot. Twin T-graphene (TTG) and twin-graphene (TG) were studied as anode materials for K-ion batteries in terms of their adsorption energies, electronic structures, theoretical capacitances, diffusion barriers, and open circuit voltages (OCV) using first-principles calculations. Seven different adsorption sites of individual K atoms on TTG and TG were investigated. The most stable adsorption sites for TTG and TG were the H2 and B sites, respectively. After K atom adsorption, both semiconducting TTG and TG transform into metals, which facilitates K-ion diffusion and migration within the anode material. The K atoms were physically adsorbed on the TTG and TG surfaces, and the K adsorbed by TG was more stable than its TTG counterpart. Both TTG and TG could accommodate up to two layers of K atoms, with a maximum theoretical capacity of 372.22 and 496.30 mA·h/g, respectively. The average OCVs of TTG and TG were 1.12 and 1.58 V, while their diffusion barriers were 0.24 and 0.30 V, respectively. Therefore, TG has better theoretical capacity than TTG, while TTG excels in average OCV and diffusion barrier performance. This study underscores the broad potential applications of both TTG and TG as new energy materials for potassium storage.