High cell voltage and storage capacity of graphyne as the anode of K-ion batteries: computational studies

Li-ion batteries have many advantages, but these batteries suffer from safety problems, short lifetime, and a high cost. Nontoxicity, wide availability, and low cost of potassium offer the K-ion batteries (KIB) as a replacement to the Li-ion batteries. The B3LYP-gCP-D3 approach of density functional theory is applied to examine the probable application of graphyne in the anode of KIBs. It is found that a triangular hollow is the most favorable site for the K or K+ adsorption, releasing energies about 16.3 or 41.1 kcal/mol. The released energies for K and K+ have been reported to be about 16.8 and 34.2 kcal/mol for graphene sheet, respectively, which generate a cell voltage of 0.75 V. A high K storage capacity of 241 mAh/g and cell voltage of 1.08 V are predicted for graphyne. The maximum barrier energies for the displacement of K or K+ on the surface of graphyne are computed to be 2.8 (similar to 3.4 for K/graphene) or 5.6 kcal/mol, representing an excellent ion mobility due to the low energy barriers. Consequently, we suggest the graphyne sheet as an anode material for the KIBs owing to its high diffusion ability, high cell voltage, and high storage capacity.