High storage capacity and small volume change of potassium-intercalation into novel vanadium oxychalcogenide monolayers V2S2O, V2Se2O and V2Te2O: An ab initio DFT investigation

A new category of two-dimensional electrode materials, i.e., V(2)Ch(2)O (Ch = S, Se and Te) monolayers was explored for K-ion batteries (PIBs) based on principle of chemical exfoliation, density functional theory and ab initio molecular dynamics simulations. The V(2)Ch(2)O monolayers show low cleavage energies and excellent thermal, dynamical and mechanical stabilities. Adsorption energies of a potassium atom on the V(2)Ch(2)O monolayers are exothermic, which are of benefit to prevent forming dendrites. The existence of electrode potentials substantially decreases the diffusion barriers of potassium atoms on the three V(2)Ch(2)O monolayers. The V(2)Ch(2)O monolayers are able to maintain their metallic characteristics and single surface phase during the whole K-intercalation process, avoiding the decrease in electronic conductivity and the appearance of potential hysteresis. The theoretical specific capacities of the V2S2O, V2Se2O and V2Te2O monolayers are predicted to be 883.6, 583.1 and 431.0 mAh g(-1), respectively, and the corresponding average open-circuit voltages are 0.449, 0.390 and 0.293 V, respectively. The maximum percentage changes in lattice parameters are 4.21%, 6.07% and 7.26% for the V2S2O, V2Se2O and V2Te2O monolayers, respectively. All the calculated properties indicate that the V(2)Ch(2)O monolayers are promising electrode materials for PIBs with high capacities and long cycle lives.