Multilayer Ion Load and Diffusion on TMD/MXene Heterostructure Anodes for Alkali-Ion Batteries

Two-dimensional (2D) material-based anodes facilitate the development of next-generation ion batteries due to their high ion loading capacity and mobility. In this study, using first-principles calculations, we confirmed that high site occupancy of ions can enhance the diffusion barrier, while the weak adhesion of the ions on heterostructures can enable easy migrations and eliminate the effects of high occupancy. First, the five-layer alkali ion (Li, Na, K) loading on transition-metal dichalcogenides (TMDs; VS2, MoS2)/MXene (Ti2CO2, V2CO2) was found, and the adsorption sites, binding energies, and charge transfers were assessed. Then, ab initio molecular dynamics (AIMD) simulations uncovered significant variations of ionic diffusivity and conductivity with ion loading concentration, which increase at first and then decrease for Li and monotonically increase for Na and K, implying discrepant interactions between ions. Systematic climbing-image nudged elastic band (CI-NEB) calculations show that the diffusion barriers of second-layer Li increase by similar to 40% when adjacent sites were occupied, while the changes of Na and K barriers are negligible. The results demonstrate that weak adhesion is vital for the fast ion migration at a high occupation. Our study provides a general framework to comprehend the ion migration at layered van der Waals structures.