Structure-transport relations for Li+ ions at the electrolyte/polymer interface from classical molecular dynamics.

Lithium-ion batteries have become indispensable in modern life due to their ability to provide efficient and reliable energy. While extensive research has been conducted on electrolyte behavior at electrode interfaces, the electrolyte/separator interface and the transport properties through it remain relatively unexplored. Yet, optimizing the transport mechanism could improve power density and reduce overheating. Lithium ions diffuse through the pore space in the separator, where an extensive interfacial surface area is in contact with the electrolyte. Experimental studies suggest that separator-electrolyte interactions may impact the surface chemistry and microscopic behavior of transport processes, but atomic-level insights are still lacking. This study uses classical molecular dynamics simulations to investigate the behavior of 1.2M LiPF6 in ethylene carbonate at the interface with a polyethylene substrate, a commonly used separator material. Our simulations reveal how the solvation structure and diffusive mechanisms change within thin interfacial films as a function of the distance from the polyethylene substrate. The results could provide a benchmark for engineering future electrolytes and separator materials to eventually control transport properties.