Simulation of the Cation Solvation Structure of the Electrolyte in Separator Nanopores of a Lithium Ion Battery

The solvation structure of Li+ plays a critical role in ion transport and electrochemical reactions in lithium-ion battery (LIB) electrolytes. To investigate the solvation structure and coordination number of Li+, we examined the impact of force field parameters using molecular dynamics simulations. In the system with mixed carbonates and lithium hexafluorophosphate (LiPF6), the total coordination number of Li+ is found to be primarily determined by nonbonded parameters of Li+. The polarity of carbonate partial charges significantly affects the Li+ solvation structure, and scaling down the partial charges promotes ion association. By simulating the solvation structure of carbonate electrolyte between two layers of polyethylene (PE) short chains as a model of separator nanopore, it is intriguingly found that linear carbonates tend to accumulate on the PE surface, increasing ion concentration and enhancing ion aggregation. Experimental measurements confirm that the nanoporous structure on the surface of the separator tends to shrink and close during battery cycling, and further influence the Li+ solvation structure as simulation exhibits and further impact the service performance of LIBs. This provides a new insight into the electrolyte-separator interaction on ion transport and electrochemical reactions.