Effect of Salt Concentration on Properties of Lithium Ion Battery Electrolytes: A Molecular Dynamics Study

Electrolyte solutions of 1 M concentration are typically used in lithium ion batteries (LIB) for optimal performance. However, recently, superconcentrated electrolytes have been proposed to be a promising alternative to 1 M solutions. Despite their improved stability features, application of the concentrated electrolytes is hindered by their poor transport properties. We probe EC-LiPF6 electrolyte system for a range of concentrations: 0.06 to 4 M using molecular dynamics simulations to study the effect of concentration on transport and structural properties. Molecular structure of the solution changes with concentration from a predominantly solvent separated ion pair (SSIP) configuration at the dilute limit to an aggregate rich configuration at high concentration. Depletion of SSIPs and formation of more aggregates at higher concentrations affect the transport properties. The present work provides insights into the relation between molecular structure and performance of the electrolyte solution and suggests ways to design novel concentrated electrolytes.