Analysis of Molecular Clusters in Simulations of Lithium-Ion Battery Electrolytes

Graph theoretic tools were used to identify and classify clusters of ions and solvent molecules in molecular dynamics simulations of lithium-ion battery electrolytes. Electrolytes composed of various concentrations of LiPF6 dissolved in ethylene carbonate (EC), dimethylene carbonate (DMC), or a 1:1 EC/DMC mixture were simulated at multiple temperatures using classical molecular dynamics. Contrary to Nernst-Einstein theory but consistent with experiment, pure DMC systems had the greatest diffusivity but the lowest conductivity. This disagreement with Nernst-Einstein theory is explained by the observed clustering behavior, which found that systems with pure EC as a solvent formed ion clusters with nonzero charge, whereas systems with pure DMC as a solvent formed primarily neutral clusters.