Understanding extreme fast charge limitations in carbonate mixtures

Abstract

Charging large format lithium ion batteries within ten to fifteen minutes requires changes to the electrolyte composition in addition to modification of electrode and cell architectures. Several approaches to address this need have been proposed; but there is not a lot of clarity on understanding which factors limit the performance of existing electrolytes. This work takes a closer look at the solvated components of a mixture of LiPF₆ in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in the context of extreme fast charging and relates these findings to cell-level requirements. Molecular dynamics studies of the Gen-2 electrolyte compositions with increasing salt concentrations, have been performed to estimate transport properties like diffusivity, transference number and conductivity. Molecular-level differences in the structure of solvation shells under extreme LiPF₆ concentrations are probed here and some key aspects on solvent structure that help overcome barriers to Li⁺ transport under extreme fast charge are discussed.