Effects of solvents on Li+ distribution and dynamics in PVDF/LiFSI solid polymer electrolytes: An all-atom molecular dynamics simulation study

Large-scale all-atom molecular dynamics simulations are used to investigate the structure and dynamics of a solid polymer electrolytes (SPE) model made up of polyvinylidene fluoride (PVDF) as the polymer matrix, lithium bis(fluorosulfonyl)imide salt (LiFSI), and six distinct solvent types in varying quantities. The influence of solvents on the physicochemical parameters of SPEs relevant to the Li-Battery sector is analysed. We prove that the presence of solvents containing oxygens atoms has different abilities to dissociate the LiFSI ions, form confined channels in the SPEs, and decrease the PVDF crystallinity. Besides, some solvents having a high affinity to the cations reduce the Li+ transport assembling in nano-domains, separated from the PVDF chains, when they present with a high amount, dramatically decreasing the Li+ transference number (tLi+). On the contrary, the ionic conductivity boosts preserving a good tLi+ for high dynamics solvents that form small Li+-solvent clusters. Our nanoscale investigations edify approaches for improving the ionic conductivity and controlling the arrangement of the ions in the SPE needed for proper battery operation by choosing a suitable solvent with a regulated amount.