  In this article, we study the transport properties of superconcentrated
electrolytes using Molecular Dynamics simulations, which have been shown
experimentally to retard elemental dissolution in vanadium containing cathode
materials. Five compositions between one and seven molar lithium
bis(trifluoromethanesulfonyl)imide in 1,3-Dioxolane and 1,2-Dimethoxyethane
solvent mixture are studied using non-polarizable Optimized Potentials for
Liquid Simulations - All Atom force field. The simulated physico-chemical
properties such as ionic conductivity, self-diffusion coefficients, and density
are observed to match well with the results obtained through experiments.
Radial Distribution Function analysis reveals a strong co-ordination between
salt anions and vanadium cations as the electrolyte transitions from a
salt-in-solvent type to solvent-in-salt type electrolyte. A high anion content
in the first solvation shell of vanadium cations is observed for
solvent-in-salt type electrolytes, through ion-clustering calculations.
Solvation free energy calculations using Free Energy Perturbation method
indicate that the active material dissolution should be retarded by using
superconcentrated electrolytes. Ion-dynamics of the clusters reveal that
vanadium cation transport occurs against its concentration gradient due to
strong coulombic interactions with the salt anions in superconcentrated
electrolytes. The improvement in the cycleability of several vanadium
containing cathode materials provides a robust proof for the theoretical
framework described in this manuscript.
