  We report the ion transport mechanisms in succinonitrile (SN) loaded solid
polymer electrolytes containing polyethylene oxide (PEO) and dissolved lithium
bis(trifluoromethane)sulphonamide (LiTFSI) salt using molecular dynamics
simulations. We investigated the effect of temperature and loading of SN on ion
transport and relaxation phenomenon in PEO-LiTFSI electrolytes. It is observed
that SN increases the ionic diffusivities in PEO-based solid polymer
electrolytes and makes them suitable for battery applications. Interestingly,
the diffusion coefficient of TFSI ions is an order of magnitude higher than the
diffusion coefficient of lithium ions across the range of temperatures and
loadings integrated. By analyzing different relaxation timescales and examining
the underlying transport mechanisms in SN-loaded systems, we find that the
diffusivity of TFSI ions correlates excellently with the Li-TFSI ion-pair
relaxation timescales. In contrast, our simulations predict distinct transport
mechanisms for Li-ions in SN-loaded PEO-LiTFSI electrolytes. Explicitly, the
diffusivity of lithium ions cannot be uniquely determined by the ion-pair
relaxation timescales but additionally depends on the polymer segmental
dynamics. On the other hand, the SN loading induced diffusion coefficient at a
given temperature does not correlate with either the ion-pair relaxation
timescales or the polymer segmental relaxation timescales.
