Ion transport in solid polymeric lithium ion electrolytes*

Understanding ion transport in solid polymeric electrolytes (SPEs) continues to be of interest concerning improving safety and energy density of lithium-ion batteries. Towards this end, we present an investigation of lithium ion transport in a baseline SPE consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in Poly(ethylene oxide) (PEO) via a combination of x-ray photon correlation spectroscopy (XPCS), x-ray absorption microscopy (XAM), continuum modelling, and molecular dynamics (MD) simulations.
Our experiments yield spatially resolved ion velocities (via XPCS) and ionic concentrations (via XAM) upon polarization of a Li/PEO-LiTFSI/Li symmetric cell, which we compare to our theoretical efforts. Particular interest lies in providing direct insight into the concentration dependent transference numbers, which can be challenging to accurately measure, but are essential to ionic transport. We realize this by variation of the input transport parameters, aided by MD simulations, within the continuum model, until a match with the experimental velocities and concentration profiles is achieved.