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Polymer battery electrolytes are a safe alternative to flammable liquid organic electrolytes; however, they suffer from low ionic conductivity and key questions remain regarding the ion transport mechanisms across multiple length-scales. To better understand this transport and to obtain insights that may lead to better electrolytes, we measured the length-scale-dependent structural dynamics of polymer diffusion related ion transport in LiTFSI (Li bis(trifluoromethylsulphonyl)imide)/PEO (poly(ethylene oxide)) using small angle X-ray photon correlation spectroscopy (XPCS). Arrhenius relationships of the obtained decorrelation times with respect to temperature closely match the Arrhenius value for ionic conductivity reported in literature [1]. This indicates a close connection between polymer self-diffusion and ion conductivity in such materials. We also present recent results on operando experiments, in which we track, under external bias, the motion of the ion front through the polymer matrix and are able to measure the ions’ velocity via heterodyne mixing.

[1] Gorecki et al., Phys.: Condens. Matter 1995, 7, 6823.