The effect of plastic-crystalline succinonitrile on the electrolyte system PEO:LiBF4: Insights from solid state NMR

• The dynamics of Li cations PEO within PEO-SN-LiBF4 solid electrolytes is investigated.
• SN acts as a solid lubricant to dramatically enhance the PEO dynamics.
• The ionic conductivity of the best samples is observed as 1.1 × 10− 3 S cm− 1.

The role of plastic-crystalline succinonitrile (SN) within the electrolyte system comprising polyethylene oxide (PEO), SN and LiBF4 is investigated. By employing solid state NMR spectroscopy and powder X-ray diffraction it is found that the SN molecules take on a double function. On the one hand, the addition of SN influences the distribution of the different phases being present in the system in such a way that the formation of amorphous salt-containing phases is favored. This results in an enhanced charge carrier concentration participating in the ion conduction. On the other hand, the SN molecules cause a drastic increase in the mobility of the PEO matrix. Thus, the SN reduces not only the PEO's tendency towards crystallization, but additionally acts as a solid lubricant for the polymer chains.