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. (C) 2014 Elsevier B.V. All rights reserved.