The salt lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) when dissolved in plastic crystal succinonitrile has been demonstrated to have particularly good conductivity even at room temperature. In-situ X-ray diffraction (XRD) measurements have previously proved invaluable in interpreting the differential scanning calorimetry (DSC) behavior, but the practical lower temperature limit of approximately −45°C was higher than the −100°C starting temperature of the DSC measurements, and the important crystalline to plastic crystal transition of succinonitrile. An improved cryo-flow system capable of capillary sample temperatures down to −192°C without icing can now easily match the DSC conditions. The previously puzzling DSC behavior of the succinonitrile–LiTFSI phase diagram at low temperatures has now been explained, with a surprising formation of a TFSI-rich adduct on heating from −100°C even at concentrations as low as 2mol%.