In-situ XRD study of the succinonitrile-lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) phase diagram

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 degrees C was higher than the - 100 degrees 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 degrees 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 degrees C even at concentrations as low as 2 mol%. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.