NMR, DSC and high pressure electrical conductivity studies of liquid and hybrid electrolytes

Electrical conductivity, differential scanning calorimetry (DSC) and Li-7 n uclear magnetic resonance (NMR) studies have been carried out on liquid ele ctrolytes such as ethylene carbonate:propylene carbonate (EC:PC) and EC:dim ethyl carbonate (DMC) containing LiPF6 (and LiCF3SO3 for NMR) and films pla sticized using the same liquid electrolytes. The films are based on poly(vi nylidene fluoride) (PVdF) copolymerized with hexafluoropropylene and contai n fumed silica. All measurements were carried out at atmospheric pressure f rom room temperature to about -150 degrees C and the electrical conductivit y studies were performed at room temperature at pressures up to 0.3 Cpa. Th e liquids and hybrid electrolytes are similar in that the electrical conduc tivity of the EC:PC-based substances exhibits Vogel-Tammann-Fulcher (VTF) b ehaviour while that for the EC:DMC-based substances does not. Part of the d eviation from VTF behaviour for the EC:DMC-based materials is attributed to crystallization. Further, the glass transition temperatures as determined from NMR, DSC and electrical conductivity measurements are about the same f or the liquids and hybrid electrolytes. However, substantial differences ar e found. The electrical conductivity of the hybrid electrolytes at room tem perature is lower than expected and, more importantly, the relative change of conductivity with pressure is larger than for the liquids. In addition, above the glass transition temperature, the NMR T-1 values are smaller and the NMR linewidths are larger for the hybrid electrolytes than for the liqu ids while at both low and high temperature the NMR linewidths are larger. C onsequently, it is concluded that significant solid matrix-lithium ion inte ractions take place. (C) 1999 Elsevier Science S.A. All rights reserved.