NMR, DSC and High Pressure Electrical Conductivity Studies on Liquid and Hybrid Electrolytes

摘要

Electrical conductivity, DSC and Li-7 NMR studies have been carried out on liquid electrolytes such as EC:PC and EC:DMC containing LiPF6 (and LiCF3SO3 for NMR) and films plasticized using the same liquid electrolytes. The films are based on poly(vinylidene fluoride) copolymerized with hexafluoropropylene and contain fumed silica. All measurements were carried out at atmospheric pressure from room temperature to about 120K and the electrical conductivity studies were performed at room temperature at pressures up to 0.3 GPa. The liquids and hybrid electrolytes are similar in that the electrical conductivity of the EC:PC based materials exhibits VTF behaviour while that for the EC:DMC based materials does not. Further, the glass transition temperatures as determined from NMR, DSC and electrical conductivity measurements are about the same for the liquids and hybrid electrolytes. However, substantial differences are found. The electrical conductivity of the hybrid electrolytes at room temperature 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 T1 values are smaller for the plasticized films than for the liquids While at both low and high temperature the NMR linewidths are larger. Consequently, it is concluded that significant solid matrix-lithium ion interactions take place.