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

• Published in: Journal of power sources Vol. 81; pp. 739 - 747
• Main Authors: Stallworth, P.E, Fontanella, J.J, Wintersgill, M.C, Scheidler, Christopher D, Immel, Jeffrey J, Greenbaum, S.G, Gozdz, A.S
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 01-09-1999; Elsevier Sequoia
• Subjects: Activation volume; Applied sciences; Electrical conductivity; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; High pressure; Lithium electrolytes; Nuclear magnetic resonance; Lithium electrolytes; Electrical conductivity; Nuclear magnetic resonance; Activation volume; High pressure; Differential scanning calorimetry; Electrolyte; Battery; Lithium; Secondary cell
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/S0378-7753(99)00144-5

Electrical conductivity, differential scanning calorimetry (DSC) and
7
Li
nuclear magnetic resonance (NMR) studies have been carried out on liquid electrolytes such as ethylene carbonate:propylene carbonate (EC:PC) and EC:dimethyl carbonate (DMC) containing LiPF
6 (and LiCF
3SO
3 for NMR) and films plasticized using the same liquid electrolytes. The films are based on poly(vinylidene fluoride) (PVdF) copolymerized with hexafluoropropylene and contain fumed silica. All measurements were carried out at atmospheric pressure from room temperature to about −150°C 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 substances exhibits Vogel–Tammann–Fulcher (VTF) behaviour while that for the EC:DMC-based substances does not. Part of the deviation 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 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
T
1 values are smaller and the NMR linewidths are larger for the hybrid electrolytes 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.