Ionic liquid-polymer gel electrolytes from hydrophilic and hydrophobic ionic liquids

Ionic liquid-polymer gels were prepared by incorporating hydrophilic EMIBF4 and EMI(triflate) (EMI+ = 1-ethyl-3-methylimidazolium) and hydrophobic BMIPF6 (BMI+ = 1-(1-butyl)-3-methylimidazolium) room-temperature ionic liquids into a poly(vinylidene fluoride)-hexafluoropropylene copolymer (PVdF(HFP)) matrix. Gel electrolytes prepared with ionic liquid:PVdF(HFP) mass ratios of 2:1 exhibited ionic conductivities of > 10(-3) S cm(-1) at room temperature and > 10(-2) S cm(-1) at 100 degrees C. The BMIPF6-PVdF(HFP) gel was incorporated into electrochemical cells, employing graphite intercalation electrodes for both the anode and cathode, to construct single and bipolar cells displaying open-circuit voltages of 3.77 and 7.86 V, respectively. New inexpensive preparative routes for the hydrophilic ionic liquids were developed that utilize the metathesis reaction of EMICl with the appropriate ammonium salt in acetone or acetonitrile to produce high purity products. (C) 1998 Elsevier Science S.A. All rights reserved.