Application of gel alkylene oxide electrolytes to rechargeable lithium batteries

Advanced gel polymer electrolytes of alkylene oxide system were prepared. The base polymer was random copolymer of alkylene oxide system (MW: 8000, ethylene oxide (EO): ca. 80%, propylene oxide (PO): ca. 20%, end functional group: acrylic group). The gel polymer electrolyte was prepared by mixing the base polymer, a solvent, a lithium salt and an initiator followed by UV irradiation. Ionic conductivity of gel polymer electrolyte was measured with ac method at temperature range between −20 and +60°C. The ionic conductivity reached over 2.5 mS cm−1 at 20°C when LiBF4/γ-butyrolactone (GBL) solution was incorporated as an electrolyte. The discharge capacity with charge-discharge cycle of test cells, Cn-Li/LiCoO2, with the gel polymer electrolyte was more stable during cycling than that with liquid organic electrolyte solution. It was affected by the kind of plasticizer in the gel electrolyte. The capacity of the test cell was limited by the weight of cathode active material (1.3 mAh). The highest discharge capacity was attained using Cn-Li/the base polymer–GBL–LiBF4/LiCoO2 and its utilization rate of the cathode material was 83%.