Synthesis and electrochemical properties of gel polymer electrolyte using poly(2-(dimethylamino)ethyl methacrylate-co-methyl methacrylate) for fabricating lithium ion polymer battery

Random copolymers comprising 2-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) are synthesized by radical polymerization using 2,2'-azobis(2-methylpropionitrile) (AIBN) as an initiator. Gel polymer electrolytes (GPEs) are prepared by in situ thermal curing using different ratios of siloxane-epoxide cross-linker to poly(DMAEMA-co-MMA) and various contents and types of liquid electrolytes. GPEs offer several advantages such as in situ thermal cross-linking without requiring an additional radical initiator, relatively shorter curing time (similar to 3 h) and lower curing temperature. When the ratio of the siloxane-epoxide cross-linker to poly(DMAEMA-co-MMA) is 1:5, the GPE with 98 wt% liquid electrolyte exhibits the highest ionic conductivity of 8.87x10(-3) S/cm at 30 A degrees C. The electrochemical stability window of the GPE is measured to be 5.1 V vs. Li/Li+. A unit cell comprising LiCoO2/GPE/graphite exhibits an initial discharge capacity of 145.6 mAh/g at 0.1 C, and the unit cell has good rate capability and cycling performance.