Polymer electrolytes based on polycarbonates and their electrochemical and thermal properties

Polycarbonates (4a-d) with various side chain lengths were synthesized by the reaction of 1,4-bis(hydroxyethoxy)benzene derivatives and triphosgene in the presence of pyridine. The polymer electrolytes composed of 4a-d with lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)(2), LiTFSI) were prepared, and their ionic conductivities and thermal and electrochemical properties were investigated. 4d-Based polymer electrolyte showed the highest ionic conductivity values of 1.0 x 10(-4) S/cm at 80 A degrees C and 1.5 x 10(-6) S/cm at 30 A degrees C, respectively, at the [LiTFSI]/[repeating unit] ratio of 1/2. Ionic conductivities of these polycarbonate-based polymer electrolytes showed the tendency of increase with increasing the chain length of oxyethylene moieties as side chains, suggestive of increased steric hindrance by side chains. Unique properties were observed for the 4a(n = 0)-based polymer electrolyte without an oxyethylene moiety. All of polycarbonate-based polymer electrolytes showed good electrochemical and thermal stabilities as polymer electrolytes for battery application.