Ion-Conductive and Mechanically Stable Copolymer Electrolytes Based on Aliphatic Carbonates

Aliphatic polycarbonate-type solid polymer electrolytes (SPEs) exhibit excellent electrochemical properties with high Li salt concentrations. A polycarbonate-based copolymer was developed by copolymerization with poly(decamethylene carbonate) [P(DMC)], pentaerythritol, triethylene glycol (TEG), 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane (spiroglycol, SPG) and was evaluated as an SPE. By comparing SPEs containing 60 wt % LiTFSI, we find that the copolymerization of SPG significantly improves the mechanical stability of SPE. branch-P(DMC/TEG/SPG) that has been copolymerized with all monomers displayed the best ionic conductivity at room temperature, a value of 7.4 × 10–6 S cm–1 at 30 °C. Vogel–Tammann–Fulcher analysis confirmed a significant improvement in the value of A, which implies an increase in carrier ions. The dissociation of Li ions from LiTFSI was probably facilitated by the increased polarity of the carbonate unit due to the SPG and TEG oxygen and by the increased segmental mobility due to branching and the presence of the ether unit.