Thermal, Mechanical, and Ion-Conductive Properties of Crosslinked Poly[(ethylene carbonate)-co-(ethylene oxide)]-Lithium Bis(fluorosulfonyl)Imide Electrolytes

A random copolymer consisting of ethylene carbonate (EC) and ethylene oxide (EO) units with allyl side groups is synthesized as a matrix for solid polymer electrolytes (SPE). By introducing crosslinking structure to the copolymer, creating a polymer matrix with superior mechanical strength while maintaining good ionic conductivity is being attempted. A tensile test indicates that introduction of the crosslinking structure improves the elastic modulus and maximum stress. When a lithium bis(fluorosulfonyl)imide is added to these polymers at 80 mol%, the conductivity of the crosslinked polymer-based electrolyte increases slightly. Vogel-Tammann-Fulcher (VTF) analysis reveals that values of the activation energy for crosslinked polymer-based electrolytes are clearly lower than those of the starting copolymer. The changes in the constant A with increasing salt concentration are very different, but the A values at 80 mol% are almost the same. This VTF behavior suggests that the crosslinking structure has a larger effect on the increase in the carrier ions and also on the decrease in the energy for ionic conduction with increasing salt concentration.