Thermal and electrochemical properties of poly(2,2-dimethoxypropylene carbonate)-based solid polymer electrolyte for polymer battery

Poly(2,2-dimethoxypropylene carbonate) (poly-1) was synthesized by bulk polymerization of 2,2-dimethoxypropylene carbonate (1) with bis(octanoic acid) Tin (II) salt (Sn(Oct)2). The polymer electrolytes composed of poly-1 with lithium salts such as lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2, LiTFSI) and lithium bis(fluorosulfonyl)imide (LiN(SO2F)2, LiFSI) were prepared, and their ionic conductivities, thermal and electrochemical properties were investigated. Polymer electrolytes at the [Li salt]/[repeating unit (RU)] ratio of 1/1 showed the ionic conductivity of 3.53 × 10− 4 S/cm at 80 °C and 1.08 × 10− 4 S/cm at 30 °C for the poly-1/LiFSI system and of 1.23 × 10− 5 S/cm at 80 °C and 1.62 × 10− 7 S/cm at 30 °C for the poly-1/LiTFSI system, respectively. Ionic conductivities of both polymer electrolytes increased with an increase in the lithium salt concentrations, but their glass transition temperatures (Tg) decreased. Transference numbers of lithium ion (t+) of the polymer electrolytes are 0.56 for the poly-1/LiTFSI system and 0.75 for the poly-1/LiFSI system, respectively. The polymer electrolytes for the poly-1/LiTFSI system were thermally more stable than those for the poly-1/LiFSI system. Decomposition temperatures of the polymer electrolytes decreased with lithium salt contents. Both polymer electrolytes had electrochemical stabilities up to 4 V. The Li/polymer electrolyte/LiFePO4 cell by using polymer electrolyte film at the [Li salt]/[RU] ratio of 1/1 for the poly-1/LiFSI system showed the capacity of 100 mAh/g at 60 °C and 0.01C.