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) , LiFSI) and lithium bis(fluorosulfonyl)imide (LiN(SO2-F)(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 x 10(-4) S/cm at 80 degrees C and 1.08 x 10(-4) S/cm at 30 degrees C for the poly-1/LiFSI system and of 1.23 x 10(-5) S/cm at 80 degrees C and 1.62 x 10(-7) S/cm at 30 degrees 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 (T-g ) 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 degrees C and 0.01C.