Transport and electrochemical characterization of plasticized poly(vinyl chloride) solid electrolytes

Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was complexed with poly(vinyl chloride) (PVC) membranes plasticized by solvents such as dibutyl phthalate (DBP) and dioctyl adipate (DOA). Plasticizing effects were reflected as a reduction in the mechanical modulus of about one to two orders of magnitude from the value for pure PVC. However, the membranes still preserved good mechanical strength. Ionic conductivity value changed from 10(-7) to 10(-4) S/cm at 25 degrees C as the weight ratio of PVC was changed from 0.67 to 0.17, keeping the weight ratio of LiTFSI to plasticizer constant at the concentration that gave the maximum conductivity of the order of 10 Slcm at 25 degrees C. Transport number for Li+ ion ranged from 0.54 to 0.98 depending on the composition and temperature. At 60 degrees C an unfavorable reaction of each plasticizer within the bulk with metallic lithium was seen to reduce the transport greatly. The electrochemically stable domain close to 4.0 V at 60 degrees C, established by cyclic voltammetry using Ni ultramicroelectrodes, was limited in the cathodic side by lithium deposition and stripping processes and in the anodic side by the oxidation of the polymer. The efficiency of lithium stripping followed by deposition was rather poor, relating to the reaction of DBP or DOA with lithium.