SOLID STATE IONICS ELWVIER Solid State Ionics 86-88 (1996) 385-393 Transport and electrochemical characterization of plasticized poly(viny1 chloride) solid electrolytes A. Mary Sukeshini, Atsushi Nishimoto, Masayoshi Watanabe* Department of Chemistry, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240, Japan Abstract 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 lo-’ to 10m4 S/cm at 25°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 1O-4 S/cm at 25°C. Transport number for Li’ ion ranged from 0.54 to 0.98 depending on the composition and temperature. At 60°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 6O”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. Keywords: Polymer electrolyte; Poly(viny1 chloride) (PVC); LiN(SO,CF,)?; Plasticizer; Ionic conductivity 1. Introduction Solid polymer electrolytes owing to their advan- tages such as viscoelasticity and flexibility in addi- tion to high ionic conductivity prove to be prospec- tive candidates for advanced electrochemical device applications. Polymer electrolytes consist of a host polymer in which electrolyte salts are dissolved. Poly(ethylene oxide) based electrolytes were the earliest and most extensively studied [1,2]. The limitation of a predominantly crystalline phase that impedes high conductivity has stimulated new direc- tions to achieving high conductivities. Choice of *Corresponding author. polymers with flexible and amorphous backbones, addition of flexible side chains, or addition of plasticizing solvents are a few among the different approaches that have been adopted to improve conductivity at ambient temperatures [ 1,2]. We have directed our attention to poly(viny1 chloride) (PVC) as a host polymer of polymer electrolytes. PVC is a commercially available inex- pensive polymer and is compatible with large amount of plasticizers such as dibutyl phthalate (DBP) and dioctyl adipate (DOA). Resulting plasti- cized PVC still preserves good mechanical strength and is widely used as films, sheets and moldings for e.g. plastic leather and curtain, lead wire coating, flooring and wallboard. The reduction of resistivity 0167-2738/96/$15.00 Copyright 01996 Elsevier Science B.V. All rights reserved PII SO167-2738(96)00156-7