Electrical conductivity effect of polyaniline addition to poly(ethylene oxide) electrolyte film containing lithium perchlorate

Abstract

The discovery of ionic conductivity in alkali cation poly(ethylene oxide) (PEO) complex [1] has greatly stimulated the development of electrochemical devices such as rechargeable batteries, electrochromic displays and sensors, since electrolytic solution free devices can be made. Numerous fundamental and technological studies on PEOs have been reported. Unfortunately, however, the technically justified level of 10 4 to 10 3 S c m -1 a t room temperature has not been achieved to date [2]. To obtain higher conductivity, we have three strategies: (i) surveying a variety of polymer types [3-6]; (ii) modifications of the-PEO system [7]; and (iii) evaluation of various additives to PEOs [8, 9]. Among the strategies, we here adopt the third one. Polyaniline (PAn), now a familiar electrically conductive polymer, is employed as an additive. PAn has high conductivity only when it is protonated and it is insoluble in common organic solvents [10]. The insolubility causes difficulties in homogeneous mixing with PEO. Although deprotonated PAn, which is soluble in common organic solvents, has no conductivity, it is attractive for our objective since it has amine and/or imine nitrogens in the polymeric backbone, Such nitrogens are expected to capture the Li ÷ ions in PEO and to enhance the mobility of the C104 ions. In this letter, we wish to show that PAn is an effective additive to enhance the ionic 4onductivity of PEO-LiC104 polymer solid electrolyte. We also suggest how PAn functions in the ion transport inside the electrolyte. Linear PEO (Aldrich, average molecular weight = 105), acetonitrile and pyridine were of reagent grade and used without further purification. Special grade anhydrous LiC104 (Wako Jun-yaku Co.) was dried in vacuum at 180 °C for 8 h. PAn was prepared by chemical oxidation of aniline [10], and was treated with NaOH solution to make it soluble in pyridine [i1]. The PEO-LiC104-PAn electrolyte was easily prepared by the following procedure. The PAnsaturated pyridine solution was uniformly mixed with acetonitrile solution containing LiC104 and PEO was dissolved in the mixture. The acetonitrilepyridine solvent was removed from the mixture by evaporation and'the stable PEO-LiC104-PAn electrolyte film was obtained. Fig. 1 shows how the electrical conductivity (o-) of the PEO electrolyte changes with the addition of