Solid State Ionics 130 (2000) 281–291 www.elsevier.com / locate / ssi Polymer electrolytes based on ethylene oxide–epichlorohydrin copolymers * ´ W.A. Gazotti, M.A.S. Spinace, E.M. Girotto, M.-A. De Paoli ´ ´ ´ Laboratorio de Polımeros Condutores e Reciclagem, Instituto de Quımica, Universidade Estadual de Campinas, C. Postal 6154, 13081-970, Campinas-SP , Brazil Received 30 August 1999; received in revised form 25 October 1999; accepted 1 February 2000 Abstract In this work we studied the ionic conductivity for three copolymers of the title co-monomers as a function of LiClO 4 content, temperature and ambient relative humidity. We also investigated the interactions between the salt and the co-monomer blocks in the copolymers and its effect on the morphology and thermal properties of the copolymer / salt 1 complexes. Our data indicate that the Li ion predominantly interacts with the ethylene oxide repeating units of the copolymers. The copolymer with the highest ionic conductivity was obtained with an ethylene oxide / epichlorohydrin ratio of 25 21 84/16 containing 5.5% (w/w) of LiClO . It showed a conductivity of 4.1 3 10 S cm (308C, humidity , 1 ppm) and 4 24 21 2.6 3 10 S cm at 84% relative humidity (248C). The potential stability window of the copolymer/salt complex is 4.0 V, as measured by cyclic voltammetry. For comparison, we also prepared a blend of the corresponding homopolymers containing LiClO ; it showed higher crystallinity and lower ionic conductivity.  2000 Elsevier Science B.V. All rights 4 reserved. Keywords: Polymeric electrolyte; Ionic conductivity; Ethylene oxide copolymers; Elastomers PACS: 61.41; 68.45; 61.20Q 1. Introduction proposal of Armand and coworkers that these sys- tems could be used in secondary batteries [2]. Since Since the 1970s great attention has been devoted that time, the research on solid polymeric elec- to the study of solid polymeric electrolytes, prepared trolytes has grown intensely and reviews with his- by dissolving inorganic salts in a polymeric matrix. toric surveys have been published [3,4]. The continu- This interest occurred mainly due to the pioneering ous and crescent interest on polymeric electrolytes is measurements of ionic conductivity in polymer–salt related to their use in different solid state electro- mixtures done by Wright and coworkers [1] and the chemical devices, such as: batteries [5–7], capacitors [7], electrochromic displays [7,8], photoelectroch- emical cells [9], light emitting electrochemical cells *Corresponding author. Tel.: 155-19-788-3022; fax: 155-19- [10] and artificial muscles [11]. 788-3023. E-mail address: mdepaoli@iqm.unicamp.br (M.-A. De Paoli) After Wright’s work [1], poly(ethylene oxide), 0167-2738 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0167-2738(00)00550-6