A polymeric solid electrolyte based on a binary blend of polyethylene oxide), polymethyl vinyl ether-maleic acid) and LiClO 4 Ana Maria Rocco a, * , Carla Polo da Fonseca b , Robson Pacheco Pereira a a Grupo de Materiais Condutores, Instituto de Quõ Âmica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, CT, Bloco A, 22949-900 Rio de Janeiro, RJ, Brazil b Faculdade de Engenharia, Universidade Sa Äo Fransisco, Itatiba, Sa Äo Paulo, Brazil Received 2 October 2001; accepted 22 February 2002 Abstract A new polymeric solid electrolyte based on a PEO/PMVE-MAc blend, complexed with LiClO 4 , was obtained and characterized by differential scanning calorimetry DSC), Fourier transform infrared spectroscopy FTIR), polarized light optical microscopy, electrochemi- cal impedance and cyclic voltammetry. DSC traces indicated miscibility for all the PSE samples. Crystallinity was suppressed for samples with LiClO 4 concentrations higher than 2.5 wt%. FTIR associated with DSC studies indicated that there is a preferential formation of complexes PEO/Li 1 /PMVE-MAc in all PSE samples studied here. The ionic conductivity of PSE reaches a maximum of about 10 25 S/cm at ambient temperature and 7.5 wt% LiClO 4 . The electrochemical stability window is 4.5 V and associated with the other characteristics, make the PSE studied here suitable for applications in `smart-windows', batteries, sensors, etc. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Blends; Solid electrolyte; Polyethylene oxide) 1. Introduction Polymeric solid electrolytes PSE) are complexes based on a polymer that acts as solvent for a cation. These systems show technological interest due to their application as solid electrolytes in electrochemical devices, such as energy conversion units batteries/fuel cells) [1], electrochromic display devices and `smart- windows' [2], photoelectrochemical cells, capacitors [3,4], etc. Among the ®rst and most studied host for PSE is polyethylene oxide) PEO), which is a polymer that dissolves high concentrations of a wide variety of salts to form polymeric electrolytes [5]. This conven- tional ion-conducting polymer has, in general, multi- phase nature, consisting of the salt-rich crystalline phase with conductivity appreciable only above 65 8C [6], pure PEO spherulite crystalline phase, and an amor- phous phase with dissolved salt. It has been revealed that the ion conduction takes place primarily in the amorphous phase and the phase diagram is affected by many factors, such as the salt species, preparation method, concentration, temperature and thermal history. At present, amorphous PEO complexes are considered to be suitable for achieving high and stable conductivity [7±9]. However, some degree of organization in the amorphous phase is required for achieving higher conductivities [10,11]. Efforts to enhance the ionic conductivity of PEO based PSE focused on suppressing its crystallization, via incorporating compounds with low T g [12] and by copolymerization of PEO with macromonomers [13]. Copolymerization is a way to lower the melting point, modulus as well as crystallinity and to increase solubi- lity and transparency [14]. Possible alternatives are grafting [15] and crosslinking [16], but these methods require a non-trivial synthetic process and this is a serious drawback to practical applications. It is impor- tant to develop an easier method for preparing the PSE with higher ionic conductivities and dimensional stabi- lity. In this regard, the preparation of polymeric electro- lytes by blending polymers is of interest [17±20]. Blending polymers is a quick and economic alternative for obtaining materials with optimized properties and easy control of physical properties by compositional change. Work has been done on binary PEO based blends, where the second component is non-crystalline and is able to inhibit crystallization of PEO [21±23]. By blending, thermal, mechanical, and adhesive properties associated with high transparency can be optimized, Polymer 43 2002) 3601±3609 0032-3861/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0032-386102)00173-8 www.elsevier.com/locate/polymer * Corresponding author. Fax: 155-21-2562-7250. E-mail address: amrocco@iq.ufrj.br A.M. Rocco).