Polymer International Polym Int 57:523–529 (2008) Composite polymer electrolyte based on (PEO) 6 :NaPO 3 dispersed with BaTiO 3 Amrtha Bhide and Krishnaswamy Hariharan ∗ Solid State Ionics Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai – 600 036, India Abstract BACKGROUND: Polymer electrolytes have attracted considerable attention as regards portable solid-state electrochemical device applications. The present investigation is focused on the characterization of a new Na + ion conducting polymer electrolyte (PEO) 6 :NaPO 3 dispersed with 3–10 wt% BaTiO 3 (0.7 μm) fillers. The composite polymer electrolytes (CPEs) were prepared by a solution-casting method and characterized using various physical measurement techniques. RESULTS: Differential scanning calorimetry results indicate a maximum reduction in the degree of crystallinity of the polymer from 62.6% for uncomplexed poly(ethylene oxide) (PEO) to 27.6% for the CPE with 6 wt% BaTiO 3 . This substantiates an enhancement in the amorphous phase of the polymer inferred from X-ray diffraction and optical micrographs. The CPE dispersed with 6 wt% BaTiO 3 is found to be the best composition exhibiting a maximum ionic conductivity of 1.2 × 10 −6 S cm −1 at 345 K with cationic transport number (t Na + ) of 0.33. CONCLUSIONS: An enhancement in the ionic conductivity of about two orders of magnitude is achieved for the composite electrolytes when compared to filler-free solid polymer electrolyte. Correlation of the temperature- dependent conductivity, activation energy for ion migration and transport number enables an understanding of the role played by the fillers in conduction characteristics of the CPEs.  2007 Society of Chemical Industry Keywords: composite polymer electrolyte; BaTiO 3 ; thermal properties; ionic transport number INTRODUCTION Polymer – metal salt complexes have been widely stud- ied over more than two decades due to their poten- tial application as electrolyte materials in solid-state electrochemical devices such as solid-state batteries, fuel cells, electrochemical capacitors, electrochromic windows and specific ion sensors. 1 Solid polymer electrolytes (SPEs) were found to be more advan- tageous when compared to the conventional solid electrolytes, because of their flexibility, ease of prepa- ration and processing into different geometries, good electrolyte–electrode contact and hence good volu- metric stability over repeated charge–discharge cycles of devices. 2 Poly(ethylene oxide) (PEO)–MX (M, alkali metal; X, anion) polymer electrolyte systems have attracted much attention because of the ability of PEO to dis- solve a variety of salts, the beneficial structure for ion migration and good electrochemical stability. 3,4 However, these electrolytes exhibit low ionic conduc- tivity below the softening temperature (ca 60 ◦ C) of the polymer host, due to low volume fraction of the amorphous phase of the PEO–metal salt complex and relatively low charge density due to the incom- plete dissociation of the salt. 5 In order to overcome these drawbacks a number of remedial methods have been reported such as preparation of polymer blends 6 and plasticized or gel electrolytes by the addition of low-molecular-weight polymers and organic sol- vents with high dielectric constant. 7,8 A new class of SPEs dispersed with nanometre- or submicrometre- sized inert fillers has been called composite poly- mer electrolytes (CPEs). A large number of CPEs are reported in the literature dispersed with a vari- ety of non-conducting fillers such as (i) inert oxides such as Al 2 O 3 , 9,10 SiO 2 , 11 TiO 2 , 10,12 BaTiO 3 13,14 and ZrO 2 ; 15 (ii) non-oxide fillers such as SiC, Si 3 N 4 , BN 16 and aluminium halides such as AlCl 3 , AlBr 3 ; 17 and (iii) layered clays such as montmorillonite 18 and microporous molecular sieves. 19 Most of these stud- ies report an enhancement in the ionic conductivity and electrochemical properties, with respect to the chemical nature and particle size of the filler addi- tives. In addition to Li + ion conducting polymer elec- trolytes, the coordination of Na + with ether oxygen has been well investigated in systems like PEO–NaX (X = I − , SCN − , ClO 4 − , CF 3 SO 3 − , BF 4 − , etc.) result- ing in a stable polymer–metal salt complex. 2 These investigations have gained significant importance in ∗ Correspondence to: Krishnaswamy Hariharan, Solid State Ionics Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai – 600 036, India E-mail: haran@iitm.ac.in (Received 9 April 2007; revised version received 22 May 2007; accepted 4 July 2007) Published online 26 October 2007; DOI: 10.1002/pi.2379  2007 Society of Chemical Industry. Polym Int 0959–8103/2007/$30.00