Journal of Power Sources 159 (2006) 1316–1321 Nanofiller incorporated poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP) composite electrolytes for lithium batteries A. Manuel Stephan a,1 , Kee Suk Nahm a,∗ , T. Prem Kumar b , M. Anbu Kulandainathan b , G. Ravi c , J. Wilson c a School of Chemical Engineering and Technology, Chonbuk National University, Chonju 561-756, South Korea b Central Electrochemical Research Institute, Karaikudi 630006, India c Department of Physics, Alagappa University, Karaikudi 630003, India Received 1 September 2005; received in revised form 10 November 2005; accepted 16 November 2005 Available online 10 January 2006 Abstract Composite polymer electrolyte (CPE) membranes, comprising poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP), aluminum oxyhy- droxide (AlO[OH] n ) of two different sizes 7 m/14 nm and LiN(C 2 F 5 SO 2 ) 2 as the lithium salt were prepared using a solution casting technique. The prepared membranes were subjected to XRD, impedance spectroscopy, compatibility and transport number studies. Also Li Cr 0.01 Mn 1.99 O 4 /CPE/Li cells were assembled and their charge–discharge profiles made at 70 ◦ C. The incorporation of nanofiller greatly enhanced the ionic conductivity and the compatibility of the composite polymer electrolyte. The film which possesses a nanosized filler offered better electrochemical properties than a film with micron sized fillers. The results are discussed based on Lewis acid–base theory. © 2005 Elsevier B.V. All rights reserved. Keywords: Composite polymer electrolyte; Ionic conductivity; Compatibility: Lewis acid–base theory 1. Introduction Very recently, studies reveal, that composite polymer elec- trolytes can alone offer a lithium battery with reliability and improved safety [1–4]. Solid polymer electrolytes derived from Li salt complexes with inorganic oxides such as TiO 2 and Al 2 O 3 have been studied previously [5–11]. On the other hand, only a very few studies have been made on other polymer hosts such as poly(acrylonitrile) (PAN) [12], poly(methyl methacrylate) (PMMA) [13] and blended poly- meric systems [14,15]. Composite polymer electrolytes based on poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP) as a host have increasingly being investigated. This polymer host has some appealing properties. This PVdF–HFP itself has a high dielectric constant, ε = 8.4 that facilitates a higher concentration of charge carriers, and also comprises both an amorphous and a crystalline phase; the amorphous phase of the polymer assists ∗ Corresponding author. Tel.: +82 63 270 2311; fax: +82 63 270 2306. E-mail address: nahmks@chonbuk.ac.kr (K.S. Nahm). 1 On deputation from CECRI, Karaikueli 630006, India. higher ionic conduction whereas the crystalline phase acts as a mechanical support for the polymer electrolyte. According to Scrosati and co-workers [1,2] and Wieczorek et al. [7] the Lewis acid–base interaction plays a vital role in the enhancement of the ionic conductivity of the composite polymer electrolytes. More- over, in the present study, the filler, AlO[OH] n a basic substance, has not been investigated as a filler. Hence, an attempt was made to study the effect of the filler in different particle sizes on ionic conductivity and the compatibility with the composite polymer electrolytes and the results are described herein. 2. Experimental procedure Poly(vinlylidene fluoride–hexafluoro propylene) (Kynar, Japan) and lithium bis perfluorosulfonyl imide (LiN(C 2 F 5 SO 2 ) 2 were dried under vacuum at 90 ◦ C for 12 h before use. The inert fillers, AlO[OH] n with different particle sizes 7 m and 14 nm were also dried at 120 ◦ C for 12 h before use. The prepa- ration of a nanocomposite electrolyte involved the dispersion of the selected inert filler and a LiN(C 2 F 5 SO 2 ) 2 salt in anhydrous tetrahydrofuran (THF), followed by the addition of PVdF–HFP of different concentrations is depicted in Table 1 and the result- 0378-7753/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2005.11.055