Appl Phys A (2009) 96: 661–670 DOI 10.1007/s00339-009-5129-y Physicochemical studies of PVdF–HFP-based polymer–ionic liquid composite electrolytes Boor Singh Lalia · K. Yamada · M.S. Hundal · Jin-Soo Park · Gu-Gon Park · Won-Yong Lee · Chang-Soo Kim · S.S. Sekhon Received: 24 September 2008 / Accepted: 2 February 2009 / Published online: 19 February 2009 © Springer-Verlag 2009 Abstract Polymer–ionic liquid compositeelectrolytes based on poly (vinylidenefluoride-co-hexafluoropropylene) (PVdF–HFP) and room temperature ionic liquid: 2,3-dimethyl-1-octylimidazolium hexafluorophosphate (DMOImPF 6 ) have been synthesized and studied. The addi- tion of dimethylacetamide (DMA) and propylene carbonate (PC), both with high dielectric constant and low viscosity, to polymer electrolytes has been found to result in an enhance- ment of conductivity by one order of magnitude. Compos- ite polymer electrolytes containing ionic liquid have been found to be thermally stable upto 300°C. Motional narrow- ing observed in the variation of line width of 1 H and 19 F NMR peaks with temperature suggests that both cations and anions are mobile in these electrolytes. PACS 61.20.Qg · 61.25.Hk · 74.25.Fy B.S. Lalia · S.S. Sekhon ( ) Department of Applied Physics, Guru Nanak Dev University, Amritsar 143005, India e-mail: sekhon_apd@yahoo.com Fax: +91-183-2258820 K. Yamada Department of Applied Molecular Chemistry, College of Industrial Technology, Nihon University, Narashino, 275-8575 Chiba, Japan M.S. Hundal Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India M.S. Hundal · J.-S. Park · G.-G. Park · W.-Y. Lee · C.-S. Kim · S.S. Sekhon Fuel Cell Research Center, New and Renewable Energy Research Division, Korea Institute of Energy Research (KIER), Daejeon 305-343, Republic of Korea 1 Introduction Polymer electrolytes with high value of proton conductiv- ity along with good mechanical strength are materials of current research interest due to their potential use in pro- ton exchange membrane fuel cells (PEFCs) and other dev ces [1–3]. Polymer gel electrolytes based on salt-solvent- polymer hybrid system, although show high conductivity (∼10 −2 S/cm),yetcan notbe easily obtained in the film form,which is generally required for theiruse in differ- entdevices [4, 5]. Thus there is a growing need to de- velop polymer electrolytes with high conductivity as well as good thermal and mechanical properties. The doping o polymer matrix with nonvolatile salt, which can also con- tribute to ionic conduction, can be a good approach. Ionic liquids is one such category of room temperature molten salts,which can be incorporated in polymer matrix to de- velop polymer electrolytes in the film form for potential use in various electrochemical devices. Ionic liquids are materials of current research interest in electrochemistry due to some of theirunique physicochemical properties, such as they are comprised entirely of ions,high ionic conductivity, good thermal, and chemical stability, neglig ble vapor pressure, wide electrochemical stability window, etc.[ 6, 7]. The ionic liquids generally consist of organic cations, such as imidazolium, phosphonium, pyridinium, ammonium, pyrazolium, triazolium, thiazolium, pyrroli- dinium,etc.[6, 8–12],and large and soft anions,such as triflate (CF 3 SO − 3 ), imide (N(CF 3 SO 2 ) − 2 ), tetrafluorob- orate (BF − 4 ), hexafluorophosphate (PF − 6 ), etc.[ 6, 13, 14]. As a large number of combinations of anions and cations are possible, the physicochemical properties of ionic liq- uids,such as conductivity, viscosity, density, hydrophobic- ity/hydrophilicity, etc., can be controlled by choosing a su able combination of cations and anions [ 6]. Ionic liquids