Poly(vinylidene fluoride) (PVdF) dissolved in organic solvents containing lithium tetrafluoroborate (LiBF 4 ) forms stable gels when the solution is cooled to room temperature. Here, we describe the effects of LiBF 4 concentration and different gelation solvents on the gelation process, and characterize the resulting structural morphology using several techniques. Diethyl carbonate (DEC), propylene carbonate (PC) and c-butyrolactone (GBL) were used as gelation solvents. Time-resolved Fourier transform infrared spectroscopic measurements showed that the conformational transition from TGT G to T 3 GT 3 G occurred with the addition of lithium salts to the PVdF/DEC gel. In addition, PVdF produces thermoreversible gels in GBL and PC containing LiBF 4 , by assuming a T 3 GT 3 G conformation regardless of the LiBF 4 concentration. Scanning electron microscopy studies have indicated the presence of spherulites in the gels. Spherulite size decreased with increasing LiBF 4 concentration, whereas gel-melting temperatures increased with an increase in LiBF 4 concentration. These results indicate that gelation of PVdF in the presence of LiBF 4 occurs as polymer chains assuming the T 3 GT 3 G conformation, imparting the resulting gels with increased thermal stability. Polymer Journal (2011) 43, 540-544; doi:10.1038/pj.2011.21; published online 13 April 2011Keywords: lithium ion; molecular conformation; polymer gel electrolyte; poly(vinylidene fluoride); thermoreversible gel INTRODUCTION Polymer electrolytes have attracted much attention in lithium-battery technology because they enable fabrication of safe and reliable highenergy, high-power secondary lithium batteries. 1 Typical examples of polymer electrolytes include complexes of a lithium salt (LiX) with PEO (polyethylene oxide). The conductivity of PEO-LiX electrolytes reaches practically useful values of B10 À4 S cm À1 at temperatures of 60-80 1C but decreases to 10 À7 S cm À1 at room temperature. 2 Decrease in the conductivity on cooling is because fast ion transport occurs only in the amorphous state of the polymer.The most promising approach for improving conductivity at room temperature is to immobilize a highly conductive liquid electrolyte within a polymer matrix. This type of electrolyte is called a polymer gel electrolyte. This system demonstrates high ionic conductivity at room temperature with sufficient mechanical strength. 3,4 Among the matrices used for polymer gel electrolytes are PVdF, 5,6 poly(methyl methacrylate), 7,8 and poly(acrylonitrile). 9,10 Gel electrolytes based on PVdF are of great interest because of their good thermal, mechanical and electrochemical stability. Recent studies have shown that the ionic conductivity of PVdF gel electrolytes is related to the morphology of the gel. 11 However, a detailed characterization of these gels with regard to the gelation process and structural morphology has not been undertaken. In a previous study, we reported our investigation of the gelation process of PVdF in a number of organic solvents without a lith...