Structure and transport properties of polymer gel electrolytes based on PVdF-HFP and LiN(C2F5SO2)(2)

Gel polymer electrolytes composed of PVdF/HFP and a non-aqueous lithium ele ctrolyte solution EC/DEC/LiN(C2F5SO2)(2) (BETI) were prepared to investigat e the conduction properties of the gel materials. Structural and micro-stru ctural characterization was carried out by means of modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM). The sam ples with polymer/solution weight ratios higher than 0.5 contain at least a n amorphous swollen gel phase and a crystalline one, while a pure liquid ph ase appears, which occupies cavities in the micrometer range in the gels wi th lower polymer content. The transport properties of the gels were investi gated by means of impedance spectroscopy for conductivity and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) for diffusion coefficients. T he results were compared with those of corresponding films prepared with Li N(CF3SO2)(2) (TFSI). The BETI-based samples showed diffusion values lower t han the TFSI-based ones. Estimation of the carrier concentration change wit h the gel composition revealed that the interaction between the host polyme r and the electrolyte in the gel especially in the polymer rich region (> 5 0 wt%). (C) 2000 Elsevier Science B.V. All rights reserved.