PVDF-based porous polymer electrolytes for lithium batteries

Gel electrolytes based on PVDF and PVDF-HFP membranes with different morphology and porosity have been prepared by means of the phase inversion technique. Diffusion coefficients and conductivity have been measured in order to investigate the role of the morphology and microstructure on the dynamics and ionic transport of these multi-phase gels. The picture emerges of a two-steps gelation process, in which the majority of the solution fills up the cavities, while a non-negligible fraction of the salt-solvent mixture swells the amorphous strands of the polymer. Pure PVDF porous membranes display one or two diffusion coefficients, depending on the level of porosity and the film morphology, The two components are attributed respectively (1) to the carriers in the swollen phase and (2) to the pure solution, whose motion can be "free" or, in such cases, partially restricted by the barriers of the cavities. A single component can be interpreted as a sort of average between the pure solution and the swollen phase, PVDF-HFP membranes generally present two diffusion coefficients and show an opposite behaviour between the cation and anion species, concerning their relative amounts. (C) 2002 Elsevier Science B.V. All rights reserved.