Plasticized microporous poly(vinylidene fluoride) separators for lithium‐ion batteries. I. Swelling behavior of dense membranes with respect to a liquid electrolyte—Characterization of the swelling equilibrium

Some poly(vinylidene fluoride) (PVdF) microporous separators for lithium‐ion batteries, used in liquid organic electrolytes based on a mixture of carbonate solvents and lithium salt LiPF₆, were characterized by the study of the swelling phenomena on dense PVdF membranes. We were interested in the evolution of the swelling ratios with respect to different parameters, such as the temperature, swelling solution composition, and salt concentration. To understand PVdF behavior in microporous membranes and, therefore, to have a means of predicting its behavior with different solvent mixtures, we correlated the swelling ratios in pure solvents and in solvent mixtures to the solvent–polymer interaction parameters and solvent–solvent interaction parameters. We attempted a parametric identification of swelling curves with a very simple Flory–Huggins model with relative success. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 532–543, 2004