A study of the mechanical and electrical properties of a polymer/carbon black binder system used in battery electrodes

The effects of carbon black content and crosslinking on the mechanical and electrical properties of a fluorinated elastomer, FC2178 (Dyneon Corp., Oakdale, MN), poly(vinylidene fluoride-co-hexafluoropropylene), were investigated and compared to those of poly(vinylidene fluoride) (PVDF). Attention was given to changes in mechanical and electrical properties of the polymers when under cyclic deformation. To describe the mechanical properties of the carbon-filled polymers in a way that is independent of the chemical details, two mechanical models were used to fit cyclic stress-strain experiments. The linear model was used to determine the effect of crosslinking on the mechanical properties of crosslinked FC2178 films. However, when carbon black was added to the polymer films, the linear model no longer fit the data well. In particular, the cyclic stress-strain curves for carbon-filled polymers showed non-linear regions and displayed the characteristic of 'memory.' A non-linear element was added in parallel with the existing elements of the linear model to successfully describe the effects of the added carbon black. (C) 2003 Wiley Periodicals, Inc.