Interaction of poly(vinylidene fluoride) with graphite particles. 1. Surface morphology of a composite film and its relation to processing parameters

In lithium ion battery composite anodes that are derived from graphite particles bound together by a polymeric binder of 5-7 wt %, it is well-known that the type and content of the binder influence the formation of a solid electrolyte interphase and the electrochemical behavior. However, the nature of the interaction between the graphite particles and binder has not been extensively studied. We describe here the interaction of poly(vinylidene fluoride) (PVDF) with graphite based on the characteristics of the precursor slurry and the surface chemistry and morphology of the final composite anodes. The slurry was characterized by dynamic viscosity measurements and the solid composite by atomic force microscopy, lateral force microscopy, electron probe X-ray microanalysis, and X-ray photoelectron spectroscopy. The final film properties correlate with the suspension viscosity, which varies over 6 orders of magnitude for eight different carbon samples. In the composite film, PVDF preferentially deposits on the edges and grain boundaries of the graphite particles with a maximum of 40% of the surface of graphite being covered by the polymer. We correlate an increase in the homogeneity of the PVDF distribution in the final composite film with an increase in the slurry viscosity and interpret this observation in terms of PVDF/graphite interaction.