Interfacial morphology and interaction of poly(vinylidene fluoride) with graphite particles

We have investigated the interfacial morphology and interaction of poly(vinylidene fluoride) (PVDF) with graphite based on the characteristics of precursor slurries and the surface chemistry and morphology of final composite films. Dynamic viscosity measurements have been used to characterize slurries and we interpret the different viscosity in terms of PVDF/graphite interaction. The morphology of PVDF on the surface of graphite has been characterized by lateral force microscopy, X-ray photoelectron spectroscopy and electron probe X-ray microanalysis. PVDF preferentially deposits on the edges and grain boundaries of the graphite with a maximum of 40% of the graphite surface being covered by the polymer. We correlate an increase in the homogeneity of the PVDF distribution with an increase in the slurry viscosity, which depends on the properties of PVDF and graphite and solvent evaporation kinetics. The PVDF distribution has been correlated with the electrochemical performance of the anodes. Samples with homogeneous PVDF distribution show higher electrochemical capacity and lower resistance.; We have evaluated the mechanical strength of composite films using a balanced beam scrape adhesion tester. The scratch adhesion strength depends on the structure of graphite particles and crystallinity of PVDF, increasing with PVDF crystallinity. The scratch adhesion has also been measured for swollen electrodes immersed in electrolytes at different temperatures.; We have determined the PVDF crystallization mechanism in the presence of graphite. Crystallization mechanism has been correlated with the interaction between graphite and PVDF and with microstructure of PVDF. We interpret these results in terms of BET surface area of carbon and a specific complex formation of PVDF with the surface oxygen of graphite.; Finally, we have investigated non-equilibrium and equilibrium behavior of PVDF in solution and in ultrathin films. A quartz crystal microbalance has been used to monitor the adsorption kinetics and equilibrium isotherms for deposition of PVDF from solution. The adsorption process is governed by diffusion for the initial few seconds and exhibits a Langmuir-like behavior. In ultrathin PVDF films, we have determined the relative ratio of polymorphic forms and the fraction of crystalline phase as a function of film thickness, annealing temperatures, and surface chemistry of substrates.