Interaction of Poly(vinylidene fluoride) with Graphite Particles. 1. Surface Morphology of a Composite Film and Its Relation to Processing Parameters

Abstract

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.

Functions of polymers in composite electrodes of lithium ion batteries

“…But PEO is usually not utilized in composite electrodes for LiB because this polymer electrochemical stability window is limited to 4 V vs. Li/ Li + , which is not suitable for high voltage positive electrodes such as LiCoO 2 . As a result, polymers with higher electrochemical stability such as poly(tetrafluoro ethylene), PTFE, or PVdF have been most widely adopted as the binder for composite electrodes in LiB [7][8][9][10]. A copolymer of vinylidene fluoride with hexafluoropropylene, PVdF-HFP, is used in both polymeric electrolyte and composite electrode of the plastic LiB technology [11].…”

Influence of polymer binder structure on the properties of the graphite anode for lithium-ion batteries

“…PVdF may have superior chemical and electrochemical stability, but this does not entirely eliminate Li-ion battery producers' problems such as having to use toxic organic solvents such as N-methylpyrrolidone (NMP), which are indispensable for dissolving polymer. In addition, the cost of PVdF-based electrodes is still a concern in the battery industry [4][5][6][7][8]. What is more, PVdF also tends to swell in organic solvents, which can lead to the active mass breaking away from the electrode current collector during battery work [1].…”

Effects of binder content on manganese dissolution and electrochemical performances of spinel lithium manganese oxide cathodes for lithium ion batteries

“…Highly conductive and adhesive polyfluorene-type binders significantly improved the electrochemical performance of high-capacity silicon electrodes by maintaining the electrical network during the charge/ discharge processes [27,28]. Because a portion of the surface of the active materials is covered with the binder film [29,30], it is usually preferred that the binder absorb a sufficient amount of electrolyte for Li þ ion transport to proceed, unless excess electrolyte uptake severely deteriorates binder adhesion [31,32]. Our recent study revealed that the relatively high electrolyte uptake of polyvinylidene fluoride (PVdF) and polyacrylonitrile (PAN) binders led to superior rate performance of the LMO electrodes due to facile Li þ ion transport, when compared to polyacrylic acid (PAA) and polyvinyl alcohol (PVA) binders [33].…”