Rotogravure Printing of Li Ion Battery Anodes

Rotogravure inks were formulated for Li-ion battery anodes. Different polymer chemistries were tested such as polyvinylidene fluoride (PVDF) with degree of polymerization of 10⁶ - 500,000. It was found that best printability can be achieved using mixed PVDF-PVP (polyvinylidene fluoride - polyvinylpyrrolidone) binders with commercial names of PVDF being Kureha 9100, 9300, and Solef 5300. As active materials, Philips 5, 10, 15 graphites (5 -15 micron) in combination with nanocarbon filler were used. Inks were dispersed in NMP (N-methyl-pyrrolidone) solvent. Particle size of graphite for most uniform printing was found to be 5 microns. Surface energy of copper foil substrate and surface tension of inks were determined. Printed copper foils were assembled into battery half cells and their irreversible capacity loss (ICL) was tested. The ICL was lower when mixed PVDF/PVP binder was employed in anode ink.