Influence of the PVdF binder on the stability of LiCoO2 electrodes

We report herein on the effect of the PVdF binder on the stability of composite LiCoO2 electrodes at elevated temperatures in 1 M LiPF6 EC/EMC solutions at open circuit conditions. The structure and morphology of composite LiCoO2 electrodes with different combinations of electrode components (LiCoO2 active material, PVdF binder, carbon black and current collector) were evaluated by Raman spectroscopy, X-ray diffraction and SEM. The content of Co ions in the electrolyte solutions was determined by ICP. A new effect was discovered, namely, a detrimental impact of the contact between PVdF and LiCoO2 on the stability of the active mass. The formation of surface Co3O4 and dissolution of Co ions at elevated temperatures is accelerated at the contact points between the active mass and the binder. The effect of water content in the electrolyte solutions on the stability of LiCoO2 was also studied. The presence of water (and/or HF) is a necessary condition for the accelerated dissolution of Co ions from the active mass. LiCoO2 oxidizes the solvents at elevated temperatures thus forming CO2.