Aging of Li2FeSiO4 Cathode Material in Fluorine containing organic Electrolytes for Lithium-Ion Batteries

Dippel C, Krüger S, Klöpsch R, Hoffmann B, Nowak S, Niehoff P, Li J, Passerini S, Winter M

Abstract

The stability vs. aging of Li2FeSiO4 (LFS) cathode material in fluorine-based electrolytes, especially at elevated temperature, was studied in this work. The LFS powder was initially synthesized using a hydrothermal route and then aged at 60°C for 40 days in LiPF6 and LiBF4-based electrolytes. The residual powder and the electrolyte were investigated afterwards. In the case of LiPF6, a structural and compositional change of LFS to Li2SiF6 was observed by XRD. SEM images confirmed that this change led to a morphology change of the aged material. XPS, EDX and ICP-OES measurements showed a large increase of fluorine content inside the residual powder. NMR investigations indicated an accelerated decomposition of electrolyte in the presence of LFS compared to the electrolyte aged without LFS. Our results suggest a degradation of LFS to Li2SiF6 in the fluorine-based electrolyte at elevated temperatures while the electrolyte decomposition is accelerated.