Investigating the solid electrolyte interphase using binder-free graphite electrodes

Binder-free (BF) electrodes simplify interpretation of solid electrolyte interphase (SEI) data obtained from studies of graphite surfaces. In this work, we prepared BF-graphite electrodes by electrophoretic deposition (EPD), and the SEI layers formed on the electrode in lithium cells containing LiPF6- and LiF2BC2O4-bearing electrolytes were examined by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results showed that the dominant SEI species were lithium alkyl carbonates (ROCO2Li) and lithium alkoxides (ROLi); Li2CO3 was conspicuously absent. Trigonal borate oligomers are most likely present in the SEI of graphite samples cycled in LiF2BC2O4 electrolyte, while lithium fluorophosphates are present on graphite samples cycled in LiPF6 electrolyte. The SEI layer coverage was greater on graphite samples cycled in LiF2BC2O4 electrolyte than in the LiPF6 electrolyte. Our results demonstrate that BF-graphite electrodes prepared by EPD are suitable for the study of SEI layer formed in various electrolyte systems.