Regulating the composition distribution of layered SEI film on Li-ion battery anode by LiDFBOP

The so-called solid-electrolyte interface (SEI) derived from the interaction between electrolyte and electrode plays a decisive role in Li-ion battery performance. Lithium difluoro(bisoxalato) phosphate (LiDFBOP) as the derivative of LiPF6 has caused great attention among the researchers. However, the mechanism of effect for LiDFBOP salt has not yet revealed, which limits the findings for the fundamental cause of performance improvement. In this work, the effect of LiDFBOP on the mesocarbon microbead (MCMB) anode electrode has been investigated with aid of surface analysis technique, such as scanning electron microscope (SEM), X-ray photoelectron spectrum (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). On the basis of the modification with LiDFBOP, the long-term cycling and degradation resistance of Li/MCMB half cells have been achieved, which results from the preferential decomposition of LiDFBOP regulating the decomposition law of the electrolyte system. The SEI film with layer structure has different composition distribution under the obstruction of LiDFBOP of the decomposition of LiPF6. The more organic ingredients are distributed in the SEI film on the electrolyte side, which leads to low impedance and fast transportation of lithium ions. The special ingredient distribution is ascribed to the obstruction of LiDFBOP on the decomposition of LiPF6. This work signifies the research of the effect of SEI film distribution on the battery performance.