Interfacial behavior of FEC and VC at graphite anode of lithium-ion batteries

doi:10.19799/j.cnki.2095-4239.2025.0217

Abstract

Abstract:

In lithium-ion batteries, electrolyte additives such as fluorinated ethylene carbonate (FEC) and vinylene carbonate (VC) have been widely employed to enhance the stability of the electrode/electrolyte interface; however, their effects on graphite electrodes remain unclear. In this study, the interfacial behavior of FEC and VC on graphite anodes in lithium-ion batteries is systematically investigated. The distinct mechanisms by which FEC and VC influence graphite surfaces are elucidated through various characterization techniques, including cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrochemical impedance results indicate that, in Li|Gr cells, the total impedance before and after solid electrolyte interphase (SEI) formation with FEC is lower than that with VC, whereas in Li|Ref|Gr cells, the total impedance with FEC is higher than that with VC. The interfacial impedances are further deconvoluted using the electrochemical impedance spectroscopy-distribution of relaxation time (EIS-DRT) method to determine the SEI impedance, the charge-exchange impedance at the SEI-graphite interface, and the SEI–electrolyte interface charge-exchange impedance in Li|Gr cells. The characteristic relaxation times of FEC and VC are essentially consistent for each component, with values of 5×10^-5 s for SEI impedance, 3×10^-4 s for SEI-graphite interface charge exchange, and 5×10^-3 s for SEI-electrolyte interface charge exchange. The results show that VC reduction at 0.77 V forms an organic-rich SEI, significantly reducing impedance at the graphite interface but exhibiting poor compatibility with lithium metal, thereby increasing the total cell impedance. In contrast, FEC reduction at 1 V forms a LiF-rich SEI on the graphite surface, which increases graphite interface impedance yet greatly improves the stability of the lithium metal electrode. The adverse effect of FEC on the graphite interface is outweighed by its stabilizing effect on lithium metal, ultimately reducing the total cell impedance. This study provides important experimental insights and theoretical guidance for the optimized design of electrolytes in lithium-ion batteries.

Key words: lithium-ion battery, electrode/electrolyte interface, fluorinated ethylene carbonate, vinylidene carbonate

CLC Number:

TQ 021.9

Yan ZHAO, Hao LIU, Zonglin YI, Li LI, Lijing XIE, Fangyuan SU. Interfacial behavior of FEC and VC at graphite anode of lithium-ion batteries[J]. Energy Storage Science and Technology, 2025, 14(9): 3249-3258.

Figures/Tables 10

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组分	EC	DMC	FEC	VC	LiPF₆
HOMO	-8.46	-8.22	-7.39	-8.97	-6.20
LUMO	-0.28	-0.07	-0.61	-0.39	-1.77