Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive

Abstract

Silicon as a negative electrode material for lithium-ion batteries has attracted tremendous attention due to its high theoretical capacity, and fluoroethylene carbonate (FEC) was used as an electrolyte additive, which significantly improved the cyclability of silicon-based electrodes in this study. The decomposition of the FEC additive was investigated by synchrotron-based X-ray photoelectron spectroscopy (PES) giving a chemical composition depth-profile. The reduction products of FEC were found to mainly consist of LiF and −CHF–OCO2-type compounds. Moreover, FEC influenced the lithium hexafluorophosphate (LiPF6) decomposition reaction and may have suppressed further salt degradation. The solid electrolyte interphase (SEI) formed from the decomposition of ethylene carbonate (EC) and diethyl carbonate (DEC), without the FEC additive present, covered surface voids and lead to an increase in polarization. However, in the presence of FEC, which degrades at a higher reduction potential than EC and DEC, instantaneously a conformal SEI was formed on the silicon electrode. This stable SEI layer sufficiently limited the emergence of large cracks and preserved the original surface morphology as well as suppressed the additional SEI formation from the other solvent. This study highlights the vital importance of how the chemical composition and morphology of the SEI influence battery performance.

A hard X-ray photoelectron spectroscopy study on the solid electrolyte interphase of a lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide based electrolyte for Si-electrodes

“…A lot of work has been done to understand the SEI on graphitic negative electrodes while the field of SEI formation on silicon is still a young area with only a rather small number of publications. [4,[7][8][9][10][11][12][13][14][15][16][17][18][19] Philippe et al have…”

Nanostructured magnesium silicide Mg2Si and its electrochemical performance as an anode of a lithium ion battery

“…For the eutectic alloy studied with electrolyte additives, the first lithiation curve shows presence of two weak cathodic peaks at 0.88 V and 1.2 V (Figure 6 (b)). As these peaks disappear after the first cycle, they can be associated with the formation of the SEI layer because of the decomposition of the electrolyte [25,26].…”

“…The addition of VC into the electrolyte increases the stability of the SEI layer. As hydrofluoric acid HF is formed during the reduction of the FEC additive, it can react with the alkali components of the SEI layer to form a more even and LiF-rich surface deposited product [26,31]. Thus, the processes of exchange of metallic lithium become easier [32].…”

“…Li per Mg 0. 26 Si 0.74 ) was obtained, with capacity retention about 49 % after 400 cycles. The Mg 2 Si/C (40% C) composite studied in [13] delivers an initial capacity of 800 mAh/g and has a good cyclic stability (400 mAh/g after 30 cycles).…”

Effect of Fluoroethylene Carbonate in the Electrolyte for LiNi0.5Mn1.5O4 Cathode in Lithium-ion Batteries

“…Simultaneously, the electrolyte plays an important role in the formation of a stable passivation film on the electrode surface, whose area increases continually because of pulverization. Among several candidates, electrolytes with large amounts of fluoroethylene carbonate (FEC) additive have been studied to cover the newly exposed electrochemically active surfaces [9][10][11]. The electrolytes for conventional graphite anodes in LIBs usually contain a small quantity of additives, less than 10 vol%.…”