What Makes Fluoroethylene Carbonate Different?

Journal Article · Thu Jul 09 04:00:00 EDT 2015 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.5b03591· OSTI ID:1392472

Shkrob, Ilya A.; Wishart, James F.; Abraham, Daniel P.

Rechargeable lithium-ion batteries containing silicon-based negative electrodes have the potential to revolutionize electrical energy storage, but carbonate solvents (such as ethylene carbonate) that are commonly used in graphite Li-ion batteries, yield unsatisfactory performance when used with such Li alloying electrodes. It has been found by trial-and-error that additions of the closely related carbonate additive, fluoroethylene carbonate (FEC) to conventional electrolytes, yields a robust solid electrolyte interphase (SEI) on the LixSiy alloy surface. Several mechanisms for this protective action have been considered in the literature and modeled theoretically; however, at present these mechanisms remain speculative. In this study, we use radiolysis, laser photoionization, electron paramagnetic resonance, and transient absorption spectroscopy to establish the redox chemistry of FEC. While the oxidation chemistry is similar to that of other carbonates, the reduction chemistry is strikingly different. Specifically, one-electron reduction of FEC causes the fission of two (instead of one) C-O bonds, resulting in concerted defluorination and decarboxylation. This reaction yields the vinoxyl radical that can abstract an H atom from FEC, initiating both the chain reaction causing FEC decomposition and radical polymerization involving the reaction products. The resulting polymer can further defluorinate yielding the interior radicals that migrate and recombine to produce a highly cross-linked network. We suggest that the outer SEI resulting from FEC addition has elastomeric properties, which account for its cohesion during expansion and contraction of silicon particles in the course of Li alloying/dealloying cycling.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1392472
• Journal Information: Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 27 Vol. 119; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

electron paramagnetic resonance
fluoroethylene carbonate
lithium-ion batteries
pulse radiolysis
radical chemistry
solid electrolyte interphase