Fluorinated Alkyl Substituted Sulfones As Electrolytes for High Voltage Lithium-Ion Battery

In an effort to enhance the energy and power density of Li-ion battery technology to facilitate the commercialization of electric vehicles, material researchers have developed new cathode materials with improved specific capacity [1] and operating voltage (5 V vs. Li⁺/Li).[2] However, the  state-of-the-art electrolyte containing 1.2 M lithium hexafluorophosophate (LiPF₆) in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) decomposes at above 4.5 V vs. Li⁺/Li which prevents the extensive use for the high voltage cathode materials. [3] Thus, the exploration of new electrolytes with elevated voltage stability has been actively pursued. [2]

In this paper, we present a novel electrolyte candidate of fluorinated sulfones for high voltage Li-ion battery. Aided by DFT computation, fluorinated sulfones with various chemical structures (trifluoromethyl)sulfonylethane (FMES), 1-(trifluoromethyl)sulfonylpropane (FMPS) and 2-(trifluoromethyl)sulfonylpropane (FMIS) were designed, synthesized and characterized with analytical methods including NMR, GC-MS and FT-IR and their oxidation stability were examined by a floating method using LiNi_0.5Mn_1.5O₄/Li cell. Sulfone with trifluoromethyl (-CF₃) substitution at alpha position possesses enhanced oxidative stability and reduced viscosity as compared to their non-fluorinated counterparts. The alpha-substituted fluorinated sulfones also showed improved wetting ability with PE/PP separators. A facile method for the synthesis of 1,1,1-trifluoro-3-(methylsulfonyl)propane (FPMS), which enabled us to produce  adequate amount of FPMS for electrolyte testing, was also developed. Unlike alpha-substituted fluorinated sulfones, the gamma-substituted fluorinated sulfones resemble the properties of their non-fluorinated ones.

References:

[1] (a) Nyten, A.; Abouimrance, A.; Armand, M.; Gustafsson, T.; Thomas, J. O. Electrochem. Commun., 2005, 7, 156-160. (b) Ellis, B. L.; Makahnoul, R. M.; Makimura, Y.; Toghill, K.; Nazar, L. F. Nat. Mater., 2007, 6, 749-753.

[2] (a) Zhang, Z.; Hu, L.; Wu, H.; Weng, W.; Koh, M.; Redfern, P. C.; Curtiss, L. A.; Amine, K. Energy Environ. Sci., 2013, 6, 1806-1810. (b) Hu, M.; Pang, X.; Zhou, Z. J. Power Sources, 2013, 237, 229-242. (c) Xu, M.; Zhou, L.; Done, Y.; Chen, Y.; Garsuch, A.; Lucht, B. L. J Electrochem. Soc. 2013, 160, A2005-A2013. (d) Von Cresce, A.; Xu, K. ECS Trans., 2012, 41, 17-22. (e) Santhanam, R.; Rambabu, B. J. Power Sources, 2010, 195, 5442-5451.

[3] a) Kunduraciz, M.; Amatucci, G.G. J Electrochem. Soc. 2006, 153, A1345-A1352. (b) Wolfenstine, J.; Aleen, J. J. Power Sources, 2005, 142, 389-390.