Electrochemical Characteristics of Novel Fluorinated Ether Solvent for Lithium-Sulfur Batteries

Introduction In recent years, the development of electric airplanes, large drones, and other equipment has created a need for batteries with high energy density and high power density. Lithium-sulfur batteries have been investigated as such batteries. Electrolyte solutions applying carbonate solvents and ether solvents have been developed as electrolyte for lithium-sulfur batteries 1 . An electrolyte with ether-based solvents is lighter than that with carbonate-based solvents, so the former is expected to be an electrolyte for lithium sulfur batteries with high energy density. However, lithium-sulfur batteries based on ether solvents have difficulty in reversible charge-discharge reactions due to the dissolution of lithium polysulfide (Li 2 S x ) that occurs during the charge-discharge process 2 . In this study, we investigate the electrochemical characteristics of electrolytes to apply a new fluorinated ether (C14) which is resistant to elution of Li 2 S x . Experimental Sulfur-carbon composite (S-C) was prepared by compositing activated carbon (C-novel, Toyo Tanso) and sulfur in a ratio of 35:65 by weight using a thermal impregnation method. S-C was used as the active material and mixed with acetylene black (AB, DENKA), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) to prepare a slurry. The cathode was obtained by coating the obtained slurry on an aluminum foil by a doctor blade method. An electrochemical cell was assembled with the obtained cathode as the working electrode, Li foil as the counter electrode, and LiTFSI dissolved in a mixture of dioxolane (DOL), dimethoxyethane (DME), and C14 at a concentration of 1 mol L -1 as the electrolyte. In order to clarify the electrochemical characteristics of the lithium sulfur battery with these electrolytes, constant current charge-discharge tests were conducted using the electrochemical cell described above. To clarify the coordination state of the solvent to lithium ions and lithium polysulfide in the electrolyte, IR spectra were measured for these electrolytes. Results and Discussion In the IR spectra for the solutions of Li 2 S x dissolved in DME, the intensity of the peak attributed to the asymmetric stretching of the C-O-C bond, which can be seen at around 1090 cm -1 , increases with increasing concentration of Li 2 S x . The change in peak intensity appears to be due to the coordination of the structure of the diether in DME to the Li + of Li 2 S x . On the other hand, in the IR spect