1,1-Difluoro-1-alkenes as new electrolyte additives for lithium ion batteries

Abstract

Five 1,1-difluoro-1-alkenes bearing aryl groups are investigated as electrolyte additives for high-charge-voltage lithium ion batteries with an aim to induce favorable solid electrolyte interphase (SEI) formation. Among them, 1,1-difluoro-4-phenylbut-1-ene (DF-1) forms appropriate SEIs on the cathode and anode by its reactions under oxidative and reductive conditions, respectively, which was suggested by linear sweep and cyclic voltammetry. The SEIs formed with the DF-1 containing electrolyte on the cathode and anode were analyzed by X-ray photoelectron spectroscopy and time of flight-secondary ion mass spectrometry, indicating the following: (i) the cathode surface has a LiF-rich layer with unsaturated hydrocarbons, and (ii) the anode surface also has a LiF-rich layer, which probably includes fluoromethylene (CHF) compounds. The formation of the SEIs on both electrodes with DF-1 results in low impedance being maintained, and thus, particularly good cycle performance even at high-charge-voltage. © 2012 Elsevier B.V. All rights reserved.