Evaluating Fluorinated Electrolyte Stabilities on Charged Ncm Cathode Surfaces with Potentiostatic Holds

Abstract

Organic carbonate electrolytes are commonly used in lithium ion batteries due to their wide electrochemical stability window and high lithium salt solubility. However, the high voltage of some cathode materials is above the stability of these conventional carbonate electrolytes (>4.5V vs. Li+/Li). One method of increasing the anodic stability of the organic carbonates is through substitution of the solvents with a fluorinated carbonates. In this work, we evaluate the stability of electrolyte formulations comprising combinations of either ethylene carbonate, fluoroethylene carbonate, or difluoroethylene carbonate as cyclic carbonates, and ethyl methyl carbonate or hexafluorodiethyl carbonate as linear carbonates. Stability of these electrolytes at both positive and negative electrodes was determined by lithium/graphite half cell tests, as well as 60 hour potentiostatic hold tests at 4.6 V vs. Li+/Li with NMC (LiNi0.5Mn0.3 Co0.2O2) cathodes and either graphite or LTO (Li4Ti5O12) anodes. In potentiostatic holds with NMC cathodes, the fluorinated electrolytes show enhanced stability (lower oxidation current) with the graphite anodes, while fluorethylene carbonate containing formulations show higher oxidation currents with the LTO anodes. These results indicate the feasibility of fluorinated electrolytes in enabling high voltage cathodes through stability of the cathode/electrolyte interface. Acknowledgements The work at Argonne National Laboratory was performed under the auspices of the U.S. Department of Energy (DOE), Office of Vehicle Technologies, under Contract No. DE-AC02-06CH11357. The submitted issue has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W-31-109-Eng-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, non-exclusive, irrevocable, worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.