Evaluation of Electrolyte Oxidation Stability on Charged LiNi0.5Co0.2Mn0.3O2 Cathode Surface through Potentiostatic Holds

The electrolyte oxidation rate was measured at 4.6 V vs. Li+/Li for a NCM/LTO full cell at temperatures ranging from room temperature to 55 degrees C. A large (similar to 2.5) N/P ratio was used in electrode fabrication to enable a stable reference in the Li4Ti5O12 electrode for both cycling and the potentiostatic hold regimes. LTO was used to prevent electrolyte reduction from contributing to the signal, as well as providing a stable impedance. For the alkyl carbonate electrolyte used, oxidation rate at room temperature to 45 degrees C approximately ranged from 1-2 mu A, as measured during the terminal 4.2 hours of a 60 hour potentiostatic hold. Many cells aged at 55 degrees C indicated increasing, unstable currents. Upon the completion of the hold, the cells were cycled to evaluate the effect of the hold and analyzed with AC impedance spectroscopy. Higher temperatures during the potentiostatic hold led to lower capacities during post-aging cycling, as well as higher impedance as measured with EIS. (C) 2016 The Electrochemical Society. All rights reserved.