Oxidative electrolyte solvent degradation in lithium-ion batteries -: An in situ differential electrochemical mass spectrometry investigation

Differential electrochemical mass spectrometry (DEMS) was used to study the electrochemical decomposition of organic carbonate electrolyte solutions at practical lithium metal oxide composite electrodes used in lithium-ion batteries. For propylene carbonate (PC), CO2 evolution was detected at LiNiO2, LiCoO2, and LiMn2O4 composite electrodes. The starting point of gas evolution was 4.2 V vs. Li/Li+ at LiNiO2, whereas at LiCoO2 and LiMn2O4, CO2 evolution was observed only above 4.8 V vs. Li/Li+. In addition, various other volatile electrolyte decomposition products of PC were detected when using LiCoO2, LiMn2O4, and carbon black electrodes. In ethylene carbonate/dimethylcarbonate, CO2 evolution was detected only at LiNiO2 electrodes, again starting at about 4.2 V vs. Li/Li+. (C) 1999 The Electrochemical Society. S0013-4651(98)09-037-5. All rights reserved.