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⁺.