A critical analysis of chemical and electrochemical oxidation mechanisms in lithium-ion batteries (LIBs) reveals that electrolyte decomposition at positive electrodes is not primarily due to electrochemical oxidation or reactions with singlet oxygen (¹O₂). Density functional theory (DFT) calculations show that electrochemical oxidation of ethylene carbonate (EC) is thermodynamically unfavorable under normal LIB operating conditions, and reactions with ¹O₂ are kinetically limited at room temperature. Instead, the study suggests that EC may react with superoxide (O₂⁻) and/or peroxide (O₂²⁻) anions, which are more likely to form at positive electrodes. These anions are believed to be intermediates in oxygen redox reactions within transition metal oxide electrodes. The study also highlights that reactions between EC and O₂⁻ or O₂²⁻ are more favorable than those with ¹O₂, and that these reactions could contribute to electrolyte degradation. The findings suggest that alternative mechanisms involving oxygen anions may be more relevant to EC decomposition in LIBs. The study also notes that further research is needed to understand the reactivity of oxygen anions at positive electrodes and to explore their potential role in electrolyte degradation. Additionally, the study emphasizes the importance of considering the role of electrode surfaces and the reactivity of salt anions in LIBs. Overall, the study provides new insights into the mechanisms of electrolyte decomposition in LIBs and highlights the need for further research to develop more stable and energy-dense LIBs.A critical analysis of chemical and electrochemical oxidation mechanisms in lithium-ion batteries (LIBs) reveals that electrolyte decomposition at positive electrodes is not primarily due to electrochemical oxidation or reactions with singlet oxygen (¹O₂). Density functional theory (DFT) calculations show that electrochemical oxidation of ethylene carbonate (EC) is thermodynamically unfavorable under normal LIB operating conditions, and reactions with ¹O₂ are kinetically limited at room temperature. Instead, the study suggests that EC may react with superoxide (O₂⁻) and/or peroxide (O₂²⁻) anions, which are more likely to form at positive electrodes. These anions are believed to be intermediates in oxygen redox reactions within transition metal oxide electrodes. The study also highlights that reactions between EC and O₂⁻ or O₂²⁻ are more favorable than those with ¹O₂, and that these reactions could contribute to electrolyte degradation. The findings suggest that alternative mechanisms involving oxygen anions may be more relevant to EC decomposition in LIBs. The study also notes that further research is needed to understand the reactivity of oxygen anions at positive electrodes and to explore their potential role in electrolyte degradation. Additionally, the study emphasizes the importance of considering the role of electrode surfaces and the reactivity of salt anions in LIBs. Overall, the study provides new insights into the mechanisms of electrolyte decomposition in LIBs and highlights the need for further research to develop more stable and energy-dense LIBs.