This article presents a critical analysis of chemical and electrochemical oxidation mechanisms in lithium-ion batteries (LIBs), focusing on the degradation of ethylene carbonate (EC) in the electrolyte at positive electrode potentials. The study uses density functional theory (DFT) to evaluate the feasibility of these mechanisms. The research challenges the prevailing notions that EC is either electrochemically or chemically oxidized by singlet oxygen (¹O₂) at high potentials. Instead, the authors propose that EC may react with superoxide (O₂⁻) and/or peroxide (O₂²⁻) anions, which are more likely to be present in the reactive environment of LIB positive electrodes. The study highlights that electrochemical oxidation of EC is thermodynamically unfavorable under normal operating conditions of LIBs. Additionally, the chemical oxidation of EC by ¹O₂ is found to be kinetically limited at room temperature, suggesting that these mechanisms are not the primary drivers of electrolyte decomposition in LIBs. The authors suggest that the degradation of EC at positive electrodes may occur through alternative pathways involving reactive oxygen species such as O₂⁻ and O₂²⁻. These anions are believed to be more reactive and prevalent in the environment of high-voltage LIBs, leading to the formation of products like water and peroxo-like species. The study also discusses the importance of understanding the reactivity of EC at positive electrodes, as this knowledge is crucial for designing stable and energy-dense LIBs. The findings suggest that further research is needed to explore the interactions between EC and reactive oxygen species, as well as to develop strategies to mitigate electrolyte degradation in LIBs. The study emphasizes the need for both computational and experimental investigations to better understand the mechanisms of electrolyte decomposition and to improve the performance and longevity of LIBs.This article presents a critical analysis of chemical and electrochemical oxidation mechanisms in lithium-ion batteries (LIBs), focusing on the degradation of ethylene carbonate (EC) in the electrolyte at positive electrode potentials. The study uses density functional theory (DFT) to evaluate the feasibility of these mechanisms. The research challenges the prevailing notions that EC is either electrochemically or chemically oxidized by singlet oxygen (¹O₂) at high potentials. Instead, the authors propose that EC may react with superoxide (O₂⁻) and/or peroxide (O₂²⁻) anions, which are more likely to be present in the reactive environment of LIB positive electrodes. The study highlights that electrochemical oxidation of EC is thermodynamically unfavorable under normal operating conditions of LIBs. Additionally, the chemical oxidation of EC by ¹O₂ is found to be kinetically limited at room temperature, suggesting that these mechanisms are not the primary drivers of electrolyte decomposition in LIBs. The authors suggest that the degradation of EC at positive electrodes may occur through alternative pathways involving reactive oxygen species such as O₂⁻ and O₂²⁻. These anions are believed to be more reactive and prevalent in the environment of high-voltage LIBs, leading to the formation of products like water and peroxo-like species. The study also discusses the importance of understanding the reactivity of EC at positive electrodes, as this knowledge is crucial for designing stable and energy-dense LIBs. The findings suggest that further research is needed to explore the interactions between EC and reactive oxygen species, as well as to develop strategies to mitigate electrolyte degradation in LIBs. The study emphasizes the need for both computational and experimental investigations to better understand the mechanisms of electrolyte decomposition and to improve the performance and longevity of LIBs.