Mechanistic Analysis of Lithium Ethylene Monocarbonate Decomposition Reaction in Battery Thermal Runaway

Abstract

To forecast the initial processes of thermal runaway and enhance the safety of lithium-ion batteries, the fundamental reaction steps involved in the thermal decomposition of specific solid electrolyte interphase (SEI) components must be investigated. This study investigates the decomposition pathway of lithium ethylene monocarbonate (LEMC), a key SEI component, using experimental and computational methods. Experimental results indicate that LEMC underwent significant mass loss at 150 °C, forming LiCO₃H and ethylene glycol. LiCO₃H then decomposes into Li₂CO₃ before 220 °C. Reactive force-field molecular dynamics calculations reveal that proton transfer reactions precede key intermediate formation, followed by C–O bond cleavage and additional proton transfer, leading to final products. Gas-phase byproducts, including CO₂ and ethylene oxide, were identified in both experiments and simulations. These findings provide insights into SEI degradation and thermal runaway initiation, contributing to improved battery safety strategies. This approach can be extended to studying SEI–electrolyte interactions in future research.