UC Berkeley

Electrolyte decomposition at the positive and negative electrodes remains a major challenge to improving lithium-ion battery lifetime. At the positive electrode, chemical oxidation of alkyl carbonate solvents by reactive lattice oxygen species (ROS) has emerged as a key degradation pathway, but the specific reactivity of different solvents toward various ROS and the underlying mechanisms remain unclear. Here, we examine the reactivity of four widely used alkyl carbonates (EC, DMC, EMC, and DEC) with singlet oxygen, peroxide, and superoxide. Gas evolution measurements were used to assess the extent of reactions, and mass spectrometry and NMR spectroscopy identified the resulting products to elucidate reaction pathways. EC was reactive toward all three ROS, with the highest reactivity for superoxide, followed by peroxide and singlet oxygen. Identified products enabled a proposed mechanism for EC oxidation, supported by DFT calculations. In contrast, the linear carbonates (DMC, EMC, and DEC) exhibited minimal reactivity under the same conditions, indicating greater resistance to ROS-induced oxidation. These findings suggest that reducing the EC content in electrolytes could mitigate degradation, particularly in next-generation cathodes with extensive oxygen redox that generate more ROS. This work provides mechanistic insight into solvent-ROS interactions and offers guidelines for designing more stable electrolytes for advanced lithium-ion batteries.