Gas evolution from cathode materials: A pathway to solvent decomposition concomitant to SEI formation

This work reports a method to explore the catalytic reactivity of electrode surfaces toward the decomposition of carbonate solvents [ethylene carbonate (EC), dimethyl carbonate (DMC), and EC/DMC]. We show that the decomposition of a 1:1 wt% EC/DMC mixture is accelerated over certain commercially available LiCoO₂ materials resulting in the formation of CO₂ while over pure EC or DMC the reaction is much slower or negligible. The solubility of the produced CO₂ in carbonate solvents is high (0.025 g mL ^-1) which masks the effect of electrolyte decomposition during storage or use. The origin of this decomposition is not clear but it is expected to be present on other cathode materials and may affect the analysis of SEI products as well as the safety of Li-ion batteries.