Decomposition of Carbonate-Based Electrolytes: Differences and Peculiarities for Liquids vs. Polymers Observed Using Operando Gas Analysis

Abstract

Direct tracking of solid polymer electrolyte (SPE) decomposition in comparison to a liquid analogue was accomplished by monitoring the evolution of volatile species using online electrochemical mass spectrometry (OEMS). Reduction of a poly(trimethylene carbonate)-based SPE was dominated by CO2 formation. Detection of CO2 and an absence of CO confirms a preferred reduction degradation pathway involving C−O bond cleavage at the carbonyl carbon, in correlation with earlier suggestions. In contrast, the alkyl carbonate-based liquid electrolyte exhibited extensive ethylene formation. Trace quantities of H2 evolution ascribed to water impurities were also observed in both systems. During oxidation, the SPE and liquid electrolyte exhibited CO2, CO and SO2 evolution synonymous with electrolyte solvent and salt degradation, albeit at different potentials. Overall, gas evolution rates and redox currents were lower in the SPE system. OEMS revealed significant gas formation independent of current response, as such highlighting the limitations of the voltammetry technique commonly used today to assess electrochemical stability.