Electrochemical Degradation Processes of Solid Polymer Electrolytes in Li-Ion Batteries: An Online Electrochemical Mass Spectrometry (OEMS) Study

Abstract

Li-ion polymer batteries are considered as a promising energy storage solution with respect to battery safety and processing flexibility. Recent advances towards fast Li+ transport and room-temperature ion-conduction in solid polymer electrolytes (SPEs) open up great possibilities promoting their implementations in all-solid-state electronics; amongst the viable candidates functionalized polycarbonates and polyesters have shown their versatility to be applied in all-solid batteries which can operate down to ambient temperatures [1]. Nevertheless, there is a general lack of knowledge about the interfacial chemistry and the electro-/chemical degradation schemes of polymer electrolytes, primarily due to the technical obstacles in sample preparation and reliable in-situ characterization.In the present study, the gaseous decomposition products from polycarbonate and polyester-based SPEs are traced by online electrochemical mass spectrometry (OEMS). An operando characterization of the evolved gases from poly(trimethylene carbonate) (PTMC)-derived SPEs using high-molecular-weight PTMC and its copolymer as the host materials is performed under both cathodic reduction and anodic oxidation regions at close to ambient temperatures (e.g., 30 °C, 50 °C). Direct correlations between the oxidation and reduction potentials with the gas evolution are observed; the evolutions of CO2 (m/z = 44) and CH4 (m/z = 16) are traced and compared with LiTFSI-containing carbonate liquid electrolyte. Meanwhile, additional gaseous products are detected, such as SO2 (m/z = 64), which could be assigned to LiTFSI decomposition. This was indicated from the detectable salt decomposition residuals in Li-cells using PTMCnLiTFSI-based SPEs by X-ray photoelectron spectroscopy (XPS) [2].