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

Tuesday, 3 October 2017: 16:20
Maryland C (Gaylord National Resort and Convention Center)
B. Sun (Paul Scherrer Institute, Electrochemistry Laboratory), C. Sångeland (Uppsala University, Department of Chemistry), D. Brandell (Department of Chemistry - Ångström, Uppsala University), J. Mindemark (Uppsala University, Department of Chemistry), and E. J. Berg (Paul Scherrer Institute, Electrochemistry Laboratory)
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].

References

[1] B. Sun, J. Mindemark, K. Edström, D. Brandell, Solid State Ionics, 262 (2014) 738-742;  J. Mindemark, B. Sun, E. Törmä, D. Brandell, J. Power Sources, 298 (2015) 166-170; Kimura, M. Yajima, Y. Tominga, Electrochem. Comm., 66 (2016) 46-48.

[2] B. Sun, C. Xu, J. Mindemark, T. Gustafsson, K. Edström, D. Brandell, J. Mater. Chem. A, 3 (2015) 13994-14000.