Deciphering the multi-step degradation mechanisms of carbonate-based electrolyte in Li batteries |
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Authors: | Gregory Gachot Sylvie Grugeon Michel Armand Serge Pilard Pierre Guenot Jean-Marie Tarascon Stephane Laruelle |
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Affiliation: | 1. LRCS, Université de Picardie Jules Verne, 33 rue de Saint Leu, 80039 Amiens, France;2. Plate-Forme Analytique, Université de Picardie Jules Verne, Amiens, France;3. Centre Régional de Mesures Physiques de l’Ouest, Université de Rennes 1, Rennes, France |
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Abstract: | Electrolytes are crucial to the safety and long life of Li-ion batteries, however, the understanding of their degradation mechanisms is still sketchy. Here we report on the nature and formation of organic/inorganic degradation products generated at low potential in a lithium-based cell using cyclic and linear carbonate-based electrolyte mixtures. The global formation mechanism of ethylene oxide oligomers produced from EC/DMC (1/1 w/w)–LiPF6 salt (1 M) electrolyte decomposition is proposed then mimicked via chemical tests. Each intermediary product structure/formula/composition is identified by means of combined NMR, FTIR and high resolution mass spectrometry (ESI-HRMS) analysis. The key role played by lithium methoxide as initiator of the electrolyte degradation is evidenced, but more importantly we isolated for the first time lithium methyl carbonate as a side product of the ethylene oxide oligomers chemical formation. The same degradation mechanism was found to hold on for another cyclic and linear carbonate-based electrolyte such as EC/DEC (1/1 w/w)–LiPF6 salt (1 M). Such findings have important implications in the choice of chemical additives for developing highly performing electrolytes. |
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Keywords: | Mass spectrometry Li-ion batteries Carbonate-based electrolyte Electrolyte degradation Ring-opening nucleophilic reactions |
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