Reaction Product Analysis of the Most Active “Inactive” Material in Lithium-Ion BatteriesThe Electrolyte. II: Battery Operation and Additive Impact

Electrolyte decomposition of lithium-ion battery as a consequence of thermal stress was investigated in Part 1 of this two-part study. The focus of Part 2 is on the influence of the battery cell operation conditions on the electrolyte during cell formation and long-term cycling. Especially, the reactivity of the negative electrode surface and the varied properties of the formed solid electrolyte interphase via vinylene carbonate addition, changing the picture of decomposition products, were addressed. With the help of liquid chromatography hyphenated to high-resolution mass spectrometryand fragmentation capabilities, structure elucidation was performed with optimal certainty. This Part 2 confirmed, summarized, and extended previous findings to 140 different carbonate, oligo phosphate, and mixed phosphate–carbonate species in the state-of-the-art electrolytes after moderate cycling conditions and contributes to a targeted investigation of LIB electrolyte aging processes. Furthermore, thermal and electrochemical aging phenomena were discussed and thermal stress-marker molecules that eased reversed-engineering were postulated.