This
study illustrates the high complexity of phosphorus-based
decomposition products in thermally treated state-of-the-art lithium
ion battery (LIB) electrolytes. Liquid chromatographic techniques
hyphenated to ion trap time-of-flight mass spectrometry reveal 122
different organophosphate (OP) and organofluorophosphate (OFP) species,
the majority of which are not reported in the literature so far. The
application of hydrophilic interaction liquid chromatography and reversed-phase
chromatography enables the investigation of the acidic as well as
nonacidic spectrum of aging products. Furthermore, the generation
of high structure certainty by consideration of (i) mass accuracy
of the precursor ions and subsequent MS2/3 fragments, (ii)
fragment intensity distribution in the mass spectra, and (iii) retention
times in hydrophilic interaction liquid chromatography (HILIC) and
reversed-phase (RP) separation allows a target analysis of further
work in the LIB electrolyte context. In an ethyl methyl carbonate-based
battery electrolyte, 82 OP compounds, 27 OFPs, and 13 cyclic O(F)Ps
are identified. Additionally, the formation of 8-membered organo(fluoro)phosphate
rings in lithium ion battery electrolytes is reported for the first
time. Since the high toxic potential of organo(fluoro)phosphates has
emerged interest in safety assessments of electrolytes, the knowledge
of possibly formed substances supports further quantification approaches
and toxicological assessments compared to nontarget investigations.