Further Insights into Structural Diversity of Phosphorus-Based Decomposition Products in Lithium Ion Battery Electrolytes via Liquid Chromatographic Techniques Hyphenated to Ion Trap-Time-of-Flight Mass Spectrometry

Abstract

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.

Mn2+ or Mn3+? Investigating transition metal dissolution of manganese species in lithium ion battery electrolytes by capillary electrophoresis

“…On the one hand, disproportionation can be accelerated at higher temperatures and, on the other hand, more acidic compounds can be formed at higher temperatures due to accelerated decomposition of the thermal labile conducting salt LiPF 6 . Previous studies demonstrated the decomposition of organic carbonates and the conducting salt at elevated temperatures to different acids, like HF or difluorophosphoric acid, especially in the presence of moisture [63–69]. As a consequence, LNMO particles are situated under acidic condition, which was shown to increase the dissolution of manganese [18, 21, 31, 34, 35].…”

Clarification of Decomposition Pathways in a State‐of‐the‐Art Lithium Ion Battery Electrolyte through 13C‐Labeling of Electrolyte Components

“…The proposed reactive species monoglycolate methyl/ethyl carbonate was claimed the key compound for the initiation of the decomposition (“intermediary A”) . The decomposition of LiPF 6 ‐based electrolytes to organo(fluoro)phosphates (O(F)Ps) was investigated intensively . Subsequent studies addressed reductively and oxidatively generated products and evolving gases separately as well as the identification of further decomposition compounds …”

Clarification of Decomposition Pathways in a State‐of‐the‐Art Lithium Ion Battery Electrolyte through 13C‐Labeling of Electrolyte Components

“…Since only the terminated products (blue background) were accessible for LC-MS measurements,the explicit initiation reaction and elongation cascade were postulated to match the obtained results.T o generate further insights into the presence of reactive species, the application of in situ techniques (e.g., IR, Raman and NMR) are possible approaches but will face challenges regarding sensitivity as well as the reliable assignment of signals without chromatographic separation in the highly complex mixture of decomposition products in LIB electrolytes with > 300 possible compounds. [25,34,35] Possible unlabeled termination molecules were DEC and lithium alkoxides (originating from DEC). Resulting leaving groups were postulated stoichiometrically.…”

“…[28,29] Besides electrochemical decomposition, thermal stress at elevated temperatures (60-80 8 8C) is another reason for aring opening polymerization of ethylene carbonate (EC) and acomparable variety of species. [25,[30][31][32][33] Overall, the identified soluble compound classes in electrolytes covered (i)o ligo carbonates,(ii)carbonate ether co-oligomers,(iii)glycols,(iv) O(F)Ps,(v) phosphate-carbonate-intermixtures and (vi)oligo phosphates,r esulting in various different species. [25,28,29,34,35] Particularly,the decomposition route to oligo phosphates via "intermediary A" was difficult to define.Recently,W ang, Xu, Eichhorn and co-workers corrected the previous assumption of lithium ethyl di-carbonate (LEDC) as am ain SEI component to the analogous monocarbonate species.…”

“…[19] Thed ecomposition of LiPF 6 -based electrolytes to organo(fluoro)phosphates (O(F)Ps) was investigated intensively. [22][23][24][25] Subsequent studies addressed reductively and oxidatively generated products and evolving gases separately [26,27] as well as the identification of further decomposition compounds. [28,29] Besides electrochemical decomposition, thermal stress at elevated temperatures (60-80 8 8C) is another reason for aring opening polymerization of ethylene carbonate (EC) and acomparable variety of species.…”