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

Abstract

The decomposition of state-of-the-art lithium ion battery (LIB) electrolytes leads to a highly complex mixture during battery cell operation. Furthermore, thermal strain by e.g., fast charging can initiate the degradation and generate various compounds. The correlation of electrolyte decomposition products and LIB performance fading over life-time is mainly unknown. The thermal and electrochemical degradation in electrolytes comprising 1 m LiPF₆ dissolved in ¹³ C₃ -labeled ethylene carbonate (EC) and unlabeled diethyl carbonate is investigated and the corresponding reaction pathways are postulated. Furthermore, a fragmentation mechanism assumption for oligomeric compounds is depicted. Soluble decomposition products classes are examined and evaluated with liquid chromatography-high resolution mass spectrometry. This study proposes a formation scheme for oligo phosphates as well as contradictory findings regarding phosphate-carbonates, disproving monoglycolate methyl/ethyl carbonate as the central reactive species.

Keywords: 13C-labeling; LC-MS; electrolyte decomposition pathways; lithium ion battery.