Quantifying Absolute Amounts of Electrolyte Components in Lithium-Ion Cells Using HPLC
Richard Stockhausen, Andreas Hofmann, Lydia Gehrlein, Thomas Bergfeldt, Marcus Müller, Helmut Ehrenberg, Anna Smith
Abstract
To quantify absolute amounts of electrolyte components in lithium-ion cells, we developed a method for electrolyte extraction from pouch cells using a diluent and subsequent analysis by high-performance liquid chromatography (HPLC) coupled to an electrospray ionization mass spectrometer and an ultraviolet/visible light detector. From LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111)/graphite lithium-ion pouch cells containing 1 M LiPF 6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) 1:1 by weight with 3 wt% vinylene carbonate (VC), electrolytes were extracted using diethyl carbonate as diluent and HPLC analyses were subsequently performed to investigate electrolyte decomposition upon electrochemical aging. Complementary analysis methods, namely X-ray photoelectron spectroscopy, gas chromatography, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma optical emission spectrometry were applied. During formation, only VC decomposition and associated deposition of polymerized VC on the anode was identified. However, after long-term cycling, EC decomposition was dominant. Furthermore, LiPF 6 decomposition and deposition of LiF on the anode were detected. Electrochemically untreated cells showed no change in electrolyte composition during storage. Unlike analyzing relative values (concentrations/quantity ratios), where only VC decomposition is detected, our approach determining absolute amounts reveals more details and allows to identify decomposition mechanisms in electrolytes upon electrochemical aging.