Study of Electrolyte Components in Li Ion Cells Using Liquid-Liquid Extraction and Gas Chromatography Coupled with Mass Spectrometry

Abstract

LiCoO2/graphite and LiNi0.33Mn0.33Co0.33O2/graphite Li-ion pouch-type cells filled with 1 M LiPF6 EC: EMC (3:7 by weight) with the additives vinylene carbonate (VC) or vinyl ethylene carbonate (VEC) were prepared. Some cells underwent partial or complete formation while others underwent full formation followed by charge-discharge cycling or high potential storage. Following a simple liquid-liquid extraction step, the mass ratios of the organic components of the electrolyte were analyzed using gas chromatography (GC) coupled with electron impact mass spectroscopy (MS). This semi-quantitative method proved to be very effective for the removal of the LiPF6 from the electrolyte, thus preventing damage to the gas chromatograph and mass spectrometer. It also allowed for a quick and simple assessment of the consumption of additives as a function of state of charge and cycling. The purpose of this paper is to make this method widely available to the Li-ion battery research community.