Extraction of lithium-ion battery electrolytes with liquid and supercritical carbon dioxide and additional solvents

A flow-through method for the extraction of lithium-ion battery electrolytes with supercritical and liquid carbon dioxide (sc and liq CO2) under the addition of different solvents has been developed and optimized to achieve quantitative extraction of the electrolyte from commercial LiNi1/3Co1/3Mn1/3O2 (NMC)/graphite 18 650 cells. Furthermore, the time-dependence of the extraction procedure was investigated and demonstrated. The extracts were analyzed with gas and ion chromatography. Linear carbonates like dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), respectively, were better extracted with liq CO2, whereas the cyclic carbonate ethylene carbonate (EC) was recovered in higher amounts with sc CO2. The addition of solvents to the CO2 resulted in improved recovery for all the ingredients but most effectively for LiPF6, which could not be obtained by extraction with CO2 only. The best results were achieved by extracting for 30 minutes with liq CO2 (25 degrees C, 60 bar) and 0.5 mL min(-1) acetonitrile (ACN)/propylene carbonate (PC) in a mixture of three to one and an additional 20 minutes with liq CO2 only, to yield (89.1 +/- 3.4) wt% electrolyte in almost its original composition of DMC, EMC, EC (1 : 1 : 1) with 1.1 mol L-1 LiPF6. Therefore, the presented method can be relevant for the recycling of lithium ion battery electrolytes but has to be validated for up-scaled processes. Furthermore, the suitability of CO2 extraction as a tool for post-mortem or aging investigations of LIB electrolytes could once more successfully be demonstrated due to the extraction of aging products like diethyl-2,5-dioxahexane dicarboxylate (DEDOHC) from a pouch cell, which was electrochemically aged for 1000 cycles at 1 C. In this context, extraction times and recovery rates were drastically improved compared to our previously reported static extraction experiments.