Research On Recycling And Reusing Of Lithium-ion Battery Electrolyte Based On Supercritical CO₂ Extraction

Lithium-ion batteries are widely used in electronic products and electric vehicles.With the substantial increase in usage,the number of used lithium-ion batteries is increasing.Since the electrolyte of Lithium-ion batteries contains toxic and harmful substances,side reactions are prone to occur in the natural environment,causing secondary pollution,so it is urgent to carry out the recovery of the electrolyte.In this thesis,the process of a combination of supercritical CO₂ static and dynamic extraction was used to extract the electrolyte,and the optimal extraction process parameters were determined by response surface analysis.The entrainment agent was selected to further improve the extraction efficiency of the electrolyte.Finally,the process of electrolyte extraction,impurity removal and reusing electrolyte for commercial18650 lithium-ion battery after aging was explored.Finally,the process of extracting,removing impurities and reusing electrolyte for commercial 18650lithium-ion battery after aging was explored.The main research contents and results were as follows:（1）In order to obtain the optimal extraction process,the thesis explored the extraction effect of different adsorption materials,and selected non-woven fabric（the main component is polypropylene PP）as the best adsorption material.Response surface analysis was used to optimize the three factors of temperature,pressure and time,and the optimal extraction process parameters were obtained:extraction pressure is 26.68 MPa,extraction temperature is40℃,extraction time includes 30 min static extraction and 20 min dynamic extraction,CO₂ flow rate was 10 m L/min,and the electrolyte extraction efficiency was 69.16%.Gas chromatography（GC）,ion chromatography（IC）,Fourier infrared spectrometer（FT-IR）,inductively coupled plasma emission spectrometer（ICP）,nuclear magnetic resonance（NMR）were used to characterize the extract,and the analysis results showed that the extraction product contained only the organic solvent components of the electrolyte and did not contain the electrolyte lithium salt,which effectively realized the separation of organic solvents and lithium salts.（2）In order to improve the extraction efficiency,the experiment introduced two types of entrainers,which are commonly used organic solvents in electrolyte and commonly used in supercritical CO₂ extraction,and discussed their mechanism in the extraction process.The optimal amounts of DMF（N,N-dimethylformamide）and GBL（γ-butylactone）were 6 wt%and 4 wt%,and the extraction rates were 84.24%and 87.20%,respectively.The optimal amount of acetone and butanone is 6 wt%,and their extraction rates are 83.55%and80.45%,respectively.When the entrainer is added,the extraction efficiency of the electrolyte increases significantly,especially when DMF and GBL were used.However,the use of GBL entrainer will accelerate the decomposition of electrolyte lithium salt,so DMF is a more suitable entrainer.（3）The commercial 18650 lithium-ion batterywas extracted and recovered.After removing impurity,the recovered products were supplemented with components and assembled into button batteries for testing.After charged and discharged 50 times at a rate of 0.2 C,the battery assembled with electrolyte had a specific discharge capacity of 127.13 m Ah/g,a capacity retention rate of89.35%,and a coulombic efficiency of 99.59%.The recoverd and resued of the electrolyte of the commercial 18650 lithium-ion battery has been relized..