Migration and Transformation Mechanism of Toxic Electrolytes During Mechanical Treatment of Spent Lithium-Ion Batteries

Abstract

Recycling spent lithium-ion batteries (LIBs) has great environmental and economic benefits. However, the potential environmental impacts of toxic electrolytes are always ignored in this process. In this paper, the migration and transformation of the toxic electrolytes including organic solvents and fluorides are studied, in which spent LIBs were mechanically treated to simulate actual operating conditions. Besides, for the convenience of analysis, LIB components were classified into strip-shaped, powdery, and liquor components according to their unique properties. The results indicated that strip-shaped components (shell, Cu/Al foil, and separator) were converted into large/middle particle size products (PSPs), while powdery components (cathode, binder, and anode) were converted into small PSPs by mechanical force. Therein, the obvious transformation and deformation of liquor electrolytes were observed, and the residual products were mainly distributed in plastics, anode, and cathode. In addition, low-boiling organic solvents escaped into air causing fire hazard and adverse health effects, and decomposed products of lithium hexafluorophosphate (LiPF 6 ) posed risk of corrosions and acute toxicity. The findings can provide instructions for preventing from hazardous pollutants in the practical application.

Recycling Hazardous and Valuable Electrolyte in Spent Lithium-Ion Batteries: Urgency, Progress, Challenge, and Viable Approach

“…These special physical and chemical properties of the electrolyte cause its recycling to be more difficult compared to other parts such as cathodes and anodes in spent LIBs. Moreover, most of the pollutants are originated from the electrolyte during the spent LIBs treatment such as discharging and crushing process. , As for the sensitive Li-based salt LiPF 6 , it will be easily hydrolyzed and decompose to produce toxic fluorine and phosphorus-containing compounds such as POF 3 , PF 5 , H 3 PO 4 , and HF when contact with trace water in the air. , Besides, the volatile carbonate solvents and toxic additives such as flame retardants in the electrolyte will also spark chemical reactions to generate VOCs during the discharging and crushing of spent LIBs…”

“…In other words, under an inert atmosphere, the crushing only needs to equip with a collecting and condensing unit for the electrolyte (Figure d). In our previous studies, we have proven that the crushing process of waste circuit board occurred in the mechanochemical reactions, which leads to the production of new organic pollutants due to the decomposition or other reactions of organics (resin and fire retardant). , In a paper just published in 2023, we also investigated the migration and transformation of the toxic electrolyte including organic solvents and fluorides during the industrialized crushing process of spent LIBs . Analogously, during the crushing process of spent LIBs, the electrolyte and other organics including plastics, separators, and binders will be subject to the mechanochemical reactions, which leads to the decomposition of electrolyte and organics in spent LIBs. , The generating gas fluorine- and phosphorus-containing products could be treated by NaOH adsorption to form NaF, Na 3 PO 4 , etc., and other hydrocarbons could be recovered as fuel.…”

“…28 In the just-published paper in 2023, we investigated the migration and transformation of the toxic electrolyte during the industrialized crushing process. 31 Through the product analysis by GC-MS and XPS, the generation of VOCs as well as toxic fluorine-and phosphorus-containing compounds was identified from the organic solvents and LiPF 6 , respectively. The schematic diagrams of LiPF 6 and VOCs release and transformation are presented in Figure 3.…”

“…According to the Web of Science (accessed December 2022), the relative number of articles on electrolyte recycling is about 10 , which accounts for only less than 1% of the total number of spent LIBs recycling (Figure ). To this March 2023, two new papers about electrolyte recycling was published, , one is our paper about the release and transformation mechanism of pollutants from electrolyte during the crushing of spent LIBs . Compared with the other components such as electrode recycling, the studies about electrolyte demonstrate neglect and initial research stages.…”

“…To this March 2023, two new papers about electrolyte recycling was published, 31,32 one is our paper about the release and transformation mechanism of pollutants from electrolyte during the crushing of spent LIBs. 31 Compared with the other components such as electrode recycling, the studies about electrolyte demonstrate neglect and initial research stages. In addition to the above hazardous property, electrolytes are potential resources if properly treated.…”