Environmentally Physical Separation and Recycling for the Spent Automotive Lithium-Ion Batteries

摘要

Nowadays, high power Lithium-ion batteries are used as power sources for automobiles in significant quantities. The environmental recycling and resources reuse of these spent automotive Lithium-ion batteries should be highly desired, after their useful lives end. An automotive Li-ion battery pack consists of hundreds of or more individual cells, which are connected and assembled into a pack with control circuitry, as well as thermal and battery management system. These components could be recycled intact from the battery pack, but the recycling process of these individual cells with different chemical compositions is more complicated. In this paper, an effective physical recycling process is put forward and applied to 60Ah prismatic Lithium-ion batteries with steel cove, which are used in electric vehicles produced by China's Beijing New Energy Automotive Corporation. The recycling process includes the first electrolyte extraction and harmless treatment, cell incision and components separation, and the recovery of active materials. The cleanly separated components such as current collectors, active materials and separator, are high-purity materials which could be reused directly as raw materials to produce another high-value product. Firstly, it is very important to ensure the safety and prevent explosion during the recycling processes, because Lithium-ion batteries contain toxic and flammable electrolyte. The pre-treatment of the individual cell includes the collection and concentration process of organic electrolyte: safe and non-toxic organic solvent was injected into the sealed cell to dissolve the electrolyte, then withdrew and distilled to reuse. The collection process was repeated, finally the sealed cell was vacuum extracted. The distilled residues contain some organic electrolyte solvents such as ethyl methyl carbonate, diethyl carbonate, and salt LiPF6. It was treated with alkali solution to reduce the toxicity of LiPF6, and the reaction product gas HF was absorbed by Ca(OH)2 to form CaF2. The harmless treatment of the LiPF6 in the electrolyte is helpful to carrying out the subsequence processes. Secondly, the individual cell without electrolyte was opened by cold cutting mode from the top, and jell roll of lithium-ion cell was withdrew from the steel can by clamp. Then jelly roll was reversely winded to part cathode electrode, anode electrode and separator. The segregation of cathode and anode electrodes is benefitial to respectively recycle high-purity different electrode materials (LiFeP04 with binder and conductive additive, graphite with binder) and Cu, Al foils, and avoid the cross contamination. It is quite different the chemical process, by which batteries are crushed, and leached the elements are leached by complicated chemical processes. High power ultrasonic system was used to exfoliate electrode materials from the current collectors. After comparing different solvents, it was verified that low concentration alkaline solution was most effective to exfoliate the cathode and anode electrode materials. Within about 10 minutes, the electrode could be separated into black electrode materials and clean metal foils with metal luster. There is no Al element detected in the solution by ICP, except the alkaline concentration is higher than 2 mol/L. This process has the advantage that almost cathode and anode components are segregated without contaminants, therefore, it is very favorable to recover the active materials by simple heat-treatment with Li salt supplement. Moreover, the recycled steel cans, clean Cu and Al foils can be reused directly. The recycled components corresponding to the separation and recycling steps are shown in Figure 1. It is difficult to recover Li element from recycled cathode material LiFeP04 by chemical precipitation. Because Fe element is very easy to form colloidal precipitation to adsorb a mass of Li+, which greatly decreases the Li recovery efficiency to 52.4%. Considering the recovery cost, it is an effective route to recover the active material LiFeP04 using the recycled materials. Although the recovery efficiency is 95.8% using the amount of cathode electrode in the spent battery as reference, the electrochemical performance of the recovered active material needs to be improved. Their discharge capacities of 120-130mAh/g are lower than original 150mAh/g. Perhaps it is reasonable that recovered materials could possibly be used in less-stringent capacity requirements. Based on our environmentally friendly separation and recycling processes, the pilot recycling demonstration line of automotive Lithium-ion batteries had been established in China's Beijing Pride Power System Technology Corporation, providing Lithium-ion battery packs for China's Beijing New Energy Automotive Corporation. The simple recycling technologies are helpful to solve the environmental and resources problems caused by the retirement of mass automotive batteries in the future, and it also needs time to improve the equipment and enact regulations to achieve the recycling goal of harmlessness,standardization and automatization and commercialization.