China Powder Network News With the continuous growth of consumer electronics and new energy vehicles and other markets, lithium-ion batteries are becoming more and more widely used. The growth of the market will generate a large number of waste lithium batteries. Discarding used lithium batteries will cause certain harm to the ecological environment. From the perspective of environmental protection and resource regeneration, the recycling of waste lithium-ion batteries has great practical significance and economic value. At present, there are many studies on the recycling of cathode materials for lithium-ion batteries, and a lot of progress has been made, but the recycling of anode materials for lithium-ion batteries is relatively weak. With the continuous deepening of ecological protection, energy saving and emission reduction, the recycling of negative electrode materials for lithium-ion batteries has also received increasing attention. According to the current research progress of recycling methods for anode materials of waste lithium-ion batteries, the editor has sorted out several mainstream methods for readers' reference.
1. Recovery by flotation
Flotation is a physical process that selectively separates hydrophobic materials from hydrophilic materials by using the difference in wettability of the substance itself, or by using the action of collectors, foaming agents and modifiers. Lithium-ion battery anode material graphite is a non-polar and hydrophobic material, and LiCoO2 in waste lithium-ion battery is an ionic crystal with strong polarity and good hydrophilicity. The flotation method utilizes the difference in wettability of the two for separation and recovery.
Some researchers used the Fenton additive flotation method to modify the electrode material under the optimum parameters of H2O2/Fe2 plus of 40/280 and liquid-solid ratio of 25/100, and then separated by flotation, the recovery rate of LiCoO2 reached 98.99 percent . . In addition, the researchers also studied the grinding flotation technology. The wettability of LiCoO2 and graphite was different by grinding. The concentrate grades of LiCoO2 and graphite after flotation were 97.13 percent and 73.56 percent , respectively, and the recoveries were 49.32 percent and 73.56 percent , respectively. The organic binder can be removed by the pyrolysis-ultrasound-assisted method, which increases the recovery rate of LiCoO2 from 74.62 percent to 93.89 percent . The flotation method realizes the simultaneous recovery of LiCoO2 positive electrode and graphite negative electrode material, which simplifies the recovery process, and is simple, efficient, and low in pollution. However, the graphite recovered by this method contains many impurities, and the purity of the graphite obtained by separation needs to be further improved.
2. Heat treatment recovery
There is a binder PVDF between the negative electrode copper foil of lithium ion battery and the active material. The heat treatment method is to place the negative electrode of waste lithium ion battery in a certain high temperature range to volatilize or decompose the binder, so that the copper foil current collector and the graphite powder of the negative electrode active material can be separated.
The heat treatment method can effectively remove the binder and separate the copper foil current collector and active material. However, this method also has shortcomings. The organic binder is easily decomposed to generate harmful gases under high temperature conditions. If no reasonable treatment is taken, secondary pollution will occur.
3. Hydrometallurgical recycling
The waste anode contains lithium (30.07 mg·g-1) which is much higher than the environmental abundance, and most of them exist in the SEI film in the form of inorganic substances Li2O, LiF, Li2CO3 and organic substances ROCO2Li, CH3OLi, (ROCO2Li)2; A small part exists in the graphite voids in the form of Li elemental substance. Among them, Li2O, ROCO2Li and CH3OLi are water-soluble, while other substances are almost insoluble in water.
The principle of hydrometallurgy is based on the fact that metals in waste lithium-ion batteries can be dissolved in acidic, alkaline solutions or other solvents, the metals are transferred into the solution, and the graphite and other metal substances are separated by filtration separation or centrifugal separation. Hydrometallurgy can recover high-quality graphite and high-yield recovery of valuable metals. The hydrometallurgical process has a low operating temperature and can effectively recover lithium salts in the negative electrode. However, due to the presence of insoluble lithium salts such as LiF, the process consumes a large amount of strong acid (sulfuric acid, hydrochloric acid) and produces more toxic hydrofluoric acid. . Therefore, an effective solution for hydrometallurgical recycling is to combine the recycling of positive and negative electrodes, which can greatly simplify the recycling process and reduce secondary pollution caused by waste acid. Hydrometallurgy has the advantages of low energy consumption, easy operation, high recovery rate and low environmental risk, but it also has problems such as electrolyte and binder residues.
4. Combined recovery of hydrometallurgy and pyrometallurgy
There are certain problems in pure hydrometallurgy, and some researchers propose to combine hydrometallurgy and pyrometallurgy.
Pyrometallurgy is to treat the pretreated waste electrode powder at high temperature to remove organic matter and at the same time make the metal and its oxides in the powder undergo redox reaction to obtain alloy and slag. It is one of the common methods for waste battery treatment.
The graphite negative electrode of waste lithium ion battery was recovered by a combination of wet method and fire method. The mixed powder of positive and negative electrodes was leached twice under the conditions of 5mol·L-1H2SO4 and 35 percent (w/w) H2O2 and then filtered to obtain a graphite filter cake. Sintered with NaOH powder at 500 degree to remove most of the impurities, washed with deionized water and dried to obtain regenerated graphite. The electrochemical performance tests of waste graphite, secondary leached graphite and regenerated graphite show that there are many impurities in the secondary leached graphite, but the initial capacity is greater than that of the regenerated graphite. It may be that the interlayer spacing is expanded by impurities, resulting in an increase in the space for lithium intercalation. The structure of recycled graphite was not destroyed during the recycling process and maintained an ideal lattice. The impurity content was significantly reduced after the ash test, and its capacity (377.3mAh·g-1 at 0.1C) met the requirements for reuse. However, the cycle performance (capacity retention rate after 100 cycles is 84.63 percent ) still needs to be improved compared with commercial graphite, but the capacity retention rate is improved compared with pure hydrometallurgy at the same number of cycles. However, this method has the problem of low recovery rate (the recovery rate is about 60 percent ). When the sintering temperature is lower than the decomposition temperature of graphite, 33 percent of the graphite is still lost during the fusion process. This method recovers the largest graphite in the process. Losses occur at this stage.
5. Electrochemical recovery
Some researchers proposed electrochemical recovery of graphite and copper foils from lithium-ion batteries, and studied the effects of various parameters (voltage, inter-electrode distance, and electrolyte concentration) on the electrolysis process. The results show that under the optimum conditions of a pole distance of 10 cm, a concentration of Na2SO4 electrolyte of 1.5 g·L-1 and a voltage of 30 V, the complete separation of copper foil and graphite can be achieved in 25 minutes of electrolysis. Li plus in the electrolyte can be further recovered by the precipitation method. However, the graphite in this method contains a small amount of binder residue, which affects its subsequent reuse value.
summary
At present, the recycling of negative electrode materials for lithium-ion batteries is still in the experimental research stage, and the recycling technology needs to be further optimized and improved. Although there is a preliminary system for the recycling of negative electrode materials for lithium-ion batteries, there is still a long way to go before the actual commercial recycling. With the continuous expansion of the new energy market, the recycling of negative electrode materials for lithium-ion batteries is the general trend. .
Reference source:
1 Liu Dongxu et al. Progress in Regeneration and Utilization of Anode Materials for Waste Li-ion Batteries. Chemical Industry and Engineering
2 Long Fei et al. Research progress on recycling of anode materials for waste lithium-ion batteries. Journal of Shanghai Second University of Technology
3 Long Lifen et al. Research progress in utilization and treatment technology of graphite anode materials for waste lithium-ion batteries. Energy storage science and technology
(Edited by China Powder Network / Wen Zheng)
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