The recycling process of used lithium-ion batteries includes pretreatment, secondary treatment and advanced treatment. Because there is still a certain amount of residual electricity in waste batteries, the pretreatment process includes deep discharge, crushing and physical separation. The purpose of the secondary treatment is to end the complete separation of the active materials of the positive and negative electrodes from the substrate. Deep processing mainly includes two processes of leaching and separation and purification to extract valuable metal data. According to the classification of extraction processes, battery recycling methods can be divided into three categories: dry recycling, wet recycling and biological recycling.
1. Dry recovery
Dry recovery refers to the recovery of materials or precious metals without a solution. At the same time, important methods are physical separation and high temperature pyrolysis.
(1) Physical separation method
The physical separation method refers to the disassembly, crushing, screening, magnetic separation, fine damage and classification of battery components such as the electrode active material, collector liquid, and battery casing of the battery to obtain valuable high-content substances. Shin et al. proposed a method to recover Li and Co from lithium-ion battery waste using sulfuric acid and hydrogen peroxide, including physical separation and chemical leaching of metal particles. At the same time, the physical separation process includes crushing, screening, magnetic separation, fine crushing and sorting. In the experiment, a set of rotating and fixed blade crushers were used for crushing. The crushed materials were screened and classified according to different apertures, and then subjected to magnetic separation treatment to prepare for the subsequent chemical leaching process.
(2) High temperature pyrolysis
The high-temperature pyrolysis method refers to a method in which lithium-ion battery data undergoes preliminary processing such as physical crushing, high-temperature cultivation and sintering differentiation, removal of organic binders, and then separation of lithium-ion battery component data. At the same time, it can also make the lithium ion battery redox and differentiation of metals and their compounds, volatilize by steam, and then collect them by methods such as condensation.
2. Wet recovery
The wet recycling process is to dissolve the waste batteries and break them, then use appropriate chemical reagents to select metal elements in the leaching solution to produce high-grade metallic cobalt or lithium carbonate, etc., and directly recover them. The wet recycling process is more suitable for recycling waste lithium-ion batteries with a relatively single chemical composition, and the equipment investment is relatively low, suitable for small and medium-scale waste lithium-ion battery recycling planning. Therefore, this method is now widely used.
(1) Alkali-acid leaching
Since the positive data of lithium-ion batteries will not dissolve in lye, and the basic aluminum foil will dissolve in lye, this method is often used to separate metal foil and lye. When Zhang Yang and others reclaimed Co and Li in the battery, they dipped the aluminum with alkali in advance, and then dipped it with dilute acid to destroy the adhesion of the organic and copper foils. However, the alkaline leaching method cannot completely eliminate polyvinylidene fluoride, which has an adverse effect on the subsequent leaching.
(2) Organic solvent extraction
The organic solvent extraction method adopts the principle of similarity and compatibility, uses a suitable organic solvent to physically dissolve the organic binder, and then weakens the adhesion of the data to the foil for separation.
(3) Ion exchange method
Ion exchange method refers to the use of ion exchange resin to collect metal ion complexes with different adsorption coefficients to end the separation and extraction of metals.
Biological leaching method has low cost, high recovery rate, low pollution and consumption, and little impact on the environment. However, it is difficult to cultivate high-efficiency microorganisms, the treatment cycle is long, and the control of leaching conditions is an important issue of this method.
4. Joint recovery
The recycling process of used lithium-ion batteries has its own advantages and disadvantages. Now there is a joint optimization of multiple recycling methods to give full play to the advantages of various recycling methods and maximize economic benefits.