Disposed battery

The recycling process of waste lithium-ion batteries mainly includes a pretreatment, secondary treatment and advanced treatment. Because there is still some electricity left in the waste battery, the pretreatment process includes deep discharge process, crushing and physical separation; The purpose of secondary treatment is to completely separate the positive and negative active materials from the substrate. Heat treatment, organic solvent dissolution, alkali solution dissolution and electrolysis are commonly used to completely separate them; Advanced treatment mainly includes two processes: leaching and separation and purification to extract valuable metal materials. According to the classification of extraction process, the recovery methods of battery can be mainly divided into three categories: dry recovery, wet recovery and biological recovery.

1. Dry recovery

Dry recovery refers to the direct recovery of materials or valuable metals without solution and other media. Among them, the main methods used are physical separation method and the high-temperature pyrolysis method.

(1) Physical sorting method

Physical separation refers to the disassembly and separation of the battery, and the crushing, screening, magnetic separation, fine crushing and classification of battery components such as electrode active substances, collector and battery shell, so as to obtain valuable high content substances

The operation of physical separation method is relatively simple, but it is not easy to completely separate lithium-ion batteries, and it is easy to have mechanical entrainment loss during screening and magnetic separation, so it is difficult to completely separate and recover metals.

(2) High-temperature pyrolysis

High-temperature pyrolysis refers to the high-temperature calcination and decomposition of lithium battery materials after preliminary separation treatment such as physical crushing, and the removal of organic adhesives, so as to separate the constituent materials of lithium batteries. At the same time, the metal and its compounds in the lithium battery can be oxidized, reduced and decomposed, volatilized in the form of steam, and then collected by condensation.

High-temperature pyrolysis treatment technology has the advantages of simple process, convenient operation, fast reaction speed and high efficiency in a high-temperature environment, and can effectively remove the adhesive; Moreover, this method does not require high components of raw materials, and is more suitable for processing a large number of or more complex batteries. However, this method requires high equipment; In the process of treatment, the organic matter decomposition of the battery will produce harmful gas, which is not friendly to the environment. It is necessary to increase purification and recovery equipment to absorb and purify harmful gas and prevent secondary pollution. Therefore, the processing cost of this method is high.

2. Wet recovery

The wet recovery process is to dissolve the waste battery after crushing, and then use appropriate chemical reagents to selectively separate the metal elements in the leaching solution to produce high-grade cobalt metal or lithium carbonate for direct recovery. Wet recycling treatment is more suitable for recycling waste lithium batteries with relatively single chemical composition. Its equipment investment cost is low, which is suitable for the recycling of small and medium-sized waste lithium batteries. Therefore, this method is also widely used.

(1) Alkali acid leaching

Since the cathode material of lithium-ion battery will not dissolve in alkaline solution, and the base aluminum foil will dissolve in alkaline solution, this method is often used to separate aluminum foil. Most of the positive active substances in lithium-ion batteries can be dissolved in acid, so the pretreated electrode materials can be leached with acid solution to separate the active substances from the collector, and then the target metal can be precipitated and purified in combination with the principle of neutralization reaction, so as to achieve the purpose of recovering high-purity components.

The acid solution used in acid leaching method includes traditional inorganic acids, including hydrochloric acid, sulfuric acid and nitric acid. However, harmful gases such as chlorine (Cl2) and sulfur trioxide (SO3) that affect the environment are often produced in the process of leaching with inorganic strong acids. Therefore, researchers try to use organic acids to treat waste lithium batteries, such as citric acid, oxalic acid, malic acid, ascorbic acid, glycine, etc.

(2) Organic solvent extraction

Organic solvent extraction method uses the principle of "similarity and compatibility" and uses appropriate organic solvent to physically dissolve the organic binder, so as to weaken the adhesion between the material and the foil and separate them.

The experimental conditions of separating material and foil by organic solvent extraction are relatively mild, but the organic solvent has certain toxicity, which may be harmful to the health of operators. At the same time, because different manufacturers have different processes for making lithium-ion batteries and choose different binders, manufacturers need to choose different organic solvents when recycling waste lithium-ion batteries according to different manufacturing processes. In addition, cost is also an important consideration for large-scale recovery and treatment operations at the industrial level. Therefore, it is very important to choose a solvent with wide sources, appropriate price, low toxicity and wide applicability.

(3) Ion exchange method

Ion exchange method is to realize metal separation and extraction by using different adsorption coefficients of ion exchange resin for metal ion complexes to be collected. The process of ion exchange method is simple and easy to operate.

3. Biological recovery

Inorganic acid and acidophilic Thiobacillus ferrooxidans are used to leach metals from waste lithium-ion batteries, and sulfuric acid and ferrous ions are used to produce metabolites such as H2SO4 and Fe3 + in the leaching medium. These metabolites help dissolve metals in waste batteries. It is found that the biological dissolution rate of cobalt is faster than that of lithium. With the progress of the dissolution process, iron ions react with the metal in the residue and precipitate, resulting in the reduction of ferrous ion concentration in the solution. With the increase of metal concentration in waste samples, the growth of cells is prevented and the dissolution rate slows down. In addition, the higher solid/liquid ratio also affects the rate of metal dissolution. The results show that almost all cobalt (99.9%) enters the solution after 6 days of bioleaching when the concentration of Cu ion is 0.75g/l, while only 43.1% of cobalt is dissolved after 10 days of reaction time without copper ion. In the presence of copper ion, the cobalt dissolution efficiency of waste lithium-ion battery is improved. Bioleaching has the advantages of low cost, high recovery efficiency, less pollution and consumption, less impact on the environment, and microorganisms can be reused. However, it is difficult to cultivate high-efficiency microorganisms, long treatment cycle and control of leaching conditions.

4. Combined recovery method

Waste lithium battery recycling processes have their own advantages and disadvantages. At present, there have been research on the recycling methods of combining and optimizing various processes, so as to give full play to the advantages of various recycling methods and maximize economic benefits.