1.3 Separation, Recovery and Utilization of Valuable Metals

The recovery and utilization of valuable metals in waste lithium-ion batteries is mainly the recovery of positive active materials. Cathode recycling and processing methods mainly include biological method, high temperature combustion method, acid dissolution method and electrochemical dissolution method.

1.3.1 Biological Law

The biological method uses the metabolic function of microorganisms to convert the metal elements in the positive electrode into soluble compounds and selectively dissolve them out. After obtaining the metal solution, the components of the positive electrode material are separated by inorganic acids, and finally the separation and recovery of valuable metals are realized. . Jia Zhizhi et al. used ferrooxidans and thiooxidans to treat waste lithium-ion batteries. This method has low recovery cost and is easy to achieve at room temperature and pressure. However, the disadvantage of this method is that the strain is not easy to cultivate and the leaching solution is difficult to separate. Zeng et al. used acidophilic bacteria to use sulfur and ferrous ions as energy sources to metabolize products such as sulfuric acid and iron ions to dissolve metal elements in waste lithium-ion batteries. However, the co-precipitation of Fe(III) with other metal elements at a higher content will reduce the solubility of metals, affect the growth rate of biological cells, and reduce the metal dissolution rate. The biological method has the characteristics of low cost, low pollution and reusability, and has become an important development direction of the recovery technology of waste lithium ion valuable metals. However, it also has problems to be solved, such as the selection and cultivation of microbial strains, the optimal leaching conditions, and the bioleaching mechanism of metals.

1.3.2 High temperature combustion method

The high-temperature combustion method refers to soaking the removed cathode material in an organic solvent, and then burning it at high temperature to obtain valuable metals. Japan's Sony and Sumitomo Corporation immersed waste lithium-ion batteries in oxalic acid and incinerated them at 1 000 ℃ to remove the electrolyte and separator, and realized the cracking of the battery. The residual material after incineration was screened and magnetically separated. To separate Fe, Cu, Al and other metals. The results show that when the oxalic acid concentration is 1.00 mol·L-1, the solid-liquid ratio is 40-45 g·L-1, and the solubility is optimal under stirring for 15-20 min at 80°C. Japan's Matsuda Guangming et al. soaked the positive electrode material and then used the mechanical breakage method to break it, and then used the muffle furnace high temperature heat treatment, flotation and other methods to separate the metal after the mechanical breakage. However, this method has high energy consumption and high temperature, and will produce waste gas to pollute the environment, and the obtained metal has a high impurity content, which requires further purification to obtain high-purity metal materials.

1.3.3 Acid dissolution method

This method refers to the use of acid to dissolve the positive electrode material, and then to extract the metal in the solution with an organic extractant to achieve the separation of metal ions, and to obtain valuable metals after treatment. At 80 °C, Halliper et al. dissolved lithium cobalt oxide in the cathode material of lithium-ion batteries at 1.5 mol/L and 0.9 mol/L H2SO4 and H2O2, respectively. Zhou Tao et al. utilize the cobalt ion solution obtained above, extract copper using extraction agent AcorgaM5640, extract cobalt using Cyanex 272, the recovery rate of copper reaches 98%, the recovery rate of cobalt is 97%, and the remaining lithium can be precipitated with sodium carbonate. come out. Wang et al. used hydrochloric acid to dissolve the cathode material, PC-88A was used as the extractant to extract cobalt ions, and cobalt sulfate was obtained after subsequent treatment. The advantage of this method is that the obtained metal is of high purity. The disadvantage is that the extractant is expensive, toxic, harmful to the human body, and the processing process is more complicated.

1.3.4 Electrochemical dissolution method

In this method, the positive electrode material is used as the cathode, the lead is used as the anode, and the mixed solution of inorganic acid (sulfuric acid or hydrochloric acid) and citric acid or hydrogen peroxide is used as the electrolyte, and the electrolysis experiment is carried out to precipitate cobalt plasma, and then the extraction agent is used to extract the metal. Chang Wei et al. used 0.4 mol/L sulfuric acid and 36 g/L citric acid as electrolyte, and electrolyzed at 25 °C for 120 min, the cobalt leaching rate reached 90.85%, and the aluminum dissolution rate was 5.8%. Lu Xiuyuan[18] adopted the orthogonal experiment method, using 3 mol/L sulfuric acid and 2.4 mol/L hydrogen peroxide, the reaction time was 20 min, and the cobalt leaching rate was as high as 99.6%. The electrochemical dissolution method is relatively simple and feasible, and the leaching rate of valuable metals is high, but the energy consumption during the electrolysis process is relatively large, so it is still necessary to continue to improve the electrochemical method to make it suitable for large-scale production. During the electrolysis process, the electrolysis reaction equation that occurs is:

cathode:
LiCoO2+4H++e-=Li++Co2++2H2O2H++2e=H2(g)

anode:
2H2O-4e-=O2(g)+4H+

2 Recycling and utilization of waste lithium-ion batteries

(1) In the process of dismantling and crushing waste lithium-ion batteries, the separation effect is still not ideal. Therefore, the safe and effective disassembly and crushing of waste lithium-ion batteries is a prerequisite for the recycling of waste batteries.

(2) At present, in the research process of valuable metals in waste lithium-ion batteries, the recovery process of valuable metals is mainly based on wet method. This method uses chemical substances such as acid and alkali, which will produce harmful waste gas and waste liquid, which will cause certain harm to people and the environment. Therefore, secondary pollution in the process is also an important problem to be solved.

(3) In the process of recovering valuable metals from waste lithium-ion batteries, most of them focus on the recovery of valuable metals in cathode materials. Neglect the negative electrode and electrolyte. In particular, the electrolyte is mostly composed of high-concentration organic solvents, electrolyte lithium salts, additives and other raw materials. These substances are toxic and pollute the environment. Therefore, it is necessary to find alternatives to these materials to reduce the harm of the electrolyte to the environment.

(4) Most of the current research is mainly on lithium iron phosphate batteries in waste lithium-ion batteries, and there is less research on nickel-cobalt lithium manganate and lithium iron phosphate batteries. Therefore, the scope of research should be expanded, and the recycling process of different types of lithium-ion batteries should be developed, so that the valuable metals of various types of waste lithium-ion batteries can be efficiently recycled.

3 Conclusion

In summary, the recycling of waste lithium-ion batteries is still in the laboratory stage, and the process of industrialization is relatively slow. In the recycling and processing of waste lithium-ion batteries, there are still some problems in how to safely dismantle, how to improve the recovery rate of valuable metals in cathode materials while avoiding secondary pollution, how to deal with the electrolyte in waste batteries in a green way, and how to effectively improve the recycling process. economic benefits and improved environmental effects. Therefore, it is urgent to strengthen the research on the recovery, treatment and utilization of lithium-ion batteries in the future, so as to truly realize the green recovery and recycling of used batteries. "