The high-efficiency recovery technology of valuable metals from waste lithium-ion batteries has become a research hotspot at home and abroad. Aiming at the current status of the recovery technology of valuable metals in waste lithium-ion batteries, this paper introduces the research methods of pretreatment and cathode material treatment in the recovery process of valuable metals, and briefly evaluates the advantages and disadvantages of various methods. During the recycling process, the technical difficulties such as the complex separation and purification process and the easy generation of secondary pollution were analyzed, and it was pointed out that the follow-up should carry out in-depth research on the recycling process, explore the efficient recycling process, and industrialize the development trend of laboratory research results.

In modern life, electronic communication devices such as cameras, video cameras, notebook computers, and mobile phones using lithium-ion batteries have been widely used by people. The main components of a lithium-ion battery are positive electrode, negative electrode, separator and electrolyte. The positive electrode of the battery is composed of a positive electrode active material, a conductive agent, a binder, a current collector, and the like. The negative electrode of the battery is mainly composed of the negative electrode active material and the current collector. A separator composed of a polymer separates the positive and negative electrodes. The electrolyte plays the role of charging and discharging the battery. However, lithium-ion batteries have a limited lifespan, typically less than 3 years. Waste batteries contain toxic substances that can damage soil and water quality in the environment. The diffusion of these toxic substances into the body of humans and animals will endanger health. Recycling valuable metals can not only improve the environment, but also improve the economic benefits of enterprises. Therefore, the green recovery and reuse technology of valuable metals in waste lithium-ion batteries has become a research hotspot in recent years. This paper mainly reviews the domestic and foreign technology methods for the recovery and treatment of valuable metals in waste lithium-ion batteries, and looks forward to the development trend of recovery technology.

1 Current status of research at home and abroad

In practical applications, the core technologies of recycling are mainly divided into two categories: fire method and wet method. The fire method is a process of extracting or separating non-ferrous metals from battery materials by heating under high temperature conditions according to the physical properties (melting point, vapor pressure) of different metals. Wet method is a recycling process that utilizes acid, alkali or organic solvent to leaching valuable metal components in batteries. The recycling process can be roughly divided into three steps: battery pretreatment, separation of active materials and current collectors, and recovery and reuse of valuable metals.

1.1 Pretreatment of waste lithium-ion batteries

1.1.1 Discharge

Used lithium-ion batteries have residual power in them. To prevent accidents during battery removal, discharge the battery before removing it. The treatment methods include physical discharge method and chemical discharge method. The physical discharge method mainly uses low-temperature forced discharge. This method is suitable for small batch production. Umicore and Toxco companies in the United States use liquid nitrogen to pretreat the battery at low temperature, and safely break the battery at a temperature of -198 ℃, but this method Higher requirements for equipment. The chemical discharge method mainly uses electrolysis to discharge. The electrolyte is mostly sodium chloride solution. When the battery is placed in the solution, the positive and negative electrodes of the battery are short-circuited in the conductive liquid, and the complete discharge of the battery is quickly realized. The disadvantage of this method is that the concentration and temperature of the electrolyte will affect the discharge rate of the battery, and the valuable metals in the battery will dissolve into the conductive liquid, reducing the metal recovery rate. At the same time, the solution containing valuable metals has strong pollution, which makes recovery difficult and increases the recovery cost.

1.1.2 Dismantling and breaking

In the laboratory, due to the small size of the battery, most of the batteries are disassembled and separated manually. In actual production, the method of mechanical crushing is often used to disassemble the battery. One method of mechanical crushing is the wet method. The wet method uses various acid and alkaline solutions as the transfer medium to transfer metal ions from the electrode material to the leaching solution, and then through ion exchange, precipitation, adsorption and other means, the metal ions are removed from the solution in the form of salts, oxides, etc. extracted. The wet recycling technology is relatively complex, but the recovery rate of valuable metals is relatively high. It is currently the main technology for processing waste nickel-hydrogen batteries and lithium-ion batteries. Wang Yuansun and others tried to soak the battery in dilute alkaline water and then smash it. This method can reduce the production of HF, but cannot effectively recover the fluorine-containing electrolyte, which is easy to cause secondary pollution. Another method is the dry method. Dry method mainly includes mechanical sorting method and high temperature pyrolysis method (or high temperature metallurgy method). The mechanical sorting method has the advantages of short recovery process and strong pertinence of recovery, which is the preliminary stage of realizing metal separation and recovery. He et al. compared the different effects of wet and mechanical sorting methods on the recycling and disposal of waste lithium-ion batteries. The results show that mechanical sorting method crushing will not break the battery components into fine particles that are easily mixed together, and the recovery rate higher. However, the mechanical sorting method cannot completely separate the components in the waste lithium-ion battery. People try to use the method of high temperature pyrolysis, that is, heating the battery in a muffle furnace to remove the organic solvent in the battery. Joo et al. used mechanical sorting and high-temperature pyrolysis to efficiently recover cobalt and lithium from waste lithium cobalt oxide batteries. However, high-temperature pyrolysis can also cause negative effects, such as the generation of harmful gases during high-temperature treatment, which can easily cause explosions, so a purification device needs to be installed.

1.2 Separation of active materials and current collectors

The separation of the positive electrode active material and the aluminum foil current collector mainly adopts two methods including organic solvent dissolution and high temperature decomposition. The organic solvent discharge mainly uses the organic solvent to dissolve the PVDF, so that the positive electrode active material and the current collector are separated. Zeng uses NMP to soak the electrode sheet, which effectively separates the active material and current collector in the battery. Yang was dissolved with the organic solvent DMAC (N,N-dimethylacetamide), and the binder on the current collector was removed under the process conditions of 100 °C and 60 min. However, the active material particles obtained by this recovery method are small, the solid-liquid separation is difficult, and the recovery investment is large. Pyrolysis is the separation of cathode materials and active bodies at high temperatures. Daniel et al. adopted a method of high temperature treatment in a vacuum environment to decompose the organic matter in the current collector at high temperature (600 °C), and part of the positive electrode material on the positive electrode material was separated from the aluminum foil. When the temperature was greater than 650 °C, the aluminum foil and the positive electrode The materials are all granular and mixed together. This method produces harmful gases and pollutes the air.