The huge market demand for lithium-ion batteries will, on the one hand, lead to the emergence of a large number of used batteries in the future. How to deal with these used lithium-ion batteries to reduce their impact on the environment is an urgent problem; on the other hand, in order to cope with the huge market Demand requires manufacturers to produce large quantities of lithium-ion batteries to supply the market. At present, the cathode materials used in the production of lithium-ion batteries mainly include lithium cobalt oxide, lithium manganate, lithium nickel cobalt manganate ternary materials and lithium iron phosphate, etc. Therefore, used lithium-ion batteries contain more cobalt (Co), lithium (Li), nickel (Ni), manganese (Mn), copper (Cu), iron (Fe) and other metal resources, including a variety of rare metal resources. Cobalt is a scarce strategic metal in my country and is mainly imported. meet growing demand. Some metal contents in used lithium-ion batteries are higher than those in natural ores, so recycling and processing used batteries has certain economic value amid the increasing shortage of production resources.

　　2. Lithium-ion battery recycling and processing technology

　　The recycling process of used lithium-ion batteries mainly includes pre-treatment, secondary treatment and advanced treatment. Since there is still some power left in used batteries, the pretreatment process includes deep discharge process, crushing, and physical sorting; the purpose of secondary treatment is to achieve complete separation of positive and negative active materials from the substrate. Commonly used heat treatment methods and organic solvent dissolution methods , alkali solution dissolution method and electrolysis method to achieve complete separation of the two; advanced treatment mainly includes two processes of leaching and separation and purification to extract valuable metal materials. According to the classification of extraction process, battery recycling methods can be mainly divided into three major categories: dry recycling, wet recycling and biological recycling.

　　1. Dry recycling

　　Dry recycling refers to the direct recovery of materials or valuable metals without using media such as solutions. Among them, the main methods used are physical separation method and high temperature pyrolysis method.

　　(1)Physical sorting method

　　The physical sorting method refers to dismantling and separating the battery, crushing, screening, magnetic separation, fine crushing and classification of battery components such as electrode active materials, current collectors and battery casings, thereby obtaining valuable high-content substances . A method proposed by Shin et al. to recover Li and Co from lithium-ion battery waste liquid using sulfuric acid and hydrogen peroxide includes two processes: physical separation of metal-containing particles and chemical leaching. Among them, the physical separation process includes crushing, screening, magnetic separation, fine crushing and classification. The experiment uses a set of rotating and fixed blade crushers for crushing, uses sieves with different apertures to classify the crushed materials, and uses magnetic separation for further processing to prepare for the subsequent chemical leaching process.

　　Based on the grinding technology and water leaching process developed by Zhang et al., Lee et al., and Saeki et al., Shu et al. developed a new method for recovering cobalt and lithium from lithium-sulfur battery waste using mechanochemical methods. This method uses a planetary ball mill to jointly grind lithium cobalt oxide (LiCoO2) and polyvinyl chloride (PVC) in the air to form Co and lithium chloride (LiCl) in a mechanochemical manner. Subsequently, the ground product is dispersed in water to extract the chloride. Grinding promotes mechanochemical reactions. As grinding proceeds, the extraction yields of both Co and Li increase. 30 minutes of grinding resulted in the recovery of more than 90% of Co and nearly 100% of lithium. At the same time, about 90% of the chlorine in the PVC sample has been converted into inorganic chlorides.

　　The operation of physical sorting method is relatively simple, but it is not easy to completely separate lithium-ion batteries, and mechanical entrainment losses are prone to occur during screening and magnetic separation, making it difficult to achieve complete separation and recovery of metals.

　　(2) High temperature pyrolysis method

　　The high-temperature pyrolysis method refers to decomposing lithium battery materials that have undergone preliminary separation treatment such as physical crushing and decomposing them at high temperature to remove the organic binder and thereby separate the constituent materials of the lithium battery. At the same time, it can also oxidize, reduce and decompose metals and their compounds in lithium batteries, volatilize them in the form of steam, and then collect them by condensation and other methods.

　　When Lee et al. used waste lithium-ion batteries to prepare LiCoO2, they used a high-temperature pyrolysis method. Lee et al. first heat-treated the LIB sample in a muffle furnace at 100-150°C for 1 hour. Second, the heat-treated cells are shredded to release the electrode material. The samples were disassembled using a high-speed crusher designed specifically for this study and classified according to size, ranging from 1 to 50 mm. Then, two steps of heat treatment are performed in the furnace. The first heat treatment is at 100-500°C for 30 minutes, and the second time is at 300-500°C for 1 hour. The electrode material is released from the current collector through vibration screening. Next, the carbon and binder are burned off by burning at a temperature of 500 to 900°C for 0.5 to 2 hours to obtain the cathode active material LiCoO2. Experimental data shows that carbon and binder are burned off at 800°C.

　　High-temperature pyrolysis treatment technology is simple in process, easy to operate, has fast reaction speed and high efficiency in high-temperature environments, and can effectively remove adhesives; and this method does not have high requirements on the composition of raw materials, and is more suitable for processing large amounts or more complex materials. Battery. However, this method has high equipment requirements; during the treatment process, the decomposition of organic matter in the battery will produce harmful gases, which is not friendly to the environment. Purification and recycling equipment needs to be added to absorb and purify harmful gases to prevent secondary pollution. Therefore, the processing cost of this method is higher.

　　2. Wet recycling

　　The wet recycling process is to crush and dissolve the waste batteries, 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, etc., for direct recycling. Wet recycling is more suitable for recycling waste lithium batteries with a relatively single chemical composition. Its equipment investment cost is low, and it is suitable for the recycling of small and medium-sized waste lithium batteries. Therefore, this method is currently widely used.

　　(1)Alkali-acid leaching method

　　Since the cathode material of lithium-ion batteries will not dissolve in alkaline solution, but the base aluminum foil will dissolve in alkaline solution, this method is often used to separate aluminum foil. When Zhang Yang et al. recycle Co and Li in batteries, they leached the aluminum with alkali in advance, and then soaked it with dilute acid to destroy the adhesion between the organic matter and the copper foil. However, the alkali leaching method cannot completely remove PVDF, which has a negative impact on subsequent leaching.

　　Most of the positive active materials in lithium-ion batteries are soluble in acid, so the pre-treated electrode materials can be leached with acid solution to separate the active materials from the current collector, and then combine the principles of neutralization reaction to target the metal. Perform precipitation and purification to achieve the purpose of recovering high-purity components.

　　The acid solutions utilized by the acid leaching method include traditional inorganic acids, including hydrochloric acid, sulfuric acid, and nitric acid. However, since harmful gases such as chlorine (Cl2) and sulfur trioxide (SO3) that have an impact on the environment are often produced during the leaching process using inorganic strong acids, researchers have tried to use organic acids, such as citric acid, to treat waste lithium batteries. , oxalic acid, malic acid, ascorbic acid, glycine, etc. Li et al. used hydrochloric acid to dissolve the recovered electrodes. Since the efficiency of the acid leaching process may be affected by hydrogen ion (H+) concentration, temperature, reaction time and solid-liquid ratio (S/L), in order to optimize the operating conditions of the acid leaching process, experiments were designed to explore the reaction time, H+ concentration and temperature effects. Experimental data show that when the temperature is 80°C, the H+ concentration is 4mol/L, and the reaction time is 2h, the leaching efficiency is the highest, in which 97% of Li and 99% of Co in the electrode material are dissolved. Zhou Tao et al. used malic acid as the leaching agent and hydrogen peroxide as the reducing agent to perform reduction leaching of the pretreated cathode active material, and studied the effects of different reaction conditions on the leaching rates of Li, Co, Ni, and Mn in the malic acid leaching solution, thereby finding out find the best reaction conditions. Research data shows that when the temperature is 80°C, the malic acid concentration is 1.2mol/L, the liquid-liquid volume ratio is 1.5%, the solid-liquid ratio is 40g/L, and the reaction time is 30 minutes, the efficiency of malic acid leaching is the highest, among which Li, The leaching rates of Co, Ni and Mn reached 98.9%, 94.3%, 95.1% and 96.4% respectively. However, compared with inorganic acids, the cost of leaching with organic acids is higher.

　　(2) Organic solvent extraction method

　　The organic solvent extraction method uses the principle of "similar compatibility" and uses a suitable organic solvent to physically dissolve the organic binder, thereby weakening the adhesion between the material and the foil and separating the two.

　　Contestabile et al. used N-methylpyrrolidone (NMP) to selectively separate components in order to better recover the active materials of the electrode when recycling lithium cobalt oxide batteries. NMP is a good solvent for PVDF (solubility is about 200g/kg), and its boiling point is relatively high, about 200°C. The study utilized NMP to treat the active material at approximately 100°C for 1 h, effectively achieving the separation of the film from its support and thus recovering the metallic form of Cu by simply filtering it out of the NMP (N-methylpyrrolidone) solution. and Al. Another benefit of this method is that the recovered Cu and Al metals can be directly reused after sufficient cleaning. In addition, recovered NMP can be recycled. Because of its high solubility in PVDF, it can be reused many times. Zhang et al. used trifluoroacetic acid (TFA) to separate the cathode material from the aluminum foil when recycling cathode waste for lithium-ion batteries. The waste lithium-ion batteries used in the experiment used polytetrafluoroethylene (PTFE) as an organic binder. The effects of TFA concentration, liquid-to-solid ratio (L/S), reaction temperature and time on the separation efficiency of cathode materials and aluminum foil were systematically studied. . Experimental results show that in a TFA solution with a mass fraction of 15, a liquid-to-solid ratio of 8.0 mL/g, a reaction temperature of 40°C, and a reaction of 180 minutes with appropriate stirring, the cathode material can be completely separated.

　　The experimental conditions for using organic solvent extraction to separate materials and foils are relatively mild, but organic solvents have certain toxicity and may be harmful to the health of operators. At the same time, because different manufacturers have different processes for making lithium-ion batteries, they choose different binders. Therefore, manufacturers need to choose different organic solvents when recycling used lithium batteries for different manufacturing processes. In addition, for large-scale recycling processing operations at an industrial level, cost is also an important consideration. Therefore, it is very important to choose a solvent with wide sources, affordable price, low toxicity and harmlessness, and wide applicability.

　　(3) Ion exchange method

　　The ion exchange method refers to the use of different adsorption coefficients of ion exchange resins for the metal ion complexes to be collected to achieve metal separation and extraction. After Wang Xiaofeng et al. acid leached the electrode material, they added an appropriate amount of ammonia to the solution to adjust the pH value of the solution and react with the metal ions in the solution to generate [Co(NH3)6]2+, [Ni(NH3) 6]2+ and other complex ions, and continuously pass pure oxygen into the solution for oxidation. Then, ammonium sulfate solutions of different concentrations are repeatedly passed through the weakly acidic cation exchange resin to selectively elute the nickel complex and trivalent cobalt ammonia complex on the ion exchange resin. Finally, a 5% H2SO4 solution is used to completely elute the cobalt complex, while the cation exchange resin is regenerated, and oxalate is used to recover the cobalt and nickel metals in the eluent respectively. The ion exchange method has a simple process and is relatively easy to operate.

　　3.Biological recycling

　　Mishra et al. used inorganic acid and acidophilic Thiobacillus ferrooxidans to leach metals from used lithium-ion batteries, and used S and ferrous ions (Fe2+) to generate H2SO4, Fe3+ and other metabolites in the leaching medium. These metabolites help dissolve metals in spent batteries. Research has found that cobalt biodissolves faster than lithium. As the dissolution process proceeds, iron ions react with metals in the residue and precipitate, causing the concentration of ferrous ions in the solution to decrease. As the metal concentration in the waste sample increases, the growth of cells is prevented and the dissolution rate slows down. . In addition, a higher solid/liquid ratio also affects the rate of metal dissolution. Zeng et al. used Thiobacillus acidophilus to bioleach metal cobalt from used lithium-ion batteries. Different from Mishra et al., this study used copper as a catalyst to analyze the effect of copper ions on the bioleaching of LiCoO2 by Thiobacillus acidophilus. . The results show that almost all cobalt (99.9%) enters the solution after 6 days of bioleaching when the Cu ion concentration is 0.75g/L, while in the absence of copper ions, only 43.1% of the cobalt enters the solution after 10 days of reaction time. Cobalt dissolves. In the presence of copper ions, the cobalt dissolution efficiency of spent lithium-ion batteries increases. In addition, Zeng et al. also studied the catalytic mechanism and explained the dissolution effect of copper ions on cobalt. LiCoO2 and copper ions undergo a cation exchange reaction to form copper cobaltate (CuCo2O4) on the surface of the sample, which is easily dissolved by iron ions.

　　The bioleaching method has low cost, high recovery efficiency, less pollution and consumption, less impact on the environment, and the microorganisms can be reused. However, it is difficult to cultivate high-efficiency microbial fungi, long processing cycle, and control of leaching conditions are several major problems required by this method.

　　4.Joint recycling method

　　Each waste lithium battery recycling process has its own advantages and disadvantages. Currently, there is research on recycling methods that combine and optimize multiple processes to give full play to the advantages of various recycling methods and maximize economic benefits.

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