Lithium-ion batteries are composed of positive and negative electrodes, binders, electrolytes, and separators. In industry, manufacturers mainly use lithium cobalt oxide, lithium manganese oxide, nickel-cobalt lithium manganese oxide ternary materials, and lithium iron phosphate as positive electrode materials for lithium-ion batteries, and natural graphite and artificial graphite as negative electrode active materials. Polyvinylidene fluoride (PVDF) is a widely used cathode binder with high viscosity, good chemical stability and physical properties. Industrially produced lithium-ion batteries mainly use lithium hexafluorophosphate (LiPF6) and an organic solvent solution as the electrolyte, and use organic membranes, such as porous polyethylene (PE) and polypropylene (PP) polymers, as the separator of the battery. Lithium-ion batteries are generally considered to be environmentally friendly and pollution-free green batteries, but improper recycling of lithium-ion batteries will also cause pollution. Although lithium-ion batteries do not contain toxic heavy metals such as mercury, cadmium, and lead, the positive and negative electrode materials and electrolytes of the battery still have a relatively large impact on the environment and human body. If ordinary waste treatment methods are used to dispose of lithium-ion batteries (landfill, incineration, composting, etc.), metals such as cobalt, nickel, lithium, manganese, and various organic and inorganic compounds in the battery will cause metal pollution, organic pollution, and dust pollution. , Acid-base pollution. Lithium-ion electrolyte machine conversion products, such as LiPF6, lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), hydrofluoric acid (HF), etc., solvents and hydrolysis products such as ethylene glycol dimethyl ether ( DME), methanol, formic acid, etc. are all toxic substances. Therefore, waste lithium-ion batteries need to be recycled to reduce the harm to the natural environment and human health.
- Production and use of lithium-ion batteries
Lithium-ion batteries have the advantages of high energy density, high voltage, small self-discharge, good cycle performance, safe operation, etc., and are relatively friendly to the natural environment, so they are widely used in electronic products such as mobile phones, tablets, laptops, and digital cameras Wait. In addition, lithium-ion batteries are widely used in energy storage power systems such as water power, fire power, wind power and solar power, and have gradually become the best choice for power batteries. The emergence of lithium iron phosphate batteries has promoted the development and application of lithium-ion batteries in the electric vehicle industry. With the gradual increase of people's demand for electronic products and the gradual acceleration of the upgrading of electronic products, and the impact of the rapid development of new energy vehicles, the global market demand for lithium-ion batteries is increasing, and the growth rate of battery production is increasing year by year.
The huge demand for lithium-ion batteries in the market, on the one hand, will lead to a large number of waste batteries in the future. How to deal with these waste lithium-ion batteries to reduce their impact on the environment is an urgent problem to be solved; on the other hand, in order to cope with the huge market Demand, manufacturers need to produce a large number of lithium-ion batteries to supply the market. At present, the positive electrode materials for the production of lithium-ion batteries mainly include lithium cobalt oxide, lithium manganese oxide, nickel-cobalt lithium manganese oxide ternary materials and lithium iron phosphate, etc. Therefore, waste lithium-ion batteries contain more cobalt (Co), lithium (Li), nickel (Ni), manganese (Mn), copper (Cu), iron (Fe) and other metal resources, which contain a variety of rare metal resources, cobalt is a scarce strategic metal in my country, mainly in the form of imports To meet the growing demand [3]. Part of the metal content in waste lithium-ion batteries is higher than that in natural ores, so it has certain economic value to recycle waste batteries under the condition of increasing shortage of production resources.Also read:48v 200ah lifepo4 battery pack
- Lithium-ion battery recycling technology
The recycling process of waste lithium-ion batteries mainly includes pretreatment, secondary treatment and advanced treatment. Since there is still some electricity left in the used battery, the pretreatment process includes deep discharge process, crushing, and physical separation; the purpose of the secondary treatment is to realize the complete separation of positive and negative active materials from the substrate, and heat treatment and organic solvent dissolution are commonly used. , alkaline solution and electrolysis to achieve complete separation of the two; advanced treatment mainly includes two processes of leaching and separation and purification to extract valuable metal materials [4]. According to the classification of extraction process, battery recycling methods can be mainly divided into three categories: dry recycling, wet recycling and biological recycling.
- Dry recycling
Dry recycling refers to the direct recovery of materials or valuable metals without using a medium such as a solution. Among them, the main methods used are physical separation method and high temperature pyrolysis method.
(1) Physical sorting method
The physical separation method refers to the disassembly and separation of batteries, and the battery components such as electrode active materials, current collectors and battery casings are crushed, sieved, magnetically separated, finely crushed and classified to obtain valuable high-content substances. . A method proposed by Shin et al. using sulfuric acid and hydrogen peroxide to recover Li and Co from lithium-ion battery waste liquid 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. In the experiment, a group of crushers with rotating and fixed blades were used for crushing, and sieves with different apertures were used to classify the crushed materials, and magnetic separation was used 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. The method uses a planetary ball mill to co-grind lithium cobaltate (LiCoO2) and polyvinyl chloride (PVC) in air to mechanochemically form Co and lithium chloride (LiCl). Subsequently, the milled product was dispersed in water to extract chlorides. Grinding promotes mechanochemical reactions. The extraction yields of both Co and Li were improved with the grinding progress. 30 min of grinding resulted in the recovery of more than 90% Co and nearly 100% Li. At the same time, about 90% of the chlorine in the PVC sample had been converted to inorganic chlorides.
The physical separation method is relatively simple to operate, 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 the decomposition of lithium battery materials that have undergone preliminary separation treatment such as physical crushing, and is fired and decomposed at high temperature to remove the organic binder, thereby separating the constituent materials of the lithium battery. At the same time, it can also redox and decompose the metals and their compounds in the lithium battery, volatilize 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 h. Second, the heat-treated battery is shredded to release the electrode material. The samples were disassembled with a high-speed pulverizer specially designed for this study, and classified according to size, ranging from 1 to 50 mm. Then, two steps of heat treatment are carried out in the furnace, the first heat treatment is at 100-500°C for 30 minutes, the second heat treatment is at 300-500°C for 1 hour, and the electrode material is released from the current collector through vibration screening. Next, by firing at a temperature of 500-900° C. for 0.5-2 hours, the carbon and the binder are burned off, and the cathode active material LiCoO2 is obtained. Experimental data show that carbon and binder are burned off at 800°C.
The high-temperature pyrolysis treatment technology has simple process, convenient operation, fast reaction speed and high efficiency in high-temperature environment, and can effectively remove binders; and this method does not have high requirements on the composition of raw materials, and is more suitable for processing a large amount or more complex Battery. However, this method requires high equipment; during the treatment process, the decomposition of organic matter in the battery will produce harmful gases, which is not friendly to the environment. It is necessary to increase purification and recovery equipment to absorb and purify harmful gases and prevent secondary pollution. Therefore, the processing cost of this method is high.
- 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, and its equipment investment cost is low, which is suitable for the recycling of small and medium-sized waste lithium batteries. Therefore, this method is widely used at present.
(1) Alkali-acid leaching method
Since the positive electrode material of lithium-ion batteries will not dissolve in lye, but the base aluminum foil will dissolve in lye, this method is often used to separate aluminum foil. Zhang Yang et al [10] used alkali leaching to remove aluminum in advance when recovering Co and Li in the battery, and then soaked in dilute acid solution to destroy the adhesion of organic matter and copper foil. However, the alkaline leaching method cannot completely remove PVDF, which has adverse effects on subsequent leaching.
Most of the positive electrode active materials in lithium-ion batteries can be dissolved in acid, so the pre-treated electrode materials can be leached with acid solution to realize the separation of active materials and current collectors, and then combined with the principle of neutralization reaction to target metals Precipitation and purification are carried out to achieve the purpose of recovering high-purity components.
The acid solution used by the pickling method includes traditional inorganic acids, including hydrochloric acid, sulfuric acid and nitric acid. However, since harmful gases such as chlorine (Cl2) and sulfur trioxide (SO3) are often produced in the process of leaching with inorganic strong acids, researchers try to use organic acids to treat waste lithium batteries, such as citric acid , 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 the 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, an experiment was designed to investigate the reaction time, H+ concentration and temperature effects. The 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 leaching agent and hydrogen peroxide as reducing agent to reduce and leaching the positive electrode active material obtained by pretreatment, and studied the influence of different reaction conditions on the leaching rate of Li, Co, Ni, and Mn in malic acid leaching solution, so as to find out the best reaction conditions. Research data show that when the temperature is 80°C, the malic acid concentration is 1.2mol/L, the liquid-to-liquid volume ratio is 1.5%, the solid-to-liquid ratio is 40g/L, and the reaction time is 30min, the leaching efficiency of malic acid 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 utilizes 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 the components in order to better recover the active material of the electrode when recycling lithium cobalt oxide batteries. NMP is a good solvent for PVDF (solubility about 200g/kg) and has a relatively high boiling point of about 200°C. Treatment of the active material with NMP at approximately 100 °C for 1 h effectively achieved the separation of the film from its support and thus the recovery of Cu in metallic form by simply filtering it out of the NMP (N-methylpyrrolidone) solution. and Al. Another benefit of this method is that the recovered metals, Cu and Al, can be directly reused after adequate 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 battery used in the experiment used polytetrafluoroethylene (PTFE) as an organic binder, and the effects of TFA concentration, liquid-solid ratio (L/S), reaction temperature and time on the separation efficiency of cathode materials and aluminum foil were systematically studied . The experimental results show that in the TFA solution with a mass fraction of 15, the liquid-solid ratio is 8.0mL/g, and the reaction temperature is 40℃, the cathode material can be completely separated under proper stirring for 180min.
The experimental conditions of using organic solvent extraction to separate materials and foils are relatively mild, but organic solvents are toxic to a certain extent and may cause harm 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, according to different manufacturing processes, manufacturers need to choose different organic solvents when recycling waste lithium batteries. In addition, cost is also an important consideration for large-scale recycling operations at an industrial level. Therefore, it is very important to choose a solvent with wide sources, reasonable price, low toxicity and harmlessness, and wide applicability.Also read:48v lithium ion battery 400ah
(3) Ion exchange method
The ion exchange method refers to the separation and extraction of metals by using the different adsorption coefficients of ion exchange resins to the metal ion complexes to be collected. Wang Xiaofeng [16] et al. added an appropriate amount of ammonia water to the solution after acid leaching treatment, adjusted the pH value of the solution, and reacted with 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 used to repeatedly pass through the weakly acidic cation exchange resin to selectively elute the nickel complex and the trivalent cobalt ammonium complex on the ion exchange resin respectively. Finally, 5% H2SO4 solution was used to completely elute the cobalt complex, and at the same time, the cation exchange resin was regenerated, and the cobalt and nickel metals in the eluent were respectively recovered by using oxalate. The ion exchange method has a simple process and is relatively easy to operate.
- Biological recycling
Mishra et al. used inorganic acids and acidophilic Thiobacillus ferrooxidans to leach metals from waste lithium-ion batteries, and used S and ferrous ions (Fe2+) to generate metabolites such as H2SO4 and Fe3+ in the leaching medium. These metabolites help dissolve metals in spent batteries. The study found that cobalt biodissolves faster than lithium. As the dissolution process proceeds, ferric ions react with the metals in the residue to precipitate, resulting in a decrease in the concentration of ferrous ions in the solution, and as the concentration of metals in the waste sample increases, cell growth is prevented and the rate of dissolution slows down . In addition, a higher solid/liquid ratio also affects the rate of metal dissolution. Zeng et al. used acidic Thiobacillus ferrooxidans to bioleave cobalt metal in waste lithium-ion batteries. Unlike Mishra et al., this study used copper as a catalyst to analyze the effect of copper ions on acidophilic Thiobacillus ferrooxidans on LiCoO2 bioleaching . The results showed that almost all of the cobalt (99.9%) entered the solution after 6 days of bioleaching at a Cu ion concentration of 0.75 g/L, whereas only 43.1% of Cobalt dissolves. In the presence of copper ions, the cobalt dissolution efficiency of spent lithium-ion batteries is enhanced. In addition, Zeng et al. also studied the catalytic mechanism and explained the dissolution 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 microorganisms can be reused. However, the cultivation of high-efficiency microbial fungi is difficult, the treatment cycle is long, and the control of leaching conditions are several major problems required by this method.
- Combined recycling method
Waste lithium battery recycling processes have their own advantages and disadvantages. At present, there have been researches on recycling methods that combine and optimize multiple processes in order to give full play to the advantages of various recycling methods and maximize economic benefits. Figure 1 is a process flow diagram of one of the combined recovery methods.
Figure 1 is a process flow diagram of a combined recovery method
- Major foreign lithium-ion battery recycling companies and their processes
- Umicore, Belgium
Belgian Umicore company independently developed the ValEas process. For battery recycling, they custom-built a furnace that uses pyrometallurgy to process lithium-ion batteries and produce cobalt hydroxide/cobalt chloride [Co(OH)2/CoCl2], graphite and organic solvents can be used as fuel. This process does not need to break the battery to solve the problem, thereby avoiding the problem of difficulty in solving the problem and reducing the safety risk in the recycling process. Moreover, the recovered Co compound has a high purity and can be directly returned to the production of lithium batteries as a raw material to realize metal recycling. In this method, while recovering valuable metals such as Co, Ni, Mn, and Cu, materials such as plastics, graphite, and aluminum foil in batteries are also reused. The recycling process is relatively simple and environmentally friendly. Umicore's Hoboken factory in Belgium processes about 7,000 tons of waste lithium batteries every year.
- American Toxco company
Toxco Corporation commercialized lithium-ion battery recycling in 1993. The company mainly uses mechanical and hydrometallurgical processes to recycle Cu, Al, Fe, Co and other metals in batteries. The company's recycling process can be carried out in a lower temperature environment, with low gas emissions, and can achieve 60% battery material recovery. The company's recycling process is shown in Figure 2.
Figure 2 Toxco's process flow chart for recycling lithium-ion batteries
- Japan OnTo Company
OnTo exclusively developed the Eco-Bat process. The process flow is shown in Figure 3. First place the battery in a dry environment with suitable pressure and temperature, dissolve the electrolyte in the battery with liquid carbon dioxide (CO2), and transport it to a recycling container. Afterwards, the CO2 is vaporized by changing the temperature and pressure, allowing the electrolyte to precipitate out of it. The process does not require high temperatures and consumes very little energy. This process mainly uses supercritical fluid CO2 as a carrier to take out the battery electrolyte, and then inject new electrolyte to restore the capacity of lithium-ion batteries.Also read:10kwh lithium battery 48v
Figure 3 OnTo company recycling lithium-ion battery process flow chart
Four. Summary
With the rapid replacement of electronic products, a large number of waste lithium batteries are produced every year, and affected by the development of new energy vehicles, there will be more waste lithium batteries in the future. Since untreated waste batteries will pollute the environment, and metal resources such as lithium and cobalt used to produce lithium-ion batteries are in short supply, recycling waste lithium-ion batteries has certain environmental safety protection and economic value. Among several technologies for recycling waste lithium-ion batteries, wet method is currently the most used technology, and bioleaching technology is the frontier of this field. Several methods have their own advantages and disadvantages. Therefore, it is the key to seek a suitable recycling process that can take advantage of various technologies, recycle renewable resources as much as possible, and improve the economic benefits of recycling. In addition, countries and regions such as the United States, Japan, and Europe have established relevant laws and waste battery recycling systems, such as the power battery cascade recycling model. Although my country has technical means to recycle waste lithium batteries, it has not yet established a suitable recycling system. , and the lack of corresponding laws and regulations. In the future, the country should establish effective laws and regulations, and establish a suitable waste battery recycling system to realize industrialized recycling of waste lithium batteries and ensure sustainable development.