Foreign lithium-ion battery recycling technology route

The lithium ion battery is composed of a positive and negative electrode sheet, a binder, an electrolyte, a separator, and the like. In the industry, manufacturers mainly use lithium cobaltate, lithium manganate, lithium nickel cobalt 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 positive electrode binder with high viscosity, good chemical stability and physical properties. Industrially produced lithium ion batteries mainly use a solution of lithium hexafluorophosphate (LiPF6) and an organic solvent as an electrolyte, and an organic film such as porous polyethylene (PE) and polypropylene (PP) is used as a separator of the battery. Lithium-ion batteries are generally considered to be environmentally friendly and non-polluting green batteries, but improper recycling of lithium-ion batteries can also cause pollution. Although lithium-ion batteries do not contain toxic heavy metals such as mercury, cadmium, and lead, the positive and negative materials and electrolytes of batteries still have a large impact on the environment and the human body. If ordinary garbage disposal methods are used to treat 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, dust pollution, acid and alkali pollution. Lithium-ion electrolyte machine converters such as LiPF6, lithium hexafluoroantimonate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), hydrofluoric acid (HF), etc., solvents and hydrolysates such as ethylene glycol dimethyl ether ( DME), methanol, formic acid, etc. are all toxic substances. Therefore, used lithium-ion batteries need to be recycled to reduce the harm to the natural environment and human health.

First, the production and use of lithium-ion batteries

Lithium-ion batteries are widely used in electronic products such as mobile phones, tablets, notebook computers and digital cameras because of their high energy density, high voltage, low self-discharge, good cycle performance, safe operation, and relative natural environment. Wait. In addition, lithium-ion batteries are widely used in energy storage systems such as hydropower, firepower, wind power and solar energy, and have gradually become the best choice for power batteries . The emergence of lithium iron phosphate battery has promoted the development and application of lithium-ion batteries in the electric vehicle industry. With the increasing demand for electronic products and the speed of electronic product replacement, and the rapid development of new energy vehicles, the demand for lithium-ion batteries in the global market 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 used 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 response to the huge market Demand, manufacturers need to produce a large number of lithium-ion batteries to supply the market. At present, the cathode material for producing lithium ion batteries mainly includes lithium cobaltate, lithium manganate, lithium nickel cobalt manganese oxide ternary material and lithium iron phosphate, so the waste lithium ion battery contains more cobalt (Co) and 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 China, mainly in the form of imports Meet the growing demand [3]. The content of some metals in the waste lithium ion battery is higher than the content of metal in the natural ore. Therefore, in the case of an increasingly shortage of production resources, recycling and disposal of used batteries has certain economic value.

Second, lithium ion battery recycling technology

The recycling process of waste lithium ion batteries mainly includes pretreatment, secondary treatment and advanced treatment. Since some electricity remains in the used battery, the pretreatment process includes deep discharge process, crushing, and physical sorting; the purpose of the secondary treatment is to achieve complete separation of the positive and negative active materials from the substrate, and common heat treatment methods and organic solvent dissolution methods. The lye dissolution method and the electrolysis method are used to achieve complete separation of the two; the deep treatment mainly includes two processes of leaching, separation and purification, and extracting valuable metal materials [4]. According to the extraction process classification, the battery recycling methods can be mainly divided into three categories: dry recovery, wet recovery and biorecycling.

Dry recycling

Dry recycling refers to the direct recovery of materials or valuable metals without passing through a medium such as a solution. Among them, the main methods used are physical sorting and high temperature pyrolysis.

(1) Physical sorting method

The physical sorting method refers to disassembling and separating the battery, and crushing, sieving, magnetic separation, fine pulverization and classification of the battery components such as the electrode active material, the current collector and the battery casing, thereby obtaining a valuable high-content substance. . A method proposed by Shin et al. for recovering Li and Co from lithium ion battery waste liquid by using sulfuric acid and hydrogen peroxide includes two processes of physically separating metal-containing particles and chemical leaching. Among them, the physical separation process includes crushing, sieving, magnetic separation, fine crushing and classification. The experiment uses a set of rotating and fixed blade crushers for crushing. The crushed materials are classified by sieves with different pore sizes, and separated by magnetic force for further processing to prepare for the subsequent chemical leaching process.

Shu et al. developed a new method for recovering cobalt and lithium from lithium-sulfur battery waste by mechanochemical methods based on the grinding technology and water leaching process developed by Zhang et al., Lee et al. and Saeki et al. The method uses a planetary ball mill to co-mill lithium cobaltate (LiCoO 2 ) and polyvinyl chloride (PVC) in air to form Co and lithium chloride (LiCl) in a mechanochemical manner. Subsequently, the ground product was dispersed in water to extract chloride. Grinding promotes mechanochemical reactions. As the grinding progresses, the extraction yields of Co and Li are both improved. Grinding for 30 minutes resulted in the recovery of more than 90% Co and nearly 100% lithium. At the same time, about 90% of the chlorine in the PVC samples has been converted to inorganic chlorides.

The operation of the physical sorting method is relatively simple, but it is not easy to completely separate the lithium ion battery, and in the screening and magnetic separation, the mechanical entrainment loss is liable to occur, and it is difficult to achieve complete separation and recovery of the metal.

(2) High temperature pyrolysis

The high-temperature pyrolysis method refers to a lithium battery material which is subjected to preliminary separation treatment such as physical crushing, is subjected to high-temperature pyrolysis decomposition, and the organic binder is removed to separate the constituent materials of the lithium battery. At the same time, the metal and its compounds in the lithium battery can be redoxed and decomposed, volatilized in the form of steam, and then collected by condensation or the like.

When Lee et al. used Lithium-ion batteries to prepare LiCoO2, a high-temperature pyrolysis method was used. Lee et al first heat-treated the LIB sample in a muffle furnace at 100-150 ° C for 1 h. Next, the heat treated battery is chopped to release the electrode material. The samples were disassembled using a high-speed pulverizer designed for the study, sorted by size, and ranged from 1 to 50 mm. Then, a two-step heat treatment was carried out in the furnace, the first heat treatment at 100 to 500 ° C for 30 min, and the second heat treatment at 300 to 500 ° C for 1 h, and the electrode material was released from the current collector by vibration screening. Next, by burning at a temperature of 500 to 900 ° C for 0.5 to 2 h, the carbon and the binder are burned off to obtain a cathode active material LiCoO 2 . Experimental data shows that carbon and binder are burned off at 800 °C.

The high-temperature pyrolysis treatment technology is simple in process, convenient in operation, fast in reaction under high temperature environment, high in efficiency, and capable of effectively removing binder; and the method has low requirements on the composition of raw materials, and is suitable for processing large or complex ones. battery. However, the method has high requirements on equipment; in the process of treatment, the decomposition of organic matter of the battery may generate harmful gas, which is unfriendly to the environment, and needs to increase purification and recovery equipment, absorb and purify harmful gases, and prevent secondary pollution. Therefore, the processing cost of this method is high.

2. Wet recycling

The wet recovery process is to dissolve the waste battery and then dissolve it, and then selectively separate the metal element in the leaching solution by using a suitable chemical reagent to produce a high-grade cobalt metal or lithium carbonate, and directly recover it. The wet recycling process is more suitable for recycling waste lithium batteries with relatively simple chemical composition, and the equipment investment cost is low, which is suitable for the recovery of small and medium-sized waste lithium batteries. Therefore, the method is currently widely used.

(1) Alkali-acid leaching

Since the positive electrode material of the lithium ion battery is not soluble in the alkali liquid, and the base aluminum foil is dissolved in the alkali liquid, the method is commonly used to separate the aluminum foil. Zhang Yang et al [10] in the recovery of Co and Li in the battery, pre-impregnated aluminum with alkali, and then used dilute acid solution to destroy the adhesion of organic matter and copper foil. However, the alkali leaching method does not completely remove PVDF and has an adverse effect on subsequent leaching.

Most of the positive active materials in the lithium ion battery can be dissolved in the acid, so the pretreated electrode material can be leached with the acid solution to separate the active material from the current collector, and the principle of the neutralization reaction can be combined with the target metal. Precipitation and purification are carried out for the purpose of recovering high purity components.

The acid solution used in the acid leaching method has a conventional inorganic acid, including hydrochloric acid, sulfuric acid, and nitric acid. However, due to the influencing of environmentally harmful gases such as chlorine (Cl2) and sulfur trioxide (SO3) during the leaching process with inorganic strong acids, researchers have tried to use organic acids to treat used lithium batteries, such as citric acid , oxalic acid, malic acid, ascorbic acid, glycine and the like. Li et al. used hydrochloric acid to dissolve the recovered electrode. 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 investigate the reaction time and H+ concentration and the effect of temperature. The experimental data showed that when the temperature was 80 °C, the H+ concentration was 4mol/L. The reaction time was 2 h, and the leaching efficiency was the highest. Among them, 97% of Li and 99% of Co in the electrode material were dissolved. Zhou Tao et al. used malic acid as leaching agent and hydrogen peroxide as reducing agent to reduce the leaching of 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. The optimal reaction conditions are obtained. The research data showed that when the temperature was 80 ° C, the concentration of malic acid was 1.2 mol / L, the volume ratio of liquid to liquid was 1.5%, the ratio of solid to liquid was 40 g / L, and the reaction time was 30 min, the efficiency of leaching with malic acid was 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, the cost of leaching with organic acids is higher than that of inorganic acids.

(2) Organic solvent extraction

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

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

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

(3) Ion exchange method

The ion exchange method refers to the separation and extraction of metal by the difference in the adsorption coefficient of the metal ion complex to be collected by the ion exchange resin. Xiaofeng Wang waited for the electrode material to undergo acid leaching treatment, added an appropriate amount of ammonia water to the solution, adjusted the pH value of the solution, and reacted with the metal ions in the solution to form [Co(NH3)6]2+, [Ni Complex ions such as (NH3)6]2+ are continuously oxidized by introducing pure oxygen into the solution. Then, the nickel complex and the trivalent cobalt ammine complex on the ion exchange resin are selectively eluted by repeatedly passing the weakly acidic cation exchange resin with different concentrations of ammonium sulfate solution. Finally, the cobalt complex was completely eluted with a 5% H2SO4 solution while the cation exchange resin was regenerated, and the cobalt and nickel metal in the eluate were separately recovered by using the oxalate. The ion exchange process is simple and easy to operate.

3. Bio-recycling

Mishra et al. use mineral acid and acidophilic Thiobacillus ferrooxidans to leach metal from waste lithium ion batteries, and use S and ferrous ions (Fe2+) to form metabolites such as H2SO4 and Fe3+ in the leaching medium. These metabolites help dissolve the metal in the spent battery. Studies have found that cobalt bio-dissolution is faster than lithium. As the dissolution process progresses, the iron ions react with the metal in the residue to precipitate, resulting in a decrease in the concentration of ferrous ions in the solution, and as the metal concentration in the waste sample increases, cell growth is prevented and the dissolution rate is slowed down. . In addition, a higher solid/liquid ratio also affects the rate at which the metal dissolves. Zeng et al. used biodegradation of metal cobalt in waste lithium ion batteries by acidophilic Thiobacillus ferrooxidans. Unlike Mishra, the 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 at a Cu ion concentration of 0.75 g/L, and in the absence of copper ions, only 43.1% after 10 days of reaction time. Cobalt is dissolved. In the presence of copper ions, the cobalt dissolution efficiency of the spent lithium ion battery is improved. In addition, Zeng et al. also studied the catalytic mechanism and explained the dissolution of cobalt by copper ions. LiCoO2 reacted with copper ions to form copper cobaltate (CuCo2O4) on the surface of the sample, which was easily dissolved by iron ions.

The bioleaching method has low cost, high recovery efficiency, less pollution and consumption, less environmental impact, and microbes can be reused. However, the cultivation of highly efficient microbial fungi, long treatment cycles, and control of leaching conditions are several major problems required by this method.

4. Joint recycling method

Waste lithium battery recycling processes have their own advantages and disadvantages. At present, there are joint and optimized recycling methods for various processes to fully exploit the advantages of various recycling methods to maximize economic benefits. Figure 1 is a process flow diagram of one of the combined recovery methods.

Third, foreign major lithium-ion battery recycling company and its technology

1. Belgium Umicore Corporation

The Umicore company in Belgium independently developed the ValEas process. For battery recycling, they custom-made a furnace that uses high-temperature metallurgy to process lithium-ion batteries and prepare cobalt hydroxide/cobalt chloride [Co(OH)2/CoCl2]. Graphite and organic solvents can be used as fuel. This process does not require the battery to be broken, so as to avoid the problem of difficult to break the problem and reduce the safety risk of the recycling process. Moreover, the recovered Co compound has a high purity, and can be directly returned to the production of a lithium battery as a raw material to realize recycling of the metal. In this method, while recovering valuable metals such as Co, Ni, Mn, and Cu, materials such as plastics, graphite, and aluminum foil in the battery are also reused. The recycling process is relatively simple and environmentally friendly. Umicore's Hoboken plant in Belgium handles about 7,000 tons of used lithium batteries every year.

2. Toxco Corporation of the United   States

Toxco achieved commercialization of lithium-ion battery recycling in 1993. The company mainly uses mechanical and hydrometallurgical processes to recover metals such as Cu, Al, Fe and Co in batteries. The company's recycling process can be carried out in a lower temperature environment, and the gas emissions are small, achieving 60% battery material recovery.

3. Japan OnTo Company

OnTo has developed the Eco-Bat process exclusively. The process flow is shown in Figure 3. The battery is first placed in a dry, pressure- and temperature-compatible environment, and the electrolyte in the battery is dissolved in liquid carbon dioxide (CO2) and transported to a recovery container. Thereafter, CO 2 is vaporized by changing the temperature and pressure, thereby allowing the electrolyte to precipitate therefrom. This process does not need to be carried out at high temperatures and requires very little energy to be consumed. The process mainly uses the supercritical fluid CO2 as a carrier to carry out the battery electrolyte, and then injects a new electrolyte to restore the capacity of the lithium ion battery.

Fourth, summary

With the rapid replacement of electronic products, a large number of used lithium batteries are produced every year, and due to the development of new energy vehicles, there will be more used lithium batteries in the future. Since untreated used batteries can pollute the environment and the metal resources such as lithium and cobalt used to produce lithium-ion batteries are scarce, recycling and disposal of used lithium-ion batteries has certain environmental safety protection and economic value. Among several technologies for recycling and disposing of used lithium-ion batteries, wet method is currently the most used technology, and bio-leaching technology is at the forefront of the field, and several methods have their own advantages and disadvantages. Therefore, it is the key to find a suitable recycling process, to take advantage of various technologies, to recover renewable resources as much as possible, and to improve the economic benefits of recycling. In addition, countries such as the United States, Japan, Europe and other countries have established relevant laws and waste battery recycling systems, such as power battery cascade recycling mode, while China has the technical means of recycling and disposing of used lithium batteries, but has not yet established a suitable recycling system. And lack of corresponding laws and regulations. In the future, the state should establish effective laws and regulations, and establish a suitable recycling system for used batteries to realize industrial recycling and disposal of used lithium batteries to ensure sustainable development.

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