Analysis of international button battery cr2032 recycling technology routes

Lithium-ion batteries are composed of positive and negative electrodes, binders, electrolytes and diaphragms. 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 positive electrode binder with high viscosity and good chemical stability and physical properties. Industrially produced lithium-ion batteries mainly use electrolyte lithium hexafluorophosphate (LiPF6) and organic solvents as electrolytes, and use organic membranes such as porous polyethylene (PE) and polypropylene (PP) polymers as battery diaphragms. 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 batteries still have a great impact on the environment and human body. If lithium-ion batteries are treated by ordinary garbage disposal methods (landfill, incineration, composting, etc.), metals such as cobalt, nickel, lithium, and manganese in the battery, as well as various organic and inorganic compounds, will cause metal pollution, organic pollution, dust pollution, and 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.

1. Production and use of lithium-ion batteries

Lithium-ion batteries have the advantages of high energy density, high voltage, low self-discharge, good cycle performance, safe operation, and are relatively friendly to the natural environment. Therefore, they are widely used in electronic products such as mobile phones, tablets, laptops, and digital cameras. In addition, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal 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 increasing demand for electronic products and the accelerated replacement 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 market demand for lithium-ion batteries 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 producing lithium-ion batteries mainly include lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese oxide ternary materials and lithium iron phosphate. Therefore, waste lithium-ion batteries contain a large amount of metal resources such as cobalt (Co), lithium (Li), nickel (Ni), manganese (Mn), copper (Cu), and iron (Fe), including a variety of rare metal resources. Cobalt is a scarce strategic metal in my country, and is mainly imported to meet the growing demand [3]. The content of some metals in waste lithium-ion batteries is higher than that in natural ores. Therefore, in the case of increasing shortage of production resources, recycling and processing waste batteries has certain economic value.

2. Lithium-ion battery recycling and processing technology

The recycling and processing process of waste lithium-ion batteries mainly includes pretreatment, secondary treatment and deep treatment. Since there is still some electricity left in the waste 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 methods include heat treatment, organic solvent dissolution, alkaline solution dissolution, and electrolysis to achieve complete separation of the two; deep treatment mainly includes two processes: leaching and separation and purification, to extract valuable metal materials [4]. According to the extraction process, battery recycling methods can be mainly divided into three major categories of technology: dry recycling, wet recycling, and biological recycling.

1. 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 sorting and high-temperature pyrolysis.

(1) Physical sorting method

Physical sorting method refers to disassembling and separating the battery, crushing, screening, magnetic separation, fine grinding and classification of battery components such as electrode active materials, current collectors and battery shells, so as to obtain valuable high-content substances. Shin et al. proposed a method for recovering Li and Co from lithium-ion battery waste liquid using sulfuric acid and hydrogen peroxide, which 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 used a set of rotating and fixed blade crushers for crushing, used sieves with different apertures to classify the crushed materials, and used magnetic separation 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 using a mechanochemical method 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 grind lithium cobalt oxide (LiCoO2) and polyvinyl chloride (PVC) together in air to form Co and lithium chloride (LiCl) in a mechanochemical manner. Subsequently, the ground product is dispersed in water to extract chloride. Grinding promotes mechanochemical reactions. As grinding proceeds, the extraction yields of Co and Li are improved. 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 had been converted into inorganic chloride.

The operation of the physical separation method is relatively simple, but it is not easy to completely separate lithium-ion batteries. In addition, 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 high-temperature calcination and decomposition of button battery cr2032 materials that have undergone preliminary separation treatments such as physical crushing, to remove organic binders and thus separate the constituent materials of lithium batteries. At the same time, the metals and their compounds in the button battery cr2032 can be oxidized, reduced and decomposed, volatilized in the form of steam, and then collected by condensation and other methods.

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

The high-temperature pyrolysis treatment technology is simple and easy to operate. It has a fast reaction speed and high efficiency under high temperature environment, and can effectively remove the binder; and this method does not require high components of raw materials, and is more suitable for processing large quantities or more complex batteries. However, this method has high requirements for 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 add purification and recovery equipment to absorb and purify harmful gases to prevent secondary pollution. Therefore, the treatment cost of this method is relatively high.

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., which can be directly recycled. Wet recycling is more suitable for recycling waste lithium batteries with relatively simple 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 positive electrode material of lithium-ion batteries will not dissolve in alkaline solution, while the base aluminum foil will dissolve in alkaline solution, this method is often used to separate aluminum foil. Zhang Yang et al. [10] used alkaline leaching to remove aluminum in advance when recovering Co and Li in batteries, and then used dilute acid to immerse to destroy the adhesion of organic matter and copper foil. However, the alkaline leaching method cannot completely remove PVDF, which has an adverse effect on subsequent leaching.

Most of the positive active materials in lithium-ion batteries can be dissolved in acid, so the pre-treated electrode materials can be leached with acid solution to achieve the separation of active materials and current collectors, and then the target metals can be precipitated and purified by combining the principle of neutralization reaction, so as to achieve the purpose of recovering high-purity components.

The acid solution used in the acid leaching 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) 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 to treat waste lithium batteries, such as citric acid, oxalic acid, malic acid, ascorbic acid, glycine, etc. Li and other electrodes recovered by dissolving with hydrochloric acid. Since the efficiency of the acid leaching process may be affected by the concentration of hydrogen ions (H+), temperature, reaction time and solid-to-liquid ratio (S/L), in order to optimize the operating conditions of the acid leaching process, experiments were designed to explore the effects of reaction time, H+ concentration and temperature. Experimental data show that when the temperature is 80℃, the H+ concentration is 4mol/L, and the reaction time is 2h, the leaching efficiency is the highest, among which 97% of Li and 99% of Co in the electrode material are dissolved. Zhou Tao et al. used malic acid as a leaching agent and hydrogen peroxide as a reducing agent to reduce and leach the positive electrode active material obtained by pretreatment, and studied the effects of different reaction conditions on the leaching rates of Li, Co, Ni, and Mn in the malic acid leaching solution to find the optimal reaction conditions. Research data show that when the temperature is 80℃, 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 30min, the efficiency of leaching using malic acid is the highest, among which the leaching rates of Li, Co, Ni, and Mn reach 98.9%, 94.3%, 95.1%, and 96.4%, respectively. However, compared with inorganic acids, the cost of leaching using organic acids is higher.

(2) Organic solvent extraction method

The organic solvent extraction method uses the principle of "like dissolves like" 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.

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

The experimental conditions for separating the material from the foil by organic solvent extraction are relatively mild, but the organic solvent has a certain toxicity and may cause harm to the health of the operator. At the same time, due to the different processes for making lithium-ion batteries by different manufacturers, the selected binders are different. Therefore, for different manufacturing processes, manufacturers need to choose different organic solvents when recycling and processing waste lithium batteries. In addition, cost is also an important consideration for large-scale recycling and processing operations at the industrial level. Therefore, it is very important to choose a solvent that is widely available, reasonably priced, low in toxicity and widely applicable.

(3) Ion exchange method

The ion exchange method refers to the use of ion exchange resins to separate and extract metals based on the different adsorption coefficients of the metal ion complexes to be collected. Wang Xiaofeng et al. [16] added an appropriate amount of ammonia water to the solution after acid leaching the electrode material, adjusted the pH value of the solution, and reacted with the metal ions in the solution to generate complex ions such as [Co(NH3)6]2+ and [Ni(NH3)6]2+, and continuously introduced pure oxygen into the solution for oxidation. Then, different concentrations of ammonium sulfate solution were 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 was used to completely elute the cobalt complex, while regenerating the cation exchange resin, and using oxalate to recover the cobalt and nickel metals in the eluent. The ion exchange method has a simple process and is relatively easy to operate.

3. Biorecycling

Mishra et al. used inorganic acids and Acidithiobacillus 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 the metals in the waste batteries. The study found that the biological dissolution rate of cobalt is faster than that of lithium. As the dissolution process proceeds, the iron ions react with the metals in the residue and precipitate, resulting in a decrease in the concentration of ferrous ions in the solution, and as the metal concentration in the waste sample increases, the growth of cells is arrested and the dissolution rate slows down. In addition, a higher solid/liquid ratio also affects the rate of metal dissolution. Zeng et al. used Acidithiobacillus ferrooxidans to bioleach metallic cobalt from waste lithium-ion batteries. Unlike Mishra et al., this study used copper as a catalyst to analyze the effect of copper ions on the bioleaching of LiCoO2 by Acidithiobacillus ferrooxidans. The results showed that almost all the cobalt (99.9%) entered the solution after 6 days of bioleaching at a Cu ion concentration of 0.75 g/L, while in the absence of copper ions, only 43.1% of the cobalt was dissolved after 10 days of reaction time. In the presence of copper ions, the cobalt dissolution efficiency of spent lithium-ion batteries is improved. In addition, Zeng et al. also studied the catalytic mechanism and explained the dissolution effect of copper ions on cobalt, in which LiCoO2 undergoes a cation exchange reaction with copper ions to form copper cobaltate (CuCo2O4) on the sample surface, which is easily dissolved by iron ions.

The bioleaching method has low cost and high recovery efficiency.The recycling rate is high, the pollution and consumption are low, the impact on the environment is also small, and the microorganisms can be reused. However, it is difficult to cultivate efficient microorganisms, the treatment cycle is long, and the control of leaching conditions are several major problems required by this method.

4. Combined recycling method

The recycling processes of waste lithium batteries have their own advantages and disadvantages. At present, there have been studies on recycling methods that combine and optimize multiple processes to give full play to the advantages of various recycling methods and maximize economic benefits. Figure 1 is a process flow chart of one of the combined recycling methods.

Figure 1 A process flow chart of a combined recycling method

III. Major foreign lithium-ion battery recycling companies and their processes

1. Umicore Company of Belgium

Umicore Company of Belgium independently developed the ValEas process. For battery recycling, they customized a furnace, used high-temperature metallurgical methods to process lithium-ion batteries and prepare cobalt hydroxide/cobalt chloride [Co(OH)2/CoCl2], and graphite and organic solvents can be used as fuel. This process does not need to break the battery, thus avoiding the problem of difficult breaking, and reducing the safety risks of the recycling process. In addition, the recovered Co compound has a high purity and can be directly returned to the production of lithium batteries as raw materials to achieve the recycling of metals. This method not only recycles valuable metals such as Co, Ni, Mn, and Cu, but also recycles plastics, graphite, aluminum foil and other materials in the battery. The recycling process is relatively simple and environmentally friendly. Umicore's Hoboken plant in Belgium processes about 7,000 tons of waste lithium batteries each year.

2. Toxco, USA

Toxco achieved commercial operation of lithium-ion battery recycling in 1993. The company mainly uses mechanical and hydrometallurgical processes to recycle metals such as Cu, Al, Fe, and Co in batteries. The company's recycling process can be carried out at a lower temperature environment, with low gas emissions, and can achieve 60% battery material recycling. The company's recycling process is shown in Figure 2.

Figure 2 Toxco's lithium-ion battery recycling process flow chart

3. OnTo, Japan

OnTo has 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 the recycling container. After that, the CO2 is gasified by changing the temperature and pressure, so that the electrolyte is precipitated from it. This process does not need to be carried out at high temperature and consumes very little energy. The process mainly uses supercritical fluid CO2 as a carrier to take out the battery electrolyte, and then injects new electrolyte to restore the capacity of the lithium-ion battery.

Figure 3 OnTo company's lithium-ion battery recycling process flow chart

IV. Summary

With the rapid replacement of electronic products, a large number of waste lithium batteries are generated every year, and under the influence of 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 in the production of lithium-ion batteries are in short supply, recycling and processing waste lithium-ion batteries has certain environmental safety protection and economic value. Among the several technologies for recycling and processing waste lithium-ion batteries, the wet method is currently the most used technology, and bioleaching technology is at the forefront of this field. Several methods have their own advantages and disadvantages. Therefore, it is key to seek a suitable recycling process that can give full play to the advantages 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 tiered recycling model. Although my country has the technical means to recycle and treat waste lithium batteries, it has not yet established a suitable recycling system and lacks corresponding laws and regulations. In the future, the country should establish effective laws and regulations, and build a suitable waste battery recycling system to achieve industrialized recycling and treatment of waste lithium batteries and ensure sustainable development.

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