What are the lithium battery recycling and processing technologies?
What are the lithium battery recycling and processing technologies?
Lithium-ion batteries are composed of positive and negative plates, binders, electrolytes, and separators. In industry, manufacturers mainly use lithium cobalt oxide, lithium manganate, lithium nickel cobalt manganese oxide ternary materials, and lithium iron phosphate as cathode materials for lithium-ion batteries, and natural graphite and artificial graphite as anode 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 organic solvents as the electrolyte and use organic membranes such as porous polyethylene (PE) and polypropylene (PP) as the battery separator.
Lithium-ion batteries are generally regarded as environmentally friendly and pollution-free 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 electrode materials and electrolytes of the battery still have a greater impact on the environment and the human body. If ordinary garbage disposal methods are used to dispose of lithium-ion batteries (landfill, incineration, composting, etc.), the cobalt, nickel, lithium, manganese, and other metals in the battery, as well as various organic and inorganic compounds will cause metal pollution, organic pollution, and dust pollution, Acid, and alkali 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, low 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, 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. As people’s demand for electronic products gradually increases and the speed of electronic product replacement is gradually accelerated and affected by the rapid development of new energy vehicles, the global market has an increasing demand for lithium-ion batteries, and the growth rate of battery production is increasing year by year.
The huge market demand for lithium-ion batteries will, on the one hand, lead to a large number of used batteries in the future. How to deal with these used lithium-ion batteries to reduce their environmental impact 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 cathode materials for the production of lithium-ion batteries mainly include lithium cobalt oxide, lithium manganate, lithium nickel cobalt manganese oxide ternary materials and lithium iron phosphate, etc. Therefore, waste lithium-ion batteries contain more cobalt (Co) and 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 imported to Meet the growing demand. Part of the metal content in waste lithium-ion batteries is higher than that in natural ore. Therefore, in the case of increasingly scarce production resources, recycling, and processing waste batteries has a certain economic value.
Lithium-ion battery recycling technology
The recycling process of used lithium-ion batteries mainly includes pretreatment, secondary treatment, and advanced treatment. Because there is still some electricity remaining in the waste battery, the pretreatment process includes a 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. Heat treatment and organic solvent dissolution are commonly used. , Lye 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 the extraction process, the battery recycling methods can be divided into three categories: dry recycling, wet recycling, and biological recycling.
1. Dry recycling
Dry recovery 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 and high-temperature pyrolysis.
(1) Physical sorting method
The physical separation method refers to the disassembly and separation of the battery, and the battery components such as the electrode active material, the current collector, and the battery casing are crushed, sieved, magnetically separated, finely crushed, and classified 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, including 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 group of rotating and fixed blade crushers for crushing, uses screens 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. The method utilizes 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 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% 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 chloride.
The operation of the physical separation method is relatively simple, but it is not easy to completely separate the lithium-ion battery, and it is prone to mechanical entrainment loss during sieving and magnetic separation, and it is difficult to achieve complete separation and recovery of metals.
(2) High-temperature pyrolysis method
The high-temperature pyrolysis method refers to the high-temperature pyrolysis of lithium battery materials that have undergone physical crushing and other preliminary separation treatments, and the organic binder is removed, thereby separating the constituent materials of the lithium battery. At the same time, the metal and its compounds in the lithium battery can be oxidized, reduced and decomposed, volatilized in the form of steam, and then collected by methods such as condensation.
Lee et al. used a high-temperature pyrolysis method when preparing 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. Second, the heat-treated battery is shredded to release the electrode material. The samples were disassembled by a high-speed crusher specially designed for this study, and classified according to size, ranging from 1 to 50 mm. Then, two-step heat treatment is performed in the furnace, the first heat treatment is performed at 100-500°C for 30 minutes, and the second heat treatment is performed at 300-500°C for 1 hour. The electrode material is released from the current collector through vibration screening. Next, by burning at a temperature of 500 to 900° C. for 0.5 to 2 hours, the carbon and the binder are burned off to obtain the cathode active material LiCoO2. Experimental data shows that carbon and binder are burned off at 800°C.
The high-temperature pyrolysis method has simple processing technology, convenient operation, fast reaction speed in high-temperature environment, high efficiency, and can effectively remove the binder; and this method does not require high raw material components, and is more suitable for processing large amounts or more complex Battery. However, this method has higher requirements for equipment; during the treatment process, the organic matter of the battery is decomposed to produce harmful gases, which are 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 processing 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 suitable chemical reagents to selectively separate the metal elements in the leaching solution to produce high-grade cobalt metal or lithium carbonate, etc., which are directly recycled. The wet recycling process is more suitable for recycling waste lithium batteries with a relatively single chemical composition, and its equipment investment cost is low, and it is suitable for the recovery 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 the lithium-ion battery will not dissolve in the lye, and the base aluminum foil will dissolve in the lye, this method is often used to separate the aluminum foil. Zhang Yang et al. used alkaline leaching to remove aluminum in advance when recovering Co and Li in batteries and then immersed 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 an adverse effect on the subsequent leaching.
Most of the positive electrode active material in lithium-ion batteries can be dissolved in acid, so the pre-treated electrode material can be leached with an acid solution to separate the active material from the current collector, and then combine the principle of neutralization reaction to target metal Carry out precipitation and purification, 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, in the process of leaching with strong inorganic acids, harmful gases such as chlorine (Cl2) and sulfur trioxide (SO3) that have an impact on the environment are often generated, so researchers try to use organic acids to dispose of used lithium batteries, such as citric acid, Oxalic acid, malic acid, ascorbic acid, glycine, etc. Li and others use hydrochloric acid to dissolve and recover 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 explore the reaction time and H+ concentration And temperature. The experimental data show that when the temperature is 80℃, the H+ concentration is 4mol/L, the reaction time is 2h, and the leaching efficiency is the highest. Among them, 97% Li and 99% 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 reduce the leaching of the positive electrode active material obtained by the pretreatment, and studied the influence of different reaction conditions on the leaching rate of Li, Co, Ni, and Mn in the malic acid leaching solution to find out Find the best reaction conditions. The research data shows 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 with malic acid is the highest. Among them, 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-methyl pyrrolidone (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 is about 200g/kg), and its boiling point is relatively high, about 200°C. The study uses NMP to treat the active material at about 100°C for 1 hour, which effectively realizes the separation of the film and its carrier, and therefore, by simply filtering it out of the NMP (N-methyl pyrrolidone) solution, the metal form of Cu is recovered. And Al. Another advantage of this method is that the recovered Cu and Al metals can be directly reused after being sufficiently cleaned. 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 cathode waste for lithium-ion batteries. The waste lithium-ion battery used in the experiment uses polytetrafluoroethylene (PTFE) as the organic binder, and the effect of TFA concentration, liquid-to-solid ratio (L/S), reaction temperature and time on the separation efficiency of cathode material and aluminum foil is systematically studied. . The experimental results show that in a TFA solution with a mass fraction of 15, the liquid-to-solid ratio is 8.0 mL/g, and the reaction temperature is 40°C, reacting for 180 minutes under appropriate stirring, the cathode material can be completely separated.
The experimental conditions of 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, the choice of binder is different. Therefore, for different manufacturing processes, manufacturers need to choose different organic solvents when recycling waste lithium batteries. In addition, the cost is also an important consideration for large-scale recycling operations at the industrial level. Therefore, it is very important to choose a solvent with a wide range of sources, a reasonable price, low toxicity, harmlessness, and wide applicability.
(3) Ion exchange method
The ion exchange method refers to the use of ion-exchange resins to achieve metal separation and extraction by different adsorption coefficients of the metal ion complexes to be collected. After the electrode material was treated by acid leaching, Wang Xiaofeng and others added an appropriate amount of ammonia to the solution, adjusted the pH of the solution, and reacted with the metal ions in the solution to form [Co(NH3)6]2+, [Ni(NH3) 6] 2+ and other complexions, 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 the trivalent cobalt ammonia complex on the ion exchange resin respectively. Finally, a 5% H2SO4 solution was used to completely elute the cobalt complex, while the cation exchange resin was regenerated, and the cobalt and nickel metals in the eluate were recovered using oxalate. The process of the ion exchange method is simple and relatively easy to operate.
3. Biorecycling
Mishra et al. used inorganic acids and acidophilic Thiobacillus ferrooxidans to extract 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. Studies have found that the biological dissolution rate of cobalt is faster than that of lithium. As the dissolution process progresses, iron ions react with the metal in the residue to precipitate, resulting in a decrease in the concentration of ferrous ions in the solution. As the metal concentration in the waste sample increases, cell growth 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 acidophilic Thiobacillus ferrooxidans to biologically leaching metal 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 acidophilic Thiobacillus ferrooxidans on LiCoO2 biological leaching. The results show that almost all cobalt (99.9%) enters the solution after 6 days of biological leaching when the Cu ion concentration is 0.75g/L, while in the absence of copper ions, after 10 days of reaction time, only 43.1% of The cobalt dissolves. In the presence of copper ions, the cobalt dissolution efficiency of waste 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. Among them, 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.
4. 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 to give full play to the advantages of various recycling methods and maximize economic benefits
