Research progress on waste cr2032 button battery recycling technology

　　1 Policies related to waste battery recycling

　　With the development of my country's lithium-ion battery industry, the effective recycling and processing of used batteries is an important issue for the healthy and sustainable development of the industry. The notice of the "Energy Saving and New Energy Automobile Industry Development Plan (2012-2020)" issued by the State Council clearly mentioned that the cascade utilization and recycling management of power batteries should be strengthened, power battery recycling management measures should be formulated, and power battery manufacturers should be guided to strengthen the management of power battery recycling. Recycling of used batteries. As the problem of power battery recycling has become increasingly prominent, in recent years, the state and local governments have issued relevant policies to regulate and supervise the development of the recycling industry. The country’s main policies on battery recycling in the past three years are shown in Table 1.

　　2 Main components of waste LiFePO4 battery recycling

　　The structure of lithium-ion batteries generally includes positive electrode, negative electrode, electrolyte, separator, casing, cover, etc. The positive electrode material is the core of the lithium battery and accounts for more than 30% of the battery cost. Table 2 shows the materials used in a batch of 5A·h wound LiFePO4 batteries produced by a battery company in Guangdong Province (the solid content of the carbon nanotube dispersion in the table is 1%). As can be seen from Table 2, positive electrode lithium iron phosphate, negative electrode graphite, electrolyte, and separator account for the largest proportions, followed by copper foil and aluminum foil. Carbon nanotubes, acetylene black, conductive graphite, PVDF, and CMC are used in small amounts. According to the quotation from Shanghai Nonferrous Network (June 29, 2018), aluminum: 14,000 yuan/ton, copper: 51,400 yuan/ton, lithium iron phosphate: 72,500 yuan/ton; according to reports from China Energy Storage Network and Battery Network, The price of ordinary graphite anode materials is (6-7) million yuan/ton, and the price of electrolyte is (5-55) yuan/ton. Materials that are used in larger amounts and are more expensive are currently the main components of used battery recycling, and the recycling process needs to consider both economic and environmental benefits.

　　3 Progress in recycling technology of waste LiFePO4 materials

　　3.1 Chemical precipitation recovery technology

　　At present, chemical precipitation wet recycling is an important method for the recycling of used batteries. Oxides or salts of Li, Co, Ni, etc. are recovered through the co-precipitation method, and then recycled in the form of chemical raw materials. The chemical precipitation method is the current industrial recycling method. The main method of lithium cobalt oxide and ternary system waste batteries. For LiFePO4 materials, through separation and precipitation methods such as high-temperature roasting, alkali dissolution, and acid leaching, the most economically valuable Li element is mainly recovered, and metals such as Fe and Al can be recovered at the same time. The positive electrode sheet is dissolved with NaOH alkali solution to make The current collector aluminum foil enters the solution in the form of NaAlO2. After filtration, the filtrate is neutralized with sulfuric acid solution and precipitates to obtain Al(OH)3, realizing the recovery of Al. The filter residue is a mixture of LiFePO4, conductive agent carbon black and LiFePO4 material surface-coated carbon. There are two ways to recover LiFePO4: method one is to use sulfuric acid and hydrogen peroxide to dissolve the filter residue, so that LiFePO4 enters the solution in the form of Fe2(SO4)3 and Li2SO4. The filtrate after separation from the carbon impurities is adjusted to pH value with NaOH and ammonia. First, the iron is dissolved in the solution. Fe(OH)3 precipitates, and the remaining liquid is precipitated with a saturated Na2CO3 solution to obtain Li2CO3; Method 2 is based on FePO4 being slightly dissolved in nitric acid, using nitric acid and hydrogen peroxide to dissolve the positive electrode material filter residue, first forming a FePO4 precipitate, and finally precipitating as Fe(OH)3. The remaining acid solution is precipitated with saturated Na2CO3 solution to precipitate Li2CO3, thereby achieving separate precipitation and recovery of Al, Fe, and Li. LI et al. [6] are based on the fact that LiFePO4 in the H2SO4+H2O2 mixed solution will be oxidized by H2O2 to Fe2+ to Fe3+, and combined with PO43− to form FePO4 precipitation, the metal Fe is recovered and separated from Li, and further based on 3Li2SO4+2Na3PO4→3Na2SO4+ 2Li3PO4↓, the precipitate is generated and then separated and collected to realize the recovery of metal Li. Oxidized materials are more easily dissolved in HCl solution. WANG et al. roasted the LiFePO4/C mixed material powder at 600°C to ensure that ferrous ions are completely oxidized and improve the solubility of LiFePO4 in acid. The recovery rate of Li reached 96%. . It is a research hotspot to decompose the recycled LiFePO4 to obtain the precursor FePO4·2H2O and Li source and then synthesize the LiFePO4 material. ZHENG et al. [8] treated the electrode sheet at high temperature to remove the binder and carbon while oxidizing the Fe2+ of LiFePO4 to Fe3+ and screening it. The powder obtained is dissolved in sulfuric acid, and the pH of the dissolved filtrate is adjusted to 2 with ammonia water to obtain FePO4 hydrate, and the FePO4 recovery product is obtained by high temperature treatment at 700°C for 5 hours. After the filtrate is concentrated, Li2CO3 is precipitated with Na2CO3 solution to realize metallurgy. of recycling. BIAN et al. [10] leached waste electrodes with phosphoric acid and then heat-treated them to obtain FePO4·2H2O. As a precursor, Li2CO3 and glucose were added and then carbothermal reduction was performed to generate LiFePO4/C composite materials. Li in the recycled materials was precipitated in the form of LiH2PO4. Realize the recycling and reuse of materials.

　　The chemical precipitation method can be used to recover useful metals from mixed cathodes. It requires low pre-treatment of scrap cathodes, which is the advantage of this method. However, for LiFePO4 materials that do not contain precious metals such as cobalt, the above methods often have long recycling processes and produce a large amount of Disadvantages of acid and alkali waste liquid and high recycling cost.

　　3.2 High temperature solid phase repair technology

　　Based on the attenuation mechanism of the LiFePO4 battery and the charge and discharge characteristics of the cathode material, the structure of the cathode LiFePO4 material is stable, and the loss of active Li is one of the main reasons for battery capacity attenuation. Therefore, it is believed that the LiFePO4 material has the ability to directly supplement active Li and other lost elements. Repair potential. At present, the main repair methods include direct high-temperature treatment and high-temperature treatment after adding corresponding element sources, which can repair impurities and supplement element sources, thereby improving the electrochemical performance of recycled materials. Xie Yinghao and others disassembled the used batteries and separated the positive electrode sheets. After carbonizing the binder by heating under nitrogen protection, they vibrated and separated and ultrasonic treated in aqueous solution to obtain the lithium iron phosphate positive electrode material. Add an appropriate amount of FeC2O4·2H2O, Li2CO3, and (NH4)2HPO4 to the collected lithium iron phosphate to adjust the molar ratio of Li, Fe, and P to 1.05:1:1, and adjust the carbon content of the reactants before calcination to 3% and 5%. and 7%, add an appropriate amount of absolute ethanol to the material and ball mill it at high speed (600r/min) in a vacuum for 4 hours, then heat it up to 700°C for 24 hours at a temperature of 5°C/min in a nitrogen atmosphere to obtain the repaired LiFePO4 material. The result is that the repair material with a carbon content of 5% has the best electrochemical performance, with a first discharge specific capacity of 148.0mA·h/g at 0.1C; after 50 cycles at 1C, the capacity retention rate is 98.9%, and the recovery The treatment process flow is shown in Figure 4. SONG et al. investigated the solid-phase high temperature effect after directly mixing new LiFePO4. When the mass ratio of doped new materials and waste recycled materials was 3:7, the electrochemical performance of the repair material was good after 8 hours at 700°C. LI et al. used the addition of Li source Li2CO3 to perform high-temperature repair reactions on the recovered LiFePO4 materials at 600°C, 650°C, 700°C, 750°C, and 800°C in an argon/hydrogen mixed gas for 1 hour. The results show that recycling without high-temperature treatment The first discharge capacity of the material is 142.9mA·h/g, and the optimal repair temperature is 650°C. The first discharge capacity of the repair material is 147.3mA·h/g, which is slightly improved, while the rate and cycle performance are significantly improved. Research by Bian Ducheng et al. shows that adding Li2CO3 with a mole fraction of 10% to the waste cathode material can effectively make up for the loss of recyclable lithium. The repaired material has a discharge specific capacity of 157mA at 0.1C and 20C rates respectively. h/g and 73mA·h/g, there is almost no capacity decay after 200 cycles at 0.5C. Adding 20% Li2CO3 will cause excessive lithium. During the roasting and repair process, the excess Li2CO3 will produce impurities such as Li2O, causing material lattice defects, so the Coulomb efficiency is low. High-temperature solid-phase repair technology only needs to supplement a small amount of Li, Fe, and P elements, does not require a large amount of acid and alkali reagents, and produces less waste acids and alkali waste liquids. The process is simple and environmentally friendly, but it requires high purity of recycled raw materials. , the presence of impurities will reduce the electrochemical performance of repair materials.

　　3.3 High temperature solid phase regeneration technology

　　Different from high-temperature solid-phase direct repair technology, high-temperature regeneration technology first processes the recycled materials into reactive precursors, which can realize the recrystallization of each element through the thermodynamic reaction process, thereby realizing the regeneration of the material. Bian Ducheng et al. kept the cathode plates at 600°C for 3 hours in the air to remove impurities such as electrolyte and polyvinylidene fluoride (PVDF), and supplemented the collected waste cathode materials with molar fractions of 0, 10%, and 20% Li2CO3 respectively. , and add 25% mass fraction of glucose (based on waste lithium iron phosphate), and obtain a regenerated LiFePO4/C cathode material through carbothermal reduction reaction at 650°C. The material has discharge specific capacities at 0.1C and 20C rates respectively. The capacity retention rate of the regenerated LiFePO4 cathode material is 91% after 1000 cycles at 10C rate. Similar to the above-mentioned literature, the author of this article explored the "oxidation-carbothermal reduction" regeneration method of waste LiFePO4 materials in the early stage. The regeneration method is mainly based on CO reduction of FePO4 and LiOH precursor to synthesize LiFePO4 material. The reaction intermediates are Li3Fe2(PO4)3 and Fe2O3, and the oxidation products of LiFePO4 are also Li3Fe2(PO4)3 and Fe2O3. Therefore, the heat treatment method will recycle the positive electrode. The binder is removed from the tablet and the oxidation of LiFePO4 is achieved at the same time. As the regeneration reaction raw materials, glucose, citric acid monohydrate, and polyethylene glycol are used as reducing agents respectively, and LiFePO4 is regenerated by high-temperature carbothermal reduction at 650-750°C. Three reducing agents Both systems can obtain regenerated LiFePO4/C materials without impurities.

　　High-temperature solid-phase regeneration technology oxidizes the recycled LiFePO4 material into a reaction intermediate at high temperature, and obtains regenerated LiFePO4 material through a carbothermal reduction reaction. The material undergoes a unified thermodynamic process of oxidation and carbothermal reduction. The recycled material is highly controllable and the process flow is Simple, but similar to high-temperature solid-phase repair technology, this method has high requirements for impurities in recycled materials, and pre-treatment of impurities in recycled materials is a necessary process step.

　　3.4 Bioleaching technology

　　In terms of recycling waste batteries, bioleaching technology was first used to recover cadmium, nickel and iron from nickel-cadmium waste batteries. CERRUTI and others used Thiobacillus ferrooxidans to dissolve and leach waste nickel-cadmium batteries. The recovery rates were 100% for cadmium and 96.5% for nickel. , iron 95%, dissolution and leaching time is 93 days. XIN et al. used a mixed system of sulfur-Thiobacillus thiooxidans, pyrite-Leptospirillum ferrophila, and (sulfur+pyrite-Thiobacillus thiooxidans+Leptospirillum ferrophila) to treat LiFePO4, LiMn2O4, and LiNixCoyMn1- respectively. x-yO2, among which, the leaching rate of Li in LiFePO4 by the sulfur-Thiobacillus thiooxidans system is 98%, the leaching rate of Li in LiMn2O4 by the mixed system is 95%, and the leaching rate of Mn is 96%. Through pH optimization, The average leaching rate of Li, Ni, Co, and Mn in the ternary material LiNixCoyMn1-x-yO2 by the mixed system is higher than 95%. The dissolution of Li is mainly due to the dissolution of H2SO4, while the dissolution of Ni, Co, and Mn is the combined effect of Fe2+ reduction and acid dissolution.

　　In bioleaching technology, the biological flora requires a long cultivation period and a long dissolution and leaching time, and during the dissolution process, the bacterial flora is easily inactivated, which limits the industrial application of this technology. Therefore, it is necessary to further increase the culture speed of bacterial strains, the adsorption speed of metal ions, etc. to increase the leaching rate of metal ions.

　　3.5 Mechanical activation treatment and recycling technology

　　Mechanochemical activation methods can cause physical and chemical changes in materials under normal temperatures and pressures, including phase changes, structural defects, strain, amorphization, and even direct reactions. Application in waste battery recycling can improve recycling efficiency at room temperature.

　　FAN and others use the method of soaking used batteries in NaCl solution to completely discharge the battery. The recovered LiFePO4 is heated at 700°C for 5 hours to remove organic impurities. Use oxalic acid as a grinding aid, mix it with recycled materials and use a planetary ball mill for mechanical activation. The mechanical activation process mainly includes three steps: particle size reduction, chemical bond breaking, and new chemical bond formation. After the grinding machine is activated, the mixed raw materials and zirconia beads are rinsed with deionized water and soaked for 30 minutes. The filtrate is stirred and evaporated at 90°C until the concentration of Li+ is greater than 5g/L. Use 1 mol/L NaOH solution to adjust the pH of the filtrate to 4, and stir continuously for more than 2 hours until the concentration of Fe2+ is less than 4 mg/L, thereby obtaining a high-purity filtrate. After filtration, adjust the pH of the purified lithium solution to 8, stir at 90°C for 2 hours, collect the precipitate and dry at 60°C for 24 hours to obtain the Li recovery product. The recovery rate of Li can reach 99%, and Fe is recovered in the form of FeC2O4·2H2O, with a recovery rate of 94%. YANG et al. separated aluminum foil and cathode materials with the assistance of ultrasonic waves. The cathode powder was mixed with disodium ethylenediaminetetraacetate (EDTA-2Na) in proportion (6:1-1:1) and then mechanically activated using a planetary ball mill. , further leaching the activated sample with dilute phosphoric acid, and vacuum filtration with a cellulose acetate membrane after stirring and leaching to obtain a filtrate containing lithium and iron metal ions. The leaching rates of Fe and Li in phosphoric acid can reach 97.67% and 94.29 respectively. %. The filtrate was refluxed with a steam condenser at 90°C for 9 hours. Metal Fe was precipitated in the form of FePO4·2H2O and Li in the form of Li3PO4. After filtration, the precipitate was collected and dried to realize metal material recovery. The total recovery rates of Fe and Li reached 93.05% and 82.55% respectively. ZHU et al. used recycled LiFePO4/C as raw material and blended it with lecithin. After chemical activation through mechanical ball milling, it was sintered at 600°C for 4 hours under the protection of Ar-H2 (10%) mixed atmosphere to obtain (C+N+P). Co-coated recycled LiFePO4 composite. The N—C bonds and P—C bonds in the recycled material coat LiFePO4, forming a stable C+N+P co-coating layer. The smaller particle size of the recycled material can shorten the diffusion path of Li+ and electrons. When the lecithin dosage is 15%, the capacity of the recycled material reaches 164.9mA·h/g at a low magnification rate of 0.2C. 3.6 Other recycling and processing technologies—electrochemical recycling and processing technology. Yang Zeheng and others used 1-methyl-2-pyrrolidone (NMP) to dissolve the used LiFePO4 pole piece binder, and then collected the recycled LiFePO4 material, and recovered the material, conductive agent, and binder. The electrode to be repaired is prepared, and the metal lithium sheet is used as the negative electrode to make a button battery. After multiple charges and discharges, lithium is embedded from the negative electrode into the positive electrode material, causing the positive electrode to change from a lithium-poor state to a lithium-rich state, achieving a repair effect. However, it is difficult to assemble the repaired electrodes into full batteries, making it difficult to guide large-scale applications.

　　4Progress in electrolyte recovery technology

　　At present, electrolyte recovery includes vacuum pyrolysis treatment, organic solvent extraction recovery treatment, and CO2 supercritical recovery method. SUN and others use vacuum pyrolysis to recycle used batteries while simultaneously processing the electrolyte. Place the separated cathode material in a vacuum furnace, the system pressure is less than 1kPa, and the condensation temperature of the cold trap is -10°C. The vacuum furnace is heated at a heating rate of 10°C/min and kept at 600°C for 30 minutes. The volatiles enter the condenser and are condensed, while the incompressible gas is extracted through the vacuum pump and finally collected by the gas collector. The binder and electrolyte are volatilized or decomposed into low molecular weight products. Most of the pyrolysis products are organic fluorocarbons, which are enriched and recycled. The organic solvent extraction method is to transfer the electrolyte into the extraction agent by adding an appropriate organic solvent as an extraction agent. After extraction, the different boiling points of the components in the extraction product solution are used to distill or fractionate the electrolyte to collect or separate the electrolyte. Tong Dongge and others cut the used batteries open under the protection of liquid nitrogen, took out the active materials, and soaked the active materials in organic solvents for a period of time to leach the electrolyte. The extraction efficiency of PC, DEC and DME for electrolyte was compared. The results showed that PC had the fastest extraction rate, and the electrolyte could be completely extracted after 2 hours, and PC could be reused many times. This may be due to the relative medium. PC with a larger electrical constant is more conducive to the dissolution of lithium salts.

　　Supercritical CO2 recycling of used lithium-ion battery electrolyte refers to the process of using supercritical CO2 as an extraction agent to separate the electrolyte adsorbed in the lithium-ion battery separator and active material. GRUETZKE et al. studied the extraction effect of liquid CO2 and supercritical CO2 on electrolyte. For electrolyte systems containing LiPF6, DMC, EMC and EC, when liquid CO2 is used, the recovery rates of DMC and EMC are higher, while the recovery rates of EC are lower. When supercritical CO2 is used, the total recovery rate is high. When the entrainer ACN/PC (3:1) is added to liquid CO2, the extraction efficiency of the electrolyte is the highest, reaching (89.1±3.4)% (mass fraction). LIU et al. studied a supercritical CO2 extraction electrolyte that combines static extraction followed by dynamic extraction, which can achieve an extraction rate of 85%. Vacuum pyrolysis technology can realize the stripping of active materials and current collectors while recycling the electrolyte, simplifying the recycling process. However, the recycling process consumes high energy and requires further processing of fluorocarbon organic compounds; the organic solvent extraction process can be recycled The main component of electrolyte, but there are problems such as high extraction solvent cost, difficult separation and subsequent new pollution of the extraction agent. Supercritical CO2 extraction technology has the advantages of no solvent residue, simple solvent separation, and good product reduction. It is an ideal choice for lithium-ion batteries. Electrolyte recycling is one of the research directions, but there are still problems such as large CO2 consumption and entrainers that may affect electrolyte reuse.

　　5. Progress in Anode Material Recycling Technology

　　From the analysis of the failure mechanism of LiFePO4 batteries, it can be seen that the performance of negative electrode graphite declines more than that of positive electrode LiFePO4 materials. Moreover, because the price of negative electrode graphite materials is relatively low and the usage is relatively small, the economics of recycling and reuse are weak. Currently, the recycling of used battery negative electrodes There are relatively few studies. Among the negative electrodes, copper foil is expensive and has a simple recycling process, so it has high recycling value. The recycled graphite powder is expected to be recycled and used in battery production after modification. Zhou Xu et al. used a combined process of hammer crushing, vibration screening and air flow sorting to separate and recycle used lithium battery negative electrode materials. The process is to put the negative electrode sample into a hammer crusher and crush it until the particle size is less than 1mm. The crushed material is placed on the fluidized bed distribution plate to form a fixed bed; the fan is turned on to adjust the gas flow rate, and the particle bed is sequentially passed through the fixed bed, The bed is loosened, initially fluidized, and fully fluidized to separate metal and non-metallic particles from each other. The light components are taken out of the fluidized bed by the air flow and collected through the cyclone separator, while the heavy components stay at the bottom of the fluidized bed. . The results show that after the negative electrode material is crushed and screened, the copper grade in the crushed material with a particle size greater than 0.250mm is 92.4%, and the carbon powder grade in the crushed material with a particle size smaller than 0.125mm is 96.6%, both of which can be directly recycled; In the crushed materials with a particle size of 0.125-0.250mm, the copper grade is relatively low, and the copper and carbon powder can be effectively separated and recycled through airflow sorting.

　　At present, the negative electrode is mainly made of water-based binder. The binder can be directly dissolved in the aqueous solution, and the negative electrode material and the current collector copper foil can be separated through a simple process. Zhu Xiaohui et al. developed a method for wet recovery of negative electrode materials using secondary ultrasound-assisted acidification. The negative electrode piece is placed in a dilute hydrochloric acid solution to directly separate the graphite sheets and the current collector copper foil. The current collector is recycled after washing and drying. The graphite material is filtered, dried, and screened to separate and obtain the recycled crude graphite product. The crude product is subjected to ultrasonic treatment in nitric acid, perchloric acid and other oxidants to remove metal compounds and binders in the material and generate functional groups on the graphite surface. The graphite material is collected and dried to obtain a secondary purified graphite material. Modified graphite powder for batteries can be obtained by immersing the secondary purified graphite material in a reducing aqueous solution of ethylenediamine or diethylenetriamine, ultrasonic treatment, and then heat-treating it under nitrogen protection to repair the graphite material. Waste battery negative electrodes often use water-based binders, so the active materials and current collector copper foil can be peeled off by simple methods. In the past, only high-value copper foil was recycled, and direct disposal of graphite materials would cause a huge waste of materials. Therefore, the modification and repair technology of graphite materials should be developed to realize the reuse of waste graphite materials in the battery industry or other industrial fields.

　　6Recycling Economic Analysis

　　The economic benefits of recycling lithium iron phosphate used batteries are greatly affected by fluctuations in raw material prices, including the recycling price of used batteries, the price of raw material lithium carbonate, the price of lithium iron phosphate, etc. Using the currently commonly used wet recycling technology route, the metal with the most economic value for recycling in waste lithium iron phosphate batteries is lithium. The recycling income is about 7,800 yuan/ton, while the recycling cost is about 8,500 yuan/ton. The recycling income cannot cover the recycling Among them, the cost of raw materials accounts for about 27% of the total cost in the recycling cost of lithium iron phosphate, and the cost of auxiliary materials accounts for about 35% of the total cost. The cost of auxiliary materials mainly includes the cost of hydrochloric acid, sodium hydroxide, hydrogen peroxide, etc. (the above data comes from the Battery Alliance and CCID consultant). Using the wet technical route, lithium cannot be completely recovered (the recovery rate of lithium is often below 90%). The recovery effect of phosphorus and iron is poor, as well as the use of a large amount of auxiliary materials. These are the main reasons why it is difficult to achieve profitability using the wet technical route. reason.

　　Waste lithium iron phosphate batteries use high-temperature solid phase method to repair or regenerate the technical route. Compared with the wet technical route, the recycling process does not require alkali dissolution of the current collector aluminum foil and acid dissolution of the cathode material lithium iron phosphate. Therefore, the use of auxiliary materials Greatly reduced, and the high-temperature solid-phase repair or regeneration technology route can achieve high recovery rates of lithium, iron, and phosphorus elements, and therefore will have higher recovery benefits. According to the predictions of Beijing Saidemei Company, the use of high-temperature repair methods The full-component recycling technology route will be able to achieve a net profit rate of approximately 20%.

　　7 Conclusion

　　When the recycled materials are mixed recycled materials with complex components, it is suitable to use chemical precipitation or biological leaching technology to recover metals and obtain reusable chemical materials. However, for LiFePO4 materials, wet recycling has a long process and requires There are many acid and alkali reagents and the problem of processing a large amount of acid and alkali waste liquid, which has the disadvantages of high recycling cost and low economic value. Compared with chemical precipitation recycling technology, high-temperature repair and high-temperature regeneration technology has the advantages of short process, less acid and alkali reagents, and less waste acid and alkali produced. However, this method requires that the recycled materials must be repaired or regenerated. Strict impurity removal is carried out before processing to avoid impurity residues affecting the electrochemical performance of the material. Impurities include a small amount of aluminum foil, copper foil, etc. The problem of impurity removal is an important issue that is rarely studied in large-scale applications of direct repair and regeneration processes but must be solved. In order to improve the economic value of used battery recycling, low-cost electrolyte and negative electrode material recycling technology should be further developed to maximize the recovery of useful substances in used batteries and maximize recycling benefits.

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