Method for preparing lithium carbonate by recycling waste batteries

Abstract

The invention discloses a method for preparing lithium carbonate by recycling a waste battery, belongs to the field of waste battery recycling, and is used for solving the technical problems that in the prior art, the leaching rate and the recycling rate of lithium in lithium iron phosphate are low, and the purity of the recycled lithium carbonate needs to be further improved. The method comprises the following steps: crushing a positive electrode material, pretreating with an N-methyl pyrrolidone solution, performing high-temperature roasting and acid leaching, adjusting the pH value, filtering with a COF membrane, and adsorbing with an aluminum-doped manganese ion sieve. According to the method, through the synergistic effect of the N-methyl pyrrolidone solution, the COF membrane and the aluminum-doped manganese ion sieve, the leaching rate and the recovery rate of lithium are increased, meanwhile, the content of lithium carbonate is increased, and the content of impurities in the lithium carbonate is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of waste battery recycling, and in particular to a method for preparing lithium carbonate by recycling waste batteries. Background Art

[0002] The rapid development of new energy vehicles has led to a surge in the use of lithium batteries, resulting in a large consumption of lithium resources and greatly increasing the pressure on lithium resources. Lithium iron phosphate batteries, as a type of lithium battery, are widely used in the automotive field due to their many characteristics such as high cycle stability and high specific energy. With the increase in the number of scrapped cars, the amount of waste lithium iron phosphate batteries has also increased significantly. If the scrapped lithium iron phosphate batteries are not properly handled, they will cause serious pollution and waste to the environment and resources.

[0003] However, most methods for recovering lithium from waste lithium iron phosphate batteries still use hydrometallurgical technology. Although hydrometallurgical technology has low recovery costs, is easy to industrialize, and can leach most of the lithium into the solution;

[0004] However, the subsequent separation and purification is relatively complicated, and the purity and impurity content of the lithium carbonate finally prepared need to be further improved. In the actual recovery of lithium, a pretreatment process of high-temperature calcination is directly carried out to remove the binder PVDF in the positive electrode material. If the HF gas generated during the calcination of PVDF is not treated, it will seriously pollute the environment.

[0005] Moreover, the lithium ions wrapped in PVDF will not be leached, which will seriously reduce the leaching rate and recovery rate of lithium ions. In addition, the ordinary precipitation method for extracting lithium carbonate is difficult to purify, which will lead to low quality of lithium carbonate and low lithium recovery rate. The use of aluminum-doped manganese ion sieve is selective and only recovers lithium ions, which can greatly improve the quality and recovery rate of lithium. Finally, the use of sodium carbonate to prepare lithium carbonate will introduce impurities, affecting the recovery rate of lithium, so the use of carbon dioxide gas is both efficient and does not introduce impurities. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for recycling waste batteries to prepare lithium carbonate, which is used to solve the technical problems in the prior art that the leaching rate and recovery rate of lithium in lithium iron phosphate are low, and the content of recovered lithium carbonate and the impurities in the lithium carbonate do not meet the requirements of battery-grade lithium carbonate.

[0007] The purpose of the present invention can be achieved by the following technical solution: A method for recycling waste batteries to prepare lithium carbonate, comprising the following steps:

[0008] S1. Discharging and disassembling discarded lithium iron phosphate batteries to obtain battery shell materials, lithium iron phosphate positive electrodes and graphite negative electrodes, and crushing the lithium iron phosphate positive electrodes to obtain lithium iron phosphate powder;

[0009] S2, pre-treating the lithium iron phosphate powder and then acid leaching and extracting it to prepare a lithium-containing solution;

[0010] S3. Add alkali to the lithium-containing solution to adjust the pH of the system to 6-7, filter it through a COF membrane, add aluminum-doped manganese ion sieve, adsorb it at 25-40°C for 1-2 hours to obtain a lithium-attached ion sieve, and desorb the lithium-attached ion sieve to obtain a regenerated aluminum-doped manganese ion sieve and a lithium ion purification solution;

[0011] S4. Precipitating lithium in the lithium ion purification solution with carbon dioxide to obtain lithium carbonate.

[0012] Furthermore, in step S2, the lithium iron phosphate powder is pretreated by adding N-methylpyrrolidone solution to the lithium iron phosphate powder, ultrasonically dispersing it at 40-60°C for 0.5-1.5h, filtering it, washing it with N-methylpyrrolidone solution 2-4 times, mixing it with sodium carbonate, and aerobically calcining it at 500-700°C for 1-2h to obtain lithium iron phosphate pretreated powder.

[0013] Reaction principle of adding N-methylpyrrolidone solution:

[0014] During the reaction, the highly polar pyrrolidone ring in the N-methylpyrrolidone solution molecules forms a directional electrostatic attraction with the fluorine atoms of PVDF through the nitrogen atoms. At the same time, hydrogen bonds and van der Waals forces destroy the forces between the PVDF molecular chains. Due to the high dielectric constant and moderate dipole moment of N-methylpyrrolidone, it can effectively penetrate the gaps between PVDF molecules. The weak polarity of PVDF and the moderate polarity of N-methylpyrrolidone follow the principle of like dissolves like, so PVDF can be dissolved and removed.

[0015] Reaction principle of aerobic roasting:

[0016] C+O2→CO2

[0017] PVDF→HF+fluorocarbon polymer

[0018] 12LiFePO4+3O2→2Fe2O3+FePO4+Li3PO4

[0019] Furthermore, the usage ratio of the lithium iron phosphate powder, N-methylpyrrolidone and sodium carbonate is 1 g:2 mL:0.5 g, and the concentration of the N-methylpyrrolidone is 80-85 wt %.

[0020] Furthermore, in step S2, the method of acid leaching the lithium iron phosphate powder after pretreatment is: first add the lithium iron phosphate pretreated powder into deionized water, stir it at 20-30°C for 30 minutes, then add inorganic acid thereto, adjust the pH of the solution to 2.0-3.0, continue stirring for 2 hours, and filter press and wash to obtain a lithium-containing solution.

[0021] Reaction principle:

[0022] Li3PO4+H + →Li + +H3PO4

[0023] Furthermore, the ratio of the oxidation mixture to deionized water is 1 g:5 mL, and the inorganic acid is a 30-37 wt % hydrochloric acid solution.

[0024] Furthermore, in step S3, the ratio of the lithium-containing solution to the aluminum-doped manganese ion sieve is 30-50 mL:1 g, and the base is a sodium hydroxide solution with a mass percentage of 5-10 wt%.

[0025] Furthermore, in step S3, the aluminum-doped manganese ion sieve is prepared by the following steps:

[0026] A1. Dissolve aluminum isopropoxide in ethanol, add manganese carbonate powder, and stir at 60-80°C for 2-4 hours to obtain a uniform sol. Dry the sol in an oven at 80°C for 24 hours to obtain a precursor powder. Pre-sinter the precursor powder in an air atmosphere at 350-450°C for 3-5 hours to obtain a pre-sintered powder.

[0027] Reaction principle:

[0028] During the reaction, aluminum isopropoxide undergoes hydrolysis and polycondensation in ethanol solvent. The Al-OH intermediate generated by hydrolysis forms an Al-O-Al network structure through condensation of hydroxyl or alkoxy groups to form an amorphous Al2O3 precursor. At the same time, manganese carbonate powder is evenly dispersed during stirring at 60-80°C, and then decomposed into MnO2 and a small amount of Mn2O3 during pre-sintering in air atmosphere at 350-450°C to achieve structural activation. During the entire process, the network formed by the hydrolysis of the aluminum source wraps the manganese source particles. After pre-sintering at high temperature, Al 3+ Part of it diffuses into the MnO2 lattice to form Al-Mn-O solid solution.

[0029] A2. After mixing the pre-sintered powder with lithium hydroxide monohydrate, the mixture was transferred to a polytetrafluoroethylene-lined autoclave, and deionized water was added. The mixture was reacted at 150-200° C. for 12-14 hours to form an aluminum-doped lithium manganate precursor.

[0030] Reaction principle:

[0031] Under hydrothermal conditions, lithium hydroxide monohydrate decomposes into Li + and OH - , MnO2 in the pre-sintered powder is oxidized by OH - The corrosion forms a soluble manganese hydroxy complex, and the Al(OH)3 generated by the hydrolysis of aluminum isopropoxide is converted into [Al(OH)4] - , Li + 、Mn 4+ 、Mn 3+ and Al 3+ Recombined in solution, through OH - Bridging to form spinel LiMn2O4 structure, Al 3+ Al-doped LiAl is formed by isomorphous substitution of some Mn sites. x Mn 2-x O4, while part of Li + Occupying tetrahedral sites forms exchangeable lithium ion channels.

[0032] A3. The aluminum-doped lithium manganate precursor is secondary calcined in an air atmosphere at 450-600°C for 6-8 hours, then immersed in a lithium hydroxide solution, stirred at 25-40°C for 4-6 hours, filtered and washed, and vacuum-dried at 60°C for 12 hours to obtain an aluminum-doped manganese ion sieve.

[0033] Reaction principle:

[0034] During the secondary calcination process, in an air atmosphere of 450-600°C, aluminum manganese oxide and lithium source undergo high-temperature solid-phase reaction to form a stable aluminum-doped lithium manganate spinel structure. Aluminum ions replace manganese sites to enhance lattice stability. The calcined product is then immersed in a lithium hydroxide solution, and selective delithiation and ion exchange occur at 25-40°C. The lithium ions in the lattice are partially replaced to produce nanoscale pores matching the target ion size, and a negatively charged manganese aluminum oxide skeleton is formed at the same time. Finally, it is filtered, washed, and vacuum-dried at 60°C to avoid the generation of impurities and maintain the pore structure, giving the material size screening and electrostatic adsorption functions to obtain an aluminum-doped manganese ion sieve.

[0035] Furthermore, in step A1, the dosage ratio of the aluminum isopropoxide, ethanol and manganese carbonate powder is 0.02-0.05 g:1 g:5-10 mL.

[0036] Furthermore, in step A2, the ratio of the pre-sintered powder, lithium hydroxide monohydrate and deionized water is 1 g:1.5-2 g:8 mL.

[0037] Furthermore, in step A3, the ratio of the aluminum-doped lithium manganate precursor to the lithium hydroxide solution is 1 g:5-10 mL, and the concentration of the lithium hydroxide solution is 1.0-4.1 wt %.

[0038] The present invention has the following beneficial effects:

[0039] 1. The lithium iron phosphate powder of the present invention is added to the N-methylpyrrolidone solution. N-methylpyrrolidone can not only dissolve the binder such as PVDF in the electrode sheet, separate the aluminum foil from the active material, avoid impurities from mixing, and improve the subsequent lithium leaching rate and recovery rate, but also remove oily impurities, residual electrolytes, etc., reduce lithium loss, avoid the generation of corrosive gases, and improve the lithium recovery rate. In addition, N-methylpyrrolidone can be recycled, which is in line with the concept of green chemistry and reduces production costs and environmental burdens. The lithium-containing solution is filtered through the COF membrane. With its clear pore structure and adjustable pore size, the COF membrane can utilize the size exclusion effect and functional group-specific adsorption to efficiently intercept impurity ions and selectively pass lithium ions, significantly improve lithium purity, and reduce the impurity content. At the same time, this method can also replace the traditional chemical precipitation method, achieve separation in one step at room temperature and pressure, simplify the process flow, and reduce costs and solid waste treatment volume.

[0040] 2. The present invention utilizes aluminum-doped manganese ion sieves. Aluminum ions can suppress Jahn-Teller distortion and reduce manganese dissolution by replacing some manganese sites, significantly improving structural stability, greatly improving the lithium adsorption capacity retention rate after cycling, reducing impurities while improving manganese recovery rate. At the same time, the aluminum-doped manganese ion sieve optimizes the pore size to match the lithium ion hydration radius, increases the surface negative charge density, enhances the selectivity and adsorption affinity for lithium ions, improves adsorption capacity, and also enhances acid and alkali resistance, resistance to impurity poisoning and cyclic regeneration performance, adapts to complex chemical environments, and improves lithium ion diffusion channels, shortens adsorption equilibrium time, improves process efficiency, and greatly improves lithium recovery rate.

[0041] 3. In the present invention, first, carbon dioxide reacts with lithium in the lithium ion purification solution without introducing other metal ions or impurities, and high-purity lithium carbonate can be directly generated, reducing the purification process. Secondly, carbon dioxide has low cost and low material consumption. The pH of the solution can be accurately adjusted by controlling the ventilation rate to avoid the formation of by-products caused by local excessive alkalinity. At the same time, lithium carbonate precipitates with uniform particles and easy to filter are formed. The reaction by-product is only water, and the treatment of washing wastewater is simple, reducing the generation of solid waste and wastewater. Finally, the gas-liquid reaction has fast mass transfer, no additional heating is required, low energy consumption, smooth connection with the previous process, and can ensure product quality. Therefore, the use of carbon dioxide and lithium ions to prepare lithium carbonate not only greatly improves the recovery rate of lithium, but also makes the lithium carbonate content reach battery-grade lithium carbonate without introducing impurity ions. DETAILED DESCRIPTION

[0042] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] In the present invention, N-methylpyrrolidone is selected from Shandong Xinyujia Chemical Co., Ltd., with a CAS number of 872-50-4, an active ingredient content of 99.9%, and a model number of ZK1230;

[0044] In the present invention, aluminum isopropoxide is selected from Jinan Huijinchuan Trading Co., Ltd., with a CAS number of 555-31-7 and an active ingredient content of 99.9%;

[0045] Example 1

[0046] This embodiment provides a method for recycling waste batteries to prepare lithium carbonate, comprising the following steps:

[0047] S1. Preparation of lithium iron phosphate powder

[0048] The discarded lithium iron phosphate batteries are discharged and disassembled to obtain battery shell materials, lithium iron phosphate positive electrodes and graphite negative electrodes. The lithium iron phosphate positive electrodes are crushed to obtain lithium iron phosphate powder.

[0049] S2. Preprocessing

[0050] Weigh: 10 g of lithium iron phosphate powder was added to 20 mL of 80 wt% N-methylpyrrolidone, ultrasonically dispersed at 40 ° C for 0.5 h, filtered, washed twice with N-methylpyrrolidone solution, mixed with 5 g of sodium carbonate, and aerobically calcined at 500 ° C for 1 h to obtain lithium iron phosphate pretreated powder.

[0051] S3, acid leaching

[0052] Weigh: 10g of lithium iron phosphate pretreated powder is added to 50mL of deionized water, stirred at 20°C for 30min, then a 30wt% hydrochloric acid aqueous solution is added thereto, the pH of the solution is adjusted to 2.0, stirring is continued for 2h, and filter pressing and washing are performed to obtain a lithium-containing solution.

[0053] S4. Preparation of aluminum-doped manganese ion sieve pre-sintered powder

[0054] Weigh: 0.2 g of aluminum isopropoxide is dissolved in 50 mL of ethanol, add 10 g of manganese carbonate powder, stir at 60°C for 2 h to obtain a uniform sol, dry the sol in an 80°C oven for 24 h to obtain a precursor powder, and then pre-sinter the precursor powder in an air atmosphere at 350°C for 3 h to obtain a pre-sintered powder.

[0055] S5. Preparation of aluminum-doped manganese ion sieve precursor

[0056] Weigh: 10g of aluminum-doped manganese ion sieve pre-sintered powder is mixed with 15g of lithium hydroxide monohydrate, transferred to a polytetrafluoroethylene-lined high-pressure reactor, and then added with 80mL of deionized water. The mixture is reacted at 150°C for 12h to form an aluminum-doped lithium manganate precursor.

[0057] S6. Preparation of aluminum-doped manganese ion sieve

[0058] Weigh: 10g of aluminum-doped lithium manganate precursor is secondary calcined in an air atmosphere at 450℃ for 6h, then immersed in 50mL of 1.0wt% lithium hydroxide aqueous solution, stirred at 25℃ for 4h, filtered and washed, and vacuum dried at 60℃ for 12h to obtain an aluminum-doped manganese ion sieve.

[0059] S7, lithium ion adsorption

[0060] Weigh 300 mL of lithium-containing solution, add 5 wt% sodium hydroxide solution, adjust the system pH to 6, filter it through a COF membrane, add 10 g of aluminum-doped manganese ion sieve, and adsorb at 25°C for 1 hour to obtain a lithium-attached ion sieve.

[0061] S8. Preparation of lithium ion purification solution

[0062] The lithium-attached ion sieve was added to a lithium hydroxide analytical solution at pH = 10, and heated to 70° C. using microwave-assisted heating and analyzed for 3 h to obtain a lithium ion purified solution.

[0063] S9. Preparation of lithium carbonate

[0064] Carbon dioxide gas was introduced into the lithium ion purification liquid. At 25° C., when the pH of the purification liquid reached 8.5, the purification liquid was filtered, the filter cake was washed with deionized water, and dried at 120° C. for 2 h to obtain lithium carbonate.

[0065] Example 2

[0066] This embodiment provides a method for recycling waste batteries to prepare lithium carbonate, comprising the following steps:

[0067] S1. Preparation of lithium iron phosphate powder

[0068] The discarded lithium iron phosphate batteries are discharged and disassembled to obtain battery shell materials, lithium iron phosphate positive electrodes and graphite negative electrodes. The lithium iron phosphate positive electrodes are crushed to obtain lithium iron phosphate powder.

[0069] S2. Preprocessing

[0070] Weigh: 10 g of lithium iron phosphate powder was added to 20 mL of 83 wt% N-methylpyrrolidone, ultrasonically dispersed at 50 ° C for 1 h, filtered, washed three times with N-methylpyrrolidone solution, mixed with 5 g of sodium carbonate, and aerobically calcined at 500 ° C for 1 h to obtain lithium iron phosphate pretreated powder.

[0071] S3, acid leaching

[0072] Weigh: 10g of lithium iron phosphate pretreated powder is added to 50mL of deionized water, stirred at 25°C for 30min, then 34wt% hydrochloric acid aqueous solution is added thereto, the pH of the solution is adjusted to 2.5, stirring is continued for 2h, and filter pressing and washing are performed to obtain a lithium-containing solution.

[0073] S4. Preparation of aluminum-doped manganese ion sieve pre-sintered powder

[0074] Weigh: 0.3 g of aluminum isopropoxide is dissolved in 80 mL of ethanol, add 10 g of manganese carbonate powder, stir at 70°C for 3 h to obtain a uniform sol, dry the sol in an 80°C oven for 24 h to obtain a precursor powder, and then pre-sinter the precursor powder in an air atmosphere at 400°C for 4 h to obtain a pre-sintered powder.

[0075] S5. Preparation of aluminum-doped manganese ion sieve precursor

[0076] Weigh: 10g of aluminum-doped manganese ion sieve pre-sintered powder is mixed with 18g of lithium hydroxide monohydrate, transferred to a polytetrafluoroethylene-lined high-pressure reactor, and then added with 80mL of deionized water. The mixture is reacted at 180°C for 13h to form an aluminum-doped lithium manganate precursor.

[0077] S6. Preparation of aluminum-doped manganese ion sieve

[0078] Weigh: 10g of aluminum-doped lithium manganate precursor is calcined twice in an air atmosphere at 5000℃ for 7h, then immersed in 80mL of 2.5wt% lithium hydroxide aqueous solution, stirred at 30℃ for 5h, filtered and washed, and vacuum dried at 60℃ for 12h to obtain aluminum-doped manganese ion sieve.

[0079] S7, lithium ion adsorption

[0080] Weigh 400 mL of lithium-containing solution, add 8 wt% sodium hydroxide solution, adjust the system pH to 6.5, filter it through a COF membrane, add 10 g of aluminum-doped manganese ion sieve, and adsorb for 1.5 hours at 30°C to obtain a lithium-attached ion sieve.

[0081] S8. Preparation of lithium ion purification solution

[0082] The lithium-attached ion sieve was added to a lithium hydroxide analytical solution at pH = 11, and heated to 75° C. using microwave-assisted heating and analyzed for 4 hours to obtain a lithium ion purified solution.

[0083] S9. Preparation of lithium carbonate

[0084] Carbon dioxide gas was introduced into the lithium ion purification liquid. At 30° C., when the pH of the purification liquid reached 8.5, the purification liquid was filtered, the filter cake was washed with deionized water, and dried at 130° C. for 2.5 h to obtain lithium carbonate.

[0085] Example 3

[0086] This embodiment provides a method for recycling waste batteries to prepare lithium carbonate, comprising the following steps:

[0087] S1. Preparation of lithium iron phosphate powder

[0088] The discarded lithium iron phosphate batteries are discharged and disassembled to obtain battery shell materials, lithium iron phosphate positive electrodes and graphite negative electrodes. The lithium iron phosphate positive electrodes are crushed to obtain lithium iron phosphate powder.

[0089] S2. Preprocessing

[0090] Weigh: 10 g of lithium iron phosphate powder was added to 20 mL of 85 wt% N-methylpyrrolidone, ultrasonically dispersed at 60 ° C for 1.5 h, filtered, washed four times with N-methylpyrrolidone solution, mixed with 5 g of sodium carbonate, and aerobically calcined at 700 ° C for 2 h to obtain lithium iron phosphate pretreated powder.

[0091] S3, acid leaching

[0092] Weigh: 10g of lithium iron phosphate pretreated powder is added to 50mL of deionized water, stirred at 30°C for 30min, then added with 37wt% hydrochloric acid aqueous solution, adjusted the solution pH to 3.0, continued stirring for 2h, and filtered and washed to obtain a lithium-containing solution.

[0093] S4. Preparation of aluminum-doped manganese ion sieve pre-sintered powder

[0094] Weigh: 0.5 g of aluminum isopropoxide is dissolved in 100 mL of ethanol, 10 g of manganese carbonate powder is added, and the mixture is stirred at 80°C for 4 h to obtain a uniform sol. The sol is dried in an oven at 80°C for 24 h to obtain a precursor powder. The precursor powder is then pre-sintered in an air atmosphere at 450°C for 5 h to obtain a pre-sintered powder.

[0095] S5. Preparation of aluminum-doped manganese ion sieve precursor

[0096] Weigh: 10g of aluminum-doped manganese ion sieve pre-sintered powder is mixed with 20g of lithium hydroxide monohydrate, transferred to a polytetrafluoroethylene-lined high-pressure reactor, and then added with 80mL of deionized water. The mixture is reacted at 200°C for 14h to form an aluminum-doped lithium manganate precursor.

[0097] S6. Preparation of aluminum-doped manganese ion sieve

[0098] Weigh: 10g of aluminum-doped lithium manganate precursor is secondary calcined in an air atmosphere at 600℃ for 8h, then immersed in 100mL of 4.1wt% lithium hydroxide aqueous solution, stirred at 40℃ for 6h, filtered and washed, and vacuum dried at 60℃ for 12h to obtain aluminum-doped manganese ion sieve.

[0099] S7, lithium ion adsorption

[0100] Weigh 500 mL of lithium-containing solution, add 10 wt% sodium hydroxide solution, adjust the system pH to 7, filter it through a COF membrane, add 10 g of aluminum-doped manganese ion sieve, and adsorb for 2 hours at 40°C to obtain a lithium-attached ion sieve.

[0101] S8. Preparation of lithium ion purification solution

[0102] The lithium-attached ion sieve was added to a lithium hydroxide analytical solution at pH = 12, and heated to 80° C. using microwave-assisted heating and analyzed for 5 h to obtain a lithium ion purified solution.

[0103] S9. Preparation of lithium carbonate

[0104] Carbon dioxide gas was introduced into the lithium ion purification liquid. At 35° C., when the pH of the purification liquid reached 9.0, the purification liquid was filtered, the filter cake was washed with deionized water, and dried at 150° C. for 3 h to obtain lithium carbonate.

[0105] Comparative Example 1 The difference between this comparative example and Example 3 is that the step of treating the lithium iron phosphate powder with N-methylpyrrolidone in step S2 is omitted, and the lithium iron phosphate powder is directly calcined to obtain the lithium iron phosphate pretreated powder.

[0106] Comparative Example 2

[0107] The difference between this comparative example and Example 3 is that the step S7 of filtering the lithium-containing solution with a COF membrane is omitted.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 3 is that step S4-6 is eliminated, and the aluminum-doped manganese-based ion sieve in step S7 is replaced by a manganese-based ion sieve.

[0110] Comparative Example 4

[0111] The difference between this comparative example and Example 3 is that step S9 is omitted and the carbon dioxide gas in S9 is replaced by sodium carbonate.

[0112] Performance testing:

[0113] The lithium leaching rate and lithium recovery rate of lithium carbonate prepared by recycling waste batteries prepared in Examples 1-3 and Comparative Examples 1-4 were determined with reference to the standard TCIECCPA 037-2024 "Technical Specifications for Wet Process Recycling of Waste Lithium Iron Phosphate Batteries - Preparation of Battery-Grade Lithium Carbonate";

[0114] With reference to the standard YS / T 582-2023 "Battery Grade Lithium Carbonate", the lithium carbonate content and impurity content in the lithium carbonate prepared by recycling waste batteries prepared in Examples 1-3 and Comparative Examples 1-4 were determined to meet the standard content. The specific test results are shown in Table 1 below:

[0115] Table 1-Performance test data of the sample

[0116]

[0117]

[0118] Data Analysis:

[0119] Comparative analysis of the data in Table 1 above shows that the lithium carbonate prepared by recycling waste batteries prepared by the present invention has a lithium leaching rate of 99.49%, a lithium recovery rate of 90.2%, and a lithium carbonate content of 99.79%, which meets the standard of battery-grade lithium carbonate. The impurity content in the lithium carbonate also meets the standard of battery-grade lithium carbonate.

[0120] Comparative Example 1 Compared with Example 3, the dissolution of PVDF leads to the release of the encapsulated lithium ions, which greatly improves the leaching rate and recovery rate of lithium ions. At the same time, no impurities are introduced. The content of lithium carbonate and the impurity content in the prepared lithium carbonate meet the standards for battery lithium carbonate.

[0121] Comparative Example 2 Compared with Example 3, the diameter of lithium ions is 0.76 nm. Due to their small size, they can enter the pores and pass through the membrane. The diameters of sodium ions, iron ions, and chloride ions in the solution are much larger than those of lithium ions and can be filtered out by the COF membrane. Therefore, the impurity content of the solution filtered by the COF membrane is greatly reduced, and the prepared lithium carbonate meets the standards for battery lithium carbonate.

[0122] Comparative Example 3 Compared with Example 3, the aluminum-doped manganese ion sieve greatly improves the recovery rate of lithium ions by ion exchange with lithium ions, and the aluminum ions can suppress Jahn-Teller distortion by replacing some manganese sites and reduce the dissolution of manganese, so the prepared lithium carbonate meets the standards of battery lithium carbonate;

[0123] Compared with Example 3, Comparative Example 4 reacts with lithium in the lithium ion purification solution without the introduction of other metal ions or impurities, and can directly generate high-purity lithium carbonate, reducing the loss of lithium ions in the purification process and improving the recovery rate of lithium carbonate. At the same time, the prepared lithium carbonate meets the standards for battery lithium carbonate.

[0124] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing lithium carbonate by recycling waste batteries, characterized in that: The following steps are involved: S1. Discharging and disassembling discarded lithium iron phosphate batteries to obtain battery shell materials, lithium iron phosphate positive electrodes and graphite negative electrodes, and crushing the lithium iron phosphate positive electrodes to obtain lithium iron phosphate powder; S2, pre-treating the lithium iron phosphate powder and then acid leaching and extracting it to prepare a lithium-containing solution; S3. Add alkali to the lithium-containing solution to adjust the pH of the system to 6-7, filter it through a COF membrane, add aluminum-doped manganese ion sieve, adsorb it at 25-40°C for 1-2 hours to obtain a lithium-attached ion sieve, and desorb the lithium-attached ion sieve to obtain a regenerated aluminum-doped manganese ion sieve and a lithium ion purification solution; S4. Precipitating lithium in the lithium ion purification solution with carbon dioxide to obtain lithium carbonate.

2. A method for preparing lithium carbonate by recycling waste batteries according to claim 1, characterized in that In step S2, the lithium iron phosphate powder is pretreated by adding N-methylpyrrolidone solution to the lithium iron phosphate powder, ultrasonically dispersing it at 40-60°C for 0.5-1.5h, filtering it, washing it with N-methylpyrrolidone solution 2-4 times, mixing it with sodium carbonate, and aerobically calcining it at 500-700°C for 1-2h to obtain lithium iron phosphate pretreated powder.

3. A method for preparing lithium carbonate by recycling waste batteries according to claim 2, characterized in that, The usage ratio of the lithium iron phosphate powder, N-methyl pyrrolidone and sodium carbonate is 1 g:2 mL:0.5 g, and the concentration of the N-methyl pyrrolidone is 80-85 wt %.

4. The method for preparing lithium carbonate by recycling waste batteries according to claim 1, wherein In step S2, the method for acid leaching the lithium iron phosphate powder after pretreatment is as follows: the lithium iron phosphate pretreated powder is first added to deionized water, stirred at 20-30°C for 30 minutes, and then an inorganic acid is added thereto to adjust the solution pH to 2.0-3.0, and stirring is continued for 2 hours, and filter pressing and washing are performed to obtain a lithium-containing solution.

5. A method for preparing lithium carbonate by recycling waste batteries according to claim 4, characterized in that: The dosage ratio of the oxidation mixture to deionized water is 1 g:5 mL, and the inorganic acid is a 30-37 wt % hydrochloric acid solution.

6. The method for preparing lithium carbonate by recycling waste batteries according to claim 1, wherein: In step S3, the ratio of the lithium-containing solution to the aluminum-doped manganese ion sieve is 30-50 mL:1 g, and the base is a sodium hydroxide solution with a mass percentage of 5-10 wt%.

7. The method for preparing lithium carbonate by recycling waste batteries according to claim 1, wherein: In step S3, the aluminum-doped manganese ion sieve is prepared by the following steps: A1. Dissolve aluminum isopropoxide in ethanol, add manganese carbonate powder, and stir at 60-80°C for 2-4 hours to obtain a uniform sol. Dry the sol in an oven at 80°C for 24 hours to obtain a precursor powder. Pre-sinter the precursor powder in an air atmosphere at 350-450°C for 3-5 hours to obtain a pre-sintered powder. A2. After mixing the pre-sintered powder with lithium hydroxide monohydrate, the mixture was transferred to a polytetrafluoroethylene-lined autoclave, and deionized water was added. The mixture was reacted at 150-200° C. for 12-14 hours to form an aluminum-doped lithium manganate precursor. A3. The aluminum-doped lithium manganate precursor is secondary calcined in an air atmosphere at 450-600°C for 6-8 hours, then immersed in a lithium hydroxide solution, stirred at 25-40°C for 4-6 hours, filtered and washed, and vacuum-dried at 60°C for 12 hours to obtain an aluminum-doped manganese ion sieve.

8. The method for preparing lithium carbonate by recycling waste batteries according to claim 7, wherein: In step A1, the ratio of aluminum isopropoxide, ethanol and manganese carbonate powder is 0.02-0.05 g:5-10 mL:1 g.

9. The method for preparing lithium carbonate by recycling waste batteries according to claim 7, wherein: In step A2, the ratio of the pre-sintered powder, lithium hydroxide monohydrate and deionized water is 1 g:1.5-2 g:8 mL.

10. The method for preparing lithium carbonate by recycling waste batteries according to claim 7, wherein: In step A3, the ratio of the aluminum-doped lithium manganate precursor to the lithium hydroxide solution is 1 g:5-10 mL, and the concentration of the lithium hydroxide solution is 1.0-4.1 wt %.

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