Resource recycling method of lithium iron phosphate
By repairing the crystal structure of lithium iron phosphate materials under supercritical conditions, the problems of complex processes and incomplete performance recovery in existing technologies have been solved, and efficient resource recycling and reuse of lithium iron phosphate has been achieved.
Patent Information
- Application Number
- CN202511345539.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-19
- Publication Date
- 2025-12-12
AI Technical Summary
Existing lithium iron phosphate recycling technologies suffer from problems such as complex processes, high costs, incomplete material repair, and unsatisfactory performance recovery.
A supercritical reactor is used to mix lithium iron phosphate black powder with lithium source, iron source, phosphorus source, carbon source and metal ion additives in a solvent at 250-400℃ and 20-30MPa to form a mixed slurry for reaction, which repairs the material's crystal lattice structure and forms a new particle size distribution.
It simplifies the process flow, improves element utilization, restores the stoichiometry and electrochemical performance of materials, and reduces material and energy consumption.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of waste lithium-ion battery recycling technology, specifically a method for the resource-based recycling and reuse of lithium iron phosphate. Background Technology
[0002] Lithium iron phosphate (LFP) batteries, as the cathode material for lithium-ion batteries, have been widely used in electric vehicles and large-scale energy storage systems due to their stable structure, low cost, and long cycle life. With the rapid development of related industries, a large number of LFP batteries have entered or are about to enter their retirement period. These retired batteries contain valuable elements such as lithium, iron, and phosphorus. Direct disposal not only wastes resources but also poses a potential threat to the environment. Therefore, the resource recycling and reuse of retired LFP batteries is a necessary step towards achieving sustainable industrial development.
[0003] Currently, the recycling technology for waste lithium iron phosphate cathode materials mainly relies on hydrometallurgy. This type of process typically involves leaching the recovered lithium iron phosphate black powder with strong acid, dissolving components such as lithium, iron, and phosphorus into the solution. Subsequently, through multi-step chemical precipitation or solvent extraction, the ions in the solution are separated and purified, ultimately yielding chemical raw materials such as lithium carbonate and iron phosphate, which are then used to resynthesize new lithium iron phosphate materials. However, this complete dismantling-reconstruction recycling path is lengthy and complex, with each separation and purification step increasing production costs and control difficulties. Furthermore, this process damages the original iron phosphate framework structure in the material, failing to fully utilize its value as a precursor, and generating large amounts of acidic wastewater and industrial salts during acid leaching and precipitation, placing high demands on subsequent environmental treatment.
[0004] To simplify the recycling process, technical solutions for directly repairing waste lithium iron phosphate materials have emerged. These solutions typically employ methods such as solid-state sintering, mixing the recovered black powder with supplementary materials like lithium salts and then subjecting the mixture to high-temperature treatment to replenish the lost lithium in the material. However, in solid-state reaction systems, the mass transfer efficiency between reactants is low, making it difficult for the added lithium source to penetrate evenly and deeply into the degraded lithium iron phosphate particles. This results in insufficient repair of the material's crystal structure, and its electrochemical performance often fails to recover to ideal levels, limiting the application value of the repaired material. Therefore, developing a recycling and reuse method that simplifies the process while effectively restoring material performance is a current technical challenge in this field. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a method for the resource-based recycling and reuse of lithium iron phosphate, which solves the problems of complex processes, high costs, incomplete material repair, and unsatisfactory performance recovery in existing lithium iron phosphate recycling technologies.
[0006] To address the aforementioned technical problems, this invention provides a technical solution for the resource-based recycling and reuse of lithium iron phosphate.
[0007] The first aspect of this invention provides a method for the resource-based recycling and reuse of lithium iron phosphate, characterized by comprising the following steps: S1: Collecting retired lithium iron phosphate black powder; S2: Test the content of each substance in the lithium iron phosphate black powder; S3: Disperse the lithium iron phosphate black powder collected in S1 in a solvent, add acid, lithium source, iron source, phosphorus source, carbon source and metal ion additives to form a mixed slurry; S4: The mixed slurry obtained in S3 is transferred to a supercritical reactor for reaction. After the reaction is completed, it is dried to obtain lithium iron phosphate cathode material for reuse.
[0008] In some embodiments of the present invention, in step S4, the reaction temperature in the supercritical reactor is 250-400°C, the reaction pressure is 20-30 MPa, and the reaction time is 1-7 hours. In the supercritical fluid environment, the reactants possess high diffusivity and solubility, enabling them to penetrate the microstructure of lithium iron phosphate black powder. Under the set temperature and pressure conditions, the supplemented lithium, iron, and phosphorus sources repair existing lattice defects or react on their surfaces, thereby supplementing the missing lithium element and repairing its crystal structure. Simultaneously, these reaction conditions can form new, smaller particles on the surface of the existing lithium iron phosphate particles, thereby altering the overall particle size distribution of the material.
[0009] In some embodiments of the present invention, in step S1, the lithium iron phosphate black powder is filtered using a 100-300 mesh sieve to remove large particulate impurities that do not meet the size requirements.
[0010] In some embodiments of the present invention, in step S2, the tested substance content includes magnetic material content, lithium content, and carbon content, so as to provide a basis for the amount of each material added in step S3.
[0011] In some embodiments of the present invention, step S3 includes: diluting the acid with water, mixing it with a solvent in which lithium iron phosphate black powder is dispersed, and stirring for 30-60 minutes, then sequentially adding the lithium source, iron source, phosphorus source, carbon source, and metal ion additive. This pretreatment step aims to activate the surface of the lithium iron phosphate black powder.
[0012] In some embodiments of the present invention, in step S4, before the reaction, an inert gas is introduced into the supercritical reactor to purge air from the reactor. The inert gas is selected from nitrogen, argon, or a mixture of nitrogen and argon to prevent side reactions from occurring during the high-temperature reaction process.
[0013] In some embodiments of the present invention, the acid is selected from one or more of phosphoric acid, sulfuric acid, hydrochloric acid, and nitric acid.
[0014] In some embodiments of the present invention, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium hydrogen phosphate; and the iron source is selected from one or more of ferric nitrate, ferric phosphate, ferric chloride, ferrous chloride, iron oxide red, and ferrous oxalate.
[0015] In some embodiments of the present invention, the phosphorus source is selected from one or more of iron phosphate, phosphoric acid, lithium dihydrogen phosphate, and lithium hydrogen phosphate; and the carbon source is selected from one or more of glucose, sucrose, PEG, PVP, and resin.
[0016] In some embodiments of the present invention, the metal ion additive is selected from one or more of titanium dioxide, vanadium pentoxide, ammonium metavanadate, niobium pentoxide, magnesium oxide, and manganese trioxide.
[0017] This invention provides a method for the resource-based recycling and reuse of lithium iron phosphate. It has the following beneficial effects: 1. This invention uses recycled lithium iron phosphate black powder as a reaction precursor to directly supplement and repair the existing material structure, rather than completely dissolving and resynthesizing it. This direct reuse method eliminates complex separation, purification, and resynthesis steps, simplifies the overall process, improves the overall utilization rate of elements such as iron and phosphorus in the recycled materials, and reduces material and energy consumption.
[0018] 2. This invention utilizes the high permeability and high solubility of supercritical fluids at specific temperatures (250-400℃) and pressures (20-30MPa). This allows the added lithium, iron, and phosphorus sources to effectively penetrate the internal microstructure of lithium iron phosphate black powder particles, achieving in-situ repair of lattice defects and replenishing lithium ions lost due to multiple cycles, thereby restoring the stoichiometry of the material.
[0019] 3. This invention induces the formation of new, smaller lithium iron phosphate grains on the surface of recovered lithium iron phosphate black powder particles by controlling the process parameters of the supercritical reaction. This secondary growth structure, formed on the basis of the original larger particles, constructs a new particle size distribution, changes the overall microstructure of the material, and increases the specific surface area and electrochemical reaction active sites of the material. Detailed Implementation
[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Example: Example 1
[0022] A method for the resource recovery and reuse of lithium iron phosphate specifically includes the following steps: (1) Collect the retired lithium iron phosphate black powder, filter the lithium iron phosphate black powder with a 200-mesh sieve, weigh 1000g of the filtered black powder and disperse it in water to prepare a precursor slurry.
[0023] (2) Add 10g of phosphoric acid to the precursor slurry prepared in step (1), dilute with water, mix and stir at room temperature for 45min.
[0024] (3) Add 25g lithium carbonate, 50g iron phosphate, 10g glucose, 5g PEG and 2g titanium dioxide to the slurry from step (2). After all materials are added, continue stirring until a uniformly mixed slurry is formed.
[0025] (4) Transfer the mixed slurry prepared in step (3) to a supercritical reactor and seal it. After purging the reactor with nitrogen to remove air, start heating and pressurizing. Control the reaction temperature in the reactor to 320°C and the reaction pressure to 25 MPa, and react under these conditions for 4 hours.
[0026] (5) After the reaction is complete, the product is vacuum dried to obtain lithium iron phosphate cathode material for secondary use.
[0027] Example 2
[0028] A method for the resource recovery and reuse of lithium iron phosphate specifically includes the following steps: (1) Collect the retired lithium iron phosphate black powder, filter the lithium iron phosphate black powder with a 100-mesh sieve, weigh 1000g of the filtered black powder and disperse it in water to prepare a precursor slurry.
[0029] (2) Add 8g of sulfuric acid to the precursor slurry prepared in step (1), dilute with water, mix and stir at room temperature for 30min.
[0030] (3) Add 20g lithium hydroxide, 40g ferrous oxalate, 8g sucrose and 1.5g magnesium oxide to the slurry from step (2). After all materials are added, continue stirring until a uniformly mixed slurry is formed.
[0031] (4) Transfer the mixed slurry prepared in step (3) to a supercritical reactor and seal it. After introducing argon gas into the reactor to remove air, start heating and pressurizing. Control the reaction temperature in the reactor to 250°C and the reaction pressure to 20 MPa, and react under these conditions for 1 hour.
[0032] (5) After the reaction is complete, the product is vacuum dried to obtain lithium iron phosphate cathode material for secondary use.
[0033] Example 3
[0034] A method for the resource recovery and reuse of lithium iron phosphate specifically includes the following steps: (1) Collect the retired lithium iron phosphate black powder, filter the lithium iron phosphate black powder with a 300-mesh sieve, weigh 1000g of the filtered black powder and disperse it in water to prepare a precursor slurry.
[0035] (2) Add a mixture of 6g nitric acid and 6g hydrochloric acid to the precursor slurry prepared in step (1), dilute with water, mix and stir at room temperature for 60 min.
[0036] (3) Add 20g of lithium carbonate, 15g of lithium dihydrogen phosphate, 30g of ferric nitrate, 30g of iron oxide red, 15g of PVP, 2g of vanadium pentoxide and 2g of niobium pentoxide to the slurry from step (2). After all materials are added, continue stirring until a uniformly mixed slurry is formed.
[0037] (4) Transfer the mixed slurry prepared in step (3) to a supercritical reactor and seal it. After introducing a mixture of nitrogen and argon into the reactor to purge air, start heating and pressurizing. Control the reaction temperature in the reactor to 400℃ and the reaction pressure to 30MPa, and react under these conditions for 7 hours.
[0038] (5) After the reaction is complete, the product is vacuum dried to obtain lithium iron phosphate cathode material for secondary use.
[0039] Comparative Example 1 The difference from Example 1 is that the reaction in step (4) is carried out at atmospheric pressure (0.1 MPa) instead of at a pressure of 25 MPa, while the rest are the same.
[0040] Comparative Example 2 Compared with Example 1, the difference is that lithium carbonate is not added in step (3), but the rest are the same.
[0041] Comparative Example 3 The difference from Example 2 is that the reaction temperature in step (4) is 200°C instead of 250°C, while the rest are the same.
[0042] Comparative Example 4 Compared with Example 2, the difference is that the acid activation process in step (2) is not performed, that is, step (3) is performed directly after step (1), and the rest are the same.
[0043] Comparative Example 5 The difference from Example 3 is that the reaction pressure in step (4) is 15 MPa instead of 30 MPa, while the rest are the same.
[0044] Comparative Example 6 Compared with Example 3, the difference is that vanadium pentoxide and niobium pentoxide are not added in step (3), but the rest are the same.
[0045] Test Example 1: Powder Compacted Density Test Experimental steps Take the powder samples prepared and dried in Examples 1-3 and Comparative Examples 1-6.
[0046] Using an electronic balance with an accuracy of 0.001g, accurately weigh 5.0g of each sample.
[0047] The weighed samples were placed into clean, dry 10mL glass graduated cylinders.
[0048] The graduated cylinder containing the sample is fixed on a powder tap density meter of model FS4.
[0049] Set the instrument's vibration frequency to 300 times / minute and the total number of vibrations to 500 times, then start the instrument to perform vibration compaction.
[0050] After the vibration program is completed, remove the graduated cylinder from the instrument and read the final volume V of the powder sample in the graduated cylinder after vibration.
[0051] The compacted density ρ of each sample was calculated using the following formula: ρ(g / cm³) = 5.0(g) / V(cm³).
[0052] Record the powder compaction density test results for each sample.
[0053] The experimental data are shown in Table 1. Table 1: Powder compaction density test results of samples obtained from each embodiment and comparative example
[0054] As shown in Table 1, the secondary lithium iron phosphate cathode materials prepared by the methods of Examples 1, 2, and 3 all have higher powder compaction densities than the materials prepared by the methods of Comparative Examples 1 to 6. This indicates that the reaction conditions and material composition during the preparation process have a direct impact on the physical properties of the final product.
[0055] Comparing Examples 1-3 with Comparative Examples 1, 3, and 5, the reaction conditions (pressure or temperature) of the latter were not within the combined range of 250-400℃ and 20-30MPa, resulting in lower powder compaction density of their products. This result shows that a specific high-temperature and high-pressure reaction environment is a necessary condition for obtaining high-compact-density powder materials. Within this specific temperature and pressure range, the reaction system is in a supercritical state, providing the physical conditions for structural repair and surface reconstruction of the material.
[0056] Comparing Example 1 with Comparative Examples 2, 4, and 6, the latter lacked a lithium source, acid activation step, or metal ion additive in their preparation processes, respectively. The powder compaction density values of these comparative examples were all lower than those of Example 1. This indicates that a complete reaction system containing acid, lithium source, iron source, phosphorus source, carbon source, and metal ion additive is the chemical basis for altering the physical properties of materials. Under supercritical conditions, these chemical components participate in the reaction together, undergoing secondary growth on the surface of the recovered lithium iron phosphate black powder, thereby changing the particle packing pattern of the final product and thus affecting its powder compaction density.
[0057] Test Example 2: Electrochemical Performance Test Experimental steps Positive electrode preparation (1) The powder samples prepared and dried in Examples 1-3 and Comparative Examples 1-6 were used as positive electrode active materials.
[0058] (2) The active material: conductive agent: binder = 90:5:5 by mass ratio, the three are placed in N-methylpyrrolidone solvent and mechanically stirred using a planetary ball mill until a uniform positive electrode slurry without particle agglomeration is formed.
[0059] (3) The prepared positive electrode slurry is uniformly coated onto the surface of the aluminum foil current collector using a coating machine, and the coating thickness is controlled.
[0060] (4) Place the coated electrode in a vacuum oven at 80°C and dry for 12 hours.
[0061] (5) After the electrode is dried, use a punching machine to punch it into a circular positive electrode with a diameter of 14mm.
[0062] Button battery assembly (1) Battery assembly was carried out in a glove box filled with argon gas and with water and oxygen content both below 0.1 ppm.
[0063] (2) The positive electrode prepared in step 1 (5) is used as the working electrode, a lithium metal sheet with a diameter of 16 mm and a thickness of 0.5 mm is used as the counter electrode, and a Celgard2400 polypropylene microporous membrane is used as the separator.
[0064] (3) Add electrolyte (1M LiPF6 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1) to the assembly system until the membrane is completely wetted.
[0065] (4) Use a packaging machine to encapsulate the above components in a CR2032 stainless steel battery case to form a button cell to be tested.
[0066] Charge and discharge performance test (1) Let each assembled coin cell stand at room temperature (25°C) for 12 hours to ensure that the electrolyte fully penetrates the electrodes.
[0067] (2) Electrochemical performance was tested using a battery testing system of model NEWA BETTS4000.
[0068] (3) First, the battery is activated by performing a charge-discharge cycle at a constant current of 0.1C within a voltage range of 2.5V to 4.2V.
[0069] (4) Subsequently, the battery was charged and discharged at a constant current of 1C, and its first discharge specific capacity was recorded.
[0070] The experimental data are shown in Table 2. Table 2: 1C discharge specific capacity test results of samples obtained from each embodiment and comparative example
[0071] As shown in Table 2, the secondary lithium iron phosphate cathode materials prepared by the methods of Examples 1, 2, and 3 all exhibit higher initial 1C discharge specific capacities than the materials prepared by the methods of Comparative Examples 1 to 6. This result indicates that the preparation method of the present invention can restore the electrochemical performance of the recovered lithium iron phosphate black powder.
[0072] Comparing the test data of Examples 1-3 with those of Comparative Examples 1, 3, and 5, the latter three either did not react under pressure or had reaction temperatures and pressures below the lower limits of 250°C and 20 MPa, resulting in a significant decrease in the discharge specific capacity of their products. This result indicates that conducting the reaction within a specific process window of 250-400°C and 20-30 MPa is necessary for restoring the electrochemical performance of materials. Under these temperature and pressure conditions, the reaction system forms a supercritical fluid, whose high diffusivity allows reactants to penetrate into the microstructure of the material, promoting the repair of lattice defects caused by cycling and providing a reaction environment for secondary growth, thereby increasing the number of electrochemically active sites.
[0073] Comparing the test data of Example 1 with those of Comparative Examples 2, 4, and 6, the discharge specific capacity of the products obtained in the absence of a lithium source (Comparative Example 2), without acid activation (Comparative Example 4), or without metal ion additives (Comparative Example 6) was lower than that of Example 1. This indicates that a complete chemical reaction system is necessary for the recovery of material performance. Specifically, the addition of a lithium source is fundamental to replenishing the lost lithium ions in the material; the acid activation step provides a reactive surface for subsequent reactions; and the introduction of metal ion additives further affects the final electrochemical performance of the material.
Claims
1. A method for the resource recovery and reuse of lithium iron phosphate, characterized in that, Includes the following steps: S1: Collecting retired lithium iron phosphate black powder; S2: Test the content of each substance in the lithium iron phosphate black powder; S3: Disperse the lithium iron phosphate black powder collected in S1 in a solvent, add acid, lithium source, iron source, phosphorus source, carbon source and metal ion additives to form a mixed slurry; S4: The mixed slurry obtained in S3 is transferred to a supercritical reactor for reaction. After the reaction is completed, it is dried to obtain lithium iron phosphate cathode material for reuse.
2. The method according to claim 1, characterized in that, In S4, the reaction temperature in the supercritical reactor is 250-400℃, the reaction pressure is 20-30MPa, and the reaction time is 1-7h.
3. The method according to claim 1, characterized in that, In step S1, the lithium iron phosphate black powder is filtered using a 100-300 mesh sieve to remove large particulate impurities.
4. The method according to claim 1, characterized in that, In S2, the tested material content includes magnetic material content, lithium content, and carbon content.
5. The method according to claim 1, characterized in that, S3 includes: diluting the acid with water, mixing it with a solvent containing lithium iron phosphate black powder and stirring for 30-60 minutes, and then sequentially adding the lithium source, iron source, phosphorus source, carbon source and metal ion additive.
6. The method according to claim 1, characterized in that, In step S4, before the reaction, an inert gas is introduced into the supercritical reactor to remove air from the reactor. The inert gas is selected from nitrogen, argon, or a mixture of nitrogen and argon.
7. The method according to claim 1, characterized in that, The acid is selected from one or more of phosphoric acid, sulfuric acid, hydrochloric acid, and nitric acid.
8. The method according to claim 1, characterized in that, The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium hydrogen phosphate. The iron source is selected from one or more of ferric nitrate, ferric phosphate, ferric chloride, ferrous chloride, iron oxide red, and ferrous oxalate.
9. The method according to claim 1, characterized in that, The phosphorus source is selected from one or more of iron phosphate, phosphoric acid, lithium dihydrogen phosphate, and lithium hydrogen phosphate. The carbon source is selected from one or more of glucose, sucrose, PEG, PVP, and resin.
10. The method according to claim 1, characterized in that, The metal ion additive is selected from one or more of titanium dioxide, vanadium pentoxide, ammonium metavanadate, niobium pentoxide, magnesium oxide, and manganese trioxide.