Method for recycling lithium iron phosphate battery cathode material

Abstract

This invention provides a method for recycling lithium iron phosphate battery cathode materials. The method involves mixing the lithium iron phosphate cathode material, calcined under an inert atmosphere, with an alkaline solution of pH 14.2-14.6 at a liquid-to-solid volume ratio of 30-50 mL / g. The mixture is first leached at a first temperature, then at a second temperature. The leachate and iron(III) oxide are separated. The pH of the leachate is adjusted to 11.5-13.5, and the solution is heated to 70-110°C for lithium precipitation. The resulting lithium phosphate and lithium precipitation mother liquor are then separated. The first temperature is 25-45°C, and the second temperature is 5-20°C lower than the first temperature. This invention employs an alkaline leaching-lithium precipitation process, achieving efficient leaching of lithium and phosphorus while simultaneously recovering lithium phosphate and iron(III) oxide through liquid-to-solid ratio control combined with pH and temperature regulation. This invention does not introduce additional lithium precipitation reagents, and the overall process is simple, efficient, and environmentally friendly, making it significant for the sustainable development of the new energy industry.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery recycling technology, specifically relating to a method for recycling positive electrode materials of lithium iron phosphate batteries. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, lithium iron phosphate (LiFePO4) batteries have become one of the mainstream power batteries due to their high safety, long cycle life, and low cost. However, the widespread use of large numbers of LiFePO4 batteries has also brought challenges to the disposal and recycling of retired batteries. Improper disposal can lead to environmental pollution and resource waste. Promoting the efficient recycling of LiFePO4 batteries can not only reduce environmental pollution but also achieve resource recycling and promote sustainable development. Therefore, researching and optimizing LiFePO4 battery recycling technologies has significant economic and environmental implications.

[0003] Wet leaching is an effective method for recovering lithium resources from batteries. Current research focuses primarily on acidic oxidative leaching for lithium extraction. Oxidative leaching yields a soluble lithium solution and iron phosphate slag. The soluble lithium solution can be converted into lithium carbonate for reuse. However, acidic oxidative leaching often uses strong acids such as sulfuric acid or hydrochloric acid as leaching agents, resulting in highly corrosive equipment and hydrogen release. Furthermore, the use of oxidants such as hydrogen peroxide or oxygen poses certain operational risks. Under acidic oxidative leaching, only lithium is effectively utilized from the positive electrode active components; phosphorus and iron are treated as ferrophosphate slag. In actual production, the regeneration of iron phosphate faces difficulties in impurity removal, leading to high production costs and low actual utilization rates. The use of strong oxidants may also cause some impurity metals, such as copper, to leach out during acidic leaching. These impurity metals entering the leaching solution require multiple extraction, precipitation, and purification steps for removal, increasing the process complexity and reducing the recovery rate and purity of the target metal.

[0004] To address this, some studies have proposed methods for lithium extraction using alkaline leaching or a combination of acid leaching and alkaline leaching. For example, patent CN120157187A discloses a method for comprehensively recovering valuable elements from waste lithium iron phosphate battery materials. This method involves first leaching waste lithium iron phosphate battery black powder and / or electrode material at 40-90°C with alkaline leaching to achieve solid-liquid separation, obtaining alkaline leaching residue and alkaline leaching solution. Acid leaching is then performed to obtain a lithium-containing solution, which is then used for further lithium extraction. This process is complex and not conducive to large-scale industrial application. Patent CN118207425A discloses a method for separating lithium iron phosphate from waste lithium iron phosphate cathode materials. This method uses a magnetic field to assist in breaking down the olivine structure of lithium iron phosphate, obtaining a mixed residue of lithium phosphate solid and iron(III) oxide. Ammonia leaching is then used to obtain a lithium-containing solution, which is then obtained through evaporation and crystallization to produce lithium phosphate products. This process is complex, energy-intensive, and generates large amounts of wastewater and waste salt.

[0005] Therefore, it is necessary to develop simpler, more efficient, and greener methods for recycling lithium iron phosphate battery cathode materials. Summary of the Invention

[0006] The purpose of this invention is to provide a simple, efficient, and environmentally friendly method for recycling lithium iron phosphate battery cathode materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for recycling lithium iron phosphate battery cathode material involves mixing the lithium iron phosphate battery cathode material calcined in an inert atmosphere with an alkaline solution with a pH of 14.2-14.6 at a liquid-to-solid volume ratio of 30-50 mL / g. The resulting mixture is first leached at a first temperature, then leached again at a second temperature, and the leachate and iron(III) oxide are obtained through solid-liquid separation. The pH of the leachate is adjusted to 11.5-13.5 using a 0.1%-1% phosphoric acid solution. The mixture is then heated to a third temperature and aged at the third temperature to precipitate lithium. After solid-liquid separation, lithium phosphate and lithium precipitation mother liquor are obtained. The first temperature is 30-40°C, the second temperature is 10-20°C lower than the first temperature, and the third temperature is 70-110°C.

[0009] In embodiments of the present invention, the pH value of the alkaline solution is 14.2 to 14.6, which refers to the pH value of the alkaline solution at 25°C, specifically such as 14.2, 14.3, 14.4, 14.5, 14.6, or any value between any two of the above.

[0010] In embodiments of the present invention, the liquid-to-solid volume ratio is the volume of the alkaline solution required per unit mass of lithium iron phosphate battery cathode material, specifically such as 30 mL / g, 31 mL / g, 32 mL / g, 33 mL / g, 34 mL / g, 35 mL / g, 36 mL / g, 37 mL / g, 38 mL / g, 39 mL / g, 40 mL / g, 41 mL / g, 42 mL / g, 43 mL / g, 44 mL / g, 45 mL / g, 46 mL / g, 47 mL / g, 48 mL / g, 49 mL / g, 50 mL / g, or any liquid-to-solid volume ratio between any two of the above.

[0011] In embodiments of the present invention, the first temperature is specifically any temperature between any two of the following: 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, or above.

[0012] In embodiments of the present invention, the second temperature is specifically 10°C, 10.5°C, 11°C, 11.5°C, 12°C, 12.5°C, 13°C, 13.5°C, 14°C, 14.5°C, 15°C, 15.5°C, 16°C, 16.5°C, 17°C, 17.5°C, 18°C, 18.5°C, 19°C, 19.5°C, or 20°C lower than the first temperature. In some preferred embodiments, the second temperature is 20-25°C.

[0013] In embodiments of the present invention, the third temperature is specifically any temperature between any two of the following: 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C, 110°C. In some preferred embodiments, the third temperature is 90°C to 105°C.

[0014] In some embodiments of the present invention, the alkaline solution is a sodium hydroxide solution and / or a potassium hydroxide solution.

[0015] Further, the concentration of the alkaline solution is 1.5~4 mol / L, for example, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3 mol / L, or any concentration between any two of the above. In some more preferred embodiments, the concentration of the alkaline solution is 2~3 mol / L.

[0016] In some embodiments of the present invention, the leaching time of the mixture at the first temperature is 1 to 24 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours, 15 hours, 15.5 hours, 16 hours, 16.5 hours, 17 hours, 17.5 hours, 18 hours, 18.5 hours, 19 hours, 19.5 hours, 20 hours, 20.5 hours, 21 hours, 21.5 hours, 22 hours, 22.5 hours, 23 hours, 23.5 hours, and 24 hours. In some more preferred embodiments, the mixture is leached at a first temperature for 1 to 12 hours, and even more preferably 1 to 8 hours.

[0017] In some embodiments of the present invention, the leaching time of the mixture at the second temperature is 0.5 to 1 hour, for example, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour.

[0018] In some embodiments of the present invention, the aging time is 1 to 3 hours, for example 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0019] In some specific and preferred embodiments of the present invention, the mixture is first leached at 30-40°C for 1-5 hours, then leached at 20-25°C for 0.5-1 hours, and the aging time is 1-3 hours.

[0020] In embodiments of the present invention, the pH of the leachate is specifically adjusted to any pH value between any two of the following: 11.5, 11.6, 11.7, 11.8, 11.9, 12, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13, 13.1, 13.2, 13.3, 13.4, 13.5, or above.

[0021] In embodiments of the present invention, the mass concentration of the phosphoric acid solution is specifically any concentration between any two of the following: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or higher.

[0022] In embodiments of the present invention, the lithium iron phosphate battery cathode material is a powder with a particle size of less than or equal to 0.5 mm, and more preferably, the lithium iron phosphate battery cathode material is a powder with a particle size of less than or equal to 0.3 mm. In some embodiments, the lithium iron phosphate battery cathode material is ground into powder, passed through a 50-100 mesh sieve, and then calcined.

[0023] In embodiments of the present invention, the inert atmosphere calcination temperature is 450~600℃, for example, any temperature between any two of the following: 450℃, 455℃, 460℃, 465℃, 470℃, 475℃, 480℃, 485℃, 490℃, 495℃, 500℃, 505℃, 510℃, 515℃, 520℃, 525℃, 530℃, 535℃, 540℃, 545℃, 550℃, 555℃, 560℃, 565℃, 570℃, 575℃, 580℃, 585℃, 590℃, 595℃, 600℃, or above.

[0024] In an embodiment of the present invention, the inert atmosphere calcination time is 1.5 to 3 hours, for example, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3 hours.

[0025] In embodiments of the present invention, the inert atmosphere calcination is carried out in a nitrogen or argon atmosphere.

[0026] In an embodiment of the present invention, the recycling method further includes cooling the lithium precipitation mother liquor to precipitate phosphate, and then separating the solid and liquid components to obtain dodecahydrate phosphate and filtrate.

[0027] In some specific embodiments of the present invention, the lithium precipitation mother liquor is cooled to 2~8°C and allowed to stand at 2~8°C for 1~24 hours before solid-liquid separation is performed to obtain dodecahydrate phosphate and filtrate.

[0028] In some specific embodiments of the present invention, the filtrate is used to prepare an alkaline solution with a pH value of 14.2 to 14.6 and is then reused in the next round of recycling of lithium iron phosphate battery cathode materials.

[0029] According to some specific embodiments of the present invention, the method for recycling the positive electrode material of the lithium iron phosphate battery specifically includes the following steps:

[0030] (1) The positive electrode material of lithium iron phosphate battery is calcined in an inert atmosphere at 450~600℃;

[0031] (2) The calcined lithium iron phosphate battery cathode material from step (1) is mixed with an alkaline solution with a pH of 14.2 to 14.6 at a liquid-to-solid volume ratio of 30 to 50 mL / g. The resulting mixed solution is first leached at the first temperature and then leached at the second temperature. After solid-liquid separation, the leachate and iron(III) oxide are obtained.

[0032] (3) The pH value of the leachate from step (2) is adjusted to 11.5 to 13.5 using a phosphoric acid solution with a mass concentration of 0.1% to 1%, heated to the third temperature and kept at the third temperature for aging and lithium precipitation, and then lithium phosphate and lithium precipitation mother liquor are obtained by solid-liquid separation.

[0033] (4) Cool the lithium precipitation mother liquor to 2~8℃, and after precipitating phosphate dodecahydrate at 2~8℃, perform solid-liquid separation. The obtained filtrate is used to prepare an alkaline solution with a pH of 14.2~14.6 as described in step (2) and reused.

[0034] More specifically, the calcination time in step (1) is 1.5~3h, and the lithium iron phosphate battery cathode material is a powder with a particle size of less than or equal to 0.5mm.

[0035] More specifically, in step (2), the liquid-to-solid volume ratio is 35-45 mL / g, the alkaline solution is a sodium hydroxide solution and / or potassium hydroxide solution with a concentration of 1.5-4 mol / L, the first temperature is 30-40°C, the leaching time at the first temperature is 2-4 h, the second temperature is 20-25°C, and the leaching time at the second temperature is 0.5-1 h.

[0036] More specifically, the heat preservation and aging temperature in step (2) is 70~110℃, and the heat preservation and aging time is 1~3h.

[0037] More specifically, when recycling the filtrate, the filtrate and the corresponding alkali are used to prepare an alkaline solution with a pH of 14.2 to 14.6 for step (1).

[0038] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0039] The present invention discloses a method for recycling lithium iron phosphate battery cathode materials using an alkaline leaching-lithium precipitation process. By selecting an appropriate liquid-solid ratio for feeding, combined with pH and temperature control, efficient leaching of lithium and phosphorus is achieved, followed by aging to obtain high-purity lithium phosphate, while simultaneously recovering iron tetroxide. This invention achieves high recovery rates without the need for additional lithium precipitation reagents. The overall process is simple, efficient, environmentally friendly, and cost-effectively controlled, making it significant for the sustainable development of the new energy industry. Attached Figure Description

[0040] Figure 1 The XRD pattern of the alkaline leaching residue obtained in the alkaline leaching step of Example 1;

[0041] Figure 2 The XRD pattern of the solid precipitate obtained in the lithium precipitation step of Example 1;

[0042] Figure 3 The XRD pattern of the alkaline leaching residue obtained in the alkaline leaching step of Comparative Example 2 is shown.

[0043] Figure 4 The XRD pattern of the alkaline leaching residue obtained in the alkaline leaching step of Comparative Example 3 is shown.

[0044] Figure 5 The image shows the XRD pattern of the alkaline leaching residue obtained in the alkaline leaching step of Comparative Example 6. Detailed Implementation

[0045] To address the common problems in existing lithium iron phosphate cathode material recycling methods, such as complex processes, low processing efficiency, high energy consumption and cost, easy generation of wastewater and waste salts, and unsatisfactory resource recovery rates and product purity, the inventors of this application, through systematic research and extensive creative exploration, have proposed a novel, highly efficient, and clean recycling process for lithium iron phosphate cathode materials. This method significantly simplifies operation, reduces energy consumption and environmental impact, while effectively improving the recovery efficiency of valuable metals and the purity of the final product, thus possessing significant triple benefits in terms of resource value, environmental impact, and economic efficiency.

[0046] Specifically, the technical solution adopted in this application is as follows: The calcined lithium iron phosphate battery cathode material is mixed with an alkaline solution with a pH value of 14.2~14.6 at a liquid-to-solid volume-to-mass ratio of 30~50 mL / g. The resulting mixture is first leached at a first temperature, then leached again at a second temperature. After solid-liquid separation, a leachate and iron(III) oxide are obtained. The pH of the leachate is adjusted to 11.5~13.5 using a 0.1%~1% phosphoric acid solution. The mixture is then heated to a third temperature and aged at the third temperature to precipitate lithium. After solid-liquid separation, lithium phosphate and lithium precipitation mother liquor are obtained. The first temperature is 30~40℃, the second temperature is 10~20℃ lower than the first temperature, and the third temperature is 70~110℃.

[0047] This application employs an alkaline leaching process. By selecting an appropriate liquid-to-solid ratio for feeding, combined with pH and temperature control, it achieves efficient leaching of lithium and phosphorus, followed by aging to obtain high-purity lithium phosphate, while simultaneously recovering iron(III) oxide (Fe3O4). In-depth research reveals that in the alkaline leaching system of this application, leaching at a first temperature rapidly disrupts the crystal structure of LiFePO4, releasing lithium ions. Further lowering the leaching temperature (i.e., the second temperature) increases the metastable region of lithium phosphate, effectively suppressing premature precipitation of lithium phosphate on the surface or in the pores of lithium iron phosphate particles caused by excessively high temperatures. Premature precipitation of lithium phosphate passivates lithium iron phosphate particles, hindering the contact between the olivine-structured LiFePO4 within the particles and the alkali, leading to a decrease in leaching rate. Simultaneously, by appropriately lowering the leaching temperature, a small amount of lithium phosphate precipitate on the surface can be redissolved, reopening the previously blocked pores. This allows the alkali to continue diffusing into the particle interior, contacting the unreacted core, thereby continuing to leach the remaining lithium and further improving the lithium leaching rate. In the alkaline leaching process of this application, the liquid-to-solid ratio and the pH value (or concentration) of the alkaline solution need to be controlled in a coordinated manner to avoid inducing lithium phosphate precipitation during alkaline leaching. Once lithium phosphate precipitation forms, it will not only be mixed in with the iron oxide slag, reducing the lithium leaching efficiency, but will also affect the subsequent separation effect due to the large amount of sodium phosphate precipitation.

[0048] Furthermore, the lithium precipitation mother liquor in this application can be cooled to precipitate phosphate, and the hydroxide-containing leachate after phosphate separation can be reused after adding an appropriate amount of alkali, effectively reducing the generation of wastewater and waste salt, making it greener and more environmentally friendly.

[0049] The technical solutions and effects of this application are further illustrated below with reference to specific embodiments and comparative examples. The embodiments provided below are for illustrative purposes only and are not intended to limit the invention unless otherwise stated. Therefore, the invention should not be considered limited to the following embodiments, but should be understood to include any and all obvious variations as a result of the teachings provided herein.

[0050] It should be understood that modifications that do not materially affect the activity of various embodiments of the present invention may also be covered within the definition of the invention provided herein. Therefore, the following examples are intended to illustrate the invention but not to limit it.

[0051] Unless otherwise specified, the operating methods involved in the embodiments and comparative examples in this application are conventional methods in the art.

[0052] In the following examples and comparative examples, the lithium iron phosphate battery cathode materials used were all recycled waste lithium iron phosphate battery cathode materials from the same batch.

[0053] In the following examples and comparative examples, operations without specific temperature instructions were performed at room temperature (25±5℃).

[0054] In this application, "lithium leaching rate" refers to the percentage of lithium mass dissolved in the leachate after leaching treatment relative to the total lithium mass in the original material. The calculation formula is: Lithium leaching rate (%) = (Leachate volume × Lithium content in leachate) / (Mass of leached material × Lithium content in material) × 100%. The lithium content in the leachate is obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) or atomic absorption spectrometry (AAS). In this application, ICP-OES is used.

[0055] In this application, "phosphorus leaching rate" refers to the percentage of phosphorus mass dissolved in the leachate after leaching treatment relative to the total phosphorus mass in the raw material. The calculation formula is: Phosphorus leaching rate (%) = (Leachate volume × Phosphorus concentration in leachate) / (Raw material mass × Phosphorus content in raw material) × 100%. The phosphorus content in the leachate is detected by inductively coupled plasma optical emission spectrometry (ICP-OES) or ammonium molybdate spectrophotometry; in this application, ICP-OES is used.

[0056] Example 1: This example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0057] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 500°C in a nitrogen or argon atmosphere for 2 hours.

[0058] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a 2 mol / L sodium hydroxide solution at a liquid-to-solid volume ratio of 40 mL / g. First, leach at 30℃ for 4 h, then cool to 20℃ and continue leaching at 20℃ for 1 h. Filter and separate the liquid as leachate and the solid as alkali leaching residue. XRD analysis shows that it is iron(III) oxide (Fe3O4). Figure 1 The tests showed that the lithium leaching rate was 99.3% and the phosphorus leaching rate was 99.1%.

[0059] (3) Lithium precipitation: The pH of the leachate was adjusted to 12 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the separated liquid was the lithium precipitation mother liquor, and the obtained solid product was identified as lithium phosphate by XRD. Figure 2 The lithium recovery rate was 98.7%.

[0060] (4) Recovery of sodium phosphate and leaching reagent: Cool the lithium precipitation mother liquor to 5°C and let it stand at 5°C for 4 hours to precipitate solid. Filter and separate the solid, which is sodium dodecahydrate byproduct. The liquid is an alkaline solution containing hydroxide ions. After adding sodium hydroxide to a concentration of 2 mol / L, it can be reused in the alkaline leaching step of the next batch of lithium iron phosphate battery cathode material recycling.

[0061] Example 2: This example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0062] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 550°C in a nitrogen or argon atmosphere for 2 hours.

[0063] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a 3 mol / L sodium hydroxide solution at a liquid-to-solid volume mass ratio of 35 mL / g. First, leach it at 30℃ for 3 hours, then cool it down to 20℃ and continue leaching at 20℃ for 1 hour. Filter the solution and separate the liquid as leachate and the solid as alkali leaching residue iron(III) oxide. The lithium leaching rate is 99.5% and the phosphorus leaching rate is 99.4%.

[0064] (3) Lithium precipitation: The pH of the leachate was adjusted to 12.5 using a 0.1 mol / L hydrochloric acid solution, heated to 100°C, and aged at 100°C for 2 hours. After filtration, the liquid obtained was lithium precipitation mother liquor, and the solid obtained was lithium phosphate. The lithium recovery rate was 98.9%.

[0065] (4) Recovery of sodium phosphate and leaching reagent: Cool the lithium precipitation mother liquor to 5°C and let it stand at 5°C for 4 hours to precipitate solid. Filter and separate the solid, which is sodium dodecahydrate byproduct. The liquid is an alkaline solution containing hydroxide ions. Sodium hydroxide can be added to the required concentration or pH value and then reused in the alkaline leaching step of the next batch of lithium iron phosphate battery cathode material recycling.

[0066] Example 3: This example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0067] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 550°C in a nitrogen or argon atmosphere for 2 hours.

[0068] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a 3 mol / L sodium hydroxide solution (from the sodium hydroxide solution recovered in Example 1 and Example 2) at a liquid-to-solid volume mass ratio of 35 mL / g. First, leach at 40°C for 2 h, then cool down to 25°C and continue leaching at 25°C for 0.5 h. Filter and separate the liquid as leachate and the solid as alkali leaching residue iron(III) oxide. The lithium leaching rate is 99.6% and the phosphorus leaching rate is 99.5%.

[0069] (3) Lithium precipitation: The pH of the leachate was adjusted to 13 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the liquid obtained was lithium precipitation mother liquor, and the solid obtained was lithium phosphate. The lithium recovery rate was 97.9%.

[0070] (4) Recovery of sodium phosphate and leaching reagent: Cool the lithium precipitation mother liquor to 3°C and let it stand at 3°C ​​for 2 hours to precipitate solid. Filter and separate the solid, which is sodium dodecahydrate byproduct. The liquid is an alkaline solution containing hydroxide ions. Sodium hydroxide can be added to the required concentration or pH value and then reused in the alkaline leaching step of the next batch of lithium iron phosphate battery cathode material recycling.

[0071] Example 4: This example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0072] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 550°C in a nitrogen or argon atmosphere for 2 hours.

[0073] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a 3 mol / L sodium hydroxide solution at a liquid-to-solid volume mass ratio of 40 mL / g. First, leach it at 40℃ for 3 h, then cool it down to 25℃ and continue leaching at 25℃ for 1 h. Filter it and separate the liquid as leachate and the solid as alkali leaching residue. XRD detection shows that it is iron(III) oxide. The lithium leaching rate is 99.4% and the phosphorus leaching rate is 99.2%.

[0074] (3) Lithium precipitation: The pH of the leachate was adjusted to 13 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the liquid obtained was lithium precipitation mother liquor, and the solid obtained was lithium phosphate. The lithium recovery rate was 97.8%.

[0075] (4) Recovery of sodium phosphate and leaching reagent: Cool the lithium precipitation mother liquor to 3°C and let it stand at 3°C ​​for 2 hours to precipitate solid. Filter and separate the solid, which is sodium dodecahydrate byproduct. The liquid is an alkaline solution containing hydroxide ions. Sodium hydroxide can be added to the required concentration or pH value and then reused in the alkaline leaching step of the next batch of lithium iron phosphate battery cathode material recycling.

[0076] Comparative Example 1: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0077] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 550°C in a nitrogen or argon atmosphere for 2 hours.

[0078] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a sodium hydroxide solution with a concentration of 2 mol / L at a liquid-to-solid volume mass ratio of 40 mL / g. Leach at 30℃ for 5 h, filter, and separate the liquid as leachate and the solid as alkali leaching residue iron(III) oxide. The lithium leaching rate is 97.2% and the phosphorus leaching rate is 96.9%.

[0079] (3) Lithium precipitation: The pH of the leachate was adjusted to 12 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the solid obtained was lithium phosphate product, with a lithium recovery rate of 95.6%.

[0080] Comparative Example 2: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0081] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 500°C in a nitrogen or argon atmosphere for 2 hours.

[0082] (2) Alkali leaching: The calcined lithium iron phosphate cathode powder was added to a 2 mol / L sodium hydroxide solution at a liquid-to-solid volume ratio of 40 mL / g and leached at 50°C for 5 h. After filtration, the separated liquid was the leachate, with a lithium leaching rate of 48.3% and a phosphorus leaching rate of 48.1%. The separated solid was the alkali leaching residue, which was characterized by XRD. Figure 3 The results show that it contains iron(III) oxide, lithium iron phosphate, and lithium phosphate.

[0083] (3) Lithium precipitation: The pH of the leachate was adjusted to 12.5 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the solid obtained was lithium phosphate product, with a lithium recovery rate of 46.8%.

[0084] Comparative Example 3: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0085] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 500°C in a nitrogen or argon atmosphere for 2 hours.

[0086] (2) Alkali leaching: The calcined lithium iron phosphate cathode powder was added to a 2 mol / L sodium hydroxide solution at a liquid-to-solid volume ratio of 40 mL / g and leached at 20°C for 5 h. After filtration, the separated liquid was the leachate, with a lithium leaching rate of 73.4% and a phosphorus leaching rate of 73.1%. The separated solid was the alkali leaching residue, which was characterized by XRD. Figure 4The product contains lithium iron phosphate and iron tetroxide.

[0087] (3) Lithium precipitation: The pH of the leachate was adjusted to 12.5 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the solid obtained was lithium phosphate product, with a lithium recovery rate of 70.2%.

[0088] Comparative Example 4: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0089] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 500°C in a nitrogen or argon atmosphere for 2 hours.

[0090] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and put it into a 3 mol / L sodium hydroxide solution at a liquid-to-solid volume mass ratio of 30 mL / g. First, leach it at 40℃ for 3 h, then cool it down to 15℃ and continue leaching at 15℃ for 1 h. Filter it and separate the liquid as leachate. The lithium leaching rate is 91.6% and the phosphorus leaching rate is 69.3%. The solid obtained is alkali leaching residue iron(III) oxide.

[0091] (3) Lithium precipitation: The pH of the leachate was adjusted to 13 using a 0.5% phosphoric acid solution, heated to 90°C, and kept at 90°C for 2 hours to precipitate and age. After filtration, the solid obtained was lithium phosphate product, with a lithium recovery rate of 63.6%.

[0092] Comparative Example 5: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0093] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 500°C in a nitrogen or argon atmosphere for 2 hours.

[0094] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a 1 mol / L sodium hydroxide solution at a liquid-to-solid volume mass ratio of 20 mL / g. First, leach it at 30℃ for 4 h, then cool it down to 20℃ and continue leaching at 20℃ for 1 h. Filter and separate the liquid as leachate. The lithium leaching rate is 23.2% and the phosphorus leaching rate is 22.8%. The separated solid is alkaline leaching residue, which mainly contains sodium phosphate and iron tetroxide.

[0095] (3) Lithium precipitation: The pH of the leachate was adjusted to 13 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the solid obtained was lithium phosphate product, and the lithium recovery rate was 18.5%.

[0096] Comparative Example 6: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0097] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined at 550°C in a nitrogen or argon atmosphere for 2 hours.

[0098] (2) Alkali leaching: The calcined lithium iron phosphate cathode powder was added to a 5 mol / L sodium hydroxide solution at a liquid-to-solid volume ratio of 60 mL / g. The solution was first leached at 40°C for 2 h, then cooled to 25°C and leached again at 25°C for 0.5 h. After filtration, the separated liquid was the leachate, with a lithium leaching rate of 63.2% and a phosphorus leaching rate of 38.8%. The separated solid was the alkaline leaching residue, which was characterized by XRD. Figure 5 The product contains iron(III) oxide, sodium phosphate, lithium iron phosphate, and lithium phosphate.

[0099] (3) Lithium precipitation: The pH of the leachate was adjusted to 13 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the solid obtained was lithium phosphate product, with a lithium recovery rate of 35.2%.

[0100] Comparative Example 7: This comparative example provides a method for recycling lithium iron phosphate battery cathode materials, which has the following characteristics:

[0101] (1) Calcination: The waste lithium iron phosphate cathode material is ground into powder, passed through a 60-mesh sieve, and calcined in air at 500°C for 2 hours.

[0102] (2) Alkali leaching: Take the calcined lithium iron phosphate cathode powder and add it to a 2 mol / L sodium hydroxide solution at a liquid-to-solid volume mass ratio of 40 mL / g. First, leach it at 30℃ for 4 h, then cool it down to 20℃ and continue leaching at 20℃ for 1 h. After filtration, the liquid obtained is the leachate and the solid is the alkali leaching residue. XRD detection shows that it is iron(III) oxide. The lithium leaching rate is 58.7% and the phosphorus leaching rate is 57.3%.

[0103] (3) Lithium precipitation: The pH of the leachate was adjusted to 12 using a 0.5% phosphoric acid solution, heated to 95°C, and aged at 95°C for 2 hours. After filtration, the separated liquid was the lithium precipitation mother liquor, and the lithium recovery rate was 10.3%.

[0104] The resulting solid product contained a large amount of ferric hydroxide impurities, preventing the preparation of high-purity lithium phosphate. Under calcination in air at 500°C, the ferrous iron in LiFePO4 was easily oxidized, transforming into Li3Fe2(PO4)3 and Fe2O3 impurity phases; the formation of Fe2O3 significantly hindered the subsequent leaching reaction. Furthermore, during the precipitation of lithium phosphate in the leachate, iron ions hydrolyzed and formed ferric hydroxide colloids, which co-precipitated with the main product, further reducing the purity of the lithium phosphate product.

[0105] As can be seen from the above embodiments and comparative examples, compared with the comparative examples, the embodiments use lithium iron phosphate cathode materials calcined in an inert atmosphere. Through the solid-liquid ratio and alkali concentration of the alkali leaching system, and the pH and temperature control in the alkali leaching-lithium precipitation process, efficient leaching of lithium and phosphorus, and efficient recovery of lithium phosphate and iron tetroxide are achieved. Furthermore, the recovered products have high purity, significantly reducing the difficulty of post-processing. The mother liquor from the lithium precipitation step can be used for further recovery of sodium phosphate and reused after alkali replenishment.

[0106] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for recycling lithium iron phosphate battery cathode material, characterized in that, The lithium iron phosphate battery cathode material calcined in an inert atmosphere is mixed with an alkaline solution with a pH of 14.2-14.6 at a liquid-to-solid volume mass ratio of 30-50 mL / g. The resulting mixture is first leached at a first temperature, then leached at a second temperature, and after solid-liquid separation, a leachate and iron(III) oxide are obtained. The pH of the leachate is adjusted to 11.5-13.5 using a 0.1%-1% phosphoric acid solution, and then heated to a third temperature for lithium precipitation. After solid-liquid separation, lithium phosphate and lithium precipitation mother liquor are obtained. The first temperature is 30-40°C, the second temperature is 10-20°C lower than the first temperature, and the third temperature is 70-110°C.

2. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The second temperature is 10-15°C lower than the first temperature.

3. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The second temperature is 20~25℃.

4. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The third temperature is 90~105℃.

5. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The alkaline solution is a sodium hydroxide solution and / or a potassium hydroxide solution.

6. The method for recycling lithium iron phosphate battery cathode material according to claim 5, characterized in that, The concentration of the alkaline solution is 1.5~4 mol / L.

7. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The mixture is leached at a first temperature for 1 to 24 hours; and / or, the mixture is leached at a second temperature for 0.5 to 1 hour; and / or, the aging time is 1 to 3 hours.

8. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The mixture is first leached at 30-40°C for 1-5 hours, then leached at 20-25°C for 0.5-1 hours, and the aging time is 1-3 hours.

9. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The positive electrode material of the lithium iron phosphate battery is a powder with a particle size of less than or equal to 0.5 mm.

10. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The inert atmosphere calcination temperature is 450~600℃.

11. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The inert atmosphere calcination time is 1.5 to 3 hours; and / or, the inert atmosphere calcination is carried out in a nitrogen or argon atmosphere.

12. The method for recycling lithium iron phosphate battery cathode material according to claim 1, characterized in that, The recycling method further includes cooling the lithium precipitation mother liquor to precipitate phosphate, and then separating the solid and liquid components to obtain dodecahydrate phosphate and filtrate.

13. The method for recycling lithium iron phosphate battery cathode material according to claim 12, characterized in that, The lithium precipitation mother liquor is cooled to 2-8°C and allowed to stand at 2-8°C for 1-24 hours before solid-liquid separation to obtain dodecahydrate phosphate and filtrate.

14. The method for recycling lithium iron phosphate battery cathode material according to claim 12, characterized in that, The filtrate is used to prepare an alkaline solution with a pH of 14.2 to 14.

6.

15. A method for recycling lithium iron phosphate battery cathode materials according to any one of claims 1 to 14, characterized in that, Specifically, it includes the following steps: (1) The positive electrode material of lithium iron phosphate battery is calcined in an inert atmosphere at 450~600℃; (2) The calcined lithium iron phosphate battery cathode material from step (1) is mixed with an alkaline solution with a pH of 14.2 to 14.6 at a liquid-to-solid volume ratio of 30 to 50 mL / g. The resulting mixed solution is first leached at the first temperature and then leached at the second temperature. After solid-liquid separation, the leachate and iron(III) oxide are obtained. (3) The pH value of the leachate from step (2) is adjusted to 11.5 to 13.5 using a phosphoric acid solution with a mass concentration of 0.1% to 1%, heated to the third temperature and kept at the third temperature for aging and lithium precipitation, and then lithium phosphate and lithium precipitation mother liquor are obtained by solid-liquid separation. (4) Cool the lithium precipitation mother liquor to 2~8℃, and after precipitating phosphate dodecahydrate at 2~8℃, perform solid-liquid separation. The obtained filtrate is used to prepare an alkaline solution with a pH of 14.2~14.6 as described in step (2) and reused.

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