Repair type lithium iron phosphate material and preparation method thereof

Abstract

The invention discloses a repair type lithium iron phosphate material and a preparation method thereof, and relates to the technical field of lithium battery materials, the preparation method comprises the following steps: S1, preparing a separating agent A and an impurity removal agent B; s2, cutting the lithium iron phosphate pole piece into standard small pieces; s3, adding the standard small pieces and a separating agent A into a separation reactor, stirring and carrying out ultrasonic separation, and separating out wet aluminum pieces and a lithium iron phosphate wet material solution; s4, drying the wet aluminum sheet to obtain an aluminum product; s5, adding an impurity removal agent B into the wet material solution, stirring, standing, and centrifuging to obtain a lithium iron phosphate wet cake; s6, drying the wet cake to obtain a lithium iron phosphate dry material; s7, performing superconducting magnetofluid density separation on the dry material to separate out impurities such as copper, aluminum and plastic, so as to obtain a purified lithium iron phosphate material; and S8, ball-milling and demagnetizing the purified material to obtain the repair type lithium iron phosphate positive electrode powder product. The method is simple and convenient in operation process, green and environment-friendly, more regular in product particles, remarkably improved in material rate capability and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of lithium battery materials, and particularly relates to a repaired lithium iron phosphate material and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy vehicle field, especially the popularization of electric vehicles, it has greatly promoted the explosive growth of battery demand. Lithium iron phosphate has the advantages of safety, environmental protection, good stability, high specific capacity, low price, etc. Therefore, as a widely used lithium ion battery material, its performance and service life are affected by various factors. However, with the popularization of new energy vehicles and the wide application of lithium iron phosphate batteries, the problem of repairing lithium iron phosphate battery materials has gradually emerged.

[0003] In the process of repairing conventional lithium iron phosphate battery materials, high-temperature calcination is a common method. However, this method has obvious drawbacks. When the battery material is calcined at high temperature, the binder will start to decompose and volatilize in the form of gas. The role of the binder is to firmly fix the active material on the surface of the current collector. Once the binder decomposes and volatilizes, the active material will lose its support, become brittle and loose, and thus easily fall off from the surface of the current collector in large quantities. During the calcination of lithium iron phosphate materials, when the temperature rises to 350 °C, the quality of the electrode sheet will also decrease significantly. This is mainly because high temperature has an adverse effect on the crystal structure and chemical stability of the active material, resulting in serious damage to the overall structure and performance of the battery material. In order to avoid the damage of high temperature to the active material of the electrode sheet, the most common current process is to select corresponding organic solvents to separate the binder according to the characteristics of different lithium iron phosphate binders. The core of this method is to dissolve and separate the binder from between the active material and the current collector through the action of organic solvents, thus avoiding the direct action of high temperature on the active material. In this way, the influence of temperature on the active material can be effectively reduced, the integrity of its structure and performance can be maintained, and thus the repair effect and service life of lithium iron phosphate battery materials can be improved.

[0004] Chinese Patent CN118073700A discloses a repair method for regenerating lithium iron phosphate, which includes the following steps: (1) placing the waste lithium iron phosphate positive electrode sheet in a calcination furnace for calcination; separating the aluminum current collector to obtain positive electrode powder; (2) putting the positive electrode powder into an acid leaching solution and stirring, and filtering to obtain a first lithium iron phosphate mixed solution; (3) adding a lithium salt solution to the first lithium iron phosphate mixed solution for lithium supplementation to obtain a second lithium iron phosphate mixed solution; (4) adding an antioxidant to the second lithium iron phosphate mixed solution, performing hydrothermal synthesis to obtain a hydrothermal product, and filtering, rinsing, and drying the hydrothermal product to obtain a regenerated lithium iron phosphate material.

[0005] The present invention proposes a new idea for applying superconducting technology to purify key materials of waste lithium-ion batteries. A repair method for regenerating lithium iron phosphate proposed by the present invention can effectively simplify the regeneration process of the lithium iron phosphate cathode material, and solve the technical problems of complex recovery process, low recovery efficiency and low purity of the lithium iron phosphate cathode material in the prior art. Summary of the Invention

[0006] The purpose of the present invention is to provide a repaired lithium iron phosphate material and its preparation method to solve the following technical problems: Provide a repaired lithium iron phosphate material and its preparation method, which improves the separation efficiency of active substances, reduces energy consumption, and then uses superconducting magnetic density separation technology for impurity removal, ball milling and demagnetization processes to re-prepare lithium iron phosphate material, making the product particles more regular, maintaining the electrochemical properties of the material, realizing the recycling of valuable metals, with simple operation, no harmful substance emissions, being green and environmentally friendly, and being more suitable for large-scale production and commercial application.

[0007] The purpose of the present invention can be achieved through the following technical solutions: In the first aspect, the present invention discloses a preparation method of a repaired lithium iron phosphate material, including the following steps: A preparation method of a repaired lithium iron phosphate material, including the following steps: S1. Prepare separation agent A and impurity removal agent B; S2. Cut the lithium iron phosphate electrode sheet into standard small pieces of lithium iron phosphate; S3. Add the standard small pieces of lithium iron phosphate and separation agent A into the separation reactor in a certain mass ratio in sequence, stir and ultrasonically separate to separate out wet aluminum sheets and a lithium iron phosphate wet material solution; S4. Dry the wet aluminum sheets to obtain aluminum products; S5. Add impurity removal agent B to the wet material solution, stir for impurity removal, stand still, and centrifuge to obtain a lithium iron phosphate wet cake; S6. Dry the wet cake to obtain dry lithium iron phosphate material; S7. Perform superconducting magnetic fluid density separation on the dry material to separate out impurities such as copper, aluminum and plastics, and obtain a purified lithium iron phosphate material; S8. After ball milling and demagnetization of the purified material, obtain a repaired lithium iron phosphate cathode powder product.

[0008] Preferably, the concentration of the separation agent A in S1 is 1-20 mol / L, and the separation agent A is any one of an N-methylpyrrolidone aqueous solution, an acetone aqueous solution, a dimethyl sulfoxide aqueous solution and an N,N-dimethylformamide aqueous solution.

[0009] Preferably, the concentration of the impurity removal agent B in S1 is 1-30 mol / L, and the impurity removal agent B is any one of a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, an ammonia aqueous solution and a sodium carbonate aqueous solution.

[0010] Preferably, the mass ratio of the standard small piece of lithium iron phosphate described in S3 to the separating agent A is 1:0.5 - 10.

[0011] Preferably, the stirring, ultrasonic separation temperature described in S3 is 25 - 100 °C, and the reaction time is 2 - 20 h.

[0012] Preferably, the drying temperature of the wet aluminum sheet described in S4 is 60 - 200 °C, and the drying time is 0.2 - 30 h.

[0013] Preferably, the drying temperature of the wet cake described in S6 is 100 - 200 °C, and the drying time is 0.2 - 20 h.

[0014] Preferably, the magnetic field strength of the superconducting magnetic fluid described in S7 is 4 - 10 T; the magnetic fluid is one or more of Fe, Ni, Co, Fe3O4, and γ-Fe2O3.

[0015] Preferably, for S8, zirconium ball milling beads are selected for ball milling, at 25 °C, the rotation speed is 300 - 1100 rpm for 1 - 12 h; the magnetic field strength of the demagnetization step is 0.1 - 2 T, the feeding speed of the material is 50 - 300 g / s, and the magnetic separation time is 0.5 - 3 h.

[0016] In a second aspect, the present invention also discloses a repaired lithium iron phosphate material obtained by using the above preparation method.

[0017] Advantages of the present invention: 1. Through the advanced superconducting magnetic fluid separation technology, the present invention utilizes the high-gradient magnetic field provided by the superconducting magnet in the nano magnetic fluid to separate impurities such as copper, aluminum, and plastic, achieving efficient removal of impurities such as copper, aluminum, and plastic in the lithium iron phosphate battery material, greatly improving the purity of the repaired lithium iron phosphate material, and having significant advantages in terms of impurity removal efficiency, energy consumption control, environmental protection, and resource utilization rate.

[0018] 2. Compared with the prior art, the present invention discloses a repaired lithium iron phosphate material and its preparation method, with a simple operation process, no harmful substance emissions during the process, being green and safe. Then, through the superconducting magnetic density separation technology, impurity removal, ball milling, and demagnetization processes are carried out to re-prepare the repaired lithium iron phosphate material. The treatment method is mild, maintaining the structural integrity of the lithium iron phosphate material, the product particles are more regular, the rate performance of the material is significantly improved, realizing metal recycling, and being more suitable for large-scale production and commercial application. Description of the Drawings

[0019] Figure 1 is the process flow chart of the present invention; Figure 2XRD structural analysis diagrams of the lithium iron phosphate materials prepared in Example 1 and Example 2 of the present invention and the lithium iron phosphate standard card; Figure 3 SEM diagram of the lithium iron phosphate material prepared in Example 1 of the present invention magnified to 2 μm Figure 4 SEM diagram of the lithium iron phosphate material prepared in Example 1 of the present invention magnified to 1 μm; Figure 5 SEM diagram of the lithium iron phosphate material prepared in Example 2 of the present invention magnified to 2 μm; Figure 6 SEM diagram of the lithium iron phosphate material prepared in Example 2 of the present invention magnified to 1 μm; Figure 7 First charge-discharge performance diagrams of the lithium iron phosphate materials prepared in Example 1 and Example 2 of the present invention. Detailed implementation manners

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention. The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and are carried out according to the technologies or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0021] The present invention discloses a preparation method of a repair-type lithium iron phosphate material, as shown in the following process flow, including the following steps: Figure 1 as shown S1. Prepare separation agent A and impurity removal agent B; S2. Cut the lithium iron phosphate electrode sheet into standard small pieces of lithium iron phosphate; S3. Add the standard small pieces of lithium iron phosphate and separation agent A into a separation reactor in a certain mass ratio in sequence, stir and ultrasonically separate to separate out wet aluminum sheets and a lithium iron phosphate wet material solution; S4. Dry the wet aluminum sheets in an oven at 60 °C for 3 h to obtain aluminum products; In this step, the selected separation agent A is any one of an N-methylpyrrolidone aqueous solution, an acetone aqueous solution, a dimethyl sulfoxide aqueous solution, and an N,N-dimethylformamide aqueous solution; the concentration of separation agent A is 1-20 mol / L; the mass ratio of the standard small pieces of lithium iron phosphate to separation agent A is 1:0.5-10.

[0022] In this step, the lithium iron phosphate electrode is cut into small pieces to increase the reaction surface area and improve the efficiency of subsequent separation and treatment. Weakly basic organic solutions such as N-methylpyrrolidone and N,N-dimethylformamide are used to soak and stir simultaneously to dissolve the binder. The binder swells / dissolves in the polar solvent, releasing the binding force between the active material and the current collector, destroying the electrode structure. This can not only separate the aluminum foil on the electrode material but also remove the binder on the electrode material, reducing the impurities in the recycled electrode material. After washing, the separated aluminum sheets can be directly recycled, while the lithium iron phosphate is dispersed in the solution to form a wet material solution.

[0023] S5. Add impurity remover B to the wet material solution, stir for impurity removal, let it stand, and centrifuge to obtain a lithium iron phosphate wet cake. The impurity remover B selected in this step includes any one of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous ammonia solution, and aqueous sodium carbonate solution; the concentration of impurity remover B is 1 - 30 mol / L.

[0024] In this step, an alkaline solution is selected as the impurity remover. Lithium iron phosphate is chemically stable within the pH range of 9 - 12 and its structure does not decompose. In an alkaline environment, the solubility of lithium iron phosphate further decreases, so it is more likely to precipitate in solid form.

[0025] S6. Dry the wet cake in an oven at 160 °C for 8 h to obtain the dry lithium iron phosphate material. S7. Perform superconducting magnetic fluid density separation on the dry material to separate impurities such as copper, aluminum, and plastic, and obtain the purified lithium iron phosphate material. In this step, the magnetic field strength of the superconducting magnetic fluid selected is 4 - 10 T; the magnetic fluid is one or more of Fe, Ni, Co, Fe3O4, and γ-Fe2O3.

[0026] In this step, the advanced technology of superconducting magnetic fluid separation is selected. Utilizing the magnetic and density characteristics of the superconducting magnetic fluid, separation is carried out according to the density and magnetic differences of the materials. The densities and magnetic properties of impurities such as copper, aluminum, and plastic are different from those of lithium iron phosphate. The high-gradient magnetic field provided by the superconducting magnet in the nanofluid is used to separate impurities such as copper, aluminum, and plastic, achieving the efficient removal of impurities such as copper, aluminum, and plastic in the lithium iron phosphate battery material.

[0027] S8. After ball milling and demagnetization of the purified material, a repaired lithium iron phosphate cathode powder product is obtained.

[0028] In this step, the ball milling uses zirconia ball milling beads and is carried out at 25 °C with a rotation speed of 300 - 1100 rpm for 1 - 12 h. The magnetic field strength of the demagnetization step is 0.1 - 2 T, the feeding speed of the material is 50 - 300 g / s, and the magnetic separation time is 0.5 - 3 h.

[0029] In this step, the purified material is ground into fine powder, while making the particles more uniform. Through the action of mechanical force, impurities on the material surface can be further removed or the microstructure of the particles can be repaired. The demagnetization process is to remove the magnetic impurities that may remain in the material to ensure the purity and performance of the lithium iron phosphate material.

[0030] Example 1

[0031] A repaired lithium iron phosphate material is prepared by the following steps: S1: Prepare an aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3 mol / L sodium hydroxide as impurity removing agent B, and fill them in two solution storage tanks. 3 N-methylpyrrolidone 50% aqueous solution as separating agent A, 3m 3 3 mol / L aqueous solution of sodium hydroxide as impurity removing agent B, and fill them in two solution storage tanks; S2: Cut 500 kg of lithium iron phosphate electrode sheets into 1 cm 1 cm standard small pieces; S3. Add the 500 kg of lithium iron phosphate standard small pieces in S2 and 1 m 3 of separating agent A solution to the separation reactor, set the temperature to 60 °C, turn on mechanical stirring and ultrasonic waves, with the stirring speed of 800 rpm, start the separation reaction. After 6 h, 75 kg of wet aluminum sheets and lithium iron phosphate wet material solution are separated; S4: Put the wet aluminum sheets into an oven, set the temperature to 60 °C, and dry for 3 h to obtain aluminum products; S5: Add 1 m 3 of impurity removing agent B to the lithium iron phosphate wet material solution, mix them, turn on mechanical stirring at 200 rpm and ultrasonic waves at 60 Hz to obtain the impurity-removed lithium iron phosphate solution, and transfer it to a centrifuge for solid-liquid separation to obtain lithium iron phosphate wet cake; S6: Transfer the lithium iron phosphate wet cake to an oven, dry at 160 °C for 8 h to obtain the lithium iron phosphate dry material; S7: Transfer it to a superconducting magnetic density separation system, set the superconducting magnet intensity to 6 T, and the magnetic fluid to γ-Fe2O3. Use the high-gradient magnetic field provided by the superconducting magnet in the nano magnetic fluid to separate impurities such as copper, aluminum, and plastic to obtain the purified lithium iron phosphate material; S8: Transfer the obtained purified lithium iron phosphate material to a ball mill for ball milling for 1 h, with the demagnetization magnetic field intensity of 0.8 T, the feeding speed of the material of 200 g / s, and the magnetic separation time of 0.5 h to finally obtain the repaired lithium iron phosphate product.

[0032] The content of aluminum impurities in the repaired lithium iron phosphate product obtained in this example is 50 ppm.

[0033] Example 2

[0034] S1: Prepare an aqueous solution of 30% N,N-dimethylformamide as separating agent A, 2m 3 N,N-dimethylformamide 30% aqueous solution as separating agent A, 2m 3An aqueous solution of potassium hydroxide at 3 mol / L is used as impurity removing agent B; S2: Cut 500 kg of lithium iron phosphate electrodes into standard small pieces of 0.5 cm × 0.5 cm; S3: Add 500 kg of the standard small pieces of lithium iron phosphate in S2 and 1 m 3 of separating agent A into a separation reactor, set the temperature to 60 °C, turn on mechanical stirring and ultrasonic waves, with a stirring speed of 800 rpm, start the separation reaction. After 6 h, 74 kg of wet aluminum sheets and a wet lithium iron phosphate solution are separated; S4: Put the wet aluminum sheets into an oven, set the temperature to 60 °C, and dry for 3 h to obtain aluminum products; S5: Add 1 m 3 of impurity removing agent B to the wet lithium iron phosphate solution in S3, mix them, turn on mechanical stirring at 100 rpm and ultrasonic waves at 60 Hz to obtain a purified lithium iron phosphate solution, and transfer it to a centrifuge for solid-liquid separation to obtain a wet lithium iron phosphate cake; S6: Transfer the wet lithium iron phosphate cake to an oven and dry it at 160 °C for 8 h to obtain dry lithium iron phosphate material; S7: Transfer it to a superconducting magnetic density separation system, set the superconducting magnet intensity to 4 T, and the magnetic fluid to γ-Fe2O3, and use the high-gradient magnetic field provided by the superconducting magnet in the nano-magnetic fluid to separate impurities such as copper, aluminum, and plastics to obtain purified lithium iron phosphate material; S8: Transfer the obtained purified lithium iron phosphate material to a ball mill for ball milling for 1 h, with a demagnetizing magnetic field intensity of 0.8 T, a feeding speed of the material of 200 g / s, and a magnetic separation time of 0.5 h to finally obtain a repaired lithium iron phosphate product.

[0035] The content of aluminum impurities in the repaired lithium iron phosphate product obtained in this example is 80 ppm.

[0036] Example 3

[0037] A repaired lithium iron phosphate material is prepared by the following steps: S1: Prepare an aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3 mol / L sodium hydroxide as impurity removing agent B, each with a volume of 2 m 3 and 3 m 3 respectively, and store them in two solution storage tanks; S2: Cut 500 kg of lithium iron phosphate electrodes into standard small pieces of 1 cm × 1 cm; S3: Add 500 kg of the standard small pieces of lithium iron phosphate in S2 and 1 m 3The separating agent A solution is added to the separation reactor, the temperature is set at 60 °C, mechanical stirring and ultrasonic are turned on, the stirring speed is 800 rpm, and the separation reaction is started. After 6 h, 75 kg of wet aluminum flakes and the wet lithium iron phosphate solution are separated; S4. Put the wet aluminum flakes into the oven, set at 60 °C, and dry for 3 h to obtain aluminum products; S5. Add 1 m 3 of impurity removing agent B, mix them, turn on mechanical stirring at 200 rpm and ultrasonic at 60 Hz to obtain the impurity-removed lithium iron phosphate solution, and transfer it to a centrifuge for solid-liquid separation to obtain the wet lithium iron phosphate cake; S6. Transfer the wet lithium iron phosphate cake to the oven and dry at 160 °C for 8 h to obtain the dry lithium iron phosphate material; S7. Transfer it to the superconducting magnetic density separation system, set the superconducting magnet intensity at 10 T, and the magnetic fluid as γ-Fe2O3, and use the high-gradient magnetic field provided by the superconducting magnet in the nanofluid to separate impurities such as copper, aluminum, and plastics to obtain the purified lithium iron phosphate material; S8. Transfer the obtained purified lithium iron phosphate material to a ball mill for ball milling for 1 h, the magnetic removal magnetic field intensity is 0.8 T, the feeding speed of the material is 200 g / s, and the magnetic separation time is 0.5 h to finally obtain the repaired lithium iron phosphate product.

[0038] The aluminum impurity content in the repaired lithium iron phosphate product obtained in this example is 30 ppm.

[0039] Example 4

[0040] A repaired lithium iron phosphate material is prepared by the following steps: S1: Prepare an aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3 mol / L sodium hydroxide as impurity removing agent B, each with a volume of 2 m 3 and 3 m 3 , and store them in two solution storage tanks; S2: Cut 500 kg of lithium iron phosphate electrode sheets into standard small pieces of 1 cm × 1 cm; S3. Add the 500 kg of lithium iron phosphate standard small pieces in S2 and 1 m 3 of the separating agent A solution to the separation reactor, set the temperature at 60 °C, turn on mechanical stirring and ultrasonic, the stirring speed is 800 rpm, start the separation reaction, and after 6 h, 75 kg of wet aluminum flakes and the wet lithium iron phosphate solution are separated; S4. Put the wet aluminum flakes into the oven, set at 60 °C, and dry for 3 h to obtain aluminum products; S5. Add 1 m 3After mixing with impurity remover B, start mechanical stirring at 200 rpm and ultrasonic at 60 Hz to obtain the lithium iron phosphate solution after impurity removal, and transfer it to a centrifuge for solid-liquid separation to obtain the wet cake of lithium iron phosphate; S6. Transfer the wet cake of lithium iron phosphate to an oven and dry it at 160 °C for 8 h to obtain the dry material of lithium iron phosphate; S7. Transfer to a superconducting magnetic density separation system, set the superconducting magnet intensity to 6 T, and the magnetic fluid to a mixture of Ni, Co, and Fe3O4. Use the high-gradient magnetic field provided by the superconducting magnet in the nano-magnetic fluid to separate impurities such as copper, aluminum, and plastic to obtain the purified material of lithium iron phosphate; S8. Transfer the obtained purified material of lithium iron phosphate to a ball mill for ball milling for 1 h. The magnetic removal magnetic field intensity is 0.8 T, the feeding speed of the material is 200 g / s, and the magnetic separation time is 0.5 h. Finally, obtain the repaired lithium iron phosphate product.

[0041] The aluminum impurity content in the repaired lithium iron phosphate product obtained in this example is 40 ppm.

[0042] Example 5

[0043] A repaired lithium iron phosphate material, adopting the following steps: S1: Prepare an aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3 mol / L sodium hydroxide as impurity remover B, and fill them in two solution storage tanks; 3 3 S2: Cut 500 kg of lithium iron phosphate electrode sheets into standard small pieces of 1 cm × 1 cm; S3. Add the 500 kg of standard small pieces of lithium iron phosphate in S2 and 1 m of separating agent A in S1 to a separation reactor, set the temperature to 60 °C, start mechanical stirring and ultrasonic, the stirring speed is 800 rpm, start the separation reaction, and after 6 h, separate 75 kg of wet aluminum sheets and the lithium iron phosphate wet material solution; 3 S4. Put the wet aluminum sheets into an oven, set the temperature to 60 °C, and dry them for 3 h to obtain aluminum products; S5. Add 1 m of impurity remover B to the lithium iron phosphate wet material solution, mix them, start mechanical stirring at 200 rpm and ultrasonic at 60 Hz to obtain the lithium iron phosphate solution after impurity removal, and transfer it to a centrifuge for solid-liquid separation to obtain the wet cake of lithium iron phosphate; 3 S6. Transfer the wet cake of lithium iron phosphate to an oven and dry it at 160 °C for 8 h to obtain the dry material of lithium iron phosphate; ​​​​​S7. Transfer to the superconducting magnetic density separation system. Set the superconducting magnet intensity to 6T, and the ferrofluid is a mixture of Fe3O4 and γ-Fe2O3. Use the high-gradient magnetic field provided by the superconducting magnet in the nanofluid to separate impurities such as copper, aluminum, and plastic, and obtain the purified lithium iron phosphate material. S8. Transfer the obtained purified lithium iron phosphate material to a ball mill for ball milling for 1h. The magnetic removal magnetic field intensity is 0.8T, the feeding speed of the material is 200g / s, and the magnetic separation time is 0.5h. Finally, obtain the repaired lithium iron phosphate product.

[0044] The aluminum impurity content in the repaired lithium iron phosphate product obtained in this example is 60ppm.

[0045] Comparative Example 1

[0046] A repaired lithium iron phosphate material is prepared by the following steps: S1: Prepare an aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3mol / L sodium hydroxide as impurity removing agent B, and fill them in two solution storage tanks. 3 An aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3mol / L sodium hydroxide as impurity removing agent B, and fill them in two solution storage tanks. 3 An aqueous solution of 50% N-methylpyrrolidone as separating agent A and an aqueous solution of 3mol / L sodium hydroxide as impurity removing agent B, and fill them in two solution storage tanks. S2: Cut 500kg of lithium iron phosphate electrode sheets into 1cm × 1cm standard small pieces. 1cm × 1cm standard small pieces. S3. Add the 500kg of lithium iron phosphate standard small pieces in S2 and 1m of separating agent A in S1 to the separation reactor, set the temperature to 60°C, turn on mechanical stirring and ultrasonic, the stirring speed is 800rpm, start the separation reaction, after 6h, separate out 75kg of wet aluminum sheets and the lithium iron phosphate wet material solution. 3 S3. Add the 500kg of lithium iron phosphate standard small pieces in S2 and 1m of separating agent A in S1 to the separation reactor, set the temperature to 60°C, turn on mechanical stirring and ultrasonic, the stirring speed is 800rpm, start the separation reaction, after 6h, separate out 75kg of wet aluminum sheets and the lithium iron phosphate wet material solution. S4. Put the wet aluminum sheets into an oven, set the temperature to 60°C, and dry for 3h to obtain aluminum products. S5. Add 1m of impurity removing agent B to the lithium iron phosphate wet material solution, mix them, turn on mechanical stirring at 200rpm and ultrasonic at 60Hz, obtain the impurity-removed lithium iron phosphate solution, and transfer it to a centrifuge for solid-liquid separation to obtain the lithium iron phosphate wet cake. 3 S5. Add 1m of impurity removing agent B to the lithium iron phosphate wet material solution, mix them, turn on mechanical stirring at 200rpm and ultrasonic at 60Hz, obtain the impurity-removed lithium iron phosphate solution, and transfer it to a centrifuge for solid-liquid separation to obtain the lithium iron phosphate wet cake. S6. Transfer the lithium iron phosphate wet cake to an oven, dry at 160°C for 8h to obtain the lithium iron phosphate dry material. S7. Transfer the obtained lithium iron phosphate dry material to a ball mill for ball milling for 1h. The magnetic removal magnetic field intensity is 0.8T, the feeding speed of the material is 200g / s, and the magnetic separation time is 0.5h. Finally, obtain the repaired lithium iron phosphate product.

[0047] The aluminum impurity content in the repaired lithium iron phosphate product obtained in this example is 600ppm.

[0048] Comparative Example 2

[0049] A repaired lithium iron phosphate material is prepared by the following steps: S1: Tear 500 kg of lithium iron phosphate electrodes into irregular small pieces about 10 cm in size. S2: Add the 500 kg of irregular small pieces of lithium iron phosphate and 1000 kg of water in S2 to a separation reactor, set the temperature at 60 °C, turn on mechanical stirring and ultrasonic waves, with the stirring speed at 800 rpm, start the separation reaction. After 6 h, 75 kg of wet aluminum sheets and a lithium iron phosphate wet material solution are separated out; S3: Put the wet aluminum sheets into an oven, set at 60 °C, and dry for 3 h to obtain aluminum products; S4: Transfer the lithium iron phosphate wet material solution to a centrifuge for solid-liquid separation to obtain a lithium iron phosphate wet cake; S5: Transfer the lithium iron phosphate wet cake to a ball mill for ball milling for 1 h. The magnetic field intensity for demagnetization is 0.8 T, the feeding speed of the material is 200 g / s, and the magnetic separation time is 0.5 h. Finally, a repaired lithium iron phosphate product is obtained.

[0050] In the repaired lithium iron phosphate product obtained in this example, the aluminum impurity content is 4000 ppm.

[0051] Comparative Example 3

[0052] A repaired lithium iron phosphate material is prepared by the following steps: S1: Tear 500 kg of lithium iron phosphate electrodes into irregular small pieces about 10 cm in size; S2: Add the 500 kg of irregular small pieces of lithium iron phosphate and 1000 kg of water in S2 to a separation reactor, set the temperature at 60 °C, turn on mechanical stirring and ultrasonic waves, with the stirring speed at 800 rpm, start the separation reaction. After 6 h, 75 kg of wet aluminum sheets and a lithium iron phosphate wet material solution are separated out; S3: Put the wet aluminum sheets into an oven, set at 60 °C, and dry for 3 h to obtain aluminum products; S4: Transfer the lithium iron phosphate solution to a centrifuge for solid-liquid separation to obtain a lithium iron phosphate wet cake; S5: Transfer it to a superconducting magnetic density separation system. Set the superconducting magnet intensity at 10 T, and the ferrofluid is a mixture of Fe3O4 and γ-Fe2O3. Use the high-gradient magnetic field provided by the superconducting magnet in the nano-ferrofluid to separate impurities such as copper, aluminum, and plastics to obtain a purified lithium iron phosphate material; S6: Transfer the obtained purified lithium iron phosphate material to a ball mill for ball milling for 1 h. The magnetic field intensity for demagnetization is 0.8 T, the feeding speed of the material is 200 g / s, and the magnetic separation time is 0.5 h. Finally, a repaired lithium iron phosphate product is obtained.

[0053] The aluminum impurity content in the repaired lithium iron phosphate product obtained in this example is 1200 ppm.

[0054] For Examples 1-5 and Comparative Examples 1-3, the performance of the prepared repaired lithium iron phosphate materials was tested. The test methods are as follows: Elemental composition test: Tested using an inductively coupled plasma spectrometer; Specific surface area test: Tested using a specific surface area tester; Tapped density: Tested using a tapped density tester; Moisture content: Tested using a Karl Fischer moisture meter; pH value: Tested using a Mettler portable pH meter; Electrochemical performance test: The material was made into a CR2032 coin cell, and the coin cell was tested for constant current charge and discharge using a BlueTEC battery test system (CT3001A), and the cyclic charge and discharge capacity curve was recorded. The test voltage range was 2.0 - 4.0 V, the test temperature was 23 ± 2 °C, and the current rate was 0.1C. The steps for constant current charge and discharge were: first stand still for 30 min, then charge at a constant current to 4.0 V, and then discharge at a constant current to 2.0 V, and charge and discharge alternately.

[0055] The test results are shown in Table 1: Table 1 Product performance test data

[0056] From Table 1 and Figure 7 It can be seen that for Examples 1-5, after impurity removal, ball milling, and demagnetization processes using the superconducting magnetic density separation technology, the aluminum impurity in the lithium iron phosphate material can be reduced to 30 ppm; the specific surface area of the repaired lithium iron phosphate material prepared in Example 2 reaches the technical index, and it has a relatively high specific surface area, indicating that the contact area between the material and the electrolyte increases, and the active sites for lithium ion insertion and extraction increase, thus improving the charge and discharge performance of the battery; the tapped densities of the repaired lithium iron phosphate materials prepared in the examples are all higher than the technical index requirement of 0.7 g / cm 3 , a high tapped density means that the particle size and distribution are more uniform and the structure is more compact, so that more lithium ions can be stored per unit volume in the battery, thus improving the energy density of the battery; the moisture content of the repaired lithium iron phosphate materials prepared in the examples is all lower than 1000 ppm, ensuring the safety performance of the lithium battery materials; the initial 0.1C charge specific capacity of the repaired materials reaches 164.32 - 170.45 mAh / g, and the initial 0.1C discharge specific capacity of the repaired materials reaches 151.13 - 156.78 mAh / g, meeting the technical requirements.

[0057] In Comparative Example 1, superconducting magnetic fluid separation was not adopted, and the aluminum content in the prepared lithium iron phosphate for repair was 600 ppm. The initial 0.1C discharge specific capacity of the repaired material reached 145.20 mAh / g, not meeting the technical standard; in Comparative Example 2, superconducting magnetic fluid separation and the impurity removal process were not adopted, and the aluminum content in the prepared lithium iron phosphate for repair was 4000 ppm. The initial 0.1C discharge specific capacity of the repaired material reached 132.06 mAh / g, not meeting the technical standard; in Comparative Example 3, superconducting magnetic fluid separation was adopted, but the impurity removal process was not carried out, and the aluminum content in the prepared lithium iron phosphate for repair was 1200 ppm. The initial 0.1C discharge specific capacity of the repaired material reached 140.62 mAh / g, not meeting the technical standard.

[0058] From Figure 2 It can be seen that the XRD of the lithium iron phosphate for repair prepared in Examples 1-2 is Figure 1 consistent with that of the lithium iron phosphate standard card, and there are no impurity peaks, indicating that the preparation method of the present invention can effectively remove impurities; from Figures 3 - 6 It can be seen that the prepared lithium iron phosphate for repair material is approximately spherical and has a uniform size distribution.

[0059] In summary, a lithium iron phosphate for repair material and its preparation method provided by the embodiments of the present invention, when treating waste lithium iron phosphate materials, by adjusting the type of separating agent, the ratio of the lithium iron phosphate electrode sheet to the separating agent, and combining the use of superconducting magnetic fluid separation technology, after ball milling and demagnetization processes, impurities such as copper, aluminum, and plastics are separated, and aluminum elements are recovered in the form of aluminum sheets, thereby improving the recovery rate of aluminum elements and realizing metal recycling. In addition, the lithium iron phosphate for repair material prepared by the method provided by the present invention has uniform particle size and excellent material properties. This method has high production efficiency, is environmentally friendly, is suitable for application in large-scale industrial production, and has high economic and social benefits.

[0060] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0061] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a repaired lithium iron phosphate material, characterized in that, It includes the following steps: S1. Prepare separation agent A and impurity removal agent B; S2. Cut the lithium iron phosphate electrode sheet into standard small pieces of lithium iron phosphate; S3. Add the standard small pieces of lithium iron phosphate and separation agent A into the separation reactor in a certain mass ratio in sequence, stir and ultrasonically separate to separate out the wet aluminum sheet and the lithium iron phosphate wet material solution; S4. Dry the wet aluminum sheet to obtain aluminum products; S5. Add impurity removal agent B to the wet material solution, stir for impurity removal, let it stand, and centrifuge to obtain the lithium iron phosphate wet cake; S6. Dry the wet cake to obtain the lithium iron phosphate dry material; S7. Perform superconducting magnetic fluid density separation on the dry material to separate out impurities such as copper, aluminum, and plastic to obtain the purified lithium iron phosphate material; S8. After ball milling and demagnetizing the purified material, obtain the repaired lithium iron phosphate cathode powder product.

2. The preparation method of the repaired lithium iron phosphate material according to claim 1, wherein, The concentration of the separation agent A described in S1 is 1 - 20 mol / L, and the separation agent A is any one of N-methylpyrrolidone aqueous solution, acetone aqueous solution, dimethyl sulfoxide aqueous solution, and N,N-dimethylformamide aqueous solution.

3. The preparation method of the repaired lithium iron phosphate material according to claim 1, wherein, The concentration of the impurity removal agent B described in S1 is 1 - 30 mol / L, and the impurity removal agent B is any one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, and sodium carbonate aqueous solution.

4. The preparation method of the repaired lithium iron phosphate material according to claim 1, characterized in that, The mass ratio of the standard small pieces of lithium iron phosphate to the separation agent A described in S3 is 1:0.5 - 10.

5. The preparation method of the repaired lithium iron phosphate material according to claim 1, wherein The temperature of the stirring and ultrasonic separation described in S3 is 25 - 100 °C, and the time is 2 - 20 h.

6. The preparation method of the repaired lithium iron phosphate material according to claim 1, characterized in that, The drying temperature of the wet aluminum sheet described in S4 is 60 - 200 °C, and the drying time is 0.2 - 30 h.

7. The preparation method of the repaired lithium iron phosphate material according to claim 1, characterized in that, The drying temperature of the wet cake described in S6 is 100 - 200 °C, and the drying time is 0.2 - 20 h.

8. The preparation method of the repaired lithium iron phosphate material according to claim 1, characterized in that The magnetic field strength of the superconducting magnetic fluid described in S7 is 4 - 10 T; the superconducting magnetic fluid is one or more of Fe, Ni, Co, Fe3O4, and γ-Fe2O3.

9. The preparation method of the repaired lithium iron phosphate material according to claim 1, wherein The ball milling described in S8 uses zirconia ball milling beads, at 25 °C, with a rotation speed of 300 - 1100 rpm for 1 - 12 h; the magnetic field strength of the demagnetization described in S8 is 0.1 - 2 T, the feeding speed of the material is 50 - 300 g / s, and the magnetic separation time is 0.5 - 3 h.

10. A lithium iron phosphate repair material, characterized in that, It is obtained by using the preparation method described in any one of claims 1 - 9.

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