A method for repairing waste lithium iron phosphate and the obtained lithium iron phosphate material

Abstract

The present application discloses a method for repairing waste lithium iron phosphate and the obtained lithium iron phosphate material, which relates to the technical field of lithium battery materials. The method specifically includes: performing degumming treatment on waste lithium iron phosphate to obtain a lithium iron phosphate recovery material; mixing the lithium iron phosphate recovery material with a reducing agent, adding a lithium source, and placing them in a fluidized bed reactor for reaction; filtering the reacted substance through a first-stage high-temperature filtration system to obtain a first filtrate; filtering the first filtrate through a second-stage high-temperature filtration system, and simultaneously spraying a carbon source. After the carbon source is gasified, it is coated on the surface of lithium iron phosphate, and the repaired lithium iron phosphate is obtained after filtration. The present application adopts a fluidized bed reaction system, which enables the full mixing and contact of lithium iron phosphate and the lithium source, thereby achieving a sufficient lithium supplementation effect. At the same time, a carbon source is sprayed during the high-temperature filtration in the second stage to form a carbon-coated structure on the surface of lithium iron phosphate, separating the repaired lithium iron phosphate from the excess lithium source.

Description

Technical Field

[0001] This application relates to the technical field of lithium battery materials, and particularly relates to a method for repairing waste lithium iron phosphate and the obtained lithium iron phosphate material. Background Art

[0002] Lithium iron phosphate (abbreviated as LFP) material, as a lithium battery material with relatively high cost performance, is widely used in various power vehicles and other large equipment, and its waste production is increasing rapidly year by year. Although the recovery processes for various valuable metals in battery materials are relatively mature now, the metal recovery value in waste lithium iron phosphate is much lower than that of other types of batteries. Therefore, the traditional leaching process for recovering elements does not have practical economic benefits for its recovery. However, benefiting from the relatively stable olivine structure of lithium iron phosphate, waste lithium iron phosphate batteries can be recycled by in-situ regeneration methods.

[0003] Chinese Patent with publication number CN106058353A in the prior art discloses a method for repairing and regenerating the cathode material of waste batteries. By qualitatively testing the ratio of lithium element to other elements, calculating the proportion of the lacking lithium element, and then supplementing the lacking lithium element directionally and sintering, the purpose of repair is achieved. In this method, the amount of the lacking lithium element needs to be accurately measured. In practical applications, there are the following problems:

[0004] On the one hand, the sources of lithium-ion batteries are complex. In the same batch of old materials, some materials may lack lithium severely, while others may not lack lithium or lack it less severely. This may lead to large errors when measuring the amount of the lacking lithium element. On the other hand, during the lithium supplementation process, if an excessive amount of lithium source is added, the excess lithium source will free-float and adhere to the surface of the cathode material, affecting the pH value of the cathode material and resulting in the performance of the battery being affected. Therefore, there is an urgent need for a lithium supplementation method that can ensure the lithium supplementation effect of waste lithium iron phosphate while avoiding the harm caused by excessive lithium supplementation. Summary of the Invention

[0005] In order to solve at least one of the problems mentioned in the above background art, this application provides a method for repairing waste lithium iron phosphate and the obtained lithium iron phosphate material. A fluidized bed reaction system is adopted to melt the lithium source into a molten salt state, and through the fluidization effect of the fluidized bed, the lithium iron phosphate and the lithium source are fully mixed and contacted, so as to achieve a sufficient lithium supplementation effect. After the fluidized bed reaction, a two-stage high-temperature filtration system is used to filter the lithium-supplemented lithium iron phosphate to make its particle size uniform. At the same time, a carbon source is sprayed during the high-temperature filtration in the second stage to form a carbon-coated structure on the surface of the lithium iron phosphate, separating the repaired lithium iron phosphate from the excess lithium source. Then, under the action of the filter screen, the lithium iron phosphate and the lithium source are completely separated, reducing the adhesion of the excess lithium source on the surface of the lithium iron phosphate, thereby making the electrochemical performance of the repaired lithium iron phosphate material better.

[0006] The specific technical solutions provided by the embodiments of the present application are as follows:

[0007] In a first aspect, a method for repairing waste lithium iron phosphate is provided. The method includes:

[0008] S1: Degumming the waste lithium iron phosphate to obtain a lithium iron phosphate recovery material;

[0009] S2: Mix the lithium iron phosphate recovery material with a reducing agent and place it in a fluidized bed reactor for reaction. The fluidized bed bed material is a lithium source, and the fluidization atmosphere is an inert reducing gas;

[0010] S3: Filter the reacted substance through a first-stage high-temperature filtration system to obtain a first filtrate, and the filtration pore size is 5 - 30 μm;

[0011] S4: Filter the first filtrate through a second-stage high-temperature filtration system, and simultaneously spray a carbon source. After the carbon source is gasified, it coats the surface of the lithium iron phosphate. After filtration, the repaired lithium iron phosphate is obtained, and the filtration pore size is less than or equal to 3 μm.

[0012] In a specific embodiment, after step S4, it further includes:

[0013] Adding the excess lithium source obtained after filtration to the fluidized bed reactor for continuous reaction.

[0014] In a specific embodiment, the mixing of the lithium iron phosphate recovery material and the reducing agent in step S2 specifically includes:

[0015] If the mass ratio of CO in the inert reducing gas is greater than 10%, no reducing agent is added;

[0016] If the mass ratio of CO in the inert reducing gas is not greater than 10%, a reducing agent is added.

[0017] In a specific embodiment, the dosage ratio of the reducing agent to the lithium iron phosphate recovery material in step S2 is 0 - 1:10 W / W.

[0018] In a specific embodiment, the reaction conditions in the fluidized bed reactor in step S2 are:

[0019] The dosage ratio of the lithium source to the lithium iron phosphate recovery material is 0.5 - 2:1 W / W, preferably 0.5 - 1.1:1 W / W;

[0020] The reaction temperature is 550 - 750 °C; the reaction time is 1 - 3 h.

[0021] In a specific embodiment, the carbon source in step S4 is a saturated hydrocarbon with 10 - 20 carbon atoms or a mixture of a saturated hydrocarbon and water.

[0022] In a specific embodiment, the dosage ratio of the carbon source to the lithium iron phosphate recovery material in step S4 is 0.2 - 2:10 W / W, preferably 0.2 - 0.8:10 W / W;

[0023] The dosage ratio of the carbon source to water is 0.3 - 0.8:1 W / W.

[0024] In a specific embodiment, the mixing method of the reducing agent and the lithium iron phosphate recovery material in step S2 is as follows:

[0025] If the reducing agent is a solid, the reducing agent and the lithium iron phosphate recovery material are ball-milled and mixed;

[0026] If the reducing agent is a liquid, the reducing agent is added to a solvent, stirred evenly and then dried.

[0027] In a specific embodiment, the inert reducing gas in step S2 includes at least one or more of carbon monoxide, carbon dioxide, nitrogen, argon.

[0028] In a second aspect, a lithium iron phosphate material is provided, and the lithium iron phosphate material is obtained by repairing waste lithium iron phosphate according to the above-mentioned repairing method.

[0029] The embodiments of the present application have the following beneficial effects:

[0030] 1. In the embodiments of the present application, the degummed waste lithium iron phosphate is mixed with a reducing agent and used as a reactant and placed in a fluidized bed reactor for reaction. The bed material of the fluidized bed is a lithium source, and the fluidization atmosphere is an inert reducing gas. Through the fluidization effect of the fluidized bed, the lithium iron phosphate and the lithium source in the molten salt state are fully mixed and contacted, so as to achieve a sufficient lithium supplement effect; then the air volume is adjusted, and the reactants are blown out of the fluidized bed reactor, filtered through the first-stage high-temperature filtration system, and by setting the particle size of the filtration system, the particles that meet the particle size of the filtration system can pass through, so that the particle size of the lithium iron phosphate after lithium supplementation is relatively uniform; a second-stage high-temperature filtration system is set, and a carbon source is sprayed when the reactants pass through the second-stage high-temperature filtration system. Under the action of high temperature, the mixture of the carbon source and water is quickly gasified. Under the action of the sieve mesh, the excess lithium source is separated from the repaired lithium iron phosphate. At the same time, the gasified carbon source substance penetrates between the repaired lithium iron phosphate and the lithium source, coats the surface of the lithium iron phosphate, and isolates the liquid-solid interface between the lithium iron phosphate and the lithium source, realizing that the surface residual lithium content of the prepared lithium iron phosphate is less than 300 ppm, meeting the application index. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0032] Figure 1 A schematic diagram showing the method for repairing waste lithium iron phosphate according to the present application. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs. The terms used in the description of the present application herein are only for the purpose of describing specific implementation manners and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0035] Embodiment 1

[0036] A method for repairing waste lithium iron phosphate, as Figure 1 shown, the method includes:

[0037] Step S1: The waste lithium iron phosphate is subjected to degumming treatment to obtain a lithium iron phosphate recovery material; among them, 10 kg of the lithium iron phosphate recovery material after removing PVDF is taken.

[0038] Step S2: The lithium iron phosphate recovery material is mixed with a reducing agent and placed in a fluidized bed reactor for reaction. The fluidized bed bed material is a lithium source. The fluidization atmosphere is nitrogen. Since the mass ratio of CO in nitrogen is not greater than 10%, a reducing agent is added.

[0039] Specifically, 10 kg of the lithium iron phosphate recovery material and 1 kg of carbon powder reducing agent are mixed. The carbon powder reducing agent is a solid. First, the carbon powder and the lithium iron phosphate recovery material are ball-milled and mixed. Then the mixture is placed in a fluidized bed reaction system. The fluidized bed bed material is lithium hydroxide. The addition amount of the lithium source bed material lithium hydroxide is 10 kg. The temperature of the fluidized bed reactor is adjusted to 550 °C, and at the same time, the fluidized bed air volume is adjusted so that all the materials are in a fluidized state in the fluidized bed. The materials react in the fluidized bed reactor for 2 h.

[0040] Step S3: Filter the reacted substances through a first-stage high-temperature filtration system to obtain a first filtrate. Specifically, the reactants are passed through a first-stage high-temperature filter screen into the second-stage high-temperature filtration system, and the filtration aperture is 12 μm.

[0041] Step S4: Filter the first filtrate through a second-stage high-temperature filtration system, and simultaneously spray a carbon source. After the carbon source is gasified, it coats the surface of lithium iron phosphate. After filtration, the repaired lithium iron phosphate is obtained, and the filtration aperture is 3 μm.

[0042] Specifically, the selected carbon source is a saturated hydrocarbon with 12 carbon atoms. The preparation process of the carbon source is as follows: 0.5 kg of sizing agent is mixed with 1 kg of water at a high speed of 3000 r / min for 30 min. Then, the prepared carbon source and the sizing agent dilution are immediately added to the second high-temperature filtration system. At this time, the pressure in the second high-temperature filtration system rapidly rises above 0.5 MPa; after reacting in the second high-temperature filtration system for 30 min, the repaired lithium iron phosphate material and the excess lithium source are obtained, and the excess lithium source is added to the fluidized bed reactor for further reaction.

[0043] After the second-stage high-temperature filtration, the lithium iron phosphate is separated from the excess lithium source. Except for being mixed with a small amount of carbon, it does not contain other impurities. The separated excess lithium source is further added to the fluidized bed reactor for further reaction. Carbon can also act as a reducing agent to play a role in reduction and repair. Therefore, the excess lithium source after filtration is continuously recycled to the fluidized bed reaction system, reducing the attachment of the lithium source on the surface of lithium iron phosphate and improving the utilization rate of the lithium source.

[0044] Example 2

[0045] Corresponding to the above embodiments, a method for repairing waste lithium iron phosphate is provided, and the method includes:

[0046] Step S1: Perform degumming treatment on waste lithium iron phosphate to obtain a lithium iron phosphate recovery material; among them, 10 kg of the lithium iron phosphate recovery material after removing PVDF is taken.

[0047] Step S2: Mix the lithium iron phosphate recovery material with a reducing agent and place it in a fluidized bed reactor for reaction. The fluidized bed material is a lithium source. The fluidization atmosphere is nitrogen. Since the mass ratio of CO in nitrogen is not greater than 10%, a reducing agent is added.

[0048] Specifically, 10 kg of lithium iron phosphate recycling material and 1 kg of carbon powder reducing agent are mixed. The carbon powder reducing agent is solid. First, the carbon powder and lithium iron phosphate recycling material are ball-milled and mixed. Then the mixture is placed in a fluidized bed reaction system. The fluidized bed material is lithium hydroxide, and the addition amount of lithium source bed material lithium hydroxide is 10 kg. The temperature of the fluidized bed reactor is adjusted to 550 °C, and at the same time, the air volume of the fluidized bed is adjusted to make all the materials in a fluidized state in the fluidized bed. The materials react in the fluidized bed reactor for 2 h.

[0049] Step S3: Filter the reacted substances through a first-stage high-temperature filtration system to obtain a first filtrate. Specifically, the reactants pass through a first-stage high-temperature filter screen and enter the second-stage high-temperature filtration system. The filtration aperture is 12 μm.

[0050] Step S4: Filter the first filtrate through a second-stage high-temperature filtration system, and at the same time spray in a carbon source. After the carbon source is gasified, it coats the surface of lithium iron phosphate. After filtration, the repaired lithium iron phosphate is obtained. The filtration aperture is 3 μm.

[0051] Specifically, the selected carbon source is a saturated hydrocarbon with 16 carbon atoms. The preparation process of the carbon source is as follows: 0.7 kg of wetting agent and 1 kg of water are mixed at a high speed of 3000 r / min for 30 min. Then the prepared carbon source as a wetting agent dilution is immediately added to the second high-temperature filtration system. At this time, the pressure in the second high-temperature filtration system rapidly rises above 0.5 MPa; after reacting in the second high-temperature filtration system for 30 min, it is filtered through a filter screen to obtain the repaired lithium iron phosphate material and the excess lithium source, and the excess lithium source is added to the fluidized bed reactor to continue the reaction.

[0052] Comparative Example 1

[0053] Corresponding to the above Example 1, a method for repairing waste lithium iron phosphate is provided. The method includes:

[0054] Step S1: The waste lithium iron phosphate is degummed to obtain lithium iron phosphate recycling material; among them, 10 kg of lithium iron phosphate recycling material after removing PVDF is taken.

[0055] Step S2: The lithium iron phosphate recycling material is mixed with a reducing agent and placed in a fluidized bed reactor for reaction. The fluidized bed material is a lithium source. The fluidizing atmosphere is nitrogen. Since the mass ratio of CO in nitrogen is not more than 10%, a reducing agent is added.

[0056] Specifically, 10 kg of lithium iron phosphate recycling material and 1 kg of carbon powder reducing agent are mixed. The carbon powder reducing agent is solid. First, the carbon powder and the lithium iron phosphate recycling material are ball-milled and mixed. Then the mixture is placed in a fluidized bed reaction system. The fluidized bed bed material is lithium hydroxide, and the addition amount of the lithium source bed material lithium hydroxide is 10 kg. The temperature of the fluidized bed reactor is adjusted to 550 °C. At the same time, the fluidized bed air volume is adjusted to make all the materials in a fluidized state in the fluidized bed. The materials react in the fluidized bed reactor for 2 h.

[0057] Step S3: Filter the reacted substance through a first-stage high-temperature filtration system to obtain a first filtrate. Specifically, the reactants pass through a first-stage high-temperature filter screen and enter the second-stage high-temperature filtration system. The filtration aperture is 5 μm.

[0058] Step S4: Filter the first filtrate through a second-stage high-temperature filtration system, and at the same time spray in a carbon source. After the carbon source is gasified, it coats the surface of the lithium iron phosphate. The repaired lithium iron phosphate is obtained after filtration. The filtration aperture is 3 μm.

[0059] Specifically, without adding a carbon source, directly add the first filtrate to the second high-temperature filtration system; after reacting in the second high-temperature filtration system for 30 min, filter through the filter screen to obtain the repaired lithium iron phosphate material and the excess lithium source, and add the excess lithium source to the fluidized bed reactor for continuous reaction.

[0060] Comparative Example 2

[0061] Corresponding to the above Example 1, a method for repairing waste lithium iron phosphate is provided. The method includes:

[0062] Step S1: Perform degumming treatment on the waste lithium iron phosphate to obtain lithium iron phosphate recycling material; among them, 10 kg of lithium iron phosphate recycling material after removing PVDF is taken.

[0063] Step S2: Mix the lithium iron phosphate recycling material with a reducing agent and place it in a fluidized bed reactor for reaction. The fluidized bed bed material is a lithium source. The fluidizing atmosphere is nitrogen. Since the mass ratio of CO in nitrogen is not more than 10%, a reducing agent is added.

[0064] Specifically, 10 kg of lithium iron phosphate recycling material and 1 kg of carbon powder reducing agent are mixed. The carbon powder reducing agent is solid. First, the carbon powder and the lithium iron phosphate recycling material are ball-milled and mixed. Then the mixture is placed in a fluidized bed reaction system. The fluidized bed bed material is lithium hydroxide, and the addition amount of the lithium source bed material lithium hydroxide is 10 kg. The temperature of the fluidized bed reactor is adjusted to 550 °C. At the same time, the fluidized bed air volume is adjusted to make all the materials in a fluidized state in the fluidized bed. The materials react in the fluidized bed reactor for 2 h.

[0065] Step S3: Filter the reacted substances through a first-stage high-temperature filtration system to obtain a first filtrate. Specifically, the reactants are passed through a first-stage high-temperature filter mesh into the second-stage high-temperature filtration system, and the filtration aperture is 5 μm.

[0066] Step S4: Filter the first filtrate through a second-stage high-temperature filtration system, and simultaneously spray in a carbon source. After the carbon source is gasified, it coats the surface of lithium iron phosphate. After filtration, the repaired lithium iron phosphate is obtained, and the filtration aperture is 3 μm.

[0067] Specifically, the selected carbon source is a saturated hydrocarbon with 12 carbon atoms. The carbon source is wetted with 0.5 kg of wetting agent without adding water. Then the wetting agent is immediately added to the second high-temperature filtration system; after reacting in the second high-temperature filtration system for 30 minutes, it is filtered through a filter mesh to obtain the repaired lithium iron phosphate material and the excess lithium source, and the excess lithium source is added to the fluidized bed reactor for continuous reaction.

[0068] The repaired lithium iron phosphate obtained by the steps in Example 1, Comparative Example 1, and Comparative Example 2 is detected. Among them, the un-repaired one is the original waste lithium iron phosphate that has not undergone the repair steps in this application. Comparative Example 1 is the repaired lithium iron phosphate obtained without adding a carbon source in the second high-temperature filtration system. Comparative Example 2 is the repaired lithium iron phosphate obtained by adding a straight-chain saturated alkane directly in the second high-temperature filtration system. The test data are shown in Table 1:

[0069] Table 1 Influence results of carbon source on the repair of lithium iron phosphate

[0070]

[0071]

[0072] From the data of the un-repaired lithium iron phosphate in Table 1 and the repaired lithium iron phosphate in Example 1 and Example 2, it can be seen that the content of lithium in the repaired lithium iron phosphate has been greatly increased compared with that before repair. Moreover, by selecting different saturated hydrocarbon infiltrants and adjusting the addition amounts of different saturated infiltrants, lithium iron phosphate with different carbon coating contents can be obtained, while avoiding the excessive free lithium on the surface of lithium iron phosphate. Thus, it is proved that under the action of high temperature, the mixture of carbon source and water gasifies rapidly. Under the action of the sieve, the excess lithium source is separated from the repaired lithium iron phosphate. At the same time, the gasified carbon source substance penetrates between the repaired lithium iron phosphate and the lithium source, coats on the surface of the lithium iron phosphate, and isolates the liquid-solid interface between the lithium iron phosphate and the lithium source, realizing that the surface residual lithium content of the prepared lithium iron phosphate is less than 300 ppm, meeting the application index. Moreover, by testing the Coulomb efficiency and specific capacity of the lithium iron phosphate before and after repair, it can be found that the Coulomb efficiency of the repaired lithium iron phosphate is above 99%, and the specific capacity after repair is above 165 mA·h / g, reaching the standards of the Coulomb efficiency and specific capacity of lithium iron phosphate. Furthermore, it is proved that the lithium iron phosphate prepared by the repair method in this application can meet the application requirements of the prepared battery.

[0073] From the comparison of the data in Comparative Example 1 and Example 1, it can be seen that without adding a carbon source to isolate the excess lithium source from the surface of lithium iron phosphate, the content of free lithium on the surface of the repaired lithium iron phosphate exceeds the standard. Moreover, the carbon content of the lithium iron phosphate obtained in Comparative Example 1 is very low, only 0.96%, indicating that the carbon coating layer is lost during the fluidization process, thus affecting the performance of the prepared battery. And when only saturated hydrocarbon is added without adding water as a dispersant, the carbon coating of the prepared lithium iron phosphate is uneven and the electrical performance is poor. Therefore, it can be obtained that adding a carbon source keeps the lithium content and carbon content on the surface of the repaired lithium iron phosphate within a suitable range, so that the performance of the prepared battery meets the application requirements.

[0074] Furthermore, the surface carbon content distribution of the prepared lithium iron phosphate in Example 1 and Comparative Example 2 was tested. Specifically, 5 different positions of the samples in Example 1 and Comparative Example 2 were randomly sampled, namely: Sampling 1, Sampling 2, Sampling 3, Sampling 4, and Sampling 5. Then, the carbon content at the 5 positions was tested, and the test data are shown in Table 2.

[0075] Table 2 Carbon Content Test Results

[0076]

[0077] As can be seen from the test results in Table 2, the carbon coating in Example 1 is relatively uniform, while the carbon coating in Comparative Example 2 is uneven, further verifying that when only saturated hydrocarbons are added without adding water as a dispersant, the carbon coating of the prepared lithium iron phosphate is uneven and the electrical properties are poor.

[0078] Comparative Example 3

[0079] Compared with Example 1 above, a method for repairing waste lithium iron phosphate is provided. The method includes:

[0080] Step S1: The waste lithium iron phosphate is subjected to degumming treatment to obtain a lithium iron phosphate recovery material; among them, 10 kg of the lithium iron phosphate recovery material after removing PVDF is taken.

[0081] Step S2: The lithium iron phosphate recovery material is mixed with a reducing agent and placed in a fluidized bed reactor for reaction. The fluidized bed bed material is a lithium source. The fluidization atmosphere is nitrogen and no reducing agent is added.

[0082] Specifically, 10 kg of the lithium iron phosphate recovery material is placed in a fluidized bed reaction system. The fluidized bed bed material is lithium hydroxide, and the addition amount of the lithium source bed material lithium hydroxide is 10 kg. The temperature of the fluidized bed reactor is adjusted to 550 °C, and at the same time, the fluidized bed air volume is adjusted so that all materials are in a fluidized state in the fluidized bed. The materials react in the fluidized bed reactor for 2 h.

[0083] Step S3: The reacted substance is filtered through a first-stage high-temperature filtration system to obtain a first filtrate. Specifically, the reactants pass through a first-stage high-temperature filter screen and enter the second-stage high-temperature filtration system. The filtration aperture is 12 μm.

[0084] Step S4: The first filtrate is filtered through a second-stage high-temperature filtration system, and at the same time, a carbon source is sprayed. After the carbon source is gasified, it is coated on the surface of the lithium iron phosphate. After filtration, the repaired lithium iron phosphate is obtained, and the filtration aperture is 3 μm.

[0085] Specifically, the selected carbon source is a saturated hydrocarbon with 12 carbon atoms. The preparation process of the carbon source is as follows: 0.5 kg of sizing agent is mixed with 1 kg of water at a high speed of 3000 r / min for 30 min. Then the prepared carbon source as a sizing agent dilution liquid is immediately added to the second high-temperature filtration system. At this time, the pressure in the second high-temperature filtration system rapidly rises above 0.5 MPa; after reacting in the second high-temperature filtration system for 30 min, it is filtered through a filter screen to obtain the repaired lithium iron phosphate material and the excess lithium source, and the excess lithium source is added to the fluidized bed reactor for continuous reaction.

[0086] Comparative Example 4

[0087] Compared with Example 1 above, a method for repairing waste lithium iron phosphate is provided. The method includes:

[0088] Step S1: The waste lithium iron phosphate is degummed to obtain lithium iron phosphate recovery material; among them, 10 kg of lithium iron phosphate recovery material after removing PVDF is taken.

[0089] Step S2: Mix the lithium iron phosphate recovery material with a reducing agent and place it in a fluidized bed reactor for reaction. The fluidized bed bed material is a lithium source. The fluidization atmosphere is nitrogen, and no reducing agent is added, but 12% by mass of CO gas is mixed in the fluidization atmosphere.

[0090] Specifically, 10 kg of lithium iron phosphate recovery material is placed in a fluidized bed reaction system. The fluidized bed bed material is lithium hydroxide, and the addition amount of the lithium source bed material lithium hydroxide is 10 kg. The temperature of the fluidized bed reactor is adjusted to 550 °C, and at the same time, the fluidized bed air volume is adjusted to make all the materials in a fluidized state in the fluidized bed. The materials react in the fluidized bed reactor for 2 h.

[0091] Step S3: Filter the reacted material through a first-stage high-temperature filtration system to obtain a first filtrate. Specifically, the reactants pass through a first-stage high-temperature filter screen and enter the second-stage high-temperature filtration system. The filtration pore size is 12 μm.

[0092] Step S4: Filter the first filtrate through a second-stage high-temperature filtration system, and at the same time spray a carbon source. After the carbon source is gasified, it coats the surface of the lithium iron phosphate. The repaired lithium iron phosphate is obtained after filtration, and the filtration pore size is 3 μm.

[0093] Specifically, the selected carbon source is a saturated hydrocarbon with 12 carbon atoms. The preparation process of the carbon source is as follows: 0.5 kg of sizing agent is mixed with 1 kg of water at a high speed of 3000 r / min for 30 min. Then the prepared carbon source as a sizing agent dilution is immediately added to the second high-temperature filtration system. At this time, the pressure in the second high-temperature filtration system rapidly rises above 0.5 MPa; after reacting in the second high-temperature filtration system for 30 min, it is filtered through a filter screen to obtain the repaired lithium iron phosphate material and the excess lithium source, and the excess lithium source is added to the fluidized bed reactor for continuous reaction.

[0094] Combined with the preparation processes in Example 1, Comparative Example 3, and Comparative Example 4, the lithium iron phosphates prepared in the three processes are tested. Among them, no reducing agent is added to the fluidized bed reactants in Comparative Example 3, and no reducing agent is added to the fluidized bed reactants in Comparative Example 4, but a certain content of CO gas is mixed in the fluidization atmosphere. The test data of the prepared lithium iron phosphate are shown in Table 3:

[0095] Table 3 Influence results of reducing agents on the repaired lithium iron phosphate

[0096]

[0097] As can be seen from the data in Table 3, the lithium content of the lithium iron phosphate prepared in Comparative Example 3 without adding any reducing agent is much lower than that of the lithium iron phosphate prepared in Example 1, indicating that the lack of a reducing agent will greatly affect the lithium compensation effect; from the comparison data of the lithium content of the lithium iron phosphate prepared in Comparative Example 4 and Example 1, it can be seen that adding carbon monoxide in the fluidized atmosphere also has a reducing effect. Although the lithium content of the lithium iron phosphate prepared at this time is lower than that of the lithium iron phosphate prepared with a reducing agent, the difference between the two is not significant, further proving the importance of adding a reducing agent in the process of repairing lithium iron phosphate.

[0098] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for repairing waste lithium iron phosphate, characterized in that, The method includes: S1: Demulcify the waste lithium iron phosphate to obtain a lithium iron phosphate recovery material; S2: Mix the lithium iron phosphate recovery material with a reducing agent and place it in a fluidized bed reactor for reaction. The fluidized bed bed material is a lithium source, and the fluidization atmosphere is an inert reducing gas; S3: Filter the reacted material through a first-stage high-temperature filtration system to obtain a first filtrate, with a filtration pore size of 5 - 30 μm; S4: Filter the first filtrate through a second-stage high-temperature filtration system. When the first filtrate passes through the second-stage high-temperature filtration system, a carbon source is simultaneously sprayed in. The carbon source is a mixture of a saturated hydrocarbon with 10 - 20 carbon atoms and water. After the carbon source gasifies and coats the surface of the lithium iron phosphate, filtration is carried out after the reaction to obtain repaired lithium iron phosphate, with a filtration pore size less than or equal to 3 μm.

2. The method for repairing waste lithium iron phosphate according to claim 1, wherein After step S4, it further includes: The excess lithium source obtained after filtration is added to the fluidized bed reactor for continuous reaction.

3. The method for repairing waste lithium iron phosphate according to claim 2, characterized in that, In step S2, the mixing of the lithium iron phosphate recovery material and the reducing agent specifically includes: If the mass ratio of CO in the inert reducing gas is greater than 10%, no reducing agent is added; If the mass ratio of CO in the inert reducing gas is not greater than 10%, a reducing agent is added.

4. The method for repairing waste lithium iron phosphate according to claim 3, wherein In step S2, the dosage ratio of the reducing agent to the lithium iron phosphate recovery material is 0 - 1:10 W / W.

5. The method for repairing waste lithium iron phosphate according to claim 4, characterized in that, In step S2, the reaction conditions in the fluidized bed reactor are: The dosage ratio of the lithium source to the lithium iron phosphate recovery material is 0.5 - 2:1 W / W; The reaction temperature is 550 - 750 °C; the reaction time is 1 - 3 h.

6. The method for repairing waste lithium iron phosphate according to claim 5, wherein The dosage ratio of the lithium source to the lithium iron phosphate recovery material is 0.5 - 1.1:1 W / W.

7. The method for repairing waste lithium iron phosphate according to claim 6, characterized in that, In step S4, the dosage ratio of the carbon source to the lithium iron phosphate recovery material is 0.2 - 2:10 W / W; The dosage ratio of the carbon source to water is 0.3 - 0.8:1 W / W.

8. The method for repairing waste lithium iron phosphate according to claim 7, wherein In step S4, the dosage ratio of the carbon source to the lithium iron phosphate recovery material is 0.2 - 0.8:10 W / W.

9. The method for repairing waste lithium iron phosphate according to claim 7, characterized in that, In step S2, the mixing method of the reducing agent and the lithium iron phosphate recovery material is: If the reducing agent is a solid, ball-mill the reducing agent and the lithium iron phosphate recovery material; If the reducing agent is a liquid, add the reducing agent to a solvent, stir evenly, and then dry.

10. The method for repairing waste lithium iron phosphate according to claim 9, wherein, The inert reducing gas in step S2 includes at least one or more of carbon monoxide, carbon dioxide, nitrogen, and argon.

11. A lithium iron phosphate material, characterized in that, The lithium iron phosphate material is repaired by the method for repairing waste lithium iron phosphate according to any one of claims 1 - 10.

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