Method for preparing battery-grade lithium phosphate and iron phosphate by recycling waste lithium iron phosphate battery

Abstract

The invention discloses a method for preparing battery-grade lithium phosphate and iron phosphate by recycling waste lithium iron phosphate batteries, and belongs to the technical field of lithium ion battery recycling. The method comprises the following steps: mixing and calcining black powder recovered from the waste lithium iron phosphate battery and sodium persulfate; adding water for dissolving, filtering to obtain a water leaching solution A and leaching residues, washing the leaching residues with water, and calcining at high temperature to obtain battery-grade iron phosphate; adding a sodium hydroxide solution into the water extract A, and reacting to obtain a water extract B; adding a trisodium phosphate solution into the water immersion liquid B, performing suction filtration after reaction to obtain lithium phosphate and filtrate, and cleaning and drying the lithium phosphate to obtain battery-grade lithium phosphate; and freezing and denitrifying the filtrate to obtain a denitrified solution, and adding the denitrified solution into the sodium hydroxide solution for recycling. The filtrate is recycled in the whole production process, zero loss of the lithium element is theoretically realized, the iron element is prevented from entering the solution, the preparation steps of the lithium phosphate are simplified, and the method has the advantages of economy and environmental protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery recycling, in particular to a method for recycling waste lithium iron phosphate battery to prepare battery-grade lithium phosphate and iron phosphate. BACKGROUND

[0002] LiFePO4 battery has attracted wide attention and application due to its excellent thermal stability and cycle performance, especially in the field of new energy vehicles. Traditional lithium batteries are gradually being replaced by LiFePO4 batteries. The rapidly growing market will inevitably lead to a large number of batteries being scrapped, so a large number of waste batteries need to be disposed of. Proper disposal of waste LiFePO4 batteries can reduce pollution caused by harmful ingredients to the environment. At present, the demand for lithium is increasing, but the natural lithium resource is limited and cannot meet the current production demand. Efficient recovery of high-value components, especially lithium and iron, in batteries can promote resource recycling and contribute to economic growth. Therefore, it is necessary to recycle waste LiFePO4 batteries.

[0003] Traditional hydrometallurgy has the advantages of high recovery rate, good selectivity and low cost, but the recovery process consumes too much chemical medicine and has a greater impact on the environment. The existing technology recovers waste lithium iron phosphate batteries through acid leaching. Patent CN108899601B discloses a method for recovering lithium and iron from lithium iron phosphate. Lithium is recovered from lithium iron phosphate by selectively leaching lithium elements. Sulfuric acid is added during the process, and iron is removed by generating hydroxide by adjusting pH. The precipitate generated during the leaching process is mainly a compound mainly composed of iron phosphate, which is further prepared into battery-grade iron phosphate. The recovered lithium phosphate in the lithium carbonate mother liquor can be further prepared into lithium carbonate. The process has a high lithium recovery rate, but the acid leaching solution contains a small amount of iron, which requires an additional step of removing iron with an oxidizing agent. The purity of the recovered lithium is not high, and a large amount of acid is consumed during the recovery process, which pollutes the environment. Therefore, a more complete system for recycling and processing retired batteries needs to be established, the process operation needs to be simplified, and the batteries need to be safely disposed of to achieve resource recycling and create higher economic value. SUMMARY

[0004] In view of the above prior art, the purpose of the present application is to provide a method for recycling waste lithium iron phosphate batteries to prepare battery-grade lithium phosphate and iron phosphate.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The first aspect of the present application provides a method for recycling waste lithium iron phosphate batteries to prepare battery-grade lithium phosphate and iron phosphate, comprising the following steps: (1) uniformly mixing lithium iron phosphate black powder separated from waste batteries with sodium persulfate by ball milling, and calcining at high temperature under inert atmosphere; (2) to the obtained calcination product, water is added, and after being fully dissolved, filtration is performed to obtain a water leaching solution A and a leaching residue, and the leaching residue is washed with water and then calcined at a high temperature in an oxygen-containing atmosphere to obtain battery-grade iron phosphate; (3) sodium hydroxide solution is added to the water leaching solution A to obtain a water leaching solution B; (4) trisodium phosphate solution is added to the water leaching solution B, and after being fully reacted, suction filtration is performed to obtain lithium phosphate and a filtrate, and the lithium phosphate is cleaned and dried to obtain battery-grade lithium phosphate; (5) the filtrate is frozen and denitration is performed to obtain a denitration solution, which can be added to the aforementioned sodium hydroxide solution for recycling.

[0006] The battery-grade iron phosphate has a ratio of iron to phosphorus close to 1:1 and low impurity content, and can be used for synthesizing lithium iron phosphate positive electrode material and assembling a battery, and through electrochemical tests such as cycle performance, while the general iron phosphate has low purity requirements.

[0007] Further, in step (1), the mass ratio of the black powder recovered from the waste lithium iron phosphate battery to sodium persulfate is 1:1-1.5.

[0008] Further, in step (1), the calcination temperature is 500-700 DEG C, and the calcination time is 6-8 h.

[0009] Further, in step (2), the calcination temperature is 700-850 DEG C, and the calcination time is 3-5 h.

[0010] Further, in step (3), the amount of sodium hydroxide solution added is: added to the solution until the PH is greater than or equal to 14.

[0011] Further, in step (4), the trisodium phosphate solution is slowly introduced into the water leaching solution B.

[0012] Further, in step (4), the amount of trisodium phosphate added is: 2%-5% excess relative to the amount of lithium hydroxide in the water leaching solution B according to the complete reaction ratio.

[0013] The beneficial effects of the present application are: 1. The present application uses sodium persulfate as a lithium ion leaching agent, and does not use acid in the process, which is lower in cost than the acid production process. Compared with the traditional wet lithium leaching method, the present application first mixes sodium persulfate powder with black powder through ball milling, and then performs high-temperature calcination reaction and water leaching, which avoids the entry of part of iron ions into the lithium-containing water leaching solution, and eliminates the subsequent step of removing iron from the water leaching solution used for lithium precipitation. The present application simplifies the steps of recycling waste lithium iron phosphate batteries to prepare battery-grade lithium phosphate, and is more environmentally friendly while reducing costs.

[0014] 2.The present application separates and recycles all iron ions and lithium ions in the black powder of waste lithium iron phosphate batteries, and obtains by-product sodium sulfate at the same time, the denitration liquid produced can be recycled and used in the next batch of sodium hydroxide solution for the preparation of lithium phosphate.The present application not only theoretically realizes the recycling process without loss of lithium ions, and the lithium extraction rate reaches 100%, but also has no waste and waste liquid generated in the whole process, is environmentally friendly, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A process flow chart for recycling waste lithium iron phosphate batteries to prepare battery-grade lithium phosphate and iron phosphate.

[0016] Figure 2 An XRD pattern of battery-grade lithium phosphate synthesized in Example 1.

[0017] Figure 3 An XRD pattern of battery-grade lithium phosphate synthesized in Example 2.

[0018] Figure 4 An XRD pattern of battery-grade lithium phosphate synthesized in Example 3. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0020] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples.

[0021] As described in the background, in order to solve the problems of low lithium extraction rate, high cost and environmental pollution in the recycling process of traditional lithium iron phosphate batteries, the present application provides a method for recycling waste lithium iron phosphate batteries to prepare battery-grade lithium phosphate and iron phosphate, which comprises the following steps: (1) The lithium iron phosphate black powder separated from the waste lithium iron phosphate battery is mixed with sodium persulfate in a mass ratio of 1:(1-1.5) by ball milling, and then calcined at 500-700℃ for 6-8h under inert atmosphere; The reaction occurring in step (1) of the present application under the protection of inert atmosphere is 2LiFePO4+Na2S2O8=2FePO4+Na2SO4+Li2SO4, wherein FePO4 is insoluble in water and is filtered out together with carbon as leaching residue in step (2); (2) After the calcination product is added with water and fully dissolved, filtration is performed to obtain water leaching liquid A and leaching residue, and the leaching residue is washed with water and then calcined at 700-850℃ for 3-5h under oxygen-containing atmosphere to obtain battery-grade iron phosphate; The reaction occurring in step (2) is C+O2=CO2, and the carbon in the black powder is removed to obtain the battery-grade FePO4; (3) adding sodium hydroxide solution to the water immersion solution A until the solution pH is greater than or equal to 14, and obtaining water immersion solution B after reaction; The reactions occurring in step (3) are 2Na2S2O8+ 4NaOH = 4Na2SO4+ O2+ 2H2O and Li2SO4+2NaOH=Na2SO4+2LiOH; (4) adding trisodium phosphate solution to the water immersion solution B, and obtaining lithium phosphate and filtrate after filtration, and the lithium phosphate is dried after washing to obtain the battery-grade lithium phosphate; The reaction occurring in step (4) is 3LiOH+2Na3PO4=3NaOH+2Li3PO4, and the battery-grade Li3PO4 is obtained, and in order to ensure complete reaction, the amount of trisodium phosphate is 2%-5% more than that of lithium hydroxide.

[0022] (5) obtaining mirabilite (sodium sulfate decahydrate, Na2SO4·10H2O) and denitration liquid (NaOH) after freezing and denitration of the filtrate, and the denitration liquid can be recycled and used in the sodium hydroxide solution.

[0023] The raw material of the application is waste lithium iron phosphate black powder, the reagents used are cheap, the process operation is simple, no waste is generated, the equipment requirement is low, the denitration liquid can be recycled and used, the environment is friendly, there is no lithium loss, and the application is suitable for large-scale production.

[0024] The test materials not specifically described in the embodiments of the application are conventional test materials in the art, and can be purchased through commercial channels.

[0025] Example 1 Steps: (1) uniformly mixing 500g of waste lithium iron phosphate black powder recovered from a lithium iron phosphate battery with 500g of sodium persulfate, and then calcining under nitrogen protection at 500℃, the temperature rising rate is kept at 10℃ / min, the holding time is 6h, and the calcined product is obtained after natural cooling; (2) adding water to the calcined product obtained in step (1) to fully dissolve, and then filtering to obtain a water immersion solution and a residue, washing the residue with water, and then calcining under air atmosphere at a temperature of 700℃, the temperature rising rate is kept at 10℃ / min, the calcining time is 3h, and the battery-grade iron phosphate (the iron-phosphorus ratio is 0.98) is obtained after natural cooling and powdering; (3) adding sodium hydroxide solution to the water immersion solution A until the solution pH is 14, and obtaining water immersion solution B after reaction; (4) Add 510 g of trisodium phosphate solution to the water immersion liquid B, and after sufficient reaction, perform suction filtration to obtain lithium phosphate and a filtrate, and the lithium phosphate, after being washed and dried, is battery-grade lithium phosphate; (5) Freeze and denitrate the filtrate to obtain a denitration liquid, which can be added to the sodium hydroxide solution in step (3) for recycling.

[0026] Example 2 Steps: (1) Mix 500 g of black powder recovered from waste lithium iron phosphate batteries with 520 g of sodium persulfate uniformly by ball milling, and then calcine under nitrogen protection at 600℃, with a heating rate of 10℃ / min and a holding time of 6 h, and after natural cooling, obtain a calcined product; (2) After adding water to the calcined product obtained in step (1) to fully dissolve and then filtering, obtain a water immersion liquid and a residue, and after washing the residue with water, perform high-temperature calcination under air atmosphere, with a temperature of 800℃, a heating rate of 10℃ / min, and a calcination time of 4 h, and after natural cooling, obtain battery-grade iron phosphate (iron-phosphorus ratio of 0.96) by powdering; (3) Add a sodium hydroxide solution to the water immersion liquid A until the solution PH=15, and after reaction, obtain a water immersion liquid B; (4) Add 520 g of trisodium phosphate solution to the water immersion liquid B, and after sufficient reaction, perform suction filtration to obtain lithium phosphate and a filtrate, and the lithium phosphate, after being washed and dried, is battery-grade lithium phosphate; (5) Freeze and denitrate the filtrate to obtain a denitration liquid, which can be added to the sodium hydroxide solution in step (3) for recycling.

[0027] Example 3 Steps: (1) Mix 600 g of black powder recovered from waste lithium iron phosphate batteries with 800 g of sodium persulfate uniformly by ball milling, and then calcine under nitrogen protection at 700℃, with a heating rate of 10℃ / min and a holding time of 7 h, and after natural cooling, obtain a calcined product; (2) After adding water to the calcined product obtained in step (1) to fully dissolve and then filtering, obtain a water immersion liquid and a residue, and after washing the residue with water, perform high-temperature calcination under air atmosphere, with a temperature of 850℃, a heating rate of 10℃ / min, and a calcination time of 5 h, and after natural cooling, obtain battery-grade iron phosphate (iron-phosphorus ratio of 0.97) by powdering; (3) Add a sodium hydroxide solution to the water immersion liquid A until the solution PH=14, and after reaction, obtain a water immersion liquid B; (4) Add 515 g of trisodium phosphate solution to the water immersion liquid B, and after sufficient reaction, perform suction filtration to obtain lithium phosphate and a filtrate, and the lithium phosphate, after being washed and dried, is battery-grade lithium phosphate; (5) The filtrate is frozen and denitration is performed to obtain a denitration solution, which can be added to the sodium hydroxide solution in step (3) for recycling.

[0028] After collecting the lithium phosphate of Example 1-Example 3, the content of the prepared lithium phosphate was measured by ICP-OES method, the purity of the lithium phosphate was obtained, and XRD test was performed. The purity measurement results are shown in Table 1, and the XRD test results are shown in Figure 1. Figures 1-3 : Table 1: Purity of lithium phosphate The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various changes and modifications to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recycling spent lithium iron phosphate battery to produce battery grade lithium phosphate and iron phosphate, characterized in that, The method comprises the following steps: (1) uniformly mixing the lithium iron phosphate black powder separated from the waste battery with sodium persulfate by ball milling, and calcining under high temperature in an inert atmosphere; (2) adding water to the obtained calcined product, fully dissolving and filtering to obtain a water immersion liquid A and an immersion residue, washing the immersion residue with water, and calcining under high temperature in an oxygen-containing atmosphere to obtain a battery-grade iron phosphate; (3) adding a sodium hydroxide solution to the water immersion liquid A to obtain a water immersion liquid B; (4) adding a trisodium phosphate solution to the water immersion liquid B, fully reacting, and then filtering to obtain lithium phosphate and a filtrate, and the lithium phosphate is cleaned and dried to obtain the battery-grade lithium phosphate; (5) freezing and removing nitrogen from the filtrate to obtain a denitration liquid, which can be added to the aforementioned sodium hydroxide solution for recycling.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of the black powder recovered from the waste lithium iron phosphate battery to sodium persulfate is 1:1-1.

5.

3. The preparation method according to claim 1, characterized in that, In step (1), the calcination temperature is 500-700℃, and the calcination time is 6-8h.

4. The method of claim 1, wherein, In step (2), the calcination temperature is 700-850℃, and the calcination time is 3-5h.

5. The preparation method according to claim 1, characterized in that, In step (3), the amount of the sodium hydroxide solution added is: added to the solution until the PH is greater than or equal to 14.

6. The method of claim 1, wherein, In step (4), the trisodium phosphate solution is slowly introduced into the water immersion liquid B.

7. The preparation method according to claim 1, characterized in that, In step (4), the amount of the trisodium phosphate added is: 2%-5% excess relative to the lithium hydroxide in the water immersion liquid B according to the complete reaction ratio.

Images