A method for recycling waste lithium iron phosphate to prepare lithium iron phosphate

Abstract

The present application discloses a method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate batteries, which comprises the following steps: oxidizing and acid-leaching the recycled lithium iron phosphate battery powder to obtain acid-leached lithium solution and iron-phosphorus filter residue; adjusting the pH of the acid-leached lithium solution for purification and concentration, adding a phosphorus source and adjusting the pH to 9.5 - 10.5 to obtain solution A; subjecting the iron-phosphorus filter residue to secondary acid-leaching, iron dissolution, adding a phosphorus source and adjusting the pH to 6.5 - 7.5 to obtain solution B; mixing solution A and solution B for coprecipitation reaction, and filtering to obtain lithium iron phosphate precursor and reaction mother liquor; subjecting the lithium iron phosphate precursor to anaerobic drying, mixing with a carbon source and sintering to prepare a carbon-coated lithium iron phosphate cathode material. The method provided by the present application has the advantages of short recycling path, few reaction by-products and environmental friendliness, and can recycle all components of lithium, iron and phosphorus in the waste lithium iron phosphate battery powder. At the same time, the by-product is ammonium sulfate, a high-quality fertilizer raw material, which has great application prospects.

Description

Technical Field

[0001] This application belongs to the technical field of lithium iron phosphate, and particularly relates to a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate. Background Art

[0002] Lithium iron phosphate (LiFePO4) is a cathode material for lithium-ion batteries, with an olivine crystal structure (orthorhombic system). Its lithium ions can be reversibly deintercalated and intercalated during charge and discharge, featuring high safety and stability. Currently, lithium iron phosphate has been widely used as a power battery and energy storage battery for new energy vehicles. However, with the explosive growth of the production and sales volume of new energy vehicles and other products, and the increasing scale of energy storage, the output of lithium iron phosphate batteries has also risen accordingly. Considering the waste generated during the production process of lithium iron phosphate batteries and the old batteries that have reached the end of their service life, a large number of waste lithium iron phosphate batteries will be generated in the future. Therefore, it is very necessary to recycle and reuse lithium iron phosphate batteries.

[0003] Currently, the treatment methods for recycling lithium iron phosphate power batteries are mainly divided into two types: one is repair and regeneration, and the other is to recover valuable elements using hydrometallurgy methods. However, the performance of lithium battery cathode materials after high-temperature repair is usually not ideal; in the wet recycling of lithium iron phosphate batteries, typical products include high-value products such as lithium carbonate and iron phosphate. However, in the past two years, with the continuous decline of lithium prices, the economy of existing recycling methods has deteriorated. Therefore, it is very necessary to research and develop short-process regeneration technologies during the recycling of lithium iron phosphate batteries.

[0004] The current mainstream lithium iron phosphate recycling process is to first extract lithium, remove some impurities such as aluminum in the lithium solution. The impurity removal process in this step is relatively simple, and then the lithium solution is prepared into lithium carbonate products. However, the subsequent process of removing aluminum from iron and phosphorus slag is relatively difficult and complex in terms of technology, and the products obtained from recycling battery powder are generally lithium carbonate and iron phosphate, with high energy consumption and a large amount of carbon emissions generated during the calcination process. After that, it is necessary to further prepare it into lithium iron phosphate, and its overall process is relatively long. And technical solutions such as the repair of positive electrode powder also result in relatively poor electrical performance of the regenerated positive electrode material due to factors such as residual impurities after repair, and its industrialization is very difficult. Summary of the Invention

[0005] In view of this, the primary objective of this application is to provide a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate, which uses the coprecipitation method to recycle and prepare regenerated lithium iron phosphate. This method solves the problems of too long recycling process and high cost of waste lithium iron phosphate battery powder. The method provided by this application has the advantages of a short recycling path, few reaction by-products, and environmental friendliness, and can recycle all components of lithium, iron, and phosphorus in waste lithium iron phosphate battery powder, with great application prospects.

[0006] To achieve the above objective, this application adopts the following technical solutions:

[0007] One aspect of the present application discloses a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate, comprising the following steps:

[0008] Oxidatively acid-leach the recycled lithium iron phosphate battery powder to obtain acid-leached lithium solution and iron-phosphorus filter residue;

[0009] Adjust the pH of the acid-leached lithium solution to above 12, filter the precipitate to obtain purified lithium solution; then concentrate the purified lithium solution, add a phosphorus source to the concentrated lithium solution and adjust the pH to 9.5 - 10.5 to obtain Solution A;

[0010] Perform secondary acid leaching on the iron-phosphorus filter residue, filter to obtain iron-phosphoric acid solution; add pure iron blocks to the iron-phosphoric acid solution for iron conversion, filter to obtain divalent iron-phosphorus solution, then add a phosphorus source and adjust the pH to 6.5 - 7.5 to obtain Solution B;

[0011] Mix Solution A and Solution B and carry out a coprecipitation reaction, filter to obtain lithium iron phosphate precursor and reaction mother liquor;

[0012] After subjecting the lithium iron phosphate precursor to anaerobic drying, mix it with a carbon source and sinter it to prepare a carbon-coated lithium iron phosphate cathode material.

[0013] Advantages of the present application:

[0014] The present application innovatively adopts the idea of directly synthesizing lithium iron phosphate precursor from waste lithium iron phosphate battery powder by combining wet method with liquid-phase coprecipitation method, avoiding the subsequent processes of preparing lithium carbonate and iron phosphate. This method not only shortens the recycling process of waste lithium iron phosphate battery powder, but also greatly reduces the recycling cost, and can remove copper and aluminum impurities during the recycling process, and the test results of the obtained cathode material are excellent. Compared with the existing wet technology, the recycling method of the present application also has relatively less carbon emissions, and the industrial production cost will be lower in the future, having obvious advantages.

[0015] The main coprecipitation reaction principle equations in the present application mainly include:

[0016] 3Li + +PO4 3- =Li3PO4↓;

[0017] 3Fe 2+ +2PO4 3- =Fe3(PO4)2↓.

[0018] After the coprecipitation reaction, there are few reaction by-products, only ammonium sulfate by-product is generated, and the subsequent treatment of waste liquid is relatively simple. And ammonium sulfate, as a high-quality fertilizer raw material, has high value and is relatively easy to sell.

[0019] In summary, the technical method of the present application can not only effectively shorten the recycling process of lithium iron phosphate battery powder, but also take into account the economy and environmental protection of the technical solution. Moreover, the test results of the final product are excellent, and it has high application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a process flow diagram for recycling waste lithium iron phosphate to prepare lithium iron phosphate in a preferred embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The embodiments of the present application will be clearly and completely described below. The technical solutions in the described embodiments are exemplary and only possible technical implementations of the present application, not all possible implementations. Those skilled in the art can fully combine the embodiments of the present application and obtain other embodiments without creative work, and these embodiments are also within the protection scope of the present application.

[0022] The present application discloses a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate. This method directly synthesizes lithium iron phosphate precursor from waste lithium iron phosphate battery powder by wet method combined with liquid phase co-precipitation method, avoiding the subsequent processes of preparing lithium carbonate and iron phosphate. This method not only shortens the recycling process of waste lithium iron phosphate battery powder, but also greatly reduces the recycling cost, and can remove copper and aluminum impurities during the recycling process, and the test results of the obtained cathode material are excellent.

[0023] Referring to Figure 1 the flowchart in, the main steps of the method of the present application are as follows:

[0024] S1. Oxidatively acid-leach the recycled lithium iron phosphate battery powder to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0025] In the present application, the recycled lithium iron phosphate battery powder is obtained by discharging, disassembling, crushing, roasting, and screening waste lithium iron phosphate batteries. This process is a conventional and well-known process in the art and will not be specifically described here.

[0026] Furthermore, acid-leached lithium solution and iron-phosphorus filter residue are obtained through oxidative acid leaching. In the present application, the oxidative acid leaching refers to adding the recycled lithium iron phosphate battery powder into a mixed solution containing an acid reagent and an oxidation reagent and fully reacting. Among them, the acid reagent and oxidation reagent used are both conventional components in the art and have no special limitations. However, considering the cost and the final effect, for example, hydrochloric acid and the like have great corrosion to the equipment, and organic acids may cause the COD of the subsequent solution to exceed the standard. Therefore, in some specific examples, preferably, the acid reagent is sulfuric acid with a mass fraction of 98%, and the oxidation reagent is hydrogen peroxide or sodium persulfate with a mass fraction of 30%, so as to reduce the cost to the greatest extent and obtain a good leaching effect.

[0027] It is understandable that there are no special restrictions on the dosages of the specific acid reagent and oxidation reagent, which can be determined by experimental methods according to the quality of the specific recovered lithium iron phosphate battery powder. In some specific examples, based on the quality of the recovered lithium iron phosphate battery powder, the added mass fraction of sulfuric acid is 23% - 28%, and the added mass fraction of hydrogen peroxide is 55% - 70%.

[0028] S2. Adjust the pH of the lithium leaching solution to above 12, filter the precipitate to obtain a purified lithium solution; then concentrate the purified lithium solution, add a phosphorus source to the concentrated lithium solution and adjust the pH to 9.5 - 10.5 to obtain solution A.

[0029] In this step, other impurities are contained in the lithium leaching solution. Therefore, by adjusting the pH to above 12 and heating (temperature ≥ 80°C), other impurities are precipitated, and then a purified lithium solution is obtained, thereby achieving the maximum degree of lithium extraction and avoiding the leaching of iron and phosphorus. Specifically, common alkali reagents in the art can be used to adjust the pH. Specific examples include NaOH with a mass fraction of 1% or Ca(OH)2 with a mass fraction of 0.8%, but are not limited thereto.

[0030] Furthermore, since the lithium concentration in the lithium solution after impurity removal is relatively low (about 4 g / L), if it is directly used for coprecipitation in the subsequent process, it will result in more filtrate and less product. Therefore, in this application, the purified lithium solution is concentrated, and the lithium concentration in the concentrated lithium solution is 13 - 15 g / L, preferably 15 g / L, so as to ensure the solid-liquid ratio of the overall reaction system and ensure the product quantity during subsequent coprecipitation. There are no particular limitations on the specific concentration method, which can be achieved by heating and evaporating the solution, or by concentration equipment such as a single-effect concentrator.

[0031] Furthermore, after the lithium solution is concentrated, a phosphorus source is added thereto and the pH is adjusted to 9.5 - 10.5 to obtain solution A. Among them, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate. Among them, the added amount of phosphorus is 1 / 3 of the molar amount of lithium element. In some specific examples, the phosphorus source is ammonium dihydrogen phosphate, making the final by-product a single ammonium sulfate. The pH regulator is at least one of ammonia water with a mass fraction of 25% - 28%, NaOH, trisodium phosphate, and ammonium phosphate, and there are no special requirements. In some specific examples, the pH regulator is preferably ammonia water with a mass fraction of 25% - 28%.

[0032] S3. Perform secondary acid leaching on the iron and phosphorus filter residue, filter to obtain an iron phosphate solution; add pure iron blocks to the iron phosphate solution for iron conversion, filter to obtain a ferrous iron and phosphorus solution, and then add a phosphorus source and adjust the pH to 6.5 - 7.5 to obtain solution B.

[0033] In this step, the iron-phosphorus filter residue is subjected to secondary acid leaching to leach out iron and phosphorus in the filter residue as much as possible. Among them, the acid reagent used for secondary acid leaching is similar to that in the previous text. Preferably, sulfuric acid with a mass fraction of 98% is used, and the dosage of the sulfuric acid is 2.0 times the molar amount of iron element in the iron-phosphorus filter residue.

[0034] Add a sufficient amount of pure iron blocks to the iron-phosphorus acid solution obtained after secondary acid leaching for iron melting. Through iron melting, ferric iron in the solution is reduced to ferrous iron, and the excessive iron blocks also achieve copper removal by displacement. After iron melting, the iron-phosphorus solution changes from reddish-brown to grass-green. In some examples, the iron melting is carried out in an oxygen-free environment, the reaction temperature is 70-80 °C, and the time is 2.5-3.5 h. Among them, oxygen isolation can be achieved by a protective gas well-known in the art, such as nitrogen, or noble gases (such as helium, argon, etc.).

[0035] Add a phosphorus source to the obtained ferrous iron-phosphorus solution and adjust the pH to 6.5-7.5 to obtain solution B. The phosphorus source and pH regulator used here are similar to those of solution A, and preferably ammonium dihydrogen phosphate. Details are not elaborated here.

[0036] It should be particularly noted that the inventors of this application have determined through a large number of experiments that the pH values of solution A and solution B need to meet the above requirements, which is crucial for the subsequent preparation of lithium iron phosphate that meets the requirements.

[0037] S4. Mix solution A and solution B and carry out a coprecipitation reaction, and filter to obtain a lithium iron phosphate precursor and a reaction mother liquor; after the lithium iron phosphate precursor is dried anaerobically, it is mixed and sintered with a carbon source to prepare a carbon-coated lithium iron phosphate cathode material.

[0038] In this step, the temperature of the coprecipitation reaction is 20-30 °C, and the reaction time is ≥30 min. After the coprecipitation reaction, a lithium iron phosphate precursor and a reaction mother liquor can be obtained. Among them, the main component of the reaction mother liquor is the by-product ammonium sulfate, and almost all of the iron and phosphorus elements are precipitated. Ammonium sulfate, as a high-quality fertilizer raw material, has a high value and can be easily sold after subsequent treatment, with high economic value.

[0039] Furthermore, the lithium iron phosphate precursor is dried anaerobically to prevent iron elements from being oxidized. Then, the dried lithium iron phosphate precursor is mixed with a carbon source and sintered to prepare a carbon-coated lithium iron phosphate cathode material.

[0040] In this application, the carbon source is not particularly limited, and a carbon source known in the art that can be used for coating lithium iron phosphate can be used. Specific examples include at least one of glucose, sucrose, and ethylene glycol, but are not limited thereto. Its specific dosage can be selected according to specific needs such as the performance requirements of the cathode material. In some examples, the addition amount of the carbon source is 7%-9% of the mass of the lithium iron phosphate precursor.

[0041] In some examples, the sintering temperature is 600 - 750 °C and the time is 6 - 9 hours, but it is not limited thereto.

[0042] Through the method in this application, the recycling and preparation of lithium iron phosphate from waste lithium iron phosphate can be achieved with a short process, and it has the advantages of low energy consumption and low cost. Its by - product is ammonium sulfate, which can be directly recycled and sold as high - quality fertilizer raw materials, and the economic benefits are significant.

[0043] The following are specific examples of this application. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of this application in any way.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0045] In addition, unless otherwise specified, the methods without specific conditions or steps recorded are all conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0046] The main elements and contents in the recycled lithium iron phosphate battery powder in the following examples and comparative examples are shown in Table 1:

[0047] Table 1 Main elements and contents in the recycled lithium iron phosphate battery powder

[0048]

[0049] These recycled lithium iron phosphate battery powders are obtained by discharging, disassembling, crushing, roasting, and screening waste lithium iron phosphate batteries.

[0050] Example 1

[0051] In this example, a method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate is disclosed, and the specific steps are as follows:

[0052] S1. Take 100 g of recycled lithium iron phosphate battery powder ①, place it in a beaker, add 700 g of pure water, 28 g of sulfuric acid, and 70 g of hydrogen peroxide, carry out an oxidation acid leaching reaction for 4 h, and then filter to obtain acid - leached lithium solution and iron - phosphorus filter residue.

[0053] S2. Adjust the pH of the acid - leached lithium solution in step S1 to 12 with NaOH, react at 80 °C for 1 h, and then filter to obtain purified lithium solution; concentrate the purified lithium solution to a Li concentration of 15 g / L, quantitatively measure the lithium solution containing 2.25 g of lithium, and add 12.58 g of ammonium dihydrogen phosphate, and adjust the pH to 9.5 with ammonia water for use as solution A.

[0054] S3. The iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 73.70 g of sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue). After the reaction, filtration is carried out to obtain an iron-phosphorus solution. Subsequently, a sufficient amount of pure iron blocks are put in, and the iron is melted at 70 °C for 3.5 h under the protection of a nitrogen atmosphere. After filtration, an iron-melting solution is obtained. A quantitatively measured iron-melting solution containing 17.69 g of iron is added with 25.18 g of ammonium dihydrogen phosphate, and the pH is adjusted to 6.5 with ammonia water for use as solution B.

[0055] S4. Solution A and solution B are mixed and subjected to a coprecipitation reaction at 25 °C for 1 h. After filtration, a lithium iron phosphate precursor is obtained and dried under the protection of nitrogen. The dried precursor material is mixed with glucose (carbon source) accounting for 7% of its mass for sand grinding and spray drying. The dried powder is sintered in a kiln at 600 °C for 6 h to finally obtain a carbon-coated lithium iron phosphate cathode material.

[0056] Example 2

[0057] In this example, a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate is disclosed, and the specific steps are as follows:

[0058] S1. Take 100 g of recycled lithium iron phosphate battery powder ①, place it in a beaker, add 700 g of pure water, 28 g of sulfuric acid and 70 g of hydrogen peroxide, and carry out an oxidation acid leaching reaction for 4 h. After filtration, an acid-leached lithium solution and an iron-phosphorus filter residue are obtained.

[0059] S2. The pH of the acid-leached lithium solution in step S1 is adjusted to 12 with NaOH, and the reaction is carried out at 80 °C for 1 h for filtration to obtain a purified lithium solution. The purified lithium solution is concentrated to a Li concentration of 15 g / L. A quantitatively measured lithium solution containing 2.25 g of lithium is added with 12.58 g of ammonium dihydrogen phosphate, and the pH is adjusted to 10.5 with ammonia water for use as solution A.

[0060] S3. The iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 73.70 g of sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue). After the reaction, filtration is carried out to obtain an iron-phosphorus solution. A sufficient amount of pure iron blocks are put in, and the iron is melted at 80 °C for 2.5 h under the protection of a nitrogen atmosphere. After filtration, an iron-melting solution is obtained. A quantitatively measured iron-melting solution containing 17.69 g of iron is added with 25.18 g of ammonium dihydrogen phosphate, and the pH is adjusted to 7.5 with ammonia water for use as solution B.

[0061] S4. Solution A and solution B are mixed and subjected to a coprecipitation reaction at 20 °C for 1 h. After filtration, a lithium iron phosphate precursor is obtained and dried under the protection of nitrogen. The dried precursor material is mixed with glucose (carbon source) accounting for 9% of its mass for sand grinding and spray drying. The dried powder is sintered in a kiln at 750 °C for 9 h to finally obtain a carbon-coated lithium iron phosphate cathode material.

[0062] Example 3

[0063] In this embodiment, a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate is disclosed, and the specific steps are as follows:

[0064] S1. Take 100 g of recycled lithium iron phosphate battery powder ②, place it in a beaker, add 700 g of pure water, 23 g of sulfuric acid and 55 g of hydrogen peroxide, filter after oxidative acid leaching reaction for 4 h to obtain acid leaching lithium solution and iron-phosphorus filter residue.

[0065] S2. Adjust the pH of the acid leaching lithium solution in step S1 to 12 with NaOH, react at 80 °C for 1 h and filter to obtain purified lithium solution; concentrate the purified lithium solution to a Li concentration of 15 g / L, quantitatively measure 2.25 g of lithium-containing lithium solution, add 12.58 g of ammonium dihydrogen phosphate, and adjust the pH to 10.0 with ammonia water for use as solution A.

[0066] S3. Perform secondary acid leaching on the iron-phosphorus filter residue in step S1 with 66.78 g of sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), filter after the reaction to obtain iron-phosphorus solution, put in sufficient pure iron blocks, and carry out iron melting for 3.0 h under nitrogen atmosphere protection at 75 °C, filter to obtain iron melting solution; quantitatively measure 17.69 g of iron-containing iron melting solution, add 25.18 g of ammonium dihydrogen phosphate, and adjust the pH to 7.0 with ammonia water for use as solution B.

[0067] S4. Mix solution A and solution B and carry out coprecipitation reaction at 25 °C for 1 h, filter to obtain lithium iron phosphate precursor, and dry it under nitrogen protection; mix the dried precursor material with 8% of its mass of glucose (carbon source), then carry out sand grinding and spray drying, and sinter the dried powder in a kiln at 675 °C for 7.5 h to finally obtain carbon-coated lithium iron phosphate cathode material.

[0068] Example 4

[0069] In this embodiment, a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate is disclosed, and the specific steps are as follows:

[0070] S1. Take 100 g of recycled lithium iron phosphate battery powder ②, place it in a beaker, add 700 g of pure water, 23 g of sulfuric acid and 55 g of hydrogen peroxide, filter after oxidative acid leaching reaction for 4 h to obtain acid leaching lithium solution and iron-phosphorus filter residue.

[0071] S2. Adjust the pH of the acid leaching lithium solution in step S1 to 12 with NaOH, react at 80 °C for 1 h and filter to obtain purified lithium solution; concentrate the purified lithium solution to a Li concentration of 15 g / L, quantitatively measure 2.25 g of lithium-containing lithium solution, add 12.58 g of ammonium dihydrogen phosphate, and adjust the pH to 9.5 with ammonia water for use as solution A.

[0072] S3. The iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 66.78 g of sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue). After the reaction, filtration is carried out to obtain an iron-phosphorus solution. A sufficient amount of pure iron blocks are added, and iron is melted for 2.5 h under nitrogen atmosphere protection at 80 °C. After filtration, an iron-melting solution is obtained; a quantitatively measured iron-melting solution containing 17.69 g of iron is taken, 25.18 g of ammonium dihydrogen phosphate is added, and the pH is adjusted to 7.5 with ammonia water for use as solution B.

[0073] S4. Solution A and solution B are mixed and subjected to coprecipitation reaction at 30 °C for 1 h. After filtration, a lithium iron phosphate precursor is obtained and dried under nitrogen protection; the dried precursor material is mixed with glucose (carbon source) accounting for 8% of its mass, followed by sand grinding and spray drying. The dried powder is sintered in a kiln at 700 °C for 7 h to finally obtain a carbon-coated lithium iron phosphate cathode material.

[0074] Example 5

[0075] In this example, a method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate is disclosed, and the specific steps are as follows:

[0076] S1. Take 100 g of recycled lithium iron phosphate battery powder ②, place it in a beaker, add 700 g of pure water, 23 g of sulfuric acid and 55 g of hydrogen peroxide, carry out oxidation acid leaching reaction for 4 h, and then filter to obtain an acid-leached lithium solution and an iron-phosphorus filter residue.

[0077] S2. The pH of the acid-leached lithium solution in step S1 is adjusted to 12 with NaOH, and the reaction is carried out at 80 °C for 1 h, followed by filtration to obtain a purified lithium solution; the purified lithium solution is concentrated to a Li concentration of 15 g / L. A quantitatively measured lithium solution containing 2.25 g of lithium is taken, 12.58 g of ammonium dihydrogen phosphate is added, and the pH is adjusted to 10.5 with ammonia water for use as solution A.

[0078] S3. The iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 66.78 g of sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue). After the reaction, filtration is carried out to obtain an iron-phosphorus solution. A sufficient amount of pure iron blocks are added, and iron is melted for 3.0 h under nitrogen atmosphere protection at 75 °C. After filtration, an iron-melting solution is obtained; a quantitatively measured iron-melting solution containing 17.69 g of iron is taken, 25.18 g of ammonium dihydrogen phosphate is added, and the pH is adjusted to 6.5 with ammonia water for use as solution B.

[0079] S4. Solution A and solution B are mixed and subjected to coprecipitation reaction at 25 °C for 1 h. After filtration, a lithium iron phosphate precursor is obtained and dried under nitrogen protection; the dried precursor material is mixed with glucose (carbon source) accounting for 7% of its mass, and then sand grinding and spray drying are carried out. The dried powder is sintered in a kiln at 750 °C for 6 h to finally obtain a carbon-coated lithium iron phosphate cathode material.

[0080] Comparative Example 1

[0081] Another method for recycling waste lithium iron phosphate to prepare lithium iron phosphate is disclosed in this comparative example. The same implementation method as in Example 1 is adopted, with the only difference being that the pH of liquid A is 12.0. All other steps and parameter conditions are the same as in Example 1.

[0082] Comparative Example 2

[0083] Another method for recycling waste lithium iron phosphate to prepare lithium iron phosphate is disclosed in this comparative example. The same implementation method as in Example 1 is adopted, with the only difference being that the pH of liquid B is 6.0. All other steps and parameter conditions are the same as in Example 1.

[0084] Comparative Example 3

[0085] Another method for recycling waste lithium iron phosphate to prepare lithium iron phosphate is disclosed in this comparative example. The same implementation method as in Example 3 is adopted, with the only difference being that iron melting is not carried out.

[0086] The recovery and preparation of lithium iron phosphate in this comparative example are specifically carried out as follows:

[0087] S1. Take 100 g of recycled lithium iron phosphate battery powder ②, place it in a beaker, add 700 g of pure water, 23 g of sulfuric acid and 55 g of hydrogen peroxide, carry out oxidation acid leaching reaction for 4 h and then filter to obtain acid leached lithium solution and iron phosphorus filter residue.

[0088] S2. Adjust the pH of the acid leached lithium solution in step S1 to 12 with NaOH, react at 80 °C for 1 h and then filter to obtain purified lithium solution; concentrate the purified lithium solution to a Li concentration of 15 g / L, quantitatively take the lithium solution containing 2.25 g of lithium, add 12.58 g of ammonium dihydrogen phosphate, and adjust the pH to 9.5 with ammonia water for use as liquid A.

[0089] S3. Carry out secondary acid leaching of the iron phosphorus residue in step S2 with 66.78 g of sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), filter after the reaction to obtain iron phosphorus solution, and do not carry out iron melting operation on the iron phosphorus solution; quantitatively take the iron phosphorus solution containing 17.69 g of iron, add 25.18 g of ammonium dihydrogen phosphate, and adjust the pH to 7.5 with ammonia water for use as liquid B.

[0090] S4. Mix liquid A and liquid B and carry out coprecipitation reaction at 30 °C for 1 h, filter to obtain lithium iron phosphate precursor, and carry out drying under nitrogen protection; mix the dried precursor material with 8% of its mass of glucose (carbon source) for sand grinding and spray drying, and sinter the dried powder in a kiln at 700 °C for 7 h to finally obtain carbon-coated lithium iron phosphate cathode material.

[0091] Result Test

[0092] The main element contents, ratios, carbon content and partial impurity contents of the carbon-coated lithium iron phosphate cathode materials prepared in the examples and comparative examples were tested respectively. The results are shown in Tables 2 and 3.

[0093] Table 2 Main Element Contents in Carbon-Coated Lithium Iron Phosphate Cathode Materials

[0094]

[0095] Table 3 Carbon Content and Partial Impurity Contents in Carbon-Coated Lithium Iron Phosphate Cathode Materials

[0096]

[0097] As can be seen from the above tables, the pH values of Liquids A and B participating in the coprecipitation reaction in Comparative Example 1 and Comparative Example 2 were different from those in the examples, and finally products with a qualified lithium-iron-phosphorus molar ratio could not be obtained. However, lithium iron phosphate products with qualified element ratios could be obtained in all the examples. In Comparative Example 3, the iron-phosphorus solution was not subjected to the iron reduction operation, and the iron element in the solution was in the trivalent state, so products with a qualified lithium-iron-phosphorus molar ratio could not be obtained either. Moreover, due to the lack of iron reduction, the impurity copper element in the iron-phosphorus solution could not be removed and was directly introduced into the final product, resulting in a high impurity content.

[0098] In summary, the method for recycling and preparing lithium iron phosphate by the coprecipitation method in this application is successful and effective. After coating and sintering, the element ratio is good and the carbon coating effect is good, and good recycled lithium iron phosphate can be obtained.

[0099] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various modifications that can be thought of by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate, characterized in that, It includes the following steps: Oxidatively acid-leach the recycled lithium iron phosphate battery powder to obtain acid-leached lithium solution and iron-phosphorus filter residue; Adjust the pH of the acid-leached lithium solution to above 12, and filter the precipitate to obtain purified lithium solution; After concentrating the purified lithium solution, add a phosphorus source thereto and adjust the pH to 9.5 - 10.5 to obtain Solution A; Perform secondary acid leaching on the iron-phosphorus filter residue, filter to obtain iron-phosphorus acid solution; add pure iron blocks to the iron-phosphorus acid solution for iron conversion, filter to obtain divalent iron-phosphorus solution; then add a phosphorus source thereto and adjust the pH to 6.5 - 7.5 to obtain Solution B; Mix Solution A and Solution B and carry out a coprecipitation reaction, filter to obtain lithium iron phosphate precursor and reaction mother liquor; After subjecting the lithium iron phosphate precursor to anaerobic drying, mix it with a carbon source and sinter it to prepare a carbon-coated lithium iron phosphate cathode material.

2. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein The acid reagent used for the oxidative acid leaching is sulfuric acid with a mass fraction of 98%, and the oxidation reagent used is hydrogen peroxide with a mass fraction of 30%.

3. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 2, wherein Based on the mass of the recycled lithium iron phosphate battery powder, the added mass fraction of the sulfuric acid is 23% - 28%, and the added mass fraction of the hydrogen peroxide is 55% - 70%.

4. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein After the purified lithium solution is concentrated, its lithium concentration is 13 - 15 g / L.

5. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein, In the step of obtaining Solution A, the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate, wherein the added amount of phosphorus is 1 / 3 of the molar amount of lithium element; and / or, the pH regulator used for the pH adjustment is at least one of ammonia water, NaOH, trisodium phosphate, and ammonium phosphate.

6. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein, The acid reagent used for the secondary acid leaching is sulfuric acid with a mass fraction of 98%, and the dosage of the sulfuric acid is 2.0 times the molar amount of iron element in the iron-phosphorus filter residue.

7. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein, The reaction temperature for the iron conversion is 70 - 80 °C, the time is 2.5 - 3.5 hours, and it is carried out in an oxygen-free environment; and / or, the oxygen-free environment is achieved by a protective gas, and the protective gas is one of nitrogen or noble gas.

8. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein In the step of obtaining Solution B, the phosphorus source is ammonium dihydrogen phosphate, and the added amount of phosphorus is in accordance with the Fe:P molar ratio of 3:

2.

9. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as claimed in claim 1, wherein, The temperature of the coprecipitation reaction is 20 - 30 °C, and the time is ≥ 30 min.

10. The method for recycling and preparing lithium iron phosphate from waste lithium iron phosphate as described in claim 1, characterized in that, The carbon source is at least one of glucose, sucrose, and ethylene glycol, and its added amount is 7% - 9% of the mass of the lithium iron phosphate precursor; and / or, the sintering temperature is 600 - 750 °C, and the time is 6 - 9 hours.

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