Method for preparing lithium iron phosphate by recycling waste lithium iron phosphate

Abstract

The invention discloses a method for preparing lithium iron phosphate by recovering waste lithium iron phosphate, which comprises the following steps: oxidizing and acid-leaching recovered lithium iron phosphate battery powder to obtain acid leaching lithium liquid and iron phosphorus filter residue; adjusting the pH value of the acid leaching lithium solution, purifying, concentrating, adding a phosphorus source, and adjusting the pH value to 9.5-10.5 to obtain a solution A; carrying out secondary acid leaching and iron melting on the iron-phosphorus filter residues, adding a phosphorus source, and adjusting the pH value to 6.5-7.5 to obtain a solution B; mixing the solution A and the solution B, carrying out coprecipitation reaction, and filtering to obtain a lithium iron phosphate precursor and a reaction mother solution; and performing oxygen-free drying on the lithium iron phosphate precursor, mixing with a carbon source, and sintering to obtain the carbon-coated lithium iron phosphate positive electrode material. The method provided by the invention has the advantages of short recovery path, few reaction byproducts and environmental protection, all components of lithium, iron and phosphorus in the waste lithium iron phosphate battery powder can be recovered, meanwhile, the byproduct is high-quality chemical fertilizer raw material ammonium sulfate, and the method has great application prospects.

Description

Technical Field

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

[0002] Lithium iron phosphate (LiFePO 4 ) is a lithium-ion battery positive electrode material with an olivine crystal structure (orthorhombic system). Its lithium ions can be reversibly deintercalated during the charge and discharge process, and it has high safety and stability. At present, lithium iron phosphate has been widely used as a power battery and energy storage battery for new energy vehicles. However, with the explosive growth in the production and sales of new energy vehicles, the scale of energy storage is also increasing, and the output of lithium iron phosphate batteries has also risen accordingly. Considering the waste generated in the production process of lithium iron phosphate batteries and old batteries that have expired, a large number of waste lithium iron phosphate batteries will be generated in the future, so it is very necessary to recycle and reuse lithium iron phosphate batteries.

[0003] At present, there are two main methods for recycling lithium iron phosphate power batteries: one is repair and regeneration, and the other is to use hydrometallurgical methods to recover valuable elements. However, the performance of lithium battery positive electrode materials after high-temperature repair is usually not ideal; and in the wet recycling of lithium iron phosphate batteries, typical products are high-priced products such as lithium carbonate and iron phosphate. However, with the continuous decline in lithium prices in the past two years, the economic efficiency of existing recycling methods has deteriorated. Therefore, it is very necessary to study and develop short-process regeneration technology in the recycling process of lithium iron phosphate batteries.

[0004] The current mainstream lithium iron phosphate recycling process is to first extract lithium and remove some impurities of aluminum in the lithium liquid. This process of impurity removal is relatively simple, and then the lithium liquid is prepared into lithium carbonate products. However, the subsequent process of removing aluminum from iron-phosphorus slag is relatively technically difficult and complex, and the products obtained from recycled battery powder are generally lithium carbonate and iron phosphate, which consumes a lot of energy and produces a large amount of carbon emissions during the calcination process. After that, it must be further prepared into lithium iron phosphate, and the overall process is relatively long. The technical solutions such as the repair of positive electrode powder also have relatively poor electrical properties 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 purpose of the present application is to provide a method for recycling waste lithium iron phosphate and preparing lithium iron phosphate, which utilizes the co-precipitation method to recycle and prepare regenerated lithium iron phosphate. This method solves the problem of long recycling process and high cost of waste lithium iron phosphate battery powder. The method provided in this application has the advantages of short recycling path, few reaction by-products and environmental protection, and can recover all components of lithium, iron and phosphorus in waste lithium iron phosphate battery powder, and has great application prospects.

[0006] In order to achieve the above objectives, this application adopts the following technical solutions: One aspect of the present application discloses a method for recovering waste lithium iron phosphate to prepare lithium iron phosphate, comprising the following steps: The recovered lithium iron phosphate battery powder is oxidized and acid-leached to obtain acid-leached lithium solution and iron-phosphorus filter residue; The pH of the acid leaching lithium solution is adjusted to above 12, and the precipitate is filtered to obtain a purified lithium solution; the purified lithium solution is then concentrated, a phosphorus source is added to the concentrated lithium solution, and the pH is adjusted to 9.5-10.5 to obtain a solution A; The iron-phosphorus filter residue is subjected to secondary acid leaching, and an iron-phosphate solution is obtained after filtering; a pure iron block is added to the iron-phosphate solution to ferricize, and a divalent iron-phosphorus solution is obtained after filtering, and then a phosphorus source is added and the pH is adjusted to 6.5-7.5 to obtain a B solution; Mixing solution A and solution B to perform a coprecipitation reaction, and filtering to obtain a lithium iron phosphate precursor and a reaction mother solution; The lithium iron phosphate precursor is dried in an oxygen-free environment, mixed with a carbon source, and sintered to obtain a carbon-coated lithium iron phosphate positive electrode material.

[0007] Beneficial effects of this application: This application pioneered the idea of ​​synthesizing lithium iron phosphate precursors directly from waste lithium iron phosphate battery powder by combining a wet method with a liquid phase co-precipitation method, avoiding the subsequent process of preparing lithium carbonate and iron phosphate. This method not only shortens the process of recycling waste lithium iron phosphate battery powder, but also greatly reduces the cost of recycling. In addition, copper and aluminum impurities can be removed during the recycling process, and the obtained positive electrode material test results are excellent. Compared with the existing wet method, the recycling method of this application will also have relatively less carbon emissions, and the cost of industrial production in the future will also be lower, which has obvious advantages.

[0008] The principle equation of the co-precipitation reaction in this application mainly includes: 3Li + +PO 4 3- =Li 3 PO 4 ↓; 3Fe 2+ +2PO 4 3- =Fe 3 (PO 4 ) 2 ↓.

[0009] After the co-precipitation reaction, there are few by-products, only ammonium sulfate by-product, and the subsequent treatment of waste liquid is relatively simple. As a high-quality fertilizer raw material, ammonium sulfate is of high value and easier to sell.

[0010] 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. The final product test results are excellent and have a high application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a process flow chart for recovering waste lithium iron phosphate and preparing lithium iron phosphate in a preferred embodiment of the present application. DETAILED DESCRIPTION

[0012] The following will clearly and completely describe the implementation methods of the present application. The technical solutions in the implementation methods described below are exemplary and are only possible technical implementations of the present application, not all possible implementations. Those skilled in the art can fully combine the implementation methods of the present application to obtain other implementation methods without creative work, and these implementation methods are also within the scope of protection of the present application.

[0013] The present application discloses a method for preparing lithium iron phosphate by recycling waste lithium iron phosphate. The method adopts a wet method combined with a liquid phase co-precipitation method to directly synthesize a lithium iron phosphate precursor from waste lithium iron phosphate battery powder, thereby avoiding the subsequent process of preparing lithium carbonate and iron phosphate. The method not only shortens the process of recycling waste lithium iron phosphate battery powder, but also greatly reduces the cost of recycling. In addition, copper and aluminum impurities can be removed during the recycling process, and the obtained positive electrode material has excellent test results.

[0014] Reference Figure 1 The main steps of the method of this application are as follows: S1. The recovered lithium iron phosphate battery powder is subjected to oxidation acid leaching to obtain acid leaching lithium solution and iron-phosphorus filter residue.

[0015] In the present application, the recycled lithium iron phosphate battery powder is obtained by discharging, disassembling, crushing, roasting and screening the waste lithium iron phosphate batteries. This process is a conventional and well-known process in the art and will not be elaborated here.

[0016] Further, acid leaching lithium solution and iron-phosphorus filter residue are obtained by oxidative acid leaching. In the present application, the oxidative acid leaching refers to adding the recovered lithium iron phosphate battery powder to a mixed solution containing an acid reagent and an oxidizing reagent, and fully reacting to achieve it. Among them, the acid reagent and oxidizing reagent used are conventional compositions in the art, without special restrictions. However, considering the cost and the final effect, for example, hydrochloric acid has a greater 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 oxidizing reagent is hydrogen peroxide or sodium persulfate with a mass fraction of 30%, so as to minimize the cost and obtain a better leaching effect.

[0017] It is understandable that there is no special restriction on the dosage of the specific acid reagent and the oxidizing reagent, which can be determined by experimental methods according to the specific mass of the recovered lithium iron phosphate battery powder. In some specific examples, based on the mass of the recovered 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%.

[0018] S2, adjusting the pH of the acid leaching lithium solution to above 12, filtering and precipitating to obtain a purified lithium solution; then concentrating the purified lithium solution, adding a phosphorus source to the concentrated lithium solution and adjusting the pH to 9.5-10.5 to obtain a solution A.

[0019] In this step, the acid leaching lithium solution contains other impurities, so by adjusting the pH to above 12 and heating (temperature ≥ 80°C), other impurities are precipitated to obtain purified lithium solution, thereby achieving the maximum lithium extraction and avoiding iron and phosphorus leaching. Specifically, the pH can be adjusted using common alkaline reagents in the field, such as 1% by mass NaOH or 0.8% by mass Ca(OH) 2 , but it is not limited to this.

[0020] 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 later, 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 the amount of product during subsequent coprecipitation. The specific concentration method is not particularly limited, and can be achieved by heating and evaporating the solution, or by a concentration device such as a single-effect concentrator.

[0021] Further, after the lithium solution is concentrated, a phosphorus source is added thereto and the pH is adjusted to 9.5-10.5 to obtain liquid A. Wherein, the phosphorus source is at least one of diammonium phosphate, diammonium phosphate, and triammonium phosphate, wherein the amount of phosphorus added is 1 / 3 of the molar amount of the lithium element. In some specific examples, the phosphorus source is diammonium phosphate, so that the final by-product is a single ammonium sulfate. The pH adjuster is at least one of ammonia water, NaOH, trisodium phosphate, and triammonium phosphate with a mass fraction of 25%-28%, without special requirements. In some specific examples, the pH adjuster is preferably ammonia water with a mass fraction of 25%-28%.

[0022] S3, subjecting the iron-phosphorus filter residue to secondary acid leaching, filtering to obtain an iron-phosphate solution; adding a pure iron block to the iron-phosphate solution for ironification, filtering to obtain a divalent iron-phosphorus solution, then adding a phosphorus source and adjusting the pH to 6.5-7.5 to obtain a B solution.

[0023] In this step, the iron-phosphorus filter residue is subjected to secondary acid leaching to leach out the iron-phosphorus in the filter residue as much as possible. The acid reagent used in the secondary acid leaching is similar to that in the above text, preferably sulfuric acid with a mass fraction of 98%, and the amount of the sulfuric acid is 2.0 times the molar amount of the iron element in the iron-phosphorus filter residue.

[0024] A sufficient amount of pure iron blocks are added to the iron phosphate solution obtained after the secondary acid leaching for iron oxidation. The trivalent iron in the solution is reduced to divalent iron by iron oxidation, and the excess iron blocks are also replaced to remove copper. After the iron oxidation is completed, the iron-phosphorus solution changes from reddish brown to grass green. In some examples, the iron oxidation is carried out in an oxygen-free environment, the reaction temperature is 70-80°C, and the time is 2.5-3.5 hours, wherein the oxygen isolation can be achieved by a protective gas well known in the art, such as nitrogen, or a rare gas (such as helium, argon, etc.).

[0025] A phosphorus source is added to the obtained divalent iron phosphorus solution and the pH is adjusted to 6.5-7.5 to obtain liquid B. The phosphorus source and pH adjuster used here are similar to those of liquid A, preferably ammonium dihydrogen phosphate. No further details are given here.

[0026] It should be noted that the inventors of the present application have determined through a large number of experiments that the pH of liquid A and liquid B must meet the above requirements, which is crucial for the subsequent preparation of lithium iron phosphate that meets the requirements.

[0027] S4, mixing liquid A and liquid B to carry out a coprecipitation reaction, filtering to obtain a lithium iron phosphate precursor and a reaction mother liquor; drying the lithium iron phosphate precursor in an oxygen-free state, mixing with a carbon source, and sintering to obtain a carbon-coated lithium iron phosphate positive electrode material.

[0028] In this step, the temperature of the coprecipitation reaction is 20-30°C, and the reaction time is ≥30min. After the coprecipitation reaction, a lithium iron phosphate precursor and a reaction mother liquor can be obtained, wherein the main component of the reaction mother liquor is the by-product ammonium sulfate, and the iron and phosphorus elements are almost completely precipitated. Ammonium sulfate is a high-quality fertilizer raw material with high value, can be easily sold after subsequent processing, and has high economic value.

[0029] Furthermore, the lithium iron phosphate precursor is dried in an oxygen-free environment to prevent the iron element from being oxidized. The dried lithium iron phosphate precursor is then mixed with a carbon source and sintered to obtain a carbon-coated lithium iron phosphate positive electrode material.

[0030] In the present application, the carbon source is not particularly limited, and any carbon source known in the art that can be used for lithium iron phosphate coating can be used, and specific examples include at least one of glucose, sucrose, and ethylene glycol, but are not limited thereto. The specific amount can be selected according to specific needs such as the performance requirements of the positive electrode material. In some examples, the amount of the carbon source added is 7% to 9% of the mass of the lithium iron phosphate precursor.

[0031] In some examples, the sintering temperature is 600-750° C. and the sintering time is 6-9 hours, but is not limited thereto.

[0032] The method of the present application can realize the recovery of waste lithium iron phosphate to prepare lithium iron phosphate in a short process, and has the advantages of low energy consumption and low cost. Its by-product is ammonium sulfate, which can be directly recovered and sold as a high-quality fertilizer raw material, with significant economic benefits.

[0033] The following are specific embodiments of the present application. It should be noted that the following specific embodiments are only for illustrative purposes and do not limit the scope of the present application in any way.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0035] In addition, unless otherwise specified, methods without specific description of conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0036] The main elements and contents of the lithium iron phosphate battery powder recovered in the following examples and comparative examples are shown in Table 1: Table 1 Main elements and contents in recycled lithium iron phosphate battery powder

[0037] These recycled lithium iron phosphate battery powders are obtained by discharging, disassembling, crushing, roasting and screening used lithium iron phosphate batteries.

[0038] Example 1 This embodiment discloses a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate, and the specific steps are as follows: S1. Take 100g of recycled lithium iron phosphate battery powder①, put it in a beaker, add 700g of pure water, 28g of sulfuric acid and 70g of hydrogen peroxide, oxidize and acid-leach for 4h, then filter to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0039] S2. The acid-leached lithium solution in step S1 is adjusted to pH 12 with NaOH, reacted at 80° C. for 1 h, and filtered to obtain a purified lithium solution; the purified lithium solution is concentrated to a Li concentration of 15 g / L, a lithium solution containing 2.25 g of lithium is quantitatively measured, 12.58 g of diammonium phosphate is added, and the pH is adjusted to 9.5 with aqueous ammonia, and the solution is used as liquid A for standby.

[0040] S3, the iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 73.70g sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), and after the reaction, the iron-phosphorus liquid is obtained by filtering; then a sufficient amount of pure iron block is added, and the iron is heated at 70°C for 3.5h under the protection of a nitrogen atmosphere, and the iron solution is obtained by filtering; the iron solution containing 17.69g of iron is quantitatively measured, 25.18g of diammonium phosphate is added, and the pH is adjusted to 6.5 with aqueous ammonia, and the solution is used as liquid B for standby.

[0041] S4. Mix liquid A and liquid B and carry out co-precipitation reaction at 25°C for 1 hour, filter to obtain lithium iron phosphate precursor, and dry under nitrogen protection; mix the dried precursor material with 7% of its mass as glucose (carbon source), sand grind and spray dry, and after drying, sinter the powder in a kiln at 600°C for 6 hours to finally obtain carbon-coated lithium iron phosphate positive electrode material.

[0042] Example 2 This embodiment discloses a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate, and the specific steps are as follows: S1. Take 100g of recycled lithium iron phosphate battery powder①, put it in a beaker, add 700g of pure water, 28g of sulfuric acid and 70g of hydrogen peroxide, oxidize and acid-leach for 4h, then filter to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0043] S2. The acid-leached lithium solution in step S1 was adjusted to pH 12 with NaOH, reacted at 80° C. for 1 h, and filtered to obtain a purified lithium solution; the purified lithium solution was concentrated to a Li concentration of 15 g / L, a lithium solution containing 2.25 g of lithium was quantitatively measured, 12.58 g of diammonium phosphate was added, and the pH was adjusted to 10.5 with aqueous ammonia, and the solution was used as liquid A for standby.

[0044] S3, the iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 73.70g sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), and after the reaction, the iron-phosphorus liquid is filtered to obtain a sufficient amount of pure iron block, and the iron is heated at 80°C for 2.5h under the protection of a nitrogen atmosphere, and the iron solution is filtered to obtain a solution; the iron solution containing 17.69g of iron is quantitatively measured, 25.18g of diammonium phosphate is added, and the pH is adjusted to 7.5 with aqueous ammonia, and the solution is used as liquid B for standby.

[0045] S4. Mix liquid A and liquid B and carry out co-precipitation reaction at 20°C for 1 hour, filter to obtain lithium iron phosphate precursor, and dry under nitrogen protection; mix the dried precursor material with 9% of its mass as glucose (carbon source), sand grind and spray dry, and sinter the dried powder in a kiln at 750°C for 9 hours to finally obtain carbon-coated lithium iron phosphate positive electrode material.

[0046] Example 3 This embodiment discloses a method for recovering waste lithium iron phosphate to prepare lithium iron phosphate, and the specific steps are as follows: S1. Take 100g of recycled lithium iron phosphate battery powder②, put it in a beaker, add 700g of pure water, 23g of sulfuric acid and 55g of hydrogen peroxide, oxidize and acid-leach for 4h, then filter to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0047] S2. The acid-leached lithium solution in step S1 was adjusted to pH 12 with NaOH, reacted at 80° C. for 1 h, and filtered to obtain a purified lithium solution; the purified lithium solution was concentrated to a Li concentration of 15 g / L, a lithium solution containing 2.25 g of lithium was quantitatively measured, 12.58 g of diammonium phosphate was added, and the pH was adjusted to 10.0 with aqueous ammonia, and the solution was used as liquid A for standby.

[0048] S3, the iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 66.78g sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), and after the reaction, the iron-phosphorus liquid is filtered to obtain a sufficient amount of pure iron block, and the iron is heated at 75°C for 3.0h in a nitrogen atmosphere, and the iron solution is filtered to obtain a solution; the iron solution containing 17.69g of iron is quantitatively measured, 25.18g of diammonium phosphate is added, and the pH is adjusted to 7.0 with ammonia water, and the solution is used as liquid B for standby.

[0049] S4. Mix liquid A and liquid B and carry out co-precipitation reaction at 25°C for 1 hour, filter to obtain lithium iron phosphate precursor, and dry under nitrogen protection; mix the dried precursor material with 8% of its mass of glucose (carbon source), sand grind and spray dry, and sinter the dried powder in a kiln at 675°C for 7.5 hours to finally obtain carbon-coated lithium iron phosphate positive electrode material.

[0050] Example 4 This embodiment discloses a method for recovering waste lithium iron phosphate to prepare lithium iron phosphate, and the specific steps are as follows: S1. Take 100g of recycled lithium iron phosphate battery powder②, put it in a beaker, add 700g of pure water, 23g of sulfuric acid and 55g of hydrogen peroxide, oxidize and acid-leach for 4h, then filter to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0051] S2. The acid-leached lithium solution in step S1 was adjusted to pH 12 with NaOH, reacted at 80° C. for 1 h, and filtered to obtain a purified lithium solution; the purified lithium solution was concentrated to a Li concentration of 15 g / L, a lithium solution containing 2.25 g of lithium was quantitatively measured, 12.58 g of diammonium phosphate was added, and the pH was adjusted to 9.5 with aqueous ammonia, and the solution was used as liquid A for standby.

[0052] S3, the iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 66.78g sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), and after the reaction, the iron-phosphorus liquid is filtered to obtain a sufficient amount of pure iron block, and the iron is heated at 80°C for 2.5h in a nitrogen atmosphere, and the iron solution is filtered to obtain a solution; the iron solution containing 17.69g of iron is quantitatively measured, 25.18g of diammonium phosphate is added, and the pH is adjusted to 7.5 with ammonia water, and the solution is used as B solution.

[0053] S4. Mix liquid A and liquid B and carry out co-precipitation reaction at 30°C for 1 hour, filter to obtain lithium iron phosphate precursor, and dry under nitrogen protection; mix the dried precursor material with 8% of its mass as glucose (carbon source), sand grind and spray dry, and after drying, sinter the powder in a kiln at 700°C for 7 hours to finally obtain carbon-coated lithium iron phosphate positive electrode material.

[0054] Example 5 This embodiment discloses a method for recycling waste lithium iron phosphate to prepare lithium iron phosphate, and the specific steps are as follows: S1. Take 100g of recycled lithium iron phosphate battery powder②, put it in a beaker, add 700g of pure water, 23g of sulfuric acid and 55g of hydrogen peroxide, oxidize and acid-leach for 4h, then filter to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0055] S2. The acid-leached lithium solution in step S1 was adjusted to pH 12 with NaOH, reacted at 80° C. for 1 h, and filtered to obtain a purified lithium solution; the purified lithium solution was concentrated to a Li concentration of 15 g / L, a lithium solution containing 2.25 g of lithium was quantitatively measured, 12.58 g of diammonium phosphate was added, and the pH was adjusted to 10.5 with aqueous ammonia, and the solution was used as liquid A for standby.

[0056] S3, the iron-phosphorus filter residue in step S1 is subjected to secondary acid leaching with 66.78g sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), and after the reaction, the iron-phosphorus liquid is filtered to obtain a sufficient amount of pure iron block, and the iron is heated at 75°C for 3.0h in a nitrogen atmosphere, and the iron solution is filtered to obtain a solution; the iron solution containing 17.69g of iron is quantitatively measured, 25.18g of diammonium phosphate is added, and the pH is adjusted to 6.5 with ammonia water, and the solution is used as B solution.

[0057] S4. Mix liquid A and liquid B and carry out co-precipitation reaction at 25°C for 1 hour, filter to obtain lithium iron phosphate precursor, and dry under nitrogen protection; mix the dried precursor material with 7% of glucose (carbon source) by weight, and then sand grind and spray dry. After drying, sinter the powder in a kiln at 750°C for 6 hours to finally obtain a carbon-coated lithium iron phosphate positive electrode material.

[0058] Comparative Example 1 This comparative example discloses another method for recovering waste lithium iron phosphate and preparing lithium iron phosphate, which adopts the same implementation as Example 1, except that the pH of liquid A is 12.0. Other steps and parameter conditions are the same as those in Example 1.

[0059] Comparative Example 2 This comparative example discloses another method for recovering waste lithium iron phosphate and preparing lithium iron phosphate, which adopts the same implementation as Example 1, except that the pH of liquid B is 6.0. The other steps and parameter conditions are the same as those in Example 1.

[0060] Comparative Example 3 This comparative example discloses another method for recovering waste lithium iron phosphate and preparing lithium iron phosphate, which adopts the same implementation as Example 3, except that no iron oxidation is performed.

[0061] The specific steps for the recovery and preparation of lithium iron phosphate in this comparative example are as follows: S1. Take 100g of recycled lithium iron phosphate battery powder②, put it in a beaker, add 700g of pure water, 23g of sulfuric acid and 55g of hydrogen peroxide, oxidize and acid-leach for 4h, then filter to obtain acid-leached lithium solution and iron-phosphorus filter residue.

[0062] S2. The acid-leached lithium solution in step S1 was adjusted to pH 12 with NaOH, reacted at 80° C. for 1 h, and filtered to obtain a purified lithium solution; the purified lithium solution was concentrated to a Li concentration of 15 g / L, a lithium solution containing 2.25 g of lithium was quantitatively taken, 12.58 g of diammonium phosphate was added, and the pH was adjusted to 9.5 with aqueous ammonia, and the solution was used as liquid A for standby.

[0063] S3, the iron-phosphorus slag in step S2 is subjected to secondary acid leaching with 66.78g sulfuric acid (the amount of sulfuric acid is 2.0 times the molar content of Fe in the filter residue), and after the reaction, the iron-phosphorus liquid is filtered to obtain the iron-phosphorus liquid, and the iron-phosphorus liquid is not subjected to the iron-making operation; the iron-phosphorus liquid containing 17.69g iron is quantitatively measured, 25.18g of diammonium phosphate is added, and the pH is adjusted to 7.5 with ammonia water, and the solution is used as liquid B for standby.

[0064] S4. Mix liquid A and liquid B and carry out co-precipitation reaction at 30°C for 1 hour, filter to obtain lithium iron phosphate precursor, and dry under nitrogen protection; mix the dried precursor material with 8% of its mass as glucose (carbon source), sand grind and spray dry, and after drying, sinter the powder in a kiln at 700°C for 7 hours to finally obtain carbon-coated lithium iron phosphate positive electrode material.

[0065] Results Test The main element content and ratio, carbon content and partial impurity content of the carbon-coated lithium iron phosphate positive electrode materials prepared in the embodiment and the comparative example were tested respectively. The results are shown in Table 2 and Table 3.

[0066] Table 2 Main element contents in carbon-coated lithium iron phosphate cathode materials

[0067] Table 3 Carbon content and some impurity content in carbon-coated lithium iron phosphate cathode materials

[0068] It can be seen from the above table that the pH of the A solution and the B solution participating in the coprecipitation reaction in Comparative Examples 1 and 2 are different from those in the examples, and ultimately no product with a qualified lithium iron phosphorus molar ratio can be obtained, while lithium iron phosphate products with qualified element ratios can be obtained in all the examples. In Comparative Example 3, the iron phosphorus solution was not subjected to the iron oxidizing operation, and the iron element in the solution was in a trivalent state, and no product with a qualified lithium iron phosphorus molar ratio could be obtained. In addition, since no iron oxidizing operation was performed, the impurity copper element in the iron phosphorus solution could not be removed and was directly brought into the final product, resulting in a high impurity content.

[0069] In summary, the method for recycling and preparing lithium iron phosphate by co-precipitation in the present application is successful and effective, and the element ratio after coating and sintering is good and the carbon coating effect is good, so that good regenerated lithium iron phosphate can be obtained.

[0070] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for recovering waste lithium iron phosphate to prepare lithium iron phosphate, characterized in that: The following steps are involved: The recovered lithium iron phosphate battery powder is oxidized and acid-leached to obtain acid-leached lithium solution and iron-phosphorus filter residue; Adjusting the pH of the acid leaching lithium solution to above 12, filtering and precipitating to obtain a purified lithium solution; After concentrating the purified lithium solution, a phosphorus source is added thereto and the pH is adjusted to 9.5-10.5 to obtain solution A; The iron-phosphorus filter residue is subjected to secondary acid leaching, and an iron-phosphate solution is obtained after filtering; a pure iron block is added to the iron-phosphate solution to ferricize, and a divalent iron-phosphorus solution is obtained after filtering; a phosphorus source is then added thereto and the pH is adjusted to 6.5-7.5 to obtain a B solution; Mixing solution A and solution B to perform a coprecipitation reaction, and filtering to obtain a lithium iron phosphate precursor and a reaction mother solution; The lithium iron phosphate precursor is dried in an oxygen-free environment, mixed with a carbon source, and sintered to obtain a carbon-coated lithium iron phosphate positive electrode material.

2. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: The acid reagent used in the oxidative acid leaching is sulfuric acid with a mass fraction of 98%, and the oxidizing reagent used is hydrogen peroxide with a mass fraction of 30%.

3. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 2, characterized in that: Based on the mass of the recovered lithium iron phosphate battery powder, the added mass fraction of the sulfuric acid is 23% to 28%, and the added mass fraction of the hydrogen peroxide is 55% to 70%.

4. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: After the purified lithium solution is concentrated, its lithium concentration is 13-15 g / L.

5. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: In the step of obtaining liquid A, the phosphorus source is at least one of diammonium phosphate, diammonium phosphate, and triammonium phosphate, wherein the amount of phosphorus added is 1 / 3 of the molar amount of lithium element; And / or, the pH adjusting agent used for the pH adjustment is at least one of ammonia water, NaOH, trisodium phosphate, and triammonium phosphate.

6. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: The acid reagent used in the secondary acid leaching is sulfuric acid with a mass fraction of 98%, and the amount of sulfuric acid used is 2.0 times the molar amount of iron element in the iron-phosphorus filter residue.

7. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: The reaction temperature of the iron oxidation 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-isolated environment is achieved by a protective gas, and the protective gas is one of nitrogen or a rare gas.

8. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: In the step of obtaining liquid B, the phosphorus source is diammonium phosphate, and the amount of phosphorus added is based on a Fe:P molar ratio of 3:

2.

9. The method for recovering waste lithium iron phosphate to prepare lithium iron phosphate according to claim 1, characterized in that: The coprecipitation reaction temperature is 20-30°C and the time is ≥30min.

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

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