A method for preparing lithium manganese iron phosphate from lithium iron phosphate

Abstract

The application discloses a method for preparing lithium manganese iron phosphate from lithium iron phosphate, and belongs to the technical field of new energy material recycling. The method comprises the following steps: reacting sulfuric acid, hydrogen peroxide and lithium iron phosphate battery powder to realize preferential leaching of lithium elements; obtaining lithium sulfate solution and iron phosphate dihydrate / graphite leaching residue after filtration; removing copper and aluminum impurities in the obtained lithium sulfate solution; dissolving the iron phosphate dihydrate / graphite leaching residue with sulfuric acid and then performing solid-liquid separation; mixing the obtained filtrate with the lithium sulfate solution after impurity removal, adding a certain amount of phosphoric acid, and adjusting pH with ammonia water to obtain a lithium phosphate and iron phosphate dihydrate mixture; adding required amounts of lithium carbonate, glucose and manganese source to the mixture, and then performing sand grinding, spraying, calcining and crushing to obtain carbon-coated lithium manganese iron phosphate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy material recycling, and particularly relates to a method for preparing lithium manganese iron phosphate from lithium iron phosphate. BACKGROUND

[0002] In recent years, with the double effects of technological progress and national policy, the market acceptance of new energy vehicles is increasing, and the production and sales are booming. Lithium ion secondary batteries are favored by many battery material manufacturers in recent years due to their high energy density, high voltage, low self-discharge, no memory effect, long cycle life and other advantages. Especially the lithium iron phosphate material, compared with other positive materials, the excellent safety performance of lithium iron phosphate enables it to always maintain a place in the range of energy storage and power battery materials, and is widely used in public transportation industry. However, the average service life of automobile power battery is about 5-8 years, and the first batch of lithium ion power batteries will usher in a large-scale retirement tide, which means that a large amount of waste lithium iron phosphate material will need to be treated in the future. Good recycling of power batteries can make new energy vehicle industry truly return to green. However, the recycling of lithium ion batteries has problems such as complex raw material composition, high recycling difficulty, and difficult treatment of wastewater and waste liquid in the recycling process, which pollutes the environment. In order to meet the practical application needs of large-scale recycling of lithium ion materials, it is of great significance to develop the corresponding recycling process. SUMMARY

[0003] The purpose of the application is to provide a method for preparing lithium manganese iron phosphate from lithium iron phosphate, so as to solve the problems of complex lithium ion battery recycling process, high recycling difficulty and environmental pollution.

[0004] The purpose of the application can be achieved by the following technical solutions:

[0005] A method for preparing lithium manganese iron phosphate from lithium iron phosphate, comprising the following steps:

[0006] S1, preferential leaching of lithium ions: mixing lithium iron phosphate battery powder with sulfuric acid and hydrogen peroxide to obtain a precursor solution, filtering the precursor solution after heating reaction to obtain a filtrate containing Li2SO4 and FePO4·2H2O / graphite composite residue;

[0007] S2, impurity removal of LiSO4 solution: adding CaO to the filtrate containing Li2SO4, adjusting pH with NaOH solution, and filtering reaction liquid A after heat preservation reaction, the filter residue is Cu(OH)2, 3CaO·Al2O3, Li3PO4 and CaF2, wherein CaO reacts with impurity ions (Al ions and F ions) in the solution under alkaline conditions to generate 3CaO·Al2O3 and CaF2.

[0008] S3, FePO4·2H2O / graphite composite slag dissolution: FePO4·2H2O / graphite composite slag is added with sulfuric acid for acidification and dissolution, and after filtration, graphite filter residue and reaction liquid B are obtained;

[0009] S4, hydrothermal reaction: reaction liquid A and reaction liquid B are mixed, H3PO4 solution is added, ammonia solution is used to adjust pH, and after hydrothermal reaction at 70-90℃, reaction is carried out for 2-4h, and then Li3PO4 and FePO4·2H2O mixture are obtained by filtration, and mother liquor is obtained by filtration and is evaporated and crystallized by MVR to obtain byproduct ammonium sulfate;

[0010] S5, lithium manganese iron phosphate coating calcination: lithium carbonate, manganese source and glucose are added to the Li3PO4 and FePO4·2H2O mixture, and after sanding, spraying, calcination and crushing, carbon-coated lithium manganese iron phosphate is obtained.

[0011] Further, the concentration of sulfuric acid in S1 is 5%-25%, and the concentration of hydrogen peroxide is 10%-28%;

[0012] Further, the molar ratio of sulfuric acid to lithium element in the precursor solution in S1 is 1.05-1.25:2;

[0013] Further, the molar amount of hydrogen peroxide in S1 is 1.1-1.5 times the molar amount of Fe 2+ oxidized to Fe 3+ in the precursor solution.

[0014] Further, the heating reaction temperature in S1 is 50-85℃, and the heating reaction time is 2-3h.

[0015] Further, the concentration of NaOH solution in S2 is 3-4mol / L, and the pH is adjusted to 10-12;

[0016] Further, the molar amount of CaO in S2 is 1.0-1.2 times the molar amount of Al 3+ and F - in the filtrate.

[0017] Further, the molar amount of sulfuric acid in S3 is 1.1-1.2 times the molar amount of FePO4·2H2O.

[0018] Further, the concentration of ammonia water in S4 is 25%-28%, and the pH is adjusted to 1.5-2.

[0019] Further, the molar amount of H3PO4 solution in S4 is 1 / 3 the molar amount of lithium element in reaction liquid A.

[0020] Further, the glucose added in S5 is 10%-15% of the mass of the Li3PO4 and FePO4·2H2O mixture.

[0021] Further, the manganese source in S5 is any one of manganese dioxide or trimanganese tetroxide.

[0022] Further, the molar ratio of lithium element, iron element, manganese element and phosphorus element in S5 is Li:(Fe+Mn):P=1.01-1.06:0.96-1:1.

[0023] Advantages of the present application:

[0024] 1. The present application realizes recycling of lithium iron phosphate batteries, the method process is simple, the raw material price is low, the recycling cost can be reduced, the generation of waste is reduced, and the resource utilization rate is improved. The purity of the product obtained by recycling is high, which can meet the use requirements of battery-grade lithium manganese iron phosphate in the industry, and the byproduct ammonium sulfate can be used as a chemical raw material. The elements in the present application can be effectively utilized, and the composite green chemical concept is realized.

[0025] 2. The product after calcination and crushing by the preparation method of the present application is LiFe 0.75 Mn 0.25 PO4@C, wherein glucose is used as a carbon source. Since the molar ratio of Li, Fe and P in the recycled lithium iron phosphate material is basically 1:1:1, the molar amount of phosphorus will be 1 / 3 more due to the additional addition of phosphoric acid. This extra phosphorus is eventually configured into lithium manganese phosphate, so Fe / Mn=3:1, and thus the product LiFe 0.75 Mn 0.25 PO4@C is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be further described below with reference to the accompanying drawings.

[0027] Figure 1 is a process flow chart of Example 1 of the present application;

[0028] Figure 2 is an SEM image of lithium manganese iron phosphate prepared in Example 1 of the present application;

[0029] Figure 3 is an XRD image of lithium manganese iron phosphate prepared in Example 1 of the present application;

[0030] Figure 4 is a rate performance graph of lithium manganese iron phosphate prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0032] Embodiment 1

[0033] A method for preparing lithium manganese iron phosphate from lithium iron phosphate, a process flow chart is shown as Figure 1 The method comprises the following steps of preparation:

[0034] S1, preferential leaching of lithium element: lithium iron phosphate recovery battery powder is mixed with 10% sulfuric acid and 20% hydrogen peroxide, the heating temperature is 60℃, the molar ratio of sulfuric acid to lithium element in the powder is 1.05:2, and the molar amount of hydrogen peroxide is 1.2 times of the molar amount of Fe 2+ oxidized to Fe 3+ in the solution, after the reaction is completed, filtration is performed to obtain a filtrate containing a Li2SO4 solution and a FePO4·2H2O / graphite composite residue;

[0035] S2, impurity removal of the Li2SO4 solution: CaO and a 3mol / L NaOH solution are added to the filtrate containing the Li2SO4 solution, the pH is adjusted to 11, and the temperature is kept at 60℃ for 2h, wherein the molar amount of CaO is 1.1 times of the molar amount of Al ions and F ions; after the reaction is completed, filtration is performed to obtain a reaction liquid A, the filter residue is Cu(OH)2, 3CaO·Al2O3, and a small amount of Li3PO4 and CaF2;

[0036] S3, dissolution of the FePO4·2H2O / graphite composite residue: 15% sulfuric acid is added to the FePO4·2H2O / graphite composite residue for acidification and dissolution, the required molar amount of sulfuric acid is 1.2 times of the molar amount of FePO4·2H2O, and after filtration, graphite and a reaction liquid B are obtained;

[0037] S4, hydrothermal reaction: after the reaction liquid A and the reaction liquid B are mixed, one-third of the molar amount of H3PO4 is added, the solution pH is adjusted to about 1.6 by using NH3·H2O, and a hydrothermal reaction is performed at 70℃ for 2h, the reaction liquid is filtered and washed to obtain a mixture of Li3PO4 and FePO4·2H2O with a molar ratio of 1:3, and the filtrate is evaporated and crystallized by using an MVR to obtain a byproduct ammonium sulfate;

[0038] S5, lithium iron manganese phosphate coated calcination: the mixture of Li3PO4 and FePO4·2H2O is added with lithium carbonate, manganese dioxide and glucose, wherein the molar ratio of lithium element, iron element, manganese element and phosphorus element is Li:(Fe+Mn):P=1.02:0.96:1, and the amount of glucose added is 10% of the mass of the mixture of Li3PO4 and FePO4·2H2O, and the carbon-coated lithium iron manganese phosphate is obtained by sanding, spraying, calcining and crushing, the calcination temperature is 700℃, the calcination time is 6h, and the calcined product is LiFe 0.75 Mn 0.25 PO4@C.

[0039] The SEM spectrum of the lithium iron manganese phosphate prepared in Example 1 is shown in Figure 2 ;

[0040] The XRD spectrum of the lithium iron manganese phosphate prepared in Example 1 is shown in Figure 3 ;

[0041] Electrochemical performance test:

[0042] The lithium iron manganese phosphate positive electrode material prepared in Example 1, acetylene black and a binder (PVDF) are mixed uniformly in a mass ratio of 8:1:1, NMP is used as a solvent, and a uniformly mixed slurry is obtained by manual grinding. The obtained slurry is coated on an aluminum foil, dried in a vacuum oven at 120℃ for 6h, and then punched into a disc-type electrode with a diameter of 8mm. A CR2025 button cell is assembled with the electrode. The constant current charge and discharge test is carried out at room temperature (25-30℃) with a limited voltage of 2-4.5V. The test shows that the 1C capacity is 137.5mAh / g, the 3C capacity is 130.2mAh / g, and the rate performance of the lithium iron manganese phosphate prepared by recycling and regeneration in Example 1 is shown in Figure 4 .

[0043] Example 2

[0044] A method for preparing lithium iron manganese phosphate from lithium iron phosphate, comprising the following steps:

[0045] S1, preferential leaching of lithium element: the lithium iron phosphate recycling battery powder is mixed with 12% sulfuric acid and 18% hydrogen peroxide, the heating temperature is 80℃, the molar ratio of sulfuric acid to lithium element in the powder is 1.06:2, and the molar amount of hydrogen peroxide is 1.3 times of the molar amount of Fe 2+ oxidized to Fe 3+ in the solution, after the reaction is completed, the filtrate containing Li2SO4 solution and FePO4·2H2O / graphite composite residue are obtained by filtration;

[0046] S2, Li SO4 solution impurity removal: CaO and 3 mol / L NaOH solution were added to the filtrate containing Li2SO4 solution, the pH was adjusted to 12, and it was incubated at 80°C for 3h. After the reaction was completed, the reaction solution A was obtained by filtration, wherein the molar amount of CaO was 1.05 times the molar amount of Al ions and F ions; the filter residue was Cu(OH)2, 3CaO·Al2O3, and a small amount of Li3PO4 and CaF2;

[0047] S3, FePO4·2H2O / graphite composite residue dissolution: 20% sulfuric acid was added to the FePO4·2H2O / graphite composite residue for acidification and dissolution, and the molar amount of sulfuric acid required was 1.1 times the molar amount of FePO4·2H2O. After filtration, graphite and reaction solution B were obtained;

[0048] S4, hydrothermal reaction: reaction solution A and reaction solution B were mixed, and one-third of the molar amount of H3PO4 was added. The solution pH was adjusted to about 2 using NH3·H2O, and a hydrothermal reaction was carried out at 80°C for 2h. The reaction solution was filtered and washed to obtain a mixture of Li3PO4 and FePO4·2H2O in a molar ratio of 1:3. The filtrate was evaporated and crystallized by MVR to obtain the byproduct ammonium sulfate;

[0049] S5, lithium manganese iron phosphate coating and calcination: the mixture of Li3PO4 and FePO4·2H2O was added with lithium carbonate, manganese dioxide and glucose, wherein the molar ratio of lithium, iron, manganese and phosphorus was Li:(Fe+Mn):P=1.03:1:1, and the amount of glucose added was 13% of the mass of the mixture of Li3PO4 and FePO4·2H2O. After sand milling, spraying, calcination and crushing, carbon-coated lithium manganese iron phosphate was obtained. The calcination temperature was 750°C, and the calcination time was 5h. The calcined product was LiFe 0.75 Mn 0.25 PO4@C.

[0050] Example 3

[0051] A method for preparing lithium manganese iron phosphate from lithium iron phosphate, comprising the following steps:

[0052] S1, preferential leaching of lithium element: lithium iron phosphate recovery battery powder was mixed with 15% sulfuric acid and 22% hydrogen peroxide, the heating temperature was 75°C, the molar ratio of sulfuric acid to lithium element in the powder was 1.1:2, and the molar amount of hydrogen peroxide was 1.4 times the molar amount of Fe 2+ oxide to Fe 3+ in the solution. After the reaction was completed, the filtrate containing Li2SO4 solution and FePO4·2H2O / graphite composite residue were obtained;

[0053] S2, Li SO4 solution impurity removal: CaO and 3 mol / L NaOH solution were added to the filtrate containing Li2SO4 solution, the pH was adjusted to 10, and the mixture was incubated at 75°C for 4h. After the reaction was completed, the reaction liquid A was obtained by filtration, wherein the molar amount of CaO was 1.2 times the molar amount of Al ions and F ions; the filter residue was Cu(OH)2, 3CaO·Al2O3, and a small amount of Li3PO4 and CaF2;

[0054] S3, FePO4·2H2O / graphite composite slag dissolution: 18% sulfuric acid was added to the FePO4·2H2O / graphite composite slag for acidification and dissolution, and the required molar amount of sulfuric acid was 1.1 times the molar amount of FePO4·2H2O. After filtration, graphite and reaction liquid B were obtained;

[0055] S4, hydrothermal reaction: after mixing reaction liquid A and reaction liquid B, one-third of the molar amount of H3PO4 was added, and the solution pH was adjusted to about 1.8 with NH3·H2O, and then the mixture was subjected to hydrothermal reaction at 90°C for 2h. The reaction liquid was filtered and washed to obtain a mixture of Li3PO4 and FePO4·2H2O in a molar ratio of 1:3, and the filtrate was evaporated by MVR to obtain byproduct ammonium sulfate;

[0056] S5, lithium manganese iron phosphate coating and calcination: the mixture of Li3PO4 and FePO4·2H2O was added with lithium carbonate, manganese dioxide and glucose, wherein the molar ratio of lithium, iron, manganese and phosphorus was Li:(Fe+Mn):P=1.06:0.97:1, and the amount of glucose added was 15% of the mass of the mixture of Li3PO4 and FePO4·2H2O. After sand milling, spraying, calcination and crushing, carbon-coated lithium manganese iron phosphate was obtained. The calcination temperature was 710°C, the calcination time was 8h, and the product obtained by calcination was LiFe 0.75 Mn 0.25 PO4@C.

[0057] The lithium manganese iron phosphate prepared in Examples 1-3 was subjected to performance testing

[0058] The carbon content was tested by a high-frequency infrared carbon-sulfur analyzer;

[0059] The tap density was tested by a tap density tester;

[0060] The specific surface area was tested by a specific surface area tester;

[0061] The pH value was tested by a pH tester;

[0062] The electrochemical performance test was the same as described in Example 1.

[0063] The results are shown in Table 1:

[0064] Table 1

[0065]

[0066]

[0067] As can be seen from Table 1, the main product lithium manganese iron phosphate obtained in Examples 1-3 can be used as a positive electrode material of a lithium ion battery, and the preparation method provided by the present application can realize recycling of lithium iron phosphate batteries.

[0068] It should be noted that, in this document, the terms such as first and second are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between such entities or operations. Moreover, the terms "comprising", "containing", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or apparatus that comprises a list of elements does not only include those elements, but also includes other elements not explicitly listed, or inherent to such process, method, article, or apparatus.

[0069] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, alternatives, and variations can be made thereto without departing from the principles and spirit of the application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing lithium manganese iron phosphate from lithium iron phosphate, characterized by, The method comprises the following steps: S1, mixing lithium iron phosphate battery powder with sulfuric acid and hydrogen peroxide to obtain a precursor solution, and filtering the precursor solution after heating reaction to obtain a filtrate containing Li2SO4 and FePO4·2H2O / graphite composite residue; S2, adding CaO to the filtrate containing Li2SO4, adjusting the pH with a NaOH solution, and filtering a reaction liquid A and a filter residue after heat preservation reaction; S3, adding sulfuric acid to the FePO4·2H2O / graphite composite residue to perform acidification and dissolution, and filtering to obtain graphite filter residue and a reaction liquid B; S4, mixing the reaction liquid A and the reaction liquid B, adding an H3PO4 solution, adjusting the pH with an ammonia solution, and filtering a Li3PO4 and FePO4·2H2O mixture after hydrothermal reaction, and evaporating and crystallizing a mother liquor by MVR to obtain a byproduct ammonium sulfate; S5, adding lithium carbonate, a manganese source and glucose to the Li3PO4 and FePO4·2H2O mixture, and obtaining carbon-coated lithium manganese iron phosphate after sand milling, spraying, calcining and crushing. The molar amount of the H3PO4 solution in S4 is 1 / 3 of the molar amount of lithium in the reaction liquid A.

2. The method for preparing lithium manganese iron phosphate from lithium iron phosphate according to claim 1, characterized in that, The concentration of sulfuric acid in S1 and S3 is 5%-25%, and the concentration of hydrogen peroxide in S1 is 10%-28%.

3. The method of claim 1, wherein the lithium manganese iron phosphate is prepared from lithium iron phosphate, and the lithium iron phosphate is prepared from lithium carbonate and iron phosphate. The molar ratio of sulfuric acid to lithium element in the precursor solution in S1 is 1.05-1.25:2, and the molar amount of hydrogen peroxide is 1.1-1.5 times the molar amount of Fe 2+ oxidized to Fe 3+ in the precursor solution.

4. The method for preparing lithium manganese iron phosphate from lithium iron phosphate according to claim 1, characterized in that, The heating reaction temperature in S1 is 50-85℃, and the heating reaction time is 2-3h, the hydrothermal reaction temperature in S4 is 70-90℃, and the hydrothermal reaction time is 2-4h.

5. The method of claim 1, wherein the lithium manganese iron phosphate is prepared from lithium iron phosphate, and the lithium iron phosphate is prepared from lithium carbonate and iron phosphate. The concentration of the NaOH solution in S2 is 3-4mol / L, and the pH is adjusted to 10-12, the concentration of the ammonia solution in S4 is 25%-28%, and the pH is adjusted to 1.5-2.

6. The method of claim 1, wherein the lithium manganese iron phosphate is prepared from lithium iron phosphate, and the lithium iron phosphate is prepared from lithium carbonate and iron phosphate. The molar amount of CaO in S2 is 1.0-1.2 times the molar amount of Al 3+ and F - in the filtrate.

7. The method of claim 1, wherein the lithium manganese iron phosphate is prepared from lithium iron phosphate, and the lithium iron phosphate is prepared from lithium carbonate and iron phosphate. The molar amount of sulfuric acid in S3 is 1.1-1.2 times the molar amount of FePO4·2H2O.

8. The method of claim 1, wherein the lithium manganese iron phosphate is prepared from lithium iron phosphate, and the lithium iron phosphate is prepared from lithium carbonate and iron phosphate. The amount of glucose added in S5 is 10%-15% of the mass of the Li3PO4 and FePO4·2H2O mixture.

9. The method of claim 1, wherein the lithium manganese iron phosphate is prepared from lithium iron phosphate, and the lithium iron phosphate is prepared from lithium carbonate and iron phosphate. The manganese source in S5 is any one of manganese dioxide or trimanganese tetraoxide.

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