A method for preparing a lithium pre-doped amine coordination manganese iron phosphate precursor from lithium manganese iron phosphate

Abstract

The application discloses a method for preparing lithium pre-doped amine coordination manganese iron phosphate precursor from lithium manganese iron phosphate, and belongs to the field of battery recycling. The method comprises the following steps: stirring and reacting lithium manganese iron phosphate battery material with a high-valence iron salt solution and a surfactant, and filtering to obtain filtrate and phosphorus iron residue; mixing the filtrate with a phosphate, adjusting the pH of the solution to 2-6, then mixing with an oxidizing agent A, and adding a mixed solution containing an organic amine compound to perform nucleation precipitation reaction, and aging to obtain the lithium pre-doped amine coordination manganese iron phosphate precursor. The application utilizes the surfactant and the high-valence iron salt to efficiently replace divalent iron under acid-free or weak acid conditions, generates a metal solution containing Li + , Fe 2+ , Mn 2+ , performs oxidation to form nucleation precipitation, adds an organic amine compound to control the morphology of the generated particles in the solution, generates the lithium-doped amine coordination manganese iron phosphate precursor, the reaction condition is mild, the energy consumption in the treatment process is low, and the economic utilization value of a manganese byproduct is improved.

Description

Technical Field

[0001] This invention relates to the field of battery recycling, and more particularly to a method for preparing lithium pre-doped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate. Background Technology

[0002] With the rapid development of new energy vehicles, lithium battery production has accelerated. In particular, lithium iron phosphate power batteries are widely used due to their good safety performance and long cycle life. Meanwhile, manganese iron phosphate is gradually being valued and entering the battery market due to its high energy density. Its properties are similar to those of lithium iron phosphate and lithium manganese phosphate, and it has better thermal stability, chemical stability and economy than ternary materials.

[0003] With the increasing application of lithium manganese iron phosphate (LFP) batteries, the disposal of waste LFP batteries needs to be considered in advance. Current technologies for recovering and extracting various metal salts from waste LFP batteries mainly involve acid leaching to form a metal solution and preparing iron phosphate and lithium carbonate. However, manganese, as an impurity element, is transferred to the solid slag during co-precipitation and is directly lost, failing to be effectively utilized. Other recycling technologies involve dissolving the positive electrode material of waste LFP batteries in an oxidizing acid solution, followed by oxidation and filtration to obtain a lithium-rich solution and manganese iron slag. The manganese iron slag is a mixture of manganese oxide and iron phosphate. The manganese iron slag is then calcined with sodium hydroxide, dissolved in water, and filtered to obtain a sodium manganate solution and iron phosphate. The sodium manganate solution is then subjected to a redox reaction with a reducing agent to obtain manganese dioxide. This method has high energy consumption, and the resulting manganese byproducts are not economically viable.

[0004] Therefore, it is necessary to develop a method for recovering lithium iron phosphate with mild reaction conditions, low acid and alkali usage, and low energy consumption, while also improving the application value of manganese by-products. Summary of the Invention

[0005] This invention provides a method for preparing lithium-predoped amine-coordinated manganese iron phosphate precursors using lithium manganese iron phosphate, wherein trivalent iron salts are used to replace Li under mild conditions. + Fe 2+ Mn 2+ The metal solution was used to prepare the Li-predoped amine-coordinated manganese iron phosphate precursor in situ, and the manganese byproduct had high application value.

[0006] To address the aforementioned technical problems, one objective of this invention is to provide a method for preparing a lithium-predoped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate, comprising the following steps:

[0007] (1) Mix the lithium manganese iron phosphate battery material with a high-valence iron salt solution, then stir and react with a surfactant, and filter to obtain filtrate and phosphorus iron slag;

[0008] (2) The filtrate is mixed with phosphate to prepare phosphorus, and acid is added to adjust the pH of the solution to 2-6 to obtain a phosphorus-prepared acid-adjusted solution;

[0009] (3) The phosphoric acid-adjusting solution and oxidant A are mixed, and then a mixed solution containing organic amine compounds is added to carry out a nucleation reaction. After aging and separation, the mother liquor and lithium pre-doped amine coordinated manganese iron phosphate precursor are obtained.

[0010] In step (1), the surfactant is an oxime acid, an amide, or a phenyl hydroxylamine compound; in step (3), the organic amine compound is a short-chain amine or an amide compound.

[0011] By employing the above scheme, this application utilizes surfactants and high-valent iron salts to efficiently replace ferrous iron under acid-free or weakly acidic conditions, generating a metal solution containing lithium, manganese, and ferrous iron. The added phosphate is a weak acid, and the solution contains monohydrogen phosphate, dihydrogen phosphate, and phosphate ions. By adding phosphate and adjusting the pH to control the phosphate concentration, lithium phosphate can precipitate together with manganese iron phosphate, achieving lithium predoping. The lower solubility product of lithium phosphate allows for preferential nucleation of some lithium in the subsequent nucleation process. An oxidant is added to the metal solution to oxidize Fe. 2+ Mn 2+ The addition of organic amine compounds for metal coordination can synergistically regulate the particle morphology generated in solution with surfactants, allowing for direct interaction in Li-containing environments. + Fe 2+ Mn 2+ A lithium-doped amine-coordinated manganese iron phosphate precursor is generated in the solution.

[0012] As a preferred embodiment, in step (1), the surfactant is at least one of octanoyloxyoxime acid, acetyloxyoxime acid, hydroxyacetamide, ethyl acetylhydroxyoxime acid, salicylic acid, hypoisohydroxyoxime acid, benzooxyoxime acid, or N-benzoyl-N-phenylhydroxylamine.

[0013] By adopting the above scheme, since the lithium manganese iron phosphate cathode powder contains organic binders, conductive carbon black, coated carbon, and other substances, its surface is hydrophobic. By adding surfactants, the surface tension of the waste lithium manganese iron phosphate is reduced, the hydrophilicity is increased to facilitate water wetting, and the Fe2+ is enhanced. 3+ The conductive effect and the replacement of Fe by lithium iron phosphate powder with manganese phosphate oxide 2+ and Mn 2+ Simultaneously, the use of surfactants with electron transport-double bond, triple bond, and benzene ring structures can increase Fe... 3+ The electron conductivity of lithium manganese iron phosphate micropowder, in synergy with substitution, accelerates the Li-P structure formation in lithium manganese iron phosphate. + Fe 2+ Mn 2+It enters the solution; the surfactant can also react with Fe. 3+ The formation of chelates reduces the precipitation of ferric iron on the surface of lithium iron phosphate slag, thereby decreasing the displacement of Fe. 2+ and Mn 2+ The channel obstruction further enhances the treatment efficiency of lithium manganese phosphate slag and improves the direct recovery rate of Li.

[0014] As a preferred embodiment, in step (1), the molar ratio of phosphorus in the iron salt and manganese iron lithium battery material is (0.8-1.1):1.

[0015] As a preferred embodiment, in step (1), the molar ratio of the surfactant to the high-valent iron salt is (0.06-0.12):1.

[0016] As a preferred embodiment, in step (1), the high-valence iron salt is an organic iron salt or an inorganic iron salt.

[0017] As a preferred embodiment, in step (1), the high-valent iron salt is one of ferric chloride, ferric nitrate, ferric sulfate, ferric oxalate, ferric citrate, and ferric acetate.

[0018] As a preferred option, in step (1), the reaction time is 8-10 hours.

[0019] As a preferred embodiment, in step (1), the lithium manganese iron phosphate battery material is waste lithium manganese iron phosphate cathode powder, waste lithium iron manganese phosphate electrode powder, or waste lithium manganese iron phosphate battery powder.

[0020] As a preferred embodiment, in step (2), the phosphate is at least one of phosphoric acid, sodium phosphate, monoammonium phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate; and the acid is an inorganic acid or an organic acid.

[0021] As a preferred embodiment, in step (2), the inorganic acid is one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; and the organic acid is one of formic acid, acetic acid, propionic acid, butyric acid, octanoic acid, adipic acid, oxalic acid, malonic acid, succinic acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, phthalic acid, terephthalic acid, valeric acid, hexanoic acid, decanoic acid, stearic acid, palmitic acid, and acrylic acid.

[0022] As a preferred embodiment, in step (3), the oxidant A is one of hydrogen peroxide, sodium peroxide, potassium peroxide, ozone, and sodium hypochlorite.

[0023] As a preferred embodiment, in step (3), the organic amine compound is at least one of methylamine, ethylamine, furfurylamine, benzylamine, isopropanolamine, ethylenediamine, propylenediamine, dicyandiamine, 1,2-propanediamine, and oxalyldiamine.

[0024] As a preferred embodiment, in step (3), the total molar ratio of the organic amine compound and the manganese iron in the solution is (0.05-0.25):1.

[0025] As a preferred embodiment, in step (3), the total molar ratio of the oxidant A and the manganese iron in the solution is (1.05-1.2):1.

[0026] As a preferred option, in step (3), the nuclear precipitation reaction temperature is 70-95℃ and the stirring rate is 250-450r / min.

[0027] As a preferred option, in step (3), the aging temperature is 80-90℃, the stirring rate is 150-350r / min, and the time is 6-12h.

[0028] As a preferred embodiment, in step (3), the mixed solution containing organic amine compounds is introduced into the solution system by spraying, and the particle size of the spray droplets is controlled at 0.8-2.5 μm. The mixed solution containing organic amine compounds also includes 0.1-0.6 wt% of the same surfactant as in step (1).

[0029] By adopting the above scheme, uniform spraying helps ethylenediamine form nucleation centers, which in turn helps manganese iron phosphate to precipitate fully.

[0030] As a preferred embodiment, in step (3), oxidant B is added to oxidize and adjust the pH of the lithium iron manganese phosphorus mother liquor. The molar ratio of oxidant B to the total manganese and iron in the mother liquor is (1-1.15):1. The pH is adjusted to 8-12 to precipitate iron and manganese metals to obtain lithium-containing liquid and precipitate residue. Carbonate is added to the lithium-containing liquid to precipitate lithium to obtain lithium carbonate.

[0031] By adopting the above scheme, Fe-containing 3+ The lithium iron manganese phosphate mother liquor can be returned to the front end for lithium extraction through displacement of lithium manganese iron phosphate, or it can be acid-dissolved and recycled after conditioning and precipitation to enhance Fe content. 3+ Increase utilization and reduce production costs.

[0032] As a preferred embodiment, the oxidant B is one of hydrogen peroxide, sodium peroxide, potassium peroxide, ozone, and sodium hypochlorite.

[0033] To address the aforementioned technical problems, a second objective of this invention is to provide a method for preparing lithium pre-doped amine-coordinated manganese iron phosphate precursors from lithium manganese iron phosphate.

[0034] As a preferred embodiment, the lithium predoped amine-coordinated manganese iron phosphate precursor contains 1.5-2.1 wt% Li, 41.4-45.8 wt% Mn, 30.5-35.4 wt% Fe and 2.6-3.7 wt% N.

[0035] To address the aforementioned technical problems, a third objective of this invention is to provide a manganese iron phosphate battery material, which is prepared using a lithium-predoped amine-coordinated manganese iron phosphate precursor.

[0036] As a preferred option, the lithium predoped amine coordinated manganese iron phosphate precursor is mixed with lithium source and carbon source, ball-milled, sintered in an inert gas atmosphere at 600-700℃ for 10-15h, and then ground and sieved to obtain lithium manganese iron phosphate material.

[0037] As a preferred embodiment, the molar ratio of the lithium predoped amine-coordinated manganese iron phosphate precursor to the lithium source is 1:(1-1.1).

[0038] As a preferred embodiment, the sucrose accounts for 2%-5% of the mass of the manganese iron phosphate battery material.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. This application utilizes surfactants and high-valent iron salts to efficiently replace divalent iron under acid-free or weakly acidic conditions, generating Li-containing compounds. + Fe 2+ Mn 2+ A metal solution, into which an oxidizing agent is added to oxidize Fe. 2+ Mn 2+ The addition of organic amine compounds for metal coordination can synergistically regulate the particle morphology generated in solution with surfactants, allowing for direct interaction in Li-containing environments. + Fe 2+ Mn 2+ The formation of lithium-doped amine-coordinated manganese iron phosphate precursors in solution can be used for the recycling of lithium manganese iron phosphate battery materials. The reaction conditions are mild, the processing has low energy consumption, and the economic utilization value of manganese by-products is improved.

[0041] 2. Because lithium manganese iron phosphate cathode powder contains organic binders, conductive carbon black, coated carbon, and other substances, its surface is hydrophobic. Adding surfactants helps to increase the surface tension of the powder, facilitating water wetting and enhancing the Fe... 3+ The conduction effect and oxidation replacement of Fe 2+ and Mn 2+ Efficiency; simultaneously, the use of surfactants with electron transport-double bond, triple bond, and benzene ring structures can increase Fe 3+ The electron conductivity of lithium manganese iron phosphate micropowder, in synergy with substitution, accelerates the Li-P structure formation in lithium manganese iron phosphate. + Fe 2+ Mn 2+ It enters the solution; the surfactant can also react with Fe. 3+ The formation of chelates reduces the precipitation of ferric iron on the surface of lithium iron phosphate slag, thereby decreasing the displacement of Fe.2+ and Mn 2+ The channel obstruction further enhances the treatment efficiency of lithium manganese phosphate slag and improves the direct recovery rate of Li.

[0042] 3. By adding organic amine compounds for metal coordination in the nuclear precipitation step, the particle morphology of lithium pre-doped amine-coordinated manganese iron phosphate precursor in solution can be synergistically controlled with surfactants. This results in a two-dimensional structure that is flat and regularly shaped, with distinct and layered superimposed contours, no particle agglomeration, and no blurred or unclear contours. Furthermore, the structure is free of doped powdery particles, which improves the electrical performance of manganese iron phosphate in subsequent applications.

[0043] 4. This application uses nuclear precipitation to separate Fe-containing molecules. 3+ The lithium iron manganese phosphate mother liquor can be returned to the upstream for lithium extraction by displacement of lithium manganese iron phosphate, or it can be acid-dissolved and recycled after conditioning and precipitation to enhance Fe content. 3+ Increase utilization and reduce production costs. Attached Figure Description

[0044] Figure 1 This is a schematic flowchart of a method for preparing lithium pre-doped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to an embodiment of the present invention.

[0045] Figure 2 : SEM image of the lithium pre-doped amine-coordinated manganese iron phosphate precursor prepared in Example 1 of this invention;

[0046] Figure 3 : SEM image of the lithium pre-doped amine-coordinated manganese iron phosphate precursor prepared in Example 2 of this invention;

[0047] Figure 4 : SEM image of the lithium pre-doped amine-coordinated manganese iron phosphate precursor prepared in Example 3 of this invention;

[0048] Figure 5 : SEM image of the lithium pre-doped amine-coordinated manganese iron phosphate precursor prepared in Comparative Example 3 of this invention;

[0049] Figure 6 : SEM image of the lithium pre-doped amine-coordinated manganese iron phosphate precursor prepared in Comparative Example 4 of this invention;

[0050] Figure 7 : This is a SEM image of the lithium pre-doped amine-coordinated manganese iron phosphate precursor prepared in Comparative Example 5 of this invention. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] A method for preparing lithium-predoped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate, such as... Figure 1 As shown, it includes the following steps:

[0054] (1) The waste lithium manganese iron phosphate battery cathode powder and the ferric sulfate aqueous solution were mixed with a solid-liquid ratio of 0.15:1 and the molar ratio of ferric sulfate to phosphorus in the waste lithium manganese iron phosphate battery cathode powder was 0.8:1. Octyloxyoxime surfactant was added and stirred for reaction. The molar ratio of octyloxyoxime to ferric sulfate was 0.06:1. The reaction time was 8h. The filtrate and phosphorus iron slag were obtained by filtration.

[0055] (2) Phosphoric acid was added to the filtrate to prepare phosphoric acid solution. The standard for phosphoric acid preparation was that the ratio of the total molar amount of manganese and iron to the molar amount of phosphorus in the solution was 0.8:1. Sulfuric acid was added to adjust the acidity of the solution to 2, and the pH value of the solution was adjusted to obtain a phosphoric acid-adjusting solution.

[0056] (3) Add hydrogen peroxide oxidant to the phosphorus acid-adjusting solution. The amount of hydrogen peroxide is 1.05 times the total molar amount of manganese and iron. Add ethylenediamine mixed solution to carry out nucleation precipitation. The ethylenediamine mixed solution includes 0.1 wt% octanoyl oxime acid and ethylenediamine accounting for 0.05 times the total molar amount of manganese and iron in the solution. The ethylenediamine mixed solution is sprayed into the solution through a 0.8 μm pore size to form small droplets that enter the solution system to react and form manganese and iron phosphate nucleation centers for precipitation. The stirring speed is 250 r / min and the reaction system temperature is 70℃.

[0057] (4) The precipitated manganese iron phosphate was aged at a stirring speed of 150 r / min, a reaction system temperature of 80℃, and an aging time of 12 h. The mother liquor containing lithium iron manganese phosphorus and the lithium predoped amine coordinated manganese iron phosphate precursor were separated.

[0058] Example 2

[0059] A method for preparing lithium-predoped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate, such as... Figure 1 As shown, it includes the following steps:

[0060] (1) The waste lithium manganese iron phosphate battery cathode powder and the ferric sulfate aqueous solution were mixed with a solid-liquid ratio of 0.25:1 and the molar ratio of ferric sulfate to phosphorus in the waste lithium manganese iron phosphate battery cathode powder was 1:1. Benzooxyoxime acid surfactant was added and stirred for reaction. The molar ratio of benzooxyoxime acid to ferric sulfate was 0.08:1 and the reaction time was 9h. The filtrate and phosphorus iron slag were obtained by filtration.

[0061] (2) Sodium phosphate was added to the filtrate to prepare phosphorus. The standard for phosphorus preparation was that the ratio of the total molar amount of manganese and iron to the molar amount of phosphorus in the solution was 1:1. Sulfuric acid was added to adjust the acidity of the solution to 4, and the pH value of the solution was adjusted to obtain a phosphorus-prepared acid-adjusting solution.

[0062] (3) Add hydrogen peroxide oxidant to the phosphorus acid-adjusting solution. The amount of hydrogen peroxide is 1.1 times the total molar amount of manganese and iron. Add dicyandiamine mixed solution to carry out nucleation precipitation. The dicyandiamine mixed solution includes 0.3 wt% benzooxyoxime acid and dicyandiamine accounting for 0.1 times the total molar amount of manganese and iron in the solution. The dicyandiamine mixed solution is sprayed into the solution through a 1.5 μm aperture to form small droplets that enter the solution system to react and form manganese and iron phosphate nucleation centers for precipitation. The stirring speed is 350 r / min and the reaction system temperature is 80 °C.

[0063] (4) The precipitated manganese iron phosphate was aged at a stirring speed of 250 r / min, a reaction system temperature of 85℃, and an aging time of 10 h. The mother liquor containing lithium iron manganese phosphorus and the lithium predoped amine coordinated manganese iron phosphate precursor were separated.

[0064] Example 3

[0065] A method for preparing lithium-predoped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate, such as... Figure 1 As shown, it includes the following steps:

[0066] (1) The waste lithium manganese iron phosphate battery cathode powder and the ferric sulfate aqueous solution were mixed with a solid-liquid ratio of 0.35:1 and the molar ratio of ferric sulfate to phosphorus in the waste lithium manganese iron phosphate battery cathode powder was 1.1:1. Salicylic acid surfactant was added and stirred for reaction. The molar ratio of salicylic acid to ferric sulfate was 0.12:1 and the reaction time was 10h. The filtrate and phosphorus iron slag were obtained by filtration.

[0067] (2) Sodium phosphate was added to the filtrate to prepare phosphorus. The standard for phosphorus preparation was that the ratio of the total molar amount of manganese and iron to the molar amount of phosphorus in the solution was 1.1:1. Sulfuric acid was added to adjust the acidity of the solution to 6, and the pH value of the solution was adjusted to obtain a phosphorus-prepared acid-adjusting solution.

[0068] (3) Add hydrogen peroxide oxidant to the phosphorus acid-adjusting solution. The amount of hydrogen peroxide is 1.2 times the total molar amount of manganese iron. Add oxalyl diamine mixed solution to carry out nucleation precipitation. The oxalyl diamine mixed solution includes 0.6 wt% salicylic acid and oxalyl diamine accounting for 0.25 times the total molar amount of manganese iron in the solution. The oxalyl diamine mixed solution is sprayed into the solution through a 2.5 μm pore size to form small droplets to enter the solution system for reaction, forming manganese iron phosphate nucleation centers for precipitation. The stirring speed is 450 r / min and the reaction system temperature is 95℃.

[0069] (4) The precipitated manganese iron phosphate was aged at a stirring speed of 350 r / min, a reaction system temperature of 90℃, and an aging time of 6 h. The mother liquor containing lithium iron manganese phosphorus and the lithium predoped amine coordinated manganese iron phosphate precursor were separated.

[0070] (5) The mother liquor of lithium iron manganese phosphorus is oxidized and adjusted with hydrogen peroxide. The amount of hydrogen peroxide added is 1 times the total molar amount of manganese and iron in the solution. The pH is adjusted to 8 to precipitate iron and manganese metal to obtain lithium-containing liquid and precipitate residue. Lithium carbonate is precipitated in the lithium-containing liquid to obtain lithium carbonate. The amount of lithium carbonate added is 1.1 times the molar amount of Li. The precipitate residue can be dissolved with sulfuric acid. The pH is adjusted to 2 with acid. Then it is reused in step (1) and mixed with waste manganese iron lithium battery positive electrode powder for iron salt leaching process.

[0071] Comparative Example 1

[0072] A method for preparing lithium predoped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate is provided. The steps, reagents, and process parameters used in each step are the same as in Example 1. The difference is that in step (1), the octanoyl oxime surfactant is not added.

[0073] Comparative Example 2

[0074] A method for preparing lithium predoped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate is provided. The steps, reagents, and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), the octanoyl oxime surfactant is replaced by an equal amount of CTAB surfactant.

[0075] Comparative Example 3

[0076] A method for preparing lithium predoped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate is provided. The steps, reagents, and process parameters used in each step are the same as in Example 1. The difference is that in step (3), the ethylenediamine mixed solution is not added.

[0077] Comparative Example 4

[0078] A method for preparing lithium predoped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate is provided. The steps, reagents, and process parameters used in each step are the same as in Example 1. The difference is that in step (2), sodium phosphate is not used for phosphorus coordination. Sulfuric acid is added to the filtrate to adjust the acidity of the solution and adjust the pH of the solution to 2 to obtain an acid-adjusted solution.

[0079] Comparative Example 5

[0080] A method for preparing lithium predoped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate is provided. The steps, reagents, and process parameters used in each step are the same as in Example 1. The difference is that in step (2), the acidity of the solution is not adjusted, and phosphoric acid is added to the filtrate to prepare phosphorus. The phosphorus preparation standard is that the ratio of the total molar amount of manganese iron to the molar amount of phosphorus in the solution is 0.8:1 to obtain the phosphorus preparation solution.

[0081] Application examples and comparative application examples

[0082] A manganese iron phosphate battery material is prepared by means of the following method: the lithium predoped amine coordinated manganese iron phosphate precursor obtained in Examples 1-3 and Comparative Examples 3-5 is used as the iron, manganese and phosphorus source and mixed with lithium carbonate (at a molar ratio of 1:1.05). At the same time, 3 wt% of sucrose is added as a carbon source. The mixture is ball-milled and then calcined at 650°C for 10 h in an inert gas atmosphere. After cooling to room temperature, the mixture is ground and passed through a 300-mesh sieve to obtain nitrogen-carbon coated manganese iron phosphate samples.

[0083] Performance testing

[0084] 1. Detect and calculate the leaching rate of different metals in the filtrate of the example and comparative example step (1). For example, the leaching rate of Li is calculated as follows: Li leaching rate = mass concentration of Li in the filtrate in step (1) * solution volume / (mass content of Li in waste manganese iron lithium battery cathode powder) × 100%. The calculation results are shown in Table 1 below.

[0085] Table 1 - Metal leaching rate in the filtrate of the embodiments and comparative examples of this application

[0086] Testing items <![CDATA[Li 2+ Leaching rate (%) <![CDATA[Mn 2+ Leaching rate (%) <![CDATA[Fe 2+ Leaching rate (%) Example 1 93 90 87 Example 2 95 93 90 Example 3 98 96 94 Comparative Example 1 61 53 43 Comparative Example 2 67 55 47

[0087] As shown in Table 1, Examples 1-3 of this application co-leached waste lithium manganese iron phosphate battery cathode powder by adding a surfactant with an electron transport-double bond, triple bond, and benzene ring structure and ferric sulfate solution. The surfactant can improve the surface tension of lithium manganese iron phosphate, facilitate solution wetting, and accelerate the electron exchange and replacement rate between Fe(III) and Fe(II) and Mn(II) in waste lithium manganese iron phosphate, and accelerate the leaching of Li. In contrast, Comparative Examples 1-2 did not add the surfactant with the electron transport-double bond, triple bond, and benzene ring structure, resulting in low leaching efficiency of Li, Fe, and Mn.

[0088] 2. The elemental content of the lithium predoped amine coordinated manganese iron phosphate precursors prepared in Examples 1-3 and Comparative Examples 1-5 was detected, and the results are shown in Table 2 below.

[0089] Table 2 - Elemental content of ferromanganese phosphate precursor in the embodiments and comparative examples of this application

[0090]

[0091]

[0092] 2. The lithium-predoped amine-coordinated manganese iron phosphate precursors prepared in Examples 1-3 and Comparative Examples 3-5 were examined by scanning electron microscopy (SEM). The results are as follows: Figure 2-7 As shown, the materials in Example 1 are as follows Figure 2 As shown, a flat and regularly shaped two-dimensional structure is formed, with distinct and clearly defined outlines in the superimposed parts, without any particle agglomeration or blurred / unclear outlines, and the structure is free of powdery particles; while the material in Comparative Example 3 is as follows... Figure 5 As shown, because no surfactant was added during nucleus precipitation, the morphology of manganese iron phosphate could not be controlled, resulting in a two-dimensional structure with a regular morphology that could not be obtained, and a large number of small particles were easily generated; the material in Comparative Example 4, for example... Figure 6 As shown, without phosphorus addition, excessive iron and manganese metals easily hydrolyze, producing tiny particles such as ferric hydroxide and manganese hydroxide, affecting the product morphology; the material in Comparative Example 5, such as... Figure 7 As shown, without adjustment, the crystals of manganese iron phosphate grow too large during precipitation, which reduces the Li ion transport efficiency and capacity utilization of the material in subsequent applications.

[0093] 3. Perform performance testing on the lithium manganese iron phosphate battery material in the application example:

[0094] The lithium manganese iron phosphate battery material samples from both the application example and the comparative application example were mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 90:4:6. The mixture was prepared using N-methylpyrrolidone as a solvent, coated onto a 16μm thick aluminum current collector foil, dried at 120℃ for 20h, punched, and pressed to form a positive electrode sheet (containing 10mg of active material) with a diameter of 14mm and a thickness of 5μm. Using lithium metal as the negative electrode and 1mol / L LiPF6 / EC+DMC (volume ratio 1:1, battery grade) as the electrolyte, CR2032 coin cells were assembled. The cells were charged at a constant current of 1.0C to 4.1V, then switched to constant voltage charging to a current of 0.1C, and finally discharged at a constant current of 1.0C to 3.6V. The reversible capacity, 200-cycle capacity, and retention rate of the lithium manganese iron phosphate battery material were measured. The test results are shown in Table 3 below.

[0095] Table 3 - Electrical performance test results of lithium manganese iron phosphate materials prepared in the application examples and comparative application examples of this application

[0096]

[0097]

[0098] As shown in Table 3, the lithium manganese iron phosphate material prepared from the lithium pre-doped amine coordinated manganese iron phosphate precursor in the embodiments of this application has higher reversible capacity and higher capacity retention after cycling, indicating good electrocycle stability.

[0099] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for preparing a lithium pre-doped amine-coordinated manganese iron phosphate precursor from lithium manganese iron phosphate, characterized in that, The method comprises the following steps: (1) mixing lithium manganese iron phosphate battery material with a high-valence iron salt solution, then stirring and reacting with a surfactant, and filtering to obtain a filtrate and a phosphorus iron residue; (2) mixing the filtrate with a phosphate salt to adjust the phosphorus content, and adding an acid to adjust the pH of the solution to 2-6 to obtain a phosphorus adjustment and acid adjustment solution; (3) mixing the phosphorus adjustment and acid adjustment solution with an oxidizing agent A, then adding a mixed solution containing an organic amine compound to perform nucleation precipitation reaction, and performing aging and separation to obtain a mother liquor and a lithium pre-doped amine complexed manganese iron phosphate precursor; In step (1), the surfactant is at least one of octanoyl hydroxamic acid, acetyl hydroxamic acid, hydroxyacetamide, acetyl hydroxamic acid ethyl ester, salicyl hydroxamic acid, secondary hydroxyl hydroxamic acid, benzyl hydroxamic acid or N-benzoyl-N-phenyl hydroxylamine.

2. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 1, characterized in that, In step (1), the surfactant is at least one of octanoyl hydroxamic acid, acetyl hydroxamic acid, hydroxyacetamide, acetyl hydroxamic acid ethyl ester, salicyl hydroxamic acid, secondary hydroxyl hydroxamic acid, benzyl hydroxamic acid or N-benzoyl-N-phenyl hydroxylamine.

3. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 1, characterized in that, In step (1), at least one of a)-d) is satisfied: a) the molar ratio of the high-valence iron salt to the phosphorus in the lithium manganese iron phosphate battery material is (0.8-1.1):1; b) the molar ratio of the surfactant to the iron salt is (0.06-0.12):1; c) the high-valence iron salt is one of ferric chloride, ferric nitrate, ferric sulfate, ferric oxalate, ferric citrate or ferric acetate; d) the reaction time is 8-10h.

4. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 1, characterized in that, In step (2), the phosphate salt is at least one of sodium phosphate, monoammonium phosphate, sodium dihydrogen phosphate or disodium hydrogen phosphate; and the acid is an inorganic acid or an organic acid.

5. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 4, characterized in that, In step (2), the inorganic acid is one of sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid; and the organic acid is one of formic acid, acetic acid, propionic acid, butyric acid, octanoic acid, adipic acid, ethanedioic acid, propanedioic acid, butanedioic acid, maleic acid, tartaric acid, benzoic acid, phenylacetic acid, phthalic acid, terephthalic acid, valeric acid, hexanoic acid, capric acid, stearic acid, palmitic acid or acrylic acid.

6. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 1, characterized in that, In step (3), at least one of a)-f) is satisfied: a) the oxidizing agent A is one of hydrogen peroxide, sodium peroxide, potassium peroxide, ozone or sodium hypochlorite; b) the organic amine compound is at least one of methylamine, ethylamine, furfurylamine, benzylamine, isopropyl alcohol amine, ethylenediamine, propylenediamine, dicyanediamine or 1,2-propylenediamine; c) the total molar amount ratio of the organic amine compound to manganese iron in the solution is (0.05-0.25):1; d) the total molar amount ratio of the oxidizing agent A to manganese iron in the solution is (1.05-1.2):1; e) the nucleation precipitation reaction temperature is 70-95℃, and the stirring rate is 250-450r / min; f) the aging temperature is 80-90℃, the stirring rate is 150-350r / min, and the time is 6-12h.

7. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 1, characterized in that, In step (3), the mixed solution containing the organic amine compound is sprayed into the solution system, the particle size of the spray droplets is controlled to be 0.8-2.5μm, and the mixed solution containing the organic amine compound further comprises 0.1-0.6wt% of the same surfactant as in step (1).

8. The method for preparing lithium pre-doped amine coordinated manganese iron phosphate precursor from lithium manganese iron phosphate according to claim 1, characterized in that, In step (3), the lithium-iron-manganese-phosphorus mother liquor is oxidized by adding an oxidant B, the molar ratio of the oxidant B to the total amount of manganese and iron in the mother liquor is (1-1.15):1, and the pH is adjusted to 8-12 to precipitate the manganese and iron metals to obtain a lithium-containing solution and a precipitate, and lithium is precipitated from the lithium-containing solution by adding a carbonate to obtain lithium carbonate.

9. A method for preparing lithium pre-doped amine-coordinated manganese iron phosphate precursor by using the lithium manganese iron phosphate prepared according to any one of claims 1-8.

10. A lithium iron manganese phosphate battery material characterized in that, The lithium pre-doped amine-coordinated manganese iron phosphate precursor is prepared by using the lithium pre-doped amine-coordinated manganese iron phosphate precursor according to claim 9.

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