An electrode active material, a preparation method thereof, and a preparation method of carbon-coated lithium manganese iron phosphate

Abstract

The present application belongs to the technical field of electrode material, and particularly relates to an electrode active material, a preparation method thereof, and a preparation method of carbon-coated lithium manganese iron phosphate. The electrode active material obtained by the method is a uniform solid solution, and each element is uniformly distributed, so that the positive electrode material is prevented from being separated, and the product is ensured to have high chemical performance. The obtained active material has a porous structure, which is helpful to realize high specific capacity, excellent rate performance and good cycle stability of the final positive electrode material. In addition, this structure is also beneficial to realize sufficient carbon coating in the production process of the positive electrode material, and further improve the performance of the material. In addition, the preparation method provided by the present application is environmentally friendly and economical, and can be produced on a large scale in a commercialized manner. After treatment, the waste gas can be discharged in a standard manner, and clean production is realized. Furthermore, the tail gas treatment system is further added, so that the hydrochloric acid generated in the production process can be recycled and used.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to an electrode active material, a preparation method thereof, and a preparation method of carbon-coated lithium manganese iron phosphate. BACKGROUND

[0002] Lithium ion batteries have high energy density, long cycle life, no memory effect and other advantages, and are widely used in electronic products, electric transportation, energy storage and other fields. The positive electrode materials of lithium ion batteries mainly include lithium cobaltate, lithium manganate, nickel-cobalt-manganese (ternary) system, lithium iron phosphate, lithium manganese iron phosphate and the like. With the application of lithium ion batteries, the cost performance of commercial products for lithium ion batteries is increasingly required, mainly reflected in the increasingly fierce competition of battery manufacturers for the cost per watt hour of the battery. In recent years, the market share of lithium iron phosphate has exceeded that of ternary, on the one hand because lithium iron phosphate is safer, and on the other hand because the price of lithium iron phosphate is lower. Lithium manganese iron phosphate is a cosolute of lithium manganese phosphate and lithium iron phosphate, has similar high safety and stability to lithium iron phosphate, and has a higher platform voltage and energy density. The working voltage (4.1V) is 20% higher than that of lithium iron phosphate (3.4V), and the theoretical energy density is about 20% higher than that of lithium iron phosphate. The theoretical cost of lithium manganese iron phosphate battery is lower than that of lithium iron phosphate, so the material end, battery end and vehicle manufacturer gradually deepen the research on lithium manganese iron phosphate, which is considered to be the most potential next-generation lithium ion power battery positive electrode material.

[0003] The synthesis method of lithium manganese iron phosphate mainly includes solid phase method and liquid phase method. The solid phase method adopts manganese source, iron source, phosphorus source and lithium source for mixed sintering, which has the advantages of simple process, less required equipment, easy production and low cost, and is widely used in the preparation of lithium manganese iron phosphate positive electrode material. The liquid phase method mainly includes sol-gel method, solvothermal method, hydrothermal method and spray drying method. Taking the sol-gel method as an example, the phosphorus source, manganese source (manganese nitrate), iron source (ferric nitrate) and lithium source are uniformly dissolved in a certain proportion to obtain a liquid slurry. After preheating, a honeycomb-shaped gel is formed, which is crushed, rolled, sintered and ground to obtain lithium manganese iron phosphate product.

[0004] However, the lithium manganese iron phosphate positive electrode material prepared by the existing solid phase method and liquid phase method is not a uniform solid solution, and there is a problem of uneven distribution of phosphorus, iron and manganese elements, which causes local manganese enrichment or iron enrichment, causes phase separation, and aggravates the Jahn-Teller effect and cooperative elastic deformation of Mn 3+ ions, thereby accelerating the distortion of the crystal structure, reducing the lithium ion transmission rate, rate performance, specific capacity and cycle performance, and making it difficult to meet the actual application requirements, thereby restricting the commercial application process of lithium manganese iron phosphate material. SUMMARY

[0005] The application aims to provide an electrode active material and a preparation method thereof, and a preparation method of carbon-coated lithium manganese iron phosphate.

[0006] To achieve the above-mentioned purpose, the application provides the following technical scheme.

[0007] The application provides a preparation method of an electrode active material, comprising the following steps.

[0008] Mixing an iron source and a hydrochloric acid solution to obtain an iron source solution;

[0009] Mixing the iron source solution and an additive to obtain a mixed solution;

[0010] Carrying out atomization and high-temperature synthesis on the mixed solution in sequence to obtain the electrode active material;

[0011] The additive comprises an additive 1, an additive 2 or an additive 3;

[0012] The additive 1 comprises a manganese source;

[0013] The additive 2 comprises a manganese source, phosphoric acid and a reducing agent;

[0014] The additive 3 comprises a manganese source, a phosphorus source, a lithium source and a reducing agent.

[0015] Preferably, the iron source comprises one or more of Fe, FeO, Fe2O3, Fe3O4, FeCl2, FeCl3, FeCO3, FeC2O4 and FeOOH;

[0016] The molar ratio of Fe element and H + in the iron source solution is 1:2-8.

[0017] Preferably, the molar ratio of Fe element and H + in the iron source solution is 1:2-8.

[0018] Preferably, the manganese source comprises one or more of Mn, MnO, MnCl2, MnCO3 and MnC2O4;

[0019] The phosphorus source comprises one or more of phosphoric acid, lithium phosphate and lithium dihydrogen phosphate;

[0020] The lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium phosphate and lithium dihydrogen phosphate.

[0021] Preferably, when the additive is additive 1, the concentration of manganese iron ions in the mixed solution is 60-300 g / L, wherein Mn 2+ The amount of substance of the substance is 0.1-1 times the amount of substance of manganese iron ions, and is not 1;

[0022] When the additive is additive 2, the concentration of manganese iron ions in the mixed solution is 60-300 g / L; wherein Mn 2+ The amount of substance of the substance is 0.1-1 times the amount of substance of manganese iron ions, and is not 1; the ratio of the total amount of substance of manganese iron ions to the amount of substance of phosphorus element is 0.95-1.0:1 in terms of the amount of substance of phosphorus element;

[0023] When the additive is additive 3, the concentration of manganese iron ions in the mixed solution is 60-300 g / L; wherein Mn 2+ The amount of substance of the substance is 0.1-1 times the amount of substance of manganese iron ions, and is not 1; the ratio of the total amount of substance of manganese iron ions to the amount of substance of phosphorus element is 0.95-1.0:1 in terms of the amount of substance of phosphorus element; the ratio of the amount of substance of lithium element to the amount of substance of phosphorus element is 0.95-1.05:1.

[0024] Preferably, the reducing agent comprises one or more of citric acid, oxalic acid, tartaric acid, formic acid and hydroxylamine hydrochloride;

[0025] The mass of the reducing agent is 1-5% of the mass of the electrode active material.

[0026] Preferably, the atomization method is gas-liquid two-fluid atomization; the atomization gas pressure is 0.3-0.8 MPa, and the average particle size of the atomized mist droplets is 10-100 μm.

[0027] Preferably, when the additive is additive 1, the high-temperature synthesis temperature is 500-1000°C, and the holding time is 10-60 s;

[0028] When the additive is additive 2, the high-temperature synthesis temperature is 500-800°C, and the holding time is 10-60 s;

[0029] When the additive is additive 3, the high-temperature synthesis temperature is 600-900°C, and the holding time is 10-60 s.

[0030] The application also provides an electrode active material prepared by the preparation method described in the above technical solution; when the additive is additive 1, the electrode active material is electrode active material 1, which is a manganese iron oxide, and the chemical composition of the manganese iron oxide is (Mn x Fe 1-x)2O3, wherein 0.1≤x<1;

[0031] When the additive is the additive 2, the electrode active material is recorded as electrode active material 2, the electrode active material 2 is ferromanganous pyrophosphate, and the chemical composition of the ferromanganous pyrophosphate is (Mn x Fe 1-x )2P2O7, wherein 0.1≤x<1;

[0032] When the additive is the additive 3, the electrode active material is recorded as electrode active material 3, the electrode active material 3 is lithium iron manganese phosphate, and the chemical composition of the lithium iron manganese phosphate is LiMn x Fe 1-x PO4, wherein 0.1≤x<1;

[0033] The electrode active material has a porous structure.

[0034] The application further provides a preparation method of the carbon-coated lithium iron manganese phosphate, comprising the following steps:

[0035] The electrode active material is provided, and the electrode active material is the electrode active material in the above technical solution.

[0036] The electrode active material is carbon-coated to obtain the carbon-coated lithium iron manganese phosphate.

[0037] When the electrode active material is the electrode active material 1, the carbon-coating process is that the electrode active material 1, lithium dihydrogen phosphate and a carbon source are mixed and calcined.

[0038] When the electrode active material is the electrode active material 2, the carbon-coating process is that the electrode active material 2, a lithium source and a carbon source are mixed and calcined; and the lithium source includes lithium carbonate or lithium hydroxide.

[0039] When the electrode active material is the electrode active material 3, the carbon-coating process is that the electrode active material 3 and a carbon source are mixed and calcined.

[0040] Preferably, the calcination temperature is 500-900℃, and the holding time is 3-20h.

[0041] The application provides a preparation method of an electrode active material, comprising the following steps: mixing a ferrous source and a hydrochloric acid solution to obtain a ferrous source solution; mixing the ferrous source solution and an additive to obtain a mixed solution; and sequentially performing atomization and high-temperature synthesis on the mixed solution to obtain the electrode active material; the additive includes an additive 1, an additive 2 or an additive 3; the additive 1 includes a manganese source; the additive 2 includes a manganese source, phosphoric acid and a reducing agent; and the additive 3 includes a manganese source, a phosphorus source, a lithium source and a reducing agent.

[0042] The present application has the advantages of:

[0043] 1. The obtained active material is a uniform solid solution, and each element is uniformly distributed, avoiding phase separation of the positive electrode material and ensuring high chemical performance of the product;

[0044] 2. The obtained active material has a porous structure, which helps to achieve high specific capacity, excellent rate performance and good cycle stability of the final positive electrode material. In addition, this structure is also beneficial to achieve sufficient carbon coating during the production process of the positive electrode material, further improving the performance of the material.

[0045] 3. Environmentally friendly and economical, large-scale commercial production can be realized; after treatment, the waste gas meets the emission standard, realizing clean production; further increasing the tail gas treatment system, so that the hydrochloric acid produced in the production process can be recycled and used.

[0046] 4. Fast reaction speed, high production efficiency, short production process; stable condition control, stable product performance, and low manufacturing cost.

[0047] The present application also provides a preparation method of carbon-coated lithium manganese iron phosphate. The carbon-coated lithium manganese iron phosphate obtained by the present application has excellent electrochemical performance as a positive electrode material of a lithium ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 It is a flowchart of the preparation method when the electrode active material is manganese iron oxide;

[0049] Figure 2 It is a flowchart of the preparation method when the electrode active material is manganese iron pyrophosphate;

[0050] Figure 3 It is a flowchart of the preparation method when the electrode active material is lithium manganese iron phosphate;

[0051] Figure 4 It is an XRD pattern of the manganese iron oxide obtained in Example 1;

[0052] Figure 5 It is an SEM pattern of the manganese iron oxide obtained in Example 1;

[0053] Figure 6 It is an XRD pattern of the manganese iron pyrophosphate obtained in Example 2;

[0054] Figure 7 It is an SEM pattern of the manganese iron pyrophosphate obtained in Example 2;

[0055] Figure 8 It is an XRD pattern of the lithium manganese iron phosphate obtained in Example 3;

[0056] Figure 9 SEM image of lithium manganese iron phosphate obtained in Example 3;

[0057] Figure 10 First discharge curve of the assembled button cell of the carbon-coated lithium manganese iron phosphate obtained in Examples 4-6. DETAILED DESCRIPTION

[0058] The application provides a preparation method of an electrode active material, comprising the following steps:

[0059] mixing an iron source and a hydrochloric acid solution to obtain an iron source solution;

[0060] mixing the iron source solution and an additive to obtain a mixed solution;

[0061] sequentially performing atomization and high-temperature synthesis on the mixed solution to obtain the electrode active material;

[0062] the additive comprises an additive 1, an additive 2 or an additive 3;

[0063] the additive 1 comprises a manganese source;

[0064] the additive 2 comprises a manganese source, phosphoric acid and a reducing agent;

[0065] the additive 3 comprises a manganese source, a phosphorus source, a lithium source and a reducing agent.

[0066] The application mixes an iron source and a hydrochloric acid solution to obtain an iron source solution.

[0067] In the application, the iron source preferably comprises one or more of Fe, FeO, Fe2O3, Fe3O4, FeCl2, FeCl3, FeCO3, FeC2O4 and FeOOH.

[0068] In the application, the concentration of H + The concentration is preferably 4-12 mol / L, and specifically can be 4.5 mol / L, 5.5 mol / L or 8 mol / L; the ratio of the amount of substance of Fe element to the amount of substance of H + In the application, the mixing is preferably performed under stirring.

[0069] In the application, the reactions of different iron sources during mixing are as follows:

[0070] Fe + 2H + = Fe 2+ + H2↑

[0071] FeO + 2H + = Fe 2+ + H2O

[0072] Fe2O3+6H + =2Fe 3+ +3H2O

[0073] Fe3O4+8H + =2Fe 3+ +Fe 2+ +4H2O

[0074] FeCO3+2H + =Fe 2+ +H2O+CO2↑

[0075] FeC2O4+2H + =Fe 2+ +H2C2O4

[0076] FeOOH+3H + =Fe 3+ +2H2O

[0077] After obtaining the iron source solution, the iron source solution and an additive are mixed to obtain a mixed solution.

[0078] In the present application, the additive comprises additive 1, additive 2 or additive 3. In the present application, the additive 1 comprises a manganese source; the additive 2 comprises a manganese source, phosphoric acid and a reducing agent; and the additive 3 comprises a manganese source, a phosphorus source, a lithium source and a reducing agent. In the present application, the manganese source preferably comprises one or more of Mn, MnO, MnCl2, MnCO3 and MnC2O4; the phosphorus source preferably comprises one or more of phosphoric acid, lithium phosphate and dihydrogen phosphate; and the lithium source preferably comprises one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium phosphate and dihydrogen phosphate.

[0079] In the present application, when the additive is additive 1, the concentration of manganese-iron ions in the mixed solution is preferably 60-300 g / L, and further preferably 80-240 g / L; and the manganese-iron ions preferably comprise Mn 2+ , Fe 2+ and Fe 3+ ; wherein the amount of substance of Mn 2+ preferably accounts for 0.1-1 of the amount of substance of manganese-iron ions, and is not 1, and further preferably 0.5-0.8.

[0080] In the present application, when the additive is additive 2, the concentration of manganese-iron ions in the mixed solution is preferably 60-300 g / L, and further preferably 80-240 g / L; and the manganese-iron ions preferably comprise Mn 2+ and Fe 2+ ; wherein the amount of substance of Mn 2+The amount of substance of Mn is preferably 0.1-1, and not 1, and further preferably 0.5-0.8, of the amount of substance of the manganese-iron ion. In the present application, the ratio of the total amount of substance of the manganese-iron ion to the amount of substance of phosphorus element is preferably 0.95-1.0:1. In the present application, the reducing agent preferably includes one or more of citric acid, oxalic acid, tartaric acid, formic acid and hydroxylamine hydrochloride; and the amount of the reducing agent is preferably 1-5% of the mass of the electrode active material. In the present application, when the additive is additive 2, the process of mixing the iron source solution and the additive is preferably as follows: the iron source solution, manganese source and reducing agent are premixed, and then phosphoric acid is added.

[0081] In the present application, when the additive is additive 3, the concentration of the manganese-iron ion in the mixed solution is preferably 60-300 g / L, and further preferably 80-240 g / L; and the manganese-iron ion preferably includes Mn 2+ and Fe 2+ ; wherein the amount of substance of Mn 2+ is preferably 0.1-1, and not 1, and further preferably 0.5-0.8, of the amount of substance of the manganese-iron ion. The ratio of the total amount of substance of the manganese-iron ion to the amount of substance of phosphorus element is preferably 0.95-1.0:1, and the ratio of the amount of substance of lithium element to the amount of substance of phosphorus element is preferably 0.95-1.05:1. In the present application, the type of the reducing agent and the amount of addition are the same as those defined in the above technical solution, and will not be described here again. In the present application, when the additive is additive 3, the process of mixing the iron source solution and the additive is preferably as follows: the iron source solution, manganese source and reducing agent are premixed, and then a phosphorus source and a lithium source are added.

[0082] In the present application, the reaction that occurs when the manganese source is added to the iron source solution is as shown below:

[0083] 2Fe 3+ + Mn = 2Fe 2+ + Mn 2+

[0084] Mn + 2H + = Mn 2+ + H2↑

[0085] MnO + 2H + = Mn 2+ + H2O

[0086] MnCO3 + 2H + = Mn 2+ + H2O + CO2↑

[0087] MnC2O4 + 2H + = Mn 2++ H2C2O4

[0088] After obtaining the mixed solution, the present application sequentially carries out atomization and high-temperature synthesis on the mixed solution to obtain the electrode active material.

[0089] Before the atomization, the present application further preferably comprises filtering the mixed solution and then transferring the mixed solution to an atomizer for atomization. In the present application, the atomization is preferably gas-liquid two-fluid atomization; when the additive is additive 1, the gas used for the atomization is preferably air or oxygen; when the additive is additive 2 or additive 3, the gas used for the atomization is preferably nitrogen; the gas pressure of the atomization is preferably 0.3-0.8 MPa, and the average particle size of the atomized mist liquid droplets is preferably 10-100 μm.

[0090] In the present application, when the additive is additive 1, the temperature of the high-temperature synthesis is preferably 500-1000 ℃, and the holding time is preferably 10-60 s; when the additive is additive 2, the temperature of the high-temperature synthesis is preferably 500-800 ℃, and the holding time is preferably 10-60 s; when the additive is additive 3, the temperature of the high-temperature synthesis is preferably 600-900 ℃, and the holding time is preferably 10-60 s. In the present application, the high-temperature synthesis is preferably carried out in an atomization high-temperature synthesis furnace, which uses an internal heating mode, i.e. heating by a burner flame, and the heat source is high-temperature gas formed after natural gas combustion; when the additive is additive 1, the oxygen content in the high-temperature gas is preferably 1%-10%; when the additive is additive 2 or additive 3, the oxygen content in the high-temperature gas is preferably less than 1%.

[0091] In the present application, when the additive is additive 1, the mist liquid droplets sequentially undergo high-temperature drying and pyrolysis reaction in the process of high-temperature synthesis to obtain solid powder and flue gas, and the reactions are as shown below:

[0092] 2Fe 3+ + 6Cl - + 3H2O = Fe2O3 + 6HCl↑

[0093] 4Fe 2+ + 8Cl - + O2 + 4H2O = 2Fe2O3 + 8HCl↑

[0094] 4Mn 2+ + 8Cl - + O2 + 4H2O = 2Mn2O3 + 8HCl↑

[0095] xMn2O3 + (1-x)Fe2O3 = (Mn x Fe 1-x )2O3

[0096] In the present application, when the additive is additive 2 or additive 3, the mist droplets sequentially undergo high-temperature drying, precipitation reaction and condensation reaction in the process of high-temperature synthesis, to obtain solid powder and flue gas; the reducing agent decomposes and carbonizes to consume oxygen in the flue gas at high temperature, preventing the oxidation of ferrous ions, and leaving a small amount of carbon residue in the solid powder.

[0097] In the present application, when the additive is additive 2, the reactions occurring in the process of high-temperature synthesis are as follows:

[0098] FeCl2+ H3PO4 = FeHPO4+ 2HCl↑

[0099] MnCl2+ H3PO4 = MnHPO4+ 2HCl↑

[0100] 2xMnHPO4+ 2(1-x)FeHPO4= (Mn x Fe 1-x )2P2O7+ H2O↑

[0101] In the present application, when the additive is additive 3, and the phosphorus source is phosphoric acid and the lithium source is lithium chloride, the reactions occurring in the process of high-temperature synthesis are as follows:

[0102] FeCl2+ H3PO4 = FeHPO4+ HCl↑

[0103] MnCl2+ H3PO4 = MnHPO4+ HCl↑

[0104] LiCl + xMnHPO4+ (1-x)FeHPO4 = LiMn x Fe 1-x PO4+ HCl↑

[0105] In the present application, the high-temperature synthesis preferably obtains solid powder and flue gas. After obtaining the flue gas, the present application further preferably comprises post-treating the flue gas, and the post-treatment preferably comprises:

[0106] carrying out gas-solid separation on the flue gas to obtain acid gas and solid particles;

[0107] carrying out acid regeneration on the acid gas, and recycling the obtained acid to the preparation process of the iron source solution for cyclic use;

[0108] mixing the solid particles and the solid powder, and then crushing to obtain the electrode active material.

[0109] In the present application, the method of crushing preferably comprises airflow crushing, mechanical crushing, dry ball milling or wet grinding.

[0110] The application further provides an electrode active material prepared by the preparation method, when the additive is additive 1, the electrode active material is recorded as electrode active material 1, the electrode active material 1 is manganese iron oxide, the chemical composition of the manganese iron oxide is (Mn x Fe 1-x )2O3, wherein 0.1≤x<1;

[0111] When the additive is additive 2, the electrode active material is recorded as electrode active material 2, the electrode active material 2 is manganese iron pyrophosphate, the chemical composition of the manganese iron pyrophosphate is (Mn x Fe 1-x )2P2O7, wherein 0.1≤x<1;

[0112] When the additive is additive 3, the electrode active material is recorded as electrode active material 3, the electrode active material 3 is lithium manganese iron phosphate, the chemical composition of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, wherein 0.1≤x<1;

[0113] The electrode active material has a porous structure.

[0114] In the application, the average particle size of the manganese iron oxide is preferably 2-10 μm, the loose bulk density is preferably 0.6-1.2 g / cm 3 , and the tap density is preferably 1.0-2.0 g / cm 3 .

[0115] In the application, the average particle size of the manganese iron pyrophosphate is preferably 2-10 μm, the loose bulk density is preferably 0.2-0.4 g / cm 3 , the tap density is preferably 0.4-0.8 g / cm 3 , and the carbon content is preferably less than 0.2%.

[0116] In the application, the average particle size of the lithium manganese iron phosphate is preferably 2-10 μm, the loose bulk density is preferably 0.2-0.6 g / cm 3 , the tap density is preferably 0.5-1.0 g / cm 3 , and the carbon content is preferably less than 0.5%.

[0117] In the application, the flowchart of the preparation method when the electrode active material is manganese iron oxide is as shown in Figure 1 , the flowchart of the preparation method when the electrode active material is manganese iron pyrophosphate is as shown in Figure 2 , and the flowchart of the preparation method when the electrode active material is lithium manganese iron phosphate is as shown in Figure 3 .

[0118] The application further provides a preparation method of the carbon-coated lithium manganese iron phosphate, comprising the following steps:

[0119] The electrode active material is provided, and the electrode active material is the electrode active material in the above technical solution.

[0120] The electrode active material is carbon-coated to obtain the carbon-coated lithium manganese iron phosphate.

[0121] When the electrode active material is the electrode active material 1, the carbon-coating process is that the electrode active material 1, lithium dihydrogen phosphate and a carbon source are mixed and calcined.

[0122] When the electrode active material is the electrode active material 2, the carbon-coating process is that the electrode active material 2, a lithium source and a carbon source are mixed and calcined; the lithium source comprises lithium carbonate or lithium hydroxide.

[0123] When the electrode active material is the electrode active material 3, the carbon-coating process is that the electrode active material 3 and a carbon source are mixed and calcined.

[0124] In the application, when the electrode active material is the electrode active material 1 or the electrode active material 2, the ratio of the total amount of substance of manganese elements and iron elements to the amount of substance of lithium elements is preferably 1:1.00-1.05 in terms of lithium elements, manganese elements and iron elements.

[0125] In the application, the carbon source preferably comprises one or more of glucose, sucrose, soluble starch and polyethylene glycol. In the application, the mass percentage of the carbon-coating layer on the carbon-coated lithium manganese iron phosphate is preferably 1.5-2.5%. In the application, the mixing mode is preferably grinding mixing. In the application, the calcination temperature is preferably 500-900℃, and further preferably 600-800℃; the holding time is preferably 3-20h, and further preferably 4-10h.

[0126] Unless otherwise specified, the materials and equipment used in the application are commercially available in the art.

[0127] The technical solutions in the application will be described clearly and completely in combination with the embodiments in the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0128] Embodiment 1

[0129] Fe2O3 is added into the hydrochloric acid solution under stirring to obtain an iron source solution, wherein the concentration of H + is 8.0 mol / L, and the molar ratio of Fe element to H + is 1:6.4;

[0130] MnCO3 is added into the iron source solution to obtain a mixed solution, wherein the concentration of manganese-iron ions is 230 g / L, and the molar ratio of Mn 2+ in the manganese-iron ions is 70%;

[0131] The obtained mixed solution is filtered and transferred to an atomizer to be atomized into mist liquid droplets, wherein the gas used for atomization is air, the atomization gas pressure is 0.45 MPa, and the average particle size of the obtained mist liquid is 38 μm;

[0132] The obtained mist liquid droplets are subjected to high-temperature synthesis at 700℃ (wherein the content of oxygen in the high-temperature gas is 9%), and the temperature is maintained for 25 s to obtain solid powder and flue gas; the flue gas is subjected to gas-solid separation to obtain acid gas and solid particles; the acid gas is subjected to acid regeneration, and the recovered acid is returned to the preparation process of the iron source solution for recycling; the solid particles and the solid powder are mixed and then crushed in an airflow crusher to obtain manganese-iron oxide (Mn 0.7 Fe 0.3 )2O3 powder, and the relevant physicochemical parameters are shown in Table 1.

[0133] Example 2

[0134] FeO is added into the hydrochloric acid solution under stirring to obtain an iron source solution, wherein the concentration of H + is 5.5 mol / L, and the molar ratio of Fe element to H + is 1:5.5;

[0135] Mn and citric acid (mass fraction of 4% of the electrode active material) are added into the iron source solution and uniformly mixed, and then phosphoric acid is added to obtain a mixed solution, wherein the concentration of manganese-iron ions is 158 g / L, the molar ratio of Mn 2+ in the manganese-iron ions is 65%, and the molar ratio of the total amount of manganese-iron ions to the amount of phosphorus element is 0.98:1;

[0136] The obtained mixed solution is filtered and transferred to an atomizer to be atomized into mist liquid droplets, wherein the gas used for atomization is nitrogen, the atomization gas pressure is 0.50 MPa, and the average particle size of the obtained mist liquid is 29 μm;

[0137] The mist liquid droplets obtained are subjected to high-temperature synthesis at 680°C (wherein the oxygen content in the high-temperature gas is 0.2%), and the temperature is kept for 20 s, to obtain solid powder and flue gas; the flue gas is subjected to gas-solid separation to obtain acid gas and solid particles; the acid gas is subjected to acid regeneration, and the recovered acid is returned to the preparation process of the iron source solution for recycling; the solid particles and the solid powder are mixed and then subjected to crushing in a mechanical crusher to obtain Mn 0.65 Fe 0.35 )2P2O7 powder, and the relevant physicochemical parameters are shown in Table 1.

[0138] Example 3

[0139] Fe is added to the hydrochloric acid solution under stirring to obtain an iron source solution, wherein the concentration of H + is 4.5 mol / L, and the amount-of-substance ratio of Fe element to H + is 1:4.5;

[0140] Mn and oxalic acid (3% of the mass fraction of the electrode active material) are added to the iron source solution and mixed uniformly, and then phosphoric acid and lithium chloride are added to obtain a mixed solution, wherein the concentration of manganese-iron ions is 138 g / L, the amount-of-substance ratio of Mn 2+ in the manganese-iron ions is 60%, the total amount-of-substance ratio of manganese-iron ions to phosphorus element is 0.99:1, and the amount-of-substance ratio of lithium element to phosphorus element is 1.02:1;

[0141] The mixed solution obtained is filtered and then transferred to an atomizer to be atomized into mist liquid droplets, wherein the gas used for atomization is nitrogen, the atomization gas pressure is 0.58 MPa, and the average particle size of the mist liquid obtained is 22 μm;

[0142] The mist liquid droplets obtained are subjected to high-temperature synthesis at 720°C (wherein the oxygen content in the high-temperature gas is 0.15%), and the temperature is kept for 30 s, to obtain solid powder and flue gas; the flue gas is subjected to gas-solid separation to obtain acid gas and solid particles; the acid gas is subjected to acid regeneration, and the recovered acid is returned to the preparation process of the iron source solution for recycling; the solid particles and the solid powder are mixed and then subjected to crushing in an airflow crusher to obtain lithium manganese iron phosphate LiMn 0.6 Fe 0.4 PO4 powder, and the relevant physicochemical parameters are shown in Table 1.

[0143] Table 1 Physicochemical parameters of the electrode active material obtained in the examples

[0144]

[0145] Example 4

[0146] 2000g of manganese iron oxide, 2650.4g of lithium dihydrogen phosphate, 160g of polyethylene glycol, and 500g of anhydrous glucose obtained in Example 1 were ground and mixed, wherein the total molar ratio of manganese and iron to lithium was 1:1.01. The resulting mixture was calcined at 745°C for 10 hours to obtain carbon-coated manganese iron phosphate. The relevant physicochemical parameters are shown in Table 2.

[0147] Example 5

[0148] 2000g of ferromanganese pyrophosphate, 262g of lithium carbonate, 50g of polyethylene glycol, and 160g of anhydrous glucose obtained in Example 2 were ground and mixed, wherein the total amount of manganese and iron and the amount of lithium were in a ratio of 1:1.01. The resulting mixture was calcined at 720°C for 8 hours to obtain carbon-coated lithium manganese iron phosphate. The relevant physicochemical parameters are shown in Table 2.

[0149] Example 6

[0150] 2000g of lithium manganese iron phosphate, 40g of polyethylene glycol, and 120g of anhydrous glucose obtained in Example 3 were ground and mixed. The resulting mixture was calcined at 700℃ for 6 hours to obtain carbon-coated lithium manganese iron phosphate. The relevant physicochemical parameters are shown in Table 2.

[0151] Table 2. Physicochemical parameters of carbon-coated lithium manganese iron phosphate obtained in the examples.

[0152]

[0153] Performance testing

[0154] Test Example 1

[0155] Figure 4 The manganese iron oxide (Mn) obtained in Example 1 0.7 Fe 0.3 The XRD pattern of )2O3 shows that the substance synthesized in Example 1 corresponds to the (Mn) standard card PDF#71-0637. 0.37 Fe 0.63 The presence of 2O3 completely corresponds to the presence of no other impurities, suggesting that the sample from Example 1 formed a manganese iron oxide solid solution. Figure 5 The image shows a SEM image of the manganese iron oxide obtained in Example 1. Figure 5 It can be seen that the sample has a porous structure, with primary particle size of approximately 200~400nm and smooth, rounded particle surface.

[0156] Figure 6 The manganese ferrous pyrophosphate (Mn) obtained in Example 2 0.65 Fe 0.35The XRD pattern of 2P2O7, from the figure, it can be seen that the substance synthesized in Example 2 corresponds to Mn2P2O7 corresponding to the standard card PDF #77-1244, without other impurities, it is inferred that the sample of Example 2 forms a pyrophosphite manganese iron solid solution. Figure 7 The SEM pattern of the pyrophosphite manganese iron obtained in Example 2, from Figure 7 It can be seen that the sample is a porous structure, the primary particle size is small, about 100-200 nm, the particle surface is smooth and round, and it is suitable for preparing high-performance carbon-coated lithium manganese iron phosphate positive electrode material.

[0157] Figure 8 The XRD pattern of lithium manganese iron phosphate LiMnPO4 obtained in Example 3, from the figure, it can be seen that the substance synthesized in Example 3 is between LiMnPO4 corresponding to the standard card PDF #77-0178 and LiFePO4 corresponding to PDF #40-1499, without other impurities, it is inferred that the sample of Example 3 forms a lithium manganese iron phosphate solid solution. 0.6 Fe 0.4 PO4, from the figure, it can be seen that the substance synthesized in Example 3 is between LiMnPO4 corresponding to the standard card PDF #77-0178 and LiFePO4 corresponding to PDF #40-1499, without other impurities, it is inferred that the sample of Example 3 forms a lithium manganese iron phosphate solid solution. Figure 9 The SEM pattern of lithium manganese iron phosphate obtained in Example 3, from Figure 9 It can be seen that the sample is a porous structure, the primary particle size is about 200-400 nm, the particle surface is smooth and round, and it is suitable for preparing high-performance carbon-coated lithium manganese iron phosphate positive electrode material.

[0158] Test Example 2

[0159] The carbon-coated lithium manganese iron phosphate positive electrode material prepared in Examples 4-6 was prepared into a positive electrode sheet, and a button cell was assembled according to the standard of GB 31241-2014. The electrochemical performance of the button cell was tested by using a blue electricity test system (range I: 10 mA; range U: 5 V). The test voltage interval was 2.5-4.5 V, and the first charge-discharge performance was tested at 0.1 C. Figure 10 The first discharge curve of the button cell assembled by the carbon-coated lithium manganese iron phosphate obtained in Examples 4-6, it can be seen that the carbon-coated lithium manganese iron phosphate positive electrode material prepared by the method has a first discharge specific capacity of 154.2 mAh / g, 157.4 mAh / g, and 159.5 mAh / g, respectively, which is higher than that of a certain commercially available product of 150.8 mAh / g.

[0160] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. A method for preparing carbon-coated lithium iron manganese phosphate, characterized in that, The method comprises the following steps: Providing an electrode active material; the electrode active material has a porous structure; Carbon-coating the electrode active material to obtain the carbon-coated lithium manganese iron phosphate; The preparation method of the electrode active material comprises the following steps: mixing an iron source and a hydrochloric acid solution to obtain an iron source solution; Mixing the iron source solution and an additive to obtain a mixed solution; and sequentially performing atomization and high-temperature synthesis on the mixed solution to obtain the electrode active material; The additive is additive 2 or additive 3; the additive 2 is an iron source, phosphoric acid and a reducing agent; the additive 3 is an iron source, a phosphorus source, a lithium source and a reducing agent; the reducing agent is one or more of citric acid, oxalic acid, tartaric acid, formic acid and hydroxylamine hydrochloride; the average particle size of the atomized mist droplets is 10-100 μm; the high-temperature synthesis is performed in a mist high-temperature synthesis furnace, which is heated by an internal heating method, i.e. by a burner flame, and the heat source is high-temperature gas formed after natural gas combustion; when the additive is additive 2, the high-temperature synthesis temperature is 500-800 ℃, and the holding time is 10-60 s; when the additive is additive 3, the high-temperature synthesis temperature is 600-900 ℃, and the holding time is 10-60 s; When the additive is additive 2, the electrode active material is recorded as electrode active material 2, the electrode active material 2 is ferromanganous pyrophosphate, the chemical composition of the ferromanganous pyrophosphate is (Mn x Fe 1-x )2P2O7, wherein 0.1≤x<1; the carbon coating process is: mixing the electrode active material 2, a lithium source and a carbon source, and performing calcination; the lithium source includes lithium carbonate or lithium hydroxide; When the additive is additive 3, the electrode active material is recorded as electrode active material 3, which is lithium manganese iron phosphate, the chemical composition of which is LiMn x Fe 1-x PO4, wherein 0.1≤x<1; the carbon coating process is: mixing electrode active material 3 and a carbon source, and roasting; The calcination temperature is 500-900 ℃, and the holding time is 3-20 h.

2. The production method according to claim 1, characterized by, The iron source includes one or more of Fe, FeO, Fe2O3, Fe3O4, FeCl2, FeCl3, FeCO3, FeC2O4 and FeOOH; H + concentration of 4-12 mol / L; The ratio of the amount of substance of Fe element and H + in the iron source solution to the amount of substance of Fe element and H 3. The preparation method according to claim 2, characterized in that, The manganese source includes one or more of Mn, MnO, MnCl2, MnCO3 and MnC2O4; The phosphorus source includes one or more of phosphoric acid, lithium phosphate and lithium dihydrogen phosphate; The lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium phosphate and lithium dihydrogen phosphate.

4. The production method according to claim 3, characterized by, When the additive is the additive 2, the concentration of the manganese-iron ion in the mixed solution is 60-300 g / L; wherein Mn 2+ The amount of substance of the substance of formula (I) accounts for 0.1-1 of the amount of substance of the manganese-iron ion, and is not 1; the ratio of the total amount of substance of the manganese-iron ion and the amount of substance of phosphorus element is 0.95-1.0:1 in terms of the amount of substance of phosphorus element; When the additive is the additive 3, the concentration of the manganese-iron ion in the mixed solution is 60-300 g / L; wherein Mn 2+ The amount of substance of the substance of formula (I) accounts for 0.1-1 of the amount of substance of the manganese-iron ion, and is not 1; the ratio of the total amount of substance of the manganese-iron ion to the amount of substance of phosphorus element is 0.95-1.0:1, and the ratio of the amount of substance of lithium element to the amount of substance of phosphorus element is 0.95-1.05:

1.

5. The preparation method according to claim 4, characterized in that, The mass of the reducing agent is 1-5% of the mass of the electrode active material.

6. The method of claim 1, wherein, The atomization method is gas-liquid two-fluid atomization; and the atomization gas pressure is 0.3-0.8 MPa.

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