Lithium manganese iron phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of new energy materials, and particularly relates to a lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source 1, a dopant 1 and a solvent 1, performing first sanding to obtain slurry A, dividing the slurry A into slurry A1 and slurry A2, and performing first spray drying on the slurry A1 to obtain a powder material B1; (2) performing first sintering on the powder material B1 obtained in the step (1), cooling, and crushing to obtain a lithium iron manganese phosphate precursor C1; (3) mixing the lithium manganese iron phosphate precursor C1 with a carbon source 2, a dopant 2 and a solvent 2, and performing second sanding to obtain slurry A3; (4) mixing the slurry A2 and the slurry A3, and performing second spray drying to obtain a powder material B2; and (5) carrying out second sintering on the powder material B2 obtained in the step (4), cooling, crushing, sieving and demagnetizing to obtain the lithium manganese iron phosphate positive electrode material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy materials, and relates to a lithium ion battery, in particular to a lithium manganese iron phosphate positive electrode material, a preparation method thereof, and a lithium ion battery using the lithium manganese iron phosphate positive electrode material. BACKGROUND

[0002] Lithium iron phosphate has been widely used in commercial lithium ion batteries due to its low price, high specific capacity, and environmental friendliness. Lithium manganese iron phosphate replaces part of the iron element with manganese element based on lithium iron phosphate. Compared with lithium iron phosphate, the voltage platform is increased from 3.2V to 3.8-4.1V, and the theoretical energy density can reach 200-230 Wh / kg, which is about 15-30% higher than that of lithium iron phosphate (150-160 Wh / kg), close to the level of ternary lithium batteries (such as NCM), and the cost is lower. However, compared with layered oxide positive electrode materials, the lithium ion conductivity and electron conduction rate in lithium manganese iron phosphate are about 1-2 orders of magnitude lower. It is necessary to improve the rate performance through nanocrystallization, carbon coating or ion doping.

[0003] Nanocrystallization of lithium manganese iron phosphate can effectively solve the problem of lithium ion transmission to a certain extent, but too small particle size (D 50 <300nm) of the material will make the specific surface area too large, and the primary particles will generally agglomerate, which seriously affects the improvement of the material compaction density, and further limits the improvement of the energy density. Increasing the particle size (D 50 ≥1μm) of the lithium manganese iron phosphate primary particles can significantly improve the material compaction density, but the discharge capacity will suddenly decrease. How to balance the contradiction between compaction and capacity is an important problem that needs to be solved in the research and development of lithium manganese iron phosphate products.

[0004] Patent CN119786544A discloses a preparation method of high-compaction lithium manganese iron phosphate positive electrode material. The method reduces the porosity by secondary grinding and secondary sintering to improve the powder compaction density of the material. All materials are prepared by the same method, and the particle size of the finished product is relatively uniform, which is difficult to balance the compaction and capacity at the same time.

[0005] Patent CN119330325A discloses a method for preparing high-compaction lithium manganese iron phosphate material by coating small particles with large particles. The particle size of the small particles is 1-4 μm, and the particle size of the large particles is as high as 5-10 μm. The powder compaction performance may be relatively high, but such high particle size is difficult to achieve good capacity.

[0006] Therefore, there is still an urgent need for a lithium manganese iron phosphate material that can balance the compaction and capacity. SUMMARY

[0007] The application provides a preparation method of a lithium iron manganese phosphate positive electrode material.

[0008] In a first aspect, the application provides a preparation method of a lithium iron manganese phosphate positive electrode material, which comprises the following steps: (1) mixing a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source 1, a dopant 1 and a solvent 1 to obtain slurry A through first sand milling, and then dividing slurry A into slurry A1 and slurry A2, and obtaining powder material B1 through first spray drying of slurry A1; (2) performing first sintering on the powder material B1 obtained in step (1), and then obtaining lithium iron manganese phosphate precursor C1 through crushing after cooling; (3) mixing the lithium iron manganese phosphate precursor C1, a carbon source 2, a dopant 2 and a solvent 2 to obtain slurry A3 through second sand milling; (4) mixing the slurry A2 prepared in step (1) and the slurry A3 prepared in step (3), and then obtaining powder material B2 through second spray drying; (5) performing second sintering on the powder material B2 obtained in step (4), and then obtaining the lithium iron manganese phosphate positive electrode material through crushing, sieving and magnetic removal after cooling.

[0009] According to some embodiments of the application, the preparation method of the lithium iron manganese phosphate positive electrode material provided by the application can further comprise the following auxiliary technical features: In some embodiments, the lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate or lithium acetate. When the lithium source comprises two or more of the above-mentioned substances, the two or more substances can be combined in any proportion.

[0010] In some embodiments, the iron source comprises at least one of iron phosphate, iron oxalate, iron nitrate, ferrous oxalate or diiron trioxide. When the iron source comprises two or more of the above-mentioned substances, the two or more substances can be combined in any proportion.

[0011] In some embodiments, the manganese source comprises at least one of manganese carbonate, trimanganese tetraoxide, manganese acetate, manganese pyrophosphate, manganese oxalate, manganese phosphate, ammonium manganese phosphate or manganous phosphate. When the manganese source comprises two or more of the above-mentioned substances, the two or more substances can be combined in any proportion.

[0012] In some embodiments, the phosphorus source includes at least one of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, lithium hydrogen phosphate, iron phosphate, or lithium phosphate. When the phosphorus source includes two or more of the above, they can be combined in any ratio.

[0013] In some embodiments, the carbon source 1 includes at least one of glucose, sucrose, fructose, starch, cellulose, graphene, citric acid, polyethylene glycol, or carbon nanotube. When the carbon source 1 includes two or more of the above, they can be combined in any ratio.

[0014] In some embodiments, the dopant 1 includes at least one of ammonium fluoride, ammonium metavanadate, magnesium oxide, niobium pentoxide, titanium dioxide, or zirconium oxide.

[0015] In some embodiments, the solvent 1 includes water.

[0016] In some embodiments, in step (1), the zirconium beads used in the first sanding have a diameter of 0.3 mm-0.5 mm. Specifically, in step (1), the zirconium beads used in the first sanding have a diameter of 0.3 mm, 0.4 mm, 0.5 mm, or any value within the above range.

[0017] In some embodiments, in step (1), the first sanding is performed for a time sufficient to sand the slurry A to a particle size D 50 of 200 nm-800 nm or 250 nm-450 nm. If the particle size D 50 of slurry A is greater than 800 nm, i.e., the sanding is insufficient, several elements in the raw materials cannot be sufficiently mixed, affecting the crystal structure of the lithium iron manganese phosphate and the material properties; the particle size D 50 of slurry A is less than 200 nm, on the one hand, the sanding efficiency is too low if the particle size is too small, and on the other hand, the small particle size in the final product is too small, which is prone to adhesion, and is not conducive to ensuring the compaction performance.

[0018] In some embodiments, in step (1), the solid raw materials include a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source 1, and a dopant 1.

[0019] In some embodiments, in the solid raw materials, the molar ratio of manganese element to iron element is (1.0-2.4):1. Specifically, in the solid raw materials, the molar ratio of manganese element to iron element is 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, or any value within the above range.

[0020] In some embodiments, the molar ratio of lithium element to the sum of manganese element and iron element in the solid raw material is (0.95-1.08):1, preferably (1.01-1.05):1. Specifically, the molar ratio of Li:(Mn+Fe) in the solid raw material is 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, or any value within the above range.

[0021] In some embodiments, the molar ratio of phosphorus element to the sum of manganese element and iron element in the solid raw material is (0.90-1.05):1, preferably (1.02-1.04):1. Specifically, the molar ratio of P:(Mn+Fe) in the solid raw material is 0.9:1.02, 1:1.02, 1.05:1.02, 0.9:1.03, 1:1.03, 1.05:1.03, 0.9:1.04, 1:1.04, 1.05:1.04, or any value within the above range.

[0022] In some embodiments, the amount of the carbon source 1 added is 2%-6% of the total mass of the solid raw material, preferably 2.5%-4.5%. Specifically, the amount of the carbon source 1 added is 2%, 3%, 4%, 5%, 6% of the total mass of the solid raw material, or any value within the above range.

[0023] In some embodiments, the amount of the doping element in the doping agent 1 added is 0.05%-0.5% of the total mass of the solid raw material. Specifically, the amount of the doping element in the doping agent 1 added is 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% of the total mass of the solid raw material, or any value within the above range. When the doping agent 1 comprises two or more of the above substances, the amount of any one doping element added should be within the range of 0.05%-0.5%, and the sum of the amounts of the multiple elements added should also be within the range of 0.05%-0.5%.

[0024] In some embodiments, the first spray drying is high-speed centrifugal atomization drying.

[0025] In some embodiments, the inlet air temperature of the first spray drying is 210℃-260℃. Specifically, the inlet air temperature of the first spray drying is 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, or any value within the above range.

[0026] In some embodiments, the out temperature of the first spray drying is 90-110°C; specifically, the out temperature of the first spray drying is 90°C, 95°C, 100°C, 105°C, 110°C, or any value within the range.

[0027] In some embodiments, the feeding speed of the first spray drying is 3-4 kg / h; specifically, the feeding speed of the first spray drying is 3 kg / h, 3.2 kg / h, 3.4 kg / h, 3.6 kg / h, 3.8 kg / h, 4.0 kg / h, or any value within the range.

[0028] In some embodiments, in step (2), the heating rate of the first sintering is 2-5°C / min. Specifically, the heating rate of the first sintering is 2°C / min, 3°C / min, 4°C / min, 5°C / min, or any value within the range.

[0029] In some embodiments, in step (2), the temperature of the first sintering is 600-900°C, preferably 680-810°C. Specifically, the temperature of the first sintering is 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or any value within the range.

[0030] In some embodiments, in step (2), the time of the first sintering is 2-10 h, preferably 6-9 h. Specifically, the time of the first sintering is 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any value within the range.

[0031] In the present application, it can be understood that the first sintering is heated to 600-900°C at a heating rate of 2-5°C / min, and then kept for 2-10 h.

[0032] In some embodiments, in step (2), the first sintering is carried out in any one of a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, or an argon atmosphere.

[0033] In some embodiments, in step (3), the carbon source 2 comprises at least one of glucose, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyacrylonitrile, polyaniline, polypyrrole, or polydopamine, preferably a mixture of glucose and polyethylene glycol.

[0034] In some embodiments, the dopant 2 comprises titanium dioxide.

[0035] In some embodiments, the solvent 2 comprises water.

[0036] In some embodiments, the amount of the carbon source 2 added is 3%-10% of the mass of the lithium manganese iron phosphate precursor C1. Specifically, the amount of the carbon source 2 added is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the mass of the lithium manganese iron phosphate precursor C1, or any value within the above range.

[0037] In some embodiments, when the carbon source 2 is a mixture of glucose and polyethylene glycol, the amount of glucose added is 3%-10% of the mass of the lithium manganese iron phosphate precursor C1, the amount of polyethylene glycol added is 3%-10% of the mass of the lithium manganese iron phosphate precursor C1, and the total mass of glucose and polyethylene glycol is 3%-10% of the mass of the lithium manganese iron phosphate precursor C1.

[0038] In some embodiments, the amount of the doping element in the dopant 2 added is 0.01%-0.2% of the mass of the lithium manganese iron phosphate precursor C1. Specifically, the amount of the doping element in the dopant 2 added is 0.01%, 0.05%, 0.1%, 0.15%, 0.2% of the mass of the lithium manganese iron phosphate precursor C1, or any value within the above range.

[0039] The present application makes the doping elements in the prepared lithium manganese iron phosphate positive electrode material present a gradient distribution through step-by-step doping, forms a synergistic effect, widens the lithium ion channel, and further improves the specific capacity and rate performance of the prepared lithium manganese iron phosphate positive electrode material.

[0040] In some embodiments, in step (4), the diameter of the zirconium beads used in the second sand milling is 0.8 mm-2.0 mm. Specifically, the diameter of the zirconium beads used in the second sand milling is 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, or any value within the above range.

[0041] In some embodiments, in step (4), the time of the second sand milling is to sand mill the slurry A3 to a particle size D 50 within the range of 500 nm-1200 nm or 700 nm-900 nm.

[0042] In some embodiments, in step (4), the particle size D 50 of the slurry A3 is within the range of 500 nm-1200 nm, preferably 700 nm-900 nm. Specifically, the particle size D 50500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, or any value within the above ranges.

[0043] In the present application, the slurry A3 is used as large particles in the grading to improve the compaction of the material, while the electrical performance cannot be too poor. If the particle size D 50 greater than 1200 nm, the second sintered particle size will be too large, resulting in poor electrical performance of the material; if the particle size D 50 less than 500 nm, large particles cannot be formed, and the compaction density of the material cannot be effectively improved.

[0044] In some embodiments, in step (4), the mass ratio of the slurry A2 and the slurry A3 is (1-9):(1-2), preferably (1.5-4):1. Specifically, the mass ratio of the slurry A2 and the slurry A3 is 1:1, 1:2, 2:1, 3:1, 3:2, 4:1, 5:1, 5:2, 6:1, 7:1, 7:2, 8:1, 9:1, 9:2, or any value within the above ranges.

[0045] In the present application, the slurry A2 is used to sinter small particles, and the slurry A3 is used to sinter large particles. The grading of large and small particles should be appropriate, and the proportion should be suitable to obtain a material that has both good electrical performance and high compaction density. If there is too much slurry A2, resulting in too many small particles, the compaction will not be high; if there is too much slurry A3, resulting in too many large particles, the electrical performance will be poor.

[0046] In some embodiments, the second spray drying uses high-speed centrifugal atomization drying.

[0047] In some embodiments, the inlet air temperature of the second spray drying is 210°C-260°C; specifically, the inlet air temperature of the second spray drying is 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, or any value within the above ranges.

[0048] In some embodiments, the outlet air temperature of the second spray drying is 90°C-110°C; specifically, the outlet air temperature of the second spray drying is 90°C, 95°C, 100°C, 105°C, 110°C, or any value within the above ranges.

[0049] In some embodiments, the second spray-drying feed rate is 3 kg / h - 4 kg / h; specifically, the second spray-drying feed rate is 3 kg / h, 3.2 kg / h, 3.4 kg / h, 3.6 kg / h, 3.8 kg / h, 4.0 kg / h, or any value within the range.

[0050] In some embodiments, in step (5), the second sintering temperature is 600℃ - 790℃, preferably 700 - 780℃. Specifically, the second sintering temperature is 600℃, 650℃, 700℃, 750℃, 790℃, or any value within the range.

[0051] In some embodiments, the second sintering temperature is 600℃ - 790℃, preferably 700 - 780℃. Specifically, the second sintering temperature is 600℃, 650℃, 700℃, 750℃, 790℃, or any value within the range.

[0052] In some embodiments, the second sintering time is 6 h - 10 h. Specifically, the second sintering time is 6 h, 7 h, 8 h, 9 h, 10 h, or any value within the range.

[0053] In the present application, it can be understood that the second sintering is heated to 600℃ - 790℃ at a heating rate of 2℃ / min - 5℃ / min, and then held for 6 h - 10 h.

[0054] In some embodiments, the second sintering is performed in any one of a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, or an argon atmosphere.

[0055] In a second aspect, the present application provides a lithium iron manganese phosphate positive electrode material prepared by the preparation method of the first aspect of the present application.

[0056] In a third aspect, the present application provides a lithium battery comprising the lithium iron manganese phosphate positive electrode material prepared by the preparation method of the first aspect of the present application or the lithium iron manganese phosphate positive electrode material of the second aspect.

[0057] The present application has the following beneficial effects: The present application prepares a compact large particle through the first sintering, improves the particle hardness of the material, and lays a foundation for improving the material compaction density; in order to ensure a high specific capacity, the large particle prepared by the first sintering is subjected to second sand milling to obtain a suitable particle size, shortens the lithium ion and electron transmission path in the large particle, and improves the electrical performance of the material.

[0058] The application makes the doping elements in the lithium manganese iron phosphate material present gradient distribution through step-by-step doping, forms a synergistic effect, widens the lithium ion channel, and further improves the specific capacity and rate performance of the material; the preparation method provided by the application has simple process flow, process parameters are easy to control, meanwhile, the final product has excellent performance, and is suitable for industrial mass production. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 SEM image of the lithium manganese iron phosphate positive electrode material prepared in Example 1 of the application.

[0060] TERMINOLOGY In the description of the application, the meaning of “a plurality of” is two or more than two, unless otherwise explicitly and specifically limited.

[0061] The term “room temperature” or “ambient temperature” means ambient temperature, which refers to a temperature of about 10°C to about 35°C, about 10°C to about 30°C, or about 20°C to 30°C, or about 25°C.

[0062] The term “wt%” means mass percentage.

[0063] In the description of the present application, the description of the terms “one embodiment”, “some embodiments”, “an example”, “a specific example”, or “some examples” means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled person in the art can combine and combine the different embodiments or examples described in the present application and the features of the different embodiments or examples without contradiction.

[0064] In the following content, all the numbers disclosed herein are approximate values, regardless of whether the words “about” or “approximately” are used. The value of each number can have a difference of 1%, 2%, 5%, 7%, 8%, 10%, 15% or 20%. Whenever a number with a value of N is disclosed, any number with a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, N+ / -10%, N+ / -15% or N+ / -20% is explicitly disclosed, wherein “+ / -” means plus or minus.

[0065] DETAILED EMBODIMENT The following description is merely exemplary of the present application and is not intended to limit the application since modifications, equivalents and alternatives thereto will be apparent to those skilled in the art without departing from the spirit and scope of the application.

[0066] The preparation method of the lithium manganese iron phosphate positive electrode material comprises the following steps: (1) mixing a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source 1, a dopant 1 and a solvent 1, and using zirconium bead sand with a diameter of 0.3 mm-0.5 mm to grind slurry A to particle size D 50 to 800 nm, slurry A is divided into slurry A1 and slurry A2, slurry A1 is subjected to first spray drying (high-speed centrifugal atomization drying, the inlet air temperature is 210℃-260℃, the outlet air temperature is 90℃-110℃, and the feeding speed is 3 kg / h-4 kg / h) to obtain powder material B1; (2) heating the powder material B1 obtained in step (1) to 600℃-900℃ at a heating rate of 2℃ / min-5℃ / min in a nitrogen atmosphere, and maintaining the temperature for 2 h-10 h. After cooling, crushing to obtain lithium manganese iron phosphate precursor C1; (3) mixing lithium manganese iron phosphate precursor C1, a carbon source 2, a dopant 2 and a solvent 2, and using zirconium bead sand with a diameter of 0.8 mm-2.0 mm to grind slurry A3 to particle size D 50 to 1200 nm; (4) mixing slurry A2 prepared in step (1) and slurry A3 prepared in step (3) in a mass ratio of (1-9):(1-2), and then subjecting to second spray drying (high-speed centrifugal atomization drying, the inlet air temperature is 210℃-260℃, the outlet air temperature is 90℃-110℃, and the feeding speed is 3 kg / h-4 kg / h) to obtain powder material B2; (5) heating the powder material B2 obtained in step (4) to 600℃-790℃ at a heating rate of 2℃ / min-5℃ / min in a nitrogen atmosphere, and maintaining the temperature for 6 h-10 h. After cooling, crushing, sieving and removing magnetism, the lithium manganese iron phosphate positive electrode material is obtained.

[0067] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conditions recorded in the description, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0068] Example 1: (1) Mix lithium source (lithium carbonate, lithium dihydrogen phosphate), iron source (iron phosphate), manganese source (manganese tetroxide), phosphorus source (lithium dihydrogen phosphate), carbon source 1 (glucose), dopant 1 (titanium dioxide and magnesium oxide) and deionized water, and grind the mixture with zirconium beads with a diameter of 0.3 mm until the particle size D of slurry A is reached. 50 To obtain powder material B1, the slurry A is divided into slurry A1 and slurry A2, with a wavelength of 300 nm. Slurry A1 is subjected to a first spray drying (using high-speed centrifugal atomization drying, inlet air temperature 220℃, outlet air temperature 100℃, and feed rate 3 kg / h) to obtain powder material B1. Among the solid raw materials (lithium source, iron source, manganese source, phosphorus source, carbon source 1 and dopant 1), the molar ratio of manganese to iron is 1.5:1, the molar ratio of Li:(Mn+Fe) is 1.043:1, the molar ratio of P:(Mn+Fe) is 1.036:1, the amount of glucose added is 4 wt% of the total mass of the solid raw materials, the amount of Ti added is 0.3 wt% of the total mass of the solid raw materials, and the amount of Mg added is 0.1 wt% of the total mass of the solid raw materials.

[0069] (2) The powder material B1 obtained in step (1) is heated to 800°C in a nitrogen atmosphere at a heating rate of 2°C / min, kept at the temperature for 8 h, cooled and then pulverized to obtain lithium manganese iron phosphate precursor C1.

[0070] (3) Mix lithium manganese iron phosphate precursor C1, carbon source 2 (a mixture of glucose and polyethylene glycol, wherein the amount of glucose added is 8% of the mass of lithium manganese iron phosphate precursor C1 and the amount of polyethylene glycol added is 1.5% of the mass of lithium manganese iron phosphate precursor C1), dopant 2 (titanium dioxide, the amount of Ti element added is 0.1% of the mass of lithium manganese iron phosphate precursor C1), and deionized water, and grind the mixture with zirconium beads with a diameter of 1.2 mm until the particle size D of slurry A3 is reached. 50 It is 700 nm.

[0071] (4) Mix the slurry A2 prepared in step (1) and the slurry A3 prepared in step (3) at a mass ratio of 7:3, and then spray dry to obtain powder material B2; (5) The powder material B2 obtained in step (4) is heated to 750°C in a nitrogen atmosphere at a heating rate of 2.4°C / min, kept at the temperature for 9 h, cooled, crushed, sieved and demagnetized to obtain the lithium manganese iron phosphate cathode material.

[0072] Example 2 The only difference between Example 2 and Example 1 is that: (2) The powder material B1 obtained in step (1) is heated to 750°C in a nitrogen atmosphere at a heating rate of 2°C / min and then kept at that temperature for 8 h.

[0073] Example 3 The only difference between Example 3 and Example 1 is that: In step (1), the slurry A is ground to a particle size D. 50 It is 400 nm.

[0074] Example 4 The only difference between Example 4 and Example 1 is that: In step (3), the slurry A3 is ground to a particle size D. 50 It is 800 nm.

[0075] Example 5 The only difference between Example 5 and Example 1 is that: In step (4), slurry A2 and slurry A3 are mixed at a mass ratio of 8:2.

[0076] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that: In step (3), the slurry A3 is ground to a particle size D. 50 It is 300 nm.

[0077] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that: In step (1), the slurry A is ground to a particle size D. 50 It is 700 nm.

[0078] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that: The amount of Ti element added in step (1) of Comparative Example 3 is the sum of the amount of Ti element added in steps (1) and (3) of Example 1, and no dopant 2 is added in step (3) of Comparative Example 3.

[0079] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that: In Comparative Example 4, no dopant 1 was added in step (1), and the dopant added in Comparative Example 4, step (3) was titanium dioxide and magnesium oxide. The amount of Ti element was the sum of the amount of Ti element added in steps (1) and (3) of Example 1, and the amount of Mg element added was 0.1 wt% of the total mass of the solid raw material described in step (1) of Example 1.

[0080] Performance testing The performance of the lithium manganese iron phosphate materials prepared in Examples 1 to 5 and Comparative Examples 1 to 4 was characterized as follows: (I) Powder compaction density test under 30000N pressure: The method was followed according to GB / T 24533-2019. An electronic pressure testing instrument (e.g., UTM7305) was used for the determination. The lithium manganese iron phosphate prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were pressurized at 30000 N for 30 seconds and then depressurized to test the compaction density. The test results are shown in Table 1.

[0081] (II) Performance testing of button cells The lithium manganese iron phosphate materials prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were used as the positive electrode active materials to be tested. The positive electrode active materials, the binder polyvinylidene fluoride (PVDF), and the conductive agent Super-P were weighed at a mass ratio of 92:4:4 and dispersed in N-methylpyrrolidone (NMP) to form a positive electrode slurry. This positive electrode slurry was coated onto aluminum foil, vacuum dried at 110°C, and then rolled and punched to obtain the positive electrode sheet. The electrolyte was 1 mol / L LiPF6, wherein the solvent of the electrolyte was a mixed solution of dimethyl carbonate: ethyl methyl carbonate: ethylene carbonate (volume ratio 1:1:1). The separator was a Celgard polypropylene membrane, and the lithium metal sheet was used as the negative electrode. All components were assembled into a coin cell in a vacuum glove box. The coin cell was electrochemically tested using a Blue Dot battery testing system, with a test voltage range of 2V to 4.4V.

[0082] The performance of each test case coin cell was obtained according to the following test method: (1) First effect: First, the batteries corresponding to the examples and comparative examples were subjected to constant current and constant voltage charging (CCCV) at a current of 0.1C and a voltage of 4.4V, and their charging capacity was measured as C0. Then, the battery under test was subjected to constant current and constant voltage discharging at a current of 0.1C and a voltage of 4.4V, and its discharging capacity was measured as C1. Therefore, the initial efficiency of the battery under test is C1 / C0×100%. The test results are shown in Table 1: (2) Discharge capacity at 0.1C: At 25°C, the batteries corresponding to the examples and comparative examples were charged to 4.4V at a constant current of 0.1C, then charged to a current of 0.05C at a constant voltage of 4.4V. After resting for 5 minutes, they were discharged to 2V at 0.1C. The discharge capacity Q1 was recorded. Therefore, the 0.1C discharge specific capacity = discharge capacity Q1 / mass of the positive electrode active material. The test results are shown in Table 1. (3) 1C discharge capacity: At 25°C, the batteries corresponding to the examples and comparative examples were charged to 4.4V at a constant current of 1C, then charged to a current of 0.05C at a constant voltage of 4.4V. After resting for 5 minutes, they were discharged to 2V at 1C. The discharge capacity Q2 was recorded. Therefore, the 1C discharge capacity = discharge capacity Q2 / mass of the positive electrode active material. The test results are shown in Table 1. Table 1: Test data of lithium manganese iron phosphate cathode materials prepared in each embodiment and comparative example

[0083] As shown in Table 1, the 0.1C discharge specific capacity of the materials prepared in the embodiments of the present invention, when made into batteries, ranges from 151 mAh / g to 153.94 mAh / g, and the discharge specific capacity at a 1C current density ranges from 139 mAh / g to 142.55 mAh / g; the powder compaction density reaches 2.28 g·cm³. -3 -2.31 g·cm -3 Therefore, it can be seen that the battery made from the material prepared in the embodiments of the present invention exhibits excellent compaction density and electrical properties, achieving a balance between compaction density and electrical performance, resulting in unexpected technical effects. While Comparative Example 1 shows a high 0.1C discharge capacity of 155.30 mAh / g and a 1C discharge capacity of 149.16 mAh / g, demonstrating improved discharge capacity, its compaction density is reduced to 2.18 g·cm³. -3 The compaction performance was poor. In Comparative Example 2, slurry A was not sufficiently ground, resulting in uneven elemental mixing in the obtained lithium manganese iron phosphate precursor. This led to crystal structure distortion, hindered lithium-ion diffusion, increased impedance, and consequently, a severe decline in electrical performance, despite a compaction density as high as 2.38 g·cm³. -3 However, the specific capacity at 0.1C was only 133.42 mAh / g, and the specific capacity at 1C was only 118.54 mAh / g, which reduced the specific capacity. In Comparative Examples 3 and 4, the dopants were added all at once, making it difficult to form internal and external gradient doping, thus failing to fully utilize the synergistic effect and adversely affecting the material's electrical properties. Although the compaction density was close to that of Examples 1-5, the initial specific capacity at 0.1C decreased to approximately 149 mAh / g, and the initial specific capacity at 1C decreased to approximately 137 mAh / g, further reducing the specific capacity. Comparative Examples 1-4 failed to balance compaction density and electrical performance.

[0084] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0085] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) The lithium source, iron source, manganese source, phosphorus source, carbon source 1, dopant 1 and solvent 1 are mixed and the mixture is ground in the first mill to obtain slurry A. Slurry A is divided into slurry A1 and slurry A2. Slurry A1 is spray dried in the first spray to obtain powder material B1. (2) The powder material B1 obtained in step (1) is subjected to a first sintering, cooled, and then pulverized to obtain lithium manganese iron phosphate precursor C1; (3) Mix lithium manganese iron phosphate precursor C1 with carbon source 2, dopant 2 and solvent 2, and then perform a second sand milling to obtain slurry A3; (4) Mix the slurry A2 prepared in step (1) and the slurry A3 prepared in step (3), and then spray dry to obtain powder material B2; (5) The powder material B2 obtained in step (4) is subjected to a second sintering, cooled and then crushed, sieved and demagnetized to obtain the lithium manganese iron phosphate cathode material.

2. The preparation method according to claim 1, characterized in that, The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, or lithium acetate. Optionally, the iron source includes at least one of ferric phosphate, ferric oxalate, ferric nitrate, ferrous oxalate, or ferric oxide; Optionally, the manganese source includes at least one of manganese carbonate, manganese tetroxide, manganese acetate, manganese pyrophosphate, manganese oxalate, manganese phosphate, ammonium manganese phosphate, or manganese phosphate. Optionally, the phosphorus source includes at least one of phosphoric acid, diammonium hydrogen phosphate, lithium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate, or lithium phosphate. Optionally, the carbon source 1 includes at least one of glucose, sucrose, fructose, starch, cellulose, graphene, citric acid, polyethylene glycol, or carbon nanotubes. Optionally, the dopant 1 includes at least one of ammonium fluoride, ammonium metavanadate, magnesium oxide, niobium pentoxide, titanium dioxide, or zirconium oxide; Optionally, the solvent 1 includes water.

3. The preparation method according to any one of claims 1-2, characterized in that, In step (1), the diameter of the zirconium beads used in the first grinding process is 0.3 mm to 0.5 mm; Optionally, the particle size D of the slurry A 50 The wavelength range is 200 nm to 800 nm, preferably 250 nm to 450 nm.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (1), the solid raw materials include lithium source, iron source, manganese source, phosphorus source, carbon source 1 and dopant 1; Optionally, in the solid raw material, the molar ratio of manganese to iron is (1.0-2.4):1; Optionally, in the solid raw material, the molar ratio of lithium to the sum of manganese and iron is (0.95-1.08):1, preferably (1.01-1.05):1; Optionally, in the solid raw material, the molar ratio of phosphorus to the sum of manganese and iron is (0.90-1.05):1, preferably (1.02-1.04):1; Optionally, the amount of carbon source 1 added is 2wt%-6wt% of the total mass of the solid raw materials, preferably 2.5wt%-4.5wt%. Optionally, the amount of dopant element added in dopant 1 is 0.05wt%-0.5wt% of the total mass of the solid raw material; Optionally, the first spray drying is performed using high-speed centrifugal atomization drying; Optionally, the inlet air temperature of the first spray dryer is 210℃-260℃; Optionally, the outlet air temperature of the first spray dryer is 90℃-110℃; Optionally, the feed rate of the first spray dryer is 3 kg / h to 4 kg / h.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the heating rate of the first sintering is 2℃ / min - 5℃ / min; Optionally, the temperature of the first sintering is 600℃-900℃, preferably 680℃-810℃; Optionally, the first sintering time is 2 h-10 h, preferably 6 h-9 h; Optionally, the first sintering is carried out in any one of a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, or an argon atmosphere.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (3), the carbon source 2 includes at least one of glucose, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol, polyacrylonitrile, polyaniline, polypyrrole, or polydopamine; Optionally, the dopant 2 comprises titanium dioxide; Optionally, the solvent 2 includes water; Optionally, the amount of carbon source 2 added is 3%-10% of the mass of the lithium manganese iron phosphate precursor C1; Optionally, the amount of dopant element added in the dopant 2 is 0.01%-0.2% of the mass of the lithium manganese iron phosphate precursor C1.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (4), the diameter of the zirconium beads used in the second grinding process is 0.8 mm to 2.0 mm; Optionally, the particle size D of the slurry A3 50 The wavelength range is 500 nm to 1200 nm, preferably 700 nm to 900 nm; Optionally, the mass ratio of slurry A2 to slurry A3 is (1-9):(1-2), preferably (1.5-4):1; Optionally, the second spray drying employs high-speed centrifugal atomization drying; Optionally, the inlet air temperature of the second spray dryer is 210°C-260°C; Optionally, the outlet air temperature of the second spray dryer is 90℃-110℃; Optionally, the feed rate of the second spray dryer is 3 kg / h - 4 kg / h.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (5), the heating rate of the second sintering is 2℃ / min-5℃ / min; Optionally, the second sintering temperature is 600℃-790℃, preferably 700-780℃; Optionally, the second sintering time is 6 h-10 h; Optionally, the second sintering is carried out in any one of the following atmospheres: nitrogen, helium, neon, or argon.

9. A lithium manganese iron phosphate cathode material, characterized in that, The lithium manganese iron phosphate cathode material is prepared by any one of claims 1-8.

10. A lithium battery, characterized in that, The lithium battery comprises lithium manganese iron phosphate cathode material obtained by any one of claims 1-8 or lithium manganese iron phosphate cathode material as described in claim 9.

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