Modified monocrystal lithium iron manganese phosphate positive electrode material and preparation method and application thereof

Abstract

The invention provides a modified monocrystal 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, a dispersing agent and a solvent to obtain mixed slurry, and carrying out spray drying treatment on the mixed slurry to obtain a lithium manganese iron phosphate intermediate; (2) carrying out jet milling treatment on the lithium manganese iron phosphate intermediate to obtain lithium manganese iron phosphate intermediate single crystal particles; and (3) calcining the lithium manganese iron phosphate intermediate single-crystal particles to obtain the modified single-crystal lithium manganese iron phosphate positive electrode material. According to the invention, the preparation process of the lithium manganese iron phosphate is sequentially optimized, and through the synergistic effect of the raw materials, the preparation of high-crystallinity and uniform single crystal particles is realized, the compaction density of the material is greatly improved while the structural stability of the material is considered, and the electrochemical performance of the lithium manganese iron phosphate positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a modified single-crystal lithium iron manganese phosphate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries have received extensive research and attention due to their advantages such as high voltage, high energy density, good cycle performance, no memory effect, and environmental friendliness. With the increasing applications of lithium-ion batteries in social life, higher requirements are put forward for the tap density of lithium-ion batteries.

[0003] As a potential cathode material for lithium-ion batteries, lithium iron manganese phosphate can improve its voltage platform and theoretical energy density by utilizing the synergistic effect of manganese and iron on the basis of inheriting the advantages of lithium iron phosphate. However, at present, the lithium iron manganese phosphate cathode material faces the problem of low tap density in practical applications, which seriously affects the comprehensive performance of the battery.

[0004] CN118183679A discloses a high-tap-density and long-cycle lithium iron manganese phosphate cathode material and a preparation method thereof, including the following steps: S1, preparing metal-doped manganese iron pyrophosphate; S2, preparing metal-doped manganese iron phosphate; S3, preparing a lithium iron manganese phosphate material; S4, performing LiPAA modification on the lithium iron manganese phosphate material. It synthesizes manganese iron compounds containing different doping elements by a liquid-phase method to improve the tap density of the manganese iron compounds. During sintering, the particles grow into different sizes and morphologies, improving the powder tap density of the lithium iron manganese phosphate material.

[0005] CN119786544A discloses a preparation method of a high-tap-density lithium iron manganese phosphate cathode material, including the following steps: placing a manganese source, an iron source, and a phosphorus source in deionized water, after stirring, first high-speed ball milling, and constant-temperature water bath, adding an oxidant and stirring for oxidation, and then drying this slurry to obtain a lithium iron manganese phosphate precursor powder; performing first sintering on the lithium iron manganese phosphate precursor powder to obtain a first-sintered lithium iron manganese phosphate material; placing the first-sintered lithium iron manganese phosphate material in deionized water, and simultaneously adding a lithium source and a carbon source, after stirring, second high-speed ball milling, and drying, to obtain a lithium iron manganese phosphate precursor powder; performing second sintering on the lithium iron manganese phosphate precursor powder, thereby obtaining the high-tap-density lithium iron manganese phosphate cathode material.

[0006] The above-mentioned solutions prepare lithium iron manganese phosphate with a high tap density by means of element doping or multiple sinterings. However, the methods described in the above-mentioned solutions will destroy the crystal form of lithium iron manganese phosphate, resulting in poor product consistency and poor grain structure stability.

[0007] In summary, there are many deficiencies in the prior art in improving the tap density of the lithium iron manganese phosphate cathode material. There is an urgent need for a new technical solution to solve these problems to meet the growing performance requirements of lithium-ion batteries. Summary of the Invention

[0008] The object of the present invention is to provide a modified single-crystal lithium iron manganese phosphate cathode material, its preparation method and application. By sequentially optimizing the preparation process of lithium iron manganese phosphate and through the synergistic effect of raw materials, the preparation of high-crystallinity and uniform single-crystal particles is achieved. While taking into account the structural stability of the material, its tap density is greatly improved, and the electrochemical performance of the lithium iron manganese phosphate cathode material is enhanced.

[0009] To achieve the object of this invention, the following technical solutions are adopted:

[0010] In the first aspect, the present invention provides a preparation method of a modified single-crystal lithium iron manganese phosphate cathode material, and the preparation method includes the following steps:

[0011] (1) Mix a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a dispersant and a solvent to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain a lithium iron manganese phosphate intermediate;

[0012] (2) Perform air jet milling on the lithium iron manganese phosphate intermediate to obtain single-crystal particles of the lithium iron manganese phosphate intermediate;

[0013] (3) Perform calcination on the single-crystal particles of the lithium iron manganese phosphate intermediate to obtain the modified single-crystal lithium iron manganese phosphate cathode material.

[0014] During the preparation process of the modified single-crystal lithium iron manganese phosphate cathode material of the present invention, adding a dispersant to the slurry can prevent the lithium source, iron source, manganese source, etc. from settling or agglomerating in the solvent, ensuring the uniform distribution of elements. The dispersant can improve the fluidity of the slurry, making the morphology of the intermediate particles after spray drying more regular and the particle size distribution narrower. By air jet milling to refine and uniformly disperse the intermediate particles before calcination, it can avoid the formation of hard lumps due to high-temperature agglomeration of particles during the calcination process, and it is easier to form single-crystal particles with uniform size during subsequent calcination. The fine particles after air jet milling have a shorter atomic diffusion path during calcination, which is beneficial to the complete growth of the single-crystal structure. The added carbon source forms an amorphous carbon layer during the calcination process, coating the surface of the single-crystal particles. The carbon layer can physically isolate the particles, limit the grain size during the calcination process, and promote the formation of single crystals.

[0015] The present invention first performs air jet milling on the lithium iron manganese phosphate intermediate, which can break open the original secondary spherical aggregates to reduce the particle size and enable the particles to be evenly redistributed and filled with each other. During the subsequent sintering process, heat can be evenly transferred to each particle, avoiding overburning caused by inconsistent internal and external temperature fields. The method of first milling and then calcining in the present invention can make the particles reach a more uniform physical state before high-temperature treatment, with more sufficient reaction, higher crystallinity and more uniform manganese / iron distribution during calcination, thereby improving the electrochemical performance of the material.

[0016] Preferably, the lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, or lithium oxalate. Typical but non-limiting combinations include the combination of lithium hydroxide and lithium carbonate, the combination of lithium acetate and lithium hydroxide, or the combination of lithium phosphate and lithium oxalate, etc.

[0017] Preferably, the iron source in step (1) includes any one or a combination of at least two of iron oxide, magnetite, ferrous oxalate, iron phosphate, iron sulfate, or iron chloride. Typical but non-limiting combinations include the combination of iron oxide and magnetite, the combination of iron phosphate and ferrous oxalate, or the combination of iron chloride and iron sulfate, etc.

[0018] Preferably, the manganese source in step (1) includes any one or a combination of at least two of manganese dioxide, manganese pentoxide, manganese tetroxide, manganese hydrogen phosphate, manganese carbonate, or manganese oxalate. Typical but non-limiting combinations include the combination of manganese dioxide and manganese pentoxide, the combination of manganese pentoxide and manganese tetroxide, or the combination of manganese carbonate and manganese oxalate, etc.

[0019] Preferably, the phosphorus source in step (1) includes any one or a combination of at least two of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, or phosphoric acid. Typical but non-limiting combinations include the combination of lithium dihydrogen phosphate and ammonium dihydrogen phosphate, the combination of ammonium dihydrogen phosphate and phosphoric acid, or the combination of lithium dihydrogen phosphate and phosphoric acid, etc.

[0020] Preferably, the carbon source in step (1) includes any one or a combination of at least two of citric acid, starch, sucrose, glucose, carbon black, or carbon nanotubes. Typical but non-limiting combinations include the combination of citric acid and starch, the combination of sucrose and glucose, or the combination of carbon black and carbon nanotubes, etc.

[0021] Preferably, the dispersant in step (1) includes any one or a combination of at least two of polyvinyl alcohol, polyethylene glycol, or oxalic acid. Typical but non-limiting combinations include the combination of polyvinyl alcohol and polyethylene glycol, the combination of polyvinyl alcohol and oxalic acid, or the combination of polyethylene glycol and oxalic acid, etc.

[0022] Preferably, the solvent in step (1) includes water.

[0023] Preferably, based on the total mass of the lithium source, iron source, manganese source, and phosphorus source being 100%, the addition amount of the dispersant is 1% - 5%, for example: 1%, 2%, 3%, 4%, or 5%, etc. It is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] Preferably, based on the total mass of the lithium source, iron source, manganese source, and phosphorus source being 100%, the addition amount of the carbon source is 7% - 15%, for example: 7%, 8%, 10%, 12%, or 15%, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0025] Preferably, the solid content of the mixed slurry in step (1) is 35% - 50%, for example: 35%, 38%, 40%, 45%, or 50%, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] Preferably, in the mixed slurry of step (1), the molar ratio of manganese element to iron element is (1 - 4):1, for example: 1:1, 1.5:1, 2:1, 2.5:1, or 4:1, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] Preferably, the mixed slurry is subjected to grinding treatment before the spray drying treatment in step (1).

[0028] Preferably, the rotation speed of the grinding treatment is 500 rpm - 2500 rpm, for example: 500 rpm, 800 rpm, 1000 rpm, 1500 rpm, or 2500 rpm, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] Preferably, the time of the grinding treatment is 3 h - 10 h, for example: 3 h, 5 h, 7 h, 8 h, or 10 h, etc.

[0030] Preferably, the target particle size of the grinding treatment is 50 nm - 500 nm, for example: 50 nm, 100 nm, 200 nm, 300 nm, or 500 nm, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] The target particle size of the grinding treatment in the present invention is the median particle size D50 of the solid materials in the slurry.

[0032] Preferably, the temperature of the spray drying treatment in step (1) is 200°C - 300°C, for example: 200°C, 220°C, 250°C, 280°C, or 300°C, etc.

[0033] Preferably, the median particle size D50 of the lithium iron manganese phosphate intermediate in step (1) is 20 μm - 40 μm, for example: 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0034] Preferably, the feeding frequency of the airflow pulverization treatment in step (2) is 10 Hz to 50 Hz, such as: 10 Hz, 20 Hz, 30 Hz, 40 Hz or 50 Hz, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0035] Preferably, the classification frequency of the airflow pulverization treatment in step (2) is 30 Hz to 70 Hz, such as: 30 Hz, 40 Hz, 50 Hz, 60 Hz or 70 Hz, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] Preferably, the pulverization pressure of the airflow pulverization treatment in step (2) is 0.2 MPa to 0.6 MPa, such as: 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or 0.6 MPa, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the median particle size D50 of the lithium iron manganese phosphate intermediate single crystal particles in step (2) is 0.8 μm to 1.6 μm, such as: 0.8 μm, 1 μm, 1.2 μm, 1.4 μm or 1.6 μm, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] Preferably, the atmosphere of the calcination treatment in step (3) includes nitrogen and / or argon.

[0039] Preferably, the calcination treatment in step (3) includes first sintering and second sintering in sequence.

[0040] Preferably, the temperature of the first sintering is 300 °C to 400 °C, such as: 300 °C, 320 °C, 350 °C, 380 °C or 400 °C, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0041] Preferably, the time of the first sintering is 2 h to 6 h, such as: 2 h, 3 h, 4 h, 5 h or 6 h, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] Preferably, the temperature of the second sintering is 600 °C to 750 °C, such as: 600 °C, 620 °C, 650 °C, 700 °C or 750 °C, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] Preferably, the time of the second sintering is 6 h to 12 h, such as: 6 h, 7 h, 8 h, 10 h or 12 h, etc., not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] In a second aspect, the present invention provides a modified single crystal lithium iron manganese phosphate positive electrode material, which is prepared by the preparation method described in the first aspect.

[0045] In a third aspect, the present invention provides a positive electrode plate, which comprises the modified single crystal lithium manganese iron phosphate positive electrode material as described in the second aspect.

[0046] In a fourth aspect, the present invention provides a lithium-ion battery, comprising the positive electrode sheet as described in the third aspect.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention achieves the preparation of high-crystallinity, uniform single-crystal particles by sequentially optimizing the preparation process of lithium iron manganese phosphate through the synergistic effect of raw materials, while taking into account the structural stability of the material while significantly improving its compaction density, thereby improving the electrochemical performance of the lithium iron manganese phosphate positive electrode material.

[0049] (2) The modified single crystal lithium manganese iron phosphate cathode material of the present invention has a compaction density of up to 2.3523 g / cm at 221.6 MPa. 3 The 0.1C discharge capacity can reach more than 151.6 mAh / g, and the 500-cycle capacity retention rate can reach more than 95.5%. By adjusting the preparation conditions, the compaction density of the modified single-crystal lithium manganese iron phosphate positive electrode material under 221.6 MPa can reach 2.3836 g / cm 3 The 0.1C discharge specific capacity can reach more than 151.6mAh / g, and the 500-cycle capacity retention rate can reach more than 98.1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is an SEM image of the modified single crystal lithium manganese iron phosphate positive electrode material obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] Example 1

[0053] This embodiment provides a modified single crystal lithium iron manganese phosphate positive electrode material, which is prepared by the following method:

[0054] (1) Mix lithium hydroxide, iron oxide, manganese dioxide, phosphoric acid, carbon nanotubes, polyvinyl alcohol and water to obtain a mixed slurry with a solid content of 40%. Ball mill at a speed of 1000 rpm for 5 h until the median particle size of the solids in the slurry is 200 nm. After spray drying at 250 °C, obtain a lithium iron manganese phosphate intermediate with a median particle size D50 of 32 μm;

[0055] In the mixed slurry, Li:(Mn + Fe) = 1.02, Mn:Fe = 2:1, and the mass ratio of the total mass of lithium hydroxide, iron oxide, manganese dioxide, and phosphoric acid to the mass of polyvinyl alcohol is 100:2. The mass ratio of the total mass of lithium hydroxide, iron oxide, manganese dioxide, and phosphoric acid to the mass of carbon nanotubes is 100:10;

[0056] (2) Add the lithium iron manganese phosphate intermediate to a jet mill for jet milling. The feeding frequency of the jet milling is 30 Hz, the classification frequency is 50 Hz, and the milling pressure is 0.4 MPa to obtain a lithium iron manganese phosphate intermediate single crystal particle with a median particle size D50 of 1.2 μm;

[0057] (3) Load the lithium iron manganese phosphate intermediate single crystal particles into a graphite crucible. Sinter at 350 °C for 4 h in a nitrogen atmosphere and then sinter at 680 °C for 8 h to obtain the modified single crystal lithium iron manganese phosphate cathode material.

[0058] Example 2

[0059] This example provides a modified single crystal lithium iron manganese phosphate cathode material, which is prepared by the following method:

[0060] (1) Mix lithium oxalate, ferrous oxalate, manganese oxalate, phosphoric acid, glucose, polyethylene glycol and water to obtain a mixed slurry with a solid content of 35%. Ball mill at a speed of 1000 rpm for 10 h until the median particle size of the solids in the slurry is 100 nm. After spray drying at 250 °C, obtain a lithium iron manganese phosphate intermediate with a median particle size D50 of 20 μm;

[0061] In the mixed slurry, Li:(Mn + Fe) = 1.02, Mn:Fe = 1.5:1, and the mass ratio of the total mass of lithium oxalate, ferrous oxalate, manganese oxalate, and phosphoric acid to the mass of polyethylene glycol is 100:1. The mass ratio of the total mass of lithium oxalate, ferrous oxalate, manganese oxalate, and phosphoric acid to the mass of carbon nanotubes is 100:7;

[0062] (2) Add the lithium iron manganese phosphate intermediate to a jet mill for jet milling. The feeding frequency of the jet milling is 10 Hz, the classification frequency is 30 Hz, and the milling pressure is 0.2 MPa to obtain a lithium iron manganese phosphate intermediate single crystal particle with a median particle size D50 of 1.6 μm;

[0063] (3) Load the lithium iron manganese phosphate intermediate single crystal particles into a graphite crucible, sinter at 300 °C for 2 h under a nitrogen atmosphere, and then sinter at 600 °C for 8 h to obtain the modified single crystal lithium iron manganese phosphate cathode material.

[0064] Example 3

[0065] This example provides a modified single crystal lithium iron manganese phosphate cathode material, which is prepared by the following method:

[0066] (1) Mix lithium carbonate, ferric chloride, manganese oxalate, ammonium dihydrogen phosphate, glucose, oxalic acid and water to obtain a mixed slurry with a solid content of 50%. Ball mill at a speed of 2500 rpm for 3 h until the median particle size of the solids in the slurry is 500 nm. After spray drying at 250 °C, a lithium iron manganese phosphate intermediate with a median particle size D50 of 40 μm is obtained;

[0067] In the mixed slurry, Li:(Mn + Fe) = 1.02, Mn:Fe = 3:1, and the mass ratio of the total mass of lithium carbonate, ferric chloride, manganese oxalate, ammonium dihydrogen phosphate to the mass of oxalic acid is 100:5, and the mass ratio of the total mass of lithium carbonate, ferric chloride, manganese oxalate, ammonium dihydrogen phosphate to the mass of glucose is 100:15;

[0068] (2) Add the lithium iron manganese phosphate intermediate to a jet mill for jet milling. The feeding frequency of the jet milling is 50 Hz, the classification frequency is 70 Hz, and the milling pressure is 0.6 MPa. The median particle size D50 of the lithium iron manganese phosphate intermediate single crystal particles is 0.8 μm;

[0069] (3) Load the lithium iron manganese phosphate intermediate single crystal particles into a graphite crucible, sinter at 400 °C for 6 h under a nitrogen atmosphere, and then sinter at 750 °C for 6 h to obtain the modified single crystal lithium iron manganese phosphate cathode material.

[0070] Example 4

[0071] The difference between this example and Example 1 is only that the mass ratio of the total mass of lithium hydroxide, iron oxide, manganese dioxide, and phosphoric acid in step (1) to the mass of polyvinyl alcohol is 100:0.5, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Example 5

[0073] The difference between this example and Example 1 is only that the mass ratio of the total mass of lithium hydroxide, iron oxide, manganese dioxide, and phosphoric acid in step (1) to the mass of polyvinyl alcohol is 100:8, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Example 6

[0075] The difference between this embodiment and Embodiment 1 is only that the pressure of the air jet milling in step (2) is 0.1 MPa, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0076] Embodiment 7

[0077] The difference between this embodiment and Embodiment 1 is only that the pressure of the air jet milling in step (2) is 0.8 MPa, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0078] Comparative Example 1 [[ID=ll]]

[0079] The difference between this comparative example and Embodiment 1 is only that two-step sintering in step (3) is carried out first and then air jet milling in step (2), and other conditions and parameters are exactly the same as those in Embodiment 1.

[0080] Comparative Example 2

[0081] The difference between this comparative example and Embodiment 1 is only that polyvinyl alcohol is not added, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Embodiment 1 is only that carbon nanotubes are not added, and other conditions and parameters are exactly the same as those in Embodiment 1.

[0084] Performance test:

[0085] The lithium iron phosphate manganese oxide cathode materials prepared in the examples and comparative examples were tested. The lithium iron phosphate manganese oxide cathode materials prepared in the examples and comparative examples were respectively made into button cells for testing. The test results are shown in Table 1:

[0086] Table 1

[0087]

[0088] [[ID=4l]]

[0089] As can be seen from Table 1, from Embodiments 1-7, it can be obtained that the compacted density of the modified single-crystal lithium iron phosphate manganese oxide cathode material of the present invention can reach 2.3523 g / cm 3 above, the discharge specific capacity at 0.1C can reach above 151.6 mAh / g, and the capacity retention rate after 500 cycles can reach above 95.5%. By adjusting the preparation conditions, the compacted density of the modified single-crystal lithium iron phosphate manganese oxide cathode material prepared can reach 2.3836 g / cm 3 above, the discharge specific capacity at 0.1C can reach above 151.6 mAh / g, and the capacity retention rate after 500 cycles can reach above 98.1%.

[0090] Comparing Example 1 with Examples 4 - 5, it can be obtained that during the preparation process of the modified single-crystal lithium manganese iron phosphate cathode material of the present invention, the addition amount of the dispersant will affect its performance. Controlling the addition amount of the dispersant within 1% - 5% of the total mass of the lithium source, iron source, manganese source, and phosphorus source results in better performance of the prepared modified single-crystal lithium manganese iron phosphate cathode material. If the addition amount of the dispersant is too high, it is easy to cause an increase in the viscosity of the slurry and a deterioration in fluidity. Excessive dispersant during the sintering process will hinder the effective combination between particles, leading to a loose internal structure of the material. If the addition amount of the dispersant is too low, during the ball milling process, when the material reaches the nanoscale, it will agglomerate under the action of electrostatic force, making it difficult to further grind and reduce the size, and the slurry has poor homogeneity.

[0091] Comparing Example 1 with Examples 6 - 7, it can be obtained that during the preparation process of the modified single-crystal lithium manganese iron phosphate cathode material of the present invention, the pressure of air jet milling will affect its performance. Controlling the pressure of air jet milling within 0.2 MPa - 0.6 MPa results in better performance of the prepared modified single-crystal lithium manganese iron phosphate cathode material. If the pressure of air jet milling is too high, the gas pressure overload will damage the equipment, and at the same time, the primary particles will be further pulverized to produce fine powder. If the pressure of air jet milling is too low, the particles cannot be broken into primary particles, and the proportion of secondary particles is too high, resulting in too long air powdering time and affecting the temperature transfer during the subsequent sintering process.

[0092] Comparing Example 1 with Comparative Example 1, it can be obtained that the traditional method uses calcination followed by air jet milling. However, after calcination, the hardness of the material increases, the energy consumption of air jet milling is high and impurities are easily introduced, and the hard agglomerates formed during calcination are difficult to completely depolymerize. During the air jet milling process, the formed crystal structure may be damaged, resulting in an increase in defects and a decrease in material performance.

[0093] Comparing Example 1 with Comparative Example 2, it can be obtained that by adding a dispersant in the present invention, the fluidity of the slurry can be improved, making the morphology of the intermediate particles after spray drying more regular and the particle size distribution narrower. Furthermore, during the subsequent air jet milling and calcination processes, the particles can still maintain a complete crystal structure, and the stability of the material is greatly improved.

[0094] Comparing Example 1 with Comparative Example 3, it can be obtained that by adding a carbon source in the present invention, an amorphous carbon layer is formed on the surface of the single-crystal particles during the calcination process. The carbon layer can physically isolate the particles, limit the grain size during the calcination process, promote the formation of single crystals, and greatly improve the capacity of the material.

[0095] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a modified single-crystal lithium iron manganese phosphate cathode material, characterized in that, The preparation method includes the following steps: (1) Mix a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a dispersant, and a solvent to obtain a mixed slurry, and perform spray drying on the mixed slurry to obtain a lithium iron manganese phosphate intermediate; (2) Perform airflow pulverization on the lithium iron manganese phosphate intermediate to obtain single crystal particles of the lithium iron manganese phosphate intermediate; (3) Perform calcination on the single crystal particles of the lithium iron manganese phosphate intermediate to obtain the modified single crystal lithium iron manganese phosphate cathode material.

2. The preparation method according to claim 1, wherein The carbon source in step (1) includes any one or a combination of at least two of citric acid, starch, sucrose, glucose, carbon black, or carbon nanotubes; Preferably, the dispersant in step (1) includes any one or a combination of at least two of polyvinyl alcohol, polyethylene glycol, or oxalic acid; Preferably, the solvent in step (1) includes water.

3. The preparation method according to claim 1, characterized in that, Based on the total mass of the lithium source, iron source, manganese source, and phosphorus source being 100%, the addition amount of the dispersant is 1% - 5%; Preferably, based on the total mass of the lithium source, iron source, manganese source, and phosphorus source being 100%, the addition amount of the carbon source is 7% - 15%.

4. The preparation method according to any one of claims 1-3, characterized in that, The solid content of the mixed slurry in step (1) is 35% - 50%; Preferably, in the mixed slurry of step (1), the molar ratio of manganese element to iron element is (1 - 4):

1.

5. The preparation method according to any one of claims 1-4, characterized in that, Before the spray drying treatment in step (1), the mixed slurry is subjected to grinding treatment; Preferably, the rotation speed of the grinding treatment is 500 rpm - 2500 rpm; Preferably, the time of the grinding treatment is 3 h - 10 h; Preferably, the target particle size of the grinding treatment is 50 nm - 500 nm; Preferably, the temperature of the spray drying treatment in step (1) is 200°C - 300°C; Preferably, the median particle size D50 of the lithium iron manganese phosphate intermediate in step (1) is 20 μm - 40 μm.

6. The preparation method according to any one of claims 1-5, characterized in that, The feeding frequency of the airflow pulverization treatment in step (2) is 10 Hz - 50 Hz; Preferably, the classification frequency of the airflow pulverization treatment in step (2) is 30 Hz - 70 Hz; Preferably, the pulverization pressure of the airflow pulverization treatment in step (2) is 0.2 MPa - 0.6 MPa; Preferably, the median particle size D50 of the single crystal particles of the lithium iron manganese phosphate intermediate in step (2) is 0.8 μm - 1.6 μm.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The atmosphere of the calcination treatment in step (3) includes nitrogen and / or argon; Preferably, the calcination treatment in step (3) includes first sintering and second sintering in sequence; Preferably, the temperature of the first sintering is 300°C - 400°C; Preferably, the time of the first sintering is 2 h - 6 h; Preferably, the temperature of the second sintering is 600°C - 750°C; Preferably, the time of the second sintering is 6 h - 12 h.

8. A modified single-crystal lithium iron manganese phosphate cathode material, characterized in that, The modified single crystal lithium iron manganese phosphate cathode material is prepared by the preparation method according to any one of claims 1 - 7.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes the modified single crystal lithium iron manganese phosphate cathode material according to claim 8.

10. A lithium-ion battery, characterized in that, The lithium ion battery includes the positive electrode sheet according to claim 9.

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