Preparation method of lithium iron phosphate material, lithium iron phosphate material and application of lithium iron phosphate material

Abstract

The invention relates to the technical field of batteries, in particular to a preparation method of a lithium iron phosphate material, the lithium iron phosphate material and application of the lithium iron phosphate material. The preparation method of the lithium iron phosphate material comprises the following steps: (a) grinding a lithium source, an iron source, a phosphorus source, a carbon source, a fluxing material and a solvent to obtain mixed slurry; the ratio of the total mass of the iron source and the phosphorus source to the mass of the fluxing material is 1: (0.001-0.015); (b) the mixed slurry is subjected to spray drying, a spray drying nozzle comprises a two-fluid nozzle, and a first material is obtained; and (c) the first material is subjected to heat treatment, heat treatment comprises first constant-temperature treatment and second constant-temperature treatment, the temperature T1 of the first constant-temperature treatment is 450-650 DEG C, and the temperature T2 of the second constant-temperature treatment is 650-850 DEG C. The lithium iron phosphate material obtained by the method has the advantages of high compaction density, high tap density, high particle strength, proper specific surface area, good conductivity and excellent processability and electrochemical performance.

Description

[0001] This application claims the priority of a Singaporean patent application with application number 10202500160V, titled "Preparation Method of Lithium Iron Phosphate Material, Lithium Iron Phosphate Material and Its Application", filed with the Singapore Patent Office on January 20, 2025, the entire content of which is incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more particularly, to a preparation method of a lithium iron phosphate material, a lithium iron phosphate material and its application. Background Art

[0003] With the rapid development of the new energy vehicle industry, the power battery industry has grown rapidly. As a cathode material for lithium-ion batteries, lithium iron phosphate has gradually become a research and application hotspot due to its abundant resources, low price, good cycle stability, stability to electrolytes at high temperatures, and a stable discharge voltage platform. Spherical lithium iron phosphate is considered to be one of the effective ways to improve the performance of lithium iron phosphate materials because of its regular particle shape, high tap density, and advantages such as facilitating electrolyte penetration and lithium ion diffusion. However, the lithium iron phosphate materials obtained by traditional preparation methods have problems such as low compaction density, poor particle strength, uneven particle size distribution, and unsuitable specific surface area.

[0004] Therefore, how to provide a lithium iron phosphate material with high compaction density, high tap density, and suitable specific surface area is crucial for the development of batteries. Summary of the Invention

[0005] This application provides a preparation method of a lithium iron phosphate material, comprising the following steps:

[0006] (a) Grinding a lithium source, an iron source, a phosphorus source, a carbon source, a flux material and a solvent to obtain a mixed slurry; the total mass ratio of the iron source and the phosphorus source to the mass of the flux material is 1:(0.001 - 0.015);

[0007] (b) Spray-drying the mixed slurry, the nozzle of the spray-drying comprising a two-fluid nozzle, the spray temperature of the spray-drying being 180 - 300 °C, the spray pressure being 0.1 - 0.8 MPa, and the feeding frequency being 20 - 50 Hz, to obtain a first material;

[0008] (c) Heat-treating the first material, the heat-treatment comprising a first constant-temperature treatment and a second constant-temperature treatment, the temperature T1 of the first constant-temperature treatment being 450 - 650 °C, and the temperature T2 of the second constant-temperature treatment being 650 - 850 °C.

[0009] In some embodiments, the flux material comprises at least one of boric acid, calcium oxide and magnesium oxide.

[0010] In some embodiments, the ratio of the total mass of the iron source and the phosphorus source to the mass of the fluxing material is 1:(0.002 - 0.01).

[0011] In some embodiments, the fluxing material includes Material A and Material B. Material A is boric acid, and Material B is calcium oxide and / or magnesium oxide. The mass ratio of Material A to Material B is (7 - 9):(1 - 3).

[0012] In some embodiments, the molar ratio of the lithium source, the iron source, and the phosphorus source in terms of lithium element, iron element, and phosphorus element respectively is (1 - 1.08):(0.95 - 1):(0.95 - 1).

[0013] In some embodiments, the ratio of the total mass of the iron source and the phosphorus source to the mass of the carbon source is 1:(0.03 - 0.15).

[0014] In some embodiments, the carbon source includes at least one of sucrose, glucose, starch, carbon black, polyethylene glycol, and phenolic resin.

[0015] In some embodiments, the spray temperature for spray drying is 200 - 260°C, the spray pressure is 0.4 - 0.6 MPa, and the feeding frequency is 30 - 45 Hz.

[0016] In some embodiments, the difference between the temperature T2 of the second constant temperature treatment and the temperature T1 of the first constant temperature treatment satisfies: 180°C ≤ T2 - T1 ≤ 250°C.

[0017] In some embodiments, the time for the first constant temperature treatment is 2 - 10 h.

[0018] In some embodiments, the time for the second constant temperature treatment is 2 - 10 h.

[0019] In some embodiments, the heating rate during the heat treatment is 0.5 - 10°C / min.

[0020] In some embodiments, the heat treatment is carried out under a protective gas condition.

[0021] In some embodiments, the temperature of the first constant temperature treatment is 500 - 600°C, and the time for the first constant temperature treatment is 3 - 8 h. The temperature of the second constant temperature treatment is 700 - 800°C, and the time for the second constant temperature treatment is 4 - 8 h;

[0022] In some embodiments, the grinding process includes a first grinding and a second grinding; the rotation speed R1 of the first grinding is 300 - 400 r / min, the rotation speed R2 of the second grinding is 500 - 700 r / min, and the ratio of the rotation speed R1 of the first grinding to the rotation speed R2 of the second grinding satisfies: 1.25 ≤ R1 / R2 ≤ 2. The time of the first grinding is 0.5 - 4 h; the time of the second grinding is 0.5 - 6 h;

[0023] In some embodiments, the solid content of the mixed slurry is 20% - 60%.

[0024] In some embodiments, the particle size D50 of the materials in the mixed slurry is 200 - 400 nm.

[0025] In some embodiments, it further includes: screening the material after heat treatment, and the mesh number of the screening process is 180 - 250 meshes.

[0026] A lithium iron phosphate material is prepared by the preparation method of the lithium iron phosphate material described above.

[0027] In some embodiments, the tap density of the lithium iron phosphate material is 2.36 - 2.55 g / cm 3 .

[0028] In some embodiments, the bulk density of the lithium iron phosphate material is 1.82 - 2.2 g / cm 3 .

[0029] In some embodiments, the particle size D50 of the lithium iron phosphate material is 8.6 - 11 μm.

[0030] In some embodiments, the specific surface area of the lithium iron phosphate material is 5 - 8 m 2 / g.

[0031] In some embodiments, the resistivity of the lithium iron phosphate material is 10 - 39.1 Ω·cm.

[0032] In some embodiments, the particle strength of the lithium iron phosphate material is 72 - 160 MPa.

[0033] An electrode sheet contains the lithium iron phosphate material prepared by the preparation method of the lithium iron phosphate material described above, or the lithium iron phosphate material described above.

[0034] A battery contains the electrode sheet.

[0035] An electrical device contains the battery. Description of the Drawings

[0036] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only exemplarily represent the embodiments of the present application, the dimensional ratios in the drawings do not directly correspond to the actual ratios of the embodiments, and at the same time, the following drawings only show some embodiments of the present application, so they should not be regarded as a limitation of the scope.

[0037] Figure 1 SEM image of the lithium iron phosphate material of Example 1;

[0038] Figure 2 CP diagram of the lithium iron phosphate material of Example 1;

[0039] Figure 3 Comparison diagram before and after the particle strength test of the lithium iron phosphate material of Example 1;

[0040] Figure 4 SEM image of the lithium iron phosphate material of Example 2;

[0041] Figure 5 SEM image of the lithium iron phosphate material of Comparative Example 1;

[0042] Figure 6 SEM image of the lithium iron phosphate material of Comparative Example 3;

[0043] Figure 7 SEM image of the lithium iron phosphate material of Comparative Example 5. Detailed implementation manners

[0044] The advantages of the embodiments in the application content will be clarified in the embodiment part of the following specification. Some are obvious according to the specification, or can be obtained through some embodiments of the embodiments of the present application.

[0045] The technical solutions of the present application will be further described below in conjunction with the accompanying drawings and through some embodiments.

[0046] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments described herein are only used to explain the present application and are not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other. Without departing from the principles of the embodiments of the present application, several improvements and retouches can also be made, and these improvements and retouches are also regarded as the protection scope of the embodiments of the present application.

[0047] According to one aspect of the present application, the present application relates to a preparation method of a lithium iron phosphate material, including the following steps:

[0048] (a) Grind a lithium source, an iron source, a phosphorus source, a carbon source, a flux material and a solvent to obtain a mixed slurry; the ratio of the total mass of the iron source and the phosphorus source to the mass of the flux material is 1:(0.001 - 0.015).

[0049] (b) Spray-dry the mixed slurry. The nozzle for spray-drying includes a two-fluid nozzle. The spray temperature for spray-drying is 180 - 300 °C, the spray pressure is 0.1 - 0.8 MPa, and the feeding frequency is 20 - 50 Hz to obtain a first material.

[0050] (c) Heat-treat the first material. The heat treatment includes a first constant-temperature treatment and a second constant-temperature treatment. The temperature T1 of the first constant-temperature treatment is 450 - 650 °C, and the temperature T2 of the second constant-temperature treatment is 650 - 850 °C.

[0051] The preparation method of the lithium iron phosphate material of the present application can solve the problems of low tap density, poor particle strength, uneven particle size distribution, and unsuitable specific surface area existing in the preparation of lithium iron phosphate materials by traditional methods. The present application uses an appropriate amount of flux material, which is beneficial to promoting the melting of the spheres and enhancing the particle strength inside the spheres; further, a two-fluid nozzle is used for spray-drying, and the temperature, pressure and feeding frequency are controlled to meet certain conditions, which can optimize the performance of the first material; on the basis of the flux material and two-fluid nozzle drying, through appropriate heat treatment conditions, the low-temperature first constant-temperature treatment can optimize carbon coating and make the reaction more complete, and the high-temperature second constant-temperature treatment is beneficial to further optimizing the tap density and particle strength of the material and obtaining a suitable specific surface area; the present application adds an appropriate flux material to the raw materials, cooperates with appropriate spray-drying conditions and heat treatment conditions, and each step and parameter conditions are coordinated, so that the obtained lithium iron phosphate material has a high tap density, a high bulk density, high particle strength, good electrical conductivity, good structural stability, and can improve the processing performance and electrochemical performance of the material.

[0052] In some embodiments, the fluxing material includes one or a combination of boric acid, calcium oxide, and magnesium oxide, such as boric acid and calcium oxide, boric acid and magnesium oxide. In some embodiments, the fluxing material includes Material A and Material B. Material A is boric acid, and Material B is calcium oxide and / or magnesium oxide. The mass ratio of Material A to Material B is (7-9):(1-3). With an appropriate mass ratio of Material A and Material B, they can better cooperate to exert their functions and improve the fluxing effect. In some embodiments, the ratio of the total mass of the iron source and the phosphorus source to the mass of the fluxing material is, for example, 1:0.001, 1:0.002, 1:0.005, 1:0.008, 1:0.009, 1:0.01, 1:0.011, 1:0.012, 1:0.015, etc. In some embodiments, the ratio of the total mass of the iron source and the phosphorus source to the mass of the fluxing material is 1:(0.002-0.01). The fluxing material of the present application needs to adopt an appropriate dosage ratio. If the dosage ratio is too low, the fluxing effect is not obvious, and the improvement of the material performance is poor. If the dosage of the fluxing material is too large, it will not only cause waste but also affect the performance of the material. By adding an appropriate dosage ratio of the fluxing material to the raw materials and combining with spray drying under appropriate conditions, it is beneficial to promote the melting of the material particles during the heat treatment process, enhance the strength of the internal particles of the material, and is beneficial to improving the processing performance and electrochemical performance of the lithium iron phosphate material.

[0053] In some embodiments, the molar ratio of the lithium source, the iron source, and the phosphorus source in terms of lithium element, iron element, and phosphorus element is (1-1.08):(0.95-1):(0.95-1), such as 1:0.95:0.95, 1.05:0.97:0.97, 1.06:1:1, etc. In some embodiments, the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium nitrate. The iron source includes one or more of iron oxide, iron phosphate, ferric oxide, and ferrous oxalate. The phosphorus source includes one or more of phosphoric acid, iron phosphate, and ammonium dihydrogen phosphate.

[0054] In some embodiments, the ratio of the total mass of the iron source and the phosphorus source to the mass of the carbon source is 1:(0.03-0.15), such as 1:0.05, 1:0.07, 1:0.09, 1:0.11, 1:0.13, or 1:0.15, etc. By adopting an appropriate dosage ratio of the carbon source in the present application, a carbon coating layer with a uniform thickness can be formed on the surface of the lithium iron phosphate material, which is beneficial to improving the electrochemical performance of the material. In some embodiments, the carbon source includes one or a combination of sucrose, glucose, starch, carbon black, polyethylene glycol, and phenolic resin, such as a combination of sucrose and glucose, a combination of carbon black and polyethylene glycol, a combination of carbon black, polyethylene glycol, and phenolic resin, etc. In some embodiments, the mass ratio of sucrose to glucose is (0.5-1):(1-2).

[0055] In some embodiments, the grinding process includes a first grinding and a second grinding. The first grinding is carried out by ball milling, and the second grinding is carried out by sand milling. The rotation speed R1 of the first grinding is 300 - 400 r / min, including but not limited to 300 r / min, 320 r / min, 350 r / min, 370 r / min, 400 r / min, etc., or the range values between any two of them. The rotation speed R2 of the second grinding is 500 - 700 r / min, including but not limited to 500 r / min, 530 r / min, 550 r / min, 580 r / min, 600 r / min, 620 r / min, 650 r / min, 700 r / min, etc., or the range values between any two of them. The ratio of the rotation speed R1 of the first grinding to the rotation speed R2 of the second grinding satisfies: 1.25 ≤ R1 / R2 ≤ 2, such as 1.25, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc., or the range values between any two of them. The time of the first grinding is 0.5 - 4 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc. The time of the second grinding is 0.5 - 6 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 5 h, 6 h, etc. The present application adopts appropriate first grinding and second grinding, and limits the ratio of the rotation speed R1 of the first grinding to the rotation speed R2 of the second grinding to meet appropriate conditions. Through the cooperation of the two, it can ensure sufficient grinding of the material to obtain a mixed slurry with appropriate particle size and solid content and uniform dispersion.

[0056] In some embodiments, the solid content of the mixed slurry is 20% - 60%, including but not limited to 20%, 25%, 30%, 35%, 40%, 45%, 55%, 60%, etc., or the range values between any two of them. In some embodiments, the particle size D50 of the material in the mixed slurry is 200 - 400 nm, including but not limited to 200 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 370 nm, 400 nm, etc., or the range values between any two of them. The mixed slurry of the present application has appropriate solid content and material particle size, which is beneficial to the subsequent spray drying process.

[0057] The spray drying in this application uses a two-fluid nozzle. The two-fluid nozzle sprays very fine mist, which is beneficial to the physical and chemical properties of the first material, making the interior of the material dense, reducing the generation of pores, and making the structural framework more stable, so that it is less likely to collapse or fall off during the preparation of the electrode sheet. In some embodiments, the spray drying temperature is 180 - 300 °C, including but not limited to 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 250 °C, 280 °C, 290 °C, 300 °C, etc., or any range value between any two of them. The spray pressure is 0.1 - 0.8 MPa, including but not limited to 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, etc., or any range value between any two of them. The feeding frequency is 20 - 50 Hz, including but not limited to 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz or 50 Hz, etc., or any range value between any two of them. In some embodiments, the spray drying temperature is 200 - 260 °C, the spray pressure is 0.4 - 0.6 MPa, and the feeding frequency is 30 - 45 Hz. By limiting the temperature, pressure and feeding frequency of spray drying within an appropriate range, this application can ensure the internal density of the material, reduce pores, improve the structural stability, and is more conducive to improving the physical and chemical properties of the first material. If the temperature, pressure and feeding frequency of spray drying do not meet the above conditions, it will affect the stability of the first material, resulting in poor strength of the final lithium iron phosphate material and reduced electrochemical performance.

[0058] In some embodiments, the difference between the temperature T2 of the second isothermal treatment and the temperature T1 of the first isothermal treatment satisfies: 180°C ≤ T2 - T1 ≤ 250°C; the difference T2 - T1 between the temperature T2 of the second isothermal treatment and the temperature T1 of the first isothermal treatment is 180°C, 190°C, 200°C, 220°C, 230°C, 250°C, etc. The difference between the temperature T2 of the second isothermal treatment and the temperature T1 of the first isothermal treatment in this application is within a suitable range, which is more conducive to improving the tap density and vibration density of the finally obtained lithium iron phosphate material, with high particle strength and a suitable specific surface area. The temperature of the first isothermal treatment is 450 - 650°C, including but not limited to 450°C, 480°C, 500°C, 510°C, 520°C, 550°C, 580°C, 600°C, 620°C or 650°C, etc., or the range values between any two of them. The time of the first isothermal treatment is 2 - 10 h, including but not limited to 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., or the range values between any two of them. The temperature of the second isothermal treatment is 650 - 850°C, including but not limited to 650°C, 680°C, 700°C, 720°C, 750°C, 780°C, 800°C, 820°C or 850°C, etc., or the range values between any two of them. The time of the second isothermal treatment is 2 - 10 h, including but not limited to 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., or the range values between any two of them. The temperature of the first isothermal treatment is 500 - 600°C, and the time of the first isothermal treatment is 3 - 8 h; the temperature of the second isothermal treatment is 700 - 800°C, and the time of the second isothermal treatment is 4 - 8 h. In some embodiments, the heating rate during the heat treatment is 0.5 - 10°C / min, including but not limited to 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 10°C / min, etc. In some embodiments, the heating rate during the heat treatment is 1.5 - 8°C / min. In some embodiments, the heat treatment is carried out under a protective gas condition, such as nitrogen, argon, helium, etc. This application adopts a suitable first isothermal treatment to facilitate carbon coating and make the reaction more complete. Adopting a suitable second isothermal treatment can further improve the strength of the material, obtain a suitable specific surface area and good conductivity. If a single isothermal treatment or two isothermal treatments do not meet the above conditions, it will affect the particle strength of the finally obtained lithium iron phosphate material, as well as its processing performance and electrochemical performance.

[0059] In some embodiments, the method for preparing the lithium iron phosphate material further includes: screening the heat-treated material to obtain a lithium iron phosphate material with a suitable particle size. The mesh number of the screening treatment is 180 - 250 meshes, such as 180 meshes, 200 meshes, 220 meshes, 250 meshes, etc., or the range values between any two of them.

[0060] According to another aspect of the present application, the present application further relates to a lithium iron phosphate material, which is prepared by the preparation method of the lithium iron phosphate material.

[0061] The lithium iron phosphate material of the present application has a high tap density, high strength, suitable specific surface area, high electrical conductivity, good processing performance, and excellent electrochemical performance.

[0062] In some embodiments, the tap density of the lithium iron phosphate material is 2.36 - 2.55 g / cm 3 , including but not limited to 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.52 g / cm 3 , 2.55 g / cm 3 and so on. In some embodiments, the bulk density of the lithium iron phosphate material is 1.82 - 2.2 g / cm 3 , including but not limited to 1.9 g / cm 3 , 1.95 g / cm 3 , 2 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 and so on. In some embodiments, the particle size D50 of the lithium iron phosphate material is 8.6 - 11 μm, such as 8.6 μm, 8.8 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, etc. In some embodiments, the specific surface area of the lithium iron phosphate material is 5 - 8 m 2 / g, such as 5 m 2 / g, 5.2 m 2 / g, 5.5 m 2 / g, 5.8 m 2 / g, 6 m 2 / g, 6.2 m 2 / g or 6.5 m 2 / g and so on. In some embodiments, the resistivity of the lithium iron phosphate material is 10 - 39.1 Ω·cm, such as 10 Ω·cm, 12 Ω·cm, 15 Ω·cm, 16 Ω·cm, 17 Ω·cm, 20 Ω·cm or 21.5 Ω·cm, etc. In some embodiments, the particle strength of the lithium iron phosphate material is 72 - 160 MPa, such as 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, etc.

[0063] According to another aspect of the present application, the present application further relates to an electrode sheet, which contains the lithium iron phosphate material prepared by the preparation method of the above-mentioned lithium iron phosphate material, or the above-mentioned lithium iron phosphate material.

[0064] In some embodiments, the electrode sheet includes a positive current collector and a positive electrode layer located on at least one surface of the positive current collector. The positive electrode layer contains the above-mentioned lithium iron phosphate material, binder, and conductive agent. In some embodiments, the mass content of the lithium iron phosphate material in the positive electrode layer is 88% to 95%.

[0065] According to another aspect of the present application, the present application also relates to a battery including the above-mentioned electrode sheet.

[0066] The battery of the present application has a high specific capacity, high Coulomb efficiency, excellent cycling performance, and safety performance.

[0067] In some embodiments, the battery includes the above-mentioned electrode sheet, negative electrode sheet, separator, and electrolyte.

[0068] According to another aspect of the present application, the present application also relates to an electrical device including the above-mentioned battery. The electrical device includes a tablet computer, a laptop computer, an electric vehicle, an electric tool, etc.

[0069] The following will be further explained with specific examples.

[0070] Example 1

[0071] A preparation method of a lithium iron phosphate material includes the following steps:

[0072] (1) Lithium carbonate, iron phosphate, a carbon source (sucrose and glucose), a flux material (boric acid), and water are mixed evenly. Li in the lithium source and Fe in the iron source are weighed according to a molar ratio of 1.05:0.97. The mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, and the mass ratio of boric acid to iron phosphate is 0.003:1 to obtain a mixed system.

[0073] (2) The above mixed system is subjected to a first grinding. The first grinding uses ball milling with a rotation speed of 350 r / min and a time of 1 h to obtain a primary ball-milled slurry; the obtained ball-milled slurry is transferred to a sand mill for further thorough grinding. The sand milling rotation speed is 600 r / min, the sand milling time is 70 min, the solid content of the slurry is controlled at 40%, and the particle size of the sand mill particles is controlled at D50 of 350 nm to obtain a sand-milled slurry.

[0074] (3) The obtained sand-milled slurry is transferred to a spray tower for precursor spray granulation; the spray temperature is 260 °C, a two-fluid spray head is selected for the spray head, the spray pressure is controlled at 0.5 MPa, and the feeding frequency is controlled at 35 Hz to obtain a spray precursor of primary spherical particles.

[0075] (4) Put the obtained spray precursor into a crucible and perform heat treatment in a nitrogen atmosphere. The heat treatment includes a first isothermal treatment and a second isothermal treatment. Control the heating rate of the box furnace to be 2.5 °C / min. The temperature of the first isothermal treatment is 550 °C, the isothermal treatment time is 6 h, the temperature of the second isothermal treatment is 760 °C, and the isothermal treatment time is 4 h to obtain a sintered finished material. Screen the finished material through a 200-mesh sieve to obtain the lithium iron phosphate material.

[0076] The scanning electron microscope image of the lithium iron phosphate material in this example is as Figure 1 shown; the CP image of the lithium iron phosphate material is as Figure 2 shown. The comparison images of the particle strength of the lithium iron phosphate material before and after testing are as Figure 3 shown, where (a) is before testing and (b) is after testing.

[0077] Example 2

[0078] A preparation method of a lithium iron phosphate material includes the following steps:

[0079] (1) Mix lithium carbonate, iron phosphate, a carbon source (sucrose and glucose), a flux material (boric acid) and water evenly. Weigh Li in the lithium source and Fe in the iron source according to a molar ratio of 1.05:0.97. The mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, and the mass ratio of boric acid to iron phosphate is 0.003:1 to obtain a mixed system.

[0080] (2) Perform a first grinding on the above mixed system. The first grinding uses ball milling with a rotation speed of 400 r / min and a time of 1 h to obtain a primary ball-milled slurry; transfer the obtained ball-milled slurry to a sand mill for further thorough grinding. The sand milling rotation speed is 650 r / min, the sand milling time is 70 min, control the solid content of the slurry to be 40%, and control the particle size of the sand milled particles to D50 of 350 nm to obtain a sand-milled slurry.

[0081] (3) Transfer the obtained sand-milled slurry to a spray tower for precursor spray granulation; the spray temperature is 220 °C, select a two-fluid spray head for the spray nozzle, control the spray pressure at 0.4 MPa, and control the feeding frequency at 32 Hz to obtain a spray precursor of primary spherical particles.

[0082] (4) Put the obtained spray precursor into a crucible and perform heat treatment in a nitrogen atmosphere. The heat treatment includes a first isothermal treatment and a second isothermal treatment. Control the heating rate of the box furnace to be 2.5 °C / min. The temperature of the first isothermal treatment is 550 °C, the isothermal treatment time is 6 h, the temperature of the second isothermal treatment is 760 °C, and the isothermal treatment time is 4 h to obtain a sintered finished material. Screen the finished material through a 200-mesh sieve to obtain the lithium iron phosphate material.

[0083] The scanning electron microscope image of the lithium iron phosphate material in this embodiment is as Figure 4 shown.

[0084] Example 3

[0085] A method for preparing a lithium iron phosphate material, comprising the following steps:

[0086] (1) Mix lithium carbonate, iron phosphate, a carbon source (sucrose and glucose), a flux material (boric acid) and water evenly. Weigh Li in the lithium source and Fe in the iron source according to a molar ratio of 1.05:0.97. The mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, and the mass ratio of boric acid to iron phosphate is 0.003:1 to obtain a mixed system.

[0087] (2) Perform a first grinding on the above mixed system. The first grinding uses ball milling at a rotation speed of 300 r / min for 1.5 h to obtain a primary ball-milled slurry; transfer the obtained ball-milled slurry to a sand mill for further thorough grinding. The sand milling speed is 500 r / min, the sand milling time is 1.5 h, control the solid content of the slurry at 35%, and control the particle size of the sand milling particles at D50 of 330 nm to obtain a sand-milled slurry.

[0088] (3) Transfer the obtained sand-milled slurry to a spray tower for precursor spray granulation; the spray temperature is 200 °C, select a two-fluid spray head for the spray nozzle, control the spray pressure at 0.4 MPa, and control the feeding frequency at 45 Hz to obtain a spray precursor of primary spherical particles.

[0089] (4) Load the obtained spray precursor into a crucible and perform heat treatment in a nitrogen atmosphere. The heat treatment includes a first constant temperature treatment and a second constant temperature treatment. Control the heating rate of the box furnace at 5 °C / min. The temperature of the first constant temperature treatment is 600 °C, the constant temperature treatment time is 5 h, the temperature of the second constant temperature treatment is 800 °C, and the constant temperature treatment time is 3 h to obtain a sintered finished product. Sieve the finished product through a 200-mesh sieve to obtain the lithium iron phosphate material.

[0090] Example 4

[0091] A method for preparing a lithium iron phosphate material, comprising the following steps:

[0092] (1) Mix lithium carbonate, iron phosphate, a carbon source (sucrose and glucose), a flux material (boric acid) and water evenly. Weigh Li in the lithium source and Fe in the iron source according to a molar ratio of 1.05:0.97. The mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, and the mass ratio of boric acid to iron phosphate is 0.003:1 to obtain a mixed system.

[0093] (2) Perform the first grinding on the above mixed system. The first grinding uses ball milling with a rotational speed of 550 r / min and a time of 1.5 h to obtain a primary ball-milled slurry. Transfer the obtained ball-milled slurry to a sand mill for further thorough grinding. The sand milling rotational speed is 600 r / min, the sand milling time is 1.5 h, control the solid content of the slurry at 35%, and control the particle size of the sand milling particles at D50 of 330 nm to obtain a sand-milled slurry.

[0094] (3) Transfer the obtained sand-milled slurry to a spray tower for precursor spray granulation. The spray temperature is 260 °C, select a two-fluid spray nozzle, control the spray pressure at 0.6 MPa, and control the feeding frequency at 30 Hz to obtain a spray precursor of primary spherical particles.

[0095] (4) Load the obtained spray precursor into a crucible and perform heat treatment in a nitrogen atmosphere. The heat treatment includes a first constant-temperature treatment and a second constant-temperature treatment. Control the heating rate of the box furnace at 5 °C / min. The temperature of the first constant-temperature treatment is 500 °C, the constant-temperature treatment time is 8 h, the temperature of the second constant-temperature treatment is 700 °C, and the constant-temperature treatment time is 8 h to obtain a sintered finished product. Screen the finished product through a 200-mesh sieve to obtain a lithium iron phosphate material.

[0096] Example 5

[0097] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0098] (1) Mix lithium carbonate, iron phosphate, a carbon source (sucrose and glucose), a flux material, and water evenly. Weigh Li in the lithium source and Fe in the iron source according to a molar ratio of 1.05:0.97. The mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, the flux material is boric acid, calcium oxide, and magnesium oxide, the mass ratio of boric acid, calcium oxide, and magnesium oxide is 8:1:1, and the mass ratio of the flux material to iron phosphate is 0.005:1 to obtain a mixed system.

[0099] (2) Perform the first grinding on the above mixed system. The first grinding uses ball milling with a rotational speed of 380 r / min and a time of 1.5 h to obtain a primary ball-milled slurry. Transfer the obtained ball-milled slurry to a sand mill for further thorough grinding. The sand milling rotational speed is 620 r / min, the sand milling time is 1.5 h, control the solid content of the slurry at 35%, and control the particle size of the sand milling particles at D50 of 330 nm to obtain a sand-milled slurry.

[0100] (3) Transfer the obtained sand-milled slurry to a spray tower for precursor spray granulation. The spray temperature is 240 °C, select a two-fluid spray nozzle, control the spray pressure at 0.5 MPa, and control the feeding frequency at 40 Hz to obtain a spray precursor of primary spherical particles.

[0101] (4) Place the obtained spray precursor into a crucible and conduct heat treatment under a nitrogen atmosphere. The heat treatment includes a first isothermal treatment and a second isothermal treatment. Control the heating rate of the box furnace to be 5 °C / min. The temperature of the first isothermal treatment is 580 °C, and the isothermal treatment time is 5 h. The temperature of the second isothermal treatment is 780 °C, and the isothermal treatment time is 3 h to obtain the sintered finished material. Screen the finished material through a 200-mesh sieve to obtain the lithium iron phosphate material.

[0102] Example 6

[0103] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0104] (1) Mix lithium carbonate, iron phosphate, a carbon source (sucrose and glucose), a flux material (boric acid) and water evenly. Weigh Li in the lithium source and Fe in the iron source according to a molar ratio of 1.05:0.97. The mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, and the mass ratio of boric acid to iron phosphate is 0.01:1 to obtain a mixed system.

[0105] (2) Conduct a first grinding on the above mixed system. The first grinding uses ball milling, with a rotation speed of 300 r / min and a time of 4 h to obtain a primary ball-milled slurry; transfer the obtained ball-milled slurry to a sand mill for further thorough grinding. The sand milling speed is 500 r / min, the sand milling time is 6 h, control the solid content of the slurry to be 45%, and control the particle size of the sand milled particles at D50 of 370 nm to obtain a sand-milled slurry.

[0106] (3) Transfer the obtained sand-milled slurry to a spray tower for precursor spray granulation; the spray temperature is 300 °C, select a two-fluid spray nozzle for the spray head, control the spray pressure at 0.8 MPa, and control the feeding frequency at 20 Hz to obtain a spray precursor of primary spherical particles.

[0107] (4) Place the obtained spray precursor into a crucible and conduct heat treatment under a nitrogen atmosphere. The heat treatment includes a first isothermal treatment and a second isothermal treatment. Control the heating rate of the box furnace to be 5 °C / min. The temperature of the first isothermal treatment is 650 °C, and the isothermal treatment time is 2 h. The temperature of the second isothermal treatment is 850 °C, and the isothermal treatment time is 2 h to obtain the sintered finished material. Screen the finished material through a 200-mesh sieve to obtain the lithium iron phosphate material.

[0108] Example 7

[0109] A preparation method of a lithium iron phosphate material, comprising the following steps:

[0110] (1) Mix lithium carbonate, iron phosphate, carbon sources (sucrose and glucose), fluxing materials (boric acid) and water evenly. Weigh Li in the lithium source and Fe in the iron source according to a molar ratio of 1.05:0.97, the mass ratio of the carbon source to iron phosphate is 0.1:1, the weight ratio of sucrose to glucose is 1:1, and the mass ratio of boric acid to iron phosphate is 0.002:1 to obtain a mixed system.

[0111] (2) Conduct the first grinding on the above mixed system. The first grinding uses ball milling with a rotation speed of 400 r / min and a time of 0.5 h to obtain a primary ball-milled slurry; transfer the obtained ball-milled slurry to a sand mill for further thorough grinding. The sand milling speed is 700 r / min, the sand milling time is 1 h, control the solid content of the slurry at 35%, and control the particle size of the sand milled particles at D50 of 300 nm to obtain a sand-milled slurry.

[0112] (3) Transfer the obtained sand-milled slurry to a spray tower for precursor spray granulation; the spray temperature is 180 °C, select a two-fluid spray nozzle, control the spray pressure at 0.1 MPa, and control the feeding frequency at 50 Hz to obtain a spray precursor of primary spherical particles.

[0113] (4) Load the obtained spray precursor into a crucible and conduct heat treatment in a nitrogen atmosphere. The heat treatment includes a first constant temperature treatment and a second constant temperature treatment. Control the heating rate of the box furnace at 5 °C / min, the temperature of the first constant temperature treatment is 450 °C, the constant temperature treatment time is 10 h, the temperature of the second constant temperature treatment is 650 °C, and the constant temperature treatment time is 10 h to obtain a sintered finished product. Screen the finished product through a 200-mesh sieve to obtain a lithium iron phosphate material.

[0114] Comparative Example 1

[0115] A preparation method of a lithium iron phosphate material, different from Example 1 in that:

[0116] Step (4): Load the obtained spray precursor into a crucible and conduct heat treatment in a nitrogen atmosphere. The heating rate of the heat treatment is 5 °C / min, the temperature of the constant temperature treatment is 750 °C, and the constant temperature treatment time is 10 h.

[0117] The scanning electron microscope image of the lithium iron phosphate material of this comparative example is as Figure 5 shown.

[0118] Comparative Example 2

[0119] A preparation method of a lithium iron phosphate material, different from Example 1 in that:

[0120] Step (4): Place the obtained spray precursor into a crucible and perform heat treatment in a nitrogen atmosphere. The heat treatment includes a first constant-temperature treatment and a second constant-temperature treatment. Control the heating rate of the box furnace to be 5 °C / min. The temperature of the first constant-temperature treatment is 700 °C, and the constant-temperature treatment time is 6 h. The temperature of the second constant-temperature treatment is 600 °C, and the constant-temperature treatment time is 4 h to obtain a sintered finished material. Screen the finished material through a 200-mesh sieve to obtain the lithium iron phosphate material.

[0121] Comparative Example 3

[0122] A preparation method of a lithium iron phosphate material, which is different from Example 1 in that:

[0123] No flux material is added in step (1).

[0124] The scanning electron microscope image of the lithium iron phosphate material in this comparative example is as Figure 6 shown.

[0125] Comparative Example 4

[0126] A preparation method of a lithium iron phosphate material, which is different from Example 1 in that:

[0127] In step (1), the mass ratio of boric acid to iron phosphate is 0.1:1.

[0128] Comparative Example 5

[0129] A preparation method of a lithium iron phosphate material, which is different from Example 1 in that:

[0130] In step (3), a centrifugal nozzle is selected for spraying, the atomizer frequency is 280 Hz, and the feeding frequency is controlled at 10 Hz.

[0131] The scanning electron microscope image of the lithium iron phosphate material in this comparative example is as Figure 7 shown.

[0132] Comparative Example 6

[0133] A preparation method of a lithium iron phosphate material, which is different from Example 1 in that:

[0134] In step (3), the spraying temperature of spray drying is 150 °C, the spraying pressure is 2 MPa, and the feeding frequency is 10 Hz.

[0135] Comparative Example 7

[0136] A preparation method of a lithium iron phosphate material, which is different from Example 1 in that:

[0137] In step (3), the spraying temperature of spray drying is 350 °C, the spraying pressure is 1.5 MPa, and the feeding frequency is 60 Hz.

[0138] Experimental Example

[0139] I. Performance Testing of Lithium Iron Phosphate Materials

[0140] The lithium iron phosphate materials prepared in each example and comparative example were respectively subjected to the following performance tests:

[0141] 1. Tap Density

[0142] The tap density was tested using a tap density tester under a pressure of 3T, GB / T 44330.

[0143] 2. Bulk Density

[0144] The bulk density was tested using a Quantachrome bulk density analyzer, GB / T 5162.

[0145] 3. Particle Size

[0146] The particle size was tested using a Malvern - 3000 particle size analyzer, GB / T 19077.

[0147] 4. Specific Surface Area

[0148] The specific surface area was tested using a DX type dynamic adsorption specific surface area analyzer, GB / T 13390.

[0149] 5. Resistivity

[0150] The resistivity was tested using a powder resistivity tester, GB / T 24521.

[0151] 6. Particle Strength

[0152] The particle strength was tested using a dynamic ultra - micro hardness tester, GB / T 41948.

[0153] The performance test results of the lithium iron phosphate materials are shown in Table 1.

[0154] Table 1

[0155]

[0156]

[0157] As can be seen from Table 1, for the methods of each example in this application, by adding a fluxing material to the raw materials, adopting appropriate spray - drying conditions and heat - treatment conditions, and coordinating each step, the obtained lithium iron phosphate materials have a high tap density and bulk density, high particle strength, appropriate D50 particle size, appropriate specific surface area, and good conductivity.

[0158] In Comparative Example 1, only one constant - temperature heat - treatment was adopted. Compared with Example 1, the tap density and bulk density of the obtained lithium iron phosphate materials were both reduced, the particle strength decreased, the specific surface area increased, and the conductivity decreased.

[0159] Although two constant temperature treatments were adopted in Comparative Example 2, the temperature of the first constant temperature treatment was higher than that of the second constant temperature treatment. Compared with Example 1, the tap density and the vibration density of the obtained lithium iron phosphate material were slightly decreased, the particle strength was decreased, and the conductivity was decreased.

[0160] In Comparative Example 3, no fluxing agent was used, and it could not play a good fluxing effect during the heat treatment process. The tap density and the vibration density of the obtained lithium iron phosphate material were decreased, the particle strength was decreased, and the conductivity was decreased.

[0161] The tap density and the vibration density of the lithium iron phosphate material obtained in Comparative Example 4 were slightly decreased, the particle strength was decreased, and the conductivity was decreased.

[0162] In Comparative Example 5, a conventional centrifugal nozzle was used, and more pores were generated. The tap density and the vibration density of the obtained lithium iron phosphate material were low, the particle strength was significantly decreased, and the conductivity was significantly decreased.

[0163] The spray drying conditions of Comparative Example 6 and Comparative Example 7 did not meet the scope defined in the present application. The tap density and the vibration density of the obtained lithium iron phosphate material were slightly lower, the particle strength was decreased, and the conductivity was decreased.

[0164] II. Battery performance test

[0165] The lithium iron phosphate materials prepared in each of the examples and comparative examples were respectively used to prepare batteries, specifically including:

[0166] The lithium iron phosphate material, the conductive agent and the binder were mixed evenly at a mass ratio of 90:5:5, coated on the aluminum foil, and then dried in a vacuum drying oven at 100 °C for 10 h to obtain a positive electrode sheet. The obtained positive electrode sheet was cut into a circular sheet with a diameter of 10 mm; a lithium sheet with a diameter of 15 mm was used as the negative electrode sheet. A battery was assembled in a glove box using the positive electrode sheet, the separator, the electrolyte and the negative electrode sheet. The battery was subjected to a 0.1C charge-discharge test at a voltage of 2-3.75V.

[0167] The test results of the batteries are shown in Table 2.

[0168] Table 2 Test results of the batteries

[0169]

[0170]

[0171] The batteries prepared from the lithium iron phosphate materials obtained in the examples of the present application have high specific capacity, high Coulomb efficiency, good cycle performance and high safety.

[0172] The batteries prepared from the lithium iron phosphate materials of Comparative Examples 1-7 have low specific capacity and poor cycle performance.

[0173] Industrial applicability

[0174] In summary, the present application provides a preparation method of a lithium iron phosphate material, the lithium iron phosphate material and its application. In the preparation method of the lithium iron phosphate material, by adding a suitable flux material to the raw materials, and in combination with suitable spray drying conditions and heat treatment conditions, each step and parameter conditions are coordinated, so that the obtained lithium iron phosphate material has a high tap density, a high bulk density, high particle strength, good conductivity, good structural stability, and can improve the processing performance and electrochemical performance of the material. The battery obtained from the lithium iron phosphate material has a high specific capacity, a high Coulomb efficiency, excellent cycle performance and safety performance.

Claims

1. A preparation method of lithium iron phosphate material, characterized in that, It includes the following steps: (a) Grind a lithium source, an iron source, a phosphorus source, a carbon source, a flux material, and a solvent to obtain a mixed slurry; the ratio of the total mass of the iron source and the phosphorus source to the mass of the flux material is 1:(0.001 - 0.015); (b) Spray-dry the mixed slurry. The nozzle for the spray drying includes a two-fluid nozzle. The spray temperature for the spray drying is 180 - 300 °C, the spray pressure is 0.1 - 0.8 MPa, and the feeding frequency is 20 - 50 Hz to obtain a first material; (c) Perform heat treatment on the first material. The heat treatment includes a first constant-temperature treatment and a second constant-temperature treatment. The temperature T1 of the first constant-temperature treatment is 450 - 650 °C, and the temperature T2 of the second constant-temperature treatment is 650 - 850 °C.

2. The preparation method of the lithium iron phosphate material according to claim 1, wherein It includes at least one of the following features (1) to (2): (1) The flux material includes at least one of boric acid, calcium oxide, and magnesium oxide; (2) The ratio of the total mass of the iron source and the phosphorus source to the mass of the flux material is 1:(0.002 - 0.01).

3. The preparation method of the lithium iron phosphate material according to claim 1 or 2, characterized in that, The flux material includes material A and material B. Material A is boric acid, and material B is calcium oxide and / or magnesium oxide. The mass ratio of material A to material B is (7 - 9):(1 - 3).

4. The preparation method of the lithium iron phosphate material according to any one of claims 1-3, characterized in that, It includes at least one of the following features (1) to (3): (1) The molar ratio of the lithium source, the iron source, and the phosphorus source in terms of lithium element, iron element, and phosphorus element respectively is (1 - 1.08):(0.95 - 1):(0.95 - 1); (2) The ratio of the total mass of the iron source and the phosphorus source to the mass of the carbon source is 1:(0.03 - 0.15); (3) The carbon source includes at least one of sucrose, glucose, starch, carbon black, polyethylene glycol, and phenolic resin.

5. The preparation method of the lithium iron phosphate material according to any one of claims 1-4, characterized in that, The spray temperature for the spray drying is 200 - 260 °C, the spray pressure is 0.4 - 0.6 MPa, and the feeding frequency is 30 - 45 Hz.

6. The preparation method of the lithium iron phosphate material according to any one of claims 1-5, characterized in that, It includes at least one of the following features (1) to (5): (1) The difference between the temperature T2 of the second constant-temperature treatment and the temperature T1 of the first constant-temperature treatment satisfies: 180 °C ≤ T2 - T1 ≤ 250 °C; (2) The time for the first constant-temperature treatment is 2 - 10 h; (3) The time for the second constant-temperature treatment is 2 - 10 h; (4) The heating rate of the heat treatment is 0.5 - 10 °C / min; (5) The heat treatment is carried out under a protective gas condition.

7. The preparation method of the lithium iron phosphate material according to claim 6, wherein The temperature of the first constant-temperature treatment is 500 - 600 °C, and the time for the first constant-temperature treatment is 3 - 8 h; The temperature of the second constant-temperature treatment is 700 - 800 °C, and the time for the second constant-temperature treatment is 4 - 8 h.

8. The preparation method of the lithium iron phosphate material according to any one of claims 1-7, characterized in that, The grinding treatment includes a first grinding and a second grinding; The rotation speed R1 of the first grinding is 300 - 400 r / min, the rotation speed R2 of the second grinding is 500 - 700 r / min, and the ratio of the rotation speed R1 of the first grinding to the rotation speed R2 of the second grinding satisfies: 1.25 ≤ R1 / R2 ≤ 2; The time for the first grinding is 0.5 - 4 h; The time of the second grinding is 0.5 to 6 h.

9. The preparation method of the lithium iron phosphate material according to any one of claims 1-8, characterized in that, It includes at least one of the following features (1) to (2): (1) The solid content of the mixed slurry is 20% to 60%; (2) The particle size D50 of the materials in the mixed slurry is 200 to 400 nm.

10. The preparation method of the lithium iron phosphate material according to any one of claims 1-9, characterized in that, It further includes: Screening the heat-treated materials, and the mesh number of the screening is 180 to 250 meshes.

11. A lithium iron phosphate material, characterized in that, It is prepared by the method for preparing lithium iron phosphate material according to any one of claims 1-10.

12. The lithium iron phosphate material according to claim 11, wherein It includes at least one of the following features (1) to (6); (1) The tap density of the lithium iron phosphate material is 2.36 to 2.55 g / cm 3 ; (2) The tap density of the lithium iron phosphate material is 1.82 to 2.2 g / cm 3 ; (3) The particle size D50 of the lithium iron phosphate material is 8.6 to 11 μm; (4) The specific surface area of the lithium iron phosphate material is 5 to 8 m 2 / g; (5) The resistivity of the lithium iron phosphate material is 10 to 39.1 Ω·cm; (6) The particle strength of the lithium iron phosphate material is 72 to 160 MPa.

13. An electrode sheet, characterized in that, It includes the lithium iron phosphate material prepared by the method for preparing lithium iron phosphate material according to any one of claims 1-10, or the lithium iron phosphate material according to claim 11 or 12.

14. A battery, characterized in that, It includes the electrode sheet according to claim 13.

15. An electrical device, characterized in that, It includes the battery according to claim 14.

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