A positive electrode material and its preparation method and application

Abstract

The present invention relates to the field of battery technology, and more particularly to a positive electrode material, a preparation method thereof, and an application thereof. The preparation method of the positive electrode material comprises the following steps: wet-grinding a lithium source, iron phosphate, and a carbon source to obtain a first mixed system; spray-drying the first mixed system to obtain a first material; and calcining the first material; wherein the D50 particle size of the first material is 1 D The maximum temperature of the calcination treatment is 1 T , let I=(100I D 2 ) / (9.41I T ), I is in the range of 0.53≤I≤1.66, and the tap density of the positive electrode material is 1.28 to 1.62. Based on the above raw materials, the present invention prepares a dense spherical positive electrode material by rationally adjusting the relationship between the calcination temperature and the D50 particle size of the first material. This can reduce the lithium ion diffusion path and improve the material's rate performance, while ensuring that the discharge capacity of the lithium iron phosphate is not lost.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4) with an olivine structure is a hot topic in current research on cathode materials for lithium-ion batteries due to its advantages such as good safety, excellent cycle performance, environmental friendliness, and abundant raw material resources. However, the rate decay problem has hindered the promotion and application of lithium-ion batteries using LiFePO4 as the cathode.

[0003] Therefore, improving the conductivity of lithium iron phosphate materials is of great significance for improving the rate discharge characteristics of lithium-ion battery systems using lithium iron phosphate as the positive electrode. Currently, improving material conductivity can be achieved through surface coating with conductive carbon materials, calcination processes, or spraying processes. However, the resulting lithium iron phosphate positive electrode materials have poor conductivity, low tap density, low volumetric capacity, and poor rate performance.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One object of the present invention is to provide a method for preparing a positive electrode material. By controlling the relationship between the D50 particle size of the first material and the maximum temperature of the calcination treatment, a positive electrode material with a suitable tap density is obtained, which can reduce the lithium ion diffusion path and improve the rate performance of the material while ensuring that the discharge capacity of the lithium iron phosphate is not lost.

[0006] Another object of the present invention is to provide a positive electrode material having a suitable tap density, and excellent capacity and rate performance.

[0007] Another object of the present invention is to provide a positive electrode sheet.

[0008] Another object of the present invention is to provide a battery.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0010] A method for preparing a positive electrode material comprises the following steps:

[0011] Wet-grinding a lithium source, iron phosphate, and a carbon source to obtain a first mixed system, spray-drying the first mixed system to obtain a first material, and calcining the first material;

[0012] The D50 particle size of the first material is 1 D The maximum temperature of the calcination treatment is 1 T , let I=(100ID 2 ) / (9.41I T ), the range of I is: 0.53≤I≤1.66, and the tap density of the positive electrode material is 1.28~1.62.

[0013] In one embodiment, the D50 particle size of the first material is D The range is: 6μm≤I D ≤10μm; the maximum temperature of the calcination treatment I T The range is: 640℃≤I T ≤720℃.

[0014] In one embodiment, the holding time of the calcination treatment is 10 to 12 hours.

[0015] In one embodiment, the calcination process is performed under protective gas conditions.

[0016] In one embodiment, the heating rate of the calcination treatment is 2-4°C / min.

[0017] In one embodiment, in the ferric phosphate, the molar ratio of iron to phosphorus is 0.99 to 1.01.

[0018] In one embodiment, the molar ratio of the lithium source to the iron phosphate is (0.95-1.05):1, calculated as lithium element and iron element, respectively.

[0019] In one embodiment, the mass ratio of the carbon source to the ferric phosphate is (0.1-0.2):1.

[0020] In one embodiment, the carbon source comprises at least one of ascorbic acid, glucose, polyethylene glycol and carbon nanotubes.

[0021] In one embodiment, the lithium source includes at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0022] In one embodiment, the solid content of the first mixed system is 20% to 40%.

[0023] In one embodiment, the wet grinding time is 3 to 5 hours, and the D50 particle size of the first mixed system is 300 to 500 nm.

[0024] In one embodiment, the calcination is followed by cooling and sieving.

[0025] A positive electrode material is prepared by the positive electrode material preparation method.

[0026] A positive electrode sheet comprises the positive electrode material prepared by the positive electrode material preparation method.

[0027] A battery comprises the positive electrode sheet.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Based on the above raw materials, the present invention prepares a dense spherical positive electrode material by reasonably adjusting the relationship between the calcination temperature and the D50 particle size of the first material, which can reduce the lithium ion diffusion path and improve the material's rate performance while ensuring that the discharge capacity of lithium iron phosphate is not lost; this method is simple, has a short cycle, and is easy to synthesize.

[0030] (2) The positive electrode material obtained by the present invention has a suitable tap density, high capacity and high rate performance.

[0031] (3) The battery of the present invention has excellent charge and discharge capacity, first efficiency and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is the first charge and discharge curve of the positive electrode material in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0035] According to one aspect of the present invention, the present invention relates to a method for preparing a positive electrode material, comprising the following steps:

[0036] Wet-grinding a lithium source, iron phosphate, and a carbon source to obtain a first mixed system, spray-drying the first mixed system to obtain a first material, and calcining the first material;

[0037] The D50 particle size of the first material is 1 D The maximum temperature of the calcination treatment is 1T , let I=(100I D 2 ) / (9.41I T ), the range of I is: the range of I is: 0.53≤I≤1.66, for example, 0.53, 0.6, 0.65, 0.68, 0.7, 0.8, 0.85, 0.88, 0.9, 0.95, 0.98, 1, 1.05, 1.1, 1.14, 1.2, 1.25, 0.13, 1.4, 1.5, 1.6, 1.66, etc., and the tap density of the positive electrode material is 1.28-1.62, for example, 1.28, 1.3, 1.35, 1.4, 1.5, 1.55, 1.58, 1.6, 1.62, etc.

[0038] Based on the above raw materials, the present invention prepares a positive electrode material with a suitable tap density by rationally adjusting the relationship between the calcination temperature and the size of the secondary spheres produced by spray drying. The positive electrode material is composed of regular spherical particles and has excellent fluidity and dispersibility due to the absence of agglomeration and particle bridging. The lithium ion diffusion path can be reduced, thereby improving the material's rate performance while ensuring that the discharge capacity of lithium iron phosphate is not lost. The method is simple, has a short cycle, and is easy to synthesize. When the I value is equal to 1, the tap density of the positive electrode material is the highest. As the I value decreases or increases, the tap density of the positive electrode material decreases, and the rate performance of the positive electrode material gradually decreases.

[0039] The size of the spherical particles after calcination is mainly affected by the size of the spray-dried spheres. If the spherical particle size after spray drying is too small or too large, the tap compaction will not be high. The calcination temperature mainly affects the size of the primary particles. If the calcination temperature is low, the primary particles are small, the resulting spherical particles have large gaps, and the tap compaction is low. If the sintering temperature is high, the primary particles will become larger, causing the secondary spheres to become irregular in shape and also causing the tap compaction to become low. Therefore, if the calcination temperature is too high or too low, the particles after spray drying are too large or too small, or the calcination temperature is not suitable for the particle size after spray drying, it will result in larger gaps between the primary particles, lower compaction, and poor stacking of the secondary spheres, which will lead to a longer lithium ion diffusion path and poor conductivity.

[0040] In one embodiment, the D50 particle size of the first material is D The range is: 6μm≤I D ≤10μm. The D50 particle size of the first material D Including but not limited to 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.2μm, 9.5μm, 10μm, etc.

[0041] In one embodiment, the maximum temperature of the calcination treatment is T The range is: 640℃≤IT ≤720℃. The maximum temperature of the calcination treatment is T Including but not limited to 640℃, 645℃, 650℃, 655℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃ or 720℃, etc.

[0042] In one embodiment, the holding time of the calcination treatment is 10 to 12 hours, for example, 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, etc.

[0043] In one embodiment, the calcination process is performed under protective gas conditions, such as nitrogen.

[0044] In one embodiment, the heating rate of the calcination treatment is 2-4°C / min, for example, 2°C / min, 3°C / min, 4°C / min, etc.

[0045] In one embodiment, the molar ratio of iron to phosphorus is 0.99 to 1.01, for example, 0.99, 1, 1.01, etc.

[0046] In one embodiment, the molar ratio of the lithium source and the iron phosphate, calculated as lithium element and iron element, respectively, is (0.95-1.05):1; for example, 0.95:1, 0.96:1, 0.98:1, 1:1, 1.04:1, 1.05:1, etc.

[0047] In one embodiment, the mass ratio of the carbon source to the ferric phosphate is (0.1-0.2):1, for example, 0.1:1, 0.12:1, 0.15:1, 0.16:1, 0.18:1, 0.2:1, etc. The carbon source and ferric phosphate of the present invention are used in an appropriate ratio to ensure that the final cathode material has excellent electrochemical properties.

[0048] In one embodiment, the carbon source comprises at least one of ascorbic acid, glucose, polyethylene glycol, and carbon nanotubes. The carbon source of the present invention can be any one of the above, or a combination of multiple ones, such as a combination of ascorbic acid and glucose, a combination of ascorbic acid and carbon nanotubes, etc.

[0049] In one embodiment, the lithium source includes at least one of lithium hydroxide, lithium carbonate, and lithium nitrate.

[0050] In one embodiment, the solid content of the first mixed system is 20% to 40%, for example, 20%, 25%, 30%, 40%, etc. The solvent of the first mixed system includes water.

[0051] In one embodiment, the wet grinding time is 3 to 5 hours, such as 3 hours, 4 hours, 5 hours, etc., until the D50 particle size of the first mixed system is 300 to 500 nm, such as 300 nm, 400 nm, 500 nm, etc.

[0052] In one embodiment, the calcination is followed by cooling and sieving. In one embodiment, the calcination is followed by cooling to room temperature in a furnace. In one embodiment, the sieving comprises: sieving through a 300 mesh sieve.

[0053] According to another aspect of the present invention, the present invention also relates to a positive electrode material prepared by the above-mentioned positive electrode material preparation method. The positive electrode material of the present invention has a suitable tap density, high capacity, and excellent rate performance.

[0054] According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising the positive electrode material prepared by the above-mentioned method for preparing the positive electrode material.

[0055] In one embodiment, the positive electrode sheet of the present invention includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the positive electrode material layer includes the positive electrode material described above. The positive electrode material layer also includes a conductive agent and a binder. A positive electrode slurry is prepared by mixing the positive electrode material, the conductive agent, the binder, and a solvent. The slurry is then applied to at least one surface of the positive electrode current collector, dried, and rolled to produce the positive electrode sheet.

[0056] According to another aspect of the present invention, the present invention also relates to a battery, comprising the positive electrode sheet.

[0057] In one embodiment, the battery of the present invention includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0058] The battery of the present invention has excellent charge and discharge capacity and rate performance.

[0059] The following is further explained with reference to specific embodiments and comparative examples.

[0060] Example 1

[0061] A method for preparing a positive electrode material comprises the following steps:

[0062] (1) lithium hydroxide and ferric phosphate were added to a grinding mill hopper at a molar ratio of 1:1, and then ascorbic acid and ferric phosphate were added to the grinding mill at a mass ratio of 0.12:1 for wet grinding. The wet grinding time was 4 hours to obtain a first mixed system. The solid content of the first mixed system was 30%, and the D50 particle size of the first mixed system was 400 nm.

[0063] (2) The first mixed system was spray-dried so that the particle size D50 after drying was maintained at 8 μm to obtain a first material; the first material was placed in a nitrogen atmosphere and heated to 680°C at a rate of 3°C / min and calcined for 10 hours, and then cooled and sieved to obtain the final positive electrode material.

[0064] Example 2

[0065] A method for preparing a positive electrode material comprises the following steps:

[0066] (1) lithium hydroxide and ferric phosphate were added to a grinding mill hopper at a molar ratio of 1:1, and then ascorbic acid and ferric phosphate were added to the grinding mill at a mass ratio of 0.12:1 for wet grinding. The wet grinding time was 4 hours to obtain a first mixed system. The solid content of the first mixed system was 30%, and the D50 particle size of the first mixed system was 400 nm.

[0067] (2) The first mixed system is spray-dried so that the particle size D50 after drying is maintained at 6 μm to obtain a first material; the first material is placed in a nitrogen atmosphere and heated to 720°C at a rate of 3°C / min and calcined for 10 hours, and then cooled and sieved to obtain the final positive electrode material.

[0068] Example 3

[0069] A method for preparing a positive electrode material comprises the following steps:

[0070] (1) lithium hydroxide and ferric phosphate were added to a grinding mill hopper at a molar ratio of 1:1, and then ascorbic acid and ferric phosphate were added to the grinding mill at a mass ratio of 0.12:1 for wet grinding. The wet grinding time was 4 hours to obtain a first mixed system. The solid content of the first mixed system was 30%, and the D50 particle size of the first mixed system was 400 nm.

[0071] (2) The first mixed system is spray-dried so that the particle size D50 after drying is maintained at 10 μm to obtain a first material; the first material is placed in a nitrogen atmosphere and heated to 640°C at a rate of 3°C / min and calcined for 10 hours, and then cooled and sieved to obtain the final positive electrode material.

[0072] Example 4

[0073] A method for preparing a positive electrode material comprises the following steps:

[0074] (1) According to the method of Example 1, a first mixed system was prepared,

[0075] (2) The first mixed system is spray-dried so that the particle size D50 after drying is maintained at 9 μm to obtain a first material; the first material is placed in a nitrogen atmosphere and heated to 700°C at a rate of 3°C / min and calcined for 10 hours, and then cooled and sieved to obtain the final positive electrode material.

[0076] Example 5

[0077] A method for preparing a positive electrode material comprises the following steps:

[0078] (1) According to the method of Example 1, a first mixed system was prepared,

[0079] (2) The first mixed system is spray-dried so that the particle size D50 after drying is maintained at 7 μm to obtain a first material; the first material is placed in a nitrogen atmosphere and heated to 660° C. at a rate of 3° C. / min and calcined for 10 h, and then cooled and sieved to obtain the final positive electrode material.

[0080] Comparative Example 1

[0081] A method for preparing a positive electrode material comprises the following steps:

[0082] (1) According to the method of Example 1, a first mixed system was prepared;

[0083] (2) The first mixed system is spray-dried so that the particle size D50 after drying is maintained at 5 μm to obtain a first material; the first material is placed in a nitrogen atmosphere and heated to 750°C at a rate of 3°C / min and calcined for 10 hours, and then cooled and sieved to obtain the final positive electrode material.

[0084] Comparative Example 2

[0085] A method for preparing a positive electrode material comprises the following steps:

[0086] (1) According to the method of Example 1, a first mixed system was prepared;

[0087] (2) The first mixed system is spray-dried so that the particle size D50 after drying is maintained at 12 μm to obtain a first material; the first material is placed in a nitrogen atmosphere and heated to 600° C. at a rate of 3° C. / min and calcined for 10 hours, and then cooled and sieved to obtain the final positive electrode material.

[0088] Experimental example

[0089] The positive electrode materials obtained in each embodiment and comparative example are respectively prepared into batteries, and the preparation method of the battery includes:

[0090] The positive electrode material, carbon black conductive agent, binder PVDF and NMP are mixed evenly, and the mass ratio of the positive electrode material, carbon black conductive agent, binder PVDF and NMP is 95:2.5:2.5:5 to obtain a positive electrode slurry; the slurry is coated on an aluminum foil with a thickness of 30 μm, and is made into a positive electrode sheet through vacuum drying and roller pressing. The lithium metal sheet is used as the negative electrode, the electrolyte is a 1.15M LiPF6 solution, the solvent of the electrolyte is EC and DMC, the volume ratio of EC and DMC is 1:1, and a button battery is assembled.

[0091] The batteries were tested at 25°C using a BlueDian battery testing system with a test voltage range of 2.0V to 3.75V. The capacity and 50-week capacity retention were tested.

[0092] The performance test results of the battery are shown in Table 1. The first charge and discharge curve of the positive electrode material in Example 1 of the present invention is shown in Table 1. Figure 1 shown.

[0093] Table 1 Battery performance test results

[0094]

[0095] As shown in Table 1, the positive electrode material obtained by the method of the present invention has a suitable tap density, which can reduce the lithium ion diffusion path and improve the rate performance of the positive electrode material, while ensuring that the discharge capacity of the lithium iron phosphate is not lost. The positive electrode materials obtained in Comparative Examples 1 and 2 have low tap densities, resulting in low initial efficiencies and relatively poor rate performance of the resulting batteries.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: The following steps are involved: Wet-grinding a lithium source, iron phosphate, and a carbon source to obtain a first mixed system, spray-drying the first mixed system to obtain a first material, and calcining the first material; The D50 particle size of the first material is 1 D The maximum temperature of the calcination treatment is 1 T , let I = (100I D 2 )∕(9.41I T ), the range of I is: 0.53≤I≤1.66, and the tap density of the positive electrode material is 1.28~1.62; The D50 particle size of the first material is D The range is: 6μm≤I D ≤10μm; The maximum temperature of the calcination treatment is T The range is: 640℃≤I T ≤720℃.

2. The method for preparing the positive electrode material according to claim 1, wherein: Contains at least one of the following features (1) to (3): (1) The holding time of the calcination treatment is 10 to 12 hours; (2) The calcination treatment is carried out under protective gas conditions; (3) The heating rate of the calcination treatment is 2~4℃ / min.

3. The method for preparing the positive electrode material according to claim 1, wherein: In the ferric phosphate, the molar ratio of iron to phosphorus is 0.99-1.01; The molar ratio of the lithium source to the iron phosphate, calculated as lithium element and iron element, is (0.95-1.05):

1.

4. The method for preparing the positive electrode material according to claim 1, wherein: The mass ratio of the carbon source to the ferric phosphate is (0.1-0.2):

1.

5. The method for preparing the positive electrode material according to claim 4, wherein: Contains at least one of the following features (1) to (2): (1) The carbon source includes at least one of ascorbic acid, glucose, polyethylene glycol and carbon nanotubes; (2) The lithium source includes at least one of lithium hydroxide, lithium carbonate and lithium nitrate.

6. The method for preparing the positive electrode material according to claim 1, wherein: Contains at least one of the following features (1) to (3): (1) The solid content of the first mixed system is 20% to 40%; (2) The wet grinding time is 3 to 5 hours, and the D50 particle size of the first mixed system is 300 to 500 nm; (3) After the calcination treatment, the product is cooled and sieved.

7. A positive electrode material, characterized in that The cathode material is prepared by the method for preparing the cathode material according to any one of claims 1 to 6.

8. A positive electrode sheet, characterized in that: A positive electrode material prepared by the method for preparing a positive electrode material according to any one of claims 1 to 6.

9. A battery, characterized in that: Including the positive electrode sheet according to claim 8.

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