A lithium iron phosphate material, a preparation method thereof and a preparation method of an electric core thereof

Abstract

The present application relates to a kind of lithium iron phosphate material, the lithium iron phosphate material has typical olivine structure, belongs to orthorhombic space group Pnma, the preparation method of the lithium iron phosphate material, comprising the following steps: (1) lithium carbonate of battery grade, boric acid, magnesium hydroxide are mixed uniformly according to certain proportion with iron phosphate, carbon source, wherein, n1 lithium carbonate: n2 iron phosphate is 1~1.02:1, the addition amount of carbon source is 10~15% of total weight, boric acid, magnesium hydroxide as additive, the content of boric acid, magnesium hydroxide is 0~2%, obtain mixture S1;(2) S1 is placed into fine grinder and is finely ground, speed 20~50r / min;Time 0.5~1h, obtain D50 particle size 0.5~0.6 μm mixed product S2;(3) S2 is sprayed in spraying equipment, obtain product S3, in roller hearth kiln sintering, sintering temperature is 650~800 DEG C, sintering atmosphere is inert gas, sintering time is 1~8h, obtain product as S4.By adding low melting point substance boric acid and magnesium hydroxide, it is conducive to sintering reaction LiFePO4 Crystal growth.

Description

A lithium iron phosphate material, its preparation method, and its battery cell preparation method. Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to a lithium iron phosphate material, its preparation method, and its cell preparation method. Background Technology

[0002] Since Sony launched the commercial application of lithium-ion batteries in 1991, lithium-ion battery technology has developed rapidly in 3C products, electric vehicles, power tools, and energy storage. Statistics show that in 2021 alone, China's new energy vehicle shipments reached 3.5 million units, with a battery installation capacity of 220GW, of which lithium iron phosphate (LFP) batteries accounted for 117GW, corresponding to approximately 300,000 tons of LFP cathode material. LFP batteries have been widely used in the new energy field due to their safety and low cost. LFP material itself has low conductivity, so carbon coating is commonly used to enhance the material's conductivity, thereby improving its electrochemical performance. In fields such as power tools, high-rate charge and discharge are required, making it crucial to improve the rate performance of LFP materials. Currently, the main methods for improving the rate performance of LFP battery cathode materials include carbon coating, particle size refinement, and element doping.

[0003] Carbon coating can improve the conductivity of lithium iron phosphate materials. However, due to the influence of the coating, excessive carbon coating can affect the processing performance of the material and has limited improvement on rate performance. Furthermore, too much carbon can affect the specific capacity of the material. Particle size reduction can shorten the lithium ion transfer path and improve the rate performance of the material. However, due to more side reactions with the electrolyte, it has a significant adverse effect on cycle life. Smaller particle size is not conducive to material processing, reduces areal density, and affects battery energy density. Element doping can improve the intrinsic ion migration rate of the material and improve its rate performance. However, the added metal oxides are often expensive, increasing the cost.

[0004] In order to solve the above problems, this invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium iron phosphate material.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A lithium iron phosphate material, wherein the lithium iron phosphate material has a typical olivine structure, belongs to the orthorhombic crystal system space group Pnma, and the unit cell can be obtained by Topas refinement software.

[0008] Another object of the present invention is to provide a method for preparing lithium iron phosphate material.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing lithium iron phosphate material includes the following steps:

[0011] (1) Iron phosphate, carbon source, battery-grade lithium carbonate, boric acid and magnesium hydroxide are mixed evenly in a certain proportion, wherein n1 lithium carbonate:n2 iron phosphate is 1 to 1.02:1, the amount of carbon source added is 10 to 15% of the total weight, and boric acid and magnesium hydroxide are used as additives with a content of 0 to 2%, to obtain mixture S1.

[0012] (2) Place S1 in a fine grinding mill for fine grinding at a speed of 20-50 r / min for 0.5-1 h to obtain a mixed product S2 with a D50 particle size of 0.5-0.6 μm;

[0013] (3) S2 is sprayed in a spraying device to obtain product S3, which is then sintered in a roller kiln at a temperature of 650-800℃, in an inert gas atmosphere, for 1-8 hours to obtain product S4.

[0014] This invention mainly involves adding low-melting-point substances boric acid and magnesium hydroxide, which are beneficial to the growth of LiFePO4 crystals during the sintering reaction, improving crystallinity, and forming a fast ion conductor layer B-Li-Mg oxide on the surface of lithium iron phosphate particles. This facilitates the transfer of lithium ions during battery charging and discharging. Furthermore, by adjusting the sintering temperature to control crystallinity and particle size, the compaction density of the material can be improved.

[0015] Preferably, in the preparation method of the lithium iron phosphate material, in step (1), the ratio of n1 lithium carbonate to n2 iron phosphate is 1.01:1, the amount of carbon source added is 12% of the total weight, boric acid is 0.5% of the total weight, and magnesium hydroxide is 1% of the total weight.

[0016] Another object of the present invention is to provide a method for preparing lithium iron phosphate battery cells.

[0017] To achieve the above objectives, the present invention adopts the following technical solution:

[0018] A method for preparing a lithium iron phosphate battery cell includes the following steps: mixing product S4 with conductive agents SP, CNT, and PVDF in a ratio of 96:(1-1.5):0.5:2.5, extruding and coating, and drying to obtain a positive electrode sheet with an areal density of 380-420 g / m2 and a roll-pressed compaction density of 2.3-2.4 g / cm3.

[0019] Preferably, the areal density is 400 g / m2, and the compaction density of the positive electrode sheet by roller pressing is 2.35 g / cm3.

[0020] Furthermore, when combined with the negative electrode, it is assembled into the 80122165 soft-pack battery cell.

[0021] Beneficial technical effects:

[0022] This invention utilizes a high-temperature solid-state method to prepare lithium iron phosphate. During the sintering process, due to the high decomposition temperature of lithium carbonate, the reaction between lithium carbonate and iron phosphate involves point-to-point material transfer. This invention primarily utilizes low-melting-point substances boric acid and magnesium hydroxide to form a liquid phase that coats the solid particles during sintering. This facilitates the reaction at a lower temperature to generate lithium iron phosphate material, improving its crystallinity and controlling grain growth, thus enhancing its compaction density and making it easier to process in slurry preparation. Furthermore, these low-melting-point substances can react with excess lithium carbonate to form a fast-ion conductor layer, which aids in lithium-ion migration and improves its rate performance. Attached Figure Description

[0023] Figure 1 shows the XRD pattern of sample S14 in Example 1 of the present invention.

[0024] Figure 2 shows the XRD pattern of sample S24 in Comparative Example 1 of this invention.

[0025] Figure 3 is a scan image of sample S34 in Embodiment 2 of the present invention.

[0026] Figure 4 is a scan image of sample S35 in Embodiment 2 of the present invention. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1:

[0029] 44.12g of battery-grade lithium carbonate and 42.38g of iron phosphate were selected, with 12g of glucose added as a carbon source for coating, and 0.5g of boric acid and 1g of magnesium hydroxide added as additives. The five substances were mixed evenly to obtain mixture S11. S11 was then fed into a fine grinder through a pipeline for fine grinding at a speed of [missing information].

[0030] The mixture was fired at 40 r / min for 1 h to obtain a mixed product S12 with a D50 particle size of 0.55 μm. S12 was then sprayed in a spraying device to obtain product S13. S13 was sintered in a roller kiln at a temperature of 700℃, a sintering atmosphere of 1 atm nitrogen, and a sintering time of 5 h to obtain product S14.

[0031] Microstructure analysis of S14 was performed, as shown in Figure 1. The XRD pattern shows that the S14 sample has a typical olivine structure and belongs to the orthorhombic crystal system space group Pnma. The unit cell was obtained by Topas refinement software, and the parameters are shown in Table 1.

[0032] Table 1

[0033]

[0034] Full cells were prepared using S14. A positive electrode slurry was prepared according to a ratio of w(lithium iron phosphate):w(SP):w(CNT):w(PVDF) = 96:1:0.5:2.5. After extrusion coating and drying, a positive electrode sheet was obtained with an areal density of 400 g / m² and a roll-pressed compaction density of 2.35 g / cm³. This positive electrode sheet was then assembled with a negative electrode sheet to form an 80122165 soft-pack cell. After formation and capacity testing, its rate discharge performance was tested, and the results are shown in Table 2.

[0035] Table 2

[0036]

[0037] Comparative Example 1:

[0038] 44.12 g of battery-grade lithium carbonate and 42.38 g of iron phosphate, with 12 g of glucose added as a carbon source for coating, were mixed evenly to obtain mixture S21. S21 was then finely ground in a fine mill at 40 r / min for 1 h to obtain mixed product S22 with a D50 particle size of 0.55 μm. S22 was then spray-treated to obtain product S23. S23 was sintered in a roller kiln at 700℃ in a 1 atm nitrogen atmosphere for 5 h to obtain product S24. The microstructure analysis of S24 is shown in Figure 1. The XRD pattern shows that the S24 sample has a typical olivine structure, belonging to the orthorhombic crystal system space group Pnma. The cell parameters obtained by Topas refinement software are shown in Table 3.

[0039] Table 3

[0040]

[0041] Full cells were prepared using S24. A positive electrode slurry was prepared according to a ratio of w(lithium iron phosphate):w(SP):w(CNT):w(PVDF) = 96:1:0.5:2.5. After extrusion coating and drying, a positive electrode sheet was obtained with an areal density of 340 g / m² and a roll-pressed compaction density of 2.2 g / cm³. This slurry was then assembled with a negative electrode sheet to form an 80122165 pouch cell. After formation and capacity testing, its rate discharge performance was tested. The test results are shown in Table 4.

[0042] Table 4

[0043]

[0044] As shown in Tables 1 and 3, S14 has a higher degree of crystallinity, indicating that the addition of boric acid and magnesium oxide facilitates the reaction and synthesis of the material.

[0045] As can be seen from Tables 2 and 4 of the capacity test data, the S14 material has better performance at high rates, which is related to the formation of a fast ion conductor layer on the surface of the material, which is conducive to the transport of lithium ions.

[0046] Example 2:

[0047] Battery-grade lithium carbonate and iron phosphate (Li / Fe) were selected with a ratio of 1.01. 10% glucose was added as a carbon source for coating, and 0.5% boric acid and 0.5% magnesium hydroxide were added as additives. The five substances were mixed thoroughly to obtain mixture S31. S31 was then finely ground in a mill at 30 r / min for 1 h to obtain a mixed product S32 with a D50 particle size of 0.6 μm. S32 was then spray-treated to obtain product S33. S33 was sintered in a roller kiln at temperatures of 660℃ and 680℃, under a nitrogen atmosphere of 1 atm, for 5 h to obtain products S34 and S35, respectively. The microstructure of the products was analyzed, as shown in Figures 3 and 4.

[0048] As shown in Figures 3 and 4, the grain size tends to increase with the increase of sintering temperature. The lithium iron phosphate particles sintered at 660℃ have complete crystal shape and form a coating layer on the surface.

[0049] Example 3:

[0050] Battery-grade lithium carbonate 45.17g and iron phosphate 43.83g were selected, with 10g of glucose added as a coating carbon source, and 0.5g of boric acid and 0.5g of magnesium hydroxide added as additives. The five substances were mixed evenly to obtain mixture S41. S41 was then finely ground in a fine mill at 30 r / min for 1 h to obtain mixed product S42 with a D50 particle size of 0.6 μm. S42 was then further processed in a spraying device...

[0051] Spray treatment was performed to obtain product S43; S43 was sintered in a roller kiln at a sintering temperature of 660℃, a sintering atmosphere of 1 atm nitrogen, and a sintering time of 5 h to obtain product S44.

Claims

1. A lithium iron phosphate material, characterized in that: The lithium iron phosphate material has a typical olivine structure and belongs to the orthorhombic crystal system space group Pnma. The unit cell can be obtained by refining with Topas refining software. The preparation method of the lithium iron phosphate material includes the following steps: (1) Iron phosphate, carbon source, battery-grade lithium carbonate, boric acid and magnesium hydroxide are mixed evenly in a certain proportion, wherein n1 lithium carbonate:n2 iron phosphate is 1~1.02:1, the amount of carbon source added is 10~15% of the total weight, and boric acid and magnesium hydroxide are used as additives. (1) The content of boric acid and magnesium hydroxide is 0~2% to obtain mixture S1; (2) S1 is put into a fine grinding mill for fine grinding at a speed of 20~50r / min for 0.5~1h to obtain mixed product S2 with D50 particle size of 0.5~0.6μm; (3) S2 is sprayed in a spraying device to obtain product S3, which is sintered in a roller kiln at a sintering temperature of 650~800℃, with an inert gas atmosphere and a sintering time of 1~8h to obtain product S4.

2. The method for preparing lithium iron phosphate material according to claim 1, characterized in that: In step (1), the ratio of n1 lithium carbonate to n2 iron phosphate is 1.01:1, the amount of carbon source added is 12% of the total weight, boric acid is 0.5% of the total weight and magnesium hydroxide is 1% of the total weight.

3. A method for preparing a lithium iron phosphate battery cell according to claim 1, characterized in that: Product S4 was mixed with conductive agents SP, CNT, and PVDF in a ratio of 96:(1-1.5):0.5:2.

5. After extrusion coating and drying, a positive electrode sheet was obtained with an areal density of 380~420 g / m2 and a compaction density of 2.3~2.4 g / cm3.

4. The method for preparing lithium iron phosphate battery cells according to claim 3, characterized in that: The areal density is 400 g / m2, and the compaction density of the positive electrode sheet is 2.35 g / cm3.

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