Method for preparing high-rate lithium iron phosphate by template method

Abstract

The invention discloses a method for preparing high-rate lithium iron phosphate by a template method, which comprises the following steps of: 1, adding a fiber material into a ferrite solution, soaking, taking out, and recording as A; step 2, adding A into a mixed solution B of phosphoric acid and hydrogen peroxide, and carrying out liquid phase precipitation and aging processes to obtain iron phosphate dihydrate with micron-sized fibers as cores; and 3, uniformly mixing the iron phosphate dihydrate obtained in the step 2, a lithium source, a carbon source, a phosphorus source and an additive, calcining at high temperature in an inert atmosphere, and crushing to obtain the high-specific-surface-area lithium iron phosphate with a micron-sized pore structure in primary particles. The lithium iron phosphate electrolyte prepared by the method is good in infiltration effect, high in conductivity and excellent in battery rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for lithium-ion batteries, and more specifically, to a method for preparing high-rate lithium iron phosphate by a template method. Background Art

[0002] In June 2022, the General Department of the National Energy Administration issued a letter soliciting opinions on the "Twenty-five Key Requirements for Preventing Power Production Accidents (2022 Edition) (Draft for Soliciting Opinions)", which clearly stated that ternary lithium batteries shall not be used in medium and large-scale electrochemical energy storage power stations. This has enabled lithium iron phosphate batteries with high safety, long cycle life, and high energy density to start emerging in the energy storage field. Moreover, with the development of electric vehicles, they also occupy a significant share in power batteries. However, the lithium iron phosphate material itself also has some defects, such as low conductivity and poor rate performance, which limit its further application.

[0003] In patent CN113044822B, petal-shaped iron phosphate was in-situ prepared by relying on the porous characteristics of sponge and space confinement, which improved the conductivity, but this morphology was difficult to maintain after high-temperature calcination; in CN115172704A, porous carbon lithium iron phosphate was prepared using metal-organic frameworks, which had a high cost and was difficult to mass-produce; in CN103066280B and CN108878848B, surfactants were used as supports to obtain mesoporous lithium iron phosphate, but the absorption of the mesopores for the electrolyte was extremely limited, and the improvement of the battery rate performance was not obvious; in CN112993245A and CN115498161A, a large number of carbon nanotubes and cavity shells were introduced, reducing the compaction density of lithium iron phosphate.

[0004] To address the above problems, the present invention uses a template method to prepare lithium iron phosphate with a high specific surface area and a micron-sized pore structure inside the primary particles, improving the electrolyte infiltration effect, thereby enhancing the ionic conductivity and rate performance; and this template will decompose and carbonize during the high-temperature calcination of lithium iron phosphate, and the residual carbon coats the inner wall of the pore structure, thus avoiding the corrosion of the cathode material by the electrolyte and improving the cycle performance. Summary of the Invention

[0005] To achieve the above object, the present invention uses fiber materials such as cotton wool, polyester, spandex, and acrylic fiber with an aspect ratio greater than one thousand and a micron-sized diameter as templates. Ferrous phosphate dihydrate nucleates and grows on the fibers, and then after being uniformly mixed with a lithium source, etc., it is sintered in a reducing atmosphere to obtain lithium iron phosphate with a high specific surface area and a micron-sized pore structure inside the primary particles.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for preparing high-rate lithium iron phosphate by a template method, comprising the following steps:

[0008] Step 1: Add the fibrous material into the ferrous salt solution, take it out after infiltration, and denote it as A.

[0009] Step 2: Add A into the mixed solution B of phosphoric acid and hydrogen peroxide, and obtain iron phosphate dihydrate with micron-scale fibers as the core through liquid-phase precipitation and aging processes.

[0010] Step 3: Mix the iron phosphate dihydrate, lithium source, carbon source, phosphorus source, and additive obtained in Step 2 evenly, then conduct high-temperature calcination under an inert atmosphere, and crush it to obtain lithium iron phosphate with a high specific surface area and micron-scale pore structures inside the primary particles.

[0011] The fibrous material is selected from one or more of cotton wool, polyester, spandex, acrylic, polypropylene, and polyamide. The aspect ratio of the fibrous material ranges from 1000 to 10000, and the diameter is 5 - 50 μm.

[0012] In the above preparation method, the ferrous salt is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, etc., preferably ferrous sulfate. The concentration of the salt solution is 0.3 - 1 mol / L, and the molar ratio of phosphoric acid, hydrogen peroxide to ferrous ions is 1 - 1.5:0.4 - 0.6:1.

[0013] In the above preparation method, the mass ratio of the addition amount of the fibrous material to the ferrous salt solution is 0.04 - 0.1:1, and the infiltration time is 5 - 100 min.

[0014] In the above preparation method, continuous stirring is required during the liquid-phase precipitation and aging processes. After reacting for 50 - 70 min, start heating for aging. The aging temperature is 80 - 100 °C. After the precipitate color turns white, keep it warm for 60 - 80 min.

[0015] In the above preparation method, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium nitrate, lithium acetate, etc., preferably lithium carbonate. The lithium-to-iron molar ratio is 1.00 - 1.05.

[0016] In the above preparation method, the carbon source is one or more of sucrose, glucose, polyethylene glycol, starch, citric acid, polyvinyl alcohol, etc., preferably sucrose, glucose, polyethylene glycol. The addition amount is 10 - 15 wt% of the iron phosphate dihydrate.

[0017] In the above preparation method, the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, etc., and the addition amount is 0.1 - 0.5 wt% of the iron phosphate dihydrate.

[0018] In the above preparation method, the additive is one or more of titanium dioxide, magnesium oxide, vanadium oxide, niobium oxide, zirconium oxide, etc., preferably titanium dioxide. The addition amount is 0.5 - 2 wt% of the iron phosphate dihydrate.

[0019] In the above preparation method, the inert atmosphere is one or more of nitrogen, argon, helium, etc., and nitrogen is preferably used.

[0020] In the above preparation method, the calcination temperature is 750 - 820 °C, the calcination time is 6 - 12 h, and the crushing particle size Dv50 is 0.8 - 1.2 μm.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1) The fiber template used in this method has a large aspect ratio, small diameter, and high specific surface area, and is composed of elements such as C, H, O, N, etc. During the pyrolysis process, H and O are discharged in the form of H2O, CO, etc., and the remaining C coated on the particle surface can improve the conductivity, and the N element can be doped into the carbon layer to further improve the conductivity. Therefore, no impurity elements are introduced.

[0023] 2) Calcination in an inert atmosphere will decompose and carbonize, and the residual carbon is coated on the inner wall of the pore channels, avoiding the collapse of the pore channel structure and at the same time improving the electronic conductivity.

[0024] 3) Due to volume changes, pore channels with a diameter of micrometers will be generated, and the pore channel structure can improve the electrolyte infiltration effect and increase the ionic conductivity.

[0025] 4) The raw material cost is low, and no additional processes are introduced, which is conducive to promotion in production. In addition, the prepared lithium iron phosphate material has excellent electrochemical performance and has good application prospects in the energy storage and power markets. Description of the Drawings

[0026] Figure 1 XRD diffraction patterns of LiFePO4 prepared in the comparative example and the examples.

[0027] Figure 2 SEM pictures of LiFePO4 prepared in the comparative example and the examples.

[0028] Figure 3 Discharge curves of the LiFePO4 coin cells prepared in the comparative example and the examples. Detailed Embodiments

[0029] In order to better explain the present invention, the following specific examples are used to further illustrate the present invention; the specific examples described below are only used to explain the present invention and are not used to limit the present invention.

[0030] Raw materials and sources: Reagents such as ferrous sulfate, hydrogen peroxide, titanium dioxide, phosphoric acid, cetyltrimethylammonium bromide, carbon nanotubes, cotton fiber, polyester, spandex, and acrylic used in the present invention were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Sucrose, glucose, and polyethylene glycol were purchased from Beian Xiangyu Jingu Biochemical Technology Co., Ltd. Lithium carbonate was purchased from Tianqi Lithium Industry Co., Ltd.

[0031] Physicochemical property tests: The crystal structure of lithium iron phosphate was characterized by a Rigaku X-ray powder diffractometer (XRD) in Japan. The morphology of lithium iron phosphate was characterized by a Zeiss Sigma 500 field emission scanning electron microscope (SEM). The specific surface area of lithium iron phosphate was measured by a Belsorp BET specific surface area analyzer. The electrochemical performance of lithium iron phosphate was tested by a Neware battery testing cabinet.

[0032] Coin-type half-cell test: The positive electrode formulation was LFP:SP:PVDF = 95.8%:2%:2.2%, the solid content was 50%, the tap density of the electrode was 2.40 g / cm 3 , and the areal density was 15 mg / cm 2 , and the aluminum foil was 13 μm; The Tianci electrolyte was used, and the test voltage was 2.0 - 3.75 V.

[0033] Comparative Example 1:

[0034] 1) Prepare 100 mL of 0.3 mol / L ferrous sulfate solution and slowly drip it into a mixed solution of 100 mL

[0035] 1 mol / L phosphoric acid, 0.6 mol / L hydrogen peroxide, and 4 g of cetyltrimethylammonium bromide, continuously stir. After reacting for 50 min, start heating and aging. The aging temperature is 80 °C. After the precipitate color turns white, keep warm for 60 min to obtain iron phosphate dihydrate;

[0036] 2) Take 10 g of iron phosphate dihydrate, 2 g of lithium carbonate, 1 g of glucose, 0.01 g of phosphoric acid, and 0.1 g of titanium dioxide, mix them evenly and sinter at 770 °C for 10 h under a nitrogen atmosphere, and crush to Dv50 of 1 μm to obtain mesoporous lithium iron phosphate using a cationic surfactant as a template;

[0037] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to the mass ratio of 47.9:1:1.1:50, coat it on an aluminum foil current collector, then dry, slice, assemble a coin-type battery, and conduct electrical performance tests.

[0038] Comparative Example 2:

[0039] 1) Prepare a 100 mL, 0.3 mol / L ferrous sulfate solution, and slowly drop it into a mixed solution of 100 mL of 1 mol / L phosphoric acid, 0.6 mol / L hydrogen peroxide, and 4 g of C124533 single-walled carbon nanotubes. Continuously stir. After reacting for 50 min, start heating and aging. The aging temperature is 80 °C. After the precipitate color turns white, keep it warm for 60 min to obtain iron phosphate dihydrate;

[0040] 2) Take 10 g of iron phosphate dihydrate, 2 g of lithium carbonate, 1 g of glucose, 0.01 g of phosphoric acid, and 0.1 g of titanium dioxide. After mixing evenly, sinter at 770 °C for 10 h under a nitrogen atmosphere, and crush it to a Dv50 of 1 μm to obtain lithium iron phosphate using carbon nanotubes as a template;

[0041] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to a mass ratio of 47.9:1:1.1:50. Then coat it on an aluminum foil current collector, and then dry, slice, assemble a button battery, and conduct electrical performance tests.

[0042] Comparative Example 3:

[0043] 1) Prepare a 100 mL, 0.3 mol / L ferrous sulfate solution, then put 4 g of D-1 sponge with an aspect ratio of 15 into it, take it out after soaking for 30 min, and put it into a mixed solution of 100 mL of 1 mol / L phosphoric acid and 0.6 mol / L hydrogen peroxide. Continuously stir. After reacting for 50 min, start heating and aging. The aging temperature is 80 °C. After the precipitate color turns white, keep it warm for 60 min to obtain iron phosphate dihydrate;

[0044] 2) Take 10 g of iron phosphate dihydrate, 2 g of lithium carbonate, 1 g of glucose, 0.01 g of phosphoric acid, and 0.1 g of titanium dioxide. After mixing evenly, sinter at 770 °C for 10 h under a nitrogen atmosphere, and crush it to a Dv50 of 1 μm to obtain lithium iron phosphate using the sponge as a template;

[0045] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to a mass ratio of 47.9:1:1.1:50. Then coat it on an aluminum foil current collector, and then dry, slice, assemble the battery, and conduct electrical performance tests.

[0046] Example 1:

[0047] 1) Prepare 100 mL of 0.3 mol / L ferrous sulfate solution, then put 4 g of SA-I medical cotton fiber into it, take it out after soaking for 30 min, and put it into a mixed solution of 100 mL of 1 mol / L phosphoric acid and 0.6 mol / L hydrogen peroxide. Keep stirring. After reacting for 50 min, start heating and aging. The aging temperature is 80 °C. After the precipitate color turns white, keep warm for 60 min to obtain iron phosphate dihydrate;

[0048] 2) Take 10 g of iron phosphate dihydrate, 2 g of lithium carbonate, 1 g of glucose, 0.01 g of phosphoric acid, and 0.1 g of titanium dioxide. After mixing evenly, sinter at 770 °C for 10 h under a nitrogen atmosphere, and crush to Dv50 of 1 μm to obtain lithium iron phosphate with a micron-scale pore structure inside the primary particles;

[0049] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to the mass ratio of 47.9:1:1.1:50, coat it on an aluminum foil current collector, then dry, slice, assemble the battery, and conduct electrical performance tests.

[0050] Example 2:

[0051] 1) Prepare 100 mL of 1 mol / L ferrous sulfate solution, then put 10 g of DYT50D polyester into it, take it out after soaking for 30 min, and put it into a mixed solution of 100 mL of 1.5 mol / L phosphoric acid and 0.4 mol / L hydrogen peroxide. Keep stirring. After reacting for 60 min, start heating and aging. The aging temperature is 90 °C. After the precipitate color turns white, keep warm for 80 min to obtain iron phosphate dihydrate;

[0052] 2) Take 10 g of iron phosphate dihydrate, 2.08 g of lithium carbonate, 1.5 g of sucrose, 0.05 g of lithium dihydrogen phosphate, and 0.2 g of titanium dioxide. After mixing evenly, sinter at 820 °C for 12 h under a nitrogen atmosphere, and crush to Dv50 of 1.2 μm to obtain lithium iron phosphate with a micron-scale pore structure inside the primary particles;

[0053] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to the mass ratio of 47.9:1:1.1:50, coat it on an aluminum foil current collector, then dry, slice, assemble the battery, and conduct electrical performance tests.

[0054] Example 3:

[0055] 1) Prepare 100 mL of 0.65 mol / L ferrous sulfate solution, then put 8 g of DY-NL102 spandex into it. After soaking for 30 min, take it out and put it into a mixed solution of 100 mL of 1.25 mol / L phosphoric acid and 0.5 mol / L hydrogen peroxide. Keep stirring continuously. After reacting for 60 min, start heating and aging. The aging temperature is 90 °C. After the precipitate color turns white, keep warm for 80 min to obtain iron phosphate dihydrate;

[0056] 2) Take 10 g of iron phosphate dihydrate, 2.04 g of lithium carbonate, 1.2 g of sucrose, 0.03 g of phosphoric acid, and 0.1 g of titanium dioxide. After mixing evenly, sinter at 800 °C for 8 h under a nitrogen atmosphere, and crush it to a Dv50 of 1 μm to obtain lithium iron phosphate with a micron-sized pore structure inside the primary particles;

[0057] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to the mass ratio of 47.9:1:1.1:50. Then coat it on an aluminum foil current collector, and then dry, slice, assemble the battery, and conduct electrical performance tests.

[0058] Example 4:

[0059] 1) Prepare 100 mL of 0.3 mol / L ferrous sulfate solution, then put 10 g of 22C acrylic fiber into it. After soaking for 30 min, take it out and put it into a mixed solution of 100 mL of 1.5 mol / L phosphoric acid and 0.6 mol / L hydrogen peroxide. Keep stirring continuously. After reacting for 70 min, start heating and aging. The aging temperature is 100 °C. After the precipitate color turns white, keep warm for 80 min to obtain iron phosphate dihydrate;

[0060] 2) Take 10 g of iron phosphate dihydrate, 2.08 g of lithium carbonate, 1.5 g of polyethylene glycol, 0.05 g of ammonium dihydrogen phosphate, and 0.15 g of titanium dioxide. After mixing evenly, sinter at 820 °C for 12 h under a nitrogen atmosphere, and crush it to a Dv50 of 1.2 μm to obtain lithium iron phosphate with a micron-sized pore structure inside the primary particles;

[0061] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to the mass ratio of 47.9:1:1.1:50. Then coat it on an aluminum foil current collector, and then dry, slice, assemble the battery, and conduct electrical performance tests.

[0062] Example 5:

[0063] 1) Prepare a 100 mL, 1 mol / L ferrous sulfate solution, then add 4 g of FDY40D polyamide fiber, take it out after soaking for 30 min, and put it into a 100 mL mixed solution of 1 mol / L phosphoric acid and 0.4 mol / L hydrogen peroxide. Stir continuously. After reacting for 70 min, start heating and aging at a temperature of 90 °C. Keep it warm for 80 min until the precipitate color turns white to obtain iron phosphate dihydrate;

[0064] 2) Take 10 g of iron phosphate dihydrate, 2 g of lithium carbonate, 1 g of polyethylene glycol, 0.01 g of ammonium dihydrogen phosphate, and 0.05 g of titanium dioxide. After mixing evenly, sinter at 750 °C for 6 h under a nitrogen atmosphere, and crush it to a Dv50 of 0.8 μm to obtain lithium iron phosphate with a micron-level pore structure inside the primary particles;

[0065] 3) Mix the lithium iron phosphate powder, SP, PVDF, and N-methylpyrrolidone solvent evenly according to a mass ratio of 47.9:1:1.1:50, coat it on an aluminum foil current collector, then dry, slice, assemble the battery, and conduct electrical performance tests.

[0066] Table 1 BET and coin cell rate performance of lithium iron phosphate

[0067]

[0068] It can be seen from the data in Table 1 that compared with Comparative Examples 1-3, the lithium iron phosphate prepared in Examples 1-5 has a higher specific surface area and better rate performance. This is mainly because the lithium iron phosphate prepared by the template method has a micron-level pore structure inside the primary particles, which has a good wetting effect on the electrolyte, a fast Li + exchange rate, and a high ionic conductivity. Therefore, the battery has excellent rate performance.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing high-rate lithium iron phosphate by a template method, comprising the following steps: Step 1: Add the fiber material into the ferrous salt solution, take it out after infiltration, and denote it as A; Step 2: Add A into the mixed solution B of phosphoric acid and hydrogen peroxide, and obtain dihydrate iron phosphate with micron-sized fibers as the core after liquid-phase precipitation and aging processes; Step 3: Mix the dihydrate iron phosphate obtained in Step 2, lithium source, carbon source, phosphorus source, and additive evenly, then perform high-temperature calcination under an inert atmosphere, and after pulverization, high-specific-surface-area lithium iron phosphate with micron-sized pore structures inside the primary particles can be obtained.

2. The method according to claim 1, characterized in that, The fiber material is selected from one or more of cotton wool, polyester, spandex, acrylic, polypropylene, and nylon. The aspect ratio of the fiber material ranges from 1000 to 10000, and the diameter is 5 - 50 μm.

3. The method according to claim 1 or 2, characterized in that, The ferrous salt is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride, etc., preferably ferrous sulfate. The concentration of the salt solution is 0.3 - 1 mol / L, and the molar ratio of phosphoric acid, hydrogen peroxide to ferrous ions is 1 - 1.5:0.4 - 0.6:

1.

4. The method according to any one of claims 1 to 3, characterized in that The mass ratio of the addition amount of the fiber material to the ferrous salt solution is 0.04 - 0.1:1, and the infiltration time is 5 - 100 min.

5. The method according to any one of claims 1 to 4, characterized in that The liquid-phase precipitation time is 50 - 70 min; and / or, the aging temperature is 80 - 100 °C. After the precipitate color turns white, Keep warm for 60 - 80 min.

6. The method according to any one of claims 1-5, characterized in that The lithium source is one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium nitrate, lithium acetate, etc., preferably lithium carbonate. The molar ratio of lithium to iron is 1.00 - 1.

05.

7. The method according to any one of claims 1-6, characterized in that, The carbon source is one or more of sucrose, glucose, polyethylene glycol, starch, citric acid, polyvinyl alcohol, etc., preferably sucrose, glucose, polyethylene glycol. The addition amount is 10 - 15 wt% of the dihydrate iron phosphate.

8. The method according to any one of claims 1 to 7, characterized in that, The phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, etc., and the addition amount is 0.1 - 0.5 wt% of the dihydrate iron phosphate.

9. The method according to any one of claims 1-8, characterized in that, The additive is one or more of titanium dioxide, magnesium oxide, vanadium oxide, niobium oxide, zirconium oxide, etc., preferably titanium dioxide. The addition amount is 0.5 - 2 wt% of the dihydrate iron phosphate; and / or, the inert atmosphere is one or more of nitrogen, argon, helium, etc., preferably nitrogen.

10. The method according to any one of claims 1-9, characterized in that, The calcination temperature is 750 - 820 °C, the calcination time is 6 - 12 h, and the pulverization particle size Dv50 is 0.8 - 1.2 μm.

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