Method for preparing lithium iron phosphate
By adding an acidic solution to modify the flake-shaped lithium iron phosphate during the preparation of lithium iron phosphate, the problem of low compaction density of flake-shaped lithium iron phosphate powder was solved, enabling the low-cost preparation of high-performance lithium iron phosphate and improving its electrochemical performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-03-10
AI Technical Summary
In existing lithium iron phosphate preparation processes, the powder compaction density of flake iron phosphate is low, and the preparation cost of high-performance lithium iron phosphate is high. In particular, when using recycled iron phosphate, the morphology is irregular, which affects the electrochemical performance.
An acidic solution, such as oxalic acid solution, is added during the batching stage of lithium iron phosphate preparation. This solution is mixed with inexpensive and readily available flake or recycled iron phosphate. After stirring to form a slurry, the mixture is milled, dried, and calcined to produce lithium iron phosphate with excellent electrochemical performance and high powder compaction density.
The powder compaction density of lithium iron phosphate was increased, the production cost was reduced, and good electrochemical performance was maintained. In particular, the modified flake lithium iron phosphate exhibited electrochemical performance similar to that of spherical lithium iron phosphate.
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Figure CN121626953A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a method for preparing lithium iron phosphate, and particularly relates to a method for preparing lithium iron phosphate by modifying iron phosphate. BACKGROUND
[0002] With the development of new energy technology, the application scenarios of lithium ion batteries are increasingly widespread. Lithium iron phosphate (LiFePO4) has become a mainstream cathode material for lithium ion batteries due to its high safety, long cycle life, and abundant raw material sources. Currently, the preparation process of lithium iron phosphate mainly uses the solid phase method of iron phosphate. The morphology of iron phosphate has a great influence on the tap density and electrochemical performance of the prepared lithium iron phosphate powder.
[0003] Generally speaking, lithium iron phosphate prepared using coral-like or molten-like spherical iron phosphate has excellent comprehensive performance, however, the synthesis process of this morphology of iron phosphate is harsh, and has a high technical threshold and preparation cost. Studies have shown that using flaky iron phosphate can prepare lithium iron phosphate with good electrochemical performance, but the tap density of the powder is low. In addition, for the recovered iron phosphate in the preparation process of lithium iron phosphate, although its price is low, due to the irregular morphology of this type of iron phosphate, it can also be used to prepare lithium iron phosphate with high performance. SUMMARY
[0004] The present application provides a method for preparing lithium iron phosphate by modifying iron phosphate, which adds an acidic solution in the batching stage of the conventional lithium iron phosphate preparation process, and uses inexpensive and readily available flaky iron phosphate and recovered iron phosphate to prepare lithium iron phosphate with excellent electrochemical performance and high powder tap density.
[0005] The method for preparing lithium iron phosphate of the present application comprises the following steps: (1) after dispersing iron phosphate with water, an acidic solution is added and stirred to obtain a first solution; (2) a lithium source, a carbon source and a doping element are added to the first solution and stirred to configure a slurry; (3) the slurry is sand-milled and dried to obtain a precursor powder, and the precursor powder is calcined and then treated to obtain a lithium iron phosphate product.
[0006] In step (1), the acidic solution is at least one of oxalic acid, phosphoric acid and nitric acid, preferably an oxalic acid solution.
[0007] In step (1), the amount of the acidic solution added is 0.01% to 3% of the mass of the iron phosphate.
[0008] In step (2), the lithium source is a lithium salt.
[0009] In step (2), the lithium salt is at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium nitrate, preferably lithium carbonate.
[0010] In step (2), the carbon source includes a macromolecular carbon source and a small molecular carbon source.
[0011] In step (2), the macromolecular carbon source is at least one of polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyaniline and starch, preferably polyethylene glycol.
[0012] In step (2), the small molecular carbon source is at least one of glucose, sucrose, citric acid and ascorbic acid, preferably glucose.
[0013] In step (2), the doping element is a titanium-containing compound.
[0014] In step (2), the titanium-containing compound is at least one of titanium dioxide, tetrabutyl titanate and titanyl oxalate, preferably titanium dioxide.
[0015] Beneficial effects: Compared with the prior art, the present application has the following remarkable advantages: (1) adding an acidic solution in the batching stage to modify the morphology of part of the iron phosphate, thereby improving the sphericity of the material and the tap density of the lithium iron phosphate powder; (2) by introducing a low-cost auxiliary process, the cheap and easily available irregular non-spherical iron phosphate is applied to the preparation of lithium iron phosphate, thereby reducing the production cost. BRIEF DESCRIPTION OF DRAWINGS
[0016] Figure 1 A scanning electron microscope (SEM) image of the flaky iron phosphate used in the present application;
[0017] Figure 2 A scanning electron microscope (SEM) image of the lithium iron phosphate prepared in the present application;
[0018] Figure 3 A scanning electron microscope (SEM) image of the lithium iron phosphate prepared using the prior art. DETAILED DESCRIPTION
[0019] The technical solutions of the present application will be further described below in combination with examples and comparative examples. Without additional description, the reagents used are commercially available reagents which are directly used without purification.
[0020] The tap density of the lithium iron phosphate and the discharge capacity of the lithium iron phosphate described in the present application are tested according to the method described in GB / T 30835-2014 Carbon composite lithium iron phosphate positive electrode material for lithium ion batteries.
[0021] Example 1
[0022] The specific surface area of the selected flaky iron phosphate is 8.63 m 2 / g, and the tap density is 0.905 g / cm 3The sheet-shaped iron phosphate was dispersed using deionized water. Oxychloride solid was weighed according to 0.8% of the mass of iron phosphate, and an oxychloride solution was prepared after dissolving the oxychloride solid in deionized water. The oxychloride solution was added to the dispersed sheet-shaped iron phosphate, and the slurry was uniformly dispersed after sufficient stirring and mixing to obtain a first solution.
[0023] Lithium carbonate was weighed according to the total molar ratio of Li:P = 1.02:1 in the system, glucose was weighed according to 8% of the mass of iron phosphate, PEG was weighed according to 3% of the mass of iron phosphate, and titanium dioxide was weighed according to 0.6% of the theoretical mass of lithium iron phosphate. The lithium source, carbon source, and doping element were added to the first solution, and the slurry was uniformly formed after stirring and mixing. Deionized water was added to adjust the solid content of the slurry to 40%.
[0024] The slurry was pumped into a sand mill containing 0.6 mm zirconium beads, and sand milling was performed to a D50 of 0.5 um. Fine grinding was performed to 0.40±0.02 um using a sand mill containing 0.3 mm zirconium beads. The sand-milled slurry was spray dried, the inlet air temperature was 220~230℃, the outlet air temperature was 80~90℃, and the atomizer speed was 16000 rpm to obtain a precursor powder. The precursor powder was loaded into a graphite crucible and calcined under an inert atmosphere, the calcination temperature was 810℃, and the calcination time was 6 h. After calcination, the product was cooled to room temperature, and the calcined product was crushed, sieved, and iron was removed to obtain a lithium iron phosphate product. The tap density of the lithium iron phosphate was measured, and the discharge capacity at 0.1C and 1C, respectively, was measured, and the results are shown in Table 1.
[0025] The sheet-shaped iron phosphate and the above lithium iron phosphate product were detected using a scanning electron microscope (SEM), and the results are shown in Figure 1 and Figure 2 .
[0026] Example 2
[0027] The sheet-shaped iron phosphate with a specific surface area of 8.63 m 2 / g and a tap density of 0.905 g / cm 3 was dispersed using deionized water. Oxychloride solid was weighed according to 3% of the mass of iron phosphate, and an oxychloride solution was prepared after dissolving the oxychloride solid in deionized water. The oxychloride solution was added to the dispersed sheet-shaped iron phosphate, and the slurry was uniformly dispersed after sufficient stirring and mixing to obtain a first solution.
[0028] Lithium carbonate was weighed according to the total molar ratio of Li:P = 1.02:1 in the system, glucose was weighed according to 8% of the mass of iron phosphate, PEG was weighed according to 3% of the mass of iron phosphate, and titanium dioxide was weighed according to 0.6% of the theoretical mass of lithium iron phosphate. The lithium source, carbon source, and doping element were added to the first solution, and the slurry was uniformly formed after stirring and mixing. Deionized water was added to adjust the solid content of the slurry to 40%.
[0029] The slurry was pumped into a sand mill with 0.6 mm zirconium beads, sand-milled to a D50 of 0.5 um, and then fine-milled to 0.40±0.02 um with a sand mill with 0.3 mm zirconium beads. The sand-milled slurry was spray dried with an inlet temperature of 220~230℃, an outlet temperature of 80~90℃, and an atomizer speed of 16000 rpm to obtain a precursor powder. The precursor powder was loaded into a graphite crucible and calcined under an inert atmosphere at a temperature of 810℃ for 6 h. After calcination, the product was cooled to room temperature, crushed, sieved, and de-ironed to obtain a lithium iron phosphate product. The tap density of the lithium iron phosphate was measured, as were the discharge capacities at 0.1C and 1C, respectively. The results are shown in Table 1.
[0030] The acidic solution in Examples 1 and 2 can also be selected from at least one of nitric acid and phosphoric acid, and the amount can be selected from the range of 0.01%~3%; the lithium source can also be selected from at least one of lithium hydroxide, lithium acetate, and lithium nitrate; the macromolecular carbon source can also be selected from at least one of polyvinyl alcohol (PVA), polyaniline, and starch; the small molecule carbon source can also be selected from at least one of sucrose, citric acid, and ascorbic acid; and the doping element can also be selected from at least one of tetrabutyl titanate and titanyl oxalate.
[0031] Comparative Example 1 A spherical lithium iron phosphate with a specific surface area of 7.35 m 2 / g and a tap density of 0.72 g / cm 3 was dispersed using deionized water. Lithium carbonate was weighed according to a total molar ratio of Li:P = 1.02:1 in the system, glucose was weighed according to 8% of the mass of the lithium iron phosphate, PEG was weighed according to 3% of the mass of the lithium iron phosphate, and titanium dioxide was weighed according to 0.6% of the theoretical mass of the lithium iron phosphate. The lithium source, carbon source, and doping element were added to the dispersed spherical lithium iron phosphate slurry, and stirred and mixed uniformly to form a slurry. Deionized water was added to adjust the solid content of the slurry to 40%.
[0032] The slurry was pumped into a sand mill with 0.6 mm zirconium beads, sand-milled to a D50 of 0.5 um, and then fine-milled to 0.40±0.02 um with a sand mill with 0.3 mm zirconium beads. The sand-milled slurry was spray dried with an inlet temperature of 220~230℃, an outlet temperature of 80~90℃, and an atomizer speed of 16000 rpm to obtain a precursor powder. The precursor powder was loaded into a graphite crucible and calcined under an inert atmosphere at a temperature of 810℃ for 6 h. After calcination, the product was cooled to room temperature, crushed, sieved, and de-ironed to obtain a lithium iron phosphate product. The tap density of the lithium iron phosphate was measured, as were the discharge capacities at 0.1C and 1C, respectively. The results are shown in Table 1.
[0033] Comparative Example 2 The specific surface area of the flaky iron phosphate was 8.63 m 2 / g, and the tap density was 0.905 g / cm 3 . Deionized water was used for dispersion. Lithium carbonate was weighed according to the total molar ratio of Li:P = 1.02:1 in the system, glucose was weighed according to 8% of the mass of iron phosphate, PEG was weighed according to 3% of the mass of iron phosphate, and titanium dioxide was weighed according to 0.6% of the theoretical mass of lithium iron phosphate. The lithium source, carbon source, and doping element were added to the dispersed flaky iron phosphate slurry, and stirred and mixed uniformly to form a slurry. Deionized water was added to adjust the solid content of the slurry to 40%.
[0034] The slurry was pumped into a sand mill containing 0.6 mm zirconium beads, and sand-milled to a D50 of 0.5 um, and then finely ground to 0.40±0.02 um using a sand mill containing 0.3 mm zirconium beads. The sand-milled slurry was spray dried, with an inlet air temperature of 220-230℃, an outlet air temperature of 80-90℃, and an atomizer speed of 16000 rpm, to obtain a precursor powder. The precursor powder was loaded into a graphite crucible and calcined under an inert atmosphere, with a calcination temperature of 810℃ and a calcination time of 6 h. After calcination, the product was cooled to room temperature, and then crushed, sieved, and iron-removed to obtain a lithium iron phosphate product. The tap density of the lithium iron phosphate was measured, as well as the discharge capacity at 0.1C and 1C, respectively, and the results are shown in Table 1.
[0035] The above lithium iron phosphate product was detected using a scanning electron microscope (SEM), and the results are shown in Figure 3 .
[0036] Comparative Example 3 The specific surface area of the flaky iron phosphate was 8.63 m 2 / g, and the tap density was 0.905 g / cm 3 . Deionized water was used for dispersion. Solid oxalic acid was weighed according to 5% of the mass of iron phosphate, and dissolved in deionized water to prepare an oxalic acid solution. The oxalic acid solution was added to the dispersed flaky iron phosphate, and stirred and mixed thoroughly to uniformly disperse the slurry, to obtain a first solution.
[0037] Lithium carbonate was weighed according to the total molar ratio of Li:P = 1.02:1 in the system, glucose was weighed according to 8% of the mass of iron phosphate, PEG was weighed according to 3% of the mass of iron phosphate, and titanium dioxide was weighed according to 0.6% of the theoretical mass of lithium iron phosphate. The lithium source, carbon source, and doping element were added to the first solution, and stirred and mixed uniformly to form a slurry. Deionized water was added to adjust the solid content of the slurry to 40%.
[0038] The slurry was pumped into a sand mill with 0.6 mm zirconium beads, sand-milled to a D50 of 0.5 um, and then fine-milled to 0.40±0.02 um with a sand mill with 0.3 mm zirconium beads. The sand-milled slurry was spray dried with an inlet temperature of 220~230℃, an outlet temperature of 80~90℃, and an atomizer speed of 16000 rpm to obtain a precursor powder. The precursor powder was loaded into a graphite crucible and calcined under an inert atmosphere at a temperature of 810℃ for 6 h. After calcination, the product was cooled to room temperature, crushed, sieved, and de-ironed to obtain a lithium iron phosphate product. The tap density of the lithium iron phosphate was measured, as well as the discharge capacity at 0.1C and 1C, respectively, and the results are shown in Table 1.
[0039] Table 1. Tap density and discharge capacity of Examples 1-6 and Comparative Examples 1-3
[0040] As shown in Table 1, Examples 1 and 2 used poorly shaped flaky iron phosphate or recycled iron phosphate as the precursor, but the lithium iron phosphate prepared had a high tap density and excellent electrochemical performance, maintaining a high discharge capacity at 0.1C and 1C. Compared to Comparative Example 1, which used spherical iron phosphate as the precursor, Examples 1 and 2 used poorly shaped flaky iron phosphate or recycled iron phosphate as the precursor to prepare lithium iron phosphate, but the electrochemical performance of the product was similar to that of the product prepared directly using spherical iron phosphate, and the tap density was significantly improved.
[0041] Comparative Example 2 used flaky iron phosphate that was not treated with an acid solution, and the tap density was significantly lower than that of Examples 1 and 2. At the same time, it can be seen from Figure 2 and Figure 3 that the lithium iron phosphate particles prepared using the present application had a high sphericity and were large in size, i.e., had a high apparent powder tap density, but the lithium iron phosphate particles prepared directly from flaky iron phosphate were significantly smaller and more irregular, resulting in a low apparent tap density. This is because in the process of preparing lithium iron phosphate according to the present application, the flaky iron phosphate is partially dissolved by treating the precursor with an acid solution during the mixing stage, which makes the morphology of the flaky iron phosphate rounder, promotes the melting and growth of the iron phosphate during the sintering stage, and promotes the formation of large particles, thereby improving the powder tap density of the material. Comparative Example 3 used an excessive amount of acid solution to treat the flaky iron phosphate, but the tap density was significantly lower than that of Examples 1 and 2, which indicates that the amount of acid solution added is not the more the better.
Claims
1. A method of preparing lithium iron phosphate, characterized by, The method comprises the following steps: (1) dispersing iron phosphate with water, adding an acid solution and stirring to obtain a first solution; (2) adding a lithium source, a carbon source and a doping element into the first solution and stirring to obtain a slurry; (3) sand grinding and drying the slurry to obtain a precursor powder, and performing post-treatment on the precursor powder after calcination to obtain a lithium iron phosphate product.
2. The method of claim 1, wherein: In step (1), the acid solution is at least one of oxalic acid, phosphoric acid and nitric acid.
3. The method of claim 1, wherein: In step (1), the acid solution is added in an amount of 0.01% to 3% of the mass of the iron phosphate.
4. The method of claim 1, wherein: In step (2), the lithium source is a lithium salt.
5. The method of claim 1, wherein: In step (2), the lithium salt is at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium nitrate.
6. The method of claim 1, wherein: In step (2), the carbon source comprises a macromolecular carbon source and a small-molecular carbon source.
7. The method of claim 6, wherein the lithium iron phosphate is prepared by: The macromolecular carbon source is at least one of polyethylene glycol, polyvinyl alcohol, polyaniline and starch.
8. The method of claim 6, wherein the lithium iron phosphate is prepared by: The small-molecular carbon source is at least one of glucose, sucrose, citric acid and ascorbic acid.
9. The method of claim 1, wherein: In step (2), the doping element is a titanium-containing compound.
10. The method of claim 9, wherein the lithium iron phosphate is prepared by: In step (2), the titanium-containing compound is at least one of titanium dioxide, tetrabutyl titanate and titanyl oxalate.