A method for preparing high-performance spherical iron phosphate
High-performance spherical lithium iron phosphate was prepared by controlling the crystallization at room temperature (-100℃) and using trace titanium salt doping. This solved the problems of harsh reaction conditions and insufficient electrical performance in the existing technology, and achieved lithium iron phosphate materials with high sphericity and high tap density.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG YOUSHAN NEW MATERIAL TECH CO LTD
- Filing Date
- 2023-10-12
- Publication Date
- 2026-05-26
AI Technical Summary
Existing methods for preparing spherical iron phosphate have stringent reaction conditions, require the addition of additional nanomaterials and strict pH control, making them unsuitable for industrial production, and their electrical properties need improvement.
A controlled crystallization method at room temperature to 100℃ was adopted. By adding trace amounts of titanium salt to adjust the pH of phosphate salt to >7.5, high-performance spherical iron phosphate was formed. Doping with Ti4+ changed the primary particle size and crystal structure, thereby improving the lithium ion diffusion rate.
High-performance spherical iron phosphate was prepared under mild reaction conditions, which is suitable for industrial production. It has high sphericity, excellent tap density and electrochemical performance, and is suitable for the preparation of lithium iron phosphate.
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Figure CN117658089B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of materials and chemical engineering technology, and specifically relates to a method for preparing high-performance spherical iron phosphate. Background Technology
[0002] Lithium iron phosphate (LFP), as a novel cathode material for lithium-ion batteries, boasts advantages such as low price, stable operating voltage, non-toxicity, environmental friendliness, structural stability, good thermal stability, and long cycle life. However, it also suffers from drawbacks including low ionic conductivity, poor low-temperature performance, and low tap density. Spheroidizing LFP is currently an effective way to address these issues, while avoiding the reduced tap density and capacity density degradation caused by carbon coating technology. Since the structure of iron phosphate, the product of electrochemical delithiation of LFP, is extremely similar to that of LFP (both belonging to the orthorhombic crystal system, possessing the same space group Pnmb, and differing in volume by only 6.8%), high-density spherical iron phosphate precursors can be used to synthesize high-tap LFP particles. Therefore, related technologies have been developed for the preparation of spherical iron phosphate.
[0003] However, most existing methods for preparing spherical iron phosphate are hydrothermal methods, which require the addition of nanomaterials. The reaction conditions are harsh and difficult to produce industrially. Some methods, however, use controlled crystallization to prepare high-density spherical iron phosphate under relatively mild reaction conditions. These methods require strict control of the pH of the raw material reaction and the pH during the reaction process. This requires a large amount of neutralizing agent and cost control, making them unsuitable for industrial production. Furthermore, the electrical properties need further improvement. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention proposes a method for preparing high-performance spherical iron phosphate, comprising the following steps:
[0005] Step S1: Take the iron salt raw material solution, add phosphate and titanium salt to it, and prepare iron-titanium salt mixed solution A;
[0006] Step S2: Prepare a phosphate raw material solution of a certain concentration and add a pH adjuster to it to prepare a phosphate mixed solution B, so that the pH of the phosphate mixed solution B is greater than 7.5;
[0007] Step S3: Mix the iron-titanium salt mixed solution A, the phosphate salt mixed solution B, and the oxidant under normal temperature and continuous conditions to make the pH greater than 2.5, raise the temperature to 60-100℃ and keep it at that temperature for 60-120 minutes to obtain seed crystal A;
[0008] Step S4: Under normal temperature and continuous stirring conditions, iron-titanium salt mixed solution A, phosphate salt mixed solution B and oxidant are added to the above seed crystal A 3-8 times simultaneously, the temperature is raised to 60-100℃ and held for 60min-120min to obtain white iron phosphate slurry B. The feeding time is 60min-120min.
[0009] Step S5: High-performance spherical iron phosphate is prepared by filtering, washing, drying and calcining iron phosphate slurry B.
[0010] Further, in step S1, the concentration of iron in the iron-titanium salt mixed solution A is 0.5-1.5 mol / L; the iron salt raw material solution is prepared from ferrous sulfate, ferrous nitrate, ferric sulfate, iron powder, and iron sheet; the amount of phosphoric acid added is: n(H3PO4:Fe) = (0.12~0.20).
[0011] Further, the titanium salt mentioned in step S1 is titanium sulfate, metatitanic acid, or titanium tetrachloride, and the amount of titanium salt added is 0.3-2% of the molar amount of iron in the iron salt.
[0012] Furthermore, the pH adjuster mentioned in step S2 is one or more of ammonia, liquid alkali, and sodium carbonate.
[0013] Furthermore, the concentration of phosphorus in the phosphate salt mixed solution B mentioned in step S2 is 0.5-1.5 mol / L; the phosphate salt raw material solution is prepared from ammonium hydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, sodium monohydrogen phosphate, and sodium dihydrogen phosphate.
[0014] Furthermore, the stirring rate described in steps S3 and S4 is 200 rpm to 800 rpm;
[0015] Furthermore, the reactions in steps S3 and S4 are divided into two stages. The first stage is the feeding stage, which is a reaction at room temperature for 30-60 minutes. The second stage is the heating stage after the feeding is completed, which is a reaction at 60-100℃ for 60-120 minutes.
[0016] Furthermore, in step S4, the total volume of the iron-titanium salt mixed solution A and the phosphate salt mixed solution B is 3-8 times the volume of the seed crystal.
[0017] Furthermore, the oxidizing agent in steps S3 and S4 is one or more of the following reagents with liquid oxidizing properties: sodium sulfate, hydrogen peroxide, perchloric acid, etc.
[0018] Furthermore, the filtration, washing, and drying methods and equipment described in step S5 are common methods or equipment in existing iron phosphate preparation technologies.
[0019] The principle of preparing high-performance spherical iron phosphate in this invention is as follows: ① In the wet reaction stage, a trace amount of titanium sulfate is added to the iron phosphate lattice to replace part of the Fe sites. According to the theory of metallic bonding, the binding energy of titanium ions with oxygen is greater than that of iron ions with oxygen. Therefore, the unit cell containing titanium ions is more tightly bound, and the size of the primary particles composed of the unit cell is smaller. In addition, titanium particle doping will inhibit the growth of iron phosphate, resulting in the shrinkage of the primary iron phosphate particles. ② The iron phosphate synthesis reaction is exothermic and proceeds rapidly at high temperatures, which is conducive to the formation of small particles; ③ By using a pH neutralizing agent to adjust the pH of the phosphate salt to >7.5, the pH of the reaction process is increased to >2.5, the supersaturation of the reaction process increases, making it easier to form smaller primary particles, improving the uniformity and sphericity of the aggregated particles, and preventing the agglomeration of secondary spherical particles into large particles; ④ The key is to prepare iron phosphate seed crystals and extend the reaction time to allow the seed crystals to grow into uniform spherical shapes; ⑤ In the downstream synthesis of lithium iron phosphate, the titanium ions in iron phosphate will reduce the diffusion barrier of lithium ions through the b-axis in the lithium iron phosphate lattice, improve the lithium ion diffusion conductivity, and improve the electrochemical performance of lithium iron phosphate materials.
[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0021] 1. Compared with other spherical iron phosphate preparation technologies, this invention only requires the addition of trace amounts of titanium salt and adjustment of phosphate salt pH to prepare high-performance spherical iron phosphate through conventional controlled crystallization. This avoids the disadvantage of maintaining a stable pH value by adjusting the neutralizing agent feeding rate in real time, which leads to high operational difficulty; it avoids the harsh reaction conditions such as high temperature and high pressure of hydrothermal methods; it avoids the addition of surfactants to the reaction system, reducing the pressure on wastewater treatment; and it avoids the disadvantage of consuming a large amount of neutralizing agent.
[0022] 2. This invention enables the preparation of high-performance spherical iron phosphate materials using a controlled crystallization method at a mild reaction temperature: room temperature to 100℃ (room temperature is 20-30℃), without the need for precise control of reaction pH, the addition of additional surfactants, the need for customized special reaction equipment, and only the addition of trace amounts (ppm level) of titanium salts. This method is suitable for industrial production.
[0023] 3. Compared with conventional iron phosphate preparation techniques, this invention uses Ti doping during the synthesis of spherical iron phosphate. 4+ , using Ti 4+ Modifying the primary particle size of iron phosphate is beneficial for the formation of a spherical structure; simultaneously, altering the crystal structure of iron phosphate is beneficial for the production of lithium iron phosphate. + This improved the electrochemical performance of the cathode material.
[0024] 4. This invention is simple to operate, and the synthesized ferric phosphate has a maximum sphericity of 0.92, with primary particles on the surface resembling fine millet grains, and a maximum tap density of 1.40 g / cm³. 3 It was prepared into lithium iron phosphate, with a compaction density reaching a maximum of 2.56 g / cm³. 3 The maximum 1C discharge capacity is 140.32 mAh / g. Attached Figure Description
[0025] Figure 1 The microstructure of the iron phosphate prepared in Example 1 is shown.
[0026] Figure 2 The microstructure of the iron phosphate prepared in Example 2 is shown.
[0027] Figure 3 The microstructure of the iron phosphate prepared in Example 2 is shown.
[0028] Figure 4 The microstructure of the iron phosphate prepared in Comparative Example 1 is shown.
[0029] Figure 5 The microstructure of the iron phosphate prepared in Comparative Example 2 is shown.
[0030] Figure 6 The microstructure of the iron phosphate prepared in Comparative Example 3 is shown.
[0031] Figure 7 The image shows the microstructure of the iron phosphate prepared in Comparative Example 4. Detailed Implementation Example 1
[0032] (1) Weigh 8004g of ferrous sulfate heptahydrate and dissolve it in deionized water. Add 498g of 85wt% phosphoric acid and 34.55g of analytical grade titanium sulfate to the solution and make up to 24L to obtain iron-titanium mixed solution A with a molar ratio of Fe:Ti = 1:0.005 and an iron concentration of 1.2mol / L.
[0033] (2) Weigh 3312g of monoammonium phosphate and dissolve it in deionized water. According to the molar ratio Fe:N=1:0.2, add 900g of 28wt% ammonia water and make up to 24L to obtain phosphate salt mixed solution B. The pH of phosphate salt mixed solution B is 7.7 and the molar concentration of phosphorus element is 1.2mol / L.
[0034] (3) Under the conditions of reaction temperature of 35℃ and 400rpm, 4L of iron salt solution, 4L of phosphate salt solution are mixed and hydrogen peroxide is mixed, and then the temperature is raised to 90℃ and kept for 30min to obtain seed crystal A;
[0035] (4) Under the conditions of reaction temperature of 35℃ and 400rpm, the remaining 20L iron-titanium mixed solution A, 20L phosphate salt solution and 1768g 30wt% hydrogen peroxide were simultaneously added to seed crystal A. The feeding time was 120min. Then the temperature was raised to 90℃ and kept for 60min to obtain white slurry B.
[0036] (5) After filtering, washing and drying the white slurry B, high-performance spherical iron phosphate is obtained. Example 2
[0037] (1) Weigh 8004g of ferrous sulfate heptahydrate and dissolve it in deionized water. Add 498g of 85wt% phosphoric acid and 69.09g of analytical grade titanium sulfate to it and make up to 24L to obtain iron-titanium mixed solution solution A. The molar ratio of Fe:Ti = 1:0.01 and the iron element concentration is 1.2mol / L.
[0038] (2) Weigh 3312g of monoammonium phosphate and dissolve it in deionized water. According to the molar ratio Fe:N=1:0.2, add 900g of 28wt% ammonia water and make up to 24L to obtain phosphate salt mixed solution B. The pH of phosphate salt mixed solution B is 7.7 and the molar concentration of phosphorus element is 1.2mol / L.
[0039] (3) Under the conditions of reaction temperature of 35℃ and 400rpm, 4L of iron salt solution, 4L of phosphate salt solution are mixed and hydrogen peroxide is mixed, and then the temperature is raised to 90℃ and kept for 30min to obtain seed crystal A;
[0040] (4) Under the conditions of reaction temperature of 35℃ and 400rpm, the remaining 20L iron-titanium mixed solution A, 20L phosphate salt solution and 1768g 30wt% hydrogen peroxide were simultaneously added to seed crystal A. The feeding time was 120min. Then the temperature was raised to 90℃ and kept for 60min to obtain white slurry B.
[0041] (5) After filtering, washing and drying the white slurry B, high-performance spherical iron phosphate is obtained. Example 3
[0042] (1) Weigh 8004g of ferrous sulfate heptahydrate and dissolve it in deionized water. Add 498g of 85wt% phosphoric acid and 103.64g of analytical grade titanium sulfate to the solution and make up to 24L to obtain iron-titanium mixed solution A. The molar ratio of Fe:Ti = 1:0.015 and the iron concentration is 1.2mol / L.
[0043] (2) Weigh 3312g of monoammonium phosphate and dissolve it in deionized water. According to the molar ratio Fe:N=1:0.2, add 900g of 28wt% ammonia water and make up to 24L to obtain phosphate salt mixed solution B. The pH of phosphate salt mixed solution B is 7.7 and the molar concentration of phosphorus element is 1.2mol / L.
[0044] (3) Under the conditions of reaction temperature of 35℃ and 400rpm, 4L of iron salt solution, 4L of phosphate salt solution are mixed and hydrogen peroxide is mixed, and then the temperature is raised to 90℃ and kept for 30min to obtain seed crystal A;
[0045] (4) Under the conditions of reaction temperature of 35℃ and 400rpm, the remaining 20L iron-titanium mixed solution A, 20L phosphate salt solution and 1768g 30wt% hydrogen peroxide were simultaneously added to seed crystal A. The feeding time was 120min. Then the temperature was raised to 90℃ and kept for 60min to obtain white slurry B.
[0046] (5) After filtering, washing and drying the white slurry B, high-performance spherical iron phosphate is obtained. Comparative Example 1
[0047] This comparative example is the same as Example 1 except that titanium salt was not added when preparing iron salt in step (1). Comparative Example 2
[0048] Except for the pH of the phosphate salt mixed solution B being 6.5, this comparative example is the same as Example 1. Comparative Example 3
[0049] Except for the addition of 17.27 g of analytical grade titanium sulfate in step (1), this comparative example is the same as Example 1. Comparative Example 4
[0050] Except for the addition of 172.7g of analytical grade titanium sulfate in step (1), this comparative example is the same as Example 1.
[0051] Experimental Section
[0052] Experiment 1
[0053] The microstructure of the ferric phosphate prepared in Example 1 was characterized, and the results are as follows: Figure 1 As shown, its sphericity is 0.92, the primary particles on the surface are fine millet-like, and its tap density is measured to be 1.35 g / cm³. 3 BET = 6.5g / cm 2 .
[0054] Lithium iron phosphate was prepared using conventional lithium iron phosphate manufacturing processes, and its compacted density was measured to be 2.56 g / cm³. 31C discharge capacity: 140.32 mAh / g.
[0055] Experiment 2
[0056] The microstructure of the ferric phosphate prepared in Example 2 was characterized, and the results are as follows: Figure 2 As shown, its sphericity is 0.90, the primary particles on the surface are fine millet-like, and its tap density is measured to be 1.40 g / cm³. 3 BET = 6.0 g / cm³ 2 .
[0057] It was prepared into lithium iron phosphate using the conventional lithium iron phosphate manufacturing process available on the market, with a compacted density of 2.53 g / cm³. 3 1C discharge capacity: 139.76 mAh / g.
[0058] Experiment 3
[0059] The microstructure of the ferric phosphate prepared in Example 3 was characterized, and the results are as follows: Figure 3 As shown, its sphericity is 0.91, the primary particles on the surface are fine millet-like, and its tap density is measured to be 1.41 g / cm³. 3 BET = 6.3 g / cm³ 2 .
[0060] It was prepared into lithium iron phosphate using the conventional lithium iron phosphate manufacturing process available on the market, with a compacted density of 2.54 g / cm³. 3 1C discharge capacity: 138.26 mAh / g.
[0061] Experiment 4
[0062] The microstructure of the ferric phosphate prepared in Comparative Example 1 was characterized, and the results are as follows: Figure 4 As shown, the sphericity of ferric phosphate is 0.75, and its tap density is measured to be 1.15 g / cm³. 3 BET = 4.6 g / cm³ 2 .
[0063] It was prepared into lithium iron phosphate using the conventional lithium iron phosphate manufacturing process available on the market, with a compacted density of 2.50 g / cm³. 3 The 1C discharge capacity is only 125.31 mAh / g.
[0064] The difference between the iron phosphate prepared in Comparative Example 1 and that in Example 2 is that the primary particles in Comparative Example 1 are in the form of thick flakes. This is because no titanium salt was added to inhibit the growth of the primary particles. When stacked, it is difficult to form a uniform sphere, so its sphericity is not high. Although the lithium iron phosphate prepared using this iron phosphate can maintain a certain compaction density, its electrical performance is poor.
[0065] Experiment 5
[0066] The microstructure of the iron phosphate prepared in Comparative Example 2 was characterized, and the results are as follows: Figure 5 As shown, the sphericity of ferric phosphate is 0.55, and the measured tap density is 0.67 g / cm³. 3 BET = 8.6 g / cm³ 2 .
[0067] It was prepared into lithium iron phosphate using the conventional lithium iron phosphate manufacturing process available on the market, with a compacted density of 2.43 g / cm³. 3 The 1C discharge capacity is only 131.23 mAh / g.
[0068] The difference between the iron phosphate prepared in Comparative Example 2 and Example 2 is that the primary particles in the comparative example are plate-like and do not form uniform spheres. The reason is that the pH value of the phosphate salt is too low at 6.5, which leads to a low degree of supersaturation in the reaction process, resulting in less nucleation in the early stage. The crystal growth rate is greater than the nucleation rate, so it is easier to form plates. Although the lithium iron phosphate prepared using this iron phosphate can maintain a certain compaction density, its electrical performance is poor.
[0069] Experiment 6
[0070] The microstructure of the ferric phosphate prepared in Comparative Example 3 was characterized, and the results are as follows: Figure 6 As shown, the sphericity of ferric phosphate is 0.83, and the measured tap density is 1.23 g / cm³. 3 BET = 6.3 g / cm³ 2 .
[0071] It was prepared into lithium iron phosphate using the conventional lithium iron phosphate manufacturing process available on the market, with a compacted density of 2.44 g / cm³. 3 The 1C discharge capacity is only 134.43 mAh / g.
[0072] The difference between the iron phosphate prepared in Comparative Example 4 and Example 2 is that a small amount of titanium sulfate was used in the comparative example, with Fe:Ti = 1:0.0025. Due to the low amount of titanium sulfate doping, the primary phosphate particles were not significantly altered and maintained their plate-like morphology, resulting in reduced sphericity and thus, the compaction density and electrical properties were at a general level.
[0073] Experiment 7
[0074] The microstructure of the ferric phosphate prepared in Comparative Example 4 was characterized, and the results are as follows: Figure 7 As shown, the sphericity of iron phosphate is 0.89, and the measured tap density is 1.34 g / cm³. 3 BET = 7.0 g / cm³ 2 .
[0075] It was prepared into lithium iron phosphate using the conventional lithium iron phosphate manufacturing process available on the market, with a compacted density of 2.52 g / cm³.3 The 1C discharge capacity is only 132.56 mAh / g.
[0076] The difference between Comparative Example 4 and Example 2 is that titanium sulfate was used in excess in the Comparative Example, with a Fe:Ti ratio of 1:0.25. Morphologically, the primary particles were reduced in size and formed spherical shapes, so its compaction density could reach 2.50 g / cm³. 3 However, due to excessive titanium sulfate doping, the lattice spacing becomes too narrow, leading to blockage of lithium-ion channels and causing FeO in the lattice to... 6 Octahedrons transformed into tiny TiO₂ 6 The octahedron shape also narrows the lithium-ion transport channels, hindering Li + The diffusion of this phosphorus leads to poor electrical performance in lithium iron phosphate prepared using this phosphorus, although it can maintain a certain compaction density.
[0077] Table 1 Performance test results of iron phosphate and lithium iron phosphate
[0078]
Claims
1. A method for preparing high-performance spherical iron phosphate, characterized in that, Includes the following steps: Step S1: Take the iron salt raw material solution, add phosphate and titanium salt to it, and prepare iron-titanium salt mixed solution A; The iron concentration in the iron-titanium salt mixed solution A is 0.5-1.5 mol / L; the iron salt raw material solution is prepared from ferrous sulfate, ferrous nitrate, ferric sulfate, iron powder or iron sheet; the amount of phosphoric acid added is: n(H3PO4:Fe) = (0.12~0.20); The titanium salt is titanium sulfate, metatitanic acid, or titanium tetrachloride, and the amount of titanium salt added is 0.3-2% of the molar amount of iron in the iron salt. Step S2: Prepare a phosphate raw material solution of a certain concentration and add a pH adjuster to it to prepare a phosphate mixed solution B, so that the pH of the phosphate mixed solution B is greater than 7.5; Step S3: Mix the iron-titanium salt mixed solution A, the phosphate salt mixed solution B, and the oxidant at room temperature with continuous stirring to make the pH greater than 2.
5. Heat to 60-100℃ and keep at that temperature for 60-120 minutes to obtain seed crystal A. Step S4: Under normal temperature and continuous stirring conditions, iron-titanium salt mixed solution A, phosphate salt mixed solution B and oxidant are added to the above seed crystal A 3-8 times simultaneously, the temperature is raised to 60-100℃ and held for 60min-120min to obtain white iron phosphate slurry B. The feeding time is 60min-120min. Step S5: High-performance spherical iron phosphate is prepared by filtering, washing, drying and calcining iron phosphate slurry B.
2. The method for preparing high-performance spherical iron phosphate according to claim 1, characterized in that: The pH adjuster mentioned in step S2 is one or more of ammonia, liquid alkali, and sodium carbonate.
3. The method for preparing high-performance spherical iron phosphate according to claim 1, characterized in that: The concentration of phosphorus in the phosphate salt mixed solution B mentioned in step S2 is 0.5-1.5 mol / L; the phosphate salt raw material solution is prepared from ammonium hydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, sodium monohydrogen phosphate or sodium dihydrogen phosphate.
4. The method for preparing high-performance spherical iron phosphate according to claim 1, characterized in that: The stirring rate described in steps S3 and S4 is 200-800 rpm.
5. The method for preparing high-performance spherical iron phosphate according to claim 1, characterized in that: The reactions in steps S3 and S4 are in two stages. The first stage is the feeding stage, which takes 30-60 minutes at room temperature. The second stage of the reaction is the heating stage after the feeding is completed, which is 60-100℃ for 60-120 minutes.
6. The method for preparing high-performance spherical iron phosphate according to claim 1, characterized in that: In step S4, the total volume of the iron-titanium salt mixed solution A and the phosphate salt mixed solution B is 3-8 times the volume of the seed crystal.
7. The method for preparing high-performance spherical iron phosphate according to claim 1, characterized in that: The oxidizing agent in steps S3 and S4 is one or more of sodium sulfate, hydrogen peroxide, and perchloric acid, which are liquid oxidizing agents.