Iron phosphate material, preparation method thereof and lithium iron phosphate positive electrode material
By controlling the molar ratio and recrystallization conditions of lithium iron phosphate liquid, a grain-shaped lithium iron phosphate material was prepared, which solved the problem of high raw material and environmental costs in the existing process and improved the performance of lithium iron phosphate cathode material.
Patent Information
- Application Number
- CN202511518982.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-22
- Publication Date
- 2026-02-10
AI Technical Summary
Existing lithium iron phosphate cathode material production processes suffer from high raw material costs or high environmental costs, making it difficult to simultaneously achieve low cost and high performance.
Using iron oxide as the iron source, by controlling the molar ratio of phosphorus to iron in the ferric phosphate solution, the recrystallization pH and temperature, granular ferric phosphate material is prepared, avoiding the use of high-purity iron powder and oxidants to generate wastewater, thus reducing raw material and environmental costs.
A lithium iron phosphate cathode material with high solid density was prepared, which improved the electrochemical performance of lithium-ion batteries and achieved a low-cost and environmentally friendly production process.
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Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of battery materials, in particular to a phosphorus iron material and a preparation method thereof and a lithium iron phosphate positive electrode material. BACKGROUND
[0002] The phosphorus iron is a precursor for producing the lithium iron phosphate positive electrode material. At present, there are two process routes for producing the battery-grade phosphorus iron in the industry. One route is to use ferrous sulfate as an iron source, a phosphate as a phosphorus source, hydrogen peroxide as an oxidizing agent, ammonia water or liquid alkali to adjust pH, and to prepare the battery-grade phosphorus iron through processes such as co-precipitation, aging and washing. The raw material cost is low in the production of the phosphorus iron by using the route, the product performance of the lithium iron phosphate positive electrode material is good, but a large amount of phosphate and hydrogen peroxide needs to be used in the process of oxidizing the ferrous sulfate into ferric iron, and then a large amount of sulfate wastewater is generated, and the environmental protection cost is high. The other route is to use phosphoric acid as a phosphorus source and iron powder as an iron source, to prepare a solution through high-temperature reaction, to add hydrogen peroxide, and to prepare the battery-grade phosphorus iron through processes such as co-precipitation, aging and washing. The production of the phosphorus iron by using the route almost does not generate wastewater, and the environmental protection cost is low, but the high-purity iron powder is used in the production route, the raw material cost is high, and the product performance of the lithium iron phosphate positive electrode material is slightly poor. SUMMARY
[0003] Therefore, it is necessary to provide a phosphorus iron material, a preparation method thereof and a lithium iron phosphate positive electrode material in view of the above problems. The preparation method of the phosphorus iron material has the advantages of low raw material cost and low environmental protection cost, and the electrochemical performance of the lithium iron phosphate positive electrode material prepared by using the preparation method is excellent.
[0004] A preparation method of a phosphorus iron material, comprising the following steps:
[0005] Mixing and reacting a phosphoric acid solution with iron oxide to prepare a phosphorus-iron solution, wherein the molar ratio of phosphorus elements to iron elements in the phosphorus-iron solution is 3:1-5:1;
[0006] Mixing the phosphorus-iron solution with a phosphorus iron yellow slurry, wherein the molar ratio of iron elements in the phosphorus-iron solution to iron elements in the phosphorus iron yellow slurry is 0.1:1-0.3:1, and then performing recrystallization by heating, wherein the pH of the recrystallization is 0.3-0.9;
[0007] Calcining the crystallization product to prepare a phosphorus iron material with granular crystal morphology and a single-peak particle size distribution peak shape diagram, wherein the molar ratio of phosphorus elements to iron elements in the phosphorus iron material is 1:0.950-1:0.965.
[0008] In one embodiment, the molar ratio of phosphorus to iron in the ferric phosphate solution is 3:1-3.5:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.960-1:0.965.
[0009] Alternatively, the molar ratio of phosphorus to iron in the ferric phosphate solution is 3.5:1-4:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.955-1:0.960.
[0010] Alternatively, the molar ratio of phosphorus to iron in the ferric phosphate solution is 4:1-5:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.950-1:0.955.
[0011] In one embodiment, the recrystallization temperature is 88°C-96°C and the duration is 2h-5h.
[0012] In one embodiment, the recrystallization is further performed by stirring at a speed of 45 rpm to 60 rpm.
[0013] In one embodiment, the step of mixing the ferric phosphate liquid with the ferric phosphate yellow slurry involves continuously feeding the ferric phosphate liquid into the ferric phosphate yellow slurry for 0.5h-1h, resulting in an iron concentration of 0.20mol / L-0.25mol / L after mixing.
[0014] In one embodiment, the calcination heating rate is 5℃ / min-10℃ / min, the temperature is 550℃-650℃, and the duration is 4h-8h.
[0015] In one embodiment, the step of mixing and reacting the phosphoric acid solution with iron oxide involves continuously feeding the iron oxide into the phosphoric acid solution for 0.5-1.0 hours, then heating to 90-100°C and holding at that temperature for 1-4 hours.
[0016] In one embodiment, the method for preparing the ferric phosphate yellow slurry includes: preparing a phosphate solution with a pH of 8-9 by mixing a phosphorus source and an oxidant; reacting the phosphate solution with a ferrous solution having an iron concentration of 1 mol / L-2 mol / L; and then filtering, washing, and pulping to obtain the ferric phosphate yellow slurry. The molar ratio of phosphorus in the phosphate solution to iron in the ferrous solution is 1:1.00-1:1.03. The particle size D of the ferric phosphate yellow slurry is... 50 The size ranges from 3μm to 8μm.
[0017] A type of iron phosphate material prepared using the above-described method for preparing iron phosphate material.
[0018] A lithium iron phosphate cathode material, wherein the lithium iron phosphate cathode material is prepared using the aforementioned iron phosphate material.
[0019] In the preparation method of the iron phosphate material of this invention, iron phosphate liquid is first prepared using iron oxide, and then the iron phosphate liquid and iron phosphate yellow slurry are recrystallized. The raw material cost is lower than that of the preparation route using high-purity iron powder as the iron source, and the environmental cost is lower than that of the preparation route using ferrous sulfate as the iron source. At the same time, by controlling the molar ratio of phosphorus to iron in the iron phosphate liquid, the molar ratio of iron in the iron phosphate liquid to iron in the iron phosphate yellow slurry, and the pH of recrystallization, iron phosphate material with a granular morphology, a single peak in the particle size distribution peak diagram, a specific molar ratio of phosphorus to iron, and low impurities can be obtained. Using this iron phosphate material, lithium iron phosphate cathode material with high compaction density can be prepared, effectively improving the electrochemical performance of lithium-ion batteries. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 Here is an electron microscope image of the iron phosphate material prepared in Example 1 of this invention;
[0022] Figure 2 This is a peak shape diagram of the particle size distribution of the iron phosphate material prepared in Example 1 of the present invention;
[0023] Figure 3 This is an electron microscope image of the iron phosphate material prepared in Example 2 of the present invention;
[0024] Figure 4 This is a peak shape diagram of the particle size distribution of the iron phosphate material prepared in Example 2 of the present invention;
[0025] Figure 5 Here is an electron microscope image of the iron phosphate material prepared in Comparative Example 4;
[0026] Figure 6 The peak shape of the particle size distribution of the iron phosphate material prepared in Comparative Example 5 is shown. Detailed Implementation
[0027] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.
[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.
[0029] The method for preparing iron phosphate material provided by the present invention includes the following steps:
[0030] Phosphoric acid solution is mixed with iron oxide to produce phosphoric iron liquid, wherein the molar ratio of phosphorus to iron in the phosphoric iron liquid is 3:1-5:1.
[0031] The ferric phosphorus solution is mixed with ferric phosphate yellow slurry, wherein the molar ratio of iron in the ferric phosphorus solution to iron in the ferric phosphate yellow slurry is 0.1:1-0.3:1, and then the mixture is heated to recrystallize, wherein the pH of the recrystallization is 0.3-0.9.
[0032] The crystalline product is calcined to obtain an iron phosphate material with a granular morphology and a single-peaked particle size distribution peak. The molar ratio of phosphorus to iron in the iron phosphate material is 1:0.950-1:0.965.
[0033] In the preparation method of the iron phosphate material of the present invention, iron oxide is first used to prepare iron phosphate liquid, and then the iron phosphate liquid and iron phosphate yellow slurry are recrystallized. This avoids the use of expensive high-purity iron powder, and also avoids the generation of wastewater containing a large amount of by-products such as ammonium sulfate or sodium sulfate due to the oxidation of divalent iron source to trivalent iron by using oxidants, phosphates and pH adjusters. Therefore, its raw material cost is lower than that of the preparation route using high-purity iron powder as iron source, and its environmental protection cost is lower than that of the preparation route using ferrous sulfate as iron source.
[0034] Meanwhile, by controlling the molar ratio of phosphorus to iron in the ferric phosphate solution, the molar ratio of iron in the ferric phosphate solution to iron in the ferric phosphate slurry, and the pH of recrystallization, it is possible to obtain ferric phosphate material with a granular morphology, a single peak in the particle size distribution diagram, a specific molar ratio of phosphorus to iron, and low impurity content. Using this ferric phosphate material, lithium iron phosphate cathode material with high compaction density can be prepared. Specifically, the compaction density of lithium iron phosphate cathode material can reach more than 2.55 g / cm³, thereby effectively improving the electrochemical performance of lithium-ion batteries.
[0035] Optionally, the molar ratio of phosphorus to iron in the ferric phosphate solution is 3:1-3.5:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.960-1:0.965; or, the molar ratio of phosphorus to iron in the ferric phosphate solution is 3.5:1-4:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.955-1:0.960; or, the molar ratio of phosphorus to iron in the ferric phosphate solution is 4:1-5:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.950-1:0.955. Therefore, by controlling the molar ratio of phosphorus to iron in the ferric phosphate solution in this manner, ferric phosphate materials with a specific molar ratio of phosphorus to iron can be prepared in a customized manner.
[0036] Optionally, the step of mixing phosphoric acid solution with iron oxide includes: first preparing phosphoric acid solution, for example, preparing a phosphoric acid solution with a mass fraction of 35%-65% from 85% phosphoric acid; then continuously feeding iron oxide into the phosphoric acid solution for 0.5-1.0 hours; stirring evenly; reacting at 90-100°C for 1-4 hours; and obtaining ferrophosphate solution after filtration. In order to reduce the amount of solvent added, it is preferable to control the iron element concentration in the ferrophosphate solution within the range of 2.0 mol / L-2.5 mol / L.
[0037] Optionally, the preparation method of the ferric phosphate yellow slurry includes: preparing a phosphate solution with a pH of 8-9 by mixing a phosphorus source and an oxidant; reacting the obtained phosphate solution with a ferrous solution with an iron concentration of 1 mol / L-2 mol / L; and then filtering, washing, and pulping to obtain the ferric phosphate yellow slurry. In order to reduce costs, ensure sufficient reaction of phosphorus, and reduce waste of phosphorus raw materials, when the phosphate solution and the ferrous solution are mixed and reacted, the molar ratio of phosphorus in the phosphate solution to iron in the ferrous solution is preferably 1:1.00-1:1.03.
[0038] Furthermore, in the step of preparing a phosphate solution with a pH of 8-9 by mixing the phosphorus source and oxidant, the mass fraction of the oxidant is controlled at 2%-3%. This ensures that the ferrous ions in the ferrous solution are completely oxidized to ferric ions during the subsequent preparation of ferric phosphate slurry. Then, the pH is adjusted to 8-9 by adding an alkaline solution, such as adjusting it to any point or range between 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, or 9. This yields a weakly alkaline phosphate solution, which is beneficial for the subsequent precipitation reaction.
[0039] The phosphorus source can be selected from any one or two of monoammonium phosphate solution and diammonium phosphate solution, preferably monoammonium phosphate solution; the oxidant can be selected from any one or more of hydrogen peroxide, sodium peroxide, ozone, sodium persulfate, and ammonium persulfate, preferably hydrogen peroxide; the alkaline solution can be selected from any one or two of ammonia water and sodium hydroxide solution, preferably ammonia water; the ferrous solution can be selected from any one or more of ferrous sulfate solution, ferrous chloride solution, and ferrous oxalate solution, preferably ferrous sulfate solution.
[0040] Optionally, after the phosphate solution reacts with the ferrous solution, it is filtered and washed to obtain ferric phosphate yellow. The ferric phosphate yellow is then mixed with a solvent and slurryed. The solvent is selected from one or more of distilled water, pure water, or deionized water. The solid content of the obtained ferric phosphate yellow slurry is preferably 15%-20%, and can be any value or a range between 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%. This solid content range is conducive to the subsequent recrystallization of the ferric phosphate yellow slurry and the ferric phosphate solution, and avoids the waste caused by using too much solvent.
[0041] To facilitate recrystallization, the particle size of the ferric phosphate yellow slurry can be controlled, with particle size D... 50 The preferred particle size is 3μm-8μm, and any value of 3μm, 4μm, 5μm, 6μm, 7μm or 8μm or any range between two can be selected. If the particle size is too large or uneven, it will lead to uneven recrystallization reaction rate, while smaller particle size helps to improve the reaction rate.
[0042] Optionally, in the step of mixing the ferric phosphate solution and the ferric phosphate yellow slurry, the ferric phosphate solution is continuously fed into the ferric phosphate yellow slurry for a feeding time of 0.5h-1h. The molar ratio of iron in the ferric phosphate solution to iron in the ferric phosphate yellow slurry can be selected from any point or range between 0.1:1, 0.2:1, or 0.3:1. Within this range, the morphology of the ferric phosphate material and the ratio of phosphorus to iron in the ferric phosphate material can be better controlled. The iron concentration in the solution after mixing is preferably 0.20mol / L-0.25mol / L, such as any point or range between 0.20mol / L, 0.21mol / L, 0.22mol / L, 0.23mol / L, 0.24mol / L, or 0.25mol / L. Within this range, a better crystallization effect can be achieved. It should be noted that the method of recrystallizing the ferric phosphate liquid with the ferric phosphate yellow slurry is beneficial for the formation of granular morphology in the ferric phosphate material.
[0043] Furthermore, to better control the recrystallization rate and obtain iron phosphate material with a good particle size distribution, specifically, the particle size distribution peak shape is a single peak, and the recrystallization temperature is preferably controlled between 88℃ and 96℃, and can be any value or a range between any two of 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, or 96℃. Simultaneously, to better control the impurity content in the iron phosphate material, the recrystallization time is preferably controlled between 2h and 5h, and can be any value or a range between any two of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h.
[0044] Furthermore, the pH for recrystallization can be controlled to any value among 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, or any range between two values. Controlling the pH within this range can inhibit the formation of ferric hydroxide and slow down the precipitation rate of FePO4, providing sufficient time for the orderly growth of crystals. The resulting ferric phosphate crystals have higher crystallinity and better particle size distribution. Specifically, the particle size distribution peak shape is a single peak.
[0045] Furthermore, in order to better promote the crystallization of ferric phosphate and obtain ferric phosphate material with better particle size distribution, the recrystallization process is also stirred, and the stirring speed is preferably 45 rpm-60 rpm.
[0046] Optionally, to effectively remove moisture from ferric phosphate dihydrate and control the morphology of the ferric phosphate material, ferric phosphate dihydrate is calcined. The preferred calcination heating rate is 5℃ / min-10℃ / min, which can be any value or a range between 5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, or 10℃ / min. The preferred calcination temperature is 550℃-650℃, which can be any value or a range between 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, or 650℃. The preferred calcination time is 4h-8h, which is beneficial for obtaining ferric phosphate material with a granular morphology.
[0047] The present invention also provides an iron phosphate material prepared using the method for preparing the iron phosphate material.
[0048] The iron phosphate material in this invention exhibits a granular morphology and a single-peaked particle size distribution. The molar ratio of phosphorus to iron in the iron phosphate material is 1:0.950-1:0.965. When iron phosphate material with the above characteristics is used to prepare lithium iron phosphate cathode material, a high compaction density can be obtained. Specifically, the compaction density can reach more than 2.55 g / cm³, thereby effectively improving the electrochemical performance of lithium-ion batteries.
[0049] The present invention also provides a lithium iron phosphate cathode material, which is prepared using the above-mentioned iron phosphate material.
[0050] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.
[0051] Example 1
[0052] A 50% phosphoric acid solution was prepared by dissolving 85% phosphoric acid. Iron oxide was continuously added to the phosphoric acid solution at a molar ratio of 3.3:1 for phosphorus to iron in the ferrophosphate solution over a period of 0.5 hours. The mixture was stirred until homogeneous and the reaction temperature was set at 95°C. After 4 hours of reaction, the mixture was filtered to obtain a ferrophosphate solution with an iron concentration of 2.1 mol / L.
[0053] A monoammonium phosphate (MAP) solution with a phosphorus concentration of 1.5 mol / L was prepared. Hydrogen peroxide was then added to the MAP solution, maintaining a hydrogen peroxide mass fraction of 3%. The pH was adjusted to 8.2 using ammonia water to obtain a phosphate solution. The phosphate solution and a ferrous sulfate solution with a ferrous iron concentration of 1.5 mol / L were added in parallel, maintaining a 1:1 molar ratio of phosphorus in the phosphate solution to iron in the ferrous sulfate solution. After reacting for 1 hour, the mixture was filtered and washed to obtain ferric phosphate yellow. Pure water was added to the ferric phosphate yellow, and the mixture was pulped to produce granules with a particle size D. 50 The ferric phosphate yellow slurry has a thickness of 4.3 μm, and the solid content of the ferric phosphate yellow slurry is controlled at 15%.
[0054] Ferric phosphate solution was continuously fed into ferric phosphate slurry over a period of 0.5 hours. The molar ratio of iron in the ferric phosphate solution to that in the ferric phosphate slurry was controlled at 0.1:1. Pure water was added until the iron concentration reached 0.25 mol / L. Recrystallization was then carried out at 95°C, with the pH adjusted to 0.67 and the stirring speed at 55 rpm for 2 hours. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 650°C at a rate of 8°C / min and calcined for 4 hours to obtain ferric phosphate material. Figure 1 As shown, the iron phosphate material exhibits a rounded grain morphology, such as... Figure 2 As shown, the particle size distribution peak shape of the iron phosphate material is a single peak.
[0055] Example 2
[0056] A 60% phosphoric acid solution was prepared by dissolving 85% phosphoric acid. Iron oxide was continuously added to the phosphoric acid solution at a molar ratio of 3.45:1 for phosphorus to iron in the ferrophosphate solution over a period of 0.5 hours. The mixture was stirred until homogeneous and the reaction temperature was set at 98°C. After 2 hours of reaction, the mixture was filtered to obtain a ferrophosphate solution with an iron concentration of 2.4 mol / L.
[0057] A monoammonium phosphate (MAP) solution with a phosphorus concentration of 1.2 mol / L was prepared. Hydrogen peroxide was then added to the MAP solution, maintaining a hydrogen peroxide mass fraction of 3%. The pH was adjusted to 8.5 using ammonia water to obtain a phosphate solution. The phosphate solution and a ferrous sulfate solution with a phosphorus concentration of 1.2 mol / L were added in parallel, maintaining a 1:1 molar ratio of phosphorus in the phosphate solution to iron in the ferrous sulfate solution. After reacting for 1 hour, the mixture was filtered and washed to obtain ferric phosphate yellow. Pure water was added to the ferric phosphate yellow, and the mixture was pulped to produce granules with a particle size D. 50 The ferric phosphate yellow slurry has a thickness of 4.6 μm, and the solid content of the ferric phosphate yellow slurry is controlled at 18%.
[0058] Ferric phosphate solution was continuously fed into ferric phosphate slurry over a period of 1 hour. The molar ratio of iron in the ferric phosphate solution to that in the ferric phosphate slurry was controlled at 0.2:1. Pure water was added until the iron concentration reached 0.22 mol / L. Recrystallization was then carried out at 95°C, with the pH adjusted to 0.68 and the stirring speed at 60 rpm for 2 hours. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 600°C at a rate of 10°C / min and calcined for 5 hours to obtain the ferric phosphate material. Figure 3 As shown, the iron phosphate material exhibits a rounded grain morphology, such as... Figure 4 As shown, the particle size distribution peak shape of the iron phosphate material is a single peak.
[0059] Example 3
[0060] Prepare a 60% phosphoric acid solution by dissolving 85% phosphoric acid. Add iron oxide continuously to the phosphoric acid solution according to the molar ratio of phosphorus to iron in the ferrophosphate solution of 3.7:1 for 0.5 hours. Stir until homogeneous, set the reaction temperature to 100℃, and filter after 1 hour of reaction to obtain a ferrophosphate solution with an iron concentration of 2.0 mol / L.
[0061] A monoammonium phosphate (MAP) solution with a phosphorus concentration of 1.0 mol / L was prepared. Hydrogen peroxide was then added to the MAP solution, controlling the hydrogen peroxide mass fraction to 2%. The pH was then adjusted to 9 using ammonia water to obtain a phosphate solution. The phosphate solution and a ferrous sulfate solution with a phosphorus concentration of 1.03 mol / L were added in parallel, controlling the molar ratio of phosphorus in the phosphate solution to iron in the ferrous sulfate solution to be 1:1.03. After reacting for 2 hours, the mixture was filtered and washed to obtain ferric phosphate yellow. Pure water was added to the ferric phosphate yellow, and the mixture was pulped to produce granules with a particle size D. 50 The ferric phosphate yellow slurry has a thickness of 6.4 μm, and the solid content of the ferric phosphate yellow slurry is controlled at 15%.
[0062] Ferric phosphate solution was continuously fed into ferric phosphate slurry over a period of 0.5 h. The molar ratio of iron in the ferric phosphate solution to that in the ferric phosphate slurry was controlled at 0.2:1. Pure water was added until the iron concentration reached 0.25 mol / L. Recrystallization was then carried out at 88 °C, with the recrystallization pH adjusted to 0.73 and the stirring speed set at 50 rpm for 5 h. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 550 °C at a rate of 5 °C / min and calcined for 8 h to obtain ferric phosphate material with a granular morphology. The particle size distribution peak of the ferric phosphate material showed a single peak.
[0063] Example 4
[0064] A 35% phosphoric acid solution was prepared by dissolving 85% phosphoric acid. Iron oxide was continuously added to the phosphoric acid solution according to the molar ratio of phosphorus to iron in the ferrophosphate solution of 4.2:1. The feeding time was 1 hour. The solution was stirred evenly and the reaction temperature was set at 90℃. After 1 hour of reaction, the solution was filtered to obtain a ferrophosphate solution with an iron concentration of 2.5 mol / L.
[0065] A monoammonium phosphate (MAP) solution with a phosphorus concentration of 2.0 mol / L was prepared. Hydrogen peroxide was then added to the MAP solution, maintaining a hydrogen peroxide mass fraction of 2%. The pH was adjusted to 8 using ammonia water to obtain a phosphate solution. The phosphate solution and a ferrous sulfate solution with a phosphorus concentration of 2.0 mol / L were added in parallel, maintaining a 1:1 molar ratio of phosphorus in the phosphate solution to iron in the ferrous sulfate solution. After reacting for 2 hours, the mixture was filtered and washed to obtain ferric phosphate yellow. Pure water was added to the ferric phosphate yellow, and the mixture was pulped to produce granules with a particle size of D. 50 The ferric phosphate yellow slurry has a thickness of 3.7 μm, and the solid content of the ferric phosphate yellow slurry is controlled at 25%.
[0066] Ferric phosphate solution was continuously fed into ferric phosphate slurry over a period of 0.5 h. The molar ratio of iron in the ferric phosphate solution to that in the ferric phosphate slurry was controlled at 0.3:1. Pure water was added until the iron concentration reached 0.20 mol / L. Recrystallization was then carried out at 96 °C, with the recrystallization pH adjusted to 0.77 and the stirring speed set at 45 rpm for 2 h. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 650 °C at a rate of 10 °C / min and calcined for 4 h to obtain ferric phosphate material with a granular morphology. The particle size distribution peak of the ferric phosphate material showed a single peak.
[0067] Example 5
[0068] The difference from Example 1 is that the pH during recrystallization is 0.3.
[0069] Example 6
[0070] The difference from Example 1 is that the pH during recrystallization is 0.9.
[0071] Comparative Example 1
[0072] A 50% phosphoric acid solution was prepared by dissolving 85% phosphoric acid. Iron oxide was continuously fed into the phosphoric acid solution at a molar ratio of 2.9:1 for phosphorus to iron in the ferric phosphate solution. The feeding time was 0.5 hours. The mixture was stirred until homogeneous. The reaction temperature was set at 95℃. After 4 hours of reaction, the iron oxide could not be completely dissolved, and amorphous iron phosphate particles were formed in the ferric phosphate solution.
[0073] Comparative Example 2
[0074] A 50% phosphoric acid solution was prepared by dissolving 85% phosphoric acid. Iron oxide was continuously added to the phosphoric acid solution at a molar ratio of 5.8:1 for phosphorus to iron in the ferrophosphate solution over a period of 0.5 hours. The solution was stirred until homogeneous and the reaction temperature was set at 95°C. After 4 hours of reaction, the solution was filtered to obtain a ferrophosphate solution with an iron concentration of 2.1 mol / L.
[0075] A monoammonium phosphate (MAP) solution with a phosphorus concentration of 1.5 mol / L was prepared. Hydrogen peroxide was then added to the MAP solution, maintaining a hydrogen peroxide mass fraction of 3%. The pH was adjusted to 8.2 using ammonia water to obtain a phosphate solution. The phosphate solution and a ferrous sulfate solution with a ferrous iron concentration of 1.5 mol / L were added in parallel, maintaining a 1:1 molar ratio of phosphorus in the phosphate solution to iron in the ferrous sulfate solution. After reacting for 1 hour, the mixture was filtered and washed to obtain ferric phosphate yellow. Pure water was added to the ferric phosphate yellow, and the mixture was pulped to produce granules with a particle size D. 50 The ferric phosphate yellow slurry has a thickness of 5.2 μm, and the solid content of the ferric phosphate yellow slurry is controlled at 15%.
[0076] Ferric phosphate solution was continuously fed into ferric phosphate slurry over a period of 0.5 hours. The molar ratio of iron in the ferric phosphate solution to that in the ferric phosphate slurry was controlled at 0.5:1. Pure water was added until the iron concentration reached 0.20 mol / L. Recrystallization was then carried out at 96℃, with the recrystallization pH adjusted to 0.56 and the stirring speed set at 50 rpm for 2 hours. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 650℃ at a rate of 10℃ / min and calcined for 4 hours to obtain ferric phosphate material with a granular morphology. The particle size distribution peak of the ferric phosphate material showed a single peak.
[0077] Comparative Example 3
[0078] The difference between Comparative Example 3 and Example 1 is that, in preparing the ferrophosphate solution, iron oxide was continuously added to the phosphoric acid solution at a molar ratio of phosphorus to iron of 5.0:1 for 1 hour. Ferric phosphate slurry was then mixed with the ferrophosphate solution prepared above, with the molar ratio of iron in the ferrophosphate solution to iron in the ferrophosphate slurry controlled at 0.05:1.
[0079] The obtained iron phosphate material exhibits a grain-like morphology, and the particle size distribution peak of the iron phosphate material is a single peak.
[0080] Comparative Example 4
[0081] A monoammonium phosphate (MAP) solution with a phosphorus concentration of 1.5 mol / L was prepared. Hydrogen peroxide was then added to the MAP solution, maintaining a hydrogen peroxide mass fraction of 3%. The pH was adjusted to 8.2 using ammonia water to obtain a phosphate solution. The phosphate solution and a ferrous sulfate solution with a ferrous iron concentration of 1.5 mol / L were added in parallel, maintaining a 1:1 molar ratio of phosphorus in the phosphate solution to iron in the ferrous sulfate solution. After reacting for 1 hour, the mixture was filtered and washed to obtain ferric phosphate yellow. Pure water was added to the ferric phosphate yellow, and the mixture was pulped to produce granules with a particle size D. 50The ferric phosphate yellow slurry has a thickness of 5.2 μm, and the solid content of the ferric phosphate yellow slurry is controlled at 15%.
[0082] A phosphoric acid solution with a mass fraction of 85% was added to ferric phosphate yellow slurry, wherein the molar ratio of phosphorus in the phosphoric acid solution to phosphorus in the ferric phosphate yellow slurry was controlled at 0.25:1. Recrystallization was then carried out at 95℃, with the recrystallization pH adjusted to 0.9, the stirring speed at 50 rpm, and the temperature maintained for 2 hours. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 650℃ at a rate of 8℃ / min and calcined for 4 hours to obtain ferric phosphate material. Figure 5 As shown, the iron phosphate material exhibits a lamellar morphology, and the particle size distribution peak of the iron phosphate material is a single peak.
[0083] Comparative Example 5
[0084] The difference between Comparative Example 5 and Example 1 is that: ferric phosphate liquid was continuously fed into ferric phosphate yellow slurry for 1 hour; the molar ratio of iron in the ferric phosphate liquid to iron in the ferric phosphate yellow slurry was controlled at 0.2:1; and pure water was added until the iron concentration reached 0.25 mol / L. Recrystallization was then carried out at 85°C, with the recrystallization pH adjusted to 0.96 and the stirring speed set at 40 rpm for 4 hours. After recrystallization, the mixture was filtered and washed to obtain ferric phosphate dihydrate. The ferric phosphate dihydrate was then heated to 550°C at a rate of 10°C / min and calcined for 8 hours to obtain ferric phosphate material with a granular morphology. Figure 6 As shown, the particle size distribution peak shape of the iron phosphate material is approximately bimodal.
[0085] The iron phosphate materials prepared in Examples 1-6 and Comparative Examples 2-5 were tested, and the data are shown in Table 1.
[0086] Table 1
[0087]
[0088] The iron phosphate materials prepared in Examples 1-6 and Comparative Examples 2-5 were used to prepare lithium iron phosphate cathode materials, and their compaction density was tested. The results are shown in Table 2.
[0089] Table 2
[0090]
[0091] As shown in Table 2, the compaction density of the lithium iron phosphate cathode materials prepared in Examples 1-6 is between 2.56 g / cm³ and 2.60 g / cm³, all greater than 2.55 g / cm³. The compaction density of the lithium iron phosphate cathode materials prepared in Comparative Examples 2-5 is lower than that in Examples 1-6.
[0092] Lithium iron phosphate cathode material, carbon black conductive agent, and polyvinylidene fluoride binder were mixed in a mass ratio of 90:5:5, and an cathode slurry was prepared using n-methylpyrrolidone as a solvent. This slurry was uniformly coated onto an aluminum foil current collector, and after drying and rolling, a lithium iron phosphate cathode sheet was obtained. In a glove box (water and oxygen content <1 ppm), a coin cell battery was assembled using polyethylene as a separator, lithium hexafluorophosphate as the lithium salt, and lithium sheets as the negative electrode. Charge-discharge tests were performed using a battery tester, and the results are shown in Table 3.
[0093] Table 3
[0094]
[0095] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0096] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A method for preparing an iron phosphate material, characterized in that, Includes the following steps: Phosphoric acid solution is mixed with iron oxide to produce phosphoric iron liquid, wherein the molar ratio of phosphorus to iron in the phosphoric iron liquid is 3:1-5:
1. The ferric phosphorus solution is mixed with ferric phosphate yellow slurry, wherein the molar ratio of iron in the ferric phosphorus solution to iron in the ferric phosphate yellow slurry is 0.1:1-0.3:1, and then the mixture is heated to recrystallize, wherein the pH of the recrystallization is 0.3-0.
9. The crystalline product is calcined to obtain an iron phosphate material with a granular morphology and a single-peaked particle size distribution peak. The molar ratio of phosphorus to iron in the iron phosphate material is 1:0.950-1:0.
965.
2. The method for preparing the iron phosphate material according to claim 1, characterized in that, The molar ratio of phosphorus to iron in the ferric phosphate solution is 3:1-3.5:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.960-1:0.
965. Alternatively, the molar ratio of phosphorus to iron in the ferric phosphate solution is 3.5:1-4:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.955-1:0.
960. Alternatively, the molar ratio of phosphorus to iron in the ferric phosphate solution is 4:1-5:1, and the molar ratio of phosphorus to iron in the ferric phosphate material is 1:0.950-1:0.
955.
3. The method for preparing the iron phosphate material according to claim 1, characterized in that, The recrystallization temperature is 88℃-96℃, and the time is 2h-5h.
4. The method for preparing the iron phosphate material according to claim 1, characterized in that, The recrystallization process also involves stirring at a speed of 45 rpm to 60 rpm.
5. The method for preparing the iron phosphate material according to claim 1, characterized in that, In the step of mixing the ferric phosphate liquid with the ferric phosphate yellow slurry, the ferric phosphate liquid is continuously fed into the ferric phosphate yellow slurry for a feeding time of 0.5h-1.0h, and the concentration of iron element after mixing is 0.20mol / L-0.25mol / L.
6. The method for preparing the iron phosphate material according to claim 1, characterized in that, The calcination heating rate is 5℃ / min-10℃ / min, the temperature is 550℃-650℃, and the duration is 4h-8h.
7. The method for preparing the iron phosphate material according to claim 1, characterized in that, In the step of mixing and reacting phosphoric acid solution with iron oxide, the iron oxide is continuously fed into the phosphoric acid solution for 0.5h-1.0h, and then the temperature is raised to 90℃-100℃ and kept at that temperature for 1h-4h.
8. The method for preparing the iron phosphate material according to claim 1, characterized in that, The preparation method of the ferric phosphate yellow slurry includes: preparing a phosphate solution with a pH of 8-9 by mixing a phosphorus source and an oxidant; reacting the phosphate solution with a ferrous solution with an iron concentration of 1 mol / L-2 mol / L; and then filtering, washing, and pulping to obtain the ferric phosphate yellow slurry. The molar ratio of phosphorus in the phosphate solution to iron in the ferrous solution is 1:1.00-1:1.
03. The particle size D of the ferric phosphate yellow slurry is... 50 The size ranges from 3μm to 8μm.
9. An iron phosphate material prepared using the method for preparing iron phosphate material as described in any one of claims 1-8.
10. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is prepared using the iron phosphate material as described in claim 9.