Iron phosphate and method for producing the same, lithium iron phosphate, battery
By controlling the content of water-soluble free phosphorus and impurity sulfur in iron phosphate, and by using specific raw material mixing and low-temperature calcination methods, the problem of impurities in iron phosphate was solved, improving battery performance and storage convenience, and realizing the preparation of high-efficiency lithium iron phosphate and lithium manganese iron phosphate materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGZHOU TINCI MATERIALS TECH
- Filing Date
- 2024-11-29
- Publication Date
- 2026-05-29
AI Technical Summary
In existing technologies, low-cost iron sources such as ferrous sulfate and titanium dioxide byproducts contain impurities that affect the structure and properties of iron phosphate, leading to a decline in battery performance. Furthermore, existing methods that increase sintering temperature or add phosphoric acid to reduce sulfur content are costly and can easily result in excessively high free phosphorus content in iron phosphate products, leading to severe moisture absorption.
By controlling the water-soluble free phosphorus content in ferric phosphate to be between 1000 and 3000 ppm and the impurity sulfur content to be no more than 50 ppm, and by adopting specific raw material mixing and treatment methods, including controlling the addition of ammonia water to the iron-phosphorus solution and calcining temperature to 530-600℃, the loss of phosphorus and the content of impurity sulfur are reduced, and the specific surface area is increased.
This method achieves excellent electrochemical performance of iron phosphate products, improves moisture absorption, facilitates storage and transportation, and obtains iron phosphate with low sulfur impurities under low-temperature sintering, thereby improving the compaction density and discharge specific capacity of lithium iron phosphate and lithium manganese iron phosphate.
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Figure CN122102076A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery materials technology, specifically relating to lithium iron phosphate precursor material—iron phosphate and its preparation method. Background Technology
[0002] With the rapid development of the new energy industry, lithium iron phosphate (LFP) batteries have attracted widespread attention due to their excellent capacity, cycle life, and rate performance, and are considered the most promising cathode material for lithium batteries. Iron phosphate is a precursor material for lithium iron phosphate, and the widespread application of LFP batteries in electric vehicles has driven the demand for iron phosphate materials.
[0003] Currently, most iron sources used in the preparation of lithium iron phosphate (LFP) batteries are low-cost ferrous sulfate or titanium dioxide byproducts, such as those specified in CN116902943A, CN117623257A, and CN110540185A. However, these low-cost iron sources contain numerous impurities, which are generally believed to affect the structure and properties of LFP, thus impacting battery performance. Therefore, low-cost and high-quality battery-grade LFP products are crucial for improving the performance of lithium iron phosphate / lithium manganese iron phosphate batteries in current technologies. Summary of the Invention
[0004] In view of the problems existing in the prior art, the main objective of this invention is to provide ferric phosphate and its preparation method.
[0005] To achieve the above objectives, the present invention provides the following specific technical solutions.
[0006] First, the present invention provides an iron phosphate, wherein the content of water-soluble free phosphorus in the iron phosphate is 1000~3000ppm; the water-soluble free phosphorus includes P2O5 and Fe(PO3)3.
[0007] In a further preferred embodiment, in the XRD pattern of the iron phosphate, (I1+I2) / I3=3%~5%; where I1 represents the characteristic peak intensity at 2θ=20.9±0.5°, I2 represents the characteristic peak intensity at 2θ=22.9±0.5°, and I3 represents the characteristic peak intensity at 2θ=25.8±0.5°.
[0008] In a further preferred embodiment, the content of impurity S in the iron phosphate does not exceed 50 ppm.
[0009] In a further preferred embodiment, the specific surface area of the iron phosphate is 8-12 m². 2 / g.
[0010] In a further preferred embodiment, the moisture content of the iron phosphate is 1500~2500ppm; after being left exposed for 2 hours, the moisture content is <4500ppm.
[0011] Secondly, this invention provides a method for preparing ferric phosphate, comprising: The iron source solution and the phosphorus source solution, which are completely oxidized, are mixed to obtain an iron-phosphorus solution. Ammonia water was added to the iron-phosphorus solution to obtain slurry I; After solid-liquid separation, slurry I is obtained as solid phase I; solid phase I is washed to obtain filter cake. The filter cake was re-pulped to obtain pulp II; phosphoric acid was added to pulp II and aged to obtain a white pulp; After solid-liquid separation, the white slurry yields solid phase II; solid phase II is then washed, dried, and calcined to obtain the iron phosphate product.
[0012] In a further preferred embodiment, the iron source is ferrous sulfate; the phosphorus source is monoammonium phosphate.
[0013] In a further preferred embodiment, the Fe content in the iron source solution is 3.5~7.0 wt%; and the P content in the phosphorus source solution is 3.5~7.0 wt%.
[0014] In a further preferred embodiment, hydrogen peroxide is added to the iron source solution to completely oxidize the iron source, resulting in a fully oxidized iron source solution. The amount of hydrogen peroxide added is further preferably determined based on the molar ratio of H₂O₂ to Fe in the iron source solution, n(H₂O₂):n(Fe) = (0.65~0.85):1.
[0015] In a further preferred embodiment, the amounts of fully oxidized iron source solution and phosphorus source solution are determined based on the molar ratio of Fe in the iron source solution to P in the phosphorus source solution, n(Fe):n(P) = (1.02~1.1):1.
[0016] In a further preferred embodiment, the pH value of the fully oxidized iron source solution is 0.4 to 2.0; and the pH value of the phosphorus source solution is 3.0 to 7.5.
[0017] In a further preferred embodiment, the amount of ammonia added to the iron-phosphorus solution is determined based on the molar ratio of NH3 to Fe in the iron source solution, n(NH3):n(Fe) = (0.75~1.04):1. The addition time of ammonia is further preferred to be 30-90 min.
[0018] In a further preferred embodiment, during the process of adding ammonia to the iron-phosphorus solution, the temperature of the system is maintained at 45~55℃; after the ammonia is added, the system is kept at this temperature for 30~60 minutes.
[0019] In a further preferred embodiment, the solid phase I is washed until the conductivity of the wash water is less than 7000 μS / cm.
[0020] In a further preferred embodiment, the solid content of slurry II is 5~20wt%.
[0021] In a further preferred embodiment, the amount of phosphoric acid added to slurry II is determined based on the ratio of the molar amount of P in phosphoric acid to the molar amount of Fe in slurry II, n(P):n(Fe) = 0.05~0.15:1.
[0022] In a further preferred embodiment, after adding phosphoric acid to slurry II, the pH value of slurry II is 1.5 to 2.5.
[0023] In a further preferred embodiment, the aging temperature is 70~99℃, and the aging time is 1~2h.
[0024] In a further preferred embodiment, the calcination temperature is 530~600℃; the calcination time is 2~5h.
[0025] Based on the same inventive concept, the present invention also provides a lithium iron phosphate, wherein the precursor material of the lithium iron phosphate is the aforementioned iron phosphate or iron phosphate prepared by the aforementioned method.
[0026] In a further preferred embodiment, the compacted density of the lithium iron phosphate is 2.55~2.70 g / m³. 3 .
[0027] In addition, the present invention provides a lithium manganese iron phosphate, wherein the precursor material of the lithium manganese iron phosphate is the aforementioned iron phosphate or iron phosphate prepared by the aforementioned method.
[0028] The present invention also provides a battery, wherein the positive electrode active material of the battery includes the above-mentioned lithium iron phosphate or lithium manganese iron phosphate.
[0029] Compared with the prior art, one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: The iron phosphate product provided by this invention has a moderate content of free phosphorus, which not only provides a good guarantee for the subsequent production of lithium iron phosphate products with excellent electrochemical performance, but also makes the iron phosphate product have a large specific surface area and can improve the moisture absorption of the iron phosphate product, making it convenient for storage and transportation.
[0030] This invention employs a specific method of adding raw materials during the synthesis of iron phosphate, directly achieving low control of the content of impurity element S through a simple process route while retaining a high proportion of free phosphorus in the system. In other words, the iron phosphate preparation method provided by this invention can effectively reduce phosphorus loss and obtain iron phosphate products with low S content at a lower calcination temperature.
[0031] The lithium iron phosphate prepared by sintering iron phosphate according to the present invention can achieve a balance between compaction density and discharge specific capacity, effectively improving compaction density without reducing discharge specific capacity. Attached Figure Description
[0032] Figure 1 The image shows the XRD pattern of the iron phosphate product obtained in Example 1.
[0033] Figure 2 The image shows the SEM image of the iron phosphate product obtained in Example 1.
[0034] Figure 3 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 1.
[0035] Figure 4 shows the XRD pattern of the iron phosphate product obtained in Comparative Example 1.
[0036] Figure 5 shows the SEM image of the iron phosphate product obtained in Comparative Example 1.
[0037] Figure 6 is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 1.
[0038] Figure 7 shows the XRD pattern of the iron phosphate product obtained in Comparative Example 2.
[0039] Figure 8 shows the SEM image of the iron phosphate product obtained in Comparative Example 2.
[0040] Figure 9 is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 2.
[0041] Figure 10 The image shows the XRD pattern of the iron phosphate product obtained in Comparative Example 3.
[0042] Figure 11 The image shows the SEM image of the iron phosphate product obtained in Comparative Example 3.
[0043] Figure 12 This is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 3.
[0044] Figure 13 The image shows the XRD pattern of the iron phosphate product obtained in Comparative Example 4.
[0045] Figure 14 The image shows the SEM image of the iron phosphate product obtained in Comparative Example 4.
[0046] Figure 15 This is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 4.
[0047] Figure 16 The image shows the XRD pattern of the iron phosphate product obtained in Example 2.
[0048] Figure 17This is a SEM image of the iron phosphate product obtained in Example 2.
[0049] Figure 18 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 2.
[0050] Figure 19 The image shows the XRD pattern of the iron phosphate product obtained in Example 3.
[0051] Figure 20 This is a SEM image of the iron phosphate product obtained in Example 3.
[0052] Figure 21 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 3.
[0053] Figure 22 The image shows the XRD pattern of the iron phosphate product obtained in Example 4.
[0054] Figure 23 This is a SEM image of the iron phosphate product obtained in Example 4.
[0055] Figure 24 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 4.
[0056] Figure 25 The image shows the XRD pattern of the iron phosphate product obtained in Example 5.
[0057] Figure 26 This is a SEM image of the iron phosphate product obtained in Example 5.
[0058] Figure 27 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 5. Detailed Implementation
[0059] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.
[0060] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0061] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.
[0062] In my country, the sulfuric acid process for titanium dioxide production generates millions of tons of ferrous sulfate as a byproduct annually. This byproduct is widely used in the synthesis of iron phosphate due to its low cost. However, for battery-grade iron phosphate products, this low-cost ferrous sulfate contains numerous impurities that affect the structure and properties of iron phosphate, thus impacting battery performance. For example, the introduction of large amounts of sulfate ions from the iron source leads to an increase in sulfur (S) content in the product. Increased S content results in a decrease in the charge / discharge capacity and cycle performance of lithium iron phosphate / lithium manganese iron phosphate batteries.
[0063] Existing technologies primarily reduce sulfur (S) content by adding large amounts of phosphoric acid to replace sulfate ions in the system or by increasing the sintering temperature. However, reducing S content is costly, and adding large amounts of phosphoric acid can easily lead to excessively high free phosphorus content in ferric phosphate products. Excessive phosphorus content in ferric phosphate products results in severe moisture absorption, making it difficult to control product moisture content, and also causes significant primary particle agglomeration, reducing the product's specific surface area.
[0064] Furthermore, the inventors discovered in their research that a moderate free phosphorus content in lithium iron phosphate products can improve the rate discharge performance and cycle performance of batteries. During the pulping process of lithium iron phosphate preparation, the dissolution reaction of residual water-soluble free phosphorus in the iron phosphate material generates a large amount of free phosphate ions. These dissolved phosphate ions can be used to replace residual sulfate ions in the system during subsequent sintering, thereby reducing the sulfur content of the lithium iron phosphate product. This eliminates the need for further phosphoric acid input or increasing the sintering temperature to reduce sulfur, lowering production costs and obtaining a low-sulfur lithium iron phosphate product. Simultaneously, a higher free phosphorus content facilitates low-temperature sintering of lithium iron phosphate, and a lower sintering temperature helps control the formation of impurities such as iron phosphide. The uniform distribution of free phosphorus in the system also ensures better compaction density, cycle performance, and battery safety of the downstream lithium iron phosphate. However, existing technologies for synthesizing iron phosphate tend to result in significant phosphorus loss, further leading to excessively low free phosphorus content in downstream lithium iron phosphate products or lithium iron phosphate, which adversely affects the battery's electrochemical performance.
[0065] Therefore, the free phosphorus content of iron phosphate products and its control are key to improving the electrochemical and cycle performance of subsequent lithium iron phosphate and battery products.
[0066] Based on this, the present invention provides an iron phosphate, wherein the content of water-soluble free phosphorus in the iron phosphate is about 1000~3000ppm; the water-soluble free phosphorus includes P2O5 and Fe(PO3)3.
[0067] In the XRD pattern of the iron phosphate, (I1+I2) / I3=3%~5%; where I1 represents the characteristic peak intensity at 2θ=20.9±0.5°, I2 represents the characteristic peak intensity at 2θ=22.9±0.5°, and I3 represents the characteristic peak intensity at 2θ=25.8±0.5°.
[0068] The content of impurity S in the iron phosphate does not exceed 50 ppm.
[0069] The specific surface area of the iron phosphate is 8-12 m². 2 / g.
[0070] The moisture content of the ferric phosphate is 1500-2500 ppm; after being left open for 2 hours, the moisture content is <4500 ppm.
[0071] Experiments have shown that when the free phosphorus content in iron phosphate products meets the above-mentioned range, it can provide a good guarantee for the subsequent production of lithium iron phosphate or lithium manganese iron phosphate products with excellent electrochemical performance. It also makes the specific surface area of iron phosphate products larger and improves the moisture absorption of iron phosphate products, making them easier to store and transport.
[0072] In addition, the present invention also provides a method for preparing iron phosphate, which will be described in detail through the following embodiments.
[0073] Example 1 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 6.0 wt%, and the pH of the iron source solution was adjusted to 1.4.
[0074] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 4.0 wt%, and adjust the pH of the phosphorus source solution to 4.5.
[0075] Hydrogen peroxide is added to the iron source solution, with the molar ratio of H2O2 in the hydrogen peroxide to the molar ratio of Fe in the iron source solution being 0.75:1, to completely oxidize the iron source solution.
[0076] Based on n(Fe):n(P)=1.05:1, the fully oxidized iron source solution and phosphorus source solution are mixed to obtain iron-phosphorus solution. The iron-phosphorus solution is clear and transparent, with no visible precipitate.
[0077] Ammonia water was slowly added to the iron-phosphorus solution, ensuring that the ammonia water was added completely within 45 minutes. The molar ratio of NH3 in the ammonia water to the molar ratio of Fe in the iron source solution was 1.02:1. After the ammonia water was added, the solution was kept at 45°C for 30 minutes to obtain slurry I.
[0078] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0079] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 15%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0080] Phosphoric acid was added to slurry II, with the molar ratio of P in the added phosphoric acid to Fe in the iron source solution being 0.09:1. After the phosphoric acid was added, the temperature was raised to 95°C and kept at that temperature for 1.5 hours to obtain a white slurry.
[0081] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 550℃ for 3 hours to obtain the ferric phosphate product.
[0082] Figure 1 The image shows the XRD pattern of the iron phosphate product obtained in Example 1.
[0083] Figure 2 The image shows the SEM image of the iron phosphate product obtained in Example 1.
[0084] Figure 3 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 1.
[0085] Comparative Example 1 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 6.0 wt%, and the pH of the iron source solution was adjusted to 1.4.
[0086] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 4.0 wt%, and adjust the pH of the phosphorus source solution to 4.5.
[0087] A small amount of water is added to the bottom of the reactor to bring the liquid level up to the stirring blades. Iron source solution, phosphorus source solution, ammonia water, and hydrogen peroxide are added to the reactor simultaneously. The molar ratio of P in the phosphorus source solution to Fe in the iron source solution is 1:1.05, the molar ratio of H2O2 in the hydrogen peroxide to Fe in the iron source solution is 0.75:1, and the molar ratio of NH3 in the ammonia water to Fe in the iron source solution is 1.02:1.
[0088] The above materials need to be added within 45 minutes, and the adding rate needs to be controlled to ensure that the difference in the finishing time of each material drop does not exceed 30 seconds. After all materials have been added, continue to keep warm at 45℃ for 30 minutes to obtain slurry I.
[0089] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0090] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 15 wt%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0091] Phosphoric acid was added to slurry II, with the molar ratio of P in the added phosphoric acid to Fe in the iron source solution being 0.09:1. After the phosphoric acid was added, the temperature was raised to 95°C and kept at that temperature for 1.5 hours to obtain a white slurry.
[0092] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 550℃ for 3 hours to obtain the ferric phosphate product.
[0093] Figure 4 shows the XRD pattern of the iron phosphate product obtained in Comparative Example 1.
[0094] Figure 5 shows the SEM image of the iron phosphate product obtained in Comparative Example 1.
[0095] Figure 6 is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 1.
[0096] Comparative Example 2 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 6.0 wt%, and the pH of the iron source solution was adjusted to 1.4.
[0097] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 4.0 wt%, and adjust the pH of the phosphorus source solution to 4.5.
[0098] Ammonia and hydrogen peroxide were added to the phosphorus source solution to prepare a phosphate solution. The molar ratio of P in the phosphorus source solution to Fe in the iron source solution was 1:1.05, the molar ratio of H2O2 in the hydrogen peroxide to Fe in the iron source solution was 0.75:1, and the molar ratio of NH3 in the ammonia solution to Fe in the iron source solution was 1.02:1.
[0099] The above phosphate solution was slowly added to the iron source solution, ensuring that the addition was completed within 45 minutes. After the addition was completed, the solution was kept at 45°C for 30 minutes to obtain slurry I.
[0100] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0101] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 15%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0102] Phosphoric acid was added to slurry II, with the ratio of the amount of phosphoric acid added to the molar amount of Fe in the iron source solution being 0.09:1. After the phosphoric acid was added, the temperature was raised to 95℃ and kept at that temperature for 1.5 hours to obtain a white slurry.
[0103] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 550℃ for 3 hours to obtain the ferric phosphate product.
[0104] Figure 7 shows the XRD pattern of the iron phosphate product obtained in Comparative Example 2.
[0105] Figure 8 shows the SEM image of the iron phosphate product obtained in Comparative Example 2.
[0106] Figure 9 is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 2.
[0107] The filtrates and wash water from Example 1, Comparative Example 1, and Comparative Example 2 were mixed respectively, and the iron and phosphorus contents were tested to obtain the amount of iron and phosphorus lost. The results are shown in Table 1.
[0108] Table 1 In Comparative Example 1, adding ammonia and iron in equal proportions carries a significant risk of localized over-alkaliness, causing iron to precipitate as other impurities and resulting in phosphorus loss. In Comparative Example 2, because the entire reaction occurs in an environment of excess iron and low phosphorus, the proportion of phosphoric acid added later in the reaction that participates in the precipitation reaction is reduced, leading to further phosphoric acid loss.
[0109] The synthesis method used in Example 1 ensured that the precipitation reaction could proceed as close to the feed ratio as possible by pre-mixing the iron and phosphorus sources. The amount of ammonia water used during the continuous dripping process was small, which also greatly reduced the formation of other possible side reactions and precipitation.
[0110] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that calcination at 520°C for 3 hours yielded the iron phosphate product.
[0111] Figure 10 The image shows the XRD pattern of the iron phosphate product obtained in Comparative Example 3.
[0112] Figure 11 The image shows the SEM image of the iron phosphate product obtained in Comparative Example 3.
[0113] Figure 12 This is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 3.
[0114] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that calcination at 620°C for 3 hours yielded the iron phosphate product.
[0115] Figure 13 The image shows the XRD pattern of the iron phosphate product obtained in Comparative Example 4.
[0116] Figure 14 The image shows the SEM image of the iron phosphate product obtained in Comparative Example 4.
[0117] Figure 15 This is a cross-sectional SEM image of the iron phosphate product obtained in Comparative Example 4.
[0118] Example 2 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 4.0 wt%, and the pH of the iron source solution was adjusted to 1.6.
[0119] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 3.5 wt%, and adjust the pH of the phosphorus source solution to 6.5.
[0120] Hydrogen peroxide is added to the iron source solution, with the molar ratio of H2O2 in the hydrogen peroxide to the molar ratio of Fe in the iron source solution being 0.80:1, to completely oxidize the iron source solution.
[0121] Based on n(Fe):n(P)=1.05:1, the fully oxidized iron source solution and phosphorus source solution are mixed to obtain iron-phosphorus solution. The iron-phosphorus solution is clear and transparent, with no visible precipitate.
[0122] Ammonia water was slowly added to the iron-phosphorus solution, ensuring that the ammonia water was added completely within 30 minutes. The molar ratio of NH3 in the ammonia water to the molar ratio of Fe in the iron source solution was 0.85:1. After the ammonia water was added, the solution was kept at 50°C for 45 minutes to obtain slurry I.
[0123] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0124] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 10%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0125] Phosphoric acid was added to slurry II, with the ratio of the amount of phosphoric acid added to the molar amount of Fe in the iron source solution being 0.12:1. After the phosphoric acid was added, the temperature was raised to 90℃ and kept at that temperature for 2 hours to obtain a white slurry.
[0126] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 570℃ for 2.5 h to obtain the ferric phosphate product.
[0127] Figure 16 The image shows the XRD pattern of the iron phosphate product obtained in Example 2.
[0128] Figure 17 This is a SEM image of the iron phosphate product obtained in Example 2.
[0129] Figure 18 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 2.
[0130] Example 3 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 7.0 wt%, and the pH of the iron source solution was adjusted to 1.2.
[0131] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 7.0 wt%, and adjust the pH of the phosphorus source solution to 3.5.
[0132] Hydrogen peroxide is added to the iron source solution, with the molar ratio of H2O2 in the hydrogen peroxide to the molar ratio of Fe in the iron source solution being 0.75:1, to completely oxidize the iron source solution.
[0133] Based on n(Fe):n(P)=1.08:1, the fully oxidized iron source solution and phosphorus source solution are mixed to obtain iron-phosphorus solution. The iron-phosphorus solution is clear and transparent, with no visible precipitate.
[0134] Ammonia water was slowly added to the iron-phosphorus solution, ensuring that the ammonia water was added completely within 45 minutes. The molar ratio of NH3 in the ammonia water to the molar ratio of Fe in the iron source solution was 1.02:1. After the ammonia water was added, the solution was kept at 45°C for 60 minutes to obtain slurry I.
[0135] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0136] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 8%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0137] Phosphoric acid was added to slurry II, with the molar ratio of P in the added phosphoric acid to Fe in the iron source solution being 0.12:1. After the phosphoric acid was added, the temperature was raised to 95°C and kept at that temperature for 1.5 hours to obtain a white slurry.
[0138] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 550℃ for 3 hours to obtain the ferric phosphate product.
[0139] Figure 19 The image shows the XRD pattern of the iron phosphate product obtained in Example 3.
[0140] Figure 20 This is a SEM image of the iron phosphate product obtained in Example 3.
[0141] Figure 21 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 3.
[0142] Example 4 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 3.5 wt%, and the pH of the iron source solution was adjusted to 1.8.
[0143] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 3.5 wt%, and adjust the pH of the phosphorus source solution to 6.5.
[0144] Hydrogen peroxide is added to the iron source solution, with the molar ratio of H2O2 in the hydrogen peroxide to the molar ratio of Fe in the iron source solution being 0.85:1, so that the iron source solution is completely oxidized.
[0145] Based on n(Fe):n(P)=1.02:1, the fully oxidized iron source solution and phosphorus source solution are mixed to obtain iron-phosphorus solution. The iron-phosphorus solution is clear and transparent, with no visible precipitate.
[0146] Slowly add ammonia water to the iron-phosphorus solution, ensuring that the ammonia water is added completely within 30 minutes. The molar ratio of NH3 in the ammonia water to the molar ratio of Fe in the iron source solution is 0.8:1. After the ammonia water is added, continue to keep it at 55℃ for 30 minutes to obtain slurry I.
[0147] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0148] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 20%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0149] Phosphoric acid was added to slurry II, with the molar ratio of P in the added phosphoric acid to Fe in the iron source solution being 0.06:1. After the phosphoric acid was added, the temperature was raised to 90℃ and kept at that temperature for 2 hours to obtain a white slurry.
[0150] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 530℃ for 5 hours to obtain the ferric phosphate product.
[0151] Figure 22 The image shows the XRD pattern of the iron phosphate product obtained in Example 4.
[0152] Figure 23 This is a SEM image of the iron phosphate product obtained in Example 4.
[0153] Figure 24 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 4.
[0154] Example 5 Ferrous sulfate was dissolved in water to prepare an iron source solution with an iron content of 6.0 wt%, and the pH of the iron source solution was adjusted to 1.4.
[0155] Dissolve monoammonium phosphate in water to prepare a phosphorus source solution with a phosphorus content of 3.5 wt%, and adjust the pH of the phosphorus source solution to 6.5.
[0156] Hydrogen peroxide is added to the iron source solution, with the molar ratio of H2O2 in the hydrogen peroxide to the molar ratio of Fe in the iron source solution being 0.80:1, to completely oxidize the iron source solution.
[0157] Based on n(Fe):n(P)=1.02:1, the fully oxidized iron source solution and phosphorus source solution are mixed to obtain iron-phosphorus solution. The iron-phosphorus solution is clear and transparent, with no visible precipitate.
[0158] Ammonia water was slowly added to the iron-phosphorus solution, ensuring that the ammonia water was added completely within 60 minutes. The molar ratio of NH3 in the ammonia water to the molar ratio of Fe in the iron source solution was 1.02:1. After the ammonia water was added, the solution was kept at 55°C for 45 minutes to obtain slurry I.
[0159] Filter slurry I and wash the filter cake until the conductivity of the wash water is less than 7000 μS / cm.
[0160] The washed filter cake was re-pulped with water to obtain slurry II with a solid content of 8%. The electrical conductivity of slurry II was less than 7000 μS / cm.
[0161] Phosphoric acid was added to slurry II, with the molar ratio of P in the added phosphoric acid to Fe in the iron source solution being 0.15:1. After the phosphoric acid was added, the temperature was raised to 90℃ and kept at that temperature for 2 hours to obtain a white slurry.
[0162] The white slurry was filtered, and the solid phase was washed until the conductivity of the wash water was less than 500 μS / cm. After drying, the washed solid phase was calcined at 600℃ for 2 hours to obtain the ferric phosphate product.
[0163] Figure 25 The image shows the XRD pattern of the iron phosphate product obtained in Example 5.
[0164] Figure 26 This is a SEM image of the iron phosphate product obtained in Example 5.
[0165] Figure 27 This is a cross-sectional SEM image of the iron phosphate product obtained in Example 5.
[0166] Test case (1) The content of free phosphorus in the ferric phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 was analyzed by the following method: Approximately 1.00 g of ferric phosphate sample was weighed on a balance, and 10.00 g of water was added to fully disperse the sample. The sample was then filtered using a sintered glass filter cup, and the precipitate was washed 5 times, each time with approximately 10.00 g of water. All water samples were collected into a 100 ml volumetric flask and diluted to 100 ml with water. The content of free phosphorus in the sample was tested by ICP.
[0167] (2) Analyze the values of (I1+I2) / I3 in the XRD spectra of the iron phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 (I1 represents the characteristic peak intensity at 2θ=20.9±0.5°, I2 represents the characteristic peak intensity at 2θ=22.9±0.5°, and I3 represents the characteristic peak intensity at 2θ=25.8±0.5°). (3) The sulfur content of the iron phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 was tested using a carbon-sulfur analyzer.
[0168] (4) The specific surface area of the iron phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 was tested in the following manner: the specific surface area was analyzed using a Tristar 3020 surface area analyzer.
[0169] (5) The iron-to-phosphorus ratio of the iron phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 was determined by the following method: refer to the test method for iron-to-phosphorus content in HG reference iron phosphate products.
[0170] (6) The moisture content of the ferric phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 was determined by the following method: Moisture content of the ferric phosphate products according to HG: Refer to the test method for moisture content in HG.
[0171] (7) The moisture content of the ferric phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 after being left open for 2 hours was determined by the following method: a crucible was placed on a balance and a sample of about 10.00g was weighed. The crucible was then placed open in a constant temperature and humidity test chamber at 25°C and 60% humidity for 2 hours. The moisture content was then tested according to the moisture test method in HG / T 4701-2014.
[0172] The analytical results of (1) to (7) above are shown in Table 2.
[0173] Table 2 Comparative analysis of the ferric phosphate products obtained in Example 1, Comparative Example 1, and Comparative Example 2 revealed that, despite differences in raw material feeding methods but identical raw material amounts and processes such as crystallization, washing, and calcination, the ferric phosphate product obtained in Example 1 exhibited a higher free phosphorus content of 2148 ppm; its (I1+I2) / I3 ratio was 3.58%, significantly higher than the (I1+I2) / I3 ratios of the ferric phosphate products obtained in Comparative Examples 1 and 2. Furthermore, the ferric phosphate product obtained in Example 1 had a lower sulfur content and a larger specific surface area. This is primarily due to the lower phosphorus loss during the synthesis of ferric phosphate using the feeding method of Example 1, which maintains a higher free phosphorus content in the ferric phosphate system before phosphoric acid crystallization and calcination. This free phosphorus dissolves during the re-pulping process, generating a large amount of free phosphate ions, resulting in a higher free phosphorus content in the system during the same crystallization and calcination steps. This effectively displaces more sulfur impurities, reducing the sulfur content in the ferric phosphate product. Furthermore, based on the specific surface area of the iron phosphate products obtained in Example 1, Comparative Example 1, and Comparative Example 2, it can be determined that free phosphorus, (I1+I2) / I3, and the specific surface area of the iron phosphate products are positively correlated.
[0174] The only difference between the ferric phosphate products prepared in Examples 1, 3, and 4 is the calcination temperature. The calcination temperature in Example 1 was 550℃, in Comparative Example 3 it was 520℃, and in Comparative Example 4 it was 620℃. As the calcination temperature increases, a large amount of residual phosphides and sulfides in the ferric phosphate structure decomposes and volatilizes, reducing the content of free phosphorus and sulfur impurities in the ferric phosphate product. The excessively high temperature also causes a large amount of primary particle aggregation, reducing the specific surface area of the ferric phosphate product. In Comparative Example 3, due to the low calcination temperature, the residual phosphides in the ferric phosphate structure did not decompose completely, resulting in an excessively high content of free phosphorus in the ferric phosphate product. This makes it more susceptible to absorbing moisture from the air, and the large amount of phosphides adsorbed within the ferric phosphate structure also contributes to the lower specific surface area of the ferric phosphate product.
[0175] The iron phosphate products obtained in Examples 1-5 and Comparative Examples 1-4 were used to prepare lithium iron phosphate materials in the following manner: The iron phosphate product obtained above was mixed with a lithium source (lithium carbonate) at a molar ratio of Fe:Li = 1:1.03, and then glucose, a carbon source, was added. The glucose content was 10% of the total material. The intermediate product was heat-treated under a nitrogen atmosphere by heating to 450°C at a rate of 2°C / min and holding for 2 hours, then heating to 780°C at a rate of 2°C / min and holding for 8 hours. Finally, lithium iron phosphate was obtained by air jet milling.
[0176] The iron phosphate product obtained in Example 1 was used to prepare lithium manganese iron phosphate material in the following manner: The obtained iron phosphate product, manganese oxide, lithium dihydrogen phosphate or ammonium dihydrogen phosphate, and lithium carbonate were mixed at a ratio of Li:(Fe+Mn):P=1:1:1. Then, glucose, a carbon source, was added, accounting for 10% of the total material. Anhydrous ethanol was used as a dispersant. The ball milling speed was 500 r / min, the ball milling time was 6 h, the ball milling bead diameter was 0.2 mm, and the ball-to-material mass ratio was 5:1. After ball milling and drying, the intermediate product was heat-treated under a nitrogen atmosphere, with the temperature increased to 600℃ at a rate of 2℃ / min and held for 10 hours. Finally, lithium manganese iron phosphate was obtained by air jet milling.
[0177] The compaction density, sulfur impurity content, and electrochemical performance of lithium iron phosphate products prepared from iron phosphate obtained in Examples 1-5, Comparative Examples 1-5, and lithium manganese iron phosphate products prepared from iron phosphate obtained in Example 1 were tested in the following manner: (1) Compacted density test: Weigh approximately 1.00g of the sample using weighing paper on a balance. The weighed sample is loaded into the mold, and the mold with the material is placed in the designated position in the middle of the compaction density meter.
[0178] The material is compressed using a 3T pressure, and then the compaction density is calculated by dividing the weight by the volume after compression.
[0179] (2) Impurity sulfur content test: The sulfur content of the above samples was tested using a carbon-sulfur analyzer.
[0180] (3) Electrochemical testing: The lithium iron phosphate / lithium manganese iron phosphate obtained from the above embodiments and comparative examples were used as the positive electrode active material. This material was mixed with conductive agent acetylene black (AB) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5, and mixed with N-methylpyrrolidone (NMP) as a solvent to prepare a positive electrode slurry. This slurry was then coated onto aluminum foil to obtain the positive electrode sheet. A lithium sheet was used as the negative electrode, the electrolyte solution was 1 M LiPF6, EC:DEC (volume 4:6), and a commercial electrolyte separator with a diameter of 16 mm was used. The batteries were assembled into coin cells in a glove box. Current charge-discharge tests were conducted on the batteries at room temperature (25°C) using the Sinovel Battery Testing System.
[0181] The results are shown in Tables 3 and 4.
[0182] Table 3 Table 4 As shown in Table 3, compared with the lithium iron phosphate prepared from iron phosphate obtained in Comparative Examples 1 and 2, the lithium iron phosphate prepared from the iron phosphate product provided by this invention has a higher compaction density. This may be because the presence of free phosphorus promotes particle agglomeration during the sintering process of lithium iron phosphate, thereby increasing the compaction density. Generally, the compaction density and discharge specific capacity of lithium iron phosphate are negatively correlated, but this invention achieves a balance between compaction density and discharge specific capacity, effectively improving the compaction density without reducing the discharge specific capacity.
[0183] As can be seen from Table 3, when the content of free phosphorus in the lithium iron phosphate product is too high, although high compaction density lithium iron phosphate can be obtained, the 1C discharge specific capacity of lithium iron phosphate decreases (as shown in Comparative Example 3). This may be because excessive free phosphorus leads to excessive particle agglomeration during the sintering process of lithium iron phosphate, resulting in a decrease in electrochemical performance. As shown in Comparative Example 4, the precursor sintering temperature is too high, and the particle agglomeration is severe, resulting in high compaction of lithium iron phosphate and extremely poor discharge performance. At the same time, the low phosphorus residue also results in excessive sulfur content in the lithium iron phosphate end product.
[0184] As can be seen from Table 4, the lithium manganese iron phosphate prepared from the iron phosphate obtained in Example 1 also has a low S content, high 1C discharge specific capacity and high compaction density.
[0185] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A battery-grade iron phosphate, characterized in that, The content of water-soluble free phosphorus in the ferric phosphate is 1000~3000ppm; the water-soluble free phosphorus includes P2O5 and Fe(PO3)3.
2. The battery-grade iron phosphate as described in claim 1, characterized in that, In the XRD pattern of the iron phosphate, (I1+I2) / I3=3%~5%; where I1 represents the characteristic peak intensity at 2θ=20.9±0.5°, I2 represents the characteristic peak intensity at 2θ=22.9±0.5°, and I3 represents the characteristic peak intensity at 2θ=25.8±0.5°.
3. The battery-grade iron phosphate as described in claim 1, characterized in that, The content of impurity S in the ferric phosphate does not exceed 50 ppm; and / or, The specific surface area of the iron phosphate is 8~12m². 2 / g; and / or, The moisture content of the ferric phosphate is 1500~2500ppm; after being left open for 2 hours, the moisture content is <4500ppm.
4. A method for preparing battery-grade iron phosphate, characterized in that, include: A fully oxidized iron source solution and a phosphorus source solution are mixed to obtain an iron-phosphorus solution. Ammonia water was added to the iron-phosphorus solution to obtain slurry I; After solid-liquid separation, slurry I yields solid phase I; Wash solid phase I to obtain filter cake; The filter cake was re-pulped to obtain pulp II; exist Phosphoric acid was added to pulp II and aged to obtain a white pulp. After solid-liquid separation, the white slurry yielded solid phase II; Solid phase II was washed, dried, and calcined to obtain the iron phosphate product.
5. The method for preparing battery-grade iron phosphate as described in claim 4, characterized in that, The iron source is ferrous sulfate; the phosphorus source is monoammonium phosphate; and / or, The iron source solution contains 3.5–7.0 wt% Fe; the phosphorus source solution contains 3.5–7.0 wt% P; and / or, The pH value of the fully oxidized iron source solution is 0.4~2.0; the pH value of the phosphorus source solution is 3.0~7.
5.
6. The method for preparing battery-grade iron phosphate as described in claim 5, characterized in that, Hydrogen peroxide is added to the iron source solution to completely oxidize the iron source, resulting in a fully oxidized iron source solution.
7. The method for preparing battery-grade iron phosphate as described in claim 6, characterized in that, The amount of hydrogen peroxide added is determined based on the molar ratio of H2O2 to Fe in the iron source solution, n(H2O2):n(Fe) = (0.65~0.85):1; and / or, The amounts of fully oxidized iron source solution and phosphorus source solution are determined based on the molar ratio of Fe in the iron source solution and P in the phosphorus source solution, n(Fe):n(P) = (1.02~1.1):
1.
8. The method for preparing battery-grade iron phosphate as described in claim 4, characterized in that, The amount of ammonia added to the iron-phosphorus solution is determined based on the molar ratio of NH3 to Fe in the iron source solution, n(NH3):n(Fe) = (0.75~1.04):1; and / or, During the process of adding ammonia to the iron-phosphorus solution, the temperature of the system should be maintained at 45~55℃; after the ammonia is added, continue to keep the system at this temperature for 30~60 minutes.
9. The method for preparing battery-grade iron phosphate as described in claim 4, characterized in that, The solid content of slurry II is 5~20wt%.
10. The method for preparing battery-grade iron phosphate as described in claim 4 or 9, characterized in that, The amount of phosphoric acid added to slurry II is determined based on the ratio of the molar amount of P in phosphoric acid to the molar amount of Fe in slurry II, n(P):n(Fe) = 0.05~0.15:
1.
11. The method for preparing battery-grade iron phosphate as described in claim 4, characterized in that, The aging temperature is 70~99℃, and the aging time is 1~2 hours; and / or, The calcination temperature is 530~600℃; the calcination time is 2~5h.
12. A lithium iron phosphate, characterized in that, The precursor material of lithium iron phosphate is battery-grade iron phosphate as described in any one of claims 1 to 3 or battery-grade iron phosphate prepared by any one of claims 4 to 11.
13. A lithium manganese iron phosphate, characterized in that, The precursor material of the lithium manganese iron phosphate is battery-grade iron phosphate as described in any one of claims 1 to 3 or battery-grade iron phosphate prepared by any one of claims 4 to 11.
14. A battery, characterized in that, The positive electrode active material of the battery includes lithium iron phosphate as described in claim 12 or lithium manganese iron phosphate as described in claim 13.