Anhydrous iron phosphate as well as preparation method and application thereof

Abstract

The invention discloses anhydrous iron phosphate as well as a preparation method and application thereof, and belongs to the technical field of battery materials. The preparation method of the anhydrous iron phosphate comprises the following steps: adding an iron phosphate dihydrate seed crystal into a mixed solution containing ferrous sulfate and first phosphoric acid, then adding a part of hydrogen peroxide to oxidize a part of Fe < 2 + > in the mixed solution into Fe < 3 + >, heating for the first time and keeping the temperature, then continuing to add hydrogen peroxide to oxidize all Fe < 2 + > in the mixed solution into Fe < 3 + >, and cooling to room temperature to obtain the anhydrous iron phosphate. Heating for the second time and preserving heat to obtain iron phosphate dihydrate; dehydrating the iron phosphate dihydrate to obtain iron phosphate; mixing iron phosphate with water and second phosphoric acid, and carrying out heat preservation to obtain hollow iron phosphate; and sintering the hollow iron phosphate to obtain the anhydrous iron phosphate. According to the method, the anhydrous iron phosphate which is relatively good in sphericity degree and has a hollow structure can be obtained, and the anhydrous iron phosphate is beneficial to further obtaining a lithium iron phosphate positive electrode material with relatively excellent performance.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to anhydrous iron phosphate, its preparation method, and its application. Background Technology

[0002] With technological advancements and economic development, the application fields of lithium-ion batteries are becoming increasingly widespread. Among various types of lithium-ion batteries, lithium iron phosphate batteries have become the mainstream choice for automotive power batteries and energy storage batteries in my country due to their advantages such as high safety, long cycle life, excellent reliability, and low cost.

[0003] As a key precursor in the preparation of lithium iron phosphate (LFP), the material properties of iron phosphate directly affect the electrochemical performance of the final product. Hollow-structured iron phosphate can increase the specific surface area of ​​LFP, thereby increasing the contact area between LFP and the electrolyte and shortening the migration path of lithium ions. Theoretically, this is beneficial for improving the rate performance of LFP batteries. However, in practice, if the hollow-structured iron phosphate has poor sphericity or excessively large particle size, the electrochemical performance of the LFP battery will be suboptimal.

[0004] Currently, there is no effective method to prepare iron phosphate materials with a hollow structure and good sphericity.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide anhydrous ferric phosphate, its preparation method and application, in order to solve or improve the above-mentioned technical problems.

[0007] This invention can be implemented as follows: In a first aspect, the present invention provides a method for preparing anhydrous ferric phosphate, comprising the following steps: Ferric phosphate seed crystals were added to a mixed solution containing ferrous sulfate and monophosphate, followed by the addition of hydrogen peroxide to remove some of the Fe in the mixed solution. 2+ Oxidized to Fe 3+ The temperature was raised and maintained for the first time, followed by the addition of hydrogen peroxide to ensure that all Fe in the mixed solution was removed. 2+ All are oxidized to Fe 3+ The temperature was raised a second time and held at that temperature to obtain ferric phosphate dihydrate. Ferric phosphate dihydrate is dehydrated to obtain ferric phosphate; Ferric phosphate is mixed with water and second phosphoric acid and kept at a certain temperature to obtain hollow ferric phosphate. Hollow ferric phosphate is sintered to obtain anhydrous ferric phosphate.

[0008] In an optional embodiment, in the mixed solution, Fe 2+ The concentration is 40 g / L~80 g / L, Fe2+ The molar ratio of P to P is 0.9:1 to 1:1.

[0009] In an optional embodiment, the amount of ferric phosphate dihydrate seed crystals added is 5wt% to 10wt% of the theoretical amount of ferric phosphate dihydrate to be generated, and the theoretical amount of ferric phosphate dihydrate to be generated is the mass of ferric phosphate dihydrate corresponding to the complete generation of ferrous sulfate in the mixed solution into ferric phosphate dihydrate. And / or, the Dv of iron phosphate dihydrate seeds 50 The range is 0.5μm to 3μm; And / or, before adding to the mixed solution, the ferric phosphate dihydrate is ground.

[0010] In an optional embodiment, the initial addition of hydrogen peroxide is used to remove 1 g / L to 3 g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ ; And / or, the temperature after the first heating is 30℃~60℃, and the holding time after the first heating does not exceed 3 hours; And / or, the temperature after the second heating is 70℃~100℃, and the holding time after the second heating is 6h~15h.

[0011] In an optional embodiment, the dehydration temperature is 150°C to 600°C.

[0012] In an optional embodiment, the dehydration temperature is 350°C to 450°C.

[0013] In an optional implementation, the dehydration time is 1 hour to 3 hours.

[0014] In an optional embodiment, the preparation of hollow ferric phosphate includes at least one of the following features: Feature 1: The mass ratio of ferric phosphate to diphosphoric acid is 10:1 to 100:1; Feature 2: The mass ratio of ferric phosphate to water is 0.1:1 to 0.45:1; Feature 3: Insulation temperature range is 50℃~95℃; Feature 4: The heat preservation time is 4h~20h.

[0015] In an optional embodiment, the sintering temperature is 550℃~650℃, and / or the sintering time is 2h~4h.

[0016] Secondly, the present invention provides anhydrous ferric phosphate, which is prepared by any of the preparation methods described in the foregoing embodiments; In an optional embodiment, anhydrous ferric phosphate has at least one of the following characteristics: Feature 5: Dv of anhydrous ferric phosphate 50The thickness is 2μm to 4μm; Feature 6: Anhydrous ferric phosphate has a hollow structure.

[0017] Thirdly, the present invention provides a lithium iron phosphate, which is prepared from anhydrous iron phosphate as described in the foregoing embodiments.

[0018] Fourthly, the present invention provides a battery comprising lithium iron phosphate as described in the foregoing embodiments.

[0019] The beneficial effects of this invention include: The method for preparing anhydrous ferric phosphate provided by this invention involves first adding a portion of hydrogen peroxide to partially dissolve the Fe in the mixed solution. 2+ Oxidized to Fe 3+ It reacts with the primary phosphoric acid to form iron phosphate nuclei, and then the added hydrogen peroxide removes the remaining Fe in the mixed solution. 2+ Oxidized to Fe 3+ It then reacts with the remaining primary phosphoric acid, continuing to generate ferric phosphate on the surface of the aforementioned ferric phosphate core, causing the ferric phosphate particles to gradually grow until the reaction is complete, yielding ferric phosphate dihydrate. Ferric phosphate dihydrate undergoes dehydration to change its crystal form, and then mixes with water and secondary phosphoric acid to undergo a hollowing reaction, yielding hollow ferric phosphate; hollow ferric phosphate is then sintered to obtain anhydrous ferric phosphate.

[0020] The above method can obtain a shape with good sphericity and Dv. 50 The smaller anhydrous iron phosphate with a hollow structure is beneficial for obtaining lithium iron phosphate cathode materials with better performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Here is a SEM image of the ferric phosphate dihydrate prepared in Example 1; Figure 2 Here is a cross-sectional SEM image of the anhydrous ferric phosphate prepared in Example 1; Figure 3 The image shows a cross-sectional SEM image of the anhydrous ferric phosphate prepared in Example 4. Figure 4 SEM image of ferric phosphate dihydrate prepared in Comparative Example 3; Figure 5 SEM image of ferric phosphate dihydrate prepared in Comparative Example 4; Figure 6 The image shows a cross-sectional SEM image of the anhydrous ferric phosphate prepared in Comparative Example 8. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] The following is a detailed description of the anhydrous ferric phosphate, its preparation method, and its applications provided by this invention.

[0025] This invention provides a method for preparing anhydrous ferric phosphate, comprising the following steps: S1: Add ferric phosphate dihydrate seed crystals to a mixed solution containing ferrous sulfate and primary phosphoric acid, then add some hydrogen peroxide to remove some of the Fe in the mixed solution. 2+ Oxidized to Fe 3+ The temperature was raised and maintained for the first time, followed by the addition of hydrogen peroxide to ensure that all Fe in the mixed solution was removed. 2+ All are oxidized to Fe 3+ The temperature was raised a second time and held at that temperature to obtain ferric phosphate dihydrate.

[0026] In the above process, the initial addition of hydrogen peroxide causes some Fe in the mixed solution to... 2+ Oxidized to Fe 3+ It reacts with the primary phosphoric acid to form ferric phosphate dihydrate on the seed crystal surface, appropriately reducing the surface energy of the seed crystal and thus preventing seed crystal aggregation; subsequently, hydrogen peroxide is added to remove the remaining Fe in the mixed solution. 2+ Oxidized to Fe 3+ It then reacts with the remaining first phosphoric acid to continue generating ferric phosphate dihydrate on the surface of the above seed crystals, causing the ferric phosphate dihydrate particles to gradually grow until the material reaction is complete, resulting in ferric phosphate dihydrate with high sphericity.

[0027] In some alternative embodiments, the mixed solution is obtained by mixing ferrous sulfate, phosphoric acid and water.

[0028] In this mixed solution, Fe 2+ The concentration can be from 40 g / L to 80 g / L, such as 40 g / L, 50 g / L, 60 g / L, 70 g / L, or 80 g / L, or other values ​​within the range of 40 g / L to 80 g / L. In the mixed solution, Fe 2+ The higher the Fe concentration, the lower the product particle size; however, if Fe... 2+Excessive Fe concentration can lead to a significant decrease in particle precipitation rate. This is mainly because increasing Fe concentration leads to an increase in phosphoric acid usage, resulting in a decrease in residual H+ in the system. + Increased concentration negatively impacts sedimentation efficiency.

[0029] In this mixed solution, Fe 2+ The molar ratio with P can be from 0.9:1 to 1:1, such as 0.9:1, 0.92:1, 0.95:1, 0.98:1 or 1:1, or other values ​​within the range of 0.9:1 to 1:1.

[0030] In some optional embodiments, the amount of ferric phosphate dihydrate seed crystals added can be 5wt% to 10wt% of the theoretical ferric phosphate dihydrate formation amount, such as 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, or other values ​​within the range of 5wt% to 10wt%. The aforementioned "theoretical ferric phosphate dihydrate formation amount" refers to the mass of ferric phosphate dihydrate corresponding to the complete formation of ferrous sulfate dihydrate from the mixed solution. Adding a larger amount of ferric phosphate dihydrate seed crystals will lead to an increase in the Dv of anhydrous ferric phosphate. 50 If the particles are too small, they will aggregate severely.

[0031] In this invention, the iron phosphate dihydrate seed crystals are first ground before being added to the mixed solution. The Dv of the ground iron phosphate dihydrate seed crystals is... 50 The range is 0.5μm to 3μm.

[0032] The aforementioned iron phosphate dihydrate seed crystals, used as inducing agents, have a Dv 50 A particle size exceeding 3 μm will result in excessively large particle sizes of the subsequently generated iron phosphate dihydrate. This invention addresses this issue by adjusting the Dv of the iron phosphate dihydrate seed crystals. 50 Controlling the particle size to 0.5μm~3μm ensures that the subsequently generated ferric phosphate dihydrate has a suitable particle size. Furthermore, this invention uses a grinding method to break the ferric phosphate dihydrate seed crystals, which not only allows for the reduction of their Dv... 50 It not only meets the requirements, but also significantly improves the activity (surface energy, etc.) of iron phosphate dihydrate seed crystals, making them more soluble in phosphoric acid, and thus causing hollowing phenomena to occur during the hollowing process.

[0033] In some alternative embodiments, the initial addition of hydrogen peroxide is used to remove 1 g / L to 3 g / L (e.g., 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, or 3 g / L) of Fe in the mixed solution. 2+ Oxidized to Fe 3+ .

[0034] If Fe is oxidized first 2+ Too little iron phosphate will result in uneven morphology and poor sphericity of the anhydrous iron phosphate particles; if the Fe is oxidized first... 2+Excessive precipitation at low temperatures results in particles that are more likely to be petal-shaped, which is detrimental to the sphericity of the product.

[0035] In some alternative implementations, the temperature after the first heating can be 30°C to 60°C, such as 30°C, 40°C, 50°C or 60°C, or other values ​​within the range of 30°C to 60°C.

[0036] The holding time after the first heating should not exceed 3 hours. For example, it can be 3 hours, 2 hours, 1 hour, or 0.5 hours, or other values ​​within the range of 3 hours. If the holding time is too long, it will affect production efficiency, and the seed crystals will be affected by the stirring shear force, leading to seed crystal breakage and an increase in the number of particles, which in turn makes it difficult to control the sphericity and smoothness of the product.

[0037] In some optional embodiments, the temperature after the second heating can be 70℃~100℃, such as 70℃, 80℃, 90℃ or 100℃, or other values ​​within the range of 70℃~100℃. If the temperature after the heating is lower than 70℃, the precipitation reaction will be incomplete, the particles will be fine and fragmented, and they will still not be able to form regular spherical shapes after heat preservation.

[0038] The holding time after the second heating can be 6h to 15h, such as 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, or other values ​​within the range of 6h to 15h.

[0039] S2: Dehydrate ferric phosphate dihydrate to obtain ferric phosphate.

[0040] In some optional embodiments, the dehydration temperature can be between 150°C and 600°C, such as 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 600°C, or other values ​​within the range of 150°C to 600°C. In some preferred embodiments, the dehydration temperature is between 350°C and 450°C. The above dehydration temperature also affects the hollow structure of the product. When the dehydration temperature is too low, although ferric phosphate dihydrate has already lost its water of crystallization, its crystal form is monoclinic and poorly soluble in acid. Therefore, an in-situ reaction of dissolution and precipitation occurs simultaneously, ultimately forming a solid structure. By controlling the dehydration temperature to 150℃~600℃ (preferably 350℃~450℃), the present invention can make the crystal form appear in a transition state from monoclinic to hexagonal. This crystal form is easily soluble in phosphoric acid, resulting in different dissolution rates inside and outside the particles. After rapid dissolution inside, it diffuses to the outside of the particles to precipitate, forming the final hollow structure.

[0041] In some alternative implementations, the dehydration time can be 1h to 3h, such as 1h, 1.5h, 2h, 2.5h or 3h, or other values ​​within the range of 1h to 3h.

[0042] S3: Mix ferric phosphate with water and second phosphoric acid and keep warm to obtain hollow ferric phosphate.

[0043] This process involves the internal dissolution of ferric phosphate by the second phosphoric acid, resulting in hollowing.

[0044] In some alternative embodiments, the mass ratio of ferric phosphate to the second phosphoric acid can be from 10:1 to 100:1, such as 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1, or other values ​​within the range of 10:1 to 100:1. In some preferred embodiments, the mass ratio of ferric phosphate to the second phosphoric acid can be from 7.5:1 to 22:1.

[0045] If the mass ratio of ferric phosphate to secondary phosphoric acid is less than 10:1 (e.g., 5:1), it will lead to excessively high P concentration, severe product agglomeration, poor sphericity, and even collapse of the hollow structure. If the mass ratio of ferric phosphate to secondary phosphoric acid is greater than 100:1 (e.g., 110:1), it will not be conducive to the preferential dissolution of internal seed crystals, making it difficult to form a hollow structure.

[0046] In some alternative embodiments, the mass ratio of ferric phosphate to water can be from 0.1:1 to 0.45:1, such as 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1 or 0.45:1, or other values ​​within the range of 0.1:1 to 0.45:1.

[0047] If the mass ratio of ferric phosphate to water is less than 0.1:1 (e.g., 0.05:1), the solution will be too dilute, making it difficult to effectively reconstruct the aqueous phase and resulting in failure of hollowing. If the mass ratio of ferric phosphate to water is greater than 0.45:1 (e.g., 0.5:1), it will be detrimental to the production of pulping and stirring.

[0048] In some alternative implementations, the insulation temperature can be 50℃~95℃, such as 50℃, 60℃, 70℃, 80℃, 90℃ or 95℃, or other values ​​within the range of 50℃~95℃.

[0049] The heat preservation time can be 4h to 20h, such as 4h, 10h, 15h or 20h, or other values ​​within the range of 4h to 20h.

[0050] Based on the fact that the dehydrated iron phosphate has a transitional crystal form from monoclinic to hexagonal, and that the seed crystals inside the iron phosphate have high activity, the rate at which the iron phosphate inside dissolves in the second phosphoric acid is higher than the rate at which the iron phosphate outside dissolves in the second phosphoric acid at the above-mentioned holding temperature, thereby achieving a hollow structure with a hollow interior and a solid exterior within the above-mentioned holding time range.

[0051] S4: Hollow iron phosphate is sintered to obtain anhydrous iron phosphate.

[0052] In some alternative embodiments, the sintering temperature can be 550℃~650℃, such as 550℃, 580℃, 600℃, 620℃ or 650℃, or other values ​​within the range of 550℃~650℃.

[0053] If the sintering temperature is below 550℃, the product will have insufficient crystallinity and residual water of crystallization.

[0054] In some alternative implementations, the sintering time can be 2h to 4h, such as 2h, 3h or 4h, or other values ​​within the range of 2h to 4h.

[0055] Accordingly, the present invention provides anhydrous ferric phosphate, which is prepared by the aforementioned preparation method; In some alternative implementations, the Dv of anhydrous ferric phosphate 50 The size ranges from 2μm to 4μm.

[0056] In some alternative implementations, anhydrous ferric phosphate has a hollow structure.

[0057] In addition, the present invention provides a lithium iron phosphate prepared from the above-mentioned anhydrous iron phosphate.

[0058] Accordingly, the present invention also provides a battery comprising the aforementioned lithium iron phosphate.

[0059] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0060] Example 1 This embodiment provides anhydrous ferric phosphate, the preparation method of which includes: S1: Raw material preparation.

[0061] FeSO4·7H2O, primary phosphoric acid (85 wt%), and water were mixed to obtain a mixed solution. In this mixed solution, Fe... 2+ The concentration was 40 g / L, Fe 2+ The molar ratio of P to P is 0.95:1.

[0062] S2: Precipitation reaction.

[0063] The above mixed solution was placed in a reaction vessel, and iron phosphate dihydrate seed crystals were added; then a small amount of hydrogen peroxide was slowly added, the temperature was raised to 30°C and held for 2 hours. After the holding time was completed, hydrogen peroxide was continued to be added to remove all the Fe in the mixed solution. 2+ All are oxidized to Fe 3+The temperature was increased to 80℃ to promote particle precipitation, and the temperature was maintained for 8 hours to obtain ferric phosphate dihydrate (e.g. Figure 1 (As shown).

[0064] The amount of the aforementioned iron phosphate dihydrate seed crystals added is 5 wt% of the theoretical amount of iron phosphate dihydrate to be formed. The Dv of this iron phosphate dihydrate seed crystal is... 50 The value is 0.5 μm; the initial addition of hydrogen peroxide is used to remove 1 g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ .

[0065] S3: Dehydration.

[0066] The above-mentioned dihydrate ferric phosphate was dehydrated at 300°C for 3 hours to obtain ferric phosphate.

[0067] S4: Hollowing out.

[0068] The above-mentioned ferric phosphate was mixed with pure water and second phosphoric acid (with a concentration of 85 wt%) at a mass ratio of 10:40:1 to obtain a reaction slurry; the reaction slurry was kept at 95℃ for 6 hours to promote the hollowing of ferric phosphate, thus obtaining hollow ferric phosphate.

[0069] S5: Sintering.

[0070] The hollowed-out ferric phosphate was sintered at 600°C for 2 hours to produce anhydrous ferric phosphate (e.g. Figure 2 (As shown).

[0071] The anhydrous ferric phosphate Dv prepared in this embodiment 50 The anhydrous ferric phosphate has a particle size of 3.2 μm and good sphericity, with the particles appearing hollow.

[0072] Example 2 This embodiment provides anhydrous ferric phosphate, the preparation method of which includes: S1: Raw material preparation.

[0073] FeSO4·7H2O, primary phosphoric acid (85 wt%), and water were mixed to obtain a mixed solution. In this mixed solution, Fe... 2+ The concentration was 60 g / L, Fe 2+ The molar ratio of P to P is 0.98:1.

[0074] S2: Precipitation reaction.

[0075] The above mixed solution was placed in a reaction vessel, and iron phosphate dihydrate seed crystals were added. Then, a small amount of hydrogen peroxide was slowly added, the temperature was raised to 40°C and maintained for 1.5 hours. After the maintenance period, hydrogen peroxide was continued to be added to remove all the Fe from the mixed solution. 2+ All are oxidized to Fe 3+The temperature was increased to 85℃ to promote particle precipitation, and the temperature was maintained for 8 hours to obtain ferric phosphate dihydrate.

[0076] The amount of the aforementioned iron phosphate dihydrate seed crystals added is 7wt% of the theoretical amount of iron phosphate dihydrate to be formed. The Dv of this iron phosphate dihydrate seed crystal is... 50 The value is 2 μm; the initial addition of hydrogen peroxide is used to remove 2 g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ .

[0077] S3: Dehydration.

[0078] The above-mentioned ferric phosphate dihydrate was dehydrated at 400°C for 3 hours to obtain ferric phosphate.

[0079] S4: Hollowing out.

[0080] The above-mentioned ferric phosphate was mixed with pure water and second phosphoric acid (with a concentration of 85 wt%) at a mass ratio of 10:40:0.1 to obtain a reaction slurry; the reaction slurry was kept at 85℃ for 10 h to promote the hollowing of ferric phosphate, thus obtaining hollow ferric phosphate.

[0081] S5: Sintering.

[0082] The hollowed-out ferric phosphate was sintered at 580°C for 2 hours to produce anhydrous ferric phosphate.

[0083] The anhydrous ferric phosphate Dv prepared in this embodiment 50 With a particle size of 3.5 μm, this anhydrous iron phosphate exhibits excellent sphericity and a high degree of particle hollowness.

[0084] Example 3 This embodiment provides anhydrous ferric phosphate, the preparation method of which includes: S1: Raw material preparation.

[0085] FeSO4·7H2O, primary phosphoric acid (85 wt%), and water were mixed to obtain a mixed solution. In this mixed solution, Fe... 2+ The concentration was 80 g / L, Fe 2+ The molar ratio of P to P is 1:1.

[0086] S2: Precipitation reaction.

[0087] The above mixed solution was placed in a reaction vessel, and iron phosphate dihydrate seed crystals were added; then a small amount of hydrogen peroxide was slowly added, the temperature was raised to 30°C and maintained for 3 hours. After the holding time was completed, hydrogen peroxide was continued to be added to remove all the Fe in the mixed solution. 2+ All are oxidized to Fe 3+ The temperature was increased to 80℃ to promote particle precipitation, and the temperature was maintained for 12 hours to obtain ferric phosphate dihydrate.

[0088] The amount of the aforementioned iron phosphate dihydrate seed crystals added is 10 wt% of the theoretical amount of iron phosphate dihydrate to be formed. The Dv of this iron phosphate dihydrate seed crystal is... 50 The value is 0.8 μm; the initial addition of hydrogen peroxide is used to remove 3 g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ .

[0089] S3: Dehydration.

[0090] The above-mentioned ferric phosphate dihydrate was dehydrated at 500°C for 3 hours to obtain ferric phosphate.

[0091] S4: Hollowing out.

[0092] The above-mentioned ferric phosphate was mixed with pure water and second phosphoric acid (with a concentration of 85 wt%) at a mass ratio of 10:25:0.5 to obtain a reaction slurry; the reaction slurry was kept at 85℃ for 20 h to promote the hollowing of ferric phosphate, thus obtaining hollow ferric phosphate.

[0093] S5: Sintering.

[0094] The hollowed-out ferric phosphate was sintered at 620°C for 2 hours to produce anhydrous ferric phosphate.

[0095] The anhydrous ferric phosphate Dv prepared in this embodiment 50 With a particle size of 2.6 μm, this anhydrous iron phosphate exhibits excellent sphericity, with the particles appearing hollow.

[0096] Example 4 This embodiment provides anhydrous ferric phosphate, the preparation method of which includes: S1: Raw material preparation.

[0097] FeSO4·7H2O, primary phosphoric acid (85 wt%), and water were mixed to obtain a mixed solution. In this mixed solution, Fe... 2+ The concentration is 50 g / L, Fe 2+ The molar ratio of P to P is 0.90:1.

[0098] S2: Precipitation reaction.

[0099] The above mixed solution was placed in a reaction vessel, and iron phosphate dihydrate seed crystals were added; then a small amount of hydrogen peroxide was slowly added, the temperature was raised to 60°C and held for 0.5 hours. After the holding period, hydrogen peroxide was continued to be added to remove all the Fe in the mixed solution. 2+ All are oxidized to Fe 3+ The temperature was increased to 70℃ to promote particle precipitation, and the temperature was maintained for 15 hours to obtain ferric phosphate dihydrate.

[0100] The amount of the aforementioned iron phosphate dihydrate seed crystals added is 6wt% of the theoretical amount of iron phosphate dihydrate to be formed. The Dv of this iron phosphate dihydrate seed crystal is... 50 The value is 3μm; the initial addition of hydrogen peroxide is used to remove 1.5g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ .

[0101] S3: Dehydration.

[0102] The above-mentioned ferric phosphate dihydrate was dehydrated at 350°C for 3 hours to obtain ferric phosphate.

[0103] S4: Hollowing out.

[0104] The above-mentioned ferric phosphate was mixed with pure water and second phosphoric acid (with a concentration of 85 wt%) at a mass ratio of 10:40:0.5 to obtain a reaction slurry; the reaction slurry was kept at 75℃ for 16 h to promote the hollowing of ferric phosphate, thus obtaining hollow ferric phosphate.

[0105] S5: Sintering.

[0106] The above-mentioned hollowed-out ferric phosphate was sintered at 590°C for 2 hours to produce anhydrous ferric phosphate (e.g. Figure 3 (As shown).

[0107] The anhydrous ferric phosphate Dv prepared in this embodiment 50 The anhydrous iron phosphate particles have a diameter of 3.8 μm, a smooth surface, good sphericity, and are partially hollow inside.

[0108] Example 5 This embodiment provides anhydrous ferric phosphate, the preparation method of which includes: S1: Raw material preparation.

[0109] FeSO4·7H2O, primary phosphoric acid (85 wt%), and water were mixed to obtain a mixed solution. In this mixed solution, Fe... 2+ The concentration was 70 g / L, Fe 2+ The molar ratio of P to P is 0.96:1.

[0110] S2: Precipitation reaction.

[0111] The above mixed solution was placed in a reaction vessel, and iron phosphate dihydrate seed crystals were added; then a small amount of hydrogen peroxide was slowly added, the temperature was raised to 40°C and held for 1 hour. After the holding period, hydrogen peroxide was added again to remove all the Fe in the mixed solution. 2+ All are oxidized to Fe 3+ The temperature was increased to 95℃ to promote particle precipitation, and the temperature was maintained for 6 hours to obtain ferric phosphate dihydrate.

[0112] The amount of the aforementioned iron phosphate dihydrate seed crystals added is 8 wt% of the theoretical amount of iron phosphate dihydrate to be formed. The Dv of this iron phosphate dihydrate seed crystal is... 50 The thickness is 1.5 μm; the initial addition of hydrogen peroxide is used to remove the 2.5 g / L Fe from the mixed solution. 2+ Oxidized to Fe 3+ .

[0113] S3: Dehydration.

[0114] The above-mentioned dihydrate ferric phosphate was dehydrated at 450°C for 3 hours to obtain ferric phosphate.

[0115] S4: Hollowing out.

[0116] The above-mentioned ferric phosphate was mixed with pure water and second phosphoric acid (with a concentration of 85 wt%) at a mass ratio of 10:30:0.75 to obtain a reaction slurry; the reaction slurry was kept at 90℃ for 6 hours to promote the hollowing of ferric phosphate, thus obtaining hollow ferric phosphate.

[0117] S5: Sintering.

[0118] The hollowed-out ferric phosphate was sintered at 650°C for 2 hours to produce anhydrous ferric phosphate.

[0119] The anhydrous ferric phosphate Dv prepared in this embodiment 50 With a diameter of 2.5 μm, this anhydrous iron phosphate exhibits excellent sphericity and a complete hollow structure.

[0120] Example 6 This embodiment provides anhydrous ferric phosphate, the preparation method of which includes: S1: Raw material preparation.

[0121] FeSO4·7H2O, primary phosphoric acid (85 wt%), and water were mixed to obtain a mixed solution. In this mixed solution, Fe... 2+ The concentration is 50 g / L, Fe 2+ The molar ratio of P to P is 0.94:1.

[0122] S2: Precipitation reaction.

[0123] The above mixed solution was placed in a reaction vessel, and iron phosphate dihydrate seed crystals were added; then a small amount of hydrogen peroxide was slowly added, the temperature was raised to 50°C and held for 1 hour. After the holding period, hydrogen peroxide was continued to be added to remove all the Fe in the mixed solution. 2+ All are oxidized to Fe 3+ The temperature was increased to 80℃ to promote particle precipitation, and the temperature was maintained for 10 hours to obtain ferric phosphate dihydrate.

[0124] The amount of the aforementioned iron phosphate dihydrate seed crystals added is 5.5 wt% of the theoretical amount of iron phosphate dihydrate to be formed. The Dv of this iron phosphate dihydrate seed crystal is...50 The value is 2 μm; the initial addition of hydrogen peroxide is used to remove the 1.8 g / L Fe in the mixed solution. 2+ Oxidized to Fe 3+ .

[0125] S3: Dehydration.

[0126] The above-mentioned dihydrate ferric phosphate was dehydrated at 630°C for 1 hour to obtain ferric phosphate.

[0127] S4: Hollowing out.

[0128] The above-mentioned ferric phosphate was mixed with pure water and second phosphoric acid (with a concentration of 85 wt%) at a mass ratio of 10:30:0.35 to obtain a reaction slurry; the reaction slurry was kept at 80℃ for 10 h to promote the hollowing of ferric phosphate, thus obtaining hollow ferric phosphate.

[0129] S5: Sintering.

[0130] The hollowed-out ferric phosphate was sintered at 630°C for 2 hours to produce anhydrous ferric phosphate.

[0131] The anhydrous ferric phosphate Dv prepared in this embodiment 50 With a diameter of 3.8 μm, this anhydrous iron phosphate exhibits excellent sphericity and a complete hollow structure.

[0132] Comparative Example 1 The difference between this comparative example and Example 1 is that no iron phosphate dihydrate crystals were added in S2.

[0133] The anhydrous ferric phosphate product prepared in this comparative example had irregular particle morphology, poor sphericity, and Dv. 50 It has a wide distribution and no obvious hollow structure.

[0134] Comparative Example 2 The difference between this comparative example and Example 1 is that in S1, the Fe in the mixed solution... 2+ The concentration is 30 g / L.

[0135] The anhydrous ferric phosphate product prepared in this comparative example has a larger particle size, Dv 50 >5μm.

[0136] Comparative Example 3 The difference between this comparative example and Example 3 is that in S1, the Fe in the mixed solution... 2+ The molar ratio of P to P is 0.85:1.

[0137] The comparative example prepared ferric phosphate dihydrate contained excess phosphorus, and the particles were lamellar spheres (e.g., ...). Figure 4 (As shown).

[0138] Comparative Example 4 The difference between this comparative example and Example 1 is that in S2, the hydrogen peroxide added first is used to remove 0.5 g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ .

[0139] The morphology of the iron phosphate dihydrate particles prepared in this comparative example was not uniform (e.g.) Figure 5 As shown), sphericity difference.

[0140] Comparative Example 5 The difference between this comparative example and Example 1 is that in S2, the temperature is increased to 60°C to cause the particles to precipitate.

[0141] The precipitation reaction in this comparative example was incomplete, resulting in finely broken particles that could not form regular spherical shapes even after aging.

[0142] Comparative Example 6 The difference between this comparative example and Example 1 is that in S4, the mass ratio of ferric phosphate to second phosphoric acid (with a concentration of 85 wt%) is 5:1.

[0143] The anhydrous iron phosphate product prepared in this comparative example had an excessively high P concentration, severe agglomeration, poor sphericity, and collapse of the hollow structure.

[0144] Comparative Example 7 The difference between this comparative example and Example 1 is that in S4, the mass ratio of ferric phosphate to water is 0.05:1.

[0145] In this comparative example, the reaction slurry was too thin, making it impossible to effectively reconstruct the aqueous phase, resulting in failure of hollowing.

[0146] Comparative Example 8 The difference between this comparative example and Example 1 is that step S4 is omitted, and sintering in S5 is performed directly after dehydration in S3.

[0147] The anhydrous ferric phosphate product prepared in this comparative example has a solid particle structure (e.g., ...). Figure 6 (As shown).

[0148] Comparative Example 9 The difference between this comparative example and Example 1 is that in S2, the amount of ferric phosphate dihydrate seed crystals added is 12wt% of the theoretical amount of ferric phosphate dihydrate generated.

[0149] The anhydrous ferric phosphate product Dv prepared in this comparative example 50 If the particles are too small, they will agglomerate severely and have poor flowability.

[0150] Comparative Example 10 The difference between this comparative example and Example 3 is that in S5, the sintering temperature is 500°C.

[0151] The anhydrous ferric phosphate product prepared in this comparative example had insufficient crystallinity, residual water of crystallization, and an impure phase.

[0152] Comparative Example 11 The difference between this comparative example and Example 3 is that in S3, the sintering temperature is 100°C.

[0153] In the preparation process of this comparative example, S3 is basically unable to form transition state ferric phosphate, and ultimately the ferric phosphate cannot be hollowed out.

[0154] Comparative Example 12 The difference between this comparative example and Example 3 is that in S3, the sintering temperature is 650°C.

[0155] In the preparation process of this comparative example, the iron phosphate obtained by S3 is more dense, making it difficult for the iron phosphate to become hollow, resulting in an unstable product.

[0156] Comparative Example 13 The difference between this comparative example and Example 3 is that in S2, the seed particle size is 4 μm; The anhydrous ferric phosphate Dv prepared in this comparative example 50 It is 6.2μm.

[0157] Test case The performance of the anhydrous ferric phosphate products prepared in Examples 1-6 and Comparative Examples 1-13 was compared, and the results are shown in Table 1.

[0158] In this process, a portion of the anhydrous ferric phosphate product was dissolved in dilute sulfuric acid to obtain anhydrous ferric phosphate solution. The iron content in the anhydrous ferric phosphate solution was then determined by potassium dichromate titration. The phosphorus content in the anhydrous ferric phosphate product was determined by quinomolybdate gravimetric method. The molar ratio of Fe to P was calculated from the iron and phosphorus contents.

[0159] The particle size distribution (Dv) was measured using a laser particle size analyzer. 50 Particle size.

[0160] The particle morphology was observed using a scanning electron microscope (SEM).

[0161] Table 1 Performance Results of Anhydrous Ferric Phosphate Products

[0162] As can be seen from Table 1, the method provided by this invention can prepare products with good sphericity and Dv. 50 Smaller anhydrous iron phosphate with a hollow structure.

[0163] As can be seen from Comparative Examples 1-13, improper methods or conditions during the preparation process can lead to a deterioration in the quality of anhydrous ferric phosphate products, such as decreased sphericity and reduced Dv.50 The product becomes larger and cannot form a hollow structure. Comparative Example 10 mainly suffers from impurities in the product phase.

[0164] In summary, this invention controls the amount of iron phosphate dihydrate seed crystals added and Dv... 50 The process of staged addition of hydrogen peroxide and dehydration temperature can effectively control the morphology, hollowness, and particle size of the final anhydrous ferric phosphate product, achieving regulation of the morphology and structure of the ferric phosphate material, and the hollowness of the anhydrous ferric phosphate can be adjusted. No other impurities, surfactants, template agents, etc., are introduced during the preparation process of this invention, making it more friendly to the reaction system and cost. The prepared anhydrous ferric phosphate has good sphericity and a particle size Dv. 50 With a particle size of 2μm~4μm, it can be directly used as a supplement to large lithium iron phosphate battery particles (typically, the Dv of small lithium iron phosphate particles is much smaller). 50 (No more than 500nm), optimizing the electrical performance of lithium iron phosphate batteries.

[0165] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing anhydrous ferric phosphate, characterized in that, Includes the following steps: Ferric phosphate seed crystals were added to a mixed solution containing ferrous sulfate and primary phosphoric acid, followed by the addition of hydrogen peroxide to remove some of the Fe in the mixed solution. 2+ Oxidized to Fe 3+ The mixture was first heated and held at that temperature, then hydrogen peroxide was added to ensure that all the Fe in the solution was removed. 2+ All are oxidized to Fe 3+ The temperature was raised a second time and held at that temperature to obtain ferric phosphate dihydrate. Ferric phosphate dihydrate is dehydrated to obtain ferric phosphate; The ferric phosphate was mixed with water and a second phosphoric acid and kept at a certain temperature to obtain hollow ferric phosphate. Hollow ferric phosphate is sintered to obtain anhydrous ferric phosphate.

2. The preparation method according to claim 1, characterized in that, In the mixed solution, Fe 2+ The concentration is 40 g / L~80 g / L, Fe 2+ The molar ratio of P to P is 0.9:1 to 1:

1.

3. The preparation method according to claim 1, characterized in that, The amount of ferric phosphate dihydrate seed crystals added is 5wt%~10wt% of the theoretical amount of ferric phosphate dihydrate generated, and the theoretical amount of ferric phosphate dihydrate generated is the mass of ferric phosphate dihydrate corresponding to when all the ferrous sulfate in the mixed solution is converted into ferric phosphate dihydrate. And / or, the Dv of the iron phosphate dihydrate seed crystals 50 The range is 0.5μm to 3μm; And / or, before adding the mixed solution, the ferric phosphate dihydrate is ground.

4. The preparation method according to claim 1, characterized in that, The initial addition of hydrogen peroxide is used to remove 1 g / L to 3 g / L of Fe from the mixed solution. 2+ Oxidized to Fe 3+ ; And / or, the temperature after the first heating is 30℃~60℃, and the holding time after the first heating does not exceed 3 hours; And / or, the temperature after the second heating is 70℃~100℃, and the holding time after the second heating is 6h~15h.

5. The preparation method according to claim 1, characterized in that, The dehydration temperature is 150℃~600℃; Preferably, the dehydration temperature is 350℃~450℃; Preferably, the dehydration time is 1 hour to 3 hours.

6. The preparation method according to claim 1, characterized in that, The preparation of the hollow ferric phosphate includes at least one of the following features: Feature 1: The mass ratio of the iron phosphate to the second phosphoric acid is 10:1 to 100:1; Feature 2: The mass ratio of the ferric phosphate to water is 0.1:1 to 0.45:1; Feature 3: Insulation temperature range is 50℃~95℃; Feature 4: The heat preservation time is 4h~20h.

7. The preparation method according to claim 1, characterized in that, The sintering temperature is 550℃~650℃, and / or the sintering time is 2h~4h.

8. An anhydrous ferric phosphate, characterized in that, The anhydrous ferric phosphate is prepared by the preparation method according to any one of claims 1 to 7; Preferably, the anhydrous ferric phosphate has at least one of the following characteristics: Feature 5: The Dv of the anhydrous ferric phosphate 50 The thickness is 2μm to 4μm; Feature 6: The anhydrous ferric phosphate has a hollow structure.

9. A lithium iron phosphate, characterized in that, The lithium iron phosphate is prepared from the anhydrous iron phosphate as described in claim 8.

10. A battery, characterized in that, The battery comprises the lithium iron phosphate as described in claim 9.

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