A low-impurity low-specific surface area iron phosphate and a method for preparing the same

Abstract

This invention relates to the preparation of ferric phosphate, and provides a low-impurity, low-specific-surface-area ferric phosphate and its preparation method, comprising the following preparation steps: (1) synthesizing amorphous ferric phosphate; (2) preparing an amorphous ferric phosphate suspension: mixing the amorphous ferric phosphate, dispersant, and phosphoric acid from step (1) and then slurrying to form a suspension; (3) aging: the suspension obtained in step (2) is introduced into a multi-channel tubular reactor for heating, crystallization, and heat preservation. After heat preservation, it is introduced into a crystallization reactor to obtain a crystallization slurry. At the same time, the suspension from step (2) is added to the crystallization reactor, and the flow rate of the crystallization slurry and the suspension are controlled. Mixing, heating, crystallization, and heat preservation are carried out in the crystallization reactor; (4) filtering, washing, and calcining the solution obtained in step (3). The low-impurity, low-specific-surface-area ferric phosphate and its preparation method of this invention can effectively adjust the specific surface area, particle size, and impurity content of ferric phosphate.

Description

Technical Field

[0001] This invention relates to the technical field of ferric phosphate preparation, and more specifically, to a low-impurity, low-specific-surface-area ferric phosphate and its preparation method. Background Technology

[0002] Lithium iron phosphate (LFP) cathode materials are favored for their advantages such as long lifespan, high discharge specific capacity, high safety, non-toxicity, and wide availability of raw materials. Experiments have shown that the performance of LFP cathode materials directly affects battery performance. Research on LFP mainly focuses on chemical, physical, and electrochemical indicators. While there is extensive research on chemical and electrochemical indicators, research on its physical indicators is relatively limited. One of the physical indicators affecting LFP is the specific surface area of ​​iron phosphate. A larger specific surface area of ​​iron phosphate can improve the compaction density of LFP. A larger specific surface area indicates more porosity, resulting in lower compaction density of the prepared LFP.

[0003] The publication number CN108455547A, entitled "A method for preparing battery-grade iron phosphate with low impurities, high iron-to-phosphorus ratio, and large specific surface area," describes a method for controlling the specific surface area of ​​iron phosphate to be between 8 and 13 m². 2 / g, when the specific surface area is too large, impurity peaks are prone to appear, and it is also not conducive to improving the compaction density of lithium iron phosphate. Publication number CN112408351A "A method for preparing high-compacted iron phosphate and lithium iron phosphate" can obtain iron phosphate with a smaller specific surface area, but directly using untreated titanium dioxide by-product ferrous sulfate will inevitably lead to unstable Ti content in the product. The use of NaOH in the preparation process will cause the Na content in the product to exceed the standard, and Ti is easily hydrolyzed into metatitanic acid, which easily adsorbs impurities. Summary of the Invention

[0004] The purpose of this invention is to provide a low-impurity, low-specific-surface-area iron phosphate and its preparation method, which can effectively adjust the specific surface area, particle size and impurity content of iron phosphate.

[0005] The embodiments of the present invention are achieved through the following technical solutions: The preparation method of the low-impurity, low-specific-surface-area iron phosphate of the present invention includes the following preparation steps: (1) Synthesis of amorphous iron phosphate: Prepare 1~1.5mol / L Fe(II) solution and 1~2mol / L phosphate solution. Mix the Fe(II) solution, phosphate solution and oxidant in a volume ratio of 1:1~1.05:0.55~0.7 and add them to the Fe(II) solution. Stir at 20~50℃ for 50~120min and then filter and wash to obtain amorphous iron phosphate. (2) Preparation of amorphous ferric phosphate suspension: The amorphous ferric phosphate, dispersant and phosphoric acid (used to adjust the pH of the system to 1.8~2) from step (1) are mixed and pulped to prepare a suspension with a solid content of ferric phosphate of 8~10%. After the suspension is prepared, it is passed through an 80~300 mesh standard sieve. (3) Aging: The suspension obtained in (2) is fed into a multi-channel tubular reactor for heating, crystallization, and heat preservation. After heat preservation, it is fed into a crystallization reactor to obtain crystallization slurry. At the same time, the suspension in (2) is added to the crystallization reactor. The flow rates of the crystallization slurry and the suspension are controlled. The crystallization slurry is mixed, heated, crystallized, and heat preserved in the crystallization reactor. The flow rate ratio of the crystallization slurry to the suspension is 1:(0.2-1), that is, the mass ratio of the two in the crystallization reactor is 1:(0.2-1). (4) After filtering the solution obtained in step (3), wash it with deionized water at 40~50℃, and vacuum dry it at 70-90℃ for 10-14h; the calcination temperature is 550~600℃ and the calcination time is 60~120min.

[0006] Further, the dispersant in step (2) is one or more of ethylene glycol, pentaerythritol glycerol, sorbitol, alkyl alcohol amide, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, C13 isopropanol amide, essential oil emulsifier, and secondary alcohol; the amount of dispersant used is 0.01~0.5% of the mass of amorphous iron phosphate.

[0007] Furthermore, in step (3), a multi-channel tubular reactor is used to heat up faster, accelerate the activation of amorphous iron phosphate molecules, and obtain iron phosphate with a smaller particle size. The heating rate is 10~15℃ / min, the crystallization temperature is 85~90℃, and the holding time is 30~60min.

[0008] Furthermore, in step (3), when using the crystallization reactor, it is necessary to mix it quickly for 5 to 10 minutes, control the heating rate at 5 to 10 °C / min, keep it warm for 90 to 120 minutes, and control the flow rate of the crystallization slurry and the suspension at 1:0.2 to 9.

[0009] Further, in step (4), the water is washed with deionized water at 40~50℃ and dried under vacuum at 70~90℃ for 10~14h; the calcination temperature is 550~600℃ and the calcination time is 60~120min.

[0010] The present invention also provides ferric phosphate prepared by the above-described method for preparing low-impurity, low-specific-surface-area ferric phosphate.

[0011] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: The present invention relates to low-impurity, low-specific-surface-area iron phosphate and its preparation method: (1) Starting from controlling crystal growth, mixing the pulping slurry with the aging slurry can increase the filling rate of the whole system. The average particle size of the pulping slurry is larger than that of the aging slurry. Therefore, after thorough mixing, the pores of the original pulping slurry will be occupied by the particles of the aging slurry, increasing the packing density between particles. At the same time, the aging slurry acts as a seed crystal. During the crystal transformation process, the seed crystal will induce that part of the pulping slurry to grow on the aging slurry, forming larger crystals, thereby controlling its specific surface area.

[0012] (2) The dispersant used in this invention is non-ionic, which on the one hand does not introduce impurities, and on the other hand can make the pulp slurry more uniformly dispersed, so that it can be filled more completely during filling. The ferric phosphate prepared by the method of this invention has a larger average particle size, a lower specific surface area, and a lower impurity content, and the product quality is stable, making it suitable for industrial production. Detailed Implementation

[0013] Example 1 This embodiment provides a method for preparing iron phosphate with low impurities and low specific surface area, including the following steps: (1) Synthesis and washing of amorphous ferric phosphate: Prepare ferrous sulfate solution and diammonium hydrogen phosphate solution, wherein the concentration of ferrous sulfate solution is 1 mol / L and the concentration of phosphate solution is 1 mol / L. Mix ferrous sulfate solution, diammonium hydrogen phosphate solution and hydrogen peroxide solution (20%) in a volume ratio of 1:1:0.6 and add them to Fe(II) solution. Stir at 50℃ for 50 min and then filter and wash to obtain amorphous ferric phosphate.

[0014] (2) Preparation of amorphous ferric phosphate suspension: The amorphous ferric phosphate from step 1) was placed in a beaker, and water, ethylene glycol, and 85% phosphoric acid were added. The amount of ethylene glycol added was 0.3% of the mass of anhydrous ferric phosphate. The dispersion was carried out using a toothed disc turbine propeller. The solid content of ferric phosphate was 10%, and the amount of phosphoric acid added was used to control the pH of the system to 1.85. The pulping time was 1 hour. After the suspension was prepared, it was passed through a 100-mesh standard sieve.

[0015] (3) The suspension obtained in (2) is fed into a multi-channel tubular reactor and heated to 90°C at a heating rate of 10°C / min. After the color turns pinkish-white, the mixture is kept at this temperature for 60 min. After the temperature is kept at this temperature, the mixture is fed into a crystallization reactor to obtain a crystallization slurry. At the same time, the suspension in (2) is added to the crystallization reactor. The flow ratio of the crystallization slurry to the suspension is 1:0.2. The mixture is rapidly mixed in the crystallization reactor for 5 min and heated to 90°C at a heating rate of 5°C / min. After the color turns pinkish-white again, the mixture is kept at this temperature for 90 min.

[0016] (4) Washing and drying: The slurry after aging in step (3) is filtered, washed with deionized water at 40°C, and vacuum dried at 80°C for 12 hours. Calcination: The calcination temperature is 590°C and the calcination time is 90 minutes.

[0017] Example 2 This embodiment provides a method for preparing iron phosphate with low impurities and low specific surface area, including the following steps: (1) Synthesis and washing of amorphous ferric phosphate: Prepare ferrous sulfate solution and diammonium hydrogen phosphate solution, wherein the concentration of ferrous sulfate solution is 1 mol / L and the concentration of phosphate solution is 1 mol / L. Mix ferrous sulfate solution, diammonium hydrogen phosphate solution and hydrogen peroxide solution (20%) in a volume ratio of 1:1:0.6 and add them to Fe(II) solution. Stir at 50℃ for 50 min and then filter and wash to obtain amorphous ferric phosphate.

[0018] (2) Preparation of amorphous ferric phosphate suspension: The amorphous ferric phosphate from step (1) is placed in a beaker, and water, ethylene glycol, and 85% phosphoric acid are added. The amount of ethylene glycol added is 0.5% of the mass of anhydrous ferric phosphate. The dispersion is carried out using a toothed disc turbine propeller. The solid content of ferric phosphate is 10%. The amount of phosphoric acid added is used to control the pH of the system to 1.85. The pulping time is 1 hour. After the suspension is prepared, it is passed through a 100-mesh standard sieve.

[0019] (3) The suspension obtained in (2) is fed into a multi-channel tubular reactor. The temperature is increased to 90°C at a rate of 10°C / min. After the color turns pinkish-white, the temperature is maintained for 30 minutes. After the temperature maintenance, the suspension is fed into a crystallization reactor to obtain a crystallization slurry. At the same time, the suspension in (2) is added to the crystallization reactor. The flow ratio of the crystallization slurry to the suspension is 1:0.5. The mixture is rapidly mixed in the crystallization reactor for 5 minutes. The temperature is increased to 90°C at a rate of 5°C / min. After the color turns pinkish-white again, the temperature is maintained for 90 minutes.

[0020] (4) Washing and drying: The slurry after aging in step (3) is filtered, washed with deionized water at 40°C, and vacuum dried at 80°C for 12 hours. Calcination: The calcination temperature is 590°C and the calcination time is 90 minutes.

[0021] Example 3 This embodiment provides a method for preparing iron phosphate with low impurities and low specific surface area, including the following steps: (1) Synthesis and washing of amorphous ferric phosphate: Prepare ferrous sulfate solution and diammonium hydrogen phosphate solution, wherein the concentration of ferrous sulfate solution is 1 mol / L and the concentration of phosphate solution is 1 mol / L. Mix ferrous sulfate solution, diammonium hydrogen phosphate solution and hydrogen peroxide solution (20%) in a volume ratio of 1:1:0.6 and add them to Fe(II) solution. Stir at 50℃ for 50 min and then filter and wash to obtain amorphous ferric phosphate.

[0022] (2) Preparation of amorphous ferric phosphate suspension: The amorphous ferric phosphate from step (1) is placed in a beaker, and water, sorbitol, and 85% phosphoric acid are added. The amount of sorbitol added is 0.3% of the mass of the anhydrous ferric phosphate. The dispersion is carried out using a toothed disc turbine propeller. The solid content of ferric phosphate is 10%, and the amount of phosphoric acid added is used to control the pH of the system to 1.85. The pulping time is 3h. After the suspension is prepared, the suspension is passed through a 100-mesh standard sieve.

[0023] (3) The suspension obtained in (2) is fed into a multi-channel tubular reactor. The temperature is increased to 90°C at a rate of 15°C / min. After the color turns pinkish-white, the temperature is maintained for 60 min. After the temperature is maintained, the suspension is fed into a crystallization reactor to obtain a crystallization slurry. At the same time, the suspension in (2) is added to the crystallization reactor. The flow ratio of the crystallization slurry to the suspension is 1:1. The mixture is rapidly mixed in the crystallization reactor for 5 min. The temperature is increased to 90°C at a rate of 5°C / min. After the color turns pinkish-white again, the temperature is maintained for 90 min.

[0024] (4) Washing and drying: The slurry after aging in step (3) is filtered, washed with deionized water at 40°C, and vacuum dried at 80°C for 12 hours. Calcination: The calcination temperature is 590°C and the calcination time is 90 minutes.

[0025] Comparative Example 1 This comparative example uses commercially available ferric phosphate as a reference, which is sourced from Guizhou Saideli New Energy Technology Co., Ltd.

[0026] Comparative Example 2 The only difference between this comparative example and Example 1 is step (3). Step (3) of this example is: place the pulped suspension in container A at 90°C, and after the color turns pinkish-white, proceed with the filtration and washing operation.

[0027] Comparative Example 3 The only difference between this comparative example and Example 1 is step (3). Step (3) of this example is: place the pulped suspension in container A at 90°C. After the color changes, transfer 20% of the total mass to container B at 90°C. Place 80% of the total mass of the next batch of pulped slurry in the aging kettle and mix it with the previous batch of aging slurry. Continue to heat to 90°C. After the system color turns pinkish-white, proceed to the filtration and washing operation.

[0028] Experimental Example Elemental analysis, particle size distribution and specific surface area analysis were performed on the anhydrous iron phosphate materials prepared in Examples 1-3. The results are shown in Table 1 below.

[0029] Table 1. Particle size distribution, specific surface area, and impurities of ferric phosphate in each group.

[0030] As can be seen from the data in Table 1, the ferric phosphate prepared by the preparation method of this application (Examples 1-3) has a larger particle size, lower specific surface area, and lower content of various impurities compared to Comparative Examples 1-3. The difference between the preparation method of Comparative Example 2 and Example 1 lies in a single aging process; the various indicators of the ferric phosphate obtained from Comparative Example 2 are not significantly different from those of commercially available ferric phosphate in Comparative Example 1. Comparative Example 3 used a two-stage aging process similar to that of this application, but there were differences in the content of substances in the two aging processes. Therefore, although the ferric phosphate obtained from Comparative Example 3 was superior to Comparative Examples 1 and 2, it was still inferior to Examples 1-3, falling somewhere in between. In summary, the applicant believes that the ferric phosphate obtained by the preparation method of this application has a more controllable specific surface area, particle size distribution, and lower impurity content, meaning it has superior performance, and the entire production process does not increase the cost of raw materials.

[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present 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 process for the preparation of low-impurity low-specific-surface-area iron phosphate, characterized in that, The preparation steps include the following: (1) Synthesis of amorphous iron phosphate; (2) Preparation of amorphous ferric phosphate suspension: After mixing the amorphous ferric phosphate, dispersant and phosphoric acid from step (1), the mixture is pulped to form a suspension. The suspension is then passed through an 80-300 mesh standard sieve and set aside for later use. (3) Aging: The suspension obtained in (2) is fed into a multi-channel tubular reactor for heating, crystallization, and heat preservation. After heat preservation, it is fed into a crystallization reactor to obtain crystallization slurry. At the same time, the suspension in (2) is added to the crystallization reactor. The flow rates of the crystallization slurry and the suspension are controlled. The crystallization slurry is mixed, heated, crystallized, and heat preserved in the crystallization reactor. The flow rate ratio of the crystallization slurry to the suspension is 1:(0.2-1). (4) The slurry obtained in step (3) is filtered, washed, and calcined; In step (3), a multi-channel tubular reactor is used to heat up faster, accelerate the activation of amorphous iron phosphate molecules, and obtain iron phosphate with a smaller particle size. The heating rate is 10~15℃ / min, the crystallization temperature is 85~90℃, and the holding time is 30~60min.

2. The method for preparing low-impurity, low-specific-surface-area iron phosphate according to claim 1, characterized in that, In step (2), phosphoric acid is used to adjust the pH of the system to 1.8~2.

3. The method for preparing low-impurity, low-specific-surface-area iron phosphate according to claim 1, characterized in that, In the suspension in step (2), the solid content of ferric phosphate is 8-10%.

4. The method for preparing low-impurity, low-specific-surface-area iron phosphate according to claim 1, characterized in that, In step (3), when using the crystallization reactor, it is necessary to mix it quickly for 5 to 10 minutes, control the heating rate at 5 to 10 °C / min, keep it warm for 90 to 120 minutes, and control the flow rate of the crystallization slurry and the suspension at 1:0.2 to 9.

5. The method for preparing low-impurity, low-specific-surface-area iron phosphate according to claim 1, characterized in that, In step (4), the water is washed with deionized water at 40-50℃ and vacuum dried at 70-90℃ for 10-14 hours; the calcination temperature is 550-600℃ and the calcination time is 60-120 minutes.

6. The method for preparing low-impurity, low-specific-surface-area iron phosphate according to claim 1, characterized in that, The dispersant in step (2) is one or more of ethylene glycol, sorbitol, alkylolamide, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, and C13 isopropanolamide; the amount of dispersant used is 0.01~0.5% of the mass of amorphous iron phosphate.

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