Process for the preparation of iron phosphate and its use

Abstract

This invention discloses a process for preparing ferric phosphate and its application, comprising the following steps: (1) adding iron-containing raw materials and phosphorus-containing raw materials into a reaction vessel and stirring evenly; (2) at the beginning of the reaction, slowly adding hydrogen peroxide to the reaction vessel; during the reaction, increasing the hydrogen peroxide dripping rate and controlling the ORP and pH of the reaction system; when the hydrogen peroxide dripping rate approaches the theoretical amount, slowing down the dripping rate, and obtaining a mixed slurry after the reaction reaches the endpoint; (3) adding an oxidation catalyst to the mixed slurry, heating to a predetermined temperature for heat preservation treatment, performing liquid-solid separation after the reaction, and obtaining ferric phosphate polyhydrate after washing; (4) calcining the ferric phosphate polyhydrate to obtain ferric phosphate product. By segmented and controlled-rate addition of hydrogen peroxide, precise control of ORP and pH, and deep oxidation with an oxidation catalyst, complete oxidation, controllable reaction, high product purity, and good batch stability are achieved, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of ferric phosphate production technology, and relates to a preparation process of ferric phosphate and its application. Background Technology

[0002] Anhydrous iron phosphate (FePO4) is an important inorganic functional material widely used in lithium-ion batteries, catalysts, pigments, adsorbents, and other fields. Especially in the field of lithium-ion battery cathode materials, anhydrous iron phosphate has become a crucial precursor for lithium iron phosphate (LiFePO4) batteries due to its excellent thermal stability, environmental friendliness, and low cost. Furthermore, anhydrous iron phosphate is widely used in various catalytic reaction systems, such as organic waste gas purification and redox reactions, due to its high surface activity, stable physicochemical properties, and excellent corrosion resistance.

[0003] Existing methods for preparing anhydrous ferric phosphate mainly include high-temperature thermal decomposition, precipitation, and solvothermal methods. The high-temperature thermal decomposition method primarily involves heating iron-containing and phosphorus-containing compounds to generate anhydrous ferric phosphate through a high-temperature decomposition reaction. However, this method requires high-temperature conditions, consumes a large amount of energy, demands sophisticated equipment, and is complex, making it unsuitable for large-scale industrial production. For example, Chinese patent CN109179353A discloses a process for preparing anhydrous ferric phosphate. This involves mixing iron oxide red with ammonium monohydrogen phosphate or ammonium dihydrogen phosphate, adding pure water to form a slurry, then grinding the slurry in a sand mill until the particle size is 500-600 nm. The slurry is then spray-dried to obtain a dried material, which is then calcined in a roller furnace or rotary kiln at 350-550℃ for 5-7 hours. The generated waste gas is absorbed by a phosphoric acid solution spray and then discharged. The calcined material is cooled, then pulverized by airflow, and finally screened to remove iron, yielding anhydrous ferric phosphate.

[0004] The precipitation method prepares ferric phosphate by co-precipitating iron-containing and phosphorus-containing solutions under certain conditions, followed by heating and drying or calcination to remove moisture and obtain anhydrous ferric phosphate. Although the precipitation method has lower energy consumption, the reaction process is difficult to control, resulting in lower purity and crystallinity of the product, and uneven particle size and morphology of the precipitate, leading to unstable performance of the final product. Furthermore, the precipitation method generates a large amount of wastewater and waste residue that requires treatment, placing a significant environmental burden on the plant. The solvothermal method obtains anhydrous ferric phosphate through a chemical reaction in a solvent environment at high temperature and pressure. This method produces ferric phosphate with good crystallinity, uniform particle size, and high purity, but it requires equipment such as autoclaves, resulting in high investment costs. Additionally, solvent recovery and treatment are difficult, making it difficult to widely apply to industrial production.

[0005] Existing technologies generally suffer from incomplete oxidation reactions and Fe 2+Problems such as incomplete conversion, high product impurity content, and poor batch stability prevent iron phosphate products from meeting the stringent requirements of precursors for high-end power batteries. Therefore, developing an iron phosphate preparation process with controllable reaction, uniform product, high purity, and suitability for industrial production has significant market value and technological importance. Summary of the Invention

[0006] To address the technical problems in the background art, this invention provides a preparation process for iron phosphate and its application. By adding hydrogen peroxide in stages at a controlled rate, precisely controlling ORP and pH, and using an oxidation catalyst for deep oxidation, complete oxidation, controllable reaction, high product purity, and good batch stability are achieved, making it suitable for large-scale industrial production.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a process for preparing iron phosphate, comprising the following steps:

[0009] (1) Add the iron-containing raw materials and phosphorus-containing raw materials to the reaction vessel and stir evenly;

[0010] (2) At the beginning of the reaction, hydrogen peroxide is slowly added to the reactor; during the reaction, the hydrogen peroxide dripping rate is increased, and the ORP and pH of the reaction system are controlled; when the amount of hydrogen peroxide added is close to the theoretical amount, the dripping rate is slowed down, and after the reaction reaches the endpoint, a mixed slurry is obtained.

[0011] (3) Add an oxidation catalyst to the mixed slurry obtained in step (2), heat it to a predetermined temperature and keep it warm, then perform liquid-solid separation after reaction, and wash it to obtain ferric phosphate polyhydrate.

[0012] (4) Calcining the ferric phosphate polyhydrate obtained in step (3) yields the ferric phosphate product.

[0013] In the preferred embodiment, the molar ratio of Fe, P and hydrogen peroxide is controlled to be 1:(1.0~1.3):(0.5~1.5).

[0014] The iron-containing raw material is selected from at least one of ferrous sulfate, ferrous chloride, or ferrous nitrate;

[0015] The phosphorus-containing raw material is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate;

[0016] The mass concentration of hydrogen peroxide is 2% to 8%.

[0017] In the preferred embodiment, in step (2), at the start of the reaction, the dropping rate of hydrogen peroxide is 0.5% to 1% of the theoretical total amount added per minute;

[0018] During the reaction, the hydrogen peroxide dripping rate was 5% to 8% of the theoretical total amount added per minute, the ORP value was controlled at +200mV to +450mV, and the pH was 0.5 to 3.

[0019] When the amount of oxidant added is close to the theoretical amount, the dropping rate of hydrogen peroxide is 0.1% to 0.5% of the theoretical total amount added per minute.

[0020] In the preferred embodiment, in step (3), the heat preservation time is 1~3h and the heat preservation temperature is 90~95℃.

[0021] In the preferred embodiment, in step (3), the filtrate is washed 3 to 5 times with deionized water at 60 to 80°C until the conductivity of the filtrate is <100 μS / cm.

[0022] In the preferred embodiment, in step (4), the calcination temperature is 550~750℃ and the calcination time is 2~4h.

[0023] In the preferred embodiment, in step (3), the amount of oxidation catalyst added is 0.1wt%~5wt% of the total mass of iron in the reaction system;

[0024] The preparation process of the oxidation catalyst is as follows:

[0025] Step a: Mix nitrogen-rich organic matter, carbon-rich organic matter, and template agent to obtain a mixture;

[0026] Step b: The mixture is subjected to a hydrothermal reaction in a high-pressure reactor to obtain the precursor;

[0027] Step c: The precursor is carbonized at high temperature in an inert atmosphere to decompose and graphitize the organic matter and form nitrogen doping sites, thus obtaining the carbonized product.

[0028] Step d: Immerse the carbonized product in concentrated hydrofluoric acid or hot sodium hydroxide solution, stir until homogeneous to dissolve and remove unstable species, wash until neutral, and dry to obtain the oxidation catalyst.

[0029] Furthermore, in step a, the nitrogen-rich organic compound is at least one of melamine, urea, polyaniline, polypyrrole, and chitosan; the carbon-rich organic compound is at least one of glucose, phenolic resin, and polyacrylonitrile; and the template agent is at least one of silica nanospheres and block copolymer F127.

[0030] In step b, the hydrothermal reaction temperature is 200~350℃, and the hydrothermal reaction time is 1~4h;

[0031] In step c, the carbonization temperature is 800~1000℃ and the carbonization time is 2~4h;

[0032] In step d, the concentration of concentrated hydrofluoric acid is 40wt%~55wt%, and the stirring time is 12~24h;

[0033] The concentration of hot sodium hydroxide is 10wt%~30wt%, the temperature is 60~90℃, and the stirring time is 12~24h.

[0034] The present invention also provides an iron phosphate product, which is prepared by the above-described preparation process.

[0035] The present invention also provides the application of the iron phosphate in the preparation of lithium-ion battery cathode materials.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1. The present invention discloses a process for preparing iron phosphate. When iron-containing raw materials, phosphorus-containing raw materials and hydrogen peroxide are mixed, hydrogen peroxide is added in stages with controlled rate and combined with closed-loop regulation of ORP / pH dual parameters to avoid excessively high local concentrations. In the early stage, high-quality seed crystals are formed slowly, the main body grows at a uniform rate in the middle stage, and the oxidation is slowed down in the final stage to ensure complete oxidation and make the iron phosphate crystals intact.

[0038] 2. In this invention, an oxidation catalyst is added during the heat preservation process to enhance Fe... 2+ Deep oxidation ultimately yields products with high purity, good crystallinity, uniform particle size, low impurity content, and good batch stability.

[0039] 3. The present invention has mild reaction conditions, low wastewater generation, high washing efficiency, and no highly toxic solvents, making it suitable for continuous industrial production. Attached Figure Description

[0040] Figure 1 This is a scanning electron microscope image of the iron phosphate particles prepared in Example 1 of the present invention.

[0041] Figure 2 The image shows the XRD pattern of the iron phosphate particles prepared in Example 1 of this invention. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The following detailed embodiments further illustrate the following:

[0044] Example 1

[0045] A process for preparing iron phosphate includes the following steps:

[0046] (1) Add ferrous sulfate and phosphoric acid to the reactor and stir evenly. At the beginning of the reaction, slowly add hydrogen peroxide to the reactor at a rate of 0.8% / min of the theoretical total amount. During the reaction, increase the rate to 6% / min of the theoretical total amount and control the ORP value to +200mV~+450mV and the pH to 0.5~3. When the amount of hydrogen peroxide added is close to the theoretical amount, reduce the rate to 0.3% / min of the theoretical total amount. After the reaction reaches the endpoint, a mixed slurry is obtained.

[0047] The molar ratio of Fe:P:H2O2 is 1:1.1:0.8, and the mass concentration of hydrogen peroxide is 5%.

[0048] (2) Add an oxidation catalyst to the mixed slurry, heat to 92°C and keep warm for 2 hours. After the reaction, perform liquid-solid separation and wash to obtain iron phosphate polyhydrate.

[0049] The oxidation catalyst was added at a rate of 1 wt%, and its preparation process was as follows:

[0050] Step a: Mix melamine, glucose and F127 to obtain a mixture;

[0051] Step b: The mixture is subjected to hydrothermal reaction in a high-pressure reactor at 250°C for 2 hours to obtain the precursor;

[0052] Step c: The precursor is carbonized at high temperature in argon gas at a temperature of 1000℃ for 2 hours to decompose and graphitize the organic matter and form nitrogen doping sites, thus obtaining the carbonized product.

[0053] Step d: Immerse the carbonized product in concentrated hydrofluoric acid (40wt%), stir for 24h to dissolve and remove unstable species, wash until neutral, and dry to obtain the oxidation catalyst.

[0054] (3) Calcine the ferric phosphate polyhydrate at 650°C for 3 hours to obtain the ferric phosphate product.

[0055] Example 2

[0056] A process for preparing iron phosphate includes the following steps:

[0057] (1) Add ferrous chloride and ammonium dihydrogen phosphate to the reactor and stir evenly. At the beginning of the reaction, slowly add hydrogen peroxide to the reactor at a rate of 0.6% / min of the theoretical total amount. During the reaction, increase the rate to 7% / min of the theoretical total amount and control the ORP value to +200mV~+450mV and the pH to 0.5~3. When the amount of hydrogen peroxide added is close to the theoretical amount, reduce the rate to 0.2% / min of the theoretical total amount. After the reaction reaches the endpoint, a mixed slurry is obtained.

[0058] The molar ratio of Fe:P:H2O2 is 1:1.2:1.0, and the mass concentration of hydrogen peroxide is 5%.

[0059] (2) Add an oxidation catalyst to the mixed slurry, heat to 90°C and keep warm for 3 hours. After the reaction, perform liquid-solid separation and wash to obtain ferric phosphate polyhydrate.

[0060] The oxidation catalyst was added at a rate of 2 wt%, and its preparation process was as follows:

[0061] Step a: Mix urea, phenolic resin and F127 to obtain a mixture;

[0062] Step b: The mixture is subjected to hydrothermal reaction in a high-pressure reactor at 250°C for 2 hours to obtain the precursor;

[0063] Step c: The precursor is carbonized at high temperature in argon gas at a temperature of 900°C for 3 hours to decompose and graphitize the organic matter and form nitrogen doping sites, thus obtaining the carbonized product.

[0064] Step d: Immerse the carbonized product in hot sodium hydroxide (20wt%) at 80°C and stir for 24 hours to dissolve and remove unstable species. Wash until neutral and dry to obtain the oxidation catalyst.

[0065] (3) Calcine the ferric phosphate polyhydrate at 750°C for 2 hours to obtain the ferric phosphate product.

[0066] Example 3

[0067] A process for preparing iron phosphate includes the following steps:

[0068] (1) Add ferrous nitrate and diammonium hydrogen phosphate to the reactor and stir evenly. At the beginning of the reaction, slowly add hydrogen peroxide to the reactor at a rate of 1.0% / min of the theoretical total amount. During the reaction, increase the rate to 5% / min of the theoretical total amount and control the ORP value to +200mV~+450mV and the pH to 0.5~3. When the amount of hydrogen peroxide added is close to the theoretical amount, reduce the rate to 0.4% / min of the theoretical total amount. After the reaction reaches the endpoint, a mixed slurry is obtained.

[0069] The molar ratio of Fe:P:H2O2 is 1:1.05:1.2, and the mass concentration of hydrogen peroxide is 5%.

[0070] (2) Add an oxidation catalyst to the mixed slurry, heat to 92°C and keep warm for 2 hours. After the reaction, perform liquid-solid separation and wash to obtain iron phosphate polyhydrate.

[0071] The oxidation catalyst was added at a rate of 0.5 wt%, and its preparation process was as follows:

[0072] Step a: Mix polyaniline, glucose, and silica nanospheres to obtain a mixture;

[0073] Step b: The mixture is subjected to hydrothermal reaction in a high-pressure reactor at 250°C for 2 hours to obtain the precursor;

[0074] Step c: The precursor is carbonized at high temperature in argon gas at a temperature of 800°C for 4 hours to decompose and graphitize the organic matter and form nitrogen doping sites, thus obtaining the carbonized product.

[0075] Step d: Immerse the carbonized product in concentrated hydrofluoric acid (40wt%), stir for 24h to dissolve and remove unstable species, wash until neutral, and dry to obtain the oxidation catalyst.

[0076] (3) Calcine the ferric phosphate polyhydrate at 750°C for 2 hours to obtain the ferric phosphate product.

[0077] Comparative Example 1 (no segmented addition, no ORP / pH adjustment)

[0078] Differences from Example 1:

[0079] Hydrogen peroxide is added dropwise at a uniform rate (the drop rate is 10% of the theoretical total amount per minute), without controlling ORP and pH.

[0080] Comparative Example 2 (without oxidation catalyst)

[0081] Differences from Example 1:

[0082] No oxidation catalyst was added, and all other conditions remained the same.

[0083] The properties of the ferric phosphates prepared in Examples 1-3 and Comparative Examples 1-2 were tested, and the details are shown in Table 1:

[0084] Table 1. Test data of various properties of ferric phosphate

[0085] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Particle size D50 (um) 2.43 2.58 2.37 1.98 4.55 <![CDATA[Specific surface area (m 2 / g)]]> 6.83 7.04 6.95 9.72 3.26 Iron-to-phosphorus ratio 0.9694 0.9693 0.9689 0.9634 0.9725 <![CDATA[Tap density (g / m 3 )]]> 0.78 0.75 0.77 0.56 0.92 S (ppm) 82 79 75 73 157 Ca (ppm) 10.54 11.32 9.58 10.37 11.45 Mg (ppm) 8.79 9.37 8.97 8.06 7.16 Cu (ppm) 0 0 0 0 0 Mn (ppm) 9.7 9.43 8.62 8.52 9.46 Ni (ppm) 0 0 0 0 0 Zn (ppm) 3.20 3.44 3.68 3.52 4.13 Cr (ppm) 10.96 12.6 13.38 13.63 15.31 Co (ppm) 1.96 2.13 2.09 2.07 2.23 Pb (ppm) 18.13 18.71 19.19 19.54 17.85 K (ppm) 5.98 33.24 36.18 42.11 45.32 Na (ppm) 1.52 19.44 18.61 17.32 17.56

[0086] The iron phosphate and lithium carbonate prepared in Examples 1-3 and Comparative Examples 1-2 were mixed at a molar ratio of 1:1.02, and then ball-milled (300 r / min for 1 hour) and sintered (700℃ for 4 hours) to prepare lithium iron phosphate cathode materials. These materials were then used to fabricate button batteries for electrochemical performance testing, as shown in Table 2.

[0087] Table 2 Electrochemical performance test data of lithium iron phosphate

[0088] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Cycle life (capacity retention after 500 charge-discharge cycles at 1C) 93.21% 91.38% 92.54% 83.17% 82.86% 0.1C initial discharge capacity (mAh / g) 158.9 159.2 158.8 157.8 158.0 First charge / discharge efficiency 99.22% 98.93% 99.07% 99.16% 99.43%

[0089] In summary, this invention achieves Fe oxidation through segmented dropwise addition and precise ORP / pH control, combined with nitrogen-doped porous carbon catalyst to enhance oxidation. 2+ Highly efficient conversion and improved product purity. This invention features a mild and controllable reaction process, produces no high-salt and highly toxic wastewater, and yields high-purity products with good crystallinity and uniform particle size, making it suitable for large-scale industrial production. The resulting iron phosphate can be used as a precursor for lithium-ion battery cathode materials, exhibiting excellent electrochemical performance and batch stability.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing iron phosphate, characterized in that, Includes the following steps: (1) Add the iron-containing raw materials and phosphorus-containing raw materials to the reaction vessel and stir evenly; (2) At the beginning of the reaction, hydrogen peroxide is slowly added to the reactor; during the reaction, the hydrogen peroxide dripping rate is increased, and the ORP and pH of the reaction system are controlled; when the amount of hydrogen peroxide added is close to the theoretical amount, the dripping rate is slowed down, and after the reaction reaches the endpoint, a mixed slurry is obtained. (3) Add an oxidation catalyst to the mixed slurry obtained in step (2), heat it to a predetermined temperature and keep it warm, then perform liquid-solid separation after reaction, and wash it to obtain ferric phosphate polyhydrate. (4) Calcining the ferric phosphate polyhydrate obtained in step (3) yields the ferric phosphate product.

2. The preparation process of iron phosphate according to claim 1, characterized in that: The molar ratio of Fe, P and hydrogen peroxide is controlled at 1:(1.0~1.3):(0.5~1.5); The iron-containing raw material is selected from at least one of ferrous sulfate, ferrous chloride, or ferrous nitrate; The phosphorus-containing raw material is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate; The mass concentration of hydrogen peroxide is 2% to 8%.

3. The preparation process of iron phosphate according to claim 1, characterized in that: In step (2), at the start of the reaction, the dropping rate of hydrogen peroxide is 0.5% to 1% of the theoretical total amount added per minute; During the reaction, the hydrogen peroxide dripping rate was 5% to 8% of the theoretical total amount added per minute, the ORP value was controlled at +200mV to +450mV, and the pH was 0.5 to 3. When the amount of oxidant added is close to the theoretical amount, the dropping rate of hydrogen peroxide is 0.1% to 0.5% of the theoretical total amount added per minute.

4. The preparation process of iron phosphate according to claim 1, characterized in that: In step (3), the heat preservation time is 1~3h and the heat preservation temperature is 90~95℃.

5. The preparation process of iron phosphate according to claim 1, characterized in that: In step (3), wash with deionized water at 60~80℃ 3~5 times until the conductivity of the filtrate is <100μS / cm.

6. The preparation process of iron phosphate according to claim 1, characterized in that: In step (4), the calcination temperature is 550~750℃ and the calcination time is 2~4h.

7. The preparation process of iron phosphate according to claim 1, characterized in that: In step (3), the amount of oxidation catalyst added is 0.1wt%~5wt% of the total mass of iron in the reaction system; The preparation process of the oxidation catalyst is as follows: Step a: Mix nitrogen-rich organic matter, carbon-rich organic matter, and template agent to obtain a mixture; Step b: The mixture is subjected to a hydrothermal reaction in a high-pressure reactor to obtain the precursor; Step c: The precursor is carbonized at high temperature in an inert atmosphere to decompose and graphitize the organic matter and form nitrogen doping sites, thus obtaining the carbonized product. Step d: Immerse the carbonized product in concentrated hydrofluoric acid or hot sodium hydroxide solution, stir until homogeneous to dissolve and remove unstable species, wash until neutral, and dry to obtain the oxidation catalyst.

8. The preparation process of iron phosphate according to claim 7, characterized in that: In step a, the nitrogen-rich organic compound is at least one of melamine, urea, polyaniline, polypyrrole, and chitosan; the carbon-rich organic compound is at least one of glucose, phenolic resin, and polyacrylonitrile; and the template agent is at least one of silica nanospheres and block copolymer F127. In step b, the hydrothermal reaction temperature is 200~350℃, and the hydrothermal reaction time is 1~4h; In step c, the carbonization temperature is 800~1000℃ and the carbonization time is 2~4h; In step d, the concentration of concentrated hydrofluoric acid is 40wt%~55wt%, and the stirring time is 12~24h; The concentration of hot sodium hydroxide is 10wt%~30wt%, the temperature is 60~90℃, and the stirring time is 12~24h.

9. A ferric phosphate product, characterized in that, It is prepared using the preparation process described in any one of claims 1 to 8.

10. The application of iron phosphate according to claim 9 in the preparation of cathode materials for lithium-ion batteries.

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