Iron phosphate, and preparation method therefor and use thereof

Abstract

Iron phosphate, and a preparation method therefor and the use thereof. The preparation method comprises the following steps: (1) mixing a ferrous salt, a phosphorus source and a solvent to obtain a mixed salt solution, and freezing the mixed salt solution to obtain a frozen mixed salt solution; (2) placing the frozen mixed salt solution in a reflux device, controlling the reflux of a hydrogen peroxide solution between the reflux device and a reaction device, controlling the concentration of hydrogen peroxide in the system, and performing a reaction until the frozen mixed salt solution is completely dissolved; and (3) adjusting the pH in the system, and subjecting same to an aging reaction and solid-liquid separation to obtain iron phosphate. The solution containing the ferrous salt and the phosphorus source is frozen in advance, hydrogen peroxide is controlled to flow through the frozen mixed salt solution, and the reaction can be slowly performed by controlling the concentration and flow rate of hydrogen peroxide, such that the iron element and the phosphorus element in the prepared iron phosphate precursor are uniformly distributed, and surface defects are few.

Description

Ferric phosphate and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials and relates to iron phosphate and a preparation method and application thereof. Background Art

[0002] Iron phosphate is a white to off-white monoclinic crystalline powder primarily used in the preparation of lithium iron phosphate cathode materials, catalysts, and ceramics. With the rapid development of lithium iron phosphate batteries, demand for iron phosphate, a key precursor for lithium iron phosphate cathode materials, has significantly increased, with annual demand expected to exceed 50,000 tons.

[0003] The structure of iron phosphate is very similar to that of lithium iron phosphate, so the performance of lithium iron phosphate can be controlled by controlling the structure, morphology and particle size of iron phosphate. Existing technologies usually use precipitation method or solid phase method to synthesize lithium iron phosphate.

[0004] CN116443834A discloses a method for continuously synthesizing ferric phosphate using a microreactor, wherein a raw material liquid for synthesizing ferric phosphate by an iron method and an oxidizing liquid are respectively introduced into a microreactor for mixing; a reaction occurs in a dynamic environment microreactor to obtain a product slurry; and the product slurry is post-treated to obtain ferric phosphate.

[0005] CN103682341A discloses a method for synthesizing a high-tap density lithium iron phosphate material, wherein a dihydrated iron phosphate precipitate is prepared by a precipitation method, and then the iron phosphate precursor is mixed with a lithium source, a carbon source, etc. and sintered to obtain a carbon-coated lithium iron phosphate positive electrode material.

[0006] The iron phosphate particles obtained by the above scheme are large and have a wide particle size distribution. When sulfate is used as the raw material for precipitation, the synthesized iron phosphate is easily entrained with sulfate ions, resulting in a high sulfur content in the synthesized iron phosphate, making it difficult to produce nano-scale iron phosphate particles.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present disclosure is to provide an iron phosphate and its preparation method and application. The method described in the present disclosure can reduce the by-products wrapped during the growth of the crystal nucleus, and the obtained nano iron phosphate particles have a stable composition, fine and uniform particles, and low sulfur content. The lithium iron phosphate positive electrode material prepared using this iron phosphate can exhibit excellent rate performance and cycle performance.

[0010] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing ferric phosphate, the preparation method comprising the following steps:

[0012] (1) mixing a ferrous salt, a phosphorus source, and a solvent to obtain a mixed salt solution, and freezing the mixed salt solution to obtain a frozen mixed salt solution;

[0013] (2) placing the frozen mixed salt solution in a reflux device, controlling the reflux of the hydrogen peroxide solution between the reflux device and the reaction device, and controlling the concentration of hydrogen peroxide in the system to react until the frozen mixed salt solution is completely dissolved;

[0014] (3) adjusting the pH in the system to perform an aging reaction, and performing solid-liquid separation to obtain the iron phosphate.

[0015] The present invention pre-freezes a solution containing a ferrous salt and a phosphorus source, and controls the flow of hydrogen peroxide through the frozen mixed salt solution. By controlling the concentration and flow rate of the hydrogen peroxide, the reaction can be slowed down, so that the iron and phosphorus elements in the prepared ferric phosphate are evenly distributed and have few surface defects.

[0016] In one embodiment, the ferrous salt in step (1) includes any one of ferrous chloride, ferrous sulfate or ferrous nitrate, or a combination of at least two thereof.

[0017] In one embodiment, the phosphorus source in step (1) includes any one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate or ammonium phosphate, or a combination of at least two thereof.

[0018] In one embodiment, the concentration of iron in the mixed salt solution in step (1) is 0.05 to 1 mol / L, for example, 0.05 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L or 1 mol / L.

[0019] In one embodiment, the concentration of phosphorus in the mixed salt solution in step (1) is 0.5 to 1 mol / L, for example, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L or 1 mol / L.

[0020] In one embodiment, the pH of the mixed salt solution in step (1) is 1.8 to 2.5, for example, 1.8, 1.9, 2, 2.2 or 2.5.

[0021] In one embodiment, the temperature of the freezing treatment in step (1) is -30 to -40°C, for example: -30°C, -32°C, -35°C, -38°C or -40°C.

[0022] In one embodiment, the freezing treatment time in step (1) is 6 to 12 hours, for example: 6 hours, 7 hours, 8 hours, 10 hours or 12 hours.

[0023] In one embodiment, the mass concentration of the hydrogen peroxide solution in step (2) is 5-10%, for example, 5%, 6%, 7%, 8% or 10%.

[0024] In one embodiment, the molar ratio of the total molar amount of hydrogen peroxide in the hydrogen peroxide solution in step (2) to the iron element in the iron source is (1-2):1, for example: 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, etc.

[0025] In one embodiment, the reflux rate of the hydrogen peroxide solution in step (2) is 50 to 100 mL / min, for example, 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min or 100 mL / min.

[0026] In one embodiment, the mass concentration of hydrogen peroxide in the reaction of step (2) is 5-10%, for example: 5%, 6%, 7%, 8% or 10%.

[0027] In one embodiment, the reaction temperature in step (2) is 40-60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C.

[0028] In one embodiment, phosphoric acid is added during the reaction of step (2) to control the pH.

[0029] In one embodiment, the pH in step (2) is controlled to be 1.8 to 2.5.

[0030] In one embodiment, the regulator for adjusting the pH in the system in step (3) includes aqueous ammonia.

[0031] In one embodiment, the pH in step (3) is 2.5 to 3.5, for example, 2.5, 2.8, 3, 3.2 or 3.5.

[0032] In one embodiment, the temperature of the aging reaction in step (3) is 40-80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C.

[0033] In one embodiment, the stirring speed of the aging reaction in step (3) is 100-200 rpm, for example, 100 rpm, 120 rpm, 150 rpm, 180 rpm or 200 rpm.

[0034] In one embodiment, the aging reaction time in step (3) is 10 to 60 hours, for example, 10 hours, 20 hours, 30 hours, 50 hours or 60 hours.

[0035] In one embodiment, the solid-liquid separation in step (3) is followed by washing and vacuum drying.

[0036] In one embodiment, the washing detergent comprises deionized water.

[0037] In one embodiment, the vacuum drying treatment is performed at a temperature of 60-100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C.

[0038] In a second aspect, the present disclosure provides iron phosphate, which is prepared by the method described in the first aspect.

[0039] In one embodiment, the particle size of the iron phosphate is 100-300 nm, for example, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm.

[0040] In a third aspect, the present disclosure provides a lithium iron phosphate, which is prepared by mixing and sintering the iron phosphate and a lithium source as described in the second aspect.

[0041] Compared with the prior art, the present disclosure has the following beneficial effects:

[0042] (1) The method disclosed herein can produce nano-scale iron phosphate, which has a stable composition, uniform element distribution, and low sulfur content. The lithium iron phosphate positive electrode material produced using the iron phosphate exhibits good rate performance and cycle performance.

[0043] (2) The lithium iron phosphate battery prepared by the method disclosed in the present invention has a 0.1C discharge capacity of more than 161.57 mAh / g, a 0.5C / 0.1C capacity retention rate of more than 97.32%, and a 100-cycle capacity retention rate of more than 98.51%.

[0044] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0046] Figure 1 is a schematic diagram of the apparatus used in the method for preparing the lithium iron phosphate positive electrode material according to an embodiment of the present disclosure, 1-frozen mixed salt solution, 2-reflux device, 3-pump, 4-reaction device, 5-stirring rod, 6-hydrogen peroxide solution, 7-feeding port.

[0047] FIG2 is a SEM image of lithium iron phosphate prepared from the iron phosphate described in Example 1 of the present disclosure.

[0048] FIG3 is a SEM image of lithium iron phosphate prepared from the iron phosphate described in Comparative Example 1. DETAILED DESCRIPTION

[0049] The technical solution of the present disclosure is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0050] Example 1

[0051] This embodiment provides a method for preparing ferric phosphate. A schematic diagram of an apparatus used in the method for preparing ferric phosphate is shown in FIG1 , wherein 1 is a frozen mixed salt solution, 2 is a reflux device, 3 is a pump, 4 is a reaction device, 5 is a stirring rod, 6 is a mixed solution, and 7 is a feeding port. The method for preparing ferric phosphate is as follows:

[0052] (1) mixing ferrous sulfate, phosphoric acid, and water to obtain a mixed salt solution having a ferrous concentration of 0.5 mol / L, a phosphorus concentration of 0.75 mol / L, and a pH of 2.1, and freezing the solution at -40°C for 8 hours to obtain a frozen mixed salt solution;

[0053] (2) placing the frozen mixed salt solution in a reflux device, controlling the mass concentration of 7% hydrogen peroxide solution to reflux between the reflux device and the reaction device at a rate of 60 mL / min, controlling the mass concentration of hydrogen peroxide in the system to remain constant at 7%, adding phosphoric acid dropwise through the feed port, maintaining the pH of the solution in the reactor at 2.1, controlling the reaction temperature at 50°C to react until the frozen mixed salt solution is completely dissolved, and the molar ratio of the total amount of hydrogen peroxide added during the reaction to the iron source is 1.5:1;

[0054] (3) The pH was adjusted to 3.1 using aqueous ammonia, the reaction temperature was controlled at 50°C, the aging reaction was carried out for 12 hours, and the stirring rate was 100 rpm. After solid-liquid separation, the solid product was washed three times with deionized water. The washed product was vacuum-dried at 80°C for 8 hours to obtain iron phosphate with a median particle size (D50) of 200 nm.

[0055] The SEM image of the positive electrode material made of iron phosphate is shown in FIG2 .

[0056] Example 2

[0057] This embodiment provides a ferric phosphate, and the preparation method of the ferric phosphate is as follows:

[0058] (1) mixing ferrous chloride, ammonium dihydrogen phosphate, and water to obtain a mixed salt solution having a ferrous concentration of 0.05 mol / L, a phosphorus concentration of 0.5 mol / L, and a pH of 1.8, and freezing the solution at -30°C for 12 hours to obtain a frozen mixed salt solution;

[0059] (2) placing the frozen mixed salt solution in a reflux device, controlling the mass concentration of 5% hydrogen peroxide solution to reflux between the reflux device and the reaction device at a rate of 80 mL / min, controlling the mass concentration of hydrogen peroxide in the system to remain constant at 7%, adding phosphoric acid dropwise through the feed port, maintaining the pH of the solution in the reactor at 1.8, controlling the reaction temperature at 40°C to react until the frozen mixed salt solution is completely dissolved, and the molar ratio of the total amount of hydrogen peroxide added during the reaction to the iron source is 1:1;

[0060] (3) The pH was adjusted to 2.5 using aqueous ammonia, the reaction temperature was controlled at 40°C, the aging reaction was carried out for 60 hours, and the stirring rate was 150 rpm. After solid-liquid separation, the solid product was washed three times with deionized water, and the washed product was vacuum-dried at 60°C for 8 hours to obtain iron phosphate with a median particle size (D50) of 230 nm.

[0061] Example 3

[0062] This embodiment provides a ferric phosphate, and the preparation method of the ferric phosphate is as follows:

[0063] (1) mixing ferrous nitrate, ammonium hydrogen phosphate, and water to obtain a mixed salt solution having a ferrous concentration of 0.1 mol / L, a phosphorus concentration of 0.1 mol / L, and a pH of 2.5, and freezing the solution at -35°C for 8 hours to obtain a frozen mixed salt solution;

[0064] (2) placing the frozen mixed salt solution in a reflux device, controlling the mass concentration of 10% hydrogen peroxide solution to reflux between the reflux device and the reaction device at a rate of 100 mL / min, controlling the mass concentration of hydrogen peroxide in the system to remain constant at 10%, adding phosphoric acid dropwise through the feed port, maintaining the pH of the solution in the reactor at 2.5, controlling the reaction temperature at 60°C to react until the frozen mixed salt solution is completely dissolved, and the molar ratio of the total amount of hydrogen peroxide added during the reaction to the iron source is 2:1;

[0065] (3) The pH value was adjusted to 3.5 using aqueous ammonia, the reaction temperature was controlled at 60°C, the aging reaction was carried out for 10 hours, and the stirring rate was 150 rpm. After solid-liquid separation, the solid product was washed three times with deionized water, and the washed product was vacuum-dried at 100°C for 6 hours to obtain iron phosphate with a median particle size (D50) of 250 nm.

[0066] Example 4

[0067] The only difference between this embodiment and embodiment 1 is that the mass concentration of hydrogen peroxide is 3%, and the mass concentration of hydrogen peroxide in the reaction system is controlled to be 3%. Other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 5

[0069] The only difference between this embodiment and embodiment 1 is that the mass concentration of hydrogen peroxide is 12%, and the mass concentration of hydrogen peroxide in the reaction system is also controlled to be 12%. Other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Example 6

[0071] The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (2) is 35° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0072] Example 7

[0073] The only difference between this embodiment and embodiment 1 is that the reaction temperature in step (2) is 65° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0074] Comparative Example 1

[0075] This comparative example provides a kind of iron phosphate, and the preparation method of the iron phosphate is as follows:

[0076] (1) mixing ferrous sulfate, phosphoric acid, and water to obtain a mixed salt solution having a ferrous concentration of 0.5 mol / L, a phosphorus concentration of 0.75 mol / L, and a pH of 2.1, and adding hydrogen peroxide having a mass concentration of 7% dropwise to the mixed salt solution, wherein the molar ratio of the total amount of hydrogen peroxide added to the iron source is 1.5:1;

[0077] (2) After the dropwise addition is completed, the pH is adjusted to 3.1 with aqueous ammonia, the reaction temperature is controlled at 50°C, the aging reaction is carried out for 12 hours, the stirring rate is 100 rpm, and the resulting suspension is transferred to a solid-liquid separator for solid-liquid separation. The solid product is washed three times with deionized water, and the washed product is vacuum-dried at 80°C for 8 hours to obtain the ferric phosphate.

[0078] The SEM image of the positive electrode material made of iron phosphate is shown in FIG3 .

[0079] Performance testing:

[0080] The iron phosphate prepared in the embodiment and the comparative example was mixed with lithium hydroxide in a molar ratio of Li:Fe=1.03:1, and glucose corresponding to 8% of the theoretical mass of the synthesized lithium iron phosphate was weighed. The above materials were wet ball-milled and dried, and then placed in a tube furnace. Under a protective atmosphere, the temperature was raised to 750°C at a rate of 3°C / min and calcined for 10 hours to obtain a carbon-coated lithium iron phosphate positive electrode material. The lithium iron phosphate positive electrode material, acetylene black and binder polytetrafluoroethylene were mixed in a mass ratio of 90:10:6, NMP was added and stirred into a slurry, and then coated on aluminum foil to prepare a positive electrode sheet. A lithium sheet was used as the negative electrode, the electrolyte was 1 mol / L LiPF6 / ethylene carbonate (EC) + dimethyl carbonate (DMC) + ethyl methyl carbonate (EMC), Celgard2400 was selected as the diaphragm material, and a button battery with a model number of CR2430 was assembled in a vacuum glove box. The charge and discharge test was carried out with a current of 0.1C and a voltage range of 2.3 to 4.2V. The test results are shown in Table 1:

[0081] Table 1

[0082] As can be seen from Table 1, from Examples 1-3, the 0.1C discharge capacity of the lithium iron phosphate battery prepared from the iron phosphate prepared by the method described in the present disclosure can reach more than 161.57 mAh / g, the 0.5C / 0.1C capacity retention rate can reach more than 97.32%, and the 100-cycle capacity retention rate can reach more than 98.51%.

[0083] By comparing Example 1 with Examples 4-5, it can be seen that in the preparation process of the ferric phosphate described in the present disclosure, the concentration of hydrogen peroxide (the concentration of hydrogen peroxide in the reaction system) affects the performance of the prepared ferric phosphate. When the mass concentration of hydrogen peroxide is controlled at 5-10%, the performance of the prepared ferric phosphate is better. If the concentration of hydrogen peroxide is too high, the oxidation precipitation process rate is too fast, the particles are easily agglomerated, and the electrochemical performance of the material is reduced. If the concentration of hydrogen peroxide is too low, the reaction rate is too slow, the reaction is not sufficient, and the valence state of the obtained material is inconsistent, which affects the electrochemical performance of the material.

[0084] By comparing Example 1 with Examples 6-7, it can be seen that in the preparation process of iron phosphate described in the present disclosure, the reaction temperature will affect the performance of the iron phosphate obtained. When the reaction temperature is controlled at 40-60°C, the performance of the iron phosphate obtained is better. If the reaction temperature is too high, the reaction rate is too fast, resulting in incomplete reaction. If the reaction temperature is too low, the reaction rate is too slow, and the grains are not easy to grow. In the later stage, after complete melting, the temperature is raised to react, which will cause the outer layer particles to be generated too quickly, and the difference in density between the inside and outside is too large, affecting the stability of the material.

[0085] As can be seen from the comparison between Example 1 and Comparative Example 1, the present disclosure pre-freezes the solution containing the ferrous salt and the phosphorus source, controls the flow of hydrogen peroxide through the frozen mixed salt solution, and controls the concentration and flow rate of the hydrogen peroxide to slow the reaction, so that the iron and phosphorus elements in the prepared ferric phosphate precursor are evenly distributed and have few surface defects.

Claims

1. A method for preparing ferric phosphate, the method comprising the following steps: (1) mixing a ferrous salt, a phosphorus source and a solvent to obtain a mixed salt solution, and freezing the mixed salt solution to obtain a frozen mixed salt solution; (2) placing the frozen mixed salt solution in a reflux device, controlling the reflux of the hydrogen peroxide solution between the reflux device and the reaction device, and controlling the concentration of hydrogen peroxide in the system to react until the frozen mixed salt solution is completely dissolved; (3) adjusting the pH in the system to carry out an aging reaction, and performing solid-liquid separation to obtain the iron phosphate.

2. The preparation method according to claim 1, wherein The ferrous salt in step (1) includes any one of ferrous chloride, ferrous sulfate or ferrous nitrate, or a combination of at least two of them.

3. The preparation method according to claim 1 or 2, wherein: The phosphorus source in step (1) includes any one of phosphoric acid, diammonium phosphate, diammonium hydrogen phosphate or ammonium phosphate, or a combination of at least two thereof.

4. The preparation method according to any one of claims 1 to 3, wherein The concentration of iron in the mixed salt solution of step (1) is 0.05-1 mol / L; Optionally, the concentration of phosphorus in the mixed salt solution in step (1) is 0.5 to 1 mol / L; Optionally, the pH of the mixed salt solution in step (1) is 1.8 to 2.

5.

5. The preparation method according to any one of claims 1 to 4, wherein: The temperature of the freezing treatment in step (1) is -30 to -40°C; Optionally, the freezing treatment time in step (1) is 6 to 12 hours.

6. The preparation method according to any one of claims 1 to 5, wherein: The mass concentration of the hydrogen peroxide solution in step (2) is 5-10%; Optionally, the molar ratio of the total molar amount of hydrogen peroxide in the hydrogen peroxide solution in step (2) to the iron element in the iron source is (1-2):

1.

7. The preparation method according to any one of claims 1 to 6, wherein: The reflux rate of the hydrogen peroxide solution in step (2) is 50 to 100 mL / min; Optionally, the mass concentration of hydrogen peroxide in the reaction in step (2) is 5-10%; Optionally, the reaction temperature in step (2) is 40-60°C.

8. The preparation method according to any one of claims 1 to 7, wherein: During the reaction of step (2), phosphoric acid is added to control the pH; Optionally, in step (2), the pH is controlled to be between 1.8 and 2.

5.

9. The preparation method according to any one of claims 1 to 8, wherein: The pH regulator in step (3) includes aqueous ammonia. Optionally, the pH in step (3) is 2.5 to 3.5; Optionally, the temperature of the aging reaction in step (3) is 40 to 80° C.; Optionally, the stirring speed of the aging reaction in step (3) is 100 to 200 rpm; Optionally, the aging reaction time in step (3) is 10 to 60 hours.

10. The preparation method according to any one of claims 1 to 9, wherein: After the solid-liquid separation in step (3), washing and vacuum drying are performed.

11. The preparation method according to claim 10, wherein: The washing detergent includes deionized water.

12. The preparation method according to claim 10 or 11, wherein: The temperature of the vacuum drying treatment is 60-100°C.

13. Iron phosphate, which is prepared by the method according to any one of claims 1 to 12.

14. The iron phosphate according to claim 13, wherein The particle size of the iron phosphate is 100-300 nm.

15. A lithium iron phosphate, which is prepared by mixing and sintering the iron phosphate as claimed in claim 13 or 14 and a lithium source.

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