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CN-118083932-B - Composite ferric phosphate and preparation method and application thereof

CN118083932BCN 118083932 BCN118083932 BCN 118083932BCN-118083932-B

Abstract

Mixing ferric salt solution and hydrochloric acid, heating and stirring, adding phosphate, regulating pH to obtain mixed solution, mixing the mixed solution with hydrogen peroxide, and performing hydrothermal reaction to obtain a mixture of ferric phosphate and ferric hydroxide; and (2) respectively placing the mixture of the ferric phosphate and the ferric hydroxide and the sodium hypophosphite in different areas of the same device, and performing heating treatment on the device to obtain the composite ferric phosphate. The invention prepares the ferric phosphate uniformly doped composite ferric phosphate by a simple hydrothermal method, and the lithium iron phosphate positive electrode material prepared from the composite ferric phosphate has higher ionic conductivity, and further has higher cycle stability and multiplying power capacity.

Inventors

  • YU HAIJUN
  • XIE YINGHAO
  • LI AIXIA
  • LI CHANGDONG

Assignees

  • 广东邦普循环科技有限公司
  • 湖南邦普循环科技有限公司

Dates

Publication Date
20260505
Application Date
20240226

Claims (20)

  1. 1. The preparation method of the composite ferric phosphate is characterized by comprising the following steps of: (1) Mixing an iron salt solution with hydrochloric acid, heating and stirring, adding phosphate, regulating pH to obtain a mixed solution, mixing the mixed solution with hydrogen peroxide, and performing hydrothermal reaction to obtain a mixture of ferric phosphate and ferric hydroxide; (2) Respectively placing the mixture of the ferric phosphate and the ferric hydroxide and sodium hypophosphite in different areas of the same device, and performing heat treatment on the device to obtain the composite ferric phosphate; wherein the molar ratio of the iron element in the ferric salt solution to the phosphorus element in the phosphate is 1 (0.97-0.99), the mass ratio of the total mass of the mixture of the ferric phosphate and the ferric hydroxide to the sodium hypophosphite is (18-20) (0.5-2.5), and the composite ferric phosphate comprises anhydrous ferric phosphate and ferric phosphide.
  2. 2. The method of claim 1, wherein the iron salt solution of step (1) comprises any one or a combination of at least two of an aqueous solution of ferric chloride, an aqueous solution of ferric nitrate, or an aqueous solution of ferric sulfate.
  3. 3. The method of claim 1, wherein the concentration of the iron salt solution is 0.5 to 2mol/L.
  4. 4. The method according to claim 1, wherein the temperature of the heating and stirring is 80-90 ℃.
  5. 5. The preparation method of claim 1, wherein the heating and stirring time is 10-20 min.
  6. 6. The method of claim 1, wherein the phosphate of step (1) comprises any one or a combination of at least two of ammonium hydrogen phosphate, ammonium phosphate, or monoammonium phosphate.
  7. 7. The method according to claim 1, wherein the phosphate is added and then stirred.
  8. 8. The method according to claim 7, wherein the stirring treatment is performed for 10 to 20 minutes.
  9. 9. The method of claim 1, wherein the pH adjusting agent in step (1) comprises hydrochloric acid or sodium hydroxide.
  10. 10. The method according to claim 1, wherein the pH is 2 to 2.5.
  11. 11. The preparation method of claim 1, wherein the mass concentration of the hydrogen peroxide is 20% -40%.
  12. 12. The preparation method of claim 1, wherein the mass ratio of the hydrogen peroxide to the mixed solution is (40-50): 100.
  13. 13. The method of claim 1, wherein the hydrothermal reaction in step (1) is performed at a temperature of 120-180 ℃.
  14. 14. The method of claim 1, wherein the hydrothermal reaction time is 3 to 10 hours.
  15. 15. The method of claim 1, wherein the mixture of iron phosphate and iron oxyhydroxide is not contacted with sodium hypophosphite in a device.
  16. 16. The method according to claim 1, wherein the temperature of the heating treatment in the step (2) is 500 to 600 ℃.
  17. 17. The method according to claim 1, wherein the heating treatment is performed for 4 to 8 hours.
  18. 18. The method of manufacturing according to claim 1, wherein the atmosphere of the heat treatment comprises an inert atmosphere.
  19. 19. A composite iron phosphate, characterized in that it is produced by the method according to any one of claims 1-18.
  20. 20. A lithium iron phosphate positive electrode material, wherein the lithium iron phosphate positive electrode material is prepared by mixing and sintering the composite ferric phosphate and a lithium source according to claim 19.

Description

Composite ferric phosphate and preparation method and application thereof Technical Field The invention belongs to the technical field of battery materials, and relates to composite ferric phosphate, a preparation method and application thereof. Background The lithium iron phosphate anode material rapidly occupies the current market because of the characteristics of good safety performance, environmental protection, high capacity, high cost performance of raw materials and the like. The LiFePO 4 has the defects of lower electronic conductivity and ionic conductivity of 10 -9 S∙cm-1 and 10 -10~10-15 cm2∙s-1 respectively, which directly lead to poor specific capacity and rate charge and discharge performance and limit the application of the LiFePO 4. The iron phosphide has better electric conduction effect, and under higher multiplying power, the electrochemical dynamic property of the material is improved, and good multiplying power performance is shown. CN103094565A discloses a lithium iron phosphate/iron phosphide/carbon composite nanofiber, which comprises, by mass, 50-99% of lithium iron phosphate, 0.5-30% of iron phosphide and 1-20% of carbon, wherein the average diameter of the lithium iron phosphate/iron phosphide/carbon composite nanofiber is 50-500 nm, and spherical particles of iron phosphide exist in the fiber. CN112864362a discloses a method for preparing iron phosphate doped lithium iron phosphate material by converting iron phosphate into iron phosphate at high temperature, which comprises the steps of reacting concentrated phosphoric acid with lithium iron phosphate to form a layer of iron phosphate on the surface of the material, reducing the material at high temperature by hydrogen to form an iron phosphate coating layer, and preparing a carbon coating layer on the surface of the iron phosphate coating layer by vapor deposition. The crystal grain growth of the lithium iron phosphate prepared by the scheme is coarse, so that the ionic conductivity of the material is reduced, and the cycling stability and the multiplying power capacity of the electrode material are further affected. Disclosure of Invention The invention aims to provide a composite ferric phosphate and a preparation method and application thereof, the invention prepares the uniformly doped composite ferric phosphate by a simple hydrothermal method, the lithium iron phosphate positive electrode material prepared from the composite ferric phosphate has higher ionic conductivity, and further has higher cycle stability and rate capacity. In order to achieve the aim of the invention, the invention adopts the following technical scheme: In a first aspect, the present invention provides a method for preparing composite ferric phosphate, the method comprising the steps of: (1) Mixing an iron salt solution with hydrochloric acid, heating and stirring, adding phosphate, regulating pH to obtain a mixed solution, mixing the mixed solution with hydrogen peroxide, and performing hydrothermal reaction to obtain a mixture of ferric phosphate and ferric hydroxide; (2) And respectively placing the mixture of the ferric phosphate and the ferric hydroxide and the sodium hypophosphite in different areas of the same device, and performing heat treatment on the device to obtain the composite ferric phosphate. In the preparation process of the composite ferric phosphate, part of iron source and hydrogen peroxide react with each other in a hydrothermal manner to form ferric hydroxide, the ferric hydroxide and ferric phosphate are synchronously generated, so that the ferric hydroxide is uniformly distributed in the ferric phosphate, then the ferric hydroxide and sodium hypophosphite are placed in a device together, the sodium hypophosphite is pyrolyzed to generate PH 3, the ferric hydroxide is fully phosphorylated to FeP in situ, and the FeP doped ferric phosphate is obtained, and the FeP is uniformly distributed in the ferric phosphate, so that the conductive effect of the ferric hydroxide is fully exerted, and the multiplying power performance of the material is provided. Preferably, the ferric salt solution in step (1) comprises any one or a combination of at least two of an aqueous solution of ferric chloride, an aqueous solution of ferric nitrate, or an aqueous solution of ferric sulfate. Preferably, the concentration of the ferric salt solution is 0.5-2 mol/L, for example, 0.5 mol/L, 0.8 mol/L, 1 mol/L, 1.5 mol/L or 2mol/L, etc. Preferably, the temperature of the heating and stirring is 80-90 ℃, for example, 80 ℃, 82 ℃, 85 ℃, 88 ℃, 90 ℃ or the like. Preferably, the heating and stirring time is 10-20 min, for example, 10min, 12 min, 15min, 18 min or 20min, etc. Preferably, the phosphate of step (1) comprises any one or a combination of at least two of ammonium hydrogen phosphate, ammonium phosphate or ammonium dihydrogen phosphate. Preferably, the molar ratio of the iron element in the iron salt solution to the phosphorus element in the phosphate i