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CN-117125690-B - Lithium iron manganese phosphate precursor and preparation method and application thereof

CN117125690BCN 117125690 BCN117125690 BCN 117125690BCN-117125690-B

Abstract

The invention provides a lithium iron manganese phosphate precursor, a preparation method and application thereof, wherein the chemical general formula of the lithium iron manganese phosphate precursor is Mn x Fe y M 1‑x‑y PO 7/2 , x is 0.5-0.7, y is 0.3-0.5, M is a doped metal element, and the lithium iron manganese phosphate precursor has smaller particle size, uniform components and high tap density, can solve the problems that the lithium iron manganese phosphate precursor has large particle size and low tap density and contains ammonium components, and generates a large amount of ammonia gas when being matched with lithium for sintering, thereby remarkably improving the compaction density and electrochemical performance of the lithium iron manganese phosphate anode material.

Inventors

  • Quan Jiazhi
  • HUA WENCHAO
  • ZHANG KUN
  • XU KAIHUA
  • JIANG XIAOPING

Assignees

  • 格林美股份有限公司

Dates

Publication Date
20260508
Application Date
20230913

Claims (20)

  1. 1. The preparation method of the lithium iron manganese phosphate precursor is characterized in that the chemical general formula of the lithium iron manganese phosphate precursor is Mn x Fe y M 1-x-y PO 7/2 , wherein x is 0.5-0.7, y is 0.3-0.5, and M is a doped metal element; The preparation method of the lithium iron manganese phosphate precursor comprises the following steps: (1) Feeding a metal salt solution, a pH regulator and a phosphate solution into a base solution, and performing coprecipitation reaction to obtain an intermediate product; The metal salt solution comprises manganese salt and ferric salt or manganese salt, ferric salt and M salt, wherein the pH value of the metal salt solution is 1-4; in the feeding process of the step (1), the pH value of the coprecipitation reaction system is gradually reduced; The pH value of the base solution in the step (1) is 7-8; After the feeding in the step (1) is finished, the pH value of the coprecipitation reaction system is 5-6; The coprecipitation reaction in the step (1) is carried out in a reaction kettle, and the addition amount of bottom liquid in the reaction kettle accounts for 1/3-2/3 of the volume of the reaction kettle; (2) Sintering the intermediate product in the step (1) to obtain the lithium iron manganese phosphate precursor; The intermediate product is ferromanganese ammonium phosphate, and NH 3 and H 2 O are removed in the sintering stage of the step (2).
  2. 2. The method of preparing a lithium iron manganese phosphate precursor according to claim 1, wherein M comprises any one or a combination of at least two of Mg, ti, nb, zr or Cu.
  3. 3. The process of claim 1, wherein the feeding of step (1) is completed for a period of 2 to 4 hours.
  4. 4. The process of claim 1, wherein the intermediate product is obtained by aging, washing and vacuum drying after the end of the feeding in step (1).
  5. 5. The method according to claim 4, wherein the number of times of washing is 3 to 5.
  6. 6. The method according to claim 4, wherein the vacuum drying temperature is 60 to 80 ℃.
  7. 7. The method of claim 1, wherein the base fluid of step (1) comprises water.
  8. 8. The method according to claim 1, wherein the concentration of phosphate in the base liquid in the step (1) is 0 to 0.5mol/L.
  9. 9. The method according to claim 1, wherein the concentration of the complexing agent in the base liquid in step (1) is 0 to 0.1mol/L.
  10. 10. The method of claim 9, wherein the complexing agent comprises any one or a combination of at least two of ammonium citrate, ammonium tartrate, ammonium ethylenediamine tetraacetate, or ammonium oxalate.
  11. 11. The method of claim 10, wherein the complexing agent is ammonium citrate and/or ammonium tartrate.
  12. 12. The method according to claim 1, wherein the concentration of total metal ions in the metal salt solution in the step (1) is 0.5 to 4mol/L.
  13. 13. The method according to claim 1, wherein the concentration of the phosphate solution in the step (1) is 0.5 to 3mol/L.
  14. 14. The method according to claim 1, wherein the concentration of the pH adjuster in the step (1) is 10 to 28%.
  15. 15. The method of claim 1, wherein the phosphate solution of step (1) comprises any one of NH 4 H 2 PO 4 、(NH 4 ) 2 HPO 4 or (NH 4 ) 3 PO 4 ) or a combination of at least two.
  16. 16. The method of claim 15, wherein the phosphate solution of step (1) is NH 4 H 2 PO 4 .
  17. 17. The method of claim 1, wherein the pH adjuster of step (1) comprises any one or a combination of at least two of ammonia, urea, or ammonium carbonate.
  18. 18. The method according to claim 1, wherein the pH adjuster in step (1) is aqueous ammonia.
  19. 19. The method according to claim 1, wherein the coprecipitation reaction of step (1) is carried out in a nitrogen atmosphere, wherein the flow rate of nitrogen is 1 to 3L/min.
  20. 20. The process according to claim 1, wherein the coprecipitation reaction of step (1) is carried out under stirring at a speed of 300 to 600r/min.

Description

Lithium iron manganese phosphate precursor and preparation method and application thereof Technical Field The invention belongs to the technical field of batteries, and relates to a lithium iron manganese phosphate precursor, a preparation method and application thereof. Background LFP (LiFePO 4) is widely used in the fields of power tools and energy storage because of its advantages of safety, environmental protection, long cycle life and wide operating temperature range, but has a low energy density due to its low capacity and operating voltage, so a material having a higher energy density and cycle performance comparable to LFP is urgently needed. The lithium iron manganese phosphate is a good choice, and the lithium iron manganese phosphate partially replaces Fe with Mn, so that the discharge platform voltage is improved (from 3.4V to 4.1V), the energy density is improved (15% -20%), and meanwhile, the lithium iron manganese phosphate has the advantages of long cycle life, high thermal stability, high safety and the like. The lithium iron manganese phosphate and the lithium iron phosphate belong to polyanion phosphate, and the preparation process is similar, wherein the solid phase method is simple in preparation, is suitable for industrial production, and the liquid phase method is complex, but the product performance is better. Differently, LFP already has a mature FePO 4 precursor process, and LFMP industry is still in the early stage of development, without precursor, raising industry technology barriers. For example, CN115974681a discloses a method for circularly preparing ferromanganese oxalate, in which manganese and iron sulfate are co-precipitated with oxalate to obtain a precursor of ferromanganese oxalate, and then a phosphorus source, a lithium source and a carbon source are matched, sanded, sprayed and sintered to obtain a lithium ferromanganese phosphate positive electrode material, but the method produces serious gas, resulting in lower compaction density of the material. CN111268664a discloses a ferromanganese phosphate intermediate, lithium ferromanganese phosphate and their manufacturing method, wherein the method for preparing the ferromanganese phosphate intermediate is to drop ferromanganese mixed solution, phosphorus source, nitrogen source and pH regulator into a reaction kettle to precipitate, the method adds various chemical reagents, and impurities are easy to introduce during precipitation, the prepared precursor is sheet-shaped, has large particle size and low tap density, and ammonia gas is generated during the lithium-compounding sintering process, resulting in too low LFMP compaction density. Moreover, since the solubility product constants of K sp＝1.3×10-32,Fe2+ and Mn 2+ of K sp＝10-36,Mn3(PO4)2 of Fe 3(PO4)2 and PO 43- are small and differ by four orders of magnitude, it is easy to precipitate out of proportion when Fe 2+ and Mn 2+ are precipitated with phosphate, and the problem of too fast growth rate and large particle size is often caused by high supersaturation. Based on the above research, it is necessary to provide a lithium iron manganese phosphate precursor, which has a higher tap density, and when the precursor is used for lithium-doped sintering, gas production is less, and the prepared lithium iron manganese phosphate has a high compacted density. Disclosure of Invention The invention aims to provide a lithium iron manganese phosphate precursor, a preparation method and application thereof, wherein the lithium iron manganese phosphate precursor has smaller particle size, uniform components and high tap density, and can solve the problems that the lithium iron manganese phosphate precursor has large particle size, low tap density and contains ammonium components, so that a large amount of ammonia gas is generated when the precursor is sintered together with lithium, thereby remarkably improving the compaction density of a lithium iron manganese phosphate positive electrode material. In order to achieve the aim of the invention, the invention adopts the following technical scheme: in a first aspect, the invention provides a lithium iron manganese phosphate precursor, which has a chemical formula of Mn xFeyM1-x-yPO7/2, wherein x is 0.5-0.7, y is 0.3-0.5, and M is a doped metal element. The precursor of the lithium iron manganese phosphate is ferric manganese pyrophosphate, but not ammonium manganese phosphate, and can avoid the generation of reducing gas in the preparation process of the lithium iron manganese phosphate positive electrode material, and as the lithium iron manganese phosphate is sintered in a reducing atmosphere to easily generate magnetic foreign matters Fe 2 P, mn 2 P and other miscellaneous phases and is harmful to the battery performance, the precursor of the lithium iron manganese phosphate positive electrode material has uniform components and high tap density and does not contain ammonium ions, thereby avoiding the generation of reducing g