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CN-121983557-A - Positive electrode active material, preparation method thereof, positive electrode plate and battery

CN121983557ACN 121983557 ACN121983557 ACN 121983557ACN-121983557-A

Abstract

The application discloses a positive electrode active material and a preparation method thereof, a positive electrode sheet and a battery, wherein the positive electrode active material comprises a matrix, a carbon coating layer and a carbon coating layer, the matrix comprises a lithium iron phosphate material, the carbon coating layer is at least partially coated on the surface of the matrix, the change rate delta b of a unit cell parameter b value of the positive electrode active material in a 4.2V charging state and a 2.5V discharging state is 0.2% <deltab <4%, delta b= (b 1 -b 2 )/b 1 ×100%,b 1 is a b value of the positive electrode active material in a state of discharging from 4.2V to 2.5V, and b 2 is a b value of the positive electrode active material in a state of charging from 4.2V), so that the positive electrode active material has a stable crystal structure and higher compaction density, and the battery prepared from the positive electrode active material has higher energy density and excellent low-temperature performance.

Inventors

  • JIN YUQIANG
  • LIU ZHIHAO
  • ZHENG CHUNYAN
  • HU YINGLI
  • LI JINGJING
  • WU LIANGCE
  • ZHANG XUEQUAN
  • LIU YAFEI
  • CHEN YANBIN

Assignees

  • 北京当升材料科技股份有限公司

Dates

Publication Date
20260505
Application Date
20260331

Claims (16)

  1. 1. A positive electrode active material, characterized by comprising: a matrix comprising a lithium iron phosphate material; the carbon coating layer at least partially coats the surface of the substrate; the change rate delta b of the unit cell parameter b value of the positive electrode active material in a 4.2V charging state and a 2.5V discharging state meets 0.2% <deltab <4%; wherein Δb= (b 1 -b 2 )/b 1 ×100%,b 1 is a b value of the positive electrode active material in a discharge state from 4.2V to 2.5V, and b 2 is a b value of the positive electrode active material in a charge state of 4.2V).
  2. 2. The positive electrode active material according to claim 1, wherein 0.5% <Δb <3%.
  3. 3. The positive electrode active material according to claim 1, wherein the matrix satisfies the general formula: Li a Fe b M c (PO 4 ) d , wherein, the a is more than or equal to 0.95 and less than or equal to 3835≤b≤1, 0 1.10,0.6 is less than or equal to b not more than 1, 0; M comprises at least one of Ti, mg, zn, cu, sr, al, zr, Y, la, ta, mn, W, ca, nb, sn, sb, mo, V, B, si, na.
  4. 4. The positive electrode active material according to claim 1 or 2, wherein the positive electrode active material has a grain size of 120nm to 200nm, optionally 130nm to 190nm.
  5. 5. The positive electrode active material according to claim 1 or 2, wherein the carbon coating layer comprises a carbon material, the mass fraction of the carbon material in the positive electrode active material being 0.9wt% to 1.7wt%, optionally 1wt% to 1.6wt%.
  6. 6. The positive electrode active material according to claim 1 or 2, wherein the positive electrode active material has a D 50 of 0.6 μm to 2.0 μm, optionally 0.7 μm to 1.8 μm, and/or, The positive electrode active material had a compacted density of 2.6g/cm 3 -2.9g/cm 3 at 226 MPa.
  7. 7. The positive electrode active material according to claim 6, wherein the positive electrode active material has a particle size volume distribution curve in which a first characteristic peak and a second characteristic peak are present, and wherein the intensity ratio of the first characteristic peak to the second characteristic peak is 0.5 to 1.9, and optionally, 0.7 to 1.6.
  8. 8. A method for producing the positive electrode active material according to any one of claims 1 to 7, characterized by comprising: dispersing a first ferric phosphate, a lithium source, a first M source, a phosphorus source and a carbon source in a solvent, and carrying out grinding treatment to obtain a first grinding material; Mixing the first abrasive, second ferric phosphate and a solvent, and grinding to obtain a second abrasive, wherein the specific surface area of the first ferric phosphate is smaller than that of the second ferric phosphate; carrying out spray drying treatment on the second grinding material to obtain spray dried material; performing first sintering treatment on the spray-dried material to obtain a sintered material; and mixing the sintering material with a second M source, and performing second sintering treatment to obtain the positive electrode active material.
  9. 9. The method of claim 8, wherein the specific surface area of the first iron phosphate is 5m 2 /g-9m 2 /g, and/or, The specific surface area of the second ferric phosphate is 8m 2 /g-14m 2 /g.
  10. 10. The method of claim 9, wherein the molar ratio of elemental iron to elemental phosphorus in the first iron phosphate is between 0.945 and 0.985, and/or, The molar ratio of the iron element to the phosphorus element in the second ferric phosphate is 0.945-0.985.
  11. 11. The method of claim 9, wherein the mass ratio of the first iron phosphate to the second iron phosphate is (1:1) - (5:1).
  12. 12. The method of claim 8, wherein the first abrasive has a D 50 of 0.1 μm to 0.6 μm and/or, The second abrasive has a D 50 of 0.3 μm to 1.2 μm.
  13. 13. The method of claim 8, wherein the first sintering process is performed at a temperature of 730 ℃ to 850 ℃ for a time of 4 hours to 18 hours, and/or, The temperature of the second sintering treatment is 700-800 ℃ and the time is 4-16 h.
  14. 14. The method of claim 8, wherein the lithium source comprises at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, and/or, The first M source and the second M source respectively and independently comprise at least one of oxide, hydroxide, carbonate, fluoride and sulfate corresponding to M element, and/or, The carbon source comprises at least one of glucose, sucrose, organic polymer, and/or, The phosphorus source comprises at least one of phosphoric acid, ammonium phosphate and ammonium dihydrogen phosphate.
  15. 15. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 7, or the positive electrode active material prepared by the method according to any one of claims 8 to 14.
  16. 16. A battery comprising the positive electrode sheet of claim 15.

Description

Positive electrode active material, preparation method thereof, positive electrode plate and battery Technical Field The application relates to the technical field of lithium batteries, in particular to a positive electrode active material, a preparation method thereof, a positive electrode plate and a battery. Background The lithium iron phosphate is used as an anode active material of the lithium ion battery, and is widely applied to electric automobiles and energy storage systems due to the advantages of high safety, long cycle life, low cost and the like. However, the related fabrication techniques still have significant drawbacks in achieving ‌ high compacted density, structural stability, and low temperature performance ‌. These defects limit the potential of lithium iron phosphate materials in high energy density and extreme environmental applications. It should be noted that the foregoing statements are merely to provide background information related to the present disclosure and may not necessarily constitute prior art. Disclosure of Invention In a first aspect of the present application, there is provided a positive electrode active material comprising a matrix comprising a lithium iron phosphate material, a carbon coating layer at least partially coating the surface of the matrix, wherein the positive electrode active material has a stable crystal structure and a high compacted density, and a battery prepared therefrom has a high energy density and excellent low temperature performance, wherein the change rate Δb of the cell parameter b value in a 4.2V charge state and a 2.5V discharge state satisfies 0.2% <Δb <4%, wherein Δb= (b 1-b2)/b1×100%,b1 is the b value of the positive electrode active material in a 4.2V discharge state and b 2 is the b value of the positive electrode active material in a 4.2V charge state). In some embodiments, 0.5% <Δb <3%. Thus, the structural stability of the positive electrode active material is further improved. In some embodiments, the matrix satisfies the general formula Li aFebMc(PO4)d, where 0.95 A≤ 1.10,0.6 b≤1, 0≤c≤ 0.6,0.90 d≤1.10, and M includes at least one of Ti, mg, zn, cu, sr, al, zr, Y, la, ta, mn, W, ca, nb, sn, sb, mo, V, B, si, na. Therefore, the doping of M element is beneficial to improving the lithium ion transmission efficiency and improving the structural stability of the positive electrode active material. In some embodiments, the positive electrode active material has a grain size of 120nm to 200nm, optionally 130nm to 190nm. Therefore, the lithium ion diffusion path is favorably shortened, and meanwhile, the positive electrode active material can better adapt to tiny volume change in the charge and discharge process, thereby being beneficial to improving the structural stability. In some embodiments, the carbon coating layer includes a carbon material, the mass fraction of the carbon material in the positive electrode active material being 0.9wt% to 1.7wt%, optionally 1wt% to 1.6wt%. Thus, the electron conductivity of the positive electrode active material is advantageously improved. In some embodiments, the positive electrode active material has a D 50 of 0.6 μm to 2.0 μm, optionally 0.7 μm to 1.8 μm. Thus, the lithium ion transmission path is shortened, and the processability of the positive electrode active material is improved. In some embodiments, the positive electrode active material has a compacted density of 2.6g/cm 3-2.9g/cm3 at 226 MPa. This is advantageous in improving the energy density of a battery using the positive electrode active material. In some embodiments, the particle size volume distribution curve of the positive electrode active material has a first characteristic peak and a second characteristic peak, the intensity ratio of the first characteristic peak to the second characteristic peak being from 0.5 to 1.9, optionally from 0.7 to 1.6. Therefore, the close packing among the positive electrode active material particles is facilitated, and the compaction density of the positive electrode active material is improved. In a second aspect of the present application, the present application provides a method for preparing the above positive electrode active material, which comprises dispersing a first iron phosphate, a lithium source, a first M source, a phosphorus source and a carbon source in a solvent, performing a grinding treatment to obtain a first abrasive, mixing the first abrasive with a second iron phosphate and the solvent, performing the grinding treatment to obtain a second abrasive, wherein the specific surface area of the first iron phosphate is smaller than the specific surface area of the second iron phosphate, performing a spray drying treatment on the second abrasive to obtain a spray-dried material, performing a first sintering treatment on the spray-dried material to obtain a sintered material, mixing the sintered material with the second M source, and performing a second sintering treatment to obtain