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CN-122025583-A - Lithium iron phosphate composite material, preparation method thereof, positive plate and secondary battery

CN122025583ACN 122025583 ACN122025583 ACN 122025583ACN-122025583-A

Abstract

The invention provides a lithium iron phosphate composite material, a preparation method thereof, a positive plate and a secondary battery. The lithium iron phosphate composite material comprises a lithium iron phosphate matrix doped with magnesium element and titanium element, and a carbon coating layer coated on at least part of the surface of the lithium iron phosphate matrix, wherein the doping amount of the magnesium element is 0.5-2.0% of the molar amount of the iron element in the lithium iron phosphate matrix, and the doping amount of the titanium element is 0.5-1.5% of the molar amount of the iron element in the lithium iron phosphate matrix. The lithium iron phosphate composite material provided by the invention adopts magnesium element and titanium element doping, the magnesium element optimizes the lattice stability, the titanium element enhances the conductivity, and the cooperative optimization of the lattice structure and the conductive network is realized by precisely controlling the doping amount, so that the cycle performance and the multiplying power performance of the secondary battery are improved.

Inventors

  • PAN KUN
  • YUAN YONG
  • KONG DEXIANG
  • ZHAO SUYING
  • LI JIGANG

Assignees

  • 天津容百斯科兰德科技有限公司

Dates

Publication Date
20260512
Application Date
20260203

Claims (10)

  1. 1. The lithium iron phosphate composite material is characterized by comprising a magnesium element and titanium element doped lithium iron phosphate matrix and a carbon coating layer coated on at least part of the surface of the lithium iron phosphate matrix; the doping amount of the magnesium element is 0.5-2.0% of the molar amount of the iron element in the lithium iron phosphate matrix, and the doping amount of the titanium element is 0.5-1.5% of the molar amount of the iron element in the lithium iron phosphate matrix.
  2. 2. The lithium iron phosphate composite material according to claim 1, wherein the molar ratio of lithium element, composite metal element and phosphorus element in the lithium iron phosphate matrix is (1.01-1.05): (0.96-0.99): 1, and the composite metal element comprises a mixture of iron element, magnesium element and titanium element.
  3. 3. The lithium iron phosphate composite material according to claim 1 or 2, wherein the carbon coating layer is formed by carbonizing a raw material comprising a reducing carbon source and a high-conductivity carbon source having a conductivity of not less than 10 -9 S/cm, and/or, The thickness of the carbon coating layer is 1-5nm.
  4. 4. The lithium iron phosphate composite material according to claim 1, wherein the compacted density of the lithium iron phosphate composite material is not less than 2.65g/cm3, and/or, The average grain diameter of the lithium iron phosphate composite material is 0.6-1.5 mu m.
  5. 5. A method of preparing the lithium iron phosphate composite material of any one of claims 1-4, comprising the steps of: Mixing raw materials comprising a lithium source, a phosphorus source, an iron source, a carbon source, a magnesium source and a titanium source, drying at 150-300 ℃, and then sequentially carrying out low-temperature sintering treatment and high-temperature sintering treatment to obtain the lithium iron phosphate composite material, wherein the temperature of the low-temperature sintering treatment is 300-400 ℃, the temperature of the high-temperature sintering treatment is 650-750 ℃, the content of magnesium element in the magnesium source is 0.5-2.0% of the total iron element molar amount in the iron source, and the content of titanium element in the titanium source is 0.5-1.5% of the total iron element molar amount in the iron source.
  6. 6. The method according to claim 5, wherein the low-temperature sintering treatment is carried out for a holding time of 2 to 4 hours and/or, The temperature rising rate of the low-temperature sintering treatment is 3-5 ℃ per minute, and/or, The heat preservation time of the high-temperature sintering treatment is 8-15h, and/or, The temperature rising rate of the high-temperature sintering treatment is 2-4 ℃ per minute, and/or, The addition amount of the carbon source is 7-26% of the mass of the lithium iron phosphate composite material.
  7. 7. The method of claim 5, wherein the lithium source comprises tri-lithium phosphate, and/or, The iron source comprises a mixture of iron phosphate, iron oxide, and/or, The carbon source comprises a mixture of a reducing carbon source and a high conductivity carbon source comprising polyethylene glycol.
  8. 8. The method according to claim 7, wherein the mass ratio of the reducing carbon source to the high-conductivity carbon source is (5-18): 2-8, and/or, The high-conductivity carbon source further comprises at least one of graphene and carbon nanotubes.
  9. 9. A positive electrode sheet comprising the lithium iron phosphate composite material according to any one of claims 1 to 4, or the lithium iron phosphate composite material produced by the production method according to any one of claims 5 to 8.
  10. 10. A secondary battery comprising the lithium iron phosphate composite material according to any one of claims 1 to 4, or the lithium iron phosphate composite material produced by the production method according to any one of claims 5 to 8, or the positive electrode sheet according to claim 9.

Description

Lithium iron phosphate composite material, preparation method thereof, positive plate and secondary battery Technical Field The invention belongs to the technical field of secondary batteries, and particularly relates to a lithium iron phosphate composite material, a preparation method thereof, a positive plate and a secondary battery. Background The lithium ion battery is used as a core power source of a new energy automobile, an energy storage system and portable electronic equipment, and the performance of the lithium ion battery is directly related to the competitiveness of a terminal product. However, with the continuous expansion of application scenes, the conventional lithium ion battery increasingly exposes a plurality of bottlenecks in comprehensive performance. At present, when commercial lithium ion batteries are pursued for high energy density, the cycle performance and the multiplying power performance are generally remarkably attenuated. The electrode material under the high energy density system has insufficient structural stability in the long-term circulation process, so that the capacity is accelerated to decline, and meanwhile, the internal resistance of the battery is increased along with the increase of the using times, so that the battery is difficult to support continuous high-rate charge and discharge. In addition, the prior art scheme focuses on the improvement of single performance parameters, and collaborative optimization between cycle life and quick charge capacity is difficult to realize. Therefore, how to simultaneously improve the cycle life and the rate performance of the lithium ion battery has become a technical problem that needs to be solved in the art. Disclosure of Invention The invention provides a lithium iron phosphate composite material which has a stable lattice structure and an excellent conductive network, and can improve the cycle performance and the rate capability of a secondary battery. The invention provides a preparation method of a lithium iron phosphate composite material, which is characterized in that the lithium iron phosphate composite material prepared by the preparation method has a stable lattice structure and an excellent conductive network, and can improve the cycle performance and the multiplying power performance of a secondary battery. The invention also provides a positive plate which comprises the lithium iron phosphate composite material or the lithium iron phosphate composite material prepared by the preparation method. Therefore, the positive electrode sheet can improve the rate performance and cycle performance of the secondary battery. The invention also provides a secondary battery, which comprises the lithium iron phosphate composite material, or the lithium iron phosphate composite material prepared by the preparation method, or the positive plate. Therefore, the secondary battery has excellent rate performance and cycle performance. The first aspect of the invention provides a lithium iron phosphate composite material, which comprises a lithium iron phosphate matrix doped with magnesium element and titanium element, and a carbon coating layer coated on at least part of the surface of the lithium iron phosphate matrix; the doping amount of the magnesium element is 0.5-2.0% of the molar amount of the iron element in the lithium iron phosphate matrix, and the doping amount of the titanium element is 0.5-1.5% of the molar amount of the iron element in the lithium iron phosphate matrix. The lithium iron phosphate composite material is characterized in that the molar ratio of lithium element, composite metal element and phosphorus element in the lithium iron phosphate matrix is (1.01-1.05): (0.96-0.99): 1, and the composite metal element comprises a mixture of iron element, magnesium element and titanium element. The lithium iron phosphate composite material as described above, wherein the carbon coating layer is formed by carbonizing a raw material including a reducing carbon source and a high-conductivity carbon source having a conductivity of not less than 10 -9 S/cm, and/or, The thickness of the carbon coating layer is 1-5nm. A lithium iron phosphate composite as described above, wherein the compacted density of the lithium iron phosphate composite is not less than 2.65g/cm3, and/or, The average grain diameter of the lithium iron phosphate composite material is 0.6-1.5 mu m. The second aspect of the invention provides a preparation method of the lithium iron phosphate composite material, which comprises the following steps: Mixing raw materials comprising a lithium source, a phosphorus source, an iron source, a carbon source, a magnesium source and a titanium source, drying at 150-300 ℃, and then sequentially carrying out low-temperature sintering treatment and high-temperature sintering treatment to obtain the lithium iron phosphate composite material, wherein the temperature of the low-temperature sintering treatment is 300-400 ℃,