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CN-122025597-A - Composite positive electrode material, preparation method thereof, positive electrode plate and lithium ion battery

CN122025597ACN 122025597 ACN122025597 ACN 122025597ACN-122025597-A

Abstract

The invention provides a composite positive electrode material, a preparation method thereof, a positive electrode plate and a lithium ion battery. The composite positive electrode material comprises a LiMn x Fe 1‑x‑a‑b La a Ce b PO 4 core, a Zr 1‑c Zn c PO 4 layer and a carbon layer which are sequentially coated on the surface of the LiMn x Fe 1‑x‑a‑b La a Ce b PO 4 core from inside to outside, wherein x is more than or equal to 0.5 and less than or equal to 0.7,0.005, a is more than or equal to 0.03,0.005 and less than or equal to 0.02,0.08, and c is more than or equal to 0.12. La 3+ in the composite positive electrode material occupies the site of Li + , is favorable for improving the diffusion speed of lithium ions, and Ce 3+ dynamically eliminates crystal lattice oxygen vacancies through a valence-changing effect and improves the dissolution activation energy of manganese, so that the dissolution of manganese ions is reduced. The Zr 1‑c Zn c PO 4 layer can block the migration path of Mn 2+ , thereby further reducing the elution of manganese ions.

Inventors

  • XU YU
  • ZHANG JIAN
  • ZHANG WEN
  • FANG YAOGUO

Assignees

  • 上海轩邑新能源发展有限公司

Dates

Publication Date
20260512
Application Date
20260313

Claims (10)

  1. 1. The composite positive electrode material is characterized by comprising a LiMn x Fe 1-x-a-b La a Ce b PO 4 core, a Zr 1-c Zn c PO 4 layer and a carbon layer which are sequentially coated on the surface of the LiMn x Fe 1-x-a-b La a Ce b PO 4 core from inside to outside, wherein x is more than or equal to 0.5 and less than or equal to 0.7,0.005, a is more than or equal to 35 and less than or equal to a 0.03,0.005 and less than or equal to 0.02,0.08, and c is more than or equal to 0.12.
  2. 2. The composite positive electrode material according to claim 1, wherein a is 0.01≤a≤0.02 and/or b is 0.01≤b≤0.02.
  3. 3. The composite positive electrode material according to claim 1 or 2, wherein the LiMn x Fe 1-x-a-b La a Ce b PO 4 core has a volume average particle diameter Dv50 of 0.1 to 5 μm, and/or the Zr 1-c Zn c PO 4 layer has a thickness of 10 to 100nm, and/or the carbon layer has a thickness of 10 to 100nm.
  4. 4. A method of producing the composite positive electrode material according to any one of claims 1 to 3, characterized by comprising: Step S1, mixing raw materials comprising a Li source, a Mn source, a Fe source, a La source, a Ce source, a first P source and water to form a first mixed solution, and then performing a first hydrothermal reaction to obtain a LiMn x Fe 1-x-a-b La a Ce b PO 4 precursor; Step S2, mixing raw materials comprising the LiMn x Fe 1-x-a-b La a Ce b PO 4 precursor, a Zr source, a Zn source, a second P source, a surfactant and water to form a second mixed solution, and then performing a second hydrothermal reaction to form a LiMn x Fe 1-x-a-b La a Ce b PO 4 core and a Zr 1-c Zn c PO 4 layer on the surface of the core to obtain an intermediate product; And step S3, mixing the raw materials comprising the intermediate product and a carbon source, and then performing sintering treatment to form a carbon layer on the outer surface of the Zr 1-c Zn c PO 4 layer far away from the LiMn x Fe 1-x-a-b La a Ce b PO 4 core, thereby obtaining the composite anode material.
  5. 5. The method according to claim 4, wherein the raw materials in the step S1 further include an antioxidant, and the amount of the antioxidant is 0.1-0.5% of the total mass of the antioxidant, the Li source, the Mn source, the Fe source, the La source, the Ce source, and the first P source; The temperature of the first hydrothermal reaction is 120-180 ℃, and/or the heat preservation time of the first hydrothermal reaction is 10-45 min, and/or the heating rate of the first hydrothermal reaction is 2-15 ℃ per min; And/or, the step S1 further comprises the step of adjusting the pH value of the first mixed solution to 4-6 and then carrying out the first hydrothermal reaction; Preferably, the first hydrothermal reaction is performed in a first ultrasonic-microwave reactor, the microwave power of the first ultrasonic-microwave reactor is 300-800W, the microwave frequency is 2.40-2.50 GHz, the ultrasonic power is 50-150W, and the ultrasonic frequency is 26-30 kHz.
  6. 6. The preparation method according to claim 4 or 5, wherein the raw materials in the step S2 further comprise a surfactant, wherein the mass of the LiMn x Fe 1-x-a-b La a Ce b PO 4 precursor is denoted as M, the total mass of the Zr source, the Zn source and the second P source is denoted as a, the mass of the surfactant is denoted as G, and the mass of the surfactant is denoted as G, wherein the ratio of M to G is 100 (1-5): 0.5-2; Preferably, the surfactant is selected from any one or more of cetyltrimethylammonium bromide, fatty alcohol polyoxyethylene ether-9 and tween-80, and further preferably, the surfactant consists of a first surfactant and a second surfactant, the mass ratio of the first surfactant to the second surfactant is 1 (1-3), the first surfactant is the cetyltrimethylammonium bromide, and the second surfactant is the fatty alcohol polyoxyethylene ether-9 and/or tween-80.
  7. 7. The method according to any one of claims 4 to 6, wherein step S2 further comprises adjusting the pH of the second mixed solution to 1 to 3 and then performing the second hydrothermal reaction; The temperature of the second hydrothermal reaction is 50-180 ℃, and/or the heat preservation time of the second hydrothermal reaction is 25-50 min, and/or the temperature rising rate of the second hydrothermal reaction is 2-15 ℃ per min; Preferably, the second hydrothermal reaction is carried out in a second ultrasonic-microwave reactor, the second hydrothermal reaction comprising a pretreatment stage, a first stage, a second stage and a third stage carried out in sequence; wherein in the pretreatment stage, the ultrasonic power of the second ultrasonic-microwave reactor is 200-350W, the temperature is 50-65 ℃, the heat preservation time is 5-10 min, and the ultrasonic frequency is 26-30 kHz; and/or the ultrasonic power of the second ultrasonic-microwave reactor in the first stage is 100-150W, the heating rate is 2-10 ℃ per minute, the temperature is 80-100 ℃, the heat preservation time is 5-10 min, the microwave power is 300-800W, the microwave frequency is 2.40-2.50 GHz, the ultrasonic frequency is 26-30 kHz, and/or the ultrasonic power of the second ultrasonic-microwave reactor in the second stage is 50-100W, the heating rate is 10-15 ℃ per minute, the temperature is 130-150 ℃, the heat preservation time is 10-20 min, the microwave power is 300-800W, the microwave frequency is 2.40-2.50 GHz, the ultrasonic frequency is 26-30 GHz, and/or the ultrasonic power of the second ultrasonic-microwave reactor in the third stage is 50-100W, the heating rate is 2-10 ℃ per minute, the temperature is 150-180 ℃ and the heat preservation time is 5-10 min, the microwave power is 300-800 kHz, the microwave frequency is 2.40-50 kHz, and the ultrasonic frequency is 26-50 kHz.
  8. 8. The production method according to any one of claims 4 to 7, characterized in that the amount of the carbon source is 1 to 5% by mass of the intermediate product; And/or the temperature of the sintering treatment is 400-750 ℃, the heat preservation time of the sintering treatment is 4-8 hours, and the temperature rising rate of the sintering treatment is 2-5 ℃ per minute; the sintering treatment comprises the steps of heating to 400-550 ℃ at a heating rate of 2-5 ℃ per minute, preserving heat for 2-4 hours, heating to 600-750 ℃ at a heating rate of 2-5 ℃ per minute, preserving heat for 2-4 hours, cooling to 400-550 ℃ at a cooling rate of 0.5-1 ℃ per minute, and finally cooling by air.
  9. 9. A positive electrode sheet, characterized in that the positive electrode sheet contains the composite positive electrode material according to any one of claims 1 to 3.
  10. 10. A lithium ion battery comprising a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate is the positive plate of claim 9.

Description

Composite positive electrode material, preparation method thereof, positive electrode plate and lithium ion battery Technical Field The invention relates to the technical field of batteries, in particular to a composite positive electrode material, a preparation method thereof, a positive electrode plate and a lithium ion battery. Background Along with the rapid development of the electric automobile field, the demand for high-performance lithium ion batteries is increasing, and the olivine structure lithium iron phosphate (LiFePO 4) has become a main stream positive electrode material of the power battery due to the advantages of high safety, long cycle life and the like. However, the discharge voltage platform is only 3.45V (vs. Li +/Li), the theoretical energy density is less than or equal to 580Wh/kg, and the higher and higher energy density requirements of the new energy automobile are difficult to meet. Although the rate performance can be improved by means of nanocrystallization, carbon coating and the like, the intrinsic voltage limitation of the material leads to low energy density improvement space. Therefore, finding a positive electrode material that can achieve both high energy density and high safety is a currently urgent problem to be solved. The lithium iron manganese phosphate (LiMn xFe1-xPO4, LMFP) improves the voltage platform to 4.1V (vs. Li +/Li) while maintaining the structural stability of the olivine, and the theoretical energy density is improved by 15-20% compared with the lithium iron phosphate. Is widely regarded as an upgrade substitute material for solving the problem of low energy density of lithium iron phosphate. However, the lithium iron manganese phosphate has two major defects of limited ion/electron conduction, namely one-dimensional lithium ion channels are blocked by PO 4 tetrahedra, the diffusion coefficient of lithium ions is as low as 10 -15cm2/S, and the electron conductivity is only 10 -13 S/cm. 2. Mn dissolution and structural distortion the Jahn-Teller effect of Mn 3+ causes lattice distortion, weakens the structural stability of the electrode, and leads to the destruction of the cathode SEI film and capacity attenuation due to Mn 2+ dissolution amount in the circulation process. At present, aiming at the problems of poor conductivity and manganese dissolution of lithium iron manganese phosphate, the conductivity and manganese dissolution of the lithium iron manganese phosphate are generally improved by means of doping, coating and the like. However, conventional hydrothermal or solid phase processes are not only time consuming but also costly. Therefore, developing a simple, efficient and low-cost preparation method is still a problem to be solved. Disclosure of Invention The invention mainly aims to provide a composite positive electrode material, a preparation method thereof, a positive electrode plate and a lithium ion battery, so as to solve the problems of low conductivity and easy dissolution of manganese ions in a lithium iron manganese phosphate material in the prior art. In order to achieve the above object, according to one aspect of the present invention, there is provided a composite cathode material, the composite positive electrode material comprises a LiMn xFe1-x-a-bLaaCebPO4 core, a Zr 1-cZncPO4 layer and a carbon layer which are sequentially coated on the surface of the LiMn xFe1-x-a-bLaaCebPO4 core from inside to outside, wherein x is more than or equal to 0.5 and less than or equal to 0.7,0.005, a is more than or equal to 0.03,0.005 and less than or equal to 0.02,0.08, and c is more than or equal to 0.12. Further, a is more than or equal to 0.01 and less than or equal to 0.02, and/or b is more than or equal to 0.01 and less than or equal to 0.02. Further, the volume average particle diameter Dv50 of the LiMn xFe1-x-a-bLaaCebPO4 core is 0.1 to 5 μm, and/or the thickness of the Zr 1-cZncPO4 layer is 10 to 100nm, and/or the thickness of the carbon layer is 10 to 100nm. According to one aspect of the invention, the preparation method of the composite positive electrode material comprises the steps of S1, mixing raw materials comprising a Li source, a Mn source, a Fe source, a La source, a Ce source, a first P source and water to form a first mixed solution, performing a first hydrothermal reaction to obtain a LiMn xFe1-x-a-bLaaCebPO4 precursor, S2, mixing raw materials comprising a LiMn xFe1-x-a-bLaaCebPO4 precursor, a Zr source, a Zn source, a second P source, a surfactant and water to form a second mixed solution, performing a second hydrothermal reaction to form a LiMn xFe1-x-a-bLaaCebPO4 core and forming a Zr 1-cZncPO4 layer on the surface of the LiMn xFe1-x-a-bLaaCebPO4 core to obtain an intermediate product, and S3, mixing raw materials comprising an intermediate product and a carbon source, performing sintering treatment, and forming a carbon layer on the outer surface of the Zr 1-cZncPO4 layer far away from the LiMn xFe1-x-a-bLaaCebPO4 co