CN115513515B - Secondary battery and preparation method thereof - Google Patents

Secondary battery and preparation method thereof Download PDF

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Publication number
CN115513515B
CN115513515B CN202211199227.4A CN202211199227A CN115513515B CN 115513515 B CN115513515 B CN 115513515B CN 202211199227 A CN202211199227 A CN 202211199227A CN 115513515 B CN115513515 B CN 115513515B
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positive electrode
active material
iron phosphate
lithium iron
electrode active
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CN115513515A (en
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张科
陈巍
褚春波
张耀
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Xinwangda Power Technology Co ltd
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Xinwangda Power Technology Co ltd
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Priority to PCT/CN2022/139492 priority patent/WO2024066071A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M2010/4292—Aspects relating to capacity ratio of electrodes/electrolyte or anode/cathode
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
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  • Inorganic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

Disclosed herein is a secondary battery and a method of manufacturing the same. The secondary battery comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer contains a positive electrode active material; the positive electrode active material includes lithium iron phosphate particles; 5 μm×5 μm is one of the unit sectional areas, based on 100% of the total amount of the lithium iron phosphate particles per unit sectional area in the positive electrode active material layer: the quantity of the lithium iron phosphate particles with the particle diameter of 0.4-2 mu m accounts for 70-95%. According to the preparation method, the lithium iron phosphate with uniform particle morphology is prepared, the particle size distribution of the lithium iron phosphate is controlled, and the capacity and the cycle performance of the battery can be remarkably improved.

Description

Secondary battery and preparation method thereof
Technical Field
The invention belongs to the field of secondary batteries, and relates to a secondary battery and a preparation method thereof.
Background
Secondary batteries, such as lithium ion batteries, are widely used in various fields such as consumer electronics, automobiles, electric vehicles, energy storage, and the like, due to their characteristics of high voltage and high energy density, and because of their cleanliness, high efficiency, and no environmental pollution. The lithium iron phosphate positive electrode active material is an ideal positive electrode active material because of low cost, no pollution and good safety performance. However, the lithium iron phosphate positive electrode active material has a problem of low theoretical capacity.
Therefore, it is necessary to provide the positive electrode sheet with a higher energy density.
Disclosure of Invention
An object of the present application is to provide a secondary battery and a method of manufacturing the same.
According to the method, the lithium iron phosphate with uniform particle morphology is prepared, the particle size distribution is controlled, and the distribution of the quantity of lithium iron phosphate particles under specific particle size in the positive electrode active material layer is controlled, so that the capacity and the cycle performance of the battery are obviously improved.
The application provides a secondary battery, which comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer contains a positive electrode active material;
the positive electrode active material includes lithium iron phosphate particles;
5 μm×5 μm is one of the unit sectional areas, based on 100% of the total amount of the lithium iron phosphate particles per unit sectional area in the positive electrode active material layer:
the quantity of the lithium iron phosphate particles with the particle diameter of 0.4-2 mu m accounts for 75-95 percent.
In the application, the total number of the lithium iron phosphate particles in the unit sectional area in the positive electrode active material layer is obtained through a scanning electron microscope test;
the particle size of the lithium iron phosphate particles is 0.4-2 μm, and the particle size value is specifically the maximum value of the measured length of single particles.
In the secondary battery described above, the number of particles having a particle diameter of > 2 μm in the lithium iron phosphate particles is 10% or less, and the number of particles having a particle diameter of 0.4 μm or less and 0.1 μm or more in the lithium iron phosphate particles is 15% or less.
In the secondary battery described above, the surface of the lithium iron phosphate material particles may have a carbon material, and the content of the carbon material may be 0.5% to 2% based on the mass of the positive electrode active material.
In the above secondary battery, the positive electrode active material layer contains an M element containing at least one of Ti, V, and Zr;
the M element content may be 100ppm to 3000ppm based on the weight of the positive electrode active material layer.
In the above secondary battery, the positive electrode active material particles satisfy at least one of the following characteristics:
(a) The Dv10 of the lithium iron phosphate particles is 0.1-0.5 mu m, the Dv50 is 0.7-1.5 mu m, and the Dv90 is 1.5-5 mu m;
(b) The lithium iron phosphate particles satisfy (Dv 90-Dv 10)/dv50=0.1 to 10.
In the application, the morphology distribution uniformity of the prepared positive electrode plate particles is improved by adjusting the particle size distribution of the lithium iron phosphate particles.
In the secondary battery, the powder compaction density of the lithium iron phosphate particles under the pressure of 30KN is more than 2.3g/cm 3 When the compaction of the powder is lower than 2.3g/cm 3 The compaction density of the lithium iron phosphate positive electrode plate is affected.
In the secondary battery, a conductive layer is disposed on the positive electrode current collector, and the thickness of the conductive layer may be 0.5 to 10 μm.
In the secondary battery, the positive electrode current collector is provided with a conductive layer, and the thickness of the conductive layer may be 0.5 μm to 3 μm.
In the secondary battery, the secondary battery further comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the specific surface area of the negative electrode active material is denoted as A 1 m 2 Per gram, the specific surface area of the positive electrode active material is denoted as A 2 m 2 Per gram, satisfies 0.05.ltoreq.A 1 /A 2 ≤0.3。
In the secondary battery, A is more than or equal to 0.5 1 ≤4，9≤A 2 ≤13。
The application also provides an electric device comprising the secondary battery.
The application has the following beneficial effects:
according to the method, the energy density of the lithium iron phosphate positive electrode plate can be remarkably improved by regulating and controlling the proportion of the quantity of lithium iron phosphate particles with the particle size of 0.4-2 mu m in the positive electrode plate to the quantity of total lithium iron phosphate particles in the unit area (5 mu m multiplied by 5 mu m).
Drawings
FIG. 1 is a CP-SEM image of a lithium iron phosphate positive electrode sheet according to example 1 of the present invention.
Detailed Description
The experimental methods used in the following examples are conventional methods unless otherwise specified.
Materials, reagents and the like used in the examples described below are commercially available unless otherwise specified.
According to the method, the particle morphology of the lithium iron phosphate material is selected, the particle size distribution of particles is optimized, and the processing technology of the positive electrode plate is adjusted, so that the quantity-to-proportion distribution condition of the positive electrode plate under the specific particle size in the cross section direction is regulated, and the energy density of the lithium iron phosphate secondary battery is remarkably improved.
The application provides a secondary battery, which comprises a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer contains a positive electrode active material;
the positive electrode active material includes lithium iron phosphate particles;
5 μm×5 μm is one of the unit sectional areas, based on 100% of the total amount of the lithium iron phosphate particles per unit sectional area in the positive electrode active material layer:
the quantity of the lithium iron phosphate particles with the particle diameter of 0.4-2 mu m accounts for 75-95 percent. For example, 75%, 78%, 80%, 83%, 85%, 88%, 90%, 92%, 95% or any two thereof. When the quantity of the lithium iron phosphate particles with the particle size of 0.4-2 mu m is in the range, the interfacial charge transfer sites of the positive electrode active material and the electrolyte on the positive electrode plate are increased, so that the charge transfer resistance at the interface is reduced; meanwhile, the anode active material and the conductive material can be uniformly mixed, the formed conductive network is better, and the capacity retention rate and the energy density of the secondary battery can be improved.
In some embodiments of the present application, the amount of lithium iron phosphate particles having a particle size of 0.4 μm to 2 μm is 82% to 95%. When the quantity of the lithium iron phosphate particles with the particle size of 0.4-2 μm is within the range, the distribution of the positive electrode active material particles in the positive electrode active material layer is more reasonable, the contact area between the particles is larger, the charge transfer resistance is smaller, the conductive network is more perfect, and the comprehensive performance of the battery is better.
In the application, the total number of the lithium iron phosphate particles in the unit sectional area in the positive electrode active material layer is obtained through a scanning electron microscope test;
the particle size of the lithium iron phosphate particles is 0.4-2 μm, and the particle size value is specifically the maximum value of the measured length of single particles.
In some embodiments of the present application, the lithium iron phosphate particles have a particle size > 2 μm and a particle count of less than or equal to 10%. For example, the ratio may be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10% or a range of any two of these. When the particle number of the lithium iron phosphate particles with the particle diameter more than 2 mu m is within the range, the particle size distribution of the positive electrode active material particles can be in a proper range, the dispersion condition of the positive electrode active material particles in the positive electrode active material layer can be in a more reasonable state, the contact points between the conductive material and the positive electrode active material are increased, the transfer of electrons is facilitated, and the secondary battery has higher energy density and better cycle performance.
In some embodiments of the present application, the lithium iron phosphate particles have a particle size > 2 μm and a particle count of less than or equal to 8%. When the particle quantity of the lithium iron phosphate particles with the particle diameter more than 2 mu m is within the range, the reduction of the utilization rate of partial space in the positive electrode plate caused by the accumulation of large particles can be reduced, the contact area between the particles is reduced, and the compaction density of the positive electrode plate is influenced, so that the secondary battery has better comprehensive performance.
In some embodiments of the present application, the lithium iron phosphate particles have a particle size > 2 μm and a particle count of greater than or equal to 0.5%. When the particle diameter of the lithium iron phosphate particles is within the above range, the overall performance of the secondary battery is superior.
In some embodiments of the present application, the number of particles of the lithium iron phosphate particles having a particle size of less than 0.4 μm and greater than or equal to 0.1 μm is less than or equal to 15%. For example, the ratio may be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15% or a range of any two of these. When the particle number of the lithium iron phosphate particles with the particle diameter smaller than 0.4 mu m and larger than or equal to 0.1 mu m is within the range, the particle diameter distribution of the positive electrode active material particles can be in a proper range, the contact surface between the positive electrode active material particles can be increased, the contact points between the conductive material and the positive electrode active material are increased, and the transfer of electrons is facilitated; meanwhile, the quantity of lithium iron phosphate particles with the particle size in the range can be controlled, so that side reactions between electrolyte and positive electrode active material particles can be reduced, and the secondary battery has higher energy density and better cycle performance.
In some embodiments of the present application, the number of particles of the lithium iron phosphate particles having a particle size of less than 0.4 μm and greater than or equal to 0.1 μm is 1% to 12%.
In some embodiments of the present application, the number of particles of the lithium iron phosphate particles having a particle size of less than 0.4 μm and greater than or equal to 0.1 μm is 2% to 10%. When the number of particles having a particle diameter of less than 0.4 μm and greater than or equal to 0.1 μm in the lithium iron phosphate particles is within the above range, the reaction area of the positive electrode active material particles and the electrolyte can be within a proper range, and unnecessary side reactions in the secondary battery can be further reduced, so that the secondary battery has better overall performance.
In some embodiments of the present application, the surface of the lithium iron phosphate particles is provided with a carbon material, and the content of the carbon material may be 0.5% to 2% based on the mass of the positive electrode active material. For example, the content may be 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.8%, 2% or a range of any two of these. When the content of the carbon material in the positive electrode active material is within the above range, the conductivity of the positive electrode active material can be improved while having less influence on the energy density of the secondary battery.
In some embodiments of the present application, the lithium iron phosphate particles are provided with a carbon material on the surface thereof, and the content of the carbon material may be 0.8% to 1.7% based on the mass of the positive electrode active material. When the content of the carbon material is within the above range, the thickness of the conductive layer on the surface of the positive electrode active material particles is within a proper range, and the conductive network is relatively complete, so that the overall performance of the secondary battery is superior.
In some embodiments of the present application, the carbon material has superior electrical conductivity properties, for example, the carbon material comprises amorphous carbon and/or conductive carbon black.
In some embodiments of the present application, the carbon material particles have a particle size of less than 0.1 times the particle size of the lithium iron phosphate. When the particle size of the carbon material is within the range, the particles of the positive electrode active material can be better coated, so that the conductive network on the surface of the particles of the positive electrode active material is more complete, the conductive network formed by the positive electrode plate is diversified, and the improvement of the comprehensive performance of the secondary battery is facilitated.
In some embodiments of the present application, the positive electrode active material layer includes an M element including at least one of Ti, V, or Zr. The M element can increase the structural stability of the positive electrode active material, and can improve the conductivity of the positive electrode plate, so that the performance of the secondary battery is better.
In some embodiments of the present application, the positive electrode active material layer includes an M element including Ti.
In some embodiments of the present application, the M element content may be 100ppm to 3000ppm based on the weight of the positive electrode active material layer. For example, it may be 100ppm, 300ppm, 500ppm, 800ppm, 1000ppm, 1200ppm, 1400ppm, 1500ppm, 1540ppm, 1568ppm, 1578ppm, 1620ppm, 1637ppm, 1659ppm, 1673ppm, 1697ppm, 1700ppm, 1701ppm, 1900ppm, 2000ppm, 2300ppm, 2500ppm, 2800ppm, 3000ppm or a range of any two of these.
In some embodiments of the present application, the M element content may be 500ppm to 2500ppm based on the weight of the positive electrode active material layer.
In some embodiments of the present application, the lithium iron phosphate particles Dv10 are 0.1 μm to 0.5 μm. For example, it may be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.37 μm, 0.38 μm, 0.39 μm, 0.35 μm, 0.4 μm, 0.41 μm, 0.45 μm, 0.5 μm or a range of any two of these.
In some embodiments of the present application, the lithium iron phosphate particles Dv50 are 0.7 μm to 1.5 μm. For example, it may be 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.08 μm, 1.07 μm, 1.1 μm, 1.11 μm, 1.13 μm, 1.2 μm, 1.3 μm, 1.5 μm, 1.51 μm or a range of any two thereof.
In some embodiments of the present application, the lithium iron phosphate particles Dv90 are 1.5 μm to 5 μm. For example, it may be 1.5 μm, 1.9 μm, 2 μm, 2.5 μm, 3 μm, 3.2 μm, 3.21 μm, 3.25 μm, 3.28 μm, 3.30 μm, 3.34 μm, 3.35 μm, 3.38 μm, 3.40 μm, 3.5 μm, 3.8 μm, 4 μm, 4.94 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.5 μm or a range composed of any two thereof.
When the volume particle size distribution of the positive electrode active material is within the above range, the particle distribution of the positive electrode active material in the positive electrode sheet can be made in a more appropriate state.
In the application, dv10, dv50 and Dv90 of the lithium iron phosphate particles can be measured by a laser particle sizer, and the dispersing agent is deionized water.
In some embodiments of the present application, the lithium iron phosphate particles satisfy (Dv 90-Dv 10)/dv50=0.1 to 10. For example, it may be 0.1, 0.5, 1, 1.5, 1.8, 2.0, 2.01, 2.2, 2.5, 2.60, 2.66, 2.68, 2.69, 2.74, 2.75, 2.8, 2.88, 3.0, 3.2, 3.5, 3.79, 3.8, 4.0, 4.04, 4.5, 4.8, 5, 6, 7, 8, 10 or a range composed of any two of them. The particle size distribution of the lithium iron phosphate particles is adjusted to improve the uniform morphology distribution of the prepared positive electrode plate particles. The secondary battery has better cycle performance and higher energy density.
In some embodiments of the present application, the lithium iron phosphate particles satisfy a (Dv 90-Dv 10)/Dv 50 range of 1.8-4.5.
In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of greater than 2.3g/cm at a pressure of 30KN 3 . In some embodiments of the present application, the lithium iron phosphate particles are powder compacted at a pressure of 30KNThe solid density is more than 2.35g/cm 3 . In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of less than or equal to 3.5g/cm at a pressure of 30KN 3 . In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of less than or equal to 3.0g/cm at a pressure of 30KN 3 . In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of 2.3 to 3.0g/cm at a pressure of 30KN 3 . In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of 2.35 to 2.9g/cm at a pressure of 30KN 3 . In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of 2.35 to 2.8g/cm at a pressure of 30KN 3 . In some embodiments of the present application, the lithium iron phosphate particles have a powder compaction density of 2.35 to 2.65g/cm at a pressure of 30KN 3 . When the powder compaction density of the lithium iron phosphate particles is in the range, the compaction density of the prepared positive electrode plate is higher, so that the secondary battery has better cycle performance and higher energy density.
In the secondary battery, the positive electrode current collector is provided with a conductive layer, and the thickness of the conductive layer may be 0.5 μm to 10 μm.
In the secondary battery, the positive electrode current collector is provided with a conductive layer, and the thickness of the conductive layer may be 0.5 μm to 3 μm. When the thickness of the conductive layer is in the above range, the conductivity of the positive electrode sheet can be further improved, and the energy density of the secondary battery is in a better range.
In the secondary battery, the secondary battery further comprises a negative electrode plate, the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the specific surface area of the negative electrode active material is denoted as A 1 m 2 Per gram, the specific surface area of the positive electrode active material is denoted as A 2 m 2 Per gram, satisfies 0.05.ltoreq.A 1 /A 2 Less than or equal to 0.3. For example, it may be 0.027, 0.05, 0.07, 0.082, 0.09, 0.095, 0.096, 0.097, 0.098, 0.099, 0.1, 0.103, 0.109, 0.13, 0.15, 0.159, 0.17, 0.177, 0.2, 0.22, 0.211, 0.239, 0.25. 0.265, 0.28, 0.3, 0.353 or any two numbers thereof. When A is 1 /A 2 In the above range, the reaction efficiency of the battery can be more matched in the charge and discharge process of the battery by the positive electrode active material and the negative electrode active material, and unnecessary side reactions are reduced, so that the overall performance of the battery is better.
In the secondary battery, A is more than or equal to 0.5 1 And is less than or equal to 4. For example, it may be 0.5, 1.0, 1.1, 1.5, 1.7, 1.8, 2.0, 2.3, 2.5, 2.7, 3.0, 3.2, 3.5, 4 or a range of any two numbers thereof.
In the secondary battery, A is more than or equal to 1.5 1 ≤4。
In the secondary battery, A is more than or equal to 9 2 And is less than or equal to 13. For example, it may be 9, 9.5, 10, 10.1, 10.5, 10.7, 11, 11.1, 11.2, 11.3, 11.5, 11.6, 12, 12.5, 12.8, 13 or a range of any two of these numbers.
The application also provides an electric device comprising the secondary battery.
In the secondary battery, the positive electrode plate comprises the following components in percentage by mass, wherein the total amount is 100 percent:
96% -99% of the positive electrode active material layer;
1% -2% of the conductive agent;
1% -2% of the binder.
In the secondary battery, the conductive agent may comprise the following components in percentage by mass:
80-90% of conductive carbon black SP and 10-20% of conductive graphite.
In the application, a conductive agent with better conductivity is selected to improve the conductivity; the consumption of the conductive agent and the binder is reduced, and the compaction density of the lithium iron phosphate positive plate is improved, so that the energy density of the secondary battery can be improved.
The application also provides a preparation method of the positive electrode plate in the secondary battery, which comprises the following steps:
mixing the positive electrode active material, the conductive agent and the binder according to a required proportion, and adding a solvent; then transferring into a vacuum stirrer for low-speed dispersion and high-speed dispersion, and performing vacuum inversion defoaming after the dispersion is finished to obtain anode slurry; uniformly coating the two sides of the positive electrode slurry on a substrate, drying, and carrying out cold pressing and cutting to obtain the positive electrode plate;
wherein the solvent comprises N-methylpyrrolidone;
the rotation speed of the low-speed dispersion can be 500 r/min-2500 r/min, for example, 500 r/min-800 r/min, 800 r/min-2500 r/min, 600-2300 r/min, 700 r/min-2000 r/min, 700 r/min-1800 r/min, 500 r/min-1000 r/min or 500 r/min-1500 r/min; the time may be 0.5 to 4 hours, for example, 0.5 to 3.5 hours, 0.5 to 3 hours, 0.5 to 2.5 hours, 0.5 to 2 hours, 0.5 to 1.5 hours, 1 to 2.5 hours, 1 to 2 hours.
The high-speed dispersion speed is 2500-5000 r/min, for example, 2500-3500 r/min, 3500-5000 r/min, 2500 r/min-4000 r/min, 2800 r/min-3800 r/min, 2800 r/min-3500 r/min or 3000-4500 r/min; the time is 3 to 8 hours, and can be specifically 3 to 4.5 hours, 4.5 to 8 hours, 4.5 to 5.5 hours, 3.5 to 7 hours, 4.0 to 7.5 hours or 4 to 6 hours; the rotating speed of the slurry during dispersion is increased, so that the conductive agent and the binder are fully and uniformly dispersed;
the viscosity of the positive electrode slurry can be 3000 mPas-5000 mPas;
the substrate is aluminum foil or carbon-coated aluminum foil, and the temperature of drying can be 100-120 ℃.
Example 1
(1) The preparation method of the positive electrode active material comprises the following specific steps:
a) Firstly, anhydrous ferric phosphate and lithium carbonate are weighed according to the mol ratio of 1:1.05, then 0.2wt% of titanium dioxide is mixed as an ion doping additive, then pure water is added to prepare slurry, and ball milling is carried out. B) The slurry after ball milling is transferred into a sand mill for sand milling, and the grain diameter D of sand milling products is controlled V 50 is 0.8 μm. C) Adding 5wt% of glucose as an organic carbon source into the sanded slurry, keeping the temperature of the slurry at 80-85 ℃ (specifically 80 ℃), slowly stirring for 2 hours, and then performing spray drying to obtain carbon-coated lithium iron phosphate precursor powder. D) Precursor is preparedTransferring the powder into a sintering furnace, heating from room temperature to 380 ℃ at a heating rate of 10 ℃/min under the protection of nitrogen, and preserving heat for 4 hours; then sintering for 10 hours at the temperature rising rate of 10 ℃/min to 700 ℃ and then naturally cooling to obtain the sintered powder. E) Pulverizing the sintered material by jet mill, and controlling pulverizing grain diameter D V 10 is in the range of 0.41 μm; d (D) V 50 particle size range 1.08 μm; d (D) V 90-degree particle size is 3.3 μm, and then the carbon-coated lithium iron phosphate anode active material (the mass percentage of carbon coated on the surface of the lithium iron phosphate material is 1.35%) is obtained through sieving and electric current iron removal.
(2) Preparing a positive electrode plate:
a) Particle size distribution Range (D) V 10 is 0.41 μm, D V 50 is 1.08 μm, D V 90 is 3.3 μm) of lithium iron phosphate positive electrode active material (specific surface area 11.3m 2 /g), binder polyvinylidene fluoride (PVDF for short), conductive agent SP and conductive graphite (80 wt%:20 wt%) mixing them according to the mass ratio of 97:1.5:1.5, adding solvent N-methyl pyrrolidone NMP; b) Then, the mixture is transferred into a vacuum stirrer to be dispersed at a low speed (the rotation speed is 800r/min, the dispersing time is 0.5 h) and at a high speed (the rotation speed is 3500r/min, the dispersing time is 4.5 h), and after the dispersing is finished, the mixture is subjected to vacuum inversion defoaming, and finally, the positive electrode slurry with the solid content of 56% and the viscosity of 4200 Pa.s is obtained; c) Uniformly coating the positive electrode slurry on two surfaces of a carbon-coated aluminum foil (the thickness of a coating layer containing double-sided carbon is 1 μm respectively) with the thickness of 14 μm; d) Drying the coated pole piece through a baking oven at 100-120 ℃; e) Cold pressing and cutting to obtain the positive pole piece.
(3) Preparing a negative electrode plate:
graphite as a negative electrode active material (specific surface area 1.1m 2 Mixing thickener sodium carboxymethyl cellulose, adhesive styrene-butadiene rubber and conductive agent acetylene black according to a mass ratio of 97:1:1:1, adding deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer; uniformly coating the negative electrode slurry on a copper foil with the thickness of 6 mu m; and transferring the coated pole piece to a baking oven at 120 ℃ for drying, and then carrying out cold pressing and slitting to obtain the negative pole piece.
(4) Preparing an electrolyte:
the organic solvent is a mixed solution containing Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20:60. At the water content<In a 10ppm argon atmosphere glove box, the LiPF was sufficiently dried 6 And dissolving lithium salt in an organic solvent, and uniformly mixing to obtain the electrolyte. Wherein the concentration of the lithium salt is 1mol/L.
(5) Preparation of a separation film:
a polypropylene isolating film of 12 μm is selected.
(6) Preparation of the battery:
and sequentially stacking the positive electrode plate, the isolating film and the negative electrode plate, enabling the isolating film to be positioned between the positive electrode plate and the negative electrode plate to play a role of isolation, winding the isolating film into square bare cells, then loading the square bare cells into a shell, baking the square bare cells at 80 ℃ to remove water, injecting corresponding nonaqueous electrolyte, sealing the square bare cells, and obtaining finished batteries after the procedures of standing, hot-cold pressing, formation, clamping, capacity division and the like.
The CP-SEM of the lithium iron phosphate positive electrode sheet in example 1 of the present invention is shown in FIG. 1.
As can be seen from FIG. 1, the lithium iron phosphate material of the present invention has uniform and moderate particle size distribution, and the particle size of LiFePO of the unit area in the unit area of the positive electrode sheet prepared by the method is 0.4-2 μm 4 The total quantity of the positive electrode plates is 93 percent, and the compacted density of the positive electrode plates is 2.71g/cm 3 。
Example 2
The preparation method and conditions are the same as in example 1 of the present invention, except that: (2) In the preparation process of the positive pole piece, a conductive agent is selected as a conductive agent SP.
Example 3
The preparation method and conditions are the same as in example 1 of the present invention, except that: (2) In the preparation process of the positive pole piece, a conductive agent SP and conductive graphite (90 wt%:10 wt%) are selected.
Example 4
The preparation method and conditions are the same as in example 1 of the present invention, except that: (2) In the preparation process of the positive pole piece, a conductive agent SP and conductive graphite (70 wt%:30 wt%) are selected.
Example 5
The preparation method and conditions are the same as in example 1 of the present invention, except that: (2) The mass ratio of the lithium iron phosphate anode active material, the binder and the conductive agent added in the preparation process of the anode sheet is 96:2:2.
example 6
The preparation method and conditions are the same as in example 1 of the present invention, except that: (2) The mass ratio of the lithium iron phosphate anode active material, the binder and the conductive agent added in the preparation process of the anode sheet is 98:1:1.
example 7
The preparation method and conditions are the same as in example 1 of the present invention, except that: (1) The content of doping additive in the preparation process of the positive electrode active material; and (2) selecting particle size range of lithium iron phosphate material (Dv 10 is 0.15 μm, dv50 is 1.11 μm, dv90 is 3.35 μm) in the preparation process of the positive electrode plate.
Example 8
The preparation method and conditions are the same as in example 1 of the present invention, except that: (1) The content of doping additive in the preparation process of the positive electrode active material; and (2) the particle size range of the lithium iron phosphate material (Dv 10 is 0.38 μm, dv50 is 1.13 μm, and Dv90 is 4.94 μm) is selected in the preparation process of the positive electrode plate.
Example 9
The preparation method and conditions are the same as in example 1 of the present invention, except that: (1) The content of doping additive in the preparation process of the positive electrode active material; and (2) selecting particle size range of lithium iron phosphate material (Dv 10 is 0.37 μm, dv50 is 1.51 μm, dv90 is 3.40 μm) in the preparation process of the positive electrode plate.
Example 10
The preparation method and conditions are the same as in example 1 of the present invention, except that: (2) The particle size range of the lithium iron phosphate material is selected in the preparation process of the positive electrode plate (Dv 10 is 0.35 mu m, dv50 is 0.8 mu m, and Dv90 is 3.38 mu m).
Example 11
The preparation method and conditions are the same as in example 1 of the present invention, except that: (3) Selecting a ratio meterArea 1.8m 2 /g of negative electrode active material graphite.
Example 12
The preparation method and conditions are the same as in example 1 of the present invention, except that: (3) The specific surface area is 0.3m 2 /g of negative electrode active material graphite.
Example 13
The preparation method and conditions are the same as in example 1 of the present invention, except that: (1) In the preparation process of the positive electrode active material, 0.2 weight percent of vanadium oxide is selected as an ion doping additive.
Example 14
The preparation method and conditions are the same as in example 1 of the present invention, except that: (1) In the preparation process of the positive electrode active material, 0.2 weight percent of zirconia is selected as an ion doping additive.
Examples 15 to 18
The preparation method and conditions were the same as in example 1, except that: (2) The preparation of the positive pole piece-B) changes the stirring time, the rotating speed and the viscosity of slurry shipment in the pulping process; wherein the dispersion time of the high speed dispersion stage in the pulping process of example 15 was 2.5h; example 16 the speed of the high speed dispersion stage of the pulping process was 2500r/min; example 17 pulping process the viscosity of the slurry shipment was 3000mpa.s; example 18 pulping process the viscosity of the slurry shipment was 600 mpa.s; the number ratio of the positive electrode active material particles having a particle diameter of 0.4 to 2 μm was made different as shown in table 2.
Examples 19 to 23
The preparation method and conditions were the same as in example 1, except that: the surface areas of the anode active materials were different as shown in table 1.
Examples 24 to 26
The preparation method and conditions were the same as in example 1, except that: in the preparation process of the positive electrode active material, the addition amount of the organic carbon source is different, and 2wt percent, 6wt percent and 7wt percent of glucose are sequentially added respectively, so that the contents of the active material surface active carbon materials are different.
Comparative example 1
The preparation method and conditions are the same as in example 1 of the present invention, except that: (1) In the preparation process of the positive electrode active material, the particle size control of broken particles is not carried out in the step E), and the lithium iron phosphate positive electrode active material with nonuniform particle size is prepared.
Comparative example 2
The preparation method and conditions are the same as in example 1 of the present invention, except that: the slurry in steps (2) -B) was dispersed at a high rate of 2000r/min.
The performance test results of the above examples and comparative examples are as follows:
LiFePO with particle size of 0.4-2 μm per unit area in pole piece CP-SEM 4 The number estimation method of (2) is a statistical average method, and is specifically: randomly selecting CP-SEM pictures of a plurality of positions of the lithium iron phosphate positive pole piece, randomly calibrating 5 groups of square grids with the size of 5 mu m multiplied by 5 mu m according to the corresponding proportion of the corresponding SEM pictures, calculating the total particle number N of particles (particles containing square side lines) in the square grids, and calculating the particle number N with the particle size of 0.4-2 mu m in the square grids, wherein the LiFePO with the particle size of 0.4-2 mu m in the unit area in the pole piece CP-SEM 4 The number of (C) is N/Nx100%. And then taking the average value of the quantity proportion of lithium iron phosphate with the particle size of 0.4-2 mu m in the unit area inside 5 square lattices, and obtaining the quantity proportion of lithium iron phosphate with the particle size of 0.4-2 mu m of the CP-SEM in the pole piece.
The testing method comprises the following steps:
1/3C first discharge gram capacity:
1. regulating the temperature of the incubator to 25 ℃, and standing for 2h
2.0.33C constant current charging to 3.65V followed by constant voltage charging to off current 0.05C
3. Standing for 5min
4.0.33C constant current discharge to 2.5V
5. Standing for 5min
Cyclic capacity retention rate:
1. regulating the temperature of the incubator to 25 ℃, and standing for 2h
2.0.33C constant current charging to 3.65V followed by constant voltage charging to off current 0.05C
3. Standing for 5min
4.0.33C constant current discharge to 2.5V
5. Standing for 5min
6.1C constant current charging to 3.65V followed by constant voltage charging to off current 0.05C
7. Standing for 5min
Constant current discharge of 8.1C to 2.5V
9. Standing for 5min
10. Repeating the steps 6-9 until 4000 cycles.
Actual energy density estimation:
the batteries prepared in the examples and the comparative examples are fully charged at 1C rate at 25 ℃, and the actual discharge energy at that time is recorded after the discharge at 1C rate; the battery was weighed using an electronic scale at 25 ℃; the ratio of the actual discharge energy of the battery 1C to the weight of the battery is the actual energy density of the battery.
Wherein the actual energy density is less than 80% of the target energy density, and the actual energy density of the battery is considered to be very low; the actual energy density is 80% or more and 95% or less of the target energy density, and the actual energy density of the battery is considered to be lower; when the actual energy density is more than or equal to 95% of the target energy density and less than 105% of the actual energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is more than or equal to 105% of the target energy density and less than 120% of the target energy density, the actual energy density of the battery is considered to be higher; when the actual energy density is 120% or more of the target energy density, the actual energy density of the battery is considered to be very high.
The test results are shown in tables 1 and 2.
Table 1 parameters of each example and comparative example
Table 2 performance testing of examples and comparative examples
From the data in tables 1 and 2, liFePO 4 The compacted density value of the pole piece is related to the ratio of the amount of lithium iron phosphate with the particle size of 0.4-2 mu m in the unit area in the pole piece to the total amount. On one hand, the compaction density of the pole piece is improved, the charge transfer sites at the interface with the electrolyte are reduced, the charge transfer resistance at the interface is increased, and the specific capacity of the lithium iron phosphate material is properly reduced. By LiFePO 4 Pole piece formula adjustment, optimization of pulping process, improvement of conductive network structure of lithium iron phosphate, so as to properly promote high-compaction LiFePO 4 Specific capacity of the pole piece. In addition, by matching the specific surface area of the anode active material with the specific surface area of the cathode active material, the capacity retention rate of the cycle can be further improved.
From examples 1 to 4, the compacted density of the positive electrode sheet can be significantly changed by adjusting the proportion of the conductive agent. Specifically, the SP has larger specific surface area, is not beneficial to the improvement of the compaction density of the pole piece, has more SP content, can cause poor slurry dispersibility, poor lithium iron phosphate particle dispersibility effect, reduced particle quantity of 0.2-4 mu m in unit area, slightly reduced pole piece compaction density, poor electronic conductive network and poor electrical property; the proportion of the conductive graphite is excessive, the improvement of an electronic conductive network is not large, the improvement of the electrical property is limited, the poor dispersibility of slurry can be caused, the dispersibility effect of lithium iron phosphate particles is slightly reduced, the number of particles with the particle size of 0.2-4 mu m in unit area is reduced, and the compaction density of pole pieces is slightly reduced; therefore, the proportion of the conductive agent SP is properly reduced, the proportion of the conductive graphite is increased, and the compaction density of the pole piece can be properly increased on the one hand; on the other hand, the mixed use of SP and conductive graphite can optimize the conductive network structure of lithium iron phosphate so as to properly promote the specific capacity of the pole piece with high compaction density. It is therefore demonstrated that the preferred proportion of the conductive agent selected in the present application is advantageous for increasing the compacted density of the pole piece.
From examples 1, 5 and 6, changing the positive electrode sheet formulation can affect the compacted density of the positive electrode sheet. Specifically, the compaction density of the pole piece with less binder and conductive agent can be obviously improved, but the conductive network structure of the lithium iron phosphate pole piece can be influenced by less conductive agent, and the risk of stripping the current collector in the repeated charging and discharging process of the active material can be caused by less binder, so that the capacity retention rate is lower. It is therefore demonstrated that the formulation of the pole piece material selected in the present application is beneficial for improving the compacted density of the pole piece.
From examples 1, 7 to 10 and comparative example 1, liFePO 4 Too wide, too narrow or uneven particle size distribution obviously leads to a proportion of the particle size of 0.4-2 μm of lithium iron phosphate in unit area, thereby reducing the compacted density of the pole piece, thus explaining the LiFePO of the application 4 The positive electrode plate prepared by grain size blending has high compacted density and high energy density.
From examples 11, 12, 19 to 23, the specific surface area of the negative electrode active material was not greatly affected by the initial discharge gram capacity of the whole battery, but the negative electrode active material having a large specific surface area increased the cycle capacity retention, but too high specific surface area easily caused uneven dispersion during pulping, but affected the cycle capacity retention. When the ratio of the specific surface area of the negative electrode active material to the specific surface area of the positive electrode active material is in the range of 0.05-0.3, the comprehensive performance of the battery is better.
From examples 13 and 14, different M elements have a small effect on the compaction of the positive electrode sheet, wherein M is Ti element, the compaction density of the positive electrode sheet is the highest, and the corresponding electrical performance test performs optimally.
From examples 1 and 24 to 26, too high or too low a surface carbon material content in the positive electrode active material is not advantageous for the practical energy density of the battery.
From examples 1, 15 to 18 and comparative example 2, the dispersion speed and stirring of the slurry suitable in the pulping process are strong, so that the active material, the conductive agent and the binder in the lithium iron phosphate pole piece are fully and uniformly dispersed, and the compaction density of the lithium iron phosphate pole piece can be improved. Therefore, the technical conditions in the optimized preparation method are beneficial to improving the compaction density of the pole piece.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (8)

1. The secondary battery comprises a positive electrode plate, and is characterized in that the positive electrode plate comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, wherein the positive electrode active material layer contains a positive electrode active material;
the positive electrode active material includes lithium iron phosphate particles;
5 μm×5 μm is one of the unit sectional areas, based on 100% of the total amount of the lithium iron phosphate particles per unit sectional area in the positive electrode active material layer:
the quantity of the lithium iron phosphate particles with the particle diameter of 0.4-2 mu m accounts for 75-95 percent;
the particle size value of the lithium iron phosphate particles refers to the maximum value of the measurement length of single particles, which is measured by a CP-SEM;
the positive electrode active material particles satisfy at least one of the following characteristics:
(a) The Dv10 of the lithium iron phosphate particles is 0.1-0.41 mu m, the Dv50 is 0.7-1.5 mu m, and the Dv90 is 1.5-5 mu m;
(b) The lithium iron phosphate particles satisfy (Dv 90-Dv 10)/dv50=0.1 to 10;
the secondary battery also comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the specific surface area of the negative electrode active material is recorded as A 1 m 2 Per gram, the specific surface area of the positive electrode active material is denoted as A 2 m 2 Per gram, satisfies 0.05.ltoreq.A 1 /A 2 ≤0.3，9≤A 2 ≤13。
2. The secondary battery according to claim 1, wherein the number of particles of the lithium iron phosphate particles having a particle diameter of > 2 μm is 10% or less, and the number of particles of the lithium iron phosphate particles having a particle diameter of less than 0.4 μm and greater than or equal to 0.1 μm is 15% or less.
3. The secondary battery according to claim 1 or 2, wherein the lithium iron phosphate particles have a carbon material on the surface thereof, the carbon material being contained in an amount of 0.5 to 2% based on the mass of the positive electrode active material.
4. The secondary battery according to claim 1, wherein the positive electrode active material layer contains an M element containing at least one of Ti, V, or Zr;
the M element content is 100ppm to 3000ppm based on the weight of the positive electrode active material layer.
5. The secondary battery according to claim 1, wherein the powder compaction density of the lithium iron phosphate particles at 30KN pressure is greater than 2.3g/cm 3 。
6. The secondary battery according to claim 1, wherein a conductive layer is provided on the positive electrode current collector, and the conductive layer has a thickness of 0.5 μm to 10 μm.
7. The secondary battery according to claim 1, wherein 0.5.ltoreq.A 1 ≤4。
8. An electric device comprising the secondary battery according to any one of claims 1 to 7.
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