WO2022047705A1 - 正极材料、正极极片、锂二次电池、电池模块、电池包及装置 - Google Patents

正极材料、正极极片、锂二次电池、电池模块、电池包及装置 Download PDF

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WO2022047705A1
WO2022047705A1 PCT/CN2020/113286 CN2020113286W WO2022047705A1 WO 2022047705 A1 WO2022047705 A1 WO 2022047705A1 CN 2020113286 W CN2020113286 W CN 2020113286W WO 2022047705 A1 WO2022047705 A1 WO 2022047705A1
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positive electrode
active material
battery
electrode active
pole piece
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PCT/CN2020/113286
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English (en)
French (fr)
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别常峰
刘宏宇
柳娜
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宁德时代新能源科技股份有限公司
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Priority to CN202080104510.7A priority Critical patent/CN116097468A/zh
Priority to PCT/CN2020/113286 priority patent/WO2022047705A1/zh
Priority to EP20951952.9A priority patent/EP4170755A4/en
Publication of WO2022047705A1 publication Critical patent/WO2022047705A1/zh
Priority to US18/063,623 priority patent/US20230108289A1/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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • 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
    • 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
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • 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

Definitions

  • the present application relates to the field of batteries, and in particular, to a positive electrode material, a positive electrode sheet, a lithium secondary battery, a battery module, a battery pack and a device.
  • lithium iron phosphate As a cathode material for lithium-ion batteries, lithium iron phosphate has advantages in safety performance, cycle performance and cost, and is widely used in buses, passenger cars and large-scale energy storage. However, the voltage platform, capacity development and electrode compaction density of lithium iron phosphate full batteries are all at a low level. Therefore, compared with the ternary cathode material battery, the energy density of the lithium iron phosphate battery is not satisfactory.
  • the coating weight of the active material per unit area of the positive electrode sheet that is, the mass surface density of the active material
  • the mass surface density of the active material can significantly improve the energy density of the lithium-ion battery, while increasing other materials (current collector, shell, electrolytic The use efficiency of liquid and separator) reduces the overall cost of the cell.
  • the positive electrode material in the lithium-ion battery is lithium iron phosphate
  • the positive electrode piece is very prone to cold-pressed stripping or delamination, and it is difficult to achieve high energy density.
  • the present application provides a positive electrode material, a positive electrode sheet, a lithium secondary battery, a battery module, a battery pack and a device.
  • the present application provides a positive electrode material comprising a first positive electrode active material represented by formula (I) and a second positive electrode active material represented by formula (II),
  • M1, M2 are each independently selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr or Ti;
  • a positive electrode active material is a single crystal particle, and the second positive electrode active material is a secondary particle.
  • the positive electrode material provided in this application includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is lithium iron phosphate single crystal particles, and the second positive electrode active material is lithium iron phosphate secondary particles .
  • lithium iron phosphate secondary particles have a low specific surface area, which can reduce the consumption of binders and solvents in the pulping process and increase the solid content of the pulp.
  • the increase of the solid content of the slurry can reduce the processing difficulty of the thick-coated pole piece: when the active material layer of the thick-coated pole piece is dried, the volatilization of the dispersing solvent is reduced, the volumetric strain of the diaphragm layer is reduced, and the bonding
  • the segregation effect of the agent in the direction perpendicular to the surface of the pole piece is suppressed, and the pole piece is not prone to powder falling, cracking, and film release.
  • the lithium iron phosphate single crystal particles are fully filled into the particle gaps of the lithium iron phosphate secondary particles, which increases the bonding force between the lithium iron phosphate secondary particles and further improves the compaction density of the pole piece; it can also improve the activity.
  • the flatness of the contact surface between the material and the current collector helps to slow down the damage of the secondary lithium iron phosphate particles to the surface of the current collector during the cold pressing of the pole piece, enhance the flexibility of the pole piece, and reduce the possibility of the pole piece breaking during processing. probability.
  • the technical solution of the present application can also reduce the overall cost of the battery cell.
  • the secondary particles are in a pomegranate-like shape formed by agglomeration of a plurality of primary particles.
  • the primary particles are single crystal nanoparticles.
  • the average particle size d of the primary particles is in the range of 20nm-500nm.
  • the particle size of the primary particles is in an appropriate range, the side reaction rate between the positive electrode material and the electrolyte and the kinetics of the battery positive electrode. The performance is at a reasonable level, and the capacity and cycle performance of the battery are better.
  • the second positive electrode active material satisfies at least one of the following conditions: (1) the median particle size Dv50 of the second positive electrode active material is 2.5 ⁇ m-10.5 ⁇ m; optionally, The median particle size Dv50 of the second positive electrode active material is 4.5 ⁇ m-8.5 ⁇ m; further optionally, the median particle size Dv50 of the second positive electrode active material is 6 ⁇ m-7 ⁇ m; (2) the second The specific surface area of the positive electrode active material is 3.5m 2 /g-10.5m 2 /g, optionally, the specific surface area of the second positive electrode active material is 5m 2 /g-9m 2 /g; further optionally, the The specific surface area of the second positive electrode active material is 6.5m 2 /g-7.5m 2 /g.
  • the particle size and specific surface area of the second positive electrode active material are moderate, which is beneficial to the adequacy of the first positive electrode active material to fill the interparticle gaps. , so that the compaction density of the pole piece is high, the contact layer between the active material and the current collector has better flatness, and the processing performance of the pole piece is good.
  • the solid content of the slurry of the cathode material mixture system is in an appropriate range, which is beneficial to improve the capacity performance and cycle performance of the battery.
  • the single crystal particles are independent particles with continuous internal lattice and almost no grain boundary separation.
  • the powder resistivity of the first positive electrode active material at 12Mpa is less than 150 ⁇ cm, and optionally, the powder resistivity of the first positive electrode active material at 12Mpa is 80 ⁇ cm cm or less, and further optionally, the powder resistivity of the first positive electrode active material at 12 Mpa is 30 ⁇ cm or less.
  • the first positive electrode active material satisfies at least one of the following conditions: (1) the median particle size Dv50 of the first positive electrode active material is 0.5 ⁇ m-2.0 ⁇ m, (2) the The specific surface area of the first positive electrode active material is 6.0 m 2 /g to 20 m 2 /g.
  • the median particle size Dv50 of the first positive electrode active material is in the range of 0.5 ⁇ m-2.0 ⁇ m, it is favorable for it to be fully filled into the interparticle gaps of the secondary particles of the second positive electrode active material lithium iron phosphate, so as to better improve the Compaction density, improve the processing performance of the pole piece.
  • the specific surface area of the first positive electrode active material is in the range of 6.0m 2 /g-20m 2 /g, it is beneficial to further reduce the consumption of the binder in the pulping process, increase the solid content of the pulp, and at the same time ensure a larger electricity Chemically reactive specific surface area.
  • the mass percentage content of the second positive electrode active material is greater than the mass percentage content of the first positive electrode active material.
  • the mass percentage of the second positive active material is 55%-90%; further optionally, the mass percentage of the second positive active material is 60%-85%; Optionally, the mass percentage of the second positive active material is 65%-80%.
  • the second active material lithium iron phosphate secondary particles have a low specific surface area, which can increase the solid content of the slurry, reduce the processing difficulty of the thick-coated pole piece, and reduce the production cost of the positive electrode material; and
  • the first active material lithium iron phosphate single crystal is filled in the particle gaps of the lithium iron phosphate secondary particles, which further improves the compaction density of the pole piece and improves the processing performance of the pole piece.
  • the compaction density and processing performance of the pole piece are further improved; at the same time, an appropriate amount of the first cathode active material needs to be added to fill the gaps between the lithium iron phosphate secondary particles, In order to increase the adhesion between the secondary particles of lithium iron phosphate, improve the compaction density and processing performance of the pole piece, improve the electron transport performance and reduce the membrane resistance.
  • the mass percentage of the second cathode active material is 60%-85%; or further 65%-80%, the first cathode active material and the second cathode active material cooperate with each other to improve the comprehensive processing performance of the slurry and pole piece electrical properties.
  • the present application provides a positive electrode sheet including a positive electrode active material layer, wherein the positive electrode active material layer includes the positive electrode material of the first aspect of the present application.
  • the single-sided coating weight per unit area of the positive electrode sheet provided in this application is 140g/m 2 -390 g/m 2 ; optionally, the single-sided coating weight per unit area is 190 g/m 2 -320 g/m 2 ; further Optionally, the coating weight per unit area on one side is 230g/m 2 -280g/m 2 .
  • the limit solid content of the positive electrode slurry is increased, a higher coating weight and a larger coating thickness can be achieved; as the coating weight and coating thickness increase , the battery volume utilization rate increases, which helps to improve the energy density, but the lithium ion migration path also becomes longer, the diffusion impedance increases, the lithium ion concentration polarization of the battery becomes larger during the discharge process, and the battery capacity performance decreases.
  • the coating weight is 230g/m 2 -280g/m 2 , the overall performance of the battery energy density and cycle performance is the best.
  • the diaphragm resistance of the positive electrode piece provided by the present application is less than 2000m ⁇ ; optionally, the diaphragm resistance is less than 800m ⁇ ; further optionally, the diaphragm resistance is less than 200m ⁇ .
  • the positive electrode sheet of the present application has lower sheet resistance, thereby promoting the energy density and cycle performance of the battery.
  • the present application provides a lithium secondary battery, which includes the positive electrode plate described in the second aspect of the present application.
  • the present application provides a battery module including the lithium secondary battery described in the third aspect of the present application.
  • the present application provides a battery pack including the battery module described in the fourth aspect of the present application.
  • the present application provides a device comprising the lithium secondary battery described in the third aspect of the present application or the battery module described in the fourth aspect of the present application or the battery pack described in the fifth aspect of the present application, wherein, The lithium secondary battery or the battery module or the battery pack serves as a power source or an energy storage unit of the device.
  • the cathode material provided by the present application has a significantly higher limit solid content of the slurry during the pulping process, the cracking of the pole piece after thick coating is improved, and the gap between the diaphragm and the current collector is improved.
  • the binding force of the lithium secondary battery is improved, and the membrane resistance is reduced.
  • the use of the positive electrode material of the present application to prepare a positive electrode plate and apply it to a lithium secondary battery can significantly improve the energy density, kinetic performance and cycle performance of the lithium secondary battery.
  • the device using the lithium secondary battery or battery module or battery pack of the present application as a power source or an energy storage unit also has better power performance.
  • 1 is a scanning electron microscope image of a second positive electrode active material according to a specific embodiment of the present application under different magnifications: wherein, the magnification of 1A is 1000X times, the magnification of 1B is 5000X times, and the magnification of 1C is 10000X times times;
  • 2 is a scanning electron microscope image of the first positive electrode active material according to a specific embodiment of the present application under different magnifications: wherein, the magnification of 2A is 10000X times, and the magnification of 2B is 30000X times;
  • FIG. 3 is a scanning electron microscope image of a section of a positive pole piece according to a specific embodiment of the present application.
  • FIG. 4 is a perspective view of a lithium secondary battery according to an embodiment of the present application.
  • Fig. 5 is an exploded view of the lithium secondary battery shown in Fig. 4;
  • FIG. 6 is a perspective view of a battery module according to an embodiment of the present application.
  • FIG. 7 is a perspective view of a battery pack according to an embodiment of the present application.
  • Figure 8 is an exploded view of the battery pack shown in Figure 7;
  • FIG. 9 is a schematic diagram of an apparatus according to an embodiment of the present application.
  • a first aspect of the present application relates to a positive electrode material comprising a first positive electrode active material represented by formula (I) and a second positive electrode active material represented by formula (II),
  • M1, M2 are each independently selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr or Ti;
  • a positive electrode active material is a single crystal particle, and the second positive electrode active material is a secondary particle.
  • the inventors of the present application have found through research that: in the production process of the lithium iron phosphate positive electrode material, in order to improve the capacity performance and kinetic performance of the positive electrode material, it generally needs to be fully nanosized.
  • the nanometerization process makes the lithium iron phosphate material have a high specific surface energy, which makes the material difficult to process.
  • the thickness of the positive electrode coating is thickened, the phenomenon of powder falling, cracking and delamination of the pole piece will be aggravated.
  • a pole piece with a high areal density requires a larger pressure of the cold pressing roller, and the positive electrode material particles will cause damage to the metal substrate in the process.
  • the defects of the pole piece during the above-mentioned cold pressing process will cause the pole piece to break during the winding of the subsequent pole piece and the hot pressing of the bare cell.
  • the second positive electrode active material lithium iron phosphate secondary particles have a low specific surface area, which can reduce the consumption of binders and solvents in the pulping process, improve pulp solid content.
  • the increase in the solid content of the slurry can reduce the processing difficulty of the thick-coated pole piece: when the active material layer of the thick-coated pole piece is dried, the volatilization of the dispersant is reduced, the volumetric strain of the diaphragm layer is reduced, and the binder The segregation effect in the direction perpendicular to the surface of the pole piece is suppressed, and the pole piece is less prone to powder falling, cracking, and film release.
  • the first positive electrode active material lithium iron phosphate single crystal is fully filled into the particle gaps of the lithium iron phosphate secondary particles, which increases the cohesive force between the lithium iron phosphate secondary particles and further improves the compaction density of the pole piece; It can also improve the flatness of the contact surface between the active material and the current collector, which helps to slow down the damage of the lithium iron phosphate secondary particles to the surface of the current collector during the cold pressing of the pole piece, enhance the flexibility of the pole piece, and reduce the processing time. Probability of pole piece breakage.
  • the lithium iron phosphate secondary particles as the second positive electrode active material are in a pomegranate-like shape formed by agglomeration of a plurality of lithium iron phosphate primary particles.
  • the primary particle of lithium iron phosphate is the smallest structural unit constituting the hierarchical structure of the secondary particle, and refers to an independent particle with low porosity, which can be observed by an electron microscope.
  • the average particle size d of the primary particles is in the range of 20nm-500nm.
  • the average particle size d of the primary particles is obtained by using the long-diameter statistical method to statistically obtain the particle size of the primary particles. Specifically, in the SEM image, the diameters in the major axis direction of a plurality of primary particles are measured and averaged.
  • the primary lithium iron phosphate particles that agglomerate to form the lithium iron phosphate secondary particles are single crystal nanoparticles.
  • Figure 1 shows the scanning electron microscope images of the second positive electrode active material under different magnifications, wherein the magnification of 1A is 1000X times, the magnification of 1B is 5000X times, and the magnification of 1C is 10000X times.
  • the median particle size Dv50 of the second positive electrode active material is 2.5 ⁇ m-10.5 ⁇ m. In some embodiments of the present application, the median particle size Dv50 of the second positive electrode active material is 4.5 ⁇ m-8.5 ⁇ m. In some embodiments of the present application, the median particle size Dv50 of the second positive electrode active material is 6 ⁇ m-7 ⁇ m.
  • the meaning of the median particle size Dv50 value is: the volume of particles with a particle size larger than this value and a particle size smaller than this value in the powder sample each account for 50% of the total volume.
  • the specific surface area of the second positive electrode active material is 3.5 m 2 /g-10.5 m 2 /g. In some embodiments of the present application, the specific surface area of the second positive electrode active material is 5 m 2 /g-9 m 2 /g. In some embodiments of the present application, the specific surface area of the second positive electrode active material is 6.5 m 2 /g-7.5 m 2 /g.
  • the particle size and specific surface area of the second positive electrode active material are moderate, which is conducive to the adequacy of the first positive electrode active material to fill in the interparticle gaps, so that the pole pieces
  • the compaction density is high, the contact layer between the active material and the current collector has good flatness, and the processing performance of the pole piece is good.
  • the solid content of the slurry of the cathode material mixing system is in an appropriate range, which is beneficial to the capacity development and cycle performance of the battery.
  • the lithium iron phosphate single crystal particles used as the first positive electrode active material are independent lithium iron phosphate particles with continuous internal lattices and almost no grain boundary separation.
  • Figure 2 shows scanning electron microscope images of the first positive electrode active material at different magnifications. Among them, the magnification of 2A is 10000X times, and the magnification of 2B is 30000X times.
  • the powder resistivity of the first positive electrode active material at 12 Mpa is 150 ⁇ cm or less. In some embodiments of the present application, the powder resistivity of the first positive electrode active material at 12 Mpa is 80 ⁇ cm or less. In some embodiments of the present application, the powder resistivity of the first positive electrode active material at 12 Mpa is 30 ⁇ cm or less.
  • the powder resistivity of the first positive electrode active material is low and the conductivity is high, which is beneficial to improve the electron transport performance between the positive electrode active materials, so that the film resistivity of the positive electrode plate is reduced accordingly, and the capacity and cycle performance of the battery are promoted. .
  • the median particle size Dv50 of the first positive electrode active material is 0.5 ⁇ m-2.0 ⁇ m, which is favorable for it to be fully filled into the interparticle gaps of the secondary particles of lithium iron phosphate of the second positive electrode active material, and more It can improve the compaction density of the pole piece and improve the processing performance of the pole piece.
  • the specific surface area of the lithium iron phosphate single crystal particles of the first positive electrode active material is 6.0 m 2 /g-20 m 2 /g, which is beneficial to further reduce the consumption of the binder in the pulping process, Increase the solid content of the slurry.
  • the mass percentage content of the second positive electrode active material is greater than the mass percentage content of the first positive electrode active material. In some embodiments of the present application, the mass percentage of the second positive active material is 55%-90%; in some embodiments of the present application, the mass percentage of the second positive active material is 60%-85%; in some embodiments of the present application, the mass percentage of the second positive active material is 65%-80%.
  • the mass percentage of the second positive active material is greater than that of the first positive active material, that is, when the mass percentage of the second positive active material is greater than 50%, a positive electrode with improved performance and lower cost can be obtained. piece.
  • the compaction density and processing performance of the pole piece are further improved; at the same time, an appropriate amount of the first cathode active material needs to be added to fill the gaps between the lithium iron phosphate secondary particles, In order to increase the adhesion between the secondary particles of lithium iron phosphate, improve the compaction density and processing performance of the pole piece, improve the electron transport performance and reduce the membrane resistance.
  • the mass percentage of the second cathode active material is 60%-85%; or further 65%-80%, the first cathode active material and the second cathode active material cooperate with each other to improve the comprehensive processing performance of the slurry and pole piece electrical properties.
  • a second aspect of the present application relates to a positive electrode sheet, comprising a positive electrode active material layer, and the positive electrode active material layer includes the positive electrode material of the first aspect of the present application.
  • FIG. 3 shows the SEM image of the section of the positive pole piece, from It can be seen from FIG. 3 that the single crystal particles of the first positive electrode active material lithium iron phosphate are filled in the particle gaps of the secondary particles of the second positive electrode active material lithium iron phosphate.
  • the single-sided coating weight of the positive electrode sheet is 140 g/m 2 -390 g/m 2 . In some embodiments of the present application, the single-sided coating weight of the positive electrode sheet is 190 g/m 2 -320 g/m 2 . In some embodiments of the present application, the single-sided coating weight of the positive electrode sheet is 230 g/m 2 -280 g/m 2 .
  • the limit solid content of the positive electrode slurry is increased, so that a higher coating weight and a larger coating thickness can be achieved; as the coating weight and coating thickness increase,
  • the increase in the volume utilization rate of the battery helps to improve the energy density, but the migration path of lithium ions also becomes longer, the diffusion resistance increases, the lithium ion concentration polarization of the battery increases during the discharge process, and the battery capacity performance decreases.
  • coating weight can affect the combined performance of battery energy density and cycling performance.
  • the membrane resistance of the positive pole piece is less than 2000 m ⁇ . In some embodiments of the present application, the membrane resistance of the positive electrode sheet is less than 800 m ⁇ . In some embodiments of the present application, the membrane resistance of the positive electrode sheet is less than 200 m ⁇ .
  • the membrane resistance of the positive electrode sheet refers to the overall resistance of the positive electrode electrode sheet after the positive electrode active material layer is provided on the upper and lower surfaces of the positive electrode current collector at room temperature.
  • the positive electrode piece provided by the embodiment of the present application has the advantages of low sheet resistance, high cell energy density, and good cycle performance.
  • a positive electrode sheet includes a positive electrode current collector and the positive electrode active material layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode active material layer may be provided on one surface of the positive electrode current collector, or may be provided on both surfaces of the positive electrode current collector.
  • the positive electrode active material layer contains the positive electrode material of the first aspect of the present application.
  • the positive electrode active material layer may further include a conductive agent and a binder, wherein the types and contents of the conductive agent and the binder are not specifically limited, and can be selected according to actual needs.
  • the binder usually includes a fluoropolyolefin-based binder, and water is usually a good solvent relative to the fluoropolyolefin-based binder, that is, the fluoropolyolefin-based binder is usually It has good solubility in water, for example, the fluorine-containing polyolefin binder can be including but not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymer or their modification (for example, carboxylic acid, acrylic acid) , modified acrylonitrile, etc.) derivatives, etc.
  • PVDF polyvinylidene fluoride
  • the mass percentage content of the binder in the positive electrode active material layer is less than or equal to 2 wt %, so as to obtain lower pole piece impedance.
  • the conductive agent of the positive electrode sheet can be various conductive agents suitable for lithium ion (secondary) batteries in the art, for example, can be including but not limited to acetylene black, conductive carbon black, carbon fiber (VGCF), carbon nanotubes A combination of one or more of (CNT), Ketjen Black, and the like.
  • the weight of the conductive agent may account for 1 wt % to 10 wt % of the total mass of the positive electrode material layer.
  • the weight ratio of the conductive agent to the positive active material in the positive electrode sheet is greater than or equal to 1.5:95.5.
  • the types of positive electrode current collectors are not specifically limited, and can be selected according to actual needs.
  • the positive electrode current collector can usually be a layer, and the positive electrode current collector is usually a structure or part that can collect current.
  • the positive electrode current collector may include but not limited to metal foil, and more specifically may include but not limited to nickel foil and aluminum foil.
  • a suitable method to prepare the positive electrode sheet may include the following steps: after mixing the positive electrode active material, binder and conductive agent of the first aspect of the present application to form a slurry, coating the positive electrode on the positive electrode on the collector.
  • a third aspect of the present application provides a lithium secondary battery, which includes the positive electrode plate described in the second aspect of the present application.
  • the lithium secondary battery may include a positive electrode sheet, a negative electrode sheet, a separator spaced between the positive electrode sheet and the negative electrode sheet, and an electrolyte.
  • the positive pole piece is the positive pole piece described in the second aspect of the application.
  • the construction and preparation method of the lithium secondary battery of the present application are well known per se, except for the use of the positive electrode sheet described in the second aspect of the present application.
  • a negative electrode sheet of a lithium secondary battery generally includes a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector, and the negative electrode active material layer generally includes a negative electrode active material.
  • the negative electrode active material can be a variety of materials suitable for negative electrode active materials of lithium secondary batteries in the art, for example, can be including but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microspheres, silicon-based A combination of one or more of materials, tin-based materials, lithium titanate, or other metals capable of alloying with lithium.
  • the graphite can be selected from a combination of one or more of artificial graphite, natural graphite and modified graphite;
  • the silicon-based material can be selected from elemental silicon, silicon-oxygen compounds, silicon-carbon composites, and silicon alloys A combination of one or more of tin-based materials;
  • the tin-based material can be selected from a combination of one or more of elemental tin, tin oxide compounds, and tin alloys.
  • the negative electrode current collector is usually a structure or part that collects current, and the negative electrode current collector can be any material suitable for use as a negative electrode current collector for lithium secondary batteries in the art.
  • the negative electrode current collector can include but not It is limited to metal foil, and more specifically can include but not limited to copper foil.
  • the negative pole piece can also be a lithium piece.
  • the separator of the lithium secondary battery may be any material suitable for the separator of the lithium secondary battery in the art, for example, it may include but not limited to polyethylene, polypropylene, polyvinylidene fluoride A combination of one or more of vinyl, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.
  • the electrolyte of the lithium secondary battery may be various electrolytes suitable for lithium secondary batteries in the art.
  • the electrolyte usually includes an electrolyte and a solvent, and the electrolyte may generally include Lithium salt, more specifically, the lithium salt may be inorganic lithium salt and/or organic lithium salt, specifically may include but not limited to LiPF 6 , LiBF 4 , LiN(SO 2 F) 2 (abbreviated as LiFSI), LiN One or more of (CF 3 SO 2 ) 2 (abbreviated as LiTFSI), LiClO 4 , LiAsF 6 , LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), LiBF 2 C 2 O 4 (abbreviated as LiDFOB) combination of species.
  • LiPF 6 LiBF 4
  • LiN(SO 2 F) 2 abbreviated as LiFSI
  • LiN One or more of (CF 3 SO 2 ) 2 abbreviated as LiTFSI
  • LiClO 4 LiAs
  • the concentration of the electrolyte may be 0.8 mol/L to 1.5 mol/L.
  • the solvent can be various solvents suitable for the electrolyte of lithium secondary batteries in the art, and the solvent of the electrolyte is usually a non-aqueous solvent, preferably an organic solvent, specifically including but not limited to ethylene carbonate, A combination of one or more of propylene carbonate, butene carbonate, pentenyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate or their halogenated derivatives.
  • the method of preparing the lithium secondary battery should be known to those skilled in the art, for example, the positive electrode sheet, the separator and the negative electrode sheet may each be a layer
  • the body can be cut to a target size and stacked in sequence, and can also be wound to a target size to form a battery cell, and can be further combined with an electrolyte to form a lithium secondary battery.
  • a lithium secondary battery 5 (hereinafter referred to as a battery cell 5 ) according to the present application includes an outer package 51 , an electrode assembly 52 , a cap assembly 53 and an electrolyte (not shown).
  • the electrode assemblies 52 are accommodated in the casing 51 , and the number of the electrode assemblies 52 is not limited, and can be one or more.
  • the battery cell 5 shown in FIG. 4 is a can type battery, but the application is not limited to this, the battery cell 5 can be a pouch type battery, that is, the casing 51 is replaced by a metal plastic film and the top cover is removed Component 53.
  • a fourth aspect of the present application provides a battery module including the lithium secondary battery described in the third aspect of the present application.
  • the lithium secondary battery can be assembled into a battery module, and the number of lithium secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 6 is a perspective view of the battery module 4 as an example.
  • the plurality of lithium secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4 . Of course, it can also be arranged in any other manner. Further, the plurality of lithium secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a case having an accommodating space in which the plurality of lithium secondary batteries 5 are accommodated.
  • a fifth aspect of the present application provides a battery pack including the battery module described in the fourth aspect of the present application.
  • the above-mentioned battery modules can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • FIG. 7 is a perspective view of the battery pack 1 as an example
  • FIG. 8 is an exploded view of the battery pack shown in FIG. 7 .
  • the battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case.
  • the battery box includes an upper box body 2 and a lower box body 3 .
  • the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • the plurality of battery modules 4 may be arranged in the battery case in any manner.
  • a sixth aspect of the present application provides a device comprising the lithium secondary battery described in the third aspect of the present application, the battery module described in the fourth aspect of the present application, or the battery pack described in the fifth aspect of the present application, wherein the The lithium secondary battery or the battery module or the battery pack is used as a power source of the device or an energy storage unit of the device.
  • the device may be, but is not limited to, mobile devices (eg, cell phones, laptops, etc.), electric vehicles (eg, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf balls) vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device may select a lithium secondary battery, a battery module or a battery pack according to its usage requirements.
  • FIG. 9 shows a schematic diagram of an apparatus according to a specific embodiment of the present application.
  • the device may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • a battery pack or a battery module may be employed.
  • the device may be a mobile phone, a tablet computer, a laptop computer, and the like.
  • the device is generally required to be thin and light, and a lithium ion secondary battery (ie, the secondary battery of the present application) can be used as a power source.
  • the first positive electrode active material single crystal lithium iron phosphate and the second positive electrode active material secondary particle lithium iron phosphate are mixed in proportion by mass percentage to obtain a positive electrode material.
  • the positive electrode material, the binder polyvinylidene fluoride (PVDF) and the conductive carbon are dry mixed in a weight ratio of 96.5:2.0:1.5, an appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and the mixture is fully stirred to form a Uniform positive electrode slurry; apply the slurry on a carbon-coated aluminum foil with a thickness of 13 ⁇ m of the positive electrode current collector, then dry and cold-press, and divide into strips for use to obtain a positive electrode pole piece.
  • NMP N-methylpyrrolidone
  • Negative pole piece fully stir and mix the negative electrode active material graphite, conductive carbon, and binder polyvinylidene fluoride (PVDF) in an appropriate amount of water solvent at a weight ratio of 95:3:2 to form a uniform negative electrode slurry ; Coat the slurry on the negative electrode current collector Cu foil, and after drying, cold-press the pole piece to the design compaction, and divide it into strips for use.
  • PVDF polyvinylidene fluoride
  • Electrolyte Lithium iron phosphate general electrolyte is used.
  • the housing material uses aluminum-plastic film.
  • the positive pole piece, the separator and the negative pole piece are wound to form a bare cell, the bare cell is encapsulated with an aluminum-plastic film, injected with an electrolyte, and a lithium secondary battery is obtained after chemical formation, exhaust gas and high temperature aging.
  • the relevant parameters of the positive electrode material, the performance of the positive electrode pole piece and the lithium secondary battery in Examples 1 to 36 and Comparative Examples 1 to 2 can be detected by conventional methods in this field.
  • the specific surface area tester was used for testing, and the test instrument model was tristar 3020.
  • the detection steps are briefly described as follows: take 2.0g-4g of the first positive active material sample; put the sample into a sample tube, put it into a heating pack, and carry out degassing treatment (the degassing condition is 200° C., 2 hours); the degassing is completed Then, when the temperature of the degassing station drops to normal temperature, remove the sample tube from the degassing station, weigh and calculate the total mass of the sample; put the sample tube into the test filling rod, perform BET test, and obtain the test result.
  • Measuring instrument laser particle size analyzer; equipment model: Malvern Mastersizer 2000E or Mastersizer 3000. Since the particle of the cathode material is irradiated by a laser beam, the angle of the scattered light is inversely proportional to the diameter of the particle, and the intensity of the scattered light decays logarithmically with the increase of the angle, and the energy distribution of the scattered light is directly related to the distribution of the particle diameter. , the particle size distribution characteristics of the particles can be obtained by accepting and measuring the energy distribution of the scattered light.
  • the solvent used in the test can be water or other organic solvents used to prepare the slurry, and the sample is dispersed by ultrasound.
  • the obtained analysis result Dv50 means that the diameter of particles occupying 50% of the total volume is larger than this value, and the diameter of other particles occupying 50% of the total volume is smaller than this value.
  • Dry the first positive electrode active material powder weigh an appropriate amount of powder, and use a powder resistivity tester, equipment model Suzhou Lattice ST2722 or Sansi Zongheng UTM7305. Put the dry powder sample in the mold/sample chamber of the resistivity tester, the depth of the sample chamber is 20mm, and the cross-sectional area is 1cm 2 , then slowly apply pressure from small to large, collect data manually, and record the corresponding powder resistivity under different pressure points Test Results.
  • the detection was carried out with reference to the detection method of the median particle diameter Dv50 of the first positive electrode active material.
  • the detection was carried out with reference to the detection method of the specific surface area BET of the first positive electrode active material.
  • the overall membrane resistance of the positive pole piece in the embodiment of the present application (with positive active material layers on both sides) is detected.
  • the gram capacity of 1/3C at 25°C is used to characterize the capacity of the battery.
  • the specific testing process is briefly described as follows: (1) Place the battery in a 25°C oven, let it stand for 2 hours, and keep the battery temperature at 25°C; (2) 1/3C DC to 2.0V; (3) Pause for 5min; (4) 1/3C CC to 3.65V and CV to I ⁇ 0.05C; (5) Pause for 5min; (6) 1/3C DC to 2.0V. This step is the actual cell test capacity, combined with the quality of the positive active material, the gram capacity can be calculated.
  • Steps (2) to (6) are one charge-discharge cycle of the battery, and steps (2) to (6) are repeated continuously until the number of cycles when the battery capacity decays to 80% of the initial value.
  • the positive electrode material of Comparative Example 1 only contains lithium iron phosphate single crystal particles. From the test data in Table 2, it can be seen that the processing performance of the positive electrode sheet of Comparative Example 1 is poor, which is manifested in the low limit solid content of the slurry of the positive electrode material, and the coating The cracking of the pole piece after the cloth is serious, and the bonding force between the diaphragm and the current collector is low. Meanwhile, the capacity exertion and cycle performance of the lithium secondary battery of Comparative Example 1 were poor.
  • the positive electrode material of Comparative Example 2 only contains lithium iron phosphate secondary particles. From the data in Table 2, it can be seen that the positive electrode piece of Comparative Example 2, although the limit solid content of the slurry is greatly improved, the cracking of the pole piece after coating is obtained. However, the bonding force between the diaphragm and the current collector is very low, and the diaphragm resistance of the positive electrode plate is relatively high, and the capacity performance and cycle performance of the battery are not ideal.
  • the positive electrode materials of Examples 1 to 36 include lithium iron phosphate single crystal particles and lithium iron phosphate secondary particles. Compared with Comparative Examples 1 and 2, the processing performance of the positive electrode sheets of Examples 1 to 36 is generally improved. The limit solid content of the positive electrode slurry is higher, the cracking of the pole piece after thick coating is improved, the bonding force between the membrane and the current collector is improved, the membrane resistance is reduced, and the battery capacity and cycle performance are excellent. For Comparative Example 1 and Comparative Example 2.
  • the positive electrode materials obtained after mixing can improve the processing performance of the pole piece, and improve the battery capacity and performance.
  • the effect of cycle performance; among them, the doping of Ti element has the most significant improvement in the capacity performance and cycle performance of the cell, and the preferred doping amount of Ti element in the positive electrode material is 2000ppm.
  • Examples 5 to 9 show the change of the powder resistivity of the lithium iron phosphate single crystal particles at 12 Mpa in the positive electrode material provided by the present application, and the influence on the processing performance of the pole piece and the performance of the battery.
  • the powder resistivity of the first positive electrode active material lithium iron phosphate single crystal particles at 12Mpa is 150 ⁇ cm or less, or 80 ⁇ cm or less, or further 30 ⁇ cm or less, with the powder resistance of the lithium iron phosphate single crystal particles.
  • the reduction of the rate, the conductivity is improved, and the electron transport performance between the positive electrode active materials is better, so that the membrane resistivity of the positive electrode plate is reduced, which is beneficial to the capacity and cycle performance of the battery.
  • Examples 5 and 10 to 17 show the influence of the change of the median particle size Dv50 of the lithium iron phosphate secondary particles on the processing performance of the pole piece and the performance of the battery in the positive electrode material provided by the present application.
  • the median particle size Dv50 of the lithium iron phosphate secondary particles is less than 2.5 ⁇ m, the specific surface area of the secondary particles is larger, which leads to enhanced liquid absorption, which can cause slight cracking during the drying process of the membrane; The uniformity of the conductive carbon distribution in the material layer is insufficient, which increases the membrane resistance.
  • the median particle size Dv50 of the lithium iron phosphate secondary particles is greater than 10.5 ⁇ m, the sufficiency of filling the first positive electrode active material in the particle gaps is weakened, which is not conducive to the improvement of the compaction density of the pole pieces, and also affects the activity.
  • the flatness of the contact layer between the material and the current collector affects the contact between the active material and the current collector, which increases the probability of the pole piece breaking during processing.
  • the processing performance of the pole piece is better, and the bonding force between the diaphragm and the current collector is also better, which is beneficial to the battery's capacity development and cycle performance to achieve the best state.
  • Examples 5 and 18 to 25 show the influence of the change of the specific surface area BET of the lithium iron phosphate secondary particles on the processing performance of the pole piece and the performance of the battery in the positive electrode material provided by the present application.
  • the specific surface area BET of the lithium iron phosphate secondary particles is lower than 3.5 m 2 /g, the electrochemical reactivity of the lithium secondary battery is low, and the cycle performance of the battery is affected to a certain extent.
  • the specific surface area BET of the lithium iron phosphate secondary particles is higher than 10.5 m 2 /g, the effect of improving the solid content of the cathode slurry and the improvement of the processing performance of the pole piece becomes insufficient.
  • the specific surface area BET of the lithium iron phosphate secondary particles is 6.5m 2 /g-7.5m 2 /g, it can not only significantly improve the solid content of the cathode slurry and improve the processing performance of the pole piece, but also ensure The electrochemical reactivity of the battery makes the battery's capacity exertion and the improvement effect of the cycle performance more obvious.
  • Examples 5 and 26 to 30 show the influence of the change in the average particle size of primary particles that agglomerate to form lithium iron phosphate secondary particles in the positive electrode material provided by the present application on the processing performance of the pole piece and the performance of the battery.
  • the average particle size d of the primary particles is in the range of 20nm-500nm, the particle size of the primary particles is in the appropriate range, the side reaction rate between the positive electrode material and the electrolyte and the kinetic performance of the battery positive electrode are at a reasonable level, and the battery’s Capacity development and cycle performance are better.
  • the average particle size d of the primary particles is less than 20 nm, the side reaction rate between the positive electrode material and the electrolyte is relatively large. Although it is beneficial to the performance of the initial capacity of the positive electrode material, the cycle performance of the battery is not high.
  • the average particle size d of the primary particles is greater than 500 nm, although the processability of the positive electrode slurry and the compaction density of the positive electrode sheet are improved, the kinetic performance of the positive electrode of the battery decreases, resulting in a decrease in the capacity of the battery.
  • Examples 5 and 31 to 36 show the influence of changes in the mass percentage of lithium iron phosphate secondary particles and lithium iron phosphate single crystal particles on the processing performance of the pole piece and battery performance in the positive electrode material provided by this application. .
  • the lithium iron phosphate secondary particles have a low specific surface area, which can increase the solid content of the slurry, reduce the processing difficulty of the thick coated pole piece, and reduce the production cost of the cathode material; while the lithium iron phosphate single crystal is filled with the lithium iron phosphate secondary In the particle gap of the particles, the compaction density of the pole piece is further improved, and the processing performance of the pole piece is improved.
  • the mass percentage of the second positive active material is greater than that of the first positive active material, that is, when the mass percentage of the second positive active material is greater than 50%, a positive electrode with improved performance and lower cost can be obtained. piece.
  • the compaction density and processing performance of the pole piece are further improved; at the same time, an appropriate amount of the first cathode active material needs to be added to fill the gaps between the lithium iron phosphate secondary particles, In order to increase the adhesion between the secondary particles of lithium iron phosphate, improve the compaction density and processing performance of the pole piece, improve the electron transport performance and reduce the membrane resistance.
  • the mass percentage of the second cathode active material is 60%-85%; or further 65%-80%, the first cathode active material and the second cathode active material cooperate with each other to improve the comprehensive processing performance of the slurry and pole piece electrical properties.
  • Examples 37 to 44 the methods for preparing positive electrode materials and lithium secondary batteries are basically the same as those in Example 5, except that the single-sided coating weight of the positive electrode sheet is changed.
  • the positive electrode sheet and the lithium secondary battery in Examples 37 to 44 were subjected to the same performance test as in Examples 1 to 36, and the energy density of the lithium secondary battery was also tested.
  • the detection method of the energy density of lithium secondary battery is as follows: (1) Put the battery in a 25°C oven environment, let it stand for 2 hours, and keep the battery temperature at 25°C; (2) 1/3C DC to 2.0V; (3) Pause for 5 minutes ; (4) 1/3C CC to 3.65V and CV to I ⁇ 0.05C; (5) Pause for 5min; (6) 1/3C DC to 2.0V.
  • This step is the actual cell test capacity, combined with the quality of the positive active material, the gram capacity can be calculated.
  • Table 4 shows the performance test results of the positive electrode sheets and lithium secondary batteries of Examples 37 to 44.
  • Examples 37 to 44 show the influence of the coating weight per unit area of the positive electrode sheet on the technical effect of the present application.
  • the positive electrode material provided in the present application can be used to prepare a positive electrode slurry with a high solid content, and further obtain a pole piece with high coating importance and high coating thickness.
  • coating weight and coating thickness With the increase of coating weight and coating thickness, the volume utilization rate of the battery increases, which helps to improve the energy density, but the migration path of lithium ions also becomes longer, the diffusion resistance increases, and the lithium ion concentration of the battery is extremely high during the discharge process. The change has increased rather than decreased.
  • the coating weight is 230g/m 2 -280g/m 2 , the overall performance of the battery energy density and cycle performance is the best.

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Abstract

本申请涉及一种正极材料、正极极片、锂二次电池、电池模块、电池包及装置。本申请所涉及的正极材料包含磷酸铁锂单晶颗粒和磷酸铁锂二次颗粒。其中，磷酸铁锂二次颗粒具有低比表面积，可减少制浆过程中对粘结剂和溶剂的消耗、提升浆料固含量，提升厚涂布极片的加工性能。同时，磷酸铁锂单晶充分填充到磷酸铁锂二次颗粒的颗粒间隙中，可进一步提升极片的压实密度，同时降低正极极片的膜片电阻，从而提高锂二次电池的克容量发挥和循环性能。

Description

正极材料、正极极片、锂二次电池、电池模块、电池包及装置 技术领域
本申请涉及电池领域，具体地讲，涉及一种正极材料、正极极片、锂二次电池、电池模块、电池包及装置。
背景技术
磷酸铁锂作为锂离子电池正极材料，在安全性能、循环性能和成本方面表现出优势，被大规模运用于大巴、乘用车和规模储能领域中。然而，磷酸铁锂全电池的电压平台、容量发挥和极片压实密度均处于较低水平。因而相比三元正极材料电池，磷酸铁锂电池的能量密度不尽人意。
通过电芯设计计算可以发现，提高正极极片的活性物质单位面积涂覆重量，即活性物质质量面密度，可以显著提高锂离子电池的能量密度，同时增加其它材料(集流体、壳体、电解液和隔离膜)的使用效率，降低电芯综合成本。但是，当锂离子电池中正极材料为磷酸铁锂时，在实际制造过程或使用的过程中，正极极片极易出现冷压断带或脱膜，较难实现高能量密度化。
由此，如何制备兼容高安全、长循环、高能量密度的锂离子电池成为业界一项急需攻克的难题。
发明内容
鉴于背景技术中存在的问题，本申请提供一种正极材料、正极极片、锂二次电池、电池模块、电池包及装置。
第一方面，本申请提供一种正极材料，其包含式(I)所示的第一正极活性物质和式(II)所示的第二正极活性物质，
LiFe 1-x1M1 x1PO 4      (I)
LiFe 1-x2M2 x2PO 4     (II)
其中，0≤x1≤0.1，0≤x2≤0.1；M1、M2各自独立地选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr或Ti中的至少一种；所述第一正极活性物质为单晶颗粒，所述第二正极活性物质为二次颗粒。
相对于现有技术，本申请至少具有以下优势：
本申请提供的正极材料中，包含第一正极活性物质和第二正极活性物质，所述第一正极活性物质为磷酸铁锂单晶颗粒，所述第二正极活性物质为磷酸铁锂二次颗粒。其中，磷酸铁锂二次颗粒具有低比表面积，可减少制浆过程中对粘结剂和溶剂的消耗、提升浆料固含量。而浆料固含量的提升可降低厚涂布极片的加工难度：厚涂布极片的活性物质层在烘干时，分散溶剂的挥发量减小，膜片层体积应变降低，且粘结剂在垂直于极片表面方向的偏析效应得到抑制，极片不易发生掉粉、裂纹、脱膜等现象。同时，磷酸铁锂单晶颗粒充分填充到磷酸铁锂二次颗粒的颗粒间隙中，增大磷酸铁锂二次颗粒之间的粘结力，进一步提升极片的压实密度；还可提升活性物质和集流体接触面的平整度，有助于减缓磷酸铁锂二次颗粒在极片冷压过程中对集流体表面的损伤，使极片的柔韧性加强，减少加工过程中极片断裂的概率。此外，由于磷酸铁锂二次颗粒的生产成本较低，本申请的技术方案也能降低电芯的综合成本。
本申请所提供的正极材料中，所述二次颗粒为由多个一次颗粒团聚形成的类石榴状形态。可选的，所述一次颗粒为单晶纳米颗粒。可选的，所述一次颗粒的平均粒径d在20nm-500nm范围内，此时，一次颗粒的粒径大小在合适范围内，正极材料与电解液发生的副反应速率和电池正极的动力学性能均处于合理水平，电池的容量发挥和循环性能较优。
本申请所提供的正极材料中，所述第二正极活性物质至少满足以下条件之一：(1)所述第二正极活性物质的中位粒径Dv50为2.5μm-10.5μm；可选的，所述第二正极活性物质的中位粒径Dv50为4.5μm-8.5μm；进一步可选的， 所述第二正极活性物质的中位粒径Dv50为6μm-7μm；(2)所述第二正极活性物质的比表面积为3.5m 2/g-10.5m 2/g，可选的，所述第二正极活性物质的比表面积为5m 2/g-9m 2/g；进一步可选的，所述第二正极活性物质的比表面积为6.5m 2/g-7.5m 2/g。
当第二正极活性物质的中位粒径Dv50和比表面积BET在本申请所提供的范围内，其的粒径和比表面积适中，有利于第一正极活性物质在其颗粒间隙中填充的充分性，使得极片压实密度较高，活性物质和集流体接触层具有较好的平整度，极片的加工性能好。同时，正极材料混合体系浆料的固含量在合适范围内，有利于提升电池的容量发挥和循环性能。
本申请所提供的正极材料中，所述单晶颗粒为内部晶格连续、几乎不存在晶界分隔的独立颗粒。
本申请所提供的正极材料中，所述第一正极活性物质在12Mpa下的粉末电阻率为150Ω·cm以下，可选的，所述第一正极活性物质在12Mpa下的粉末电阻率为80Ω·cm以下，进一步可选的，所述第一正极活性物质在12Mpa下的粉末电阻率为30Ω·cm以下。
随着第一正极活性物质的粉末电阻率的降低，其导电性得到提高，有利于提升正极活性物质间的电子传输性能，使正极极片的膜片电阻率随之降低，促进电池的容量发挥和循环性能。
本申请提供的正极材料中，所述第一正极活性物质至少满足以下条件之一：(1)所述第一正极活性物质的中位粒径Dv50为0.5μm-2.0μm，(2)所述第一正极活性物质的比表面积为6.0m 2/g-20m 2/g。
当第一正极活性物质的中位粒径Dv50在0.5μm-2.0μm范围内，有利于其充分填充到第二正极活性物质二次颗粒磷酸铁锂的颗粒间隙中，更好地提升极片的压实密度、提升极片的加工性能。当第一正极活性物质的比表面积为6.0m 2/g-20m 2/g范围内，有利于进一步减少制浆过程中对粘结剂的消耗，提升浆料固含量，同时保证较大的电化学反应活性比表面积。
本申请提供的正极材料中，所述第二正极活性物质的质量百分含量大于所述第一正极活性物质的质量百分含量。可选的，所述第二正极活性物质的质量百分含量为55％-90％；进一步可选的，所述第二正极活性物质的质量百分含量为60％-85％；更进一步可选的，所述第二正极活性物质的质量百分含量为65％-80％。
在本申请的实施方式中，第二活性物质磷酸铁锂二次颗粒具有低比表面积，可提升浆料固含量、降低厚涂布极片的可加工难度，并降低正极材料的生产成本；而第一活性物质磷酸铁锂单晶填充于磷酸铁锂二次颗粒的颗粒间隙中，进一步提升极片的压实密度，提高极片加工性能。当第二正极活性物质的质量百分含量大于第一正极活性物质的质量百分含量，即第二正极活性物质的质量百分含量大于50％时，可获得性能提升、成本较低的正极极片。随着第二正极活性物质含量的进一步增大，极片的压实密度和加工性能也进一步提升；同时需要适量的第一正极活性物质的加入，填充进磷酸铁锂二次颗粒间隙之间，以增大磷酸铁锂二次颗粒之间的粘结力，提升极片的压实密度和加工性能，提升电子传输性能并降低膜片电阻。当第二正极活性物质的质量百分含量为60％-85％；或进一步为65％-80％时，第一正极活性物质和第二正极活性物质相互协同作用，提升浆料的综合加工性能和极片电性能。
第二方面，本申请提供了一种正极极片，包括正极活性物质层，且所述正极活性物质层中包含本申请第一方面的正极材料。
本申请所提供的正极极片的单面单位面积涂布重量为140g/m 2-390g/m 2；可选的，单面单位面积涂布重量为190g/m 2-320g/m 2；进一步可选的，单面单位面积涂布重量为230g/m 2-280g/m 2。
本申请所提供的正极极片中，由于正极浆料的极限固含量得到了提高，从而可实现较高的涂布重量和较大的涂布厚度；随着涂布重量和涂布厚度的提升，电池体积利用率提高，有助于能量密度提升，但是锂离子迁移路径也随之变长，扩散阻抗增加，电池在放电过程中锂离子浓差极化变大，电池容量发挥 反而有所下降。当涂布重量为230g/m 2-280g/m 2时，电池能量密度和循环性能综合表现最佳。
本申请所提供的正极极片的膜片电阻小于2000mΩ；可选的，膜片电阻小于800mΩ；进一步可选的，膜片电阻小于200mΩ。本申请的正极极片具有较低的膜片电阻，从而可促进电池的能量密度和循环性能。
第三方面，本申请提供一种锂二次电池，其包括本申请第二方面所述的正极极片。
第四方面，本申请提供一种电池模块，其包括本申请第三方面所述的锂二次电池。
第五方面，本申请提供一种电池包，其包括本申请第四方面所述的电池模块。
第六方面，本申请提供一种装置，其包括本申请第三方面所述的锂二次电池或本申请第四方面所述的电池模块或本申请第五方面所述的电池包，其中，所述锂二次电池或所述电池模块或所述电池包用作所述装置的电源或能量存储单元。
本申请所提供的正极材料相比传统的磷酸铁锂材料，在制浆过程中的浆料极限固含量显著提升，进行厚涂布后的极片开裂情况得到改善，且膜片和集流体间的结合力得到提高，膜片电阻得到降低，使用本申请的正极材料制备正极极片并应用于锂二次电池中，可显著改善锂二次电池的能量密度、动力学性能和循环性能，同时也使得以本申请的锂二次电池或电池模块或电池包作为电源或能量存储单元的装置也具有较好的动力性能。
附图说明
图1是根据本申请一具体实施方式的第二正极活性物质在不同放大倍数下的扫描电镜图：其中，1A的放大倍数为1000X倍，1B的放大倍数为5000X倍，1C的放大倍数为10000X倍；
图2是根据本申请一具体实施方式的第一正极活性物质在不同放大倍数下的扫描电镜图：其中，2A的放大倍数为10000X倍，2B的放大倍数为30000X倍；
图3是根据本申请一具体实施方式的正极极片断面的扫描电镜图；
图4是根据本申请一具体实施方式的锂二次电池的立体图；
图5是图4所示锂二次电池的分解图；
图6是根据本申请一具体实施方式的电池模块的立体图；
图7是根据本申请一具体实施方式的电池包的立体图；
图8是图7所示电池包的分解图；
图9是根据本申请一具体实施方式的装置的示意图。
其中，附图标记说明如下：
1 电池包
2 上箱体
3 下箱体
4 电池模块
5 锂二次电池
51 壳体
52 电极组件
53 顶盖组件
具体实施方式
下面结合具体实施例，进一步阐述本申请。应理解，这些具体实施例仅用于说明本申请而不用于限制本申请的范围。
正极材料
本申请的第一方面涉及一种正极材料，其包含式(I)所示的第一正极活性物质和式(II)所示的第二正极活性物质，
LiFe 1-x1M1 x1PO 4       (I)
LiFe 1-x2M2 x2PO 4       (II)
其中，0≤x1≤0.1，0≤x2≤0.1；M1、M2各自独立地选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr或Ti中的至少一种；所述第一正极活性物质为单晶颗粒，所述第二正极活性物质为二次颗粒。
本申请发明人经研究发现：磷酸铁锂正极材料在生产过程中，为了提升正极材料的容量发挥和动力学性能，一般都需要充分的纳米化。但纳米化过程使得磷酸铁锂材料具有了高的比表面能，造成材料难以加工，在正极涂布厚度加厚的情况下，极片的掉粉、裂纹、脱膜现象会加剧。同时，达到相同的极片压实密度，高面密度的极片需要更大的冷压辊压力，在该过程中正极材料颗粒会对金属基材造成损伤。而极片在上述冷压过程中产生的缺陷，会造成后续极片在卷绕和裸电芯在热压过程中极片断裂。
本申请发明人经进一步研究发现：在本申请的实施方式中，第二正极活性物质磷酸铁锂二次颗粒具有低比表面积，可减少制浆过程中对粘结剂和溶剂的消耗、提升浆料固含量。浆料固含量的提升可降低厚涂布极片的加工难度：厚涂布极片的活性物质层在烘干时，分散剂的挥发量减小，膜片层体积应变降低，且粘结剂在垂直于极片表面方向的偏析效应得到抑制，极片不易发生掉粉、裂纹、脱膜等现象。同时，第一正极活性物质磷酸铁锂单晶充分填充到磷酸铁锂二次颗粒的颗粒间隙中，增大磷酸铁锂二次颗粒之间的粘结力，进一步提升极片的压实密度；还可提升活性物质和集流体接触面的平整度，有助于减缓磷酸铁锂二次颗粒在极片冷压过程中对集流体表面的损伤，使极片的柔韧性加强，减少加工过程中极片断裂的概率。
在本申请的部分实施方式中，作为第二正极活性物质的磷酸铁锂二次颗粒为由多个磷酸铁锂一次颗粒团聚形成的类石榴状形态。所述磷酸铁锂一次颗粒是构成二次颗粒分级结构的最小结构单元，指含有低孔隙率的独立的粒子，它能被电子显微镜观察到。
在本申请的部分实施方式中，所述一次颗粒的平均粒径d在20nm-500nm范围内。本申请中，当一次颗粒的平均粒径d在上述范围内时，形成的正极材料与电解液发生的副反应速率和电池正极的动力学性能均处于合理水平，电池的容量发挥和循环性能较优。所述一次颗粒的平均粒径d为采用长径统计法对一次颗粒的粒径进行统计得到。具体为：在SEM图中，测量多个一次颗粒的长轴方向的直径并取平均值。
在本申请的部分实施方式中，团聚形成所述磷酸铁锂二次颗粒的磷酸铁锂一次颗粒为单晶纳米颗粒。图1示出了第二正极活性物质在不同放大倍数下的扫描电镜图，其中，1A的放大倍数为1000X倍，1B的放大倍数为5000X倍，1C的放大倍数为10000X倍。
在本申请的部分实施方式中，所述第二正极活性物质的中位粒径Dv50为2.5μm-10.5μm。在本申请的部分实施方式中，所述第二正极活性物质的中位粒径Dv50为4.5μm-8.5μm。在本申请的部分实施方式中，所述第二正极活性物质的中位粒径Dv50为6μm-7μm。其中，中位粒径Dv50值的含义为：粉体样品中粒径大于该值和小于该值的颗粒体积各占总体体积的50％。
在本申请的部分实施方式中，所述第二正极活性物质比表面积为3.5m 2/g-10.5m 2/g。在本申请的部分实施方式中，所述第二正极活性物质比表面积为5m 2/g-9m 2/g。在本申请的部分实施方式中，所述第二正极活性物质比表面积为6.5m 2/g-7.5m 2/g。
当第二正极活性物质的中位粒径Dv50和比表面积BET在上述范围内，其的粒径和比表面积适中，有利于第一正极活性物质在其颗粒间隙中填充的充分性，使得极片压实密度较高，活性物质和集流体接触层具有较好的平整度，极片的加工性能好。同时，正极材料混合体系浆料的固含量在合适范围内，有利于电池的容量发挥和循环性能。
在本申请的部分实施方式中，作为第一正极活性物质的磷酸铁锂单晶颗粒，为内部晶格连续、几乎不存在晶界分隔的磷酸铁锂独立颗粒。图2示出 了第一正极活性物质在不同放大倍数下的扫描电镜图。其中，2A的放大倍数为10000X倍，2B的放大倍数为30000X倍。
在本申请的部分实施方式中，第一正极活性物质在12Mpa下的粉末电阻率为150Ω·cm以下。在本申请的部分实施方式中，第一正极活性物质在12Mpa下的粉末电阻率为80Ω·cm以下。在本申请的部分实施方式中，第一正极活性物质在12Mpa下的粉末电阻率为30Ω·cm以下。
第一正极活性物质的粉末电阻率较低，导电性较高，有利于提升正极活性物质间的电子传输性能，使正极极片的膜片电阻率随之降低，促进电池的容量发挥和循环性能。
在本申请的部分实施方式中，第一正极活性物质的中位粒径Dv50为0.5μm-2.0μm，有利于其充分填充到第二正极活性物质二次颗粒磷酸铁锂的颗粒间隙中，更好地提升极片的压实密度、提升极片的加工性能。
在本申请的部分实施方式中，第一正极活性物质磷酸铁锂单晶颗粒的比表面积为6.0m 2/g-20m 2/g，有利于进一步减少制浆过程中对粘结剂的消耗，提升浆料固含量。
在本申请的部分实施方式中，第二正极活性物质的质量百分含量大于第一正极活性物质的质量百分含量。在本申请的部分实施方式中，所述第二正极活性物质的质量百分含量为55％-90％；在本申请的部分实施方式中，所述第二正极活性物质的质量百分含量为60％-85％；在本申请的部分实施方式中，所述第二正极活性物质的质量百分含量为65％-80％。
当第二正极活性物质的质量百分含量大于第一正极活性物质的质量百分含量，即第二正极活性物质的质量百分含量大于50％时，可获得性能提升、成本较低的正极极片。随着第二正极活性物质含量的进一步增大，极片的压实密度和加工性能也进一步提升；同时需要适量的第一正极活性物质的加入，填充进磷酸铁锂二次颗粒间隙之间，以增大磷酸铁锂二次颗粒之间的粘结力，提升极片的压实密度和加工性能，提升电子传输性能并降低膜片电阻。当第二正 极活性物质的质量百分含量为60％-85％；或进一步为65％-80％时，第一正极活性物质和第二正极活性物质相互协同作用，提升浆料的综合加工性能和极片电性能。
正极极片
本申请的第二方面涉及一种正极极片，包括正极活性物质层，且所述正极活性物质层中包含本申请第一方面的正极材料。
取本申请部分实施方式的正极极片，采用氩离子束垂直于极片表面方向将极片切开，暴露出正极极片的断面，图3示出了正极极片断面的扫描电镜图，从图3可以看到，第一正极活性物质磷酸铁锂单晶颗粒填充于第二正极活性物质磷酸铁锂二次颗粒的颗粒间隙中。
在本申请的部分实施方式中，正极极片的单面单位面积涂布重量为140g/m 2-390g/m 2。在本申请的部分实施方式中，正极极片的单面单位面积涂布重量为190g/m 2-320g/m 2。在本申请的部分实施方式中，正极极片的单面单位面积涂布重量为230g/m 2-280g/m 2。
本申请实施方式提供的正极极片，正极浆料的极限固含量得到了提高，从而可实现较高的涂布重量和较大的涂布厚度；随着涂布重量和涂布厚度的提升，电池体积利用率提高，有助于能量密度提升，但是锂离子迁移路径也随之变长，扩散阻抗增加，电池在放电过程中锂离子浓差极化变大，电池容量发挥反而有所下降。因而，涂布重量可影响电池能量密度和循环性能的综合表现。
在本申请的部分实施方式中，正极极片的膜片电阻小于2000mΩ。在本申请的部分实施方式中，正极极片的膜片电阻小于800mΩ。在本申请的部分实施方式中，正极极片的膜片电阻小于200mΩ。所述正极极片的膜片电阻是指在室温下、正极集流体的上下表面均设置正极活性物质层后正极极片的整体电阻。本申请的实施方式所提供的正极极片具有膜片电阻低、电芯能量密度高、循环性能好的优势。
在本申请的部分实施方式中，正极极片包括正极集流体以及设置在正 极集流体至少一个表面上的所述正极活性物质层。所述正极活性物质层可设置在正极集流体的其中一个表面上，也可以设置在正极集流体的两个表面上。所述正极活性物质层中包含了本申请第一方面的正极材料。
在本申请的部分实施方式中，正极活性物质层还可包括导电剂以及粘结剂，其中导电剂以及粘结剂的种类和含量不受具体的限制，可根据实际需求进行选择。所述粘结剂通常包括含氟聚烯烃类粘结剂，相对于所述含氟聚烯烃类粘结剂来说，水通常是良溶剂，即所述含氟聚烯烃类粘结剂通常在水中具有良好的溶解性，例如，所述含氟聚烯烃类粘结剂可以是包括但不限于聚偏氟乙烯(PVDF)、偏氟乙烯共聚物或它们的改性(例如，羧酸、丙烯酸、丙烯腈等改性)衍生物等。在所述正极活性物质层中，由于粘结剂本身的导电性较差，因此粘结剂的用量不能过高。可选的，正极活性物质层中粘结剂的质量百分含量小于等于2wt％，以获得较低的极片阻抗。所述正极极片的导电剂可以是本领域各种适用于锂离子(二次)电池的导电剂，例如，可以是包括但不限于乙炔黑、导电炭黑、碳纤维(VGCF)、碳纳米管(CNT)、科琴黑等中的一种或多种的组合。所述导电剂的重量可以占正极材料层总质量的1wt％～10wt％。可选的，正极极片中导电剂与正极活性物质的重量比大于等于1.5:95.5。
在本申请的部分实施方式中，正极集流体的种类也不受具体的限制，可根据实际需求进行选择。所述正极集流体通常可以为层体，所述正极集流体通常是可以汇集电流的结构或零件，所述正极集流体可以是本领域各种适用于作为电化学储能装置正极集流体的材料，例如，所述正极集流体可以是包括但不限于金属箔，更具体可以是包括但不限于镍箔、铝箔。
本领域技术人员可选择合适的方法制备所述正极极片，例如，可以包括如下步骤：将本申请第一方面的正极活性材料、粘结剂、导电剂混合形成浆料后，涂布于正极集流体上。
锂二次电池
本申请的第三方面提供一种锂二次电池，其包括本申请第二方面所述 的正极极片。
在本申请的部分实施方式中，锂二次电池可包括正极极片、负极极片、间隔于正极极片和负极极片之间的隔离膜、电解液。其中，所述正极极片为本申请第二方面所述的正极极片。
除了使用本申请第二方面所述的正极极片外，本申请的锂二次电池的构造和制备方法本身是公知的。
在本申请的部分实施方式中，锂二次电池的负极极片通常包括负极集流体和位于负极集流体表面的负极活性材料层，所述负极活性材料层通常包括负极活性材料。所述负极活性材料可以是本领域各种适用于锂二次电池的负极活性材料的材料，例如，可以是包括但不限于石墨、软碳、硬碳、碳纤维、中间相碳微球、硅基材料、锡基材料、钛酸锂或其他能与锂形成合金的金属中的一种或多种的组合。其中，所述石墨可选自人造石墨、天然石墨以及改性石墨中的一种或多种的组合；所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅合金中的一种或多种的组合；所述锡基材料可选自单质锡、锡氧化合物、锡合金中的一种或多种的组合。所述负极集流体通常是汇集电流的结构或零件，所述负极集流体可以是本领域各种适用于作为锂二次电池负极集流体的材料，例如，所述负极集流体可以是包括但不限于金属箔，更具体可以是包括但不限于铜箔。此外，负极极片也可为锂片。
在本申请的部分实施方式中，锂二次电池的隔离膜可以是本领域各种适用于锂二次电池隔离膜的材料，例如，可以是包括但不限于聚乙烯、聚丙烯、聚偏氟乙烯、芳纶、聚对苯二甲酸乙二醇酯、聚四氟乙烯、聚丙烯腈、聚酰亚胺，聚酰胺、聚酯和天然纤维中的一种或多种的组合。
在本申请的部分实施方式中，锂二次电池的电解液可以是本领域各种适用于锂二次电池的电解液，例如，所述电解液通常包括电解质和溶剂，所述电解质通常可以包括锂盐，更具体的，所述锂盐可以是无机锂盐和/或有机锂盐，具体可以是包括但不限于LiPF 6、LiBF 4、LiN(SO 2F) 2(简写为LiFSI)、 LiN(CF 3SO 2) 2(简写为LiTFSI)、LiClO 4、LiAsF 6、LiB(C 2O 4) 2(简写为LiBOB)、LiBF 2C 2O 4(简写为LiDFOB)中的一种或多种的组合。再例如，所述电解质的浓度可以为0.8mol/L～1.5mol/L。所述溶剂可以是本领域各种适用于锂二次电池的电解液的溶剂，所述电解液的溶剂通常为非水溶剂，优选可以为有机溶剂，具体可以是包括但不限于碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、碳酸戊烯酯、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯或它们的卤代衍生物中的一种或多种的组合。
在本申请的部分实施方式中，制备所述锂二次电池的方法对于本领域技术人员来说应该是已知的，例如，所述正极极片、隔离膜和负极极片各自都可以是层体，从而可以裁剪成目标尺寸后依次叠放，还可以卷绕至目标尺寸，以用于形成电芯，并可以进一步与电解液结合以形成锂二次电池。
图4示出了根据本发明一具体实施方式的锂二次电池的立体图，图5是图4所示锂离子二次电池的分解图。参看图4和图5，根据本申请的锂二次电池5(以下简称电池单体5)包括外包装51、电极组件52、顶盖组件53和电解液(未示出)。其中电极组件52收容于壳体51内，电极组件52的数量不受限制，可以为一个或多个。
需要说明的是，图4所示的电池单体5为罐型电池，但本申请并不限于此，电池单体5可以是袋型电池，即壳体51由金属塑膜替代且取消顶盖组件53。
电池模块
本申请的第四方面提供一种电池模块，其包括本申请第三方面所述的锂二次电池。在一些实施方式中，所述锂二次电池可以组装成电池模块，电池模块所含的锂二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。图6是作为一个示例的电池模块4的立体图。参照图6，在电池模块4中，多个锂二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个 锂二次电池5进行固定。可选地，电池模块4还可以包括具有容纳空间的壳体，多个锂二次电池5容纳于该容纳空间。
电池包
本申请的第五方面提供一种电池包，其包括本申请第四方面所述的电池模块。在一些实施方式中，上述电池模块可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。图7是作为一个示例的电池包1的立体图，图8是图7所示电池包的分解图。参照图7和图8，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
装置
本申请的第六方面提供一种装置，其包括本申请第三方面所述的锂二次电池或本申请第四方面所述的电池模块或本申请第五方面所述的电池包，所述锂二次电池或所述电池模块或所述电池包用作所述装置的电源或所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述装置可以根据其使用需求来选择锂二次电池、电池模块或电池包。
图9示出了根据本申请一具体实施方式的装置的示意图。该装置可以为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子二次电池(即本申请的二次电池)的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用锂离子二次电池(即本申请的二次电池)作为电源。
本领域技术人员可以理解：以上提到的本申请的不同实施例中对于电 化学活性材料中的组分选择、组分含量和材料理化性能参数的各种限定或优选范围可以任意组合，其组合而得到的各种实施例仍然在本申请范围内，且视为本说明书公开内容的一部分。
除非特别规定，本说明书中涉及的各种参数具有本领域公知的通用含义，可以按本领域公知的方法进行测量。例如，可以按照在本申请的实施例中给出的方法进行测试。另外，各种优选实施例中给出的各种不同参数的优选范围和选项可以进行任意组合，由此得到的各种组合都视为在本申请的公开范围之内。
以下结合具体实施例进一步说明本申请的优势。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
(一)第一活性物质和第二活性物质的参数对本申请技术效果的影响
实施例1～36、对比例1～2
1、制备正极材料：
将第一正极活性物质单晶磷酸铁锂和第二正极活性物质二次颗粒磷酸铁锂，按照质量百分含量配比混合，得到正极材料。
2、制备正极极片：
将正极材料、粘结剂聚偏二氟乙烯(PVDF)与导电炭按96.5:2.0:1.5的重量比干混，加入适量的N-甲基吡咯烷酮(NMP)溶剂，充分搅拌混合，使其形成均匀的正极浆料；将此浆料涂覆于正极集流体厚度为13μm的涂碳铝箔上，随后进行烘干冷压，分条备用，得到正极极片。
3、按照本领域常规方法获得负极极片、隔离膜、电解液和壳体：
负极极片：将负极活性材料石墨与导电炭、粘结剂聚偏二氟乙烯(PVDF)按95:3:2重量比在适量的水溶剂中充分搅拌混合，使其形成均匀的负极浆料；将此浆料涂覆于负极集流体Cu箔上，干燥后把极片冷压到设计压密，分条备用。
隔离膜：采用12μm的PP隔离膜。
电解液：采用磷酸铁锂通用电解液。
壳体：壳体材料使用铝塑膜。
4、制备锂二次电池：
将正极极片，隔离膜，负极极片卷绕形成裸电芯，用铝塑膜将裸电芯进行封装，注入电解液，通过化成、排气和高温老化后得到锂二次电池。
实施例1～36、对比例1～2中的正极材料的相关参数、正极极片和锂二次电池的性能，可通过本领域内常规方法进行检测，以下为检测方法的举例：
1、第一正极活性物质的比表面积BET：
采用比表面积测试仪进行检测，测试仪器型号为：tristar 3020。检测步骤简述如下：取第一正极活性物质样品2.0g-4g；将样品放入样品管，放入加热包中，进行脱气处理(脱气条件为200℃，2小时)；脱气完成后，等脱气站温度降到常温时，将样品管从脱气站卸下，称量计算样品总质量；将样品管放入测试填充棒，进行BET测试，得到检测结果。
2、第一正极活性物质的中位粒径Dv50：
测定仪器：激光粒度分析仪；设备型号：马尔文Mastersizer 2000E或者Mastersizer 3000。由于正极材料的颗粒在激光束的照射下，其散射光的角度与颗粒的直径成反比关系而散射光强随角度的增加呈对数规律衰减，散射光的能量分布与颗粒直径的分布直接相关，通过接受和测量散向光的能量分布就可以得出颗粒的粒度分布特征。测试所用溶剂可以是水或者制备浆料所使用的其他有机溶剂，样品采用超声进行分散。所得分析结果Dv50即占总体积50％的颗粒直径大于此值，另有占总体积50％的颗粒直径小于此值。
3、第一正极活性物质在12Mpa下的粉末电阻率：
将第一正极活性物质粉末干燥，称取适量粉末，使用粉末电阻率测试仪，设备型号苏州晶格ST2722或者三思纵横UTM7305。将干燥粉末样品放于电阻率测试仪的模具/样品仓中，样品仓深度20mm，截面积1cm 2，然后从小到大缓慢施加压力，手动采集数据，记录不同压力点下对应的的粉末电阻率测试 结果。
4、第二正极活性物质的中位粒径Dv50：
参照第一正极活性物质的中位粒径Dv50的检测方法进行检测。
5、第二正极活性物质的比表面积BET：
参照第一正极活性物质的比表面积BET的检测方法进行检测。
6、正极极片的膜片电阻：
使用杭州川源科技有限公司ACCFLM膜片电阻测试系统，采用双探针法，对本申请实施方式中的正极极片(双面设置正极活性物质层)检测正极极片整体的膜片电阻。
7、膜片和集流体结合力检测：
取待待测试正极极片，用刀片截取宽30mm*长度为100-160mm的试样；同时，将双面胶贴于钢板上，胶带宽度20mm*长度90-150mm。将截取的极片试样贴在双面胶上，测试面朝下。将宽度与极片等宽，长度大于试样长度80-200mm的纸带插入极片下方，并且用皱纹胶固定，然后使用三思拉力机检测膜片和集流体的结合力。
8、克容量发挥：
采用25℃下1/3C的克容量来表征电池的容量发挥，具体检测流程简述如下：(1)将电池置于25℃烘箱环境，静置2h，待电池温度保持25℃；(2)1/3C DC to 2.0V；(3)暂停5min；(4)1/3C CC to 3.65V and CV to I≤0.05C；(5)暂停5min；(6)1/3C DC to 2.0V。此步为实际电芯测试容量，结合正极活性物质质量，即可计算得到克容量发挥。
9、循环性能测试：
采用60℃下1C/1C循环，检测电池容量衰减至初始值的80％时的循环圈数，具体流程简述如下：(1)将电池置于45℃烘箱中，静置2h，待电池温度保持25℃；(2)1C电流恒流充电到3.65V，继续恒压充电，直至充电电流小于0.05C后截止；(3)暂停5min；(4)1C电流恒流放电到2.5V；(5)暂停 5min。步骤(2)至(6)为电池的一个充放电循环，不断重复步骤(2)至(6)，直至电池容量衰减到初始值的80％时的循环圈数。
实施例1～36、对比例1～2的正极材料的相关参数如表1所示。
表1
Figure PCTCN2020113286-appb-000001
实施例1～36、对比例1～2的性能检测结果如表2所示。
表2
Figure PCTCN2020113286-appb-000002
数据讨论：
(1)实施例1～36、对比例1～2：
对比例1的正极材料仅包含磷酸铁锂单晶颗粒，从表2检测数据可知，对比例1的正极极片的加工性能较差，具体表现在正极材料的浆料极限固含量很低，涂布后极片的开裂情况严重，且膜片和集流体的结合力低。同时，对比例1的锂二次电池的容量发挥和循环性能表现不佳。
对比例2的正极材料仅包含磷酸铁锂二次颗粒，从表2数据可知，对比例2的正极极片，虽然浆料的极限固含量得到很大提升、涂布后的极片开裂情况得到改善，然而膜片和集流体的结合力很低，且正极极片的膜片电阻较高，电池的容量发挥和循环性能也不理想。
实施例1～36的正极材料包含了磷酸铁锂单晶颗粒和磷酸铁锂二次颗粒，相对于对比例1和对比例2，实施例1～36的正极极片的加工性能得到普遍提升，正极浆料的极限固含量较高，进行厚涂布后的极片开裂情况得到改善，且膜片和集流体间的结合力得到提高，膜片电阻得到降低，电池容量发挥和循环性能均优于对比例1和对比例2。
此外，从实施例1～5可知，采用不同元素掺杂的磷酸铁锂二次颗粒和磷酸铁锂单晶颗粒，混合后得到的正极材料均能实现改善极片加工性能、提高电池容量发挥和循环性能的效果；其中，Ti元素掺杂对于电芯的容量发挥和循环性能的提升最为显著，且Ti元素在正极材料中较佳的掺杂量为2000ppm。
(2)实施例5～9：
实施例5～9示出了本申请所提供的正极材料中，磷酸铁锂单晶颗粒在12Mpa下的粉末电阻率的变化，对极片加工性能和电池性能的影响。
第一正极活性物质磷酸铁锂单晶颗粒在12Mpa下的粉末电阻率为150Ω·cm以下、或为80Ω·cm以下、或进一步为30Ω·cm以下，随着磷酸铁锂单晶颗粒的粉末电阻率的降低，其导电性得到提高，正极活性物质间的电子传输性能较好，使正极极片的膜片电阻率随之降低，有利于电池的容量发挥和 循环性能。
(3)实施例5、10～17：
实施例5、10～17示出了本申请所提供的正极材料中，磷酸铁锂二次颗粒的中位粒径Dv50的变化，对极片加工性能和电池性能的影响。
当磷酸铁锂二次颗粒的中位粒径Dv50小于2.5μm时，二次颗粒的比表面积较大，导致吸液性加强，可造成膜片烘干过程中的轻微开裂；同时涂布后活性物质层的导电碳分布的均匀性有所不足，使膜片电阻升高。当磷酸铁锂二次颗粒的中位粒径Dv50大于10.5μm时，对第一正极活性物质在其颗粒间隙中填充的充分性有所减弱，不利于极片压实密度的提高，也影响活性物质和集流体接触层的平整度，导致活性物质和集流体之间的接触受到影响，反而增大加工过程中极片断裂的概率。当磷酸铁锂二次颗粒的Dv50为6μm-7μm时，极片加工性能较好，膜片和集流体结合力也较佳，有利于电池的容量发挥和循环性能达到最佳状态。
(4)实施例5、18～25：
实施例5、18～25示出了本申请所提供的正极材料中，磷酸铁锂二次颗粒的比表面积BET的变化，对极片加工性能和电池性能的影响。
当磷酸铁锂二次颗粒的比表面积BET低于3.5m 2/g时，导致锂二次电池的电化学反应活性较低，使电池的循环性能受到一定的影响。当磷酸铁锂二次颗粒的比表面积BET高于10.5m 2/g时，对正极浆料固含量的提升作用以及对极片加工性能改善作用变得不够明显。当磷酸铁锂二次颗粒的比表面积BET为6.5m 2/g-7.5m 2/g时，既能显著发挥对正极浆料固含量的提升作用以及对极片加工性能改善作用，也能保证电池的电化学反应活性，使得电池的容量发挥和循环性能的改善效果较为明显。
(5)实施例5、26～30：
实施例5、26～30示出了本申请所提供的正极材料中，团聚形成磷酸铁锂二次颗粒的一次颗粒的平均粒径变化，对极片加工性能和电池性能的影响。
当一次颗粒的平均粒径d在20nm-500nm范围内，一次颗粒的粒径大小在合适范围内，正极材料与电解液发生的副反应速率和电池正极的动力学性能均处于合理水平，电池的容量发挥和循环性能较优。当一次颗粒的平均粒径d小于20nm时，正极材料与电解液发生的副反应速率较大，虽然有利于正极材料初始容量的发挥，但电池的循环性能不高。当一次颗粒的平均粒径d大于500nm时，正极浆料的可加工性能和正极极片的压实密度虽得到提升，但电池正极动力学性能有所下降，导致了电池容量发挥也发生下降。
(6)实施例5、31～36：
实施例5、31～36示出了本申请所提供的正极材料中，磷酸铁锂二次颗粒和磷酸铁锂单晶颗粒的质量百分含量的变化，对极片加工性能和电池性能的影响。
磷酸铁锂二次颗粒具有低比表面积，可提升浆料固含量、降低厚涂布极片的可加工难度，并降低正极材料的生产成本；而磷酸铁锂单晶填充于磷酸铁锂二次颗粒的颗粒间隙中，进一步提升极片的压实密度，提高极片加工性能。当第二正极活性物质的质量百分含量大于第一正极活性物质的质量百分含量，即第二正极活性物质的质量百分含量大于50％时，可获得性能提升、成本较低的正极极片。随着第二正极活性物质含量的进一步增大，极片的压实密度和加工性能也进一步提升；同时需要适量的第一正极活性物质的加入，填充进磷酸铁锂二次颗粒间隙之间，以增大磷酸铁锂二次颗粒之间的粘结力，提升极片的压实密度和加工性能，提升电子传输性能并降低膜片电阻。当第二正极活性物质的质量百分含量为60％-85％；或进一步为65％-80％时，第一正极活性物质和第二正极活性物质相互协同作用，提升浆料的综合加工性能和极片电性能。
(二)正极极片的单面单位面积涂布重量对本申请技术效果的影响
实施例37～44
实施例37～44中，制备正极材料、锂二次电池的方法与实施例5基本相同，不同之处仅在于改变了正极极片的单面涂布重量。
此外，对实施例37～44中的正极极片和锂二次电池，除了进行实施例1～36相同的性能检测之外，还进行了锂二次电池能量密度的检测。
锂二次电池能量密度的检测方法如下：(1)将电池置于25℃烘箱环境，静置2h，待电池温度保持25℃；(2)1/3C DC to 2.0V；(3)暂停5min；(4)1/3C CC to 3.65V and CV to I≤0.05C；(5)暂停5min；(6)1/3C DC to 2.0V。此步为实际电芯测试容量，结合正极活性物质质量，即可计算得到克容量发挥。通过电压-容量曲线积分即可计算电芯能量，能量值/电芯重量值＝能量密度。
实施例37～44的正极材料的相关参数如表3所示。
表3
Figure PCTCN2020113286-appb-000003
实施例37～44的正极极片和锂二次电池的性能检测结果如表4所示。
表4
Figure PCTCN2020113286-appb-000004
数据讨论：
实施例37～44示出了正极极片的单面单位面积涂布重量对本申请技术效果的影响。
采用本申请所提供的正极材料可制备固含量较高的正极浆料，并进一步获得高涂布重要和高涂布厚度的极片。随着涂布重量和涂布厚度的提升，电池体积利用率提高，有助于能量密度提升，但是锂离子迁移路径也随之变长，扩散阻抗增加，电池在放电过程中锂离子浓差极化变大反而有所下降。当涂布重量为230g/m 2-280g/m 2时，电池能量密度和循环性能综合表现最优。
根据上述说明书的揭示和教导，本领域技术人员还可以对上述实施方式进行变更和修改。因此，本申请并不局限于上面揭示和描述的具体实施方式，对本申请的一些修改和变更也应当落入本申请的权利要求的保护范围内。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本申请构成任何限制。

Claims (14)

  1. 一种正极材料，其中，包含式(I)所示的第一正极活性物质和式(II)所示的第二正极活性物质，
    LiFe 1-x1M1 x1PO 4  (I)
    LiFe 1-x2M2 x2PO 4  (II)
    其中，0≤x1≤0.1，0≤x2≤0.1，M1、M2各自独立地选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr或Ti中的至少一种；
    所述第一正极活性物质为单晶颗粒，所述第二正极活性物质为二次颗粒。
  2. 根据权利要求1所述的正极材料，其中，所述二次颗粒为由多个一次颗粒团聚形成的类石榴状形态，
    可选的，所述一次颗粒为单晶纳米颗粒，
    可选的，所述一次颗粒的粒径d在20nm-500nm范围内。
  3. 根据权利要求1或2所述的正极材料，其中，所述第二正极活性物质至少满足以下条件之一：
    (1)所述第二正极活性物质的中位粒径Dv50为2.5μm-10.5μm；可选的，为4.5μm-8.5μm；进一步可选的，为6μm-7μm；
    (2)所述第二正极活性物质比表面积为3.5m 2/g-10.5m 2/g；可选的，为5m 2/g-9m 2/g；进一步可选的，为6.5m 2/g-7.5m 2/g。
  4. 根据权利要求1所述的正极材料，其中，所述单晶颗粒为内部晶格连续、几乎不存在晶界分隔的独立颗粒。
  5. 根据权利要求1或4所述的正极材料，其中，所述第一正极活性物质在12Mpa下的粉末电阻率为150Ω·cm以下；可选的，为80Ω·cm以下；进一步可选的，为30Ω·cm以下。
  6. 根据权利要求1或4或5所述的正极材料，其中，所述第一正极活性物质至少满足以下条件之一：
    (1)所述第一正极活性物质的中位粒径Dv50为0.5μm-2.0μm；
    (2)所述第一正极活性物质的比表面积为6.0m 2/g-20m 2/g。
  7. 根据权利要求1至6任一项所述的正极材料，其中，所述第二正极活性物质的质量百分含量大于所述第一正极活性物质的质量百分含量，可选的，所述第二正极活性物质的质量百分含量为55％-90％；进一步可选的为60％-85％；更进一步可选的为65％-80％。
  8. 一种正极极片，包括正极活性物质层，其中，所述正极活性物质层中包含根据权利要求1～7中任一项所述的正极材料。
  9. 根据权利要求8所述的正极极片，其中，所述正极极片的单面单位面积涂布重量为140g/m 2-390g/m 2；可选的为190g/m 2-320g/m 2；进一步可选的为230g/m 2-280g/m 2。
  10. 根据权利要求8或9所述的正极极片，其中，所述正极极片的膜片电阻小于2000mΩ；可选的小于800mΩ；进一步可选的小于200mΩ。
  11. 一种锂二次电池，其中，包括根据权利要求8至10中任一项所述的正极极片。
  12. 一种电池模块，其中，包括根据权利要求11所述的锂二次电池。
  13. 一种电池包，其中，包括根据权利要求12所述的电池模块。
  14. 一种装置，其中，包括根据权利要求11所述的锂二次电池或根据权利要求12所述的电池模块或根据权利要求13所述的电池包，所述锂二次电池或所述电池模块或所述电池包用作所述装置的电源或所述装置的能量存储单元。
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WO2023206131A1 (zh) * 2022-04-27 2023-11-02 宁德时代新能源科技股份有限公司 磷酸铁锂正极极片及其相关的二次电池、电池模块、电池包和用电装置
CN115832183A (zh) * 2022-05-05 2023-03-21 宁德时代新能源科技股份有限公司 正极极片及其制备方法、二次电池、电池模块、电池包及用电装置
WO2024087388A1 (zh) * 2022-10-27 2024-05-02 欣旺达动力科技股份有限公司 一种二次电池及用电设备
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