WO2022067812A1 - 混合正极材料、正极极片及制备方法、电池和装置 - Google Patents

混合正极材料、正极极片及制备方法、电池和装置 Download PDF

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WO2022067812A1
WO2022067812A1 PCT/CN2020/119743 CN2020119743W WO2022067812A1 WO 2022067812 A1 WO2022067812 A1 WO 2022067812A1 CN 2020119743 W CN2020119743 W CN 2020119743W WO 2022067812 A1 WO2022067812 A1 WO 2022067812A1
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positive electrode
electrode material
chemical system
mixed
iron phosphate
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PCT/CN2020/119743
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English (en)
French (fr)
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别常峰
胡霞
刘倩
柳娜
徐晓富
倪欢
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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 PCT/CN2020/119743 priority Critical patent/WO2022067812A1/zh
Priority to EP20955832.9A priority patent/EP4071855A4/en
Priority to CN202080097180.3A priority patent/CN115280551A/zh
Publication of WO2022067812A1 publication Critical patent/WO2022067812A1/zh
Priority to US17/863,295 priority patent/US20220359874A1/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
    • 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
    • H01M4/36—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
    • 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
    • H01M4/04—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
    • H01M4/04—Processes of manufacture in general
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • H01M4/0435—Rolling or calendering
    • 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
    • H01M4/48—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
    • 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
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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 application belongs to the technical field of lithium ion batteries, and in particular relates to a mixed positive electrode material, a positive electrode sheet and a preparation method, a battery and a device.
  • lithium-ion batteries Because of its high energy density, long cycle life, no memory effect, and green environmental protection, lithium-ion batteries have strong competitiveness in the field of secondary batteries. They are not only widely used in mobile phones, notebook computers and other terminal electronic products, but also Applications in electric vehicles, large-scale energy storage equipment and other fields are also gradually increasing.
  • cathode materials for lithium-ion batteries the most mature and commonly used lithium iron phosphate material systems (such as lithium iron phosphate or doped modified lithium iron phosphate materials) and ternary material systems (such as nickel cobalt lithium manganate) and nickel-cobalt-aluminate lithium system materials).
  • Lithium-ion batteries with ternary system materials as cathode active materials have received attention in the industry during a certain period of development due to their higher energy density and better power performance, and have become a research direction.
  • the two types of materials have their own advantages and disadvantages. With the deepening of cognition and research, how to use their respective advantages has also begun to attract attention.
  • the present application provides a mixed positive electrode material, which solves the problem of easy agglomeration when mixing different types of materials by screening and reasonably matching the types and microscopic morphology of the materials used, and makes the compatibility and processing performance of the mixed positive electrode material better. Well, it is beneficial to ensure the safety performance and cycle life improvement of lithium-ion batteries.
  • the present application also provides a positive electrode plate, which is prepared by using the mixed positive electrode material of the present application, which can improve the distribution uniformity of the positive electrode material on the positive electrode plate, and can better meet the electrochemical performance of the lithium ion battery.
  • the present application also provides a method for preparing a positive electrode plate.
  • the preparation method of the present application adopts the mixed positive electrode material of the present application, which can improve the uniform distribution of the positive electrode material on the positive electrode plate, improve the performance of the electrode plate, and better meet the requirements of lithium ion batteries. Electrochemical performance requirements.
  • the present application also provides a battery, which adopts the positive electrode plate of the present application to achieve the purpose of improving the energy density and at the same time having good electrochemical performance.
  • the present application also provides a device comprising the battery of the present application, the battery being used to provide a power source for the device and/or an energy storage unit for the device.
  • This application proposes a mixed cathode material, which includes a mixed component composed of a lithium iron phosphate chemical system material and a ternary chemical system material.
  • the lithium iron phosphate chemical system material is secondary particles with low specific surface area, and the average specific surface area does not exceed 10 m 2 /g of secondary particles.
  • the lithium iron phosphate chemical system material is secondary particles with an average specific surface area not exceeding 6 m 2 /g.
  • the secondary particles of the lithium iron phosphate material used in the present application should also be understood as the above-mentioned processed and agglomerated material particles. In a specific embodiment, it may refer to secondary particles obtained by hard agglomeration of primary particles of a nanoscale lithium iron phosphate chemical system.
  • the specific surface area of the secondary particles of the lithium iron phosphate chemical system is no more than 10 m 2 /g. Specifically, it may be no more than 9 m 2 /g, no more than 8 m 2 /g, and no more than 7 m 2 /g. Further, it may be no more than 6m 2 /g, no more than 5m 2 /g, no more than 4m 2 /g, no more than 3m 2 /g.
  • the specific surface area of the secondary particles of the lithium iron phosphate chemical system when mixed with the ternary chemical system material, it can avoid the high viscosity of the slurry caused by the agglomeration problem during the pulping process. The problem of uneven coating on the sheet, thereby improving the feasibility of the processing of mixed cathode materials.
  • the particle size distribution of the secondary particles of the lithium iron phosphate chemical system satisfies: 0.1 ⁇ D v 50/(D v 90-D v 10) ⁇ 10. Further 0.3 ⁇ D v 50/(D v 90-D v 10) ⁇ 5, and further 0.5 ⁇ D v 50/(D v 90-D v 10) ⁇ 1.
  • the obtained mixed positive electrode material is more conducive to the formation of a more uniform mixed positive electrode slurry during the pulping process.
  • D v 10 and D v 90 can be further defined respectively, and the proportion of particles with smaller particle size and larger particle size can be controlled, so that the secondary particles of the lithium iron phosphate chemical system can be controlled.
  • the slurry processability of the mixed system with the ternary chemical system material is further optimized.
  • the particle size distribution of the secondary particles of the lithium iron phosphate chemical system can satisfy: D v 10 ⁇ 0.6 ⁇ m, D v 90 ⁇ 30 ⁇ m; for example, D v 10 ⁇ 0.8 ⁇ m, D v 90 ⁇ 25 ⁇ m; further, such as D v 10 ⁇ 1 ⁇ m, D v 90 ⁇ 20 ⁇ m; D v 10 ⁇ 1.2 ⁇ m, D v 90 ⁇ 25 ⁇ m; D v 10 ⁇ 2 ⁇ m, D v 90 ⁇ 22 ⁇ m; D v 10 ⁇ 3 ⁇ m, D v 90 ⁇ 18 ⁇ m; D v 10 ⁇ 4 ⁇ m , D v 90 ⁇ 15 ⁇ m; D v 10 ⁇ 5 ⁇ m, D v 90 ⁇ 12 ⁇ m.
  • the median particle size distribution of the secondary particles of the lithium iron phosphate chemical system satisfies: 2 ⁇ m ⁇ D v 50 ⁇ 9 ⁇ m.
  • the introduced secondary particles of the lithium iron phosphate chemical system material have a suitable median particle size distribution while satisfying a smaller specific surface area, it is more beneficial to the secondary particles of the lithium iron phosphate chemical system and the ternary chemical system. Homogeneous mixing of materials, thereby improving the processability of mixed cathode materials.
  • the average particle size distribution d of the primary particles constituting the secondary particles of the lithium iron phosphate chemical system satisfies: 20nm ⁇ d ⁇ 800nm.
  • d may satisfy: 300nm ⁇ d ⁇ 500nm, further 300nm ⁇ d ⁇ 350nm, 350nm ⁇ d ⁇ 400nm, 400nm ⁇ d ⁇ 450nm, 450nm ⁇ d ⁇ 500nm.
  • the ternary chemical system material can be further prevented from causing kinetic performance and low temperature performance due to the introduction of the LFP secondary particle material. deterioration, at the same time, the hybrid system can guarantee a better long-term life.
  • the powder resistivity of the secondary particles of the lithium iron phosphate chemical system is not greater than 100 ⁇ cm. Specifically, it can be: no greater than 80 ⁇ cm, no greater than 75 ⁇ cm, no greater than 70 ⁇ cm, no greater than 65 ⁇ cm, no greater than 60 ⁇ cm, no greater than 55 ⁇ cm, 50 ⁇ cm, no greater than 45 ⁇ cm cm, not more than 40 ⁇ cm, not more than 30 ⁇ cm, not more than 20 ⁇ cm, not more than 10 ⁇ cm.
  • the resistance of the positive electrode sheet can be effectively regulated, thereby helping to ensure the cycle performance of the lithium ion battery.
  • the mass percentage content of the secondary particles in the lithium iron phosphate chemical system is controlled to be 20%-70%.
  • the mass percentage of the secondary particles in the lithium iron phosphate chemical system can be 20%-25%, 25%-35%, 35%-45%, 45%-55%, 55%-65%, 65% -70%.
  • the energy density and safety of the battery can be further optimized.
  • the lithium iron phosphate chemical system material may use a lithium-containing compound with the general formula LiFe 1-x M x PO 4 , wherein 0 ⁇ x ⁇ 0.1, M may be selected from Cu, Mn, Cr , one or more of Zn, Pb, Ca, Co, Ni, Sr or Ti.
  • the ternary chemical system material may be a nickel cobalt lithium manganate chemical system material and/or a nickel cobalt lithium aluminate chemical system material.
  • the general formula of the chemical system of nickel cobalt manganese oxide can be LiNi x M y Co 1-xy O 2 , where 1>x>0, 1>y>0, x+y ⁇ 0.95; lithium nickel cobalt aluminate
  • the general formula of the chemical system material can be LiNi x Co y Al 1-xy O 2 , wherein 1>x>0.6, 0.4>y>0.1.
  • the mixed positive electrode material described in this application solves the problem of agglomeration when the ternary chemical system material is blended with the lithium iron phosphate chemical system material by controlling the specific surface area of the secondary particles of the lithium iron phosphate chemical system, and improves the performance of the mixed positive electrode material. Processing performance, realize the slurry is not easy to agglomerate, and improve the good compatibility between different materials. The stability of the slurry is enhanced, the maximum storage time of the slurry is increased, and the filtration performance is improved.
  • the mixed positive electrode material of the present application is used to prepare the positive electrode plate, the mixed components can be uniformly distributed on the positive electrode plate, which is beneficial to adjust the uniformity of the resistance distribution of the electrode plate, thereby improving the electrochemical performance of the battery.
  • the present application proposes a positive electrode sheet, which includes a positive electrode material layer containing the above-mentioned mixed positive electrode material.
  • the mass per unit area of the positive electrode material layer is 150-250 g/m 2 .
  • the lower limit of the mass per unit area of the positive electrode material layer may be: not lower than 150 g/m 2 , not lower than 160 g/m 2 , not lower than 170 g/m 2 , not lower than 180 g/m 2 , not lower than 190g/m 2 , not lower than 200g/m 2 , not lower than 210g/m 2 , not lower than 220g/m 2 , not lower than 230g/m 2 , not lower than 240g/m 2 .
  • the upper limit of the mass per unit area of the positive electrode material layer may be: not higher than 160g/m 2 , not higher than 170g/m 2 , not higher than 180g/m 2 , not higher than 190g/m 2 , not higher than 200g/m 2 , not higher than 220g/m 2 , not higher than 210g/m 2 , not higher than 230g/m 2 , not higher than 240g/m 2 , not higher than 250g/m 2 .
  • the compaction density of the positive electrode material layer is 2.6-3.5 g/cm 3 .
  • the lower limit of the compaction density of the positive electrode material layer may be 2.6 g/cm 3 , 2.7 g/cm 3 , 2.8 g/cm 3 , 2.9 g/cm 3 , 3 g/cm 3 , 3.1 g/cm 3 , 3.2 g/cm 3 , 3.3 g/cm 3 , 3.4 g/cm 3 .
  • the upper limit of the compaction density of the positive electrode material layer may be 2.7g/ cm3 , 2.8g/ cm3 , 2.9g/ cm3 , 3g/ cm3 , 3.1g/ cm3 , 3.2g/ cm3 , 3.3g/cm3 3 , 3.4g/cm 3 , 3.5g/cm 3 .
  • the resistivity of the positive electrode sheet and the capacity of the positive electrode sheet per unit area can be adjusted, thereby ensuring that the prepared battery has higher dynamic performance and high energy density.
  • the positive electrode sheet further contains a conductive agent and a binder.
  • the conductive agent and the binder are conventional materials in the art, for example, the conductive agent can be selected from at least one of carbon black, graphene, carbon nanotubes, Ketjen black, and carbon fibers, and the binder can be selected from polytetrafluoroethylene At least one of ethylene, polystyrene butadiene rubber, and sodium carboxymethyl cellulose.
  • the mass ratio of the mixed positive electrode material, the conductive agent and the binder is about (90-98):(1-5):(1-5). For example 96.5:1.5:2, 92:2:3, 93:3:2, 97:5:1, 98:1:5, 95:3.5:4.
  • the positive electrode plate of the present application because of the use of the above-mentioned mixed positive electrode material, can realize the uniform distribution of the mixed positive electrode material on the positive electrode electrode plate, which is beneficial to improve the uniformity of electrode resistance and can better meet the electrochemical performance of lithium ion batteries.
  • the method for preparing a positive electrode sheet proposed in this application includes the following steps: mixing the mixed positive electrode materials, filtering and collecting the slurry, coating the slurry on the current collector, removing the solvent, and rolling Pressing and slicing to obtain a positive pole piece.
  • the preparation method of the present application adopts the mixed positive electrode material of the present application, which is beneficial to make the mixed positive electrode material distribute more uniformly on the positive electrode sheet, improve the performance of the positive electrode sheet, and better meet the electrochemical performance requirements of lithium ion batteries.
  • the present application provides a battery including the above-mentioned positive electrode.
  • the mixed positive electrode material is uniformly distributed on the positive electrode electrode sheet, it is beneficial to improve the uniformity of the electrode sheet resistance, so that the prepared battery has higher energy density and better cycle performance.
  • the battery of the present application has high energy density and also has good electrochemical performance.
  • the present application proposes a device comprising the above-mentioned battery, the battery is used to provide power for the device and/or an energy storage unit for the device, and the device is selected from the group consisting of electric vehicles, electric ships, electric tools, electronic equipment and storage devices. one or more of the energy systems.
  • the device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric vehicles, etc.) scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • mobile devices such as mobile phones, laptop computers, etc.
  • electric vehicles such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric vehicles, etc.
  • scooters electric golf carts, electric trucks, etc.
  • electric trains ships and satellites, energy storage systems, etc.
  • Fig. 1 is the SEM image of the positive pole piece of embodiment 1;
  • Fig. 2 is the SEM image of the positive pole piece prepared by traditional single crystal 523 ternary material
  • 3a and 3b are SEM images of different magnifications of positive pole pieces prepared from LFP material secondary particles in an embodiment of the present application
  • Fig. 4 is the long-diameter statistical schematic diagram of some primary particles in Fig. 3a;
  • Example 7 is a schematic diagram of the lithium-ion battery of Example 1.
  • FIG. 8 is a schematic diagram of one embodiment of a device in which a lithium ion battery is used as a power source.
  • lithium iron phosphate system materials mixed with ternary system materials as cathode materials to improve the safety performance and cycle life of ternary system batteries. Since the structural stability of lithium iron phosphate itself is better than that of ternary materials, it has become a consensus in the industry that a small amount of lithium iron phosphate can be mixed in the ternary cathode material to improve the structural stability of the battery material system.
  • the screening and mixing are improper, the performance and quality of the battery may be unstable due to the high defective rate of the positive electrode, and the positive electrode will be unstable in severe cases. The material system and the overall performance of the battery are adversely affected. There may be many factors affecting the defect rate.
  • the poor compatibility of the two materials leads to poor stability of the mixed slurry used to prepare the pole piece, and is prone to agglomeration, which makes the distribution of the positive electrode material in the active material layer of the pole piece. non-uniformity, thereby deteriorating the electrochemical performance of the battery.
  • this application proposes a mixed positive electrode material, which includes a mixed component consisting of a lithium iron phosphate chemical system material and a ternary chemical system material.
  • the lithium iron phosphate chemical system material is secondary particles with a low specific surface area and a specific surface area. Secondary particles with an average value not exceeding 10 m 2 /g. In some embodiments, the lithium iron phosphate chemical system material is secondary particles having an average specific surface area of no more than 6 m 2 /g.
  • the particles When the particles are very fine, they have a large specific surface area, and the larger the specific surface area, the larger the surface energy.
  • the small particles with large surface energy are easily combined due to weak van der Waals forces and hydrogen bonds and other interaction forces, and agglomeration occurs, that is, many small particles combine twice to form larger secondary particles, that is, small particles.
  • the primary particles are agglomerated in a certain way, which can be called secondary particles.
  • the agglomeration of particles can be divided into soft agglomeration or hard agglomeration.
  • the agglomeration caused by physical bonding is soft agglomeration
  • the agglomeration caused by chemical bonding is Hard reunion.
  • Soft agglomerates can be opened using mechanical force, but hard agglomerates are difficult to open. Therefore, the product form that can usually be called secondary particles should refer to the product obtained by processing the primary particles by some artificial means to make them agglomerate.
  • the mixed positive electrode material of the present application introduces the lithium iron phosphate chemical system material mainly in the form of secondary particles.
  • the secondary particles of the lithium iron phosphate material used in this application should also be understood as the above-mentioned processed and agglomerated material particles. In a specific embodiment, it may refer to secondary particles obtained by hard agglomeration of primary particles of a nanoscale lithium iron phosphate chemical system.
  • the lithium iron phosphate chemical system material in the mixed positive electrode material mainly exists in the form of secondary particles, and a small amount of primary particles are inevitably doped in the mixed components, which are all within the protection scope of this application.
  • the chemical system of the positive electrode material is divided according to the type of active material, and the auxiliary materials doped or added are not limited.
  • the material whose active material is lithium iron phosphate (including element-doped) can be defined as Lithium iron phosphate chemical system material
  • the active material is the material represented by the nickel cobalt lithium manganate system (generally referred to as NCM) and the nickel cobalt lithium aluminate system (generally called NCA), which is defined as a ternary chemical material system.
  • the specific surface area between the lithium iron phosphate chemical system particles and the ternary chemical system particles is significantly different, and it is easy to agglomerate when mixing.
  • the inventors have found through a large number of experimental studies that the secondary particles of the lithium iron phosphate chemical system with a smaller average specific surface area can be used, specifically, no more than 9m 2 /g, no more than 8m 2 /g, no more than 7m 2 /g . Further, it may be no more than 6m 2 /g, no more than 5m 2 /g, no more than 4m 2 /g, no more than 3m 2 /g.
  • D v X is defined as follows: the particles are arranged in ascending order of volume and are numbered 1, 2, 3...n..., where the nth particle and all particles whose volume is less than or equal to the nth particle have a volume The sum accounts for X% of the total volume of all particles, and the particle size value of the nth particle is recorded as D v X.
  • D v 50 is the particle size value of the corresponding nth particle when the sum of the volumes of the first n particles accounts for 50% of the total volume.
  • D v 50 is used to represent the median particle size distribution.
  • D v 10 refers to the particle size value of the corresponding nth particle when the sum of the volume of the first n particles accounts for 10% of the total volume.
  • D v 90 refers to the particle size value of the corresponding nth particle when the sum of the volume of the first n particles accounts for 90% of the total volume.
  • the particle size distribution of the secondary particles satisfies: 0.1 ⁇ D v 50/(D v 90-D v 10) ⁇ 10, further 0.3 ⁇ D v 50/(D v 90-D v 10) ⁇ 5, Furthermore, when 0.5 ⁇ D v 50/(D v 90-D v 10) ⁇ 1, the obtained mixed positive electrode material is more favorable for forming a more uniform mixed positive electrode slurry during the pulping process.
  • D v 10 When D v 10 is too small, there may be agglomeration of small particles.
  • D v 90 When D v 90 is too large, the filter element of the lithium-ion battery slurry production equipment may be blocked, and the ternary material with smaller particle size cannot be used. Particles form well packed and fit.
  • D v 10 and D v 90 can be further defined respectively, and the proportion of particles with smaller particle size and larger particle size can be controlled, so that the secondary particles of the lithium iron phosphate chemical system can be controlled.
  • the particle size distribution of secondary particles can satisfy: D v 10 ⁇ 0.6 ⁇ m, D v 90 ⁇ 30 ⁇ m, such as D v 10 ⁇ 0.8 ⁇ m, D v 90 ⁇ 25 ⁇ m, further such as D v 10 ⁇ 1 ⁇ m, D v 90 ⁇ 20 ⁇ m; D v 10 ⁇ 1.2 ⁇ m, D v 90 ⁇ 25 ⁇ m; D v 10 ⁇ 2 ⁇ m, D v 90 ⁇ 22 ⁇ m; D v 10 ⁇ 3 ⁇ m, D v 90 ⁇ 18 ⁇ m; D v 10 ⁇ 4 ⁇ m, D v 90 ⁇ 15 ⁇ m; D v 10 ⁇ 5 ⁇ m, D v 90 ⁇ 12 ⁇ m.
  • the introduced secondary particles of the lithium iron phosphate chemical system material when the introduced secondary particles of the lithium iron phosphate chemical system material have a suitable median particle size distribution while satisfying a small specific surface area, it is more beneficial to the secondary particles of the lithium iron phosphate chemical system and the ternary chemical system material. uniform mixing, thereby improving the processing performance of the mixed cathode material.
  • the median particle size distribution of the secondary particles satisfies: 2 ⁇ m ⁇ D v 50 ⁇ 9 ⁇ m, for example, 3 ⁇ m ⁇ D v 50 ⁇ 6 ⁇ m, 2 ⁇ m ⁇ D v 50 ⁇ 4 ⁇ m, 4 ⁇ m ⁇ D v 50 ⁇ 7 ⁇ m, 5 ⁇ m ⁇ D v 50 ⁇ 8 ⁇ m, 6 ⁇ m ⁇ D v 50 ⁇ 9 ⁇ m.
  • the electrochemical performance of the lithium ion battery prepared from the hybrid cathode material of the present application can be further improved.
  • the average particle size of the primary particles is too small, the storage performance and cycle life of the hybrid system are poor; when the average particle size of the primary particles is too large, the low-temperature performance and rate discharge performance of the hybrid system are poor.
  • the average particle size distribution d of the primary particles constituting the secondary particles satisfies: 20nm ⁇ d ⁇ 800nm, for example, when the control d satisfies: 300nm ⁇ d ⁇ 500nm, further 300nm ⁇ d ⁇ 350nm, 350nm ⁇ d ⁇ 400nm, 400nm ⁇ d ⁇ 450nm, 450nm ⁇ d ⁇ 500nm, so that the ternary chemical system material will not deteriorate the kinetic performance and low temperature performance due to the introduction of the LFP secondary particle material. Guarantees better long-term life.
  • the powder resistivity of the LFP secondary particles will indirectly affect the resistance of the positive electrode sheet. Therefore, the properties of the secondary particles of the lithium iron phosphate chemical system can be further defined by the powder resistivity, for example, the powder resistivity of the secondary particles of the lithium iron phosphate chemical system can be controlled to be no greater than 100 ⁇ cm. Specifically, it can be: no greater than 80 ⁇ cm, no greater than 75 ⁇ cm, no greater than 70 ⁇ cm, no greater than 65 ⁇ cm, no greater than 60 ⁇ cm, no greater than 55 ⁇ cm, 50 ⁇ cm, no greater than 45 ⁇ cm cm, not more than 40 ⁇ cm, not more than 30 ⁇ cm, not more than 20 ⁇ cm, not more than 10 ⁇ cm.
  • the powder resistivity of the secondary particles of the lithium iron phosphate chemical system changes within the above range, the resistance of the positive electrode sheet can be effectively regulated, thereby helping to ensure the cycle performance of the lithium ion battery.
  • the battery performance can be further optimized by adjusting the content of secondary particles of the lithium iron phosphate chemical system in the mixed cathode material. Specifically, taking the mass of the mixed components as 100%, the mass percentage content of the secondary particles of the lithium iron phosphate chemical system is controlled to be 20%-70%. For example 20%-25%, 25%-35%, 35%-45%, 45%-55%, 55%-65%, 65%-70%. In the present application, by adjusting the content of the secondary particles of the lithium iron phosphate chemical system in the mixed positive electrode material within the above range, the energy density and safety performance of the battery can be further ensured.
  • a lithium iron phosphate chemical system material with the general formula LiFe 1-x M x PO 4 can be used, wherein 0 ⁇ x ⁇ 0.1, M can be selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni One or more of , Sr or Ti.
  • the ternary chemical system material may be a nickel cobalt lithium manganate chemical system material and/or a nickel cobalt lithium aluminate chemical system material.
  • the general formula of the chemical system of nickel cobalt manganese oxide can be LiNi x M y Co 1-xy O 2 , where 1>x>0, 1>y>0, x+y ⁇ 0.95; lithium nickel cobalt aluminate
  • the general formula of the chemical system material can be LiNi x Co y Al 1-xy O 2 , wherein 1>x>0.6, 0.4>y>0.1.
  • the lithium iron phosphate chemical system material in the present application may be one in which at least part of the surface of at least part of the particle is formed with a carbon coating.
  • the preparation method of carbon-coated lithium iron phosphate utilizes a compound reaction system containing a lithium source, a phosphorus source and a carbon source, and obtains carbon-coated iron phosphate by controlling the thermodynamic and kinetic factors in the reaction process. Lithium particles. It can be understood that the thickness and uniformity of the carbon coating will also affect the electrical conductivity. When the thickness of the carbon coating on the surface of all particles is substantially uniform, the electrical conductivity is the best.
  • the preparation method of the secondary particles of the lithium iron phosphate chemical system is as follows:
  • the lithium source, the iron source, the phosphorus source compound, the optional dopant and the carbon source are uniformly mixed, and then pre-sintered at a low temperature under a protective gas to obtain a pre-sintered material.
  • the phosphorus source iron source can be selected from one or a combination of iron phosphate or iron phosphate dihydrate, the lithium source is one or more of lithium phosphate, lithium carbonate, and lithium nitrate; the carbon source is selected from One or at least two combinations of ascorbic acid, cellulose, polypropylene, epoxy resin, sucrose, glucose, fructose, citric acid, polyethylene glycol, starch, and phenolic resin, the above materials are conventional raw materials in the art, The addition ratio may be sufficient as long as the present application can be realized.
  • the mixed positive electrode material of the present application by controlling the specific surface area of the secondary particles of the lithium iron phosphate chemical system, solves the problem of agglomeration when the ternary chemical system material is blended with the lithium iron phosphate chemical system material, and improves the processing performance of the mixed positive electrode material. , to realize that the slurry is not easy to agglomerate, and the two materials are well compatible. The stability of the slurry is enhanced, the maximum storage time of the slurry is increased, and the filtration performance is improved.
  • the mixed positive electrode material of the present application is used to prepare the positive electrode sheet, the uniform distribution of the positive electrode material on the positive electrode sheet can be effectively controlled, which is beneficial to adjust the distribution uniformity of the resistance of the electrode sheet.
  • the present application proposes a positive electrode sheet, which includes a positive electrode material layer containing the above-mentioned mixed positive electrode material.
  • the resistivity of the positive electrode sheet can be further adjusted.
  • the mass per unit area of the positive electrode material layer is 150-250 g/m 2 .
  • the lower limit of the mass per unit area of the positive electrode material layer may be: not lower than 150 g/m 2 , not lower than 160 g/m 2 , not lower than 170 g/m 2 , not lower than 180 g/m 2 , not lower than 190g/m 2 , not lower than 200g/m 2 , not lower than 210g/m 2 , not lower than 220g/m 2 , not lower than 230g/m 2 , not lower than 240g/m 2 .
  • the upper limit of the mass per unit area of the positive electrode material layer may be: not higher than 160g/m 2 , not higher than 170g/m 2 , not higher than 180g/m 2 , not higher than 190g/m 2 , not higher than 200g/m 2 , not higher than 220g/m 2 , not higher than 210g/m 2 , not higher than 230g/m 2 , not higher than 240g/m 2 , not higher than 250g/m 2 .
  • the compaction density of the positive electrode material layer is 2.6-3.5 g/cm 3 .
  • the lower limit of the compaction density of the positive electrode material layer may be 2.6 g/cm 3 , 2.7 g/cm 3 , 2.8 g/cm 3 , 2.9 g/cm 3 , 3 g/cm 3 , 3.1 g/cm 3 , 3.2 g/cm 3 , 3.3 g/cm 3 , 3.4 g/cm 3 .
  • the upper limit of the compaction density of the positive electrode material layer may be 2.7g/ cm3 , 2.8g/ cm3 , 2.9g/ cm3 , 3g/ cm3 , 3.1g/ cm3 , 3.2g/ cm3 , 3.3g/cm3 3 , 3.4g/cm 3 , 3.5g/cm 3 .
  • the resistivity of the positive electrode sheet and the capacity of the positive electrode sheet per unit area can be adjusted, thereby ensuring that the prepared battery has higher dynamic performance and high energy density.
  • the positive electrode sheet further contains a conductive agent and a binder.
  • a conductive agent and a binder are conventional materials in the art, for example, the conductive agent can be selected from at least one of carbon black, graphene, carbon nanotubes, Ketjen black, and carbon fibers, and the binder can be selected from polytetrafluoroethylene At least one of ethylene, polystyrene butadiene rubber, and sodium carboxymethyl cellulose.
  • the mass ratio of the mixed components, the conductive agent and the binder is about (90-98):(1-5):(1-5), for example, 96.5:1.5:2,92 :2:3, 93:3:2, 97:5:1, 98:1:5, 95:3.5:4.
  • the positive electrode plate of the present application has good distribution uniformity of the mixed positive electrode material on the positive electrode electrode plate, which is beneficial to improve the distribution uniformity of the resistance of the positive electrode electrode plate, and can better satisfy the electrochemical performance of the lithium ion battery.
  • the method for preparing a positive electrode sheet proposed in this application includes the following steps: mixing the mixed positive electrode materials, filtering and collecting the slurry, coating the slurry on the current collector, removing the solvent, and rolling Pressing and slicing to obtain a positive pole piece.
  • the preparation method of the present application adopts the mixed positive electrode material of the present application, which is beneficial to improve the distribution uniformity of the positive electrode material on the positive electrode plate, improve the resistance uniformity of the positive electrode plate, and can better meet the electrochemical performance requirements of the lithium ion battery.
  • the present application provides a battery including the above-mentioned positive electrode.
  • the mixed positive electrode material since the mixed positive electrode material has a good distribution on the positive electrode electrode plate, it is beneficial to improve the distribution uniformity of the electrode plate resistance, so that the prepared battery has higher energy density and better cycle performance.
  • the battery of the present application has high energy density and also has good electrochemical performance.
  • the present application proposes a device, comprising the above-mentioned battery, the battery is used to provide power for the device and/or an energy storage unit for the device, and the device is selected from the group consisting of electric vehicles, electric ships, electric tools, electronic equipment and One or more of the energy storage systems.
  • the device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric vehicles, etc.) scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • mobile devices such as mobile phones, laptop computers, etc.
  • electric vehicles such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric vehicles, etc.
  • scooters electric golf carts, electric trucks, etc.
  • electric trains ships and satellites, energy storage systems, etc.
  • the instrument After inputting the corresponding parameters, the instrument automatically measures and obtains the result.
  • the particle size is counted by the long diameter statistical method: as shown in Figure 3a and Figure 4, the length of the line segment marked in Figure 4 is the length of the long diameter direction of the primary particle in Figure 3a. Measure the diameters in the long axis direction of the three groups of primary particles in Figure 4, at least 10 in each group, and take the average value of the three groups to obtain the particle size of the primary particles.
  • Test method Put a certain mass of mixed cathode material sample in the feeding cup of the resistivity tester, then compact the sample, collect data manually, and record the powder resistivity test results at different pressure points.
  • Sample weighing take a certain weight of sample, and control the sample weight within 0.8-2.4g;
  • Feeding add the weighed sample to the feeding cup to ensure that all the weighed samples are added to the feeding cup;
  • Test instrument Accuracy: ⁇ 1% FS, Brookfield DV2T viscometer;
  • Test methods 1-7 are based on the tests performed synchronously in the preparation process of the positive lithium-ion battery. If the lithium-ion battery that has been prepared is tested, the following steps can be added:
  • the battery is fully discharged when the voltage is 2.0V;
  • the dry mixture powder is dispersed in a liquid medium (the density of the liquid medium is greater than 1.2 g/cm 3 , eg, nitrobenzene, bromobenzene, carbon tetrachloride, etc.), and stirred to make it substantially uniformly mixed.
  • a liquid medium the density of the liquid medium is greater than 1.2 g/cm 3 , eg, nitrobenzene, bromobenzene, carbon tetrachloride, etc.
  • the density difference between the ternary chemical system material and the lithium iron phosphate chemical system material is smaller than the difference between the positive electrode material and the conductive carbon, when separating the ternary positive electrode material and the lithium iron phosphate positive electrode material, it is necessary to further use the surface wetting of the two.
  • a suitable liquid medium such as water, ethylene glycol or glycerol, etc.
  • a suitable flotation agent such as fat oil 190, fusel, etc.
  • the specific steps are: take 1Kg of the mixed positive electrode material in the liquid medium, adjust to a more suitable solid content, add a flotation agent, stir to generate bubbles, collect the floating foam, wash and dry, and then obtain the lithium iron phosphate chemical system material ; Collect the slurry at the bottom, wash and dry to obtain the ternary chemical system material.
  • the capacity is expressed as a constant current of 1/3C at 25°C (wherein, the charge/discharge current is the rate multiplied by the rated capacity of the cell, and the rated capacity is determined by the cell, or the battery module to which the cell belongs, or the cell.
  • the capacity of the battery cell identified in the GBT certification document of the battery pack to which the cell belongs shall prevail), charge and discharge within the working voltage range specified in the GBT certification document, and measure the capacity of the battery cell.
  • the number of cycles when the capacity decays to 80% of the initial value (Note: when the system is a pure lithium iron phosphate system, the charge cut-off voltage is 3.65V, and the discharge cut-off voltage is 2.5V; when the system is a pure ternary chemical system or mixed When there is a ternary chemical system, the charge cut-off voltage is 4.35V, and the discharge cut-off voltage is 2.8V).
  • the specific process is as follows:
  • Step 2)-Step 6) is a charge-discharge cycle of the battery, and FIG. 5 shows the number of cycles when the above steps 2-step 6 are continuously cycled until the capacity decays to 80% of the initial value.
  • the PVDF used in the examples and comparative examples of the present application was purchased from Solvay Co., Ltd., model 5130, with an average molecular weight of 800,000-1,500,000;
  • CMC Sodium carboxymethyl cellulose
  • the separator was purchased from Enjie New Materials Co., Ltd., which is a ceramic separator for lithium iron phosphate lithium-ion batteries;
  • the electrolyte was purchased from Guangdong Tianci New Materials Co., Ltd., which is the electrolyte for lithium iron phosphate lithium-ion batteries;
  • An example of the preparation method of the negative pole piece of the present application is as follows:
  • negative pole piece artificial graphite, conductive carbon black, binder (styrene-butadiene rubber) and sodium carboxymethyl cellulose (CMC) are dissolved in a solvent according to the proportion, stirred evenly and made into a slurry. It is evenly coated on the copper foil current collector, and after drying, cold rolling, slitting and cutting in sequence, a negative pole piece is obtained.
  • Example 1 proposes a mixed positive electrode material, a positive electrode sheet prepared therefrom, and a lithium ion battery.
  • the mixed positive electrode material of Example 1 includes a mixed component composed of secondary particles of a lithium iron phosphate chemical system with a mass ratio of about 3:7 and a ternary chemical system powder.
  • the specific composition parameters are shown in Table 1.
  • the molecular formula of the ternary chemical system powder is LiNi 0.5 Co 0.2 Mn .0.3 O 2 , the specific surface area is about 1.2 m 2 /g, and the D v 50 is about 3 ⁇ m.
  • the mixed cathode material of Example 1 further includes conductive carbon black and PVDF, wherein the mass ratio of the mixed components to the conductive carbon black and PVDF is about 96.5:1.5:2.
  • the above mixed positive electrode materials are mixed at a speed of about 500 r/min, then N-methylpyrrolidone (NMP) is added, and the mixture is stirred uniformly at a speed of about 2000 r/min. Then filter with a filter screen of about 200 mesh to obtain a slurry with a viscosity of about 8000 mPa ⁇ S, and measure the solid content in the slurry. It is coated on aluminum foil with a thickness of about 13 ⁇ m, then evaporated to remove NMP, rolled and sliced to obtain a positive electrode sheet with a compacted density of about 3.1 g/cm 3 and a coating weight of about 190 g/m 2 .
  • NMP N-methylpyrrolidone
  • Figure 2 is a cross-sectional SEM image of a positive electrode piece prepared from a traditional single crystal 523 ternary positive electrode material. Although the ternary material particles are evenly distributed, there are many unfilled spaces between the particles.
  • Figures 3a and 3b are SEM images of different magnifications of the LFP material secondary particle positive pole piece. Similarly, although the secondary particles are uniformly distributed, there are also many unfilled spaces between the particles. At the same time, there are a large number of nano grain boundaries inside the secondary particles, and the secondary particles have a dense structure.
  • the LFP secondary particles and the ternary material in the mixed cathode material are uniformly and densely distributed, and no agglomeration occurs.
  • Figure 5 illustrates a graph of the three charge-discharge cycles of the lithium-ion battery of Example 1, which is obtained by testing the same lithium-ion battery for three consecutive cycles under the same test conditions. It can be seen that the difference between the three charge-discharge cycles Not big, the three curves almost overlap, and there is almost no capacity fading.
  • Figure 6 shows the decay of the cycle capacity retention rate of the lithium-ion battery of Example 1.
  • the two curves respectively record the decay of the cycle capacity retention rate of the two lithium-ion batteries.
  • the decay of the two tests is almost the same, Not much difference. It can be seen from the trend of the curve that the capacity of the lithium-ion battery prepared in Example 1 has an upward trend in the first few laps, mainly because with the progress of the cycle, the interior of the material is continuously activated, and the electrolyte is fully infiltrated, which causes the activation of the battery. Its attenuation factor, so that the capacity can be improved.
  • Example 2-25 According to the specific components and proportions shown in Table 1, the method shown in Example 1 was used to prepare a positive electrode and a lithium ion battery.
  • Embodiment 26 provides a device, and the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle or the like.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle or the like.
  • a battery pack or battery module prepared from the above-mentioned lithium-ion batteries can be used.
  • Embodiment 27 provides a mobile device, and the mobile device may be a mobile phone, a tablet computer, a notebook computer, or the like.
  • the device is generally required to be thin and light, and the above-mentioned lithium-ion battery is used as a power source.
  • Comparative Example 1 proposes a mixed positive electrode material, a positive electrode sheet prepared therefrom, and a lithium ion battery.
  • Comparative Example 1 The only difference between Comparative Example 1 and Example 2 is that the average specific surface area of the LiFe 0.98 Mn 0.02 PO 4 secondary particles in Comparative Example 1 is about 12 m 2 /g, which constitutes the primary particles of the LiFe 0.98 Mn 0.02 PO 4 secondary particles.
  • the diameter is about 10 nm, and other steps and parameters are the same.
  • Comparative Example 2 proposes a mixed positive electrode material, a positive electrode sheet prepared therefrom, and a lithium ion battery.
  • Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that the average specific surface area of the secondary particles of LiFe 0.98 Mn 0.02 PO 4 in Comparative Example 2 is about 17 m 2 /g, and other steps and parameters are the same.
  • Comparative Example 3 proposes a mixed positive electrode material, a positive electrode sheet prepared therefrom, and a lithium ion battery.
  • Comparative Example 3 includes primary particles of lithium iron phosphate chemical system with a mass ratio of about 3:7 and ternary chemical system powder, LiFe 0.98 Mn 0.02 PO 4 primary particles
  • the specific surface area is about 16 m 2 /g
  • D v 50 is about 1.1 ⁇ m
  • D v 10 is about 0.25 ⁇ m
  • D v 90 is about 18.5 ⁇ m
  • other steps and parameters are the same.
  • the slurry could not pass through the 150-mesh wire screen continuously and stably, and the agglomerated slurry was blocked on one side of the screen, and the filtration could not be completed.
  • the viscosity of the slurry before and after mixing was tested, and it was found that after the slurry was mixed, the viscosity increased significantly, and the fluidity became significantly worse, indicating that a relatively serious agglomeration occurred.
  • the mixed slurry could continuously and stably pass through the 150-mesh steel wire screen without clogging, indicating that no agglomeration occurred.
  • the viscosity of the slurry was measured, and it was found that the viscosity of the mixed slurry did not change much compared with that before mixing.
  • Example 1-6 Comparing the solid content of the mixed slurry of Example 1-6 and Comparative Example 1-3, it can be seen that the specific surface area of the secondary particles in Example 1-6 is not greater than 10 m 2 /g, and the solid content of the finally obtained mixed slurry is Much larger than Comparative Examples 1-3, the reason for analysis is mainly because the mixed cathode materials of Examples 1-6 did not agglomerate during the preparation process, and still have better slurry stability and processing at higher solid content. performance. However, the mixed cathode materials of Comparative Examples 1-3 will agglomerate during the preparation process. When the solid content increases, the agglomeration phenomenon is more serious, so the solid content of the finally prepared mixed cathode materials will also decrease.
  • the low solid content slurry is prone to the problems of film cracking and uneven coating thickness control during the coating process, which affects the energy density and cycle performance of the battery.
  • Comparative Example 3 when the nano-scale lithium iron phosphate primary particles are used as the mixed material, the solid content of the mixed slurry is only 46%, which is much smaller than the mixed slurry of Examples 1-6. The solid content of the material seriously affects the energy density and cycle performance of the battery.
  • Comparing Table 3 it can be seen from Comparative Examples 1-6 and Comparative Examples 1-2 that by using the average value of the LFP specific surface area of the examples of the present application, the energy density of the lithium battery finally prepared is improved, and finally the initial discharge capacity, the first Under the condition that the cycle efficiency is basically the same, the number of cycles when the capacity decays to 80% of the initial value increases significantly, which is much greater than that of the comparative example, and the cycle performance of the lithium battery increases significantly.
  • the hybrid cathode material of the present application by controlling the specific surface area of the secondary particles of the lithium iron phosphate chemical system, solves the problem of agglomeration when the ternary chemical system material is blended with the lithium iron phosphate chemical system material, and improves the mixed cathode material.
  • the processing performance is excellent, the slurry is not easy to agglomerate, and the two materials are well compatible.
  • the mixed positive electrode material of the present application is used to prepare the positive electrode plate, the positive electrode material can be uniformly distributed on the positive electrode plate, which is beneficial to adjust the uniformity of the distribution of the resistance value of the electrode plate, so that the prepared lithium ion battery has higher energy density and Better cycle performance.

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Abstract

一种混合正极材料、正极极片及制备方法、电池和装置，该混合正极材料包括磷酸铁锂化学体系材料和三元化学体系材料的混合组分，所述磷酸铁锂化学体系材料为比表面积平均值不超过10m 2/g的二次颗粒。该混合正极材料通过引入低比表面积二次颗粒磷酸铁锂，提高了混合正极材料的加工性能，实现浆料不易团聚，二种材料之间良好相容。当采用该混合正极材料制备正极极片时，能够有效提高正极材料在正极极片上分布均匀，利于调节极片电阻的分布均匀性，从而提升电池的电化学性能。

Description

混合正极材料、正极极片及制备方法、电池和装置 技术领域
本申请属于锂离子电池技术领域，具体涉及一种混合正极材料、正极极片及制备方法、电池和装置。
背景技术
锂离子电池因其具有能量密度高、循环寿命长、无记忆效应且绿色环保等特点，在二次电池领域具有很强的竞争力，不仅广泛适用于手机、笔记本电脑等终端电子产品领域，同时在电动汽车、大型储能设备等领域的应用也逐步增加。作为锂离子电池的正极材料，目前比较成熟且普遍应用的主要是磷酸铁锂材料体系(例如磷酸铁锂或掺杂改性的磷酸铁锂材料)和三元材料体系(例如镍钴锰酸锂和镍钴铝酸锂体系材料)。以三元体系材料为正极活性材料的锂离子电池因具有更高的能量密度和更好的功率性能，在一定发展时期曾受到行业内关注，成为研究的方向。但是两类材料各有特长和缺陷，随着认知和研究的深入，如何利用其各自优势也开始引起关注。
然而如何实现锂离子电池性能提升和稳定，确保锂离子电池的电性能，同时保证制备过程的加工性能较好，成为亟待解决的技术问题之一。
发明内容
本申请提供了一种混合正极材料，通过对所用材料的种类、微观形貌进行筛选和合理匹配，解决了不同类型材料混合时容易团聚的问题，使混合正极材料的相容性和加工性能较好，有利于保证锂离子电池的安全性能和循环寿命的提升。
本申请还提供了一种正极极片，采用本申请的混合正极材料制备，能够提高正极材料在正极极片上分布均匀性，更能满足锂离子电池的电化学性能。
本申请还提供了一种正极极片的制备方法，本申请的制备方法采用本申请的混合正极材料，能够提高正极材料在正极极片上分布均匀，提升极 片性能，更能满足锂离子电池的电化学性能要求。
本申请还提供了一种电池，采用本申请的正极极片，达到提高能量密度的同时，还具有良好电化学性能的目的。
本申请还提供了一种装置，包括本申请的电池，电池用于为装置提供电源和/或用于装置的能量存储单元。
本申请提出的技术方案是：
本申请提出了一种混合正极材料，包括由磷酸铁锂化学体系材料和三元化学体系材料组成的混合组分，磷酸铁锂化学体系材料为低比表面积二次颗粒，比表面积平均值不超过10m 2/g的二次颗粒。
在本申请的一些实施方式中，磷酸铁锂化学体系材料为比表面积平均值不超过6m 2/g的二次颗粒。
本申请所使用的磷酸铁锂材料的二次颗粒也应该理解为上述经加工而团聚的材料颗粒。在具体的实施方案中，可以是指纳米级磷酸铁锂化学体系一次颗粒经硬团聚后得到的二次颗粒。
在本申请的一些实施方式中，磷酸铁锂化学体系二次颗粒的比表面积为不超过10m 2/g。具体地，可以为不超过9m 2/g，不超过8m 2/g，不超过7m 2/g。进一步可以为不超过6m 2/g，不超过5m 2/g，不超过4m 2/g，不超过3m 2/g。本申请中，当磷酸铁锂化学体系二次颗粒的比表面积在上述范围时，与三元化学体系材料混合时，可以避免在制浆过程中由于团聚问题导致的浆料粘度大，在正极极片上涂布不均等问题，从而提高了混合正极材料的加工的可行性。
在本申请的一些实施方式中，磷酸铁锂化学体系二次颗粒的粒径分布满足：0.1≤D v50/(D v90-D v10)≤10。进一步地0.3≤D v50/(D v90-D v10)≤5，更进一步地0.5≤D v50/(D v90-D v10)≤1。本申请中，当磷酸铁锂化学体系二次颗粒的粒径分布在上述范围内时，得到的混合正极材料，在制浆过程中，更有利于形成更加均匀的混合正极浆料。
在本申请的一些实施方式中，可以分别对D v10和D v90作进一步限定，控制粒径较小和粒径较大的颗粒的占比，从而可以对磷酸铁锂化学体系二次颗粒与三元化学体系材料的混合体系的浆料加工性进一步优化。例如，磷酸铁锂化学体系二次颗粒的粒径分布可以满足：D v10≥0.6μm，D v90≤30μm； 比如D v10≥0.8μm，D v90≤25μm；进一步如D v10≥1μm，D v90≤20μm；D v10≥1.2μm，D v90≤25μm；D v10≥2μm，D v90≤22μm；D v10≥3μm，D v90≤18μm；D v10≥4μm，D v90≤15μm；D v10≥5μm，D v90≤12μm。
本申请的一些实施方案中，磷酸铁锂化学体系二次颗粒的中位粒度分布满足：2μm≤D v50≤9μm。例如，3μm≤D v50≤6μm，2μm≤D v50≤4μm，4μm≤D v50≤7μm，5μm≤D v50≤8μm，6μm≤D v50≤9μm。本申请中，当所引入的磷酸铁锂化学体系材料二次颗粒在满足较小比表面积的同时，还具有合适的中位粒度分布时，更利于磷酸铁锂化学体系二次颗粒与三元化学体系材料的均匀混合，进而提高混合正极材料的加工性能。
在本申请的一些实施方式中，组成磷酸铁锂化学体系二次颗粒的一次颗粒平均粒径分布d满足：20nm≤d≤800nm。例如，d可以满足：300nm≤d≤500nm，进一步地300nm≤d≤350nm，350nm≤d≤400nm，400nm≤d≤450nm，450nm≤d≤500nm。本申请中，当控制组成LFP二次颗粒的一次颗粒的粒径在上述范围内时，可以进一步使得三元化学体系材料不会由于LFP二次颗粒材料的引入，而导致动力学性能和低温性能恶化，同时，混合体系可以保证较好的长期寿命。
在本申请的一些实施方式中，磷酸铁锂化学体系二次颗粒的粉末电阻率不大于100Ω·cm。具体的，可以为：不大于80Ω·cm，不大于75Ω·cm，不大于70Ω·cm，不大于65Ω·cm，不大于60Ω·cm，不大于55Ω·cm，50Ω·cm，不大于45Ω·cm，不大于40Ω·cm，不大于30Ω·cm，不大于20Ω·cm，不大于10Ω·cm。本申请中，通过对磷酸铁锂化学体系二次颗粒的粉末电阻率进一步限定，可以有效调控正极极片电阻，从而有利于保证锂离子电池的循环性能。
在本申请的一些实施方式中，以混合组分的质量为100％计，控制磷酸铁锂化学体系二次颗粒的质量百分含量为20％-70％。具体的，磷酸铁锂化学体系二次颗粒的质量百分含量可以为20％-25％，25％-35％，35％-45％，45％-55％，55％-65％，65％-70％。本申请中，通过调节混合正极材料中磷酸铁锂化学体系二次颗粒的含量在上述范围内，可以进一步优化电池的能量密度及安全性。
在本申请的一些实施方式中，磷酸铁锂化学体系材料可以采用通式为LiFe 1-xM xPO 4的含锂化合物，其中，0<x≤0.1，M可以选自Cu、Mn、Cr、 Zn、Pb、Ca、Co、Ni、Sr或Ti中的一种以上。
在本申请的一些实施方式中，三元化学体系材料可以为镍钴锰酸锂化学体系材料和/或镍钴铝酸锂化学体系材料。例如，镍钴锰酸锂化学体系材料通式可以为LiNi xMn yCo 1-x-yO 2，其中，1＞x＞0，1＞y＞0，x+y≤0.95；镍钴铝酸锂化学体系材料通式可以为LiNi xCo yAl 1-x-yO 2，其中，1＞x＞0.6，0.4＞y＞0.1。
本申请所述的混合正极材料，通过控制磷酸铁锂化学体系二次颗粒的比表面积，解决了三元化学体系材料与磷酸铁锂化学体系材料共混时的团聚问题，提高了混合正极材料的加工性能，实现浆料不易团聚，提高了不同材料之间良好相容。浆料稳定性增强，浆料最长可放置时间增加，同时可过滤性能提升。当采用本申请的混合正极材料制备正极极片时，能够使混合组分在正极极片上分布均匀，有利于调节极片电阻分布均匀性，从而提升电池的电化学性能。
第二方面，本申请提出了一种正极极片，包括含有上述的混合正极材料的正极材料层。
在本申请的一些实施方式中，正极材料层的单位面积质量为150-250g/m 2。具体地，正极材料层的单位面积质量的下限可以为：不低于150g/m 2，不低于160g/m 2，不低于170g/m 2，不低于180g/m 2，不低于190g/m 2，不低于200g/m 2，不低于210g/m 2，不低于220g/m 2，不低于230g/m 2，不低于240g/m 2。正极材料层的单位面积质量的上限可以为：不高于160g/m 2，不高于170g/m 2，不高于180g/m 2，不高于190g/m 2，不高于200g/m 2，不高于220g/m 2，不高于210g/m 2，不高于230g/m 2，不高于240g/m 2，不高于250g/m 2。
在本申请的一些实施方式中，正极材料层的压实密度为2.6-3.5g/cm 3。具体地，正极材料层的压实密度的下限可以为2.6g/cm 3，2.7g/cm 3，2.8g/cm 3，2.9g/cm 3，3g/cm 3，3.1g/cm 3，3.2g/cm 3，3.3g/cm 3，3.4g/cm 3。正极材料层的压实密度的上限可以为2.7g/cm 3，2.8g/cm 3，2.9g/cm 3，3g/cm 3，3.1g/cm 3，3.2g/cm 3，3.3g/cm 3，3.4g/cm 3，3.5g/cm 3。
本申请中，通过对正极材料层的单位面积质量以及压实密度进一步调整，可以调节正极极片的电阻率以及单位面积正极极片可发挥的容量，由此可以保证制备的电池具有较高的动力学性能以及较高的能量密度。
在本申请的一些实施方式中，正极极片中还含有导电剂和粘结剂。导电剂和粘结剂均为本领域常规的材料，例如导电剂可以选自炭黑、石墨烯、碳纳米管、科琴黑、碳纤维中的至少一种，粘结剂可以选自聚四氟乙烯、聚丁苯橡胶、羧甲基纤维素钠中的至少一种。在本申请的具体实施方式中，混合正极材料、导电剂与粘结剂的质量比约为(90-98):(1-5):(1-5)。例如96.5:1.5:2，92:2:3，93:3:2，97:5:1，98:1:5，95:3.5:4。
本申请的正极极片，由于使用上述混合正极材料，能够实现混合正极材料在正极极片上分布均匀，利于提高极片电阻均匀性，更能满足锂离子电池的电化学性能。
第三方面，本申请提出了的正极极片的制备方法，包括如下步骤：将混合正极材料进行混合，然后过滤并收集浆料，再将浆料涂覆在集流体上，去除溶剂后进行辊压、切片，得到正极极片。
本申请的制备方法采用本申请的混合正极材料，有利于使混合正极材料在正极极片上分布更加均匀，有利于提升正极极片性能，更能满足锂离子电池的电化学性能要求。
第四方面，本申请提出了一种电池，包括上述的正极极片。
本申请的正极极片，由于混合正极材料在正极极片上的分布均匀，有利于提高极片电阻均匀性，从而制备的电池具有更高的能量密度以及更好的循环性能。本申请的电池，能量密度高，同时还具有很好的电化学性能。
第五方面，本申请提出了一种装置，包括上述电池，电池用于为装置提供电源和/或用于装置的能量存储单元，装置选自电动车辆、电动船舶、电动工具、电子设备及储能***中的一种或多种。
在本申请具体实施方式中，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***等。
本申请的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本申请的实践了解到。
附图说明
图1是实施例1的正极极片的SEM图；
图2是传统单晶523三元材料制备的正极极片的SEM图；
图3a和3b是本申请一实施例中LFP材料二次颗粒制备的正极极片的不同放大倍数的SEM图；
图4为图3a中部分一次颗粒的长径统计示意图；
图5为实施例1的锂离子电池充放电曲线图；
图6为实施例1的锂离子电池循环容量保持率曲线图；
图7为实施例1的锂离子电池的示意图；
图8是锂离子电池用作电源的装置的一实施方式的示意图。
具体实施方式
目前已有研究采用磷酸铁锂体系材料与三元体系材料混合作为正极材料，用以改善三元体系电池的安全性能和循环寿命。由于磷酸铁锂本身的结构稳定性优于三元材料，因此，在三元正极材料中微量混掺磷酸铁锂后可以提升电池材料体系的结构稳定性，也成为业内共识。但是，作为两类在结构和性质上都有很大差异的材料，若筛选和混配不当，轻则也易因正极的不良率高而导致电池的性能和质量不稳定，重则会导致正极材料体系以及电池综合性能反受损害。不良率的影响因素可能会多方面，例如，两种材料相容性不好而导致用于制备极片的混合浆料稳定性差，容易发生团聚，使得正极材料在极片活性物质层中的分布不均匀，进而恶化电池的电化学性能。
第一方面，本申请提出了一种混合正极材料，包括由磷酸铁锂化学体系材料和三元化学体系材料组成的混合组分，磷酸铁锂化学体系材料为低比表面积二次颗粒，比表面积平均值不超过10m 2/g的二次颗粒。在一些实施例中，磷酸铁锂化学体系材料为比表面积平均值不超过6m 2/g的二次颗粒。
颗粒非常细小时具有很大的比表面积，比表面积越大其表面能也就越大。表面能大的细小颗粒之间容易由于弱的范德华力和氢键等相互作用力结合在一起，发生团聚，也就是很多个细小颗粒二次组合，形成更大的二次颗粒，即，细小的一次颗粒经某种方式被团聚，即可称为二次颗粒。作为公知，颗粒的团聚方式可以分为软团聚或硬团聚，一般情况下，物理键合(如范德华力，氢键等分子间作用力等)引起的团聚为软团聚，化学键合引起的 团聚为硬团聚。使用机械力可以打开软团聚，但是很难打开硬团聚。所以，通常能称为二次颗粒的产品形式，应该是指通过某些人为手段对一次颗粒进行加工使之团聚而得到的产物。作为正极活性材料的组成之一，本申请的混合正极材料引入了主要以二次颗粒存在的磷酸铁锂化学体系材料，该二次颗粒能够稳定(不易被打开)是本申请所要求的，所以，本申请所使用的磷酸铁锂材料的二次颗粒也应该理解为上述经加工而团聚的材料颗粒。在具体的实施方案中，可以是指纳米级磷酸铁锂化学体系一次颗粒经硬团聚后得到的二次颗粒。
本申请中，混合正极材料中的磷酸铁锂化学体系材料主要是以二次颗粒的形式存在，在混合组分中不可避免掺杂少量一次颗粒等，均在本申请的保护范围内。
在本领域中，正极材料的化学体系是按照活性物质种类划分，对其掺杂或添加的辅料不作限定，例如，活性物质为磷酸铁锂(包括经元素掺杂的)的材料均可以定义为磷酸铁锂化学体系材料，活性物质为以镍钴锰酸锂体系(一般简称NCM)的材料、和镍钴铝酸锂体系(一般称NCA)为代表的材料，定义为三元化学材料体系。
通常情况下，磷酸铁锂化学体系颗粒与三元化学体系颗粒之间的比表面积具有明显差异，混合时很容易产生团聚。发明人经大量实验研究发现，采用比表面积平均值较小的磷酸铁锂化学体系二次颗粒，具体地，可以为不超过9m 2/g，不超过8m 2/g，不超过7m 2/g。进一步可以为不超过6m 2/g，不超过5m 2/g，不超过4m 2/g，不超过3m 2/g。当比表面积在上述的磷酸铁锂化学体系二次颗粒与三元化学体系材料混合时，可以避免在制浆过程中由于团聚问题导致的浆料粘度大，在正极极片上涂布不均等问题，从而提高了混合正极材料的加工的可行性。
本申请中，D vX定义如下：将颗粒按体积从小到大排列，并标号为1，2，3…n…，其中，第n个颗粒以及所有体积小于或等于第n个颗粒的颗粒体积之和占所有颗粒总体积的X％，则第n个颗粒的粒径值记为D vX。
D v50即为前n个颗粒体积之和占总体积50％时，所对应的第n个颗粒的粒径值，本申请用D v50表示中位粒度分布。D v10则指前n个颗粒体积之和占总体积10％时，所对应的第n个颗粒的粒径值。D v90则是指前n个颗 粒体积之和占总体积90％时，所对应的第n个颗粒的粒径值。
本申请中，二次颗粒的粒径分布越窄，D v90越小，D v10越大时，越有利于二次颗粒与三元化学体系材料的适配。例如，当二次颗粒的粒径分布满足：0.1≤D v50/(D v90-D v10)≤10，进一步地0.3≤D v50/(D v90-D v10)≤5，更进一步地0.5≤D v50/(D v90-D v10)≤1时，得到的混合正极材料，在制浆过程中，更有利于形成更加均匀的混合正极浆料。
当D v10过小时，有可能会出现小颗粒团聚的现象，当D v90过大时，又可能会堵塞锂离子电池浆料生产设备的滤芯，且无法和粒径较小的三元材料颗粒形成很好的填充和配合。在本申请的具体实施方式中，可以分别对D v10和D v90作进一步限定，控制粒径较小和粒径较大的颗粒的占比，从而可以对磷酸铁锂化学体系二次颗粒与三元化学体系材料的混合体系作进一步优化，例如，二次颗粒的粒径分布可以满足：D v10≥0.6μm，D v90≤30μm，比如D v10≥0.8μm，D v90≤25μm，进一步如D v10≥1μm，D v90≤20μm；D v10≥1.2μm，D v90≤25μm；D v10≥2μm，D v90≤22μm；D v10≥3μm，D v90≤18μm；D v10≥4μm，D v90≤15μm；D v10≥5μm，D v90≤12μm。
本申请的正极材料，当所引入的磷酸铁锂化学体系材料二次颗粒在满足较小比表面积同时，具有合适的中位粒度分布，更利于磷酸铁锂化学体系二次颗粒与三元化学体系材料的均匀混合，进而提高混合正极材料的加工性能。本申请的一些实施方案中，二次颗粒的中位粒度分布满足：2μm≤D v50≤9μm，例如，3μm≤D v50≤6μm，2μm≤D v50≤4μm，4μm≤D v50≤7μm，5μm≤D v50≤8μm，6μm≤D v50≤9μm。
通过控制组成LFP二次颗粒的一次颗粒的粒径，可以进一步提高由本申请的混合正极材料制备的锂离子电池的电化学性能。当一次颗粒平均粒径过小时，混合体系的存储性能和循环寿命较差，当一次粒子平均粒径过大时，混合体系低温性能和倍率放电性能较差。在本申请的具体实施方式中，组成二次颗粒的一次颗粒平均粒径分布d满足：20nm≤d≤800nm，例如，当控制d满足：300nm≤d≤500nm，进一步地300nm≤d≤350nm，350nm≤d≤400nm，400nm≤d≤450nm，450nm≤d≤500nm，使得三元化学体系材料不会由于LFP二次颗粒材料的引入，而导致动力学性能和低温性能恶化，同时，混合体系可以保证较好的长期寿命。
本领域技术人员可以理解，LFP二次颗粒的粉末电阻率会间接影响正极极片的电阻。因此，可以通过粉末电阻率对磷酸铁锂化学体系二次颗粒的性质进一步限定，例如控制磷酸铁锂化学体系二次颗粒的粉末电阻率不大于100Ω·cm。具体的，可以为：不大于80Ω·cm，不大于75Ω·cm，不大于70Ω·cm，不大于65Ω·cm，不大于60Ω·cm，不大于55Ω·cm，50Ω·cm，不大于45Ω·cm，不大于40Ω·cm，不大于30Ω·cm，不大于20Ω·cm，不大于10Ω·cm。本申请中，当磷酸铁锂化学体系二次颗粒的粉末电阻率在上述范围内变化时，可以有效调控正极极片电阻，从而利于保证锂离子电池的循环性能。
本申请中，可以通过调节混合正极材料中磷酸铁锂化学体系二次颗粒的含量，进一步优化电池性能。具体地，以混合组分的质量为100％计，控制磷酸铁锂化学体系二次颗粒的质量百分含量为20％-70％。例如20％-25％，25％-35％，35％-45％，45％-55％，55％-65％，65％-70％。本申请中，通过调节混合正极材料中磷酸铁锂化学体系二次颗粒的含量在上述范围内，可以进一步保证电池的能量密度和安全性能。
在本申请中，对化学体系材料的选择不作限定。例如，可以采用通式为LiFe 1-xM xPO 4的磷酸铁锂化学体系材料，其中，0<x≤0.1，M可以选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr或Ti中的一种以上。
在本申请中，三元化学体系材料可以为镍钴锰酸锂化学体系材料和/或镍钴铝酸锂化学体系材料。例如，镍钴锰酸锂化学体系材料通式可以为LiNi xMn yCo 1-x-yO 2，其中，1＞x＞0，1＞y＞0，x+y≤0.95；镍钴铝酸锂化学体系材料通式可以为LiNi xCo yAl 1-x-yO 2，其中，1＞x＞0.6，0.4＞y＞0.1。
本领域技术人员公知，磷酸铁锂化学体系颗粒制备过程中会通过进一步实施对颗粒的碳包覆以提高正极材料的导电率。本申请中的磷酸铁锂化学体系材料可以是其中至少部分颗粒表面的至少部分区域形成有碳包覆。碳包覆的磷酸铁锂的制备方法例如参考专利申请CN101453030A，利用含有锂源、磷源和碳源的化合物反应体系，通过控制反应过程中的热力学和动力学因素，得到碳包覆的磷酸铁锂颗粒。可以理解，碳包覆的厚度以及均匀程度也会影响导电性，当所有颗粒表面的碳包覆厚度基本均匀一致时，其导电性最好。
在本申请的具体实施方式中，磷酸铁锂化学体系二次颗粒的制备方法如下：
(1)采用球磨机，将锂源、铁源、磷源化合物、任选的掺杂物及碳源均匀混合后在保护性气体下低温预烧结，得到预烧料。其中，磷源铁源可以选自磷酸铁、或者二水磷酸铁中的一种或者两种的组合，锂源为磷酸锂、碳酸锂、硝酸锂中的一种或者几种；碳源选自抗坏血酸、纤维素、聚丙烯、环氧树脂、蔗糖、葡萄糖、果糖、柠檬酸、聚乙二醇、淀粉、酚醛树脂中的1种或至少2种的组合，以上材料均为本领域常规原料，其添加比例只要能够实现本申请即可。
(2)将上述预烧料与分散剂、溶剂(去离子水或者甲醇)混合，用砂磨机进行超细磨，得到磷酸铁锂化学体系一次颗粒。在具体实施方式中，还可以在超细磨时加入少量碳源，以进一步提升后续烧结产物的导电性，同时增强包覆。
(3)将超细磨后的磷酸铁锂化学体系一次颗粒进行喷雾干燥，蒸发掉溶剂后形成单分散的微球，然后将上述微球在氮气保护气氛下烧结进一步反应(反应温度相对于预烧结温度稍有提高)，得到磷酸铁锂化学体系二次颗粒。也可以通过进一步气相沉积，在磷酸铁锂二次颗粒表面进行进一步碳包覆，提升材料导电性。
本申请的混合正极材料，通过控制磷酸铁锂化学体系二次颗粒的比表面积，解决了三元化学体系材料与磷酸铁锂化学体系材料共混时的团聚问题，提高了混合正极材料的加工性能，实现浆料不易团聚，二种材料之间良好相容。浆料稳定性增强，浆料最长可放置时间增加，同时可过滤性能提升。当采用本申请的混合正极材料制备正极极片时，能够有效控制正极材料在正极极片上分布均匀，利于调节极片电阻的分布均匀性。
第二方面，本申请提出了一种正极极片，包括含有上述的混合正极材料的正极材料层。
本申请中，通过控制单位面积正极材料的质量以及正极材料的压实密度，可以进一步地调节正极极片的电阻率。在本申请的一些实施方式中，正极材料层的单位面积质量为150-250g/m 2。具体地，正极材料层的单位面积质量的下限可以为：不低于150g/m 2，不低于160g/m 2，不低于170g/m 2，不低于180g/m 2，不低于190g/m 2，不低于200g/m 2，不低于210g/m 2，不低于220g/m 2，不低于230g/m 2，不低于240g/m 2。正极材料层的单位面积质量的 上限可以为：不高于160g/m 2，不高于170g/m 2，不高于180g/m 2，不高于190g/m 2，不高于200g/m 2，不高于220g/m 2，不高于210g/m 2，不高于230g/m 2，不高于240g/m 2，不高于250g/m 2。
在本申请的一些实施方式中，正极材料层的压实密度为2.6-3.5g/cm 3。具体地，正极材料层的压实密度的下限可以为2.6g/cm 3，2.7g/cm 3，2.8g/cm 3，2.9g/cm 3，3g/cm 3，3.1g/cm 3，3.2g/cm 3，3.3g/cm 3，3.4g/cm 3。正极材料层的压实密度的上限可以为2.7g/cm 3，2.8g/cm 3，2.9g/cm 3，3g/cm 3，3.1g/cm 3，3.2g/cm 3，3.3g/cm 3，3.4g/cm 3，3.5g/cm 3。
本申请中，通过对正极材料层的单位面积质量以及压实密度进一步调整，可以调节正极极片的电阻率以及单位面积正极极片可发挥的容量，由此可以保证制备的电池具有较高的动力学性能以及较高的能量密度。
在本申请的一些实施方式中，正极极片还含有导电剂和粘结剂。导电剂和粘结剂均为本领域常规的材料，例如导电剂可以选自炭黑、石墨烯、碳纳米管、科琴黑、碳纤维中的至少一种，粘结剂可以选自聚四氟乙烯、聚丁苯橡胶、羧甲基纤维素钠中的至少一种。在本申请的具体实施方式中，混合组分、导电剂与粘结剂的质量比约为(90-98):(1-5):(1-5)，例如96.5:1.5:2，92:2:3，93:3:2，97:5:1，98:1:5，95:3.5:4。
本申请的正极极片，由于混合正极材料在正极极片上分布均匀性良好，有利于提升正极极片电阻的分布均匀性，更能满足锂离子电池的电化学性能。
第三方面，本申请提出了的正极极片的制备方法，包括如下步骤：将混合正极材料进行混合，然后过滤并收集浆料，再将浆料涂覆在集流体上，去除溶剂后进行辊压、切片，得到正极极片。
本申请的制备方法采用本申请的混合正极材料，有利于提高正极材料在正极极片上分布均匀性，提升正极极片的电阻均匀性，更能满足锂离子电池的电化学性能要求。
第四方面，本申请提出了一种电池，包括上述的正极极片。
本申请的正极极片，由于混合正极材料在正极极片上的分布均匀良好，有利于提高极片电阻的分布均匀性，从而制备的电池具有更高的能量密度以及更好的循环性能。
本申请的电池，能量密度高，同时还具有很好的电化学性能。
第五方面，本申请提出了一种装置，包括上述的电池，电池用于为装置提供电源和/或用于装置的能量存储单元，装置选自电动车辆、电动船舶、电动工具、电子设备及储能***中的一种或多种。
在本申请具体实施方式中，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***等。
本申请的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本申请的实践了解到。
下面详细描述本申请的实施例，所述实施例是示例性的，旨在用于解释本申请，而不能理解为对本申请的限制。
以下实施例和对比例中，进行如下测试：
1、二次颗粒比表面积测试
参考标准：GB/T 19587-2004《气体吸附BET法测定固态物质比表面积》
作为示例具体流程如下：
(1)取一定量的样品：如果是磷酸铁锂二次颗粒，需要2.0-4g；如果是三元材料，需要8.0-15.0g；
(2)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)；
(3)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；
(4)将样品管放入测试填充棒，进行BET测试。
2、二次颗粒粒度分布测试
参考标准：GB/T 19077.1-2016
作为示例具体流程如下：
(1)取一洁净烧杯，加入待测试样品(样品浓度保证遮光度为8％-12％即可)；
(2)加入约20g酒精溶液，同时外超声5min，确保样品完全分散；
(3)打开进样***，再打开光路***，预热30min，进行测试；
(4)输入相应参数后，仪器自动测量得到结果。
3、SEM图片获取
取冷压后的极片，通过Ar粒子束垂直极片大面方向将极片切开，暴露出端面，通过扫描电子显微镜获得图片。
4、一次颗粒粒径测试
采用长径统计法对颗粒粒径进行统计：如图3a和图4所示，图4中标示出的线段长度即为图3a中一次颗粒的长径方向的长度，根据SEM图片显示的尺寸分别测量图4中三组一次颗粒的长轴方向的直径，每组至少测量10个，取三组平均值，即得到一次颗粒的粒径。
5、粉末电阻率测试
参考标准：GB/T 30835-2014《锂离子电池用碳复合磷酸铁锂正极材料》
测试方法：将一定质量的混合正极材料样品放于电阻率测试仪的加料杯中，然后将样品压实，手动采集数据，记录不同压力点下的粉末电阻率测试结果。
作为示例具体流程如下：
(1)样品称重：称取一定重量的样品，样品重量控制在0.8-2.4g；
(2)加料：将称好重量的样品加到加料杯中，确保称重的样品全部加入到加料杯；
(3)加压：将样品压实，并保证压实压力为8MPa；
(4)采集数据：当压力为8MPa时，收集粉末电阻率数据。
6、浆料粘度测试方法
参考标准：GB/T 10247-2008粘度测量方法，测试温度25℃
测试仪器：精度:±1％FS，博勒飞DV2T粘度仪；
原理说明：当转子(圆筒)在流体中持续旋转时，流体的粘性扭矩作用于转子(圆筒)，在一定转速下，流体的动力粘度与扭矩成正比。
7、浆料固含量测试方法
称取一定量的锂离子电池浆料，于120-125℃干燥至质量恒定，干 燥后试样质量占原样质量的质量分数作为浆料的固含量。
作为示例具体流程如下：
(1)取充分搅拌均匀的浆料试样(3.0±0.2g)置于预先干燥并称量(称准至0.0002g)过的称量瓶中，迅速加盖，称量(称准至0.0002g)，晃动摊平；
(2)打开瓶盖，将称量瓶和瓶盖放入预先鼓风并已经加热到120-125℃的干燥箱中，在鼓风条件下，干燥1h；
(3)从干燥箱中取出称量瓶，立即盖上盖在空气中冷却约3min后放入干燥器中，冷却至室温，称量；
(4)结果计算:固含量＝(干燥后固体物总重量/干燥前浆料总重量)。
测试方法1-7均是基于正向的锂离子电池的制备过程所同步进行的测试，若对已经制备完成的锂离子电池进行测试，可以增加如下步骤：
1)电池拆解
a.电池满放到电压为2.0V的满放态；
b.在手套箱中拆解电池，并控制手套箱中湿度在2％以内；
c.分离出电池中的正极极片，然后用DMC(碳酸二甲酯)浸泡并充分洗涤掉正极极片上的电解液；
d.取出正极极片并置于真空干燥箱中，在80℃温度下干燥5h。
2)活性物质分离
a.将干燥的正极极片活性物质层和集流体分离；
b.将分离后的活性物质研磨至粉末状，并在加热条件下用NMP(N-甲基吡咯烷酮)溶解，然后过滤并收集滤渣，重复溶解过滤步骤，直至充分去除PVDF粘结剂；
c.将充分洗涤掉粘结剂的混合物过滤干燥。
d.导电碳分离
将干燥的混合物粉末分散于液体介质中(液体介质的密度大于1.2g/cm 3，例如，硝基苯，溴苯，四氯化碳等)，搅拌使其基本均匀混合。静置足够长时间后，溶液分层，上层为导电碳，下层为活性物质材料。
3)磷酸铁锂化学体系材料和三元化学体系材料分离
原理：由于三元化学体系材料和磷酸铁锂化学体系材料密度差异较 正极材料和导电碳的差异要小，在分离三元正极材料和磷酸铁锂正极材料时，需要进一步利用二者表面润湿性能的差异：磷酸铁锂化学体系材料表面具有碳包覆，表面憎水；三元化学体系材料表面亲水较强。
具体步骤：
a.将下层的活性物质材料干燥，得到混合物粉末；
b.类似于煤的筛选过程，选用合适的液相介质(例如水，乙二醇或丙三醇等)和合适的浮选剂(例如脂油190，杂醇等)，采用气泡浮选法进行分离。
具体步骤为：取1Kg混合物正极材料于液相介质中，调节至较为合适的固含量，加入浮选剂，搅拌产生气泡，收集上浮的泡沫，并洗涤干燥，即可得到磷酸铁锂化学体系材料；收集底部的浆液，并洗涤干燥，即可得到三元化学体系材料。
c.将分离后的三元化学体系材料和磷酸铁锂化学体系材料干燥后分别进行后续表征分析。
8、电池容量和电池能量密度的测试(注：当体系为纯磷酸铁锂体系时，充电截止电压为3.65V，放电截止电压为2.0V；当体系为纯三元化学体系或者混合有三元的化学体系时，充电截止电压为4.35V，放电截止电压为2.8V)
本申请中容量均表示为25℃下，以1/3C恒流(其中，充/放电电流为倍率乘以电芯额定容量，额定容量以该电芯、或该电芯所属电池模组或该电芯所属电池包的GBT认证文件中所认定的电芯容量为准)、在GBT认证文件所规定的工作电压区间内进行充放电，测得电芯容量，示例具体流程如下：
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恒流放电到放电截止电压；
3)暂停5min；
4)1/3C恒流充电充电截止电压，继续恒压充电，直至充电电流小于0.05C后截止；
5)暂停5min；
6)1/3C恒流放电到放电截止电压(此步为实际电池测试容量，结合阴极活性物质质量，即可计算得到正极材料克容量发挥；通过电压-容量曲线 积分即可计算电池能量，能量值/电池重量值＝电池质量能量密度)。
9、电池循环性能测试
容量衰减至初始值的80％时的循环圈数(注：当体系为纯磷酸铁锂体系时，充电截止电压为3.65V，放电截止电压为2.5V；当体系为纯三元化学体系或者混合有三元的化学体系时，充电截止电压为4.35V，放电截止电压为2.8V)，具体流程如下：
1)45℃，1C/1C循环测试流程：
2)将电池置于45℃烘箱中，静置2h，待电池温度保持45℃；
3)1C电流恒流充电到充电截止电压，继续恒压充电，直至充电电流小于0.05C后截止；
4)暂停5min；
5)1C电流恒流放电到放电截止电压；
6)暂停5min；
步骤2)-步骤6)为电池的一个充放电循环，图5示出了不断循环以上步骤2-步骤6，直至容量衰减到初始值的80％时的循环圈数。
本申请各实施例、对比例所用PVDF购自苏威有限公司，型号5130，平均分子量为80-150万；
羧甲基纤维素钠(CMC)购自佛山市瑞美达新材料，锂电池系列CMC；
隔离膜购自恩捷新材料股份有限公司，为磷酸铁锂锂离子电池用陶瓷隔离膜；
电解液购自广东天赐新材料股份有限公司，为磷酸铁锂锂离子电池用电解液；
本申请负极极片制备方法示例如下：
负极极片的制备：将人造石墨，导电炭黑，粘结剂(丁苯橡胶)和羧甲基纤维素钠(CMC)按照比例溶于溶剂中，搅拌均匀并制成浆料，将浆料均匀涂覆在铜箔集流体上，依次经烘干、冷轧、分条、裁片后，得到负极极片。
下面通过具体实施例详细描述本申请：
实施例1
实施例1提出了一种混合正极材料、由其制备的正极极片以及锂离子电池。
(1)混合正极材料
实施例1的混合正极材料包括质量比大约为3:7的磷酸铁锂化学体系二次颗粒与的三元化学体系粉末组成的混合组分，具体组成参数见表1。
其中，磷酸铁锂化学体系二次粒的分子式为：LiFe 0.98Mn 0.02PO 4，比表面积平均值约为10m 2/g，D v50约为5μm，D v10约为1.5μm，D v90约为13.5μm，计算得到D v50/(D v90-D v10)＝0.42，组成磷酸铁锂二次颗粒的一次颗粒粒径约为400nm。
三元化学体系粉末的分子式为LiNi 0.5Co 0.2Mn .0.3O 2，比表面积约为1.2m 2/g，D v50约为3μm。
实施例1的混合正极材料中还包括导电炭黑和PVDF，其中，混合组分与导电炭黑和PVDF按照质量比约为96.5:1.5:2。
(2)正极极片及其制备方法
将上述混合正极材料在大约为500r/min转速下混合，然后加入N-甲基吡咯烷酮(NMP)，在大约为2000r/min转速下搅拌均匀。再用200目左右的过滤筛网进行过滤，得到粘度约为8000mPa·S的浆料，并测定浆料中的固含量。涂覆在厚度为13μm左右的铝箔上，然后蒸发去除NMP，并进行辊压、切片，得到压实密度约为3.1g/cm 3，涂布重量约为190g/m 2的正极极片，其SEM结果见图1。
图2为传统单晶523三元正极材料制备的正极极片的断面SEM图，虽然三元材料颗粒分布均匀，但是颗粒之间存在较多未填充空间。图3a和图3b为LFP材料二次颗粒正极极片的不同放大倍数的SEM图，同样地，虽然二次颗粒分布均匀，但是颗粒之间也存在较多未填充的空间。同时，二次颗粒内部存在大量纳米晶界，二次颗粒具有致密结构。
如图1所示，混合正极材料中的LFP二次颗粒与三元材料分布均匀且致密，没有发生团聚现象。另外，还可以看到LFP二次颗粒内部具有明显的纳米晶界。
(3)锂离子电池及其制备方法
依次将上述正极极片与隔离膜、负极极片叠合，然后卷绕得到裸电池，再经封装、注液、化成抽气得到锂离子电池，如图7所示，并测量其能量密度、循环性能，结果见表3、图5和图6。
图5示例了实施例1的锂离子电池的三次充放电循环的曲线图，是在相同的测试条件下，对同一个锂离子电池连续循环测试三次得到的，可以看出，三次充放电循环差别不大，三条曲线几乎重合，几乎没有容量衰减。
图6示出了实施例1的锂离子电池的循环容量保持率的衰减情况，两条曲线分别记录了两个锂离子电池的循环容量保持率的衰减情况，两次测试的衰减情况几乎相同，没有太大差异。从曲线趋势可以看出，实施例1制备的锂离子电池容量在前几圈具有上升趋势，主要是由于随着循环的进行，材料内部不断活化，电解液充分浸润，导致电池活化的因素大于使其衰减的因素，从而使容量得到提升。继续进行循环，由于容量衰减因素增加，大于活化因素，从而使电池容量不断衰减，但是衰减缓慢，直至循环到225圈，容量保持率仍然接近98％。从图6可以看出，实施例1的锂离子电池具有很好的循环性能。
实施例2-25
实施例2-25按照表1所示的具体成分与比例，采用实施例1所示的方法制备正极极片和锂离子电池。
实施例26
如图8所示，实施例26提供了一种装置，该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该设备对锂离子电池的高功率和高能量密度的需求，可以采用由上述锂离子电池制备得到的电池包或电池模块。
实施例27
实施例27提供了一种移动设备，该移动设备可以是手机、平板电脑、笔记本电脑等。该设备通常要求轻薄化，采用上述锂离子电池作为电源。
对比例1
对比例1提出了一种混合正极材料、由其制备的正极极片以及锂离子电池。
对比例1与实施例2的区别仅在于，对比例1的LiFe 0.98Mn 0.02PO 4 二次颗粒比表面积平均值约为12m 2/g，组成LiFe 0.98Mn 0.02PO 4二次颗粒的一次颗粒粒径约为10nm，其他步骤和参数均相同。
对比例2
对比例2提出了一种混合正极材料、由其制备的正极极片以及锂离子电池。
对比例2与实施例2的区别仅在于，对比例2的LiFe 0.98Mn 0.02PO 4二次颗粒比表面积平均值约为17m 2/g，其他步骤和参数均相同。
对比例3
对比例3提出了一种混合正极材料、由其制备的正极极片以及锂离子电池。
对比例3与实施例2的区别在于，对比例3的混合正极材料包括质量比大约为3:7的磷酸铁锂化学体系一次颗粒与的三元化学体系粉末，LiFe 0.98Mn 0.02PO 4一次颗粒的比表面积约为16m 2/g，D v50约为1.1μm，D v10约为0.25μm，D v90约为18.5μm，其他步骤和参数均相同。
实施例1-25和对比例1-3的混合组分的具体参数见表1。
表1
Figure PCTCN2020119743-appb-000001
Figure PCTCN2020119743-appb-000002
测量实施例1-6与对比例1-3的混合浆料固含量，并测量其电池能量密度、循环性能，结果见表2。
表2
Figure PCTCN2020119743-appb-000003
测量实施例1-25与对比例1-3的正极极片电阻，以及包括正极极片的锂离子电池的能量密度、循环性能，结果见表3。
表3
Figure PCTCN2020119743-appb-000004
Figure PCTCN2020119743-appb-000005
对比例1-3在制备过程中，浆料无法连续稳定通过150目钢丝筛网，团聚的浆料在滤网一侧发生堵塞，无法完成过滤。除此之外，对混合前后浆料的粘度进行测试发现，浆料混合后，粘度明显上升，流动性明显变差，说明产生了较为严重的团聚现象。而实施例1-25在制备过程中，混合浆料可以连续稳定通过150目钢丝筛网，没有发生堵塞，说明没有发生团聚现象。同时测量浆料粘度，发现混合浆料的粘度与混合前相比，变化不大。
对比实施例1-6与对比例1-3的混合浆料固含量，可以看出，实施例1-6中的二次颗粒比表面积不大于10m 2/g，最终得到的混合浆料固含量远大于对比例1-3，分析原因，主要是因为实施例1-6的混合正极材料在制备过程中没有发生团聚，在较高的固含量下，仍具有较好的浆料稳定性和加工性能。而对比例1-3的混合正极材料在制备过程中，会发生团聚，当固含量提高时，团聚现象更加严重，因而最终制备得到的混合正极材料中的固含量也会 降低。低固含量浆料在涂布过程中易于产生膜片开裂和涂布厚度控制不均的问题，从而影响了电池能量密度和循环性能。尤其是，如对比例3所示，同时比较表2和表3，当混合材料采用纳米级磷酸铁锂一次颗粒时，混合浆料固含量只有46％，远小于实施例1-6的混合浆料固含量，严重影响了电池的能量密度和循环性能。
比较表3，对比实施例1-6和对比例1-2可看出，采用本申请实施例的LFP比表面积平均值，最终制备得到的锂电池的能量密度提高，最终在初始放电容量、首圈效率基本相同的情况下，容量衰减至初始值的80％时的循环圈数明显增加，远大于对比例的循环圈数，锂电池的循环性能明显增加。
对比实施例7-9和12-14和实施例10、11、15、16可以看出，D v50、D v10、D v90以及D v50/(D v90-D v10)的取值分布，对极片电阻率和循环寿命的均有影响。本申请实施例7-9和12-14的混合正极材料，D v50、D v10、D v90以及D v50/(D v90-D v10)的取值保证在合适的范围，最终制备得到的正极极片电阻值较低，在初始放电容量、首圈效率基本相同的情况下，容量衰减至初始值的80％时的循环圈数明显增加，说明合适的二次颗粒粒径分布对电池性能的影响很大。
比较实施例17-21和实施例22-24可以看出，混合正极材料的比例对正极极片阻值、锂电池的能量密度和循环性能均有较大影响。从实施例17-21可以看出，随着磷酸铁锂二次颗粒质量分数的增加，正极极片阻值降低，电池能量密度稍有降低，循环性能增加。实施例22-24可以看出，过量添加三元材料会使电池能量循环性能可能会受到影响，能量密度的提高有限。
综上，本申请的混合正极材料，通过控制磷酸铁锂化学体系二次颗粒的比表面积，解决了三元化学体系材料与磷酸铁锂化学体系材料共混时的团聚问题，提高了混合正极材料的加工性能，实现浆料不易团聚，二种材料之间良好相容。当采用本申请的混合正极材料制备正极极片时，能够使正极材料在正极极片上分布均匀，利于调节极片电阻值的分布均匀性，从而制备得到的锂离子电池具有更高的能量密度以及更好的循环性能。
在本说明书的描述中，参考术语“一个实施例”、“一些实施例”、“示例”、“具体示例”、或“一些示例”等的描述意指结合该实施例或示例描述的具体特征、结构、材料或者特点包含于本申请的至少一个实施例或示例中。在 本说明书中，对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不相互矛盾的情况下，本领域的技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。
尽管上面已经示出和描述了本申请的实施例，可以理解的是，上述实施例是示例性的，不能理解为对本申请的限制，本领域的普通技术人员在本申请的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (17)

  1. 一种混合正极材料，其中，包括由磷酸铁锂化学体系材料和三元化学体系材料组成的混合组分，所述磷酸铁锂化学体系材料为比表面积平均值不超过10m 2/g的二次颗粒。
  2. 根据权利要求1所述的混合正极材料，其中，所述磷酸铁锂化学体系材料为比表面积平均值不超过6m 2/g的二次颗粒。
  3. 根据权利要求1或2所述的混合正极材料，其中，所述二次颗粒的粒径分布满足：0.1≤D v50/(D v90-D v10)≤10。
  4. 根据权利要求1-3任一项所述的混合正极材料，其中，所述二次颗粒的粒径分布满足：D v10≥0.6μm，D v90≤30μm。
  5. 根据权利要求1-4任一项所述的混合正极材料，其中，所述二次颗粒中位粒度分布满足：2μm≤D v50≤9μm。
  6. 根据权利要求5所述的混合正极材料，其中，所述二次颗粒中位粒度分布满足：3μm≤D v50≤6μm。
  7. 根据权利要求1-6任一项所述的混合正极材料，其中，组成所述二次颗粒的一次颗粒平均粒径分布d满足：20nm≤d≤800nm。
  8. 根据权利要求1-7任一项所述的混合正极材料，其中，所述磷酸铁锂化学体系二次颗粒的粉末电阻率不大于100Ω·cm。
  9. 根据权利要求1-8任一项所述的混合正极材料，其中，以所述混合组分的质量为100％计，所述磷酸铁锂化学体系二次颗粒的含量为20％-70％。
  10. 根据权利要求9所述的混合正极材料，其中，所述磷酸铁锂化学体系二次颗粒的含量为25％-45％。
  11. 根据权利要求1-10任一项所述的混合正极材料，其中，所述混合组分中：
    所述磷酸铁锂化学体系材料通式为LiFe 1-xM xPO 4，其中，0<x≤0.1，M选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr和Ti中的一种或多种；和/或
    所述三元化学体系材料为镍钴锰酸锂化学体系材料和/或镍钴铝酸锂化学体系材料，所述镍钴锰酸锂化学体系材料通式为LiNi xMn yCo 1-x-yO 2，其中，1＞x＞0，1＞y＞0，x+y≤0.95；所述镍钴铝酸锂化学体系材料通式为LiNi xCo yAl 1-x-yO 2，其中，1＞x＞0.6，0.4＞y＞0.1。
  12. 一种正极极片，包括含有根据权利要求1-11任一项所述的混合正极材料的正极材料层。
  13. 根据权利要求12所述的正极极片，其中，所述正极材料层的单位面积质量为150-250g/m 2，和/或
    所述正极材料层的压实密度为2.6-3.5g/cm 3。
  14. 根据权利要求12所述的正极极片，其中，所述正极材料层中还含有导电剂和粘结剂，所述混合正极材料、所述导电剂与所述粘结剂的质量比为(90-98):(1-5):(1-5)。
  15. 一种如权利要求12-14任一项所述的正极极片的制备方法，其中，包括如下步骤：
    将如权利要求1-11任一项所述混合正极材料进行混合，
    过滤并收集浆料，
    将所述浆料涂覆在集流体上，
    去除溶剂后进行辊压、切片，
    得到正极极片。
  16. 一种电池，包括权利要求12-14所述的正极极片。
  17. 一种装置，包括权利要求16所述的电池，所述电池用于为所述装置提供电源和/或用于所述装置的能量存储单元，所述装置选自电动车辆、电动船舶、电动工具、电子设备及储能***中的一种或多种。
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