WO2021258900A1 - 正极片及电池 - Google Patents

正极片及电池 Download PDF

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Publication number
WO2021258900A1
WO2021258900A1 PCT/CN2021/093563 CN2021093563W WO2021258900A1 WO 2021258900 A1 WO2021258900 A1 WO 2021258900A1 CN 2021093563 W CN2021093563 W CN 2021093563W WO 2021258900 A1 WO2021258900 A1 WO 2021258900A1
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positive electrode
electrode active
layer
main
electrode material
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PCT/CN2021/093563
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English (en)
French (fr)
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阮泽文
陈娜
郝嵘
潘仪
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比亚迪股份有限公司
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Priority to EP21830200.8A priority Critical patent/EP4174980A1/en
Priority to JP2022580298A priority patent/JP2023531266A/ja
Priority to US18/012,599 priority patent/US20230253549A1/en
Priority to KR1020237001997A priority patent/KR20230027203A/ko
Publication of WO2021258900A1 publication Critical patent/WO2021258900A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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
    • H01M4/362—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
    • 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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 invention relates to the technical field of batteries, in particular to a positive electrode sheet and a battery.
  • Lithium-ion batteries have the advantages of high energy density, small size, light weight, long cycle life, and no memory effect. They are widely used in the field of portable electronic equipment and new energy electric vehicle batteries.
  • layered cathode materials have become the focus of attention of cathode materials due to their advantages of high energy density, low cost, and high platform voltage.
  • the area density and pressure of the electrode sheet The solid density also puts forward higher requirements.
  • the lithium ion migration path in the electrode sheet far away from the electrolyte is extended, the electrode sheet is partially deintercalated with lithium unevenly, and the large size of the electrode sheet ,
  • the speed at which all the small particles are completely released/embedded is inconsistent, resulting in uneven distribution of the state of charge between the particles, causing problems such as large battery impedance, poor magnification, and fast cycle attenuation, and at the same time bury potential safety hazards.
  • a positive electrode sheet includes a current collector and a positive electrode active layer disposed on the current collector, and the positive electrode active layer includes m-layer positive active sublayers. , each active sub-layer positive electrode active material of positive electrode material and a positive electrode comprising a main auxiliary cathode material, and the D layer of the positive electrode active material in the positive electrode 50 of the primary particle diameter satisfies:
  • the m is an integer greater than or equal to 2
  • the n is any integer from 2 to m
  • the D 501 represents the D 50 particle size of the main cathode material in the first layer of the anode active sublayer
  • the D 50 n represents the D 50 particle size of the main positive electrode material in the nth positive electrode active sublayer
  • the distance between the nth positive electrode active sublayer and the current collector is greater than the distance between the n-1th positive electrode active sublayer and the current collector.
  • the D 90 particle size of the auxiliary positive electrode material is smaller than the D 10 particle size of the main positive electrode material in the first positive electrode active sublayer.
  • a battery including the positive electrode sheet as described above.
  • the particle size of the main positive electrode material in each layer of the positive electrode active sublayer in the positive electrode active layer is set to satisfy:
  • the particle size of the main positive electrode material of the positive electrode active layer gradually increases from the side adjacent to the current collector to the side away from the current collector, so that the release/intercalation rate of lithium ions in the entire positive electrode active layer is uniform, so that the thickness of the positive electrode sheet
  • the charge distribution between adjacent particles in the direction is uniform, and can reduce the polarization caused by the difference in the charge state between the thickness direction of the positive electrode sheet and the large and small particles; the auxiliary positive electrode material of small particles is filled between the main positive electrode material of large particles
  • the gap effectively increases the compaction density of the positive electrode sheet.
  • FIG. 1 is a Raman spectrum imaging diagram of a microscopic area of a positive electrode prepared by one of the embodiments and the comparative example provided by the present disclosure.
  • An embodiment of the present disclosure provides a positive electrode sheet.
  • the positive electrode sheet includes a current collector and a positive electrode active layer disposed on the current collector.
  • the positive electrode active layer includes m layers of positive electrode active sublayers, and each positive electrode active sublayer
  • the positive electrode active material in the positive electrode active layer includes a main positive electrode material and an auxiliary positive electrode material, and the D 50 particle size of the main positive electrode material in the positive electrode active layer satisfies:
  • the m is an integer greater than or equal to 2
  • the n is any integer from 2 to m
  • the D 501 represents the D 50 particle size of the main cathode material in the first layer of the anode active sublayer
  • the D 50 n represents the D 50 particle size of the main positive electrode material in the nth positive electrode active sublayer
  • the distance between the nth positive electrode active sublayer and the current collector is greater than the distance between the n-1th positive electrode active sublayer and the current collector. State the distance of the current collector.
  • the D 90 particle size of the auxiliary positive electrode material is smaller than the D 10 particle size of the main positive electrode material in the first positive electrode active sublayer. That is, the particle size of the auxiliary positive electrode material and the particle size of the main positive electrode material in the first positive electrode active sublayer satisfy: D 90 auxiliary ⁇ D 101 , where D 90 auxiliary represents the D of the auxiliary positive electrode material 90 particle size, the D 101 represents the D 10 particle size of the main positive electrode material in the first positive electrode active sublayer.
  • the m-layer positive active sub-layer is arranged on the same side of the current collector, from the direction away from the current collector, the m-layer positive active sub-layer includes the first positive active sub-layer and the second positive active sub-layer in turn.
  • Layer optionally The m-1th layer of positive electrode active sublayer, the mth layer of positive electrode active sublayer, wherein the first layer of positive electrode active sublayer is in direct contact with the current collector.
  • the D 50 particle size of the main cathode material in the cathode active layer satisfies:
  • the D 50 particle size of the active sub-layer to the m-th positive active sub-layer gradually increases.
  • the first positive active sub-layer close to the current collector has the smallest D 50 particle size, and the m-th layer farthest from the current collector
  • the D 50 particle size in the active sublayer of the positive electrode is the largest, and the middle layer has a gradient distribution with a small particle size gradually transitioning to a large particle size.
  • the particle size of the main cathode material of the positive electrode active layer gradually increases from the current collector to the side away from the current collector, so that the release/intercalation rate of lithium ions in the entire positive electrode active layer Uniformity, so that the charge distribution between adjacent particles in the thickness direction of the positive electrode sheet is uniform, and the polarization caused by the difference in the charge state between the thickness direction of the positive electrode sheet and the large and small particles can be reduced, and the conductivity of the prepared battery can be improved. Performance, improve the rate performance and safety performance of the prepared battery. There are two main aspects that affect the transmission of lithium ions in the battery.
  • One is solid phase diffusion, that is, the particle size of the active material in the electrode
  • the other is liquid phase diffusion, that is, the diffusion of lithium ions in a liquid environment. distance.
  • the particle size of the positive electrode material particles at each position of the entire positive electrode active layer is not distributed according to the above-mentioned relational formula 1, for example, the particle size of the positive electrode material particles in the entire positive electrode active layer is the same, and the lithium ion is solidified in the active material.
  • the distance of the phase diffusion is the same, but the distance between the active material and the solid-liquid interface on the different thickness of the pole piece is different, resulting in different distances of the lithium ions in the liquid phase; in this case, it will be on the surface of the pole piece.
  • the active material (close to the diaphragm) releases lithium fast, and the active material in the inner layer of the pole piece (close to the current collector) releases lithium slowly, which leads to uneven distribution of the state of charge between the active material particles, causing the battery
  • the problems of large impedance, poor magnification, and fast cycle attenuation The deintercalation speed of lithium ions on large particles of positive electrode material particles is slower than that of small particles of main positive electrode material particles, which will lead to uneven distribution of the state of charge between the positive electrode material particles, resulting in large battery impedance , The problem of poor magnification and fast cycle attenuation.
  • the large-diameter cathode material particles have a slower rate of desorption/intercalation of lithium
  • the small-diameter cathode material particles have a faster rate of desorption/intercalation of lithium.
  • the particle size of the main positive electrode material particles in the positive electrode active sublayer on one side is set to be larger, and the particle size of the main positive electrode material particles in the positive electrode active sublayer far from the electrolyte (or the side adjacent to the current collector) is set to be larger.
  • the lithium removal/intercalation rate of the large-diameter main cathode material particles closer to the electrolyte is equivalent to the lithium removal/intercalation rate of the small-diameter main cathode material particles far away from the electrolyte
  • the The lithium extraction/intercalation rate of the positive electrode active material in the positive electrode active sublayer of the layer is the same, which improves the uniformity of the lithium extraction/intercalation rate of the overall positive electrode active layer.
  • the particle size of the main positive electrode material is the smallest, and the time for lithium ions to precipitate from the main positive electrode material particles is relatively short, but the first positive electrode active sublayer is the farthest away from the electrolyte.
  • Lithium ions need a long time to enter the electrolyte, and in the m-th layer of the positive electrode active sublayer, the particle size of the main positive electrode material is the largest, and the time for lithium ions to separate from the main positive electrode material particles is longer, but the m-th layer
  • the active sub-layer of the positive electrode is closest to the electrolyte, and the precipitated lithium ions can enter the electrolyte in a short time.
  • lithium ions are precipitated from the main positive electrode material particles in the first active sub-layer of the positive electrode.
  • the total time to reach the electrolyte and the total time for lithium ions to precipitate from the main positive electrode material particles of the m-th positive electrode active sublayer and reach the electrolyte can tend to be the same, that is, the desorption of lithium ions in the first positive electrode active sublayer.
  • the intercalation rate is equivalent to the deintercalation rate of lithium ions in the active sub-layer of the m-th positive electrode.
  • the desorption/intercalation rate of lithium ions in the second positive active layer and the m-1th positive active layer is equivalent, and the desorption/intercalation of lithium ions in the adjacent nth and n-1th positive active sublayers
  • the intercalation rate is also equivalent, in other words, the desorption/intercalation rate of lithium ions in any two positive active sublayers in the positive active layer is equivalent.
  • the D 50 particle size of each of the positive electrode active sub-layer of the positive electrode active layer of the primary positive electrode material according to a distribution of the above relationship, the entire release lithium ions in the positive electrode active layer, /The embedding speed is uniform, so that the charge distribution between adjacent particles in the thickness direction of the positive electrode sheet is uniform, and the polarization caused by the difference in the charge state between the thickness direction of the positive electrode sheet and the large and small particles can be reduced.
  • the positive electrode active material in the present application is also provided with an auxiliary positive electrode material layer, and the particle size of the auxiliary positive electrode material and the particle size of the main positive electrode material in the first positive electrode active sublayer satisfy: D 90 auxiliary ⁇ D 101 , that is, on the whole
  • the particle size of 90% of the auxiliary positive electrode material is less than 10% of the particle size of the main positive electrode material of the positive electrode active sublayer.
  • the small particle size of the auxiliary positive electrode material is distributed in each layer of the positive electrode active sublayer. The gap between the particles effectively increases the compaction density of the positive electrode sheet.
  • the main cathode material is preferably a layered cathode material
  • the auxiliary cathode material is preferably a polyanionic cathode material.
  • the polyanionic cathode material has excellent structural stability, and the polyanionic cathode is not easy to react with the electrolyte or react with The electrolyte reaction has little effect on the structure of the positive electrode active layer, and will not damage the structural stability of the positive electrode active layer.
  • the composite use of the polyanionic positive electrode material and the layered positive electrode material can improve the cycle and safety performance of the positive electrode sheet.
  • the layered positive electrode material may be a layered positive electrode material formed by coating and compacting the main positive electrode material.
  • the auxiliary positive electrode material of small particles is also filled in The gap between the large particles of the main positive electrode material can improve the uniformity of the charge distribution between adjacent particles in the thickness direction of the positive electrode sheet, and can reduce the polarity caused by the difference in the charge state between the thickness direction of the positive electrode sheet and the large and small particles. In the case of chemical conversion, the compaction density of the positive electrode sheet is further effectively increased.
  • the D 50 particle size of the auxiliary cathode material is less than or equal to 200 nm. That is, the particle diameter of the auxiliary positive electrode material satisfies: D 50 auxiliary ⁇ 200 nm, and the D 50 auxiliary represents the D 50 particle diameter of the auxiliary positive electrode material.
  • the auxiliary positive electrode material can be better distributed among the particles of the main positive electrode material to further increase the compaction density of the positive electrode sheet.
  • the D 90 particle size of the main positive electrode material in the n-1th positive active sublayer is less than or equal to the D 10 particle size of the main positive electrode material in the nth positive active sublayer. That is, the particle size of the main positive electrode material in the n-1th positive electrode active sublayer and the particle size of the main positive electrode material in the nth positive electrode active sublayer satisfy: D 90 n-1 ⁇ D 10 n, where The D 90 n-1 represents the D 90 particle size of the main positive electrode material in the n-1th positive active sublayer, and the D 10 n represents the D 10 particle size of the main positive electrode material in the n-th positive active sublayer.
  • 90% of the main positive electrode material has a particle size smaller than 10% of the main positive electrode material in the nth positive electrode active sublayer. This can ensure that the particle size of the main positive electrode material particles in the two adjacent layers gradually transition from small particle size to large particle size. For the entire positive electrode active layer, the size of the main positive electrode material particles in each positive electrode active sublayer can be further improved. Gradient regularity of particle size distribution.
  • the particle size of the main positive electrode material in the positive electrode active layer also satisfies: 4.0 ⁇ m ⁇ D 50 [m/2]+1 ⁇ 8.0 ⁇ m, and the [m/2] represents an integer down,
  • the D 50 [m/2]+1 represents the D 50 particle size of the main cathode material in the [m/2]+1th layer of the anode active sublayer.
  • the particle size of the main positive electrode material in the positive electrode active layer satisfies: 4.0 ⁇ m ⁇ D 503 ⁇ 8.0 ⁇ m, that is to say, the D 50 particle size of the third layer of positive electrode active sub-layer is 4.0 ⁇ m to 8.0 Between ⁇ m.
  • the primary particle diameter satisfies a positive electrode active material in the positive electrode layer: 4.0 ⁇ m ⁇ D 503 ⁇ 8.0 ⁇ m, particle diameter D 50 that is the third layer of the positive electrode active sub-layer of 4.0 ⁇ m to 8.0 ⁇ m in between.
  • the above setting limits the particle size of the main positive electrode material close to the intermediate layer or the intermediate layer. According to the particle size distribution relationship equation 1 in each layer, it can be known that the first layer of positive electrode active sublayer to the last layer of positive electrode active sublayer The particle size distribution of the main cathode material in the layer.
  • the areal density of the main positive electrode material in the first positive active sublayer to the m-th positive active sublayer in the positive active layer accounts for the percentage of the areal density of the main positive electrode material in the positive active layer, respectively It is normally distributed.
  • the areal density of the main positive electrode material in the positive electrode active layer refers to the mass of the main positive electrode material in the positive electrode active layer per unit area under a specified thickness
  • the areal density of the main positive electrode material in the positive electrode active sublayer is Refers to the mass of the main positive electrode material in the positive electrode active sublayer per unit area under the specified thickness.
  • the area density of the main positive electrode material in the positive electrode active sublayers at both ends of the positive electrode active layer is small, and the area density of the main positive electrode material in the positive electrode active sublayer of the intermediate layer is large.
  • This distribution can increase the phase density of the positive electrode sheet in the thickness direction.
  • the uniformity of charge distribution between adjacent particles Since the particle size of the main positive electrode material in the positive electrode active sublayers at both ends has the largest difference, the difference in the speed of lithium ion extraction/intercalation on the main positive electrode material particles at both ends is the largest.
  • the surface of the main positive electrode material in the positive electrode active sublayers A smaller density setting can reduce the amount of main cathode material particles with a large difference in lithium ion deintercalation/intercalation speed at both ends, thereby improving the uniformity of the lithium ion deintercalation speed in the entire positive electrode active layer, thereby improving the positive electrode sheet The uniformity of the charge distribution between adjacent particles in the thickness direction.
  • the percentage of the areal density of the main positive electrode material in each positive electrode active sublayer to the areal density of the main positive electrode material in the positive electrode active layer satisfies:
  • the m is an integer greater than or equal to 3
  • the ⁇ 1 represents the percentage of the areal density of the main positive electrode material in the first positive electrode active sublayer to the areal density of the main positive electrode material in the positive electrode active layer
  • the ⁇ 2 the second layer represents a positive electrode active sub-layer surface-density of the positive electrode active material
  • the surface density [rho] m represents the m-th layer of the positive electrode active material of the positive electrode of the main sub-layer accounts for positive
  • the percentage of the areal density of the main positive electrode material in the active layer where ⁇ m-1 represents the percentage of the areal density of the main positive electrode material in the positive active sublayer of the m-1th layer to the areal density of the main positive electrode material in the positive electrode active layer;
  • the ⁇ m/2 represents the percentage of the area density of the main positive electrode material in the positive electrode active sublayer of the [m/2]+1th layer to
  • each positive active sublayer further includes a conductive agent and a binder.
  • the area density of the positive electrode active layer satisfies: 300 g/m 2 ⁇ 500 g/m 2 , where ⁇ represents the area density of the positive electrode active layer.
  • the positive electrode active layer includes the main positive electrode material, the auxiliary positive electrode material, the conductive agent, and the binder.
  • the area density of the positive electrode active layer refers to all the main positive electrode materials and auxiliary positive electrode materials in the positive electrode active layer per unit area under a specified thickness. , The quality of conductive agent and adhesive.
  • the surface density of the positive electrode active layer of the present application is relatively large, between 300 g/m 2 and 500 g/m 2 , and has a relatively high electric capacity.
  • a positive electrode active layer with a larger areal density has a larger thickness on a positive electrode sheet of the same area.
  • the above-mentioned particle size distribution relationship of each positive electrode active sublayer is adopted for a positive electrode active layer with a larger thickness.
  • Formula 1 the state of charge distribution among the positive electrode material particles of the positive electrode sheet is improved more obviously.
  • the conductive agent is at least one of conductive carbon black, acetylene black, carbon nanotubes and graphene
  • the binder is polyvinylidene fluoride or a copolymer containing vinylidene fluoride.
  • the area density of the positive electrode active layer satisfies: 350 g/m 2 ⁇ 450 g/m 2 . In an embodiment, the area density of the positive electrode active layer satisfies: 400 g/m 2 ⁇ 450 g/m 2 .
  • the mass of the auxiliary positive electrode material accounts for 0.5% to 20.0% of the mass of the positive electrode active material in the positive electrode active layer. With the above-mentioned mass ratio, the obtained positive electrode sheet has a better compaction density.
  • the mass of the auxiliary positive electrode material accounts for 4.0%-12.0% of the mass of the positive electrode active material in the positive electrode active layer.
  • the layered cathode material is at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate;
  • the polyanionic cathode material is phosphoric acid At least one of lithium iron, lithium iron manganese phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium vanadium fluorophosphate, lithium manganese silicate, lithium iron silicate, and lithium cobalt silicate.
  • the present disclosure also provides a battery, which includes the positive electrode sheet as described in any one of the above. Placing the above-mentioned electrode sheet in the battery can reduce the polarization caused by the difference in the thickness direction of the positive electrode sheet and between the large and small particles, eliminate the polarization caused by uneven lithium extraction/intercalation, reduce the impedance of the battery, and improve the battery Electrochemical performance and cycle performance at different rates.
  • the positive electrode active material, the conductive agent and the binder are dissolved in a solvent of nitrogen methyl pyrrolidone at a mass ratio of 94:3.0:3.0 and dispersed uniformly to prepare a slurry;
  • the positive electrode active material includes a layered positive electrode material and Polyanionic cathode material, in which the layered cathode material is LiNi 0.83 Co 0.13 Mn 0.04O2 , the polyanionic cathode material is lithium iron phosphate cathode material, and the mass percentage of the lithium iron phosphate cathode material to the cathode active material is 6.5%.
  • the first positive electrode slurry, the second positive electrode slurry, the third positive electrode slurry, and the fourth positive electrode slurry are sequentially coated on the current collector to form the first positive electrode active sublayer and the second positive electrode
  • the active sub-layer, the third positive active sub-layer and the fourth positive active sub-layer, the four positive active sub-layers constitute the positive active layer of the positive sheet;
  • the positive sheet coated with the slurry is continuously shaken to make
  • the particle size of the positive electrode active material particles in each layer of the positive electrode active sub-layer in the positive electrode sheet is in a gradient distribution, which reduces the difference in particle size of the interface layer;
  • the positive electrode sheet is baked, rolled, and then cut into specific sizes for use; the first layer of positive electrode active sublayer, the second layer of positive electrode active sublayer, the third layer of positive electrode active sublayer, and the fourth layer of positive electrode
  • the area density of the main positive electrode material in the active sublayer accounts for 8.0%, 45.0%, 38.0%, and 9.0% of the main positive electrode material in the positive electrode active layer, respectively; the area density of the positive electrode active layer is 420 g/m 2 .
  • the D 50 particle size of LiNi 0.83 Co 0.13 Mn 0.04O2 in the four positive active sub-layers above satisfies:
  • Example 1 Following the same method of preparing a positive electrode sheet, except that the layered cathode active material for preparing the positive electrode sublayer selected particle size D 50 of three kinds, the first sub-layer of the positive electrode active layer, a second layer
  • the D 50 particle size of the layered cathode material in the positive electrode active sublayer and the third layer of the positive electrode active sublayer are 2.0 ⁇ m, 6.5 ⁇ m, and 15.0 ⁇ m, respectively.
  • the D 50 particle size in the three layers satisfies the relational formula 1, and the other conditions are the same as In the same manner as in Example 1, a positive electrode sheet was prepared.
  • Example 1 Following the same method of preparing a positive electrode sheet, except that the layered cathode active material for the positive electrode preparation of the selected sublayers D 50 particle size of 5 kinds of positive electrode active sub-layer of the first layer, the second layer the positive electrode active sub-layer, a third layer of the positive electrode active sub-layer, the fourth layer of the positive electrode active sublayer and D 50 particle size of the fifth layer of the positive electrode active sub-layer layered cathode material are 0.5 ⁇ m, 1.5 ⁇ m, 4.5 ⁇ m, 8.0 ⁇ m, 18.0 ⁇ m, the D 50 particle size in the 5 layers satisfies the relational formula 1, and other conditions are the same as in Example 1, and a positive electrode sheet is prepared;
  • the positive electrode sheet was prepared according to the same method as in Example 1, except that the selected layered positive electrode material was lithium cobalt oxide and lithium nickel cobalt aluminate, and the molar ratio of the two was 1:1; the positive electrode sheet was prepared.
  • the positive electrode sheet was prepared according to the same method as in Example 1, except that the content of lithium iron phosphate in the positive electrode active material was 15.0%; the positive electrode sheet was prepared.
  • the positive electrode sheet was prepared according to the same method as in Example 1, except that the content of lithium iron phosphate in the positive electrode active material was 2.0%; the positive electrode sheet was prepared.
  • the positive electrode sheet was prepared according to the same method as in Example 1, except that the polyanion in the positive electrode active material was lithium iron manganese phosphate; the positive electrode sheet was prepared.
  • the positive electrode sheet was prepared according to the same method as in Example 1, except that the positive electrode active material did not contain a polyanionic positive electrode; the positive electrode sheet was prepared.
  • Example 1 Following the same method of preparing a positive electrode sheet, except that the layered cathode active material for preparing the positive electrode sublayer selected particle size D 50 of four kinds, a first sub-layer of the positive electrode active layer, a second layer
  • the D 50 particle diameters of LiNi 0.83 Co 0.13 Mn 0.04O2 in the positive electrode active sub-layer, the third positive active sub-layer and the fourth positive active sub-layer are 0.6 ⁇ m, 3.0 ⁇ m, 7.0 ⁇ m, and 20.0 ⁇ m, respectively; the positive electrode is prepared piece.
  • the positive electrode sheets in the foregoing Example 1 to Example 9 and Comparative Example 1 to Comparative Example 4 were all prepared according to the following method to obtain the corresponding battery: the positive electrode sheet, the separator, and the negative electrode sheet were stacked in order to obtain a bare cell, and then Put the electric core into the shell, bake and dry, inject electrolyte, weld and seal, and go through high-temperature aging, chemical conversion, aging and other processes to obtain the battery.
  • Impedance performance test method Fully charge with 0.2C constant current and constant voltage at 25°C, then discharge to 2.5V at 0.2C constant current after shelving, repeat 3 times, record the third discharge capacity as C0, and use 0.2C0 current Adjust the battery to 50% SOC, and then test the 1.5C constant current discharge for 30s to calculate the impedance value.
  • Rate performance test method Fully charge with 0.2C constant current and constant voltage at 25°C, and then discharge to 2.5V at 0.2C constant current after shelving, repeat 3 times, record the third discharge capacity as C0, respectively with 0.2C0 , 5.0C0 constant current and constant voltage is fully charged, and then discharged with the same current, based on 0.2C0 discharge capacity, 5.0C0 discharge capacity and its ratio as an index for evaluating rate performance.
  • Cycle performance test method Fully charge at 0.2C constant current and constant voltage at 25°C, and then discharge to 2.5V at 0.2C constant current after shelving, repeat 3 times, record the third discharge capacity as C0, at 45°C environment Next, fully charge with 1.0C0 constant current and constant voltage, then discharge with 1.0C0 constant current, and cycle for 500 weeks to record the capacity retention rate.
  • Safety performance test method Use DSC to test electrode stability as an index to evaluate safety performance. Fully charge the battery, take out the positive electrode sheet in the glove box, scrape an appropriate amount of positive electrode material and place it in a crucible, and then add a certain amount of electrolyte , Transfer to the equipment, test atmosphere with pure argon, heating rate 2°C/min, record thermal runaway start temperature, thermal runaway peak temperature and heat release power respectively.
  • SOC State of charge performance test method: quickly fully charge the battery with 2.0C current, take out the positive electrode sheet in the glove box, cut it with an Ar ion beam to obtain the pole piece section, and then place it in the pull Raman spectroscopy on a cross-sectional scanning, different metal and oxygen / vibration level different metals with different valences and oxygen peaks in the Raman spectrum, peak shape, peak intensity different to 550cm -1 and 470cm -1 peak peak peak.
  • the area ratio of is used as an index to evaluate the SOC state, and the ratio of each point in the scanning area can be obtained, and the SOC distribution in the area can be obtained, and then the average value of the SOC in the area can be calculated to characterize the actual SOC state of the pole piece.
  • Figure 1 Please refer to Figure 1.
  • the left side of Figure 1 is the SOC distribution of the battery prepared in Example 1
  • the right side of Figure 1 is the SOC distribution of the battery prepared in Comparative Example 3. It can be seen that the positive electrode prepared in Example 1
  • the SOC distribution in the sheet is significantly more uniform, indicating that the polarization of the positive electrode sheet is smaller, which is more conducive to the insertion/extraction of lithium ions.
  • Example 1 in terms of battery impedance in Example 1 to Example 9, the battery impedance value is the lowest. Reaching 151m ⁇ , the lower the battery impedance, the better the battery’s electrical conductivity; in terms of rate performance, the rate ratio is 99.3% at the highest and 86.2% at the lowest. The higher the rate ratio, the better the electrochemical performance of the battery at different rates. Stability means better rate performance; in terms of cycle performance, the highest cycle capacity retention rate is 93.2%, and the lowest is 82.0%. The higher the cycle capacity retention rate, the more stable the battery performance and the longer the service life.
  • Comparative Example 1 since the particle size of the layered cathode material particles in the positive electrode active layer in Comparative Example 1 is only one, the particle size distribution that satisfies the relational formula 1 is not adopted as in Example 1, and the battery prepared is in Impedance, rate, cycle capacity retention, safety performance, and SOC are all worse than Example 1.
  • the battery impedance in Comparative Example 1 is 195m ⁇ , which is larger than Example 1, indicating that the electrical conductivity of the battery is reduced; Only 87.8%, the capacity retention rate is only 76.8%, the thermal runaway initiation temperature and the thermal runaway peak temperature are lower than those of the first embodiment, the heat release function is greater than that of the first embodiment, and the SOC ratio is lower than that of the first embodiment.
  • Comparative Example 2 no polyanionic positive electrode material is added in Comparative Example 2, which will affect the compaction density of the positive electrode sheet, and then affect the electrical conductivity of the positive electrode sheet. From the data of Comparative Example 2, it can be seen that the preparation obtained in Comparative Example 2 The battery is inferior to Example 1 in terms of impedance, rate, cycle capacity retention, safety performance, and SOC.
  • Comparative Example 3 there is only one particle size in Comparative Example 3, and no polyanionic cathode material is added. From the data of Comparative Example 3, it can be seen that the battery prepared in Comparative Example 3 exhibits resistance, rate, cycle The capacity retention rate, safety performance, and SOC are all inferior to Example 1.
  • Comparative Example 4 in Comparative Example 4, the D 50 particle size of LiNi 0.83 Co 0.13 Mn 0.04O2 in the four-layer positive electrode active sublayer does not satisfy the relational formula 1 of the present disclosure, that is to say, the particle size between the layers The diameter does not show a regular distribution in relational formula 1. From the data of Comparative Example 4, it can be seen that the battery prepared in Comparative Example 4 is better than Example 1 in terms of impedance, rate, cycle capacity retention, safety performance, and SOC. Poor, this shows that setting the D 50 particle size of LiNi 0.83 Co 0.13 Mn 0.04O2 in each positive electrode active sublayer according to the relational formula 1 in the present disclosure can improve the electrical performance of the battery.
  • Example 5 Comparing Example 5 with Example 1 and Example 4, it can be seen that the performance and effect of the positive electrode sheet prepared by using lithium iron phosphate with a D 50 particle size ⁇ 200 nm is better.
  • Example 7 and Example 8 Comparing Example 7 and Example 8 with Example 1, it can be seen that the positive electrode sheet prepared by using the lithium iron phosphate positive electrode material to account for 6.5% by weight of the positive electrode active material has better performance and effect.
  • the present disclosure finds that through more experimental data The performance of the prepared positive electrode sheet is better when the auxiliary positive electrode material accounts for 4.0%-12.0% of the mass of the positive electrode active material in the positive electrode active layer.

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Abstract

一种正极片，包括集流体以及设置在所述集流体上的正极活性层，所述正极活性层包括m层正极活性子层，每层正极活性子层中的正极活性材料包括主正极材料和辅助正极材料，且所述正极活性层中主正极材料的D50粒径满足（aa）；所述辅助正极材料的D90粒径小于所述第一层正极活性子层中主正极材料的D10粒径。

Description

正极片及电池
相关申请的交叉引用
本申请要求比亚迪股份有限公司于2020年06月24日提交的、申请名称为“正极片及电池”的、中国专利申请号“202010585072.2”的优先权。
技术领域
本发明涉及电池技术领域，具体涉及一种正极片及电池。
背景技术
锂离子电池具有能量密度高、体积小，重量轻、循环寿命长、无记忆效应等优点，被广泛应用于便携式电子设备及新能源电动汽车电池领域。在锂电池体系中，层状正极材料凭借高能量密度、低成本、平台电压高等优点成为正极材料的关注焦点，尤其是随着人们对高能量密度的迫切需求，对电极片的面密度和压实密度也提出了更高的要求，然而在高面密度和高压实下，远离电解液侧电极片中的锂离子迁移路径延长，电极片局部脱嵌锂不均匀，并且电极片中的大、小颗粒全部完成脱/嵌的速度不一致，导致了颗粒间的荷电状态分布不均，引起电池阻抗大、倍率差、循环衰减快的问题，同时埋下安全隐患。
发明内容
本申请内容旨在至少解决现有技术中存在的技术问题之一。为此，在本申请的第一个方面，提供一种正极片，所述正极片包括集流体以及设置在所述集流体上的正极活性层，所述正极活性层包括m层正极活性子层，每层正极活性子层中的正极活性材料包括主正极材料和辅助正极材料，且所述正极活性层中主正极材料的D 50粒径满足：
Figure PCTCN2021093563-appb-000001
Figure PCTCN2021093563-appb-000002
其中，所述m为大于或等于2的整数，所述n为2至m中的任一整数，所述D 501表示第一层正极活性子层中主正极材料的D 50粒径，所述D 50 n表示第n层正极活性子层中的主正极材料的D 50粒径，所述第n层正极活性子层距所述集流体的距离大于第n-1层正极活性子层距所述集流体的距离；
所述辅助正极材料的D 90粒径小于所述第一层正极活性子层中主正极材料的D 10粒径。
在本申请的第二个方面，提供一种电池，所述电池包括如上面所述的正极片。
本公开的有益效果：本公开提供的正极片中通过将正极活性层中的各层正极活性 子层中的主正极材料的粒径设置为满足：
Figure PCTCN2021093563-appb-000003
使得正极活性层的主正极材料的粒径自邻近集流体的一侧向远离集流体的一侧逐渐增加，使锂离子在整个正极活性层中的脱/嵌速度均匀，从而使得正极片在厚度方向相邻颗粒间的荷电分布均匀，并且可以减小正极片厚度方向以及大小颗粒之间荷电状态不同引起的极化；将小颗粒的辅助正极材料填充于大颗粒的主正极材料之间的缝隙，有效的增加了正极片的压实密度。
附图说明
图1为本公开提供的其中一个实施例和对比例制备得到正极片的微观区域的拉曼光谱成像图。
具体实施方式
以下所述是本公开的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本公开原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也视为本公开的保护范围。
本公开一实施例提供一种正极片，所述正极片包括集流体以及设置在所述集流体上的正极活性层，所述正极活性层包括m层正极活性子层，每层正极活性子层中的正极活性材料包括主正极材料和辅助正极材料，且所述正极活性层中主正极材料的D 50粒径满足：
Figure PCTCN2021093563-appb-000004
其中，所述m为大于或等于2的整数，所述n为2至m中的任一整数，所述D 501表示第一层正极活性子层中主正极材料的D 50粒径，所述D 50 n表示第n层正极活性子层中的主正极材料的D 50粒径，所述第n层正极活性子层距所述集流体的距离大于第n-1层正极活性子层距所述集流体的距离。
所述辅助正极材料的D 90粒径小于所述第一层正极活性子层中主正极材料的D 10粒径。即所述辅助正极材料的粒径与所述第一层正极活性子层中主正极材料的粒径满足：D 90 辅助＜D 101，其中，所述D 90 辅助表示所述辅助正极材料的D 90粒径，所述D 101表示第一层正极活性子层中主正极材料的D 10粒径。
其中，m层正极活性子层设置在集流体的同一侧，自远离所述集流体的方向，m层正极活性子层依次包括叠加设置的第一层正极活性子层、第二层正极活性子层……第m-1层正极活性子层、第m层正极活性子层，其中，第一层正极活性子层与所述集流体直接接触。在一个实施例中，所述m为3-6之间的整数。更在一个实施例中，所述m＝4。
其中，所述正极活性层中主正极材料的D 50粒径满足：
Figure PCTCN2021093563-appb-000005
也就是说m层正极活性子层中任一层正极活性子层的D 50粒径与第一正极活性子层的D 50粒径具有上述关系式一，从关系式一可知，第一层正极活性子层至第m层正极活性子层中的D 50粒径是逐渐增加的，靠近集流体侧的第一层正极活性子层的D 50粒径最小，距集流体最远的第m层正极活性子层中的D 50粒径最大，中间层为小粒径逐渐过渡到大粒径的梯度分布。
关系式一的这种梯度分布的粒径关系，正极活性层的主正极材料的粒径自集流体向远离集流体的一侧逐渐增加，使锂离子在整个正极活性层中的脱/嵌速度均匀，从而使得正极片在厚度方向相邻颗粒间的荷电分布均匀，并且可以减小正极片厚度方向以及大小颗粒之间荷电状态不同引起的极化，进而可以提高所制备的电池的导电性能、提高所制备的电池的倍率性能以及安全性能等。影响锂离子在电池中的传输主要包括两个方面，一是固相扩散，即电极中活性材料的颗粒粒径的大小，另一方面是液相扩散，即锂离子在液相环境中的扩散距离。当正极材料颗粒在整个正极活性层的各个位置的粒径没有按照上述关系式一的规律分布时，例如在整个正极活性层中的正极材料颗粒的粒径相同，锂离子在活性材料中的固相扩散的距离是相同的，但是极片不同厚度上活性材料距固液界面的距离是不同的，造成其液相中锂离子的脱嵌距离不同；这种情况下就会导致处于极片表层(靠近隔膜的位置)的活性材料脱嵌锂速度快，极片里层(靠近集流体位置)的活性材料脱嵌锂速度慢，进而导致活性材料颗粒间的荷电状态分布不均匀，引起电池阻抗大、倍率差、循环衰减快的问题。锂离子在大颗粒的正极材料颗粒上完成脱嵌的速度比小颗粒的主正极材料颗粒上完成脱嵌的速度慢，这会导致正极材料颗粒间的荷电状态分布不均匀，引起电池阻抗大、倍率差、循环衰减快的问题。
一般而言，大粒径的正极材料颗粒脱/嵌锂的速度较慢，小粒径的正极材料颗粒脱/嵌锂的速度较快，本申请中，将邻近电解液(或者说远离集流体一侧)的正极活性子层中的主正极材料颗粒的粒径设置较大，将远离电解液(或者说邻近集流体一侧)的正极活性子层中的主正极材料颗粒的粒径设置较小，这样就使距电解液较近的大粒径主正极材料颗粒的脱/嵌锂速度，与距电解液较远的小粒径主正极材料颗粒的脱/嵌锂速度相当，进而使得每层正极活性子层中的正极活性材料的脱/嵌锂速度相同，提高了整体正极活性层的脱/嵌 锂速度一致性。
例如，在第一层正极活性子层中主正极材料颗粒粒径最小，锂离子从主正极材料颗粒上析出的时间较短，但第一层正极活性子层距离电解液最远，该析出的锂离子需要较长的时间才能进入到电解液中，而在第m层正极活性子层中主正极材料颗粒粒径最大，锂离子从主正极材料颗粒上析出的时间较长，但第m层正极活性子层距离电解液最近，该析出的锂离子仅需要较短的时间就能进入到电解液中，由此可看出锂离子从第一层正极活性子层的主正极材料颗粒上析出并到达电解液的总时间与锂离子从第m层正极活性子层的主正极材料颗粒上析出并到达电解液的总时间可趋向一致，也就是第一层正极活性子层中锂离子的脱/嵌速度与第m层正极活性子层中锂离子的脱/嵌速度相当。同样的，第二层正极活性层和第m-1层正极活性层中锂离子的脱/嵌速度相当，相邻的第n层和第n-1层正极活性子层中锂离子的脱/嵌速度也相当，或者说正极活性层中任意两层正极活性子层中的锂离子的脱/嵌速度相当。因此，对于整个正极活性层而言，将正极活性层中的各正极活性子层中的主正极材料的D 50粒径按照上述关系式一来分布，使锂离子在整个正极活性层中的脱/嵌速度均匀，从而使得正极片在厚度方向相邻颗粒间的荷电分布均匀，并且可以减小正极片厚度方向以及大小颗粒之间荷电状态不同引起的极化。
另外，本申请中正极活性材料中还设有辅助正极材料层，辅助正极材料的粒径与第一层正极活性子层中主正极材料的粒径满足：D 90 辅助＜D 101，即整体上90％的辅助正极材料的粒径是小于10％的正极活性子层主正极材料的粒径，将小粒径的辅助正极材料分布于各层正极活性子层中相对粒径大的主正极材料颗粒的颗粒间隙处，有效的增加了正极片的压实密度。
在本申请中，主正极材料优选为层状正极材料，辅助正极材料优选为聚阴离子正极材料，所述聚阴离子正极材料具有优异的结构稳定性，聚阴离子正极不容易与电解液反应，或者与电解液反应时对正极活性层的结构影响较小，不会破坏正极活性层的结构稳定，通过聚阴离子正极材料与层状正极材料复合使用可以提高正极片循环和安全性能。其中层状正极材料可以是主正极材料通过涂布压实方式形成的层状正极材料。
本公开提供的正极片中在通过将正极活性层中的各层正极活性子层中的主正极材料的粒径设置为满足上述关系式一的情况下，还将小颗粒的辅助正极材料填充于大颗粒的主正极材料之间的缝隙，可以在提高正极片在厚度方向相邻颗粒间的荷电分布均匀性，并且可以减小正极片厚度方向以及大小颗粒之间荷电状态不同引起的极化的情况下，进一步有效的增加了正极片的压实密度。
在一个实施例中，所述辅助正极材料的D 50粒径小于或等于200nm。即，所述辅助正极材料的粒径满足：D 50 辅助≤200nm，所述D 50 辅助表示所述辅助正极材料的D 50粒径。当辅助正极材料的D 50粒径小于或等于200nm时，辅助正极材料可以更好的分布于主正极材料颗粒之间， 进一步提高正极片的压实密度。
在一个实施例中，第n-1层正极活性子层中主正极材料的D 90粒径小于或等于所述第n层正极活性子层中主正极材料的D 10粒径。即，第n-1层正极活性子层中主正极材料的粒径与所述第n层正极活性子层中主正极材料的粒径满足：D 90 n-1≤D 10 n，其中，所述D 90 n-1表示第n-1层正极活性子层中主正极材料的D 90粒径，所述D 10 n表示第n层正极活性子层中主正极材料的D 10粒径。在第n-1层正极活性子层中，90％的主正极材料的粒径小于第n层正极活性子层中10％的主正极材料的粒径。这样可以保证相邻两层中的主正极材料颗粒的粒径是从小粒径逐渐过渡到大粒径的，对于整个正极活性层而言，可以进一步提升各正极活性子层中主正极材料颗粒的粒径分布的梯度规律性。
在一个实施例中，所述正极活性层中主正极材料的粒径还满足：4.0μm≤D 50 [m/2]+1≤8.0μm，所述[m/2]表示向下取整数，所述D 50 [m/2]+1表示第[m/2]+1层正极活性子层中主正极材料的D 50粒径。例如，当m为4时，在正极活性层中主正极材料的粒径满足：4.0μm≤D 503≤8.0μm，也就是说第三层正极活性子层的D 50粒径在4.0μm至8.0μm之间。当m为5时，在正极活性层中主正极材料的粒径满足：4.0μm≤D 503≤8.0μm，也就是说第三层正极活性子层的D 50粒径在4.0μm至8.0μm之间。
上述设置限定了靠近中间层或者中间层中的主正极材料的粒径大小，通过上述各层中的粒径分布关系式一，可以得知第一层正极活性子层至最后一层正极活性子层中的主正极材料的粒径分布。
在一个实施例中，所述正极活性层中第一层正极活性子层至第m层正极活性子层中主正极材料的面密度分别占所述正极活性层中主正极材料的面密度的百分数呈正态分布。在此处，所述正极活性层中主正极材料的面密度是指在指定厚度下的单位面积上正极活性层中主正极材料的质量，所述正极活性子层中主正极材料的面密度是指在指定厚度下的单位面积上正极活性子层中主正极材料的质量。
也就是说在正极活性层中两端的正极活性子层中主正极材料的面密度小，中间层的正极活性子层中主正极材料的面密度大，这种分布可以提升正极片在厚度方向相邻颗粒间的荷电分布均匀性。由于两端的正极活性子层中主正极材料的粒径大小相差最大，锂离子在两端的主正极材料颗粒上脱/嵌的速度差最大，因此将两端的正极活性子层中主正极材料的面密度设置较小，可减小两端锂离子脱/嵌速度相差较大的主正极材料颗粒的量，从而可提升整个正极活性层中的锂离子脱嵌速度的一致性，进而可提升正极片在厚度方向相邻颗粒间的荷电分布均匀性。
在一个实施例中，在所述正极活性层中，各层正极活性子层中主正极材料的面密度占所述正极活性层中主正极材料的面密度的百分数满足：
ρ 1≤10.0％，ρ m≤10.0％；
ρ 2≥10.0％，ρ m-1≥10.0％；
40.0％≤ρ m/2≤60.0％；
其中，所述m为大于或等于3的整数，所述ρ 1表示第一层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述ρ 2表示第二层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述ρ m表示第m层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述ρ m-1表示第m-1层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数；当m为奇数时，所述ρ m/2表示第[m/2]+1层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述[m/2]表示向下取整数；当m为偶数时，所述ρ m/2表示第[m/2]层正极活性子层和第[m/2]+1层正极活性子层中的至少一个中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数。
例如，当m等于4时，ρ 1＝8％，ρ 2＝45％，ρ 3＝38％，ρ 4＝9％。
当m等于5时，ρ 1＝8％，ρ 2＝17％，ρ 3＝50％，ρ 4＝17％，ρ 5＝8％。当m等于6时，ρ 1＝5％，ρ 2＝10％，ρ 3＝40％，ρ 4＝30％，ρ 5＝10％，ρ 6＝5％。即两端的正极活性子层中主正极材料的面密度小，中间的正极活性子层中主正极材料的面密度大。
在一个实施例中，每层正极活性子层还包括导电剂和粘结剂。
优选地，所述正极活性层的面密度满足：300g/m 2≤ρ≤500g/m 2，所述ρ表示正极活性层的面密度。其中所述正极活性层包括主正极材料、辅助正极材料、导电剂以及粘结剂，正极活性层的面密度是指在指定厚度下的单位面积上正极活性层中所有主正极材料、辅助正极材料、导电剂以及粘结剂的质量。
本申请的正极活性层的面密度较大，在300g/m 2和500g/m 2之间，具有较高的电容量。另一方面来说，面密度较大的正极活性层在同样面积的正极片上具有更大的厚度，本申请中，对于厚度越大的正极活性层采用上述各正极活性子层的粒径分布关系式一，正极片的正极材料颗粒间的荷电状态分布改善的更明显。或者说，对于厚度越大的正极片，采用上述关系式一的设置，正极片的电性能改善的效果越明显，具体表现为可降低正极片的阻抗、提升正极片的荷电均匀性以及提升所制备的电池的倍率性能。
其中，所述导电剂为导电炭黑、乙炔黑、碳纳米管和石墨烯中的至少一种，所述粘结剂为聚偏氟乙烯或者为含偏氟乙烯的共聚物。
在一个实施例中，所述正极活性层的面密度满足为：350g/m 2≤ρ≤450g/m 2。更在一个实施例中，所述正极活性层的面密度满足为：400g/m 2≤ρ≤450g/m 2。
在一个实施例中，所述辅助正极材料的质量占所述正极活性层中正极活性材料质量的 0.5％-20.0％。采用上述质量比，得到的正极片的极片压实密度较佳。
更在一个实施例中，所述辅助正极材料的质量占所述正极活性层中正极活性材料质量的4.0％-12.0％。
在一个实施例中，所述层状正极材料为钴酸锂、镍酸锂、锰酸锂、镍钴锰酸锂和镍钴铝酸锂中的至少一种；所述聚阴离子正极材料为磷酸铁锂、磷酸铁锰锂、磷酸锰锂、磷酸钒锂、氟磷酸钒锂、硅酸锰锂、硅酸铁锂和硅酸钴锂中的至少一种。
本公开还提供一种电池，所述电池包括如上述任一项所述的正极片。将上述电极片设置在电池中，可以减小正极片厚度方向以及大小颗粒之间荷电不同引起的极化，可以消除脱/嵌锂不均引起的极化，可以降低电池的阻抗，提高电池在不同倍率电化学性能以及循环性能。
为了更好的说明本公开的技术方案，下面结合多个具体实施例进行说明。
实施例1
(1)将正极活性材料、导电剂和粘结剂按照质量比为94∶3.0∶3.0溶解在氮甲基吡咯烷酮的溶剂中，分散均匀，制得浆料；正极活性材料包括层状正极材料和聚阴离子正极材料，其中层状正极材料为LiNi 0.83Co 0.13Mn 0.04O2，聚阴离子正极材料为磷酸铁锂正极材料，磷酸铁锂正极材料占正极活性材料的质量百分数为6.5％。
(2)依照上述步骤制得第一正极浆料，其中第一正极浆料包含D 50＝0.80μm的LiNi 0.83Co 0.13Mn 0.04O2和D 50＝200nm的磷酸铁锂正极；
依照上述步骤制得第二正极浆料，其中第二正极浆料包含D 50＝2.2μm的LiNi 0.83Co 0.13Mn 0.04O2和D 50＝200nm的磷酸铁锂正极；
依照上述步骤制得第三正极浆料，其中第三正极浆料包含D 50＝5.2μm的LiNi 0.83Co 0.13Mn 0.04O2和D 50＝200nm的磷酸铁锂正极；
依照上述步骤制得第四正极浆料，其中第四正极浆料包含D 50＝12.0μm的LiNi 0.83Co 0.13Mn 0.04O2和D 50＝200nm的磷酸铁锂正极。
(3)按照第一正极浆料、第二正极浆料、第三正极浆料及第四正极浆料的顺序，依次涂覆在集流体上形成第一层正极活性子层、第二层正极活性子层、第三层正极活性子层以及第四层正极活性子层，4层正极活性子层构成正极片的正极活性层；连续将经过4道浆料涂覆的正极片进行震荡，使正极片内各层正极活性子层中的正极活性材料颗粒粒径呈梯度分布，降低界面层的粒径差；
(4)将正极片经烘烤、辊压后分切成特定尺寸待用；上述第一层正极活性子层、第二层正极活性子层、第三层正极活性子层以及第四层正极活性子层中主正极材料在正极活性层中主正极材料的面密度占比分别为8.0％、45.0％、38.0％和9.0％；正极活性层的面密度为 420g/m 2。上述四层正极活性子层中的LiNi 0.83Co 0.13Mn 0.04O2的D 50粒径满足：
Figure PCTCN2021093563-appb-000006
Figure PCTCN2021093563-appb-000007
实施例2
按照与实施例1相同的方法制备正极片，不同之处在于选取的用于制备正极活性子层的层状正极材料的D 50粒径为3种，第一层正极活性子层、第二层正极活性子层以及第三层正极活性子层中的层状正极材料的D 50粒径分别是2.0μm、6.5μm、15.0μm，3层中的D 50粒径满足关系式一，其他条件与实施例1相同，制备得到正极片。
实施例3
按照与实施例1相同的方法制备正极片，不同之处在于选取的用于制备正极活性子层的层状正极材料的D 50粒径为5种，第一层正极活性子层、第二层正极活性子层、第三层正极活性子层、第四层正极活性子层以及第五层正极活性子层中的层状正极材料的D 50粒径分别是0.5μm、1.5μm、4.5μm、8.0μm、18.0μm，5层中的D 50粒径满足关系式一，其他条件与实施例1相同，制备得到正极片；
实施例4
按照与实施例1相同的方法制备正极片，不同之处在于选取的磷酸铁锂D 50粒径＝125nm，制备得到正极片。
实施例5
按照与实施例1相同的方法制备正极片，不同之处在于选取的磷酸铁锂D 50粒径＝300nm，制备得到正极片。
实施例6
按照与实施例1相同的方法制备正极片，不同之处在于选取的层状正极材料为钴酸锂和镍钴铝酸锂，两者摩尔比为1∶1；制备得到正极片。
实施例7
按照与实施例1相同的方法制备正极片，不同之处在于正极活性材料中磷酸铁锂的含量为15.0％；制备得到正极片。
实施例8
按照与实施例1相同的方法制备正极片，不同之处在于正极活性材料中磷酸铁锂的含量为2.0％；制备得到正极片。
实施例9
按照与实施例1相同的方法制备正极片，不同之处在于正极活性材料中聚阴离子为磷酸铁锰锂；制备得到正极片。
对比例1
按照与实施例1相同的方法制备正极片，不同之处在于正极活性材料中只包含D 50＝5.4μm的LiNi 0.83Co 0.13Mn 0.04O2；制备得到正极片。
对比例2
按照与实施例1相同的方法制备正极片，不同之处在于正极活性材料中不含有聚阴离子正极；制备得到正极片。
对比例3
按照与实施例1相同的方法制备正极片，不同之处在于正极活性材料中只包含D 50＝5.4μm的LiNi 0.83Co 0.13Mn 0.04O2，且正极活性材料中不含有聚阴离子正极；制备得到正极片。
对比例4
按照与实施例1相同的方法制备正极片，不同之处在于选取的用于制备正极活性子层的层状正极材料的D 50粒径为4种，第一层正极活性子层、第二层正极活性子层、第三层正极活性子层以及第四层正极活性子层中LiNi 0.83Co 0.13Mn 0.04O2的D 50粒径分别是0.6μm、3.0μm、7.0μm、20.0μm；制备得到正极片。
将上述实施例1-实施例9和对比例1-对比例4中的正极片均按照如下方法制备得到对应的电池：将正极片与隔膜、负极片按顺序叠好，得到裸电芯，然后将电芯套入外壳，烘烤干燥后，注入电解液，焊接密封，经过高温陈化、化成、老化等工序得到电池。
将上述实施例1-实施例9和对比例1-对比例4中的正极片对应制备得到的电池进行性能测试，包括阻抗性能测试、倍率性能测试、循环性能测试、安全性能测试以及荷电状态性能测试，具体数据件图1和表1。
阻抗性能测试方法：在25℃下，以0.2C恒流恒压充满电，搁置后再以0.2C恒流放电至2.5V，重复3次，记第3次放出容量为C0，以0.2C0电流调整电池至50％SOC，再测试1.5C恒流放电30s，计算出阻抗值的大小。
倍率性能测试方法：在25℃下，以0.2C恒流恒压充满电，搁置后再以0.2C恒流放电至2.5V，重复3次，记第3次放出容量为C0，分别以0.2C0、5.0C0恒流恒压充满电，再以同样大小的电流放完电，以0.2C0放电容量为基准，5.0C0放电容量与其比值作为评价倍率性能的指标。
循环性能测试方法：在25℃下，以0.2C恒流恒压充满电，搁置后再以0.2C恒流放电至2.5V，重复3次，记第3次放出容量为C0，在45℃环境下，以1.0C0恒流恒压充满电，再以1.0C0恒流放电，如此循环500周，记录容量保持率。
安全性能测试方法：以DSC测试电极稳定性作为评价安全性能的指标，将电池充满电，在手套箱内将正极片取出，刮取适量的正极料置于坩埚中，再添加一定量的电解液，转移 到设备中，测试氛围纯氩气，升温速率2℃/min，分别记录热失控起始温度、热失控峰值温度和放热功率。
荷电状态(state of charge，SOC)性能测试方法：以2.0C电流将电池快速充满电，并在手套箱内将正极片取出，用Ar离子束进行剖切得到极片截面，再置于拉曼光谱上进行截面扫描，不同金属与氧/不同价态金属与氧的振动能级不同，在拉曼光谱上的峰位、峰型、峰强不同，以550cm -1峰和470cm -1峰的面积比值作为评价SOC态的指标，可以得到扫描面积内各点的比值，即可得到面积内的SOC分布情况，再求出面积内的SOC的平均值，表征该极片的实际SOC态。
请参阅图1，在图1中左边为实施例1对应制备的电池的SOC分布情况，图1中右边为对比例3对应制备的电池的SOC分布情况，可以看出实施例1制得的正极片中SOC分布明显更均一，说明正极片极化更小，更有利于锂离子的嵌入/脱出。
表1
Figure PCTCN2021093563-appb-000008
从表1可以看出，实施例1-实施例9的效果比对比例1-4的效果要好，在一个实施例 中：实施例1-实施例9中在电池阻抗方面，电池阻抗值最低可达到151m·Ω，电池阻抗值越低说明电池的导电性能越好；在倍率性能方面，倍率比值最高有99.3％，最低有86.2％，倍率比值越高说明电池在不同倍率下的电化学性能越稳定，即倍率性能更佳；在循环性能方面，循环容量保持率最高有93.2％，最低有82.0％，循环容量保持率越高说明电池性能越稳定，使用寿命越长；在安全性能方面，热失控起始温度最高有204.2℃，热失控峰值温度最高有210.2℃，放热功率最低有948.4J/g，热失控起始温度和热失控峰值温度越高说明电池更耐高温、更安全，放热功率越低说明电池更不易产热而更加安全；在SOC方面，最高有98.7％，SOC比值越高，说明正极片中的SOC更均匀。
对于对比例1，由于对比例1中的正极活性层中的层状正极材料颗粒的粒径只有一种，没有如实施例1一样采用满足关系式一的粒径大小分布，制备得到的电池在阻抗、倍率、循环容量保持率、安全性能以及SOC方面均比实施例1较差，其中对比例1中的电池阻抗为195m·Ω，比实施例1要大，说明电池的导电性能下降；倍率仅有87.8％，容量保持率仅有76.8％，热失控起始温度和热失控峰值温度比实施例1要低，放热功能比实施例1要大，且SOC比值比实施例1低。
对于对比例2，在对比例2中没有添加聚阴离子正极材料，会影响正极片的压实密度，进而影响正极片的导电性能，从对比例2的数据可以看出，对比例2制备得到的电池在阻抗、倍率、循环容量保持率、安全性能以及SOC方面均比实施例1较差。
对于对比例3，在对比例3中仅有一种粒径大小的颗粒，且没有添加聚阴离子正极材料，从对比例3的数据可以看出，对比例3制备得到的电池在阻抗、倍率、循环容量保持率、安全性能以及SOC方面均比实施例1较差。
对于对比例4，在对比例4中，四层正极活性子层中的LiNi 0.83Co 0.13Mn 0.04O2的D 50粒径不满足本公开的关系式一，也就是说各层之间的颗粒粒径大小没有呈关系式一中规律性分布，从对比例4的数据可以看出，对比例4制备得到的电池在阻抗、倍率、循环容量保持率、安全性能以及SOC方面均比实施例1较差，这说明按照本公开中的关系式一来设置各正极活性子层中的LiNi 0.83Co 0.13Mn 0.04O2的D 50粒径可以提升电池的电性能。
实施例5与实施例1、实施例4相比可知，采用D 50粒径≤200nm的磷酸铁锂制备的正极片的性能效果更好。
实施例7、实施例8与实施例1相比可知，采用磷酸铁锂正极材料占正极活性材料的质量百分数为6.5％制备的正极片的性能效果更好，本公开通过更多的实验数据发现辅助正极材料占所述正极活性层中正极活性材料质量的4.0％-12.0％时制备的正极片的性能较佳。
综上所述，从表1中的实施例和对比例的实验结果，可以看出按照满足本公开关系式一粒径分布的正极片，可以减小正极片厚度方向以及大小颗粒之间SOC态不同引起的极化， 可以消除嵌锂不均引起的极化，降低电池阻抗，提高倍率和循环性能；而聚阴离子正极材料具有优异的结构稳定性，通过复合使用，不仅还提高了循环性能，安全性能(热稳定性)也得到了改善。
以上所述实施例仅表达了本公开的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本公开专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本公开构思的前提下，还可以做出若干变形和改进，这些都属于本公开的保护范围。因此，本公开专利的保护范围应以所附权利要求为准。

Claims (13)

  1. 一种正极片，其特征在于，所述正极片包括集流体以及设置在所述集流体上的正极活性层，所述正极活性层包括m层正极活性子层，每层正极活性子层中的正极活性材料包括主正极材料和辅助正极材料，且所述正极活性层中主正极材料的D50粒径满足：
    Figure PCTCN2021093563-appb-100001
    Figure PCTCN2021093563-appb-100002
    其中，所述m为大于或等于2的整数，所述n为2至m中的任一整数，所述D 501表示第一层正极活性子层中主正极材料的D 50粒径，所述D 50 n表示第n层正极活性子层中的主正极材料的D 50粒径，所述第n层正极活性子层距所述集流体的距离大于第n-1层正极活性子层距所述集流体的距离；
    所述辅助正极材料的D 90粒径小于所述第一层正极活性子层中主正极材料的D 10粒径。
  2. 如权利要求1所述的正极片，其特征在于，所述辅助正极材料的D 50粒径小于或等于200nm。
  3. 如权利要求1或2所述的正极片，其特征在于，第n-1层正极活性子层中主正极材料的D 90粒径小于或等于第n层正极活性子层中主正极材料的D 10粒径。
  4. 如权利要求3所述的正极片，其特征在于，所述正极活性层中主正极材料的粒径还满足：4.0μm≤D50[m/2]+1≤8.0μm，所述[m/2]表示向下取整数，所述D 50 [m/2]+1表示第[m/2]+1层正极活性子层中主正极材料的D 50粒径。
  5. 如权利要求1-4中任一项所述的正极片，其特征在于，所述正极活性层中第一层正极活性子层至第m层正极活性子层中主正极材料的面密度各自占所述正极活性层中主正极材料的面密度的百分数呈正态分布。
  6. 如权利要求1-5中任一项所述的正极片，其特征在于，在所述正极活性层中，各层正极活性子层中主正极材料的面密度占所述正极活性层中主正极材料的面密度的百分数满足：
    ρ 1≤10.0％，ρ m≤10.0％；
    ρ 2≥10.0％，ρ m-1≥10.0％；
    40.0％≤ρ m/2≤60.0％；
    其中，所述m为大于或等于3的整数，所述ρ 1表示第一层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述ρ 2表示第二层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述ρ m表示第m层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述ρ m-1表示第m-1层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密 度的百分数；其中，当m为奇数时，所述ρ m/2表示第[m/2]+1层正极活性子层中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数，所述[m/2]表示向下取整数；当m为偶数时，所述ρ m/2表示第[m/2]层正极活性子层和第[m/2]+1层正极活性子层中的至少一个中主正极材料的面密度占正极活性层中主正极材料的面密度的百分数。
  7. 如权利要求1-6中任一项所述的正极片，其特征在于，每层正极活性子层还包括导电剂和粘结剂，所述正极活性层的面密度满足：300g/m 2≤ρ≤500g/m 2，所述ρ表示正极活性层的面密度。
  8. 如权利要求1-7中任一项所述的正极片，其特征在于，所述辅助正极材料的质量占所述正极活性层中正极活性材料质量的0.5％-20.0％。
  9. 如权利要求1-8中任一项所述的正极片，其特征在于，所述m为3-6之间的整数。
  10. 如权利要求1-9中任一项所述的正极片，其特征在于，所述m＝4。
  11. 如权利要求1-10中任一项所述的正极片，其特征在于，所述主正极材料为层状正极材料；所述辅助正极材料为聚阴离子正极材料。
  12. 如权利要求11所述的正极片，其特征在于，所述层状正极材料为钴酸锂、镍酸锂、锰酸锂、镍钴锰酸锂和镍钴铝酸锂中的至少一种；
    所述聚阴离子正极材料为磷酸铁锂、磷酸铁锰锂、磷酸锰锂、磷酸钒锂、氟磷酸钒锂、硅酸锰锂、硅酸铁锂和硅酸钴锂中的至少一种。
  13. 一种电池，其特征在于，所述电池包括如权利要求1-12任一项所述的正极片。
PCT/CN2021/093563 2020-06-24 2021-05-13 正极片及电池 WO2021258900A1 (zh)

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