WO2020211452A1 - 正极极片、电化学装置及装置 - Google Patents

正极极片、电化学装置及装置 Download PDF

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WO2020211452A1
WO2020211452A1 PCT/CN2019/129354 CN2019129354W WO2020211452A1 WO 2020211452 A1 WO2020211452 A1 WO 2020211452A1 CN 2019129354 W CN2019129354 W CN 2019129354W WO 2020211452 A1 WO2020211452 A1 WO 2020211452A1
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layer
conductive
active material
electrode active
current collector
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PCT/CN2019/129354
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English (en)
French (fr)
Inventor
李静
薛庆瑞
李伟
张子格
张扬
杨献伟
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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 EP19924802.2A priority Critical patent/EP3940817B1/en
Publication of WO2020211452A1 publication Critical patent/WO2020211452A1/zh
Priority to US17/501,895 priority patent/US20220037667A1/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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • H01M4/662—Alloys
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/668—Composites of electroconductive material and synthetic resins
    • 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

  • This application relates to the field of batteries, and in particular to a positive pole piece, electrochemical device and device.
  • Lithium-ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages of high energy density, high output power, long cycle life and low environmental pollution. With the continuous expansion of the application range of lithium-ion batteries, the requirements for the weight energy density and volume energy density of lithium-ion batteries are getting higher and higher.
  • lithium-ion batteries with higher mass energy density and volumetric energy density
  • improvements are usually made to lithium-ion batteries: (1) Choose a positive electrode material or negative electrode material with a high specific discharge capacity; (2) Optimize the mechanical design of lithium-ion batteries , To minimize its volume; (3) Choose a positive pole piece or negative pole piece with high compaction density; (4) Reduce the weight of each component of the lithium ion battery.
  • the improvement of the current collector is usually to select a lighter or thinner current collector.
  • a perforated current collector or a metal-plated plastic current collector can be used.
  • this application proposes a positive pole piece, electrochemical device and device.
  • the present application relates to a positive pole piece, which includes a current collector and an electrode active material layer disposed on at least one surface of the current collector, wherein the current collector includes a support layer and at least one The conductive layer on the surface, the single-sided thickness D2 of the conductive layer satisfies: 30nm ⁇ D2 ⁇ 3 ⁇ m, the thickness D1 of the support layer satisfies: 1 ⁇ m ⁇ D1 ⁇ 30 ⁇ m, and the support layer is a polymer material or a polymer composite material; said electrode active material layer comprises a total thickness D of the electrode active material, a conductive agent and a binder, the electrode active material layer is not more than a total of 170 m, and the resistive membrane electrode active material layer is 0.1 Euro to 10 Euro.
  • the present application relates to an electrochemical device, including a positive pole piece, a negative pole piece, a separator and an electrolyte, wherein the positive pole piece is the positive pole piece described in the first aspect of the application.
  • the present application relates to a device, including the electrochemical device described in the second aspect of the present application.
  • the positive pole piece of the present application and the electrochemical device (such as a lithium ion battery) containing the positive pole piece have both excellent energy density, good electrochemical performance and safety performance.
  • the positive pole piece of the present application uses a composite current collector, which can significantly improve the energy density of the electrochemical device, such as the weight energy density;
  • the conductive layer in the positive electrode composite current collector of the present application is relatively thin (the metal burr is also small when abnormalities such as nails occur) and because the support layer is made of polymer materials or polymer composite materials, it has a relatively high High short circuit internal resistance, thus improving the safety performance of nail penetration;
  • the membrane resistance of the electrode active material layer of the positive pole piece is 0.1 ohm to 10 ohm, so the positive pole piece and electrochemical device have good electrochemical performance, and also have good nail penetration safety performance.
  • the content of the binder and/or the content of the conductive agent in the electrode active material layer of the positive pole piece preferably has a non-uniform composition state in the thickness direction, which can not only be very good Overcome the shortcomings of poor conductivity of the composite current collector and easy damage of the conductive layer in the composite current collector.
  • By effectively repairing and constructing a conductive network between the current collector, the conductive primer layer and the active material the electron transmission efficiency is improved and the current collector is reduced.
  • the resistance between the electrode active material layer and the electrode assembly can effectively reduce the DC internal resistance of the electrode assembly, improve the power performance of the electrode assembly, and ensure that the electrode assembly is not prone to large polarization and lithium evolution during long-term cycling.
  • the compaction density of the area This special partition design can effectively suppress the curvature and edge warping of the composite current collector and electrode pads due to rolling, etc., so that the electrode pads can maintain better pole pieces after rolling.
  • the flatness is good for protecting the conductive layer from damage, so that the pole piece has good electrochemical performance.
  • the device of the present application includes the electrochemical device described in the second aspect of the present application, and therefore has at least the same advantages as the electrochemical device.
  • the positive pole piece, electrochemical device, and device of the present application have good and balanced electrochemical performance, safety performance and processing performance.
  • FIG. 1 is a schematic cross-sectional structure diagram of a positive electrode current collector according to a specific embodiment of this application;
  • FIG. 2 is a schematic cross-sectional structure diagram of a cathode current collector according to another specific embodiment of this application;
  • FIG. 3 is a schematic cross-sectional structure diagram of a cathode current collector according to another specific embodiment of this application.
  • FIG. 4 is a schematic cross-sectional structure diagram of a positive electrode current collector according to another specific embodiment of this application.
  • FIG. 5 is a schematic cross-sectional structure diagram of a positive pole piece according to a specific embodiment of this application.
  • FIG. 6 is a schematic cross-sectional structure diagram of a positive pole piece according to another specific embodiment of this application.
  • FIG. 7 is a schematic diagram of a top view structure of a positive pole piece according to a specific embodiment of this application.
  • FIG. 8 is a schematic diagram of measuring the sheet resistance of the electrode active material layer according to the present application.
  • FIG. 9 is a schematic diagram of an embodiment of the electrochemical device of this application.
  • FIG. 10 is a schematic diagram of an embodiment of the battery module of this application.
  • FIG. 11 is a schematic diagram of an embodiment of the battery pack of this application.
  • Figure 12 is an exploded view of Figure 11;
  • FIG. 13 is a schematic diagram of an embodiment of the electrochemical device of the application as a power source device
  • the first aspect of the application relates to a positive pole piece, which includes a current collector and an electrode active material layer disposed on at least one surface of the current collector, wherein the current collector includes a support layer and at least one The conductive layer on the surface, the single-sided thickness D2 of the conductive layer satisfies: 30nm ⁇ D2 ⁇ 3 ⁇ m, the thickness D1 of the support layer satisfies: 1 ⁇ m ⁇ D1 ⁇ 30 ⁇ m, and the support layer is a polymer material or a polymer composite material ; the electrode active material layer comprises an electrode active material, a conductive agent and a binder, the total thickness D of the total electrode active material layer is not more than 170 m, the membrane resistance and the electrode active material layer is 0.1 ohm to 10 ohms.
  • the current collector used for the positive pole piece of the first aspect of the application is a composite current collector, which is a composite of at least two materials.
  • the current collector includes a support layer and a conductive layer disposed on at least one surface of the support layer, the single-sided thickness D2 of the conductive layer satisfies: 30nm ⁇ D2 ⁇ 3 ⁇ m, and the thickness D1 of the support layer satisfies: 1 ⁇ m ⁇ D1 ⁇ 30 ⁇ m. Therefore, the conductive layer is the conductive layer in the current collector.
  • the thickness D2 of the conductive layer is much smaller than the thickness of the commonly used Al foil metal current collector in the prior art (the thickness of the commonly used Al foil metal current collector is usually 12 ⁇ m), and the support layer is made of polymer material or polymer composite material, so The weight energy density of an electrochemical device (such as a lithium battery) using the pole piece can be improved.
  • the composite current collector when the composite current collector is applied to the positive electrode current collector, it can also greatly improve the nail penetration safety performance of the positive electrode sheet, because the conductive layer in the positive electrode current collector is thin, and the metal burr generated when the nail penetration occurs is also Smaller, and due to the existence of the support layer, its short-circuit internal resistance is larger, so it is less likely to cause a short-circuit.
  • the electrode active material layer is specially designed, which can make the positive pole piece and the electrochemical device (such as lithium ion battery) containing the positive pole piece have good energy density.
  • Electrochemical performance and safety performance are particularly, since the membrane resistance of the electrode active material layer is controlled within a certain range, the nail penetration safety performance and electrochemical performance of the electrochemical device can be further improved.
  • the polymer support layer of the composite current collector has a greater rebound degree than the traditional metal current collector, if the current collector is coated and then compacted by a rolling process according to the traditional process, it will also cause a series of other problem. Due to the rebound of the support layer, the edges on both sides of the pole piece will be upturned, causing the pole piece to be curved as a whole, thereby causing the pole piece to deform. Deformation of the pole piece may cause separation of the electrode active material layer from the composite current collector, breakage of the conductive layer, peeling of the conductive layer from the support layer, etc., thereby deteriorating the electrochemical performance of the pole piece.
  • the deformation of the pole pieces will also make the positive and negative pole pieces unable to accurately align. Therefore, electrode pads made of composite current collectors are prone to technical problems such as large internal resistance and large polarization.
  • the lateral direction of the active material layer of the electrode pole piece is also determined. The material distribution is specially designed.
  • This special partition design can effectively suppress the curvature and edge warping of the composite current collector and electrode pads due to rolling, etc. So that the electrode pole piece maintains a good pole piece flatness after rolling, eliminates or reduces technical problems such as large internal resistance and large polarization of the pole piece, and is beneficial to protect the conductive layer from being damaged, thereby making the electrode The sheet and electrochemical device have good electrochemical performance.
  • the content of the binder and/or the content of the conductive agent in the electrode active material layer preferably has a non-uniform composition state in the thickness direction.
  • the weight percentage of the binder in the inner region of the electrode active material layer close to the current collector is higher than that of the electrode active material layer away from the current collector.
  • the weight percent content of the binder in the outer region of the current collector, so the inner region with a higher binder content can significantly improve the interface between the composite current collector and the electrode active material layer, and improve the relationship between the current collector and the electrode active material layer.
  • the binding force ensures that the electrode active material layer is more firmly set on the surface of the composite current collector; in addition, because the electrode active material layer can be more firmly set on the surface of the composite current collector, the electrode active material layer can be more firmly set on the surface of the composite current collector.
  • the active material layer can more effectively wrap the burrs generated in the conductive layer, and better improve the nail penetration safety; third, the proportion of electrochemically active material in the outer region with lower binder content can be higher, so the positive electrode
  • the electrochemical performance of the pole piece (such as electrochemical capacity and energy density) is better.
  • the weight percentage of the conductive agent in the inner region of the electrode active material layer close to the current collector is higher than that of the electrode active material layer away from the current collector.
  • the current collector has poor conductivity and the conductive layer in the composite current collector is easily damaged.
  • the electron transmission efficiency is improved, and the resistance of the pole piece containing the composite current collector is reduced, thereby effectively reducing the DC internal resistance of the electrode assembly ( DCR), improve the power performance of the electrode assembly, and ensure that the electrode assembly is not prone to large polarization and lithium evolution during long-term cycling, which effectively improves the long-term reliability of the electrode assembly.
  • the proportion of the electrochemically active material in the outer region with a lower conductive agent content may be higher, so the electrochemical performance (such as electrochemical capacity and energy density) of the positive pole piece is better.
  • the conductive layer plays a role of conduction and current collection, and is used to provide electrons to the electrode active material layer.
  • the material of the conductive layer is selected from at least one of metal conductive materials and carbon-based conductive materials.
  • the metal conductive material is preferably at least one of aluminum, nickel, titanium, silver, and aluminum-zirconium alloy;
  • the carbon-based conductive material is preferably at least one of graphite, acetylene black, graphene, and carbon nanotubes;
  • the material of the conductive layer is preferably a metal conductive material, that is, the conductive layer is preferably a metal conductive layer.
  • the current collector is the positive electrode current collector
  • aluminum is usually used as the material of the conductive layer.
  • the conductivity of the conductive layer When the conductivity of the conductive layer is poor or the thickness is too small, the internal resistance of the battery will be large, and the polarization will be large. When the thickness of the conductive layer is too large, it is not enough to improve the weight energy density and volume energy density of the battery. Effect.
  • the single-sided thickness of the conductive layer is D2, and D2 preferably satisfies: 30nm ⁇ D2 ⁇ 3 ⁇ m, more preferably 300nm ⁇ D2 ⁇ 2 ⁇ m, most preferably 500nm ⁇ D2 ⁇ 1.5 ⁇ m; in order to better ensure the lightweight performance of the current collector It also has good electrical conductivity.
  • the upper limit of the single-sided thickness D2 of the conductive layer may be 3 ⁇ m, 2.5 ⁇ m, 2 ⁇ m, 1.8 ⁇ m, 1.5 ⁇ m, 1.2 ⁇ m, 1 ⁇ m, 900 nm
  • the lower limit of the single-sided thickness D2 of the conductive layer may be It is 800nm, 700nm, 600nm, 500nm, 450nm, 400nm, 350nm, 300nm, 100nm, 50nm, 30nm
  • the range of the single-sided thickness D2 of the conductive layer can be composed of any upper limit or lower limit.
  • cracks exist in the conductive layer of the positive pole piece described in this application.
  • the cracks in the conductive layer usually exist irregularly in the conductive layer. They can be elongated cracks, cross-shaped cracks, divergent cracks, etc.; they can be cracks that penetrate the entire conductive layer, or they can be in the conductive layer. Cracks formed on the surface layer. Cracks in the conductive layer are usually caused by the rolling during the pole piece processing, the excessive amplitude of the welding tab, and the excessive tension of the substrate winding.
  • the conductive layer can be formed on the support layer by at least one of mechanical rolling, bonding, vapor deposition, and electroless plating.
  • the vapor deposition method is preferably Physical Vapor Deposition (PVD). ); the physical vapor deposition method is preferably at least one of evaporation and sputtering; the evaporation method is preferably vacuum evaporation, thermal evaporation (thermal evaporation), electron beam evaporation (electron beam evaporation), At least one of EBEM), the sputtering method is preferably magnetron sputtering (Magnetron sputtering).
  • At least one of vapor deposition or electroless plating is preferred to make the bonding between the support layer and the conductive layer stronger.
  • the supporting layer plays a role of supporting and protecting the conductive layer. Since the support layer generally uses organic polymer materials or polymer composite materials, the density of the support layer is usually lower than that of the conductive layer, so that the weight energy density of the battery can be significantly increased compared with traditional metal current collectors.
  • the conductive layer adopts a metal layer with a smaller thickness, which can further increase the weight energy density of the battery.
  • the support layer can play a good bearing and protection effect on the conductive layer on its surface, it is not easy to produce the common pole piece fracture phenomenon in traditional current collectors.
  • the material of the support layer can be specifically selected from at least one of insulating polymer materials, insulating polymer composite materials, conductive polymer materials, and conductive polymer composite materials.
  • the insulating polymer material is for example selected from polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, aramid, polyphenylene diamide, acrylonitrile -Butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, poly Phenyl sulfide, polyvinylidene fluoride, silicone rubber, polycarbonate, cellulose and its derivatives, starch and its derivatives, protein and its derivatives, polyvinyl alcohol and its cross-linked products, polyethylene glycol and its At least one of cross-linked products.
  • the insulating polymer composite material is, for example, selected from composite materials formed by insulating polymer materials and inorganic materials, and the inorganic material is preferably at least one of ceramic materials, glass materials, and ceramic composite materials.
  • the conductive polymer material is, for example, selected from polysulfur nitride polymer materials or doped conjugated polymer materials, such as at least one of polypyrrole, polyacetylene, polyaniline, and polythiophene.
  • the conductive polymer composite material is, for example, selected from composite materials formed by insulating polymer materials and conductive materials, where the conductive material is selected from at least one of conductive carbon materials, metal materials, and composite conductive materials, and the conductive carbon materials are selected from carbon black, At least one of carbon nanotubes, graphite, acetylene black, and graphene, the metal material is selected from at least one of nickel, iron, copper, aluminum or alloys of the foregoing metals, and the composite conductive material is selected from nickel-coated graphite powder , At least one of nickel-coated carbon fibers.
  • the material of the support layer in this application is preferably an insulating polymer material or an insulating polymer composite material, especially when the current collector is a positive electrode current collector.
  • the safety performance of the battery can be significantly improved by using a special current collector supported by an insulating layer and a conductive layer with a specific thickness.
  • the insulating layer is non-conductive, its resistance is relatively large, which can increase the short-circuit resistance of the battery when a short circuit occurs under abnormal conditions, and greatly reduce the short-circuit current. Therefore, it can greatly reduce the short-circuit heat generation and improve the safety performance of the battery;
  • the conductive layer is relatively thin. Therefore, under abnormal circumstances such as nail penetration, the local conductive network is cut off, preventing a large area of the electrochemical device or even the entire electrochemical device from short-circuiting, which can reduce the damage of the electrochemical device caused by nail penetration. The damage is limited to the puncture site, only forming a "point disconnection", and does not affect the normal operation of the electrochemical device within a certain period of time.
  • the thickness of the support layer is D1, and D1 preferably satisfies: 1 ⁇ m ⁇ D1 ⁇ 30 ⁇ m; more preferably 1 ⁇ m ⁇ D1 ⁇ 15 ⁇ m.
  • the support layer is too thin, the mechanical strength of the support layer is insufficient, and it is easy to break during the pole piece processing process; if the support layer is too thick, the volumetric energy density of the battery using the current collector will be reduced.
  • the upper limit of the thickness D1 of the support layer can be 30 ⁇ m, 25 ⁇ m, 20 ⁇ m, 15 ⁇ m, 12 ⁇ m, 10 ⁇ m, 8 ⁇ m, and the lower limit can be 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m; the thickness of the support layer D1
  • the range of can be composed of any number of upper or lower limit.
  • the specific thickness of the present application can further ensure that the current collector has a larger resistance, and significantly reduce the battery heating when an internal short circuit occurs.
  • the conductive layer is aluminum, it can also significantly reduce or prevent the aluminum heat of the positive electrode current collector. Response to ensure that the battery has good safety performance.
  • the conductive layer is a metal conductive layer
  • the normal temperature Young's modulus of the support layer satisfies: 20GPa ⁇ E ⁇ 4GPa.
  • the testing method of the normal temperature Young's modulus of the support layer described in this application is as follows:
  • metal Since metal is relatively rigid relative to polymers or polymer composites, that is, it deforms less during the rolling process of pole piece processing, so in order to ensure that the deformation difference between the support layer and the conductive layer is not too large, so
  • the conductive layer is torn, and the normal temperature Young's modulus of the support layer should preferably meet: 20GPa ⁇ E ⁇ 4Gpa, so that the support layer can have a certain rigidity, and the rigidity matching between the support layer and the conductive layer can be further improved Therefore, during the processing of the current collector and the pole piece, it is ensured that the deformation of the support layer and the conductive layer will not be too different.
  • the current collector Since the support layer has a certain rigidity (20GPa ⁇ E ⁇ 4GPa), the current collector is not easy to deform or stretch too much during the processing of the current collector and the pole piece, so that the support layer and the conductive layer can be firmly bonded. It is not easy to detach, and can prevent the conductive layer from being "forced" to expand and causing damage to the conductive layer.
  • the current collector according to the present application has a certain degree of toughness, so that the current collector and the pole piece have a certain ability to withstand deformation and are not easy to break.
  • the Young's modulus of the support layer should not be too large, otherwise the rigidity will be too strong, which will cause difficulty in winding and winding, and poor workability.
  • the support layer can be guaranteed to have a certain degree of flexibility, and the pole piece can also have a certain ability to withstand deformation.
  • the thermal shrinkage rate of the support layer at 90° C. is not greater than 1.5%, so that the thermal stability of the current collector can be better ensured during the pole piece processing.
  • the current collector is further provided with a protective layer, and the protective layer is provided on one surface of the conductive layer of the current collector or on two of the conductive layers of the current collector. On the surface, that is, on the surface of the conductive layer away from the support layer and on the surface facing the support layer.
  • the protective layer can be a metal protective layer or a metal oxide protective layer.
  • the protective layer can prevent the conductive layer of the current collector from being damaged by chemical corrosion or mechanical damage, and can also enhance the mechanical strength of the current collector.
  • the protective layer is provided on both surfaces of the conductive layer of the current collector.
  • the lower protective layer of the conductive layer that is, the protective layer provided on the surface of the conductive layer facing the support layer
  • the technical effect of the upper protective layer of the conductive layer is mainly to prevent the conductive layer from being damaged and corroded during processing (such as electrolyte immersion, rolling, etc.)
  • the surface of the conductive layer affects).
  • the metal protective layer can not only further improve the mechanical strength and corrosion resistance of the conductive layer, but also reduce the polarization of the pole piece.
  • the material of the metal protective layer is, for example, selected from at least one of nickel, chromium, nickel-based alloys, and copper-based alloys, preferably nickel or nickel-based alloys.
  • the nickel-based alloy is an alloy formed by adding one or more other elements to pure nickel as the matrix.
  • it is a nickel-chromium alloy.
  • the nickel-chromium alloy is an alloy formed of metallic nickel and metallic chromium.
  • the molar ratio of nickel element to chromium element is 1:99-99:1.
  • Copper-based alloy is an alloy formed by adding one or more other elements to pure copper as the matrix. Preferably, it is a copper-nickel alloy. Optionally, in the copper-nickel alloy, the molar ratio of nickel to copper is 1:99-99:1.
  • metal oxide When metal oxide is selected for the protective layer, due to its low ductility, large specific surface area, and high hardness, it can also form effective support and protection for the conductive layer, and improve the bonding force between the support layer and the conductive layer. Has a good technical effect.
  • the material of the metal oxide protective layer is, for example, at least one selected from aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide.
  • the protective layer of the composite current collector preferably adopts metal oxides, so as to achieve good technical effects of support and protection, while further improving the safety performance of the positive pole piece and the battery.
  • the thickness of the protective layer is D3, and D3 preferably satisfies: D3 ⁇ 1/10D2 and 1nm ⁇ D3 ⁇ 200nm. If the protective layer is too thin, it will not be enough to protect the conductive layer; if the protective layer is too thick, it will reduce the weight energy density and volume energy density of the battery. More preferably, 5nm ⁇ D3 ⁇ 500nm, further preferably 10nm ⁇ D3 ⁇ 200nm, most preferably 10nm ⁇ D3 ⁇ 50nm.
  • the materials of the protective layers on the two surfaces of the conductive layer can be the same or different, and the thickness can be the same or different.
  • the thickness of the lower protective layer is smaller than the thickness of the upper protective layer to help improve the weight energy density of the battery.
  • the ratio of the thickness D3" of the lower protective layer to the thickness D3' of the upper protective layer is: 1/2D3' ⁇ D3" ⁇ 4/5D3'.
  • the current collector is the positive electrode current collector
  • aluminum is usually used as the material of the conductive layer
  • the lower protective layer is preferably a metal oxide material.
  • the metal oxide material has a larger resistance. Therefore, this type of lower protective layer can further increase the resistance of the positive electrode current collector to a certain extent, thereby further improving the abnormality of the battery.
  • the short circuit resistance in the event of a short circuit improves the safety performance of the battery.
  • the lower protective layer is preferably a metal oxide material
  • the upper protective layer is a metal material or a metal oxide material
  • the upper protective layer is preferably also a metal oxide material.
  • FIGS 1 to 4 show schematic structural diagrams of current collectors used in positive pole pieces according to some embodiments of the present application.
  • the positive current collector 10 includes a positive current collector support layer 101 and a positive current collector conductive layer 102 disposed on two opposite surfaces of the positive current collector support layer 101, and also includes a positive current collector conductive layer 102
  • the positive current collector protective layer 103 on the lower surface is the lower protective layer.
  • the positive electrode current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector conductive layer 102 provided on two opposite surfaces of the positive electrode current collector support layer 101, and also includes a positive electrode current collector conductive layer 102 The positive current collector protective layer 103 on the opposite two surfaces, namely the lower protective layer and the upper protective layer.
  • the positive current collector 10 includes a positive current collector support layer 101 and a positive current collector conductive layer 102 disposed on one surface of the positive current collector support layer 101, and also includes a positive current collector disposed on the positive current collector conductive layer 102.
  • the positive current collector protective layer 103 on the surface of the fluid supporting layer 101 is the lower protective layer.
  • the positive current collector 10 includes a positive current collector support layer 101 and a positive current collector conductive layer 102 disposed on one surface of the positive current collector support layer 101, and also includes two oppositely disposed on the positive current collector conductive layer 102.
  • the positive current collector protective layer 103 on the surface, namely the lower protective layer and the upper protective layer.
  • the material of the protective layer on the two opposite surfaces of the conductive layer can be the same or different, and the thickness can be the same or different.
  • a conductive layer may be provided on two opposite surfaces of the support layer, or as shown in FIG. 3 and FIG. As shown in 4, a conductive layer may be provided on only one side of the support layer.
  • the composite current collector used in the positive pole piece of the present application preferably contains a current collector protective layer as shown in Figures 1 to 4, it should be understood that the current collector protective layer is not a necessary structure of the current collector, and is used in some embodiments.
  • the current collector may not contain a current collector protective layer.
  • the electrode active material layer used in the positive pole piece of the present application generally includes an electrode active material, a binder, and a conductive agent. According to needs, the electrode active material layer may further include optional other additives or auxiliary agents.
  • the average particle size D50 of the active material in the electrode active material layer is 5 ⁇ m to 15 ⁇ m. If the D50 is too small, the porosity of the pole piece after compaction is small, which is not conducive to the infiltration of the electrolyte, and its larger specific surface area is likely to produce more side reactions with the electrolyte, reducing the reliability of the electrode assembly; if If D50 is too large, it is easy to cause greater damage to the composite current collector during the pole piece compaction process. D50 refers to the particle size when the cumulative volume percentage of the active material reaches 50%, that is, the median particle size of the volume distribution. D50 can be measured using, for example, a laser diffraction particle size distribution measuring instrument (such as Malvern Mastersizer 3000).
  • the positive electrode active material can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, transition Metal phosphate, lithium iron phosphate, etc., but the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials of lithium ion batteries can also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • the positive electrode active material may be selected from LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 ( One or more of NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , and LiMnPO 4 .
  • LiCoO 2 LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 ( One or more of NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)
  • the total thickness D of the total electrode active material layer is not more than 170 ⁇ m, D total ⁇ 170 ⁇ m.
  • the electrode active material layer coated on one side of the technical solution the total thickness D of the electrode active material layer that is the total thickness D4 sided electrode active material layer; applying a double-sided electrode active material layer for technical solution, the total thickness D of the electrode active material layer is always one-sided thickness D4 of the electrode active material layer twice, i.e. 2D4.
  • the total calculation of D4 and D should include all (that is, each layer) electrode active material layer. If D total >170 ⁇ m, the dynamic performance of the battery is poor.
  • the sheet resistance of the electrode active material layer of the positive pole piece is 0.1 ohm to 10 ohm.
  • the applicant of the present application found that when the membrane resistance is within an appropriate range, the nail penetration safety performance of the battery can be further guaranteed, and good electrochemical performance of the battery can be guaranteed. If the diaphragm resistance is too small, it is not enough to ensure the safety of nail penetration, if it is too large, the electrochemical performance is poor.
  • the intrinsic resistivity of the active material the content of the conductive agent, the content of the binder, the particle size of the active material, the conductivity of the electrolyte, the compaction density (the greater the resistance is), the thickness of the active material layer, etc. It will affect the diaphragm resistance of the active material layer. Therefore, the sheet resistance of the active material layer can be adjusted by adjusting or controlling these parameters.
  • the sheet resistance of the electrode active material layer described in this application can be tested, for example, by the following method:
  • a pole piece coated with a positive electrode active material layer on both sides is taken as an example.
  • the positive electrode active material layer should be folded in half placed in the middle of the probe of the film resistance meter (as shown in Figure 8), and then tested to obtain the measured pole piece
  • the membrane resistance of the active material layer is measured on 5 pole piece samples and the average value is obtained, which is the membrane resistance of the active material layer.
  • the positive electrode piece (and electrochemical device) of the present application can have both good electrochemical performance and good nail penetration Safety performance.
  • the diaphragm resistance is 0.6 ohm to 0.9 ohm, it can further ensure that the pole piece has good nail penetration safety performance, and at the same time, it can ensure that the pole piece has good electrochemical performance.
  • the binder content in the electrode active material layer is not less than 1 wt%, preferably not less than 1.5 wt%, and more preferably not less than 2 wt%.
  • the binder content in the electrode active material layer is not less than 1 wt%, preferably not less than 1.5 wt%, and more preferably not less than 2 wt%.
  • the active material layer and the current collector have a better binding force, so that under abnormal conditions such as nail penetration, the active material layer can more effectively wrap the metal burrs generated in the conductive layer , In order to improve the safety performance of battery nail penetration.
  • the content of the binder and/or the conductive agent in the electrode active material layer The content preferably has a non-uniform composition state in the thickness direction.
  • the conductive agent used in the electrode active material layer is preferably at least one of a conductive carbon material and a metal material.
  • the conductive carbon material is selected from zero-dimensional conductive carbon (such as acetylene black, conductive carbon black), one-dimensional conductive carbon (such as carbon nanotubes), two-dimensional conductive carbon (such as conductive graphite, graphene), three-dimensional conductive carbon (such as Reduced graphene oxide); the metal material is selected from at least one of aluminum powder, iron powder and silver powder.
  • zero-dimensional conductive carbon such as acetylene black, conductive carbon black
  • one-dimensional conductive carbon such as carbon nanotubes
  • two-dimensional conductive carbon such as conductive graphite, graphene
  • three-dimensional conductive carbon such as Reduced graphene oxide
  • the metal material is selected from at least one of aluminum powder, iron powder and silver powder.
  • a slurry composed of an electrode active material, a conductive agent and a binder is coated on the electrode current collector, and then dried and other post-treatments can be used to obtain the desired electrode active material layer.
  • the positive pole piece of the present application can uniformly coat the electrode active material layer in the coating area of the entire pole piece surface like a traditional positive pole piece, and then cold press (roll) the entire surface of the pole piece, thereby
  • the compaction density of the electrode active material layer on the obtained pole piece is basically the same, and there is no significant difference.
  • the compaction density of the middle region is higher than the compaction density of the two sides. Because after cold pressing (rolling) and other processes, the compaction density on both sides of the pole piece is low, while the compaction density in the middle area is high, that is, the area on both sides of the pole piece is subjected to cold pressing (rolling).
  • the pressure is less than the middle area, which can avoid the edge warpage and curvature of the composite current collector and the electrode pole piece caused by the rebound of the composite current collector during the pole piece processing, which is beneficial to the formation of a smooth surface pole piece, thereby It helps to ensure the electrochemical performance of the electrochemical device.
  • the "length direction” and “width direction” of the surface of the electrode pole piece refer to the two dimensions of the surface respectively, where the length direction refers to the main dimension direction (that is, the direction with larger dimensions), and the width direction refers to The secondary dimension direction (that is, the direction of the smaller size).
  • the length direction is consistent with the coating direction of each material layer (such as electrode active material layer) during the processing of the pole piece, and is also consistent with the winding direction of the pole piece during the manufacturing process of an electrochemical device (such as a battery) ;
  • the width direction is perpendicular to the length direction.
  • the compaction density of the middle area is higher than the compaction density of the two sides
  • the compaction density of the symmetrical areas on both sides is the same.
  • the 2n+1 regions of the active material layer based on the compaction density according to the present application, it can be realized by a partition coating method, that is, using baffles or spacers to divide different regions (or boundaries) on the surface of the pole piece , Each area is coated with different weight of electrode active material slurry, so that the active material layer area with different compaction density is formed after rolling.
  • the compaction density of each area on both sides is preferably the same symmetrically. Such a design helps to better ensure the flatness of the electrode pole pieces.
  • the content of the conductive agent in the electrode active material layer has an uneven distribution in the thickness direction, that is, the weight percentage of the conductive agent in the electrode active material layer is not uniform in the thickness direction. Uniform and variable. More specifically, based on the total weight of the electrode active material layer, the weight percentage of the conductive agent in the inner region of the electrode active material layer (also referred to as “lower electrode active material”) is higher than that of the electrode active material layer. The weight percentage of the conductive agent in the outer region (also called “the upper electrode active material”). Preferably, the weight percentage of the electrochemically active material in the inner region is lower than the weight percentage of the electrochemically active material in the outer region.
  • the “inside” of the electrode active material refers to the side of the electrode active material layer close to the current collector in the thickness direction.
  • the “outside” of the electrode active material refers to the The electrode active material layer is away from the side of the current collector in the thickness direction.
  • the conductive agent has an uneven distribution in the thickness direction
  • the weight percentage of the conductive agent in the inner region of the electrode active material layer is higher than the weight percentage of the conductive agent in the outer region of the electrode active material layer.
  • the “partial content” can have many different implementations.
  • the weight percentage of the conductive agent in the electrode active material layer may gradually decrease along the thickness direction from the inner region to the outer region; or the electrode active material layer may be divided into two or more in the thickness direction The area (that is, divided into two, three or more layers), and the weight percentage of the conductive agent in the area closest to the current collector is greater than the weight percentage of the conductive agent in each area far from the current collector.
  • the electrode active material layer is divided into two regions in the thickness direction (ie, divided into two electrode active material layers), and the weight percentage of the conductive agent in the lower (inner) electrode active material is The content is greater than the weight percentage of the conductive agent in the upper (outer) electrode active material.
  • the electrode active material layer is divided into two regions in the thickness direction, namely, an inner region and an outer region.
  • the amount of conductive agent in the inner region is The weight percentage is 10% to 99% by weight, preferably 20% to 80% by weight, and more preferably 50% to 80% by weight.
  • the weight percentage of the conductive agent in the outer region is preferably 0.5 wt% to 10 wt%.
  • the inner area with a higher conductive agent content can play the role of a conductive primer layer between the conductive layer of the current collector and the electrode active material layer, which can well overcome the poor conductivity of the composite current collector and the problems in the composite current collector.
  • the conductive layer is easy to break and other disadvantages.
  • the electron transmission efficiency is improved, and the resistance of the pole piece containing the composite current collector is reduced, thereby effectively reducing the DC internal resistance of the electrode assembly ( DCR), improve the power performance of the electrode assembly, and ensure that the electrode assembly is not prone to large polarization and lithium evolution during long-term cycling, which effectively improves the long-term reliability of the electrode assembly.
  • the proportion of the electrochemically active material in the outer region with a lower conductive agent content may be higher, so the electrochemical performance (such as electrochemical capacity and energy density) of the positive pole piece is better.
  • the conductive agent in the inner region contains a one-dimensional conductive carbon material (such as carbon nanotubes) and/or a two-dimensional conductive carbon material.
  • a one-dimensional conductive carbon material such as carbon nanotubes
  • the two-dimensional conductive carbon material in the inner area of the electrode active material layer can produce "horizontal sliding" during the compaction process of the pole piece, thereby acting as a buffer and reducing the impact during the compaction process. Destruction of the conductive layer of the current collector, thereby reducing cracks.
  • the particle size D50 of the preferred two-dimensional conductive carbon material is 0.01 to 0.1 ⁇ m.
  • the one-dimensional conductive carbon material due to the special morphology of the one-dimensional conductive carbon material, it can improve the conductivity of the inner region after adding, especially when the amount of conductive agent is added, the one-dimensional conductive carbon material can be compared with other types of conductive materials. Better improve the conductivity of the inner area.
  • the one-dimensional conductive carbon material is preferably carbon nanotubes, and the aspect ratio is preferably 1,000 to 5,000.
  • the one-dimensional conductive carbon material and/or the two-dimensional conductive carbon material in the inner region account for 1% to 50% by weight of the conductive agent in the inner region, and the remaining conductive agent can be other types of conductive agents, preferably zero.
  • Dimensional carbon materials The one-dimensional conductive carbon material and/or the two-dimensional conductive carbon material and the zero-dimensional carbon material can work together to better improve the conductive performance of the inner region and the performance as a conductive primer.
  • the preferred conductive agent in the inner region is a mixed material of conductive carbon black and carbon nanotubes.
  • the conductive agent in the outer region preferably also contains a two-dimensional conductive carbon material, or in order to better play the role of conduction, the conductive agent in the outer region also preferably contains a one-dimensional conductive carbon material (E.g. carbon nanotubes).
  • the conductive agents in the inner region and the outer region both contain carbon nanotubes; more preferably, the conductive agents in the inner region and the outer region are both a mixture of carbon nanotubes and conductive carbon black.
  • the content of the binder and the active material in the electrode active material may also vary in the thickness direction.
  • the binder used in the electrode active material layer can be selected from, for example, styrene-butadiene rubber, oily polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer (such as PVDF-HFP copolymer, PVDF-TFE copolymer), carboxymethyl Sodium cellulose, polystyrene, polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide, water-based PVDF, polyurethane, polyvinyl alcohol, polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, polyacrylate -At least one of polyacrylonitrile copolymers.
  • PVDF oily polyvinylidene fluoride
  • PVDF-HFP copolymer such as PVDF-HFP copolymer, PVDF-TFE copolymer
  • carboxymethyl Sodium cellulose polystyrene
  • polyacrylic acid polytetrafluoro
  • the adhesive in the inner region is preferably an aqueous adhesive, such as those in aqueous PVDF, polyacrylic acid, polyurethane, polyvinyl alcohol, polyacrylate, polyacrylic acid-polyacrylonitrile copolymer, and polyacrylate-polyacrylonitrile copolymer. At least one, the DCR growth of such electrochemical devices is small.
  • aqueous polymer material means that the polymer molecular chain is fully extended and dispersed in water
  • “oily” polymer material means that the polymer molecular chain is fully extended and dispersed in an oily solvent.
  • the same type of polymer material can be dispersed in water and oil respectively, that is, by using a suitable surfactant, the same type of polymer material can be made into water-based Polymer materials and oily polymer materials.
  • those skilled in the art can modify PVDF into aqueous PVDF or oily PVDF as needed.
  • the binding force between the active material layer and the current collector is better, so that abnormal conditions such as nail penetration Below, the active material layer can effectively wrap the metal burrs generated in the conductive layer to improve the safety performance of the battery.
  • the binder content is too high, the content of the active material will decrease, which is not conducive to ensuring the battery has a higher electrochemical capacity.
  • the content of the binder in the electrode active material layer has a non-uniform composition state in the thickness direction, wherein the The total weight, the weight percentage of the binder in the inner region of the electrode active material layer close to the current collector is higher than the binder in the outer region of the electrode active material layer away from the current collector The weight percentage of the agent.
  • the electrode active material layer is divided into two regions in the thickness direction, namely an inner region and an outer region, wherein, based on the total weight of the electrode active material layer at the inner region, the inner region is bonded
  • the weight percentage content of the agent is 1wt% to 90wt%, preferably 20wt% to 80wt%, more preferably 20wt% to 50wt%.
  • the weight percentage of the binder in the outer region is preferably 1 wt% to 5 wt%.
  • the inner area with a higher binder content can significantly improve the interface between the composite current collector and the electrode active material layer, increase the binding force between the current collector and the electrode active material layer, and ensure that the electrode active material layer is more firmly placed on the The surface of the composite current collector; in addition, since the electrode active material layer can be more firmly placed on the surface of the composite current collector, when an abnormal situation such as nail piercing occurs, the inner area with a higher binder content can serve as the glue layer The electrode active material layer can more effectively wrap the burrs generated in the conductive layer, and further improve the safety performance of nail penetration; third, the proportion of electrochemically active material in the outer area with lower binder content can be higher High, so the electrochemical performance (such as electrochemical capacity and energy density) of the positive pole piece is better.
  • the electrode active material layer is divided into two regions in the thickness direction, namely an inner region and an outer region, wherein, based on the total weight of the electrode active material layer at the inner region, the conductive agent in the inner region
  • the weight percentage content of the adhesive is 10wt% to 99wt%, preferably 20wt% to 80wt%, more preferably 50wt% to 80wt%; the weight percentage of the binder in the inner region is 1% to 90%, preferably 20% to 80%, more preferably 20%-50%; and the balance is the electrode active material.
  • the content of the electrode active material in the inner region may be 0%.
  • the content of the conductive agent is preferably 10% to 98% by weight, and the content of the binder is preferably 1% to 89% by weight,
  • the content of the electrode (positive electrode) active material is preferably 1 wt% to 89 wt%.
  • the binder content in the outer region of the electrode active material layer (relative to the total weight of the outer region of the electrode active material layer) is not less than 1wt%, preferably not less than 1.5wt%, and most preferably Not less than 2wt%.
  • the binder content in the outer region is maintained at a certain amount, and the bonding force between the inner region and the outer region of the active material layer is better, so that the entire active material layer can effectively wrap the conductive material under abnormal conditions such as nail penetration. Metal burrs generated in the layer to improve the safety performance of battery nail penetration.
  • the electrode active material layer is divided into two regions, an inner region and an outer region in the thickness direction
  • the electrode active material, conductive agent, and binder selected for the inner region and the outer region may be the same or different .
  • the inner region preferably uses the conductive agent and water-based binder containing the one-dimensional conductive carbon material and/or the two-dimensional conductive carbon material preferred in the present application, and the outer region can use the same or different conductive agents and binders.
  • the positive active material in the inner region may be the same as or different from the positive active material in the outer region; the positive active material in the inner region is preferably a material with high thermal stability, such as phosphoric acid At least one of lithium iron, lithium iron manganese phosphate, lithium manganate, lithium manganese phosphate, NCM333, NCM523, and the like.
  • the electrode active material layer in which the conductive agent/binder has an uneven distribution in the thickness direction can be prepared by a method known in the art, for example, a multilayer coating method, such as a two coating method, a three coating method, can be used Etc., but this application is not limited to this.
  • Figures 5 and 6 show schematic structural diagrams of positive pole pieces according to some embodiments of the present application.
  • the positive pole piece includes a positive current collector 10 and a positive active material layer 11 disposed on two opposite surfaces of the positive current collector 10.
  • the positive current collector 10 includes a positive current collector support layer 101 and a positive current collector support layer 101.
  • the positive electrode current collector conductive layer 102 on the two opposite surfaces of the fluid support layer 101 and the positive electrode protective layer 103 (not shown in the figure) disposed on one or both sides of the positive electrode conductive layer 102.
  • the positive electrode sheet includes a positive electrode current collector 10 and a positive electrode active material layer 11 arranged on one surface of the positive electrode current collector 10.
  • the positive electrode current collector 10 includes a positive electrode current collector support layer 101 and a positive electrode current collector support layer.
  • the positive electrode current collector conductive layer 102 on one surface of 101 and the positive electrode protective layer 103 (not shown in the figure) disposed on one or both sides of the positive electrode conductive layer 102.
  • the electrode active material layer can be provided on one surface of the current collector or on both surfaces of the current collector.
  • the positive pole piece when a current collector provided with a double-sided conductive layer is used, the positive pole piece can be coated on both sides (that is, the electrode active material layer is provided on both surfaces of the current collector), or only on one side. Coating (that is, the electrode active material layer is only provided on one surface of the current collector); and when the current collector provided with only a single-sided conductive layer is used, the positive pole piece can only be coated on one side, and the electrode active material layer It can only be coated on the side of the current collector provided with the conductive layer.
  • Fig. 7 shows a schematic top view of a positive pole piece according to some embodiments of the present application.
  • the blank area on the pole piece is set for processing convenience or safety considerations, and the blank area itself is optional; according to needs, the pole piece may contain 0, 1, or 2 blank areas ( There is one outside each of the two low-pressure solid areas).
  • the ratio of the intermediate high-density area to the total coating area (in this example, the ratio of the sum of 514 width and 513 width + 514 width + 515 width) can be, for example, 20 to 80%, preferably It is 30 to 70%, preferably 40 to 60%, or more preferably 45 to 55%.
  • the widths of the two low-pressure solid areas may be the same or different, preferably the same.
  • the compaction density of the low-pressure compaction area may be about 5-30% lower than the compaction density of the high-pressure compaction area, such as 7-25%, such as 8-20%, such as 8-18%.
  • the second aspect of the present application relates to an electrochemical device, including a positive pole piece, a negative pole piece, a separator and an electrolyte, wherein the positive pole piece is the positive pole piece according to the first aspect of the present application.
  • the electrochemical device may be a capacitor, a primary battery, or a secondary battery.
  • it may be a lithium ion capacitor, a lithium ion primary battery, or a lithium ion secondary battery.
  • the structure and preparation method of these electrochemical devices are well known per se. Due to the use of the positive pole piece of the present application, the electrochemical device can have high energy density, improved safety (such as nail penetration safety) and electrochemical performance.
  • the positive pole piece of the present application is easy to process, so the manufacturing cost of an electrochemical device using the positive pole piece of the present application can be reduced.
  • the specific types and compositions of the negative pole piece, separator, and electrolyte are not specifically limited, and can be selected according to actual needs.
  • the isolation film can be selected from polyethylene film, polypropylene film, polyvinylidene fluoride film and their multilayer composite film.
  • a non-aqueous electrolyte is generally used as the electrolyte.
  • a lithium salt solution dissolved in an organic solvent is generally used as the non-aqueous electrolyte.
  • the lithium salt is, for example, LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 and other inorganic lithium salts, or LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiN(CF 3 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F 2n+1 SO 3 (n ⁇ 2) and other organic lithium salts.
  • the organic solvent used in the non-aqueous electrolyte is, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.
  • the negative electrode piece a negative electrode piece formed of various negative electrode active materials commonly used in the art can be selected.
  • the negative electrode active material can be selected from carbonaceous materials such as graphite (artificial graphite or natural graphite), conductive carbon black, carbon fiber, etc., such as metals or semi-metals such as Si, Sn, Ge, Bi, Sn, and In. Metal material or its alloy, lithium-containing nitride or lithium-containing oxide, lithium metal or lithium aluminum alloy, etc.
  • the electrochemical device may include an outer package for packaging the positive pole piece, the negative pole piece, and the electrolyte.
  • the positive pole piece, the negative pole piece and the separator can be laminated or wound to form a laminated structure electrode assembly or a wound structure electrode assembly, the electrode assembly is encapsulated in an outer package; the electrolyte can be an electrolyte, which is infiltrated In the electrode assembly.
  • the number of electrode assemblies in the electrochemical device can be one or several, which can be adjusted according to requirements.
  • the outer packaging of the electrochemical device may be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag can be plastic, for example, it can include one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • the outer packaging of the electrochemical device can also be a hard shell, such as an aluminum shell.
  • Fig. 9 is an electrochemical device 5 with a square structure as an example.
  • the electrochemical device can be assembled into a battery module, and the number of electrochemical devices contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 10 shows the battery module 4 as an example.
  • a plurality of electrochemical devices 5 may be arranged in order along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of electrochemical devices 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodation space, and a plurality of electrochemical devices 5 are accommodated in the accommodation space.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • FIG. 11 and FIG. 12 are the battery pack 1 as an example. 11 and 12, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3.
  • the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4.
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the third aspect of the application relates to a device, including the electrochemical device described in the second aspect of the application.
  • the electrochemical device provides power to the device.
  • 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 scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • electric trains, ships, and satellites are all vehicles and belong to vehicles in a broad sense.
  • the device can select an electrochemical device, a battery module or a battery pack according to its usage requirements.
  • Figure 13 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • battery packs or battery modules can be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the device usually requires lightness and thinness, and an electrochemical device can be used as a power source.
  • a support layer of a certain thickness is selected, and a conductive layer of a certain thickness is formed on the surface by vacuum evaporation, mechanical rolling or bonding.
  • the formation conditions of the vacuum evaporation method are as follows: the support layer with the surface cleaning treatment is placed in the vacuum coating chamber, and the high-purity metal wire in the metal evaporation chamber is melted and evaporated at a high temperature of 1600°C to 2000°C. The evaporated metal After the cooling system in the vacuum coating chamber, it is finally deposited on the surface of the support layer to form a conductive layer.
  • the forming conditions of the mechanical rolling method are as follows: the foil of the conductive layer material is placed in a mechanical roller, and it is rolled to a predetermined thickness by applying a pressure of 20t to 40t, and then it is placed and subjected to surface cleaning treatment The surface of the support layer is finally placed in a mechanical roller, and the two are tightly combined by applying a pressure of 30t to 50t.
  • the formation conditions of the bonding method are as follows: the foil of the conductive layer material is placed in a mechanical roller, and it is rolled to a predetermined thickness by applying a pressure of 20t to 40t; and then the surface cleaning treatment of the support layer The surface is coated with a mixed solution of PVDF and NMP; finally, the conductive layer with the predetermined thickness is adhered to the surface of the support layer and dried at 100°C.
  • a protective layer is provided on the surface of the support layer by vapor deposition or coating, and then a conductive layer with a certain thickness is formed on the surface of the support layer with the protective layer by vacuum evaporation, mechanical rolling or bonding.
  • the protective layer is located between the support layer and the conductive layer
  • the surface of the conductive layer away from the support layer can be vapor-deposited in situ Forming method or coating method to form another protective layer to prepare a current collector with protective layer (the protective layer is located on two opposite surfaces of the conductive layer);
  • a protective layer is formed on one surface of the conductive layer by vapor deposition, in-situ formation or coating, and then the conductive layer with the protective layer is placed on the support by mechanical rolling or bonding.
  • Layer surface, and the protective layer is arranged between the support layer and the conductive layer to prepare a current collector with a protective layer (the protective layer is located between the support layer and the conductive layer); in addition, on the basis of the above, the conductive layer
  • another protective layer is formed by vapor deposition, in-situ formation or coating to prepare a current collector with a protective layer (the protective layer is located on two opposite surfaces of the conductive layer);
  • a protective layer is formed on one surface of the conductive layer by vapor deposition, in-situ formation or coating, and then the conductive layer with the protective layer is placed on the support by mechanical rolling or bonding. Layer surface, and the protective layer is arranged on the surface of the conductive layer away from the support layer to prepare a current collector with a protective layer (the protective layer is located on the surface of the conductive layer away from the support layer);
  • a protective layer is formed on the two surfaces of the conductive layer by vapor deposition, in-situ formation or coating, and then the conductive layer with the protective layer is placed on the conductive layer by mechanical rolling or bonding.
  • the surface of the support layer to prepare a current collector with a protective layer (the protective layer is located on two opposite surfaces of the conductive layer);
  • the vapor deposition method uses a vacuum evaporation method
  • the in-situ formation method uses an in-situ passivation method
  • the coating method uses a doctor blade coating method.
  • the formation conditions of the vacuum evaporation method are as follows: put the sample with surface cleaning treatment in the vacuum plating chamber, melt and evaporate the protective layer material in the evaporation chamber at a high temperature of 1600°C to 2000°C, and the evaporated protective layer material passes through the vacuum coating chamber The cooling system is finally deposited on the surface of the sample to form a protective layer.
  • the formation conditions of the in-situ passivation method are as follows: the conductive layer is placed in a high-temperature oxidizing environment, the temperature is controlled at 160°C to 250°C, while the oxygen supply is maintained in the high-temperature environment, and the treatment time is 30 minutes, thereby forming metal oxides.
  • the protective layer is controlled at 160°C to 250°C, while the oxygen supply is maintained in the high-temperature environment, and the treatment time is 30 minutes, thereby forming metal oxides.
  • the formation conditions of the gravure coating method are as follows: the protective layer material and NMP are stirred and mixed, and then the slurry of the protective layer material (solid content of 20% to 75%) is coated on the surface of the sample, and then the gravure roll is used to control the coating The thickness is finally dried at 100°C to 130°C.
  • the composite current collector used is: a 1 ⁇ m thick Al metal layer is vapor-deposited on both surfaces of a 10 ⁇ m PET.
  • the two surfaces of the composite current collector are coated by extrusion coating, that is, the middle is the high coating weight area, and the two sides are the low coating weight area (can be achieved by extrusion gasket or baffle), at 85°C Dry down.
  • the width of the high coat weight area is 4 cm
  • the width of the low coat weight area is 2.1 cm.
  • the compacted density of the high coat weight area is 3.45 g/cm 3
  • the compacted density of the low coat weight area is 3.3 g/cm 3 .
  • Compaction density test method first cut 30 small current collector discs with area S to measure their weight and thickness, calculate the weight average value m 1 and height average value H 1 , and then cut out the very small piece with area S 30 discs, calculate the weight average m 2 and height average H 2 , then:
  • the current collector is also prepared using the above-mentioned 10 ⁇ m thick PET Al-plated composite current collector, which is similar to the preparation method of the positive electrode sheet above, but the positive electrode active material layer slurry is directly uniformly coated on the two surfaces of the composite current collector On top, that is, no partition treatment is performed, and a uniformly coated comparative positive pole piece is obtained after post-treatment.
  • the compaction density of the positive electrode active material layer is 3.4 g/cm 3 .
  • the current collector is a metal Al foil with a thickness of 12 ⁇ m. Similar to the preparation method of the comparative positive electrode above, the positive electrode active material layer slurry is directly and uniformly coated on the two surfaces of the Al foil current collector, and then Processing to obtain conventional positive pole piece.
  • the flatness test of the pole piece is characterized by measuring the arc height of the pole piece relative to the reference plane.
  • the specific measurement method of arc height is as follows:
  • the width of the plane is slightly smaller than the length of the electrode pad sample, and then place an equal weight on each side of the sample (1Kg) weight to make the sample close to the plane. Then use a soft ruler to measure the height of the middle of the sample above the plane. The height above is the arc height.
  • the pole pieces with arc height less than or equal to 2mm are flat, and the positive and negative pole pieces can be accurately aligned when assembled into a battery.
  • the conventional positive pole piece using metal current collector meets the requirement of pole piece flatness (the arc height is less than or equal to 2mm), and can achieve accurate alignment during battery assembly.
  • the composite current collector is uniformly coated according to the conventional process, the arc height of the pole piece is relatively large (greater than 5 mm), the flatness of the pole piece is not good, and it is difficult to achieve precise alignment during battery assembly.
  • the partition coating process of the present application the arc height is significantly reduced to a degree similar to that of conventional pole pieces, and precise alignment during battery assembly can be achieved.
  • the following describes the influence of the structure and composition of the electrode pads (for example, the composition of the current collector, the presence of the conductive primer layer, the thickness and composition of the electrode active material layer, etc.) on the battery performance.
  • the active material layer is applied in regions to ensure the flatness of the final pole piece and the accuracy of the electrochemical performance measurement results, but those skilled in the art It can be understood that the partition coating of the active material layer is not the only way to achieve a flat pole piece, and those skilled in the art can also use other alternative methods to obtain a flat pole piece.
  • a two-time coating method is used to coat a positive electrode sheet having a lower positive electrode active material layer (inner area) and an upper positive electrode active material layer (outer area).
  • conductive agent such as conductive carbon black
  • binder such as PVDF or polyacrylic acid, etc.
  • positive electrode active material such as NMP or water
  • the primer layer ie, the lower positive active material layer
  • 92wt% of the positive active material NCM333 is used by default if no specific material is specified
  • 5wt% of the conductive agent Super-P abbreviated as "SP"
  • 3wt% PVDF 3wt% PVDF, using NMP as the solvent, and mixing uniformly to form the upper layer slurry (the composition of the active material layer slurry in some embodiments may be changed, at this time, the specific instructions in this embodiment shall prevail)
  • the upper layer slurry was coated on the surface of the dried undercoat layer by extrusion coating; the positive electrode active material layer was obtained after drying at 85°C.
  • the preparation method is similar to the preparation method of the positive electrode plate (two coatings) of the above embodiment, but the upper layer slurry is directly applied to the surface of the composite current collector in sections without the lower positive electrode active material layer (undercoating). Floor).
  • the current collector is an Al foil with a thickness of 12 ⁇ m, which is similar to the preparation method of the positive electrode (single coating) above.
  • the upper slurry is directly and evenly coated on the surface of the Al foil current collector, and then the result is obtained by post-processing Conventional positive pole piece.
  • the partition coating method described in this application is used to coat the active material slurry, wherein the specific parameters of the partition coating are set, such as each The area width and compaction density, etc., are set similar to the settings described in the section "Position Coated Positive Pole Pieces".
  • the positive pole piece (compact density: 3.4g/cm 3 ), PP/PE/PP separator and negative pole piece (compact density: 1.6g/cm 3 ) are wound together to form an electrode assembly , Then put into the battery case, inject electrolyte (EC:EMC volume ratio is 3:7, LiPF 6 is 1mol/L), followed by sealing, chemical conversion and other processes, and finally get a lithium ion secondary battery (hereinafter referred to as battery).
  • electrolyte ECC volume ratio is 3:7, LiPF 6 is 1mol/L
  • Adjust the secondary battery to 50% SOC with 1C current at 25°C, and record the voltage U1. Then discharge with 4C current for 30 seconds, and record the voltage U2. DCR (U1-U2)/4C. Then the battery is subjected to a 1C/1C charge-discharge cycle for 500 weeks, and the DCR of the 500th week is recorded. The DCR of the 500th week is divided by the DCR of the first week and subtracted by 1 to obtain the DCR growth rate of the 500th week.
  • the secondary batteries (10 samples) were fully charged to the charge cut-off voltage with a current of 1C, and then charged at a constant voltage until the current dropped to 0.05C, and the charging was stopped.
  • the current collector weight percentage refers to the percentage of the weight of the positive current collector per unit area divided by the weight of the conventional positive current collector per unit area.
  • Lithium-ion batteries using composite current collectors have a thinner conductive layer than traditional metal current collectors, resulting in smaller metal burrs under abnormal conditions such as nail penetration, and the support layer of the composite current collector has a larger short-circuit resistance. Conducive to improving the safety performance of battery nail penetration. As can be seen from the above table, conventional batteries will suffer thermal runaway and destruction under nail penetration and cannot pass the nail penetration safety test. All lithium-ion batteries using composite current collectors can pass the nail penetration safety test.
  • Table 3 shows the cycle performance data measured after assembling the battery with the pole pieces (single coating) listed in Table 2.
  • the cycle life of the battery using the composite current collector is good, which is equivalent to the cycle performance of the conventional battery.
  • the battery capacity retention rate of a battery made of a current collector containing a protective layer can be further improved compared to a battery made of a current collector without a protective layer, indicating that the battery is more reliable.
  • the electrode active material layer is divided into two parts: an inner region (which can be referred to as a "lower electrode active material layer”) and an outer region (which can be referred to as an "upper electrode active material layer"). Since the content of the conductive agent in the lower active material layer is higher than the content of the conductive agent in the upper active material layer, the lower electrode active material layer can also be referred to as a conductive primer layer (or simply a primer layer).
  • Table 4 shows the specific composition and related parameters of the batteries of each embodiment and comparative example, as well as the electrode pads and current collectors used therein.
  • Table 5 shows the performance measurement results of each battery.
  • the composite current collector has a higher conductivity than the traditional metal current collector Poor, and the conductive layer in the composite current collector is easy to be damaged.
  • the DCR of the battery is large and the cycle capacity retention rate is low.
  • the conductive primer layer effectively repairs and constructs a conductive network between the current collector, the conductive primer layer and the active material, which improves the electron transmission efficiency and reduces the current collector and the electrode.
  • the resistance between the active material layers can effectively reduce DCR.
  • the DCR of the battery can be improved to a greater extent.
  • flake graphite can produce "horizontal sliding", it acts as a buffer and reduces the damage to the conductive layer of the current collector during the compaction process, thereby reducing cracks, so the introduction of flake graphite can further reduce the battery DCR (positive electrode) Pole piece 24 vs. positive pole piece 29).
  • the DCR of the battery can also be more significantly improved.
  • the thickness of the conductive primer layer is too large, it is not conducive to the improvement of the energy density of the battery.
  • the introduction of the primer layer can effectively repair and construct the conductive network between the current collector, the conductive primer layer and the active material, improve the electron transmission efficiency, and reduce The resistance between the current collector and the electrode active material layer can effectively reduce the DCR.
  • the specific test method is: charge and discharge the lithium-ion battery at 25°C, that is, charge to 4.2V with a current of 0.5C, then discharge to 2.8V with a current of 1C, and record the discharge capacity in the first week; Then the battery is subjected to a 05C/1C charge-discharge cycle for 1000 cycles, and the battery discharge capacity at the 1000th week is recorded. The discharge capacity at the 1000th week is divided by the discharge capacity at the first week to obtain the capacity retention rate at the 1000th week.
  • the battery has both good cycle performance and good Safety performance of nail penetration. Especially when the diaphragm resistance is 0.6 ohm to 0.9 ohm, the cycle performance and nail penetration safety performance are very excellent.
  • the binder content of the primer layer in the inner region is usually higher, so the bonding force between the primer layer and the current collector is stronger.
  • the bonding force between the upper electrode active material layer (ie, the outer region) and the undercoat layer (ie, the inner region) is affected by the binder content in the upper active material layer.
  • the binder content in the upper active material that is, the outer region
  • the positive electrode pieces were prepared according to the method described in the previous embodiment, but the composition of the upper layer slurry was adjusted to prepare multiple positive electrode pieces with different binder content in the upper positive electrode active material layer.
  • the specific pole piece composition is shown in the table below.
  • Table 10 shows the nail penetration test results when the above-mentioned different positive pole pieces are assembled into a battery. The results show that the higher the content of the binder in the upper positive active material layer, the better the nail penetration safety performance of the corresponding battery.
  • the binder content in the upper positive active material layer is not less than 1 wt%, more preferably not less than 1.5 wt%, and most preferably not less than 2 wt%.

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Abstract

一种正极极片(PP)、电化学装置(5)及装置，正极极片(PP)包括集流体(10)和设置于所述集流体(10)至少一个表面上的电极活性材料层(11)，其中，所述集流体(10)包括支撑层(101)和设置于支撑层(101)至少一个表面上的导电层(102)，所述导电层(102)的单面厚度D2满足：30nm≤D2≤3μm，所述支撑层(101)的厚度D1满足：1μm≤D1≤30μm，且支撑层(101)为高分子材料或高分子复合材料；所述电极活性材料层(11)包括电极活性材料、粘结剂和导电剂，电极活性材料层(11)的总厚度D 总为不大于170μm，且所述电极活性材料层(11)的膜片电阻为0.1欧至10欧。包含该正极极片(PP)的电化学装置(5)具有高的能量密度和良好的安全性能（尤其是穿钉安全性能）及电化学性能。

Description

正极极片、电化学装置及装置 技术领域
本申请涉及电池领域，具体地讲，涉及一种正极极片、电化学装置及装置。
背景技术
锂离子电池由于具备能量密度大、输出功率高、循环寿命长和环境污染小等优点而被广泛应用于电动汽车以及消费类电子产品中。随着锂离子电池的应用范围不断扩大，大家对锂离子电池的重量能量密度和体积能量密度的要求也越来越高。
为了得到质量能量密度和体积能量密度较高的锂离子电池，通常对锂离子电池进行如下改进：(1)选择放电比容量高的正极材料或负极材料；(2)优化锂离子电池的机械设计，使其体积最小化；(3)选择高压实密度的正极极片或负极极片；(4)对锂离子电池的各部件进行减重。
其中，对集流体的改进通常是选择重量较轻或厚度较小的集流体，例如可以采用打孔集流体或镀有金属层的塑料集流体等。
对于采用镀有金属层的塑料集流体的极片和电池来说，虽然能量密度得以提高，但是有可能带来加工性能和电化学性能等方面的一些性能劣化。要得到电化学性能好的极片和集流体，还需要很多方面的改进。
为了克服现有技术之不足，特提出本申请。
发明内容
鉴于此，本申请提出一种正极极片、电化学装置及装置。
第一方面，本申请涉及一种正极极片，其包括集流体和设置于所述集流体至少一个表面上的电极活性材料层，其中，所述集流体包括支撑层和设置于支撑层至少一个表面上的导电层，所述导电层的单面厚度D2满足：30nm≤D2≤3μm，所述支撑层的厚度D1满足：1μm≤D1≤30μm，且所述支撑层为高分子材料或高分子复合材料；所述电极活性材料层包括电极活性材料、粘结剂和导电剂，所述电极活性材料层的总厚度D 总为不大于170μm，且所述电极活性材料层的膜片电阻为0.1欧至10欧。
第二方面，本申请涉及一种电化学装置，包括正极极片、负极极片、隔离膜和电解液，其中所述正极极片为本申请第一方面所述的正极极片。
第三方面，本申请涉及一种装置，包括本申请第二方面所述的电化学装置。
本申请的技术方案至少具有以下有益的效果：
本申请的正极极片和含有该正极极片的电化学装置(例如锂离子电池)兼具优异的能量密度、良好的电化学性能和安全性能。
第一，本申请的正极极片采用复合集流体，可以显著改善电化学装置的能量密度， 例如重量能量密度；
第二，本申请的正极复合集流体中的导电层较薄(在发生穿钉等异常情况时产生的金属毛刺也较小)且由于支撑层为高分子材料或高分子复合材料，因此具有较高的短路内阻，因此改善了穿钉安全性能；
第三，正极极片的电极活性材料层的膜片电阻为0.1欧至10欧，因此该正极极片和电化学装置具有良好的电化学性能，且还具有良好的穿钉安全性能。
此外，根据本申请某些优选实施方式的正极极片的电极活性材料层中的粘结剂的含量和/或导电剂的含量优选在厚度方向上具有不均匀的组成状态，不仅可以很好地克服复合集流体导电能力较差、且复合集流体中的导电层易于破损等缺点，通过有效修补并构筑集流体、导电底涂层与活性物质间的导电网络，提高电子传输效率，降低集流体与电极活性材料层之间的电阻，从而可以有效降低电极组件直流内阻，提高电极组件功率性能，并保证电极组件在长期循环过程中不易于发生较大的极化及析锂等现象，即有效改善了电极组件的长期可靠性，还可以明显改善复合集流体与电极活性材料层之间的界面，提高集流体和电极活性材料层之间的结合力，保证电极活性材料层更牢固地设置于复合集流体的表面。
此外，根据本申请某些优选实施方式的电极极片，电极活性材料层基于压实密度包括2n+1(n＝1、2或3)个区域，且中间区域的压实密度高于两侧区域的压实密度，这种特殊的分区设计可以有效抑制复合集流体及电极极片由于辊压等而导致的弧度和边缘翘曲，从而使得电极极片在辊压之后保持较好的极片平整度，且有利于保护导电层不易破损，从而使得极片具有良好的电化学性能。
本申请的装置包括本申请第二方面所述的电化学装置，因而至少具有与所述电化学装置相同的优势。
因此，本申请的正极极片、电化学装置及装置具有良好且均衡的电化学性能、安全性能和加工性能。
附图说明
下面结合附图和具体实施方式，对本申请的正极极片、电化学装置、装置及其有益效果进行详细说明。
图1为本申请某一具体实施方式的正极集流体的剖视结构示意图；
图2为本申请又一具体实施方式的正极集流体的剖视结构示意图；
图3为本申请又一具体实施方式的正极集流体的剖视结构示意图；
图4为本申请又一具体实施方式的正极集流体的剖视结构示意图；
图5为本申请某一具体实施方式的正极极片的剖视结构示意图；
图6为本申请又一具体实施方式的正极极片的剖视结构示意图；
图7为本申请某一具体实施方式的正极极片的俯视结构示意图；
图8为根据本申请测量电极活性材料层的膜片电阻的示意图；
图9为本申请的电化学装置的一实施方式的示意图；
图10为本申请的电池模块的一实施方式的示意图；
图11为本申请的电池包的一实施方式的示意图；
图12是图11的分解图；
图13为本申请的电化学装置作为电源的装置的一实施方式的示意图；
其中：
PP-正极极片；
10-正极集流体；
101-正极支撑层；
102-正极导电层；
103-正极保护层；
11-正极活性材料层；
511-极耳；
512-空白区；
513-第一低压实区域；
514-高压实区域；
515-第二低压实区域；
1-电池包；
2-上箱体；
3-下箱体；
4-电池模块；
5-电化学装置。
具体实施方式
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
本申请的第一方面涉及一种正极极片，其包括集流体和设置于所述集流体至少一个表面上的电极活性材料层，其中，所述集流体包括支撑层和设置于支撑层至少一个表面上的导电层，所述导电层的单面厚度D2满足：30nm≤D2≤3μm，所述支撑层的厚度D1满足：1μm≤D1≤30μm，且支撑层为高分子材料或高分子复合材料；所述电极活性材料层包括电极活性材料、粘结剂和导电剂，电极活性材料层的总厚度D 总为不大于170μm，且电极活性材料层的膜片电阻为0.1欧至10欧。
用于本申请第一方面所述正极极片的集流体是一种复合集流体，其由至少两种材料复合而成。在结构上，所述集流体包括支撑层和设置于支撑层至少一个表面上的导电层，所述导电层的单面厚度D2满足：30nm≤D2≤3μm，所述支撑层的厚度D1满足：1μm≤D1≤30μm。因此，所述集流体中起导电作用的是导电层。该导电层厚度D2远小于现有技术中常用的诸如Al箔金属集流体的厚度(常用的Al箔金属集流体的厚度通常为12μm)，且支撑层为高分子材料或高分子复合材料，因此可以提高使用该极片的电化学装置(例如锂电池)的重量能量密度。此外，该复合集流体应用于正极集流体时，还可以大大改善正极极片的穿钉安全性能，因为正极集流体中的导电层较薄，在发生穿钉等异常情况时产生的金属毛刺也较小，且由于支撑层的存在，其短路 内阻较大，因此更不容易引起短路。
此外，在根据本申请的正极极片中，对于电极活性材料层进行了特殊设计，可以使得该正极极片和含有该正极极片的电化学装置(例如锂离子电池)兼具良好的能量密度、电化学性能和安全性能。具体而言，由于将电极活性材料层的膜片电阻控制在一定范围内，可以进一步改善电化学装置的穿钉安全性能和电化学性能。
另外，由于复合集流体的高分子支撑层的反弹程度较传统金属集流体大，因此如果按照传统工艺，对集流体进行涂布后再经辊压工艺进行压实，还会导致一系列的其它问题。由于支撑层的反弹，会导致极片两侧的边缘上翘，使得极片整体产生弧度，从而导致极片变形。极片变形有可能导致电极活性材料层与复合集流体分离、导电层破损、导电层从支撑层剥离等，进而使极片电化学性能劣化。另一方面，极片的变形也会使得正负极极片无法精确对准。因此，由复合集流体制备的电极极片容易产生内阻偏大、极化较大等技术问题。现有技术中为了解决复合集流体导致的极片变形问题往往要在活性材料浆料干燥过程或者辊压过程中采用一些特殊技术手段来释放应力，或者采用常规工艺而不得不牺牲良品率。鉴于此，在本申请的优选实施方式中，除了对电极极片的厚度方向的材料分布进行设计外，还对电极极片的活性材料层的横向方向(即与极片表面平行的方向)的材料分布进行了特殊设计。根据本申请的该优选实施方式，电极极片的电极活性材料层基于压实密度包括沿极片宽度方向(即与涂布方向垂直的方向)分布的2n+1(n＝1、2或3)个区域，且中间区域的压实密度高于两侧区域的压实密度，这种特殊的分区设计可以有效抑制复合集流体及电极极片由于辊压等而导致的弧度和边缘翘曲，从而使得电极极片在辊压之后仍保持较好的极片平整度，消除或减小极片内阻偏大、极化较大等技术问题，且有利于保护导电层不易破损，从而使得极片和电化学装置具有良好的电化学性能。
根据本申请的某些优选实施方式，所述电极活性材料层中的粘结剂的含量和/或导电剂的含量优选在厚度方向上具有不均匀的组成状态。
其中基于电极活性材料层的总重量，在所述电极活性材料层的靠近所述集流体的内侧区域中的粘结剂的重量百分含量高于所述电极活性材料层的远离所述集流体的外侧区域中的粘结剂的重量百分含量，因此粘结剂含量较高的内侧区域可以明显改善复合集流体与电极活性材料层之间的界面，提高集流体和电极活性材料层之间的结合力，保证电极活性材料层更牢固地设置于复合集流体的表面；另外，由于电极活性材料层可以更牢固地设置于复合集流体的表面，因此在穿钉等异常情况发生时，电极活性材料层可以更有效地包裹导电层中产生的毛刺，更好地改善穿钉安全性能；第三，粘结剂含量较低的外侧区域中电化学活性材料的占比可以较高，因此正极极片的电化学性能(例如电化学容量和能量密度)更好。
此外，基于电极活性材料层的总重量，在所述电极活性材料层的靠近所述集流体的内侧区域中的导电剂的重量百分含量高于所述电极活性材料层的远离所述集流体的外侧区域中的导电剂的重量百分含量，从而导电剂含量较高的内侧区域可以发挥集流体的导电层与电极活性材料层之间的导电底涂层的作用，可以很好地克服复合集流体导电能力较差、且复合集流体中的导电层易于破损等缺点。所述内侧区域通过有效修补并构筑集流体、导电底涂层与活性物质间的导电网络，提高电子传输效率，降低含 有复合集流体的极片电阻，从而可以有效降低电极组件的直流内阻(DCR)，提高电极组件的功率性能，并保证电极组件在长期循环过程中不易于发生较大的极化及析锂等现象，即有效改善了电极组件的长期可靠性。此外，导电剂含量较低的外侧区域中电化学活性材料的占比可以较高，因此正极极片的电化学性能(例如电化学容量和能量密度)更好。
下面对本申请实施方式涉及的正极极片(以及其中的集流体)的结构、材料和性能等进行详细描述。
[集流体导电层]
相对于传统的金属集流体来说，在本申请实施方式的集流体中，导电层起到导电和集流的作用，用于为电极活性材料层提供电子。
导电层的材料选自金属导电材料、碳基导电材料中的至少一种。
所述金属导电材料优选铝、镍、钛、银、铝锆合金中的至少一种；
所述碳基导电材料优选石墨、乙炔黑、石墨烯、碳纳米管中的至少一种；
导电层的材料优选为金属导电材料，即导电层优选为金属导电层。其中，当集流体为正极集流体时，通常采用铝为导电层的材料。
当导电层的导电性较差或厚度太小时，会造成电池的内阻较大、极化较大，当导电层的厚度太大时，则不足以起到改善电池重量能量密度和体积能量密度的效果。
所述导电层的单面厚度为D2，D2优选满足：30nm≤D2≤3μm，更优选300nm≤D2≤2μm，最优选为500nm≤D2≤1.5μm；以便更好的保证集流体的轻质性能并兼具良好的导电性能。
在本申请优选实施方式中，导电层的单面厚度D2的上限可为3μm、、2.5μm、2μm、1.8μm、1.5μm、1.2μm、1μm、900nm，导电层的单面厚度D2的下限可为800nm、700nm、600nm、500nm、450nm、400nm、350nm、300nm、100nm、50nm、30nm；导电层的单面厚度D2的范围可由上限或下限的任意数值组成。优选地，300nm≤D2≤2μm；更优选为500nm≤D2≤1.5μm。
由于本申请中导电层的厚度较小，因此在极片制作等过程中，易产生裂纹等破损。
通常，在本申请所述正极极片的导电层中有裂纹存在。导电层中的裂纹通常不规则地存在于导电层中，可以是长条形裂纹、可以为交叉型裂纹、可以为发散状裂纹等；可以是贯穿整个导电层的裂纹，也可以是在导电层的表层形成的裂纹。导电层中的裂纹通常是由于在极片加工过程中的辊压、焊接极耳振幅过大、基材收卷张力过大，等情况造成的。
导电层可通过机械辊轧、粘结、气相沉积法(vapor deposition)、化学镀(Electroless plating)中的至少一种形成于支撑层上，气相沉积法优选物理气相沉积法(Physical Vapor Deposition，PVD)；物理气相沉积法优选蒸发法、溅射法中的至少一种；蒸发法优选真空蒸镀法(vacuum evaporating)、热蒸发法(Thermal Evaporation Deposition)、电子束蒸发法(electron beam evaporation method，EBEM)中的至少一种，溅射法优选磁控溅射法(Magnetron sputtering)。
优选气相沉积法或化学镀中的至少一种，以使得支撑层与导电层之间的结合更牢 固。
[集流体支撑层]
在本申请实施方式的集流体中，支撑层对导电层起到支撑和保护的作用。由于支撑层一般采用有机高分子材料或高分子复合材料，因此支撑层的密度通常小于导电层的密度，从而较传统的金属集流体可显著提升电池的重量能量密度。
并且，导电层采用厚度较小的金属层，可进一步提高电池的重量能量密度。并且由于支撑层可以对位于其表面的导电层起到良好的承载和保护作用，因而不易产生传统集流体中常见的极片断裂现象。
所述支撑层的材料具体可选自绝缘高分子材料、绝缘高分子复合材料、导电高分子材料、导电高分子复合材料中的至少一种。
绝缘高分子材料例如选自聚酰胺、聚对苯二甲酸酯、聚酰亚胺、聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、芳纶、聚二甲酰苯二胺、丙烯腈-丁二烯-苯乙烯共聚物、聚对苯二甲酸丁二醇酯、聚对苯二甲酰对苯二胺、聚丙乙烯、聚甲醛、环氧树脂、酚醛树脂、聚四氟乙烯、聚苯硫醚、聚偏氟乙烯、硅橡胶、聚碳酸酯、纤维素及其衍生物、淀粉及其衍生物、蛋白质及其衍生物、聚乙烯醇及其交联物、聚乙二醇及其交联物中的至少一种。
绝缘高分子复合材料例如选自绝缘高分子材料与无机材料形成的复合材料，其中无机材料优选陶瓷材料、玻璃材料、陶瓷复合材料中的至少一种。
导电高分子材料例如选自聚氮化硫类高分子材料或经掺杂的共轭类高分子材料，比如聚吡咯、聚乙炔、聚苯胺、聚噻吩等中的至少一种。
导电高分子复合材料例如选自绝缘高分子材料与导电材料形成的复合材料，其中导电材料选自导电碳材料、金属材料、复合导电材料中的至少一种，其中导电碳材料选自碳黑、碳纳米管、石墨、乙炔黑、石墨烯中的至少一种，金属材料选自镍、铁、铜、铝或上述金属的合金中的至少一种，复合导电材料选自镍包覆的石墨粉、镍包覆的碳纤维中的至少一种。
根据应用环境的实际需要和成本等因素，本领域技术人员可以合理地选择和确定支撑层的材料。本申请中所述支撑层的材料优选为绝缘高分子材料或绝缘高分子复合材料，尤其是当集流体为正极集流体时。
当集流体为正极集流体时，通过采用具有绝缘层支撑、且具有特定厚度的导电层的特殊集流体，可以明显改善电池的安全性能。由于绝缘层不导电，因此其电阻较大，可以提高电池在异常情况下发生短路时的短路电阻，使短路电流大幅度减小，因此可极大地降低短路产热量，从而改善电池的安全性能；且导电层较薄，因此在穿钉等异常情况下，局部的导电网络被切断，防止电化学装置大面积甚至整个电化学装置发生内短路，这就可以将穿钉等造成的电化学装置的损坏局限于刺穿位点，仅形成“点断路”，而不影响电化学装置在一定时间内的正常工作。
支撑层的厚度为D1，D1优选满足：1μm≤D1≤30μm；更优选1μm≤D1≤15μm。
若支撑层太薄的话，则支撑层的机械强度不够，很容易在极片加工工艺等过程中发生断裂；支撑层太厚的话，则会降低使用该集流体的电池的体积能量密度。
其中，支撑层的厚度D1的上限可为30μm、25μm、20μm、15μm、12μm、10μm、8μm，下限可为1μm、1.5μm、2μm、3μm、4μm、5μm、6μm、7μm；支撑层的厚度D1的范围可由上限或下限的任意数值组成。优选的，1μm≤D1≤15μm；更优选2μm≤D1≤10μm；最优选3μm≤D1≤8μm。
同时，本申请特定的厚度可以进一步保证该集流体具有较大的电阻，显著降低电池在发生内短路时的电池升温，当导电层为铝时，还可显著减少或防止正极集流体的铝热反应，从而保证电池具有良好的安全性能。
此外，当导电层为金属导电层时，优选支撑层的常温杨氏模量满足：20GPa≥E≥4GPa。
本申请中所述支撑层的常温杨氏模量的测试方法如下：
取支撑层样品裁剪成15mm×200mm，用万分尺量取样品的厚度h(μm)，常温常压下使用高铁拉力机进行拉伸测试，设置初始位置，并使夹具之间样品为50mm长，拉伸以50mm/min速度进行，记录拉伸至断裂的载荷L(N)，设备位移y(mm)，则应力ε＝L/(15*h)*1000，应变η＝y/50*100，绘制应力应变曲线，取初始线性区曲线，该曲线的斜率既为杨氏模量E。
由于金属相对于高分子或高分子复合材料刚性较强，即在极片加工的辊压等过程中变形较小，因此为了确保支撑层和导电层之间的形变差别不至于过大，以至于将导电层撕裂，所述支撑层的常温杨氏模量最好满足：20GPa≥E≥4Gpa，从而可以使得支撑层具有一定的刚性，且可进一步提高支撑层与导电层之间的刚性匹配性，从而在集流体、极片的加工过程中，保证支撑层与导电层的形变量不会差别太大。
由于支撑层具有一定的刚性(20GPa≥E≥4GPa)，因此在集流体、极片的加工过程中，集流体不易变形或不易延展太大，从而可使得支撑层与导电层之间结合牢固，不易脱离，且可防止导电层“被迫”延展而导致的导电层破损。且根据本申请的集流体具有一定的韧性，从而可使得集流体和极片具有一定的承受变形的能力，不易于断带。
但是支撑层的杨氏模量不能过大，否则刚性过强，会造成收卷及卷绕困难、可加工性变差。当20GPa≥E，可以保证支撑层具有一定的柔性，还可使得极片具有一定的承受变形的能力。
此外，优选支撑层在90℃的热收缩率不大于1.5％，从而在极片加工过程中，可以更好的保证集流体的热稳定性。
[集流体的保护层]
在本申请的一些优选实施方式中，所述集流体还设置有保护层，所述保护层设置于所述集流体的导电层的一个表面上或设置于所述集流体的导电层的两个表面上，即导电层的远离支撑层的表面上和面对支撑层的表面上。
保护层可为金属保护层或金属氧化物保护层。保护层可以防止集流体的导电层受到化学腐蚀或机械损坏而导致的破损，此外还可以增强集流体的机械强度。
优选保护层设置于集流体的导电层的两个表面上。导电层的下保护层(即设置于导电层的面对支撑层的表面上的保护层)不仅可以防止导电层受到损坏、增强集流体 的机械强度，还可以增强支撑层与导电层之间的结合力，防止脱膜(即支撑层与导电层分离)。
导电层的上保护层(即设置于导电层的远离支撑层的表面上的保护层)的技术效果主要是防止加工过程中导电层被破坏、腐蚀等(例如电解液浸泡、辊压等都会对导电层表面造成影响)。
由于良好的导电性，金属保护层不仅可以进一步改进导电层的机械强度和耐蚀性，还能降低极片的极化。所述金属保护层的材料例如选自镍、铬、镍基合金、铜基合金中的至少一种，优选镍或镍基合金。
其中，镍基合金是以纯镍为基体加入一种或几种其他元素所构成的合金。优选为镍铬合金，镍铬合金是金属镍和金属铬形成的合金，可选的，镍元素与铬元素的摩尔比为1：99～99：1。
铜基合金是以纯铜为基体加入一种或几种其他元素所构成的合金。优选为铜镍合金，可选的，在铜镍合金中，镍元素与铜元素的摩尔比为1：99～99：1。
保护层选用金属氧化物时，由于金属氧化物的延展性小、比表面积大、硬度大，同样也可形成对导电层的有效支撑和保护，并对于改善支撑层与导电层之间的结合力具有良好的技术效果。金属氧化物保护层的材料例如选自氧化铝、氧化钴、氧化铬、氧化镍中的至少一种。
根据本申请的复合集流体的保护层优选采用金属氧化物，以在达到良好的支撑和保护的技术效果的同时，进一步改善正极极片和电池的安全性能。
所述保护层的厚度为D3，D3优选满足：D3≤1/10D2且1nm≤D3≤200nm。如果保护层太薄，则不足以起到保护导电层的作用；保护层太厚，则会降低电池的重量能量密度和体积能量密度。更优选的，5nm≤D3≤500nm，进一步优选10nm≤D3≤200nm，最优选10nm≤D3≤50nm。
位于导电层的两个表面上的保护层的材料可相同或不同，厚度可相同或不同。
优选，下保护层的厚度小于上保护层的厚度，以有利于改善电池的重量能量密度。
进一步可选的，下保护层厚度D3”与上保护层厚度D3'的比例关系为：1/2D3'≤D3”≤4/5D3'。
当集流体为正极集流体时，通常采用铝为导电层的材料，下保护层优选选用金属氧化物材料。相对于下保护层的材料选用金属来讲，金属氧化物材料具有较大电阻，因此该类型的下保护层可以在一定程度上进一步增大正极集流体的电阻，从而进一步的提高电池异常情况下发生短路时的短路电阻，改善电池的安全性能。此外，由于金属氧化物的比表面积更大，所以金属氧化物材料的下保护层与支撑层之间的结合力增强；同时由于金属氧化物的比表面积更大，因此下保护层可以增加支撑层表面的粗糙度，起到增强导电层与支撑层之间的结合力的作用，从而提高了集流体整体的强度。因此，当集流体为正极集流体时，下保护层优选为金属氧化物材料，上保护层为金属材料或金属氧化物材料，优选上保护层也为金属氧化物材料。
[集流体]
图1至图4示出了根据本申请某些实施方式的正极极片中所采用的集流体的结构 示意图。
在图1中，正极集流体10包括正极集流体支撑层101和设置于正极集流体支撑层101相对的两个表面上的正极集流体导电层102，还包括设置于正极集流体导电层102的下表面(即朝向正极集流体支撑层101的面)上的正极集流体保护层103，即下保护层。
在图2中，正极集流体10包括正极集流体支撑层101和设置于正极集流体支撑层101相对的两个表面上的正极集流体导电层102，还包括设置于正极集流体导电层102的相对两个表面上的正极集流体保护层103，即下保护层和上保护层。
在图3中，正极集流体10包括正极集流体支撑层101和设置于正极集流体支撑层101一个表面上的正极集流体导电层102，还包括设置于正极集流体导电层102的朝向正极集流体支撑层101的面上的正极集流体保护层103，即下保护层。
在图4中，正极集流体10包括正极集流体支撑层101和设置于正极集流体支撑层101一个表面上的正极集流体导电层102，还包括设置于正极集流体导电层102的相对两个表面上的正极集流体保护层103，即下保护层和上保护层。
位于导电层的两个相对的表面上的保护层的材料可相同或不同，厚度可相同或不同。
其中，对于用于根据本申请的正极极片的集流体而言，如图1、图2所示，可在支撑层的相对的两个表面上均设置有导电层，或者如图3、图4所示，也可在仅支撑层的一面上设置有导电层。
虽然本申请的正极极片所采用的复合集流体优选地如图1至4所示含有集流体保护层，但是应该理解：集流体保护层并非集流体的必须结构，在某些实施方式中所用的集流体可以不含集流体保护层。
[正极极片的电极活性材料层]
用于本申请正极极片的电极活性材料层通常包括电极活性材料、粘结剂和导电剂。根据需要，电极活性材料层还可以包括可选的其它添加剂或助剂。
对于本申请的正极极片来说，优选电极活性材料层中的活性材料的平均粒径D50为5μm～15μm。如果D50太小，则压实后，极片的孔隙率较小，不利于电解液的浸润，且其较大的比表面积易与电解液产生较多副反应，降低电极组件的可靠性；如果D50太大，则易于在极片压实过程中对复合集流体造成较大的损坏。D50指活性材料累计体积百分数达到50％时所对应的粒径，即体积分布中位粒径。D50例如可以使用激光衍射粒度分布测量仪(例如Malvern Mastersizer 3000)进行测量。
对于本申请的正极极片而言，可以选用本领域常用的各种电极活性材料(即正极活性材料)。例如，对于锂电池来说，正极活性材料可选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、过渡金属磷酸盐、磷酸铁锂等，但本申请并不限定于这些材料，还可以使用其他可被用作锂离子电池正极活性物质的传统公知的材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。优选地，正极活性材料可选自LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2 (NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4、LiMnPO 4中的一种或几种。
本申请的正极极片的一个重要特征是电极活性材料层的总厚度D 总为不大于170μm，D 总≤170μm。在本申请中，对于电极活性材料层单面涂布的技术方案而言，电极活性材料层的总厚度D 总即是电极活性材料层的单面厚度D4；对于电极活性材料层双面涂布的技术方案而言，电极活性材料层的总厚度D 总是电极活性材料层的单面厚度D4的二倍，即2D4。另外，如果电极活性材料层采用多次分层涂布法进行涂布时，则D4和D 总的计算要包括所有的(即每一层的)电极活性材料层。若D 总>170μm，则电池的动力学性能较差。
在D 总≤170μm的情况下，本申请的正极极片的另一个重要特征是正极极片的电极活性材料层的膜片电阻为0.1欧至10欧。本申请的申请人发现，当膜片电阻处于适当的范围内时，可以进一步保证电池的穿钉安全性能，且可以保证电池良好的电化学性能。如果膜片电阻太小，则不足以保证穿钉安全，若太大，则电化学性能较差。活性材料的本征电阻率、导电剂的含量、粘结剂的含量、活性材料的粒径、电解液的电导率、压实密度(越大，电阻越小)、活性材料层的厚度等均会对活性材料层的膜片电阻产生影响。因此，可以通过调节或控制这些参数来调整活性材料层的膜片电阻。
本申请中所述的电极活性材料层的膜片电阻可以例如通过以下的方法进行测试：
在5％湿度及室温环境下，取100mm×100mm大小的、浸泡过锂离子电池电解液的极片1片，从中间对折后(这里以双面涂布正极活性材料层的极片为例，对于单面涂布正极活性材料层的极片，则正极活性材料层朝外进行对折)置于膜片电阻仪探针中间(如图8所示)，然后进行测试，得到被测极片的活性材料层的膜片电阻，对5个极片样品进行测试后求取平均值，即为活性材料层的膜片电阻。
当电极活性材料层的总厚度为不大于170μm且其膜片电阻为0.1欧至10欧时，本申请的正极极片(及电化学装置)可以兼具良好的电化学性能和良好的穿钉安全性能。尤其是当膜片电阻为0.6欧至0.9欧时，可进一步保证极片具有良好的穿钉安全性能，且同时可保证极片具有良好的电化学性能。
根据本申请的某些优选实施方式，基于电极活性材料层的总重量，电极活性材料层中的粘结剂含量不小于1wt％，优选不小于1.5wt％，更优选不小于2wt％。对于本申请的正极极片来说，当电极活性材料层中的粘结剂的含量较高时，则可以增强活性材料层与复合集流体之间的结合力，从而可以抑制由于加工过程中支撑层的较大反弹而导致的复合集流体与电极活性材料层之间的结合力劣化，并且使得在穿钉等异常情况下，活性材料层可有效地包裹导电层中产生的金属毛刺，以改善电池的穿钉安全性能。粘结剂含量保持在这一范围内，则活性材料层与集流体间的结合力较好，从而使得在穿钉等异常情况下，活性材料层可更有效地包裹导电层中产生的金属毛刺，以改善电池的穿钉安全性能。
然而当提高电极活性材料层中的粘结剂含量时，活性材料的占比会下降，从而不利于得到电化学容量高和能量密度高的极片和电化学装置。因此，在电极活性材料层的膜片电阻满足0.1欧至10欧的情况下，根据本申请的某些优选实施方式，所述电极活性材料层中的粘结剂的含量和/或导电剂的含量优选在厚度方向上具有不均匀的组 成状态。
电极活性材料层中所用导电剂优选为导电碳材料、金属材料中的至少一种。
例如，导电碳材料选自零维导电碳(如乙炔黑、导电炭黑)，一维导电碳(如碳纳米管)，二维导电碳(如导电石墨、石墨烯)，三维导电碳(如还原后的氧化石墨烯)中的至少一种；金属材料选自铝粉，铁粉以及银粉中的至少一种。
本领域技术人员熟知，将电极活性材料、导电剂和粘结剂等组成的浆料涂覆到电极集流体上，再经干燥等后处理即可得所需的电极活性材料层。
本申请的正极极片可以像传统的正极极片那样在整个极片表面的涂覆区域内均匀涂覆电极活性材料层，然后对极片表面整体进行冷压(辊压)操作，由此所得到的极片上的电极活性材料层的压实密度是基本一致的，不会有明显差异。如前所述，由于复合集流体的特殊性，这种涂布方法可能造成极片在辊压过程中边缘上翘、整体形成弧度，从而降低极片的良品率。因此，在本申请的一些优选实施方式中，从所述正极极片被涂布表面的宽度方向看，涂布的电极活性材料层基于压实密度包括2n+1(n＝1、2或3)个区域，且中间区域的压实密度高于两侧区域的压实密度。由于在冷压(辊压)等过程之后，极片两侧区域的压实密度低，而中间区域的压实密度高，即在冷压(辊压)等过程中极片两侧区域处承受的压力小于中间区域，由此可以避免极片加工过程中由于复合集流体的反弹而导致的复合集流体和电极极片易于产生的边缘翘曲和弧度，有利于形成表面平整的极片，从而有利于保证电化学装置的电化学性能。
在本申请中，电极极片表面的“长度方向”和“宽度方向”分别是指表面的两个维度，其中长度方向是指主要维度方向(即尺寸较大的方向)，而宽度方向是指次要维度方向(即尺寸较小的方向)。通常，长度方向与极片加工过程中的各个材料层(例如电极活性材料层)的涂覆方向是一致的，也与电化学装置(例如电池)制造过程中极片的卷绕方向是一致的；而宽度方向是与长度方向垂直的。
“中间区域的压实密度高于两侧区域的压实密度”表示中间区域的压实密度最高，两侧区域的压实密度由中间向边缘逐级降低。优选地，两侧对称区域的压实密度是相同的。
要形成根据本申请的基于压实密度的活性材料层的2n+1个区域，可以采用分区涂布的方法实现，即利用挡板或垫片在极片表面划分出不同的区域(或界限)，在每个区域涂覆不同重量的电极活性材料浆料，这样在辊压之后就形成了压实密度不同的活性材料层区域。此外，两侧各个区域的压实密度优选为对称相同的，这样的设计有利于更好地保证电极极片的平整度。
考虑到工艺复杂性和成本问题，涂布的电极活性材料层基于压实密度优选包括3个(n＝1)或5个(n＝2)区域，最优选3个区域。
根据本申请的某些优选实施方式，电极活性材料层中的导电剂的含量在厚度方向上具有不均匀的分布，即导电剂在电极活性材料层中的重量百分含量在厚度方向上是不均匀的、有变化的。更具体地说，基于电极活性材料层的总重量，在所述电极活性材料层的内侧区域(也可称“下层电极活性材料”)中的导电剂的重量百分含量高于电极活性材料层的外侧区域(也可称“上层电极活性材料”)中的导电剂的重量百分含量。优选，在内侧区域中的电化学活性材料的重量百分含量低于外侧区域中的电化学活性 材料的重量百分含量。
本申请中，在提及电极活性材料的“内侧”时，是指所述电极活性材料层在厚度方向上靠近集流体的一侧，在提及电极活性材料的“外侧”时，是指所述电极活性材料层在厚度方向上远离集流体的一侧。
“导电剂在厚度方向上具有不均匀的分布”和“在所述电极活性材料层的内侧区域中的导电剂的重量百分含量高于电极活性材料层的外侧区域中的导电剂的重量百分含量”可以有多种不同实施方式。例如，所述电极活性材料层中导电剂的重量百分含量可以沿着从内侧区域到外侧区域的厚度方向逐渐减小；或者所述电极活性材料层在厚度方向分为两个或更多个区域(即分成两层、三层或更多层)，且最靠近集流体的区域中导电剂的重量百分含量都大于每一个远离集流体的区域中导电剂的重量百分含量。在本申请的一个具体实施方式中，所述电极活性材料层在厚度方向分为两个区域(即分成两层电极活性材料层)，且下层(内侧)电极活性材料中导电剂的重量百分含量都大于上层(外侧)电极活性材料中导电剂的重量百分含量。
在本申请的一个优选实施方式中，电极活性材料层在厚度方向分为两个区域，即内侧区域和外侧区域，基于所述电极活性材料层的内侧区域的总重量，内侧区域中导电剂的重量百分含量为10wt％～99wt％，优选20wt％～80wt％，更优选为50wt％～80wt％。基于所述电极活性材料层的外侧区域的总重量，优选外侧区域中的导电剂的重量百分含量为0.5wt％～10wt％。
因此导电剂含量较高的内侧区域可以发挥集流体的导电层与电极活性材料层之间的导电底涂层的作用，可以很好地克服复合集流体导电能力较差、且复合集流体中的导电层易于破损等缺点。所述内侧区域通过有效修补并构筑集流体、导电底涂层与活性物质间的导电网络，提高电子传输效率，降低含有复合集流体的极片电阻，从而可以有效降低电极组件的直流内阻(DCR)，提高电极组件的功率性能，并保证电极组件在长期循环过程中不易于发生较大的极化及析锂等现象，即有效改善了电极组件的长期可靠性。此外，导电剂含量较低的外侧区域中电化学活性材料的占比可以较高，因此正极极片的电化学性能(例如电化学容量和能量密度)更好。
优选的，内侧区域中的导电剂含有一维导电碳材料(例如碳纳米管)和/或二维导电碳材料。因为加入二维导电碳材料后，在极片压实过程中，电极活性材料层的内侧区域中的二维导电碳材料可以产生“水平滑动”，从而起到缓冲作用，减少压实过程中对集流体的导电层的破坏，从而减少裂纹。优选的二维导电碳材料的粒径D50为0.01～0.1μm。另外由于一维导电碳材料的形貌特殊，因此添加后可以改善内侧区域的导电性，尤其是在导电剂的添加量一定的情况下，一维导电碳材料相较于其他类型的导电材料可以更好的改善内侧区域的导电性。一维导电碳材料优选碳纳米管，其长径比优选为1000～5000。
优选地，在内侧区域中一维导电碳材料和/或二维导电碳材料占所述内侧区域中导电剂的1wt％～50wt％，其余的导电剂可以为其他类型的导电剂，优选为零维碳材料。一维导电碳材料和/或二维导电碳材料与零维碳材料可以一起作用，更好地改善内侧区域的导电性能和作为导电底涂层的性能。优选的内侧区域中的导电剂为导电炭黑与碳纳米管的混合材料。
当然为了更好地起到缓冲作用，外侧区域中的导电剂也优选含有二维导电碳材料，或者为了更好地起到导电的作用，外侧区域中的导电剂也优选含有一维导电碳材料(例如碳纳米管)。
优选地内侧区域和外侧区域中的导电剂均含有碳纳米管；更优选的内侧区域和外侧区域中的导电剂均为碳纳米管与导电炭黑的混合物。
由于导电剂含量的不均匀分布，所述电极活性材料中粘结剂和活性材料的含量沿厚度方向也可能有变化。
电极活性材料层中所用粘结剂例如可选自丁苯橡胶，油性聚偏氟乙烯(PVDF)，聚偏氟乙烯共聚物(如PVDF-HFP共聚物、PVDF-TFE共聚物)、羧甲基纤维素钠，聚苯乙烯，聚丙烯酸，聚四氟乙烯，聚丙烯腈、聚酰亚胺、水性PVDF、聚氨酯、聚乙烯醇、聚丙烯酸酯、聚丙烯酸-聚丙烯腈共聚物、聚丙烯酸酯-聚丙烯腈共聚物中的至少一种。
内侧区域中的粘结剂优选水性粘结剂，如水性PVDF、聚丙烯酸、聚氨酯、聚乙烯醇、聚丙烯酸酯、聚丙烯酸-聚丙烯腈共聚物、聚丙烯酸酯-聚丙烯腈共聚物中的至少一种，这样电化学装置的DCR增长较小。在本申请中，“水性”高分子材料是指高分子分子链完全伸展开分散在水中，“油性”高分子材料是指高分子分子链完全伸展开分散在油性溶剂中。本领域技术人员理解，通过采用合适的表面活性剂可以将同一类的高分子材料分别分散在水中和油中，即通过采用合适的表面活性剂，同一类的高分子材料可以被分别做成水性高分子材料和油性高分子材料。例如，本领域技术人员可以根据需要，将PVDF改性为水性PVDF或油性PVDF。
此外，对于本申请的正极极片来说，当电极活性材料层中的粘结剂的含量较高时，则活性材料层与集流体之间的结合力较好从而使得在穿钉等异常情况下，活性材料层可有效地包裹导电层中产生的金属毛刺，以改善电池的穿钉安全性能。然而如果粘结剂含量偏高，活性材料的含量则会降低，从而不利于保证电池具有较高的电化学容量。因此，就进一步改善电池安全性以及保证电池的高容量而言，优选地所述电极活性材料层中的粘结剂的含量在厚度方向上具有不均匀的组成状态，其中基于电极活性材料层的总重量，在所述电极活性材料层的靠近所述集流体的内侧区域中的粘结剂的重量百分含量高于所述电极活性材料层的远离所述集流体的外侧区域中的粘结剂的重量百分含量。
在本申请的一个优选实施方式中，电极活性材料层在厚度方向分为两个区域，即内侧区域和外侧区域，其中，基于内侧区域处的电极活性材料层的总重量，内侧区域中粘结剂的重量百分含量为1wt％～90wt％，优选20wt％～80wt％，更优选为20wt％～50wt％。基于外侧区域处的电极活性材料层的总重量，优选外侧区域中的粘结剂的重量百分含量为1wt％～5wt％。
因此粘结剂含量较高的内侧区域可以明显改善复合集流体与电极活性材料层之间的界面，提高集流体和电极活性材料层之间的结合力，保证电极活性材料层更牢固地设置于复合集流体的表面；另外，由于电极活性材料层可以更牢固地设置于复合集流体的表面，因此在穿钉等异常情况发生时，粘结剂含量较高的内侧区域可以起到胶层的作用，电极活性材料层可以更有效地包裹导电层中产生的毛刺，进一步更好地改 善穿钉安全性能；第三，粘结剂含量较低的外侧区域中电化学活性材料的占比可以较高，因此正极极片的电化学性能(例如电化学容量和能量密度)更好。
在本申请的一个优选实施方式中，电极活性材料层在厚度方向分为两个区域，即内侧区域和外侧区域，其中，基于内侧区域处的电极活性材料层的总重量，内侧区域中导电剂的重量百分含量为10wt％～99wt％，优选20wt％～80wt％，更优选为50wt％～80wt％；内侧区域中粘结剂的重量百分含量为1％～90％，优选20％～80％，更优选为20％～50％；而余量为电极活性材料。但是，在此实施方式中，内侧区域中电极活性材料的含量可以为0％。
在本申请的另一个优选实施方式中，基于内侧区域电极(正极)活性材料层的总重量，导电剂的含量优选为10wt％～98wt％，粘结剂的含量优选为1wt％～89wt％，电极(正极)活性材料的含量优选为1wt％～89wt％。
为了进一步改善电池穿钉安全性，优选的电极活性材料层外侧区域中的粘结剂含量(相对于电极活性材料层外侧区域总重量)不小于1wt％，优选的不小于1.5wt％，最优选不小于2wt％。外侧区域中的粘结剂含量保持在一定量，则活性材料层的内侧区域与外侧区域之间的结合力较好，从而使得在穿钉等异常情况下，整个活性材料层可有效地包裹导电层中产生的金属毛刺，以改善电池的穿钉安全性能。
需注意，在电极活性材料层在厚度方向分为内侧区域和外侧区域两个区域的实施方式中，所述内侧区域和外侧区域所选用的电极活性材料、导电剂和粘结剂可以相同或不同。所述内侧区域优选使用本申请优选的含有一维导电碳材料和/或二维导电碳材料的导电剂和水性粘结剂，而外侧区域可以选用相同或不同的导电剂和粘结剂。对于这种实施方式的正极极片而言，内侧区域中的正极活性材料可以与外侧区域中的正极活性材料相同或不同；内侧区域中的正极活性材料优选为热稳定性高的材料，例如磷酸铁锂、磷酸锰铁锂、锰酸锂、磷酸锰锂、NCM333、NCM523等中的至少一种。
导电剂/粘结剂在厚度方向上具有不均匀分布的电极活性材料层可以采用本领域已知的方法进行制备，例如可以采用多层涂布法，例如两次涂布法、三次涂布法等，但本申请不限于此。
[正极极片]
图5、图6示出了根据本申请某些实施方式的正极极片的结构示意图。
在图5中，正极极片包括正极集流体10和设置于正极集流体10相对的两个表面上的正极活性材料层11，而正极集流体10包括正极集流体支撑层101和设置于正极集流体支撑层101相对的两个表面上的正极集流体导电层102以及设置于正极导电层102一侧或两侧的正极保护层103(图中未示出)。
在图6中，正极极片包括正极集流体10和设置于正极集流体10一个表面上的正极活性材料层11，而正极集流体10包括正极集流体支撑层101和设置于正极集流体支撑层101一个表面上的正极集流体导电层102以及设置于正极导电层102一侧或两侧的正极保护层103(图中未示出)。
如图5至图6所示，电极活性材料层可以设置于集流体的一个表面上，也可以设置于集流体的两个表面。
本领域技术人员可以理解：当采用设置有双面导电层的集流体时，正极极片既可以双面涂布(即电极活性材料层设置于集流体的两个表面)，也可以仅单面涂布(即电极活性材料层仅设置于集流体的一个表面上)；而当采用仅设置有单面导电层的集流体时，正极极片也仅能单面涂布，且电极活性材料层仅能涂布在集流体设置有导电层的一面。
图7示出了根据本申请某些实施方式的正极极片的俯视结构示意图。正极极片PP包括极片本体和一个或多个与其电连接的极耳511；根据涂覆的电极活性材料层的不同，极片本体包括四个区域：与极耳511直接相连的空白区512(即集流体的表面未涂覆有活性材料层的区域)、第一低压实区域513、高压实区域514和第二低压实区域515。即，从正极极片PP被涂布表面的宽度方向看，电极活性材料层基于压实密度包括3个区域(即2n+1个区域，其中n＝1)。且中间区域514的压实密度高于两侧区域513、515的压实密度。
本领域技术人员明白，极片上的空白区是为了加工方便或安全等考虑而设置的，空白区本身是可选的；根据需要，极片可以包含0个、1个、或2个空白区(两个低压实区域外侧各有一个)。
在本申请中，中间高压实区域占涂布总区域的比例(在本例中，即514宽度与513宽度+514宽度+515宽度之和的比值)，可以例如为20～80％，优选为30～70％，优选地40～60％，或者更优选地45～55％。两个低压实区域的宽度可以相同或不同，优选相同。
在本申请中，低压实区域的压实密度比高压实区域的压实密度可以低约5～30％，例如7～25％，例如8～20％，例如8～18％。
[电化学装置]
本申请的第二方面涉及一种电化学装置，包括正极极片、负极极片、隔离膜和电解液，其中所述正极极片为根据本申请的第一方面所述的正极极片。
所述电化学装置可以为电容器、一次电池或二次电池。例如可以为锂离子电容器、锂离子一次电池或锂离子二次电池。除了使用了本申请的正极极片外，这些电化学装置的构造和制备方法本身是公知的。由于使用了本申请的正极极片，所述电化学装置可以具有高的能量密度、改善的安全性(如穿钉安全性)和电化学性能。并且本申请的正极极片容易加工，因此可以降低使用了本申请的正极极片的电化学装置的制造成本。
在本申请的电化学装置中，负极极片、隔离膜以及电解液的具体种类及组成均不受具体的限制，可根据实际需求进行选择。具体地，所述隔离膜可选自聚乙烯膜、聚丙烯膜、聚偏氟乙烯膜以及它们的多层复合膜。当电池为锂离子电池时，通常使用非水电解液作为电解质。作为非水电解液，通常使用在有机溶剂中溶解的锂盐溶液。锂盐例如是LiClO 4、LiPF 6、LiBF 4、LiAsF 6、LiSbF 6等无机锂盐、或者LiCF 3SO 3、LiCF 3CO 2、Li 2C 2F 4(SO 3) 2、LiN(CF 3SO 2) 2、LiC(CF 3SO 2) 3、LiC nF 2n+1SO 3(n≥2)等有机锂盐。非水电解液中使用的有机溶剂例如是碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、碳酸亚乙烯酯等环状碳酸酯，碳酸二甲酯、碳酸二乙酯、碳酸甲基乙酯等链状碳酸酯，丙酸甲酯等链状酯，γ-丁内酯等环状酯，二甲氧基乙烷、二乙醚、二甘醇二甲醚、三甘醇二甲醚 等链状醚，四氢呋喃、2-甲基四氢呋喃等环状醚，乙腈、丙腈等腈类，或者这些溶剂的混合物。对于负极极片而言，可以选用本领域常用的各种负极活性材料形成的负极极片。例如，对于锂电池来说，负极活性材料可选自例如石墨(人造石墨或天然石墨)、导电炭黑、碳纤维等碳质材料，例如Si、Sn、Ge、Bi、Sn、In等金属或半金属材料或其合金，含锂氮化物或含锂氧化物，锂金属或锂铝合金等。
在一些实施例中，电化学装置可以包括外包装，用于封装正极极片、负极极片和电解质。作为一个示例，正极极片、负极极片和隔离膜可经叠片或卷绕形成叠片结构电极组件或卷绕结构电极组件，电极组件封装在外包装内；电解质可采用电解液，电解液浸润于电极组件中。电化学装置中电极组件的数量可以为一个或几个，可以根据需求来调节。
在一些实施例中，电化学装置的外包装可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。电化学装置的外包装也可以是硬壳，例如铝壳等。
本申请对电化学装置的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图9是作为一个示例的方形结构的电化学装置5。
在一些实施例中，电化学装置可以组装成电池模块，电池模块所含电化学装置的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图10是作为一个示例的电池模块4。参照图10，在电池模块4中，多个电化学装置5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个电化学装置5进行固定。
可选地，电池模块4还可以包括具有容纳空间的壳体，多个电化学装置5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图11和图12是作为一个示例的电池包1。参照图11和图12，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
[装置]
本申请的第三方面涉及一种装置，包括本申请第二方面所述的电化学装置。所述电化学装置为所述装置提供电源。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。此外，电气列车、船舶及卫星均是运载工具，属于广义上的车辆(vehicle)。
所述装置可以根据其使用需求来选择电化学装置、电池模块或电池包。
图13是作为一个示例的装置。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。为了满足该装置对电化学装置的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用电化学装置作为电源。
本领域技术人员可以理解：以上提到的本申请的不同实施方式中对于极片、电极活性材料层等的组分选择、组分含量和材料理化性能参数的各种限定或优选范围可以任意组合，其组合而得到的各种实施方式仍然在本申请范围内，且视为本说明书公开内容的一部分。
除非特别规定，本说明书中涉及的各种参数具有本领域公知的通用含义，可以按本领域公知的方法进行测量。例如，可以按照在本申请的实施例中给出的方法进行测试。另外，各种优选实施方式中给出的各种不同参数的优选范围和选项可以进行任意组合，由此得到的各种组合都视为在本申请的公开范围之内。
以下结合实施例进一步说明本申请的有益效果。
实施例
一)集流体的准备
各实施例和对比例中的电极极片所用的集流体制备方法如下：
1、不具有保护层的集流体的制备：
选取一定厚度的支撑层，在其表面通过真空蒸镀、机械辊轧或粘结的方式形成一定厚度的导电层。
其中，
(1)真空蒸镀方式的形成条件如下：将经过表面清洁处理的支撑层置于真空镀室内，以1600℃至2000℃的高温将金属蒸发室内的高纯金属丝熔化蒸发，蒸发后的金属经过真空镀室内的冷却系统，最后沉积于支撑层的表面，形成导电层。
(2)机械辊轧方式的形成条件如下：将导电层材料的箔片置于机械辊中，通过施加20t至40t的压力将其碾压为预定的厚度，然后将其置于经过表面清洁处理的支撑层的表面，最后将两者置于机械辊中，通过施加30t至50t的压力使两者紧密结合。
(3)粘结方式的形成条件如下：将导电层材料的箔片置于机械辊中，通过施加20t至40t的压力将其碾压为预定的厚度；然后在经过表面清洁处理的支撑层的表面涂布PVDF与NMP的混合溶液；最后将上述预定厚度的导电层粘结于支撑层的表面，并于100℃下烘干。
2、具有保护层的集流体的制备：
制备具有保护层的集流体有如下几种方式：
(1)先通过气相沉积法或涂布法在支撑层表面设置保护层，然后通过真空蒸镀、机械辊轧或粘结的方式，在上述具有保护层的支撑层表面形成一定厚度的导电层，以制备具有保护层的集流体(保护层位于支撑层与导电层之间)；此外，也可在上述基础上，再在导电层的远离支撑层方向的表面上通过气相沉积法、原位形成法或涂布法形成另外一层保护层，以制备具有保护层的集流体(保护层位于导电层的两个相对的表面)；
(2)先通过气相沉积法、原位形成法或涂布法在导电层的一个表面上形成保护 层，然后通过机械辊轧或粘结的方式，将上述具有保护层的导电层设置于支撑层表面，且保护层设置于支撑层与导电层之间，以制备具有保护层的集流体(保护层位于支撑层与导电层之间)；此外，也可在上述基础上，再在导电层的远离支撑层方向的表面上通过气相沉积法、原位形成法或涂布法形成另外一层保护层，以制备具有保护层的集流体(保护层位于导电层的两个相对的表面)；
(3)先通过气相沉积法、原位形成法或涂布法在导电层的一个表面上形成保护层，然后通过机械辊轧或粘结的方式，将上述具有保护层的导电层设置于支撑层表面，且保护层设置于导电层的远离支撑层的表面上，以制备具有保护层的集流体(保护层位于导电层的远离支撑层的表面)；
(4)先通过气相沉积法、原位形成法或涂布法在导电层的两个表面上形成保护层，然后通过机械辊轧或粘结的方式，将上述具有保护层的导电层设置于支撑层表面，以制备具有保护层的集流体(保护层位于导电层的两个相对的表面)；
(5)在上述“不具有保护层的集流体的制备”的基础上，再在导电层的远离支撑层方向的表面上通过气相沉积法、原位形成法或涂布法形成另外一层保护层，以制备具有保护层的集流体(保护层位于导电层的远离支撑层的表面)。
在制备实例中，气相沉积法采用真空蒸镀方式，原位形成法采用原位钝化方式，涂布法采用刮刀涂布方式。
真空蒸镀方式的形成条件如下：将经过表面清洁处理的样品置于真空镀室内，以1600℃至2000℃的高温将蒸发室内的保护层材料熔化蒸发，蒸发后的保护层材料经过真空镀室内的冷却系统，最后沉积于样品的表面，形成保护层。
原位钝化法的形成条件如下：将导电层置于高温氧化环境中，温度控制在160℃至250℃，同时在高温环境中维持氧气供应，处理时间为30min，从而形成金属氧化物类的保护层。
凹版涂布方式的形成条件如下：将保护层材料与NMP进行搅拌混合，然后在样品表面涂布上述保护层材料的浆料(固含量为20％至75％)，其次用凹版辊控制涂布的厚度，最后在100℃至130℃下进行干燥。
二)电极活性材料层的区域分布对电极极片平整性的影响
下面说明在本申请的实施方式中，电极活性材料层的不同的涂布方式对于电极极片平整性的影响。本申请分别比较了以下3种不同类型的正极极片的平整度。
1)分区涂布的正极极片：
采用的复合集流体为：10μm的PET的两个表面上分别气相沉积有1μm厚的Al金属层。
将92wt％正极活性材料NCM333、5wt％导电剂Super-P(简称“SP”)和3wt％PVDF，以NMP为溶剂，搅拌均匀配成正极活性材料层浆料。
在复合集流体的两个表面通过挤压涂布进行分区涂布，即中间为高涂布重量区域，两边为低涂布重量区域(可通过挤压垫片或挡板实现)，在85℃下烘干。其中，高涂布重量区域宽度为4cm，低涂布重量区域宽度均为2.1cm。
然后进行冷压、切割，再在85℃真空条件下烘干4小时，焊接极耳，得到正极极 片。
高涂布重量区域的压实密度为3.45g/cm 3，低涂布重量区域的压实密度均为3.3g/cm 3。
压实密度测试方法：首先裁取面积为S的集流体小圆片30片测量其重量及厚度，求取重量平均值m 1及高度平均值H 1，再裁取面积为S的极片小圆片30片，求取重量平均值m 2及高度平均值H 2，则：
压实密度＝(m 2-m 1)/((H 2-H 1)*S)
2)均匀涂布的对比正极极片：
集流体同样采用上面提到的10μm厚PET镀Al复合集流体，类似于上面的正极极片的制备方法进行制备，但是将正极活性材料层浆料直接均匀涂布到复合集流体的两个表面上，即不进行分区处理，再经后处理得到均匀涂布的对比正极极片。正极活性材料层的压实密度为：3.4g/cm 3。
3)常规正极极片
集流体是厚度为12μm的金属Al箔片，类似于上面对比正极极片的制备方法，将正极活性材料层浆料直接均匀地涂布到Al箔片集流体的两个表面上，再经后处理得到常规正极极片。
对以上3种不同的极片测量极片平整度。极片平整度的测试是通过测量极片相对于参考平面的弧高来表征的。弧高的具体测量方法如下：
取长度为2m的电极极片样品，将样品置于参考平面上并沿着该平面的宽度方向展开，该平面的宽度略小于电极极片样品的长度，然后在样品的两边各放置一个重量相等(1Kg)的重物，以使样品与该平面紧贴。然后用软尺测量样品中间位置高出该平面的高度，该高出的高度即为弧高。实际生产中，一般认为弧高小于等于2mm的极片是平整的，组装成电池时可以实现正负极片的精确对准。
下表为具体测量结果：
极片 弧高
分区涂布的正极极片 小于2mm
均匀涂布的对比正极极片 大于5mm
常规正极极片 小于2mm
根据上表的测量结果可知，采用金属集流体的常规正极极片是满足极片平整度要求的(弧高小于或等于2mm)，可以实现电池组装时的精确对准。而按照常规工艺对于复合集流体进行均匀涂布，则极片的弧高较大(大于5mm)，极片平整度不好，在电池组装时难以实现精确对准。而采用本申请的分区涂布工艺后，弧高明显降低，达到与常规极片近似的程度，可以实现电池组装时的精确对准。这说明，采用活性材料 层分区涂布的特殊设计，可以消除或降低含有复合集流体的电极极片在辊压之后可能产生的边缘翘曲和弧度，提高极片平整度，从而实现电池组装时的精确对准，同时可以使电池具有复合集流体所带来的优异的电化学性能和安全性能。
三)电极极片的其他结构和组成等因素对于改善电池的电化学性能的作用
下面说明电极极片的结构和组成(例如集流体的组成、导电底涂层的存在、电极活性材料层的厚度和组成等)对于电池性能的影响。
需注意的是，下面使用复合集流体制备极片的实施例中采用了活性材料层分区涂布的方式来保证最终极片的平整度和电化学性能测量结果的准确性，但是本领域技术人员可以明白：活性材料层分区涂布并非实现平整极片的唯一方式，本领域技术人员也可以采用其他替代方式来得到平整的极片。
1、极片的制备：
1)实施例的正极极片(两次涂布)：
采用两次涂布法涂布具有下层正极活性材料层(内侧区域)和上层正极活性材料层(外侧区域)的正极极片。
采用一定配比的导电剂(如导电炭黑)、粘结剂(如PVDF或聚丙烯酸等)和可选的正极活性材料溶于适当的溶剂中(例如NMP或水中)，搅拌均匀配成底涂浆料。
将底涂浆料(即下层正极活性材料层浆料)均匀双面涂覆于按照上述方法制备的复合集流体上，涂布速度20m/min，并对底涂层进行干燥，烘箱温度为70～100℃，烘干时间为5min。
待底涂层(即下层正极活性材料层)完全干燥后，再将92wt％正极活性材料(未指明具体材料的情况下，缺省使用NCM333)、5wt％导电剂Super-P(简称“SP”)和3wt％PVDF，以NMP为溶剂，搅拌均匀配成上层浆料(某些实施例的活性材料层浆料组成可能有所变化，此时以该实施例中特别注明的为准)，采用挤压涂布将上层浆料分区涂布于干燥的底涂层表面；在85℃下烘干后得到正极活性材料层。
然后对带有各涂层的集流体进行冷压，然后切割，再在85℃真空条件下烘干4小时，焊接极耳，得到正极极片。
2)实施例的正极极片(单次涂布)：
类似于上面实施例的正极极片(两次涂布)的制备方法进行制备，但是其中将上层浆料直接分区涂布到复合集流体的表面上，而不设置下层正极活性材料层(底涂层)。
3)常规正极极片：
集流体是厚度为12μm的Al箔片，类似于上面正极极片(单次涂布)的制备方法，将上层浆料直接均匀涂布到Al箔片集流体的表面上，再经后处理得到常规正极极片。
4)常规负极极片：
将负极活性物质人造石墨、导电剂Super-P、增稠剂CMC、粘接剂SBR按质量比96.5:1.0:1.0:1.5加入到溶剂去离子水中混合均匀制成负极活性材料层浆料；采用挤压涂布将负极活性材料层浆料均匀涂布于厚度为8μm的Cu箔片(负极集流体)两面；在 85℃下烘干后得到负极活性材料层，再经后处理得到常规负极极片。
以上正极极片的制备过程中，对于复合集流体，为了能得到平整的极片采用本申请所述的分区涂布方式进行活性材料浆液的涂布，其中分区涂布的具体参数设置，例如各区域宽度和压实密度等，采用类似于前面“分区涂布的正极极片”部分所述的设置。
2、电池的制备：
通过常规的电池制作工艺，将正极极片(压实密度：3.4g/cm 3)、PP/PE/PP隔膜和负极极片(压实密度：1.6g/cm 3)一起卷绕成电极组件，然后置入电池壳体中，注入电解液(EC:EMC体积比为3:7，LiPF 6为1mol/L)，随之进行密封、化成等工序，最终得到锂离子二次电池(以下简称电池)。
3、电池测试方法：
1)锂离子电池循环寿命测试方法：
将锂离子电池于45℃下进行充放电，即先以1C的电流充电至4.2V，然后再以1C的电流放电至2.8V，记录下第一周的放电容量；然后使电池进行1C/1C充放电循环1000周，记录第1000周的电池放电容量，将第1000周的放电容量除以第一周的放电容量，得到第1000周的容量保有率。
2)DCR增长率的测试方法：
在25℃下，以1C电流将二次电池调整至50％SOC，记录电压U1。然后以4C电流放电30秒，记录电压U2。DCR＝(U1-U2)/4C。然后使电池进行1C/1C充放电循环500周，记录第500周的DCR，将第500周的DCR除以第一周的DCR并减1，得到第500周的DCR增长率。
3)针刺测试：
将二次电池(10个样品)以1C电流满充至充电截止电压，再恒压充电至电流降至0.05C，停止充电。用φ8mm的耐高温钢针，以25mm/s的速度，从垂直于电池极板的方向贯穿，贯穿位置宜靠近所刺面的几何中心，钢针停留在电池中，观察电池是否有燃烧、爆炸现象。
4、测试结果和讨论：
4.1复合集流体在改善电池重量能量密度方面的作用
各实施例的集流体及其极片具体参数如表1所示(表1中所列各实施例的集流体均未设置保护层)。在表1中，集流体重量百分数是指单位面积正极集流体重量除以单位面积常规正极集流体重量的百分数。
表1
Figure PCTCN2019129354-appb-000001
Figure PCTCN2019129354-appb-000002
根据表1可知，本申请采用的正极集流体的重量相对于传统的集流体(Al，12μm)都得到了不同程度的减轻，从而可提升电池的重量能量密度。不过当导电层的厚度大于1.5μm以后，对于集流体的减重改善程度变小。
另外，还考察了复合集流体对于改善电池穿钉安全的作用。测试的正极极片组成见下表1-1(其中各极片采用了单次涂布)，穿钉实验结果见表1-2。
表1-1
Figure PCTCN2019129354-appb-000003
表1-2
电池编号 正极极片 负极极片 穿钉实验结果
电池60 常规正极极片 常规负极极片 全部不通过
电池61 正极极片11 常规负极极片 全部通过
电池62 正极极片12 常规负极极片 全部通过
电池63 正极极片13 常规负极极片 全部通过
电池64 正极极片14 常规负极极片 全部通过
电池65 正极极片15 常规负极极片 全部通过
电池66 正极极片16 常规负极极片 全部通过
采用复合集流体的锂离子电池，由于导电层较传统的金属集流体薄，在穿钉等异常情况下产生的金属毛刺较小，且复合集流体的支撑层具有较大的短路电阻，因此有利于改善电池的穿钉安全性能。从上表中可以看出，常规电池在穿钉情况下会发生热失控和毁坏，不能通过穿钉安全测试。而采用了复合集流体的锂离子电池，均可以通过穿钉安全测试。
4.2保护层在改善复合集流体的电化学性能方面的作用
在表1中所列各实施例的集流体基础上，进一步形成保护层，以便研究保护层对于改善复合集流体的电化学性能方面的作用。表2中“正极集流体2-1”表示在表1中“正极集流体2”的基础上形成保护层所得集流体，其它集流体的编号含义类似。
表2
Figure PCTCN2019129354-appb-000004
表3示出了以表2中所列极片(单次涂布)组装成电池后测得的循环性能数据。
表3
Figure PCTCN2019129354-appb-000005
如表3所示，与采用常规的正极极片和常规的负极极片的电池1相比，采用复合集流体的电池的循环寿命良好，与常规的电池的循环性能相当。尤其是含有保护层的集流体制成的电池，相对于不含保护层的集流体制成的电池，其电池的容量保有率可进一步获得提升，说明电池的可靠性更好。
4.3底涂层(即内侧区域)在改善电池的电化学性能方面的作用
本实施例中采用了双层涂布法来在集流体上形成电极活性材料层来形成极片。因此，电极活性材料层分成了内侧区域(可称为“下层电极活性材料层”)和外侧区域(可称为“上层电极活性材料层”)两部分。由于下层活性材料层导电剂含量高于上层活性 材料层的导电剂含量，所以下层电极活性材料层亦可以称之为导电底涂层(或简称底涂层)。
下面说明底涂层、以及底涂层的组成等因素对于改善电池的电化学性能方面的作用。表4示出了各个实施例和对比例的电池以及其中采用的电极极片和集流体的具体组成和相关参数。表5示出了各电池的性能测量结果。
表4
Figure PCTCN2019129354-appb-000006
Figure PCTCN2019129354-appb-000007
表5
Figure PCTCN2019129354-appb-000008
从以上测试数据可以看出：
1)采用导电层较薄的复合集流体时(即没有采用双层涂布法涂布而不含导电底涂层的对比正极极片20)，由于复合集流体导电能力较传统的金属集流体差、且复合集流体中的导电层易于破损等缺点，电池的DCR较大、循环容量保持率较低。而在通过双层涂布法引入了导电底涂层后，导电底涂层通过有效修补并构筑集流体、导电底涂层与活性物质间的导电网络，提高电子传输效率，降低集流体与电极活性材料层之间的电阻，从而可以有效降低DCR。
2)随着导电底涂层中的导电剂含量的提高(正极极片21至26)，电池的DCR可得到较大程度的改善。
3)在相同的组成下，水性粘结剂的引入较油性粘结剂可使得DCR的改善程度更明显(正极极片24vs.正极极片27以及正极极片25vs.正极极片28)。
4)由于片状石墨可产生“水平滑动”，从而起到缓冲作用，减少压实过程中对集流体 的导电层的破坏，从而减少裂纹，因此片状石墨的引入可进一步降低电池DCR(正极极片24vs.正极极片29)。
5)随着导电底涂层的厚度的增大(正极极片30至正极极片32)，电池的DCR也可得到更明显的改善。但是若导电底涂层的厚度过大，则不利于电池的能量密度的改进。
4.4底涂层中电极活性材料的影响
上面的实施例中，为了研究的方便，所有底涂层中未加入电极活性材料。下面测试在底涂层中引入正极活性材料后对于电池性能的影响。具体极片组成和电池组成见表6、表7。
表6
Figure PCTCN2019129354-appb-000009
表7
Figure PCTCN2019129354-appb-000010
Figure PCTCN2019129354-appb-000011
从以上测试数据可以看出：无论底涂层是否含有电极活性材料，底涂层的引入都可以有效修补并构筑集流体、导电底涂层与活性物质间的导电网络，提高电子传输效率，降低集流体与电极活性材料层之间的电阻，从而可以有效降低DCR。
4.5电极活性材料层膜片电阻对于改善电池电化学性能方面的作用
使用前述集流体来制备正极极片，调整活性材料层的组成，以期调整膜片电阻，将所得正极极片(活性材料层单面厚度D4为55μm)与常规负极极片组装成电池，测量其穿钉性能和循环寿命。结果如下表所示。
表8
Figure PCTCN2019129354-appb-000012
*具体测试方法为：将锂离子电池于25℃下进行充放电，即先以0.5C的电流充电至4.2V，然后再以1C的电流放电至2.8V，记录下第一周的放电容量；然后使电池进行05C/1C充放电循环1000 周，记录第1000周的电池放电容量，将第1000周的放电容量除以第一周的放电容量，得到第1000周的容量保有率。
从以上测试结果可知，无论是否设置底涂层，当电极活性材料层的总厚度为不大于170μm且活性材料层的膜片电阻为0.1至10欧时，电池兼具良好的循环性能和良好的穿钉安全性能。尤其是当膜片电阻为0.6欧至0.9欧时，循环性能和穿钉安全性能都非常优异。
4.6电极活性材料层中的外侧区域的粘结剂的含量在改善电池的电化学性能方面的作用
内侧区域的底涂层粘结剂含量通常较高，因此底涂层与集流体之间的结合力较强。但是上层电极活性材料层(即外侧区域)与底涂层(即内侧区域)间的结合力受上层活性材料层中的粘结剂含量影响。为了使得在穿钉等异常情况下，整个电极活性材料层可有效地包裹导电层中产生的金属毛刺，以改善电池的穿钉安全性能，上层活性材料(即外侧区域)中的粘结剂含量优选应该高于一个下限值。
下面以从电池穿钉安全的角度来说明上层电极活性材料层中的粘结剂的含量在改善电池的电化学性能方面的作用。
按照前面实施例所述方法制备正极极片，但是调整上层浆料的组成，制得上层正极活性材料层中粘结剂含量不同的多个正极极片。具体极片组成见下表。
表9
Figure PCTCN2019129354-appb-000013
Figure PCTCN2019129354-appb-000014
表10
Figure PCTCN2019129354-appb-000015
表10示出了上述不同正极极片组装成电池时的穿钉测试结果。结果表明上层正极活性材料层中的粘结剂的含量越高时，相应电池的穿钉安全性能越好。优选地，基于上层活性材料层的总重量，上层正极活性材料层中的粘结剂含量不小于1wt％，更优选不小于1.5wt％，最优选不小于2wt％。
本领域技术人员可以理解：以上仅以锂电池为例示出了本申请的极片的应用实例，但是本申请的极片同样可以应用于其它类型的电化学装置，而仍然可以获得本申请的良好技术效果。
根据上述说明书的揭示和教导，本申请所属领域的技术人员还可以对上述实施方式进行适当的变更和修改。因此，本申请并不局限于上面揭示和描述的具体实施方式，对本申请的一些修改和变更也应当落入本申请的权利要求的保护范围内。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本申请构成任何限制。

Claims (11)

  1. 一种正极极片，包括集流体和设置于所述集流体至少一个表面上的电极活性材料层，其中，
    所述集流体包括支撑层和设置于所述支撑层至少一个表面上的导电层，所述导电层的单面厚度D2满足：30nm≤D2≤3μm，所述支撑层的厚度D1满足：1μm≤D1≤30μm，且所述支撑层为高分子材料或高分子复合材料；
    所述电极活性材料层包括电极活性材料、粘结剂和导电剂，所述电极活性材料层的总厚度D 总为不大于170μm，且所述电极活性材料层的膜片电阻为0.1欧至10欧。
  2. 根据权利要求1所述的正极极片，其中，所述电极活性材料层中的粘结剂含量不小于1wt％，优选不小于1.5wt％，更优选不小于2wt％。
  3. 根据权利要求1至2任一项所述的正极极片，其中，所述电极活性材料层中的粘结剂的含量在厚度方向上具有不均匀的组成状态，其中基于所述电极活性材料层的总重量，在所述电极活性材料层的靠近所述集流体的内侧区域中的粘结剂的重量百分含量高于所述电极活性材料层的远离所述集流体的外侧区域中的粘结剂的重量百分含量；
    优选基于所述电极活性材料层的外侧区域的总重量，所述外侧区域中的粘结剂的重量百分含量为1wt％～5wt％，和/或，
    优选基于所述电极活性材料层的内侧区域的总重量，所述内侧区域中的粘结剂的重量百分含量为1wt％～90wt％，更优选20wt％～80wt％，最优选为20wt％～50wt％。
  4. 根据权利要求1至3任一项所述的正极极片，其中，所述电极活性材料层中的导电剂的含量在厚度方向上具有不均匀的组成状态，其中基于所述电极活性材料层的总重量，在所述电极活性材料层的靠近所述集流体的内侧区域中的导电剂的重量百分含量高于所述电极活性材料层的远离所述集流体的外侧区域中的导电剂的重量百分含量，
    优选基于所述电极活性材料层的外侧区域的总重量，所述外侧区域中的导电剂的重量百分含量为0.5wt％～10wt％；
    优选基于所述电极活性材料层的内侧区域的总重量，所述内侧区域中的导电剂的重量百分含量为10wt％～99wt％，更优选20wt％～80wt％，最优选为50wt％～80wt％。
  5. 根据权利要求1至4任一项所述的正极极片，其中，所述导电层为金属导电层，所述金属导电层的材料优选铝、镍、钛、银、铝锆合金中的至少一种；和/或，
    所述支撑层的材料选自绝缘高分子材料、绝缘高分子复合材料、导电高分子材料、导电高分子复合材料中的至少一种，
    优选地，所述绝缘高分子材料选自聚酰胺、聚对苯二甲酸酯、聚酰亚胺、聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、芳纶、聚二甲酰苯二胺、丙烯腈-丁二烯-苯乙烯共聚物、聚对苯二甲酸丁二醇酯、聚对苯二甲酰对苯二胺、聚丙乙烯、聚甲醛、环氧树脂、酚醛树脂、聚四氟乙烯、聚苯硫醚、聚偏氟乙烯、硅橡胶、聚碳酸酯、纤维素及其衍生物、淀粉及其衍生物、蛋白质及其衍生物、聚乙烯醇及其交联物、聚乙二醇及其交 联物中的至少一种；
    优选地，所述绝缘高分子复合材料选自绝缘高分子材料与无机材料形成的复合材料，其中，所述无机材料优选陶瓷材料、玻璃材料、陶瓷复合材料中的至少一种，
    优选地，所述导电高分子材料选自聚氮化硫类高分子材料或经掺杂的共轭类高分子材料，更优选地，所述导电高分子材料选自聚吡咯、聚乙炔、聚苯胺、聚噻吩等中的至少一种；
    优选地，所述导电高分子复合材料选自绝缘高分子材料与导电材料形成的复合材料，更优选地，所述导电材料选自导电碳材料、金属材料、复合导电材料中的至少一种，所述导电碳材料选自碳黑、碳纳米管、石墨、乙炔黑、石墨烯中的至少一种，所述金属材料选自镍、铁、铜、铝或上述金属的合金中的至少一种，所述复合导电材料选自镍包覆的石墨粉、镍包覆的碳纤维中的至少一种；
    所述支撑层的材料优选为绝缘高分子材料或绝缘高分子复合材料。
  6. 根据权利要求1至5任一项所述的正极极片，其中，所述支撑层的厚度D1满足：1μm≤D1≤15μm；和/或，
    所述支撑层的常温杨氏模量E满足：20GPa≥E≥4GPa；和/或，
    所述导电层中有裂纹；和/或，
    所述电极活性材料的平均粒径D50为：5μm～15μm；和/或，
    所述导电层的单面厚度D2满足300nm≤D2≤2μm，更优选为500nm≤D2≤1.5μm。
  7. 根据权利要求1至6任一项所述的正极极片，其中，所述导电层表面还设置有保护层，所述保护层仅设置于所述集流体的导电层的一个表面上或设置于所述集流体的导电层的两个表面上；
    优选地，所述保护层的厚度D3满足：D3≤1/10D2且1nm≤D3≤200nm，优选10nm≤D3≤50nm。
  8. 根据权利要求1至7任一项所述的正极极片，其中，
    所述导电剂为导电碳材料、金属材料中的至少一种；其中，所述导电碳材料选自零维导电碳，优选为乙炔黑、导电炭黑；一维导电碳，优选为碳纳米管；二维导电碳，优选为导电石墨、石墨烯；三维导电碳，优选为还原后的氧化石墨烯中的至少一种；金属材料选自铝粉，铁粉以及银粉中的至少一种；
    优选的，内侧区域中的导电剂含有碳纳米管，更优选的内侧区域和外侧区域中的导电剂均含有碳纳米管；更优选的内侧区域中的导电剂为碳纳米管与导电炭黑的混合物；更优选的内侧区域和外侧区域中的导电剂均为碳纳米管与导电炭黑的混合物；
    所述粘结剂选自丁苯橡胶，油性聚偏氟乙烯(PVDF)，聚偏氟乙烯共聚物(如PVDF-HFP共聚物、PVDF-TFE共聚物)、羧甲基纤维素钠，聚苯乙烯，聚丙烯酸，聚四氟乙烯，聚丙烯腈、聚酰亚胺、水性PVDF、聚氨酯、聚乙烯醇、聚丙烯酸酯、聚丙烯酸-聚丙烯腈共聚物、聚丙烯酸酯-聚丙烯腈共聚物中的至少一种。
  9. 根据权利要求1至8任一项所述的正极极片，其中，从所述电极极片被涂布表面的宽度方向看，所述电极活性材料层基于压实密度包括2n+1个区域，且中间区域的压实密度高于两侧区域的压实密度；优选地，n＝1、2或3；更优选地，n＝1。
  10. 一种电化学装置，包括正极极片、负极极片、隔离膜和电解液，其中，所述正极极片为权利要求1至权利要求9中任一项所述的正极极片。
  11. 一种装置，其中，包括权利要求10所述的电化学装置。
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