WO2020098787A1 - 一种正极极片及电化学装置 - Google Patents

一种正极极片及电化学装置 Download PDF

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WO2020098787A1
WO2020098787A1 PCT/CN2019/118825 CN2019118825W WO2020098787A1 WO 2020098787 A1 WO2020098787 A1 WO 2020098787A1 CN 2019118825 W CN2019118825 W CN 2019118825W WO 2020098787 A1 WO2020098787 A1 WO 2020098787A1
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conductive
battery
pole piece
lithium
coating
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PCT/CN2019/118825
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English (en)
French (fr)
Inventor
李星
李振华
金海族
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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 US17/043,711 priority Critical patent/US11133564B2/en
Priority to EP19884550.5A priority patent/EP3796422B1/en
Publication of WO2020098787A1 publication Critical patent/WO2020098787A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/572—Means for preventing undesired use or discharge
    • H01M50/574—Devices or arrangements for the interruption of current
    • H01M50/581—Devices or arrangements for the interruption of current in response to temperature
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H01G11/28—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features arranged or disposed on a current collector; Layers or phases between electrodes and current collectors, e.g. adhesives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/66—Current collectors
    • H01G11/70—Current collectors characterised by their structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • 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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/10—Primary casings; Jackets or wrappings
    • H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
    • H01M50/103—Primary casings; Jackets or wrappings characterised by their shape or physical structure prismatic or rectangular
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H01M50/207—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape
    • H01M50/209—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape adapted for prismatic or rectangular cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/50—Methods or arrangements for servicing or maintenance, e.g. for maintaining operating temperature
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2200/00—Safety devices for primary or secondary batteries
    • H01M2200/10—Temperature sensitive devices
    • H01M2200/106—PTC
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the field of electrochemical technology. More specifically, the present application relates to a positive pole piece and an electrochemical device including the positive pole piece.
  • Lithium ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution.
  • lithium-ion batteries are susceptible to fire and explosion when they are subject to abnormal conditions such as crushing, collision, or puncture, causing serious harm. Therefore, the safety of lithium-ion batteries greatly limits the application and popularization of lithium-ion batteries.
  • PTC Positive Temperature Coefficient
  • a PTC material layer (safety coating) is separately provided between the current collector of the battery and the electrode active material layer.
  • the resistance of the PTC material layer increases, thereby increasing the resistance between the current collector and the electrode active material layer, or even powering off, thereby playing a safety role in preventing the electrochemical reaction from continuing.
  • the solvent such as NMP
  • the solvent in the slurry will dissolve the PTC material in the PTC layer and enter the upper active material layer, not only The PTC layer loses the PTC effect and deteriorates the electrical performance.
  • the PTC material layer is easily squeezed to the edge, causing the electrode active material layer to directly contact the current collector, thereby losing the effect of improving safety performance.
  • the performance of the PTC material layer such as response speed and current blocking effect, needs to be greatly improved.
  • An object of the present application is to provide a pole piece and an electrochemical device with improved safety and electrical performance.
  • the present application provides a positive electrode sheet including a current collector and a safety coating, an insoluble layer, and a positive electrode active material layer that are sequentially disposed on the current collector, the safety coating includes a polymer matrix, a conductive material, and an inorganic filler
  • the safety coating includes a polymer matrix, a conductive material, and an inorganic filler
  • the poorly soluble layer contains a binder and a conductive agent, and the solubility of the binder in the poorly soluble layer in an oily solvent is less than the solubility of the polymer matrix in the safety coating.
  • the binder in the insoluble layer is one of an oily binder or an aqueous binder
  • the oily binder is selected from oily polyacrylonitrile, oily polyacrylic acid, oily polyacrylate, At least one of oily polyacrylic acid-acrylate, oily polyacrylonitrile-acrylic acid, oily polyacrylonitrile-acrylic acid
  • the water-based binder is selected from water-based polyacrylic acid, water-based polyurethane, water-based polyvinyl alcohol, water-based polyacrylic acid At least one of ester, water-based polytetrafluoroethylene, water-based polyacrylonitrile.
  • the polymer matrix is fluorinated polyolefin and / or chlorinated polyolefin.
  • the weight percentage of the polymer matrix is 35wt% -75wt%, preferably 50wt% -75wt%; the weight percentage of the conductive material is 5wt% -25wt%, preferably 5wt% -20wt%; the weight percentage of the inorganic filler is 10wt% -60wt%, preferably 15wt% -45wt%.
  • the present application also provides an electrochemical device, which includes the positive pole piece of the present application, and the electrochemical device is preferably a capacitor, a primary battery, or a secondary battery.
  • FIG. 1 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application, wherein 10—current collector; 12—safety coating (ie, PTC safety coating); 13—insoluble layer; 14—positive electrode active material layer.
  • 10 current collector
  • 12 safety coating (ie, PTC safety coating)
  • 13 insoluble layer
  • 14 positive electrode active material layer.
  • FIG. 2 is a perspective view of an embodiment of a lithium ion battery.
  • FIG. 3 is an exploded view of FIG. 2.
  • FIG. 4 is a perspective view of an embodiment of a battery module.
  • FIG. 5 is a perspective view of an embodiment of a battery pack.
  • Fig. 6 is an exploded view of Fig. 5.
  • FIG. 7 is a schematic diagram of an embodiment of a device using a lithium ion battery as a power source.
  • the present application discloses a positive pole piece, which includes a current collector and a safety coating, an insoluble layer and a positive electrode active material layer sequentially arranged on the current collector, the safety coating includes a polymer matrix, a conductive material and an inorganic filler
  • the poorly soluble layer contains a binder and a conductive agent, and the solubility of the binder in the poorly soluble layer in an oily solvent is less than the solubility of the polymer matrix in the safety coating.
  • FIG. 1 shows a schematic structural view of a positive electrode sheet according to some embodiments of the present application, where 10—current collector; 12—safety coating (ie, PTC safety coating); 13—insoluble layer; 14—positive electrode active material Floor.
  • 10 current collector
  • 12 safety coating (ie, PTC safety coating)
  • 13 insoluble layer
  • 14 positive electrode active material Floor.
  • FIG. 1 shows that the PTC safety coating layer 12, the insoluble layer 13 and the positive electrode active material layer 14 are provided only on one side of the positive electrode current collector 10, in other embodiments, the positive electrode collector
  • the fluid 10 may be provided with a PTC safety coating layer 12, a poorly soluble layer 13, and a positive electrode active material layer 14 on both sides.
  • Traditional coatings with PTC effect used in batteries usually include a polymer matrix and conductive materials.
  • polyethylene, polypropylene or ethylene propylene copolymers are usually used as PTC matrix materials; in this case, the PTC matrix Additional binder is added to materials and conductive materials. If the binder content is too small, the adhesion between the coating and the current collector will be poor. If the binder content is too large, it will affect the response temperature and response speed of the PTC effect. .
  • the solvent such as NMP, etc.
  • electrolyte in the positive electrode active material layer on the upper layer of the safety coating will cause dissolution, swelling and other defects of the polymer material in the safety coating
  • the safety coating will be damaged, affecting the performance of the PTC effect.
  • the inorganic filler is equivalent to a barrier substance, which is beneficial to eliminate the above-mentioned adverse effects of dissolution and swelling, and is conducive to stabilizing the safety coating.
  • the addition of inorganic fillers also helps to ensure that the safety coating is not easily deformed during the compaction of the pole piece. Therefore, the addition of the inorganic filler can ensure that the safety coating is stably located between the current collector and the positive electrode active material layer, preventing direct contact between the current collector and the positive electrode active material layer, thereby improving the safety performance of the battery.
  • the inorganic filler can play the role of stabilizing the safety coating from the following two aspects: (1) hinder the solvent (usually organic oily solvent, such as NMP, etc.) in the positive electrode active material layer or the electrolyte to the safety coating
  • the high molecular material has the adverse effects of dissolution and swelling; (2) It is helpful to ensure that the safety coating is not easily deformed during the compaction of the pole piece.
  • the inventor also unexpectedly found that inorganic fillers can also improve the performance of the safety coating, such as response speed.
  • the working principle of the safety coating is: at normal temperature, the safety coating relies on a good conductive network formed between the conductive materials to conduct electron conduction; when the temperature increases, the volume of the polymer matrix material begins to expand, and between the particles of the conductive material As the spacing increases, the conductive network is partially blocked, and the resistance of the safety coating gradually increases; when a certain temperature (such as actuation temperature) is reached, the conductive network is almost completely blocked, and the current approaches zero.
  • the conductive network is partially restored, so after reaching a certain temperature (such as the operating temperature), the resistance of the safety coating is not as large as expected, and it is still There is very little current.
  • the inorganic filler may be at least one selected from the group consisting of metal oxides, non-metal oxides, metal carbides, non-metal carbides, and inorganic salts, or the conductive carbon coating modification and conductive metal coating modification of the above materials At least one of the modified or conductive polymer coating modified material.
  • Adding inorganic fillers to the safety coating can help the safety coating resist the damage of solvents or electrolytes. On this basis, it is also possible to further eliminate the influence caused by the solvent or electrolyte by introducing a structural layer with barrier properties between the safety coating and the positive electrode active material layer.
  • Such a structural layer needs to include a conductive agent to maintain the electrical conductivity of the pole piece, and also needs to include an adhesive to maintain the structural integrity.
  • the solubility of the binder in this structural layer in the organic oily solvent must be less than the solubility of the polymer matrix in the safety coating in the organic oily solvent, in order to further eliminate the solvent or electrolyte on the safety coating.
  • the polymer matrix such as fluorinated polyolefin and / or chlorinated polyolefin
  • organic oily solvents such as NMP, etc.
  • the polymer matrix such as fluorinated polyolefin and / or chlorinated polyolefin
  • organic oily solvents such as NMP, etc.
  • this structural layer may include a conductive agent and a binder, and preferably consists essentially of the conductive agent and the binder.
  • this structural layer may be referred to as a "barrier layer" or "insoluble layer”.
  • the oily binder is preferably at least one selected from the group consisting of oily polyacrylonitrile, oily polyacrylic acid, oily polyacrylate, oily polyacrylic acid-acrylate, oily polyacrylonitrile-acrylic acid, and oily polyacrylonitrile-acrylate;
  • the water-based binder is at least one selected from water-based polyacrylic acid, water-based polyurethane, water-based polyvinyl alcohol, water-based polyacrylate, water-based polytetrafluoroethylene, and water-based polyacrylonitrile.
  • the positive electrode sheet includes a safety coating, a poorly soluble layer (barrier layer) and a positive electrode active material layer that are sequentially coated on the current collector, and the safety coating includes a polymer matrix , A conductive material and an inorganic filler, the poorly soluble layer includes a conductive agent and a binder whose solubility in an oily solvent (preferably NMP) is less than the solubility of the polymer matrix in the safety coating.
  • an oily solvent preferably NMP
  • the insoluble layer acts as a barrier to hinder the fluorinated polyolefins and / or chlorine in the safety coating
  • organic oily solvents such as NMP, etc.
  • the safety coating of the positive electrode sheet of the present application includes a polymer matrix, a conductive material and an inorganic filler. Its function principle is: at normal temperature, the safety coating relies on a good conductive network formed between conductive materials to conduct electronic conduction; when the temperature increases, the volume of the polymer matrix material starts to expand, and the spacing between the conductive material particles increases , The conductive network is partially blocked, the resistance of the safety coating gradually increases; and when a certain temperature (such as the operating temperature) is reached, the conductive network is almost completely blocked, and the current approaches zero, thereby protecting the use of the safety coating Electrochemical device.
  • the safety coating of the positive electrode sheet of the present application can be formed by conventional methods. For example, by dissolving the polymer matrix material, conductive material, inorganic filler and optional other additives in a solvent and stirring to form a slurry, and then coating the slurry on the current collector, heating and drying to obtain Safety coating is required.
  • the safety coating of the positive electrode sheet of the present application may be substantially composed of the polymer matrix, conductive material and inorganic filler, that is, not containing a significant amount (for example, content ⁇ 3% , ⁇ 1%, or ⁇ 0.5%), and the polymer matrix is a fluorinated polyolefin or chlorinated polyolefin material.
  • the safety coating directly adheres to the current collector and is arranged between the current collector and the insoluble layer.
  • the thickness H of the safety coating can be reasonably determined according to actual needs.
  • the thickness H of the safety coating is generally not more than 40 ⁇ m, preferably not more than 25 ⁇ m, and more preferably not more than 20 ⁇ m, 15 ⁇ m or 10 ⁇ m.
  • the coating thickness of the safety coating layer is usually 1 ⁇ m or more, preferably 2 ⁇ m or more, and more preferably 3 ⁇ m or more. If the thickness is too small, it is not enough to ensure the effect of the safety coating on improving the safety performance of the battery; if it is too large, it will cause the internal resistance of the battery to increase seriously, thereby affecting the electrochemical performance of the battery during normal operation.
  • the bonding force between the safety coating and the current collector is preferably equal to or greater than 10 N / m.
  • the bonding force between the safety coating and the current collector can be increased by introducing an additional binder or by cross-linking the polymer matrix. The larger bonding force can better improve the safety performance of the pole piece through the nail.
  • the weight percentage of the polymer matrix is 35wt% -75wt%, preferably 40wt% -75wt%, more preferably 50wt% -75wt%.
  • the polymer matrix material as a safety coating can be polyolefin material or other polymer materials, such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer Materials, polyamide, polystyrene, polyacrylonitrile, thermoplastic elastomer, epoxy resin, polyacetal, thermoplastic modified cellulose, polysulfone, polymethyl (meth) acrylate, including (meth) acrylate Copolymers, etc.
  • the safety coating additionally contains a binder for enhancing the adhesion between the polymer matrix material and the current collector.
  • the binder may be, for example, PVDF, PVDC, SBR, etc., or may be selected from CMC, polyacrylate, polycarbonate, polyethylene oxide, rubber, polyurethane, sodium carboxymethyl cellulose, polyacrylic acid, Aqueous binders such as acrylonitrile multi-component copolymers, gelatin, chitosan, sodium alginate, coupling agents, cyanoacrylates, polymeric cyclic ether derivatives, and hydroxyl derivatives of cyclodextrin.
  • CMC polyacrylate, polycarbonate, polyethylene oxide, rubber, polyurethane, sodium carboxymethyl cellulose, polyacrylic acid
  • Aqueous binders such as acrylonitrile multi-component copolymers, gelatin, chitosan, sodium alginate, coupling agents, cyanoacrylates, polymeric cyclic ether derivatives, and hydroxyl derivatives of cyclodextrin.
  • polyethylene, polypropylene or ethylene propylene copolymers are usually used as PTC matrix materials.
  • an additional binder needs to be added to the PTC matrix material and the conductive material. If the binder content is too small, the adhesion between the coating and the current collector will be poor. If the binder content is too large, the PTC effect will be affected. The response temperature and response speed and other performance.
  • fluorinated polyolefin or chlorinated polyolefin can be used as a polymer matrix material for safety coating, the amount of which (for example, 35wt% -75wt% relative to the total weight of the safety coating) is much higher than that of fluorination
  • the amount of polyolefin or chlorinated polyolefin used as a binder (usually less than 15% or less than 10% relative to the total weight of the coating).
  • the fluorinated polyolefin and / or chlorinated polyolefin material actually plays two roles, serving as both a PTC matrix and a binder. In this way, the influence of the adhesive on the coating, the response temperature and the response speed of the PTC effect due to the difference between the binder and the PTC matrix material are avoided.
  • the safety coating composed of fluorinated polyolefin and / or chlorinated polyolefin material and conductive material can play the role of PTC thermistor layer, the operating temperature range is appropriate, can be 80 °C to 160 °C, so it can be very Improve the high temperature safety performance of the battery.
  • the fluorinated polyolefin and / or chlorinated polyolefin used as the polymer matrix material of the safety coating can be used as both the PTC matrix and the binder, thereby also facilitating the preparation of thinner safety coatings without affecting The adhesion of the safety coating.
  • the solvent (such as NMP, etc.) or electrolyte in the positive electrode active material layer on the upper layer of the safety coating will have adverse effects on the dissolution and swelling of the polymer material in the safety coating.
  • PVDF safety coatings it is easy to cause poor adhesion; for safety coatings with a high content of fluorinated polyolefins and / or chlorinated polyolefins, such adverse effects can be relatively small.
  • the polymer matrix is preferably a fluorinated polyolefin and / or chlorinated polyolefin, namely polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), modified PVDF, and / or modified PVDC.
  • the polymer matrix may be selected from PVDF, carboxylic acid modified PVDF, acrylic modified PVDF, PVDF copolymer, PVDC, carboxylic acid modified PVDC, acrylic modified PVDC, PVDC copolymer or their Any mixture.
  • the fluorinated polyolefin and / or chlorinated polyolefin polymer based on the total weight of the safety coating (or based on the total weight of the polymer matrix, conductive material and inorganic filler), the fluorinated polyolefin and / or chlorinated polyolefin polymer
  • the weight percentage of the matrix is 35wt% -75wt%. If the content is too small, the PTC effect of the safety coating cannot be well guaranteed; if the content is too high, the performance of the safety coating, such as response speed, may be affected.
  • the weight percentage of the fluorinated polyolefin and / or chlorinated polyolefin polymer matrix is preferably 40 wt% to 75 wt%, and more preferably 50 wt% to 75 wt%.
  • the fluorinated polyolefin and / or chlorinated polyolefin polymer matrix materials used in the safety coating of the positive electrode sheet of this application these materials themselves have good adhesion in addition to being used as matrix materials It can be used as a binder; therefore, when using this type of polymer matrix material, the safety coating does not need to use other additional binders, which can simplify the process and save costs. Therefore, in a preferred embodiment of the present application, the polymer matrix is a fluorinated polyolefin and / or chlorinated polyolefin, and the safety coating is substantially free of other binders than the polymer matrix material ( "Substantially free" means content ⁇ 3%, ⁇ 1%, or ⁇ 0.5%).
  • the polymer matrix is at least partially cross-linked, that is, it contains a polymer matrix material with a cross-linked structure, preferably a fluorinated polyolefin and / or chlorine with a cross-linked structure Chemical polyolefin.
  • Cross-linking treatment can be more conducive to hindering the negative effects of solvents (such as NMP, etc.) or electrolytes in the positive electrode active material layer on the polymer materials in the safety coating, such as dissolution and swelling, and preventing the positive electrode active material due to uneven stress Cracking of the layer;
  • solvents such as NMP, etc.
  • electrolytes in the positive electrode active material layer on the polymer materials in the safety coating, such as dissolution and swelling, and preventing the positive electrode active material due to uneven stress Cracking of the layer;
  • the cross-linking treatment can be achieved by introducing an activator and a cross-linking agent.
  • a strong alkali weak acid salt such as sodium silicate or potassium silicate can be used.
  • the weight ratio of the activator to the polymer matrix is usually 0.5% to 5%.
  • the crosslinking agent may be selected from polyisocyanates (JQ-1, JQ-1E, JQ-2E, JQ-3E, JQ-4, JQ-5, JQ-6, PAPI, emulsifiable MDI, tetraisocyanate) , Polyamines (propylene diamine, MOCA), polyols (polyethylene glycol, polypropylene glycol, trimethylolpropane), glycidyl ether (polypropylene glycol glycidyl ether), inorganic substances (zinc oxide, chloride Aluminum, aluminum sulfate, sulfur, boric acid, borax, chromium nitrate), glyoxal, aziridine, silicones (ethyl orthosilicate, methyl orthosilicate, trimethoxysilane), benzenesulfonic acid ( P-toluenesulfonic acid, p-toluenesulfonyl chloride), ethy
  • the weight ratio of the cross-linking agent to the polymer matrix is 0.01% to 5%. Too little cross-linking agent, the degree of cross-linking of the polymer matrix is low, can not completely eliminate cracking. Too much cross-linking agent may cause gelation during stirring.
  • the activator and the cross-linking agent can be added after the slurry for preparing the safety coating is stirred, and after the cross-linking reaction is performed, the coating is evenly stirred to prepare a safety coating.
  • the weight percentage of the inorganic filler is usually 10% to 60% by weight relative to the total weight of the total weight of the polymer matrix, the conductive material and the inorganic filler. If the content of inorganic filler is too small, it is not enough to stabilize the safety coating; if the content is too large, it will affect the PTC performance of the safety coating.
  • the weight percentage of the inorganic filler is preferably 15% to 45% by weight.
  • the average particle diameter D of the inorganic filler in the safety coating satisfies 100 nm ⁇ D ⁇ 10 ⁇ m, and more preferably 1 ⁇ m ⁇ D ⁇ 6 ⁇ m.
  • the specific surface area (BET) of the inorganic filler in the safety coating layer is not more than 500 m 2 / g.
  • the specific surface area of the inorganic filler When the specific surface area of the inorganic filler is increased, side reactions will increase and affect the performance of the battery; and when the specific surface area of the inorganic filler is too large, a higher proportion of binder needs to be consumed, which will cause a gap between the safety coating and the current collector and positive electrode active material layer The cohesive force is reduced, and the internal resistance growth rate is higher.
  • the specific surface area (BET) of the inorganic filler is not greater than 500 m2 / g, it can provide a better overall effect.
  • the inorganic filler is selected from at least one of metal oxides, non-metal oxides, metal carbides, non-metal carbides, and inorganic salts, or conductive carbon coating modification, conductive metal coating modification of the above materials or The conductive polymer coats at least one of the modified materials.
  • the inorganic filler may be selected from magnesium oxide, alumina, titania, zirconia, silica, silicon carbide, boron carbide, calcium carbonate, aluminum silicate, calcium silicate, potassium titanate, barium sulfate, cobalt acid Lithium, lithium manganate, lithium nickelate, lithium nickel manganate, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, silicic acid At least one of lithium vanadium, lithium cobalt silicate, lithium manganese silicate, lithium titanate, or the conductive carbon coating modification, conductive metal coating modification or conductive polymer coating modification of the above materials At least one.
  • the inorganic filler In addition to the above-mentioned role of stabilizing the safety coating (impeding the dissolution and swelling of the organic solvent on the polymer material and ensuring that the safety coating is not easily deformed) and improving the response speed of the safety coating, the inorganic filler In addition to performance, it can also play the following two roles: (1) improve the overcharge performance of the battery: PTC safety coating system composed of fluorinated polyolefin and / or chlorinated polyolefin polymer matrix and conductive material
  • the electrochemically active material has the characteristics of intercalating and deintercalating lithium ions, at the normal operating temperature of the battery, the electrochemically active material can be used as the "active site" participating in the conductive network, that is, the "active site” in the safety coating Increased, in the process of overcharging, electrochemically active materials will delithium and become more and more difficult to delithium, and the impedance continues to increase, so when the current passes, the heat generation power increases, and the temperature of the primer
  • the material of the positive electrode electrochemically active material or the conductive carbon coating modification of the positive electrode electrochemically active material, the conductive metal coating modification or the conductive polymer coating modification is used as the safety coating Inorganic fillers are the most preferred.
  • the positive electrode electrochemically active material is preferably selected from lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron manganese phosphate, silicic acid Lithium iron, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganate, spinel lithium nickel manganate, lithium titanate, or their conductive carbon coating modified materials, At least one of a conductive metal-coated modified material or a conductive polymer-coated modified material.
  • these electrochemically active materials modified by conductive carbon coating such as conductive carbon coated modified lithium cobalt oxide, conductive carbon coated modified nickel manganese lithium cobalt oxide, conductive carbon coated modified nickel manganese Lithium aluminate, conductive carbon coated modified lithium iron phosphate, conductive carbon coated modified lithium vanadium phosphate, conductive carbon coated modified lithium cobalt phosphate, conductive carbon coated modified lithium manganese phosphate, conductive carbon Coated modified lithium iron manganese phosphate, conductive carbon coated modified lithium iron silicate, conductive carbon coated modified lithium vanadium silicate, conductive carbon coated modified lithium cobalt silicate, conductive carbon coated Modified lithium manganese silicate, conductive carbon coated modified spinel lithium manganate, conductive carbon coated modified spinel lithium nickel manganate, conductive carbon coated modified lithium titanate At least one.
  • conductive carbon coated modified lithium cobalt oxide such as conductive carbon coated modified lithium cobalt oxide, conductive carbon coated modified nickel manganese lithium cobalt oxide, conductive carbon coated modified nickel manga
  • electrochemically active materials and conductive carbon-coated modified electrochemically active materials are commonly used materials in the manufacture of lithium batteries, and most of them can be purchased directly through commercial channels.
  • the types of conductive carbon can be graphite, graphene, conductive carbon black, carbon nanotubes, etc.
  • the electrical conductivity of the inorganic filler can be adjusted by adjusting the coating content of the conductive carbon.
  • the weight percentage of the conductive material is 5 wt% to 25 wt%, preferably 5 wt% to 20 wt%.
  • the conductive material may be selected from at least one of a conductive carbon-based material, a conductive metal material, and a conductive polymer material.
  • the conductive carbon-based material may be selected from at least one of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, and carbon nanofibers;
  • the conductive metal material may be selected from Al powder, Ni powder, and gold powder At least one of;
  • the conductive polymer material may be selected from at least one of conductive polythiophene, conductive polypyrrole, conductive polyaniline.
  • the conductive material may be used alone or in combination of two or more.
  • the conductive material is usually used in the form of powder or granules. Depending on the specific application environment, its particle size may be 5nm-500nm, such as 10nm-300nm, 15nm-200nm, 15nm-100nm, 20nm-400nm, 20nm-150nm, etc.
  • the weight percentage of the conductive material is 5 wt% to 25 wt%, preferably 5 wt% to 20 wt%.
  • the weight ratio of the polymer matrix material to the conductive material is greater than or equal to 2. Under this dosage ratio, the safety of nail penetration can be further improved. If the weight ratio of the polymer matrix material to the conductive material is less than 2, the content of the conductive material is relatively high, and when the temperature increases, the conductive network may not be sufficiently disconnected, thereby affecting the PTC effect. If the weight ratio of the polymer matrix material to the conductive material is too high, the content of the conductive material is relatively low, which will cause a large increase in the DCR of the battery during normal operation. Preferably, the weight ratio of the polymer matrix to the conductive material is 2 or more and 8 or less.
  • the insoluble layer includes a conductive agent and a binder, and other optional additives.
  • the poorly soluble layer consists essentially of a conductive agent and a binder.
  • the formation method of the insoluble layer is similar to the safety coating.
  • the slurry can be formed by stirring the conductive agent and the binder in an appropriate solvent (such as NMP or water), and then the slurry is applied to the surface of the safety coating. Heating and drying can get the required insoluble layer.
  • the binder in the insoluble layer may be an oily binder or an aqueous binder, and the oily binder is selected from oily polyacrylonitrile, oily polyacrylic acid, oily polyacrylate, oily polyacrylic acid-acrylate , Oily polyacrylonitrile-acrylic acid, oily polyacrylonitrile-acrylate, at least one of the water-based binder is selected from water-based polyacrylic acid, water-based polyurethane, water-based polyvinyl alcohol, water-based polyacrylate, water-based polytetrafluoroethylene At least one of ethylene and water-based polyacrylonitrile.
  • the structural layer may be referred to as a “barrier layer” or "insoluble layer”.
  • the aqueous binder refers to a polymer material in which polymer molecular chains are fully extended and dispersed in water
  • the oily binder refers to a polymer material in which polymer molecular chains are fully extended and dispersed in an oily solvent.
  • suitable surfactants that is, the same type of polymer materials can be made into water-based adhesives by using suitable surfactants. Bonding agent and oily binder.
  • a person skilled in the art may appropriately select water-based polyacrylonitrile or oily polyacrylonitrile as the binder in the insoluble layer, or water-based polyacrylate or oily polyacrylate as the adhesive in the insoluble layer. Nodule.
  • the solubility of fluorinated polyolefin and / or chlorinated polyolefin polymer materials such as PVDF and PVDC in NMP is 100%
  • the solubility of the binder in the poorly soluble layer in NMP is basically not greater than 30%.
  • the solubility of oily polyacrylonitrile in NMP is about 8%, and that of oily polyacrylate is 15%
  • the solubility of waterborne polymer materials such as waterborne polyacrylic acid, waterborne polyurethane, waterborne polyvinyl alcohol in NMP is basically no more than 5 %.
  • the conductive agent may be selected from at least one of a conductive carbon-based material, a conductive metal material, and a conductive polymer material.
  • the conductive carbon-based material may be selected from at least one of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, and carbon nanofibers;
  • the conductive metal material may be selected from Al powder, Ni powder, and gold powder At least one of;
  • the conductive polymer material may be selected from at least one of conductive polythiophene, conductive polypyrrole, conductive polyaniline.
  • the conductive agent may be used alone or in combination of two or more.
  • the conductive agent is usually used in the form of powder or granules. Depending on the specific application environment, its particle size may be 5nm-500nm, such as 10nm-300nm, 15nm-200nm, 15nm-100nm, 20nm-400nm, 20nm-150nm, etc.
  • the conductive agent in the insoluble layer and the conductive material in the safety coating may be the same or different.
  • the weight ratio of the binder to the conductive agent is preferably 9: 1 to 1: 9.
  • the thickness of the poorly soluble layer is generally smaller than the thickness of the safety coating, preferably between 0.5 ⁇ m and 3 ⁇ m.
  • the thickness of the insoluble layer is less than 0.5 ⁇ m, the improvement effect may not be obvious; when the thickness of the insoluble layer is greater than 3 ⁇ m, the energy density of the battery may be reduced.
  • the positive electrode active material layer used in the positive electrode sheet of the present application can be selected from various conventional positive electrode active material layers commonly used in the art, and its composition and preparation method are well known in the art and are not particularly limited.
  • the positive electrode active material layer contains a positive electrode active material, and various positive electrode active materials known to those skilled in the art for preparing a positive electrode of a lithium ion secondary battery can be used.
  • the positive electrode active material is a lithium-containing composite metal oxide, specifically
  • the material is, for example, one or more of LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiFePO 4 , lithium nickel cobalt manganese oxide (such as LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) and one of lithium nickel manganese oxide kind or several.
  • the positive electrode electrochemically active material (or its coating modified material) is used as the inorganic filler of the safety coating of the positive electrode sheet
  • the positive electrode electrochemically active material in the safety coating and the positive electrode active material layer used in The positive electrode active materials may be the same or different.
  • the current collector For the material of the current collector, materials commonly used in the art may be used, and metal current collectors such as stainless steel, aluminum, copper, titanium and other metal sheets or metal foils are preferred.
  • the current collector is a porous current collector (for example, porous aluminum foil). Under abnormal conditions such as nail penetration, the use of porous aluminum foil can reduce the probability of occurrence of metal burrs, and thereby reduce the probability of occurrence of severe aluminothermic reaction, so the safety of the electrochemical device can be further improved.
  • porous aluminum foil can also improve the electrolyte infiltration pole piece, and thus improve the dynamic performance of lithium-ion batteries; and the safety coating can cover the surface of the porous aluminum foil to prevent the upper active material layer in the coating process Leakage phenomenon.
  • the elongation at break ⁇ of the current collector is preferably 0.8% ⁇ ⁇ ⁇ 4%. It has been found that if the elongation at break of the current collector is too large, the metal burrs are large when punctured, which is not conducive to improving the safety performance of the battery; otherwise, if the elongation at break of the current collector is too small, it is compacted at the pole piece It is easy to break during processing or when the battery is pressed or collided, which reduces the quality or safety of the battery. Therefore, in order to further improve safety, especially nailing safety, the elongation at break ⁇ of the current collector should be no more than 4% and no less than 0.8%.
  • the elongation at break of the metal current collector can be adjusted by changing the purity, impurity content and additives of the metal current collector, billet production process, rolling speed, heat treatment process, etc.
  • the negative electrode tab may include a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material, a binder, a conductive material, and the like.
  • the negative electrode active material is, for example, a carbonaceous material such as graphite (artificial graphite or natural graphite), conductive carbon black, carbon fiber, etc., for example, metal or semi-metallic materials such as Si, Sn, Ge, Bi, Sn, In or their alloys, containing lithium Nitride or lithium-containing oxide, lithium metal or lithium aluminum alloy, etc.
  • a carbonaceous material such as graphite (artificial graphite or natural graphite), conductive carbon black, carbon fiber, etc.
  • metal or semi-metallic materials such as Si, Sn, Ge, Bi, Sn, In or their alloys, containing lithium Nitride or lithium-containing oxide, lithium metal or lithium aluminum alloy, etc.
  • the present application also discloses an electrochemical device including the positive electrode sheet according to 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 construction and preparation methods of these electrochemical devices are known per se.
  • the electrochemical device may have improved safety (such as nail-penetrating safety) and electrical performance.
  • the positive electrode tab of the present application is easy to process, so the manufacturing cost of the electrochemical device using the positive electrode tab of the present application can be reduced.
  • the electrochemical device is a lithium ion battery.
  • FIG. 2 is a perspective view of an embodiment of a lithium ion battery 5.
  • FIG. 3 is an exploded view of FIG. 2. 2 to 3, the lithium ion battery 5 includes a case 51, an electrode assembly 52, a top cover assembly 53, and an electrolyte (not shown).
  • the electrode assembly 52 is accommodated in the case 51.
  • the number of electrode assemblies 52 is not limited, and may be one or more.
  • the electrode assembly 52 includes a positive pole piece, a negative pole piece, and a separator.
  • the separator separates the positive pole piece from the negative pole piece.
  • the electrolyte is injected into the case 51 and impregnates the electrode assembly 52, which includes, for example, a first pole piece, a second pole piece, and a separator.
  • the lithium-ion battery 5 shown in FIG. 2 is a can-type battery, but it is not limited thereto.
  • the lithium-ion battery 5 may be a pouch-type battery, that is, the case 51 is replaced by a metal plastic film and the top cover assembly 53 is eliminated.
  • FIG. 4 is a perspective view of an embodiment of the battery module 4.
  • the battery module 4 provided by the embodiment of the present application includes the lithium ion battery 5 of the present application.
  • the battery module 4 includes a plurality of batteries 5.
  • a plurality of lithium ion batteries 5 are arranged in the longitudinal direction.
  • the battery module 4 can serve as a power source or an energy storage device.
  • the number of lithium ion batteries 5 in the battery module 4 can be adjusted according to the application and capacity of the battery module 4.
  • FIG. 5 is a perspective view of an embodiment of the battery pack 1.
  • Fig. 6 is an exploded view of Fig. 5.
  • the battery pack 1 provided by the present application includes the battery module 4 according to an embodiment of the present application.
  • the battery pack 1 includes an upper case 2, a lower case 3 and a battery module 4.
  • the upper case 2 and the lower case 3 are assembled together and form a space for accommodating the battery module 4.
  • the battery module 4 is placed in the space of the upper case 2 and the lower case 3 assembled together.
  • the output pole of the battery module 4 passes through one or both of the upper case 2 and the lower case 3 to supply power to or charge from the outside.
  • the number and arrangement of battery modules 4 used in the battery pack 1 can be determined according to actual needs.
  • FIG. 7 is a schematic diagram of an embodiment of a device using a lithium ion battery as a power source.
  • the device provided by the present application includes the lithium ion battery 5 according to an embodiment of the present application, and the lithium ion battery 5 can be used as a power source of the device.
  • the device using the lithium ion battery 5 is an electric car.
  • the device using the lithium-ion battery 5 may be any electric vehicle (for example, electric bus, electric tram, electric bicycle, electric motorcycle, electric scooter, electric golf cart, electric truck) other than electric cars ), Electric ships, electric tools, electronic equipment and energy storage systems.
  • the electric vehicle may be an electric pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • the device provided in this application may include the battery module 4 described in this application.
  • the device provided in this application may also include the battery pack 1 described in this application.
  • the safety coating is prepared by one of the following two methods.
  • the polymer matrix is not cross-linked:
  • NMP N-methyl-2-pyrrolidone
  • NMP N-methyl-2-pyrrolidone
  • Insoluble layer dissolve the binder and conductive material in a suitable solvent (such as NMP or water), stir evenly, and coat on the safety coating of the current collector prepared according to the above method; at 85 °C drying.
  • a suitable solvent such as NMP or water
  • Positive electrode active material layer Then, 90wt% positive electrode active material, 5wt% SP and 5wt% PVDF are mixed with NMP as a solvent, and then evenly coated on the insoluble layer of the current collector prepared according to the above method; After drying at 85 ° C, a positive electrode active material layer was obtained.
  • PVDF manufactured by Manufacturing “Solvay”, model 5130), PVDC;
  • Crosslinking agent tetraisocyanate, polyethylene glycol, acrylonitrile
  • Conductive material conductive agent: Super-P (Swiss TIMCAL company, referred to as SP);
  • Binder oily polyacrylonitrile, water-based polyacrylic acid, water-based polyurethane, water-based polyvinyl alcohol;
  • Inorganic fillers alumina, lithium iron phosphate (LFP for short), carbon-coated modified lithium iron phosphate (abbreviated as LFP / C), carbon-coated modified lithium titanate (abbreviated as Li 4 Ti 5 O 12 / C);
  • Positive electrode active material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ).
  • the above materials are common and commonly used materials in the field of lithium battery industry, and can be easily obtained through corresponding suppliers through commercial channels.
  • Negative pole piece Add active material graphite, conductive agent Super-P, thickener CMC, adhesive SBR according to the mass ratio of 96.5: 1.0: 1.0: 1.5 to the solvent deionized water and mix to make anode slurry; The slurry is coated on the surface of the negative electrode metal current collector copper foil and dried at 85 ° C, then trimmed, cut, and slitted, and then dried at 110 ° C for 4 hours under vacuum conditions, and welded to the ear The negative pole piece of the secondary battery that meets the requirements.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 3: 5: 2 to obtain an EC / EMC / DEC mixed solvent, and then the fully dried lithium salt LiPF 6 is dissolved in a mixed solvent to obtain a solution with a concentration of 1M, that is, an electrolyte is obtained.
  • separator Using a 12 ⁇ m polypropylene film as the separator, stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is in the middle of the positive pole piece and the negative pole piece to play the role of isolation, and then wound into a bare battery core.
  • Vacuum-bake at 75 ° C for 10 hours inject the electrolyte (prepared as described in "Preparation of Electrolyte” above), vacuum encapsulate and let stand for 24 hours, then charge to 4.2V with a constant current of 0.1C, and then Charge at a constant voltage of V until the current drops to 0.05C, then discharge to 3.0V at a constant current of 0.1C, repeat the charge and discharge twice, and finally charge to 3.8V at a constant current of 0.1C, that is, the preparation of the secondary battery is completed.
  • the powder sample of the material is dispersed in a dispersion medium (distilled water), and a Malvern laser particle size analyzer MS2000 is used, and the average value is measured 5 times and the unit is ⁇ m.
  • a dispersion medium distilled water
  • MS2000 Malvern laser particle size analyzer MS2000
  • the specific surface area of the powder sample of the material was tested with a Quadrasorb SI specific surface tester, and the average value was measured 5 times and the unit was m 2 / g.
  • Coating thickness, diaphragm layer thickness The thickness of the current collector is measured first, and then the total thickness is measured after the coating is applied. The difference between the two is taken as the coating thickness.
  • the thickness of the diaphragm layer adopts a similar method.
  • the absence of cracks in the 100m2 pole piece is defined as no cracking.
  • the polymer material is made into a film of about 7 ⁇ m, cut into 20mm * 50mm strips, weighed and recorded as M1;
  • NMP N-methylpyrrolidone
  • GBT31485-2015 Safety requirements and test methods for power batteries for electric vehicles was used to evaluate the safety of the secondary batteries of the examples and comparative examples, and the test results were recorded.
  • the high temperature resistant steel needle (the cone angle of the needle tip is 45 °), penetrates at a speed of 25mm / s from the direction perpendicular to the battery plate, the penetration position should be close to the geometric center of the puncture surface, the steel needle stays in the battery, Observe whether the battery is burning or exploding.
  • the test conditions for the number of cycles are: at 25 ° C, the secondary battery is subjected to a 1C / 1C cycle test, and the charging and discharging voltage range is 2.8 to 4.2V, and the capacity is reduced to 80% of the first discharge specific capacity to stop the test.
  • the secondary battery was adjusted to 50% SOC at a current of 1C, and the voltage U1 was recorded. Then discharge at a current of 4C for 30 seconds, and record the voltage U2.
  • DCR (U1-U2) / 4C.
  • the cell DCR is used as a reference and recorded as 100%, and the DCR of other cells and its ratio are calculated and recorded.
  • the conventional pole piece P is basically prepared according to the method described in "1.1 Preparation of the positive pole piece", but a safety coating is not provided, that is, the positive electrode active material layer is directly coated on the current collector, and the conventional pole piece N is prepared according to "1.2 Preparation of pole pieces ".
  • Table 1-1 and Table 1-2 show that the introduction of a safety coating using PVDF or PVDC as a polymer matrix greatly improves the needle safety performance of the battery, especially when inorganic fillers are added Significantly. From the DC resistance growth rate data in Table 1-3, it can be seen that the safety coating composed of PVDF and conductive materials does have a PTC effect, and the addition of inorganic fillers significantly improves the DC resistance growth rate of the battery at high temperatures, that is, PTC The effect is more significant.
  • the corresponding safety coating In order to further study the influence of the content of components in the safety coating, the corresponding safety coating, the specific materials and dosages listed in Table 2-1 below are used to prepare the corresponding safety coating, Positive pole piece, negative pole piece and battery, and then test according to the method specified in "3. Battery Performance Test". In order to ensure the accuracy of the data, 4 batteries of each type (10 batteries for acupuncture test) were prepared and tested independently. The final test results were averaged and summarized in Table 2-2.
  • the weight percentage of the polymer matrix is 35wt% -75wt%
  • the weight percentage of the conductive material is 5wt% -25wt%;
  • the weight percentage of the inorganic filler is 10wt% -60wt%.
  • the content of each component of the safety coating is within the above range, the effect of improving the safety and electrical performance (such as cycle performance) of the battery can be achieved.
  • the cross-linking agent is not added to the pole piece 2-51 to cross-link the polymer matrix, the pole piece cracks and severely cracks.
  • the addition of cross-linking agent has a significant effect on improving the cracking of the pole piece. No cracks occurred in the pole pieces 2-53 to 2-56. Similar experiments with PVDC (pole pieces 2-57 and 2-58) have similar results. It can be seen that the addition of cross-linking agent obviously eliminates the cracking of pole piece coating.
  • the above data shows that PVDF / PVDC can be used as a PTC layer polymer matrix material regardless of cross-linking or not.
  • the resulting battery has high safety (excellent results of acupuncture test experiment), and shows that cross-linking treatment It will have a negative impact on the protective effect of the safety coating.
  • the cross-linking treatment improves the cracking of the pole piece, from severe cracking to no cracking or mild cracking.
  • the cross-linking treatment reduces the swelling of the polymer matrix in the electrolyte, thereby reducing DCR by 15% to 25%, thereby improving the electrical performance of the battery.
  • pole piece of the present application is only illustrated with a lithium battery as an example, but the pole piece of the present application can also be applied to other types of batteries or electrochemical devices, and the Good technical effect.

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Abstract

本申请涉及一种正极极片及电化学装置。该正极极片包括集流体和依次设置于集流体之上的安全涂层、难溶层和正极活性材料层，所述安全涂层包含高分子基体、导电材料和无机填料，所述难溶层包含粘结剂和导电剂，在油性溶剂中所述粘结剂的溶解度小于所述安全涂层中的高分子基体的溶解度。该正极极片可以在电化学装置(例如电容器、一次电池或二次电池等)处于高温条件或发生内短路时迅速断开电路，从而改善电化学装置的高温安全性。

Description

一种正极极片及电化学装置
相关申请的交叉引用
本申请要求享有于2018年11月16日提交的名称为“一种正极极片及电化学装置”的中国专利申请201811371594.1的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于电化学技术领域，更具体地说，本申请涉及一种正极极片和包括该正极极片的电化学装置。
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。然而锂离子电池在受到挤压、碰撞或穿刺等异常情况时很容易发生着火、爆炸，从而引起严重危害。因此锂离子电池的安全问题很大程度地限制了锂离子电池的应用和普及。
大量实验结果表明，电池内短路是造成锂离子电池安全隐患的根本所在。为了避免发生电池内短路，研究者们试图从许多方面来进行改进，其中包括利用PTC材料的特性来提升锂离子电池的安全性能方面的研究。PTC(Positive Temperature Coefficient)材料即正温度系数热敏材料，它具有电阻率随温度升高而增大的特性，当温度超过一定的温度时，它的电阻率呈阶跃性的迅速增高。
在利用PTC材料的特性来提升锂离子电池的安全性能方面的研究中，有些研究是在电池的电极活性材料层中添加PTC材料。当电池温度升高时，PTC材料的电阻增大，从而导致整个电极活性材料层的电阻变大，甚至使得整个电极活性材料层的导电通路被破坏，从而起到断电、阻止电化学反应继续进行的安全效 果。然而在这种改进方式中，在电极活性材料层中添加的PTC材料会对电池的电化学性能产生不良的影响。
还有些研究是在电池的集流体与电极活性材料层之间单独设置PTC材料层(安全涂层)。当电池温度升高时，PTC材料层的电阻增大，从而使得集流体与电极活性材料层之间电阻增大、甚至断电，从而起到阻止电化学反应继续进行的安全效果。然而在这种改进方式中，在PTC材料层表面涂覆活性物质浆料时，浆料中的溶剂(如NMP等)会将PTC层中的PTC材料溶解，并进入上层活性物质层中，不仅使PTC层失去PTC效应，而且会恶化电性能。另外，在极片制作过程中的压实步骤中，PTC材料层极易被挤压至边缘，导致电极活性材料层与集流体直接接触，从而失去提高安全性能的作用。另外，PTC材料层的响应速度、阻断电流的效果等性能均需要大幅改善。
有鉴于此，确有必要提供一种能够解决上述问题的具有改善的安全性和电池性能的极片及电池。
发明内容
本申请的一个目的在于：提供一种具有改善的安全性和电性能的极片及电化学装置。
本申请提供了一种正极极片，包括集流体和依次设置于集流体之上的安全涂层、难溶层和正极活性材料层，所述安全涂层包含高分子基体、导电材料和无机填料，所述难溶层包含粘结剂和导电剂，且在油性溶剂中所述难溶层中的粘结剂的溶解度小于所述安全涂层中的高分子基体的溶解度。
优选地，所述难溶层中的粘结剂为油性粘结剂或水性粘结剂中的一种，所述油性粘结剂选自油性聚丙烯腈、油性聚丙烯酸、油性聚丙烯酸酯、油性聚丙烯酸-丙烯酸酯、油性聚丙烯腈-丙烯酸、油性聚丙烯腈-丙烯酸酯中的至少一种，所述水性粘结剂选自水性聚丙烯酸、水性聚氨酯、水性聚乙烯醇、水性聚丙烯酸酯、水性聚四氟乙烯、水性聚丙烯腈中的至少一种。
优选地，在所述安全涂层中，所述高分子基体是氟化聚烯烃和/或氯化聚烯烃。优选地，基于高分子基体、导电材料和无机填料的总重量，所述高分子基体的重量百分比为35wt％-75wt％，优选为50wt％-75wt％；所述导电材料的重量百分比为5wt％-25wt％，优选为5wt％-20wt％；所述无机填料的重量百分比为10wt％-60wt％，优选为15wt％-45wt％。
本申请还提供了一种电化学装置，其包括本申请的正极极片，所述电化学装置优选为电容器、一次电池或二次电池。
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、电化学装置及其有益效果进行详细说明。
图1为根据本申请实施例的正极极片的结构示意图，其中10—集流体；12—安全涂层(即PTC安全涂层)；13—难溶层；14—正极活性材料层。
图2是锂离子电池的一实施方式的立体图。
图3是图2的分解图。
图4是电池模块的一实施方式的立体图。
图5是电池包的一实施方式的立体图。
图6是图5的分解图。
图7是锂离子电池作为电源的装置的一实施方式的示意图。
其中，附图标记说明如下：
1电池包
2上箱体
3下箱体
4电池模块
5电池
51壳体
52电极组件
53顶盖组件
具体实施方式
本申请公开了一种正极极片，包括集流体和依次设置于集流体之上的安全涂层、难溶层和正极活性材料层，所述安全涂层包含高分子基体、导电材料和无机填料，所述难溶层包含粘结剂和导电剂，在油性溶剂中所述难溶层中的粘结剂的溶解度小于所述安全涂层中的高分子基体的溶解度。
图1示出了根据本申请某些实施例的正极极片的结构示意图，其中10—集流体；12—安全涂层(即PTC安全涂层)；13—难溶层；14—正极活性材料层。
易于理解的是，虽然图1中示出的是仅在正极极集流体10的单面设置PTC安全涂层12、难溶层13和正极活性材料层14，但在其他实施例中，正极集流体10可以在双面设置PTC安全涂层12、难溶层13和正极活性材料层14。
传统的用于电池中的具有PTC效应的涂层通常包括高分子基体和导电材料，其中，通常使用聚乙烯、聚丙烯或乙烯丙烯共聚物等作为PTC基体材料；这种情况下需要在PTC基体材料和导电材料中额外加入粘结剂，粘结剂含量过小则涂层与集流体的粘结性较差，粘结剂含量过大则会影响到PTC效应的响应温度和响应速度等性能。另外发现，在PTC材料层表面涂覆活性物质浆料时，浆料中的溶剂(如NMP等)会将PTC层中的PTC材料溶解，并进入上层活性物质层中，不仅使PTC层失去PTC效应，而且会恶化电性能。为了克服以上缺陷，本申请从多个方面着手，采用多种技术手段协同处理来改善PTC安全涂层的性能和稳定性。
首先，发明人发现，在正极极片的安全涂层中加入无机填料可以起到稳定安全涂层的作用。
已发现当安全涂层中不含有无机填料时，处于安全涂层上层的正极活性材 料层中的溶剂(如NMP等)或电解液会对安全涂层中的高分子材料产生溶解、溶胀等不良影响，从而安全涂层会遭到破坏，影响PTC效应的性能。安全涂层中添加了无机填料后，该无机填料相当于一种阻隔物质，从而有利于消除上述溶解、溶胀等不良影响，有利于稳定安全涂层。此外，还发现无机填料的添加还有利于保证在极片压实过程中，安全涂层不易变形。因此无机填料的添加可以很好地保证安全涂层稳定地处于集流体与正极活性材料层之间，防止集流体与正极活性材料层直接接触，从而可以改善电池的安全性能。
概括而言，无机填料可以从如下两方面起到稳定安全涂层的作用：(1)阻碍正极活性材料层中的溶剂(通常为有机油性溶剂，如NMP等)或电解液对安全涂层中的高分子材料产生溶解、溶胀等不良影响；(2)有利于保证在极片压实过程中，安全涂层不易变形。
发明人还出人意料地发现，无机填料还可以改善安全涂层的响应速度等性能。安全涂层的作用原理为：在常温下，安全涂层依靠导电材料之间形成的良好的导电网络，进行电子传导；温度升高时，高分子基体材料的体积开始膨胀，导电材料颗粒之间间距增大，导电网络被部分阻隔，安全涂层的电阻逐渐增大；当达到一定的温度(例如作动温度)时，导电网络几乎完全被隔断，电流趋近为零。然而通常情况下，当安全涂层内部达到一种动态平衡后，导电网络又部分得到恢复，因此在达到一定温度(例如作动温度)后，安全涂层的电阻不如预期的那样大，且仍有很小的电流通过。发明人发现，当加入无机填料后，在高分子基体材料的体积膨胀后，无机填料与体积增大的高分子基体材料都可以起到阻隔导电网络的效果。因此在加入无机填料后，在作动温度范围内，安全涂层可以更好地产生PTC效应，即高温下电阻值增加速度更快，PTC响应速度更快。从而可以更好地改善电池的安全性能。
所述无机填料可以是选自金属氧化物、非金属氧化物、金属碳化物、非金属碳化物、无机盐中的至少一种，或上述材料的导电碳包覆改性、导电金属包覆改 性或导电聚合物包覆改性的材料中的至少一种。
其次，发明人发现，可以通过引入难溶层来进一步改善安全涂层的稳定性和性能。
在安全涂层中加入无机填料可以帮助安全涂层抵御溶剂或电解液对其的破坏。在此基础上，还可以通过在安全涂层和正极活性材料层之间引入一层有阻隔性质的结构层来进一步消除溶剂或电解液造成的影响。
这样的结构层需要包括导电剂来保持极片的电导性，同时还需包括粘结剂来保持结构完整性。且这一结构层中的粘结剂在有机油性溶剂中的溶解度需小于所述安全涂层中的高分子基体在有机油性溶剂中的溶解度，才可以达到进一步消除溶剂或电解液对安全涂层中的高分子基体的溶胀、溶解造成的影响的技术效果。
若不设置这一结构层的话，则易带来如下技术问题：
(1)由于安全涂层中的高分子基体(例如氟化聚烯烃和/或氯化聚烯烃)在有机油性溶剂(如NMP等)和电解液中具有较大的溶解、溶胀，因此在安全涂层的上方涂布正极活性材料层时，若涂布速度较快，则易于由于应力不均导致正极活性材料层的开裂；
(2)由于安全涂层中的高分子基体(例如氟化聚烯烃和/或氯化聚烯烃)在有机油性溶剂(如NMP等)和电解液中具有较大的溶解、溶胀，因此安全涂层的引入，会引起较大的电池DCR(直流内阻)增长，不利于电池的动力学性能改善。
本申请的发明人发现，在油性溶剂中溶解度小于所述安全涂层中的高分子基体的溶解度的油性粘结剂或水性粘结剂特别适合于解决上述技术问题中的一个或两个，因为它们较安全涂层中的高分子基体而言，较难溶于电池制造过程中常用的NMP等有机油性溶剂，且自身可以兼做粘结剂。因此，这一结构层可以包括导电剂和粘结剂，优选地基本由导电剂和粘结剂组成。为了方便，该结构层 可以被称为“阻隔层”或“难溶层”。所述油性粘结剂优选选自油性聚丙烯腈、油性聚丙烯酸、油性聚丙烯酸酯、油性聚丙烯酸-丙烯酸酯、油性聚丙烯腈-丙烯酸、油性聚丙烯腈-丙烯酸酯中的至少一种；所述水性粘结剂选自水性聚丙烯酸、水性聚氨酯、水性聚乙烯醇、水性聚丙烯酸酯、水性聚四氟乙烯、水性聚丙烯腈中的至少一种。
因此，在本申请的实施方式中，正极极片包括了依次涂覆在集流体上的安全涂层、难溶层(阻隔层)和正极活性材料层，且所述安全涂层包括高分子基体、导电材料和无机填料，所述难溶层包括导电剂和在油性溶剂(优选NMP)中溶解度小于所述安全涂层中的高分子基体的溶解度的粘结剂。
由于在油性溶剂中难溶类高分子材料的溶解度小于氟化聚烯烃和/或氯化聚烯烃的溶解度，因此难溶层作为阻挡层阻碍了安全涂层中的氟化聚烯烃和/或氯化聚烯烃在有机油性溶剂(如NMP等)和电解液中的溶解、溶胀过大，从而解决了开裂问题和DCR增长过大的问题。
下面对本申请的正积极片的各结构层及其组成成分分别进行具体描述。
安全涂层
本申请的正极极片的安全涂层包括高分子基体、导电材料和无机填料。其作用原理为：在常温下，安全涂层依靠导电材料之间形成的良好的导电网络，进行电子传导；温度升高时，高分子基体材料的体积开始膨胀，导电材料颗粒之间间距增大，导电网络被部分阻隔，安全涂层的电阻逐渐增大；而当达到一定的温度(例如作动温度)时，导电网络几乎完全被隔断，电流趋近为零，从而保护使用该安全涂层的电化学装置。
本申请的正极极片的安全涂层可以通过常规方法来形成。例如，通过将高分子基体材料、导电材料、无机填料和可选的其他助剂溶解在溶剂中并搅拌形成浆料，然后将浆料涂覆到集流体之上，加热烘干即可得到所需安全涂层。
此外，在本申请的一些优选实施方式中，本申请的正极极片的安全涂层可以 基本上由所述高分子基体、导电材料和无机填料组成，即不含显著量(例如含量≤3％、≤1％、或≤0.5％)的其他组分，且所述高分子基体是氟化聚烯烃或氯化聚烯烃材料。
安全涂层直接粘附在集流体之上，设置于集流体和难溶层之间。所述安全涂层的厚度H可以根据实际需要进行合理确定。所述安全涂层的厚度H通常为不大于40μm，优选的为不大于25μm，更优选的为不大于20μm、15μm或10μm。安全涂层的涂布厚度通常为大于或等于1μm，优选的为大于或等于2μm，更优选为大于或等于3μm。厚度过小，不足以保证安全涂层改善电池安全性能的效果；过大，会造成电池内阻增大严重，从而影响电池正常工作时的电化学性能。优选地1μm≤H≤20μm，更优选地3μm≤H≤10μm。
安全涂层与集流体之间的结合力优选大于等于10N/m。例如，通过引入额外的粘结剂或通过对高分子基体进行交联处理可以增大安全涂层与集流体之间的结合力。较大的结合力可以更好地改善极片的穿钉安全性能。
安全涂层中的高分子基体
相对于高分子基体、导电材料和无机填料的总重量，所述高分子基体的重量百分比为35wt％-75wt％，优选为40wt％-75wt％，更优选为50wt％-75wt％。
作为安全涂层的高分子基体材料可以是聚烯烃材料或其他高分子材料，如聚乙烯、聚丙烯、乙烯-乙酸乙烯酯共聚物(EVA)、乙烯-丙烯酸共聚物、乙烯-甲基丙烯酸共聚物、聚酰胺、聚苯乙烯、聚丙烯腈、热塑性弹性体、环氧树脂、聚缩醛、热塑性改性纤维素、聚砜、聚(甲基)丙烯酸甲酯、包含(甲基)丙烯酸酯的共聚物等等。此时，优选地，所述安全涂层还额外含有用于增强高分子基体材料与集流体之间的粘结力的粘结剂。所述粘结剂可以是例如PVDF、PVDC、SBR等，也可以是选自CMC、聚丙烯酸酯、聚碳酸酯、聚环氧乙烷、橡胶、聚氨酯、羧甲基纤维素钠、聚丙烯酸、丙烯腈多元共聚物、明胶、壳聚糖、海藻酸钠、偶联剂、氰基丙烯酸酯、聚合环醚衍生物、环糊精的羟基衍生物等的水性粘结剂。
在传统的用于电池中的具有PTC效应的涂层中，通常使用聚乙烯、聚丙烯或乙烯丙烯共聚物等作为PTC基体材料。这种情况下需要在PTC基体材料和导电材料中额外加入粘结剂，粘结剂含量过小则涂层与集流体的粘结性较差，粘结剂含量过大则会影响到PTC效应的响应温度和响应速度等性能。而发明人发现，不使用聚乙烯、聚丙烯或乙烯丙烯共聚物等传统PTC基体材料，而是在集流体与正极活性材料层之间使用大量的氟化聚烯烃和/或氯化聚烯烃材料，仍可以起到PTC热敏电阻层的作用，而且能帮助消除现有PTC安全涂层所面临的各种问题。因此，以氟化聚烯烃和/或氯化聚烯烃材料作为高分子基体材料是更优选的。
在本申请中，氟化聚烯烃或氯化聚烯烃可以作为安全涂层高分子基体材料使用，其用量(例如相对于安全涂层总重的35wt％-75wt％)要远远高于氟化聚烯烃或氯化聚烯烃作为粘结剂的用量(相对于涂层总重通常小于15％或小于10％)。
在这种安全涂层中，氟化聚烯烃和/或氯化聚烯烃材料实际上起到了两方面的作用，其既作为PTC基体，又作为粘结剂。这样避免了由于粘结剂与PTC基体材料的不同，而造成的对涂层的粘结性、PTC效应的响应温度和响应速度等的影响。
首先，氟化聚烯烃和/或氯化聚烯烃材料与导电材料组成的安全涂层可以起到PTC热敏电阻层的作用，作动温度范围适当，可为80℃至160℃，因此可以很好地改善电池的高温安全性能。
其次，作为安全涂层的高分子基体材料的氟化聚烯烃和/或氯化聚烯烃，既作为PTC基体，又作为粘结剂，从而还有利于制备较薄的安全涂层，且不影响安全涂层的粘结性。
另外，处于安全涂层上层的正极活性材料层中的溶剂(如NMP等)或电解液会对安全涂层中的高分子材料产生溶解、溶胀等不良影响，对于仅含有常规粘结剂用量的PVDF的安全涂层来说，易于造成粘结性变差；而对于氟化聚烯烃 和/或氯化聚烯烃的含量较高的安全涂层而言，这种不良影响可相对较小。
所以，作为本申请的一方面的改进，所述高分子基体优选是氟化聚烯烃和/或氯化聚烯烃，即聚偏氟乙烯(PVDF)、聚偏氯乙烯(PVDC)、经改性的PVDF、和/或经改性的PVDC。例如，所述高分子基体可以选自PVDF、羧酸改性的PVDF、丙烯酸改性的PVDF、PVDF共聚物、PVDC、羧酸改性的PVDC、丙烯酸改性的PVDC、PVDC共聚物或它们的任意混合物。
在本申请的这种优选实施方式中，基于安全涂层的总重量(或基于高分子基体、导电材料和无机填料的总重量)，所述氟化聚烯烃和/或氯化聚烯烃高分子基体的重量百分比为35wt％-75wt％。含量过小，则无法很好地保证安全涂层的PTC效应；含量过高则可能会影响安全涂层的响应速度等性能。所述氟化聚烯烃和/或氯化聚烯烃高分子基体的重量百分比优选为40wt％-75wt％，更优选为50wt％-75wt％。
当本申请的正极极片的安全涂层中所用氟化聚烯烃和/或氯化聚烯烃高分子基体材料时，这些材料本身除了作为基体材料使用外，其本身还具有很好的粘结性，可以作为粘结剂使用；因此，使用这类高分子基体材料时，安全涂层不需再使用其他额外的粘结剂，这可以简化工艺节约成本。因此，在本申请的优选实施方式中，所述高分子基体是氟化聚烯烃和/或氯化聚烯烃，所述安全涂层基本不含所述高分子基体材料以外的其他粘结剂(“基本不含”表示含量≤3％、≤1％、或≤0.5％)。
在本申请的一些优选实施方式中，所述高分子基体是至少部分交联的，即包含具有交联结构的高分子基体材料，优选地是具有交联结构的氟化聚烯烃和/或氯化聚烯烃。
交联处理可以更有利于阻碍正极活性材料层中的溶剂(如NMP等)或电解液对安全涂层中的高分子材料产生溶解、溶胀等不良影响，防止由于应力不均导致的正极活性材料层的开裂；
第二，对于未进行交联处理的高分子基体，其在电解液中的溶解、溶胀较大，因此安全涂层的引入会引起较大的电池DCR增长，不利于电池的动力学性能改善；而在交联处理之后，有效抑制了高分子基体的溶解度，因此可明显降低由于安全涂层的引入而引起的DCR增长。
交联处理的操作过程是现有技术已知的。例如，对于氟化聚烯烃和/或氯化聚烯烃高分子基体来说，交联处理可以通过引入活化剂和交联剂来实现。活化剂的作用是使氟化聚烯烃和/或氯化聚烯烃脱去HF或HCl，生成C＝C双键；交联剂的作用是使C＝C双键交联。对于活化剂，可以采用例如硅酸钠或硅酸钾等强碱弱酸盐。所述活化剂与高分子基体的重量之比通常为0.5％至5％。所述交联剂可以是选自多异氰酸酯类(JQ-1、JQ-1E、JQ-2E、JQ-3E、JQ-4、JQ-5、JQ-6、PAPI、可乳化MDI、四异氰酸酯)、多元胺类(丙二胺、MOCA)、多元醇类(聚乙二醇、聚丙二醇、三羟甲基丙烷)、缩水甘油醚(聚丙二醇缩水甘油醚)、无机物(氧化锌、氯化铝、硫酸铝、硫黄、硼酸、硼砂、硝酸铬)、乙二醛、氮丙啶、有机硅类(正硅酸乙酯、正硅酸甲酯、三甲氧基硅烷)、苯磺酸类(对甲苯磺酸、对甲苯磺酰氯)、烯属不饱和化合物(苯乙烯、a-甲基苯乙烯、丙烯腈、丙烯酸、甲基丙烯酸、丙烯酸酯类(二丙烯酸-1，4-丁二醇酯、二甲基丙烯酸乙二醇酯、TAC、丙烯酸丁酯、HEA、HPA、HEMA、HPMA、MMA))、有机过氧化物(过氧化二异丙苯，过氧化双2，4-二氯苯甲酰)、金属有机化合物(异丙醇铝、醋酸锌、乙酰丙酮钛)中的至少一种。
所述交联剂与高分子基体的重量之比为0.01％至5％。交联剂太少，高分子基体交联程度较低，不能完全消除开裂。交联剂过多，在搅拌过程中易造成凝胶。所述活化剂和交联剂可在制备安全涂层的浆料搅拌完成后加入，进行交联反应后，搅拌均匀后涂布，以制备安全涂层。
安全涂层中的无机填料
相对于高分子基体、导电材料和无机填料的总重量的总重量，所述无机填料的重量百分比通常为10wt％-60wt％。无机填料含量过小，不足以稳定安全涂层；含量过大，则会影响安全涂层的PTC性能。无机填料的重量百分比优选为15wt％-45wt％。
当无机填料的颗粒粒径过小时，比表面积增大，副反应会增多；过大时，会造成安全涂层的涂布厚度过大且厚度易不均匀。优选地，安全涂层中的无机填料的平均粒径D满足100nm≤D≤10μm，更优选为1μm≤D≤6μm。无机填料的颗粒粒径处于上述范围时，还可以改善高温下阻隔导电网络的效果，从而改善其作为安全涂层的响应速度。还优选地，安全涂层中的无机填料的比表面积(BET)为不大于500m 2/g。无机填料比表面积增大时，副反应会增多影响电池性能；而且无机填料比表面积过大时，需消耗更高比例的粘结剂，会造成安全涂层与集流体、正极活性材料层之间的粘结力降低，内阻增长率较高。当无机填料的比表面积(BET)为不大于500m2/g时，可以提供更好的综合效果。
所述无机填料选自金属氧化物、非金属氧化物、金属碳化物、非金属碳化物、无机盐中的至少一种，或上述材料的导电碳包覆改性、导电金属包覆改性或导电聚合物包覆改性的材料中的至少一种。
例如，所述无机填料可以选自氧化镁、氧化铝、二氧化钛、氧化锆、二氧化硅、碳化硅、碳化硼、碳酸钙、硅酸铝、硅酸钙、钛酸钾、硫酸钡、钴酸锂、锰酸锂、镍酸锂、镍锰酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、钛酸锂中的至少一种，或上述材料的导电碳包覆改性、导电金属包覆改性或导电聚合物包覆改性的材料中的至少一种。
尤其是，发明人发现，当安全涂层用于正极极片时，使用正极电化学活性材料或正极电化学活性材料的导电碳包覆改性、导电金属包覆改性或导电聚合物包覆改性的材料作为无机填料具有特别的优势。这种情况下，无机填料除了上面 提到的稳定安全涂层的作用(阻碍有机溶剂对高分子材料产生溶解、溶胀等不良影响和保证安全涂层不易变形)和改善安全涂层的响应速度等性能外，进一步地，还可以发挥如下两方面的作用：(1)改善电池的过充性能：在氟化聚烯烃和/或氯化聚烯烃高分子基体、导电材料组成的PTC安全涂层体系中，由于电化学活性材料具有嵌脱锂离子的特点，因此在电池正常工作温度下，电化学活性材料可作为参与导电网络的“活性点位”，即安全涂层中的“活性点位”增多，在过充过程中，电化学活性材料会脱锂且脱锂难度越来越大，阻抗不断增加，因此当电流通过时，产热功率增大，底涂层温度增加速度更快，从而PTC效应响应速度更快，进而可以在电池产生过充安全问题之前产生PTC效应，改善电池的过充安全；(2)贡献充放电容量：由于电化学活性材料可以在电池正常工作温度下贡献一定的充放电容量，因此可使得在正常工作温度下安全涂层对电池的容量等电化学性能的影响降至最低。
因此，对于正极极片而言，使用正极电化学活性材料或正极电化学活性材料的导电碳包覆改性、导电金属包覆改性或导电聚合物包覆改性的材料作为安全涂层中的无机填料是最优选的。所述正极电化学活性材料优选是选自钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂、钛酸锂、或它们的导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。尤其是经导电碳包覆改性的这些电化学活性材料，例如导电碳包覆改性的钴酸锂、导电碳包覆改性的镍锰钴酸锂、导电碳包覆改性的镍锰铝酸锂、导电碳包覆改性的磷酸铁锂、导电碳包覆改性的磷酸钒锂、导电碳包覆改性的磷酸钴锂、导电碳包覆改性的磷酸锰锂、导电碳包覆改性的磷酸锰铁锂、导电碳包覆改性的硅酸铁锂、导电碳包覆改性的硅酸钒锂、导电碳包覆改性的硅酸钴锂、导电碳包覆改性的硅酸锰锂、导电碳包覆改性的尖晶石型锰酸锂、导电碳包覆改性的尖晶石型镍锰酸锂、导电碳包覆改性的钛酸锂中的 至少一种。这些电化学活性材料和导电碳包覆改性的电化学活性材料是锂电池制造中的常用材料，大部分可通过商业途径直接购买获得。其中导电碳的种类可以采用石墨、石墨烯、导电炭黑、碳纳米管等。此外，通过调节导电碳的包覆含量可以调节无机填料的电导率。
安全涂层中的导电材料
相对于高分子基体、导电材料和无机填料的总重量，所述导电材料的重量百分比为5wt％-25wt％，优选为5wt％-20wt％。
所述导电材料可以选自导电碳基材料、导电金属材料和导电聚合物材料中的至少一种。作为示例性说明，导电碳基材料可以选自导电炭黑、乙炔黑、石墨、石墨烯、碳纳米管、碳纳米纤维中的至少一种；导电金属材料可以选自Al粉、Ni粉、金粉中的至少一种；导电聚合物材料可以选自导电聚噻吩、导电聚吡咯、导电聚苯胺中的至少一种。导电材料可单独使用一种或组合使用两种以上。
导电材料通常以粉末或颗粒的形式使用。取决于具体应用环境，其粒径可以是5nm-500nm，例如10nm-300nm、15nm-200nm、15nm-100nm、20nm-400nm、20nm-150nm等等。
在本申请中，相对于安全涂层的总重量，所述导电材料的重量百分比为5wt％-25wt％，优选为5wt％-20wt％。优选地，所述高分子基体材料与导电材料的重量比大于等于2。在这种用量比例下，可以进一步改善穿钉安全性。如果高分子基体材料与导电材料的重量比小于2，则导电材料的含量相对较高，则温度升高时，导电网络可能无法充分断开，从而影响PTC效应。若所述高分子基体材料与导电材料的重量比过高，则导电材料的含量相对较低，则会造成正常工作时电池的DCR增长较大。优选地，所述高分子基体与所述导电材料的重量比大于等于2且小于等于8。
难溶层
难溶层包括导电剂和粘结剂以及其他可选的助剂。优选地，难溶层基本上由导电剂和粘结剂组成。难溶层的形成方法与安全涂层类似，例如可以通过将导电剂和粘结剂在适当的溶剂(例如NMP或水)中搅拌形成浆料，然后将浆料涂覆到安全涂层表面，加热烘干即可得到所需难溶层。
所述难溶层中的粘结剂可为油性粘结剂或水性粘结剂，所述油性粘结剂选自油性聚丙烯腈、油性聚丙烯酸、油性聚丙烯酸酯、油性聚丙烯酸-丙烯酸酯、油性聚丙烯腈-丙烯酸、油性聚丙烯腈-丙烯酸酯中的至少一种，所述水性粘结剂选自水性聚丙烯酸、水性聚氨酯、水性聚乙烯醇、水性聚丙烯酸酯、水性聚四氟乙烯、水性聚丙烯腈中的至少一种。
为了方便，该结构层可以被称为“阻隔层”或“难溶层”。
在本申请中，水性粘结剂是指高分子分子链完全伸展开分散在水中的高分子材料，油性粘结剂是指高分子分子链完全伸展开分散在油性溶剂中的高分子材料。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为分别做成水性粘结剂和油性粘结剂。例如，本领域技术人员可以根据需要，适当选用水性聚丙烯腈或油性聚丙烯腈作为难溶层中的粘结剂，也可以选用水性聚丙烯酸酯或油性聚丙烯酸酯作为难溶层中的粘结剂。
PVDF、PVDC等氟化聚烯烃和/或氯化聚烯烃高分子材料在NMP中的溶解度为100％的话，优选的难溶层中的粘结剂在NMP中的溶解度基本都不大于30％。例如，油性聚丙烯腈在NMP中的溶解度大约为8％，油性聚丙烯酸酯为15％；水性聚丙烯酸、水性聚氨酯、水性聚乙烯醇等水性高分子材料在NMP中的溶解度基本都不大于5％。
由于加入水性粘结剂作为难溶层的粘结剂之后，涂层的脆性有可能会增加，不利于电池的安全性能的改善和循环寿命的改善，因此优选加入油性粘结剂作 为难溶层的粘结剂。所述导电剂可以选自导电碳基材料、导电金属材料和导电聚合物材料中的至少一种。作为示例性说明，导电碳基材料可以选自导电炭黑、乙炔黑、石墨、石墨烯、碳纳米管、碳纳米纤维中的至少一种；导电金属材料可以选自Al粉、Ni粉、金粉中的至少一种；导电聚合物材料可以选自导电聚噻吩、导电聚吡咯、导电聚苯胺中的至少一种。导电剂可单独使用一种或组合使用两种以上。
导电剂通常以粉末或颗粒的形式使用。取决于具体应用环境，其粒径可以是5nm-500nm，例如10nm-300nm、15nm-200nm、15nm-100nm、20nm-400nm、20nm-150nm等等。
需注意，难溶层中的导电剂与安全涂层中的导电材料可以相同也可以不同。
在难溶层中，粘结剂与导电剂的重量比优选为9:1至1:9。
难溶层的厚度通常小于安全涂层的厚度，优选在0.5μm至3μm之间。难溶层厚度小于0.5μm时，改善效果可能不够明显；难溶层厚度大于3μm时，可能会降低电池的能量密度。
正极活性材料层
用于本申请正极极片的正极活性材料层可以选用本领域常用的各种常规正极活性材料层，其构成和制备方法是本领域公知的，并无特殊限制。所述正极活性材料层中含有正极活性物质，可以使用本领域技术人员公知的各种用于制备锂离子二次电池正极的正极活性物质，例如该正极活性物质为含锂复合金属氧化物，具体材料例如是LiCoO 2、LiNiO 2、LiMn 2O 4、LiFePO 4、锂镍钴锰氧化物中的一种或几种(如LiNi 0.5Co 0.2Mn 0.3O 2)和锂镍锰氧化物中的一种或几种。
当使用正极电化学活性材料(或其包覆改性材料)作为正极极片的安全涂层的无机填料时，在安全涂层中的正极电化学活性材料和在正极活性材料层中所使用的正极活性物质可以相同也可以不同。
集流体
对于集流体的材料，可以使用本领域常用的材料，优选金属集流体，例如不锈钢、铝、铜、钛等金属薄片或金属箔。优选地，所述集流体为多孔集流体(例如多孔铝箔)。由于在穿钉等异常情况下，多孔铝箔的使用可以降低金属毛刺的产生概率，并进而降低发生剧烈铝热反应的概率，因此可以进一步改善电化学装置的安全性。此外，多孔铝箔的使用还可以改善电解液浸润极片，并进而改善锂离子电池的动力学性能；而安全涂层则可以覆盖在多孔铝箔的表面，防止上层活性材料层在涂布过程中的漏涂现象。
另外，考虑到穿钉安全性，集流体的断裂伸长率δ优选为0.8％≤δ≤4％。业已发现，如果集流体的断裂伸长率过大，则被穿刺时金属毛刺较大，不利于改善电池的安全性能；反之，如果集流体的断裂伸长率过小，则在极片压实等加工过程中或电池受到挤压或碰撞时容易出现断裂，降低电池质量或安全性。因此，为了进一步改善安全性，尤其是穿钉安全性，集流体的断裂伸长率δ应该不大于4％且不小于0.8％。金属集流体的断裂伸长率可通过改变金属集流体的纯度、杂质含量和添加剂、坯料生产工艺、轧制速度、热处理工艺等进行调整。
用于与本申请的正极极片配合使用的负极极片可以选用本领域常用的各种常规负极极片，其构成和制备方法是本领域公知的。例如，负极极片可以包括负极集流体和设置于负极集流体上负极活性材料层，所述负极活性材料层可以包括负极活性材料、粘结剂和导电材料等。负极活性材料例如为诸如石墨(人造石墨或天然石墨)、导电炭黑、碳纤维等的碳质材料，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。
本申请还公开了一种电化学装置，该电化学装置包含了根据本申请的正极 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改善的安全性(如穿钉安全性)和电性能。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。
在本申请的一个具体实施方式中，电化学装置为锂离子电池。图2是锂离子电池5的一实施方式的立体图。图3是图2的分解图。参照图2至图3，锂离子电池5包括壳体51、电极组件52、顶盖组件53以及电解液(未示出)。
电极组件52收容于壳体51内。电极组件52的数量不受限制，可以为一个或多个。电极组件52包括正极极片、负极极片、隔离膜。隔离膜将正极极片和负极极片隔开。电解液注入在壳体51内并浸渍电极组件52，所述电极组件包括例如第一极片、第二极片以及隔离膜。
注意的是图2所示的锂离子电池5为罐型电池，但不限于此，锂离子电池5可以是袋型电池，即壳体51由金属塑膜替代且取消顶盖组件53。
接下来说明本申请又一方面的电池模块。
图4是电池模块4的一实施方式的立体图。
本申请的实施方式提供的电池模块4包括本申请的锂离子电池5。
参照图4，电池模块4包括多个电池5。多个锂离子电池5沿纵向排列。电池模块4可以作为电源或储能装置。电池模块4中的锂离子电池5的数量可以根据电池模块4的应用和容量进行调节。
接下来说明本申请又一方面的电池包。
图5是电池包1的一实施方式的立体图。图6是图5的分解图。
本申请提供的电池包1包括本申请的一实施方式所述的电池模块4。
具体地，参照图5和图6，电池包1包括上箱体2、下箱体3以及电池模块4。上箱体2和下箱体3组装在一起并形成收容电池模块4的空间。电池模块4置于组装在一起的上箱体2和下箱体3的空间内。电池模块4的输出极从上箱体2和下箱体3的其中之一或二者之间穿出，以向外部供电或从外部充电。电池包1采用的电池模块4的数量和排列可以依据实际需要来确定。
接下来说明本申请又一方面的装置。
图7是锂离子电池作为电源的装置的一实施方式的示意图。
本申请提供的装置包括本申请的一实施方式所述的锂离子电池5，所述锂离子电池5可以用作所述装置的电源。在图7中，采用锂离子电池5的装置为电动汽车。当然不限于此，采用锂离子电池5的装置可以为除电动汽车外的任何电动车辆(例如电动大巴、电动有轨电车、电动自行车、电动摩托车、电动踏板车、电动高尔夫球车、电动卡车)、电动船舶、电动工具、电子设备及储能系统。电动汽车可以为电动纯电动车、混合动力电动车、插电式混合动力电动车。当然，依据实际使用形式，本申请提供的装置可包括本申请所述的电池模块4，当然，本申请提供的装置也可包括本申请的所述的电池包1。
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安全涂层中组分选择、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。
实施例
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例进一步详细描述本申请。但是，应当理解的是，本申请的实施例仅仅是为了 解释本申请，并非为了限制本申请，且本申请的实施例并不局限于说明书中给出的实施例。实施例中未注明实验条件采用常规条件，或采用材料供应商或设备供应商推荐的条件。
1、制备方法
1.1 正极极片的制备
1)安全涂层：
取决于安全涂层中高分子基体材料是否进行交联处理，安全涂层采用以下两种方法之一进行制备。
未对高分子基体交联处理：
采用一定配比的高分子基体材料、导电材料、无机填料，以N-甲基-2-吡咯烷酮(NMP)为溶剂，搅拌均匀后涂布在金属集流体的两个表面上，在85℃下烘干后得PTC层(即安全涂层)。
对高分子基体进行交联处理：
采用一定配比的高分子基体材料、导电材料、无机填料，以N-甲基-2-吡咯烷酮(NMP)为溶剂，搅拌均匀后，再加入活化剂(硅酸钠)和交联剂，再搅拌均匀后涂布在金属集流体的两个表面上，在85℃下烘干后得安全涂层。
2)难溶层：将粘结剂和导电材料溶于适当的溶剂中(例如NMP或水中)，搅拌均匀后涂布在按照上述方法所制备的集流体的安全涂层上；在85℃下烘干。
3)正极活性材料层：然后再将90wt％正极活性材料、5wt％SP和5wt％PVDF，以NMP为溶剂，搅拌均匀后涂布在按照上述方法所制备的集流体的难溶层上；在85℃下烘干后得到正极活性材料层。
3)后处理：然后对带有三层正极活性材料层的集流体进行冷压，然后切边、裁片、分条，再在85℃真空条件下烘干4小时，焊接极耳，制成满足要求的二次电池正极极片。
在各具体实施例的安全涂层中使用的主要材料如下：
高分子基体：PVDF(厂家“苏威”，型号5130)，PVDC；
交联剂：四异氰酸酯、聚乙二醇、丙烯腈；
导电材料(导电剂)：Super-P(瑞士TIMCAL公司，简称SP)；
粘结剂：油性聚丙烯腈、水性聚丙烯酸、水性聚氨酯、水性聚乙烯醇；
无机填料：氧化铝、磷酸铁锂(简称LFP)，碳包覆改性的磷酸铁锂(简写为LFP/C)，碳包覆改性的钛酸锂(简写为Li 4Ti 5O 12/C)；
正极活性材料：NCM811(LiNi 0.8Co 0.1Mn 0.1O 2)。
以上所用材料均为锂电池工业领域常见和常用材料，可以通过相应的供应商通过商业途径方便地得到。
1.2 负极极片的制备
负极极片：将活性物质石墨、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阳极浆料；将阳极浆料涂布负极金属集流体铜箔表面上，并在85℃下烘干，然后进行切边、裁片、分条，再在110℃真空条件下烘干4小时，焊接极耳，制成满足要求的二次电池负极极片。
1.3 电解液的配制
将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照3∶5∶2体积比进行混合得EC/EMC/DEC混合溶剂，接着将充分干燥的锂盐LiPF 6溶解于混合溶剂中得浓度为1M的溶液，即得电解液。
1.4 电池的制备
以12μm的聚丙烯薄膜作为隔离膜，将正极极片、隔离膜和负极极片按顺序叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，然后卷绕成裸电芯。在75℃下真空烘烤10h，注入(按照上面“电解液的配制”所述配制的)电解液，经过真空封装、静置24h，之后用0.1C的恒定电流充电至4.2V，然后 以4.2V恒压充电至电流下降到0.05C，再以0.1C的恒定电流放电至3.0V，重复2次充放电，最后以0.1C的恒定电流充电至3.8V，即完成二次电池的制备。
2、材料性能的测试
在各实施例和对比例中，除非另有指明，对于材料的物理性能参数均采用本领域的常用公知方法进行测量。
一些具体参数采用以下方法进行测试。
2.1 粒径
将材料的粉末样品分散于分散介质(蒸馏水)中，使用马尔文激光粒度仪MS2000，测量5次取平均值，单位μm。
2.2 BET(比表面积)
使用Quadrasorb SI比表面测试仪测试材料的粉末样品的比表面积，测量5次取平均值，单位m 2/g。
2.3 膜片层与集流体之间的结合力
将含集流体的双面具有膜片层的极片裁切为宽度为2cm，长度15cm的待测样品，将待测样品的一面在25℃、常压条件下，使用3M双面胶均匀贴于不锈钢板上，将待测样品的一端固定在高铁拉力机上，使用高铁拉力机将待测样品的膜片层与集流体剥离，根据拉力和位移的数据图，读取最大拉力，将读取的值(单位N)除以样品宽度(0.02m)，计算得到结合力(N/m)。
2.4 集流体断裂伸长率
在集流体上取2个长度为200mm，宽度为15mm的样片，用万分尺量取样品的厚度h(μm)。然后将样片固定于拉力机(型号AI7000)上，以50mm/min速度进行拉伸。2次测试的算数平均值为测试结果。记录初始长度L0，启动拉力机测试，直至样片断裂，从拉力机上读取断裂时样片的位移L1。断裂伸长率＝(L1-L0)/L0*100％。
2.5 集流体厚度、涂层厚度、膜片层厚度
集流体厚度：采用万分尺测量，测量5处取平均值。
涂层厚度、膜片层厚度：先测量集流体厚度，涂覆涂层后再测量总厚度，以两者之差作为涂层厚度。膜片层厚度采用类似的方法。
2.6 涂层开裂状况
在烘干并得到正极活性材料层之后，100m2极片不出现裂纹定义为不开裂。100m2极片裂纹出现次数≤3，定义为轻度开裂。100m2极片裂纹出现次数＞3，定义为严重开裂。
2.7 高分子材料在油性溶剂中的溶解度
将高分子材料制成约7μm胶膜，裁剪成20mm*50mm长条，称重并记为M1；
将胶膜置于NMP(N-甲基吡咯烷酮)溶剂中，130℃下放置5min，取出，100℃下真空烘干；真空烘干后称量重量并记为M2；
则溶解度＝(M1-M2)/M1*100％
3、电池的性能测试
采用GBT31485-2015《电动汽车用动力蓄电池安全要求及试验方法》对各实施例和对比例的二次电池的安全性进行评估，并记录测试结果。
3.1 针刺测试：
将二次电池以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
Figure PCTCN2019118825-appb-000001
的耐高温钢针(针尖的圆锥角度为45°)，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。
3.2 过充测试：
将二次电池以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。然后，以1C电流恒流至充电终止电压的1.5倍或充电1h后停止充电。
3.3 循环性能测试：
循环次数测试条件为：在25℃下，将二次电池进行1C/1C循环测试，充放电电压范围2.8～4.2V，容量衰减至首次放电比容量的80％时停止测试。
3.4 PTC效应测试
将二次电池以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，测试电芯直流电阻(4C电流放电10s)。然后将电芯放置于130℃下恒温1h，测试直流电阻，计算直流电阻增长率；然后将电芯放置于130℃下恒温2h，测试直流电阻，计算直流电阻增长率。
3.5 DCR测试
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。
本申请中，为方便比较，以使用非交联的PVDF基体的
电芯DCR作为参比，记为100％，计算和记录其它电芯的DCR和其比值。
4、性能测试结果
4.1 安全涂层的防护效果(PTC效应)和对电池性能的影响
为了验证安全涂层的防护效果，以下面表1-1中所列出的具体材料和用量，按照“1、制备方法”所描述的方法和步骤制备出相应的安全涂层、正极极片、负极极片和电池，然后按照“3、电池的性能测试”部分规定方法进行测试。为了保证数据准确，每种电池制备4个(用于针刺测试的电池制备10个)并独立测试，最终测试结果取平均值，示于表1-2和表1-3。
其中，常规极片P基本按照“1.1正极极片的制备”所述方法进行制备，但是不设置安全涂层，即正极活性材料层直接涂覆在集流体上，常规极片N按 照“1.2负极极片的制备”所述方法制备。
表1-1：极片组成
Figure PCTCN2019118825-appb-000002
表1-2：锂离子电池的性能测试结果
电池No. 正极极片 负极极片 针刺测试
电池1 常规极片P 常规极片N 10个全部不通过
电池2 对比极片CP 常规极片N 2个通过，8个不通过
电池3 极片1 常规极片N 10个全部通过
电池4 极片2 常规极片N 10个全部通过
表1-3：锂离子电池的性能测试结果
Figure PCTCN2019118825-appb-000003
表1-1和表1-2的数据表明：引入以PVDF或PVDC作为高分子基体的安全涂层大大改善了电池的针刺安全性能，尤其是在加入了无机填料的情况下，改善更为显著。从表1-3的直流电阻增长率数据可以看出：PVDF与导电材料构成的安全涂层确有PTC效应，且无机填料的添加非常明显地改善了高温下电池的直流电阻增长率，即PTC效应更为显著。
4.2 安全涂层中组分含量的影响
为了进一步研究安全涂层中组分含量的影响，以下面表2-1中所列出的具体材料和用量，按照“1、制备方法”所描述的方法和步骤制备出相应的安全涂层、正极极片、负极极片和电池，然后按照“3、电池的性能测试”部分规定方法进行测试。为了保证数据准确，每种电池制备4个(用于针刺测试的电池制备10个)并独立测试，最终测试结果取平均值，总结于表2-2。
表2-1：极片组成
Figure PCTCN2019118825-appb-000004
表2-2：锂离子电池的性能测试结果
电池 正极 负极 针刺测试 循环寿命(cycle)
电池6 对比极片2-1 常规极片N 5个不通过，5个通过 2502
电池7 极片2-2 常规极片N 10个全部通过 2351
电池8 极片2-3 常规极片N 10个全部通过 2205
电池9 极片2-4 常规极片N 10个全部通过 2251
电池10 极片2-5 常规极片N 10个全部通过 2000
电池11 极片2-6 常规极片N 10个全部通过 2408
电池12 极片2-7 常规极片N 10个全部通过 2707
电池13 极片2-8 常规极片N 10个全部通过 2355
电池14 极片2-9 常规极片N 10个全部通过 1800
电池15 对比极片2-10 常规极片N 4个不通过，6个通过 1715
表2-1和表2-2的数据表明：(1)无机填料含量过低，则安全涂层的稳定性不足够高，因此电池的安全性能不能得到充分改善；无机填料含量过高，则高分子基体含量会过低，则也无法保证安全涂层正常发挥作用；(2)导电材料对电池的内阻、极化的影响较大，因此会影响电池的循环寿命，导电材料含量越高，则电池的内阻、极化越小，则循环寿命越好。
经实验发现安全涂层的各组分的适当含量范围如下：
高分子基体的重量百分比为35wt％-75wt％；
导电材料的重量百分比为5wt％-25wt％；
无机填料的重量百分比为10wt％-60wt％。
只要安全涂层的各组分含量在以上范围内，就可以实现改善电池的安全性和电性能(如循环性能)的效果。
4.3 无机填料种类对电池性能的影响
为了进一步研究安全涂层中材料选择对极片和电池性能的影响，以下面表3-1中所列出的具体材料和用量，按照“1、制备方法”所描述的方法和步骤制备出相应的安全涂层、正极极片、负极极片和电池，然后按照“3、电池的性能测试”部分规定方法进行测试。为了保证数据准确，每种电池制备4个(用于针刺测试的电池制备10个)并独立测试，最终测试结果取平均值，总结于表3-2。
表3-1：极片组成
Figure PCTCN2019118825-appb-000005
表3-2：锂离子电池的性能测试结果
电池 正极 负极 针刺测试 过充测试 循环测试(cycle)
电池46 极片2-41 常规极片N 10个全部通过 10个全部不通过 2200
电池47 极片2-42 常规极片N 10个全部通过 10个全部通过 2300
电池48 极片2-43 常规极片N 10个全部通过 10个全部通过 2500
电池49 极片2-44 常规极片N 10个全部通过 10个全部通过 2700
电池50 极片2-45 常规极片N 10个全部通过 10个全部通过 2900
电池51 极片2-46 常规极片N 10个全部通过 10个全部通过 3000
表3-1和表3-2的数据表明，相对于其他材料(例如氧化铝)来说，电化学活性材料明显改善了电池的过充安全性能；此外碳包覆的电化学活性材料还改善了电池的循环寿命。
4.4 交联对极片和电池性能的影响
以下面表4-1中所列出的具体材料和用量，按照上述的方法和步骤制备出相应的安全涂层、正极极片、负极极片和电池，然后按照规定方法进行测试以便研究交联对于涂层开裂情况、DCR的影响。
表4-1：交联剂的影响
Figure PCTCN2019118825-appb-000006
在正极活性材料层的涂布速度为50m/min的情况下，极片2-51中没有加入交联剂对高分子基体进行交联，则极片发生开裂且严重开裂。交联剂的加入对改善极片开裂情况具有很明显的作用。极片2-53至极片2-56均没有发生开裂。针对PVDC进行的类似实验(极片2-57和2-58)，结果也类似。由此可见，交联剂的加入明显消除了极片涂布开裂。
表4-2：锂离子电池的性能测试结果
电池 正极 负极 电池DCR 针刺测试
电池52 极片2-51 常规极片N 100％ 10个全部通过
电池53 极片2-52 常规极片N 80％ 10个全部通过
电池54 极片2-53 常规极片N 85％ 10个全部通过
电池55 极片2-54 常规极片N 78％ 10个全部通过
电池56 极片2-55 常规极片N 75％ 10个全部通过
电池57 极片2-56 常规极片N 84％ 10个全部通过
极片2-51中没有加入交联剂对高分子基体进行交联，高分子基体在电解液中溶胀较大，导致DCR较大。交联剂的加入降低了高分子基体在电解液中溶胀，对DCR具有很明显的降低作用。由此可见，交联剂的加入明显降低了电池的DCR。
另外，以上数据说明了，无论是否交联，PVDF/PVDC都能作为PTC层高分子基体材料使用，所得电池具有很高的安全性(针刺测试实验结果优异)，并且表明了交联处理不会对安全涂层的防护作用带来负面影响。而且进一步，与未经交联的PVDC/PVDF相比，交联处理改善了极片开裂，由严重开裂降低至不开裂或轻度开裂。交联处理降低了高分子基体在电解液中的溶胀，从而降低DCR，降幅达15％～25％，从而改善了电池的电性能。
4.5 难溶层对极片和电池性能的影响
为了进一步研究引入难溶层对极片和电池性能的影响，以下面表5-1中所列出的具体材料和用量，按照“1、制备方法”所描述的方法和步骤制备出相应的安全涂层、正极极片、负极极片和电池，然后按照“3、电池的性能测试”部分规定方法进行测试。为了保证数据准确，每种电池制备4个(用于针刺测试的电池制备10个)并独立测试，最终测试结果取平均值，总结于表5-2。
表5-1和表5-2的数据表明，当不存在难溶层时，极片严重开裂。而当存在难溶层时，均不开裂。这是难溶层阻隔了上层活性物质浆料中的有机油性溶剂对安全涂层中的PVDF高分子基体的溶解和溶胀，从而减少开裂，大幅提高生产效率。而且，引入难溶层后，电池仍然保持非常好的安全性，针刺测试结果优异，说明难溶层的引入对于安全涂层的防护作用未造成负面影响。
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池或电化学装置，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。
表5-1：极片组成
Figure PCTCN2019118825-appb-000007
表5-2：锂离子电池的性能测试结果
Figure PCTCN2019118825-appb-000008

Claims (13)

  1. 一种正极极片，包括集流体和依次设置于所述集流体之上的安全涂层、难溶层和正极活性材料层，所述安全涂层包含高分子基体、导电材料和无机填料，所述难溶层包含粘结剂和导电剂，且在油性溶剂中所述难溶层中的粘结剂的溶解度小于所述安全涂层中的高分子基体的溶解度。
  2. 根据权利要求1所述的正极极片，其中所述难溶层中的粘结剂为油性粘结剂或水性粘结剂中的一种，
    所述油性粘结剂选自油性聚丙烯腈、油性聚丙烯酸、油性聚丙烯酸酯、油性聚丙烯酸-丙烯酸酯、油性聚丙烯腈-丙烯酸、油性聚丙烯腈-丙烯酸酯中的至少一种，
    所述水性粘结剂选自水性聚丙烯酸、水性聚氨酯、水性聚乙烯醇、水性聚丙烯酸酯、水性聚四氟乙烯、水性聚丙烯腈中的至少一种。
  3. 根据权利要求1所述的正极极片，其中在所述安全涂层中，相对于所述高分子基体、所述导电材料和所述无机填料的总重量，
    所述高分子基体的重量百分比为35wt％-75wt％，
    所述导电材料的重量百分比为5wt％-25wt％，
    所述无机填料的重量百分比为10wt％-60wt％。
  4. 根据权利要求1所述的正极极片，其中所述高分子基体是氟化聚烯烃和/或氯化聚烯烃，优选地，所述氟化聚烯烃和/或氯化聚烯烃选自聚偏氟乙烯(PVDF)、羧酸改性的PVDF、丙烯酸改性的PVDF、聚偏氯乙烯(PVDC)、羧酸改性的PVDC、丙烯酸改性的PVDC、PVDF共聚物、PVDC共聚物中的至少一种。
  5. 根据权利要求1所述的正极极片，其中所述导电材料和所述导电剂分别独立选自导电碳基材料、导电金属材料和导电聚合物材料中的至少一种，
    优选地，所述导电碳基材料选自导电炭黑、乙炔黑、石墨、石墨烯、碳纳米管、碳纳米纤维中的至少一种；
    优选地，所述导电金属材料选自Al粉、Ni粉、金粉中的至少一种；
    优选地，所述导电聚合物材料选自导电聚噻吩、导电聚吡咯、导电聚苯胺中的至少一种。
  6. 根据权利要求1所述的正极极片，其中所述无机填料选自金属氧化物、非金属氧化物、金属碳化物、非金属碳化物、无机盐中的至少一种，或上述材料的导电碳包覆改性、导电金属包覆改性或导电聚合物包覆改性的材料中的至少一种；
    优选地，所述安全涂层中的无机填料为氧化镁、氧化铝、二氧化钛、氧化锆、二氧化硅、碳化硅、碳化硼、碳酸钙、硅酸铝、硅酸钙、钛酸钾、硫酸钡、钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂、钛酸锂、或上述材料的导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种；
    优选地，所述无机填料的平均粒径D为100nm≤D≤10μm；
    优选地，所述无机填料的比表面积(BET)为不大于500m 2/g。
  7. 根据权利要求1所述的正极极片，其中在所述难溶层中，所述粘结剂与所述导电剂的重量比为9:1～1:9。
  8. 根据权利要求1所述的正极极片，其中所述安全涂层中的高分子基体是具有交联结构的氟化聚烯烃和/或氯化聚烯烃。
  9. 根据权利要求1-8任一项所述的正极极片，其中所述难溶层的厚度为0.5μm至3μm之间；和/或，所述安全涂层的厚度H为1μm≤H≤20μm。
  10. 一种电化学装置，包括根据权利要求1至9任一项所述的正极极片，所述电化学装置为电容器、一次电池或二次电池。
  11. 一种电池模块，其特征在于，包括根据权利要求10所描述的电池。
  12. 一种电池包，其特征在于，包括根据权利要求11所述的电池模块。
  13. 一种装置，其特征在于，包括根据权利要求10所描述的电池，所述电池作为所述装置的电源；优选地，所述装置包括电动车辆、混合动力电动车辆、插电式混合动力电动车辆、电动自行车、电动踏板车、电动高尔夫球车、电动卡车、电动船舶、储能系统。
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