WO2020098769A1 - 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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WO2020098769A1
WO2020098769A1 PCT/CN2019/118695 CN2019118695W WO2020098769A1 WO 2020098769 A1 WO2020098769 A1 WO 2020098769A1 CN 2019118695 W CN2019118695 W CN 2019118695W WO 2020098769 A1 WO2020098769 A1 WO 2020098769A1
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conductive
battery
positive electrode
pole piece
lithium
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PCT/CN2019/118695
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English (en)
French (fr)
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李伟
薛庆瑞
李静
张子格
徐建宝
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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 US16/969,475 priority Critical patent/US11575134B2/en
Priority to PL19883827T priority patent/PL3742529T3/pl
Priority to EP19883827.8A priority patent/EP3742529B1/en
Priority to ES19883827T priority patent/ES2914708T3/es
Publication of WO2020098769A1 publication Critical patent/WO2020098769A1/zh

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    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • 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
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    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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    • 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.
  • ternary materials have become one of the main cathode materials used in commercial lithium-ion batteries, especially in the field of lithium-ion batteries for electric vehicles.
  • High-nickel ternary materials (such as NCM622 and NCM811) are expected to become the main cathode materials for new-generation lithium-ion batteries for electric vehicles due to their high energy density.
  • the thermal stability of high-nickel ternary materials is poor. At high temperatures, substances with strong oxidizability will be released, oxidizing non-aqueous electrolytes and deteriorating the high-temperature performance of lithium-ion batteries, which will cause serious safety problems.
  • the lithium-ion battery of the high-nickel ternary material system is more likely to cause fire, explosion and other risks, thus causing serious harm. Therefore, these problems greatly limit the application and popularization of high-nickel ternary materials.
  • PTC Positive Temperature Coefficient
  • PTC Positive Temperature Coefficient
  • the resistance of the PTC material increases, which causes the resistance of the entire electrode active material layer to increase, and even causes the conductive path of the entire electrode active material layer to be destroyed, thereby playing a power off and preventing the electrochemical reaction from continuing The safety effect carried out.
  • the PTC material added in the electrode active material layer will adversely affect the electrochemical performance of the battery.
  • a PTC material layer (safety coating) is separately provided between the metal 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 metal 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 in the slurry such as NMP
  • the PTC material usually polyethylene, polypropylene or ethylene propylene
  • Copolymers and other materials dissolve and enter the upper active material layer, which not only makes the PTC layer lose the PTC effect, but also deteriorates the electrical properties.
  • the PTC material layer is easily squeezed to the edge, causing the electrode active material layer to directly contact the metal current collector, thereby losing the effect of improving safety performance.
  • This traditional PTC material layer has proved to be unsuitable for high nickel ternary materials.
  • An object of the present application is to provide a pole piece and an electrochemical device using high-nickel ternary materials with improved safety and electrical performance.
  • a further object of the present application is to provide a pole piece and an electrochemical device with good safety and improved electrical performance, especially with improved safety for nail penetration.
  • the present application provides a positive electrode sheet including a metal current collector, a positive electrode active material layer and a safety coating disposed between the metal current collector and the positive electrode active material layer
  • Inorganic filler in the safety coating, relative to the total weight of the polymer matrix, conductive material and inorganic filler, the weight percentage of the inorganic filler is 10wt% -60wt%, the weight percentage of the polymer matrix is 35wt%- 75wt%, the weight percentage of the conductive material is 5wt% -25wt%;
  • the positive electrode active material layer contains Li 1 + x Ni a Co b Me (1-ab) O 2 , where -0.1 ⁇ x ⁇ 0.2, 0.6 ⁇ a ⁇ 1,0 ⁇ b ⁇ 1,0 ⁇ (1-ab) ⁇ 1, Me is at least selected from Mn, Al, Mg, Zn, Ga, Ba, Fe, Cr, Sn, V, Sc, Ti, Zr One; and the metal current collector is an aluminum-containing porous current collector.
  • 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, in which 10- metal current collector; 14- positive electrode active material layer; 12- safety coating (ie, PTC safety coating).
  • 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 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 well ensure that the safety coating is stably located between the metal current collector and the positive electrode active material layer, and prevent the metal current collector from directly contacting the positive electrode active material layer, thereby improving the safety performance of the battery.
  • 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 can play the role of stabilizing the safety coating from the following two aspects: (1) hinder the solvent (such as NMP, etc.) in the positive electrode active material layer or the electrolyte from dissolving the polymer material in the safety coating , Swelling and other adverse effects; (2) helps to ensure that the safety coating is not easily deformed during the compaction of the pole piece.
  • hinder the solvent such as NMP, etc.
  • the weight percentage of the inorganic filler is usually 10% to 60% by weight. 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 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.
  • 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 greater than 500 m2 / 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 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 further 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 performance of the safety coating can be greatly improved, so that it can be used for high nickel ternary The application environment of the material.
  • the PTC safety coating layer in addition to the inorganic filler, also contains a polymer matrix material (PTC matrix material) and a conductive material.
  • 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.
  • EVA ethylene-vinyl acetate copolymer
  • the safety coating may additionally contain 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.
  • PVDF Fluorinated polyolefin or chlorinated polyolefin
  • the material can still function as a PTC thermistor layer, and the safety coating with fluorinated polyolefin and / or chlorinated polyolefin as the polymer matrix is more suitable for the application environment of high nickel ternary materials.
  • the weight percentage of the fluorinated polyolefin and / or chlorinated polyolefin as the polymer matrix material is 35 wt% to 75 wt%. This amount is much higher than the amount of fluorinated polyolefin or chlorinated polyolefin (such as PVDF) commonly used as a binder in the prior art PTC thermistor layer.
  • 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 use of fluorinated polyolefins and / or chlorinated polyolefins as the polymer matrix material of the PTC layer has particular advantages, which helps to eliminate the various defects faced by the existing PTC layer.
  • the fluorinated polyolefin and / or chlorinated polyolefin matrix material itself has good adhesion, when using such a polymer matrix material, the safety coating can eliminate the need to use other additional adhesives.
  • the fluorinated polyolefin and / or chlorinated polyolefin is preferably polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), modified PVDF, or modified PVDC.
  • the binder 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 weight percentage of the fluorinated polyolefin and / or chlorinated polyolefin polymer matrix is 35 wt% to 75 wt%. 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 polymer matrix in the safety coating of the positive electrode sheet is preferably cross-linked, that is, a polymer matrix material having a cross-linked structure, preferably having a cross-linked structure Of fluorinated polyolefins and / or chlorinated polyolefins.
  • 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 swelling in the electrolyte is large, so the introduction of the safety coating will cause a large increase in the DCR (DC internal resistance) of the battery, which is not conducive to the dynamic performance of the battery Improvement; and after the cross-linking treatment, the swelling rate of the polymer matrix is effectively suppressed, so the growth of DCR due to the introduction of the safety coating can be significantly reduced.
  • DCR DC internal resistance
  • 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, ethylenically unsaturated compounds (styrene, a-methylstyrene, acrylonitrile, acrylic acid, methacrylic acid, acrylate Class (-1,4-butanediol diacrylate, ethylene glycol dimethacryl
  • 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 safety coating provided between the metal current collector and the positive electrode active material layer also contains a conductive material.
  • 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 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 8 or less. In a specific embodiment of the present application, preferably, the weight ratio of the polymer matrix to the conductive material is greater than or equal to 3 and less than or equal to 8
  • 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 safety coating may also contain other materials or components, such as other binders that promote adhesion between the coating and the substrate as a current collector. Those skilled in the art can select other additives according to actual needs.
  • the safety coating may further include other binders.
  • the safety coating may further include other polymer substrates different from the polymer substrate.
  • the safety coating is basically Contains no binder or other polymer matrix other than the polymer matrix ("substantially free” means content ⁇ 3%, ⁇ 1%, or ⁇ 0.5%).
  • the safety coating may consist essentially of the polymer matrix, the conductive material, and the inorganic filler, that is, it does not contain a significant amount (eg, content ⁇ 3%, ⁇ 1%, or ⁇ 0.5%) of other components.
  • the thickness H of the safety coating can be reasonably determined according to actual needs.
  • the thickness H of the safety coating is usually not greater than 40 ⁇ m, preferably not greater than 25 ⁇ m, and more preferably not greater 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. However, it is preferable to satisfy 1 ⁇ m ⁇ H ⁇ 20 ⁇ m, and more preferably 3 ⁇ m ⁇ H ⁇ 10 ⁇ m.
  • FIG. 1 shows a schematic structural diagram of a positive electrode sheet according to some embodiments of the present application, wherein 10-metal current collector, 14-positive electrode active material layer, and 12-safety coating (i.e., PTC safety coating).
  • 12-safety coating i.e., PTC safety coating
  • FIG. 1 shows that only one side of the positive electrode metal current collector 10 is provided with a safety coating layer and a positive electrode active material layer, in other embodiments, the positive electrode metal current collector 10 may be separated on both sides.
  • the safety coating 12 and the positive electrode active material layer 14 are provided.
  • the safety coating ie, safety coating
  • the safety coating not only increases resistance when the temperature increases, but also plays the technical effect of PTC, and can also be used in abnormal situations such as nail penetration. Wrap metal burrs that may be generated in the current collector to prevent short circuits in the battery. Taking into account the safety of nail penetration, the elongation at break of the current collector has a great influence on the safety of the battery.
  • the elongation at break of the current collector is too large, the metal burr is large, which is not conducive to improving the safety performance of the battery; if the elongation at break of the current collector is too small, the battery may be squeezed during processing such as pole piece compaction It is easy to break when 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 material of the metal current collector for the material of the metal current collector, materials commonly used in the art, such as metal sheets or metal foils such as stainless steel, aluminum, copper, and titanium, can be used.
  • the thickness of the metal current collector is 4 ⁇ m to 16 ⁇ m.
  • the current collector is a porous aluminum-containing 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 combination of a porous aluminum-containing current collector and an inorganic filler-containing safety coating is particularly suitable for high nickel ternary materials. Since the aluminum metal content per unit area in the thickness direction of the cell is reduced, and the safety coating can wrap the burrs generated in the current collector under abnormal conditions such as nail penetration, and the safety coating also has the effect of PTC, it can further improve the battery Safety performance. In addition, it can also reduce the probability of a violent thermite reaction (thermite reaction is a serious problem for high-nickel ternary materials), so it can also further improve the safety performance of the battery.
  • the thickness of the metal current collector is preferably 4 ⁇ m to 16 ⁇ m.
  • the proportion of the pore area of the aluminum-containing porous current collector is preferably 5% to 75%.
  • the present application does not specifically limit the composition of the upper active material layer of the positive electrode sheet, the present application is particularly suitable for a positive electrode sheet containing a high nickel ternary material as the positive electrode active material. Therefore, in a preferred embodiment of the present application, the positive electrode active material layer contains Li 1 + x Ni a Co b Me (1-ab) O 2 , where -0.1 ⁇ x ⁇ 0.2, 0.6 ⁇ a ⁇ 1 (preferably , 0.8 ⁇ a ⁇ 1), 0 ⁇ b ⁇ 1, 0 ⁇ (1-ab) ⁇ 1, Me is selected from Mn, Al, Mg, Zn, Ga, Ba, Fe, Cr, Sn, V, Sc, Ti , At least one of Zr (preferably Mn or Al).
  • the positive electrode active material layer may contain a variety of positive electrode active materials, for example, in addition to the above-mentioned Li 1 + x Ni a Co b Me (1-ab) O 2 , the positive electrode active material layer may also contain LiCoO 2 , LiNiO 2. One or more of LiMn 2 O 4 , LiFePO 4 and the like. Other materials in the positive electrode active material layer (for example, binder, conductive agent, and optional other additives) are conventionally selected by those skilled in the art.
  • the safety coating and the positive electrode active material layer are separately formed on the current collector, the two are bonded together, and it is not easy to distinguish in appearance.
  • the coating is peeled off from the current collector, a whole coating is generally obtained. Therefore, the safety coating and the positive electrode active material layer are generally collectively referred to as the membrane layer.
  • the elongation of the membrane layer is greater than or equal to 30%, preferably greater than or equal to 80%.
  • the advantage of the larger elongation rate is that under abnormal conditions such as nail penetration, the membrane layer with greater elongation rate can wrap the metal burrs that may be generated in the current collector to prevent the occurrence of short circuits in the battery, thereby greatly improving the battery nailing safety (For the conventional positive electrode active material layer, the elongation rate is generally not more than 1%, which can not play the role of wrapping metal burrs; in this application, due to the introduction of the safety coating, the elongation rate of the diaphragm layer is obtained A great improvement.).
  • the elongation of the membrane layer is 80% or more and 300% or less.
  • the thickness of one side of the membrane layer is 30 ⁇ m to 80 ⁇ m.
  • the bonding force between the membrane layer and the current collector is greater than or equal to 10 N / m.
  • a larger binding force can improve the safety performance of the battery through the nail.
  • 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, that is, the bonding force between the membrane layer and the current collector can be increased.
  • 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 pole piece 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. Due to the use of the positive pole piece of the present application, the electrochemical device may have improved safety (such as nail-penetrating safety) and electrical performance.
  • 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 for 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
  • 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 safety coating of the current collector prepared according to the above method; After drying at 85 ° C, a positive electrode active material layer was obtained.
  • Crosslinking agent tetraisocyanate, polyethylene glycol, acrylonitrile
  • Conductive material conductive agent: Super-P (Swiss TIMCAL company, referred to as SP);
  • Positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811);
  • 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);
  • the materials used above are common and commonly used materials in the 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 100 m 2 pole piece is defined as no cracking.
  • 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 DCR of a cell using a non-crosslinked PVDF matrix is used as a reference, 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.
  • the corresponding positive electrode is prepared according to the methods and steps described in "1, preparation method” with the specific materials and dosages listed in Table 5-1 below The pole piece, the negative pole piece and the battery (but changing the material of the current collector), and then perform the test according to the method specified in the section "3. Battery Performance Test".

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Abstract

一种正极极片及电化学装置。该正极极片包括金属集流体（10）、正极活性材料层（14）和设置于金属集流体（10）与正极活性材料层（14）之间的安全涂层（12），所述安全涂层（12）包含高分子基体、导电材料和无机填料，正极活性材料层（14）包含Li 1+xNi aCo bMe (1-a-b)O 2，其中-0.1≤x≤0.2，0.6≤a<1，0<b<1，0<(1-a-b)<1，Me选自Mn、Al、Mg、Zn、Ga、Ba、Fe、Cr、Sn、V、Sc、Ti、Zr中的至少一种；且金属集流体（10）为含铝多孔集流体。该正极极片可以改善电化学装置的电性能和安全性能。

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201811366548.2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。
目前，三元材料已成为商用锂离子电池主要使用的正极材料之一，尤其是在电动汽车用锂离子电池领域。高镍三元材料(比如NCM622、NCM811)由于能量密度高，因此有望成为新一代的电动汽车用锂离子电池的主要正极材料。但是，高镍三元材料的热稳定性较差，高温下会释放具有强氧化性的物质，氧化非水电解液并恶化锂离子电池的高温性能，并由此带来严重的安全性问题。特别是在锂离子电池受到挤压、碰撞或穿刺等异常情况时，高镍三元材料体系的锂离子电池更容易导致发生着火、爆炸等风险，从而引起严重危害。因此，这些问题很大程度地限制了高镍三元材料的应用和普及。
现有技术中，常用PTC材料来增强锂电池的安全性。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金属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，从而使得金属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(通常为聚乙烯、聚丙烯或乙烯丙烯共聚物等材料)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金属集流体直接接触，从而失去提高安全性能的作用。这种传统的PTC材料层已被证明并不适合于高镍三元材料。
有鉴于此，确有必要提供一种能够避免现有技术中的上述问题、改善高镍三元材料电池的性能和安全性的电极极片及电池。
发明内容
本申请的一个目的在于：提供一种使用高镍三元材料、具有改善的安全性和电性能的极片及电化学装置。
本申请的进一步目的在于：提供一种具有良好的安全性和改善的电性能，尤其是具有改善的穿钉安全性的极片及电化学装置。
本申请提供了一种正极极片，包括金属集流体、正极活性材料层和设置于金属集流体与正极活性材料层之间的安全涂层，所述安全涂层包含高分子基体、 导电材料和无机填料，在安全涂层中，相对于高分子基体、导电材料和无机填料的总重量，所述无机填料的重量百分比为10wt％-60wt％，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％；正极活性材料层包含Li 1+xNi aCo bMe (1-a-b)O 2，其中-0.1≤x≤0.2，0.6≤a<1，0<b<1，0<(1-a-b)<1，Me选自Mn、Al、Mg、Zn、Ga、Ba、Fe、Cr、Sn、V、Sc、Ti、Zr中的至少一种；且金属集流体为含铝多孔集流体。
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为根据本申请一实施方式所描述的正极极片的结构示意图，其中10—金属集流体；14—正极活性材料层；12—安全涂层(即PTC安全涂层)。
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
发明人发现，在电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金属集流体与正极活性材料层之间，防止金属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。
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。
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(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。
基于安全涂层的总重量，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％。
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。
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500m2/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。
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。
因此，通过在正极极片的安全涂层中引入无机填料，尤其是正极电化学活性材料(或其包覆改性材料)，可以大大改善安全涂层的性能，从而可以用于高镍三元材料的应用环境。
在本申请中，PTC安全涂层除了含有无机填料以外，还含有高分子基体材料(PTC基体材料)和导电材料。
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，所述安全涂层还可以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，这种情况下通常需要在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金属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。氟化聚烯烃或氯化聚烯烃(例如PVDF)就是一种常用的粘结剂。作为粘结剂使用时，PVDF的用量要远小于基体材料的用量。例如在传统PTC涂层之中的PVDF粘结剂相对于涂层总重通常小于15％或10％，甚至更低。
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，而是在金属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，且以氟化聚烯烃和/或氯化聚烯烃作为高分子基体的安全涂层更适合于高镍三元材料的应用环境。相对于安全涂层的总重量，作为高分子基体材料的氟化聚烯烃和/或氯化聚烯烃重量百分比为35wt％-75wt％。这一用量远高于现有技术PTC热敏电阻层中通常作为粘结剂使用的氟化聚烯烃或氯化聚烯烃(例如PVDF)的用量。
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。
因此，使用氟化聚烯烃和/或氯化聚烯烃作为PTC层的高分子基体材料具有特别的优势，有助于消除现有PTC层所面临的各种缺陷。例如，由于氟化聚烯烃和/或氯化聚烯烃基体材料本身具有很好的粘结性，使用这类高分子基体材料时，安全涂层可以不需再使用其他额外的粘结剂。
所述氟化聚烯烃和/或氯化聚烯烃优选是聚偏氟乙烯(PVDF)、聚偏氯乙烯(PVDC)、经改性的PVDF、或经改性的PVDC。例如，所述粘结剂可以选自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，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％。
另外，作为本申请的一种进一步改进，正极极片的安全涂层中的高分子基体优选是经过交联处理的，即是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。
另外，对于未进行交联处理的高分子基体，其在电解液中的溶胀较大，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；而在交联处理之后，有效抑制了高分子基体的溶胀率，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、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)、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。
设置于金属集流体与正极活性材料层之间的安全涂层还包含导电材料。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。
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小于等于8。在本申请的一个具体实施方式中，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3且小于等于8
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。
除了高分子基体、导电材料和无机填料外，安全涂层也可以包含其他材料或组分，例如促进涂层与作为集流体的基材之间的粘附性的其他粘结剂等。本领域技术人员可以根据实际需要选择其他助剂。例如，在本申请的另一些实施方式中，所述安全涂层还可以包括其他粘结剂。在本申请的另一些实施方式中，所述安全涂层还可以包括与所述高分子基体不同的其他高分子基体。在以氟化聚烯烃和/或氯化聚烯烃作为高分子基体时，由于安全涂层中所用高分子基体本身具有良好的粘附性，出于简化工艺节约成本考虑，所述安全涂层基本不含所述高分子基体以外的其他粘结剂或其他高分子基体(“基本不含”表示含量≤3％、≤1％、或≤0.5％)。
此外，在本申请的一些优选实施方式中，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。
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。但是优选满足1μm≤H≤20μm，更优选地3μm≤H≤10μm。
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—金 属集流体，14—正极活性材料层，12—安全涂层(即PTC安全涂层)。
易于理解的是，虽然图1中示出的是仅在正极金属集流体10的单面设置安全涂层和正极活性材料层，但在其他实施例中，正极金属集流体10可以在双面分别设置安全涂层12和正极活性材料层14。
另外还发现，在本申请的正极极片中，安全涂层(即安全涂层)不仅在温度升高时电阻变大，而起到PTC的技术效果，还可以在穿钉等异常情况下，包裹集流体中可能产生的金属毛刺，防止电池内短路的发生。考虑到穿钉安全性，集流体的断裂伸长率对于电池安全性有很大影响。如果集流体的断裂伸长率过大，则金属毛刺较大，不利于改善电池的安全性能；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。
在本申请的正极极片中，对于金属集流体的材料，可以使用本领域常用的材料，例如不锈钢、铝、铜、钛等金属薄片或金属箔。金属集流体的厚度为4μm～16μm。优选地，所述集流体为多孔含铝集流体(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。
已经发现，多孔含铝集流体和含无机填料的安全涂层的组合特别适合于高镍三元材料。由于减少了电芯厚度方向上单位面积内的铝金属含量，且安全涂层可以包裹穿钉等异常情况下集流体中产生的毛刺，且安全涂层还具有PTC的 效应，因此可以进一步改善电池的安全性能。另外，还可以降低发生剧烈铝热反应的概率(铝热反应对于高镍三元材料是一个比较严重的问题)，因此也可以进一步改善电池的安全性能。优选金属集流体的厚度为4μm～16μm。含铝多孔集流体的孔面积占比优选为5％至75％。
虽然本申请对于正极极片的上层活性材料层的组成并无特殊限制，但是本申请特别适合于含有高镍三元材料作为正极活性材料的正极极片。因此，在本申请的优选实施方式中，正极活性材料层中包含Li 1+xNi aCo bMe (1-a-b)O 2，其中-0.1≤x≤0.2，0.6≤a<1(优选地，0.8≤a<1)，0<b<1，0<(1-a-b)<1，Me选自Mn、Al、Mg、Zn、Ga、Ba、Fe、Cr、Sn、V、Sc、Ti、Zr中的至少一种(优选是Mn或Al)。这些材料是本领域公知的，其构成和制备方法也是本领域公知的。当然，所述正极活性材料层中可以含有多种正极活性物质，例如除了上述Li 1+xNi aCo bMe (1-a-b)O 2之外，正极活性材料层还可以含有LiCoO 2、LiNiO 2、LiMn 2O 4、LiFePO 4等中的一种或几种。正极活性材料层中的其他材料(例如粘结剂、导电剂和可选的其他添加剂)是本领域技术人员可以常规选择的。
安全涂层和正极活性材料层分别形成在集流体上之后，两者粘结在一起，在外观上不易区分。将涂层从集流体上剥离，一般也会得到一个涂层整体。因此，通常将安全涂层和正极活性材料层统称为膜片层。
发明人发现，本申请正极极片的膜片层的延展率对于极片的穿钉安全性能也有影响。
作为本申请的一种进一步改进，所述膜片层的延展率为大于等于30％，优选大于等于80％。较大延展率的好处是：在穿钉等异常情况下，延展率较大的膜片层可以包裹集流体中可能产生的金属毛刺，防止电池内短路的发生，从而大大改善电池的穿钉安全性(对于常规的正极活性材料层来说，其延展率一般不超过1％，无法起到包裹金属毛刺的作用；而在本申请中，由于安全涂层的引入，膜片层的延展率得到了很大的提高。)。
若增大安全涂层中的高分子基体的含量，则必然会对膜片层的延展率的提高有影响。然而若安全涂层中的高分子基体的含量过大，则会造成导电材料的含量相对较低，由此造成正常工作时电池的DCR增长较大。因此优选膜片层的延展率大于等于80％且小于等于300％。
优选地，膜片层的单面厚度为30μm～80μm。
进一步地，膜片层与集流体之间的结合力大于等于10N/m。较大的结合力可以改善电池的穿钉安全性能。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，即增大膜片层与集流体之间的结合力。
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。
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各组分选择、组分含量和材料理化性能参数(厚度、粒径、比表面积、断裂伸长率等)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、无机填料以及交联剂，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)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安全涂层上；在85℃下烘干后得到正极活性材料层。
3)后处理：然后对带有两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：
粘结剂：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)；
正极活性材料：LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)；
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)；
集流体：多孔铝箔(厚度为12μm，孔面积占比为32％)、非多孔的普通铝箔(厚度为12μm)。
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，100m 2极片不出现裂纹定义为不开裂。100m 2极片裂纹出现次数≤3，定义为轻度开裂。100m 2极片裂纹出现次数＞3，定义为严重开裂。
2.7 膜片层的延展率
取极片并去除集流体：将正极极片从电芯中取出，加入电解液，使极片完全浸泡于电解液中，置于90℃下存储48h以上，然后取出极片，正极极片的膜片层即可从集流体上剥落。
将去除集流体后的膜片层，制成宽度20mm、长度50mm的试样，用万分尺量取样品的厚度h(μm)。然后将试样固定于拉力机(型号AI7000)上，记录初始长度L0。启动拉力机，以50mm/min速度进行拉伸，直至试样断裂。从拉力机上读取断裂时试样的位移L1。延展率＝(L1-L0)/L0*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 PCTCN2019118695-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。
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 PCTCN2019118695-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 PCTCN2019118695-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 PCTCN2019118695-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 PCTCN2019118695-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 PCTCN2019118695-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 集流体是否多孔对电池性能的影响
为了进一步研究集流体是否多孔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正极极片、负极极片和电池(但是改变集流体的材料)，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20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：极片组成及材料性能
Figure PCTCN2019118695-appb-000007
表5-2：锂离子电池的性能测试结果
Figure PCTCN2019118695-appb-000008
表5-1和表5-2的数据表明，集流体是否多孔的选择对电池的性能和安全性会有一定影响。相对于普通铝箔，采用多孔铝箔进一步改善了安全性能(提高了针刺测试通过率)，同时也提高了循环寿命。
综合以上实验数据可知：在PTC安全涂层中添加无机填料消除了传统PTC安全涂层一些固有的缺陷，改进了电池性能；再结合特定集流体的选择，大幅提高了NCM811电池的电性能和安全性，从而为NCM811等高镍材料的商业化应用铺平了道路。
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正极极片的应用实例，但是本申请的正极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。

Claims (13)

  1. 一种正极极片，包括金属集流体、正极活性材料层和设置于所述金属集流体与所述正极活性材料层之间的安全涂层，其中：
    所述安全涂层包含高分子基体、导电材料和无机填料，
    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，
    所述无机填料的重量百分比为10wt％-60wt％，
    所述高分子基体的重量百分比为35wt％-75wt％，且
    所述导电材料的重量百分比为5wt％-25wt％；
    所述正极活性材料层包含Li 1+xNi aCo bMe (1-a-b)O 2，其中-0.1≤x≤0.2，0.6≤a<1，0<b<1，0<(1-a-b)<1，Me选自Mn、Al、Mg、Zn、Ga、Ba、Fe、Cr、Sn、V、Sc、Ti、Zr中的至少一种；
    且所述金属集流体为含铝多孔集流体。
  2. 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。
  3. 根据权利要求1所述的正极极片，其中所述导电材料选自导电碳基材料、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。
  4. 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。
  5. 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高分子基体，优选地是具有交联结构的氟化聚烯烃和/或氯化聚烯烃。
  6. 根据权利要求1所述的正极极片，其中在所述安全涂层中，相对于所述无机填料、所述高分子基体和所述导电材料的总重量，
    所述高分子基体的重量百分比为50wt％-75wt％，
    所述导电材料的重量百分比为5wt％-20wt％，且
    所述无机填料的重量百分比为15wt％-45wt％。
  7. 根据权利要求1所述的正极极片，其中所述高分子基体与所述导电材料的重量比大于等于2；优选大于等于3且小于等于8。
  8. 根据权利要求1所述的正极极片，其中所述金属集流体的断裂伸长率δ满足0.8％≤δ≤4％；和/或，所述集流体的厚度为4μm～16μm。
  9. 根据权利要求1所述的正极极片，其中由所述安全涂层和所述正极活性材料层一起形成的膜片层的延展率为大于等于80％；优选大于等于80％且小于等于300％；优选膜片层的单面厚度为30μm～80μm。
  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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