WO2019091392A1 - 一种正极极片、电化学装置及安全涂层 - Google Patents

一种正极极片、电化学装置及安全涂层 Download PDF

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WO2019091392A1
WO2019091392A1 PCT/CN2018/114298 CN2018114298W WO2019091392A1 WO 2019091392 A1 WO2019091392 A1 WO 2019091392A1 CN 2018114298 W CN2018114298 W CN 2018114298W WO 2019091392 A1 WO2019091392 A1 WO 2019091392A1
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conductive
positive electrode
weight
inorganic filler
coating
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PCT/CN2018/114298
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English (en)
French (fr)
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张小文
金海族
李星
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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 EP18875836.1A priority Critical patent/EP3694027B1/en
Priority to ES18875836T priority patent/ES2897512T3/es
Priority to US16/762,507 priority patent/US11349126B2/en
Publication of WO2019091392A1 publication Critical patent/WO2019091392A1/zh

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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
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    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
    • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
    • C09D127/04—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing chlorine atoms
    • C09D127/08—Homopolymers or copolymers of vinylidene chloride
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    • C09D127/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers
    • C09D127/02—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
    • C09D127/12—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C09D127/16—Homopolymers or copolymers of vinylidene fluoride
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    • 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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
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    • 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
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    • 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
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    • 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
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2227—Oxides; Hydroxides of metals of aluminium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/32—Phosphorus-containing compounds
    • C08K2003/321—Phosphates
    • C08K2003/324—Alkali metal phosphate
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/001—Conductive additives
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
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    • 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
    • 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
    • H01M4/625—Carbon or graphite
    • 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
    • H01M4/626—Metals
    • 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 invention belongs to the field of electrochemical technology, and more particularly to a positive electrode tab and an electrochemical device including the same.
  • Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, long cycle life and low environmental pollution.
  • lithium-ion batteries are prone to fire and explosion when subjected to abnormal conditions such as crushing, bumping or puncture, causing serious damage. Therefore, the safety of lithium-ion batteries greatly limits the application and popularity of lithium-ion batteries.
  • PTC Positive Temperature Coefficient
  • the PTC material layer is easily pressed 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 the response speed and the effect of blocking the current needs to be greatly improved.
  • Another object of the present invention is to provide a positive electrode tab and an electrochemical device which have both good safety and electrical properties (e.g., cycle performance).
  • the invention provides a positive electrode pole piece, comprising a current collector, a positive active material layer and a safety coating disposed between the current collector and the positive active material layer, the safety coating comprising a polymer matrix, a conductive material and an inorganic filler
  • the polymer matrix is a polyvinylidene fluoride and/or a polyvinylidene chloride polymer matrix, wherein the weight percentage of the polymer matrix is from 35 wt% to 75 wt%, preferably 50 wt%, based on the total weight of the security coating.
  • the conductive material is 5 wt% to 25 wt%, preferably 5 wt% to 15 wt%; and the inorganic filler is 10 wt% to 60 wt%, preferably 15 wt% to 45 wt%.
  • the inorganic filler is a carbon-coated positive electrode electrochemically active material.
  • the present invention also provides an electrochemical device comprising the positive electrode tab of the present invention, which is preferably a capacitor, a primary battery or a secondary battery.
  • the invention also provides a safety coating for a positive electrode tab, comprising: a polymer matrix, a conductive material and an inorganic filler, wherein the polymer matrix is a poly (perfluoro) olefin and/or a poly(vinylidene) polymer matrix, based on
  • the total weight of the safety coating layer is 35 wt% to 75 wt%, preferably 50 wt% to 75 wt%;
  • the conductive material is 5 wt% to 25 wt%, preferably 5 wt% -15 wt%;
  • the inorganic filler is from 10% by weight to 60% by weight, preferably from 15% by weight to 45% by weight.
  • the inorganic filler is a carbon-coated positive electrode electrochemically active material.
  • FIG. 1 is a schematic structural view of a positive electrode tab according to an embodiment of the present invention, wherein 10 - current collector; 14 - positive active material layer; 12 - safety coating (ie, PTC safety coating).
  • the invention discloses a positive electrode pole piece, comprising a current collector, a positive active material layer and a safety coating disposed between the current collector and the positive active material layer, the safety coating comprising polyvinylidene fluoride and/or polypolarization A chloroolefin polymer matrix, a conductive material, and an inorganic filler.
  • FIG. 1 shows a schematic structural view of a positive electrode tab according to some embodiments of the present invention, wherein 10 - current collector, 14 - positive active material layer, 12 - security coating (ie, PTC security coating).
  • the PTC security coating 12 and the positive active material layer 14 are provided only on one side of the positive electrode current collector 10 in FIG. 1, in other embodiments, the positive current collector 10 may be in the double The PTC security coating 12 and the positive active material layer 14 are provided.
  • the polyvinylidene fluoride and/or polyvinylidene chloride as a polymer matrix material of a safety coating means polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), modified PVDF, or modified PVDC.
  • PVDF polyvinylidene fluoride
  • PVDC polyvinylidene chloride
  • modified PVDF or modified PVDC.
  • the polyvinylidene fluoride and/or polychloroolefin may be selected from the group consisting of PVDF, carboxylic acid modified PVDF, acrylic modified PVDF, PVDF copolymer, PVDC, carboxylic acid modified PVDC, acrylic modified PVDC, PVDC copolymer or any mixture thereof.
  • polyethylene, polypropylene or ethylene propylene copolymer or the like is generally used as the PTC base material.
  • a binder if the binder content is too small, the adhesion between the coating and the current collector is poor, and if the binder content is too large, the response temperature and response speed of the PTC effect are affected.
  • Polyvinylidene fluorides and/or polychloroolefins such as PVDF are a common binder. When used as a binder, the amount of PVDF used is much less than the amount of the base material.
  • PVDF binders in conventional PTC coatings are typically less than 15% or 10%, or even lower, relative to the total weight of the coating.
  • Some documents (such as CN105594019A, CN06558676A) also mention that PVDF itself may be used as a PTC matrix material, but most of them are theoretically guessed, and the effect of PVDF as a PTC matrix material has not been actually verified.
  • other literature (such as paragraph [0071] of CN104823313A) clearly states that PVDF is not suitable for use as a PTC matrix material.
  • the safety coating provided between the current collector and the positive electrode active material layer can function as a PTC thermistor layer by using a polyvinylidene fluoride and/or a polyvinylidene chloride as a polymer base material.
  • the weight percentage of the polyvinylidene fluoride and/or the polyvinylidene chloride as the polymer matrix material is from 35 wt% to 75 wt%, relative to the total weight of the safety coating. This amount is much higher than the amount of polyvinylidene fluoride and/or polychloroolefin (e.g., PVDF) typically used as a binder in prior art PTC thermistor layers.
  • PVDF polychloroolefin
  • the polyvinylidene fluoride and/or polyvinylidene chloride material actually functions in two ways, both as a PTC matrix and as a binder. This avoids the influence on the adhesion of the coating, the response temperature of the PTC effect, and the response speed due to the difference between the binder and the PTC base material.
  • the safety coating composed of the polyvinylidene fluoride and/or the polyvinylidene chloride material and the conductive material can function as a PTC thermistor layer, and the operating temperature range is appropriately, and can be 80 ° C to 160 ° C, so it can be very Goodly improve the high temperature safety performance of the battery.
  • polyvinylidene fluoride and/or polyvinylidene chloride as a polymer matrix material of the safety coating serve as both a PTC matrix and a binder, thereby facilitating the preparation of a thinner safety coating without affecting The adhesion of the safety coating.
  • a solvent such as NMP or the like
  • an electrolyte solution in the electrode active material layer on the upper layer of the safety coating layer may adversely affect dissolution, swelling, and the like of the polymer material in the safety coating layer, and PVDF containing only the amount of the binder.
  • a solvent such as NMP or the like
  • an electrolyte solution in the electrode active material layer on the upper layer of the safety coating layer may adversely affect dissolution, swelling, and the like of the polymer material in the safety coating layer, and PVDF containing only the amount of the binder.
  • the adverse effect is negligible due to the large content of polyvinylidene fluoride and/or polychloroolefin .
  • the weight percentage of the polyvinylidene fluoride and/or polyvinylidene chloride polymer matrix is from 35 wt% to 75 wt%, based on the total weight of the safety coating. If the content is too small, the PTC effect of the safety coating cannot be well ensured; if the content is too high, the content of the conductive material and the inorganic filler is too small, which also affects the response speed of the safety coating.
  • the weight percentage of the polyvinylidene fluoride and/or polyvinylidene chloride polymer matrix is preferably from 40% by weight to 75% by weight, more preferably from 50% by weight to 75% by weight.
  • the security coating disposed between the current collector and the positive active material layer further includes 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, wherein the conductive carbon-based material is selected from the group consisting of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, carbon At least one of the nanofibers; the conductive metal material is at least one selected from the group consisting of Al powder, Ni powder, and gold powder; and the conductive polymer material is at least one selected from the group consisting of conductive polythiophene, conductive polypyrrole, and conductive polyaniline.
  • the conductive materials may be used alone or in combination of two or more.
  • the working principle of the safety coating of the invention is that at a normal temperature, the safety coating relies on a good conductive network formed between the conductive materials to conduct electron conduction; when the temperature rises, the volume of the polymer matrix material begins to expand, and the conductive material begins to expand. The spacing between the particles increases, the conductive network is partially blocked, and the resistance of the safety coating gradually increases. When a certain temperature (for example, the operating temperature) is reached, the conductive network is almost completely blocked, and the current approaches zero. An electrochemical device that uses the security coating is protected. Therefore, the amount of conductive material is important for the correct functioning of the PTC layer.
  • the conductive material has a weight percentage of 5 wt% to 25 wt%, preferably 5 wt% to 15 wt%, based on the total weight of the security coating.
  • Conductive materials are typically used in the form of powders or granules.
  • the particle diameter may be 5 nm to 500 nm, for example, 10 nm to 300 nm, 15 nm to 200 nm, 15 nm to 100 nm, 20 nm to 400 nm, 20 nm to 150 nm, or the like, depending on the specific application environment.
  • the safety coating provided between the current collector and the positive electrode active material layer further contains an inorganic filler.
  • the solvent such as NMP or the like
  • the electrolyte in the positive active material layer of the upper layer of the safety coating may cause dissolution, swelling, etc. of the polymer material in the safety coating.
  • the effect is that the safety coating will be destroyed, affecting the performance of the PTC effect.
  • the inorganic filler acts as a barrier substance, thereby facilitating the elimination of the above-mentioned adverse effects such as dissolution and swelling, and is advantageous for stabilizing the safety coating.
  • the addition of the inorganic filler is also advantageous in ensuring that the security coating is not easily deformed during the pole piece compaction process. Therefore, the addition of the inorganic filler can well ensure that the safety coating is stably between the current collector and the positive active material layer, and the current collector is prevented from directly contacting the positive active material layer, thereby improving the safety performance of the battery.
  • the inventors have also unexpectedly discovered that inorganic fillers can also improve the response speed of the safety coating and the like.
  • 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 rises, the volume of the polymer matrix material begins to expand, and between the conductive material particles As the pitch increases, the conductive network is partially blocked, and the resistance of the safety coating gradually increases. When a certain temperature (for example, the operating temperature) is reached, the conductive network is almost completely blocked, and the current approaches zero. However, in general, when the internal balance of the safety coating reaches a dynamic equilibrium, the conductive network is partially recovered.
  • the resistance of the safety coating is not as large as expected, and still There is very little current flowing through.
  • the inventors have found that, after the addition of the inorganic filler, the inorganic filler and the increased volume of the polymer matrix material can function to block the conductive network after the volume expansion of the polymer matrix material. Therefore, after the addition of the inorganic filler, the safety coating can better produce the PTC effect in the operating temperature range, that is, the resistance value increases at a higher temperature and the PTC response speed is faster. Thereby, the safety performance of the battery can be better improved.
  • the inorganic filler has a weight percentage of 10% by weight to 60% by weight based on the total weight of the safety coating.
  • the inorganic filler content is too small 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 from 15% by weight to 45% by weight.
  • the inorganic filler can function to stabilize the safety coating from the following two aspects: (1) hindering the solvent (such as NMP, etc.) in the positive electrode active material layer or the electrolyte to dissolve or swell the polymer material in the safety coating. The effect; (2) is beneficial to ensure that the safety coating is not easily deformed during the pole piece compaction process.
  • hindering the solvent such as NMP, etc.
  • the inorganic filler is selected from at least one of a metal oxide, a non-metal oxide, a metal carbide, a non-metal carbide, and an inorganic salt, or a conductive carbon coating modification of the above material, a conductive metal coating modification or The conductive polymer coats at least one of the modified materials.
  • the inorganic filler may be selected from the group consisting of magnesium oxide, aluminum oxide, titanium dioxide, zirconium oxide, silicon dioxide, silicon carbide, boron carbide, calcium carbonate, aluminum silicate, calcium silicate, potassium titanate, barium sulfate, and cobalt acid.
  • the positive electrode electrochemically active material as the inorganic filler functions in addition to the above-mentioned stable safety coating (prevents the adverse effects of the organic solvent on the dissolution, swelling, and the like of the polymer material and ensures that the safety coating is not easily deformed) and improves.
  • the safety coating such as the response speed, it can also play the following two roles: (1) Improve the overcharge performance of the battery: PTC composed of a polyvinylidene fluoride and/or a polyvinylidene chloride polymer matrix and a conductive material.
  • the electrochemically active material has the characteristics of lithium ion intercalation
  • the electrochemically active material can be used as an "active site" in the conductive network at the normal operating temperature of the battery, that is, in the safety coating.
  • the active site is increased.
  • the electrochemically active material will de-lithium and the de-lithium is more and more difficult, and the impedance is increasing. Therefore, when the current passes, the heat-generating power increases, and the temperature of the primer layer increases.
  • a particularly preferred positive electrode electrochemically active material suitable for such use is selected from the group consisting of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminate, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, silicon. At least one of lithium iron phosphate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, lithium spinel lithium manganate, lithium spinel lithium nickel manganese oxide, and lithium titanate.
  • the inventors have found that when the positive electrode electrochemically active material is used as the filler, the conductivity of the filler is improved, and the performance of the entire pole piece is further improved.
  • the main reasons are as follows: increasing the conductivity, the internal resistance of the battery can be lowered, and the improvement is further improved.
  • the safety coating causes an increase in the internal resistance of the battery, thereby improving the electrochemical performance such as the cycle life of the battery; those skilled in the art will appreciate that the conductivity of the inorganic filler can be improved by means of material modification or modification commonly used in the art, for example,
  • the inorganic filler is coated and modified using conductive carbon, a conductive metal or a conductive polymer.
  • either an unmodified electrochemically active material or an electroconductive carbon coating modification, a conductive metal coating modification or a conductive polymer coating modification electrochemical reaction may be used.
  • Active material it is preferable to use a material of a conductive carbon coating modification, a conductive metal coating modification or a conductive polymer coating modification of a positive electrode electrochemical active material as an inorganic filler.
  • the inorganic filler in the safety coating of the present invention is preferably a conductive carbon coated modified electrochemically active material, such as conductive carbon coated modified lithium cobalt oxide, conductive carbon coated modified Nickel manganese manganese cobaltate, conductive carbon coated modified lithium manganese manganese aluminate, conductive carbon coated modified lithium iron phosphate, conductive carbon coated modified vanadium phosphate, conductive carbon coated modified phosphoric acid Cobalt lithium, conductive carbon coated modified lithium manganese phosphate, conductive carbon coated modified lithium iron silicate, conductive carbon coated modified 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 At least one of lithium titanate.
  • a conductive carbon coated modified electrochemically active material such as conductive carbon coated modified lithium cobalt oxide, conductive carbon coated modified Nickel manganese manganese cobaltate,
  • conductive carbon-coated modified electrochemically active materials are commonly used materials in the manufacture of lithium batteries, and most of them are commercially available directly.
  • the type of conductive carbon may be graphite, graphene, conductive carbon black, carbon nanotubes or the like. Further, the conductivity of the inorganic filler can be adjusted by adjusting the coating content of the conductive carbon.
  • the weight percentage of carbon is from 0.5% by weight to 5% by weight based on the weight of the carbon-coated positive electrode electrochemically active material. If the carbon coating content is too small, the effect of improving the conductivity will not be obvious; if the content is too large, the PTC effect of the PTC safety coating will be affected to some extent.
  • the security coating employed in the present invention may also comprise other materials or components, such as adhesions that promote adhesion between the coating and the substrate as a current collector.
  • adhesions that promote adhesion between the coating and the substrate as a current collector.
  • An additive an additive that can improve the processing properties of a pole piece, and the like. Those skilled in the art can select other auxiliaries according to actual needs.
  • the security coating layer is substantially free of other binders other than the polymer matrix material.
  • substantially free means content ⁇ 3%, ⁇ 1%, or ⁇ 0.5%).
  • the security coating is substantially free of aqueous binders (eg, CMC, polyacrylate, polycarbonate, polyethylene oxide, rubber, polyurethane, sodium carboxymethylcellulose, Polyacrylic acid, acrylonitrile multicomponent copolymer, gelatin, chitosan, sodium alginate, coupling agent, cyanoacrylate, polymeric cyclic ether derivative, hydroxyl derivative of cyclodextrin, etc.).
  • aqueous binders eg, CMC, polyacrylate, polycarbonate, polyethylene oxide, rubber, polyurethane, sodium carboxymethylcellulose, Polyacrylic acid, acrylonitrile multicomponent copolymer, gelatin, chitosan, sodium alginate, coupling agent, cyanoacrylate, polymeric cyclic ether derivative, hydroxyl derivative of cyclodextrin, etc.
  • the security coating of the present invention may consist essentially of the polymeric matrix, electrically conductive material, and inorganic filler, ie, without significant amounts (eg, content ⁇ 3%, ⁇ 1%, or ⁇ 0.5%) Other components.
  • the coating thickness H of the security coating layer is not more than 40 ⁇ m, preferably not more than 25 ⁇ m, more preferably not more than 20 ⁇ m, 15 ⁇ m or 10 ⁇ m.
  • the coating thickness of the security coating layer is greater than or equal to 1 ⁇ m, preferably greater than or equal to 2 ⁇ m, and more preferably greater than or equal to 3 ⁇ m. If the thickness is too small, it is not enough to ensure the safety coating improves the safety performance of the battery; if it is too large, the internal resistance of the battery will increase seriously, which will affect the electrochemical performance of the battery during normal operation.
  • a safety coating is applied over the positive electrode current collector.
  • materials commonly used in the art such as metal flakes or metal foils such as stainless steel, aluminum, copper, titanium, etc., can be used.
  • a positive electrode active material layer is provided outside the safety coating.
  • the positive electrode active material layer used in the present invention various positive electrode active material layers suitable for use in a lithium battery, which are well known in the art, can be selected, and the constitution and preparation method thereof are well known in the art.
  • the positive electrode active material layer contains a positive electrode active material, and various positive electrode active materials for preparing a lithium ion secondary battery positive electrode known to those skilled in the art may be used.
  • the positive electrode active material is a lithium-containing composite metal oxide, specifically The material is, for example, one 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 lithium nickel manganese oxide.
  • the material is, for example, one 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
  • the negative electrode tab used in combination with the positive electrode tab of the present invention may be various negative electrode tabs commonly used in lithium batteries.
  • the negative electrode active material layer used in the negative electrode tab may be selected from various negative electrode active material layers suitable for use in lithium batteries known in the art, and the constitution and preparation method thereof are well known in the art.
  • the negative electrode active material layer contains a negative electrode active material, and various negative electrode active materials for preparing a lithium ion secondary battery negative electrode known to those skilled in the art, such as, for example, graphite (artificial graphite or natural graphite), conductive carbon, can be used.
  • a carbonaceous material such as black or carbon fiber, for example, a metal or a semimetal material such as Si, Sn, Ge, Bi, Sn, or In or an alloy thereof, a lithium-containing nitride or a lithium-containing oxide, a lithium metal or a lithium aluminum alloy.
  • the positive electrode electrochemically active material in the safety coating layer and the positive electrode active material used in the positive electrode active material layer may be the same or different.
  • the present application also discloses an electrochemical device comprising a positive electrode tab according to the present invention.
  • 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 can have improved safety and electrical properties (e.g., cycle performance) due to the use of the positive electrode tab of the present invention. Further, since the positive electrode tab of the present invention is easy to process, the manufacturing cost of the electrochemical device using the positive electrode tab of the present invention can be reduced.
  • NMP N-methyl-2-pyrrolidone
  • the main materials used in the safety coatings of the specific examples are as follows:
  • Polymer matrix material PVDF, PVDC;
  • Conductive material conductive agent: Super-P (TIMCAL, Switzerland, SP);
  • Inorganic filler lithium iron phosphate (LFP for short) and carbon coated lithium iron phosphate (abbreviated as LFP/C), lithium cobalt oxide (LCO) and carbon coated lithium cobalt oxide (abbreviated as LCO/) C), lithium titanate (Li 4 Ti 5 O 12 ) and carbon coated modified lithium titanate (abbreviated as Li 4 Ti 5 O 12 /C), alumina.
  • the materials used above are common and commonly used materials in the lithium battery industry and can be conveniently obtained commercially by the corresponding suppliers.
  • Positive electrode tab with safety coating 90 wt% ternary material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), 5 wt% SP and 5 wt% PVDF, using NMP as solvent, stirring uniformly and coating according to 1.1 above
  • the prepared positive electrode current collector aluminum foil surface is used as a positive electrode active material layer; it is dried at 85 ° C, then cold pressed, then cut, cut, and stripped, and then dried under vacuum at 85 ° C. After 4 hours, the tabs were welded to prepare a positive electrode tab (ie, a cathode tab) of the secondary battery that satisfies the requirements.
  • Conventional positive electrode tab Same as the preparation method described above except that there is no safety coating on the surface of the positive current collector aluminum foil.
  • Conventional negative electrode piece the active material graphite, conductive agent Super-P, thickener CMC, adhesive SBR are added to the solvent deionized water at a mass ratio of 96.5:1.0:1.0:1.5 to form an anode slurry;
  • the anode slurry is coated on the surface of the negative current collector copper foil, and dried at 85 ° C, then trimmed, cut, and stripped, and then dried under vacuum at 110 ° C for 4 hours to weld the tabs.
  • a secondary battery negative electrode piece ie, an anode pole piece that satisfies the requirements.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 3:5:2 to obtain an EC/EMC/DEC mixed solvent, followed by a sufficiently dried lithium salt LiPF6.
  • the solution was dissolved in a mixed solvent to obtain a solution having a concentration of 1 M.
  • the 12 ⁇ m polypropylene film is used as the separator, and the positive electrode, the separator and the negative electrode are stacked in order, so that the separator is in the middle of the positive electrode and the negative electrode, and then wound into a bare battery. core.
  • the electrolyte (prepared as described in "1.4 Electrolyte Preparation" above) was injected, vacuum-packed, allowed to stand for 24 h, then charged to 4.2 V with a constant current of 0.1 C, and then 4.2V constant voltage charging until the current drops to 0.05C, and then discharges to 3.0V with a constant current of 0.1C, repeats the charge and discharge twice, and finally charges to 3.8V with a constant current of 0.1C, that is, the preparation of the secondary battery is completed.
  • the secondary battery is fully charged to the charge cut-off voltage with a current of 1 C, and then charged to a constant current until the current drops to 0.05 C to stop charging.
  • the high temperature resistant steel needle (the taper angle of the needle tip is 45°), penetrates from the direction perpendicular to the battery plate at a speed of 25 mm/s, and the penetration position should be close to the geometric center of the razor surface, and the steel needle stays in the battery. Observe whether the battery is burning or exploding.
  • the secondary battery is fully charged to the charge cut-off voltage with a current of 1 C, and then charged to a constant current until the current drops to 0.05 C to stop charging. Then, the charging was stopped by a constant current of 1 C to 1.5 times the charging termination voltage or after charging for 1 hour.
  • the test conditions of the number of cycles were as follows: the secondary battery was subjected to a 1 C/1 C cycle test at 25 ° C, and the charge and discharge voltage range was 2.8 to 4.2 V, and the test was stopped when the capacity was attenuated to 80% of the first discharge specific capacity.
  • the secondary battery is fully charged to the charge cut-off voltage with a current of 1 C, and then the current is reduced to 0.05 C by constant voltage charging, the charging is stopped, and the DC resistance of the battery is tested (4 C current discharge for 10 s). Then, the cell was placed at 130 ° C for 1 h, the DC resistance was tested, and the DC resistance growth rate was calculated. Then, the cell was placed at 130 ° C for 2 h, and the DC resistance was tested to calculate the DC resistance growth rate.
  • the corresponding safety coating, positive electrode tab and negative electrode were prepared according to the specific materials and amounts listed in Table 1-1 below, according to the methods and procedures described in "1. Preparation method”. The pole piece and the battery are then tested according to the method specified in section 2. Performance Test of the Battery. In order to ensure accurate data, 4 batteries were prepared for each battery (10 batteries for the needle test) and tested independently. The final test results were averaged and shown in Table 1-2 and Table 1-3.
  • the corresponding safety coating is prepared according to the specific materials and amounts listed in Table 2-1 below, according to the methods and procedures described in "1. Preparation method”. The positive pole piece, the negative pole piece and the battery are then tested according to the method specified in "2. Performance test of the battery”. In order to ensure the accuracy of the data, 4 batteries were prepared for each battery (10 for the acupuncture test) and tested independently. The final test results were averaged and summarized in Table 2-2.
  • the weight percentage of the polymer matrix is from 35 wt% to 75 wt%;
  • the weight percentage of the conductive material is 5 wt% to 25 wt%;
  • the weight percentage of the inorganic filler is from 10% by weight to 60% by weight.

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Abstract

本发明涉及一种正极极片、电化学装置及安全涂层。该正极极片包括集流体、正极活性材料层和设置于集流体与正极活性材料层之间的安全涂层，所述安全涂层包含聚偏氟烯烃和/或聚偏氯烯烃高分子基体、导电材料和无机填料。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、电化学装置及安全涂层
相关申请的交叉引用
本申请要求于2017年11月8日递交的中国发明申请201711091425.8的权益，所述中国发明申请的全部内容通过引用并入本文。
技术领域
本发明属于电化学技术领域，更具体地说，本发明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、***，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(如循环性能)的极片及电池。
发明内容
本发明的一个目的在于：提供一种具有改善的安全性和电性能(如循环性能)的正极极片及电化学装置。
本发明的另一个目的在于：提供一种兼具良好的安全性和电性能(如循环性能)的正极极片及电化学装置。
本发明的进一步目的在于：提供一种具有良好的安全性、改善的电性能(如循环性能)、易加工性等优良性能的适于大规模生产和应用的极片及电化学装置。
本发明提供了一种正极极片，包括集流体、正极活性材料层和设置于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，所述高分子基体是聚偏氟烯烃和/或聚偏氯烯烃高分子基体，其中基于安全涂层的总重量：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％-15wt％；所述无机填料的重量百分比为10wt％-60wt％，优选为15wt％-45wt％。优选地，其中所述无机填料为碳包覆的正极电化学活性材料。
本发明还提供了一种电化学装置，其包括本发明的正极极片，所述电化学装置优选为电容器、一次电池或二次电池。
本发明还提供了一种正极极片用安全涂层，其包含：高分子基体、导电材料和无机填料，所述高分子基体是聚偏氟烯烃和/或聚偏氯烯烃高分子基体，基于所述安全涂层的总重量，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％-15wt％；所述无机填料的重量百分比为10wt％-60wt％，优选为15wt％-45wt％。优选地，其中所述无机填料为碳包覆的正极电化学活性材料。
附图说明
下面结合附图和具体实施方式，对本发明的正极极片、电化学装置及其有益效果进行详细说明。
图1为根据本发明实施例的正极极片的结构示意图，其中10—集流体；14—正极活性材料层；12—安全涂层(即PTC安全涂层)。
具体实施方式
本发明公开了一种正极极片，包括集流体、正极活性材料层和设置于集流体与正极活性材料层之间的安全涂层，所述安全涂层包含聚偏氟烯烃和/或聚偏氯烯烃高分子基体、导电材料和无机填料。
图1示出了根据本发明某些实施例的正极极片的结构示意图，其中10—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极集流体10的单面设置PTC安全涂层12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和正极活性材料层14。
在本发明中，作为安全涂层的高分子基体材料的所述聚偏氟烯烃和/或聚偏氯烯烃是指聚偏氟乙烯(PVDF)、聚偏氯乙烯(PVDC)、经改性的PVDF、或经改性的PVDC。例如，所述聚偏氟烯烃和/或聚偏氯烯烃可以选自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。聚偏氟烯烃和/或聚偏氯烯烃(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。某些文献(例如CN105594019A、CN06558676A)也提到PVDF本身有可能作为PTC基体材料使用，但多是出于理论上的猜测，并未实际验证PVDF作为PTC基体材料的使用效果。同时，另外一些文献(例如CN104823313A的[0071]段)则明确提出PVDF不适合作为PTC基体材料使用。
在本发明中，设置于集流体与正极活性材料层之间的安全涂层使用聚偏氟烯烃和/或聚偏氯烯烃作为高分子基体材料，仍可以起到PTC热敏电阻层的作用。相对于安全涂层的总重量，作为高分子基体材料的聚偏氟烯烃和/或聚偏氯烯烃重量百分比为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聚偏氟烯烃和/或聚偏氯烯烃(例如PVDF)的用量。
在本发明中，聚偏氟烯烃和/或聚偏氯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。
其次，聚偏氟烯烃和/或聚偏氯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。
此外，作为安全涂层的高分子基体材料的聚偏氟烯烃和/或聚偏氯烯烃，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电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；而对于本申请的安全涂层来说，由于聚偏氟烯烃和/或聚偏氯烯烃的含量较大，因此这种不良影响可忽略。
在本发明的电极极片中，基于安全涂层的总重量，所述聚偏氟烯烃和/或聚偏氯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，则导电材料与无机填料的含量过小，则也会影响安全涂层的响应速度等性能。所述聚偏氟烯烃和/或聚偏氯烯烃高分子基体的重量百分比优选为40wt％-75wt％，更优选为50wt％-75wt％。
在本发明中，设置于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，其中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；导电金属材料选自Al粉、Ni粉、金粉中的至少一种；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。导电材料可单独使用一种或组合使用两种以上。
本发明的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；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。因此，导电材料的用量对于PTC层正确发挥作用很重要。在本发明中，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％-15wt％。
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。
在本发明中，设置于集流体与正极活性材料层之间的安全涂层，还包含无机填料。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。发明人发现，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。
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。
基于安全涂层的总重量，所述无机填料的重量百分比为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％。
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。
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。
作为本发明的一种进一步改进，当本发明的安全涂层用于正极极片时，使用正极电化学活性材料(以下亦简称“电化学活性材料”)作为无机填料具有特别的优势。
发明人发现，使用电化学活性材料作为无机填料具有特别的优势。这种情况下，作为无机填料的正极电化学活性材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，还可以发挥如下两方面的作用： (1)改善电池的过充性能：在聚偏氟烯烃和/或聚偏氯烯烃高分子基体、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。
适合于这种用途的特别优选的正极电化学活性材料是选自钴酸锂、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、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、钛酸锂中的至少一种。
另外，发明人发现，当使用正极电化学活性材料作为填料时，提高填料的导电性能，会进一步改善整个极片的性能，主要原因如下：增加导电性能，可以降低电池的内阻，进一步改善由于安全涂层导致的电池内阻的增加，从而改善电池的循环寿命等电化学性能；本领域技术人员可以理解,可以通过本领域常用的材料修饰或改性手段来改善无机填料的导电性能，例如使用导电碳、导电金属或导电聚合物对无机填料进行包覆改性。
所以，在本发明的安全涂层中，既可以使用未经修饰的电化学活性材料，也可以使用导电碳包覆改性、导电金属包覆改性或导电聚合物包覆改性的电化学活性材料。但是，优选使用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。
在一些优选的实施方式中，本发明的安全涂层中的无机填料优选为导电碳包覆改性的电化学活性材料，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。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。
进一步优选的，在碳包覆的正极电化学活性材料中，基于碳包覆的正极电化学活性材料的重量，碳的重量百分比为0.5wt％-5wt％。碳包覆含量过小，则起不到明显的改善导电的作用；含量过大，则会在一定程度上影响PTC安全涂层正常发挥PTC效应。
除了所述高分子基体、导电材料和无机填料外，本发明采用的安全涂层还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粘结剂、可以改善极片加工性能的添加剂等。本领域技术人员可以根据实际需要选择其他助剂。
由于本发明的安全涂层中所用高分子基体材料本身具有良好的粘附性，在本发明的一些实施方式中，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％)。在本发明的一些实施方式中，所述安全涂层基本不含水性粘结剂(例如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)。
在一些实施方式中，本发明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。
本领域技术人员可以理解：以上提到的本发明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发明范围内，且视为本说明书公开内容的一部分。
在本发明中，所述安全涂层的涂布厚度H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。
在本发明的正极极片中，安全涂层涂布于正极集流体之上。对于集流体，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。
在本发明的正极极片中，在安全涂层外设置有正极活性材料层。
用于本发明中的正极活性材料层可以选用本领域公知的适于锂电池使用的各种正极活性材料层，其构成和制备方法是本领域公知的。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。
与本发明的正极极片配对使用的负极极片可以是锂电池常用的各种负极极片。用于负极极片中的负极活性材料层可以选用本领域公知的适于锂电池使用的各种负极活性材料层，其构成和制备方法是本领域公知的。所述负极活性材料层中含有负极活性物质，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负极的负极活性物质，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。
需注意的是，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。
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发明的正极极片。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。除了使用了本发明的正极极片外，这些电化学装置的构造和制备方法本身是公知的。由于使用了本发明的正极极片，所述电化学装置可以具有改善的安全性和电性能(如循环性能)。并且本发明的正极极片容易加工，因此可以降低使用了本发明的正极极片的电化学装置的制造成本。
实施例
为了使本发明的发明目的、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发明。但是，应当理解的是，本发明的实施例仅仅是为了解释本发明，并非为了限制本发明，且本发明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 安全涂层的制备
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，搅拌均匀后涂布在集流体(正极集流体铝箔或负极集流体铜箔)上，烘干后得PTC层(即安全涂层)。
在各具体实施例的安全涂层中使用的主要材料如下：
高分子基体材料：PVDF，PVDC；
导电材料(导电剂)：Super-P(瑞士TIMCAL公司，简称SP)；
无机填料：磷酸铁锂(简称LFP)和碳包覆改性的磷酸铁锂(简写为LFP/C)，钴酸锂(简称LCO)和碳包覆改性的钴酸锂(简写为LCO/C)，钛酸锂(Li 4Ti 5O 12)和碳包覆改性的钛酸锂(简写为Li 4Ti 5O 12/C)，氧化铝。
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 正极极片的制备
带有安全涂层的正极极片：采用90wt％三元材料NCM811(LiNi 0.8Co 0.1Mn 0.1O 2)、5wt％SP和5wt％PVDF，以NMP为溶剂，搅拌均匀后涂布在按照上述1.1所制备的正极集流体铝箔表面的安全涂层上，作为正极活性物质层；在85℃下烘干后进行冷压，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(即阴极极片)。
常规正极极片：与上面描述的制备方法相同，除了正极集流体铝箔表面没有安全涂层。
1.3 负极极片的制备
常规负极极片：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；将阳极浆料涂布在负极集流体铜箔表面上，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(即阳极极片)。
1.4 电解液的配制
将碳酸乙烯酯(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LiPF6溶解于混合溶剂中得浓度为1M的溶液，即得电解液。
1.5 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“1.4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、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。
2.1 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 PCTCN2018114298-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、***现象。
2.2 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。
2.3 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。
2.4 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、性能测试结果
3.1 安全涂层的防护效果(PTC效应)和对电池性能的影响
为了验证本发明的防护效果，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“2、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。
表1-1：极片组成
Figure PCTCN2018114298-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 PCTCN2018114298-appb-000003
Figure PCTCN2018114298-appb-000004
表1-1、表1-2和表1-3的数据表明：本申请的正极极片可以大大改善电池的针刺安全性能，且无机填料的添加可以非常明显地改善高温下电池的直流电阻增长率，从而改善电池针刺安全性能测试的通过率。
3.2 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“2、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 PCTCN2018114298-appb-000005
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PTC效应无法百分百地得到发挥，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PTC效应；(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％。
3.3 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“2、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 PCTCN2018114298-appb-000006
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16 对比极片2-11 常规极片N 10个全部通过 10个全部不通过 2200
电池17 对比极片2-12 常规极片N 10个全部通过 10个全部通过 2300
电池18 极片2-13 常规极片N 10个全部通过 10个全部通过 2500
电池19 极片2-14 常规极片N 10个全部通过 10个全部通过 2700
电池20 极片2-15 常规极片N 10个全部通过 10个全部通过 2900
电池21 极片2-16 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 活性材料可以明显改善电池的过充安全性能；此外碳包覆的电化学活性材料还可以改善电池的循环寿命。
本领域技术人员可以理解：以上仅以锂电池为例示出了本发明的安全涂层的应用实例，但是本发明的安全涂层同样可以应用于其它类型的电池或电化学装置，而仍然可以获得本发明的良好技术效果。
根据上述说明书的揭示和教导，本发明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，本发明并不局限于上面揭示和描述的具体实施方式，对本发明的一些修改和变更也应当落入本发明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，并不对本发明构成任何限制。

Claims (10)

  1. 一种正极极片，包括集流体、正极活性材料层和设置于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，所述高分子基体是聚偏氟烯烃和/或聚偏氯烯烃高分子基体，基于所述安全涂层的总重量，
    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％，
    所述无机填料为碳包覆的正极电化学活性材料。
  2. 根据权利要求1所述的正极极片，所述高分子基体选自聚偏氟乙烯(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，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，
    其中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；
    导电金属材料选自Al粉、Ni粉、金粉中的至少一种；
    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，所述无机填料选自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。
  5. 根据权利要求1-4任一项所述的正极极片，所述安全涂层的厚度H为1μm≤H≤20μm，优选地3μm≤H≤10μm。
  6. 根据权利要求1-4任一项所述的正极极片，所述碳包覆的正极电化学活性材料中，基于碳包覆的正极电化学活性材料的重量，碳的重量百分比为0.5wt％-5wt％。
  7. 根据权利要求1-4任一项所述的正极极片，其中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％-15wt％，所述无机填料的重量百分比为15wt％-45wt％。
  8. 一种电化学装置，包括根据权利要求1至7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。
  9. 一种正极极片用安全涂层，所述安全涂层包含高分子基体、导电材料和无机填料，所述高分子基体是聚偏氟烯烃和/或聚偏氯烯烃高分子基体，基于所述安全涂层的总重量，
    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％，
    所述无机填料为碳包覆的正极电化学活性材料。
  10. 根据权利要求9所述的正极极片用安全涂层，其中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％-15wt％，所述无机填料的重量百分比为15wt％-45wt％。
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