WO2023123087A1 - 一种水系正极极片及包含该极片的二次电池及用电装置 - Google Patents

一种水系正极极片及包含该极片的二次电池及用电装置 Download PDF

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WO2023123087A1
WO2023123087A1 PCT/CN2021/142609 CN2021142609W WO2023123087A1 WO 2023123087 A1 WO2023123087 A1 WO 2023123087A1 CN 2021142609 W CN2021142609 W CN 2021142609W WO 2023123087 A1 WO2023123087 A1 WO 2023123087A1
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positive electrode
active material
current collector
material layer
electrode sheet
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PCT/CN2021/142609
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English (en)
French (fr)
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程丛
裴海乐
陈均桄
张盛武
王星会
李世松
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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 PCT/CN2021/142609 priority Critical patent/WO2023123087A1/zh
Priority to EP21964279.0A priority patent/EP4254560A1/en
Priority to CN202180092928.5A priority patent/CN116830312A/zh
Priority to US18/324,680 priority patent/US20230361305A1/en
Publication of WO2023123087A1 publication Critical patent/WO2023123087A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of secondary batteries, in particular to a water-based positive electrode sheet with improved mechanical and electrical properties, and a secondary battery, a battery pack, and an electrical device including the positive electrode sheet.
  • Lithium iron phosphate (LFP) cathode material lithium-ion batteries are extremely safe in terms of safety due to the stable structure and high-temperature decomposition characteristics of lithium iron phosphate materials. It has great advantages, and the lithium iron phosphate material does not contain heavy metals, and the cost is also low. It has developed rapidly in recent years.
  • deionized water can be used instead of solvent NMP in the water-based binder system
  • the water-based binders for secondary batteries developed on the market such as styrene-butadiene emulsion (SBR), hydroxymethyl cellulose (CMC), polyacrylic acid Ester (PAA), polytetrafluoroethylene emulsion (PTFE) and other common problems such as uneven dispersion of solid matter, poor consistency of water-based positive electrode slurry, low stability, prone to sedimentation, poor adhesion and high brittleness of the electrode sheet , can not meet the requirements for the use of lithium-ion batteries.
  • SBR styrene-butadiene emulsion
  • CMC hydroxymethyl cellulose
  • PAA polyacrylic acid Ester
  • PTFE polytetrafluoroethylene emulsion
  • other common problems such as uneven dispersion of solid matter, poor consistency of water-based positive electrode slurry, low stability, prone to sedimentation, poor adhesion
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a water-based positive pole piece to solve the technical problems of improving the mechanical properties of the pole piece, especially the flexibility, and further improving the kinetic performance of the battery.
  • the first aspect of the present application provides a water-based positive electrode sheet, including a current collector and a positive active material layer disposed on at least one surface of the current collector, the positive active material layer includes a water-based binder, wherein the adhesive force AT between the positive electrode active material layer and the current collector and the cohesive force CT of the positive electrode active material layer itself satisfy the following relationship: 1 ⁇ CT/AT ⁇ 10. In a further embodiment, the ratio of CT to AT is in the range of 2-8, alternatively 3-5.
  • the balance of the cohesive force of the pole piece and the adhesion of the film layer in the water-based positive pole piece can be adjusted.
  • the contact angle between the current collector and water is 5°-90°, optionally 20°-70°.
  • the adhesive force AT between the positive electrode active material layer and the current collector is 6-45N/m, optionally 10-35N/m.
  • the cohesion CT of the positive electrode active material layer is 40-140 N/m, optionally 60-120 N/m. Setting the adhesive force AT and the cohesive force CT within a specific range can further improve the performance of the pole piece.
  • the proportion of the aqueous binder in the positive active material layer is 0.5-10% by weight, optionally 1.5-5% by weight, based on the total weight of the positive active material layer .
  • the proportion of the water-based binder in the positive electrode active material layer can be maintained, which is beneficial to the maintenance of battery capacity.
  • the current collector comprises a surface modified aluminum foil.
  • the surface-modified aluminum foil can further improve the adhesion to the positive electrode active material layer and the kinetic performance of the battery.
  • the current collector includes a pre-treated current collector activated by high surface energy, and the pre-treatment process includes corona treatment, plasma treatment, rolling, polar solvent coating or a combination thereof.
  • the high surface energy activation pretreatment of the current collector can further improve the adhesion between the current collector and the positive electrode active material layer.
  • the treatment voltage in the corona treatment is 5-30kV, optionally 10-25kV.
  • the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material is selected from the group consisting of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel One or more of lithium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide.
  • the positive electrode active material layer contains a conductive agent, and the conductive agent includes one of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes. one or more species. The selection of the positive electrode active material and the conductive agent can broaden the structure and type of the positive electrode active material layer of the positive electrode sheet, and achieve a wider adjustment range.
  • the aqueous adhesive comprises soluble polysaccharides and derivatives thereof, water-soluble or water-dispersible polymers or mixtures thereof.
  • the aqueous binder is methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyethyleneimine and its salts, Polyacrylamide, acrylonitrile-acrylic acid copolymer and its derivatives, or mixtures of the above substances.
  • the water-based adhesive is a compound mixture of soluble polysaccharides and derivatives thereof and water-soluble or water-dispersed polymers, and the compounding ratio is 2:1-1:15, which can be The selection is 1:2-1:14.
  • the water-based adhesive is a compound mixture of xanthan gum and polyethyleneimine, and the compounding ratio is 2:1-1:15, optionally 1:2-1:14 ;
  • the average molecular weight Mn of xanthan gum is 300000-2000000g/mol
  • the average molecular weight Mn of polyethyleneimine is 2000-50000g/mol.
  • the positive electrode sheet has a sheet resistance of 0.3 to 1 ⁇ .
  • the positive electrode sheet resistance of the present application is significantly reduced, further improving the kinetic performance of the secondary battery including the positive electrode sheet.
  • the second aspect of the present application provides a secondary battery, which includes the aqueous positive electrode sheet selected from the first aspect of the present application.
  • a third aspect of the present application provides a battery pack including the secondary battery selected from the second aspect of the present application.
  • a fourth aspect of the present application provides an electric device, which includes the secondary battery selected from the second aspect of the present application or the battery pack of the third aspect of the present application.
  • FIG. 1 is a schematic diagram of corona treatment on one side and/or both sides of a positive electrode current collector in one embodiment of the present application.
  • Fig. 2 shows the change of the contact angle with water before and after corona treatment of the aluminum foil current collector in one embodiment of the present application.
  • FIG. 3 is a schematic diagram of a lithium ion secondary battery in one embodiment of the present application.
  • FIG. 4 is an exploded view of the lithium-ion secondary battery in one embodiment of the present application shown in FIG. 3 .
  • Fig. 5 is a schematic diagram of a battery pack in an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack shown in FIG. 5 in one embodiment of the present application.
  • Fig. 7 is a schematic diagram of a device in which a battery pack is used as a power source in an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or individual value may serve as a lower or upper limit by itself in combination with any other point or individual value or with other lower or upper limits to form an unexpressly recited range.
  • the current adhesives mainly include the following categories: butadiene-styrene copolymer (SBR) and its derivatives, sodium carboxymethylcellulose (CMC-Na) and its derivatives, acrylonitrile-acrylate copolymer and Its derivatives (LA series), etc.
  • SBR butadiene-styrene copolymer
  • CMC-Na sodium carboxymethylcellulose
  • LA series acrylonitrile-acrylate copolymer and Its derivatives
  • thermoelastic adhesives such as SBR and silicone rubber are used for the water-based positive pole piece, although the problem of brittleness of the pole piece can be effectively solved, the adhesion between the current collector of the pole piece and the film layer of the pole piece is insufficient.
  • the inventors have found through research that, on the one hand, by optimizing the type and proportion of the binder of the water-based positive electrode sheet, and on the other hand, by roughening the substrate and modifying the polar adhesive, the adhesion of the current collector and the positive active material layer can be achieved.
  • the first aspect of the present application provides a water-based positive electrode sheet, including a current collector and a positive active material layer disposed on at least one surface of the current collector, and the positive active material layer includes a water-based binder, wherein the The adhesive force AT between the positive electrode active material layer and the current collector and the cohesive force CT of the positive electrode active material layer itself satisfy the following relationship: 1 ⁇ CT/AT ⁇ 10.
  • the ratio of CT to AT is in the range of 2-8, alternatively 3-5.
  • the ratio of CT/AT is too small, the cohesion of the positive electrode active material layer itself is insufficient, and it is easy to crack internally; if the ratio of CT/AT is too large, the adhesion between the current collector and the film layer of the pole piece is insufficient, and the pole piece It is easy to produce powder drop, or even large-area peeling off, resulting in an increase in the internal resistance of the battery polarization, affecting the battery rate and cycle performance.
  • the contact angle of the current collector with water is 5°-90°, optionally 20°-70°.
  • the contact angle between the current collector and water can be adjusted by selecting the type of the current collector and performing surface treatment on the current collector. By adjusting the contact angle between the current collector and water and setting it within a specific range, the bonding performance between the current collector and the positive electrode active material layer can be adjusted.
  • the adhesive force AT between the positive electrode active material layer and the current collector is 6-45 N/m, optionally 10-35 N/m.
  • the cohesion CT of the positive electrode active material layer is 40-140 N/m, optionally 60-120 N/m. Setting the adhesive force AT and the cohesive force CT within a specific range can further improve the performance of the pole piece. If AT and CT are too high or too low, the balance between them will be easily destroyed, which will increase the brittleness of the pole piece, deteriorate the flexibility, and reduce the electrical performance of the secondary battery.
  • the proportion of the aqueous binder in the positive active material layer is 0.5-10% by weight, optionally 1.5-5% by weight, based on the total weight of the positive active material layer . If the proportion of the water-based adhesive is too low, the bonding effect will be insufficient; if the proportion of the water-based adhesive is too high, the proportion of the active material in the electrode formulation will drop significantly, which is not conducive to the maintenance of battery capacity and cannot Meet the demand for high energy density of the battery. By adjusting the proportion of the water-based binder in the positive electrode active material layer, the proportion of the active material in the electrode sheet formula can be maintained, and the capacity retention rate of the battery is improved.
  • the current collector comprises a surface-modified aluminum foil.
  • the surface-modified aluminum foil is selected as the current collector, which can combine high conductivity, high stability, high flexibility and good adhesive performance, and can further improve the adhesive force with the positive active material layer and the battery kinetic performance.
  • the current collector includes a pre-treated current collector activated by high surface energy
  • the pre-treatment process includes corona treatment, plasma treatment, rolling, polar solvent coating, or a combination thereof. It is advantageous to choose corona treatment to make the current collector have high surface energy, which is conducive to the uniform spreading of the positive electrode slurry on the current collector, and improves the adhesion between the positive electrode active material layer and the current collector.
  • FIG. 1 shows a schematic diagram of corona treatment on one side and/or both sides of a positive electrode current collector in one embodiment of the present application.
  • the treatment voltage in the corona treatment is 5-30 kV, optionally 10-25 kV.
  • the surface roughness and surface energy of the current collector after corona treatment are significantly increased, and the water-based positive electrode slurry spreads rapidly on the current collector.
  • the bonding strength between the positive electrode active material layer and the current collector can be significantly increased.
  • the conductivity between the positive electrode active material layer and the current collector is greatly increased, and the polarization is reduced, which can significantly improve the cycle performance of the battery.
  • Fig. 2 shows the change of the contact angle with water before and after corona treatment of the aluminum foil current collector in one embodiment of the present application.
  • the contact angle between the aluminum foil current collector and water is reduced from 91.86° to 33.86°, which makes the water-based positive electrode slurry spread on the current collector more quickly, and improves the bonding strength and conductivity. Therefore, by selecting an appropriate corona treatment voltage, further improvements in sheet resistance as well as cell kinetics can be achieved.
  • the positive electrode active material layer contains a positive electrode active material, and the positive electrode active material is selected from the group consisting of lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel One or more of lithium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide.
  • the positive electrode active material layer contains a conductive agent, and the conductive agent includes one of conductive carbon black, superconducting carbon black, conductive graphite, acetylene black, Ketjen black, graphene, and carbon nanotubes. one or more species. The selection of the positive electrode active material and the conductive agent can broaden the structure and type of the positive electrode active material layer of the positive electrode sheet, and achieve a wider adjustment range.
  • the water-based adhesive comprises soluble polysaccharides and derivatives thereof, water-soluble or water-dispersible polymers or mixtures thereof.
  • the aqueous binder is methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyethyleneimine and its salts, Polyacrylamide, acrylonitrile-acrylic acid copolymer and its derivatives, or mixtures of the above substances.
  • the water-based adhesive is a compound mixture of soluble polysaccharides and their derivatives and water-soluble or water-dispersed polymers, and the compounding ratio is 2:1-1:15, which can be The selection is 1:2-1:14.
  • the water-based adhesive is a compound mixture of xanthan gum and polyethyleneimine, and the compounding ratio is 2:1-1:15, optionally 1:2-1:14 ;
  • the average molecular weight Mn of xanthan gum is 300000-2000000g/mol
  • the average molecular weight Mn of polyethyleneimine is 2000-50000g/mol.
  • the combination of the selected specific water-based binder and its ratio can achieve the best performance improvement, including the mechanical properties of the positive electrode sheet and the kinetic performance of the battery.
  • the present invention optimizes the formula and adopts flexible water-based adhesives, such as hydroxypropyl methylcellulose HPMC, xanthan gum XG, polyethyleneimine, etc. Na, under the premise of ensuring the high stability of the slurry, it can achieve a better balance between the cohesion and adhesion of the pole piece.
  • flexible water-based adhesives such as hydroxypropyl methylcellulose HPMC, xanthan gum XG, polyethyleneimine, etc. Na
  • the water-based binder is used as the binder and the deionized water is used as the solvent to mix and stir to form a slurry, the slurry is uniform, the dispersion effect of the conductive agent and the binder is good, and the surface of the coated pole piece is smooth and free of particles
  • the protrusions are firmly bonded to the current collector, and the positive electrode material is not easy to drop powder and release the film during the winding process, which meets the high-speed winding requirements of the pole piece, and the assembled battery is stable.
  • the film layer of the pole piece does not shed powder and film during the charging and discharging process of the battery, and the structure is stable, which can effectively inhibit the polarization of the pole piece and reduce the internal resistance of the battery, thereby improving the capacity retention of the battery;
  • the pole piece is flexible and can withstand the increased stress caused by the expansion of the pole piece during the charging and discharging process of the battery. The pole piece will not break, ensuring the safety and reliability of the battery application.
  • the positive electrode sheet has a sheet resistance of 0.3 to 1 ⁇ .
  • the sheet resistance of the positive pole piece of the present application is significantly lower than that of the conventionally used positive pole piece, which further improves the kinetic performance of the battery comprising the positive pole piece.
  • the second aspect of the present application provides a secondary battery, which includes the water-based positive electrode sheet of the first aspect of the present application.
  • the secondary battery is a lithium ion secondary battery.
  • the lithium ion secondary battery has a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet includes a positive electrode current collector and a positive active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode The active material layer contains a positive electrode active material and a conductive agent.
  • the battery cells of the secondary battery will be described in detail below.
  • a lithium-ion secondary battery typically includes a positive pole piece, a negative pole piece, a separator, and an electrolyte.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolytic solution includes electrolyte salts and solvents.
  • the electrolyte salt can be a common electrolyte salt in lithium-ion secondary batteries, such as lithium salt, including the above-mentioned lithium salt as a high thermal stability salt, lithium salt as a low-impedance additive, or lithium salt that inhibits aluminum foil corrosion. Salt.
  • the electrolyte salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide), LiTFSI (bistrifluoromethane Lithium sulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorodifluorooxalate phosphate), LiSO 3 F (lithium fluorosulfonate), NDFOP (difluorodioxalate), Li 2 F(SO 2 N) 2 SO 2 F, KFSI, CsFSI, Ba(FSI) 2 and LiFSO 2 NSO 2 CH 2 CH 2 CF 3 more than one of them
  • the solvent is not particularly limited, and can be selected according to actual needs.
  • the solvent is a non-aqueous solvent.
  • the solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylates.
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl Carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), Fluoroethylene Carbonate (FEC), Methyl Formate (MF), Methyl Acetate Ester (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB) , e
  • the electrolyte may optionally include other additives.
  • additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc.
  • the additive is selected from cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate ester compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds , aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic acid anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, and carboxylate compounds.
  • the positive pole piece includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, and the positive active material layer includes a positive active material and a conductive agent.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector can be formed by metal materials (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the positive electrode active material layer provided on the surface of the positive electrode current collector includes a positive electrode active material.
  • the cathode active material used in the present application may have any conventional cathode active material used in secondary batteries.
  • the positive electrode active material may contain one or more selected from the group consisting of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium manganese iron phosphate, lithium manganese iron phosphate One or more of the composite materials with carbon and their modified compounds. These materials are all commercially available. Carbon may be coated on the surface of the positive electrode active material.
  • the positive active material layer optionally includes a conductive agent.
  • a conductive agent there is no specific limitation on the type of conductive agent, which can be selected by those skilled in the art according to actual needs.
  • the conductive agent used for the positive electrode material can be selected from more than one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive active material layer may also optionally include a binder.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid ( One or more of PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode sheet can be prepared according to methods known in the art.
  • a positive electrode active material coated with carbon, a conductive agent and a binder can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode On the current collector, after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material.
  • Composite current collectors can be formed by metal materials (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the negative electrode material layer usually includes negative electrode active material and optional binder, optional conductive agent and other optional additives, usually formed by coating and drying negative electrode slurry into.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring them evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of lithium ion secondary batteries can be used, and those skilled in the art can select according to actual needs.
  • the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, simple silicon, silicon oxide compounds, silicon-carbon composites, and lithium titanate. kind.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), One or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • CMC-Na sodium carboxymethylcellulose
  • a separator is also included in a lithium ion secondary battery using an electrolytic solution.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from more than one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • a lithium ion secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer package of the lithium-ion secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the lithium-ion secondary battery may also be a soft bag, such as a pouch-type soft bag.
  • the material of the soft bag may be plastic, and examples of plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 3 shows a square-shaped lithium-ion secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the lithium-ion secondary battery can be assembled into a battery module 4, and the number of lithium-ion secondary batteries contained in the battery module 4 can be one or more, and the specific number can be determined by those skilled in the art according to the application of the battery module 4 and capacity selection.
  • a plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module. Of course, it can also be arranged in any other manner. Furthermore, the plurality of lithium-ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may also include a housing with a containing space in which a plurality of lithium-ion secondary batteries 5 are housed.
  • the above-mentioned lithium-ion secondary batteries 5 or battery modules 4 can be assembled into a battery pack 1, and the number of lithium-ion secondary batteries 5 or battery modules 4 contained in the battery pack 1 can be determined by those skilled in the art according to the battery pack 1 Choose from your application and capacity.
  • the battery pack 1 may include a battery box and a plurality of battery cells disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating battery cells.
  • the present application also provides a device, which includes the battery pack provided in the present application.
  • the battery pack can be used as a power source for the device and also as an energy storage unit for the device.
  • the device can be, but not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a battery pack can be selected according to its usage requirements.
  • Figure 7 is an example device.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • battery packs or battery modules can be employed.
  • Li iron phosphate cathode active material LPF, conductive agent conductive carbon black, and water-based binder at a weight ratio of 96:1:3, wherein the water-based binder uses xanthan gum (molecular weight is about 1,000,000 g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) and polyethyleneimine (molecular weight is about 10000g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), the compounding weight ratio is 3:0 (that is, in the embodiment In 1, the water-based binder used is only xanthan gum); the balance is stirred and mixed evenly with deionized water as a solvent to obtain a positive electrode slurry with a solid content of 50%.
  • xanthan gum molecular weight is about 1,000,000 g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.
  • polyethyleneimine molecular weight is about 10000g/mol, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.
  • corona pretreatment was performed on the positive electrode current collector of the aluminum foil, and the treatment voltage was 20kV, and then the positive electrode slurry was evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet.
  • a 2 ⁇ m thick ceramic coating was coated with a PE porous film as a separator.
  • Example 5 Other steps are the same as in Example 5 except that the current collector corona treatment applies a difference in electrode voltage.
  • Example 1 the positive pole piece, the separator, and the negative pole piece are stacked in order, so that the separator is between the positive and negative pole pieces to play the role of isolation, and then the bare battery is obtained by winding, and the tabs are welded to the bare battery, and Put the bare battery into the aluminum case, and bake it at 80°C to remove water, then inject the electrolyte and seal it to get an uncharged battery.
  • the uncharged battery is then subjected to standing, hot and cold pressing, formation, shaping, capacity testing and other processes in sequence to obtain the lithium ion secondary battery product of Example 1.
  • the lithium ion secondary battery products of Examples 2-13 and Comparative Examples 1-2 were also prepared according to the above steps.
  • test methods for the parameters of the positive pole piece and the battery are as follows:
  • the contact angle refers to the angle ⁇ between the tangent of the gas-liquid interface at the intersection of gas, liquid and solid and the solid-liquid boundary line, which is a measure of the degree of wetting. If ⁇ 90°, the solid is lyophilic, that is, the liquid can wet the solid, and the smaller the angle, the better the wettability; if ⁇ >90°, the solid is lyophobic, that is, the liquid does not wet the solid, It moves easily on the surface and cannot enter the pores. In the present invention, the contact angle test is directly performed with reference to the GB/T 30693-2014 standard document, and the liquid reagent is deionized water.
  • Adhesion test is the test of 180°peel strength.
  • the high-speed rail tensile machine AI-7000S is selected, and the test standard is GB/T 36363-2018.
  • Take the pole piece to be tested (the positive pole piece with the active material layer coated on both sides of the current collector), the appearance of the pole piece is good, and no defective products are allowed.
  • the cohesion test is the 180° shear strength test. Choose the high-speed rail tensile machine AI-7000S. Take the pole piece to be tested (the positive pole piece with the active material layer coated on both sides of the current collector), the appearance of the pole piece is good, and no defective products are allowed. Use a blade to cut a sample with a width of 30mm and a length of 100-160mm. Stick the special double-sided adhesive NITTO.NO5000NS on the steel plate, the width of the tape is 20mm, and the length is 90-150mm.
  • Positive pole sheet winding hot pressing test Wind the positive electrode sheet, separator, and negative electrode sheet into a square battery, then perform hot pressing at 90°C and 0.8MPa pressure, then disassemble the battery and observe the creases Whether there is light leakage or not, the battery obtained by winding has a total of 45 creases. Each group was tested 5 times and the average value was taken.
  • Positive electrode membrane folding test After folding the positive electrode membrane in half, use a 2kg roller to roll back and forth 3 times, then spread the positive electrode membrane flat, and repeat the above operation until light leaks at the half fold, and record the number of folds. Each group was tested 5 times and the average value was taken.
  • CRM-01 sheet resistance tester Use the CRM-01 sheet resistance tester to test the sheet resistance of the positive electrode sheet. Each group was tested 5 times and the average value was taken.
  • Example 1 the DC impedance test process of the battery is as follows: at 25°C, charge the battery corresponding to Example 1 with a constant current of 1/3C to 3.65V, and then charge it with a constant voltage of 3.65V to a current of 0.05C , after resting for 5min, record the voltage V1. Then discharge at 1/3C for 30s, record the voltage V2, then (V2-V1)/1/3C, get the internal resistance DCR of the battery.
  • the battery capacity retention test process is as follows: at 25°C, charge the battery corresponding to Example 1 with a constant current of 1/3C to 3.65V, and then charge it with a constant voltage of 3.65V to a current of 0.05 C, put it aside for 5 minutes, and then discharge it to 2.7V at 1/3C, and record the resulting capacity as the initial capacity C0.
  • the battery capacity retention data corresponding to Example 1 in Table 1 is the data measured after 800 cycles under the above test conditions, that is, the value of P800.
  • the test process of Comparative Example 1 and other embodiments is the same as above.
  • Examples 1-7 when the current collector is corona treated and the voltage is maintained at 20kV, the specific ratio of xanthan gum and polyethyleneimine in the water-based adhesive makes the performance of the positive electrode sheet and the secondary battery A further improvement occurred.
  • Examples 8-12 when the ratio of xanthan gum and polyethyleneimine in the water-based adhesive is kept constant, the voltage during corona treatment is maintained at 10-25kV, which can produce further reduced sheet resistance.
  • the ratio of CT/AT is higher than 10 because no corona treatment is performed on the positive current collector. Although the capacity retention rate of the secondary battery is still high, the resistance of the positive pole piece is obviously increased, and the DC resistance of the secondary battery is also high.
  • Comparative Example 1 uses a voltage of 20kV to corona treat the positive current collector, but uses a conventional adhesive composed of sodium carboxymethylcellulose and acrylonitrile-acrylic acid ester copolymer, and its positive electrode sheet
  • the CT/AT value is higher than 10.
  • the ratio of CT/AT of the positive pole piece in the range of 1 to 10, especially in the range of 1 to 8, by adjusting the voltage of the corona treatment to a specific range and adding xanthogen in the adhesive
  • the ratio of the glue and polyethyleneimine is adjusted to a specific range, the performance of the positive electrode sheet and the secondary battery made therefrom can be further improved.

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Abstract

本申请涉及一种水系正极极片，其包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，其中所述正极活性物质层与所述集流体之间的粘接力AT和所述正极活性物质层自身的内聚力CT满足以下关系式：1≤CT/AT≤10。本申请还涉及包含所述水系正极极片的二次电池、包含所述二次电池的电池包以及包含所述电池包的用电装置。

Description

一种水系正极极片及包含该极片的二次电池及用电装置 技术领域
本申请涉及二次电池领域，尤其涉及一种具有改善的力学性能以及电学性能的水系正极极片，以及包含该正极极片的二次电池、电池包及其用电装置。
背景技术
二次电池因其成本低、寿命长，安全性好等特点成为最受欢迎的能量存储***，现已被广泛应用于纯电动汽车、混合电动汽车以及智能电网等领域。高安全性与低成本是动力/储能电池市场技术持续发展的重点方向，磷酸铁锂(LFP)正极材料锂离子电池因磷酸铁锂材料稳定的结构与耐高温分解特性在安全性上具有极大优势，且磷酸铁锂材料不含重金属，成本亦较低，近年来发展愈发迅猛。
现有动力电池正极大多采用油系配方进行浆料制作，其普遍为粘接剂聚偏二氟乙烯(PVDF)和溶剂N-甲基吡咯烷酮(NMP)组成的体系。但是，PVDF和NMP均为石油衍生化学产品,在浆料搅拌和涂布过程中，大量NMP毒性气体会挥发到空气中，污染环境并对人体产生危害。另外，NMP和PVDF合成及后处理过程复杂，能耗高，应用成本很高。基于此，电池行业也在尝试开发水系正极体系，一方面可避免有机溶剂NMP的使用，减小对环境及人类危害，另一方面不涉及氟聚合物PVDF的大量使用及其NMP溶剂的复杂回收，其电池制作成本低，可实现规模化降低成本应用。
虽然在水性粘接剂体系中可使用去离子水代替溶剂NMP使用，但市 面上开发的二次电池用水性粘结剂如丁苯乳液(SBR)、羟甲基纤维素(CMC)、聚丙烯酸酯(PAA)、聚四氟乙烯乳液(PTFE)等普遍存在固体物质分散不均匀，水性正极浆料一致性较差，稳定性不高，易发生沉降，极片粘接力差和脆性高等问题，不能满足锂离子电池的使用要求。虽然行业内有报道可通过增塑剂的添加来改善极片脆性，但改善效果有限。
因此，目前的水系正极极片在改善极片力学性能以及电池动力学性能方面仍不太令人满意。本领域中仍然需要具有改善的特性的水系正极极片。
发明内容
本申请是鉴于上述课题而进行的，其目的在于提供一种水系正极极片，以解决改善极片力学性能，特别是柔韧性，以及进一步改善电池动力学性能的技术问题。
为了达到上述目的，本申请第一方面提供一种水系正极极片，包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，其中所述正极活性物质层与所述集流体之间的粘接力AT和所述正极活性物质层自身的内聚力CT满足以下关系式：1≤CT/AT≤10。在进一步的实施方案中，CT与AT比值的范围为2-8，可选地为3-5。通过设定正极活性物质层自身的内聚力CT与正极活性物质层与集流体之间的粘接力AT的比值范围，可以调节水系正极极片中的极片内聚力及膜层粘接力的平衡。
在任意实施方案中，所述集流体与水的接触角为5°-90°，可选地为20°-70°。通过调节集流体与水的接触角，可调节集流体与正极活性物质层之间的粘接性能。
在任意实施方案中，所述正极活性物质层与所述集流体之间的粘接力 AT为6-45N/m，可选地为10-35N/m。在任意实施方案中，所述正极活性物质层的内聚力CT为40-140N/m，可选地为60-120N/m。将粘接力AT以及内聚力CT设置在特定范围内，可实现对于极片性能的进一步改善。
在任意实施方案中，所述水性粘接剂在所述正极活性物质层中的比例为0.5-10重量％，可选地为1.5-5重量％，基于所述正极活性物质层的总重量计。通过调节水性粘接剂在正极活性物质层中的比例，可以保持正极活性物质在极片配方中的占比，有利于电池容量的保持。
在任意实施方案中，所述集流体包含表面改性的铝箔。经过表面改性的铝箔可进一步改善与正极活性物质层的粘接力以及电池动力学性能。
在任意实施方案中，所述集流体包括经高表面能活化预处理的集流体，所述预处理工艺包含电晕处理、等离子体处理、辊压、极性溶剂涂敷或其组合。将集流体进行高表面能活化预处理，可进一步改善集流体与正极活性物质层的粘接力。
在任意实施方案中，所述电晕处理中处理电压为5-30kV，可选地为10-25kV。通过选择电晕处理对集流体进行高表面能活化，并进一步选择合适的处理电压，可实现对于膜片电阻以及电池动力学的进一步改善。
在任意实施方案中，所述正极活性物质层中含有正极活性材料，所述正极活性材料选自包含磷酸铁锂、磷酸锰锂、磷酸钴锂、磷酸铁锰锂、锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物中的一种或多种。在任意实施方案中，所述正极活性物质层中含有导电剂，所述导电剂包含导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或多种。对正极活性材料与导电剂的选择可拓宽所述正极极片的正极活性物质层的结构和种类，实现更宽的调节范围。
在任意实施方案中，所述水性粘接剂包含可溶性多糖类及其衍生物、 水溶性或水分散液高分子聚合物或其混合物。在进一步的实施方案中，所述水性粘接剂为甲基纤维素及其盐、黄原胶及其盐、壳聚糖及其盐、海藻酸及其盐、聚乙烯亚胺及其盐、聚丙烯酰胺、丙烯腈-丙烯酸共聚物及其衍生物，或上述物质的混合物。通过选择特定的水性粘接剂种类，可实现正极极片的力学性能的持续改善，尤其是柔韧性。
在任意实施方案中，所述水性粘接剂为可溶性多糖类及其衍生物与水溶性或水分散液高分子聚合物的复配混合物，复配比例为2:1-1:15，可选地为1:2-1:14。在进一步的实施方案中，所述水性粘接剂为黄原胶和聚乙烯亚胺的复配混合物，复配比例为2:1-1:15，可选地为1:2-1:14；可选地，黄原胶的平均分子量Mn为300000-2000000g/mol，聚乙烯亚胺的平均分子量Mn为2000-50000g/mol。所选择的具体的水性粘接剂的组合以及其配比可实现最佳的性能提升，包括正极极片力学性能以及电池的动力学性能。
在任意实施方案中，所述正极极片的膜片电阻为0.3至1Ω。本申请的正极膜片电阻得到了显著降低，进一步改善了包含所述正极极片的二次电池的动力学性能。
本申请的第二方面提供一种二次电池，其包括选自本申请的第一方面的水系正极极片。
本申请的第三方面提供一种电池包，其包括选自本申请的第二方面的二次电池。
本申请的第四方面提供一种用电装置，其包括选自本申请的第二方面的二次电池或者本申请的第三方面的电池包。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请实施例中所需要使用的附图作简单的介绍。显而易见地，下面所描述的附图仅仅是本申 请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的一个实施方式中对正极集流体进行单面和/或双面电晕处理的示意图。
图2示出了本申请一个实施方式中铝箔集流体进行电晕处理之前和之后与水的接触角变化。
图3是本申请一个实施方式中的锂离子二次电池的示意图。
图4是图3所示的本申请一个实施方式中的锂离子二次电池的分解图。
图5是本申请一个实施方式中的电池包的示意图。
图6是图5所示的本申请一个实施方式中的电池包的分解图。
图7是本申请一个实施方式中的电池包用作电源的装置的示意图。
附图标记说明
1电池包
2上箱体
3下箱体
4电池模块
5锂离子二次电池
51壳体
52电极组件
53盖板
具体实施方式
为了简明，本申请具体地公开了一些数值范围。然而，任意下限可以与任意上限组合形成未明确记载的范围；以及任意下限可以与其它下限组 合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在水系正极极片组成中，水性粘接剂的选型相当重要。当前粘接剂主要有以下几类：丁二烯-苯乙烯共聚物(SBR)及其衍生物、羧甲基纤维素钠(CMC-Na)及其衍生物、丙烯腈-丙烯酸酯共聚物及其衍生物(LA系列)等。其中，若水系正极极片仅采用SBR、有机硅橡胶等热弹性粘接剂，虽能有效解决极片脆性问题，但极片集流体与极片膜层之间的粘接力不足，极片易产生掉粉，甚至大面积脱膜，导致电池极化内阻增加，影响电池倍率和循环性能，严重时甚至会影响电池安全性能。尤其是SBR分子内含有双键，其应用于高压正极体系易氧化分解，还会给电池性能带来一定的副作用。而CMC-Na和LA系列由于主链上羧酸钠离子键和极性官能团的存在，导致聚合物分子间/内作用力大，涂布干燥时聚合物内应力过大，极片脆性增加，柔韧性变差，易产生涂布开裂，干燥后极片弯折时易断裂，无法实现卷绕。采用多种粘接剂复配体系，虽可平衡极片内聚力和膜层粘接力，但改善效果非常有限。更为重要的是由于粘接剂种类和含量较高，导致极片配方中活性物质的占比大幅下降，不利于电池容量的保持，无法满足电池高能量密度的迫切需求。
本发明人经研究发现，通过一方面进行水系正极极片的粘接剂类型和配比优化，另一方面进行基材粗糙化极性粘接改性，实现集流体及正极活性物质层的粘接力和正极活性物质层自身的内聚力的平衡，在保证正极活性物质层不掉粉、脱膜的前提下，实现极片高柔韧性性能，尤其是厚涂布、高压密极片柔韧性的保持。
具体的，本申请第一方面提供一种水系正极极片，包括集流体及设置 在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，其中所述正极活性物质层与所述集流体之间的粘接力AT和所述正极活性物质层自身的内聚力CT满足以下关系式：1≤CT/AT≤10。在进一步的实施方案中，CT与AT比值的范围为2-8，可选地为3-5。如果CT/AT的比值过小，则正极活性物质层自身的内聚力不足，容易内部开裂；如果CT/AT的比值过大，则集流体与极片膜层之间的粘接力不足，极片易产生掉粉，甚至大面积脱膜，导致电池极化内阻增加，影响电池倍率和循环性能。通过设定正极活性物质层自身的内聚力CT与正极活性物质层与集流体之间的粘接力AT的比值范围，可以调节水系正极极片中的极片内聚力及膜层粘接力的平衡。
在一些实施方案中，所述集流体与水的接触角为5°-90°，可选地为20°-70°。集流体与水的接触角可通过对集流体的种类的选择以及对集流体进行表面处理而进行调节。通过调节集流体与水的接触角设定在特定范围内，可调节集流体与正极活性物质层之间的粘接性能。
在一些实施方案中，所述正极活性物质层与所述集流体之间的粘接力AT为6-45N/m，可选地为10-35N/m。在一些实施方案中，所述正极活性物质层的内聚力CT为40-140N/m，可选地为60-120N/m。将粘接力AT以及内聚力CT设置在特定范围内，可实现对于极片性能的进一步改善。AT与CT过高或者过低，都容易破坏二者的平衡，使得极片脆性增加，柔韧性变差，同时使得二次电池的电学性能降低。
在一些实施方案中，所述水性粘接剂在所述正极活性物质层中的比例为0.5-10重量％，可选地为1.5-5重量％，基于所述正极活性物质层的总重量计。如果水性粘接剂的比例过低，则其粘接效果不足；如果水性粘接剂的比例过高，则会导致极片配方中活性物质的占比大幅下降，不利于电池容量的保持，无法满足电池高能量密度的需求。通过调节水性粘接剂在正 极活性物质层中的比例，可以保持活性物质在极片配方中的占比，改善了电池的容量保持率。
在一些实施方案中，所述集流体包含表面改性的铝箔。选择经过表面改性的铝箔作为集流体，可兼具高导电性、高稳定性、高柔韧性以及良好的粘接性能，可进一步改善与正极活性物质层的粘接力以及电池动力学性能。
在一些实施方案中，所述集流体包括经高表面能活化预处理的集流体，所述预处理工艺包含电晕处理、等离子体处理、辊压、极性溶剂涂敷或其组合。有利的是选择电晕处理来使得所述集流体具有高表面能，这有利于正极浆料在集流体上的均匀铺展，且提升正极活性物质层与集流体之间的粘接力。图1示出了本申请的一个实施方式中对正极集流体进行单面和/或双面电晕处理的示意图。在一些实施方案中，所述电晕处理中处理电压为5-30kV，可选地为10-25kV。本发明中经电晕处理后的集流体，表面粗糙度及表面能显著增加，水性正极浆料在集流体上铺展迅速，一方面可使正极活性物质层与集流体的粘接强度显著增加，电池卷绕过程中不脱膜；另一方面，正极活性物质层与集流体之间的导电性大幅度增加，极化减小，可显著改善电池的循环性能。图2示出了本申请一个实施方式中铝箔集流体进行电晕处理之前和之后与水的接触角变化。经过电晕处理，铝箔集流体与水的接触角从91.86°减小为33.86°，使得水性正极浆料在集流体上铺展更加迅速，提高了粘接强度以及导电性。因此，通过选择合适的电晕处理电压，可实现对于膜片电阻以及电池动力学的进一步改善。
在一些实施方案中，所述正极活性物质层中含有正极活性材料，所述正极活性材料选自包含磷酸铁锂、磷酸锰锂、磷酸钴锂、磷酸铁锰锂、锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物中的一种或多种。在一些实施方案中，所述正极活性物质 层中含有导电剂，所述导电剂包含导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或多种。对正极活性材料与导电剂的选择可拓宽所述正极极片的正极活性物质层的结构和种类，实现更宽的调节范围。
在一些实施方案中，所述水性粘接剂包含可溶性多糖类及其衍生物、水溶性或水分散液高分子聚合物或其混合物。在进一步的实施方案中，所述水性粘接剂为甲基纤维素及其盐、黄原胶及其盐、壳聚糖及其盐、海藻酸及其盐、聚乙烯亚胺及其盐、聚丙烯酰胺、丙烯腈-丙烯酸共聚物及其衍生物，或上述物质的混合物。通过选择特定的水性粘接剂种类，可实现正极极片的力学性能的持续改善，尤其是柔韧性。
在一些实施方案中，所述水性粘接剂为可溶性多糖类及其衍生物与水溶性或水分散液高分子聚合物的复配混合物，复配比例为2:1-1:15，可选地为1:2-1:14。在进一步的实施方案中，所述水性粘接剂为黄原胶和聚乙烯亚胺的复配混合物，复配比例为2:1-1:15，可选地为1:2-1:14；可选地，黄原胶的平均分子量Mn为300000-2000000g/mol，聚乙烯亚胺的平均分子量Mn为2000-50000g/mol。所选择的具体的水性粘接剂的组合以及其配比可实现最佳的性能提升，包括正极极片力学性能以及电池的动力学性能。
本发明通过配方优化，采用柔性水性粘接剂，如羟丙基甲基纤维素HPMC、黄原胶XG、聚乙烯亚胺等，相比于常规水性粘接剂羧甲基纤维素钠CMC-Na，在保证浆料高稳定性的前提下，使极片内聚力和粘接力达到更好的平衡。本发明以水性粘结剂作为粘结剂、去离子水作为溶剂混合搅拌成浆料，浆料均匀，导电剂、粘结剂分散效果良好，涂布制得的极片表面外观光滑，无颗粒突起，与集流体的粘合牢靠，正极材料在卷绕过程中不易掉粉和脱膜，满足极片的高速卷绕需求，组装的电池稳定。这样带来的效果是，一方面，电池充放电应用过程中极片膜层不掉粉脱膜，结构 稳定，可有效抑制极片极化，减低电池内阻，从而改善电池的容量保持率；另一方面，极片柔韧性强，可承受电池充放电过程因极片膨胀而带来的应力增加，极片不会产生断裂，保障电池应用时的安全可靠性。
在一些实施方案中，所述正极极片的膜片电阻为0.3至1Ω。本申请的正极极片的膜片电阻相较于常规使用的正极极片显著降低，进一步改善了包含所述正极极片的电池的动力学性能。
本申请第二方面提供一种二次电池，其包括本申请的第一方面的水系正极极片。在一些实施方案中，所述二次电池为锂离子二次电池。所述锂离子二次电池具有正极极片、负极极片、隔离膜及电解液，所述正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极活性物质层，所述正极活性物质层包含正极活性材料和导电剂。
下面对所述二次电池的电池单体进行详细阐述。
通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[电解液]
电解液在正极极片和负极极片之间起到传导离子的作用。电解液包括电解质盐和溶剂。
在本申请中，电解质盐可为锂离子二次电池中的常用电解质盐，例如锂盐，包括可为上述作为高热稳定性盐的锂盐、作为低阻抗添加剂的锂盐或抑制铝箔腐蚀的锂盐。作为实例，电解质盐可选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二 草酸磷酸锂)、LiSO 3F(氟磺酸锂)、NDFOP(二氟二草酸盐)、Li 2F(SO 2N) 2SO 2F、KFSI、CsFSI、Ba(FSI) 2及LiFSO 2NSO 2CH 2CH 2CF 3中的一种以上。
所述溶剂的种类没有特别的限制，可根据实际需求进行选择。在一些实施方式中，所述溶剂为非水性溶剂。可选地，所述溶剂可包括链状碳酸酯、环状碳酸酯、羧酸酯中的一种或几种。在一些实施方式中，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、四氢呋喃、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种以上。
在一些实施方式中，所述电解液中还可选地包括其他添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、以及改善电池低温性能的添加剂等。作为示例，所述添加剂选自含有不饱和键的环状碳酸酯化合物、卤素取代的环状碳酸酯化合物、硫酸酯化合物、亚硫酸酯化合物、磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、磷腈化合物、环状酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物、羧酸酯化合物中的至少一种。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极活性物质层，所述正极活性物质层包括正极活性材料和导电剂。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性物质层设置在正极集流体相对的两个表面的其中任意一者或两者上。
本申请的锂离子二次电池中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(例如铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
设置于正极集流体的表面上的正极活性物质层包括正极活性材料。本申请中所用的正极活性材料可具有二次电池中使用的任意常规正极活性材料。在一些实施方式中，所述正极活性材料可包含选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。正极活性材料表面上可包覆有碳。
正极活性物质层可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材 料的导电剂可以选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
正极活性物质层还可选地包括粘结剂。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将包覆碳的正极活性材料、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮(NMP))中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极材料层设置在负极集流体相对的两个表面中的任意一者或两者上。
本申请的锂离子二次电池中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(例如铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
本申请的锂离子二次电池中，所述负极材料层通常包含负极活性物质以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂 布干燥而成的。负极浆料涂通常是将负极活性物质以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水。
所述负极活性物质的具体种类不做限制，可以采用本领域已知的能够用于锂离子二次电池负极的活性物质，本领域技术人员可以根据实际需求进行选择。作为示例，负极活性物质可选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或几种。
作为示例，导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种以上。
其他可选助剂例如是增稠剂(如羧甲基纤维素钠(CMC-Na))等。
[隔离膜]
采用电解液的锂离子二次电池中还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种以上。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，锂离子二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对锂离子二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图3是作为一个示例的方形结构的锂离子二次电池5。
在一些实施方式中，参照图4，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。锂离子二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，锂离子二次电池可以组装成电池模块4，电池模块4所含锂离子二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块4的应用和容量进行选择。在电池模块4中，多个锂离子二次电池5可以是沿电池模块的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个锂离子二次电池5进行固定。可选地，电池模块4还可以包括具有容纳空间的外壳，多个锂离子二次电池5容纳于该容纳空间。
在一些实施方式中，上述锂离子二次电池5或者电池模块4可以组装成电池包1，电池包1所含锂离子二次电池5或者电池模块4的数量可由本领域技术人员根据电池包1的应用和容量进行选择。
图5和图6是作为一个示例的电池包1。参照图5和图6，在电池包1中可以包括电池箱和设置于电池箱中的多个电池单体。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池单体的封闭空间。
另外，本申请还提供一种装置，所述装置包括本申请提供的电池包。所述电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能***等。
作为所述装置，可以根据其使用需求来选择电池包。
图7是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
正极极片的制备
将磷酸铁锂正极活性材料LPF、导电剂导电碳黑、水性粘结剂按重量比为96：1：3混合，其中水性粘接剂采用黄原胶(分子量约为1000000g/mol，购自上海阿拉丁生化科技股份有限公司)和聚乙烯亚胺(分子量约为10000g/mol，购自上海阿拉丁生化科技股份有限公司)的复配混合物，复配重量比例为3:0(即在实施例1中，所用水性粘接剂仅为黄原胶)；余量用溶剂去离子水搅拌混合均匀，得到固含量为50％的正极浆料。之后将铝箔正极集流体进行电晕预处理，处理电压为20kV，然后将正极浆料均匀涂覆于正极集流体上，之后经过烘干、冷压、分切，得到正极极片。
负极极片的制备
将活性物质人造石墨、导电剂碳黑、粘结剂丁苯橡胶(SBR)、增稠剂羟甲基纤维素钠(CMC)按照重量比为96.2：0.8：0.8：1.2溶于溶剂去离子水中，混合均匀后制备成负极浆料；将负极浆料多次均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。
电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5％LiPF 6锂盐溶解于有机溶剂中，搅拌均匀，得到电解液。
隔离膜
以PE多孔薄膜涂布2μm厚的陶瓷涂层后作为隔离膜。
实施例2-7
除水性粘接剂黄原胶和聚乙烯亚胺复配比例差异外，其他步骤与实施例1相同。
实施例8-12
除集流体电晕处理应用电极电压差异外，其他步骤与实施例5相同。
实施例13
除集流体不采用电晕处理外，其他步骤与实施例5相同。
对比例1
除水性粘接剂材料不同外，其他步骤与实施例5相同。
对比例2
除集流体不采用电晕处理外，其他步骤与对比例1相同。
锂离子电池的制备
将实施例1正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，然后卷绕得到裸电池，给裸电池焊接极耳，并将裸电池装入铝壳中，并在80℃下烘烤除水，随即注入电解液并封口，得到不带电的电池。不带电的电池再依次经过静置、热冷压、化成、整形、容量测试等工序，获得实施例1的锂离子二次电池产品。
实施例2-13以及对比例1-2的锂离子二次电池产品同样按照上述步骤制备。
实施例1-13以及对比例1-2的正极极片以及锂离子二次电池的制备参数均列于下表1中。
正极极片以及电池的各项参数的测试方法如下：
1)接触角测试：接触角是指气、液、固三相交点处所作的气-液界面的切线与固-液交界线之间的夹角θ，是润湿程度的量度。若θ＜90°，则固体是亲液的，即液体可润湿固体，其角越小，润湿性越好；若θ＞ 90°，则固体是憎液的，即液体不润湿固体，容易在表面上移动，不能进入毛细孔。本发明中接触角测试直接参考GB/T 30693-2014标准文件执行，液体试剂采用去离子水。
2)正极片外观测试：观察制备的正极片的外观，并按照以下标准分类：
如果外观无划痕、凸点等异常现象，则记为优；
如果外观划痕小于1处，且不露金属或凸点≤3处，则记为良；
如果外观划痕大于1处或凸点＞3处，则记为差。
3)粘接力测试：
粘接力测试即180°剥离强度的测试。选用高铁拉力机AI-7000S，测试标准：GB/T 36363-2018。取待测试极片(集流体双面涂敷活性物质层的正极极片)，极片外观良好，不允许外观坏品。用刀片截取宽30mm、长度为100-160mm的试样。将专用双面胶NITTO.NO5000NS贴于钢板上，胶带宽度20mm、长度90-150mm。将上述截取的固定尺寸极片试样贴在双面胶上，测试面朝下，后用3kg压辊沿在正极片的表面同一个方向滚压三次。将宽度与极片等宽，长度大于试样长度80-200mm的纸带***极片下方，并且用皱纹胶固定。然后将该样品固定在试验机上，钢板未贴极片的一端用下夹具固定，将纸带向上翻折，用上夹具固定，极片轴线方向与施力方向保持一致，选用高铁拉力机AI-7000S试验机以10mm/min剥离速度加载，直至正极片断裂，停止测试，记录最大负载力为F(单位N)，极片宽度L＝20mm，根据f1＝F/L，计算剥离强度f1(单位N/m)。
4)内聚力测试：
内聚力测试即180°剪切强度测试。选用高铁拉力机AI-7000S。取待测试极片(集流体双面涂敷活性物质层的正极极片)，极片外观良好，不允许外观坏品。用刀片截取宽30mm、长度为100-160mm的试样。将专 用双面胶NITTO.NO5000NS贴于钢板上，胶带宽度20mm、长度90-150mm。将上述截取的固定尺寸极片试样贴在双面胶上，测试面朝上，然后将宽度为20mm，长度大于试样长度80-200mm的低粘绿胶带MD-XTG-620-2335L平整的粘在测试面表面，后用3kg压辊沿在正极片的表面同一个方向滚压三次。然后将该样品固定在试验机上，钢板未贴极片的一端用下夹具固定，将绿胶向上翻折，用上夹具固定，极片轴线方向与施力方向保持一致，试验机以10mm/min剥离速度加载，直至正极片断裂，停止测试，记录最大负载力为F(单位N)，极片宽度L＝20mm，根据f1＝F/L，计算剪切强度f2(单位N/m)。
5)正极极片卷绕热压测试：将正极片、隔离膜、负极片卷绕成方型的电池，之后90℃、0.8MPa压力下进行热压，之后将电池拆解，观察折痕处是否漏光，其中，在卷绕得到的电池中，共计45个折痕。每组测试5次，取平均值。
6)正极膜片对折测试：将正极膜片对折后使用重量为2kg的压辊来回辊压3次，之后将正极膜片铺平，重复上述操作，直至对折处漏光，记录对折次数。每组测试5次，取平均值。
7)正极极片的膜片电阻测试：
使用CRM-01膜片电阻测试仪测试正极极片的膜片电阻。每组测试5次，取平均值。
8)电池直流阻抗测试：
以实施例1为例，电池直流阻抗测试过程如下：在25℃下，将实施例1对应的电池，以1/3C恒流充电至3.65V，再以3.65V恒定电压充电至电流为0.05C，搁置5min后，记录电压V1。然后再以1/3C放电30s，记录电压V2，则(V2-V1)/1/3C，得到电池的内阻DCR。
9)电池容量保持率测试：
以实施例1为例，电池容量保持率测试过程如下：在25℃下，将实施例1对应的电池，以1/3C恒流充电至3.65V，再以3.65V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.7V，所得容量记为初始容量C0。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的放电容量Cn，则每次循环后电池容量保持率Pn＝Cn/C0*100％。该测试过程中，第一次循环对应n＝1、第二次循环对应n＝2、……第100次循环对应n＝100。表1中实施例1对应的电池容量保持率数据是在上述测试条件下循环800次之后测得的数据，即P800的值。对比例1以及其他实施例的测试过程同上。
对各实施例中所制备的正极极片以及电池进行测试，测试结果显示于表1中。
表1：实施例1-13以及对比例1-2的正极极片以及电池的性能测试
Figure PCTCN2021142609-appb-000001
由表1可见，对于本发明的实施例1-12的锂离子二次电池来说，当其正极极片的CT/AT的比值在1至10范围内时，极片外观优良，极片卷绕热压折痕漏光极少或没有，极片对折漏光的次数也较高，膜片电阻较低。同时，由该正极极片制成的锂离子二次电池的直流阻抗较低，而电池容量保持率很高。当正极极片的CT/AT的比值在1至8范围内时，以上特性基本上得到了进一步的提高。其中，对于实施例1-7，当对集流体进行电晕处理且电压保持在20kV时，水性粘接剂中黄原胶和聚乙烯亚胺的特定比例使得正极极片以及二次电池的性能产生了进一步的提升。对于实施例8-12，当水性粘接剂中黄原胶和聚乙烯亚胺的比例保持恒定时，电晕处理时的电压保持在10-25kV可以产生进一步降低的膜片电阻。
对于实施例13，由于其未对正极集流体进行电晕处理，因此其CT/AT的比值高于10。虽然其二次电池的容量保持率仍然很高，但是其正极极片的电阻明显升高，且二次电池的直流阻抗也较高。
与之相比，对比例1使用20kV的电压对正极集流体进行电晕处理，但是使用了常规的羧甲基纤维素钠与丙烯腈-丙烯酸酯共聚物组成的粘接剂，其正极极片的CT/AT值高于10。结果显示，对比例1制得的正极极片外观较差，极片卷绕热压折痕漏光较多且膜片电阻明显升高，而由此得到的二次电池的直流阻抗较高，容量保持率也明显下降。对比例2在对比例1的基础上，省去了对正极集流体进行电晕处理的步骤，结果是其正极极片和二次电池的特性在对比例1的基础上又有不同程度的劣化。
另外，在保持正极极片的CT/AT的比值在1至10范围、特别是1至8范围内的基础上，通过将电晕处理的电压调制到特定范围内并且将粘接剂中黄原胶和聚乙烯亚胺的比例调节至特定范围，正极极片以及由其制得的二次电池的性能均可实现进一步的提升。
虽然已经参考实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (19)

  1. 一种水系正极极片，包括集流体及设置在所述集流体至少一个表面上的正极活性物质层，所述正极活性物质层包括水性粘接剂，
    其中所述正极活性物质层与所述集流体之间的粘接力AT和所述正极活性物质层自身的内聚力CT满足以下关系式：1≤CT/AT≤10。
  2. 根据权利要求1所述的正极极片，其中所述集流体与水的接触角为5°-90°，可选地为20°-70°。
  3. 根据权利要求1至2中任一项所述的正极极片，其中所述正极活性物质层与所述集流体之间的粘接力AT为6-45N/m，可选地为10-35N/m。
  4. 根据权利要求1至3中任一项所述的正极极片，其中所述正极活性物质层的内聚力CT为40-140N/m，可选地为60-120N/m。
  5. 根据权利要求1至4中任一项中所述的正极极片，其中CT与AT比值的范围为2-8，可选地为3-5。
  6. 根据权利要求1至5中任一项所述的正极极片，其中所述水性粘接剂在所述正极活性物质层中的比例为0.5-10重量％，可选地为1.5-5重量％，基于所述正极活性物质层的总重量计。
  7. 根据权利要求1至6中任一项所述的正极极片，其中所述集流体包含表面改性的铝箔。
  8. 根据权利要求1至7中任一项所述的正极极片，其中所述集流体包括经高表面能活化预处理的集流体，所述预处理工艺包含电晕处理、等离子体处理、辊压、极性溶剂涂敷或其组合。
  9. 根据权利要求8所述的正极极片，其中所述电晕处理中处理电压为5-30kV，可选地为10-25kV。
  10. 根据权利要求1至9中任一项所述的正极极片，其中所述正极活 性物质层中含有正极活性材料，所述正极活性材料选自包含磷酸铁锂、磷酸锰锂、磷酸钴锂、磷酸铁锰锂、锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物中的一种或多种。
  11. 根据权利要求1至10中任一项所述的正极极片，其中所述正极活性物质层中含有导电剂，所述导电剂包含导电炭黑、超导炭黑、导电石墨、乙炔黑、科琴黑、石墨烯、碳纳米管中的一种或多种。
  12. 根据权利要求1至11中任一项所述的正极极片，其中所述水性粘接剂包含可溶性多糖类及其衍生物、水溶性或水分散液高分子聚合物或其混合物。
  13. 根据权利要求1至12中任一项所述的正极极片，其中所述水性粘接剂为甲基纤维素及其盐、黄原胶及其盐、壳聚糖及其盐、海藻酸及其盐、聚乙烯亚胺及其盐、聚丙烯酰胺、丙烯腈-丙烯酸共聚物及其衍生物，或上述物质的混合物。
  14. 根据权利要求1至13中任一项所述的正极极片，其中所述水性粘接剂为可溶性多糖类及其衍生物与水溶性或水分散液高分子聚合物的复配混合物，复配比例为2:1-1:15，可选地为1:2-1:14。
  15. 根据权利要求1至14中任一项所述的正极极片，其中所述水性粘接剂为黄原胶和聚乙烯亚胺的复配混合物，复配比例为2:1-1:15，可选地为1:2-1:14；可选地，黄原胶的平均分子量Mn为300000-2000000g/mol，聚乙烯亚胺的平均分子量Mn为2000-50000g/mol。
  16. 根据权利要求1至15中任一项所述的正极极片，其中，所述正极极片的膜片电阻为0.3至1Ω。
  17. 一种二次电池，其包括选自权利要求1-16中任一项所述的水系正极极片。
  18. 一种电池包，其包括权利要求17所述的二次电池。
  19. 一种用电装置，其包括权利要求17所述的二次电池或者权利要求18所述的电池包。
PCT/CN2021/142609 2021-12-29 2021-12-29 一种水系正极极片及包含该极片的二次电池及用电装置 WO2023123087A1 (zh)

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EP21964279.0A EP4254560A1 (en) 2021-12-29 2021-12-29 Aqueous positive electrode plate, secondary battery including same, and electric apparatus
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