WO2020134707A1 - 一种复合正极极片及其制备方法及含有该极片的锂离子电池 - Google Patents

一种复合正极极片及其制备方法及含有该极片的锂离子电池 Download PDF

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WO2020134707A1
WO2020134707A1 PCT/CN2019/119260 CN2019119260W WO2020134707A1 WO 2020134707 A1 WO2020134707 A1 WO 2020134707A1 CN 2019119260 W CN2019119260 W CN 2019119260W WO 2020134707 A1 WO2020134707 A1 WO 2020134707A1
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positive electrode
coating
pole piece
active material
water
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English (en)
French (fr)
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樊亚楠
李素丽
李俊义
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • 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
    • H01M4/136—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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of 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
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of lithium ion batteries, and in particular relates to a composite positive pole piece, a preparation method thereof, and a lithium ion battery containing the pole piece.
  • lithium ion secondary batteries gradually occupy most of the battery industry due to their unique advantages of high capacity, long cycle life, no memory effect, high energy density, clean and pollution-free, etc.
  • lithium-ion batteries are currently used in mobile phones, laptop computers and electric vehicles.
  • the safety performance of lithium-ion batteries has greatly restricted its application.
  • lithium-containing oxide positive electrodes lithium cobalt oxide, nickel cobalt manganese oxide, nickel cobalt aluminum aluminate, lithium iron phosphate, etc.
  • negative electrodes natural graphite, artificial graphite , Hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbon, silicon oxide, etc. any one or a combination of several
  • organic electrolyte and separator lithium-containing oxide positive electrodes (lithium cobalt oxide, nickel cobalt manganese oxide, nickel cobalt aluminum aluminate, lithium iron phosphate, etc.), and negative electrodes (natural graphite, artificial graphite , Hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbon, silicon oxide, etc. any one or a combination of several), organic electrolyte and separator.
  • lithium ions are deintercalated on the positive and negative electrodes to form a path to achieve the purpose of charging and discharging the lithium ion battery.
  • the reactions are not only the deintercalation of lithium ions and the redox of metal ions, but also many side reactions, such as the oxidative decomposition of the electrolyte, the collapse of the positive electrode structure, The decomposition and reorganization of the SEI and CEI films on the surface of the material, the reaction of the electrolyte with the positive and negative electrode materials, and the thermal decomposition reaction of the positive electrode material, etc.
  • side reactions such as the oxidative decomposition of the electrolyte, the collapse of the positive electrode structure, The decomposition and reorganization of the SEI and CEI films on the surface of the material, the reaction of the electrolyte with the positive and negative electrode materials, and the thermal decomposition reaction of the positive electrode material, etc.
  • the above-mentioned side reactions occur to a lesser extent, and the impact on the entire battery system is smaller.
  • One of the purposes of this application is to provide a composite positive pole piece, which contains a positive internal coating that can improve the safety performance of a lithium battery.
  • the coating is a positive electrode water-based coating, which is very similar to the positive electrode external active coating Good compatibility, at the same time, it can avoid the problem of dissolution of the internal coating of the double-layer coating, prevent the appearance of the pole piece from causing many pits on the surface of the pole piece, and can effectively improve the safety performance of the lithium ion battery.
  • the rate performance and cycle performance have also been improved;
  • the second objective of this application is to provide a method for preparing a composite positive pole piece
  • the third object of the present application is to provide a lithium ion battery using the composite positive pole piece.
  • a composite positive pole piece is a positive pole piece with a double-layer coating structure, including a current collector, a positive electrode inner coating and a positive electrode outer coating, the positive electrode inner coating is coated on the current collector
  • the outer coating of the positive electrode is coated on the inner coating of the positive electrode
  • the inner coating of the positive electrode is a water-soluble coating
  • the outer coating of the positive electrode is an oil-soluble coating.
  • the material of the internal coating of the positive electrode includes a positive electrode active material containing a lithium source, a conductive agent, a water-soluble binder, and a water-soluble thickener.
  • the mass percentages of the positive electrode active material, conductive agent, water-soluble binder, and water-soluble thickener are 80.0%-96.0%, 0.5%-6.0%, 1.5%-10.0%, 2.0%-4.0, respectively. %.
  • the positive electrode active material is one or a combination of one or more of lithium iron phosphate, lithium cobaltate, nickel cobalt manganate, nickel cobalt lithium aluminate, and lithium manganate;
  • the conductive agent is conductive graphite, Conductive carbon black, Ketjen black, acetylene black, carbon fiber, single-arm carbon nanotubes, multi-arm carbon nanotubes, or a combination of one or more of graphene;
  • the water-soluble thickener is carboxymethyl cellulose One or a combination of sodium, hydroxyethyl cellulose, hydroxypropyl cellulose, Dingyou gum, polyvinyl alcohol, polyacrylic acid;
  • the water-soluble binder is polyacrylamide, polyethylene oxide, poly A combination of one or more of vinylpyrrolidone, acrylamide-acrylonitrile copolymer, acrylic acid-acrylate copolymer, acrylic acid-acrylamide-acrylonitrile copolymer, acrylic acid-acrylate-acrylonitrile copoly
  • the pH value of the water-soluble binder is 4-5.
  • a method for preparing a composite positive pole piece includes the following steps:
  • Step 1 Mix the acidic aqueous solution and the proportion of the positive electrode active material uniformly to obtain a uniform homogenate, and the pH value of the uniform homogenate is 7-8;
  • Step 2 Add the conductive agent and water-soluble thickener to the homogeneous homogenate in step one, adjust the slurry to be dough-shaped, stir it evenly, then add deionized water to dilute the slurry to Viscosity is 4000-6000mPa.s, then add a certain amount of water-soluble binder and continue to stir for 0.5-3h, and finally vacuum to remove air bubbles, after filtering through the screen to obtain the positive electrode inner slurry, the positive electrode inner slurry
  • the solid content is 30%-50%, the viscosity is 500-4000mPa.s;
  • Step 3 Evenly coat the positive electrode inner layer slurry on the current collector, heat and bake to volatilize the solvent water in the acidic aqueous solution to obtain a current collector coated with the positive electrode inner layer slurry;
  • Step 4 Dry the current collector coated with the positive electrode inner layer slurry to obtain a current collector coated with the positive electrode inner coating; the thickness of the positive electrode inner coating is 1-20 ⁇ m, and the areal density is 0.1-10 g/m 2 ;
  • Step 5 Coating the positive electrode outer layer slurry on the positive electrode inner coating in step 4, and baking and rolling to obtain a composite positive electrode sheet.
  • step one an acidic aqueous solution is added to the positive electrode active material while stirring within a temperature range of 5-10°C, the acidic aqueous solution is a weakly acidic aqueous solution, and the volume percentage concentration of the acidic aqueous solution is 1%-5 %.
  • the acidic aqueous solution is one or more of phosphoric acid, oxalic acid, acetic acid, carbonic acid, citric acid, malonic acid, adipic acid, succinic acid, salicylic acid, phthalic acid, toluenesulfonic acid, tartaric acid A mixed solution of various species.
  • the positive electrode outer layer slurry includes an oil-soluble binder, a dispersant, and a positive electrode active material and a conductive agent.
  • oil-soluble binder is polyvinylidene fluoride
  • dispersant is N-methylpyrrolidone
  • a lithium ion battery containing the composite positive pole piece, the lithium ion battery includes the above composite positive pole piece, negative electrode piece, separator and electrolyte.
  • the positive electrode active material is used as the internal coating material of the positive electrode, which can effectively improve the energy density of the battery;
  • Aqueous positive electrode slurry is applied as the inner layer of the positive electrode, which can effectively prevent the dissolution of the inner coating of the positive electrode during the coating of the outer layer of the positive electrode oil slurry, and prevent the formation of many pits on the surface of the pole piece.
  • the appearance of the film is poor, improving the appearance of the pole piece and the yield of the battery;
  • the positive electrode double-layer coating method can increase the resistance between the pole piece and the current collector, and effectively improve the safety performance of the battery;
  • a weak acidic aqueous solution is used to modify the high pH positive electrode active material, which can neutralize the alkalinity of the high pH positive electrode active material, thereby avoiding the phenomenon of gel generation. Therefore, the expansion problem of the positive electrode material during storage can be improved, and the calendar life of the lithium ion battery can be extended.
  • Example 1 is a graph of rate discharge curves of Example 1, Example 4 and Comparative Example 2;
  • Example 2 is a storage thickness expansion diagram of Example 2, Example 4 and Comparative Example 1, Comparative Example 3;
  • Example 3 is a graph of the room temperature cycle of Example 1, Example 4 and Comparative Example 1 and Comparative Example 2;
  • FIG. 4 is a data graph of temperature changes with time in the overcharge experiments of Example 1 and Comparative Example 1.
  • FIG. 4 is a data graph of temperature changes with time in the overcharge experiments of Example 1 and Comparative Example 1.
  • a composite positive pole piece is a positive pole piece with a double-layer coating structure, including a current collector, a positive electrode inner coating and a positive electrode outer coating, the positive electrode inner coating is coated on the current collector
  • the outer coating of the positive electrode is coated on the inner coating of the positive electrode
  • the inner coating of the positive electrode is a water-soluble coating
  • the outer coating of the positive electrode is an oil-soluble coating.
  • the material of the internal coating of the positive electrode includes a positive electrode active material containing a lithium source, a water-soluble binder, a water-soluble thickener, and a conductive agent.
  • the mass percentages of the positive electrode active material, the conductive agent, the water-soluble binder, and the water-soluble thickener in the positive electrode internal coating are 80.0%-96.0%, 0.5%-6.0%, 1.5%-10.0%, 2.0%-4.0%.
  • the positive electrode active material is one or a combination of lithium iron phosphate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and lithium manganate;
  • the conductive agent is conductive graphite, One or a combination of conductive carbon black, Ketjen black, acetylene black, carbon fiber, single-arm carbon nanotubes, multi-arm carbon nanotubes, graphene;
  • the water-soluble thickener is carboxymethyl cellulose One or a combination of sodium, hydroxyethyl cellulose, hydroxypropyl cellulose, Dingyou gum, polyvinyl alcohol, polyacrylic acid;
  • the water-soluble binder is polyacrylamide, polyethylene oxide, poly One or a combination of vinylpyrrolidone, acrylamide-acrylonitrile copolymer, acrylic acid-acrylate copolymer, acrylic acid-acrylamide-acrylonitrile copolymer, acrylic acid-acrylate-acrylonitrile copolymer.
  • the pH value of the water-soluble binder is 4-5.
  • a method for preparing the above composite positive pole piece includes the following steps:
  • Step 1 Mix the acidic aqueous solution with the positive electrode active material that accounts for 80.0%-96.0% of the internal coating material of the positive electrode to obtain a uniform homogenate, and the pH value of the uniform homogenate is 7-8;
  • Step 2 Add the conductive agent that accounts for 0.5%-6.0% of the internal coating material of the positive electrode and 2.0%-4.0% of the water-soluble thickener for the internal coating material of the positive electrode in the homogeneous homogenate in step one, adjust the slurry
  • the material is in the shape of a dough.
  • Step 3 Evenly coat the positive electrode inner layer slurry on the current collector, heat and bake to volatilize the solvent water in the acidic aqueous solution to obtain a current collector coated with the positive electrode inner layer slurry;
  • Step 4 Dry the current collector coated with the positive electrode inner layer slurry to obtain a current collector coated with the positive electrode inner coating, the thickness of the positive electrode inner coating is 1-20 ⁇ m, and the areal density is 0.1-10 g/m 2 ;
  • Step 5 Coating the positive electrode outer layer slurry on the positive electrode inner coating in step 4, and baking and rolling to obtain a composite positive electrode sheet.
  • step one an acidic aqueous solution is added to the positive electrode active material while stirring within a temperature range of 5-10°C, the acidic aqueous solution is a weakly acidic aqueous solution, and the volume percentage concentration of the acidic aqueous solution is 1%-5 %.
  • the acidic aqueous solution is one or more of phosphoric acid, oxalic acid, acetic acid, carbonic acid, citric acid, malonic acid, adipic acid, succinic acid, salicylic acid, phthalic acid, toluenesulfonic acid, tartaric acid A mixed solution of various species.
  • step three the coating process uses transfer, spraying, and printing processes, and the coating speed is 20-35 m/s.
  • step three the current collector coated with the positive electrode inner layer slurry is heated and baked in a five-stage oven to volatilize the solvent water in the acidic aqueous solution.
  • the temperature of the five-stage oven is 60°C, 70°C, and 90, respectively.
  • °C, 120°C, 120°C, each section of the oven is 1-2m, by adjusting the coating speed, changing the time of the pole piece in the oven, the main purpose of this step of baking is to make the pole piece not stick to the roller during the winding process.
  • step four the current collector coated with the positive electrode inner layer slurry is dried, the oven temperature is 50-150°C, the baking time is 1-20h, and the oven atmosphere is one of nitrogen or inert gas Or a combination of several.
  • the positive electrode outer layer slurry includes an oil-soluble binder, a dispersant, and a positive electrode active material and a conductive agent.
  • the solid content of the positive electrode outer layer slurry is 65%-80%, and the viscosity is
  • step five the positive electrode outer layer slurry is baked in a five-stage oven during the coating process, and the temperature settings of the five-stage oven are respectively 70°C, 80°C, 95°C, 120°C, and 120°C.
  • the current collector coated with the positive electrode outer layer slurry is placed in an oven at 100-120°C for 4-8 hours, and the dispersant of the positive electrode outer layer slurry is completely evaporated to obtain a coating
  • the protective gas in the oven is one or a combination of several types of nitrogen or inert gas, and the pole pieces after baking are rolled with a roller machine to obtain a compacted density of 3.65 -4.15g/cm 3 composite positive pole piece.
  • the mass percentages of the positive electrode active material, the conductive agent, and the oil-soluble binder in the positive electrode outer coating are 88.0%-98.5%, 0.6%-5.0%, 0.9%-7.0%, respectively.
  • oil-soluble binder is polyvinylidene fluoride
  • dispersant is N-methylpyrrolidone
  • a lithium ion battery containing the above composite positive pole piece, the lithium ion battery includes the above composite positive pole piece, a negative pole piece, a separator and an electrolyte.
  • the negative electrode sheet includes a negative electrode slurry and a negative electrode current collector.
  • the negative electrode slurry includes a negative electrode active material, a conductive agent, a negative electrode binder, a negative electrode thickener, and a negative electrode dispersant.
  • the solid content of the negative electrode slurry is 40%-70%, and the viscosity is 1000-5000 mPa.s.
  • the negative electrode active material includes one or a combination of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbon, and silicon oxide;
  • the negative electrode binder It is styrene-butadiene rubber;
  • the negative electrode thickener is sodium hydroxymethyl cellulose;
  • the negative electrode dispersant is distilled water.
  • the negative electrode slurry is dried to obtain a negative electrode coating.
  • the mass percentage of the negative electrode active material, conductive agent, negative electrode binder, and negative electrode thickener in the negative electrode coating is 89.0%-97.0%, 0.2%-3.5% , 1.2%-4%, 1.6%-3.5%.
  • the diaphragm is made of polypropylene as a base material, or a rubber-coated diaphragm coated with ceramic on one side or both sides on this basis.
  • the electrolyte includes a lithium salt and a non-aqueous organic solvent
  • the lithium salt is LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , Li(CF 3 SO 2 ) 2 N
  • the non-aqueous organic solvent includes cyclic carbonate and chain carbonate
  • the cyclic carbonate is ethylene carbonate (EC), propylene carbonate (PC), ⁇ -butyrolactone (GBL), one or a combination of butene carbonate (BC)
  • the chain carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC ), at least one of ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).
  • the lithium ion battery has a wound structure or a laminated structure.
  • a composite positive pole piece is a positive pole piece with a double-layer coating structure, including a current collector, a positive electrode inner coating and a positive electrode outer coating, the positive electrode inner coating is coated on the current collector
  • the outer coating of the positive electrode is coated on the inner coating of the positive electrode
  • the inner coating of the positive electrode is a water-soluble coating
  • the outer coating of the positive electrode is an oil-soluble coating.
  • the material of the internal coating of the positive electrode includes a positive electrode active material containing a lithium source, a water-soluble binder, a water-soluble thickener, and a conductive agent, and the positive electrode active material is LiNi 0.5 Co 0.2 Mn 0.3 O 2 ,
  • the conductive agent is Super-P
  • the water-soluble thickener is sodium carboxymethyl cellulose (CMC)
  • the water-soluble binder is acrylic acid-acrylate copolymer
  • positive electrode active material positive electrode active material
  • conductive agent water-soluble
  • the mass percentages of organic thickener and water-soluble binder are 92%, 2.5%, 2% and 3.5%, respectively, and the proportion of acrylic monomer in the water-soluble binder is between 30% and 40%.
  • a polymer binder with a pH value of 4 to 5 is selected to further neutralize the alkaline component in the positive electrode active material.
  • a method for preparing the above composite positive pole piece includes the following steps:
  • Step 1 Add the matching amount of LiNi 0.5 Co 0.2 Mn 0.3 O 2 to the double planetary mixer, adjust the temperature in the mixing tank to 5-10°C by circulating water, slowly add the 5% oxalic acid aqueous solution by volume percentage, adjust the revolution At a speed of 10 rpm and stirring for 30 min, slowly add an aqueous solution of oxalic acid to the system while stirring until the pH of the system is 7-8;
  • Step 2 Add the mixed amount of ground conductive agent and water-soluble thickener to the mixing tank, adjust the addition ratio to make the slurry dough-like, and continue to stir for 2 hours; then add deionized water to adjust the slurry viscosity It is 4000-6000mPa.s, then add water-soluble binder, and stir at the speed of 15rpm for 30min. Continue to add deionized water to adjust the final viscosity to 500-4000mPa.s, evacuate and stir for 30min, and filter with a 200 mesh screen to obtain the positive electrode inner layer slurry;
  • Step 3 Control the coating speed to 30m/s, apply the positive electrode inner layer slurry to the two surfaces of the 10 ⁇ m thick aluminum foil with a sprayer, and heat and bake in a five-stage oven to volatilize the solvent water in the acidic aqueous solution
  • a current collector coated with the positive electrode inner layer slurry in which the temperature of the five-stage oven is 60°C, 70°C, 90°C, 120°C, and 120°C, and each section of the oven is 1-2m, by adjusting the coating speed .
  • the main purpose of this step of baking is to make the pole piece not stick to the roller during the winding process;
  • Step 4 Place the current collector coated with the positive electrode inner layer slurry in an oven and dry it to obtain the current collector coated with the positive electrode inner coating.
  • the temperature of the oven is 120°C, bake for 6 hours, and the oven is filled with nitrogen as Shielding gas; the thickness of the internal coating of the positive electrode is 10 ⁇ m, and the areal density is 5 g/m 2 ;
  • Step 5 The external coating of the positive electrode is formulated with a conventional oil-based slurry, the positive electrode active material of the positive electrode outer slurry is LiCoO 2 , the conductive agent is Super-P, and the oil-soluble binder is polyvinylidene fluoride (PVDF) ), N-methylpyrrolidone (NMP) is used as the dispersant, the ratio of the positive electrode active material LiCoO 2 , the conductive agent Super-P, and the oil-soluble binder PVDF is 97%: 1.5%: 1.5%.
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • the temperature of the five-stage oven is set to 70°C, 80°C, 95°C, At 120°C and 120°C, after five stages of baking, the current collector coated with the positive electrode outer layer slurry is placed in a 100°C oven for 8 hours, and the dispersant of the positive electrode outer layer slurry is completely evaporated to obtain The current collector coated with the outer coating of the positive electrode was rolled on the current collector after baking, and the compacted density was 4.0 g/cm 3 to prepare a composite positive electrode sheet.
  • a lithium ion battery containing the above composite positive pole piece, the lithium ion battery includes the above composite positive pole piece, a negative pole piece, a separator and an electrolyte.
  • the negative electrode plate is prepared by using the conventional negative electrode formula.
  • the negative electrode slurry includes artificial graphite, superconducting carbon black (Super-P), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and distilled water.
  • Super-P superconducting carbon black
  • CMC sodium carboxymethyl cellulose
  • SBR styrene-butadiene rubber
  • Preparation of lithium-ion battery using conventional electrolyte formulation, LiPF 6 as lithium salt, using a mixture of ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC) as a solvent, and then adding electrolyte additive.
  • EC ethylene carbonate
  • PC propylene carbonate
  • DMC dimethyl carbonate
  • the diaphragm used is a single-sided ceramic + double-sided oily LBG rubber coated diaphragm.
  • the positive pole piece, the negative pole piece, and the separator are wound to make an electric core, which is encapsulated with an aluminum plastic film.
  • the temperature is controlled at 120° C., baked for 36 hours, the electrolyte is injected, and the chemical composition is selected.
  • a soft-pack lithium ion battery with a capacity of 5 Ah is finally obtained.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 lies in that LiNi 0.8 Co 0.15 Al 0.05 O 2 material is used as the cathode active material in the cathode internal coating in this embodiment, and the rest is the same as Embodiment 1.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 lies in that the positive electrode active material in the internal coating of this embodiment is LiFePO 4 material, and the rest is the same as Embodiment 1.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 lies in that LiCoO 2 material is used for the positive electrode active material in the positive electrode internal coating in this embodiment, and the rest is the same as in Embodiment 1.
  • Example 1 The difference between this example and Example 1 is that the positive electrode active material in the positive electrode outer coating in this example is LiNi 0.5 Co 0.2 Mn 0.3 O 2 , and the rest is the same as Example 1.
  • the preparation process of the lithium ion battery of this comparative example is as follows:
  • the positive pole is formulated with conventional oil-based slurry, the positive electrode active material is LiCoO 2 , the conductive agent is superconducting carbon black, the binder is polyvinylidene fluoride (PVDF), and the solvent is N- The mass percentages of methylpyrrolidone (NMP), LiCoO 2 , Super-P and PVDF are 97%, 1.5% and 1.5%, respectively.
  • NMP methylpyrrolidone
  • LiCoO 2 LiCoO 2
  • Super-P and PVDF are 97%, 1.5% and 1.5%, respectively.
  • the temperature of the five-stage oven is set to 70°C, 80°C, 95°C, 120°C, and 120°C, respectively (the cathode oil
  • the baking temperature of the slurry in the coating needs to be higher to ensure complete drying
  • the collector coated with the positive electrode oil slurry is placed in a 100°C oven for 8 hours , The dispersant of the positive electrode oil-based slurry was completely volatilized to obtain a current collector coated with a positive electrode coating, which was rolled after drying, and the compacted density was 4.0 g/cm 3 to obtain a positive electrode sheet.
  • the negative electrode plate is prepared by using the conventional negative electrode formula.
  • the negative electrode materials include artificial graphite, Super-P, CMC, SBR and distilled water. The above materials are mixed to make negative electrode slurry. It was coated and dried on 8 ⁇ m copper foil, and the baking conditions were 100° C., 4 h, and rolling, to obtain a negative pole piece with a compact density of 1.65 g/cm 3 .
  • LiPF 6 is used as a lithium salt
  • EC ethylene carbonate
  • PC propylene carbonate
  • DMC dimethyl carbonate
  • the diaphragm used is a single-sided ceramic + double-sided oily LBG rubber coated diaphragm.
  • the positive pole piece, the negative pole piece, and the separator are wound to make an electric core, which is encapsulated with an aluminum plastic film, controlled in a nitrogen-protected oven, controlled at 120°C, baked for 36 hours, injected with electrolyte, and selected for chemical composition, etc. In the process, a soft-pack lithium ion battery with a capacity of 5 Ah is finally obtained.
  • the preparation process of the lithium ion battery of this comparative example is as follows:
  • the positive electrode active material is LiNi 0.5 Co 0.2 Mn 0.3 O 2
  • the conductive agent is Super-P
  • the binder is polyvinylidene fluoride (PVDF)
  • the solvent is N-methylpyrrolidone (NMP)
  • the ratio of LiNi 0.5 Co 0.2 Mn 0.3 O 2 , Super-P, PVDF is 97%: 1.5%: 1.5%.
  • the positive-electrode inner layer oil-based slurry is directly coated on the surface of the current collector, and after being baked in a five-stage oven, the solvent N-methylpyrrolidone is volatilized to obtain a current collector coated with the positive-electrode inner layer slurry, wherein,
  • the temperature of the five-stage oven is 70°C, 80°C, 95°C, 120°C, and 120°C (the baking temperature of the positive electrode inner layer oil-based slurry in the coating needs to be higher to ensure complete drying).
  • the main purpose of this step of baking is to make the pole piece not stick to the roller during the winding process;
  • the fluid was placed in an oven for drying.
  • the temperature of the oven was 100°C, and the oven was baked for 8 hours.
  • the oven was filled with nitrogen as a protective gas to obtain an internal coating of the oil-based positive electrode.
  • the positive pole uses the formula of conventional oil-based slurry, the positive electrode active material is LiCoO 2 , the conductive agent is Super-P, the binder is polyvinylidene fluoride (PVDF), and the solvent is N- The mass percentages of methylpyrrolidone (NMP), LiCoO 2 , Super-P, and PVDF are 97%, 1.5%, and 1.5%, respectively.
  • NMP methylpyrrolidone
  • LiCoO 2 , Super-P, and PVDF are 97%, 1.5%, and 1.5%, respectively.
  • the negative electrode plate is prepared by using the conventional negative electrode formulation.
  • the negative electrode materials include artificial graphite, Super-P, CMC and SBR and distilled water. The above materials are mixed to make negative electrode slurry. Coated on an 8 ⁇ m copper foil, the baking temperature was 100° C., baked for 4 h, and rolled to obtain a negative pole piece with a compacted density of 1.65 g/cm 3 .
  • LiPF 6 is used as a lithium salt
  • a mixture of ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC) is used as a solvent, and then Add electrolyte additives.
  • the diaphragm used is a single-sided ceramic + double-sided oily LBG rubber coated diaphragm.
  • the positive pole piece, the negative pole piece, and the separator are wound to make an electric core, which is encapsulated with an aluminum plastic film.
  • the temperature is controlled at 120° C., baked for 36 hours, the electrolyte is injected, and the chemical composition is selected.
  • a soft-pack lithium ion battery with a capacity of 5 Ah is finally obtained.
  • the difference between the present comparative example and the comparative example 2 lies in that the material of the positive electrode active material in the positive electrode inner layer oil-based slurry in this embodiment is LiNi 0.8 Co 0.15 Al 0.05 O 2 material.
  • FIG. 1 shows Example 1, Example 4 and The rate discharge curve of Comparative Example 2;
  • Figure 2 is the storage thickness expansion diagram of Example 2, Example 4 and Comparative Example 1, Comparative Example 3;
  • Figure 3 is the Example 1, Example 4 and Comparative Example 1, Comparative Example The normal temperature cycle curve graph of FIG. 2;
  • FIG. 4 is a data graph of temperature changes with time in the overcharge experiments of Example 1 and Comparative Example 1.
  • Example 4 compared with Comparative Example 1, after coating a layer of water-based positive electrode internal coating on the surface of aluminum foil, the energy density of the battery cell can be effectively improved;
  • Example 2 compares with Example 4 in the activity of the positive electrode internal coating After the material was changed to LiNi 0.8 Co 0.15 Al 0.05 O 2 , the energy density increased significantly, reaching 741.3Wh/kg.
  • Example 2 Compared with Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1, Comparative Example 2, Comparative Example 3, after coating a layer of water-based positive electrode internal coating on the aluminum foil surface, it can be very The peeling force of the positive pole piece is obviously increased to prevent the positive electrode active material from falling off from the current collector during circulation.
  • Example 1 Comparing Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1, Comparative Example 2, and Comparative Example 3, after coating the internal coating of the positive electrode, the rate performance of the material became significantly better.
  • the coating of the aqueous positive electrode internal coating improves the battery rate performance better than the oil-based positive electrode internal coating.
  • the internal coating of the aqueous positive electrode can significantly reduce the expansion during high-temperature storage to prevent battery failure due to gas production.
  • Example 1 Example 3, Example 4, and Example 5, compared with Comparative Example 1, the addition of an aqueous positive electrode internal coating between the positive electrode material and the current collector did not sacrifice the cycling performance of the battery.
  • Comparative Example 2 and Comparative Example 3 the oil-based LiNi 0.8 Co 0.15 Al 0.05 O 2 positive electrode internal coating significantly reduces the cycleability of the battery, but the positive electrode internal coating slurry system is replaced with an aqueous system After the slurry, the cycle performance of the battery has improved.
  • Example 3 Example 4, and Example 5 with Comparative Example 1, the design idea of increasing the internal coating of the water-based positive electrode can indeed greatly improve the penetration rate of the battery needling by adding the water-based positive electrode All batteries with internal coatings can pass the needling experiment. At the same time, the heat generated during the needling process is relatively small, indicating that the presence of the internal coating of the positive electrode of the water system can protect the active material from direct contact with the current collector and cause thermal runaway.
  • Example 1 The effect of LiCoO 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiFePO 4 water-based positive electrode internal coating in Example 1, Example 2, and Example 3 compared with Example 4.
  • LiCoO 2 has the smallest impact on cycling.
  • LiNi 0.5 Co 0.2 Mn 0.3 O 2 has the best safety performance
  • LiNi 0.8 Co 0.15 Al 0.05 O 2 The safety performance of the material is relatively weak.
  • the maximum temperature of the cell during the needling process was 78.9°C, which was much lower than 331.2°C of Comparative Example 1.
  • Example 1 compared with Comparative Example 1, the cells containing the internal coating of the LiNi 0.5 Co 0.2 Mn 0.3 O 2 aqueous positive electrode can pass 2C-6V overcharge, but the conventional LiCoO 2 battery cannot pass this test. Thermal runaway will occur later in the test, which will cause the battery to catch fire.
  • this application applies an aqueous coating of lithium cobalt oxide, lithium nickel cobalt manganese oxide, nickel nickel cobalt aluminum aluminate, and lithium iron phosphate to the cathode current collector by coating a layer of the cathode internal coating, and then applies the aqueous cathode Continuously coating the positive electrode active material on the internal coating layer can effectively improve the binding force between the positive electrode active material and the current collector, and prevent the circulation capacity from declining due to the shedding of the positive electrode active material.
  • the presence of the internal coating of the positive electrode of the water system has greatly improved the rate performance of the battery cell, and in particular, has greatly improved the safety performance of the battery cell.

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Abstract

一种复合正极极片及其制备方法及含有该极片的锂离子电池，属于锂离子电池技术领域，该方法制备的正极片为多层涂覆极片，在集流体上涂布正极活性材料之前，预先在集流体上涂布含有正极活性材料的水系涂层；含有正极活性材料的水系涂层成分包括含有锂源的正极活性材料、导电剂、粘结剂、增稠剂。通过使用水系涂层作为内部涂层，有效的避免双层涂布中，外部涂层对内部涂层的溶解作用，保护极片的外观。该涂层的存在有效的提高正极活性材料与集流体之间的粘结力，可以防止正极活性材料在循环中的脱落。该涂层的存在有效阻止了正极集流体与负极活性材料的接触，降低了电池滥用过程中短路的风险，有效的提高了锂离子电池的安全性能。

Description

一种复合正极极片及其制备方法及含有该极片的锂离子电池
本申请要求于2018年12月24日提交中国专利局、申请号为201811582874.7、申请名称为“一种复合正极极片及其制备方法及含有该极片的锂离子电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请属于锂离子电池技术领域，尤其涉及一种复合正极极片及其制备方法及含有该极片的锂离子电池。
背景技术
近几年，随着科技的进展，锂离子二次电池凭借其独特的高容量、循环寿命长、无记忆效应、较高的能量密度、清洁无污染等优势，逐渐占据了电池行业的大部分市场，目前锂离子电池多应用在手机、笔记本电脑以及电动汽车领域。但是，锂离子电池的安全性能极大的制约了它的应用。
目前，市场上多见的聚合物锂离子电池是由含锂氧化物正极(钴酸锂、镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂等组成)，负极(天然石墨、人造石墨、硬炭、中间相碳微球、钛酸锂、硅炭、氧化亚硅等其中的任意一种或几种的组合)、有机电解液以及隔膜组成。在电池的工作过程中，锂离子在正负极上进行脱嵌，形成通路，以达到对锂离子电池充放电的目的。然而，在锂离子电池充放电的过程中，存在的反应不仅是锂离子的脱嵌和金属离子的氧化还原，还会存在着许多的副反应，如电解液的氧化分解、正极结构的坍塌、材料表面的SEI膜和CEI膜的分解和重组、电解液与正负极材料的反应以及正极材料的热分解反应等等。当然，在现有的锂离子电池正常工作的过程中，以上副反应发生的程度较低，对整个电池体系的影响较小。然而，一旦电池发生滥用，如过充电、高温放置、重物冲击、外部短路以及震荡等情况，电池内部温度升高，导致上述副反应剧烈，并会在短时间内释放较高的热量，当电池产热速率极大的高于散热速率时，就会发生热失控，如果热失控没有被及时有效的制止，则电池很有可能会发 生起火、燃烧等安全事故。近年来，也有许多学者将研究的重点放在了电池安全性的改善方面，在电池内部增加保护板等机制，但是随着我们对电池能量密度以及电池尺寸的要求，越来越多的人关注电池裸电芯的安全性能，同时，较高的能量密度，也会使电池发生热失控的风险增加。
近年的研究中，也提到了多种改善安全性能的方法：在中国专利申请《一种双层复合锂离子电池的电极及生产方法》(申请号CN201210212137.4)中，公开了一种在集流体上涂覆双层磷酸铁锂来提高电池的稳定性，但在该方案中，两层磷酸铁锂的稳定性不同，对安全性改善效果并不明显；在中国专利申请《一种锂电池极片及其制作方法》(申请号CN201510555564.6)中，提及了一种正极双涂层来改善安全性能的方法，正极活性物质采用钴酸锂、镍钴锰酸锂、磷酸铁锂等材料，但在该方案中，正极极片内外两层均采用油系涂层，这会导致在外层涂布时，对内部涂层有一定程度的溶解，严重降低了电池的良率；也有许多报道提出在集流体表面涂覆一层热敏性材料复合导电剂制成的PTC材料，该种电池结构可以极大的提高电池的稳定性，但随之而来的是电池性能的牺牲，同时，当温度急剧升高时，也会产生NPC效应，降低电池的安全性。
发明内容
本申请的目的之一是提供一种复合正极极片，该复合正极极片含有可以改善锂电池安全性能的正极内部涂层，该涂层为正极水系涂层，与正极外部活性涂层有很好的兼容性，同时可以避免双层涂布对内部涂层的溶解问题，防止极片表面产生许多凹坑而导致的极片外观不良，可有效的提高锂离子电池的安全性能，对电池的倍率性能、循环性能也有一定的提高；
本申请的目的之二提供一种复合正极极片的制备方法；
本申请的目的之三是提供一种使用该复合正极极片的锂离子电池。
为了实现上述目的，本申请采取如下技术方案：
一种复合正极极片，所述复合正极极片为双层涂覆结构的正极极片，包括集流体、正极内部涂层和正极外部涂层，所述正极内部涂层涂布在集流体上，所述正极外部涂层涂布在正极内部涂层上，所述正极内部涂层为水溶性涂层，所述正极外部涂层为油溶性涂层。
进一步的，所述正极内部涂层的材料包括含有锂源的正极活性材料、导电剂、水溶性粘结剂、水溶性增稠剂。
进一步的，所述正极活性材料、导电剂、水溶性粘结剂、水溶性增稠剂的质量百分比分别为80.0％-96.0％、0.5％-6.0％、1.5％-10.0％、2.0％-4.0％。
进一步的，所述正极活性材料为磷酸铁锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂中的一种或多种的组合；所述导电剂为导电石墨、导电炭黑、科琴黑、乙炔黑、碳纤维、单臂碳纳米管、多臂碳纳米管、石墨烯中的一种或多种的组合；所述水溶性增稠剂为羧甲基纤维素钠、羟乙基纤维素、羟丙基纤维素、定优胶、聚乙烯醇、聚丙烯酸中一种或多种的组合；所述水溶性粘结剂为聚丙烯酰胺、聚氧化乙烯、聚乙烯吡咯烷酮、丙烯酰胺-丙烯腈共聚物、丙烯酸-丙烯酸酯共聚物、丙烯酸-丙烯酰胺-丙烯腈共聚物、丙烯酸-丙烯酸酯-丙烯腈共聚物中的一种或多种的组合。
进一步的，所述水溶性粘结剂的pH值为4～5。
一种复合正极极片的制备方法，包括如下步骤：
步骤一：将酸性水溶液与配比量的所述正极活性材料混合均匀，得到均一匀浆，所述均一匀浆的pH值为7-8；
步骤二：在步骤一中所述均一匀浆里加入配比量的所述导电剂和水溶性增稠剂，调节浆料呈面团状，搅拌均匀后，再加入去离子水将浆料稀释至粘度为4000-6000mPa.s，再加入配比量的水溶性粘结剂继续搅拌0.5-3h，最后抽真空脱除气泡，筛网过滤后得到正极内层浆料，所述正极内层浆料的固含量为30％-50％，粘度为500-4000mPa.s；
步骤三：将上述正极内层浆料均匀涂布在集流体上，加热烘烤使酸性水溶液中的溶剂水挥发，得到涂覆有正极内层浆料的集流体；
步骤四：将涂覆有正极内层浆料的集流体进行干燥得到涂覆有正极内部涂层的集流体；所述正极内部涂层的厚度为1-20μm，面密度为0.1-10g/m 2；
步骤五：在步骤四中所述正极内部涂层上涂覆正极外层浆料，经过烘烤、辊压得到复合正极极片。
进一步的，在步骤一中，在5-10℃温度范围内边搅拌边往正极活性材料中加入酸性水溶液，所述酸性水溶液为弱酸性水溶液，所述酸性水溶液的体积百分比浓度为1％-5％。
进一步的，所述酸性水溶液为磷酸、草酸、乙酸、碳酸、柠檬酸、丙二酸、己二酸、琥珀酸、水杨酸、邻苯二甲酸、甲苯磺酸、酒石酸中的一种或几种的混合配制的水溶液。
进一步的，在步骤五中，所述正极外层浆料包括油溶性粘结剂、分散剂以及正极活性材料和导电剂。
进一步的，所述油溶性粘结剂为聚偏四氟乙烯，所述分散剂为N-甲基吡咯烷酮。
一种含有所述复合正极极片的锂离子电池，所述锂离子电池包括上述复合正极极片、负极片、隔膜和电解液。
本申请相对于现有技术的有益效果：
(1)通过在含有正极活性材料的正极外部涂层与集流体之间增加一层正极内部涂层，可以有效的增加极片的粘接性，保证电池在循环过程中，正极粉料不易脱落，有效提高循环效率；
(2)采用正极活性材料作为正极内部涂层材料，可有效的提高电池的能量密度；
(3)采用水系正极浆料作为正极内层涂布，可有效的防止正极外层油系浆料涂布过程中对正极内部涂层的溶解，防止极片表面产生许多凹坑而导致的极片外观不良，提高极片的外观及电池的良率；
(4)通过正极双层涂布的手段，可以增大极片与集流体之间的电阻，有效的提高电池的安全性能；
(5)本申请在制备正极内层浆料时，采用弱酸性水溶液对高pH的正极活性材料进行改性，可以中和高pH的正极活性材料的碱性，从而避免产生凝胶的现象，也因此可以改善正极材料储存过程中的膨胀问题，延长了锂离子电池的日历寿命。
附图说明
图1为实施例1、实施例4和对比例2的倍率放电曲线图；
图2为实施例2、实施例4和对比例1、对比例3的储存厚度膨胀图；
图3为实施例1、实施例4和对比例1、对比例2的常温循环曲线图；
图4为实施例1和对比例1的过充实验，温度随时间变化的数据图。
具体实施方式
为使本申请实施例的目的、技术方案和优点更加清楚，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
具体实施方式一
一种复合正极极片，所述复合正极极片为双层涂覆结构的正极极片，包括集流体、正极内部涂层和正极外部涂层，所述正极内部涂层涂布在集流体上，所述正极外部涂层涂布在正极内部涂层上，所述正极内部涂层为水溶性涂层，所述正极外部涂层为油溶性涂层。
进一步的，所述正极内部涂层的材料包括含有锂源的正极活性材料、水溶性粘结剂、水溶性增稠剂、导电剂。
进一步的，正极内部涂层中的正极活性材料、导电剂、水溶性粘结剂、水溶性增稠剂的质量百分比分别为80.0％-96.0％、0.5％-6.0％、1.5％-10.0％、2.0％-4.0％。
进一步的，所述正极活性材料为磷酸铁锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂中的一种或几种的组合；所述导电剂为导电石墨、导电炭黑、科琴黑、乙炔黑、碳纤维、单臂碳纳米管、多臂碳纳米管、石墨烯中的一种或几种的组合；所述水溶性增稠剂为羧甲基纤维素钠、羟乙基纤维素、羟丙基纤维素、定优胶、聚乙烯醇、聚丙烯酸中一种或几种的组合；所述水溶性粘结剂为聚丙烯酰胺、聚氧化乙烯、聚乙烯吡咯烷酮、丙烯酰胺-丙烯腈共聚物、丙烯酸-丙烯酸酯共聚物、丙烯酸-丙烯酰胺-丙烯腈共聚物、丙烯酸-丙烯酸酯-丙烯腈共聚物中的一种或几种的组合。
进一步地，所述水溶性粘结剂的pH值为4～5。
一种上述复合正极极片的制备方法，包括如下步骤：
步骤一：将酸性水溶液与占正极内部涂层材料的80.0％-96.0％的所述正极活性材料混合均匀，得到均一匀浆，所述均一匀浆的pH值为7-8；
步骤二：在步骤一中所述均一匀浆里加入占正极内部涂层材料0.5％-6.0％的所述导电剂和占正极内部涂层材料2.0％-4.0％水溶性增稠剂，调节浆料呈面团状，搅拌均匀后，再加入去离子水将浆料稀释至粘度为4000-6000mPa.s，再加入占正极内部涂层材料1.5％-10.0％的水溶性粘结剂继续搅拌0.5-3h，最后抽真空脱除气泡，筛网过滤后得到正极内层浆料，所述正极内层浆料的固含量为30％-50％，粘度为500-4000mPa.s；
步骤三：将上述正极内层浆料均匀涂布在集流体上，加热烘烤使酸性水溶液中的溶剂水挥发，得到涂覆有正极内层浆料的集流体；
步骤四：将涂覆有正极内层浆料的集流体进行干燥得到涂覆有正极内部涂层的集流体，所述正极内部涂层的厚度为1-20μm，面密度为0.1-10g/m 2；
步骤五：在步骤四中所述正极内部涂层上涂覆正极外层浆料，经过烘烤、辊压得到复合正极极片。
进一步的，在步骤一中，在5-10℃温度范围内边搅拌边往正极活性材料中加入酸性水溶液，所述酸性水溶液为弱酸性水溶液，所述酸性水溶液的体积百分比浓度为1％-5％。
进一步的，所述酸性水溶液为磷酸、草酸、乙酸、碳酸、柠檬酸、丙二酸、己二酸、琥珀酸、水杨酸、邻苯二甲酸、甲苯磺酸、酒石酸中的一种或几种的混合配制的水溶液。
进一步的，在步骤三中，涂布工艺采用转移、喷涂、印刷工艺，涂布速度为20-35m/s。
进一步的，在步骤三中，涂覆有正极内层浆料的集流体以五段烘箱进行加热烘烤使酸性水溶液中的溶剂水挥发，五段烘箱的温度分别为60℃、70℃、90℃、120℃、120℃，每段烘箱1-2m，通过调节涂布速度，改变极片在烘箱中的时间，此步烘烤的主要目的是使极片在收卷过程中不沾辊。
进一步的，在步骤四中，对涂覆有正极内层浆料的集流体进行干燥，烘箱温度为50-150℃，烘烤时间为1-20h，烘箱气氛为氮气或惰性气体中的一种或几种的组合。
进一步的，在步骤五中，所述正极外层浆料包括油溶性粘结剂、分散剂以及正极活性材料和导电剂。
进一步的，所述正极外层浆料的固含量为65％-80％，粘度为
3000-7000mPa.s。
进一步的，在步骤五中，所述正极外层浆料在涂布过程中经过五段烘箱烘烤，五段烘箱的温度设置分别为70℃、80℃、95℃、120℃、120℃，经五段烘烤后，再将涂覆有正极外层浆料的集流体置于100-120℃的烘箱中烘烤4-8h，将正极外层浆料的分散剂挥发完全，得到涂覆有正极外部涂层的集流体，烘箱中的保护气体为氮气或者惰性气体的一种或几种的组合，对烘烤后的极片，使用对辊机进行辊压，得到压实密度在3.65-4.15g/cm 3的复合正极极片。
进一步的，正极外部涂层中的正极活性材料、导电剂、油溶性粘结剂、的质量百分比分别为88.0％-98.5％、0.6％-5.0％、0.9％-7.0％。
进一步的，所述油溶性粘结剂为聚偏四氟乙烯，所述分散剂为N-甲基吡咯烷酮。
一种含有上述复合正极极片的锂离子电池，所述锂离子电池包括上述复合正极极片、负极片、隔膜和电解液。
进一步的，所述负极片包括负极浆料和负极集流体，所述负极浆料包括负极活性物质、导电剂、负极粘结剂、负极增稠剂及负极分散剂。
进一步的，所述负极浆料的固含量为40％-70％，粘度为1000-5000mPa.s。
进一步的，所述负极活性物质包含人造石墨、天然石墨、硬炭、中间相碳微球、钛酸锂、硅炭、氧化亚硅中的一种或几种的组合；所述负极粘结剂为丁苯橡胶；所述负极增稠剂为羟甲基纤维素钠；所述负极分散剂为蒸馏水。
进一步的，负极浆料被烘干后得到负极涂层，负极涂层中负极活性物质、导电剂、负极粘结剂、负极增稠剂的质量百分比为89.0％-97.0％、0.2％-3.5％、1.2％-4％、1.6％-3.5％。
进一步的，所述隔膜为聚丙烯为基材的材料，或在此基础上单面或双面涂覆陶瓷的涂胶隔膜。
进一步的，所述电解液中包括锂盐以及非水性有机溶剂，所述锂盐为LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiCF 3SO 3、Li(CF 3SO 2) 2N中的一种或几 种组合；所述非水性有机溶剂包括环状碳酸酯和链状碳酸酯；所述环状碳酸酯为碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、γ-丁内酯(GBL)、碳酸丁烯酯(BC)中的一种或几种的组合；所述链状碳酸酯为碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲乙酯(EMC)、碳酸甲丙酯(MPC)以及碳酸乙丙酯(EPC)中的至少一种。
进一步的，所述锂离子电池为卷绕结构或叠片结构。
下面，通过具体实施例和对比例对本申请作进一步说明。下述说明中所使用到的仪器、材料以及试剂如没有特殊的说明，均为常规仪器、常规材料及常规试剂。
实施例1
一种复合正极极片，所述复合正极极片为双层涂覆结构的正极极片，包括集流体、正极内部涂层和正极外部涂层，所述正极内部涂层涂布在集流体上，所述正极外部涂层涂布在正极内部涂层上，所述正极内部涂层为水溶性涂层，所述正极外部涂层为油溶性涂层。
进一步的，所述正极内部涂层的材料包括含有锂源的正极活性材料、水溶性粘结剂、水溶性增稠剂、导电剂，所述正极活性材料为LiNi 0.5Co 0.2Mn 0.3O 2，导电剂为超导炭黑(Super-P)，水溶性增稠剂为羧甲基纤维素钠(CMC)，水溶性粘结剂为丙烯酸-丙烯酸酯共聚物，正极活性材料、导电剂、水溶性增稠剂、水溶性粘结剂质量百分比分别为92％、2.5％、2％、3.5％，丙烯酸单体占所述水溶性粘结剂的比例在30％～40％之间，水溶性较好，选用pH值为4～5的聚合物粘结剂，可进一步中和正极活性材料中的碱性成分。
一种上述复合正极极片的制备方法，包括如下步骤：
步骤一：向双行星搅拌机中加入配比量的LiNi 0.5Co 0.2Mn 0.3O 2，通过循环水调整搅拌罐内温度为5-10℃，缓慢加入体积百分比浓度为5％的草酸水溶液，调整公转速度为10rpm，搅拌30min，一边搅拌一边缓慢向体系中加入草酸水溶液，直到体系pH值为7-8；
步骤二：向搅拌罐中加入配比量的研磨后的导电剂和水溶性增稠剂，调整加入比例，使浆料呈面团状，继续搅拌2个小时；然后加入去离子水调整浆料粘度为4000-6000mPa.s，再加入水溶性粘结剂，以公转15rpm的 速度搅拌30min。继续加入去离子水调节最终粘度为500-4000mPa.s，抽真空搅拌30min，用200目的筛网过滤，得到正极内层浆料；
步骤三：控制涂布速度为30m/s，将正极内层浆料用喷涂机涂布到10μm厚的铝箔的两个表面后，以五段烘箱进行加热烘烤使酸性水溶液中的溶剂水挥发，得到涂覆有正极内层浆料的集流体，其中，五段烘箱的温度分别为60℃、70℃、90℃、120℃、120℃，每段烘箱1-2m，通过调节涂布速度，改变极片在烘箱中的时间，此步烘烤的主要目的是使极片在收卷过程中不沾辊；
步骤四：将涂覆有正极内层浆料的集流体放入烘箱中干燥，得到涂覆有正极内部涂层的集流体，其中，烘箱温度为120℃，烘烤6h，烘箱中充氮气作为保护气；所述正极内部涂层的厚度为10μm，面密度为5g/m 2；
步骤五：正极外部涂层采用常规的油系浆料的配方，正极外层浆料的正极活性材料为LiCoO 2，导电剂为Super-P，油溶性粘结剂采用聚偏四氟乙烯(PVDF)，分散剂采用N-甲基吡咯烷酮(NMP)，正极活性材料LiCoO 2、导电剂Super-P、油溶性粘结剂PVDF的配比为97％：1.5％：1.5％。首先在双行星搅拌罐中加入配比量的LiCoO 2和Super-P，以公转30rpm，自转1500rpm搅拌10min，向体系中加入配比量的PVDF和一定量的NMP，搅拌2h，调节浆料粘度为3000-7000mPa.s，抽真空搅拌30min后，用200目筛网进行过滤，得到正极外层浆料。将正极外层浆料涂覆在LiNi 0.5Co 0.2Mn 0.3O 2正极内部涂层上面，经过五段烘箱烘烤后收卷，五段烘箱的温度设置分别为70℃、80℃、95℃、120℃、120℃，经五段烘烤后，再将涂覆有正极外层浆料的集流体置于100℃的烘箱中烘烤8h，将正极外层浆料的分散剂挥发完全，得到涂覆有正极外部涂层的集流体，对烘烤后的集流体进行辊压，压实密度为4.0g/cm 3，制得复合正极极片。
一种含有上述复合正极极片的锂离子电池，所述锂离子电池包括上述复合正极极片、负极片、隔膜和电解液。
负极片的制备：采用常规的负极配方制备负极极片，负极浆料包括人造石墨、超导炭黑(Super-P)、羧甲基纤维素钠(CMC)、丁苯橡胶(SBR)和蒸馏水，将以上物料混合制成负极浆料，将负极浆料涂布在8μm的铜箔上烘干，烘烤温度为100℃，烘烤4h，并辊压，得到压实密度为1.65g/cm 3 的负极极片。
锂离子电池的制备：采用常规的电解液配方，LiPF 6作为锂盐，以碳酸乙烯酯(EC)、碳酸丙烯酯(PC)和碳酸二甲酯(DMC)的混合物为溶剂，再加入电解液添加剂。
采用的隔膜为单面陶瓷+双面油性LBG涂胶隔膜。
将正极极片、负极极片、隔膜通过卷绕制成电芯，用铝塑膜封装，在氮气保护的烘箱中，控制温度为120℃，烘烤36h，注入电解液，进行化成分选等工序，最终得到容量为5Ah的软包锂离子电池。
实施例2
本实施例与实施例1不同的地方在于：本实施例中的正极内部涂层中正极活性材料选用的是LiNi 0.8Co 0.15Al 0.05O 2材料，其余与实施例1相同。
实施例3
本实施例与实施例1不同的地方在于：本实施例中的正极内部涂层中正极活性材料选用的是LiFePO 4材料，其余与实施例1相同。
实施例4
本实施例与实施例1不同的地方在于：本实施例中的正极内部涂层中正极活性材料选用的是LiCoO 2材料，其余与实施例1相同。
实施例5
本实施例与实施例1不同的地方在于：本实施例中的正极外部涂层中正极活性材料选用的是LiNi 0.5Co 0.2Mn 0.3O 2材料，其余与实施例1相同。
对比例1
本对比例锂离子电池的制备工艺如下：
(1)正极极片制备：正极采用常规油系浆料的配方，正极活性材料为LiCoO 2，导电剂为超导炭黑，粘结剂采用聚偏四氟乙烯(PVDF)，溶剂采用N-甲基吡咯烷酮(NMP)，LiCoO 2、Super-P和PVDF的质量百分比分别为97％、1.5％、1.5％。首先在双行星搅拌罐中加入配比量的LiCoO 2和Super-P，以公转30rpm，自转1500rpm搅拌10min，向体系中加入配比量的PVDF和一定量的NMP，搅拌2h，调节浆料粘度为3000-7000mPa.s，抽真空搅拌30min后，用200目筛网进行过滤，得到正极油系浆料。将正极油系浆料直接涂覆在集流体表面，经过五段烘箱烘烤后收卷，五段烘箱 的温度设置分别为70℃、80℃、95℃、120℃、120℃，(正极油系浆料在涂布中的烘烤温度需高些，以保证干燥完全)经五段烘烤后，再将涂覆有正极油系浆料的集流体置于100℃的烘箱中烘烤8h，将正极油系浆料的分散剂挥发完全，得到涂覆有正极涂层的集流体，烘干后进行辊压，压实密度为4.0g/cm 3，制得正极极片。
(2)负极片的制备：采用常规的负极配方制备负极极片，负极物料包括人造石墨、Super-P、CMC、SBR和蒸馏水，将以上几种物料混合制成负极浆料，将负极浆料涂布在8μm的铜箔上烘干，烘烤条件为，温度100℃，烘烤4h，并辊压，得到压实密度为1.65g/cm 3的负极极片。
(3)锂离子电池的制备：采用常规的电解液配方，LiPF 6作为锂盐，以碳酸乙烯酯(EC)、碳酸丙烯酯(PC)和碳酸二甲酯(DMC)的混合物为溶剂，再加入电解液添加剂。
采用的隔膜为单面陶瓷+双面油性LBG涂胶隔膜。
将正极极片、负极极片、隔膜通过卷绕制成电芯，用铝塑膜封装，在氮气保护的烘箱，控制温度为120℃，中烘烤36h，注入电解液，进行化成分选等工序，最终得到容量为5Ah的软包锂离子电池。
对比例2
本对比例锂离子电池的制备流程如下：
(1)正极内部涂层材料的制备：正极内层油系浆料配方中，正极活性材料为LiNi 0.5Co 0.2Mn 0.3O 2，导电剂为Super-P，粘结剂采用聚偏四氟乙烯(PVDF)，溶剂采用N-甲基吡咯烷酮(NMP)，LiNi 0.5Co 0.2Mn 0.3O 2、Super-P、PVDF的配比为97％：1.5％：1.5％。首先在双行星搅拌罐中加入LiCoO 2和Super-P，以公转30rpm，自转1500rpm搅拌10min，向体系中加入PVDF和一定量的NMP，搅拌2h，调节浆料粘度为500-3000mPa.s，抽真空搅拌30min后，用200目筛网进行过滤，得到正极内层油系浆料。将正极内层油系浆料直接涂覆在集流体表面，经五段烘箱烘烤后收卷，使溶剂N-甲基吡咯烷酮挥发，得到涂覆有正极内层浆料的集流体，其中，五段烘箱的温度分别为70℃、80℃、95℃、120℃、120℃(正极内层油系浆料在涂布中的烘烤温度需高些，以保证干燥完全)，每段烘箱1-2m，通过调节涂布速度，改变极片在烘箱中的时间，此步烘烤的主要目的是使极 片在收卷过程中不沾辊；将涂覆有正极内层浆料的集流体放入烘箱中干燥，烘箱温度为100℃，烘烤8h，烘箱中充氮气作为保护气，得到油系正极内部涂层。
(2)正极极片的制备：正极采用常规油系浆料的配方，正极活性材料为LiCoO 2，导电剂为Super-P，粘结剂采用聚偏四氟乙烯(PVDF)，溶剂采用N-甲基吡咯烷酮(NMP)，LiCoO 2、Super-P、PVDF的质量百分比分别为97％、1.5％、1.5％。首先在双行星搅拌罐中加入LiCoO 2和Super-P，以公转30rpm，自转1500rpm搅拌10min，向体系中加入PVDF和一定量的NMP，搅拌2h，调节浆料粘度为3000-7000mPa.s，抽真空搅拌30min后，用200目筛网进行过滤，得到正极油系浆料。将正极油系浆料涂覆在油系正极内部涂层的表面，经五段烘箱烘烤后收卷，然后100℃烘烤8h，对烘烤后的集流体进行辊压，压实密度为4.0g/cm 3，制得复合正极极片。
(3)负极片的制备：采用常规的负极配方制备负极极片，负极物料包括人造石墨、Super-P、CMC和SBR和蒸馏水，将以上几种物料混合制成负极浆料，将负极浆料涂布在8μm的铜箔上，烘烤温度为100℃，烘烤4h，并辊压，得到压实密度为1.65g/cm 3的负极极片。
(4)锂离子电池的制备：采用常规的电解液配方，LiPF 6作为锂盐，以碳酸乙烯酯(EC)、碳酸丙烯酯(PC)和碳酸二甲酯(DMC)的混合物为溶剂，再加入电解液添加剂。
采用的隔膜为单面陶瓷+双面油性LBG涂胶隔膜。
将正极极片、负极极片、隔膜通过卷绕制成电芯，用铝塑膜封装，在氮气保护的烘箱中，控制温度为120℃，烘烤36h，注入电解液，进行化成分选等工序，最终得到容量为5Ah的软包锂离子电池。
对比例3
本对比例与对比例2不同的地方在于：本实施例中的正极内层油系浆料中正极活性材料选用的是LiNi 0.8Co 0.15Al 0.05O 2材料。
将实施例1-5和对比例1-3制得的电池进行测试，测试方法参照企业标准，测试结果如表1和图1至图4所示，图1为实施例1、实施例4和对比例2的倍率放电曲线图；图2为实施例2、实施例4和对比例1、对比例3 的储存厚度膨胀图；图3为实施例1、实施例4和对比例1、对比例2的常温循环曲线图；图4为实施例1和对比例1的过充实验，温度随时间变化的数据图。
表1
Figure PCTCN2019119260-appb-000001
从表1可以看出，含水系正极内部涂层的复合正极极片的剥离力明显上升，倍率性能优异，膨胀方面明显减小，循环容量保持率与未涂正极内部涂层的纯LiCoO 2相比在同一个水平。
实施例4与对比例1相比，在铝箔表面涂覆一层水系正极内部涂层后，可以有效的提高电芯的能量密度；实施例2与实施例4相比，正极内部涂层的活性材料更换成LiNi 0.8Co 0.15Al 0.05O 2后，能量密度明显提升，可达到741.3Wh/kg。
实施例1、实施例2、实施例3、实施例4、实施例5和对比例1、对比例2、对比例3相比，在铝箔表面涂覆一层水系正极内部涂层后，可以很明显的增大正极极片的剥离力，防止正极活性物质在循环中从集流体上脱落。
实施例1、实施例2、实施例3、实施例4、实施例5和对比例1、对 比例2、对比例3对比，涂覆正极内部涂层后，材料的倍率性能明显变好。尤其，对比实施例1与对比例1，实施例2与对比例2，涂覆水系正极内部涂层对电池倍率性能的提升优于油系正极内部涂层。
实施例2与对比例2同比，在高镍含量的体系中，水系正极内部涂层可以明显的降低在高温储存中的膨胀，防止电池由于产气而导致的失效。
实施例1、实施例3、实施例4、实施例5与对比例1相比，在正极材料与集流体之间增加一个水系正极内部涂层后，并没有牺牲电池的循环性能。特别的，对比实施例2与对比例3，油系的LiNi 0.8Co 0.15Al 0.05O 2正极内部涂层明显对电池的循环性有很大降低，但将正极内部涂层浆料体系换成水系浆料后，电池的循环性能有所改善。
实施例1、实施例3、实施例4、实施例5与对比例1相比，增加水系正极内部涂层的设计思路的确可以在极大地程度上提升电池针刺的通过率，加入了水系正极内部涂层的电池全部可以通过针刺实验，同时在针刺的过程中，产热量也比较小，说明水系正极内部涂层的存在可以保护活性材料直接与集流体接触而引起的热失控。
实施例1、实施例2、实施例3与实施例4相对比，LiCoO 2、LiNi 0.8Co 0.15Al 0.05O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiFePO 4四款水系正极内部涂层的效果不同，其中针对循环来讲，LiCoO 2对循环的影响最小，就几组实验结果的安全性来讲，LiNi 0.5Co 0.2Mn 0.3O 2材料的安全性能最好，LiNi 0.8Co 0.15Al 0.05O 2材料的安全性能相对而言弱一些。对于实施例1，在针刺的过程中电芯的最高温度为78.9℃远低于对比例1的331.2℃。
实施例1与对比例1相比，含有LiNi 0.5Co 0.2Mn 0.3O 2水系正极内部涂层的电芯可以通过2C-6V的过充，而常规的LiCoO 2电池无法通过该项测试，电池在测试后期会发生热失控，进而导致电池着火。
综上所述，本申请通过采用钴酸锂、镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂水性浆料在正极集流体上涂覆一层正极内部涂层，继而向该水系正极内部涂层上继续涂布正极活性材料，可以有效的提高正极活性材料与集流体之间的粘结力，防止由于正极活性材料的脱落而导致的循环容量衰减。同时水系正极内部涂的存在极大地提升了电芯的倍率性能，特别的，对电芯的安全性能有一个很大的改善。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本申请。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本申请的精神或范围的情况下，在其它实施例中实现。因此，本申请将不会被限制于本文所示的实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽范围。

Claims (11)

  1. 一种复合正极极片，其中，所述复合正极极片为双层涂覆结构的正极极片，包括集流体、正极内部涂层和正极外部涂层，所述正极内部涂层涂布在集流体上，所述正极外部涂层涂布在正极内部涂层上，所述正极内部涂层为水溶性涂层，所述正极外部涂层为油溶性涂层。
  2. 根据权利要求1所述的复合正极极片，其中，所述正极内部涂层的材料包括含有锂源的正极活性材料、导电剂、水溶性粘结剂、水溶性增稠剂。
  3. 根据权利要求2所述的复合正极极片，其中，所述正极活性材料、导电剂、水溶性粘结剂、水溶性增稠剂的质量百分比分别为80.0％-96.0％、0.5％-6.0％、1.5％-10.0％、2.0％-4.0％。
  4. 根据权利要求3所述的复合正极极片，其中，所述正极活性材料为磷酸铁锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂中的一种或多种的组合；所述导电剂为导电石墨、导电炭黑、科琴黑、乙炔黑、碳纤维、单臂碳纳米管、多臂碳纳米管、石墨烯中的一种或多种的组合；所述水溶性增稠剂为羧甲基纤维素钠、羟乙基纤维素、羟丙基纤维素、定优胶、聚乙烯醇、聚丙烯酸中一种或多种的组合；所述水溶性粘结剂为聚丙烯酰胺、聚氧化乙烯、聚乙烯吡咯烷酮、丙烯酰胺-丙烯腈共聚物、丙烯酸-丙烯酸酯共聚物、丙烯酸-丙烯酰胺-丙烯腈共聚物、丙烯酸-丙烯酸酯-丙烯腈共聚物中的一种或多种的组合。
  5. 根据权利要求3或4所述的复合正极极片，其中，所述水溶性粘结剂的pH值为4～5。
  6. 一种权利要求3-5任一项所述的复合正极极片的制备方法，其中，包括如下步骤：
    步骤一：将酸性水溶液与配比量的正极活性材料混合均匀，得到均一匀浆，所述均一匀浆的pH值为7-8；
    步骤二：在步骤一中所述均一匀浆里加入配比量的导电剂和水溶性增稠剂，调节浆料呈面团状，搅拌均匀后，再加入去离子水将浆料稀释至粘度为4000-6000mPa.s,再加入配比量的水溶性粘结剂继续搅拌0.5-3h，最后抽真空脱除气泡，筛网过滤后得到正极内层浆料，所述正极内层浆料的固含量为30％-50％，粘度为500-4000mPa.s；
    步骤三：将所述正极内层浆料均匀涂布在集流体上，加热烘烤使酸性水溶液中的溶剂水挥发，得到涂覆有正极内层浆料的集流体；
    步骤四：将涂覆有正极内层浆料的集流体进行干燥得到涂覆有正极内部涂层的集流体；所述正极内部涂层的厚度为1-20μm，面密度为0.1-10g/m 2；
    步骤五：在步骤四中所述正极内部涂层上涂覆正极外层浆料，经过烘烤、辊压得到复合正极极片。
  7. 根据权利要求6所述的复合正极极片的制备方法，其中，在步骤一中，在5-10℃温度范围内边搅拌边往所述正极活性材料中加入所述酸性水溶液，所述酸性水溶液为弱酸性水溶液，所述酸性水溶液的体积百分比浓度为1％-5％。
  8. 根据权利要求7所述的复合正极极片的制备方法，其中，所述酸性水溶液为磷酸、草酸、乙酸、碳酸、柠檬酸、丙二酸、己二酸、琥珀酸、水杨酸、邻苯二甲酸、甲苯磺酸、酒石酸中的一种或几种的混合配制的水溶液。
  9. 根据权利要求6所述的复合正极极片的制备方法，其中，在步骤五中，所述正极外层浆料包括油溶性粘结剂、分散剂以及正极活性材料和导电剂。
  10. 根据权利要求9所述的复合正极极片的制备方法，其中，所述油溶性粘结剂为聚偏四氟乙烯，所述分散剂为N-甲基吡咯烷酮。
  11. 一种锂离子电池，其特征在于：所述锂离子电池包括权利要求1-5任一 项所述的复合正极极片、负极片、隔膜和电解液。
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