WO2023236158A1 - 正极极片、二次电池、电池模块、电池包及用电装置 - Google Patents

正极极片、二次电池、电池模块、电池包及用电装置 Download PDF

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WO2023236158A1
WO2023236158A1 PCT/CN2022/097967 CN2022097967W WO2023236158A1 WO 2023236158 A1 WO2023236158 A1 WO 2023236158A1 CN 2022097967 W CN2022097967 W CN 2022097967W WO 2023236158 A1 WO2023236158 A1 WO 2023236158A1
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positive electrode
polymer
battery
structural units
units derived
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PCT/CN2022/097967
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English (en)
French (fr)
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李�诚
刘会会
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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 KR1020247001598A priority Critical patent/KR20240022600A/ko
Priority to CN202280045807.XA priority patent/CN117581391A/zh
Priority to PCT/CN2022/097967 priority patent/WO2023236158A1/zh
Priority to EP22945302.2A priority patent/EP4379839A1/en
Priority to US18/498,969 priority patent/US20240063393A1/en
Publication of WO2023236158A1 publication Critical patent/WO2023236158A1/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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • 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
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/668—Composites of electroconductive material and synthetic resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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 technical field of lithium batteries, and in particular to a positive electrode plate, a secondary battery and an electrical device.
  • lithium-ion batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the popularity of lithium-ion battery applications, higher requirements have been placed on both performance and cost.
  • the existing traditional binder PVDF as a commonly used binder, has problems such as poor compatibility with electrode active materials and weak bonding force, resulting in poor stability and difficulty in molding of pole pieces using it as a binder. Therefore, it is urgently needed.
  • a new binder and positive electrode sheet were developed.
  • This application was made in view of the above-mentioned problems, and its purpose is to provide a positive electrode sheet with good molding quality and strong adhesive force, thereby improving the cycle performance of the battery.
  • a first aspect of the present application provides a positive electrode sheet, which includes a current collector, an undercoat layer disposed on at least one surface of the current collector, and a cathode diaphragm disposed on the undercoat layer.
  • the undercoat layer contains a component capable of being dissolved in Polymer A of an aqueous solvent, polymer A comprising a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structure derived from a monomer containing an ester group unit.
  • This application improves the molding quality, bonding force and flexibility of the positive electrode piece by using polymer A in the base coating of the positive electrode piece, and optimizes the cycle performance of the battery.
  • the weight average molecular weight of polymer A in the base coat layer is 1.5 ⁇ 10 5 to 2 ⁇ 10 5 .
  • Appropriate weight average molecular weight can improve the molding quality of the electrode piece, take into account the processability and adhesion of the undercoat, and ensure that the polymer A in the undercoat has a certain diffusivity when the cathode slurry is coated, thereby further Improve the adhesion of the pole pieces and the cycle performance of the battery.
  • the mass content of polymer A in the base coating is 5% to 40%, optionally 5% to 30%, optionally 5% to 20%, based on the total mass of the base coating. .
  • the quality of polymer A in the base coating is within this range, the appearance quality and brittleness of the pole piece are improved, and the bonding performance of the pole piece and the cycle performance of the battery are improved.
  • the base coating further includes a conductive agent, and the conductive agent is selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.
  • Adding a conductive agent to the base coating can reduce the interface resistance between the positive electrode diaphragm and the current collector, improve the charge and discharge rate performance of the battery, and extend the cycle life of the battery.
  • the thickness of the primer layer is 1 to 20 ⁇ m.
  • the thickness of the undercoat within this range can take into account the bonding performance of the pole piece and the power performance and cycle performance of the battery.
  • the coating area density of the positive electrode membrane is not less than 20 mg/cm 2 .
  • the undercoating of the present application in the electrode piece, it can be ensured that the positive electrode piece is loaded with a certain content of positive electrode active material, thereby ensuring the power performance of the battery.
  • the positive electrode membrane includes a positive electrode active material, a binder and a conductive agent.
  • the binder includes a polymer A capable of being dissolved in an oily solvent.
  • the polymer A contains a polymer derived from a monomer containing a cyano group. Structural units, structural units derived from monomers containing amide groups and structural units derived from monomers containing ester groups.
  • polymer A that can be dissolved in oily solvents is used as a binder to diffusely connect with the polymer A in the undercoat layer, which can further enhance the bonding force between the undercoat layer and the positive electrode diaphragm and improve the electrode piece. It improves the appearance quality and brittleness, improves the bonding performance of the pole pieces and the cycle performance of the battery.
  • the positive electrode membrane contains the polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 .
  • Controlling the weight average molecular weight of polymer A can further reduce the cycle internal resistance growth rate of the battery while improving the adhesion of the positive electrode sheet.
  • the positive electrode membrane further contains polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 .
  • Polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 plays the role of a dispersant in the positive electrode diaphragm. Its addition can further improve the dispersion of the positive electrode active material in the positive electrode diaphragm, making the prepared electrode The sheet has higher adhesion and the battery has lower cycle internal resistance growth rate.
  • the positive active material is a lithium-containing transition metal oxide
  • the positive active material can be lithium iron phosphate, or their doping modified materials, or their conductive carbon coating modified materials, conductive metals At least one of the modified materials is coated or the conductive polymer is coated.
  • the mass content of the positive electrode active material is 70%-99.5%, optionally 88%-99.5%, based on the total mass of the positive electrode membrane.
  • the mass content of the positive active material is within this range, which can ensure the loading capacity of the positive active material and improve the power performance of the battery.
  • the mass content of polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 in the positive electrode membrane is 0.4%-5.5%, and/or the weight average molecular weight of the positive electrode membrane is 1 ⁇
  • the mass content of 10 5 to 2.5 ⁇ 10 5 polymer A is 0.05%-0.5%, based on the mass of the positive electrode membrane.
  • the monomer containing a cyano group in polymer A is selected from one or more of acrylonitrile and butenenitrile;
  • the monomer containing an amide group is selected from methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide Amide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, One or more types of N,N-diethylmethacrylamide;
  • the monomer containing an ester group is selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, isopentyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, acrylic acid One or more hydroxypropyl esters.
  • the molar content of structural units derived from monomers containing cyano groups in polymer A is 50% to 70%, and the molar content of structural units derived from monomers containing ester groups is is 10% to 30%, and the molar content of structural units derived from monomers containing amide groups is 10% to 30%, based on the total molar content of structural units in polymer A.
  • a secondary battery including the positive electrode plate of the first aspect of the present application.
  • a battery module including the secondary battery of the second aspect of the present application.
  • a battery pack including the battery module of the third aspect of the present application.
  • an electrical device including at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, or the battery pack of the fourth aspect of the present application.
  • FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • Figure 7 is a schematic diagram of the adhesive force test of the pole piece.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • Lithium iron phosphate cathode active material has received widespread attention in the industry due to its low cost, high performance and safety.
  • the lithium iron phosphate cathode active material has the characteristics of large specific surface area, small particle size, large amount of carbon element coating on the surface after carbon coating, and high degree of graphitization. Therefore, using lithium iron phosphate as the cathode active material uses the traditional binder PVDF.
  • the slurry used as a binder has poor dispersion, is easy to precipitate, has high viscosity, and has low solid content.
  • the surface of the pole piece prepared by it is prone to defects such as cracking, peeling, particle scratches, pinholes, etc., and the positive active material in the pole piece is prone to defects. Uneven distribution and uneven pole piece quality.
  • this application proposes a positive electrode slurry for batteries, which includes a positive electrode active material, a conductive agent and a binder.
  • the binder includes polymer A, and polymer A includes a monomer derived from a cyano group-containing unit. structural units derived from monomers containing amide groups and structural units derived from monomers containing ester groups.
  • binder refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.
  • polymer includes on the one hand an assembly of macromolecules that are chemically homogeneous but differ in degree of polymerization, molar mass and chain length, prepared by polymerization reactions.
  • the term on the other hand also includes derivatives of aggregates of macromolecules formed by polymerization reactions which are obtainable by reaction, for example addition or substitution, of functional groups in said macromolecules and which may be chemically homogeneous or chemically A non-homogeneous compound or mixture.
  • positive electrode also refers to the "cathode” in the secondary battery.
  • cyano group refers to the -CN group.
  • amide group refers to the -CONH group.
  • ester group refers to a -COOR 1 group, with R 1 selected from C 1-9 alkyl groups substituted or unsubstituted.
  • substituents in the term "substituted by a substituent" are each independently selected from: hydroxyl, mercapto, amino, cyano, nitro, aldehyde, halogen atom, alkenyl, alkynyl, aryl, hetero Aryl group, C 1-6 alkyl group, C 1-6 alkoxy group.
  • C 1-6 alkyl refers to a straight or branched hydrocarbon chain radical consisting exclusively of carbon and hydrogen atoms, with no unsaturation present in the radical, having from one to five carbon atoms, and Attached to the rest of the molecule by a single bond.
  • C 1-9 alkyl should be interpreted accordingly. Examples of C 1-6 alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, pentyl.
  • polymer A refers to a polymer containing structural units derived from monomers containing cyano groups, structural units derived from monomers containing amide groups, and monomers derived from monomers containing ester groups. structural units of polymers.
  • Polymer A is soluble in oily solvents. In some embodiments, Polymer A is soluble in aqueous solvents.
  • oily solvents include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethylcellulose, polycarbonate.
  • aqueous solvents include, but are not limited to, water. It can be understood that the structural units in polymer A can be proportioned in any proportion, polymer A can have different molecular weights, and polymer A can be prepared by different methods, such as suspension method, emulsion method, etc.
  • a dispersion medium is included in the cathode slurry.
  • the dispersion medium of the cathode slurry is an oily solvent.
  • the dispersion medium of the cathode slurry is an aqueous solvent.
  • the binder is used to bind the positive active material and/or the conductive agent together to form a slurry, and can fix them in place and adhere them to the conductive metal components to form the positive electrode.
  • Polymer A is acrylonitrile-acrylamide-methyl acrylate copolymer, acrylonitrile-acrylamide-ethyl acrylate copolymer, acrylonitrile-acrylamide-propyl acrylate copolymer, acrylonitrile-propylene One or more of the amide-isooctyl acrylate copolymers.
  • the present application uses structural units derived from monomers containing cyano groups, structural units derived from monomers containing amide groups, and structural units derived from monomers containing ester groups in the positive electrode slurry.
  • the polymer is used as a binder to improve the stability and processability of the cathode slurry and improve the bonding force of the cathode sheet.
  • Polymer A has abundant polar groups, such as the cyano group located in the main chain segment of polymer A. Due to the dipolar interaction between the cyano group and the electronegativity of the cathode current collector, polymer A is The current collector has strong adhesion, which improves the bonding force of the pole piece and avoids processing abnormalities such as peeling off and powder loss of the pole piece during the coating or cold pressing process.
  • the ester-containing functional groups in polymer A have a certain ability to absorb electrolyte and retain electrolyte, which can improve the problem of poor ionic conductivity of traditional binders such as polyvinylidene fluoride.
  • the abundant groups on polymer A can improve the compatibility of polymer A with various cathode active materials and improve the versatility of polymer A as a binder.
  • the binder includes Polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 .
  • the weight average molecular weight of polymer A can be selected from 7 ⁇ 10 5 to 9.5 ⁇ 10 5 , or from 7 ⁇ 10 5 to 9 ⁇ 10 5 , or from 7 ⁇ 10 5 to 8.5 ⁇ 10 5 , Or 7 ⁇ 10 5 to 8 ⁇ 10 5 , or 7.5 ⁇ 10 5 to 1 ⁇ 10 6 , or 8 ⁇ 10 5 to 1 ⁇ 10 6 , or 8.5 ⁇ 10 5 to 1 ⁇ 10 6 , or 9 ⁇ 10 5 to 1 ⁇ 10 6 , or 9.5 ⁇ 10 5 to 1 ⁇ 10 6 .
  • weight average molecular weight refers to the sum of the weight fractions of molecules of different molecular weights in the polymer multiplied by their corresponding molecular weights.
  • Controlling the weight average molecular weight of polymer A can further reduce the cycle internal resistance growth rate of the battery while improving the stability and processability of the cathode slurry and the adhesive force of the cathode sheet.
  • the binder further includes polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 .
  • the weight average molecular weight of polymer A can be selected from 1.5 ⁇ 10 5 to 2.5 ⁇ 10 5 , or from 2 ⁇ 10 5 to 2.5 ⁇ 10 5 , or from 1 ⁇ 10 5 to 2 ⁇ 10 5 , Or 1 ⁇ 10 5 ⁇ 1.5 ⁇ 10 5 .
  • polymer A with a lower weight average molecular weight in the slurry its electrostatic repulsion or steric hindrance can be used to avoid agglomeration between positive electrode active materials (such as lithium iron phosphate LFP powder particles); at the same time, the Other small molecular substances play the role of dispersion and suspension, so that the slurry will not settle for a short time and the stability will be increased.
  • polymer A with a low weight average molecular weight has a low glass transition temperature, which can further improve the flexibility of the pole piece.
  • polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 acts as a dispersant in the cathode slurry, and its addition further improves the stability and processability of the slurry, and the electrode piece
  • the adhesive force reduces the cycle internal resistance growth rate of the battery.
  • the mass content of polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 is 0.4%-5.5%, based on the total mass of the positive electrode active material, conductive agent and binder. If too much polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 is added, the power performance and cycle performance of the battery will be reduced. Polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 within this mass content range can improve the stability and processability of the slurry, the adhesion of the pole pieces, and at the same time greatly reduce the cycle internal resistance of the battery. growth rate.
  • the mass content of polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 is 0.05%-0.5%, based on the total mass of the cathode active material, conductive agent and binder.
  • polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 is added too much, it will increase the swelling of the pole pieces and affect the normal temperature power performance of the battery.
  • Polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 within this mass content range can further improve the stability and processability of the slurry and the adhesion of the pole pieces, while significantly reducing the battery cycle Internal resistance growth rate.
  • the cyano group-containing monomer is selected from one or more of acrylonitrile and butenenitrile.
  • the monomer containing an amide group is selected from the group consisting of methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N- Isopropylmethacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N- One or more of diethyl acrylamide and N,N-diethylmethacrylamide.
  • the monomer containing an ester group is selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, isopentyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, One or more of hydroxyethyl acrylate and hydroxypropyl acrylate.
  • the above-mentioned materials are simple and easy to obtain and can significantly reduce the manufacturing cost of the adhesive.
  • the molar content of structural units derived from monomers containing cyano groups in polymer A is 50% to 70%, and the molar content of structural units derived from monomers containing ester groups is is 10% to 30%, and the molar content of structural units derived from monomers containing amide groups is 10% to 30%, based on the total molar content of structural units in polymer A.
  • the reasonable combination of structural units derived from monomers containing various groups can take into account the strength, flexibility, bonding performance and swelling resistance of polymer A, so that the pole piece has excellent bonding force and processing performance.
  • the positive active material is a lithium-containing transition metal oxide, which may be lithium iron phosphate, or their doped modified materials, or their conductive carbon coating modified materials, conductive metal coating modified materials, etc. At least one of the modified materials is coated with a conductive material or a conductive polymer.
  • the lithium iron phosphate cathode active material has a microporous structure, and its surface has a high degree of graphitization after carbon coating.
  • the above structural characteristics lead to poor wettability in slurry solvents (such as N-methylpyrrolidone NMP), which results in poor stability of the slurry, low solid content, easy to become sticky after being placed, and cannot be used normally.
  • Polymer A contains groups with good affinity for carbon materials with a high degree of graphitization, such as N-containing groups (cyano groups, amide groups), oxygen-containing groups (ester groups, amide groups) group), thereby effectively improving the wettability of lithium iron phosphate powder in solvents (such as NMP), thereby improving the stability and processing performance of the cathode slurry.
  • the mass content of the cathode active material is 70% to 99.5%, optionally 88.0% to 99.5%, based on the total mass of the cathode active material, conductive agent and binder.
  • the mass content of the positive active material is within this range, which can ensure the loading capacity of the positive active material and improve the power performance of the battery.
  • the conductive agent is selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass content of the conductive agent is 0.2%-6.0%, based on the total mass of the positive active material, the conductive agent and the binder.
  • a positive electrode sheet which includes a current collector, an undercoat layer disposed on at least one surface of the current collector, and a cathode diaphragm disposed on the undercoat layer.
  • the undercoat layer contains a material capable of dissolving Polymer A in an aqueous solvent, polymer A comprising a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structural unit derived from a monomer containing an ester group. Structural units.
  • current collector refers to any conductive substrate capable of conducting current to an electrode during discharge or charge of a secondary battery.
  • positive electrode membrane refers to the coating formed after the positive electrode slurry is coated and dried.
  • Small particle cathode active materials have the advantage of large specific surface area and can fully react with the electrolyte. However, their large specific surface area also brings the disadvantage of poor adhesion with the current collector, causing the cathode slurry to easily appear during the coating process. Decoating phenomenon. If the amount of binder in the positive electrode slurry is increased, the electrode piece will be brittle during the cold pressing process and the compacted density will be reduced. Therefore, a special primer coating needs to be added to the current collector to improve the connection between the positive electrode diaphragm and the collector. The bonding force between fluids.
  • the polymer A in the base coating that is soluble in aqueous solvents contains cyano groups, amide groups and ester groups, it comes into contact with the oily solvent (such as NMP) of the cathode slurry during the coating process of the cathode slurry. ), appropriate swelling can occur but will not dissolve.
  • Mutual diffusion can be achieved by molecular contact between the polymer A in the primer layer and the binder in the cathode slurry, which can greatly improve the bonding force between the cathode diaphragm and the current collector.
  • the ester group in polymer A can form strong hydrogen bonds with the hydroxyl groups in the oxide layer on the surface of the current collector to ensure that the positive electrode membrane is firmly attached to the current collector.
  • Polymer A that can be dissolved in aqueous solvent means that polymer A can be dissolved in aqueous solvent to form a solution or dispersion system, and the solubility of polymer A in aqueous solvent is not less than 1g.
  • the solubility of polymer A in the aqueous solvent is not less than 10 g.
  • the polymer A in the base coat that is soluble in an aqueous solvent is formed through bulk polymerization, suspension polymerization, emulsion polymerization or solution polymerization.
  • the polymer A in the base coating that can be dissolved in an aqueous solvent is formed by an emulsion method, which is easy to mass-produce, simple and environmentally friendly.
  • This application improves the molding quality, bonding force and flexibility of the positive electrode piece by using polymer A in the base coating of the positive electrode piece, and optimizes the cycle performance of the battery.
  • the weight average molecular weight of polymer A in the base coat layer is 1.5 ⁇ 10 5 to 2 ⁇ 10 5 .
  • An appropriate weight average molecular weight can improve the molding quality of the electrode piece, take into account the processability and adhesion of the base coating, and at the same time ensure that the polymer A in the base coating has a certain diffusivity when the cathode slurry is coated.
  • the mass content of polymer A in the base coating is 5% to 40%, optionally 5% to 30%, optionally 5% to 20%, based on the total mass of the base coating. .
  • the amount of polymer A in the undercoat is too large, it will reduce the stability of the undercoat and the cycle performance of the battery.
  • the quality of polymer A in the base coating is within this range, the appearance quality and brittleness of the pole piece are improved, and the bonding performance of the pole piece and the cycle performance of the battery are improved.
  • the undercoat layer also contains a conductive agent, and the conductive agent is selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.
  • Adding a conductive agent to the base coating can reduce the interface resistance between the positive electrode diaphragm and the current collector, improve the charge and discharge rate performance of the battery, and extend the cycle life of the battery.
  • the thickness of the primer layer is 1-20 ⁇ m.
  • the thickness of the undercoat is too large, the current collector will have poor conductivity. If the thickness of the undercoat is too small, it cannot ensure effective bonding in the pole piece.
  • the thickness of the base coating is within this range, which can take into account the bonding performance of the pole piece and the power performance and cycle performance of the battery.
  • the coating area density of the positive electrode membrane is not less than 20 mg/cm 2 .
  • area density is calculated by dividing the mass by the corresponding area.
  • the undercoating of the present application in the electrode piece, it can be ensured that the positive electrode piece is loaded with a certain content of positive electrode active material, thereby ensuring the power performance of the battery.
  • the positive electrode membrane includes a positive electrode active material, a binder and a conductive agent.
  • the binder includes a polymer A capable of being dissolved in an oily solvent.
  • the polymer A contains a polymer derived from a monomer containing a cyano group. Structural units, structural units derived from monomers containing amide groups and structural units derived from monomers containing ester groups.
  • Polymer A that can be dissolved in an oily solvent means that polymer A can be dissolved in an oily solvent to form a solution or dispersion system, and the solubility of polymer A in an oily solvent is not less than 1g.
  • the solubility of polymer A in oily solvent is not less than 10 g.
  • polymer A that can be dissolved in oily solvents is used as a binder to diffusely connect with the polymer A in the undercoat layer, which can further enhance the bonding force between the undercoat layer and the positive electrode diaphragm and improve the electrode piece. It improves the appearance quality and brittleness, improves the bonding performance of the pole pieces and the cycle performance of the battery.
  • the positive electrode membrane contains the polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 .
  • Controlling the weight average molecular weight of polymer A can further reduce the cycle internal resistance growth rate of the battery while improving the adhesion of the positive electrode sheet.
  • the positive electrode membrane further contains polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 .
  • Polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 plays the role of a dispersant in the positive electrode diaphragm. Its addition can further improve the dispersion of the positive electrode active material in the positive electrode diaphragm, making the prepared electrode The sheet has higher adhesion and the battery has lower cycle internal resistance growth rate.
  • polymer A with a lower weight average molecular weight in the slurry for forming the positive electrode membrane Due to the large specific surface area and large number of small particles of some positive active materials (such as lithium iron phosphate LFP), the slurry that forms the positive electrode membrane is prone to agglomeration during the preparation process, causing the filter to become clogged.
  • polymer A with a lower weight average molecular weight in the slurry for forming the positive electrode membrane By using polymer A with a lower weight average molecular weight in the slurry for forming the positive electrode membrane, its electrostatic repulsion or steric hindrance can be used to avoid agglomeration between positive electrode active materials (such as lithium iron phosphate LFP powder particles); at the same time, It plays a role in dispersing and suspending other small molecule substances in the positive electrode diaphragm, so that the slurry will not settle for a short time and its stability will be increased.
  • polymer A with a low weight average molecular weight has
  • the positive active material is a lithium-containing transition metal oxide
  • the positive active material can be lithium iron phosphate, or their doping modified materials, or their conductive carbon coating modified materials, conductive metals At least one of the modified materials is coated or the conductive polymer is coated.
  • Polyacrylic acid is often used as a binder in the base coating of traditional lithium iron phosphate systems.
  • the polarity of polyacrylic acid and the traditional binder polyvinylidene fluoride in the cathode diaphragm are quite different, and the bonding force between the two is low.
  • the polyacrylic acid in the undercoat has poor solubility in the positive electrode slurry solvent, and cannot form an effective diffusion connection between the undercoat and the positive electrode diaphragm when the slurry coating is dried.
  • NMP N-methylpyrrolidone
  • the mass content of the positive electrode active material is 70%-99.5%, optionally 88.0%-99.5%, based on the total mass of the positive electrode membrane.
  • the mass content of the positive active material is within this range, which can ensure the loading capacity of the positive active material and improve the power performance of the battery.
  • the mass content of polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 in the positive electrode membrane is 0.4%-5.5%, and/or the weight average molecular weight of the positive electrode membrane is 1 ⁇
  • the mass content of 10 5 to 2.5 ⁇ 10 5 polymer A is 0.05%-0.5%, based on the mass of the positive electrode membrane.
  • Polymer A with a weight average molecular weight of 7 ⁇ 10 5 to 1 ⁇ 10 6 within this mass content range can improve the stability and processability of the slurry, the adhesion of the pole pieces, and at the same time greatly reduce the cycle internal resistance of the battery. growth rate. If polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 is added too much, it will increase the swelling of the pole pieces and affect the normal temperature power performance of the battery. Polymer A with a weight average molecular weight of 1 ⁇ 10 5 to 2.5 ⁇ 10 5 within this mass content range can further improve the stability and processability of the slurry and the adhesion of the pole pieces, while significantly reducing the battery cycle Internal resistance growth rate.
  • the monomer containing a cyano group in polymer A is selected from one or more of acrylonitrile and butenenitrile;
  • the monomer containing an amide group is selected from methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide Amide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, One or more types of N,N-diethylmethacrylamide;
  • the monomer containing an ester group is selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, isopentyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, acrylic acid One or more hydroxypropyl esters.
  • the above-mentioned materials are simple and easy to obtain and can significantly reduce the manufacturing cost of the adhesive.
  • the molar content of structural units derived from monomers containing cyano groups in polymer A is 50% to 60%, and the molar content of structural units derived from monomers containing ester groups is is 10% to 20%, and the molar content of structural units derived from monomers containing amide groups is 20% to 30%, respectively based on the total molar content of structural units in polymer A.
  • a reasonable combination of structural units derived from monomers containing various groups can take into account the strength, flexibility, adhesion and swelling resistance of polymer A.
  • the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the cathode active material may be a cathode active material known in the art for batteries.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (can also be abbreviated to NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (can also be abbreviated to NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (can also be abbreviated to NCM 622 ), LiNi At least one of 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as Li Li
  • the olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composites of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate and carbon.
  • At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • the positive electrode membrane optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative active material may be a negative active material known in the art for batteries.
  • the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer optionally also includes other auxiliaries, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • auxiliaries such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally further includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • a secondary battery including an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode piece, a separator, and a negative electrode piece.
  • the positive electrode piece is prepared from the positive electrode slurry of any embodiment. .
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 1 shows a square-structured 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 side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • an electrical device including at least one of a secondary battery of any embodiment, a battery module of any embodiment, or a battery pack of any embodiment.
  • the electrical device includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG. 6 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This adhesive is used for pole pieces.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2.
  • the prepared polymer A-1 has The weight average molecular weight is 800,000.
  • Example 2 Dissolve the lithium iron phosphate LFP active material, conductive agent carbon black, and polymer A-1 of Example 1 in N-methylpyrrolidone (NMP) solution at a weight ratio of 93:4:3, stir and mix evenly, and obtain a positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the slurry has a solid content of 55%; the positive electrode slurry is then evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode piece.
  • SBR styrene-butadiene rubber
  • CMC thickener sodium hydroxymethylcellulose
  • Example 1 Stack the positive electrode piece, isolation film, and negative electrode piece in order in Example 1 so that the isolation film plays an isolation role between the positive and negative electrode pieces, then wind it to obtain a bare battery core, and weld the tabs to the bare battery core. , put the bare battery core into an aluminum case, bake it at 80°C to remove water, then inject electrolyte and seal it to obtain an uncharged battery. The uncharged battery then undergoes processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This binder is used for dispersion in the pole piece slurry.
  • the molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in polymer A-2 is 5:3:2.
  • NMP N-methylpyrrolidone
  • Example 11 the total amount of polymer A added is kept unchanged, and the ratio of added polymer A-1 and polymer A-2 is adjusted. Other parameters and steps are the same as in Example 1. The specific parameters are shown in Table 1. .
  • the preparation method of polymer A-1 in Example 17 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 400 mg of calcium sulfate and 80 mg of calcium phosphate. Then 420 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 3.003 mmol AIBN (0.39% based on total monomer molar content) were added. Finally, 0.10g of magnesium sulfate aqueous solution dissolved in 50ml of deionized water was added, the suspension was heated to 65°C, and reacted for 5 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This adhesive is used for pole pieces.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2.
  • the prepared polymer A-1 has The weight average molecular weight is 700,000.
  • the preparation method of polymer A-1 in Example 18 is as follows: dissolve 0.20g of suspension agent in 150ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 400mg of calcium sulfate and 80mg of calcium phosphate. Then 420 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 3.003 mmol AIBN (0.39% based on total monomer molar content) were added. Finally, 0.13 g of magnesium sulfate aqueous solution dissolved in 50 ml of deionized water was added, and the suspension was heated to 75°C and reacted for 6 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This adhesive is used for pole pieces.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2.
  • the prepared polymer A-1 has The weight average molecular weight is 1 million.
  • the preparation method of polymer A-1 in Example 19 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 400 mg of calcium sulfate and 80 mg of calcium phosphate. Then 420 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 3.003 mmol AIBN (0.39% based on total monomer molar content) were added. Finally, 0.1 g of magnesium sulfate aqueous solution dissolved in 50 ml of deionized water was added, and the suspension was heated to 65°C and reacted for 4 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C. At constant weight, a white powder was obtained.
  • This adhesive is used for pole pieces.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2.
  • the prepared polymer A-1 has The weight average molecular weight is 600,000.
  • the preparation method of polymer A-1 in Example 20 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 400 mg of calcium sulfate and 80 mg of calcium phosphate. Then 420 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 3.003 mmol AIBN (0.39% based on total monomer molar content) were added. Finally, 0.18g of magnesium sulfate aqueous solution dissolved in 50ml of deionized water was added, the suspension was heated to 80°C, and reacted for 7 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This adhesive is used for pole pieces.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2.
  • the prepared polymer A-1 has The weight average molecular weight is 1.1 million.
  • Example 21 the weight average molecular weight of polymer A-2 was adjusted, and other parameters and steps were the same as in Example 1. See Table 1 for specific parameters.
  • the preparation method of polymer A-2 in Example 21 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 300 mg of calcium sulfate and 60 mg of calcium phosphate. Then 350 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 2.25 mmol AIBN (0.3% based on total monomer molar content) were added. Finally, 0.05g of magnesium sulfate aqueous solution dissolved in 50ml of deionized water was added, and the suspension was heated to 46°C and reacted for 2.0 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This binder is used for dispersion in the pole piece slurry.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2.
  • the prepared polymer A-2 has The weight average molecular weight is 100,000.
  • the preparation method of polymer A-2 in Example 22 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 300 mg of calcium sulfate and 60 mg of calcium phosphate. Then 350 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 2.25 mmol AIBN (0.3% based on total monomer molar content) were added. Finally, 0.08 g of magnesium sulfate aqueous solution dissolved in 50 ml of deionized water was added, and the suspension was heated to 50°C and reacted for 3.5 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This binder is used for dispersion in the pole piece slurry.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2.
  • the prepared polymer A-2 has The weight average molecular weight is 250,000.
  • the preparation method of polymer A-2 in Example 23 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 300 mg of calcium sulfate and 60 mg of calcium phosphate. Then 350 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 2.25 mmol AIBN (0.3% based on total monomer molar content) were added. Finally, 0.03g of magnesium sulfate aqueous solution dissolved in 50ml of deionized water was added, the suspension was heated to 40°C, and reacted for 1.5 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This binder is used for dispersion in the pole piece slurry.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2.
  • the prepared polymer A-2 has The weight average molecular weight is 50,000. .
  • the preparation method of polymer A-2 in Example 24 is as follows: dissolve 0.20g of the suspension agent in 150 ml of deionized water, blow with dry nitrogen for 30 minutes, and then use 300 mg of calcium sulfate and 60 mg of calcium phosphate. Then 350 mmol acrylonitrile, 140 mmol methyl acrylate, 210 mmol acrylamide, 2.25 mmol AIBN (0.3% based on total monomer molar content) were added. Finally, 0.10g of magnesium sulfate aqueous solution dissolved in 50ml of deionized water was added, the suspension was heated to 58°C, and reacted for 4 hours.
  • the suspension was cooled, and the product was filtered, washed, and then vacuum dried at 70°C to At constant weight, a white powder was obtained.
  • This binder is used for dispersion in the pole piece slurry.
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2.
  • the prepared polymer A-2 has The weight average molecular weight is 400,000.
  • Example 1 Directly dissolve the positive active material, LFP lithium iron phosphate active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 92:4:4. Stir thoroughly and mix evenly to obtain the positive electrode slurry; then apply the positive electrode slurry evenly on the positive electrode current collector, and then dry, cold press, and cut to obtain the positive electrode sheet of Comparative Example 1. Other preparation steps are the same as Example 1.
  • NMP N-methylpyrrolidone
  • the molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-3 is 3:1:1, and the weight average molecular weight of polymer A-3 to 180,000.
  • Preparation of the base coating The prepared emulsion containing polymer A-3 and the conductive agent are mixed at a mass ratio of 30:70, using the kneading method to completely infiltrate the conductive agent with deionized water, and finally add deionized water to make the slurry
  • the solid content is 15%, stir well and the slurry has a shipping viscosity of 200-800mpa.s.
  • gravure coating the gravure roller is engraved with pits. During coating, the slurry is injected into the pits (30 ⁇ m). After the roller surface leaves the liquid surface, the smooth area is scraped off by a scraper. Under the action of the pressure roller, the pits are formed. The slurry in the coating is transferred to the surface of the substrate, and the thickness of the single-sided coating after drying is about 5 ⁇ m. Prepare primed aluminum foil and set aside.
  • the preparation of the positive electrode sheet is the same as in Example 12.
  • Lithium iron phosphate: conductive agent SP: polymer A-1: polymer A-2 is dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 92: 4: 3.8: 0.2 solution, stir and mix evenly to obtain a positive electrode slurry; then, the positive electrode slurry is evenly coated on the prepared aluminum foil with primer, and then dried, cold pressed, and cut to obtain a positive electrode piece.
  • the coating prepared by the positive electrode slurry is called the positive electrode diaphragm.
  • the surface density of the single-sided coating of the positive electrode diaphragm is about 20mg/cm 2
  • the compacted density of the single-sided coating of the positive electrode diaphragm is about 2.3g/cm 3 .
  • Embodiment 25 is the same as those of Embodiment 12.
  • Example 26 the mass ratios of the emulsion containing polymer A-3 and the conductive agent were respectively adjusted to 40:60, 50:50, 60:40, and 70:30. Other steps were the same as in Example 12.
  • Example 30 the preparation of the positive electrode sheet includes nickel cobalt manganese oxide (NCM), lithium iron phosphate: conductive agent SP: polymer A-1: polymer A-2 in a mass ratio of 82: 10: 4: 3.8:0.2 is dissolved in N-methylpyrrolidone (NMP) solution, stir and mix evenly to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the prepared aluminum foil with primer, and then dried, cold pressed, Cut it to obtain the positive electrode piece.
  • NMP N-methylpyrrolidone
  • the base coating in Comparative Example 3 is a PAA base coating, and the positive electrode plate is the same as Comparative Example 2.
  • the preparation method of the PAA base coating is as follows: Prepare a water-based emulsion containing PAA. The solid content of the emulsion is about 20%. The mass ratio of the emulsion and conductive agent is 50:50. The kneading method is used to completely infiltrate the conductive agent with deionized water. Finally, add deionized water to make the solid content of the slurry 15%, stir thoroughly and evenly, and the shipping viscosity of the slurry is 200-800 mpa.s. When gravure coating is used, the gravure roller is engraved with pits.
  • the slurry is injected into the pits (30 ⁇ m). After the roller surface leaves the liquid surface, the smooth area is scraped off by a scraper. Under the action of the pressure roller, the pits are formed. The slurry in the coating is transferred to the surface of the substrate, and the thickness of the single-sided coating after drying is about 5 ⁇ m. Prepare primed aluminum foil and set aside.
  • the polymers, pole pieces and batteries obtained in the above-mentioned Examples 1 to 24 and Comparative Example 1 were subjected to performance tests.
  • the test results are shown in Table 1; the polymers obtained in the above-mentioned Examples 25-30 and Comparative Examples 2-3 were Conduct performance tests on objects, pole pieces and batteries.
  • the test results are shown in Table 2.
  • the test method is as follows:
  • Double-sided tape 7 is pasted on one side of the pole piece 6, and pressed with a pressure roller to completely fit it with the pole piece; the other side of the double-sided tape 7 is pasted on the surface of the steel plate 8, and one end of the current collector 61 is bent in the opposite direction.
  • the bending angle is 180°, as shown by the arrow in Figure 7; a high-speed rail tensile machine is used for testing.
  • One end of the steel plate 8 is fixed on the lower clamp of the tensile machine, and the bent end of the current collector 61 is fixed on the upper clamp. Adjust the angle of the current collector to ensure that it is up and down.
  • the end is in a vertical position, and then the sample is stretched at a speed of 50mm/min until the current collector 61 is completely peeled off from the coating 62 on the surface of the current collector 61.
  • the displacement and force during the process are recorded, and the force when the force is balanced is taken as The bonding force of pole piece 6.
  • the battery DC impedance test process is as follows: at 25°C, charge the battery in the example or comparative example with a constant current of 1/3C to 3.65V, then charge with a constant voltage of 3.65V until the current is 0.05C, and leave it aside for 5 minutes. Record the voltage V 1 . Then discharge at 1/3C for 30 seconds and record the voltage V 2 . Then the internal resistance DCR 1 of the battery after the first cycle can be obtained through the formula 3*(V 2 -V 1 )/C.
  • Battery cycle number is derived from capacity testing.
  • the test process is as follows: at 25°C, charge the battery corresponding to Example 1 to 3.65V with a constant current of 1/3C, then charge with a constant voltage of 3.65V until the current is 0.05C, leave it aside for 5 minutes, and then discharge it with a constant current of 1/3C. to 2.5V, the obtained capacity is recorded as the initial capacity C 0 , and the cut-off condition P n ⁇ 70% C 0 . Repeat the above steps for the same battery, and record the discharge capacity C n of the battery after the nth cycle.
  • the positive electrode slurry in Comparative Example 1 uses PVDF as a binder, and the positive active material in the positive electrode slurry is prone to agglomeration.
  • the stability and processability of the positive electrode slurry are poor, and it is difficult to produce high-quality positive electrode sheets. This in turn causes the internal resistance growth rate to increase after battery cycling.
  • Embodiments 1 to 24 provide a positive electrode slurry, which includes a positive electrode active material, a conductive agent, and a binder.
  • the binder includes polymer A, and polymer A includes structural units derived from acrylonitrile, and derived from acrylamide. structural units and structural units derived from methyl acrylate. From the comparison between Example 5 and Comparative Example 1, it can be seen that polymer A has achieved good results as a binder in the cathode slurry, improving the stability and processability of the cathode slurry, and improving the adhesion of the electrode pieces. performance.
  • the binder contains polymer A-1 with a weight average molecular weight of 700,000 to 1,000,000. Compared with the polymer A-1 with a weight average molecular weight of 600,000 or 1.1 million in Examples 19 and 20, they both achieved better results, improved the stability and processability of the cathode slurry, and improved the electrode piece. It also improves the bonding performance and further reduces the cycle internal resistance growth rate of the battery.
  • the binder further includes polymer A-2 with a weight average molecular weight of 100,000 to 250,000.
  • polymer A-2 acts as a dispersant in the slurry due to its small molecular weight.
  • the addition of polymer A-2 further improves the stability and processability of the slurry, improves the bonding performance of the pole pieces, and at the same time reduces the cycle internal resistance growth rate of the battery.
  • the mass content of polymer A-1 is 0.4%-5.5%, based on the total mass of the positive electrode active material, conductive agent and binder.
  • the polymer A-1 within this range improves the stability and processability of the slurry, improves the bonding performance of the pole piece, and greatly reduces the battery cycle. Internal resistance growth rate.
  • the mass content of polymer A-2 is 0.05%-0.5%, based on the total mass of the positive active material, conductive agent and binder.
  • the addition of polymer A-2 within this range improves the stability and processability of the slurry, improves the bonding performance of the pole pieces, and can significantly reduce the cycle internal resistance of the battery. growth rate.
  • Embodiments 25 to 30 provide a positive electrode sheet, which includes a current collector, an undercoat layer disposed on one surface of the current collector, and a positive electrode membrane disposed on the undercoat layer.
  • the undercoat layer contains a water-soluble Polymer A-3 of the solvent, polymer A-3 includes structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate.
  • the mass content of polymer A-3 in the base coating is 5% to 40%, based on the total mass of the base coating.
  • the appearance quality and brittleness of the pole pieces in this embodiment are improved, and the bonding performance of the pole pieces and the cycle performance of the battery are improved.
  • the mass content of polymer A-3 in the undercoat layer is 5% to 30% or 5% to 20%, based on the total mass of the undercoat layer, the cycle performance of the battery is greatly improved.
  • the positive electrode membrane includes a positive electrode active material, a binder and a conductive agent.
  • the binder includes polymer A-1 and polymer A-2.
  • polymer A-1 and polymer A-2 Contains structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate.

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Abstract

本申请提供了一种正极极片、二次电池、电池模块、电池包及用电装置。该正极极片包含集流体、设置在集流体至少一个面上的底涂层以及设置在底涂层上的正极膜片，底涂层中包含能够溶解于水性溶剂的聚合物A，聚合物A包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。本申请通过在正极极片的底涂层中使用聚合物A，提高了正极极片的成型质量、粘结力和极片柔性，优化了电池的循环性能。

Description

正极极片、二次电池、电池模块、电池包及用电装置 技术领域
本申请涉及锂电池技术领域，尤其涉及一种正极极片、二次电池及用电装置。
背景技术
近年来，锂离子电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着锂离子电池应用的普及，对其性能和成本均提出了更高的要求。
现有的传统粘结剂PVDF作为一种常用粘结剂，存在与电极活性材料相容性差、粘结力弱等问题，导致以其作为粘结剂的极片稳定性差、成型困难，因此亟待开发出一种新型粘结剂和正极极片。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种极片成型质量好、粘结力强的正极极片，进而能够提高电池的循环性能。
本申请的第一方面，提供一种正极极片，包含集流体、设置在集流体至少一个面上的底涂层以及设置在底涂层上的正极膜片，底涂层中包含能够溶解于水性溶剂的聚合物A，聚合物A包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
本申请通过在正极极片的底涂层中使用聚合物A，提高了正极极片的成型质量、粘结力和极片柔性，优化了电池的循环性能。
在任意实施方式中，底涂层中的聚合物A的重均分子量为1.5×10 5～2×10 5。
合适的重均分子量可以提高极片的成型质量，兼顾底涂层的工艺 性与粘结性，同时保证底涂层中的聚合物A在正极浆料涂敷时具有一定的扩散性，从而进一步提高极片的粘结力和电池的循环性能。
在任意实施方式中，底涂层中的聚合物A的质量含量为5％～40％，可选为5％～30％，可选为5％～20％，基于底涂层的总质量计。
底涂层中聚合物A的质量在此范围内使得极片的外观质量和脆性有所改善，极片的粘结性能和电池的循环性能有所提高。
在任意实施方式中，底涂层中还包含导电剂，导电剂选自炭黑、乙炔黑、碳纤维、石墨、碳纳米管中的一种或多种。
底涂层中增加导电剂，能够降低正极膜片与集流体之间的界面电阻，提高电池的充、放电倍率性能，并延长电池的循环寿命。
在任意实施方式中，底涂层的厚度为1～20μm。
底涂层的厚度在此范围内可以兼顾极片的粘结性能和电池的功率性能以及循环性能。
在任意实施方式中，正极膜片的涂布面密度不小于20mg/cm 2。
通过在极片中设置本申请的底涂层，能够保证正极极片中负载有一定含量的正极活性物质，进而保证电池的功率性能。
在任意实施方式中，正极膜片包含正极活性物质、粘结剂和导电剂，粘结剂包含能够溶解于油性溶剂的聚合物A，聚合物A含有衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
在正极膜片中采用能够溶解于油性溶剂的聚合物A作为粘结剂与底涂层中的聚合物A发生扩散连接，能够进一步增强底涂层与正极膜片的粘结力，改善极片的外观质量和脆性，提高极片的粘结性能和电池的循环性能。
在任意实施方式中，正极膜片中包含重均分子量为7×10 5～1×10 6的所述聚合物A。
控制聚合物A的重均分子量能够在提高正极极片的粘结力的同时进一步降低电池的循环内阻增长率。
在任意实施方式中，正极膜片中还包含重均分子量为1×10 5～2.5×10 5的聚合物A。
重均分子量为1×10 5～2.5×10 5的聚合物A在正极膜片中起到分散剂的作用，其的加入能够进一步提高正极膜片中正极活性物质的分散性，使得制备的极片具有更高的粘结力，电池具有更低的循环内阻增长率。
在任意实施方式中，正极活性物质为含锂的过渡金属氧化物，正极活性物质可选为磷酸铁锂、或它们的掺杂改性材料、或它们的导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
在任意实施方式中，正极活性物质的质量含量为70％-99.5％，可选为88％～99.5％，基于正极膜片的总质量计。正极活性物质的质量含量在此范围内，可以保证正极活性物质的负载量，提高电池的功率性能。
在任意实施方式中，正极膜片中重均分子量为7×10 5～1×10 6的聚合物A的质量含量为0.4％-5.5％，和/或正极膜片中重均分子量为1×10 5～2.5×10 5的聚合物A的质量含量为0.05％-0.5％，基于正极膜片的质量计。
在任意实施方式中，聚合物A中含有氰基基团的单体选自丙烯腈和丁烯腈中的一种或多种；
含有酰胺基团的单体选自甲基丙烯酰胺、N-甲基甲基丙烯酰胺、N-乙基甲基丙烯酰胺、N-正丙基甲基丙烯酰胺、N-异丙基甲基丙烯酰胺、N-正丁基甲基丙烯酰胺、N-异丁基甲基丙烯酰胺、N,N-二甲基丙烯酰胺、N,N-二甲基甲基丙烯酰胺、N,N-二乙基丙烯酰胺、N,N-二乙基甲基丙烯酰胺的一种或多种；
含有酯基基团的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
在任意实施方式中，聚合物A中衍生自含有氰基基团的单体的结构单元的摩尔含量为50％～70％，衍生自含有酯基基基团的单体的结构单元的摩尔含量为10％～30％，衍生自含有酰胺基团的单体的结构单元的摩尔含量为10％～30％，基于聚合物A中结构单元的总摩尔 含量计。
在本申请的第二方面，提供一种二次电池，包括本申请第一方面的正极极片。
在本申请的第三方面，提供一种电池模块，包括本申请第二方面的二次电池。
在本申请的第四方面，提供一种电池包，包括本申请第三方面的电池模块。
在本申请的第五方面，提供一种用电装置，包括本申请第二方面的二次电池、第三方面的电池模块或第四方面的电池包中的至少一种。
附图说明
图1是本申请一实施方式的二次电池的示意图。
图2是图1所示的本申请一实施方式的二次电池的分解图。
图3是本申请一实施方式的电池模块的示意图。
图4是本申请一实施方式的电池包的示意图。
图5是图4所示的本申请一实施方式的电池包的分解图。
图6是本申请一实施方式的二次电池用作电源的用电装置的示意图。
图7为极片的粘结力测试示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53顶盖组件；6极片；61集流体62集流体上的涂层；7双面胶；8钢板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的粘结剂、制备方法、电极、电池及用电装置的实施方式。但是会有省略不必要的 详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包 括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
磷酸锂铁正极活性物质因其低成本、高性能和安全性得到了业界的广泛关注。然而，磷酸锂铁正极活性物质具有比表面积大、颗粒度小、碳包覆后表面碳元素包覆量大、石墨化程度高等特点，导致以磷酸锂铁作为正极活性物质以传统粘结剂PVDF作为粘结剂的浆料分散性差、易沉淀、粘度大、固含量低，进而其制备的极片表面容易出现开裂、脱膜、颗粒划痕、针孔等缺陷且极片中的正极活性物质分布不均匀、极片质量不均一。
[正极浆料]
基于此，本申请提出了一种用于电池的正极浆料，包含正极活性物质、导电剂和粘结剂，粘结剂包含聚合物A，聚合物A包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
在本文中，术语“粘结剂”是指在分散介质中形成胶体溶液或胶体分散液的化学化合物、聚合物或混合物。
在本文中，术语“聚合物”一方面包括通过聚合反应制备的化学上均一的、但在聚合度、摩尔质量和链长方面不同的大分子的集合体。该术语另一方面也包括由聚合反应形成的这样的大分子集合体的衍生物，即可以通过上述大分子中的官能团的反应，例如加成或取代获得的并且可以是化学上均一的或化学上不均一的化合物或混合物。
在本文中，术语“正极”也指二次电池中的“阴极”。
在本文中，术语“氰基基团”指的是-CN基团。
在本文中，术语“酰胺基团”指的是-CONH基团。
在本文中，术语“酯基基团”指的是-COOR 1基团，R 1选自被取代基取代或未取代的C 1-9烷基。
在本文中，术语“被取代基取代的”中的取代基各自独立地选自：羟基、巯基、氨基、氰基、硝基、醛基、卤素原子、烯基、炔基、芳基、杂芳基、C 1-6烷基、C 1-6烷氧基。
在本文中，术语“C 1-6烷基”是指仅由碳和氢原子组成的直链或支链烃链基团，基团中不存在不饱和，具有从一至五个碳原子，并且通过单键附接到分子的其余部分。术语“C 1-9烷基”应相应解释。C 1-6烷基的示例包括但不限于：甲基、乙基、正丙基、1-甲基乙基(异丙基)、丁基、戊基。
在本文中，术语“聚合物A”是指包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元的聚合物。
在一些实施例中，聚合物A能够溶解于油性溶剂。在一些实施例中，聚合物A能够溶解于水性溶剂中。油性溶剂的示例包括但不限于二甲基乙酰胺、N，N-二甲基甲酰胺、N-甲基吡咯烷酮、丙酮、碳酸二甲酯、乙基纤维素、聚碳酸酯。水性溶剂的示例包括但不限于水。可以理解，聚合物A中的结构单元可以以任意比例配比，聚合物A可以具有不同的分子量，聚合物A可以以不同的方法制备，如悬浮法、乳液法等。
在一些实施方式中，正极浆料中包含分散介质。在一些实施方式中，正极浆料的分散介质是油性溶剂。在一些实施方式中，正极浆料的分散介质是水性溶剂。
在一些实施方式中，粘结剂用于将正极活性物质及/或导电剂粘结在一起形成浆料，并可以使其固定在合适位置并将它们粘附在导电金属部件以形成正极电极。
在一些实施方式中，聚合物A为丙烯腈-丙烯酰胺-丙烯酸甲酯共聚物，丙烯腈-丙烯酰胺-丙烯酸乙酯共聚物，丙烯腈-丙烯酰胺-丙烯酸丙酯共聚物，丙烯腈-丙烯酰胺-丙烯酸异辛酯共聚物中的一种或多种。
本申请通过在正极浆料中使用包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元的聚合物作为粘结剂，改善了正极浆料的 稳定性和加工性，并且提高了正极极片的粘结力。
聚合物A中具有丰富的极性基团，如氰基基团位于聚合物A的主链段，由于氰基基团和正极集流体电负性之间的偶极相互作用，聚合物A对集流体具有很强的粘附性，提高了极片的粘结力，避免了极片在涂布或冷压过程中出现脱膜、掉粉等加工异常。另外，聚合物A中的含酯类官能团具备一定的吸收电解液和保持电解液的能力，可改善传统粘结剂单纯聚偏氟乙烯的离子电导性差的问题。再者，聚合物A上的丰富的基团可以提高聚合物A与各种正极活性物质的相容性，提高聚合物A作为粘结剂的通用性。
在一些实施方式中，粘结剂包含重均分子量为7×10 5～1×10 6的聚合物A。在一些实施方式中，聚合物A的重均分子量可选为7×10 5～9.5×10 5，或为7×10 5～9×10 5，或为7×10 5～8.5×10 5，或为7×10 5～8×10 5，或为7.5×10 5～1×10 6，或为8×10 5～1×10 6，或为8.5×10 5～1×10 6，或为9×10 5～1×10 6，或为9.5×10 5～1×10 6。
在本文中，术语“重均分子量”是指聚合物中用不同分子量的分子所占的重量分数与其对应的分子量乘积的总和。
控制聚合物A的重均分子量在提高正极浆料的稳定性、加工性以及正极极片的粘结力的同时能够进一步降低电池的循环内阻增长率。
在一些实施方式中，粘结剂还包含重均分子量为1×10 5～2.5×10 5的聚合物A。在一些实施方式中，聚合物A的重均分子量可选为1.5×10 5～2.5×10 5，或为2×10 5～2.5×10 5，或为1×10 5～2×10 5，或为1×10 5～1.5×10 5。
由于一些正极活性物质(如磷酸铁锂LFP)的比表面积较大且小颗粒较多，导致浆料在制备过程中容易产生团聚，致使滤网堵塞。通过在浆料中使用重均分子量较低的聚合物A，可以利用其静电排斥或空间位阻作用避免正极活性物质(如磷酸铁锂LFP粉体颗粒)间的团聚；同时对浆料中的其他小分子物质起到分散和悬浮的作用，使得浆料短时间放置不沉降、稳定性增加。另外，重均分子量低的聚合物A的玻璃化转变温度低，进而可以提高极片的柔性。
综上，重均分子量为1×10 5～2.5×10 5的聚合物A在正极浆料中起到分散剂的作用，其的加入进一步提高了浆料的稳定性和加工性，极片的粘结力，降低了电池的循环内阻增长率。
在一些实施方式中，重均分子量为7×10 5～1×10 6的聚合物A的质量含量为0.4％-5.5％，基于正极活性物质、导电剂和粘结剂的质量总和计。若重均分子量为7×10 5～1×10 6的聚合物A加入过多，会降低电池的功率性能和循环性能。在此质量含量范围内的重均分子量7×10 5～1×10 6的聚合物A可以提高浆料的稳定性和加工性、极片的粘结性，同时大幅度降低电池的循环内阻增长率。
在一些实施方式中，重均分子量为1×10 5～2.5×10 5的聚合物A的质量含量为0.05％-0.5％，基于正极活性物质、导电剂和粘结剂的质量总和计。
若重均分子量为1×10 5～2.5×10 5的聚合物A加入过多，会增加极片的溶胀，影响电池的常温功率性能。在此质量含量范围内的重均分子量为1×10 5～2.5×10 5的聚合物A可以进一步提高浆料的稳定性和加工性、极片的粘结力，同时大幅度降低电池的循环内阻增长率。
在一些实施方式中，含有氰基基团的单体选自丙烯腈和丁烯腈中的一种或多种。
在一些实施方式中，含有酰胺基团的单体选自甲基丙烯酰胺、N-甲基甲基丙烯酰胺、N-乙基甲基丙烯酰胺、N-正丙基甲基丙烯酰胺、N-异丙基甲基丙烯酰胺、N-正丁基甲基丙烯酰胺、N-异丁基甲基丙烯酰胺、N,N-二甲基丙烯酰胺、N,N-二甲基甲基丙烯酰胺、N,N-二乙基丙烯酰胺、N,N-二乙基甲基丙烯酰胺的一种或多种。
在一些实施方式中，含有酯基基团的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
上述材料简单易得，能够大幅度降低粘结剂的制造成本。
在一些实施方式中，聚合物A中衍生自含有氰基基团的单体的结构单元的摩尔含量为50％～70％，衍生自含有酯基基基团的单体的结构单元的摩尔含量为10％～30％，衍生自含有酰胺基团的单体的结 构单元的摩尔含量为10％～30％，基于聚合物A中结构单元的总摩尔含量计。
衍生自含有各基团的单体的结构单元的合理搭配可以兼顾聚合物A的强度、柔性、粘结性能和抗溶胀性，使得极片具有优异的粘结力和加工性能。
在一些实施方式中，正极活性物质为含锂的过渡金属氧化物，可选为磷酸铁锂、或它们的掺杂改性材料、或它们的导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
磷酸铁锂正极活性物质具有微孔结构，且在碳包覆后其表面石墨化度较高。上述结构特征导致其在浆料溶剂(如N-甲基吡咯烷酮NMP)中的浸润性较差，进而使得浆料稳定性差、固含量低、放置后容易掉粘，无法正常使用。聚合物A中含有对石墨化度高的碳材料亲和性较好的基团，如含N基团(氰基基团、酰胺基团)，含氧基团(酯基基团、酰胺基团)，从而有效提高磷酸锂铁粉体在溶剂(如NMP)中的浸润性，进而提高正极浆料的稳定性和加工性能。
在一些实施方式中，正极活性物质的质量含量为70％～99.5％，可选为88.0％～99.5％，基于正极活性物质、导电剂和粘结剂的质量总和计。正极活性物质的质量含量在此范围内，可以保证正极活性物质的负载量，提高电池的功率性能。
在一些实施方式中，导电剂选自超导碳、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或多种。
在一些实施方式中，导电剂的质量含量为0.2％-6.0％，基于正极活性物质、导电剂和粘结剂的质量总和计。
[正极极片]
本申请的一个实施方式中，提供一种正极极片，包含集流体、设置在集流体至少一个面上的底涂层以及设置在底涂层上的正极膜片，底涂层中包含能够溶解于水性溶剂的聚合物A，聚合物A包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
在本文中，术语“集流体”是指在二次电池的放电或充电期间能够 传导电流至电极的任何导电基底。
术语“正极膜片”是指正极浆料涂布干燥后形成的涂层。
小颗粒正极活性物质具有比表面积大、能够与电解液充分反应的优点，然而其大的比表面积也带来了与集流体粘结性差的弊端，导致正极浆料在涂布的过程中容易出现脱膜现象。如果增加正极浆料中粘结剂的用量则会导致极片在冷压过程中出现脆性问题，压实密度降低，因而需要在集流体上增加特殊的底涂层用于提高正极膜片与集流体间的粘结力。
由于底涂层中能够溶解于水性溶剂的聚合物A含有氰基基团、酰胺基团和酯基基团，其在正极浆料涂敷的过程中接触到正极浆料的油性溶剂(如NMP)时，能够发生适当溶胀，但是不会溶解。通过底涂层中的聚合物A与正极浆料中的粘结剂形成分子接触可以实现相互扩散，能够大幅度提高正极膜片与集流体之间的粘结力。且聚合物A中的酯基基团能够与集流体表面氧化层中的羟基基团形成较强的氢键，以确保正极膜片牢固附着在集流体上。
能够能溶解于水性溶剂的聚合物A是指聚合物A能够溶解于水性溶剂中形成溶液或分散体系，聚合物A在水性溶剂中的溶解度不小于1g。可选地，聚合物A在水性溶剂中的溶解度不小于10g。
在一些实施方式中，底涂层中能够溶解于水性溶剂的聚合物A通过本体聚合、悬浮聚合、乳液聚合或溶液聚合成型。在一些实施方式中，底涂层中能够溶解于水性溶剂的聚合物A通过乳液法成型，该方法易于量产、简单环保。
本申请通过在正极极片的底涂层中使用聚合物A，提高了正极极片的成型质量、粘结力和极片柔性，优化了电池的循环性能。
在一些实施方式中，底涂层中的聚合物A的重均分子量为1.5×10 5～2×10 5。
合适的重均分子量可以提高极片的成型质量，兼顾底涂层的工艺性与粘结性，同时保证底涂层中的聚合物A在正极浆料涂敷时具有一定的扩散性。
在一些实施方式中，底涂层中的聚合物A的质量含量为5％～40％， 可选为5％～30％，可选为5％～20％，基于底涂层的总质量计。
如果底涂层中，聚合物A的用量过大会降低底涂层的稳定性和电池的循环性能。底涂层中聚合物A的质量在此范围内使得极片的外观质量和脆性有所改善，极片的粘结性能和电池的循环性能有所提高。
在一些实施方式中，底涂层中还包含导电剂，导电剂选自炭黑、乙炔黑、碳纤维、石墨、碳纳米管中的一种或多种。
底涂层中增加导电剂，能够降低正极膜片与集流体之间的界面电阻，提高电池的充、放电倍率性能，并延长电池的循环寿命。
在一些实施方式中，底涂层的厚度为1～20μm。
若底涂层厚度过大，集流体导电性差，若底涂层厚度过小，无法保证在极片中起到有效的粘结作用。底涂层的厚度在此范围内，可以兼顾极片的粘结性能和电池的功率性能以及循环性能。
在一些实施方式中，正极膜片的涂布面密度不小于20mg/cm 2。
在本文中，术语“面密度”是通过质量除以相应面积计算的。
通过在极片中设置本申请的底涂层，能够保证正极极片中负载有一定含量的正极活性物质，进而保证电池的功率性能。
在一些实施方式中，正极膜片包含正极活性物质、粘结剂和导电剂，粘结剂包含能够溶解于油性溶剂的聚合物A，聚合物A含有衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
能够能溶解于油性溶剂的聚合物A是指聚合物A能够溶解于油性溶剂中形成溶液或分散体系，聚合物A在油性溶剂中的溶解度不小于1g。可选地，聚合物A在油性溶剂中的溶解度不小于10g。
在正极膜片中采用能够溶解于油性溶剂的聚合物A作为粘结剂与底涂层中的聚合物A发生扩散连接，能够进一步增强底涂层与正极膜片的粘结力，改善极片的外观质量和脆性，提高极片的粘结性能和电池的循环性能。
在一些实施方式中，正极膜片中包含重均分子量为7×10 5～1×10 6的所述聚合物A。
控制聚合物A的重均分子量能够在提高正极极片的粘结力的同时进一步降低电池的循环内阻增长率。
在一些实施方式中，正极膜片中还包含重均分子量为1×10 5～2.5×10 5的聚合物A。
重均分子量为1×10 5～2.5×10 5的聚合物A在正极膜片中起到分散剂的作用，其的加入能够进一步提高正极膜片中正极活性物质的分散性，使得制备的极片具有更高的粘结力，电池具有更低的循环内阻增长率。
由于一些正极活性物质(如磷酸铁锂LFP)的比表面积较大且小颗粒较多，导致形成正极膜片的浆料在制备过程中容易产生团聚，致使滤网堵塞。通过在正极膜片成型的浆料中使用重均分子量较低的聚合物A，可以利用其静电排斥或空间位阻作用避免正极活性物质(如磷酸铁锂LFP粉体颗粒)间的团聚；同时对正极膜片中的其他小分子物质起到分散和悬浮的作用，使得浆料短时间放置不沉降、稳定性增加。另外，重均分子量低的聚合物A的玻璃化转变温度低，进而可以提高正极膜片的柔性。
在一些实施方式中，正极活性物质为含锂的过渡金属氧化物，正极活性物质可选为磷酸铁锂、或它们的掺杂改性材料、或它们的导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
传统磷酸铁锂体系中底涂层常使用聚丙烯酸作为粘结剂，然而聚丙烯酸与正极膜片中的传统粘结剂聚偏二氟乙烯极性差异较大，两者之间粘结力低，且底涂层中的聚丙烯酸在正极浆料溶剂中的溶解性差，无法在浆料涂布干燥时在底涂层与正极膜片间形成有效扩散连接。
通过使用本申请提供的能被N-甲基吡咯烷酮(NMP)二次湿润的聚合物A作为底涂层中的粘结剂，能够实现底涂层与正极膜片中粘结剂的相互扩散以增加粘接力，进一步改善极片的外观质量和脆性，提高极片的粘结性能和电池的循环性能。
在一些实施方式中，正极活性物质的质量含量为70％-99.5％，可选为88.0％～99.5％，基于正极膜片的总质量计。正极活性物质的质量 含量在此范围内，可以保证正极活性物质的负载量，提高电池的功率性能。
在一些实施方式中，正极膜片中重均分子量为7×10 5～1×10 6的聚合物A的质量含量为0.4％-5.5％，和/或正极膜片中重均分子量为1×10 5～2.5×10 5的聚合物A的质量含量为0.05％-0.5％，基于正极膜片的质量计。
若重均分子量为7×10 5～1×10 6的聚合物A加入过多，会降低电池的功率性能和循环性能。在此质量含量范围内的重均分子量7×10 5～1×10 6的聚合物A可以提高浆料的稳定性和加工性、极片的粘结性，同时大幅度降低电池的循环内阻增长率。若重均分子量为1×10 5～2.5×10 5的聚合物A加入过多，会增加极片的溶胀，影响电池的常温功率性能。在此质量含量范围内的重均分子量为1×10 5～2.5×10 5的聚合物A可以进一步提高浆料的稳定性和加工性、极片的粘结力，同时大幅度降低电池的循环内阻增长率。
在一些实施方式中，聚合物A中含有氰基基团的单体选自丙烯腈和丁烯腈中的一种或多种；
含有酰胺基团的单体选自甲基丙烯酰胺、N-甲基甲基丙烯酰胺、N-乙基甲基丙烯酰胺、N-正丙基甲基丙烯酰胺、N-异丙基甲基丙烯酰胺、N-正丁基甲基丙烯酰胺、N-异丁基甲基丙烯酰胺、N,N-二甲基丙烯酰胺、N,N-二甲基甲基丙烯酰胺、N,N-二乙基丙烯酰胺、N,N-二乙基甲基丙烯酰胺的一种或多种；
含有酯基基团的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
上述材料简单易得，能够大幅度降低粘结剂的制造成本。
在一些实施方式中，聚合物A中衍生自含有氰基基团的单体的结构单元的摩尔含量为50％～60％，衍生自含有酯基基基团的单体的结构单元的摩尔含量为10％～20％，衍生自含有酰胺基团的单体的结构单元的摩尔含量为20％～30％，分别基于聚合物A中结构单元的总摩尔含量计。
衍生自含有各基团的单体的结构单元的合理搭配可以兼顾聚合物A的强度、柔性、粘结性和抗溶胀性。
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，正极膜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。
在一些实施方式中，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(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。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、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(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。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(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、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中的至少一种。
在一些实施方式中，正极膜片还可选地包括导电剂。作为示例， 所述导电剂可以包括超导碳、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至少一种。
[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膜层，所述负极膜层包括负极活性材料。
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，负极膜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。
在一些实施方式中，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(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。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述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)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。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至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠 剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、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、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。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至少一种。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，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，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
[二次电池]
本申请的一个实施方式中，提供一种二次电池，包括电极组件和电解液，电极组件包括正极极片、隔离膜、负极极片，正极极片由任意实施方式的正极浆料制备而得。
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，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，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对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1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图2，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。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。
[电池模块]
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含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的应用和容量进行选择。
图3是作为一个示例的电池模块4。参照图5，在电池模块4中，多个二次电池5可以是沿电池模块4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，多个二次电池5容纳于该容纳空间。
[电池包]
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块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包的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和图5，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模块4。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模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
[用电装置]
本申请的一个实施方式中，提供一种用电装置，包括任意实施方式的二次电池、任意实施方式的电池模块或任意实施方式的电池包中的至少一种。
所述用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(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、储能系统等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对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。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
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
1)正极膜片中的重均分子量为60万～100万的聚合物A(聚合物A-1)的制备
悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用400mg硫酸钙和80mg磷酸钙。然后420mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，3.003mmolAIBN(基于总单体摩尔含量的0.39％)添加。最后将0.1g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到70℃，反应5小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片。聚合物A-1中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为6﹕3﹕2，制备得到的聚合物A-1的重均分子量为80万。
2)正极极片的制备
将实施例1的磷酸铁锂LFP活性材料、导电剂碳黑、聚合物A-1按重量比为93﹕4﹕3溶于N-甲基吡咯烷酮(NMP)溶液，搅拌混合 均匀，得到正极浆料，浆料固含量为55％；之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。
3)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；将负极浆料一次或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。
4)隔离膜
以聚丙烯膜作为隔离膜。
5)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LiPF 6锂盐溶解于有机溶剂中，搅拌均匀，配制1M LiPF 6EC/EMC溶液得到电解液。
6)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，然后卷绕得到裸电芯，给裸电芯焊接极耳，并将裸电芯装入铝壳中，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的锂离子电池产品。
实施例2～实施例9中调节加入的正极活性物质和聚合物A-1的比例，其他参数和步骤同实施例1，具体参数见表1。
实施例10
正极膜片中的重均分子量为10万～25万的聚合物A(聚合物A-2)的制备：
悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用300mg硫酸钙和60mg磷酸钙。然后350mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，2.25mmolAIBN(基于总单体摩尔含 量的0.3％)添加。最后将0.06g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到46℃，反应2.5小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片浆料中分散作用。聚合物A-2中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为5﹕3﹕2，聚合物A-2的重均分子量为17万。
正极极片的制备：
将磷酸铁锂LFP活性材料、导电剂碳黑、聚合物A-1、聚合物A-2按重量比为92﹕4﹕3.95﹕0.05溶于N-甲基吡咯烷酮(NMP)溶液，搅拌混合均匀，得到正极浆料，浆料固含量为55％；之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。
其他步骤和参数同实施例1，具体参数见表1。
实施例11～实施例16中保持聚合物A加入的总量不变，调节加入的聚合物A-1和聚合物A-2的比例，其他参数和步骤同实施例1，具体参数见表1。
实施例17～实施例20中调整聚合物A-1的重均分子量，不同重均分子量的聚合物A-1的制备方法如下：
实施例17中聚合物A-1的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用400mg硫酸钙和80mg磷酸钙。然后420mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，3.003mmolAIBN(基于总单体摩尔含量的0.39％)添加。最后将0.10g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到65℃，反应5小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片。聚合物A-1中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为6﹕3﹕2，制备得到的聚合物A-1的重均分子量为70万。
实施例18中聚合物A-1的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用400mg硫酸钙和80mg 磷酸钙。然后420mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，3.003mmolAIBN(基于总单体摩尔含量的0.39％)添加。最后将0.13g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到75℃，反应6小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片。聚合物A-1中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为6﹕3﹕2，制备得到的聚合物A-1的重均分子量为100万。
实施例19中聚合物A-1的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用400mg硫酸钙和80mg磷酸钙。然后420mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，3.003mmolAIBN(基于总单体摩尔含量的0.39％)添加。最后将0.1g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到65℃，反应4小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片。聚合物A-1中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为6﹕3﹕2，制备得到的聚合物A-1的重均分子量为60万。
实施例20中聚合物A-1的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用400mg硫酸钙和80mg磷酸钙。然后420mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，3.003mmolAIBN(基于总单体摩尔含量的0.39％)添加。最后将0.18g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到80℃，反应7小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片。聚合物A-1中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为6﹕3﹕2，制备得到的聚合物A-1的重均分子量为110万。
实施例21～实施例24中调整聚合物A-2的重均分子量，其他参数和步骤同实施例1，具体参数见表1。
实施例21中聚合物A-2的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用300mg硫酸钙和60mg磷酸钙。然后350mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，2.25mmolAIBN(基于总单体摩尔含量的0.3％)添加。最后将0.05g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到46℃，反应2.0小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片浆料中分散作用。聚合物A-2中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为5﹕3﹕2，制备得到的聚合物A-2的重均分子量为10万。
实施例22中聚合物A-2的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用300mg硫酸钙和60mg磷酸钙。然后350mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，2.25mmolAIBN(基于总单体摩尔含量的0.3％)添加。最后将0.08g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到50℃，反应3.5小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片浆料中分散作用。聚合物A-2中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为5﹕3﹕2，制备得到的聚合物A-2的重均分子量为25万。
实施例23中聚合物A-2的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用300mg硫酸钙和60mg磷酸钙。然后350mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，2.25mmolAIBN(基于总单体摩尔含量的0.3％)添加。最后将0.03g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到40℃，反应1.5小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片浆料中分散作用。聚合物A-2中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为5﹕3﹕2，制备得到的聚合物A-2的重均分子量为5万。.
实施例24中聚合物A-2的制备方法如下：悬浮剂0.20g溶解在150ml去离子水中，用干燥的氮气吹30min,再用300mg硫酸钙和60mg磷酸钙。然后350mmol丙烯腈,140mmol丙烯酸甲酯，210mmol丙烯酰胺，2.25mmolAIBN(基于总单体摩尔含量的0.3％)添加。最后将0.10g溶于50ml去离子水的硫酸镁水溶液被添加，将悬浮液加热到58℃，反应4小时，反应结束时，悬浮液冷却，产品经过过滤、洗涤，然后在70℃真空干燥至恒重，得到白色粉末。此粘结剂用于极片浆料中分散作用。聚合物A-2中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为5﹕3﹕2，制备得到的聚合物A-2的重均分子量为40万。
对比例1
直接将正极活性物质，LFP磷酸铁锂活性材料、导电剂碳黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为92﹕4﹕4溶于溶剂N-甲基吡咯烷酮(NMP)，充分搅拌混合均匀后得到正极浆料；之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，得到对比例1的正极极片。其他制备步骤同实施例1。
上述实施例1～24、对比例1的正极制备的相关参数如下述表1所示。
实施例25
底涂层中能够溶解于水性溶剂的聚合物A的制备(聚合物A-3)：
称取1.84mmol十二烷基苯磺酸钠和400ml去离子水加入搅拌容器中，加入0.63mol丙烯腈，0.21mol甲基丙烯酸甲酯，0.21mol丙烯酰胺，控制搅拌转速500rpm，搅拌加热至74±1℃，然后加入1.2份硫酸铵，保持75℃搅拌反应6h后升温至80℃，继续反应3h，得到固含量约为20％乳液。此乳液用于底涂。聚合物A-3中衍生自丙烯腈的结构单元，衍生自丙烯酰胺的结构单元，和衍生自丙烯酸甲酯的结构单元的摩尔比为3﹕1﹕1，聚合物A-3的重均分子量为18万。
底涂层制备：将制备的含有聚合物A-3的乳液和导电剂按质量比30﹕70，采用捏合的方法，使得去离子水完全浸润导电剂，最后加入去离子水，使得浆料的固含量为15％，充分搅拌均匀，浆料出货粘度 为200-800mpa.s。采用凹版涂布时，凹版辊上刻有凹坑，涂布时浆料注入凹坑(30μm)中，辊面离开液面后平滑处浆料由刮刀刮去，在压辊作用下，凹坑中的浆料被转移到基材表面上,烘干后单面涂层的厚度约为5μm。制备的带底涂铝箔备用。
正极极片制备同实施例12，将磷酸铁锂﹕导电剂SP﹕聚合物A-1﹕聚合物A-2按质量比为92﹕4﹕3.8﹕0.2溶于N-甲基吡咯烷酮(NMP)溶液，搅拌混合均匀，得到正极浆料；之后将正极浆料均匀涂覆于制备的带底涂的铝箔上，之后经过烘干、冷压、分切，得到正极极片。正极浆料制备的涂层称为正极膜片，正极膜片的单面涂层的面密度约为20mg/cm 2，正极膜片的单面涂层的压实密度约为2.3g/cm 3。
实施例25的其他步骤和实施例12相同。
实施例26～29中分别调整含有聚合物A-3的乳液和导电剂的质量比为40﹕60，50﹕50，60﹕40，70﹕30，其他步骤和实施例12相同。
实施例30中，正极极片的制备包括将镍钴锰氧化物(NCM)、磷酸铁锂﹕导电剂SP﹕聚合物A-1﹕聚合物A-2按质量比为82﹕10﹕4﹕3.8﹕0.2溶于N-甲基吡咯烷酮(NMP)溶液，搅拌混合均匀，得到正极浆料；之后将正极浆料均匀涂覆于制备的带底涂的铝箔上，之后经过烘干、冷压、分切，得到正极极片，其他步骤同实施例12。
对比例2中不设置底涂层，正极极片同实施例25；
对比例3中的底涂层为PAA底涂层，正极极片同对比例2。PAA类底涂层制备方法如下：制备的含有PAA的水性乳液，乳液固含量为约20％，乳液和导电剂按质量比50﹕50，采用捏合的方法，使得去离子水完全浸润导电剂，最后加入去离子水，使得浆料的固含量为15％，充分搅拌均匀，浆料出货粘度为200-800mpa.s。采用凹版涂布时，凹版辊上刻有凹坑，涂布时浆料注入凹坑(30μm)中，辊面离开液面后平滑处浆料由刮刀刮去，在压辊作用下，凹坑中的浆料被转移到基材表面上,烘干后单面涂层的厚度约为5μm。制备的带底涂铝箔备用。
上述实施例25～30、对比例2～3的制备的相关参数如下述表2所示。
另外，将上述实施例1～24和对比例1中得到的聚合物、极片和电池进行性能测试，测试结果见表1；将上述实施例25～30和对比例2～3中得到的聚合物、极片和电池进行性能测试，测试结果见表2。测试方法如下：
1、聚合物的结构单元种类测试-红外光谱测试
采用压片透射法，将样品进行KBr压片，通过透射法扣除KBr背景空白，得到样品测试谱图，仪器型号：Nicolet 5700(美国Thermo Nicolet公司)，标准线性度：优于0.07％，分辨率：0.09cm -1，波数范围：400～4000cm -1，灵敏度<9.65*10 -5Abls。用于检测分子的结构和化学键。
2、重均分子量测试
采用Waters 2695 Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的粘结剂胶液，配置好的溶液静置一天，备用。测试时，先用注射器吸取四氢呋喃，进行冲洗，重复几次。然后吸取5ml实验溶液，排除注射器中的空气，将针尖擦干。最后将试样溶液缓缓注入进样口。待测试完后输出流出曲线图，分子量分布曲线图以及分子量统计结果。
3、浆料粘度测试
选取合适的转子，固定好粘度计，将正极浆料置于粘度计下方，浆料恰好淹没转子的刻度线，仪器型号：上海方瑞NDJ-5S，转子：63#(2000-10000mPa.s)、64#(10000-50000mPa.s)，转速：12r/min，测试温度：25℃，测试时间为5min，待示数稳定读取数据。
4、浆料过滤性能测试
取500ml烧杯置于200目滤网支架下端，取浆料500ml,置于滤网中过滤，记录烧杯中浆料体积到达300ml时的时间，此时间用于判段浆料的过滤性能，过滤时间低于120s，表明浆料的过滤性能OK；若浆料不能透过滤网，表明浆料的过滤性能差，判定为“NG”。
5、浆料流动性测试：
用药匙取适量正极浆料，观察正极浆料的自然下流是否流畅。若自然下流顺畅判定为OK；若流动性不好，浆料出现果冻状，成块，表明出现凝胶，判定为NG。
6、极片外观测试:
正极极片制备完成后观察正极极片的表面状态，包括是否平整、是否有裂痕以及是否有颗粒团聚等，若均无上述现象，记录为OK，若存在其中一种现象，予以记录。
7、粘结力测试：
将实施例中的正极极片裁剪为20*100mm尺寸的测试试样，备用，测试方法如图7所示。双面胶7粘贴于极片6的一面，并用压辊压实，使之与极片完全贴合；双面胶7的另外一面粘贴于钢板8的表面，将集流体61一端反向弯曲，弯曲角度为180°，如图7中箭头所示；采用高铁拉力机测试，将钢板8的一端固定于拉力机下方夹具，集流体61的弯曲末端固定于上方夹具，调整集流体角度，保证上下端位于垂直位置，然后以50mm/min的速度拉伸试样，直到集流体61全部从集流体61表面的涂层62剥离，记录过程中的位移和作用力，将受力平衡时的力作为极片6的粘结力。
8、极片脆性测试
将实施例中的正极极片裁剪为20*100mm尺寸的测试试样，备用。将极片弯曲对折固定好，使用2kg重的碾压辊碾压一次，查看极片对折处是否透光漏金属；若无透光漏金属，.再将极片反过来对折固定住，使用2kg的碾压辊碾压一次，查看极片对折处是否透光漏金属，重复以上步骤，直至极片对折处透光漏金属为止。
9、电池直流阻抗测试
电池直流阻抗测试过程如下：在25℃下，将实施例或对比例中的电池，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V 1。然后再以1/3C放电30s，记录电压V 2，则通过公式3*(V 2-V 1)/C得到第一次循环后电池的内阻DCR 1。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的内阻DCR n(n＝1、2、3……100)，将上述DCR 1、DCR 2、 DCR 3……DCR 100这100个点值为纵坐标，以对应的循环次数为横坐标，得到正极活性物质对应的电池放电DCR与循环次数的曲线图。
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DCR增大率＝(DCR 500-DCR 1)/DCR 1*100％，对比例1以及其他实施例的测试过程同上。
10、电池循环圈数测试
电池循环圈数从容量测试中得出。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2.5V，所得容量记为初始容量C 0,截止条件P n≦70％C 0。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C n，则每次循环后电池容量保持率P n＝C n/C 0*100％，以P 1、P 2……P n这n个点值为纵坐标，以对应的循环次数为横坐标，对应的电池容量保持率与循环次数的曲线图。当P n≦70％C 0，停止测试，记录循环次数。
Figure PCTCN2022097967-appb-000001
Figure PCTCN2022097967-appb-000002
Figure PCTCN2022097967-appb-000003
Figure PCTCN2022097967-appb-000004
Figure PCTCN2022097967-appb-000005
根据上述结果可知，对比例1中正极浆料以PVDF作为粘结剂，正极浆料中的正极活性物质容易出现团聚，正极浆料的稳定性和加工性差，难以生产高质量的正极极片，进而使得电池循环后内阻增长率增加。
实施例1～24中提供了一种正极浆料，包含正极活性物质、导电剂和粘结剂，粘结剂包含聚合物A，聚合物A包含衍生自丙烯腈的结构单元、衍生自丙烯酰胺的结构单元以及衍生自丙烯酸甲酯的结构单元。从实施例5与对比例1的对比可见，聚合物A在正极浆料中作为粘结剂取得了良好的效果，改善了正极浆料的稳定性和加工性，并且提高了极片的粘结性能。
实施例1～18、21～24中粘结剂包含重均分子量为70万～100万的聚合物A-1。相比于实施例19、20中重均分子量为60万或110万的聚合物A-1，其均取得了更好的效果，改善了正极浆料的稳定性和加工性，提高了极片的粘结性能，同时进一步降低了电池的循环内阻增长率。
实施例10～24中粘结剂还包含重均分子量为10万～25万的聚合物A-2。相比于实施例5，聚合物A-2由于分子量小，在浆料中起到了分散剂的作用。聚合物A-2的加入进一步改善了浆料的稳定性和加工性，提高了极片的粘结性能，同时降低了电池的循环内阻增长率。
实施例2～8、10～24中，聚合物A-1的质量含量为0.4％-5.5％，基于正极活性物质、导电剂和粘结剂的质量总和计。相比于实施例1和实施例9，在此范围区间内的聚合物A-1改善了浆料的稳定性和加工性，提高了极片的粘结性能，同时大幅度降低了电池的循环内阻增长率。
实施例10～实施例15中，聚合物A-2的质量含量为0.05％-0.5％，基于正极活性物质、导电剂和粘结剂的质量总和计。相比于实施例16，在此范围区间内聚合物A-2的加入改善了浆料的稳定性和加工性，提高了极片的粘结性能，同时能够大幅度降低了电池的循环内阻增长率。
实施例25～30中提供了一种正极极片，包含集流体、设置在集流体一个面上的底涂层以及设置在底涂层上的正极膜片，底涂层中包含能够溶解于水性溶剂的聚合物A-3，聚合物A-3包含衍生自丙烯腈的结构单元、衍生自丙烯酰胺的结构单元以及衍生自丙烯酸甲酯的结构单元。通过设置该底涂层，相比于对比例2～3，极片的外观质量和脆性有所改善，极片的粘结性能和电池的循环性能实现大幅度提高。
实施例25～30中，底涂层中聚合物A-3的质量含量为5％～40％，基于底涂层的总质量计。相比于对比例2～3，该实施例中极片的外观质量和脆性有所改善，极片的粘结性能和电池的循环性能有所提高。当底涂层中聚合物A-3的质量含量为5％～30％或5％～20％时，基于底涂层的总质量计，电池的循环性能得到大幅度提高。
实施例25～30中，正极膜片包含正极活性物质、粘结剂和导电剂，粘结剂包含聚合物A-1和聚合物A-2，聚合物A-1和聚合物A-2中包含衍生自丙烯腈的结构单元、衍生自丙烯酰胺的结构单元以及衍生自丙烯酸甲酯的结构单元。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其他方式也包含在本申请的范围内。

Claims (17)

  1. 一种正极极片，其特征在于，包含集流体、设置在所述集流体至少一个面上的底涂层以及设置在所述底涂层上的正极膜片，所述底涂层中包含能够溶解于水性溶剂的聚合物A，所述聚合物A包含衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
  2. 根据权利要求1所述的正极极片，其特征在于，所述底涂层中的所述聚合物A的重均分子量为1.5×10 5～2×10 5。
  3. 根据权利要求1至2中任一项所述的正极极片，其特征在于，所述底涂层中的所述聚合物A的质量含量为5％～40％，可选为5％～30％，可选为5％～20％，基于所述底涂层的总质量计。
  4. 根据权利要求1至3中任一项所述的正极极片，其特征在于，所述底涂层中还包含导电剂，所述导电剂选自炭黑、乙炔黑、碳纤维、石墨、碳纳米管中的一种或多种。
  5. 根据权利要求1至4中任一项所述的正极极片，其特征在于，所述底涂层的厚度为1～20μm。
  6. 根据权利要求1至5中任一项所述的正极极片，其特征在于，所述正极膜片包含正极活性物质、粘结剂和导电剂，所述粘结剂包含能够溶解于油性溶剂的聚合物A，所述聚合物A含有衍生自含有氰基基团的单体的结构单元、衍生自含有酰胺基团的单体的结构单元以及衍生自含有酯基基团的单体的结构单元。
  7. 根据权利要求6中所述的正极极片，其特征在于，所述正极 膜片中包含重均分子量为7×10 5～1×10 6的所述聚合物A。
  8. 根据权利要求7中所述的正极极片，其特征在于，所述正极膜片中还包含重均分子量为1×10 5～2.5×10 5的所述聚合物A。
  9. 根据权利要求6至8中任一项所述的正极极片，其特征在于，所述正极活性物质为含锂的过渡金属氧化物，所述正极活性物质可选为磷酸铁锂、或它们的掺杂改性材料、或它们的导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
  10. 根据权利要求6至9中任一项所述的正极极片，其特征在于，所述正极活性物质的质量含量为70％-99.5％，可选为88％～99.5％，基于所述正极膜片的质量计。
  11. 根据权利要求6至10中任一项所述的正极极片，其特征在于，所述正极膜片中所述重均分子量为7×10 5～1×10 6的所述聚合物A的质量含量为0.4％-5.5％，和/或所述正极膜片中所述重均分子量为1×10 5～2.5×10 5的所述聚合物A的质量含量为0.05％-0.5％，基于所述正极膜片的质量计。
  12. 根据权利要求1至11中任一项所述的正极极片，其特征在于，
    所述聚合物A中所述含有氰基基团的单体选自丙烯腈和丁烯腈中的一种或多种；
    所述含有酰胺基团的单体选自甲基丙烯酰胺、N-甲基甲基丙烯酰胺、N-乙基甲基丙烯酰胺、N-正丙基甲基丙烯酰胺、N-异丙基甲基丙烯酰胺、N-正丁基甲基丙烯酰胺、N-异丁基甲基丙烯酰胺、N,N-二甲基丙烯酰胺、N,N-二甲基甲基丙烯酰胺、N,N-二乙基丙烯酰胺、N,N-二乙基甲基丙烯酰胺的一种或多种；
    所述含有酯基基团的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸 丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
  13. 根据权利要求1至12中任一项所述的正极极片，其特征在于，
    所述聚合物A中衍生自含有氰基基团的单体的结构单元的摩尔含量为50％～70％，衍生自含有酯基基基团的单体的结构单元的摩尔含量为10％～30％，衍生自含有酰胺基团的单体的结构单元的摩尔含量为10％～30％，分别基于所述聚合物A中结构单元的总摩尔含量计。
  14. 一种二次电池，其特征在于，包括电极组件和电解液，所述电极组件包括如权利要求1～13中任一项所述的正极极片、隔离膜和负极极片。
  15. 一种电池模块，其特征在于，包括权利要求14所述的二次电池。
  16. 一种电池包，其特征在于，包括权利要求15所述的电池模块。
  17. 一种用电装置，其特征在于，包括选自权利要求14所述的二次电池、权利要求15所述的电池模块或权利要求16所述的电池包中的至少一种。
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