WO2024082336A1 - 聚合物、导电浆料、正极极片、二次电池和用电装置 - Google Patents

聚合物、导电浆料、正极极片、二次电池和用电装置 Download PDF

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WO2024082336A1
WO2024082336A1 PCT/CN2022/128800 CN2022128800W WO2024082336A1 WO 2024082336 A1 WO2024082336 A1 WO 2024082336A1 CN 2022128800 W CN2022128800 W CN 2022128800W WO 2024082336 A1 WO2024082336 A1 WO 2024082336A1
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polymer
positive electrode
monomer
formula
conductive
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PCT/CN2022/128800
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English (en)
French (fr)
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冯伟
欧阳楚英
孙成栋
刘会会
冯凌云
段连威
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宁德时代新能源科技股份有限公司
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
    • C08F214/18—Monomers containing fluorine
    • C08F214/22—Vinylidene fluoride
    • C08F214/225—Vinylidene fluoride with non-fluorinated comonomers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F293/00—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule
    • 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
    • H01M4/139—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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/04—Acids; Metal salts or ammonium salts thereof
    • C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
    • 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 battery production, and in particular to a polymer, a conductive slurry, a positive electrode sheet, a secondary battery and an electrical device.
  • Secondary batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes and electric tools, etc.
  • the pole pieces in the secondary batteries are usually optimized and improved.
  • the performance of the film layer in the pole piece is currently uneven, and when it is used in secondary batteries, the electrochemical performance of the secondary battery is poor.
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a polymer, a conductive paste, a positive electrode sheet, a secondary battery and an electrical device.
  • the first aspect of the present application provides a polymer, wherein the polymer comprises a structural unit represented by formula (1) and a structural unit represented by formula (2),
  • R 1 , R 2 and R 3 are each independently selected from hydrogen atom, halogen atom or substituted or unsubstituted C1-C10 alkyl; alternatively, R 1 , R 2 and R 3 are each independently selected from hydrogen atom, halogen atom or substituted or unsubstituted C1-C5 alkyl.
  • the polymer of the embodiment of the present application has good dispersibility and still has certain adhesion.
  • the polymer when used in secondary batteries, especially in the preparation of conductive slurries, it can be used as a dispersant and at the same time can be used as an auxiliary material for the binder to reduce the use of binders with higher adhesion properties, so that the particles in the slurry are not easy to agglomerate and can be evenly dispersed, and can improve the adhesion between particles and the adhesion between particles and current collectors, thereby ensuring the structural stability of the pole piece and thus ensuring the electrochemical performance of the secondary battery.
  • the structural unit represented by formula (2) includes one or more structural units represented by formula (2-1) to formula (2-10):
  • the weight average molecular weight of the polymer is from 1.5 ⁇ 10 5 Da to 2.0 ⁇ 10 5 Da.
  • the number of structural units represented by formula (1) is n, 100 ⁇ n ⁇ 150; and/or the number of structural units represented by formula (2) is m, 100 ⁇ m ⁇ 150.
  • the weight average molecular weight of the polymer is within the above range, a certain solubility of the polymer can be ensured, thereby ensuring the viscosity of the polymer; and the viscosity rebound is small, and it can adhere well to the active material and the like.
  • the polymer satisfies at least one of conditions (1) to (3): (1) the viscosity of the polymer is C mPa*s, 500 ⁇ C ⁇ 3000; (2) the glass transition temperature of the polymer is Tg°C, 150 ⁇ Tg ⁇ 180; (3) the crystallinity of the polymer under differential scanning calorimetry (DSC) test is 40% to 50%.
  • the viscosity of the polymer of the present application when the viscosity of the polymer of the present application is within the above range, its viscosity is moderate; when the polymer is applied to a secondary battery, it can evenly disperse the active material particles, etc., and is not easy to cause agglomeration between the particles, so that the performance of the pole piece is more uniform, which is conducive to giving full play to the electrochemical performance of the secondary battery.
  • the glass transition temperature of the polymer is within the above range, it can improve the toughness of the pole piece, enhance the mechanical properties of the pole piece, and make the viscosity of the polymer moderate.
  • the crystallinity of the polymer when the crystallinity of the polymer is within the above range, it basically does not affect the circulation of molecules in the electrolyte, and can ensure the charge and discharge performance of the secondary battery.
  • the polymer is in granular form, and the volume average particle size of the polymer is Dv50 ⁇ m, 1 ⁇ Dv50 ⁇ 5.
  • the volume average particle size of the polymer is within the above range, it can be dissolved in the slurry system to a certain extent, and plays the role of a binder and a dispersant.
  • the second aspect of the present application also provides a method for preparing a polymer, the method comprising: providing a first monomer and a second monomer comprising a structural unit represented by formula (2); polymerizing the first monomer and the second monomer in the presence of a free radical initiator to form a polymer, wherein the first monomer comprises vinylidene fluoride; the structural unit represented by formula (2) is as follows:
  • R 1 , R 2 and R 3 are each independently selected from hydrogen atom, halogen atom or substituted or unsubstituted C1-C10 alkyl; alternatively, R 1 , R 2 and R 3 are each independently selected from hydrogen atom, halogen atom or substituted or unsubstituted C1-C5 alkyl.
  • the step of polymerizing the first monomer and the second monomer in the presence of a free radical initiator to form a polymer includes: homopolymerizing the first monomer in the presence of a free radical initiator to form a first block polymer; copolymerizing the first monomer, the second monomer and the first block polymer in the presence of a free radical initiator to form a second block polymer; copolymerizing the first monomer and the second block polymer in the presence of a free radical initiator to form a polymer.
  • the ratio of the mole percentage of the second monomer to the mole percentage of the first monomer is A, and 0.10 ⁇ A ⁇ 0.30.
  • the third aspect of the present application also provides a method for preparing a conductive paste, the method comprising: adding a polymer to a solvent to mix into a prefabricated glue solution; dispersing a conductive agent in the prefabricated glue solution to form a conductive paste, wherein the polymer comprises a polymer according to any embodiment of the first aspect of the present application or a polymer obtained according to the method of any embodiment of the second aspect of the present application.
  • the mass content of the polymer is recorded as p%; based on the total mass of the conductive paste, the mass content of the conductive agent is recorded as q%, 2 ⁇ q/p ⁇ 20, and further optionally, 3 ⁇ q/p ⁇ 15.
  • the fourth aspect of the present application further provides a conductive paste, which includes a conductive agent and a polymer, wherein the polymer includes a polymer according to any embodiment of the first aspect of the present application and a polymer obtained by a method according to any embodiment of the second aspect of the present application.
  • the mass content of the polymer is recorded as p%; based on the total mass of the conductive paste, the mass content of the conductive agent is recorded as q%, 2 ⁇ q/p ⁇ 20, and further optionally, 3 ⁇ q/p ⁇ 15.
  • the fifth aspect of the present application also provides a method for preparing a positive electrode plate, the method comprising: providing a positive electrode collector; adding a positive electrode active material, a polymer, a conductive agent and a binder into a solvent to mix into a positive electrode slurry, coating the positive electrode slurry on the positive electrode collector, and curing to form a positive electrode plate; wherein the polymer comprises a polymer according to any embodiment of the first aspect of the present application or a polymer obtained by the method according to any embodiment of the second aspect of the present application.
  • the step of adding positive electrode active material, polymer, conductive agent and binder into solvent to mix into positive electrode slurry includes: adding polymer into solvent to mix into pre-made glue solution; dispersing conductive agent in pre-made glue solution to form conductive slurry; mixing conductive slurry and active material into positive electrode slurry.
  • the mass content of the polymer is recorded as p%; based on the total mass of the conductive paste, the mass content of the conductive agent is recorded as q%, 2 ⁇ q/p ⁇ 20, and further optionally, 3 ⁇ q/p ⁇ 15.
  • the sixth aspect of the present application also provides a positive electrode plate, which is prepared by the method described in any embodiment of the fifth aspect of the present application.
  • the seventh aspect of the present application also provides a secondary battery, comprising the positive electrode plate described in any embodiment of the sixth aspect of the present application.
  • the eighth aspect of the present application also provides an electrical device, comprising the secondary battery as described in the seventh aspect of the present application.
  • FIG. 1 is a schematic diagram of an embodiment of a secondary battery of the present application.
  • FIG. 2 is an exploded schematic diagram of an embodiment of the secondary battery of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.
  • FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.
  • the terms “installed”, “connected”, “connected”, and “attached” should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements.
  • installed should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements.
  • a and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone.
  • the character "/" in this application generally indicates that the associated objects before and after are in an "or" relationship.
  • the pole piece usually includes a current collector and a film layer disposed on the current collector.
  • the active material is bonded to the current collector.
  • a binder is usually used to ensure the bonding performance; and it is conducive to the formation of an interface film on the surface of the film layer.
  • Binders are generally polymer compounds, usually polyvinyl alcohol PVA, polytetrafluoroethylene PTFE, polyvinylidene fluoride PVDF, etc.
  • Polyvinylidene fluoride PVDF has excellent chemical properties, physical properties and thermal processing properties, so it has been widely and deeply studied.
  • PVDF when used as a binder in secondary batteries, too much PVDF may cause agglomeration between active material particles, resulting in uneven distribution of active material particles and easily leading to an increase in the internal resistance of the secondary battery.
  • N-methylpyrrolidone NMP as a dispersant, and the two are used in combination with each other; too little PVDF may result in poor film-forming effect, and the film layer may easily fall off the current collector during the charge and discharge process.
  • the inventors improved the composition structure of PVDF in order to improve the performance of PVDF itself, so that the improved PVDF can have good dispersibility and retain a certain degree of adhesion; the technical solution of this application is described in detail below.
  • the present application proposes a polymer.
  • the polymer comprises a structural unit represented by formula (1),
  • the polymer also includes a structural unit represented by formula (2):
  • the structural unit shown in formula (1) is derived from vinylidene fluoride VDF, which is the main monomer for synthesizing polymers.
  • VDF vinylidene fluoride
  • the carbon chain of the polymer part formed by VDF is zigzag-shaped. After the hydrogen atoms are replaced by fluorine atoms with greater electronegativity, they repel each other with adjacent fluorine atoms, so that the fluorine atoms are not in the same plane and are distributed in a spiral along the carbon chain.
  • the carbon chain is surrounded by a series of fluorine atoms with stable properties, forming a certain space barrier so that other atoms or groups are not easy to enter its structure and destroy the carbon chain, thereby showing extremely high chemical stability and thermal stability; and because the polarizability of the carbon-fluorine bond in the polymer is low, the molecular structure is dense, and it has good hydrophobicity, which is reflected in lipophilicity.
  • the polymer also shows high insulation.
  • the structural unit shown in formula (2) contains a carboxyl grafted group, which can enhance the cohesion of the polymer. Since the carboxyl group is a polar group, the introduction of a polar group into the side chain of the polymer can improve the dispersibility of the polymer. When the polymer is applied to a secondary battery, the polymer is more likely to wet the surface of particles such as a conductive agent, thereby increasing the wetting speed.
  • the structural unit represented by formula (1) exhibits lipophilicity
  • the structural unit represented by formula (2) exhibits hydrophilicity.
  • the structural unit represented by formula (1) and the structural unit represented by formula (2) are used in combination so that the polymer has both lipophilicity and hydrophilicity, and can evenly disperse particles such as conductive agents in the system, exhibiting good dispersibility.
  • the structural unit represented by formula (1) and the structural unit represented by formula (2) are used in combination so that the composed polymer has an appropriate degree of crystallinity, thereby being able to improve the cohesion of the polymer itself and ensure that the polymer still has a certain degree of adhesion.
  • its adhesion strength is relatively poor and can be used together with other adhesives to supplement and improve the adhesion performance to conductive agents, etc.
  • the polymer of the embodiment of the present application has good dispersibility and still has certain adhesion.
  • the polymer when used in secondary batteries, especially in the preparation of conductive slurry, it can be used as a dispersant and at the same time can be used as an auxiliary material for the binder to reduce the use of binders with higher adhesion properties, so that the particles in the slurry are not easy to agglomerate and can be evenly dispersed, and can improve the adhesion between the particles and the adhesion between the particles and the current collector, thereby ensuring the structural stability of the electrode and thus ensuring the electrochemical performance of the secondary battery.
  • R1 is selected from hydrogen atom, halogen atom or substituted or unsubstituted C1-C10 alkyl
  • R2 and R3 are each independently selected from hydrogen atom, halogen atom or substituted or unsubstituted C1-C10 alkyl.
  • the substituent may be a halogen atom, or other atoms such as a sulfur atom.
  • the halogen atom may be a fluorine atom, a chlorine atom, a bromine atom or the like.
  • the alkyl group may be a straight or linear alkyl group.
  • the alkyl group may be a C1-C10 alkyl group, a C1-C8 alkyl group, a C1-C5 alkyl group, a C2-C8 alkyl group, a C2-C6 alkyl group.
  • the alkyl group may include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a heptyl group, a cycloheptyl group, an octyl group, a cyclooctyl group, a nonyl group, and a decyl group.
  • the alkyl group may be optionally substituted; its substituent may be a halogen atom, or may be other atoms such as a sulfur atom.
  • the structural units represented by formula (2) can be directly connected to each other, and the structural units represented by formula (2) can also be alternately connected with the structural units represented by formula (1).
  • the C atom connected to R1 in formula (2) can be connected to -CH2 in formula (1)
  • the C atom connected to R2 in formula (2) can be connected to -CF2 in formula (1).
  • the polymerization mode is mainly linear polymerization; that is, when the structural unit shown in formula (2) is polymerized, the side chain will basically not interfere with the polymerization process, thereby ensuring the normal progress of the polymerization, and the structural symmetry of the molecular chain of the formed polymer is high, and the polymer is easier to crystallize, thereby further improving the adhesion of the polymer; and the number of carbon atoms in the side chain structure increases, and its hydrophobic property shows an increasing trend.
  • the relatively short side chain can ensure the overall hydrophilic property of the structural unit shown in formula (2).
  • R 1 , R 2 and R 3 are each independently selected from a hydrogen atom, a halogen atom or a substituted or unsubstituted C1-C5 alkyl group.
  • the structural unit represented by formula (2) includes one or more structural units represented by formula (2-1) to formula (2-10):
  • the structural unit shown in formula (2) of the above structure can ensure that when the structural unit shown in formula (2) is introduced into the polymer, on the one hand, it can enhance the cohesion of the polymer and improve its bonding performance; on the other hand, it can introduce hydrophilic properties and improve the dispersibility of the polymer.
  • the weight average molecular weight of the polymer is from 1.5 ⁇ 10 5 Da to 2.0 ⁇ 10 5 Da.
  • the weight average molecular weight of the polymer When the weight average molecular weight of the polymer is within the above range, a certain solubility of the polymer can be ensured, thereby ensuring the viscosity of the polymer; and the viscosity rebound is small, and it can adhere well to active materials, etc.
  • the weight average molecular weight of the polymer can be 1.5 ⁇ 10 5 Da, 1.6 ⁇ 10 5 Da, 1.7 ⁇ 10 5 Da, 1.8 ⁇ 10 5 Da, 1.9 ⁇ 10 5 Da or 2.0 ⁇ 10 5 Da, etc., or a range consisting of any two of the above values.
  • the number of structural units represented by formula (1) is n, 100 ⁇ n ⁇ 150; optionally, 100 ⁇ n ⁇ 133.
  • n can be 100, 110, 120, 125, 130, 133, 138, 140, 145, 150 or a range consisting of any two of the above values.
  • the structural units shown in formula (1) constitute the molecular chain of the polymer
  • the symmetry of the molecular chain is high and the crystallization performance of the polymer is good, and it mainly contributes to the bonding performance of the polymer; therefore, when the number n of the structural units shown in formula (1) is within the above range, it can ensure that the viscosity of the polymer is moderate and it is not easy to cause agglomeration of active materials, conductive agents, etc.
  • the number of structural units shown in formula (2) is m, 100 ⁇ m ⁇ 150; optionally, 100 ⁇ m ⁇ 133.
  • m can be 100, 110, 120, 125, 130, 133, 138, 140, 145, 150 or a range consisting of any two of the above values.
  • the introduction of functional groups such as carboxyl groups into the side chains of the polymer can improve the hydrophilicity of the polymer, thereby improving the dispersion performance of the polymer; and the introduction of carboxyl groups can also improve the cohesion of the polymer and enhance the bonding performance of the polymer; therefore, when the number m of the structural units shown in formula (2) is within the above range, it can ensure that the viscosity of the polymer is moderate and can make the polymer have a certain degree of dispersibility.
  • the viscosity of the polymer is C mPa*s, 500 ⁇ C ⁇ 3000.
  • the viscosity of the polymer When the viscosity of the polymer is within the above range, its viscosity is moderate; when the polymer is applied to a secondary battery, it can evenly disperse the active material particles, etc., and is not easy to cause agglomeration between the particles, so that the performance of the pole piece is more uniform, which is conducive to giving full play to the electrochemical performance of the secondary battery.
  • the viscosity of the polymer can be 500mPa*s, 600mPa*s, 700mPa*s, 800mPa*s, 900mPa*s, 1000mPa*s, 1200mPa*s, 1500mPa*s, 1800mPa*s, 1900mPa*s, 2000mPa*s, 2500mPa*s or a range consisting of any two of the above values.
  • the polymer has a glass transition temperature, Tg°C, 150 ⁇ Tg ⁇ 180°C.
  • the glass transition temperature of the polymer is within the above range, the toughness of the pole piece can be improved, the mechanical properties of the pole piece can be enhanced, and the viscosity of the polymer can be moderate.
  • the glass transition temperature of the polymer can be 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, or a range consisting of any two of the above values.
  • the polymer has a crystallinity of 40% to 50% as measured by differential scanning calorimetry (DSC).
  • the crystallinity of the polymer When the crystallinity of the polymer is within the above range, it will not substantially affect the flow of molecules in the electrolyte, and can ensure the charge and discharge performance of the secondary battery.
  • the crystallinity of the polymer can be 40%, 42%, 45%, 48%, 49%, 50%, or a range consisting of any two of the above values.
  • the polymer is in a granular form, and the volume average particle size of the polymer is Dv50 ⁇ m, and 1 ⁇ Dv50 ⁇ 5.
  • the volume average particle size of the polymer When the volume average particle size of the polymer is within the above range, it can be dissolved in the slurry system to a certain extent, and play the role of a binder and a dispersant.
  • the volume average particle size Dv50 ⁇ m of the polymer can be 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m or 5 ⁇ m; or a range consisting of any two of the above values.
  • the volume average particle size Dv50 of the material has a well-known meaning in the art, which indicates the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be tested using instruments and methods known in the art. For example, it can be conveniently tested using a laser particle size analyzer with reference to GB/T 19077-2016 particle size distribution laser diffraction method, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.
  • the specific surface area of a material has a well-known meaning in the art and can be tested using instruments and methods well-known in the art. For example, it can be tested by nitrogen adsorption specific surface area analysis test method with reference to GB/T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method.
  • the nitrogen adsorption specific surface area analysis test can be performed using the Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.
  • the present application provides a method for preparing a polymer, which can prepare a polymer according to any embodiment of the first aspect of the present application.
  • the method comprises:
  • Step S100 providing a first monomer and a second monomer including a structural unit represented by formula (2);
  • Step S200 polymerizing the first monomer and the second monomer in the presence of a free radical initiator to form a polymer
  • the first monomer includes vinylidene fluoride; the structural unit shown in formula (2) is as follows:
  • R1 is selected from a hydrogen atom, a halogen atom or a substituted or unsubstituted C1-C10 alkyl group
  • R 2 and R 3 are each independently selected from a hydrogen atom, a halogen atom or a substituted or unsubstituted C1-C10 alkyl group.
  • R 1 , R 2 and R 3 are each independently selected from a hydrogen atom, a halogen atom or a substituted or unsubstituted C1-C5 alkyl group.
  • the first monomer and the second monomer are copolymerized to form a polymer, and the order of adding the first monomer and the second monomer can be adjusted according to production requirements; for example, part of the first monomer can be added first, and the first monomers are homopolymerized; then the second monomer and the first monomer are added, and the first monomer, the second monomer, etc. are copolymerized. Or the first monomer is added first, and the first monomers are copolymerized; then the second monomer is added, and the second monomers are copolymerized; then the block polymer obtained by copolymerizing the first monomer and the block polymer obtained by copolymerizing the second monomer are polymerized.
  • the polymer formed can be based on -CH2-CF2- as the basic main chain, supplemented by the structural unit shown in formula (2), and a carboxyl group can be introduced into the side chain of the polymer to improve the adhesion and dispersibility of the polymer.
  • the polymerization method of the present application is relatively simple, and the polymer formed has good dispersibility and still has a certain adhesion.
  • the polymerization of polymers can be carried out by suspension polymerization or emulsion polymerization.
  • the amount of dispersant adsorbed on the polymer formed by suspension polymerization is small and easy to remove, the purity of the product is high; and the post-processing process is relatively simple.
  • the polymerization rate of emulsion polymerization is fast, the molecular weight of the product is relatively high, and the polymerization can be carried out at a relatively high temperature.
  • Suspension polymerization can be carried out in the following process: add a certain amount of deionized water and dispersant into the reactor, seal the reactor, evacuate, replace oxygen with an inert gas such as nitrogen, evacuate again, and fill with nitrogen to make the pressure in the reactor slightly higher than the atmospheric pressure and the oxygen content in the reactor meet the standard. Stir the system in the reactor, and raise the temperature to about 50°C and the pressure to about 3.5MPa. Add some monomers and initiators to start polymerization; during the polymerization process, continue to add monomers and initiators to maintain the temperature and pressure in the reactor until all the monomers are added, reduce the pressure to about 2.8MPa, stop stirring, and the reaction is over.
  • Emulsion polymerization can be carried out in the following process: evacuate the reactor and replace the oxygen with an inert gas such as nitrogen to ensure that the oxygen content in the reactor meets the standard. Add deionized water, emulsifiers and initiators into the reactor, and add a small amount of monomers; heat the reactor to the reaction temperature, continue to add monomers as the reaction proceeds, and maintain the pressure in the reactor until the reaction is completed; during the reaction, the polymer undergoes processes such as coagulation, washing and drying to obtain the final polymer product.
  • an inert gas such as nitrogen
  • step S200 includes:
  • Step S210 homopolymerizing the first monomer in the presence of a free radical initiator to form a first block polymer.
  • the first monomer is pre-homopolymerized to form the first block polymer, which can ensure that the molecular chain of the polymer is a linear main chain, thereby ensuring a certain regularity of the polymer, which is beneficial to improving the crystallization ability of the polymer.
  • Step S220 copolymerizing the first monomer, the second monomer, and the first block polymer in the presence of a free radical initiator to form a second block polymer.
  • the second monomer is introduced, and the first monomer and the second monomer continue to polymerize on the basis of the first block polymer, and a carboxyl group is introduced into the side chain of the polymer to improve the adhesion and dispersibility of the polymer.
  • Step S230 copolymerizing the first monomer and the second block polymer in the presence of a free radical initiator to form the polymer.
  • the polymerization of the first monomer is continued to ensure that the entire polymer is a linear molecular chain.
  • a ratio of the molar percentage of the second monomer to the molar percentage of the first monomer is A, and 0.10 ⁇ A ⁇ 0.30.
  • the total molar amount of the first monomer and the second monomer refers to the sum of the molar amount of the added first monomer and the molar amount of the added second monomer during the entire reaction process.
  • the molar percentage of the first monomer refers to the percentage of the molar amount of the first monomer to the total molar amount.
  • the molar percentage of the second monomer refers to the percentage of the molar amount of the second monomer to the total molar amount.
  • the ratio A of the molar percentage of the second monomer to the molar percentage of the first monomer can be 0.10, 0.15, 0.20, 0.25, 0.30 or a range consisting of any two of the above values.
  • emulsifiers and solvents may be added to facilitate emulsion polymerization.
  • Emulsifiers include alkali metal perfluorooctanoate and the like.
  • the present application proposes a method for preparing a conductive paste.
  • conductive agents such as conductive carbon black are important components in the battery production process. Their dispersibility in the slurry has a great influence on the pole piece resistance and the performance of the secondary battery.
  • the conductive carbon black particles are micron-sized, with a large specific surface area and are very easy to agglomerate.
  • the traditional feeding method is to directly mix the conductive carbon black dry powder and the positive electrode active material and add them to the solvent. Mechanical stirring is difficult to disperse evenly, and a long time of stirring and slurrying is required, which affects the production efficiency and also affects its conductivity.
  • conductive carbon black is also prefabricated into conductive slurry, but other additives such as dispersants and surfactants need to be added to the conductive slurry.
  • the additives of different systems are different, and the problem of incompatibility with the slurry system is prone to occur during the preparation of secondary battery slurry.
  • the binder PVDF used in the battery production process has a molecular weight of 500,000 to 1.2 million, and the viscosity of the glue is large. It is difficult to evenly disperse the conductive carbon black, and the pole piece resistance is high. Even if the stirring time is extended to disperse evenly, the dispersed carbon black particles will agglomerate after the slurry is left to stand, and the slurry will also increase in viscosity and gel, affecting its production and use.
  • the inventors proposed a method for preparing a conductive paste, the method comprising:
  • the polymer includes the polymer described in any embodiment of the first aspect of the present application or the polymer obtained by the method described in any embodiment of the second aspect of the present application.
  • the polymer powder can be added to the solvent and mixed into a pre-made glue solution; then the conductive agent, such as conductive carbon black, is dispersed in the pre-made glue solution to prepare a conductive slurry.
  • the conductive agent in the conductive slurry prepared in this way is more evenly dispersed, and will not agglomerate in large quantities due to the small particle size of the conductive agent.
  • the distribution of the conductive agent is more uniform, which can reduce the resistance of the positive electrode film layer to a certain extent and improve the electrochemical performance of the secondary battery.
  • the solvent in the pre-made glue solution can be selected from the types of solvents commonly used in positive electrode slurries, such as N-methylpyrrolidone NMP.
  • the mass content of the polymer is recorded as p%, and 0.5 ⁇ q ⁇ 2.5.
  • the conductive agent can be uniformly dispersed in the polymer, and the conductive paste has a certain viscosity, for example, greater than 40mPa*s, the conductive paste has high stability, and the conductive agent is not easy to settle; and the viscosity of the conductive paste is moderate, and basically no problems such as viscosity rebound and gelation will occur, which is conducive to the long-term storage of the conductive paste.
  • the mass content of the polymer can be 0.5%, 1%, 1.5%, 2% or 2.5%; or a range consisting of any two of the above values.
  • the mass content of the conductive agent is recorded as q%, and 7.5 ⁇ q ⁇ 15.5.
  • the mass content of the conductive agent is within the above range, the content of the solvent can be guaranteed, which is conducive to the dissolution and dispersion of the polymer; and the amount of the conductive agent is moderate, the overall fluidity of the conductive paste is good, which is conducive to the addition of materials in industrial production.
  • the mass content of the conductive agent can be 7.5%, 8%, 8.5%, 9%, 9.5%, 10.5%, 11.0%, 12.0%, 13.0%, 13.5%, 14.0%, 15.0%, 15.5% or a range consisting of any two of the above values.
  • q/p 2 ⁇ q/p ⁇ 20.
  • 3 ⁇ q/p ⁇ 15 q/p can be 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 16, 18, 19, 20 or a range consisting of any two of the above values.
  • q/p is within the above range, the dispersant polymer has better dispersibility for the conductive agent, the conductive agent is evenly dispersed, and the conductive slurry formed has stable performance, which is beneficial to reduce the membrane resistance of the positive electrode sheet when applied to the positive electrode sheet.
  • the present application proposes a conductive paste.
  • the conductive paste includes a conductive agent and a polymer, wherein the polymer includes the polymer described in any embodiment of the first aspect of the present application or a polymer obtained by the method described in any embodiment of the second aspect of the present application.
  • the conductive paste can also be prepared by the method of any embodiment of the third aspect of the present application.
  • the conductive slurry of the present application has good dispersibility, is not easy to agglomerate and settle, and can ensure uniform and stable performance during long-term storage.
  • the mass content of the polymer is recorded as p%; based on the total mass of the conductive paste, the mass content of the conductive agent is recorded as q%, 2 ⁇ q/p ⁇ 20, and further optionally, 3 ⁇ q/p ⁇ 15.
  • the present application proposes a positive electrode plate.
  • the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode current collector has two surfaces opposite to each other in the thickness direction thereof, 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 film layer includes a polymer according to any embodiment of the first aspect of the present application or a polymer prepared as in any embodiment of the second aspect of the present application. Since the polymer has good dispersibility and certain bonding properties, it can be used as a dispersant in the positive electrode film layer, as well as an auxiliary agent for the binder. No other dispersants need to be introduced into the positive electrode film layer, thereby reducing the risk of damage to the positive electrode active material caused by other dispersants and ensuring the structural stability of the positive electrode film layer.
  • the positive electrode film layer includes a positive electrode active material
  • the positive electrode active material can be a positive electrode active material for a secondary battery known in the art.
  • the positive electrode active material may include at least one of the following materials: a layered structure positive electrode active material (such as ternary, lithium nickelate/sodium, lithium cobaltate/sodium, lithium manganate/sodium, lithium/sodium-rich layered and rock salt phase layered materials), an olivine-type phosphate active material, a spinel structured positive electrode active material (such as spinel lithium manganate, spinel nickel lithium manganate, lithium-rich spinel lithium manganate, and lithium nickel lithium manganate, etc.).
  • a layered structure positive electrode active material such as ternary, lithium nickelate/sodium, lithium cobaltate/sodium, lithium manganate/sodium, lithium/sodium-rich layered and rock salt phase layered materials
  • an olivine-type phosphate active material such as spinel lithium manganate,
  • the general formula of the layered positive electrode active material is: LixAyNiaCobMncM (1-abc) Yz , wherein 0 ⁇ x ⁇ 2.1, 0 ⁇ y ⁇ 2.1, and 0.9 ⁇ x+y ⁇ 2.1; 0 ⁇ a ⁇ 1 , 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, and 0.1 ⁇ a+b+c ⁇ 1; 1.8 ⁇ z ⁇ 3.5;
  • A is selected from one or more of Na, K, and Mg;
  • M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce;
  • Y is selected from one or more of O and F.
  • the layered structure positive active material may include one or more of lithium cobalt oxide LCO, lithium nickel oxide LNO, lithium manganese oxide LMO, LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), and LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523).
  • the general formula of the olivine -type phosphate active material is: LixAyMeaMbP1 - cXcYz , wherein 0 ⁇ x ⁇ 1.3 , 0 ⁇ y ⁇ 1.3, and 0.9 ⁇ x+y ⁇ 1.3; 0.9 ⁇ a ⁇ 1.5, 0 ⁇ b ⁇ 0.5, and 0.9 ⁇ a+b ⁇ 1.5; 0 ⁇ c ⁇ 0.5; 3 ⁇ z ⁇ 5;
  • A is selected from one or more of Na, K, and Mg;
  • Me is selected from one or more of Mn, Fe, Co, and Ni;
  • M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce;
  • X is selected from one or more of S, Si, Cl, B, C, and N; and Y is selected from one or more of O
  • the general formula of the positive electrode active material with a spinel structure is: LixAyMnaM2 - aYz , wherein 0 ⁇ x ⁇ 2 , 0 ⁇ y ⁇ 1, and 0.9 ⁇ x+y ⁇ 2; 0.5 ⁇ a ⁇ 2; 3 ⁇ z ⁇ 5;
  • A is selected from one or more of Na, K, and Mg;
  • M is selected from one or more of Ni, Co, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; and Y is selected from one or more of O and F.
  • the positive electrode active material of the spinel structure includes one or more of LiMn 2 O 4 , LiNi 0.5 Mn 1.5 O 4 , LiCr 0.3 Mn 1.7 O 4 , Li 1.1 Al 0.1 Mn 1.9 O 4 , Li 2 Mn 2 O 4 , and Li 1.5 Mn 2 O 4 .
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil an aluminum foil or an aluminum alloy foil may be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include a combination of one or more selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy
  • the polymer material base layer may include a combination of one or more selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).
  • the positive electrode film layer may further include a positive electrode conductive agent.
  • a positive electrode conductive agent includes a combination of one or more selected from superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass percentage of the positive electrode conductive agent is less than 5%.
  • the positive electrode film layer may also optionally include a positive electrode binder.
  • the present application does not particularly limit the type of positive electrode binder.
  • the positive electrode binder may include a combination of one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer vinylidene fluoride-hexafluoropropylene-
  • the mass percentage of the positive electrode binder is less than 5%; optionally, the mass percentage of the positive electrode binder is 1.0% to 2.5%.
  • the molecular weight of the positive electrode binder is 500,000 to 2 million.
  • the molecular weight of the polyvinylidene fluoride PVDF used in the positive electrode binder is 500,000 to 2 million.
  • the polymer in the embodiment described in the first aspect of the present application can be used as an auxiliary agent for the positive electrode binder, which can improve the bonding performance of the positive electrode film layer and reduce the risk of agglomeration of the positive electrode active material.
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them evenly.
  • the positive electrode sheet is prepared by the following steps: providing a positive current collector; adding a positive active material, a polymer, a conductive agent, and a binder into a solvent to mix into a positive active slurry, coating the positive active slurry on the positive current collector, and curing to form a positive electrode sheet.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the conductive agent may be prepared in advance as a conductive slurry, and then the conductive slurry and the positive electrode active material may be mixed to form a positive electrode slurry.
  • the conductive slurry may be prepared by the method of any embodiment of the third aspect of the present application, or may be prepared by the conductive slurry of any embodiment of the fourth aspect of the present application.
  • the conductive slurry may be prepared directly by using the polymer described in any embodiment of the first aspect of the present application or the polymer obtained by the method of any embodiment of the second aspect of the present application.
  • the polymer powder can be added to the solvent and mixed into a pre-made glue solution; then the conductive agent such as conductive carbon black is dispersed in the pre-made glue solution to prepare a conductive slurry, and then the positive electrode active material, positive electrode binder, etc. are dispersed in the conductive slurry to prepare a positive electrode slurry; the conductive agent in the conductive slurry prepared in this way is more evenly dispersed, and will not agglomerate in large quantities due to the small particle size of the conductive agent.
  • the distribution of the conductive agent is more uniform, which can reduce the resistance of the positive electrode film layer to a certain extent and improve the electrochemical performance of the secondary battery.
  • the solvent in the pre-made glue solution can be selected from the type of solvent commonly used in the positive electrode slurry, such as N-methylpyrrolidone NMP, etc.
  • the present application proposes a secondary battery.
  • the secondary battery comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet to isolate the positive electrode sheet from the negative electrode sheet.
  • the positive electrode plate may adopt the positive electrode plate of any embodiment of the fifth aspect of the present application, thereby reducing the plate resistance and improving the cycle performance and charge and discharge performance of the secondary battery.
  • the negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.
  • the negative electrode film layer includes a polymer according to any embodiment of the first aspect of the present application or a polymer prepared as in any embodiment of the second aspect of the present application. Since the polymer has good dispersibility and certain bonding properties, it can be used as a dispersant in the negative electrode film layer, as well as an auxiliary agent for the binder. Other dispersants do not need to be introduced into the negative electrode film layer, reducing the risk of other dispersants causing damage to the negative electrode active material and ensuring the structural stability of the negative electrode film layer.
  • the negative electrode current collector has two surfaces opposite to each other in its 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 metal foil copper foil may 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 substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode active material may adopt the negative electrode active material for the battery known in the art.
  • the negative electrode 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, etc.
  • 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 negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode film layer may also optionally include a negative electrode binder.
  • the negative electrode binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the mass percentage of the negative electrode binder is less than 5%; optionally, the mass percentage of the negative electrode binder is 1.5% to 3%.
  • the molecular weight of the negative electrode binder is 500,000 to 2 million.
  • the molecular weight of the styrene-butadiene rubber SBR used in the negative electrode binder is 500,000 to 2 million.
  • the polymer in the embodiment described in the first aspect of the present application can be used as an auxiliary agent for the styrene-butadiene rubber binder, which can improve the bonding particle size of the negative electrode film layer and reduce the risk of agglomeration of the styrene-butadiene rubber active material.
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the optional conductive agent, the optional binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the secondary battery also includes an electrolyte, which plays a role in conducting ions between the positive electrode and the negative electrode.
  • an electrolyte which plays a role in conducting ions between the positive electrode and the negative electrode.
  • the present application does not specifically limit the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be liquid, gel or all-solid.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the lithium salt may include a combination of one or more selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium te
  • the organic solvent may include a combination of one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).
  • EC ethylene carbon
  • the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • additives such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane may include a combination of one or more selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.
  • the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly by a winding process or a lamination process.
  • FIG1 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.
  • the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the positive electrode sheet, the separator and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying, and the secondary battery is obtained through vacuum packaging, standing, forming, shaping and other processes.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG3 is a schematic diagram of 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. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 are housed in the housing space.
  • the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.
  • FIG4 and FIG5 are schematic diagrams of a battery pack 1 as an example.
  • 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 body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 may be arranged in the battery box in any manner.
  • the present application provides an electrical device, which includes at least one of the secondary battery, battery module and battery pack of the present application.
  • the secondary battery, battery module and battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.
  • the electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • the electric device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • Fig. 6 is a schematic diagram of an electric device as an example.
  • the electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack 1 or a battery module can be used.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the electric device is usually required to be light and thin, and a secondary battery may be used as a power source.
  • Step S1 30 kg of deionized water (conductivity is less than or equal to 2 ⁇ s/cm), 15 g of 100% emulsifier perfluorooctanoic acid alkali metal salt, and 36 g of initiator (5% concentration potassium persulfate solution) accounting for 40% of the total amount are added into a 50 L reactor in sequence, and the reactor is closed;
  • Step S2 evacuating the reactor and filling it with nitrogen, and repeating the operation until the oxygen concentration in the reactor is less than 100 ppm;
  • Step S3 introducing vinylidene fluoride monomer into the reactor until the pressure in the reactor reaches 7.0 MPa;
  • Step S4 the temperature in the reactor is raised to 80° C. to start the reaction, and vinylidene fluoride monomer is continuously introduced during the reaction to maintain the reaction pressure in the reactor unchanged;
  • Step S5 when 50% of the total amount of vinylidene fluoride monomer, i.e. 2.4 kg, is introduced, 36 g of an initiator (5% potassium persulfate solution) is added, accounting for 40% of the total amount, and a mixed gas of vinylidene fluoride monomer and a second monomer is introduced into the reactor while maintaining the reaction pressure at 7.0 MPa (the vinylidene fluoride monomer and the second monomer methacrylic acid monomer are added simultaneously at a mass ratio of 1:1);
  • an initiator 5% potassium persulfate solution
  • Step S6 all 1.2 kg of the second monomer is added, and when the amount of vinylidene fluoride added accounts for 80% of the total amount, i.e. 3.6 kg, the remaining 20% of the initiator 18 g is added, and the remaining 20% of the vinylidene fluoride monomer 1.2 kg is introduced into the reactor while maintaining the reaction pressure at 7.0 MPa;
  • Step S7 when the reaction is completed, the pressure in the reactor will reach 2.0 MPa, and the unreacted vinylidene fluoride monomer is recovered;
  • Step S8 the reaction product is condensed, washed, separated, dried and crushed to obtain polymer PVDF.
  • Example 1-2 and Example 1-3
  • Example 1-2 and Example 1-3 were prepared using a method similar to Example 1-1 to prepare a dispersant PVDF.
  • Example 1-1 The difference between Example 1-1 and Example 1-2 is that the molar ratio of the second monomer is adjusted in Example 1-3.
  • Example 1-4 and Example 1-5 were prepared by a method similar to Example 1-1, and the dispersant PVDF was
  • Example 1-1 The difference between Example 1-1 and Example 1-4 is that at least one of the reaction temperature of step S4 and the reaction pressure of step S3 is adjusted in Example 1-5.
  • Example 1-6 The dispersant PVDF was prepared according to a method similar to Example 1-1. The difference from Example 1-1 was that the type of the second monomer was adjusted in Example 1-6.
  • Example 1-7 to Example 1-9 prepare the dispersant PVDF in a similar manner to Example 1-1, and
  • Example 1-1 and Example 1-7 to Example 1-9 The difference between Example 1-1 and Example 1-7 to Example 1-9 is that the reaction rate is adjusted by adjusting the amount of the initiator, thereby adjusting the particle size of the polymer. For example, compared with Example 1-1, the amount of the initiator in Example 1-7 is increased by 10%;
  • Example 1-8 the initiator dosage was increased by 5%; in Example 1-9, the initiator dosage was increased by 2%.
  • the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2
  • polyvinylidene fluoride are added to the conductive slurry and stirred to form a uniform positive electrode slurry with a solid content of 73%.
  • the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.
  • the molecular weight of polytetrafluoroethylene (PTFE) is 800,000.
  • the mass ratio of positive electrode active material, conductive carbon black powder, polyvinylidene fluoride, and NMP is 96.9:2.1:1:21.
  • a copper foil with a thickness of 8 ⁇ m was used as the negative electrode current collector.
  • the negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are fully stirred and mixed in an appropriate amount of solvent deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode collector copper foil, and after drying and cold pressing, a negative electrode sheet is obtained.
  • SBR binder styrene-butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • Super P conductive agent carbon black
  • a porous polyethylene (PE) membrane was used as the isolation membrane.
  • non-aqueous organic solvents ethylene carbonate EC and diethyl carbonate DMC are mixed in a volume ratio of 1:1 to obtain an electrolyte solvent, and then lithium salt and the mixed solvent are mixed to prepare an electrolyte with a lithium salt concentration of 1 mol/L.
  • the positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.
  • Example 2-2 Secondary batteries were prepared in Example 2-2 to Example 2-9 in a similar manner to Example 2-1.
  • the difference from Example 2-1 was that the types of dispersant PVDF were adjusted in Example 2-2 to Example 2-9, and the dispersant PVDF prepared in Example 1-2 to Example 1-9 was used respectively.
  • Example 2-10 Secondary batteries were prepared in Example 2-10 to Example 2-13 in a manner similar to that in Example 2-1. The difference from Example 2-1 was that the amount of the dispersant PVDF was adjusted in Example 2-10 to Example 2-13.
  • Comparative Example A secondary battery was prepared according to a method similar to that of Example 2-1. Unlike Example 2-1, the comparative example adjusted the preparation method of the positive electrode slurry, which was specifically as follows: the positive electrode active material (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ), conductive carbon black powder, polyvinylidene fluoride, and NMP were fully stirred and mixed in a mass ratio of 96.9:2.1:1:21 to form a uniform positive electrode slurry; the positive electrode slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained.
  • the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2
  • conductive carbon black powder LiNi 0.6 Co 0.2 Mn 0.2 O 2
  • conductive carbon black powder LiNi 0.6 Co 0.2 Mn 0.2 O 2
  • polyvinylidene fluoride polyvinylidene fluoride
  • NMP NMP
  • a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141) was used.
  • a polystyrene solution sample with a mass fraction of 3.0% was used as a reference, and a matching chromatographic column (oily: Styragel HT5DMF7.8 ⁇ 300mm+Styragel HT4) was selected.
  • a 3.0% polymer solution was prepared with purified N-methylpyrrolidone (NMP) solvent, and the prepared solution was allowed to stand for one day for use. During the test, tetrahydrofuran was first drawn with a syringe and rinsed, and repeated several times.
  • NMP N-methylpyrrolidone
  • the bonding test process of the embodiment and comparative example is as follows: Use a blade to cut a sample with a width of 30mm and a length of 100-160mm, and stick the special double-sided tape on the steel plate, the tape width is 20mm, and the length is 90-150mm. Stick the insulating coating surface of the pole piece sample cut earlier on the double-sided tape, and then roll it three times in the same direction with a 2kg roller. Fix a paper tape with a width equal to the pole piece and a length of 250mm on the current collector and fix it with wrinkled glue.
  • the indicator light is on, adjust the limit block to the appropriate position, and fix the end of the steel plate without the pole piece with the lower clamp. Fold the paper tape upwards and fix it with the upper clamp, and use the "up” and “down” buttons on the manual controller attached to the tensile machine to adjust the position of the upper clamp. Then test and read the value, the tensile speed is 50mm/min. The force when the pole piece is under force balance divided by the width of the tape is taken as the bonding force of the positive electrode film layer per unit length to characterize the bonding strength between the positive electrode film layer and the current collector.
  • the secondary battery DC impedance test process is as follows: at 25°C, the battery corresponding to Example 1 is charged to 4.3V at a constant current of 1/3*C, and then charged to a current of 0.05C at a constant voltage of 4.3V, and after standing for 5 minutes, the voltage V1 is recorded. Then, it is discharged at 1/3C for 30 seconds, and the voltage V2 is recorded, and the internal resistance DCR of the secondary battery is obtained by 3*(V2-V1)/C.
  • the comparative example uses conductive carbon black powder to be directly mixed with the positive electrode active material to form a positive electrode slurry.
  • the risk of conductive carbon black agglomeration is high, which makes the electrode sheet resistance high and the dynamic performance relatively poor.
  • the conductive carbon black powder is pre-prepared as a conductive slurry.
  • the polymer can effectively disperse the conductive carbon black powder evenly as a dispersant, so that the conductive slurry has better dispersion performance, is not easy to settle, and has more uniform performance.
  • the resistance of the positive electrode sheet can be improved, and the dynamic performance of the positive electrode sheet can be improved.
  • the polymer has a certain viscosity, it can help improve the bonding force within the positive electrode sheet.
  • the storage performance of the embodiment is relatively stable, and gel sedimentation is not easy to occur after standing for 24 hours, and gel sedimentation still does not occur after 60 days (60D) of storage.
  • the degree of dispersion of the conductive agent can be adjusted to reduce the electrode resistance, and the viscosity can be regulated to a certain extent to adjust the bonding strength within the electrode.

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Abstract

本申请涉及一种聚合物、导电浆料、正极极片、二次电池和用电装置。所述聚合物包括式(1)所示的结构单元和式(2)所示的结构单元，式(2)中，R1、R2和R3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基。本申请实施例的聚合物具有良好的分散性，在聚合物应用于二次电池时，尤其是应用于导电浆料的制备时，可以作为分散剂使用，使得浆料中的颗粒不易发生团聚，并能够均匀分散，从而保证二次电池的电化学性能。

Description

聚合物、导电浆料、正极极片、二次电池和用电装置
相关申请的交叉引用
本申请要求享有于2022年10月17日提交的名称为“聚合物、导电浆料、正极极片、二次电池和用电装置”的中国专利申请202211266304.3的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请涉及电池生产技术领域，特别是涉及一种聚合物、导电浆料、正极极片、二次电池和用电装置。
背景技术
二次电池具有容量高、寿命长等特性，因此广泛应用于电子设备，例如手机、笔记本电脑、电瓶车、电动汽车、电动飞机、电动轮船、电动玩具汽车、电动玩具轮船、电动玩具飞机和电动工具等等。
随着电池应用范围越来越广泛，对二次电池性能的要求也逐渐严苛。为了提高二次电池的性能，通常对二次电池内的极片进行优化改善。然而，目前极片中的膜层的性能不均一，其应用于二次电池时，二次电池的电化学性能较差。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种聚合物、导电浆料、正极极片、二次电池和用电装置。
本申请的第一方面提供了一种聚合物，所述聚合物包括式(1)所示的结构单元和式(2)所示的结构单元，
Figure PCTCN2022128800-appb-000001
Figure PCTCN2022128800-appb-000002
式(2)中，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基；可选地，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C5烷基。
本申请实施例的聚合物具有良好的分散性，并同时仍具有一定的粘结性，在聚合物应用于二次电池时，尤其是应用于导电浆料的制备时，可以作为分散剂使用，并同时能够作为粘结剂的辅助用料，降低粘附性能较高的粘结剂的使用量，使得浆料中的颗粒不易发生团聚，并能够均匀分散，且能够改善颗粒之间的粘结力，以及颗粒和集流体之间的粘结力，保证极片的结构稳定性，从而保证二次电池的电化学性能。
在一些实施方式中，式(2)所示的结构单元包括式(2-1)至式(2-10)所示的结构单元中的一种或多种：
Figure PCTCN2022128800-appb-000003
Figure PCTCN2022128800-appb-000004
在一些实施方式中，聚合物的重均分子量为1.5×10 5Da至2.0×10 5Da。
在一些实施方式中，式(1)所示的结构单元的数量为n，100≤n≤150；和/或式(2)所示的结构单元的数量为m，100≤m≤150。聚合物的重均分子量在上述范围时，能够保证聚合物一定的溶解度，从而保证聚合物的粘度；且粘度反弹小，能够与活性材料等较好的粘附。
在一些实施方式中，聚合物满足条件(1)至条件(3)中的至少一条：(1)聚合物的粘度为C mPa*s，500≤C≤3000；(2)聚合物的玻璃化转变温度Tg℃，150≤Tg≤180；(3)聚合物于差示扫描量热仪DSC测试下的结晶度为40％至50％。
由此，本申请的聚合物的粘度在上述范围时，其粘度适中；在将聚合物应用于二次电池时，能够均匀分散活性材料颗粒等，不易引起颗粒之间的团聚，使得极片的性能更均一，有利于充分发挥二次电池的电化学性能。聚合物的玻璃化转变温度在上述范围时，能够改善极片的韧性，增强极片的力学性能，并且能够使得聚合物的粘度适中。聚合物的结晶度在上述范围时，其基本不会对电解液中的分子的流通造成影响，能够保证二次电池的充放电性能。
在一些实施方式中，聚合物为颗粒状；聚合物的体积平均粒径为Dv50μm，1≤Dv50≤5。聚合物的体积平均粒径在上述范围时，其能够在一定程度上溶解于浆料体系中，起到粘结剂和分散剂的作用。
本申请的第二方面还提供了一种制备聚合物的方法，所述方法包括：提供第一单体和包含式(2)所示的结构单元的第二单体；将第一单体和第二单体在自由基引发剂的存在下，聚合形成聚合物，其中，第一单体包括偏氟乙烯；式(2)所示的结构单元如下：
Figure PCTCN2022128800-appb-000005
式(2)中，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基；可选地，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C5烷基。
在一些实施方式中，将第一单体和第二单体在自由基引发剂的存在下，聚合形成聚合物的步骤，包括：将第一单体在自由基引发剂的存在下均聚形成第一嵌段聚合物；将第一单体和第二单体以及第一嵌段聚合物在自由基引发剂的存在下共聚形成第二嵌段聚合物；将第一单体和第二嵌段聚合物在自由基引发剂的存在下共聚形成聚合物。
在一些实施方式中，基于第一单体和第二单体的总摩尔量计，第二单体的摩尔百分含量与第一单体的摩尔百分含量的比值为A，0.10≤A≤0.30。
本申请第三方面还提供了一种制备导电浆料的方法，所述方法包括：将聚合物加入溶剂中混合为预制胶液；将导电剂分散于预制胶液中形成导电浆料，其中，所述聚合物包括根据本申请第一方面任一实施方式的聚合物或根据本申请第二方面任一实施方式的方法得到的聚合物。
在一些实施方式中，基于导电浆料的总质量计，聚合物的质量含量记为p％；基于导电浆料的总质量计，导电剂的质量含量记为q％，2≤q/p≤20，进一步可选地，3≤q/p≤15。
本申请第四方面还提供了一种导电浆料，所述导电浆料包括导电剂和聚合物，所述聚合物包括根据本申请第一方面任一实施方式的聚合物、根据本申请第二方面任一实施方式的方法得到的聚合物。
在一些实施方式中，基于导电浆料的总质量计，聚合物的质量含量记为p％；基于导电浆料的总质量计，导电剂的质量含量记为q％，2≤q/p≤20，进一步可选地，3≤q/p≤15。
本申请第五方面还提供了一种制备正极极片的方法，所述方法包括：提供正极集流体；将正极活性材料、聚合物、导电剂和粘结剂加入溶剂中混合为正极浆料，将正极浆料涂覆于正极集流体上，经固化形成正极极片；其中，聚合物包括根据本申请第一方面任一实施方式的聚合物或根据本申请第二方面任一实施方式的方法得到的聚合物。
在一些实施方式中，将正极活性材料、聚合物、导电剂和粘结剂加入溶剂中混合为正极浆料的步骤，包括：将聚合物加入溶剂中混合为预制胶液；将导电剂分散于预制胶液中形成导电浆料；将导电浆料和活性材料混合为正极浆料。
在一些实施方式中，基于导电浆料的总质量计，聚合物的质量含量记为p％； 基于导电浆料的总质量计，导电剂的质量含量记为q％，2≤q/p≤20，进一步可选地，3≤q/p≤15。
本申请第六方面还提供了一种正极极片，由本申请第五方面任一实施方式所述的方法制备得到。
本申请第七方面还提供了一种二次电池，包括本申请第六方面任一实施方式所述的正极极片。
本申请第八方面还提供了一种用电装置，包括如本申请第七方面所述的二次电池。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
附图未必按照实际的比例绘制。
附图标记说明如下：
1、电池包；2、上箱体；3、下箱体；4、电池模块；
5、二次电池；51、壳体；52、电极组件；
53、盖板；
6、用电装置。
具体实施方式
使本申请实施例的目的、技术方案和优点更加清楚，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
除非另有定义，本申请所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同；本申请中在申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请；本申请的说明书和权利要求书及上述附图说明中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的 包含。本申请的说明书和权利要求书或上述附图中的术语“第一”、“第二”等是用于区别不同对象，而不是用于描述特定顺序或主次关系。
在本申请中提及“实施例”意味着，结合实施例描述的特定特征、结构或特性可以包含在本申请的至少一个实施例中。在说明书中的各个位置出现该短语并不一定均是指相同的实施例，也不是与其它实施例互斥的独立的或备选的实施例。
在本申请的描述中，需要说明的是，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”、“附接”应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本申请中的具体含义。
本申请中术语“和/或”，仅仅是一种描述关联对象的关联关系，表示可以存在三种关系，例如，A和/或B，可以表示：单独存在A，同时存在A和B，单独存在B这三种情况。另外，本申请中字符“/”，一般表示前后关联对象是一种“或”的关系。
在本申请的实施例中，相同的附图标记表示相同的部件，并且为了简洁，在不同实施例中，省略对相同部件的详细说明。应理解，附图示出的本申请实施例中的各种部件的厚度、长宽等尺寸，以及集成装置的整体厚度、长宽等尺寸仅为示例性说明，而不应对本申请构成任何限定。
本申请中出现的“多个”指的是两个以上(包括两个)。
极片通常包括集流体和设置于集流体上的膜层。在制备极片时，将活性材料粘结于集流体上，为了保证活性材料的颗粒之间的粘结力，以及活性材料和集流体之间的粘结力，通常采用粘结剂以保证粘结性能；并且有利于在膜层的表面形成界面膜。粘结剂一般都是高分子化合物，通常可以采用聚乙烯醇PVA、聚四氟乙烯PTFE、聚偏氟乙烯PVDF等。聚偏氟乙烯PVDF具有优良的化学性能、物理性能和热加工性能，因此得到了广泛且深入的研究。
发明人发现，PVDF作为粘结剂应用于二次电池时，PVDF用量过高可能会引发活性材料颗粒之间的团聚，导致活性材料颗粒分布不均匀，且容易导致二次电池的内阻增大，一般需要额外引入N-甲基吡咯烷酮NMP作为分散剂，二者相互配合使用；PVDF用量过少可能会使得成膜效果较差，在充放电过程中，膜层容易从集流体上脱落。
故，发明人从改善PVDF自身的性能出发，对PVDF的组成结构进行改进，以使改进后的PVDF能够具有良好的分散性，并保有一定的粘结性；接下来对本申请的技术方案进行详细说明。
聚合物
第一方面，本申请提出了一种聚合物。
所述聚合物包括式(1)所示的结构单元，
Figure PCTCN2022128800-appb-000006
所述聚合物还包括式(2)所示的结构单元：
Figure PCTCN2022128800-appb-000007
式(1)所示的结构单元来源于偏氟乙烯VDF，其是合成聚合物的主要单体，VDF所形成的聚合物部分的碳链呈锯齿形，其氢原子被电负性较大的氟原子取代后，与相邻的氟原子相互排斥，从而使得氟原子不在同一平面内，并沿碳链作螺旋分布，故在碳链的四周被一系列性质稳定的氟原子所包围，形成了一定的空间屏障使得其它原子或基团不易进入其结构内部而破坏碳链，因而表现出极高的化学稳定性和热稳定性；并且由于聚合物中碳氟键的极化率较低，分子结构致密，具有较好的疏水性，体现为亲油性，其聚合物还表现出高度的绝缘性。
式(2)所示的结构单元中包含羧基接枝基团，羧基能够增强聚合物的内聚力，且由于羧基为极性基团，在聚合物的侧链中引入极性基团能够改善聚合物分散性，在将该聚合物应用于二次电池时，该聚合物更易于浸润导电剂等颗粒的表面，提高润湿速度。
式(1)所示的结构单元表现为亲油性，式(2)所示的结构单元表现为亲水性，式(1)所示的结构单元和式(2)所示的结构单元配合使用，使得聚合物兼顾亲油性和亲水性，能够将导电剂等颗粒均一分散于体系中，表现为良好的分散性能。
式(1)所示的结构单元和式(2)所示的结构单元配合使用，使得所组成的聚合物具有适当的结晶度，从而能够改善聚合物自身的内聚力，保证聚合物仍具有一定的粘结性，但是其粘结力度相对较差，可以配合其它粘结剂共同使用，补足提高对导电剂等的粘附性能。
由此，本申请实施例的聚合物具有良好的分散性，并同时仍具有一定的粘结性，在聚合物应用于二次电池时，尤其是应用于导电浆料的制备时，可以作为分散剂使用，并同时能够作为粘结剂的辅助用料，降低粘附性能较高的粘结剂的使用量，使得浆料中的颗粒不易发生团聚，并能够均匀分散，且能够改善颗粒之间的粘结力，以及颗粒和集流体之间的粘结力，保证极片的结构稳定性，从而保证二次电池的电化学性能。
在一些实施方式中，式(2)中，R 1选自氢原子、卤素原子或者取代或未取代的C1-C10烷基；R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基。当经取代时，取代基可以任选为卤素原子，也可以为硫原子等其它原子等。
卤素原子可以为氟原子、氯原子、溴原子等。
烷基可以为直链或直链烷基。例如，烷基可以为C1-C10烷基、C1-C8烷基、C1-C5烷基、C2-C8烷基、C2-C6烷基。具体地，烷基可以包括甲基、乙基、丙基、异 丙基、丁基、异丁基、仲丁基、叔丁基、环丁基、戊基、异戊基、新戊基、叔戊基、环戊基、己基、环己基、庚基、环庚基、辛基、环辛基、壬基和癸基等。另外，烷基可以是任选地被取代的；其取代基可以为卤素原子，也可以为硫原子等其它原子。
式(2)所示的结构单元在组成聚合物的一部分时，式(2)所示的结构单元之间可以直接连接，式(2)所示的结构单元也可以与式(1)所示的结构单元交替连接，例如，式(2)中与R 1连接的C原子可以与式(1)中的-CH 2连接，式(2)中与R 2连接的C原子可以与式(1)中的-CF 2连接。
由于R 1、R 2和R 3的碳原子数量相对较少，式(2)所示的结构单元的侧链结构不会过长，在聚合过程中不易形成三维交联聚合，聚合方式主要体现为线性聚合；即在式(2)所示的结构单元聚合时，侧链基本不会对聚合过程造成干扰，从而保证聚合的正常进行，且所形成的聚合物的分子链的结构对称性较高，聚合物更容易结晶，从而进一步改善聚合物的粘结性；且侧链结构中的碳原子的数量增多，其疏水性能呈现增强趋势，相对较短的侧链能够保证式(2)所示的结构单元整体的亲水性能。
可选地，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C5烷基。
可选地，式(2)所示的结构单元包括式(2-1)至式(2-10)所示的结构单元中的一种或多种：
Figure PCTCN2022128800-appb-000008
Figure PCTCN2022128800-appb-000009
上述结构的式(2)所示的结构单元能够保证式(2)所示的结构单元在引入聚合物时，一方面增强聚合物的内聚力，改善其粘结性能；另一方面能够引入亲水性能，改善聚合物的分散性。
在一些实施方式中，聚合物的重均分子量为1.5×10 5Da至2.0×10 5Da。
聚合物的重均分子量在上述范围时，能够保证聚合物一定的溶解度，从而保证聚合物的粘度；且粘度反弹小，能够与活性材料等较好的粘附。示例性地，聚合物的重均分子量可以为1.5×10 5Da、1.6×10 5Da、1.7×10 5Da、1.8×10 5Da、1.9×10 5Da或2.0×10 5Da等等，或者是上述任意两个数值组成的范围。
在一些实施方式中，式(1)所示的结构单元的数量为n，100≤n≤150；可选地，100≤n≤133。示例性地，n可以为100、110、120、125、130、133、138、140、145、150或是上述任意两个数值组成的范围。
式(1)所示的结构单元在组成聚合物的分子链时，其分子链的对称度较高，聚合物的结晶性能较好，其主要为聚合物贡献粘结性能；故式(1)所示的结构单元的数量n在上述范围时，能够保证聚合物的粘度适中，不易引发活性材料、导电剂等的团聚现象。
在一些实施方式中，式(2)所示的结构单元的数量为m，100≤m≤150；可选地，100≤m≤133。示例性地，m可以为100、110、120、125、130、133、138、140、145、150或是上述任意两个数值组成的范围。
式(2)所示的结构单元在组成聚合物分子链时，其为聚合物的侧链引入羧基等功能基团，能够改善聚合物的亲水性，从而改善聚合物的分散性能；并且引入羧基还能够改善聚合物的内聚力提高聚合物的粘结性能；故式(2)所示结构单元的数量m在上述范围时，能够保证聚合物的粘度适中，且能够使得聚合物具有一定的分散性。
在一些实施方式中，聚合物的粘度为C mPa*s，500≤C≤3000。
聚合物的粘度在上述范围时，其粘度适中；在将聚合物应用于二次电池时，能够均匀分散活性材料颗粒等，不易引起颗粒之间的团聚，使得极片的性能更均一，有利于充分发挥二次电池的电化学性能。示例性地，聚合物的粘度可以为500mPa*s、 600mPa*s、700mPa*s、800mPa*s、900mPa*s、1000mPa*s、1200mPa*s、1500mPa*s、1800mPa*s、1900mPa*s、2000mPa*s、2500mPa*s或是上述任意两个数值组成的范围。
在一些实施方式中，聚合物的玻璃化转变温度Tg℃，150≤Tg≤180。
聚合物的玻璃化转变温度在上述范围时，能够改善极片的韧性，增强极片的力学性能，并且能够使得聚合物的粘度适中。示例性地，聚合物的玻璃化转变温度可以为150℃、155℃、160℃、165℃、170℃、175℃、180℃或是上述任意两个数值组成的范围。
在一些实施方式中，聚合物于差示扫描量热仪DSC测试下的结晶度为40％至50％。
聚合物的结晶度在上述范围时，其基本不会对电解液中的分子的流通造成影响，能够保证二次电池的充放电性能。示例性地，聚合物的结晶度可以为40％、42％、45％、48％、49％、50％或是上述任意两个数值组成的范围。
在一些实施方式中，聚合物为颗粒状，聚合物的体积平均粒径为Dv50μm，1≤Dv50≤5。
聚合物的体积平均粒径在上述范围时，其能够在一定程度上溶解于浆料体系中，起到粘结剂和分散剂的作用。示例性地，聚合物的体积平均粒径Dv50μm可以为1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、4.5μm或5μm；或者是上述任意两个数值组成的范围。
在本申请中，材料的体积平均粒径Dv50为本领域公知的含义，其表示材料累计体积分布百分数达到50％时所对应的粒径，可以用本领域公知的仪器及方法进行测试。例如可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测试，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪。
在本申请中，材料的比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测试。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(BrunauerEmmett Teller)法计算得出，氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
制备聚合物的方法
第二方面，本申请提出了一种制备聚合物的方法。所述方法能够制备得到本申请第一方面任一实施方式的聚合物。
所述方法包括：
步骤S100，提供第一单体和包含式(2)所示的结构单元的第二单体；
步骤S200，将第一单体和第二单体在自由基引发剂的存在下，聚合形成聚合物，
其中，第一单体包括偏氟乙烯；式(2)所示的结构单元如下：
Figure PCTCN2022128800-appb-000010
式(2)中，
R 1选自氢原子、卤素原子或者取代或未取代的C1-C10烷基；
R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基。可选地，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C5烷基。
第一单体和第二单体发生共聚形成聚合物，第一单体和第二单体的加入顺序可以根据生产需求进行调整；例如，可以先加入部分第一单体，第一单体之间进行均聚；然后再加入第二单体和第一单体，第一单体、第二单体等进行共聚。或者先加入第一单体，第一单体之间进行共聚；然后加入第二单体，第二单体之间进行共聚；再然后将第一单体共聚后的嵌段聚合物和第二单体共聚后的嵌段聚合物进行聚合。
无论何种聚合方式，其所形成的聚合物均可以以-CH2-CF2-为基本主链，辅以式(2)所示的结构单元，且能够在聚合物的侧链上引入羧基基团，以改善聚合物的粘结性和分散性。本申请的聚合方式较为简便，且所形成的聚合物具有良好的分散性，且同时仍具有一定的粘结性。
聚合物的聚合可以采用悬浮聚合或乳液聚合。悬浮聚合所形成的聚合物上吸附的分散剂的量少，且容易脱除，产品的纯度较高；且后处理工序较为简单。乳液聚合的聚合速率较快，产物分子量相对较高，可以在相对较高的温度下聚合。
悬浮聚合可以采用如下过程：在反应釜内加入一定量的去离子水和分散剂，密闭反应釜，抽取真空，采用惰性气体如氮气置换氧气，再抽真空，充入氮气，使得反应釜内的压力略高于大气压，且使反应釜内的氧气含量达标。搅拌反应釜内的体系，并将温度升高至50℃左右，压力升高至3.5MPa左右。加入部分单体和引发剂等，开始聚合；在聚合过程中，继续加入单体和引发剂等，维持反应釜内的温度及压力，直至单体全部加完，降压至2.8MPa左右，停止搅拌，反应结束。
乳液聚合可以采用如下过程：将反应釜抽真空、采用惰性气体如氮气置换氧气，以使反应釜内的氧气含量达标。在反应釜内投加去离子水、乳化剂和引发剂等，并加入少量的单体；将反应釜加热至反应温度，随着反应的进行，持续加入单体，并保持反应釜内的压力，直至反应结束；在反应过程中，聚合物经过凝聚、洗涤及干燥等过程得到最终的聚合物产品。
在一些实施方式中，步骤S200包括：
步骤S210，将所述第一单体在自由基引发剂的存在下均聚形成第一嵌段聚合物。
第一单体预先均聚形成第一嵌段聚合物能够保证聚合物的分子链为线性主 链，从而保证聚合物的一定的规整性，有利于提升聚合物的结晶能力。
步骤S220，将所述第一单体和所述第二单体以及所述第一嵌段聚合物在自由基引发剂的存在下共聚形成第二嵌段聚合物。
引入第二单体，第一单体和第二单体在第一嵌段聚合物的基础上继续聚合，在聚合物的侧链上引入羧基，以改善聚合物的粘结性和分散性。
步骤S230，将所述第一单体和所述第二嵌段聚合物在自由基引发剂的存在下共聚形成所述聚合物。
在第二嵌段聚合物的基础上，继续进行第一单体的聚合，保证聚合物整体为线性分子链。
在一些实施方式中，基于所述第一单体和所述第二单体的总摩尔量计，所述第二单体的摩尔百分含量与所述第一单体的摩尔百分含量的比值为A，0.10≤A≤0.30。
第一单体和第二单体的总摩尔量是指在整个反应过程中，投加的第一单体的摩尔量以及投加的第二单体的摩尔量的加和。第一单体的摩尔百分含量指第一单体的摩尔量与总摩尔量的百分比。第二单体的摩尔百分含量指第二单体的摩尔量与总摩尔量的百分比。示例性地，第二单体的摩尔百分含量与第一单体的摩尔百分含量的比值A可以为0.10、0.15、0.20、0.25、0.30或是上述任意两个数值组成的范围。
第二单体的摩尔百分含量与第一单体的摩尔百分含量的比值A在上述范围时，既能够保证聚合物的粘结性，又能够保证聚合物的分散性。
在一些实施方式中，可以加入乳化剂和溶剂，以便于乳化聚合。
乳化剂包括全氟辛酸碱金属盐等。
制备导电浆料的方法
第三方面，本申请提出了一种制备导电浆料的方法。
发明人发现，导电剂例如导电炭黑作为电池生产过程中的重要组成部分，其在浆料中的分散性对极片电阻和二次电池的性能影响很大，导电炭黑颗粒尺寸为微米级，比表面积大，极易团聚，传统加料方式是将导电炭黑干粉和正极活性材料直接混合加入溶剂中，机械搅拌难分散均匀，需长时间搅拌制浆，即影响了生产效率，也影响发挥其导电性；相关技术中也有将导电炭黑预制为导电浆料，但是导电浆料中需要额外添加分散剂、表面活性剂等其他添加剂，但不同体系的添加剂不同，在二次电池合浆制备过程中易发生与浆料体系不相容的问题。并且电池生产过程中使用的粘结剂PVDF，分子量在50万至120万，胶液粘度大，导电炭黑均匀分散难度大，极片电阻高。即使延长搅拌时间分散均匀，浆料静置后分散开的炭黑颗粒还会团聚，且浆料还会出现粘度增大，凝胶现象，影响其生产使用。
针对上述问题，发明人提出了一种制备导电浆料的方法，所述方法包括：
将聚合物加入溶剂中混合为预制胶液；
将导电剂分散于所述预制胶液中形成导电浆料，
其中，所述聚合物包括根据本申请第一方面任一实施方式所述的聚合物或根据本申请第二方面任一实施方式所述的方法得到的聚合物。
具体地，可以将聚合物粉末加入溶剂中，混合为预制胶液；然后将导电剂例如导电炭黑分散于预制胶液中，制备形成导电浆料，如此制备得到的导电浆料中的导电剂的分散更为均匀，不会因为导电剂的粒径较小而发生大量团聚等现象，导电剂的分布更为均匀，可以在一定程度上降低正极膜层的电阻，改善二次电池的电化学性能。本申请中，预制胶液中的溶剂可以选用正极浆料中常用的溶剂类型，例如N-甲基吡咯烷酮NMP等。
进一步地，基于导电浆料的总质量计，聚合物的质量含量记为p％，0.5≤q≤2.5。
聚合物的质量含量在上述范围时，能够保证导电剂在聚合物中均匀分散，且导电浆料具有一定的粘度例如大于40mPa*s，导电浆料的稳定性较高，导电剂不容易发生沉降；且导电浆料的粘度适中，基本不会发生粘度反弹产生凝胶等问题，有利于导电浆料的长期保存。示例性地，聚合物的质量含量可以为0.5％、1％、1.5％、2％或2.5％；或者是上述任意两个数值组成的范围。
进一步地，基于导电浆料的总质量计，导电剂的质量含量记为q％，7.5≤q≤15.5。
导电剂的质量含量在上述范围时，能够保证溶剂的含量，从而有利于聚合物的溶解和分散；并且导电剂的用量适中，导电浆料的整体流动性较好，有利于工业化生产中的加料。示例性地，导电剂的质量含量可以为7.5％、8％、8.5％、9％、9.5％、10.5％、11.0％、12.0％、13.0％、13.5％、14.0％、15.0％、15.5％或是上述任意两个数值组成的范围。
更进一步地，2≤q/p≤20。可选地，3≤q/p≤15。示例性地，q/p可以为3、4、5、6、7、8、9、10、12、15、16、18、19、20或是上述任意两个数值组成的范围。q/p在上述范围时，分散剂聚合物对导电剂的分散性能更好，导电剂分散均匀，且所形成的导电浆料性能稳定，在应用于正极极片时，有利于降低正极极片的膜片电阻。
导电浆料
第四方面，本申请提出了一种导电浆料。
所述导电浆料包括导电剂和聚合物，所述聚合物包括根据本申请第一方面任一实施方式所述的聚合物或根据本申请第二方面任一实施方式所述的方法得到的聚合物。
所述导电浆料也可以由本申请第三方面任一实施方式的方法制备得到。
本申请的导电浆料分散性能较好，不易团聚和沉降，在长时间存储过程中能够保证性能均一且稳定。
可选地，基于导电浆料的总质量计，聚合物的质量含量记为p％；基于导电浆料的总质量计，导电剂的质量含量记为q％，2≤q/p≤20，进一步可选地，3≤q/p≤15。
正极极片
第五方面，本申请提出了一种正极极片。
在一些实施方式中，正极极片包括正极集流体以及设置在正极集流体至少一个表面上的正极膜层。例如，正极集流体具有在自身厚度方向相对的两个表面，正极膜层设置于正极集流体的两个相对表面中的任意一者或两者上。所述正极膜层包括本申请第一方面任一实施方式的聚合物或如本申请第二方面任一实施方式制备得到的聚合物。聚合物由于具有良好的分散性能和一定的粘结性能，其可以作为正极膜层中的分散剂，以及粘结剂的辅助用剂。正极膜层中可以不用引入其他的分散剂，降低其他分散剂对正极活性材料造成损伤的风险，保证正极膜层的结构稳定性。
所述正极膜层包括正极活性材料，所述正极活性材料可采用本领域公知的用于二次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：层状结构正极活性材料(例如三元、镍酸锂/钠、钴酸锂/钠、锰酸锂/钠、富锂/钠层状和岩盐相层状等材料)、橄榄石型磷酸盐活性材料、尖晶石结构的正极活性材料(例如尖晶石锰酸锂、尖晶石镍锰酸锂、富锂的尖晶石锰酸锂和镍锰酸锂等)。
示例性地，层状结构正极活性材料的通式为：Li xA yNi aCo bMn cM (1-a-b-c)Y z，其中，0≤x≤2.1，0≤y≤2.1，且0.9≤x+y≤2.1；0≤a≤1，0≤b≤1，0≤c≤1，且0.1≤a+b+c≤1；1.8≤z≤3.5；A选自Na、K、Mg中的一种或几种；M选自B、Mg、Al、Si、P、S、Ca、Sc、Ti、V、Cr、Fe、Cu、Zn、Sr、Y、Zr、Nb、Mo、Cd、Sn、Sb、Te、Ba、Ta、W、Yb、La、Ce中的一种或几种；Y选自O、F中的一种或几种。可选地，y＝0。具体地，层状结构正极活性材料可以包括钴酸锂LCO、镍酸锂LNO、锰酸锂LMO、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)和LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)中的一种或多种。
示例性地，橄榄石型磷酸盐活性材料的通式为：Li xA yMe aM bP 1-cX cY z，其中，0≤x≤1.3，0≤y≤1.3，且0.9≤x+y≤1.3；0.9≤a≤1.5，0≤b≤0.5，且0.9≤a+b≤1.5；0≤c≤0.5；3≤z≤5；A选自Na、K、Mg中的一种或几种；Me选自Mn、Fe、Co、Ni中的一种或几种；M选自B、Mg、Al、Si、P、S、Ca、Sc、Ti、V、Cr、Cu、Zn、Sr、Y、Zr、Nb、Mo、Cd、Sn、Sb、Te、Ba、Ta、W、Yb、La、Ce中的一种或几种；X选自S、Si、Cl、B、C、N中的一种或几种；Y选自O、F中的一种或几种。具体地，橄榄石型磷酸盐活性材料包括LiFePO 4、LiMnPO 4、LiNiPO 4、和LiCoPO 4中的一种或多种。
示例性地，尖晶石结构的正极活性材料的通式为：Li xA yMn aM 2-aY z，其中，0≤x≤2，0≤y≤1，且0.9≤x+y≤2；0.5≤a≤2；3≤z≤5；A选自Na、K、Mg中的一种或几种；M选自Ni、Co、B、Mg、Al、Si、P、S、Ca、Sc、Ti、V、Cr、Fe、Cu、Zn、Sr、Y、Zr、Nb、Mo、Cd、Sn、Sb、Te、Ba、Ta、W、Yb、La、Ce中的一种或几种；Y选自O、F中的一种或几种。具体地，尖晶石结构的正极活性材料包括LiMn 2O 4、LiNi 0.5Mn 1.5O 4、LiCr 0.3Mn 1.7O 4、Li 1.1Al 0.1Mn 1.9O 4、Li 2Mn 2O 4和Li 1.5Mn 2O 4中的一种或多种。
在一些实施方式中，正极集流体可采用金属箔片或复合集流体。作为金属 箔片的示例，可采用铝箔或铝合金箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层，作为示例，金属材料可包括选自铝、铝合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种的组合，高分子材料基层可包括选自聚丙烯(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)和聚乙烯(PE)中的一种或多种的组合。
在一些实施方式中，正极膜层还可选地包括正极导电剂。本申请对正极导电剂的种类没有特别的限制，作为示例，正极导电剂包括选自超导碳、导电炭黑、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的一种或多种的组合。在一些实施方式中，基于正极膜层的总质量，正极导电剂的质量百分含量在5％以下。
在一些实施方式中，正极膜层还可选地包括正极粘结剂。本申请对正极粘结剂的种类没有特别的限制，作为示例，正极粘结剂可包括选自聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物和含氟丙烯酸酯类树脂中的一种或多种的组合。在一些实施方式中，基于正极膜层的总质量，正极粘结剂的质量百分含量在5％以下；可选地，正极粘结剂的质量百分含量为1.0％至2.5％。在本申请中，正极粘结剂的分子量为50万至200万，例如正极粘结剂所采用的聚偏氟乙烯PVDF的分子量为50万至200万，本申请第一方面所述的实施方式中的聚合物可以作为正极粘结剂的辅助用剂，能够改善正极膜层的粘结性能，并能够降低正极活性材料发生团聚的风险。
正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。
在一些实施方式中，正极极片经以下步骤制备得到：提供正极集流体；将正极活性材料、聚合物、导电剂和粘结剂加入溶剂中混合为正极活性浆料，将正极活性浆料涂覆于正极集流体上，经固化形成正极极片。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
在一些实施方式中，可以将导电剂预先制备为导电浆料，然后将导电浆料和正极活性材料混合为正极浆料。导电浆料可以采用本申请第三方面任一实施方式的方法制备得到的导电浆料，也可以采用本申请第四方面任一实施方式的导电浆料。或者直接采用本申请第一方面任一实施方式所述的聚合物或根据本申请第二方面任一实施方式所述的方法得到的聚合物，制备导电浆料。
具体地，可以将聚合物粉末加入溶剂中，混合为预制胶液；然后将导电剂例如导电炭黑分散于预制胶液中，制备形成导电浆料，然后将正极活性材料、正极粘结剂等分散于导电浆料中制备形成正极浆料；如此制备得到的导电浆料中的导电剂的分散更为均匀，不会因为导电剂的粒径较小而发生大量团聚等现象，导电剂的分布更为均匀，可以在一定程度上降低正极膜层的电阻，改善二次电池的电化学性能。本申 请中，预制胶液中的溶剂可以选用正极浆料中常用的溶剂类型，例如N-甲基吡咯烷酮NMP等。
二次电池
第六方面，本申请提出了一种二次电池。
所述二次电池包括正极极片、负极极片和隔离膜，隔离膜设置于正极极片和负极极片之间，以起到隔绝正极极片和负极极片的作用。
在一些实施方式中，所述正极极片可以采用本申请第五方面任一实施方式的正极极片，由此能够降低极片电阻，改善二次电池的循环性能和充放电性能。
负极极片
所述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。所述负极膜层包括本申请第一方面任一实施方式的聚合物或如本申请第二方面任一实施方式制备得到的聚合物。聚合物由于具有良好的分散性能和一定的粘结性能，其可以作为负极膜层中的分散剂，以及粘结剂的辅助用剂。负极膜层中可以不用引入其他的分散剂，降低其他分散剂对负极活性材料造成损伤的风险，保证负极膜层的结构稳定性。
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导电剂。导电剂可选自超导碳、乙炔黑、导电炭黑、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，负极膜层还可选地包括负极粘结剂。所述负极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，基于负极膜层的总质量，负极粘结剂的质量百分含量在5％以下；可选地，负极粘结剂的质量百分含量为1.5％至3％。在本申请中，负极粘结剂的分子量为50万至200万，例如负极粘结剂所采用的丁苯橡胶SBR的分子量为50万至200万，本申请第一方面所述的实施方式中的聚合物可以作为丁苯橡胶粘结剂的辅助用剂，能够改善负极膜层的粘结粒度，并能够降低丁苯橡胶活性材料发生团聚的风险。
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、可选的导电剂、可选的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]
二次电池还包括电解质，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。
作为示例，锂盐可包括选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)和四氟草酸磷酸锂(LiTFOP)中的一种或多种的组合。
作为示例，有机溶剂可包括选自碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)和二乙砜(ESE)中的一种或多种的组合。
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，隔离膜的材质可以包括选自玻璃纤维、无纺布、聚乙 烯、聚丙烯和聚偏二氟乙烯中的一种或多种的组合。隔离膜可以是单层薄膜，也可以是多层复合薄膜。当隔离膜为多层复合薄膜时，各层的材料相同或不同。
在一些实施方式中，正极极片、隔离膜和负极极片可通过卷绕工艺或叠片工艺制成电极组件。
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。如图1是作为一个示例的方形结构的二次电池5。
在一些实施例中，如图1和图2所示，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用于盖设开口，以封闭容纳腔。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封装于容纳腔。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，可根据需求来调节。
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
在本申请的一些实施例中，根据本申请的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多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4的示意图。如图3所示，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。
在一些实施例中，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根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，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用于盖设下箱体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
第七方面，本申请提供一种用电装置，用电装置包括本申请的二次电池、电池模块和电池包中的至少一种。二次电池、电池模块和电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
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的示意图。该用电装置6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高功率和高能量密度的需求，可以采用电池包1或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电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
分散剂聚偏氟乙烯的制备
实施例1-1
步骤S1，将30Kg的去离子水(电导率小于等于2μs/cm)、100％的乳化剂全氟辛酸碱金属盐15g、占总量40％的引发剂(5％浓度的过硫酸钾溶液)36g依次加入50L反应釜内，关闭反应釜；
步骤S2，反应釜内抽真空，充氮气，重复操作至反应釜内氧气浓度小于100ppm；
步骤S3，向反应釜内通入偏氟乙烯单体至反应釜内压力为7.0MPa；
步骤S4，反应釜内升温至80℃开始反应，反应过程中不断通入偏氟乙烯单体维持反应釜内反应压力不变；
步骤S5，通入偏氟乙烯单体占总量的50％即2.4Kg时，加入占总量40％的引发剂(5％浓度的过硫酸钾溶液)36g，维持反应压力7.0MPa向反应釜内通入偏氟乙烯单体和第二单体混合气体(偏氟乙烯单体和第二单体甲基丙烯酸单体按质量比1：1同时加入)；
步骤S6，第二单体1.2Kg全部加入，偏氟乙烯加入量占总量的80％即3.6Kg时，加入剩余20％的引发剂18g，维持反应压力7.0MPa向反应釜内通入剩余的20％偏氟乙烯单体1.2Kg；
步骤S7，反应完成时反应釜内压力将至2.0MPa，回收未反应的偏氟乙烯单体；
步骤S8，反应产物经凝聚、洗涤、分离、干燥、粉碎得到聚合物PVDF。
实施例1-2和实施例1-3
实施例1-2和实施例1-3按照实施例1-1类似的方法制备分散剂PVDF，与
实施例1-1不同的是，实施例1-2和实施例1-3调整了第二单体的摩尔比。
实施例1-4和实施例1-5
实施例1-4和实施例1-5按照实施例1-1类似的方法制备分散剂PVDF，与
实施例1-1不同的是，实施例1-4和实施例1-5调整了步骤S4的反应温度和步骤S3的反应压力中的至少一者。
实施例1-6
实施例1-6按照实施例1-1类似的方法制备分散剂PVDF，与实施例1-1不同的是，实施例1-6调整了第二单体的种类。
实施例1-7至实施例1-9
实施例1-7至实施例1-9按照实施例1-1类似的方法制备分散剂PVDF，与
实施例1-1不同的是，实施例1-7至实施例1-9通过调整引发剂的用量调整反应速率，从而调整聚合物的粒径，例如：相较于实施例1-1，实施例1-7中引发剂量增加10％；
实施例1-8中引发剂量增加5％；实施例1-9中引发剂量增加2％。
实施例1-1至实施例1-9的各参数如表1所示。
表1
Figure PCTCN2022128800-appb-000011
实施例2
实施例2-1
1、正极极片的制备
1.1采用厚度为12μm的铝箔作为正极集流体。
1.2导电浆料的制备
将溶剂氮甲基吡咯烷酮16000g加入至搅拌罐内；
将实施例1-1所制备的分散剂PVDF 300g加入搅拌罐的溶剂NMP内，在室温下，以1000rpm的转速搅拌60min，得到预制胶液；
经1600g导电炭黑粉末加入预制胶液中，以800rpm的转速搅拌60min，搅拌罐开启冷却水循环，搅拌结束后得到导电浆料。
1.3正极浆料的制备
将正极活性材料(LiNi 0.6Co 0.2Mn 0.2O 2)、聚偏二氟乙烯加入导电浆料中充分搅拌混合，形成均匀的正极浆料，正极浆料的固含量为73％；将正极浆料均匀涂覆于正极集流体铝箔的表面上，经干燥、冷压后，得到正极极片。其中，聚四氟乙烯(PTFE)的分子量为80万。其中，正极活性材料、导电炭黑粉末、聚偏二氟乙烯、NMP的质量比为96.9:2.1:1:21。
2、负极极片的制备
采用厚度为8μm的铜箔作为负极集流体。
将负极活性材料石墨、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)、导电剂炭黑(Super P)按重量比96.2:1.8:1.2:0.8在适量的溶剂去离子水中充分搅拌混合，形成均匀的负极浆料；将负极浆料均匀涂覆于负极集流体铜箔的表面上，经干燥、冷压后，得到负极极片。
3、隔离膜
采用多孔聚乙烯(PE)膜作为隔离膜。
4、电解液的制备
在含水量小于10ppm的环境下，将非水有机溶剂碳酸乙烯酯EC、碳酸二乙酯DMC按照体积比1:1进行混合得到电解液溶剂，随后将锂盐和混合后的溶剂混合，配置成锂盐浓度为1mol/L的电解液。
5、二次电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正极极片和负极极片之间起到隔离作用，然后卷绕得到电极组件；将电极组件置于外包装壳中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到锂离子电池。
实施例2-2至实施例2-9
实施例2-2至实施例2-9按照实施例2-1类似的方法制备二次电池，与实施例2-1不同的是，实施例2-2至实施例2-9调整了分散剂PVDF的种类，分别采用实施例1-2至实施例1-9制备的分散剂PVDF。
实施例2-10至实施例2-13
实施例2-10至实施例2-13按照实施例2-1类似的方法制备二次电池，与实施例2-1不同的是，实施例2-10至实施例2-13调整了分散剂PVDF的用量。
对比例
对比例按照实施例2-1类似的方法制备二次电池，与实施例2-1不同的是，对比例调整了正极浆料的制备方法，具体如下：将正极活性材料(LiNi 0.6Co 0.2Mn 0.2O 2)、导电炭黑粉末、聚偏二氟乙烯、NMP按质量比为96.9:2.1:1:21充分搅拌混合，形成均匀的正极浆料；将正极浆料均匀涂覆于正极集流体铝箔的表面上，经干燥、冷压后，得到正极极片。
实施例2-1至实施例2-13以及对比例的各参数如表2所示。
测试部分
一、聚合物的性能测试
1、聚合物重均分子量测试
采用Waters 2695 Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。以质量分数为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％的聚合物溶液，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。待示数稳定后获取数据，读取重均分子量。
2、导电浆料的粘度测试
使用旋转粘度剂测量导电浆料的粘度。选取合适的转子，固定好粘度计转子，将导电浆料放置于粘度计转子下方，导电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：12转/分钟，测试温度：25℃，测试时间为5分钟，待示数稳定读取数据。
3、导电浆料的过滤性能测试
取500ml烧杯置于200目滤网支架下端，取导电浆料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”。
4、导电浆料静置24小时之后上/下层固含量的差值
取小片极片于水分测定仪内称重，记为M0，清零；取上层导电浆料，少量涂覆与极片上，然后放入水分测定仪内称重，记为M1；合上设备，开始烘干；结束后，记录称重数据，记录为M2，并计算固含量，固含量为(M2-M0)/(M1-M0)；以同样的方法测量下层导电浆料的固含量，以下层导电浆料的固含量减上层导电浆料的固含量作为导电浆料静置24小时之后上/下层固含量的差值。
二、二次电池性能测试
5、正极极片的粘结力
参考GB-T2790-1995国标《胶粘剂180°剥离强度实验方法》，实施例和对比例的粘结力测试过程如下：用刀片截取宽度为30mm，长度为100-160mm的试样，将专用双面胶贴于钢板上，胶带宽度20mm，长度90-150mm。将前面截取的极片试样的绝缘涂层面贴在双面胶上，后用2kg压辊沿同一个方向滚压三次。将宽度与极片等宽，长度为250mm的纸带固定于集流体上，并且用皱纹胶固定。打开三思拉力机电源(灵敏度为1N)，指示灯亮，调整限位块到合适位置，将钢板未贴极片的一端用下夹具固定。将纸带向上翻折，用上夹具固定，利用拉力机附带的手动控制器上的“上行”和“下行”按钮调整上夹具的位置。然后进行测试并读取数值，拉伸速度为50mm/min。将极片受力平衡时的力除以胶带的宽度作为单位长度的正极膜层的粘结力，以表征正极膜层与集流体之间的粘结强度。
6、正极极片的膜片电阻
在正极极片左、中、右处裁剪烘干后的极片，裁剪为3mm直径的小圆片。开启元能科技极片电阻仪电源，将其置于极片电阻仪“探头”合适位置，点击“开始”按钮，待示数稳定，读取即可。每个小圆片测试两个位置，最后计算六次测量的平均值，即为该极片的膜层电阻。
7、二次电池直流阻抗DCR(Ω)
二次电池直流阻抗测试过程如下：在25℃下，将实施例1对应的电池，以1/3*C恒流充电至4.3V，再以4.3V恒定电压充电至电流为0.05C，搁置5min后，记录电压V1。然后再以1/3C放电30s，记录电压V2，则3*(V2-V1)/C，得到二次电池的内阻DCR。
测试结果
本申请改善二次电池的性能的作用如表2所示。
表2
Figure PCTCN2022128800-appb-000012
由表2可知，对比例采用导电炭黑粉末直接与正极活性材料混合为正极浆料，导电炭黑发生团聚的风险较高，使得极片电阻较高，动力学性能相对较差。而本申请实施例2-1至实施例2-9将导电炭黑粉末预先制备为导电浆料，聚合物作为分散剂可以有效地将导电炭黑粉末均匀分散，使得导电浆料的分散性能较好，且不容易发生沉降，性能较为均一。在将导电浆料和正极活性材料混合为正极浆料时，可以改善正极极片的电阻，改善正极极片的动力学性能。并且由于聚合物带有一定的粘性，可以辅助提高正极极片内的粘结力。且实施例的存储性能较为稳定，静置24h后不易发生凝胶沉降，在存储60天(60D)后仍不发生凝胶沉降。
实施例2-10至实施例2-13通过调节分散剂聚合物的用量，可以调整对导电剂的分散程度，降低极片电阻，且可以在一定程度上调控粘度，调节极片内的粘结强度。
虽然已经参考优选实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件，尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (20)

  1. 一种聚合物，包括式(1)所示的结构单元和式(2)所示的结构单元，
    Figure PCTCN2022128800-appb-100001
    式(2)中，
    R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基。
  2. 根据权利要求1所述的聚合物，其中，R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C5烷基。
  3. 根据权利要求1或2所述的聚合物，其中，所述式(2)所示的结构单元包括式(2-1)至式(2-10)所示的结构单元中的一种或多种：
    Figure PCTCN2022128800-appb-100002
    Figure PCTCN2022128800-appb-100003
  4. 根据权利要求1至3中任一项所述的聚合物，其中，所述聚合物满足条件(I)至条件(III)中的至少一条：
    (I)所述聚合物的重均分子量为1.5×10 5Da至2.0×10 5Da；
    (II)所述式(1)所示的结构单元的数量为n，100≤n≤150；
    (III)所述式(2)所示的结构单元的数量为m，100≤m≤150。
  5. 根据权利要求1至4中任一项所述的聚合物，其中，所述聚合物满足条件(1)至条件(3)中的至少一条：
    (1)所述聚合物的粘度为C mPa*s，500≤C≤3000；
    (2)所述聚合物的玻璃化转变温度Tg℃，150≤Tg≤180；
    (3)所述聚合物于差示扫描量热仪DSC测试下的结晶度为40％至50％。
  6. 根据权利要求1至5中任一项所述的聚合物，其中，所述聚合物为颗粒状；所述聚合物的体积平均粒径为Dv50μm，1≤Dv50≤5。
  7. 一种制备聚合物的方法，包括：
    提供第一单体和包含式(2)所示的结构单元的第二单体；
    将所述第一单体和所述第二单体在自由基引发剂的存在下，聚合形成聚合物，其中，
    所述第一单体包括偏氟乙烯；
    所述式(2)所示的结构单元如下：
    Figure PCTCN2022128800-appb-100004
    式(2)中，
    R 1、R 2和R 3各自独立地选自氢原子、卤素原子或者取代或未取代的C1-C10烷基。
  8. 根据权利要求7所述的方法，其中，所述将所述第一单体和所述第二单体在自由基引发剂的存在下，聚合形成聚合物的步骤，包括：
    将所述第一单体在自由基引发剂的存在下均聚形成第一嵌段聚合物；
    将所述第一单体和所述第二单体以及所述第一嵌段聚合物在自由基引发剂的存在下共聚形成第二嵌段聚合物；
    将所述第一单体和所述第二嵌段聚合物在自由基引发剂的存在下共聚形成所述聚合物。
  9. 根据权利要求7或8所述的方法，其中，基于所述第一单体和所述第二单体的总摩尔量计，所述第二单体的摩尔百分含量与所述第一单体的摩尔百分含量的比值为A，0.10≤A≤0.30。
  10. 一种制备导电浆料的方法，包括：
    将聚合物加入溶剂中混合为预制胶液；
    将导电剂分散于所述预制胶液中形成导电浆料，
    其中，所述聚合物包括根据权利要求1至6中任一项所述的聚合物或根据权利要求7至9中任一项所述的方法得到的聚合物。
  11. 根据权利要求10所述的方法，其中，
    基于所述导电浆料的总质量计，所述聚合物的质量含量记为p％；
    基于所述导电浆料的总质量计，所述导电剂的质量含量记为q％，
    2≤q/p≤20。
  12. 根据权利要求11所述的方法，其中，3≤q/p≤15。
  13. 一种导电浆料，包括导电剂和聚合物，所述聚合物包括根据权利要求1至6中 任一项所述的聚合物或根据权利要求7至9中任一项所述的方法得到的聚合物。
  14. 根据权利要求13所述的导电浆料，其中，
    基于所述导电浆料的总质量计，所述聚合物的质量含量记为p％；
    基于所述导电浆料的总质量计，所述导电剂的质量含量记为q％，
    2≤q/p≤20。
  15. 根据权利要求14所述的导电浆料，其中，3≤q/p≤15。
  16. 一种制备正极极片的方法，包括：
    提供正极集流体；
    将正极活性材料、聚合物、导电剂和粘结剂加入溶剂中混合为正极浆料，将所述正极浆料涂覆于所述正极集流体上，经固化形成正极极片；其中，所述聚合物包括根据权利要求1至6中任一项所述的聚合物或根据权利要求7至9中任一项所述的方法得到的聚合物。
  17. 根据权利要求16所述的方法，其中，所述将正极活性材料、聚合物、导电剂和粘结剂加入溶剂中混合为正极浆料的步骤，包括：
    将所述聚合物加入溶剂中混合为预制胶液；
    将所述导电剂分散于所述预制胶液中形成导电浆料；
    将所述导电浆料和所述正极活性材料混合为正极浆料。
  18. 一种正极极片，由如权利要求16或17所述的方法制备得到。
  19. 一种二次电池，包括根据权利要求18所述的正极极片。
  20. 一种用电装置，包括根据权利要求19所述的二次电池。
PCT/CN2022/128800 2022-10-17 2022-10-31 聚合物、导电浆料、正极极片、二次电池和用电装置 WO2024082336A1 (zh)

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