WO2024045471A1 - Polymère ayant une structure noyau-enveloppe et son procédé de préparation et son utilisation, pâte d'électrode positive, batterie secondaire, module de batterie, bloc-batterie et dispositif électrique - Google Patents

Polymère ayant une structure noyau-enveloppe et son procédé de préparation et son utilisation, pâte d'électrode positive, batterie secondaire, module de batterie, bloc-batterie et dispositif électrique Download PDF

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WO2024045471A1
WO2024045471A1 PCT/CN2023/071572 CN2023071572W WO2024045471A1 WO 2024045471 A1 WO2024045471 A1 WO 2024045471A1 CN 2023071572 W CN2023071572 W CN 2023071572W WO 2024045471 A1 WO2024045471 A1 WO 2024045471A1
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core
shell structure
positive electrode
polymer
structure polymer
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PCT/CN2023/071572
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Chinese (zh)
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李�诚
曾子鹏
刘会会
王景明
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宁德时代新能源科技股份有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 secondary batteries, and in particular to a core-shell structure polymer, preparation methods and uses, positive electrode slurry, secondary batteries, battery modules, battery packs and electrical devices.
  • secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields. Due to the great development of lithium-ion batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance.
  • PVDF polyvinylidene fluoride
  • This application was made in view of the above problems, and its purpose is to provide a core-shell structure polymer including: a core part, which is a fluorine-containing polymer containing a structural unit derived from the monomer represented by Formula I. ; And a shell part, the shell part is a non-fluoropolymer containing structural units derived from the monomers represented by formula II and formula III, the shell part at least partially covers the surface of the core part,
  • R 1 and R 2 are each independently selected from hydrogen, fluorine, chlorine or at least one fluoro-substituted C 1-3 alkyl group;
  • R 3 , R 4 and R 5 are each independently selected from hydrogen or substituted or unsubstituted C 1-5 alkyl.
  • the core-shell structure polymer can improve the flexibility of the binder, improve the flexibility of the pole piece and the safety performance of the battery; at the same time, it can also ensure the adhesive force of the pole piece, thereby ensuring the performance and service life of the battery.
  • the core-shell structure polymer helps to improve the dispersion of the cathode slurry, which can reduce the resistance of the electrode sheet film and improve the battery cycle performance.
  • the core-shell structure polymer is used in combination with a binder, the flexibility of the pole piece and the dispersion of the slurry can be improved at the same time, and the pole piece has good bonding properties.
  • R 1 and R 2 are each independently selected from hydrogen, fluorine, or at least one fluoro-substituted C 1-3 alkyl group.
  • the core in the core-shell polymer contains structural units derived from the monomer represented by Formula I.
  • a fluoropolymer, and R 1 and R 2 are each independently selected from hydrogen, fluorine or at least one fluorine-substituted C 1-3 alkyl group, which can reduce the viscosity of the positive electrode slurry and the resistance of the positive electrode film layer, and improve the resistance of the electrode piece.
  • the bonding force and the number of rolling cycles can be improved, as well as the capacity retention rate of the battery after 500 cycles.
  • the mass content of the core part is 5% to 9%, and the mass content of the shell part is 91% to 95%, based on the total mass of the core-shell structure polymer.
  • the content of the core and shell is within this range, it can increase the plastic strain stress of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery, and ensuring that the pole piece has sufficient adhesion, thereby ensuring Battery performance and lifespan.
  • the molar content of the structural units derived from the monomer represented by Formula II is 20% to 50%, based on the total molar amount of the non-fluoropolymer.
  • the core-shell structure polymer within this content range can ensure that the pole piece has good flexibility, thereby ensuring that the battery has excellent electrical performance and cycle performance while improving safety performance.
  • non-fluoropolymer further includes structural units derived from monomers represented by Formula IV,
  • R 6 is selected from amide group or cyano group
  • R 7 is selected from hydrogen, substituted or unsubstituted C 1-5 alkyl group.
  • the polar group contained in the monomer represented by formula IV can form better adsorption performance or affinity with the positive electrode active material, which helps to improve the agglomeration of the positive electrode active material, thereby improving the slurry It improves the stability of the material, improves the processing performance of the pole piece and improves the film resistance of the pole piece.
  • the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 50%, based on the total molar amount of the non-fluoropolymer.
  • the mass content of the monomer shown in Formula IV within a suitable range can have sufficient adsorption performance or affinity for the positive electrode active material, effectively improve the dispersion of the slurry, thereby reducing the electrode sheet film resistance and improving battery cycle performance.
  • the weight average molecular weight of the fluorine-containing polymer is 20,000 to 200,000.
  • the weight average molecular weight of the fluorine-containing polymer is 20,000 to 150,000.
  • the fluoropolymer is polyvinylidene fluoride or a modified polymer thereof;
  • the non-fluoropolymer is a copolymer of styrene and tert-butyl acrylate, acrylonitrile, styrene and Copolymer of tert-butyl acrylate, one or a combination of copolymers of acrylamide, styrene and methyl acrylate.
  • the fluorine-containing polymer has stable chemical properties, excellent electrical properties, and good mechanical properties.
  • the non-fluorine polymer has relatively soft chain segments, which can significantly improve the flexibility of the binder and the plastic strain stress of the pole piece film layer, thereby improving the flexibility of the pole piece; at the same time, the polar functional groups of the non-fluorine polymer It also has good adsorption performance and/or affinity, and can be stably attached to the surface of cathode active materials including lithium iron phosphate and lithium nickel cobalt manganese oxide, thereby improving the dispersion of the slurry and the film resistance of the pole piece, and thus Improve battery cycle performance.
  • the core-shell structure polymer has a median particle diameter Dv50 of 2 ⁇ m to 10 ⁇ m.
  • the particle size of the core-shell structure polymer within a suitable range is beneficial to dissolution in the positive electrode slurry solvent, such as N-methylpyrrolidone, reducing the processing difficulty of the binder glue and improving battery processing efficiency.
  • the viscosity of the glue solution is 50-180 mPa ⁇ s.
  • the core-shell structure The polymer is dissolved in N-methylpyrrolidone to prepare a glue solution.
  • a core-shell structure polymer with a mass ratio of core and shell within a suitable range can have both good flexibility and adsorption of positive electrode active materials, which can improve the uniformity of the slurry coating on the pole piece and improve the pole piece. Flexibility, while taking into account the bonding performance of the adhesive, reducing battery safety hazards and improving the long-term cycle performance of the battery.
  • the second aspect of the application also provides a method for preparing a core-shell structure polymer, including:
  • Preparing the core part at least one monomer represented by the following formula I is polymerized under the first polymerization condition to obtain an emulsion of fluorine-containing polymer;
  • Preparing a core-shell structure polymer The emulsion of the fluorine-containing polymer and at least two monomers represented by the following formula V are polymerized under the second polymerization condition to prepare a non-fluorine polymer, and the non-fluorine polymer is polymerized as a core-shell structure
  • the shell part of the object at least partially covers the surface of the core part;
  • R 1 and R 2 are each independently selected from hydrogen, fluorine, chlorine or C 1-3 alkyl substituted by at least one fluoro group;
  • R 8 and R 9 are each independently selected from hydrogen, amide group, cyano group, substituted or unsubstituted phenyl group, or -CO 2 R 10 ; R 10 is selected from substituted or unsubstituted C 1-5 alkyl group.
  • the polymerization conditions in this preparation method are safe and controllable, which is beneficial to the continuous production of the core-shell structure polymer.
  • the core-shell structure polymer can improve the flexibility of the binder, improve the flexibility of the pole piece and the safety performance of the battery; at the same time, it can also ensure the adhesive force of the pole piece, thereby ensuring the performance and service life of the battery.
  • the core-shell structure polymer prepared by this method has good affinity and/or adsorption properties for the cathode active material, which can help the cathode active material disperse in the slurry; and can also reduce the direct contact between the cathode active material and the electrolyte. contact, thereby improving the long-term cycle performance of the battery.
  • the preparation of the non-fluoropolymer under the second polymerization conditions includes the following steps:
  • the emulsion of the fluorine-containing polymer, at least two monomers represented by formula V and the second initiator are swollen in the second solvent, and polymerization ligands and catalysts are added to perform the polymerization reaction.
  • the preparation of the non-fluoropolymer under the second polymerization conditions includes the following steps:
  • the dispersed fluoropolymer emulsion, at least two monomers represented by formula V and the second initiator are swollen in the second solvent for 0.5 hours to 2 After an hour, the polymerization ligand and catalyst are added, and the polymerization reaction is carried out for 1 to 5 hours.
  • the preparation method of the polymer shell has low raw material cost and mild reaction conditions, and can obtain a core-shell structure polymer with a specific and stable structure.
  • preparing the fluoropolymer under first polymerization conditions includes the steps of:
  • the preparation method of the polymer core has low raw material costs, relatively small environmental hazards to the reagents, and mild reaction conditions, which is conducive to the expanded production of the core.
  • a third aspect of the application also provides a cathode slurry, including a cathode active material, a conductive agent, a binder and the core-shell structure polymer described in the first aspect of the application.
  • the positive electrode slurry has good bonding performance, dispersibility and processability, which is beneficial to the processing of the electrode piece.
  • the positive active material is a lithium-containing transition metal oxide with a carbon coating layer on the surface.
  • the lithium-containing transition metal oxide can be selected from lithium iron phosphate and lithium nickel cobalt manganese oxide. one or more of them.
  • the carbon coating layer on the surface of the cathode active material can form a physical barrier to prevent or reduce the chemical erosion of the cathode active material by the electrolyte, thereby reducing the dissolution of transition metals; and it can also promote electronic and/or ion conductivity and improve conductive performance.
  • the graphitization degree of the carbon coating layer is 0.2% to 0.35%, optionally 0.2% to 0.3%.
  • Controlling the graphitization degree of the carbon coating layer of the cathode active material within an appropriate range can make the cathode active material have appropriate conductivity, corrosion resistance and machining performance, and help improve the processing performance of the slurry and the performance of the pole piece. Conductive properties and long-term cycle performance of secondary batteries.
  • the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is 1% to 3%, optionally 1.4 % ⁇ 2.4%.
  • the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is within a suitable range, which helps to balance the bonding performance of the slurry and the flexibility of the pole piece.
  • the mass ratio of the core-shell structure polymer and the binder is 0.05-5, optionally 0.5-2.
  • the mass ratio of the core-shell structure polymer and the binder within an appropriate range helps to balance the dispersion of the cathode slurry and the flexibility of the pole piece, reduces the use of other additives in the slurry, and helps Improve the loading capacity of the positive active material of the pole piece and the energy density of the battery.
  • the viscosity of the cathode slurry is 5000-50000 mPa ⁇ s, optionally 5000-32000 mPa ⁇ s, and the viscosity of the cathode slurry is
  • the optional solvent used is N-methylpyrrolidone.
  • the viscosity of the positive electrode slurry within a suitable range helps to improve the processability of the pole piece and the bonding performance of the pole piece film layer.
  • the binder is polyvinylidene fluoride or a modified polymer thereof, and the weight average molecular weight of the binder is 700,000 to 1.1 million.
  • the adhesive has good compatibility with the core-shell structure polymer provided in this application, and can maintain good bonding performance while improving flexibility.
  • a fourth aspect of the application also provides an application of the core-shell structure polymer described in the first aspect of the application or the core-shell structure polymer prepared by the method described in the second aspect of the application in secondary batteries.
  • the core-shell structure polymer can improve the dispersion, stability and processability of the cathode slurry, improve the flexibility of the pole piece, and improve the processing performance and battery cycle performance of the pole piece.
  • a fifth aspect of the present application provides a secondary battery, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte.
  • the positive electrode sheet includes a positive electrode current collector and a battery disposed on at least one surface of the positive electrode current collector.
  • the positive electrode film layer is prepared from the positive electrode slurry described in the third aspect of the present application; optionally, the secondary battery is a lithium ion battery.
  • the bonding force per unit length between the positive electrode film layer and the positive electrode current collector is 10 N/m to 35 N/m.
  • the positive electrode film layer of the electrode piece has high bonding strength with the positive electrode current collector. During use, the positive electrode film layer is not easily detached from the positive electrode current collector, which helps to improve the cycle performance and safety of the battery.
  • the membrane resistance of the positive electrode piece is 0.4 ⁇ ⁇ 1 ⁇ .
  • the electrode piece has low diaphragm resistance, indicating that the materials in the positive electrode film layer are evenly dispersed, and the positive electrode film layer has good electron transmission efficiency, which is conducive to the performance of the battery.
  • the positive electrode piece after the positive electrode piece undergoes no less than 2.3 bending tests, the positive electrode piece appears to be light-transmissive.
  • the pole piece can pass no less than 2.3 bending tests, indicating that the pole piece has good flexibility and is not prone to cracking during the production process or brittle fracture during use, which helps improve the battery's performance. Yield rate and improve battery safety performance.
  • a sixth aspect of the present application provides a battery module including the secondary battery of the fifth aspect of the present application.
  • a seventh aspect of the present application provides a battery pack, including the battery module of the sixth aspect of the present application.
  • An eighth aspect of the present application provides an electrical device, including at least one selected from the secondary battery of the fifth aspect of the present application, the battery module of the sixth aspect of the present application, or the battery pack of the seventh aspect of the present application. kind.
  • Figure 1 is a schematic diagram of the core-shell structure polymer of the present application.
  • Figure 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • Figure 3 is an exploded view of the secondary battery according to an embodiment of the present application shown in Figure 2;
  • FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 5;
  • FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • Cathode active materials such as lithium iron phosphate, often have characteristics such as large specific surface area and small particle size. After coating treatment, they have poor compatibility with the binder, causing the prepared slurry to agglomerate and block the filter. Using this The surface of the pole piece prepared from the slurry is prone to defects such as cracking, peeling, particle scratches, pinholes, etc., and due to the uneven distribution of the positive active material in the pole piece, the film layer resistance is high and the cycle performance of the battery is reduced.
  • the electrode film layer at the corner of the innermost cathode is easily broken due to insufficient tensile strength, causing the electrode piece to transmit light, thereby causing the electrode piece to be brittle (or brittle). problem and reduce the safety of the battery.
  • the brittleness of the pole piece will also cause the positive active material to come into direct contact with the electrolyte, which will then be chemically corroded and reduce the cycle performance of the battery.
  • this application proposes a core-shell structure polymer, including: a core part, which is a fluoropolymer containing structural units derived from the monomer shown in Formula I; and a shell part, which The shell part is a non-fluorine polymer containing structural units derived from monomers represented by Formula II and Formula III, and the shell part at least partially covers the surface of the core part,
  • R 1 and R 2 are each independently selected from hydrogen, fluorine, chlorine or at least one fluoro-substituted C 1-3 alkyl group;
  • R 3 , R 4 and R 5 are each independently selected from hydrogen or substituted or unsubstituted C 1-5 alkyl.
  • polymer includes on the one hand an assembly of macromolecules that are chemically homogeneous but differ in degree of polymerization, molar mass and chain length, prepared by polymerization reactions.
  • the term on the other hand also includes derivatives of aggregates of macromolecules formed by polymerization reactions which are obtainable by reaction, for example addition or substitution, of functional groups in said macromolecules and which may be chemically homogeneous or chemically non-uniform compounds.
  • substituted means that at least one hydrogen atom of the compound or chemical moiety is replaced by a substituent of another chemical moiety, where each substituent is independently selected from: hydroxyl, mercapto, amino, cyano , nitro group, aldehyde group, halogen atom, alkenyl group, alkynyl group, aryl group, heteroaryl group, C 1-3 alkyl group or C 1-3 alkoxy group.
  • C 1-5 alkyl refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturated bonds present in the group, and having from one to five carbon atoms, And attached to the rest of the molecule by a single bond, exemplary C 1-5 alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n-pentyl.
  • C 1-3 alkyl refers to a straight or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, with no unsaturated bonds present in the group, and having from one to three carbon atoms, And attached to the rest of the molecule by a single bond, exemplary C 1-3 alkyl groups such as methyl, ethyl, propyl, isopropyl.
  • C 1-3 alkoxy refers to a group formed by connecting a saturated alkyl group with one to three carbon atoms to an oxygen atom.
  • Exemplary C 1-3 alkoxy groups such as methoxy , ethoxy.
  • weight average molecular weight refers to the sum of the weight fractions of molecules of different molecular weights in the polymer multiplied by their corresponding molecular weights.
  • core-shell polymer can have the same meaning as “core-shell polymer” and "core-shell polymer”, which means that the core and the shell are respectively enriched by two or more polymers.
  • the force between the core and the shell is not limited to chemical cross-linking, but may also include physical deposition, hydrogen bonding force, etc.
  • the schematic diagram of the core-shell structure polymer 6 is shown in FIG. 1 .
  • the core portion 61 is inside the core-shell structure polymer 6 , and the outer periphery of the core portion 61 is wrapped with a shell portion 62 .
  • the fluoro-substituted C 1-3 alkyl group is selected from -CF 3 , -CHF 2 , CH 3 CF 3 -, CH 3 CHF 2 -, or C 2 F 6 -. In some embodiments, the fluoro-substituted C 1-3 alkyl is -CF 3 (or trifluoromethyl).
  • R 1 and R 2 are each independently selected from hydrogen, fluorine, or at least one fluoro-substituted C 1-3 alkyl group.
  • the weight average molecular weight of the fluoropolymer in the core is 20,000 to 200,000, optionally 20,000 to 150,000.
  • the weight average molecular weight of the core polymer can be measured using measurement methods commonly used in this field, or using methods such as those in the examples.
  • the molecular weight of the non-fluorine polymer in the shell part can be estimated based on the degree of polymerization or the molecular weight can be theoretically calculated.
  • the degree of polymerization is a measure of the size of the polymer molecules. Based on the number of repeating units, that is, the average number of repeating units contained in the polymer macromolecular chain,
  • Degree of polymerization average molecular weight of polymer ⁇ molecular weight of polymerized units
  • the degree of polymerization of the non-fluorine polymer in the shell can also be confirmed/estimated based on the weight average molecular weight.
  • the core-shell structure polymer can improve the flexibility of the binder, improve the flexibility of the pole piece and the safety performance of the battery; at the same time, it can also ensure the adhesive force of the pole piece, thereby ensuring the performance and service life of the battery.
  • the core-shell structure polymer helps to improve the dispersion of the cathode slurry, which can reduce the resistance of the electrode sheet film and improve the battery cycle performance.
  • the core-shell structure polymer can simultaneously improve the flexibility of the pole piece and the dispersion of the slurry, and make the pole piece have good bonding properties, which helps to reduce the loss of other additives in the slurry. Used to improve battery safety and battery cycle performance, and help increase battery energy density.
  • auxiliary agent refers to auxiliary chemicals added to improve the production process of the pole piece and improve the quality of the pole piece.
  • This article refers to other substances in the cathode slurry except the cathode active material, conductive agent and solvent.
  • the mass content of the core part is 5% to 9%, and the mass content of the shell part is 91% to 95%, based on the total mass of the core-shell structure polymer.
  • the mass content of the core part is 5% to 8.5%, 5% to 8%, 5% to 7.5%, 5.5% to 8.5% or 6% to 8.5%, based on the core-shell structure Total mass of polymer.
  • the mass content of the shell part is 90% to 95%, 90% to 94.5%, 90% to 94%, 90.5% to 95% or 91% to 94%, based on the core-shell structure Total mass of polymer.
  • the content of the core and shell is within this range, it can increase the plastic strain stress of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety performance of the battery, and ensuring that the pole piece has sufficient adhesion, thereby ensuring Battery performance and lifespan.
  • the molar content of the structural units derived from the monomer represented by Formula III is 30% to 50%, based on the total molar amount of the non-fluoropolymer.
  • the molar content of the structural units derived from the monomer represented by Formula III is 30% to 45%, 30% to 40%, 35% to 50% or 40% to 50%, based on the Total moles of non-fluoropolymers.
  • the molar content of the structural units derived from the monomer represented by Formula II is 20% to 50%, based on the total molar amount of the non-fluoropolymer.
  • the molar content of the structural units derived from the monomer represented by Formula II is 20% to 50%, 30% to 50%, or 20% to 30%, based on the total amount of the non-fluoropolymer. Molometer.
  • the core-shell structure polymer within this content range can ensure that the pole piece has good flexibility, thereby ensuring that the battery has excellent electrical performance and cycle performance while improving safety performance.
  • the non-fluoropolymer further includes structural units derived from monomers represented by Formula IV,
  • R 6 is selected from amide group or cyano group
  • R 7 is selected from hydrogen, substituted or unsubstituted C 1-5 alkyl group.
  • the polar group contained in the monomer represented by formula IV can form better adsorption performance or affinity with the positive active material, which helps to improve the agglomeration of the positive active material, thereby improving the slurry stability, improve the processing performance of the pole piece and improve the film resistance of the pole piece.
  • the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 50%, based on the total molar amount of the non-fluoropolymer.
  • the molar content of the structural units derived from the monomer represented by Formula IV is 40% to 47%, 40% to 45%, 43% to 50% or 45% to 50%, based on the Total moles of non-fluoropolymers.
  • the mass content of the structural units derived from the monomer shown in Formula IV within a suitable range can have sufficient adsorption performance or affinity for the positive electrode active material, effectively improve the dispersion of the slurry, thereby reducing the electrode sheet film resistance and improving the battery Cycle performance.
  • the fluoropolymer is polyvinylidene fluoride or modified polymers thereof. In some embodiments, the fluoropolymer is polyvinylidene fluoride.
  • the core has stable chemical properties, excellent electrical properties, and good mechanical properties, which is helpful for preparing pole pieces with good electrical properties and mechanical properties.
  • the non-fluorine polymer is one or a combination of a copolymer of styrene and tert-butyl acrylate, a copolymer of acrylonitrile, styrene and tert-butyl acrylate, and a copolymer of acrylamide, styrene and methyl acrylate. .
  • the non-fluoropolymer is a copolymer of styrene and t-butyl acrylate. In some embodiments, the non-fluoropolymer is a copolymer of acrylonitrile, styrene, and t-butyl acrylate. In some embodiments, the non-fluoropolymer is a copolymer of acrylamide, styrene, and methyl acrylate. In some embodiments, the non-fluoropolymer is polystyrene-t-butyl acrylate. In some embodiments, the non-fluoropolymer is polyacrylonitrile-styrene-t-butyl acrylate. In some embodiments, the non-fluoropolymer is polyacrylamide-styrene-t-butyl acrylate.
  • the structural units derived from the monomer shown in Formula II in the non-fluorine polymer have ester groups that can form soft segments that have large free volumes and can absorb external energy through segment motion. It has the effect of energy absorption and toughening; at the same time, its strong polarity can generate large intermolecular forces, making the core-shell structure polymer have excellent softening effect and bonding performance.
  • the structural unit derived from the monomer represented by formula III in the non-fluorine polymer has a phenyl group, and the free volume of this chain segment is relatively limited, so that the core-shell structure polymer has good mechanical properties and processing strength.
  • the polar functional groups of non-fluorine polymers also have good adsorption properties and/or affinity, and can be stably attached to the surface of cathode active materials including lithium iron phosphate and lithium nickel cobalt manganese oxide, thereby improving the dispersion of the slurry. and the film resistance of the electrode plate, thereby improving the cycle performance of the battery; it can also reduce the direct contact between the positive active material and the electrolyte, thereby improving the long-term cycle performance of the battery.
  • the non-fluoropolymer coats or partially coats the surface of the fluoropolymer, increasing the dispersion of the fluoropolymer in the non-fluoropolymer and interacting with the fluoropolymer.
  • Forming a strong connection makes the structure of the core part and the shell part more stable, allowing the core-shell structure polymer to exert a long-lasting toughening effect.
  • the force between the core and the shell of the core-shell structure polymer is not limited to chemical cross-linking, but may also include physical deposition, hydrogen bonding force, etc.
  • the viscosity of the glue solution is 50 to 180 mPa ⁇ s.
  • the viscosity of the glue prepared by dissolving the core-shell polymer in N-methylpyrrolidone 50 ⁇ 160mPa ⁇ s, 50 ⁇ 140mPa ⁇ s, 50 ⁇ 120mPa ⁇ s, 50 ⁇ 100mPa ⁇ s, 50 ⁇ 80mPa ⁇ s, 60 ⁇ 180mPa ⁇ s, 70 ⁇ 180mPa ⁇ s, 80 ⁇ 180mPa ⁇ s, 90 ⁇ 180mPa ⁇ s, 100 ⁇ 180mPa ⁇ s, 120 ⁇ 180mPa ⁇ s or 140 ⁇ 180mPa ⁇ s.
  • the viscosity of the core-shell structure polymer is higher than 180 mPa ⁇ s (mass content is 7%), the chain segment movement of the core-shell structure polymer is restricted, which is not conducive to improving the flexibility of the pole piece; when the viscosity of the core-shell structure polymer When it is lower than 50 mPa ⁇ s (mass content is 7%), the bonding performance of the slurry will be affected, and the defect of pole piece defilming will easily occur.
  • Controlling the viscosity of the core-shell structure polymer within a suitable range can take into account the flexibility of the pole piece and the adhesiveness of the binder, improve the uniformity and processability of the pole piece coating, maintain good flexibility while maintaining appropriate
  • the adhesive force helps to reduce the resistance of the film layer and improve the cycle performance, and improves the safety of the long-term cycle of the battery.
  • film layer refers to the coating formed after the positive electrode or negative electrode slurry is coated and dried.
  • the core-shell structure polymer has a median particle size Dv50 of 2 to 10 ⁇ m.
  • the core-shell structure polymer has a median particle size Dv50 of 2 to 9 um, 2 to 7 um, 2 to 5 um, 3 to 7 um or 5 to 7 um.
  • the term “median particle size Dv50” refers to the particle size corresponding to when the cumulative particle size distribution percentage of the measured sample reaches 50%. Its physical meaning is that 50% of the particles have a particle size smaller (or larger) than it.
  • the particle size of the core-shell structure polymer within a suitable range is beneficial to dissolution in the positive electrode slurry solvent, such as N-methylpyrrolidone, reducing the processing difficulty of the binder glue and improving battery processing efficiency.
  • This application also provides a method for preparing a core-shell structure polymer, including:
  • Preparing the core part at least one monomer represented by the following formula I is polymerized under the first polymerization condition to obtain an emulsion of fluorine-containing polymer;
  • Preparing a core-shell structure polymer The emulsion of the fluorine-containing polymer and at least two monomers represented by the following formula V are polymerized under the second polymerization condition to prepare a non-fluorine polymer, and the non-fluorine polymer is polymerized as a core-shell structure
  • the shell part of the object at least partially covers the surface of the core part;
  • R 1 and R 2 are each independently selected from hydrogen, fluorine, chlorine or at least one fluorine-substituted C 1-3 alkyl group;
  • R 8 and R 9 are each independently selected from hydrogen, amide group, cyano group, substituted Or unsubstituted phenyl, or -CO 2 R 10 ;
  • R 10 is selected from substituted or unsubstituted C 1-5 alkyl.
  • the fluoro-substituted C 1-3 alkyl group is selected from -CF 3 , -CHF 2 , CH 3 CF 3 -, CH 3 CHF 2 -, or C 2 F 6 -. In some embodiments, the fluoro-substituted C 1-3 alkyl is -CF 3 (or trifluoromethyl).
  • the C 1-5 alkyl group is selected from methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, or n-pentyl.
  • each of R 1 , R 2 , and R 9 is independently selected from hydrogen.
  • R 8 is selected from cyano, phenyl or -CO 2 R 10 ;
  • R 10 is selected from substituted or unsubstituted C 1-5 alkyl.
  • the R 8 is selected from cyano.
  • the R 8 is selected from phenyl.
  • the R 8 is selected from -CO 2 R 10 ; R 10 is selected from substituted or unsubstituted C 1-5 alkyl. In some embodiments, R 8 is selected from -CO 2 R 10 ; R 10 is selected from n-butyl.
  • the at least two monomers represented by the following formula V respectively include phenyl and -CO 2 R 10 ; R 10 is selected from substituted or unsubstituted C 1-5 alkyl.
  • the at least two monomers represented by the following formula V respectively include phenyl, -CO 2 R 10 and cyano; R 10 is selected from substituted or unsubstituted C 1-5 alkyl.
  • the at least two monomers represented by Formula V below include phenyl, -CO 2 R 10 and amide groups respectively; R 10 is selected from substituted or unsubstituted C 1-5 alkyl groups.
  • the preparation of the non-fluoropolymer under the second polymerization condition includes the following steps: under an inert gas atmosphere, an emulsion of the fluoropolymer, at least two monomers represented by Formula V and a second initiator Swell in the second solvent, add polymerization ligands and catalysts, and perform polymerization.
  • the prepared non-fluoropolymer at least partially covers the surface of the fluoropolymer.
  • the fluoropolymer serves as the core part and the non-fluoropolymer serves as the shell part.
  • the prepared product is a core-shell structure polymer.
  • the preparation method of the core-shell structure polymer includes the following steps: under an inert gas atmosphere, an emulsion of fluoropolymer, at least two monomers represented by formula V and a second initiator are added in a second Swell in the solvent, add polymerization ligands and catalysts, carry out polymerization, stop the reaction, collect the solid phase, and obtain a core-shell structure polymer.
  • inert gas refers to a gas that does not participate in the polymerization reaction.
  • exemplary inert gases include any or a combination of argon, helium, and nitrogen.
  • initiator refers to a substance that initiates the polymerization of monomers during a polymerization reaction.
  • the second initiator is selected from one or more of 2-bromopropionic acid methyl ester, 2-ethyl peroxydicarbonate and peroxytert-amyl pivalate.
  • the second initiator is methyl 2-bromopropionate.
  • the second solvent is selected from deionized water, benzene or dimethylformamide.
  • the second solvent is deionized water, which is beneficial to reducing harm to the environment.
  • swelling refers to the phenomenon of volume expansion of polymers in solvents.
  • polymerization ligand refers to a compound that can form coordination with polymerized monomers and/or transition metals in a coordination polymerization reaction initiated by a complex catalyst composed of two or more components.
  • the polymerization reaction ligand is selected from one of N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine and pentamethyldiethylenetriamine.
  • the polymerization ligand is pentamethyldiethylenetriamine.
  • catalyst refers to a substance that can change the chemical reaction rate (increase or decrease) of reactants in a chemical reaction without changing the chemical equilibrium, and its own quality and chemical properties do not change before and after the chemical reaction.
  • the catalyst is selected from copper, titanium chloride or vanadium tetrachloride.
  • the catalyst is copper.
  • the polymerization conditions in this preparation method are safe and controllable, which is beneficial to the continuous production of the core-shell structure polymer.
  • the core-shell structure polymer can improve the flexibility of the binder, improve the flexibility of the pole piece and the safety performance of the battery; at the same time, it can also ensure the adhesive force of the pole piece, thereby ensuring the performance and service life of the battery.
  • the core-shell structure polymer prepared by this method has good affinity and/or adsorption properties for the positive electrode active material, and can help the positive electrode active material to be dispersed in the slurry, thereby improving the film resistance and electrical properties of the electrode piece; it also It can reduce the direct contact between the positive active material and the electrolyte and improve the long-term cycle performance of the battery.
  • the preparation of the non-fluoropolymer under the second polymerization conditions includes the following steps:
  • the dispersed fluoropolymer emulsion, at least two monomers represented by formula V and the second initiator are swollen in the second solvent for 0.5 hours to 2 After an hour, the polymerization ligand and catalyst are added, and the polymerization reaction is carried out for 1 to 5 hours.
  • normal pressure refers to a standard atmospheric pressure, which is 101KPa.
  • dispersion processing methods include but are not limited to ultrasonic and stirring.
  • the reaction temperature is 22°C to 30°C, 22°C to 28°C, or 23°C to 26°C, such as 25°C.
  • the polymerization reaction time is 1 hour to 4 hours, 1 hour to 3 hours, 1 hour to 2 hours, 2 hours to 5 hours, 3 hours to 5 hours, or 3 hours to 4 hours.
  • the preparation method of the core-shell structure polymer has low raw material cost and mild reaction conditions; the shell part and the core part of the polymer have good binding force and stability, and the core-shell structure polymerization with a stable and specific structure can be obtained things.
  • preparing the fluoropolymer under first polymerization conditions includes the steps of:
  • the reaction temperature is 60°C to 68°C, 60°C to 66°C, 60°C to 64°C, 62°C to 70°C, 64°C to 70°C or 66°C to 70°C.
  • the reaction time is 4 hours to 7 hours, 4 hours to 6 hours, 4 hours to 5 hours, 6 hours to 8 hours or 7 hours to 8 hours.
  • preparing the core fluoropolymer under first polymerization conditions includes the steps of:
  • the first initiator is selected from one or more of 2-ethyl peroxydicarbonate and peroxytert-amyl pivalate. In some embodiments, the first initiator is 2-ethylperoxydicarbonate.
  • pH adjuster refers to a substance that changes the pH of a solution or dispersion medium, including increasing the acidity or increasing the alkalinity.
  • exemplary pH adjusting agents include sodium bicarbonate, sodium carbonate and sodium hydroxide.
  • dispersing aid refers to substances that can promote the uniform dispersion of monomers in the medium during synthesis reactions.
  • exemplary dispersing aids include carboxyethyl cellulose ether.
  • the first solvent is deionized water, which is beneficial to reducing harm to the environment.
  • the pH is adjusted to 6.5, 6.8 or 7.
  • the stirring time is 30 minutes to 55 minutes, 30 minutes to 50 minutes, 30 minutes to 45 minutes, 35 minutes to 60 minutes, 40 minutes to 60 minutes or 45 minutes to 60 minutes.
  • the preparation method of the core part has low raw material cost, controllable environmental hazards, and mild reaction conditions, which is beneficial to the expanded production of the core part.
  • the weight average molecular weight of the fluoropolymer in the core is 20,000 to 150,000.
  • step-by-step preparation a core-shell polymer with a stable core-shell structure can be obtained, and the method has high repeatability.
  • This application also provides a positive electrode slurry, which includes a positive electrode active material, a conductive agent, a binder, and the core-shell structure polymer mentioned above in this application or the core-shell structure polymer prepared by the above method.
  • the positive electrode slurry has good bonding performance, dispersibility and processability, which is beneficial to the processing of the electrode piece.
  • the positive active material is a lithium-containing transition metal oxide with a carbon coating layer on the surface.
  • the lithium-containing transition metal oxide can be selected from lithium iron phosphate and lithium nickel cobalt manganese oxide. of one or more.
  • the carbon coating layer on the surface of the cathode active material can form a physical barrier to prevent or reduce the chemical erosion of the cathode active material by the electrolyte, thereby reducing the dissolution of transition metals; and it can also promote electronic and/or ion conductivity and improve conductive performance.
  • the carbon coating layer can be coated with an organic carbon source.
  • organic carbon sources include glucose, tannic acid, polyvinylpyrrolidone, etc.
  • the graphitization degree of the coating layer is 0.2% to 0.35%, optionally 0.2% to 0.3%.
  • the graphitization degree of the coating layer is 0.2% to 0.3%, 0.2% to 0.25%, 0.25% to 0.35%, or 0.3% to 0.35%. In some embodiments, the coating layer has a degree of graphitization of 0.3%.
  • the graphitization degree of the carbon coating layer of the positive active material is higher than 0.35%, the compatibility between the positive active material and the binder is further reduced, resulting in poor dispersion of the slurry; and the conductive properties of the positive active material will also be reduced. , thereby reducing the electrical performance of the battery.
  • the graphitization degree of the carbon coating layer of the cathode active material is less than 0.2%, the coating layer of the cathode active material is not enough to form a physical barrier and cannot prevent or mitigate the chemical erosion of the cathode active material by the electrolyte, resulting in the dissolution of the transition metal and the cathode Active material structure collapses.
  • Controlling the graphitization degree of the carbon coating layer of the cathode active material within an appropriate range can make the cathode active material have appropriate conductivity, corrosion resistance and machining performance, and help improve the processing performance of the slurry and the performance of the pole piece. Conductive properties and long-term cycle performance of secondary batteries.
  • the thickness of the coating layer of the positive active material does not exceed 100 nm.
  • the mass percentage of the composition consisting of the core-shell structure polymer and the binder and the cathode active material is 1% to 3%.
  • the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is 0.5% to 3%, 0.8% to 3% , 1% to 3%, 1.2% to 3%, 1.5% to 3%, 2% to 3%, 0.5% to 2.8%, 0.5% to 2.5%, 0.5% to 2.4%, 0.5% to 2% or 0.5 % ⁇ 1.4%.
  • the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is higher than 3%, the binding performance of the slurry is too high, resulting in reduced dispersion and processability of the slurry. ; Moreover, excessive dosage will also lead to increased brittleness of the pole piece.
  • the mass percentage of the composition composed of the core-shell structure polymer and the binder and the cathode active material is less than 0.5%, the bonding performance of the slurry is significantly reduced, resulting in a decrease in the bonding performance of the slurry.
  • the adhesion of the prepared pole pieces is insufficient. It is easy to produce peeling defects. As the cycle proceeds, the electrolyte will decompose to produce hydrofluoric acid.
  • the mass percentage of the composition composed of the core-shell structure polymer and the binder and the positive electrode active material is within a suitable range, which helps to take into account the flexibility, dispersion and bonding properties of the slurry, so that the electrode piece has Good flexibility, adhesion and processability, thereby improving the electrical properties of the pole piece.
  • the mass ratio of the core-shell structure polymer and the binder is 0.05 to 5:1.
  • the mass ratio of the core-shell structure polymer and the binder is 0.1 ⁇ 5:1, 0.5 ⁇ 5:1, 0.5 ⁇ 2:1, 1 ⁇ 4:1, 1 ⁇ 3:1 or 1 ⁇ 2:1.
  • the mass ratio of the core-shell structure polymer and the binder is higher than 5:1
  • the increase of the core-shell structure polymer in the slurry significantly improves the flexibility of the binder and the dispersion of the slurry, but This leads to a decrease in the bonding performance of the slurry, which is not conducive to the preparation of safe and stable pole pieces.
  • the mass ratio of the core-shell structure polymer and the binder is less than 0.05:1, the content of the soft segments in the core-shell structure polymer is insufficient, making it difficult to increase the plastic strain stress of the film layer; and, the core-shell structure polymer
  • the adsorption capacity of the structural polymer to the cathode active material is limited, and it is unable to improve the dispersion of the slurry and effectively wrap/coat the cathode active material, resulting in a reduction in the flexibility and cycle performance of the pole piece, which is not conducive to improving the battery's performance. electrical properties.
  • the mass ratio of the core-shell structure polymer and the binder within a suitable range helps to balance the flexibility of the pole piece and the dispersion of the cathode slurry, improve the processability of the pole piece, and reduce the film layer of the pole piece resistance and improve battery cycle performance.
  • composition of the core-shell structure polymer and the binder within the above range also helps to reduce the use of other additives in the slurry, and helps to increase the loading capacity of the positive active material of the electrode sheet and the energy density of the battery.
  • the viscosity of the cathode slurry is 5,000 to 50,000 mPa ⁇ s.
  • the viscosity of the positive electrode slurry is 5000 ⁇ 32000mPa ⁇ s, 8000 ⁇ 48000mPa ⁇ s, 10000 ⁇ 48000mPa ⁇ s, 12000 ⁇ 48000mPa ⁇ s , 13000 ⁇ 48000mPa ⁇ s, 15000 ⁇ 48000mPa ⁇ s, 16000 ⁇ 48000mPa ⁇ s, 18000 ⁇ 48000mPa ⁇ s, 20000 ⁇ 48000mPa ⁇ s, 25000 ⁇ 48000mPa ⁇ s, 30000 ⁇ 48000mPa ⁇ s, 35000 ⁇ 4800 0mPa ⁇ s, 40000 ⁇ 48000mPa ⁇ s or 45000 ⁇ 48000mPa ⁇ s.
  • the solvent used in the cathode slurry is N-methylpyrrolidone.
  • the viscosity of the cathode slurry When the viscosity of the cathode slurry is higher than 50,000 mPa ⁇ s, the dispersion and stability of the slurry are poor, which in turn leads to an increase in film layer resistance and a decrease in battery cycle performance.
  • the viscosity of the positive electrode slurry When the viscosity of the positive electrode slurry is lower than 5000 mPa ⁇ s, the viscosity of the slurry is too low, resulting in insufficient bonding force of the produced electrode piece, causing potential safety hazards for the battery.
  • the viscosity of the positive electrode slurry within a suitable range helps to improve the processing performance of the pole piece and the bonding performance of the pole piece film layer.
  • the binder is polyvinylidene fluoride or a modified polymer thereof, and the weight average molecular weight of the binder is 700,000 to 1.1 million.
  • the binder is polyvinylidene fluoride.
  • the weight average molecular weight of the binder is 700,000-1,000,000, 700,000-900,000, 800,000-1.1 million, 900,000-1.1 million or 1 million-1.1 million. In some embodiments, the binder has a weight average molecular weight of 700,000.
  • the adhesive has good compatibility with the core-shell structure polymer provided in this application, and can maintain good bonding performance while improving flexibility.
  • This application also provides the application of the above-mentioned core-shell structure polymer or the core-shell structure polymer prepared by the above-mentioned method in secondary batteries.
  • the core-shell structure polymer or the core-shell structure polymer prepared by the above method is used to improve the dispersion of battery slurry.
  • the core-shell structure polymer or the core-shell structure polymer prepared by the above method is used to improve the flexibility of the battery pole piece.
  • the core-shell structure polymer described in this application has the effect of improving the dispersion of the cathode slurry and the flexibility of the pole piece while taking into account the bonding performance. It helps to reduce the amount of additives in the slurry and improves the electrode performance. The processability and cycle performance of the sheet can be improved, as well as helping to improve the energy density of the battery.
  • a secondary battery is provided, and the secondary battery is a lithium-ion battery.
  • a secondary battery typically includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.
  • the positive electrode sheet 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 facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the cathode active material may be a cathode active material known in the art for batteries.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (can also be abbreviated to NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (can also be abbreviated to NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (can also be abbreviated to NCM 622 ), LiNi At least one of 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as Li Li
  • the olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composites of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate and carbon.
  • At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • the positive electrode film layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the positive electrode film layer optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative active material may be a negative active material known in the art for batteries.
  • the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally further includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece, and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic. Examples of plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 2 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 4 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • Fig. 7 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the composition consisting of the binder and the core-shell structure polymer, the conductive agent carbon black, and the carbon-coated lithium iron phosphate LFP are added according to the weight ratio of 2:4:100, and N-methylpyrrolidone is added to prepare a solid content of 58 % of the cathode slurry.
  • the mass content of the carbon coating layer of lithium iron phosphate is 1.2%
  • the graphitization degree G is 0.3%.
  • the binder is PVDF (purchased from Arkema France Co., Ltd.) with a weight average molecular weight of 700,000.
  • the mass ratio of the core-shell structure polymer to the binder is 0.5:1.
  • the specific parameters are shown in Table 1.
  • the positive electrode slurry is evenly coated on both surfaces of the aluminum foil positive electrode current collector, and then dried to obtain a film layer; it is then cold pressed and cut to obtain the positive electrode sheet.
  • SBR binder styrene-butadiene rubber
  • CMC thickener sodium carboxymethylcellulose
  • the positive electrode sheet, isolation film and negative electrode sheet prepared in Example 1 are stacked in order so that the isolation film is between the positive and negative electrode sheets to play an isolation role. Then, the bare battery core is obtained by winding and welding to the bare battery core. The tabs are removed, and the bare battery core is put into an aluminum case, baked at 80°C to remove water, and then electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.
  • the preparation method of the secondary batteries of Examples 2 to 5 is similar to that of the secondary battery of Example 1, but the mass content of the fluorine-containing polymer in the core-shell structure polymer is adjusted.
  • the different product parameters are detailed in Table 1.
  • the preparation method of the secondary battery of Example 6 is similar to that of the secondary battery of Example 1, but the weight average molecular weight of the core-shell structure polymer core is adjusted to 200,000.
  • the preparation method is as follows:
  • 1.7g of the above PVDF emulsion was dispersed in 35g of deionized water, ultrasonic treated for 40 minutes, stirred at 25°C at 150rpm, and nitrogen was passed through to eliminate oxygen.
  • St purified styrene
  • tBA tert-butyl acrylate
  • MBP 2-bromopropyl Methyl acid ester
  • PMDETA 2-bromopropyl Methyl acid ester
  • the reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 5 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.
  • the preparation method of the secondary battery of Example 7 is similar to that of the secondary battery of Example 1, but the weight average molecular weight of the core-shell structure polymer core is adjusted to 150,000.
  • the preparation method is as follows:
  • the preparation method of the secondary battery of Example 8 is similar to that of the secondary battery of Example 1, but the weight average molecular weight of the core-shell structure polymer core is adjusted to 20,000.
  • the preparation method is as follows:
  • the preparation method of the secondary battery of Example 9 is similar to that of the secondary battery of Example 1, but the median particle size Dv50 of the core-shell structure polymer is adjusted to 1 ⁇ m.
  • the preparation method of the secondary battery of Examples 10-11 is similar to the preparation method of the secondary battery of Example 1, but the graphitization degree is adjusted.
  • the different product parameters are detailed in Table 1.
  • the preparation method of the secondary battery of Example 12 is similar to the preparation method of the secondary battery of Example 1, but the positive active material is adjusted to be lithium iron phosphate without a coating layer.
  • the preparation method of the secondary battery of Examples 13 to 17 is similar to the preparation method of the secondary battery of Example 1, but the mass ratio of the composition composed of the binder and the core-shell structure polymer and the positive electrode active material is adjusted. Different Product parameters are detailed in Table 1.
  • the preparation method of the secondary battery of Examples 18 to 23 is similar to the preparation method of the secondary battery of Example 1, but the mass ratio of the core-shell structure polymer and the binder is adjusted.
  • the different product parameters are detailed in Table 1.
  • the preparation method of the secondary battery of Examples 24 to 25 is similar to the preparation method of the secondary battery of Example 1, but the weight average molecular weight of the PVDF binder in the core-shell structure is adjusted to 900,000 and 1.1 million respectively.
  • Binder PVD with weight average molecular weights of 900,000 and 1.1 million was purchased from Solvay (Shanghai) Co., Ltd., see Table 1 for details.
  • the positive active material in Example 25 is lithium nickel cobalt manganese oxide.
  • the secondary battery preparation method of Example 26 is similar to the secondary battery preparation method of Example 1, but the weight average molecular weight of the core-shell polymer core is 120,000 and the type of core-shell polymer is adjusted. See Table 1 for details. ; Its preparation method is as follows:
  • the reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 3 hours, the copper wire was taken out and the reaction was stopped to obtain a core with PVDF as the core and acrylamide-styrene-tert-butyl acrylate as the shell. Shell structure polymer.
  • the preparation method of the secondary battery in Example 27 is similar to that of Example 1, but the type of core-shell structure polymer is adjusted, as shown in Table 1 for details; the preparation method of the core-shell structure polymer is as follows:
  • the preparation method of PVDF emulsion is the same as the preparation method of PVDF emulsion in Example 1.
  • PVDF emulsion Disperse 1.7g of PVDF emulsion (the amount of PVDF polymer is 0.51g) in 35g of deionized water. After ultrasonic treatment for 40 minutes, stir at 25°C and 150rpm, and pass in nitrogen to eliminate oxygen. Add 2.55g of purified styrene (St) and 3.24g of tert-butyl acrylate (tBA) (molar ratio 5:5), as well as 2% of the total monomer mass of the initiator methyl 2-bromopropionate (MBP). After swelling for 1 hour, add the ligand pentamethyldiethylenetriamine (PMDETA) (2% of the total monomer mass), and then add the catalyst copper wire after 10 minutes.
  • St purified styrene
  • tBA tert-butyl acrylate
  • MBP methyl 2-bromopropionate
  • the reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 5 hours, the copper wire was taken out to stop the reaction, and a core-shell structure with PVDF as the core and styrene-tert-butyl acrylate as the shell was obtained. polymer.
  • the preparation method of the secondary battery in Example 28 is similar to that of Example 1, but the type of core-shell structure polymer is adjusted, as shown in Table 1 for details; the preparation method of the core-shell structure polymer is as follows:
  • the preparation method of the secondary battery in Example 29 is similar to that of Example 1, but the type of core-shell structure polymer is adjusted, as shown in Table 1 for details; the preparation method of the core-shell structure polymer is as follows:
  • the secondary battery preparation method of Examples 30 to 31 is similar to the secondary battery preparation method of Example 1, but the mass ratio of the core-shell structure polymer and the binder is adjusted, and the binder and core-shell structure polymer are adjusted.
  • the mass ratio of the composition and the positive active material is 3.0:100, see Table 1 for details.
  • the secondary battery preparation method of Example 32 is similar to the secondary battery preparation method of Example 1, but the weight average molecular weight of the core part of the core-shell structure polymer is adjusted to 200,000, and the binder and core-shell structure polymer are adjusted.
  • the mass ratio of the composition and the positive active material is 3.0:100, see Table 1 for details; the preparation method is as follows:
  • the reaction system was evacuated 5 times to make the system reach an oxygen-free or low-oxygen atmosphere. After 5 hours, the copper wire was taken out to stop the reaction, and PVDF was used as the core and acrylonitrile-styrene-tert-butyl acrylate was used as the shell. Core-shell polymer.
  • the secondary battery preparation method of Example 33 is similar to the secondary battery preparation method of Example 10, but in the process of preparing the core-shell structure polymer, the molar ratio of acrylonitrile, styrene, and polytert-butyl acrylate is adjusted to 4 :3:3.
  • Comparative Example 1 only a PVDF binder with a weight average molecular weight of 700,000 was used to prepare a secondary battery, and other steps were the same as the preparation method of the secondary battery in Example 1.
  • the preparation method of the secondary battery of Comparative Example 2 is the same as that of Example 1, but the shell part is adjusted to be polytert-butyl acrylate. See Table 1 for details.
  • the shell preparation method was similar to Example 1, except that only 2.1 g of tert-butyl acrylate was added.
  • the preparation method of the secondary battery of Comparative Example 3 is the same as that of Example 1, but the shell part is adjusted to be polystyrene. See Table 1 for details.
  • the shell preparation method is similar to Example 1, except that only 2.55g of styrene is added.
  • the GB/T 19077-2016 particle size distribution laser diffraction method weigh 0.1g to 0.13g of the polymer sample to be tested in a 50mL beaker, add 5g of absolute ethanol, put in a stirrer of about 2.5mm, and seal it with plastic wrap. After ultrasonic treatment for 5 minutes, the samples were transferred to a magnetic stirrer and stirred at 500 rpm for more than 20 minutes. Two samples were taken from each batch of products for testing. The test was carried out using the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the UK.
  • NMP N-methylpyrrolidone
  • the degree of graphitization was characterized using a French HORIBA Jobin Yvon high-resolution Raman spectrometer, model LabRAM HR Evlution. After subtracting the detection background, the following Gaussian function was used for fitting.
  • Raman spectrum test conditions wavelength 532nm, scanning range 200-4000cm -1 , accumulation twice, measuring 10 points for each sample, taking the average value for fitting:
  • G is the degree of graphitization
  • a i , Vi and w i are the peak intensity, peak position and peak width respectively.
  • the method for measuring the cycle capacity retention rate of lithium iron phosphate system is as follows:
  • Example 1 the battery capacity retention rate test process is as follows: at 25°C, charge the battery corresponding to Example 1 with a constant current of 1/3C to 3.65V, and then charge with a constant voltage of 3.65V until the current is 0.05 C, leave it for 5 minutes, and then discharge it to 2.5V at 1/3C. The resulting capacity is recorded as the initial capacity C 0 . Repeat the above steps for the same battery and record the discharge capacity C n of the battery after the nth cycle. Then the battery capacity retention rate after each cycle is:
  • the battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 500 cycles under the above test conditions, that is, the value of P500.
  • the testing procedures of Comparative Example 1 and other examples are the same as above;
  • the measurement method is as follows:
  • Example 25 the battery DC impedance DCR test process is as follows: at 25°C, charge the battery corresponding to Example 25 with a constant current of 1/3C to 4.4V, and then charge with a constant voltage of 4.4V until the current is 0.05 C. After leaving it for 5 minutes, record the voltage V1. Then discharge at 1/3C for 30 seconds and record the voltage V2, then (V2-V1)/1/3C, we get the internal resistance DCR1 of the battery after the first cycle. Other steps are the same as above.
  • the viscosity of the slurry was measured using a rotational viscometer. Select the appropriate rotor, fix the viscometer rotor, and place the positive slurry under the viscometer rotor so that the slurry just submerges the scale line of the rotor.
  • a core-shell structure polymer and a binder are used to prepare secondary batteries.
  • the core of the core-shell structure polymer is polyvinylidene fluoride or its modified polymer.
  • the shell structure polymer shell part is acrylonitrile-styrene-tert-butyl acrylate polymer, acrylamide-styrene-tert-butyl acrylate polymer or styrene-tert-butyl acrylate polymer.
  • Comparative Example 2 shows that due to polytert-butyl acrylate, the electrode piece absorbs a large amount of liquid, and the battery capacity decays extremely quickly, making the capacity retention rate of the battery after 500 cycles lower than that of the Example 1 to 33, indicating that the combination of specific types of shell polymers in core-shell structure polymers can help improve battery cycle performance; in addition, Comparative Example 3 shows that polystyrene causes poor dispersion of the cathode slurry, resulting in poor dispersion of the cathode plate. The diaphragm resistance is higher than that of Examples 1 to 33, indicating that the combination of specific types of shell polymers in the core-shell structure polymer can help improve the conductive performance of the battery.
  • Example 1 Comparing Example 1, Examples 3 to 4 with Example 2 and Example 5, it can be seen that the mass content of the core part in the core-shell structure polymer is controlled to be 5% to 9%, and the mass content of the shell part is 91% to 95%. , based on the total mass of the core-shell structure polymer, is conducive to further reducing the membrane resistance of the positive electrode piece, increasing the number of rolling times of the positive electrode piece and the capacity retention rate of the battery after 500 cycles.
  • Example 1 Comparing Example 1, Examples 6 to 8 and Comparative Examples 1 to 3, it can be seen that controlling the weight average molecular weight of the fluoropolymer in the core-shell structure polymer to 20,000 to 200,000 can reduce the viscosity of the positive electrode slurry and the positive electrode film resistance, and improve the capacity retention rate of the battery after 500 cycles, indicating that the core-shell structure polymer containing a fluoropolymer with a weight average molecular weight of 20,000 to 200,000 is beneficial to improving the dispersion of the cathode slurry and improving the performance of the cathode.
  • Example 1 Comparison between Example 1, Examples 7-8 and Example 6 shows that controlling the weight average molecular weight of the fluoropolymer in the core-shell structure polymer to 20,000-150,000 can further reduce the viscosity of the positive electrode slurry and the positive electrode film.
  • the layer resistance is greatly improved, and the bonding force of the positive electrode sheet, the number of rolling times and the capacity retention rate of the battery after 500 cycles are greatly improved, and the bonding force, flexibility, conductive performance and battery cycle performance of the positive electrode sheet are improved to a greater extent.
  • Example 1 Comparing Example 1, Examples 7 to 8 with Examples 6 and 9, it can be seen that controlling the median particle size Dv50 of the core-shell structure polymer to 2 ⁇ m to 10 ⁇ m can further increase the number of rolling of the positive electrode sheet and the battery life.
  • the capacity retention rate after 500 cycles improves the flexibility of the positive electrode sheet and the battery cycle performance to a greater extent.
  • Example 12 The cathode active material in Example 12 was not coated. Compared with Examples 1 and 10 in which the cathode active material was coated with a carbon layer, the cycle performance and pole piece flexibility of the batteries in Example 1 and Example 10 were It is obviously better than Example 12, and the slurry viscosity in Example 1 and Example 10 is reduced, indicating that the core-shell structure polymer has good affinity to the carbon layer of the cathode active material and can coat the carbon layer of the cathode active material. The surface promotes the dispersion of positive active materials, thereby improving the cycle performance of the battery and the flexibility of the pole piece. In Example 11, a cathode active material with a graphitization degree of 0.5% was used to prepare a battery.
  • Example 11 Compared with Example 1 and Example 10, the viscosity of the slurry in Example 11 was significantly higher than that in Example 1 and Example 10. Viscosity, which leads to poor dispersion properties of the slurry, further increases the film resistance and reduces the adhesion and flexibility of the pole pieces, ultimately leading to reduced cycle performance of the battery.
  • Example 1 Comparing Example 1, Examples 13 to 16 and Example 17, it can be seen that the mass percentage of the composition of the core-shell structure polymer and the binder and the cathode active material is controlled to be 1% to 3%. , the slurry viscosity and cathode film layer resistance were significantly reduced, and accordingly, the capacity retention rate of the battery after 500 cycles was significantly increased, indicating that the core-shell structure polymer can significantly improve the dispersion and stability of the cathode slurry, helping Improving the coating of the positive electrode slurry improves the cycle performance of the battery.
  • Example 14-15 and Implementation Comparing Example 13 and Example 14 it can be seen that the mass percentage of the core-shell structure polymer and binder composition and the positive electrode active material can be controlled to 1.4% to 2.4%, which can take into account the viscosity of the positive electrode slurry and the flexibility of the electrode piece. , and battery cycle performance.
  • Example 1 Comparison between Example 1, Examples 19-22, and Example 18 and Example 23 shows that by controlling the mass ratio of the core-shell structure polymer and the binder to 0.05-5:1, the slurry viscosity is improved, and the viscosity of the slurry is improved.
  • the resistance of the positive electrode film layer was significantly reduced, and the capacity retention rate of the battery after 500 cycles was significantly improved, indicating that the core-shell structure polymer and binder can significantly improve the dispersion and dispersion of the positive electrode slurry within the above mass ratio range.
  • the stability of the positive electrode plate has also been improved, indicating that the core-shell structure polymer helps to improve the flexibility of the binder and the flexibility of the electrode plate.
  • Example 1 Comparison between Example 1, Examples 24-25 and Comparative Examples 1-3 shows that controlling the weight average molecular weight of the polyvinylidene fluoride binder to 700,000-1.1 million can be applied to different cathode active materials and reduce the cost of the cathode.
  • the viscosity of the slurry and the resistance of the positive electrode film, the adhesion of the electrode piece and the number of rolling times, and the capacity retention rate of the battery after 500 cycles are improved.
  • the shell part in the core-shell polymer is polyacrylamide-styrene-tert-butyl acrylate or polystyrene-tert-butyl acrylate, which can reduce the density of the positive electrode slurry. viscosity and positive electrode film resistance, improve the adhesive force of the electrode piece and the number of rolling times, and improve the capacity retention rate of the battery after 500 cycles.
  • Example 1 Comparison between Example 1 and Examples 28-29 shows that compared to the core in the core-shell polymer being polychlorotrifluoroethylene or vinylidene fluoride-chlorotrifluoroethylene copolymer, the core in the core-shell polymer is Partly composed of polyvinylidene fluoride, it can reduce the viscosity of the positive electrode slurry and the resistance of the positive electrode film, improve the adhesive force of the electrode piece and the number of rolling times, and improve the capacity retention rate of the battery after 500 cycles.
  • Example 16 Examples 30-31 and Example 32 Comparing Example 16, Examples 30-31 and Example 32, it can be seen that the mass ratio of the core-shell structure polymer and the binder is controlled to be in the range of 0.5-2:1.
  • the slurry of Example 16, Examples 30-31 The material viscosity, positive electrode film layer resistance, positive electrode sheet rolling times, and battery capacity retention rate after 500 cycles are all significantly better than those in Example 32, indicating that the polyvinylidene fluoride core with a weight average molecular weight of 80,000 has a core-shell structure.
  • the core-shell structure polymer improves the cycle performance of secondary batteries and increases the flexibility of the pole piece.

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Abstract

La présente invention concerne un polymère ayant une structure noyau-enveloppe et son procédé de préparation et son utilisation, une pâte d'électrode positive, une batterie secondaire, un module de batterie, un bloc-batterie et un dispositif électrique. Le polymère ayant une structure noyau-enveloppe comprend : une partie noyau, qui est un polymère contenant du fluor contenant une unité structurale dérivée d'un monomère tel que représenté par la formule I ; et une partie enveloppe, qui est un polymère non fluoré contenant des motifs structuraux dérivés de monomères tels que représentés par la formule II et la formule III, et recouvre au moins partiellement la surface de la partie noyau. Le polymère ayant une structure noyau-enveloppe peut améliorer la flexibilité d'un liant, et améliorer la flexibilité d'une feuille d'électrode et les performances de sécurité d'une batterie ; de plus, le polymère peut également assurer la force d'adhérence de la feuille d'électrode, ce qui permet d'assurer les performances et la durée de vie de la batterie.
PCT/CN2023/071572 2022-08-30 2023-01-10 Polymère ayant une structure noyau-enveloppe et son procédé de préparation et son utilisation, pâte d'électrode positive, batterie secondaire, module de batterie, bloc-batterie et dispositif électrique WO2024045471A1 (fr)

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