WO2024045619A1 - 粘结剂、制备方法、正极极片、二次电池及用电装置 - Google Patents

粘结剂、制备方法、正极极片、二次电池及用电装置 Download PDF

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WO2024045619A1
WO2024045619A1 PCT/CN2023/087056 CN2023087056W WO2024045619A1 WO 2024045619 A1 WO2024045619 A1 WO 2024045619A1 CN 2023087056 W CN2023087056 W CN 2023087056W WO 2024045619 A1 WO2024045619 A1 WO 2024045619A1
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formula
preparation
polymer
monomer represented
binder
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PCT/CN2023/087056
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English (en)
French (fr)
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段连威
孙成栋
刘会会
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宁德时代新能源科技股份有限公司
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Publication of WO2024045619A1 publication Critical patent/WO2024045619A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—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
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application relates to the technical field of secondary batteries, and in particular to an adhesive, a preparation method, a positive electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device.
  • secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the popularization of secondary battery applications, higher requirements have been placed on its cycle performance and service life.
  • Binders are commonly used materials in secondary batteries and are in great demand for battery pole pieces, separators, packaging, etc.
  • the existing adhesive requires a large amount of addition to ensure that the pole pieces have sufficient adhesion.
  • the adhesive cannot maintain sufficient flexibility during the cycle, making the pole pieces prone to brittle fracture, which in turn causes safety issues. Therefore, existing adhesives still need to be improved.
  • This application was made in view of the above problems, and its purpose is to provide a binder that can make the pole piece have excellent bonding force at a low addition amount, and at the same time, the binder can improve the polarity.
  • the flexibility of the sheet improves the cycle performance of the battery.
  • the present application provides a binder, which is a polymer containing a structural unit shown in Formula I and a structural unit shown in Formula II,
  • R 1 is selected from one or more types of fluorine, chlorine, and C 1-3 alkyl groups containing at least one fluorine atom, and the weight average molecular weight of the polymer is 5 million to 9 million.
  • This binder can ensure sufficient adhesion of the pole piece at a low addition amount, and can further improve the flexibility of the pole piece and reduce the probability of brittle fracture of the pole piece, thus improving the safety and cycle performance of the battery.
  • the mass fraction of the structural unit represented by Formula II is 0.5% to 15%, based on the total mass of the polymer.
  • the binder When the mass fraction of the structural unit represented by Formula II is within an appropriate range, the binder enables the pole piece to have both excellent flexibility and good adhesion, allowing the battery to maintain high capacity performance during cycling.
  • the polymer has a polydispersity coefficient of 1.7 to 2.3.
  • the polydispersity coefficient of the polymer is 1.85 to 2.25.
  • the polydispersity coefficient of the polymer is within a suitable range, the weight average molecular weight of the polymer is uniformly distributed, and the performance is balanced, which can ensure that the binder has excellent flexibility and adhesion at a low addition amount, and the battery Capacity retention during cycling is further improved.
  • the polymer has a Dv50 particle size of 100 ⁇ m to 200 ⁇ m, optionally, the polymer has a Dv50 particle size of 105 ⁇ m to 185 ⁇ m.
  • the ultra-high molecular weight polymer still has good processing properties and can ensure the production efficiency of the pole piece and battery.
  • the polymer has a crystallinity of 30% to 40%.
  • the polymer has a crystallinity of 31% to 39%.
  • Controlling the crystallinity of the polymer within an appropriate range allows the pole piece to have excellent flexibility, reduces the risk of breakage or light leakage during the winding and hot pressing processes, and can improve the safety performance of the battery.
  • the polymer is vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer.
  • Ethylene-tetrafluoroethylene copolymer vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene- One or more hexafluoropropylene copolymers.
  • the second aspect of the present application also provides a method for preparing a binder, which includes the following steps: providing a monomer represented by Formula III, a monomer represented by Formula IV and a reaction solvent, and performing a first-stage polymerization reaction to obtain the first-stage polymerization reaction. a product;
  • R 2 is selected from one or more types of fluorine, chlorine, and C 1-3 alkyl containing at least one fluorine atom;
  • the first product is subjected to a second-stage polymerization reaction in a water-insoluble gas atmosphere;
  • This preparation method can prepare ultra-high molecular weight polymer binder through segmented polymerization.
  • This binder can ensure sufficient adhesion of the pole piece at a low addition amount, and can further improve the flexibility of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety and cycle of the battery. performance.
  • the mass fraction of the monomer represented by Formula IV is 0.5% to 15%, based on the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the pole piece When the mass fraction of the monomer represented by Formula IV is within an appropriate range, the pole piece has both excellent flexibility and good adhesion, allowing the battery to maintain a high cycle capacity during cycling.
  • the monomer represented by Formula IV is one or more of chlorotrifluoroethylene, tetrafluoroethylene, and hexafluoropropylene.
  • the above-mentioned raw materials are simple and easy to obtain, which can significantly reduce production costs and increase output.
  • the reaction temperature of the first-stage polymerization reaction is 45°C to 60°C
  • the reaction time is 4 hours to 10 hours
  • the initial pressure is 4MPa to 6MPa.
  • the reaction temperature of the second stage polymerization reaction is 60°C to 80°C
  • the reaction time is 2 hours to 4 hours
  • the reaction pressure is 6MPa to 8MPa.
  • reaction time of the third stage polymerization reaction is 1 hour to 2 hours.
  • Controlling the reaction pressure, reaction time, and reaction temperature of each stage of the polymerization reaction within a suitable range can not only increase the weight average molecular weight of the polymer, but also ensure the uniformity of the weight average molecular weight of the polymer, so that the polymer has a lower polypeptide.
  • the dispersion coefficient improves the balance of polymer properties, and at the same time allows the pole piece to have excellent flexibility and adhesion with a low amount of binder added, and the cycle capacity retention rate of the battery can be further improved.
  • the chain transfer agent includes one or more of cyclohexane, isopropanol, methanol, and acetone.
  • the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.
  • the amount of chain transfer agent used is 1.5% to 3% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the first stage polymerization reaction includes the following steps:
  • the amount of water solvent used is 2 to 8 times the total mass of the monomer represented by formula III and the monomer represented by formula IV.
  • the dispersant includes one or both of cellulose ether and polyvinyl alcohol.
  • the cellulose ether includes one or both of methyl cellulose ether and carboxyethyl cellulose ether.
  • the amount of dispersant used is 0.1% to 0.3% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the initiator is an organic peroxide.
  • the organic peroxide includes t-amyl peroxypivalate, t-amyl peroxypivalate, 2-ethylperoxydicarbonate, diisopropylperoxydicarbonate, One or more types of tert-butyl peroxypivalate.
  • the amount of initiator used is 0.15% to 1% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.
  • the pH adjuster includes one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and ammonia.
  • the amount of pH adjuster used is 0.05% to 0.2% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • a third aspect of the present application provides a positive electrode sheet, including 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 film layer includes a positive electrode active material, a conductive agent, and a binder in any embodiment.
  • the adhesive prepared by the preparation method in any embodiment.
  • the positive electrode sheet has both excellent flexibility and good adhesion.
  • the mass fraction of the binder is 0.8% to 1%, based on the total mass of the positive electrode film layer.
  • Controlling the mass fraction of the binder within an appropriate range enables the pole piece to have both excellent flexibility and adhesion, allowing the battery to have a high cycle capacity retention rate during cycling.
  • a secondary battery including an electrode assembly and an electrolyte.
  • the electrode assembly includes a negative electrode sheet, a separator and a positive electrode sheet of the third aspect of the present application.
  • two Secondary batteries are lithium-ion batteries and sodium-ion batteries.
  • an electrical device including the secondary battery of the fourth aspect of the present application.
  • Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • Figure 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in Figure 1;
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG 5 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 4;
  • FIG. 6 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • 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).
  • Polyvinylidene fluoride is currently one of the most widely used binder types in secondary batteries.
  • the bonding force of traditional polyvinylidene fluoride is insufficient, and a large amount of addition is often required to ensure effective bonding of active materials, so that the pole pieces can achieve effective bonding force.
  • increasing the amount of polyvinylidene fluoride binder will, on the one hand, reduce the load of active materials in the pole pieces, affecting the improvement of battery power performance. On the other hand, it will reduce the flexibility of the pole pieces, making the pole pieces prone to brittle fracture and difficult to Meet the requirements for battery cycle performance and safety performance.
  • this application proposes a binder, which is a polymer containing structural units shown in Formula I and structural units shown in Formula II,
  • R 1 is selected from one or more types of fluorine, chlorine, and C 1-3 alkyl groups containing at least one fluorine atom, and the weight average molecular weight of the polymer is 5 million to 9 million.
  • binder refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.
  • polymer includes on the one hand a collection of chemically homogeneous macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass and chain length.
  • 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 uneven product.
  • 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.
  • the dispersion medium of the binder is an oily solvent.
  • the oily solvent include but are not limited to dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dicarbonate Methyl ester, ethyl cellulose, polycarbonate. That is, the binder is dissolved in the oily solvent.
  • a binder is used to fix the electrode active material and/or conductive agent in place and adhere them to the conductive metal component to form an electrode.
  • the binder serves as a positive electrode binder and is used to bind the positive electrode active material and/or conductive agent to form an electrode.
  • the binder serves as a negative electrode binder and is used to bind the negative electrode active material and/or conductive agent to form an electrode.
  • fluoro refers to the -F group.
  • chlorine refers to the -Cl group.
  • C 1-3 alkyl group containing at least one fluorine atom refers to an alkyl group containing 1 to 3 Cs in which at least one H atom is replaced by an F atom.
  • the C 1-3 alkyl group containing one fluorine atom is selected from -CF 3 group, -C 2 F 6 group.
  • the binder is a halogenated hydrocarbon copolymer, which can be selected from the group consisting of vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, Vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene One or more of vinyl chloride-tetrafluoroethylene-hexafluoropropylene copolymers.
  • the fluorine element contained in the polymer forms hydrogen bonds with the hydroxyl groups or/and carboxyl groups on the surface of the active material and the current collector surface, which can improve the adhesion of the pole piece.
  • Polymers with a weight average molecular weight of 5 million to 9 million have great cohesion and intermolecular forces, which can improve the adhesion of the pole pieces at low addition amounts.
  • the structural unit represented by formula II in the polymer can introduce disordered units into the crystallization region of the periodically arranged chain segments formed by the structural unit represented by formula I, thereby reducing the crystallinity of the polymer and increasing the mobility of the chain segments.
  • the polymer contains the structural unit represented by formula II, which can reduce the content of the structural unit represented by formula I, reduce the crystallization caused by the polymerization of the structural unit represented by formula I, thereby further improving the pole piece.
  • the flexibility of the piece improves the flexibility of the pole piece.
  • the weight average molecular weight of the polymer is too large, the too high weight average molecular weight will reduce the flexibility of the pole piece; if the weight average molecular weight of the polymer is too small, the pole piece cannot be guaranteed to have the properties of a low binder addition. Sufficient adhesion.
  • This binder can ensure sufficient adhesion of the pole piece at a low addition amount, and can further improve the flexibility of the pole piece, reduce the probability of brittle fracture of the pole piece, thereby improving the safety and cycle performance of the battery. .
  • the weight average molecular weight of the polymer can be measured using methods known in the art, such as gel chromatography, such as Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). carry out testing.
  • the test method is to use a polystyrene solution sample with a mass fraction of 3.0% as a reference and select a matching chromatographic column (oil: Styragel HT5DMF7.8*300mm+Styragel HT4).
  • NMP N-methylpyrrolidone
  • the mass fraction of the structural unit represented by Formula II is 0.5% to 15%, based on the total mass of the polymer.
  • the mass fraction of the structural unit represented by Formula II can be selected from 0.5% to 1%, 1% to 2%, 3% to 4%, 4% to 5%, 5% to 6%, 6 % ⁇ 7%, 7% ⁇ 8%, 8% ⁇ 9%, 9% ⁇ 10%, 10% ⁇ 11%, 11% ⁇ 12%, 12% ⁇ 13%, 13% ⁇ 14%, 14% ⁇ 15%, 0.5% ⁇ 3%, 3% ⁇ 6%, 6% ⁇ 9%, 9% ⁇ 12%, 12% ⁇ 15%, 0.5% Any one of 5%, 5% to 10%, and 10% to 15%.
  • the pole piece can have both excellent flexibility and good adhesion with a low amount of binder added, making the battery more durable during cycling. Maintain good capacity performance.
  • the polymer has a polydispersity coefficient of 1.7 to 2.3.
  • the polydispersity coefficient of the polymer can be selected from any one of 1.7 to 1.85, 1.85 to 1.95, 1.95 to 2.05, 2.05 to 2.15, and 1.85 to 2.25.
  • polydispersity coefficient refers to the ratio of the weight average molecular weight of the polymer to the number average molecular weight of the polymer.
  • number average molecular weight refers to the sum of the mole fractions of molecules of different molecular weights in the polymer multiplied by their corresponding molecular weights.
  • the order of the polymer will be low, which will affect the dispersion of the binder, reduce the flexibility of the pole piece, and also reduce the solid content of the slurry, increasing production costs; if The polydispersity coefficient of the polymer is too small, the preparation process is difficult, and the yield rate is low, resulting in high production costs.
  • the polydispersity coefficient of the polymer is within a suitable range, the weight average molecular weight of the polymer is uniformly distributed, and the performance is balanced, which can ensure that the binder has excellent flexibility and adhesion at a low amount of addition, and the battery can be used during cycling The capacity retention rate during the process is further improved.
  • a suitable polydispersity coefficient of the polymer can effectively increase the solid content of the slurry and reduce production costs.
  • the polydispersity coefficient can be tested using methods known in the art, such as gel chromatography, such as Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141).
  • gel chromatography such as Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141).
  • a polystyrene solution sample with a mass fraction of 3.0% is used as a reference to select a matching chromatography column (oil: Styragel HT5DMF7.8 ⁇ 300mm+Styragel HT4).
  • NMP N-methylpyrrolidone
  • the polymer has a Dv50 particle size of 100 ⁇ m to 200 ⁇ m.
  • the Dv50 particle size of the polymer can be selected from 105 ⁇ m to 115 ⁇ m, 115 ⁇ m to 125 ⁇ m, 125 ⁇ m to 135 ⁇ m, 135 ⁇ m to 145 ⁇ m, 145 ⁇ m to 155 ⁇ m, 155 ⁇ m to 165 ⁇ m, 165 ⁇ m to 175 ⁇ m, 175 ⁇ m to 185 ⁇ m, 185 ⁇ m to 195 ⁇ m. , any one of 105 ⁇ m ⁇ 125 ⁇ m, 125 ⁇ m ⁇ 145 ⁇ m, 145 ⁇ m ⁇ 165 ⁇ m, 165 ⁇ m ⁇ 185 ⁇ m, 105 ⁇ m ⁇ 185 ⁇ m, 125 ⁇ m ⁇ 185 ⁇ m.
  • Dv50 particle size refers to the particle size corresponding to when the cumulative particle size distribution number of particles reaches 50% in the particle size distribution curve. Its physical meaning is that particles with a particle size smaller (or larger) than it account for 50%. %.
  • the Dv50 particle size of the polymer is too large, it will be relatively difficult to dissolve the polymer, and the dispersibility of the binder will be reduced, which will reduce the flexibility of the pole piece. At the same time, it will be difficult for the polymer to dissolve, which will reduce the speed of the pulping process; if the polymer The Dv50 particle size is too small, and the bonding force of the pole piece decreases.
  • Controlling the Dv50 particle size of the polymer within an appropriate range can improve the solubility of the binder, improve the flexibility of the pole piece, and make the pole piece have better adhesion.
  • a suitable range of Dv50 particle size of the polymer can also control the amount of binder at a low level without excessive negative impact on the bonding performance, thus effectively improving the performance of high-dose adhesive in traditional technology. The performance of the pole piece and battery is damaged due to the binder.
  • the polymer has a crystallinity of 30% to 40%.
  • the crystallinity of the polymer can be selected from 30% to 32%, 32% to 34%, 34% to 36%, 36% to 38%, 38% to 39%, 31% to 33%, 33% to Any one of 35%, 35% to 37%, 37% to 39%, and 31% to 39%.
  • crystallity refers to the proportion of crystalline areas in the polymer. There are some areas with stable and regularly arranged molecules in the microstructure. Areas where the molecules are regularly and closely arranged are called crystalline areas.
  • the crystallinity of the polymer is too large, the mobility of the polymer chain segments is reduced, which affects the flexibility of the pole piece. At the same time, the dissolution of the polymer is difficult and the speed of the pulping process is reduced; if the crystallinity of the polymer is too small, the polymerization The degree of regular and dense packing of the molecular chains is reduced, which affects the chemical stability and thermal stability of the binder.
  • the pole piece By controlling the crystallinity of the polymer within an appropriate range so that the amount of binder is at a low level, the pole piece can have both excellent flexibility and good adhesion, which in turn helps to increase the loading capacity of active materials and Battery cycle performance.
  • the crystallinity can be tested using methods known in the art, such as differential scanning thermal analysis.
  • 0.5 g of polymer is placed in an aluminum dry pot, shaken flat, and the crucible lid is covered. Under a nitrogen atmosphere, a purge gas of 50 ml/min and a protective gas of 70 ml/min are used. The heating rate is 10°C per minute, and the test temperature range is -100°C to 400°C.
  • a differential scanning calorimeter (DSC) of the American TA Instrument model Discovery 250 is used to test and eliminate thermal history.
  • the polymer is vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene.
  • Vinylidene fluoride copolymer vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene One or more copolymers.
  • a method for preparing an adhesive comprising: Next steps:
  • R 2 is selected from one or more types of fluorine, chlorine, and C 1-3 alkyl containing at least one fluorine atom;
  • the first product is subjected to a second-stage polymerization reaction in a water-insoluble gas atmosphere;
  • multiple parts of the first product are mixed, and the second stage polymerization reaction is performed under a water-insoluble gas atmosphere. It can be understood that multiple portions of the first product can be simultaneously prepared through multiple reaction kettles, or can be prepared multiple times through one reaction kettle. The uniformity of the polymer can be improved through multiple, segmented synthesis methods.
  • the polymerization reaction using the segmented method can prepare ultra-high molecular weight polymers, so that the binder can meet the adhesive strength requirements of the pole pieces at a low addition amount, and at the same time, the pole pieces have excellent flexibility, which is conducive to improving the battery Capacity retention during cycling.
  • a first product with a relatively low weight average molecular weight is formed in the first stage of polymerization reaction, and a molecular chain segment with a target molecular weight is formed in the second stage of polymerization reaction.
  • the third stage of polymerization reaction is used to control the molecular weight of the polymer and avoid polymerization. The randomness of the weight average molecular weight is too high, which improves the uniformity of the polymer.
  • staged polymerization can not only improve the utilization rate of the reactor during the polymer preparation process, but also save time and reduce the residence time of the polymer in the reactor.
  • the production efficiency of the polymer can be further improved.
  • the first product can be a reaction liquid formed by the monomer represented by Formula III, the monomer represented by Formula IV and the reaction solvent, or can be a product after processing and purification of the above reaction liquid.
  • the mass fraction of the monomer represented by Formula IV is 0.5% to 15%, based on the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the mass fraction of the monomer shown in Formula IV can be selected from 0.5% to 1%, 1% to 2%, 3% to 4%, 4% to 5%, 5% to 6%, 6% to 7 %, 7% to 8%, 8% to 9%, 9% to 10%, 10% to 11%, 11% to 12%, 12% to 13%, 13% to 14%, 14% to 15%, Any of 0.5% to 3%, 3% to 6%, 6% to 9%, 9% to 12%, 12% to 15%, 0.5% to 5%, 5% to 10%, 10% to 15% A sort of.
  • the pole piece When the mass fraction of the monomer represented by Formula IV is within an appropriate range, the pole piece has both excellent flexibility and good adhesion, allowing the battery to maintain a high cycle capacity during cycling.
  • the monomer represented by Formula IV is one or more of chlorotrifluoroethylene, tetrafluoroethylene, and hexafluoropropylene.
  • the above-mentioned raw materials are simple and easy to obtain, which can significantly reduce production costs and increase output.
  • the reaction temperature of the first stage polymerization reaction is 45°C to 60°C. In some embodiments, the reaction temperature of the first-stage polymerization reaction can be selected from any one of 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, and 45°C to 55°C.
  • the reaction time of the first stage polymerization reaction is 4 hours to 10 hours. In some embodiments, the reaction time of the first stage polymerization reaction can be selected from 4 hours to 5 hours, 5 hours to 6 hours, 6 hours to 7 hours, 7 hours to 8 hours, 8 hours to 9 hours, 9 hours to Any one of 10 hours, 4 hours to 6 hours, 6 hours to 8 hours, 8 hours to 10 hours, 5 hours to 10 hours.
  • the initial pressure of the first stage polymerization reaction is 4MPa ⁇ 6MPa. In some embodiments, the initial pressure of the first stage polymerization reaction is 4MPa ⁇ 5MPa or 5MPa ⁇ 6MPa.
  • the reaction temperature of the second stage polymerization reaction is 60°C to 80°C. In some embodiments, the reaction temperature of the second stage polymerization reaction is 60°C to 70°C or 70°C to 80°C.
  • reaction time of the second stage polymerization reaction is 2 hours to 4 hours. In some embodiments, the reaction time of the second stage polymerization reaction is 2 hours to 3 hours. hour or 3 to 4 hours.
  • the reaction pressure of the second stage polymerization reaction is 6MPa ⁇ 8MPa. In some embodiments, the reaction pressure of the second stage polymerization reaction is 6MPa ⁇ 7MPa or 7MPa ⁇ 8MPa.
  • the reaction time of the third stage polymerization reaction is 1 hour to 2 hours.
  • the uniformity of the weight average molecular weight of the polymerized product can be controlled to ensure that the product has a lower molecular weight.
  • the dispersion coefficient improves the uniformity of product performance.
  • the prepared polymer enables the pole piece to have excellent flexibility and adhesion at a low addition amount, and the cycle capacity retention rate of the battery can be further improved.
  • the chain transfer agent includes one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.
  • Water-insoluble gas refers to a gas with a gas solubility less than 0.1L.
  • Gas solubility refers to the volume of gas when it is dissolved in 1L of water and reaches saturation when the pressure of the gas is 1.013 ⁇ 10 5 Pa at 20°C.
  • the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.
  • the water-insoluble gas is selected from one or more of nitrogen, oxygen, hydrogen, and methane.
  • the amount of chain transfer agent used is 1.5% to 3% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.
  • the amount of chain transfer agent used may also be, for example, 2% or 2.5% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • Controlling the amount of chain transfer agent within an appropriate range can control the polymer chain length, thereby obtaining a polymer with an appropriate molecular weight range.
  • the first stage polymerization reaction includes the following steps:
  • the materials Before raising the temperature to carry out the polymerization reaction, the materials should be mixed evenly first to make the reaction proceed more thoroughly and the polydispersity coefficient, crystallinity and particle size of the resulting polymer to be more uniform.
  • the amount of water solvent used is 2 to 8 times the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the amount of water solvent used may be, for example, 3, 4, 5, 6 or 7 times the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the water solvent is deionized water.
  • the dispersant includes one or both of cellulose ether and polyvinyl alcohol.
  • the cellulose ether includes one or both of methyl cellulose ether and carboxyethyl cellulose ether.
  • the amount of dispersant is 0.1% to 0.3% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the amount of dispersant used may also be, for example, 0.2% of the total mass of the monomer represented by formula III and the monomer represented by formula IV.
  • the initiator is an organic peroxide.
  • the organic peroxide includes tert-amyl peroxypivalate, tert-amyl peroxypivalate, 2-ethylperoxydicarbonate, diisopropylperoxydicarbonate, One or more types of tert-butyl peroxypivalate.
  • the amount of initiator used is 0.15% to 1% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the amount of initiator used can also be selected as 0.2%, 0.4%, 0.6% or 0.8% of the total mass of the monomer represented by formula III and the monomer represented by formula IV, for example.
  • the pH adjuster includes one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and ammonia.
  • the amount of pH adjuster is 0.05% to 0.2% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the amount of pH adjuster used may also be, for example, 0.1% or 0.15% of the total mass of the monomer represented by Formula III and the monomer represented by Formula IV.
  • the positive electrode sheet has both excellent flexibility and good adhesion.
  • the mass fraction of the binder is 0.8% to 1%, based on the positive electrode film The total mass of the layer.
  • Controlling the mass fraction of the binder within an appropriate range can enable the pole piece to have both excellent flexibility and adhesion, allowing the battery to have a high cycle capacity retention rate during cycling.
  • 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 film layer includes a positive electrode active material, a conductive agent and a binder in some embodiments or prepared by a preparation method in some embodiments. Binder.
  • the positive electrode sheet has both excellent flexibility and good adhesion.
  • the mass fraction of the binder is 0.8% to 1%, based on the total mass of the positive electrode film layer. In some embodiments, the mass fraction of the binder can be selected from any one of 0.8% to 0.85%, 0.85% to 0.9%, 0.9% to 0.95%, 0.95% to 1%, and 0.85% to 0.95%.
  • the binder coating layer covering the surface of the positive electrode active material will be too thick, resulting in the electrode piece being brittle and having poor toughness.
  • too much binder will cause the load capacity of the positive active material in the pole piece to decrease, resulting in a reduction in the energy density of the battery and a reduction in battery capacity.
  • Controlling the mass fraction of the binder within an appropriate range enables the pole piece to have both excellent flexibility and good adhesion, allowing the battery to have good cycle capacity retention during cycling.
  • 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.
  • Composite current collection The body can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base material (such as polypropylene (PP), polyethylene terephthalate It is formed on base materials such as alcohol 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 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, It can also be a multi-layer composite film without 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.
  • a fourth aspect of the present application provides a secondary battery, including an electrode assembly and an electrolyte.
  • the electrode assembly includes a negative electrode sheet, a separator, and the positive electrode sheet of the third aspect of the present application.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 1 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • a battery module including the secondary battery of the fourth aspect of the present application.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • a battery pack is provided, including the battery module of the fifth aspect of the present application.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • an electrical device including at least one of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect, or the battery pack of the sixth aspect of the present application.
  • 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 may be used as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG. 6 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the first stage of polymerization reaction Add 4kg of deionized water and 2.5g of methylcellulose ether to the 10L autoclave of No.1 and No.2, evacuate and replace O2 with N2 three times, and then add 5g of tert-butyl hydrochloride Oxidize pivalate and 2g of sodium bicarbonate, and fill in 0.94kg of vinylidene fluoride and 0.06kg of chlorotrifluoroethylene to bring the pressure to 5MPa. Mix and stir for 30 minutes, raise the temperature to 45°C, and react for 4 hours;
  • the second stage of polymerization reaction transfer the reaction liquid in No. 1 and No. 2 reactors to No. 3 reactor, fill with nitrogen to a pressure of 7MPa, raise the temperature to 70°C, and stir for 3 hours;
  • the third stage of polymerization reaction add 38g of cyclohexane and continue the reaction for 1 hour, then stop the reaction.
  • the reaction system is centrifuged and the solid phase is collected, washed and dried to obtain a vinylidene fluoride-chlorotrifluoroethylene copolymer binder.
  • NMP N-methylpyrrolidone
  • the viscosity is high, add NMP solution to reduce it to the above viscosity range, then stir for 30 minutes at a revolution speed of 25 r/min and a rotation speed of 1250 r/min to obtain the positive electrode slurry.
  • the prepared cathode slurry is scraped onto the carbon-coated aluminum foil with a scraping weight of 550mg/(1540mm 2 ) on one side, baked at 110°C for 15 minutes, cold-pressed to a density of 2.7g/cm 3 and then cut into circles with a diameter of 15mm. slice to obtain the positive electrode slice.
  • Metal lithium sheets are used as negative electrode sheets.
  • Example 1 The positive electrode sheet, negative electrode sheet, separator and electrolyte in Example 1 were assembled into a button battery in a buck box.
  • Example 1 Basically the same as Example 1, the difference is that the reaction times in the first stage polymerization reaction are adjusted to 5h, 6h, 7h, and 8h respectively, and the chain transfer agent cyclohexane in the third stage polymerization reaction is adjusted to 33g, 28g, 23g, 18g, the specific parameters are shown in Table 1.
  • Example 1 Basically the same as Example 1, the difference is that the total amount of vinylidene fluoride and chlorotrifluoroethylene monomers added is kept unchanged, and the mass fraction of chlorotrifluoroethylene is adjusted. Based on the total amount of vinylidene fluoride and chlorotrifluoroethylene monomers, Mass meter, the specific parameters are shown in Table 1.
  • Example 2 It is basically the same as Example 1, except that the mass fraction of the vinylidene fluoride-chlorotrifluoroethylene copolymer binder is adjusted, based on the total mass of the positive electrode film layer.
  • the specific parameters are as shown in Table 1.
  • Example 1 Basically the same as Example 1, the difference is that 0.06kg chlorotrifluoroethylene is replaced with 0.06kg tetrafluoroethylene, 0.06kg hexafluoropropylene, 0.03kg chlorotrifluoroethylene + 0.03kg tetrafluoroethylene, 0.03kg chlorotrifluoroethylene Ethylene + 0.03kg hexafluoropropylene, 0.03kg tetrafluoroethylene + 0.03kg hexafluoropropylene, 0.02kg chlorotrifluoroethylene + 0.02kg tetrafluoroethylene + 0.02kg hexafluoropropylene.
  • Table 1 The specific parameters are shown in Table 1.
  • Example 1 Basically the same as Example 1, the polymerized monomer is only 1kg vinylidene fluoride, and the specific parameters are as shown in Table 1.
  • Example 2 Basically the same as Example 2, the polymerized monomer is only 1kg vinylidene fluoride, and the specific parameters are shown in Table 1.
  • Example 3 Basically the same as Example 3, the polymerized monomer is only 1kg vinylidene fluoride, and the specific parameters are shown in Table 1.
  • Example 4 Basically the same as Example 4, the polymerized monomer is only 1kg vinylidene fluoride, and the specific parameters are shown in Table 1.
  • Example 5 Basically the same as Example 5, the polymerized monomer is only 1kg vinylidene fluoride, and the specific parameters are shown in Table 1.
  • the binder is polyvinylidene fluoride with a weight average molecular weight of 800,000, purchased from Huaan Company, model number 605, and the mass fraction of the binder is adjusted to 2.5%, based on the positive electrode film layer Total mass meter, specific parameters are shown in Table 1.
  • DSC differential scanning calorimeter
  • the indicator light is on, adjust the limit block to the appropriate position, and fix the end of the steel plate that is not attached to the pole piece with the lower clamp. Fold the paper tape upward and fix it with the upper clamp. Use the "up” and “down” buttons on the manual controller that comes with the tensile machine to adjust the position of the upper clamp. Then perform the test and read the values. Divide the force of the pole piece when the force is balanced by the width of the tape as the bonding force of the pole piece per unit length to characterize the bonding strength between the positive electrode film layer and the current collector.
  • the battery capacity retention rate data corresponding to Examples 1 to 15 or Comparative Examples 1 to 6 in Table 1 is the data measured after 500 cycles under the above test conditions, that is, the value of P500.
  • the binders in Examples 1 to 19 all contain polymers.
  • the compound contains structural units derived from vinylidene fluoride and at least one structural unit derived from chlorotrifluoroethylene, tetrafluoroethylene, and hexafluoropropylene, and the weight average molecular weight of the polymer is 5 million to 9 million.
  • Example 5 Comparison with Comparative Example 5 shows that the introduction of comonomers in the polymer can improve the flexibility of the pole piece without significantly reducing the adhesive force of the pole piece, and reduce breakage or light leakage during the winding and hot pressing processes. risk and improve battery safety performance.
  • Examples 1 to 19 have vinylidene fluoride-chlorotrifluoroethylene copolymer binders, vinylidene fluoride-tetrafluoroethylene copolymer binders, and vinylidene fluoride-chlorotrifluoroethylene copolymer binders with weight average molecular weights of 5 million to 9 million.
  • Vinylidene fluoride-hexafluoropropylene copolymer adhesive, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene copolymer adhesive, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer adhesive, fluoride Ethylene-tetrafluoroethylene-hexafluoropropylene copolymer binder or vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer binder can ensure sufficient adhesion of the pole piece at a low addition amount. At the same time, it can further improve the flexibility of the pole piece, thereby improving the capacity retention rate of the battery during the cycle, effectively improving the performance damage of the pole piece and battery caused by the high amount of binder in traditional technology.
  • vinylidene fluoride-chlorotrifluoroethylene copolymer binders vinylidene fluoride-tetrafluoroethylene copolymer binders, and vinylidene fluoride-hexafluoroethylene copolymers with polydispersity coefficients of 1.7 to 2.3
  • the vinyl fluoride-hexafluoropropylene copolymer binder gives the pole piece excellent flexibility and adhesion at a low addition amount, allowing the battery to
  • vinylidene fluoride-chlorotrifluoroethylene copolymer binders vinylidene fluoride-tetrafluoroethylene copolymer binders, and vinylidene fluoride-chlorotrifluoroethylene copolymer binders with crystallinity of 30% to 40% Hexafluoropropylene copolymer binder, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene copolymer binder, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer binder, vinylidene fluoride-tetrafluoroethylene copolymer binder Vinyl fluoride-hexafluoropropylene copolymer binder or vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer binder enables the pole

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Abstract

本申请提供了一种粘结剂、制备方法、正极极片、二次电池及用电装置。该粘结剂为含有如式I所示的结构单元和式II所示的结构单元的聚合物，其中，R1选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种，聚合物的重均分子量为500万～900万。该粘结剂在低添加量下就能够保证极片具有足够的粘结力，同时可以进一步提升极片的柔性，降低极片发生脆断的概率，从而提高电池的安全性和循环性能。

Description

粘结剂、制备方法、正极极片、二次电池及用电装置
交叉引用
本申请引用于2022年8月30日递交的名称为“粘结剂、制备方法、正极极片、二次电池及用电装置”的第202211043966.4号中国专利申请，其通过引用被全部并入本申请。
技术领域
本申请涉及二次电池技术领域，尤其涉及一种粘结剂、制备方法、正极极片、二次电池、电池模块、电池包及用电装置。
背景技术
近年来，二次电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着二次电池应用的普及，对其循环性能、使用寿命等也提出了更高的要求。
粘结剂是二次电池中的常用材料，在电池的极片、隔离膜、封装处等均有很大需求。但是现有的粘结剂需要大量添加才能够保证极片具有足够的粘结力，同时在循环过程中粘结剂无法保持足够的柔性，使得极片容易发生脆断，进而引发安全问题。因此，现有的粘结剂仍有待改进。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种粘结剂，该粘结剂在低添加量下就可以使得极片具有优异的粘结力，同时该粘结剂能够提高极片的柔韧性，进而提高电池的循环性能。
为了达到上述目的，本申请提供了一种粘结剂，该粘结剂为含有如式I所示的结构单元和式II所示的结构单元的聚合物，
其中，R1选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种，聚合物的重均分子量为500万～900万。
该粘结剂在低添加量下就能够保证极片具有足够的粘结力，同时可以进一步提升极片的柔性，降低极片发生脆断的概率，从而提高电池的安全性和循环性能。
在任意实施方式中，式II所示的结构单元的质量分数为0.5％～15％，基于聚合物总质量计。
式II所示的结构单元的质量分数在合适范围内时，该粘结剂使得极片兼具优异的柔韧性和良好的粘结力，使得电池在循环过程中保持高的容量性能。
在任意实施方式中，聚合物的多分散系数为1.7～2.3。可选地，聚合物的多分散系数为1.85～2.25。
聚合物的多分散系数在合适范围内，聚合物的重均分子量分布均匀，性能均衡，能够保证粘结剂在低添加量的情况下，使得极片具有优异的柔韧性和粘结力，电池在循环过程中的容量保持率进一步提高。
在任意实施方式中，聚合物的Dv50粒径为100μm～200μm，可选地，聚合物的Dv50粒径为105μm～185μm。
控制聚合物的Dv50粒径在合适范围内，超高分子量的聚合物依然具有良好的加工性能，能够保证极片和电池的生产效率。
在任意实施方式中，聚合物的结晶度为30％～40％。可选地，聚合物的结晶度为31％～39％。
控制聚合物的结晶度在合适范围内，使得极片具有优异的柔韧性，减少在卷绕和热压工序中出现断裂或漏光的风险，能够提高电池的安全性能。
在任意实施方式中，聚合物为偏氟乙烯-三氟氯乙烯共聚物、偏氟乙烯-四氟乙烯共聚物、偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯 乙烯-四氟乙烯共聚物、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物、偏氟乙烯-四氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物中的一种或多种。
本申请的第二方面还提供一种粘结剂的制备方法，包括以下步骤：提供式III所示的单体、式Ⅳ所示的单体和反应溶剂，进行第一段聚合反应，得到第一产物；
其中，R2选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种；
将第一产物在非水溶性气体氛围下进行第二段聚合反应；
加入链转移剂，进行第三段聚合反应，得到重均分子量为500万～900万的聚合物。
该制备方法通过分段聚合，能够制备出超高分子量的聚合物粘结剂。该粘结剂在低添加量的情况下，就能够保证极片具有足够的粘结力，同时可以进一步提升极片的柔性，降低极片发生脆断的概率，从而提高电池的安全性和循环性能。
任意实施方式中，式Ⅳ所示的单体的质量分数为0.5％～15％，基于式III所示的单体和式Ⅳ所示的单体的总质量计。
式Ⅳ所示的单体的质量分数在合适范围内时，极片兼具优异的柔韧性和良好的粘结力，使得电池在循环过程中能够保持高的循环容量。
任意实施方式中，式Ⅳ所示的单体为三氟氯乙烯、四氟乙烯、六氟丙烯中的一种或多种。
上述原材料简单易得，能够大幅度降低生产成本，提高产量。
在任意实施方式中，第一段聚合反应的反应温度为45℃～60℃，反应时间为4小时～10小时，初始压力为4MPa～6MPa。
在任意实施方式中，第二段聚合反应的反应温度为60℃～80℃，反应时间为2小时～4小时，反应压力为6MPa～8MPa。
在任意实施方式中，第三段聚合反应的反应时间为1小时～2小时。
控制各个阶段聚合反应的反应压力、反应时间、反应温度在合适的范围内，在提高聚合物的重均分子量的同时，可以保证聚合物重均分子量的均匀性，使得聚合物具有较低的多分散系数，提高聚合物性能的均衡度，同时使得极片在粘结剂低添加量下即具有优异的柔韧性和粘结力，且电池的循环容量保持率能够进一步提高。
在任意实施方式中，链转移剂包括环己烷、异丙醇、甲醇以及丙酮中的一种或多种。
在任意实施方式中，非水溶性气体选自氮气、氧气、氢气、甲烷中的一种或多种。
在任意实施方式中，链转移剂的用量为式III所示的单体和式IV所示的单体总质量的1.5％～3％。
在任意实施方式中，第一段聚合反应包括以下步骤：
向容器中加入水溶剂和分散剂，去除反应体系中的氧气；
向所述容器中加入引发剂和pH调节剂，调节pH值至6.5～7，然后加入式III所示的单体和式IV所示的单体，使容器中的压力达到4MPa～6MPa；
搅拌30分钟～60分钟后，升温至45℃～60℃，进行第一段聚合反应。
在任意实施方式中，水溶剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的2～8倍。
在任意实施方式中，分散剂包括纤维素醚、聚乙烯醇中的一种或两种。
在任意实施方式中，纤维素醚包括甲基纤维素醚、羧乙基纤维素醚中的一种或两种。
在任意实施方式中，分散剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的0.1％～0.3％。
在任意实施方式中，引发剂为有机过氧化物。
在任意实施方式中，有机过氧化物包括过氧化新戊酸叔戊酯、过氧化叔戊基新戊酸酯、2-乙基过氧化二碳酸酯、二异丙基过氧化二碳酸酯、叔丁基过氧化新戊酸酯中的一种或多种。
在任意实施方式中，引发剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的0.15％～1％。
在任意实施方式中，pH调节剂包括碳酸钾、碳酸氢钾、碳酸钠、碳酸氢钠、氨水中的一种或多种。
在任意实施方式中，pH调节剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的0.05％～0.2％。
本申请的第三方面提供一种正极极片，包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，正极膜层包括正极活性材料、导电剂和任意实施方式中的粘结剂或任意实施方式中的制备方法制备的粘结剂。
该正极极片兼具优异的柔韧性和良好的粘结力。
在任意实施方式中，粘结剂的质量分数为0.8％～1％，基于正极膜层的总质量计。
控制粘结剂的质量分数在合适的范围内，使得极片兼具优异的柔韧性和粘结力，使得电池在循环过程中具有高的循环容量保持率。
在本申请的第四方面提供，提供一种二次电池，包括电极组件和电解液，所述电极组件包括负极极片、隔离膜和本申请第三方面的正极极片，可选地，二次电池为锂离子电池和钠离子电池。
在本申请的第五方面，提供一种用电装置，包括本申请第四方面的二次电池。
附图说明
图1是本申请一实施方式的二次电池的示意图；
图2是图1所示的本申请一实施方式的二次电池的分解图；
图3是本申请一实施方式的电池模块的示意图；
图4是本申请一实施方式的电池包的示意图；
图5是图4所示的本申请一实施方式的电池包的分解图；
图6是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的正极活性材料及其制造方法、正极极片、二次电池、电池模块、电池包和电学装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征 可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
聚偏氟乙烯是目前二次电池中使用最为广泛的粘结剂种类之一。然而，传统聚偏氟乙烯的粘结力不足，往往需要大量添加才能保证活性物质的有效粘结，从而使得极片达到有效的粘结力。然而聚偏氟乙烯粘结剂用量的提高一方面会降低活性材料在极片中的负载量，影响电池功率性能的提升，一方面会降低极片的柔性，使得极片易于发生脆断，难以满足对于电池循环性能和安全性能的要求。
[粘结剂]
基于此，本申请提出了一种粘结剂，该粘结剂为含有如式I所示的结构单元和式II所示的结构单元的聚合物，
其中，R1选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种，聚合物的重均分子量为500万～900万。
在本文中，术语“粘结剂”是指在分散介质中形成胶体溶液或胶体分散液的化学化合物、聚合物或混合物。
在本文中，术语“聚合物”一方面包括通过聚合反应制备的化学上均一的、但在聚合度、摩尔质量和链长方面不同的大分子的集合体。该术语另一方面也包括由聚合反应形成的这样的大分子集合体的衍生物，即可以通过上述大分子中的官能团的反应，例如加成或取代获得的并且可以是化学上均一的或化学上不均一的产物。
在本文中，术语“重均分子量”是指聚合物中用不同分子量的分子所占的重量分数与其对应的分子量乘积的总和。
在一些实施方式中，粘结剂的分散介质是油性溶剂，油性溶剂的示例包括但不限于二甲基乙酰胺、N，N-二甲基甲酰胺、N-甲基吡咯烷酮、丙酮、碳酸二甲酯、乙基纤维素、聚碳酸酯。即，粘结剂溶解于油性溶剂中。
在一些实施方式中，粘结剂用于将电极活性物质及/或导电剂固定在合适位置并将它们粘附在导电金属部件以形成电极。
在一些实施方式中，粘结剂作为正极粘结剂，用于粘结正极活性材料及/或导电剂以形成电极。
在一些实施方式中，粘结剂作为负极粘结剂，用于粘结负极活性材料及/或导电剂以形成电极。
在本文中，术语“氟”指的是-F基团。
在本文中，术语“氯”指的是-Cl基团。
在本文中，术语“至少含有一个氟原子的C1-3烷基”是指至少有一个H原子被F原子取代的含有1-3个C的烷基。在一些实施方式中，含有一个氟原子的C1-3烷基选自-CF3基团、-C2F6基团。
在一些实施方式中，粘结剂为卤代烃共聚物，可选自偏氟乙烯-三氟氯乙烯共聚物、偏氟乙烯-四氟乙烯共聚物、偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物、偏氟乙烯-四氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物中的一种或多种。
聚合物含有的氟元素与活性材料表面及集流体表面的羟基或/和羧基形成氢键作用，能够提高极片的粘结力。重均分子量为500万～900万的聚合物具有极大的内聚力和分子间作用力，能够在低添加量下提高极片的粘结力。聚合物中式Ⅱ所示的结构单元，能够在式Ⅰ所示的结构单元形成的周期排列的链段的结晶区中引入无序单元，进而降低聚合物的结晶度，增加链段的可移动性，提高极片的柔韧性，同时聚合物中包含式Ⅱ所示的结构单元，能够降低式Ⅰ所示的结构单元的含量，减少式Ⅰ所示的结构单元聚合导致的结晶，从而进一步提高极片的柔韧性。
若聚合物的重均分子量过大，过高的重均分子量会降低极片的柔韧性；若聚合物的重均分子量过小，在粘结剂低添加量的情况下，无法保证极片具有足够的粘结力。
该粘结剂在较低的添加量下就能够保证极片具有足够的粘结力，同时可以进一步改善极片的柔性，降低极片发生脆断的概率，从而提高电池的安全性和循环性能。
在本申请中，聚合物的重均分子量的测试可以选用本领域已知的方法进行测试，例如采用凝胶色谱法进行测试，如采用Waters 2695Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)进行测试。在一些实施方式中，测试方法为以质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的聚合物胶液，配置好的溶液静置一天，备用。测试时，先用注射器吸取四氢呋喃，进行冲洗，重复几次。然后吸取5ml实验溶液，排除注射器中的空气，将针尖擦干。最后将试样溶液缓缓注入进样口。待示数稳定后获取数据，读取重均分子量。
在一些实施方式中，式II所示的结构单元的质量分数为0.5％～15％，基于聚合物的总质量计。在一些实施方式中，式II所示的结构单元的质量分数可选为0.5％～1％，1％～2％，3％～4％，4％～5％，5％～6％，6％～7％，7％～8％，8％～9％，9％～10％，10％～11％，11％～12％， 12％～13％，13％～14％，14％～15％，0.5％～3％，3％～6％，6％～9％，9％～12％，12％～15％，0.5％～5％，5％～10％，10％～15％中的任意一种。
若式II所示的结构单元的质量分数过低，达不到改善极片柔韧性的目的；若式II所示的结构单元的质量分数过高，极片的粘结力下降，影响电池的循环性能。
式II所示的结构单元的质量分数在合适范围内时，使得极片在粘结剂低添加量的情况下就能兼具优异的柔韧性和良好的粘结力，使得电池在循环过程中保持良好的容量性能。
在一些实施方式中，聚合物的多分散系数为1.7～2.3。在一些实施方式中，聚合物的多分散系数可选为1.7～1.85、1.85～1.95、1.95～2.05、2.05～2.15、1.85～2.25中的任意一种。
在本文书，术语“多分散系数”指聚合物的重均分子量与聚合物的数均分子量的比值。
在本文中，术语“数均分子量”是指聚合物中用不同分子量的分子所占的摩尔分数与其对应的分子量乘积的总和。
若聚合物的多分散系数过大，则聚合物的有序性较低，影响粘结剂的分散性，使得极片的柔韧性下降，同时也使得浆料固含量下降，增加生产成本；若聚合物的多分散系数过小，制备工艺难度较大，且优率较低，导致生产成本较高。
聚合物的多分散系数在合适范围内，聚合物的重均分子量分布均匀，性能均衡，能够保证粘结剂在低添加量下就使得极片具有优异的柔韧性和粘结力，电池在循环过程中的容量保持率进一步提高。另外合适的聚合物的多分散系数，能有效提升浆料固含量，降低生产成本。
本申请中，多分散系数的测试可以选用本领域已知的方法进行测试，例如采用凝胶色谱法进行测试，如采用Waters 2695Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)进行测试。在一些实施方式中，以质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8×300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的聚合物胶液，配置好 的溶液静置一天，备用。测试时，先用注射器吸取四氢呋喃，进行冲洗，重复几次。然后吸取5ml实验溶液，排除注射器中的空气，将针尖擦干。最后将试样溶液缓缓注入进样口。待示数稳定后获取数据。分别读取重均分子量a和数均分子量b。多分散系数＝a/b。
在一些实施方式中，聚合物的Dv50粒径为100μm～200μm。在一些实施方式中，聚合物的Dv50粒径可选为105μm～115μm、115μm～125μm、125μm～135μm、135μm～145μm、145μm～155μm、155μm～165μm、165μm～175μm、175μm～185μm、185μm～195μm、105μm～125μm、125μm～145μm、145μm～165μm、165μm～185μm、105μm～185μm、125μm～185μm中的任意一种。
在本文中，术语“Dv50粒径”指在粒度分布曲线中，颗粒的累计粒度分布数达到50％时所对应的粒径，它的物理意义是粒径小于(或大于)它的颗粒占50％。
若聚合物的Dv50粒径过大，聚合物溶解相对困难，粘结剂的分散性降低，使得极片的柔韧性下降，同时聚合物溶解困难，会降低制浆过程的速度；若聚合物的Dv50粒径过小，极片的粘结力下降。
控制聚合物的Dv50粒径在合适范围内，可以提高粘结剂的溶解性，提高极片的柔韧性，并使得极片具有较好粘结力。同时合适范围的聚合物的Dv50粒径，还能使得粘结剂的用量被控制在较低的水平，且不会对粘结性能造成过大的负面影响，从而有效改善了传统技术中高用量粘结剂带来的极片和电池性能受损的情况。
参照GB/T 19077-2016粒度分布激光衍射法，用50ml烧杯称量0.1g～0.13g的聚合物粉料，再称取5g无水乙醇，加入到装有聚合物粉料的烧杯中，放入长度约2.5mm搅拌子，并用保鲜膜密封。将样品放入超声机超声5分钟，转移到磁力搅拌机用500转/分钟的速度搅拌20分钟以上，每批次产品抽取2个样品测试取平均值。采用激光粒度分析仪进行测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪进行测试。
在一些实施方式中，聚合物的结晶度为30％～40％。在一些实施 方式中，聚合物的结晶度可选为30％～32％、32％～34％、34％～36％、36％～38％、38％～39％、31％～33％、33％～35％、35％～37％、37％～39％、31％～39％中的任意一种。
在本文中，术语“结晶度”指聚合物中结晶区域所占的比例，微观结构中存在一些具有稳定规整排列的分子的区域，分子有规则紧密排列的区域称为结晶区域。
若聚合物的结晶度过大，聚合物链段的可移动性降低，影响极片的柔韧性，同时聚合物的溶解困难，降低制浆过程的速度；若聚合物的结晶度过小，聚合物分子链的规整密堆积程度下降，影响粘结剂的化学稳定性和热稳定性。
控制聚合物的结晶度在合适范围内，使得粘结剂用量在较低水平时，极片就能兼具优异的柔韧性和良好的粘结力，进而有助于提高活性物质的负载量和电池的循环性能。
本申请中，结晶度的测试可以选用本领域已知的方法进行测试，如采用差式扫描热分析法进行测试。在一些实施例中，将0.5g聚合物置于铝制干锅中，抖平，盖上坩埚盖子，在氮气气氛下，以50毫升/分钟的吹扫气，以70毫升/分钟的保护气，升温速率为每分钟10℃，测试温度范围-100℃～400℃，利用美国TA仪器型号为Discovery 250的差示扫描量热仪(DSC)进行测试并消除热历史。
此测试将会得到聚合物的DSC曲线，对曲线进行积分，峰面积即为聚合物的熔融焓ΔH(J/g)，聚合物结晶度＝(ΔH/ΔHm)×100％，其中ΔHm为聚偏氟乙烯的标准熔融焓(晶态熔化热)，ΔHm＝104.7J/g。
在一些实施方式中，聚合物为偏氟乙烯-三氟氯乙烯共聚物、偏氟乙烯-四氟乙烯共聚物、偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物、偏氟乙烯-四氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物中的一种或多种。
本申请的一个实施方式中，提供一种粘结剂的制备方法，包括以 下步骤：
提供式III所示的单体、式Ⅳ所示的单体和反应溶剂，进行第一段聚合反应，得到第一产物；
其中，R2选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种；
将第一产物在非水溶性气体氛围下进行第二段聚合反应；
加入链转移剂，进行第三段聚合反应，得到重均分子量为500万～900万的聚合物。
在一些实施方式中，将多份第一产物混合，在非水溶性气体氛围下进行第二段聚合反应。可以理解，多份第一产物可以通过多个反应釜同步制备，也可以通过一个反应釜多次制备。通过多次、分段合成的方法可以提高聚合物的均匀度。
采用分段法进行聚合反应能够制备得到超高分子量的聚合物，使得粘结剂在低添加量下即可以满足极片粘结力的需求，同时使得极片具有优异的柔韧性，利于提高电池在循环过程中的容量保持率。同时先在第一段聚合反应中形成重均分子量相对较低的第一产物，第二段聚合反应形成目标分子量的分子链段，第三段聚合反应用以调控聚合物的分子量，避免聚合物的重均分子量随机性过高，提高聚合物的均一性。而且分段聚合不仅能够提升聚合物制备过程中反应器的利用率，还能够节约时间，减少聚合物在反应器中的停留时间。通过第一段聚合反应、第二段聚合反应、第三段聚合反应相互配合，可以进一步提升聚合物的生产效率。
可以理解，第一产物既可以为式III所示的单体、式Ⅳ所示的单体和反应溶剂形成的反应液，也可以为上述反应液加工提纯后的产物。
在一些实施方式中，式Ⅳ所示的单体的质量分数为0.5％～15％，基于式III所示的单体和式Ⅳ所示的单体的总质量计。在一些实施方 式中，式Ⅳ所示的单体的质量分数可选为0.5％～1％，1％～2％，3％～4％，4％～5％，5％～6％，6％～7％，7％～8％，8％～9％，9％～10％，10％～11％，11％～12％，12％～13％，13％～14％，14％～15％，0.5％～3％，3％～6％，6％～9％，9％～12％，12％～15％，0.5％～5％，5％～10％，10％～15％中的任意一种。
若式Ⅳ所示的单体的质量分数过低，达不到改善极片柔韧性的目的；若式Ⅳ所示的单体的质量分数过高，极片的粘结力下降，影响电池的循环性能。
式Ⅳ所示的单体的质量分数在合适范围内时，极片兼具优异的柔韧性和良好的粘结力，使得电池在循环过程中能够保持高的循环容量。
在一些实施方式中，式Ⅳ所示的单体为三氟氯乙烯、四氟乙烯、六氟丙烯中的一种或多种。
上述原材料简单易得，能够大幅度降低生产成本，提高产量。
在一些实施方式中，第一段聚合反应的反应温度为45℃～60℃。在一些实施方式中，第一段聚合反应的反应温度可选为45℃～50℃、50℃～55℃、55℃～60℃、45℃～55℃中的任意一种。
在一些实施方式中，第一段聚合反应的反应时间为4小时～10小时。在一些实施方式中，第一段聚合反应的反应时间可选为4小时～5小时、5小时～6小时、6小时～7小时、7小时～8小时、8小时～9小时、9小时～10小时、4小时～6小时、6小时～8小时、8小时～10小时、5小时～10小时中的任意一种。
在一些实施方式中，第一段聚合反应的初始压力为4MPa～6MPa。在一些实施方式中，第一段聚合反应的初始压力为4MPa～5MPa或5MPa～6MPa。
在一些实施方式中，第二段聚合反应的反应温度为60℃～80℃。在一些实施方式中，第二段聚合反应的反应温度为60℃～70℃或70℃～80℃。
在一些实施方式中，第二段聚合反应的反应时间为2小时～4小时。在一些实施方式中，第二段聚合反应的反应时间为2小时～3小 时或3小时～4小时。
在一些实施方式中，第二段聚合反应的反应压力为6MPa～8MPa。在一些实施方式中，第二段聚合反应的反应压力为6MPa～7MPa或7MPa～8MPa。
在一些实施方式中，第三段聚合反应的反应时间为1小时～2小时。
控制各个阶段聚合反应的反应压力、反应时间、反应温度在合适的范围内，在实现提高聚合物的重均分子量的同时，可以控制聚合产物重均分子量的均匀性，保证产物具有较低的多分散系数，提高产物性能的均一性，制备的聚合物使得极片在低添加量下即具有优异的柔韧性和粘结力，且电池的循环容量保持率能够进一步提高。
在一些实施方式中，链转移剂包括环己烷、异丙醇、甲醇以及丙酮中的一种或多种。
非水溶性气体是指气体溶解度小于0.1L的气体。气体溶解度是指在20℃时，气体的压强为1.013×105Pa，在1L水里溶解达到饱和状态时气体的体积。在一些实施方式中，非水溶性气体选自氮气、氧气、氢气、甲烷中的一种或多种。
在一些实施方式中，非水溶性气体选自氮气、氧气、氢气、甲烷中的一种或多种。
在一些实施方式中，链转移剂的用量为式III所示单体和式IV所示单体总质量的1.5％～3％。链转移剂的用量例如还可以是式III所示单体和式IV所示单体总质量的2％或2.5％。
链转移剂的用量控制在合适范围内，能使得聚合物链长可控，从而获得合适分子量范围的聚合物。
在一些实施方式中，第一段聚合反应包括以下步骤：
向容器中加入水溶剂和分散剂，去除反应体系中的氧气；
向所述容器中加入引发剂和pH调节剂，调节pH值至6.5～7，然后加入式III所示单体和式IV所示单体，使容器中的压力达到4MPa～6MPa；
搅拌30分钟～60分钟后，升温至45℃～60℃，进行第一段聚合反应。
升温进行聚合反应前，先将物料混合均匀，能使反应进行得更彻底，所得的聚合物的多分散系数、结晶度以及粒径更均匀。
在一些实施方式中，水溶剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的2～8倍。水溶剂的用量例如还可以是式III所示的单体和式Ⅳ所示的单体的总质量的3、4、5、6或7倍。在一些实施方式中，水溶剂为去离子水。
在一些实施方式中，分散剂包括纤维素醚、聚乙烯醇中的一种或两种。
在一些实施方式中，纤维素醚包括甲基纤维素醚、羧乙基纤维素醚中的一种或两种。
在一些实施方式中，分散剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的0.1％～0.3％。分散剂的用量例如还可以是式III所示的单体和式IV所示的单体总质量的0.2％。
在一些实施方式中，引发剂为有机过氧化物。
在一些实施方式中，有机过氧化物包括过氧化新戊酸叔戊酯、过氧化叔戊基新戊酸酯、2-乙基过氧化二碳酸酯、二异丙基过氧化二碳酸酯、叔丁基过氧化新戊酸酯中的一种或多种。
在一些实施方式中，引发剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的0.15％～1％。引发剂的用量例如还可选为式III所示的单体和式IV所示的单体总质量的0.2％、0.4％、0.6％或0.8％。
在一些实施方式中，pH调节剂包括碳酸钾、碳酸氢钾、碳酸钠、碳酸氢钠、氨水中的一种或多种。
在一些实施方式中，pH调节剂的用量为式III所示的单体和式Ⅳ所示的单体的总质量的0.05％～0.2％。pH调节剂的用量例如还可以是式III所示单体和式IV所示单体总质量的0.1％或0.15％。
该正极极片兼具优异的柔韧性和良好的粘结力。
在一些实施方式中，粘结剂的质量分数为0.8％～1％，基于正极膜 层的总质量计。
控制粘结剂的质量分数在合适的范围内能够使得极片兼具优异的柔韧性和粘结力，使得电池在循环过程中具有高的循环容量保持率。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，正极膜层包括正极活性材料、导电剂和一些实施方式中的粘结剂或一些实施方式中的制备方法制备的粘结剂。
该正极极片兼具优异的柔韧性和良好的粘结力。
在一些实施方式中，粘结剂的质量分数为0.8％～1％，基于正极膜层的总质量计。在一些实施方式中，粘结剂的质量分数可选为0.8％～0.85％、0.85％～0.9％、0.9％～0.95％、0.95％～1％、0.85％～0.95％中的任意一种。
若粘结剂的质量分数过高，导致包覆于正极活性材料表面的粘结剂包覆层过厚，导致极片较脆、韧性较差。另外过多的粘结剂会造成正极活性材料在极片中的负载量下降，导致电池的能量密度降低，降低电池的容量。
若粘结剂的质量分数过低，达不到足够的粘结效果，一方面无法将足量的导电剂和正极活性材料粘结到一起，极片的粘结力小；另一方面粘结剂无法紧密结合于活性物质表面，导致极片表面容易脱粉，造成电池的循环性能下降。
控制粘结剂的质量分数在合适的范围内，使得极片兼具优异的柔韧性和良好的粘结力，使得电池在循环过程中具有良好的循环容量保持率。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流 体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO2)、锂镍氧化物(如LiNiO2)、锂锰氧化物(如LiMnO2、LiMn2O4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi1/3Co1/3Mn1/3O2(也可以简称为NCM333)、LiNi0.5Co0.2Mn0.3O2(也可以简称为NCM523)、LiNi0.5Co0.25Mn0.25O2(也可以简称为NCM211)、LiNi0.6Co0.2Mn0.2O2(也可以简称为NCM622)、LiNi0.8Co0.1Mn0.1O2(也可以简称为NCM811)、锂镍钴铝氧化物(如LiNi0.85Co0.15Al0.05O2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜， 也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
[二次电池]
在本申请的第四方面提供一种二次电池，包括电极组件和电解液，所述电极组件包括负极极片、隔离膜和本申请第三方面的正极极片。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
[电池模块]
在本申请的第五方面，提供一种电池模块，包括本申请第四方面的二次电池。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图3是作为一个示例的电池模块4。参照图3，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
[电池包]
在本申请的第六方面，提供一种电池包，包括本申请第五方面的电池模块。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和图5，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
[用电装置]
在本申请的第七方面，提供一种用电装置，包括本申请第四方面的二次电池、第五方面的电池模块或第六方面的电池包中的至少一种。
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
1)粘结剂的制备
第一段聚合反应：在1号、2号10L的高压釜中加入4kg的去离子水和2.5g的甲基纤维素醚，抽真空并用N2置换O2三次，再次加入5g叔丁基过氧化新戊酸酯和2g的碳酸氢钠，并充入0.94kg的偏氟乙烯和0.06kg三氟氯乙烯，使压力达到5MPa，混合搅拌30min，升温到45℃，反应4h；
第二段聚合反应：将1号、2号反应釜中的反应液转移到3号反应釜当中，充入氮气至压力7MPa，升温到70℃，搅拌反应3h；
第三段聚合反应：加入38g环己烷后继续反应1h，停止反应。将反应体系离心后收集固相，洗涤、干燥即得到偏氟乙烯-三氟氯乙烯共聚物粘结剂。
2)正极极片的制备
将3961.8g磷酸铁锂，32.8g的聚偏氟乙烯粘结剂，57.4g的乙炔黑在行星式搅拌罐中，公转转速25r/min，搅拌20～30min，其中粘结剂的质量分数为0.6％，基于正极膜层的总质量计；
在搅拌罐中加入2.4kg的N-甲基吡咯烷酮(NMP)溶液，公转速度25r/min，自转速度900r/min，搅拌70min；
在搅拌罐中加入12.3g分散剂，以公转速度25r/min，自转速度1300r/min搅拌60min；
搅拌结束，测试浆料粘度，粘度控制在8000～15000mPa·s。
如粘度偏高，添加NMP溶液使之降低到上述粘度区间后按照公转速度25r/min，自转速度1250r/min，搅拌30min，得到正极浆料。将制得的正极浆料刮涂到涂碳铝箔上面，刮涂重量单面550mg/(1540mm2)，110℃烘烤15min，冷压到压密2.7g/cm3后裁剪成直径15mm的圆片，即得到正极极片。
3)负极极片
以金属锂片作为负极极片。
4)隔离膜
以聚丙烯膜作为隔离膜。
5)电解液的制备
在氩气气氛手套箱中(H2O<0.1ppm，O2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入LiPF6锂盐溶解于有机溶剂中，搅拌均匀，配置1M LiPF6EC/EMC溶液得到电解液。
6)电池的制备
将实施例1中的正极极片、负极极片、隔离膜和电解液在扣电箱中组装成扣式电池。
实施例2～5
与实施例1基本相同，区别在于，将第一段聚合反应中的反应时间分别调整为5h、6h、7h、8h，将第三段聚合反应中的链转移剂环己烷分别调整为33g、28g、23g、18g，具体参数如表1所示。
实施例6～9
与实施例1基本相同，区别在于，保持加入的偏氟乙烯和三氟氯乙烯单体总量不变，调整三氟氯乙烯的质量分数，基于偏氟乙烯和三氟氯乙烯单体的总质量计，具体参数如表1所示。
实施例10～13
与实施例1基本相同，区别在于，调整了偏氟乙烯-三氟氯乙烯共聚物粘结剂的质量分数，基于正极膜层的总质量计，具体参数如表1所示。
实施例14～19
与实施例1基本相同，区别在于，将0.06kg三氟氯乙烯分别替换成0.06kg四氟乙烯、0.06kg六氟丙烯、0.03kg三氟氯乙烯+0.03kg四氟乙烯、0.03kg三氟氯乙烯+0.03kg六氟丙烯、0.03kg四氟乙烯+0.03kg六氟丙烯、0.02kg三氟氯乙烯+0.02kg四氟乙烯+0.02kg六氟丙烯。具体参数如表1所示。
对比例1
与实施例1基本相同，聚合单体只有1kg偏氟乙烯，具体参数如表1所示。
对比例2
与实施例2基本相同，聚合单体只有1kg偏氟乙烯，具体参数如表1所示。
对比例3
与实施例3基本相同，聚合单体只有1kg偏氟乙烯，具体参数如表1所示。
对比例4
与实施例4基本相同，聚合单体只有1kg偏氟乙烯，具体参数如表1所示。
对比例5
与实施例5基本相同，聚合单体只有1kg偏氟乙烯，具体参数如表1所示。
对比例6
与实施例1基本相同，该粘结剂为重均分子量为80万的聚偏氟乙烯，购买于华安公司，型号为605牌号，调整粘结剂的质量分数为2.5％，基于正极膜层的总质量计，具体参数如表1所示。
二、电池性能测试
1、粘结剂性质测试
1)重均分子量测试
采用Waters 2695Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。以质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的粘结剂胶液，配置好的溶液静置一天，备用。测试时，先用注射器吸取四氢呋喃，进行冲洗，重复几次。然后吸取5ml实验溶液，排除注射器中的空气，将针尖擦干。最后将试样溶液缓缓注入进样口。待示数稳定后获取数据，读取重均分子量。
2)多分散系数测试
采用Waters 2695Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。以质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的粘结剂胶液，配置好的溶液静置一天，备用。测试时，先用注射器吸取四氢呋喃，进行冲洗，重复几次。然后吸取5ml实验溶液，排除注射器中的空气，将针尖擦干。最后将试样溶液缓缓注入进样口。待示数稳定后获取数据。分别读取重均分子量a和数均分子量b。多分散系数＝a/b。
3)Dv50测试
参照GB/T 19077-2016粒度分布激光衍射法，用50ml烧杯称量0.1g～0.13g的粘结剂粉料，再称取5g无水乙醇，加入到装有粘结剂粉料的烧杯中，放入长度约2.5mm搅拌子，并用保鲜膜密封。将样品放入超声机超声5min，转移到磁力搅拌机用500r/min的速度搅拌20min以上。采用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪进行测试。
4)结晶度测试
将0.5g粘结剂置于铝制干锅中，抖平，盖上坩埚盖子，在氮气气氛下，以50ml/min的吹扫气，以70ml/min的保护气，升温速率 为10℃/min，测试温度范围-100℃～400℃，利用美国TA仪器型号为Discovery 250的差示扫描量热仪(DSC)进行测试并消除热历史。
此测试将会得到粘结剂的DSC/(Mw/mg)随温度变化曲线，并进行积分，峰面积即为粘结剂的熔融焓ΔH(J/g)，粘结剂结晶度＝(ΔH/ΔHm)×100％，其中ΔHm为聚偏氟乙烯的标准熔融焓(晶态熔化热)，ΔHm＝104.7J/g。
2、极片性能测试
1)粘结力测试
参考GB-T2790-1995国标《胶粘剂180°剥离强度实验方法》，本申请实施例和对比例的粘结力测试过程如下：
用刀片截取宽度为30mm，长度为100-160mm的试样，将专用双面胶贴于钢板上，胶带宽度20mm，长度90-150mm。将前面截取的极片试样的正极膜层面贴在双面胶上，后用2kg压辊沿同一个方向滚压三次。
将宽度与极片等宽，长度为250mm的纸带固定于极片集流体上，并且用皱纹胶固定。
打开三思拉力机电源(灵敏度为1N)，指示灯亮，调整限位块到合适位置，将钢板未贴极片的一端用下夹具固定。将纸带向上翻折，用上夹具固定，利用拉力机附带的手动控制器上的“上行”和“下行”按钮调整上夹具的位置。然后进行测试并读取数值。将极片受力平衡时的力除以胶带的宽度作为单位长度的极片的粘结力，以表征正极膜层与集流体之间的粘结强度。
3、电池性能测试
1)电池容量保持率测试
电池容量保持率测试过程如下：在25℃下，将扣式电池以1/3C恒流充电至3.65V，再以3.65V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.5V，所得容量记为初始容量C0。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的放电容量Cn，则每次循环后电池容量保持率Pn＝Cn/C0*100％，以P1、 P2……P500这500个点值为纵坐标，以对应的循环次数为横坐标，得到电池容量保持率与循环次数的曲线图。
该测试过程中，第一次循环对应n＝1、第二次循环对应n＝2、……第500次循环对应n＝500。表1中实施例1～15或对比例1～6对应的电池容量保持率数据是在上述测试条件下循环500次之后测得的数据，即P500的值。
三、各实施例、对比例测试结果分析
按照上述方法分别制备各实施例和对比例的电池，并测量各项性能参数，结果见下表1和表2。
表1
表2
根据上述结果可知，实施例1～19中的粘结剂均包含聚合物，聚 合物包含衍生自偏氟乙烯的结构单元以及包含至少一种衍生自三氟氯乙烯、四氟乙烯、六氟丙烯的结构单元，且该聚合物的重均分子量为500万～900万。从实施例1和对比例1的对比，实施例2、实施例6～9和对比例2的对比，实施例3和对比例3的对比，实施例4和对比例4的对比，实施例5和对比例5的对比可知，聚合物中共聚单体的引入能够在不明显降低极片粘结力的情况下，提高极片的柔韧性，减少在卷绕和热压工序中出现断裂或漏光风险，提高电池的安全性能。
实施例1～19与对比例6相比，重均分子量为500万～900万的偏氟乙烯-三氟氯乙烯共聚物粘结剂、偏氟乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-四氟乙烯-六氟丙烯共聚物粘结剂或偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物粘结剂在低添加量下就能够保证极片具有足够的粘结力，同时可以进一步提升极片的柔性，进而能够提高电池在循环过程中的容量保持率，有效改善了传统技术中高用量粘结剂带来的极片和电池性能受损的情况。
从实施例1、实施例6、实施例8和实施例7、实施例9对比可知，当偏氟乙烯-三氟氯乙烯共聚物中三氟氯乙烯的质量分数0.5％～15％，基于偏氟乙烯-三氟氯乙烯共聚物的总质量计，该粘结剂使得极片兼具优异的柔韧性和粘结力，使得电池在循环过程中保持良好的容量性能。
从实施例1～19中可知，多分散系数为1.7～2.3的偏氟乙烯-三氟氯乙烯共聚物粘结剂、偏氟乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-四氟乙烯-六氟丙烯共聚物粘结剂或偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物粘结剂在低添加量下即使得极片兼具优异的柔韧性和粘结力，使得电池在循环过程中具有高的容量保持率。
从实施例1～19中得知，Dv50粒径为100μm～200μm的偏氟乙烯 -三氟氯乙烯共聚物粘结剂、偏氟乙烯-四氟乙烯共聚物粘结剂或、氟乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-四氟乙烯-六氟丙烯共聚物粘结剂或偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物粘结剂在低添加量下即使得极片兼具优异的柔韧性和粘结力，使得电池在循环过程中具有高的容量保持率。
从实施例1～19中得知，结晶度为30％～40％的偏氟乙烯-三氟氯乙烯共聚物粘结剂、偏氟乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物粘结剂、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物粘结剂、偏氟乙烯-四氟乙烯-六氟丙烯共聚物粘结剂或偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物粘结剂在低添加量下使得极片兼具优异的柔韧性和粘结力，使得电池在循环过程中具有高的容量保持率。
从实施2、实施例11～12和实施例10、实施例13对比可知，当偏氟乙烯-三氟氯乙烯共聚物粘结剂基于正极膜层总质量的质量分数为0.8％～1％时，该粘结剂可以使得极片兼具优异的柔韧性和良好粘结力，使得电池在循环过程中具有高的容量保持率。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (30)

  1. 一种粘结剂，其特征在于，所述粘结剂为含有如式I所示的结构单元和式II所示的结构单元的聚合物，
    其中，R1选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种，所述聚合物的重均分子量为500万～900万。
  2. 根据权利要求1所述的粘结剂，其特征在于，所述式II所示的结构单元的质量分数为0.5％～15％，基于所述聚合物的总质量计。
  3. 根据权利要求1或2所述的粘结剂，其特征在于，所述聚合物的多分散系数为1.7～2.3。
  4. 根据权利要求1至3中任一项所述的粘结剂，其特征在于，所述聚合物的Dv50粒径为100μm～200μm。
  5. 根据权利要求1至4中任一项所述的粘结剂，其特征在于，所述聚合物的结晶度为30％～40％。
  6. 根据权利要求1至5中任一项所述的粘结剂，其特征在于，所述聚合物为偏氟乙烯-三氟氯乙烯共聚物、偏氟乙烯-四氟乙烯共聚物、偏氟乙烯-六氟丙烯、偏氟乙烯-三氟氯乙烯-四氟乙烯共聚物、偏氟乙烯-三氟氯乙烯-六氟丙烯共聚物、偏氟乙烯-四氟乙烯-六氟丙烯共聚物、偏氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物中的一种或多种。
  7. 一种粘结剂的制备方法，其特征在于，包括以下步骤：
    提供式III所示的单体、式Ⅳ所示的单体和反应溶剂，进行第一段聚合反应，得到第一产物；
    其中，R2选自氟、氯、至少含有一个氟原子的C1-3烷基中的一种或多种；
    将所述第一产物在非水溶性气体氛围下进行第二段聚合反应；
    加入链转移剂，进行第三段聚合反应，得到重均分子量为500万～900万的聚合物。
  8. 根据权利要求7所述的制备方法，其特征在于，所述式Ⅳ所示的单体的质量分数为0.5％～15％，基于所述式III所示的单体和式Ⅳ所示的单体的总质量计。
  9. 根据权利要求7或8所述的制备方法，其特征在于，所述式Ⅳ所示的单体为三氟氯乙烯、四氟乙烯、六氟丙烯中的一种或多种。
  10. 根据权利要求7至9中任一项所述的制备方法，其特征在于，所述第一段聚合反应的反应温度为45℃～60℃，反应时间为4小时～10小时，初始压力为4MPa～6MPa。
  11. 根据权利要求7至10中任一项所述的制备方法，其特征在于，所述第二段聚合反应的反应温度为60℃～80℃，反应时间为2小时～4小时，反应压力为6MPa～8MPa。
  12. 根据权利要求7至11中任一项所述的制备方法，其特征在于，所述第三段聚合反应的反应时间为1小时～2小时。
  13. 根据权利要求7至12中任一项所述的制备方法，其特征在于，所述链转移剂包括环己烷、异丙醇、甲醇以及丙酮中的一种或多种。
  14. 根据权利要求7至13中任一项所述的制备方法，其特征在于，所述非水溶性气体选自氮气、氧气、氢气、甲烷中的一种或多种。
  15. 根据权利要求7至14中任一项所述的制备方法，其特征在于，所述链转移剂的用量为所述式III所示的单体和式IV所示的单体的总质量的1.5％～3％。
  16. 根据权利要求7至15中任一项所述的制备方法，其特征在于，所述第一段聚合反应包括以下步骤：
    向容器中加入水溶剂和分散剂，去除反应体系中的氧气；
    向所述容器中加入引发剂和pH调节剂，调节pH值至6.5～7，然后加入式III和式Ⅳ所示单体，使所述容器中的压力达到4MPa～6MPa；
    搅拌30分钟～60分钟后，升温至45℃～60℃，进行第一段聚合反应。
  17. 根据权利要求16所述的制备方法，其特征在于，所述水溶剂的用量为所述式III所示的单体和式Ⅳ所示的单体的总质量的2～8倍。
  18. 根据权利要求16或17所述的制备方法，其特征在于，所述分散剂包括纤维素醚、聚乙烯醇中的一种或两种。
  19. 根据权利要求18所述的制备方法，其特征在于，所述纤维素醚包括甲基纤维素醚、羧乙基纤维素醚中的一种或两种。
  20. 根据权利要求16至19中任一项所述的制备方法，其特征在于，所述分散剂的用量为所述式III所示的单体和式Ⅳ所示的单体的总质量的0.1％～0.3％。
  21. 根据权利要求16至20中任一项所述的制备方法，其特征在 于，所述引发剂为有机过氧化物。
  22. 根据权利要求21所述的制备方法，其特征在于，所述有机过氧化物包括过氧化新戊酸叔戊酯、过氧化叔戊基新戊酸酯、2-乙基过氧化二碳酸酯、二异丙基过氧化二碳酸酯、叔丁基过氧化新戊酸酯中的一种或多种。
  23. 根据权利要求16至22中任一项所述的制备方法，其特征在于，所述引发剂的用量为所述式III所示的单体和式Ⅳ所示的单体的总质量的0.15％～1％。
  24. 根据权利要求16至23中任一项所述的制备方法，其特征在于，所述pH调节剂包括碳酸钾、碳酸氢钾、碳酸钠、碳酸氢钠、氨水中的一种或多种。
  25. 根据权利要求至16至24中任一项所述的制备方法，其特征在于，所述pH调节剂的用量为所述式III所示的单体和式Ⅳ所示的单体的总质量的0.05％～0.2％。
  26. 一种正极极片，包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括正极活性材料、导电剂和权利要求1至6中任一项所述的粘结剂或如权利要求7至25中任一项所述的制备方法制备的粘结剂。
  27. 根据权利要求26所述的正极极片，其特征在于，所述粘结剂的质量分数为0.8％～1％，基于所述正极膜层的总质量计。
  28. 一种二次电池，其特征在于，包括电极组件和电解液，所述电极组件包括负极极片、隔离膜和权利要求26或27所述的正极极片。
  29. 根据权利要求28所述的二次电池，其特征在于，所述二次电池为锂离子电池或钠离子电池。
  30. 一种用电装置，其特征在于，包括权利要求28或29所述的二次电池。
PCT/CN2023/087056 2022-08-30 2023-04-07 粘结剂、制备方法、正极极片、二次电池及用电装置 WO2024045619A1 (zh)

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CN115117357B (zh) * 2022-08-30 2023-05-16 宁德时代新能源科技股份有限公司 粘结剂、制备方法、正极极片、二次电池及用电装置

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