WO2024045554A1 - 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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Publication number
WO2024045554A1
WO2024045554A1 PCT/CN2023/081622 CN2023081622W WO2024045554A1 WO 2024045554 A1 WO2024045554 A1 WO 2024045554A1 CN 2023081622 W CN2023081622 W CN 2023081622W WO 2024045554 A1 WO2024045554 A1 WO 2024045554A1
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Prior art keywords
polyvinylidene fluoride
binder
positive electrode
preparation
mass
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PCT/CN2023/081622
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English (en)
French (fr)
Inventor
段连威
孙成栋
刘会会
张文帅
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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 WO2024045554A1 publication Critical patent/WO2024045554A1/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
    • H01M4/623—Binders being polymers fluorinated polymers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F114/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
    • C08F114/18—Monomers containing fluorine
    • C08F114/22—Vinylidene fluoride
    • 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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of 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 binders have poor adhesion and often require a large amount of addition to meet the adhesive strength requirements of the pole pieces, which will limit the improvement of battery energy density. Therefore, existing adhesives still need to be improved.
  • This application was made in view of the above-mentioned problems, and its purpose is to provide a binder that can exert excellent bonding force at a low addition amount, so that the pole piece has sufficient bonding strength, and Can improve battery cycle performance.
  • this application provides a binder.
  • the binder includes a first polyvinylidene fluoride and a second polyvinylidene fluoride.
  • the weight average molecular weight of the first polyvinylidene fluoride is 1.8 million to 5 million.
  • the weight average molecular weight of the second polyvinylidene fluoride is smaller than the weight average molecular weight of the first polyvinylidene fluoride.
  • This binder can ensure sufficient adhesion of the pole pieces at a low addition amount and improve the cycle performance of the battery.
  • the polydispersity coefficient of the first polyvinylidene fluoride is 2 to 2.3, optionally 2.1 to 2.3.
  • the binder can provide excellent adhesive force to the pole piece at a low addition amount, further improving the capacity retention rate of the battery during cycling.
  • the Dv50 particle size of the first polyvinylidene fluoride is 50 ⁇ m to 150 ⁇ m, optionally 60 ⁇ m to 150 ⁇ m.
  • the binder can make the pole piece have excellent bonding force at a low addition amount, and the capacity retention rate of the battery during cycling can be further improved.
  • the crystallinity of the first polyvinylidene fluoride is 40% to 45%, optionally 42% to 45%.
  • the binder can make the pole piece have excellent adhesion and flexibility at a low addition amount, and the capacity retention rate of the battery during cycling can be further improved.
  • the viscosity of the glue containing 4% of the first polyvinylidene fluoride prepared by dissolving the first polyvinylidene fluoride in N-methylpyrrolidone is 2500mPa ⁇ s ⁇ 5000mPa. ⁇ s, optional 3600mPa ⁇ s ⁇ 5000mPa ⁇ s.
  • Controlling the viscosity of the first polyvinylidene fluoride glue within an appropriate range and adding a low amount of binder can ensure that the pole piece has excellent bonding force.
  • the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 ⁇ 4:1.
  • the pole piece By controlling the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride within an appropriate range, the pole piece has both good processing performance and adhesion, and the capacity retention rate of the battery during cycling can be further improved.
  • the second polyvinylidene fluoride has a weight average molecular weight of 600,000 to 1.1 million.
  • the pole piece has excellent adhesion, and the capacity retention rate of the battery during cycling can be improved.
  • a second aspect of the application also provides a method for preparing a binder, including the following steps: preparing a first polyvinylidene fluoride: polymerizing vinylidene fluoride monomer under polymerizable conditions to prepare a first polyvinylidene fluoride. Vinylidene fluoride, the weight average molecular weight of the first polyvinylidene fluoride is 1.8 million to 5 million; blending: the first polyvinylidene fluoride and the second polyvinylidene fluoride are blended to prepare a binder, wherein , the weight average molecular weight of the second polyvinylidene fluoride is smaller than the weight average molecular weight of the first polyvinylidene fluoride.
  • the preparation method of the binder is simple, environmentally friendly, has reduced costs and is conducive to industrial production.
  • the binder prepared by this method can meet the requirements for the adhesive force of the electrode piece at a low addition amount, which helps to increase the loading capacity of the positive active material in the electrode piece and improves the capacity retention rate of the battery during the cycle.
  • the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 ⁇ 4:1.
  • the pole piece By controlling the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride within an appropriate range, the pole piece will have excellent adhesion with a low amount of binder added, and the capacity of the battery will be maintained during the cycle. rate further increased.
  • the polymerization reaction to prepare the first polyvinylidene fluoride includes the following steps:
  • the weight average molecular weight of the first polyvinylidene fluoride can be controlled, so that the electrode piece has excellent adhesion, so that the battery has excellent performance during the cycle. Better cycle capacity retention.
  • the chain transfer agent includes one or more of cyclohexane, isopropanol, methanol, and acetone.
  • the amount of chain transfer agent used is the mass of vinylidene fluoride monomer. 1.5% ⁇ 3%.
  • Controlling the amount of the chain transfer agent within a suitable range can control the chain length of the first polyvinylidene fluoride, thereby obtaining the first polyvinylidene fluoride in a suitable weight average molecular weight range.
  • the polymerization reaction to prepare the first polyvinylidene fluoride further 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 solvent used is 2 to 8 times the mass of the vinylidene fluoride monomer.
  • the dispersant includes one or more of cellulose ethers and polyvinyl alcohol.
  • the cellulose ether includes one or more of methyl cellulose ether and carboxyethyl cellulose ether.
  • the amount of dispersant is 0.1% to 0.3% based on the mass of vinylidene fluoride monomer.
  • the initiator is an organic peroxide.
  • the organic peroxide includes t-amyl peroxypivalate, t-amyl peroxypivalate, 2-ethylperoxydicarbonate, diisopropylperoxydicarbonate, and One or more types of tert-butyl peroxypivalate.
  • the amount of initiator used is 0.15% to 1% based on the mass of vinylidene fluoride monomer.
  • the pH adjusting agent includes one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and ammonia.
  • the pH adjuster is used in an amount of the vinylidene fluoride monomer 0.05% ⁇ 0.2% of the amount.
  • 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 excellent bonding force with a low additive amount of binder.
  • the mass fraction of the binder is 0.8% to 1.6%, based on the total mass of the positive electrode film layer.
  • Controlling the mass fraction of the binder within an appropriate range, while ensuring that the electrode pieces have sufficient adhesion, can increase the loading of active materials in the battery electrode pieces, helping to further improve the power performance of the battery.
  • the positive active material is a lithium-containing transition metal oxide.
  • the lithium-containing transition metal oxide is at least one of lithium iron phosphate and its modified materials, lithium nickel cobalt manganese oxide and its modified materials, and the modified materials are obtained by doping, It is prepared by one or more modification methods of conductive carbon coating, conductive metal coating, and conductive polymer coating.
  • a fourth aspect of the present application provides a secondary battery, including an electrode assembly and an electrolyte.
  • the electrode assembly includes the positive electrode sheet, the separator and the negative electrode sheet of the third aspect of the present application.
  • 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.
  • FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1;
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG 5 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 4;
  • FIG. 6 is an illustration of an electrical device using a secondary battery as a power source according to an embodiment of the present application. intention.
  • 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 viscosity of traditional polyvinylidene fluoride is low, and a large amount of addition is often required to ensure effective bonding of active materials, thereby enabling the pole pieces to achieve effective bonding force.
  • increasing the dosage of traditional polyvinylidene fluoride will reduce the load of active materials in the pole pieces, affecting the improvement of battery power performance and making it difficult to meet the requirements for battery cycle performance.
  • the binder includes a first polyvinylidene fluoride and a second polyvinylidene fluoride.
  • the first polyvinylidene fluoride has a weight average molecular weight of 1.8 million to 5 million
  • the second polyvinylidene fluoride has a weight average molecular weight of 1.8 million to 5 million.
  • the weight average molecular weight of the polyvinylidene fluoride is less than the weight average molecular weight of the first polyvinylidene fluoride.
  • binder refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.
  • polyvinylidene fluoride refers to polyvinylidene fluoride as the main synthetic Polymers of monomers, which on the one hand include aggregates 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.
  • Polyvinylidene fluoride herein includes both homopolymers and copolymers.
  • the first polyvinylidene fluoride includes polyvinylidene fluoride homopolymer, 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-hexafluoroethylene One or more of propylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.
  • the second polyvinylidene fluoride includes polyvinylidene fluoride homopolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene copolymer , Vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer one or more of the things.
  • 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 adhesive 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.
  • binders are used to hold electrode active materials and/or conductive agents in place and adhere them to conductive metal components to form electrodes.
  • 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.
  • the structural formula of the first polyvinylidene fluoride is shown in formula I, and the structural formula of the second polyvinylidene fluoride is shown in formula II.
  • m and n are integers, respectively representing the degree of polymerization of the first polyvinylidene fluoride and the second polyvinylidene fluoride.
  • m is greater than n, that is, the degree of polymerization and weight average molecular weight of the first polyvinylidene fluoride are greater than that of the second polyvinylidene fluoride.
  • the fluorine element contained in the first polyvinylidene fluoride and the second polyvinylidene fluoride forms hydrogen bonds with the hydroxyl groups or/and carboxyl groups on the surface of the active material and the surface of the current collector, which can improve the adhesive force of the pole piece.
  • the first polyvinylidene fluoride with a weight average molecular weight of 1.8 million to 5 million has great cohesion and intermolecular force, which can improve the adhesion of the pole pieces at low levels of addition and improve the battery's performance during cycling. capacity retention rate.
  • the addition of the second polyvinylidene fluoride to the binder can greatly reduce the cost of the binder.
  • the first polyvinylidene fluoride and the second polyvinylidene fluoride have the same structural units and excellent compatibility, they can During the drying process of preparing pole pieces, the pole pieces will not delaminate, and high-quality pole pieces can be obtained.
  • the above-mentioned binder can ensure sufficient adhesion of the electrode piece at a low addition amount, which is beneficial to improving the energy density of the battery and the cycle performance of the battery.
  • the weight average molecular weight of the first polyvinylidene fluoride 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) for testing.
  • the testing 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 first polyvinylidene fluoride has a polydispersity coefficient of 2 to 2.3.
  • the polydispersity coefficient of the first polyvinylidene fluoride can be selected from any one of 2 to 2.1, 2 to 2.2, 2 to 2.3, 2.1 to 2.2, and 2.1 to 2.3.
  • 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 polydispersity coefficient of the first polyvinylidene fluoride is too large, the polymerization degree of the first polyvinylidene fluoride will be relatively dispersed, affecting the uniformity of the binder, and the binder will not be able to uniformly adhere the positive electrode active material to the On the current collector, it affects the cycle performance of the battery, and also reduces the solid content of the slurry, making it impossible to further improve the energy density of the battery; if the polydispersity coefficient of the first polyvinylidene fluoride is too small, the preparation process will be difficult and the optimal The rate is lower, resulting in higher production costs.
  • the polydispersity coefficient of the first polyvinylidene fluoride is within an appropriate range, so that the electrode piece has excellent adhesion and improves the capacity retention rate of the battery during cycling.
  • a suitable polydispersity coefficient of the first polyvinylidene fluoride can effectively increase the solid content of the slurry and reduce production costs.
  • the polydispersity coefficient of the first polyvinylidene fluoride can be tested using methods known in the art, such as gel chromatography, such as Waters 2695 Isocratic HPLC gel chromatograph (differential differential chromatography). Refractive index detector 2141) for testing.
  • gel chromatography such as Waters 2695 Isocratic HPLC gel chromatograph (differential differential chromatography).
  • Refractive index detector 2141) for testing.
  • a polystyrene solution sample with a mass fraction of 3.0% is used as a reference to select a matching chromatographic column (oil: Styragel HT5DMF7.8*300mm+Styragel HT4).
  • NMP N-methylpyrrolidone
  • the Dv50 particle size of the first polyvinylidene fluoride is 50 ⁇ m ⁇ 150 ⁇ m, optional 60 ⁇ m ⁇ 150 ⁇ m. In some embodiments, the Dv50 particle size of the first polyvinylidene fluoride can be selected from 50 ⁇ m ⁇ 60 ⁇ m, 60 ⁇ m ⁇ 70 ⁇ m, 70 ⁇ m ⁇ 80 ⁇ m, 80 ⁇ m ⁇ 90 ⁇ m, 90 ⁇ m ⁇ 100 ⁇ m, 100 ⁇ m ⁇ 110 ⁇ m, 110 ⁇ m ⁇ 120 ⁇ m, 120 ⁇ m ⁇ 130 ⁇ m, 130 ⁇ m ⁇ 140 ⁇ m, 140 ⁇ m ⁇ 150 ⁇ m, 50 ⁇ m ⁇ 70 ⁇ m, 70 ⁇ m ⁇ 90 ⁇ m, 90 ⁇ m ⁇ 110 ⁇ m, 110 ⁇ m ⁇ 130 ⁇ m, 130 ⁇ m ⁇ 150 ⁇ m, 60 ⁇ m ⁇ 80 ⁇ m, 80 ⁇ m ⁇ 100 ⁇ m, 60 ⁇ m ⁇ 140 ⁇ m, 60 ⁇ m ⁇ 1 Any of 50 ⁇ 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 first polyvinylidene fluoride is too large, it will be relatively difficult to dissolve the first polyvinylidene fluoride, which will reduce the dispersion of the binder, affect the uniform distribution of the positive active material on the current collector, and affect the cycle of the battery. At the same time, the dissolution of the first polyvinylidene fluoride is difficult, which reduces the speed of the pulping process; if the Dv50 particle size of the first polyvinylidene fluoride is too small, the adhesive force of the pole piece decreases.
  • the Dv50 particle size of the first polyvinylidene fluoride By controlling the Dv50 particle size of the first polyvinylidene fluoride within an appropriate range, a low content of binder can make the electrode piece have sufficient adhesive force and improve the capacity retention rate of the battery during cycling. At the same time, the Dv50 particle size of the first polyvinylidene fluoride in the appropriate range can also control the amount of binder at a low level without causing too much negative impact on the bonding performance, thus effectively improving The performance of pole pieces and batteries is limited due to the high amount of binder used in traditional technology.
  • the Dv50 particle size of the first polyvinylidene fluoride can be tested using methods known in the art. For example, refer to the GB/T 19077-2016 particle size distribution laser diffraction method and weigh 0.1g in a 50ml beaker. ⁇ 0.13g of the first polyvinylidene fluoride powder, then weigh 5g of absolute ethanol, add it to the beaker containing the first polyvinylidene fluoride powder, put in a stirrer with a length of about 2.5mm, and use Seal with plastic wrap. Put the sample into an ultrasonic machine for 5 minutes, transfer to a magnetic stirrer and stir at a speed of 500 rpm for more than 20 minutes. Take 2 samples from each batch of products and test them and take the average. Use a laser particle size analyzer for measurement, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Co., Ltd. in the UK. analyzer for testing.
  • a laser particle size analyzer for measurement such as the Mastersizer 2000
  • the first polyvinylidene fluoride has a crystallinity of 40% to 45%, optionally 42% to 45%.
  • the crystallinity of the first polyvinylidene fluoride can be selected from 40% to 42%, 42% to 43%, 43% to 45%, 40% to 43%, 41% to 42%, 41 Any one of % to 43%, 43% to 44%, 41% to 44%, and 42% to 45%.
  • 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 crystallization of the first polyvinylidene fluoride is too large, the mobility of the first polyvinylidene fluoride chain segment is reduced, which affects the flexibility of the pole piece. At the same time, it is difficult to dissolve the first polyvinylidene fluoride, which reduces the manufacturing process. The speed of the slurry process. If the crystallization of the first polyvinylidene fluoride is too small, the degree of regular and dense packing of the polymer molecular chains will be reduced, which will affect the chemical stability and thermal stability of the binder.
  • the binder By controlling the crystallinity of the first polyvinylidene fluoride within an appropriate range, the binder enables the pole piece to have excellent adhesion, which can improve the capacity retention rate of the battery during cycling.
  • the crystallinity can be tested using methods known in the art, such as differential scanning thermal analysis.
  • 0.5 g of the first polyvinylidene fluoride is placed in an aluminum crucible, shaken flat, and the crucible lid is covered. Under a nitrogen atmosphere, a purge gas of 50 ml/min is used, and a purge gas of 70 ml/min is used. minutes of protective gas, a heating rate of 10°C per minute, a test temperature range of -100°C to 400°C, and a differential scanning calorimeter (DSC) of the American TA Instruments model Discovery 250 for testing and elimination of thermal history.
  • DSC differential scanning calorimeter
  • the viscosity of the glue containing 4% mass content of the first polyvinylidene fluoride prepared by dissolving the first polyvinylidene fluoride in N-methylpyrrolidone is 2500 mPa ⁇ s to 5000 mPa ⁇ s. , optional 3600mPa ⁇ s ⁇ 5000mPa ⁇ s.
  • the first polyvinylidene fluoride is dissolved in N-methylpyrrolidone and contains a mass containing
  • the viscosity of the first polyvinylidene fluoride glue solution with an amount of 4% can be selected from 2500mPa ⁇ s ⁇ 3000mPa ⁇ s, 3000mPa ⁇ s ⁇ 3300mPa ⁇ s, 3300mPa ⁇ s ⁇ 3500mPa ⁇ s, 3500mPa ⁇ s ⁇ 3800mPa ⁇ s, 3800mPa ⁇ s ⁇ 4000mPa ⁇ s, 4000mPa ⁇ s ⁇ 4200mPa ⁇ s, 4200mPa ⁇ s ⁇ 4600mPa ⁇ s, 4600mPa ⁇ s ⁇ 5000mPa ⁇ s, 3100mPa ⁇ s ⁇ 3400mPa ⁇ s, 3400mPa ⁇ s ⁇ 3800mPa ⁇ s, Any one of 3800mPa ⁇ s ⁇ 4600mPa ⁇ s, 3600mPa ⁇ s ⁇ 5000mPa,
  • the viscosity of the first polyvinylidene fluoride is too high, the viscosity of the prepared binder glue will be too high, making it difficult to stir, reducing the dispersibility of the binder, making it difficult for the binder to evenly adhere the positive active material to the on the current collector, affecting the cycle performance of the battery.
  • the viscosity of the binder glue is too high, which reduces the speed of the pulping process; if the viscosity of the first polyvinylidene fluoride is too small, the viscosity of the prepared binder glue will be If it is too small, it will be difficult for the pole piece to have sufficient bonding force at low addition amounts.
  • the binder when preparing the positive electrode slurry, the binder needs to have a certain viscosity to prevent the positive electrode active materials and conductive agents and other additives from settling, so that the slurry can be stored stably.
  • a binder with a mass content of at least 7% is required.
  • the first polyylidene fluoride of the present application Ethylene can achieve the expected viscosity of the glue at a dosage of 4%, which provides a basis for reducing the content of the binder in the positive electrode film layer.
  • Controlling the viscosity of the first polyvinylidene fluoride glue within an appropriate range allows the pole piece to have excellent bonding performance with a low amount of binder added, thereby improving the capacity retention rate of the battery during cycling.
  • the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 1:1 ⁇ 4:1. In some embodiments, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride can be selected from 1:1 to 2:1, 1:1 to 3:1, or 2:1 to 3:1. , 2:1 ⁇ 4:1, 3:2 ⁇ 5:2, 4:3 ⁇ 7:2, 5:3 ⁇ 7:3, 8:3 ⁇ 10:3, 5:4 ⁇ 7:4, 9 : Any one of 4 ⁇ 11:4, 13:4 ⁇ 15:4, 3:2 ⁇ 7:2, 4:3 ⁇ 11:3, 5:4 ⁇ 15:4, 6:5 ⁇ 19:5 kind.
  • the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is too large, that is, the The quality of the first polyvinylidene fluoride is too high and the purpose of cost reduction cannot be achieved; if the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is too small, that is, the quality of the first polyvinylidene fluoride is too high. If it is low, the bonding force of the pole pieces will decrease, which will affect the cycle performance of the battery.
  • the binder can be added in a low amount so that the pole piece has excellent bonding force, which can improve the performance of the battery during the cycle. Capacity retention rate.
  • the second polyvinylidene fluoride has a weight average molecular weight of 600,000 to 1.1 million.
  • the weight average molecular weight of the second polyvinylidene fluoride can be selected from 600,000 to 700,000, 600,000 to 800,000, 600,000 to 900,000, 600,000 to 1 million, 600,000 to 1.1 million, 700,000 to 800,000, 700,000 to 900,000, 700,000 to 1 million, 700,000 to 1.1 million, 800,000 to 900,000, 800,000 to 1 million, 800,000 to 1.1 million, 900,000 to 1 million, 800,000 to 1.1 million, 900,000 to 1 million, 900,000 ⁇ 1.1 million, any one of 1 million ⁇ 1.1 million.
  • the binder By controlling the weight average molecular weight of the second polyvinylidene fluoride within an appropriate range, the binder enables the electrode piece to have excellent bonding force, improving the capacity retention rate of the battery during cycling while controlling the production cost of the binder. .
  • a method for preparing an adhesive including the following steps:
  • Preparing the first polyvinylidene fluoride polymerizing the vinylidene fluoride monomer under polymerizable conditions to prepare the first polyvinylidene fluoride.
  • the weight average molecular weight of the first polyvinylidene fluoride is 1.8 million to 500 Ten thousand;
  • Blending The first polyvinylidene fluoride and the second polyvinylidene fluoride are blended to prepare a binder, wherein the weight average molecular weight of the second polyvinylidene fluoride is less than the weight average of the first polyvinylidene fluoride. molecular weight.
  • blending refers to the process of making a macroscopically uniform material from two or more substances under certain conditions such as temperature and/or shear stress.
  • the preparation method of the binder is simple, environmentally friendly, has reduced costs and is conducive to industrial production. At the same time, the binder prepared by this method enables the pole piece to have excellent bonding force and improves the capacity retention rate of the battery during cycling.
  • the first polyvinylidene fluoride and the second polyvinylidene fluoride The mass ratio of vinylidene fluoride is 1:1 to 4:1.
  • the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride can be selected from 1:1 to 2:1, 1:1 to 3:1, or 2:1 to 3:1. , 2:1 ⁇ 4:1, 3:2 ⁇ 5:2, 4:3 ⁇ 7:2, 5:3 ⁇ 7:3, 8:3 ⁇ 10:3, 5:4 ⁇ 7:4, 9 : Any one of 4 ⁇ 11:4, 13:4 ⁇ 15:4, 3:2 ⁇ 7:2, 4:3 ⁇ 11:3, 5:4 ⁇ 15:4, 6:5 ⁇ 19:5 kind.
  • the binder can make the pole piece have excellent bonding force at a low addition amount, and can improve the cycle performance of the battery. Capacity retention during the process.
  • the synthesis step of the first polyvinylidene fluoride includes: reacting vinylidene fluoride monomer in a non-reactive gas atmosphere, a reaction pressure of 6MPa to 8MPa, and a reaction temperature of 45°C to 60°C 6 hours to 12 hours; add chain transfer agent, wait until the pressure in the reaction system drops to 2MPa ⁇ 2.5MPa, stop the reaction, separate the solid and liquid, and retain the solid phase.
  • non-reactive gas refers to a gas that does not react with the reactants in the reaction system.
  • Common non-reactive gases are inert gases such as argon and nitrogen.
  • the reaction pressure is one of 6MPa ⁇ 6.5MPa, 6.5MPa ⁇ 7MPa, 7MPa ⁇ 7.5MPa, 7.5MPa ⁇ 8MPa, 6MPa ⁇ 7MPa, 7MPa ⁇ 8MPa.
  • the reaction temperature is one of 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, 45°C to 55°C, and 50°C to 60°C.
  • the polymerization reaction time is 6 hours to 7 hours, 7 hours to 8 hours, 8 hours to 9 hours, 9 hours to 10 hours, 10 hours to 11 hours, 11 hours to 12 hours, 6 hours to 8 hours, 6 hours to 10 hours.
  • the pressure of the polymerization reaction is relatively large, and the pressure of monomers entering the reaction solution is relatively large. More monomers enter the reaction solution, which can lead to the occurrence of a large-scale polymerization reaction, causing the polydispersity coefficient of the first polyvinylidene fluoride to be generated to increase. With the reduction of monomers, the polymerization reaction lacks the supply of monomers, resulting in a relatively small weight average molecular weight of the first polyvinylidene fluoride, which affects the adhesive force of the pole piece and the battery cycle capacity retention rate.
  • the polymerization reaction pressure is small, the pressure for the monomers to enter the reaction solution is small, and the reaction monomers cannot be continuously replenished, which is not conducive to the continuous progress of the polymerization.
  • the first polyvinylidene fluoride produced The weight average molecular weight of ethylene is too low to meet the adhesive force requirements, and the battery cycle performance is also reduced.
  • the polymerization reaction temperature is relatively low, the driving force for copolymerization is small, the polymerization reaction is insufficient, and the molecular weight of the first polyvinylidene fluoride prepared is relatively small, resulting in a significant decrease in adhesive force and a significant decrease in cycle performance.
  • the polymerization reaction temperature is relatively high and a large-scale polymerization reaction occurs, resulting in an increase in the amount of the first polyvinylidene fluoride produced.
  • the polymerization reaction lacks the supply of monomers, resulting in the formation of the first polyvinylidene fluoride.
  • the weight average molecular weight of vinyl fluoride is relatively small, which affects the adhesion of the pole pieces and the battery cycle capacity retention rate.
  • the polymerization reaction time is short, the polymerization reaction cannot continue, and the weight average molecular weight of the first polyvinylidene fluoride prepared is small, which will also cause a decrease in the adhesive force and cycle performance.
  • the polymerization reaction time is long. As the monomers continue to be consumed and the pressure decreases, the conditions for polymerization are no longer reached. Extending the reaction time will not continue the polymerization reaction and reduce production efficiency.
  • the weight average molecular weight of the first polyvinylidene fluoride can be controlled, so that the electrode piece has excellent adhesion, so that the battery has excellent performance during the cycle. Better cycle capacity retention.
  • the chain transfer agent includes one or more of cyclohexane, isopropanol, methanol, and acetone.
  • the amount of chain transfer agent used is 1.5% to 3% of the mass of vinylidene fluoride monomer.
  • the amount of chain transfer agent may also be, for example, 2% or 2.5% of the mass of vinylidene fluoride monomer. Controlling the amount of the chain transfer agent within a suitable range can control the chain length of the first polyvinylidene fluoride, thereby obtaining the first polyvinylidene fluoride in a suitable weight average molecular weight range.
  • the polymerization reaction includes the following steps: adding a solvent and a dispersant to the container, evacuating the container and filling it with a non-reactive gas; adding an initiator and a pH adjuster to the container, and adjusting the pH value to 6.5-6.5. 7. Then add vinylidene fluoride monomer to bring the pressure in the container to 6MPa ⁇ 8MPa; after stirring for 30 to 60 minutes, raise the temperature to 45°C to 60°C to carry out polymerization reaction.
  • 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 solvent used is 2 to 8 times the mass of vinylidene fluoride monomer.
  • the amount of solvent used may also be, for example, 3, 4, 5, 6 or 7 times the mass of vinylidene fluoride monomer.
  • the solvent is an aqueous solvent, optionally deionized water.
  • the dispersant includes one or more of cellulose ethers and polyvinyl alcohol.
  • the cellulose ether includes one or more of methyl cellulose ether and carboxyethyl cellulose ether.
  • the amount of dispersant is 0.1% to 0.3% based on the mass of vinylidene fluoride monomer.
  • the amount of dispersant used may also be, for example, 0.2% by mass of the vinylidene fluoride monomer.
  • the initiator is an organic peroxide.
  • organic peroxides include t-amyl peroxypivalate, t-amyl peroxypivalate, 2-ethylperoxydicarbonate, diisopropylperoxydicarbonate, and One or more types of tert-butyl peroxypivalate.
  • the amount of initiator used is 0.15% to 1% of the monomer mass of vinylidene fluoride.
  • the amount of initiator used may also be, for example, 0.2%, 0.4%, 0.6% or 0.8% based on the mass of vinylidene fluoride monomer.
  • the pH adjusting agent 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% based on the mass of vinylidene fluoride monomer.
  • the amount of pH adjuster used may also be, for example, 0.1% or 0.15% of the mass of the vinylidene fluoride monomer.
  • 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 excellent bonding force with a low additive amount of binder.
  • the mass fraction of the binder is 0.8% to 1.6%, based on the total mass of the positive electrode film layer.
  • the mass fraction of the binder can be selected from 0.8% to 9%, 0.9% to 1%, 1% to 1.1%, 1.1% to 1.2%, 1.2% to 1.3%, 1.3% to 1.4% , 1.4% to 1.5%, 1.5% to 1.6%, 0.8% to 1%, 1% to 1.2%, 1.2% to 1.4%, 1.4% to 1.6%, 0.8% to 1.3%, 1.3% to 1.6% Any kind.
  • Controlling the mass fraction of the binder within an appropriate range enables the pole piece to have excellent bonding force and improve the capacity retention rate of the battery during cycling.
  • the cathode active material is a lithium-containing transition metal oxide.
  • the positive active material is at least one of lithium iron phosphate and its modified materials, lithium nickel cobalt manganese oxide and its modified materials, and the modified materials are obtained by doping, conductive carbon coating It is prepared by one or more modification methods of , conductive metal coating, and conductive polymer coating.
  • a method for preparing a positive electrode sheet including the following steps: first stage: preparing the positive active material, the conductive agent and the binder in any embodiment or by the preparation method in any embodiment Mix the binder and perform the first stirring; the second stage: add the solvent and perform the second stirring; the third stage: add the dispersant and perform the third stirring to obtain a slurry, and control the viscosity of the slurry to be between 8000mPa ⁇ s and 15000mPa ⁇ s; The fourth stage: Coat the slurry on the positive electrode current collector to obtain the positive electrode piece.
  • the preparation method is simple and convenient for industrial production. This preparation method is beneficial to reducing the sedimentation of the high molecular weight first polyvinylidene fluoride in the slurry, and is helpful to improve the quality of the slurry and the uniformity of the positive electrode sheet.
  • the stirring revolution speed is 25 rpm and the stirring time is 30 minutes.
  • the stirring revolution speed is 25 rpm
  • the stirring rotation speed is 800-1000 rpm
  • the stirring time is 50-80 minutes.
  • the stirring rotation speed is 1200-1500 rpm, and the stirring time is 50-70 minutes.
  • the dispersant is at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethylcellulose, polyacrylamide, polyacrylic acid, sodium polyacrylate, and polyacetimide. A sort of.
  • the mass fraction of the dispersant is 0.2% to 0.5%, based on the total mass of the positive electrode film layer.
  • 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 0.8 Co 0.1 Mn 0.1 O 2 (can also be abbreviated to NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiN
  • lithium-containing phosphates with an olivine structure 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 ), phosphoric acid At least one of a composite material of lithium manganese and carbon, a composite material of lithium manganese iron phosphate, or a composite material of lithium manganese iron 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
  • phosphoric acid At least one of a composite material of lithium manganese and carbon, a composite material of lithium manganese iron phosphate, or a composite material of lithium manganese iron 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 the following materials: At least one: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate, etc.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as 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 can be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, Lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium triflate, lithium difluorophosphate, lithium difluoroxaloborate, dioxaloborate At least one of lithium, 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 material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 1 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • this application also provides an electrical device, the electrical device includes the application's At least one of a secondary battery, a battery module, or a battery pack is provided.
  • 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.
  • Preparation of the first polyvinylidene fluoride Add 4kg of deionized water and 2g of methylcellulose ether to a 10L autoclave, evacuate and replace O2 with N 2 three times, and then add 5g of tert-butyl peroxide neopentyl acid ester and 2g of sodium bicarbonate, and filled with 1kg of vinylidene fluoride to bring the system pressure to 7MPa. Mix and stir for 30 minutes, raise the temperature to 45°C, and after 6 hours of reaction, add 30g of cyclohexane to continue the reaction. When the reaction kettle is Stop the reaction when the pressure drops to 2MPa answer. The reaction system is centrifuged and the solid phase is collected, washed and dried to obtain the first polyvinylidene fluoride.
  • the second polyvinylidene fluoride purchased from Shandong Deyi New Materials Co., Ltd., model DY-5, weight average molecular weight 800,000, polydispersity coefficient 1.85, Dv50 15 ⁇ m, crystallinity 40%, dissolved in N -The viscosity of the glue with a mass fraction of 7% after methylpyrrolidone is 2300 mPa ⁇ s.
  • the first polyvinylidene fluoride and the second polyvinylidene fluoride are blended, and the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 3:1 to obtain the first polyvinylidene fluoride.
  • Binder for ethylene and a second vinylidene fluoride are blended, and the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 3:1 to obtain the first polyvinylidene fluoride.
  • NMP N-methylpyrrolidone
  • NMP N-methylpyrrolidone
  • 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 2 It is basically the same as Example 1, except that the polymerization reaction time of the first polyvinylidene fluoride is adjusted to 10h and 12h respectively, and the mass of cyclohexane is adjusted to 20g and 15g respectively to adjust the polymerization reaction time of the first polyvinylidene fluoride.
  • the weight average molecular weight of vinyl fluoride, the specific parameters are shown in Table 1.
  • Example 2 It is basically the same as Example 1, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride during the blending process is adjusted.
  • the specific parameters are as shown in Table 1.
  • Example 2 It is basically the same as Example 1, except that the mass fraction of the binder is adjusted, based on the total mass of the positive electrode film layer.
  • the specific parameters are as shown in Table 1.
  • Example 2 It is basically the same as Example 1, except that the second polyvinylidene fluoride is 605 purchased from Huaan Company, with a weight average molecular weight of 600,000, a polydispersity coefficient of 2.05, a Dv50 of 13.4 ⁇ m, a crystallinity of 42%, and a dissolved
  • the viscosity of the glue with a mass fraction of 7% after N-methylpyrrolidone was 3000 mPa ⁇ s.
  • Example 2 It is basically the same as Example 1, except that the second polyvinylidene fluoride is 202E purchased from Shenzhou Company, with a weight average molecular weight of 1.1 million, a polydispersity coefficient of 2.0, a Dv50 of 11.5 ⁇ m, a crystallinity of 42%, and a dissolved
  • the viscosity of the glue formulated with a mass fraction of 7% after N-methylpyrrolidone is 4100 mPa ⁇ s.
  • Example 1 Basically the same as Example 1, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 0.8%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 1 Basically the same as Example 1, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride during the blending process was adjusted, and the mass fraction of the binder was adjusted to 1.6%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 2 Basically the same as Example 2, except that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 0.8%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 2 It is basically the same as Example 2, except that the mass fraction of the binder is adjusted to 0.8%, based on the total mass of the positive electrode film layer.
  • the specific parameters are as shown in Table 1.
  • Example 2 Basically the same as Example 2, except that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 0.8%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 2 It is basically the same as Example 2, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride during the blending process is adjusted.
  • the specific parameters are as shown in Table 1.
  • Example 2 Basically the same as Example 2, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 1.6%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 2 It is basically the same as Example 2, except that the mass fraction of the binder is adjusted to 1.6%, based on the total mass of the positive electrode film layer.
  • the specific parameters are as shown in Table 1.
  • Example 2 Basically the same as Example 2, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 1.6%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 3 Basically the same as Example 3, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 0.8%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 3 It is basically the same as Example 3, except that the mass fraction of the binder is adjusted to 0.8%, based on the total mass of the positive electrode film layer.
  • the specific parameters are as shown in Table 1.
  • Example 3 Basically the same as Example 3, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 0.8%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 3 It is basically the same as Example 3, except that the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride during the blending process is adjusted.
  • the specific parameters are as shown in Table 1.
  • Example 3 Basically the same as Example 3, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 1.6%, based on the positive electrode The total mass of the film layer is measured, and the specific parameters are shown in Table 1.
  • Example 3 It is basically the same as Example 3, except that the mass fraction of the binder is adjusted to 1.6%, based on the total mass of the positive electrode film layer.
  • the specific parameters are as shown in Table 1.
  • Example 3 Basically the same as Example 3, the difference is that during the blending process, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride was adjusted, and the mass fraction of the binder was adjusted to 1.6%, based on the positive electrode film The total mass of the layer is measured, and the specific parameters are shown in Table 1.
  • Example 2 Basically the same as Example 2, the difference is that the polymerized monomers are adjusted to 0.94kg of vinylidene fluoride and 0.06kg of chlorotrifluoroethylene to prepare a vinylidene fluoride-chlorotrifluoroethylene copolymer.
  • the specific parameters are as shown in the table 1 shown.
  • Example 2 Basically the same as Example 2, except that the polymerized monomers were adjusted to 0.94kg of vinylidene fluoride and 0.06kg of tetrafluoroethylene to prepare a vinylidene fluoride-tetrafluoroethylene copolymer.
  • the specific parameters are as shown in Table 1. Show.
  • Example 2 It is basically the same as Example 2, except that the polymerized monomers are adjusted to 0.94kg of vinylidene fluoride and 0.06kg of hexafluoropropylene to prepare a vinylidene fluoride-hexafluoropropylene copolymer.
  • the specific parameters are as shown in Table 1. Show.
  • Example 2 It is basically the same as Example 2, except that the second polyvinylidene fluoride is replaced with a vinylidene fluoride-chlorotrifluoroethylene copolymer with a weight average molecular weight of 800,000, purchased from Huaxia Shenzhou New Materials Co., Ltd., model number 202D, the specific parameters are shown in Table 1.
  • Example 2 It is basically the same as Example 1, except that the binder only contains the second polyvinylidene fluoride, and the specific parameters are as shown in Table 1.
  • Example 2 Basically the same as Example 1, except that the polymerization temperature of the first polyvinylidene fluoride was adjusted to 38°C, the polymerization pressure was adjusted to 5MPa, the polymerization time was adjusted to 3h, and cyclohexane was adjusted to 36g, The molecular weight of the first polyvinylidene fluoride prepared after the reaction was 1.2 million.
  • the GB/T 19077-2016 particle size distribution laser diffraction method use a 50ml beaker to weigh 0.1g ⁇ 0.13g of the first polyvinylidene fluoride powder, then weigh 5g of absolute ethanol, and add it to the container containing the first polyvinylidene fluoride.
  • a stirrer with a length of about 2.5mm and seal it with plastic wrap. Put the sample into the ultrasonic machine for 5 minutes, transfer to the magnetic stirrer and stir at 500r/min for more than 20 minutes. Take 2 samples from each batch of products for testing and take the average value.
  • Use a laser particle size analyzer for measurement such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the United Kingdom.
  • the battery capacity retention rate data corresponding to Examples 1 to 41 or Comparative Examples 1 to 3 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 45 all include a first polyvinylidene fluoride and a second polyvinylidene fluoride, and the weight average molecular weight of the first polyvinylidene fluoride is 1.8 million to 5 million. , the weight average molecular weight of the second polyvinylidene fluoride is smaller than the weight average molecular weight of the first polyvinylidene fluoride.
  • Comparing Examples 1 to 45 with Comparative Example 2 it can be seen that when the amount of binder added is low, Under this condition, the binder including the first polyvinylidene fluoride and the second polyvinylidene fluoride enables the pole piece to have excellent bonding force, improves the capacity retention rate of the battery during the cycle, and effectively improves the high performance of the traditional technology. The performance of the pole piece and battery is limited due to the amount of binder used.
  • the polydispersity coefficient of the first polyvinylidene fluoride in the binder is 2.1 to 2.3.
  • a low amount of binder can make the electrode piece have excellent bonding force, and the battery can High capacity retention during cycling.
  • the Dv50 particle size of the first polyvinylidene fluoride in the binder is 50 ⁇ m to 150 ⁇ m.
  • a low addition amount of binder can make the pole piece have excellent adhesive force, and the battery High capacity retention during cycling.
  • the crystallinity of the first polyvinylidene fluoride in the binder is 42% to 45%, and a low amount of binder can make the pole piece have excellent bonding force.
  • the battery has high capacity retention during cycling.
  • the viscosity of the glue containing 4% mass content of the first polyvinylidene fluoride prepared by dissolving the first polyvinylidene fluoride in N-methylpyrrolidone in the binder It is known from Examples 1 to 45 that the viscosity of the glue containing 4% mass content of the first polyvinylidene fluoride prepared by dissolving the first polyvinylidene fluoride in N-methylpyrrolidone in the binder It is 2500mPa ⁇ s ⁇ 5000mPa ⁇ s, which enables the binder to ensure sufficient bonding force of the pole piece at a low addition amount.
  • Example 7 From the comparison of Example 1, Examples 4 to 6 and Example 7, it can be seen that when the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in the binder is 1:1 to 4:1, the lower The added amount of binder makes the pole piece have excellent bonding force, and the capacity retention rate of the battery during cycling can be further improved.
  • Example 1 It is known from Example 1 and Examples 12 to 13 that the weight average molecular weight of the second polyvinylidene fluoride in the binder is 600,000 to 1.1 million, and the binder can make the pole piece have Excellent adhesion, the capacity retention rate of the battery during cycling is improved.
  • Example 1 From the comparison of Example 1, Examples 8 to 9 and Example 10, it can be seen that when the mass fraction of the binder is 0.8% to 1.6%, based on the total mass of the positive electrode film layer, the binder can ensure that the electrode piece has sufficient The adhesive force is improved, and the capacity retention rate of the battery during cycling is further improved. From the comparison of Example 1, Examples 8 to 9 and Example 11, it can be seen that when the binder mass fraction is 2.0%, excessively high binder content will not significantly improve the adhesive force of the pole piece and the cycle performance of the battery. , which is not conducive to the improvement of battery energy density.
  • the first polyvinylidene fluoride in the binder is vinylidene fluoride homopolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride - Tetrafluoroethylene copolymer or vinylidene fluoride-hexafluoropropylene copolymer, low addition amount of binder can make the pole piece have excellent bonding force, and the battery has a high capacity retention rate during cycling.
  • the second polyvinylidene fluoride in the binder is a vinylidene fluoride homopolymer or a vinylidene fluoride-chlorotrifluoroethylene copolymer.
  • the agent can make the electrode piece have excellent adhesion, and the battery has a high capacity retention rate during cycling.

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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。粘结剂包括第一聚偏二氟乙烯和第二聚偏二氟乙烯，第一聚偏二氟乙烯的重均分子量为180万～500万，第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。该粘结剂在低添加量下就可以使得极片具有高的粘结力，并能提高电池的循环性能。

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202211052046.9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。但是现有的粘结剂粘结性差，往往需要大量添加才能满足极片粘结力的要求，这会限制电池能量密度的提升。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即可以发挥优异的粘结力，使得极片具有足够的粘结强度，并且能够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，粘结剂包括第一聚偏二氟乙烯和第二聚偏二氟乙烯，第一聚偏二氟乙烯的重均分子量为180万～500万，第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。
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，提高电池的循环性能。
在任意实施方式中，第一聚偏二氟乙烯的多分散系数为2～2.3，可选为2.1～2.3。
控制第一聚偏二氟乙烯的多分散系数在合适范围内，粘结剂在低添加量下就能使得极片具有优异的粘结力，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，第一聚偏二氟乙烯的Dv50粒径为50μm～150μm，可选为60μm～150μm。
控制第一聚偏二氟乙烯的Dv50粒径在合适范围内，粘结剂在低添加量下就能使得极片具有优异的粘结力，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，第一聚偏二氟乙烯的结晶度为40％～45％，可选为42％～45％。
控制第一聚偏二氟乙烯的结晶度在合适范围内，粘结剂在低添加量下就能使得极片具有优异的粘结力和柔性，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，第一聚偏二氟乙烯溶于N-甲基吡咯烷酮制得的含有质量含量为4％的所述第一聚偏二氟乙烯的胶液的粘度为2500mPa·s～5000mPa·s，可选为3600mPa·s～5000mPa·s。
控制第一聚偏二氟乙烯的胶液的粘度在合适范围内，低添加量的粘结剂就能够保证极片具有优异的粘结力。
在任意实施方式中，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比为1：1～4：1。
控制第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比在合适范围内，极片兼具好的加工性能和粘结力，电池在循环过程中的容量保持率能够进一步提高。
在任意实施方式中，第二聚偏二氟乙烯的重均分子量为60万～110万。
控制第二聚偏二氟乙烯的重均分子量在合适范围内，极片具有优异的粘结力，电池在循环过程中的容量保持率能够提高。
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：制备第一聚偏二氟乙烯：在可聚合条件下，将偏二氟乙烯单体进行聚合反应制备第一聚偏二氟乙烯，第一聚偏二氟乙烯的重均分子量为180万～500万；共混：将第一聚偏二氟乙烯与第二聚偏二氟乙烯共混制备粘结剂，其中，第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。
该粘结剂的制备方法简单，对环境友好，成本降低，利于工业化生产。同时该方法制备的粘结剂在低添加量下即可以满足极片粘结力的要求，有助于提高极片中正极活性材料的负载量，利于提高电池在循环过程中的容量保持率。
在任意实施方式中，共混步骤中，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比为1：1～4：1。
控制第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比在合适范围内，极片在粘结剂低添加量下即具有优异的粘结力，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，制备第一聚偏二氟乙烯的聚合反应包括以下步骤：
将偏二氟乙烯单体在非反应性气体氛围、6MPa～8MPa的反应压力、45℃～60℃的反应温度下反应6小时～12小时；
加入链转移剂，待反应体系中压力降至2MPa～2.5MPa，停止反应，固液分离，保留固相。
控制聚合反应的反应压力、反应温度、反应时间在合适的范围内，可以控制第一聚偏二氟乙烯的的重均分子量，使得极片具有优异的粘结力，使得电池在循环过程中具有较好的循环容量保持率。
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，链转移剂的用量为偏二氟乙烯单体质量的 1.5％～3％。
链转移剂的用量控制在合适范围内，能使得第一聚偏二氟乙烯的链长可控，从而获得合适重均分子量范围的第一聚偏二氟乙烯。
在任意实施方式中，制备第一聚偏二氟乙烯的聚合反应还包括以下步骤：
向容器中加入溶剂和分散剂，对容器抽真空后充入非反应性气体；
向容器中加入引发剂和pH调节剂，调节pH值至6.5～7，然后加入偏二氟乙烯单体，使容器中的压力达到6MPa～8MPa；
搅拌30分钟～60分钟后，升温至45℃～60℃，进行聚合反应。
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。
在任意实施方式中，溶剂的用量为所述偏二氟乙烯单体质量的2～8倍。
在任意实施方式中，分散剂包括纤维素醚和聚乙烯醇中的一种或多种。
在任意实施方式中，纤维素醚包括甲基纤维素醚和羧乙基纤维素醚中的一种或多种。
在任意实施方式中，分散剂的用量为偏二氟乙烯单体质量的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以及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，引发剂的用量为偏二氟乙烯单体质量的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、碳酸氢钠以及氨水中的一种或多种。
在任意实施方式中，pH调节剂的用量为所述偏二氟乙烯单体质 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。
该正极极片在粘结剂低添加量下具有优异的粘结力。
在任意实施方式中，粘结剂的质量分数为0.8％～1.6％，基于正极膜层的总质量计。
控制粘结剂的质量分数在合适范围内在确保极片具有足够粘结力的情况下，能够提高电池极片中活性材料的负载量，有助于进一步提高电池的功率性能。
在任意实施方式中，正极活性材料为含锂的过渡金属氧化物。
在任意实施方式中，含锂的过渡金属氧化物为磷酸铁锂及其改性材料、锂镍钴锰氧化物及其改性材料中的至少一种，所述改性材料是通过掺杂、导电碳包覆、导电金属包覆、导电聚合物包覆中的一种或多种改性方式制备的。
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，所述电极组件包括本申请第三方面的正极极片、隔离膜和负极极片。
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)。
聚偏二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，传统聚偏二氟乙烯的粘度低，往往需要大量添加才能保证活性材料的有效粘结，从而使得极片达到有效的粘结力。然而传统聚偏二氟乙烯用量的提高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，难以满足对于电池循环性能的要求。
[粘结剂]
本申请提供了一种粘结剂，粘结剂包括第一聚偏二氟乙烯和第二聚偏二氟乙烯，第一聚偏二氟乙烯的重均分子量为180万～500万，第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。
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“聚偏二氟乙烯”是指以偏二氟乙烯为主要合成 单体的聚合物，聚合物一方面包括通过聚合反应制备的化学上均一的、但在聚合度、摩尔质量和链长方面不同的大分子的集合体。该术语另一方面也包括由聚合反应形成的这样的大分子集合体的衍生物，即可以通过上述大分子中的官能团的反应，例如加成或取代获得的并且可以是化学上均一的或化学上不均一的化合物。本文中的聚偏二氟乙烯既包括均聚物，也包括共聚物。
在一些实施方式中，第一聚偏二氟乙烯包括聚偏二氟乙烯均聚物、偏二氟乙烯-三氟氯乙烯共聚物、偏二氟乙烯-四氟乙烯共聚物、偏二氟乙烯-六氟丙烯共聚物、偏二氟乙烯-三氟氯乙烯-四氟乙烯共聚物、偏二氟乙烯-三氟氯乙烯-六氟丙烯共聚物、偏二氟乙烯-四氟乙烯-六氟丙烯共聚物、偏二氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物中的一种或多种。
在一些实施方式中，第二聚偏二氟乙烯包括聚偏二氟乙烯均聚物、偏二氟乙烯-三氟氯乙烯共聚物、偏二氟乙烯-三氟氯乙烯-四氟乙烯共聚物、偏二氟乙烯-三氟氯乙烯-六氟丙烯共聚物、偏二氟乙烯-四氟乙烯-六氟丙烯共聚物、偏二氟乙烯-三氟氯乙烯-四氟乙烯-六氟丙烯共聚物中的一种或多种。
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，粘接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材料及/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。
第一聚偏二氟乙烯的结构式如式I所示，第二聚偏二氟乙烯的结构式如式Ⅱ所示，
其中，m、n为整数，分别表示第一聚偏二氟乙烯和第二聚偏二氟乙烯的聚合度，m大于n，即第一聚偏二氟乙烯的聚合度和重均分子量大于第二聚偏二氟乙烯的聚合度和重均分子量。
第一聚偏二氟乙烯和第二聚偏二氟乙烯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180万～500万的第一聚偏二氟乙烯，具有极大的内聚力和分子间作用力，能够在低水平添加量下提高极片的粘结力，提高电池在循环过程中的容量保持率。第二聚偏二氟乙烯在粘结剂中的加入可以大大降低粘结剂成本，同时由于第一聚偏二氟乙烯与第二聚偏二氟乙烯的结构单元相同、相容性优异，在制备极片的烘干过程中，极片不会出现分层现象，能够得到高品质极片。
上述粘结剂在低添加量下就能够保证极片具有足够的粘结力，有利于提高电池的能量密度以及电池的循环性能。
在本申请中，第一聚偏二氟乙烯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 2695 Isocratic 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。
在一些实施方式中，第一聚偏二氟乙烯的多分散系数为2～2.3。在一些实施方式中，第一聚偏二氟乙烯的多分散系数可选为2～2.1、2～2.2、2～2.3、2.1～2.2、2.1～2.3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。
若第一聚偏二氟乙烯的多分散系数过大，则第一聚偏二氟乙烯的聚合度较为分散，影响粘结剂的均匀性，粘结剂无法将正极活性材料均匀的粘附在集流体上，影响电池的循环性能，同时也使得浆料固含量下降，无法进一步提高电池的能量密度；若第一聚偏二氟乙烯的多分散系数过小，制备工艺难度较大，且优率较低，导致生产成本较高。
第一聚偏二氟乙烯的多分散系数在合适范围内，使得极片具有优异的粘结力，提高电池在循环过程中的容量保持率。另外合适的第一聚偏二氟乙烯的多分散系数，能有效提升浆料固含量，降低生产成本。
本申请中，第一聚偏二氟乙烯的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 2695 Isocratic 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。
在一些实施方式中，第一聚偏二氟乙烯的Dv50粒径为 50μm～150μm，可选为60μm～150μm。在一些实施方式中，第一聚偏二氟乙烯的Dv50粒径可选为50μm～60μm、60μm～70μm、70μm～80μm、80μm～90μm、90μm～100μm、100μm～110μm、110μm～120μm、120μm～130μm、130μm～140μm、140μm～150μm、50μm～70μm、70μm～90μm、90μm～110μm、110μm～130μm、130μm～150μm、60μm～80μm、80μm～100μm、60μm～140μm、60μm～150μm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％。
若第一聚偏二氟乙烯的Dv50粒径过大，第一聚偏二氟乙烯溶解相对困难，降低粘结剂的分散性，影响正极活性材料在集流体上的均匀分布，影响电池的循环性能，同时第一聚偏二氟乙烯的溶解困难，降低制浆过程的速度；若第一聚偏二氟乙烯的Dv50粒径过小，极片的粘结力下降。
控制第一聚偏二氟乙烯的Dv50粒径在合适范围内，低含量的粘结剂就能够使得极片具有足够的粘结力，并且能够提高电池在循环过程中的容量保持率。同时合适范围的第一聚偏二氟乙烯的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导致的极片和电池性能受限的情况。
本申请中，第一聚偏二氟乙烯的Dv50粒径的测试可以选用本领域已知的方法进行测试，例如，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的第一聚偏二氟乙烯粉料，再称取5g无水乙醇，加入到装有第一聚偏二氟乙烯粉料的烧杯中，放入长度约2.5mm的搅拌子，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，第一聚偏二氟乙烯的结晶度为40％～45％，可选为42％～45％。在一些实施方式中，第一聚偏二氟乙烯的结晶度可选为40％～42％、42％～43％、43％～45％、40％～43％、41％～42％、41％～43％、43％～44％、41％～44％、42％～45％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。
若第一聚偏二氟乙烯的结晶度过大，第一聚偏二氟乙烯链段的可移动性降低，影响极片的柔韧性，同时第一聚偏二氟乙烯的溶解困难，降低制浆过程的速度。若第一聚偏二氟乙烯的结晶度过小，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。
控制第一聚偏二氟乙烯的结晶度在合适范围内，粘结剂使得极片具有优异的粘结力，能够提高电池在循环过程中的容量保持率。
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第一聚偏二氟乙烯置于铝制坩埚中，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。
此测试将会得到第一聚偏二氟乙烯的DSC曲线，并对曲线进行积分，峰面积即为第一聚偏二氟乙烯的熔融焓ΔH(J/g)，粘结剂结晶度＝(ΔH/ΔHm)×100％，其中ΔHm为聚偏二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，第一聚偏二氟乙烯溶于N-甲基吡咯烷酮制得的含有质量含量为4％的第一聚偏二氟乙烯的胶液的粘度为2500mPa·s～5000mPa·s，可选为3600mPa·s～5000mPa·s。在一些实施方式中，第一聚偏二氟乙烯溶于N-甲基吡咯烷酮制得的含有质量含 量为4％的第一聚偏二氟乙烯的胶液的粘度可选为2500mPa·s～3000mPa·s、3000mPa·s～3300mPa·s、3300mPa·s～3500mPa·s、3500mPa·s～3800mPa·s、3800mPa·s～4000mPa·s、4000mPa·s～4200mPa·s、4200mPa·s～4600mPa·s、4600mPa·s～5000mPa·s、3100mPa·s～3400mPa·s、3400mPa·s～3800mPa·s、3800mPa·s～4600mPa·s、3600mPa·s～5000mPa·s中的任意一种。
若第一聚偏二氟乙烯的粘度过大，制备的粘结剂胶液的粘度过大，难以搅动，降低粘结剂的分散性，使得粘结剂难以将正极活性材料均匀的粘附在集流体上，影响电池的循环性能，同时粘结剂胶液粘度过大，降低制浆过程的速度；若第一聚偏二氟乙烯的粘度过小，制备的粘结剂胶液的粘度会过小，极片在低添加量下难以具有足够的粘结力。
另外制备正极浆料时，粘结剂需要具有一定的粘度，才能防止正极活性材料以及导电剂等助剂的沉降，使浆料能稳定地存储。传统技术中，要达到2500mPa·s～5000mPa·s的胶液粘度，至少需要含有质量含量为7％的粘结剂才能实现，基于胶液的质量计，而本申请的第一聚偏二氟乙烯在4％的用量下就可以实现胶液的预期粘度，为降低粘结剂在正极膜层中的含量提供了基础。
控制第一聚偏二氟乙烯胶液的粘度在合适范围内，使得极片在粘结剂低添加量的情况下就能具有优异的粘结性能，提高电池在循环过程中的容量保持率。
在一些实施方式中，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比为1：1～4：1。在一些实施方式中，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比可选为1：1～2：1、1：1～3：1、2：1～3：1、2：1～4：1、3：2～5：2、4：3～7：2、5：3～7：3、8：3～10：3、5：4～7：4、9：4～11：4、13：4～15：4、3：2～7：2、4：3～11：3、5：4～15：4、6：5～19：5中的任意一种。
若第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比过大，即第 一聚偏二氟乙烯的质量过高，无法达到降低成本的目的；若第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比过小，即第一聚二氟乙烯的质量过低，极片的粘结力下降，影响电池的循环性能。
控制第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比在合适范围内，粘结剂在低添加量下使得极片具有优异的粘结力，能够提高电池在循环过程中的容量保持率。
在一些实施方式中，第二聚偏二氟乙烯的重均分子量为60万～110万。在一些实施方式中，第二聚偏二氟乙烯的重均分子量可选为60万～70万、60万～80万、60万～90万、60万～100万、60万～110万、70万～80万、70万～90万、70万～100万、70万～110万、80万～90万、80万～100万、80万～110万、90万～100万、90万～110万、100万～110万中的任意一种。
控制第二聚偏二氟乙烯的重均分子量在合适范围内，粘结剂使得极片具有优异的粘结力，提高电池在循环过程中的容量保持率的同时能够控制粘结剂的生产成本。
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：
制备第一聚偏二氟乙烯：在可聚合条件下，将偏二氟乙烯单体进行聚合反应制备第一聚偏二氟乙烯，第一聚偏二氟乙烯的重均分子量为180万～500万；
共混：将第一聚偏二氟乙烯与第二聚偏二氟乙烯共混制备粘结剂，其中，第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。
在本文中，术语“共混”指两种或两种以上物质，在一定温度和/或剪切应力等条件下，制成宏观均匀材料的过程。
该粘结剂的制备方法简单，对环境友好，成本降低，利于工业化生产。同时该方法制备的粘结剂，使得极片具有优异的粘结力，提高电池在循环过程中的容量保持率。
在一些实施方式中，共混步骤中，第一聚偏二氟乙烯与第二聚 偏二氟乙烯的质量比为1：1～4：1。在一些实施方式中，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比可选为1：1～2：1、1：1～3：1、2：1～3：1、2：1～4：1、3：2～5：2、4：3～7：2、5：3～7：3、8：3～10：3、5：4～7：4、9：4～11：4、13：4～15：4、3：2～7：2、4：3～11：3、5：4～15：4、6：5～19：5中的任意一种。
控制第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比在合适范围内，粘结剂在低添加量下就能够使得极片具有优异的粘结力，且能够提高电池在循环过程中的容量保持率。
在一些实施方式中，第一聚偏二氟乙烯的合成步骤包括：将偏二氟乙烯单体在非反应性气体氛围、6MPa～8MPa的反应压力、45℃～60℃的反应温度下反应6小时～12小时；加入链转移剂，待反应体系中压力降至2MPa～2.5MPa，停止反应，固液分离，保留固相。
本文中，术语“非反应性气体”指不与反应体系中反应物进行反应的气体，常见的非反应性气体为氩气等惰性气体以及氮气。
在一些实施方式中，反应压力为6MPa～6.5MPa、6.5MPa～7MPa、7MPa～7.5MPa、7.5MPa～8MPa、6MPa～7MPa、7MPa～8MPa中的一种。
在一些实施方式中，反应温度为45℃～50℃、50℃～55℃、55℃～60℃、45℃～55℃、50℃～60℃中的一种。
在一些实施方式中，聚合反应的时间为6小时～7小时、7小时～8小时、8小时～9小时、9小时～10小时、10小时～11小时、11小时～12小时、6小时～8小时、6小时～10小时。
聚合反应压力较大，单体进入反应溶液的压力较大，单体进入反应溶液中较多，可导致大范围聚合反应的发生，使得生成的第一聚偏二氟乙烯多分散系数增大，随着单体的减少，聚合反应缺少单体的供给，导致生成的第一聚偏二氟乙烯的重均分子量相对较小，影响极片的粘结力和电池循环容量保持率。
聚合反应压力较小，单体进入反应溶液的压力较小，反应单体不能持续的补充，不利于聚合的持续进行，制得的第一聚偏二氟乙 烯的重均分子量过低，无法满足粘结力需求，且电池循环性能也有所下降。
聚合反应温度偏低，共聚的促动力较小，聚合反应不充分，制备的第一聚偏二氟乙烯的分子量偏小，造成粘结力的大幅下降，以及循环性能的明显下降。
聚合反应温度偏高，大范围聚合反应的发生，导致生成的第一聚偏二氟乙烯的数量增多，随着单体的减少，聚合反应缺少单体的供给，导致生成的第一聚偏二氟乙烯的重均分子量相对较小，影响极片的粘结力和电池循环容量保持率。
聚合反应时间较短，聚合反应不能持续进行，制备的第一聚偏二氟乙烯的重均分子量偏小，同样会造成粘结力和循环性能的下降。
聚合反应时间较长，随着单体的持续消耗，压力的降低，已达不到聚合的条件，延长反应时间并不能持续进行聚合反应，降低生产效率。
控制聚合反应的反应压力、反应温度、反应时间在合适的范围内，可以控制第一聚偏二氟乙烯的的重均分子量，使得极片具有优异的粘结力，使得电池在循环过程中具有较好的循环容量保持率。
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。
在一些实施方式中，链转移剂的用量为偏二氟乙烯单体质量的1.5％～3％，链转移剂的用量例如还可以是偏二氟乙烯单体质量的2％或2.5％。链转移剂的用量控制在合适范围内，能使得第一聚偏二氟乙烯的链长可控，从而获得合适重均分子量范围的第一聚偏二氟乙烯。
在一些实施方式中，聚合反应包括以下步骤：向容器中加入溶剂和分散剂，对容器抽真空后充入非反应性气体；向容器中加入引发剂和pH调节剂，调节pH值至6.5～7，然后加入偏二氟乙烯单体，使容器中的压力达到6MPa～8MPa；搅拌30分钟～60分钟后，升温至45℃～60℃，进行聚合反应。
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，溶剂的用量为偏二氟乙烯单体质量的2～8倍。溶剂的用量例如还可以是偏二氟乙烯单体质量的3、4、5、6或7倍。在一些实施方式中，溶剂为水溶剂，可选为去离子水。
在一些实施方式中，分散剂包括纤维素醚和聚乙烯醇中的一种或多种。
在一些实施方式中，纤维素醚包括甲基纤维素醚和羧乙基纤维素醚中的一种或多种。
在一些实施方式中，分散剂的用量为偏二氟乙烯单体质量的0.1％～0.3％。分散剂的用量例如还可以是偏二氟乙烯单体质量的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以及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，引发剂的用量为偏二氟乙烯的单体质量的0.15％～1％。引发剂的用量例如还可以是偏二氟乙烯单体质量的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、碳酸氢钠以及氨水中的一种或多种。
在一些实施方式中，pH调节剂的用量为偏二氟乙烯单体质量的0.05％～0.2％。pH调节剂的用量例如还可以是偏二氟乙烯单体质量的0.1％或0.15％。
[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。
该正极极片在粘结剂低添加量下具有优异的粘结力。
在一些实施方式中，粘结剂的质量分数为0.8％～1.6％，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％～9％、0.9％～1％、1％～1.1％、1.1％～1.2％、1.2％～1.3％、1.3％～1.4％、1.4％～1.5％、1.5％～1.6％、0.8％～1％、1％～1.2％、1.2％～1.4％、1.4％～1.6％、0.8％～1.3％、1.3％～1.6％中的任意一种。
若粘结剂的质量分数过高，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材料表面，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，使得极片具有优异的粘结力，提高电池在循环过程中的容量保持率。
在一些实施方式中，正极活性材料为含锂的过渡金属氧化物。
在一些实施方式中，正极活性材料为磷酸铁锂及其改性材料、锂镍钴锰氧化物及其改性材料中的至少一种，所述改性材料是通过掺杂、导电碳包覆、导电金属包覆、导电聚合物包覆中的一种或多种改性方式制备的。
在一些实施方式中，提供一种正极极片的制备方法，包括以下步骤：第一阶段：将正极活性材料、导电剂和任意实施方式中的粘结剂或如任意实施方式中的制备方法制备的粘结剂混合，进行第一搅拌；第二阶段：加入溶剂进行第二搅拌；第三阶段：加入分散剂进行第三搅拌，得到浆料，控制浆料粘度为在8000mPa·s～15000mPa·s；第四阶段：在正极集流体上涂布浆料，得到正极极片。
该制备方法简单，利于工业生产。该制备方法有利于减少高分子量的第一聚偏二氟乙烯在浆料中的沉降，有助于提升浆料品质和正极极片的均匀性。
在一些实施方式中，第一搅拌中，搅拌公转速度为25转/分钟，搅拌时间为30分钟。
在一些实施方式中，第二搅拌中，搅拌公转速度为25转/分钟，搅拌自转速度800～1000转/分钟，搅拌时间为50～80分钟。
在一些实施方式中，第三搅拌中，搅拌自转速度1200～1500转/分钟，搅拌时间为50～70分钟。
在一些实施方式中，分散剂为聚乙二醇辛基苯基醚、聚乙烯吡咯烷酮、聚乙烯醇、羧甲基纤维素、聚丙烯酰胺、聚丙烯酸、聚丙烯酸钠、聚乙酰亚胺中至少一种。
在一些实施方式中，分散剂的质量分数为0.2％～0.5％，基于正极膜层的总质量计。
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。
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。
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。
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。
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。
一、制备方法
实施例1
1)粘结剂的制备
制备第一聚偏二氟乙烯：在10L的高压釜中加入4kg的去离子水和2g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1kg的偏二氟乙烯，使体系压力达到7MPa，混合搅拌30min，升温到45℃，反应6h后加入30g的环己烷继续反应，当反应釜内压力降到2MPa时停止反 应。将反应体系离心后收集固相，洗涤、干燥即得到第一聚偏二氟乙烯。
第二聚偏二氟乙烯：购买于山东德宜新材料有限公司，型号为DY-5，重均分子量为80万，多分散系数为1.85，Dv50为15μm，结晶度为40％，溶解于N-甲基吡咯烷酮后配置为质量分数7％的胶液的粘度为2300mPa·s。
将第一聚偏二氟乙烯与第二聚偏二氟乙烯共混，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比为3:1，得到包含第一聚偏二氟乙烯和第二偏二氟乙烯的粘结剂。
2)正极极片的制备
将3973.6g磷酸铁锂，49.1g的粘结剂，57.4g的乙炔黑在行星式搅拌罐中，公转转速25r/min，搅拌30min，其中粘结剂的质量分数为1.2％，基于正极膜层总质量计；
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的聚乙烯吡咯烷酮分散剂，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，加入N-甲基吡咯烷酮(NMP)溶液使得粘度降低到上述范围，加入NMP溶液后按照公转速度25r/min，自转速度1200～1500r/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，110℃烘烤15min，冷压后裁剪成直径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2～3
与实施例1基本相同，区别在于，分别将第一聚偏二氟乙烯的聚合反应时间调整为10h、12h，并且分别将环己烷的质量调整为20g、15g，以调整第一聚偏二氟乙烯的重均分子量，具体参数如表1所示。
实施例4～7
与实施例1基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比，具体参数如表1所示。
实施例8～11
与实施例1基本相同，区别在于，调整了粘结剂的质量分数，基于正极膜层总质量计，具体参数如表1所示。
实施例12
与实施例1基本相同，区别在于，第二聚偏二氟乙烯为购买自华安公司的605，重均分子量为60万，多分散系数为2.05，Dv50为13.4μm，结晶度为42％，溶解于N-甲基吡咯烷酮后配置为质量分数7％的胶液的粘度为3000mPa·s。
实施例13
与实施例1基本相同，区别在于，第二聚偏二氟乙烯为购买自神州公司的202E，重均分子量为110万，多分散系数为2.0，Dv50为11.5μm，结晶度为42％，溶解于N-甲基吡咯烷酮后配置为质量分数7％的胶液的粘度为4100mPa·s。
实施例14～16
与实施例1基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例17～19
与实施例1基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例20～21
与实施例2基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例22
与实施例2基本相同，区别在于，将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例23
与实施例2基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例24～26
与实施例2基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，具体参数如表1所示。
实施例27～28
与实施例2基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例29
与实施例2基本相同，区别在于，将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例30
与实施例2基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例31～32
与实施例3基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例33
与实施例3基本相同，区别在于，将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例34
与实施例3基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为0.8％，基于正极膜层总质量计，具体参数如表1所示。
实施例35～37
与实施例3基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，具体参数如表1所示。
实施例38～39
与实施例3基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，并且将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例40
与实施例3基本相同，区别在于，将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例41
与实施例3基本相同，区别在于，调整了共混过程中，第一聚偏二氟乙烯与第二聚偏二氟乙烯质量比，将粘结剂的质量分数调整为1.6％，基于正极膜层总质量计，具体参数如表1所示。
实施例42
与实施例2基本相同，区别在于，将聚合单体调整为0.94kg的偏二氟乙烯和0.06kg的三氟氯乙烯，制备得到偏二氟乙烯-三氟氯乙烯共聚物，具体参数如表1所示。
实施例43
与实施例2基本相同，区别在于，将聚合单体调整为0.94kg的偏二氟乙烯和0.06kg的四氟乙烯，制备得到偏二氟乙烯-四氟乙烯共聚物，具体参数如表1所示。
实施例44
与实施例2基本相同，区别在于，将聚合单体调整为0.94kg的偏二氟乙烯和0.06kg的六氟丙烯，制备得到偏二氟乙烯-六氟丙烯共聚物，具体参数如表1所示。
实施例45
与实施例2基本相同，区别在于，将第二聚偏二氟乙烯替换成重均分子量为80万的偏二氟乙烯-三氟氯乙烯共聚物，购买自华夏神州新材料有限公司，型号为202D，具体参数如表1所示。
对比例1
与实施例1基本相同，区别在于，粘结剂中只含有第二聚偏二氟乙烯，具体参数如表1所示。
对比例2
与对比例1基本相同，区别在于，将粘结剂的质量分数调整为2.5％，基于正极膜层总质量计，具体参数如表1所示。
对比例3
与实施例1基本相同，区别在于，将第一聚偏二氟乙烯的聚合反应温度调整为38℃，聚合反应压力调整为5MPa，聚合反应时间调整为3h，并且将环己烷调整为36g，反应后制备的第一聚偏二氟乙烯的分子量为120万。
二、电池性能测试
1、第一聚偏二氟乙烯性质测试
1)重均分子量测试
采用Waters 2695 Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。以质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的粘结剂胶液，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 2695 Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。以质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的粘结剂胶液，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的第一聚偏二氟乙烯粉料，再称取5g无水乙醇，加入到装有第一聚偏二氟乙烯粉料的烧杯中，放入长度约2.5mm的搅拌子，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的搅拌20min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。
4)结晶度测试
将0.5g第一聚偏二氟乙烯置于铝制坩埚中，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。
此测试将会得到第一聚偏二氟乙烯的DSC曲线，并对曲线进行积分，峰面积即为第一聚偏二氟乙烯的熔融焓ΔH(J/g)，粘结剂结晶度＝(ΔH/ΔHm)×100％，其中ΔHm为聚偏二氟乙烯的标准熔融焓(晶态熔化热)，ΔHm＝104.7J/g。
5)胶液粘度测试
用500ml烧杯分别称取14g第一聚偏二氟乙烯和336g N-甲基吡咯烷酮(NMP)，配置成质量分数4％的胶液，使用力辰高速研磨机搅拌分散，转速800r/min，搅拌时间120min后超声震荡30min去除气泡。在室温下，使用力辰科技NDJ-5S旋转粘度计进行测试，选用3号转子插入胶液，保证转子液面标志和胶液液面相平，以12r/min的转子转速测试粘度，6min后读取粘度数据即可。
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1～41或对比例1～3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。
上述实施例1～45和对比例1～3中得到粘结剂、极片和电池进行性能测试结果如表1所示。
上述实施例1～45和对比例1～3中得到粘结剂、极片和电池进行性能测试结果如表1所示。
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。
表1实施例和对比例的制备参数和测试结果


根据上述结果可知，实施例1～45中的粘结剂均包括第一聚偏二氟乙烯和第二聚偏二氟乙烯，第一聚偏二氟乙烯的重均分子量为180万～500万，第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。
实施例1～7、实施例12～13、实施例24～26、实施例35～37、实施例42～45与对比例1、对比例3的对比可知，包含第一聚偏二氟乙烯和第二聚偏二氟乙烯的粘结剂在低添加量下即使得极片具有优异的粘结力，提高电池在循环过程中的容量保持率。
实施例1～45与对比例2对比可知，在粘结剂添加量较低的情 况下，包含第一聚偏二氟乙烯和第二聚偏二氟乙烯的粘结剂使得极片具有优异的粘结力，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导致的极片和电池性能受限的情况。
从实施例1～45中可知，粘结剂中第一聚偏二氟乙烯的多分散系数为2.1～2.3，低添加量的粘结剂就能够使得极片具有优异的粘结力，电池在循环过程中具有高的容量保持率。
从实施例1～45中得知，粘结剂中第一聚偏二氟乙烯的Dv50粒径为50μm～150μm，低添加量的粘结剂就能够使得极片具有优异的粘结力，电池在循环过程中具有高的容量保持率。
从实施例1～45中得知，粘结剂中第一聚偏二氟乙烯的结晶度为42％～45％，低添加量的粘结剂就能够使得极片具有优异的粘结力，电池在循环过程中具有高的容量保持率。
从实施例1～45中得知，粘结剂中第一聚偏二氟乙烯溶解于N-甲基吡咯烷酮制得的含有质量含量为4％的第一聚偏二氟乙烯的胶液的粘度为2500mPa·s～5000mPa·s，这使得粘结剂在低添加量下就能够保证极片具有足够的粘结力。
从实施例1、实施例4～6和实施例7对比可知，粘结剂中第一聚偏二氟乙烯与第二聚偏二氟乙烯的质量比为1：1～4：1时，低添加量的粘结剂使得极片具有优异的粘结力，电池在循环过程中的容量保持率能够进一步提高。
从实施例1、实施例12～13中得知，粘结剂中第二聚偏二氟乙烯的重均分子量为60万～110万，粘结剂在低添加量下就能够使得极片具有优异的粘结力，电池在循环过程中的容量保持率有所提高。
从实施1、实施例8～9和实施例10对比可知，当粘结剂的质量分数为0.8％～1.6％，基于正极膜层的总质量计时，粘结剂就能够保证极片具有足够的粘结力，且电池在循环过程中的容量保持率进一步提高。从实施例1、实施例8～9和实施例11对比可知，当粘结剂质量分数为2.0％时，过高的粘结剂含量不会显著提升极片的粘结力和电池的循环性能，反而不利于电池能量密度的提高。
从实施例1、实施例42～44中得知，粘结剂中第一聚偏二氟乙烯为偏二氟乙烯均聚物、偏二氟乙烯-三氟氯乙烯共聚物、偏二氟乙烯-四氟乙烯共聚物或偏二氟乙烯-六氟丙烯共聚物，低添加量的粘结剂就能够使得极片具有优异的粘结力，电池在循环过程中具有高的容量保持率。
从实施例1、实施例45中得知，粘结剂中第二聚偏二氟乙烯为偏二氟乙烯均聚物或偏二氟乙烯-三氟氯乙烯共聚物，低添加量的粘结剂就能够使得极片具有优异的粘结力，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 (28)

  1. 一种粘结剂，其特征在于，所述粘结剂包括第一聚偏二氟乙烯和第二聚偏二氟乙烯，所述第一聚偏二氟乙烯的重均分子量为180万～500万，所述第二聚偏二氟乙烯的重均分子量小于所述第一聚偏二氟乙烯的重均分子量。
  2. 根据权利要求1所述的粘结剂，其特征在于，所述第一聚偏二氟乙烯的多分散系数为2～2.3。
  3. 根据权利要求1或2所述的粘结剂，其特征在于，所述第一聚偏二氟乙烯的Dv50粒径为50μm～150μm。
  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，所述第一聚偏二氟乙烯的结晶度为40％～45％。
  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，所述第一聚偏二氟乙烯溶解于N-甲基吡咯烷酮制得的含有质量含量为4％的所述第一聚偏二氟乙烯的胶液的粘度为2500mPa·s～5000mPa·s。
  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，所述第一聚偏二氟乙烯与所述第二聚偏二氟乙烯的质量比为1：1～4：1。
  7. 根据权利要求1至6中任一项所述的粘结剂，其特征在于，所述第二聚偏二氟乙烯的重均分子量为60万～110万。
  8. 一种粘结剂的制备方法，其特征在于，包括以下步骤：
    制备第一聚偏二氟乙烯：在可聚合条件下，将偏二氟乙烯单体进行聚合反应制备第一聚偏二氟乙烯，所述第一聚偏二氟乙烯的重均分子量为180万～500万；
    共混：将所述第一聚偏二氟乙烯与第二聚偏二氟乙烯共混制备 所述粘结剂，其中，所述第二聚偏二氟乙烯的重均分子量小于第一聚偏二氟乙烯的重均分子量。
  9. 根据权利要求8所述的制备方法，其特征在于，所述共混步骤中，所述第一聚偏二氟乙烯与所述第二聚偏二氟乙烯的质量比为1：1～4：1。
  10. 根据权利要求8或9所述的制备方法，其特征在于，所述制备第一聚偏二氟乙烯的聚合反应包括以下步骤：
    将偏二氟乙烯单体在非反应性气体氛围、6MPa～8MPa的反应压力、45℃～60℃的反应温度下反应6小时～12小时；
    加入链转移剂，待反应体系中压力降至2MPa～2.5MPa，停止反应，固液分离，保留固相。
  11. 根据权利要求10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。
  12. 根据权利要求10或11所述的制备方法，其特征在于，所述链转移剂的用量为所述偏二氟乙烯单体质量的1.5％～3％。
  13. 根据权利要求8至12中任一项所述的制备方法，其特征在于，所述制备第一聚偏二氟乙烯的聚合反应还包括以下步骤：
    向容器中加入溶剂和分散剂，对所述容器抽真空后充入非反应性气体；
    向所述容器中加入引发剂和pH调节剂，调节pH值至6.5～7，然后加入偏二氟乙烯单体，使所述容器中的压力达到6MPa～8MPa；
    搅拌30分钟～60分钟后，升温至45℃～60℃，进行聚合反应。
  14. 根据权利要求13所述的制备方法，其特征在于，所述溶剂的用量为所述偏二氟乙烯单体质量的2～8倍。
  15. 根据权利要求13或14所述的制备方法，其特征在于，所述分散剂包括纤维素醚和聚乙烯醇中的一种或多种。
  16. 根据权利要求15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和羧乙基纤维素醚中的一种或多种。
  17. 根据权利要求13至16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偏二氟乙烯单体质量的0.1％～0.3％。
  18. 根据权利要求13至17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。
  19. 根据权利要求18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以及叔丁基过氧化新戊酸酯中的一种或多种。
  20. 根据权利要求13至19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偏二氟乙烯单体质量的0.15％～1％。
  21. 根据权利要求13至20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、碳酸氢钠以及氨水中的一种或多种。
  22. 根据权利要求13至21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偏二氟乙烯单体质量的0.05％～0.2％。
  23. 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7中任一项所述的粘结剂或权利要求8至22中任一项所述的制备方法制备的粘结剂。
  24. 根据权利要求23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％～1.6％，基于所述正极膜层的总质量计。
  25. 根据权利要求23或24所述的正极极片，其特征在于，所述正极活性材料为含锂的过渡金属氧化物。
  26. 根据权利要求25所述的正极极片，其特征在于，所述含锂的过渡金属氧化物为磷酸铁锂及其改性材料、锂镍钴锰氧化物及其改性材料中的至少一种，所述改性材料是通过掺杂、导电碳包覆、导电金属包覆、导电聚合物包覆中的一种或多种改性方式制备的。
  27. 一种二次电池，其特征在于，包括电极组件和电解液，所述电极组件包括隔离膜、负极极片和如权利要求23至26中任一项所述的正极极片。
  28. 一种用电装置，其特征在于，包括权利要求27所述的二次电池。
PCT/CN2023/081622 2022-08-30 2023-03-15 粘结剂、制备方法、正极极片、二次电池及用电装置 WO2024045554A1 (zh)

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