Core-shell structured polymers, conductive pastes, secondary batteries and electrical devices

Abstract

A core-shell polymer (6), a conductive paste, a secondary battery (5), and an electrical device are disclosed. The core-shell polymer (6) includes a core (61) and a shell (62) that at least partially covers the core (61). The core (61) comprises structural units derived from monomers of Formula I and Formula II, and the shell (62) comprises structural units derived from monomers of Formula I and Formula III. In Formulas (I), (II), and (III), R1, R2, and R3 are each independently selected from hydrogen-, fluorine-, chlorine-, and fluorine-substituted C. 1‑3 One or more alkyl groups, wherein R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen, substituted or unsubstituted C. 1‑5 One or more of the alkyl groups.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a core-shell structure polymer, a preparation method thereof, a conductive paste, a preparation method of the conductive paste, a secondary battery, a battery module, a battery pack and an electrical device. BACKGROUND

[0002] In the production of secondary batteries, the conductivity of active materials is usually improved by adding a conductive agent, thereby improving the overall performance of the battery. However, the specific surface area of the existing conductive agent is generally large, and under the action of van der Waals force, it is prone to agglomeration, affecting its conductivity effect, and at the same time, it is easy to cause uneven distribution of the pole piece, affecting the performance of the active material. Therefore, it is urgent to solve this technical problem. SUMMARY

[0003] The present application is carried out in view of the above-mentioned problems, and the purpose is to provide a core-shell structure polymer and a conductive paste containing the same, so as to improve the dispersion performance, processing performance and storage performance of the conductive paste, and thereby improve the battery performance.

[0004] The first aspect of the present application provides a core-shell structure polymer, comprising a core part and a shell part covering at least part of the core part, the core part comprising structural units derived from a monomer represented by formula I and structural units derived from a monomer represented by formula II, and the shell part comprising structural units derived from a monomer represented by formula I and structural units derived from a monomer represented by formula III,

[0005]

[0006] wherein R1, R2, R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, fluorine-substituted C 1-3 alkyl, R4, R5, R6, R7, R8, R9 are each independently selected from one or more of hydrogen, substituted or unsubstituted C 1-5 alkyl.

[0007] In any embodiment, R1 in formula I is fluorine, and R2, R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, trifluoromethyl.

[0008] The core-shell structure polymer provided by the present application can optimize the viscosity of the paste, so that the paste has excellent anti-settling property, anti-gelling property and filtration performance, and can alleviate the settling and agglomeration of the conductive agent without additional addition of a dispersing agent, thereby improving the quality of the pole piece and the performance of the battery.

[0009] In any embodiment, the mass content of the core part is 70%-90%, and the mass content of the shell part is 10%-30%, based on the mass of the core-shell structure polymer.

[0010] The core part controls the mass content within a suitable range, and the core-shell structure polymer can further optimize the viscosity of the slurry, and comprehensively improve the processing performance and use performance of the conductive slurry.

[0011] In any embodiment, the molar content of the structural unit derived from the monomer shown in formula I is 50%-80%, based on the total number of moles of all structural units in the core-shell structure polymer.

[0012] Controlling the molar content of the structural unit derived from the monomer shown in formula I within a suitable range can further optimize the viscosity of the slurry, and comprehensively improve the processing performance and adhesion performance of the conductive slurry.

[0013] In any embodiment, the molar content of the structural unit derived from the monomer shown in formula II is 10%-20%, and the molar content of the structural unit derived from the monomer shown in formula III is 10%-30%, based on the total number of moles of all structural units in the core-shell structure polymer.

[0014] Controlling the molar content of the structural unit derived from the monomer shown in formula II and the structural unit derived from the monomer shown in formula III within a suitable range can further optimize the viscosity of the slurry, and comprehensively improve the processing performance and adhesion performance of the conductive slurry.

[0015] In any embodiment, the mass content of the structural unit derived from the monomer shown in formula I in the core part is 85%-95%, based on the total mass of the structural unit derived from the monomer shown in formula I in the core-shell structure polymer.

[0016] Because a large number of fluorine-containing structural units are located in the core part of the core-shell polymer, it helps to slow down the gelation of the slurry, improve the storage performance of the conductive slurry, which further reduces the production cost of the conductive slurry and improves the production efficiency of the conductive slurry.

[0017] In any embodiment, the weight average molecular weight of the core-shell structure polymer is 100,000-300,000.

[0018] Controlling the weight average molecular weight of the core-shell structure polymer within a suitable range can take into account the adhesion of the pole piece and the filterability of the slurry, and comprehensively improve the adhesion performance and processing performance of the pole piece.

[0019] In any embodiment, the Dv50 particle size of the core-shell structure polymer is 100 nm-8 μm. The core-shell structure polymer with a suitable particle size helps to improve the uniformity of the conductive slurry and prepare pole pieces with uniform quality.

[0020] In any embodiment, the monomer shown in formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropylene.

[0021] In any embodiment, the monomer of Formula II is selected from one or more of acrylamide, methacrylamide, crotonamide.

[0022] In any embodiment, the monomer of Formula III is selected from one or more of acrylonitrile, methacrylonitrile, 2-methyl-2-butenenitrile, 3-butenenitrile.

[0023] A second aspect of the present application provides a method for preparing a core-shell structure polymer, the method comprising the steps of,

[0024] polymerizing the monomer of Formula I and the monomer of Formula II under polymerizable conditions to prepare a core part of the core-shell structure polymer, and polymerizing the monomer of Formula I and the monomer of Formula III to prepare a shell part of the core-shell structure polymer, the shell part at least partially covering the core part,

[0025]

[0026] wherein R1, R2, R3are each independently selected from one or more of hydrogen, fluorine, chlorine, fluorine-substituted C 1-3 alkyl, R4, R5, R6, R7, R8, R9are each independently selected from one or more of hydrogen, substituted or unsubstituted C 1-5 alkyl.

[0027] The core-shell structure polymer prepared by the method can reduce the viscosity of the slurry, improve the filterability of the conductive slurry, so that the slurry does not gel after standing for 60 days, improve the anti-gelling property and storage property of the conductive slurry, significantly widen the process window of the conductive slurry, improve the processability of the conductive slurry, so that the conductive slurry can meet the production requirements of the conductive slurry without adding a dispersant, thereby further reducing the direct current impedance of the battery.

[0028] In any embodiment, R1in Formula I is fluorine, and R2, R3are each independently selected from one or more of hydrogen, fluorine, chlorine, trifluoromethyl.

[0029] In any embodiment, the molar content of the monomer of Formula I is 50%-80%, based on the total moles of the monomer of Formula I, the monomer of Formula II, and the monomer of Formula III.

[0030] In any embodiment, the molar content of the monomer of Formula II is 10%-20%, based on the total moles of the monomer of Formula I, the monomer of Formula II, and the monomer of Formula III.

[0031] In any embodiment, the mole content of the monomer of formula III is 10%-30%, based on the total moles of the monomer of formula I, the monomer of formula II and the monomer of formula III.

[0032] In any embodiment, the polymerization reaction comprises a first-stage polymerization and a second-stage polymerization,

[0033] The first-stage polymerization: the initiator, the first emulsifier, at least one monomer of formula I, at least one monomer of formula II and the aqueous medium are added into a reaction container to carry out the first-stage polymerization, and the monomer of formula I is continuously fed to maintain the reaction pressure constant;

[0034] The second-stage polymerization: after a period of reaction, the initiator, the second emulsifier, at least one monomer of formula III and the aqueous medium are added into the reaction container to carry out the second-stage polymerization to obtain the core-shell structure polymer, and the monomer of formula I is continuously fed until all the monomer of formula I is fed into the reaction container, and the reaction is stopped when the reaction pressure drops to 0-0.2 MPa.

[0035] The method provided in the application first feeds a large amount of the monomer of formula I and the monomer of formula II to form a fluorine-containing core part, so that the core part has high thermal stability; and then feeds a small amount of the monomer of formula I and the monomer of formula III to form a shell part surrounding the core part. In the emulsion system, the core-shell structure polymer is obtained by stepwise addition of monomers with different hydrophilicities, and the core-shell structure polymer exists in the form of core-shell structure in the aqueous medium. Compared with the non-core-shell structure polymer prepared by feeding all the monomers into the reaction container at the same time, the stability and dispersibility of the core-shell structure polymer are greatly improved, which helps to improve the filtration and storage performance of the conductive slurry. In addition, when the monomer of formula III is fed into the reaction container to carry out the second-stage polymerization, the monomer of formula I is continuously fed into the reaction container, which increases the compatibility of the core part and the shell part of the core-shell polymer and improves the stability of the core-shell structure polymer.

[0036] In any embodiment, the second-stage polymerization comprises: after the initiator is added into the reaction container, a premix liquid comprising the second emulsifier, at least one monomer of formula III and the aqueous medium is added.

[0037] In any embodiment, the mass of the monomer of formula I fed in the first-stage polymerization is 85%-95% of the total mass of the monomer of formula I fed in the polymerization reaction, and the mass of the monomer of formula I fed in the second-stage polymerization is 5%-15% of the total mass of the monomer of formula I fed in the polymerization reaction.

[0038] Since a large number of fluorinated structural units are located in the core of the core-shell polymer, they help to slow down the gelation of the slurry and improve the storage performance of the conductive slurry. This will further reduce the production cost of the conductive slurry and improve its production efficiency.

[0039] In any embodiment, the percentage of the total mass of the initiator added in the first polymerization stage and the second polymerization stage is 1%-2%, based on the total mass of the monomers shown in Formula I, Formula II and Formula III.

[0040] In any embodiment, the first emulsifier has a mass percentage of 0.1%-0.5% based on the total mass of the monomers shown in Formula I, Formula II, and Formula III; the second emulsifier has a mass percentage of 0.5%-5% based on the mass of the monomers shown in Formula III.

[0041] In any embodiment, the mass percentage of the aqueous medium provided in the first polymerization stage is 400%-600%, based on the total mass of the monomers shown in Formula I, Formula II and Formula III.

[0042] In any embodiment, the reaction pressure of the first polymerization stage is 6.0 MPa to 9.0 MPa, and the reaction temperature is 80°C to 100°C.

[0043] In any embodiment, the initial reaction pressure of the second polymerization stage is lower than the reaction pressure of the first polymerization stage, and the reaction temperature of the second polymerization stage is higher than the reaction temperature of the first polymerization stage.

[0044] In any embodiment, the first emulsifier is a perfluorooctanoic acid alkali metal salt, and the second emulsifier is polyoxyethylene-4-phenolic ether ammonium sulfate.

[0045] In any embodiment, the initiator is one or both of N,N-dimethylbenzylamine and ammonium persulfate.

[0046] A third aspect of this application provides the application of the core-shell structured polymer of the first aspect in secondary batteries.

[0047] A fourth aspect of this application provides an emulsion comprising an aqueous medium, an emulsifier, and a core-shell polymer of the first aspect.

[0048] A fifth aspect of this application provides a conductive paste, the conductive paste comprising a conductive agent, an aqueous medium, and an emulsion as described in the fourth aspect.

[0049] Compared to existing technologies that directly add conductive agents during the preparation of negative electrode slurry, the conductive slurry provided in this application can improve the dispersibility of conductive agents in negative electrode slurry, enhance the conductivity of conductive agents in the electrode sheet, and thus effectively reduce the content of conductive agents in the electrode sheet. This is beneficial for further increasing the loading of active materials in the negative electrode sheet and improving battery power performance.

[0050] In any embodiment, the conductive agent has a mass fraction of 10.0% to 15.0%, based on the total mass of the conductive paste.

[0051] By controlling the mass fraction of the conductive agent within a suitable range, the viscosity of the conductive slurry can be optimized, thereby comprehensively improving the slurry's processing and performance.

[0052] In any embodiment, the mass fraction of the core-shell structured polymer is 0.5% to 2.5%, based on the total mass of the conductive paste.

[0053] By controlling the mass fraction of the core-shell polymer within a suitable range, and based on the total mass of the conductive slurry, the slurry has a suitable viscosity, which enables the electrode to have good adhesion, thus comprehensively improving the processing performance and performance of the slurry.

[0054] In any embodiment, the solid content of the conductive paste is 12% to 17%, and the viscosity of the conductive paste is 500 mPa·s to 1500 mPa·s.

[0055] Conductive pastes with a solid content of 12% to 17% and a viscosity of 500 mPa·s to 1500 mPa·s can be directly mixed with active materials and binders to prepare negative electrode pastes without the need for additional additives, which helps to improve production efficiency and reduce production costs.

[0056] A sixth aspect of this application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material, a conductive agent and a binder, wherein the conductive agent is a deposit of the conductive paste of the fifth aspect.

[0057] Compared to the negative electrode sheets prepared by directly adding conductive agent powder in the prior art, the conductive agent in the negative electrode sheet disclosed in this application exists in the form of conductive slurry deposits, which helps to further reduce the impedance of the battery.

[0058] In any embodiment, the adhesion force per unit length between the negative electrode film layer and the negative electrode current collector is not less than 12 N / m.

[0059] A seventh aspect of this application provides a secondary battery, comprising a positive electrode, a separator, an electrolyte, and a negative electrode as provided in the sixth aspect of this application. Optionally, the secondary battery comprises at least one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, and a potassium-ion battery.

[0060] The eighth aspect of this application provides a battery module, including the secondary battery of the seventh aspect of this application.

[0061] The ninth aspect of this application provides a battery pack, including a secondary battery of the seventh aspect of this application or a battery module of the eighth aspect of this application.

[0062] The tenth aspect of this application provides an electrical device, including at least one selected from the seventh aspect of this application, the eighth aspect of this application, and the ninth aspect of this application. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the core-shell structured polymer according to one embodiment of the application;

[0064] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0065] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0066] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0067] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0068] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0069] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0070] Figure label:

[0071] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Core-shell structure polymer; 61 Core; 62 Shell. Detailed Implementation

[0072] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the adhesive, preparation method, electrode, battery, and power device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0073] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 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. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0075] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0076] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0077] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0078] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the 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).

[0079] In the manufacturing process of secondary batteries, conductive agents are typically added to improve electron transport performance, thereby enhancing the overall performance of the battery. However, existing conductive agents generally have a large specific surface area, making them prone to aggregation under van der Waals forces, affecting their conductivity and leading to uneven electrode distribution, thus impacting the performance of active materials. Adding dispersants helps improve the dispersion of conductive agents, but their introduction into the slurry is detrimental to subsequent electrode preparation, easily causing problems such as slurry gelation, shortened process windows, and poor batch-to-batch slurry stability. Based on these technical problems, this application develops a polymer that imparts suitable viscosity and excellent filterability, anti-settling properties, and anti-gelling properties to conductive slurries, thereby improving production efficiency and quality.

[0080] [Core-shell polymers]

[0081] Based on this, this application provides a core-shell structured polymer, comprising a core and a shell at least partially covering the core, wherein the core comprises structural units derived from monomers of formula I and formula II, and the shell comprises structural units derived from monomers of formula I and formula III.

[0082]

[0083] Among them, R1, R2, and R3 are each independently selected from C atoms substituted with hydrogen, fluorine, chlorine, or fluorine. 1-3 One or more alkyl groups, wherein R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen, substituted or unsubstituted C. 1-5 One or more of the alkyl groups.

[0084] In this document, the term "polymer" includes, on the one hand, an aggregate of chemically homogeneous macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass, and chain length. On the other hand, the term also includes derivatives of such aggregates of macromolecules formed by polymerization reactions, i.e., products that can be obtained by reactions of the functional groups in the aforementioned macromolecules, such as addition or substitution, and can be chemically homogeneous or chemically heterogeneous.

[0085] In this article, the term "C" 1-3 "Alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms. The group is not unsaturated, has one to three carbon atoms, and is attached to the rest of the molecule by single bonds.

[0086] In this article, the term "C" 1-5 "alkyl" can be referenced from the term "C". 1-3 We can understand this by referring to the definition of "alkyl".

[0087] In this document, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is replaced by a substituent in another chemical moiety, wherein each substituent is independently selected from: hydroxyl, mercapto, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 Alkyl group.

[0088] In some embodiments, R1 in Formula I is fluorine, and R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl.

[0089] In this article, the term "trifluoromethyl" refers to the -CF3 group.

[0090] In some embodiments, the monomer represented by Formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropylene.

[0091] In some embodiments, the monomer represented by Formula II is selected from one or more of acrylamide, methacrylamide, and butenamide.

[0092] In some embodiments, the monomer represented by Formula III is selected from one or more of acrylonitrile, methacrylonitrile, 2-methyl-2-butenonitrile, and 3-butenonitrile.

[0093] Figure 1 This is a schematic diagram of a core-shell structured polymer according to one embodiment of this application. The core-shell structured polymer 6 includes a core portion 61 and a shell portion 62, with the shell portion 62 covering the surface of the core portion 61. The core portion 61 contains structural units derived from the monomer shown in Formula I and structural units derived from the monomer shown in Formula II. The core portion 61 also contains fluorinated structural units, which can increase the thermal stability and adhesive properties of the structure. The shell portion contains structural units derived from the monomer shown in Formula I and structural units derived from the monomer shown in Formula III. The shell portion contains cyano groups, which can improve the adhesive properties of the polymer.

[0094] Compared to traditional polyvinylidene fluoride, core-shell structured polymers can reduce the contact area between fluorinated structural units and solvents, thereby reducing slurry viscosity, stabilizing the slurry, mitigating slurry sedimentation, and effectively improving the slurry's filterability.

[0095] The core-shell structured polymer provided in this application can optimize the viscosity of the slurry, giving the slurry excellent anti-settling, anti-gelling, and filtration properties. It can alleviate the sedimentation and agglomeration of conductive agents without the need for additional dispersants, thereby improving electrode quality and battery performance.

[0096] In some embodiments, the core content is 70%-90% by mass, and the shell content is 10%-30% by mass, based on the mass of the core-shell polymer. In some embodiments, the core content can be selected from any one of 70%, 75%, 80%, 85%, and 90%, based on the mass of the core-shell polymer. In some embodiments, the shell content can be selected from any one of 10%, 15%, 20%, 25%, and 30%, based on the mass of the core-shell polymer.

[0097] By controlling the mass content of the core within a suitable range, the viscosity of the core-shell structured polymer can be further optimized, avoiding the decrease in coating drying efficiency and adhesion caused by excessively low viscosity, or the difficulty in leveling and coating processing caused by excessively high viscosity, thus comprehensively improving the processing performance and performance of conductive paste.

[0098] In some embodiments, the molar content of the structural units of the monomer derived from Formula I is 50%-80%, based on the total molar number of all structural units in the core-shell polymer. In some embodiments, the molar content of the structural units of the monomer derived from Formula I may be selected as any one of 50%, 60%, 70%, and 80%, based on the total molar number of all structural units in the core-shell polymer.

[0099] By controlling the molar content of the structural units derived from the monomer shown in Formula I within a suitable range, the viscosity of the slurry can be further optimized, thereby comprehensively improving the processing and bonding properties of the conductive slurry.

[0100] In some embodiments, the molar content of the structural units of the monomer derived from Formula II is 10%-20%, and the molar content of the structural units of the monomer derived from Formula III is 10%-30%, based on the total molar number of all structural units in the core-shell polymer. In some embodiments, the molar content of the structural units of the monomer derived from Formula II may be any one of 10%, 15%, and 20%, based on the total molar number of all structural units in the core-shell polymer. In some embodiments, the molar content of the structural units of the monomer derived from Formula III may be any one of 10%, 20%, and 30%, based on the total molar number of all structural units in the core-shell polymer.

[0101] By controlling the molar content of the structural units of the monomers derived from Formula II and Formula III within a suitable range, the viscosity of the slurry can be further optimized, thereby comprehensively improving the processing and bonding properties of the conductive slurry.

[0102] In some embodiments, the mass content of structural units derived from the monomer shown in Formula I in the core is 85%-95%, based on the total mass of structural units derived from the monomer shown in Formula I in the core-shell polymer. In some embodiments, the mass content of structural units derived from the monomer shown in Formula I in the core may be selected as 85%, 90%, or 95%, based on the total mass of structural units derived from the monomer shown in Formula I in the core-shell polymer.

[0103] Since a large number of fluorinated structural units are located in the core of the core-shell polymer, they help to slow down the gelation of the slurry and improve the storage performance of the conductive slurry. This will further reduce the production cost of the conductive slurry and improve its production efficiency.

[0104] In some embodiments, the weight-average molecular weight of the core-shell polymer is between 100,000 and 300,000. In some embodiments, the weight-average molecular weight of the core-shell polymer can be selected from any one of 100,000, 200,000, and 300,000.

[0105] In this paper, the term "weight-average molecular weight" refers to the sum of the products of the weight fraction of molecules of different molecular weights in a polymer and their corresponding molecular weights.

[0106] In this application, the weight-average molecular weight of the polymer can be determined using methods known in the art, such as gel permeation chromatography (GPC), e.g., using a Waters 2695 Isocratic HPLC gel permeation chromatograph (differential refractive index detector 2141). In some embodiments, the test method uses a 3.0% polystyrene solution sample as a reference, selecting a matched chromatographic column (oil-based: Styragel HT5DMF7.8*300mm + Styragel HT4). A 3.0% core-shell polymer gel solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day for later use. During testing, tetrahydrofuran is first drawn into a syringe for rinsing, repeated several times. Then, 5 ml of the experimental solution is drawn, air is expelled from the syringe, and the needle tip is dried. Finally, the sample solution is slowly injected into the injection port. After the reading stabilizes, the data is acquired, and the weight-average molecular weight is read.

[0107] By controlling the weight-average molecular weight of the core-shell polymer within a suitable range, the core-shell polymer exhibits good solubility in the slurry, is less prone to agglomeration with the conductive agent, and ensures that the conductive agent is uniformly dispersed in the slurry. At the same time, the suitable weight-average molecular weight facilitates the formation of a three-dimensional network bonding structure by the binder, thereby achieving an effective bonding effect. This approach can balance the adhesion of the electrode sheet and the filtration properties of the slurry, comprehensively improving the adhesion and processing performance of the electrode sheet.

[0108] In some embodiments, the Dv50 particle size of the core-shell polymer is 100 nm to 8 μm. In some embodiments, the Dv50 particle size of the core-shell polymer can be selected from any one of 100 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, and 8 μm.

[0109] In this paper, the term "Dv50 particle size" refers to the particle size at which the cumulative particle size distribution number of particles reaches 50% in the particle size distribution curve. Its physical meaning is that 50% of the particles are smaller (or larger) than it.

[0110] Core-shell structured polymers with suitable particle size help improve the uniformity of conductive pastes and produce electrodes with uniform quality.

[0111] In one embodiment of this application, a method for preparing a core-shell structured polymer is provided, the method comprising the following steps:

[0112] Under polymerizable conditions, the core of the core-shell polymer is prepared by polymerizing the monomers shown in Formula I and Formula II, and the shell of the core-shell polymer is prepared by polymerizing the monomers shown in Formula I and Formula III, wherein the shell at least partially covers the core.

[0113]

[0114] Among them, R1, R2, and R3 are each independently selected from C atoms substituted with hydrogen, fluorine, chlorine, or fluorine. 1-3 One or more alkyl groups, wherein R4, R5, R6, R7, R8, and R9 are each independently selected from hydrogen, substituted or unsubstituted C. 1-5 One or more of the alkyl groups.

[0115] In this document, the term "polymerizable conditions" refers to those conditions, including temperature, pressure, reactant concentration, optional solvent / diluent, reactant mixing / addition parameters selected by those skilled in the art, and other conditions that facilitate the reaction of one or more monomers within at least one polymerization reactor.

[0116] The core-shell structured polymer prepared by this method can reduce the viscosity of the slurry, improve the filterability of the slurry, significantly broaden the process window of the slurry, and improve the processability of the slurry. This allows the slurry to meet the production requirements of water-based conductive slurries without the need for the addition of dispersants, which is beneficial for optimizing the production process of water-based conductive slurries and improving their production efficiency.

[0117] In some embodiments, the molar content of the monomer shown in Formula I is 50%-80%, based on the total molar number of the monomers shown in Formula I, Formula II, and Formula III. In some embodiments, the molar content of the monomer shown in Formula I can be selected as any one of 50%, 60%, 70%, and 80%, based on the total molar number of the monomers shown in Formula I, Formula II, and Formula III.

[0118] In some embodiments, the molar content of the monomer shown in Formula II is 10%-20%, based on the total molar number of the monomers shown in Formula I, Formula II, and Formula III. In some embodiments, the molar content of the monomer shown in Formula II may be selected as any one of 10%, 15%, and 20%, based on the total molar number of the monomers shown in Formula I, Formula II, and Formula III.

[0119] In some embodiments, the molar content of the monomer shown in Formula III is 10%-30%, based on the total molar number of the monomers shown in Formula I, Formula II, and Formula III. In some embodiments, the molar content of the monomer shown in Formula III may be any one of 10%, 20%, and 30%, based on the total molar number of the monomers shown in Formula I, Formula II, and Formula III.

[0120] In some embodiments, the preparation method includes a first-stage polymerization and a second-stage polymerization.

[0121] First stage polymerization: an initiator, a first emulsifier, at least one monomer of formula I, at least one monomer of formula II, and an aqueous medium are added to the reaction vessel to carry out the first stage polymerization. The monomer of formula I is continuously fed into the first stage polymerization to maintain a constant reaction pressure.

[0122] Second stage polymerization: After a period of reaction, an initiator, a second emulsifier, at least one monomer of Formula III, and an aqueous medium are added to the reaction vessel to carry out the second stage polymerization reaction to obtain a core-shell structured polymer. During the second stage polymerization reaction, the monomer of Formula I is continuously fed until all the monomer of Formula I is fed into the reaction vessel. The reaction is stopped when the reaction pressure drops to 0-0.2 MPa.

[0123] In this article, "continuous feeding" refers to adding slowly, steadily, and gradually during the polymerization process.

[0124] The method provided in this application first introduces a large amount of monomers shown in Formula I and Formula II to form a fluorinated core, resulting in high thermal stability of the core; then, a small amount of monomers shown in Formula I and Formula III are introduced to form a shell at least surrounding the core. In an emulsion system, a core-shell structured polymer is obtained by stepwise addition of monomers with different hydrophilicities. This core-shell structured polymer exists in an aqueous medium in a core-shell structure form. Compared to non-core-shell structured polymers prepared by simultaneously introducing all monomers into the reaction vessel, the stability and dispersibility of the core-shell structured polymer are significantly improved, which helps to improve the filterability and storage performance of conductive slurries.

[0125] In some embodiments, the mass of the monomer of Formula I introduced in the first stage of polymerization is 85% to 95% of the total mass of the monomer of Formula I supplied in the polymerization reaction, and the mass of the monomer of Formula I introduced in the second stage of polymerization is 5% to 15% of the total mass of the monomer of Formula I supplied in the polymerization reaction.

[0126] Since a large number of fluorinated structural units are located in the core of the core-shell polymer, they help to slow down the gelation of the slurry and improve the storage performance of the conductive slurry. This will further reduce the production cost of the conductive slurry and improve its production efficiency.

[0127] In some embodiments, the second polymerization stage includes adding an initiator to a reaction vessel, followed by adding a premix containing a second emulsifier, at least one monomer of Formula II, a monomer of Formula III, and an aqueous medium.

[0128] In some embodiments, the percentage of the total mass of the initiator added in the first polymerization stage and the second polymerization stage is 1%-2%, based on the total mass of the monomers shown in Formula I, Formula II and Formula III.

[0129] In some embodiments, the initiator provided in the first polymerization stage is 0.05% to 1.5% by mass, and the initiator provided in the second polymerization stage is 0.005% to 0.5% by mass, based on the total mass of the monomers shown in Formula I, Formula II, and Formula III.

[0130] In some embodiments, the first emulsifier is 0.1% to 0.5% by mass, based on the total mass of the monomers shown in Formula I, Formula II, and Formula III.

[0131] In some embodiments, the second emulsifier is 0.5% to 5% by mass, based on the mass of the monomer shown in Formula III.

[0132] In some embodiments, the mass percentage of the aqueous medium provided in the first polymerization stage is 400% to 600%, and the mass percentage of the aqueous medium provided in the second polymerization stage is 100% to 300%, based on the total mass of the monomers shown in Formula I, Formula II, and Formula III.

[0133] In some embodiments, the aqueous medium provided in the first polymerization stage and the aqueous medium provided in the second polymerization stage are deionized water with a conductivity of less than or equal to 2 μs / cm.

[0134] In some embodiments, the reaction pressure of the first stage polymerization is 6.0 MPa to 9.0 MPa, and the reaction temperature is 80°C to 100°C.

[0135] In some embodiments, the reaction pressure of the second polymerization is 4.0 MPa to 7.0 MPa, and the reaction temperature is 86°C to 95°C.

[0136] In some embodiments, the first initiator and the second initiator may be selected from one or both of N,N-dimethylbenzylamine and ammonium persulfate.

[0137] N,N-dimethylbenzylamine and ammonium persulfate can both decompose effectively above 60℃, generating free radical ions or ionic free radicals, making them suitable as initiators for emulsion polymerization.

[0138] In some embodiments, the first emulsifier is an alkali metal salt of perfluorooctanoic acid, which may be sodium perfluorooctanoic acid.

[0139] Perfluorooctanoic acid (PFOA) alkali metal salts are commonly used as emulsifiers or dispersants in the polymerization reactions of fluorinated monomers.

[0140] In some embodiments, the second emulsifier is one or both of polyoxyethylene-4-phenolic ether ammonium sulfate and nonylphenol polyoxyethylene ether ammonium sulfate.

[0141] Both polyoxyethylene-4-phenolic ether ammonium sulfate and nonylphenol polyoxyethylene ether ammonium sulfate are anionic-nonionic emulsifiers, possessing both anionic and nonionic properties. They can be used alone in emulsion polymerization without needing to be used in combination with other emulsifiers.

[0142] In one embodiment of this application, the application of a core-shell structured polymer in any embodiment is provided in a secondary battery. Optionally, the secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

[0143] In some embodiments, core-shell polymers are used as binders in secondary batteries.

[0144] In some embodiments, core-shell structured polymers are used as binders in conductive pastes in secondary batteries.

[0145] [Conductive paste]

[0146] One embodiment of this application provides a conductive paste comprising a binder, a conductive agent, and an aqueous medium, wherein the binder comprises a core-shell structured polymer as described in any manner.

[0147] In this document, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0148] In some embodiments, the dispersion medium of the adhesive is an aqueous medium, such as deionized water. That is, the adhesive is dissolved in an aqueous medium.

[0149] Compared to non-core-shell polymers, core-shell polymers exhibit improved stability and dispersibility, which helps to enhance the filterability, dispersibility, and storage performance of conductive slurries, thereby improving battery performance.

[0150] In some embodiments, the core-shell polymer is added to the conductive slurry in the form of an emulsion containing the core-shell polymer.

[0151] The core-shell structured polymer prepared by the preparation method in any of the above embodiments exists in the form of an emulsion and can be directly added to conductive pastes for use, thereby reducing production costs and improving production efficiency.

[0152] In some embodiments, the conductive agent has a mass fraction of 10.0% to 15.0%, based on the total mass of the conductive paste.

[0153] When the mass fraction of the conductive agent is less than 10.0% based on the total mass of the conductive slurry, the remaining solvent amount is too small during the slurry mixing process of the battery cell electrode preparation, which is not conducive to the dissolution and dispersion of the binder; when the mass fraction of the conductive agent is greater than 15.0% based on the total mass of the conductive slurry, the viscosity of the conductive slurry is high, the viscosity rebound is large and the fluidity becomes poor, which is not conducive to feeding in industrial production.

[0154] In some embodiments, the core-shell polymer has a mass fraction of 0.5% to 2.5% based on the total mass of the conductive paste.

[0155] When the mass fraction of the core-shell polymer is less than 0.5% based on the total mass of the conductive slurry, the bonding performance of the conductive slurry deteriorates; when the mass fraction of the core-shell polymer is greater than 2.5% based on the total mass of the conductive slurry, the viscosity of the conductive slurry is high, the uniformity of the electrode sheet deteriorates, which is not conducive to the reduction of battery impedance.

[0156] In some embodiments, when the solid content of the conductive paste is 12% to 17%, the viscosity of the conductive paste is 500 mPa·s to 1500 mPa·s. In some embodiments, the viscosity of the conductive paste is 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, or 1500 mPa·s. Conductive pastes with a solid content of 12% to 17% and a viscosity of 500 mPa·s to 1500 mPa·s provide suitable viscosity for conductive pastes prepared from core-shell structured polymers, eliminating the need for additional dispersants or thickeners to improve processing performance, thus contributing to increased production efficiency and optimized production processes.

[0157] In one embodiment of this application, a secondary battery is provided, comprising a positive electrode, a separator, a negative electrode, and an electrolyte. In some embodiments, the secondary battery is at least one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, and a potassium-ion battery. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0158] [Positive electrode plate]

[0159] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0160] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0161] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0162] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0163] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0164] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the conductive slurry of any embodiment onto the surface of the current collector, drying it to form an aqueous conductive slurry, i.e., an aqueous primer current collector; then coating the positive electrode slurry onto the aqueous primer current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0166] [Negative electrode plate]

[0167] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, a conductive agent, and a binder. The conductive agent is a deposit of the conductive slurry in any embodiment of this application.

[0168] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0169] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0170] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, 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. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0171] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0172] In some embodiments, the negative electrode film may optionally include 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.

[0173] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0174] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive paste in any embodiment of this application, the binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode paste; coating the negative electrode paste onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0175] [Electrolytes]

[0176] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0177] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0178] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0179] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0180] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0181] [Isolation membrane]

[0182] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0183] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0184] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0185] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0186] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0187] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0188] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0189] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0190] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0191] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0192] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0193] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0194] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0195] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0196] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0197] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0198] Example

[0199] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0200] I. Preparation Method

[0201] Example 1

[0202] 1) Preparation of core-shell structured polymers

[0203] First stage polymerization: 21 kg of deionized water, 17.45 g of sodium perfluorooctanoate, 84.77 g of N,N-dimethylbenzylamine, and 905 g of acrylamide monomer, wherein the conductivity of the deionized water is less than or equal to 2 μs / cm, are added to the reactor in sequence, and the reactor is then closed.

[0204] The reactor was evacuated and then filled with nitrogen. This process was repeated until the oxygen concentration inside the reactor was less than 100 ppm.

[0205] Vinylidene fluoride monomer is introduced into the reactor until the pressure inside the reactor reaches 8.0 MPa; the temperature inside the reactor is raised to 85°C to start the reaction, and during the reaction, vinylidene fluoride monomer is continuously introduced to maintain a constant reaction pressure inside the reactor;

[0206] Second stage polymerization: 9 kg of deionized water (the conductivity of deionized water is less than or equal to 2 μs / cm), 10.14 g of polyoxyethylene-4-phenolic ether ammonium sulfate, and 1014 g of acrylonitrile monomer were added to a mixing tank and stirred until homogeneous to obtain a premixed solution.

[0207] When the total amount of vinylidene fluoride monomer introduced is 3877g, 16.22g of 5% ammonium persulfate is added, the reaction pressure is adjusted to 7.0MPa, the temperature is raised to 95℃, and the premixed solution is slowly added to the reactor. The total addition time of the premixed solution is 1.0 hour. At the same time, the remaining 204g of vinylidene fluoride monomer is gradually introduced.

[0208] The reaction stops when the pressure inside the reactor drops to 0.2 MPa.

[0209] After cooling to room temperature, the material was filtered to obtain an emulsion containing a core-shell polymer. The core of the core-shell polymer mainly consists of vinylidene fluoride and acrylamide, while the shell consists of a small amount of vinylidene fluoride and acrylonitrile. The Dv50 particle size of the core-shell vinylidene fluoride-acrylamide-acrylonitrile copolymer is 260 nm.

[0210] 2) Preparation of conductive paste

[0211] The solid content of the emulsion of core-shell structured vinylidene fluoride-acrylamide-acrylonitrile copolymer was adjusted to 40%.

[0212] Weigh 16.4 kg of deionized water and 1 kg of emulsion of core-shell structured vinylidene fluoride-acrylamide-acrylonitrile copolymer and add them sequentially into a 35 L mixing tank; stir at a stirring speed of 1000 rpm for 60 minutes to obtain a pre-formulated adhesive solution of core-shell structured vinylidene fluoride-acrylamide-acrylonitrile copolymer.

[0213] Weigh 2.6 kg of conductive carbon black powder and add it to a mixing jar containing the pre-mixed adhesive solution. Stir at 1000 rpm for 60 minutes.

[0214] The above slurry was filtered through a 300-mesh filter to obtain a conductive slurry.

[0215] 3) Preparation of negative electrode sheet

[0216] The active material artificial graphite, the above-mentioned conductive slurry, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are mixed in deionized water to make the weight ratio of artificial graphite, conductive carbon black, SBR and CMC 96.2:0.8:0.8:1.2. After being mixed evenly, a negative electrode slurry is prepared. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed and slit to obtain the negative electrode sheet.

[0217] 4) Preparation of positive electrode sheet

[0218] Lithium nickel cobalt manganese (NCM) material, conductive carbon black, polyvinylidene fluoride binder, and N-methylpyrrolidone (NMP) were mixed evenly in a weight ratio of 96.9:2.1:1:21 to obtain a positive electrode slurry with a solid content of 73%. The positive electrode slurry was then uniformly coated onto the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0219] 5) Separating membrane

[0220] Polypropylene film is used as the separator.

[0221] 6) Preparation of electrolyte

[0222] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. 12.5% ​​LiPF6 lithium salt was added and dissolved in the organic solvent and stirred evenly to obtain the electrolyte of Example 1.

[0223] 7) Battery manufacturing

[0224] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound, tabs are welded onto it, and the cell is placed in an aluminum casing. It is then baked at 80°C to remove moisture, followed by the injection of electrolyte and sealing to obtain a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

[0225] Examples 2 to 5

[0226] The preparation method is basically the same as that in Example 1, except that the molar content of the core and shell in the synthesis of the core-shell structured polymer and the ratio of each monomer are adjusted. The specific parameters are shown in Table 1 and Table 2.

[0227] Examples 6 to 9

[0228] The preparation method is basically the same as that in Example 1, except that the initiator mass and reaction temperature in the synthesis of the core-shell structured polymer were adjusted so that the core-shell structured polymers have different weight-average molecular weights. The specific parameters are shown in Table 1 and Table 2.

[0229] Specifically, in the preparation method of the core-shell structured polymer with a weight-average molecular weight of 100,000 in Example 6, the amount of N,N-dimethylbenzylamine added was adjusted to 89.0g.

[0230] In Example 7, the reaction temperature was adjusted to 80°C and the amount of N,N-dimethylbenzylamine added was adjusted to 80.53g in the preparation method of the core-shell structured polymer with a weight-average molecular weight of 300,000.

[0231] In Example 8, the amount of N,N-dimethylbenzylamine added was adjusted to 93.25g in the preparation method of the fluoropolymer with a weight-average molecular weight of 50,000.

[0232] In Example 9, the reaction temperature was adjusted to 80°C and the amount of N,N-dimethylbenzylamine added was adjusted to 76.29 g in the preparation method of the fluoropolymer with a weight-average molecular weight of 400,000.

[0233] Examples 10 to 12

[0234] The preparation method is basically the same as that in Example 1, except that the types of comonomers in the synthesis of the core-shell structure polymer are adjusted. For specific parameters, please refer to Table 1 and Table 2.

[0235] Examples 13 to 16

[0236] The preparation method is basically the same as that in Example 1, except that the mass fraction of the core-shell structured polymer in the conductive paste is adjusted. For specific parameters, please refer to Table 1 and Table 2.

[0237] Examples 17 to 20

[0238] The preparation method is basically the same as that in Example 1, except that the mass fraction of the conductive agent in the conductive slurry is adjusted. For specific parameters, please refer to Table 1 and Table 2.

[0239] Comparative Example 1

[0240] The preparation method is basically the same as that in Example 1, except that vinylidene fluoride polymer is used instead of core-shell structure polymer in conductive paste.

[0241] Comparative Example 2

[0242] The preparation method is basically the same as in Example 1, except that vinylidene fluoride-acrylamide polymer is used instead of the core-shell structure polymer in the conductive paste. The preparation method is as follows:

[0243] 30 kg of deionized water, 17.45 g of sodium perfluorooctanoate, 84.77 g of N,N-dimethylbenzylamine, 905 g of acrylamide monomer, 10.14 g of polyoxyethylene-4-phenolic ether ammonium sulfate, and 1014 g of acrylonitrile monomer were added sequentially into the reactor. The conductivity of the deionized water was less than or equal to 2 μs / cm. The reactor was then shut off.

[0244] The reactor was evacuated and then filled with nitrogen. This process was repeated until the oxygen concentration inside the reactor was less than 100 ppm.

[0245] Vinylidene fluoride monomer is introduced into the reactor until the pressure inside the reactor reaches 8.0 MPa; the temperature inside the reactor is raised to 85°C to start the reaction, and during the reaction, vinylidene fluoride monomer is continuously introduced to maintain a constant reaction pressure inside the reactor;

[0246] After all 4081g of vinylidene fluoride monomer was introduced, the reaction was stopped when the pressure inside the reactor dropped to 0.2MPa.

[0247] After cooling to room temperature, the material is filtered out to obtain a copolymer of vinylidene fluoride and acrylamide.

[0248] Comparative Example 3

[0249] The preparation method is basically the same as that of Example 1, except that the conductive paste uses vinylidene fluoride-acrylonitrile polymer instead of core-shell structure polymer, and its preparation method is similar to that of Comparative Example 2.

[0250] Comparative Example 4

[0251] The preparation method is basically the same as in Example 1, except that the core-shell structured vinylidene fluoride-acrylamide-acrylonitrile copolymer emulsion is replaced with a vinylidene fluoride-acrylamide-acrylonitrile copolymer emulsion prepared by a conventional method. The synthesis method is as follows:

[0252] Add 30 kg of deionized water (with a conductivity of less than or equal to 2 μS / cm), 17.45 g of perfluorooctanoic acid alkali metal salt, 84.77 g of N,N-dimethylbenzylamine, 10.14 g of polyoxyethylene-4-phenolic ether ammonium sulfate, 16.22 g of 5% ammonium persulfate solution, 1014 g of acrylonitrile, and 905 g of acrylamide into the reactor in sequence, and then close the reactor.

[0253] Vacuum the reactor, purge with nitrogen, and repeat the process until the oxygen concentration inside the reactor is less than 100 ppm.

[0254] Vinylidene fluoride monomer was introduced into the reactor until the pressure inside the reactor reached 8.0 MPa; the temperature inside the reactor was raised to 85°C to start the reaction. During the reaction, vinylidene fluoride monomer was continuously introduced to maintain a constant reaction pressure inside the reactor. The total mass of vinylidene fluoride monomer introduced was 4.08 kg.

[0255] The reaction is stopped when the pressure inside the reactor drops to 0.2 MPa, and the unreacted vinylidene fluoride monomer is recovered.

[0256] After cooling to room temperature, the material is filtered out to obtain an emulsion containing a vinylidene fluoride-acrylamide-acrylonitrile copolymer.

[0257] In Comparative Example 5, conductive paste was not added during the preparation of the negative electrode sheet; instead, an equivalent mass of conductive carbon black was added.

[0258] In Comparative Example 6, a conductive paste was added during the preparation of the negative electrode sheet. The preparation method of the conductive paste was similar to that of the conductive paste in Example 1, except that the same mass of sodium carboxymethyl cellulose (CMC) was used to replace the core-shell structure vinylidene fluoride-acrylamide-acrylonitrile copolymer.

[0259] II. Testing Methods

[0260] 1. Characterization of the properties of core-shell structured polymers

[0261] (1) Measurement of weight-average molecular weight of core-shell structured polymers

[0262] The emulsion containing the core-shell polymer was vacuum dried at 100°C for 180 minutes to obtain the core-shell polymer powder.

[0263] A Waters 2695 Isocratic HPLC gel electrophoresis system (differential refractive index detector 2141) was used. A 3.0% (w / w) polystyrene solution was used as a reference, and a matched column (oil-based: Styragel HT5DMF7.8×300mm + Styragel HT4) was selected. A 3.0% core-shell polymer solution was prepared using purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day. For testing, tetrahydrofuran was first used to flush the solution, repeated several times. Then, 5 ml of the experimental solution was drawn, air was expelled from the syringe, and the needle tip was dried. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the data was acquired, and the weight-average molecular weight was recorded.

[0264] (2) Dv50 particle size test of core-shell structured polymers

[0265] Following GB / T 19077-2016 Laser Diffraction Method for Particle Size Distribution, 0.1g–0.13g of core-shell polymer emulsion was weighed into a 50ml beaker. 5g of deionized water was added to the beaker containing the emulsion, and a stir bar approximately 2.5mm in length was placed inside. The beaker was then sealed with plastic wrap. The sample was sonicated for 5 minutes, then transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were taken from each batch for testing. Particle size distribution was determined using a laser particle size analyzer, such as the Mastersizer 2000E from Malvern Instruments Ltd. (UK).

[0266] 2. Properties testing of conductive paste

[0267] (1) Filtration performance test

[0268] Place a 500ml beaker at the bottom of a 200-mesh filter holder, put 500ml of conductive slurry into the filter, and record the time when the volume of the slurry in the beaker reaches 300ml.

[0269] (2) Solid content of conductive paste and the difference in solid content between the upper and lower layers after standing for 24 hours.

[0270] Weigh the copper foil in the weight loss rate measuring instrument and record the weight as M0, then zero the instrument.

[0271] Take a small amount of conductive paste, coat it onto copper foil, and then weigh it in a moisture analyzer. Record the weight as M1.

[0272] Close the equipment and begin drying;

[0273] After completion, record the weighing data as M2, and calculate the solid content as (M2-M0) / (M1-M0);

[0274] The solid content of the upper and lower conductive slurries was measured using the same method after standing for 24 hours. The difference between the solid content of the upper and lower conductive slurries after standing for 24 hours was taken as the solid content of the upper and lower conductive slurries.

[0275] (3) Test of the gel state of conductive paste after standing for 60 days

[0276] Use a steel ruler to lift the slurry in the beaker and judge whether the slurry has gelled based on its flow pattern. If the slurry has not gelled, mark it as "OK"; if the slurry has gelled, mark it as "NG".

[0277] Gel formation: The slurry clumps together or fails to flow naturally and continues to flow.

[0278] No gel: The slurry flows naturally and continuously, and flows horizontally on the surface of the steel ruler without clumping.

[0279] 3. Adhesion of the electrode sheet

[0280] Referring to GB-T2790-1995 national standard "Test Method for 180° Peel Strength of Adhesives", the adhesion test process of the embodiments and comparative examples in this application is as follows: A sample with a width of 30mm and a length of 100-160mm is cut with a blade. Special double-sided adhesive tape is applied to a steel plate, with a tape width of 20mm and a length of 90-150mm. The negative electrode film layer of the previously cut electrode sample is attached to the double-sided adhesive tape, and then rolled three times in the same direction using a 2kg pressure roller. A paper strip with a width equal to the electrode and a length of 250mm is fixed to the electrode current collector and secured with wrinkle adhesive. The power of the Sansi tensile testing machine (sensitivity 1N) is turned on; the indicator light illuminates. The limit block is adjusted to a suitable position, and the end of the steel plate without the electrode attached is fixed with the lower clamp. The paper strip is folded upwards and fixed with the upper clamp. The position of the upper clamp is adjusted using the "up" and "down" buttons on the manual controller attached to the tensile testing machine. Then, tests were conducted and values ​​were recorded at a stretching speed of 50 mm / min. The force when the electrode is in equilibrium was divided by the width of the tape to obtain the adhesive force per unit length of the negative electrode sheet, which characterizes the bond strength between the negative electrode film and the current collector.

[0281] 4. Battery performance testing

[0282] (1) Battery DC resistance

[0283] At 25℃, the secondary battery was charged at a constant current rate of 1 / 3C to 4.2V, then charged at a constant voltage of 4.2V to a current of 0.05C, and left to stand for 5 minutes. Then it was discharged at a rate of 1 / 3C for 90 minutes, the electrode assembly was adjusted to 50% SOC, left to stand for 60 minutes, and then discharged at a rate of 4C for 30 seconds. The discharge DCR at 50% SOC was obtained based on the test data.

[0284] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0285] Core-shell structured polymers, conductive slurries, negative electrode sheets, and secondary batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in Tables 1 and 2 below.

[0286] Table 1. Preparation parameters and test results of the examples and comparative examples.

[0287]

[0288]

[0289]

[0290] Table 2. Preparation parameters and test results of the examples and comparative examples.

[0291]

[0292]

[0293]

[0294] Examples 1-20 all utilize the core-shell structured polymers disclosed in this application, comprising a core and a shell at least partially covering the core. The core comprises structural units derived from fluorinated monomers (vinylidene fluoride or trifluorochloroethylene) and structural units derived from unsaturated monomers containing amide groups (acrylamide or methacrylamide). The shell comprises structural units derived from fluorinated monomers (vinylidene fluoride or trifluorochloroethylene) and structural units derived from unsaturated monomers containing cyano groups (acrylonitrile or methacrylonitrile). A comparison of Examples 1-20 with Comparative Examples 1-4 shows that the core-shell structured polymers disclosed in this application, compared to non-core-shell structured polymers prepared by conventional methods, can effectively adjust the viscosity of the conductive slurry, giving it both good anti-settling properties and filterability. The preparation of core-shell structured polymers significantly slows down the gelation of the conductive slurry, improves the storage performance of the conductive slurry, and reduces the DC impedance of the battery. As can be seen from Examples 1 to 5, based on the total mass of the core-shell structured polymer, the mass content of the core is 70%-90% and the mass content of the shell is 10%-30%. The above-mentioned core-shell structured polymer can further optimize the viscosity of the slurry and comprehensively improve the processing performance and bonding performance of the conductive slurry.

[0295] As can be seen from Examples 1-5, based on the total molar number of all structural units in the core-shell polymer, the molar content of structural units derived from vinylidene fluoride is 50%-80%. The aforementioned core-shell polymer can further optimize the viscosity of the slurry, comprehensively improving the processing and bonding properties of the conductive slurry.

[0296] As can be seen from Examples 1-5, based on the total molar number of all structural units in the core-shell polymer, the molar content of structural units derived from acrylamide is 10%-20%. The above-mentioned core-shell polymer can further optimize the viscosity of the slurry and comprehensively improve the processing and bonding properties of the conductive slurry.

[0297] As seen in Examples 1-5, based on the total molar number of all structural units in the core-shell polymer, the molar content of structural units derived from acrylonitrile is 10%-30%. The aforementioned core-shell polymer can further optimize the viscosity of the slurry, comprehensively improving the processing and bonding properties of the conductive slurry. As seen in Examples 1 and 6-9, when the weight-average molecular weight of the core-shell polymer is 100,000-300,000, the core-shell polymer can balance the adhesion of the electrode and the filterability of the slurry, comprehensively improving the bonding and processing properties of the electrode.

[0298] As can be seen from Examples 1 and 13-16, based on the total mass of the conductive slurry, when the mass fraction of the core-shell structure polymer is 0.5% to 2.5%, the core-shell structure polymer can balance the high adhesion of the electrode and the low impedance of the battery, thus comprehensively improving the adhesion performance and electrochemical performance of the battery.

[0299] As can be seen from Examples 1 and 17-20, when the mass fraction of the conductive agent is 10.0% to 15.0%, based on the total mass of the conductive slurry, the core-shell structure polymer can achieve both high adhesion of the electrode and low impedance of the battery, thus comprehensively improving the adhesion and electrochemical performance of the battery.

[0300] As can be seen from the comparison between the examples and Comparative Example 5, the aqueous conductive slurry prepared using the core-shell structure polymer disclosed in this application can improve the adhesion of the electrode and reduce the film resistance of the electrode compared with the direct addition of conductive carbon black.

[0301] As can be seen from the comparison between the examples and Comparative Example 6, the aqueous conductive slurry prepared using the core-shell structure polymer disclosed in this application, compared with the conductive slurry using traditional CMC dispersant as a binder, can not only effectively improve the dispersibility, anti-settling and anti-gelling properties of the slurry, but also effectively reduce the amount of traditional dispersant used in the battery, improve the adhesion of the electrode sheet, and further reduce the battery impedance.

[0302] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A core-shell structured polymer, characterized by, comprises a core part and a shell part at least partially covering the core part, the core part comprising structural units derived from a monomer represented by Formula I and structural units derived from a monomer represented by Formula II, and the shell part comprising structural units derived from a monomer represented by Formula I and structural units derived from a monomer represented by Formula III, Formula I Formula II Formula III wherein R1, R2, R3are each independently selected from the group consisting of hydrogen, fluorine, chlorine, fluorine-substituted C 1-3 one or more of alkyl, R4, R5, R6, R7, R8, R9are each independently selected from the group consisting of hydrogen, substituted or unsubstituted C 1-5 one or more of alkyl.

2. The core-shell structured polymer according to claim 1, wherein R1 in the Formula I is fluorine, and R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine and trifluoromethyl.

3. The core-shell structured polymer according to claim 1, wherein The mass content of the core part is 70%-90%, and the mass content of the shell part is 10%-30%, based on the mass of the core-shell structured polymer.

4. The core-shell structured polymer according to claim 1, wherein The molar content of the structural units derived from the monomer represented by Formula I is 50%-80%, based on the total moles of all structural units in the core-shell structured polymer.

5. The core-shell structured polymer according to claim 1, wherein The molar content of the structural units derived from the monomer represented by Formula II is 10%-20%, and the molar content of the structural units derived from the monomer represented by Formula III is 10%-30%, based on the total moles of all structural units in the core-shell structured polymer.

6. The core-shell structured polymer according to claim 1, wherein The mass content of the structural units derived from the monomer represented by Formula I in the core part is 85%-95%, based on the total mass of the structural units derived from the monomer represented by Formula I in the core-shell structured polymer.

7. The core-shell structured polymer according to any one of claims 1 to 6, wherein The weight average molecular weight of the core-shell structured polymer is 100,000-3,000,000.

8. The core-shell structured polymer according to any one of claims 1 to 6, wherein The monomer represented by Formula I is selected from one or more of vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene and hexafluoropropylene.

9. The core-shell structured polymer according to any one of claims 1 to 6, wherein The monomer represented by Formula II is selected from one or more of acrylamide, methacrylamide and crotonamide.

10. The core-shell structured polymer according to any one of claims 1 to 6, wherein The monomer represented by Formula III is selected from one or more of acrylonitrile, methacrylonitrile, 2-methyl-2-butenenitrile and 3-butenenitrile.

11. The core-shell structured polymer according to any one of claims 1 to 6, wherein The Dv50 particle size of the core-shell structured polymer is 100 nm-8 μm.

12. A method for preparing a core-shell structured polymer, characterized by, The preparation method comprises the following steps: polymerizing the monomer represented by Formula I and the monomer represented by Formula II under polymerizable conditions to prepare the core part of the core-shell structured polymer, and polymerizing the monomer represented by Formula I and the monomer represented by Formula III to prepare the shell part of the core-shell structured polymer, the shell part at least partially covering the core part, Formula I Formula II Formula III wherein R1, R2, R3are each independently selected from the group consisting of hydrogen, fluorine, chlorine, fluorine-substituted C 1-3 one or more of alkyl, R4, R5, R6, R7, R8, R9are each independently selected from the group consisting of hydrogen, substituted or unsubstituted C 1-5 one or more of alkyl.

13. The method for preparing the core-shell structured polymer according to claim 12, characterized in that, R1 in the Formula I is fluorine, and R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine and trifluoromethyl.

14. The method for preparing the core-shell structured polymer according to claim 12, characterized in that, The molar content of the monomer represented by Formula I is 50%-80%, based on the total moles of the monomer represented by Formula I, the monomer represented by Formula II and the monomer represented by Formula III.

15. The method for preparing the core-shell structured polymer according to claim 12, characterized in that, The molar content of the monomer represented by Formula II is 10%-20%, based on the total moles of the monomer represented by Formula I, the monomer represented by Formula II and the monomer represented by Formula III.

16. The method for preparing the core-shell structured polymer according to claim 12, characterized in that, The molar content of the monomer represented by Formula III is 10%-30%, based on the total moles of the monomer represented by Formula I, the monomer represented by Formula II and the monomer represented by Formula III.

17. The method of preparing a core-shell structured polymer according to any one of claims 12 to 16, characterized in that, The polymerization reaction comprises a first-stage polymerization and a second-stage polymerization, the first-stage polymerization: adding an initiator, a first emulsifier, at least one monomer represented by Formula I, at least one monomer represented by Formula II and an aqueous medium into a reaction vessel to perform the first-stage polymerization, and continuously feeding the monomer represented by Formula I in the first-stage polymerization to maintain the reaction pressure constant; Second-stage polymerization: after a period of time, an initiator, a second emulsifier, at least one monomer of formula III, and an aqueous medium are added to the reaction vessel to perform a second-stage polymerization to obtain a core-shell structure polymer, and the monomer of formula I is continuously fed into the reaction vessel during the second-stage polymerization until all the monomer of formula I is fed into the reaction vessel, and the reaction is stopped when the reaction pressure drops to 0-0.2 MPa.

18. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The second-stage polymerization comprises: After the initiator is added to the reaction vessel, a premix solution containing the second emulsifier, at least one monomer of formula III, and an aqueous medium is added.

19. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The mass of the monomer of formula I fed into the first-stage polymerization is 85%-95% of the total mass of the monomer of formula I fed into the polymerization, and the mass of the monomer of formula I fed into the second-stage polymerization is 5%-15% of the total mass of the monomer of formula I fed into the polymerization.

20. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The total mass of the initiator added in the first-stage polymerization and the second-stage polymerization is 1%-2% of the total mass of the monomer of formula I, the monomer of formula II, and the monomer of formula III.

21. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The mass percentage of the first emulsifier is 0.1%-0.5% of the total mass of the monomer of formula I, the monomer of formula II, and the monomer of formula III, and the mass percentage of the second emulsifier is 0.5%-5% of the mass of the monomer of formula III.

22. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The mass percentage of the aqueous medium provided in the first-stage polymerization is 400%-600% of the total mass of the monomer of formula I, the monomer of formula II, and the monomer of formula III.

23. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The reaction pressure of the first-stage polymerization is 6.0 MPa-9.0 MPa, and the reaction temperature is 80°C-100°C.

24. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The initial reaction pressure of the second-stage polymerization is lower than the reaction pressure of the first-stage polymerization, and the reaction temperature of the second-stage polymerization is higher than the reaction temperature of the first-stage polymerization.

25. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The first emulsifier is an alkali metal salt of perfluorooctanoic acid, and the second emulsifier is an ammonium salt of polyoxyethylene-4-phenol ether sulfate.

26. The method for preparing the core-shell structured polymer according to claim 17, characterized in that, The initiator is one or both of N,N-dimethylbenzylamine and ammonium persulfate.

27. Use of the core-shell structure polymer of any one of claims 1-11 in a secondary battery.

28. An emulsion characterized by, An aqueous medium, an emulsifier, and the core-shell structure polymer of any one of claims 1-11.

29. An electrically conductive paste, characterized by A conductive agent, an aqueous medium, and the core-shell structure polymer of any one of claims 1-11 or the emulsion of claim 28.

30. The conductive paste of claim 29, wherein, The mass fraction of the conductive agent is 10.0%-15.0% of the total mass of the conductive slurry.

31. The conductive paste of claim 29, wherein, The mass fraction of the core-shell structure polymer is 0.5%-2.5% of the total mass of the conductive slurry.

32. The conductive paste of claim 29, wherein, The solid content of the conductive slurry is 12%-17%, and the viscosity of the conductive slurry is 500 mPa·s-1500 mPa·s. 33.A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, a conductive agent, and a binder, and the conductive agent is a deposit of the conductive paste according to any one of claims 29 to 32.

34. The negative electrode sheet according to claim 33, wherein The adhesion per unit length between the negative electrode film layer and the negative electrode current collector is not less than 12 N / m.

35. A secondary battery, characterized by comprising: The secondary battery comprises at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

36. The secondary battery of claim 35, wherein, The secondary battery comprises at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

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