Fluoropolymer, conductive paste, negative electrode sheet, secondary battery, and electric device

Abstract

The application provides a fluorine-containing polymer, a conductive paste, a negative electrode sheet, a secondary battery and an electric device. The fluorine-containing polymer comprises at least one structural unit derived from a monomer shown in formula I and at least one structural unit derived from a monomer shown in formula II, wherein R1, R2 and R3 are each independently selected from hydrogen, fluorine, chlorine or C 1‑3 alkyl containing at least one fluorine atom, R4, R5, R6 and R7 are each independently selected from hydrogen or substituted or unsubstituted C 1‑15 alkyl, and R4, R5, R6 and R7 contain at least two -COOM, and M is selected from hydrogen, NH4 or alkali metal. The fluorine-containing polymer can improve the cohesion of the electrode sheet, reduce the electrode sheet rebound rate after cold pressing for 24 hours, and improve the use quality of the electrode sheet.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more particularly to a fluoropolymer, conductive paste, negative electrode sheet, secondary battery, and electrical device. Background Technology

[0002] Secondary batteries have many advantages, such as high volumetric and gravimetric energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field.

[0003] The fabrication of secondary batteries involves multiple processes, primarily including electrode cold pressing, electrode die-cutting, assembly, baking, and electrolyte injection. Electrode manufacturing, being a front-end process, plays a crucial role in the overall process. The quality of the electrodes directly affects the progress of the mid-stage assembly process and also influences the subsequent stages and the electrochemical performance of the secondary battery. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a fluoropolymer and a conductive paste containing the fluoropolymer, which can improve the cohesiveness of the electrode, reduce the electrode rebound rate after 24 hours of cold pressing, and improve the quality of the electrode, while improving the dispersibility of the conductive paste and slowing down the gelation of the conductive paste.

[0005] The first aspect of this application provides a fluoropolymer comprising at least one structural unit derived from a monomer shown in Formula I and at least one structural unit derived from a monomer shown in Formula II.

[0006]

[0007] Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C4 groups. 1-15 Alkyl groups, R4, R5, R6 and R7 contain at least two -COOM, where M is selected from hydrogen, NH4 or an alkali metal.

[0008] The fluoropolymer provided in this application can act as a dispersant, significantly alleviating gelation of conductive slurry during storage, improving the anti-gelling and storage properties of conductive slurry, reducing the film resistance of the electrode, reducing the DC internal resistance of the battery, and thus improving the dynamic performance of the battery. On the other hand, the fluoropolymer can increase the cohesion of the electrode, reduce the irreversible expansion of the electrode during the manufacturing process, reduce the rebound rate of the electrode after 24 hours of cold pressing, and improve the quality of the electrode.

[0009] In any embodiment, M comprises one or more of lithium, sodium, and potassium.

[0010] The introduction of lithium, sodium, or potassium into fluoropolymers can form ion exchanges with active ions during charging and discharging, further increasing the mobility of active ions, reducing the DC internal resistance of the battery, and improving the battery's dynamic performance.

[0011] In any embodiment, R1 is fluorine, and R2 and R3 are each independently selected from hydrogen, fluorine, chlorine or trifluoromethyl.

[0012] In any embodiment, the molar content of the structural units derived from the monomer shown in Formula I is 60%-80%, based on the total molar number of all structural units in the fluoropolymer.

[0013] 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 conductive paste, the cohesion of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing can be taken into account, thereby comprehensively improving the processing performance and performance of the conductive paste.

[0014] In any embodiment, the molar content of the structural units derived from the monomer shown in Formula II is 20%-40%, based on the total molar number of all structural units in the fluoropolymer.

[0015] By controlling the molar content of the structural units derived from the monomer shown in Formula II within a suitable range, the viscosity of the conductive paste, the cohesion of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing can be taken into account, thereby comprehensively improving the processing performance and performance of the conductive paste.

[0016] In any embodiment, the weight-average molecular weight of the fluoropolymer is 80,000 to 120,000.

[0017] By controlling the weight-average molecular weight of fluoropolymers within a suitable range, the viscosity of conductive paste, the cohesive force of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing can be balanced, thereby comprehensively improving the processing and performance of conductive paste.

[0018] In any embodiment, the monomer shown in Formula I is selected from one or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropylene.

[0019] In any embodiment, the monomer shown in Formula II is selected from one or more of allylmalonic acid, 2-pentenonic acid, lithium 2-pentenonic acid, lithium allylmalonic acid, lithium methylenemalonic acid, lithium vinylmalonic acid, lithium allylbutyric acid, lithium pentenonic acid, lithium maleate, lithium trans-pentenonic acid, lithium hexenedioic acid, lithium heptenonic acid, lithium octenonic acid, sodium allylmalonic acid, sodium methylenemalonic acid, sodium vinylmalonic acid, sodium allylbutyric acid, sodium 2-(4-pentenyl)malonic acid, sodium maleate, sodium trans-pentenonic acid, sodium hexenedioic acid, sodium heptenonic acid, sodium octenonic acid, potassium allylmalonic acid, potassium methylenemalonic acid, potassium vinylmalonic acid, and potassium heptenonic acid.

[0020] In any embodiment, the fluoropolymer includes one or more of the following: vinylidene fluoride-allylpropanediol copolymer, vinylidene fluoride-allyl malonic acid copolymer, vinylidene fluoride-sodium allyl malonate copolymer, vinylidene fluoride-2-pentenic lithium copolymer, vinylidene fluoride-trifluorochloroethylene-allylpropanediol copolymer, tetrafluoroethylene-allylpropanediol copolymer, and vinylidene fluoride-hexafluoropropylene-allylpropanediol copolymer.

[0021] A second aspect of this application provides a method for preparing a fluoropolymer, comprising the following steps:

[0022] Under polymerizable conditions, at least one monomer of Formula I and at least one monomer of Formula II are polymerized to form a polymer product.

[0023]

[0024] Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C4 groups. 1-15 Alkyl groups, wherein R4, R5, R6, and R7 contain at least two -COOH groups.

[0025] Optionally, the polymerization product is neutralized with a neutralizing agent, the neutralization reaction causing at least a portion of the -COOH in the polymerization product to be converted to -COOM, where M is selected from NH4 or an alkali metal.

[0026] Compared to traditional dispersants, the fluoropolymer prepared by this method can not only improve the dispersibility of conductive slurry, alleviate gelation of conductive slurry during storage, improve the anti-gelling and storage properties of conductive slurry, reduce the film resistance of electrode, reduce the DC internal resistance of battery, and improve the dynamic performance of battery, but also improve the cohesion of electrode, reduce irreversible expansion of electrode during manufacturing, reduce the rebound rate of electrode after 24 hours of cold pressing, and improve the quality of electrode.

[0027] In any embodiment, M comprises one or more of lithium, sodium, and potassium.

[0028] In any embodiment, R1 is fluorine, and R2 and R3 are each independently selected from hydrogen, fluorine, chlorine or trifluoromethyl.

[0029] In any embodiment, the molar content of the monomer shown in Formula I is 60%-80%, based on the total molar number of the monomer shown in Formula I and the monomer shown in Formula II.

[0030] In any embodiment, the molar content of the monomer shown in Formula II is 20%-40%, based on the total molar number of the monomers shown in Formula I and Formula II.

[0031] In any embodiment, the polymerization reaction specifically includes:

[0032] First stage polymerization: an initiator, an emulsifier, at least one monomer of Formula I and a solvent are provided to carry out the first stage polymerization, wherein the monomer of Formula I is continuously fed in during the first stage polymerization to maintain the initial reaction pressure;

[0033] Second stage polymerization: After a period of reaction, the monomers shown in Formula I and Formula II are fed into the reaction vessel to carry out the second stage polymerization. The monomers shown in Formula I are continuously fed into the second stage polymerization.

[0034] Optionally, the neutralizing agent is added to the reactor after the second polymerization reaction is completed to carry out a neutralization reaction.

[0035] The method provided in this application first continuously feeds in the monomer shown in Formula I to form fluorinated segments, resulting in a fluorinated polymer with high thermal stability. Then, the monomer shown in Formula II is introduced to reduce the contact between the fluorinated segments and the external environment, effectively mitigating the gelation phenomenon caused by fluorine. Compared to fluorinated polymers prepared by simultaneously polymerizing all monomers in the reaction vessel, the fluorinated polymer prepared by this method effectively improves the stability and dispersibility of the conductive slurry, reduces the film resistance of the electrode and the DC internal resistance of the battery, and improves the kinetic performance of the battery. Furthermore, while feeding the monomer shown in Formula II into the reaction vessel for the second-stage polymerization reaction, continuing to feed the monomer shown in Formula I into the reaction vessel helps improve the compatibility between the segments generated in the first-stage polymerization reaction and those generated in the second-stage polymerization reaction, thereby improving the stability of the fluorinated polymer.

[0036] In any embodiment, the mass of the monomer of Formula I introduced in the first stage of polymerization is 30%-70% 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 30%-70% of the total mass of the monomer of Formula I supplied in the polymerization reaction.

[0037] In any embodiment, the neutralizing agent includes one or more of lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia.

[0038] A third aspect of this application provides the application of the fluoropolymer of the first aspect in secondary batteries.

[0039] A fourth aspect of this application provides a conductive paste comprising a conductive agent, an aqueous medium, and the fluoropolymer described in the first aspect.

[0040] Compared to existing technologies that directly add conductive agents during the preparation of negative electrode slurry, the conductive slurry provided in this application can reduce the rebound rate of the electrode after 24 hours of cold pressing, improve the quality of the electrode, and at the same time improve the dispersibility of the conductive agent in the negative electrode slurry, thereby enhancing the conductivity of the conductive agent in the electrode and effectively reducing the content of conductive agent in the electrode. This is beneficial to further increase the loading of negative electrode active material in the electrode and improve the battery power performance.

[0041] In any embodiment, the mass fraction of the conductive agent is 1.5%-4.5%, based on the total mass of the conductive paste.

[0042] By controlling the mass fraction of the conductive agent within a suitable range, the slurry has a suitable viscosity based on the total mass of the conductive slurry, while the electrode has a low rebound rate after 24 hours of cold pressing, thus comprehensively improving the processing and performance of the slurry.

[0043] In any embodiment, the fluoropolymer has a mass fraction of 0.5%-1.5% based on the total mass of the conductive paste.

[0044] By controlling the mass fraction of fluoropolymer within a suitable range, the slurry has a suitable viscosity based on the total mass of the conductive slurry, while the electrode has a low rebound rate after 24 hours of cold pressing, thus comprehensively improving the processing and performance of the slurry.

[0045] In any embodiment, the solid content of the conductive paste is 1%-10%, and the viscosity of the conductive paste is 500mPa·s-5000mPa·s.

[0046] With a solid content of 1%-10% and a viscosity of 500mPa·s-5000mPa·s, it can be directly mixed with active materials and binders to prepare negative electrode slurry without the need for additional additives, which helps to improve production efficiency and reduce production costs.

[0047] The fifth aspect of this application provides a negative electrode sheet, including 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 including a negative electrode active material, a conductive agent and a binder, the conductive agent comprising a deposit of the conductive paste of the fourth aspect.

[0048] Compared to existing technologies that directly add conductive agent powder to prepare negative electrode sheets, the conductive agent in the negative electrode sheet disclosed in this application exists in the form of conductive slurry deposits. On the one hand, this can improve the cohesion of the electrode sheet, reduce the rebound rate after 24 hours of cold pressing, and improve the quality of the electrode sheet. On the other hand, adding it in the form of conductive slurry can improve the dispersion performance of conductive materials, so that the negative electrode sheet can have low film resistance even with low amounts of conductive agent added, which provides the possibility of further increasing the loading of negative electrode active materials in the electrode sheet.

[0049] In any embodiment, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 -1.8g / cm 3 At that time, the electrode rebound rate of the negative electrode sheet after cold pressing for 24 hours is not higher than 7.0%.

[0050] In any implementation, the cohesive force of the negative electrode sheet is not less than 73 N / m, and can be selected as not less than 80 N / m.

[0051] In any embodiment, based on the total mass of the negative electrode film, the mass content of the conductive agent is 0.2%-2%, and the film resistance of the negative electrode film is not higher than 0.15Ω.

[0052] The sixth aspect of this application provides a secondary battery, characterized in that it includes the negative electrode sheet of the fifth aspect.

[0053] In any embodiment, the secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

[0054] The seventh aspect of this application provides an electrical device, including the secondary battery of the sixth aspect. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0056] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0057] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0058] Figure 4This is a schematic diagram of a battery pack according to one embodiment of this application;

[0059] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0060] Figure 6 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.

[0061] Explanation of reference numerals in the attached figures:

[0062] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0063] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the fluoropolymer, conductive paste, negative electrode sheet, secondary battery, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically 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.

[0064] 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.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0067] 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.

[0068] 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.

[0069] 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).

[0070] As the energy density of rechargeable batteries gradually increases, battery manufacturers are increasing the compaction density of electrode sheets to pack more sheets into a limited casing volume, thereby improving the energy density of the cell. However, in the actual production process of electrode sheets, as the compaction density increases, the cold pressing process can damage the active material. Insufficient gaps between particles and excessive internal repulsive forces can lead to increased electrode thickness after cold pressing, causing electrode rebound and affecting subsequent battery assembly processes.

[0071] [Fluoropolymers]

[0072] Based on this, this application proposes a fluoropolymer comprising at least one structural unit derived from a monomer shown in Formula I and at least one structural unit derived from a monomer shown in Formula II.

[0073]

[0074] Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C4 groups. 1-15 Alkyl groups, R4, R5, R6 and R7 contain at least two -COOM, where M is selected from hydrogen, NH4 or an alkali metal.

[0075] In this paper, the term "fluoropolymer" refers to a polymer whose structural unit contains fluorine.

[0076] 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.

[0077] In this article, the term "C" 1-3 "Alkyl" refers to a branched and straight-chain saturated aliphatic monovalent hydrocarbon group with a specified number of carbon atoms. The group is not unsaturated, has one to three carbon atoms, and is attached to the rest of the molecule by a single bond.

[0078] In this article, the term "C containing at least one fluorine atom" is used. 1-3 "Alkyl" refers to an alkyl group containing 1-3 carbon atoms, in which at least one hydrogen atom is replaced by a fluorine atom. In some embodiments, the carbon atom contains one fluorine atom. 1-3 Alkyl groups include -CF3 groups and -C2F6 groups.

[0079] In this article, the term "C" 1-15 "Alkyl" refers to a branched and straight-chain saturated aliphatic monovalent hydrocarbon group with a specified number of carbon atoms. The group is not unsaturated, has one to fifteen carbon atoms, and is attached to the rest of the molecule by a single bond.

[0080] 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.

[0081] In some embodiments, R1 is fluorine, and R2 and R3 are each independently selected from hydrogen, fluorine, chlorine or trifluoromethyl.

[0082] In this paper, the term "alkali metals" refers to the six metallic elements in Group IA of the periodic table, excluding hydrogen (H): lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

[0083] In some implementations, -COOM includes any one of -COOH, -COONH4, -COOLi, -COONa, and -COOK.

[0084] In some implementations, R4, R5, R6, and R7 contain at least two -COOH groups.

[0085] In some implementations, R4, R5, R6, and R7 contain at least two -COO NH4 groups.

[0086] In some implementations, R4, R5, R6, and R7 contain at least two -COOLi.

[0087] In some implementations, R4, R5, R6, and R7 contain at least two -COONa.

[0088] In some implementations, R4, R5, R6, and R7 contain at least two -COOKs.

[0089] In some implementations, R4, R5, R6, and R7 independently contain any two or more of -COOH, -COONH4, -COOLi, -COONa, and -COOK.

[0090] In some implementations, R4 and R5 are independently selected from any one of -COOH, -COONH4, -COOLi, -COONa, and -COOK.

[0091] In some embodiments, R6 and R7 are independently selected from any one of -COOH, -COONH4, -COOLi, -COONa, and -COOK.

[0092] In some implementations, R4 and R6 are independently selected from any one of -COOH, -COONH4, -COOLi, -COONa, and -COOK.

[0093] In some implementations, R4 comprises two or more -COOH, -COONH4, -COOLi, -COONa, or -COOK.

[0094] In some embodiments, the monomer represented by Formula I is selected from one or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropylene.

[0095] In some embodiments, the monomer shown in Formula II is selected from one or more of allylmalonic acid, 2-pentenonic acid, lithium 2-pentenonic acid, lithium allylmalonic acid, lithium methylenemalonic acid, lithium vinylmalonic acid, lithium allylbutyric acid, lithium pentenonic acid, lithium maleate, lithium trans-pentenonic acid, lithium hexenedioic acid, lithium heptenonic acid, lithium octenonic acid, sodium allylmalonic acid, sodium methylenemalonic acid, sodium vinylmalonic acid, sodium allylbutyric acid, sodium 2-(4-pentenyl)malonic acid, sodium maleate, sodium trans-pentenonic acid, sodium hexenedioic acid, sodium heptenonic acid, sodium octenonic acid, potassium allylmalonic acid, potassium methylenemalonic acid, potassium vinylmalonic acid, and potassium heptenonic acid.

[0096] In this article, the term "process window" refers to the process range that can guarantee product quality, including but not limited to temperature range, pressure range, storage time length, etc. It can be understood that the wider the process window, the lower the requirement for process precision.

[0097] In this paper, the term "carboxylate group" refers to -COONH4, -COOLi, -COONa, -COOK, -COORb, -COOCs, and -COOFr.

[0098] In some embodiments, the polymer comprises one or more structural units derived from the monomers shown in Formula I. In some embodiments, the polymer comprises one or more structural units derived from the monomers shown in Formula II. In some embodiments, the polymer includes, but is not limited to, fluoropolymers including vinylidene fluoride-allylpropylene glycol dilithium copolymer, vinylidene fluoride-allyl malonic acid copolymer, vinylidene fluoride-sodium allyl malonate copolymer, vinylidene fluoride-2-pentenediol copolymer, vinylidene fluoride-trifluorochloroethylene-allyl malonate copolymer, and hexafluoropropylene-vinyl malonate copolymer.

[0099] The fluorine element in the structural unit of the monomer derived from Formula I can form hydrogen bonds with the hydroxyl and / or carboxyl groups on the surface of the active material. Additionally, the carboxyl and / or carboxyl groups in the structural unit of the monomer derived from Formula II can also form hydrogen bonds with the hydroxyl and / or carboxyl groups on the surface of the active material. These two factors work together to increase the cohesive force of the electrode, reduce irreversible expansion of the electrode during manufacturing, decrease the rebound rate after 24 hours of cold pressing, and improve the quality of the electrode. Furthermore, the structural unit of the monomer derived from Formula II can effectively reduce the fluorine content of the fluoropolymer, mitigating the fluorine-induced slurry gelation phenomenon. Moreover, the structural unit of the monomer derived from Formula II can further increase the steric hindrance of the fluoropolymer, reducing the aggregation of fluorine-containing units, thereby reducing slurry viscosity, alleviating slurry gelation, and effectively improving the slurry's filterability. The structural unit derived from the monomer shown in Formula II contains at least two carboxyl and / or carboxylate groups, which can further improve the cohesion of the electrode, reduce the rebound rate of the electrode after cold pressing, reduce the viscosity of the conductive paste, improve the filterability of the conductive paste, make the conductive paste less prone to gelation during storage, improve the anti-gelling and storage properties of the conductive paste, and further reduce the DC impedance of the battery.

[0100] In summary, the fluoropolymer provided in this application can act as a dispersant, significantly alleviating gelation of conductive slurry during storage, improving the anti-gelling and storage properties of conductive slurry, reducing the film resistance of the electrode, reducing the DC internal resistance of the battery, and thus improving the kinetic performance of the battery. On the other hand, the fluoropolymer can increase the cohesive force of the electrode, reduce the irreversible expansion of the electrode during the manufacturing process, reduce the rebound rate of the electrode after 24 hours of cold pressing, and improve the quality of the electrode.

[0101] In some embodiments, M is selected from one or more of lithium, sodium, and potassium.

[0102] In some implementations, -COOM can be any one of -COOLi, -COONa, or -COOK.

[0103] The introduction of lithium, sodium, or potassium into fluoropolymers can form ion exchanges with active ions during charging and discharging, further increasing the mobility of active ions, reducing the DC internal resistance of the battery, and improving the battery's dynamic performance.

[0104] In some embodiments, the molar content of the structural units derived from the monomer shown in Formula I is 60%-80%, based on the total molar number of all structural units in the fluoropolymer.

[0105] In some embodiments, the molar content of the structural units derived from the monomer shown in Formula I can be selected as any value from 60%, 70%, 80%, or a range of any two of these values, based on the total molar number of all structural units in the fluoropolymer.

[0106] 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 conductive paste, the cohesion of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing can be taken into account, thereby comprehensively improving the processing performance and performance of the conductive paste.

[0107] In some embodiments, the molar content of the structural units derived from the monomer shown in Formula II is 20%-40%, based on the total molar number of all structural units in the fluoropolymer. In some embodiments, the molar content of the structural units derived from the monomer shown in Formula II may be selected as any value from 20%, 30%, 40%, or a range of any two of these values, based on the total molar number of all structural units in the fluoropolymer.

[0108] By controlling the molar content of the structural units derived from the monomer shown in Formula II within a suitable range, the viscosity of the conductive paste, the cohesiveness of the electrode, and the rebound rate after the electrode is cold-pressed for 24 hours can be taken into account, thereby comprehensively improving the processing performance and performance of the conductive paste.

[0109] In some embodiments, the weight-average molecular weight of the fluoropolymer is 80,000 to 120,000. In some embodiments, the weight-average molecular weight of the fluoropolymer can be selected as any value from 80,000, 90,000, 100,000, 110,000, and 120,000, or a range consisting of any two of these values.

[0110] 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.

[0111] 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), specifically 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% fluoropolymer gel solution is prepared using purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day. During testing, tetrahydrofuran is first drawn into a syringe for rinsing, repeated several times. Then, 5 ml of the test 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.

[0112] Controlling the weight-average molecular weight of the fluoropolymer within a suitable range ensures that the slurry has appropriate viscosity, which is beneficial for the subsequent preparation of the negative electrode slurry. At the same time, the fluoropolymer with an appropriate weight-average molecular weight is conducive to the formation of a three-dimensional network bonding structure, resulting in good cohesion of the electrode and a low rebound rate after 24 hours of cold pressing. This approach can balance the viscosity of the conductive slurry, the cohesion of the electrode, and the rebound rate after 24 hours of cold pressing, thereby comprehensively improving the processing and performance of the conductive slurry.

[0113] One embodiment of this application provides a method for preparing a fluoropolymer, comprising the following steps:

[0114] Under polymerizable conditions, at least one monomer of Formula I and at least one monomer of Formula II are polymerized to form a polymer product.

[0115]

[0116] Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C atoms. 1-15 Alkyl groups, wherein R4, R5, R6, and R7 contain at least two -COOH groups.

[0117] Optionally, the polymerization product is neutralized with a neutralizing agent, the neutralization reaction causing at least a portion of the -COOH in the polymerization product to be converted to -COOM, where M contains NH4 or an alkali metal.

[0118] In some embodiments, the method for preparing fluoropolymers includes the following steps:

[0119] Under polymerizable conditions, at least one monomer of Formula I and at least one monomer of Formula II are polymerized to form a polymer product.

[0120]

[0121] Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C atoms. 1-15 Alkyl groups, wherein R4, R5, R6 and R7 contain at least two -COOH groups.

[0122] In some embodiments, the method for preparing fluoropolymers includes the following steps:

[0123] Under polymerizable conditions, at least one monomer of Formula I and at least one monomer of Formula II are polymerized to form a polymer product.

[0124]

[0125] Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C atoms. 1-15 Alkyl groups, wherein R4, R5, R6, and R7 contain at least two -COOH groups.

[0126] The polymerization product is neutralized with a neutralizing agent, the neutralization reaction causing at least a portion of the -COOH in the polymerization product to be converted to -COOM, where M contains NH4 or an alkali metal.

[0127] In some embodiments, the neutralizing agent includes one or more of lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia.

[0128] Compared to traditional dispersants, the fluoropolymer prepared by this method not only improves the dispersibility of conductive slurry, alleviates gelation of conductive slurry during storage, enhances the anti-gelling and storage properties of conductive slurry, reduces the film resistance of electrode, reduces the DC internal resistance of battery, and improves the kinetic performance of battery, but also enhances the cohesive force of electrode, reduces irreversible expansion of electrode during manufacturing, reduces the rebound rate of electrode after 24 hours of cold pressing, and improves the quality of electrode.

[0129] In some implementations, M comprises one or more of lithium, sodium, and potassium.

[0130] In some embodiments, R1 is fluorine, and R2 and R3 are each independently selected from hydrogen, fluorine, chlorine or trifluoromethyl.

[0131] In some embodiments, the molar content of the monomer shown in Formula I is 60%-80%, based on the total molar number of the monomer shown in Formula I and the monomer shown in Formula II.

[0132] In some embodiments, the molar content of the monomer shown in Formula II is 20%-40%, based on the total molar number of the monomers shown in Formula I and Formula II.

[0133] In some implementations, the polymerization reaction specifically includes:

[0134] First stage polymerization: an initiator, an emulsifier, at least one monomer of Formula I and a solvent are provided to carry out the first stage polymerization, wherein the monomer of Formula I is continuously fed in during the first stage polymerization to maintain the initial reaction pressure;

[0135] Second stage polymerization: After the reaction has been going on for a period of time, the monomers shown in Formula I and Formula II are fed into the reaction vessel to carry out the second stage polymerization. The monomers shown in Formula I are continuously fed into the second stage polymerization.

[0136] Optionally, the neutralizing agent is added to the reactor after the second polymerization reaction is completed to carry out a neutralization reaction.

[0137] In some implementations, the polymerization reaction specifically includes:

[0138] First stage polymerization: an initiator, an emulsifier, at least one monomer of Formula I and a solvent are provided to carry out the first stage polymerization, wherein the monomer of Formula I is continuously fed in during the first stage polymerization to maintain the initial reaction pressure;

[0139] Second stage polymerization: After a period of reaction, monomers shown in Formula I and Formula II are fed into the reaction vessel for second stage polymerization, during which monomers shown in Formula I are continuously fed.

[0140] In some implementations, the polymerization reaction specifically includes:

[0141] First stage polymerization: an initiator, an emulsifier, at least one monomer of Formula I and a solvent are provided to carry out the first stage polymerization, wherein the monomer of Formula I is continuously fed in during the first stage polymerization to maintain the initial reaction pressure;

[0142] Second stage polymerization: After the reaction has been going on for a period of time, the monomers shown in Formula I and Formula II are fed into the reaction vessel to carry out the second stage polymerization. The monomers shown in Formula I are continuously fed into the second stage polymerization.

[0143] After the second stage of polymerization is completed, the neutralizing agent is added to the reactor to carry out a neutralization reaction.

[0144] The method provided in this application first continuously feeds in the monomer shown in Formula I to form fluorinated segments, giving the fluorinated polymer high thermal stability. Then, the monomer shown in Formula II is introduced to reduce the contact between the fluorinated segments and the external environment, effectively mitigating the gelation phenomenon caused by fluorine. Compared to fluorinated polymers prepared by simultaneously polymerizing all monomers in the reaction vessel, the fluorinated polymer prepared by this method effectively improves the stability of the conductive slurry, enhances the slurry's dispersibility, increases the cohesive force of the electrode, reduces the electrode rebound rate after 24 hours of cold pressing, lowers the film resistance of the electrode and the DC internal resistance of the battery, and improves the battery's kinetic performance. Furthermore, while feeding the monomer shown in Formula II into the reaction vessel for the second-stage polymerization reaction, continuing to feed the monomer shown in Formula I into the reaction vessel helps improve the compatibility between the segments generated in the first-stage polymerization reaction and those generated in the second-stage polymerization reaction, thus improving the stability of the fluorinated polymer.

[0145] In some embodiments, the mass of the monomer of Formula I introduced in the first stage of polymerization is 30%-70% 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 30%-70% of the total mass of the monomer of Formula I supplied in the polymerization reaction.

[0146] In some embodiments, the initiator is 0.5%-1.5% by mass, based on the total mass of the monomers shown in Formula I and Formula II.

[0147] In some embodiments, the emulsifier is 0.1%-0.5% by mass, based on the total mass of the monomers shown in Formula I and Formula II.

[0148] In some embodiments, the mass percentage of the aqueous medium provided in the polymerization reaction is 400%-600%, based on the total mass of the monomers shown in Formula I and Formula II.

[0149] In some embodiments, the polymerization reaction pressure is 7 MPa-9 MPa, and the polymerization reaction temperature is 80°C-120°C.

[0150] In some embodiments, the initiator is one or both of N,N-dimethylbenzylamine and N-methylamphetamine.

[0151] In some embodiments, the emulsifier is at least one of perfluorooctanoic acid alkali metal salt, polyoxyethylene-4-phenolic ether ammonium sulfate, and nonylphenol polyoxyethylene ether ammonium sulfate.

[0152] In one embodiment of this application, the application of fluoropolymers 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.

[0153] [Conductive paste]

[0154] In one embodiment of this application, a conductive paste is provided, comprising a conductive agent, an aqueous medium, and the fluoropolymer described in any embodiment.

[0155] Compared to existing technologies that directly add conductive agents during the negative electrode slurry preparation process, the conductive slurry provided in this application can improve the dispersibility of the conductive agent in the negative electrode slurry, enhance the conductivity of the conductive agent in the electrode, and thus effectively reduce the conductive agent content in the electrode, which is beneficial for further increasing the electrode loading and improving battery power performance. Furthermore, the fluoropolymer in the conductive slurry can simultaneously act as a binder and dispersant. While improving the dispersibility of the conductive slurry and the conductive agent in the electrode, and reducing the DC impedance of the battery, it can also increase the cohesion of the electrode, reduce the rebound rate after cold pressing, and improve the quality of the electrode.

[0156] In some implementations, the aqueous medium includes deionized water.

[0157] In some embodiments, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0158] In some implementations, the conductive agent includes carbon nanotubes.

[0159] One-dimensional linear carbon nanotubes form a long-range conductive network in the electrode. This conductive network can connect the active material particles together, keeping them in electrical contact. The battery has low DC resistance. At the same time, this conductive network can limit the mutual repulsion between the active material particles after cold pressing, reduce the rebound rate of the electrode after cold pressing, and improve the quality of the electrode.

[0160] In some embodiments, the conductive agent has a mass fraction of 1.5% to 4.5%, based on the total mass of the conductive paste.

[0161] In some embodiments, the mass fraction of the conductive agent can be selected as any value or a range of any two of 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, based on the total mass of the conductive slurry.

[0162] By controlling the mass fraction of the conductive agent within a suitable range, the slurry has a suitable viscosity based on the total mass of the conductive slurry, while the electrode has a low rebound rate after 24 hours of cold pressing, thus comprehensively improving the processing and performance of the slurry.

[0163] In some embodiments, the fluoropolymer content is 0.5%-1.5% by mass, based on the total mass of the conductive paste. In some embodiments, the fluoropolymer content is any value or a range of any two of 0.5%, 0.75%, 1%, 1.25%, and 1.5% by mass, based on the total mass of the conductive paste.

[0164] By controlling the mass fraction of fluoropolymer within a suitable range, the slurry has a suitable viscosity based on the total mass of the conductive slurry, while the electrode has a low rebound rate after 24 hours of cold pressing, thus comprehensively improving the processing and performance of the slurry.

[0165] In any embodiment, the solid content of the conductive paste is 1%-10%, and the viscosity of the conductive paste is 500mPa·s-5000mPa·s.

[0166] In some embodiments, the solid content of the conductive paste can be selected as any value from 1%, 3%, 5%, 6%, 10%, or a range of any two of these values.

[0167] In some embodiments, the viscosity of the conductive paste can be selected from any value or a range of any two of the following: 500 mPa·s, 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, 1500 mPa·s, 2000 mPa·s, 2500 mPa·s, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, and 5000 mPa·s.

[0168] With a solid content of 1%-10% and a viscosity of 500mPa·s-5000mPa·s, it can be directly mixed with active materials and binders to prepare negative electrode slurry without the need for additional additives, which helps to improve production efficiency and reduce production costs.

[0169] [Negative electrode plate]

[0170] The fifth aspect of this application provides a negative electrode sheet, including 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 including a negative electrode active material, a conductive agent and a binder, the conductive agent comprising a deposit of the conductive paste of the fourth aspect.

[0171] 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.

[0172] Compared to existing technologies that directly add conductive agent powder to prepare negative electrode sheets, the conductive agent in the negative electrode sheet disclosed in this application exists in the form of conductive slurry deposits. On the one hand, this can improve the cohesion of the electrode sheet, reduce the rebound rate after 24 hours of cold pressing, and improve the quality of the electrode sheet. On the other hand, adding it in the form of conductive slurry can improve the dispersion performance of conductive materials, so that the negative electrode sheet can have low film resistance even with low amounts of conductive agent added, which provides the possibility of further increasing the loading of negative electrode active materials in the electrode sheet.

[0173] In some embodiments, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 -1.8g / cm 3 At that time, the electrode rebound rate of the negative electrode sheet after cold pressing for 24 hours is not higher than 7.0%.

[0174] In this paper, the rebound rate of the negative electrode sheet after cold pressing for 24 hours has a meaning known in the art and can be determined using instruments and methods known in the art. As an example, the coated negative electrode sheet is cold-pressed to a fixed compaction density (1.5 g / cm³). 3 The thickness of the negative electrode sheet was measured and recorded as h1; after the cold-pressed electrode sheet was left to stand for 24 hours, the thickness of the negative electrode sheet was measured again and recorded as h2.

[0175] The rebound rate (%) of the electrode after 24 hours of cold pressing is (h2-h1) / h1×100%.

[0176] While meeting the requirements for high compaction density of the negative electrode sheet and improving the energy density of the battery, the negative electrode sheet of this application has a low rebound rate after 24 hours of cold pressing, which improves the quality of the electrode sheet and facilitates subsequent battery assembly processes.

[0177] In some embodiments, the compaction density of the electrode sheet can be selected as 1.3 g / cm³. 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 Any value in or a range consisting of any two values ​​in it.

[0178] In some implementations, the electrode rebound rate after cold pressing of the negative electrode sheet for 24 hours can be selected as any one of not higher than 7.0%, not higher than 6.0%, and not higher than 5.0%.

[0179] In some implementations, the cohesive force of the negative electrode sheet is not less than 73 N / m, and can be selected as not less than 80 N / m.

[0180] In this paper, the cohesive force of the negative electrode sheet is defined in a way known in the art and can be measured using instruments and methods known in the art. As an example, double-sided tape is used to attach the negative electrode sheet to a steel plate. A strip of negative electrode sheet with a length of 20 cm and a width of 20 mm is cut and attached to the double-sided tape. A single-sided adhesive paper (width × length = 20 mm × 80 mm) for testing the cohesive force of the negative electrode sheet is centered and attached to cover the strip. A strip of white paper with a width × length = 20 mm × 60 mm is cut and inserted between the steel plate and the single-sided adhesive paper, with an overlap length of about 15 mm. The strip is rolled back and forth four times with a roller. The white paper is clamped in the tensile testing machine fixture, and the tensile testing machine is turned on to separate the single-sided adhesive paper adhering to the negative electrode film layer of the strip from the strip. The cohesive force value is obtained after the test is completed.

[0181] In some embodiments, based on the total mass of the negative electrode film, the mass content of the conductive agent is 0.2%-2%, and the film resistance of the negative electrode film is not higher than 0.15Ω.

[0182] In some embodiments, based on the total mass of the negative electrode film, the mass content of the conductive agent can be selected as any value from 0.2%, 0.5%, 1%, 1.5%, 2%, or a range of any two of these values.

[0183] In some embodiments, the film resistance of the negative electrode film can be selected as no higher than 0.15Ω, 0.1Ω, or 0.05Ω.

[0184] In this document, the film resistance of the negative electrode layer has a meaning known in the art and can be measured using instruments and methods known in the art. As an example, after drying, the electrode is cut into small circular pieces with a diameter of 10mm at the left, center, and right edges. The Yuaneng Technology electrode resistance meter is powered on, placed at the appropriate position of the probe, and the "Start" button is clicked. Once the reading stabilizes, it is read. Two positions are tested for each small circular piece, and the average of the six measurements is calculated; this is the film resistance of the electrode.

[0185] 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.

[0186] 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.).

[0187] 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.

[0188] 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).

[0189] 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.

[0190] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0191] In some embodiments, the negative electrode sheet can be prepared by: mixing the above-mentioned components for preparing the negative electrode sheet, for example, first stirring a fluoropolymer, a conductive agent, and deionized water to prepare a conductive slurry; dispersing the negative electrode active material, binder, conductive slurry, and any other components in deionized water to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector; and after drying, cold pressing, and other processes, the negative electrode sheet can be obtained.

[0192] [Positive electrode plate]

[0193] 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, the positive electrode film layer including a positive electrode active material.

[0194] 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.

[0195] 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.).

[0196] 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 Mn0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 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.

[0197] 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.

[0198] 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.

[0199] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0200] [Electrolytes]

[0201] 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.

[0202] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] [Isolation membrane]

[0207] 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.

[0208] 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.

[0209] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0210] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0211] 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.

[0212] 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 1 This is an example of a square-structured secondary battery 5.

[0213] In some implementations, refer to Figure 2The 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.

[0214] 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.

[0215] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0216] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0217] 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.

[0218] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The 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.

[0219] 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.

[0220] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0221] Figure 6 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.

[0222] 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.

[0223] Example

[0224] 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.

[0225] Example 1

[0226] 1) Preparation of fluoropolymers

[0227] First stage polymerization: Add 30 kg of deionized water (conductivity less than or equal to 2 μs / cm), 15 g of sodium perfluorooctanoate, and 54 g of N,N-dimethylbenzylamine to a 50 L reactor and close the reactor.

[0228] Vacuum the reactor, purge with nitrogen, and repeat the process until the oxygen concentration inside the reactor is less than 100 ppm.

[0229] Vinylidene fluoride monomer is introduced into the reactor until the pressure inside the reactor reaches 8.0 MPa;

[0230] The reaction begins when the temperature inside the reactor is raised to 100°C. During the reaction, vinylidene fluoride monomer is continuously introduced to maintain a constant reaction pressure inside the reactor.

[0231] Second stage polymerization: When the mass of vinylidene fluoride monomer introduced is 1411.1g, the reaction pressure is maintained at 8.0MPa and the temperature at 100℃, and another 1411.1g of vinylidene fluoride monomer and 3177.8g of allyl malonic acid monomer are introduced into the reactor, and the reaction continues for 8h.

[0232] When the reaction is complete, the pressure inside the reactor drops to 0.2 MPa, and the unreacted vinylidene fluoride monomer is recovered.

[0233] The reaction product was coagulated, washed, and neutralized with 1625.58g of lithium carbonate, and stirred for 2 hours. Subsequently, it was separated and concentrated to obtain a vinylidene fluoride-allyl lithium malonate copolymer emulsion with a solid content of 25%, wherein the weight average molecular weight of the vinylidene fluoride-allyl lithium malonate copolymer was 100,000.

[0234] 2) Preparation of conductive paste

[0235] 18400g of deionized water and 800g of vinylidene fluoride-lithium allyl malonate copolymer emulsion were added to a 35L mixing tank and stirred at 800rpm for 30min to obtain a pre-mixed adhesive solution.

[0236] Next, 800g of carbon nanotubes were added to the pre-mixed adhesive solution and stirred at 800rpm for 180min. Cooling water circulation was then activated to obtain a conductive slurry. The solid content of the conductive slurry was 5%.

[0237] 3) Preparation of negative electrode sheet

[0238] Artificial graphite (active material), SiO2 (active material), styrene-butadiene rubber (SBR) (binder), sodium carboxymethyl cellulose (CMC) (thickener), and the above-mentioned conductive paste are added to deionized water and mixed evenly to prepare a negative electrode paste. The negative electrode paste is uniformly coated onto the copper foil of the negative electrode current collector once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet. The weight ratio of the deposits of artificial graphite (active material), SiO2 (active material), styrene-butadiene rubber (SBR) (binder), sodium carboxymethyl cellulose (CMC) (thickener), and conductive paste in the negative electrode film layer is 90.8%:5%:3%:1%:0.2%.

[0239] 4) Preparation of positive electrode sheet

[0240] 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.

[0241] 5) Separating membrane

[0242] Polypropylene film is used as the separator.

[0243] 6) Preparation of electrolyte

[0244] 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.

[0245] 7) Battery manufacturing

[0246] In Example 1, 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.

[0247] In Examples 2-5, the molar ratio of each monomer in the fluoropolymer was adjusted, while other parameters remained the same as in Example 1. Specific parameters are shown in Table 1.

[0248] In Examples 6-9, the experimental parameters of the preparation method of the fluoropolymer were adjusted so that the fluoropolymer had different weight-average molecular weights. Other parameters remained the same as in Example 1. Specific parameters are shown in Tables 1 and 2.

[0249] Specifically, the preparation method of the fluoropolymer with a weight-average molecular weight of 60,000 in Example 6 is basically the same as that in Example 1, except that the amount of N,N-dimethylbenzylamine added is adjusted to 59.4g and the reaction temperature is adjusted to 105℃.

[0250] The preparation method of the fluoropolymer with a weight-average molecular weight of 80,000 in Example 7 is basically the same as that in Example 1, except that the amount of N,N-dimethylbenzylamine added is adjusted to 56.7g and the reaction temperature is adjusted to 105℃.

[0251] The preparation method of the fluoropolymer with a weight-average molecular weight of 120,000 in Example 8 is basically the same as that in Example 1, except that the reaction temperature is adjusted to 95°C and the amount of N,N-dimethylbenzylamine added is adjusted to 51.3g.

[0252] The preparation method of the fluoropolymer with a weight-average molecular weight of 150,000 in Example 9 is basically the same as that in Example 1, except that the reaction temperature is adjusted to 95°C and the amount of N,N-dimethylbenzylamine added is adjusted to 48.6g.

[0253] In Examples 10-13, the mass fraction of fluoropolymer in the conductive paste was adjusted, while other parameters remained the same as in Example 1. Specific parameters are shown in Table 1.

[0254] In Examples 14-17, the mass fraction of the conductive agent in the conductive primer slurry was adjusted, while other parameters remained the same as in Example 1. Specific parameters are shown in Table 1.

[0255] In Example 18, the allylmalonic acid monomer was replaced with the 2-pentenic acid monomer, and other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0256] In Example 19, 1411.1g of vinylidene fluoride monomer in the first polymerization stage and 1411.1g in the second polymerization stage were replaced with 960.5g of vinylidene fluoride and 815.3g of trifluorochloroethylene monomer, respectively. Other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0257] In Example 20, lithium carbonate was not added for neutralization after polymerization. Other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0258] In Comparative Example 1, the fluoropolymer in the conductive paste was replaced with the dispersant polyvinylpyrrolidone (PVP), and other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0259] In Comparative Example 2, polyvinylidene fluoride emulsion was used as the fluoropolymer, and other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0260] In Comparative Example 3, lithium allyl malonate emulsion was used as the fluoropolymer, and other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0261] In Comparative Example 4, the allyl malondiic acid monomer was replaced with the 4-pentenoic acid monomer, and other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0262] In Comparative Example 5, conductive carbon black was used to replace conductive paste to directly prepare the negative electrode sheet. Other parameters were the same as in Example 1. For specific parameters, please refer to Table 1.

[0263] In Comparative Example 6, the mass content of conductive carbon black was adjusted to 2.0%. Based on the total mass of the negative electrode film, other parameters were basically the same as those in Comparative Example 5. For specific parameters, please refer to Table 1.

[0264] II. Testing Methods

[0265] 1. Characterization of the properties of fluoropolymers

[0266] (1) Measurement of weight-average molecular weight of fluoropolymers

[0267] A Waters 2695 Isocratic HPLC gel electrophoresis system (differential refractive index detector 2141) was used. A 3.0% polystyrene solution was used as a reference, and a matched column (oil-based: Styragel HT5DMF 7.8×300mm + Styragel HT4) was selected. A 3.0% fluoropolymer 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 read.

[0268] 2. Properties testing of conductive paste

[0269] (1) Viscosity test of conductive paste

[0270] The viscosity of the primer slurry was measured using a rotational viscometer. A suitable rotor was selected and fixed in place. The primer slurry was placed below the rotor, just submerging the scale lines. The instrument model was Shanghai Fangrui NDJ-5S, with a 62# rotor at 30 rpm (measurable viscosity range: 0-1000 mPa·s); a 63# rotor at 30 rpm (measurable viscosity range: 0-2000 mPa·s); and a 63# rotor at 12 rpm (measurable viscosity range: 2000-10000 mPa·s). The test temperature was 25℃, and the test time was 5 minutes. The data was read after the reading stabilized.

[0271] (2) Filtration performance test of conductive paste

[0272] Place a 500ml beaker at the bottom of a 200-mesh filter screen holder. Take 500ml of conductive slurry and place it in the filter screen for filtration. Record the time it takes for the volume of slurry in the beaker to reach 300ml. This time is used to judge the filtration performance of the slurry. If the filtration time is less than 120s, it indicates that the filtration performance of the slurry is good, and it is recorded as "Y". If the slurry cannot pass through the filter screen, it indicates that the filtration performance of the slurry is poor, and it is judged as "N".

[0273] (3) Solid content of conductive paste and the difference in solid content between the upper and lower layers after standing for 24 hours.

[0274] Weigh the copper foil in the weight loss rate measuring instrument and record the weight as M0, then zero the instrument.

[0275] 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.

[0276] Close the equipment and begin drying;

[0277] After completion, record the weighing data as M2, and calculate the solid content as (M2-M0) / (M1-M0);

[0278] The solid content of the upper and lower conductive pastes was measured using the same method after standing for 24 hours. The difference between the solid content of the upper and lower conductive pastes after standing for 24 hours was taken as the solid content of the upper and lower conductive pastes.

[0279] (4) Test of the gel state of conductive paste after standing for 60 days

[0280] 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, record it as "No"; if the slurry has gelled, record it as "Yes".

[0281] Gel formation: The slurry clumps together or fails to flow naturally and continues to flow.

[0282] No gel: The slurry flows naturally and continuously, and flows horizontally on the surface of the steel ruler without clumping.

[0283] 3. Electrode performance testing

[0284] (1) Cohesion of the electrode

[0285] Double-sided tape is used to attach the negative electrode sheet to the steel plate. A strip of negative electrode sheet with a length of 20cm and a width of 20mm is cut and attached to the double-sided tape. A single-sided adhesive paper (width × length = 20mm × 80mm) for testing the cohesion of the negative electrode sheet is placed in the center and covered the strip. A strip of white paper with a width × length = 20mm × 60mm is cut and inserted between the steel plate and the single-sided adhesive paper, with an overlap length of about 15mm. The strip is rolled back and forth 4 times with a roller. The white paper is clamped in the tensile testing machine fixture and the tensile testing machine is turned on to test, so that the single-sided adhesive paper adhering to the negative electrode film layer of the strip separates from the strip. The cohesion value is obtained after the test is completed.

[0286] (2) Electrode rebound rate after 24 hours of cold pressing

[0287] The coated negative electrode sheet is cold-pressed to a fixed compaction density (1.65 g / cm³). 3The thickness of the negative electrode sheet was measured and recorded as h1; after the cold-pressed electrode sheet was left to stand for 24 hours, the thickness of the negative electrode sheet was measured again and recorded as h2.

[0288] The rebound rate (%) of the electrode after 24 hours of cold pressing is (h2-h1) / h1×100%.

[0289] (3) Film resistance of the electrode

[0290] Cut the dried electrode into small round pieces with a diameter of 10mm from the left, center, and right sides. Turn on the Yuaneng Technology electrode resistance meter, place it at the appropriate position of the probe, and click the "Start" button. Once the reading stabilizes, take the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements, which is the film resistance of the electrode.

[0291] 4. Battery performance testing

[0292] (1) Battery DC impedance test

[0293] 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.

[0294] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0295] Fluoropolymers, conductive pastes, 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.

[0296] Table 1. Preparation parameters and results of the fluoropolymers in Examples and Comparative Example 1

[0297]

[0298]

[0299] Table 2. Preparation parameters and test results of the examples and comparative example 1.

[0300]

[0301]

[0302] As can be seen from Tables 1 and 2, the fluoropolymers of Examples 1-20 contain structural units derived from vinylidene fluoride or trifluorochloroethylene, and also contain structural units derived from allyl dilithium, allyl dicitonic acid or lithium 2-pentenedioic acid.

[0303] As can be seen from the comparison of Examples 1-9, Examples 18-20 and Comparative Example 1, compared with the traditional polyvinylpyrrolidone dispersant, the fluoropolymer disclosed in this application can improve the cohesive force of the electrode, reduce the rebound rate of the electrode after 24 hours of cold pressing, improve the quality of the electrode, and at the same time significantly alleviate the gelation of the conductive slurry during storage, improve the anti-gelling and storage properties of the conductive slurry, reduce the film resistance of the electrode, reduce the DC internal resistance of the battery, and thus improve the dynamic performance of the battery.

[0304] As can be seen from the comparison of Examples 1-9, Examples 18-20 and Comparative Example 2, compared with polyvinylidene fluoride, the fluoropolymer provided in this application can reduce the viscosity of the conductive slurry, improve the filterability of the conductive slurry, and make the conductive slurry less prone to gelation during storage, thereby improving the anti-gelling and storage properties of the conductive slurry. Due to the improved dispersion performance of the conductive slurry, the DC impedance of the battery is further reduced.

[0305] A comparison of Examples 1-5, Example 19, and Comparative Example 3 shows that, compared to lithium polyallyl malonate, the vinylidene fluoride-allyl malonate copolymer, vinylidene fluoride-2-pentenic acid copolymer, vinylidene fluoride-trifluorochloroethylene-allyl malonate copolymer, and vinylidene fluoride-allyl malonate copolymer disclosed in this application can improve the cohesiveness of the electrode, reduce the rebound rate after 24 hours of cold pressing, and improve the quality of the electrode. Simultaneously, it can also improve the anti-settling properties of the conductive slurry, improve the adhesion of the electrode, and reduce the DC internal resistance of the battery. A comparison of Examples 1-5 and Comparative Example 4 shows that the vinylidene fluoride-allyl malonate copolymer disclosed in this application can improve the cohesiveness of the electrode, reduce the rebound rate after 24 hours of cold pressing, and improve the quality of the electrode. It can also reduce the viscosity of the conductive slurry, improve the filterability of the conductive slurry, making it less prone to gelation during storage, and improving the anti-gelling and storage properties of the conductive slurry. The improved dispersion properties of the conductive slurry further reduced the DC resistance of the battery.

[0306] As can be seen from the comparison between Example 1 and Example 20, compared with the structural unit derived from allylmalonic acid, the presence of lithium allylmalonic acid-derived in the fluoropolymer can reduce the DC internal resistance of the battery and improve the battery's dynamic performance.

[0307] As can be seen from the comparison between Examples 1-3 and Examples 4-5, the molar content of the structural units derived from vinylidene fluoride is 60%-80%. Based on the total molar number of all structural units in the fluoropolymer, the viscosity of the conductive paste, the cohesive force of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing can be taken into account, thus comprehensively improving the processing performance and performance of the conductive paste.

[0308] As can be seen from the comparison between Examples 1-3 and Examples 4-5, the molar content of the structural units derived from allylpropanedilithium is 20%-40%. Based on the total molar number of all structural units in the fluoropolymer, the viscosity of the conductive paste, the cohesive force of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing can be taken into account, thus comprehensively improving the processing performance and performance of the conductive paste.

[0309] As can be seen from the comparison between Examples 1 and 7-8 and Examples 6 and 9, the weight-average molecular weight of the fluoropolymer is 80,000-120,000, which can take into account the viscosity of the conductive paste, the cohesion of the electrode, and the rebound rate of the electrode after 24 hours of cold pressing, thus comprehensively improving the processing performance and performance of the conductive paste.

[0310] The conductive pastes in Examples 1-20 all include carbon nanotubes, deionized water, and vinylidene fluoride-allyl propylene glycol copolymer, vinylidene fluoride-2-pentenedioic acid copolymer, vinylidene fluoride-trifluorochloroethylene-allyl propylene glycol copolymer, and vinylidene fluoride-allyl malonic acid copolymer.

[0311] As seen in Examples 1 and 10-13, the mass fraction of the fluoropolymer is 0.5%-1.5% based on the total mass of the conductive paste. The paste has a suitable viscosity, while the electrode exhibits a low rebound rate after 24 hours of cold pressing, thus comprehensively improving the processing and performance of the paste.

[0312] As seen in Examples 1 and 14-17, the mass fraction of the conductive agent is 1.5%-4.5% based on the total mass of the conductive slurry. The slurry has a suitable viscosity, while the electrode exhibits a low rebound rate after 24 hours of cold pressing, thus comprehensively improving the processing and performance of the slurry.

[0313] As can be seen from Examples 1-20, the solid content of the conductive paste is 1%-10%, and the viscosity of the conductive paste is 500mPa·s-5000mPa·s. The conductive paste prepared by fluoropolymer does not require the addition of additional dispersants or thickeners to improve processing performance, which helps to improve production efficiency and optimize production process.

[0314] The negative electrode sheets in Examples 1-20 all include 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 contains a deposit of conductive slurry.

[0315] As can be seen from the comparison between Examples 1-20 and Comparative Example 6, compared with the negative electrode sheets prepared by directly adding conductive agent powder commonly used in the prior art, the negative electrode sheet of this application contains conductive agent in the form of conductive slurry deposits, which is beneficial to reduce the rebound rate of the electrode sheet after cold pressing for 24 hours, improve the cohesion of the electrode sheet, improve the quality of the electrode sheet, and at the same time, it can also reduce the film resistance of the electrode sheet and the DC internal resistance of the battery, and improve the dynamic performance of the battery.

[0316] As can be seen from the comparison between Examples 1-20 and Comparative Example 7, compared with the negative electrode sheets commonly prepared by directly adding conductive agent powder in the prior art, the negative electrode sheet disclosed in this application contains conductive agent in the form of conductive slurry deposits, which can effectively reduce the rebound rate of the electrode sheet after cold pressing for 24 hours and improve the quality of the electrode sheet. At the same time, it can also reduce the content of conductive agent that needs to be added to the negative electrode sheet, which is beneficial to improving the energy density of the battery.

[0317] 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 fluoropolymer, characterized in that, It comprises at least one structural unit derived from the monomer shown in Formula I and at least one structural unit derived from the monomer shown in Formula II. Formula I Formula II Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C4 groups. 1-15 Alkyl groups, R4, R5, R6 and R7 contain at least two -COOM, where M is selected from hydrogen, NH4 or an alkali metal; The molar content of the structural units derived from the monomer shown in Formula I is 60%-80%, based on the total molar number of all structural units in the fluoropolymer. The weight-average molecular weight of the fluoropolymer is 80,000 to 120,000.

2. The fluoropolymer according to claim 1, characterized in that, M contains one or more of lithium, sodium, and potassium.

3. The fluoropolymer according to claim 1, characterized in that, R1 is fluorine, and R2 and R3 are each independently selected from hydrogen, fluorine, chlorine or trifluoromethyl.

4. The fluoropolymer according to claim 1, characterized in that, The molar content of the structural units of the monomer derived from Formula II is 20%-40%, based on the total molar number of all structural units in the fluoropolymer.

5. The fluoropolymer according to claim 1, characterized in that, The monomer shown in Formula I contains one or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropylene.

6. The fluoropolymer according to claim 1, characterized in that, The monomer shown in Formula II comprises one or more of allylmalonic acid, 2-pentenonic acid, lithium 2-pentenonic acid, lithium allylmalonic acid, lithium methylenemalonic acid, lithium vinylmalonic acid, lithium allylbutyric acid, lithium pentenonic acid, lithium maleate, lithium trans-pentenonic acid, lithium hexenedioic acid, lithium heptenonic acid, lithium octenonic acid, sodium allylmalonic acid, sodium methylenemalonic acid, sodium vinylmalonic acid, sodium allylbutyric acid, sodium 2-(4-pentenyl)malonic acid, sodium maleate, sodium trans-pentenonic acid, sodium hexenedioic acid, sodium heptenonic acid, sodium octenonic acid, potassium allylmalonic acid, potassium methylenemalonic acid, potassium vinylmalonic acid, and potassium heptenonic acid.

7. The fluoropolymer according to any one of claims 1 to 6, characterized in that, The fluoropolymers include one or more of the following: vinylidene fluoride-allylpropanediol copolymer, vinylidene fluoride-allyl malonic acid copolymer, vinylidene fluoride-sodium allyl malonate copolymer, vinylidene fluoride-2-pentenic lithium copolymer, vinylidene fluoride-trifluorochloroethylene-allylpropanediol copolymer, tetrafluoroethylene-allylpropanediol copolymer, and vinylidene fluoride-hexafluoropropylene-allylpropanediol copolymer.

8. A method for preparing a fluoropolymer, characterized in that, Includes the following steps: Under polymerizable conditions, at least one monomer of Formula I and at least one monomer of Formula II are polymerized to form a polymer product. Formula I Formula II Among them, R1, R2, and R3 are each independently selected from hydrogen, fluorine, chlorine, or C atoms containing at least one fluorine atom. 1-3 Alkyl groups, R4, R5, R6, and R7 are each independently selected from hydrogen or substituted or unsubstituted C4 groups. 1-15 Alkyl groups, R4, R5, R6, and R7 contain at least two -COOH groups; The molar content of the structural units derived from the monomer shown in Formula I in the fluoropolymer is 60%-80%, based on the total molar number of all structural units in the fluoropolymer. The weight-average molecular weight of the fluoropolymer is 80,000 to 120,000.

9. The preparation method according to claim 8, characterized in that, It also includes the following steps: The polymerization product is neutralized with a neutralizing agent, which causes at least a portion of the -COOH in the polymerization product to be converted to -COOM, where M is selected from NH4 or an alkali metal.

10. The preparation method according to claim 9, characterized in that, M contains one or more of lithium, sodium, and potassium.

11. The preparation method according to claim 8, characterized in that, R1 is fluorine, and R2 and R3 are each independently selected from hydrogen, fluorine, chlorine, or trifluoromethyl.

12. The preparation method according to claim 8, characterized in that, The molar content of the monomer shown in Formula I is 60%-80%, based on the total molar number of the monomers shown in Formula I and Formula II.

13. The preparation method according to any one of claims 8 to 12, characterized in that, The molar content of the monomer shown in Formula II is 20%-40%, based on the total molar number of the monomers shown in Formula I and Formula II.

14. The preparation method according to claim 9, characterized in that, The polymerization reaction specifically includes: First stage polymerization: an initiator, an emulsifier, at least one monomer of Formula I and a solvent are provided to carry out the first stage polymerization, wherein the monomer of Formula I is continuously fed in during the first stage polymerization to maintain the initial reaction pressure; Second stage polymerization: After a period of reaction, monomers shown in Formula I and Formula II are fed into the reaction vessel for second stage polymerization, during which monomers shown in Formula I are continuously fed.

15. The preparation method according to claim 14, characterized in that, The polymerization reaction further includes: After the second stage of polymerization is completed, the neutralizing agent is added to the reactor to carry out a neutralization reaction.

16. The preparation method according to claim 14, characterized in that, The mass of the monomer of Formula I introduced in the first stage of polymerization is 30%-70% 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 30%-70% of the total mass of the monomer of Formula I supplied in the polymerization reaction.

17. The preparation method according to claim 9, characterized in that, The neutralizing agent includes one or more of lithium carbonate, sodium carbonate, potassium carbonate, lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia.

18. The use of the fluoropolymer according to any one of claims 1 to 7 in a secondary battery.

19. A conductive paste, characterized in that, The conductive paste comprises a conductive agent, an aqueous medium, and a fluoropolymer as described in any one of claims 1 to 7.

20. The conductive paste according to claim 19, characterized in that, The conductive agent has a mass fraction of 1.5%-4.5%, based on the total mass of the conductive slurry.

21. The conductive paste according to claim 19, characterized in that, The fluoropolymer has a mass fraction of 0.5%-1.5%, based on the total mass of the conductive paste.

22. The conductive paste according to any one of claims 19 to 21, characterized in that, The conductive paste has a solid content of 1%-10% and a viscosity of 500 mPa·s-5000 mPa·s.

23. A negative electrode sheet, characterized in that, It includes 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, the conductive agent comprising a deposit of the conductive slurry according to any one of claims 19 to 22.

24. The negative electrode sheet according to claim 23, characterized in that, The compaction density of the negative electrode sheet is 1.5 g / cm³. 3 -1.8g / cm 3 At that time, the rebound rate of the negative electrode sheet after cold pressing for 24 hours is not higher than 7.0%.

25. The negative electrode sheet according to claim 23, characterized in that, The cohesive force of the negative electrode sheet is not less than 73 N / m.

26. The negative electrode sheet according to claim 23, characterized in that, The cohesive force of the negative electrode sheet is not less than 80 N / m.

27. The negative electrode sheet according to any one of claims 23 to 26, characterized in that, Based on the total mass of the negative electrode film, the mass content of the conductive agent is 0.2%-2%, and the film resistance of the negative electrode film is not higher than 0.15Ω.

28. A secondary battery, characterized in that, Includes the negative electrode sheet according to any one of claims 23 to 27.

29. The secondary battery according to claim 28, characterized in that, The secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

30. An electrical device, characterized in that, Includes the secondary battery selected from claims 28 or 29.

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