Fluorine-containing polymer, primer paste, secondary battery, and power consumption device

Abstract

The present application provides a fluorine-containing polymer, a primer paste, a secondary battery, and a power consumption device. The fluorine-containing polymer includes a structural unit derived from a monomer represented by formula I and a structural unit derived from a monomer represented by formula II, and the molar content of the structural unit derived from the monomer represented by formula I is 70% to 90% of the total number of moles of the structural units in the fluorine-containing polymer, and R1, R2, and R3 are each independently hydrogen, fluorine, chlorine, or C substituted with fluorine. 1~3 alkyl groups, and R, R, and R are each independently hydrogen, substituted or unsubstituted C 1~5 alkyl groups, and R7 is selected from one or more of substituted or unsubstituted C 1~9 The alkyl group is selected from the group consisting of:

Description

[Technical Field]

[0001] The present application relates to the field of secondary battery technology, and in particular to fluorine-containing polymers, primer pastes, secondary batteries, and power consuming devices. [Background technology]

[0002] During the manufacturing process of polar sheets for secondary batteries, a primer layer is applied between the current collector and the active material layer to provide electrical conductivity between the active material layer and the current collector, thereby reducing the contact resistance between the active material layer and the current collector. The primer layer is typically produced by applying a primer paste containing a binder, conductive agent, and additives to the surface of the current collector. However, conventional primer pastes have a short process window, poor filterability, and are prone to precipitation and pipe clogging, which severely impacts the production efficiency of polar sheets. Therefore, to improve paste processability, there is a need to develop a polymer that can act as a binder while also providing good dispersibility in the paste. Summary of the Invention

[0003] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide a fluorine-containing polymer and a primer layer containing the fluorine-containing polymer in order to optimize the process window for producing a primer layer and improve the production efficiency of the primer layer.

[0004] A first aspect of the present application provides a fluorine-containing polymer, comprising a structural unit derived from a monomer represented by formula I and a structural unit derived from a monomer represented by formula II, wherein the molar content of the structural unit derived from the monomer represented by formula I is 70% to 90% based on the total number of moles of structural units in the fluorine-containing polymer; JPEG2025537508000002.jpg21164 where R1, R2, and R3 are each independently hydrogen, fluorine, chlorine, or fluorine-substituted C. 1~3alkyl groups, and R, R, and R are each independently hydrogen, substituted or unsubstituted C 1~5 alkyl groups, and R7 is selected from one or more of substituted or unsubstituted C 1~9 The alkyl group is selected from the group consisting of:

[0005] The fluorine-containing polymer provided by the present application reduces the viscosity of the paste, improves the filterability, and improves the processability of the primer paste compared to the general polyvinylidene fluoride binder used in the prior art. This can meet the production needs of primer paste without the need to add a dispersant to the primer paste, and is useful for optimizing the production process of the primer paste and improving its production quality.

[0006] In any embodiment, R1 is fluorine, R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R5 and R6 are each independently selected from one or two of hydrogen and methyl.

[0007] In any embodiment, the molar content of the structural units derived from the monomer represented by formula II is 10% to 30% relative to the total number of moles of structural units in the fluorine-containing polymer.

[0008] When the molar content of the constituent units derived from the monomer represented by formula II is 10% to 30% of the total molar number of the constituent units of the fluorine-containing polymer, the viscosity of the fluorine-containing polymer is appropriate, the processability and adhesiveness of the paste are comprehensively improved, and the processability and usability of the primer layer can be both achieved.

[0009] In an optional embodiment, the weight average molecular weight of the fluorine-containing polymer is 400,000 to 500,000.

[0010] A fluorine-containing polymer with a weight-average molecular weight of 400,000 to 500,000 has an appropriate viscosity, which comprehensively improves the processability and adhesiveness of the paste, and can achieve both the processability and usability of the primer layer.

[0011] In any embodiment, the monomer shown in Formula I is selected from one or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene.

[0012] In any embodiment, the monomer shown in Formula II is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate.

[0013] A second aspect of the present application provides a method for producing a fluorine-containing polymer, comprising the steps of:

[0014] Under polymerizable conditions, at least one monomer represented by formula I and at least one monomer represented by formula II are polymerized, and the molar content of the monomer represented by formula I is 70% to 90% based on the total molar amount of the monomer represented by formula I and the monomer represented by formula II; JPEG2025537508000003.jpg21164 where R1, R2, and R3 are each independently hydrogen, fluorine, chlorine, or fluorine-substituted C 1~3 alkyl groups, and R, R, and R are each independently hydrogen, substituted or unsubstituted C 1~5 alkyl groups, and R7 is selected from one or more of substituted or unsubstituted C 1~9 The alkyl group is selected from the group consisting of:

[0015] The fluorine-containing polymer produced by this method can improve the stability and adhesion of the primer paste compared to conventional binders, significantly widening the process window of the primer paste and improving the use performance of the primer paste.

[0016] In any embodiment, R1 is fluorine, R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R5 and R6 are each independently selected from one or two of hydrogen and methyl.

[0017] In any embodiment, the molar content of the monomer represented by formula II is 10% to 30% based on the total number of moles of the monomer represented by formula I and the monomer represented by formula II.

[0018] When the molar content of the constituent units derived from the monomer represented by formula II is 10% to 30% of the total molar content of the constituent units of the fluorine-containing polymer, the viscosity of the fluorine-containing polymer is appropriate, and the processability and adhesiveness of the paste are comprehensively improved, thereby achieving both the processability and usability of the primer layer.

[0019] In an optional embodiment, the polymerization reaction comprises a first stage polymerization and a second stage polymerization; First-stage polymerization: A first-stage polymerization is carried out by adding an initiator, a first emulsifier, at least one monomer represented by Formula I and an aqueous medium to a reaction vessel, and in the first-stage polymerization, the monomer represented by Formula I is continuously fed.

[0020] Second-stage polymerization: After reacting for a certain time, an initiator, a second emulsifier, at least one monomer represented by formula II and an aqueous medium are added to the reaction vessel to carry out second-stage polymerization, and in the second-stage polymerization, the monomer represented by formula I is continuously fed.

[0021] The method provided herein first ensures high adhesion of the fluorine-containing polymer by continuously feeding the monomer represented by Formula I to form a fluorine-containing segment, and then introduces the monomer represented by Formula II to reduce contact between the fluorine-containing segment and the external environment, thereby effectively reducing the viscosity of the paste. The fluorine-containing polymer produced by this method can more effectively improve the stability and adhesion of the primer paste than a fluorine-containing polymer produced by simultaneously introducing all the monomers into a reaction vessel, further widening the process window and shelf life of the primer paste and helping to reduce the production cost of the primer layer.

[0022] In any embodiment, the mass of the monomer represented by formula I introduced in the first-stage polymerization is 90% to 95% of the total mass of the monomer represented by formula I supplied in the polymerization reaction, and the mass of the monomer represented by formula I introduced in the second-stage polymerization reaction is 5% to 10% of the total mass of the monomer represented by formula I supplied in the polymerization reaction.

[0023] In an optional embodiment, the initiator provided in the first stage polymerization and the initiator provided in the second stage polymerization are both persulfate salts, the weight percentage of the initiator provided in the first stage polymerization is 0.05% to 0.1% based on the total weight of the monomer represented by Formula I and the monomer represented by Formula II, and the weight percentage of the initiator provided in the second stage polymerization is 0.05% to 0.1% based on the weight of the monomer represented by Formula II.

[0024] In any embodiment, the weight percentage of the first emulsifier is 0.2% to 0.7% based on the total weight of the monomer represented by formula I and the monomer represented by formula II.

[0025] In any embodiment, the weight percentage of the second emulsifier is 0.5% to 1.5% based on the weight of the monomer shown in Formula II.

[0026] In any embodiment, the mass percentage of the aqueous medium provided in the first-stage polymerization is 200% to 500%, and the mass percentage of the aqueous medium provided in the second-stage polymerization is 100% to 200%, based on the total mass of the monomer represented by Formula I and the monomer represented by Formula II.

[0027] In an optional embodiment, the reaction pressure of the first stage polymerization is 5.5 to 7.5 MPa, and the reaction temperature is 75°C to 85°C.

[0028] In an optional embodiment, the reaction pressure of the second-stage polymerization is 4.5 to 6.5 MPa, and the reaction temperature is 86 to 95°C.

[0029] In any embodiment, after reacting for a certain period of time, adding an initiator, a second emulsifier, at least one monomer represented by Formula II, and an aqueous medium into the reaction vessel to carry out second-stage polymerization, The method includes adding an initiator to a reaction vessel, followed by adding a premix containing the initiator, a second emulsifier, at least one monomer represented by formula II, and an aqueous medium.

[0030] In an optional embodiment, the first emulsifier is an alkali metal perfluorooctanoate.

[0031] In any embodiment, the second emulsifier is one or two of polyoxyethylene-4-phenol ether ammonium sulfate, nonylphenol polyoxyethylene ether ammonium sulfate.

[0032] A third aspect of the present application provides use of the fluorine-containing polymer of the first aspect in a secondary battery, optionally wherein the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0033] A fourth aspect of the present application provides a primer paste comprising a binder, a conductive agent, and a solvent, wherein the binder comprises the fluorine-containing polymer of the first aspect of the present application.

[0034] The primer paste is easy to process and manufacture, has good uniformity, and is useful for improving battery production capacity.

[0035] In any embodiment, the mass fraction of the binder is 0.5% to 5% with respect to the mass of the conductive agent.

[0036] In any embodiment, the solid content of the primer paste is 15% to 30%, and the viscosity of the primer paste is 100 mPa·s to 1000 mPa·s.

[0037] Primer pastes with a solids content of 15% to 30% have a viscosity of 100 mPa·s to 1000 mPa·s, which eliminates the need for additional dispersants or thickeners to improve processability, helping to improve production efficiency and optimize the production process. Primer pastes with this viscosity range also offer stability, fluidity, and adhesive properties, improving the adhesion of the primer layer and ensuring uniform application, helping to improve the stability of primer layer batch production.

[0038] In any embodiment, the solvent is an organic solvent.

[0039] In any embodiment, the solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide, and 3-butoxy-N-methylpropionamide.

[0040] A fifth aspect of the present application provides a method for producing a primer layer, comprising the following steps:

[0041] The method includes gravure coating the primer paste of the fourth aspect of the present application onto the surface of a current collector and drying it to obtain a primer layer, the thickness of the primer layer being 1 um to 3 um.

[0042] The primer paste is gravure coated onto the current collector surface and dried to obtain a primer layer with a thickness of 1 to 3 μm, which has lower sheet resistance, ensures the electrical properties of the polar sheet, and at the same time, maintains the adhesive strength of the primer layer.

[0043] A sixth aspect of the present application provides a secondary battery including a positive electrode sheet, a negative electrode sheet including the primer layer of the fifth aspect of the present application, a separator, and an electrolyte.

[0044] In any embodiment, the secondary battery comprises at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0045] A seventh aspect of the present application provides a battery module including the secondary battery according to the sixth aspect of the present application.

[0046] An eighth aspect of the present application provides a battery pack including the secondary battery according to the sixth aspect of the present application or the battery module according to the seventh aspect of the present application.

[0047] A ninth aspect of the present application provides a power consumption device including at least one selected from the secondary battery according to the sixth aspect of the present application, the battery module according to the seventh aspect of the present application, or the battery pack according to the eighth aspect of the present application. [Brief explanation of the drawings]

[0048] [Figure 1] FIG. 1 is a schematic diagram of a gravure coating process according to an embodiment of the present application. [Figure 2] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Figure 3] FIG. 3 is an exploded view of the secondary battery shown in FIG. 2 according to the embodiment of the present invention. [Figure 4] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 5] 1 is a schematic diagram of a battery pack according to an embodiment of the present application; [Figure 6] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to the embodiment of the present invention. [Figure 7] 1 is a schematic diagram of a power consuming device that uses a secondary battery as a power source according to an embodiment of the present application; DETAILED DESCRIPTION OF THE INVENTION

[0049] Hereinafter, with appropriate reference to the drawings, specific disclosed embodiments of the binder, preparation method, electrode, battery, and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and redundant description of actually identical structures may be omitted. This is to avoid the following description becoming unnecessarily long and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0050] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, with the selected lower and upper limits defining the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, the ranges 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range "a to b" represents a shorthand notation for any combination of real numbers a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that this specification has already listed all real numbers between "0-5," and "0-5" is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise stated, all embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0052] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0053] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order, and for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0054] Unless otherwise specified, the terms "comprise" and "include" used in this application may be open-ended or closed-ended. For example, the terms "comprise" and "include" may indicate that other components not listed may be further included or included, or that only the listed components may be included or included.

[0055] Unless otherwise stated, in this application, the term "or" is inclusive. 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 either A being true (or present) and B being false (or absent), or A being false (or absent) and B being true (or present), or both A and B being true (or present).

[0056] Electrode conductivity is one of the most important research topics in secondary batteries. During the manufacturing process of secondary battery polar sheets, a primer layer is applied between the current collector and the active material layer to provide electrical conductivity between the active material layer and the current collector, thereby reducing the contact resistance between the active material layer and the current collector and improving battery performance. In conventional technologies, primer layers are generally manufactured using binders and conductive agents. However, traditional polyvinylidene fluoride binders increase the viscosity of the paste, making it difficult to filter, and making it difficult to achieve a uniform coating. Therefore, it is necessary to add a dispersant during the paste manufacturing process to improve the paste's processability. This undoubtedly complicates the paste production process, impacts production efficiency, and reduces paste stability between batches. To address this technical issue, the present application develops a polymer that can act as a binder and dispersant in the primer paste, improves the filterability and stability of the primer paste, and is advantageous for improving the production efficiency and production quality of the primer layer.

[0057] Based on this, the present application provides a fluorine-containing polymer, comprising a structural unit derived from a monomer represented by formula I and a structural unit derived from a monomer represented by formula II, wherein the molar content of the structural unit derived from the monomer represented by formula I is 70% to 90% based on the total number of moles of the fluorine-containing polymer; JPEG2025537508000004.jpg21164 where R1, R2, and R3 are each independently hydrogen, fluorine, chlorine, or fluorine-substituted C 1~3 alkyl groups, and R, R, and R are each independently hydrogen, substituted or unsubstituted C 1~5 alkyl groups, and R7 is selected from one or more of substituted or unsubstituted C 1~9 The alkyl group is selected from the group consisting of:

[0058] As used herein, the term "fluorine-containing polymer" refers to a polymer containing fluorine elements in its constitutional units.

[0059] In this specification, the term "polymer" refers, on the one hand, to a collection of chemically uniform macromolecules produced via a polymerization reaction, but differing in the aspects of their degree of polymerization, molar mass and chain length, and, on the other hand, also to derivatives of such a collection of macromolecules formed by a polymerization reaction, i.e., products that can be obtained by reaction, for example addition or substitution, of functional groups in the macromolecules and that may be chemically uniform or chemically heterogeneous.

[0060] As used herein, "C 1~5 The term "alkyl group" refers to a straight or branched hydrocarbon chain group composed solely of carbon and hydrogen, the group being free of unsaturation, having from 1 to 5 carbon atoms, and attached to the remainder of the molecule by a single bond. 1~3 The term "alkyl group" and "C 1~9 The term "alkyl group" should be construed accordingly. 1~5 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, and pentyl. In some embodiments, fluorine-substituted C 1~3 The alkyl groups are -CF3, -CH3CH2F, and -CH2FCH2F. C 1~9 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, and n-nonyl.

[0061] As used herein, the term "substituted" refers to at least one hydrogen atom of the compound or chemical moiety being replaced by a substituent of another chemical moiety, each of which is independently selected from the group consisting of hydroxyl, mercapto, amino, cyano, nitro, aldehyde, halogen, alkenyl, alkynyl, aryl, heteroaryl, C 1~6 Alkyl group, C 1~6 It is an alkoxy group.

[0062] As used herein, the term "process window" refers to a process range within which product quality can be guaranteed, including but not limited to a temperature range, a pressure range, a length of storage time, etc. It can be understood that the wider the process window, the lower the requirements for process precision.

[0063] In some embodiments, R1 is fluorine, R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R5 and R6 are each independently selected from one or two of hydrogen and methyl.

[0064] In some embodiments, the monomer shown in Formula I is selected from one or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene.

[0065] In some embodiments, the monomer shown in Formula II is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate.

[0066] In some embodiments, the polymer comprises one or more constitutional units derived from a monomer having Formula I. In some embodiments, the polymer comprises one or more constitutional units derived from a monomer having Formula II. In some embodiments, the polymer comprises one or more constitutional units derived from a monomer having Formula II. In some embodiments, the polymer is selected from vinylidene fluoride-methyl acrylate copolymer, vinylidene fluoride-ethyl acrylate copolymer, vinylidene fluoride-butyl acrylate copolymer, vinylidene fluoride-isoamyl acrylate copolymer, vinylidene fluoride-isooctyl acrylate copolymer, vinylidene fluoride-methyl methacrylate copolymer, vinylidene fluoride-ethyl methacrylate copolymer, vinylidene fluoride-2-hydroxyethyl acrylate copolymer, vinylidene fluoride-2-hydroxypropyl acrylate copolymer, vinylidene fluoride -tetrafluoroethylene-butyl acrylate copolymer, vinylidene fluoride-tetrafluoropropene-methyl acrylate copolymer, vinylidene fluoride-vinyl fluoride-butyl acrylate copolymer, vinylidene fluoride-chlorotrifluoroethylene-butyl acrylate copolymer, vinylidene fluoride-hexafluoropropylene-butyl acrylate copolymer, vinylidene fluoride-hexafluoropropylene-methyl acrylate copolymer, vinylidene fluoride-hexafluoropropylene-isooctyl acrylate copolymer.

[0067] In some embodiments, the molar content of the constitutional units derived from the monomer represented by Formula I may be selected from 70%, 75%, 80%, 85%, or 90% based on the total number of moles of constitutional units in the fluorine-containing polymer.

[0068] The fluorine element in the structural unit derived from the monomer represented by formula I and the hydroxyl and / or carboxyl groups on the current collector surface can form hydrogen bonds, which provides good adhesion to the primer layer and reduces the risk of peeling during production and use, leading to safety hazards. The structural unit derived from the monomer represented by formula II can effectively reduce the fluorine content of the fluorine-containing polymer, and by setting the mass content of the structural unit derived from the monomer represented by formula I to 70% to 90%, it helps to adjust the viscosity of the paste, alleviating the phenomenon of excessive viscosity of the primer paste due to fluorine element and improving the processability of the paste.

[0069] The fluorine-containing polymer provided by the present application reduces the viscosity of the paste, improves the filterability, and improves the processability of the primer paste compared to the general polyvinylidene fluoride binder used in the prior art. This can meet the production needs of primer paste without the need to add a dispersant to the primer paste, and is useful for optimizing the production process of the primer paste and improving its production quality.

[0070] In some embodiments, the molar content of the structural units derived from the monomer represented by Formula II is 10% to 30% relative to the total number of moles of structural units in the fluorine-containing polymer. In some embodiments, the molar content of the structural units derived from the monomer represented by Formula II may be selected from any one of 12%, 15%, 18%, 20%, 22%, 25%, and 30% relative to the total number of moles of structural units in the fluorine-containing polymer.

[0071] When the molar content of the constituent units derived from the monomer represented by formula II is 10% to 30% of the total molar content of the constituent units of the fluorine-containing polymer, the viscosity of the fluorine-containing polymer is appropriate, so that the polar sheet has good adhesive strength. At the same time, the appropriate viscosity ensures that the paste has good fluidity and filterability, which comprehensively improves the processability and adhesiveness of the paste and achieves both the processability and use performance of the primer layer.

[0072] In some embodiments, the weight average molecular weight of the fluorine-containing polymer is 400,000 to 500,000. In some embodiments, the weight average molecular weight of the fluorine-containing polymer may be selected from any one of 430,000, 450,000, and 480,000.

[0073] As used herein, the term "weight average molecular weight" refers to the sum of the products of the weight fractions of molecules of different molecular weights in a polymer and their corresponding molecular weights.

[0074] In this application, the weight-average molecular weight of a polymer can be measured using methods known in the art, for example, gel chromatography, such as a Waters 2695 Isocratic HPLC Gel Chromatograph (Differential Refractive Index Detector 2141). In some embodiments, the measurement method uses a 3.0% mass fraction polystyrene solution sample as a reference and selects a suitable chromatography column (oil-based: Styragel HT5 DMF 7.8 * 300 mm + Styragel HT4). A 3.0% fluorine-containing polymer binder solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day for later use. During measurement, tetrahydrofuran is first aspirated into a syringe and washed, and this process is repeated several times. Then, 5 ml of test solution is aspirated, the air is expelled from the syringe, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the injection port. After the display stabilizes, data is acquired and the weight-average molecular weight is read.

[0075] Fluorine-containing polymers with a weight-average molecular weight of 400,000 to 500,000 have an appropriate viscosity, which allows the polar sheet to have good adhesion. At the same time, the appropriate viscosity is advantageous for subsequent coating operations, comprehensively improving the processability and adhesion of the paste, and achieving both the processability and usability of the primer layer.

[0076] In one embodiment of the present application, there is provided a method for producing a fluorine-containing polymer, comprising the steps of:

[0077] Under polymerizable conditions, at least one monomer represented by formula I and at least one monomer represented by formula II are polymerized, and the molar content of the monomer represented by formula I is 70% to 90% based on the total molar amount of the monomer represented by formula I and the monomer represented by formula II; JPEG2025537508000005.jpg21164 where R1, R2, and R3 are each independently hydrogen, fluorine, chlorine, or fluorine-substituted C 1~3 alkyl groups, and R, R, and R are each independently hydrogen, substituted or unsubstituted C 1~5 alkyl groups, and R7 is selected from one or more of substituted or unsubstituted C 1~9 The alkyl group is selected from the group consisting of:

[0078] As used herein, the term "polymerization conditions" includes conditions such as temperature, pressure, reactant concentrations, optional solvents / diluents, reactant mixing / addition parameters, and other conditions conducive to the reaction of one or more monomers in at least one polymerization reactor, selected by one skilled in the art.

[0079] The fluorine-containing polymer produced by this method can improve the stability and adhesion of the primer paste compared to conventional binders, significantly widening the process window of the primer paste and improving the use performance of the primer paste.

[0080] In some embodiments, R1 is fluorine, R2 and R3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl, and R5 and R6 are each independently selected from one or two of hydrogen and methyl.

[0081] In some examples, the molar content of the monomer represented by formula II is 10% to 30% based on the total number of moles of the monomer represented by formula I and the monomer represented by formula II. In some embodiments, the molar content of the constitutional unit derived from the monomer represented by formula II may be selected from any one of 12%, 15%, 18%, 20%, 22%, 25%, and 30% based on the total number of moles of the monomer represented by formula I and the monomer represented by formula II.

[0082] When the molar content of the constituent units derived from the monomer represented by formula II is 10% to 30% of the total molar content of the constituent units of the fluorine-containing polymer, the viscosity of the fluorine-containing polymer is appropriate, and the processability and adhesiveness of the paste are comprehensively improved, thereby achieving both the processability and usability of the primer layer.

[0083] In some embodiments, the polymerization reaction comprises a first stage polymerization and a second stage polymerization; First-stage polymerization: A first-stage polymerization is carried out by adding an initiator, a first emulsifier, at least one monomer represented by formula I and an aqueous medium to a reaction vessel, and in the first-stage polymerization, the monomer represented by formula I is continuously fed.

[0084] Second-stage polymerization: After reacting for a certain time, an initiator, a second emulsifier, at least one monomer represented by formula II and an aqueous medium are added to the reaction vessel to carry out second-stage polymerization, and in the second-stage polymerization, the monomer represented by formula I is continuously fed.

[0085] As used herein, the term "continuously feeding" refers to the slow, small, incremental addition of monomer.

[0086] The method provided herein first ensures high adhesion of the fluorine-containing polymer by continuously feeding the monomer represented by Formula I to form a fluorine-containing segment, and then introduces the monomer represented by Formula II to reduce contact between the fluorine-containing segment and the external environment, thereby effectively reducing the viscosity of the paste. The fluorine-containing polymer produced by this method can more effectively improve the stability and adhesion of the primer paste than a fluorine-containing polymer produced by simultaneously introducing all the monomers into a reaction vessel, further widening the process window and shelf life of the primer paste and helping to reduce the production cost of the primer layer.

[0087] In some embodiments, the initiator provided in the first-stage polymerization and the initiator provided in the second-stage polymerization are both persulfate salts, the weight percentage of the initiator provided in the first-stage polymerization is 0.05% to 0.1% based on the total weight of the monomer represented by Formula I and the monomer represented by Formula II, and the weight percentage of the initiator provided in the second-stage polymerization is 0.05% to 0.1% based on the weight of the monomer represented by Formula II.

[0088] In some embodiments, the initiator persulfate may be selected to be potassium persulfate, which effectively decomposes at temperatures above 60° C. to generate radical ions or ion radicals, making it suitable as an initiator for emulsion polymerization.

[0089] In some embodiments, the weight percent of initiator provided in the first-stage polymerization is 0.05%, 0.07%, 0.09%, or 0.1%, based on the total weight of the monomers of Formula I and Formula II.

[0090] In some embodiments, the weight percent of initiator provided in the second stage polymerization is 0.05%, 0.07%, 0.09%, or 0.1%, based on the weight of the monomer shown in Formula II.

[0091] In some embodiments, the weight percent of the first emulsifier is 0.2% to 0.7% based on the total weight of the monomer represented by Formula I and the monomer represented by Formula II. In some embodiments, the weight percent of the first emulsifier is 0.2%, 0.5%, or 0.7% based on the total weight of the monomer represented by Formula I and the monomer represented by Formula II.

[0092] In some embodiments, the first emulsifier is an alkali metal perfluorooctanoate.

[0093] In some embodiments, the weight percent of the second emulsifier is 0.5% to 1.5% based on the weight of the monomer of Formula II. In some embodiments, the weight percent of the second emulsifier is 0.5%, 0.75%, 1.0%, 1.25%, or 1.5% based on the weight of the monomer of Formula II.

[0094] In some embodiments, the second emulsifier is one or two of polyoxyethylene-4-phenol ether ammonium sulfate, nonylphenol polyoxyethylene ether ammonium sulfate.

[0095] In some embodiments, the weight percent of the aqueous medium provided in the first polymerization stage is 200% to 500% relative to the total weight of the monomers represented by Formula I and Formula II, and the weight percent of the aqueous medium provided in the second polymerization stage is 100% to 200%. In some embodiments, the weight percent of the aqueous medium provided in the first polymerization stage is 200%, 300%, 400%, or 500% relative to the total weight of the monomers represented by Formula I and Formula II, and the weight percent of the aqueous medium provided in the second polymerization stage is 100%, 150%, or 200%. In some embodiments, the aqueous medium is a water solvent, and deionized water or a mixture of deionized water with another hydrophilic solvent such as alcohol or ethyl acetate may be selected.

[0096] In some embodiments, the reaction pressure in the first stage polymerization is 5.5 to 7.5 MPa, and the reaction temperature is 75 to 85° C. In some embodiments, the reaction pressure in the first stage polymerization is 5.5 MPa, 6.5 MPa, or 7.5 MPa, and the reaction temperature is 75° C., 80° C., or 85° C.

[0097] In some embodiments, the reaction pressure in the second stage polymerization is 4.5 to 6.5 MPa, and the reaction temperature is 86 to 95° C. In some embodiments, the reaction pressure in the second stage polymerization is 4.5 MPa, 5.5 MPa, or 6.5 MPa, and the reaction temperature is 86° C., 90° C., or 95° C.

[0098] In some embodiments, the mass of the monomer represented by formula I introduced in the first-stage polymerization is 90% to 95% of the total mass of the monomer represented by formula I supplied in the polymerization reaction, and the mass of the monomer represented by formula I introduced in the second-stage polymerization is 5% to 10% of the total mass of the monomer represented by formula I supplied in the polymerization reaction. In some embodiments, the mass of the monomer represented by formula I introduced in the first-stage polymerization is 90%, 92%, or 95% of the total mass of the monomer represented by formula I supplied in the polymerization reaction, and the mass of the monomer represented by formula I introduced in the second-stage polymerization is 5%, 7%, or 10% of the total mass of the monomer represented by formula I supplied in the polymerization reaction.

[0099] In some embodiments, after reacting for a certain period of time, adding an initiator, a second emulsifier, at least one monomer represented by Formula II, and an aqueous medium into the reaction vessel to perform a second stage polymerization, The method includes adding an initiator to a reaction vessel, followed by adding a premix containing the initiator, a second emulsifier, at least one monomer represented by formula II, and an aqueous medium.

[0100] In one embodiment of the present application, there is provided a use of the fluorine-containing polymer according to any of the embodiments in a secondary battery, and optionally the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery. In some embodiments, the fluorine-containing polymer is used as a binder in the secondary battery. In some embodiments, the fluorine-containing polymer is used as a binder of a primer layer in the secondary battery.

[0101] [Primer paste] In one embodiment of the present application, there is provided a primer paste including a binder including a fluorine-containing polymer in any embodiment, a conductive agent, and a solvent.

[0102] As used herein, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or dispersion in a carrier medium.

[0103] In this application, the term "conductive agent" refers to a substance that acts to collect minute currents, and includes, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the solvent is an organic solvent.

[0105] An organic solvent is a solvent made of an organic compound containing carbon atoms. Organic solvents can dissolve some water-insoluble substances. By using an organic solvent as the solvent for the primer layer, the primer paste can be properly prepared for the primer layer of the negative electrode sheet. The primer layer is less likely to dissolve during the manufacturing process of the negative electrode film layer, and has high stability.

[0106] In some embodiments, the solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide, and 3-butoxy-N-methylpropionamide.

[0107] The primer paste is easy to process and manufacture, has good uniformity, and is useful for improving battery production capacity.

[0108] In some embodiments, the mass fraction of the binder is 0.5% to 5% relative to the mass of the conductive agent. In some embodiments, the mass content of the binder may be selected from any one of 0.5%, 1.0%, 2.0%, 4.0%, and 5.0% relative to the mass of the conductive agent.

[0109] When the binder mass content is within an appropriate range, sufficient adhesion is maintained between the primer layer and the current collector, preventing the primer layer from falling off during cell use. At the same time, when the binder mass content is within an appropriate range, the primer paste has an appropriate viscosity, which allows the paste to have good fluidity and filterability, which is advantageous for subsequent coating operations.

[0110] In some embodiments, the solids content of the primer paste is 15% to 30%, and the viscosity of the primer paste is 100 mPa·s to 1000 mPa·s. In some embodiments, when the solids content of the primer paste is 15% to 30%, the viscosity of the primer paste is 100 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, or 1000 mPa·s.

[0111] If the viscosity of the primer paste is within an appropriate range, it is advantageous for the subsequent application and drying operations, and furthermore, an appropriate viscosity can improve the stability of the paste and give the paste good fluidity and filterability.

[0112] In the present application, the viscosity of the fluorine-containing polymer primer paste can be measured by selecting a method known in the art, for example, by using a rotational viscometer.

[0113] Primer pastes with a solids content of 15% to 30% have a viscosity of 100 mPa·s to 1000 mPa·s, which eliminates the need for additional dispersants or thickeners to improve processability, helping to improve production efficiency and optimize the production process. Primer pastes with this viscosity range also offer stability, fluidity, and adhesive properties, improving the adhesion of the primer layer and ensuring uniform application, helping to improve the stability of primer layer batch production.

[0114] In one embodiment of the present application, there is provided a method for producing a primer layer, comprising the following steps:

[0115] In any embodiment, the primer paste is gravure coated onto the surface of the current collector, and the primer paste is dried to obtain a primer layer.

[0116] In some embodiments, the gravure coating process is as shown in Figure 1, where a portion of a gravure roll 62 in a gravure coating apparatus 6 is immersed in the paste in the paste grooves 65, and the paste moves as the gravure roll 62 rotates. A blade 64 scrapes off the paste from the smooth portion of the gravure roll 62, and the paste remaining in the surface recesses of the gravure roll 62 is transferred to the surface of a current collector 63 by the pressure of a pressure roll 61, where the rotation direction of the gravure roll 62 is opposite to the movement direction of the pressure roll 61. The depth of the surface recesses of the gravure roll 62 can be adjusted depending on the desired thickness of the primer layer, and the depth of the recesses can optionally be 10 to 100 µm.

[0117] The primer layer produced by gravure coating has a rough surface, which can improve the adhesion between the primer layer and the film layer or current collector through the anchoring effect, so that the polar sheet has better adhesion.

[0118] In some embodiments, the thickness of the primer layer is 1 um to 3 um.

[0119] The primer paste is gravure coated onto the surface of the current collector and dried to obtain a primer layer with a thickness of 1 to 3 um. This primer layer has excellent adhesion and low sheet resistance, and can ensure the mechanical, electrical, and chemical properties of the polar sheet.

[0120] In one embodiment of the present application, there is provided a secondary battery including a positive electrode sheet, a negative electrode sheet including the primer layer of any embodiment, a separator, and an electrolyte. In some embodiments, the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0121] During the charge and discharge process of a battery, active ions are inserted and removed between the positive and negative electrode sheets. The electrolyte serves to conduct ions between the positive and negative electrode sheets. The separator, placed between the positive and negative electrode sheets, primarily serves to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0122] [Positive electrode sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector.

[0123] As an example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two facing surfaces of the positive electrode current collector.

[0124] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of the metal foil include aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0125] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries known in the art. For example, the positive electrode active material may include at least one of an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and a modified compound thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (may be abbreviated as "LiNi") 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (may be abbreviated as "LiNi") 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (may be abbreviated as "LiNi") 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (may be abbreviated as "LiNi") 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. The lithium-containing phosphate having an olivine structure may include, but is not limited to, for example, at least one of lithium iron phosphate (e.g., LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0126] In some embodiments, the positive electrode film layer may further include a binder, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0127] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the positive electrode sheet can be manufactured by the following method: Components for manufacturing the positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode paste, which is then applied to a positive electrode current collector, followed by processes such as drying and cold pressing, to obtain a positive electrode sheet.

[0129] [Negative electrode sheet] The negative electrode sheet includes a negative electrode current collector, a primer layer disposed on at least one surface of the negative electrode current collector, and a negative electrode film layer disposed on the primer layer, and the negative electrode film layer includes a negative electrode active material.

[0130] As an example, the negative electrode current collector has two surfaces facing each other in the thickness direction thereof, and the negative electrode film layer is provided on one or both of the two facing surfaces of the negative electrode current collector.

[0131] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. The metal foil may be, for example, a copper foil. The composite current collector may include a polymer base layer 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 (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0132] In some embodiments, the negative electrode active material may be a battery negative electrode active material known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicone-based material, a tin-based material, and lithium titanate. The silicone-based material may be selected from at least one of a silicone element, a silicone oxide, a silicone carbon composite, a silicone nitrogen composite, and a silicone alloy. The tin-based material may be selected from at least one of a tin element, a tin oxide, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative electrode active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0133] In some embodiments, the negative electrode membrane layer optionally further comprises a binder, which 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).

[0134] In some embodiments, the negative electrode film layer further optionally includes a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0135] In some embodiments, the negative electrode film layer optionally further comprises other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0136] In some embodiments, a negative electrode sheet can be manufactured by the following method: Components for manufacturing the primer layer, such as a fluorine-containing polymer and a conductive agent, are dispersed in N-methyl-2-methylpyrrolidone to form a primer paste, which is then gravure-coated onto the surface of a copper foil current collector to obtain a current collector with a primer layer. Components for manufacturing the negative electrode film layer, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode paste, which is then applied to a current collector with a primer layer, followed by drying, cold pressing, and other processes to obtain a negative electrode sheet.

[0137] [Electrolyte] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte may be liquid, gel, or all solid.

[0138] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0139] In some embodiments, the electrolyte salt may be chosen 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0140] In some embodiments, the solvent may be chosen from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene 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, ethyl methyl sulfone, and diethyl sulfone.

[0141] In some embodiments, the electrolyte solution further optionally contains additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives that can improve some battery performance, such as an additive that improves the overcharge performance of the battery, or an additive that improves the high-temperature or low-temperature performance of the battery.

[0142] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator with good chemical stability and mechanical stability may be selected.

[0143] In some embodiments, the separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without any particular limitations. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without any particular limitations.

[0144] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be wound or stacked to form an electrode assembly.

[0145] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0146] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The pouch may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0147] The present application does not particularly limit the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. For example, Fig. 2 shows a secondary battery 5 having a rectangular structure as an example.

[0148] In some embodiments, referring to FIG. 3 , the exterior material 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, forming a receiving cavity surrounded by the bottom plate and side plates. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 may cover the opening and seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be wound or stacked to form an electrode assembly 52. ​​The electrode assembly 52 is packaged in the receiving cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select the number according to actual needs.

[0149] In some embodiments, the secondary batteries can be assembled into a battery module, and the number of secondary batteries included in the battery module can be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0150] FIG. 4 shows an example of a battery module 4. Referring to FIG. 4, in the battery module 4, a plurality of secondary batteries 5 can be arranged in order along the length of the battery module 4. Of course, any other arrangement method may also be used. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0151] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in this accommodating space.

[0152] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0153] 5 and 6 show an example of a battery pack 1. Referring to FIGS. 5 and 6, the battery pack 1 may include a battery case and a plurality of battery modules 4 installed in the battery case. The battery case includes an upper housing 2 and a lower housing 3, and the upper housing 2 can be fitted over the lower housing 3 to form a sealed space for accommodating the plurality of battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0154] The present application also provides a power consuming device, the power consuming device including at least one of a secondary battery, a battery module, or a battery pack according to the present application. The secondary battery, the battery module, or the battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming 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, satellites, energy storage systems, etc.

[0155] The power consumption device can be selected from a secondary battery, a battery module, or a battery pack according to its usage requirements.

[0156] 7 shows an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the demand for high power output and high energy density of the secondary battery of this power consuming device, a battery pack or battery module can be used.

[0157] Other examples of the device may be a mobile phone, a tablet computer, a laptop computer, etc. These devices are generally required to be lightweight and can use a secondary battery as a power source.

[0158] Example The following describes examples of the present application. The examples described below are illustrative and are intended only to interpret the present application and should not be understood as limitations on the present application. If specific techniques or conditions are not specified in the examples, they will be carried out according to the techniques or conditions described in literature in the field or in accordance with the product specifications. If the manufacturer of the reagents or instruments used is not specified, they are all ordinary products that are commercially available.

[0159] 1. Manufacturing method Example 1 1) Production of fluorine-containing polymers 26 kg of deionized water, 37.3 g of sodium perfluorooctanoate, and 112 g of 5% potassium persulfate solution, of which the conductivity of the deionized water is less than 2 μs / cm, are added to the reactor in order, and the reactor is closed.

[0160] The inside of the reactor is evacuated and filled with nitrogen gas, and this operation is repeated until the oxygen concentration inside the reactor is less than 100 ppm.

[0161] Vinylidene fluoride monomer is introduced into the reactor, and the reaction begins when the pressure inside the reactor reaches 7.5 MPa and the temperature inside the reactor rises to 85°C. During the reaction, vinylidene fluoride monomer is continuously introduced to maintain the reaction pressure inside the reactor constant.

[0162] 11.2 kg of deionized water, 29.8 g of polyoxyethylene-4-phenol ether ammonium sulfate, and 23.3 mol of butyl acrylate were added to a stirring tank and stirred uniformly, and the conductivity of the deionized water was 2 μs / cm or less to obtain a premixed liquid.

[0163] When the total amount of vinylidene fluoride monomer introduced is 66.5 mol, add 44.8 g of 5% ammonium persulfate, adjust the reaction pressure to 6.0 MPa, raise the temperature to 90 ° C, slowly add the pre-mixture to the reactor, the time for adding all the pre-mixture is 2.5 hours, and at the same time, gradually add the remaining 3.5 mol of vinylidene fluoride monomer.

[0164] When the pressure inside the vessel drops to 0.2 MPa, the reaction is stopped.

[0165] The reaction product is cooled to room temperature, and then subjected to coagulation, washing, separation, drying, and pulverization to obtain a vinylidene fluoride-butyl acrylate copolymer binder.

[0166] 2) Primer paste manufacturing 5.88 kg of conductive carbon black and 0.12 kg of vinylidene fluoride-butyl acrylate copolymer binder are weighed and added in this order to a stirring tank, and the stirring speed is set to 300 rpm, followed by stirring for 10 minutes.

[0167] 14 kg of N-methylpyrrolidone is weighed and added to the stirring tank, and the stirring speed is set to 1200 rpm and stirred for 120 minutes.

[0168] Furthermore, 10 kg of N-methylpyrrolidone is weighed and added to the stirring tank, and the stirring speed is set to 1500 rpm and stirred for 120 minutes.

[0169] The paste is filtered through a 200 mesh filter to obtain a primer paste.

[0170] 3) Preparation of primer layer The primer paste is coated using the gravure coating device shown in Figure 1. First, the primer paste is poured into the paste grooves, and then the gravure roll is rotated to carry the primer paste. A blade is used to scrape off the primer paste from the smooth areas, leaving the remaining primer paste only in the recesses on the gravure roll surface. The recesses are 50 μm deep, and the pressure of the pressure roll transfers the primer paste in the recesses to the surface of the copper foil current collector substrate, where it is dried to obtain a primer layer with a thickness of 2 μm.

[0171] 4) Manufacturing of negative electrode sheets Graphite material, conductive agent carbon black, styrene butadiene binder, carboxymethyl cellulose sodium, and N-methylpyrrolidone (NMP) were mixed uniformly in a weight ratio of 97.15:0.04:1.95:0.5:0.36 to obtain a negative electrode paste, the solid content of which was 64%.

[0172] The negative electrode paste is uniformly applied onto the primer layer, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0173] In Examples 2 and 3, the compounding ratio of each monomer in the fluorine-containing polymer was adjusted, and other parameters remained the same as in Example 1. The specific parameters are as shown in Tables 1 and 2.

[0174] In Examples 4 to 7, the reaction conditions for synthesizing the fluorine-containing polymer were adjusted so that the fluorine-containing polymer had different weight-average molecular weights, while other parameters remained the same as in Example 1. The specific parameters are as shown in Tables 1 and 2. Specifically, the method for producing the fluorine-containing polymer having a weight-average molecular weight of 300,000 in Example 4 was substantially the same as in Example 1, except that the amount of 5% potassium persulfate solution added was adjusted to 99.00 g.

[0175] The method for preparing a fluorine-containing polymer having a weight average molecular weight of 400,000 in Example 5 is substantially the same as that in Example 1, except that the amount of potassium persulfate solution with a concentration of 5% is adjusted to 99.45 g.

[0176] The method for producing a fluorine-containing polymer having a weight-average molecular weight of 500,000 in Example 6 is substantially the same as that in Example 1, except that the reaction temperature is adjusted to 80°C and the amount of 5% potassium persulfate solution added is adjusted to 89.45g.

[0177] The method for producing a fluorine-containing polymer having a weight-average molecular weight of 600,000 in Example 7 is substantially the same as that in Example 1, except that the reaction temperature is adjusted to 80°C and the amount of 5% potassium persulfate solution added is adjusted to 81.00 g.

[0178] In Examples 8 to 11, the mass fraction of the binder in the primer paste was adjusted, and other parameters remained the same as in Example 1. The specific parameters are as shown in Tables 1 and 2.

[0179] In Examples 12 to 15, the solid content of the primer paste was adjusted, and other parameters remained the same as those in Example 1, and the specific parameters are as shown in Tables 1 and 2.

[0180] In Example 16, the ethyl acrylate monomer was replaced with isooctyl acrylate monomer, and the other parameters were the same as those in Example 1, and the specific parameters are as shown in Tables 1 and 2.

[0181] In Example 17, the primer layer was prepared using the blade coating method, and the other methods were the same as those in Example 1, with the specific parameters as shown in Tables 1 and 2.

[0182] In Example 18, the manufacturing method remains the same as that of Example 1, except that the binder in the primer layer is vinylidene fluoride-butyl acrylate copolymer manufactured by conventional methods, and the synthesis method is as follows:

[0183] 37.2 kg of deionized water (conductivity of 2 μs / cm or less), 37.3 g of perfluorooctanoic acid sodium salt, 112 g of 5% potassium persulfate solution, 44.8 g of 5% ammonium persulfate solution, and 29.8 g of polyoxyethylene-4-phenol ether ammonium sulfate are added to the reaction vessel in this order, and the reaction vessel is closed.

[0184] The inside of the reactor is evacuated and filled with nitrogen gas, and this operation is repeated until the oxygen concentration inside the reactor is less than 100 ppm.

[0185] Vinylidene fluoride monomer and 23.3 mol of butyl acrylate were introduced into the reactor until the pressure inside the reactor reached 7.5 MPa.

[0186] The reaction starts when the temperature inside the vessel rises to 85°C. During the reaction, vinylidene fluoride monomer is continuously introduced to maintain the reaction pressure inside the vessel constant, and the number of moles of vinylidene fluoride monomer introduced is 70 mol.

[0187] The reaction is stopped when the pressure inside the vessel drops to 0.2 MPa.

[0188] The mixture is cooled to room temperature, and then subjected to coagulation, washing, separation, drying, and pulverization to obtain a fluorine-containing polymer, namely, vinylidene fluoride-butyl acrylate copolymer.

[0189] In Comparative Example 1, the manufacturing method remains the same as that of Example 1, the difference is that in Comparative Example 1, vinylidene fluoride polymer is used as the binder of the primer paste, which is the product number of Arkema, France, HSV900.

[0190] Comparative Example 2 is substantially the same as Comparative Example 1, except that the manufacturing method of the primer layer was adjusted, and the specific manufacturing method is as follows.

[0191] The primer paste is applied to the surface of the copper foil current collector substrate using a blade and dried to obtain a primer layer with a thickness of 2 um.

[0192] In Comparative Examples 3 and 4, the compounding ratio of each monomer in the fluorine-containing polymer was adjusted, and other parameters remained the same as in Example 1. Specific parameters are as shown in Tables 1 and 2.

[0193] The relevant parameters of the primer pastes and coating layers of Examples 1 to 18 and Comparative Examples 1 to 4 are shown in Tables 1 and 2 below.

[0194] Furthermore, the primer pastes and coating layers obtained in Examples 1 to 18 and Comparative Examples 1 to 4 were subjected to property tests.

[0195] II. Test Method 1. Weight average molecular weight test A Waters 2695 Isocratic HPLC gel chromatograph (refractive index detector 2141) is used. A 3.0% mass fraction polystyrene solution sample is used as a reference and a suitable chromatography column (oil-based: Styragel HT5 DMF 7.8 x 300 mm + Styragel HT4) is selected. A 3.0% fluorine-containing polymer solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day for later use. For measurement, first, tetrahydrofuran is aspirated into the syringe and washed, and this process is repeated several times. Then, 5 ml of the test solution is aspirated, the air is expelled from the syringe, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the injection port. After the display stabilizes, data is acquired and the weight-average molecular weight is read.

[0196] 2. Viscosity test of primer paste Use a rotational viscometer to measure the viscosity of the paste. Select an appropriate rotor, secure the viscometer rotor, and place the primer paste under the rotor so that it just immerses at the rotor's graduations. Model number: Shanghai Fangrui NDJ-5S. Rotor 62#: Measurable paste viscosity range at 30 rpm is 0-1000 mPa·s. Rotor 63#: Measurable paste viscosity range at 30 rpm is 0-2000 mPa·s. Test temperature: 25°C. Test time: 5 minutes. Wait for the display to stabilize before reading the data.

[0197] 3. Filtration characteristic test of primer paste Take a 500ml beaker and place it on the bottom of a 200 mesh filter holder. Take 500ml of primer paste and put it into the filter to filter. If the filtration time when the volume of the paste in the beaker reaches 300ml is less than 120 seconds, it indicates that the filtration performance of the paste is good and is judged as "Y". If the paste does not pass through the filter within 120 seconds, it indicates that the filtration performance of the paste is poor and is judged as "N".

[0198] 4. Difference in solid content of primer paste and solid content after 24 hours of standing Take the copper foil and weigh it with a weight loss rate measuring instrument, set it as M0, and clear the display on the weight loss rate measuring instrument.

[0199] Take the primer paste, apply a small amount to the copper foil, and then weigh it with a weight loss rate measuring instrument to obtain M1.

[0200] Close the device and begin drying.

[0201] After completion, the weighing data is recorded and designated as M2, and the solid content is calculated as (M2-M0) / (M1-M0).

[0202] Using the same method, measure the solids content of the upper and lower layer primer pastes after 24 hours of standing, and subtract the solids content of the upper layer primer paste from the solids content of the lower layer primer paste to obtain the difference in solids content of the primer pastes after 24 hours of standing.

[0203] 5. Adhesion strength of polar sheet Referring to the GB-T2790-1995 national standard "Test Method for 180° Peel Strength of Binders," the adhesion test procedure for the examples and comparative examples in this application was as follows: A 30mm wide, 150mm long sample was cut using a cutter, and a 20mm wide, 100mm long double-sided tape was attached to a steel plate. The negative electrode film layer of the cut polar sheet sample was then attached to the double-sided tape, and rolled three times in the same direction using a 2kg pressure roll. A 250mm long paper tape, the same width as the polar sheet, was attached to the polar sheet current collector and secured in place with masking tape. The Sansi tensioning device was powered on (sensitivity 1N), the indicator light was turned on, the stopper was adjusted to the appropriate position, and the end of the steel plate not attached to the polar sheet was secured with the lower clamp. The paper tape was folded back and secured with the upper clamp, and the position of the upper clamp was adjusted using the "up" and "down" buttons on the tensioning device's manual controller. The test is then performed and the numerical value is read at a pulling speed of 50 mm / min. The force when the force applied to the polar sheet is balanced is divided by the tape width to obtain the adhesive force of the negative electrode sheet per unit length, which characterizes the adhesive strength between the film layer in the current collector and the current collector.

[0204] 6. Sheet resistance of polar sheet The left, middle, and right sections of the polar sheet are cut and dried, then cut into small circular sheets with a diameter of 30 mm. Simply power on the Yuan Neng Technology polar sheet resistance meter, place it on the polar sheet resistance meter's "probe" in the appropriate position, press the "Start" button, and wait until the display stabilizes before taking a reading. Each circular sheet is measured in two positions, and the average of the six measurements is finally calculated, which is the film layer resistance of the polar sheet.

[0205] 7. Thickness of primer layer Place the smooth-sided copper foil on a flat table surface, with the foil extending approximately 5 cm beyond the table surface, and press the copper foil against the table surface to prevent movement.

[0206] The micrometer was started and the display was cleared. The micrometer was purchased from Mitutoyo in Japan.

[0207] Tests are carried out at different positions on the copper foil in turn, and the average value of the five points is calculated and designated as L1.

[0208] A copper foil is gravure coated on one side and dried, then placed on a flat table surface. The copper foil extends about 5 cm beyond the table surface, and the copper foil on the table surface is pressed to prevent movement.

[0209] Activate the micrometer and clear the display.

[0210] Tests are carried out at different positions on the copper foil in turn, and the average value of the five points is calculated and designated as L2.

[0211] Thickness of primer layer = (L2-L1).

[0212] 3. Results analysis [Table 1-1] [Table 1-2] [Table 2-1] [Table 2-2] [Table 2-3]

[0213] As can be seen from the results in Table 1, the binders in Examples 1 to 18 were all fluorine-containing polymers containing structural units derived from vinylidene fluoride and structural units derived from acrylic ester, and the molar content of the structural units derived from vinylidene fluoride in the polymer was 70% to 90% of the total number of moles of the structural units in the fluorine-containing polymer. Using the above fluorine-containing polymers as binders provided good effects in all cases, and compared with polyvinylidene fluoride in Comparative Example 1, the fluorine-containing polymers provided by the present application reduced the viscosity of the paste, improved filterability, and were suitable for producing primer layers.

[0214] As can be seen from a comparison of Examples 1 to 3 with Comparative Examples 3 and 4, when the molar content of the structural units derived from acrylic ester in the fluorine-containing polymer is 10% to 30% of the total molar content of all structural units in the fluorine-containing polymer, the viscosity of the fluorine-containing polymer is appropriate, the processability and adhesiveness of the paste are improved overall, and both the processability and usability of the primer layer can be achieved.

[0215] As can be seen from a comparison of Examples 4 to 7, when the weight-average molecular weight of the fluorine-containing polymer is 400,000 to 500,000, the viscosity of the fluorine-containing polymer is appropriate, which comprehensively improves the processability and adhesiveness of the paste, and achieves both the processability and usability of the primer layer.

[0216] As can be seen from Examples 8 to 11, when the mass fraction of the fluorine-containing polymer is 0.5% to 5% relative to the mass of the conductive agent, the viscosity of the fluorine-containing polymer is appropriate, which is suitable for producing a uniform primer layer, and the processability and adhesiveness of the paste are comprehensively improved, thereby achieving both the processability and usability of the primer layer.

[0217] As can be seen from Examples 12 to 15, the viscosity of primer pastes with a fluorine-containing polymer mass fraction of 0.5% to 5% and a solids content of 15% to 30% is 100 mPa·s to 1000 mPa·s, which means that primer pastes made from fluorine-containing polymers do not require the addition of additional dispersants or thickeners to improve processability, which helps reduce paste variation between batches, improves production efficiency, and optimizes the production process.

[0218] As can be seen from a comparison of Examples 1 to 16 and Example 18, the fluorine-containing polymers prepared by the methods disclosed herein can more effectively improve paste stability, widen the process window for paste application, and improve paste processability compared to fluorine-containing copolymers synthesized by conventional methods.

[0219] As can be seen from a comparison between Examples 1 to 16 and Example 17, the primer layer produced by gravure coating has higher adhesive strength than the primer layer produced by the blade method commonly used in the prior art.

[0220] As can be seen from a comparison between Examples 1 to 16 and Comparative Example 2, the primer layer produced by the gravure coating method used in the present application has polar sheet adhesion strength equivalent to that of a primer layer produced without gravure coating using a paste containing a conventional binder in the prior art, and has excellent prospects for use.

[0221] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and achieves the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. It should be noted that various modifications that a person skilled in the art can make to the embodiments and other forms formed by combining some of the components of the embodiments are also included within the scope of the present application, as long as they do not deviate from the spirit of the present application. [Explanation of symbols]

[0222] 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 housing, 52 electrode assembly, 53 cover plate, 6 gravure coating device, 61 pressure roll, 62 gravure roll, 63 current collector, 64 blade, 65 paste groove

Claims

1. A fluorine-containing polymer comprising a structural unit derived from a monomer represented by formula I and a structural unit derived from a monomer represented by formula II, wherein the molar content of the structural unit derived from the monomer represented by formula I is 70% to 90% based on the total number of moles of structural units in the fluorine-containing polymer; Here, R 1 , R 2 , R 3 are each independently hydrogen, fluorine, chlorine, or C substituted with fluorine. 1~3 alkyl groups, R 4 , R 5 , R 6 are each independently hydrogen or substituted or unsubstituted C 1~5 alkyl groups, R 7 is a substituted or unsubstituted C 1~9 A fluorine-containing polymer, characterized in that the fluorine-containing polymer is selected from alkyl groups.

2. The R 1 is fluorine, and R 2 , R 3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl; R 5 , R 6 2. The fluorine-containing polymer according to claim 1, wherein each of is independently selected from one or two of hydrogen and methyl.

3. 3. The fluorine-containing polymer according to claim 1, wherein the molar content of the constitutional units derived from the monomer represented by formula II is 10% to 30% based on the total number of moles of constitutional units of the fluorine-containing polymer.

4. The fluorine-containing polymer according to any one of claims 1 to 3, wherein the weight average molecular weight of the fluorine-containing polymer is 400,000 to 500,000.

5. 2. The fluorine-containing polymer of claim 1, wherein the monomer shown in formula I is selected from one or more of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene.

6. The fluorine-containing polymer according to any one of claims 1 to 5, wherein the monomer represented by formula II is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate.

7. Polymerizing at least one monomer of formula I and at least one monomer of formula II under polymerizable conditions, wherein the molar content of the monomer of formula I is 70% to 90% based on the total moles of the monomer of formula I and the monomer of formula II; Here, R 1 , R 2 , R 3 are each independently hydrogen, fluorine, chlorine, or C substituted with fluorine. 1~3 alkyl groups, R 4 , R 5 , R 6 are each independently hydrogen, substituted or unsubstituted C 1~5 alkyl groups, R 7 is a substituted or unsubstituted C 1~9 A method for producing a fluorine-containing polymer, wherein the alkyl group is selected from alkyl groups.

8. The R 1 is fluorine, and R 2 , R 3 are each independently selected from one or more of hydrogen, fluorine, chlorine, and trifluoromethyl; R 5 , R 6 and each independently is selected from one or two of hydrogen and methyl.

9. The method according to claim 7 or 8, wherein the molar content of the monomer represented by formula II is 10% to 30% based on the total number of moles of the monomer represented by formula I and the monomer represented by formula II.

10. The polymerization reaction includes a first stage polymerization and a second stage polymerization, a first stage polymerization is carried out by adding an initiator, a first emulsifier, at least one monomer represented by Formula I, and an aqueous medium to a reaction vessel, wherein the monomer represented by Formula I is continuously fed in the first stage polymerization; The method according to any one of claims 7 to 9, characterized in that after reacting for a certain time, an initiator, a second emulsifier, at least one monomer represented by formula II and an aqueous medium are added to the reaction vessel to carry out second-stage polymerization, and in the second-stage polymerization, the monomer represented by formula I is continuously fed.

11. The method according to claim 10, wherein the mass of the monomer represented by formula I introduced in the first-stage polymerization is 90% to 95% of the total mass of the monomer represented by formula I supplied in the polymerization reaction, and the mass of the monomer represented by formula I introduced in the second-stage polymerization is 5% to 10% of the total mass of the monomer represented by formula I supplied in the polymerization reaction.

12. The method according to claim 10 or 11, wherein the initiator provided in the first-stage polymerization and the initiator provided in the second-stage polymerization are both persulfates, the weight percentage of the initiator provided in the first-stage polymerization is 0.05% to 0.1% based on the total weight of the monomer represented by Formula I and the monomer represented by Formula II, and the weight percentage of the initiator provided in the second-stage polymerization is 0.05% to 0.1% based on the weight of the monomer represented by Formula II.

13. The method according to any one of claims 10 to 12, characterized in that the mass percentage of the first emulsifier is 0.2% to 0.7% based on the total mass of the monomer shown in formula I and the monomer shown in formula II.

14. The method according to any one of claims 10 to 13, characterized in that the weight percentage of the second emulsifier is 0.5% to 1.5% relative to the weight of the monomer shown in formula II.

15. The method according to any one of claims 10 to 14, characterized in that the weight percentage of the aqueous medium provided in the first-stage polymerization is 200% to 500% and the weight percentage of the aqueous medium provided in the second-stage polymerization is 100% to 200% relative to the total weight of the monomer represented by formula I and the monomer represented by formula II.

16. The method according to any one of claims 10 to 15, wherein the reaction pressure of the first-stage polymerization is 5.5 to 7.5 MPa and the reaction temperature is 75 to 85°C.

17. The method according to any one of claims 10 to 16, wherein the reaction pressure of the second-stage polymerization is 4.5 to 6.5 MPa and the reaction temperature is 86 to 95°C.

18. After the reaction for a certain period of time, an initiator, a second emulsifier, at least one monomer represented by formula II, and an aqueous medium are added to the reaction vessel to carry out second-stage polymerization. The method according to any one of claims 10 to 17, further comprising adding a premixed liquid containing an initiator, a second emulsifier, at least one monomer represented by formula II, and an aqueous medium after adding the initiator to the reaction vessel.

19. The method according to any one of claims 10 to 18, wherein the first emulsifier is an alkali metal salt of perfluorooctanoic acid.

20. The method according to any one of claims 10 to 19, wherein the second emulsifier is one or two of polyoxyethylene-4-phenol ether ammonium sulfate and nonylphenol polyoxyethylene ether ammonium sulfate.

21. Use of the fluorine-containing polymer according to any one of claims 1 to 6 in a secondary battery.

22. A primer paste comprising a binder, a conductive agent, and a solvent, wherein the binder comprises the fluorine-containing polymer according to any one of claims 1 to 6.

23. The primer paste according to claim 22, wherein the mass fraction of the binder is 0.5% to 5% relative to the mass of the conductive agent.

24. 24. The primer paste according to claim 22 or 23, characterized in that the solid content is 15% to 30% and the viscosity is 100 mPa·s to 1000 mPa·s.

25. The primer paste according to any one of claims 22 to 24, wherein the solvent is an organic solvent.

26. 26. The primer paste according to any one of claims 22 to 25, characterized in that the solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide and 3-butoxy-N-methylpropionamide.

27. A method for producing a primer layer, comprising: gravure coating a surface of a current collector with the primer paste according to any one of claims 22 to 26; and drying the primer paste to obtain a primer layer.

28. A secondary battery comprising: a positive electrode sheet; a negative electrode sheet including a primer layer produced by the method of claim 27; a separator; and an electrolyte solution.

29. 30. The secondary battery of claim 28, wherein the secondary battery comprises at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

30. A battery module comprising the secondary battery according to claim 28 or 29.

31. A battery pack comprising at least one of the secondary battery according to claim 28 or 29 and the battery module according to claim 30.

32. 32. A power consuming device comprising at least one selected from the group consisting of the secondary battery according to claim 28 or 29, the battery module according to claim 30, and the battery pack according to claim 31.

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