Binder composition, positive plate, secondary battery and electrical equipment

Abstract

The present application provides a binder composition, wherein the binder composition comprises a first fluorine-containing polymer and a second fluorine-containing polymer, wherein the first fluorine-containing polymer comprises polyvinylidene difluoride having a weight average molecular weight of 5 million to 9 million, and the weight average molecular weight of the second fluorine-containing polymer does not exceed 600,000. This binder composition has good processability and can enable the electrode plate to have high adhesion even with a low amount of additive, and can improve the cycle performance of the battery.

Description

Technology Field

[0001] The present application relates to PCT patent application No. PCT / CN2022 / 099187, filed on June 16, 2022, titled 'Binder and method of manufacturing the same and application'; CN patent application No. 202211044631.4, filed on August 30, 2022, titled 'Fluorine-containing polymer, method of manufacturing the same and use thereof, anode slurry, secondary battery, battery module, battery pack and electrical equipment'; CN patent application No. 202211052014.9, filed on August 30, 2022, titled 'Fluorine-containing polymer, method of manufacturing the same and use thereof, anode slurry, secondary battery, battery module, battery pack and electrical equipment'; and CN patent application No. 202211052014.9, filed on August 30, 2022, titled 'Binder, manufacturing method, anode plate, secondary battery and electrical equipment' Claiming priority to CN patent application No. 202211046282.X, CN patent application No. 202211044756.7 filed on August 30, 2022, titled 'Binder, manufacturing method, anode plate, secondary battery and electrical device', and CN patent application No. 202211043966.4 filed on August 30, 2022, titled 'Binder, manufacturing method, anode plate, secondary battery and electrical device', all of which are incorporated into the present application by reference.

[0002] The present application relates to the field of secondary battery technology, and in particular to fluorine-containing polymers, manufacturing methods, binder compositions, positive plates, secondary batteries, and electrical devices. Background Technology

[0003] In recent years, secondary batteries have been widely applied in various fields, including energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As the application of secondary batteries becomes more widespread, higher requirements are being placed on their cycle performance and service life.

[0004] Binders are common materials in secondary batteries and are widely used in electrode plates, separators, and packaging. However, conventional binders have poor adhesive properties, often requiring large amounts to meet electrode adhesion requirements, which limits the improvement of battery energy density. Therefore, existing binders still need improvement.

[0005] This application has been made in consideration of the above-mentioned problem, and its purpose is to provide a binder composition, which can exhibit excellent adhesive strength even with a low amount of addition and has good processability.

[0006] To achieve the above objective, in the first aspect of the present application, a binder composition is provided, wherein the binder composition comprises a first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer, wherein the weight average molecular weight of the first fluorine-containing polymer is 3 million to 10 million, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1.1 million, and the weight average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000.

[0007] This binder composition ensures that the electrode plate has sufficient adhesion even with a low amount of additive and can improve the cycle performance of the battery, and furthermore, this binder composition possesses excellent flexibility and processability simultaneously, which can further enhance the safety and cycle performance of the battery.

[0008] In any embodiment, the mass content of the first fluorine-containing polymer is 10% to 86% when calculated based on the total mass of the binder composition.

[0009] By controlling the mass content of the first fluorine-containing polymer within an appropriate range, it is possible to ensure that the binder composition has sufficient adhesion, thereby preventing the film from detaching during the battery cycling process. In addition, a certain amount of the first fluorine-containing polymer can effectively reduce the amount of binder composition used and improve the active material loading of the electrode plate.

[0010] In any embodiment, the mass content of the second fluorine-containing polymer is 10% to 86% when calculated based on the total mass of the binder composition.

[0011] The weight-average molecular weight of the second fluorine-containing polymer is relatively low, which effectively improves the crystallinity of the first fluorine-containing polymer, enhances the flexibility of the electrode plate, and lowers battery costs.

[0012] In any embodiment, the degree of crystallinity of the binder composition does not exceed 40%, and optionally 5% to 40%.

[0013] Adding a second fluorine-containing polymer and a third fluorine-containing polymer to the first fluorine-containing polymer can effectively lower the crystallinity of the binder, improve electrode plate flexibility and slurry processing performance, and improve the cycle performance of the battery.

[0014] In any embodiment, the first fluorine-containing polymer comprises a structural unit derived from vinylidene difluoride.

[0015] In any embodiment, the first fluorine-containing polymer further comprises a structural unit represented by Formula I, and

[0016] Formula I

[0017] Here, R1 is hydrogen, fluorine, chlorine, and C containing at least one fluorine atom. 1-3 It includes one or more of the alkyl groups.

[0018] In any embodiment, the first fluorine-containing polymer comprises one or more of polyvinylidene difluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

[0019] In any embodiment, the second fluorine-containing polymer comprises a structural unit represented by Formula II, and

[0020] Formula II

[0021] Here, R2 and R3 are each independently C containing hydrogen, a halogen, and at least one fluorine atom. 1-3 It includes at least one of the alkyl groups.

[0022] The above second fluorine-containing polymer contains chlorine.

[0023] A second fluorine-containing polymer containing chlorine can further lower the crystallinity of the binder composition, improve the flexibility of the electrode plate, and improve the safety performance of the battery.

[0024] In any embodiment, when calculated based on the total mass of the second fluorine-containing polymer, the chlorine content in the second fluorine-containing polymer does not exceed 8%.

[0025] A second fluorine-containing polymer with a chlorine content not exceeding 8% has a low degree of crystallinity, so the flexibility of the electrode plate can be significantly improved.

[0026] In any embodiment, the degree of crystallization of the second fluorine-containing polymer does not exceed 47%, and optionally does not exceed 30%.

[0027] In any embodiment, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000.

[0028] In any embodiment, the second fluorine-containing polymer comprises at least one of polyvinylidene difluoride, chlorinated polyvinylidene difluoride, chlorinated poly(vinylidene difluoride-hexafluoropropylene), and poly(vinylidene difluoride-chlorotrifluoroethylene).

[0029] In any embodiment, the third fluorine-containing polymer comprises a structural unit represented by Formula III.

[0030] Formula III

[0031] Here, R4 and R5 each independently include at least one of hydrogen, fluorine, chlorine, or trifluoromethyl group.

[0032] In any embodiment, the terminal group of the third fluorine-containing polymer includes a hydroxyl group or an ester group. In any embodiment, the third fluorine-containing polymer comprises one of polytetrafluoroethylene, polyvinylidene difluoride, poly(vinylidene difluoride-hexafluoropropylene) copolymer, poly(vinylidene difluoride-tetrafluoroethylene) copolymer, poly(vinylidene difluoride-chlorotrifluoroethylene) copolymer, and poly(vinylidene difluoride-vinylidene tetrafluoride-hexafluoropropylene) copolymer.

[0033] In a second aspect of the present application, a fluorine-containing polymer is provided, wherein the fluorine-containing polymer comprises a structural unit derived from vinylidene difluoride and a structural unit represented by Formula IV, and

[0034] Formula IV

[0035] Here, R6 contains at least one of hydrogen, Cl, and F.

[0036] In any embodiment, when calculated based on the total mass of the fluorine-containing polymer, the chlorine content in the fluorine-containing polymer does not exceed 8%.

[0037] In any embodiment, the degree of crystallization of the fluorine-containing polymer does not exceed 30%. In any embodiment, the weight average molecular weight of the fluorine-containing polymer is 600,000 to 1,100,000.

[0038] In any embodiment, the fluorine-containing polymer comprises at least one of chlorinated polyvinylidene difluoride, chlorinated poly(vinylidene difluoride-hexafluoropropylene), and poly(vinylidene difluoride-chlorotrifluoroethylene).

[0039] In a third aspect of the present application, a method for manufacturing a fluorine-containing polymer is provided, wherein the method comprises the step of manufacturing a fluorine-containing polymer by chlorinating polyvinylidene fluoride using a chlorinating agent.

[0040] In any embodiment, the manufacturing method specifically comprises the step of preparing a polyvinylidene fluoride suspension by dispersing polyvinylidene fluoride in a solvent; and the step of preparing a fluorine-containing polymer by adding an initiator and a chlorinating agent to chlorine the polyvinylidene fluoride.

[0041] In any embodiment, the chlorinating agent comprises at least one of chlorine, hydrogen chloride, phosphorus pentachloride, phosphorus trichloride, sulfuryl chloride (SO2Cl2), and phosgene (COCl2).

[0042] In any embodiment, the initiator comprises at least one of dibenzoyl peroxide, lauroyl peroxide, azobis(isobutyronitrile) (AIBN), and 2,2'-azobis(2,4-dimethylvaleronitrile) (ABVN).

[0043] In any embodiment, the solvent comprises at least one of carbon tetrachloride and water.

[0044] In a fourth aspect of the present application, an anode plate is provided, comprising an anode current collector and an anode film layer installed on at least one surface of the anode current collector, wherein the anode film layer comprises an anode active material, a conductive agent, and a binder according to any embodiment or a binder composition prepared by a manufacturing method according to any embodiment.

[0045] This anode plate has excellent adhesion with a low amount of binder.

[0046] In any embodiment, the mass fraction of the binder composition does not exceed 1.5%, optionally 0.8% to 1.2%, and is calculated based on the total mass of the anode film layer.

[0047] By controlling the mass fraction of the binder composition within an appropriate range, it is possible to ensure that the electrode plate has sufficient adhesion while simultaneously considering the flexibility of the electrode plate, thereby improving the cycle performance and safety performance of the battery.

[0048] In any embodiment, the positive electrode active material is a lithium-containing transition metal oxide.

[0049] In any embodiment, the lithium-containing transition metal oxide is at least one of lithium iron phosphate or lithium nickel cobalt manganese oxide, or a doped modified material thereof, or a conductive carbon coating modified material, a conductive metal coating modified material, or a conductive polymer coating modified material thereof.

[0050] In the fifth aspect of the present application, a secondary battery is provided comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a separator, a negative electrode plate and a positive electrode plate according to the fourth aspect of the present application.

[0051] In the sixth aspect of the present application, an electric device is provided, comprising a secondary battery according to the fifth aspect of the present application. Brief explanation of the drawing

[0052] FIG. 1 is a schematic diagram of a secondary battery according to one embodiment of the present application. FIG. 2 is an exploded view of a secondary battery according to one embodiment of the present application illustrated in FIG. 1. FIG. 3 is a schematic diagram of a battery module according to one embodiment of the present application. FIG. 4 is a schematic diagram of a battery pack according to one embodiment of the present application. FIG. 5 is an exploded view of a battery pack according to one embodiment of the present application shown in FIG. 4. FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to one embodiment of the present application. Explanation of the symbols: 1-Battery pack; 2-Upper case; 3-Lower case; 4-Battery module; 5-Secondary battery; 51-Housing; 52-Electrode assembly; 53-Cover plate. Specific details for implementing the invention

[0053] Embodiments of the positive active material, the method for manufacturing the same, the positive plate, the secondary battery, the battery module, the battery pack, and the electrical device of the present application are described and disclosed in detail below with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of known matters or repetitive descriptions of substantially identical structures may be omitted. This is to avoid making the following description unnecessarily long and to aid the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided to facilitate a sufficient understanding of the present application by those skilled in the art and are not intended to limit the essence described in the claims.

[0054] The 'range' disclosed in this application is limited in the form of a lower limit and an upper limit, and a given range is limited by the selection of one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. A range limited in this way may include or not include boundary values, and may also be arbitrarily combined. That is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it can be understood that ranges of 60 to 110 and 80 to 120 are also expected. Additionally, if minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are listed, ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 can all be expected. In this application, unless otherwise noted, the value range 'a to b' represents an abbreviated expression of any combination of real numbers from a to b, where a and b are both real numbers. For example, the value range '0 to 5' indicates that all real numbers between '0 to 5' are listed here, and '0 to 5' is merely an abbreviated expression of such combination of values. Additionally, if a specific parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that this parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present application may be combined with one another to form a new technical solution.

[0056] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with one another to form a new technical solution.

[0057] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, but sequentially is preferred. For example, if the method comprises steps (a) and (b), it indicates that the method may comprise steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, if the method further comprises step (c), it indicates that step (c) may be added to the method in any order. For example, the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0058] Unless otherwise specified, the terms 'include' and 'have' as used in this application are open forms and may also be closed forms. For example, the terms 'include' and 'have' may indicate that other unlisted components are included, or that only the listed components are included.

[0059] Unless otherwise specified, the term 'or' in this application is inclusive. For example, the phrase 'A or B' indicates 'A, B, or A and B'. More specifically, any of the following conditions satisfy the condition 'A or B': A being true (or existing) and B being false (or absent); A being false (or absent) and B being true (or existing); or both A and B being true (or existing).

[0060] Fluorine-containing polymers are currently one of the most widely used binders in secondary batteries. However, conventional fluorine-containing polymers have low viscosity, often requiring large amounts to ensure effective adhesion of the active material and enable the electrode plates to achieve effective bonding. Conversely, increasing the usage of conventional fluorine-containing polymers lowers the active material load on the electrode plates, thereby affecting the improvement of battery energy density; on the other hand, if the binder content is low, it is difficult to guarantee sufficient bonding strength during use, making it difficult to meet market requirements for battery cycle performance.

[0061] [Binder composition]

[0062] The present application provides a binder composition, wherein the binder composition comprises a first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer, wherein the weight average molecular weight of the first fluorine-containing polymer is 3 million to 10 million, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1.1 million, and the weight average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000.

[0063] In this specification, the term 'binder composition' means a mixture that forms a colloidal solution or a colloidal dispersion in a dispersion medium.

[0064] In this specification, the term 'fluorine-containing polymer' refers to a polymer that uses a fluorine-containing monomer as the primary monomer for synthesis, and the polymer comprises, on the one hand, an assembly of polymers that are chemically homogeneous but differ in degree of polymerization, molar mass, and chain length, prepared through a polymerization reaction. On the other hand, the term includes derivatives of such polymer assemblies formed by a polymerization reaction, that is, chemically homogeneous or non-chemically homogeneous compounds that can be obtained through the reaction of functional groups in said polymers, for example, addition or substitution. Fluorine-containing polymers in this specification include copolymers as well as homopolymers.

[0065] In this specification, the term 'weight average molecular weight' refers to the sum of the products of the weight fraction of molecules with different molecular weights in a polymer and the corresponding molecular weights.

[0066] In some embodiments, the dispersion medium of the binder composition is an oily solvent, and examples of oily solvents include, but are not limited to, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethylcellulose, and polycarbonate. That is, the binder is dissolved in an oily solvent.

[0067] In some embodiments, the binder composition is used to form an electrode by fixing the electrode active material and / or conductive agent in appropriate positions and attaching them to a conductive metal member.

[0068] In some embodiments, the binder composition is used as an anode binder to form an electrode by adhering an anode active material and / or a conductive agent.

[0069] In some embodiments, the binder composition is used to form an electrode by bonding a cathode active material and / or a conductive agent as a cathode binder.

[0070] In some embodiments, the weight average molecular weight of the first fluorine-containing polymer is 3 million to 10 million. In some embodiments, the weight average molecular weight of the first fluorine-containing polymer is 3 million, 3.5 million, 4 million, 4.5 million, 5 million, 5.5 million, 6 million, 6.5 million, 7 million, 7.5 million, 8 million, 8.5 million, 9 million, 9.5 million, 10 million, or any of these values.

[0071] In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000. In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is optionally 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,050,000, or any of these values.

[0072] In some embodiments, the weight average molecular weight of the third fluorine-containing polymer is 0.5 million to 150,000. In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is optionally 0.5 million, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, or any of these values.

[0073] In this application, the weight-average molecular weight of the fluorine-containing polymer may be tested using methods known in the art, for example, by gel chromatography, for example using a Waters 2695 Isocratic HPLC-type gel chromatograph (differential refractive index detector 2141). In some embodiments, the test method involves referencing a polystyrene solution sample with a mass fraction of 3.0% and selecting a matching chromatography column (planet: Styragel HT5DMF 7.8*300mm + Styragel HT4). A 3.0% binder colloidal solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is left to stand for one day to await use. When testing, tetrahydrofuran is first drawn into a syringe and washed repeatedly. Then, 5 ml of the test solution is drawn to remove air from the syringe and wipe the needle tip. Finally, the sample solution is slowly injected into the sample inlet. After the numerical display stabilizes, acquire the data and read the weight-average molecular weight.

[0074] A first fluorine-containing polymer with a weight average molecular weight of 3 million to 10 million can improve the adhesion of the electrode plate with a low amount of addition and improve the capacity retention rate of the battery during the cycling process, and the addition of a second fluorine-containing polymer and a third fluorine-containing polymer with low molecular weight can effectively improve the processing performance of the slurry, improve the quality of the electrode plate, improve the brittleness problem of the electrode plate, and lower processing, manufacturing, and raw material costs, and a uniform binder composition can further improve the cycling performance of the battery.

[0075] In some embodiments, the mass content of the first fluorine-containing polymer is 10% to 86% when calculated based on the total mass of the binder composition.

[0076] In some embodiments, when calculated based on the total mass of the binder composition, the mass content of the first fluorine-containing polymer is optionally 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 86%, or any of these values.

[0077] By controlling the mass content of the first fluorine-containing polymer within an appropriate range, it is possible to ensure that the binder composition has sufficient adhesion, thereby preventing the film from detaching during the battery cycling process. In addition, a certain amount of the first fluorine-containing polymer can effectively reduce the amount of binder composition used and improve the active material loading of the electrode plate.

[0078] In some embodiments, the mass content of the second fluorine-containing polymer is 10% to 86% when calculated based on the total mass of the binder composition.

[0079] In some embodiments, when calculated based on the total mass of the binder composition, the mass content of the second fluorine-containing polymer is optionally 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 86%, or any of these values.

[0080] The weight-average molecular weight of the second fluorine-containing polymer is relatively low, which effectively improves the crystallinity of the first fluorine-containing polymer, enhances the flexibility of the electrode plate, and lowers battery costs.

[0081] In some embodiments, the degree of crystallinity of the binder composition does not exceed 40%, and optionally is 5% to 40%.

[0082] In some embodiments, the degree of crystallinity of the binder composition is optionally 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or any of these values.

[0083] In this specification, the term 'degree of crystallization' refers to the proportion of the crystalline region in a polymer, and the microstructure contains regions with stable and regularly arranged molecules, and the regions where molecules are regularly and closely arranged are called crystallized regions.

[0084] In this application, the degree of crystallinity may be tested using methods known in the art, such as using differential scanning calorimetry. In some embodiments, 0.5 g of the binder composition is placed in an aluminum crucible, shaken evenly, and then the crucible lid is closed. Then, the test is performed using a differential scanning calorimeter (DSC) of the Discovery 250 model from TA, USA, in a nitrogen gas atmosphere with a purge gas of 50 ml / min, a shielding gas of 70 ml / min, a heating temperature of 10°C / min, and a test temperature range of -100°C to 400°C, and the thermal history is removed.

[0085] Through this test, the DSC / (Mw / mg) change curve according to temperature of the binder composition is obtained and integrated, and the peak area is the melting enthalpy ΔH (J / g) of the fluorine-containing polymer composition, and the binder crystallinity = ΔH / (ΔHm) × 100%, where ΔHm is the standard melting enthalpy (crystalline heat of dissolution) of the fluorine-containing polymer, and ΔHm = 104.7 J / g.

[0086] Adding a second fluorine-containing polymer and a third fluorine-containing polymer to the first fluorine-containing polymer can effectively lower the crystallinity of the binder, improve electrode plate flexibility and slurry processing performance, and improve the cycle performance of the battery.

[0087] In some embodiments, the first fluorine-containing polymer comprises a structural unit derived from vinylidene difluoride. In some embodiments, the first fluorine-containing polymer is a vinylidene difluoride homopolymer. In some embodiments, the first fluorine-containing polymer is a vinylidene difluoride copolymer.

[0088] In some embodiments, the first fluorine-containing polymer further comprises a structural unit represented by Formula I, and

[0089] Formula I

[0090] Here, R1 is hydrogen, fluorine, chlorine, and C containing at least one fluorine atom. 1-3 It includes one or more of the alkyl groups.

[0091] In some embodiments, R1 comprises one or more of hydrogen, fluorine, chlorine, and trifluoromethyl groups.

[0092] In some embodiments, the first fluorine-containing polymer comprises one or more of polyvinylidene difluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

[0093] In some embodiments, the second fluorine-containing polymer includes a structural unit represented by Formula II, and

[0094] Formula II

[0095] Here, R2 and R3 are each independently C containing hydrogen, a halogen, and at least one fluorine atom. 1-3 It includes at least one of the alkyl groups.

[0096] In some embodiments, R2 and R3 each independently contain hydrogen, fluorine, chlorine, or a trifluoromethyl group.

[0097] In some embodiments, the second fluorine-containing polymer contains chlorine.

[0098] A second fluorine-containing polymer containing chlorine can further lower the crystallinity of the binder composition, improve the flexibility of the electrode plate, and improve the safety performance of the battery.

[0099] In some embodiments, the second fluorine-containing polymer is prepared by chlorinating the fluorine-containing polymer.

[0100] In some embodiments, the second fluorine-containing polymer is prepared by copolymerizing a polyvinylidene difluoride monomer and a chlorine-containing monomer.

[0101] In some embodiments, the chlorine content in the second fluorine-containing polymer, calculated based on the total mass of the second fluorine-containing polymer, does not exceed 8%. In some embodiments, the chlorine content in the second fluorine-containing polymer, calculated based on the total mass of the second fluorine-containing polymer, is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any of these values.

[0102] A second fluorine-containing polymer with a chlorine content not exceeding 8% has a low degree of crystallinity, so the flexibility of the electrode plate can be significantly improved.

[0103] In some embodiments, the degree of crystallization of the second fluorine-containing polymer does not exceed 47%, optionally not exceed 30%. In some embodiments, the degree of crystallization of the second fluorine-containing polymer is 47%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 4%, 3%, or any of these values. In some embodiments, the weight-average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000. In some embodiments, the weight-average molecular weight of the second fluorine-containing polymer is 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, or any of these values.

[0104] In some embodiments, the second fluorine-containing polymer comprises at least one of polyvinylidene difluoride, chlorinated polyvinylidene difluoride, chlorinated poly(vinylidene difluoride-hexafluoropropylene), and poly(vinylidene difluoride-chlorotrifluoroethylene).

[0105] In some embodiments, the third fluorine-containing polymer comprises a structural unit represented by Formula III, and

[0106] Formula III

[0107] Here, R4 and R5 each independently include at least one of hydrogen, fluorine, chlorine, or trifluoromethyl group.

[0108] In some embodiments, the terminal group of the third fluorine-containing polymer includes a hydroxyl group or an ester group.

[0109] Since the third fluorine-containing polymer has a low weight-average molecular weight and a high mass content of terminal groups, the terminal groups have a relatively significant influence on the performance of the third fluorine-containing polymer. The inclusion of hydroxyl or ester groups in the terminal groups of the third fluorine-containing polymer effectively improves the adhesion of the third fluorine-containing polymer and can reduce the decrease in electrode plate adhesion caused by the addition of the third fluorine-containing polymer with a low molecular weight.

[0110] The terminal group structure of polymers can be studied through nuclear magnetic resonance. 19 F-NMR and 1 The terminal group structure of a polymer can be analyzed using H-NMR. As an example, using dimethyl sulfoxide as a solvent and CFCl3 19 Based on F-NMR, TMS 1 Based on H-NMR.

[0111] In some embodiments, the third fluorine-containing polymer comprises one of polytetrafluoroethylene, polyvinylidene difluoride, poly(vinylidene difluoride-hexafluoropropylene) copolymer, poly(vinylidene difluoride-tetrafluoroethylene) copolymer, poly(vinylidene difluoride-chlorotrifluoroethylene) copolymer, and poly(vinylidene difluoride-vinylidene tetrafluoride-hexafluoropropylene) copolymer.

[0112] In one embodiment of the present application, a fluorine-containing polymer is provided, said fluorine-containing polymer comprises a structural unit derived from vinylidene difluoride and a structural unit represented by Formula IV, and

[0113] Formula IV

[0114] Here, R6 contains at least one of hydrogen, Cl, and F.

[0115] Fluorine-containing polymers containing chlorine can further lower the crystallinity of the binder composition, improve the flexibility of the electrode plate, and improve the safety performance of the battery.

[0116] In some embodiments, the fluorine-containing polymer is prepared after the fluorine-containing polymer is chlorinated.

[0117] In some embodiments, the fluorine-containing polymer is prepared by copolymerizing vinylidene difluoride with a chlorine-containing monomer.

[0118] In some embodiments, the chlorine content in the fluorine-containing polymer, calculated based on the total mass of the fluorine-containing polymer, does not exceed 8%. In some embodiments, the chlorine content in the fluorine-containing polymer, calculated based on the total mass of the fluorine-containing polymer, is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any of these values.

[0119] Fluorine-containing polymers with a chlorine content not exceeding 8% have a low degree of crystallinity, so the flexibility of the electrode plate can be significantly improved.

[0120] In some embodiments, the degree of crystallization of the fluorine-containing polymer does not exceed 30%.

[0121] In some embodiments, the degree of crystallinity of the fluorine-containing polymer is optionally 30%, 25%, 20%, 15%, 10%, 5%, or any of these values. In some embodiments, the weight average molecular weight of the fluorine-containing polymer is 600,000 to 1,100,000. In some embodiments, the weight average molecular weight of the fluorine-containing polymer is 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, or any of these values.

[0122] In some embodiments, the fluorine-containing polymer comprises at least one of polyvinylidene difluoride, chlorinated polyvinylidene difluoride, chlorinated poly(vinylidene difluoride-hexafluoropropylene), and poly(vinylidene difluoride-chlorotrifluoroethylene).

[0123] One embodiment of the present application provides a method for manufacturing a fluorine-containing polymer, the method comprising the step of manufacturing a fluorine-containing polymer by chlorinating polyvinylidene fluoride using a chlorinating agent.

[0124] In some embodiments, the manufacturing method specifically comprises the step of preparing a polyvinylidene fluoride suspension by dispersing polyvinylidene fluoride in a solvent; and the step of preparing a fluorine-containing polymer by chlorinating the polyvinylidene fluoride by adding an initiator and a chlorinating agent.

[0125] In some embodiments, the chlorinating agent comprises at least one of chlorine, phosphorus pentachloride (PCl5), hydrogen chloride (HCl), phosphorus trichloride (PCl3), sulfuryl chloride (SO2Cl2), and phosgene (COCl2).

[0126] In some embodiments, the initiator comprises at least one of dibenzoyl peroxide, lauroyl peroxide, azobis(isobutyronitrile) (AIBN), and 2,2'-azobis(2,4-dimethylvaleronitrile) (ABVN).

[0127] In some embodiments, the solvent comprises at least one of carbon tetrachloride and water.

[0128] In one embodiment of the present application, a method for manufacturing a binder composition is provided, specifically,

[0129] Step of preparing a first fluorine-containing polymer - preparing a first fluorine-containing polymer by carrying out a first polymerization reaction on a raw material containing vinylidene difluoride monomer under polymerizable conditions, wherein the weight average molecular weight of the first fluorine-containing polymer is 3 million to 10 million - ;

[0130] Step of preparing a third fluorine-containing polymer - preparing a second fluorine-containing polymer by carrying out a second polymerization reaction under polymerizable conditions, wherein the weight-average molecular weight of the third fluorine-containing polymer does not exceed 600,000 - ;

[0131] Blending step - preparing a binder composition by blending a first fluorine-containing polymer, a second fluorine-containing polymer having a weight average molecular weight of 600,000 to 1,100,000, and a third fluorine-containing polymer - ; includes.

[0132] In this specification, the term 'blending' refers to the process of combining two or more materials into a macroscopically uniform material under conditions such as constant temperature and / or shear stress.

[0133] The manufacturing method of this binder is simple, environmentally friendly, and cost-effective, making it advantageous for industrial production. At the same time, the binder composition produced by this method can improve the battery's capacity retention rate during the cycling process by considering both electrode plate flexibility and battery cycle performance simultaneously with a low additive amount.

[0134] In some embodiments, the synthesis step of the first fluorine-containing polymer comprises: a step of carrying out a polymerization reaction for 6 to 10 hours in a non-reactive gas atmosphere, a reaction pressure of 6 MPa to 8 MPa, and a reaction temperature of 45°C to 60°C with respect to a raw material containing vinylidene fluoride monomer; a step of adding a chain transfer agent and stopping the reaction when the pressure of the reaction system drops to 2 MPa to 2.5 MPa, and preparing the first fluorine-containing polymer by leaving a solid phase through solid-liquid separation.

[0135] In some embodiments, the synthesis step of the first fluorine-containing polymer comprises: a step of providing a raw material containing a vinylidene fluoride monomer and a reaction solvent and carrying out a first-stage polymerization reaction to obtain a first product; a step of carrying out a second-stage polymerization reaction on the first product in a non-aqueous gas atmosphere; and a step of adding a chain transfer agent and carrying out a third-stage polymerization reaction to obtain the first fluorine-containing polymer.

[0136] The first product may refer to the reaction solution obtained after the first stage polymerization reaction, or it may be the product obtained after purifying the reaction solution after the first stage polymerization reaction.

[0137] In some embodiments, multiple batches of the first product are mixed and a second-stage polymerization reaction is carried out in an insoluble gas atmosphere. That is, the second-stage polymerization reaction is the self-polymerization of the first product. It can be understood that multiple batches of the first product may be produced simultaneously through multiple reactors or may be produced multiple times through a single reactor. The uniformity of the polymerization product can be improved through a multiple-step synthesis method.

[0138] By carrying out the polymerization reaction using a stepwise method, ultra-high molecular weight polyvinylidene fluoride can be produced, which allows the requirements for electrode adhesion to be met with a low amount of binder, helps improve the loading of the positive electrode active material, and is advantageous for improving the battery capacity retention rate during the cycling process. At the same time, a first product is formed in the first step of the polymerization reaction, a molecular chain of the target molecular weight is formed in the second step, and the third step is used to control the molecular weight of the polymer to improve product uniformity and avoid lowering the uniformity of the weight-average molecular weight of polyvinylidene fluoride due to excessively high molecular weight. Furthermore, stepwise polymerization improves reactor utilization and saves time during the polyvinylidene fluoride manufacturing process, and can reduce the residence time of polyvinylidene fluoride in the reactor. The mutual cooperation of the first, second, and third step polymerization reactions further enhances the production efficiency of polyvinylidene fluoride.

[0139] In some embodiments, the reaction temperature of the first stage polymerization reaction is 45°C to 60°C. In some embodiments, the reaction temperature of the first stage polymerization reaction is optionally 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, or 45°C to 55°C.

[0140] In some embodiments, the reaction time of the first stage polymerization reaction is 4h to 10h. In some embodiments, the reaction time of the first stage polymerization reaction is optionally 4h to 5h, 5h to 6h, 6h to 7h, 7h to 8h, 8h to 9h, 9h to 10h, 4h to 6h, 6h to 8h, 8h to 10h, and 5h to 10h.

[0141] In some embodiments, the initial polymerization pressure is 4 MPa to 6 MPa. In some embodiments, the initial polymerization pressure is optionally 4 MPa to 5 MPa or 5 MPa to 6 MPa. In some embodiments, the initial polymerization pressure is higher than the critical pressure of vinylidene fluoride.

[0142] In some embodiments, the reaction temperature of the second stage polymerization reaction is 60°C to 80°C. In some embodiments, the reaction temperature of the second stage polymerization reaction is optionally 60°C to 70°C or 70°C to 80°C.

[0143] In some embodiments, the reaction time of the second stage polymerization reaction is 2h to 4h. In some embodiments, the reaction time of the second stage polymerization reaction is optionally 2h to 3h or 3h to 4h.

[0144] In some embodiments, the reaction pressure of the second stage polymerization reaction is 6 MPa to 8 MPa. In some embodiments, the reaction pressure of the second stage polymerization reaction is optionally 6 MPa to 7 MPa or 7 MPa to 8 MPa.

[0145] In some embodiments, the reaction time of the third stage polymerization reaction is 1h to 2h.

[0146] By controlling the reaction pressure, reaction time, and reaction temperature of each step of the polymerization reaction within an appropriate range, the weight-average molecular weight of polyvinylidene fluoride can be improved, and the uniformity of the weight-average molecular weight of the polymerization product can be controlled, thereby ensuring that the product has a relatively low polydispersity index and improving the performance balance of the first polyvinylidene fluoride so that the electrode plate has excellent adhesion with a low amount of binder, and further improving the cycle capacity retention rate of the battery.

[0147] In some embodiments, the chain transfer reactant comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0148] Insoluble gases refer to gases with a solubility less than 0.1 L. The gas solubility at 20°C is 1.013 × 10⁻⁶. 5 It refers to the volume of gas when dissolved in 1 L of water at a pressure of Pa and reaching a saturated state. In some embodiments, the water-insoluble gas is one or more selected from nitrogen gas, oxygen gas, hydrogen gas, and methane.

[0149] In some embodiments, the amount of chain transfer reactant used is 1.5% to 3% of the total mass of vinylidene fluoride monomer. The amount of chain transfer reactant used may be, for example, 2% or 2.5%.

[0150] By controlling the amount of chain transfer agent used within an appropriate range, the chain length of the polymer can be controlled, allowing for the acquisition of a polymer with an appropriate molecular weight range and a uniform distribution.

[0151] In some embodiments, the first step polymerization reaction is,

[0152] A step of removing oxygen gas from the reaction system by adding an aqueous solvent and a dispersant to a container;

[0153] A step of adding a first initiator and a pH adjuster to the above container to adjust the pH value to 6.5~7, and then adding a vinylidene fluoride monomer to adjust the pressure inside the container to 4MPa~6MPa;

[0154] The step of carrying out the first stage polymerization reaction by stirring for 30 min to 60 min and then heating to 45℃ to 60℃; is included.

[0155] If the materials are mixed uniformly before heating to perform the polymerization reaction, the reaction can proceed more thoroughly, and the weight-average molecular weight, degree of crystallinity, and particle size of the manufactured polymer can be made more uniform.

[0156] In some embodiments, in the process of manufacturing the first fluorine-containing polymer, the amount of aqueous solvent used is 2 to 8 times the total mass of the vinylidene fluoride monomer. The amount of solvent used may be, for example, 3, 4, 5, 6, or 7 times the total mass of the vinylidene fluoride monomer. In some embodiments, the aqueous solvent is deionized water.

[0157] In some embodiments, in the process of manufacturing the first fluorine-containing polymer, the dispersant comprises one or more of cellulose ether and polyvinyl alcohol.

[0158] In some embodiments, in the process of manufacturing the first fluorine-containing polymer, the dispersant comprises one or more of methyl cellulose ether and carboxyethyl cellulose ether.

[0159] In some embodiments, in the process of manufacturing the first fluorine-containing polymer, the amount of dispersant used is 0.1% to 0.3% of the total mass of the vinylidene fluoride monomer. The amount of dispersant used may be, for example, 0.2% of the total mass of the vinylidene fluoride monomer.

[0160] In some embodiments, the first initiator is an organic peroxide.

[0161] In some embodiments, the first initiator comprises one or more of tert-amyl perpivalate, tert-amyl perpivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate and tert-butyl peroxypivalate.

[0162] In some embodiments, in the process of manufacturing the first fluorine-containing polymer, the amount of the first initiator used is 0.15% to 1% of the total mass of the vinylidene fluoride monomer. The amount of the first initiator used may be, for example, 0.2%, 0.4%, 0.6%, or 0.8% of the mass of the vinylidene fluoride monomer.

[0163] In some embodiments, the pH adjuster comprises one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and ammonia water.

[0164] In some embodiments, the amount of pH adjuster used is 0.05% to 0.2% of the total mass of vinylidene fluoride monomer. The amount of pH adjuster used may be, for example, 0.1% or 0.15% of the total mass of vinylidene fluoride monomer.

[0165] In some embodiments, the method for manufacturing the third fluorine-containing polymer specifically includes,

[0166] The method comprises the step of carrying out a second polymerization reaction for at least one monomer represented by Formula V at a reaction temperature of 60°C to 90°C and a non-reactive gas atmosphere for 0.5 to 8 hours, stopping the reaction, and obtaining a third fluorine-containing polymer by leaving a solid phase through solid-liquid separation.

[0167] Formula V

[0168] Here, R4 and R5 are each independently C containing hydrogen, a halogen, or at least one fluorine atom. 1-3 It is selected from alkyl groups.

[0169] In some embodiments, the reaction pressure of the second polymerization reaction is 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, or any of these values.

[0170] In some embodiments, the reaction temperature of the second polymerization reaction is 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any of these values.

[0171] Conducting a polymerization reaction at high temperature and high pressure can improve reaction efficiency, reduce reaction time, increase reaction conversion rate, and enhance the uniformity and purity of the product.

[0172] In some embodiments, the second polymerization reaction is,

[0173] A step of adding a solvent and a dispersant to a container, and filling the container with a non-reactive gas;

[0174] The method further includes the step of adding a monomer represented by Formula III, heating to 60°C to 90°C, and then adding a second initiator and a chain transfer agent.

[0175] In some embodiments, the second initiator comprises an inorganic peroxide and may be selected from potassium persulfate or ammonium persulfate.

[0176] Nuclear magnetic resonance results indicate that when an inorganic peroxide is used as an initiator, the terminal groups of the second fluorine-containing polymer contain -CF2-CH2OH or -CF2-CH2OOCCH3. The presence of hydroxyl groups and ester groups in the terminal groups effectively improves the adhesion of the second fluorine-containing polymer and can reduce the degradation of the adhesive performance of the binder composition caused by its addition.

[0177] In some embodiments, the mass content of the initiator is 3% to 12% when calculated based on the total mass of the monomer represented by the formula V.

[0178] A high content of initiator helps improve reaction efficiency, reduce reaction time, and enhance the uniformity and consistency of the product.

[0179] In some embodiments, the chain transfer reactant comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0180] [Polar Plate]

[0181] The anode plate comprises an anode current collector and an anode film layer installed on at least one surface of the anode current collector, and the anode film layer comprises an anode active material, a conductive agent, and a binder composition according to some embodiments.

[0182] This anode plate has excellent adhesion even when the amount of binder composition added is low.

[0183] In some embodiments, the mass fraction of the binder composition does not exceed 1.5%, optionally 0.8% to 1.2%, and is calculated based on the total mass of the anode film layer. In some embodiments, the mass content of the binder composition is 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any of these values.

[0184] The binder composition can effectively improve the adhesion performance of the electrode plate even with a low addition amount, and enables the electrode plate to have excellent flexibility and processability, allowing the battery to achieve high energy density and cycle performance.

[0185] In some embodiments, the positive active material is a lithium-containing transition metal oxide.

[0186] In some embodiments, the positive active material is at least one of lithium iron phosphate or lithium nickel cobalt manganese oxide, or a doped modified material thereof, or a conductive carbon coating modified material, a conductive metal coating modified material, or a conductive polymer coating modified material thereof.

[0187] In some embodiments, the positive current collector may use a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0188] In some embodiments, the positive active material may be a positive active material for a battery known in the art. As an example, the positive active material may include at least one of a lithium-containing phosphate with an olivine-type structure, 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 positive active materials for batteries may also be used. Such positive 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., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), 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 (can be abbreviated as ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM 523 (can be abbreviated as ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (NCM 211 (can be abbreviated as ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM 622 (can be abbreviated as ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM 811 (may be abbreviated as)), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05It may include, but is not limited to, at least one of O2) and its modified compounds. Examples of lithium-containing phosphates with an olivine-type structure may include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may be abbreviated 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 iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0189] In some embodiments, the anode film layer further optionally comprises a conductive agent. As an example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers.

[0190] In some embodiments, the anode plate may be manufactured in the following manner. An anode slurry may be formed by dispersing the components for manufacturing the anode plate, such as an anode active material, a conductive agent, and a binder, and any other components in a solvent (e.g., N-methylpyrrolidone), and the anode slurry may be coated onto an anode current collector and the anode plate may be obtained through processes such as drying and cold rolling.

[0191] [Cathode]

[0192] The cathode plate comprises a cathode current collector and a cathode film layer installed on at least one surface of the cathode current collector, and the cathode film layer comprises a cathode active material.

[0193] As an example, the cathode current collector has two opposing surfaces in its thickness direction, and the cathode film layer is installed on either one or both of the two opposing surfaces of the cathode current collector.

[0194] In some embodiments, the negative current collector may use a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0195] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of synthetic graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be at least one selected from solid silicon, silicon compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be at least one selected from solid tin, tin compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. Such negative electrode active materials may be used alone or in combination of two or more.

[0196] In some embodiments, the cathode film layer further optionally comprises a binder. The binder may be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0197] In some embodiments, the cathode film layer further optionally comprises a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon quantum dots, carbon nanotubes, graphene, and carbon nanofibers.

[0198] In some embodiments, the cathode film layer more optionally includes other auxiliary agents such as a thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0199] In some embodiments, the cathode plate may be manufactured in the following manner. Components for manufacturing the cathode plate, such as a cathode active material, a conductive agent, and a binder, and any other components may be dispersed in a solvent (e.g., deionized water) to form a cathode slurry, the cathode slurry may be coated onto a cathode current collector, and the cathode plate may be obtained through processes such as drying and cold rolling.

[0200] [Electrolyte]

[0201] The electrolyte acts to conduct ions between the positive plate and the negative plate. In this application, the type of electrolyte is not specifically limited and may be selected as needed. For example, the electrolyte may be a liquid, a gel, or a solid.

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

[0203] In some embodiments, the electrolyte salt may be at least one selected from 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.

[0204] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,2-butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, tetramethylene sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0205] In some embodiments, the electrolyte further optionally includes additives. For example, the additives may include a cathode film forming additive and an anode film forming additive, and may also include additives that can improve some performance of the battery, such as an additive that improves battery overcharge performance, an additive that improves battery high or low temperature performance, etc.

[0206] [Separator]

[0207] 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 excellent chemical stability and mechanical stability may be selected.

[0208] In some embodiments, the material of the separator may be at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and fluorine-containing polymer. The separator may be a single-layer thin film or a multilayer composite thin film, and there are no particular limitations. If the separator is a multilayer composite thin film, the materials of each layer may be the same or different from each other, and there are no particular limitations.

[0209] In some embodiments, the positive plate, the negative plate, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

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

[0211] In some embodiments, the outer packaging of the secondary battery may be a rigid case, such as a rigid plastic case, an aluminum case, a steel case, etc. The outer packaging of the secondary battery may also be a pouch, such as a pocket-type pouch. The material of the pouch may be plastic, and the plastic may be, for example, polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0212] In this application, the shape of the secondary battery is not specifically limited and may be cylindrical, prismatic, or any other shape. For example, FIG. 1 is a secondary battery (5) with a prismatic structure as an example.

[0213] In some embodiments, referring to FIG. 2, the outer packaging may include a housing (51) and a cover plate (53). Here, the housing (51) may include a bottom plate and a side plate connected to the bottom plate, and may form a receiving chamber by surrounding the bottom plate and the side plate. The housing (51) has an opening communicating with the receiving chamber, and the cover plate (53) may cover the opening to seal the receiving chamber. The positive plate, the negative plate, and the separator may form an electrode assembly (52) through a winding process or a lamination process. The electrode assembly (52) is packaged within the receiving chamber. The electrolyte is impregnated into the electrode assembly (52). The number of electrode assemblies (52) included in the secondary battery (5) may be one or many, and a person skilled in the art may select according to specific actual needs.

[0214] In some embodiments, the secondary battery may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or many, and a person skilled in the art may select a specific number depending on the application and capacity of the battery module.

[0215] FIG. 3 shows a battery module (4) as an example. Referring to FIG. 3, in the battery module (4), a plurality of secondary batteries (5) may be arranged sequentially along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary manner. Furthermore, a plurality of secondary batteries (5) may be fixed by a fixing member.

[0216] Optionally, the battery module (4) may further include an outer casing having a receiving space, and a plurality of secondary batteries (5) are received in this receiving space.

[0217] In some embodiments, the battery module may also be assembled into a battery pack, and the number of battery modules included in the battery pack may be one or many, and a person skilled in the art may select a specific number depending on the application and capacity of the battery pack.

[0218] FIGS. 4 and 5 illustrate a battery pack (1) as an example. Referring to FIGS. 4 and 5, the battery pack (1) may include a battery case and a plurality of battery modules (4) installed within the battery case. The battery case includes an upper case (2) and a lower case (3), and the upper case (2) may cover the lower case (3) to form a sealed space for accommodating the battery modules (4). The plurality of battery modules (4) may be arranged within the battery case in any manner.

[0219] Furthermore, the present application also provides an electric device, said electric device comprising at least one of a secondary battery, a battery module, or a battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source for said electric device or as an energy storage unit for said electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0220] Depending on the usage requirements of the above electrical device, a secondary battery, battery module, or battery pack can be selected.

[0221] FIG. 6 is an example of an electric device. This electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To satisfy the requirements of the electric device for high power and high energy density of a secondary battery, a battery pack or a battery module may be used.

[0222] Other examples of such devices include mobile phones, tablet PCs, and laptops. Since these devices generally require lightweight design, secondary batteries can be used as a power source.

[0223] a. Examples

[0224] The embodiments of this application are described below. The embodiments described below are illustrative and are intended for interpretation purposes only and should not be construed as a limitation to this application. Specific techniques or conditions not specified in the embodiments shall follow the techniques or conditions or product descriptions found in literature in the field. Any test pieces or equipment used without manufacturer's indication are commercially available conventional products.

[0225] Example 1

[0226] 1) Preparation of binder composition

[0227] Preparation of the first fluorine-containing polymer:

[0228] First stage polymerization reaction: 4 kg of deionized water and 2 g of methyl cellulose ether are added to 10 L high-pressure reactors No. 1 and 2, vacuumed, and then O2 is substituted with N2 three times. Then, 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate are added, and 1 kg of vinylidene fluoride monomer is added to reach a pressure of 5 MPa. Mixing and stirring are performed for 30 min, then heated to 45°C and reacted for 4 h.

[0229] Second stage polymerization reaction: The reaction solution in reactors 1 and 2 is transferred to reactor 3, nitrogen gas is filled until the pressure reaches 7 MPa, heated to 70°C, stirred for 3 hours, and the reaction is carried out.

[0230] Third step polymerization reaction: 40g of cyclohexane is added and the reaction is continued for 1 hour, after which the reaction is stopped. The reaction system is centrifuged to collect the solid phase, and the polyvinylidene fluoride binder is obtained through washing and drying.

[0231] Preparation of a second fluorine-containing polymer:

[0232] A certain amount of PVDF powder with a weight-average molecular weight of 1 million (commercially available) and a reaction medium (carbon tetrachloride) were prepared as a suspension and added to a 500 ml three-necked flask. While stirring, N2 was injected, the mixture was heated to 75°C, and refluxed for 15 minutes (temperature controlled by a constant temperature water bath). Then, an initiator (5 g / L BPO was used as the initiator) and a chlorinating agent (the chlorinating agent is Cl2, and the flow rate is 170 mL / min) were added simultaneously. The HCl produced in the reaction was absorbed with water, and the degree of chlorination of the PVDF was controlled by weighing the amount of absorbed HCl. After the reaction was completed, nitrogen was continuously injected to remove residual chlorine. The product was washed with alcohol, filtered, and then dried under vacuum to a constant weight. Finally, PVDF with a chlorine content of approximately 8.0% was obtained.

[0233] Preparation of 3rd Fluorine-Containing Polymers:

[0234] 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose are added to a 0.5 L high-pressure reactor, and oxygen is removed by purging with nitrogen gas several times, after which 120 g of vinylidene fluoride monomer gas is added. After adding the monomer, the reaction temperature is controlled to 82°C, and the reaction is started after adding a water-soluble ammonium persulfate initiator and 0.12 g of isopropyl alcohol chain transfer agent; the amount of initiator added is approximately 8% of the total amount of added monomer. The polymerization reaction time is 1.5 h, and the pressure is maintained at 4.4 MPa. Polyvinylidene difluoride polymer is obtained by washing and drying the reaction product with water.

[0235] A first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer are blended, and the mass ratio of the first fluorine-containing polymer, the second fluorine-containing polymer, and the third fluorine-containing polymer is 86:10:4, and a binder composition comprising the first fluorine-containing polymer, the second fluorine-containing polymer, and the third fluorine-containing polymer is obtained.

[0236] The manufacturing methods of Examples 2 to 9 are the same as those of Example 1, the only difference being that the mass ratio of each fluorine-containing polymer in the binder composition is changed, specifically as shown in the table.

[0237] The manufacturing method of Examples 10 to 13 is the same as that of Example 3, the only difference being that the degree of chlorination of PVDF is changed, specifically as shown in the table.

[0238] The method of preparation for Example 14 is the same as that of Example 3, the only difference being that the second fluorine-containing polymer is replaced with a (vinylidene difluoride-chlorotrifluoroethylene) copolymer.

[0239] The manufacturing method of Comparative Example 1 is the same as that of Example 1, the difference being that the binder composition contains only polyvinylidene difluoride with a weight average molecular weight of 5 million.

[0240] The binder composition used in Examples 15 to 17 and 20 is the same as that in Examples 10, 11, 3, and 12, and a battery is manufactured using this binder composition as a binder, and the specific method is as follows.

[0241] 2) Manufacture of the anode plate

[0242] Lithium iron phosphate, a binder composition, and acetylene black are stirred in a planetary mixer at an orbital speed of 25 r / min for 30 min, wherein the mass fraction of the binder composition is 1% and is calculated based on the total mass of the anode film layer,

[0243] 2.4 kg of N-methylpyrrolidone (NMP) solution is added to a stirring tank and stirred for 70 min at an orbital speed of 25 r / min and a rotational speed of 900 r / min;

[0244] 12.3g of polyvinylpyrrolidone dispersant is added to a stirring tank and stirred for 60 min at an orbital speed of 25 r / min and a rotational speed of 1300 r / min;

[0245] After stirring is finished, the slurry viscosity is tested and controlled to 8000~15000 MPa·s.

[0246] If the viscosity is high, an N-methylpyrrolidone (NMP) solution is added to lower the viscosity to the above range, and after adding the NMP solution, the anode slurry is obtained by stirring for 30 minutes at an orbital speed of 25 r / min and a rotational speed of 1200 to 1500 r / min, the prepared anode slurry is coated onto a carbon-coated aluminum foil, baked at 110°C for 15 minutes, and then cold-rolled and cut into a disc with a diameter of 15 mm to obtain an anode plate.

[0247] 3) Cathode plate

[0248] A metal lithium plate is used as the negative electrode.

[0249] 4) Separator

[0250] Polypropylene membrane is used as a separator.

[0251] 5) Preparation of electrolyte

[0252] In an argon gas atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are uniformly mixed in a volume ratio of 3 / 7, and LiPF6 lithium salt is added to the organic solvent and dissolved, then uniformly stirred to prepare a 1M LiPF6EC / EMC solution to obtain an electrolyte.

[0253] 6) Manufacturing of batteries

[0254] The positive plate, negative plate, separator, and electrolyte according to Example 1 are assembled into a button battery in a glove box for a button battery.

[0255] The manufacturing method of the battery in Examples 18, 19, 21, and 22 is basically the same as in Example 20, the difference being that the amount of binder composition used in the electrode plate is changed, specifically as shown in the table.

[0256] The method of manufacturing the battery in Examples 23 to 26 is basically the same as in Example 20, the difference being that the ratio of each fluorine-containing polymer in the binder composition is changed, specifically as shown in the table.

[0257] The method of manufacturing the battery in Examples 27 to 29 is basically the same as in Example 20, the only difference being that the weight average molecular weight of the third fluorine-containing polymer is changed.

[0258] In Example 27, a method for preparing polyvinylidene difluoride having a weight-average molecular weight of 0.5,000 includes the following steps.

[0259] 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose are added to a 0.5 L high-pressure reactor, and oxygen is removed by purging with nitrogen gas several times, after which 120 g of vinylidene fluoride monomer gas is added. After adding the monomer, the reaction temperature is controlled to 87°C, and the reaction is started after adding a water-soluble ammonium persulfate initiator and 0.15 g of isopropyl alcohol chain transfer agent, with the amount of initiator added being approximately 8% of the total amount of added monomer. The polymerization reaction time is 0.8 h, and the pressure is maintained at 4.4 MPa. The reaction product is washed with water and dried to obtain a polyvinylidene difluoride polymer.

[0260] In Example 28, the method for preparing polyvinylidene difluoride having a weight-average molecular weight of 20,000 includes the following steps.

[0261] 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose are added to a 0.5 L high-pressure reactor, and oxygen is removed by purging with nitrogen gas several times, after which 120 g of vinylidene fluoride monomer gas is added. After adding the monomer, the reaction temperature is controlled to 83°C, and the reaction is started after adding a water-soluble ammonium persulfate initiator and 0.14 g of isopropyl alcohol chain transfer agent; the amount of initiator added is approximately 8% of the total amount of added monomer. The polymerization reaction time is 1 hour, and the pressure is maintained at 4.4 MPa. Polyvinylidene difluoride polymer is obtained by washing and drying the reaction product with water.

[0262] In Example 29, the method for preparing polyvinylidene difluoride having a weight-average molecular weight of 150,000 includes the following steps.

[0263] 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose are added to a 0.5 L high-pressure reactor, and oxygen is removed by purging with nitrogen gas several times, after which 120 g of vinylidene fluoride monomer gas is added. After adding the monomer, the reaction temperature is controlled to 79°C, and a water-soluble ammonium persulfate initiator and 0.12 g of isopropyl alcohol chain transfer agent are added to start the reaction. The amount of initiator added is approximately 7.0% of the total amount of added monomer, the polymerization reaction time is 1.5 h, and the pressure is maintained at 4.4 MPa. The reaction product is washed with water and dried to obtain a polyvinylidene difluoride polymer.

[0264] The method of manufacturing the battery in Examples 30 and 31 is basically the same as in Example 20, the only difference being that the weight average molecular weight of the second fluorine-containing polymer is changed.

[0265] The method of manufacturing the battery in Examples 32 and 33 is basically the same as in Example 20, the only difference being that the weight average molecular weight of the first fluorine-containing polymer is changed.

[0266] The method for preparing polyvinylidene difluoride with a weight-average molecular weight of 3 million in Example 32 is as follows.

[0267] 4 kg of deionized water and 2 g of methyl cellulose ether are added to a 10 L high-pressure reactor and vacuumed, then O2 is replaced with N2 three times, then 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate are added, and 1 kg of vinylidene fluoride monomer is filled so that the pressure reaches 7 MPa, and the mixture is mixed and stirred for 30 min and heated to 45°C to carry out the polymerization reaction. After 10 hours of polymerization, 20 g of cyclohexane is added to continue the reaction, and the reaction is stopped when the pressure inside the reactor drops to 2 MPa. The reaction system is centrifuged to collect the solid phase, and a polyvinylidene fluoride binder is obtained through washing and drying.

[0268] The method for preparing polyvinylidene difluoride with a weight-average molecular weight of 10 million in Example 33 is as follows.

[0269] First stage polymerization reaction: 4 kg of deionized water and 2 g of methyl cellulose ether are added to 10 L high-pressure reactors No. 1 and 2, vacuumed, and then O2 is substituted with N2 three times. Then, 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate are added, and 1 kg of vinylidene fluoride monomer is added to reach a pressure of 5 MPa. Mixing and stirring are performed for 30 min, then heated to 45°C and reacted for 9 h.

[0270] Second stage polymerization reaction: The reaction solution in reactors 1 and 2 is transferred to reactor 3, nitrogen gas is filled until the pressure reaches 7 MPa, heated to 70°C, stirred for 3 hours, and the reaction is carried out.

[0271] Third step polymerization reaction: 20g of cyclohexane is added and the reaction is continued for 1 hour, after which the reaction is stopped. The reaction system is centrifuged to collect the solid phase, and the polyvinylidene fluoride binder is obtained through washing and drying.

[0272] The method of manufacturing the battery in Examples 34 and 35 is basically the same as in Example 20, the difference being that the type of the second fluorine-containing polymer is changed, and the second fluorine-containing polymer in Example 34 is vinylidene difluoride-chlorotrifluoroethylene copolymer, and the second fluorine-containing polymer in Example 35 was not chlorinated.

[0273] The method for preparing the vinylidene difluoride-chlorotrifluoroethylene copolymer in Example 34 is as follows.

[0274] 0.8g of benzoyl peroxide (BPO) is weighed and added to a 1L high-pressure reactor containing 1,1,2-trichlorotrifluoroethane (400mL). The reactor is sealed, cooled in a dry ice bath, vacuumed, 25g of chlorotrifluoroethylene is injected, followed by 420g of vinylidene fluoride. The mixture is heated to room temperature, then heated to 45°C and reacted for 7.5 hours. After cooling to room temperature and releasing unreacted gas, the reactor is opened to remove the colorless precipitate from the solution. The solution is then dried in a vacuum dryer at 55°C for 8 hours to finally obtain a P(VDF-TrFE) copolymer.

[0275] In Example 36, the method of manufacturing the battery is basically the same as in Example 20, the difference being that the type of the first fluorine-containing polymer in the binder composition is changed to a (vinylidene difluoride-hexafluoropropylene) copolymer and the third fluorine-containing polymer is changed to a (vinylidene difluoride-hexafluoropropylene) copolymer.

[0276] The method for preparing a (vinylidene difluoride-hexafluoropropylene) copolymer with a weight average molecular weight of 5 million is as follows.

[0277] First stage polymerization reaction: 4 kg of deionized water and 2.5 g of methyl cellulose ether are added to 10 L high-pressure reactors No. 1 and 2, vacuumed, and then O2 is substituted with N2 three times. Then, 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate are added, and 0.94 kg of vinylidene fluoride and 0.06 kg of hexafluoropropylene are added to reach a pressure of 5 MPa. Mixing and stirring are performed for 30 min, then heated to 45°C and reacted for 4 h.

[0278] Second stage polymerization reaction: The reaction solution in reactors 1 and 2 is transferred to reactor 3, nitrogen gas is filled until the pressure reaches 7 MPa, heated to 70°C, stirred for 3 hours, and the reaction is carried out.

[0279] Step 3 polymerization reaction: 38 g of cyclohexane is added and the reaction is continued for 1 hour, after which the reaction is stopped. The reaction system is centrifuged to collect the solid phase, and after washing and drying, a vinylidene fluoride-chlorotrifluoroethylene copolymer binder is obtained.

[0280] The method for preparing a (vinylidene difluoride-hexafluoropropylene) copolymer with a weight-average molecular weight of 80,000 is as follows.

[0281] 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose are added to a 0.5 L high-pressure reactor and oxygen is removed by purging with nitrogen gas several times, then 100 g of vinylidene fluoride monomer gas and 11.9 g of hexafluoropropylene are added. After adding the monomers, the reaction temperature is controlled to 85°C. After adding a water-soluble ammonium persulfate initiator and 0.12 g of isopropyl alcohol chain transfer agent, the reaction is started, and the amount of initiator added is approximately 8% of the total amount of monomers. The polymerization reaction time is 1 hour, and the pressure is maintained at 4.6 MPa. The reaction product is washed with water and dried to obtain a secondary fluorine-containing polymer.

[0282] The composition of the binder composition in Comparative Examples 1 to 3 is different, and specifically refer to Table 1 and Table 2.

[0283] B. Battery Performance Test

[0284] 1. Polymer property test

[0285] 1) Weight-average molecular weight test

[0286] Use a Waters 2695 isocratic HPLC-type gel chromatograph (differential refractive index detector 2141). Select a matched chromatography column (planet: Styragel HT5DMF 7.8*300mm + Styragel HT4) based on a polystyrene solution sample with a mass fraction of 3.0%. Prepare a 3.0% polymer colloidal solution using purified N-methylpyrrolidone (NMP) solvent and allow the prepared solution to stand for one day. For testing, first draw tetrahydrofuran into the syringe and wash it repeatedly. Then, draw in 5 ml of the experimental solution to remove air from the syringe and wipe the needle tip. Finally, slowly inject the sample solution into the sample inlet. After the display stabilizes, acquire the data and read the weight-average molecular weight.

[0287] 2) Crystallinity test

[0288] 0.5g of fluorine-containing polymer is placed in an aluminum crucible, shaken evenly, and then the crucible lid is closed. Then, the sample is tested using a Differential Scanning Calorimeter (DSC) of the Discovery 250 model from TA, USA, in a nitrogen gas atmosphere with a purge gas of 50ml / min, a shielding gas of 70ml / min, a heating temperature of 10℃ / min, and a test temperature range of -100℃ to 400℃, and the thermal history is removed.

[0289] Through this test, the DSC / (Mw / mg) change curve of the fluorine-containing polymer with respect to temperature is obtained and integrated, and the peak area is the melting enthalpy ΔH (J / g) of the fluorine-containing polymer composition, and the degree of binder crystallinity = ΔH / (ΔHm100%)*100%, where ΔHm100% is the standard melting enthalpy (heat of crystalline dissolution) of the fluorine-containing polymer, and ΔHm100% = 104.7 J / g.

[0290] 3) Chlorine content test

[0291] The chlorine content of chlorinated PVDF is measured using the alkali melting method, and the specific procedure is as follows. Accurately weigh 0.6 grams (with an accuracy of up to 1 mg) of the ground secondary fluorine-containing polymer and place it in a 40 ml porcelain crucible. First, spread a mixture of anhydrous sodium carbonate and potassium nitrate at the bottom of the porcelain crucible, add the sample, and then cover the top with the mixture of anhydrous sodium carbonate and potassium nitrate. The mass ratio of anhydrous sodium carbonate to potassium nitrate is 3:2, and both are chlorine-free reagents. The amount of this mixture used for each sample is approximately 10 g. Cover the crucible containing the sample with a lid, but do not seal it tightly so that gas can still leak out. Place the crucible in a muffle furnace and gradually heat it to 600°C. Melt it for about 4 hours until no foul-smelling gas volatilizes, and stop heating when the melt is uniform and there are no black spots. Remove the crucible and let it cool slightly, then add boiling water to dissolve it. After cooling, transfer it to a 250 ml quantitative flask and add deionized water up to the mark. Take 5 ml of the solution and place it in an Erlenmeyer flask. Add 1 drop of bromophenol blue indicator, then add 5 drops of ethanol dropwise and shake to mix. First, neutralize most of the alkali with concentrated nitric acid, then add nitric acid with a concentration of 0.2 ml / L dropwise to turn the bromophenol blue yellow, and then add a few more drops to adjust the pH of the solution to 1.5–2. Add 5 drops of diphenyl carbazone solution dropwise and titrate with a standard mercury nitrate solution. At the endpoint, the color changes from yellowish-red to purplish-red, and a blank test is performed under the same conditions. Test each of the above samples three times.

[0292] The mass fraction of chlorine (Cl%) is calculated using the following formula.

[0293] Cl%=[(Vl-V2)×C×35.46×2 / W]×100

[0294] In the formula: V1 and V2 are the volumes of mercury nitrate standard solution consumed in the titration sample and blank test, respectively, in mL; C is the concentration of the mercury nitrate standard solution, in mol / L; and W is the mass of the sample, in mg.

[0295] 2. Slurry Performance Test

[0296] 1) Slurry fluidity test

[0297] Take an appropriate amount of anode slurry with a measuring spoon and observe whether the natural downward flow of the anode slurry is smooth. If the natural flow is smooth, it is judged as OK; if the fluidity is poor and jelly-like lumps form in the slurry, it means that gel has formed and it is judged as NG.

[0298] 2) Slurry filtration performance test

[0299] A 500ml beaker is placed under a 200 mesh filter screen support, 500ml of slurry is collected and placed on the filter screen for filtration, and the time taken for the volume of the slurry in the beaker to reach 300ml is recorded. This time is used to judge the filtration performance of the slurry. If the filtration time is less than 120s, the filtration performance of the slurry is judged as 'OK', and if the slurry does not pass through the filter screen, it indicates that the filtration performance of the slurry is poor and is judged as 'NG'.

[0300] 3. Plate Performance Test

[0301] 1) Adhesion test

[0302] Referring to GB-T2790-1995 International Method for Testing 180° Peel Strength of Adhesives, the adhesion strength test process according to the examples and comparative examples of the present application is as follows.

[0303] Cut a sample with a width of 30 mm and a length of 100 to 160 mm using a knife, and attach a dedicated double-sided tape with a width of 20 mm and a length of 90 to 150 mm to a steel plate. Attach the side of the previously cut electrode plate sample containing the anode film layer to the double-sided tape, and then roll it three times along the same direction with a 2 kg roller.

[0304] After fixing a paper tape with a width equal to that of the electrode plate and a length of 250 mm onto the electrode plate current collector, secure it with masking tape.

[0305] Turn on the power to the SASTest tensioner (sensitivity 1N). When the indicator light turns on, adjust the limit block to the appropriate position and secure the unattached end of the steel plate with the lower clamp. Fold the paper tape upward and secure it with the upper clamp, then adjust the position of the upper clamp using the 'Up' and 'Down' buttons on the manual controller provided with the tensioner. Next, perform the test and read the value. The adhesion strength between the anode film layer and the current collector is characterized by dividing the force at which the plate stress is balanced by the width of the tape to obtain the adhesion force of the plate per unit length.

[0306] 2) Measurement of anode film layer resistance:

[0307] The dried anode slurry (film layer) is cut from the left, middle, and right sides of the anode plate and cut into small discs with a diameter of 3 mm. Turn on the power of the IEST electrode resistance meter, place it in the appropriate position on the electrode resistance meter 'probe', press the 'Start' button, and read the value once the display stabilizes. Each small disc measures two positions, and the average value of the last six measurements is calculated to obtain the film layer resistance of this electrode plate.

[0308] 3) Electrode brittleness test

[0309] The anode plate according to the embodiment is prepared by cutting it into a test sample of 20×100mm size. The anode plate is folded in half and fixed, then rolled once with a 2kg roller, and then inspected for light transmission and metal exposure in the folded portion of the anode plate; if there is no light transmission and metal exposure, the anode plate is folded in half again in the opposite direction and fixed, then rolled once with a 2kg roller, and then inspected for light transmission and metal exposure in the folded portion of the anode plate, and the above procedure is repeated until light transmission and metal exposure are found in the folded portion of the anode plate, and the number of times the anode plate is folded in half and transmitted is recorded. Three sets are tested simultaneously and the average value is calculated.

[0310] 4. Battery Performance Test

[0311] 1) Battery capacity retention rate test

[0312] The battery capacity retention rate test process is as follows. A button-type battery is charged to 3.65V at 25℃ with a constant current of 1 / 3C, then charged to a constant voltage of 3.65V until the current becomes 0.05C, left for 5 minutes, and then discharged again to 2.5V with 1 / 3C, and the obtained capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and simultaneously, the discharge capacity Cn of the battery is recorded after the nth cycle. After each cycle, the battery capacity retention rate Pn = Cn / C0 * 100%, and a curve graph of the battery capacity retention rate and the number of cycles is obtained by using 500 values ​​from P1, P2… … P500 as the vertical axis and the corresponding number of cycles as the horizontal axis.

[0313] In this test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and … the 500th cycle corresponds to n=500. In the table, the battery capacity retention rate data corresponding to the example and comparative example is the data measured after 500 cycles under the above test conditions, i.e., the value of P500.

[0314] C. Analysis of test results for each example and comparative example

[0315] Each battery of each example and comparative example is manufactured according to the above method, and each performance parameter is measured, and the results can be seen by referring to Table 1 and Table 2 below.

[0316]

[0317]

[0318]

[0319]

[0320]

[0321]

[0322]

[0323] Comparing Examples 1 to 14 with Comparative Example 1, it can be seen that the degree of crystallization of the polymer can be lowered by including fluorine-containing polymers with different weight-average molecular weights in the binder composition. In Examples 1 to 9, it can be seen that the degree of crystallization of the binder composition decreases as the content of the second fluorine-containing polymer increases. In Examples 10 to 13, it can be seen that the chlorinated polyvinylidene difluoride has a degree of crystallization of only 4.2% when the chlorine content is 8%, and is basically in an amorphous state.

[0324] In Example 14, it can be seen that the (vinylidene difluoride-chlorotrifluoroethylene) copolymer can effectively lower the degree of crystallinity of the binder composition even as a second fluorine-containing polymer. However, it can be seen that when the chlorine content of the (vinylidene difluoride-chlorotrifluoroethylene) copolymer is 8%, its degree of crystallinity is higher than that of chlorinated polyvinylidene difluoride.

[0325] Comparing Examples 15 to 36 with Comparative Examples 1 to 2, it can be seen that the binder composition can significantly reduce the amount of fluorine-containing polymer used, and that when a third fluorine-containing polymer is included in the binder composition, high adhesion performance can be ensured while effectively improving the processing performance of the slurry and enhancing the flexibility of the battery, thereby optimizing the cycle performance of the battery.

[0326] Comparing Examples 15–17 and 20 with Examples 35 and 36, it can be seen that the addition of a chlorinated second fluorine-containing polymer can further improve the flexibility of the polymer and reduce the possibility of brittle fracture of the electrode plate.

[0327] In Examples 18 to 22, it can be seen that as the amount of binder composition used increases, the adhesion of the electrode plate continues to increase, and the flexibility and cycle capacity retention rate increase first and then decrease.

[0328] It should be noted that the present application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiments having substantially the same configuration as the technical concept and producing the same effect within the scope of the technical solution of the present application are included within the technical scope of the present application. Furthermore, other forms configured by applying various modifications that a person skilled in the art could conceive of to the embodiments without deviating from the essence of the present application, and by combining some of the components of the embodiments, are also included within the scope of the present application.

Claims

Claim 1 A binder composition comprising a first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer, wherein the weight average molecular weight of the first fluorine-containing polymer is 3 million to 10 million, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1.1 million, the weight average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000, and the degree of crystallinity of the binder composition does not exceed 40%. Claim 2 A binder composition according to claim 1, characterized in that, when calculated based on the total mass of the binder composition, the mass content of the first fluorine-containing polymer is 10% to 86%. Claim 3 A binder composition according to claim 1, characterized in that, when calculated based on the total mass of the binder composition, the mass content of the second fluorine-containing polymer is 10% to 86%. Claim 4 A binder composition according to claim 1, characterized in that the first fluorine-containing polymer comprises a structural unit derived from vinylidene difluoride. Claim 5 In claim 1, the first fluorine-containing polymer further comprises a structural unit represented by Formula I, and Formula I where R1 is fluorine, chlorine, or C containing at least one fluorine atom 1-3 A binder composition characterized by comprising one or more of alkyl groups. Claim 6 A binder composition according to claim 1, wherein the first fluorine-containing polymer comprises one or more of polyvinylidene difluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer. Claim 7 In claim 1, the second fluorine-containing polymer comprises a structural unit represented by Formula II, and Equation II Here, R2 and R3 are each independently hydrogen, a halogen, or C containing at least one fluorine atom. 1-3 A binder composition characterized by comprising at least one alkyl group. Claim 8 A binder composition according to claim 1, characterized in that the second fluorine-containing polymer contains chlorine. Claim 9 A binder composition according to claim 1, characterized in that, when calculated based on the total mass of the second fluorine-containing polymer, the chlorine content in the second fluorine-containing polymer does not exceed 8%. Claim 10 A binder composition according to claim 1, characterized in that the degree of crystallization of the second fluorine-containing polymer does not exceed 47%. Claim 11 A binder composition according to claim 1, characterized in that the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000. Claim 12 A binder composition according to claim 1, wherein the second fluorine-containing polymer comprises at least one of polyvinylidene difluoride, chlorinated polyvinylidene difluoride, chlorinated poly(vinylidene difluoride-hexafluoropropylene), and poly(vinylidene difluoride-chlorotrifluoroethylene). Claim 13 In claim 1, the third fluorine-containing polymer comprises a structural unit represented by Formula III, and Formula III, wherein R4 and R5 each independently comprise at least one of hydrogen, fluorine, chlorine, or trifluoromethyl group, characterized in that the binder composition is Claim 14 A binder composition according to claim 1, characterized in that the terminal group of the third fluorine-containing polymer includes a hydroxyl group or an ester group. Claim 15 A binder composition according to claim 1, wherein the third fluorine-containing polymer comprises one of polytetrafluoroethylene, polyvinylidene difluoride, poly(vinylidene difluoride-hexafluoropropylene) copolymer, poly(vinylidene difluoride-tetrafluoroethylene) copolymer, poly(vinylidene difluoride-chlorotrifluoroethylene) copolymer, or poly(vinylidene difluoride-vinylidene tetrafluoride-hexafluoropropylene) copolymer. Claim 16 A positive plate comprising a positive current collector and a positive film layer installed on at least one surface of the positive current collector, wherein the positive film layer comprises a positive active material, a conductive agent, and a binder composition according to any one of claims 1 to 15. Claim 17 An anode plate according to claim 16, characterized in that the mass fraction of the binder composition does not exceed 1.5% and is calculated based on the total mass of the anode film layer. Claim 18 A positive plate according to claim 16, characterized in that the positive active material is at least one of a lithium-containing transition metal oxide, a doping modified material thereof, or a conductive carbon coating modified material, a conductive metal coating modified material thereof, or a conductive polymer coating modified material thereof. Claim 19 A secondary battery comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a separator, a negative electrode plate and a positive electrode plate according to claim 16. Claim 20 An electric device characterized by including a secondary battery according to claim 19. Claim 21 delete Claim 22 delete Claim 23 delete Claim 24 delete Claim 25 delete Claim 26 delete Claim 27 delete Claim 28 delete Claim 29 delete Claim 30 delete

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