Fluorine-free polymer, method for producing the same, and use thereof, insulating coating and method for producing the same, battery and electric device

Abstract

The present application provides a fluorine-free polymer, a preparation method and application thereof, an insulating coating and a preparation method thereof, a secondary battery, and an electric device. The fluorine-free polymer comprises a structural unit derived from an olefin monomer, a structural unit derived from a monomer represented by Formula I, and a structural unit derived from a monomer represented by Formula II; wherein R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or a substituted or unsubstituted C 1‑6 alkyl group, and R7 is selected from a substituted or unsubstituted C 1‑8 alkyl group.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a fluoropolymer, its preparation method and application, an insulating coating and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] With the increasingly widespread application of batteries, ensuring battery safety is crucial in battery production and application. Thermal runaway caused by short circuits is one of the main factors affecting battery safety. To prevent short circuits between the positive and negative electrodes due to thermal shrinkage of the separator, an insulating coating is commonly used on the electrodes. However, the peel strength of current insulating coatings is poor, and they are prone to detachment, severely affecting the use of the electrodes. Therefore, there is an urgent need to develop an adhesive to improve the performance of the insulating coating. Summary of the Invention

[0004] In view of the problems existing in the background art, this application provides a fluoropolymer and an insulating coating containing the fluoropolymer, which can improve the peel strength of the insulating coating, improve the adhesion stability of the insulating coating during battery cycling, and improve the performance of the insulating coating.

[0005] The first aspect of this application provides a fluorine-free polymer comprising structural units derived from olefin monomers, structural units derived from monomers shown in Formula I, and structural units derived from monomers shown in Formula II.

[0006]

[0007] Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or substituted or unsubstituted C. 1-6 Alkyl group, R7 is selected from substituted or unsubstituted C4 groups. 1-8 alkyl.

[0008] The fluorine-free polymer provided in this application contains hard segments of structural units derived from olefin monomers, which can reduce the swelling of the electrode in the electrolyte. It also contains soft segments of structural units derived from formula II. The combination of hard and soft segments gives the fluorine-free polymer a suitable glass transition temperature and excellent mechanical strength. Furthermore, the carboxyl groups in the structural units derived from formula I can form hydrogen bonds with the hydroxyl and / or carboxyl groups on the current collector surface, resulting in excellent adhesion of the insulating coating. Both of these factors work together to improve the peel strength of the insulating coating. Simultaneously, the coating exhibits excellent electrolyte resistance. The combined effect of excellent peel strength and electrolyte resistance improves the adhesion stability of the insulating coating during battery cycling, thereby enhancing its stability and overall performance.

[0009] In any embodiment, R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or C. 1-3 Alkyl group, R7 is selected from C 1-3 alkyl.

[0010] In any embodiment, the molar content of the structural units derived from the monomer shown in Formula II is 10%-60%, based on the total molar number of all structural units in the fluoropolymer.

[0011] By controlling the molar content of the structural units of the monomer derived from Formula II within a suitable range, the cutting burrs of the electrode sheet are effectively reduced, the laser cutting quality of the electrode sheet is improved, the insulating coating has excellent peel strength and electrolyte resistance, the bonding stability of the insulating coating during battery cycling is improved, the performance of the insulating coating is improved, and the battery safety performance is improved.

[0012] In any embodiment, the molar content of the structural units derived from the monomer shown in Formula I is 5%-20%, based on the total number of moles of structural units in the fluoropolymer.

[0013] Controlling the molar content of the structural units derived from the monomer shown in Formula I within a suitable range,

[0014] It effectively reduces cutting burrs on the electrode sheets, improves the laser cutting quality of the electrode sheets, and the insulating coating has excellent peel strength and electrolyte resistance. It also improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, and improves battery safety performance.

[0015] In any embodiment, the molar content of the structural units derived from olefin monomers is 20%-85%, based on the total molar number of all structural units in the fluoropolymer.

[0016] By controlling the molar content of structural units derived from olefin monomers within a suitable range, the cutting burrs of the electrode sheet are effectively reduced, the laser cutting quality of the electrode sheet is improved, the insulating coating has excellent peel strength and electrolyte resistance, the adhesion stability of the insulating coating during battery cycling is improved, the performance of the insulating coating is improved, and the battery safety performance is improved.

[0017] In any embodiment, the weight-average molecular weight of the fluorine-free polymer is 100,000 to 1,500,000.

[0018] By controlling the weight-average molecular weight of the fluoropolymer within a suitable range, the cutting burrs of the electrode sheet are effectively reduced, the laser cutting quality of the electrode sheet is improved, the insulating coating has excellent peel strength and electrolyte resistance, the adhesion stability of the insulating coating during battery cycling is improved, the performance of the insulating coating is improved, and the battery safety performance is improved.

[0019] In any embodiment, the olefin monomer comprises one or more of ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0020] In any embodiment, the monomer shown in Formula I comprises one or more of acrylic acid, methacrylic acid, and ethylacrylic acid.

[0021] In any embodiment, the monomer shown in Formula II comprises one or more of methyl acrylate, methyl methacrylate, ethyl ethyl acrylate, and butyl acrylate.

[0022] The second aspect of this application provides a method for preparing a fluorine-free polymer, characterized in that the preparation method includes:

[0023] An intermediate polymer is formed by polymerizing at least one olefin monomer and at least one monomer of Formula II, the intermediate polymer containing ester groups.

[0024]

[0025] R4, R5, and R6 are each independently selected from hydrogen or substituted or unsubstituted C. 1-6 Alkyl group, R7 is selected from substituted or unsubstituted C4 groups. 1-8 alkyl;

[0026] The intermediate polymer is mixed with an aqueous solution of an alkaline substance and reacts to hydrolyze at least some of the ester groups in the intermediate polymer into carboxyl groups.

[0027] This method is simple to prepare, uses abundant raw materials, and is low in cost. Through the hydrolysis of ester groups under alkaline conditions, at least partially converting them into carboxyl groups, the adhesion of the insulating coating is improved. Simultaneously, the polymerization of olefin monomers forms the hard segments of the fluorine-free polymer, reducing the swelling of the electrode in the electrolyte. The ester-containing segments form the soft segments of the fluorine-free polymer. The combination of hard and soft segments gives the fluorine-free polymer a suitable glass transition temperature and excellent mechanical strength. Both work together to improve the peel strength of the insulating coating. Furthermore, the coating exhibits excellent electrolyte resistance. The combined effect of excellent peel strength and electrolyte resistance improves the adhesion stability of the insulating coating during battery cycling, enhancing its overall stability and performance.

[0028] In any embodiment, R4, R5, and R6 are each independently selected from hydrogen or C. 1-3 Alkyl group, R7 is selected from C 1-3 alkyl.

[0029] In any embodiment, the molar content of the olefin monomer is 20%-85%, based on the total molar number of the olefin monomer and the monomer shown in Formula II.

[0030] By controlling the molar content of olefin monomers within a suitable range, the cutting burrs of the electrode sheet can be effectively reduced, the laser cutting quality of the electrode sheet can be improved, the insulating coating has excellent peel strength and electrolyte resistance, the adhesion stability of the insulating coating during battery cycling can be improved, the performance of the insulating coating can be improved, and the battery safety performance can be improved.

[0031] In any embodiment, the molar ratio of the monomer shown in Formula II to the alkaline substance is 1:0.1 to 1:0.5.

[0032] Controlling the molar ratio of monomer to alkaline substance as shown in Formula II within a suitable range can control the degree of hydrolysis of ester groups, control the molar content of ester and carboxyl groups within a suitable range, effectively reduce cutting burrs on the electrode, improve the laser cutting quality of the electrode, and give the insulating coating excellent peel strength and electrolyte resistance, improve the adhesion stability of the insulating coating during battery cycling, improve the performance of the insulating coating, and improve battery safety performance.

[0033] In any embodiment, the preparation method further includes:

[0034] After the reaction is complete, add an acidic solution to the reaction product to adjust the pH of the reaction solution to 5.0-7.0.

[0035] In any embodiment, the alkaline substance is selected from one or more of lithium hydroxide, sodium hydroxide, and ammonia. These materials are simple, readily available, low in cost, and easy to promote and apply.

[0036] In any embodiment, the reaction temperature for the intermediate polymer to react with the aqueous solution of the alkaline substance is 35°C-120°C, or 60-90°C. Controlling the reaction temperature within a suitable range can control the degree of hydrolysis of the ester groups, control the molar content of ester and carboxyl groups within a suitable range, effectively reduce cutting burrs on the electrode, improve the laser cutting quality of the electrode, and give the insulating coating excellent peel strength and electrolyte resistance. This also improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, and improves battery safety.

[0037] In any embodiment, the reaction time for the intermediate polymer to react with the aqueous solution of the alkaline substance is 1-24 hours, or 4-10 hours. Controlling the reaction temperature within a suitable range can control the degree of hydrolysis of the ester groups and the molar content of the ester and carboxyl groups within a suitable range, effectively reducing cutting burrs on the electrode sheet, improving the laser cutting quality of the electrode sheet, and giving the insulating coating excellent peel strength and electrolyte resistance. This also improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, and improves battery safety.

[0038] In any embodiment, the olefin monomer comprises one or more of ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0039] In any embodiment, the monomer shown in Formula II comprises one or more of methyl acrylate, methyl methacrylate, ethyl ethyl acrylate, and butyl acrylate.

[0040] The third aspect of this application provides an application of the fluorine-free polymer provided in the first aspect of this application in a secondary battery.

[0041] The fourth aspect of this application provides an insulating coating comprising an adhesive and an inorganic insulating material, wherein the adhesive is a fluorine-free polymer provided in the first aspect of this application or a fluorine-free polymer prepared by the preparation method provided in the second aspect of this application.

[0042] In any embodiment, the fluoropolymer content is 15%-30% by mass, based on the total mass of the insulating coating.

[0043] By controlling the mass content of fluoropolymers within a suitable range, the adhesion stability of the insulating coating during battery cycling can be improved, the performance of the insulating coating can be enhanced, the cutting burrs on the electrode sheets can be reduced, and the laser cutting quality of the electrode sheets can be improved.

[0044] In any embodiment, the inorganic insulating material has a mass content of 70%-85%, based on the total mass of the insulating coating.

[0045] Controlling the mass content of inorganic insulating materials within a suitable range improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, reduces cutting burrs on the electrode sheets, and improves the laser cutting quality of the electrode sheets.

[0046] In any embodiment, the Dv50 of the inorganic insulating material is 0.1-5 μm.

[0047] Controlling the Dv50 of the electrodeless insulating material within a suitable range can improve the peel strength of the insulating coating, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, effectively reduce the virtual edge of the insulating coating, improve the positioning accuracy of the identification system, reduce burrs in electrode cutting, and improve the laser cutting quality of the electrode.

[0048] In any embodiment, the inorganic insulating material comprises hydroxides or hydrated oxides.

[0049] In any embodiment, the inorganic insulating material comprises one or more of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, hydrated alumina, and hydrated magnesium silicate.

[0050] The fifth aspect of this application provides a method for preparing an insulating coating, comprising first stirring, second stirring, and coating.

[0051] First mixing: The binder and inorganic insulating filler are first mixed to obtain a dry mixture, wherein the binder contains the fluorine-free polymer provided in the first aspect of this application;

[0052] Second stirring: The dry mixture and solvent are stirred for the second time to obtain the insulating coating slurry;

[0053] Coating: Apply the insulating coating slurry onto the current collector to prepare the insulating coating.

[0054] In any embodiment, the stirring speed of the first stirring is 50-1000 r / min, and the stirring time is 5-30 min.

[0055] Controlling the stirring speed of the first stirring step within a suitable range can reduce the virtual edges of the insulating coating, decrease the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce burrs during electrode cutting, and improve the laser cutting quality of the electrode.

[0056] Controlling the stirring time of the first stirring step within a suitable range can reduce the virtual edges of the insulating coating, decrease the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce burrs in electrode cutting, and improve the laser cutting quality of the electrode.

[0057] In any embodiment, the stirring speed of the second stirrer is 1000-3000 r / min, and the stirring time is 1-3 h.

[0058] Controlling the stirring speed of the second stirrer within a suitable range can reduce the virtual edges of the insulating coating, improve the peel strength of the insulating coating, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce burrs in electrode cutting, and improve the laser cutting quality of the electrode.

[0059] Controlling the stirring time of the second stirring within a suitable range can improve the peel strength of the insulating coating, enhance the adhesion stability of the insulating coating during battery cycling, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce electrode cutting burrs, and improve the laser cutting quality of the electrode.

[0060] In any embodiment, the second stirring temperature is 10-60°C.

[0061] Controlling the stirring temperature of the second stirrer within a suitable range can improve the peel strength of the insulating coating, reduce the coating edge defects, decrease the electrolyte swelling rate of the coating, and improve the electrolyte resistance of the coating.

[0062] In any implementation, the coating step specifically includes:

[0063] An insulating coating slurry is applied to a current collector and dried at a temperature of 90-130℃ to prepare the insulating coating.

[0064] A suitable drying temperature can reduce the virtual edges of the insulating coating, improve the positioning accuracy of the laser recognition system, increase the peel strength of the insulating coating, and also save energy and reduce costs.

[0065] In any embodiment, the solid content of the insulating coating slurry is 20%-50%.

[0066] Controlling the solid content in the insulating coating slurry within a suitable range can improve the adhesion of the insulating coating, enabling it to maintain excellent adhesion after 500 battery cycles. It can also effectively reduce electrode cutting burrs and improve the laser cutting quality of the electrodes.

[0067] The sixth aspect of this application provides a secondary battery including a positive electrode and a negative electrode, wherein the positive electrode and / or the negative electrode includes an insulating coating provided in the fourth aspect of this application.

[0068] In any embodiment, the secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

[0069] The seventh aspect of this application provides an electrical device, including the secondary battery provided in the sixth aspect of this application. Attached Figure Description

[0070] Figure 1This is a schematic diagram of an electrode sheet including an insulating coating;

[0071] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0072] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0073] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0074] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0075] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0076] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application;

[0077] Figure label:

[0078] 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrode sheet; 61 Current collector; 62 Active material layer; 63 Insulating coating. Detailed Implementation

[0079] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the adhesive, preparation method, electrode, battery, and power device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0080] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0081] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0082] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0083] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0084] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0085] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0086] Safety is one of the most important research topics in rechargeable batteries. For example... Figure 1 As shown, during the preparation of electrode 6, an insulating coating 63 is applied between the current collector 61 used to form the electrode tab and the active material layer 62 to prevent direct contact between the positive and negative electrodes during use, which could lead to a short circuit, safety accidents, or even fires and explosions. Due to the high resistance of inorganic materials, they are often dispersed in a binder to form a slurry for preparing the insulating coating. However, with traditional binders, the inorganic material in the insulating coating may fall off during subsequent electrode processing and battery cycling, potentially causing safety accidents.

[0087] In view of the above problems, this application proposes a fluorine-free polymer and an insulating coating containing the fluorine-free polymer, which can improve the peel strength of the insulating coating, improve the adhesion stability of the insulating coating during battery cycling, improve the performance of the insulating coating, and improve the safety performance of the battery.

[0088] [Fluoropolymer]

[0089] This application proposes a fluorine-free polymer comprising structural units derived from olefin monomers, structural units derived from monomers shown in Formula I, and structural units derived from monomers shown in Formula II.

[0090]

[0091] Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or substituted or unsubstituted C. 1-6 Alkyl group, R7 is selected from substituted or unsubstituted C4 groups. 1-8 alkyl.

[0092] In this article, the term "fluorine-free polymer" refers to a polymer that does not contain fluorine.

[0093] In this document, the term "polymer" includes, on the one hand, an aggregate of chemically homogeneous macromolecules prepared by polymerization reactions, but differing in degree of polymerization, molar mass, and chain length. On the other hand, the term also includes derivatives of such aggregates of macromolecules formed by polymerization reactions, i.e., compounds that can be obtained through reactions of the functional groups in the aforementioned macromolecules, such as addition or substitution, and which may be chemically homogeneous or chemically heterogeneous.

[0094] In this document, the term "C1-C6 alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without any unsaturation, having one to six carbon atoms, and attached to the rest of the molecule by single bonds. Examples of C1-C6 alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, and n-hexyl. The term "C1-C8 alkyl" should be interpreted accordingly.

[0095] In this document, the term “substitution” means being substituted by a substituent, wherein each substituent is independently selected from: hydroxyl, mercapto, amino, cyano, nitro, aldehyde, and halogen atom.

[0096] In this paper, the term "olefin" refers to hydrocarbons containing C=C bonds.

[0097] In some embodiments, the olefin monomer comprises one or more of ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0098] In some embodiments, the monomer represented by Formula I comprises one or more of acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0099] In some embodiments, the monomer shown in Formula II comprises one or more of methyl acrylate, methyl methacrylate, ethyl 2-ethyl acrylate, and butyl acrylate.

[0100] The fluorine-free polymer provided in this application contains hard segments of structural units derived from olefin monomers, which can reduce the swelling of the electrode in the electrolyte. It also contains soft segments of structural units derived from formula II. The combination of hard and soft segments gives the fluorine-free polymer a suitable glass transition temperature and excellent mechanical strength. Furthermore, the carboxyl groups in the structural units derived from formula I can form hydrogen bonds with the hydroxyl and / or carboxyl groups on the surface of the current collector and / or inorganic insulating material, resulting in excellent adhesion of the insulating coating. Both of these factors work together to improve the peel strength of the insulating coating. Simultaneously, the coating exhibits excellent electrolyte resistance. This superior peel strength and electrolyte resistance work together to improve the adhesion stability of the insulating coating during battery cycling, thereby increasing its stability and reducing the likelihood of expansion, peeling, or other phenomena during subsequent battery operation, thus improving battery safety. In addition, compared to the binders of fluorinated polymers in the prior art, using the fluorine-free polymer of this application in the insulating coating can reduce costs.

[0101] In some embodiments, R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or C. 1-3Alkyl group, R7 is selected from C 1-3 alkyl.

[0102] In this document, the term "C1-C3 alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without any unsaturation, having one to three carbon atoms, and attached to the rest of the molecule by a single bond. Examples of C1-C3 alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, and isopropyl.

[0103] In some embodiments, the molar content of the structural units derived from the monomer shown in Formula II is 10%-60%, based on the total molar number of all structural units in the fluoropolymer. In some embodiments, the molar content of the structural units derived from the monomer shown in Formula II may be selected from any one of 10%-20%, 10%-30%, 10%-40%, 10%-50%, 10%-60%, 20%-30%, 20%-40%, 20%-50%, 20%-60%, 30%-40%, 30%-50%, 30%-60%, 40%-50%, 40%-60%, and 50%-60%.

[0104] In some embodiments, the molar content of the structural units derived from the monomer shown in Formula I is 5%-20%, based on the total number of moles of structural units in the fluoropolymer. In some embodiments, the molar content of the structural units derived from the monomer shown in Formula I may be selected from any one of 5%-10%, 5%-15%, 5%-20%, 10%-15%, 10%-20%, and 15%-20%.

[0105] In some embodiments, the molar content of structural units derived from olefin units is 20%-85%, based on the total molar number of all structural units in the fluoropolymer. In some embodiments, the molar content of the structural units derived from olefin units can be selected from any one of 20%-30%, 20%-40%, 20%-50%, 20%-60%, 20%-70%, 20%-80%, 20%-85%, 30%-40%, 30%-50%, 30%-60%, 30%-70%, 30%-80%, 30%-85%, 40%-50%, 40%-60%, 40%-70%, 40%-80%, 40%-85%, 50%-60%, 50%-70%, 50%-80%, 50%-85%, 60%-70%, 60%-80%, 60%-85%, 70%-80%, 70%-85%, and 80%-85%.

[0106] In this paper, the term "virtual edge of insulating coating" refers to the maximum width of the insulating coating area that migrates into the active material layer area after the electrode has dried.

[0107] The structural units derived from olefin monomers and those derived from the monomer shown in Formula II constitute oleophilic segments, while the structural units derived from the monomer shown in Formula I constitute oleophobic segments. By controlling the molar content of the structural units derived from the monomer shown in Formula II, the monomer shown in Formula I, and the olefin-derived units within a suitable range, the surface tension of the insulating coating slurry can be adjusted to be similar to that of the active material layer slurry. This prevents the insulating coating slurry from climbing or fusing into the active material layer during electrode drying, reduces the virtual edges of the insulating coating, improves the positioning accuracy of the identification system, and enhances the dimensional accuracy of electrode die-cutting, thus avoiding adverse effects on battery safety due to incorrect electrode dimensions. Simultaneously controlling the molar ratio of the three structural units within a suitable range results in excellent peel strength and electrolyte resistance in the coating, both of which work together to improve the adhesion stability of the insulating coating during battery cycling.

[0108] In addition, the carboxyl groups contained in fluoropolymers can form hydrogen bonds with the hydroxyl and / or carboxyl groups in inorganic insulating materials, which improves the compatibility between fluoropolymers and inorganic insulating materials, improves the dispersibility of fluoropolymers and inorganic insulating materials, is beneficial to the uniformity and thickness consistency of insulating coating, improves laser energy utilization and transmission uniformity, reduces cutting burrs on electrodes, and improves the laser cutting quality of electrodes.

[0109] In summary, controlling the molar content of structural units derived from olefin monomers, structural units derived from monomers shown in Formula II, and structural units derived from monomers shown in Formula I within a suitable range can effectively reduce the virtual edges of the insulating coating, improve the positioning accuracy of the identification system, effectively reduce cutting burrs on the electrode sheets, improve the laser cutting quality of the electrode sheets, improve the adhesion stability of the insulating coating during battery cycling, improve the stability of the insulating coating, improve the performance of the electrode sheets, and improve the safety performance of the battery.

[0110] In some embodiments, the weight-average molecular weight of the fluoropolymer is 100,000 to 1,500,000. The weight-average molecular weight of the fluoropolymer can be selected from any value or a range of any two of the following: 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, and 1,500,000.

[0111] When the weight-average molecular weight of the fluoropolymer is within a suitable range, the insulating coating slurry prepared from the fluoropolymer has a suitable viscosity, which allows for uniform coating on the current collector, resulting in a uniformly distributed insulating coating. This effectively reduces cutting burrs on the electrode and improves the laser cutting quality of the electrode. In addition, the fluoropolymer has a suitable weight-average molecular weight, exhibiting excellent peel strength and electrolyte resistance, which improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, and improves battery safety.

[0112] In some embodiments, a method for preparing a fluoropolymer is provided, the method comprising:

[0113] An intermediate polymer is formed by polymerizing at least one olefin monomer and at least one monomer of Formula II, the intermediate polymer containing ester groups.

[0114]

[0115] R4, R5, and R6 are each independently selected from hydrogen or substituted or unsubstituted C. 1-6 Alkyl group, R7 is selected from substituted or unsubstituted C4 groups. 1-8 alkyl;

[0116] The intermediate polymer reacts with an aqueous solution of an alkaline substance, causing at least some of the ester groups in the intermediate polymer to hydrolyze into carboxyl groups.

[0117] In some embodiments, at least one olefin monomer and at least one monomer represented by Formula II are subjected to free radical polymerization to form an intermediate polymer.

[0118] In this paper, the term "radical polymerization" refers to a polymerization reaction initiated by free radicals, in which chain-growing (chain-growth) free radicals continuously grow.

[0119] In this paper, at least one olefin monomer and at least one monomer represented by Formula II are emulsion polymerized to form an intermediate polymer.

[0120] In this paper, the term "emulsion polymerization" refers to polymerization in which monomers are dispersed in an aqueous medium to form an emulsion. The polymerization system generally includes monomers, an aqueous medium, an initiator, and an emulsifier.

[0121] In some embodiments, the olefin monomer comprises one or more of ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0122] In some embodiments, the monomer shown in Formula II comprises one or more of methyl acrylate, methyl methacrylate, ethyl ethyl acrylate, and butyl acrylate.

[0123] This method is simple to prepare, uses abundant raw materials, and is low in cost. Through the hydrolysis of ester groups under alkaline conditions, at least partially converting them into carboxyl groups, the adhesion of the insulating coating is improved. Simultaneously, the polymerization of olefin monomers forms the hard segments of the fluorine-free polymer, reducing the swelling of the electrode in the electrolyte. The ester-containing segments form the soft segments of the fluorine-free polymer. The combination of hard and soft segments gives the fluorine-free polymer a suitable glass transition temperature and excellent mechanical strength. Both work together to improve the peel strength of the insulating coating, enhance its adhesion stability during battery cycling, improve its overall stability, and improve its performance.

[0124] In some embodiments, R4, R5, and R6 are each independently selected from hydrogen or C. 1-3 Alkyl group, R7 is selected from C 1-3 alkyl.

[0125] In some embodiments, the molar content of the olefin monomer is 20%-85%, based on the total molar number of the olefin monomer and the monomer shown in Formula II.

[0126] In some embodiments, based on the total molar number of the olefin monomer and the monomer shown in Formula II, the molar content of the olefin monomer can be selected as 20%-30%, 20%-40%, 20%-50%, 20%-60%, 20%-70%, 20%-80%, 20%-85%, 30%-40%, 30%-50%, 30%-60%, 30%-70%, 30%-85 ... Any one of the following: 0%, 30%-85%, 40%-50%, 40%-60%, 40%-70%, 40%-80%, 40%-85%, 50%-60%, 50%-70%, 50%-80%, 50%-85%, 60%-70%, 60%-80%, 60%-85%, 70%-80%, 70%-85%, 80%-85%.

[0127] By controlling the molar content of olefin monomers within a suitable range, the cutting burrs of the electrode sheet can be effectively reduced, the laser cutting quality of the electrode sheet can be improved, the insulating coating has excellent peel strength and electrolyte resistance, the adhesion stability of the insulating coating during battery cycling can be improved, the performance of the insulating coating can be improved, and the battery safety performance can be improved.

[0128] In some embodiments, the molar ratio of the monomer shown in Formula II to the alkaline substance is 1:0.1-1:0.5. In some embodiments, the molar ratio of the monomer shown in Formula II to the alkaline substance can be selected from any one of 1:0.1-1:0.5, 1:0.1-1:0.4, 1:0.1-1:0.3, 1:0.1-1:0.2, 1:0.2-1:0.5, 1:0.2-1:0.4, 1:0.2-1:0.3, 1:0.3-1:0.5, 1:0.3-1:0.4, and 1:0.4-1:0.5.

[0129] Controlling the molar ratio of monomer to alkaline substance as shown in Formula II within a suitable range can control the degree of hydrolysis of ester groups, control the molar content of ester and carboxyl groups within a suitable range, effectively reduce the false edge of the insulating coating, improve the positioning accuracy of the identification system, reduce the electrolyte swelling rate of the electrode, and improve the electrochemical performance of the battery.

[0130] In some embodiments, the preparation method further includes: after the reaction is completed, adding an acidic solution to the reaction product to adjust the pH of the reaction solution to 5.0-7.0.

[0131] In some embodiments, an acidic solution is added to the reaction product to adjust the pH of the reaction solution to any one of 5.0-6.0, 5.0-7.0, or 6.0-7.0. In some embodiments, the acidic solution is one or more of hydrochloric acid, sulfuric acid, oxalic acid, and acetic acid. In some embodiments, the mass fraction of the acidic solution is 5%-20%.

[0132] In some embodiments, the alkaline substance is selected from one or more of lithium hydroxide, sodium hydroxide, and ammonia. In some embodiments, the alkaline substance is an organic base. The above materials are simple, readily available, and inexpensive, facilitating widespread application.

[0133] In some embodiments, the reaction temperature for the intermediate polymer to react with an aqueous solution of an alkaline substance is 35°C-120°C, or 60-90°C.

[0134] In some embodiments, the reaction temperature for the intermediate polymer to react with an aqueous solution of an alkaline substance is 35°C-120°C. In some embodiments, the reaction temperature is any value or a range of any two of the following: 35°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, and 120°C.

[0135] In some embodiments, the reaction temperature for the intermediate polymer to react with an aqueous solution of an alkaline substance is 60-90°C. In some embodiments, the reaction temperature is any value or a range of any two of 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C.

[0136] Regulating the reaction temperature within a suitable range can control the degree of hydrolysis of ester groups and the molar content of ester and carboxyl groups within a suitable range, effectively reducing cutting burrs on the electrode sheet, improving the laser cutting quality of the electrode sheet, and giving the insulating coating excellent peel strength and electrolyte resistance. This also improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, and improves battery safety.

[0137] In some embodiments, the reaction time for the intermediate polymer to react with an aqueous solution of an alkaline substance is 1-24 hours or 4-10 hours.

[0138] In some embodiments, the reaction time is 1-24 hours. In some embodiments, the reaction time is any value or a range of any two values ​​from 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, to 24 hours.

[0139] In some embodiments, the reaction time is 4-10 hours. In some embodiments, the reaction time is any value or a range of any two of the following: 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, and 10 hours.

[0140] Regulating the reaction temperature within a suitable range can control the degree of hydrolysis of ester groups and the molar content of ester and carboxyl groups within a suitable range, effectively reducing cutting burrs on the electrode sheet, improving the laser cutting quality of the electrode sheet, and giving the insulating coating excellent peel strength and electrolyte resistance. This also improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, and improves battery safety.

[0141] In some embodiments, the use of a fluoropolymer in a secondary battery is provided.

[0142] In some embodiments, an insulating coating is provided, comprising an adhesive and an inorganic insulating material, wherein the adhesive comprises a fluoropolymer as described in some embodiments or a fluoropolymer prepared by the preparation method described in some embodiments.

[0143] In this document, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0144] In some embodiments, the dispersion medium of the adhesive is an aqueous solvent, such as water. In some embodiments, the dispersion medium of the adhesive is an oily solvent, examples of which include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate.

[0145] In this application, the term "inorganic insulating material" refers to a material with a resistivity greater than 10. 6 Inorganic materials and their precursors with an Ω·cm value, including but not limited to aluminum hydroxide, magnesium hydroxide, calcium hydroxide, hydrated alumina, and hydrated magnesium silicate.

[0146] In some embodiments, the inorganic insulating material comprises hydroxides or hydrated oxides.

[0147] In some embodiments, the inorganic insulating material comprises one or more of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, hydrated alumina, and hydrated magnesium silicate.

[0148] In some embodiments, the inorganic insulating material includes hydroxides. Hydroxides contain abundant hydroxide ions, which form hydrogen bonds with the carboxyl groups in the fluoropolymer, improving their compatibility and resulting in a denser coating surface. This is beneficial for coating uniformity and thickness consistency, improving the temperature uniformity across the insulating coating area to the current collector during laser cutting of the electrode tabs, reducing cutting burrs on the electrode sheet, and improving the laser cutting quality of the electrode sheet.

[0149] In some embodiments, the inorganic insulating material includes hydrated oxides. The high crystallinity of the hydrated oxides is beneficial for forming an insulating coating with high regularity and density, thereby improving the processing performance of the insulating coating. At the same time, the high crystallinity of the hydrated oxides has better thermal conductivity, which improves the temperature uniformity from the insulating coating area to the current collector when the electrode tab is laser cut, reduces the cutting burrs of the electrode, and improves the laser cutting quality of the electrode.

[0150] In some implementations, an adhesive is used to hold inorganic insulating materials in place and adhere them to the current collector to form an insulating coating.

[0151] This insulating coating is easy to process and has good uniformity, which helps to improve battery production capacity.

[0152] In some embodiments, the fluoropolymer content is 15%-30% by mass, based on the total mass of the insulating coating. In some embodiments, the fluoropolymer content, based on the total mass of the insulating coating, can be selected from any one of 15%-20%, 15%-25%, 15%-30%, 20%-25%, 20%-30%, and 25%-30%.

[0153] Controlling the mass content of fluoropolymers within a suitable range improves the adhesion stability of the insulating coating during battery cycling, enhances its performance, reduces cutting burrs on the electrodes, and improves the quality of laser cutting of the electrodes. Simultaneously, within a suitable mass content range of inorganic polymers, the insulating coating slurry exhibits appropriate viscosity and excellent stability, resulting in superior storage and processability.

[0154] In some embodiments, the inorganic insulating material has a mass content of 70%-85% based on the total mass of the insulating coating. In some embodiments, the mass content of the inorganic insulating material, based on the total mass of the insulating coating, can be selected from any one of 70%-75%, 70%-80%, 70%-85%, 75%-80%, 75%-85%, and 80%-85%.

[0155] Controlling the mass content of inorganic insulating material within a suitable range improves the adhesion stability of the insulating coating during battery cycling, enhances its performance, reduces cutting burrs on the electrode sheets, and improves the laser cutting quality of the electrodes. Simultaneously, with an appropriate mass content of inorganic insulating material within a suitable range, the insulating coating slurry exhibits suitable viscosity and excellent stability, resulting in superior storage and processability.

[0156] In some implementations, the Dv50 of the inorganic insulating material is 0.1-5 μm.

[0157] In some embodiments, the Dv50 of the inorganic insulating material can be selected from any one of 0.1-1μm, 0.1-2μm, 0.1-3μm, 0.1-4μm, 0.1-5μm, 1-2μm, 1-3μm, 1-4μm, 1-5μm, 2-3μm, 2-4μm, 2-5μm, 3-4μm, 3-5μm, and 4-5μm.

[0158] Controlling the Dv50 of inorganic insulating materials within a suitable range avoids pipe blockage and particle scratches during coating, which is conducive to forming a smooth and dense insulating coating. Coating can improve the peel strength of the insulating coating, reduce the electrolyte swelling rate of the electrode, effectively reduce the virtual edge of the insulating coating, improve the positioning accuracy of the identification system, reduce burrs in electrode cutting, and improve the laser cutting quality of the electrode.

[0159] In some embodiments, a method for preparing an insulating coating is provided, comprising first stirring, second stirring, and coating.

[0160] First mixing: The binder and inorganic insulating filler are first mixed to obtain a dry mixture, wherein the binder contains the fluoropolymer in any embodiment;

[0161] Second stirring: The dry mixture and solvent are stirred for the second time to obtain the insulating coating slurry;

[0162] Coating: Apply the insulating coating slurry onto the current collector to prepare the insulating coating.

[0163] In some embodiments, the solvent is an aqueous solvent, such as water. In some embodiments, the solvent is an oily solvent, examples of which include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate.

[0164] In some embodiments, the stirring speed of the first stirring is 50-1000 r / min, and the stirring time is 5-30 min.

[0165] By controlling the stirring speed of the first stirring process within a suitable range, the insulating coating slurry can achieve excellent dispersibility, resulting in a highly regular and dense insulating coating. This reduces the coating edge defects, decreases the electrolyte swelling rate of the electrode, reduces burrs during electrode cutting, and improves the laser cutting quality of the electrode.

[0166] In some embodiments, the stirring speed of the first stirring can be selected as 50-100 r / min, 50-200 r / min, 50-300 r / min, 50-400 r / min, 50-500 r / min, 50-600 r / min, 50-700 r / min, 50-800 r / min, 50-900 r / min, 50-1000 r / min, 100-200 r / min, 100-300 r / min, 100-400 r / min, 100- 500r / min, 100-600r / min, 100-700r / min, 100-800r / min, 100-900r / min, 100-1000r / min, 200-300r / min, 200-4 00r / min, 200-500r / min, 200-600r / min, 200-700r / min, 200-800r / min, 200-900r / min, 200-1000r / min, 300-40 0r / min, 300-500r / min, 300-600r / min, 300-700r / min, 300-800r / min, 300-900r / min, 300-1000r / min, 400-50 0r / min, 400-600r / min, 400-700r / min, 400-800r / min, 400-900r / min, 400-1000r / min, 500-600r / min, 500-700 Any one of the following speeds: r / min, 500-800 r / min, 500-900 r / min, 500-1000 r / min, 600-700 r / min, 600-800 r / min, 600-900 r / min, 600-1000 r / min, 700-800 r / min, 700-900 r / min, 700-1000 r / min, 800-900 r / min, 800-1000 r / min, 900-1000 r / min.

[0167] In some embodiments, the stirring time of the first stirring can be selected from any one of 5-15 min, 5-30 min, 15-30 min, and 20-30 min.

[0168] By controlling the stirring time of the first stirring within a suitable range, the insulating coating slurry can have excellent dispersibility, resulting in a highly regular and dense insulating coating. This can reduce the coating edge defects, decrease the electrolyte swelling rate of the electrode, reduce burrs during electrode cutting, and improve the laser cutting quality of the electrode.

[0169] In some embodiments, the stirring speed of the second stirrer is 1000-3000 r / min, and the stirring time is 1-3 h.

[0170] In some embodiments, the stirring speed of the second stirrer can be selected from any one of 1000-2000 r / min, 1000-3000 r / min, and 2000-3000 r / min.

[0171] By controlling the stirring speed of the second stirrer within a suitable range, the insulating coating slurry can be made to have excellent dispersibility, resulting in a highly regular and dense insulating coating. This can reduce the coating edge defects, improve the peel strength of the insulating coating, reduce the electrolyte swelling rate of the electrode, reduce burrs during electrode cutting, and improve the laser cutting quality of the electrode.

[0172] In some embodiments, the stirring time of the second stirring can be selected as any one of 1-2h, 1-3h, or 2-3h.

[0173] Controlling the stirring time of the second stirring is within a suitable range, so that the insulating coating slurry has excellent dispersibility, and the insulating coating has high regularity and excellent density. This can improve the peel strength of the insulating coating, improve the adhesion stability of the insulating coating during battery cycling, reduce the electrolyte swelling rate of the electrode, reduce electrode cutting burrs, and improve the laser cutting quality of the electrode.

[0174] In some embodiments, the second stirring temperature is 10-60°C.

[0175] In some embodiments, the second stirring temperature can be selected from any one of 10-30℃, 10-50℃, 10-60℃, 20-30℃, 20-50℃, 20-60℃, 30-50℃, and 30-60℃.

[0176] By controlling the second stirring temperature within a suitable range, the insulating coating slurry can be made to have excellent dispersibility, resulting in a highly regular and dense insulating coating. This can improve the peel strength of the insulating coating, reduce the coating edge defects, and decrease the electrolyte swelling rate of the electrode sheet.

[0177] In some embodiments, the coating step specifically includes:

[0178] An insulating coating slurry is applied to a current collector and dried at a temperature of 90-130℃ to prepare the insulating coating.

[0179] In some embodiments, the drying temperature can be selected from any one of 90-100℃, 90-110℃, 90-120℃, 90-130℃, 100-110℃, 100-120℃, 100-130℃, 110-120℃, 110-130℃, and 120-130℃.

[0180] Controlling the coating drying temperature within a suitable range ensures that the dried coating has high smoothness and excellent density, reduces the coating edge defects of the insulating coating, improves the positioning accuracy of the laser recognition system, and increases the peel strength of the insulating coating. At the same time, keeping the coating drying temperature within a suitable range can save energy and reduce costs while ensuring that the coating is fully dried, which is beneficial for industrial production.

[0181] In some embodiments, the solid content of the insulating coating slurry is 20%-50%.

[0182] In some embodiments, the solid content of the insulating coating slurry can be selected from any one of 20%-30%, 20%-40%, 20%-50%, 30%-40%, 30%-50%, and 40%-50%.

[0183] The insulating coating slurry has a suitable solid content to prevent the insulating coating film area from seeping into the positive electrode material film area during the coating process, forming a large blank edge in the insulating coating, which would affect the subsequent die-cutting process and be detrimental to the subsequent coating drying process. In addition, the insulating coating slurry has a suitable solid content to reduce the risk of gelation and tube bursting caused by increased coating pump pressure.

[0184] In some embodiments, the fluoropolymer in any embodiment can be used in a secondary battery. Optionally, the secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

[0185] [Positive electrode plate]

[0186] The positive electrode sheet includes a positive current collector and a positive active material layer and an insulating coating disposed on at least one surface of the positive current collector.

[0187] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer and the insulating coating are disposed on either or both of the two opposite surfaces of the positive current collector.

[0188] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide.

[0189] In some embodiments, the positive electrode active material is at least one of lithium iron phosphate and its modified materials, lithium nickel cobalt manganese oxide and its modified materials, and the modified material is prepared by one or more modification methods selected from doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0190] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0191] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi)0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0192] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode active material layer, such as the positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; obtaining an insulating coating slurry using the above-described method for preparing an insulating coating slurry; coating the positive electrode slurry and the insulating coating slurry onto the positive electrode current collector, wherein the insulating coating slurry is coated on both sides of the active material layer; and obtaining the positive electrode sheet after processes such as drying and cold pressing.

[0194] [Negative electrode plate]

[0195] The negative electrode sheet includes a negative current collector and a negative active material layer and an insulating coating disposed on at least one surface of the negative current collector.

[0196] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0197] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0198] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0199] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0200] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0201] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0202] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode active material layer, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; obtaining an insulating coating slurry using the above-described method for preparing an insulating coating slurry; coating the negative electrode slurry and the insulating coating slurry onto the negative electrode current collector, wherein the insulating coating slurry is coated on both sides of the active material layer; and obtaining the negative electrode sheet after processes such as drying and cold pressing.

[0203] [Electrolytes]

[0204] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0205] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0206] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0207] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0208] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0209] [Isolation membrane]

[0210] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0211] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0212] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0213] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0214] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0215] [Rechargeable Battery]

[0216] In one embodiment of this application, a secondary battery is provided, including a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the binder in the active material layer of the positive electrode includes polymers according to any embodiment of this application.

[0217] In some embodiments, the secondary battery is a lithium-ion battery or a sodium-ion battery. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. A separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0218] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0219] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0220] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0221] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0222] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0223] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0224] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0225] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0226] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0227] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0228] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0229] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0230] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0231] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0232] Example

[0233] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0234] Example 1

[0235] 1) Preparation of fluoropolymers

[0236] Preparation of intermediate polymer: 68.6g of methyl acrylate, 200mL of deionized water, 1.3g of emulsifier alkylphenol polyoxyethylene ether OP-10, and 2.0g of ammonium persulfate as initiator were added to a high-pressure reactor. After stirring and mixing, the temperature was raised to 90℃, and 33.6g of ethylene was introduced. The reaction was carried out at a pressure of 10MPa for 6h. After the reaction was completed, the reaction emulsion was placed at 0℃ for 10h to precipitate solids. The solids were then filtered and dried to obtain ethylene-methyl acrylate polymer, i.e., intermediate polymer.

[0237] Preparation of fluorine-free polymer: 100g of ethylene-methyl acrylate polymer powder and 300mL of deionized water were added to a reaction vessel and stirred for 30min to mix evenly. Then, 4.84g of LiOH was dissolved in 50mL of deionized water to prepare an alkaline solution, which was added to the reaction vessel. Next, the reaction vessel temperature was raised to 90℃ and reacted for 4h. After the reaction, the reaction vessel temperature was allowed to return to room temperature. A 5% acetic acid solution was prepared and added dropwise to the reaction vessel to adjust the pH of the product to 5.0-6.0. Stirring was continued for 2h. The product was then dried, washed three times with deionized water, and dried again. The modification reaction converted some of the ester functional groups derived from methyl acrylate on the intermediate polymer into -COOH groups, yielding an ethylene-acrylate polymer with a weight-average molecular weight of 500,000.

[0238] 2) Preparation of insulating coating slurry

[0239] Add 50g of ethylene-acrylic acid-acrylate polymer and 200g of aluminum hydroxide powder with a particle size Dv50 of 1μm into a disperser. The first stirring is carried out at a linear speed of 500r / min for 10min for dry mixing and dispersion.

[0240] While stirring, add 375g of N-methylpyrrolidone solvent to the disperser. After the solvent is added, increase the stirring speed to 2000r / min, turn on the circulating cooling water to control the slurry temperature at 20℃, and continue dispersing and stirring for 120min. After dispersion and slurry preparation, filter using a 150-mesh filter to obtain the insulating coating slurry.

[0241] 3) Preparation of positive electrode sheet

[0242] Polyvinylidene fluoride, lithium iron phosphate positive electrode active material, conductive agent carbon black, and N-methylpyrrolidone (NMP) were mixed evenly in a weight ratio of 1.28:62.2:0.52:36 to obtain a positive electrode active material slurry. Then, the positive electrode active material slurry and the insulating coating slurry were uniformly coated on the positive electrode current collector, with the insulating coating applied to both sides of the positive electrode active material film area. The mixture was dried at 110°C, and then cold-pressed, slit, and laser-cut to obtain the positive electrode sheet.

[0243] 4) Preparation of negative electrode sheet

[0244] The active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water at a weight ratio of 96.2:0.8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0245] 5) Separating membrane

[0246] Polypropylene film is used as the separator.

[0247] 6) Preparation of electrolyte

[0248] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3 / 7. LiPF6 lithium salt was then dissolved in the organic solvent to prepare a 12.5% ​​solution, thus obtaining the electrolyte.

[0249] 9) Battery manufacturing

[0250] The positive electrode, separator, and negative electrode prepared in Example 1 are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed to obtain a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

[0251] The preparation methods in Examples 2 to 56 are similar to those in Example 1. Specific adjustments to the preparation parameters are shown in Tables 1, 2, and 3. In Examples 9-12, the weight-average molecular weight of the fluorine-free polymer was adjusted by changing the polymerization time of the intermediate polymer and the amount of initiator, as detailed below:

[0252] Preparation of intermediate polymer: 68.6g of methyl acrylate, 200mL of deionized water, 1.3g of emulsifier alkylphenol polyoxyethylene ether OP-10, and 2.0g of ammonium persulfate as initiator were added to a high-pressure reactor. After stirring and mixing, the temperature was raised to 90℃, and 33.6g of ethylene was introduced. The reaction was carried out at a pressure of 10MPa for 6h. After the reaction was completed, the reaction emulsion was placed at 0℃ for 10h to precipitate solids. The solids were then filtered and dried to obtain ethylene-methyl acrylate polymer, i.e., intermediate polymer.

[0253] Example 9; (Preparation of 100,000) The preparation method is similar to that of Example 1, except that the amount of ammonium persulfate initiator is 10.0g, and the reaction yields an intermediate polymer with a molecular weight of 100,000.

[0254] Example 10: (Preparation of 1.5 million) The preparation method is similar to that of Example 1, except that the amount of ammonium persulfate initiator is 0.5g, and the reaction is carried out at 40°C for 12h to obtain an intermediate polymer with a molecular weight of 1.5 million.

[0255] Example 11; (Preparation of 50,000)

[0256] Similar to the preparation method in Example 1, except that the amount of methyl acrylate added is 65.2g and the amount of ammonium persulfate initiator added is 10.0g, and the reaction yields an intermediate polymer with a molecular weight of 50,000.

[0257] Example 12: (Preparation of 1.7 million) The preparation method is similar to that of Example 1, except that the amount of ammonium persulfate initiator is 0.5g, and the reaction is carried out at 20°C for 15h to obtain an intermediate polymer with a molecular weight of 1.7 million.

[0258] Comparative Example 1

[0259] Comparative Example 1 was prepared in a similar manner to Example 1, except that the binder in the insulating coating was replaced with polyvinylidene fluoride with a weight-average molecular weight of 500,000. For specific parameters, please refer to Table 1.

[0260] Comparative Examples 2-4

[0261] The preparation methods of Comparative Examples 2 to 4 are similar to those of Example 1. For specific adjustments to the preparation parameters, please refer to Table 1.

[0262] II. Testing Methods

[0263] 1. Weight-average molecular weight test of fluoropolymers

[0264] A Waters 2695 Isocratic HPLC gel electrophoresis system (differential refractive index detector 2141) was used. A 3.0% (w / w) polystyrene solution was used as a reference, and a matched column (oil-based: Styragel HT5DMF 7.8×300mm + Styragel HT4) was selected. A 3.0% fluorine-free polymer solution was prepared using purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day. For testing, tetrahydrofuran was first used to flush the sample, repeated several times. Then, 5 ml of the experimental solution was drawn, air was expelled from the syringe, and the needle tip was dried. Finally, the sample solution was slowly injected into the injection port. After the reading stabilized, the data was acquired, and the weight-average molecular weight was read.

[0265] 4. The false edges of the insulating coating

[0266] Take the coated positive electrode sheet and measure the maximum width of the insulating coating that migrates to the positive electrode active material film area on the dried electrode sheet under a fully automatic camera positioning and cutting machine (CCD). This is the virtual edge of the insulating coating.

[0267] 5. Peel strength

[0268] The insulating coating slurry was scraped onto the aluminum foil and dried in an oven at 110℃. The thickness of the dried coating was controlled to be 30μm. Then, a 10*2.5cm strip sample was cut and pasted onto a stainless steel plate. The peel strength was tested according to the GB / T2790 coating peel test method.

[0269] 7. Electrolyte Swelling Resistance Test

[0270] The insulating coating slurry was scraped onto aluminum foil and dried thoroughly in a 110℃ oven, maintaining a coating thickness of 30μm after drying. A 5*5cm area was cut off and weighed, recorded as m0. The sample was then immersed in an electrolyte solution and stored at 60℃ for 7 days. After quickly wiping away any residual electrolyte, the sample was weighed and recorded as m1. The coating swelling rate can be calculated using the following formula:

[0271] Coating swelling rate (%) = (m1 – m0) / m0 × 100%

[0272] 8. Laser cutting of electrode tab burrs

[0273] Take the positive electrode sheet after the laser-cut tab and observe it under CCD to check for burrs and molten beads at the laser-cut interface aluminum foil. If burrs or molten beads are observed, it is considered NG; if no burrs or molten beads are observed, it is considered OK.

[0274] 9. Cyclic stability of the insulating coating:

[0275] The lithium-ion battery prepared above was charged at 1C to 3.65V at a constant temperature of 60℃ and a voltage of 2.5~3.65V. Then, it was charged at a constant voltage of 3.65V until the current was ≤0.05mA. After standing for 5 minutes, it was discharged at 1C to 2.5V. The capacity was recorded as Dn (n=0,1,2……). The above operation was repeated for 500 cycles. After 500 cycles, the cell was disassembled to check whether there was any delamination of the insulating coating.

[0276] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0277] The fluoropolymers and insulating coatings of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in Tables 1, 2, 3 and 4 below.

[0278] Table 1

[0279]

[0280]

[0281] Table 2

[0282]

[0283]

[0284]

[0285] Table 3

[0286]

[0287]

[0288]

[0289] Table 4

[0290]

[0291]

[0292]

[0293] According to the results in Tables 1-4, the fluorine-free polymers in Examples 1-56 contain structural units derived from ethylene or 1-butene, structural units derived from acrylic acid or methacrylic acid, and structural units derived from methyl acrylate, butyl acrylate, or methyl methacrylate.

[0294] As can be seen from the comparison between Examples 1-8, 13-15 and Comparative Example 1, compared with the insulating coating containing polyvinylidene fluoride, the insulating coating containing ethylene-acrylic acid-methyl acrylate copolymer, 1-butene-acrylic acid-methyl acrylate copolymer, ethylene-acrylic acid-butyl acrylate copolymer, and ethylene-methacrylic acid-methyl methacrylate copolymer can improve the peel strength of the insulating coating, improve the adhesion stability of the insulating coating during battery cycling, improve the stability of the insulating coating, and improve the performance of the insulating coating.

[0295] As can be seen from the comparison between Examples 1-8 and Comparative Examples 2-4, compared with insulating coatings containing ethylene-methyl acrylate, ethylene-acrylic acid, or methyl acrylate-acrylic acid copolymers, insulating coatings containing ethylene-acrylic acid-methyl acrylate copolymers improve the adhesion stability of the insulating coating during battery cycling, improve the stability of the insulating coating, and improve the performance of the coating.

[0296] A comparison of Examples 1-5 with Comparative Examples 1-4 shows that when the molar content of structural units derived from methyl acrylate monomers is 10%-60%, the molar content of structural units derived from acrylic acid monomers is 5%-20%, and the molar content of structural units derived from ethylene is 20%-85%, based on the total molar number of structural units in the fluoropolymer, it can effectively reduce the false edges of the insulating coating, improve the positioning accuracy of the identification system, effectively reduce the cutting burrs of the electrode sheet, improve the laser cutting quality of the electrode sheet, improve the adhesion stability of the insulating coating during battery cycling, improve the stability of the insulating coating, and improve the performance of the electrode sheet.

[0297] A comparison of Examples 1-5 with Examples 6-8 shows that when the molar content of structural units derived from methyl acrylate monomers is 10%-60%, the molar content of structural units derived from acrylic acid monomers is 5%-20%, and the molar content of structural units derived from ethylene is 20%-85%, based on the total molar number of structural units in the fluoropolymer, the cutting burrs of the electrode sheet are effectively reduced, the laser cutting quality of the electrode sheet is improved, the insulating coating has excellent peel strength and electrolyte resistance, the adhesion stability of the insulating coating during battery cycling is improved, the performance of the insulating coating is improved, and the battery safety performance is improved.

[0298] A comparison of Examples 1 and 9-10 with Examples 11-12 shows that the weight-average molecular weight of the fluoropolymer is controlled between 100,000 and 1,500,000, which effectively reduces the cutting burrs of the electrode sheet, improves the laser cutting quality of the electrode sheet, and the insulating coating has excellent peel strength and electrolyte resistance, improves the adhesion stability of the insulating coating during battery cycling, improves the performance of the insulating coating, and improves the battery safety performance.

[0299] The insulating coatings in Examples 1-56 comprise an adhesive of ethylene-acrylate-methyl acrylate copolymer, 1-butene-acrylate-methyl acrylate copolymer, ethylene-acrylate-butyl acrylate copolymer, or ethylene-methacrylate-methyl methacrylate copolymer, and inorganic insulating materials of magnesium hydroxide, aluminum hydroxide, hydrated alumina, or hydrated magnesium silicate.

[0300] A comparison of Examples 1, 16-17 and Examples 18-19 shows that the mass content of the fluoropolymer in the insulating coating is 15%-30%. Based on the total mass of the insulating coating, this improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, reduces cutting burrs on the electrode sheet, and improves the laser cutting quality of the electrode sheet.

[0301] A comparison of Examples 1, 16-17 and Examples 18-19 shows that the inorganic insulating slurry content in the insulating coating is 70%-85% by mass. Based on the total mass of the insulating coating, this improves the adhesion stability of the insulating coating during battery cycling, enhances the performance of the insulating coating, reduces cutting burrs on the electrode sheet, and improves the laser cutting quality of the electrode sheet.

[0302] A comparison of Examples 1, 20-21 and Examples 22-23 shows that the Dv50 of the inorganic insulating material is 0.1-5μm, which can improve the peel strength of the insulating coating, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, effectively reduce the virtual edge of the insulating coating, improve the positioning accuracy of the identification system, reduce the burrs of the electrode cutting, and improve the laser cutting quality of the electrode.

[0303] The preparation method of the insulating coating in Examples 1-56 includes first stirring, second stirring, and coating.

[0304] First mixing: The binder of ethylene-acrylic acid-methyl acrylate copolymer, 1-butene-acrylic acid-methyl acrylate copolymer, ethylene-acrylic acid-butyl acrylate copolymer or ethylene-methacrylic acid-methyl methacrylate copolymer is mixed with inorganic insulating materials of magnesium hydroxide, aluminum hydroxide, hydrated alumina or hydrated magnesium silicate to obtain a dry mixture.

[0305] The second stirring involves mixing the dry mixture with N-methylpyrrolidone to obtain an insulating coating slurry.

[0306] Coating: Apply the insulating coating slurry onto the aluminum foil to obtain the insulating coating.

[0307] A comparison of Examples 1, 29-30 with Examples 31-32 shows that, during the preparation of the insulating coating slurry, a first stirring time of 5-30 minutes can reduce the coating edge defects, decrease the electrolyte swelling rate, improve the electrolyte resistance, reduce burrs during electrode cutting, and improve the laser cutting quality of the electrode.

[0308] A comparison of Examples 1, 33-34 and Examples 35-36 shows that, during the preparation of the insulating coating slurry, controlling the stirring speed of the first stirring to 50-1000 r / min can reduce the virtual edges of the insulating coating, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce burrs in electrode cutting, and improve the laser cutting quality of the electrode.

[0309] A comparison of Examples 1, 37-38 with Examples 39-40 shows that controlling the stirring speed of the second stirrer to 1000-3000 r / min can reduce the coating edge of the insulating coating, improve the peel strength of the insulating coating, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce the burrs in the electrode cutting, and improve the laser cutting quality of the electrode.

[0310] A comparison of Examples 1, 41-42 and Examples 43-44 shows that controlling the second stirring time to 1-3 hours can improve the peel strength of the insulating coating, improve the adhesion stability of the insulating coating during battery cycling, reduce the electrolyte swelling rate of the coating, improve the electrolyte resistance of the coating, reduce electrode cutting burrs, and improve the laser cutting quality of the electrode.

[0311] A comparison of Examples 1, 45-46, 48 and Example 47 shows that controlling the stirring temperature of the second stirring to 10-60°C can improve the peel strength of the insulating coating, reduce the coating edge defects, reduce the electrolyte swelling rate of the coating, and improve the electrolyte resistance of the coating.

[0312] As can be seen from the comparison between Examples 1 and 49-50 and Examples 51-52, coating and drying at a temperature of 90-130℃ during the preparation of the insulating coating slurry reduces the virtual edges of the insulating coating, improves the positioning accuracy of the laser recognition system, increases the peel strength of the insulating coating, and can also save energy and reduce costs.

[0313] A comparison of Examples 1, 53-54 and Examples 55-56 shows that controlling the solid content in the insulating coating slurry to be 20%-50% improves the adhesion stability of the insulating coating during battery cycling, and can also effectively reduce electrode cutting burrs and improve the laser cutting quality of the electrode.

[0314] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a secondary battery, characterized in that, Includes first stirring, second stirring, and coating. First mixing: The binder and inorganic insulating material are first mixed to obtain a dry mixture, wherein the binder contains a fluoropolymer; Second stirring: The dry mixture and solvent are stirred for the second time to obtain the insulating coating slurry; Coating: The insulating coating slurry is applied onto the current collector to obtain an insulating coating; The insulating coating is applied to the positive electrode and / or negative electrode to form a secondary battery. The stirring speed of the first stirrer is 50-1000 r / min, and the stirring time is 5-30 min; The stirring speed of the second stirring is 1000-3000 r / min, and the stirring time is 1-3 h; The second stirring temperature is 10-60℃; the solid content of the insulating coating slurry is 20%-50%. The fluoropolymer comprises structural units derived from olefin monomers, structural units derived from monomers shown in Formula I, and structural units derived from monomers shown in Formula II. Formula I Formula II Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or substituted or unsubstituted C. 1-6 Alkyl group, R7 is selected from substituted or unsubstituted C4 groups. 1-8 alkyl; The molar content of the structural units derived from the olefin unit is 20%-85%, the molar content of the structural units derived from the monomer shown in Formula II is 10%-60%, and the molar content of the structural units derived from the monomer shown in Formula I is 5%-20%, based on the total molar number of all structural units in the fluorinated polymer; the weight-average molecular weight of the fluorinated polymer is 100,000-1,500,000. The inorganic insulating material has a Dv50 of 0.1-5 μm; the fluoropolymer has a mass content of 15%-30% based on the total mass of the insulating coating.

2. The preparation method according to claim 1, characterized in that, R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen or C. 1-3 Alkyl group, R7 is selected from C 1-3 alkyl.

3. The preparation method according to claim 1, characterized in that, The olefin monomer comprises one or more of ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

4. The preparation method according to claim 1, characterized in that, The monomer represented by Formula I comprises one or more of acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

5. The preparation method according to claim 1, characterized in that, The monomer shown in Formula II comprises one or more of methyl acrylate, methyl methacrylate, ethyl 2-ethyl acrylate, and butyl acrylate.

6. The preparation method according to claim 1, characterized in that, The coating step specifically includes: The insulating coating slurry is applied to the current collector and dried at 90-130°C to obtain the insulating coating.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The method for preparing the fluoropolymer includes: An intermediate polymer is formed by polymerizing at least one olefin monomer and at least one monomer of Formula II, the intermediate polymer containing ester groups. Formula II R4, R5, and R6 are each independently selected from hydrogen or substituted or unsubstituted C. 1-6 Alkyl group, R7 is selected from substituted or unsubstituted C4 groups. 1-8 alkyl; The intermediate polymer is reacted with an aqueous solution of an alkaline substance, and the reaction causes at least some of the ester groups in the intermediate polymer to hydrolyze into carboxyl groups.

8. The preparation method according to claim 7, characterized in that... : The molar ratio of the monomer shown in Formula II to the alkaline substance is 1:0.1 to 1:0.

5.

9. The preparation method according to claim 7, characterized in that, Also includes: After the reaction is completed, an acidic solution is added to the reaction product to adjust the pH of the reaction solution to 5.0-7.

0.

10. The preparation method according to claim 7, characterized in that, The alkaline substance is selected from one or more of lithium hydroxide, sodium hydroxide, and ammonia.

11. The preparation method according to claim 7, characterized in that... : The reaction temperature for the intermediate polymer to react with an aqueous solution of an alkaline substance is 35℃-120℃.

12. The preparation method according to claim 11, characterized in that... : The reaction temperature for the intermediate polymer to react with an aqueous solution of an alkaline substance is 60-90℃.

13. The preparation method according to claim 7, characterized in that... : The reaction time for the intermediate polymer to react with the aqueous solution of the alkaline substance is 1-24 hours.

14. The preparation method according to claim 13, characterized in that... The reaction time for the intermediate polymer to react with the aqueous solution of the alkaline substance is 4-10 hours.

15. The preparation method according to any one of claims 1 to 6, characterized in that, The inorganic insulating material has a mass content of 70%-85%, based on the total mass of the insulating coating.

16. The preparation method according to any one of claims 1 to 6, characterized in that, The inorganic insulating material contains hydroxides or hydrated oxides.

17. The preparation method according to any one of claims 1 to 6, characterized in that, The inorganic insulating material comprises one or more of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, hydrated aluminum oxide, and hydrated magnesium silicate.

18. A secondary battery, characterized in that, The secondary battery includes those prepared by the preparation method described in any one of claims 1-17.

19. The secondary battery according to claim 18, characterized in that, The secondary battery includes at least one of lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, and potassium-ion batteries.

20. An electrical appliance, characterized in that, This includes secondary batteries prepared by the preparation method according to any one of claims 1-17 and / or secondary batteries according to claim 18 or 19.

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