Polymers, preparation methods, negative electrode sheets, secondary batteries, and electrical devices

Abstract

This application provides a polymer, a preparation method, a negative electrode sheet, a secondary battery, and an electrical device. The polymer contains constituent units derived from unsaturated carboxylic acid monomers, constituent units derived from unsaturated cyano monomers, and constituent units derived from flexible monomers, the glass transition temperature of the flexible monomers being -60°C to 0°C, and selectively -55°C to -15°C. The polymer can reduce sheet warping and widen the processing window of the sheet.

Description

[Technical Field]

[0001] This application relates to the technical field of secondary batteries, and more particularly to polymers, preparation methods, negative electrode sheets, secondary batteries, and electrical devices. [Background technology]

[0002] In recent years, secondary batteries have been widely applied in various fields, including energy storage and power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0003] Non-fluorinated polymer binders containing unsaturated carboxylic acid monomers have advantages such as low cost, strong binding strength, and high water solubility, and are commonly used as negative electrode binders in secondary batteries. However, they face drawbacks such as a narrow processing window and difficulty in meeting the demand for high-performance active materials, which significantly limits their application. Therefore, conventional polymer binders still have room for improvement. [Overview of the Initiative]

[0004] This application has been made in view of the above-mentioned problems, and aims to provide a polymer that can improve the warping phenomenon in the sheet manufacturing process and widen the processing window of the sheet.

[0005] To achieve the above objective, this application provides a polymer containing constituent units derived from an unsaturated carboxylic acid monomer, constituent units derived from an unsaturated cyano monomer, and constituent units derived from a flexible monomer, wherein the glass transition temperature of the flexible monomer is -60°C to 0°C, and selectively -55°C to -15°C.

[0006] The constituent units derived from unsaturated carboxylic acid monomers contained in the polymer can improve the water solubility of the polymer and provide ion transport channels to lithium ions, which is advantageous for improving the kinetic properties of the battery. The constituent units derived from unsaturated cyano monomers can improve the bonding strength between the polymer and the active material and current collector. The constituent units derived from flexible monomers can effectively lower the glass transition temperature of the polymer, improve the flexibility of the polymer, reduce the phenomenon of uneven shrinkage and stress concentration that occurs during the oven drying process of the slurry, and further mitigate the degree of sheet warping, widen the processing window of the sheet, and improve the processability and quality stability of the sheet.

[0007] In any embodiment, the flexible monomer comprises a structure represented by formula I, [ka] In the formula, R1, R2, and R3 are each independently hydrogen, or substituted or unsubstituted carbon. 1-5 It contains an alkyl group, and R4 is C 1-5 Hydroxyalkyl group, C 1-5 Alkyl and C 1-5 It contains one or more alkoxy groups.

[0008] In any embodiment, the unsaturated carboxylic acid monomer comprises the structure represented by formula II, and the unsaturated cyano monomer comprises the structure represented by formula III. [ka] In the formula, R5, R6, R7, R8, R9, R 10 Each is independently hydrogen, or substituted or unsubstituted C 1-5 Contains alkyl groups.

[0009] In any embodiment, the polymer further comprises a constituent unit derived from an unsaturated amide monomer, the unsaturated amide monomer comprising a structure represented by formula IV, [Chemical formula] In the formula, R 11 , R 12 , R 13 , R 14 , R 15 are each independently hydrogen or a substituted or unsubstituted C 1-5 alkyl group.

[0010] When the polymer contains a structural unit derived from an unsaturated amide monomer, after the amide groups in the polymer dissolve in water and dissociate, the polymer has a negative charge, and due to the presence of electrostatic repulsive forces between different chains in the polymer, the polymer can extend and spread in the solution and entangle with each other, thereby improving the viscosity of the negative electrode slurry, enhancing the stability of the negative electrode slurry, and further optimizing the processing performance of the sheet.

[0011] In any embodiment, the flexible monomer includes one or more of hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0012] The flexible monomer not only has a low glass transition temperature, but also has high compatibility with the structural units derived from unsaturated carboxylic acid monomers and the structural units derived from unsaturated cyano-based monomers, and can effectively lower the glass transition temperature of the polymer. In addition, the flexible monomer can effectively lower the surface tension of the slurry by groups such as ester groups, hydroxy groups, and alkoxy groups, further reduce the warpage of the sheet, and improve the processing performance and quality stability of the sheet.

[0013] In any embodiment, the flexible monomer includes at least two of hydroxyethyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0014] By combining two different types of flexible monomers, it is possible to achieve both polymer bonding performance and suppression of sheet rebound, while further improving the flexibility of the polymer and expanding the processing window and application scenarios of the polymer.

[0015] In any embodiment, the unsaturated carboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid, ethacrylic acid, and crotonic acid; the unsaturated cyano monomer comprises one or more of acrylonitrile, crotononitrile, methacrylonitrile, and ethacrylonitrile; and the unsaturated amide monomer comprises one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N-methylacrylamide.

[0016] In any embodiment, the molar proportion of constituent units derived from the flexible monomer is 5% to 50%, and selectively 20% to 35%, based on the total number of moles of all constituent units in the polymer.

[0017] Polymers in which the molar proportion of flexible monomer components is 5% to 50% have a low glass transition temperature, which can mitigate sheet warping and improve sheet processing performance. Polymers in which the molar proportion of flexible monomer components is 20% to 35% can achieve both polymer flexibility and bonding performance, reducing the risk of edge cracking due to cold pressing and interface wrinkles and film shedding due to full charge during sheet processing, thereby improving production efficiency and yield. Furthermore, they can maintain high bonding strength and low rebound rate in the sheet, and can comprehensively improve the battery cycle stability.

[0018] In any embodiment, based on the total number of moles of all constituent units in the polymer, the molar proportion of constituent units derived from the unsaturated carboxylic acid monomer is 10% to 60%, selectively 30% to 50%, and / or the molar proportion of constituent units derived from the unsaturated cyano monomer is 10% to 60%, selectively 15% to 45%, and / or the molar proportion of constituent units derived from the unsaturated amide monomer is 0% to 30%, selectively 5% to 20%.

[0019] Polymers whose constituent units fall within the above content range can achieve both improved flexibility and a balance of binding strength and solubility.

[0020] In any embodiment, the glass transition temperature of the polymer is 40°C to 105°C, and selectively 40°C to 90°C.

[0021] When the glass transition temperature of a polymer is between 40°C and 105°C, the polymer has good flexibility, and the sheet exhibits low warping and good processability. Polymers with a glass transition temperature between 40°C and 90°C can further reduce the occurrence of edge cracking during edge roll pressing of batteries, further widen the processing window of the sheet, and improve the processing performance of the sheet.

[0022] In any embodiment, the weight-average molecular weight of the polymer is between 500,000 and 2,000,000, and selectively between 800,000 and 1,500,000.

[0023] When the weight-average molecular weight of the polymer is between 500,000 and 2,000,000, the viscosity of the aqueous solution of the polymer at a certain solid content is within an appropriate range, the sheet has good processability and bonding performance, and the battery has good cycle stability.

[0024] In any embodiment, the viscosity of an aqueous solution with a solid content of 6 wt% prepared by dissolving the polymer in deionized water is 8000 MPa·s to 30000 MPa·s, and selectively 10000 MPa·s to 20000 MPa·s.

[0025] When the viscosity of an aqueous solution with a solid content of 6 wt%, prepared by dissolving the polymer in deionized water, is within the above range, the slurry will have stability and processability, the sheet will have excellent processability and bonding performance, and the battery will have good cycle stability.

[0026] In any embodiment, the polymer comprises at least one of the following copolymers: acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-hydroxyethyl acrylate copolymer, methacrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-methacrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-methacrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-2-hydroxybutyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxypropyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer, and acrylic acid-acrylonitrile-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer.

[0027] A second aspect of this application provides a method for preparing a polymer by polymerizing raw materials containing a flexible monomer, an unsaturated carboxylic acid monomer, and an unsaturated cyano monomer under polymerizable conditions, wherein the glass transition temperature of the flexible monomer is -60°C to 0°C, and selectively -55°C to -15°C.

[0028] In any embodiment, the preparation method specifically involves polymerizing an initiator, a flexible monomer represented by formula I, an unsaturated carboxylic acid monomer represented by formula II, an unsaturated cyano monomer represented by formula III, and an unsaturated amide monomer represented by formula IV in an aqueous solvent. [ka] In the formula, R1, R2, R3, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 Each is independently hydrogen, or substituted or unsubstituted C 1-5 It contains an alkyl group, and R4 is C 1-5 Hydroxyalkyl group, C 1-5 Alkyl and C 1-5 It contains one or more alkoxy groups. By preparing the polymer by solution polymerization, the reaction temperature can be well controlled, which is advantageous for preparing polymers with appropriate molecular weights, and the polymers synthesized by solution polymerization have good water solubility.

[0029] In any embodiment, the initiator comprises an inorganic peroxide initiator, the inorganic peroxide initiator comprising one of ammonium persulfate, potassium persulfate, or sodium persulfate.

[0030] In any embodiment, the mass of the initiator is 0.01% to 0.1% of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer, and selectively 0.03% to 0.08%.

[0031] When the amount of initiator used is within the above range, the polymerization reaction rate slows down, the system is heated uniformly, the gel effect is weakened, and the polymerization of the polymer is uniform, thereby obtaining a polymer with an appropriate weight-average molecular weight.

[0032] In any embodiment, the polymerization reaction is (1) The reaction environment for the polymerization reaction is a water-insoluble gas atmosphere, (2) The reaction temperature of the polymerization reaction is 60°C to 100°C, (3) The stirring speed of the polymerization reaction is 200 rpm to 800 rpm, (4) The reaction time of the polymerization reaction is 8 to 12 hours, and at least one of the following conditions is met.

[0033] When the polymerization reaction temperature is between 60°C and 100°C, the reactivity of radicals in the solution is within an appropriate range, the rates of chain transfer and chain growth are moderate, and consequently the molecular weight of the polymer is within an appropriate range.

[0034] When the polymerization reaction time is between 8 and 12 hours, the monomer conversion rate is within an appropriate range, and the polymer has an appropriate weight-average molecular weight.

[0035] In some embodiments, the water-insoluble gas is one or more selected from nitrogen, oxygen, hydrogen, and methane.

[0036] A third aspect of this application provides a negative electrode sheet comprising a negative electrode film layer, wherein the negative electrode film layer comprises a binder, and the binder comprises a polymer in any embodiment or a polymer prepared by a preparation method in any embodiment.

[0037] In any embodiment, the mass percentage of the binder is 0.5% to 3%, and selectively 1% to 2%, based on the total mass of the negative electrode film layer.

[0038] In the prior art, polymers containing constituent units derived from unsaturated carboxylic acid monomers cause serious warping and edge cracking in the sheet when roll-pressed, even with an additive amount of just 1%, making it difficult to meet production requirements. Even with a high additive amount of 3% of the polymer provided in the examples of this application, the sheet still exhibits good processing performance, and therefore, the cycle stability of secondary batteries can be further improved by increasing the amount of binder used.

[0039] In any embodiment, the curvature height of the negative electrode sheet is 0 mm to 20 mm.

[0040] The polymer has a low glass transition temperature and high flexibility, which effectively improves the uneven shrinkage and stress concentration phenomena that occur during the oven drying process, and can mitigate the warping phenomenon of the sheet.

[0041] In any embodiment, the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

[0042] Silicon-based materials have high capacity and can significantly improve the energy density of batteries. However, due to the large expansion rate of silicon-based materials during the cycle process, the force applied to the sheet tends to be uneven, making it prone to phenomena such as wrinkling of the sheet. The corners of the inner ring of the cell are subjected to more severe forces, resulting in conditions such as film formation, foaming, and cracking, and in some cases, even peeling of film fragments. The polymer provided in the embodiment of this application can also be applied to silicon-based systems, reducing the uneven stress distribution of the sheet, effectively improving conditions such as film formation, foaming, and cracking of the sheet when fully charged, and further improving the cycle stability of the battery.

[0043] In any embodiment, the pressure density of the negative electrode sheet is 1.45 g / cm³. 3 ~1.95g / cm 3 That is the case.

[0044] Anode sheets with high compression density are more susceptible to brittle fracture during the cycling process, and consequently, there is a risk of cracking during the hot pressing process after winding. The polymers provided in the embodiments of this application can also be applied to high-pressure density sheets, improving their flexibility and reducing the probability of cracking and brittle fracture during the production and use of the sheets.

[0045] A fourth aspect of this application provides a secondary battery including the negative electrode sheet described in the third aspect of this application.

[0046] A fifth aspect of this application provides an electrical device including a secondary battery as described in the fourth aspect of this application. [Brief explanation of the drawing]

[0047] [Figure 1] This is a schematic diagram of a secondary battery according to one embodiment of the present application. [Figure 2] Figure 1 is an exploded view of a secondary battery according to one embodiment of this application. [Figure 3] This is a schematic diagram of a battery module according to one embodiment of the present application. [Figure 4] This is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 5] Figure 4 is an exploded view of a battery pack according to one embodiment of this application. [Figure 6] This is a schematic diagram of an electrical device in which a secondary battery is used as a power source according to one embodiment of this application. [Modes for carrying out the invention]

[0048] The following describes in detail embodiments specifically disclosing the polymer, preparation method, negative electrode sheet, secondary battery, and electrical device of this application, with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of well-known matters and redundant explanations of identical structures may be omitted. This is to avoid unnecessarily verbose explanations, making it easier for those skilled in the art to understand. Furthermore, the drawings and the following explanation are provided to enable those skilled in the art to fully understand this application and are not intended to limit the intent of the claims.

[0049] The “range” disclosed in this application is limited by a lower and upper limit, and a given range is limited by selecting one lower limit and one upper limit, and the boundaries of the special range are limited by the selected lower and upper limits. Such limited ranges may or may not include endpoint values ​​and can be combined arbitrarily, that is, any lower limit and any upper limit can be combined to form a single range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, the ranges 60-110 and 80-120 are also understood to be predictable. Similarly, if the minimum range values ​​are listed as 1 and 2, and the maximum range values ​​are listed as 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all predictable. In this application, unless otherwise specified, the numerical range “a-b” represents an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated representation of combinations of these numbers. Furthermore, when a parameter is described as being an integer of 2 or more, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technological solutions.

[0051] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but preferably sequentially. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, when the method further includes step (c), it means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), or otherwise.

[0053] Unless otherwise specified, the terms "includes" and "incorporates" in this application are open, but may also be closed. For example, the terms "includes" and "incorporates" may further include or incorporate other components not listed, or may include or incorporate only the listed components.

[0054] 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, any of the following conditions satisfy the "A or B" condition: 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).

[0055] Non-fluorinated polymers containing unsaturated carboxylic acid monomers have advantages such as low cost, strong binding strength, and high water solubility, and their application in secondary batteries has been widely studied in recent years. To meet the binding strength requirements of sheets, such binders always use large amounts of unsaturated carboxylic acid monomers and unsaturated monomers containing cyano groups as copolymer units, improving the binding performance of the sheet through the interaction between the carboxyl and cyano groups and the current collector. However, in practice, slurries containing such polymers have been shown to easily cause significant warping of the sheet during the oven drying process after coating, affecting subsequent roll press manufacturing of the sheet and the stability of the sheet quality.

[0056] [polymer] Based on this, the present application provides a polymer. The polymer contains constituent units derived from an unsaturated carboxylic acid monomer, constituent units derived from an unsaturated cyano monomer, and constituent units derived from a flexible monomer, wherein the glass transition temperature of the flexible monomer is -60°C to 0°C, and selectively -55°C to -15°C.

[0057] In this specification, the term “polymer” includes, on the one hand, a collection of polymers that are chemically homogeneous but differ in degree of polymerization, molar mass and chain length, prepared by polymerization reactions. On the other hand, the term also includes derivatives of such polymer collections formed by polymerization reactions, i.e., compounds obtained by reactions of functional groups in the polymers, such as addition or substitution, which may be chemically homogeneous or heterogeneous.

[0058] In this specification, the term "unsaturated carboxylic acid monomer" refers to an unsaturated monomer that contains a -COOH group in its molecule.

[0059] In this specification, the term "unsaturated cyano monomer" refers to an unsaturated monomer that contains a -CN group in its molecule.

[0060] In this specification, the term "flexible monomer" refers to a monomer whose homopolymer has a low glass transition temperature, which can improve the brittleness of the polymer and enhance its flexibility.

[0061] In this specification, the term "glass transition temperature" refers to the temperature at which a polymer transitions from a glassy state to a highly elastic state, and is abbreviated as Tg. The glass transition temperature of a flexible monomer is generally obtained by measuring the glass transition temperature of a homopolymer of the flexible monomer, and may also be obtained by referring to reference books.

[0062] In some embodiments, the glass transition temperature of the flexible monomer is -60°C, -55°C, -50°C, -45°C, -40°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, or any number in between.

[0063] The constituent units derived from unsaturated carboxylic acid monomers contained in the polymer can improve the water solubility of the polymer and provide ion transport channels to lithium ions, which is advantageous for improving the kinetic properties of the battery. The constituent units derived from unsaturated cyano monomers can improve the bonding strength between the polymer and the active material and current collector. The constituent units derived from flexible monomers can effectively lower the glass transition temperature of the polymer, improve the flexibility of the polymer, reduce the phenomenon of uneven shrinkage and stress concentration that occurs during the oven drying process of the slurry, and further mitigate the degree of sheet warping, widen the processing window of the sheet, and improve the processability and quality stability of the sheet.

[0064] In some embodiments, the flexible monomer comprises a structure represented by formula I, [ka] In the formula, R1, R2, and R3 are each independently hydrogen, or substituted or unsubstituted carbon. 1-5 It contains an alkyl group, and R4 is C 1-5 Hydroxyalkyl group, C1-5 Alkyl and C 1-5 It contains one or more alkoxy groups.

[0065] In this specification, the term "substituted" means that at least one hydrogen atom of the compound or chemical moiety is substituted with a substituent of another chemical moiety, where each substituent is independently a hydroxyl group, a mercapto group, an amino group, a cyano group, a nitro group, an aldehyde group, a halogen atom, an alkenyl group, an alkynyl group, an aryl group, a heteroaryl group, or C 1-6 Alkyl alkyl group, C 1-6 Selected from alkoxy groups.

[0066] In this specification, the term "C 1-5 A "hydroxyalkyl group" refers to a group consisting of an alkyl group and a hydroxyl group, which is not unsaturated, has 1 to 5 carbon atoms, and is bonded to the remainder of the molecule by a single bond. This includes, but is not limited to, hydroxymethyl, hydroxyethyl, hydroxypropyl, and 4-hydroxybutyl groups.

[0067] In this specification, the term "C 1-5 "Alkyl group" refers to a linear or branched hydrocarbon group consisting only of carbon and hydrogen atoms, having 1 to 5 carbon atoms, and bonded to the remainder of the molecule by a single bond. This includes, but is not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, and pentyl groups.

[0068] In this specification, the term "C 1-5 An "alkoxy group" refers to a group consisting of an alkyl group and an oxygen atom, having 1 to 5 carbon atoms, and being bonded to the rest of the molecule by a single bond. Common examples include the methoxy group (CH3O-), ethoxy group (C2H5O-), and propoxy group (C3H7O-).

[0069] In some embodiments, R1, R2, and R3 are each independently hydrogen or C 1-5 It contains an alkyl group, and R4 is C 1-4Contains a hydroxyalkyl group.

[0070] In some embodiments, the flexible monomer comprises one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0071] In some embodiments, the flexible monomer comprises one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate.

[0072] The above-mentioned flexible monomers not only have a low glass transition temperature, but also exhibit high compatibility with constituent units derived from unsaturated carboxylic acid monomers and unsaturated cyano monomers, effectively lowering the glass transition temperature of the polymer. Furthermore, the above-mentioned flexible monomers can effectively reduce the surface tension of the slurry through groups such as ester groups, hydroxyl groups, and alkoxy groups, thereby reducing sheet warping and improving the processability and quality stability of the sheet.

[0073] In some embodiments, the flexible monomer comprises at least two of the following: hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

[0074] In some embodiments, the flexible monomer comprises at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate.

[0075] By combining two different types of flexible monomers, it is possible to achieve both polymer bonding performance and suppression of sheet rebound, while further improving the flexibility of the polymer and expanding the processing window and application scenarios of the polymer.

[0076] In some embodiments, the unsaturated carboxylic acid monomer comprises the structure shown in formula II, and the unsaturated cyano monomer comprises the structure shown in formula III. [ka] In the formula, R5, R6, R7, R8, R9, R 10 Each is independently hydrogen, or substituted or unsubstituted C 1-5 Contains alkyl groups.

[0077] In some embodiments, the unsaturated carboxylic acid monomer includes one or more of acrylic acid, methacrylic acid, ethacrylic acid, and crotonic acid.

[0078] In some embodiments, the unsaturated cyano monomer comprises one or more of acrylonitrile, crotononitrile, methacrylonitrile, and ethacrylonitrile. In some embodiments, the polymer further comprises a constituent unit derived from an unsaturated amide monomer, the unsaturated amide monomer comprising a structure represented by formula IV, [ka] In the formula, R 11 , R 12 , R 13 , R 14 , R 15 Each is independently hydrogen, or substituted or unsubstituted C 1-5 Contains alkyl groups.

[0079] In this specification, the term "unsaturated amide monomer" refers to an unsaturated monomer that contains -CO-N- in its molecule.

[0080] When a polymer contains constituent units derived from unsaturated amide monomers, the amide groups in the polymer dissociate after dissolving in water, resulting in a negative charge on the polymer. The presence of electrostatic repulsion between different chains in the polymer allows the polymer to spread and entangle with each other in the solution, thereby improving the viscosity and stability of the negative electrode slurry and further optimizing the processing performance of the sheet.

[0081] In some embodiments, the unsaturated amide monomer comprises one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N-methylacrylamide.

[0082] In some embodiments, the molar proportion of constituent units derived from the flexible monomer is 5% to 50%, and selectively 20% to 35%, based on the total number of moles of all constituent units in the polymer.

[0083] In some embodiments, the molar proportion of the constituent units derived from the flexible monomer is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any number in between, based on the total number of moles of all constituent units in the polymer.

[0084] Polymers in which the molar proportion of flexible monomer components is 5% to 50% have a low glass transition temperature, which can mitigate sheet warping and improve sheet processing performance. Polymers in which the molar proportion of flexible monomer components is 20% to 35% can achieve both polymer flexibility and bonding performance, reducing the risk of edge cracking due to cold pressing and interface wrinkles and film shedding due to full charge during sheet processing, thereby improving production efficiency and yield. Furthermore, they can maintain high bonding strength and low rebound rate in the sheet, and can comprehensively improve the battery cycle stability.

[0085] In some embodiments, based on the total number of moles of all constituent units in the polymer, the molar proportion of constituent units derived from the unsaturated carboxylic acid monomer is 10% to 60%, selectively 30% to 50%, and / or the molar proportion of constituent units derived from the unsaturated cyano monomer is 10% to 60%, selectively 15% to 45%, and / or the molar proportion of constituent units derived from the unsaturated amide monomer is 0% to 30%, selectively 5% to 20%.

[0086] In some embodiments, the molar proportion of the constituent units derived from the unsaturated carboxylic acid monomer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any number in between, based on the total number of moles of all constituent units in the polymer.

[0087] In some embodiments, the molar proportion of the constituent units derived from the unsaturated cyano monomer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any number in between, based on the total number of moles of all constituent units in the polymer.

[0088] In some embodiments, the molar proportion of the constituent units derived from the unsaturated amide monomer is 0%, 5%, 10%, 15%, 20%, 25%, 30%, or any value in between, based on the total number of moles of all constituent units in the polymer.

[0089] Polymers whose constituent units fall within the above content range can achieve both improved flexibility and high binding strength and solubility. In some embodiments, the glass transition temperature of the polymer is 40°C to 105°C, and selectively 40°C to 90°C.

[0090] In this application, the glass transition temperature of a polymer can be tested using a method known in the art, for example, by using a differential scanning calorimeter (Q1000 model) manufactured by TA Corporation. A polymer sample of 6-9 g is taken and heated from room temperature to 200°C at a heating rate of 10°C / min, and then incubated at 200°C for 3 hours to remove the thermal history. After cooling, the sample is heated again from room temperature to 200°C at a heating rate of 10°C / min, and the differential scanning calorimetry curve obtained from this scan is analyzed to determine the glass transition temperature of the polymer, in units of °C.

[0091] In some embodiments, the glass transition temperature of the polymer is 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 105°C, or any number in between.

[0092] When the glass transition temperature of a polymer is within the above range, the polymer has good flexibility, and the sheet has low warping and good processing performance. Polymers with a glass transition temperature of 40°C to 90°C can further reduce the occurrence of edge cracking during edge roll press processing of batteries, further widen the processing window of the sheet, and improve the processing performance of the sheet.

[0093] In some embodiments, the weight-average molecular weight of the polymer is between 500,000 and 2,000,000, and selectively between 800,000 and 1,500,000.

[0094] In this specification, the term "weight-average molecular weight" refers to the sum of the products of the weight fractions of molecules with different molecular weights in a polymer and their corresponding molecular weights.

[0095] In this application, the weight-average molecular weight of polymers can be tested using methods known in the art, such as gel chromatography, and can be tested using a Waters 2695 Isocratic HPLC-type gel chromatograph (differential refractive index detector 2141). In some embodiments, the test method is as follows: A 3.0% polystyrene solution sample is used as a reference, and a matched chromatography column (oil-based: Styragel HT5DMF 7.8*300mm + Styragel HT4) is selected. A 3.0% polymer gel solution is prepared in purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for 1 day to prepare it for use. During the test, tetrahydrofuran is first drawn into the syringe, washed, and repeated several times. Next, 5 ml of the experimental solution is drawn into the syringe, air is removed, and the tip of the needle is wiped dry. Finally, the sample solution is gradually injected into the inlet. After the displayed value stabilizes, the data is acquired and the weight-average molecular weight is read.

[0096] In some embodiments, the weight-average molecular weight of the polymer is 500,000, 700,000, 800,000, 900,000, 1,000,000, 1,200,000, 1,400,000, 1,500,000, 1,600,000, 1,800,000, 2,000,000, or any number in between.

[0097] When the weight-average molecular weight of the polymer is within the above range, the viscosity of the aqueous solution of the polymer at a certain solid content is within an appropriate range, the sheet has good processability and bonding performance, and the battery has good cycle stability.

[0098] In some embodiments, the viscosity of an aqueous solution with a solid content of 6 wt% prepared by dissolving the polymer in deionized water is 8000 MPa·s to 30000 MPa·s, and selectively 10000 MPa·s to 20000 MPa·s.

[0099] In this application, the viscosity of the polymer solution can be tested using methods known in the art. For example, 24 g of polymer and 376 g of water are weighed into 500 ml beakers to prepare an aqueous solution with a solid content of 6%, which is then stirred and dispersed using a Lichen high-speed polishing machine. After stirring at a rotation speed of 800 r / min for 120 min, the mixture is shaken with ultrasound for 30 min to remove air bubbles. Using a Lichen NDJ-5S rotational viscometer, rotor number 64 is selected and inserted so that the aqueous solution is above the scale line, and the viscosity is tested at 12 r / min. The viscosity data is then read after 6 min.

[0100] In some embodiments, the viscosity of an aqueous solution with a solid content of 6 wt% prepared by dissolving the polymer in deionized water is 8000 MPa·s, 10000 MPa·s, 15000 MPa·s, 20000 MPa·s, 25000 MPa·s, 30000 MPa·s, or any value in between.

[0101] When the viscosity of an aqueous solution with a solid content of 6 wt%, prepared by dissolving the polymer in deionized water, is within the above range, the slurry will have stability and processability, the sheet will have excellent processability and bonding performance, and the battery will have good cycle stability.

[0102] In some embodiments, the polymer comprises at least one of the following copolymers: acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-hydroxyethyl acrylate copolymer, methacrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-methacrylonitrile-acrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-methacrylamide-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-2-hydroxybutyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxypropyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer, and acrylic acid-acrylonitrile-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer.

[0103] A second aspect of this application provides a method for preparing a polymer by polymerizing raw materials containing a flexible monomer, an unsaturated carboxylic acid monomer, and an unsaturated cyano monomer under polymerizable conditions, wherein the glass transition temperature of the flexible monomer is -60°C to 0°C, and selectively -55°C to -15°C.

[0104] In some embodiments, the preparation method specifically involves polymerizing an initiator, a flexible monomer represented by formula I, an unsaturated carboxylic acid monomer represented by formula II, an unsaturated cyano monomer represented by formula III, and an unsaturated amide monomer represented by formula IV in an aqueous solvent. [ka] In the formula, R1, R2, R3, R5, R6, R7, R8, R9, R 10 , R 11 , R 12 , R 13 , R 14 , R 15 Each is independently hydrogen, or substituted or unsubstituted C1-5 It contains an alkyl group, and R4 is C 1-5 Hydroxyalkyl group, C 1-5 Alkyl and C 1-5 It contains one or more alkoxy groups.

[0105] By preparing polymers using solution polymerization, the reaction temperature can be well controlled, which is advantageous for preparing polymers with appropriate molecular weights, and polymers synthesized by solution polymerization have good water solubility.

[0106] In some embodiments, the initiator comprises an inorganic peroxide initiator, the inorganic peroxide initiator comprising one of ammonium persulfate, potassium persulfate, or sodium persulfate.

[0107] In some embodiments, the mass of the initiator is 0.01% to 0.1% of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer, and selectively 0.03% to 0.08%.

[0108] In some embodiments, the mass of the initiator is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, or any value in between, of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer.

[0109] When the amount of initiator used is within the above range, the polymerization reaction rate slows down, the system is heated uniformly, the gel effect is weakened, and the polymerization of the polymer is uniform, resulting in a polymer with an appropriate weight-average molecular weight.

[0110] In some embodiments, the polymerization reaction is carried out as follows: (1) The reaction environment for the polymerization reaction is a water-insoluble gas atmosphere, (2) The reaction temperature of the polymerization reaction is 60°C to 100°C, (3) The stirring speed of the polymerization reaction is 200 rpm to 800 rpm, (4) The reaction time of the polymerization reaction is 8 to 12 hours, and at least one of the following conditions is met.

[0111] Non-water-soluble gases refer to gases with a gas solubility of less than 0.1 L. Gas solubility is calculated at 20°C and under a gas pressure of 1.013 × 10⁻¹⁰. 5 In the case of Pa, it refers to the volume of gas when dissolved in 1 liter of water and reaching a saturated state.

[0112] In some embodiments, the water-insoluble gas is one or more selected from nitrogen, oxygen, hydrogen, and methane.

[0113] In some embodiments, the reaction temperature of the polymerization reaction is 60°C, 70°C, 80°C, 90°C, 100°C, or any value in between.

[0114] When the polymerization reaction temperature is within the above range, the reaction activity of radicals in the solution is within an appropriate range, the rates of chain transfer and chain growth are moderate, and consequently the weight-average molecular weight of the polymer is within an appropriate range.

[0115] In some embodiments, the stirring speed of the polymerization reaction is 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, or any number in between.

[0116] In some embodiments, the reaction time for the polymerization reaction is 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, or any number in between.

[0117] If the reaction time of the polymerization reaction is within the above range, the monomer conversion rate is within an appropriate range, and the polymer has an appropriate weight-average molecular weight.

[0118] [Negative electrode sheet] In some embodiments, the negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a binder, the binder includes a polymer in any embodiment or a polymer prepared by a preparation method in any embodiment.

[0119] In this specification, the term "binding agent" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0120] In some embodiments, the dispersion medium for the binder is an aqueous solvent such as water. That is, the binder dissolves in the aqueous solvent.

[0121] In some embodiments, the mass percentage of the binder is 0.5% to 3% and selectively 1% to 2% based on the total mass of the negative electrode film layer.

[0122] In some embodiments, the mass percentage of the binder is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any value in between, based on the total mass of the negative electrode film layer.

[0123] In the prior art, polymers containing constituent units derived from unsaturated carboxylic acid monomers cause serious warping and edge cracking in the sheet when roll-pressed, even with an additive amount of just 1%, making it difficult to meet production requirements. Even with a high additive amount of 3% of the polymer provided in the examples of this application, the sheet still exhibits good processing performance, and therefore, the cycle stability of secondary batteries can be further improved by increasing the amount of binder used.

[0124] In some embodiments, the curvature height of the negative electrode sheet is 0 mm to 20 mm.

[0125] In this application, the warp height of the negative electrode sheet can be tested by selecting a method known in the art. For example, a negative electrode slurry is applied to the negative electrode current collector, baked at 100°C for 1 minute to remove most of the water, then cut into 10 negative electrode sheets measuring 4 cm x 4 cm, and then placed on the top surface of a heating plate maintained at 120°C for 1 minute. The height at which the four corners of each negative electrode sheet warp from the plane of the heating plate is measured using a scale and recorded as h1, h2, h3, and h4, respectively. The average value of the corresponding h1, h2, h3, and h4 for each negative electrode sheet is calculated and recorded as H. The average value of the corresponding average H of the 10 negative electrode sheets is taken as the warp height of the negative electrode sheet.

[0126] In some embodiments, the curvature height of the negative electrode sheet is 0 mm, 2 mm, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, or any number in between.

[0127] The polymer has a low glass transition temperature and high flexibility, which effectively improves the uneven shrinkage and stress concentration phenomena that occur during the oven drying process, and can mitigate the warping phenomenon of the sheet.

[0128] In some embodiments, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

[0129] In some embodiments, the silicon-based material includes at least one of elemental silicon, nanosilicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys.

[0130] Silicon-based materials have high capacity and can significantly improve the energy density of batteries. However, due to the large expansion rate of silicon-based materials during the cycle process, the force applied to the sheet tends to be uneven, making it prone to phenomena such as wrinkling of the sheet. The corners of the inner ring of the cell are subjected to more severe forces, resulting in conditions such as film formation, foaming, and cracking, and in some cases, even peeling of film fragments. The polymer provided in the embodiment of this application can also be applied to silicon-based systems, reducing the uneven stress distribution of the sheet while maintaining the low rebound rate of the sheet, effectively improving conditions such as film formation, foaming, and cracking of the sheet when fully charged, and further improving the cycle stability of the battery.

[0131] In some embodiments, the negative electrode film layer comprises a negative electrode active material and a binder, the negative electrode active material comprises a silicon-based material, the binder comprises a polymer, the polymer comprises constituent units derived from unsaturated carboxylic acid monomers, constituent units derived from unsaturated cyano monomers and constituent units derived from flexible monomers, the flexible monomer comprises at least two of hydroxyethyl acrylate, hydroxypropyl acrylate and 4-hydroxybutyl acrylate, and the glass transition temperature of the polymer is 40°C to 75°C.

[0132] In some embodiments, the pressure density of the negative electrode sheet is 1.45 g / cm³. 3 , 1.55 g / cm³ 3 1.60 g / cm³ 3 1.65 g / cm³ 3 1.75 g / cm³ 3 1.85 g / cm³ 3 1.95 g / cm³ 3 Or any number between those two values.

[0133] Anode sheets with high compression density are more prone to brittle fracture during the cycling process, and consequently, there is a risk of cracking during the hot pressing process after winding. The polymers provided in the embodiments of this application can also be applied to high-pressure density sheets, improving the flexibility of the high-pressure density sheets while maintaining the low rebound rate of the sheets, and reducing the probability of cracking and brittle fracture during the production and use processes of the sheets.

[0134] In some embodiments, the pressure density of the negative electrode sheet is 1.60 g / cm³. 3 ~1.95g / cm 3 The negative electrode film layer contains a binder, the binder contains a polymer, the polymer contains constituent units derived from unsaturated carboxylic acid monomers, constituent units derived from unsaturated cyano monomers, constituent units derived from unsaturated amide monomers, and constituent units derived from flexible monomers, the flexible monomers contain at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, and 4-hydroxybutyl acrylate, and the glass transition temperature of the polymer is 40°C to 90°C.

[0135] In some embodiments, a metal foil or a composite current collector can be used as the negative electrode current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector can be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0136] In some embodiments, the negative electrode film layer further selectively comprises a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the negative electrode film layer further comprises other additives, such as a selective thickener (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0138] In some embodiments, the negative electrode sheet can be manufactured as follows: Components for manufacturing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is applied to a negative electrode current collector; and the negative electrode sheet can be obtained through processes such as oven drying and cold pressing.

[0139] [Positive electrode sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer containing a positive electrode active material.

[0140] For example, a positive electrode current collector has two opposing surfaces in the thickness direction of itself. The positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0141] In some embodiments, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate layer and a metal layer formed on at least one surface of the polymer material substrate layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (for example, a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0142] In some embodiments, the positive electrode active material can be any positive electrode active material known in the art for batteries. For example, the positive electrode active material may include at least one of olivine-structured lithium-containing phosphates, lithium transition metal oxides, and modified compounds of each thereof. However, this application is not limited to these materials, and other conventional materials usable as positive electrode active materials for batteries may be used. These positive electrode active materials may be used individually or in combination of two or more. Here, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (Can also be abbreviated as LiNi) 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (Can also be abbreviated as LiNi) 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (Can also be abbreviated as LiNi) 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (Can also be abbreviated as LiNi) 0.8 Co 0.1 Mn 0.1 O2(NCM 811 (It can also be abbreviated as LiNi) Lithium nickel cobalt aluminum oxide (for example, LiNi 0.85 Co 0.15 Al 0.05It may include, but is not limited to, at least one of O2) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure include, but is not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (also abbreviated as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0143] In some embodiments, the positive electrode film layer selectively further comprises a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0144] In some embodiments, the cathode film layer selectively further comprises a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0145] In some embodiments, the positive electrode sheet can be manufactured as follows: Components for manufacturing the above-mentioned positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, the positive electrode slurry is applied to a positive electrode current collector, and the positive electrode sheet can be obtained through processes such as oven drying and cold pressing.

[0146] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. In this application, the type of electrolyte is not specifically limited and can be selected as needed. For example, the electrolyte may be liquid, gel-like, or all-solid.

[0147] In some embodiments, the electrolyte is an electrolyte solution, which comprises an electrolyte salt and a solvent.

[0148] In some embodiments, the electrolyte salt may be at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0149] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethylmethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethylmethyl sulfone, and diethyl sulfone.

[0150] In some embodiments, the electrolyte further selectively includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may further include additives that can improve certain aspects of the battery's performance, such as additives that can improve the battery's overcharge performance, or additives that can improve the battery's high-temperature or low-temperature performance.

[0151] [Separator] In some embodiments, the secondary battery further includes a separator. In this application, the type of separator is not particularly limited, and any known porous structure separator having good chemical and mechanical stability can be selected.

[0152] In some embodiments, the material of the separator may be at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. If the separator is a multilayer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0153] In some embodiments, the positive electrode sheet, negative electrode sheet, and separator can be assembled into an electrode assembly by a winding process or a lamination process.

[0154] In some embodiments, the secondary battery may include an casing. This casing can be used to enclose the electrode assembly and electrolyte.

[0155] In some embodiments, the casing of the secondary battery may be a rigid case, such as a hard plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0156] In this application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows a rectangular secondary battery 5 as an example. Selectively, the secondary battery may be a lithium-ion battery or a sodium-ion battery.

[0157] In some embodiments, referring to Figure 2, the exterior may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround the case 51 to form a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the cover plate 53 can cover the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet and separator can be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and a person skilled in the art can select according to the specific actual needs.

[0158] In some embodiments, the secondary battery may be assembled as a battery module, and the number of secondary batteries included in the battery module may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0159] Figure 3 shows an example of a battery module 4. Referring to Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fastening members.

[0160] Selectively, the battery module 4 may further include a housing having a housing space, in which a plurality of secondary batteries 5 are housed.

[0161] In some embodiments, the battery modules may be assembled as a battery pack, and the number of battery modules included in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery pack.

[0162] Figures 4 and 5 show an example of a battery pack 1. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided within the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 covering the lower box 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged within the battery box in any manner.

[0163] Furthermore, this application provides an electrical device comprising at least one of the secondary battery, battery module, or battery pack provided herein. The secondary battery, battery module, or battery pack may 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.), trains, ships and satellites, energy storage systems, etc.

[0164] The aforementioned electrical device can be selected as a secondary battery, battery module, or battery pack, depending on its intended use.

[0165] Figure 6 shows an example of an electrical device. This electrical device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the requirements for high power output and high energy density of secondary batteries, this electrical device may use a battery pack or battery module.

[0166] Other examples of devices may include mobile phones, tablet computers, and laptop computers. These devices are typically required to be lightweight and thin, and may use rechargeable batteries as a power source.

[0167] Examples Preparation method Examples of the present application are described below. The examples described below are illustrative and are for interpretive purposes only, and should not be understood as limiting this application. Unless otherwise specified in the examples, specific techniques or conditions are followed in accordance with the techniques or conditions or product specifications described in the literature in the art. Unless otherwise specified, the reagents or equipment used are common commercially available products.

[0168] 1. Preparation method Example 1 1) Preparation of polymers Hydroxyethyl acrylate (HEA), acrylic acid, acrylonitrile, and acrylamide were placed in a molar ratio of 35:30:25:10 in a three-necked flask equipped with a reflux condenser and stirrer. Deionized water and ammonium persulfate initiator, comprising 0.05% of the total monomer mass, were added. The mixture was then reacted at a constant temperature under a nitrogen atmosphere at 80°C with a rotation speed of 500 rpm for 8 hours. After the reaction was complete, an acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate copolymer was obtained. The weight-average molecular weight of the copolymer was 800,000, and the viscosity of an aqueous solution containing 6 wt% solids of the copolymer was 8,000 MPa·s to 30,000 MPa·s.

[0169] 2) Manufacturing of positive electrode sheets LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were added to N-methylpyrrolidone in a weight ratio of 92:4:4, stirred, and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was uniformly applied to two surfaces of an aluminum foil positive electrode current collector, then dried to obtain a film layer, which was then cold-pressed and cut to obtain a positive electrode sheet. Here, the binder was PVDF with a weight-average molecular weight of 700,000, purchased from Arkema France Ltd.

[0170] 3) Manufacturing of negative electrode sheets Common graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, the polymer prepared in Example 1, and sodium carboxymethyl cellulose (CMC-Na) as the thickener were dissolved in deionized water as the solvent at a weight ratio of 96.5:0.5:1:1:1, stirred at 1800 r / min under the condition of 25 °C for 3 h, and uniformly mixed to obtain a negative electrode slurry. The negative electrode slurry was uniformly applied to two surfaces of a copper foil as the negative electrode current collector once or multiple times, and after oven drying, cold pressing, and cutting, a negative electrode sheet was obtained, and the tap density was 1.5 g / cm 3 It was.

[0171] 4) Separator A polypropylene film was used as the separator.

[0172] 5) Preparation of electrolyte In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as organic solvents were uniformly mixed at a volume ratio of 3 / 7, and LiPF6 lithium salt was dissolved in the organic solvent and uniformly stirred to prepare a 1 M LiPF6 electrolyte.

[0173] 6) Manufacture of battery The manufactured positive electrode sheet, separator, and negative electrode sheet were stacked in this order so that the separator played a role of separating them between the positive electrode sheet and the negative electrode sheet, and then wound to obtain a bare cell. Tabs were welded to the bare cell, the bare cell was placed in an aluminum case, baked at 80 °C to remove water, and then immediately the electrolyte was injected and sealed to obtain an uncharged battery. The uncharged battery was sequentially subjected to processes such as standing, hot pressing, cold pressing, forming, and capacity testing to obtain the lithium-ion battery product of Example 1.

[0174] The batteries of Examples 2 to 13 were the same as the manufacturing method of the battery of Example 1 except that the molar ratios of acrylic acid, acrylonitrile, acrylamide, and hydroxyethyl acrylate monomers were adjusted and the usage amount of the initiator changed correspondingly. The specific parameters are as shown in Table 1.

[0175] The batteries of Examples 14 to 16 are manufactured in the same manner as the battery of Example 1, except that the mass fraction of the polymer is adjusted and the mass of the negative electrode active material changes accordingly based on the total mass of the negative electrode film layer. The specific parameters are shown in Table 1.

[0176] The batteries in Examples 17-20 were manufactured in the same manner as the battery in Example 1, except that the amount of initiator used was adjusted to 0.1%, 0.05%, 0.03%, and 0.03% of the total monomer mass, and the reaction times were set to 8 hours, 10 hours, 10 hours, and 12 hours, respectively, thereby adjusting the molecular weight of the polymer. The specific parameters are shown in Table 1.

[0177] The battery in Example 21 is the same as the battery manufacturing method in Example 1, except that the hydroxyethyl acrylate monomer is replaced with 4-hydroxybutyl acrylate (4-HBA) monomer and the molar ratio remains unchanged. The specific parameters are shown in Table 1.

[0178] The battery of Example 22 is the same as the battery manufacturing method of Example 1, except that the hydroxyethyl acrylate monomer is replaced with hydroxypropyl acrylate monomer, the molar ratio is set to 25%, and the molar ratio of acrylic acid monomer changes accordingly. The specific parameters are shown in Table 1.

[0179] The battery of Example 23 is the same as the battery of Example 1 in terms of manufacturing method, except that the acrylic acid monomer is replaced with methacrylic acid monomer. The specific parameters are shown in Table 1.

[0180] The battery in Example 24 is the same as the battery in Example 1 in terms of manufacturing method, except that the acrylonitrile monomer is replaced with methacrylonitrile monomer and the molar ratio does not change. The specific parameters are shown in Table 1.

[0181] The battery in Example 25 is the same as the battery in Example 1 in terms of manufacturing method, except that the acrylamide monomer is replaced with methacrylamide monomer and the molar ratio does not change. The specific parameters are shown in Table 1.

[0182] Example 26 1) Preparation of polymers Hydroxyethyl acrylate, 4-hydroxybutyl acrylate, acrylic acid, acrylonitrile, and acrylamide were placed in a molar ratio of 5:15:35:40:5 in a three-necked flask equipped with a reflux condenser and stirrer. Deionized water and ammonium persulfate initiator, comprising 0.05% of the total mass of monomers, were added. The reaction was carried out at a constant temperature of 500 rpm under a nitrogen atmosphere at 80°C for 8 hours. After the reaction was complete, an acrylic acid-acrylonitrile-acrylamide-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer was obtained. The weight-average molecular weight of the polymer was 800,000.

[0183] 2) Manufacturing of positive electrode sheets LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were added to N-methylpyrrolidone in a weight ratio of 92:4:4, stirred, and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was uniformly applied to two surfaces of an aluminum foil positive electrode current collector, then dried to obtain a film layer, which was then cold-pressed and cut to obtain a positive electrode sheet. Here, the binder was PVDF with a weight-average molecular weight of 700,000, purchased from Arkema France Ltd.

[0184] 3) Manufacturing of negative electrode sheets High-density graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, the polymer prepared in Example 1, and sodium carboxymethylcellulose (CMC-Na) as the thickener are dissolved in deionized water as the solvent in a weight ratio of 96.5:0.5:1:1:1. The mixture is stirred for 3 hours at 1800 r / min and 25°C to obtain a negative electrode slurry. The negative electrode slurry is then uniformly applied to two surfaces of copper foil, which is the negative electrode current collector, one or more times. After oven drying, cold pressing, and cutting, a negative electrode sheet is obtained with a pressure density of 1.75 g / cm³. 3 That was the case.

[0185] 4) Separator A polypropylene film is used as the separator.

[0186] 5) Preparation of the electrolyte In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC), which are organic solvents, were uniformly mixed in a 3 / 7 volume ratio. LiPF6 lithium salt was dissolved in the organic solvent and uniformly stirred to prepare a 1 M LiPF6EC / EMC solution, thereby obtaining the electrolyte.

[0187] 6) Battery manufacturing A positive electrode sheet, a separator, and a negative electrode sheet were stacked in this order, with the separator acting to separate them from each other. These were then wound to obtain a bare cell. Tabs were welded to the bare cell, the bare cell was placed in an aluminum case, baked at 80°C to remove water, and then immediately injected with electrolyte and sealed to obtain an uncharged battery. The uncharged battery was then subjected to a series of processes including standing, hot pressing, cold pressing, chemical conversion, molding, and capacity testing to obtain the lithium-ion battery product of Example 26.

[0188] The batteries of Examples 27 and 28 are manufactured in the same manner as the battery of Example 26, but differ in that the molar ratios of hydroxyethyl acrylate and 4-hydroxybutyl acrylate are adjusted. The specific parameters are shown in Table 3.

[0189] Example 29 1) Preparation of Polymer Hydroxyethyl acrylate, 4-hydroxybutyl acrylate, acrylic acid, and acrylonitrile were placed in a three-neck flask equipped with a reflux condenser and a stirrer at a molar ratio of 20:20:40:20. Deionized water and an ammonium persulfate initiator accounting for 0.05% of the total mass of the monomers were added. Under a nitrogen atmosphere and at a temperature of 80 °C, a constant-temperature reaction was carried out at a rotation speed of 500 rmp for 8 hours. After the reaction was completed, an acrylic acid-acrylonitrile-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer was obtained. The weight-average molecular weight of the polymer was 800,000.

[0190] 2) Manufacture of Positive Electrode Sheet LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were added to N-methylpyrrolidone at a weight ratio of 92:4:4, and stirred to be uniformly mixed to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on two surfaces of an aluminum foil positive electrode current collector, and then dried to obtain a film layer. After that, through cold pressing and cutting, a positive electrode sheet was obtained. Here, the binder was PVDF with a weight-average molecular weight of 700,000 purchased from Arkema France Co., Ltd.

[0191] 3) Manufacture of Negative Electrode Sheet A common graphite material as the negative electrode active material, a silicon carbon material, carbon black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, the polymer prepared in Example 1, and sodium carboxymethyl cellulose (CMC-Na) as the thickener were dissolved in deionized water as the solvent at a weight ratio of 66.5:30:0.5:1:1:1, and stirred at 1800 r / min and 25 °C for 3 h. After being uniformly mixed, it was used as a negative electrode slurry. The negative electrode slurry was uniformly coated on two surfaces of a copper foil as the negative electrode current collector once or multiple times, and after oven drying, cold pressing, and cutting, a negative electrode sheet was obtained, and the tap density was 1.50 g / cm 3 It was.

[0192] 4) Separator A polypropylene film is used as the separator.

[0193] 5) Preparation of the electrolyte In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC), which are organic solvents, were uniformly mixed in a 3 / 7 volume ratio. LiPF6 lithium salt was dissolved in the organic solvent and uniformly stirred to prepare a 1 M LiPF6EC / EMC solution, thereby obtaining the electrolyte.

[0194] 6) Battery manufacturing A positive electrode sheet, a separator, and a negative electrode sheet were stacked in this order, with the separator acting to separate them from each other. These were then wound to obtain a bare cell, tabs were welded to the bare cell, the bare cell was placed in an aluminum case, and after baking at 80°C to remove water, electrolyte was immediately injected and the case was sealed to obtain an uncharged battery. The uncharged battery was then subjected to sequential processes such as standing, hot pressing, cold pressing, chemical conversion, molding, and capacity testing to obtain the lithium-ion battery product of Example 29.

[0195] The batteries of Examples 30-31 are manufactured in the same manner as the battery of Example 30, but differ in that the molar ratios of hydroxyethyl acrylate and 4-hydroxybutyl acrylate are adjusted. The specific parameters are shown in Table 3.

[0196] The battery of Comparative Example 1 was manufactured in the same manner as the battery of Example 1, except that the binder for the negative electrode sheet was a polyacrylic acid binder with a weight-average molecular weight of 800,000, which was LA133 purchased from Yindi Le. The specific parameters are shown in Table 1.

[0197] The battery in Comparative Example 2 was manufactured in the same manner as the battery in Example 1, except that the polymerization monomers available were limited to acrylic acid, acrylonitrile, and acrylamide monomer. The specific parameters are shown in Table 1.

[0198] The battery of Comparative Example 3 was manufactured in the same manner as the battery of Example 26, except that the binder for the negative electrode sheet was a polyacrylic acid binder with a weight-average molecular weight of 800,000, which was LA133 purchased from Yindi Le. The specific parameters are shown in Table 3.

[0199] The battery in Comparative Example 4 was manufactured in the same way as the battery in Example 26, except that the polymerization monomers were limited to acrylic acid, acrylonitrile, and acrylamide monomer. The specific parameters are shown in Table 3.

[0200] The battery of Comparative Example 5 was manufactured in the same manner as the battery of Example 29, except that the binder for the negative electrode sheet was a polyacrylic acid binder with a weight-average molecular weight of 800,000, which was LA133 purchased from Yindi Le. The specific parameters are shown in Table 3.

[0201] The battery of Comparative Example 6 was manufactured in the same manner as the battery of Example 29, except that the polymerization monomers were limited to acrylic acid, acrylonitrile, and acrylamide monomer. The specific parameters are shown in Table 3.

[0202] 2. Test Method 1. Polymer property testing 1) Glass transition temperature test The glass transition temperature was tested using a differential scanning calorimeter (Q1000 model) manufactured by TA Corporation. 6-9 g of polymer samples were taken and heated from room temperature to 200°C at a heating rate of 10°C / min. The samples were then held at 200°C for 3 hours to remove the thermal history. After cooling, the samples were heated again from room temperature to 200°C at a heating rate of 10°C / min. The differential scanning calorimeter curve obtained from this scan was analyzed to determine the glass transition temperature of the polymer, in degrees Celsius.

[0203] 2) Weight-average molecular weight test A Waters 2695 isocratic HPLC-type gel chromatograph (differential refractive index detector 2141) was used. A 3.0% polystyrene solution sample was used as a reference, and a matched chromatography column (oil-based: Styragel HT5DMF 7.8*300mm + Styragel HT4) was selected. A 3.0% polymer solution was prepared in purified N-methylpyrrolidone (NMP) solvent, and the prepared solution was allowed to stand for 1 day to prepare for use. During the test, tetrahydrofuran was first drawn into the syringe, washed, and repeated several times. Next, 5 ml of the experimental solution was drawn into the syringe, the air in the syringe was removed, and the tip of the needle was wiped dry. Finally, the sample solution was gradually injected into the inlet. After the displayed values ​​stabilized, data was acquired, and the weight-average molecular weight was read.

[0204] 3) Viscosity of an aqueous solution with a solid content of 6 wt% Weigh 24g of polymer and 376g of water into 500ml beakers to prepare an aqueous solution with a solid content of 6%. Disperse the solution by stirring in a Lichen high-speed polishing machine, stirring at 800 r / min for 120 minutes, and then remove air bubbles by shaking with ultrasound for 30 minutes. Using a Lichen NDJ-5S rotational viscometer, select and insert rotor number 64 so that the aqueous solution is above the scale line, test the viscosity at 12 r / min, and read the viscosity data after 6 minutes.

[0205] 2. Performance testing of the negative electrode sheet 1) Test to determine whether or not there are edge cracks caused by roll pressing. After applying the slurry, the sheet was placed on a roll press machine, and the roll gap thickness and roll press pressure were adjusted to appropriate values. Roll pressing was then performed, and it was observed whether the film layer and current collector of the sheet were torn at the boundary. If there was no tearing, it was determined that no edge cracking had occurred; if there was tearing, it was determined that edge cracking had occurred.

[0206] 2) Sheet rebound rate 48 hours after roll pressing The thickness of the negative electrode sheet was obtained by testing with calipers. The initial thickness D0 of the negative electrode sheet after roll pressing was used as the reference, and the thickness of the negative electrode sheet after being left to stand for 48 hours after roll pressing was defined as D1. The rebound rate of the sheet 48 hours after roll pressing was [(D1-D0) / D0]×100%.

[0207] 3) Curve height The negative electrode slurry was applied to the negative electrode current collector and baked at 100°C for 1 minute to remove most of the water. Then, it was cut into 10 negative electrode sheets measuring 4 cm x 4 cm. After that, the cut negative electrode sheets were placed on the top surface of a heating plate at 120°C and held for 1 minute. The height at which each of the four corners of each negative electrode sheet curled from the plane of the heating plate was measured using a scale and labeled h1, h2, h3, and h4. The average value of the corresponding h1, h2, h3, and h4 for each negative electrode sheet was calculated and labeled H. The average value H of the corresponding values ​​for the 10 negative electrode sheets was taken as the curl height of the negative electrode sheet.

[0208] 4) Folding count test The negative electrode sheet after cold pressing is 20*100mm 2 The material was cut into test samples of the specified size, folded in half in the forward direction, flattened with a 2kg press roll, unfolded, and exposed to light to check whether light could pass through the fold. If light could not be transmitted, it was folded in half in the reverse direction, flattened with a 2kg press roll, and exposed to light again for inspection. This process was repeated until light transmission occurred at the fold, and the number of folds was recorded. The test was repeated three times, and the average value was taken to determine the number of folds in the sheet.

[0209] 5) Test to determine whether or not film shedding has occurred at the corners. After completing the cell capacity test, the cell was disassembled while fully charged, and the presence or absence of film layer shedding and powder shedding was observed at the convex corner of the negative electrode sheet. If only powder shedding occurred, it was marked as Grade 1; if film shedding occurred, it was marked as Grade 2; and if film formation and foaming occurred, it was marked as Grade 3.

[0210] 6) Sheet bonding strength test Referring to the Chinese national standard "Experimental Method for 180° Peel Strength of Adhesives," the bonding strength test procedure is as follows: A sample measuring 30mm wide and 100-160mm long was cut using a blade, and special double-sided tape was attached to the steel plate. The tape was 20mm wide and 90-150mm long. The previously cut sheet sample was attached to the double-sided tape, with the test surface facing downwards, and then roll-pressed three times in the same direction using a press roll.

[0211] A piece of paper tape, whose width was the same as the sheet width and whose length was 80-200 mm longer than the length of the sample, was inserted below the sheet and secured with masking tape.

[0212] The power to the tensile strength machine was turned on (sensitivity set to 1N), the indicator lamp was illuminated, the stopper was adjusted to the appropriate position, and the end of the steel plate that was not covered with the sheet was secured with the lower jig. The paper tape was folded upwards and secured with the upper jig, and the position of the upper jig was adjusted using the "up" and "down" buttons on the manual controller attached to the tensile strength machine. Next, the test was performed and the values ​​were read.

[0213] 3. Battery performance testing 1) Battery capacity retention rate test At 25°C, the battery was charged with a constant current of 1 / 3C to 4.25V, then charged with a constant voltage of 4.25V until the current dropped to 0.05C, left for 5 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity was defined as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after n cycles was recorded. The battery capacity retention rate after each cycle was calculated as Pn = Cn / C0 * 100%, and the battery cycle capacity retention rate after 500 cycles was recorded.

[0214] III. Analysis of the test results of each example and comparative example. Batteries for each example and comparative example were manufactured according to the method described above, and each performance parameter was measured. The results are shown in the table below.

[0215] [Table 1-1] Table 1-2 Table 1-3 Table 1-4

[0216] Table 2-1 Table 2-2

[0217] Table 3-1 Table 3-2 Table 3-3

[0218] Table 4-1 Table 4-2

[0219] The glass transition temperature of hydroxyethyl acrylate is -15°C, the glass transition temperature of hydroxypropyl acrylate is -30°C, and the glass transition temperature of 4-hydroxybutyl acrylate is -55°C. As can be seen from Tables 1 to 4, the polymers in Examples 1 to 31 all contain constituent units derived from unsaturated carboxylic acid monomers, constituent units derived from unsaturated cyano monomers, and constituent units derived from flexible monomers, and the glass transition temperature of the flexible monomers is -60°C to 0°C, and selectively -55°C to -15°C.

[0220] As can be seen from Tables 1 and 2, when the negative electrode sheet contains the above polymer, the cohesive force of the binder in the sheet is low, resulting in a low warp height and good molding quality for the negative electrode sheet.

[0221] As can be seen from Table 1, when the glass transition temperature of the polymer is 40°C to 105°C, the negative electrode sheet has low warp height and good molding quality. When the glass transition temperature of the negative electrode polymer is 40°C to 90°C, the negative electrode sheet does not develop edge cracks during roll pressing, and production efficiency and quality are greatly improved.

[0222] As can be seen from Examples 1-5 in Table 1, when the molar proportion of constituent units derived from hydroxyethyl acrylate is 5% to 50% based on the total number of moles of all constituent units in the polymer, the sheet exhibits low warp height and excellent molding stability. When the molar proportion is 20% to 35%, the negative electrode sheet does not experience edge cracking during roll pressing, improving production efficiency, maintaining high sheet bonding strength and low sheet rebound rate, and further enhancing the overall cycle stability of the battery.

[0223] As can be seen from Examples 1, 6-13 in Table 1, when the molar proportion of constituent units derived from unsaturated cyano monomers is 10% to 45% based on the total number of moles of all constituent units in the polymer, the sheet exhibits good bonding performance and the battery has excellent cycle stability.

[0224] As can be seen from Examples 1, 10-13 in Table 1, when the molar content of constituent units derived from unsaturated amide monomers is 0% to 30% based on the total number of moles of all constituent units in the polymer, the negative electrode slurry has an appropriate viscosity, is advantageous for slurry coating and molding, and improves the quality of the negative electrode sheet.

[0225] As can be seen from Examples 1 and 14-16, the polymer mass content is 0.5% to 3% of the total mass of the negative electrode film layer, the negative electrode sheet has low warp height and good bonding performance, and the battery has excellent cycle stability.

[0226] As can be seen from Examples 1 and 17-20, when the weight-average molecular weight of the polymer is between 500,000 and 2,000,000, the negative electrode sheet exhibits both low warpage and good bonding performance, and the battery has excellent cycle stability.

[0227] As can be seen from the comparison of the examples and comparative examples in Table 3, the polymer provided in this application is similarly applied to high-pressure density graphite anode sheet systems to reduce the sheet's warp height.

[0228] When the polymer contains two types of flexible monomers, hydroxyethyl acrylate and 2-hydroxybutyl acrylate, it is possible to achieve both high bonding strength and low rebound rate of the sheet, improve the flexibility of the high-pressure density anode sheet, increase the number of folds the sheet can be made, meet the usage requirements for the high-pressure density anode sheet, and improve the cycle stability of the battery through an overall effect.

[0229] As can be seen from the comparison of the examples and comparative examples in Table 3, the polymer provided in this application is similarly applied to a silicon anode system to reduce the sheet's warp height.

[0230] When the polymer simultaneously contains two flexible monomers, hydroxyethyl acrylate and 2-hydroxybutyl acrylate, it can achieve both high adhesion and low repulsion rate, reduce the occurrence of film peeling phenomenon at the corners of the silicon negative electrode, meet the usage requirements of the silicon negative electrode system, and improve the cycle stability of the battery through comprehensive effects.

[0231] It should be noted that this application is not limited to the above embodiments. The above embodiments are merely illustrative. Embodiments that have substantially the same technical idea within the scope of the technical solution of this application and exhibit the same functions and effects are all included in the technical scope of this application. Also, within the scope not departing from the gist of this application, various modifications conceivable by those skilled in the art can be added to the embodiments, and other forms constituted by combining some of the components in the embodiments are also considered to be included in the scope of this application.

Description of Reference Numerals

[0232] 1 Battery Pack 2 Upper Box 3 Lower Box 4 Battery Module 5 Secondary Battery 51 Case 52 Electrode Assembly 53 Cover Plate

Claims

1. A polymer comprising constituent units derived from an unsaturated carboxylic acid monomer, constituent units derived from an unsaturated cyano monomer, and constituent units derived from a flexible monomer, wherein the glass transition temperature of the flexible monomer is -60°C to 0°C, and selectively -55°C to -15°C.

2. The aforementioned flexible monomer comprises the structure represented by formula I, 【Chemistry 1】 In the formula, R １ , R ２ , R ３ Each is independently hydrogen, or substituted or unsubstituted C １－５ Contains alkyl groups, R ４ is C １－５ Hydroxyalkyl group, C １－５ Alkyl and C １－５ The polymer according to claim 1, characterized by comprising one or more alkoxy groups.

3. The aforementioned unsaturated carboxylic acid monomer includes the structure shown in formula II, 【Chemistry 2】 The aforementioned unsaturated cyano monomer includes the structure represented by formula III, 【Transformation 3】 wherein R ５ , R ６ , R ７ , R ８ , R ９ , R １０ are each independently hydrogen or a substituted or unsubstituted C １－５ alkyl group, and the polymer according to claim 1 or 2.

4. The polymer further contains constituent units derived from an unsaturated amide monomer, the unsaturated amide monomer having a structure represented by formula IV, 【Chemistry 4】 In the formula, R １１ , R １２ , R １３ , R １４ , R １５ Each is independently hydrogen, or substituted or unsubstituted C １－５ A polymer according to any one of claims 1 to 3, characterized by containing an alkyl group.

5. The polymer according to any one of claims 1 to 4, characterized in that the flexible monomer comprises one or more of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

6. The polymer according to any one of claims 1 to 4, characterized in that the flexible monomer comprises at least two of hydroxyethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl acrylate, ethyl acrylate, and n-butyl acrylate.

7. The polymer according to any one of claims 4 to 6, characterized in that the unsaturated carboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid, ethacrylic acid, and crotonic acid; the unsaturated cyano monomer comprises one or more of acrylonitrile, crotononitrile, methacrylonitrile, and ethacrylonitrile; and the unsaturated amide monomer comprises one or more of acrylamide, methacrylamide, N,N-dimethylacrylamide, and N-methylacrylamide.

8. The polymer according to any one of claims 1 to 7, characterized in that, on a basis of the total number of moles of all constituent units in the polymer, the molar proportion of constituent units derived from the flexible monomer is 5% to 50%, and selectively 20% to 35%.

9. Based on the total number of moles of all constituent units in the polymer, the molar proportion of constituent units derived from the unsaturated carboxylic acid monomer is 10% to 60%, selectively 30% to 50%, and / or The molar proportion of constituent units derived from the unsaturated cyano monomer is 10% to 60%, selectively 15% to 45%, and / or The polymer according to any one of claims 4 to 8, characterized in that the molar proportion of constituent units derived from the unsaturated amide monomer is 0% to 30%, and selectively 5% to 20%.

10. The polymer according to any one of claims 1 to 9, characterized in that the glass transition temperature of the polymer is 40°C to 105°C, and selectively 40°C to 90°C.

11. The polymer according to any one of claims 1 to 10, characterized in that the weight-average molecular weight of the polymer is 500,000 to 2,000,000, and selectively 800,000 to 1,500,000.

12. The polymer according to any one of claims 1 to 11, characterized in that the viscosity of an aqueous solution with a solid content of 6 wt%, prepared by dissolving the polymer in deionized water, is 8,000 mPa·s to 30,000 mPa·s, and selectively 10,000 mPa·s to 20,000 mPa·s.

13. The polymer is characterized by comprising at least one of the following: acrylic acid-acrylonitrile-acrylamido-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-hydroxyethyl acrylate copolymer, methacrylic acid-acrylonitrile-acrylamido-hydroxyethyl acrylate copolymer, acrylic acid-methacrylonitrile-acrylamido-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-methacrylamido-hydroxyethyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamido-2-hydroxybutyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamido-hydroxypropyl acrylate copolymer, acrylic acid-acrylonitrile-acrylamido-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer, or acrylic acid-acrylonitrile-hydroxyethyl acrylate-2-hydroxybutyl acrylate copolymer.

14. A method for preparing a polymer, comprising the step of preparing a polymer by polymerizing raw materials containing a flexible monomer, an unsaturated carboxylic acid monomer, and an unsaturated cyano monomer under polymerizable conditions, wherein the glass transition temperature of the flexible monomer is -60°C to 0°C, and selectively -55°C to -15°C.

15. The aforementioned preparation method specifically includes, This involves polymerizing an initiator, a flexible monomer represented by formula I, an unsaturated carboxylic acid monomer represented by formula II, an unsaturated cyano monomer represented by formula III, and an unsaturated amide monomer represented by formula IV in an aqueous solvent. 【Transformation 5】 In the formula, R １ , R ２ , R ３ , R ５ , R ６ , R ７ , R ８ , R ９ , R １０ , R １１ , R １２ , R １３ , R １４ , R １５ Each is independently hydrogen, or substituted or unsubstituted C １－５ Contains alkyl groups, R ４ is C １－５ Hydroxyalkyl group, C １－５ Alkyl and C １－５ The preparation method according to claim 14, characterized by comprising one or more alkoxy groups.

16. The preparation method according to claim 15, characterized in that the initiator comprises an inorganic peroxide initiator, and the inorganic peroxide initiator comprises one of ammonium persulfate, potassium persulfate, and sodium persulfate.

17. The preparation method according to claim 15 or 16, characterized in that the mass of the initiator is 0.01% to 0.1% of the total mass of the flexible monomer, the unsaturated carboxylic acid monomer, the unsaturated cyano monomer, and the unsaturated amide monomer, and is selectively 0.03% to 0.08%.

18. The polymerization reaction described above is (1) The reaction environment for the polymerization reaction is a water-insoluble gas atmosphere, (2) The reaction temperature of the polymerization reaction is 60°C to 100°C, (3) The stirring speed of the polymerization reaction is 200 rpm to 800 rpm, (4) The preparation method according to any one of claims 14 to 17, characterized in that at least one of the following conditions is met: (4) The reaction time of the polymerization reaction is 8 to 12 hours.

19. The preparation method according to claim 18, characterized in that the non-water-soluble gas includes one or more of nitrogen, oxygen, hydrogen, and methane.

20. A negative electrode sheet comprising a negative electrode film layer, wherein the negative electrode film layer comprises a binder, and the binder comprises a polymer according to any one of claims 1 to 13 or a polymer prepared by the preparation method according to any one of claims 14 to 19.

21. The anode sheet according to claim 20, characterized in that the mass percentage of the binder is 0.5% to 3%, and selectively 1% to 2%, based on the total mass of the anode film layer.

22. The negative electrode sheet according to claim 20 or 21, characterized in that the curvature height is 0 mm to 20 mm.

23. A negative electrode sheet according to any one of claims 20 to 22, characterized in that it includes a negative electrode active material, wherein the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, and silicon-based materials.

24. The pressure density is 1.45 g / cm³. ３ ~1.95 g / cm ３ The negative electrode sheet according to any one of claims 20 to 23, characterized in that it is the negative electrode sheet according to any one of claims 20 to 23.

25. A secondary battery characterized by comprising a negative electrode sheet according to any one of claims 20 to 24.

26. An electrical device characterized by including the secondary battery described in claim 25.

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