Positive electrode plate, secondary battery, battery module, battery pack, and power consumption device

Abstract

The present application provides a positive electrode plate, a secondary battery, a battery module, a battery pack, and a power consumption device. The positive electrode plate includes a current collector, an undercoat layer disposed on at least one surface of the current collector, and a positive electrode film disposed on the undercoat layer, and the undercoat layer includes a polymer A soluble in an aqueous solvent, the polymer A including a structural unit derived from a cyano group-containing monomer, a structural unit derived from an amide group-containing monomer, and a structural unit derived from an ester group-containing monomer. The present application uses the polymer A in the undercoat layer of the positive electrode plate to improve the molding quality, adhesion, and flexibility of the positive electrode plate, and optimize the cycle performance of the battery.

Description

[Technical Field]

[0001] This application relates to the field of lithium battery technology, and more particularly to positive electrodes, secondary batteries, and power consumption devices. [Background technology]

[0002] In recent years, lithium-ion 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 electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the increasing prevalence of lithium-ion battery applications, there is a growing demand for higher performance and lower costs. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] Current conventional adhesives, such as PVDF, have problems as commonly used adhesives, including poor compatibility with electrode active materials and weak adhesive strength. As a result, electrode plates using PVDF as an adhesive are unstable and difficult to mold. Therefore, the rapid development of new adhesives and positive electrode plates has been urgently needed.

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode plate that can further improve the cycle performance of a battery, has good molding quality, and has strong adhesive strength. [Means for solving the problem]

[0005] A first aspect of this application provides a positive electrode plate comprising a current collector, a primer layer placed on at least one surface of the current collector, and a positive electrode film placed on the primer layer, wherein the primer layer contains a polymer A soluble in an aqueous solvent, and polymer A comprises structural units derived from a cyano group-containing monomer, a structural unit derived from an amide group-containing monomer, and a structural unit derived from an ester group-containing monomer.

[0006] This application describes how using polymer A in the undercoat layer of the positive electrode plate improves the molding quality, adhesive strength, and flexibility of the electrode plate, thereby optimizing the battery's cycle performance.

[0007] In any embodiment, the weight-average molecular weight of polymer A in the undercoat layer is 1.5 × 10⁻⁶. 5 ~2×10 5 That is the case.

[0008] An appropriate weight-average molecular weight improves the molding quality of the electrode plates, ensures both processability and adhesion of the undercoat layer, and guarantees that polymer A in the undercoat layer has a certain degree of diffusivity when the positive electrode slurry is applied, thereby further improving the adhesion strength of the electrode plates and the cycle performance of the battery.

[0009] In any embodiment, the mass content of polymer A in the undercoat layer is 5% to 40%, optionally 5% to 30%, and optionally 5% to 20%, based on the total mass of the undercoat layer.

[0010] By keeping the mass of polymer A in the undercoat layer within the above range, the appearance quality and brittleness of the electrode plates were improved, and the adhesive performance of the electrode plates and the cycle performance of the battery were enhanced.

[0011] In any embodiment, the undercoat layer further comprises a conductive agent, which is selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.

[0012] By adding a conductive agent to the undercoat layer, the interfacial resistance between the positive electrode film and the current collector can be reduced, improving the battery's charge / discharge rate performance and extending its cycle life.

[0013] In any embodiment, the thickness of the undercoat layer is 1 to 20 μm.

[0014] By keeping the thickness of the undercoat layer within this range, it is possible to achieve a balance between the adhesive performance of the electrode plates and the power performance and cycle performance of the battery.

[0015] In any embodiment, the coating surface density of the positive electrode film is 20 mg / cm 2 or more.

[0016] By providing the undercoat layer of the present application on the electrode plate, it is possible to ensure that a certain content of the positive electrode active material is supported on the positive electrode plate, and further ensure the power performance of the battery.

[0017] In any embodiment, the positive electrode film includes a positive electrode active material, an adhesive, and a conductive agent. The adhesive includes a polymer A that is soluble in an oily solvent. The polymer A contains a structural unit derived from a cyano group-containing monomer, a structural unit derived from an amide group-containing monomer, and a structural unit derived from an ester group-containing monomer.

[0018] By adopting the polymer A that is soluble in an oily solvent as an adhesive in the positive electrode film and making it diffusion-connected with the polymer A in the undercoat layer, the adhesive force between the undercoat layer and the positive electrode film can be further strengthened, the appearance quality and brittleness of the electrode plate can be improved, and the adhesion performance of the electrode plate and the cycle performance of the battery can be improved.

[0019] In any embodiment, the positive electrode film contains the polymer A having a weight average molecular weight of 7×10 [[ID=二十二]] 5 ~1×10 6 .

[0020] By controlling the weight average molecular weight of the polymer A, the adhesive force of the positive electrode plate can be improved, and the increase rate of the internal resistance of the battery during cycling can be further reduced.

[0021] In any embodiment, the positive electrode film further contains a polymer A having a weight average molecular weight of 1×10 5 ~2.5×10 5 .

[0022] The weight average molecular weight is 1×10 5 ~2.5×10 5Polymer A acts as a dispersant in the positive electrode film, and its addition further improves the dispersibility of the positive electrode active material in the positive electrode film, resulting in a manufactured electrode plate with higher adhesion and a battery with a lower rate of increase in cycle internal resistance.

[0023] In any embodiment, the positive electrode active material is a lithium-containing transition metal oxide, and the positive electrode active material is optionally lithium iron phosphate, or a doped modified material thereof, or at least one of a conductive carbon-coated modified material, a conductive metal-coated modified material, or a conductive polymer-coated modified material thereof.

[0024] In any embodiment, the mass content of the positive electrode active material is 70% to 99.5% of the total mass of the positive electrode film, and optionally 88% to 99.5%. Having the mass content of the positive electrode active material within this range ensures the amount of positive electrode active material supported and improves the power performance of the battery.

[0025] In any embodiment, the weight-average molecular weight of the positive electrode film is 7 × 10⁻⁶, based on the mass of the positive electrode film. 5 ~1 × 10 6 The mass content of polymer A is 0.4% to 5.5%, and / or the weight-average molecular weight in the cathode film is 1 × 10⁻⁶. 5 ~2.5×10 5 The mass content of polymer A is 0.05% to 0.5%.

[0026] In any embodiment, the cyano group-containing monomer in polymer A is selected from one or more of acrylonitrile and butenenitrile. The amide group-containing monomer is selected from one or more of the following: methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, and N,N-diethylmethacrylamide. The ester group-containing monomer is selected from one or more of the following: methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0027] In any embodiment, with respect to the total molar content of structural units in polymer A, the molar content of structural units derived from cyano group-containing monomers is 50% to 70%, the molar content of structural units derived from ester group-containing monomers is 10% to 30%, and the molar content of structural units derived from amide group-containing monomers is 10% to 30%.

[0028] A second aspect of this application provides a secondary battery including the positive electrode plate of the first aspect of this application.

[0029] A third aspect of this application provides a battery module including a secondary battery according to the second aspect of this application.

[0030] A fourth aspect of this application provides a battery pack including the battery module of the third aspect of this application.

[0031] A fifth aspect of this application provides a power consumption device including at least one of the secondary battery of the second aspect of this application, the battery module of the third aspect, or the battery pack of the fourth aspect. [Brief explanation of the drawing]

[0032] [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 one embodiment of a power consumption device in which the secondary battery of this application is used as a power source. [Figure 7] This is a schematic diagram of the electrode plate adhesive strength test. [Modes for carrying out the invention]

[0033] The following descriptions will detail embodiments of the adhesive, manufacturing method, electrode, battery, and power consumption device disclosed in 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 structures that are actually the same may be omitted. This is to avoid making the following explanation unnecessarily long and to make it easily understandable to those skilled in the art. The drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in the claims.

[0034] The “range” disclosed in this application is limited in the form of a lower limit and an upper limit, and a given range is limited by selecting one lower limit and one upper limit that define the boundary of a particular range. The range thus limited may or may not include the endpoints, and may be in any combination, that is, any lower limit and any upper limit may be combined to form a single range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​1 and 2 and the maximum range values ​​3, 4 and 5 are listed, then the following ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 are all expected. In this application, unless otherwise stated, the numerical range “a-b” is an abbreviated expression representing all combinations of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed herein, and "0 to 5" is merely an abbreviation for combinations of these numbers. Also, when it is stated that a parameter is an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical concepts.

[0037] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the fact that the method referred to above may further include step (c) 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), and so on.

[0038] Unless otherwise specified, the terms “includes” and “inclusion” as used in this application may be open or closed. For example, “includes” and “inclusion” may mean that other components not listed may be included or included, or that only the listed components may be included or included.

[0039] 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 one of the following conditions satisfies the condition "A or B": 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).

[0040] Lithium iron phosphate cathode active material has attracted widespread attention in the industry due to its low cost, high performance, and safety. However, lithium iron phosphate cathode active material has characteristics such as a large specific surface area, small particle size, a large amount of surface carbon coating after carbon coating, and a high degree of graphitization. As a result, slurries using lithium iron phosphate as the cathode active material and conventional PVDF adhesive as the adhesive have poor dispersibility, are prone to precipitation, have high viscosity, and have a low solid content. Furthermore, defects such as cracks, delamination, particle scratches, and pinholes are likely to occur on the surface of the manufactured electrode plate, and the distribution of the cathode active material on the electrode plate is uneven, resulting in uneven quality of the electrode plate.

[0041] [Positive electrode slurry] Based on this, the present application provides a positive electrode slurry for use in a battery, which comprises a positive electrode active material, a conductive agent, and an adhesive, wherein the adhesive comprises polymer A, which includes structural units derived from a cyano group-containing monomer, structural units derived from an amide group-containing monomer, and structural units derived from an ester group-containing monomer.

[0042] In this specification, the term “adhesive” refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0043] In this specification, the term “polymer” includes, on the one hand, a collection of large molecules that are chemically homogeneous but differ in degree of polymerization, molar mass, and chain length, produced by polymerization reactions. On the other hand, the term also includes derivatives of such large molecule collections formed by polymerization reactions, i.e., those obtained by reactions of functional groups in the large molecules, such as addition or substitution, and may be chemically homogeneous or chemically heterogeneous compounds or mixtures.

[0044] In this specification, the term "positive electrode" also refers to the "cathode" in a secondary battery.

[0045] In this specification, the term "cyano group" refers to the -CN group.

[0046] In this specification, the term "amide group" refers to the -CONH group.

[0047] In this specification, the term "ester group" refers to a -COOR1 group, where R1 is a substituted or unsubstituted C 1-9 Selected from alkyl groups.

[0048] In this specification, the term "substituted with substituents" refers independently to hydroxyl groups, mercapto groups, amino groups, cyano groups, nitro groups, aldehyde groups, halogen atoms, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, and C 1-6 Alkyl alkyl group, C 1-6 Selected from alkoxy groups.

[0049] In this specification, the term "C 1-6 An alkyl group refers to a linear or branched hydrocarbon chain group consisting only of carbon and hydrogen atoms, without unsaturation, having one to five carbon atoms, and bonded to the rest of the molecule by single bonds. 1-9 The term "alkyl" should be interpreted accordingly. 1-6 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, and pentyl groups.

[0050] In this specification, the term "polymer A" refers to a polymer containing structural units derived from cyano group-containing monomers, structural units derived from amide group-containing monomers, and structural units derived from ester group-containing monomers.

[0051] In some embodiments, polymer A is soluble in oily solvents. In some embodiments, polymer A is soluble in aqueous solvents. Examples of oily solvents include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethylcellulose, and polycarbonate. Examples of aqueous solvents include, but are not limited to, water. To be understood, the structural units in polymer A may be blended in any proportion, polymer A may have different molecular weights, and polymer A may be produced by different methods, such as suspension or emulsion.

[0052] In some embodiments, the positive electrode slurry contains a dispersion medium. In some embodiments, the dispersion medium of the positive electrode slurry is an oily solvent. In some embodiments, the dispersion medium of the positive electrode slurry is an aqueous solvent.

[0053] In some embodiments, an adhesive is used to bond positive electrode active material and / or conductive material to form a slurry, which can then be fixed in place and adhered to a conductive metal member to form a positive electrode.

[0054] In some embodiments, polymer A is one or more of the following: acrylonitrile-acrylamide-methyl acrylate copolymer, acrylonitrile-acrylamide-ethyl acrylate copolymer, acrylonitrile-acrylamide-propyl acrylate copolymer, and acrylonitrile-acrylamide-isooctyl acrylate copolymer.

[0055] This application improves the stability and processability of a positive electrode slurry and enhances the adhesive strength of the positive electrode plate by using a polymer containing structural units derived from cyano group-containing monomers, structural units derived from amide group-containing monomers, and structural units derived from ester group-containing monomers as an adhesive in the positive electrode slurry.

[0056] Polymer A possesses a rich array of polar groups; for example, cyano groups are located in the main chain segment of polymer A. Due to the dipole interaction between the cyano groups and the electronegativity of the positive electrode current collector, polymer A exhibits extremely strong adhesion to the current collector, improving the adhesion strength of the electrode plates and avoiding processing abnormalities such as peeling and powder shedding of the electrode plates during coating or cold pressing processes. Furthermore, the ester-containing functional groups in polymer A possess a certain electrolyte absorption and retention capacity, improving the problem of poor ionic conductivity of conventional adhesives such as simple polyvinylidene fluoride. In addition, the rich array of groups on polymer A improves the compatibility of polymer A with various positive electrode active materials, thereby increasing the versatility of polymer A as an adhesive.

[0057] In some embodiments, the adhesive has a weight-average molecular weight of 7 × 10 5 ~1 × 10 6 The polymer A is included. In some embodiments, the important average molecular weight of polymer A is optionally 7 × 10 5 ~9.5×10 5 It is, or 7 × 10 5 ~9×10 5 It is, or 7 × 10 5 ~8.5×10 5 It is, or 7 × 10 5 ~8×10 5 It is, or 7.5 × 10 5 ~1 × 10 6 and, or 8 × 10 5 ~1 × 10 6 It is, or 8.5 × 10 5 ~1× 106 and, or 9 × 10 5 ~1 × 10 6 It is, or 9.5 × 10 5 ~1 × 10 6 That is the case.

[0058] 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.

[0059] By controlling the weight-average molecular weight of polymer A, the stability, processability, and adhesive strength of the positive electrode slurry can be improved, and the rate of increase in the battery's cycle internal resistance can be further reduced.

[0060] In some embodiments, the adhesive has a weight-average molecular weight of 1 × 10 5 ~2.5×10 5 The present invention further comprises polymer A, which is a polymer. In some embodiments, the weight-average molecular weight of polymer A is optionally 1.5 × 10⁻⁶. 5 ~2.5×10 5 It is, or 2 × 10 5 ~2.5×10 5 It is, or 1 × 10 5 ~2×10 5 It is, or 1 × 10 5 ~1.5×10 5 That is the case.

[0061] Because some positive electrode active materials (e.g., lithium iron phosphate LFP) have large and small specific surface areas, the slurry tends to aggregate during the manufacturing process, causing screen clogging. By using polymer A, which has a low weight-average molecular weight, aggregation between positive electrode active materials (e.g., lithium iron phosphate LFP powder particles) can be avoided due to its electrostatic repulsion or steric hindrance. At the same time, it plays a role in dispersing and suspending other small molecular substances in the slurry, preventing sedimentation even when the slurry is left standing for a short time, thus increasing its stability. Furthermore, polymer A, with its low weight-average molecular weight, has a low glass transition temperature, which can further improve the flexibility of the electrode plate.

[0062] In summary, the weight-average molecular weight is 1 × 10⁻⁶ 5 ~2.5×10 5 Polymer A acts as a dispersant in the positive electrode slurry, and its addition further improves the stability and processability of the slurry, as well as the adhesion strength of the electrode plates, thereby reducing the rate of increase in the battery's cycle internal resistance.

[0063] In some embodiments, the weight-average molecular weight is 7 × 10⁻¹⁰ based on the total mass of the positive electrode active material, conductive agent, and adhesive. 5 ~1 × 10 6 The mass content of polymer A is 0.4% to 5.5%. The weight-average molecular weight is 7 × 10⁻⁶. 5 ~1 × 10 6 When polymer A is added in excess, it reduces the power performance and cycle performance of the battery. The weight-average molecular weight within this mass content range is 7 × 10 5 ~1 × 10 6 Polymer A improves the stability and processability of the slurry and the adhesion of the electrode plates, while also significantly reducing the rate of increase in the battery's cycle internal resistance.

[0064] In some embodiments, the weight-average molecular weight is 1 × 10⁻¹⁶ based on the total mass of the positive electrode active material, conductive agent, and adhesive. 5 ~2.5×10 5 The mass content of polymer A is 0.05% to 0.5%.

[0065] Weight-average molecular weight is 1 × 10 5 ~2.5×10 5 When polymer A is added in excess, it increases the swelling of the electrode plates and affects the battery's room-temperature power performance. A weight-average molecular weight within this mass content range is 1 × 10⁻⁶. 5 ~2.5×10 5 Polymer A further improves the stability and processability of the slurry and the adhesive strength of the electrode plates, while also significantly reducing the rate of increase in the battery's cycle internal resistance.

[0066] In some embodiments, the cyano group-containing monomer is selected from one or more of acrylonitrile and butenenitrile.

[0067] In some embodiments, the amide group-containing monomer is selected from one or more of the following: methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, and N,N-diethylmethacrylamide.

[0068] In some embodiments, the ester group-containing monomer is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0069] The above materials are readily available and can significantly reduce the manufacturing cost of adhesives.

[0070] In some embodiments, based on the total molar content of structural units in polymer A, the molar content of structural units derived from cyano group-containing monomers is 50% to 70%, the molar content of structural units derived from ester group-containing monomers is 10% to 30%, and the molar content of structural units derived from amide group-containing monomers is 10% to 30%.

[0071] By rationally combining structural units derived from monomers containing each group, polymer A can achieve a balance of strength, flexibility, adhesive properties, and swelling resistance, thereby providing the electrode plate with excellent adhesive strength and processability.

[0072] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide, optionally lithium iron phosphate, or a doped modified material thereof, or at least one of a conductive carbon-coated modified material, a conductive metal-coated modified material, or a conductive polymer-coated modified material thereof.

[0073] The lithium iron phosphate cathode active material has a microporous structure and a high degree of graphitization on its surface after carbon coating. Due to these structural characteristics, it has poor penetration in slurry solvents (e.g., N-methylpyrrolidone NMP), poor slurry stability, low solid content, and the adhesive part easily peels off after standing, rendering it unusable. By including groups in polymer A that have excellent affinity for carbon materials with a high degree of graphitization, such as N-containing groups (cyano groups, amide groups) and oxygen-containing groups (ester groups, amide groups), the penetration of lithium iron phosphate powder in solvents (e.g., NMP) is effectively improved, further enhancing the stability and processability of the cathode slurry.

[0074] In some embodiments, the mass content of the positive electrode active material is 70% to 99.5%, and optionally 88.0% to 99.5%, based on the total mass of the positive electrode active material, conductive agent, and adhesive. By having the mass content of the positive electrode active material within the above range, the amount of positive electrode active material supported can be guaranteed, and the power performance of the battery can be improved.

[0075] In some embodiments, the conductive agent is selected from one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjenblack, carbon spots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In some embodiments, the mass content of the conductive agent is 0.2% to 6.0% based on the total mass of the positive electrode active material, conductive agent, and adhesive.

[0077] [Positive plate] In one embodiment of this application, a positive electrode plate is provided, which includes a current collector, a primer layer placed on at least one surface of the current collector, and a positive electrode film placed on the primer layer, wherein the primer layer contains polymer A soluble in an aqueous solvent, and polymer A includes structural units derived from cyano group-containing monomers, structural units derived from amide group-containing monomers, and structural units derived from ester group-containing monomers.

[0078] In this specification, the term "current collector" refers to any conductive substrate capable of conducting current to electrodes during the discharge or charging of a secondary battery.

[0079] The term "positive electrode film" refers to the coating that forms after the positive electrode slurry is applied and dried.

[0080] Small-particle positive electrode active material has the advantage of a large specific surface area, allowing it to react sufficiently with the electrolyte. However, this large specific surface area also leads to poor adhesion to the current collector, making delamination more likely during the coating process of the positive electrode slurry. Increasing the amount of adhesive used in the positive electrode slurry leads to problems such as brittleness of the electrode plate during the cold pressing process and a decrease in press density. Therefore, it is necessary to add a special undercoat layer on the current collector to improve the adhesion between the positive electrode film and the current collector.

[0081] Because polymer A, which is soluble in aqueous solvents in the undercoat layer, contains cyano groups, amide groups, and ester groups, when it comes into contact with the oily solvent (e.g., NMP) of the positive electrode slurry during the positive electrode slurry coating process, moderate swelling may occur, but it will not dissolve. Molecular contact between polymer A in the undercoat layer and the adhesive in the positive electrode slurry enables interdiffusion, significantly improving the adhesion between the positive electrode film and the current collector. Furthermore, the ester groups in polymer A form strong hydrogen bonds with the hydroxyl groups in the oxide layer on the surface of the current collector, ensuring that the positive electrode film adheres firmly to the current collector.

[0082] A polymer A that is soluble in an aqueous solvent is one in which polymer A can dissolve in an aqueous solvent to form a solution or dispersion, and the solubility of polymer A in the aqueous solvent is 1 g or more. Optionally, the solubility of polymer A in the aqueous solvent is 10 g or more.

[0083] In some embodiments, polymer A, which is soluble in an aqueous solvent in the undercoat layer, is formed by bulk polymerization, suspension polymerization, emulsion polymerization, or solution polymerization. In some embodiments, polymer A, which is soluble in an aqueous solvent in the undercoat layer, is formed by an emulsion method, which is easy to mass-produce, simple, and environmentally friendly.

[0084] This application describes how using polymer A in the undercoat layer of the positive electrode plate improves the molding quality, adhesive strength, and flexibility of the electrode plate, thereby optimizing the battery's cycle performance.

[0085] In some embodiments, the weight-average molecular weight of polymer A in the undercoat layer is 1.5 × 10⁻⁶. 5 ~2×10 5 That is the case.

[0086] An appropriate weight-average molecular weight improves the molding quality of the electrode plate, ensures both processability and adhesion of the undercoat layer, and guarantees that polymer A in the undercoat layer has a certain degree of diffusivity when the positive electrode slurry is applied.

[0087] In some embodiments, the mass content of polymer A in the undercoat layer is 5% to 40%, optionally 5% to 30%, and optionally 5% to 20%, based on the total mass of the undercoat layer.

[0088] If the amount of polymer A used in the undercoat layer is too large, it reduces the stability of the undercoat layer and the battery's cycle performance. When the mass of polymer A in the undercoat layer is within the above range, the appearance quality and brittleness of the electrode plates are improved, and the adhesion performance of the electrode plates and the battery's cycle performance are enhanced.

[0089] In some embodiments, the undercoat layer further includes a conductive agent, which is selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.

[0090] By adding a conductive agent to the undercoat layer, the interfacial resistance between the positive electrode film and the current collector can be reduced, improving the battery's charge / discharge rate performance and extending its cycle life.

[0091] In some embodiments, the thickness of the undercoat layer is 1 to 20 μm.

[0092] If the undercoat layer is too thick, the conductivity of the current collector will be poor, and if the undercoat layer is too thin, it cannot be guaranteed that it will provide effective adhesion to the electrode plates. By keeping the undercoat layer thickness within this range, it is possible to achieve a balance between the adhesion performance of the electrode plates and the power and cycle performance of the battery.

[0093] In some embodiments, the coating density of the positive electrode film is 20 mg / cm². 2 That's all.

[0094] In this specification, the term "surface density" is calculated by dividing the mass by the corresponding area.

[0095] By applying the undercoat layer of this invention to the electrode plate, it is possible to ensure that a certain amount of positive electrode active material is supported on the positive electrode plate, and furthermore, to guarantee the power performance of the battery.

[0096] In some embodiments, the positive electrode film comprises a positive electrode active material, an adhesive, and a conductive agent, wherein the adhesive comprises polymer A soluble in an oily solvent, and polymer A contains structural units derived from cyano group-containing monomers, structural units derived from amide group-containing monomers, and structural units derived from ester group-containing monomers.

[0097] A polymer A that is soluble in an oily solvent is one in which polymer A can dissolve in an oily solvent to form a solution or dispersion, and the solubility of polymer A in the oily solvent is 1 g or more. Optionally, the solubility of polymer A in the oily solvent is 10 g or more.

[0098] By using polymer A, which is soluble in an oily solvent, as an adhesive in the positive electrode film and diffusing it with polymer A in the undercoat layer, the adhesion between the undercoat layer and the positive electrode film can be further strengthened, improving the appearance quality and brittleness of the electrode plate, and enhancing the adhesive performance of the electrode plate and the cycle performance of the battery.

[0099] In some embodiments, the cathode film has a weight-average molecular weight of 7 × 10 5 ~1 × 10 6 The polymer A is included.

[0100] By controlling the weight-average molecular weight of polymer A, the adhesive strength of the positive electrode plate can be improved, and the rate of increase in the battery's cycle internal resistance can be further reduced.

[0101] In some embodiments, the cathode film has a weight-average molecular weight of 1 × 10 5 ~2.5×10 5 It further contains polymer A.

[0102] Weight-average molecular weight is 1 × 10 5 ~2.5×10 5 Polymer A acts as a dispersant in the positive electrode film, and its addition further improves the dispersibility of the positive electrode active material in the positive electrode film, resulting in a manufactured electrode plate with higher adhesion and a battery with a lower rate of increase in cycle internal resistance.

[0103] Because some positive electrode active materials (e.g., lithium iron phosphate LFP) have large specific surface areas and many small particles, the slurry used to form the positive electrode film tends to aggregate during the manufacturing process, causing screen clogging. By using polymer A, which has a low weight-average molecular weight, in the slurry used to form the positive electrode film, aggregation between positive electrode active materials (e.g., lithium iron phosphate LFP powder particles) can be avoided due to its electrostatic repulsion or steric hindrance. At the same time, it plays a role in dispersing and suspending other small molecular substances in the positive electrode film, preventing sedimentation even when the slurry is left standing for a short time, thus increasing its stability. Furthermore, polymer A, with its low weight-average molecular weight, has a low glass transition temperature, which can further improve the flexibility of the positive electrode film.

[0104] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide, and the positive electrode active material is optionally lithium iron phosphate, or a doped modified material thereof, or at least one of a conductive carbon-coated modified material, a conductive metal-coated modified material, or a conductive polymer-coated modified material thereof.

[0105] In conventional lithium iron phosphate systems, polyacrylic acid is generally used as an adhesive for the undercoat layer. However, polyacrylic acid and polyvinylidene fluororide, a conventional adhesive used in the cathode film, have significantly different polarities, resulting in low adhesion between them. Furthermore, polyacrylic acid in the undercoat layer has poor solubility in the cathode slurry solvent, making it impossible to form an effective diffusion bond between the undercoat layer and the cathode film during slurry coating and drying.

[0106] By using polymer A, which is secondary wettable with N-methylpyrrolidone (NMP), as an adhesive in the undercoat layer according to this application, mutual diffusion of the adhesive between the undercoat layer and the positive electrode film is achieved, increasing the adhesive strength, further improving the appearance quality and brittleness of the electrode plate, and enhancing the adhesive performance of the electrode plate and the cycle performance of the battery.

[0107] In some embodiments, the mass content of the positive electrode active material is 70% to 99.5% of the total mass of the positive electrode film, and optionally 88.0% to 99.5%. By having the mass content of the positive electrode active material within the above range, the amount of positive electrode active material supported can be guaranteed, and the power performance of the battery can be improved.

[0108] In some embodiments, the weight-average molecular weight of the positive electrode film is 7 × 10⁻⁶, relative to the mass of the positive electrode film. 5 ~1 × 10 6 The mass content of polymer A is 0.4% to 5.5%, and / or the weight-average molecular weight in the cathode film is 1 × 10⁻⁶. 5 ~2.5×10 5 The mass content of polymer A is 0.05% to 0.5%.

[0109] Weight-average molecular weight is 7 × 10 5 ~1 × 10 6 When polymer A is added in excess, it reduces the power performance and cycle performance of the battery. The weight-average molecular weight within this mass content range is 7 × 10 5 ~1 × 10 6 Polymer A improves the stability and processability of the slurry and the adhesion of the electrode plates, while also significantly reducing the rate of increase in the battery's cycle internal resistance. Its weight-average molecular weight is 1 × 10⁻⁶. 5 ~2.5×10 5 When polymer A is added in excess, it increases the swelling of the electrode plates and affects the battery's room-temperature power performance. A weight-average molecular weight within this mass content range is 1 × 10⁻⁶. 5 ~2.5×10 5 Polymer A further improves the stability and processability of the slurry and the adhesive strength of the electrode plates, while also significantly reducing the rate of increase in the battery's cycle internal resistance.

[0110] In some embodiments, the cyano group-containing monomer in polymer A is selected from one or more of acrylonitrile and butenenitrile. The amide group-containing monomer is selected from one or more of the following: methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, and N,N-diethylmethacrylamide. The ester group-containing monomer is selected from one or more of the following: methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0111] The above materials are readily available and can significantly reduce the manufacturing cost of adhesives.

[0112] In some embodiments, based on the total molar content of structural units in polymer A, the molar content of structural units derived from cyano group-containing monomers is 50% to 60%, the molar content of structural units derived from ester group-containing monomers is 10% to 20%, and the molar content of structural units derived from amide group-containing monomers is 20% to 30%.

[0113] By rationally combining structural units derived from monomers containing each group, polymer A can achieve a balance of strength, flexibility, adhesive properties, and swelling resistance.

[0114] For example, a positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is placed on one or both of the two opposing surfaces of the positive electrode current collector.

[0115] In some embodiments, the positive electrode current collector may employ a metal foil sheet or a composite current collector. For example, as the metal foil, aluminum foil may be employed. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In some embodiments, the positive electrode active material may employ a positive electrode active material for a battery well-known in the art. As an example, the positive electrode active material may include at least one material among lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone, or two or more of them may be used in combination. Here, examples of lithium transition metal oxides are 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 (which may be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn0.2 O2(NCM 622 (It may also be abbreviated as LiNi) 0.8 Co 0.1 Mn 0.1 O2(NCM 811 (May be abbreviated as LiNi) Lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 It may include, but is not limited to, at least one of O2) and its modified compounds. 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 (which may be abbreviated as LFP)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), composite materials of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite materials of lithium manganese iron phosphate and carbon.

[0117] In some embodiments, the cathode film optionally 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.

[0118] [negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer containing a negative electrode active material.

[0119] For example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is placed on one or both of the two opposing surfaces of the negative electrode current collector.

[0120] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (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)).

[0121] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries that is well known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may be selected from at least one of elemental tin, tin oxide, and tin alloy. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used individually or in combination of two or more.

[0122] In some embodiments, the negative electrode film layer optionally further comprises an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0123] In some embodiments, the negative electrode film layer optionally further comprises a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the negative electrode film layer optionally further comprises other auxiliary agents, such as thickeners (e.g., sodium carboxymethylcellulose (CMC-Na)).

[0125] In some embodiments, a negative electrode plate can be manufactured by the following method: The above components for manufacturing a negative electrode plate, such as a negative electrode active material, a conductive agent, an adhesive, 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 a negative electrode plate is obtained through processes such as drying and cold pressing.

[0126] [Electrolytes] The electrolyte plays a role in conducting ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, which can be selected according to the requirements. For example, the electrolyte may be a liquid, a gel, or all-solid.

[0127] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0128] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)borate, and lithium tetrafluoro(oxalato)phosphate.

[0129] In some embodiments, the solvent may be selected from at least one of 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.

[0130] In some embodiments, the electrolyte optionally further comprises additives. For example, the additives may include a negative electrode film-forming additive and a positive electrode film-forming additive, or may further include additives that can improve some of the battery's performance, such as an additive that improves the battery's overcharge performance or an additive that improves the battery's high-temperature or low-temperature performance.

[0131] [Separator] In some embodiments, the secondary battery further includes a separator. This application does not particularly limit the type of separator, and any well-known porous separator having good chemical and mechanical stability may be selected.

[0132] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluororide. The separator may be a single-layer thin film or a multilayer composite thin film, and there are no particular limitations. If the separator is a multilayer composite thin film, the materials of each layer may be the same or different, and there are no particular limitations.

[0133] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator may be manufactured as an electrode assembly by a winding process or a lamination process.

[0134] In some embodiments, the secondary battery may include an outer casing. This casing may be used to package the electrode assembly and the electrolyte.

[0135] In some embodiments, the casing of the secondary battery may be a rigid shell such as a rigid plastic shell, an aluminum shell, or a steel shell. The casing of the secondary battery may also be flexible packaging, for example, a bag-type flexible packaging. The material of the flexible packaging may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0136] [Secondary battery] In one embodiment of this application, a secondary battery is provided, which comprises an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode plate, a separator and a negative electrode plate, the positive electrode plate being manufactured from a positive electrode slurry of any embodiment.

[0137] In some embodiments, the positive electrode plate, negative electrode plate, and separator may be manufactured as an electrode assembly by a winding process or a lamination process.

[0138] In some embodiments, the secondary battery may include an outer casing. This casing may be used to package the electrode assembly and the electrolyte.

[0139] In some embodiments, the casing of the secondary battery may be a rigid shell such as a rigid plastic shell, an aluminum shell, or a steel shell. The casing of the secondary battery may also be flexible packaging, for example, a bag-type flexible packaging. The material of the flexible packaging may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0140] This application does not impose any particular restrictions on the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows a rectangular secondary battery 5 as an example.

[0141] In some embodiments, referring to Figure 2, the exterior may include a housing 51 and a cover plate 53. Here, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround and form a housing cavity. The housing 51 has an opening that communicates with the housing cavity, and the cover plate 53 can close the housing cavity by covering the opening. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged in the housing cavity. The electrolyte permeates 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 may select according to the actual specific requirements.

[0142] [Battery Module] In some embodiments, secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0143] Figure 3 shows an example of a battery module 4. Referring to Figure 5, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged according to any other method. Furthermore, the multiple secondary batteries 5 may be fixed with fasteners.

[0144] Optionally, the battery module 4 may further include a housing having a housing space, and a plurality of secondary batteries 5 are housed in the housing space.

[0145] [Battery pack] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0146] 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 case and a plurality of battery modules 4 installed in the battery case. The battery case includes an upper case 2 and a lower case 3, the upper case 2 covering the lower case 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged inside the battery case in any manner.

[0147] [Power consumption equipment] One embodiment of this application provides a power consumption device that includes at least one of a secondary battery of any embodiment, a battery module of any embodiment, or a battery pack of any embodiment.

[0148] The power consumption device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may include, but is not limited to, mobile equipment (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0149] As the power consumption device, a secondary battery, battery module, or battery pack may be selected depending on the usage requirements.

[0150] Figure 6 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the requirements of the power consumption device for high output and high energy density of secondary batteries, a battery pack or battery module can be used.

[0151] Other examples of such devices may include mobile phones, tablet computers, and laptop computers. These devices generally require lightweight designs and can utilize rechargeable batteries as their power source.

[0152] Examples The following describes embodiments of this application. The embodiments described below are illustrative and are used solely for interpreting this application and should not be understood as limiting this application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in the art or in product descriptions shall be followed. Unless the manufacturer is specified for the reagents or equipment used, they are all common products that can be purchased commercially.

[0153] Example 1 1) Production of polymer A (polymer A-1) with a weight-average molecular weight of 600,000 to 1,000,000 in the cathode film. 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and blown with dry nitrogen gas for 30 minutes. Then, 400 mg of calcium sulfate and 80 mg of calcium phosphate were added. Next, 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.1 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 70°C and reacted for 5 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for electrode plates. The molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in polymer A-1 is 6:3:2, and the weight-average molecular weight of polymer A-1 obtained is 800,000.

[0154] 2) Manufacturing of positive electrode plates In Example 1, the lithium iron phosphate LFP active material, the conductive agent carbon black, and polymer A-1 were dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 93:4:3, and the mixture was stirred to obtain a positive electrode slurry. The solid content of the slurry was 55%. The positive electrode slurry was then uniformly applied to a positive electrode current collector, and subsequently dried, cold pressed, and slit to obtain a positive electrode plate.

[0155] 3) Manufacturing of the negative electrode plate The active material, artificial graphite, the conductive agent, carbon black, the adhesive, styrene-butadiene rubber (SBR), and the thickener, sodium carboxymethylcellulose (CMC), were dissolved in deionized water as a solvent in a weight ratio of 96.2:0.8:0.8:1.2. After stirring and uniformly mixing, a negative electrode slurry was produced. The negative electrode slurry was then uniformly applied to the copper foil of the negative electrode current collector one or more times, and a negative electrode plate was obtained by drying, cold pressing, and slitting.

[0156] 4) Separator A polypropylene film is used as the separator.

[0157] 5) Manufacturing of electrolyte In a glove box under an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) and methyl ethyl carbonate (EMC) 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.

[0158] 6) Battery manufacturing The positive electrode plate, separator, and negative electrode plate of Example 1 were stacked in order, with the separator positioned between the positive and negative electrode plates to provide isolation, and then wound up to obtain a bare cell. Tabs were welded to the bare cell, the bare cell was placed in an aluminum case, and the case was fired at 80°C to remove moisture. The electrolyte was immediately injected and the case was sealed to obtain an uncharged battery. The uncharged battery was subjected to a series of processes including standing, hot and cold pressing, chemical conversion, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.

[0159] In Examples 2 to 9, the ratio of the positive electrode active material to polymer A-1 added is adjusted, and other parameters and steps are the same as in Example 1. For specific parameters, please refer to Table 1.

[0160] Example 10 Manufacturing of polymer A(A-2) with a weight-average molecular weight of 100,000 to 250,000 in the cathode film: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and blown with dry nitrogen gas for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate were added. Next, 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.06 g of magnesium sulfate in 50 ml of deionized water was added. The suspension was heated to 46°C and reacted for 2.5 hours. At the end of the reaction, the suspension was cooled, the product was filtered and washed, and then vacuum-dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for dispersion in electrode plate slurries. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-2 is 5:3:2, and the weight-average molecular weight of polymer A-2 is 170,000.

[0161] Manufacturing of positive electrode plates: Lithium iron phosphate LFP active material, conductive carbon black, polymer A-1, and polymer A-2 were dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 92:4:3.95:0.05, and the mixture was stirred to obtain a positive electrode slurry. The solid content of the slurry was 55%. The positive electrode slurry was then uniformly applied to a positive electrode current collector, and subsequently dried, cold pressed, and slit to obtain a positive electrode plate.

[0162] The other steps and parameters are the same as in Example 1; refer to Table 1 for specific parameters.

[0163] In Examples 11 to 16, the total amount of polymer A added was kept the same, and the ratio of polymer A-1 to polymer A-2 added was adjusted. Other parameters and steps were the same as in Example 1; see Table 1 for specific parameters.

[0164] In Examples 17 to 20, the weight-average molecular weight of polymer A-1 was adjusted, and the methods for producing polymer A-1 with different weight-average molecular weights are as follows.

[0165] The method for producing polymer A-1 in Example 17 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 400 mg of calcium sulfate and 80 mg of calcium phosphate were added. Next, 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.10 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 65°C and reacted for 5 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for electrode plates. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-1 is 6:3:2, and the weight-average molecular weight of polymer A-1 obtained by production is 700,000.

[0166] The method for producing polymer A-1 in Example 18 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 400 mg of calcium sulfate and 80 mg of calcium phosphate were added. Next, 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.13 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 75°C and reacted for 6 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for electrode plates. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-1 is 6:3:2, and the weight-average molecular weight of polymer A-1 obtained by production is 1 million.

[0167] The method for producing polymer A-1 in Example 19 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 400 mg of calcium sulfate and 80 mg of calcium phosphate were added. Next, 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.1 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 65°C and reacted for 4 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for electrode plates. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-1 is 6:3:2, and the weight-average molecular weight of polymer A-1 obtained by production is 600,000.

[0168] The method for producing polymer A-1 in Example 20 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 400 mg of calcium sulfate and 80 mg of calcium phosphate were added. Next, 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.18 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 80°C and reacted for 7 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for electrode plates. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-1 is 6:3:2, and the weight-average molecular weight of polymer A-1 obtained by production is 1.1 million.

[0169] In Examples 21 to 24, the weight-average molecular weight of polymer A-2 was adjusted, and the other parameters and steps were the same as in Example 1. For specific parameters, please refer to Table 1.

[0170] The method for producing polymer A-2 in Example 21 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate were added. Next, 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.05 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 46°C and reacted for 2.0 hours, and at the end of the reaction, the suspension was cooled, the product was filtered and washed, and then vacuum-dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for dispersion in electrode plate slurries. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-2 is 5:3:2, and the weight-average molecular weight of polymer A-2 obtained by production is 100,000.

[0171] The method for producing polymer A-2 in Example 22 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate were added. Next, 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.08 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 50°C and reacted for 3.5 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for dispersion in electrode plate slurries. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-2 is 5:3:2, and the weight-average molecular weight of polymer A-2 obtained by production is 250,000.

[0172] The method for producing polymer A-2 in Example 23 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate were added. Next, 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.03 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 40°C and reacted for 1.5 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for dispersion in electrode plate slurries. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-2 is 5:3:2, and the weight-average molecular weight of polymer A-2 obtained by production is 50,000.

[0173] The method for producing polymer A-2 in Example 24 is as follows: 0.20 g of the suspension agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate were added. Next, 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on total monomer molar content) were added. Finally, an aqueous solution obtained by dissolving 0.10 g of magnesium sulfate in 50 ml of deionized water was added, the suspension was heated to 58°C and reacted for 4 hours, and at the end of the reaction the suspension was cooled, the product was filtered and washed, and then vacuum dried at 70°C until constant weight was obtained to obtain a white powder. This adhesive is used for dispersion in electrode plate slurries. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-2 is 5:3:2, and the weight-average molecular weight of polymer A-2 obtained by production is 400,000.

[0174] Comparative Example 1 Lithium iron phosphate (LFP) active material, which is the positive electrode active material, carbon black as a conductive agent, and polyvinylidene fluorolide (PVDF) as an adhesive were dissolved in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 92:4:4. After thorough stirring and homogeneous mixing, a positive electrode slurry was obtained. The positive electrode slurry was then applied to the positive electrode current collector, and subsequently dried, cold pressed, and slit to obtain the positive electrode plate of Comparative Example 1. The other manufacturing steps were the same as in Example 1.

[0175] The relevant parameters for the manufacturing of the positive electrode in Examples 1 to 24 and Comparative Example 1 are shown in Table 1 below.

[0176] Example 25 Preparation of polymer A soluble in aqueous solvents for the undercoat layer (polymer A-3): 1.84 mmol of sodium dodecylbenzenesulfonate and 400 ml of deionized water were weighed and added to a stirring vessel. 0.63 mol of acrylonitrile, 0.21 mol of methyl methacrylate, and 0.21 mol of acrylamide were added. The stirring speed was controlled to 500 rpm, and the mixture was heated to 74 ± 1°C while stirring. Then, 1.2 parts of ammonium sulfate were added, and the reaction was stirred while maintaining the temperature at 75°C for 6 hours. After that, the temperature was raised to 80°C and the reaction was continued for 3 hours to obtain an emulsion with a solid content of approximately 20%. This emulsion is used as a primer. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in polymer A-3 is 3:1:1, and the weight-average molecular weight of polymer A-3 is 180,000.

[0177] Preparation of the undercoat layer: The prepared polymer A-3-containing emulsion and conductive agent were kneaded in a mass ratio of 30:70 so that the conductive agent was fully immersed in deionized water. Finally, deionized water was added so that the solid content of the slurry was 15%, and the mixture was stirred thoroughly and uniformly to achieve a viscosity of 200-800 MPa.s for the slurry at the time of shipment. When gravure coating was used, a recess was engraved on the gravure roller. During coating, the slurry was poured into the recess (30 μm), and after the roller surface lifted from the liquid surface, the slurry from the smooth part was scraped off with a doctor blade. The slurry in the recess was then transferred to the substrate surface by the action of the pressure roller, and the thickness of the single-sided coating after drying was approximately 5 μm. The prepared aluminum foil with undercoat was prepared for use.

[0178] The manufacturing of the positive electrode plate was the same as in Example 12. Lithium iron phosphate, conductive agent SP, polymer A-1, and polymer A-2 were dissolved in an N-methylpyrrolidone (NMP) solution in a mass ratio of 92:4:3.8:0.2, stirred, and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to an aluminum foil with a primer coating, followed by drying, cold pressing, and slitting to obtain the positive electrode plate. The coating produced by the positive electrode slurry is called the positive electrode film, and the surface density of the single-sided coating of the positive electrode film is approximately 20 mg / cm². 2Therefore, the press density of the single-sided coating of the positive electrode film is approximately 2.3 g / cm³. 3 That is the case.

[0179] The other steps in Example 25 are the same as in Example 12.

[0180] In Examples 26-29, the mass ratio of the polymer A-3-containing emulsion to the conductive agent was adjusted to 40:60, 50:50, 60:40, and 70:30, respectively, while the other steps were the same as in Example 12.

[0181] In Example 30, the production of the positive electrode plate involves dissolving nickel cobalt manganese oxide (NCM), lithium iron phosphate, conductive agent SP, polymer A-1, and polymer A-2 in an N-methylpyrrolidone (NMP) solution in a mass ratio of 82:10:4:3.8:0.2, stirring to mix uniformly, obtaining a positive electrode slurry, then uniformly applying the positive electrode slurry onto a pre-coated aluminum foil, followed by drying, cold pressing, and slitting to obtain a positive electrode plate. The other steps are the same as in Example 12.

[0182] In Comparative Example 2, no undercoat layer was applied, and the positive electrode plate was the same as in Example 25. In Comparative Example 3, the undercoat layer is a PAA undercoat layer, and the positive electrode plate is the same as in Comparative Example 2. The manufacturing method for the PAA-based undercoat layer is as follows: The manufactured PAA-containing aqueous emulsion has a solid content of approximately 20%. The emulsion and conductive agent are mixed in a mass ratio of 50:50 so that the conductive agent is fully immersed in deionized water. Finally, deionized water is added so that the solid content of the slurry becomes 15%, and the mixture is stirred thoroughly and uniformly to achieve a viscosity of 200-800 mPa.s at the time of shipment. When gravure coating is used, a recess is engraved on the gravure roller. During coating, the slurry is poured into the recess (30 μm), and after the roller surface leaves the liquid surface, the slurry from the smooth part is scraped off with a doctor blade. The slurry in the recess is then transferred to the substrate surface by the action of the pressure roller, and the thickness of the single-sided coating after drying is approximately 5 μm. The manufactured aluminum foil with undercoat is prepared for use.

[0183] The relevant manufacturing parameters for Examples 25-30 and Comparative Examples 2-3 are shown in Table 2 below.

[0184] Furthermore, performance tests were conducted on the polymers, electrodes, and batteries obtained in Examples 1-24 and Comparative Example 1. See Table 1 for the test results. Performance tests were also conducted on the polymers, electrodes, and batteries obtained in Examples 25-30 and Comparative Examples 2-3. See Table 2 for the test results. The test methods are as follows.

[0185] 1. Testing the types of polymer structural units - Infrared spectroscopy In the tablet press transmission method, the sample was pressed into a KBr tablet, the KBr background blank was removed by transmission, and the sample test spectrum was obtained. The instrument model number was Nicolet 5700 (Thermo Nicolet, USA), the standard linearity was better than 0.07%, and the resolution was 0.09 cm². -1 The wavenumber range is 400-4000 cm. -1 Therefore, sensitivity <9.65*10 -5 ABLs is used to detect the structure and chemical bonds of molecules.

[0186] 2. Weight-average molecular weight test A Waters 2695 isocratic HPLC-type gel chromatograph (differential refractive photodetector 2141) was used. A polystyrene solution sample with a mass fraction of 3.0% was used as the reference sample, and a matching chromatographic column (oil-based: Styragel HT5 DMF 7.8*300 mm + Styragel HT4) was selected. A 3.0% adhesive colloid solution was placed in purified N-methylpyrrolidone (NMP) solvent, and the solution was allowed to stand for one day in preparation for use. During testing, tetrahydrofuran was first drawn using a syringe, flushed, and repeated several times. Then, 5 ml of the experimental solution was drawn, air was removed from the syringe, and the needle tip was dried. Finally, the sample solution was gradually injected into the sample inlet. After the test was completed, the efflux graph, molecular weight distribution graph, and molecular weight statistics were output.

[0187] 3. Slurry viscosity test A suitable rotor was selected, the viscometer was fixed in place, and the positive electrode slurry was placed under the viscometer so that the slurry was just embedded in the rotor's scale line. The instrument model number was Shanghai Fangrui NDJ-5S, the rotor was 63# (2000-10000 mPa.s) and 64# (10000-50000 mPa.s), the rotation speed was 12 r / min, the test temperature was 25°C, the test time was 5 minutes, and the data was read after the indicated values ​​stabilized.

[0188] 4. Slurry filtration performance test A 500 ml beaker is placed on the lower end of a 200-mesh screen support stand. 500 ml of slurry is taken and filtered through the screen. The time it takes for the volume of slurry in the beaker to reach 300 ml is recorded. This time is used to determine the filtration performance of the slurry. If the filtration time is less than 120 seconds, the slurry's filtration performance is considered OK. If the slurry cannot pass through the screen, the slurry's filtration performance is considered poor and is judged as "NG".

[0189] 5. Fluidity test of the slurry: An appropriate amount of positive electrode slurry was taken with a spoon, and the smooth flow of the slurry by gravity was observed. If the flow by gravity was smooth, it was judged as OK. If the fluidity was poor and the slurry solidified into a jelly-like substance, it was judged as NG, indicating that gel formation had occurred.

[0190] 6. Visual inspection of the electrode plates: After the manufacturing of the positive electrode plate was completed, the surface condition of the positive electrode plate was observed, including whether it was flat, whether there were any cracks, and whether there was any particle aggregation. If none of the above phenomena were present, it was recorded as OK; if any of these phenomena were present, it was recorded.

[0191] 7. Adhesion strength test: The positive electrode plate in the embodiment was cut into a test sample of size 20*100mm and prepared for use, and the test method is as shown in Figure 7. Double-sided tape 7 was attached to one surface of the electrode plate 6 and pressed with a pressure roller to ensure complete adhesion to the electrode plate, the other side of the double-sided tape 7 was attached to the surface of the steel plate 8, one end of the current collector 61 was bent in the opposite direction to a bending angle of 180°, as shown by the arrow in Figure 7, and the test was performed using a high-strength tensile machine. One end of the steel plate 8 was fixed to the jig below the tensile machine, and the curved end of the current collector 61 was fixed to the jig above. After adjusting the angle of the current collector so that the upper and lower ends were in a vertical position, the sample was pulled at a speed of 50 mm / min and continued until the entire current collector 61 was peeled off from the coating 62 on the surface of the current collector 61. The displacement and applied force during the process were recorded, and the force when the forces were balanced was defined as the adhesive force of the electrode plate 6.

[0192] 8. Brittleness test of electrode plates The positive electrode plate in the example was cut into a test sample measuring 20*100mm and prepared for use. The electrode plate was folded in half and fixed in place, and then pressed once using a 2kg rolling roller. It was checked whether light could pass through the folded portion of the electrode plate and whether metal was leaking. If light could not pass through and metal was not leaking, the electrode plate was turned over, folded in half and fixed in place, and pressed once using a 2kg rolling roller. It was checked whether light could pass through the folded portion of the electrode plate and whether metal was leaking. The above steps were repeated until light could pass through the folded portion of the electrode plate and metal was leaking.

[0193] 9. DC impedance test of the battery The DC impedance test process for the battery is as follows: At 25°C, the battery in the example or comparative example was charged with a constant current of 1 / 3C to 3.65V, then charged with a constant voltage of 0.05C at 3.65V, left for 5 minutes, and the voltage V1 was recorded. Then, it was discharged at 1 / 3C for 30s, and the voltage V2 was recorded. The internal resistance DCR1 of the battery after the first cycle was obtained using formula 3*(V2-V1) / C. The above steps were repeated for the same battery, and the internal resistance DCR1 of the battery after the nth cycle was obtained. n(n=1, 2, 3...100) were recorded, and the above DCR1, DCR2, DCR3...DCR 100 The values ​​of these 100 points were used as the vertical coordinate, and the corresponding number of cycles was used as the horizontal coordinate, resulting in a graph of the battery discharge DCR and number of cycles corresponding to the positive electrode active material.

[0194] In this test process, the first cycle corresponds to n=1, the second cycle to n=2, ... the 100th cycle to n=100. DCR increase rate in Table 1 = (DCR 500 -DCR1) / DCR1*100%, and the test process for Comparative Example 1 and the other examples is the same as described above.

[0195] 10. Battery cycle count test The number of battery cycles was obtained from capacity testing. The test process was as follows: At 25°C, the battery corresponding to Example 1 was charged with a constant current of 1 / 3C to 3.65V, then charged with a constant voltage of 0.05C at 3.65V, left for 5 minutes, and then discharged to 2.5V at 1 / 3C. The resulting initial capacity C0 was recorded, and the cutoff condition Pn ≤ 70%C0 was set. The above steps were repeated for the same battery, and the discharge capacity C of the battery after the nth cycle was measured. n When recording the battery capacity retention rate P after each cycle, n =C n / C0*100%, and P1, P2...P n The values ​​of the n points were used as the vertical coordinate, and the corresponding number of cycles was used as the horizontal coordinate, resulting in a graph of the corresponding battery capacity retention rate and number of cycles. n If the value was ≤70%C0, the test was stopped and the number of cycles was recorded.

[0196] [Table 1] JPEG0007867532000002.jpg251139JPEG0007867532000003.jpg251139JPEG0007867532000004.jpg252165

[0197] [Table 2]

[0198] As can be seen from the results above, in Comparative Example 1, PVDF was used as an adhesive for the positive electrode slurry, which made the positive electrode active material in the slurry prone to aggregation. This resulted in poor stability and processability of the positive electrode slurry, making it difficult to produce high-quality positive electrode plates, and further increasing the rate of increase in internal resistance after battery cycling.

[0199] Examples 1 to 24 provide a positive electrode slurry, which comprises a positive electrode active material, a conductive agent, and an adhesive. The adhesive contains polymer A, which includes structural units derived from acrylonitrile, acrylamide, and methyl acrylate. As can be seen by comparing Example 5 with Comparative Example 1, polymer A exhibits a good effect as an adhesive in the positive electrode slurry, improving the stability and processability of the positive electrode slurry, and enhancing the adhesive performance of the electrode plates.

[0200] In Examples 1-18 and 21-24, the adhesive contains polymer A-1 with a weight-average molecular weight of 700,000 to 1,000,000. Compared to polymer A-1 with a weight-average molecular weight of 600,000 or 1,100,000 in Examples 19 and 20, both yielded better results, improving the stability and processability of the positive electrode slurry, enhancing the adhesive performance of the electrode plates, and further reducing the rate of increase in the battery's cycle internal resistance.

[0201] In Examples 10-24, the adhesive further contains polymer A-2, which has a weight-average molecular weight of 100,000 to 250,000. Compared to Example 5, polymer A-2 has a smaller molecular weight and therefore acted as a dispersant in the slurry. The addition of polymer A-2 further improved the stability and processability of the slurry, enhanced the adhesion performance of the electrode plates, and reduced the rate of increase in the battery's cycle internal resistance.

[0202] In Examples 2-8 and 10-24, the mass content of polymer A-1 was 0.4% to 5.5% based on the total mass of the positive electrode active material, conductive agent, and adhesive. Compared to Examples 1 and 9, polymer A-1 within this range improved the stability and processability of the slurry, enhanced the adhesion performance of the electrode plates, and significantly reduced the rate of increase in the battery's cycle internal resistance.

[0203] In Examples 10 to 15, the mass content of polymer A-2 is 0.05% to 0.5% based on the total mass of the positive electrode active material, conductive agent, and adhesive. Compared to Example 16, adding polymer A-2 within this range improves the stability and processability of the slurry, enhances the adhesion performance of the electrode plates, and significantly reduces the increase in the battery's cycle internal resistance.

[0204] Examples 25-30 provide a positive electrode plate comprising a current collector, an undercoat layer placed on at least one surface of the current collector, and a positive electrode film placed on the undercoat layer. The undercoat layer contains polymer A-3, which is soluble in an aqueous solvent, and polymer A-3 comprises structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate. By applying this undercoat layer, the appearance quality and brittleness of the electrode plate were improved compared to Comparative Examples 2-3, and the adhesion performance of the electrode plate and the cycle performance of the battery were significantly improved.

[0205] In Examples 25-30, the mass content of polymer A-3 in the undercoat layer was 5%-40% based on the total mass of the undercoat layer. Compared to Comparative Examples 2-3, the appearance quality and brittleness of the electrode plates were improved in these examples, and the adhesive performance of the electrode plates and the cycle performance of the battery were improved. When the mass content of polymer A-3 in the undercoat layer was 5%-30% or 5%-20% based on the total mass of the undercoat layer, the cycle performance of the battery was significantly improved.

[0206] In Examples 25-30, the positive electrode film comprises a positive electrode active material, an adhesive, and a conductive agent. The adhesive comprises polymer A-1 and polymer A-2, and polymers A-1 and A-2 contain structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate.

[0207] It should be noted that this application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiments that have substantially the same configuration as the technical concept and produce similar functions and effects within the scope of the technical proposal of this application are all included within the scope of the technical proposal. Furthermore, other forms that are constructed by combining some of the components of the embodiments, by implementing various modifications to the embodiments that a person skilled in the art could conceive of, without departing from the spirit of this application, are also included within the scope of this application. [Explanation of symbols]

[0208] 1: Battery pack, 2: Upper case, 3: Lower case, 4: Battery module, 5: Rechargeable battery, 51: Housing, 52: Electrode assembly, 53: Top cover assembly, 6: Electrode plate, 61: Current collector, 62: Coating on current collector, 7: Double-sided tape, 8: Steel plate

Claims

1. A positive electrode plate comprising a current collector, an undercoat layer placed on at least one surface of the current collector, and a positive electrode film placed on the undercoat layer, The aforementioned undercoat layer contains polymer A soluble in an aqueous solvent, and polymer A comprises structural units derived from cyano group-containing monomers, structural units derived from amide group-containing monomers, and structural units derived from ester group-containing monomers. A positive electrode plate characterized in that, based on the total mass of the undercoat layer, the mass content of polymer A in the undercoat layer is 5% to 16.67%.

2. The weight-average molecular weight of polymer A in the aforementioned undercoat layer is 1.5 × 10 ５ ~2 x 10 ５ The positive electrode plate according to claim 1.

3. The positive electrode plate according to claim 1 or 2, characterized in that the undercoat layer further contains a conductive agent, the conductive agent being selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.

4. The positive electrode plate according to claim 1 or 2, characterized in that the thickness of the undercoat layer is 1 to 20 μm.

5. The positive electrode film comprises a positive electrode active material, an adhesive, and a conductive agent. The positive electrode plate according to claim 1, characterized in that the adhesive contains polymer A soluble in an oily solvent, and polymer A contains structural units derived from a cyano group-containing monomer, structural units derived from an amide group-containing monomer, and structural units derived from an ester group-containing monomer.

6. The aforementioned positive electrode film has a weight-average molecular weight of 7 × 10 ５ ~1 x 10 ６ The positive electrode plate according to claim 5, characterized in that it contains the polymer A.

7. The aforementioned positive electrode film has a weight-average molecular weight of 1 × 10 ５ ~2.5 x 10 ５ The positive electrode plate according to claim 6, further comprising the polymer A.

8. The positive electrode plate according to any one of claims 5 to 7, characterized in that the positive electrode active material is a lithium-containing transition metal oxide, and the positive electrode active material is optionally at least one of lithium iron phosphate, or a doped modified material thereof, or a conductive carbon-coated modified material thereof, a conductive metal-coated modified material, or a conductive polymer-coated modified material thereof.

9. The positive electrode plate according to any one of claims 5 to 7, characterized in that, with respect to the mass of the positive electrode film, the mass content of the positive electrode active material is 70% to 99.5%, and optionally 88% to 99.5%.

10. Based on the mass of the positive electrode film, the mass content of the polymer A in the positive electrode film with a weight average molecular weight of 7×10 ５ ~1×10 ６ is 0.4% to 5.5%, and / or the mass content of the polymer A in the positive electrode film with a weight average molecular weight of 1×10 ５ ~2.5×10 ５ is 0.05% to 0.5%. The positive electrode plate according to claim 6 or 7, characterized in that.

11. The cyano group-containing monomer in polymer A is selected from one or more of acrylonitrile and butenenitrile. The amide group-containing monomer is selected from one or more of the following: methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-n-propylmethacrylamide, N-isopropylmethacrylamide, N-n-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, and N,N-diethylmethacrylamide. The positive electrode plate according to claim 1 or 2, characterized in that the ester group-containing monomer is selected from one or more of methyl acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

12. The positive electrode plate according to claim 1 or 2, characterized in that, based on the total molar content of structural units in polymer A, the molar content of structural units derived from cyano group-containing monomers in polymer A is 50% to 70%, the molar content of structural units derived from ester group-containing monomers is 10% to 30%, and the molar content of structural units derived from amide group-containing monomers is 10% to 30%.

13. A secondary battery comprising an electrode assembly and an electrolyte, The electrode assembly is characterized by comprising a positive electrode plate, a separator, and a negative electrode plate as described in claim 1 or 2, in a secondary battery.

14. A battery module characterized by including a secondary battery as described in claim 13.

15. A battery pack characterized by including the battery module described in claim 14.

16. A power consumption device characterized by including a secondary battery as described in claim 13.

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