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

Abstract

The present application provides a positive electrode slurry, a secondary battery, a battery module, a battery pack, and a power consumption device. The positive electrode slurry includes a positive electrode active material, a conductive agent, and an adhesive, and the adhesive includes a 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 improves the stability and processability of the positive electrode slurry and improves the adhesive strength of the positive electrode plate by using the polymer A as the adhesive of the positive electrode slurry.

Description

[Technical Field]

[0001] The present application relates to the field of lithium battery technology, and in particular to positive electrode slurries, secondary batteries, battery modules, battery packs, and power consuming devices. [Background technology]

[0002] In recent years, lithium ion batteries have been widely applied in energy storage power systems such as hydroelectric power, thermal power, wind power and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the widespread application of lithium ion batteries, higher requirements are being placed on both their performance and cost.

[0003] The current conventional adhesive PVDF, as a commonly used adhesive, has problems such as poor compatibility with electrode active materials and weak adhesive strength. In addition, the stability of positive electrode slurries made with it is poor, making them difficult to process during the application process. Therefore, the development of a new adhesive and positive electrode slurry was eagerly awaited. Summary of the Invention

[0004] The present application has been made in view of the above problems, and its object is to provide a positive electrode slurry that is highly stable, easy to process, and has strong adhesive strength.

[0005] A first aspect of the present application provides a positive electrode slurry, the positive electrode slurry including a positive electrode active material, a conductive agent, and an adhesive, the adhesive including a polymer A including 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.

[0006] The present application improves the stability and processability of the positive electrode slurry and enhances the adhesive strength of the positive electrode plate by using, as an adhesive in a positive electrode slurry, a polymer A that includes 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.

[0007] Polymer A contains abundant polar groups, such as cyano groups, located in the main chain segment of Polymer A. The dipole-dipole interaction between the cyano groups and the electronegativity of the positive electrode current collector provides Polymer A with extremely strong adhesion to the current collector, improving the adhesion strength of the electrode plate and preventing processing anomalies such as electrode plate peeling and powder shedding during the coating or cold pressing process. Furthermore, the ester-containing functional groups provide a certain level of electrolyte absorption and retention, improving the poor ionic conductivity of conventional adhesives, such as simple polyvinylidene fluoride. Furthermore, the abundant groups on Polymer A improve the compatibility of Polymer A with various positive electrode active materials, enhancing Polymer A's versatility as an adhesive.

[0008] In an optional embodiment, the adhesive has a weight average molecular weight of 7×10 5 ~1×10 6 By controlling the weight-average molecular weight of polymer A, the stability and processability of the positive electrode slurry and the adhesive strength of the positive electrode plate can be improved, and the rate of increase in the internal resistance of the battery during cycling can be further reduced.

[0009] In an optional embodiment, the adhesive has a weight average molecular weight of 1×10 5 ~2.5×10 5 The polymer A further comprises a polymer A having a weight average molecular weight of 1×10 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 and the adhesive strength of the electrode plates, thereby reducing the rate of increase in internal resistance during battery cycling.

[0010] In an optional embodiment, the weight average molecular weight is 7×10 based on the total mass of the positive electrode active material, the conductive agent, and the adhesive. 5 ~1×10 6 The mass content of polymer A is 0.4% to 5.5%. The weight average molecular weight within this mass content range is 7×10 5 ~1×10 6Polymer A can improve the stability and processability of the slurry and the adhesiveness of the electrode plates, and can also significantly reduce the rate of increase in the internal resistance of the battery during cycling.

[0011] In an optional embodiment, the weight average molecular weight is 1×10 based on the total mass of the positive electrode active material, the conductive agent, and the adhesive. 5 ~2.5×10 5 The mass content of polymer A is 0.05% to 0.5%. 5 ~2.5×10 5 Polymer A can further improve the stability and processability of the slurry and the adhesive strength of the electrode plates, and can also significantly reduce the rate of increase in the internal resistance of the battery during cycling.

[0012] In an optional embodiment, the cyano group-containing monomer is selected from one or more of acrylonitrile and butenenitrile.

[0013] In an optional embodiment, the amide group-containing monomer is selected from one or more of methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide.

[0014] In an optional embodiment, 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, hydroxypropyl acrylate.

[0015] The above materials are readily available and can significantly reduce the manufacturing costs of adhesives.

[0016] In any embodiment, 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 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%.

[0017] In any embodiment, the active cathode material is a lithium-containing transition metal oxide, optionally at least one of lithium iron phosphate, or doped modifications thereof, or conductive carbon-coated, conductive metal-coated, or conductive polymer-coated modifications thereof, or mixtures thereof with other lithium-containing transition metal oxides.

[0018] By including in Polymer A a group that has excellent affinity with highly graphitized carbon materials, such as an N-containing group (cyano group, amide group) or an oxygen-containing group (ester group, amide group), the wettability of the lithium iron phosphate powder in a solvent (e.g., N-methylpyrrolidone) can be effectively improved, and the stability and processability of the positive electrode slurry can be further improved.

[0019] In any embodiment, 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.

[0020] In an optional embodiment, the conductive agent is selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon spots, carbon nanotubes, graphene, and carbon nanofibers.

[0021] In any embodiment, the mass content of the conductive agent is 0.2% to 6.0% based on the total mass of the positive electrode active material, the conductive agent, and the adhesive.

[0022] In a second aspect of the present application, there is provided a secondary battery, the secondary battery including an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode plate made from the positive electrode slurry of the first aspect of the present application, a separator, and a negative electrode plate.

[0023] In a third aspect of the present application, there is provided a battery module including the secondary battery of the second aspect of the present application.

[0024] In a fourth aspect of the present application, there is provided a battery pack including the battery module of the third aspect of the present application.

[0025] A fifth aspect of the present application provides a power consumption device including at least one of the secondary battery of the second aspect of the present application, the battery module of the third aspect, or the battery pack of the fourth aspect. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; [Figure 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application; [Figure 5] FIG. 5 is an exploded view of the battery pack according to the embodiment of the present application shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of a power consuming device in which a secondary battery of the present application is used as a power source; [Figure 7] FIG. 1 is a schematic diagram of a test for adhesive strength of electrodes. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, with reference to the accompanying drawings as appropriate, detailed descriptions will be given of embodiments specifically disclosing the adhesive, manufacturing method, electrode, battery, and power consumption device of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of structures that are actually the same may be omitted. This is to avoid the following description becoming unnecessarily long and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0028] The "ranges" disclosed herein are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit that define the boundaries of the particular range. Such defined ranges may or may not include the end values, and may be arbitrarily combined; i.e., any lower limit and any upper limit may be combined to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​1 and 2 and maximum range values ​​3, 4, and 5 are listed, the following ranges are also contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, a numerical range "a to b" is a shorthand expression representing all combinations of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed herein, with "0-5" merely being a shorthand notation for combinations of these numbers. Also, stating that a parameter is an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise stated, all embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution.

[0030] Unless otherwise stated, all technical features and optional technical features in the present application may be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, a description of a method including steps (a) and (b) means that the method may include sequential steps (a) and (b), or sequential steps (b) and (a). For example, a description of a method mentioned above that 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 may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0032] Unless otherwise specified, the terms "comprise" and "comprises" used in this application may be open-ended or closed-ended. For example, the terms "comprise" and "comprises" may further include or include other components not listed, or may include or include only the listed components.

[0033] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, 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).

[0034] Lithium iron phosphate positive electrode active material has attracted widespread attention in the industry due to its low cost, high performance, and safety. However, due to its characteristics of large specific surface area, small particle size, high surface carbon coverage after carbon coating, and high degree of graphitization, slurries using lithium iron phosphate as the positive electrode active material and the conventional adhesive PVDF as the adhesive have poor dispersibility, are prone to settling, have high viscosity, and have low solid content. Furthermore, the produced electrode plates are prone to surface defects such as cracks, peeling, particle scratches, and pinholes, and the positive electrode active material is unevenly distributed in the electrode plates, resulting in uneven electrode plate quality.

[0035] [Positive electrode slurry] Based on this, the present application provides a positive electrode slurry for use in a battery, which includes a positive electrode active material, a conductive agent, and an adhesive, and the adhesive includes a polymer A including 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.

[0036] As used herein, the term "adhesive" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or dispersion in a carrier medium.

[0037] As used herein, the term "polymer" includes, on the one hand, chemically uniform aggregates of macromolecules produced by polymerization reactions, but which differ in terms of their degree of polymerization, molar mass and chain length. On the other hand, the term also includes derivatives of such macromolecular aggregates formed by polymerization reactions, i.e., those obtained by reactions, such as addition or substitution, of functional groups on the macromolecules, and may be chemically uniform or chemically heterogeneous compounds or mixtures.

[0038] As used herein, the term "positive electrode" also refers to the "negative electrode" in a secondary battery.

[0039] As used herein, the term "cyano" refers to a -CN group.

[0040] As used herein, the term "amide group" refers to a -CONH group.

[0041] As used herein, the term "ester group" refers to a -COOR group, where R is a C 1-9 The alkyl group is selected from the group consisting of:

[0042] As used herein, the substituents in the term "substituted by substituents" each independently include a hydroxyl group, a mercapto group, an amino group, a cyano group, a nitro group, an aldehyde group, a halogen atom, an alkenyl group, an alkynyl group, an aryl group, a heteroaryl group, a C 1-6 Alkyl group, C 1-6 The alkoxy group is selected from the group consisting of alkoxy groups.

[0043] As used herein, the term "C 1-6 "Alkyl group" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, free of unsaturation, having from one to five carbon atoms and attached to the remainder of the molecule by a single bond. 1-9 "Alkyl" should be construed accordingly. 1-6 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, and pentyl groups.

[0044] As used herein, 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.

[0045] In some embodiments, polymer A can be dissolved in an oil-based solvent. In some embodiments, polymer A can be dissolved in an aqueous solvent. Examples of oil-based solvents include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate. Examples of aqueous solvents include, but are not limited to, water. As can be appreciated, the structural units in polymer A can be blended in any ratio, polymer A can have different molecular weights, and polymer A can be produced by different methods, such as a suspension method, an emulsion method, etc.

[0046] In some embodiments, the positive electrode slurry includes a dispersion medium. In some embodiments, the dispersion medium of the positive electrode slurry is an oil-based solvent. In some embodiments, the dispersion medium of the positive electrode slurry is an aqueous solvent.

[0047] In some embodiments, an adhesive is used to bond the positive electrode active material and / or conductive agent to form a slurry, which can be fixed in place and adhered to a conductive metal member to form the positive electrode.

[0048] In some embodiments, polymer A is one or more of acrylonitrile-acrylamide-methyl acrylate copolymer, acrylonitrile-acrylamide-ethyl acrylate copolymer, acrylonitrile-acrylamide-propyl acrylate copolymer, acrylonitrile-acrylamide-isooctyl acrylate copolymer.

[0049] The present application improves the stability and processability of a positive electrode slurry and enhances the adhesive strength of a positive electrode plate by using a polymer containing 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 as an adhesive in a positive electrode slurry.

[0050] Polymer A contains abundant polar groups, such as cyano groups, located in the main chain segment of Polymer A. The dipole-dipole interaction between the cyano groups and the electronegativity of the positive electrode current collector gives Polymer A extremely strong adhesion to the current collector, improving the adhesion strength of the electrode plate and preventing processing anomalies such as electrode plate peeling and powder shedding during the coating or cold pressing process. Furthermore, the ester-containing functional groups in Polymer A provide a certain level of electrolyte absorption and retention, thereby alleviating the poor ionic conductivity of conventional adhesives, such as simple polyvinylidene fluoride. Furthermore, the abundant groups on Polymer A improve the compatibility of Polymer A with various positive electrode active materials, enhancing Polymer A's versatility as an adhesive.

[0051] In some embodiments, the adhesive has a weight average molecular weight of 7×10 5 ~1×10 6 In some embodiments, the weight average molecular weight of polymer A is optionally 7×10 5 ~9.5×10 5 or 7 x 10 5 ~9×10 5 or 7 x 10 5 ~8.5×10 5 or 7 x 10 5 ~8×10 5 or 7.5 x 10 5 ~1×10 6 or 8 x 10 5 ~1×10 6 or 8.5 x 10 5 ~1×10 6 or 9 x 10 5 ~1×10 6 or 9.5 x 10 5 ~1×10 6 is.

[0052] As used herein, the term "weight average molecular weight" refers to the sum of the products of the weight fractions of molecules of different molecular weights in a polymer and the corresponding molecular weights.

[0053] By controlling the weight average molecular weight of polymer A, the stability and processability of the positive electrode slurry and the adhesive strength of the positive electrode plate can be improved, and the rate of increase in the internal resistance of the battery during cycling can be further reduced.

[0054] In some embodiments, the adhesive has a weight average molecular weight of 1×10 5 ~2.5×10 5 In some embodiments, the weight average molecular weight of polymer A is optionally 1.5×10 5 ~2.5×10 5 or 2 x 10 5 ~2.5×10 5 or 1 x 10 5 ~2×10 5 or 1 x 10 5 ~1.5×10 5 is.

[0055] Some positive electrode active materials (e.g., lithium iron phosphate LFP) have a large specific surface area and many small particles, which can easily cause the slurry to aggregate during the manufacturing process and lead to screen clogging. The use of polymer A, which has a low weight-average molecular weight, in the slurry prevents aggregation between the positive electrode active material (e.g., lithium iron phosphate LFP powder particles) through electrostatic repulsion or steric hindrance. It also acts as a dispersant and suspender for other small molecule materials in the slurry, preventing settling even after short periods of standing, increasing the slurry's stability. Furthermore, polymer A's low weight-average molecular weight has a low glass transition temperature, further improving the flexibility of the electrode plate.

[0056] Weight average molecular weight is 1×10 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 and the adhesive strength of the electrode plates, thereby reducing the rate of increase in internal resistance during battery cycling.

[0057] In some embodiments, the weight average molecular weight is 7×10 based on the total mass of the positive electrode active material, the conductive agent, and the adhesive. 5 ~1×10 6 The mass content of polymer A having a weight average molecular weight of 7×10 is 0.4% to 5.5%. 5 ~1×10 6 If polymer A having a weight average molecular weight of 7×10 is added in excess, the power performance and cycle performance of the battery will be reduced. 5 ~1×10 6 Polymer A can improve the stability and processability of the slurry and the adhesion of the electrode plates, and can also significantly reduce the rate of increase in the internal resistance of the battery during cycling.

[0058] In some embodiments, the weight average molecular weight is 1×10 based on the total mass of the positive electrode active material, the conductive agent, and the adhesive. 5 ~2.5×10 5 The mass content of polymer A is 0.05% to 0.5%.

[0059] Weight average molecular weight is 1×10 5 ~2.5×10 5 If polymer A is added in excess, it will increase the swelling of the electrode plate and affect the room temperature power performance of the battery. 5 ~2.5×10 5 Polymer A further improves the stability and processability of the slurry and the adhesive strength of the electrode plates, and can also significantly reduce the rate of increase in the internal resistance of the battery during cycling.

[0060] In some embodiments, the cyano group-containing monomer is selected from one or more of acrylonitrile and butenenitrile.

[0061] In some embodiments, the amide group-containing monomer is selected from one or more of methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide.

[0062] 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, hydroxypropyl acrylate.

[0063] The above materials are readily available and can significantly reduce the manufacturing costs of adhesives.

[0064] 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 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%.

[0065] By rationally combining structural units derived from monomers containing each group, polymer A can achieve both strength, flexibility, adhesive performance and swelling resistance, giving the electrode plate excellent adhesive strength and processability.

[0066] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide, optionally lithium iron phosphate, or doped modifications thereof, or at least one of conductive carbon-coated, conductive metal-coated, or conductive polymer-coated modifications thereof.

[0067] The lithium iron phosphate positive electrode active material has a microporous structure and a high degree of graphitization on its surface after carbon coating. Due to these structural characteristics, the slurry exhibits poor wettability in a slurry solvent (e.g., N-methylpyrrolidone (NMP)), poor stability, a low solids content, and easy peeling of adhesive areas after storage, making it unusable. By incorporating groups with excellent affinity for highly graphitized carbon materials, such as N-containing groups (cyano groups, amide groups) and oxygen-containing groups (ester groups, amide groups), into Polymer A, the wettability of the lithium iron phosphate powder in a solvent (e.g., NMP) is effectively improved, further improving the stability and processability of the positive electrode slurry.

[0068] 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 ensuring that the mass content of the positive electrode active material is within this range, the loading amount of the positive electrode active material can be ensured, and the power performance of the battery can be improved.

[0069] In some embodiments, the conductive agent is selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon spots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] 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, the conductive agent, and the adhesive.

[0071] [Positive electrode] In one embodiment of the present application, there is provided a positive electrode plate, the positive electrode plate including 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, the undercoat layer including 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.

[0072] As used herein, the term "current collector" refers to any conductive substrate capable of conducting electrical current to an electrode during discharging or charging of a secondary battery.

[0073] The term "cathode film" refers to the coating formed after applying and drying the cathode slurry.

[0074] While small-particle size positive electrode active materials have the advantage of a large specific surface area, allowing for sufficient reaction with the electrolyte, the large specific surface area also results in poor adhesion to the current collector, making peeling more likely during the positive electrode slurry application process. Increasing the amount of adhesive used in the positive electrode slurry can lead to issues with brittleness of the electrode plate during the cold pressing process and a decrease in press density, making it necessary to add a special undercoat layer on the current collector to improve adhesion between the positive electrode film and the current collector.

[0075] Because the aqueous-soluble polymer A in the undercoat layer contains cyano, amide, and ester groups, it may swell moderately when it comes into contact with the oil-based solvent (e.g., NMP) of the positive electrode slurry during the positive electrode slurry application process, but it does not dissolve. The polymer A in the undercoat layer and the adhesive in the positive electrode slurry form molecular contacts, allowing for 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 current collector surface, ensuring strong adhesion of the positive electrode film to the current collector.

[0076] Polymer A that is soluble in an aqueous solvent refers to polymer A that can be dissolved 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.

[0077] In some embodiments, the aqueous-soluble polymer A in the primer layer is formed by bulk polymerization, suspension polymerization, emulsion polymerization, or solution polymerization. In some embodiments, the aqueous-soluble polymer A in the primer layer is formed by an emulsion method, which is easy for mass production, simple, and environmentally friendly.

[0078] In some embodiments, the present application uses Polymer A in the undercoat layer of the positive electrode plate to improve the forming quality, adhesion, and flexibility of the positive electrode plate, thereby optimizing the cycling performance of the battery.

[0079] In some embodiments, the weight average molecular weight of polymer A in the primer layer is 1.5×10 5 ~2×10 5 is.

[0080] An appropriate weight-average molecular weight improves the forming quality of the electrode plate, balances the processability and adhesiveness of the undercoat layer, and ensures that polymer A in the undercoat layer has a certain degree of diffusibility when the positive electrode slurry is applied.

[0081] In some embodiments, the weight content of polymer A in the primer layer is 5% to 40%, optionally 5% to 30%, and optionally 5% to 20%, based on the total weight of the primer layer.

[0082] If the amount of polymer A in the undercoat layer is too high, it will reduce the stability of the undercoat layer and the cycle performance of the battery. By keeping the mass of polymer A in the undercoat layer within this range, the appearance quality and brittleness of the electrode plate are improved, and the adhesion performance of the electrode plate and the cycle performance of the battery are improved.

[0083] In some embodiments, the primer layer further comprises a conductive agent, the conductive agent being selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.

[0084] 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 charge / discharge rate performance of the battery and extending the cycle life of the battery.

[0085] In some embodiments, the thickness of the primer layer is from 1 to 20 μm.

[0086] If the thickness of the undercoat layer is too large, the conductivity of the current collector will be poor, and if the thickness of the undercoat layer is too small, it will not be possible to ensure effective adhesion of the electrode plate. By keeping the thickness of the undercoat layer within this range, it is possible to achieve both the adhesive properties of the electrode plate and the power and cycle performance of the battery.

[0087] In some embodiments, the cathode membrane has an areal coating density of 20 mg / cm 2 That's all.

[0088] As used herein, the term "areal density" is calculated by dividing the mass by the corresponding area.

[0089] By providing the undercoat layer of the present invention on the electrode plate, it is possible to ensure that a certain amount of positive electrode active material is carried on the positive electrode plate, and further ensure the power performance of the battery.

[0090] In some embodiments, the positive electrode membrane includes a positive electrode active material, an adhesive, and a conductive agent, the adhesive includes a polymer A that is soluble in an oil-based solvent, and the polymer A includes 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.

[0091] Polymer A that is soluble in an oily solvent means that polymer A can be dissolved 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.

[0092] By using polymer A, which is soluble in an oil-based solvent, as an adhesive in the positive electrode film and diffusing and connecting it with polymer A in the undercoat layer, the adhesive strength between the undercoat layer and the positive electrode film can be further strengthened, improving the appearance quality and brittleness of the electrode plate, and improving the adhesive performance of the electrode plate and the cycle performance of the battery.

[0093] In an optional embodiment, the cathode film has a weight average molecular weight of 7×10 5 ~1×10 6 The polymer A includes the polymer A, which is

[0094] By controlling the weight-average molecular weight of polymer A, it is possible to improve the adhesive strength of the positive electrode plate and further reduce the rate of increase in the internal resistance of the battery during cycling.

[0095] In an optional embodiment, the cathode film has a weight average molecular weight of 1×10 5 ~2.5×10 5 Further included is a polymer A in which:

[0096] 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 can further improve the dispersibility of the positive electrode active material in the positive electrode film, resulting in a battery with higher adhesive strength and a lower cycle internal resistance increase rate.

[0097] Some positive electrode active materials (e.g., lithium iron phosphate LFP) have large specific surface areas and many small particles, which can easily cause the slurry used to form the positive electrode film to aggregate and clog the screen during the manufacturing process. By using Polymer A with a low weight-average molecular weight in the slurry used to form the positive electrode film, the electrostatic repulsion or steric hindrance of the polymer A can prevent aggregation between the positive electrode active material (e.g., lithium iron phosphate LFP powder particles). At the same time, it also acts as a dispersant and suspender for other small molecule materials in the positive electrode film, preventing settling even when the slurry is left standing for a short period of time, increasing its stability. Furthermore, the low glass transition temperature of Polymer A with a low weight-average molecular weight further improves the flexibility of the positive electrode film.

[0098] In some embodiments, the active cathode material is a lithium-containing transition metal oxide, and the active cathode material is optionally lithium iron phosphate, or a doped modification thereof, or at least one of a conductive carbon-coated, a conductive metal-coated, or a conductive polymer-coated modification thereof.

[0099] In conventional lithium iron phosphate systems, the undercoat layer generally uses polyacrylic acid as an adhesive. However, the polarity of polyacrylic acid is significantly different from that of polyvinylidene fluoride, the conventional adhesive used in the positive electrode membrane, resulting in low adhesive strength between the two. Furthermore, the polyacrylic acid in the undercoat layer has poor solubility in the positive electrode slurry solvent, making it impossible to form an effective diffusion connection between the undercoat layer and the positive electrode membrane when the slurry is applied and dried.

[0100] By using the N-methylpyrrolidone (NMP)-wettable polymer A of the present application as an adhesive in the undercoat layer, interdiffusion of the adhesive between the undercoat layer and the positive electrode membrane can be achieved, increasing the adhesive strength, further improving the appearance quality and brittleness of the electrode plate, and improving the adhesive performance of the electrode plate and the cycle performance of the battery.

[0101] 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 membrane. By ensuring that the mass content of the positive electrode active material is within this range, the amount of the positive electrode active material supported can be ensured, and the power performance of the battery can be improved.

[0102] In some embodiments, the weight average molecular weight of the positive electrode film is 7×10 5 ~1×10 6 The mass content of polymer A is 0.4% to 5.5%, and / or the weight average molecular weight of the positive electrode film is 1×10 5 ~2.5×10 5 The mass content of polymer A is 0.05% to 0.5%.

[0103] Weight average molecular weight is 7 x 10 5 ~1×10 6 If polymer A having a weight average molecular weight of 7×10 is added in excess, the power performance and cycle performance of the battery will be reduced. 5 ~1×10 6 Polymer A, which has a weight-average molecular weight of 1×10, can improve the stability and processability of the slurry and the adhesion of the electrode plates, and can also significantly reduce the rate of increase in internal resistance during battery cycling. 5 ~2.5×10 5 If polymer A is added in excess, it will increase the swelling of the electrode plate and affect the room temperature power performance of the battery. 5 ~2.5×10 5 Polymer A further improves the stability and processability of the slurry and the adhesive strength of the electrode plates, and can also significantly reduce the rate of increase in the internal resistance of the battery during cycling.

[0104] 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 methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide; 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, hydroxypropyl acrylate.

[0105] The above materials are readily available and can significantly reduce the manufacturing costs of adhesives.

[0106] In some embodiments, the molar content of structural units derived from cyano group-containing monomers in polymer A 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%, each based on the total molar content of structural units in polymer A.

[0107] By rationally combining structural units derived from monomers containing each group, polymer A can achieve strength, flexibility, adhesive performance, and swelling resistance all at the same time.

[0108] For example, the positive electrode current collector has two surfaces that face each other in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two facing surfaces of the positive electrode current collector.

[0109] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric base layer and a metal layer formed on at least one surface of the polymeric base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0110] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries well known in the art. For example, the positive electrode active material may include at least one of a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and a modified compound of each. However, the present application is not limited to these materials, and other conventional materials usable as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (may be abbreviated as "LiNi") 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (may be abbreviated as "LiNi") 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (may be abbreviated as "LiNi") 0.6 Co 0.2 Mn0.2 O2(NCM 622 (may be abbreviated as "LiNi") 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0111] In some embodiments, the positive electrode membrane layer optionally further comprises a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers, by way of example only.

[0112] In some embodiments, the positive electrode plate can be manufactured by the following method: The components for manufacturing the positive electrode plate, such as the positive electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then applied to a positive electrode current collector, followed by drying, cold pressing, and other processes to obtain the positive electrode plate.

[0113] [Negative electrode] 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 including a negative electrode active material.

[0114] For example, the negative electrode current collector has two surfaces that face each other in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two facing surfaces of the negative electrode current collector.

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

[0116] In some embodiments, the negative electrode active material may be a battery negative electrode active material 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, a silicon-based material, a tin-based material, and lithium titanate. The silicon-based material may be selected from at least one of silicon elemental, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be selected from at least one of tin elemental, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials usable as a battery negative electrode active material may also be used. These negative electrode active materials may be used alone or in combination.

[0117] In some embodiments, the negative electrode membrane layer optionally further comprises an adhesive, which may be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0118] In some embodiments, the negative electrode film layer optionally further comprises a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some embodiments, the negative electrode membrane layer optionally further comprises other auxiliary agents, such as a thickener (eg, sodium carboxymethylcellulose (CMC-Na)).

[0120] In some embodiments, the negative electrode plate can be manufactured by the following method: The components for manufacturing the negative electrode plate, such as the negative electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then applied to a negative electrode current collector, followed by drying, cold pressing, and other processes to obtain the negative electrode plate.

[0121] [Electrolyte] The electrolyte serves to conduct ions between the positive and negative electrodes. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte may be liquid, gel, or all solid.

[0122] In some embodiments, the electrolyte employs an electrolytic solution, the electrolytic solution including an electrolyte salt and a solvent.

[0123] 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.

[0124] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0125] In some embodiments, the electrolyte solution optionally further comprises additives, such as an anode film-forming additive and a cathode film-forming additive, or an additive that can improve some battery performance, such as an additive that improves the overcharge performance of the battery or an additive that improves the high-temperature or low-temperature performance of the battery.

[0126] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any separator with a well-known porous structure having good chemical and mechanical stability may be selected.

[0127] In some embodiments, the separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film, without any particular limitation. When the separator is a multi-layer composite thin film, the materials of the layers may be the same or different, without any particular limitation.

[0128] In some embodiments, the positive and negative electrode plates and separator may be wound or stacked to form an electrode assembly.

[0129] In some embodiments, the secondary battery may include an outer casing, which may be used to package the electrode assembly and electrolyte.

[0130] In some embodiments, the secondary battery may be packaged in a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The secondary battery may also be packaged in a flexible packaging, such as a bag-type flexible packaging. The flexible packaging may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0131] [Secondary battery] In one embodiment of the present application, there is provided a secondary battery, the secondary battery including an electrode assembly and an electrolyte, the electrode assembly including a positive electrode plate, a separator, and a negative electrode plate, the positive electrode plate being manufactured using the positive electrode slurry of any embodiment.

[0132] In some embodiments, the positive and negative electrode plates and separator may be wound or stacked to form an electrode assembly.

[0133] In some embodiments, the secondary battery may include an outer casing, which may be used to package the electrode assembly and electrolyte.

[0134] In some embodiments, the secondary battery may be packaged in a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The secondary battery may also be packaged in a flexible packaging, such as a bag-type flexible packaging. The flexible packaging may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0135] In the present application, there is no particular limitation on the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0136] In some embodiments, referring to FIG. 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 receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided to cover the opening and close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. An electrolyte permeates the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be selected by those skilled in the art according to actual specific needs.

[0137] [Battery module] In some embodiments, the 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, with the specific number being selectable by those skilled in the art based on the application and capacity of the battery module.

[0138] Fig. 5 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fastened with fasteners.

[0139] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0140] [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.

[0141] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 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, and the upper case 2 is provided to cover the lower case 3 and can form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0142] [Power consumption equipment] In one embodiment of the present application, there is provided a power consuming device including at least one of the secondary battery according to any of the embodiments, the battery module according to any of the embodiments, or the battery pack according to any of the embodiments.

[0143] The power consuming device includes at least one of a secondary battery, a battery module, or a battery pack provided by the present application. The secondary battery, the battery module, or the battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile 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 and satellites, energy storage systems, etc.

[0144] The power consumption device may be a secondary battery, a battery module, or a battery pack, depending on the requirements of the use.

[0145] 6 shows an example of a power consumption device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, which may employ a battery pack or a battery module to meet the high power and high energy density requirements of secondary batteries.

[0146] Other example devices may be mobile phones, tablet computers, laptop computers, etc. These devices are generally required to be lightweight and may employ secondary batteries as their power source. [Example]

[0147] Examples of the present application are described below. The examples described below are illustrative and are used only to interpret the present application, and should not be understood as limiting the present application. In the examples, specific techniques or conditions are not specified, but are carried out according to the techniques or conditions described in the literature in the field or the product instructions. Reagents or equipment used without a specified manufacturer are all common products that can be purchased commercially.

[0148] Example 1 1) Preparation of polymer A (polymer A-1) having a weight-average molecular weight of 600,000 to 1,100,000 in the positive electrode film 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 400 mg of calcium sulfate and 80 mg of calcium phosphate were then added. Then, 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on the total monomer molar content) were added. Finally, an aqueous solution of 0.1 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 70 °C and reacted for 5 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70 °C to a constant weight, yielding a white powder. This adhesive was used for electrode plates. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in Polymer A-1 was 6:3:2, and the weight-average molecular weight of the resulting Polymer A-1 was 800,000.

[0149] 2) Manufacturing of positive electrode plates The lithium iron phosphate LFP active material of Example 1, carbon black as a conductive agent, 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 uniformly mix to obtain a positive electrode slurry. The solid content of the slurry was 55%. The positive electrode slurry was then uniformly applied onto a positive electrode current collector, followed by drying, cold pressing, and slitting to obtain a positive electrode plate.

[0150] 3) Manufacturing of negative electrode plates The active material, artificial graphite, the conductive agent, carbon black, the adhesive, styrene butadiene rubber (SBR), and the thickener, sodium carboxymethyl cellulose (CMC), were dissolved in deionized water as a solvent in a weight ratio of 96.2:0.8:0.8:1.2, and the mixture was stirred to form a uniform mixture to produce a negative electrode slurry. The negative electrode slurry was then uniformly applied to a copper foil negative electrode current collector once or multiple times, followed by drying, cold pressing, and slitting to obtain a negative electrode plate.

[0151] 4) Separator A polypropylene membrane serves as the separator.

[0152] 5) Electrolyte production In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3 / 7, LiPF6 lithium salt was dissolved in the organic solvent, and the mixture was stirred uniformly to prepare a 1M LiPF6EC / EMC solution, thereby obtaining the electrolyte.

[0153] 6) Battery manufacturing The positive electrode plate, separator, and negative electrode plate of Example 1 were stacked in this order, with a separator positioned between the positive and negative electrodes to provide isolation, and then wound to obtain a bare cell. Tabs were welded to the bare cell, which was then inserted into an aluminum case and baked at 80°C to remove moisture. An electrolyte was immediately poured into the case and sealed to obtain an uncharged battery. The uncharged battery was then subjected to a series of processes, including standing, hot and cold pressing, chemical formation, shaping, and capacity testing, to obtain the lithium-ion battery product of Example 1.

[0154] In Examples 2 to 9, the proportions of the positive electrode active material and polymer A-1 added were adjusted, and other parameters and steps were the same as those in Example 1. See Table 1 for specific parameters.

[0155] Example 10 Preparation of polymer A (A-2) having a weight average molecular weight of 50,000 to 400,000 in the positive electrode film: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 300 mg of calcium sulfate and 60 mg of calcium phosphate were then added. 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.06 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 46°C and reacted for 2.5 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight to obtain a white powder. This adhesive was used as a dispersant in electrode plate slurries. The molar ratio of structural units derived from acrylonitrile, acrylamide, and methyl acrylate in Polymer A-2 was 5:3:2, and the weight-average molecular weight of Polymer A-2 was 170,000.

[0156] Positive plate manufacturing: The lithium iron phosphate LFP active material, the conductive agent 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, which was then dried, cold-pressed, and slit to obtain a positive electrode plate.

[0157] The other steps and parameters are the same as those in Example 1, and the specific parameters are shown in Table 1.

[0158] In Examples 11 to 16, the total amount of polymer A added was kept the same, and the ratio of polymer A-1 and polymer A-2 added was adjusted. Other parameters and steps were the same as in Example 1. For specific parameters, see Table 1.

[0159] In Examples 17 to 20, the weight average molecular weight of the polymer A-1 was adjusted, and the methods for producing polymers A-1 with different weight average molecular weights were as follows.

[0160] The preparation method for Polymer A-1 in Example 17 was as follows: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 400 mg of calcium sulfate and 80 mg of calcium phosphate were then added. 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.10 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 65°C and reacted for 5 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight, yielding a white powder. This adhesive was 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 was 6:3:2, and the weight average molecular weight of the produced Polymer A-1 was 700,000.

[0161] The preparation method for Polymer A-1 in Example 18 was as follows: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 400 mg of calcium sulfate and 80 mg of calcium phosphate were then added. 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.13 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 75°C and reacted for 6 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight, yielding a white powder. This adhesive was 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 was 6:3:2, and the weight average molecular weight of the produced Polymer A-1 was 1,000,000.

[0162] The preparation method for Polymer A-1 in Example 19 was as follows: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 400 mg of calcium sulfate and 80 mg of calcium phosphate were then added. 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.1 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 65°C and reacted for 4 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight, yielding a white powder. This adhesive was 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 was 6:3:2, and the weight average molecular weight of the produced Polymer A-1 was 600,000.

[0163] The preparation method for Polymer A-1 in Example 20 was as follows: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 400 mg of calcium sulfate and 80 mg of calcium phosphate were then added. 420 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 3.003 mmol of AIBN (0.39% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.18 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 80°C and reacted for 7 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C until a constant weight was obtained, yielding a white powder. This adhesive was 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 was 6:3:2, and the weight average molecular weight of the produced Polymer A-1 was 1.1 million.

[0164] In Examples 21 to 24, the weight average molecular weight of the polymer A-2 was adjusted, and other parameters and steps were the same as those in Example 1. See Table 1 for specific parameters.

[0165] The preparation method for Polymer A-2 in Example 21 was as follows: 0.20 g of a suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 300 mg of calcium sulfate and 60 mg of calcium phosphate were then added. 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.05 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 46°C and reacted for 2.0 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight, yielding a white powder. This adhesive was used as a dispersant in the electrode slurry. The molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in Polymer A-2 was 5:3:2, and the weight average molecular weight of the produced Polymer A-2 was 100,000.

[0166] The preparation method for Polymer A-2 in Example 22 was as follows: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 300 mg of calcium sulfate and 60 mg of calcium phosphate were then added. 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.08 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 50°C and reacted for 3.5 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight, yielding a white powder. This adhesive was used as a dispersant in the electrode slurry. The molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in Polymer A-2 was 5:3:2, and the weight average molecular weight of the produced Polymer A-2 was 250,000.

[0167] The preparation method for Polymer A-2 in Example 23 was as follows: 0.20 g of a suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 300 mg of calcium sulfate and 60 mg of calcium phosphate were then added. 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.03 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 40°C and reacted for 1.5 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C to a constant weight, yielding a white powder. This adhesive was used as a dispersant in the electrode slurry. The molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in Polymer A-2 was 5:3:2, and the weight average molecular weight of the produced Polymer A-2 was 50,000.

[0168] The preparation method for Polymer A-2 in Example 24 was as follows: 0.20 g of the suspending agent was dissolved in 150 ml of deionized water and sprayed with dry nitrogen gas for 30 minutes. 300 mg of calcium sulfate and 60 mg of calcium phosphate were then added. 350 mmol of acrylonitrile, 140 mmol of methyl acrylate, 210 mmol of acrylamide, and 2.25 mmol of AIBN (0.3% based on the total monomer molar content) were then added. Finally, an aqueous solution of 0.10 g of magnesium sulfate dissolved in 50 ml of deionized water was added, and the suspension was heated to 58°C and reacted for 4 hours. Upon completion of the reaction, the suspension was cooled, filtered, washed, and vacuum dried at 70°C until a constant weight was obtained, yielding a white powder. This adhesive was used as a dispersant in the electrode slurry. The molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in Polymer A-2 was 5:3:2, and the weight average molecular weight of the produced Polymer A-2 was 400,000.

[0169] Comparative Example 1 The positive electrode active material, LFP lithium iron phosphate active material, the conductive agent, carbon black, and the adhesive, polyvinylidene fluoride (PVDF), were dissolved in the solvent, N-methylpyrrolidone (NMP), in a weight ratio of 92:4:4, and after thorough stirring and uniform mixing, a positive electrode slurry was obtained. The positive electrode slurry was then applied to a positive electrode current collector, followed by drying, cold pressing, and slitting to obtain a positive electrode plate of Comparative Example 1. The other manufacturing steps were the same as in Example 1.

[0170] The relevant parameters for manufacturing the positive electrodes of Examples 1 to 24 and Comparative Example 1 are as shown in Table 1 below.

[0171] Example 25 Preparation of aqueous soluble polymer A in the primer 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 at 500 rpm, and the mixture was heated to 74±1°C while stirring. 1.2 parts of ammonium sulfate was added, and the mixture was maintained at 75°C and stirred for 6 hours. The temperature was then increased to 80°C and the reaction was continued for 3 hours, yielding an emulsion with a solids content of approximately 20%. This emulsion is used for undercoating. The molar ratio of structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate in Polymer A-3 was 3:1:1, and the weight-average molecular weight of Polymer A-3 was 180,000.

[0172] Preparation of the primer layer: The prepared polymer A-3-containing emulsion and conductive agent were mixed in a 30:70 mass ratio, ensuring that the conductive agent was fully immersed in deionized water. Finally, deionized water was added to achieve a 15% solids content, and the mixture was thoroughly and uniformly stirred to achieve a slurry viscosity of 200-800 MPa. When using gravure coating, the gravure roller had grooves cut into it. During application, the slurry was poured into the grooves (30 μm). After the roller surface separated from the liquid surface, the smooth portions of the slurry were scraped off with a doctor blade. The pressure roller transferred the slurry from the grooves to the substrate surface, resulting in a single-sided coating thickness of approximately 5 μm after drying. The prepared primer-coated aluminum foil was then ready for use.

[0173] The positive electrode plate was manufactured in the same manner 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, and the mixture was stirred to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to a primed aluminum foil, which was then dried, cold-pressed, and slit to obtain a positive electrode plate. The coating produced by the positive electrode slurry was called a positive electrode film, and the surface density of the positive electrode film coating on one side was approximately 20 mg / cm. 2The press density of the positive electrode film on one side is approximately 2.3 g / cm 3 is.

[0174] Other steps of Example 25 are the same as those of Example 12.

[0175] In Examples 26 to 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, and the other steps were the same as in Example 12.

[0176] In Example 30, the positive electrode plate was prepared by 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, and stirring to uniformly mix them to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to the prepared undercoated aluminum foil, followed by drying, cold pressing, and slitting to obtain a positive electrode plate; the other steps were the same as those in Example 12.

[0177] In Comparative Example 2, no undercoat layer was provided, and the positive electrode plate was the same as in Example 25. In Comparative Example 3, the undercoat layer was a polyacrylic acid (PAA) undercoat layer, and the positive electrode plate was the same as in Comparative Example 2. The PAA undercoat layer was manufactured as follows: The PAA-containing aqueous emulsion manufactured had a solids content of approximately 20%. The emulsion and conductive agent were mixed in a 50:50 mass ratio so that the conductive agent was fully immersed in deionized water. Finally, deionized water was added to the slurry so that the solids content was 15%. The mixture was thoroughly and uniformly stirred, resulting in a slurry with a shipping viscosity of 200-800 MPa. When gravure coating was used, the gravure roller had grooves engraved on it. During coating, the slurry was poured into the grooves (30 μm). After the roller surface separated from the liquid surface, the slurry on the smooth areas was scraped off with a doctor blade. The slurry in the grooves was transferred to the substrate surface by the action of a pressure roller, resulting in a single-sided coating thickness of approximately 5 μm after drying. The manufactured undercoated aluminum foil was then ready for use.

[0178] The relevant parameters for the production of Examples 25 to 30 and Comparative Examples 2 and 3 are as shown in Table 2 below.

[0179] In addition, performance tests were conducted on the polymers, electrodes, and batteries obtained in Examples 1 to 24 and Comparative Example 1, and the test results are shown in Table 1. Performance tests were conducted on the polymers, electrodes, and batteries obtained in Examples 25 to 30 and Comparative Examples 2 and 3, and the test results are shown in Table 2. The test methods were as follows.

[0180] 1. Polymer structural unit type test - infrared spectroscopy test In the tablet press transmission method, the sample was pressed into a KBr tablet, and the KBr background blank was removed by the transmission method to obtain the sample test spectrum. The instrument model was Nicolet 5700 (Thermo Nicolet, USA). The standard linearity was better than 0.07%, and the resolution was 0.09 cm. -1 and the wavenumber range is 400 to 4000 cm -1 and sensitivity <9.65*10 -5 Abls. Used to detect molecular structure and chemical bonds.

[0181] 2. Weight average molecular weight test A Waters 2695 Isocratic HPLC gel chromatography system (differential refractive index detector 2141) was used. A 3.0% mass fraction polystyrene solution sample was used as the reference, and a matching chromatography column (oil-based: Styragel HT5 DMF 7.8*300mm + Styragel HT4) was selected. A 3.0% adhesive colloid solution was prepared using purified N-methylpyrrolidone (NMP) solvent. The prepared solution was allowed to stand for one day before use. During the test, tetrahydrofuran was first drawn into the syringe and flushed several times. Then, 5 ml of the experimental solution was drawn into the syringe, removing any air in the syringe and allowing the needle tip to dry. Finally, the sample solution was slowly injected into the sample inlet. After the test was completed, a flow graph, molecular weight distribution graph, and molecular weight statistics were output.

[0182] 3. Slurry viscosity test Select an appropriate rotor, fix the viscometer, place the positive electrode slurry under the viscometer so that the slurry is just submerged under the rotor graduations, the model number of the instrument is Shanghai Fangrui NDJ-5S, the rotor is 63# (2000-10000mPa.s), 64# (10000-50000mPa.s), the rotation speed is 12 r / min, the test temperature is 25°C, the test time is 5 min, and the data is read after the displayed value stabilizes.

[0183] 4. Slurry filtration performance test A 500 ml beaker is placed on the bottom of a 200 mesh screen support, and 500 ml of slurry is taken and placed on the screen to filter. The time it takes for the volume of the slurry in the beaker to reach 300 ml is recorded and used to judge the filtration performance of the slurry. If the filtration time is less than 120 seconds, it indicates that the filtration performance of the slurry is OK. If the slurry cannot pass through the screen, it indicates that the filtration performance of the slurry is poor and is judged as "NG".

[0184] 5. Slurry fluidity test: An appropriate amount of positive electrode slurry was taken with a spoon and observed to see if it flowed naturally. If it flowed naturally, it was judged as OK. If the fluidity was poor and the slurry solidified into a jelly-like substance, this indicated the formation of gel and was judged as NG.

[0185] 6. Appearance test of electrode plates: After the production 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 cracks, whether there was particle aggregation, etc. If none of the above phenomena were present, it was recorded as OK, and if any of the phenomena were present, it was recorded.

[0186] 7. Adhesion test: The positive electrode plate in this example was cut into a test specimen measuring 20*100 mm for use. The test method was as shown in Figure 7. Double-sided tape 7 was attached to one side of electrode plate 6 and pressed with a pressure roller to ensure complete adhesion to the electrode plate. The other side of double-sided tape 7 was attached to the surface of steel plate 8. One end of current collector 61 was bent in the opposite direction to a bending angle of 180°, as shown by the arrow in Figure 7. The test was carried out using a high-strength tensile test machine. One end of steel plate 8 was fixed to the lower fixture of the tensile test machine, and the curved end of current collector 61 was fixed to the upper fixture. The angle of the current collector was adjusted so that the upper and lower ends were vertical. The specimen was then pulled at a speed of 50 mm / min until the entire current collector 61 was peeled off from the coating 62 on the surface of current collector 61. The displacement and applied force during the process were recorded, and the force when the forces were balanced was taken as the adhesive strength of electrode plate 6.

[0187] 8. Plate brittleness test The positive electrode plate in the example was cut into a test sample measuring 20 x 100 mm and prepared for use. The electrode plate was folded in half and fixed, and then rotated once using a 2 kg roller to check whether there was any metal leakage by passing light through the folded portion of the electrode plate. If there was no metal leakage by passing light through the folded portion of the electrode plate, the electrode plate was turned over, folded in half, fixed, and rotated once using a 2 kg roller to check whether there was any metal leakage by passing light through the folded portion of the electrode plate. The above steps were repeated until there was any metal leakage by passing light through the folded portion of the electrode plate.

[0188] 9. Battery DC Impedance Test The DC impedance test process for the battery is as follows: At 25°C, the battery in the example or comparative example was charged at a constant current of 1 / 3 C to 3.65 V, then charged at a constant voltage of 0.05 C at 3.65 V, and left for 5 minutes, after which the voltage V1 was recorded. The battery was then discharged at 1 / 3 C for 30 seconds, and the voltage V2 was recorded. The internal resistance DCR1 of the battery after the first cycle was calculated using the formula 3*(V2-V1) / C. The above steps were repeated for the same battery, and the internal resistance DCR of the battery after the nth cycle was calculated. n(n=1, 2, 3……100) were recorded and the above DCR1, DCR2, DCR3……DCR 100 The values ​​of the 100 points are taken as the ordinate and the corresponding number of cycles as the abscissa, and a graph of the battery discharge DCR and number of cycles corresponding to the positive electrode active material is obtained.

[0189] In this test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and so on until the 100th cycle corresponds to n=100. 500 -DCR1) / DCR1*100%, and the test process of Comparative Example 1 and other Examples is the same as above.

[0190] 10. Battery cycle test The cycle number of the battery was obtained from the capacity test. The test process is as follows: At 25°C, the battery corresponding to Example 1 was charged at a constant current of 1 / 3 C to 3.65 V, then charged at a constant voltage of 0.05 C at 3.65 V, left for 5 minutes, and then discharged at 1 / 3 C to 2.5 V. The obtained initial capacity was denoted as C0, and the cutoff condition P n ≦70%C0. The above steps are repeated for the same battery, and the discharge capacity C of the battery after the nth cycle is n When recording the battery capacity retention rate P after each cycle n =C n / C0*100%, P1, P2……P n The values ​​of the n points are taken as the ordinate and the corresponding number of cycles as the abscissa, and a graph of the corresponding battery capacity retention rate and number of cycles is obtained. n If <70% C0, the test was stopped and the number of cycles was recorded.

[0191] [Table 1] TIFF0007734759000002.tif248168TIFF0007734759000003.tif248168TIFF0007734759000004.tif248168

[0192] [Table 2]

[0193] As can be seen from the above results, the positive electrode slurry in Comparative Example 1 used PVDF as an adhesive, and the positive electrode active material in the positive electrode slurry was prone to agglomeration. 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.

[0194] Examples 1 to 24 provide positive electrode slurries containing a positive electrode active material, a conductive agent, and an adhesive, and the adhesive contains Polymer A, which contains structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate. As can be seen from comparing Example 5 with Comparative Example 1, Polymer A exerts a good effect as an adhesive in the positive electrode slurry, improves the stability and processability of the positive electrode slurry, and enhances the adhesive performance of the electrode plate.

[0195] In Examples 1 to 18 and 21 to 24, the adhesive contains polymer A-1 having a weight-average molecular weight of 700,000 to 1,000,000. Compared with polymer A-1 having a weight-average molecular weight of 600,000 or 1,100,000 in Examples 19 and 20, it exhibits better effects in all cases, improving the stability and processability of the positive electrode slurry, improving the adhesive performance of the electrode plate, and further reducing the rate of increase in internal resistance during cycling of the battery.

[0196] In Examples 10 to 24, the adhesive further contained a polymer A-2 having a weight-average molecular weight of 100,000 to 250,000. Compared to Example 5, polymer A-2 had 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 adhesive performance of the electrode plates, and reduced the rate of increase in internal resistance during cycling of the battery.

[0197] In Examples 2 to 8 and 10 to 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 adhesive performance of the electrode plates, and significantly reduced the rate of increase in internal resistance during cycling of the battery.

[0198] 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, improves the adhesive performance of the electrode plate, and significantly reduces the rate of increase in internal resistance during cycling of the battery.

[0199] Examples 25 to 30 provide positive electrode plates comprising 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. The undercoat layer contains a polymer A-3 soluble in an aqueous solvent, the polymer A-3 containing structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate. By providing this undercoat layer, the appearance quality and brittleness of the electrode plates were improved compared to Comparative Examples 2 and 3, and the adhesion performance of the electrode plates and the cycle performance of the battery were significantly improved.

[0200] In Examples 25 to 30, the mass content of polymer A-3 in the undercoat layer was 5% to 40% based on the total mass of the undercoat layer. Compared with Comparative Examples 2 and 3, the appearance quality and brittleness of the electrode plates in these Examples were improved, and the adhesive performance of the electrode plates and the cycle performance of the battery were also improved. When the mass content of polymer A-3 in the undercoat layer was 5% to 30% or 5% to 20% based on the total mass of the undercoat layer, the cycle performance of the battery was significantly improved.

[0201] In Examples 25 to 30, the positive electrode membrane contains a positive electrode active material, an adhesive, and a conductive agent, the adhesive contains polymer A-1 and polymer A-2, and polymer A-1 and polymer A-2 contain structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate.

[0202] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and provides similar functions and effects within the scope of the technical solution of the present application is also within the technical scope of the present application. Furthermore, various modifications that a person skilled in the art may make to the embodiments without departing from the spirit of the present application, and other forms constructed by combining some of the components of the embodiments are also within the scope of the present application. [Explanation of symbols]

[0203] 1 battery pack 2 Upper case 3 Lower case 4 Battery Module 5 Secondary battery 51 Case 52 Electrode Assembly 53 Top cover assembly 6 plate 61 Current collector 62 Coating on current collector 7 double-sided tape 8 steel plate

Claims

1. A positive electrode slurry comprising a positive electrode active material, a conductive agent, and an adhesive, wherein the adhesive comprises polymer A-1 and polymer A-2 each comprising 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, and the adhesive comprises polymer A-1 having a weight-average molecular weight of 7×10 5 to 1×10 6 and polymer A-2 having a weight-average molecular weight of 1×10 5 to 2.5×10 5 .

2. The weight average molecular weight is 7×10 based on the total mass of the positive electrode active material, the conductive agent, and the adhesive. ５ ~1 x 10 ６ 2. The positive electrode slurry according to claim 1, wherein the mass content of the polymer A-1 is 0.4% to 5.5%.

3. The weight average molecular weight is 1×10 based on the total mass of the positive electrode active material, the conductive agent, and the adhesive. ５ ~2.5 x 10 ５ 2. The positive electrode slurry according to claim 1, wherein the mass content of the polymer A-2 is 0.05% to 0.5%.

4. 2. The positive electrode slurry according to claim 1, wherein the cyano group-containing monomer is selected from one or more of acrylonitrile and butenenitrile.

5. 2. The positive electrode slurry of claim 1, wherein the amide group-containing monomer is selected from one or more of 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.

6. 2. The positive electrode slurry of claim 1, wherein 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.

7. 2. The positive electrode slurry according to claim 1, wherein, based on the total molar content of structural units in the polymers A-1 and A-2, the molar content of structural units derived from cyano group-containing monomers in the polymers A-1 and A-2 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%.

8. 2. The positive electrode slurry according to claim 1, wherein the positive electrode active material is at least one of lithium iron phosphate, a doped modification thereof, a conductive carbon-coated modification thereof, a conductive metal-coated modification thereof, a conductive polymer-coated modification thereof, or a mixture thereof with another lithium-containing transition metal oxide.

9. 2. The positive electrode slurry according to claim 1, wherein a mass content of the positive electrode active material is 70% to 99.5% based on a total mass of the positive electrode active material, the conductive agent, and the adhesive.

10. 2. The positive electrode slurry of claim 1, wherein the conductive agent is selected from one or more of acetylene black, carbon black, ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

11. 2. The positive electrode slurry according to claim 1, wherein the mass content of the conductive agent is 0.2% to 6.0% based on the total mass of the positive electrode active material, the conductive agent, and the adhesive.

12. A secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode plate manufactured using the positive electrode slurry of claim 1, a separator, and a negative electrode plate.

13. A battery module comprising the secondary battery according to claim 12.

14. A battery pack comprising the battery module according to claim 13.

15. A power consumption device, comprising at least one selected from the group consisting of the secondary battery according to claim 12, the battery module according to claim 13, and the battery pack according to claim 14.

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