Positive electrode slurry, secondary battery, battery module, battery pack, and electric device

Abstract

The application provides a positive electrode slurry, a secondary battery, a battery module, a battery pack, and a power utilization device. The positive electrode slurry contains a positive electrode active material, a conductive agent, and a binder, and the binder contains a polymer A, the polymer A contains a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structural unit derived from a monomer containing an ester group. By using the polymer A as the binder of the positive electrode slurry, the stability and processability of the positive electrode slurry are improved, and the adhesion of the positive electrode plate is improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a positive electrode slurry, a secondary battery, a battery module, a battery pack, and an electrical device. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the widespread use of lithium-ion batteries, higher requirements have been placed on their performance and cost.

[0003] The existing traditional binder PVDF is a commonly used binder, but it has problems such as poor compatibility with electrode active materials and weak bonding strength. As a result, the positive electrode slurry using it as a binder has poor stability and high difficulty in coating process. Therefore, it is urgent to develop a new binder and positive electrode slurry. Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode slurry with strong stability, good processability and strong binding force.

[0005] The first aspect of the present application provides a positive electrode slurry comprising a positive electrode active material, a conductive agent and a binder, the binder comprising a polymer A, the polymer A comprising a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group and a structural unit derived from a monomer containing an ester group.

[0006] The present application improves the stability and processability of the positive electrode slurry and enhances the bonding strength of the positive electrode sheet by using a polymer A comprising structural units derived from a monomer containing a cyano group, structural units derived from a monomer containing an amide group, and structural units derived from a monomer containing an ester group as a binder in the positive electrode slurry.

[0007] Polymer A is rich in polar groups, such as cyano groups located in the main chain segment of polymer A. Due to the dipole interaction between the cyano groups and the electronegativity of the positive electrode current collector, polymer A has strong adhesion to the current collector, which improves the bonding strength of the electrode and avoids processing anomalies such as demolding and powder loss during the coating or cold pressing process of the electrode. In addition, the ester functional group has a certain ability to absorb and retain electrolytes, which can improve the poor ionic conductivity of the traditional binder pure polyvinylidene fluoride. Furthermore, the rich groups on polymer A can improve the compatibility of polymer A with various positive electrode active materials and improve the versatility of polymer A as a binder.

[0008] In any embodiment, the binder comprises a weight average molecular weight of 7×105 ~1×10 6 Controlling the weight average molecular weight of polymer A can improve the stability, processability and adhesion of the positive electrode slurry and further reduce the cycle internal resistance growth rate of the battery.

[0009] In any embodiment, the binder further comprises a 5 ~2.5×10 5 The weight average molecular weight of polymer A is 1×10 5 ~2.5×10 5 The polymer A acts as a dispersant in the positive electrode slurry. Its addition further improves the stability and processability of the slurry, the adhesion of the pole pieces, and reduces the cycle internal resistance growth rate of the battery.

[0010] In any embodiment, the weight average molecular weight is 7×10 5 ~1×10 6 The mass content of polymer A is 0.4%-5.5%, based on the total mass of the positive electrode active material, the conductive agent and the binder. The weight average molecular weight within this mass content range is 7×10 5 ~1×10 6 Polymer A can improve the stability, processability and adhesion of the slurry, while significantly reducing the growth rate of the battery's cycle internal resistance.

[0011] In any embodiment, the weight average molecular weight is 1×10 5 ~2.5×10 5 The mass content of polymer A is 0.05%-0.5%, based on the total mass of the positive electrode active material, the conductive agent and the binder. The weight average molecular weight within this mass content range is 1×10 5 ~2.5×10 5 Polymer A can further improve the stability, processability and adhesion of the slurry, while significantly reducing the growth rate of the battery's cycle internal resistance.

[0012] In any embodiment, the monomer containing a cyano group is selected from one or more of acrylonitrile and crotononitrile.

[0013] In any embodiment, the monomer containing an amide group 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.

[0014] In any embodiment, the monomer containing an ester group 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.

[0015] The above materials are simple and easy to obtain, and can significantly reduce the manufacturing cost of the adhesive.

[0016] In any embodiment, the molar content of the structural units derived from the monomer containing a cyano group in polymer A is 50% to 60%, the molar content of the structural units derived from the monomer containing an ester group is 10% to 20%, and the molar content of the structural units derived from the monomer containing an amide group is 20% to 30%, based on the total molar content of the structural units in polymer A.

[0017] In any embodiment, the positive electrode active material is a lithium-containing transition metal oxide, which can be selected from lithium iron phosphate, or their doped modified materials, or their conductive carbon-coated modified materials, conductive metal-coated modified materials, conductive polymer-coated modified materials, or at least one of their mixtures with other lithium-containing transition metal oxides.

[0018] Polymer A contains groups with good affinity for highly graphitized carbon materials, such as N-containing groups (cyano groups, amide groups, etc.) and oxygen-containing groups (ester groups, amide groups, etc.), which can effectively improve the wettability of lithium iron phosphate powder in solvents (such as N-methylpyrrolidone), thereby improving the stability and processing performance of the positive electrode slurry.

[0019] In any embodiment, the mass content of the positive electrode active material is 70% to 99.5%, optionally 88.0% to 99.5%, based on the total mass of the positive electrode active material, the conductive agent, and the binder.

[0020] In any embodiment, the conductive agent is selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

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

[0022] In a second aspect of the present application, a secondary battery is provided, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a separator and a negative electrode sheet, and the positive electrode sheet is prepared from the positive electrode slurry of the first aspect of the present application.

[0023] In a third aspect of the present application, a battery module is provided, comprising the secondary battery according to the second aspect of the present application.

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

[0025] In a fifth aspect of the present application, an electrical device is provided, comprising at least one of the secondary battery of the second aspect, the battery module of the third aspect, or the battery pack of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a secondary battery according to one embodiment of the present application.

[0027] Figure 2 yes Figure 1 FIG. 1 is an exploded view of a secondary battery according to an embodiment of the present application.

[0028] Figure 3 Schematic diagram of a battery module according to one embodiment of the present application.

[0029] Figure 4 Schematic diagram of a battery pack according to one embodiment of the present application.

[0030] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0031] Figure 6 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0032] Figure 7 Schematic diagram of the electrode adhesion test.

[0033] Description of reference numerals:

[0034] 1 Battery pack; 2 Upper case; 3 Lower case; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 6 Pole sheet; 61 Current collector; 62 Coating on current collector; 7 Double-sided tape; 8 Steel plate. DETAILED DESCRIPTION

[0035] Below, the embodiments of the binder, preparation method, electrode, battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, 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.

[0036] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating 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.

[0040] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0041] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0042] Lithium iron phosphate (LiFePO4) cathode active materials have attracted widespread attention in the industry due to their low cost, high performance, and safety. However, LiFePO4 cathode active materials have the characteristics of large specific surface area, small particle size, high carbon content after carbon coating, and high degree of graphitization. As a result, slurries using LiFePO4 as the cathode active material and the traditional binder PVDF as the binder have poor dispersibility, easy precipitation, high viscosity, and low solid content. Consequently, the electrode surfaces prepared with LiFePO4 are prone to defects such as cracking, film release, particle scratches, and pinholes. Furthermore, the distribution of the cathode active material in the electrode is uneven, and the electrode quality is uneven.

[0043] [Cathode slurry]

[0044] Based on this, the present application proposes a positive electrode slurry for a battery, comprising a positive electrode active material, a conductive agent and a binder, the binder comprising a polymer A, and the polymer A comprising a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structural unit derived from a monomer containing an ester group.

[0045] As used herein, the term "binder" refers to a chemical compound, polymer, or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.

[0046] As used herein, the term "polymer" includes, on the one hand, a collection of chemically homogeneous macromolecules prepared by polymerization, but differing in degree of polymerization, molar mass, and chain length. The term also includes derivatives of such a collection of macromolecules formed by polymerization, i.e., compounds or mixtures that can be obtained by reaction, for example, addition or substitution, of functional groups in the aforementioned macromolecules and that can be chemically homogeneous or chemically heterogeneous.

[0047] Herein, the term "positive electrode" also refers to the "cathode" in a secondary battery.

[0048] As used herein, the term "cyano group" refers to a -CN group.

[0049] As used herein, the term "amide group" refers to a -CONH group.

[0050] In this context, the term "ester group" refers to a -COOR1 group, wherein R1 is selected from C 1-9 alkyl.

[0051] In the present invention, the substituents in the term "substituted by a substituent" are each independently selected from: hydroxyl, thiol, amino, cyano, nitro, aldehyde, halogen atom, alkenyl, alkynyl, aryl, heteroaryl, C 1-6 Alkyl, C 1-6 Alkoxy.

[0052] In this article, the term “C 1-6 "Alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from one to five carbon atoms, and attached to the remainder of the molecule by a single bond. 1-9 "Alkyl" should be interpreted accordingly. C 1-6 Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, and pentyl.

[0053] Herein, the term "polymer A" refers to a polymer comprising a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structural unit derived from a monomer containing an ester group.

[0054] In some embodiments, polymer A is soluble in an oily solvent. In some embodiments, polymer A is soluble in an aqueous solvent. Examples of oily 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. It will be appreciated that the structural units in polymer A can be formulated in any proportion, polymer A can have different molecular weights, and polymer A can be prepared using various methods, such as suspension methods and emulsion methods.

[0055] In some embodiments, the positive electrode slurry comprises a dispersion medium. In some embodiments, the dispersion medium of the positive electrode slurry is an oily solvent. In some embodiments, the dispersion medium of the positive electrode slurry is an aqueous solvent.

[0056] In some embodiments, the binder is used to bind the positive active material and / or the conductive agent together to form a slurry, and can fix them in a suitable position and adhere them to a conductive metal component to form a positive electrode.

[0057] 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, and acrylonitrile-acrylamide-isooctyl acrylate copolymer.

[0058] The present application improves the stability and processability of the positive electrode slurry and enhances the bonding strength of the positive electrode sheet by using a polymer comprising structural units derived from a monomer containing a cyano group, structural units derived from a monomer containing an amide group, and structural units derived from a monomer containing an ester group as a binder in the positive electrode slurry.

[0059] Polymer A is rich in polar groups, such as cyano groups located in the main chain segment of polymer A. Due to the dipole interaction between the cyano groups and the electronegativity of the positive electrode current collector, polymer A has strong adhesion to the current collector, which improves the bonding strength of the electrode and avoids processing anomalies such as demolding and powder loss during the coating or cold pressing process of the electrode. In addition, the ester-containing functional groups in polymer A have a certain ability to absorb and retain electrolytes, which can improve the poor ionic conductivity of the traditional binder pure polyvinylidene fluoride. Furthermore, the rich groups on polymer A can improve the compatibility of polymer A with various positive electrode active materials and improve the versatility of polymer A as a binder.

[0060] In some embodiments, the binder comprises a weight average molecular weight of 7×10 5 ~1×10 6 In some embodiments, the weight average molecular weight of polymer A can be 7×10 5 ~9.5×10 5 , or 7×10 5 ~9×10 5 , or 7×10 5 ~8.5×10 5 , or 7×10 5 ~8×10 5 , or 7.5×10 5 ~1×10 6 , or 8×10 5 ~1×10 6 , or 8.5×10 5 ~1×10 6 , or 9×10 5 ~1×10 6 , or 9.5×10 5 ~1×10 6 .

[0061] As used herein, the term "weight average molecular weight" refers to the sum of the weight fractions of molecules of different molecular weights in a polymer multiplied by their corresponding molecular weights.

[0062] Controlling the weight-average molecular weight of polymer A can further reduce the cycle internal resistance growth rate of the battery while improving the stability and processability of the positive electrode slurry and the bonding strength of the positive electrode sheet.

[0063] In some embodiments, the binder further comprises a 5 ~2.5×10 5 In some embodiments, the weight average molecular weight of polymer A can be 1.5×10 5 ~2.5×10 5 , or 2×10 5 ~2.5×10 5 , or 1×10 5 ~2×10 5 , or 1×10 5 ~1.5×10 5 .

[0064] Some positive electrode active materials (such as lithium iron phosphate LFP) have a large specific surface area and a large number of small particles, which makes the slurry easily agglomerated during the preparation process, thereby causing the filter to clog. By using polymer A with a low weight-average molecular weight in the slurry, its electrostatic repulsion or steric hindrance can be used to avoid agglomeration between positive electrode active materials (such as lithium iron phosphate LFP powder particles); at the same time, it can disperse and suspend other small molecules in the slurry, so that the slurry does not settle after being placed for a short time and its stability is increased. In addition, polymer A with a low weight-average molecular weight has a low glass transition temperature, which can improve the flexibility of the electrode.

[0065] The weight average molecular weight is 1×10 5 ~2.5×10 5 The polymer A acts as a dispersant in the positive electrode slurry. Its addition further improves the stability and processability of the slurry, the adhesion of the pole pieces, and reduces the cycle internal resistance growth rate of the battery.

[0066] In some embodiments, the weight average molecular weight is 7×10 5 ~1×10 6 The mass content of polymer A is 0.4%-5.5%, based on the total mass of the positive electrode active material, the conductive agent and the binder. 5 ~1×10 6 Adding too much polymer A will reduce the power performance and cycle performance of the battery. 5 ~1×10 6 Polymer A can improve the stability and processability of the slurry and the adhesion of the electrode, while significantly reducing the growth rate of the battery's cycle internal resistance.

[0067] In some embodiments, the weight average molecular weight is 1×10 5 ~2.5×10 5The mass content of polymer A is 0.05%-0.5%, based on the total mass of the positive electrode active material, the conductive agent and the binder.

[0068] If the weight average molecular weight is 1×10 5 ~2.5×10 5 Adding too much polymer A will increase the swelling of the electrode and affect the room temperature power performance of the battery. The weight average molecular weight within this mass content range is 1×10 5 ~2.5×10 5 Polymer A can further improve the stability and processability of the slurry and the adhesion of the electrode, while significantly reducing the growth rate of the battery's cycle internal resistance.

[0069] In some embodiments, the monomer containing a cyano group is selected from one or more of acrylonitrile and crotononitrile.

[0070] In some embodiments, the monomer containing an amide group 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.

[0071] In some embodiments, the monomer containing an ester group 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.

[0072] The above materials are simple and easy to obtain, and can greatly reduce the manufacturing cost of the adhesive.

[0073] In some embodiments, the molar content of structural units derived from monomers containing cyano groups in polymer A is 50% to 70%, the molar content of structural units derived from monomers containing ester groups is 10% to 30%, and the molar content of structural units derived from monomers containing amide groups is 10% to 30%, based on the total molar content of structural units in polymer A.

[0074] The rational combination of structural units derived from monomers containing various groups can take into account the strength, flexibility, bonding properties and anti-swelling properties of polymer A, so that the electrode has excellent bonding force and processing performance.

[0075] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide, which can be lithium iron phosphate, or their doped modified materials, or their conductive carbon coated modified materials, conductive metal coated modified materials or conductive polymer coated modified materials.

[0076] The lithium iron phosphate positive electrode active material has a microporous structure, and its surface graphitization degree is high after carbon coating. The above structural characteristics lead to its poor wettability in slurry solvents (such as N-methylpyrrolidone NMP), which in turn makes the slurry poorly stable, low in solid content, and easy to fall off after being placed, making it impossible to use normally. Polymer A contains groups with good affinity for carbon materials with high graphitization degree, such as N-containing groups (cyano groups, amide groups) and oxygen-containing groups (ester groups, amide groups), thereby effectively improving the wettability of lithium iron phosphate powder in solvents (such as NMP), thereby improving the stability and processing performance of the positive electrode slurry.

[0077] In some embodiments, the mass content of the positive electrode active material is 70% to 99.5%, optionally 88.0% to 99.5%, based on the total mass of the positive electrode active material, conductive agent, and binder. Within this range, the mass content of the positive electrode active material can ensure the loading of the positive electrode active material and improve the power performance of the battery.

[0078] In some embodiments, the conductive agent is selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] In some embodiments, the mass content of the conductive agent is 0.2%-6.0%, based on the total mass of the positive electrode active material, the conductive agent, and the binder.

[0080] [Positive electrode]

[0081] In one embodiment of the present application, a positive electrode sheet is provided, comprising a current collector, a primer layer arranged on at least one surface of the current collector, and a positive electrode membrane arranged on the primer layer, wherein the primer layer comprises a polymer A that can be dissolved in an aqueous solvent, and the polymer A comprises a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structural unit derived from a monomer containing an ester group.

[0082] As used herein, the term "current collector" refers to any conductive substrate capable of conducting current to an electrode during discharge or charge of a secondary battery.

[0083] The term "positive electrode film" refers to the coating formed after the positive electrode slurry is applied and dried.

[0084] Small-particle positive electrode active materials have the advantages of large specific surface area and sufficient reaction with the electrolyte. However, this large specific surface area also brings the disadvantage of poor adhesion to the current collector, resulting in the positive electrode slurry easily peeling off during the coating process. Increasing the amount of binder in the positive electrode slurry will cause the electrode to become brittle during the cold pressing process and reduce the compaction density. Therefore, it is necessary to add a special primer to the current collector to improve the adhesion between the positive electrode film and the current collector.

[0085] Since the polymer A that can be dissolved in an aqueous solvent in the primer layer contains a cyano group, an amide group, and an ester group, it can swell appropriately when it comes into contact with the oily solvent (such as NMP) of the positive electrode slurry during the coating process of the positive electrode slurry, but it will not dissolve. The molecular contact formed by the polymer A in the primer layer and the binder in the positive electrode slurry can achieve mutual diffusion, which can greatly improve the bonding force between the positive electrode diaphragm and the current collector. The ester group in the polymer A can form a strong hydrogen bond with the hydroxyl group in the oxide layer on the surface of the current collector to ensure that the positive electrode diaphragm is firmly attached to the current collector.

[0086] The polymer A being soluble in an aqueous solvent means that the polymer A can be dissolved in the aqueous solvent to form a solution or dispersion, and the solubility of the polymer A in the aqueous solvent is not less than 1 g. Alternatively, the solubility of the polymer A in the aqueous solvent is not less than 10 g.

[0087] In some embodiments, the polymer A soluble in an aqueous solvent in the primer layer is formed by bulk polymerization, suspension polymerization, emulsion polymerization, or solution polymerization. In some embodiments, the polymer A soluble in an aqueous solvent in the primer layer is formed by an emulsion method, which is easy to mass produce, simple, and environmentally friendly.

[0088] In some embodiments, the present application improves the molding quality, adhesion and flexibility of the positive electrode sheet and optimizes the cycle performance of the battery by using polymer A in the bottom coating layer of the positive electrode sheet.

[0089] In some embodiments, the weight average molecular weight of polymer A in the primer layer is 1.5×10 5 ~2×10 5 .

[0090] The appropriate weight-average molecular weight can improve the molding quality of the electrode, take into account the processability and adhesion of the primer layer, and at the same time ensure that the polymer A in the primer layer has a certain diffusivity when the positive electrode slurry is applied.

[0091] In some embodiments, the mass content of polymer A in the primer layer is 5% to 40%, optionally 5% to 30%, optionally 5% to 20%, based on the total mass of the primer layer.

[0092] If the amount of polymer A in the primer layer is too high, the stability of the primer layer and the cycle performance of the battery will be reduced. If the mass of polymer A in the primer layer is within this range, the appearance quality and brittleness of the electrode will be improved, and the bonding performance of the electrode and the cycle performance of the battery will be improved.

[0093] In some embodiments, the primer layer further comprises a conductive agent, and the conductive agent is selected from one or more of carbon black, acetylene black, carbon fiber, graphite, and carbon nanotubes.

[0094] Adding a conductive agent to the base coat can reduce the interface resistance between the positive electrode membrane and the current collector, improve the charge and discharge rate performance of the battery, and extend the cycle life of the battery.

[0095] In some embodiments, the primer layer has a thickness of 1 to 20 μm.

[0096] If the primer layer is too thick, the current collector conductivity will be poor. If the primer layer is too thin, it cannot ensure effective bonding in the electrode. Within this range, the primer layer thickness can balance the bonding performance of the electrode and the power performance and cycle performance of the battery.

[0097] In some embodiments, the coating area density of the positive electrode film is not less than 20 mg / cm 2 .

[0098] As used herein, the term "areal density" is calculated by dividing the mass by the corresponding area.

[0099] By providing the primer layer of the present application in the electrode sheet, it is possible to ensure that a certain content of positive electrode active material is loaded in the positive electrode sheet, thereby ensuring the power performance of the battery.

[0100] In some embodiments, the positive electrode membrane comprises a positive electrode active material, a binder and a conductive agent, the binder comprises a polymer A that can be dissolved in an oily solvent, and the polymer A contains a structural unit derived from a monomer containing a cyano group, a structural unit derived from a monomer containing an amide group, and a structural unit derived from a monomer containing an ester group.

[0101] The polymer A being soluble in an oily solvent means that the polymer A can be dissolved in the oily solvent to form a solution or dispersion, and the solubility of the polymer A in the oily solvent is not less than 1 g. Alternatively, the solubility of the polymer A in the oily solvent is not less than 10 g.

[0102] In the positive electrode membrane, polymer A that can be dissolved in an oily solvent is used as a binder to diffusely connect with polymer A in the primer layer, which can further enhance the bonding force between the primer layer and the positive electrode membrane, improve the appearance quality and brittleness of the electrode, and improve the bonding performance of the electrode and the cycle performance of the battery.

[0103] In any embodiment, the positive electrode film contains a weight average molecular weight of 7×10 5 ~1×10 6 of the polymer A.

[0104] Controlling the weight-average molecular weight of polymer A can improve the bonding strength of the positive electrode sheet while further reducing the cycle internal resistance growth rate of the battery.

[0105] In any embodiment, the positive electrode film further comprises a 5 ~2.5×10 5 of polymer A.

[0106] The weight average molecular weight is 1×10 5 ~2.5×10 5 The polymer A acts as a dispersant in the positive electrode membrane. Its addition can further improve the dispersibility of the positive electrode active material in the positive electrode membrane, so that the prepared electrode has higher adhesion and the battery has a lower cycle internal resistance growth rate.

[0107] Because some positive electrode active materials (such as lithium iron phosphate LFP) have a large specific surface area and a large number of small particles, the slurry that forms the positive electrode membrane is prone to agglomeration during the preparation process, causing the filter to clog. By using polymer A with a low weight-average molecular weight in the slurry for forming the positive electrode membrane, its electrostatic repulsion or steric hindrance can be used to avoid agglomeration between positive electrode active materials (such as lithium iron phosphate LFP powder particles); at the same time, it has the effect of dispersing and suspending other small molecules in the positive electrode membrane, so that the slurry does not settle after being placed for a short time and its stability is increased. In addition, the glass transition temperature of polymer A with a low weight-average molecular weight is low, which can further improve the flexibility of the positive electrode membrane.

[0108] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide, and the positive electrode active material can be selected from lithium iron phosphate, or their doped modified materials, or their conductive carbon-coated modified materials, conductive metal-coated modified materials, or conductive polymer-coated modified materials.

[0109] In traditional lithium iron phosphate systems, polyacrylic acid is often used as a binder for the undercoat layer. However, the polarity of polyacrylic acid is significantly different from that of polyvinylidene fluoride, a traditional binder in positive electrode membranes, resulting in low bonding strength. In addition, 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.

[0110] By using the polymer A provided in this application that can be secondary wetted by N-methylpyrrolidone (NMP) as a binder in the primer layer, mutual diffusion of the primer layer and the binder in the positive electrode membrane can be achieved to increase the adhesion, further improve the appearance quality and brittleness of the electrode, and improve the bonding performance of the electrode and the cycle performance of the battery.

[0111] 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 film. Within this range, the mass content of the positive electrode active material can ensure the loading of the positive electrode active material and improve the power performance of the battery.

[0112] 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%-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%-0.5%, based on the mass of the positive electrode membrane.

[0113] If the weight average molecular weight is 7×10 5 ~1×10 6 Adding too much polymer A will reduce the power performance and cycle performance of the battery. 5 ~1×10 6 The polymer A can improve the stability and processability of the slurry and the adhesion of the electrode, while significantly reducing the cycle internal resistance growth rate of the battery. 5 ~2.5×10 5 Adding too much polymer A will increase the swelling of the electrode and affect the room temperature power performance of the battery. The weight average molecular weight within this mass content range is 1×10 5 ~2.5×10 5 Polymer A can further improve the stability and processability of the slurry and the adhesion of the electrode, while significantly reducing the growth rate of the battery's cycle internal resistance.

[0114] In some embodiments, the monomer containing a cyano group in polymer A is selected from one or more of acrylonitrile and crotononitrile;

[0115] The monomer containing an amide group 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;

[0116] The monomer containing an ester group 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.

[0117] The above materials are simple and easy to obtain, and can greatly reduce the manufacturing cost of the adhesive.

[0118] In some embodiments, the molar content of structural units derived from monomers containing cyano groups in polymer A is 50% to 60%, the molar content of structural units derived from monomers containing ester groups is 10% to 20%, and the molar content of structural units derived from monomers containing amide groups is 20% to 30%, respectively based on the total molar content of structural units in polymer A.

[0119] The rational combination of structural units derived from monomers containing various groups can take into account the strength, flexibility, adhesion and anti-swelling properties of polymer A.

[0120] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0121] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used 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. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0123] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0124] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0125] [Negative electrode]

[0126] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0127] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0128] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0129] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0130] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0131] In some embodiments, the negative electrode film layer may further include 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.

[0132] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0133] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0134] [Electrolytes]

[0135] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0136] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0137] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0138] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0139] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0140] [Isolation film]

[0141] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0142] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0143] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0144] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0145] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0146] [Secondary battery]

[0147] In one embodiment of the present application, a secondary battery is provided, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet is prepared from the positive electrode slurry of any embodiment.

[0148] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0149] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0150] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0151] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 1 The secondary battery 5 is a square structure as an example.

[0152] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0153] [Battery Module]

[0154] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0155] Figure 5 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0156] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0157] [Battery Pack]

[0158] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0159] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0160] [Electrical devices]

[0161] In one embodiment of the present application, an electric device is provided, comprising at least one of a secondary battery according to any embodiment, a battery module according to any embodiment, or a battery pack according to any embodiment.

[0162] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but is not limited thereto.

[0163] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0164] Figure 6 This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0165] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0166] Example

[0167] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0168] Example 1

[0169] 1) Preparation of polymer A (polymer A-1) with a weight average molecular weight of 600,000 to 1.1 million in the positive electrode membrane

[0170] 0.20g of suspending agent is dissolved in 150ml of deionized water, blown with dry nitrogen for 30 minutes, and then 400mg of calcium sulfate and 80mg of calcium phosphate are added. Then 420mmol of acrylonitrile, 140mmol of methyl acrylate, 210mmol of acrylamide, and 3.003mmol of AIBN (based on 0.39% of the total monomer molar content) are added. Finally, 0.1g of an aqueous solution of magnesium sulfate dissolved in 50ml of deionized water is added, the suspension is heated to 70°C, and reacted for 5 hours. At the end of the reaction, the suspension is cooled, the product is filtered and washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for the electrode. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2, and the weight-average molecular weight of the prepared polymer A-1 is 800,000.

[0171] 2) Preparation of positive electrode sheet

[0172] The lithium iron phosphate LFP active material, conductive agent carbon black, and polymer A-1 of Example 1 were dissolved in N-methylpyrrolidone (NMP) solution in a weight ratio of 93:4:3, and stirred to mix evenly to obtain a positive electrode slurry with a solid content of 55%. The positive electrode slurry was then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0173] 3) Preparation of negative electrode sheet

[0174] The active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are dissolved in the solvent deionized water in a weight ratio of 96.2:0.8:0.8:1.2, and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode collector copper foil once or multiple times, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0175] 4) Isolation film

[0176] Polypropylene film is used as the isolation film.

[0177] 5) Preparation of electrolyte

[0178] In an argon atmosphere glove box (H2O < 0.1ppm, O2 < 0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3 / 7, LiPF6 lithium salt was added and dissolved in the organic solvent, and stirred uniformly to prepare a 1MLiPF6EC / EMC solution to obtain an electrolyte.

[0179] 6) Preparation of batteries

[0180] The positive electrode sheet, separator, and negative electrode sheet of Example 1 were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells were then wound to obtain a bare cell. The tabs were welded to the bare cell and placed in an aluminum casing. The cells were then baked at 80°C to remove moisture. The electrolyte was then injected and sealed to obtain an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion battery product of Example 1.

[0181] In Examples 2 to 9, the ratio of the added positive electrode active material and polymer A-1 was adjusted, and other parameters and steps were the same as in Example 1. Specific parameters are shown in Table 1.

[0182] Example 10

[0183] Preparation of polymer A (polymer A-2) with a weight average molecular weight of 50,000 to 400,000 in the positive electrode membrane:

[0184] 0.20g of suspending agent is dissolved in 150ml of deionized water, blown with dry nitrogen for 30 minutes, and then 300mg of calcium sulfate and 60mg of calcium phosphate are added. Then 350mmol of acrylonitrile, 140mmol of methyl acrylate, 210mmol of acrylamide, and 2.25mmol of AIBN (based on 0.3% of the total monomer molar content) are added. Finally, 0.06g of magnesium sulfate aqueous solution dissolved in 50ml of deionized water is added, the suspension is heated to 46°C, and the reaction is carried out for 2.5 hours. At the end of the reaction, the suspension is cooled, the product is filtered and washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for dispersion in the electrode slurry. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2, and the weight-average molecular weight of polymer A-2 is 170,000.

[0185] Preparation of positive electrode:

[0186] The lithium iron phosphate LFP active material, conductive agent carbon black, polymer A-1, and polymer A-2 are dissolved in N-methylpyrrolidone (NMP) solution in a weight ratio of 92:4:3.95:0.05, and stirred to mix evenly to obtain a positive electrode slurry with a solid content of 55%; the positive electrode slurry is then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

[0187] Other steps and parameters are the same as in Example 1, and the specific parameters are shown in Table 1.

[0188] In Examples 11 to 16, the total amount of polymer A added was kept unchanged, and the ratio of polymer A-1 to polymer A-2 added was adjusted. Other parameters and steps were the same as in Example 1. Specific parameters are shown in Table 1.

[0189] In Examples 17 to 20, the weight average molecular weight of polymer A-1 was adjusted. The preparation methods of polymer A-1 with different weight average molecular weights are as follows:

[0190] The preparation method of polymer A-1 in Example 17 is as follows: 0.20g of suspending agent is dissolved in 150ml of deionized water and blown with dry nitrogen for 30 minutes. Then, 400mg of calcium sulfate and 80mg of calcium phosphate are added. Then, 420mmol of acrylonitrile, 140mmol of methyl acrylate, 210mmol of acrylamide, and 3.003mmol of AIBN (0.39% based on the total monomer molar content) are added. Finally, 0.10g of an aqueous solution of magnesium sulfate dissolved in 50ml of deionized water is added. The suspension is heated to 65°C and reacted for 5 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for the electrode. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2. The weight-average molecular weight of the prepared polymer A-1 is 700,000.

[0191] The preparation method of polymer A-1 in Example 18 is as follows: 0.20g of suspending agent is dissolved in 150ml of deionized water and blown with dry nitrogen for 30 minutes. Then, 400mg of calcium sulfate and 80mg of calcium phosphate are added. Then, 420mmol of acrylonitrile, 140mmol of methyl acrylate, 210mmol of acrylamide, and 3.003mmol of AIBN (0.39% based on the total monomer molar content) are added. Finally, 0.13g of an aqueous solution of magnesium sulfate dissolved in 50ml of deionized water is added. The suspension is heated to 75°C and reacted for 6 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for the electrode. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2. The weight-average molecular weight of the prepared polymer A-1 is 1 million.

[0192] The preparation method of polymer A-1 in Example 19 is as follows: 0.20g of suspending agent is dissolved in 150ml of deionized water and blown with dry nitrogen for 30 minutes. 400mg of calcium sulfate and 60mg of calcium phosphate are then added. Then, 420mmol of acrylonitrile, 140mmol of methyl acrylate, 210mmol of acrylamide, and 3.003mmol of AIBN (0.39% based on the total monomer molar content) are added. Finally, 0.1g of an aqueous solution of magnesium sulfate dissolved in 50ml of deionized water is added. The suspension is heated to 65°C and reacted for 4 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for the electrode. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2. The weight-average molecular weight of the prepared polymer A-1 is 600,000.

[0193] The preparation method of polymer A-1 in Example 20 is as follows: 0.20g of suspending agent is dissolved in 150ml of deionized water, blown with dry nitrogen for 30 minutes, and then 400mg of calcium sulfate and 80mg of calcium phosphate are added. Then, 420mmol of acrylonitrile, 140mmol of methyl acrylate, 210mmol of acrylamide, and 3.003mmol of AIBN (0.39% based on the total monomer molar content) are added. Finally, 0.18g of an aqueous solution of magnesium sulfate dissolved in 50ml of deionized water is added. The suspension is heated to 80°C and reacted for 7 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for the electrode. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-1 is 6:3:2. The weight-average molecular weight of the prepared polymer A-1 is 1.1 million.

[0194] In Examples 21 to 24, the weight average molecular weight of polymer A-2 was adjusted, and other parameters and steps were the same as in Example 1. Specific parameters are shown in Table 1.

[0195] The preparation method for polymer A-2 in Example 21 is as follows: 0.20 g of suspending agent is dissolved in 150 ml of deionized water and purged with dry nitrogen for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate are added. Then, 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) are added. Finally, 0.05 g of an aqueous solution of magnesium sulfate dissolved in 50 ml of deionized water is added. The suspension is heated to 46°C and allowed to react for 2 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for dispersion in the electrode slurry. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2. The weight-average molecular weight of the prepared polymer A-2 is 100,000.

[0196] The preparation method for polymer A-2 in Example 22 is as follows: 0.20 g of suspending agent is dissolved in 150 ml of deionized water and purged with dry nitrogen for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate are added. Then, 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) are added. Finally, 0.08 g of an aqueous solution of magnesium sulfate dissolved in 50 ml of deionized water is added. The suspension is heated to 50°C and allowed to react for 3.5 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for dispersion 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 is 5:3:2. The weight-average molecular weight of the prepared polymer A-2 is 250,000.

[0197] The preparation method for polymer A-2 in Example 23 is as follows: 0.20 g of suspending agent is dissolved in 150 ml of deionized water and purged with dry nitrogen for 30 minutes. 300 mg of calcium sulfate and 60 mg of calcium phosphate are then added. Then, 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) are added. Finally, 0.03 g of an aqueous solution of magnesium sulfate dissolved in 50 ml of deionized water is added. The suspension is heated to 40°C and allowed to react for 1.5 hours. At the end of the reaction, the suspension is cooled, filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for dispersion 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 is 5:3:2. The weight-average molecular weight of the prepared polymer A-2 is 50,000.

[0198] The preparation method for polymer A-2 in Example 24 is as follows: 0.20 g of suspending agent is dissolved in 150 ml of deionized water and purged with dry nitrogen for 30 minutes. Then, 300 mg of calcium sulfate and 60 mg of calcium phosphate are added. Then, 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) are added. Finally, 0.10 g of an aqueous solution of magnesium sulfate dissolved in 50 ml of deionized water is added. The suspension is heated to 58°C and allowed to react for 4 hours. At the end of the reaction, the suspension is cooled, the product is filtered, washed, and then vacuum-dried at 70°C to constant weight to obtain a white powder. This binder is used for dispersion in the electrode slurry. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-2 is 5:3:2. The weight-average molecular weight of the prepared polymer A-2 is 400,000.

[0199] Comparative Example 1

[0200] The positive electrode active material, LFP lithium iron phosphate active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were directly dissolved in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 92:4:4, and thoroughly stirred and mixed to obtain a positive electrode slurry. The positive electrode slurry was then evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet of Comparative Example 1. The other preparation steps were the same as those in Example 1.

[0201] The relevant parameters for the positive electrode preparation of the above-mentioned Examples 1 to 24 and Comparative Example 1 are shown in Table 1 below.

[0202] Example 25

[0203] Preparation of polymer A soluble in aqueous solvent in the primer layer (polymer A-3):

[0204] 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 then added. The stirring speed was controlled at 500 rpm and heated to 74±1°C. Then, 1.2 parts of ammonium sulfate was added. The mixture was stirred at 75°C for 6 hours, then the temperature was raised to 80°C and the reaction was continued for 3 hours to obtain an emulsion with a solids content of approximately 20%. This emulsion was used for primer coating. The molar ratio of the structural units derived from acrylonitrile, the structural units derived from acrylamide, and the structural units derived from methyl acrylate in polymer A-3 was 3:1:1. The weight-average molecular weight of polymer A-3 was 180,000.

[0205] Preparation of the primer: The prepared emulsion containing polymer A-3 and the conductive agent are mixed in a mass ratio of 30:70, kneading the mixture until the deionized water completely soaks the conductive agent. Finally, deionized water is added to achieve a slurry with a solids content of 15%. The mixture is thoroughly stirred and the slurry has an outgoing viscosity of 200-800 mPa.s. When using gravure coating, the slurry is injected into the 30 μm pits engraved on the gravure roller during coating. The slurry is scraped off the smooth surface of the roller after it leaves the liquid surface. The slurry in the pits is then transferred to the substrate surface by the pressure roller. After drying, the single-sided coating thickness is approximately 5 μm. The prepared primer-coated aluminum foil is set aside for use.

[0206] The preparation of the positive electrode sheet was the same as in Example 12. Lithium iron phosphate: conductive agent SP: polymer A-1: ​​polymer A-2 were dissolved in N-methylpyrrolidone (NMP) solution at a mass ratio of 92:4:3.8:0.2 and stirred to obtain a positive electrode slurry. The positive electrode slurry was then evenly coated on the prepared aluminum foil with a primer. After drying, cold pressing, and slitting, the positive electrode sheet was obtained. The coating prepared with the positive electrode slurry is called a positive electrode film. The surface density of the coating on one side of the positive electrode film is about 20 mg / cm 2 The compaction density of the single-sided coating of the positive electrode membrane is about 2.3g / cm 3 .

[0207] The other steps of Example 25 are the same as those of Example 12.

[0208] In Examples 26 to 29, the mass ratios of the emulsion containing polymer A-3 and the conductive agent were adjusted to 40:60, 50:50, 60:40, and 70:30, respectively. Other steps were the same as in Example 12.

[0209] In Example 30, the preparation of the positive electrode plate includes dissolving nickel cobalt manganese oxide (NCM), lithium iron phosphate: conductive agent SP: polymer A-1: ​​polymer A-2 in an N-methylpyrrolidone (NMP) solution in a mass ratio of 82:10:4:3.8:0.2, stirring and mixing evenly to obtain a positive electrode slurry; then, the positive electrode slurry is evenly coated on the prepared aluminum foil with a primer, and then dried, cold pressed, and cut to obtain a positive electrode plate. The other steps are the same as Example 12.

[0210] In Comparative Example 2, no primer layer was provided, and the positive electrode sheet was the same as in Example 25;

[0211] The primer layer in Comparative Example 3 is a polyacrylic acid (PAA) primer layer, and the positive electrode is the same as in Comparative Example 2. The PAA primer layer is prepared as follows: an aqueous emulsion containing PAA is prepared, with an emulsion solid content of approximately 20%. The emulsion and conductive agent are in a mass ratio of 50:50. The emulsion is kneaded to completely soak the conductive agent with deionized water. Finally, deionized water is added to achieve a slurry solid content of 15%. The mixture is thoroughly stirred and the slurry has a shipping viscosity of 200-800 mPa.s. When gravure coating is used, pits are engraved on the gravure roller. During coating, the slurry is injected into the pits (30 μm). After the roller surface leaves the liquid surface, the slurry is scraped off with a scraper. Under the action of the pressure roller, the slurry in the pits is transferred to the substrate surface. After drying, the thickness of the single-sided coating is approximately 5 μm. The prepared primer-coated aluminum foil is ready for use.

[0212] The relevant parameters for the preparation of the above-mentioned Examples 25 to 30 and Comparative Examples 2 to 3 are shown in Table 2 below.

[0213] In addition, the polymers, electrodes, and batteries obtained in Examples 1 to 24 and Comparative Example 1 were subjected to performance tests, and the test results are shown in Table 1; the polymers, electrodes, and batteries obtained in Examples 25 to 30 and Comparative Examples 2 to 3 were subjected to performance tests, and the test results are shown in Table 2. The test methods are as follows:

[0214] 1. Polymer structural unit type test - infrared spectrum test

[0215] The sample was pressed into a KBr pellet using the pellet transmission method. The KBr background blank was subtracted 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 , wave number range: 400~4000cm -1 , sensitivity <9.65*10 -5 Abls. Used to examine the structure and chemical bonds of molecules.

[0216] 2. Weight average molecular weight test

[0217] A Waters 2695 Isocratic HPLC gel chromatography instrument (differential refractive index detector 2141) was used. A 3.0% polystyrene solution sample was used as a reference, and a matching chromatographic column was selected (oil-based: Styragel HT5 DMF 7.8*300mm + Styragel HT4). A 3.0% adhesive solution was prepared using purified N-methylpyrrolidone (NMP) solvent. The prepared solution was allowed to stand for one day before use. During testing, tetrahydrofuran was first drawn into a syringe and rinsed several times. Then, 5 ml of the experimental solution was drawn, the air in the syringe was expelled, and the needle tip was wiped dry. Finally, the sample solution was slowly injected into the inlet. After the test was completed, an effluent curve, a molecular weight distribution curve, and molecular weight statistical results were output.

[0218] 3. Slurry viscosity test

[0219] Select a suitable rotor, fix the viscometer, place the positive electrode slurry under the viscometer, and the slurry just submerges the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 63# (2000-10000mPa.s), 64# (10000-50000mPa.s), speed: 12r / min, test temperature: 25℃, test time is 5min, and read the data when the display is stable.

[0220] 4. Slurry filtration performance test

[0221] Take a 500ml beaker and place it at the lower end of the 200-mesh filter holder. Take 500ml of slurry and place it in the filter to filter. Record the time when the volume of the slurry in the beaker reaches 300ml. This time is used to judge the filtration performance of the slurry. If the filtration time is less than 120s, it indicates that the filtration performance of the slurry is OK. If the slurry cannot pass through the filter, it indicates that the filtration performance of the slurry is poor and is judged as "NG".

[0222] 5. Slurry fluidity test:

[0223] Use a spatula to take an appropriate amount of positive electrode slurry and observe whether it flows smoothly. If it flows smoothly, it is judged as OK. If the fluidity is poor, the slurry becomes jelly-like and lumpy, indicating gelation, it is judged as NG.

[0224] 6. Pole appearance test:

[0225] After the positive electrode sheet is prepared, observe the surface condition of the positive electrode sheet, including whether it is flat, whether there are cracks, and whether there are particle agglomerations. If none of the above phenomena exist, record it as OK. If any of the above phenomena exists, record it.

[0226] 7. Adhesion test:

[0227] The positive electrode sheet in the embodiment is cut into test samples with a size of 20*100 mm and set aside. The test method is as follows Figure 7 As shown. Double-sided tape 7 is pasted on one side of the electrode 6 and compacted with a roller to make it completely fit the electrode; the other side of the double-sided tape 7 is pasted on the surface of the steel plate 8, and one end of the current collector 61 is bent in the opposite direction with a bending angle of 180°, as shown. Figure 7 As indicated by the middle arrow; a high-speed rail tensile testing machine is used for testing. One end of the steel plate 8 is fixed to the lower fixture of the tensile testing machine, and the bent end of the current collector 61 is fixed to the upper fixture. The angle of the current collector is adjusted to ensure that the upper and lower ends are in a vertical position. Then, the sample is stretched at a speed of 50 mm / min until the current collector 61 is completely peeled off from the coating 62 on the surface of the current collector 61. The displacement and force during the process are recorded, and the force when the force is balanced is used as the bonding force of the electrode 6.

[0228] 8. Pole brittleness test

[0229] Cut the positive electrode sheet from the example into test specimens measuring 20 x 100 mm and set aside. Bend the sheet in half, secure it, and roll it once with a 2 kg roller to check if the folded section is light-permeable and leaking metal. If not, fold the sheet in half again, secure it, and roll it once with a 2 kg roller to check if the folded section is light-permeable and leaking metal. Repeat this step until light-permeable and metal leaking are confirmed.

[0230] 9. Battery DC impedance test

[0231] The battery DC impedance test process is as follows: At 25°C, charge the battery in the embodiment or comparative example at a constant current of 1 / 3C to 3.65V, then charge at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, record the voltage V1. Then discharge at 1 / 3C for 30 seconds, record the voltage V2, and calculate the internal resistance DCR1 of the battery after the first cycle using the formula 3*(V2-V1) / C. Repeat the above steps for the same battery and simultaneously record the internal resistance DCR of the battery after the nth cycle. n (n=1, 2, 3......100), the above DCR1, DCR2, DCR3......DCR 100 These 100 point values ​​are the vertical coordinates, and the corresponding cycle numbers are the horizontal coordinates, so as to obtain a curve graph of battery discharge DCR and cycle number corresponding to the positive electrode active material.

[0232] During the test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, ..., the 100th cycle corresponds to n=100. In Table 1, the DCR increase rate = (DCR 500 -DCR1) / DCR1*100%, the testing process of Comparative Example 1 and other embodiments is the same as above.

[0233] 10. Battery cycle test

[0234] The number of battery cycles is obtained from the capacity test. The test process is as follows: at 25°C, the battery corresponding to Example 1 is charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, left for 5 minutes, and then discharged at 1 / 3C to 2.5V. The obtained capacity is recorded as the initial capacity C0, and the cut-off condition P n ≤70% C0. Repeat the above steps for the same battery and record the discharge capacity C of the battery after the nth cycle. n , then the battery capacity retention rate P after each cycle n =C n / C0*100%, based on P1, P2...P n The n points are the vertical coordinates, and the corresponding number of cycles is the horizontal coordinate, and the corresponding battery capacity retention rate and cycle number are plotted. n ≤70% C0, stop the test and record the number of cycles.

[0235]

[0236]

[0237]

[0238]

[0239]

[0240] According to the above results, the positive electrode slurry in Comparative Example 1 uses PVDF as a binder, the positive electrode active material in the positive electrode slurry is prone to agglomeration, the stability and processability of the positive electrode slurry are poor, and it is difficult to produce high-quality positive electrode sheets, which in turn increases the internal resistance growth rate after battery cycling.

[0241] Examples 1 to 24 provide a positive electrode slurry comprising a positive electrode active material, a conductive agent, and a binder. The binder comprises polymer A, which comprises structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate. A comparison of Example 5 with Comparative Example 1 demonstrates that polymer A performs well as a binder in the positive electrode slurry, improving the stability and processability of the positive electrode slurry and enhancing the bonding performance of the electrode sheet.

[0242] The binder in Examples 1-18 and 21-24 included polymer A-1 with a weight-average molecular weight of 700,000 to 1,000,000. Compared to the polymer A-1 with a weight-average molecular weight of 600,000 or 1,100,000 in Examples 19 and 20, these achieved superior results, improving the stability and processability of the positive electrode slurry, enhancing the bonding performance of the electrode sheet, and further reducing the cycle internal resistance growth rate of the battery.

[0243] In Examples 10-24, the binder also includes polymer A-2 with a weight-average molecular weight of 100,000 to 250,000. Compared to Example 5, polymer A-2, due to its lower molecular weight, acts as a dispersant in the slurry. The addition of polymer A-2 further improves the slurry's stability and processability, enhances the electrode sheet's bonding performance, and reduces the battery's cycle internal resistance growth rate.

[0244] In Examples 2-8 and 10-24, the mass content of Polymer A-1 was 0.4%-5.5%, based on the combined mass of the positive electrode active material, conductive agent, and binder. Compared to Examples 1 and 9, Polymer A-1 within this range improved slurry stability and processability, enhanced electrode sheet adhesion, and significantly reduced the battery's cycle internal resistance growth rate.

[0245] In Examples 10 to 15, the mass content of polymer A-2 was 0.05% to 0.5%, based on the combined mass of the positive electrode active material, conductive agent, and binder. Compared to Example 16, the addition of polymer A-2 within this range improved the stability and processability of the slurry, enhanced the bonding performance of the electrode sheet, and significantly reduced the cycle internal resistance growth rate of the battery.

[0246] Examples 25-30 provide a positive electrode sheet comprising a current collector, a primer layer disposed on one surface of the current collector, and a positive electrode membrane disposed on the primer layer. The primer layer comprises a polymer A-3 soluble in an aqueous solvent, comprising structural units derived from acrylonitrile, acrylamide, and methyl acrylate. The primer layer improves the appearance and brittleness of the electrode sheet compared to Comparative Examples 2-3, significantly enhancing the electrode sheet's bonding performance and battery cycle performance.

[0247] In Examples 25-30, the mass content of polymer A-3 in the primer layer ranged from 5% to 40% based on the total mass of the primer layer. Compared to Comparative Examples 2-3, the electrode appearance and brittleness of these examples were improved, as were the electrode bonding performance and battery cycling performance. When the mass content of polymer A-3 in the primer layer ranged from 5% to 30% or 5% to 20% based on the total mass of the primer layer, the battery cycling performance was significantly improved.

[0248] In Examples 25 to 30, the positive electrode membrane includes a positive electrode active material, a binder and a conductive agent, the binder includes polymer A-1 and polymer A-2, and polymer A-1 and polymer A-2 include structural units derived from acrylonitrile, structural units derived from acrylamide, and structural units derived from methyl acrylate.

[0249] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical idea and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode plate, characterized in that: The invention comprises a current collector, a primer layer provided on at least one surface of the current collector, and a positive electrode film provided on the primer layer, wherein the positive electrode film comprises a positive electrode active material, a conductive agent and a binder, wherein the binder comprises a conductive agent with a weight average molecular weight of 7×10 5 ~1×10 6 The polymer A has a weight average molecular weight of 1×10 5 ~2.5×10 5 Polymer A, Based on the total mass of the positive electrode active material, the conductive agent and the binder, the weight average molecular weight is 7×10 5 ~1×10 6 The mass content of the polymer A is 0.4%-5.5%, and the weight average molecular weight is 1×10 5 ~2.5×10 5 The mass content of the polymer A is 0.05%-0.5%; The primer layer contains a weight average molecular weight of 1.5×10 5 ~2×10 5 The polymer A, based on the total mass of the primer layer, the mass content of the polymer A in the primer layer is 5%-20%; The polymer A comprises structural units derived from monomers containing cyano groups, structural units derived from monomers containing amide groups, and structural units derived from monomers containing ester groups; the molar content of the structural units derived from monomers containing cyano groups in the polymer A is 50% to 70%, the molar content of the structural units derived from monomers containing ester groups is 10% to 30%, and the molar content of the structural units derived from monomers containing amide groups is 10% to 30%, based on the total molar content of the structural units in the polymer A.

2. The positive electrode sheet according to claim 1, characterized in that: The monomer containing a cyano group is selected from one or more of acrylonitrile and crotononitrile.

3. The positive electrode sheet according to claim 1, characterized in that: The monomer containing an amide group 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.

4. The positive electrode sheet according to claim 1, characterized in that: The monomer containing an ester group 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.

5. The positive electrode sheet according to claim 1, characterized in that: The positive electrode active material is a lithium-containing transition metal oxide.

6. The positive electrode sheet according to claim 1, characterized in that: The positive electrode active material is selected from at least one of lithium iron phosphate, or their doped modified materials, or their conductive carbon coated modified materials, conductive metal coated modified materials, conductive polymer coated modified materials, or their mixtures with other lithium-containing transition metal oxides.

7. The positive electrode sheet according to claim 1, characterized in that: The mass content of the positive electrode active material is 70% to 99.5%, based on the total mass of the positive electrode active material, the conductive agent and the binder.

8. The positive electrode sheet according to claim 1, characterized in that: The mass content of the positive electrode active material is 88.0% to 99.5%, based on the total mass of the positive electrode active material, the conductive agent, and the binder.

9. The positive electrode sheet according to claim 1, characterized in that: The conductive agent is selected from one or more of carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The mass content of the conductive agent is 0.2%-6.0%, based on the total mass of the positive electrode active material, the conductive agent and the binder.

11. A secondary battery, characterized in that: The invention comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a separator, and a negative electrode sheet according to any one of claims 1 to 10.

12. A battery module, characterized in that: The secondary battery according to claim 11 is included.

13. A battery pack, characterized in that: A battery module comprising the battery module according to claim 12.

14. An electrical device, characterized in that: The battery comprises at least one selected from the group consisting of the secondary battery according to claim 11, the battery module according to claim 12, and the battery pack according to claim 13.

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