Preparation method of positive pole piece, positive pole piece, battery monomer, battery and electric device

Abstract

The embodiment of the invention provides a preparation method of a positive pole piece, the positive pole piece, a battery monomer, a battery and a power utilization device. The preparation method of the positive pole piece comprises the following steps: preparing positive slurry which comprises a polyurethane prepolymer; coating at least one side of a positive electrode current collector with the positive electrode slurry; and drying the positive electrode slurry coated on at least one side of the positive electrode current collector to prepare the positive electrode plate. According to the technical scheme provided by the invention, the performance of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for preparing a positive electrode sheet, a positive electrode sheet, a battery cell, a battery and an electrical device. Background Art

[0002] In recent years, the application scope of lithium-ion batteries has become increasingly wide. They are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] As a component of the battery, the performance of the positive electrode sheet is crucial to the performance of the battery. Therefore, how to provide a positive electrode sheet to improve the performance of the battery is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application is made in view of the above-mentioned technical problems, and its purpose is to provide a method for preparing a positive electrode sheet, to prepare a positive electrode sheet with good performance, and to improve the performance of a battery containing the positive electrode sheet.

[0005] In order to achieve the above-mentioned objectives, the embodiments of the present application provide a method for preparing a positive electrode sheet, a positive electrode sheet, a battery cell, a battery and an electrical device.

[0006] In a first aspect, a method for preparing a positive electrode plate is provided, comprising: preparing a positive electrode slurry, wherein the positive electrode slurry comprises a polyurethane prepolymer; coating the positive electrode slurry on at least one side of a positive electrode collector; and drying the positive electrode slurry coated on at least one side of the positive electrode collector to obtain the positive electrode plate.

[0007] In the preparation method of the positive electrode sheet provided in the embodiment of the present application, the positive electrode slurry includes a polyurethane prepolymer, and after the positive electrode slurry is coated on at least one side of the positive electrode current collector, the positive electrode slurry coated on at least one side of the positive electrode current collector is dried. In the process of drying the positive electrode slurry, the polyurethane prepolymer in the positive electrode slurry will be cross-linked and cured to form a polyurethane cross-linked substance with a large molecular weight. The polyurethane cross-linked substance has a cross-linked network structure and a long molecular chain substance. Compared with the general crystalline binder substance, it has good bonding strength and toughness, thereby improving the toughness of the positive electrode sheet and obtaining a positive electrode sheet with good performance. At the same time, polyurethane is conducive to improving the transmission rate of active metal ions (such as lithium ions), thereby improving the internal resistance of the battery and improving the cycle performance of the battery. In the technical solution provided in the embodiment of the present application, the polyurethane prepolymer that has not been cross-linked and cured has a lower viscosity. When added to the positive electrode slurry, the solid content of the polyurethane binder in the positive electrode slurry can be increased, and the positive electrode slurry is easy to disperse during coating, thereby improving the processing efficiency of the positive electrode sheet. In the process of drying the positive electrode slurry coated on at least one side of the positive electrode current collector, the polyurethane prepolymer is cross-linked and cured to form a large molecular weight cross-linked substance with good bonding strength and toughness, which can improve the performance of the positive electrode sheet and thus improve the performance of the battery.

[0008] In a possible implementation, the drying temperature of the positive electrode slurry is in the range of 60°C to 150°C. Optionally, the drying temperature is in the range of 80°C to 140°C.

[0009] The drying temperature of the positive electrode slurry is set within the above range, which is conducive to the cross-linking and curing of the polyurethane prepolymer and the drying of the slurry, and is conducive to the preparation of a positive electrode sheet with good performance.

[0010] In a possible implementation, the preparing of the positive electrode slurry includes: preparing a binder precursor solution, adding a positive electrode active material, a conductive agent, a dispersant and a cross-linking agent into the binder precursor solution, and mixing to obtain the positive electrode slurry.

[0011] Conductive agents collect microcurrents between active materials to reduce the contact resistance of the electrode and accelerate the movement rate of electrons. They can also effectively increase the migration rate of metal ions in the electrode material, thereby improving the charge and discharge efficiency of the electrode. Dispersants are conducive to the uniform dispersion of solids in the positive electrode slurry in the solvent. Crosslinking agents are conducive to catalyzing the crosslinking and curing of polyurethane prepolymers. Including the above substances in the positive electrode slurry is conducive to the preparation of positive electrode sheets with good performance.

[0012] In a possible implementation, the conductive agent includes at least one of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0013] Due to the unique composition of carbon structure, carbon material conductive agent has good conductivity. For example, conductive carbon black has low resistance and high conductivity, small particle size, large and rough specific surface area, high structure, clean surface (few compounds), etc. Ketjen black has a unique branched chain morphology, so it has high conductivity; carbon atoms in carbon nanotubes adopt SP 2 Hybridization, thus having high modulus and high strength, carbon nanotubes also have good flexibility, stretchability and conductivity. Conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers can be used as conductive agents to improve the conductivity of batteries.

[0014] In a possible implementation, the dispersant includes polyvinyl pyrrolidone.

[0015] Polyvinyl pyrrolidone has good stability and has the advantages of colloidal protection, film-forming, adhesiveness, hygroscopicity, solubilization or coagulation in the reaction system.

[0016] In a possible implementation, the cross-linking agent includes at least one of sucrose, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethyltoluenediamine, dimethylthiotoluenediamine, three-arm polycaprolactone, and four-arm polycaprolactone.

[0017] In a possible implementation, the preparing the binder precursor solution includes: preparing the polyurethane prepolymer; dispersing the polyurethane prepolymer in N-methylpyrrolidone solvent to obtain the binder precursor solution.

[0018] In a possible implementation, the preparation of the polyurethane prepolymer includes: drying polyether polyol and / or polyester polyol; mixing the dried polyether polyol and / or polyester polyol with isocyanate and a catalyst to carry out a prepolymerization reaction; after the prepolymerization reaction is completed, adding a blocking agent to the reaction product to obtain the polyurethane prepolymer.

[0019] A blocking agent is added to the reaction product of the prepolymerization reaction. The blocking agent can make the isocyanate active group inactive at a lower temperature. When the coated electrode is baked at a high temperature in an oven, the blocking agent loses its effect, exposing the isocyanate group.

[0020] In a possible implementation, the drying temperature of the polyether polyol and / or the polyester polyol is in the range of 90° C. to 95° C., and the drying time is in the range of 2 to 3 hours.

[0021] The drying temperature and drying time are set within the above ranges, which is beneficial for the polyether polyol and / or polyester polyol to reach a state suitable for polymerization reaction, and is beneficial for prepolymerization reaction with isocyanate.

[0022] In a possible implementation, the isocyanate includes diisocyanate, and the diisocyanate includes at least one of aromatic diisocyanate and aliphatic diisocyanate.

[0023] In one possible implementation, the isocyanate includes at least one of isotoluene-2,3-diisocyanate, toluene-2,4-diisocyanate, toluene-2,5-diisocyanate, toluene-2,6-diisocyanate, toluene-3,4-diisocyanate, toluene-3,5-diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, L-lysine ethyl diisocyanate, hydrogenated toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate.

[0024] In a possible implementation, the molar ratio R of isocyanate to hydroxyl in the polyurethane prepolymer is in the range of 1.1 to 2.0. Optionally, the molar ratio R is in the range of 1.2 to 1.8.

[0025] The molar ratio of isocyanate to hydroxyl in the polyurethane prepolymer is set within the above range, which is conducive to the subsequent cross-linking and curing reaction of the polyurethane prepolymer.

[0026] In a possible implementation, the polyether polyol includes at least one of polyethylene glycol, polypropylene oxide glycol, polyethylene oxide glycol, polytetramethylene glycol, and polyethylene glycol-propylene glycol copolymer.

[0027] In a possible implementation, the polyester polyol includes at least one of polycaprolactone, polycarbonate diol, polylactic acid diol, and polyglycolide-lactide copolymer.

[0028] In a possible implementation, the catalyst includes at least one of an organic tin catalyst, an organic bismuth catalyst, and a tertiary amine catalyst.

[0029] In a possible implementation, the catalyst includes at least one of dibutyltin dilaurate, stannous octoate, N-ethylmorpholine, N-methylmorpholine, and triethylamine.

[0030] The above substances can effectively catalyze the prepolymerization reaction of polyether polyol and / or polyester polyol with isocyanate.

[0031] In one possible implementation, the blocking agent includes at least one of trichloroethanol, trifluoroethanol, dodecyl mercaptan, triphenyl mercaptan, hexanethiol, N,N-butanediol acetamide, ethylene glycol monohexyl ether, N,N-diol amide, phenol, pyridine, methyl ethyl ketone oxime, caprolactam, and ethyl acetoacetate.

[0032] In a possible implementation, based on the total mass of the reaction raw materials for the prepolymerization reaction, the mass percentage content of the catalyst in the reaction raw materials for the prepolymerization reaction ranges from 0.001% to 1.0%.

[0033] Controlling the catalyst within the above range is beneficial to catalyzing the prepolymerization reaction of polyether polyol and / or polyester polyol with isocyanate.

[0034] In a second aspect, a positive electrode sheet is provided that is produced according to the preparation method in the first aspect and any possible implementation thereof.

[0035] In a possible implementation, the positive electrode plate includes a positive electrode active material layer, and based on the total mass of the positive electrode active material layer, the mass percentage of the binder in the positive electrode active material layer is in a range of 0.3% to 4.2%.

[0036] The mass percentage of the binder in the positive electrode active material layer is set within the above range, which is beneficial to improving the performance of the positive electrode sheet.

[0037] In a third aspect, a battery cell is provided, comprising the positive electrode plate described in the second aspect.

[0038] In a fourth aspect, a battery is provided, comprising the battery cell described in the third aspect.

[0039] In a fifth aspect, an electrical device is provided, comprising the battery described in the fourth aspect.

[0040] The embodiment of the present application provides a method for preparing a positive electrode sheet, wherein the positive electrode slurry includes a polyurethane prepolymer, and after the positive electrode slurry is coated on at least one side of the positive electrode current collector, the positive electrode slurry coated on at least one side of the positive electrode current collector is dried. In the process of drying the positive electrode slurry, the polyurethane prepolymer in the positive electrode slurry is cross-linked and cured to form a polyurethane cross-linked substance with a large molecular weight. The polyurethane cross-linked substance has a cross-linked network structure and a long molecular chain structure. Compared with the general crystalline binder substance, it has good bonding strength and toughness, thereby improving the toughness of the positive electrode sheet and obtaining a positive electrode sheet with good performance. At the same time, polyurethane is conducive to improving the transmission rate of active metal ions (such as lithium ions), thereby improving the internal resistance of the battery and improving the cycle performance of the battery. In the technical solution provided by the embodiment of the present application, the polyurethane prepolymer that has not been cross-linked and cured has a lower viscosity. When added to the positive electrode slurry, the solid content of the polyurethane binder in the positive electrode slurry can be increased, and the positive electrode slurry is easy to disperse during coating, thereby improving the processing efficiency of the positive electrode sheet. In the process of drying the positive electrode slurry coated on at least one side of the positive electrode current collector, the polyurethane prepolymer is cross-linked and cured to form a large molecular weight cross-linked substance with good bonding strength and toughness, which can improve the performance of the positive electrode sheet and thus improve the performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0042] Figure 1 A schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application;

[0043] Figure 2 A schematic diagram of a positive electrode sheet according to an embodiment of the present application;

[0044] Figure 3 A schematic diagram of a positive electrode sheet according to an embodiment of the present application;

[0045] Figure 4 A schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application;

[0046] Figure 5 A schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application;

[0047] Figure 6 A schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application;

[0048] Figure 7is a schematic diagram of a battery cell disclosed in an embodiment of the present application;

[0049] Figure 8 is a schematic diagram of the exploded structure of a battery cell disclosed in one embodiment of the present application;

[0050] Fig. 9 is a schematic diagram of the exploded structure of a battery disclosed in one embodiment of the present application;

[0051] Fig.10 is a schematic diagram of an electrical device disclosed in one embodiment of the present application;

[0052] In the drawings, the drawings are not drawn to scale. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0054] Below, the embodiments of the electrode plates, battery cells, batteries and electrical devices of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are 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 the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0056] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a 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 a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present 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 real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0057] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means 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), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0058] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended. For example, the "include" and "comprising" may mean including or comprising other components not listed.

[0059] If not specifically stated, in this application, the term "and / or" is inclusive. For example, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0060] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0061] 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.

[0062] Secondary batteries are widely used in mobile phones, electric vehicles, power stations, etc. due to their high energy density, high voltage, long life, etc. As a component of the battery, the performance of the positive electrode is crucial to the performance of the battery.

[0063] Binder is an important factor affecting the performance of positive electrode sheets. In the preparation process of positive electrode sheets, binders are usually added to the positive electrode slurry. The positive electrode active material and the conductive agent are adhered to the positive electrode collector by the binder to maintain the structural stability of the positive electrode sheet. Polyurethane binders are widely used because of their good bonding force, storage stability and more active metal ion channels. However, the molecular weight of the cross-linked and cured polyurethane binder is relatively large. Adding it to the positive electrode slurry will greatly increase the viscosity of the positive electrode slurry and reduce the uniformity of the solid dispersion in the positive electrode slurry. When the positive electrode slurry is coated on the positive electrode collector, it is difficult to apply it evenly, which increases the difficulty of production and reduces production efficiency. In order to ensure the availability of the positive electrode slurry, the molecular weight of the polyurethane binder must be controlled not to be too large, which greatly reduces the bonding performance of the polyurethane binder and is not conducive to the preparation of positive electrode sheets with good performance.

[0064] In view of this, the embodiment of the present application provides a method for preparing a positive electrode sheet, wherein a polyurethane prepolymer is included in the positive electrode slurry, and after the positive electrode slurry is coated on at least one side of the positive electrode current collector, the positive electrode slurry coated on at least one side of the positive electrode current collector is dried. In the process of drying the positive electrode slurry, the polyurethane prepolymer in the positive electrode slurry is cross-linked and cured to form a polyurethane cross-linked substance with a large molecular weight. The polyurethane cross-linked substance has a cross-linked network structure and a long molecular chain structure. Compared with the general crystalline binder material, it has good bonding strength and toughness, thereby improving the toughness of the positive electrode sheet and obtaining a positive electrode sheet with good performance. At the same time, polyurethane is conducive to improving the transmission rate of active metal ions (such as lithium ions), thereby improving the internal resistance of the battery and improving the cycle performance of the battery. In the technical solution provided in the embodiment of the present application, the polyurethane prepolymer that has not been cross-linked and cured has a lower viscosity. When added to the positive electrode slurry, the solid content of the polyurethane binder in the positive electrode slurry can be increased, and the positive electrode slurry is easy to disperse during coating, thereby improving the processing efficiency of the positive electrode sheet. In the process of drying the positive electrode slurry coated on at least one side of the positive electrode current collector, the polyurethane prepolymer is cross-linked and cured to form a large molecular weight cross-linked substance with good bonding strength and toughness, which can improve the performance of the positive electrode sheet and thus improve the performance of the battery.

[0065] Several embodiments of the present application are described in detail below.

[0066] [Method for preparing positive electrode sheet]

[0067] Figure 1 FIG. 1 is a schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application. Figure 1 As shown, the preparation method includes the following steps.

[0068] Step 101, preparing positive electrode slurry.

[0069] Wherein, the positive electrode slurry includes polyurethane prepolymer.

[0070] Step 102: coating the positive electrode slurry on at least one side of the positive electrode current collector.

[0071] Step 103, drying the positive electrode slurry coated on at least one side of the positive electrode current collector to obtain a positive electrode sheet.

[0072] In the preparation method of the positive electrode sheet provided by the embodiment of the present application, a positive electrode slurry containing a polyurethane prepolymer is provided, and after the positive electrode slurry is coated on at least one side of the positive electrode current collector, the positive electrode slurry coated on at least one side of the positive electrode current collector is dried. In the process of drying the positive electrode slurry, the polyurethane prepolymer in the positive electrode slurry will be cross-linked and cured to form a polyurethane cross-linked substance with a large molecular weight. The polyurethane cross-linked substance has a cross-linked network structure and a long molecular chain structure. Compared with the general crystalline binder material, it has good bonding strength and toughness, thereby improving the toughness of the positive electrode sheet and obtaining a positive electrode sheet with good performance. At the same time, polyurethane is conducive to improving the transmission rate of active metal ions (such as lithium ions), thereby improving the internal resistance of the battery and improving the cycle performance of the battery. In the technical solution provided by the embodiment of the present application, the polyurethane prepolymer that has not been cross-linked and cured has a lower viscosity. When added to the positive electrode slurry, the solid content of the polyurethane binder in the positive electrode slurry can be increased, and the positive electrode slurry is easy to disperse during coating, thereby improving the processing efficiency of the positive electrode sheet. In the process of drying the positive electrode slurry coated on at least one side of the positive electrode current collector, the polyurethane prepolymer is cross-linked and cured to form a large molecular weight cross-linked substance with good bonding strength and toughness, which can improve the performance of the positive electrode sheet and thus improve the performance of the battery.

[0073] Figure 2 Schematic diagram of a positive electrode sheet according to an embodiment of the present application. Figure 2 As shown, the positive electrode sheet 2 includes a positive electrode current collector 21 and a positive electrode material layer 22. The positive electrode material layer 22 is formed by coating the positive electrode slurry on the positive electrode current collector 21 and drying the positive electrode material layer 22. Figure 2 The positive electrode current collector 21 and the positive electrode material layer 22 are arranged in sequence.

[0074] The positive electrode current collector 21 has two surfaces arranged along its thickness direction. Figure 1As shown, positive electrode material layers 22 are provided on both surfaces of the positive electrode current collector 21 .

[0075] Figure 3 Schematic diagram of a positive electrode sheet of an embodiment of the present application. In some other embodiments, such as Figure 3 As shown, a positive electrode material layer 22 is provided on one of two surfaces of the positive electrode collector 21 that are opposite to each other in the thickness direction.

[0076] Optionally, in some embodiments, the drying temperature of the positive electrode slurry ranges from 60°C to 150°C. Optionally, the drying temperature ranges from 80°C to 140°C.

[0077] Specifically, the drying temperature of the positive electrode slurry can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or a value between any two of the above values.

[0078] The drying temperature of the positive electrode slurry is set within the above range, which is conducive to the cross-linking and curing of the polyurethane prepolymer and the drying of the slurry, and is conducive to the preparation of a positive electrode sheet with good performance.

[0079] Optionally, in some embodiments, preparing the positive electrode slurry includes: preparing a binder precursor solution, adding a positive electrode active material, a conductive agent, a dispersant and a cross-linking agent to the binder precursor solution, and mixing to obtain the positive electrode slurry. Figure 4 , Figure 4 Schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application. Figure 4 Steps 403-404 in are similar to steps 102-103 in the aforementioned embodiment, and reference may be made to the aforementioned embodiment. For the sake of brevity, they will not be described in detail here.

[0080] Step 401, preparing a binder precursor solution.

[0081] Step 402: Add positive electrode active material, conductive agent, dispersant and cross-linking agent into the binder precursor solution, mix them, and prepare positive electrode slurry.

[0082] Conductive agents collect microcurrents between active materials to reduce the contact resistance of the electrode and accelerate the movement rate of electrons. They can also effectively increase the migration rate of metal ions in the electrode material, thereby improving the charge and discharge efficiency of the electrode. Dispersants are conducive to the uniform dispersion of solids in the positive electrode slurry in the solvent. Crosslinking agents are conducive to catalyzing the crosslinking and curing of polyurethane prepolymers. Including the above substances in the positive electrode slurry is conducive to the preparation of positive electrode sheets with good performance.

[0083] Optionally, in some embodiments, the conductive agent includes at least one of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0084] Due to the unique composition of carbon structure, carbon material conductive agent has good conductivity. For example, conductive carbon black has low resistance and high conductivity, small particle size, large and rough specific surface area, high structure, clean surface (few compounds), etc. Ketjen black has a unique branched chain morphology, so it has high conductivity; carbon atoms in carbon nanotubes adopt SP 2 Hybridization, thus having high modulus and high strength, carbon nanotubes also have good flexibility, stretchability and conductivity. Conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers can be used as conductive agents to improve the conductivity of batteries.

[0085] Optionally, in some embodiments, the dispersant comprises polyvinyl pyrrolidone.

[0086] Polyvinyl pyrrolidone has good stability and has the advantages of colloidal protection, film-forming, adhesiveness, hygroscopicity, solubilization or coagulation in the reaction system.

[0087] Optionally, in some embodiments, the cross-linking agent includes at least one of sucrose, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethyltoluenediamine, dimethylthiotoluenediamine, three-arm polycaprolactone, and four-arm polycaprolactone.

[0088] Optionally, in some embodiments, preparing the binder precursor solution includes: preparing a polyurethane prepolymer; dispersing the polyurethane prepolymer in an N-methylpyrrolidone solvent to obtain the binder precursor solution. Figure 5 , Figure 5 Schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application. Figure 5 Steps 503-505 in are similar to steps 402-404 in the aforementioned embodiment, and reference may be made to the aforementioned embodiment. For the sake of brevity, they will not be described in detail here.

[0089] Step 501, preparing a polyurethane prepolymer.

[0090] Step 502: Disperse the polyurethane prepolymer in N-methylpyrrolidone solvent to obtain a binder precursor solution.

[0091] Optionally, in some embodiments, providing a polyurethane prepolymer includes: drying polyether polyol and / or polyester polyol; mixing the dried polyether polyol and / or polyester polyol with isocyanate and a catalyst to perform a prepolymerization reaction; after the prepolymerization reaction is completed, adding a blocking agent to the reaction product to obtain a polyurethane prepolymer. Figure 6 , Figure 6 Schematic diagram of a method for preparing a positive electrode sheet according to an embodiment of the present application. Figure 6 Steps 604-607 in are similar to steps 502-505 in the aforementioned embodiment, and reference may be made to the aforementioned embodiment. For the sake of brevity, they will not be described in detail here.

[0092] Step 601, drying polyether polyol and / or polyester polyol.

[0093] Step 602: Mix the dried polyether polyol and / or polyester polyol with isocyanate and a catalyst to perform a prepolymerization reaction.

[0094] Step 603, adding a blocking agent to the reaction product of the prepolymerization reaction to obtain a polyurethane prepolymer.

[0095] A blocking agent is added to the reaction product of the prepolymerization reaction. The blocking agent can make the isocyanate active group inactive at a lower temperature. When the coated electrode is baked at a high temperature in an oven, the blocking agent loses its effect, exposing the isocyanate group.

[0096] Optionally, in some embodiments, the drying temperature of the polyether polyol and / or the polyester polyol is in the range of 90° C. to 95° C., and the drying time is in the range of 2 to 3 hours.

[0097] Specifically, the drying temperature of the polyether polyol and / or polyester polyol can be 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, or a value between any two of the above values; the drying time can be 2 hours, 2.5 hours, 3 hours, or a value between any two of the above values.

[0098] The drying temperature and drying time are set within the above ranges, which is beneficial for the polyether polyol and / or polyester polyol to reach a state suitable for polymerization reaction, and is beneficial for prepolymerization reaction with isocyanate.

[0099] Optionally, in some embodiments, the isocyanate includes a diisocyanate, and optionally, the diisocyanate includes at least one of an aromatic diisocyanate and an aliphatic diisocyanate.

[0100] Specifically, the isocyanate may include at least one of isotoluene-2,3-diisocyanate, toluene-2,4-diisocyanate, toluene-2,5-diisocyanate, toluene-2,6-diisocyanate, toluene-3,4-diisocyanate, toluene-3,5-diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, L-lysine ethyl diisocyanate, hydrogenated toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate.

[0101] Optionally, in some embodiments, the polyether polyol includes at least one of polyethylene glycol, polypropylene oxide glycol, polyethylene oxide glycol, polytetramethylene glycol, and polyethylene glycol-propylene glycol copolymer.

[0102] Optionally, in some embodiments, the polyester polyol includes at least one of polycaprolactone, polycarbonate diol, polylactic acid diol, and polyglycolide-lactide copolymer.

[0103] Optionally, in some embodiments, the molar ratio R of isocyanate to hydroxyl in the polyurethane prepolymer is in the range of 1.1 to 2.0. Optionally, R is in the range of 1.2 to 1.8.

[0104] Specifically, the molar ratio R of isocyanate to hydroxyl in the polyurethane prepolymer can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or a value between any two of the above values.

[0105] The molar ratio of isocyanate to hydroxyl in the polyurethane prepolymer is set within the above range, which is conducive to the subsequent cross-linking and curing reaction of the polyurethane prepolymer.

[0106] Optionally, in some embodiments, the catalyst includes at least one of an organic tin catalyst, an organic bismuth catalyst, and a tertiary amine catalyst.

[0107] Specifically, the catalyst may include at least one of dibutyltin dilaurate, stannous octoate, N-ethylmorpholine, N-methylmorpholine, and triethylamine.

[0108] The above substances can effectively catalyze the prepolymerization reaction of polyether polyol and / or polyester polyol with isocyanate.

[0109] Optionally, in some embodiments, the sealing agent includes at least one of trichloroethanol, trifluoroethanol, dodecyl mercaptan, triphenyl mercaptan, hexanethiol, N,N-butanediol acetamide, ethylene glycol monohexyl ether, N,N-diol amide, phenol, pyridine, methyl ethyl ketone oxime, caprolactam, and ethyl acetoacetate.

[0110] Optionally, in some embodiments, based on the total mass of the reaction raw materials for the prepolymerization reaction, the mass percentage of the catalyst in the reaction raw materials for the prepolymerization reaction ranges from 0.001% to 1.0%.

[0111] Specifically, the mass percentage of the catalyst in the reaction raw materials of the prepolymerization reaction can be 0.001%, 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, or a value between any two of the above values.

[0112] [Positive electrode]

[0113] The present application embodiment provides a positive electrode sheet prepared according to the above preparation method, referring to Figure 2-3 The positive electrode sheet 2 includes a positive electrode current collector 21 and a positive electrode material layer 22 .

[0114] The positive electrode material layer 22 includes a binder. Based on the total mass of the positive electrode material layer 22 , the mass percentage of the binder in the positive electrode material layer 22 ranges from 0.3% to 4.2%.

[0115] Specifically, the mass percentage of the binder in the positive electrode material layer 22 can be 0.3%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.2%, or a value between any two of the above values.

[0116] In some embodiments, the adhesive comprises a polyurethane adhesive, which has excellent shear strength and impact resistance, and has excellent flexibility.

[0117] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0118] 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.).

[0119] In some embodiments, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material may be a positive electrode active material for lithium ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates containing 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 lithium ion batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, 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 / 3Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure 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.

[0120] In some embodiments, the binder may also include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0121] [Negative electrode]

[0122] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0123] 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 any one or both of the two opposite surfaces of the negative electrode current collector.

[0124] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery 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 oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, 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.

[0126] 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).

[0127] 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.

[0128] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0129] In some embodiments, the negative electrode sheet can be prepared in the following manner: 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 collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0130] [Electrolytes]

[0131] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0132] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0133] In some embodiments, the electrolyte salt can 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.

[0134] 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, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0135] In some embodiments, the electrolyte may further include additives, such as 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, additives that improve battery high or low temperature performance, etc.

[0136] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0137] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0138] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0139] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 7 The battery cell 70 is a square structure as an example.

[0140] In some embodiments, reference Figure 8 , the outer packaging may include a shell 71 and a cover plate 73. Among them, the shell 71 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 71 has an opening connected to the receiving cavity, and the cover plate 73 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 72 through a winding process or a lamination process. The electrode assembly 72 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 72. The number of electrode assemblies 72 contained in the battery cell 70 can be one or more, and those skilled in the art can choose according to specific actual needs.

[0141] In some embodiments, the battery 80 may include a plurality of battery cells 70. For example, Fig. 9 , which is a schematic diagram of the structure of a battery 80 according to an embodiment of the present application, wherein the battery 80 may include a plurality of battery cells 70. The battery 80 may also include a box 81, wherein the box 81 is a hollow structure, and the plurality of battery cells 70 are accommodated in the box 81. For example, the plurality of battery cells 70 are connected in parallel, in series, or in a mixed combination and then placed in the box 81.

[0142] Optionally, the battery 80 may also include other structures, which are not described one by one here. For example, the battery 80 may also include a busbar component, which is used to realize electrical connection between multiple battery cells 70, such as parallel connection, series connection or mixed connection. Specifically, the busbar component can realize electrical connection between battery cells 70 by connecting the electrode terminals of the battery cells 70. Further, the busbar component can be fixed to the electrode terminals of the battery cells 70 by welding. The electrical energy of multiple battery cells 70 can be further led out through the box 81 through a conductive mechanism. Optionally, the conductive mechanism may also belong to the busbar component.

[0143] According to different power requirements, the number of battery cells 70 can be set to any value. Multiple battery cells 70 can be connected in series, parallel or hybrid to achieve a larger capacity or power. Since the number of battery cells 70 included in each battery 80 may be large, for ease of installation, the battery cells 70 can be grouped, and each group of battery cells 70 constitutes a battery module. The number of battery cells 70 included in the battery module is not limited and can be set according to demand. The battery can include multiple battery modules, which can be connected in series, parallel or hybrid.

[0144] In addition, the present application also provides an electric device, which includes at least one of the battery cells, battery modules or batteries provided in the present application. The battery cells, battery modules or batteries can be used as the power source of the electric device, and can also be used as the energy storage unit of the electric device. The electric 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 are not limited thereto.

[0145] As the electrical device, a battery cell, a battery module or a battery can be selected according to its usage requirements.

[0146] Fig.10 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for battery cells, batteries or battery modules can be used.

[0147] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0148] [Example]

[0149] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0150] 1. Preparation of positive electrode sheet

[0151] Positive electrode 1:

[0152] 100.000 kg of polyethylene glycol (PEG, molecular weight of 1000) was added to the reactor and dried at 95°C for 3 hours. Then, 18.500 kg of hexamethylene diisocyanate was added to the reactor, and 2.405 g of catalyst triethylamine was added to the reactor. The reaction was carried out at 75°C. The isocyanate group (-NCO) content was detected during the reaction until the -NCO content reached the theoretical value. Then, 1.742 kg of blocking agent methyl ethyl ketone oxime was added to the reactor to continue the reaction. After the reaction, a polyurethane prepolymer was obtained.

[0153] 97.300 kg of positive electrode active material lithium iron phosphate (LiFePO4), 1.000 kg of polyurethane prepolymer, and 1.400 kg of conductive agent acetylene black were stirred in a planetary stirring tank at an orbital speed of 25 r / min for 20 min; 53.850 kg of N-methylpyrrolidone (NMP) solution was added to the stirring tank, and stirred at an orbital speed of 25 r / min and a rotation speed of 900 r / min for 50 min; 300.000 g of dispersant polyvinylpyrrolidone (PVP) and 0.487 kg of cross-linking agent triethylenetetramine were added to the stirring tank, and stirred at an orbital speed of 25 r / min and a rotation speed of 1400 r / min for 50 min to prepare a positive electrode slurry.

[0154] The positive electrode slurry prepared above was scraped onto a carbon-coated aluminum foil and baked at a temperature of 110° C. for 15 minutes to obtain a positive electrode sheet 1.

[0155] The detection of the isocyanate group (-NCO) content mentioned above can be carried out according to the detection method of the isocyanate group content provided in the national standard GB / T 12009.4. The theoretical value of the -NCO content is a theoretical value obtained by theoretical calculation based on the ratio of the reaction raw materials of the polyurethane prepolymerization reaction in the embodiment.

[0156] Positive electrode plate 2: The preparation of positive electrode plate 2 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 2, the amount of hexamethylene diisocyanate added is 20.177 kg, the amount of catalyst triethylamine added is 2.473 g, the amount of sealing agent methyl ethyl ketone oxime added is 3.485 kg, and the amount of cross-linking agent triethylenetetramine added is 0.975 kg, so as to obtain positive electrode plate 2.

[0157] Positive electrode sheet 3: The preparation of positive electrode sheet 3 is similar to that of positive electrode sheet 1, except that, in the process of preparing positive electrode sheet 3, the amount of hexamethylene diisocyanate added is 21.858 kg, the amount of catalyst triethylamine added is 2.542 g, the amount of sealing agent methyl ethyl ketone oxime added is 5.227 kg, and the amount of cross-linking agent triethylenetetramine added is 1.462 kg, so as to obtain positive electrode sheet 3.

[0158] Positive electrode plate 4: The preparation of positive electrode plate 4 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 4, the amount of hexamethylene diisocyanate added is 23.540 kg, the amount of catalyst triethylamine added is 2.610 g, the amount of sealing agent methyl ethyl ketone oxime added is 6.970 kg, and the amount of cross-linking agent triethylenetetramine added is 1.950 kg, so as to obtain positive electrode plate 4.

[0159] Positive electrode plate 5: The preparation of positive electrode plate 5 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 5, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode plate 5.

[0160] Positive electrode plate 6: The preparation of positive electrode plate 6 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 6, the amount of hexamethylene diisocyanate added is 26.902 kg, the amount of catalyst triethylamine added is 2.747 g, the amount of sealing agent methyl ethyl ketone oxime added is 10.454 kg, and the amount of cross-linking agent triethylenetetramine added is 2.925 kg, so as to obtain positive electrode plate 6.

[0161] Positive electrode plate 7: The preparation of positive electrode plate 7 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 7, the amount of hexamethylene diisocyanate added is 28.584 kg, the amount of catalyst triethylamine added is 2.816 g, the amount of sealing agent methyl ethyl ketone oxime added is 12.197 kg, and the amount of cross-linking agent triethylenetetramine added is 3.412 kg, so as to obtain positive electrode plate 7.

[0162] Positive electrode plate 8: The preparation of positive electrode plate 8 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 8, the amount of hexamethylene diisocyanate added is 30.265 kg, the amount of catalyst triethylamine added is 2.884 g, the amount of sealing agent methyl ethyl ketone oxime added is 13.939 kg, and the amount of cross-linking agent triethylenetetramine added is 3.899 kg, so as to obtain positive electrode plate 8.

[0163] Positive electrode plate 9: The preparation of positive electrode plate 9 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 9, the amount of hexamethylene diisocyanate added is 33.638 kg, the amount of catalyst triethylamine added is 3.021 g, the amount of sealing agent methyl ethyl ketone oxime added is 17.424 kg, and the amount of cross-linking agent triethylenetetramine added is 4.874 kg, so as to obtain positive electrode plate 9.

[0164] Positive electrode plate 10: The preparation of positive electrode plate 10 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 10, the amount of PEG added is 60.000 kg, and 40.000 kg of polybutylene glycol (PTMG, molecular weight 1000) is added as a reaction raw material of polyurethane prepolymer, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode plate 10.

[0165] Positive electrode plate 11: The preparation of positive electrode plate 11 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 11, the amount of PEG added is 60.000 kg, and 40.000 kg of polycaprolactone (PCL, molecular weight 1000) is added as a reaction raw material of polyurethane prepolymer, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode plate 11.

[0166] Positive electrode plate 12: The preparation of positive electrode plate 12 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 12, the amount of PEG added is 60.000 kg, and 40.000 kg of polycarbonate diol (PCDL, molecular weight 1000) is added as a reaction raw material of polyurethane prepolymer, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode plate 12.

[0167] Positive electrode plate 13: The preparation of positive electrode plate 13 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 13, the amount of PEG added is 60.000 kg, and 40.000 kg of polypropylene glycol (PPG, molecular weight 1000) is added as a reaction raw material of polyurethane prepolymer, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode plate 13.

[0168] Positive electrode plate 14: The preparation of positive electrode plate 14 is similar to that of positive electrode plate 1, except that, in the process of preparing positive electrode plate 14, the amount of PEG added is 60.000 kg, and 40.000 kg of polydimethylsiloxane (PDMS, molecular weight 1000) is added as a reaction raw material of polyurethane prepolymer, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode plate 14.

[0169] Positive electrode sheet 15: The preparation of positive electrode sheet 15 is similar to that of positive electrode sheet 1, except that, in the process of preparing positive electrode sheet 15, the amount of PEG added is 60.000 kg, and 40.000 kg of polylactic acid-hydroxyacetic acid copolymer (PLGA, molecular weight 1000) is added as the reaction raw material of polyurethane prepolymer, the amount of hexamethylene diisocyanate added is 25.221 kg, the amount of catalyst triethylamine added is 2.679 g, the amount of sealing agent methyl ethyl ketone oxime added is 8.712 kg, and the amount of cross-linking agent triethylenetetramine added is 2.437 kg, so as to obtain positive electrode sheet 15.

[0170] Positive electrode sheet 16: Add 100.000 kg of polyethylene glycol (PEG, molecular weight 1000) to the reactor and dry it at 95°C for 3 hours. Then add 25.221 kg of hexamethylene diisocyanate, 2.679 g of catalyst triethylamine, and 0.487 kg of cross-linking agent triethylenetetramine to the reactor, and react at 115°C to obtain a polyurethane adhesive.

[0171] 97.300 kg of positive electrode active material LiFePO4, 1.000 kg of polyurethane binder, and 1.400 kg of conductive agent acetylene black were stirred in a planetary stirring tank at an orbital speed of 25 r / min for 20 min; 53.850 kg of NMP solution was added to the stirring tank and stirred at an orbital speed of 25 r / min and a rotation speed of 900 r / min for 50 min; 300.000 g of dispersant PVP was added to the stirring tank and stirred at an orbital speed of 25 r / min and a rotation speed of 1400 r / min for 50 min to prepare a positive electrode slurry.

[0172] The positive electrode slurry prepared above was scraped onto a carbon-coated aluminum foil and baked at a temperature of 110° C. for 15 minutes to obtain a positive electrode sheet 16 .

[0173] Positive electrode sheet 17: 3.97 kg of positive electrode active material LiFePO4, 16.4 g of binder polyvinylidene fluoride, and 57.4 g of conductive agent acetylene black were placed in a planetary stirring tank, and stirred at an orbital speed of 25 r / min for 20 min. 2.4 kg of NMP solution was added to the stirring tank, and stirred at an orbital speed of 25 r / min and a self-rotation speed of 900 r / min for 50 min. 12.3 g of dispersant PVP was added to the stirring tank, and stirred at an orbital speed of 25 r / min and a self-rotation speed of 1400 r / min for 50 min to obtain a positive electrode slurry.

[0174] The positive electrode slurry prepared above was scraped onto the carbon-coated aluminum foil and baked at 110° C. for 15 min to obtain the positive electrode sheet 17 .

[0175] According to the positive electrode sheet prepared by the preparation method of the positive electrode sheet provided in the embodiment of the present application, the dried positive electrode slurry in the prepared positive electrode sheet is scraped off from the positive electrode collector and dissolved with NMP solution. The polyurethane therein cannot be redissolved due to its large molecular weight and remains solid in the solvent.

[0176] 2. Preparation of battery cells

[0177] [Example 1]

[0178] (1) Positive electrode

[0179] The positive electrode sheet adopts the positive electrode sheet 1 prepared as above.

[0180] (2) Preparation of negative electrode sheet

[0181] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR), and CMC are dissolved in deionized water as a solvent in a weight ratio of 95.5:1.2:1.3:1.5, and are evenly mixed to prepare a negative electrode slurry; the negative electrode slurry is then evenly coated on the negative electrode collector, dried to obtain a negative electrode film, and then cold pressed and cut to obtain a negative electrode sheet.

[0182] (3) Preparation of electrolyte

[0183] In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt (LiPF6) was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 20:20:60, and then the additive vinylene carbonate (VC) was added and mixed evenly to obtain an electrolyte. The concentration of the lithium salt was 1 mol / L.

[0184] (4) Preparation of isolation membrane

[0185] A conventional polypropylene film was used as the isolation film.

[0186] (5) Assembly of lithium-ion batteries

[0187] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, so that the isolation film is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in a battery casing, and after drying, the electrolyte is injected, and then a lithium-ion battery 1 is obtained through processes such as formation and standing, as Example 1.

[0188] [Example 2-15, Comparative Example 1-2]

[0189] The preparation methods of the lithium-ion batteries of Examples 2-15 and Comparative Examples 1-2 are similar to those of the lithium-ion battery of Example 1, except that different positive electrode sheets are used (among which, Example 1-15 uses positive electrode sheet 1-15, and Comparative Example 1-2 uses positive electrode sheet 16-17), as shown in Table 1 for details.

[0190] 3. Performance test of positive electrode

[0191] (1) Adhesion test of the binder in the positive electrode

[0192] Refer to the national standard "Adhesive 180° Peel Strength Test Method", use a blade to cut a positive electrode sheet with a width of 30mm and a length of 100-160mm, and stick a special double-sided tape on the steel plate. The double-sided tape is 20mm wide and 90-150mm long. Stick the cut positive electrode sheet on the double-sided tape with the test side facing down, and then roll it three times in the same direction with a roller.

[0193] Insert a paper tape with the same width as the positive electrode sheet and 80-200mm longer than the length of the positive electrode sheet under the positive electrode sheet and fix it with wrinkle glue.

[0194] Turn on the power of the Sansi tensile testing machine (sensitivity is 1N), the indicator light is on, adjust the limit block to the appropriate position, and fix the end of the steel plate without the positive electrode with the lower clamp. Fold the paper tape upwards and fix it with the upper clamp, and use the "up" and "down" buttons on the manual controller attached to the tensile testing machine to adjust the position of the upper clamp. Then perform the test and read the value.

[0195] (2) Test of the membrane resistance of the positive electrode

[0196] The prepared positive electrode was tested using a four-probe resistance meter. Three parallel samples were tested for each sample and the average value was taken.

[0197] 4. Battery performance test

[0198] (1) Initial Direct Current Resistance (DCR) Test

[0199] At room temperature, the batteries of the embodiments and comparative examples are charged to 3.65V at 0.5C constant current, and then charged to 0.05C at constant voltage; the battery is discharged at 0.5C constant current for 60 minutes to adjust the battery to 50% SOC, at which time the battery voltage is recorded as U1; the battery is discharged at 4C constant current for 30 seconds, with 0.1 second sampling, and the voltage at the end of discharge is recorded as U2. The discharge DCR of the battery at 50% SOC represents the initial DCR of the battery, and the initial DCR of the battery = (U1-U2) / 4C.

[0200] (2) Battery capacity retention test

[0201] At 25°C, the lithium-ion battery is charged to 3.65V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 3.65V, left for 5 minutes, and then discharged to 2.5V at 1 / 3C. The obtained capacity is recorded as the initial capacity C0. Repeat the above steps and record the discharge capacity Cn of the battery after the nth cycle at the same time. The battery capacity retention rate (%) after n cycles = (Cn / C0) × 100%.

[0202] For example, the capacity retention rate (%) of a lithium-ion battery after 500 cycles at 25° C. = (discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0203] The product parameters of different embodiments and comparative examples, as well as the test results of the performance tests of the prepared positive electrode sheets 1-17 according to the above method, are shown in Table 1. The R value of the polyurethane prepolymer in Table 1 refers to the molar ratio of isocyanate to hydroxyl in the polyurethane prepolymer as R. The test results of the battery performance tests of the prepared comparative examples 1-2 and embodiments 1-15 according to the above method are shown in Table 2.

[0204] Table 1: Product parameters of the embodiments and comparative examples and performance test results of positive electrode sheets 1-17

[0205]

[0206] Table 2: Performance test results of Examples 1-15 and Comparative Examples 1-2

[0207]

[0208] From the comparison of the results of Comparative Example 1-2 and Example 1-15, it can be seen that in the preparation of the positive electrode sheet, the positive electrode slurry contains a polyurethane prepolymer, the prepared positive electrode sheet has good bonding force and a small film resistance of the positive electrode sheet. The corresponding lithium-ion battery has a small DCR and a good capacity retention rate of the lithium-ion battery.

[0209] From the comparison of the results of Examples 1-9, it can be seen that the ratio of the reaction raw materials PEG and hexamethylene diisocyanate in the prepolymerization reaction of the polyurethane prepolymer is controlled, thereby controlling the molar ratio R of isocyanate to hydroxyl in the polyurethane prepolymer, and setting R within an appropriate range, the performance of the positive electrode sheet and the performance of the lithium ion battery are better. In the present application, under the condition of other conditions being constant, the molar ratio R of isocyanate to hydroxyl in the polyurethane prepolymer is controlled within the range of 1.2 to 1.8, the bonding force of the positive electrode sheet is better, and the film resistance of the positive electrode sheet is also smaller; the corresponding DCR of the lithium ion battery is smaller, and the capacity retention rate of the lithium ion battery is better.

[0210] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a positive electrode sheet, comprising: preparing a positive electrode slurry, wherein the positive electrode slurry comprises a polyurethane prepolymer; Applying the positive electrode slurry to at least one side of the positive electrode current collector; The positive electrode slurry coated on at least one side of the positive electrode current collector is dried to obtain the positive electrode sheet.

2. The preparation method according to claim 1, characterized in that: The drying temperature of the positive electrode slurry ranges from 60°C to 150°C. Optionally, the drying temperature ranges from 80°C to 140°C.

3. The preparation method according to claim 1 or 2, characterized in that: The preparation of the positive electrode slurry comprises: preparing a binder precursor solution; The positive electrode slurry is prepared by adding a positive electrode active material, a conductive agent, a dispersant and a cross-linking agent into the binder precursor solution and mixing them.

4. The preparation method according to claim 3, characterized in that: The conductive agent includes at least one of conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

5. The preparation method according to claim 3 or 4, characterized in that: The dispersant includes polyvinyl pyrrolidone.

6. The preparation method according to any one of claims 3 to 5, characterized in that: The cross-linking agent includes at least one of sucrose, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethyltoluenediamine, dimethylthiotoluenediamine, three-arm polycaprolactone, and four-arm polycaprolactone.

7. The preparation method according to any one of claims 3 to 6, characterized in that: The preparation of the binder precursor solution comprises: preparing the polyurethane prepolymer; The polyurethane prepolymer is dispersed in N-methylpyrrolidone solvent to prepare the binder precursor solution.

8. The preparation method according to claim 7, characterized in that: The preparation of the polyurethane prepolymer comprises: Dry polyether polyol, and / or polyester polyol; Mixing the dried polyether polyol and / or the polyester polyol with isocyanate and a catalyst to perform a prepolymerization reaction; After the prepolymerization reaction is completed, a blocking agent is added to the reaction product to obtain the polyurethane prepolymer.

9. The preparation method according to claim 8, characterized in that: The drying temperature of the polyether polyol and / or the polyester polyol is in the range of 90° C. to 95° C., and the drying time is in the range of 2 to 3 hours.

10. The preparation method according to claim 8 or 9, characterized in that: The isocyanate includes diisocyanate. Optionally, the diisocyanate includes at least one of aromatic diisocyanate and aliphatic diisocyanate.

11. The preparation method according to any one of claims 8 to 10, characterized in that: The isocyanate includes at least one of isotoluene-2,3-diisocyanate, toluene-2,4-diisocyanate, toluene-2,5-diisocyanate, toluene-2,6-diisocyanate, toluene-3,4-diisocyanate, toluene-3,5-diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, L-lysine ethyl diisocyanate, hydrogenated toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate.

12. The preparation method according to any one of claims 8 to 11, characterized in that The molar ratio R of isocyanate to hydroxyl in the polyurethane prepolymer is in the range of 1.1 to 2.

0. Optionally, the molar ratio R is in the range of 1.2 to 1.

8.

13. The preparation method according to any one of claims 8 to 12, characterized in that: The polyether polyol includes at least one of polyethylene glycol, polypropylene oxide glycol, polyethylene oxide glycol, polytetramethylene glycol, and polyethylene glycol-propylene glycol copolymer.

14. The preparation method according to any one of claims 8 to 13, characterized in that: The polyester polyol includes at least one of polycaprolactone, polycarbonate diol, polylactic acid diol, and polyglycolide-lactide copolymer.

15. The preparation method according to any one of claims 8 to 14, characterized in that: The catalyst includes at least one of an organic tin catalyst, an organic bismuth catalyst, and a tertiary amine catalyst.

16. The preparation method according to any one of claims 8 to 15, characterized in that: The catalyst includes at least one of dibutyltin dilaurate, stannous octoate, N-ethylmorpholine, N-methylmorpholine and triethylamine.

17. The preparation method according to any one of claims 8 to 16, characterized in that: The blocking agent includes at least one of trichloroethanol, trifluoroethanol, dodecyl mercaptan, triphenyl mercaptan, hexanethiol, N,N-butanediol acetamide, ethylene glycol monohexyl ether, N,N-diol amide, phenol, pyridine, methyl ethyl ketone oxime, caprolactam, and ethyl acetoacetate.

18. The preparation method according to any one of claims 8 to 17, characterized in that: Based on the total mass of the reaction raw materials for the prepolymerization reaction, the mass percentage content of the catalyst in the reaction raw materials for the prepolymerization reaction ranges from 0.001% to 1.0%.

19. A positive electrode sheet obtained by the preparation method according to any one of claims 1 to 18.

20. The positive electrode sheet according to claim 19, characterized in that: The positive electrode plate comprises a positive electrode material layer. Based on the total mass of the positive electrode material layer, the mass percentage of the binder in the positive electrode material layer is in the range of 0.3% to 4.2%.

21. A battery cell comprising the positive electrode sheet according to claim 19 or 20.

22. A battery comprising the battery cell according to claim 21.

23. An electrical device comprising the battery according to claim 22.

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