Method for preparing positive electrode slurry, positive electrode slurry, positive electrode sheet, secondary battery, and electric device

Abstract

The application provides a preparation method of a positive electrode slurry, the positive electrode slurry, a positive electrode tab, a secondary battery and an electric device. The preparation method of the positive electrode slurry comprises first stirring, second stirring and third stirring. In the first stirring, a positive electrode active material is mixed and stirred with a binder to prepare a dry mixture. In the second stirring, a solvent is kneaded with the dry mixture to prepare a primary slurry. In the third stirring, a conductive agent, the solvent and the binder are mixed and stirred with the primary slurry to prepare the positive electrode slurry. The preparation method has universality and is suitable for a slurry containing different molecular weight binders, especially a high molecular weight binder, so that the gel resistance and the sedimentation resistance of the slurry are effectively improved, the uniformity of the slurry is optimized, and the cost of preparation is reduced and the production efficiency is improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a method for preparing a positive electrode slurry, a positive electrode sheet, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide range of applications of secondary batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] Electrode slurry is the foundation for electrode molding and the first step in secondary battery production. The characteristics of the electrode slurry significantly impact subsequent electrode production and battery performance. The positive electrode slurry is primarily a solid-liquid phase mixture formed by positive electrode active materials, conductive agents, binders, and solvents. This system is in a metastable state, and the slurry preparation process—that is, the method of slurry preparation—has a crucial influence on the slurry's dispersibility, uniformity, and stability. Current slurry preparation processes are often one-step methods, directly mixing the components of the positive electrode slurry. However, this one-step method is not suitable for binders with different molecular weights. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for preparing a positive electrode slurry for secondary batteries to meet the manufacturing needs of binders with different molecular weights, broaden the process window for coating positive electrode slurry, and improve the processing performance of positive electrode slurry.

[0005] To achieve the above objectives, this application provides a method for preparing a positive electrode slurry, comprising a first stirring, a second stirring, and a third stirring; in the first stirring, a positive electrode active material and a binder are mixed and stirred to prepare a dry mixture; in the second stirring, a solvent is kneaded with the dry mixture to prepare a primary slurry; in the third stirring, a conductive agent, a solvent, and a binder are mixed and stirred with the primary slurry to prepare a positive electrode slurry.

[0006] The preparation method disclosed in this application has broad applicability and is applicable to binders of different molecular weights, especially high molecular weight binders. This effectively improves the anti-gelling property of slurries containing high molecular weight binders, optimizes the uniformity of the slurry, and helps to reduce preparation costs and improve production efficiency.

[0007] In any embodiment, the binder in the first stirring and / or the binder in the third stirring comprises at least one fluoropolymer with a weight-average molecular weight of 1.5 million to 8 million.

[0008] Fluoropolymers possess excellent bonding properties and electrochemical stability, but agglomeration and gelation are prone to occur during their preparation. The preparation method described in this application is applicable to high molecular weight fluoropolymers and can effectively alleviate gelation and sedimentation phenomena in different slurries, thereby improving production efficiency and broadening the process window for slurry coating.

[0009] In any embodiment, the binder in the first stirring and / or the binder in the third stirring comprises at least two fluoropolymers with a weight-average molecular weight difference of no more than 6.5 million.

[0010] Existing cathode slurry preparation methods suffer from poor compatibility and cannot adapt to differences in the weight-average molecular weight of binders within the slurry, thus imposing high precision requirements on the materials. This application addresses this by combining and controlling a stepwise slurry mixing and kneading process, thereby reducing the final viscosity of the cathode slurry, mitigating gelation, and improving its anti-settling and anti-gelling properties. This allows slurries with high weight-average molecular weight binders to maintain low final viscosity and anti-gelling properties, enhancing the versatility of the preparation method. The preparation method described in this application is applicable to high molecular weight binders, effectively mitigating gelation and sedimentation in different slurries, contributing to improved production efficiency and broadening the process window for slurry coating.

[0011] In any embodiment, the fluoropolymer includes polyvinylidene fluoride.

[0012] In any embodiment, the binder in the first stirring and the binder in the third stirring comprise the same fluoropolymer.

[0013] The first and third stirring processes use a binder containing the same polymer, which can effectively alleviate the slurry segregation phenomenon and improve the slurry's processability.

[0014] In any embodiment, the solvent used in the second stirring has a mass percentage of 5%-25%, optionally 10%-20%, based on the total mass of the positive electrode active material and the binder.

[0015] In any embodiment, the solvent used in the third stirring has a mass percentage of 25%-45%, optionally 30%-40%, based on the total mass of the positive electrode active material and the binder.

[0016] In any embodiment, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 40%-80%, optionally 50%-70%, and the mass percentage of the binder used in the third stirring is 20%-60%, optionally 30%-50%.

[0017] By properly controlling the proportion of binder added in batches, the agglomeration of high molecular weight polymers can be effectively reduced, the viscosity of the slurry at the time of shipment and after standing for 24 hours can be adjusted, the coatability and processability of the slurry can be improved, and the anti-settling and anti-gelling properties of the slurry can be enhanced.

[0018] In any embodiment, the stirring time in the first stirring is 5 minutes to 25 minutes, and can be selected as 10 minutes to 20 minutes.

[0019] In any embodiment, the revolution speed in the first stirring is 15 rpm to 35 rpm, and can be selected as 20 rpm to 30 rpm.

[0020] In any embodiment, the stirring time in the second stirring is 20 minutes to 60 minutes, and can be selected as 30 minutes to 50 minutes.

[0021] In any embodiment, the revolution speed in the second stirring is 15 rpm to 35 rpm, and can be selected as 20 rpm to 30 rpm.

[0022] In any embodiment, the rotation speed of the second stirring is 300 rpm to 700 rpm, and can be selected as 400 rpm to 600 rpm.

[0023] In any embodiment, the stirring time in the third stirring is 90 minutes to 130 minutes, and can be selected as 100 minutes to 120 minutes.

[0024] In any embodiment, the revolution speed in the third stirring is 15 rpm to 35 rpm, and can be selected as 20 rpm to 30 rpm.

[0025] In any embodiment, the rotation speed of the third stirring is 900 rpm to 1300 rpm, and can be selected as 1000 rpm to 1200 rpm.

[0026] By controlling the above parameters within a suitable range, it is possible to reduce the viscosity of the slurry at the time of shipment and after standing for 24 hours, improve the coatability and processability of the slurry, enhance the anti-settling and anti-gelling properties of the slurry, improve the storability of the slurry, and broaden the process window for slurry coating, while also taking cost-effectiveness into account.

[0027] In any embodiment, the mass ratio of the total mass of the positive electrode active material, the total mass of the binder, and the mass of the conductive agent in the positive electrode slurry is (90-99.8):(0.1-5):(0.1-5), and can be selected as (92-96):(2-4):(2-4).

[0028] The preparation method disclosed in this application makes full use of the excellent adhesion of high molecular weight polymers, which can effectively increase the loading of active materials in the electrode, so that the slurry containing a high content of positive electrode active material still has low shipping viscosity and anti-gelling properties, which can meet the high energy density requirements of batteries.

[0029] In any embodiment, the positive electrode active material comprises at least one of lithium iron phosphate and its modified materials, lithium cobalt oxide and its modified materials, and lithium manganese oxide and its modified materials, wherein the modified material is prepared by one or more modification methods selected from doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0030] The second aspect of this application provides a positive electrode slurry, which is prepared by the preparation method of the first aspect of this application.

[0031] In any embodiment, the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 7000mPa·s-39000mPa·s, optionally 7600mPa·s-24000mPa·s.

[0032] The slurry of this application retains a suitable viscosity even at high solids content and has excellent processability. The slurry can be directly used in subsequent coating processes, which can improve production efficiency.

[0033] In any embodiment, after being left to stand for 24 hours after shipment, the viscosity of the positive electrode slurry does not exceed 50,000 mPa·s.

[0034] A third aspect of this application provides a positive electrode sheet, including a positive electrode film layer, which is mainly prepared from the positive electrode slurry provided in the second aspect of this application.

[0035] A fourth aspect of this application provides a secondary battery, including the positive electrode provided in the third aspect of this application.

[0036] In any embodiment, the secondary battery is any one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, and a potassium-ion battery.

[0037] The fifth aspect of this application provides an electrical device, including the secondary battery provided in the fourth aspect of this application. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0039] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown;

[0040] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0041] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0042] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0043] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0046] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode slurry preparation method, the positive electrode slurry, the positive electrode sheet, the secondary battery, and the power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0047] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0049] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0050] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0051] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0052] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0053] Studies have shown that using high molecular weight polymers as binders can effectively improve the adhesion of electrodes and increase the loading of active materials at low dosages, thereby improving the energy density of batteries. However, the existing slurry mixing process has poor applicability and cannot meet the processing requirements of polymers with different molecular weights. In particular, the slurry containing high molecular weight polymers has poor stability, is prone to sedimentation and gelation, and is difficult to meet the production requirements of electrodes.

[0054] Based on this, this application proposes a method for preparing a positive electrode slurry, including a first stirring, a second stirring, and a third stirring; in the first stirring, a positive electrode active material and a binder are mixed and stirred to prepare a dry mixture; in the second stirring, a solvent is kneaded with the dry mixture to prepare a primary slurry; in the third stirring, a conductive agent, a solvent, a binder, and the primary slurry are mixed and stirred to prepare a positive electrode slurry.

[0055] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials 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 include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0056] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] In some embodiments, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0058] In some implementations, the solvent is an aqueous medium, such as deionized water.

[0059] In some embodiments, the solvent is an oily medium selected from one or more of N-methyl-2-pyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide, and 3-butoxy-N-methylpropionamide.

[0060] In this article, the term "kneading" refers to the process of adding a small amount of liquid to a solid powder and mixing it uniformly to prepare a plastic or paste-like material.

[0061] In this article, the term "process window" refers to the process range that can guarantee product quality, including but not limited to temperature range, pressure range, storage time length, etc. It can be understood that the wider the process window, the lower the requirement for process precision.

[0062] In this preparation method, the positive electrode active material and binder are first stirred to obtain a dry mixture, which facilitates the uniform dispersion and bonding of the binder to the surface of the positive electrode active material. Then, a small amount of solvent is added for kneading. The positive electrode active material and binder absorb the solvent simultaneously, making the slurry in a moderately wet state to facilitate the kneading process. This prevents the positive electrode active material and binder from agglomerating during kneading, enhancing the dispersibility of the slurry. At the same time, under the wetting effect of the solvent, the chain segments of the binder further extend, and the binder tightly wraps the surface of the positive electrode active material. Finally, the conductive agent, solvent, and binder are added again to change the slurry from a kneaded state to a solution state. Under the strong shearing action induced by stirring, the various components are evenly dispersed, improving the dispersibility and stability of the slurry. In addition, in the solution state, the chain segments of the binder can fully extend and tightly coat the positive electrode active material and conductive agent, playing a stabilizing and dispersing role in the materials in the slurry and slowing down the gelation of the slurry. By using a stepwise addition method of binder, the polymer can be gradually dissolved and effectively dispersed, which is especially suitable for the processing and manufacturing of high molecular weight polymers and improves the uniformity of the slurry.

[0063] The preparation method disclosed in this application has broad applicability and is applicable to binders of different molecular weights, especially high molecular weight binders. This effectively improves the anti-gelling property of slurries containing high molecular weight binders, optimizes the uniformity of the slurry, and helps to reduce preparation costs and improve production efficiency.

[0064] In some embodiments, the binder in the first stirring and / or the binder in the third stirring comprises at least one fluoropolymer with a weight-average molecular weight of 1.5 million to 8 million.

[0065] In some embodiments, the weight-average molecular weight of the fluoropolymer is any one or more of 1.5 million, 2 million, 2.5 million, 3 million, 3.5 million, 4 million, 4.5 million, 5 million, 5.5 million, 6 million, 6.5 million, 7 million, 7.5 million, and 8 million.

[0066] In this document, the term "weight-average molecular weight" is common knowledge in the art and has a commonly known meaning, and can be determined using instruments and methods known in the art. For example, gel permeation chromatography can be used, referring to the GB / T21863-2008 standard.

[0067] In this document, the term "fluoropolymer" refers to a polymer having fluorinated groups.

[0068] In some embodiments, the fluoropolymer includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0069] In some embodiments, the fluoropolymer includes polyvinylidene fluoride.

[0070] Fluoropolymers possess excellent bonding properties and electrochemical stability, but agglomeration and gelation are prone to occur during their preparation. The preparation method described in this application is applicable to high molecular weight fluoropolymers and can effectively alleviate gelation and sedimentation phenomena in different slurries, thereby improving production efficiency and broadening the process window for slurry coating.

[0071] In some embodiments, the binder in the first stirring and / or the binder in the third stirring comprises at least two fluoropolymers with a weight-average molecular weight difference of no more than 6.5 million.

[0072] In some embodiments, the adhesive contains two or more polyvinylidene fluoride (PVDF) compounds with different weight-average molecular weights, wherein the difference in weight-average molecular weight between the PVDF compounds is no higher than 6.5 million, 6 million, 5 million, 4 million, 3 million, 2 million, 1 million, 500,000, or any value between them.

[0073] Existing cathode slurry preparation methods suffer from poor compatibility and cannot accommodate variations in the weight-average molecular weight of binders within the slurry, thus imposing high precision requirements on the materials. This application addresses this by combining and controlling a stepwise slurry mixing and kneading process, thereby reducing the final viscosity of the cathode slurry, mitigating gelation, and improving its anti-settling and anti-gelling properties. This allows slurries with binders of different weight-average molecular weights to maintain low final viscosity and anti-gelling characteristics, enhancing the versatility of the preparation method.

[0074] The applicant unexpectedly discovered that the preparation method disclosed in this application can effectively adapt to cathode slurries containing various weight-average molecular weight binders. Unlike the phenomenon in the prior art where binders of different molecular weights easily lead to increased slurry sedimentation, the cathode slurry prepared using the method of this application can effectively utilize the characteristics of polyvinylidene fluoride binders of different molecular weights, improving the slurry's anti-settling properties through the interaction of large and small chain segments and steric hindrance.

[0075] In some embodiments, the binder in the first stirring and the binder in the third stirring comprise the same fluoropolymer.

[0076] The first and third stirring processes use a binder containing the same fluoropolymer, which effectively alleviates slurry segregation and improves slurry processability.

[0077] In some embodiments, the solvent used in the second stirring has a mass percentage of 5%-25%, optionally 10%-20%, based on the total mass of the positive electrode active material and the binder.

[0078] In some embodiments, the mass percentage of the solvent used in the second stirring is 5%, 10%, 15%, 20%, 25%, or any value between them, based on the total mass of the positive electrode active material and the binder.

[0079] Controlling the quality of the solvent used in the second stirring process, based on the ratio of the total mass of the positive electrode active material and the binder within a suitable range, can reduce the slurry's discharge viscosity and viscosity after standing for 24 hours, improve the slurry's coatability and processability, enhance its anti-settling and anti-gelling properties, improve its storage properties, and broaden the slurry coating process window, while also taking cost-effectiveness into account.

[0080] In some embodiments, based on the total mass of the positive electrode active material and the binder, the mass percentage of the solvent used in the third stirring is 25%-45%, optionally 30%-40%. In some embodiments, based on the total mass of the positive electrode active material and the binder, the mass ratio of the solvent used in the third stirring can be 25%, 30%, 35%, 40%, 45%, or any value between these values.

[0081] Controlling the quality of the solvent used in the third stirring process, based on the ratio of the total mass of the positive electrode active material and the binder within a suitable range, can reduce the slurry's discharge viscosity and viscosity after standing for 24 hours, improve the slurry's coatability and processability, enhance its anti-settling and anti-gelling properties, improve its storage properties, and broaden the slurry coating process window, while also taking cost-effectiveness into account.

[0082] In some embodiments, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 40%-80%, optionally 50%-70%, and the mass percentage of the binder used in the third stirring is 20%-60%, optionally 30%-50%.

[0083] In some embodiments, based on the total mass of the binder, the first stirring uses 40% by mass and the third stirring uses 60% by mass. In some embodiments, based on the total mass of the binder, the first stirring uses 50% by mass and the third stirring uses 50% by mass. In some embodiments, based on the total mass of the binder, the first stirring uses 60% by mass and the third stirring uses 40% by mass. In some embodiments, based on the total mass of the binder, the first stirring uses 70% by mass and the third stirring uses 30% by mass. In some embodiments, based on the total mass of the binder, the first stirring uses 80% by mass and the third stirring uses 20% by mass. By properly controlling the proportion of binder added in batches, the agglomeration of high molecular weight polymers can be effectively reduced, the viscosity of the slurry at the time of shipment and after standing for 24 hours can be adjusted, the coatability and processability of the slurry can be improved, and the anti-settling and anti-gelling properties of the slurry can be enhanced.

[0084] In some embodiments, the stirring time in the first stirring is 5 minutes to 25 minutes, and can be selected as 10 minutes to 20 minutes.

[0085] In some embodiments, the stirring time in the first stirring can be selected as 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or any value between them.

[0086] Reasonable control of the first stirring time is conducive to further uniform dispersion of the binder and the positive electrode active material, so that the binder is further bonded to the surface of the positive electrode active material, improving the dispersibility of the dry mix, effectively adjusting the viscosity of the slurry at the time of delivery and the viscosity after standing for 24 hours, improving the coating and processability of the slurry, and improving the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0087] In some embodiments, the revolution speed in the first stirring is 15 rpm to 35 rpm, and can be selected as 20 rpm to 30 rpm.

[0088] In some embodiments, the revolution speed in the first stirring is 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, or any value between them.

[0089] In this article, the term "revolution speed" refers to the speed at which the agitator rotates around the vessel containing the material.

[0090] Reasonable control of the revolution speed of the first stirring is conducive to the further uniform dispersion of the binder and the positive electrode active material, so that the binder is further bonded to the surface of the positive electrode active material, improving the dispersibility of the dry mix, effectively adjusting the viscosity of the slurry at the time of delivery and the viscosity after standing for 24 hours, improving the coating and processability of the slurry, and improving the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0091] In some embodiments, the stirring time in the second stirring is 20-60 minutes, and optionally 30-50 minutes.

[0092] In some embodiments, the stirring time in the second stirring is 20 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 60 minutes or any value between them.

[0093] Reasonable control of the stirring time of the second stirring is beneficial to improve the dispersibility of the primary slurry, effectively adjust the slurry's output viscosity and viscosity after standing for 24 hours, improve the slurry's coatability and processability, and enhance the slurry's anti-settling and anti-gelling properties while taking cost-effectiveness into account.

[0094] In some embodiments, the revolution speed in the second stirring is 15 rpm to 35 rpm, and can be selected as 20 rpm to 30 rpm.

[0095] In some embodiments, the revolution speed in the second stirring is 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, or any value between them.

[0096] By properly controlling the revolution speed of the second agitator, the viscosity of the slurry at the time of delivery and after standing for 24 hours can be effectively adjusted, thereby improving the coating and processability of the slurry, enhancing its anti-settling and anti-gelling properties, and taking into account cost-effectiveness.

[0097] In some embodiments, the rotation speed of the second stirring is 300 rpm to 700 rpm, and can be selected as 400 rpm to 600 rpm.

[0098] In some embodiments, the rotation speed of the second stirring is 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, or any value between them.

[0099] In this article, the term "rotation speed" refers to the speed at which the stirrer rotates about its own axis.

[0100] By properly controlling the rotation speed of the second agitator, the viscosity of the slurry at the point of shipment and after standing for 24 hours can be effectively adjusted, improving the coating and processability of the slurry, enhancing its anti-settling and anti-gelling properties, while also taking cost-effectiveness into account.

[0101] In some embodiments, the stirring time in the third stirring is 90-130 minutes, and can be selected as 100-120 minutes.

[0102] In some embodiments, the stirring time in the third stirring is 90 minutes, 100 minutes, 110 minutes, 120 minutes, 130 minutes, or any value between them.

[0103] Reasonable control of the third stirring time is conducive to the full dispersion of conductive agent and binder around the positive electrode active material, effectively adjusting the slurry's output viscosity and viscosity after standing for 24 hours, improving the slurry's coatability and processability, and enhancing its anti-settling and anti-gelling properties while taking cost-effectiveness into account.

[0104] In some embodiments, the revolution speed in the third stirring is 15 rpm to 35 rpm, and can be selected as 20 rpm to 30 rpm.

[0105] In some embodiments, the revolution speed in the third stirring is 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, or any value between them.

[0106] By properly controlling the revolution speed of the third agitator, the viscosity of the slurry at the point of shipment and after standing for 24 hours can be effectively adjusted, improving the coating and processability of the slurry, enhancing its anti-settling and anti-gelling properties, while also taking cost-effectiveness into account.

[0107] In some embodiments, the rotation speed of the third stirring is 900 rpm to 1300 rpm, and can be selected as 1000 rpm to 1200 rpm.

[0108] In some embodiments, the rotation speed of the third stirring is 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, or any value between them.

[0109] By properly controlling the rotation speed of the third agitator, the viscosity of the slurry at the point of shipment and after standing for 24 hours can be effectively adjusted, improving the coating and processability of the slurry, enhancing its anti-settling and anti-gelling properties, while also taking cost-effectiveness into account.

[0110] In some embodiments, the mass ratio of the total mass of the positive electrode active material, the total mass of the binder, and the mass of the conductive agent in the positive electrode slurry is (90-99.8):(0.1-5):(0.1-5), and can be selected as (92-96):(2-4):(2-4).

[0111] In some embodiments, the mass ratio of positive electrode active material, binder and conductive agent in the positive electrode slurry can be selected as any one of 92:4:4, 93:3:4, 94:4:2, 95:3:2, 96:2:4, 95:2:3, 96:2.5:1.5, and 98:1:1.

[0112] The preparation method disclosed in this application makes full use of the excellent adhesion of high molecular weight polymers, which can effectively increase the loading of active materials in the electrode, so that the slurry containing a high content of positive electrode active material still has low shipping viscosity and anti-gelling properties, which can meet the high energy density requirements of batteries.

[0113] In some embodiments, the positive electrode active material comprises at least one of lithium iron phosphate and its modified materials, lithium cobalt oxide and its modified materials, and lithium manganese oxide and its modified materials, wherein the modified material is prepared by one or more modification methods selected from doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0114] The second aspect of this application provides a positive electrode slurry, which is prepared by a positive electrode slurry preparation method according to any embodiment.

[0115] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 7000mPa·s-39000mPa·s, optionally 7600mPa·s-24000mPa·s.

[0116] The slurry preparation method provided in this application can effectively increase the solid content of the slurry. Low-solid-content slurries require more solvent evaporation during the electrode drying process, leading to reduced coating speed and increased equipment energy consumption. Simultaneously, excessively low solid content slurries necessitate extended heating and drying times during coating, potentially causing electrode edge curling, cracking, and reduced adhesion due to binder floating. The high-solid-content slurry disclosed in this application not only meets the requirements for faster coating but also satisfies the requirements for longer slurry storage time and a wider process window, effectively improving production efficiency and reducing costs. In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry can be selected from 7000 mPa·s, 7600 mPa·s, 8000 mPa·s, 10000 mPa·s, 15000 mPa·s, 20000 mPa·s, 24000 mPa·s, 25000 mPa·s, 30000 mPa·s, 35000 mPa·s, 39000 mPa·s or any value between them.

[0117] The shipping viscosity refers to the viscosity of the cathode slurry immediately after preparation.

[0118] The slurry of this application has a suitable viscosity and excellent processability. The slurry can be directly used in subsequent coating processes, which can improve production efficiency.

[0119] In some embodiments, after being left to stand for 24 hours after shipment, the viscosity of the positive electrode slurry does not exceed 50,000 mPa·s.

[0120] In some embodiments, after being left to stand for 24 hours after shipment, the viscosity of the positive electrode slurry does not exceed any one of 50000 mPa·s, 45000 mPa·s, 40000 mPa·s, 35000 mPa·s, 30000 mPa·s, 25000 mPa·s, 20000 mPa·s, 15000 mPa·s, or 10000 mPa·s.

[0121] The cathode slurry provided in this application has excellent storage performance and broadens the process window of the slurry.

[0122] In some implementations, after being left to stand for 24 hours after shipment, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed 1.5%.

[0123] In some implementations, after being left to stand for 24 hours after shipment, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed any one of 1.5%, 1%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1%.

[0124] A third aspect of this application provides a positive electrode sheet, including a positive electrode film layer, said positive electrode film layer being mainly prepared from a positive electrode slurry of any embodiment.

[0125] A fourth aspect of this application provides a secondary battery including a positive electrode sheet of any embodiment.

[0126] In some embodiments, the secondary battery is any one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, or a potassium-ion battery.

[0127] [Positive electrode plate]

[0128] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer is prepared from a slurry prepared by the preparation method in any embodiment of this application.

[0129] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0130] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0131] In some embodiments, the positive electrode sheet can be prepared by coating the positive electrode slurry prepared by any of the above preparation methods onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0132] [Negative electrode plate]

[0133] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0134] As an example, the negative electrode current collector has two surfaces opposite each other in its own 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.

[0135] 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 substrate and a metal layer formed on at least one surface of the polymer 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0136] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. 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, and 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, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0137] In some embodiments, the negative electrode film layer may optionally 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).

[0138] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0139] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0140] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0141] [Electrolytes]

[0142] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0143] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0144] 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0145] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0146] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0147] [Isolation membrane]

[0148] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0149] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0150] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0151] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0152] 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. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0153] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0154] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0155] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0156] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0157] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0158] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0159] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0160] In addition, this application also provides an electrical device, which 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, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0161] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0162] Figure 6 This is an example of an electrical device. The device could be 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 for this device, a battery pack or battery module can be used.

[0163] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0164] Example

[0165] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0166] I. Preparation Method

[0167] Example 1

[0168] 1) Preparation of positive electrode slurry

[0169] First mixing: 960 kg of positive electrode active material and 13.3 kg of polyvinylidene fluoride with a weight average molecular weight of 1.5 million were added to a 1300 L double planetary mixer for the first mixing. The first mixing speed was 25 rpm and the mixing time was 15 minutes to obtain a dry mixture.

[0170] Second stirring: 146 kg of NMP (N-methylpyrrolidone) solvent was added to a double planetary mixer and mixed with the dry mixture for a second stirring. The mass of NMP solvent added in the second stirring was 15% of the total mass of the positive electrode active material and the binder. The revolution speed was 25 rpm, the rotation speed was 500 rpm, and the stirring time was 40 minutes to obtain the primary slurry.

[0171] Third stirring: 20 kg of conductive carbon black, 6.7 kg of polyvinylidene fluoride, and 340.6 kg of NMP solvent are mixed with the primary slurry for a third stirring. The mass of NMP solvent added in the third stirring is 35% of the total mass of the positive electrode active material and binder. The revolution speed is 25 rpm, the rotation speed is 1100 rpm, and the stirring time is 110 minutes to obtain the positive electrode slurry with a solid content of 70%.

[0172] Example 2-55

[0173] The process is basically the same as in Example 1, except that the preparation parameters of the positive electrode slurry were adjusted. For specific parameters, please refer to Table 1. In Examples 5-7, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 2:1. In Examples 8-10, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, and the third polyvinylidene fluoride is 3:2:1. In Example 11, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, the third polyvinylidene fluoride, and the fourth polyvinylidene fluoride is 4:3:2:1.

[0174] Comparative Example 1

[0175] 960 kg of positive electrode active material and 13.3 kg of polyvinylidene fluoride with a weight average molecular weight of 1.5 million were added to a 1300 L double planetary mixer and mixed for 10 minutes at a revolution speed of 25 rpm to obtain a dry mixture.

[0176] 392 kg of NMP (N-methylpyrrolidone) solvent, 20 kg of conductive carbon black, and 6.7 kg of binder were added to a double planetary mixer and mixed with the dry mixture. The planetary speed was 25 rpm, the mixing time was 150 minutes, and the rotation speed was 1100 rpm to obtain the positive electrode slurry.

[0177] Comparative Example 2-12

[0178] The preparation methods of Comparative Examples 2-11 are basically the same as those of Comparative Example 1, except that the composition and weight-average molecular weight of the binder are adjusted. In Comparative Examples 5-7, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 2:1. In Comparative Examples 8-10, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, and the third polyvinylidene fluoride is 3:2:1. In Comparative Example 11, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, the third polyvinylidene fluoride, and the fourth polyvinylidene fluoride is 4:3:2:1. For specific parameters, please refer to Table 1.

[0179] The preparation method of Comparative Example 12 is basically the same as that of Example 2, except that the binder in Comparative Example 12 is not added in the first stirring, but only in the third stirring, and the amount added is the total amount of binder in Example 2.

[0180] II. Testing Methods

[0181] 1. Test of the difference in solid content between the upper and lower layers of the slurry after 24 hours of settling.

[0182] Weigh the aluminum foil in a moisture analyzer and record the weight as M0. The model of the moisture analyzer is MOC-120H.

[0183] After the slurry has been left to stand for 24 hours, take a small amount of the upper slurry and coat it onto aluminum foil. Zero the moisture analyzer and then weigh it in the moisture analyzer. Record this as M1.

[0184] Close the equipment and begin drying;

[0185] After completion, record the weighing data as M2, and calculate the solid content as (M2-M0) / (M1-M0);

[0186] The solid content of the lower layer slurry was measured using the same method. The difference between the solid content of the lower layer slurry and the solid content of the upper layer slurry was taken as the solid content difference between the upper and lower layers after the slurry had been left to stand for 24 hours.

[0187] 2. Viscosity test of the shipped slurry

[0188] The prepared positive electrode slurry was left to stand for 10 minutes before being shipped. The viscosity value measured using a Dveslvtjo rotational viscometer (BROOKFIELD) was recorded as the shipping viscosity. The test conditions were: 25℃, rotation speed 12 rpm. A 64 rotor was used when the slurry viscosity was not less than 2000 mPa·s, and a 62 rotor was used when the slurry viscosity was less than 2000 mPa·s. Three parallel measurements were performed, and the average value was taken.

[0189] 3. Viscosity test of slurry after standing for 24 hours

[0190] After the prepared positive electrode slurry was left to stand for 24 hours, the viscosity value measured using a Dveslvtjo rotational viscometer (BROOKFIELD) was recorded as the 24-hour viscosity. The test conditions were: 25℃, rotation speed 12 rpm. A 64 rotor was used when the slurry viscosity was not lower than 2000 mPa·s, and a 62 rotor was used when the slurry viscosity was less than 2000 mPa·s. Three parallel measurements were performed, and the average value was taken.

[0191] 4. Gelation test of slurry after standing for 24 hours

[0192] After the slurry has been left to stand for 24 hours, use a steel ruler to lift the slurry in the beaker and judge whether the slurry is non-gelled, slightly gelled, moderately gelled, or severely gelled based on its flow state.

[0193] gel-free state: The slurry flows naturally and continuously, and flows horizontally on the surface of the steel ruler without clumping;

[0194] Slightly gelled state: The slurry flows naturally and continuously, but the fluid is relatively fine. The slurry is basically spread evenly on the surface of the steel ruler, with slight small lumps.

[0195] The state of moderate gelation: the slurry drips naturally, intermittently; it flows discontinuously, and the slurry cannot be spread evenly on the steel ruler surface, with obvious lumps and agglomerations;

[0196] Severe gelling condition: The slurry cannot flow down, it clumps up and falls off, or it stays directly on the steel ruler and cannot flow down.

[0197] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0198] The positive electrode slurries of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in Table 1 and Table 2 below.

[0199] Table 1

[0200]

[0201]

[0202]

[0203] Table 2

[0204]

[0205]

[0206]

[0207] The positive electrode slurry in the embodiments is prepared using the slurry preparation method disclosed in this application, including a first stirring, a second stirring and a third stirring; in the first stirring, the positive electrode active material and the binder are mixed and stirred to prepare a dry mixture; in the second stirring, the solvent is kneaded with the dry mixture to prepare a primary slurry; in the third stirring, the conductive agent, the solvent, the binder and the primary slurry are mixed and stirred to prepare the positive electrode slurry.

[0208] As can be seen from the comparison between the examples and the comparative examples, the preparation method disclosed in this application has broad applicability and is applicable to binders with different weight-average molecular weights. It can improve the anti-settling and anti-gelling properties of the slurry, which is beneficial to improving processing efficiency and reducing processing costs.

[0209] As can be seen from the comparison between the examples and the comparative examples, the binder in the first stirring and the binder in the third stirring both contain at least one polyvinylidene fluoride with a weight average molecular weight of 1.5 million to 8 million.

[0210] As can be seen from the comparative examples, existing preparation processes struggle to reduce the final viscosity of high molecular weight binders, resulting in severe gelation of the slurry. However, the preparation method disclosed in this application ensures that slurries containing binders with a weight-average molecular weight as high as 8 million still exhibit good anti-settling and anti-gelling properties, meeting the requirements for next-generation high molecular weight binders.

[0211] As can be seen from the comparison between Examples 5-11 and Comparative Examples 5-11, this application is also applicable to slurries with binders having different weight-average molecular weights. Unlike the preparation methods in the prior art, the preparation method disclosed in this application can effectively overcome the slurry gelation phenomenon caused by large differences in the molecular weight of the binders. This preparation method has broader applicability.

[0212] As can be seen from the comparison of Examples 2 and 12-15, controlling the mass percentage of the solvent used in the second stirring to be 10% to 20% of the total mass of the positive electrode active material and binder can further reduce the discharge viscosity of the slurry and the viscosity of the slurry after standing for 24 hours while maintaining the high solid content of the slurry. It can also reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, improve the anti-settling and anti-gelling properties of the slurry, improve the storage performance of the slurry, and broaden the process window for slurry coating.

[0213] As can be seen from the comparison of Examples 2 and 16-19, controlling the mass content of the solvent used in the third stirring to be 30% to 40% of the total mass of the positive electrode active material and binder can further reduce the discharge viscosity of the slurry and the viscosity of the slurry after standing for 24 hours while maintaining the high solid content of the slurry. It can also reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness, improve the storage performance of the slurry, and broaden the process window for slurry coating.

[0214] As can be seen from the comparison of Examples 2 and 20-23, based on the total mass of the binder, the mass ratio of the binder used in the first stirring is 50%-70%, and the mass ratio of the binder used in the third stirring is 30%-50%. This can further reduce the discharge viscosity of the slurry and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, improve the anti-settling and anti-gelling properties of the slurry, improve the storage performance of the slurry, and broaden the process window for slurry coating.

[0215] As can be seen from the comparison of Examples 2 and 24-27, the stirring time in the first stirring is 10-20 minutes, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, improve the anti-settling and anti-gelling properties of the slurry, improve the storage performance of the slurry, and broaden the process window for slurry coating.

[0216] As can be seen from the comparison of Examples 2 and 28-31, the revolution speed in the first stirring is 20 rpm to 30 rpm, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0217] As can be seen from the comparison of Examples 2 and 32-35, the revolution speed of the second stirring is 20 rpm to 30 rpm, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0218] As can be seen from the comparison of Examples 2 and 36-39, the rotation speed of the second stirrer is 400 rpm to 600 rpm, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0219] As can be seen from the comparison of Examples 2 and 40-43, the stirring time of the second stirring is 30-50 minutes, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0220] As can be seen from the comparison of Examples 2 and 44-47, the revolution speed in the third stirring is 20 rpm to 30 rpm, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0221] As can be seen from the comparison of Examples 2 and 48-51, the rotation speed in the third stirring is 1000 rpm to 1200 rpm, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0222] As can be seen from the comparison of Examples 2 and 52-55, the stirring time in the third stirring is 100-120 minutes, which helps to further reduce the viscosity of the slurry at the time of delivery and the viscosity of the slurry after standing for 24 hours, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and improve the anti-settling and anti-gelling properties of the slurry while taking into account cost-effectiveness.

[0223] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a positive electrode slurry, characterized in that, The preparation method includes a first stirring, a second stirring, and a third stirring. In the first stirring, the positive electrode active material and the binder are mixed and stirred to prepare a dry mixture; In the second stirring process, the solvent is kneaded with the dry mixture to prepare a primary slurry; In the third stirring process, the conductive agent, solvent, binder and primary slurry are mixed and stirred to prepare the positive electrode slurry; The binder in the first stirring and / or the binder in the third stirring comprises at least one fluoropolymer with a weight-average molecular weight of 1.5 million to 6 million. The stirring time of the first mixer is 10-25 minutes, and the revolution speed is 20-35 revolutions per minute; based on the total mass of the binder, the mass percentage of the binder used in the first mixer is 50%-70%; The second stirring has a revolution speed of 20-35 rpm and a rotation speed of 400-700 rpm; the stirring time is 30-60 minutes; and the solvent used in the second stirring has a mass percentage of 10%-25% based on the total mass of the positive electrode active material and binder. The stirring time of the third stirring is 100-130 minutes, the revolution speed is 20-35 rpm, and the rotation speed is 1000-1300 rpm; based on the total mass of the positive electrode active material and the binder, the mass percentage of the solvent used in the third stirring is 30%-45%.

2. The preparation method according to claim 1, characterized in that, The binder in the first stirring and / or the binder in the third stirring comprises at least two fluoropolymers with a weight-average molecular weight difference of no more than 6.5 million.

3. The preparation method according to claim 2, characterized in that, The fluoropolymer includes polyvinylidene fluoride.

4. The preparation method according to claim 2, characterized in that, The binder in the first stirring and the binder in the third stirring both comprise the same fluoropolymer.

5. The preparation method according to claim 1, characterized in that, Based on the total mass of the positive electrode active material and the binder, the solvent used in the second stirring process has a mass percentage of 10%-20%, and / or Based on the total mass of the positive electrode active material and the binder, the solvent used in the third stirring has a mass percentage of 30%-40%.

6. The preparation method according to claim 1, characterized in that, The first stirring satisfies at least one of the following conditions: (i) Stirring time is 10-20 minutes; (ii) The revolution speed is 20 revolutions per minute to 30 revolutions per minute.

7. The preparation method according to claim 1, characterized in that, The second stirring satisfies at least one of the following conditions: (i) The stirring time is 30-50 minutes; (ii) The revolution speed is 20 revolutions per minute to 30 revolutions per minute; (iii) The rotation speed is 400 rpm - 600 rpm.

8. The preparation method according to claim 1, characterized in that, The third stirring satisfies at least one of the following conditions: (i) The stirring time is 100-120 minutes; (ii) The revolution speed is 20 revolutions per minute to 30 revolutions per minute; (iii) The rotation speed is 1000 rpm - 1200 rpm.

9. The preparation method according to claim 1, characterized in that, In the positive electrode slurry, the mass ratio of the total mass of the positive electrode active material, the total mass of the binder, and the mass of the conductive agent is (90-99.8):(0.1-5):(0.1-5).

10. The preparation method according to claim 9, characterized in that, In the positive electrode slurry, the mass ratio of the total mass of the positive electrode active material, the total mass of the binder, and the mass of the conductive agent is (92-96):(2-4):(2-4).

11. A positive electrode slurry, characterized in that, The positive electrode slurry is prepared by the preparation method according to any one of claims 1 to 10.

12. The positive electrode slurry according to claim 11, wherein the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 7000 mPa·s-39000 mPa·s.

13. The positive electrode slurry according to claim 12, wherein the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 7600 mPa·s-24000 mPa·s.

14. A positive electrode plate, characterized in that, It includes a positive electrode film layer, which is prepared from the positive electrode slurry according to any one of claims 11 to 13.

15. A secondary battery, characterized in that, Includes the positive electrode sheet as described in claim 14.

16. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 15.

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