Preparation method of positive electrode slurry, positive electrode slurry, positive electrode sheet, secondary battery and electrical device

Abstract

This application provides a method for preparing a positive electrode slurry, a positive electrode slurry, a positive electrode sheet, a secondary battery, and an electrical device. The method for preparing the positive electrode slurry includes 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 the primary slurry are mixed and stirred to prepare a positive electrode slurry, wherein the binder contains at least one fluoropolymer with a weight-average molecular weight of 150,000 to 1,500,000.

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 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 slurry preparation method—has a crucial influence on the slurry's dispersibility, uniformity, and stability. Current slurry preparation processes are often one-step methods, directly mixing and stirring the components of the positive electrode active slurry. However, this one-step method cannot meet the manufacturing requirements of binders with different weight-average molecular weights, resulting in poor versatility and hindering cost reduction. Therefore, a new slurry preparation method needs to be developed to be applicable to binders with different weight-average 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, so as to adapt to binders with different weight-average 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, including a first stirring, a second stirring, and a third stirring;

[0006] In the first stirring, the positive electrode active material and the binder are mixed and stirred to prepare a dry mixture;

[0007] In the second mixing process, the solvent and dry mixture are kneaded together to prepare a primary slurry;

[0008] In the third stirring process, the conductive agent, solvent and primary slurry are mixed and stirred to prepare the positive electrode slurry;

[0009] The adhesive contains at least one fluoropolymer with a weight-average molecular weight of 150,000 to 1,500,000.

[0010] The preparation method disclosed in this application is universally applicable to both low-molecular-weight and high-molecular-weight fluoropolymer binders, effectively mitigating gelation phenomena in different slurries, thus improving production efficiency and broadening the coating window of the slurry. The preparation method disclosed in this application is applicable to binders with a weight-average molecular weight as high as 1.5 million, ensuring that slurries containing high weight-average molecular weight binders still exhibit low shipping viscosity, anti-gelling properties, and anti-settling properties, meeting the application requirements of next-generation binders.

[0011] In any embodiment, the binder comprises at least two fluoropolymers with a weight-average molecular weight difference of no more than 1.5 million.

[0012] 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 fluoropolymer binders of different molecular weights, improving the slurry's anti-settling properties through the interaction of large and small chain segments and steric hindrance.

[0013] In any embodiment, the fluoropolymer includes polyvinylidene fluoride.

[0014] In any embodiment, the solvent used in the second stirring is the same as the solvent used in the third stirring, and the mass content of the solvent used in the second stirring is 10% to 20% based on the total mass of the positive electrode active material and the binder.

[0015] Controlling the mass content of the solvent used in the second stirring within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0016] In any embodiment, the solvent content used in the third stirring is 20% to 30% based on the total mass of the positive electrode active material and the binder.

[0017] Controlling the mass content of the solvent used in the third stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0018] In any embodiment, the revolution speed in the first stirring is 10 rpm to 20 rpm.

[0019] Controlling the revolution speed during the first stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance, and stability of the slurry.

[0020] In any embodiment, the stirring time in the first stirring is 10 to 20 minutes.

[0021] Controlling the stirring time in the first stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0022] In any embodiment, the revolution speed in the second stirring is 20 rpm to 30 rpm.

[0023] Controlling the revolution speed in the second stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0024] In any embodiment, the stirring time in the second stirring is 20 to 30 minutes.

[0025] Controlling the stirring time in the second stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0026] In any embodiment, the revolution speed in the third stirring is 20 rpm to 30 rpm.

[0027] Controlling the revolution speed in the third stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0028] In any implementation, the rotation speed of the third stirring is 1000 rpm to 1200 rpm.

[0029] Controlling the rotation speed in the third stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0030] In any implementation, the stirring time in the third stirring is 100 to 120 minutes.

[0031] Controlling the stirring time in the third stirring process within a suitable range ensures that the slurry has low delivery viscosity, low viscosity after 24 hours of standing storage, and excellent anti-settling and anti-gelling properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0032] In any embodiment, the mass ratio of positive electrode active material, binder and conductive agent in the positive electrode slurry is (92-96):(2-4):(2-4).

[0033] The preparation method of this application is more universal than existing cathode slurry preparation methods, applicable to slurries with different contents of cathode active materials. It can effectively alleviate the gelation phenomenon of different slurries, helping to improve production efficiency and broaden the coating window of the slurry. At the same time, the preparation method disclosed in this application can be applied to slurries with high contents of cathode active materials, so that slurries containing high contents of cathode active materials still have low shipping viscosity, excellent anti-settling and anti-gelling properties, and can meet the requirements of high energy density batteries.

[0034] In any embodiment, the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 4500 mPa·s to 40000 mPa·s, optionally 4500 mPa·s to 20000 mPa·s.

[0035] The slurry prepared by the method 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.

[0036] In any embodiment, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the viscosity of the positive electrode slurry does not exceed 50,000 mPa·s, and may be selected to be no more than 30,000 mPa·s.

[0037] The slurry prepared by the method of this application has excellent storage properties and broadens the process window of the slurry.

[0038] A second aspect of this application also provides a positive electrode slurry, which is prepared by the method for preparing the positive electrode slurry of the first aspect.

[0039] A third aspect of this application provides a positive electrode sheet, including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, which is obtained from a positive electrode slurry prepared by the method for preparing the positive electrode slurry of the first aspect.

[0040] The fourth aspect of this application provides a secondary battery, including a separator, a negative electrode, and a positive electrode as described in the third aspect.

[0041] The fifth aspect of this application provides an electrical device, characterized in that it includes a secondary battery as described in the fourth aspect. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0043] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0044] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0045] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0046] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0047] 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.

[0048] Explanation of reference numerals in the attached figures:

[0049] 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

[0050] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical 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.

[0051] 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.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] Positive electrode slurry is primarily a solid-liquid phase mixture system composed of positive electrode active material, conductive agent, binder, and solvent. To improve the uniformity of the distribution of different components in the system, processes such as stirring, ball milling, and ultrasonication are commonly used for slurry preparation. However, existing slurry preparation processes are generally only applicable to slurry systems with fixed components, lacking versatility. When the physical properties of the components in the slurry change, the slurry preparation process often needs adjustment. For example, existing slurry preparation processes are not suitable for high molecular weight binders, nor for binders with high weight-average molecular weight dispersion and poor batch stability. Slurries prepared using the same existing slurry preparation process with different batches of binders exhibit significant performance differences, are prone to gelation, and fail to meet the production requirements of electrode sheets.

[0058] [Preparation Method]

[0059] 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;

[0060] In the first stirring, the positive electrode active material and the binder are mixed and stirred to prepare a dry mixture;

[0061] In the second mixing process, the solvent and dry mixture are kneaded together to prepare a primary slurry;

[0062] In the third stirring process, the conductive agent, solvent and primary slurry are mixed and stirred to prepare the positive electrode slurry;

[0063] The adhesive contains at least one fluoropolymer with a weight-average molecular weight of 150,000 to 1,500,000.

[0064] In some embodiments, the adhesive comprises at least one fluoropolymer with a weight-average molecular weight of 150,000 to 1,500,000. In some embodiments, the fluoropolymer has a weight-average molecular weight of any one or more of the following: 150,000, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,050,000, 1,100,000, 1,150,000, 1,200,000, 1,250,000, 1,300,000, 1,350,000, 1,400,000, 1,450,000, and 1,500,000.

[0065] In this document, the term "fluoropolymer" refers to a polymer having fluorinated groups.

[0066] 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.

[0067] In some embodiments, the fluoropolymer includes polyvinylidene fluoride.

[0068] In this document, the term "weight-average molecular weight" refers to the statistical average molecular weight of a polymer by mass, obtained by averaging per unit weight, and can be determined using instruments and methods known in the art. For example, gel permeation chromatography can be used, with reference to the standard GB / T21863-2008.

[0069] In some embodiments, the positive electrode active material includes 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. The modified materials are prepared by one or more modification methods selected from doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0070] In some embodiments, the conductive agent may include at least one of superconducting carbon, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0071] In some embodiments, the solvent is an aqueous medium, such as deionized water. 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.

[0072] 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.

[0073] 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.

[0074] 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 liquid is added for kneading. The positive electrode active material and binder absorb the liquid 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, a conductive agent and solvent are added 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 the conductive agent, playing a stabilizing and dispersing role in the materials in the slurry and slowing down the gelation of the slurry.

[0075] 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 to reduce the output viscosity of the cathode slurry, alleviate gelation, and improve its anti-settling and anti-gelling properties. This allows slurries with high weight-average molecular weight binders to maintain low output viscosity and anti-gelling properties, enhancing the versatility of the preparation method. The preparation method presented in this application is applicable not only to low weight-average molecular weight binders but also to high weight-average molecular weight binders, effectively mitigating gelation and sedimentation phenomena in different slurries, thereby improving production efficiency and broadening the process window for slurry coating.

[0076] In some embodiments, the adhesive comprises at least two fluoropolymers with a weight-average molecular weight difference not exceeding 1.5 million. In some embodiments, the adhesive comprises two or more fluoropolymers with different weight-average molecular weights, wherein the weight-average molecular weight difference between the fluoropolymers is not higher than 1.45 million, 1.4 million, 1.35 million, 1.3 million, 1.25 million, 1.2 million, 1.15 million, 1.1 million, 1.05 million, 1 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 250,000, 200,000, 150,000, 100,000, or 50,000.

[0077] 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 fluoropolymer binders of different molecular weights, improving the slurry's anti-settling properties through the interaction of large and small chain segments and steric hindrance.

[0078] In some embodiments, the solvent used in the second stirring is the same as the solvent used in the third stirring, and the mass content of the solvent used in the second stirring is 10% to 20% based on the total mass of the positive electrode active material and the binder.

[0079] In some embodiments, the mass content of the solvent used in the second stirring is any one of 10% to 15%, 10% to 20%, or 15% to 20%, based on the total mass of the positive electrode active material and the binder.

[0080] Controlling the solvent content used in the second stirring process within a suitable range can reduce the slurry's output viscosity and viscosity after 24 hours of standing, improve its coatability and processability, enhance its resistance to sedimentation and gelation, improve its storage properties, and broaden the coating process window. Simultaneously, controlling the solvent content in the second stirring process within a suitable range can reduce solvent usage and lower costs without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, solids content difference between upper and lower layers after 24 hours of standing, or gelation phenomenon, thus achieving a balance between slurry quality and cost.

[0081] In some embodiments, the solvent used in the second stirring is the same as the solvent used in the third stirring, and the mass content of the solvent used in the third stirring is 20% to 30% based on the total mass of the positive electrode active material and the binder.

[0082] In some embodiments, based on the total mass of the positive electrode active material and the binder, the mass content of the solvent used in the third stirring can be selected as any one of 20% to 25%, 20% to 30%, or 25% to 30%.

[0083] Controlling the solvent content used in the third stirring process within a suitable range can reduce the slurry's output viscosity and viscosity after 24 hours of standing, improve its coatability and processability, enhance its resistance to sedimentation and gelation, improve its storage properties, and broaden the coating process window. Simultaneously, controlling the solvent content in the third stirring process within a suitable range can reduce solvent usage and lower costs without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, solids content difference between upper and lower layers after 24 hours of standing, or gelation phenomenon, thus achieving a balance between slurry quality and cost.

[0084] In some embodiments, the revolution speed in the first stirring is 10 to 20 revolutions per minute.

[0085] In some embodiments, the revolution speed in the first stirring can be selected as any one of 10 rpm to 15 rpm, 10 rpm to 20 rpm, or 15 rpm to 20 rpm.

[0086] In this article, the term "rotation speed" refers to the speed at which the stirrer rotates about its own axis.

[0087] In this article, the term "revolution speed" refers to the speed at which the agitator rotates around the vessel containing the material.

[0088] Controlling the revolution speed during the first stirring process within a suitable range is beneficial for the further uniform dispersion of the binder and the positive electrode active material, and for the binder to further adhere to the surface of the positive electrode active material. This improves the dispersibility of the dry mix, effectively reduces the slurry's output viscosity and viscosity after 24 hours of standing, enhances the slurry's coatability and processability, improves its anti-settling and anti-gelling properties, improves its storage properties, and broadens the process window for slurry coating. Simultaneously, controlling the revolution speed during the first stirring process within a suitable range, without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers after 24 hours of standing, or the slurry's gelation phenomenon, can reduce the power of the agitator, saving energy and balancing slurry quality and cost.

[0089] In some embodiments, the stirring time in the first stirring is 10 to 20 minutes.

[0090] In some embodiments, the stirring time in the first stirring is any one of 10-15 minutes, 10-20 minutes, or 15-20 minutes.

[0091] Controlling the stirring time within a suitable range during the first stirring step is beneficial for the further uniform dispersion of the binder and the positive electrode active material, and for the binder to further adhere to the surface of the positive electrode active material. This improves the dispersibility of the dry mix, effectively reduces the slurry's output viscosity and viscosity after 24 hours of standing, enhances the slurry's coatability and processability, improves its anti-settling and anti-gelling properties, improves its storage properties, and broadens the process window for slurry coating. Simultaneously, controlling the stirring time within a suitable range during the first stirring step, without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers after 24 hours of standing, or the gelation phenomenon, can reduce the slurry preparation time, improve slurry preparation efficiency, and lower costs.

[0092] In some embodiments, the revolution speed in the second stirring is 20 rpm to 30 rpm. In some embodiments, the revolution speed in the second stirring can be selected from any one of 20 rpm to 25 rpm, 20 rpm to 30 rpm, or 25 rpm to 30 rpm.

[0093] Controlling the revolution speed in the second agitator within a suitable range is beneficial for improving the dispersibility of the primary slurry, effectively reducing the slurry's output viscosity and viscosity after 24 hours of standing, improving its coatability and processability, enhancing its anti-settling and anti-gelling properties, improving its storage properties, and broadening the coating process window. Simultaneously, controlling the revolution speed in the second agitator within a suitable range, without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers after 24 hours of standing, or the gelation phenomenon, can reduce the agitator power, save energy, and balance slurry quality and cost.

[0094] In some embodiments, the stirring time in the second stirring is 20 to 30 minutes. In some embodiments, the stirring time in the second stirring can be any one of 20 to 25 minutes, 25 to 30 minutes, or 20 to 30 minutes.

[0095] Controlling the stirring time in the second stirring process within a suitable range is beneficial for improving the dispersibility of the primary slurry, effectively reducing the slurry's output viscosity and viscosity after 24 hours of standing, improving its coatability and processability, enhancing its anti-settling and anti-gelling properties, improving its storage properties, and broadening the coating process window. Simultaneously, controlling the stirring time in the second stirring process within a suitable range, without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers after 24 hours of standing, or the gelation phenomenon, can reduce the slurry preparation time, improve efficiency, and lower costs.

[0096] In some embodiments, the revolution speed in the third stirring is 20 rpm to 30 rpm. In some embodiments, the revolution speed in the third stirring can be selected from any one of 20 rpm to 25 rpm, 20 rpm to 30 rpm, or 25 rpm to 30 rpm.

[0097] Controlling the revolution speed during the third stirring process within a suitable range facilitates the thorough dispersion of conductive agents and binders around the positive electrode active material. This effectively reduces the slurry's output viscosity and viscosity after 24 hours of standing, improves its coatability and processability, enhances its anti-settling and anti-gelling properties, improves its storage properties, and broadens the coating process window. Simultaneously, controlling the revolution speed within the appropriate range allows for reduced agitator power and energy savings without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, solids content difference between upper and lower layers after 24 hours of standing, or gelation phenomena. This balances slurry quality and cost.

[0098] In some embodiments, the rotation speed of the third stirring is 1000 rpm to 1200 rpm. In some embodiments, the rotation speed of the third stirring can be selected from any one of 1000 rpm to 1100 rpm, 1000 rpm to 1200 rpm, or 1100 rpm to 1200 rpm.

[0099] Controlling the rotation speed of the third agitator within a suitable range facilitates the thorough dispersion of conductive agents and binders around the positive electrode active material, effectively reducing the slurry's output viscosity and viscosity after 24 hours of standing, improving its coatability and processability, enhancing its anti-settling and anti-gelling properties, improving its storage properties, and broadening the coating process window. Simultaneously, controlling the rotation speed within a suitable range, without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers after 24 hours of standing, or the gelation phenomenon, allows for a reduction in agitator power, saving energy and balancing slurry quality and cost.

[0100] In some embodiments, the stirring time in the third stirring is 100 to 120 minutes. In some embodiments, the stirring time in the third stirring is any one of 100 to 110 minutes, 100 to 120 minutes, or 110 to 120 minutes.

[0101] Controlling the stirring time in the third stirring process within a suitable range is beneficial for the conductive agent and binder to be fully dispersed around the positive electrode active material, effectively reducing the slurry's output viscosity and viscosity after 24 hours of standing, improving the slurry's coatability and processability, as well as its anti-settling and anti-gelling properties, improving its storage properties, and broadening the process window for slurry coating. Simultaneously, controlling the stirring time in the third stirring process within a suitable range, without significantly altering the slurry's output viscosity, viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers after 24 hours of standing, or the slurry's gelation phenomenon, can reduce the slurry preparation time, improve slurry preparation efficiency, and lower costs.

[0102] In some embodiments, the mass ratio of positive electrode active material, binder and conductive agent in the positive electrode slurry is (92-96):(2-4):(2-4).

[0103] 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.

[0104] The preparation method of this application is more universal than existing cathode slurry preparation methods, applicable to slurry systems with different contents of cathode active materials. It can effectively alleviate the gelation phenomenon of different slurries, helping to improve production efficiency and broaden the coating window of the slurry. The preparation method disclosed in this application is applicable to high contents of cathode active materials, ensuring that slurries containing high contents of cathode active materials still have low shipping viscosity and anti-gelling properties, meeting the high energy density requirements of batteries.

[0105] In some embodiments, the solid content of the cathode slurry is 65%-75%, and the shipping viscosity of the cathode slurry is 4500 mPa·s to 40000 mPa·s.

[0106] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the delivery viscosity of the positive electrode slurry can be selected from 4500 mPa·s to 10000 mPa·s, 4500 mPa·s to 15000 mPa·s, 4500 mPa·s to 20000 mPa·s, 4500 mPa·s to 25000 mPa·s, 4500 mPa·s to 30000 mPa·s, 4500 mPa·s to 35000 mPa·s, 4500 mPa·s to 40000 mPa·s, 10000 mPa·s to 15000 mPa·s, 10000 mPa·s to 20000 mPa·s, 10000 mPa·s to 25000 mPa·s, and 10000 mPa·s to 30000 mPa·s. s, 10000mPa·s~35000mPa·s, 10000mPa·s~40000mPa·s, 20000mPa·s~25000mPa·s, 20000mPa·s~30000mPa·s, 20000mPa·s~35000mPa·s, 20000mPa·s~40000mPa·s, 25 Any one of the following: 000mPa·s~30000mPa·s, 25000mPa·s~35000mPa·s, 25000mPa·s~40000mPa·s, 30000mPa·s~35000mPa·s, 30000mPa·s~40000mPa·s, 35000mPa·s~40000mPa·s.

[0107] In some embodiments, the solid content of the cathode slurry is 65%-75%, and the shipping viscosity of the cathode slurry is 4500 mPa·s to 20000 mPa·s.

[0108] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the delivery viscosity of the positive electrode slurry can be selected from any one of 4500mPa·s to 10000mPa·s, 4500mPa·s to 15000mPa·s, 4500mPa·s to 20000mPa·s, 10000mPa·s to 15000mPa·s, and 10000mPa·s to 20000mPa·s.

[0109] The shipping viscosity refers to the viscosity of the cathode slurry immediately after preparation.

[0110] The slurry prepared by the method 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.

[0111] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the viscosity of the positive electrode slurry does not exceed 50,000 mPa·s after standing for 24 hours.

[0112] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, 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, and 10000 mPa·s.

[0113] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the viscosity of the positive electrode slurry does not exceed 30000 mPa·s after standing for 24 hours.

[0114] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the viscosity of the positive electrode slurry does not exceed any one of 30000mPa·s, 25000mPa·s, 20000mPa·s, 15000mPa·s, or 10000mPa·s.

[0115] The slurry prepared by the method of this application has excellent storage properties and broadens the process window of the slurry.

[0116] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed 1.5%.

[0117] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, 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%.

[0118] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed 0.2%.

[0119] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed any one of 0.2%, 0.15%, 0.1%, or 0.8%.

[0120] The slurry prepared by the method of this application has excellent anti-settling properties and broadens the process window of the slurry.

[0121] In one embodiment of this application, a positive electrode slurry is provided, which is prepared by the positive electrode slurry preparation method in any embodiment.

[0122] In some embodiments, the solid content of the cathode slurry is 65%-75%, and the shipping viscosity of the cathode slurry is 4500 mPa·s to 40000 mPa·s.

[0123] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the delivery viscosity of the positive electrode slurry can be selected from 4500 mPa·s to 10000 mPa·s, 4500 mPa·s to 15000 mPa·s, 4500 mPa·s to 20000 mPa·s, 4500 mPa·s to 25000 mPa·s, 4500 mPa·s to 30000 mPa·s, 4500 mPa·s to 35000 mPa·s, 4500 mPa·s to 40000 mPa·s, 10000 mPa·s to 15000 mPa·s, 10000 mPa·s to 20000 mPa·s, 10000 mPa·s to 25000 mPa·s, and 10000 mPa·s to 30000 mPa·s. s, 10000mPa·s~35000mPa·s, 10000mPa·s~40000mPa·s, 20000mPa·s~25000mPa·s, 20000mPa·s~30000mPa·s, 20000mPa·s~35000mPa·s, 20000mPa·s~40000mPa·s, 25 Any one of the following: 000mPa·s~30000mPa·s, 25000mPa·s~35000mPa·s, 25000mPa·s~40000mPa·s, 30000mPa·s~35000mPa·s, 30000mPa·s~40000mPa·s, 35000mPa·s~40000mPa·s.

[0124] In some embodiments, the solid content of the cathode slurry is 65%-75%, and the shipping viscosity of the cathode slurry is 4500 mPa·s to 20000 mPa·s.

[0125] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the delivery viscosity of the positive electrode slurry can be selected from any one of 4500mPa·s to 10000mPa·s, 4500mPa·s to 15000mPa·s, 4500mPa·s to 20000mPa·s, 10000mPa·s to 15000mPa·s, and 10000mPa·s to 20000mPa·s.

[0126] The cathode slurry provided in this application has a suitable viscosity and excellent processability.

[0127] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the viscosity of the positive electrode slurry does not exceed 50,000 mPa·s after standing for 24 hours.

[0128] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, 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, and 10000 mPa·s.

[0129] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the viscosity of the positive electrode slurry does not exceed 30000 mPa·s after standing for 24 hours.

[0130] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the viscosity of the positive electrode slurry does not exceed any one of 30000mPa·s, 25000mPa·s, 20000mPa·s, 15000mPa·s, or 10000mPa·s.

[0131] The cathode slurry provided in this application has excellent storage performance and broadens the process window of the slurry.

[0132] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed 1.5%.

[0133] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, 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%.

[0134] In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and after standing for 24 hours, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed 0.2%.

[0135] In some embodiments, after standing for 24 hours, the difference in solid content between the upper and lower layers of the positive electrode slurry does not exceed any one of 0.2%, 0.15%, 0.1%, or 0.8%.

[0136] The slurry of this application has excellent anti-settling properties, which broadens the process window of the slurry.

[0137] In some embodiments, a positive electrode sheet is provided, including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, which is obtained by preparing a positive electrode slurry by any method of preparing a positive electrode slurry in any embodiment or by preparing a positive electrode slurry in any embodiment.

[0138] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0139] In one embodiment of this application, a secondary battery is provided, including a separator, a negative electrode, and a positive electrode as described in any embodiment.

[0140] In some implementations, the secondary battery is any one of a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, or a potassium-ion battery.

[0141] During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, placed between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0142] [Positive electrode plate]

[0143] 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.

[0144] 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.

[0145] 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.).

[0146] 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 0.2 O2 (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.

[0147] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0148] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0149] 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.

[0150] [Negative electrode plate]

[0151] 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.

[0152] 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.

[0153] 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.).

[0154] 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.

[0155] 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).

[0156] 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.

[0157] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0158] 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.

[0159] [Electrolytes]

[0160] 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.

[0161] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] [Isolation membrane]

[0166] 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.

[0167] 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.

[0168] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a 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.

[0173] 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.

[0174] 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.

[0175] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0176] 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.

[0177] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The 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.

[0178] 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.

[0179] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0180] Figure 6This 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.

[0181] 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.

[0182] Example

[0183] 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.

[0184] I. Preparation Method

[0185] Example 1

[0186] 1) Preparation of positive electrode slurry

[0187] First mixing: 960 kg of lithium iron phosphate and 20 kg of polyvinylidene fluoride with a weight average molecular weight of 800,000 were added to a 1300 L double planetary mixer for the first mixing. The first mixing speed was 15 rpm and the mixing time was 15 minutes to obtain a dry mixture.

[0188] Second stirring: 147 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 and the stirring time was 25 minutes to obtain the primary slurry.

[0189] Third stirring: 20 kg of conductive carbon black and 245 kg of NMP solvent are mixed with the primary slurry for third stirring. The mass of NMP solvent added in the third stirring is 25% 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.

[0190] Examples 2-50

[0191] This is basically the same as Example 1, except that the preparation parameters of the positive electrode slurry were adjusted. See Table 1 for specific parameters.

[0192] In Examples 6-11, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 2:1. In Example 12, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, and the third polyvinylidene fluoride is 3:2:1.

[0193] Comparative Example 1

[0194] 960 kg of positive electrode active material and 20 kg of polyvinylidene fluoride with a weight average molecular weight of 800,000 were added to a 1300 L double planetary mixer and mixed. The first mixing speed was 25 rpm and the mixing time was 70 minutes to obtain a dry mixture.

[0195] 392 kg of NMP (N-methylpyrrolidone) solvent and 20 kg of conductive carbon black were added to a double planetary mixer and mixed with the dry mixture. The planetary speed was 30 rpm, the mixing time was 110 minutes, and the rotation speed was 1100 rpm to obtain the positive electrode slurry.

[0196] Comparative Examples 2-3

[0197] It is basically the same as Comparative Example 1, except that the mass ratio of positive electrode active material: binder: conductive agent was adjusted. See Table 1 for specific parameters.

[0198] Comparative Examples 4-6

[0199] The results are basically the same as those in Comparative Example 1, except that the weight-average molecular weight of polyvinylidene fluoride was adjusted to 150,000, 500,000, and 1,000,000, respectively. For details, please refer to Table 1.

[0200] Comparative Example 7

[0201] The results are basically the same as those in Comparative Example 1, except that the adhesive is adjusted to contain two types of polyvinylidene fluoride with different weight average molecular weights. The first type of polyvinylidene fluoride has a weight average molecular weight of 800,000, and the second type of polyvinylidene fluoride has a weight average molecular weight of 1,400,000. The two types of polyvinylidene fluoride are mixed and used in a mass ratio of 2:1. The specific parameters are shown in Table 1.

[0202] II. Testing Methods

[0203] 1. Test of the difference in solid content between the upper and lower layers of the slurry after 24 hours of settling.

[0204] Weigh the aluminum foil in a moisture analyzer and record the weight as M0. The model of the moisture analyzer is MOC-120H.

[0205] 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.

[0206] Close the equipment and begin drying;

[0207] After completion, record the weighing data as M2, and calculate the solid content as (M2-M0) / (M1-M0);

[0208] The solids content of the lower layer slurry was measured using the same method. The difference between the solids content of the lower layer slurry and the solids content of the upper layer slurry was taken as the difference in solids content between the upper and lower layers after the slurry had stood for 24 hours.

[0209] 2. Viscosity test of the shipped slurry

[0210] 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.

[0211] 3. Viscosity test of slurry after standing for 24 hours

[0212] 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.

[0213] 4. Gelation test of slurry after standing for 24 hours

[0214] 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.

[0215] gel-free state: The slurry flows naturally and continuously, and flows horizontally on the surface of the steel ruler without clumping;

[0216] 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.

[0217] 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;

[0218] 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.

[0219] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0220] 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.

[0221] Table 1

[0222]

[0223]

[0224] Table 2

[0225]

[0226]

[0227] According to the results in Tables 1 and 2, the positive electrode slurries in Examples 1-50 were all 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, and the primary slurry are mixed and stirred to prepare a positive electrode slurry. The binder contains at least one fluoropolymer with a weight-average molecular weight of 150,000 to 1,500,000.

[0228] As can be seen from the comparison of Examples 1-4, 7, 49, and 50 with Comparative Examples 1-7, the preparation method disclosed in this application has broad applicability and is applicable to slurries of one or more fluoropolymer binders with a weight average molecular weight of 150,000 to 1,500,000. This preparation method is universally applicable to both low and high weight average molecular weight fluoropolymer binders, and helps to reduce preparation costs and improve production efficiency.

[0229] As can be seen from Comparative Example 6, the existing preparation process is insufficient to reduce the discharge viscosity of the slurry for binders with a weight-average molecular weight of 1 million, resulting in severe gelation. However, the preparation method disclosed in this application enables slurries containing binders with a weight-average molecular weight as high as 1.5 million to still exhibit low discharge viscosity, anti-settling properties, and anti-gelling characteristics, thus meeting the requirements for the use of next-generation high molecular weight binders.

[0230] As can be seen from the comparison between Examples 6-13 and Comparative Example 7, 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.

[0231] As can be seen from Examples 1, 49, 50 and Comparative Examples 1-3, the existing preparation processes are insufficient to reduce the slurry's output viscosity for slurries with high cathode active material content, and severe gelation may occur. However, the preparation method disclosed in this application enables slurries with high cathode active material content to still exhibit low output viscosity, anti-settling properties, and anti-gelling characteristics, thus meeting the requirements of high-energy-density batteries.

[0232] As can be seen from the comparison of Examples 8 and 4, Examples 10 and 5, and Examples 11 and 1, the slurry containing binders of different molecular weights prepared by the preparation method of this application has a lower viscosity after standing for 24 hours and a lower difference in solid content between the upper and lower layers after standing for 24 hours. The slurry has better anti-settling properties.

[0233] A comparison of Examples 1, 14, and 15 with Example 13 shows that controlling the solvent content used in the second stirring to 10%–20% of the total mass of the positive electrode active material and binder can reduce the slurry's discharge viscosity and viscosity after 24 hours of standing, reduce the solid content difference between the upper and lower layers after 24 hours of standing, improve the slurry's anti-settling and anti-gelling properties, improve its storage performance, and broaden the slurry coating process window. A comparison of Examples 1, 14, and 15 with Example 16 shows that, without significantly changing the slurry's discharge viscosity, viscosity after 24 hours of standing, solid content difference between the upper and lower layers after 24 hours of standing, or gelation phenomenon, controlling the solvent content used in the second stirring to 10%–20% of the total mass of the positive electrode active material and binder can reduce solvent usage, lower costs, and balance slurry quality and cost.

[0234] A comparison of Examples 1, 18-19 with Example 17 shows that controlling the solvent content used in the third stirring to 20%-30% of the total mass of the positive electrode active material and binder can reduce the slurry's output viscosity and viscosity after 24 hours of standing, improve the slurry's coatability and processability, reduce the solid content difference between the upper and lower layers after 24 hours of standing, slow down the slurry's gelation phenomenon, improve the slurry's anti-settling and anti-gelling properties, improve the slurry's storage properties, and broaden the slurry coating process window. A comparison of Examples 1, 18-19 with Example 20 shows that, without significantly changing the slurry's output viscosity, viscosity after 24 hours of standing, solid content difference between the upper and lower layers after 24 hours of standing, or gelation phenomenon, controlling the solvent content used in the third stirring to 20%-30% of the total mass of the positive electrode active material and binder can reduce solvent usage, lower costs, and balance slurry quality and cost.

[0235] A comparison of Examples 1, 26-27 with Example 25 shows that controlling the revolution speed during the first stirring process to 10-20 rpm can reduce the output viscosity and the viscosity after 24 hours of standing, improve the coatability and processability of the slurry, reduce the solid content difference between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the anti-settling and anti-gelling properties of the slurry, and improve the stability and storage properties of the slurry. A comparison of Examples 1, 26-27 with Example 28 shows that, without significantly changing the output viscosity, the viscosity after 24 hours of standing, the solid content difference between the upper and lower layers after 24 hours of standing, or the gelation phenomenon of the slurry, controlling the revolution speed during the first stirring process to 10-20 rpm reduces the power of the stirrer, saves energy, and balances the quality and cost of the mixed slurry.

[0236] A comparison of Examples 1, 22-23 with Example 21 shows that controlling the stirring time in the first stirring stage to 10-20 minutes can reduce the output viscosity and the viscosity after 24 hours of standing, improve the coatability and processability of the slurry, reduce the solid content difference between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the anti-settling and anti-gelling properties of the slurry, and improve the stability and storage properties of the slurry. A comparison of Examples 1, 22-23 with Example 24 shows that, without significantly changing the output viscosity, the viscosity after 24 hours of standing, the solid content difference between the upper and lower layers after 24 hours of standing, or the gelation phenomenon of the slurry, controlling the stirring time in the first stirring stage to 10-20 minutes can reduce the working time of slurry preparation, improve the efficiency of slurry preparation, and reduce costs.

[0237] A comparison of Examples 1, 30-31 with Example 29 shows that controlling the revolution speed in the second stirring process to 20-30 rpm can reduce the discharge viscosity and the viscosity after 24 hours of standing, improve the coatability and processability of the slurry, reduce the solid content difference between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the anti-settling and anti-gelling properties of the slurry, and improve the stability and storage properties of the slurry. A comparison of Examples 1, 30-31 with Example 32 shows that, without significantly changing the discharge viscosity, the viscosity after 24 hours of standing, the solid content difference between the upper and lower layers after 24 hours of standing, or the gelation phenomenon of the slurry, controlling the revolution speed in the second stirring process to 20-30 rpm reduces the power of the stirrer, saves energy, and balances the quality and cost of the mixed slurry.

[0238] A comparison of Examples 1, 34-35 with Example 33 shows that controlling the stirring time in the second stirring process to 20-30 minutes can reduce the slurry's output viscosity and viscosity after 24 hours of standing, improve the slurry's coatability and processability, reduce the difference in solid content between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the slurry's anti-settling and anti-gelling properties, and improve the slurry's stability and storage properties. A comparison of Examples 1, 34-35 with Example 36 shows that, without significantly changing the slurry's output viscosity, viscosity after 24 hours of standing, difference in solid content between the upper and lower layers after 24 hours of standing, or gelation phenomenon, controlling the stirring time in the second stirring process to 20-30 minutes can reduce the slurry preparation time, improve the efficiency of slurry preparation, and reduce costs.

[0239] A comparison of Examples 1, 42-43 with Example 41 shows that controlling the revolution speed in the third stirring process to 20-30 rpm can reduce the discharge viscosity and the viscosity after 24 hours of standing, improve the coatability and processability of the slurry, reduce the solid content difference between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the anti-settling and anti-gelling properties of the slurry, and improve the stability and storage properties of the slurry. A comparison of Examples 1, 42-43 with Example 44 shows that, without significantly changing the discharge viscosity, the viscosity after 24 hours of standing, the solid content difference between the upper and lower layers after 24 hours of standing, or the gelation phenomenon of the slurry, controlling the revolution speed in the third stirring process to 20-30 rpm reduces the power of the stirrer, saves energy, and balances the quality and cost of the mixed slurry.

[0240] A comparison of Examples 1, 46-47 with Example 45 shows that controlling the rotation speed of the third agitator to 1000 rpm to 1200 rpm can reduce the discharge viscosity and the viscosity after 24 hours of standing, improve the coatability and processability of the slurry, reduce the solid content difference between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the anti-settling and anti-gelling properties of the slurry, and improve the stability and storage properties of the slurry. A comparison of Examples 1, 46-47 with Example 48 shows that, without significantly changing the discharge viscosity, the viscosity after 24 hours of standing, the solid content difference between the upper and lower layers after 24 hours of standing, or the gelation phenomenon of the slurry, controlling the rotation speed of the third agitator to 1000 rpm to 1200 rpm reduces the power of the agitator, saves energy, and balances the quality and cost of the mixed slurry.

[0241] A comparison of Examples 1, 38-39 with Example 37 shows that controlling the stirring time in the third stirring process to 100-120 minutes can reduce the slurry's output viscosity and viscosity after 24 hours of standing, improve the slurry's coatability and processability, reduce the difference in solid content between the upper and lower layers after 24 hours of standing, slow down the gelation phenomenon, improve the slurry's anti-settling and anti-gelling properties, and improve the slurry's stability and storage properties. A comparison of Examples 1, 38-39 with Example 40 shows that, without significantly changing the slurry's output viscosity, viscosity after 24 hours of standing, difference in solid content between the upper and lower layers after 24 hours of standing, or gelation phenomenon, controlling the stirring time in the third stirring process to 100-120 minutes can reduce the slurry preparation time, improve the efficiency of slurry preparation, and reduce costs.

[0242] As can be seen from Examples 1 and 49-50, the preparation method of this application is applicable to slurry systems with a mass ratio of positive electrode active material, binder and conductive agent of (92-96):(2-4):(2-4). The prepared slurry has low delivery viscosity and viscosity after standing for 24 hours. The slurry has excellent anti-settling and anti-gelling properties, which can meet the requirements of high energy density of batteries.

[0243] As can be seen from Examples 1 to 50, the shipping viscosity of the positive electrode slurry is 4500 mPa·s to 40000 mPa·s. The slurry has a suitable viscosity, which can improve the coating and processability of the slurry. At the same time, the suitable slurry viscosity makes the slurry have good anti-settling and anti-gelling properties, and improves the stability and storage of the slurry.

[0244] As can be seen from Examples 1 to 50, the viscosity of the positive electrode slurry after standing for 24 hours does not exceed 50,000 mPa·s, and the slurry has good storage properties.

[0245] 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 by, The first stirring, the second stirring and the third stirring are included. In the first stirring, the positive active material is mixed with the binder 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 and the solvent are mixed with the primary slurry to prepare a positive electrode slurry; The binder comprises at least one fluoropolymer with a weight average molecular weight of 150-1500 thousand; The stirring time of the first stirring is 15-20 minutes; The revolution speed of the first stirring is 15-20 revolutions per minute; The stirring time of the second stirring is 25-30 minutes; The revolution speed of the second stirring is 20-30 revolutions per minute; The mass content of the solvent used in the second stirring is 15-20% based on the total mass of the positive active material and the binder; The stirring time of the third stirring is 110-120 minutes; The revolution speed of the third stirring is 20-30 revolutions per minute; The rotation speed of the third stirring is 1100-1200 revolutions per minute; The mass content of the solvent used in the third stirring is 25-30% based on the total mass of the positive active material and the binder.

2. The production method according to claim 1, characterized by, The binder comprises at least two fluoropolymers with a difference of weight average molecular weight of no more than 1500 thousand.

3. The preparation method according to claim 1, characterized in that, The fluoropolymer comprises polyvinylidene fluoride.

4. The preparation method according to claim 1, characterized in that, The solvent used in the second stirring is the same as the solvent used in the third stirring.

5. The preparation method according to claim 1, characterized in that, In the positive electrode slurry, the mass ratio of the positive active material, the binder and the conductive agent is (92-96):(2-4):(2-4).

6. The preparation method according to claim 1, characterized in that, The solid content of the positive electrode slurry is 65-75%, and the delivery viscosity of the positive electrode slurry is 4500-40000 mPa·s.

7. The production method according to claim 6, wherein The solid content of the positive electrode slurry is 65-75%, and the delivery viscosity of the positive electrode slurry is 4500-20000 mPa·s.

8. The method of claim 1, wherein, The solid content of the positive electrode slurry is 65-75%, and the viscosity of the positive electrode slurry after standing for 24 hours is no more than 50000 mPa·s.

9. The production method according to claim 8, characterized by, The solid content of the positive electrode slurry is 65-75%, and the viscosity of the positive electrode slurry after standing for 24 hours is no more than 30000 mPa·s.

10. A positive electrode slurry, characterized by, The positive electrode slurry is prepared by the method for preparing a positive electrode slurry according to any one of claims 1-9.

11. A positive electrode sheet characterized by comprising: The positive electrode film layer is prepared by the method for preparing a positive electrode slurry according to any one of claims 1-9.

12. A secondary battery characterized by comprising: The secondary battery according to claim 12 is included.

13. An electrical device, characterized by The secondary battery according to claim 12 is included.

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