Preparation method for positive electrode slurry, positive electrode slurry, positive electrode sheet, secondary battery, and electric device

Abstract

A preparation method for a positive electrode slurry, a positive electrode slurry, a positive electrode sheet, a secondary battery, and an electric device. The preparation method for the positive electrode slurry comprises first stirring, second stirring, and 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 and the dry mixture are kneaded to prepare a primary slurry; and in the third stirring, a 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 having a weight-average molecular weight of 150 thousand to 1.5 million. The preparation method has universal applicability to a low-molecular-weight fluoropolymer binder and a high-molecular-weight fluoropolymer binder, can effectively reduce the occurrence of gelling of different slurries, can improve the production efficiency, widens the coating window of a slurry, and can be suitable for a binder having a weight-average molecular weight up to 1.5 million, such that a slurry containing a binder having a high weight-average molecular weight still has low delivery viscosity, gelling resistance, and sedimentation resistance, and the method can be suitable for a slurry containing high content of a positive electrode active substance, such that the slurry containing high content of a positive electrode active substance still has low delivery viscosity, thereby satisfying the requirement for high energy density in batteries.

Description

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

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202310785726.X filed on June 29, 2023, entitled “Method for preparing positive electrode slurry, positive electrode slurry, positive electrode sheet, secondary battery and electrical device”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, 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 Art

[0004] In recent years, as the application scope of secondary batteries has become increasingly wider, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] Electrode slurry is the basis for forming electrodes and is also the first step in the production of secondary batteries. The characteristics of electrode slurry have a significant impact on subsequent electrode production and battery performance. Positive electrode slurry is mainly a solid-liquid phase mixed system formed by positive electrode active material, conductive agent, binder and solvent. This system is in a metastable state. The slurrying process, that is, the preparation method of the slurry has a crucial influence on the dispersibility, uniformity, stability and other properties of the slurry. The slurrying process in the prior art is often a one-step method, in which the components in the positive electrode active slurry are directly mixed and stirred. However, the one-step preparation method cannot meet the manufacturing requirements of binders with different weight-average molecular weights, and the slurrying process has poor versatility, which is not conducive to reducing manufacturing costs. Therefore, it is necessary to develop a new slurry preparation method that is suitable for binders with different weight-average molecular weights.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned issues, and its purpose is to provide a method for preparing a positive electrode slurry for a secondary battery to adapt to binders with different weight-average molecular weights, broaden the process window for coating the positive electrode slurry, and improve the processing performance of the positive electrode slurry.

[0008] In order to achieve the above-mentioned purpose, the present 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, the positive electrode active material and the binder are mixed and stirred to prepare a dry mixture; in the second stirring, the solvent and the dry mixture are kneaded 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; wherein the binder comprises at least one fluorine-containing polymer having a weight-average molecular weight of 150,000 to 1.5 million.

[0009] The preparation method disclosed in this application is universally applicable to both low-molecular-weight and high-molecular-weight fluoropolymer binders, effectively alleviating the gelation phenomenon of different slurries, helping to improve production efficiency and broaden the slurry coating window. The preparation method disclosed in this application is applicable to binders with a weight-average molecular weight of up to 1.5 million, allowing slurries containing high-weight-average molecular weight binders to maintain low shipping viscosity, anti-gelation, and anti-settling properties, meeting the requirements of the new generation of binders.

[0010] In any embodiment, the binder comprises at least two fluoropolymers having a weight average molecular weight difference of no more than 1.5 million.

[0011] The applicant unexpectedly discovered that the preparation method disclosed in this application can effectively adapt to positive electrode slurries containing binders of various weight-average molecular weights. Unlike the prior art, where binders of varying molecular weights tend to exacerbate slurry sedimentation, the positive electrode slurry prepared using the method of this application effectively leverages the properties of fluoropolymer binders of varying molecular weights, improving the slurry's anti-settling properties through the interaction of large and small chain segments and steric hindrance.

[0012] In any embodiment, the fluoropolymer comprises polyvinylidene fluoride.

[0013] 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.

[0014] The mass content of the solvent used in the second stirring is controlled within an appropriate range so that the slurry has low shipping viscosity, low viscosity after static storage for 24 hours, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0015] In any embodiment, the solvent used in the third stirring may be present in an amount of 20% to 30% by mass based on the total mass of the positive electrode active material and the binder.

[0016] The mass content of the solvent used in the third stirring is controlled within an appropriate range so that the slurry has low shipping viscosity, low viscosity after static storage for 24 hours, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0017] In any embodiment, the revolution speed during the first stirring is 10 to 20 rpm.

[0018] The revolution speed in the first stirring is controlled within an appropriate range so that the slurry has low shipping viscosity, low viscosity after 24 hours of static storage, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0019] In any embodiment, the stirring time in the first stirring is 10 to 20 minutes.

[0020] Controlling the stirring time in the first stirring within an appropriate range allows the slurry to have low shipping viscosity, low viscosity after 24 hours of static storage, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0021] In any embodiment, the revolution speed during the second stirring is 20 to 30 rpm.

[0022] The revolution speed in the second stirring is controlled within an appropriate range so that the slurry has low shipping viscosity, low viscosity after 24 hours of static storage, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0023] In any embodiment, the stirring time in the second stirring is 20 minutes to 30 minutes.

[0024] Controlling the stirring time in the second stirring within an appropriate range allows the slurry to have low shipping viscosity, low viscosity after 24 hours of static storage, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0025] In any embodiment, the revolution speed during the third stirring is 20 to 30 rpm.

[0026] The revolution speed in the third stirring is controlled within an appropriate range so that the slurry has low shipping viscosity, low viscosity after static storage for 24 hours, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0027] In any embodiment, the rotation speed during the third stirring is 1000 rpm to 1200 rpm.

[0028] Controlling the rotation speed in the third stirring within an appropriate range allows the slurry to have low shipping viscosity, low viscosity after 24 hours of static storage, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0029] In any embodiment, the stirring time in the third stirring is 100 minutes to 120 minutes.

[0030] Controlling the stirring time in the third stirring within an appropriate range allows the slurry to have low shipping viscosity, low viscosity after 24 hours of static storage, excellent anti-settling and anti-gel properties, which is beneficial to improving the coating performance, processing performance and stability of the slurry.

[0031] In any embodiment, the mass ratio of the positive electrode active material, the binder, and the conductive agent is (92-96): (2-4): (2-4).

[0032] Compared with existing positive electrode slurry preparation methods, the preparation method of the present application is universal and applicable to slurries with different contents of positive electrode active materials. It can effectively alleviate the gelation phenomenon of different slurries, help improve production efficiency, and widen the coating window of the slurry. At the same time, the preparation method disclosed in the present application can be applied to slurries with high contents of positive electrode active materials, so that the slurry containing high contents of positive electrode active materials still has low shipping viscosity, excellent anti-settling and anti-gel properties, and can meet the demand for high energy density of batteries.

[0033] The second aspect of the present application further provides a positive electrode slurry, which is prepared by the positive electrode slurry preparation method of the first aspect.

[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 4500mPa·s to 40000mPa·s, and can be optionally 4500mPa·s to 20000mPa·s.

[0035] The slurry formed by the preparation method of the present application has suitable viscosity and excellent processability. The above slurry can be directly used in the subsequent coating process, 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 can optionally be no more than 30,000 mPa·s.

[0037] The slurry formed by the preparation method of the present application has excellent storage performance and broadens the process window of the slurry.

[0038] The third aspect of the present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer being prepared by the positive electrode slurry prepared by the positive electrode slurry preparation method of the first aspect or the positive electrode slurry of the second aspect.

[0039] A fourth aspect of the present application provides a secondary battery comprising a separator, a negative electrode plate and the positive electrode plate of the third aspect.

[0040] A fifth aspect of the present application provides an electrical device, characterized in that it includes the secondary battery of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0042] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0043] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0044] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0045] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0046] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0047] Description of reference numerals:

[0048] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0049] Below, with appropriate reference to the accompanying drawings, the embodiments of the positive electrode slurry preparation method, positive electrode slurry, positive electrode sheet, secondary battery and electric device of the present application are described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0050] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0052] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0053] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0054] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0055] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0056] The positive electrode slurry is mainly a solid-liquid phase mixed system formed by the positive electrode active material, the conductive agent, the binder and the solvent. In order to improve the uniformity of the distribution of different components in the system, slurry is often mixed by stirring, ball milling, ultrasound and other processes. However, the slurry mixing process in the prior art is usually only applicable to slurry systems with fixed components, and has poor versatility. After the physical properties of the components in the slurry change, the slurry mixing process often needs to be adjusted. For example, the slurry mixing process in the prior art cannot be applied to high molecular weight binders, nor can it be applied to binders with large weight average molecular weight dispersibility and poor batch stability. The performance of slurries using different batches of binders prepared using the same slurry mixing process in the prior art is very different, and the slurry is prone to gel, which makes it difficult to meet the production requirements of the electrode.

[0057] [Preparation method]

[0058] Based on this, the present application proposes a method for preparing a positive electrode slurry, including first stirring, second stirring and 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 and the dry mixture are kneaded 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; wherein the binder contains at least one fluorine-containing polymer with a weight-average molecular weight of 150,000 to 1.5 million.

[0059] In some embodiments, the weight average molecular weight of the fluoropolymer is 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, 1,050,000, 1,100,000, 1,150,000, 1,200,000, 1,250,000, 1,300,000, 1,350,000, 1,400,000, 1,450,000, 1,500,000, or any value therebetween.

[0060] As used herein, the term "fluoropolymer" refers to a polymer having fluorine-containing groups.

[0061] In some embodiments, the fluoropolymer includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0062] In some embodiments, the fluoropolymer comprises polyvinylidene fluoride.

[0063] As used herein, the term "weight average molecular weight" refers to the statistical average molecular weight of a polymer by mass, which is the average molecular weight per unit weight. It can be determined using instruments and methods known in the art, such as gel permeation chromatography, in accordance with GB / T 21863-2008.

[0064] In some embodiments, the conductive agent may include at least one of superconducting carbon, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0065] 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.

[0066] In this context, the term "kneading" refers to the operation of adding a small amount of liquid to a solid powder and uniformly mixing them to prepare a plastic material or a paste-like material.

[0067] In this article, the term "process window" refers to the process range that can ensure 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 accuracy.

[0068] In this preparation method, the positive electrode active material and the binder are first stirred to obtain a dry mixture, which is conducive to the uniform dispersion and riveting of the binder on the surface of the positive electrode active material; then a small amount of liquid is added for kneading, and the positive electrode active material and the binder absorb the liquid at the same time, so that the slurry is in a state of moderate dryness and wetness, so as to facilitate the kneading process, so that the positive electrode active material and the binder in the slurry do not agglomerate during the kneading process, thereby enhancing the dispersibility of the slurry. At the same time, under the wetting action of the solvent, the chain segments of the binder are further extended, and the binder is tightly wrapped on the surface of the positive electrode active material; finally, a conductive agent and a solvent are added to transform the slurry from a kneaded state into a solution state, so that under the strong shear action promoted by stirring, various components of the slurry are evenly dispersed, thereby improving the dispersibility and stability of the slurry. In addition, in the solution state, the chain segments of the binder can be fully extended and tightly coated on the positive electrode active material and the conductive agent, thereby maintaining the dispersion of the materials in the slurry and slowing down the gelation of the slurry.

[0069] The preparation method of the positive electrode slurry in the prior art has poor compatibility and cannot adapt to the difference in the weight average molecular weight of the binder in the slurry. Therefore, a very high precision requirement is put forward for the material. The present application reduces the shipping viscosity of the positive electrode slurry, alleviates the gelation phenomenon of the positive electrode slurry, improves the anti-sedimentation and anti-gelation properties of the slurry, and makes the slurry with a high weight average molecular weight binder still have low shipping viscosity and anti-coagulation properties, thereby improving the universality of the preparation method. The preparation method of the present application is not only applicable to binders with low weight average molecular weight, but also to binders with high weight average molecular weight. It can effectively alleviate the gelation and sedimentation phenomena of different slurries, which helps to improve production efficiency and broaden the process window of slurry coating.

[0070] In some embodiments, the binder comprises at least two fluoropolymers having a weight average molecular weight difference of no more than 1.5 million. In some embodiments, the binder comprises two or more fluoropolymers having different weight average molecular weights, wherein the weight average molecular weight difference between the fluoropolymers is no more 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, 50,000, or any value therebetween.

[0071] The applicant unexpectedly discovered that the preparation method disclosed in this application can effectively adapt to positive electrode slurries containing binders of various weight-average molecular weights. Unlike the prior art, where binders of varying molecular weights tend to exacerbate slurry sedimentation, the positive electrode slurry prepared using the method of this application effectively leverages the properties of fluoropolymer binders of varying molecular weights, improving the slurry's anti-settling properties through the interaction of large and small chain segments and steric hindrance.

[0072] 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.

[0073] In some embodiments, the mass content of the solvent used in the second stirring is any one of 10% to 15%, 10% to 20%, and 15% to 20% based on the total mass of the positive electrode active material and the binder.

[0074] Controlling the mass content of the solvent used in the second stirring within an appropriate range can reduce the slurry's shipping viscosity and viscosity after standing for 24 hours, improve the slurry's coating and processability, and improve the slurry's anti-settling and anti-gel properties, improve the slurry's storage properties, and broaden the slurry coating process window. At the same time, controlling the mass content of the solvent used in the second stirring within an appropriate range can reduce the use of solvent and reduce costs without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation phenomenon of the slurry, thereby achieving a balance between slurry quality and cost.

[0075] 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.

[0076] In some embodiments, the mass content of the solvent used in the third stirring may be any one of 20% to 25%, 20% to 30%, and 25% to 30%, based on the total mass of the positive electrode active material and the binder.

[0077] Controlling the mass content of the solvent used in the third stirring within an appropriate range can reduce the slurry's shipping viscosity and viscosity after standing for 24 hours, improve the slurry's coating and processability, and improve the slurry's anti-settling and anti-gel properties, improve the slurry's storage properties, and broaden the slurry coating process window. At the same time, controlling the mass content of the solvent used in the third stirring within an appropriate range can reduce the use of solvent and reduce costs without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation phenomenon of the slurry, thereby achieving a balance between slurry quality and cost.

[0078] In some embodiments, the revolution speed during the first stirring is 10 rpm to 20 rpm.

[0079] In some embodiments, the revolution speed during the first stirring can be selected from any one of 10 rpm to 15 rpm, 10 rpm to 20 rpm, and 15 rpm to 20 rpm.

[0080] As used herein, the term "rotational speed" refers to the speed at which the agitator rotates about its own axis.

[0081] As used herein, the term "revolution speed" refers to the speed at which the agitator rotates around the vessel containing the material.

[0082] Controlling the revolution speed during the first stirring within an appropriate range is beneficial to further uniform dispersion of the binder and the positive electrode active material, further bonding of the binder to the surface of the positive electrode active material, improving the dispersibility of the dry mix, effectively reducing the slurry's shipping viscosity and viscosity after standing for 24 hours, improving the slurry's coating and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the slurry coating process window. At the same time, controlling the revolution speed during the first stirring within an appropriate range can reduce the power of the agitator, save energy, and balance the slurry quality and cost without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation of the slurry.

[0083] In some embodiments, the stirring time in the first stirring is 10 minutes to 20 minutes.

[0084] In some embodiments, the stirring time in the first stirring is any one of 10 minutes to 15 minutes, 10 minutes to 20 minutes, and 15 minutes to 20 minutes.

[0085] Controlling the stirring time in the first stirring within an appropriate range is conducive to further uniform dispersion of the binder and the positive electrode active material, further bonding of the binder to the surface of the positive electrode active material, improving the dispersibility of the dry mix, effectively reducing the slurry's shipping viscosity and viscosity after standing for 24 hours, improving the slurry's coating and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the slurry coating process window. At the same time, controlling the stirring time in the first stirring within an appropriate range, without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation phenomenon of the slurry, can reduce the working time of slurry preparation, improve the working efficiency of slurry preparation, and reduce costs.

[0086] In some embodiments, the revolution speed during the second stirring is 20 rpm to 30 rpm. In some embodiments, the revolution speed during the second stirring can be selected from any one of 20 rpm to 25 rpm, 20 rpm to 30 rpm, and 25 rpm to 30 rpm.

[0087] Controlling the revolution speed during the second stirring process within an appropriate range is beneficial to improving the dispersibility of the primary slurry, effectively reducing the slurry's shipping viscosity and viscosity after standing for 24 hours, improving the slurry's coatability and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the process window for slurry coating. Simultaneously, controlling the revolution speed during the second stirring process within an appropriate range can reduce the power of the agitator, save energy, and achieve a balance between slurry quality and cost, without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, or the gelation of the slurry.

[0088] In some embodiments, the stirring time in the second stirring is 20 minutes to 30 minutes. In some embodiments, the stirring time in the second stirring can be any one of 20 minutes to 25 minutes, 25 minutes to 30 minutes, and 20 minutes to 30 minutes.

[0089] Controlling the stirring time in the second stirring process within an appropriate range is beneficial to improving the dispersibility of the primary slurry, effectively reducing the slurry's shipping viscosity and viscosity after standing for 24 hours, improving the slurry's coating and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the process window for slurry coating. At the same time, controlling the stirring time in the second stirring process within an appropriate range, without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation phenomenon of the slurry, can reduce the working time of slurry preparation, improve the working efficiency of slurry preparation, and reduce costs.

[0090] In some embodiments, the revolution speed during the third stirring is 20 rpm to 30 rpm. In some embodiments, the revolution speed during the third stirring can be selected from any one of 20 rpm to 25 rpm, 20 rpm to 30 rpm, and 25 rpm to 30 rpm.

[0091] Controlling the revolution speed during the third stirring process within an appropriate range facilitates the full dispersion of the conductive agent and binder around the positive electrode active material, effectively reducing the slurry's shipping viscosity and viscosity after 24 hours of standing, improving the slurry's coating and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the slurry coating process window. Simultaneously, controlling the revolution speed during the third stirring process within an appropriate range can reduce the power of the agitator, save energy, and balance slurry quality and cost without significantly changing the slurry's shipping viscosity, the slurry's viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers of the slurry after 24 hours of standing, or the gelation of the slurry.

[0092] In some embodiments, the rotation speed during the third stirring is 1000 rpm to 1200 rpm. In some embodiments, the rotation speed during the third stirring can be selected from any one of 1000 rpm to 1100 rpm, 1000 rpm to 1200 rpm, and 1100 rpm to 1200 rpm.

[0093] Controlling the rotation speed during the third stirring process within an appropriate range facilitates the full dispersion of the conductive agent and binder around the positive electrode active material, effectively reducing the slurry's shipping viscosity and viscosity after 24 hours of standing, improving the slurry's coating and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the slurry coating process window. Simultaneously, controlling the rotation speed during the third stirring process within an appropriate range can reduce the power of the agitator, save energy, and balance slurry quality and cost, without significantly changing the slurry's shipping viscosity, the slurry's viscosity after 24 hours of standing, the difference in solid content between the upper and lower layers of the slurry after 24 hours of standing, or the gelation of the slurry.

[0094] 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, and 110 to 120 minutes.

[0095] Controlling the stirring time in the third stirring process within an appropriate range is conducive to the full dispersion of the conductive agent and binder around the positive electrode active material, effectively reducing the slurry's shipping viscosity and viscosity after standing for 24 hours, improving the slurry's coating and processability, and improving the slurry's anti-settling and anti-gel properties, improving the slurry's storage properties, and widening the slurry coating process window. At the same time, controlling the stirring time in the third stirring process within an appropriate range, without significantly changing the slurry's shipping viscosity, the slurry's viscosity after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation phenomenon of the slurry, can reduce the working time of slurry preparation, improve the working efficiency of slurry preparation, and reduce costs.

[0096] In some embodiments, the mass ratio of the positive electrode active material, the binder, and the conductive agent is (92-96): (2-4): (2-4).

[0097] In some embodiments, the mass ratio of the positive electrode active material, the binder, and the conductive agent may be 92:4:4, 93:3:4, 94:4:2, 95:3:2, 96:2:4, 95:2:3, 96:2.5:1.5, or any value therebetween.

[0098] Compared with existing positive electrode slurry preparation methods, the preparation method of the present application is universal and applicable to slurry systems with different contents of positive electrode active materials. It can effectively alleviate the gelation phenomenon of different slurries, help improve production efficiency, and broaden the coating window of the slurry. The preparation method disclosed in the present application can be applied to high-content positive electrode active materials, so that the slurry containing high content of positive electrode active materials still has low shipping viscosity and anti-gel properties, which can meet the high energy density requirements of batteries.

[0099] In one embodiment of the present application, a positive electrode slurry is provided. The positive electrode slurry is prepared by the method for preparing the positive electrode slurry in any embodiment.

[0100] In some embodiments, 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.

[0101] 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 4500mPa·s to 10000mPa·s, 4500mPa·s to 15000mPa·s, 4500mPa·s to 20000mPa·s, 4500mPa·s to 25000mPa·s, 4500mPa·s to 30000mPa·s, 4500mPa·s to 35000mPa·s, 4500mPa·s to 40000mPa·s, 10000mPa·s to 15000mPa·s, 10000mPa·s to 20000mPa·s, 10000mPa·s to 25000mPa·s, 10000mPa·s to 30000mPa·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 1000mPa·s~30000mPa·s, 25000mPa·s~35000mPa·s, 25000mPa·s~40000mPa·s, 30000mPa·s~35000mPa·s, 30000mPa·s~40000mPa·s, and 35000mPa·s~40000mPa·s.

[0102] In some embodiments, 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 20000 mPa·s.

[0103] Shipping viscosity refers to the viscosity of the positive electrode slurry when it is just prepared.

[0104] The slurry formed by the preparation method of the present application has suitable viscosity and excellent processability. The above slurry can be directly used in the subsequent coating process, which can improve production efficiency.

[0105] 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 50,000 mPa·s.

[0106] 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 50000mPa·s, 45000mPa·s, 40000mPa·s, 35000mPa·s, 30000mPa·s, 25000mPa·s, 20000mPa·s, 15000mPa·s, and 10000mPa·s.

[0107] 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 30,000 mPa·s.

[0108] The positive electrode slurry provided in this application has excellent storage performance and broadens the process window of the slurry.

[0109] 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%.

[0110] 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%, 1%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1% or any value therebetween.

[0111] 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%.

[0112] The positive electrode slurry of the present application has excellent anti-settling properties, which broadens the process window of the slurry.

[0113] [Positive electrode]

[0114] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. The positive electrode film layer is prepared by the positive electrode slurry prepared by the preparation method in any embodiment of the present application or the positive electrode slurry in any embodiment.

[0115] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0116] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0117] In some embodiments, the positive electrode active material may adopt the positive electrode active material for batteries that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0118] In some embodiments, the positive electrode active material comprises at least one of lithium iron phosphate and its modified materials, lithium cobaltate and its modified materials, lithium manganate and its modified materials, and the modified material is prepared by one or more modification methods of doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0119] In some embodiments, the positive electrode sheet can be prepared by the following method: the positive electrode slurry prepared by the preparation method in any of the above embodiments or the positive electrode slurry in any embodiment is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0120] [Negative electrode]

[0121] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0122] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0125] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0128] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0129] [Electrolytes]

[0130] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0131] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0132] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0133] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0134] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0135] [Isolation film]

[0136] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0137] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0138] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0139] The present application has no particular limitation on the type of secondary battery. For example, in some embodiments, the secondary battery is any one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0140] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0141] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0142] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 with a square structure as an example.

[0143] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0144] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0145] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0146] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0147] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0148] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0149] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0150] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0151] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0152] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0153] Example

[0154] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0155] 1. Preparation method

[0156] Example 1

[0157] 1) Preparation of positive electrode slurry

[0158] First stirring: 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 and mixed for first stirring at a revolution speed of 15 rpm for 15 minutes to obtain a dry mix;

[0159] Second stirring: 147 kg of NMP (N-methylpyrrolidone) solvent was added to a double planetary mixer and mixed with the dry mix to perform a second stirring, wherein the mass of the 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 a primary slurry;

[0160] Third stirring: 20 kg of conductive carbon black and 245 kg of NMP solvent were mixed with the primary slurry for third stirring, wherein the mass of the NMP solvent added in the third stirring was 25% of the total mass of the positive electrode active material and the binder, the revolution speed was 25 rpm, the rotation speed was 1100 rpm, and the stirring time was 110 minutes to obtain a positive electrode slurry.

[0161] Examples 2 to 50

[0162] The method is basically the same as Example 1, except that the preparation parameters of the positive electrode slurry are adjusted. For specific parameters, see Table 1.

[0163] In Examples 6 to 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 to the second polyvinylidene fluoride to the third polyvinylidene fluoride is 3:2:1.

[0164] Comparative Example 1

[0165] 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 for stirring. The revolution speed of the first stirring was 25 rpm and the stirring time was 70 minutes to obtain a dry mix.

[0166] 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 for stirring at an orbital speed of 30 rpm, a stirring time of 110 minutes, and a rotation speed of 1100 rpm to obtain a positive electrode slurry.

[0167] Comparative Examples 2-3

[0168] The method is basically the same as Comparative Example 1, except that the mass ratio of positive electrode active material: binder: conductive agent is adjusted. For specific parameters, see Table 1.

[0169] Comparative Examples 4 to 6

[0170] The results are basically the same as those in Comparative Example 1, except that the weight average molecular weight of polyvinylidene fluoride is adjusted to 150,000, 500,000, and 1,000,000, respectively. The specific parameters are shown in Table 1.

[0171] Comparative Example 7

[0172] It is basically the same as Comparative Example 1, except that the binder is adjusted to contain two weight-average molecular weights of polyvinylidene fluoride, the weight-average molecular weight of the first polyvinylidene fluoride is 800,000, and the weight-average molecular weight of the second polyvinylidene fluoride is 1.4 million. The two weight-average molecular weights of polyvinylidene fluoride are mixed and used. The mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 2:1. The specific parameters are shown in Table 1.

[0173] 2. Test Method

[0174] 1. Test the solid content difference between the upper and lower layers of the slurry after it has been allowed to stand for 24 hours

[0175] Weigh the aluminum foil in a moisture meter, record it as M0, the model of the moisture meter is MOC-120H;

[0176] After the slurry has been allowed to stand for 24 hours, take the upper slurry and apply a small amount of it on aluminum foil. Reset the moisture meter to zero, then put it into the moisture meter and weigh it, which is recorded as M1.

[0177] Close the device and start drying;

[0178] After the end, record the weighing data, record it as M2, and calculate the solid content, the solid content is (M2-M0) / (M1-M0);

[0179] The solid content of the lower slurry was measured in the same way, and the solid content of the lower slurry minus the solid content of the upper slurry was taken as the difference in solid content of the upper and lower layers after the slurry was allowed to stand for 24 hours.

[0180] 2. Viscosity test of shipped slurry

[0181] The prepared positive electrode slurry was allowed to stand for 10 minutes before being shipped. The viscosity was measured using a Brookfield Dveslvtjo rotary viscometer at 25°C and 12 rpm. A 64-spindle was used for slurry viscosity not less than 2000 mPa·s, and a 62-spindle was used for slurry viscosity less than 2000 mPa·s. Three replicate measurements were performed, and the average value was taken.

[0182] 3. Viscosity test of the slurry after standing for 24 hours

[0183] After the prepared positive electrode slurry was allowed to stand for 24 hours, the viscosity was measured using a Brookfield rotary viscometer. The 24-hour viscosity was recorded. The test conditions were: 25°C, 12 rpm, a 64-spindle for slurry viscosity not less than 2000 mPa·s, and a 62-spindle for slurry viscosity less than 2000 mPa·s. Three replicate measurements were performed, and the average value was calculated.

[0184] 4. Gel state test after the slurry has been allowed to stand for 24 hours

[0185] After the slurry has been allowed to stand for 24 hours, use a steel ruler to pick up the slurry in the beaker and judge whether the slurry is non-gel, slightly gelled, moderately gelled, or severely gelled based on the flow state of the slurry.

[0186] Gel-free state: the slurry flows naturally and continuously, and the slurry flows flat on the surface of the steel ruler without lumps;

[0187] Slightly gelled state: The slurry flows naturally and continuously, but the fluid is relatively thin. The slurry is basically spread evenly on the surface of the steel ruler, with slight lumps;

[0188] Moderate gel state: The slurry drips naturally and intermittently; it does not flow continuously, and the slurry cannot be spread evenly on the surface of the steel ruler, with obvious block agglomerations;

[0189] Severe gelation: The slurry cannot flow down in a stream, falls down in lumps or remains directly on the steel ruler and cannot flow down.

[0190] 3. Analysis of test results of various embodiments and comparative examples

[0191] The positive electrode slurries of the embodiments and comparative examples were prepared according to the above method, and various parameters were measured. The results are shown in Tables 1 and 2 below.

[0192] Table 1

[0193] Table 2

[0194] According to the results in Table 1 and Table 2, the positive electrode slurries in Examples 1-50 are all prepared by the slurry preparation method disclosed in the present application, including first stirring, second stirring and 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 and the dry mixture are kneaded 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; wherein the binder comprises at least one fluorine-containing polymer having a weight-average molecular weight of 150,000 to 1.5 million.

[0195] From the comparison of Examples 1 to 4, 7, 49, and 50 with Comparative Examples 1 to 7, it can be seen that the preparation method disclosed in the present application has wide versatility and is applicable to slurries of one or more fluoropolymer binders with a weight-average molecular weight of 150,000 to 1.5 million. The preparation method is universal for low-weight-average molecular weight fluoropolymer binders and high-weight-average molecular weight fluoropolymer binders, which helps to reduce preparation costs and improve production efficiency.

[0196] As can be seen from Comparative Example 6, the prior art preparation process is unable to reduce the shipping viscosity of the slurry for a binder with a weight-average molecular weight of 1 million, resulting in severe gelation. However, the preparation method disclosed in this application enables a slurry containing a binder with a weight-average molecular weight of up to 1.5 million to still have low shipping viscosity, anti-settling and anti-gel properties, meeting the requirements for the use of the new generation of high molecular weight binders.

[0197] As can be seen from the comparison of Examples 6-13 with Comparative Example 7, this application is also applicable to slurries containing binders with 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 binder molecular weights. This preparation method has wider applicability.

[0198] As can be seen from Examples 1, 49, and 50 and Comparative Examples 1-3, the prior art preparation processes have difficulty reducing the shipping viscosity of slurries with high contents of positive electrode active materials, and can also cause severe gelation. However, the preparation method disclosed in this application enables slurries with high contents of positive electrode active materials to maintain low shipping viscosity, anti-settling properties, and anti-gelation properties, meeting the requirements of high-energy-density batteries.

[0199] From the comparison between Example 8 and Example 4, the comparison between Example 10 and Example 5, and the comparison between Example 11 and Example 1, it can be seen that the slurry containing binders of different molecular weights prepared by the preparation method of the present application has a lower viscosity after standing for 24 hours and a lower solid content difference between the upper and lower layers after standing for 24 hours, and the slurry has better anti-settling properties.

[0200] From the comparison of Examples 1, 14, and 15 with Example 13, it can be seen that controlling the mass content of the solvent used in the second stirring to 10% to 20% of the total mass of the positive electrode active material and the binder can reduce the shipping 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 slurry's anti-settling and anti-gel properties, improve the slurry's storage performance, and broaden the slurry coating process window. From the comparison of Examples 1, 14, and 15 with Example 16, it can be seen that controlling the mass content of the solvent used in the second stirring to 10% to 20% of the total mass of the positive electrode active material and the binder without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, and the gelation phenomenon of the slurry can reduce the use of solvent, reduce costs, and balance the quality and cost of the slurry.

[0201] From the comparison of Examples 1, 18 to 19 with Example 17, it can be seen that controlling the mass content of the solvent used in the third stirring to 20% to 30% of the total mass of the positive electrode active material and the binder can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and can reduce the solid content difference between the upper and lower layers of the slurry after standing for 24 hours, slow down the gelation of the slurry, improve the anti-settling and anti-gelation properties of the slurry, improve the storage properties of the slurry, and widen the process window for slurry coating. From the comparison of Examples 1, 18 to 19 with Example 20, it can be seen that controlling the mass content of the solvent used in the third stirring to 20% to 30% of the total mass of the positive electrode active material and the binder without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the solid content difference between the upper and lower layers of the slurry after standing for 24 hours, and the gelation of the slurry can reduce the use of solvent, reduce costs, and balance the quality and cost of the slurry.

[0202] From the comparison of Examples 1, 26 to 27 with Example 25, it can be seen that controlling the revolution speed in the first stirring to 10 to 20 rpm can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers after standing for 24 hours, slow down the gelation of the slurry, improve the anti-sedimentation and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 26 to 27 with Example 28, it can be seen that controlling the revolution speed in the first stirring to 10 to 20 rpm without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, and the gelation of the slurry can reduce the power of the agitator, save energy, and take into account both the quality and cost of the slurry.

[0203] From the comparison of Examples 1, 22 to 23 with Example 21, it can be seen that controlling the stirring time in the first stirring to 10 to 20 minutes can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers after standing for 24 hours, slow down the gelation of the slurry, improve the anti-settling and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 22 to 23 with Example 24, it can be seen that controlling the stirring time in the first stirring to 10 to 20 minutes without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, and the gelation of the slurry can reduce the working time of slurry preparation, improve the working efficiency of slurry preparation, and reduce costs.

[0204] From the comparison of Examples 1, 30 to 31 with Example 29, it can be seen that controlling the revolution speed in the second stirring to 20 to 30 rpm can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers after standing for 24 hours, slow down the gelation of the slurry, improve the anti-sedimentation and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 30 to 31 with Example 32, it can be seen that controlling the revolution speed in the second stirring to 20 to 30 rpm without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, and the gelation of the slurry can reduce the power of the agitator, save energy, and take into account both the quality and cost of the slurry.

[0205] From the comparison of Examples 1, 34 to 35 with Example 33, it can be seen that controlling the stirring time in the second stirring to 20 to 30 minutes can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers after standing for 24 hours, slow down the gelation of the slurry, improve the anti-settling and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 34 to 35 with Example 36, it can be seen that controlling the stirring time in the second stirring to 20 to 30 minutes without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, and the gelation of the slurry can reduce the working time of slurry preparation, improve the working efficiency of slurry preparation, and reduce costs.

[0206] From the comparison of Examples 1, 42 to 43 with Example 41, it can be seen that controlling the revolution speed during the third stirring to 20 to 30 rpm can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, slow down the gelation of the slurry, improve the anti-settling and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 42 to 43 with Example 44, it can be seen that controlling the revolution speed during the third stirring to 20 to 30 rpm without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, or the gelation of the slurry, reduces the power of the agitator, saves energy, and can balance the quality and cost of the slurry.

[0207] From the comparison of Examples 1, 46 to 47 with Example 45, it can be seen that controlling the rotation speed in the third stirring process to 1000 to 1200 rpm can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers after standing for 24 hours, slow down the gelation of the slurry, improve the anti-settling and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 46 to 47 with Example 48, it can be seen that controlling the rotation speed in the third stirring process to 1000 to 1200 rpm can reduce the power of the agitator, save energy, and balance the quality and cost of the slurry without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, and the gelation of the slurry.

[0208] From the comparison of Examples 1, 38 to 39 with Example 37, it can be seen that controlling the stirring time in the third stirring to 100 minutes to 120 minutes can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and reduce the difference in solid content between the upper and lower layers after standing for 24 hours, slow down the gelation of the slurry, improve the anti-settling and anti-gelation properties of the slurry, and improve the stability and storage properties of the slurry. From the comparison of Examples 1, 38 to 39 with Example 40, it can be seen that controlling the stirring time in the third stirring to 100 minutes to 120 minutes without significantly changing the shipping viscosity of the slurry, the viscosity of the slurry after standing for 24 hours, the difference in solid content between the upper and lower layers after standing for 24 hours, and the gelation of the slurry can reduce the working time of slurry preparation, improve the working efficiency of slurry preparation, and reduce costs.

[0209] It can be seen from Examples 1 and 49 to 50 that the preparation method of the present application is applicable to the slurry system in which the mass ratio of the positive electrode active material, the binder and the conductive agent is (92 to 96): (2 to 4): (2 to 4), and the prepared slurry has a low shipping viscosity and a viscosity after standing for 24 hours. The slurry has excellent anti-sedimentation and anti-gel properties, which can meet the high energy density requirements of the battery.

[0210] It can be seen from Examples 1 to 50 that 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-gel properties, thereby improving the stability and storage properties of the slurry.

[0211] It can be seen from Examples 1 to 50 that 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.

[0212] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a positive electrode slurry, characterized in that: 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 mixed material 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; Wherein, the binder comprises at least one fluorine-containing polymer with a weight average molecular weight of 150,000 to 1.5 million.

2. The preparation method according to claim 1, characterized in that: The binder comprises at least two fluorine-containing polymers whose difference in weight average molecular weight is not greater than 1.5 million.

3. The preparation method according to claim 1 or 2, characterized in that: The fluorine-containing polymer includes polyvinylidene fluoride.

4. The preparation method according to any one of claims 1 to 3, characterized in that 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%-20% based on the total mass of the positive electrode active material and the binder, and / or The mass content of the solvent used in the third stirring is 20%-30% based on the total mass of the positive electrode active material and the binder.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The first stirring satisfies at least one of the following conditions: (i) stirring time is 10 minutes to 20 minutes; (ii) The revolution speed is 10 rpm to 20 rpm.

6. The preparation method according to any one of claims 1 to 5, characterized in that The second stirring satisfies at least one of the following conditions: (i) stirring time is 20 minutes to 30 minutes; (ii) The revolution speed is 20 rpm to 30 rpm.

7. The preparation method according to any one of claims 1 to 6, characterized in that The third stirring satisfies at least one of the following conditions: (i) stirring time is 100 minutes to 120 minutes; (ii) the revolution speed is 20 rpm to 30 rpm; (iii) The rotation speed is 1000 rpm to 1200 rpm.

8. The preparation method according to any one of claims 1 to 7, characterized in that The mass ratio of the positive electrode active material, the binder and the conductive agent is (92-96):(2-4):(2-4).

9. A positive electrode slurry, characterized in that: The positive electrode slurry is prepared by the method for preparing the positive electrode slurry according to any one of claims 1 to 8.

10. The positive electrode slurry according to claim 9, characterized in that: The solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 4500mPa·s-40000mPa·s, and can be selected as 4500mPa·s-20000mPa·s.

11. The positive electrode slurry according to claim 9 or 10, characterized in that: 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 50000 mPa·s, and can be selected to be no more than 30000 mPa·s.

12. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer is prepared by the positive electrode slurry prepared by the method for preparing the positive electrode slurry according to any one of claims 1 to 8 or the positive electrode slurry according to any one of claims 9 to 11.

13. A secondary battery, characterized in that: It comprises a separator, a negative electrode sheet and the positive electrode sheet as claimed in claim 12.

14. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 13.

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