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

Abstract

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

Description

Technical Field

[0001] 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 sheet, a secondary battery and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] 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. The positive electrode slurry is mainly a solid-liquid mixed system formed by positive electrode active materials, conductive agents, binders and solvents. This system is in a metastable state. The slurry mixing process, that is, the preparation method of the slurry, has a crucial influence on the dispersion, uniformity, stability and other properties of the slurry. The slurry mixing process in the prior art is often a one-step process, in which the components in the positive electrode slurry are directly mixed and stirred. However, the one-step preparation method is not applicable to binders with different molecular weights. Summary of the invention

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

[0005] 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 is kneaded with the dry mixture to prepare a primary slurry; in the third stirring, the conductive agent, the solvent, the binder and the primary slurry are mixed and stirred to prepare a positive electrode slurry.

[0006] The preparation method disclosed in the present application has broad versatility and is applicable to binders of different molecular weights, especially high molecular weight binders, so that the anti-gelling property of the slurry containing the high molecular weight binder is effectively improved, the slurry uniformity is optimized, and it helps to reduce the preparation cost and improve the production efficiency.

[0007] In any embodiment, the first stirred binder and / or the third stirred binder comprises at least one fluorine-containing polymer having a weight average molecular weight of 1.5 million to 8 million.

[0008] Fluorine-containing polymers have excellent bonding properties and electrochemical stability, but they are prone to agglomeration and gelation during the preparation process. The preparation method of the present application is suitable for high molecular weight fluorine-containing polymers, which can effectively alleviate the gelation and sedimentation phenomena of different slurries, help improve production efficiency, and broaden the process window of slurry coating.

[0009] In any embodiment, the first stirred binder and / or the third stirred binder comprises at least two fluorine-containing polymers having a weight average molecular weight difference of no more than 6.5 million.

[0010] The preparation method of positive electrode slurry in the prior art has poor compatibility and cannot adapt to the difference in 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, and improves the anti-sedimentation and anti-gelation properties of the slurry through the coordination and regulation of the step-by-step slurry mixing and kneading process, so that the slurry with a high weight average molecular weight binder still has low shipping viscosity and anti-coagulation properties, thereby improving the universality of the preparation method. The preparation method of the present application is suitable for high molecular weight binders, which can effectively alleviate the gelation and sedimentation phenomena of different slurries, help to improve production efficiency and broaden the process window of slurry coating.

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

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

[0013] The first stirring and the third stirring use a binder comprising the same polymer, which can effectively alleviate the stratification phenomenon of the slurry and improve the processability of the slurry.

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

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

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

[0017] Reasonable control of the proportion of binder added in batches can effectively reduce the agglomeration of high molecular weight polymers, adjust the viscosity of the slurry at delivery and after standing for 24 hours, improve the coating and processability of the slurry, and enhance the anti-settling and anti-gel properties of the slurry.

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

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

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

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

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

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

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

[0025] In any embodiment, the rotation speed in the third stirring is 900 rpm-1300 rpm, and can be optionally 1000 rpm-1200 rpm.

[0026] Controlling the above parameters within an appropriate range can reduce the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, improve the anti-settling and anti-gel properties of the slurry, improve the storage properties of the slurry, broaden the process window of slurry coating, and take into account cost-effectiveness.

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

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

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

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

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

[0032] The slurry of the present application still maintains a suitable viscosity at a high solid content and has excellent processability. The above slurry can be directly used in the subsequent coating process, which can improve production efficiency.

[0033] In any embodiment, after being left to stand for 24 hours after shipment, the viscosity of the positive electrode slurry does not exceed 50000 mPa·s.

[0034] The third aspect of the present application provides a positive electrode plate, including a positive electrode film layer, wherein the positive electrode film layer is mainly prepared from the positive electrode slurry provided in the second aspect of the present application.

[0035] The fourth aspect of the present application provides a secondary battery, comprising the positive electrode plate provided in the third aspect of the present application.

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

[0037] The fifth aspect of the present application provides an electrical device, comprising the secondary battery provided in the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

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

[0040] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0041] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

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

[0043] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0044] Description of reference numerals:

[0045] 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

[0046] Below, the preparation method of the positive electrode slurry, the positive electrode slurry, the positive electrode sheet, the secondary battery and the implementation method of the electric device of the present application are specifically disclosed with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same 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 descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0047] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] 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.

[0050] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0051] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0052] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0053] Studies have shown that using high molecular weight polymers as binders can effectively improve the bonding strength of the pole piece at a low usage amount, increase the loading amount of active materials, and thus improve the energy density of the battery. However, the slurry mixing process in the prior art has poor applicability and cannot meet the processing requirements of polymers with different molecular weights. In particular, the prepared slurry containing high molecular weight polymers has poor stability, is easy to settle and gel, and is difficult to meet the production requirements of pole pieces.

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

[0055] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 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 0.2O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

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

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

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

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

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

[0061] 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.

[0062] In the 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 solvent is added for kneading, and the positive electrode active material and the binder absorb the solvent 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 effect 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, the conductive agent, solvent, and binder are added again to transform the slurry from the kneading state to the solution state, so that under the strong shearing effect caused 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. The method of adding the binder step by step allows the polymer to be gradually dissolved and effectively dispersed, which is particularly suitable for the processing and manufacturing of high molecular weight polymers and improves the uniformity of the slurry.

[0063] The preparation method disclosed in the present application has broad versatility and is applicable to binders of different molecular weights, especially high molecular weight binders, so that the anti-gelling property of the slurry containing the high molecular weight binder is effectively improved, the slurry uniformity is optimized, and it helps to reduce the preparation cost and improve the production efficiency.

[0064] In some embodiments, the binder in the first mixing and / or the binder in the third mixing comprises at least one fluorine-containing polymer having a weight average molecular weight of 1.5 million to 8 million.

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

[0066] In this article, the term "weight average molecular weight" is common knowledge in the art and has a well-known meaning in the art, and can be measured using instruments and methods known in the art, such as gel permeation chromatography, and referring to GB / T21863-2008 standard.

[0067] As used herein, the term "fluoropolymer" refers to a polymer having fluorine-containing groups.

[0068] In some embodiments, the fluorine-containing polymer 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.

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

[0070] Fluorine-containing polymers have excellent bonding properties and electrochemical stability, but they are prone to agglomeration and gelation during the preparation process. The preparation method of the present application is suitable for high molecular weight fluorine-containing polymers, which can effectively alleviate the gelation and sedimentation phenomena of different slurries, help improve production efficiency, and broaden the process window of slurry coating.

[0071] In some embodiments, the first stirred binder and / or the third stirred binder comprises at least two fluorine-containing polymers having a weight average molecular weight difference of no more than 6.5 million.

[0072] In some embodiments, the binder contains two or more polyvinylidene fluoride with different weight average molecular weights, and the difference in weight average molecular weight between the polyvinylidene fluoride is not higher than 6.5 million, 6 million, 5 million, 4 million, 3 million, 2 million, 1 million, 500,000 or any value therebetween.

[0073] The preparation methods of positive electrode slurries in the prior art have poor compatibility and cannot adapt to the differences in the weight average molecular weight of the binder in the slurry. Therefore, very high precision requirements are placed on the materials. The present application reduces the shipping viscosity of the positive electrode slurry, alleviates the gelation phenomenon of the positive electrode slurry, improves the slurry's anti-sedimentation and anti-gel properties, and enables slurries with binders of different weight average molecular weights to still have low shipping viscosity and anti-coagulation properties, thereby improving the universality of the preparation method.

[0074] The applicant unexpectedly discovered that the preparation method disclosed in the present application can effectively adapt to positive electrode slurries containing a variety of weight-average molecular weight binders. Unlike the phenomenon in the prior art that binders of different molecular weights easily lead to aggravated slurry sedimentation, the positive electrode slurry prepared by the method of the present application can effectively exert the characteristics of polyvinylidene fluoride binders of different molecular weights, and improve the anti-sedimentation property of the slurry through the mutual coordination of large and small chain segments and steric hindrance.

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

[0076] The first stirring and the third stirring use a binder including the same fluorine-containing polymer, which can effectively alleviate the stratification phenomenon of the slurry and improve the processability of the slurry.

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

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

[0079] Controlling the mass of the solvent used in the second stirring within a suitable range based on the ratio 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, improve the anti-sedimentation and anti-gel properties of the slurry, improve the storage properties of the slurry, broaden the process window of slurry coating, and take into account cost-effectiveness.

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

[0081] Controlling the mass of the solvent used in the third stirring within a suitable range based on the ratio 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, improve the anti-sedimentation and anti-gel properties of the slurry, improve the storage properties of the slurry, broaden the process window of slurry coating, and take into account cost-effectiveness.

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

[0083] In some embodiments, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 40%, and the mass percentage of the binder used in the third stirring is 60%. In some embodiments, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 50%, and the mass percentage of the binder used in the third stirring is 50%. In some embodiments, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 60%, and the mass percentage of the binder used in the third stirring is 40%. In some embodiments, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 70%, and the mass percentage of the binder used in the third stirring is 30%. In some embodiments, based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 80%, and the mass percentage of the binder used in the third stirring is 20%. Reasonable control of the proportion of binder added in batches can effectively reduce the agglomeration of high molecular weight polymers, adjust the viscosity of the slurry at delivery and after standing for 24 hours, improve the coating and processability of the slurry, and enhance the anti-settling and anti-gel properties of the slurry.

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

[0085] In some embodiments, the stirring time in the first stirring may be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or any value therebetween.

[0086] Reasonable control of the first stirring time is conducive to further uniform dispersion of the binder and the positive electrode active material, so that the binder is further riveted to the surface of the positive electrode active material, improving the dispersibility of the dry mixture, and can effectively adjust the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, improve the anti-sedimentation and anti-gel properties of the slurry, while taking into account cost-effectiveness.

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

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

[0089] As used herein, the term "orbital speed" refers to the speed at which the agitator rotates around the vessel containing the material.

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

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

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

[0093] Reasonable control of the stirring time of the second stirring is beneficial to improving the dispersibility of the primary slurry, effectively adjusting the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improving the coating and processability of the slurry, and improving the anti-settling and anti-gel properties of the slurry while taking into account cost-effectiveness.

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

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

[0096] Reasonable control of the revolution speed of the second stirring can effectively adjust the shipping viscosity of the slurry and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and improve the anti-settling and anti-gel properties of the slurry while taking into account cost-effectiveness.

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

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

[0099] As used herein, the term "rotational speed" refers to the speed at which the agitator rotates about its own axis.

[0100] Reasonable control of the rotation speed of the second stirring can effectively adjust the viscosity of the slurry at delivery and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and improve the anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0101] In some embodiments, the stirring time in the third stirring is 90 minutes to 130 minutes, and optionally 100 minutes to 120 minutes.

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

[0103] Reasonable control of the third stirring time is conducive to the full dispersion of the conductive agent and the binder around the positive electrode active material, effectively adjusting the viscosity of the slurry at the time of shipment and the viscosity after standing for 24 hours, improving the coating and processability of the slurry, improving the anti-sedimentation and anti-gel properties of the slurry, and taking into account cost-effectiveness.

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

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

[0106] Reasonable control of the revolution speed of the third stirring can effectively adjust the viscosity of the slurry at delivery and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and improve the anti-settling and anti-gel properties of the slurry while taking into account cost-effectiveness.

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

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

[0109] Reasonable control of the rotation speed of the third stirring can effectively adjust the viscosity of the slurry at delivery and the viscosity after standing for 24 hours, improve the coating and processability of the slurry, and improve the anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

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

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

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

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

[0114] A second aspect of the present application provides a positive electrode slurry, which is prepared by the method for preparing a positive electrode slurry of any embodiment.

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

[0116] The slurry preparation method provided in the present application can effectively increase the solid content of the slurry. Slurries with low solid content need to evaporate more solvents during the drying process of coating the pole pieces, resulting in a decrease in coating speed and an increase in equipment energy consumption; at the same time, if the solid content of the slurry is too low, the heating and drying time needs to be extended during coating, which may cause problems such as pole piece warping, cracking, and poor adhesion caused by the floating of the adhesive. The high-solid content slurry disclosed in the present application can not only meet the requirements of coating speed-up, but also meet the requirements of long slurry storage time and wide process window, effectively improving production efficiency and reducing costs. In some embodiments, the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry can be selected as 7000mPa·s, 7600mPa·s, 8000mPa·s, 10000mPa·s, 15000mPa·s, 20000mPa·s, 24000mPa·s, 25000mPa·s, 30000mPa·s, 35000mPa·s, 39000mPa·s or any value therebetween.

[0117] Shipping viscosity refers to the viscosity of the positive electrode slurry when it is just prepared.

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

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

[0120] In some embodiments, after standing for 24 hours after shipment, 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.

[0121] The positive electrode slurry provided in the present application has excellent storage performance and broadens the process window of the slurry.

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

[0123] In some embodiments, after being shipped and allowed to stand 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%, and 0.1%.

[0124] A third aspect of the present application provides a positive electrode plate, comprising a positive electrode film layer, wherein the positive electrode film layer is mainly prepared from the positive electrode slurry of any embodiment.

[0125] A fourth aspect of the present application provides a secondary battery, comprising a positive electrode sheet according to any embodiment.

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

[0127] [Positive electrode]

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

[0129] 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 any one or both of the two opposite surfaces of the positive electrode current collector.

[0130] 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.).

[0131] In some embodiments, the positive electrode sheet can be prepared by the following method: the positive electrode slurry prepared by any of the above preparation methods is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0132] [Negative electrode]

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

[0134] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0135] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0136] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0137] 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).

[0138] 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.

[0139] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0140] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0141] [Electrolytes]

[0142] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

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

[0144] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

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

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

[0147] [Isolation film]

[0148] 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 stability and mechanical stability can be selected.

[0149] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0150] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0151] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0152] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0153] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0154] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

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

[0156] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0157] 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.

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

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

[0160] In addition, the present application also provides an electrical 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 electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

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

[0162] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0163] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0164] Example

[0165] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0166] 1. Preparation method

[0167] Example 1

[0168] 1) Preparation of positive electrode slurry

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

[0170] Second stirring: 146 kg of NMP (N-methylpyrrolidone) solvent was added to a double planetary mixer and mixed with the dry blend 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, the rotation speed was 500 rpm, and the stirring time was 40 minutes to obtain a primary slurry;

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

[0172] Example 2-55

[0173] It 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, wherein the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride in Examples 5-7 is 2:1, and in Examples 8-10, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride and the third polyvinylidene fluoride is 3:2:1. In Example 11, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, the third polyvinylidene fluoride and the fourth polyvinylidene fluoride is 4:3:2:1.

[0174] Comparative Example 1

[0175] 960 kg of positive electrode active material and 13.3 kg of polyvinylidene fluoride having a weight average molecular weight of 1.5 million were added into a 1300 L double planetary mixer for mixing and stirring at an orbital speed of 25 revolutions per minute for 10 minutes to obtain a dry mixture;

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

[0177] Comparative Examples 2-12

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

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

[0180] 2. Test Method

[0181] 1. Test on the difference in solid content between the upper and lower layers of the slurry after it has been left to stand for 24 hours

[0182] Weigh the aluminum foil in a moisture meter, record it as M0, the model of the moisture meter is MOC-120H;

[0183] After the slurry is left 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.

[0184] Close the device and start drying;

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

[0186] 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 between the upper and lower layers after the slurry was left standing for 24 hours.

[0187] 2. Viscosity test of shipped slurry

[0188] The prepared positive electrode slurry was placed for 10 minutes before shipment. The viscosity value measured by Dveslvtjo rotary viscosity tester (BROOKFIELD) was recorded as the shipping viscosity, where the test conditions were: 25°C, 12 rpm, 64 rotor when the slurry viscosity was not less than 2000 mPa·s, and 62 rotor when the slurry viscosity was less than 2000 mPa·s. The measurement was repeated three times and the average value was taken.

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

[0190] After the prepared positive electrode slurry was placed for 24 hours, the viscosity value measured by Dveslvtjo rotary viscosity tester (BROOKFIELD) was recorded as the 24-hour viscosity, wherein the test conditions were: 25°C, rotation speed 12 rpm, when the slurry viscosity was not less than 2000 mPa·s, a 64 rotor was used, and when the slurry viscosity was less than 2000 mPa·s, a 62 rotor was used. The measurement was repeated three times and the average value was taken.

[0191] 4. Gel state test after the slurry has been left to stand for 24 hours

[0192] After the slurry has been allowed to stand for 24 hours, a steel ruler is used to pick up the slurry in the beaker, and the slurry is judged according to the flow state of the slurry to determine whether it is non-gel, slightly gelled, moderately gelled, or severely gelled.

[0193] Gel-free state: the slurry flows naturally and continuously, and the slurry flows on the surface of the steel ruler without lumps;

[0194] Slightly gelled state: the slurry flows naturally and continuously, but the fluid is thin, and the slurry is basically spread evenly on the surface of the steel ruler, with slight small pieces;

[0195] Moderate gel state: the slurry drips naturally and intermittently; it does not flow continuously, the slurry cannot be spread evenly on the surface of the steel ruler, and there are obvious block agglomerations;

[0196] Severe gel state: The slurry cannot flow down in a stream, falls off in lumps or remains directly on the steel ruler and cannot flow down.

[0197] III. Analysis of test results of various embodiments and comparative examples

[0198] 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.

[0199] Table 1

[0200]

[0201]

[0202]

[0203] Table 2

[0204]

[0205]

[0206]

[0207] The positive electrode slurries in the embodiments 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 is kneaded with the dry mixture to prepare a primary slurry; in the third stirring, the conductive agent, solvent, binder and the primary slurry are mixed and stirred to prepare a positive electrode slurry.

[0208] From the comparison between the examples and the comparative examples, it can be seen that the preparation method disclosed in the present application has wide versatility, is applicable to binders with different weight-average molecular weights, can improve the anti-settling and anti-gel properties of the slurry, and is beneficial to improving processing efficiency and reducing processing costs.

[0209] From the comparison between the embodiment and the comparative example, it can be seen that the binder in the first stirring and the binder in the third stirring both contain at least one polyvinylidene fluoride having a weight average molecular weight of 1.5 million to 8 million.

[0210] As can be seen from the comparative examples, the preparation process in the prior art is difficult to reduce the shipping viscosity of the high molecular weight binder, and the slurry will have serious gelation. However, the preparation method disclosed in the present application enables the slurry containing the binder with a weight average molecular weight of up to 8 million to still have good anti-settling and anti-gel properties, which can meet the use requirements of the new generation of high molecular weight binders.

[0211] From the comparison between Examples 5-11 and Comparative Examples 5-11, it can be seen that the present application is also applicable to slurries with binders of different weight average molecular weights. Different from the preparation methods in the prior art, the preparation method disclosed in the present application can effectively overcome the slurry gel phenomenon caused by large differences in binder molecular weights. The preparation method has wider universality.

[0212] From the comparison of Examples 2 and 12-15, it can be seen that controlling the mass percentage 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 further reduce the shipping viscosity of the slurry and the viscosity of the slurry after standing for 24 hours while maintaining a high solid content of the slurry, 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-sedimentation and anti-gel properties, improve the slurry's storage performance, and broaden the process window for slurry coating.

[0213] From the comparison of Examples 2 and 16-19, it can be seen that controlling the mass content of the solvent used in the third stirring to 30% to 40% of the total mass of the positive electrode active material and the binder can further reduce the shipping viscosity of the slurry and the viscosity of the slurry after standing for 24 hours while maintaining a high solid content of the slurry, reduce the difference in solid content between the upper and lower layers of the slurry after standing for 24 hours, improve the anti-sedimentation and anti-gel properties of the slurry while taking into account both cost and benefit, improve the storage performance of the slurry, and broaden the process window for slurry coating.

[0214] From the comparison of Examples 2 and 20-23, it can be seen that, based on the total mass of the binder, the mass ratio of the binder used in the first stirring is 50%-70%, and the mass ratio of the binder used in the third stirring is 30%-50%, which can further 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-sedimentation and anti-gel properties, improve the slurry's storage performance, and broaden the process window for slurry coating.

[0215] From the comparison of Examples 2 and 24-27, it can be seen that the stirring time in the first stirring is 10 minutes to 20 minutes, which helps to further 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-sedimentation and anti-gel properties, improve the slurry's storage performance, and broaden the process window for slurry coating.

[0216] From the comparison of Examples 2 and 28-31, it can be seen that the revolution speed in the first stirring is 20 rpm-30 rpm, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0217] From the comparison of Examples 2 and 32-35, it can be seen that the revolution speed of the second stirring is 20 rpm-30 rpm, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0218] From the comparison of Examples 2 and 36-39, it can be seen that the rotation speed of the second stirring is 400 rpm-600 rpm, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0219] From the comparison of Examples 2 and 40-43, it can be seen that the stirring time of the second stirring is 30 minutes to 50 minutes, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0220] From the comparison of Examples 2 and 44-47, it can be seen that the revolution speed in the third stirring is 20 rpm-30 rpm, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0221] From the comparison of Examples 2 and 48-51, it can be seen that the rotation speed in the third stirring is 1000 rpm-1200 rpm, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0222] From the comparison of Examples 2 and 52-55, it can be seen that the stirring time in the third stirring is 100 minutes-120 minutes, which helps to further 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 anti-sedimentation and anti-gel properties of the slurry while taking into account cost-effectiveness.

[0223] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining 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: The preparation method comprises 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, the binder and the primary slurry are mixed and stirred to prepare the positive electrode slurry.

2. The preparation method according to claim 1, characterized in that: The binder in the first stirring and / or the binder in the third stirring comprises at least one fluorine-containing polymer having a weight average molecular weight of 1.5 million to 8 million.

3. The preparation method according to claim 1 or 2, characterized in that: The binder in the first stirring and / or the binder in the third stirring comprises at least two fluorine-containing polymers whose difference in weight average molecular weight is not greater than 6.5 million.

4. The preparation method according to any one of claims 1 to 3, characterized in that The fluorine-containing polymer includes polyvinylidene fluoride.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The first stirred binder and the third stirred binder include the same fluoropolymer.

6. The preparation method according to any one of claims 1 to 5, characterized in that Based on the total mass of the positive electrode active material and the binder, the mass percentage of the solvent used in the second stirring is 5%-25%, optionally 10%-20%, and / or Based on the total mass of the positive electrode active material and the binder, the mass percentage of the solvent used in the third stirring is 25%-45%, and can be 30%-40%.

7. The preparation method according to any one of claims 1 to 6, characterized in that Based on the total mass of the binder, the mass percentage of the binder used in the first stirring is 40%-80%, optionally 50%-70%, and the mass percentage of the binder used in the third stirring is 20%-60%, optionally 30%-50%.

8. The preparation method according to any one of claims 1 to 7, characterized in that The first stirring satisfies at least one of the following conditions: (i) stirring time is 5 minutes to 25 minutes, and can be 10 minutes to 20 minutes; (ii) The revolution speed is 15 rpm to 35 rpm, and can be optionally 20 rpm to 30 rpm.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The second stirring satisfies at least one of the following conditions: (i) stirring time is 20 minutes to 60 minutes, and can be 30 minutes to 50 minutes; (ii) the revolution speed is 15 rpm to 35 rpm, and can be optionally 20 rpm to 30 rpm; (iii) The rotation speed is 300 rpm to 700 rpm, and can be optionally 400 rpm to 600 rpm.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The third stirring satisfies at least one of the following conditions: (i) stirring time is 90 minutes to 130 minutes, and can be 100 minutes to 120 minutes; (ii) the revolution speed is 15 rpm to 35 rpm, and can be optionally 20 rpm to 30 rpm; (iii) The rotation speed is 900 rpm to 1300 rpm, and can be optionally 1000 rpm to 1200 rpm.

11. The preparation method according to any one of claims 1 to 10, characterized in that: In the positive electrode slurry, the mass ratio of the total mass of the positive electrode active material, the total mass of the binder, and the mass ratio of the conductive agent is (90-99.8):(0.1-5):(0.1-5), and can be optionally (92-96):(2-4):(2-4).

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

13. The positive electrode slurry according to claim 12, wherein the solid content of the positive electrode slurry is 65%-75%, and the shipping viscosity of the positive electrode slurry is 7000mPa·s-39000mPa·s, and can be optionally 7600mPa·s-24000mPa·s.

14. A positive electrode sheet, characterized in that: It comprises a positive electrode film layer, and the positive electrode film layer is mainly prepared from the positive electrode slurry according to claim 12 or 13.

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

16. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 15.

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