Positive electrode slurry preparation method, positive electrode plate, secondary battery, and power consumption device

Abstract

The present application provides a method for preparing a positive electrode slurry, a positive electrode plate, a secondary battery, and a power consumption device. The method for preparing a positive electrode slurry includes a first stirring, a second stirring, a third stirring, and a fourth stirring, and during the first stirring, a positive electrode active material and an adhesive are mixed and stirred to prepare a dry mixture, during the second stirring, an adhesive and a solvent are mixed and stirred to prepare an adhesive liquid, during the third stirring, the dry mixture and the adhesive liquid are mixed and stirred to prepare a primary slurry, and during the fourth stirring, a positive electrode active material, a conductive agent, a solvent, and the primary slurry are mixed and stirred to prepare a positive electrode slurry, and the adhesive used in the first stirring is the same as the adhesive used in the second stirring.

Description

[Technical field]

[0001] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode slurry preparation method, a positive electrode plate, a secondary battery, and a power consuming device. [Background technology]

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

[0003] Electrode slurry is the basis for forming electrodes and is also the first step in the production of secondary batteries. The properties of the electrode slurry have a significant impact on the subsequent electrode production and battery performance. The positive electrode slurry is a solid-liquid phase mixture system mainly consisting of a positive electrode active material, a conductive agent, an adhesive and a solvent. The slurry preparation method in the prior art is often a one-step method, which can be obtained by directly mixing and stirring each component in the positive electrode slurry, but the one-step preparation method cannot meet the preparation demand of adhesives with different mass average molecular weights, the versatility of the mixing process is poor, and it is disadvantageous in reducing the preparation cost. Therefore, it is necessary to develop a new slurry preparation method to apply to adhesives with different mass average molecular weights. Summary of the Invention

[0004] The present application has been made in view of the above problems, and an object of the application is to provide a method for preparing a positive electrode slurry for application to adhesives with different mass average molecular weights.

[0005] According to a first aspect of the present application, there is provided a method for preparing a positive electrode slurry, the method including first stirring, second stirring, third stirring and fourth stirring, During the first stirring, the positive electrode active material and the adhesive are mixed and stirred to prepare a dry mixture; During the second stirring, the adhesive and the solvent are mixed and stirred to prepare an adhesive liquid; During the third stirring, the dry mixture and the adhesive liquid are mixed and stirred to prepare a primary slurry; During the fourth stirring, the positive electrode active material, the conductive agent, the solvent, and the primary slurry are mixed and stirred to prepare a positive electrode slurry; The adhesive used in the first mixing and the adhesive used in the second mixing are the same.

[0006] The positive electrode slurry preparation method disclosed in the present application has wider versatility than conventional positive electrode slurry preparation methods and is applicable to slurries containing adhesives with different mass average molecular weights. Compared with conventional preparation methods, the present application allows the adhesive to be uniformly coated on the positive electrode active material by adding and mixing the adhesive multiple times, and can effectively disperse the adhesive in the slurry and avoid serious aggregation of the adhesive, thereby improving the applicability of the preparation method of the present application to adhesives with large molecular weights, improving the versatility of the slurry preparation method, and reducing the preparation cost.

[0007] In any embodiment, the adhesive includes at least one polyvinylidene fluoride having a weight average molecular weight of 1 million to 8 million.

[0008] The preparation method disclosed in the present application is versatile for low molecular weight polyvinylidene fluoride adhesives and high molecular weight polyvinylidene fluoride adhesives, broadens the application window of the slurry, and still has suitable viscosity for the slurry containing an adhesive with a mass average molecular weight of up to 8 million, while ensuring that the electrode plate has excellent adhesive performance, and can meet the demand for the use of next-generation adhesives.

[0009] In any embodiment, the adhesive includes at least two polyvinylidene fluorides having a difference in mass average molecular weight of 7 million or less.

[0010] The positive electrode slurry prepared by the preparation method disclosed in the present application can effectively exert the properties of polyvinylidene fluoride adhesives with different molecular weights, and the mutual bonding and steric hindrance between the large and small segments ensures that the slurry has an appropriate viscosity and that the electrode plate has relatively high adhesive strength, shear strength and cohesive strength.

[0011] In any embodiment, with respect to the total mass of the adhesive used in the first mixing and the adhesive used in the second mixing, the mass content of the adhesive used in the first mixing is 30% to 50%, and the mass content of the adhesive used in the second mixing is 50% to 70%.

[0012] By controlling the mass content of the adhesive used in the first mixing to 30% to 50% and the mass content of the adhesive used in the second mixing to 50% to 70% relative to the total mass of the adhesive used in the first mixing and the adhesive used in the second mixing, it is possible to ensure that the viscosity of the slurry is within an appropriate range and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0013] In any embodiment, the revolution speed of the first stirring is 10 revolutions / minute to 20 revolutions / minute.

[0014] By controlling the revolution speed of the first stirring to 10 rpm to 20 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0015] In any embodiment, the rotation speed of the first agitation is 0.

[0016] By controlling the rotation speed of the first stirrer to 0, the shear force of the first stirrer is reduced, the possibility of the positive electrode active material and the adhesive being excessively pulverized is reduced, the positive electrode active material and the adhesive have a certain particle size and specific surface area, the dispersion effect of the positive electrode active material and the adhesive is improved, and the viscosity of the slurry is reduced, which contributes to improving the adhesion, shear strength and cohesive force of the electrode plate.

[0017] In any embodiment, the stirring time of the first stirring is 10 minutes to 20 minutes.

[0018] By controlling the stirring time of the first stirring to 10 to 20 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0019] In any embodiment, the revolution speed of the second stirring is 20 revolutions / minute to 30 revolutions / minute.

[0020] By controlling the revolution speed of the second stirring to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0021] In any embodiment, the rotation speed of the second stirring is 1100 rpm to 1300 rpm.

[0022] By controlling the rotation speed of the second agitator to 1100 rpm to 1300 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the second agitator being too high, which may affect the service life of the device, and to reduce cost loss.

[0023] In any embodiment, the stirring time of the second stirring is 60 minutes to 80 minutes.

[0024] By controlling the stirring time of the second stirring to 60 to 80 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a reduction in production efficiency due to an excessively long stirring time of the second stirring, and to save production costs.

[0025] In any embodiment, the revolution speed of the third stirring is 20 revolutions / minute to 30 revolutions / minute.

[0026] By controlling the revolution speed of the third agitator to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid the load on the device being too large due to the revolution speed of the third agitator being too high, which may affect the service life of the device, and to reduce cost losses.

[0027] In any embodiment, the rotation speed of the third stirring is 500 rpm to 800 rpm.

[0028] By controlling the rotation speed of the third agitator to 500 rpm to 800 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the third agitator being too high, which may affect the service life of the device, and to reduce cost loss.

[0029] In any embodiment, the stirring time of the third stirring is 40 minutes to 60 minutes.

[0030] By controlling the stirring time of the third stirring to 40 to 60 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a reduction in production efficiency due to a too long stirring time of the third stirring, and to save production costs.

[0031] In any embodiment, the revolution speed of the fourth stirring is 20 revolutions / minute to 30 revolutions / minute.

[0032] By controlling the revolution speed of the fourth agitator to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid the load on the device being too large due to the revolution speed of the fourth agitator being too high, which may affect the service life of the device, and to reduce cost losses.

[0033] In any embodiment, the rotation speed of the fourth stirring is 1100 rpm to 1400 rpm.

[0034] By controlling the rotation speed of the fourth stirrer to 1100 rpm to 1400 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid the load on the device being too large due to the rotation speed of the fourth stirrer being too high, which may affect the service life of the device, and to reduce cost loss.

[0035] In any embodiment, the stirring time of the fourth stirring is 100 minutes to 120 minutes.

[0036] By controlling the stirring time of the fourth stirring to 100 to 120 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a reduction in production efficiency due to an excessively long stirring time of the fourth stirring, and to save production costs.

[0037] In any embodiment, when the solid content of the positive electrode slurry is 68%, the viscosity of the positive electrode slurry is 8000 mPa·s to 41000 mPa·s.

[0038] The positive electrode slurry with a solid content of 68% has a viscosity of 8000 mPa·s to 41000 mPa·s. This positive electrode slurry has good application and processability, widening the process window for slurry application.

[0039] In any embodiment, the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring are the same, and the mass content of the positive electrode active material used in the first stirring is 50% to 70%, and the mass content of the positive electrode active material used in the fourth stirring is 30% to 50%, relative to the total mass of the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring.

[0040] By controlling the mass content of the positive electrode active material used in the first stirring to 50% to 70% and the mass content of the positive electrode active material used in the fourth stirring to 30% to 50% relative to the total mass of the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring, the viscosity of the slurry can be reduced, and the adhesive strength, shear strength and cohesive strength of the electrode plates can be improved, the process window for slurry application can be widened, and the performance of the electrode plates can be improved.

[0041] In any embodiment, the solvent used in the second stirring and the solvent used in the fourth stirring are the same, and the mass content of the solvent used in the second stirring is 35% to 40%, and the mass content of the solvent used in the fourth stirring is 5% to 10%, relative to the total mass of the conductive agent, the positive electrode active material used in the first stirring, the positive electrode active material used in the fourth stirring, the adhesive used in the first stirring, and the adhesive used in the second stirring.

[0042] In any one of the embodiments, the mass ratio of the total mass of the positive electrode active material, the total mass of the adhesive, and the conductive agent in the positive electrode slurry is (86 to 98):(1 to 8):(1 to 6). The positive electrode slurry within the above range has good processability and provides the formed positive electrode plate with excellent adhesive performance and electrochemical performance.

[0043] In any of the embodiments, the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide, which is advantageous in providing the battery with a high energy density and improving the cycle performance of the battery.

[0044] In any embodiment, the conductive agent is one or more of conductive carbon black, graphite, and carbon nanotubes, which are advantageous in improving the electrical conductivity of the battery.

[0045] According to a second aspect of the present application, there is provided a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer being manufactured from a positive electrode slurry prepared by the preparation method according to the first aspect of the present application.

[0046] In any embodiment, the adhesive strength per unit length between the positive electrode film layer and the positive electrode current collector is 20 N / m to 30 N / m.

[0047] In any embodiment, the positive electrode membrane layer has a shear strength of 0.64 mPa to 0.91 mPa.

[0048] In any embodiment, the cohesive strength of the positive electrode membrane layer is 70 N / m to 90 N / m.

[0049] According to a third aspect of the present application, there is provided a secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a separator, a negative electrode plate, and the positive electrode plate according to the second aspect of the present application.

[0050] In any of the embodiments, the secondary battery is one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

[0051] According to a fourth aspect of the present application, there is provided a battery module including the secondary battery according to the third aspect of the present application.

[0052] According to a fifth aspect of the present application, there is provided a battery pack including the secondary battery according to the third aspect of the present application or the battery module according to the fourth aspect of the present application.

[0053] According to a sixth aspect of the present application, there is provided a power consuming device including at least one selected from the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application. [Brief description of the drawings]

[0054] [Figure 1] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Diagram 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. [Diagram 3] FIG. 1 is a schematic diagram of a battery module according to an embodiment of the present application. [Figure 4] FIG. 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Diagram 5] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application. [Figure 6]1 is a schematic diagram of a power consuming device using a secondary battery as a power source according to an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the adhesive, preparation method, electrode, battery, and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and duplicated description of structures that are actually the same may be omitted. This is to avoid the following description becoming unnecessarily long and to allow those skilled in the art to easily understand. Note that the drawings and the following description are provided to allow those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0056] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisaged. It is noted that if 1 and 2 are listed as the minimum range values, and 3, 4, and 5 are listed as the maximum range values, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisaged. In this application, unless otherwise specified, a numerical range "a-b" represents a shorthand representation of any combination of real numbers a-b, where a and b are both real numbers. For example, the numerical range "0-5" represents a list of all real numbers between "0-5" already listed in this specification, and "0-5" is only a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] Unless otherwise stated, all the embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0058] Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0059] Unless otherwise stated, all steps in this application may be performed in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b) to mean that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, the method mentioned above may further include step (c) to mean that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0060] Unless otherwise stated, the terms "comprise" and "include" referred to in this application may be open ended or closed ended. For example, the terms "comprise" and "include" may further include or include other ingredients not listed, or may include or include only the listed ingredients.

[0061] Unless otherwise 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, "A or B" is satisfied if A is true (or exists) and B is false (or does not exist), if A is false (or does not exist) but B is true (or exists), or if both A and B are true (or exist).

[0062] The positive electrode slurry is a solid-liquid phase mixture mainly composed of a positive electrode active material, a conductive agent, an adhesive and a solvent. The slurry preparation method in the prior art can only be applied to a slurry containing a low molecular weight adhesive, and cannot meet the preparation demand of the next generation of high molecular weight adhesives. The applicant's research has found that a high molecular weight adhesive is useful for improving the loading amount of the active material in the electrode plate, which is advantageous for improving the energy density and capacity of the battery. However, when forming a slurry containing a high molecular weight adhesive in the prior art slurry preparation method, the viscosity of the slurry increases rapidly, making it difficult to apply and reducing the performance of the electrode plate.

[0063] [Positive electrode slurry preparation method] On this basis, the present application proposes a method for preparing a positive electrode slurry, which includes first stirring, second stirring, third stirring, and fourth stirring, in which, during the first stirring, a positive electrode active material and an adhesive are mixed and stirred to prepare a dry mixture, during the second stirring, an adhesive and a solvent are mixed and stirred to prepare an adhesive liquid, during the third stirring, the dry mixture and the adhesive liquid are mixed and stirred to prepare a primary slurry, and during the fourth stirring, a positive electrode active material, a conductive agent, a solvent, and the primary slurry are mixed and stirred to prepare a positive electrode slurry, and the adhesive used in the first stirring and the adhesive used in the second stirring are the same.

[0064] In this preparation method, the positive electrode active material and a part of the adhesive are firstly stirred to obtain a dry mixture, and the first stirring mechanically crimps the two together to form a tight entanglement; the remaining adhesive and a part of the solvent are then mixed and secondly stirred to obtain an adhesive liquid, and the second stirring contributes to uniformly dispersing the adhesive in the solvent; the dry mixture prepared by the first stirring and the adhesive liquid prepared by the second stirring are then thirdly stirred to obtain a primary slurry, and the third stirring contributes to uniformly dispersing the positive electrode active material in the primary slurry system, and the positive electrode active material is uniformly covered by the adhesive and can be entangled with the adhesive; finally, the remaining positive electrode active material, the conductive agent, the solvent and the primary slurry are fourthly stirred to obtain a positive electrode slurry, and the fourth stirring contributes to thoroughly mixing the conductive agent and the positive electrode active material, uniformly dispersing the positive electrode active material and the conductive agent in the slurry, and uniformly covering the adhesive on the surfaces of the positive electrode active material and the conductive agent.

[0065] In the present application, by dispersing and mixing, the adhesive can be uniformly coated on the positive electrode active material and the conductive agent, and the adhesive and the positive electrode active material can be effectively dispersed in the slurry while avoiding serious aggregation of the adhesive, thereby improving the applicability of the preparation method to adhesives with large molecular weights, improving the versatility of the slurry preparation method, and reducing the preparation cost.

[0066] In some embodiments, the adhesive comprises at least one polyvinylidene fluoride having a weight average molecular weight of 1 million to 8 million. In some embodiments, the weight average molecular weight of the polyvinylidene fluoride is optionally any one of 1 million, 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.

[0067] As used herein, the term "weight average molecular weight" refers to the average molecular weight of a polymer calculated statistically based on mass, ie, the molecular weight obtained by averaging over unit mass.

[0068] In this application, the weight average molecular weight of the polymer can be tested by methods known in the art, such as gel chromatography, for example, gel chromatography on a Waters 2695 Isocratic HPLC model number (differential refractive index detector 2141). A polystyrene solution sample with a mass fraction of 3.0% is used as a reference to select a matching chromatography column (oil-based: Styragel HT5DMF7.8×300 mm+Styragel HT4). A 3.0% adhesive solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day. During the test, first, tetrahydrofuran is drawn into the syringe, washed, and repeated several times. Then, 5 ml of the test solution is drawn, the air in the syringe is removed, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the injection port. When the displayed number does not change, data is acquired and the weight average molecular weight is read.

[0069] By using the preparation method disclosed in this application, the slurry containing the polyvinylidene fluoride adhesive with a mass average molecular weight of up to 8 million still has an appropriate viscosity, and the adhesive strength, shear strength and cohesive strength of the electrode plate all meet the product requirements, and can meet the use demand of next-generation high molecular weight adhesives.

[0070] In some embodiments, the adhesive comprises at least two polyvinylidene fluorides having a difference in mass average molecular weight of 7 million or less. In some embodiments, the difference in mass average molecular weight of the two or more polyvinylidene fluorides is optionally any one of 100,000, 500,000, 1 million, 1 million, 2 million, 3 million, 4 million, 5 million, 6 million, and 7 million.

[0071] The positive electrode slurry prepared by the preparation method disclosed in the present application can effectively exhibit the properties of polyvinylidene fluoride adhesives with different molecular weights, and due to the mutual bonding and steric hindrance between the large and small segments, the slurry has an appropriate viscosity, and the positive electrode plate manufactured with this slurry has high adhesive strength, shear strength and cohesive strength.

[0072] In this specification, adhesion is used to characterize the adhesive strength between a membrane layer made of a positive electrode slurry and a current collector mainly in a positive electrode plate, and can be tested by any known method.

[0073] In this specification, shear strength is used primarily to characterize the shear resistance strength of the membrane layer made of the positive electrode slurry in the positive electrode plate, and can be tested by any known method.

[0074] In this specification, cohesion is mainly used to characterize the internal adhesive strength of the membrane layer made of the positive electrode slurry in the positive electrode plate, which can indicate the adhesive strength between the positive electrode active material and the adhesive, and can be tested by any known method.

[0075] In some embodiments, the mass content of the adhesive used in the first mixing is 30% to 50%, and the mass content of the adhesive used in the second mixing is 50% to 70%, relative to the total mass of the adhesive used in the first mixing and the adhesive used in the second mixing.

[0076] In some embodiments, the mass content of the adhesive used in the first mixing may be selected from 30%, 35%, 40%, 45% or 50%, and the mass content of the adhesive used in the second mixing may be selected from 50%, 55%, 60%, 65% or 70%, relative to the total mass of the adhesive used in the first mixing and the adhesive used in the second mixing.

[0077] If the mass content of the adhesive used in the first stirring is too small or the mass content of the adhesive used in the second stirring is too large, the mass of the adhesive coated on the surface of the positive electrode active material during the first stirring is too low, and the viscosity of the adhesive liquid prepared during the second stirring is too high, the adhesive cannot be effectively coated on the surface of the positive electrode active material, so that the positive electrode active material cannot be effectively dispersed in the adhesive liquid, and the viscosity of the slurry becomes too high, making it difficult for the adhesive to disperse in the positive electrode active material to exert its adhesive performance, and the adhesive strength, shear strength and cohesive strength of the electrode plate are all reduced.

[0078] If the mass content of the adhesive used in the first mixing is too large or the mass content of the adhesive used in the second mixing is too small, and the mass of the adhesive coated on the surface of the positive electrode active material during the first mixing is too high, it is likely to cause entanglement of the adhesive, which is unfavorable to the mechanical crimping due to the mutual bonding between the positive electrode active material and the adhesive surface, and it becomes impossible to improve the adhesive strength, shear strength, and cohesive strength of the electrode plate.

[0079] By controlling the mass content of the adhesive used in the first stirring to 30% to 50% and the mass content of the adhesive used in the second stirring to 50% to 70% relative to the total mass of the adhesive used in the first stirring and the adhesive used in the second stirring, it is possible to ensure that the viscosity of the slurry is within an appropriate range and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0080] As used herein, the term "process window" refers to a process interval within which product quality can be ensured, including but not limited to a temperature interval, a pressure interval, storage time length, etc., and as can be appreciated, the wider the process window, the lower the demand for process precision.

[0081] In some embodiments, the revolution speed of the first agitation is 10 rpm to 20 rpm. In some embodiments, the revolution speed of the first agitation is optionally any one of 10 rpm, 12 rpm, 15 rpm, 18 rpm, and 20 rpm.

[0082] In some embodiments, the stirring time of the first stirring is 10 minutes to 20 minutes. In some embodiments, the stirring time of the first stirring is optionally any one of 10 minutes, 12 minutes, 15 minutes, 18 minutes, and 20 minutes.

[0083] As used herein, the term "orbital speed" refers to the speed at which the agitator rotates around the kettle loaded with material.

[0084] In some embodiments, the stirring device is a planetary mixer. The working principle of the planetary mixer is that after the mixer is started, the planetary carrier rotates, rotating the stirring shaft in the box, revolving around the axis of the material cylinder and rotating at high speed, so that the material undergoes strong shearing and kneading action. As can be understood, the preparation method according to the present application is applicable to any type of planetary mixer.

[0085] If the revolution speed of the first stirring is too slow or the stirring time is too short, the positive electrode active material and the adhesive cannot be effectively mixed, the viscosity of the slurry is too high, and the adhesive performance of the electrode plate is poor. On the other hand, if the revolution speed of the first stirring is too high or the stirring time is too long, the positive electrode active material and the adhesive are easily crushed, the adhesive performance of the adhesive is reduced, and the adhesive strength, shear strength, and cohesive strength of the electrode plate are reduced.

[0086] In summary, by controlling the revolution speed of the first stirring to 10 rpm to 20 rpm or the stirring time of the first stirring to 10 minutes to 20 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0087] In some embodiments, the rotation speed of the first agitation is 0.

[0088] As used herein, the term "rotation speed" refers to the speed at which the agitator rotates about its own axis.

[0089] By controlling the rotation speed of the first stirrer to 0, the shear force of the first stirrer is reduced, the possibility of the positive electrode active material and adhesive being excessively pulverized is reduced, the positive electrode active material and adhesive have a certain particle size and specific surface area, the dispersion effect of the positive electrode active material and adhesive is improved, and the viscosity of the slurry is reduced, which contributes to improving the adhesive strength, shear strength and cohesive strength of the positive electrode plate manufactured with the slurry.

[0090] In some embodiments, the revolution speed of the second stirring is 20 rpm to 30 rpm. In some embodiments, the revolution speed of the second stirring is optionally any one of 10 rpm, 15 rpm, 20 rpm, 25 rpm, and 30 rpm.

[0091] If the revolution speed of the second stirring is too small, the adhesive cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive electrode plate is poor, which cannot meet the demand of the product; on the other hand, if the revolution speed of the second stirring is too large, the adhesive is at risk of being crushed, which will result in a decrease in molecular chains and a decrease in adhesive performance.

[0092] By controlling the revolution speed of the second stirring to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0093] In some embodiments, the rotation speed of the second agitation is 1100 rpm to 1300 rpm. In some embodiments, the rotation speed of the second agitation is optionally any one of 1100 rpm, 1150 rpm, 1200 rpm, 1250 rpm, and 1300 rpm.

[0094] If the rotation speed of the second stirring is too low, the adhesive cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive electrode plate is poor, and the product demand cannot be met. On the other hand, if the rotation speed of the second stirring is too high, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the electrode plate cannot be significantly improved. If the rotation speed is too high, the load on the device will be increased, which will affect the service life of the device and increase the production cost.

[0095] By controlling the rotation speed of the second agitator to 1100 rpm to 1300 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the second agitator being too high, which may affect the service life of the device, and reduce cost losses.

[0096] In some embodiments, the stirring time of the second stirring is 60 minutes to 80 minutes. In some embodiments, the stirring time of the second stirring is optionally any one of 60 minutes, 65 minutes, 70 minutes, 75 minutes, and 80 minutes.

[0097] If the stirring time of the second stirring is too short, the adhesive cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive electrode plate is poor, which cannot meet the demand of the product. On the other hand, if the stirring time of the second stirring is too long, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the electrode plate cannot be significantly improved. The excessively long stirring time will instead result in energy waste and reduce production efficiency.

[0098] By controlling the stirring time of the second stirring to 60 to 80 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a situation where the stirring time of the second stirring is too long, which would result in a reduction in production efficiency, and to save production costs.

[0099] In some embodiments, the revolution speed of the third agitation is 20 rpm to 30 rpm. In some embodiments, the revolution speed of the third agitation is optionally any one of 20 rpm, 22 rpm, 25 rpm, 28 rpm, and 30 rpm.

[0100] If the revolution speed of the third stirring is too low, the dry mixture and the adhesive liquid cannot be mixed uniformly, that is, the positive active material and the adhesive cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive plate is poor and cannot meet the demand of the product. On the other hand, if the revolution speed of the third stirring is too high, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the plate cannot be significantly improved, and the rotation speed that is too high will increase the load of the device, affect the service life of the device and increase the production cost.

[0101] By controlling the revolution speed of the third agitator to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plates have high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device becoming too large due to the revolution speed of the third agitator being too high, which may affect the service life of the device, and reduce cost losses.

[0102] In some embodiments, the rotation speed of the third agitation is 500 rpm to 800 rpm. In some embodiments, the rotation speed of the third agitation is optionally any one of 500 rpm, 600 rpm, 700 rpm, 750 rpm, and 800 rpm.

[0103] If the rotation speed of the third stirring is too low, the dry mixture and the adhesive liquid cannot be mixed uniformly, that is, the positive active material and the adhesive cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive plate is poor, which cannot meet the demand of the product. On the other hand, if the rotation speed of the third stirring is too high, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the plate cannot be significantly improved. In this case, the rotation speed that is too high will increase the load of the device, affect the service life of the device and increase the production cost.

[0104] By controlling the rotation speed of the third agitator to 500 rpm to 800 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the third agitator being too high, which may affect the service life of the device, and reduce cost losses.

[0105] In some embodiments, the stirring time of the third stirring is 40 minutes to 60 minutes. In some embodiments, the stirring time of the third stirring is optionally any one of 40 minutes, 45 minutes, 50 minutes, 55 minutes, and 60 minutes.

[0106] If the stirring time of the third stirring is too short, the dry mixture and the adhesive liquid cannot be mixed uniformly, that is, the positive active material and the adhesive cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive plate is poor and cannot meet the product demand. On the other hand, if the stirring time of the third stirring is too long, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the plate cannot be significantly improved. The too long stirring time will instead result in energy waste and reduce production efficiency.

[0107] By controlling the stirring time of the third stirring to 40 to 60 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a situation where the stirring time of the third stirring is too long, which would result in a reduction in production efficiency, and to save production costs.

[0108] In some embodiments, the revolution speed of the fourth agitation is 20 rpm to 30 rpm. In some embodiments, the revolution speed of the fourth agitation is optionally any one of 20 rpm, 23 rpm, 25 rpm, 27 rpm, and 30 rpm.

[0109] If the revolution speed of the fourth stirring is too low, the positive active material, adhesive and conductive agent cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive plate is poor, which cannot meet the demand of the product. On the other hand, if the revolution speed of the fourth stirring is too high, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the plate cannot be significantly improved. In this case, the rotation speed is too high, which increases the load on the device, affects the service life of the device and increases the production cost.

[0110] By controlling the revolution speed of the fourth agitator to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device becoming too large due to the revolution speed of the fourth agitator being too high, which may affect the service life of the device, and to reduce cost losses.

[0111] In some embodiments, the rotation speed of the fourth agitation is 1100 rpm to 1400 rpm. In some embodiments, the rotation speed of the fourth agitation is optionally any one of 1100 rpm, 1150 rpm, 1200 rpm, 1250 rpm, 1300 rpm, and 1400 rpm.

[0112] If the rotation speed of the fourth stirring is too low, the positive active material, adhesive and conductive agent cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive plate is poor, which cannot meet the demand of the product. On the other hand, if the rotation speed of the fourth stirring is too high, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the plate cannot be significantly improved. In this case, the rotation speed is too high, which will increase the load of the device, affect the service life of the device and increase the production cost.

[0113] By controlling the rotation speed of the fourth stirrer to 1100 rpm to 1400 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the fourth stirrer being too high, which may affect the service life of the device, and reduce cost losses.

[0114] In some embodiments, the stirring time of the fourth stirring is 100 minutes to 120 minutes. In some embodiments, the stirring time of the fourth stirring is any one of 100 minutes, 105 minutes, 110 minutes, 115 minutes, and 120 minutes.

[0115] If the stirring time of the fourth stirring is too short, the positive active material, adhesive and conductive agent cannot be effectively dispersed in the solvent, the viscosity of the slurry is too high, and the adhesive performance of the positive electrode plate is poor, which cannot meet the product demand. On the other hand, if the stirring time of the fourth stirring is too long, the viscosity of the slurry and the adhesive strength, shear strength and cohesive strength of the electrode plate cannot be significantly improved. The excessively long stirring time will instead result in energy waste and reduce production efficiency.

[0116] By controlling the stirring time of the fourth stirring to 100 to 120 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a situation where the stirring time of the fourth stirring is too long, which would result in a reduction in production efficiency, and to save production costs.

[0117] In some embodiments, when the solids content of the cathode slurry is 68%, the viscosity of the cathode slurry is 8000 mPa·s to 41000 mPa·s. In some embodiments, the viscosity of the cathode slurry is optionally 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, 11000 mPa·s, 12000 mPa·s, 13000 mPa·s, 14000 mPa·s, 15000 mPa·s, 16000 mPa·s, 17000 mPa·s, 18000 mPa·s, 19000 mPa·s, 20000 mPa·s, 210000 mPa·s, 220000 mPa·s, 230000 mPa·s, 240000 mPa·s, 250000 mPa·s, 260000 mPa·s, 270000 mPa·s, 280000 mPa·s, 290000 mPa·s, 300000 mPa·s, 310000 mPa·s, 320000 mPa·s, 330000 mPa·s, 340000 mPa·s, 350000 mPa·s, 360000 mPa·s, 370000 mPa·s, 380000 mPa·s, 390000 mPa·s, 400000 mPa·s, 410000 mPa·s, 420000 mPa·s, 430000 mPa·s, 440000 mPa·s, 450000 mPa·s, 460000 mPa·s, The value is one of the following: 22000mPa·s, 24000mPa·s, 25000mPa·s, 26000mPa·s, 28000mPa·s, 30000mPa·s, 32000mPa·s, 34000mPa·s, 35000mPa·s, 36000mPa·s, 38000mPa·s, 40000mPa·s, 41000mPa·s.

[0118] In this application, the viscosity of the positive electrode slurry can be tested by methods known in the art, such as a rotational viscometer, for example, by selecting an appropriate rotor, fixing the viscometer rotor, placing the positive electrode slurry under the viscometer rotor so that the slurry just immerses the graduation lines of the rotor, the model number of the instrument is Shanghai Fangrui NDJ-5S, using rotor model 63 to measure the viscosity of the slurry of 2000-10000 mPa s, and using rotor model 64 to measure the viscosity of the slurry of 10000-50000 mPa s, the rotation speed is 12 rpm, the test temperature is 25° C., the test time is 5 minutes, and the data is read when the displayed number does not change.

[0119] The viscosity of the positive electrode slurry with a solid content of 68% is 8000 mPa·s to 41000 mPa·s, and this positive electrode slurry has good coating properties and processability, widening the coating process window.

[0120] In some embodiments, the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring are the same, and the mass content of the positive electrode active material used in the first stirring is 50% to 70%, and the mass content of the positive electrode active material used in the fourth stirring is 30% to 50%, relative to the total mass of the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring.

[0121] In some embodiments, the mass content of the positive electrode active material used in the first stirring relative to the total mass of the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring may be selected from 50%, 53%, 55%, 58%, 60%, 62%, 67% or 70%, and the mass content of the positive electrode active material used in the fourth stirring may be selected from 30%, 33%, 38%, 40%, 42%, 45%, 47% or 50%.

[0122] The mass content of the positive active material used in the first stirring is too small, i.e., the mass content of the positive active material used in the fourth stirring is too large, which is unfavorable to control the dispersion of the positive active material into the slurry during the fourth stirring, so the viscosity of the slurry is too high and the adhesive performance of the positive electrode plate is poor; the mass content of the positive active material used in the first stirring is too large, i.e., the mass content of the positive active material used in the fourth stirring is too small, which is unfavorable to control the mechanical crimping between the positive active material and the adhesive during the first stirring, so the dispersibility of the dry mixture prepared in the first stirring into the subsequent slurry is poor, and the viscosity of the slurry is too high and the adhesive performance of the positive electrode plate is poor.

[0123] By controlling the mass content of the positive electrode active material used in the first stirring to 50% to 70% and the mass content of the positive electrode active material used in the fourth stirring to 30% to 50% relative to the total mass of the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring, the viscosity of the slurry can be reduced, and the adhesive strength, shear strength and cohesive strength of the electrode plates can be improved, the process window for slurry application can be widened, and the performance of the electrode plates can be improved.

[0124] In some embodiments, the solvent used in the second stirring and the solvent used in the fourth stirring are the same, and the mass content of the solvent used in the second stirring is 35% to 40%, and the mass content of the solvent used in the fourth stirring is 5% to 10%, relative to the total mass of the conductive agent, the positive electrode active material used in the first stirring, the positive electrode active material used in the fourth stirring, the adhesive used in the first stirring, and the adhesive used in the second stirring.

[0125] In some embodiments, the mass content of the solvent used in the second stirring may be selected from 35%, 36%, 37%, 38%, 39% or 40%, and the mass content of the solvent used in the fourth stirring may be selected from 5%, 6%, 7%, 8%, 9% or 10%, relative to the total mass of the conductive agent, the positive electrode active material used in the first stirring, the positive electrode active material used in the fourth stirring, the adhesive used in the first stirring and the adhesive used in the second stirring.

[0126] In some embodiments, the mass ratio of the total mass of the positive electrode active material, the total mass of the adhesive, and the conductive agent in the positive electrode slurry is (86 to 98):(1 to 8):(1 to 6). In some embodiments, the mass ratio of the total mass of the positive electrode active material, the total mass of the adhesive, and the conductive agent is optionally any one of 96:2:2, 96:3:1, 97:1:2, and 98:1:1.

[0127] A positive electrode slurry within the above range has good processability and provides the formed positive electrode plate with excellent electrochemical properties.

[0128] In some embodiments, the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide.

[0129] The above positive electrode active material provides a battery with a high energy density, and is advantageous in improving the cycle performance of the battery.

[0130] In some embodiments, the conductive agent is one or more of conductive carbon black, graphite, and carbon nanotubes.

[0131] The conductive agent is advantageous in improving the electrical conductivity of the electrode plate.

[0132] [Positive electrode plate] The present application provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer is manufactured with a positive electrode slurry prepared by the preparation method in any of the embodiments of the present application.

[0133] For example, a positive electrode current collector has two surfaces that are opposite each other in the thickness direction of the positive electrode current collector, and a positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0134] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, an aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries known in the art. As an example, the positive electrode active material may include at least one of 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 conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Here, an example of a lithium transition metal oxide is lithium cobalt oxide (e.g., LiCoO 2 ), lithium nickel oxide (e.g. LiNiO 2 ), lithium manganese oxide (e.g. LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g. LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM 333 (may be abbreviated as LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 523 (may be abbreviated as LiNi 0.5 Co 0.25 Mn0.25 O 2 (NCM 211 (may be abbreviated as LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622 (may be abbreviated as LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811 Lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and modified compounds thereof. An example of a lithium-containing phosphate having an olivine structure is lithium iron phosphate (e.g., LiFePO 4 (which may be abbreviated as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO 4 ), a composite of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite of lithium iron manganese phosphate and carbon.

[0136] In some embodiments, the adhesive strength per unit length between the positive electrode film layer and the positive electrode current collector is 20 N / m to 30 N / m. In some embodiments, the adhesive strength per unit length between the positive electrode film layer and the positive electrode current collector is optionally any one of 20 N / m, 21 N / m, 22 N / m, 23 N / m, 24 N / m, 25 N / m, 26 N / m, 26.5 N / m, 27 N / m, 27.5 N / m, 28 N / m, 29 N / m, and 30 N / m.

[0137] In this application, the adhesive strength per unit length between the positive electrode film layer and the positive electrode current collector can be tested by a method known in the art, for example, see the Chinese standard GB-T2790-1995 "Adhesive 180° Peel Strength Test Method". Cut a sample with a width of 30 mm and a length of 100-160 mm with a blade, and attach a special double-sided tape with a width of 20 mm and a length of 90-150 mm to a steel plate. The positive electrode film layer surface of the electrode plate sample cut before this is attached to the double-sided tape, and then rolled three times in the same direction with a 2 kg rolling roller. A paper tape with a width equal to the electrode plate and a length of 250 mm is fixed to the electrode plate current collector, and then fixed with crepe tape. Turn on the power (sensitivity is 1N) of Sanshisha's tension machine, the lamp is lit, adjust the stopper block to the appropriate position, and fix the end of the steel plate where the electrode plate is not attached with the lower jig. The paper tape is folded upwards and fixed with the upper jig, and the position of the upper jig is adjusted with the "up" and "down" buttons on the manual controller with the tensioner. Then the test is performed and the numerical value is read, and the tension speed is 50mm / min. The force when the plate forces are balanced is divided by the tape width to obtain the plate adhesive strength per unit length, which characterizes the adhesive strength between the positive electrode film layer and the current collector.

[0138] In some embodiments, the shear strength of the positive electrode membrane layer is 0.64 mPa to 0.91 mPa. In some embodiments, the shear strength of the positive electrode membrane layer is optionally any one of 0.64 mPa, 0.68 mPa, 0.72 mPa, 0.74 mPa, 0.78 mPa, 0.80 mPa, 0.81 mPa, 0.83 mPa, 0.86 mPa, 0.88 mPa, 0.90 mPa, and 0.91 mPa.

[0139] In this application, the shear strength of the positive electrode membrane layer can be tested by a method known in the art, such as a tensile machine, by cutting a double-sided tape with a length of about 60 mm, attaching the double-sided tape along the longitudinal direction of the electrode plate, cutting the electrode plate along the edge of the double-sided tape with a blade, selecting a steel plate with a flat appearance, polishing the surface of the steel plate with sandpaper, applying alcohol to cotton gauze, wiping the surface of the steel plate, drying it, attaching the double-sided tape to the steel plate, and the distance between the bottom edge of the tape and the bottom edge of the steel plate is >1 cm, and placing the steel plate in an oven at 60-80°C. Leave it for 5 minutes, take out the steel plate, lightly scrape off the upper release paper of the tape with a blade, attach the previously cut electrode plate to the double-sided tape of the steel plate with the test surface facing downwards, roll it back and forth three times with a 2 kg rolling roller, turn on the Sanshisha tensile machine, the light turns on, adjust the stopper block to the appropriate position, fix the end of the steel plate where the electrode plate is not attached with the lower jig, fix the end of the electrode plate where the steel plate is not attached with the upper jig, and then perform the test and read the values, the tensile speed is 10 mm / min.

[0140] In some embodiments, the cohesive strength of the positive electrode membrane layer is 70 N / m to 90 N / m. In some embodiments, the cohesive strength of the positive electrode membrane layer is optionally any one of 72 N / m, 74 N / m, 76 N / m, 78 N / m, 80 N / m, 82 N / m, 84 N / m, 86 N / m, 88 N / m, and 90 N / m.

[0141] In the present application, the cohesive strength of the positive electrode film layer can be tested by a method known in the art, for example, a tensile machine, by cutting a plate sample with a width of 30 mm and a length of 90 to 150 mm with a blade, cutting a dedicated double-sided tape with a width of 20 mm and a length of 90 to 150 mm, attaching the cut dedicated double-sided tape to a steel plate, attaching the cut plate sample to the cut double-sided tape with the test surface facing upward, and attaching a low-viscosity grease with a width of 20 mm and a length 80 to 200 mm longer than the length of the sample. The green tape is glued flat on the test surface, rolled three times in the same direction with a rolling roller, turned on the Sanshisha tensile machine, the light turned on, adjusted the stopper block to the appropriate position, fixed the end of the steel plate that does not have a pole attached with the lower jig, folded the green tape with the hard paper attached upwards and fixed with the upper jig, adjusted the position of the upper jig with the "up" and "down" buttons on the manual controller with the tensile machine, and then performed the test and read the values, the tensile speed is 10mm / min.

[0142] In some embodiments, a positive electrode plate can be manufactured in the following manner: A positive electrode slurry is prepared by the positive electrode slurry preparation method according to any embodiment of the present application using the above-mentioned components for manufacturing a positive electrode plate, such as a positive electrode active material, a conductive agent, an adhesive, and a solvent (e.g., N-methylpyrrolidone), and the prepared positive electrode slurry is applied to a positive electrode current collector, and a positive electrode plate is obtained after processes such as drying and cold pressing.

[0143] [Negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0144] For example, the negative electrode current collector has two surfaces that are opposite each other in the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0145] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, a copper foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0146] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicone-based material, tin-based material, lithium titanate, and the like. The silicone-based material may be selected from at least one of silicone alone, silicone oxide, silicone carbon composite, silicone nitrogen composite, and silicone alloy. The tin-based material may be selected from at least one of tin alone, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may be used. These negative electrode active materials may be used alone or in combination of two or more.

[0147] In some embodiments, the negative electrode membrane layer further optionally includes an adhesive, which 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).

[0148] In some embodiments, the negative electrode membrane layer further optionally includes 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.

[0149] In some embodiments, the negative electrode membrane layer further optionally includes other auxiliary agents, such as a thickening agent (eg, sodium carboxymethylcellulose (CMC-Na)).

[0150] In some embodiments, the negative electrode plate can be manufactured in the following manner: Components for manufacturing the negative electrode plate, such as a negative electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then applied onto a negative electrode current collector, and the negative electrode plate is obtained after processes such as drying and cold pressing.

[0151] [Electrolytes] The electrolyte serves to conduct ions between the positive and negative electrodes. The present application is not specifically limited to the type of electrolyte, which can be selected according to need. For example, the electrolyte may be liquid, gel, or all solid.

[0152] In some embodiments, the electrolyte is an electrolytic solution, the electrolytic solution including an electrolyte salt and a solvent.

[0153] 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(trifluoromethanesulfonate), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0154] In some embodiments, the solvent may 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, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0155] In some embodiments, the electrolyte solution further optionally includes additives. For example, the additives may include anode film-forming additives, cathode film-forming additives, and may further include additives that can improve some performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[0156] [Separator] In some embodiments, the secondary battery further includes a separator. The present application is not particularly limited to the type of separator, and any known porous structure separator having good chemical stability and mechanical stability may be selected.

[0157] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single layer film or a multi-layer composite film, and there is no particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

[0158] In some embodiments, the positive and negative plates and the separator can be fabricated into an electrode assembly by a winding or lamination process.

[0159] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0160] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0161] The present application is not particularly limited to the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, FIG. 1 shows a secondary battery 5 with a rectangular structure as an example.

[0162] In some embodiments, referring to FIG. 2, the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening to seal the receiving cavity. The positive electrode plate, the negative electrode plate and the separator can form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is infiltrated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can specifically select according to actual needs.

[0163] In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0164] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fasteners.

[0165] Optionally, the battery module 4 may further include a housing having an accommodating space, and the multiple secondary batteries 5 are accommodated in the accommodating space.

[0166] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0167] 4 and 5 show an example of a battery pack 1. Referring to Fig. 4 and Fig. 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box may include an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by the lower housing 3 to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0168] The present application further provides a power consuming device, the power consuming device including at least one of the secondary battery, the battery module, or the battery pack according to the present application. The secondary battery, the battery module, or the battery pack may be used as a power source for the power consuming device, or may be used as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0169] The power consumption device can be a secondary battery, a battery module, or a battery pack depending on the usage demand.

[0170] 6 shows an example of a power consumption device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack or a battery module can be used to meet the demand for high power and high energy density of the secondary battery of the power consumption device.

[0171] Other exemplary devices may be mobile phones, tablet computers, notebook computers, etc. These devices are generally required to be lightweight and can use secondary batteries as a power source.

[0172] Working Example The following describes the examples of the present application. The examples in the following description are illustrative and are only for interpreting the present application, and should not be understood as limitations on the present application. If no specific techniques or conditions are specified in the examples, they will be performed according to the techniques or conditions described in the literature in the field, or according to the product specifications. If the manufacturer is not specified for the reagents or instruments used, they are all ordinary products that are commercially available.

[0173] 1. Preparation method Example 1 Preparation of cathode slurry Weighing of raw materials: 1200 kg of lithium iron phosphate as a positive electrode active material, 25 kg of polyvinylidene fluoride as an adhesive, and 25 kg of conductive carbon black as a conductive agent were weighed in advance. Here, the mass average molecular weight of polyvinylidene fluoride was 1.8 million, First mixing: 720 kg of lithium iron phosphate and 10 kg of polyvinylidene fluoride were mixed in a double planetary mixer, and the first mixing was performed for 15 minutes with a revolution speed of 15 revolutions per minute and a rotation speed of 0 to obtain a dry mixture. Second mixing: 15 kg of polyvinylidene fluoride and 437.5 kg of N-methylpyrrolidone (NMP) solvent were mixed in a double planetary mixer, and second mixing was performed for 70 minutes at a revolution speed of 25 rpm and a rotation speed of 1200 rpm to obtain an adhesive liquid. Third mixing: The dry mixture prepared in the first mixing is added to the adhesive liquid prepared in the second mixing, and the third mixing is carried out for 50 minutes at a revolution speed of 25 rpm and a rotation speed of 600 rpm to obtain a primary slurry; Fourth stirring: 480 kg of lithium iron phosphate, 25 kg of conductive carbon black, and 125 kg of N-methylpyrrolidone (NMP) solvent were added to the primary slurry prepared in the third stirring, and the fourth stirring was performed for 110 minutes at a revolution speed of 25 rpm and a rotation speed of 1300 rpm, to obtain a positive electrode slurry with a solid content of 68%.

[0174] Examples 2 to 7 Except for adjusting the mass average molecular weight of the polyvinylidene fluoride adhesive, the procedure is basically the same as in Example 1. For specific parameters, please refer to Table 1.

[0175] Examples 8 to 10 Other than adding various adhesives with different weight average molecular weights, it is basically the same as Example 1, and the specific parameters can be seen in Table 1. In Example 8, the mass ratio of polyvinylidene fluoride with a weight average molecular weight of 1 million to polyvinylidene fluoride with a weight average molecular weight of 8 million was 1:1, in Example 9, the mass ratio of polyvinylidene fluoride with a weight average molecular weight of 1 million to polyvinylidene fluoride with a weight average molecular weight of 4 million to polyvinylidene fluoride with a weight average molecular weight of 8 million was 1:1:1. In Example 10, the mass ratio of polyvinylidene fluoride with a weight average molecular weight of 1.8 million to polyvinylidene fluoride with a weight average molecular weight of 6 million was 1:1.

[0176] Examples 11 to 14 The first mixing step is basically the same as that in Example 2, except for adjusting the mass content of polyvinylidene fluoride adhesive during stirring. For specific parameters, please refer to Table 1.

[0177] Examples 15 to 60 Except for adjusting the stirring parameters, the process is basically the same as in Example 2. For the specific parameters, please refer to Table 1.

[0178] Examples 61 to 64 Except for adjusting the mass content of lithium iron phosphate in the first stirring, the process is basically the same as in Example 2. For specific parameters, please refer to Table 1.

[0179] Comparative Example 1 Weighing of raw materials: 1200 kg of lithium iron phosphate as a positive electrode active material, 25 kg of polyvinylidene fluoride as an adhesive, and 25 kg of conductive carbon black as a conductive agent were weighed in advance. Here, the mass average molecular weight of polyvinylidene fluoride was 1.8 million, First mixing: 1200 kg of lithium iron phosphate and 25 kg of conductive carbon black are mixed and thoroughly mixed for 15 minutes at a revolution speed of 15 rpm and a rotation speed of 0 to obtain a dry mixture. Second mixing: 25 kg of polyvinylidene fluoride was added to 437.5 kg of NMP solvent, and the mixture was thoroughly mixed for 70 minutes at a revolution speed of 25 rpm and a rotation speed of 1200 rpm to obtain an adhesive liquid. Third mixing: The dry mixture is added to the adhesive liquid and thoroughly mixed for 50 minutes at a revolution speed of 25 rpm and a rotation speed of 600 rpm to obtain a primary slurry. Fourth stirring: 125 kg of NMP solvent was added to the primary slurry, and the mixture was stirred for 110 minutes at a revolution speed of 25 rpm and a rotation speed of 1300 rpm to obtain a positive electrode slurry with a solid content of 68%.

[0180] Comparative Examples 2 to 5 Except for the mass average molecular weight of polyvinylidene fluoride being 2 million, 3 million, 4 million, and 8 million, respectively, the results are basically the same as those of Comparative Example 1. For specific parameters, please refer to Table 1.

[0181] II. Test Method 1. Viscosity test of positive electrode slurry The viscosity of the undercoat slurry was measured with a rotational viscometer. Select an appropriate rotor, fix the viscometer rotor, and place the undercoat slurry under the viscometer rotor so that the slurry just immerses the graduation lines of the rotor. The model number of the instrument is Shanghai Fangrui NDJ-5S, rotor number 63 is used to measure the viscosity of the slurry between 2000 and 10000 mPa·s, and rotor number 64 is used to measure the viscosity of the slurry between 10000 and 50000 mPa·s. The rotation speed is 12 rpm, the test temperature is 25°C, and the test time is 5 minutes. The data is read when the display number does not change.

[0182] 2. Adhesion test of electrodes Referring to the Chinese standard GB-T2790-1995 "Test method for adhesive 180° peel strength", the adhesive strength test process of the examples and comparative examples of this application was as follows. A blade was used to cut a sample with a width of 30 mm and a length of 100-160 mm, and a dedicated double-sided tape with a width of 20 mm and a length of 90-150 mm was attached to the steel plate. The positive electrode film layer surface of the electrode plate sample cut before this was attached to the double-sided tape, and then rolled three times in the same direction with a 2 kg rolling roller. A paper tape with a width equal to the electrode plate and a length of 250 mm was fixed to the electrode plate current collector and fixed with crepe tape. The power supply (sensitivity is 1N) of Sanshisha's tension machine was turned on, the lamp was turned on, the stopper block was adjusted to the appropriate position, and the end of the steel plate where the electrode plate was not attached was fixed with the lower jig. The paper tape was folded upwards and fixed with the upper jig, and the position of the upper jig was adjusted with the "up" and "down" buttons on the manual controller with the tensioner. Then the test was performed and the numerical value was read, and the tension speed was 50 mm / min. The force when the plate forces were balanced was divided by the tape width to obtain the adhesive strength of the plate per unit length, which characterized the adhesive strength between the positive electrode film layer and the current collector.

[0183] 3. Shear strength test of electrode plates Cut a piece of double-sided tape with a length of about 60 mm and paste it along the longitudinal direction of the electrode plate. Cut the electrode plate along the edge of the double-sided tape with a blade. Select a steel plate with a flat appearance. Polish the surface of the steel plate with sandpaper. Apply alcohol to cotton gauze and wipe the surface of the steel plate. Dry it. Paste the double-sided tape on the steel plate. The distance between the bottom edge of the tape and the bottom edge of the steel plate is >1 cm. Leave the steel plate in an oven at 60-80 ° C for 5 min. Take out the steel plate and lightly scrape off the upper layer release paper of the tape with a blade. Paste the previously cut electrode plate on the double-sided tape of the steel plate so that the test surface faces downward. Roll it back and forth three times with a 2 kg rolling roller. Turn on the Sanshisha tension machine, the lamp is lit, adjust the stopper block to the appropriate position, fix the end of the steel plate where the electrode plate is not attached with the lower jig, clamp the end of the electrode plate where the steel plate is not attached with the upper jig, and then perform the test to read the numerical value. The tensile speed is 10 mm / min.

[0184] 4. Cohesion test of electrode plates Cut out a plate sample with a width of 30 mm and a length of 90-150 mm with a blade, cut a special double-sided tape with a width of 20 mm and a length of 90-150 mm, attach the cut special double-sided tape to a steel plate, attach the cut plate sample to the cut double-sided tape so that the test surface faces upwards, and flatly attach a low-viscosity green tape with a width of 20 mm and a length 80-200 mm longer than the length of the sample to the test surface, roll it three times in the same direction with a rolling roller, turn on the Sanshisha tensioning machine, the light is on, adjust the stopper block to the appropriate position, fix the end of the steel plate where the plate is not attached with the lower jig, fold the green tape with the hard paper attached up and fix it with the upper jig, adjust the position of the upper jig with the "up" and "down" buttons on the manual controller with the tensioning machine, and then perform the test and read the numerical value, and the tensioning speed is 10 mm / min.

[0185] 3. Analysis of the Test Results of Each Example and Comparative Example According to the above-mentioned method, the positive electrode slurries of the examples and comparative examples were prepared, and the parameters were measured. The results are shown in Table 1 below.

[0186] Table 1 Preparation parameters and test results for the examples and comparative examples TIFF2025515880000002.tif206166 TIFF2025515880000003.tif239166 TIFF2025515880000004.tif239166 TIFF2025515880000005.tif178166

[0187] As can be seen from the results in Table 1, the positive electrode slurries in Examples 1 to 64 were all prepared by the slurry preparation method disclosed in the present application, including the first stirring, second stirring, third stirring, and fourth stirring. During the first stirring, the lithium iron phosphate positive electrode active material and the polyvinylidene fluoride adhesive are mixed and stirred to prepare a dry mixture. During the second stirring, the polyvinylidene fluoride and the N-methylpyrrolidone (NMP) solvent are mixed and stirred to prepare an adhesive liquid. During the third stirring, the dry mixture prepared in the first stirring and the adhesive liquid prepared in the second stirring are mixed and stirred to prepare a primary slurry. During the fourth stirring, the lithium iron phosphate, the conductive carbon black as a conductive agent, the NMP solvent, and the primary slurry prepared in the third stirring are mixed and stirred to prepare a positive electrode slurry.

[0188] As can be seen from a comparison between Examples 1 to 10 and Comparative Examples 1 to 4, the preparation method disclosed in the present application has wide versatility and is applicable to slurries of one or more polyvinylidene fluoride adhesives having a mass average molecular weight of 1 million to 8 million, and this preparation method has versatility for polyvinylidene fluoride adhesives having low mass average molecular weights and polyvinylidene fluoride adhesives having high mass average molecular weights, contributing to reducing preparation costs and improving production efficiency.

[0189] As can be seen from Comparative Examples 3 to 5, when using a polyvinylidene fluoride adhesive with a mass average molecular weight of 3 million, the preparation process in the prior art is difficult to reduce the viscosity of the slurry, making it impossible to apply the slurry. The preparation method of the present application makes it possible to produce a slurry containing a polyvinylidene fluoride adhesive with a mass average molecular weight of 8 million that still has an appropriate viscosity, and the adhesive strength, shear strength and cohesive strength of the electrode plate all meet the product demands, and can meet the demands for the use of next-generation high molecular weight adhesives.

[0190] As can be seen from Examples 8 to 10, when the slurry synthesized by this preparation method contains an adhesive with a mass average molecular weight difference of 7 million or less, the slurry can still maintain a low viscosity, and the electrode plates can maintain high adhesive strength, shear strength and cohesive strength.

[0191] As can be seen from a comparison between Examples 8 to 10 and Examples 5 to 6, when the slurry synthesized by this preparation method contains adhesives with a difference in mass average molecular weight of 7 million or less, the slurry containing adhesives with different mass average molecular weights can have a further reduced viscosity and further improved adhesive strength, shear strength, or cohesive strength compared to a slurry containing only an adhesive with a single mass average molecular weight.

[0192] As can be seen from Example 2 and Examples 11 to 14, by controlling the ratio of polyvinylidene fluoride adhesive added during the first stirring to 30% to 50% of the total mass of polyvinylidene fluoride adhesive, this preparation method ensures that the slurry has a suitable viscosity, and also improves the adhesive strength, shear strength and cohesive strength of the electrode plates, widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0193] As can be seen from Examples 2 and 15 to 18, by controlling the revolution speed of the first stirring to 10 rpm to 20 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0194] As can be seen from Example 2 and Examples 19 to 22, by controlling the stirring time of the first stirring to 10 to 20 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0195] As can be seen from Example 2 and Examples 23 to 26, by controlling the revolution speed of the second stirring to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength, thereby widening the electrode plate manufacturing process window and improving the adhesive performance of the electrode plates.

[0196] As can be seen from Example 2 and Examples 27 to 30, by controlling the rotation speed of the second agitator to 1100 rpm to 1300 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the second agitator being too high, which may affect the service life of the device, and reduce cost loss.

[0197] As can be seen from Example 2 and Examples 31 to 34, by controlling the stirring time of the second stirring to 60 to 80 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a situation where the stirring time of the second stirring is too long, which would result in a reduction in production efficiency, and to save production costs.

[0198] As can be seen from Example 2 and Examples 35 to 38, by controlling the revolution speed of the third agitation to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. It is also possible to avoid the load on the device being too large due to the revolution speed of the third agitation being too high, which may affect the service life of the device, and reduce cost losses.

[0199] As can be seen from Example 2 and Examples 39 to 43, by controlling the rotation speed of the third stirrer to 500 rpm to 800 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the third stirrer being too high, which may affect the service life of the device, and reduce cost loss.

[0200] As can be seen from Example 2 and Examples 44 to 47, by controlling the stirring time of the third stirring to 40 to 60 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength. It is also possible to avoid the stirring time of the third stirring being too long, which would result in a reduction in production efficiency, and to save production costs.

[0201] As can be seen from Example 2 and Examples 48 to 51, by controlling the revolution speed of the fourth agitator to 20 rpm to 30 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the revolution speed of the fourth agitator being too high, which may affect the service life of the device, and reduce cost losses.

[0202] As can be seen from Example 2 and Examples 52 to 56, by controlling the rotation speed of the fourth stirrer to 1100 rpm to 1400 rpm, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the plate has high adhesive strength, shear strength and cohesive strength. At the same time, it is possible to avoid the load on the device being too large due to the rotation speed of the fourth stirrer being too high, which may affect the service life of the device, and reduce cost loss.

[0203] As can be seen from Examples 2 and 57 to 60, by controlling the stirring time of the fourth stirring to 100 to 120 minutes, it is possible to ensure that the viscosity of the slurry is within an appropriate range, and also to ensure that the electrode plates have high adhesive strength, shear strength and cohesive strength. It is also possible to avoid a situation where the stirring time of the fourth stirring is too long, which would result in a reduction in production efficiency, and to save production costs.

[0204] As can be seen from the examples, the positive electrode slurry having a solid content of 68% disclosed in the present application has a viscosity of 8000 mPa·s to 41000 mPa·s, and this positive electrode slurry has good coatability and processability.

[0205] As can be seen from Example 2 and Examples 61 to 64, by controlling the mass content of lithium iron phosphate used in the first stirring to 50% to 70%, the viscosity of the slurry can be reduced, the adhesive strength, shear strength and cohesive strength of the electrode plate can be improved, the process window of the slurry application can be widened, and the performance of the electrode plate can be improved.

[0206] It should be noted that the present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is merely an example, and any embodiment having substantially the same configuration as the technical idea and the same effect within the scope of the technical proposal of the present application is included in the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiment and other forms configured by combining some of the components in the embodiment are also included in the scope of the present application, within the scope of the purpose of the present application. [Explanation of symbols]

[0207] 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate.

Claims

1. 1. A method for preparing a positive electrode slurry, comprising first stirring, second stirring, third stirring, and fourth stirring, During the first stirring, the positive electrode active material and the adhesive are mixed and stirred to prepare a dry mixture; During the second stirring, the adhesive and the solvent are mixed and stirred to prepare an adhesive liquid; During the third stirring, the dry mixture and the adhesive liquid are mixed and stirred to prepare a primary slurry; During the fourth stirring, the positive electrode active material, the conductive agent, the solvent, and the primary slurry are mixed and stirred to prepare a positive electrode slurry; the adhesive used in the first mixing and the adhesive used in the second mixing are the same.

2. The preparation method according to claim 1, characterized in that the adhesive comprises at least one polyvinylidene fluoride having a weight average molecular weight of 1 million to 8 million.

3. The preparation method according to claim 1 or 2, characterized in that the adhesive contains at least two polyvinylidene fluorides having a difference in mass average molecular weight of 7 million or less.

4. The mass content of the adhesive used in the first stirring is 30% to 50%, and the mass content of the adhesive used in the second stirring is 50% to 70%, relative to the total mass of the adhesive used in the first stirring and the adhesive used in the second stirring. The preparation method according to any one of claims 1 to 3, characterized in that

5. The preparation method according to any one of claims 1 to 4, characterized in that the revolution speed of the first stirring is 10 rpm to 20 rpm.

6. The preparation method according to any one of claims 1 to 5, characterized in that the rotation speed of the first stirring is 0.

7. The method according to any one of claims 1 to 6, characterized in that the stirring time of the first stirring is 10 minutes to 20 minutes.

8. The preparation method according to any one of claims 1 to 7, characterized in that the revolution speed of the second stirring is 20 rpm to 30 rpm.

9. The method according to any one of claims 1 to 8, characterized in that the rotation speed of the second stirring is 1100 rpm to 1300 rpm.

10. The preparation method according to any one of claims 1 to 9, characterized in that the stirring time of the second stirring is 60 minutes to 80 minutes.

11. The preparation method according to any one of claims 1 to 10, characterized in that the revolution speed of the third stirring is 20 rpm to 30 rpm.

12. The preparation method according to any one of claims 1 to 11, characterized in that the rotation speed of the third stirring is 500 rpm to 800 rpm.

13. The preparation method according to any one of claims 1 to 12, characterized in that the stirring time of the third stirring is 40 minutes to 60 minutes.

14. The preparation method according to any one of claims 1 to 13, characterized in that the revolution speed of the fourth stirring is 20 rpm to 30 rpm.

15. The method according to any one of claims 1 to 14, characterized in that the rotation speed of the fourth stirring is 1100 rpm to 1400 rpm.

16. The method according to any one of claims 1 to 15, wherein the stirring time of the fourth stirring is 100 minutes to 120 minutes.

17. 17. The method according to claim 1, wherein the viscosity of the cathode slurry is 8000 mPa·s to 41000 mPa·s when the solid content of the cathode slurry is 68%.

18. The positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring are the same, and the mass content of the positive electrode active material used in the first stirring is 50% to 70%, and the mass content of the positive electrode active material used in the fourth stirring is 30% to 50%, relative to the total mass of the positive electrode active material used in the first stirring and the positive electrode active material used in the fourth stirring. The preparation method according to any one of claims 1 to 17,

19. The solvent used in the second stirring and the solvent used in the fourth stirring are the same, and the conductive agent, the positive electrode active material used in the first stirring, the positive electrode active material used in the fourth stirring, the adhesive used in the first stirring, and the adhesive used in the second stirring are the same. The mass content of the solvent used in the second stirring is 35% to 40%, and the mass content of the solvent used in the fourth stirring is 5% to 10%, relative to the total mass of the conductive agent, the positive electrode active material used in the first stirring, the positive electrode active material used in the fourth stirring, the adhesive used in the first stirring, and the adhesive used in the second stirring. The preparation method according to any one of claims 1 to 18, characterized in that

20. 20. The method according to claim 1, wherein a mass ratio of the total mass of the positive electrode active material, the total mass of the adhesive, and the conductive agent in the positive electrode slurry is (86 to 98):(1 to 8):(1 to 6).

21. 21. The method of any one of claims 1 to 20, wherein the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium nickel cobalt manganese oxide.

22. 22. The method according to any one of claims 1 to 21, wherein the conductive agent is one or more of conductive carbon black, graphite, and carbon nanotubes.

23. A positive electrode plate, comprising: a positive electrode current collector; and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer being manufactured from a positive electrode slurry prepared by the preparation method according to any one of claims 1 to 22.

24. The positive electrode plate according to claim 23, wherein the adhesive strength per unit length between the positive electrode film layer and the positive electrode current collector is 20 N / m to 30 N / m.

25. The positive electrode plate according to claim 23 or 24, characterized in that the positive electrode film layer has a shear strength of 0.64 mPa to 0.91 mPa.

26. The positive electrode plate according to any one of claims 23 to 25, characterized in that the cohesive strength of the positive electrode film layer is 70 N / m to 90 N / m.

27. 27. A secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a separator, a negative electrode plate, and the positive electrode plate according to any one of claims 23 to 26.

28. 28. The secondary battery of claim 27, wherein the secondary battery is any one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

29. A battery module comprising the secondary battery according to claim 27 or 28.

30. A battery pack comprising at least one of the secondary battery according to claim 27 or 28 and the battery module according to claim 29.

31. 31. A power consuming device comprising at least one selected from the group consisting of the secondary battery according to claim 27 or 28, the battery module according to claim 29, and the battery pack according to claim 30.

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