Positive electrode paste manufacturing method, secondary battery, battery pack, and power consumption device

Abstract

This application provides a method for manufacturing a positive electrode paste, a secondary battery, a battery pack, and a power consumption device. The manufacturing method includes first stirring, second stirring, and third stirring. The first stirring involves mixing and stirring a binder and a solvent to produce a binder liquid. The second stirring involves mixing and stirring a positive electrode active material, a conductive agent, and the binder liquid to produce a mixed material. The third stirring involves mixing and stirring the mixed material with the binder and solvent to obtain a positive electrode paste. The binder and solvent used in the first stirring are the same as those used in the third stirring, respectively. The weight percentage of the binder used in the first stirring is 50% to 70% and the weight percentage of the binder used in the third stirring are 30% to 50% relative to the total weight of the binder used in the first stirring and the binder used in the third stirring. The weight percentage of the solvent used in the first stirring is 50% to 70% and the weight percentage of the solvent used in the third stirring are 30% to 50% relative to the total weight of the solvent used in the first stirring and the solvent used in the third stirring.

Description

[Technical Field]

[0001] The present application relates to the field of secondary battery technology, and in particular to a method for manufacturing a positive electrode paste, a secondary battery, a battery pack, and a power consumption 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 supply systems such as hydroelectric power, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment and aerospace.

[0003] Electrode paste is the basis for forming electrodes and the first step in the production of secondary batteries. The properties of the electrode paste have a significant impact on subsequent electrode production and battery performance. Positive electrode paste is a solid-liquid mixed system primarily composed of a positive electrode active material, a conductive agent, a binder, and a solvent. This system is in a metastable state, and the paste mixing process, i.e., the paste manufacturing method, has a significant impact on the paste's properties, such as dispersibility, uniformity, and stability. Conventional paste mixing processes are typically one-step processes, which directly mix and stir the components of the positive electrode active material paste. However, one-step manufacturing methods cannot meet the needs of binders with different weight-average molecular weights, making the paste mixing process less versatile and disadvantageous for reducing production costs. Therefore, there is a need to develop new paste manufacturing methods that can accommodate binders with different weight-average molecular weights. Summary of the Invention

[0004] The present application has been made in view of the above-mentioned problems, and its purpose is to provide a method for manufacturing a positive electrode paste for a secondary battery that is adaptable to binders with different weight-average molecular weights, widens the process window for coating the positive electrode paste, and improves the processability of the positive electrode paste.

[0005] To achieve the above object, the present application provides a method for manufacturing a positive electrode paste, including first stirring, second stirring, and third stirring. In the first stirring, a binder and a solvent are mixed and stirred to produce a binder liquid. In the second stirring, a positive electrode active material, a conductive agent, and the binder liquid are mixed and stirred to produce a mixed material. In the third stirring, the binder and the solvent are mixed and stirred to produce a positive electrode paste. The binder and solvent used in the first stirring are the same as those used in the third stirring, respectively. The binder and solvent used in the first stirring are 50% to 70% by mass and 30% to 50% by mass relative to the total mass of the binder used in the first stirring and the third stirring. The solvent used in the first stirring is 50% to 70% by mass and 30% to 50% by mass relative to the total mass of the solvent used in the first stirring and the third stirring.

[0006] As a result, the positive electrode paste manufacturing method disclosed herein has broader versatility than conventional positive electrode paste manufacturing methods and is adaptable to pastes containing binders with different weight average molecular weights. Compared to conventional manufacturing methods, the present invention performs paste mixing in separate steps, thereby reducing the viscosity of the positive electrode paste at the time of shipment, mitigating the gelation phenomenon of the positive electrode paste, and improving the adaptability of the manufacturing method to high molecular weight binders. This broadens the process window for applying the positive electrode paste, and improves the processability of the positive electrode paste.

[0007] In an optional embodiment, the binder contains at least polyvinylidene fluoride having a weight average molecular weight of 150,000 to 1,500,000.

[0008] The manufacturing method disclosed herein is universal for both low-molecular-weight and high-molecular-weight polyvinylidene fluoride binders, and can effectively mitigate the gelation phenomenon of different pastes, helping to improve production efficiency and widen the application window of the paste. The manufacturing method disclosed herein can be applied to binders with a weight-average molecular weight of up to 1.5 million, so that pastes containing binders with high weight-average molecular weights still have low viscosity at shipping and anti-gelling properties, meeting the needs of next-generation binders.

[0009] In an optional embodiment, the binder comprises at least two polyvinylidene fluorides having a difference in weight average molecular weight of 1.5 million or less.

[0010] The applicants have discovered that the manufacturing method disclosed herein can be effectively applied to positive electrode pastes containing binders of various weight average molecular weights. Unlike conventional techniques, where binders of different molecular weights easily cause the paste to gel, the positive electrode paste manufactured using the method disclosed herein can effectively utilize the properties of polyvinylidene fluoride binders of different molecular weights, and further alleviate the paste gelation phenomenon through the mutual combination of large and small segments and steric hindrance.

[0011] In any embodiment, the revolution speed of the first stirring is 20 rpm to 40 rpm, and the rotation speed of the first stirring is 100 rpm to 800 rpm. By setting the first stirring speed within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0012] In any embodiment, the stirring time of the first stirring is 20 to 50 minutes. The first stirring time within the appropriate range helps to further alleviate the gelling phenomenon of the paste and improve the paste processability.

[0013] In any embodiment, the rotation speed of the second stirring is 800 rpm to 1500 rpm. A rotation speed of the second stirring within an appropriate range helps to further alleviate the gelation phenomenon of the paste and improve the paste process performance.

[0014] In any embodiment, the revolution speed of the second stirring is 5 rpm to 10 rpm faster than the revolution speed of the first stirring. By setting the revolution speed of the second stirring within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0015] In any embodiment, the stirring time of the second stirring is 30 to 80 minutes. By setting the second stirring time within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0016] In any embodiment, the stirring time of the third stirring is 100 to 130 minutes. By setting the third stirring time within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0017] In some embodiments, the positive electrode paste has a solids content of 60% to 75% and a viscosity of 10,000 mPa·s to 30,000 mPa·s. The paste produced by the method of the present application has a high solids content, an appropriate viscosity, and excellent processability. The paste can be directly used in a subsequent coating process, thereby improving production efficiency.

[0018] In an optional embodiment, the ratio of the mass of the positive electrode active material to the total mass of the binder is 50:1 to 60:1, and the ratio of the mass of the conductive agent to the total mass of the binder is 0.3:1 to 0.5:1. A positive electrode paste within the above ranges not only has good processability, but also provides a formed positive electrode sheet with excellent electrical and chemical properties.

[0019] In any embodiment, the solvent is one or more of N-methyl-2-pyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide, and 3-butoxy-N-methylpropionamide.

[0020] The above solvent has good solubility for any of the binders, and can effectively disperse each material such as the binder, positive electrode active material, and conductive agent, which helps to improve the quality of the paste coating.

[0021] According to a second aspect of the present application, there is provided a positive electrode paste, the positive electrode paste having a solids content of 60% to 75%, an initial viscosity of 10,000 mPa·s to 30,000 mPa·s, and a viscosity of less than 50,000 mPa·s after standing for 24 hours.

[0022] The paste of the present invention has a high solid content, suitable viscosity, and excellent processability and storage stability. The paste can be used directly in the subsequent coating process, thereby improving production efficiency.

[0023] In an optional embodiment, the positive electrode paste includes at least polyvinylidene fluoride having a weight-average molecular weight of 150,000 to 1,500,000. The positive electrode paste of the present application is compatible with binders of different weight-average molecular weights and can effectively mitigate the gelation phenomenon for binders of different weight-average molecular weights, thereby improving production efficiency and widening the process window for applying the paste.

[0024] In an optional embodiment, the binder comprises at least two polyvinylidene fluorides having a weight average molecular weight difference of 1.5 million or less. By including binders having different weight average molecular weights in the paste, the gelling phenomenon of the paste can be further alleviated.

[0025] In any embodiment, the positive electrode paste is manufactured by the method for manufacturing a positive electrode paste according to the first aspect of the present application. The paste formed by the manufacturing method according to the present application has a high solid content, suitable viscosity, and excellent processability, and can be directly used in a subsequent coating process, thereby improving production efficiency.

[0026] According to a third aspect of the present invention, there is provided a secondary battery including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet is manufactured from a positive electrode paste produced by the method for manufacturing a positive electrode paste according to the first aspect. The positive electrode sheet has high quality and production efficiency.

[0027] In any embodiment, the secondary battery is a lithium ion battery, a sodium ion battery, a magnesium ion battery, or a potassium ion battery.

[0028] According to a fourth aspect of the present invention, there is further provided a battery module including the secondary battery according to the third aspect of the present invention.

[0029] 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.

[0030] According to a sixth aspect of the present application, there is provided a power consumption device including at least one selected from the secondary battery according to the third aspect of the present application, the battery module according to the fourth aspect of the present application, or the battery pack according to the fifth aspect of the present application. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application. [Figure 2] FIG. 2 is an exploded view of the secondary battery shown in FIG. 1 according to the embodiment of the present invention. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application; [Figure 5]FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to the embodiment of the present invention. [Figure 6] 1 is a schematic diagram of a power consumption device that uses a secondary battery according to an embodiment of the present application as a power source; DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments specifically disclosing the present application's cathode active material and manufacturing method thereof, cathode sheet, secondary battery, battery module, battery pack, and power consumption device will be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and redundant description of actually identical structures may be omitted. This is to avoid unnecessary lengthening of the following description and to facilitate easy understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0033] The "ranges" disclosed herein 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, with the selected lower and upper limits defining the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of their endpoints, and are arbitrarily combinable; i.e., any lower limit can be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, the ranges 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range "a to b" is a shorthand representation of any combination of real numbers a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that this specification has already listed all real numbers between "0-5," and "0-5" is merely 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.

[0034] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0035] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0036] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order, and for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, the terms "comprise" and "include" used herein may be open-ended or closed-ended. For example, the terms "comprise" and "include" may indicate that other components not listed may be further included or included, or that only the listed components may be included or included.

[0038] Unless otherwise stated, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0039] Positive electrode paste is a solid-liquid mixture primarily composed of a positive electrode active material, a conductive agent, a binder, and a solvent. To improve the uniformity of the distribution of the different components in the system, paste mixing is typically performed using processes such as stirring, ball milling, and ultrasonication. However, conventional paste mixing processes are generally only applicable to paste systems with fixed components, resulting in limited versatility. Changes in the physical properties of the components in the paste often necessitate adjustments to the paste mixing process. For example, conventional paste mixing processes are not applicable to high-molecular-weight binders, nor are they applicable to binders with high weight-average molecular weight dispersion and poor batch production stability. Pastes using different batches of binder produced using the same conventional paste mixing process result in significant performance differences and are prone to gel formation in the paste, making it difficult to meet the production needs of polar sheets.

[0040] [Positive electrode paste manufacturing method] Based on this, the present application provides a method for manufacturing a positive electrode paste, which includes first stirring, second stirring, and third stirring. In the first stirring, a binder and a solvent are mixed and stirred to produce a binder liquid. In the second stirring, a positive electrode active material, a conductive agent, and the binder liquid are mixed and stirred to produce a mixed material. In the third stirring, the binder, the solvent, and the mixed material are mixed and stirred to obtain a positive electrode paste. The binder and the solvent used in the first stirring are the same as those used in the third stirring, respectively. The weight percentage of the binder used in the first stirring is 50% to 70% and the weight percentage of the binder used in the third stirring are 30% to 50% relative to the total weight of the binder used in the first stirring and the binder used in the third stirring. The weight percentage of the solvent used in the first stirring is 50% to 70% and the weight percentage of the solvent used in the third stirring are 30% to 50% relative to the total weight of the solvent used in the first stirring and the solvent used in the third stirring.

[0041] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide, and in some embodiments, the positive electrode active material is at least one of lithium iron phosphate and modified materials thereof, and lithium nickel cobalt manganese oxide and modified materials thereof, and the modified materials are prepared by one or more of the following modification methods: doping, conductive carbon coating, conductive metal coating, and conductive polymer coating.

[0042] In some embodiments, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0043] In this manufacturing method, a binder and a solvent are first mixed and stirred to produce a binder liquid. The binder mass used in the first stirring is 50% to 70% of the total binder mass in the paste, and the solvent mass used in the first stirring is 50% to 70% of the total solvent mass in the paste. This step effectively disperses the binder in the solvent and avoids the aggregation and solidification that would occur if the binder were directly mixed and stirred with other materials. Next, a positive electrode active material, a conductive agent, and the binder liquid are mixed and stirred to produce a mixed material. The second stirring effectively disperses the positive electrode active material and the conductive agent in the binder liquid. The binder in the binder liquid improves the paste stability through electrostatic and steric hindrance effects, reducing aggregation and sedimentation of the positive electrode active material and the conductive agent. The binder and solvent are further mixed with the mixed material and subjected to a third stirring to obtain a positive electrode paste, and the mass percentage of the binder used in the third stirring is 30% to 50% and the mass percentage of the solvent used in the third stirring is 30% to 50% relative to the total mass of the binder used in the first stirring and the binder used in the third stirring. The third stirring serves to stably disperse the materials in the paste by coating the positive electrode active material and conductive agent with the binder added again, and can delay gelation of the paste.

[0044] If the mass of the binder added in the first stirring is too large or too small, the gelling phenomenon of the paste cannot be effectively improved.

[0045] In some embodiments, vacuuming is initiated during the third stirring step. In the prior art, the entire stirring process is typically performed under vacuum conditions. In the present application, vacuuming is initiated during the third stirring step, which can reduce solvent loss and simultaneously expel gases in the paste, further improving the uniformity of the paste.

[0046] Prior art positive electrode paste manufacturing methods had low compatibility and were unable to accommodate differences in the weight-average molecular weight of binders in the paste, resulting in high material precision requirements. The present invention uses separate paste mixing steps to reduce the shipping viscosity of the positive electrode paste and mitigate the gelation phenomenon of the positive electrode paste. Therefore, pastes with high weight-average molecular weight binders still have low shipping viscosity and anti-gelation properties, improving the versatility of the manufacturing method. The present manufacturing method is compatible with not only low weight-average molecular weight binders but also high weight-average molecular weight binders, effectively mitigating the gelation phenomenon of different pastes, improving production efficiency, and widening the paste coating process window.

[0047] In some embodiments, the binder comprises at least polyvinylidene fluoride having a weight average molecular weight of 150,000 to 1.5 million. In some embodiments, the weight average molecular weight of the polyvinylidene fluoride is any one or more of 150,000, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,050,000, 1,100,000, 1,150,000, 1,200,000, 1,250,000, 1,300,000, 1,350,000, 1,400,000, 1,450,000, and 1.5 million.

[0048] As used herein, the term "weight average molecular weight" refers to the statistical average molecular weight by mass of polymer averaged over unit weight.

[0049] The paste mixing process in the prior art is difficult to adapt to binders with high weight-average molecular weights, and the resulting paste has high viscosity at shipping, making it difficult to meet coating requirements, and the paste suffers from serious gelling. The manufacturing method disclosed in this application can be applied to binders with a weight-average molecular weight of up to 1.5 million, so that pastes containing binders with high weight-average molecular weights still have low viscosity at shipping and anti-gelling properties, meeting the needs of next-generation binders.

[0050] In some embodiments, the binder comprises at least two polyvinylidene fluorides having a difference in weight average molecular weight of 1.5 million or less. In some embodiments, the binder comprises two or more polyvinylidene fluorides having different weight average molecular weights, wherein the difference in weight average molecular weight between the polyvinylidene fluorides is 1.45 million, 1.4 million, 1.35 million, 1.3 million, 1.25 million, 1.2 million, 1.15 million, 1.1 million, 1.05 million, 1.0 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 250,000, 200,000, 150,000, 100,000, or 50,000 or less.

[0051] The applicants have discovered that the manufacturing method disclosed herein can be effectively applied to positive electrode pastes containing binders of various weight average molecular weights. Unlike conventional techniques, where binders of different molecular weights easily cause gelation to worsen, the positive electrode paste manufactured using the method disclosed herein can effectively utilize the properties of polyvinylidene fluoride binders of different molecular weights, further mitigating the gelation phenomenon of the paste through the mutual combination of large and small segments and steric hindrance.

[0052] In some embodiments, the revolution speed of the first agitation is 20 rpm to 40 rpm, and the rotation speed of the first agitation is 100 rpm to 800 rpm. In some embodiments, the revolution speed of the first agitation is any one of 20 rpm, 25 rpm, 30 rpm, 35 rpm, and 40 rpm. In some embodiments, the rotation speed of the first agitation is any one of 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, and 800 rpm.

[0053] As used herein, the term "rotation speed" refers to the speed at which the agitator rotates about its own axis.

[0054] As used herein, the term "orbital speed" refers to the speed at which the agitator rotates around the tank containing the material.

[0055] In some embodiments, the agitator is a planetary mixer. The working principle of a planetary mixer is that after the mixer is started, the planetary carrier rotates, rotating the agitator shaft inside the box, revolving around the axis of the material cylinder and simultaneously rotating at high speed, thereby subjecting the material to strong shearing and kneading action. Note that the manufacturing method provided herein is suitable for all types of planetary mixers.

[0056] If the revolution speed of the first stirring is too low or too high, or if the rotation speed of the first stirring is too low, both will result in uneven dispersion of the binder, which will cause the viscosity of the paste to be too high at the time of shipment, and the viscosity of the paste to increase rapidly during the standing process, causing the paste to gel.

[0057] If the rotation speed of the first stirring is too high, the binder liquid will become too thin, which will affect the anti-settling effect of the binder, and the difference in solid content between the upper and lower layers will increase after the paste is left to stand for 24 hours.

[0058] By setting the first stirring speed within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0059] In some embodiments, the stirring time of the first stirring is 20 minutes to 50 minutes, hi some embodiments, the stirring time of the first stirring is 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, or 50 minutes.

[0060] If the first stirring time is too short, the binder will not be effectively dispersed in the solvent, and gel will likely appear in the paste.If the first stirring time is too long, the binder's ability to disperse materials such as the positive electrode active material will be reduced, the paste will be prone to settling, and energy will be wasted, resulting in reduced production efficiency.

[0061] A first stirring time within an appropriate range helps to further alleviate the gelling phenomenon of the paste, and improves the paste process performance.

[0062] In some embodiments, the rotation speed of the second agitation is 800 rpm to 1500 rpm. In some embodiments, the rotation speed of the second agitation may be selected from any one of 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm, 1200 rpm, 1250 rpm, 1300 rpm, 1350 rpm, 1400 rpm, 1450 rpm, and 1500 rpm.

[0063] If the rotation speed of the second stirring is too low or too high, the positive electrode active material and the conductive agent will not be effectively dispersed in the binder liquid, and the viscosity of the paste will be too high at the time of shipping, which will not meet production needs.

[0064] The rotation speed of the second stirring within an appropriate range can further alleviate the gelling phenomenon of the paste, improving the paste process performance.

[0065] In some embodiments, the revolution speed of the second agitation is 5 rpm to 10 rpm faster than the revolution speed of the first agitation. In some embodiments, the revolution speed of the second agitation is 5 rpm, 6 rpm, 7 rpm, 8 rpm, 9 rpm, or 10 rpm faster than the revolution speed of the first agitation.

[0066] If the revolution speed of the second stirring is too low, it is not favorable for the dispersion of the positive electrode active material and the conductive agent in the binder liquid, and gel is likely to appear in the paste.If the revolution speed of the second stirring is too high, the positive electrode active material and the conductive agent are likely to be crushed, the paste is likely to settle, and gelation is accelerated.

[0067] By setting the revolution speed of the second stirring within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0068] In some embodiments, the stirring time of the second stirring is 30 to 80 minutes, or any one of 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, and 80 minutes.

[0069] If the stirring time of the second stirring is too short, it is not favorable for the dispersion of the positive electrode active material and the conductive agent in the binder liquid, and gel is likely to appear in the paste.If the stirring time of the second stirring is too long, the positive electrode active material and the conductive agent are likely to be crushed, and the paste is likely to settle.

[0070] By setting the second stirring time within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0071] In some embodiments, the stirring time of the third stirring is 100 minutes to 130 minutes. In some embodiments, the stirring time of the third stirring is any one of 100 minutes, 105 minutes, 110 minutes, 115 minutes, 120 minutes, 125 minutes, and 130 minutes.

[0072] If the stirring time of the third stirring is too short, it is not favorable for uniform dispersion of the paste and gel is likely to appear in the paste, whereas if the stirring time of the third stirring is too long, the positive electrode active material and conductive agent are likely to be crushed, the paste is likely to settle, and gelation is accelerated.

[0073] By setting the third stirring time within an appropriate range, the paste can have both good anti-gelling properties and good anti-settling properties.

[0074] In some embodiments, the viscosity of a positive electrode paste having a solids content of 60% to 75% is 10,000 mPa·s to 30,000 mPa·s. In some embodiments, the viscosity of a positive electrode paste having a solids content of 60% to 75% is any one of 11,000 mPa·s, 12,000 mPa·s, 13,000 mPa·s, 14,000 mPa·s, 15,000 mPa·s, 16,000 mPa·s, 17,000 mPa·s, 18,000 mPa·s, 19,000 mPa·s, 20,000 mPa·s, 21,000 mPa·s, 22,000 mPa·s, 23,000 mPa·s, 24,000 mPa·s, 25,000 mPa·s, 26,000 mPa·s, 27,000 mPa·s, 28,000 mPa·s, 29,000 mPa·s, and 30,000 mPa·s.

[0075] The paste formed by the manufacturing method of the present invention has a high solid content, suitable viscosity, and excellent processability, and the paste can be directly used in the subsequent coating process, thereby improving production efficiency.

[0076] In some embodiments, the ratio of the mass of the positive electrode active material to the total mass of the binder is 50:1 to 60:1, and the ratio of the mass of the conductive agent to the total mass of the binder is 0.3:1 to 0.5:1. In some embodiments, the ratio of the mass of the positive electrode active material to the total mass of the binder is 50:1, 51:1, 52:1, 53:1, 54:1, 55:1, 56:1, 57:1, 58:1, 59:1, or 60:1. In some embodiments, the ratio of the mass of the conductive agent to the total mass of the binder is 0.3:1, 0.35:1, 0.4:1, 0.45:1, or 0.5:1.

[0077] The total mass of the binder is the sum of the mass of the binder added in the first stirring and the mass of the binder added in the third stirring. Note that the total amount of the binder, positive electrode active material, conductive agent, and solvent to be added can be determined by one skilled in the art based on the rated range of the stirring device.

[0078] A positive electrode paste within the above range not only has good processability, but also provides a positive electrode sheet after molding with excellent electrical and chemical properties.

[0079] In some embodiments, the solvent is one or more of N-methyl-2-pyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide, and 3-butoxy-N-methylpropionamide.

[0080] The above solvent has good solubility for any of the binders, and can effectively disperse each material such as the binder, positive electrode active material, and conductive agent, which helps to improve the quality of the paste coating.

[0081] [Positive electrode paste] The present application further provides a positive electrode paste, the positive electrode paste having a solids content of 60% to 75%, an initial viscosity of 10,000 mPa·s to 30,000 mPa·s, and after standing for 24 hours, the viscosity of the positive electrode paste is less than 50,000 mPa·s. In some embodiments, the viscosity of a positive electrode paste having a solids content of 60% to 75% is any one of 11,000 mPa·s, 12,000 mPa·s, 13,000 mPa·s, 14,000 mPa·s, 15,000 mPa·s, 16,000 mPa·s, 17,000 mPa·s, 18,000 mPa·s, 19,000 mPa·s, 20,000 mPa·s, 21,000 mPa·s, 22,000 mPa·s, 23,000 mPa·s, 24,000 mPa·s, 25,000 mPa·s, 26,000 mPa·s, 27,000 mPa·s, 28,000 mPa·s, 29,000 mPa·s, and 30,000 mPa·s. In some embodiments, after standing for 24 hours, the viscosity of the positive electrode paste is less than 50,000 mPa·s, 45,000 mPa·s, 40,000 mPa·s, 35,000 mPa·s, 30,000 mPa·s, 25,000 mPa·s, 20,000 mPa·s, or 15,000 mPa·s.

[0082] The initial viscosity is the viscosity at the time of shipping when the production of the positive electrode paste is completed.

[0083] The paste of the present invention has a high solid content, suitable viscosity, and excellent processability and storage stability. The paste can be used directly in the subsequent coating process, thereby improving production efficiency.

[0084] In some embodiments, the positive electrode paste includes at least polyvinylidene fluoride having a weight-average molecular weight of 150,000 to 1.5 million. In some embodiments, the weight-average molecular weight of polyvinylidene fluoride is any one or more of 150,000, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,050,000, 1,100,000, 1,150,000, 1,200,000, 1,250,000, 1,300,000, 1,350,000, 1,400,000, 1,450,000, and 1.5 million.

[0085] The positive electrode paste of the present application is compatible with binders of different weight average molecular weights and can effectively mitigate the gelation phenomenon for all binders of different weight average molecular weights, which helps improve production efficiency and widen the process window for paste application.

[0086] In some embodiments, the binder comprises at least two polyvinylidene fluorides having a difference in weight average molecular weight of 1.5 million or less. In some embodiments, the binder comprises two or more polyvinylidene fluorides having different weight average molecular weights, wherein the difference in weight average molecular weight between the polyvinylidene fluorides is 1.45 million, 1.4 million, 1.35 million, 1.3 million, 1.25 million, 1.2 million, 1.15 million, 1.1 million, 1.05 million, 1.0 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 250,000, 200,000, 150,000, 100,000, or 50,000 or less.

[0087] By including binders with different weight average molecular weights in the paste, the gelling phenomenon of the paste can be further alleviated.

[0088] In some embodiments, the positive electrode paste is produced by the manufacturing method of the first aspect of the present application. The paste formed by the manufacturing method of the present application has a high solid content, suitable viscosity, and excellent processability, and the paste can be directly used in a subsequent coating process, thereby improving production efficiency.

[0089] Furthermore, the secondary battery, battery module, battery pack, and power consuming device of the present application will be described below with reference to the drawings as appropriate.

[0090] In one embodiment of the present application, a secondary battery is provided.

[0091] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are inserted and removed between the positive and negative electrode sheets. The electrolyte serves to conduct ions between the positive and negative electrode sheets. The separator, located between the positive and negative electrode sheets, primarily serves to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0092] [Positive electrode sheet] The positive electrode sheet 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 sheet is manufactured from a positive electrode paste manufactured by the method for manufacturing a positive electrode paste in any embodiment.

[0093] As an example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode film layer is provided on one or both of the two facing surfaces of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of the metal foil include aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0095] In some embodiments, the positive electrode active material may be a positive electrode active material for batteries known in the art. For 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 a modified compound thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (may be abbreviated as "LiNi") 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (may be abbreviated as "LiNi") 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (may be abbreviated as "LiNi") 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (may be abbreviated as "LiNi") 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. The lithium-containing phosphate having an olivine structure may include, but is not limited to, for example, at least one of lithium iron phosphate (e.g., LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0096] In some embodiments, the positive electrode film layer may further include a binder, such as at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0097] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, a positive electrode sheet can be manufactured by the following method. A positive electrode paste is manufactured from the components for manufacturing the positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and a solvent (e.g., N-methyl-2-pyrrolidone), using the method for manufacturing a positive electrode paste according to any embodiment of the present application. The manufactured positive electrode paste is applied to a positive electrode current collector, and then subjected to processes such as drying and cold pressing to obtain a positive electrode sheet.

[0099] [Negative electrode sheet] The negative electrode sheet includes a negative electrode active material and includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0100] As an example, the negative electrode current collector has two surfaces facing each other in the thickness direction thereof, and the negative electrode film layer is provided on one or both of the two facing surfaces of the negative electrode current collector.

[0101] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. The metal foil may be, for example, a copper foil. 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, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0102] In some embodiments, the negative electrode active material may be a battery negative electrode active material 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, a silicone-based material, a tin-based material, and lithium titanate. The silicone-based material may be selected from at least one of a silicone element, a silicone oxide, a silicone carbon composite, a silicone nitrogen composite, and a silicone alloy. The tin-based material may be selected from at least one of a tin element, a tin oxide, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative electrode active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0103] In some embodiments, the negative electrode membrane layer optionally further comprises a binder, 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).

[0104] In some embodiments, the negative electrode film 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.

[0105] In some embodiments, the negative electrode membrane layer further optionally includes other auxiliary agents, such as a thickener (e.g., carboxymethylcellulose sodium (CMC-Na)).

[0106] In some embodiments, the negative electrode sheet can be manufactured in the following manner: Components for manufacturing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode paste, which is then applied to a negative electrode current collector, dried, cold-pressed, and other processes to obtain a negative electrode sheet.

[0107] [Electrolyte] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of electrolyte, and the electrolyte may be selected according to needs. For example, the electrolyte may be liquid, gel, or all solid.

[0108] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0109] In some embodiments, the electrolyte salt may be chosen from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0110] In some embodiments, the solvent may be chosen 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.

[0111] In some embodiments, the electrolyte solution further optionally contains additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives that can improve some battery performance, such as an additive that improves the overcharge performance of the battery, or an additive that improves the high-temperature or low-temperature performance of the battery.

[0112] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator with good chemical stability and mechanical stability may be selected.

[0113] In some embodiments, the separator may be made of at least one material selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without any particular limitations. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without any particular limitations.

[0114] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be wound or stacked to form an electrode assembly.

[0115] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0116] 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 pouch may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0117] The present application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0118] 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, where the bottom plate and the side plate together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening and seal the accommodating cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the accommodating cavity. An electrolyte is impregnated 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 select the number according to actual needs.

[0119] 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.

[0120] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0121] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in this accommodating space.

[0122] 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.

[0123] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 4 and 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 includes an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by the lower housing 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0124] The present application also provides a power consuming device, the power consuming device including at least one of a secondary battery, a battery module, or a 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 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, satellites, energy storage systems, etc.

[0125] The power consumption device can be selected from a secondary battery, a battery module, or a battery pack depending on its usage needs.

[0126] 6 shows an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, in which a battery pack or a battery module can be used to meet the demand for high power output and high energy density of the secondary battery of the power consuming device.

[0127] Other examples of the device may be a mobile phone, a tablet computer, a laptop computer, etc. These devices are generally required to be lightweight and can use secondary batteries as a power source.

[0128] Example The following examples of the present application are described. The examples described below are illustrative and are intended only to explain the present application and should not be understood as limitations on the present application. If specific techniques or conditions are not specified in the examples, they will be carried out according to the techniques or conditions described in literature in the field or in accordance with the product specifications. If the manufacturer of the reagents or instruments used is not specified, they are all ordinary products that are commercially available.

[0129] 1. Preparation method Example 1 Positive electrode paste production: 1) 15 kg of binder polyvinylidene fluoride with a weight average molecular weight of 150,000 and 375 kg of solvent N-methyl-2-pyrrolidone are mixed in a double planetary mixer and subjected to first stirring to produce a binder liquid, the revolution speed of the first stirring is 25 rpm, the rotation speed of the first stirring is 500 rpm, the stirring time of the first stirring is 40 minutes, and the temperature of the paste is always controlled at 50°C during the paste production process.

[0130] 2) 1200 kg of the positive electrode active material lithium iron phosphate, 9 kg of conductive carbon black (SP), and the binder liquid were mixed and a second stirring was performed to produce a mixed material, where the rotation speed of the second stirring was 1300 rpm, the revolution speed of the second stirring was 30 rpm, and the stirring time of the second stirring was 60 minutes.

[0131] 3) Mix the mixed materials with 7.5 kg of polyvinylidene fluoride binder with a weight average molecular weight of 150,000 and 187.5 kg of N-methyl-2-pyrrolidone solvent, and perform the third stirring to produce a paste with a solid content of 68%, with a deviation of plus or minus 5%. During the third stirring process, the stirrer is evacuated, the vacuum level is less than -20 MPa, the stirring time is 120 minutes, the revolution speed is 30 rpm, the rotation speed is 1300 rpm, and the paste viscosity is 12000-18000 mPa·s.

[0132] 4) Add cooling water to cool the mixture to 25°C, complete the stirring and remove the mixture.

[0133] Examples 2 to 5 The manufacturing method is substantially the same as that of Example 1, except that the weight average molecular weight of the binder added is adjusted, and the specific parameters are as shown in Tables 1 and 2.

[0134] Examples 6 to 12 The manufacturing method is substantially the same as that of Example 1, except that a plurality of binders with different weight average molecular weights are added, and the specific parameters are as shown in Tables 1 and 2. In Examples 6 to 11, the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 2:1, and in Example 12, the mass ratio of the first polyvinylidene fluoride, the second polyvinylidene fluoride, and the third polyvinylidene fluoride is 3:2:1.

[0135] Examples 13 to 16 The manufacturing method is essentially the same as that of Example 3, except that the total mass of the added solvent, N-methyl-2-pyrrolidone, is adjusted to vary the solid content of the positive electrode paste. The specific parameters are as shown in Tables 1 and 2.

[0136] Examples 17 to 46 The manufacturing method is substantially the same as that of Example 3, except that the stirring parameters are adjusted, and the specific parameters are as shown in Tables 1 and 2.

[0137] Comparative Example 1 1) 22.5 kg of polyvinylidene fluoride binder with a weight average molecular weight of 150,000 and 562.5 kg of N-methyl-2-pyrrolidone solvent were added to a double planetary mixer, the mass ratio of binder to solvent was 0.04:1, the mixing time was 40 minutes, the revolution speed was 25 rpm, and the rotation speed was 400 rpm.

[0138] 2) The revolution speed and rotation speed of the stirring device were increased, and the stirring time was 60 minutes, the revolution speed was 30 rpm, and the rotation speed was 1300 rpm.

[0139] 3) 1200 kg of lithium iron phosphate as a positive electrode active material was added, and the stirring time was 60 minutes, the revolution speed was 30 rpm, and the rotation speed was 1300 rpm.

[0140] 4) Add 9 kg of conductive carbon black (SP), evacuate the inside of the stirring device, the degree of vacuum is less than -50 MPa, the stirring time is 120 minutes, the revolution speed is 30 rpm, and the rotation speed is 1300 rpm, and a paste with a solid content of 68% is obtained.

[0141] 5) Cool by introducing cooling water, cool to 25°C, complete stirring and remove from the container.

[0142] Comparative Examples 2 to 4 This is substantially the same as Comparative Example 1, except that the weight average molecular weight of polyvinylidene fluoride is adjusted to 500,000, 800,000, and 1,000,000, respectively, and the specific parameters are as shown in Tables 1 and 2.

[0143] Comparative Example 5 This is essentially the same as Comparative Example 1, except that the binder is adjusted to polyvinylidene fluorides with two weight average molecular weights, the first polyvinylidene fluoride having a weight average molecular weight of 800,000 and the second polyvinylidene fluoride having a weight average molecular weight of 1.4 million. The two weight average molecular weight polyvinylidene fluorides are mixed and used, and the mass ratio of the first polyvinylidene fluoride to the second polyvinylidene fluoride is 2:1. The specific parameters are as shown in Tables 1 and 2.

[0144] Comparative Examples 6-7 The manufacturing method is substantially the same as that of Example 3, except that the mass of the binder added in the first stirring and the third stirring is adjusted, and the specific parameters are as shown in Tables 1 and 2.

[0145] 2. Paste characteristic test 1. Paste viscosity test The manufactured positive electrode paste is left to stand for 10 minutes before shipping, and the viscosity measured using a Dveslvtjo rotational viscometer (BROOKFIELD) is recorded as the viscosity at shipping. The test conditions are 25°C, rotation speed 12 rpm, and if the viscosity of the paste is 2000 mPa·s or higher, a 64 rotor is used, and if the viscosity of the paste is less than 2000 mPa·s, a 62 rotor is used. The measurement is carried out three times in parallel, and the average value is calculated.

[0146] 2. Viscosity test after leaving the paste to stand for 24 hours After leaving the prepared positive electrode paste to stand for 24 hours, the viscosity value measured using a Dveslvtjo rotational viscometer (BROOKFIELD) was recorded as the 24-hour viscosity. The test conditions were 25°C, rotation speed 12 rpm. If the viscosity of the paste was 2000 mPa·s or higher, a 64 rotor was used, and if the viscosity of the paste was less than 2000 mPa·s, a 62 rotor was used. The measurement was carried out three times in parallel, and the average value was calculated.

[0147] 3. Paste viscosity change test The viscosity change value of the paste is calculated by subtracting the viscosity of the paste at the time of shipment from the viscosity of the paste at 24 hours.

[0148] 4. Gel state test after leaving the paste undisturbed for 24 hours After the paste is allowed to stand for 24 hours, the paste in the beaker is pulled up with a steel ruler, and based on the fluidity of the paste, it is determined whether the paste is ungelled, slightly gelled, moderately gelled, or heavily gelled.

[0149] No gelation: The paste flows naturally without interruption, flows over the surface of the steel ruler, and is free of lumps.

[0150] Slightly gelled state: The paste flows naturally but is thin and the paste is essentially flat on the surface of a steel ruler, with slight lumps.

[0151] Moderate gelation: The paste drips spontaneously, but intermittently, without a continuous flow, the paste does not lie flat on the surface of a steel ruler, and there are obvious lumpy clumps.

[0152] Severe Gelling: The paste does not flow, falls in clumps or remains intact on the steel ruler and does not flow.

[0153] 5. The difference in solid content between the upper and lower layers after the paste is left to stand for 24 hours a) Take the aluminum and weigh it with a moisture meter, and it will be M0. The display will be cleared. The model number of the moisture meter is MOC-120H.

[0154] b) After leaving the paste to stand for 24 hours, remove the upper layer of paste, apply a small amount to aluminum foil, place it in a moisture meter, weigh it, and call it M1.

[0155] c) Close the device and begin drying.

[0156] d) After completion, record the weighing data and record it as M2, and calculate the solid content, which is (M2-M0) / (M1-M0).

[0157] The solid content of the lower layer paste is measured in the same manner, and the solid content of the upper layer paste is subtracted from the solid content of the lower layer paste to obtain the difference in solid content between the upper and lower layers after the paste has been left to stand for 24 hours.

[0158] [Table 1-1] [Table 1-2] [Table 1-3] [Table 1-4]

[0159] [Table 2-1] [Table 2-2] [Table 2-3] [Table 2-4] [Table 2-5] [Table 2-6] [Table 2-7]

[0160] 3. Analysis of the test results of each example and comparative example The positive electrode pastes of the examples and comparative examples were prepared according to the above methods, and the parameters and performance measurement results are shown in Tables 1 and 2.

[0161] As can be seen from the results in Tables 1 and 2, the positive electrode pastes in Examples 1 to 46 were all produced using the paste production method disclosed herein, and included first, second, and third stirring. In the first stirring, a binder and a solvent were mixed and stirred to produce a binder liquid. In the second stirring, a positive electrode active material, a conductive agent, and the binder liquid were mixed and stirred to produce a mixed material. In the third stirring, the binder and the solvent were mixed and stirred to produce a positive electrode paste. The binder and the solvent used in the first stirring were the same as those used in the third stirring, and the mass percentage of the binder used in the first stirring was 50% to 70% and the mass percentage of the binder used in the third stirring was 30% to 50% of the total mass of the binder used in the first stirring and the binder used in the third stirring. With respect to the total mass of the solvent used in the first stirring and the solvent used in the third stirring, the mass percentage of the solvent used in the first stirring is 50% to 70%, and the mass percentage of the solvent used in the third stirring is 30% to 50%.

[0162] As can be seen from comparing Examples 1 to 5 and Example 7 with Comparative Examples 1 to 5, the manufacturing method disclosed in the present application has a wide range of versatility and is applicable to pastes of one or more polyvinylidene fluoride binders having a weight-average molecular weight of 150,000 to 1,500,000. The manufacturing method is universal for polyvinylidene fluoride binders having low weight-average molecular weights and polyvinylidene fluoride binders having high weight-average molecular weights, which helps reduce manufacturing costs and improve production efficiency.

[0163] As can be seen from Comparative Example 4, the prior art manufacturing process has difficulty in reducing the viscosity of the paste at the time of shipment for a binder with a weight-average molecular weight of 1 million, and the paste suffers from serious gelation. By using the manufacturing method disclosed herein, a paste containing a binder with a weight-average molecular weight of up to 1.5 million still has low viscosity at the time of shipment and anti-gelling properties, which can meet the needs of next-generation high molecular weight binders.

[0164] As can be seen from comparing Examples 6 to 12 with Comparative Example 5, the present invention is also applicable to pastes having binders with different weight-average molecular weights. Unlike the manufacturing methods of the prior art, the manufacturing method disclosed in the present invention can effectively eliminate the gelation phenomenon of the paste caused by large differences in the molecular weight of the binders. This manufacturing method has wider general applicability.

[0165] As can be seen from comparing Example 4 with Example 8, Example 10 with Example 5, and Example 11 with Example 3, pastes containing binders of different molecular weights prepared using the manufacturing method of the present invention have lower shipping viscosities and better anti-gelling properties.

[0166] As can be seen from Examples 13 to 16, by controlling the solid content of the paste to 60% to 75%, the paste can achieve both good anti-gelling properties and good anti-settling properties.

[0167] As can be seen from comparing Examples 3, 17, and 18 with Comparative Examples 6 and 7, by controlling the proportion of binder added in the first stirring to 50% to 70% of the total binder mass, it is possible to effectively mitigate the gelation of the paste, improve the shelf life of the paste, and widen the process window for coating the paste.

[0168] As can be seen from a comparison of Examples 3, 21, and 22 with Examples 19 and 20, controlling the revolution speed of the first stirring to 20 to 40 rpm effectively alleviates gelation of the paste, improves paste shelf life, and widens the process window for coating the paste.

[0169] As can be seen from a comparison of Examples 3, 23, and 24 with Examples 25 and 26, by controlling the rotation speed of the first stirring to 100 rpm to 800 rpm, the paste can achieve both good anti-gelling properties and anti-settling properties.

[0170] As can be seen from a comparison of Examples 3, 28, and 29 with Examples 27 and 30, by controlling the stirring time of the first stirring to 20 to 50 minutes, the paste can achieve both good anti-gelling properties and good anti-settling properties.

[0171] As can be seen from comparing Examples 3, 31, and 32 with Examples 33 and 34, controlling the rotation speed of the second stirring to 800 rpm to 1500 rpm can effectively alleviate the gelation of the paste, improve the shelf life of the paste, and widen the process window for coating the paste.

[0172] As can be seen from a comparison of Examples 3, 36, and 37 with Examples 35 and 38, by making the revolution speed of the second stirring 5 to 10 revolutions per minute faster than the revolution speed of the first stirring, the paste can achieve both good anti-gelling properties and anti-settling properties.

[0173] As can be seen from a comparison of Examples 3, 40, and 41 with Examples 39 and 42, by controlling the stirring time of the second stirring to 30 to 80 minutes, the paste can achieve both good anti-gelling properties and good anti-settling properties.

[0174] As can be seen from a comparison of Examples 3, 44, and 45 with Examples 43 and 46, by controlling the stirring time of the third stirring to 100 to 130 minutes, the paste can achieve both good anti-gelling properties and good anti-settling properties.

[0175] As can be seen from the examples, the viscosity of the positive electrode paste disclosed in the present application with a solid content of 60% to 75% is 10,000 mPa·s to 30,000 mPa·s, and the positive electrode paste has good coating properties and processability.

[0176] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and achieves the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. Furthermore, various modifications conceivable by those skilled in the art to the embodiments, as well as other forms constructed by combining some of the components of the embodiments, are also included within the scope of the present application, as long as they do not deviate from the gist of the present application. [Explanation of symbols]

[0177] 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. A method for producing a positive electrode paste, comprising first stirring, second stirring, and third stirring, In the first stirring, a binder and a solvent are mixed and stirred to prepare a binder liquid; In the second stirring, the positive electrode active material, the conductive agent, and the binder liquid are mixed and stirred to produce a mixed material; In the third stirring, the binder and the solvent are mixed and stirred with the mixed material to obtain a positive electrode paste, the binder and the solvent used in the first stirring are the same as the binder and the solvent used in the third stirring, respectively; the mass percentage of the binder used in the first stirring is 50% to 70% and the mass percentage of the binder used in the third stirring is 30% to 50% relative to the total mass of the binder used in the first stirring and the binder used in the third stirring; the mass percentage of the solvent used in the first stirring is 50% to 70% and the mass percentage of the solvent used in the third stirring is 30% to 50% relative to the total mass of the solvent used in the first stirring and the solvent used in the third stirring.

2. The method for producing a positive electrode paste according to claim 1, wherein the binder contains at least polyvinylidene fluoride having a weight average molecular weight of 150,000 to 1,500,000.

3. 3. The method for producing a positive electrode paste according to claim 1, wherein the binder contains at least two polyvinylidene fluorides having a difference in weight average molecular weight of 1.5 million or less.

4. 4. The method for producing a positive electrode paste according to claim 1, wherein the revolution speed of the first stirring is 20 rpm to 40 rpm, and the rotation speed of the first stirring is 100 rpm to 800 rpm.

5. The method for producing a positive electrode paste according to any one of claims 1 to 4, wherein the first stirring is performed for a period of 20 to 50 minutes.

6. The method for producing a positive electrode paste according to any one of claims 1 to 5, wherein the rotation speed of the second stirring is 800 rpm to 1500 rpm.

7. The method for producing a positive electrode paste according to any one of claims 1 to 6, wherein the revolution speed of the second stirring is 5 rpm to 10 rpm faster than the revolution speed of the first stirring.

8. The method for producing a positive electrode paste according to any one of claims 1 to 7, wherein the second stirring is performed for a period of 30 to 80 minutes.

9. The method for producing a positive electrode paste according to any one of claims 1 to 8, wherein the third stirring is performed for a stirring time of 100 to 130 minutes.

10. The method for producing a positive electrode paste according to any one of claims 1 to 9, wherein the positive electrode paste has a solid content of 60% to 75% and a viscosity of 10,000 mPa·s to 30,000 mPa·s.

11. 11. The method for producing a positive electrode paste according to claim 1, wherein a ratio of a mass of the positive electrode active material to a total mass of the binder is 50:1 to 60:1, and a ratio of a mass of the conductive agent to a total mass of the binder is 0.3:1 to 0.5:

1.

12. The method for producing a positive electrode paste according to any one of claims 1 to 11, wherein the solvent is one or more of N-methyl-2-pyrrolidone, N,N-dimethylpropionamide, N,N-diethylpropionamide, N,N-dipropylpropionamide, N,N-dibutylpropionamide, N,N-dimethylethylpropionamide, and 3-butoxy-N-methylpropionamide.

13. A positive electrode paste, wherein the positive electrode paste has a solids content of 60% to 75%, an initial viscosity of 10,000 mPa·s to 30,000 mPa·s, and after being allowed to stand for 24 hours, the viscosity of the positive electrode paste is less than 50,000 mPa·s.

14. The positive electrode paste according to claim 13, comprising at least polyvinylidene fluoride having a weight average molecular weight of 150,000 to 1,500,000.

15. The positive electrode paste according to claim 13 or 14, wherein the binder contains at least two polyvinylidene fluorides having a difference in weight average molecular weight of 1.5 million or less.

16. The positive electrode paste according to any one of claims 13 to 15, characterized in that it is produced by the method for producing a positive electrode paste according to any one of claims 1 to 12.

17. A secondary battery comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet is manufactured from a positive electrode paste manufactured by the method for manufacturing a positive electrode paste according to any one of claims 1 to 12.

18. 18. The secondary battery according to claim 17, which is any one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.

19. A battery module comprising the secondary battery according to claim 17 or 18.

20. A battery pack comprising at least one of the secondary battery according to claim 17 or 18 and the battery module according to claim 19.

21. 21. A power consumption device comprising at least one selected from the group consisting of the secondary battery according to claim 17 or 18, the battery module according to claim 19, and the battery pack according to claim 20.

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