Manufacturing method of secondary battery

Abstract

To provide a manufacturing method of a secondary battery.SOLUTION: A manufacturing method of a secondary battery according to the present invention includes a negative electrode plate manufacturing step of manufacturing a negative electrode plate, a positive electrode plate manufacturing step of manufacturing a positive electrode plate, an electrolyte solution preparation step, and a secondary battery fabrication step of sequentially stacking a negative electrode plate, a separator, and the positive electrode plate to form a cell and then injecting an electrolyte solution to fabricate a secondary battery. The negative electrode plate manufacturing step includes an adhesive pretreatment step of pretreating an emulsion-type adhesive by at least one of a kneading operation, a dilution and sedimentation operation, a dilution and ultrasonic operation, a centrifugation operation, and a sedimentation operation, a first mixture preparation step of mixing a negative electrode active material, a conductive agent, and an additive in a predetermined ratio to obtain a first mixture, a negative electrode slurry preparation step of mixing the pretreated emulsion-type adhesive, the first mixture, and a diluent to obtain a negative electrode slurry, and a negative electrode plate formation step of applying the negative electrode slurry to at least one surface of a current collector and obtaining a negative electrode plate after drying.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to the field of lithium battery technology, and in particular to a negative electrode plate, a method for manufacturing the same, a secondary battery including the negative electrode plate, a battery module, a battery pack, and a power consumption device. [Background technology]

[0002] In recent years, secondary batteries have been widely used in many fields. However, during the manufacturing process of the negative electrode plate of a secondary battery, especially during the drying process of the negative electrode plate, the negative electrode adhesive tends to float up significantly as the water evaporates, resulting in uneven distribution of the adhesive in the negative electrode film layer, poor adhesion between the negative electrode active material, and defects such as powder shedding and cracking on the electrode plate, which negatively impacts battery performance. Summary of the Invention

[0003] The present application has been made in view of the above-mentioned problems, and its object is to provide a negative electrode plate in which the adhesive is uniformly distributed and which is less likely to cause powder falling and cracking, a method for manufacturing the same, and a secondary battery manufactured using the negative electrode plate.

[0004] To achieve the above object, the present application provides a negative electrode plate and a manufacturing method thereof.

[0005] A first aspect of the present application provides a negative electrode plate, the negative electrode plate comprising: a current collector and a negative electrode film layer located on at least one surface of the current collector, wherein the negative electrode film layer includes a negative electrode active material and an emulsion-type adhesive, and at least a portion of the emulsion-type adhesive exhibits an irregular film-like distribution on the surface of the negative electrode active material; The irregular film-like distribution refers to a state in which, in an image of the negative electrode film layer taken by a scanning electron microscope (SEM) at a magnification of 10K, the emulsion-type adhesive is not distributed in the form of single particles or clusters of single particles, but is distributed on the surface of the negative electrode active material in the form of an irregular film.

[0006] In some embodiments, on the surface of the negative electrode active material, in the SEM photograph of the negative electrode film layer taken by a scanning electron microscope, at a magnification of 10K, an emulsion-type adhesive showing an irregular film-like distribution at any one location is selected, a closed region is constructed along the edge of the film-like structure, and the radius of the standard circle formed by normalizing the closed region is not less than 500 nm.

[0007] Thereby, in the present application, on the negative electrode active material, the adhesion and cohesion of the negative electrode plate are improved by an emulsion-type adhesive that at least partially shows an irregular film-like distribution, and the battery performance is improved.

[0008] In some embodiments, for the negative electrode film layer, at a magnification of 10K, in the SEM photograph, if the total area of the region where the emulsion-type adhesive shows an irregular film-like distribution is A, and the total area of the region where the emulsion-type adhesive is distributed in a single-particle shape or a cluster shape composed of single particles is B, then the ratio of A to (A + B) is at least 10:100, optionally 60:100 to 100:100, and more optionally 80:100 to 98:100.

[0009] By increasing the average area ratio of the irregular film-like distribution of the emulsion-type adhesive, the cohesion and adhesion of the negative electrode plate can be improved, thereby improving the structural stability of the electrode plate.

[0010] In some embodiments, in the negative electrode plate, in the direction from the outer surface of the negative electrode film layer toward the current collector along the outer surface of the negative electrode film layer, if the ratio of the longitudinal depth of the negative electrode film layer to the total thickness of the entire negative electrode film layer is d, and the ratio of the mass content of the emulsion-type adhesive in the negative electrode film layer with the longitudinal depth to the mass content of the emulsion-type adhesive in the entire negative electrode film layer is x, here, when the total thickness of the entire negative electrode film layer is set to 1 and the mass content of the emulsion-type adhesive in the entire negative electrode film layer is set to 1, then 0 < d < 1, 0 < x < 1, and x and d satisfy 1 < x / d ≤ 1.8, optionally 1 < x / d ≤ 1.5.

[0011] By improving the uniformity and consistency of the emulsion adhesive distribution in the thickness direction of the negative electrode film layer, the mechanical stability of the negative electrode plate is improved.

[0012] In one embodiment, the negative electrode film layer includes two sub-layer regions having the same thickness on the surface of the same side of the current collector, and the mass content of the emulsion adhesive in the lower half layer of the negative electrode film layer is smaller than the mass content of the emulsion adhesive in the upper half layer along the outer surface of the negative electrode film layer toward the current collector, the difference being no more than 12%, and the lower half layer and the upper half layer are separated by half the thickness of the negative electrode film layer located on the same side of the current collector. By improving the uniformity and consistency of the emulsion adhesive distribution in the thickness direction of the negative electrode film layer, the mechanical stability of the negative electrode plate is improved.

[0013] In any embodiment, the emulsion adhesive is at least one selected from styrene butadiene rubber (SBR), polyacrylate, ethylene propylene rubber, nitrile rubber, and polyvinylidene fluoride (PVDF). By selecting an appropriate emulsion adhesive, better adhesive performance can be obtained.

[0014] A second aspect of the present application further provides a method for manufacturing a negative electrode plate, the method comprising: The method includes the steps of: pretreating an emulsion adhesive, the pretreatment method including at least one of ultrasonic waves, sedimentation, centrifugation, and kneading; mixing a negative electrode active material, a conductive agent, and an additive in a predetermined proportion to obtain a first mixture; mixing the pretreated emulsion adhesive, the first mixture, and deionized water to obtain a negative electrode slurry; and applying the negative electrode slurry to at least one surface of a current collector and obtaining the negative electrode plate after drying, and optionally: The method comprises: The method includes the steps of: mixing a negative electrode active material, a conductive agent, and an additive in a predetermined proportion to obtain a first mixture; uniformly mixing the emulsion-type adhesive, the first mixture, and deionized water by kneading and stirring to obtain a negative electrode slurry; and applying the negative electrode slurry to at least one surface of a current collector and drying it to obtain the negative electrode plate, where: the negative electrode plate includes a current collector and a negative electrode film layer located on at least one surface of the current collector, wherein the negative electrode film layer includes a negative electrode active material and an emulsion-type adhesive, and most or all of the emulsion-type adhesive exhibits an irregular film-like distribution on the surface of the negative electrode active material; The irregular film-like distribution refers to a state in which, in an SEM photograph of the negative electrode film layer taken by a scanning electron microscope at a magnification of 10K, the emulsion-type adhesive is not distributed in the form of single particles or clusters consisting of single particles, but is distributed on the surface of the negative electrode active material in the form of an irregular film.

[0015] Therefore, the present application changes the conventional method of adding emulsion-type adhesives by adjusting the process, so that part or most of the adhesive exhibits irregular film-like distribution characteristics on the surface of the negative electrode active material, thereby improving the cohesion and adhesion of the negative electrode plate and improving battery performance.

[0016] A third aspect of the present application provides a secondary battery, the battery including a negative electrode plate according to the first aspect of the present application.

[0017] A fourth aspect of the present application provides a battery module, which includes the secondary battery of the third aspect of the present application.

[0018] A fifth aspect of the present application provides a battery pack, which includes the battery module of the fourth aspect of the present application.

[0019] A sixth aspect of the present application provides a power consumption device, the 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. [Effects of the Invention]

[0020] Compared with the prior art, the present invention provides a negative electrode plate containing an emulsion adhesive, at least some of which exhibits an irregular film distribution, obtained by adjusting the manufacturing process. During the drying process of the negative electrode plate, the emulsion adhesive is prevented from migrating to the surface of the negative electrode film layer and floating up, thereby improving the adhesive strength and cohesive strength of the negative electrode plate and at least achieving the beneficial technical effects of improving the cycle performance of the battery. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an SEM image of the negative electrode film layer on the negative electrode plate of Example 1, which shows representative emulsion-type adhesives with different state distributions: Region 1 is an emulsion-type adhesive with an irregular film-like distribution, Region 2 is an emulsion-type adhesive with a single-particle distribution, and Region 3 is an emulsion-type adhesive with a cluster-like distribution consisting of single-particle particles. [Figure 2] 1 is an SEM image of a negative electrode film layer on a negative electrode plate of Comparative Example 1. [Figure 3] 1 is an SEM image of the negative electrode film layer on the negative electrode plate of Example 5, which shows the emulsion-type adhesive exhibiting irregular film-like distribution. [Figure 4] 10 shows test results of cycle retention rates of secondary batteries assembled using Example 5 and Comparative Example 1. [Figure 5] 10 shows the results of a direct current internal resistance (DCR) test of secondary batteries assembled using Example 5 and Comparative Example 1. [Figure 6] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; [Figure 7] FIG. 7 is an exploded view of the secondary battery shown in FIG. 6 according to the embodiment of the present application. [Figure 8] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 9] 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 10]FIG. 10 is an exploded view of the battery pack shown in FIG. 9 according to an embodiment of the present application. [Figure 11] 1 is a schematic diagram of a power consumption device powered by a secondary battery according to an embodiment of the present application; DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, the specifically disclosed embodiments of the present application, including a negative electrode plate and a manufacturing method thereof, a secondary battery, a battery module, a battery pack, and an electrical 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 the following description becoming unnecessarily long and to facilitate 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.

[0023] 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 any combination is possible; 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 of 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" represents a shorthand notation for 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 all real numbers between "0-5" have already been listed in this specification, 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.

[0024] Unless otherwise stated, all embodiments and optional embodiments in the present application can be combined with each other to form a new technical solution.

[0025] 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.

[0026] 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 may include 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. 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.

[0027] Unless otherwise specified, the terms "comprise" and "include" used in this application 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.

[0028] 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 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).

[0029] Currently, secondary battery negative electrodes generally use emulsion adhesives as negative electrode adhesives. However, emulsion adhesives exist in the form of dispersed micelles in the slurry, and negative electrodes manufactured using such slurries often suffer from poor adhesion, resulting in insufficient adhesion between the negative electrode active materials or between the active material layer and the current collector, which can lead to powdering of the active material, cracking of the negative electrode film layer, or peeling of the negative electrode film layer, thereby deteriorating battery performance.

[0030] In view of the above problems, the inventors have developed a negative electrode plate in which an adhesive is distributed in the form of an irregular film on the surface of the negative electrode active material, and the negative electrode active material particles of this negative electrode plate have significantly improved cohesion, and the negative electrode film layer of this negative electrode plate has significantly improved adhesion to the current collector. This significantly improves the problems that reduce the yield of the plate, such as powdering of the active material, cracking of the negative electrode film layer, and peeling off of the negative electrode film layer, and the cycle performance of secondary batteries manufactured using the negative electrode plate of the present invention is significantly improved.

[0031] [Negative electrode plate] The present application proposes a negative electrode plate, comprising a current collector and a negative electrode film layer located on at least one surface of the current collector, wherein the negative electrode film layer comprises a negative electrode active material and an emulsion-type adhesive, wherein: At least a portion of the emulsion adhesive exhibits an irregular film-like distribution on the surface of the negative electrode active material, The "irregular film distribution" refers to a state in which, in a scanning electron microscope (SEM) photograph of the negative electrode film layer at a magnification of 10K, the emulsion adhesive is not distributed in the form of single particles or clusters of single particles, but is distributed on the surface of the negative electrode active material in the form of an irregular film. For example, referring to the SEM photograph of Figure 1, the irregular film-like material in one area of ​​the photograph is an emulsion adhesive exhibiting an "irregular film distribution." Figure 3 shows an emulsion adhesive with an irregular film distribution.

[0032] An "emulsion adhesive" is a water-based emulsion adhesive of a water-insoluble polymer, and may be an adhesive containing a resin-type emulsion and a rubber-type latex. It is an important water-based adhesive. It should be noted that the term "emulsion adhesive" refers to the adhesive product located within the negative electrode membrane layer and formed after dehydration during the drying process of the electrode plate. It refers to the type of adhesive, not the form of the adhesive on the surface of the negative electrode active material. The emulsion adhesive of the present application is selected from at least one of styrene butadiene rubber, polyacrylate, ethylene propylene rubber, nitrile rubber, and polyvinylidene fluoride.

[0033] On the surface of the negative electrode active material, "at least a portion" of the emulsion adhesive exhibits an irregular film-like distribution. "At least a portion" refers to the presence of emulsion adhesive distributed in single particles or clusters of single particles on the surface of the negative electrode active material in addition to the emulsion adhesive distributed in an irregular film-like manner. For example, referring to the SEM photograph of Figure 1, Region 1 in the figure is an emulsion adhesive with an irregular film-like distribution, Region 2 is an emulsion adhesive with a single particle-like distribution, and the relatively dark-colored materials in Region 3 clearly represent emulsion adhesive with a cluster-like distribution of single particles. The SEM photograph of Figure 2 more clearly shows the emulsion adhesive with a single particle-like distribution. The SEM photograph of Figure 3 is a schematic diagram of an emulsion adhesive with an irregular film-like distribution.

[0034] "Surface of negative electrode active material" means the surface of a negative electrode active material particle (for example, graphite) in an SEM photograph at a magnification of 10K.

[0035] Compared with the adhesives of the prior art that are "distributed in the form of single particles or clusters consisting of single particles" on the surface of the negative active material of the negative electrode plate of the present application, the emulsion-type adhesive of the present application adheres to the surface of the negative active material in the form of "irregular film-like distribution", on the one hand, significantly increasing the adhesion area between particles of the negative active material, significantly increasing the cohesive force, and further improving the prevention of powdering of the active material and cracking of the negative electrode film layer, and on the other hand, increasing the adhesion area between the negative active material and the current collector, significantly increasing the adhesion force between the two, and further improving the prevention of the drop-off of the negative electrode film layer, so that the cycle performance of secondary batteries manufactured using the negative electrode plate of the present application is significantly improved.

[0036] In a preferred embodiment, in the negative electrode plate of the present application, all of the emulsion-type adhesives exhibit an irregular film-like distribution on the surface of the negative electrode active material.

[0037] Unlike the present application, referring to the SEM photograph of Comparative Example 1 in FIG. 2, after cold pressing in the conventional negative electrode plate, the adhesive still has a clear particulate distribution, and as a result, the adhesive strength between the negative electrode active material particles and between the negative electrode active material and the current collector is significantly inferior to that of the negative electrode plate of the present application.

[0038] In some embodiments, an emulsion adhesive is selected that exhibits an irregular film-like distribution at any one location in a SEM image of the negative electrode film layer taken on the surface of the negative electrode active material described herein at a magnification of 10K using a scanning electron microscope, and a closed region is constructed along the edge of the film-like structure. The radius of the standard circle obtained by normalizing the closed region is not smaller than 500 nm. The irregular film-like distribution can significantly strengthen the cohesive strength and adhesive strength of the negative electrode plate.

[0039] Regarding the "normalized radius of the standard circle," the area of ​​the closed region is obtained as S using the SEM area test tool, and S = πR 2 is equivalent to the area of ​​a standard circle, the calculated R is the "radius of the normalized standard circle" described in this application.

[0040] In some embodiments, optionally, when the emulsion adhesive exhibits a single particle distribution or a cluster distribution consisting of single particles on the surface of the negative electrode active material, the increase rate of the maximum particle size of a single particle relative to the particle size when the emulsion adhesive exhibits an emulsion state is ≦150%.

[0041] The "particle size when the emulsion adhesive is in an emulsion state" refers to the particle size of a single micelle in a commercially available emulsion that is in an emulsion state as a raw material in a manufacturing method, and the particle size is generally 50 to 300 nm.

[0042] The "maximum particle size" is the longest diameter of an irregularly shaped, roughly spherical, single particle emulsion adhesive in an SEM photograph of the negative electrode film layer taken by a scanning electron microscope at a magnification of 10K.

[0043] In one embodiment, when a portion of the emulsion adhesive on the surface of the negative electrode active material exhibits a monoparticulate distribution, the increase rate of the maximum particle size of the emulsion adhesive with the monoparticulate distribution relative to the particle size when the emulsion adhesive is in an emulsion state is ≦150%.

[0044] It should be noted that the adhesive with a single particle distribution contained in the negative electrode film layer of the present application basically maintains the basic shape and size of the emulsion-type adhesive when it is in an emulsion state, and does not significantly improve the technical effect of the present application, namely, significantly strengthening the cohesive strength and adhesive strength of the negative electrode plate. In fact, the technical effect of the present application is mainly achieved by the emulsion-type adhesive with the irregular film distribution, which is achieved by optimizing the manufacturing method of the negative electrode plate. That is, the irregular film distribution of the adhesive significantly improves the cohesive strength and adhesive strength of the negative electrode plate.

[0045] In some embodiments, optionally, in an SEM photograph of the negative electrode film layer at a magnification of 10K, if the total area of ​​the region where the emulsion adhesive exhibits an irregular film-like distribution is A and the total area of ​​the region where the emulsion adhesive is distributed in the form of single particles or clusters of single particles is B, the ratio of A to (A+B) is at least 10:100, optionally 60:100 to 100:100, and further optionally 80:100 to 98:100.

[0046] The inventors have discovered that by increasing the area proportion of the irregular film distribution of the emulsion adhesive, the adhesive action between particles of the negative electrode active material and the adhesive strength between the negative electrode active material and the current collector can be improved, and the cohesive force and adhesive force of the negative electrode plate can be further improved, resulting in relatively high electrode plate structural stability and improved electrode plate cycle performance.

[0047] (A + B) can be tested by the following method. At the same magnification (10K or 20K), randomly select 20 different positions on the same negative electrode plate and take pictures. Calculate the total area of the regions where the emulsion-type adhesive exhibits an irregular film-like distribution and the total area of the regions where the emulsion-type adhesive exhibits a clustered distribution consisting of particles or single particles in each imaging photo. Then, based on these 20 imaging photos, calculate the average value of their respective total areas, and this average value is the total area of the corresponding distribution region.

[0048] The "cohesive force" described in this application means the adhesion performance between the particles of the active material in the negative electrode film layer.

[0049] The "adhesive force" described in this application means the adhesion performance between the negative electrode film layer and the current collector, and between the negative electrode active material and the current collector.

[0050] In some embodiments, in the direction from the outer surface of the negative electrode film layer towards the current collector, let the ratio of the longitudinal depth of the negative electrode film layer to the total thickness of the entire negative electrode film layer be d, and let the ratio of the mass content of the emulsion-type adhesive in the negative electrode film layer with the longitudinal depth to the mass content of the emulsion-type adhesive in the entire negative electrode film layer be x. Here, when the total thickness of the entire negative electrode film layer is set to 1 and the mass content of the emulsion-type adhesive in the entire negative electrode film layer is set to 1, 0 < d < 1, 0 < x < 1, x and d satisfy 1 < x / d ≤ 1.8, and optionally 1 < x / d ≤ 1.5.

[0051] The magnitude of the difference (x / d) − 1 represents the degree of deviation of the mass content of the emulsion-type adhesive in the negative electrode film layer with a certain longitudinal depth from this uniform distribution state with respect to the ideal state where the emulsion-type adhesive is uniformly distributed throughout the negative electrode film layer (i.e., x / d = 1), thereby representing the degree of lifting of the emulsion-type adhesive in the thickness direction of the negative electrode film layer.

[0052] The fact that the negative electrode plate of the present application has x / d≦1.8 indicates that the phenomenon of uneven adhesive distribution (floating problem) is improved, and the structural stability of the negative electrode plate and the performance of a secondary battery using this negative electrode plate are optimized.

[0053] The test process of any d in this application is to select a negative electrode film layer on one side of a current collector, measure the thickness of the negative electrode film layer as D, and use SAICAS (Surface and Interface Cutting Analysis System) to peel the negative electrode film layer corresponding to the predetermined depth D1 (i.e., the thickness of the peeled negative electrode film layer is D1) along the thickness direction of the negative electrode film layer from the surface of the negative electrode film layer to a predetermined depth D1, where d=D1 / D; Any x test process in this application is tested using pyrolysis-mass spectrometry (Py-MS), and the mass of the emulsion adhesive in the entire negative electrode film layer is X, and the mass of the emulsion adhesive in the negative electrode film layer remaining after the negative electrode film layer having a thickness of D1 is peeled off is Y1, where x=(X-Y1) / X.

[0054] In some embodiments, optionally, in the negative electrode plate of the present application, the mass content of the emulsion adhesive in the lower half layer of the negative electrode film layer is smaller than the mass content of the emulsion adhesive in the upper half layer, the difference being no more than 12%, and the lower half layer and the upper half layer are separated by half the thickness of the negative electrode film layer located on the same side of the current collector.

[0055] In some embodiments, on the same surface of a current collector, the negative electrode film layer includes four sub-membrane layer regions having the same film layer thickness, and along the outer surface of the negative electrode film layer in the direction toward the current collector, the four sub-membrane layers are, in order, a first sub-membrane layer, a second sub-membrane layer, a third sub-membrane layer, and a fourth sub-membrane layer, and the emulsion adhesive content therein decreases sequentially, with the difference in the emulsion adhesive content between the first sub-membrane layer and the third sub-membrane layer not exceeding 15%, optionally not exceeding 10%, and the difference in the emulsion adhesive content between the second sub-membrane layer and the fourth sub-membrane layer not exceeding 18%, optionally not exceeding 15%.

[0056] The inventors have further found that the difference in emulsion adhesive content between the sub-layers of each subdivided negative electrode film layer is at most 18%, which indicates that the uniformity and consistency of adhesive distribution in the thickness direction of the negative electrode film layer of the present invention is improved, which is beneficial to improving the cycle retention rate of the electrochemical device.

[0057] The difference in mass content of emulsion adhesive between the two negative electrode membrane sub-layers is calculated by the following formula: (S1-S2) / S2*100%.

[0058] Here, on the same side of the negative electrode plate, along the outer surface of the negative electrode film layer in the direction toward the current collector, S1 is the mass content of the emulsion adhesive in the sublayer farther from the current collector, and S2 is the mass content of the emulsion adhesive in the sublayer closer to the current collector.

[0059] 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 base layer. 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 base material (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0060] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art and used in batteries. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of silicon elemental, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy. The tin-based material may be selected from at least one of tin elemental, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0061] In some embodiments, the negative electrode film layer optionally further includes a conductive agent, which may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0062] Compared with the adhesives of the prior art that are "distributed in the form of single particles or clusters consisting of single particles" on the surface of the negative active material of the negative electrode plate of the present application, the emulsion-type adhesive of the present application adheres to the surface of the negative active material in the form of "irregular film-like distribution", on the one hand, significantly increasing the adhesion area between particles of the negative active material, significantly increasing the cohesive force, and further improving the prevention of powdering of the active material and cracking of the negative electrode film layer, and on the other hand, increasing the adhesion area between the negative active material and the current collector, significantly increasing the adhesion force between the two, and further improving the prevention of the drop-off of the negative electrode film layer, so that the cycle performance of secondary batteries manufactured using the negative electrode plate of the present application is significantly improved.

[0063] [Method of manufacturing negative electrode plate] The method for manufacturing the negative electrode plate is as follows: A step of pretreating the emulsion adhesive, the pretreatment method including at least one of ultrasonic waves, sedimentation, centrifugation, and kneading; mixing a negative electrode active material, a conductive agent, and an additive in a predetermined proportion to obtain a first mixture; mixing the pretreated emulsion adhesive, the first mixture, and deionized water to obtain a negative electrode slurry; applying the negative electrode slurry to at least one surface of a current collector and obtaining the negative electrode plate after drying, wherein: the negative electrode plate includes a current collector and a negative electrode film layer located on at least one surface of the current collector, wherein the negative electrode film layer includes a negative electrode active material and an emulsion-type adhesive, and most or all of the emulsion-type adhesive exhibits an irregular film-like distribution on the surface of the negative electrode active material; The irregular film-like distribution refers to a state in which, in an SEM photograph of the negative electrode film layer taken by a scanning electron microscope at a magnification of 10K, the emulsion-type adhesive is not distributed in the form of single particles or clusters of single particles, but is distributed on the surface of the negative electrode active material in the form of an irregular film.

[0064] The inventors have discovered that by using the ultrasonic waves, sedimentation, centrifugation or kneading operations, the micelle housing of the emulsion adhesive is destroyed, thereby changing the form of the emulsion adhesive and its distribution on the surface of the negative electrode active material, so that part or most of it exhibits the characteristics of a film-like distribution, thereby suppressing the floating of the adhesive, improving the cohesive force and adhesive force of the negative electrode plate, and improving the performance of the secondary battery, for example, improving cycle performance and reducing the internal resistance of the battery.

[0065] In some embodiments, the method for manufacturing a negative electrode plate of the present invention includes the following steps.

[0066] (a) mixing a negative electrode active material, a conductive agent, and an additive in a predetermined proportion to obtain a first mixture; (b) uniformly mixing the emulsion-type adhesive, the first mixture, and deionized water by kneading and stirring to obtain a negative electrode slurry; (c) applying the negative electrode slurry to at least one surface of a current collector, and obtaining the negative electrode plate after drying;

[0067] In some embodiments, step (b) specifically comprises the steps of:

[0068] (b-1) Add the emulsion adhesive to the first mixture obtained in step (a), and add deionized water to adjust the mass fraction of the solid component to be within the range of 63-68% by weight to obtain an initial slurry; (b-2) kneading and stirring the initial slurry obtained in step (b-1); (b-3) adding deionized water to adjust the mass fraction of the solid component to 50-60% by weight to obtain a negative electrode slurry; Here, the steps (b-1), (b-2) and (b-3) are carried out in order.

[0069] In some embodiments, in step (a), the mass fraction of the negative electrode active material relative to the total solids of the negative electrode slurry is 90 to 98 wt %, the mass fraction of the conductive agent relative to the total solids of the negative electrode slurry is 0.5 to 2 wt %, the mass fraction of the additive relative to the total solids of the negative electrode slurry is 0.5 to 2 wt %, and optionally the mass ratio of the negative electrode active material, the conductive agent, and the additive is optionally 96:1:1.5.

[0070] In some embodiments, in step (b), the kneading time is 2 to 100 minutes, optionally 20 to 80 minutes, and the revolution speed is 20 to 200 rpm, optionally 50 to 150 rpm. Appropriate mechanical strength and kneading time not only ensure sufficient adhesion between the emulsion adhesive and the negative electrode active material, but also save energy.

[0071] In some embodiments, the emulsion adhesive may be pretreated using ultrasonic waves, sedimentation, centrifugation, kneading, or other conventional treatment methods, such as dilution. Alternatively, the emulsion adhesive may be pretreated using a combination of dilution and ultrasonic waves, or a combination of dilution and sedimentation.

[0072] In some embodiments, the ultrasonic operation is performed at a temperature of 30 to 70°C, optionally 40 to 60°C, with a power range of 30 to 60 kHz, optionally 35 to 50 kHz, and with an ultrasonic time of 10 to 50 minutes, optionally 20 to 40 minutes. Appropriate ultrasonic action can not only sufficiently destroy the micelle housing of the emulsion adhesive, but also further save energy.

[0073] In some embodiments, the precipitating agent used in the precipitating operation is selected from alcohols such as methyl alcohol, butanol, isopropanol, etc., or carbonates such as methyl ethyl carbonate (EMC), dimethyl carbonate, ethylene carbonate, diethyl carbonate, propylene carbonate, etc., and the ratio of the mass of the precipitating agent to the mass of the solid components of the emulsion adhesive is 2:98 to 10:90, optionally 4:96 to 6:94. By using an appropriate precipitating agent and controlling the mass ratio of the precipitating agent to the solid components of the emulsion adhesive, it is possible not only to sufficiently destroy the micelle housing of the emulsion adhesive, but also to further reduce costs.

[0074] In some embodiments, the diluent used in the dilution step is deionized water, and the solid content of the emulsion adhesive after dilution is 5 to 20 wt %, optionally 8 to 16 wt %, calculated based on the total weight of the diluted slurry. Dilution with deionized water disrupts the metastable balance between the surface emulsifier and the solvent in the emulsion adhesive, making it easier for the sedimentation, ultrasonic waves, and kneading to disrupt the micelle housing of the emulsion adhesive.

[0075] In some embodiments, the rotation speed in the centrifugation step is 2000 to 4000 rpm, optionally 2500 to 3500 rpm, and the duration is 5 to 20 minutes, optionally 7 to 15 minutes. By selecting an appropriate rotation speed and centrifugation time, not only can the micelle housing of the emulsion adhesive be sufficiently destroyed, but energy can also be saved.

[0076] In some embodiments, the additive may also include an adhesive that is different from the emulsion adhesive, and therefore, in the present disclosure, the emulsion adhesive is also referred to as the first adhesive and the adhesive is also referred to as the second adhesive.

[0077] Optionally, the mass ratio of the solid components of the emulsion adhesive (first adhesive) to the other adhesive (second adhesive) is 1:4 to 4:1, optionally 1:2 to 2:1, and optionally the other adhesive (second adhesive) is a non-emulsion adhesive, such as modified or unmodified polyamide, polyacrylic acid, sodium carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, or chitosan. Adding additives is advantageous for improving the stability of the slurry.

[0078] The secondary battery, battery module, battery pack, and power consumption device of the present application will be described below with appropriate reference to the drawings.

[0079] In one embodiment of the present application, a secondary battery is provided.

[0080] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During charging and discharging of the battery, active ions are repeatedly inserted and removed between the positive and negative electrodes. The electrolyte functions as ion conduction between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short-circuiting between the positive and negative electrodes and allows ions to pass through.

[0081] [Positive electrode plate] The positive electrode plate 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 includes the positive electrode active material of the first aspect of the present application.

[0082] For example, the positive electrode current collector has two surfaces that face each other in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on either one or both of the two facing surfaces of the positive electrode current collector.

[0083] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, 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 alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0084] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art and used in batteries. 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 positive electrode active materials in batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides 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 0.05Examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may be abbreviated 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.

[0085] In some embodiments, the positive electrode membrane layer optionally further includes an adhesive, which may include 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.

[0086] In some embodiments, the positive electrode film layer optionally further includes a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the positive electrode plate may be manufactured by the following method: The components for manufacturing the positive electrode plate, such as the positive electrode active material, conductive agent, adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then applied to a positive electrode current collector, and the positive electrode plate is obtained after processes such as drying and cold pressing.

[0088] [Electrolyte] The electrolyte functions to conduct ions between the positive and negative electrodes. The present application does not specifically limit the type of electrolyte, and it may be selected according to needs. For example, the electrolyte may be liquid, gel, or all-solid.

[0089] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0090] In some embodiments, the electrolyte salt can be at least one selected from 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.

[0091] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl 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, sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0092] In some embodiments, the electrolyte solution may further optionally contain additives. For example, the additives may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may further include additives that can improve some performance of the battery, 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.

[0093] [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 having good chemical stability and mechanical stability can be selected and used.

[0094] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0095] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0096] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0097] 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-type pouch. The pouch may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0098] 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. 6 shows an example of a secondary battery 5 with a rectangular structure.

[0099] In some embodiments, referring to FIG. 7 , 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 to seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 through 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 this can be selected by those skilled in the art according to specific actual needs.

[0100] 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 based on the application and capacity of the battery module.

[0101] Fig. 8 shows an example of a battery module 4. Referring to Fig. 8, in the battery module 4, the 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.

[0102] 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.

[0103] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0104] 9 and 10 show an example battery pack 1. Referring to FIGS. 9 and 10, 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 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.

[0105] 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.

[0106] The power consumption device can be selected from a secondary battery, a battery module, or a battery pack depending on its usage needs.

[0107] 11 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, which may employ a battery pack or a battery module to meet the high power and high energy density demands of secondary batteries.

[0108] Other exemplary devices may be mobile phones, tablet computers, laptop computers, etc. These devices generally require a thin design and may employ secondary batteries as their power source.

[0109] Example The following describes examples of the present application. The examples described below are illustrative and are intended only to interpret 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 in accordance with the specifications of techniques, conditions, or products described in literature in the field. If the manufacturer of the reagents or instruments used is not specified, they are all common commercially available products.

[0110] I. Manufacturing method Example 1 [Negative electrode plate] Step 1: Add graphite, superconducting carbon, and sodium carboxymethyl cellulose (CMC) in a weight ratio of 96:1:1.5 into a double planetary mixer equipped with a kneading double paddle, and stir for 15 minutes at a revolution speed of 20 rpm without starting rotation. After uniform mixing, a first mixture is obtained; Step 2: Add styrene butadiene rubber emulsion (SBR emulsion, solid content is 50% by weight) into the first mixture obtained in step 1 according to a mass ratio of SBR solid component to CMC of 1:1; Step 3: Add deionized water to the mixture containing SBR obtained in Step 2 to adjust the solid mass fraction of the slurry to 65% by weight (calculated based on the total weight of the slurry) to obtain an initial slurry; Step 4: The initial slurry obtained in Step 3 is mixed and stirred for 2 minutes at a revolution speed of 100 rpm without starting rotation. Step 5: Add deionized water to the slurry obtained in Step 4 to adjust the solid mass fraction of the slurry to 55 wt % (calculated based on the total weight of the slurry), and continue stirring for 90 minutes at an orbital speed of 20 rpm and a rotation speed of 1000 rpm to obtain a negative electrode slurry.

[0111] Step 6: The negative electrode slurry prepared above is mixed with 0.2 g / 1540.25 mm 2 The coating weight is then applied, dried, cold pressed, and slit to produce a negative electrode plate.

[0112] [Positive electrode plate] Positive electrode ternary material (NCM 811 ), superconducting carbon, and adhesive polyvinylidene fluoride (PVDF) are mixed uniformly in a weight ratio of 96:2.5:1.5, and then solvent N-methylpyrrolidone (NMP) is added to adjust the solid mass fraction to 75% by weight. After uniform stirring, a positive electrode slurry is obtained, which is then coated, dried, cold pressed, and slit to produce a positive electrode plate.

[0113] [Electrolyte] In an argon gas atmosphere, EC (ethylene carbonate) and EMC (methyl ethyl carbonate) are mixed according to a mass ratio of 3:7, and LiPF6 is added to form an electrolyte solution, in which the mass content of LiPF6 is 12.5%.

[0114] [Separator] Polypropylene Separator

[0115] [Secondary battery] A positive electrode plate, a separator, and a negative electrode plate are stacked in this order, with a separator positioned between the positive and negative plates to provide isolation. The stack is then wound into a rectangular bare cell, which is then packed into a case. The appropriate electrolyte is then injected, sealed, and the secondary battery is obtained after undergoing processes such as standing, hot and cold pressing, chemical formation, clamping, and classification.

[0116] Examples 2-8 The manufacturing methods of the negative electrode plates in Examples 2-8 and Example 1 are the same, except that the kneading and stirring time in step 4 is adjusted, and the specific values ​​are 5, 10, 20, 50, 60, 70, and 80 minutes, respectively.

[0117] Example 9 [Negative electrode plate] Step 1: Add graphite, superconducting carbon, and sodium carboxymethyl cellulose (CMC) in a mass ratio of 96:1:1.5 into a double planetary mixer equipped with a kneading double paddle, and stir for 15 minutes at a revolution speed of 20 rpm without turning on the rotation. After uniform mixing, a first mixture is obtained. Step 2: Add deionized water to the first mixture obtained in step 1 to adjust the solid mass fraction of the slurry to 65% by weight to obtain an initial slurry; Step 3: The initial slurry obtained in Step 2 is stirred for 30 minutes at a revolution speed of 20 rpm and a rotation speed of 200 rpm to obtain a mixture. Step 4: SBR emulsion pretreatment process (dilution + precipitation): add absolute ethanol to the SBR emulsion in advance to make the ratio of the mass of the added absolute ethanol to the mass of the SBR solid component 5:95, and then add deionized water to dilute it until the content of the SBR solid component reaches 15% by weight, at which point the pretreatment process is completed.Then, add the pretreated SBR emulsion into the mixture of Step 3, and add the amount of SBR emulsion so that the mass ratio of the SBR solid component to CMC in the mixing system is 1:1.

[0118] Step 5: Add deionized water to the mixture obtained in step 4 to adjust the solid mass fraction of the slurry to 55% by weight, and stir at an orbital speed of 20 rpm and a rotation speed of 1000 rpm for 60 minutes to obtain a negative electrode slurry.

[0119] Step 6: The negative electrode slurry prepared above was mixed with 0.2 g / 1540.25 mm 2 The coating is applied at a desired coating weight, then dried, cold pressed, and slit into a negative electrode plate.

[0120] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0121] Example 10 The manufacturing process of the negative electrode plate is similar to that in Example 9, except that the pretreatment process of the SBR emulsion in step 4 is changed to dilution + ultrasonic, in which the SBR emulsion is diluted with deionized water to a solid content of 10 wt%, and then ultrasonically treated at 40 kHz power and 50°C for 30 minutes.

[0122] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0123] Example 11 The manufacturing process of the negative electrode slurry is similar to that of Example 9, except that the pretreatment process of the SBR emulsion in step 4 is changed to centrifugation, and the SBR emulsion is centrifuged at 3000 rpm for 10 minutes.

[0124] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0125] Example 12 The manufacturing process of the negative electrode slurry is similar to that in Example 9, except that the pretreatment process of the SBR emulsion in step 4 is changed to precipitation, and methyl ethyl carbonate (EMC) is added into the SBR emulsion, where the ratio of the mass of the added EMC to the mass of the SBR solid component is 5:95.

[0126] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0127] Example 13 The manufacturing process of the negative electrode slurry is similar to that of Example 1, except that the SBR emulsion in step 2 is replaced with an ethylene propylene rubber emulsion, and the kneading and stirring time in step 4 is changed to 50 minutes.

[0128] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0129] Example 14 The manufacturing process of the negative electrode slurry is similar to that of Example 1, except that in step 2, the SBR emulsion is replaced with an acrylate emulsion, and the kneading and stirring time in step 4 is changed to 50 minutes.

[0130] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0131] Comparative Example 1 The manufacturing process of the negative electrode slurry is similar to that of Example 9, except that the pretreatment process for the emulsion in Step 4 is omitted, and the SBR emulsion is directly added to the mixture in Step 3, with the mass ratio of the SBR solid component to CMC being 1:1.

[0132] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0133] Comparative Example 2 The manufacturing process of the negative electrode slurry is similar to that of Example 9, except that the pretreatment process for the emulsion in Step 4 is omitted, and the ethylene propylene rubber emulsion is directly added to the mixture in Step 3, so that the mass ratio of the ethylene propylene rubber solid component to CMC is 1:1.

[0134] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0135] Comparative Example 3 The manufacturing process of the negative electrode slurry is similar to that in Example 9, except that the pretreatment process for the emulsion in Step 4 is omitted, and the acrylate emulsion is directly added to the mixture in Step 3, with the mass ratio of the acrylate solid component to CMC being 1:1.

[0136] The other manufacturing processes for the positive electrode plate, the electrolyte, the separator, and the secondary battery are the same as those in Example 1.

[0137] II. Test method for each parameter [Negative electrode plate parameter test] 1. Area A of the region where the emulsion adhesive exhibits an irregular film-like distribution, and area B of the region where the emulsion adhesive is distributed in the form of single particles or clusters of single particles Randomly select 20 different positions on the negative electrode plate of the present invention and perform SEM imaging (Sigma-02-33 scanning electron microscope, SEM, Zeiss, Germany) at the same magnification (10K or 20K) to obtain 20 SEM images. Using the area test tool attached to the SEM instrument, first calculate the total area of ​​the area where the emulsion adhesive exhibits an irregular film-like distribution in each image. Add up the total areas of the 20 images and divide the resulting value by 20 to obtain the average total area of ​​the irregular film-like distribution area, which is the total area A described in the present application. Similarly, the total area B of the area distributed in the form of single particles or clusters of single particles is simultaneously obtained.

[0138] 2. Adhesion test The negative electrode plates of each example and comparative example were cut into test samples measuring 100 mm in length and 10 mm in width. A 25 mm wide stainless steel plate was attached with double-sided tape (11 mm wide). The test sample was then attached to the stainless steel plate and rolled back and forth three times at a speed of 300 mm / min using a 2000 g press roll. One end of the test sample was then bent 180 degrees, and the negative electrode film layer and current collector of the test sample were manually peeled 25 mm along the longitudinal direction. The test sample was then fixed on a testing machine (e.g., an Instron 336). The peeling surface was aligned with the line of force of the testing machine (the pulling direction of the testing machine was kept parallel to the longitudinal direction of the electrode plate). The testing machine was then used to continuously peel at a speed of 30 mm / min to obtain a peel force curve. The peel force F0 corresponding to the stable portion of the peel force curve was taken, and the adhesive strength between the negative electrode film and current collector of the test sample (F = F0 / width of the test sample) (F is measured in N / m).

[0139] 3. Cohesion test The negative electrode plates of each example and comparative example were cut into test samples measuring 100 mm in length and 10 mm in width. A 25 mm wide stainless steel plate was attached with double-sided tape (11 mm wide). The test sample was then attached to the double-sided tape on the stainless steel plate, and the surface was rolled back and forth three times at a speed of 300 mm / min using a 2000 g press roll. Low-viscosity green glue was applied to the surface of the negative electrode film layer of the test sample (the adhesive strength of the low-viscosity green glue was 350 ± 20 g / 25 mm). One end of the test sample was then bent 180 degrees, and the negative electrode film layer and the green glue were manually peeled off 25 mm along the longitudinal direction. The test sample was then fixed on a testing machine (e.g., an Instron 336) and the peeling surface was aligned with the force line of the testing machine (the pulling direction of the testing machine was kept parallel to the longitudinal direction of the electrode plate). The testing machine was then used to continuously peel the negative electrode film layer and the green glue at a speed of 30 mm / min to obtain a peel force curve. The peel force N0 corresponding to the stable portion on the peel force curve is taken, and the adhesive force N between the negative electrode film and the current collector in the test sample is N=N0 / width of the test sample (unit of measurement of N: N / m).

[0140] 4. Testing x and d The test process of any d in this application is to select a negative electrode film layer on one side of a current collector, measure the thickness D of the negative electrode film layer, and use SAICAS (Surface and Interface Cutting Analysis System, Daipla Wintes Japan) to peel the negative electrode film layer corresponding to the predetermined depth D1 (i.e., the thickness of the peeled negative electrode film layer is D1) along the thickness direction of the negative electrode film layer from the surface of the negative electrode film layer to a predetermined depth D1, where d=D1 / D; The test process for any x in this application is to test the adhesive content X of the entire negative electrode film layer using pyrolysis-mass spectrometry (Shimadzu Py-GCMS QP-2020), and the adhesive content in the negative electrode film layer remaining after peeling off a negative electrode film layer with a thickness of D1 is Y1, where x = (X - Y1) / X. For SBR, the styrene fragment is the characteristic ion, the reserve time is 4.075 minutes, and the molecular weight is 104.

[0141] [Secondary battery performance test] 1. Battery cycle performance test At 45°C, the secondary batteries prepared in each example and comparative example were charged at a constant current of 0.5C to a charge cutoff voltage of 4.25V, then charged at a constant voltage of 0.05C or less. The battery capacity at this time was recorded as C0, and the battery was allowed to stand for 10 minutes. It was then discharged at a constant current of 0.5C to a discharge cutoff voltage of 2.8V, and allowed to stand for 10 minutes. This constitutes one charge-discharge cycle. According to this method, the batteries were subjected to 50 charge-discharge cycle tests, and the corresponding battery discharge capacity C at the end of the final cycle was recorded. The cycle capacity retention rate = C / C0 * 100%.

[0142] 2.Method of measuring state of charge (SOC) and DC internal resistance (DCR) At SOC: 25°C, the secondary batteries prepared in each example and comparative example were charged at a constant current of 0.5C up to a charge cut-off voltage of 4.25V, then charged at a constant voltage of 0.05C or less and allowed to stand for 10 minutes. Then, they were discharged at a constant current of 0.5C up to a discharge cut-off voltage of 2.8V and allowed to stand for 10 minutes. This constitutes one charge-discharge cycle.

[0143] Thereafter, at 25°C, the secondary batteries produced in each of the examples and comparative examples were charged at a constant current of 0.5C up to a charge cutoff voltage of 4.25V, and then charged at a constant voltage of 0.05C or less. The battery capacity at this time was recorded as 100% SOC. Thereafter, the battery was discharged at a constant current of 1C for 6 minutes at 25°C and allowed to stand for 1 hour. The capacity at this time was 90% SOC, and the voltage was recorded as U0. The battery was then discharged at a current of I at 5C for 10 seconds, and the voltage was recorded as U1. 90% SOC DCR = (U0 - U1) / I.

[0144] Follow the same method to test 1C depth of discharge is 50% and DCR is 20% SOC.

[0145] III. Performance Evaluation Distribution of adhesive on the surface of the negative electrode active material As can be seen from FIGS. 1 and 2, some of the adhesive in Example 1 exhibited an irregular film-like distribution on the negative electrode active material, which significantly increased the cohesive force between particles of the negative electrode active material and the adhesive force between the negative electrode film layer and the current collector. In contrast, the adhesive on the surface of the negative electrode active material in Comparative Example 1 was distributed only in the form of a single particle, resulting in poor adhesive and cohesive forces.

[0146] Performance test of negative electrode plate and secondary battery The negative electrode plates and secondary batteries manufactured in Examples 1-14 and Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Tables 1 and 2.

[0147] [Table 1] Note: The " / " in "Pretreatment method for emulsion adhesives" indicates that no pretreatment or mixing was performed, and the " / " in "A / (A+B)" indicates that an irregular film distribution has never been observed.

[0148] Comparing the results of Examples 1-5 and Comparative Example 1 in Table 1, it can be seen that kneading the emulsion-type adhesive SBR with superconducting carbon, graphite active material, and sodium carboxymethyl cellulose at 100 rpm changes the distribution morphology of the SBR on the surface of the graphite active material, and changes the ratio A of the total area of ​​the regions exhibiting irregular film-like distribution of the SBR to B of the total area of ​​the regions distributed in single particle or cluster form consisting of single particles. As the kneading time increases, A / (A+B) gradually improves, the adhesive strength and cohesive strength of the electrode plate increase, and the cycle retention rate at 50 cycles of the corresponding battery also increases.

[0149] As can be seen from the results of Examples 6-8, when the other conditions are kept the same and the kneading time is increased in the presence of SBR, the A / (A+B) ratio in the electrode plates is greater than 80:100, and the adhesive strength, cohesive strength, and cycle capacity retention rate at 50 cycles of the produced batteries all remain at relatively high levels.

[0150] As can be seen from Examples 9-12, by adopting other pretreatment methods for emulsion adhesives, such as sedimentation, ultrasonic, centrifugation, or dilution for SBR emulsion, the stability of emulsion particles in emulsion-type SBR can be reduced, and a relatively large ratio of A / (A+B) can be obtained, which improves the adhesive strength and cohesive strength of the produced electrode plate, and also improves the 50-cycle cycle capacity retention rate of the battery produced using this electrode plate.

[0151] As can be seen from the comparison of the results of Examples 13 and 14 with Comparative Examples 2 and 3, by using other emulsion-type adhesives (e.g., ethylene propylene rubber, polyacrylate emulsion) as adhesives and using the manufacturing method of the present invention, it is possible to improve the adhesive strength and cohesive strength of the electrode plates and the cycle capacity retention rate of the manufactured batteries after 50 cycles.

[0152] Determination of mass content of emulsion adhesives

[0153] [Table 2]

[0154] As can be seen from the results in Table 2, with the increase in the kneading time, the maximum value of x / d gradually decreases, the difference in mass content of SBR between the upper and lower half layers of the negative electrode film layer gradually decreases, and the SBR distribution in the negative electrode film layer tends to become more uniform, which inhibits the adhesive from lifting up and strengthens the adhesive strength and cohesive strength of the produced electrode plate, thereby improving the 50-cycle cycle capacity retention rate of the battery produced using this electrode plate.

[0155] Test results for DC internal resistance (DCR) of secondary batteries The secondary batteries manufactured in Comparative Example 1 and Example 5 were measured for state of charge (SOC) and direct current internal resistance (DCR) using the above-described measurement method, and the results are shown in Figure 5. As shown in the figure, the secondary battery of Example 5 of the present invention has a lower direct current internal resistance than that of Comparative Example 1 at the same SOC. This is because in the present invention, the emulsion adhesive is more uniformly distributed in the electrode plate membrane layer, reducing the degree of emulsion adhesive aggregation in the upper layer, thereby reducing lithium ion transition inhibition due to SBR aggregation in the upper layer, thereby improving the direct current internal resistance (DCR) of the manufactured electrochemical device (Example 5 and Comparative Example 1).

[0156] 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. In addition, various modifications that a person skilled in the art can make to the embodiments without departing from the spirit of the present application, and other methods constructed by combining some of the components of the embodiments, are also included within the scope of the present application. [Explanation of symbols]

[0157] 1 battery pack 2 Upper housing 3 Lower housing 4 Battery Module 5 Secondary battery 51 cases 52 Electrode Assembly 53 Cover plate

Claims

1. A method for manufacturing a secondary battery, a negative electrode plate manufacturing step of manufacturing a negative electrode plate; a positive electrode plate manufacturing step of manufacturing a positive electrode plate; an electrolyte preparation step; a secondary battery fabrication step of stacking the negative electrode plate, a separator, and the positive electrode plate in this order to form a cell, and then injecting an electrolyte solution to fabricate a secondary battery; Including, The negative electrode plate manufacturing step includes: an adhesive pretreatment step in which the emulsion-type adhesive is pretreated by at least one operation selected from the group consisting of a kneading operation, a dilution and sedimentation operation, a dilution and ultrasonic operation, a centrifugation operation, and a sedimentation operation; a first mixture preparation step of mixing a negative electrode active material, a conductive agent, and an additive in a predetermined ratio to obtain a first mixture; a negative electrode slurry preparation step of mixing the pretreated emulsion adhesive, the first mixture, and a diluent to obtain a negative electrode slurry; a negative electrode plate forming step of applying the negative electrode slurry to at least one surface of a current collector and obtaining the negative electrode plate after drying; Including, A method for manufacturing a secondary battery comprising the steps of:

2. the kneading operation is an operation of treating the emulsion adhesive under conditions of a predetermined revolution speed, a predetermined kneading time, and no rotation, The dilution and sedimentation operation is an operation of adding a sedimentation agent to the emulsion adhesive, adjusting the ratio of the mass of the sedimentation agent to the mass of the solid components of the emulsion adhesive to a predetermined ratio, and then adding a diluent to dilute the emulsion adhesive, The dilution ultrasonic treatment is a treatment in which a diluent is added to the emulsion adhesive and ultrasonic treatment is carried out under conditions of a predetermined power, a predetermined temperature and a predetermined time, the centrifugal operation is an operation of subjecting the emulsion adhesive to a centrifugal treatment under conditions of a predetermined rotation speed and a predetermined time, The sedimentation operation is an operation in which a sedimentation agent is added to the emulsion adhesive, the ratio of the mass of the sedimentation agent to the mass of the solid components of the emulsion adhesive is set to a predetermined ratio, and sedimentation is carried out. The method for manufacturing a secondary battery according to claim 1 .

3. 3. The method for manufacturing a secondary battery according to claim 2, wherein in the negative electrode slurry preparation step, the emulsion-type adhesive, the first mixture, and deionized water are mixed by kneading and stirring to obtain the negative electrode slurry.

4. The negative electrode slurry preparation step includes: an initial slurry preparation step of adding the pretreated emulsion adhesive to the first mixture and then adding a diluent to adjust the mass fraction of the solid component to 63 to 68 wt % to obtain an initial slurry; a kneading and stirring step of kneading and stirring the initial slurry obtained in the initial slurry preparation step; a negative electrode slurry formation step of adding a diluent to the kneaded and stirred slurry to adjust the mass fraction of the solid component to 50 to 60 wt % to obtain a negative electrode slurry; Including, 4. The method for manufacturing a secondary battery according to claim 3.

5. the mass fraction of the negative electrode active material relative to the total solids of the negative electrode slurry is 90 to 98 wt %, the mass fraction of the conductive agent relative to the total solids of the negative electrode slurry is 0.5 to 2 wt %; 3. The method for producing a secondary battery according to claim 2, wherein a mass fraction of the additive to the total solids of the negative electrode slurry is 0.5 to 2% by weight.

6. 5. The method for producing a secondary battery according to claim 4, wherein the kneading time is 2 to 100 minutes and the revolution speed is 20 to 200 rpm in the kneading and stirring.

7. 3. The method for producing a secondary battery according to claim 2, wherein in the kneading operation, the revolution speed is 100 rpm and the kneading time is 2 minutes.

8. 3. The method for manufacturing a secondary battery according to claim 2, wherein in the dilution and sedimentation operation, the ratio of the mass of the sedimentation agent to the mass of the solid components of the emulsion-type adhesive is set to 5:95, and a diluent is added to dilute the emulsion-type adhesive until the content of the solid components becomes 15% by weight.

9. 3. The method for producing a secondary battery according to claim 2, wherein in the dilution ultrasonic operation, the predetermined power is 30 to 60 kHz, the predetermined temperature is 30 to 70° C., and the predetermined time is 10 to 50 minutes.

10. 3. The method for producing a secondary battery according to claim 2, wherein in the centrifugation step, the predetermined rotation speed is 2000 to 4000 rpm, and the predetermined time is 5 to 20 minutes.

11. 11. The method for manufacturing a secondary battery according to claim 2, wherein the precipitating agent is selected from alcohols.

12. 11. The method for manufacturing a secondary battery according to claim 1, wherein the diluent is deionized water.

13. 11. The method for manufacturing a secondary battery according to claim 1, wherein the additive includes another adhesive different from the emulsion-type adhesive.

14. 14. The method for manufacturing a secondary battery according to claim 13, wherein a mass ratio of the solid component of the emulsion adhesive to the other adhesive is 1:4 to 4:1.

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