Dry electrode film, method of manufacturing the same, and secondary battery

Abstract

The application belongs to the technical field of batteries, and particularly relates to a dry-method electrode film, a preparation method thereof and a secondary battery. The preparation method of the dry-method electrode film comprises the following steps: mixing an electrode active material, a conductive agent and a binder by a dry method and performing fiberization treatment to obtain a fiberized mixture; performing tabletting treatment on the fiberized mixture to obtain an initial film tablet; performing crushing treatment on the initial film tablet to obtain a crushed mixture; and performing compression molding on the crushed mixture to obtain the dry-method electrode film. In the preparation method of the dry-method electrode film, tabletting treatment is performed on the fiberized mixture, and subsequent crushing treatment is performed, so that the particle agglomeration phenomenon is reduced, and the production quality of the electrode film is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a dry electrode film, its preparation method, and a secondary battery. Background Technology

[0002] Dry electrode forming technology has become an important development direction in electrode preparation technology due to its advantages of being solvent-free, environmentally friendly, and highly efficient. However, due to the severe particle agglomeration and insufficient interparticle forces of fibrous cathode powders (such as fibrous lithium iron phosphate and fibrous ternary cathode materials), direct application of dry forming technology can easily lead to problems such as poor formability, low electrode sheet density, and insufficient strength, which further restricts the industrial application of dry electrodes.

[0003] To address the aforementioned issues, existing technologies have disclosed numerous pretreatment methods. However, current pretreatment methods primarily focus on chemical modification or simple mechanical dispersion, making it difficult to simultaneously and effectively address the agglomeration phenomenon, forces, and pore structure of powders, resulting in poor dry molding performance.

[0004] Therefore, how to significantly improve the dispersion uniformity and interparticle forces of dry electrode powder and improve the production quality of dry electrode film is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a dry-process electrode membrane, its preparation method, and a secondary battery. In the dry-process electrode membrane preparation method provided by the present invention, after the mixed material is fiberized, it undergoes sequential pressing and subsequent pulverization, thereby reducing particle agglomeration and improving the production quality of the electrode membrane.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a dry electrode film, the method comprising the following steps: Electrode active material, conductive agent and binder are dry-mixed and then subjected to fibrosis treatment to obtain fibrous mixture; The fibrous mixture is compressed into tablets to obtain initial films; The initial membrane was pulverized to obtain a pulverized mixture; The pulverized mixture is pressed into shape to obtain a dry electrode film.

[0007] In one embodiment, the fibrous mixture is subjected to tableting treatment, which includes: rolling the fibrous mixture through one or more sets of pressing rollers to obtain an initial film.

[0008] In one embodiment, each set of pressing rollers includes a first sub-roller and a second sub-roller arranged parallel to a preset roll gap, and the differential speed ratio between the first sub-roller and the second sub-roller is 1:(1.1~10).

[0009] In one embodiment, the preset roll gap is 300μm~5mm.

[0010] In one embodiment, the fibrous mixture is subjected to roll pressing treatment by multiple sets of pressing rollers, including: rolling the fibrous mixture with increasing and then decreasing pressure along the conveying direction; wherein the conveying direction is the same as the conveying direction of the initial film.

[0011] In one embodiment, the fibrous mixture is subjected to a temperature roll pressing process along the conveying direction, with the temperature first increasing and then decreasing.

[0012] In one embodiment, the pressure of each group of pressing rollers for roller pressing is 5MPa~20MPa, the temperature is 25℃~200℃, and the transmission speed is 1m / min~60m / min.

[0013] In one embodiment, the distance between two adjacent sets of pressing rollers increases sequentially along the conveying direction.

[0014] In one embodiment, along the conveying direction, the tension between two adjacent sets of pressing rollers increases sequentially.

[0015] In one embodiment, the fibrous mixture is processed by pressing with pressure rollers that first increase and then decrease along the conveying direction, including: pressing the fibrous mixture with pressure rollers that increase sequentially along the conveying direction to obtain a first film, and pressing the first film with pressure rollers that decrease sequentially along the conveying direction to obtain an initial film.

[0016] In one embodiment, the maximum pressure in the successively increasing pressure is greater than the maximum pressure in the successively decreasing pressure; and the thickness of the first diaphragm is 1 mm to 1.5 mm, and the thickness of the initial diaphragm is 300 μm to 1 mm.

[0017] In one embodiment, the process of pressing the fibrous mixture with pressure rollers that first increase and then decrease along the conveying direction further includes: heating the fibrous mixture with a gradually increasing temperature along the conveying direction by a portion of the pressing roller group to obtain a first film; and heating the first film with a gradually decreasing temperature along the conveying direction by the remaining portion of the pressing roller group.

[0018] In one embodiment, the highest temperature in the successively increasing temperatures is higher than the highest temperature in the successively decreasing temperatures.

[0019] In one embodiment, the electrode active material, conductive agent, and binder are dry-mixed and then fibrous to obtain a fibrous mixture, comprising: The electrode active material and the conductive agent are dry-mixed in a first ratio to obtain a first dry mixture; The first dry mixture and the fiberized binder are dry-mixed in a second ratio to obtain a fiberized mixture.

[0020] In one embodiment, the D of the pulverized mixture v The particle size of 50 particles ranges from 5μm to 20μm.

[0021] Secondly, the present invention provides a dry electrode membrane, which is prepared by the method for preparing the dry electrode membrane provided in the first aspect.

[0022] Thirdly, the present invention provides a secondary battery, which includes an electrode sheet and an electrolyte, wherein the electrode sheet includes the dry electrode membrane provided in the second aspect.

[0023] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a dry electrode film. The method involves sequentially pressing and pulverizing a fibrous mixture obtained by fiberizing a dry mixture to form a film. The pressing process reorients the three-dimensionally agglomerated particles in the fibrous mixture, exposing them fully to the two-dimensional film surface of the initial film. Pulverizing the initial film obtained by pressing effectively disperses the agglomerated particles within the two-dimensional film surface, thus achieving a thorough dispersion of the agglomerated particles. Therefore, the resulting pulverized mixture has uniformly dispersed particles, reducing particle agglomeration, optimizing the binding force between particles, and improving the forming effect of the dry electrode film. Attached Figure Description

[0024] Figure 1 This is an X-ray image of the dry cathode film prepared in Example 1.

[0025] Figure 2 This is an X-ray image of the dry cathode film prepared in Example 3.

[0026] Figure 3 This is an X-ray image of the dry cathode film prepared in Comparative Example 1. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to specific embodiments and accompanying drawings. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0028] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0029] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0030] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0031] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0032] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0033] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0034] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0035] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0036] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0037] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0038] This invention relates to a method for preparing dry electrode films. In the prior art, the preparation of dry electrode films typically involves directly pulverizing a dry mixture after fiberization, followed by pressing and molding to obtain the dry electrode film. However, the above preparation method has the following two problems: Firstly, due to the increased binding force of the binder after fiberization, agglomeration is easily caused. During the pulverization process, the agglomerated particles tend to adhere to the blades of the pulverizer, hindering the dispersion of agglomerated particles and resulting in poor dispersion. Excessive pulverization shear force can also cause the binder fibers to break, leading to binder failure and preventing the electrode sheet from being formed. Secondly, this pulverization method directly pulverizes the dry powder in a three-dimensional bulk phase. Even if it has a certain dispersing effect on large agglomerates, the buffering effect of external particles on the pulverization shear force makes it difficult to effectively disperse particles within the agglomerates and small agglomerates encapsulated within the powder, thus the dispersion effect is not ideal.

[0039] Based on this, in a first aspect, the present invention provides a method for preparing a dry electrode film, the method comprising the following steps: Electrode active material, conductive agent and binder are dry-mixed and then fiberized to obtain a fiberized mixture. The fibrous mixture is compressed into tablets to obtain initial films; The initial membrane was pulverized to obtain a pulverized mixture; The pulverized mixture is pressed into shape to obtain a dry electrode film.

[0040] It is understood that the dry mixing method of this invention refers to the absence of any additional liquid reagents besides the raw materials mentioned. Furthermore, this invention does not provide detailed limitations on the specific dry mixing and fiberization processes. Any known details of specific dry mixing and fiberization processes are applicable without departing from the overall technical concept of this invention; for example, conventional mechanical dry mixing methods can be used for dry mixing.

[0041] This invention provides a method for preparing a dry electrode membrane. By sequentially pressing and pulverizing a fibrous mixture, the resulting powder has advantages such as small particle size, good particle size uniformity, increased degree of fibrosis, and strong adhesion. The resulting dry electrode membrane has good dispersibility, low agglomeration, and high compaction density, thereby improving the energy density and cycle stability of the secondary battery.

[0042] Compared with the preparation methods of the prior art, in the technical solution of the present invention, in the early stage of tableting, large agglomerates are reoriented and effectively dispersed under the action of strong roller shearing force. After being pressed into thin sheets, the three-dimensional bulk dry powder can be transformed into a two-dimensional film surface. Even if there are fine particle agglomerates, they can be clearly exposed on the surface of the film layer, which makes it easy to directly disperse them during the crushing process, thereby further improving the dispersion effect.

[0043] In some embodiments, the fibrous mixture is subjected to tableting, which includes: rolling the fibrous mixture through one or more sets of pressing rollers to obtain an initial film.

[0044] In some embodiments, each set of pressing rollers includes a first sub-roller and a second sub-roller arranged parallel to a preset roll gap. The differential speed ratio between the first sub-roller and the second sub-roller is 1:(1.1~10), for example, it can be 1:1.1, 1:1.2, 1:1.5, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] This invention further enhances the shearing action by adjusting the differential speed ratio between the first and second sub-rollers to a reasonable range, thereby further reducing particle porosity and agglomeration.

[0046] In some implementations, the preset roller gap is 300μm to 5mm, for example, it can be 300μm, 500μm, 1mm, 2mm, 3mm, 4mm or 5mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, thereby enabling better control of pressure changes during the tableting process.

[0047] In some embodiments, the fibrous mixture is rolled through multiple sets of pressing rollers, including: rolling the fibrous mixture with increasing and then decreasing pressure along the conveying direction; wherein the conveying direction is the same as the conveying direction of the initial film.

[0048] This invention employs multiple sets of pressing rollers for roller pressing and further regulates the pressure change trend during the roller pressing process. When the roller pressing pressure increases, the particle dispersion effect can be improved. When a certain thickness (1mm~1.5mm) is reached, the pressure decreases to avoid excessive pressure from damaging the surface active particles.

[0049] In some embodiments, the fibrous mixture is rolled along the conveying direction with a temperature that increases first and then decreases.

[0050] This invention employs multiple sets of pressing rollers for roller pressing and further controls the temperature change trend during the roller pressing process. By first hot pressing the fibrous mixture to release internal stress, and then cold pressing to solidify the overall structure, cohesion is avoided.

[0051] In some embodiments, the pressure of each group of pressing rollers for roller pressing is 5MPa~20MPa, the temperature is 25℃~200℃, and the transmission speed is 1m / min~60m / min.

[0052] Specifically, the pressure of the rolling process can be, for example, 5MPa, 5MPa, 5MPa, 5MPa, 5MPa, or 20MPa, the temperature can be, for example, 25℃, 50℃, 80℃, 100℃, 120℃, 150℃, 180℃, or 200℃, and the conveying speed can be, for example, 1m / min, 5m / min, 10m / min, 20m / min, 30m / min, 40m / min, 50m / min, or 60m / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] In some implementations, the distance between adjacent sets of pressing rollers increases sequentially along the conveying direction.

[0054] In some implementations, the tension between adjacent sets of pressing rollers increases sequentially along the conveying direction.

[0055] In some embodiments, the fibrous mixture is processed by pressing with pressure rollers that increase in pressure and then decrease in pressure along the conveying direction, including: pressing the fibrous mixture with a portion of the pressing roller group with pressure rollers that increase in pressure in sequence along the conveying direction to obtain a first film, and pressing the first film with a remaining portion of the pressing roller group with pressure rollers that decrease in pressure in sequence along the conveying direction to obtain an initial film.

[0056] In some embodiments, the maximum pressure in the successively increasing pressure is greater than the maximum pressure in the successively decreasing pressure; and the thickness of the first diaphragm is 1 mm to 1.5 mm, and the thickness of the initial diaphragm is 300 μm to 1 mm.

[0057] Specifically, the thickness of the first membrane can be, for example, 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, or 1.5 mm, and the thickness of the initial membrane can be, for example, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or 1 mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] In some embodiments, the process of pressing the fibrous mixture with pressure rollers that first increase and then decrease along the conveying direction further includes: heating the fibrous mixture with a gradually increasing temperature along the conveying direction by a portion of the pressing roller group to obtain a first film; and heating the first film with a gradually decreasing temperature along the conveying direction by the remaining portion of the pressing roller group.

[0059] In some implementations, the highest temperature in the series of increasing temperatures is higher than the highest temperature in the series of decreasing temperatures.

[0060] In some embodiments, the electrode active material, conductive agent and binder are dry-mixed and fiberized to obtain a fiberized mixture, including: dry-mixing the electrode active material and conductive agent in a first ratio to obtain a first dry mixture; and dry-mixing the first dry mixture with the fiberized binder in a second ratio to obtain a fiberized mixture.

[0061] In some embodiments, the electrode active material includes a positive electrode active material.

[0062] In some embodiments, the positive electrode active material includes compounds capable of reversibly inserting and deintercalating lithium ions.

[0063] In some embodiments, the positive electrode active material comprises one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), or vanadium (V) and combinations thereof.

[0064] In some embodiments, the positive electrode active material is one of layered oxides, spinel, and polyanionic materials. For example, layered oxides (e.g., rock salt layered oxides) comprise one or more lithium-based positive electrode active materials selected from: LiCoO2 (LCO), LiNi x Mn y Co 1xy O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1xy Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1x O2 (where 0 ≤ x ≤ 1) or Li 1+xMO2 (where M is one of Mn, Ni, Co, or Al, 0 ≤ x ≤ 1). Spinel contains one or more lithium-based cathode active materials selected from LiMn2O4 (LMO) and LiNi. x Mn 1.5 O4. The olivine type contains one or more lithium-based positive electrode active materials, LiMPO4 (where M is at least one of Fe, Ni, Co, or Mn). The polyanionic cation contains, for example, phosphates such as LiV2(PO4). 24 And / or silicates such as LiFeSiO4.

[0065] The binder enhances the bonding between the positive electrode active material particles and the conductive agent particles.

[0066] The binder includes a fiberizable binder, which achieves bonding of the positive electrode active material and the conductive agent by transforming from particulate to fibrous form under high shear stress.

[0067] In some embodiments, the fiberizable binder includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polypropylene, polyethylene, or polyimide.

[0068] In some embodiments, to further enhance the adhesion of the binder to the positive electrode, the binder may further include at least one of the following: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0069] Conductive agents impart conductivity to electrodes. Conductive agents can include any conductive material, as long as it does not cause a chemical change.

[0070] The present invention does not limit the type of conductive agent. Exemplarily, the conductive agent includes any one or a combination of at least two of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. These are all common conductive agents in the art and are merely examples, not limitations.

[0071] In some embodiments, the mass ratio of electrode active material to conductive agent in the fibrous mixture is (80~98):(0.1~10), more preferably (90~93):(3~6), for example, it can be 80:10, 85:8, 90:5, 95:3 or 98:0.1, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0072] In some embodiments, the mass ratio of electrode active material to binder in the fibrous mixture is (80~98):(0.1~10), preferably (85~96):(1.5~5), more preferably (90~93):(2.5~4), for example, it can be 80:10, 85:5, 90:4, 93:2.5, 96:1.5 or 98:0.1, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0073] In some embodiments, the D of the pulverized mixture v The particle size is 5μm to 20μm, for example, it can be 5μm, 8μm, 10μm, 12μm, 15μm, 18μm or 20μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] In some implementations, the pulverization method includes mechanical pulverization and / or air jet pulverization.

[0075] In some implementations, compression molding methods include die pressing and / or roll pressing.

[0076] Secondly, the present invention provides a dry electrode membrane, which is prepared by the method for preparing the dry electrode membrane provided in the first aspect.

[0077] Thirdly, the present invention provides a secondary battery, which includes an electrode sheet and an electrolyte, wherein the electrode sheet includes the dry electrode membrane provided in the second aspect.

[0078] In some embodiments, the dry electrode film includes a dry positive electrode film.

[0079] In some embodiments, the dry cathode membrane further includes a cathode current collector, on which at least one side surface is coated with the dry cathode membrane.

[0080] In some embodiments, the positive current collector includes a metallic material that can conduct electrons; for example, the positive current collector includes at least one of aluminum, nickel, tin, copper, or stainless steel.

[0081] In some embodiments, the positive current collector can be made of high-purity aluminum foil or aluminum alloy foil with a purity of not less than 99.6% and a thickness of 10μm to 20μm (e.g., 10μm, 13μm, 15μm, 18μm or 20μm, etc.).

[0082] In some embodiments, the surface of the aluminum foil may be anodized to form a nanoscale aluminum oxide layer, thereby enhancing its corrosion resistance and interfacial bonding with the cathode material.

[0083] In some embodiments, the aluminum alloy foil may contain trace amounts of titanium (Ti) or (Si) to enhance mechanical strength and high-temperature stability.

[0084] In some embodiments, the aluminum foil may also be a carbon-coated aluminum foil.

[0085] In some embodiments, the composite method in this invention is roll forming.

[0086] The electrode sheet in the secondary battery having the dry electrode film of the present invention has a dense structure, strong adhesion and high mechanical strength, so the energy density and cycle life of the secondary battery are significantly improved.

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0088] Example 1 This embodiment provides a dry-process positive electrode film and its preparation method. The preparation method of the dry-process positive electrode film includes the following steps: S1, the positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2, NCM811), acetylene black conductive agent and polyvinylidene fluoride (PVDF) binder are dry-mixed in a mixer at a mass ratio of 80:10:10 to obtain a mixture.

[0089] S2. The mixture is subjected to fiberization treatment in a high-speed shearing machine to obtain a fiberized mixture.

[0090] S3. The fibrous mixture is added to the pressing roller for rolling to obtain an initial film with a thickness of 320 μm; the rolling conditions are shown in Table 1.

[0091] S4. The initial membrane sheet is added to a pulverizer for pulverization to obtain D. v 50 particles of material with a diameter of 12μm were crushed and then rolled into shape using a roller pressing device to obtain a dry cathode membrane.

[0092] This embodiment also provides a positive electrode sheet, which includes an aluminum foil and the aforementioned dry-process positive electrode film laminated on both sides of the aluminum foil.

[0093] Example 2 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (LiNi) is used. 0.8 Co 0.1 Mn 0.1 O2, NCM811) were replaced with an equal mass of lithium iron phosphate, and the D of the material obtained after the initial membrane was crushed was... vThe particle size of 50 particles was 17 μm, and everything else was the same as in Example 1.

[0094] Example 3 The dry electrode films of Examples 3 to 10 are prepared in a similar manner to those of Example 1, except that the rolling conditions for forming the initial film are different, as detailed in Table 1.

[0095] Comparative Example 1 The difference between this comparative example and Example 1 is that step S3 is omitted, and the fibrous mixture obtained in step S2 is directly processed in step S4. Everything else is the same as in Example 1.

[0096] Comparative Example 2 The difference between this comparative example and Comparative Example 1 is that the positive electrode active material (LiNi) is used. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was replaced with an equal mass of lithium iron phosphate, and everything else was the same as in Comparative Example 1.

[0097] Test conditions The morphology of the dry cathode films provided in the above embodiments and comparative examples was tested using a microfocus X-ray inspection device. The test results are shown in Table 1 below. Table 1 In Table 1 above, there are multiple roller groups. The roller pressure and roller temperature are the pressure and temperature of each roller group set along the transmission direction. Each roller group adopts the same differential speed ratio. The roller gap of each roller group decreases sequentially along the transmission direction. Table 1 only shows the roller gap of the last roller group.

[0098] As can be seen from Table 1, according to Examples 1 and 2 and Comparative Examples 1 and 2, the agglomeration problem of the positive electrode sheet is significantly improved by first rolling it to form a primary film and then crushing it. According to Examples 1, 3, 4 and 5, as the number of rolling cycles increases, the continuity and uniformity of the primary film formation gradually improve, and the particle agglomeration problem is further improved. In Example 3, the rolling pressure and temperature first gradually increase and then gradually decrease, and the improvement effect on particle agglomeration is the most significant.

[0099] Please refer to Figures 1-3 ,from Figure 1 and Figure 3 The comparison also shows that the dry cathode film obtained by the preparation method provided by this invention has better dispersion effect and the agglomeration problem is significantly improved. Figure 1 and Figure 2 It can be seen that the preparation method in Example 3 significantly improves the agglomeration problem.

[0100] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a dry electrode film, characterized in that, The method for preparing the dry electrode film includes the following steps: The electrode active material, conductive agent and binder are dry-mixed and then fiberized to obtain a fiberized mixture. The fibrous mixture is compressed into tablets to obtain an initial film; The initial membrane was pulverized to obtain a pulverized mixture; The pulverized mixture is pressed into shape to obtain the dry electrode film.

2. The method for preparing the dry electrode film according to claim 1, characterized in that, The step of compressing the fibrous mixture into tablets includes: passing the fibrous mixture through one or more sets of pressing rollers to obtain the initial film; Each of the pressing roller groups includes a first sub-roller and a second sub-roller arranged parallel to a preset roll gap, and the differential speed ratio between the first sub-roller and the second sub-roller is 1:(1.1~10). Preferably, the preset roll gap is 300μm~5mm.

3. The method for preparing the dry electrode film according to claim 2, characterized in that, The step of rolling the fibrous mixture through multiple sets of pressing rollers includes: rolling the fibrous mixture along the conveying direction with a pressure that first increases and then decreases; wherein the conveying direction is the same as the conveying direction of the initial film; Preferably, the fibrous mixture is subjected to roller pressing treatment along the conveying direction with a temperature that first increases and then decreases; Preferably, the pressure of each group of pressing rollers for the roller pressing process is 5MPa~20MPa, the temperature is 25℃~200℃, and the transmission speed is 1m / min~60m / min.

4. The method for preparing the dry electrode film according to claim 3, characterized in that, Along the conveying direction, the distance between two adjacent sets of pressing rollers increases sequentially; Preferably, along the conveying direction, the tension between two adjacent sets of pressing rollers increases sequentially.

5. The method for preparing the dry electrode film according to claim 3, characterized in that, The process of pressing the fibrous mixture with pressure rollers that first increase and then decrease along the conveying direction includes: a portion of the pressing roller group pressing the fibrous mixture with pressure rollers that increase sequentially along the conveying direction to obtain a first film; and the remaining portion of the pressing roller group pressing the first film with pressure rollers that decrease sequentially along the conveying direction to obtain the initial film. Wherein, the maximum pressure in the successively increasing pressure is greater than the maximum pressure in the successively decreasing pressure; and, the thickness of the first diaphragm is 1mm~1.5mm, and the thickness of the initial diaphragm is 300μm~1mm.

6. The method for preparing a dry electrode film according to claim 5, characterized in that, The process of pressing the fibrous mixture with pressure rollers that first increase and then decrease along the conveying direction further includes: a portion of the pressing roller group heating the fibrous mixture with a temperature that increases sequentially along the conveying direction to obtain the first film; and the remaining portion of the pressing roller group heating the first film with a temperature that decreases sequentially along the conveying direction. The highest temperature among the successively increasing temperatures is higher than the highest temperature among the successively decreasing temperatures.

7. The method for preparing a dry electrode film according to claim 1, characterized in that, The process of dry mixing and fiberizing the electrode active material, conductive agent, and binder to obtain a fiberized mixture includes: The electrode active material and the conductive agent are dry-mixed in a first ratio to obtain a first dry mixture; The first dry mixture is dry-mixed with the fiberized binder in a second ratio to obtain the fiberized mixture.

8. The method for preparing a dry electrode film according to claim 1, characterized in that, The D of the pulverized mixture v The particle size of 50 particles ranges from 5μm to 20μm.

9. A dry electrode film, characterized in that, The dry electrode film is prepared by the method of any one of claims 1 to 8.

10. A secondary battery, characterized in that, The secondary battery includes electrode sheets and an electrolyte, wherein the electrode sheets include the dry electrode film as described in claim 9.

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