Pole piece and manufacturing method thereof, rolling system and secondary battery

Abstract

The invention provides a pole piece and a manufacturing method thereof, a rolling system and a secondary battery, and the manufacturing method of the pole piece comprises the following steps: coating slurry on a current collector and drying to obtain a dried pole piece; the difference between the thickness of the dried pole piece and the preset thickness after rolling is used as the total rolling reduction; the dried pole piece is subjected to continuous multi-stage rolling, adjacent two-stage rolling is carried out, the percentage of the rolling reduction of the previous-stage rolling in the total rolling reduction is larger than or equal to the percentage of the rolling reduction of the next-stage rolling in the total rolling reduction, and the sum of the rolling reduction of all stages of rolling is equal to the total rolling reduction; in the multi-stage rolling, the rolling reduction of each stage of rolling is gradually reduced on the whole; and the multi-stage rolling is cold pressing. According to the manufacturing method of the pole piece, the multi-stage rolling mode is adopted, the rolling reduction decreasing and roller gap adjusting mode is adopted, the diameter, roughness and hardness of the roller body are combined to adapt to different rolling reduction, and finally the consistency of stress release and the pole piece is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a pole piece, a manufacturing method thereof, a rolling system and application. BACKGROUND

[0002] In the design and production of batteries, the adhesion strength between the active material and the foil can be enhanced after the pole piece is rolled, and the porosity between the active material, the conductive agent and the binder in the pole piece can be reduced, and the resistance of the pole piece can be reduced, and finally the performance of the battery can be improved. However, the mechanical rebound and the thickness fluctuation in the width direction of the pole piece after rolling cannot be precisely controlled by the current rolling technology, and the multi-stage rolling technology has the risk of residual stress accumulation, and processes such as hot rolling can easily cause local enrichment of the binder, which can aggravate the porosity and ion transmission polarization. In addition, the actual roll gap of the current rolling process deviates from the set value (on the one hand, the objective conditions of the roll deformation determine it, and on the other hand, the rebound caused by the movement of the pole piece outlet end face to the laser thickness measuring instrument causes the error), which finally leads to the hysteresis of the control and the overpressure. SUMMARY

[0003] Therefore, one purpose of the present application is to provide a manufacturing method of a pole piece, which adopts a multi-stage continuous rolling and a whole decreasing reduction method, reduces the reduction of the end roller to release the stress, reduces the mechanical rebound rate of the pole piece, and improves the consistency of the pole piece.

[0004] Another purpose of the present application is to provide a rolling system.

[0005] Still another purpose of the present application is to provide a pole piece.

[0006] Still another purpose of the present application is to provide a secondary battery.

[0007] To achieve the above purpose, the first aspect of the present application provides a manufacturing method of a pole piece, comprising:

[0008] coating a slurry on the current collector and drying to obtain a dried pole piece;

[0009] taking the difference between the thickness of the dried pole piece and the preset thickness after rolling as the total reduction;

[0010] continuously rolling the dried pole piece in multiple stages, and the percentage of the reduction of the previous stage rolling to the total reduction is greater than or equal to the percentage of the reduction of the next stage rolling to the total reduction, and the sum of the reductions of each stage rolling is equivalent to the total reduction; in the multiple-stage rolling, the reduction of each stage rolling decreases as a whole; and the multiple-stage rolling is cold rolling.

[0011] In some embodiments, the percentage of the total reduction in thickness of the front stage of rolling is greater than the percentage of the total reduction in thickness of the next stage of rolling.

[0012] In some embodiments, the linear speed of the rollers of the last stage of rolling is used as a reference to set the linear speed of the rollers of the other stages of rolling.

[0013] In some embodiments, the diameter of the rollers of the front stage of rolling is less than or equal to the diameter of the rollers of the next stage of rolling, and the diameter of the rollers of the stages of rolling changes from small to large as a whole.

[0014] Optionally, the diameter of the rollers of the front stage of rolling is less than the diameter of the rollers of the next stage of rolling.

[0015] In some embodiments, the linear speed of the rollers of the front stage of rolling is less than the linear speed of the rollers of the next stage of rolling.

[0016] In some embodiments, the roughness of the rollers of the front stage of rolling is greater than or equal to the roughness of the rollers of the next stage of rolling, and the roughness of the rollers of the stages of rolling changes from large to small as a whole.

[0017] Optionally, the roughness of the rollers of the front stage of rolling is greater than the roughness of the rollers of the next stage of rolling.

[0018] In some embodiments, the total reduction in thickness is distributed to the stages of rolling by means of adjusting the gap between the rollers.

[0019] In some embodiments, the gap between the rollers of the front stage of rolling is greater than or equal to the gap between the rollers of the next stage of rolling.

[0020] In some embodiments, the material of the roller body of the rollers used in at least the first stage of rolling is alloy tool steel, and the material of the roller body of the rollers used in the last stage of rolling is alloy tool steel coated with tungsten carbide.

[0021] In some embodiments, a two-high rolling mill is used in at least the first stage of rolling, and a four-high rolling mill is used in at least the last stage of rolling.

[0022] In some embodiments, the temperature of the cold pressing is 5-15°C.

[0023] In some embodiments, the areal density of the dried pole piece is 150-550 g / m 3 .

[0024] In some embodiments, the method for manufacturing the pole piece further comprises the step of obtaining a total reduction rate according to the total reduction in thickness.

[0025] In some embodiments, the total reduction is 5-110 μm.

[0026] In some embodiments, the total reduction rate is 10-50%.

[0027] In some embodiments, the multi-stage rolling comprises a first stage rolling, a second stage rolling, a third stage rolling, a fourth stage rolling and a fifth stage rolling performed in sequence, wherein:

[0028] In some embodiments, the reduction of the first stage rolling is 40-60% of the total reduction, and / or, the roll diameter of the first stage rolling is 200-400 mm, and / or, the first stage rolling is performed by a two-high rolling mill, and / or, the roll body of the roll used in the first stage rolling is alloy tool steel, and / or, the roll roughness of the first stage rolling is 0.5-1.0 μm.

[0029] In some embodiments, the reduction of the second stage rolling is 20-30% of the total reduction, and / or, the roll diameter of the second stage rolling is 300-500 mm, and / or, the second stage rolling is performed by a two-high rolling mill, and / or, the roll body of the roll used in the second stage rolling is alloy tool steel, and / or, the roll roughness of the second stage rolling is 0.5-1.0 μm.

[0030] In some embodiments, the reduction of the third stage rolling is 10-20% of the total reduction, and / or, the roll diameter of the third stage rolling is 400-600 mm, and / or, the third stage rolling is performed by a two-high rolling mill, and / or, the roll body of the roll used in the third stage rolling is alloy tool steel, and / or, the roll roughness of the third stage rolling is 0.3-0.5 μm.

[0031] In some embodiments, the reduction of the fourth stage rolling is 5-15% of the total reduction, and / or, the roll diameter of the fourth stage rolling is 600-1000 mm, and / or, the fourth stage rolling is performed by a four-high rolling mill, and / or, the roll body of the roll used in the fourth stage rolling is alloy tool steel, and / or, the roll roughness of the fourth stage rolling is 0.1-0.3 μm.

[0032] In some embodiments, the reduction of the fifth stage rolling is 2-10% of the total reduction, and / or, the roll diameter of the fifth stage rolling is 800-1200 mm, and / or, the fifth stage rolling is performed by a four-high rolling mill, and / or, the roll body of the roll used in the fifth stage rolling is alloy tool steel coated with sprayed tungsten carbide, and / or, the roll roughness of the fifth stage rolling is 0.1-0.3 μm.

[0033] The second aspect of the present application provides a rolling system for the manufacturing method of the pole piece, comprising a unwinding device for unwinding the dried pole piece, a plurality of groups of rollers for the multi-stage rolling, and a winding device for winding the obtained pole piece after the multi-stage rolling.

[0034] Each group of rollers is used for one stage of the multi-stage rolling.

[0035] Tension roller groups are arranged between adjacent two groups of rollers, between the first group of rollers and the unwinding device, and between the last group of rollers and the winding device.

[0036] The third aspect of the present application provides a pole piece prepared by the manufacturing method of the pole piece or the rolling system.

[0037] The fourth aspect of the present application provides a secondary battery comprising a positive pole piece, a negative pole piece, and a separator, wherein the positive pole piece or the negative pole piece is the pole piece.

[0038] The manufacturing method of the pole piece can at least bring the following beneficial effects:

[0039] 1. The multi-stage continuous rolling and the decreasing reduction are adopted to reduce the reduction of the end roller to release the stress, reduce the mechanical rebound rate of the pole piece, and improve the consistency of the pole piece.

[0040] 2. In the multi-stage rolling process, the roller diameter changes from small to large, and the roller surface roughness changes from large to small, especially when the roller diameter gradually increases and the roller surface roughness gradually decreases, the thickness consistency of the pole piece surface can be effectively improved, and the friction during rolling is reduced to improve the problem of easy breaking of the belt during multi-pass rolling extension.

[0041] 3. Through the above improvement of the thickness consistency of the pole piece, the SEI film is uniformly formed, the ion transmission path of the pole piece is improved, the interface contact resistance is reduced, and finally the initial efficiency of the battery is improved.

[0042] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0043] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings,

[0044] In which:

[0045] Figure 1 The flowchart of the manufacturing method of the pole piece is shown in an exemplary embodiment of the present application.

[0046] Figure 2This is a schematic diagram of the structure of a roller pressing system shown in an exemplary embodiment of this application.

[0047] Figure 3 The figures show a comparison of the electrode effects after five-stage rolling in Example 1 and conventional rolling in Comparative Example 1. (a) is a top view of the electrode after five-stage rolling in Example 1 and conventional rolling in Comparative Example 1, (b) is a cross-sectional view of the conventionally rolled electrode, and (c) is a cross-sectional view of the five-stage rolled electrode in Example 1.

[0048] Figure label:

[0049] 1-Unwinding device; 2-Rewinding device; 3-Multiple sets of rolls; 301-Primary rolling roll; 302-Roughing roll; 303-Finishing roll; 304-Precision rolling roll; 305-Dressing roll; 4-Tension roll group. Detailed Implementation

[0050] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0051] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0052] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0053] When the term “and / or” is used in a list containing two or more items, it means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression “A and / or B” is intended to mean A or B or A and B, that is, A only, B only, or a combination of A and B.

[0054] <Methods for making polarized film>

[0055] Figure 1 A flowchart illustrating a method for manufacturing an electrode sheet as an exemplary embodiment of this application.

[0056] like Figure 1 As shown, the method for manufacturing this electrode includes the following steps:

[0057] S101. Coat the current collector with slurry and dry it to obtain the dried electrode.

[0058] In some embodiments, the slurry is a positive electrode slurry. In the embodiments of this application, the composition of the positive electrode slurry is not limited; it can be any positive electrode slurry well known in the art, or it can be a positive electrode slurry with the following composition:

[0059] Positive electrode slurry includes positive electrode active material, positive electrode conductive agent, positive electrode binder, positive electrode dispersant, positive electrode solvent, etc.

[0060] For example, a method for preparing a positive electrode slurry includes: adding a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, a positive electrode dispersant, etc., in a certain proportion to an appropriate amount of positive electrode solvent to obtain a positive electrode slurry.

[0061] For example, the positive electrode active material includes, but is not limited to, at least one of lithium iron phosphate, lithium nickel cobalt manganese, and sodium copper iron manganese.

[0062] For example, the mass content of the positive electrode active material in the positive electrode slurry is 80-98%, including but not limited to 82%, 84%, 86%, 88%, 90%, 92%, 94% or 96%.

[0063] For example, the positive electrode conductive agent includes, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNT), and vapor-grown carbon fiber (VGCF).

[0064] For example, the mass content of the positive electrode conductive agent in the positive electrode slurry is 0.5-15%, including but not limited to 1%, 3%, 5%, 7%, 9%, 11%, 13% or 15%.

[0065] For example, the positive electrode binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polyacrylonitrile copolymer (PAN), etc.

[0066] For example, the mass content of the positive electrode binder in the positive electrode slurry is 0.5-15%, including but not limited to 1%, 3%, 5%, 7%, 9%, 11%, 13% or 15%.

[0067] For example, the positive electrode dispersant includes, but is not limited to, at least one of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), etc.

[0068] For example, the mass content of the positive electrode dispersant in the positive electrode slurry is 0.1-0.5%, including but not limited to 0.2%, 0.3% or 0.4%.

[0069] For example, the positive electrode solvent includes, but is not limited to, at least one of N-methylpyrrolidone (NMP), water, etc.

[0070] For example, the solid content of the positive electrode slurry is 45-65 wt%, including but not limited to 50 wt%, 55 wt%, or 60 wt%.

[0071] In some embodiments, when the slurry is a positive electrode slurry, the current collector is a positive electrode current collector. In the embodiments of this application, the type of positive electrode current collector is not limited; it can be any positive electrode current collector well-known in the art that can be used in secondary batteries such as lithium-ion batteries and sodium-ion batteries. For example, aluminum foil, carbon-coated aluminum foil, or composite current collectors. In this case, the electrode preparation method of the embodiments of this application prepares a positive electrode sheet.

[0072] In other embodiments, the slurry is a negative electrode slurry. In the embodiments of this application, the composition of the negative electrode slurry is not limited; it can be any negative electrode slurry well known in the art, or it can be a negative electrode slurry with the following composition:

[0073] Negative electrode slurry includes positive electrode active material, negative electrode conductive agent, negative electrode binder, negative electrode thickener, negative electrode dispersant, negative electrode solvent, etc.

[0074] For example, a method for preparing a negative electrode slurry includes: adding a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, a negative electrode thickener, a negative electrode dispersant, etc., in a certain proportion to an appropriate amount of negative electrode solvent to obtain a negative electrode slurry.

[0075] For example, the negative electrode active material includes, but is not limited to, at least one of graphite, hard carbon, silicon carbide, etc.

[0076] For example, the mass content of the negative electrode active material in the negative electrode slurry is 80-98%, including but not limited to 82%, 84%, 86%, 88%, 90%, 92%, 94% or 96%.

[0077] For example, the negative electrode conductive agent includes, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNT), and vapor-grown carbon fiber (VGCF).

[0078] For example, the mass content of the negative electrode conductive agent in the negative electrode slurry is 0.5-15%, including but not limited to 1%, 3%, 5%, 7%, 9%, 11%, 13% or 15%.

[0079] For example, the negative electrode binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), etc.

[0080] For example, the mass content of the negative electrode binder in the negative electrode slurry is 0.5-15%, including but not limited to 1%, 3%, 5%, 7%, 9%, 11%, 13% or 15%.

[0081] For example, the negative electrode thickener includes, but is not limited to, at least one of lithium carboxymethyl cellulose (CMC-Li), sodium carboxymethyl cellulose (CMC-Na), and carboxymethyl cellulose (CMC).

[0082] For example, the mass content of the negative electrode thickener in the negative electrode slurry is 0.5-3%, including but not limited to 1%, 1.5%, 2%, 2.5% or 3%.

[0083] For example, negative electrode dispersants include, but are not limited to, at least one of polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), etc.

[0084] For example, the mass content of the negative electrode dispersant in the negative electrode slurry is 0-0.5%, including but not limited to 0, 0.4%, 0.3%, 0.2%, 0.1%, 0.2%, 0.3%, or 0.4%. When the mass content is 0, it means that no negative electrode dispersant is added to the negative electrode slurry.

[0085] For example, the negative electrode solvent includes, but is not limited to, at least one of N-methylpyrrolidone (NMP), water, etc.

[0086] For example, the solid content of the negative electrode slurry is 45-65 wt%, including but not limited to 50 wt%, 55 wt%, or 60 wt%.

[0087] In some embodiments, when the slurry is a negative electrode slurry, the current collector is a negative electrode current collector. In the embodiments of this application, the type of negative electrode current collector is not limited; it can be any negative electrode current collector well-known in the art that can be used in secondary batteries such as lithium-ion batteries and sodium-ion batteries. For example, copper foil, carbon-coated copper foil, or composite current collectors. In this case, the electrode preparation method of the embodiments of this application prepares a negative electrode sheet.

[0088] In some embodiments, the areal density of the dried electrode sheet is 150-550 g / m³. 3 including but not limited to 200g / m 3 250g / m 3 300g / m 3 350g / m 3 400g / m 3 450g / m 3 500g / m 3 Or 550g / m 3 wait.

[0089] S102. The difference between the thickness of the dried electrode obtained in step S101 and the preset thickness after rolling is used as the total reduction.

[0090] In some embodiments, the thickness of the dried electrode sheet is measured using a laser thickness gauge, a micrometer, or the like.

[0091] In some embodiments, the method for manufacturing the electrode further includes the step of obtaining a total reduction rate based on the total reduction amount.

[0092] In some implementations, the total reduction rate is calculated according to the following formula:

[0093] Total reduction rate = thickness of the dried electrode sheet / preset thickness after rolling - 1.

[0094] In some implementations, the total reduction rate is 10-50%, including but not limited to 15%, 20%, 25%, 30%, 35%, 40%, or 45%.

[0095] In some embodiments, the preset thickness after rolling is 80-450μm, including but not limited to 100μm, 150μm, 200μm, 250μm, 300μm, 350μm or 400μm.

[0096] In some implementations, the total reduction is 5-110 μm, including but not limited to 10 μm, 30 μm, 50 μm, 80 μm or 100 μm.

[0097] S103. The dried electrode obtained in step S101 is subjected to continuous multi-stage rolling, and the percentage of the reduction amount of the previous rolling stage to the total reduction amount is greater than or equal to the percentage of the reduction amount of the subsequent rolling stage to the total reduction amount. The sum of the reduction amounts of each rolling stage is equivalent to the total reduction amount. In the multi-stage rolling, the reduction amount of each rolling stage decreases as a whole. All multi-stage rolling is cold pressing.

[0098] In the embodiments of this application, in the multi-stage rolling process, the reduction amount of each stage of rolling decreases overall. This reduces the reduction amount of the final roller to release stress, lowers the mechanical rebound rate of the electrode, and improves the consistency of the electrode.

[0099] It is understandable that in multi-stage rolling, the reduction amount of each stage of rolling decreases overall, which means:

[0100] In some implementations, in a multi-stage rolling process, the first stage of rolling has the largest reduction, the last stage has the smallest reduction, and the reduction of the intermediate stages can be at least partially equal. However, the reduction of the intermediate stages must be less than the reduction of the first stage and greater than or equal to the reduction of the last stage, while ensuring that the reduction from the first stage to the last stage generally decreases (from large to small).

[0101] In other embodiments, between adjacent rolling stages, the percentage of reduction in the total reduction of the preceding rolling stage is greater than the percentage of reduction in the total reduction of the following rolling stage. In this case, in the multi-stage rolling process, the percentage of reduction in the total reduction of each rolling stage decreases progressively (from the first rolling stage to the last rolling stage). In the embodiments of this application, the rolls are arranged in a continuous rolling manner, and the reduction is differentiated according to the characteristics of each rolling stage. From beginning to end, the reduction decreases, which is beneficial for stress release and gradually improves the thickness control accuracy.

[0102] In some implementations, in adjacent rolling stages, the diameter of the preceding rolling stage is less than or equal to the diameter of the following rolling stage.

[0103] As an optional example, in the multi-stage rolling process, the roller diameter of each stage varies from small to large. This effectively improves the thickness uniformity of the electrode surface, especially when the roller diameter is large and the reduction is small, the thickness uniformity is further improved.

[0104] In some cases, in multi-stage rolling, the roller diameters used from the first stage to the last stage are generally smaller and larger. The roller diameters of the intermediate stages may be the same (for example, the roller diameters of the intermediate stages are all equal, but all are larger than the roller diameter of the first stage and smaller than the roller diameter of the last stage; or, the roller diameters of some of the intermediate stages are equal, but the entire multi-stage rolling still meets the requirement that the roller diameters are generally smaller and larger).

[0105] In other cases, between adjacent rolling stages, the roller diameter of the preceding stage is smaller than that of the following stage. That is, in multi-stage rolling, the roller diameter increases progressively with each stage (from the first stage to the last). Compared to the situation where the roller diameters used from the first to the last stage are generally smaller and larger, with the intermediate stages potentially having the same roller diameter, this setup effectively improves the thickness uniformity of the electrode surface, especially when using large roller diameters with small reduction amounts, where thickness uniformity is further improved.

[0106] For example, in a multi-stage rolling process, the diameter of the first-stage rolling mill is 200-400mm, including but not limited to 250mm, 300mm or 350mm.

[0107] For example, in a multi-stage rolling process, the diameter of the last rolling stage is 800-1200mm, including but not limited to 900mm, 1000mm, 1100mm or 1200mm.

[0108] In some embodiments, in the multi-stage rolling process, the linear speed of the last rolling stage is used as a reference, and the linear speeds of the remaining rolling stages are set sequentially. The purpose of this is that the linear speed of the last rolling stage is the output speed of the rolling process, determining the rolling capacity and facilitating the design of equipment compatibility between processes.

[0109] Specifically, if multi-stage rolling is continuous rolling, the speed of the last stage's rolling line rate is used as a reference, and the speed of the previous stage's rolling line rate decreases progressively, meaning the last stage has the highest rolling line rate (which determines rolling efficiency and production capacity). If it is staged rolling, the speed can be set according to continuous rolling or according to elongation requirements. Generally, the greater the reduction, the lower the rolling line rate, and the more rolling passes, the greater the elongation. Greater elongation makes the electrode sheet more prone to breakage, and thinner foil is more suitable for low elongation. However, the lower the elongation, the greater the rebound of the electrode sheet if stress is not fully released; therefore, the more rolling stages, the more fully the stress is released, and the higher the rolling line rate can be selected, improving production efficiency while reducing elongation.

[0110] For example, the basis for setting the linear speed of the remaining rollers in the above-mentioned step-by-step manner is: the larger the number of rollers, the greater the linear speed.

[0111] Based on the principle of constant volume, the linear speed of the subsequent roller (i.e., the rear roller speed) is greater than the linear speed of the preceding roller (i.e., the front roller speed). The formula is: Rear roller gap × Rear roller speed = Front roller gap × Front roller speed. Dynamic fine-tuning using tension ensures continuous production. The roller gap adjustment method is the design of this application (as described below), avoiding the lag in electrode thickness measurement.

[0112] For example, the linear speed of the last stage of rolling is 60-140 m / min, including but not limited to 70 m / min, 80 m / min, 90 m / min, 100 m / min, 110 m / min, 120 m / min or 130 m / min.

[0113] For example, the linear speed of the first-stage roller is 35-125 m / min, including but not limited to 45 m / min, 55 m / min, 65 m / min, 75 m / min, 85 m / min, 95 m / min, 105 m / min or 115 m / min.

[0114] In the embodiments of this application, the friction force is related to the roughness of the roller surface (i.e., the roller roughness). The greater the roughness, the greater the friction force, and the greater the extension of the electrode sheet after rolling. The electrode sheet is more likely to break during the rolling process. Furthermore, under multiple rolling passes, the material contained in the electrode sheet will flow and extend. The current collector is stretched due to the ductility of the metal, and eventually, the current collector is more likely to break.

[0115] Therefore, in some embodiments, between two adjacent rolling stages, the roll roughness of the preceding rolling stage is greater than or equal to the roll roughness of the following rolling stage.

[0116] As an alternative example, in multi-stage rolling, the roughness of each stage of rolling varies from large to small. This setup can effectively improve the thickness uniformity of the electrode surface while reducing friction during rolling to mitigate the problem of large stretching and easy breakage during multi-pass rolling.

[0117] In some cases, in multi-stage rolling, the surface roughness of the rollers used from the first stage to the last stage generally decreases from large to small. The surface roughness of the rollers used in the intermediate stages may overlap (for example, the surface roughness of the rollers used in the intermediate stages may be equal, but less than the surface roughness of the rollers used in the first stage, and greater than or equal to the surface roughness of the rollers used in the last stage; or, the surface roughness of the rollers used in some of the intermediate stages may be equal, but the entire multi-stage rolling still meets the requirement that the surface roughness generally decreases from large to small).

[0118] In other cases, the roller roughness of the preceding roller stage is greater than that of the following roller stage in adjacent roller pressing stages. That is, in multi-stage roller pressing, the roller roughness decreases progressively with each stage (from the first to the last stage). This configuration, compared to the situation where the overall roller roughness from the first to the last stage is initially large and then decreases, with the intermediate stages potentially having similar roller roughness, effectively improves the thickness uniformity of the electrode surface. It also better addresses the problem of excessive stretching and potential breakage during multi-pass roller pressing by reducing friction as the roller diameter gradually increases.

[0119] For example, the roller roughness of the first-stage roller pressing is 0.5-1.0μm, including but not limited to 0.6μm, 0.7μm, 0.8μm or 0.9μm.

[0120] For example, the roll roughness of the last stage of rolling is 0.1-0.3μm, including but not limited to 0.15μm, 0.2μm or 0.25μm.

[0121] In some implementations, in multi-stage rolling, the total reduction is distributed to each stage of rolling by adjusting the roll gap.

[0122] In some implementations, between two adjacent rolling stages, the roll gap of the preceding rolling stage is greater than or equal to the roll gap of the following rolling stage.

[0123] For example, in multi-stage rolling, the roll gap of the first stage rolling is 85-480μm, including but not limited to 100μm, 200μm, 300μm, 400μm or 450μm.

[0124] For example, in multi-stage rolling, the roll gap of the last stage is 80-450μm, including but not limited to 100μm, 200μm, 300μm, 400μm or 450μm.

[0125] In some embodiments, in the multi-stage rolling process, at least the first stage rolling process uses rollers made of alloy tool steel, and the last stage rolling process uses rollers made of alloy tool steel coated with tungsten carbide. This arrangement aims to enhance the hardness of the roller surface, reduce elastic deformation of the roller body, and improve the thickness uniformity of the rolled electrode sheets.

[0126] It should be noted that, in the embodiments of this application, the roller body, roller diameter, and roller roughness involved in multi-stage rolling all refer to the roller body, roller diameter, and roughness of the roller that contacts the electrode in the corresponding stage of rolling.

[0127] In some embodiments, in the multi-stage rolling process, at least the first stage of rolling employs a two-high mill, and at least the last stage employs a four-high mill. This arrangement aims to: use a two-high, small-diameter mill for the first stage of rolling to roll at the optimal plasticity of the electrode sheet with a high-pressure reduction rate, thereby improving the extension and diffusion of non-current collector materials, reducing the extension and stretching of current collector materials, and ultimately lowering the risk of strip breakage; and use a four-high process for the last stage of rolling to ensure uniform pressure on the work rolls, improving the thickness consistency in the width direction of the electrode sheet. The advantage of a four-high mill over a two-high mill is its enhanced consistency in the width direction; therefore, using a four-high mill in the later stages of the multi-stage rolling process is essential.

[0128] In the embodiments of this application, all multi-stage rolling is cold rolling (cold rolling). This is done to prevent roller sticking, reduce micro-protrusions caused by uneven viscosity within the electrode due to the accumulation of binders on the electrode surface, and ultimately improve electrode thickness uniformity and surface quality. Compared to alternating hot rolling (hot rolling) and ambient rolling (room temperature rolling), the advantages are: reduced roller sticking and improved electrode thickness consistency. Compared to all hot rolling (hot rolling), the advantages are: significantly reduced roller sticking and improved electrode thickness consistency. Compared to all ambient rolling (room temperature rolling), the advantages are: reduced roller sticking and improved surface quality.

[0129] In some embodiments, the cold pressing temperature in multi-stage rolling is 5-15°C, including but not limited to 7°C, 9°C, 11°C or 13°C.

[0130] In the embodiments of this application, cold pressing requires cold pressing pressure, which is mainly represented by the amount of reduction. The greater the amount of reduction, the higher the pressure. This invention reduces the pressure of each stage of roller pressing by distributing the amount of reduction. Through multi-stage roller pressing, the particles diffuse and move sufficiently, which can avoid the material brittle cracking problem that may be caused by a simple cold pressing process.

[0131] As an optional example, the multi-stage rolling process includes a first-stage rolling process, a second-stage rolling process, a third-stage rolling process, a fourth-stage rolling process, and a fifth-stage rolling process performed sequentially. In this case:

[0132] In some embodiments, the reduction of the first-stage roller is 40-60% of the total reduction, including but not limited to 45%, 50% or 55%.

[0133] In some embodiments, the diameter of the first-stage roller is 200-400mm, including but not limited to 250mm, 300mm or 350mm.

[0134] In some implementations, the first stage of rolling is performed using a two-roll mill.

[0135] In some embodiments, the rollers used in the first-stage rolling process are made of alloy tool steel.

[0136] In some embodiments, the roughness of the first-stage roller is 0.5-1.0 μm, including but not limited to 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0137] In some embodiments, the reduction of the second-stage roller is 20-30% of the total reduction, including but not limited to 22.5%, 25% or 27.5%.

[0138] In some embodiments, the diameter of the second-stage roller is 300-500mm, including but not limited to 350mm, 400mm or 450mm.

[0139] In some implementations, the second-stage rolling process uses a two-roll mill.

[0140] In some embodiments, the rollers used in the second-stage rolling process are made of alloy tool steel.

[0141] In some embodiments, the roughness of the second-stage roller is 0.5-1.0 μm, including but not limited to 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0142] In some embodiments, the reduction of the third-stage roller is 10-20% of the total reduction, including but not limited to 12.5%, 15% or 17.5%.

[0143] In some embodiments, the diameter of the third-stage roller is 400-600mm, including but not limited to 450mm, 500mm or 550mm.

[0144] In some embodiments, the third-stage rolling mill is a two-roll mill.

[0145] In some embodiments, the rollers used in the third-stage rolling process are made of alloy tool steel.

[0146] In some embodiments, the roughness of the third-stage roller is 0.3-0.5 μm, including but not limited to 0.35 μm, 0.4 μm or 0.45 μm.

[0147] In some embodiments, the reduction of the fourth-stage roller is 5-15% of the total reduction, including but not limited to 7.5%, 10% or 12.5%.

[0148] In some embodiments, the diameter of the fourth-stage roller is 600-1000mm, including but not limited to 650mm, 700mm, 750mm, 800mm, 850mm, 900mm or 950mm.

[0149] In some embodiments, the fourth stage of rolling is performed using a four-high rolling mill.

[0150] In some embodiments, the rollers used in the fourth-stage rolling process are made of alloy tool steel.

[0151] In some embodiments, the roller roughness of the fourth-stage roller pressing is 0.1-0.3 μm, including but not limited to 0.15 μm, 0.2 μm or 0.25 μm.

[0152] In some embodiments, the reduction of the fifth-stage roller is 2-10% of the total reduction, including but not limited to 3%, 4%, 5%, 6%, 7%, 8% or 9%.

[0153] In some embodiments, the diameter of the fifth-stage roller is 800-1200mm, including but not limited to 850mm, 900mm, 950mm, 1000mm, 1050mm, 1100mm or 1150mm.

[0154] In some embodiments, the fifth rolling process uses a four-roll mill.

[0155] In some embodiments, the rollers used in the fifth-stage rolling process are made of alloy tool steel coated with tungsten carbide (i.e., alloy tool steel coated with tungsten carbide).

[0156] This application does not limit the composition, thickness, etc. of the tungsten carbide coating. For example, the thickness of the tungsten carbide coating is 0.1-0.5 mm, such as 0.2 mm, 0.3 mm, or 0.4 mm; the tungsten carbide coating is composed of tungsten carbide (WC), cobalt (Co), and chromium (Cr), wherein the mass ratio of WC, Co, and Cr (WC:Co:Cr) is (88-95):(3-11):(1.8-2.2), such as 88:10:2, 90:8:2, or 92:6:2, etc., and 88:10:2 is optional.

[0157] In some embodiments, the roughness of the fifth-stage roller is 0.1-0.3 μm, including but not limited to 0.15 μm, 0.2 μm or 0.25 μm.

[0158] In some implementations, this application is used. Figure 2 The roller pressing system shown realizes the above-mentioned multi-stage roller pressing, including five-stage roller pressing.

[0159] In the embodiments of this application, when the above-mentioned five-stage rolling is used, the first stage of rolling compacts the floating powder, ensuring a smoother surface when the electrode enters the next stage. A two-roll small-diameter mill is used to roll the electrode at its optimal plasticity with a high reduction rate, improving the extension and diffusion of non-current collector materials and reducing the extension and stretching of current collector materials, ultimately reducing the risk of strip breakage. The second and third stages of rolling reduce stress concentration within the material by gradually adjusting the roll gap and further reducing the reduction amount. Gradually increasing the roll diameter and reducing the roll body roughness reduces extension and increases electrode flatness. The fourth stage... The fifth-stage rolling process further optimizes the roller body hardness based on the increased roller diameter and uses a four-roll process to ensure uniform roller body pressure, which improves the thickness consistency in the width direction of the electrode sheet. At the same time, the rolling process is carried out with a smaller reduction amount, which releases the stress in the previous stage and produces a pre-finished electrode sheet with a better surface condition. The fifth-stage rolling process further optimizes the roller body hardness based on the fourth-stage rolling process and uses the designed thickness as the roller gap to trim the electrode sheet surface to further improve the thickness consistency in the width direction, ensure the accuracy of the thickness and prevent over-pressure.

[0160] The method for manufacturing the electrode sheet according to the embodiments of this application can bring at least the following beneficial effects:

[0161] 1. By adopting multi-stage continuous rolling and decreasing or equal reduction, the reduction of the end roll is reduced to release stress, reduce the mechanical rebound rate of the electrode, and improve the consistency of the electrode.

[0162] 2. During the multi-stage rolling process, the overall roller diameter changes from small to large and the overall roller surface roughness changes from large to small. In particular, when the roller diameter gradually increases and the roller surface roughness gradually decreases, the thickness uniformity of the electrode surface can be effectively improved while reducing the friction during rolling to improve the problem of easy strip breakage due to large elongation during multi-stage rolling.

[0163] 3. By improving the uniformity of electrode thickness as described above, the SEI film is formed uniformly, the ion transport path of the electrode is improved, the interfacial contact resistance is reduced, and the first efficiency of the battery is ultimately improved.

[0164] It should be noted that, in the embodiments of this application, the rebound rate is calculated according to the following formula:

[0165] Rebound rate = (Thickness after 24 hours of rolling - Thickness after 0 hours of rolling) / Thickness after 0 hours of rolling

[0166] The thickness after 24 hours of rolling refers to the thickness 24 hours after the last rolling stage in multi-stage rolling (if multiple locations are tested, it can be the average of the thicknesses at these locations). The thickness after 0 hours of rolling refers to the thickness 0 hours after the last rolling stage in multi-stage rolling (i.e., the roll gap height of the last rolling stage) (if multiple locations are tested, it can be the average of the thicknesses at these locations).

[0167] <Roller pressing system>

[0168] The rolling system of this application embodiment can be used in the electrode fabrication method of this application embodiment.

[0169] Figure 2 This is a schematic diagram of the structure of a roller pressing system shown in an exemplary embodiment of this application.

[0170] like Figure 2 As shown, the rolling system includes an unwinding device 1 for unwinding the dried electrode sheet, multiple sets of rollers 3 for multi-stage rolling, and a winding device 2 for winding the obtained electrode sheet after multi-stage winding; each set of rollers is used for one stage of the multi-stage rolling; tension roller sets 4 are provided between adjacent sets of rollers, between the first set of rollers and the unwinding device 1, and between the last set of rollers and the winding device 2.

[0171] In some embodiments, when the multi-stage rolling process includes the aforementioned five-stage rolling process, the multiple sets of rolls 3 include a primary rolling roll 301, a roughing roll 302, a finishing roll 303, a finishing roll 304, and a dressing roll 305 arranged sequentially. Specifically, the primary rolling roll 301 is used for the first stage of rolling, the roughing roll 302 for the second stage, the finishing roll 303 for the third stage, the finishing roll 304 for the fourth stage, and the dressing roll 305 for the fifth stage. In this case:

[0172] In some embodiments, the diameter of the primary roll 301 is 200-400mm, including but not limited to 250mm, 300mm or 350mm.

[0173] In some embodiments, the primary roll 301 is a two-roll mill.

[0174] In some embodiments, the roll body of the primary roll 301 is made of alloy tool steel.

[0175] In some embodiments, the roughness of the primary roll 301 is 0.5-1.0 μm, including but not limited to 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0176] In some embodiments, the diameter of the roughing roll 302 is 300-500mm, including but not limited to 350mm, 400mm or 450mm.

[0177] In some embodiments, the roughing roll 302 is a two-roll mill.

[0178] In some embodiments, the body of the roughing roll 302 is made of alloy tool steel.

[0179] In some embodiments, the roughness of the roughing roll 302 is 0.5-1.0 μm, including but not limited to 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm.

[0180] In some embodiments, the diameter of the finishing roll 303 is 400-600mm, including but not limited to 450mm, 500mm or 550mm.

[0181] In some embodiments, the finishing roll 303 is a two-roll mill.

[0182] In some embodiments, the roll body of the finishing roll 303 is made of alloy tool steel.

[0183] In some embodiments, the roughness of the finishing roll 303 is 0.3-0.5 μm, including but not limited to 0.35 μm, 0.4 μm or 0.45 μm.

[0184] In some embodiments, the diameter of the superior rolling roll 304 is 600-1000mm, including but not limited to 650mm, 700mm, 750mm, 800mm, 850mm, 900mm or 950mm.

[0185] In some embodiments, the superior roll 304 is a four-high rolling mill.

[0186] In some embodiments, the roll body of the superior roll 304 is made of alloy tool steel.

[0187] In some embodiments, the roughness of the superior roll 304 is 0.1-0.3μm, including but not limited to 0.15μm, 0.2μm or 0.25μm.

[0188] In some embodiments, the diameter of the trimming roller 305 is 800-1200mm, including but not limited to 850mm, 900mm, 950mm, 1000mm, 1050mm, 1100mm or 1150mm.

[0189] In some embodiments, the dressing roll 305 is a four-high mill.

[0190] In some embodiments, the roller body of the dressing roller 305 is made of alloy tool steel coated with tungsten carbide (i.e., alloy tool steel coated with tungsten carbide).

[0191] This application does not limit the composition, thickness, etc. of the tungsten carbide coating. For example, the thickness of the tungsten carbide coating is 0.1-0.5 mm, such as 0.2 mm, 0.3 mm, or 0.4 mm; the tungsten carbide coating is composed of tungsten carbide (WC), cobalt (Co), and chromium (Cr), wherein the mass ratio of WC, Co, and Cr (WC:Co:Cr) is (88-95):(3-11):(1.8-2.2), such as 88:10:2, 90:8:2, or 92:6:2, etc., and 88:10:2 is optional.

[0192] In some embodiments, the roughness of the dressing roller 305 is 0.1-0.3 μm, including but not limited to 0.15 μm, 0.2 μm or 0.25 μm.

[0193] As an optional example, a method for multi-stage rolling using the aforementioned primary roll 301, roughing roll 302, finishing roll 303, finishing roll 304, and dressing roll 305 includes:

[0194] The dried electrode sheets from the unwinding device pass sequentially through the primary roll, roughing roll, finishing roll, superior roll, and dressing roll. The gaps between the rolls are adjusted, and the linear speed of each roll is controlled by the system program based on the principle of constant volume. This ensures that the reduction of the first stage of the primary roll is 40-60% of the total reduction, the reduction of the second stage of the roughing roll is 20-30%, the reduction of the third stage of the finishing roll is 10-20%, the reduction of the fourth stage of the superior roll is 5-15%, and the reduction of the fifth stage of the dressing roll is 2-10%. These reductions are then used to adjust the gaps between the rolls, ultimately resulting in a reduction that decreases as the electrode sheet is rolled.

[0195] The aforementioned "adjusting the gaps between each roller, with the linear speed of each roller controlled by the system program based on the principle of constant volume" specifically refers to the speed formula between the front and rear rollers according to the principle of constant volume: rear roller gap × rear roller linear speed = front roller gap × front roller linear speed. Dynamic fine-tuning is performed using tension rollers to ensure continuous production.

[0196] In the embodiments of this application (including the aforementioned manufacturing method), the reduction ratio is calculated according to the following formula:

[0197] Reduction rate = Thickness before rolling / Thickness after rolling - 1.

[0198] In the above formula, the thickness before rolling is the thickness of the electrode sheet before rolling; the thickness after rolling is the final thickness of the electrode sheet after passing through multiple rolling stages (replaced by the roll gap of the last rolling stage).

[0199] It should be noted that in the embodiments of this application, only the total reduction rate is given, not the reduction rate of each stage. Each stage only has the reduction amount or the reduction amount percentage. The reduction amount is the thickness before rolling minus the thickness after rolling, and the sum of the reduction amount percentages is 1.

[0200] In some embodiments, the rolling system of this application further includes a roll gap detection device for determining the roll gap size. For example, each rolling device (i.e., each set of rollers) of the multiple sets of rollers 3 used for the multi-stage rolling process is equipped with a roll gap detection device.

[0201] In the roll forming system of this application embodiment, the unwinding device, the winding device, the tension roller group, and the roll gap detection device are all existing structural equipment. For example, the roll gap detection device can adopt a hydraulic automatic thickness control system (hereinafter referred to as hydraulic AGC or HAGC), etc., which will not be described in detail here.

[0202] For example, in the above-mentioned hydraulic automatic thickness control system, the displacement sensor device for roll gap detection is generally installed inside the servo hydraulic cylinder, and the extension of the hydraulic cylinder can represent the roll gap size.

[0203] Currently, rolling mill rolls consist of fixed rolls and movable rolls. The roll gap data can be obtained simply by detecting the displacement of the movable rolls, resulting in high direct measurement accuracy. Between adjacent sets of rolls, thickness gauges are typically used to monitor the roll exit side, and the two can work together. However, if a thickness gauge, an indirect measurement method, is used in this application, the roll gap measurement will have a lag. Therefore, a hydraulic automatic thickness control system is generally used.

[0204] In the embodiments of this application, a multi-roller continuous rolling system is used. The reduction amount is diverted by adjusting the roll gap. This is combined with five cold pressing processes: initial rolling, roughing rolling, finishing rolling, fine rolling, and finishing rolling. Following the principle of constant output volume, the speed of the preceding rolls is set step-by-step based on the linear velocity of the final finishing roll. This is then integrated with a roll gap detection device to form a joint control system. Feedback from the tension roll group allows for real-time adjustment of the speed ratio to maintain constant tension. The resulting electrode sheet exhibits minimal thickness fluctuation in the width direction, minimal mechanical rebound, and avoids over-pressure.

[0205] <Extreme Film>

[0206] The electrode sheets in this application embodiment are prepared using the electrode sheet manufacturing method of this application embodiment or the rolling system of this application embodiment.

[0207] In some implementations, the electrode is a positive electrode.

[0208] In other embodiments, the electrode is a negative electrode.

[0209] The electrode sheets of this application embodiment have at least the beneficial effects of the electrode sheet manufacturing method of this application embodiment.

[0210] Secondary batteries

[0211] The secondary battery of this application embodiment includes a positive electrode, a negative electrode, and a separator, wherein the positive electrode or the negative electrode is the electrode of this application embodiment.

[0212] In some embodiments, the secondary battery includes, but is not limited to, lithium-ion batteries, sodium-ion batteries, etc.

[0213] In the embodiments of this application, the separator and other components of the secondary battery are not limited, and can be any separator or other material well-known and recognized in the art that can be used in the corresponding secondary battery.

[0214] The electrode sheets of this application embodiment have at least the beneficial effects of the electrode sheet manufacturing method of this application embodiment.

[0215] The following non-limiting embodiments further illustrate certain features of the present technology.

[0216] I. Examples and Comparative Examples

[0217] The graphite 1 and graphite 2 involved in the following embodiments and comparative examples are different types of graphite. Among them,

[0218] Graphite 1 is a single-particle negative electrode graphite with a volumetric particle size D50 of 10.5 μm, a Dmax of 40 μm, a span of 1.6, and a tap density of 0.95 g / cm³. 3 ;

[0219] Graphite 2 is a secondary particle negative electrode graphite with a volumetric particle size D50 of 15 μm, a Dmax of 48 μm, a span of 1.4, and a tap density of 1.13 g / cm³. 3 .

[0220] Example 1

[0221] The method for manufacturing the electrode sheet in this embodiment includes the following steps:

[0222] (1) Graphite 1, conductive agent Super P, CMC, and SBR were added to an appropriate amount of pure water in a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry with a solid content of 52wt%. Then, the negative electrode slurry was subjected to a process of adding 180g / m... 2 The areal density is uniformly coated on both opposite surfaces of a 6μm thick copper foil. After thorough drying, the thickness of the electrode (i.e., the thickness of the dried electrode) is 170μm, according to 1.49g / cm³. 3 The requirement for electrode compaction is to control the thickness of the electrode after roller pressing (i.e., the preset thickness after roller pressing) to be 120μm, so the calculated total pressing amount requirement (i.e., total pressing amount) is 50μm.

[0223] (2) The dried electrode sheet is subjected to first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling and fifth-stage rolling under cold pressing conditions at 10℃ to obtain a negative electrode sheet with a thickness of 120μm.

[0224] in:

[0225] In the first stage of rolling, a two-roll mill is used, with the reduction accounting for 50% of the total reduction. The roll diameter is 300 mm, the roll body is made of alloy tool steel, the roll roughness is 1 μm, the roll gap is 145 μm, and the roll linear speed is 99.3 m / min.

[0226] In the second-stage rolling process, a two-roll mill is used, with a reduction of 25% of the total reduction. The roll diameter is 400 mm, the roll body is made of alloy tool steel, the roll roughness is 0.75 μm, the roll gap is 132.5 μm, and the roll linear speed is 108.7 m / min.

[0227] In the third stage of rolling, a four-high mill is used, with the reduction accounting for 12.5% ​​of the total reduction. The roll diameter is 500 mm, the roll body is made of alloy tool steel, the roll roughness is 0.5 μm, the roll gap is 126.25 μm, and the roll linear speed is 114.1 m / min.

[0228] In the fourth stage of rolling, a two-roll mill is used, with the reduction accounting for 6.25% of the total reduction. The roll diameter is 800 mm, the roll body is made of alloy tool steel, the roll roughness is 0.3 μm, the roll gap is 123.125 μm, and the roll linear speed is 117 m / min.

[0229] In the fifth-stage rolling process, a four-high mill is used, with a reduction accounting for 6.25% of the total reduction. The roll diameter is 1000 mm, and the roll body is made of alloy tool steel coated with tungsten carbide. The roll surface roughness is 0.1 μm, the roll gap is 120 μm, and the roll linear speed is 120 m / min. The tungsten carbide coating thickness is 0.1 mm. The tungsten carbide coating is composed of tungsten carbide (WC), cobalt (Co), and chromium (Cr), with a WC:Co:Cr mass ratio of 88:10:2.

[0230] In the first-stage, second-stage, third-stage, fourth-stage, and fifth-stage rolling processes, the roller body, roller diameter, and roller roughness all refer to the roller body that contacts the electrode sheet, as well as the roller diameter and roughness of that roller body.

[0231] Example 2

[0232] This embodiment is basically the same as Embodiment 1, except that:

[0233] In step (2), the first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling, and fifth-stage rolling are performed using... Figure 2 The rolling system shown is used for the first stage of rolling, the second stage of rolling, the third stage of rolling, the fourth stage of rolling, and the fifth stage of rolling.

[0234] Example 3

[0235] The method for manufacturing the electrode sheet in this embodiment includes the following steps:

[0236] (1) Graphite 2, conductive agent Super P, CMC, and SBR were added to an appropriate amount of pure water in a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry with a solid content of 54wt%. Then, the negative electrode slurry was added at a rate of 200g / m 2 The areal density is uniformly coated on both opposite surfaces of a 6μm thick copper foil. After thorough drying, the thickness of the electrode (i.e., the thickness of the dried electrode) is 180μm, according to 1.47g / cm³. 3 The requirement for electrode compaction is to control the thickness of the electrode after roller pressing (i.e., the preset thickness after roller pressing) to be 135μm. Therefore, the calculated total pressing amount requirement (i.e., the total pressing amount) is 45μm.

[0237] (2) The dried electrode sheet is subjected to first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling and fifth-stage rolling under cold pressing conditions at 5°C to obtain a negative electrode sheet with a thickness of 135μm.

[0238] in:

[0239] In the first stage of rolling, a two-roll mill is used, with the reduction accounting for 40% of the total reduction. The roll diameter is 300 mm, the roll body is made of alloy tool steel, the roll roughness is 1 μm, the roll gap is 162 μm, and the roll linear speed is 66.7 m / min.

[0240] In the second stage of rolling, a two-roll mill is used, with the reduction accounting for 20% of the total reduction. The roll diameter is 400 mm, the roll body is made of alloy tool steel, the roll roughness is 0.75 μm, the roll gap is 153 μm, and the roll linear speed is 70.6 m / min.

[0241] In the third stage of rolling, a four-high mill is used, with the reduction accounting for 20% of the total reduction. The roll diameter is 500 mm, the roll body is made of alloy tool steel, the roll roughness is 0.5 μm, the roll gap is 144 μm, and the roll linear speed is 75 m / min.

[0242] In the fourth stage of rolling, a two-roll mill is used, with the reduction accounting for 10% of the total reduction. The roll diameter is 800 mm, the roll body is made of alloy tool steel, the roll roughness is 0.3 μm, the roll gap is 139.5 μm, and the roll linear speed is 77.4 m / min.

[0243] In the fifth-stage rolling process, a four-high mill is used, with a reduction accounting for 10% of the total reduction. The roll diameter is 1000 mm, and the roll body is made of alloy tool steel coated with tungsten carbide. The roll roughness is 0.1 μm, the roll gap is 135 μm, and the roll linear speed is 80 m / min. The tungsten carbide coating thickness is 0.3 mm. The tungsten carbide coating is composed of tungsten carbide (WC), cobalt (Co), and chromium (Cr), with a WC:Co:Cr mass ratio of 88:10:2.

[0244] In the first-stage, second-stage, third-stage, fourth-stage, and fifth-stage rolling processes, the roller body, roller diameter, and roller roughness all refer to the roller body that contacts the electrode sheet, as well as the roller diameter and roughness of that roller body.

[0245] Example 4

[0246] This embodiment is basically the same as embodiment 3, except that:

[0247] In step (2), the first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling, and fifth-stage rolling are performed using... Figure 2 The rolling system shown is used for the first stage of rolling, the second stage of rolling, the third stage of rolling, the fourth stage of rolling, and the fifth stage of rolling.

[0248] Example 5

[0249] The method for manufacturing the electrode sheet in this embodiment includes the following steps:

[0250] (1) Lithium iron phosphate, conductive agent Super P, PVDF, and dispersant HFF-2968 (Shenzhen Haofei) were added to an appropriate amount of NMP in a mass ratio of 93:5:1.8:0.2 and mixed evenly to obtain a positive electrode slurry with a solid content of 63wt%. Then, the positive electrode slurry was subjected to a reaction at 380g / m³. 2 The areal density is uniformly coated on both opposite surfaces of an aluminum foil with a thickness of 15 μm. After thorough drying, the thickness of the electrode (i.e., the thickness of the dried electrode) is 215 μm, according to 2.27 g / cm³. 3 The requirement for electrode compaction is to control the thickness of the electrode after roller pressing (i.e., the preset thickness after roller pressing) to be 165μm, so the calculated total pressing amount requirement (i.e., total pressing amount) is 50μm.

[0251] The lithium iron phosphate particles have a volumetric particle size (D50) of 0.745 μm, a Dmax of 7.6 μm, a span of 3.2, and a compaction density of 2.35 g / cm³. 3 .

[0252] (2) The dried electrode sheet is subjected to first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling and fifth-stage rolling under cold pressing conditions at 15°C to obtain a negative electrode sheet with a thickness of 165μm.

[0253] in:

[0254] In the first stage of rolling, a two-roll mill is used, with the reduction accounting for 60% of the total reduction. The roll diameter is 300 mm, the roll body is made of alloy tool steel, the roll roughness is 1 μm, the roll gap is 185 μm, and the roll linear speed is 89.2 m / min.

[0255] In the second stage of rolling, a two-roll mill is used, with the reduction accounting for 20% of the total reduction. The roll diameter is 400 mm, the roll body is made of alloy tool steel, the roll roughness is 0.75 μm, the roll gap is 175 μm, and the roll linear speed is 94.3 m / min.

[0256] In the third stage of rolling, a four-high mill is used, with the reduction accounting for 10% of the total reduction. The roll diameter is 500 mm, the roll body is made of alloy tool steel, the roll roughness is 0.5 μm, the roll gap is 170 μm, and the roll linear speed is 97.1 m / min.

[0257] In the fourth stage of rolling, a two-roll mill is used, with a reduction of 8% of the total reduction. The roll diameter is 800 mm, the roll body is made of alloy tool steel, the roll roughness is 0.3 μm, the roll gap is 166 μm, and the roll linear speed is 99.4 m / min.

[0258] In the fifth-stage rolling process, a four-high mill is used, with a reduction of 2% of the total reduction. The roll diameter is 1000 mm, and the roll body is made of alloy tool steel coated with tungsten carbide. The roll roughness is 0.1 μm, the roll gap is 165 μm, and the roll linear speed is 100 m / min. The tungsten carbide coating has a thickness of 0.5 μm and is composed of tungsten carbide (WC), cobalt (Co), and chromium (Cr), with a mass ratio of WC:Co:Cr of 88:10:2.

[0259] In the first-stage, second-stage, third-stage, fourth-stage, and fifth-stage rolling processes, the roller body, roller diameter, and roller roughness all refer to the roller body that contacts the electrode sheet, as well as the roller diameter and roughness of that roller body.

[0260] Example 6

[0261] This embodiment is basically the same as embodiment 5, except that:

[0262] In step (2), the first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling, and fifth-stage rolling are performed using... Figure 2 The rolling system shown is used for the first stage of rolling, the second stage of rolling, the third stage of rolling, the fourth stage of rolling, and the fifth stage of rolling.

[0263] Example 7

[0264] This embodiment is basically the same as embodiment 6, except that:

[0265] In step (2):

[0266] In the first stage of rolling, a two-roll mill is used, with the reduction accounting for 40% of the total reduction. The roll diameter is 200 mm, the roll body is made of alloy tool steel, the roll roughness is 0.6 μm, the roll gap is 195 μm, and the roll linear speed is 84.6 m / min.

[0267] In the second stage of rolling, a two-roll mill is used, with the reduction accounting for 30% of the total reduction. The roll diameter is 300 mm, the roll body is made of alloy tool steel, the roll roughness is 0.5 μm, the roll gap is 180 μm, and the roll linear speed is 91.7 m / min.

[0268] In the third stage of rolling, a four-high mill is used, with the reduction accounting for 15% of the total reduction. The roll diameter is 400 mm, the roll body is made of alloy tool steel, the roll roughness is 0.5 μm, the roll gap is 172.5 μm, and the roll linear speed is 95.7 m / min.

[0269] In the fourth stage of rolling, a two-roll mill is used, with the reduction accounting for 10% of the total reduction. The roll diameter is 600 mm, the roll body is made of alloy tool steel, the roll roughness is 0.3 μm, the roll gap is 167.5 μm, and the roll linear speed is 98.5 m / min.

[0270] In the fifth stage of rolling, a four-roll mill is used, the reduction accounts for 5% of the total reduction, the roll diameter is 800mm, the roll body is made of alloy tool steel with tungsten carbide coating, the roll roughness is 0.3μm, the roll gap is 165μm, and the roll linear speed is 100m / min.

[0271] Example 8

[0272] This embodiment is basically the same as embodiment 6, except that:

[0273] In step (2):

[0274] In the first stage of rolling, a two-roll mill is used, with the reduction accounting for 48% of the total reduction. The roll diameter is 400 mm, the roll body is made of alloy tool steel, the roll roughness is 0.75 μm, the roll gap is 191 μm, and the roll linear speed is 86.4 m / min.

[0275] In the second stage of rolling, a two-roll mill is used, with the reduction accounting for 20% of the total reduction. The roll diameter is 500 mm, the roll body is made of alloy tool steel, the roll roughness is 0.6 μm, the roll gap is 181 μm, and the roll linear speed is 91.2 m / min.

[0276] In the third stage of rolling, a four-high mill is used, with the reduction accounting for 15% of the total reduction. The roll diameter is 500 mm, the roll body is made of alloy tool steel, the roll roughness is 0.5 μm, the roll gap is 173.5 μm, and the roll linear speed is 95.1 m / min.

[0277] In the fourth stage of rolling, a two-roll mill is used, with the reduction accounting for 15% of the total reduction. The roll diameter is 1000mm, the roll body is made of alloy tool steel, the roll roughness is 0.2μm, the roll gap is 166μm, and the roll linear speed is 99.4m / min.

[0278] In the fifth stage of rolling, a four-high mill is used, the reduction accounts for 2% of the total reduction, the roll diameter is 1200mm, the roll body is made of alloy tool steel with tungsten carbide coating, the roll roughness is 0.1μm, the roll gap is 165μm, and the roll linear speed is 100m / min.

[0279] Example 9

[0280] This embodiment is basically the same as embodiment 6, except that:

[0281] Step (1) involves uniformly mixing lithium iron phosphate, conductive agent Super P, PVDF, and dispersant HFF-2968 (Shenzhen Haofei) in a mass ratio of 80:15:4.8:0.2 with an appropriate amount of NMP to obtain a positive electrode slurry with a solid content of 63wt%. Then, the positive electrode slurry is mixed at a concentration of 150g / m³. 2 The areal density is uniformly coated on both opposite surfaces of an aluminum foil with a thickness of 15 μm. After thorough drying, the thickness of the electrode (i.e., the thickness of the dried electrode) is 95 μm, according to 1.74 g / cm³. 3 The requirement for electrode compaction is to control the thickness of the electrode after roller pressing (i.e., the preset thickness after roller pressing) to be 85μm, so the calculated total pressing amount requirement (i.e., total pressing amount) is 10μm.

[0282] The lithium iron phosphate particles have a volumetric particle size (D50) of 0.745 μm, a Dmax of 7.6 μm, a span of 3.2, and a compaction density of 2.35 g / cm³. 3 .

[0283] Example 10

[0284] This embodiment is basically the same as embodiment 6, except that:

[0285] Step (1) involves adding lithium iron phosphate, conductive agent Super P, PVDF, and dispersant HFF-2968 (Shenzhen Haofei) to an appropriate amount of NMP in a mass ratio of 97:0.5:2.3:0.2 and mixing them uniformly to obtain a positive electrode slurry with a solid content of 63wt%. Then, the positive electrode slurry is mixed at a concentration of 550g / m³. 2 The areal density is uniformly coated on both opposite surfaces of an aluminum foil with a thickness of 15 μm. After thorough drying, the thickness of the electrode (i.e., the thickness of the dried electrode) is 315 μm, according to 2.58 g / cm³. 3 The requirement for electrode compaction is to control the thickness of the electrode after roller pressing (i.e., the preset thickness after roller pressing) to be 210μm, so the calculated total pressing amount requirement (i.e., total pressing amount) is 105μm.

[0286] The lithium iron phosphate particles have a volumetric particle size (D50) of 0.745 μm, a Dmax of 7.6 μm, a span of 3.2, and a compaction density of 2.35 g / cm³. 3 .

[0287] Comparative Example 1

[0288] This comparative example is basically the same as Example 2, except that:

[0289] Step (2) is as follows: After drying, the electrode sheet is rolled using a conventional roller to finally obtain a negative electrode sheet with a thickness of 120μm.

[0290] The conventional roll is a two-roll mill with a roll body roughness of 1.0μm. The roll body is made of alloy tool steel. The process parameters for rolling with conventional rolls are: one-time rolling, and the rolling pressure and roll gap are adjusted by the electrode size obtained by the laser thickness gauge after the roll.

[0291] Comparative Example 2

[0292] This comparative example is basically the same as Example 2, except that:

[0293] In step (2), the first rolling is hot-pressed at 95°C, the second rolling is hot-pressed at 25°C, and the remaining third, fourth and fifth rolling are still cold-pressed at 10°C.

[0294] II. Performance Testing

[0295] 1. Electrode rebound rate

[0296] The rebound rate of the electrode sheets produced in each embodiment or comparative example was tested. The test method was as follows: 0h after the electrode sheet was rolled (i.e., the electrode sheet that has not been rolled out after the fifth stage of rolling or the electrode sheet that has not been rolled out after conventional rolling in Comparative Example 1), the thickness of the electrode sheet at multiple positions in the width direction (excluding the stripping area, which is close to the tab and parallel to the tab, and is generally 1 to 10 mm wide) was measured with a micrometer. The thickness of the electrode sheet was calculated and marked as the first variance. After waiting for 24h, the thickness of the electrode sheet at multiple positions in the width direction other than the stripping area was measured and the variance of the first variance was calculated and marked as the second variance. The rebound rate of the electrode sheet was calculated according to formula (1). The first variance and the second variance were both calculated according to formula (2).

[0297] Rebound rate = (Thickness after 24 hours of rolling - Thickness after 0 hours of rolling) / Thickness after 0 hours of rolling * 100% (Equation 1)

[0298] In formula (1), the thickness after 24 hours of rolling is the first variance, and the thickness after 0 hours of rolling is the second variance.

[0299]

[0300] In equation (2), σ 2 Let X be the variance, i be the i-th position, n be the total number of positions, and X be the variance. i Let the thickness be at position i. This represents the average thickness at multiple locations.

[0301] 2. Electrode elongation

[0302] The elongation of the electrode sheets prepared in each embodiment or comparative example was tested separately. The test method was as follows:

[0303] Before the electrode is rolled, a rectangular area on the electrode is selected and marked as region A1. The length of region A1 is defined as along the electrode's belt direction, and the width is defined as along the electrode's width direction. The length is 1m, and the width is the same as the electrode's width and covers the entire width of the electrode. The area of ​​region A1 is calculated as S1. After the electrode is rolled, the region corresponding to region A1 is found and marked as region A2. The length and width of region A2 are measured, and its area is calculated as S2. The elongation is S2 / S1-1.

[0304] 3. Battery first-time efficiency

[0305] The electrode sheets prepared in each embodiment and comparative example were assembled into pouch cells with a nominal capacity of 3Ah, and the initial efficiency of the cells was tested. Among them:

[0306] When the electrode in each embodiment or comparative example is a negative electrode, the battery assembly method is as follows:

[0307] (1) Preparation of the positive electrode sheet: The areal density was set to 1.13 with an NP ratio (NP ratio = negative electrode capacity per unit area / positive electrode capacity per unit area), and the sheets were cut into 59*90.5mm pieces. The positive electrode active material was lithium iron phosphate, with a volumetric particle size D50 of 0.745μm, a Dmax of 7.6μm, a span of 3.2, and a powder compaction density of 2.35g / cm³. 3 .

[0308] (2) Preparation of electrolyte: The electrolyte was injected with a filling coefficient of 4.0. The electrolyte consisted of solvent and lithium salt. The solvent consisted of ethyl acetate (EA), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and ethylene carbonate (EC). The volume ratio of EA, DMC, EMC, VC, and EC was 10:20:30:5:35. The lithium salt consisted of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). The mass ratio of LiPF6 to LiFSI was 3:2. The mass content of lithium salt in the electrolyte was 14.8%.

[0309] (3) Selection of diaphragm: A 7+2+2 single-sided coated diaphragm is used (where 7 refers to the thickness of the base membrane 7μm, the first 2 is the thickness of the ceramic layer 2μm, the second 2 is the thickness of the PVDF 2μm, the base membrane (diaphragm itself) is made of PP (polypropylene), and the coating material is PVDF), with the coated side facing the positive electrode.

[0310] (4) Assembly: The positive electrode, separator and negative electrode are stacked and then liquid is injected, formed and capacity tested to obtain a soft pack battery with a nominal capacity of 3Ah.

[0311] When the electrode in each embodiment or comparative example is a positive electrode, the battery assembly method is as follows:

[0312] (1) Preparation of negative electrode sheet: The areal density is set with an NP ratio of 1.13, and the electrode sheet is cut into 62*93.5mm.

[0313] (2) Preparation of electrolyte: The electrolyte was injected with a filling coefficient of 4.0. The electrolyte consisted of solvent and lithium salt. The solvent consisted of ethyl acetate (EA), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and ethylene carbonate (EC). The volume ratio of EA, DMC, EMC, VC, and EC was 10:20:30:5:35. The lithium salt consisted of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). The mass ratio of LiPF6 to LiFSI was 3:2. The mass content of lithium salt in the electrolyte was 14.8%.

[0314] (3) Selection of diaphragm: A 7+2+2 single-sided coated diaphragm is used (where 7 refers to the thickness of the base membrane 7μm, the first 2 is the thickness of the ceramic layer 2μm, the second 2 is the thickness of the PVDF 2μm, the base membrane (diaphragm itself) is made of PP (polypropylene), and the coating material is PVDF), with the coated side facing the positive electrode.

[0315] (4) Assembly: The positive electrode, separator and negative electrode are stacked and then liquid is injected, formed and capacity tested to obtain a soft pack battery with a nominal capacity of 3Ah.

[0316] The test method for the first-time efficiency of the battery is as follows: For lithium iron phosphate batteries (the batteries assembled with electrode sheets in each embodiment and comparative example are all lithium iron phosphate batteries), the first charge and discharge are performed, with a charge and discharge rate of 0.33C, a charging cut-off voltage of 3.65V, and a discharge cut-off voltage of 2.5V. The first-time efficiency is obtained by dividing the discharge capacity by the charging capacity. For lithium iron phosphate batteries, the first charge and discharge are performed, with a charge and discharge rate of 0.33C, a charging cut-off voltage of 4.2V, and a discharge cut-off voltage of 2.75V. The first-time efficiency is obtained by dividing the discharge capacity by the charging capacity.

[0317] The rebound rate, elongation rate, and first-efficiency test results of the electrodes prepared in each embodiment and their corresponding batteries are shown in Table 1.

[0318] Table 1. Rebound rate, elongation rate, and first-effect test results

[0319]

[0320] As can be seen from Table 1, compared with the comparative example, the electrode rebound rate and elongation obtained by the multi-stage roll forming method of this application embodiment are significantly reduced, the thickness variance consistency is better, and the corresponding battery first efficiency is significantly improved.

[0321] In summary, this application mainly uses a multi-stage rolling process, employing decreasing reduction and roll gap adjustment, and adapting different reduction amounts to the diameter, roughness, and hardness of the roll body, ultimately achieving stress release (manifested as low mechanical rebound rate and small variation in electrode thickness variance) and electrode consistency (manifested as small thickness variance in the electrode width direction and high initial efficiency).

[0322] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0323] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0324] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for manufacturing an electrode sheet, characterized in that, include: A slurry is coated onto the current collector and dried to obtain a dried electrode sheet. The difference between the thickness of the dried electrode sheet and the preset thickness after rolling is used as the total reduction. The dried electrode sheet is subjected to continuous multi-stage rolling, and the percentage of the reduction amount of the previous rolling stage to the total reduction amount is greater than or equal to the percentage of the reduction amount of the next rolling stage to the total reduction amount. The sum of the reduction amounts of each rolling stage is equivalent to the total reduction amount. In the multi-stage rolling process, the amount of pressure applied by each stage of the rolling process decreases overall; all stages of the rolling process are cold pressing.

2. The manufacturing method according to claim 1, characterized in that, In two adjacent rolling stages, the percentage of the reduction amount of the preceding rolling stage in the total reduction amount is greater than the percentage of the reduction amount of the following rolling stage in the total reduction amount.

3. The manufacturing method according to claim 1, characterized in that, In the case of two adjacent rolling stages, the diameter of the preceding rolling stage is less than or equal to the diameter of the following rolling stage, and in the multi-stage rolling process, the diameter of each rolling stage generally changes from small to large. And / or, in two adjacent rolling stages, the roller roughness of the preceding rolling stage is greater than or equal to the roller roughness of the following rolling stage, and in the multi-stage rolling process, the roller roughness of each rolling stage changes from large to small overall. And / or, the temperature of the cold pressing is 5-15°C; And / or, in the multi-stage rolling process, the roller linear speed of the last stage of rolling is used as a reference, and the roller linear speeds of the remaining stages of rolling are set step by step.

4. The manufacturing method according to claim 3, characterized in that, In two adjacent rolling stages, the diameter of the roller in the previous rolling stage is smaller than that in the next rolling stage. And / or, in two adjacent rolling stages, the roll roughness of the preceding rolling stage is greater than that of the following rolling stage.

5. The manufacturing method according to claim 4, characterized in that, In two adjacent rolling stages, the linear speed of the roller in the preceding rolling stage is less than that in the following rolling stage.

6. The manufacturing method according to claim 1, characterized in that, The total reduction is distributed to each stage of roller pressing by adjusting the roller gap. And / or, in two adjacent rolling stages, the roll gap of the preceding rolling stage is greater than or equal to the roll gap of the following rolling stage; And / or, in the multi-stage rolling process, at least the first stage rolling process uses rollers made of alloy tool steel, and the last stage rolling process uses rollers made of alloy tool steel coated with tungsten carbide. And / or, in the multi-stage rolling process, at least the first stage rolling process uses a two-roll mill, and at least the last stage rolling process uses a four-roll mill; And / or, the areal density of the dried electrode sheet is 150-550 g / m³. 3 ; And / or, the method for manufacturing the electrode further includes the step of obtaining the total reduction rate based on the total reduction amount; Optionally, the total reduction is 5-110 μm, and / or the total reduction rate is 10-50%.

7. The manufacturing method according to any one of claims 1 to 6, characterized in that, The multi-stage rolling process includes sequentially performed first-stage rolling, second-stage rolling, third-stage rolling, fourth-stage rolling, and fifth-stage rolling, wherein: The reduction of the first-stage rolling mill is 40-60% of the total reduction, and / or the diameter of the first-stage rolling mill is 200-400 mm, and / or the first-stage rolling mill uses a two-roll mill, and / or the roll body of the first-stage rolling mill is made of alloy tool steel, and / or the roughness of the first-stage rolling mill is 0.5-1.0 μm; And / or, the reduction of the second-stage roll forming is 20-30% of the total reduction, and / or, the roll diameter of the second-stage roll forming is 300-500 mm, and / or, the second-stage roll forming uses a two-roll mill, and / or, the roll body of the roll used in the second-stage roll forming is alloy tool steel, and / or, the roll roughness of the second-stage roll forming is 0.5-1.0 μm; And / or, the reduction of the third-stage rolling mill is 10-20% of the total reduction, and / or, the diameter of the third-stage rolling mill is 400-600 mm, and / or, the third-stage rolling mill uses a two-roll mill, and / or, the roll body of the third-stage rolling mill is made of alloy tool steel, and / or, the roughness of the third-stage rolling mill is 0.3-0.5 μm; And / or, the reduction of the fourth-stage roll forming is 5-15% of the total reduction, and / or, the roll diameter of the fourth-stage roll forming is 600-1000 mm, and / or, the fourth-stage roll forming uses a four-roll mill, and / or, the roll body of the rolls used in the fourth-stage roll forming is alloy tool steel, and / or, the roll roughness of the fourth-stage roll forming is 0.1-0.3 μm; And / or, the reduction of the fifth-stage roll forming is 2-10% of the total reduction, and / or, the roll diameter of the fifth-stage roll forming is 800-1200 mm, and / or, the fifth-stage roll forming uses a four-high mill, and / or, the roll body of the fifth-stage roll forming is alloy tool steel coated with tungsten carbide, and / or, the roll roughness of the fifth-stage roll forming is 0.1-0.3 μm.

8. A rolling system for use in the manufacturing method as described in any one of claims 1 to 7, characterized in that, It includes an unwinding device for unwinding the dried electrode sheet, a multi-group of rollers for multi-stage rolling, and a winding device for winding the obtained electrode sheet after multi-stage winding. Each set of rollers is used for one of the multiple stages of rolling; Tension roller sets are provided between adjacent sets of rollers, between the first set of rollers and the unwinding device, and between the last set of rollers and the winding device.

9. An electrode sheet, characterized in that, Prepared using the manufacturing method as described in any one of claims 1 to 7 or the rolling system as described in claim 8.

10. A secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, The positive electrode or the negative electrode is the electrode as described in claim 9.

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