Pole piece, secondary battery and electronic device

Abstract

The invention provides a pole piece, a secondary battery and an electronic device. The pole piece comprises a current collector and a material layer arranged on at least one surface of the current collector, the material layer comprises an electrode active material and a binding agent, the binding agent comprises a fibrous binding agent and a granular binding agent, based on the total surface area of the electrode active material, the proportion of the area, covered by the binding agent, of the electrode active material is A, and A is larger than or equal to 5% and smaller than or equal to 25%. The secondary battery provided by the invention has good dynamic performance and cycle performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a pole piece, a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in fields such as smartphones, wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. However, the preparation of wet electrodes by the traditional slurry coating method requires the use of a large amount of toxic solvents (such as N-methylpyrrolidone) and high-energy drying equipment, which is not environmentally friendly and has high preparation costs. In addition, the surface of the electrode active material in the electrode plate prepared by the wet method is heavily coated with a binder, which reduces the reactive area of ​​the electrode active material. During the drying process, the binder will float up, making the above problems more serious and bringing the risk of clogging the pores in the upper layer of the material layer, affecting the kinetic performance and cycle performance of the lithium-ion battery. Summary of the Invention

[0003] The purpose of this application is to provide a pole piece, a secondary battery, and an electronic device to improve the dynamic performance and cycle performance of the secondary battery. The specific technical solution is as follows:

[0004] The first aspect of the present application provides a pole piece, which includes a current collector and a material layer disposed on at least one surface of the current collector, the material layer including an electrode active material and a binder, the binder including a fibrous binder and a granular binder, and based on the total surface area of ​​the electrode active material, the area of ​​the electrode active material covered by the binder accounts for A, 5%≤A≤25%. The pole piece of the present application can reduce the amount of fibrous binder used by combining the granular binder and the fibrous binder, thereby reducing the coating of the electrode active material by the binder, and can increase the reactive area of ​​the electrode active material. In addition, when the area of ​​the electrode active material covered by the binder accounts for A within this range, the bonding effect can be ensured, the energy density can be increased, and the dynamic performance and cycle performance of the secondary battery can be improved.

[0005] In some embodiments of the present application, 5%≤A≤20%. A value within the above range is beneficial to further improve the kinetic performance and cycle performance of the secondary battery.

[0006] In some embodiments of the present application, based on the total surface area of ​​the electrode active material covered by the binder, the area of ​​the electrode active material covered by the fibrous binder is represented by B, and the area of ​​the electrode active material covered by the granular binder is represented by C, where 50% ≤ B ≤ 98%, and 2% ≤ C ≤ 50%. Values ​​of B and C within the above ranges are beneficial for reducing the coating of the electrode active material by the binder, increasing the reactive area of ​​the electrode active material, and thereby improving the kinetic performance and cycle performance of the secondary battery.

[0007] In some embodiments of the present application, 1≤B / C≤9. When the value of B / C is within the above range, the fibrous binder and the particulate binder act synergistically, which is beneficial to further improve the dynamic performance and cycle performance of the secondary battery.

[0008] In some embodiments of the present application, the length of the fibrous binder is L μm, the diameter of the fibrous binder is D nm, 5≤L≤100, 10≤D≤200. The values ​​of L and D of the fibrous binder within the above range are beneficial to improving the dynamic performance and cycle performance of the secondary battery.

[0009] In some embodiments of the present application, the average particle size of the particulate binder is 0.1 μm to 5 μm. The average particle size of the particulate binder within the above range is beneficial to improving the dynamic performance and cycle performance of the secondary battery.

[0010] In some embodiments of the present application, the binder has a mass percentage of 1% to 10% based on the mass of the material layer. The binder mass percentage within the above range is conducive to making the secondary battery have a higher energy density, while also having good kinetic performance and cycle performance.

[0011] In some embodiments of the present application, the mass ratio of the fibrous binder to the particulate binder is (1 to 9) : 1. The mass ratio of the fibrous binder to the particulate binder within the above range is beneficial to improving the dynamic performance and cycle performance of the secondary battery.

[0012] In some embodiments of the present application, the fibrous binder includes at least one of polytetrafluoroethylene, polytetrafluoroethylene-perfluorosulfonyl copolymer, polyacrylonitrile, or sericin; and the granular binder includes at least one of polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, paraffin wax, polylactic acid, polyurethane, acrylonitrile-butadiene-styrene copolymer, or styrene-butadiene rubber. The use of these fibrous and granular binders can improve the dynamic and cycling performance of secondary batteries.

[0013] In some embodiments of the present application, the electrode active material includes a positive electrode active material and a negative electrode active material, wherein the Dv50 of the positive electrode active material is 5 μm to 35 μm, and the Dv50 of the negative electrode active material is 5 μm to 35 μm. The Dv50 of the positive electrode active material and the negative electrode active material within the above range is conducive to reducing the coating of the binder on the electrode active material and increasing the reactive area of ​​the electrode active material, thereby facilitating the improvement of the kinetic performance and cycle performance of the secondary battery.

[0014] In some embodiments of the present application, the binder mass percentage variation rate for a given electrode sheet of the same area, measured perpendicular to the thickness direction, is between 1% and 4%. A binder mass percentage variation rate within this range indicates that the binder is evenly distributed throughout the material layer, which is beneficial for improving the kinetic and cycling performance of the secondary battery.

[0015] The second aspect of the present application provides a secondary battery, which includes the electrode provided in the first aspect of the present application. The secondary battery of the present application has good dynamic performance and cycle performance.

[0016] The third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0017] Beneficial effects of this application:

[0018] The present application provides a pole piece, a secondary battery, and an electronic device. The pole piece includes a current collector and a material layer disposed on at least one surface of the current collector. The material layer includes an electrode active material and a binder. The binder includes a fibrous binder and a granular binder. Based on the total surface area of ​​the electrode active material, the area of ​​the electrode active material covered by the binder accounts for A, 5%≤A≤25%. The pole piece of the present application can reduce the amount of fibrous binder used by the combined use of a granular binder and a fibrous binder, thereby reducing the coating of the electrode active material by the binder, and can increase the reactive area of ​​the electrode active material. In addition, when the area of ​​the electrode active material covered by the binder accounts for A within this range, it can ensure the bonding effect and increase the energy density, while also improving the dynamic performance and cycle performance of the secondary battery.

[0019] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 This is a schematic structural diagram of a material layer along a direction perpendicular to the thickness in one embodiment of the present application.

[0022] Reference numerals: material layer 10 , electrode active material 11 , fibrous binder 12 , granular binder 13 . DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0024] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0025] The first aspect of the present application provides a pole piece, which includes a current collector and a material layer disposed on at least one surface of the current collector, the material layer including an electrode active material and a binder, the binder including a fibrous binder and a granular binder, and based on the total surface area of ​​the electrode active material, the area of ​​the electrode active material covered by the binder accounts for A, 5%≤A≤25%, preferably, 5%≤A≤20%. For example, the value of A can be 5%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, 17%, 18%, 19%, 20%, 22%, 24%, 25%, or a range consisting of any two of these values.

[0026] The electrode of the present application can obtain a material layer by dry powder mixing, which can reduce the use of toxic solvents (such as N-methylpyrrolidone) and high-energy drying equipment, reduce the cost of electrode preparation and be environmentally friendly. In addition, the binder of the electrode of the present application includes a fibrous binder and a granular binder. During the preparation of the electrode, the fibrous binder forms a fibrous bond to the electrode active material through shear force, and the granular binder forms a point bond at the contact site between the electrode active materials through heating, so that the A value is within the above range. The binder covers less of the electrode active material, which can increase the effective area of ​​the electrode active material participating in the electrochemical reaction, that is, the reaction active area. The binder is evenly distributed in the material layer and the content is appropriate, which is conducive to improving the floating problem of the binder, reducing the risk of the pores in the upper layer of the material layer being blocked, improving the liquid phase transmission capacity of lithium ions and the reaction rate of the electrode active material particles to deintercalate lithium, reducing polarization, and at the same time, the cohesion of the material layer and the bonding force between the material layer and the current collector are large, and the risk of the material layer falling off during the cycle is low, and the expansion is small, thereby improving the dynamic performance and cycle performance of the secondary battery.

[0027] When the value of A is too small, for example, less than 5%, although the reactive area of ​​the electrode active material is large, the content of the binder in the material layer is too low, the cohesive force of the material layer is too small, the mechanical strength is too low, and the bonding between the material layer and the current collector is also poor, making the material layer easy to fall off during the cycle and swell more severely, which is not conducive to improving the kinetic performance and cycle performance of the secondary battery. When the value of A is too large, for example, greater than 25%, the content of the binder in the material layer is too high and the content of the electrode active material is too low, which affects the energy density of the secondary battery. In addition, the binder covers the electrode active material severely, reducing the reactive area of ​​the electrode active material, affecting the transmission of lithium ions in the material layer and the reaction rate of lithium insertion and deintercalation of the electrode active material particles, which is not conducive to improving the kinetic performance and cycle performance of the secondary battery.

[0028] In some embodiments, the total surface area of ​​the electrode active material and the area of ​​the electrode active material covered by the binder can refer to the area obtained by scanning electron microscopy (SEM) testing, or can be the area obtained by other testing methods, as long as the purpose of this application is achieved. In some embodiments, the A value of the electrode sheet satisfies 5% ≤ A ≤ 25%, which can be satisfied in the entire area of ​​the material layer or in any part of the material layer.

[0029] For example, the length direction of the material layer itself is defined as X, and the width direction is defined as Y. The material layer usually has a long side and a short side. The length direction is the extension direction of the long side of the material layer. It should be understood that the above definition of direction is for the purpose of convenient description of this application. Figure 1As shown, the material layer 10 includes an electrode active material 11 and a binder, and the binder includes a fibrous binder 12 and a granular binder 13 .

[0030] In some embodiments of the present application, based on the total surface area of ​​the electrode active material covered by the binder, the area ratio of the electrode active material covered by the fibrous binder is B, and the area ratio of the electrode active material covered by the granular binder is C, 50%≤B≤98%, and 2%≤C≤50%. For example, the value of B can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or a range consisting of any two of these values, and the value of C can be 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of these values. When the values ​​of B and C are within the above ranges, the fibrous binder and the granular binder act synergistically, which is beneficial to reducing the coating of the binder on the electrode active material, increasing the reaction active area of ​​the electrode active material, improving the reaction rate of lithium insertion and extraction of the electrode active material particles, reducing polarization, and at the same time strengthening the bonding network in the material layer, improving the cohesion of the material layer and the bonding force between the material layer and the current collector, reducing the risk of the material layer falling off, and reducing the probability of electrical deactivation of the electrode active material, thereby helping to improve the kinetic performance and cycle performance of the secondary battery.

[0031] In some embodiments of the present application, 1≤B / C≤9. For example, the value of B / C can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or a range consisting of any two of these values. When the value of B / C is within the above range, the fibrous binder and the granular binder can work together better, which is beneficial to further strengthen the bonding network in the material layer, improve the cohesion of the material layer and the bonding force between the material layer and the current collector, reduce the risk of the material layer falling off, and reduce the probability of electrical deactivation of the electrode active material, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0032] In some embodiments of the present application, the length of the fibrous binder is L μm, the diameter of the fibrous binder is D nm, 5≤L≤100, and 10≤D≤200. For example, the value of L can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or a range consisting of any two values ​​therein, and the value of D can be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a range consisting of any two values ​​therein. The values ​​of L and D of the fibrous binder are within the above range, which is conducive to making the fibrous binder have higher mechanical strength, improving the cohesion of the material layer and the bonding force between the material layer and the current collector, and at the same time helping to reduce the coating of the binder on the electrode active material, increasing the reaction active area of ​​the electrode active material, and being easy to implement in terms of process, which is conducive to improving the processing performance of the electrode sheet, thereby helping to improve the dynamic performance and cycle performance of the secondary battery.

[0033] In some embodiments, the length of the fibrous binder is L μm, the diameter of the fibrous binder is D nm, and 0.025 ≤ L / D ≤ ​​10. For example, the value of L / D can be 0.025, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two of these values. When the value of L / D is within the above range, the fibrous binder has a suitable aspect ratio, which is beneficial for the fibrous binder to have high mechanical strength, improve the cohesion of the material layer and the adhesion between the material layer and the current collector, and also help reduce the coating of the binder on the electrode active material, increase the reactive area of ​​the electrode active material, and be easy to implement in the process, which is beneficial for improving the processing performance of the electrode sheet, thereby improving the dynamic performance and cycle performance of the secondary battery.

[0034] In some embodiments of the present application, the average particle size of the granular binder is 0.1 μm to 5 μm. For example, the average particle size of the granular binder can be 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm or a range consisting of any two of these values. The average particle size of the granular binder within the above range is beneficial to improving the cohesion of the material layer and the adhesion between the material layer and the current collector, while also helping to reduce the coating of the binder on the electrode active material, increase the reactive area of ​​the electrode active material, increase the reaction rate of the electrode active material particles in lithium insertion and extraction, reduce polarization, and thus help to improve the kinetic performance and cycle performance of the secondary battery. In the present application, the average particle size of the granular binder refers to the average diameter of the circumscribed circle of the granular binder.

[0035] In some embodiments of the present application, based on the mass of the material layer, the mass percentage of the binder is 1% to 10%. For example, the mass percentage of the binder can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of these values. The mass percentage of the binder in the material layer is within the above range, which is conducive to making the secondary battery have a higher energy density, while making the cohesion of the material layer and the bonding force between the material layer and the current collector larger, reducing the risk of the material layer falling off, and the binder has less coating on the electrode active material, and the reactive area of ​​the electrode active material is larger, which is conducive to improving the reaction rate of the electrode active material particles to deintercalate and deintercalate lithium, reducing polarization, thereby helping to improve the kinetic performance and cycle performance of the secondary battery, while having a higher energy density.

[0036] In some embodiments of the present application, the mass ratio of the fibrous binder to the granular binder is (1 to 9):1. For example, the mass ratio of the fibrous binder to the granular binder can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or a range consisting of any two values ​​therein. When the mass ratio of the fibrous binder to the granular binder is within the above range, the fibrous binder and the granular binder act synergistically, so that the A value is within the range of the present application, which is conducive to forming a good bonding network in the material layer, improving the cohesion of the material layer and the bonding force between the material layer and the current collector, and at the same time, it is also conducive to reducing the coating of the binder on the electrode active material, increasing the reactive area of ​​the electrode active material, improving the lithium intercalation and deintercalation reaction rate of the electrode active material particles, reducing polarization, and thus helping to improve the kinetic performance and cycle performance of the secondary battery.

[0037] In some embodiments, based on the mass of the material layer, the mass percentage of the fibrous binder is 2.5% to 4.9%, and the mass percentage of the particulate binder is 0.6% to 1.9%. For example, the mass percentage of the fibrous binder may be 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.9%, or a range consisting of any two of these values, and the mass percentage of the particulate binder may be 0.6%, 1.0%, 1.2%, 1.5%, 1.7%, 1.9%, or a range consisting of any two of these values.

[0038] In some embodiments of the present application, the fibrous binder includes at least one of polytetrafluoroethylene, polytetrafluoroethylene-perfluorosulfone copolymer, polyacrylonitrile, or sericin. The use of the above-mentioned fibrous binder is beneficial for improving the dynamic performance and cycle performance of the secondary battery.

[0039] In some embodiments of the present application, the granular binder includes at least one of polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, paraffin wax, polylactic acid, polyurethane, acrylonitrile-butadiene-styrene copolymer, or styrene-butadiene rubber. The use of such granular binders is beneficial for improving the dynamic performance and cycle performance of the secondary battery.

[0040] In some embodiments of the present application, the electrode active material includes a positive electrode active material and a negative electrode active material, the Dv50 of the positive electrode active material is 5 μm to 35 μm, and the Dv50 of the negative electrode active material is 5 μm to 35 μm. For example, the Dv50 of the positive electrode active material can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, or a range consisting of any two of the values, and the Dv50 of the negative electrode active material can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, or a range consisting of any two of the values. The Dv50 of the positive and negative active materials within the above range is beneficial to reducing the coating of the electrode active materials by the binder, increasing the reactive area of ​​the electrode active materials, improving the reaction rate of the electrode active material particles in the lithium intercalation and deintercalation reaction, and reducing the risk of agglomeration of the electrode active materials during the preparation process. This allows for a uniform distribution of the components in the material layer, resulting in a continuous and uniform electrode sheet with a bonding network and a conductive network, thereby improving the kinetic performance and cycle performance of the secondary battery. In this application, Dv50 refers to the particle size that reaches 50% of the volume accumulation, measured from the smallest particle size, in the volume-based particle size distribution of the material.

[0041] In some embodiments of the present application, the rate of change of the binder mass percentage for any electrode of the same area taken on the surface perpendicular to the thickness direction is 1% to 4%. For example, the rate of change of the binder mass percentage can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0% or a range consisting of any two values ​​therein. The rate of change of the binder mass percentage within the above range indicates that the binder is evenly distributed in the material layer, which is beneficial to improving the problem of the binder floating up, reducing the risk of pores in the upper layer of the material layer being blocked, and enhancing the liquid phase transmission capacity of lithium ions, thereby helping to improve the kinetic performance and cycle performance of the secondary battery.

[0042] In some embodiments, the rate of change of the binder mass percentage in any electrode of the same thickness taken along the thickness direction is 1% to 4%. For example, the rate of change of the binder mass percentage can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, or a range consisting of any two values ​​therein. The rate of change of the binder mass percentage within the above range indicates that the binder is evenly distributed in the material layer, which is beneficial to improving the binder floating problem, reducing the risk of pores in the upper layer of the material layer being blocked, and enhancing the liquid phase transmission capacity of lithium ions, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0043] The present application does not impose any particular restrictions on the preparation method of the electrode sheet, as long as the purpose of the present application can be achieved. For example, in some embodiments, the preparation of the electrode sheet may include, but is not limited to, the following steps: after uniformly mixing the electrode active material and the conductive agent, adding a fibrous binder and a granular binder, and mixing them uniformly to obtain a material layer dry powder. The material layer dry powder is subjected to high-speed mixing and shearing to fiberize to obtain a fiberized material. The fiberized material is hot-pressed and thinned to obtain a self-supporting membrane. The self-supporting membrane is hot-pressed and composited with a current collector to obtain a electrode sheet.

[0044] In some embodiments, the temperature for mixing the electrode active material and the conductive agent may be 20° C. to 30° C., the rotation speed may be 1000 rpm to 3000 rpm, and the time may be 20 min to 60 min. For example, the temperature for mixing the electrode active material and the conductive agent may be 20° C., 22° C., 25° C., 28° C., 30° C., or a range consisting of any two values ​​thereof, the rotation speed may be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or a range consisting of any two values ​​thereof, and the time may be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or a range consisting of any two values ​​thereof.

[0045] In some embodiments, the temperature when the binder is added can be 0° C. to 18° C., the rotation speed can be 1000 rpm to 3000 rpm, and the time can be 20 min to 60 min. For example, the temperature when the binder is added can be 0° C., 2° C., 5° C., 8° C., 10° C., 12° C., 15° C., 18° C., or a range consisting of any two values ​​thereof, the rotation speed can be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, or a range consisting of any two values ​​thereof, and the time can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or a range consisting of any two values ​​thereof.

[0046] In some embodiments, the temperature of high-speed mixed shearing fiberization can be 60°C to 120°C, the rotation speed can be 3000rpm to 5000rpm, and the time can be 20min to 60min. For example, the temperature of high-speed mixed shearing fiberization can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C or a range consisting of any two values ​​therein, the rotation speed can be 3000rpm, 3500rpm, 4000rpm, 4500rpm, 5000rpm or a range consisting of any two values ​​therein, and the time can be 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min or a range consisting of any two values ​​therein. By regulating the process parameters of high-speed mixed shearing fiberization within the above range, it is beneficial to fiberize the fibrous binder, while reducing the risk of breakage of the fibrous binder, making it have higher mechanical strength, facilitating the processing and preparation of the material layer and reducing the expansion of the electrode active material, thereby improving the dynamic performance and cycle performance of the secondary battery.

[0047] In some embodiments, the temperature of hot pressing and thinning can be 80°C to 180°C, and the pressure can be 1 ton to 30 tons. For example, the temperature of hot pressing and thinning can be 80°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 180°C or a range consisting of any two values ​​therein, and the pressure can be 1 ton, 3 tons, 5 tons, 10 tons, 15 tons, 20 tons, 25 tons, 30 tons or a range consisting of any two values ​​therein. By regulating the process parameters of hot pressing and thinning within the above range, it is beneficial to improve the cohesion of the material layer and the adhesion between the material layer and the current collector, reduce the effect of excessively high processing temperature on the electrochemical performance of the secondary battery, and thus help improve the kinetic performance and cycle performance of the secondary battery.

[0048] In some embodiments, the temperature for hot-pressing the self-supporting film and the current collector can be 80° C. to 180° C., and the pressure can be 1 ton to 50 tons. For example, the temperature for hot-pressing the self-supporting film and the current collector can be 80° C., 100° C., 110° C., 120° C., 130° C., 140° C., 150° C., 160° C., 180° C., or a range consisting of any two values ​​thereof, and the pressure can be 1 ton, 5 tons, 10 tons, 15 tons, 20 tons, 25 tons, 30 tons, 35 tons, 40 tons, 45 tons, 50 tons, or a range consisting of any two values ​​thereof.

[0049] In the present application, the A value can be controlled by regulating the binder mass percentage and the mass ratio of the fibrous binder to the granular binder in the material layer. For example, when other conditions remain unchanged, an increase in the binder mass percentage increases the A value; a decrease in the binder mass percentage decreases the A value. When other conditions remain unchanged, an increase in the mass ratio of the fibrous binder to the granular binder increases the A value; a decrease in the mass ratio of the fibrous binder to the granular binder decreases the A value. The length L and diameter D of the fibrous binder, the average particle size of the granular binder, and the Dv50 of the electrode active material also affect the A value.

[0050] In the present application, the B value and the C value can be controlled by regulating the mass ratio of the fibrous binder to the granular binder. For example, when other conditions remain unchanged, the mass ratio of the fibrous binder to the granular binder increases, the B value increases, and the C value decreases; when the mass ratio of the fibrous binder to the granular binder decreases, the B value decreases, and the C value increases. When the material layer contains both fibrous binder and granular binder, when other conditions remain unchanged, the mass percentage of the binder in the material layer will also affect the B value and the C value. In addition, during the preparation of the pole piece, the process parameters of high-speed mixed shear fiberization (for example, rotation speed and time) will also affect the B value and the C value by affecting the degree of fiberization of the fibrous binder. The greater the degree of fiberization of the fibrous binder, the greater the B value and the smaller the C value.

[0051] In the present application, the length L and diameter D of the fibrous binder can be controlled by regulating the rotation speed and the time of high-speed mixed shear fiberization. For example, when other conditions remain unchanged, the rotation speed of high-speed mixed shear fiberization increases, and the L value increases; the rotation speed of high-speed mixed shear fiberization decreases, and the L value decreases. When other conditions remain unchanged, the time of high-speed mixed shear fiberization is prolonged, and the L value increases; the time of high-speed mixed shear fiberization is shortened, and the L value decreases. When other conditions remain unchanged, the rotation speed of high-speed mixed shear fiberization increases, and the D value decreases; the rotation speed of high-speed mixed shear fiberization decreases, and the D value increases. When other conditions remain unchanged, the time of high-speed mixed shear fiberization is prolonged, and the D value decreases; the time of high-speed mixed shear fiberization is shortened, and the D value increases.

[0052] In the present application, granular binders of varying average particle sizes can be obtained by mechanical crushing (e.g., ball milling). For example, the average particle size of the granular binder can be controlled by regulating the ball milling time and ball milling speed. For example, when other conditions remain unchanged, increasing the ball milling time decreases the average particle size of the granular binder; shortening the ball milling time increases the average particle size of the granular binder. When other conditions remain unchanged, increasing the ball milling speed decreases the average particle size of the granular binder; decreasing the ball milling speed increases the average particle size of the granular binder.

[0053] In the present application, electrode active materials with different Dv50 values ​​can be obtained by mechanical crushing (e.g., ball milling). For example, the Dv50 value of the electrode active material can be controlled by regulating the ball milling time and ball milling speed. For example, when other conditions remain unchanged, the Dv50 value of the electrode active material decreases with increasing the ball milling time, while the Dv50 value of the electrode active material increases with decreasing the ball milling time. When other conditions remain unchanged, the Dv50 value of the electrode active material decreases with increasing the ball milling speed, while the Dv50 value of the electrode active material increases with decreasing the ball milling speed.

[0054] In the present application, the electrode sheet may be a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0055] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0056] The positive electrode material layer of the present application includes a positive electrode active material, and the positive electrode active material includes a substance that can reversibly embed and extract active ions such as lithium ions. The positive electrode material layer can be one layer or more layers, and each layer in the multilayer positive electrode material layer can contain the same or different positive electrode active materials. The present application has no special restrictions on the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95),LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.5 Co 0.2 Mn 0.3O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111).

[0057] In some embodiments, the mass percentage of the positive electrode active material is 85% to 98% based on the mass of the positive electrode material layer. For example, the mass percentage of the positive electrode active material can be 85%, 87%, 89%, 90%, 91%, 93%, 95%, 96%, 97%, 98%, or a range consisting of any two of these values.

[0058] The positive electrode material layer of the present application also includes a positive electrode conductive agent. The present application has no particular restrictions on the positive electrode conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent may include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0059] In some embodiments, the mass percentage of the positive electrode conductive agent is 0.5% to 5% based on the mass of the positive electrode material layer. For example, the mass percentage of the positive electrode conductive agent can be 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values.

[0060] The present application does not particularly limit the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector can be 6 μm to 25 μm. The present application does not particularly limit the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of a single-sided positive electrode material layer can be 50 μm to 120 μm.

[0061] In the present application, the electrode sheet may be a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be provided on one surface of the negative electrode current collector along its own thickness direction, or may be provided on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of ​​the surface of the negative electrode current collector, or may be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0062] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector or a titanium-copper composite current collector, etc.

[0063] The negative electrode material layer of the present application includes a negative electrode active material. The present application has no particular restrictions on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0064] In some embodiments, the mass percentage of the negative electrode active material is 85% to 98% based on the mass of the negative electrode material layer. For example, the mass percentage of the negative electrode active material can be 85%, 87%, 89%, 90%, 91%, 93%, 95%, 96%, 97%, 98%, or a range consisting of any two of these values.

[0065] The negative electrode material layer of the present application may further include a negative electrode conductive agent. For example, the negative electrode conductive agent may be at least one of the positive electrode conductive agents described above. In some embodiments, the weight percentage of the negative electrode conductive agent is 0.5% to 5% based on the weight of the negative electrode material layer. For example, the weight percentage of the negative electrode conductive agent may be 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values.

[0066] The present application has no particular limitation on the thickness of the negative electrode material layer and the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be 30 μm to 200 μm, and the thickness of the negative electrode current collector can be 4 μm to 15 μm.

[0067] The second aspect of the present application provides a secondary battery, which includes the electrode provided in the first aspect of the present application. The secondary battery of the present application has good dynamic performance and cycle performance.

[0068] In the present application, the secondary battery includes a separator. The present application has no particular restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0069] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0070] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0071] In some embodiments, the inorganic layer includes ceramic particles and an inorganic layer binder. The application is not particularly limited to ceramic particles. For example, ceramic particles may include at least one of silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The application is not particularly limited to the inorganic layer binder. For example, the inorganic layer binder may include but is not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride. In some embodiments, the polymer layer includes a polymer, and the material of the polymer may include but is not limited to at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0072] In the present application, there is no particular limitation on the thickness of the isolation film, as long as the purpose of the present application can be achieved. For example, the thickness of the isolation film can be 3 μm to 20 μm.

[0073] In the present application, the secondary battery further includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.

[0074] The present application does not specifically limit the lithium salt, as long as the objectives of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate. The present application does not specifically limit the content of the lithium salt in the electrolyte, as long as the objectives of the present application can be achieved.

[0075] The present application has no particular limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0076] Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC).Above-mentioned cyclic carbonate compound can include but not limited to at least one in ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorocarbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0077] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal, and a metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0078] The secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In some embodiments, the secondary battery may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0079] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator, the negative electrode sheet, and the separator in order, and winding, folding, and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator, the negative electrode sheet, and the separator in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0080] The third aspect of the present application provides an electronic device, which includes the secondary battery provided by the second aspect of the present application. The electronic device of the present application has a long service life and good performance.

[0081] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0082] Example

[0083] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0084] Test methods and equipment:

[0085] A value, B value, C value, L value, D value, average particle size test of granular binder

[0086] After the lithium-ion battery was discharged to 3V at 0.2C, the electrode was disassembled and cleaned with dimethyl carbonate (DMC) and then dried at 60°C. The surface of the electrode perpendicular to the thickness direction was observed using a scanning electron microscope (SEM) with a magnification of 5000×. Five observation areas were selected, and the size of the observation area was 100μm×100μm. Combined with an energy dispersive X-ray spectrometer (EDS), the characteristic elements were selected as C, Si, O, N, F, etc. Within the selected observation area, the length and diameter of 10 fibrous binders and the maximum diameter of the circumscribed circle of 10 granular binders were tested. The average value was calculated as the L value, D value, and average particle size of the granular binder in a single observation area. The observation area image was processed using HALCON image processing software. The pixel size was calibrated using the scale of the observation area image. The number of pixels representing the total surface area of ​​the electrode active material, the area of ​​the electrode active material covered by the fibrous binder, and the area of ​​the electrode active material covered by the granular binder were calculated. These values ​​were then multiplied by the calibrated single pixel area to obtain the total surface area of ​​the electrode active material, the area of ​​the electrode active material covered by the fibrous binder, and the area of ​​the electrode active material covered by the granular binder within each observation area. The A value, B value, and C value for each observation area were then calculated. The average of these test results across the five observation areas was calculated as the final values ​​for the fibrous binder length L and diameter D, the average particle size of the granular binder, and the A value, B value, and C value.

[0087] Dv50 test of electrode active materials

[0088] According to the national standard “Particle size distribution laser diffraction method” (GB / T19077-2016), the Dv50 of the electrode active material was tested using a laser particle size analyzer (model MS3000).

[0089] Binder mass percentage and its change rate test

[0090] After the lithium-ion battery is discharged to 3V at 0.2C, the negative electrode is disassembled and cleaned with dimethyl carbonate (DMC) and dried at 60℃. An area of ​​1540.25mm is punched at any position of the negative electrode. 2Take the test sample, scrape off the material layer powder, weigh its mass, and record it as m1 mg. Heat treat the material layer powder at 450°C in nitrogen for 2 hours, weigh its mass, and record it as m2 mg. The mass percentage of the binder M1 (%) = (m1-m2) / m1 × 100%. Take samples five times at different locations on the negative electrode and repeat the above test process. The resulting mass percentages of the binder are recorded as M1, M2, M3, M4, and M5, respectively. Calculate the average value as the mass percentage of the binder in the material layer, M. The rate of change of the mass percentage of the binder is calculated by the following formula: a = |M1-M| / M×100%, b = |M2-M| / M×100%, c = |M3-M| / M×100%, d = |M4-M| / M×100%, e = |M5-M| / M×100%, the rate of change of the mass percentage of the binder (%) = (a+b+c+d+e) / 5×100%.

[0091] Rate performance test

[0092] At 25°C, after the lithium-ion battery has been allowed to stand for 5 minutes, it is charged to 4.53V at a constant current of 0.5C, then charged to 0.05C at a constant voltage of 4.53V, and allowed to stand for 5 minutes. Then, it is discharged to 3.0V at a constant current of 0.2C. The discharge capacity of the lithium-ion battery at this time is tested and recorded as the 0.2C discharge capacity. Then, after standing for 5 minutes, it is charged to 4.53V at a constant current of 0.5C, then charged to 0.05C at a constant voltage of 4.53V, and allowed to stand for 5 minutes. Then, it is discharged to 3.0V at a constant current of 2C. The discharge capacity of the lithium-ion battery at this time is tested and recorded as the 2C discharge capacity. 2C discharge capacity / 0.2C discharge capacity (%) = 2C discharge capacity / 0.2C discharge capacity × 100%. The kinetic performance of lithium-ion batteries is characterized by 2C discharge capacity / 0.2C discharge capacity. The larger the 2C discharge capacity / 0.2C discharge capacity, the better the kinetic performance of the lithium-ion battery; the smaller the 2C discharge capacity / 0.2C discharge capacity, the worse the kinetic performance of the lithium-ion battery.

[0093] Cyclic performance test

[0094] At 25°C, charge the lithium-ion battery at a constant current of 0.5C to a voltage of 4.53V, charge it at a constant voltage of 4.53V to a current of 0.025C, and then discharge it at a constant current of 0.5C to a voltage of 3.0V. The discharge capacity of the lithium-ion battery at this time is measured and recorded as the discharge capacity of the first cycle. Then, perform the above charge and discharge steps for 500 cycles and measure the discharge capacity of the 500th cycle. Cycle capacity retention (%) = discharge capacity of the 500th cycle / discharge capacity of the first cycle × 100%.

[0095] Example 1-1

[0096] <Preparation of negative electrode sheet>

[0097] Artificial graphite, a negative electrode active material, a silicon-carbon composite material (silicon to carbon mass ratio of 1:1), and carbon nanotubes (carbon nanotubes) were added to a vacuum mixer and mixed at 2000 rpm for 30 minutes at 25°C. Then, fibrous polytetrafluoroethylene (PTFE) and granular polyurethane (PU) were added and mixed at 2000 rpm for 30 minutes at 15°C to obtain a uniformly mixed dry powder for the negative electrode material layer. The mass ratio of artificial graphite, silicon-carbon composite material, carbon nanotubes, PTFE, and PU was 47.5:47.5:1:4. The mass ratio of fibrous to granular binders is shown in Table 1. The dry powder for the negative electrode material layer was added to a high-speed mixer and mixed at 4500 rpm for 30 minutes at 100°C to achieve high-speed mixing and shearing fiberization. The resulting fiberized material was then sieved to obtain a fibrous material. The above-mentioned fibrous material is placed in a hot rolling roller for multiple differential hot pressing thinning at a temperature of 100°C and a pressure of 5 tons to obtain a negative electrode self-supporting membrane. The negative electrode self-supporting membrane is placed on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and hot pressed and compounded at 120°C with a pressure of 10 tons to obtain a negative electrode pole piece with a negative electrode material layer on one side. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode pole piece with a negative electrode material layer on both sides. After cold pressing, cutting, and welding the pole ears, a negative electrode pole piece with a specification of 96mm×1000mm is obtained for standby use. Among them, the thickness of the single-sided negative electrode material layer is 30μm, and the compaction density of the negative electrode material layer is 1.7g / cm 3 The length L and diameter D of the fibrous binder, the average particle size of the granular binder, and the Dv50 of the negative electrode active materials artificial graphite and silicon-carbon composite material are shown in Table 2.

[0098] <Preparation of positive electrode sheet>

[0099] The positive electrode active material, lithium cobalt oxide (LiCoO2), and the positive electrode conductive agent, conductive carbon black (Super P), were added to a vacuum mixer and mixed at 2000 rpm for 30 minutes at 25°C. The positive electrode binder, fibrous polytetrafluoroethylene (PTFE), and granular polyurethane (PU), were then added and mixed at 2000 rpm for 30 minutes at 15°C to obtain a uniformly mixed positive electrode material layer dry powder. The mass ratio of the positive electrode active material, lithium cobalt oxide (LiCoO2), the positive electrode conductive agent, conductive carbon black (Super P), the positive electrode binder, PTFE, and the PU was 95:1:4, and the mass ratio of the fibrous binder to the granular binder was 5:1. The positive electrode material layer dry powder was added to a high-speed mixer and mixed at 4500 rpm for 30 minutes at 100°C for high-speed mixing and shearing to obtain a fiberized material. After mixing, the material was sieved to obtain a fiberized material. The above-mentioned fibrous material is placed in a hot rolling roller for multiple differential hot pressing thinning at a temperature of 100°C and a pressure of 5 tons to obtain a positive electrode self-supporting membrane. The positive electrode self-supporting membrane is placed on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and hot pressed and compounded at 120°C with a pressure of 20 tons to obtain a positive electrode pole piece with a positive electrode material layer on one side. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode pole piece with a positive electrode material layer on both sides. After cold pressing, cutting, and welding the pole ears, a positive electrode pole piece with a specification of 92mm×1000mm is obtained for standby use. Among them, the thickness of the single-sided positive electrode material layer is 57μm, and the compaction density of the positive electrode material layer is 4.3g / cm 3 , the Dv50 of the positive electrode active material is shown in Table 3.

[0100] <Isolation Film>

[0101] A polyethylene porous polymer film with a thickness of 7 μm (manufacturer: Celgard Membrane Co., Ltd., USA) was used as a separator.

[0102] <Preparation of Electrolyte>

[0103] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 10:30:60 to obtain a base solvent. The lithium salt LiPF6 was then added and stirred to obtain an electrolyte. The mass percentage of the lithium salt LiPF6, based on the total mass of the electrolyte, was 12.5%, with the remainder being the base solvent.

[0104] <Preparation of lithium-ion batteries>

[0105] The positive electrode sheet, separator, negative electrode sheet, and separator are stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and injected with the prepared electrolyte. The lithium-ion battery is obtained through vacuum packaging, standing, forming, and shaping processes, wherein the upper limit of the formation voltage is 4.53V, the formation temperature is 85°C, and the formation time is 60 minutes.

[0106] Example 1-2 to Example 1-10

[0107] The preparation parameters in the "Preparation of Negative Electrode Sheet" were adjusted according to Table 1, and the remainder was the same as in Example 1-1. When the mass percentage of the negative electrode binder changed, the mass percentage of the negative electrode active material, artificial graphite, also changed, while the mass percentages of the negative electrode active material, silicon-carbon composite material, and the negative electrode conductive agent remained unchanged.

[0108] Example 2-1 to Example 2-6

[0109] The preparation parameters in the "Preparation of Negative Electrode Sheet" were adjusted according to Table 2, and the remainder was the same as in Example 1-1. Specifically, in the "Preparation of Negative Electrode Sheet," the length L and diameter D of the fibrous binder were controlled by adjusting the rotational speed of the high-speed mixed shear fiberization process, the average particle size of the granular binder was controlled by adjusting the ball milling time of the granular binder, and the Dv50 of the negative electrode active material was controlled by adjusting the ball milling time of the negative electrode active material.

[0110] Example 3-1 to Example 3-2

[0111] The preparation parameters in the preparation of the positive electrode sheet were adjusted according to Table 3, and the rest was the same as in Example 1-1. The Dv50 of the positive electrode active material was adjusted by adjusting the ball milling time of the positive electrode active material.

[0112] Comparative Example 1

[0113] Except that the following preparation methods are used for <Preparation of Negative Electrode Sheet> and <Preparation of Positive Electrode Sheet>, the rest are the same as Example 1-1.

[0114] <Preparation of negative electrode sheet>

[0115] Artificial graphite (a negative electrode active material), a silicon-carbon composite material (a silicon-to-carbon mass ratio of 1:1), carbon nanotubes (a negative electrode conductive agent), and polyacrylic acid and carboxymethyl cellulose (CMC) (a polyacrylic acid-to-CMC mass ratio of 3:1) were mixed in a mass ratio of 47.5:47.5:1:4. Deionized water was added as a solvent to form a slurry with a solids content of 45 wt%. After uniform mixing using a vacuum mixer, the negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of an 8 μm thick negative electrode current collector copper foil and dried at 100°C to obtain a negative electrode sheet coated on one side with the negative electrode material layer. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with the negative electrode material layer. After drying at 100°C, the sheet was cold pressed, cut into pieces, and the tabs were welded to obtain a negative electrode sheet measuring 96 mm x 1000 mm for later use. The thickness of the single-sided negative electrode material layer is 30 μm, and the compaction density of the negative electrode material layer is 1.7 g / cm 3 The Dv50 of the negative electrode active material artificial graphite and silicon-carbon composite material is the same as that of Example 1-1.

[0116] <Preparation of positive electrode sheet>

[0117] The positive electrode active material lithium cobalt oxide (LiCoO2), the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride are mixed in a mass ratio of 95:1:4, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm and dried at 100°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. After drying at 100°C, the sheet is cold pressed, cut into pieces, and the tabs are welded to obtain a positive electrode sheet with a specification of 92mm×1000mm for use. The thickness of the single-sided positive electrode material layer is 57μm, and the compaction density of the positive electrode material layer is 4.3g / cm 3 , the Dv50 of the positive electrode active material is 20μm.

[0118] Comparative Example 2 to Comparative Example 3

[0119] The preparation parameters in the "Preparation of Negative Electrode Sheet" were adjusted according to Table 1, and the remainder was the same as in Example 1-1. When the mass percentage of the negative electrode binder changed, the mass percentage of the negative electrode active material, artificial graphite, also changed, while the mass percentages of the negative electrode active material, silicon-carbon composite material, and the negative electrode conductive agent remained unchanged.

[0120] Comparative Example 4

[0121] Except that the following preparation method is used for <Preparation of Negative Electrode Sheet>, the rest is the same as Example 1-1.

[0122] <Preparation of negative electrode sheet>

[0123] Artificial graphite, a silicon-carbon composite material (silicon to carbon mass ratio of 1:1), and carbon nanotubes (carbon nanotubes) were added to a vacuum mixer and mixed at 2000 rpm for 30 minutes at 25°C. Polytetrafluoroethylene (PTFE) was then added and mixed at 2000 rpm for 30 minutes at 18°C ​​to obtain a uniformly mixed dry powder for the negative electrode material layer. The mass ratio of artificial graphite, silicon-carbon composite, carbon nanotubes, and PTFE was 47.5:47.5:1:4. The dry powder was then added to a high-speed mixer and mixed at 4500 rpm for 30 minutes at 100°C for high-speed mixing and shearing to produce a fiberized material. The fiberized material was then sieved to obtain a fiberized material. The fiberized material was then placed on a hot roller and subjected to multiple differential hot pressing cycles at 100°C and 5 tons to obtain a self-supporting negative electrode membrane. Place the negative electrode self-supporting film on one surface of the negative electrode current collector copper foil with a thickness of 8μm, and hot press it at 120℃ with a pressure of 10 tons to obtain a negative electrode sheet with a negative electrode material layer on one side. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer on both sides. After cold pressing, cutting and welding the tabs, a negative electrode sheet with a specification of 96mm×1000mm is obtained for use. Among them, the thickness of the single-sided negative electrode material layer is 30μm, and the compaction density of the negative electrode material layer is 1.7g / cm 3 The Dv50 of the negative electrode active material artificial graphite and silicon-carbon composite material is the same as that of Example 1-1.

[0124] Comparative Example 5

[0125] Except that the following preparation method is used for <Preparation of Negative Electrode Sheet>, the rest is the same as Example 1-1.

[0126] <Preparation of negative electrode sheet>

[0127] Artificial graphite, a negative electrode active material, a silicon-carbon composite material (silicon to carbon mass ratio of 1:1), and carbon nanotubes (carbon nanotubes) were added to a vacuum mixer and mixed at 2000 rpm for 30 minutes at 25°C. Polyurethane granules were then added and mixed at 2000 rpm for 30 minutes at 18°C ​​to obtain a uniformly mixed dry powder for the negative electrode material layer. The mass ratio of artificial graphite, silicon-carbon composite material, carbon nanotubes, and polyurethane was 47.5:47.5:1:4. The dry powder was then placed on hot rollers and subjected to multiple differential hot pressing cycles at 180°C and 5 tons of pressure to obtain a self-supporting negative electrode film. The self-supporting negative electrode film was then placed on one surface of an 8μm thick negative electrode current collector copper foil and hot pressed at 180°C and 10 tons of pressure to obtain a negative electrode sheet with a negative electrode material layer on one side. The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer on both sides. After cold pressing, cutting, and welding the tabs, a negative electrode sheet with a specification of 96mm×1000mm is obtained for use. The thickness of the negative electrode material layer on one side is 30μm, and the compaction density of the negative electrode material layer is 1.7g / cm 3 The Dv50 of the negative electrode active material artificial graphite and silicon-carbon composite material is the same as that of Example 1-1.

[0128] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0129] Table 1

[0130]

[0131]

[0132] Note: “ / ” in Table 1 indicates no corresponding parameter.

[0133] From Examples 1-1 to 1-10 and Comparative Examples 1 to 5, it can be seen that the electrode sheets of the present application, by adjusting the binder and the A value within the scope of the present application, have a greater 2C discharge capacity / 0.2C discharge capacity and a cycle capacity retention rate of the lithium-ion battery, indicating that the lithium-ion battery of the present application has good kinetic performance and cycle performance. However, the lithium-ion battery of Comparative Example 1 was prepared using a wet process and had an A value outside the scope of the present application. The A values ​​of the lithium-ion batteries of Comparative Examples 2 to 3 were also outside the scope of the present application. The binder used in the material layer of the lithium-ion batteries of Comparative Examples 4 to 5 was also outside the scope of the present application. The lithium-ion batteries had even lower 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention rates, indicating that the lithium-ion batteries had poor kinetic performance and cycle performance.

[0134] The weight percentage of the binder affects the kinetic and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-4, when the weight percentage of the binder is within the range of this application, the lithium-ion batteries exhibit high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating that the lithium-ion batteries of this application exhibit good kinetic and cycling performance.

[0135] The mass ratio of fibrous binder to particulate binder affects the dynamic and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-5, and 1-8, when the mass ratio of fibrous binder to particulate binder is within the range of this application, the lithium-ion batteries exhibit high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating that the lithium-ion batteries of this application exhibit good dynamic and cycling performance.

[0136] The type of fibrous and particulate binder affects the dynamic and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-9, and 1-10, using fibrous and particulate binders within the scope of this application results in a lithium-ion battery with a high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention rate, indicating that the lithium-ion battery of this application exhibits good dynamic and cycling performance.

[0137] The values ​​of B, C, and B / C affect the kinetic performance and cycling performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-10, when the values ​​of B, C, and B / C are within the ranges of this application, the lithium-ion battery exhibits high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating good kinetic performance and cycling performance of the lithium-ion battery of this application.

[0138] Table 2

[0139]

[0140]

[0141] Note: The length L and diameter D of the fibrous binder and the average particle size of the granular binder in Table 2 are parameter characteristics of the negative electrode binder in the negative electrode sheet.

[0142] The length L and diameter D of the fibrous binder affect the dynamic and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1, and 2-2, when the length L and diameter D of the fibrous binder are within the ranges of this application, the lithium-ion battery exhibits high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating good dynamic and cycling performance of the lithium-ion battery of this application.

[0143] The average particle size of the granular binder affects the kinetic and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-3, and 2-4, when the average particle size of the granular binder is within the range of this application, the lithium-ion battery exhibits high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating that the lithium-ion battery of this application exhibits good kinetic and cycling performance.

[0144] The Dv50 of the negative electrode active material affects the kinetic and cycling performance of the lithium-ion battery. As can be seen from Examples 1-1, 2-5, and 2-6, when the Dv50 of the negative electrode active material is within the range of this application, the lithium-ion battery exhibits high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating good kinetic and cycling performance of the lithium-ion battery of this application.

[0145] Table 3

[0146]

[0147] The Dv50 of the positive electrode active material affects the kinetic and cycling performance of the lithium-ion battery. As can be seen from Examples 1-1, 3-1, and 3-2, when the Dv50 of the positive electrode active material is within the range of this application, the lithium-ion battery exhibits high 2C discharge capacity / 0.2C discharge capacity and cycle capacity retention, indicating good kinetic and cycling performance of the lithium-ion battery of this application.

[0148] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such process, method or article.

[0149] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0150] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A pole piece comprising a current collector and a material layer disposed on at least one surface of the current collector, wherein the material layer comprises an electrode active material and a binder, wherein the binder comprises a fibrous binder and a granular binder, and based on the total surface area of ​​the electrode active material, the area of ​​the electrode active material covered by the binder accounts for A, 5%≤A≤25%.

2. The pole piece according to claim 1, wherein: 5％≤A≤20％。 3. The pole piece according to claim 1, wherein: Based on the total surface area of ​​the electrode active material covered by the binder, the area ratio of the electrode active material covered by the fibrous binder is B, the area ratio of the electrode active material covered by the granular binder is C, 50%≤B≤98%, 2%≤C≤50%.

4. The pole piece according to claim 3, wherein: 1≤B / C≤9.

5. The pole piece according to claim 1, wherein: The length of the fibrous binder is L μm, the diameter of the fibrous binder is D nm, 5≤L≤100, 10≤D≤200.

6. The pole piece according to claim 1, wherein: The average particle size of the particulate binder is 0.1 μm to 5 μm.

7. The pole piece according to any one of claims 1 to 6, wherein: Based on the mass of the material layer, the mass percentage of the binder is 1% to 10%.

8. The pole piece according to claim 7, wherein: The mass ratio of the fibrous binder to the granular binder is (1 to 9):

1.

9. The pole piece according to any one of claims 1 to 6, wherein: The fibrous binder comprises at least one of polytetrafluoroethylene, polytetrafluoroethylene-perfluorosulfone copolymer, polyacrylonitrile or sericin; The granular binder includes at least one of polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, paraffin wax, polylactic acid, polyurethane, acrylonitrile-butadiene-styrene copolymer or styrene-butadiene rubber.

10. The pole piece according to any one of claims 1 to 6, wherein: The electrode active material includes a positive electrode active material and a negative electrode active material. The Dv50 of the positive electrode active material is 5 μm to 35 μm, and the Dv50 of the negative electrode active material is 5 μm to 35 μm.

11. The pole piece according to any one of claims 1 to 6, wherein: For the pole piece of the same area randomly selected on the surface perpendicular to the thickness direction, the change rate of the mass percentage of the binder is 1% to 4%. 12 . A secondary battery comprising the electrode according to claim 1 . 13 . An electronic device comprising the secondary battery according to claim 12 .

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