Electrode sheet and battery

Abstract

Provided in the present application are an electrode sheet and a battery. The electrode sheet comprises a current collector, and an active substance layer which is provided on at least one functional surface of the current collector, wherein the active substance layer contains graphite. In the extension direction of the current collector, the active substance layer comprises recesses and a main body portion, wherein each of the recesses is provided with a groove, which does not penetrate the recess, in the side of the recess that faces away from the current collector, and each of the recesses comprises a first region that faces away from a surface of the current collector and a second region which is close to the surface of the current collector. The degree of orientation of graphite in the first region is lower than the degree of orientation of graphite in the main body portion, wherein the degree of orientation of graphite refers to the intensity ratio of the diffraction peak of the 004 crystal plane of the graphite to the diffraction peak of the 110 crystal plane of the graphite. By means of applying the electrode sheet to a battery, the quick charge performance of the battery can be improved, and the cyclic expansion rate of the battery can be lowered.

Description

Electrode sheet and battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on October 25, 2023, with application number 202311395793.7 and application name “An Electrode Sheet and Battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of lithium-ion batteries, and specifically relates to an electrode sheet and a battery. Background Art

[0003] With the rapid development of new energy vehicles and large-scale energy storage industries, higher requirements are placed on the fast charging performance, cycle performance and other performance of lithium-ion batteries. At present, in order to meet the high energy density requirements of lithium-ion batteries, most of them are achieved by reducing the proportion of inactive substances or increasing the thickness and compaction density of the active material layer. However, as the proportion of inactive substances decreases and the thickness and compaction density of the active material layer increase, the porosity decreases after rolling, especially the surface of the active material layer is subjected to large forces, the compaction is higher, and the porosity is lower, resulting in a longer migration path of lithium ions in the active material layer in the direction perpendicular to the current collector, a longer electrolyte transmission path, an increase in internal resistance, and thus a decrease in lithium ion transmission efficiency. The electrolyte infiltration efficiency of the electrode sheet becomes lower, resulting in poor kinetic performance of the electrode sheet, especially the risk of lithium plating increases during fast charging, and the thickness expansion increases during cycling.

[0004] Summary of the Invention

[0005] The present application provides an electrode sheet, which can increase the surface area of ​​the active material layer, improve the permeation rate of the electrolyte, and enhance the transmission of ions and electrons by providing grooves and limiting the graphite orientation in the grooves to be smaller than the graphite orientation in other areas. The electrode sheet is applied to a battery to improve the fast charging performance and cycle expansion rate of the battery.

[0006] The present application also provides a battery, which includes the above-mentioned electrode sheet and can effectively improve the fast charging performance and reduce the cycle expansion rate.

[0007] In a first aspect of the present application, an electrode sheet is provided, comprising a current collector, an active material layer disposed on at least one functional surface of the current collector, wherein the active material layer comprises graphite;

[0008] Along the extension direction of the current collector, the active material layer includes a concave portion and a main portion, and a groove that does not penetrate the concave portion is provided on a side of the concave portion away from the current collector;

[0009] The recess includes a first region facing away from the current collector surface and a second region close to the current collector surface;

[0010] The orientation degree of graphite in the first region is smaller than that in the main body, wherein the orientation degree of graphite refers to the intensity ratio of the diffraction peaks of the 004 crystal plane and the 110 crystal plane of graphite.

[0011] In the electrode sheet as described above, the first region occupies 20 to 80% of the volume of the recess.

[0012] The electrode sheet as described above, wherein the orientation degree of graphite in the first region is 0.1 to 2; and / or,

[0013] The orientation degree of the graphite in the main body is 3-15.

[0014] The electrode sheet as described above, wherein the groove is in the shape of a strip on the side of the active material layer away from the current collector, and the groove is multiple;

[0015] The plurality of grooves are spaced apart along the length direction of the current collector, and the grooves extend along the width direction of the current collector; or,

[0016] The plurality of grooves are spaced apart along the width direction of the current collector, and the grooves extend along the length direction of the current collector.

[0017] In the electrode sheet as described above, every two adjacent grooves are connected by a protrusion, and the size of the protrusion in the length direction of the current collector is 10-500 μm, or the size of the protrusion in the second direction of the current collector is 10-500 μm.

[0018] The electrode sheet as described above, wherein the ratio of the orthographic projection area of ​​the groove on the current collector to the orthographic projection area of ​​the active material layer on the current collector is (0.1-0.5):1; and / or,

[0019] The size of the groove in the third direction of the current collector is 1 to 50 μm; and / or,

[0020] The size of the concave portion in the second direction of the current collector is A, the size of the groove in the second direction of the current collector is B, AB=0.5-10 mm; the size of the groove in the first direction of the current collector is 1-30 μm, or,

[0021] The size of the concave portion in the first direction of the current collector is C, the size of the groove in the first direction of the current collector is D, CD=0-3 mm, and the size of the groove in the second direction of the current collector is 1-30 μm.

[0022] The electrode sheet as described above, wherein the recessed portions and the main portions are alternately arranged along the width direction of the current collector; or

[0023] The recessed portions and the main body portions are alternately arranged along a length direction of the current collector.

[0024] In the electrode sheet as described above, the graphite sheet surface in the first region has an angle α with the plane where the current collector is located, and the graphite sheet surface in the main body has an angle β with the plane where the current collector is located, and α>β.

[0025] The electrode sheet as described above, wherein the angle α satisfies: 0°<α≤90°; and / or,

[0026] The angle β satisfies: 0°≤β≤50°.

[0027] The electrode sheet as described above, wherein in the first region, at least 50% by mass of the graphite has one end surface facing the center of the groove.

[0028] The electrode sheet as described above, wherein the porosity of the recessed portion is greater than the porosity of the main body portion.

[0029] The electrode sheet as described above, wherein the porosity of the recessed portion is 30% to 60%; and / or,

[0030] The porosity of the main body is 15-35%.

[0031] In a second aspect of the present application, a battery is provided, comprising the electrode sheet as described above.

[0032] The implementation of this application has at least the following beneficial effects:

[0033] The electrode sheet provided in the present application is provided with grooves, which increase the exposed sites of the active material layer, thereby increasing the contact area between the electrolyte and the electrode sheet, which is beneficial to improving the infiltration rate of the electrolyte into the electrode sheet, increasing the transmission rate of lithium ions and electrons, and improving the dynamic performance of the electrode sheet, thereby improving the fast charging performance of the battery; by limiting the graphite orientation at the groove to be smaller than the graphite orientation in the main body, the graphite is embedded with lithium in multiple directions and is subjected to more uniform stress. At the same time, the groove provides a buffering space for the expansion of the electrode sheet, thereby reducing the cycle expansion rate of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic structural diagram of an electrode sheet in one embodiment of the present application;

[0035] FIG2 is a schematic diagram of a partial structure of an electrode sheet in one embodiment of the present application;

[0036] FIG3 is a schematic diagram of a top view of an electrode sheet in one embodiment of the present application;

[0037] FIG4 is a schematic diagram of a top view of an electrode sheet in another embodiment of the present application;

[0038] FIG5 is a schematic top view of the electrode sheet in another embodiment of the present application;

[0039] FIG6 is a schematic top view of the electrode sheet in another embodiment of the present application;

[0040] FIG7 is a SEM image of an electrode sheet in one embodiment of the present application, wherein the white arrows indicate grooves;

[0041] FIG8 is a partial SEM enlarged view of an electrode sheet in one embodiment of the present application, wherein the white arrows indicate grooves;

[0042] FIG9 is an SEM enlarged view of an electrode sheet from a top view angle in one embodiment of the present application;

[0043] FIG10 is an SEM enlarged view of an electrode sheet according to another embodiment of the present application from another top view angle;

[0044] FIG11 is a partial structural diagram of graphite in an active material layer according to an embodiment of the present application;

[0045] FIG12 is a top view of an electrode sheet according to an embodiment of the present application;

[0046] FIG13 is a microscope image of the surface of the active material layer in the electrode sheet of FIG12 facing away from the current collector;

[0047] FIG14 is a top view of an electrode sheet according to another embodiment of the present invention;

[0048] FIG15 is a microscopic image of the surface of the active material layer in the electrode sheet of FIG14 facing away from the current collector;

[0049] FIG16 is a cross-sectional SEM image of the active material layer in an electrode sheet according to one embodiment of the present application;

[0050] FIG17 is a peel strength curve diagram of the negative electrode sheet and the separator in Example 2 and Comparative Example 1 of the present application.

[0051] Explanation of reference numerals: 1 - current collector; 11 - active material layer; 101 - recessed portion; 102 - main body portion; 103 - groove; 104 - raised portion; 110 - active layer region; 120 - hollow foil region; 1011 - first region; 1012 - second region. DETAILED DESCRIPTION

[0052] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0053] It should be noted that, in FIG. 1 to FIG. 6 and FIG. 11 , the X direction is the first direction of the current collector, the Y direction is the second direction of the current collector, and the Z direction is the third direction of the current collector.

[0054] As shown in Figure 1, the first aspect of the present application provides an electrode sheet, which includes a current collector 1 and an active material layer 11 arranged on at least one functional surface of the current collector 1, and the active material layer 11 contains graphite; along the extension direction of the current collector, the active material layer 11 includes a recess 101 and a main body 102, and a groove 103 that does not penetrate the recess is provided on the side of the recess 101 away from the current collector; the recess 101 includes a first area away from the surface of the current collector and a second area close to the surface of the current collector; and the orientation degree of the graphite in the first area is less than the orientation degree of the graphite in the main body 102, wherein the graphite orientation degree refers to the intensity ratio of the diffraction peaks of the 004 crystal plane and the 110 crystal plane of the graphite.

[0055] The current collector 1 has two largest functional surfaces that are arranged opposite each other. These two functional surfaces are used to coat the active material layer 11. The active material layer 11 can be coated on only one functional surface of the current collector 1, or on both functional surfaces of the current collector 1. When the active material layer is coated on both functional surfaces of the current collector 1, grooves can be provided in the active material layer on each functional surface.

[0056] The active material layer 11 comprises graphite, for example, flake graphite. Because flake graphite has a two-dimensional, layered structure, it significantly increases contact between the various material particles in the active material layer, thereby improving conductivity. In addition to graphite, the active material layer may also include other active materials, depending on the specific selection of the electrode sheet.

[0057] The electrode sheet can be either a negative or positive electrode sheet, and the materials of the current collector 1 and active material layer 11 are determined by the specific electrode sheet selection. For example, when the electrode sheet is a negative electrode sheet, the current collector 1 is copper foil, and the active material layer 11 can contain only graphite or a silicon-based negative electrode active material. When the electrode sheet is a positive electrode sheet, the current collector 1 is aluminum foil, and the active material layer 11 contains graphite and a positive electrode active material such as a ternary material or lithium iron phosphate.

[0058] The extension direction of the current collector 1 refers to the first direction (X direction) of the current collector, for example, it can be the length direction of the current collector, or the second direction (Y direction) of the current collector, for example, it can be the length direction of the current collector. This application does not limit it here. For example, taking the active material layer on one side of the current collector 1 as an example, as shown in Figures 3, 4 and 11, in one embodiment, along the first direction (X direction) of the current collector, the active material layer is divided into a recessed portion 101 and a main body 102. In another embodiment, as shown in Figures 5, 6, 7 to 10, along the second direction of the current collector, the active material layer 11 is divided into a recessed portion 101 and a main body 102.

[0059] A groove 103 that does not penetrate the recess 11 is provided on the side facing away from the current collector 1. That is, the wall of the groove 103 is the surface of the recess 101 facing away from the current collector 1. The groove 103 can be provided on the active layer on one side of the current collector 1, or on the active layers on both sides of the current collector 1.

[0060] The third direction (Z direction) of the current collector can be, for example, the thickness direction of the current collector. In the third direction of the current collector, the recess can be divided into a first region away from the surface of the current collector and a second region close to the surface of the current collector. At this time, the wall of the groove is the side of the first region away from the surface of the current collector. In this way, it can be ensured that the first region is exposed on the surface. Since the graphite orientation in the first region is small, the graphite has multiple directions of lithium insertion, which can increase the insertion path of lithium ions and improve the dynamic performance of the electrode sheet, thereby improving the fast charging performance and cycle performance of the battery. Among them, the wall of the groove includes the bottom wall and side walls of the groove.

[0061] Taking the electrode sheet as the negative electrode sheet as an example, during the process of graphite intercalation, lithium ions will be embedded in the interlayer spacing of graphite, causing the interlayer spacing to expand and the volume to increase. This expansion is irreversible. The size of the expansion is related to the orientation of the graphite, where the orientation = I004 / I110 can be calculated through X-ray diffraction (XRD) data. Anisotropic graphite materials tend to undergo lattice expansion in the same direction (the C-axis direction of the graphite crystal) during the lithium intercalation process, which will cause the battery to undergo a large volume expansion. The present application makes the orientation of the graphite in the first region smaller than the orientation of the graphite in the main body, so that the graphite is intercalated with lithium in multiple directions, the stress it is subjected to is more uniform, and the expansion is reduced.

[0062] According to the research of this application, the application of the above-mentioned electrode sheet in the battery is conducive to improving the fast charging performance and cycle expansion rate of the battery. This is because, on the one hand, by providing the groove, the groove increases the exposed sites of the active material layer, thereby increasing the contact area between the electrolyte and the electrode sheet, which is conducive to improving the electrolyte infiltration rate of the electrode sheet, improving the transmission rate of lithium ions and electrons, and improving the dynamic performance of the electrode sheet and improving the fast charging performance of the battery. At the same time, the groove provides a buffer space for the expansion of the electrode sheet, which is conducive to reducing the cycle expansion rate of the battery; on the other hand, by limiting the graphite orientation degree at the groove to be less than the graphite orientation degree in the main body, the graphite is embedded with lithium in multiple directions, and the stress it is subjected to is more uniform, thereby further reducing the cycle expansion rate of the battery.

[0063] The electrode sheet is preferably a negative electrode sheet. This is because the lithium plating problem mainly occurs on the negative electrode sheet. When only the kinetic performance of the positive electrode sheet is improved, it means that the rate of lithium ion release from the positive electrode is increased. At this time, if the kinetic performance of the negative electrode sheet cannot keep up, lithium plating will become more serious. Therefore, in one embodiment of the present application, the above-mentioned electrode sheet is a negative electrode sheet, and the positive electrode sheet can be a conventional positive electrode sheet in the field.

[0064] This application does not limit the specific ratio of the first region to the concave portion. For example, in some embodiments, the first region accounts for 20-80% of the volume of the concave portion. In other words, as shown in Figures 1 and 11, the concave portion 101 is divided into a first region 1011 and a second region 1012. The volume of the concave portion 101 is the sum of the volumes of the first region 1011 and the second region 1012. The first region 1011 accounts for 20-80% of the volume of the concave portion 101.

[0065] This application does not limit the specific value of the graphite orientation degree in the active material layer, as long as the graphite orientation degree in the first region is less than the graphite orientation degree in the main body. In some embodiments, the graphite orientation degree in the first region is 0.1 to 2; and / or the graphite orientation degree in the main body is 3 to 15.

[0066] This application does not limit the shape, number and arrangement of the groove 103. The shape of the groove 103 on the side of the active material layer away from the current collector can be at least one of a circle, a rectangle, and a diamond. The groove 103 can extend along the first direction or the second direction of the current collector, or it can extend along a direction inclined relative to the first direction and the second direction. In some embodiments, the shape of the groove on the side of the active material layer away from the current collector is a strip, and there are multiple grooves; as shown in Figures 1 to 4, the multiple grooves are spaced apart along the first direction (X direction) of the current collector, and the grooves extend along the second direction (Y direction) of the current collector; or, as shown in Figures 5 and 6, the multiple grooves are spaced apart along the second direction (Y direction) of the current collector, and each groove extends along the first direction of the current collector.

[0067] The multiple grooves can provide multiple buffer spaces, thereby effectively releasing the expansion stress; at the same time, the multiple grooves can provide multiple infiltration paths for the electrolyte, thereby improving the wettability. In some embodiments, the penetration rate of the electrolyte in the electrode sheet is 0.15 to 0.35 mm / (s -0.5 ).

[0068] As shown in Figures 3 and 4, when the grooves 103 extend along the first direction of the current collector 1, the grooves 103 are distributed in strips in the second direction of the current collector 1; when the grooves extend along the second direction of the current collector, the grooves are distributed in strips in the first direction of the current collector.

[0069] Among them, taking the battery cell as an example of a wound battery cell, the electrode sheet usually needs to be wound multiple times around the winding axis of the battery cell. When the winding axis is parallel to the second direction of the electrode sheet, at this time, the groove is preferably strip-shaped and extends along the second direction of the current collector, and multiple grooves are spaced apart along the first direction of the current collector, which can effectively alleviate the expansion of the electrode sheet in the first direction.

[0070] This application does not limit the size parameters of the groove 103, as long as the recess 1 is provided with the groove 103. In some embodiments, the ratio of the orthogonal projection area of ​​the groove 103 on the current collector to the orthogonal projection area of ​​the active material layer on the current collector is (0.1-0.5):1, wherein, when the active material layer includes a recess and a main body, the orthogonal projection area of ​​the active material layer on the current collector refers to the sum of the orthogonal projection areas of the recess and the main body on the current collector.

[0071] When there are multiple grooves, spaced apart along the length of the current collector and extending along the width of the current collector, as shown in Figure 2, a raised portion 104 is formed between each two adjacent grooves. The dimension w of the raised portion 104 along the length of the current collector is 10 to 500 μm. In some embodiments, the dimension m of the groove along the length of the current collector is 1 to 30 μm, where m refers to the maximum dimension of each groove along the length of the current collector. In this case, the raised portion between two adjacent grooves is essentially the surface of the main body facing away from the current collector. In a battery, the electrolyte enters through the ends of the cell along the winding direction. In other words, the ends of the electrode sheet along the second direction first come into contact with the electrolyte. In some embodiments, as shown in Figure 3, the ends of the grooves along the second direction of the current collector extend to the edge of the active material layer; that is, the grooves extend to the ends of the current collector in the second direction. The dimension A of the recess in the second direction of the current collector is equal to the dimension B of the recess in the second direction of the current collector, where A=B. This allows the grooves to directly absorb the electrolyte, providing a high-speed infiltration channel for the electrolyte, which helps improve the battery's wettability. In other embodiments, as shown in FIG4 , the size of the concave portion in the second direction of the current collector is A, the size of the groove in the second direction of the current collector is B, and AB=0.5-10 mm.

[0072] In another embodiment, as shown in FIG6 , the size of the recess in the first direction of the current collector is C, the size of the groove in the first direction of the current collector is D, and CD=0 to 3 mm. This avoids contact with the empty foil area during the formation of the groove, thereby effectively avoiding the risk of breaking the empty aluminum foil at the edge.

[0073] As shown in Figure 2, in some embodiments, the dimension n of the groove in the third direction of the current collector is 1 to 50 μm. If the dimension n of the groove in the third direction of the current collector is less than 1 μm, the buffer space provided by the groove is limited and the expansion stress cannot be effectively released. At the same time, the surface area of ​​the exposed groove is also limited and cannot absorb sufficient electrolyte. If the dimension n of the groove in the third direction of the current collector is greater than 50 μm, a large amount of active material layer needs to be removed to achieve this, resulting in a reduction in battery capacity and affecting the battery's energy density.

[0074] The present application does not limit the proportion of the recess and the main body. For example, in one embodiment, the active material layer is divided into a recess and a main body along the first direction of the current collector. At this time, the size of the recess in the second direction of the current collector is 5 to 200 μm, and the size of the main body in the second direction of the current collector is 5 to 200 μm. In another embodiment, the active material layer is divided into a recess and a main body along the second direction of the current collector. At this time, the size of the recess in the first direction of the current collector is 5 to 200 μm, and the size of the main body in the first direction of the current collector is 5 to 200 μm.

[0075] This application does not limit the arrangement of the recesses and the main body, as long as the active material layer includes both the recesses and the main body. For example, in one embodiment, as shown in Figure 6, the recesses 101 and the main body 102 are alternately arranged along the second direction of the current collector. At this time, strip grooves are provided on each recess, which is conducive to the grooves being spaced apart along the second direction of the current collector. In another embodiment, as shown in Figures 1 to 4 and Figures 12 to 15, the recesses and the main body are alternately arranged along the first direction of the current collector. At this time, strip grooves are provided on each recess, which is conducive to the grooves being spaced apart along the first direction of the current collector.

[0076] As shown in Figures 11 and 16, the flaky graphite has a flaky face and an end face that are perpendicular to each other. The active material including the flaky graphite is coated on the current collector and rolled to form an electrode sheet. During the rolling process, the flaky face of the flaky graphite tends to be parallel to the plane where the current collector is located (that is, the angle between the flaky face of the graphite and the plane where the current collector is located tends to be 0). At this time, the electrolyte tends to enter from the flaky face of the graphite. In the present application, in some embodiments, the flaky face of the graphite in the first region has an angle α with the plane where the current collector is located, and the flaky face of the graphite in the main body has an angle β with the plane where the current collector is located, α>β. By limiting α>β, the present application is conducive to shortening the embedding path of lithium ions, improving the kinetic performance of the electrode sheet, and reducing the risk of lithium plating. This is because the applicant believes that the energy barrier for lithium ions to enter from the end face of graphite is the lowest, and the energy barrier for entering from the flaky face is higher. The sum of the angle between the flaky surface of graphite and the plane where the current collector is located and the angle between the end face of graphite and the plane where the current collector is located is 90°. If the angle between the flaky surface of graphite and the plane where the current collector is located is smaller, the angle between the end face of the flaky graphite and the plane where the current collector is located is larger, and the electrolyte is more inclined to enter through the flaky surface of graphite, which is not conducive to shortening the embedding path of lithium ions and leads to poor kinetics; if the angle between the flaky surface of graphite and the plane where the current collector is located is larger, the angle between the end face of the flaky graphite and the plane where the current collector is located is smaller, and the electrolyte is more inclined to enter through the end face of graphite, which is conducive to shortening the embedding path of lithium ions.

[0077] This application does not limit the specific values ​​of angles α and β. For example, in some embodiments, angle α satisfies the following: 0° < α ≤ 90°, preferably 50° < α ≤ 90°; and / or angle β satisfies the following: 0° ≤ β ≤ 50°. Angle α refers to the angle between the graphite flaky surface in the first region and the plane of the current collector. This application does not limit the angle between the graphite flaky surface in the second region and the plane of the current collector; for example, it can be 0 to 50°.

[0078] In some embodiments, as shown in FIG6 , the current collector includes an active layer region 110 and a hollow foil region 120 , the active material layer 11 is disposed in the active layer region 110 , the groove 103 is disposed in the active material layer 11 , and the hollow foil region 120 is used to dispose the tab 2 .

[0079] The present application does not impose too many restrictions on the preparation process of the above-mentioned electrode sheet. An initial electrode sheet can be prepared by conventional methods, and then the corresponding position of the initial electrode sheet is subjected to subtractive treatment to form a groove to obtain the electrode sheet of the present application. Among them, the subtractive treatment can be methods such as scraping, friction, peeling, ablation, ion beam, etc. After the subtractive treatment, in some embodiments, in the first region, at least 50% of the mass of the graphite has one end face facing the center of the groove. In this way, the graphite in the first region is oriented at a certain angle to form a path with a specific orientation, which is conducive to achieving an orientation degree of graphite in the first region that is less than the orientation degree of graphite in the main body. By limiting the proportion and size parameters of the active layer of the subtractive treatment or using friction materials of different roughness or types, it is conducive to further regulating the orientation degree of graphite in the first region to 0.1 to 2. In addition, by limiting the proportion and size parameters of the active layer of the subtractive treatment or using friction materials of different roughness or types, it is conducive to achieving that the first region occupies 20 to 80% of the volume of the recess.

[0080] Subtractive processing essentially involves partially removing the active layer from the initial electrode sheet. Due to the removal of the active layer, the weight and energy density of the electrode sheet decrease. To balance the fast-charging performance, cycle expansion rate, and energy density of the electrode sheet, in some embodiments, the weight loss rate of the electrode sheet is 0.01% to 3.0%. The weight loss rate is calculated as (mass of the initial electrode sheet - mass of the electrode sheet after subtractive processing) / mass of the initial electrode sheet.

[0081] In this application, the initial electrode sheet is placed on sandpaper and subjected to subtractive processing using equipment used for subtractive processing. During the subtractive processing, some impurities, such as artificial diamond, glass, aluminum oxide, silicon oxide, and silicon carbide, are inevitably dropped. Therefore, in some embodiments, the groove contains at least one of artificial diamond, glass, aluminum oxide, silicon oxide, and silicon carbide.

[0082] In the present application, a subtractive treatment is performed on the surface of the active material layer away from the current collector. This is because, in the prior art, the preparation of the initial electrode sheet is usually to first coat the active material on the current collector, and then obtain the initial electrode sheet after rolling. The porosity is reduced after rolling. During the rolling process, the surface of the active material layer is subjected to great force, the compaction is higher, and the porosity is lower. The present application performs a subtractive treatment on the surface of the active material layer away from the current collector, which is not only conducive to the formation of grooves, but also can remove part of the active layer with a sudden drop in porosity, thereby avoiding the occurrence of situations such as the migration path of lithium ions becoming longer and the transmission path of the electrolyte becoming longer. Therefore, in the electrode sheet of the present application, in some embodiments, the porosity of the recessed portion is greater than the porosity of the main portion, which is conducive to improving the transmission path of the electrolyte.

[0083] The porosity of the active material layer determines the diffusion and transport of lithium ions. The higher the porosity, the more conducive it is to the infiltration of the electrolyte and the transport of lithium ions, promoting the increased speed of lithium ion and electrolyte transport into the interior of the electrode sheet. It also helps increase the channels and directions for lithium ion insertion and extraction in the active material layer, thereby enabling the battery to have excellent high-rate charge and discharge performance. However, the higher the porosity, the lower the volume density of the active material layer and the lower the energy density of the battery. In some embodiments, the porosity of the recessed portion is 30% to 60%; and / or the porosity of the main body is 15% to 35%.

[0084] In a second aspect of the present application, a battery is provided, comprising the electrode sheet according to the first aspect.

[0085] Specifically, the electrode sheets include a negative electrode sheet and a positive electrode sheet. The negative electrode sheet, the positive electrode sheet, and the separator can form a battery cell, wherein at least one of the negative electrode sheet and the positive electrode sheet is the electrode sheet of the first aspect described above. By installing the battery cell and the protection circuit together inside the battery casing, a battery for charge and discharge can be formed. The quality of the battery cell directly determines the quality of the battery. Due to the use of the above-mentioned electrode sheets, the battery of the present application performs excellently in terms of fast charging performance and cyclic expansion rate.

[0086] Due to the unique structure of the electrode sheet in this application, the interfacial strength between the electrode sheet and the separator in the battery is improved, further reducing the cycle expansion rate. In this battery, the peel strength between the electrode sheet and the separator is 1.2 to 3.0 mN / mm.

[0087] The present application will be further described below through specific examples and comparative examples.

[0088] Example 1

[0089] 1. Preparation of negative electrode sheet

[0090] (1) Graphite, styrene-butadiene latex (SBR), and sodium carboxymethyl cellulose (CMC) in a mass ratio of 96.5:2:1.5 were dissolved in deionized water. A double planetary mixer was used with a rotation of 1200 r / min and a revolution of 20 r / min. After stirring for 5 h, a negative electrode slurry was obtained. The negative electrode slurry was coated on both surfaces of a negative electrode current collector with a thickness of 6 μm using an extrusion coater. The coating surface density was 9.88 mg / cm 2 , roller compaction density 1.7g / cm 3 , obtaining an initial negative electrode sheet with a thickness of 119 μm;

[0091] (2) As shown in FIG6 , the active material layer on the initial negative electrode sheet on both sides of the current collector is subjected to a subtractive treatment to form grooves, wherein on one side of the current collector, the ratio of the orthographic projection area of ​​the groove on the current collector to the orthographic projection area of ​​the active material layer on the current collector is 0.1:1. Specifically, the active material layer is scraped every 30 to 100 μm along the width direction of the current collector to form grooves, and the depth of the groove (the dimension in the thickness direction of the current collector is 2 μm; the dimension difference between the groove and the active layer in the length direction of the current collector is 1 mm, and the distance between the groove closest to the edge of the current collector in the length direction and the edge of the current collector in the length direction is 0 to 3 mm.

[0092] 2. Preparation of positive electrode

[0093] (1) Lithium iron phosphate, polyvinylidene fluoride, and Super P in a mass ratio of 95:2:3 were dissolved in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 55%; the positive electrode slurry was coated on both surfaces of a 10 μm thick rolled aluminum foil and dried at 90°C. The coating surface density was 14.5 mg / cm 2 ; Then follow 4.0g / cm 3 The compaction density was rolled to obtain a positive electrode sheet with a thickness of 81 μm.

[0094] 3. Preparation of batteries

[0095] (1) Using a polyethylene (PE) porous polymer film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain a battery cell;

[0096] (2) Preparation of electrolyte: In a dry argon environment, lithium hexafluorophosphate (LiPF6) was added to a solvent solution of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1, and the mixture was uniformly mixed, wherein the concentration of LiPF6 was 1.12 mol / L, and then 10 wt% of fluoroethylene carbonate (FEC) was added and mixed uniformly to obtain an electrolyte;

[0097] (3) The battery cell is encapsulated into the punched hole of the packaging film (the aluminum-plastic film contains an outer layer of nylon, a middle layer of Al, and an inner layer of PP). After the battery cell is dried, the electrolyte is injected and encapsulated. After formation, degassing, and trimming, a full battery is obtained, and the electrical performance of the full battery is tested.

[0098] Example 2

[0099] The preparation process is basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, the groove depth of 2 μm is replaced by the groove depth (dimension in the thickness direction of the current collector) of 5 μm. Other conditions remain unchanged to obtain the negative electrode sheet of this embodiment.

[0100] The negative electrode sheet of the embodiment is replaced with the negative electrode sheet of this embodiment, and other conditions remain unchanged, and the battery of this embodiment is assembled.

[0101] Example 3

[0102] The preparation process is basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, the groove depth of 2 μm is replaced by the groove depth (dimension in the thickness direction of the current collector) of 10 μm. Other conditions remain unchanged to obtain the negative electrode sheet of this embodiment.

[0103] The negative electrode sheet of the embodiment is replaced with the negative electrode sheet of this embodiment, and other conditions remain unchanged, and the battery of this embodiment is assembled.

[0104] Example 4

[0105] The preparation process is basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, the groove depth of 2 μm is replaced by a groove depth (dimension in the thickness direction of the current collector) of 15 μm. Other conditions remain unchanged to obtain the negative electrode sheet of this embodiment.

[0106] The negative electrode sheet of the embodiment is replaced with the negative electrode sheet of this embodiment, and other conditions remain unchanged, and the battery of this embodiment is assembled.

[0107] Example 5

[0108] The preparation process is basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, the groove depth of 2 μm is replaced by "the groove depth (dimension in the thickness direction of the current collector) 5 μm", and the ratio of the orthographic projection area of ​​the groove on the current collector to the orthographic projection area of ​​the active material layer on the current collector is replaced by "a ratio of 0.3:1" in the preparation process of the negative electrode sheet of this embodiment.

[0109] The negative electrode sheet of the embodiment is replaced with the negative electrode sheet of this embodiment, and other conditions remain unchanged, and the battery of this embodiment is assembled.

[0110] Example 6

[0111] The preparation process was basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, the groove depth of 2 μm was replaced by "the groove depth (dimension in the thickness direction of the current collector) 5 μm", and the ratio of the orthographic projection area of ​​the groove on the current collector to the orthographic projection area of ​​the active material layer on the current collector was replaced by "a ratio of 0.4:1"; other conditions remained unchanged, and the negative electrode sheet of this embodiment was obtained;

[0112] The negative electrode sheet of the embodiment is replaced with the negative electrode sheet of this embodiment, and other conditions remain unchanged, and the battery of this embodiment is assembled.

[0113] Example 7

[0114] The preparation process is basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, the groove depth of 2 μm is replaced by “the groove depth (dimension in the thickness direction of the current collector) 5 μm”, and the ratio of the orthographic projection area of ​​the groove on the current collector to the orthographic projection area of ​​the active material layer on the current collector of 0.1:1 is replaced by “a ratio of 0.5:1”. Other conditions remain unchanged to obtain the negative electrode sheet of this embodiment;

[0115] The negative electrode sheet of the embodiment is replaced with the negative electrode sheet of this embodiment, and other conditions remain unchanged, and the battery of this embodiment is assembled.

[0116] Comparative Example 1

[0117] The preparation process is basically the same as that of Example 1, except that, in the preparation process of the negative electrode sheet, step (2) is omitted, other conditions remain unchanged, and the initial negative electrode sheet is directly used as the negative electrode sheet to assemble the battery to obtain the battery of this comparative example.

[0118] Test example

[0119] 1. Rate performance measurement

[0120] At room temperature, the sample was completely discharged and fully charged at constant current and constant voltage of 0.2C / 0.5C / 1C / 1.5C / 2C respectively. The discharge was carried out at a constant current of 0.2C to the discharge cut-off voltage. The charging capacity in the constant current stage is calculated as: C c1 , C c2 , C c3 , C c4 , C c5 The total charging capacity is counted as C1, C2, C3, C4, and C5, which are respectively included in the constant current charging ratio under each charging rate. The constant current charging ratio is constant current charging capacity / total charging capacity.

[0121] 2. Electrolyte penetration rate test in electrode sheet

[0122] (1) Testing the volatilization amount of the electrolyte to obtain the volatilization amount of the electrolyte at different times;

[0123] (2) Immersing the electrode sheet in the same amount and type of electrolyte as in step (1), and after immersion, measuring the amount of electrolyte reduction at different times;

[0124] (3) The amount of electrolyte reduced in step (2) minus the amount of electrolyte volatilized in step (1) at the same time is used to obtain the actual liquid absorption amount Δm of the electrode sheet. The actual wetting curve of the electrode sheet is obtained using the Lucas-Washburn equation. The slope of the actual wetting curve is the wetting rate of the electrolyte in the electrode sheet.

[0125] The wetting rate equation based on the modified Lucas-Washburn equation is as follows:

[0126] Where: t-time; Δm-change in electrode weight during the wetting process; ρ sol -Electrolyte density; A e - electrode sheet cross-sectional area; K - electrolyte wetting rate in the porous electrode sheet; P - electrode sheet porosity; The effective aperture of the electrode sheet; γ lv -Surface tension of the electrolyte; θ-contact angle between the electrolyte and the electrode; η-viscosity of the electrolyte.

[0127] 3. Lithium deposition window test

[0128] The batteries were charged at 1C constant current and constant voltage to 4.35V at 0°C, left to rest for 10 minutes, and then discharged at 0.7C to 3.0V. Each battery group was cycled 20 times and dissected to observe lithium deposition. The lithium deposition ratio = area of ​​the lithium deposition region / projected area of ​​the active material layer.

[0129] 4. Peel strength test between electrode sheet and isolation film

[0130] The negative electrode sheet and separator used in this example were hot-pressed at 2.0 MPa and 85°C for 10 seconds to form a composite material. The composite material was then cut into composite samples measuring 20 × 100 mm. The ends of the composite sample were separated, with one end fixed to the upper end of a tensile testing machine and the other to the other end, with a bending angle of 180°. Testing was performed using a high-speed rail tensile testing machine, with the sample angle adjusted to ensure the upper and lower ends were vertical. The sample was then stretched at a rate of 50 mm / min until the negative electrode and separator were completely separated. The displacement and applied force during the process were recorded, as well as the force at equilibrium. Ten measurements were averaged, and the average of these values ​​was taken as the peel strength between the negative electrode sheet and the separator. Figure 17 shows the peel strength data for multiple samples from Example 1 and the comparative example.

[0131] 5. Cell cycle thickness expansion rate

[0132] Charge the battery to full charge and use a flat thickness gauge to measure the thickness of the battery, which is recorded as T0. Cycle the battery for 25, 50, 100, 150, 200, and 300 times respectively. The thickness of the battery at each node is recorded as T i (i=1,2,3,4), Swelling Ratio %=(T i -T0) / T0×100%.

[0133] The above tests were performed on the batteries of the embodiment and the comparative example, and the results are shown in Table 1.

[0134] Table 1

[0135] By comparing Examples 1-7 and Example 1, it can be seen that after the negative electrode sheet is subjected to subtractive processing to form grooves, the peel strength between the negative electrode sheet and the separator is improved, which is beneficial to improving the interface strength between the separator and the negative electrode sheet, thereby reducing the cycle expansion rate of the battery cell during the cycle; the electrolyte penetration rate of the negative electrode sheet is also improved, which is beneficial to shortening the processing time of the aging process in the battery cell manufacturing process, reducing the manufacturing cycle of the battery cell and reducing the manufacturing cost; the lithium plating window of the negative electrode sheet is significantly improved, which is beneficial to improving the fast charging performance of the battery cell, especially the fast charging performance under extreme conditions.

[0136] By comparing Examples 1-7, it can be seen that increasing the groove depth and the total area of ​​the grooves is beneficial to improving the interface strength and improving lithium plating, but it will also have a certain loss on ED. Therefore, by adjusting the size and proportion of the grooves, the energy density, cycle performance and fast charging performance of the battery can be taken into account.

[0137] The above describes in detail the preferred embodiments and experimental verifications of the present application. It should be understood that ordinary skill in the art can make numerous modifications and variations based on the concepts of the present application without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art based on the concepts of the present application through logical analysis, reasoning, or limited experimentation on the basis of the existing technology should be within the scope of protection defined by the claims.

Claims

1. An electrode sheet, wherein: The electrode sheet comprises a current collector and an active material layer disposed on at least one functional surface of the current collector, wherein the active material layer comprises graphite; Along the extension direction of the current collector, the active material layer includes a main body and a concave portion, and a groove that does not penetrate the concave portion is provided on a side of the concave portion away from the current collector; The recess includes a first region away from the current collector surface and a second region close to the current collector surface; And the orientation degree of graphite in the first region is smaller than that of graphite in the main body, wherein the orientation degree of graphite refers to the intensity ratio of the diffraction peaks of the 004 crystal plane and the 110 crystal plane of graphite.

2. The electrode sheet according to claim 1, wherein: The first region occupies 20 to 80% of the volume of the recess.

3. The electrode sheet according to claim 1, wherein: The orientation degree of graphite in the first region is 0.1 to 2; and / or, The orientation degree of graphite in the main body is 3-15.

4. The electrode sheet according to any one of claims 1 to 3, wherein: The groove is in the shape of a strip on the side of the active material layer away from the current collector, and there are a plurality of grooves; A plurality of the grooves are arranged at intervals along the length direction of the current collector, and the grooves extend along the width direction of the current collector; or, A plurality of the grooves are arranged at intervals along a width direction of the current collector, and the grooves extend along a length direction of the current collector.

5. The electrode sheet according to claim 4, wherein: Every two adjacent grooves are connected by a protrusion, and the size of the protrusion in the first direction of the current collector is 10 to 500 μm, or the size of the protrusion in the second direction of the current collector is 10 to 500 μm.

6. The electrode sheet according to claim 4 or 5, wherein: The ratio of the orthographic projection area of ​​the groove on the current collector to the orthographic projection area of ​​the active material layer on the current collector is (0.1-0.5):1; and / or, The size of the groove in the thickness direction of the current collector is 1 to 50 μm; and / or, The size of the concave portion in the second direction of the current collector is A, the size of the groove in the second direction of the current collector is B, AB=0.5-10 mm, or, The size of the concave portion in the first direction of the current collector is C, and the groove in the first direction of the current collector is The dimension in the first direction is D, CD=0-3 mm.

7. The electrode sheet according to claim 6, wherein: The size of the groove in the first direction of the current collector is 1 to 30 μm; The size of the groove in the second direction of the current collector is 1 to 30 μm.

8. The electrode sheet according to any one of claims 1 to 7, wherein: The recessed portions and the main body portions are alternately arranged along the first direction of the current collector; or, The recessed portions and the main body portions are alternately arranged along a second direction of the current collector.

9. The electrode sheet according to any one of claims 1 to 8, wherein: The graphite flake surface in the first region has an angle α with the plane where the current collector is located, and the graphite flake surface in the main body has an angle β with the plane where the current collector is located, α>β.

10. The electrode sheet according to claim 9, wherein: The angle α satisfies: 0°<α≤90°; and / or, The angle β satisfies: 0°≤β≤50°.

11. The electrode sheet according to any one of claims 1 to 10, wherein: In the first region, at least 50% by mass of the graphite has one end surface facing the center of the groove.

12. The electrode sheet according to any one of claims 1 to 10, wherein: The porosity of the recessed portion is greater than the porosity of the main body portion.

13. The electrode sheet according to claim 12, wherein: The porosity of the recess is 30% to 60%; and / or, The porosity of the main body is 15-35%.

14. A battery, wherein: The electrode sheet comprises the electrode sheet according to any one of claims 1 to 13.

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