Electrode sheet and preparation method therefor, electrode assembly, and lithium ion battery

Abstract

An electrode sheet, an electrode assembly, and a lithium ion battery. The electrode sheet (1) comprises a conductive current collector (10), an electrode active layer (20), and a tackifying layer (30), wherein the electrode active layer (20) covers a middle area of the conductive current collector (10) in a first direction, and the tackifying layer (30) at least covers a part of the surface of the side of the electrode active layer (20) facing away from the conductive current collector (10).

Description

Electrode sheet and preparation method thereof, electrode assembly and lithium ion battery

[0001] Related applications

[0002] This application claims priority to Chinese patent application number 2023116231170, filed on November 30, 2023, entitled “Electrode sheet and preparation method thereof, electrode assembly and lithium-ion battery”, the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application relates to the technical field of lithium-ion batteries, and in particular to an electrode sheet and a preparation method thereof, an electrode assembly and a lithium-ion battery. Background Art

[0004] With the rapid development of energy storage technology, the market has put forward higher and higher requirements for the performance of lithium-ion batteries in all aspects, and the pressure on the cost side is also increasing. Among them, the improvement of diaphragms is very effective in reducing costs. If dry coating of diaphragms is used, the unit price of diaphragms can be reduced by more than 60%, and the corresponding Wh cost of battery cells can be reduced by about 10%. Therefore, the use of the above-mentioned diaphragms in lithium-ion batteries will help to significantly reduce production costs.

[0005] However, due to the dry coating method of the diaphragm, the diaphragm loses its coating, resulting in serious wrinkling of the electrode plates of the electrode assembly (winding structure) or poor electrode coverage (laminated structure), which poses a very large safety hazard. Therefore, it is necessary to further improve the production process of lithium-ion batteries so that the device can smoothly introduce the above-mentioned diaphragm without safety risks, thereby improving product competitiveness. Summary of the Invention

[0006] An embodiment of the present application provides an electrode sheet, comprising a conductive current collector, an electrode active layer, and an adhesion-promoting layer, wherein the electrode active layer covers a central region of the conductive current collector along a first direction, and the adhesion-promoting layer covers at least a portion of the surface of the electrode active layer on a side facing away from the conductive current collector.

[0007] In one embodiment, the adhesion-promoting layer covers the surface of the electrode active layer facing away from the conductive current collector, and the adhesion-promoting layer includes adhesion-promoting strips, and the number of the adhesion-promoting strips n is ≥1.

[0008] In one embodiment, the tackifying strip is rectangular.

[0009] In one embodiment, the number n of the tackifying strips is greater than 1, and each of the tackifying strips is spaced apart and arranged in the same direction;

[0010] The width direction of each of the adhesion-promoting strips is parallel to the first direction; or

[0011] The length direction of each of the adhesion-promoting strips is parallel to the first direction.

[0012] In one embodiment, the number n of the tackifying strips is greater than 1, and the tackifying strips are arranged in a grid shape, the width direction of at least one of the tackifying strips is parallel to the first direction, and the length directions of the other tackifying strips are parallel to the first direction.

[0013] In one embodiment, the thickness of the electrode active layer is T1, the thickness of the adhesion-promoting layer on the surface of the electrode active layer facing away from the conductive current collector is T2, and T2<T1.

[0014] In one embodiment, 0 μm<T2≤10 μm.

[0015] In one embodiment, in the region corresponding to the conductive current collector, the adhesion-promoting layer further covers at least one side surface of the electrode active layer that is perpendicular to the conductive current collector.

[0016] In one embodiment, the thickness of the electrode active layer is T1, the thickness of the adhesion-promoting layer covering the side surface is T3, and T3 ≤ (T1+10) μm;

[0017] The adhesion-promoting layer covering the side surface has a width W1 perpendicular to the first direction, and 0 mm ≤ W1 ≤ 15 mm.

[0018] In one embodiment, the projected area of ​​the adhesion-promoting layer on the conductive current collector is 5% to 110% of the projected area of ​​the electrode active layer on the conductive current collector.

[0019] In one embodiment, the material of the adhesion-promoting layer includes one or more of an active material, a binder, a conductive agent, and a dispersant.

[0020] In one embodiment, the material of the adhesion-promoting layer is selected from the adhesive and the conductive agent.

[0021] In one embodiment, the mass ratio of the binder to the conductive agent is (10-50): (10-90).

[0022] One embodiment of the present application provides a method for preparing the electrode sheet described in any of the above embodiments, comprising the following steps:

[0023] Coating the central region of the conductive current collector along a first direction to form an electrode active layer;

[0024] An adhesion-promoting layer is formed by coating at least a portion of the surface of the electrode active layer away from the conductive current collector.

[0025] An embodiment of the present application provides an electrode assembly, including a cathode electrode sheet, an anode electrode sheet and a diaphragm, wherein the cathode electrode sheet and the anode electrode sheet are separated by the diaphragm, and at least one of the cathode electrode sheet and the anode electrode sheet is the electrode sheet described in any of the above embodiments.

[0026] An embodiment of the present application provides a lithium-ion battery comprising the electrode assembly described in any of the above embodiments.

[0027] In addition to the conductive current collector and electrode active layer, the electrode sheet also includes an adhesion-enhancing layer. The adhesion-enhancing layer covers at least a portion of the surface of the electrode active layer facing away from the conductive current collector. This improves the adhesion between the electrode sheet and the separator, particularly the uncoated separator, and resolves wrinkling issues that can occur during winding of uncoated separator electrode assemblies or poor coverage during lamination, thereby improving the service life of the electrode assembly and reducing safety risks. The use of the electrode sheet makes it easier to incorporate uncoated separators, which helps reduce the production cost of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without any creative work.

[0029] FIG1 is a schematic front view of an electrode sheet with n=1 adhesion-promoting strips in one embodiment.

[0030] FIG2 is a schematic top view of an electrode sheet with the number of adhesion-promoting strips n=1 in one embodiment.

[0031] FIG3 is a schematic top view of an electrode sheet in an embodiment in which the number of adhesion-promoting strips n>1 and the width direction of each adhesion-promoting strip is parallel to the first direction.

[0032] FIG4 is a left side schematic diagram of an electrode sheet in an embodiment in which the number of adhesion promoting strips n>1 and the width direction of each adhesion promoting strip is parallel to the first direction.

[0033] FIG5 is a schematic top view of an electrode sheet in another embodiment in which the number of adhesion-promoting strips n is greater than 1 and the length direction of each adhesion-promoting strip is parallel to the first direction.

[0034] FIG6 is a schematic front view of an electrode sheet in another embodiment in which the number of adhesion-promoting strips n is greater than 1 and the length direction of each adhesion-promoting strip is parallel to the first direction.

[0035] FIG7 is a schematic top view of an electrode sheet in which the number of adhesion-enhancing strips n>1 and the adhesion-enhancing strips are arranged in a grid pattern in one embodiment.

[0036] 8 is a schematic front view of an electrode sheet in which the adhesion-promoting layer also covers at least one side of the electrode active layer perpendicular to the conductive current collector in the region corresponding to the conductive current collector in one embodiment.

[0037] FIG9 is a partially enlarged schematic diagram of FIG8 .

[0038] Explanation of reference numerals: 1: electrode sheet; 10: conductive current collector; 20: electrode active layer; 30: adhesion-enhancing layer; 310: adhesion-enhancing strip. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in 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.

[0040] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0042] In this application, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0043] It should be noted that when an element is referred to as being “fixed to” another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or there may be an intermediate element.

[0044] In this application, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0045] In addition, the drawings are not drawn in a 1:1 scale, and the relative sizes of the elements are drawn in the drawings only as examples to facilitate understanding of the present application, but are not necessarily drawn in true proportion. The proportions in the drawings do not constitute a limitation to the present application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0047] The present application provides an electrode sheet and a preparation method thereof, an electrode assembly and a lithium-ion battery. The above-mentioned electrode sheet can improve the problems of wrinkling of the wound electrode group or poor coverage of the laminated electrode group, make it easier to introduce an uncoated diaphragm, and reduce the production cost of the lithium-ion battery.

[0048] As shown in Figures 1 to 8, an embodiment of the present application provides an electrode sheet 1, including a conductive current collector 10, an electrode active layer 20 and an adhesion-promoting layer 30, wherein the electrode active layer 20 covers the central area of ​​the conductive current collector 10 along a first direction X, and the adhesion-promoting layer 30 covers at least a portion of the surface of the electrode active layer 20 on the side away from the conductive current collector 10.

[0049] In addition to the conductive current collector 10 and the electrode active layer 20, the electrode sheet 1 also includes an adhesion-promoting layer 30. The adhesion-promoting layer 30 covers at least a portion of the surface of the electrode active layer 20 facing away from the conductive current collector 10. This can enhance the adhesion between the electrode sheet 1 and the separator, especially between the electrode sheet 1 and the uncoated separator, thereby resolving the wrinkling problem that occurs when the uncoated separator electrode assembly is wound, or the poor coverage problem that occurs when the sheets are stacked, thereby improving the service life of the electrode assembly and reducing safety risks. The use of the electrode sheet 1 makes it easier to introduce the uncoated separator, which is conducive to reducing the production cost of lithium-ion batteries.

[0050] As shown in Figures 1 to 6, the adhesion layer covers the surface of the electrode active layer 20 facing away from the conductive current collector 10. The adhesion layer 30 includes adhesion strips 310. The number of adhesion strips 310 is n ≥ 1. The adhesion strips 310 are rectangular.

[0051] As shown in FIG. 1 and FIG. 2 , in one embodiment, the number n of the adhesion promoting strips 310 is 1, and the adhesion promoting layer 30 covers the entire surface of the electrode active layer 20 facing away from the conductive current collector 10 .

[0052] Referring to Figures 3 to 6 , in one embodiment, the number of tackifying strips n is greater than 1, and each tackifying strip 310 is spaced apart and arranged in the same direction. Furthermore, referring to Figures 3 and 4 , the width direction of each tackifying strip 310 is parallel to the first direction X, or, referring to Figures 5 and 6 , the length direction of each tackifying strip 310 is parallel to the first direction X.

[0053] 7 , in one embodiment, the number of tackifying strips n>1, and the tackifying strips 310 are arranged in a grid pattern, with the width direction of at least one tackifying strip 310 parallel to the first direction X, and the length directions of the other tackifying strips 310 parallel to the first direction X.

[0054] It is understandable that the adhesion layer 30 only needs to cover the portion of the surface of the electrode active layer 20 facing away from the conductive current collector 10. It can cover all, partially, or even exceed the surface coverage. The shape and arrangement of the adhesion layer 30 are not limited to the technical solutions in any of the above embodiments. Other arbitrary shapes and arbitrary arrangements can be adopted, such as irregular coverage, discontinuous coverage, etc. As long as they can achieve the adhesion effect, they should be understood to be within the scope of protection of this application. It is understandable that the adhesion layer 30 can be, for example, but not limited to, covered on the surface of the electrode active layer 20 by gravure coating, spraying, intermittent coating, etc., as long as the effect of fixing the adhesion layer 30 can be achieved.

[0055] 8 , in one embodiment, in the region corresponding to the conductive current collector 10 , the adhesion-promoting layer 30 further covers at least one side surface of the electrode active layer 20 that is perpendicular to the conductive current collector 10 .

[0056] Referring to Figure 9, further, the thickness of the electrode active layer 20 is T1, and the thickness of the adhesion-promoting layer 30 on the surface of the electrode active layer 20 facing away from the conductive current collector 10 is T2, where T2 < T1. The thickness T2 of the adhesion-promoting layer 30 is less than the thickness T1 of the electrode active layer 20, which is beneficial for ensuring good electrical performance of the electrode sheet 1. Furthermore, 0μm < T2 ≤ 10μm. The thickness T2 of the adhesion-promoting layer 30 within this range can ensure good adhesion and ensure that the released ions can pass through the coating normally, thereby not affecting the electrical performance. In one embodiment, 0.5μm ≤ T2 ≤ 5μm.

[0057] Referring to Figure 9 , the thickness of the electrode active layer 20 is T1, and the thickness of the adhesion-promoting layer 30 covering the side surfaces is T3, where T3 ≤ (T1 + 10) μm. The thickness of the adhesion-promoting layer 30 covering the side surfaces is controlled to not exceed the thickness range of the electrode active layer 20, thereby minimizing the impact on the electrical performance of the electrode sheet 1. In one embodiment, T1 - 5 μm ≤ T3 ≤ T1 + 5 μm.

[0058] It can be understood that the thickness T1 of the electrode active layer 20 can be the conventional thickness of the electrode active layer in the lithium battery, for example, T1 is 60 μm to 100 μm.

[0059] Referring to Figure 9 , the width of the adhesion-promoting layer 30 covering the side surfaces in a direction perpendicular to the first direction X is W1, where 0 mm ≤ W1 ≤ 15 mm. Similarly, when the width of the adhesion-promoting layer 30 covering the side surfaces in a direction perpendicular to the first direction X is within this range, poor welding can be avoided and a reduction in energy density can be effectively prevented. In one embodiment, 0.5 mm ≤ W1 ≤ 7 mm.

[0060] In one embodiment, the projected area of ​​the adhesion-promoting layer 30 on the conductive current collector 10 is 5% to 110% of the projected area of ​​the electrode active layer 20 on the conductive current collector 10. When the projected area of ​​the adhesion-promoting layer 30 on the conductive current collector 10 is within the above range, the adhesion between the electrode sheet 1 and the separator, especially the uncoated separator, can be effectively improved, thereby improving the problem of wrinkling or poor coverage of the electrode assembly.

[0061] In some embodiments, the material of the adhesion-promoting layer 30 includes one or more of an active material, a binder, a dispersant, and a conductive agent. Further, the adhesion-promoting layer 30 includes an active material, a binder, a dispersant, and a conductive agent in a mass ratio of (0-90): (5-90): (0.1-2): (5-90). It can be understood that if the electrode sheet 1 is an anode electrode sheet, the active material is selected from the anode active material, and if the electrode sheet 1 is a cathode electrode sheet, the active material is selected from the cathode active material. Further, the material of the adhesion-promoting layer 30 is selected from a binder and a conductive agent. Furthermore, the mass ratio of the binder and the conductive agent is (10-50): (10-90). The increase in the proportion of conductive agent improves the conductivity, which is beneficial to improving the cycle performance of the battery. However, as the proportion of conductive agent increases, the proportion of binder will decrease. If the binder proportion is too low, the bonding force will be reduced to an unreasonable level. Appropriate bonding force is beneficial to improving the bonding effect between the electrode and the diaphragm, reducing the wrinkling problem, and preventing the problem of lithium precipitation during cycling caused by wrinkling, thereby improving the cycle performance. If the bonding force is too low, the conductivity and bonding force will be seriously unbalanced, which will lead to a decrease in battery performance. Controlling the mass ratio of the binder and the conductive agent in the adhesion layer 30 within the above range can maintain a better balance between the conductivity and bonding force of the electrode.

[0062] Furthermore, the conductive agent may include, for example but not limited to, carbon black.

[0063] Furthermore, the adhesive may include, for example but not limited to, styrene-butadiene rubber.

[0064] An embodiment of the present application provides an electrode assembly, including a cathode electrode sheet, an anode electrode sheet and a diaphragm. The cathode electrode sheet and the anode electrode sheet are separated by the diaphragm, and at least one of the cathode electrode sheet and the anode electrode sheet is the electrode sheet 1 in any of the above embodiments.

[0065] It is understandable that in some embodiments, the cathode electrode sheet may be the electrode sheet 1 in any of the above embodiments, and the anode electrode sheet may be a conventional anode electrode sheet. In other embodiments, the anode electrode sheet may be the electrode sheet 1 in any of the above embodiments, and the cathode electrode sheet may be a conventional cathode electrode sheet. In yet other embodiments, both the cathode electrode sheet and the anode electrode sheet may be the electrode sheet 1 in any of the above embodiments. It is understandable that for the cathode electrode sheet, the conductive current collector 10 may be a conventional cathode conductive current collector, and the electrode active layer 20 may be a conventional cathode electrode active layer; for the anode electrode sheet, the conductive current collector 10 may be a conventional anode conductive current collector, and the electrode active layer 20 may be a conventional anode electrode active layer.

[0066] In some embodiments, the electrode sheet 1 provided in any of the above embodiments is an anode electrode sheet, and the anode electrode active layer includes an anode active material. Furthermore, the anode active material includes one or more of artificial graphite, natural graphite, mesophase carbon microbeads, composite graphite, hard carbon, soft carbon, silicon-carbon material, silicon-oxygen material, silicon-based alloy material, lithium titanate, other non-carbon materials and the like. Furthermore, the anode electrode active layer also includes a binder, a dispersant and a conductive agent. Furthermore, the anode electrode active layer includes anode active material, a binder, a dispersant and a conductive agent in a mass ratio of (90-99): (1-5): (0.1-2): (1-5). In one embodiment, the anode electrode active layer includes anode active material, a binder, a dispersant and a conductive agent in a mass ratio of 95-97: 2-3: 0.1-0.5: 1-2.

[0067] In some embodiments, the electrode sheet 1 provided in any of the above embodiments is an anode electrode sheet, and the anode conductive current collector includes copper foil.

[0068] It is understood that when the electrode sheet 1 provided in any of the above embodiments is a cathode electrode sheet, the cathode electrode active layer also includes materials such as an active material, a binder, and a conductive agent. The active material may include, but is not limited to, one or a combination of materials such as lithium iron phosphate, lithium cobalt oxide, and lithium manganese oxide. It is understood that the cathode electrode current collector may be, for example, aluminum foil.

[0069] In some embodiments, the separator may be one or more of PP, PE, PP / PE / PP composite film, aramid and non-woven fabric.

[0070] In some embodiments, the electrode assembly further includes an encapsulation layer that encapsulates the cathode electrode sheet, the anode electrode sheet, and the separator. Furthermore, the encapsulation layer may be, for example, an aluminum-plastic film, an aluminum shell, a steel shell, or other materials, and the shell shape of the encapsulation layer may be, for example, a cylinder, a polygonal prism, or the like.

[0071] An embodiment of the present application provides a lithium-ion battery comprising the electrode assembly of any of the above embodiments.

[0072] The following are specific examples.

[0073] Example 1

[0074] Step 1: Refer to Figures 5 and 6 to prepare the anode electrode sheet:

[0075] (1) Graphite, carbon black, and sodium carboxymethyl cellulose were dry-mixed in a mass ratio of 95.9%:1.1%:1.1%, deionized water was added, and the mixture was stirred. Finally, 1.9% by mass of styrene-butadiene rubber was added and uniformly dispersed to obtain an anode electrode active layer slurry. The anode electrode active layer slurry was uniformly coated along a first direction X on the central region of the copper foil of the conductive current collector 10, and dried to form an electrode active layer 20. The thickness of the electrode active layer T1 was 80 μm.

[0076] (2) Carbon black and styrene-butadiene rubber were dry-mixed in a mass ratio of 4:1, and deionized water was added and stirred to obtain an adhesion-promoting layer slurry. The adhesion-promoting layer slurry was evenly coated on the surface of the electrode active layer 20 facing away from the conductive current collector 10. The coating method was intermittent coating to form four rectangular adhesion-promoting strips 310 spaced apart. The length direction of each adhesion-promoting strip 310 was parallel to the first direction X. After drying, an adhesion-promoting layer 30 was formed. The thickness of the adhesion-promoting layer 30 on the surface of the electrode active layer 20 facing away from the conductive current collector 10 was T2 = 1.5 μm.

[0077] The projected area of ​​the adhesion promoting layer 30 on the conductive current collector 10 is 60% of the projected area of ​​the electrode active layer 20 on the conductive current collector 10 .

[0078] (3) Cold pressing, die cutting and slitting are performed to obtain anode electrode sheets.

[0079] Step 2: Prepare cathode electrode sheet:

[0080] Lithium iron phosphate, carbon black, and polyvinylidene fluoride are dry-mixed in a mass ratio of 96.5%:1.5%:2%, and then N-methylpyrrolidone is added as a solvent. The mixture is stirred evenly in a blender to obtain a cathode active layer slurry. The cathode active layer slurry is evenly coated on aluminum foil, dried, cold-pressed, die-cut, and slit to obtain cathode electrode sheets.

[0081] Step 3: Prepare lithium-ion battery:

[0082] The anode electrode sheet prepared in step 1, the cathode electrode sheet prepared in step 2 and the PP-based separator are combined and wound to obtain a bare cell, and then a lithium-ion battery is obtained through conventional assembly, liquid injection, formation, capacity division and other processes.

[0083] Example 2

[0084] The embodiment is substantially the same as the embodiment 1, except that, in the anode electrode sheet of the embodiment 2, the mass ratio of carbon black and styrene-butadiene rubber in the material of the adhesion-promoting layer 30 is 1:1.

[0085] Example 3

[0086] The embodiment is substantially the same as the embodiment 1, except that, in the anode electrode sheet of the embodiment 3, the mass ratio of carbon black to styrene-butadiene rubber in the material of the adhesion-promoting layer 30 is 2:1.

[0087] Example 4

[0088] The embodiment is substantially the same as the embodiment 1, except that, in the anode electrode sheet of the embodiment 4, the mass ratio of carbon black to styrene-butadiene rubber in the material of the adhesion-promoting layer 30 is 3:1.

[0089] Example 5

[0090] The embodiment is substantially the same as the embodiment 1, except that, in the anode electrode sheet of the embodiment 5, the mass ratio of carbon black to styrene-butadiene rubber in the material of the adhesion-promoting layer 30 is 5:1.

[0091] Example 6

[0092] It is substantially the same as Example 1, except that in the anode electrode sheet of Example 6, the thickness T2 of the adhesion-promoting layer 30 is 10 μm.

[0093] Example 7

[0094] It is substantially the same as Example 1, except that in the anode electrode sheet of Example 7, the thickness T2 of the adhesion-promoting layer 30 is 5 μm.

[0095] Example 8

[0096] The structure of the anode electrode sheet is shown in Figures 3 and 4.

[0097] It is substantially the same as Example 1, except that, in the anode electrode sheet of Example 8, the width direction of each adhesion-enhancing strip 310 is parallel to the first direction, and the number of adhesion-enhancing strips 310 is 3.

[0098] Example 9

[0099] Please refer to Figure 7 for the structure of the anode electrode sheet.

[0100] It is substantially the same as Example 1, except that, in the anode electrode sheet of Example 9, the adhesion promoting strips 310 are arranged in a grid pattern, wherein the width directions of three adhesion promoting strips 310 are parallel to the first direction, and the length directions of the other three adhesion promoting strips 310 are parallel to the first direction.

[0101] The projected area of ​​the adhesion promoting layer 30 on the conductive current collector 10 is 80% of the projected area of ​​the electrode active layer 20 on the conductive current collector 10 .

[0102] Example 10

[0103] The structure of the anode electrode sheet is shown in Figures 1 and 2.

[0104] It is substantially the same as Example 1, except that, in the anode electrode sheet of Example 10, the adhesion promoting layer 30 covers the entire surface of the electrode active layer 20 on the side away from the conductive current collector 10 , and the number of the adhesion promoting strips 310 is one.

[0105] The projected area of ​​the adhesion promoting layer 30 on the conductive current collector 10 is 100% of the projected area of ​​the electrode active layer 20 on the conductive current collector 10 .

[0106] Example 11

[0107] Please refer to Figure 8 for the structure of the anode electrode sheet.

[0108] The embodiment is substantially the same as Example 1, except that in the anode electrode sheet of Example 11, the adhesion-promoting layer 30 covers the entire surface of the electrode active layer 20 facing away from the conductive current collector 10, and the number of adhesion-promoting strips 310 on this surface is one. Furthermore, within the region corresponding to the conductive current collector 10, the adhesion-promoting layer 30 also covers the two side surfaces of the electrode active layer 20 perpendicular to the conductive current collector 10.

[0109] The thickness of the adhesion promoting layer covering the side surface is T3 = 81.5 μm; the width of the adhesion promoting layer covering the side surface in the direction perpendicular to the first direction X is W1 = 5 mm.

[0110] The projected area of ​​the adhesion promoting layer 30 on the conductive current collector 10 is 105% of the projected area of ​​the electrode active layer 20 on the conductive current collector 10 .

[0111] Comparative Example 1

[0112] It is substantially the same as Example 1, except that the anode electrode sheet of Comparative Example 1 does not contain an adhesion-promoting layer.

[0113] The adhesion and cycle performance tests were performed on the lithium-ion batteries prepared in Examples 1 to 11 and Comparative Example 1. The test results are shown in Table 1 below.

[0114] (1) Adhesion test: The adhesion between the electrode and the diaphragm is tested on the core after winding and hot pressing to evaluate the adhesion effect.

[0115] (2) Cycle performance test: The lithium-ion battery was subjected to a cycle test under the following test conditions: 45°C, 1C / 1C charge and discharge, and a voltage range of 2.5 to 2.65V.

[0116] Table 1 Test results of adhesion and cycle performance of lithium-ion batteries

[0117] As can be seen from Table 1, by comparing Examples 1 to 11 with Comparative Example 1, Examples 1 to 11 can significantly enhance the bonding force between the electrode sheet and the separator in the battery cell, and have little effect on the cycle performance of the lithium battery.

[0118] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. An electrode sheet, characterized in that: It comprises a conductive current collector, an electrode active layer and an adhesion-promoting layer, wherein the electrode active layer covers the middle region of the conductive current collector along a first direction, and the adhesion-promoting layer covers at least a portion of the surface of the electrode active layer on a side away from the conductive current collector.

2. The electrode sheet according to claim 1, characterized in that: The adhesion-promoting layer covers the surface of the electrode active layer on the side away from the conductive current collector, and the adhesion-promoting layer includes adhesion-promoting strips, and the number of the adhesion-promoting strips n≥1.

3. The electrode sheet according to claim 2, characterized in that: The tackified strips are rectangular.

4. The electrode sheet according to claim 2 or 3, characterized in that: The number of the adhesion-enhancing strips n>1, and each of the adhesion-enhancing strips is arranged at intervals along the same direction; The width direction of each of the adhesion-promoting strips is parallel to the first direction; or The length direction of each of the adhesion-promoting strips is parallel to the first direction.

5. The electrode sheet according to claim 2 or 3, characterized in that: The number n of the tackifying strips is greater than 1, and the tackifying strips are arranged in a grid shape, the width direction of at least one of the tackifying strips is parallel to the first direction, and the length directions of the other tackifying strips are parallel to the first direction.

6. The electrode sheet according to any one of claims 1 to 5, characterized in that: The thickness of the electrode active layer is T1, and the thickness of the adhesion-promoting layer on the surface of the electrode active layer facing away from the conductive current collector is T2, where T2<T1.

7. The electrode sheet according to claim 6, characterized in that: 0μm<T2≤10μm.

8. The electrode sheet according to any one of claims 1 to 7, characterized in that: In the region corresponding to the conductive current collector, the adhesion promoting layer also covers at least one side surface of the electrode active layer that is perpendicular to the conductive current collector.

9. The electrode sheet according to claim 8, characterized in that: The thickness of the electrode active layer is T1, the thickness of the adhesion-promoting layer covering the side surface is T3, T3≤(T1+10)μm; The width of the adhesion-promoting layer covering the side surface in a direction perpendicular to the first direction is W1, and 0mm≤W1≤15mm.

10. The electrode sheet according to any one of claims 1 to 9, characterized in that: The projected area of ​​the adhesion-promoting layer on the conductive current collector is 5% to 110% of the projected area of ​​the electrode active layer on the conductive current collector.

11. The electrode sheet according to any one of claims 1 to 10, characterized in that: The material of the adhesion-promoting layer includes one or more of an active material, a binder, a conductive agent and a dispersant.

12. The electrode sheet according to claim 11, characterized in that: The material of the adhesion-promoting layer is selected from the binder and the conductive agent.

13. The electrode sheet according to claim 12, characterized in that: The mass ratio of the binder to the conductive agent is (10-50):(10-90).

14. A method for preparing an electrode sheet according to any one of claims 1 to 13, characterized in that: The steps include: Coating the middle region of the conductive current collector along a first direction to form an electrode active layer; An adhesion-promoting layer is formed by coating at least a portion of the surface of the electrode active layer away from the conductive current collector.

15. An electrode assembly, characterized in that: The invention comprises a cathode electrode sheet, an anode electrode sheet and a separator, wherein the cathode electrode sheet and the anode electrode sheet are separated by the separator, and at least one of the cathode electrode sheet and the anode electrode sheet is the electrode sheet according to any one of claims 1 to 13.

16. A lithium ion battery, characterized in that: The electrode assembly comprises the electrode assembly according to claim 15.

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