Electrode sheet, electrode assembly and battery

Abstract

Disclosed in the present application are an electrode sheet, an electrode assembly and a battery. The electrode sheet comprises a main body portion and a plurality of protrusions, wherein each protrusion is formed by means of bending part of the electrode sheet towards one side of the main body portion, and has an inner surface connected to one surface of the main body portion and an outer surface connected to another surface of the main body portion; and the area of the outer surface of each protrusion is S1, the projection area of the outer surface of each protrusion in the direction of the thickness of the electrode sheet is S2, and S1 and S2 meet 1.01≤S1 / S2≤1.7. Reduction in damage to the electrode sheet is facilitated, and the electrode sheet is not stretched and extended too much; and the protrusions provided have good structural stability, are configured to support a separator, and cause an appropriate gap between the main body portion and the separator, thereby facilitating an improvement in the performance of a battery.

Description

Electrode pieces, electrode assemblies and batteries Technical Field

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

[0002] Cycle life is a key performance of lithium-ion batteries. Improving cycle life is a long-term and continuous research and development direction. In addition to improving the battery material end through optimization and innovation, its cycle life can also be effectively contributed through structural design and improvement. This also places more design requirements on the winding method of the battery cell electrode. Summary of the Invention

[0003] The inventors found that there will be extrusion between the layers of the electrode. When the support stability of the interlayer structure of the electrode is poor, the interlayer extrusion leads to insufficient electrolyte between the layers and poor wetting, which easily leads to interface deterioration and even abnormal conditions such as poor wetting and cycle failure.

[0004] The embodiments of the present application provide a pole piece, an electrode assembly, and a battery, which can solve the problem of poor support stability between pole piece layers.

[0005] In the first aspect, an embodiment of the present application provides a pole piece, which includes a main body and a plurality of protrusions, each of the protrusions being formed by bending a portion of the pole piece toward one side of the main body; the protrusion has an inner surface connected to one surface of the main body and an outer surface connected to another surface of the main body.

[0006] The area of ​​the outer surface of the convex portion is S1, and the projected area of ​​the outer surface of the convex portion in the thickness direction of the electrode is S2, and S1 and S2 satisfy: 1.01≤S1 / S2≤1.7, preferably, 1.05≤S1 / S2≤1.5, and further preferably, 1.05≤S1 / S2≤1.3.

[0007] The convex portion has a preset spherical diameter SD, which includes an inner spherical diameter SD1 of the inner surface and an outer spherical diameter SD2 of the outer surface. The inner spherical diameter SD1 is a first diameter of a first circumscribed sphere on which the inner surface is located, and the outer spherical diameter SD2 is a second diameter of a second circumscribed sphere on which the outer surface is located; wherein, SD2>SD1, and 1.5mm≤SD1≤30mm; and / or, 1.5mm≤SD2≤30mm.

[0008] In some exemplary embodiments, the outer surface of the protrusion has a first edge line, the first edge line is formed at the connection between the outer surface and the main body, and the perimeter of the first edge line is C sd , C sd Meet: 1.0mm≤Csd ≤7.8mm, preferably, 4.5mm≤C sd ≤7.8mm.

[0009] In some exemplary embodiments, the convex portion also has a first transition arc surface connected to the first edge line of the outer surface, and the first transition arc surface has a second edge line connected to the main body; the outer surface of the convex portion is connected to the surface of the main body through the first transition arc surface, and the first transition arc surface is a concave arc surface.

[0010] In some exemplary embodiments, the central angle of the first transition arc surface is γ, and γ satisfies: 0°<γ≤90°; and / or the radius of the first transition arc surface is r, and r satisfies: 0.1mm≤r≤5mm.

[0011] In some exemplary embodiments, 5.0 mm ≤ SD1 ≤ 10 mm.

[0012] In some exemplary embodiments, the first circumscribed sphere and the second circumscribed sphere are disposed at the same center; and the shape of the inner surface of the convex portion is similar to the shape of the outer surface.

[0013] In some exemplary embodiments, the outer surface of the protrusion has a first edge line, the first circumscribed sphere has a first tangent line at the first edge line, and the angle between the extension of the surface of the main body connected to the protrusion and the corresponding first tangent line of the protrusion is the first angle α1, where α1 satisfies the following: 15°≤α1≤75°. The outer surface has an outer peripheral edge line connected to the surface of the main body, the first circumscribed sphere has a first tangent line at the outer peripheral edge line, and the angle between the extension of the surface of the main body connected to the protrusion and the corresponding first tangent line of the protrusion is the first angle.

[0014] In some exemplary embodiments, the compressive strength per unit length of the pole piece is N, and N satisfies 0.05N / mm≤N≤1N / mm.

[0015] In some exemplary embodiments, the protrusion has a supporting force P, which satisfies the following conditional formula (1): P = 2N × sinα1 × C sd (1)

[0016] Wherein, N is the compressive strength per unit length of the electrode;

[0017] C sd is the perimeter of the first edge line of the outer surface of the convex portion;

[0018] α1 is the first angle;

[0019] P satisfies 0.026N≤P≤9.66N.

[0020] In some exemplary embodiments, the outer surface of the convex portion includes a main surface and a top surface connected to the main surface, the top surface is an arc surface located in the second circumscribed sphere, and the edge line of the main surface away from the top surface forms a first edge line; the curvature of the main surface is equal to the curvature of the top surface; or, the curvature of the main surface is smaller than the curvature of the top surface, the first edge line forms a polygon, and the vertices of the first edge line of the polygon are all located in the second circumscribed sphere; or, the curvature of the main surface is smaller than the curvature of the top surface, the first edge line forms a circle, and the circular first edge line is located in the second circumscribed sphere.

[0021] In some exemplary embodiments, each of the protrusions has a central axis passing through the center of a first circumscribed sphere on the outer surface and extending along the thickness direction of the pole piece, and the vertical spacing between the central axes of two adjacent protrusions is a first spacing L1, and L1 satisfies: 2.0mm≤L1≤8.0mm.

[0022] In some exemplary embodiments, within a unit area, in the thickness direction of the pole piece, the ratio of the projected area of ​​the outer surfaces of all the protrusions to the projected area of ​​the pole piece is T, and T satisfies: 20%≤T≤40%.

[0023] In some exemplary embodiments, a plurality of the protrusions are arranged side by side and spaced apart along a first direction of the pole piece to form a group of protrusion units, and in a second direction of the pole piece, two adjacent protrusion units are spaced apart, and the first direction, the second direction and the thickness direction of the pole piece are perpendicular to each other.

[0024] In some exemplary embodiments, the protrusions of two adjacent protrusion units are collinearly arranged in the second direction; or one of the protrusion units is translated relative to the other protrusion unit by a predetermined distance A in the first direction, where A satisfies the following: 0.3L2≤A≤L2; wherein each protrusion has a central axis passing through the center of a first circumscribed sphere of the outer surface and extending along the thickness direction of the pole piece, and the vertical spacing between the central axes of two adjacent protrusions in the first direction is a second spacing L2. Preferably, 0.6L2≤A≤0.9L2.

[0025] In some exemplary embodiments, in the thickness direction of the pole piece, all of the protrusions are bent toward the same side of the main body; or, in the thickness direction of the pole piece, some of the protrusions are bent toward one side of the main body, and another part of the protrusions are bent toward the other side of the main body.

[0026] In a second aspect, an embodiment of the present application provides an electrode assembly, comprising the electrode piece as described above.

[0027] In some exemplary embodiments, the protrusions on the electrode assembly all protrude toward the interior of the electrode assembly. This provides stable support, effectively achieving good structural stability. Furthermore, this can improve the cycling performance and volumetric energy density of the subsequently assembled battery.

[0028] In a third aspect, an embodiment of the present application provides a battery, comprising a housing and an electrode assembly as described above, wherein the electrode assembly is disposed in an internal space of the housing.

[0029] Based on the pole piece, electrode assembly and battery of the embodiment of the present application, by setting the area S1 of the outer surface of the protrusion and the projected area S2 of the outer surface of the protrusion in the thickness direction of the pole piece to satisfy: 1.01≤S1 / S2≤1.7, the protrusion of the above specifications is used to facilitate the adjustment of the protrusion so that the coverage area of ​​the protrusion in the thickness direction of the pole piece is appropriate while satisfying the required support height. The protrusion is not easy to collapse and deform under the action of extrusion force and extension force. The protrusion has good structural stability for supporting the isolation membrane, so that the gap between the main body and the isolation membrane is appropriate, which helps to improve the performance of the battery using the pole piece of the present application. In addition, it is convenient to set the angles between the inner surface and the outer surface of the protrusion and the surface of the main body to be appropriate, so as to prevent the connection between the inner surface and the outer surface of the protrusion and the surface of the main body from being too steep, causing the protrusion to be easy to break. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0031] FIG1 is a partial cross-sectional schematic diagram of an electrode assembly including a pole piece according to an embodiment of the present application;

[0032] FIG2 is a schematic diagram of the unfolded structure of a pole piece according to an embodiment of the present application;

[0033] FIG3 is a partial cross-sectional schematic diagram of a pole piece provided with a convex portion according to an embodiment of the present application;

[0034] FIG4 is a cross-sectional schematic diagram of a pole piece in which a first transition arc surface is connected to an outer surface according to an embodiment of the present application;

[0035] FIG5 is a partial cross-sectional diagram of a pole piece provided with a protrusion according to another embodiment of the present application;

[0036] FIG6 is a schematic structural diagram of two adjacent groups of convex units arranged in a staggered manner according to an embodiment of the present application;

[0037] FIG7 is a partial cross-sectional schematic diagram of an electrode assembly including a pole piece according to an embodiment of the present application, in which adjacent protrusions protrude toward opposite sides.

[0038] Figure markings: 100, electrode assembly; 101, straight portion; 102, corner portion; 200, pole piece; 2011, central area; 2012, edge area; 201, first edge, 202, second edge, 203, third edge; 204, fourth edge; 211, first boundary; 212, second boundary; 213, third boundary; 214, fourth boundary; m, first tangent; H, center axis; Q, support vertex; 300, isolation membrane; 410, positive pole piece; 420, negative pole piece; 210, main body; 220, convex portion; 221, inner surface; 222, outer surface; 2221, top surface; 2222, main surface; 2201, first edge line; 2202, first transition arc surface; 2203, second edge line; 2204, second transition arc surface. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0040] The inventors found that during the battery charging and discharging process, the electrode sheets expand and the interlayer extrusion of the electrode assembly will be further aggravated, resulting in insufficient electrolyte between the layers of the electrode assembly, poor infiltration, and easy interface deterioration, and even cycle failure.

[0041] The inventors also discovered that during the electrode assembly process, the positive electrode sheet, separator, and negative electrode sheet are stacked and wound multiple times in sequence to form an electrode body with multiple winding units. Protrusions are provided on the electrode sheets, along with supporting structures such as protective adhesive, to support adjacent winding units. This increases the spacing between adjacent winding units, thereby improving the problem of interlayer compression in the electrode assembly, which can lead to poor battery performance. Because the protrusions are also subject to interlayer compression, improperly designed protrusions can easily deform under this pressure. This can affect the stability of the electrode assembly's interlayers and, in severe cases, worsen battery performance.

[0042] Based on this, the embodiments of the present application provide a pole piece, an electrode assembly and a battery, designing the structure of the protrusion to improve the structural stability of the protrusion provided on the pole piece, so that the protrusion can play an effective supporting stability, thereby effectively improving the electrolyte infiltration and pole piece interface problems.

[0043] As shown in FIG1 , a partial cross-sectional structural schematic diagram of an electrode assembly 100 including the electrode sheets according to an embodiment of the present application is shown. The electrode assembly 100 includes a plurality of electrode sheets 200 and a separator 300, which are alternately stacked and wound. As shown in FIG2 , a front structural schematic diagram of one of the electrode sheets 200 is shown in an unfolded state. The electrode sheets 200 have a length direction X, a width direction Y, and a thickness direction Z that are perpendicular to each other, and the length directions X, width directions Y, and thickness directions Z of the plurality of electrode sheets 200 are consistent. The separator 300 is provided between two electrode sheets 200 of opposite polarity in the thickness direction Z of the electrode sheets 200. One of the two electrode sheets 200 of opposite polarity is a positive electrode sheet 410 and the other is a negative electrode sheet 420. The separator 300 has insulating properties and is used to separate the positive electrode sheet 410 from the negative electrode sheet 420 to prevent the positive electrode sheet 410 and the negative electrode sheet 420 from shorting. In the embodiment of the present application, the isolation membrane 300 and the two electrode pieces 200 are wound multiple times along the length direction X of the electrode piece 200 to form an electrode body. The electrode body is flat, and each circle of the electrode piece 200 includes two straight parts 101 and two corner parts 102. The two straight parts 101 are connected between the two corner parts 102.

[0044] The pole piece 200 includes a main body 210 and a plurality of protrusions 220, each of which is formed by bending a portion of the pole piece 200 toward one side of the main body 210. Specifically, when the pole piece 200 is in a flat state, the main body 210 is flat, and the protrusion 220 protrudes along one side of the main body 210 in the thickness direction Z of the pole piece 200. In this way, after the pole piece 200 is wound, the protrusion 220 can contact the isolation membrane 300 to provide support. When the electrode assembly 100 expands, the protrusion 220 can still support the isolation membrane 300. The contact area between the protrusion 220 and the isolation membrane 300 is small, so that there is space between the pole piece 200 and the isolation membrane 300 to accommodate electrolyte, thereby preventing abnormal conditions such as insufficient electrolyte and poor wetting between the pole piece 200 and the isolation membrane 300 due to expansion and extrusion.

[0045] The straight portion 101 of each circle of electrode pieces 200 may be provided with a plurality of protrusions 220, and the corner portion 102 of each circle of electrode pieces 200 may also be provided with a plurality of protrusions 220. Since the corner portions 102 of two adjacent circles of electrode pieces 200 are prone to mutual compression, the straight portion 101 and the corner portion 102 of each circle of electrode pieces 200 are also compressed, making the corner portion 102 a high-incidence area for compression of the electrode body. Therefore, when the protrusions 220 are provided on the electrode pieces 200, the embodiment of the present application preferably provides the protrusions 220 on the corner portion 102.

[0046] The pole piece 200 of the embodiment of the present application includes a current collector and an active material layer disposed on the surface of the current collector. The protrusion 220 can be formed by a portion of the current collector and a portion of the active material layer. For example, the protrusion 220 of the embodiment of the present application can be formed by rolling. Specifically, the rolling equipment acts on a portion of the pole piece 200 on one side, causing the current collector and the active material layer in the region to deform and bend toward the same side, thereby forming the protrusion 220.

[0047] The convex portion 220 is spaced apart from the edge of the pole piece 200 to prevent the convex portion 220 from being too close to the edge of the pole piece 200, causing the edge of the pole piece 200 to be bent unevenly due to rolling stress. Specifically, the pole piece 200 includes a first edge 201 and a second edge 202 arranged oppositely in the length direction X of the pole piece 200, and a third edge 203 and a fourth edge 204 arranged oppositely in the width direction Y of the pole piece 200. The pole piece also has a central area 2011, and the convex portion 220 is formed in the central area 2011 of the pole piece 200. The central area 2011 has a first boundary 211 and a second boundary 212 arranged oppositely in the length direction X of the pole piece 200. 2. The third boundary 213 and the fourth boundary 214 are relatively arranged in the width direction Y of the pole piece 200. An edge area 2012 is formed between the first boundary 211 and the first edge 201 and between the second boundary 212 and the second edge 202. An end avoidance zone is formed between the third boundary 213 and the third edge 203 and between the fourth boundary 214 and the fourth edge 204. Optionally, in the length direction X of the pole piece 200, the width of the end avoidance zone between the third boundary 213 and the third edge 203 and the width of the end avoidance zone between the fourth boundary 214 and the fourth edge 204 may be equal to or different.

[0048] Among them, the active material layer of the pole piece 200 is provided on the surface of the current collector, and in the thickness direction Z of the pole piece 200, the active material layer covers the entire surface of the current collector; in some other embodiments, the current collector includes a coating portion and a hollow foil portion, and the hollow foil portion is connected to the outside of the coating portion in the width direction Y of the pole piece 200. The active material layer covers the entire surface of the coating portion and avoids the surface of the hollow foil portion. This design can better reduce lithium plating, reduce the impact of cold pressing on cell deformation, and improve the safety performance of the battery. The first edge 201, second edge 202, third edge 203 and fourth edge 204 described above are the edges of the active material layer facing away from the surface of the current collector.

[0049] The convex portion 220 has an inner surface 221 connected to one surface of the main body 210 and an outer surface 222 connected to the other surface of the main body 210. The shape of the convex portion 220 is mainly defined by the inner surface 221 and the outer surface 222. The inner surface 221 is a concave surface, and the outer surface 222 is a convex surface. For example, the pole piece 200 includes a first surface and a second surface arranged opposite to each other in the thickness direction Z of the pole piece 200. A portion of the first surface is recessed toward the side where the other surface is located to form the inner surface 221 of the convex portion 220, and a portion of the second surface is convex toward the side away from the first surface to form the outer surface 222 of the convex portion 220.

[0050] The area of ​​the outer surface 222 of the protrusion 220 is S1, and S1 is calculated using the formula S1 = 2л*SD2*m1. The outer surface 222 of the protrusion 220 has a projected area S2 in the thickness direction Z of the electrode 200. Among them, S1 and S2 satisfy: 1.01≤S1 / S2≤1.7, which facilitates the regulation of the volume of space occupied by the protrusion 220 to be appropriate, and helps to improve the energy density of the battery when the electrode assembly 100 is used in the battery. Furthermore, it is preferred that 1.01≤S1 / S2≤1.5. When the range of S1 and S2 satisfies this relationship, the cycle performance of the battery at room temperature and high temperature can be further improved, especially the charge and discharge performance under high energy density conditions will also be improved. In addition, the shape and size of the protrusion will be within the appropriate range, thereby reducing the degree of damage to the electrode. Further, if 1.01≤S1 / S2≤1.3 is satisfied, the cycle performance of the battery will be further improved, and the degree of damage to the electrode itself will be further reduced.

[0051] The protrusion 220 has a predetermined diameter SD, where SD satisfies the following conditions: 1.5 mm ≤ SD ≤ 30 mm. Specifically, as shown in FIG3 , the predetermined diameter SD includes an inner diameter SD1 of the inner surface 221 and an outer diameter SD2 of the outer surface 222. The inner diameter SD1 is the first diameter of the first circumscribed sphere U1 on which the inner surface 221 is located, and the outer diameter SD2 is the second diameter of the second circumscribed sphere U2 on which the outer surface 222 is located. Furthermore, SD2 > SD1, and 1.5 mm ≤ SD1 ≤ 30 mm and / or 1.5 mm ≤ SD2 ≤ 30 mm.

[0052] It is understandable that after the electrode assembly 100 is wound and formed, the protrusion 220 is susceptible to interlayer squeezing force, and when the electrode assembly 100 expands, the protrusion 220 is also subject to expansion squeezing force. In addition, during the winding process of the electrode 200, the electrode 200 bends, and the protrusion 220 is also subject to the extension force generated by the bending of the electrode 200. These squeezing and extension forces may cause the protrusion 220 to deform. The better the structural stability of the protrusion 220, the less likely the protrusion 220 is to deform when subjected to squeezing and extension forces. Among them, the structural stability of the protrusion 220 is closely related to the structural design of the protrusion 220. For example, the shape of the inner surface 221 and the outer surface 222 of the protrusion 220, the support height of the protrusion 220 in the thickness direction Z of the electrode 200, the area covered by the protrusion 220 in the thickness direction Z of the electrode 200, the angle between the protrusion 220 and the main body 210, and other related parameters will affect the structural stability of the protrusion 220. At the same time, the height of the protrusion 220 affects the gap between the main body 210 and the isolation membrane 300 , and directly affects the infiltration effect of the electrolyte. After comprehensively considering the above-mentioned structural conditions, the embodiment of the present application sets the inner spherical diameter SD1 of the inner surface 221 of the protrusion 220 to satisfy 1.5mm≤SD1≤30mm, and the outer spherical diameter SD2 of the outer surface 222 of the protrusion 220 to satisfy 1.5mm≤SD2≤30mm. The use of the protrusion 220 within the above-mentioned spherical diameter range facilitates the adjustment of the protrusion 220 so that the coverage area of ​​the protrusion 220 in the thickness direction Z of the pole piece 200 is appropriate while meeting the required support height. The protrusion 220 is not easily collapsed and deformed under the action of the extrusion force and the extension force. The protrusion 220 has good structural stability for supporting the isolation membrane 300, so that there is a gap between the main body 210 and the isolation membrane 300. In addition, it is convenient to set the angles between the inner surface 221 and the outer surface 222 of the protrusion 220 and the surface of the main body 210 to be appropriate, so as to prevent the connection between the inner surface 221 and the outer surface 222 of the protrusion 220 and the surface of the main body 210 from being too steep, which may cause the protrusion 220 to be easily broken.

[0053] When SD1 and SD2 are greater than 30mm, the area covered by the protrusion 220 in the thickness direction Z of the pole piece 200 is too large to meet the required support height, and the protrusion 220 is prone to collapse when subjected to compression or extension force. When SD1 and SD2 are less than 5mm, the inner surface 221 and outer surface 222 of the protrusion 220 are prone to excessively steep junctions with the surface of the main body 210 to meet the required support height, causing the protrusion 220 to easily break. Moreover, when SD1 and SD2 are too small, the protrusion 220 also has difficulty meeting the required support height. Preferably, 5.0mm≤SD1≤10mm.

[0054] In addition, in the embodiment of the present application, SD1 is set to satisfy 1.5mm≤SD1≤30mm and SD2 is set to satisfy 1.5mm≤SD2≤30mm. After determining the support height of the protrusion 220 in the thickness direction Z of the pole piece 200, a tool with a working surface corresponding to SD2 is selected, and the position of the tool is adjusted. The working surface of the tool acts on the surface of the pole piece 200, and the protrusion 220 with good structural strength can be directly processed on the pole piece 200. The processing method is simple.

[0055] As shown in Figures 2 and 3, the outer surface 222 of the protrusion 220 has a first edge line 2201, which is formed at the connection between the outer surface 222 and the main body 210. The outer surface 222 of the protrusion 220 protrudes from the first edge line 2201 in a direction away from the main body 210 to form a convex surface. The circumference of the first edge line 2201 is Csd, and Csd satisfies: 1.0mm≤Csd≤7.8mm. By setting the circumference Csd of an edge line within the above range, on the one hand, it is convenient to make the area covered by the protrusion 220 in the thickness direction Z of the electrode 200 appropriate. On the other hand, Csd cooperates with SD1 to facilitate setting the support height of the protrusion 220 in the thickness direction Z of the electrode 200 within an appropriate range, preventing the support height of the protrusion 220 from being too small, resulting in insufficient support, or preventing the support height of the protrusion 220 from being too large, resulting in an excessive gap between the isolation membrane 300 and the main body 210, thereby preventing the improper support height of the protrusion 220 from reducing the energy density of the battery. Furthermore, satisfying 4.5mm≤Csd≤7.8mm can improve the high-rate cycle performance of the battery at high and normal temperatures, improve the infiltration effect of the electrolyte in the battery cell, increase the liquid retention to a certain extent, and reduce the degree of damage to the electrode.

[0056] As shown in Figure 4, the convex portion 220 also has a first transition arc surface 2202 connected to the first edge line 2201 of the outer surface 222. The first transition arc surface 2202 has a second edge line 2203 connected to the main body 210. The outer surface 222 of the convex portion 220 is connected to the surface of the main body 210 through the first transition arc surface 2202. The first transition arc surface 2202 is a concave arc surface. The first transition arc surface 2202 is used to transition between the outer surface 222 of the convex portion 220 and the surface of the main body 210, thereby improving the stress resistance of the connection between the outer surface 222 of the convex portion 220 and the surface of the main body against external forces, making it less likely to break. Correspondingly, the protrusion 220 also has a second transition arc surface 2204 connected to the inner surface 221. The second transition arc surface 2204 connects between the inner surface 221 of the protrusion 220 and the surface of the main body 210. The second transition arc surface 2204 is a convex arc surface, so that the inner surface 221 of the protrusion 220 and the surface of the main body 210 also form an arc-shaped transition connection. Of course, in some other embodiments, the protrusion 220 may not have the first transition arc surface 2202 and the second transition arc surface 2204. The first edge line 2201 of the outer surface 222 is directly connected to the surface of the main body 210, and the inner surface 221 is directly connected to the surface of the main body 210. When the protrusion 220 of the embodiment of the present application is processed using a rolling process, the protrusion 220 has the first transition arc surface 2202 and the second transition arc surface 2204. The first transition arc surface 2202 and the second transition arc surface 2204 can each be a circular arc surface. Furthermore, the first transition arc surface 2202 and the second transition arc surface 2204 are arranged concentrically.

[0057] As shown in FIG3 , the outer surface 222 of the convex portion 220 has a support vertex Q. The point on the outer surface 222 of the convex portion 220 that is farthest from the first edge line 2201 in the thickness direction Z of the pole piece 200 is the support vertex Q of the outer surface 222. In conjunction with FIG3 and FIG4 , the support height of the convex portion 220 in the thickness direction Z of the pole piece 200 described in the embodiment of the present application is: the distance between the support vertex Q in the thickness direction Z of the pole piece 200 and the second edge line 2203, that is, the support height of the convex portion 220 in the thickness direction Z of the pole piece 200 is the sum of the height m1 of the convex portion 220 in the thickness direction Z of the pole piece 200 and the height of the first transition arc surface 2202 in the thickness direction Z of the pole piece 200, wherein the height m1 of the convex portion 220 in the thickness direction Z of the pole piece 200 is the distance between the support vertex Q in the thickness direction Z of the pole piece 200 and the first edge line 2201. It can be seen that the support height of the protrusion 220 in the thickness direction Z of the pole piece 200 is also related to the height m2 of the first transition arc surface 2202 in the thickness direction Z of the pole piece 200. In the embodiment of the present application, the height m2 of the first transition arc surface 2202 in the thickness direction Z of the pole piece 200 can be controlled to be within an appropriate range by setting the central angle γ of the first transition arc surface 2202 and the radius r of the first transition arc surface 2202.

[0058] Optionally, the central angle of the first transition arc surface 2202 is γ, where γ satisfies the following: 0° < γ ≤ 90°. For example, γ can be 5°, 10°, 15°, 30°, 45°, or 60°. When γ is greater than 90°, the curvature of the first transition arc surface 2202 is too large, resulting in an acute angle between the tangent line of the outer surface 222 of the protrusion 220 at the first edge line 2201 and the surface of the main body 210, which can easily cause the connection between the protrusion 220 and the main body 210 to be squeezed and fractured. The corresponding second transition arc surface 2204 can be arranged concentrically with the first transition arc surface 2202, and the central angles of the two are equal.

[0059] Optionally, the radius of the first transition arc surface 2202 is r, where r satisfies the following: 0.1 mm ≤ r ≤ 5 mm. For example, r can be 0.1 mm, 0.2 mm, 0.5 mm, 1.0 mm, 1.5 mm, 3.0 mm, etc. When r is less than the lower limit of 0.1 mm, the transition stress of the first transition arc surface 2202 is poor and fails to exert its effect. When r is greater than the upper limit of 5 mm, the first transition arc surface 2202 occupies too much space, which can easily lead to unstable support of the protrusion 220.

[0060] The first circumscribed ball U1 and the second circumscribed ball U2 are arranged co-centrically. The inner surface 221 of the protrusion 220 has a shape similar to that of the outer surface 222. This facilitates ensuring that the radial thickness of the protrusion 220 in the first circumscribed ball U1 is approximately equal, thus ensuring good structural stability. Of course, in other embodiments, the portion of the protrusion 220 adjacent to the main body 210 may have a greater radial thickness in the first circumscribed ball U1, while the portion of the protrusion 220 distal from the main body 210 may have a smaller radial thickness in the first circumscribed ball U1, thereby ensuring good connection strength between the protrusion 220 and the main body 210.

[0061] As shown in Figures 3 and 4 , the first circumscribed sphere U1 has a first tangent line m at a first edge line 2201. The angle between the extended surface of the main body 210 connecting to the protrusion 220 and the corresponding first tangent line m of the protrusion 220 is a first angle α1, where α1 satisfies the following: 15°≤α1≤75°. For example, α1 can be 15°, 20°, 30°, 45°, or 60°. Setting α1 within this range ensures that the outer surface 222 of the protrusion 220 has an appropriate inclination relative to the surface of the main body 210, thereby preventing deformation at the connection between the protrusion 220 and the main body 210. When α1 is lower than the lower limit of 15°, the protrusion of the protrusion 220 is too small to meet the support requirements. When α1 is higher than the upper limit of 75°, the connection between the outer surface 222 of the protrusion 220 and the main body 210 is too steep. When the protrusion 220 is subjected to extrusion force, the connection between the outer surface 222 of the protrusion 220 and the main body 210 is prone to breakage.

[0062] Correspondingly, the second circumscribed ball U2 has a second tangent at the connection between the inner surface 221 of the convex portion 220 and the second transition arc surface 2204. The angle between the second tangent and the corresponding extended surface of the surface of the main body 210 is a second angle α2, α2≥α1. For example, when the radial thickness of the convex portion 220 in the first circumscribed ball U1 is close to equal, α2=α1; when the thickness of the portion of the convex portion 220 adjacent to the main body 210 in the radial direction of the first circumscribed ball U1 is greater than the thickness of the portion of the convex portion 220 away from the main body 210, α2>α1.

[0063] Optionally, the compressive strength per unit length of the pole piece 200 is N, where N satisfies 0.05N / mm≤N≤1N / mm. The compressive strength per unit length of the pole piece 200 is measured by the following method: a standard protrusion 220 is made on the pole piece, the protrusion 220 has a shape of Csd=2mm, α1=30°, a pole piece per unit length containing n protrusions 220 is cut, that is, a pole piece containing n protrusions 220 per unit area is flattened using a press, and the maximum rebound force F during the flattening process is recorded; the compressive strength per unit length of the pole piece 200 is N=F / n / sin(30°) / 2. The material of the pole piece 200 can be selected so that the compressive strength per unit length of the pole piece 200 satisfies the above range, thereby making the protrusion 220 have good supporting strength and tensile strength.

[0064] Optionally, the protrusion 220 has a supporting force P, which satisfies the following conditional formula (1): P = 2N × sinα1 × Csd (1)

[0065] Wherein, N is the compressive strength of 200 unit length of the pole piece;

[0066] Csd is the perimeter of the first edge line 2201 of the outer surface 222 of the convex portion 220;

[0067] α1 is the first angle;

[0068] P satisfies 0.026N≤P≤9.66N.

[0069] The supporting force P of the protrusion 220 of the embodiment of the present application is in the range of 0.026 to 9.66. The protrusion 220 has good supporting strength and tensile strength, which can effectively improve the electrolyte infiltration effect, thereby improving the battery performance when the electrode assembly 100 is used in the battery. In addition, the material of the pole piece 200 and the various parameters of the protrusion 220 can be selected based on the range of the supporting force P, so that the various parameters of the protrusion 220 can be flexibly adjusted, thereby facilitating the processing of a pole piece 200 with good structural stability in response to different processing conditions.

[0070] In the embodiment of the present application, at least a portion of the outer surface 222 of the protrusion 220 is an arcuate surface located within the second circumscribed sphere U2. Specifically, the outer surface 222 of the protrusion 220 includes a main surface 2222 and a top surface 2221 connected to the main surface 2222. The top surface 2221 is an arcuate surface located within the second circumscribed sphere U2 and has a support vertex Q. The top surface 2221 is the surface of the protrusion 220 that contacts the isolation membrane 300 to prevent the top surface 2221 of the protrusion 220 from damaging the isolation membrane 300. The edge of the main surface 2222 away from the top surface 2221 forms a first edge line 2201.

[0071] In the embodiment of the present application, the shape of the protrusion 220 can be set to various shapes.

[0072] Optionally, the curvature of the main surface 2222 is equal to the curvature of the top surface 2221, that is, as shown in Figure 3, the outer surface 222 of the convex portion 220 is a convex arc surface on the second circumscribed sphere U2 as a whole. At this time, at the first edge line 2201, the curvatures of the outer surface 222 of the convex portion 220 and the first transition arc surface 2202 are opposite in sign, that is, adjacent to the first edge line 2201, the first transition arc surface 2202 is a concave arc surface, and the outer surface 222 is a convex arc surface.

[0073] Alternatively, as shown in FIG5 , the curvature of the main surface 2222 is smaller than that of the top surface 2221. For example, the main surface 2222 may be an arcuate surface having a smaller curvature than that of the top surface 2221. Alternatively, the main surface 2222 may extend from the first edge line 2201 in a direction forming an angle with the first tangent line m to connect with the top surface 2221. In this case, the first edge line 2201 may form a polygon, with all vertices of the polygon located on the second circumscribed sphere U2. Alternatively, the first edge line 2201 may form a circle, with the first edge line 2201 forming the circle located on the second circumscribed sphere U2.

[0074] In the embodiment of the present application, the spacing between two adjacent protrusions 220 is also designed to reduce the interference between the two adjacent protrusions 220. Optionally, please refer to Figure 3 again. Each protrusion 220 has a central axis H that passes through the center of the circumscribed sphere of the outer surface 222 and extends along the thickness direction Z of the electrode 200. The vertical spacing between the central axes H of the two adjacent protrusions 220 is a first spacing L1. L1 satisfies: 2.0mm≤L1≤8.0mm. When L1 is less than the lower limit of 2.0mm, the spacing between the two adjacent protrusions 220 is too small during the rolling process, and the electrode 200 is prone to low flatness due to the stress generated during the rolling process. When L1 is greater than the upper limit of 8.0mm, the spacing between the two adjacent protrusions 220 is too large, which easily leads to the protrusions 220 being too dispersed and insufficient in support area, making it difficult to improve the infiltration effect of the electrolyte.

[0075] It should be noted that the first spacing L1 between two adjacent protrusions 220 is: when the pole piece 200 is in the unfolded state, the minimum distance between the center axes H of the two adjacent protrusions 220 in the direction parallel to the plate surface of the pole piece 200; or, when the pole piece 200 is in the wound state, the first spacing L1 between the two adjacent protrusions 220 of the straight part 101 of the pole piece 200 is: the minimum spacing between the center axes H of the two adjacent protrusions 220 in the direction parallel to the surface of the straight part 101, and the first spacing L1 between the two adjacent protrusions 220 of the corner part 102 of the pole piece 200 is: the minimum spacing between the center axes H of the two adjacent protrusions 220 in the winding direction of the corner part 102. 2 , the first spacing L1 includes at least a transverse spacing l1 in the length direction X of the electrode 200 and a longitudinal spacing l2 in the width direction Y of the electrode 200 , where l1 satisfies: 2.0 mm ≤ l1 ≤ 8.0 mm, and l2 satisfies: 2.0 mm ≤ l2 ≤ 8.0 mm.

[0076] Please refer to Figure 2 again. A plurality of protrusions 220 are arranged side by side and spaced apart along the first direction of the pole piece 200 to form a group of protrusion units. In the second direction of the pole piece 200, two adjacent protrusion units are arranged side by side and spaced apart. The first direction, the second direction and the thickness direction Z of the pole piece 200 are perpendicular to each other, that is, one of the first direction and the second direction is the length direction X of the pole piece 200, and the other is the width direction Y of the pole piece 200.

[0077] Furthermore, as shown in FIG2 , the protrusions 220 of two adjacent protrusion units are collinearly arranged in the second direction; or, as shown in FIG6 , one protrusion unit is translated relative to the other protrusion unit by a preset distance A in the first direction, so that the protrusions 220 of the two adjacent protrusion units are staggered in the second direction, and A satisfies the following: 0.3L2≤A≤L2, where the central axes H of the two adjacent protrusions 220 are perpendicular to the second distance L2 in the first direction. In this case, when the electrode assembly 100 is used in a battery, it has a better improvement effect on the electrolyte. Preferably, 0.6L2≤A≤0.9L2.

[0078] When the first direction is the length direction X of the electrode 200 , the second spacing L2 is the transverse spacing l1 ; when the first direction is the width direction Y of the electrode 200 , the second spacing L2 is the longitudinal spacing l2 .

[0079] Optionally, within a unit area, in the thickness direction Z of the pole piece 200, the ratio of the projected area of ​​the outer surface 222 of all the protrusions 220 (i.e., the sum of S2 of all the protrusions 220 within the unit area of ​​the pole piece 200) to the projected area of ​​the pole piece 200 is T, and T satisfies: 20%≤T≤40%.

[0080] Furthermore, when T satisfies 20%≤T≤40%, combined with the spacing L1 between the first edge lines 2201 of two adjacent protrusions 220 satisfying 2.0mm≤L1≤8.0mm, the distribution density of the protrusions 220 can be controlled appropriately, which not only improves the supporting stability of the protrusions 220, but also helps to improve the wetting effect of the electrolyte.

[0081] Optionally, in the thickness direction Z of the pole piece 200, all the protrusions 220 are bent toward the same side of the main body 210. For example, the protrusions 220 of each wound circle of the pole piece 200 all protrude toward the winding center, or the protrusions 220 of each wound circle of the pole piece 200 all protrude toward the side away from the winding center, or one of the protrusions 220 protrudes toward the winding center, and the protrusions 220 of the other circles of the pole piece 200 protrude toward the side away from the winding center.

[0082] Optionally, in the thickness direction Z of the pole piece 200, part of the protrusion 220 is bent toward one side of the main body 210, and another part of the protrusion 220 is bent toward the other side of the main body 210. For example, as shown in Figure 7, one of the protrusions 220 protrudes toward the winding center, and the adjacent protrusion 220 protrudes toward the side away from the winding center.

[0083] The electrode assembly 100 of the present embodiment includes two types of electrode sheets 200 with opposite polarities, namely a positive electrode sheet 410 and a negative electrode sheet 420. The electrode assembly 100 also includes a positive electrode tab electrically connected to the positive electrode sheet 410 and a negative electrode tab electrically connected to the negative electrode sheet 420.

[0084] The embodiments of the present application have no particular restrictions on the positive electrode sheet 410 , the negative electrode sheet 420 , the separator 300 , the positive electrode tab, and the negative electrode tab. Various components that are well known in the art and can be used as the electrode assembly 100 are applicable to the present application.

[0085] In some exemplary embodiments, the negative electrode plate 420 may include a negative electrode current collector and a negative electrode active material layer disposed on the surface of the negative electrode current collector. Exemplarily, the negative electrode current collector may be at least one of copper foil, aluminum foil, nickel foil, or a carbon-based current collector; the thickness of the negative electrode current collector may be 1 μm to 200 μm. The negative electrode active material layer may be disposed on one surface or two opposing surfaces of the negative electrode current collector. Furthermore, in the thickness direction Z of the negative electrode plate 420, the negative electrode active material layer may be coated only on a portion of the negative electrode current collector. Exemplarily, the thickness of the negative electrode active material layer may be 10 μm to 500 μm.

[0086] The negative electrode active material layer includes a negative electrode active material. Exemplarily, the negative electrode active material includes at least one of lithium metal, natural graphite, artificial graphite, or a silicon-based material. The silicon-based material includes at least one of silicon, a silicon oxide compound, a silicon carbon compound, or a silicon alloy. The negative electrode active material layer may further include a conductive agent and / or a binder. Exemplarily, the conductive agent in the negative electrode active material layer may include at least one of carbon black, acetylene black, Ketjen black, flake graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. The binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylic acid salt, polyacrylate, polyvinyl pyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0087] In some exemplary embodiments, the positive electrode sheet 410 includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. For example, the positive electrode current collector may be made of aluminum foil, although other common positive electrode current collectors in the art may also be used. The thickness of the positive electrode current collector may be 1 μm to 200 μm. The positive electrode active material layer may be disposed on one surface or two opposing surfaces of the positive electrode current collector. Furthermore, in the thickness direction Z of the positive electrode sheet 410, the positive electrode active material layer may be coated only on a portion of the positive electrode current collector. The thickness of the positive electrode active material layer may be 10 μm to 500 μm.

[0088] The positive electrode active material layer includes positive electrode active materials, and the positive electrode active materials include LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y M y O2、LiNi 1-y M y O2、LiMn 2-y M y O4、LiNi x Co y Mn z M 1-x-y-zO2, wherein M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, or Ti, and 0≤y≤1, 0≤x≤1, 0≤z≤1, and x+y+z≤1. For example, the positive electrode active material may include at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide, or lithium nickel manganate. The positive electrode active material may be doped and / or coated. The positive electrode active material layer further includes a binder and a conductive agent. Illustratively, the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene; the conductive agent in the positive electrode active material layer may include at least one of conductive carbon black, acetylene black, Ketjen black, flake graphite, graphene, carbon nanotubes or carbon fibers.

[0089] In some exemplary embodiments, separator 300 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in preventing short circuits and can improve the stability of electrode assembly 100 through a shutdown effect. Separator 300 has a thickness ranging from approximately 3 μm to 500 μm.

[0090] The present invention also provides a battery comprising a housing and the electrode assembly 100 described above, wherein the electrode assembly 100 is disposed within the interior space of the housing. The battery also comprises an electrolyte, which fills the interior space of the housing and impregnates the electrode assembly 100. The present invention also provides no particular limitations on the electrolyte; any material known in the art for use as an electrolyte is suitable for use in the present invention.

[0091] The present application will be further described below using the electrode assembly 100 of a lithium-ion battery as an example and in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0092] In each embodiment and comparative example of the present application, lithium-ion batteries were prepared and their performance was tested using the following method:

[0093] 1. Preparation method of lithium-ion battery

[0094] (1) Preparation of positive electrode sheet 410

[0095] The positive electrode active material, lithium cobalt oxide (LiCoO2), the conductive agent, conductive carbon black, and the binder, polyvinylidene fluoride (PVDF), were dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 97.9:0.9:1.2 to form a positive electrode slurry. A 9μm thick, 62mm wide, and 1182mm long aluminum foil was used as the positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector, which were arranged oppositely in the thickness direction Z. After drying, cold pressing, and cutting, the positive electrode sheet 410 was obtained. The compacted density of the positive active material layer of the positive electrode sheet 410 was 4.2g / cm 3 The thickness of the positive electrode sheet 410 is 0.092 mm.

[0096] In the following embodiments and comparative examples, a plurality of protrusions 220 were formed in the central region 2011 of the positive electrode sheet 410 by rolling. The central region 2011 of the positive electrode sheet 410, where the protrusions 220 were located, was rectangular in shape, similar to the outer contour of the positive electrode sheet 410. The dimensions of each edge region 2012 of the positive electrode sheet in the width direction and the dimensions of each end clearance region of the positive electrode sheet in the length direction were equal, and both were T1, with T1 being 3 mm.

[0097] (2) Preparation of negative electrode sheet 420

[0098] The negative electrode active material, artificial graphite, the binder, styrene-butadiene rubber (SBR), and the thickener, sodium carboxymethyl cellulose (CMC), were dissolved in deionized water at a weight ratio of 97.4:1.4:1.2 to form a negative electrode slurry. A copper foil with a thickness of 6 μm, a width of 63.1 mm, and a length of 1250 mm was used as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector, which were arranged oppositely in the thickness direction Z. After drying, cold pressing, and cutting, the negative electrode sheet 420 was obtained. The compacted density of the negative electrode active material layer of the negative electrode sheet 420 was 1.8 g / cm 3 The thickness of the negative electrode sheet 420 is 0.105 mm.

[0099] (3) Preparation of isolation film 300

[0100] The separator substrate is made of 5μm-thick polyethylene (PE). A 2μm-thick alumina ceramic layer is coated on one side of the separator substrate. Finally, a 2.5mg / 1540.25mm² binder (PVDF) is applied to both sides of the single-layer ceramic-coated separator substrate and dried to form a porous layer. The porous layer of separator 300 has a porosity of 39%.

[0101] (4) Preparation of electrolyte

[0102] In an environment with a water content of less than 10 ppm, ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), diethyl carbonate (abbreviated as DEC), ethyl propionate (abbreviated as EP), and propyl propionate (abbreviated as PP) are mixed uniformly in a mass ratio of 1:1:1:1:1, and then the electrolyte salt LiPF6 is dissolved in the above-mentioned non-aqueous solvent. After uniform mixing, an electrolyte is formed, wherein the mass percentage of LiPF6 based on the mass of the electrolyte is 12.5%.

[0103] (5) Assembly of lithium-ion batteries

[0104] The positive electrode tab is mounted on the edge region 2012 of the positive electrode sheet 410 by rolling, and the negative electrode tab is mounted on the edge region 2012 of the negative electrode sheet 420 by rolling. The positive electrode sheet 410 with the positive electrode tab, the separator 300, and the negative electrode sheet 420 with the negative electrode tab are stacked in sequence, with the separator 300 positioned between the positive electrode sheet 410 and the negative electrode sheet 420 to act as an insulator, and then wound to obtain the electrode assembly 100. The electrode assembly 100 is placed in an outer packaging aluminum-plastic film, dehydrated at 80°C, injected with the above-mentioned electrolyte and packaged, and a lithium-ion battery is obtained through a process of formation, degassing, and trimming. The following describes the test methods for various parameters of various embodiments of the present application.

[0105] 2. Performance test of lithium-ion batteries

[0106] (1) 25℃ cycle test

[0107] In an environment of 25°C, the lithium-ion battery in (5) above is charged at a constant current of 5C at a charging current of 2C / 5C to the full charge voltage (the battery is designed for a maximum voltage of 4.5V). Then, constant voltage charging is performed at the maximum voltage until the current reaches 0.02C. Then, constant current discharge is performed at a discharge current of 0.5C until the final voltage reaches 3.0V. The discharge capacity of the first cycle is recorded. The above steps are then repeated for charging and discharging cycles, and the cycle number N at which the cycle capacity retention rate begins to drop to ≤80% is recorded.

[0108] Cycle capacity retention rate=(discharge capacity at the Nth cycle / discharge capacity at the first cycle)×100%.

[0109] (2) 45℃ cycle test

[0110] In an environment of 45°C, the lithium-ion battery in (5) above is charged at a constant current of 2C / 5C to the full charge voltage (the battery is designed for a maximum voltage of 4.5V). Then, constant voltage charging is performed at the maximum voltage until the current reaches 0.02C. Then, constant current discharge is performed at a discharge current of 0.5C until the final voltage reaches 3.0V. The discharge capacity of the first cycle is recorded. The above steps are then repeated for charge and discharge cycles, and the number of cycles N at which the cycle capacity retention rate is ≤80% is recorded.

[0111] Cycle capacity retention rate=(discharge capacity at the Nth cycle / discharge capacity at the first cycle)×100%.

[0112] (3) Wetting improvement effect test

[0113] After the electrode assembly 100 is placed in the outer packaging aluminum-plastic film injection process, it is left at room temperature (25°C) for 24 hours, and the isolation membrane 300 is disassembled and observed for wetting. The area size of the wetted part is estimated and compared, and is divided into three levels: significant (wetting area of ​​60% to 100%), moderate (wetting area of ​​30% to 60%), and slight (wetting area of ​​0% to 30%). The unwetted area is usually an irregular water pattern boundary, and the difference in area size can be directly observed visually.

[0114] (4) Liquid retention test

[0115] The electrolyte retention volume is the amount of electrolyte that is ultimately retained in the lithium-ion battery. To ensure the consumption of electrolyte during the formation of the lithium-ion battery, a certain amount of electrolyte is usually injected, and then the excess electrolyte is withdrawn after formation. It is measured by weighing, with the injection volume n1 and the withdrawal volume n2.

[0116] Liquid retention volume = n1-n2.

[0117] (5) Pole 200 damage degree test

[0118] Take a 30X30cm electrode for penetration test. Apply the penetrant on one side of the electrode, let it stand for 60 minutes, and then visually inspect whether there is any penetration of the penetrant. For samples that cannot be judged visually, observe the back of the electrode under a microscope at 20X to see if there is any penetration of the penetrant; record the degree of penetration (none, slight, moderate, severe).

[0119] None: No penetration observed visually or under a microscope

[0120] Slight: No penetration by visual inspection, slight penetration by microscope observation;

[0121] Medium: Visually observed dotted penetration;

[0122] Serious: Visual observation shows flaky penetration.

[0123] In Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-2, the parameters of the electrode 200 are shown in Table I.

[0124] Table I

[0125] In Table 1, the parameters and performance test results of the lithium-ion batteries in Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-2 are shown in Table 1.

[0126] Table 1

[0127] Table 1 shows that, based on Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-2, when the S1 / S2 ratio of the protrusion 220 is within the range of 1.01 to 1.70, the lithium-ion battery exhibits good high-rate charge-discharge cycle performance and minimal damage to the electrode sheet 200. When S1 / S2 is less than the lower limit of 1.01, the high-rate charge-discharge cycle performance of the lithium-ion battery deteriorates. When S1 / S2 is greater than the upper limit of 1.7, the electrode sheet 200 is severely damaged. This is because a larger S1 / S2 ratio indicates greater stretching and elongation of the electrode sheet. When S1 / S2 is greater than the upper limit of 1.7, the electrode sheet approaches its maximum elongation limit, and significant electrode sheet damage begins to occur. Conversely, when S1 / S2 is less than the lower limit of 1.01, the protrusion is very shallow and weak, resulting in minimal stretching and elongation. While the electrode sheet is largely undamaged, the protrusion is too shallow and weak to form a channel, causing the improvement effect to gradually diminish.

[0128] According to Examples 1-2, 1-8 to 1-9, and 1-10 to 1-11, when the total area ratio T of the protrusion 220 per unit area of ​​the electrode 200 is in the range of 20% to 40%, the lithium-ion battery has good high-rate charge and discharge cycle performance. This is because within this range, the protrusion is large enough and provides sufficient effective support to form a stable channel, while the stretching of the electrode does not exceed the upper limit of its extension, thus preventing damage to the electrode.

[0129] In Table 2, the differences between Examples 2-1 to 2-20 and Example 1-1 are the parameters SD1, α1, r, and Csd. The parameters and performance test results of the lithium-ion batteries in Examples 2-1 to 2-20 and Example 1-1 are shown in Table 2.

[0130] Table 2

[0131] Table 2 shows that, according to Examples 1-1 to 2-4, 2-14 to 2-15, and 2-19 to 2-10, the inner sphere diameter SD1 of the inner surface 221 of the protrusion 220 of the electrode 200 ranges from 1.5 mm to 30 mm, effectively improving the high and low temperature cycling performance of the lithium-ion battery and minimizing damage to the electrode 200. When SD1 is less than the lower limit of 1.5 mm, the protrusion is too small, the morphology becomes sharper, and it is more likely to puncture the electrode. With other conditions remaining unchanged, a larger protrusion results in a smoother transition, which is less likely to damage the electrode. However, due to the geometric relationship, α decreases, resulting in a weakened support capacity of the protrusion. Although a large protrusion is formed, the support capacity is insufficient. The protrusion is more likely to be flattened during winding, and an effective channel cannot be established. This weakens the wettability improvement and the cycling performance improvement effect, and causes severe damage to the electrode 200. When SD1 is greater than the upper limit of 30mm, the high-rate cycle performance of the lithium-ion battery is poor, and the electrolyte infiltration effect and liquid retention of the lithium-ion battery are poor. In addition, as SD1 decreases, the charge and discharge cycle performance, electrolyte infiltration effect, and liquid retention of the lithium-ion battery gradually increase. This is because as SD1 decreases, the support capacity of a single convex portion increases, making it more difficult for the convex portion to be flattened during winding. Under the same conditions, the smaller the convex portion, the more stable the channel formed.

[0132] According to Examples 2-5 to 2-9, 2-16, and 2-18 to 2-20, it can be seen that the first angle α1 of the protrusion 220 of the electrode 200 is in the range of 15° to 75°, and the charge and discharge cycle performance, electrolyte infiltration, and liquid retention of the lithium-ion battery are all good. Moreover, as α1 increases, the charge and discharge cycle performance, electrolyte infiltration effect, and liquid retention of the lithium-ion battery are gradually enhanced. This is because, when other parameters remain unchanged, the larger α1 is, the stronger the supporting capacity of the protrusion is, the more difficult it is to be flattened by winding, and the formed channel is larger and more stable, which can accommodate more electrolyte, resulting in an increase in liquid retention. When α1 is lower than the lower limit of 15° or higher than the upper limit of 75°, the high-rate cycle performance of the lithium-ion battery is poor, and the electrolyte infiltration effect and liquid retention of the lithium-ion battery are poor. This is because the smaller α1 is, the weaker the supporting ability of the protrusion is, and the more difficult it is to support the formation of an effective channel, resulting in a decrease in the electrolyte storage capacity; the larger α1 is, the stronger the supporting ability is, and it should be able to form a larger and more stable channel to store the electrolyte. However, when it is higher than the upper limit of 75°, the electrode is easily damaged. After the electrode is damaged, the supporting ability of the protrusion will decrease, the size of the channel formed fluctuates greatly, the structure is unstable, and it is more likely to be flattened and crushed, and the liquid retention capacity will also decrease accordingly.

[0133] According to Examples 2-10 to 2-13 and 2-17, it can be seen that when the radius r of the first transition arc surface 2202 is between 0.1 mm and 5 mm, the charge-discharge cycle performance, electrolyte wetting, and liquid retention of the lithium-ion battery are all good. When r exceeds the upper limit of 5 mm, the area occupied by the first transition arc surface 2202 in the thickness direction of the electrode 200 is too large, which not only easily leads to a decrease in the energy density of the lithium-ion battery, but also, due to the excessively large r, it can cause serious damage and weaken the effect of supporting the formation of the channel during winding. Excessive r will lead to poor support of the r transition area of ​​the protrusion, resulting in a slight decrease in the support height of the protrusion, resulting in a smaller channel, poor electrolyte wetting, and low liquid retention. This leads to poor electrolyte wetting and liquid retention, ultimately affecting the charge-discharge cycle performance.

[0134] According to Examples 1-1 to 2-4, 2-14, and 2-15, it can be seen that the perimeter C of the first edge line 2201 of the outer surface 222 of the convex portion 220 is sD The result of comprehensive selection of SD1 and α1, the perimeter C of the first edge line 2201 sd The range of C is 1.0mm~10mm, and the charge and discharge cycle performance, electrolyte infiltration effect, liquid retention and electrode 200 damage effect of lithium-ion batteries are all good. sd When the Csd is less than the lower limit of 1.0mm, the charge and discharge cycle performance, electrolyte infiltration effect, liquid retention and electrode 200 damage effect of the lithium-ion battery are all poor. This is because when Csd is too small, the convex morphology is too small, the support height will also become smaller, the distribution will also appear sparse, and the channel between points will collapse, resulting in discontinuous channels, poor infiltration effect, liquid retention, and ultimately affecting the cycle performance. sD When the diameter is greater than the upper limit of 7.8 mm, although the damage to the electrode 200 is small, the charge and discharge cycle performance, electrolyte infiltration effect and liquid retention of the lithium-ion battery are poor. This is because when Csd is too large, the morphology of the protrusion will become larger, the protrusion will become flatter, and α1 will become smaller, resulting in a weakening of the protrusion support capacity. The protrusion is more likely to be flattened during winding, affecting the infiltration and liquid retention, thereby affecting the cycle performance.

[0135] In Table 3, the differences between Examples 3-1 to 3-17 and Example 1-6 lie in the parameters P, l1, and l2. The parameters and performance test results of the lithium-ion batteries in Examples 3-1 to 3-17 and Example 1-6 are shown in Table 3.

[0136] Table 3

[0137] Table 3 shows that, according to Examples 3-1 to 3-4 and 3-12 to 3-13, the support force P of the protrusion 220 of the electrode 200 ranges from 0.026 to 9.66, resulting in good lithium-ion battery performance. Furthermore, as the support force P gradually increases, the high-rate charge-discharge cycle performance and liquid retention of the lithium-ion battery gradually improve. When P is less than the lower limit of 0.026, the high-rate charge-discharge cycle performance and liquid retention of the lithium-ion battery are both poor. When P is greater than the upper limit of 9.66, the electrode 200 is severely damaged. This is because when P is greater than the upper limit, the electrode itself becomes brittle while increasing in strength, its ductility deteriorates, and it is more susceptible to brittle cracking, making it difficult to form a sufficiently large protrusion structure.

[0138] According to Examples 3-8 to 3-11, 3-5 to 3-7, and 3-14 to 3-17, it can be seen that the range of the horizontal spacing l1 and the vertical spacing l2 between two adjacent protrusions 220 is 2.0 mm to 8.0 mm, and the high-rate charge-discharge cycle performance and liquid retention effect of the lithium-ion battery are both good, and the damage to the electrode 200 is relatively small. When l1 and l2 are less than the lower limit of 2.0 mm, or l1 and l2 are greater than the upper limit of 8.0 mm, the high-rate charge-discharge cycle performance and liquid retention effect of the lithium-ion battery are both poor. This is because when the spacing is less than the lower limit, the protrusions are extremely densely distributed. Although the support channel is more sufficient and the channel is more stable, the excessive protrusions occupy the electrolyte storage space, resulting in a decrease in the liquid retention. Conversely, when the spacing is greater than the upper limit of 8.0 mm, the protrusions become very sparsely distributed, and the channel support points between the protrusions are insufficient, which is easily collapsed by winding, squeezing, and resulting in the channel being divided and unable to form a continuous effective channel, which affects the infiltration effect. Preferably, the range of l1 is 3.0 mm to 6.0 mm, and the range of l2 is 4.0 mm to 6.0 mm.

[0139] The same or similar numbers in the drawings of this embodiment correspond to the same or similar parts; in the description of this application, it should be understood that if the terms "upper", "lower", "left", "right", etc. indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the drawings. This is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as a limitation on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0140] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A pole piece includes a main body portion and a plurality of convex portions, and each of the convex portions is formed by bending a part of the pole piece toward one side of the main body portion; The convex portion has an inner surface that abuts one surface of the main body portion and an outer surface that abuts the other surface of the main body portion; The area of the outer surface of the convex portion is S1, and the projected area of the outer surface of the convex portion in the thickness direction of the electrode tab is S2. S1 and S2 satisfy: 1.01 ≤ S1 / S2 ≤ 1.7; the outer surface of the convex portion has a first edge line formed at the connection between the outer surface and the main body portion, and the perimeter of the first edge line is C sd , C sd satisfies: 1.0 mm ≤ C sd ≤ 7.8 mm.

2. The pole piece according to claim 1, characterized in that, 1.01 ≤ S1 / S2 ≤ 1.

5.

3. The pole piece according to claim 1, characterized in that, 1.01 ≤ S1 / S2 ≤ 1.

3.

4. The pole piece according to claim 1, characterized in that, 4.5mm ≤ C sd ≤ 7.8mm.

5. The pole piece according to claim 1, wherein The convex portion further has a first transition arc surface connected to the first edge line of the outer surface, and the first transition arc surface has a second edge line connected to the main body portion; The outer surface of the convex portion is connected to the surface of the main body portion through the first transition arc surface, and the first transition arc surface is a concave arc surface.

6. The pole piece according to claim 5, wherein The central angle of the first transition arc surface is γ, and γ satisfies: 0° < γ ≤ 90°; and / or, The radius of the first transition arc surface is r, and r satisfies: 0.1 mm ≤ r ≤ 5 mm.

7. The electrode tab according to claim 1, characterized in that, The inner surface of the convex portion has a first circumscribed sphere, and the outer surface of the convex portion has a second circumscribed sphere. The first circumscribed sphere and the second circumscribed sphere are arranged with the same center of the sphere; the shape of the inner surface of the convex portion is similar to the shape of the outer surface of the convex portion.

8. The electrode sheet according to claim 1, characterized in that, The outer surface of the convex portion has a first edge line. The first circumscribed sphere has a first tangent line at the first edge line. The included angle between the extension surface of the surface where the main body portion is connected to the convex portion and the corresponding first tangent line of the convex portion is the first included angle α1, and α1 satisfies: 15° ≤ α1 ≤ 75°.

9. The pole piece according to claim 1, characterized in that, The compressive strength per unit length of the pole piece is N, and N satisfies 0.05 N / mm ≤ N ≤ 1 N / mm.

10. The pole piece according to claim 1, characterized in that, The convex portion has a supporting force P, and P satisfies the following conditional formula (1), P = 2N × sinα1 × C sd (1) wherein, N is the compressive strength per unit length of the pole piece; C sd is the perimeter of the first edge line of the outer surface of the convex portion; α1 is the first included angle; P satisfies 0.026 N ≤ P ≤ 9.66 N.

11. The electrode sheet according to claim 1, characterized in that, The outer surface of the convex portion has a second circumscribed sphere. The outer surface of the convex portion includes a main surface and a top surface connected to the main surface. The top surface is an arc surface on the second circumscribed sphere. The edge line of the main surface away from the top surface forms a first edge line; The curvature of the main surface is equal to the curvature of the top surface; or, The curvature of the main surface is less than the curvature of the top surface. The first edge line forms a polygon, and the vertices of the first edge line in the shape of a polygon are all on the second circumscribed sphere; or, The curvature of the main surface is less than the curvature of the top surface. The first edge line forms a circle, and the first edge line in the shape of a circle is located on the second circumscribed sphere.

12. The pole piece according to claim 1, wherein, Each convex portion has a central axis passing through the center of the sphere of the first circumscribed sphere of the outer surface and extending along the thickness direction of the pole piece. The vertical distance between the central axes of two adjacent convex portions is the first distance L1, and L1 satisfies: 2.0 mm ≤ L1 ≤ 8.0 mm.

13. The pole piece according to claim 1, characterized in that, In the thickness direction of the pole piece per unit area, the ratio of the projected area of the outer surfaces of all the convex portions to the projected area of the pole piece is T, and T satisfies: 20% ≤ T ≤ 40%.

14. The pole piece according to claim 1, characterized in that, The convex portion has a preset spherical diameter SD, and the preset spherical diameter SD includes an inner spherical diameter SD1 of the inner surface and an outer spherical diameter SD2 of the outer surface. The inner spherical diameter SD1 is the first diameter of the first circumscribed sphere where the inner surface is located, and the outer spherical diameter SD2 is the second diameter of the second circumscribed sphere where the outer surface is located; wherein, SD2>SD1, and 1.5mm≤SD1≤30mm; and / or, 1.5mm≤SD2≤30mm.

15. The pole piece according to claim 14, characterized in that, 5.0mm≤SD1≤10mm.

16. The electrode sheet according to claim 1, wherein, A plurality of the convex portions are arranged side by side and at intervals along a first direction of the pole piece to form a set of convex portion units. In a second direction of the pole piece, adjacent two of the convex portion units are arranged at intervals. The first direction, the second direction, and the thickness direction of the pole piece are perpendicular to each other in pairs.

17. The pole piece according to claim 16, wherein the convex portions of adjacent two of the convex portion units are arranged collinearly in the second direction; or, one of the convex portion units is translated a preset distance A in the first direction relative to the other convex portion unit, and A satisfies: 0.3L2≤A≤L2; wherein, each of the convex portions has a central axis passing through the center of the first circumscribed sphere of the outer surface and extending along the thickness direction of the pole piece, and the vertical distance in the first direction between the central axes of adjacent two of the convex portions is a second distance L2.

18. The pole piece according to claim 17, wherein 0.6L2≤A≤0.9L2.

19. The pole piece according to claim 1, wherein in the thickness direction of the pole piece, all of the convex portions are bent toward the same side of the main body portion; or, in the thickness direction of the pole piece, some of the convex portions are bent toward one side of the main body portion, and the other convex portions are bent toward the other side of the main body portion.

20. An electrode assembly, characterized in that, Comprising: the pole piece according to any one of the above claims 1-19.

21. The electrode assembly according to claim 20, wherein The convex portions on the electrode assembly all protrude toward the inside of the electrode assembly.

22. A battery, characterized in that, Comprising: a housing; and, the electrode assembly according to claim 20 above, and the electrode assembly is arranged in the internal space of the housing.

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