Composite current collector and battery

Abstract

The utility model discloses a composite current collector and a battery, comprising: a base material layer, at least one surface of which is provided with a plurality of projections, the projections are arc-shaped, and the ratio of the height of the projections to the thickness of the base material layer is 1: 90-4: 90; and the conductive layer is arranged on the surface of the base material layer and wraps the bulges. By adopting the structure, the outer surface of the conducting layer, which is far away from the base material layer, is also provided with an arc-shaped bulge, so that the binding force between the subsequently coated active material and the conducting layer is favorably improved, the coating uniformity and smoothness of the active material are ensured, the elongation rate of the composite current collector is high, and the base material layer and the conducting layer are tightly combined.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a composite current collector and battery. Background Technology

[0002] Composite current collectors mainly adopt a sandwich structure of "metal-polymer material-metal", with polymer materials such as PET / PP / PI as the middle substrate layer, and metal deposited on the upper and lower layers to form a metal conductive layer.

[0003] The composite current collector is composed of a substrate layer and a conductive layer. Since these two materials have different properties, defects or stress concentration areas may exist at their interface, affecting the overall elongation of the composite current collector. Under tensile or other external forces, the poor deformation coordination between the substrate layer and the conductive layer can easily lead to excessive local stress, causing problems such as fracture and reducing elongation. Furthermore, the weak bonding force between the substrate layer and the conductive layer affects conductivity.

[0004] Therefore, it is necessary to improve the existing technology to overcome the aforementioned defects. Utility Model Content

[0005] The purpose of this invention is to provide a composite current collector and battery with high elongation and a tight bond between the substrate layer and the conductive layer.

[0006] The purpose of this utility model is achieved through the following technical solution: a composite current collector, comprising:

[0007] The substrate layer has at least one surface provided with a plurality of protrusions, the protrusions being arc-shaped, and the ratio of the height of the protrusions to the thickness of the substrate layer being 1:90 to 4:90;

[0008] A conductive layer is disposed on the surface of the substrate layer and covers the protrusion.

[0009] Furthermore, the height of the protrusion gradually increases from both ends toward the center, and the ratio of the center height of the protrusion to the thickness of the substrate layer is 1:90 to 4:90.

[0010] Furthermore, the height ratio of the end of any side of the protrusion to the height of the center position is 1:2 to 1:3.

[0011] Furthermore, the openings of two adjacent protrusions are arranged opposite to each other and enclose each other to form an elliptical ring protrusion.

[0012] Furthermore, the ratio of the length of the major axis to the length of the corresponding minor axis of the elliptical annular protrusion cross-section is 1.2:1 to 2.5:1.

[0013] Furthermore, the conductive layer includes an intermediate layer and a metal layer sequentially stacked along the surface of the substrate layer, and the ratio of the height of the elliptical annular protrusion to the thickness of the intermediate layer is 1:2 to 1:3.

[0014] Furthermore, the number of elliptical annular protrusions in the substrate layer per unit millimeter area is not less than 20.

[0015] Furthermore, the elliptical annular protrusion includes a first end face that is in contact with the substrate layer and a second end face that is away from the substrate layer. In the direction from the first end face to the second end face, the outer circumferential dimension of the elliptical annular protrusion gradually increases and the inner circumferential dimension gradually decreases.

[0016] Furthermore, the ratio of the outer major axis length of the first end face to the outer minor axis length of the second end face is 1:1.5 to 1:2.5, and the ratio of the outer minor axis length of the first end face to the outer major axis length of the second end face is the same as the ratio of the outer major axis length of the first end face to the outer minor axis length of the second end face.

[0017] Furthermore, the major axis of the elliptical annular protrusion is parallel to the TD direction, and its minor axis is parallel to the MD direction. The elliptical annular protrusion is provided on both surfaces of the substrate layer, and multiple elliptical annular protrusions are distributed along the TD and MD directions.

[0018] Furthermore, the elliptical annular protrusions on the two surfaces of the substrate layer are staggered along the long axis.

[0019] Furthermore, in the same plane, the distance between two adjacent elliptical annular protrusions in the TD direction is 1.2 to 1.5 times the length of the major axis of the elliptical annular protrusion, and the distance between two adjacent elliptical annular protrusions in the MD direction is 1.0 to 1.2 times the length of the minor axis of the elliptical annular protrusion.

[0020] In addition, this utility model also provides a battery including the aforementioned composite current collector.

[0021] Compared with the prior art, the present invention has the following beneficial effects: By adopting the above structure, when the conductive layer is disposed on the surface of the substrate layer, on the one hand, due to the presence of the arc-shaped protrusions on the surface of the substrate layer, the outer surface of the conductive layer away from the substrate layer will also form arc-shaped protrusions, which is beneficial to improving the bonding force between the active material subsequently coated on the outer surface of the conductive layer and the conductive layer. At the same time, the arc-shaped structure on the outer surface of the conductive layer can prevent the flow of the active material in multiple directions, ensuring the uniformity and smoothness of the active material coating. On the other hand, the conductive layer wraps around the arc-shaped protrusions, which can act as anchor points, forming more contact points and a larger contact area between the substrate layer and the conductive layer, thereby improving the bonding force between the metal atoms of the conductive layer and the substrate layer. To prevent electrolyte corrosion at the junction of the conductive layer and the substrate layer during subsequent battery assembly, thus improving the adhesion of the conductive layer; in addition, when the composite current collector is subjected to external forces such as tension, the arc-shaped protrusions can guide the stress distribution along its periphery to disperse the stress, avoid stress concentration in a single direction, delay the overall fracture of the composite current collector, and improve the elongation; the elliptical ring protrusions formed by the relatively arranged arc-shaped protrusions, after the conductive layer is placed on the substrate layer, the elliptical ring protrusions formed on the outer surface of the substrate layer can further prevent the flow of active materials, ensure the uniformity of active material coating, and guide the stress distribution along the ring path during stretching, avoiding stress concentration in a single direction, further delaying the overall fracture of the composite current collector, and improving the elongation. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the arc-shaped arrangement of protrusions in this utility model;

[0023] Figure 2 This is a schematic diagram of the structure of an embodiment of the arc-shaped protrusion in this utility model;

[0024] Figure 3 This is a schematic diagram of the arrangement of the elliptical and annular protrusions of this utility model;

[0025] Figure 4 This is a cross-sectional schematic diagram of the elliptical annular protrusion of this utility model;

[0026] Figure 5 This is a cross-sectional schematic diagram of the composite current collector with an elliptical annular protrusion of this utility model.

[0027] Explanation of reference numerals in the attached figures:

[0028] 100, Substrate layer; 200, Conductive layer; 210, Intermediate layer; 220, Metal layer; 300, Elliptical annular protrusion; 310, First end face; 320, Second end face; 330, Recessed area; 400, Protrusion. Detailed Implementation

[0029] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0030] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] Please see Figure 1 As shown, the composite current collector corresponding to a preferred embodiment of the present invention includes a substrate layer 100 and a conductive layer 200. At least one protrusion 400 is provided on the surface of the substrate layer 100. The protrusion 400 is arc-shaped, and the ratio of the height of the protrusion 400 to the thickness of the substrate layer 100 is 1:90 to 4:90. The conductive layer 200 is disposed on the surface of the substrate layer 100 and covers the protrusion 400. It can be understood that the arc-shaped protrusion 400 refers to the fact that both edges along the protrusion direction are arc-shaped, for example, the arc shape is C-shaped.

[0033] By employing the above-described structure, when the conductive layer 200 is disposed on the surface of the substrate layer 100, on the one hand, due to the presence of the arc-shaped protrusions 400 on the surface of the substrate layer 100, the conductive layer 200, facing away from the outer surface of the substrate layer 100, also forms arc-shaped protrusions. This is beneficial for improving the bonding force between the active material subsequently coated on the outer surface of the conductive layer 200 and the conductive layer 200. Simultaneously, the arc-shaped structure can prevent the flow of the active material in multiple directions, ensuring the uniformity and smoothness of the active material coating. On the other hand, the conductive layer 200 encloses the arc-shaped protrusions 400, and the arc-shaped protrusions 400... It can act as an anchor point, forming more contact points and a larger contact area between the substrate layer 100 and the conductive layer 200, thereby improving the bonding force between the metal atoms of the conductive layer 200 and the substrate layer 100. This prevents the electrolyte from corroding the connection between the conductive layer 200 and the substrate layer 100 during subsequent battery assembly, thus improving the adhesion of the conductive layer 200. In addition, when the composite current collector is subjected to external forces such as tension, the arc-shaped protrusion 400 can guide the stress distribution along its periphery to disperse the stress, avoid stress concentration in a single direction, delay the overall fracture of the composite current collector, and improve the elongation.

[0034] Furthermore, the ratio of the height of the arc-shaped protrusion 400 to the thickness of the substrate layer 100 is 1:90 to 4:90. Controlling this ratio within this range can, on the one hand, prevent the arc-shaped protrusion 400 from being too high, which would cause it to bend and deform easily during subsequent rolling and coating of active materials on the composite current collector, leading to the detachment of the conductive layer 200. On the other hand, it can prevent the arc-shaped protrusion 400 from being too low, which would make it difficult to form an arc-shaped protrusion on the surface of the conductive layer 200, thus failing to prevent the coating of active materials from flowing and affecting the uniformity of the active materials. In addition, too low a height would also result in insufficient contact area between the substrate layer 100 and the conductive layer 200, poor locking effect, and limited improvement in bonding force.

[0035] Furthermore, in one embodiment, the height of the end of the arc-shaped protrusion 400 is the same as the height of the center. In this embodiment, referring to... Figure 2 As shown, the height of the arc-shaped protrusion 400 gradually increases from both ends towards the center, meaning the center of the arc-shaped protrusion 400 is higher than both ends. At this point, the ratio of the center height of the arc-shaped protrusion 400 to the thickness of the substrate layer 100 is 1:90 to 4:90.

[0036] The present invention adopts the above-mentioned structure, with the 400 protrusions of varying heights. The shape of the center being high and the sides being low can smoothly disperse external pressure or internal expansion stress along the arc, avoid local stress concentration, and reduce the risk of cracking in the conductive layer 200.

[0037] Specifically, in a preferred embodiment, the height ratio of the end of any side of the arc-shaped protrusion 400 to the center is 1:2 to 1:3. By controlling the height ratio within this range, it is beneficial to ensure that the stress is smoothly distributed along the arc. If the height ratio is too small, it is easy to create a steep arc slope, forming an isolated peak in the middle. The top of the high protrusion, lacking support, is prone to buckling deformation or even collapse during subsequent rolling processes, causing the metal layer 220 to fall off. If the height difference ratio is too large, that is, the height of the center and both ends of the arc-shaped protrusion 400 tends to be the same, resulting in the loss of the gradient change in the height of the protrusion 400, which easily causes stress concentration and increases the risk of cracking.

[0038] Furthermore, as a preferred embodiment, the curvature directions of two adjacent arc-shaped protrusions 400 are opposite, that is, the openings of two adjacent arc-shaped protrusions 400 can be arranged opposite each other (the openings face each other). It is understood that the curvature direction of the arc-shaped protrusion 400 refers to the direction of the arc's concavity.

[0039] Furthermore, refer to Figure 3 As shown, the two ends of two adjacent arc-shaped protrusions 400 with opposite openings extend towards each other to enclose and form an elliptical annular protrusion 300. It can be understood that the elliptical annular protrusion 300 is a three-dimensional closed ring formed by two coplanar concentric ellipses extending in a direction away from the substrate layer 100, preferably perpendicular to the substrate layer 100. By using the elliptical annular protrusion 300, the elliptical annular protrusion formed on the outer surface of the conductive layer 200 can further prevent the flow of active material, ensuring the uniformity of active material coating. Furthermore, the conductive layer 200 is deposited in the middle of the elliptical annular protrusion 300 and surrounds it. The elliptical annular protrusion 300 on the surface of the substrate layer 100 can form more contact points and a larger contact area between the substrate layer 100 and the conductive layer 200, increasing the effective contact area of ​​the conductive layer 200, further enhancing the bonding force, and forming a three-dimensional conductive network, thereby improving conductivity. Meanwhile, the elliptical annular protrusion 300 can disperse stress when the composite current collector is subjected to tensile force in any direction, thereby improving the tensile strength and elongation of the composite current collector in any direction.

[0040] Furthermore, in a preferred embodiment, the ratio of the length of the major axis to the corresponding minor axis of the cross-section of the elliptical annular protrusion 300 is 1.2:1 to 2.5:1, that is, the ratio of the length of the outer major axis to the outer minor axis of the cross-section of the elliptical annular protrusion 300 is 1.2:1 to 2.5:1, and / or the ratio of the length of the length of the inner major axis to the length of the inner minor axis of the elliptical annular protrusion 300 is 1.2:1 to 2.5:1. It should be noted that the outer major axis and outer minor axis of the elliptical annular protrusion 300 refer to the major axis and minor axis corresponding to the outer ellipse of the cross-section, and the inner major axis and inner minor axis of the elliptical annular protrusion 300 refer to the major axis and minor axis corresponding to the inner ellipse of the cross-section.

[0041] If the length ratio is less than 1.2, the peripheral contour of the elliptical annular protrusion 300 tends to be circular. Since the curvature of a circle is the same in all directions, it is impossible to optimize the stress distribution for the principal stress direction, especially in the MD direction (the direction of the principal stress during processing). When the length ratio is greater than 2.5, the elliptical annular protrusion 300 is too long and narrow in the TD direction. The conductive path in the TD direction is long, but the minor axis in the MD direction is short, resulting in poor bonding strength. Furthermore, the conductive layer 200 is prone to detachment due to the small size of the central concave region 330. It should be noted that the MD direction is the mechanical direction, that is, the direction along which the substrate layer 100 moves during the production process, and the TD direction is the transverse direction, that is, the direction perpendicular to the machine direction.

[0042] Furthermore, the substrate layer 100 can be made of thin film materials such as polypropylene, polyethylene terephthalate, and polyimide, and the conductive layer 200 is prepared on the surface of the substrate layer 100 by deposition. In this embodiment, the conductive layer 200 includes an intermediate layer 210 and a metal layer 220 sequentially stacked along the surface of the substrate layer 100. The intermediate layer 210 can be made of materials such as nickel, chromium, or nickel-chromium alloy, and the metal layer 220 can be made of copper.

[0043] When preparing the conductive layer 200, an intermediate layer 210 can be prepared on at least one surface of the substrate layer 100 by deposition. During deposition, the intermediate layer 210 is prepared by magnetron sputtering, and the thickness of the intermediate layer 210 is 10 nm to 100 nm. After the magnetron sputtering is completed, the metal layer 220 is thickened by electroplating, and the total thickness of the metal layer 220 is controlled to be 0.5 μm to 2 μm.

[0044] In this embodiment, elliptical annular protrusions 300 are provided on both surfaces of the substrate layer 100, and conductive layers 200 are deposited on different surfaces of the substrate layer 100.

[0045] Furthermore, if the ratio of the height of the elliptical annular protrusion 300 to the thickness of the intermediate layer 210 is too small, i.e., the height of the elliptical annular protrusion 300 is low, the interlocking ability between the elliptical annular protrusion 300 and the intermediate layer 210 is poor, resulting in poor bonding force. If the ratio of the height of the elliptical annular protrusion 300 to the thickness of the intermediate layer 210 is too large, i.e., the height of the elliptical annular protrusion 300 is too high, the intermediate layer 210 will not be able to completely cover the elliptical annular protrusion 300, resulting in light transmission. As a preferred embodiment, the ratio of the height of the elliptical annular protrusion 300 to the thickness of the intermediate layer 210 is 1:2 to 1:3. When the height of the arc-shaped protrusion 400 gradually increases from the center of both ends, the height of the elliptical annular protrusion 300 refers to the height of its center. By limiting the above parameters, the interlocking ability between the elliptical ring protrusion 300 and the intermediate layer 210 is good, and the intermediate layer 210 can completely cover the elliptical ring protrusion 300 to prevent light transmission. It also avoids the intermediate layer 210 being loose and porous, which would result in poor density of the metal layer 220 and further reduce the adhesion of the metal layer 220.

[0046] Furthermore, in any direction on the surface of the substrate layer 100, there are no fewer than 20 elliptical annular protrusions 300 per unit area of ​​1mm*1mm. If there are fewer than 20 elliptical annular protrusions 300 per unit millimeter area, the interlocking effect between the substrate layer 100 and the conductive layer 200 may be affected due to the small number and sparse distribution of the elliptical annular protrusions 300, thus reducing the bonding force.

[0047] Furthermore, referring to Figure 4 As shown, the elliptical annular protrusion 300 includes a first end face 310 that is in contact with the substrate layer 100 and a second end face 320 that is away from the substrate layer 100. In the direction from the first end face 310 to the second end face 320, the outer peripheral dimension of the elliptical annular protrusion 300 gradually increases and the inner peripheral dimension gradually decreases. Specifically, the outer major axis and outer minor axis of the cross-section of the elliptical annular protrusion 300 gradually increase, while the inner major axis and inner minor axis gradually decrease. A concave region 330 is formed at the center of the elliptical annular protrusion 300.

[0048] The above structure allows corner regions to be formed both inside and outside the elliptical annular protrusion 300. Metal ions are deposited in these corner regions, creating an interlocking state between the substrate layer 100 and the conductive layer 200, thus improving the bonding strength between them. Furthermore, when subjected to external forces, the elliptical annular protrusion 300 also acts as a buffer, uniformly transferring the force to the substrate layer 100 and preventing stress concentration. This further enhances the tightness between the substrate layer 100 and the conductive layer 200. Preferably, the outer and inner ellipses at the cross-section of the elliptical annular protrusion 300 are coaxial similar ellipses, with their major axes and minor axes coinciding, allowing for more uniform stress distribution.

[0049] Furthermore, in a preferred embodiment, when the cross-section of the elliptical annular protrusion 300 is elliptical, the ratio of the length of the outer major axis of the first end face 310 and the second end face 320 is 1:1.5 to 1:2.5, and the ratio of the length of the outer minor axis of the first end face 310 and the second end face 320 is the same as the ratio of the length of the outer major axis of the first end face 310 and the second end face 320.

[0050] By limiting the ratio to the range described above, it is possible to prevent the size of the first end face 310 from being too small and the size of the second end face 320 from being too large due to a small ratio. Therefore, when the conductive layer 200 is magnetron sputtered, the sputtering path of the metal particles will not be blocked by the second end face 320, ensuring that the metal particles are deposited at the end where the elliptical annular protrusion 300 is connected to the substrate layer 100. That is, the conductive layer 200 can reliably mechanically interlock with the elliptical annular protrusion 300, improving the bonding force between them. At the same time, it can also prevent the elliptical annular protrusion 300 from easily breaking under bending or external force due to the small size of the first end face 310.

[0051] Furthermore, by limiting the ratio to the range described above, it is possible to prevent the dimensions of the first end face 310 and the second end face 320 from becoming too close due to an excessively large ratio. This also prevents the cross-section of the elliptical annular protrusion 300 perpendicular to the TD and MD directions from becoming rectangular, thereby losing the corner area formed inside and outside the elliptical annular protrusion 300. Consequently, the substrate layer 100 and the conductive layer 200 cannot form an interlocking state, which is not conducive to improving the bonding strength.

[0052] Furthermore, the major axis of the elliptical annular protrusion 300 is parallel to the TD direction, and its minor axis is parallel to the MD direction. Elliptical annular protrusions 300 are provided on both surfaces of the substrate layer 100. The major axis of the elliptical annular protrusion 300 is set along the TD direction, and the minor axis is set along the MD direction. Multiple elliptical annular protrusions 300 are distributed along the TD and MD directions. By setting the minor axis along the MD direction (the direction in which the material bears the main mechanical stress during processing and use), and distributing the elliptical annular protrusions 300 along the MD direction, the minor axis structure is more prone to elastic compression or extension, absorbing energy, reducing stress concentration, and better adapting to deformation. This prevents excessive deformation from causing the conductive layer 200 to peel off from the substrate layer 100, maintaining the contact integrity between the conductive layer 200 and the substrate layer 100. Moreover, the multiple elliptical annular protrusions 300 distributed along the TD and MD directions help improve the bonding force between the conductive layer 200 and the substrate layer 100.

[0053] Preferably, refer to Figure 5 As shown, the elliptical annular protrusions 300 on the two surfaces of the substrate layer 100 are staggered along the TD direction, which is conducive to stress release and improves product performance, and avoids stress concentration and reduced elongation caused by the corresponding arrangement of the elliptical annular protrusions 300 on the two surfaces.

[0054] Furthermore, as a preferred embodiment, in the same plane, the distance between two adjacent elliptical annular protrusions 300 in the TD direction is 1.2 to 1.5 times the length of the major axis of the elliptical annular protrusion 300, and the distance between two adjacent elliptical annular protrusions 300 in the MD direction is 1.0 to 1.2 times the length of the minor axis of the elliptical annular protrusion 300. It should be noted that the major axis and minor axis of the elliptical annular protrusion 300 refer to the outer major axis and outer minor axis.

[0055] By limiting the above parameters, when magnetron sputtering the intermediate layer 210, it is possible to avoid the situation where the spacing between two adjacent elliptical annular protrusions 300 is too small, making it difficult to deposit metal particles in the area between adjacent elliptical annular protrusions 300. This ensures that the metal particles uniformly cover the elliptical annular protrusions 300 and ensures conductivity. At the same time, it is also possible to avoid the situation where the spacing between two adjacent elliptical annular protrusions 300 is too large, resulting in too few elliptical annular protrusions 300 structures per unit area. This ensures the bonding force between the substrate layer 100 and the intermediate layer 210.

[0056] In addition, this utility model also provides a battery, including a positive electrode, a separator and a negative electrode stacked together, wherein the current collector in the positive electrode and / or the current collector in the negative electrode is the aforementioned composite current collector.

[0057] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A composite current collector, characterized in that, include: The substrate layer (100) has at least one surface provided with a plurality of protrusions (400), the protrusions (400) being arc-shaped, and the ratio of the height of the protrusions (400) to the thickness of the substrate layer (100) being 1:90 to 4:90; A conductive layer (200) is disposed on the surface of the substrate layer (100) and covers the protrusion (400).

2. The composite current collector as described in claim 1, characterized in that, The height of the protrusion (400) gradually increases from both ends toward the center, and the ratio of the center height of the protrusion (400) to the thickness of the substrate layer (100) is 1:90 to 4:

90.

3. The composite current collector as described in claim 2, characterized in that, The height ratio of the end of any side of the protrusion (400) to the height of the center position is 1:2 to 1:

3.

4. The composite current collector as described in claim 1, characterized in that, The openings of two adjacent protrusions (400) are arranged opposite to each other and enclose each other to form an elliptical annular protrusion (300).

5. The composite current collector as described in claim 4, characterized in that, The ratio of the length of the major axis to the length of the corresponding minor axis of the cross-section of the elliptical annular protrusion (300) is 1.2:1 to 2.5:

1.

6. The composite current collector as described in claim 4, characterized in that, The conductive layer (200) includes an intermediate layer (210) and a metal layer (220) stacked sequentially along the surface of the substrate layer (100), and the ratio of the height of the elliptical annular protrusion (300) to the thickness of the intermediate layer (210) is 1:2 to 1:

3.

7. The composite current collector as described in claim 4, characterized in that, The number of elliptical annular protrusions (300) in the substrate layer (100) per unit millimeter area is not less than 20.

8. The composite current collector as described in claim 4, characterized in that, The elliptical annular protrusion (300) includes a first end face (310) that is in contact with the substrate layer (100) and a second end face (320) that is away from the substrate layer (100). In the direction from the first end face (310) to the second end face (320), the outer peripheral dimension of the elliptical annular protrusion (300) gradually increases and the inner peripheral dimension gradually decreases.

9. The composite current collector as described in claim 8, characterized in that, The ratio of the outer major axis length of the first end face (310) and the second end face (320) is 1:1.5 to 1:2.5, and the ratio of the outer minor axis length of the first end face (310) and the second end face (320) is the same as the ratio of the outer major axis length of the first end face (310) and the second end face (320).

10. The composite current collector as described in claim 4, characterized in that, The major axis of the elliptical annular protrusion (300) is parallel to the TD direction, and the minor axis is parallel to the MD direction. The elliptical annular protrusion (300) is provided on both surfaces of the substrate layer (100). Multiple elliptical annular protrusions (300) are distributed along the TD and MD directions.

11. The composite current collector as described in claim 4, characterized in that, The elliptical annular protrusions (300) on the two surfaces of the substrate layer (100) are staggered along the long axis.

12. The composite current collector as described in claim 4, characterized in that, In the same plane, the distance between two adjacent elliptical annular protrusions (300) in the TD direction is 1.2 to 1.5 times the length of the major axis of the elliptical annular protrusion (300), and the distance between two adjacent elliptical annular protrusions (300) in the MD direction is 1.0 to 1.2 times the length of the minor axis of the elliptical annular protrusion (300).

13. A battery, characterized in that, Includes the composite current collector as described in any one of claims 1 to 12.

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