Composite current collector, preparation method thereof and secondary battery

Abstract

The invention provides a composite current collector, a preparation method thereof and a secondary battery, and belongs to the technical field of composite current collector manufacturing. The two sides of the polymer base material layer are each provided with a plurality of first protrusions and a plurality of second protrusion sets, the first protrusions are distributed at intervals, the height of each first protrusion is H1, the outer diameter of the root of each first protrusion is L1, the height of each second protrusion is H2, the outer diameter of the root of each second protrusion is L2, H1 is larger than 5H2, L1 is larger than 4L2, and the second protrusion sets are arranged between at least part of every two adjacent first protrusions; transition layers are arranged on the two sides of the polymer base material layer, and the thickness of each transition layer is D1; the composite current collector comprises a polymer substrate layer and two transition layers, conductive layers are arranged on the sides, away from the polymer substrate layer, of the two transition layers, the thickness of each conductive layer is D2, H2: (D1 + D2) = 1: (4-20), and the composite current collector can relieve stress concentration and has excellent tensile strength.

Description

Technical Field

[0001] The present application relates to the technical field of composite current collector manufacturing, and in particular, to a composite current collector, a preparation method thereof, and a secondary battery. Background Art

[0002] When the composite current collector is installed, disassembled, or subjected to external collision and extrusion, additional mechanical stress is generated, which may cause the conductive layer to rupture after long-term accumulation. In addition, during high-temperature charging, low-temperature discharging, or when the product is in an extreme temperature environment, due to the difference in thermal expansion coefficients of the various layers of materials in the composite current collector, the degree of shrinkage is inconsistent, which easily generates internal stress between the layers and also easily causes the rupture of the conductive layer. The rupture of the conductive layer will affect the effective contact with the active material, resulting in blocked charge transfer, thereby reducing the energy density of the battery and significantly weakening the battery life of the device. The rupture site is prone to form a local electrochemically unstable region during the charge and discharge process of the battery, accelerating the imbalance of chemical reactions inside the battery, greatly shortening the cycle life of the battery, and increasing the frequency of battery replacement.

[0003] Currently, patents such as CN108155387A, CN117304541A, and CN117304541A combine the high flexibility of the polymer substrate layer with the wrinkled structure of the conductive layer to improve the cracks caused by mechanical deformation of the electrode sheet and internal expansion of each layer of materials. However, the stress concentration in the groove area between the wrinkles is 6-8 times that in the wrinkled area, and it is easily broken after being stretched, making it difficult to effectively improve the problem of easy crack generation. In addition, patent CN118824606A forms an elastomer layer on the surface layer of the base film with porous pits to reduce interface stress concentration, thereby reducing the occurrence of cracking. However, its pit structure is still a stress concentration area, and it is extremely easy to form cracks due to stress concentration. Moreover, punching the ultra-thin base film easily leads to a reduction in mechanical strength and easy film breakage.

[0004] Therefore, there is an urgent need to develop a composite current collector that can effectively relieve stress concentration in the conductive layer and has excellent tensile strength to meet the continuously improving requirements for the cycle performance and safety performance of lithium batteries. Summary of the Invention

[0005] The purpose of the present application is to provide a composite current collector, a preparation method thereof, and a secondary battery, and the composite current collector can relieve stress concentration in the conductive layer and has excellent tensile strength.

[0006] The embodiments of the present application are implemented as follows: In a first aspect, an embodiment of the present application provides a composite current collector, including a polymer substrate layer, a transition layer, and a conductive layer. Both sides of the polymer substrate layer in the thickness direction have a plurality of first protrusions distributed at intervals and a plurality of second protrusion groups distributed at intervals. Among them, the height of the first protrusion is H1, the outer diameter of the root is L1, the height of each second protrusion in the second protrusion group is H2, and the outer diameter of the root is L2. H1 > 5H2 and L1 > 4L2. There is a second protrusion group between at least some adjacent first protrusions; in the thickness direction, transition layers are provided on both sides of the polymer substrate layer, and each transition layer covers a plurality of first protrusions and a plurality of second protrusion groups on the same side. The thickness of a single transition layer is D1; on the side of the two transition layers facing away from the polymer substrate layer, there are conductive layers. The material of the conductive layer is different from that of the transition layer and the compactness of the conductive layer < the compactness of the transition layer. The thickness of a single conductive layer is D2, and H2: (D1 + D2) = 1: (4 - 20).

[0007] In the prior art, in order to improve the tensile strength of the composite current collector and delay the concentration of stress in the conductive layer, it is usually to make the surface of the conductive layer have a plurality of protrusions with similar shapes and sizes and distributed at intervals. However, the inventor's research found that the concave areas between these adjacent protrusions are still areas with relatively serious stress concentration. The stress in the concave area is approximately 6 - 8 times that in the non-concave area, and the improvement of the tensile strength of the composite current collector is also relatively limited. In the present application, by providing a plurality of first protrusions distributed at intervals and a plurality of second protrusion groups (including second protrusions) distributed at intervals on both surfaces of the polymer substrate layer, and there is a second protrusion group between at least some adjacent first protrusions. Specifically, the height of the first protrusion is H1, the outer diameter of the root is L1, the height of each second protrusion in the second protrusion group is H2, and the outer diameter of the root is L2. H1 > 5H2 and L1 > 4L2; at the same time, a transition layer is added between the polymer substrate layer and the conductive layer. Among them, the material of the conductive layer is different from that of the transition layer and the compactness of the conductive layer < the compactness of the transition layer (adding a transition layer can effectively improve the problem that the conductive layer and the polymer substrate layer are likely to fall off during plastic deformation due to the mismatch of the expansion coefficient and elastic modulus), and H2: (D1 + D2) = 1: (4 - 20) is also set, which can make the surface of the conductive layer of the composite current collector also have a plurality of large protrusions with large sizes and distributed at intervals, and there are small protrusions between at least some adjacent large protrusions. Through the mutual cooperation of the large protrusions and the small protrusions, the stress concentration in the concave area and the non-concave area of the conductive layer can be relieved simultaneously and effectively, and the composite current collector has excellent tensile strength.

[0008] In some alternative embodiments, in a first direction and a second direction, a second protrusion group is provided between any two adjacent first protrusions, and a first protrusion is provided between any two adjacent second protrusion groups. The first direction is perpendicular to the second direction, and both are perpendicular to the thickness direction.

[0009] In the above technical solution, in the first direction and the second direction that are perpendicular to each other, a second protrusion group is provided between any two adjacent first protrusions, and a first protrusion is provided between any two adjacent second protrusion groups, so that a plurality of first protrusions and a plurality of second protrusion groups on the same side of the polymer substrate layer are staggered in the first direction and the second direction, which can provide more stress points, thereby better relieving the stress concentration in the concave area. At the same time, it can also make the composite current collector have better tensile strength. In addition, the above layout form also makes the composite current collector have the advantages of a relatively regular overall structure and being convenient for manufacturing.

[0010] In some alternative embodiments, the first direction is the width direction, the second direction is the length direction, the second protrusion group includes a plurality of second protrusions, and the plurality of second protrusions in each second protrusion group are arranged at intervals along the second direction.

[0011] In the above technical solution, the second protrusion group includes a plurality of second protrusions distributed at intervals, and the plurality of second protrusions are arranged at intervals along the length direction, which has the advantage of a relatively reasonable layout.

[0012] In some alternative embodiments, in the thickness direction, the first protrusions on one side of the polymer substrate layer are arranged opposite to the second protrusion group on the other side of the polymer substrate layer.

[0013] In the above technical solution, the first protrusions on the first side of the polymer substrate layer are arranged corresponding to the second protrusion group on the opposite second side. Correspondingly, the second protrusion group on the first side of the polymer substrate layer will also correspond to the first protrusions on the opposite second side, which can further increase the number of stress points, so as to better relieve the stress concentration in the concave area. At the same time, it can also further improve the tensile strength of the composite current collector.

[0014] In some alternative embodiments, in the first direction, the distance between two adjacent first protrusions is 250 - 2500 nm; in the second direction, the distance between two adjacent first protrusions is 500 - 5000 nm.

[0015] In the above technical solution, the distances between two adjacent first protrusions in the first direction and the second direction are respectively limited to the above ranges, so that the concave area has a more appropriate size. On this basis, further adding a second protrusion group in the concave area can better relieve the stress concentration in the concave area and better improve the tensile strength of the composite current collector.

[0016] In some alternative embodiments, H1 is 600 - 3000 nm, L1 is 1000 - 10000 nm, H2 is 60 - 500 nm, L2 is 100 - 2000 nm; and / or, D1 is 2 - 100 nm, D2 is 1000 - 2000 nm.

[0017] In the above technical solution, H1, L1, H2, L2, D1, and D2 are respectively limited within the above ranges so that each parameter can be better matched, so that the surface of the conductive layer has large protrusions and small protrusions with appropriate sizes, quantities, and reasonable arrangement methods, thereby better alleviating the stress concentration in the concave area and better improving the tensile strength of the composite current collector.

[0018] In some alternative embodiments, L1 / H1 = AL2 / H2, where A is 0.6 - 1.0, and / or, the thickness of the polymer substrate layer is D3, and D3:H1 = (5 - 10):1.

[0019] In the above technical solution, setting L1 / H1 = AL2 / H2, where A is 0.6 - 1.0, enables the surface of the conductive layer to have large protrusions and small protrusions with more reasonable size differences, thereby better alleviating the stress concentration in the concave area and better improving the tensile strength of the composite current collector; in addition, setting D3:H1 = (5 - 10):1 facilitates the formation of the first protrusions and the second protrusion groups on the surface of the polymer substrate layer.

[0020] In a second aspect, the present application provides a method for preparing a composite current collector as in the first aspect embodiment, including the following steps: S1 Form first protrusions and second protrusion groups on both sides in the thickness direction of the polymer substrate layer by using a hot embossing technique to obtain a composite current collector precursor.

[0021] S2 Form a transition layer and a conductive layer on both sides of the composite current collector precursor respectively and sequentially by using a magnetron sputtering coating technique to obtain a composite current collector.

[0022] In the above technical solution, the method of using a hot embossing technique in combination with a magnetron sputtering technique to prepare a composite current collector has the advantages of simple and easy process and high quality of the prepared composite current collector.

[0023] In some alternative embodiments, the step of forming first protrusions and second protrusion groups on both sides in the thickness direction of the polymer substrate layer by using a hot embossing technique includes: On one surface of a first polymer substrate, a first set of protrusions and a second set of protrusions are formed by a hot embossing technique; on one surface of a second polymer substrate, a first set of protrusions and a second set of protrusions are formed by a hot embossing technique; the other surface of the first polymer substrate and the other surface of the second polymer substrate are respectively laminated on two surfaces of a third polymer substrate to form a polymer substrate layer.

[0024] In the above technical solution, the first set of protrusions and the second set of protrusions are first formed separately on two polymer substrates, and then the two substrates with the first set of protrusions and the second set of protrusions and the two surfaces of an additional substrate are laminated to prepare a polymer substrate layer with the first set of protrusions and the second set of protrusions on both side surfaces. This preparation process has the advantages of low equipment requirements and simple and easy operation.

[0025] In a third aspect, an embodiment of the present application provides a secondary battery, including the composite current collector provided in the embodiment of the first aspect.

[0026] In the above technical solution, the secondary battery includes the composite current collector provided in the embodiment of the first aspect. Since the composite current collector can effectively relieve the concentration of stress in the conductive layer and has excellent tensile strength, the prepared secondary battery has the advantages of good cycling performance and high safety. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a schematic structural diagram of a polymer substrate layer provided by an embodiment of the present application; Figure 2 It is a schematic structural diagram of a polymer substrate layer provided by an embodiment of the present application after a transition layer is provided; Figure 3 It is a schematic structural diagram of a transition layer provided by an embodiment of the present application after a conductive layer is provided; Figure 4 It is a schematic structural diagram of another polymer substrate layer provided by an embodiment of the present application.

[0029] Icons: 10 - composite current collector; 100 - polymer substrate layer; 100a - first polymer substrate; 100b - second polymer substrate; 100c - third polymer substrate; 110 - first protrusion; 120 - second protrusion group; 121 - second protrusion; 200 - transition layer; 300 - conductive layer; a - first direction; b - second direction; c - thickness direction. Detailed implementation manners

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0032] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0033] In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of this application is usually placed during use. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second", "third", etc. are only used for descriptive distinction and cannot be understood as indicating or implying relative importance.

[0034] In addition, terms such as "horizontal" and "overhanging" do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0035] In the description of the present application, it should also be noted that unless otherwise clearly specified and limited, the terms "arranged", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0036] In the prior art, in order to improve the tensile strength of the composite current collector and delay the concentration of stress in the conductive layer (which is likely to cause the conductive layer of the composite current collector to crack when subjected to a large external force impact or used at extreme temperatures), it is usually to make the surface of the conductive layer have a plurality of protrusions with similar shapes and sizes and spaced apart. However, the inventor has found through research that the concave regions between these adjacent protrusions are still regions where stress concentration is relatively severe. The stress in the concave region is approximately 6 to 8 times that in the non-concave region, and the improvement in the tensile strength of the composite current collector is also relatively limited, such that the conductive layer is still likely to crack when stress accumulates and plastic deformation occurs.

[0037] On this basis, the inventor further found through research that by adding smaller protrusions in the concave regions, the stress concentration in the concave regions can be effectively alleviated and the tensile strength of the composite current collector can be further improved, thereby being able to improve the problem that the conductive layer of the composite current collector is likely to crack during use (especially when subjected to a large external force impact or used at extreme temperatures).

[0038] The following specifically describes a composite current collector, a preparation method thereof, and a secondary battery provided by the present application.

[0039] Refer to Figure 1 、 Figure 2 and Figure 3, in a first aspect, an embodiment of the present application provides a composite current collector 10, including a polymer substrate layer 100, a transition layer 200, and a conductive layer 300. Both sides of the polymer substrate layer 100 in the thickness direction c have a plurality of first protrusions 110 distributed at intervals and a plurality of second protrusion groups 120 distributed at intervals. Among them, the height of the first protrusion 110 is H1, and the root outer diameter is L1. The height of each second protrusion 121 in the second protrusion group 120 is H2, and the root outer diameter is L2. H1 > 5H2 and L1 > 4L2. There is a second protrusion group 120 between at least some adjacent first protrusions 110; in the thickness direction c, both sides of the polymer substrate layer 100 have a transition layer 200. Each transition layer 200 covers a plurality of first protrusions 110 and a plurality of second protrusion groups 120 on the same side. The thickness of a single transition layer 200 is D1; on the side of the two transition layers 200 facing away from the polymer substrate layer 100, there is a conductive layer 300. The material of the conductive layer 300 is different from that of the transition layer 200, and the density of the conductive layer 300 < the density of the transition layer 200. The thickness of a single conductive layer 300 is D2, and H2:(D1 + D2) = 1:(4~20).

[0040] In the present application, by providing a plurality of first protrusions 110 distributed at intervals and a plurality of second protrusion groups 120 (including second protrusions 121) distributed at intervals on both surfaces of the polymer substrate layer 100, and there is a second protrusion group 120 between at least some adjacent first protrusions 110. Specifically, the height of the first protrusion 110 is H1, and the root outer diameter is L1. The height of each second protrusion 121 in the second protrusion group 120 is H2, and the root outer diameter is L2. H1:H1 > 5H2 and L1 > 4L2; at the same time, a transition layer 200 is added between the polymer substrate layer 100 and the conductive layer 300. Among them, the material of the conductive layer 300 is different from that of the transition layer 200, and the density of the conductive layer 300 < the density of the transition layer 200 (adding the transition layer 200 can effectively improve the problem that the conductive layer 300 and the polymer substrate layer 100 are prone to peeling during plastic deformation due to the mismatch of the expansion coefficient and elastic modulus), and H2:(D1 + D2) = 1:(4~20) is also set, which can make the surface of the conductive layer 300 of the composite current collector 10 also have a plurality of large-sized and spaced-apart large protrusions, and there are also small protrusions between at least some adjacent large protrusions. Through the mutual cooperation of the large protrusions and the small protrusions, the stress concentration in the concave and non-concave regions of the conductive layer 300 can be relieved simultaneously and effectively, and the composite current collector 10 has excellent tensile strength, thereby improving the problem that the conductive layer 300 is prone to cracking when the composite current collector 10 is subjected to a large external force impact or used at an extreme temperature.

[0041] It should be noted that the materials of each functional layer are not limited and can be set according to the conventional selection in the art.

[0042] As an example, the material of the polymer substrate layer 100 is selected from at least one of PET, PP, PE, PI, PVDF, PTFE, PVDF, FEP, PS, and PC. Among them, the materials of the first protrusion 110 and the second protrusion 121 are the same as those of the polymer substrate layer 100.

[0043] As an example, the material of the transition layer 200 is selected from at least one of nickel, chromium, nickel-chromium alloy, titanium, lead, platinum, molybdenum, zinc, graphite, alumina, and copper oxide.

[0044] As an example, the material of the conductive layer 300 is selected from at least one of copper, aluminum, stainless steel, gold, silver, carbon fiber, and carbon nanotubes.

[0045] It should be noted that the outer contour shapes of the first protrusion 110 and the second protrusion 121 are not limited and can be adaptively adjusted according to actual needs. For example, they can be hemispherical or conical. In the embodiments of the present application, the conical shape is taken as an example. Among them, the root outer diameter refers to the maximum outer diameter.

[0046] It should be noted that in the present application, it is simultaneously defined that H1 > 5H2, L1 > 4L2, and H2:(D1 + D2)=1:(4 - 20). This is because the inventors have found through research that only by controlling the relevant parameters within this range can the stress concentration in the concave region of the conductive layer 300 be effectively delayed and the tensile strength of the composite current collector 10 be effectively improved.

[0047] As an example, 5H2 < H1 < 25H2. For example, but not limited to, H1 can be any point value among 6H2, 8H2, 10H2, 12H2, 14H2, 16H2, 18H2, 20H2, 22H2, 24H2, and 25H2 or the range value between any two of them; 4L2 < L1 < 26L2. For example, but not limited to, L1 can be any point value among 5L2, 8L2, 10L2, 12L2, 15L2, 18L2, 20L2, and 25L2 or the range value between any two of them.

[0048] In this embodiment, by controlling the relevant parameters within the above range, the stress concentration in the concave region of the conductive layer 300 can be more effectively delayed and the tensile strength of the composite current collector 10 can be more effectively improved.

[0049] It should be noted that the polymer substrate layer 100 can be of an integral structure or in the form of a multi-layer composite, and can be specifically adaptively adjusted according to the actual preparation process.

[0050] Refer to Figure 1, as an example, the polymer substrate layer 100 is in the form of a multi-layer composite, specifically including: a second polymer substrate 100b, and a first polymer substrate 100a and a third polymer substrate 100c located on both sides of the second polymer substrate 100b, and both the side of the first polymer substrate 100a and the side of the third polymer substrate 100c facing away from each other have a first protrusion 110 and a second protrusion group 120.

[0051] As an example, the first polymer substrate 100a and the third polymer substrate 100c are respectively bonded to the second polymer substrate 100b, wherein the bonding material is selected from at least one of polyacrylic acid, polyurethane, epoxy resin, silicone, acrylate and polyvinyl alcohol.

[0052] Refer to Figure 3 , as an example, in the first direction a and the second direction b, a second protrusion group 120 is provided between any two adjacent first protrusions 110, and a first protrusion 110 is provided between any two adjacent second protrusion groups 120, and the first direction a is perpendicular to the second direction b and both are perpendicular to the thickness direction c.

[0053] In this embodiment, in the mutually perpendicular first direction a and second direction b, a second protrusion group 120 is provided between any two adjacent first protrusions 110, and a first protrusion 110 is provided between any two adjacent second protrusion groups 120, so that the multiple first protrusions 110 and multiple second protrusion groups 120 on the same side of the polymer substrate layer 100 are staggered in the first direction a and the second direction b, which can provide more stress points, thereby better relieving the stress concentration in the concave area. At the same time, it can also make the composite current collector 10 have better tensile strength. In addition, the above layout form also makes the composite current collector 10 have the advantages of a relatively regular overall structure and being convenient for manufacturing.

[0054] In other possible embodiments, it can also be that the multiple first protrusions 110 and multiple second protrusion groups 120 on the same side of the polymer substrate layer 100 satisfy: a second protrusion group 120 is provided between some adjacent first protrusions 110, and a first protrusion 110 is provided between some adjacent second protrusion groups 120, that is, the first protrusions 110 and the second protrusion groups 120 are only spaced apart in a single direction.

[0055] In other possible embodiments, it can also be that multiple first protrusions 110 and multiple second protrusion groups 120 on the same side of the polymer substrate layer 100 only satisfy in the first direction a or the second direction b that: there is a second protrusion group 120 between any two adjacent first protrusions 110, and there is a first protrusion 110 between any two adjacent second protrusion groups 120, that is, the first protrusions 110 and the second protrusion groups 120 are only spaced apart in a single direction.

[0056] Referring to Figure 3 , as an example, the first direction a is the width direction, the second direction b is the length direction, and the second protrusion group 120 includes multiple second protrusions 121, and the multiple second protrusions 121 of each second protrusion group 120 are arranged at intervals along the second direction b.

[0057] In this embodiment, the second protrusion group 120 includes multiple second protrusions 121 distributed at intervals, and the multiple second protrusions 121 are arranged at intervals along the length direction, which has the advantage of a more reasonable layout.

[0058] It should be noted that the number of second protrusions 121 in each second protrusion group 120 is not limited and can be adaptively adjusted according to actual needs. For example, it can be 1, 2, 3, 4, or 5.

[0059] Referring to Figure 4 , as an example, in the thickness direction c, the first protrusions 110 on one side of the polymer substrate layer 100 are arranged opposite to the second protrusion group 120 on the other side of the polymer substrate layer 100.

[0060] In this embodiment, the first protrusions 110 on the first side of the polymer substrate layer 100 are arranged corresponding to the second protrusion group 120 on the opposite second side. Correspondingly, the second protrusion group 120 on the first side of the polymer substrate layer 100 will also be arranged corresponding to the first protrusions 110 on the opposite second side, which can further increase the number of stress points to better relieve the stress concentration in the concave area. At the same time, it can also further improve the tensile strength of the composite current collector 10.

[0061] Referring to Figure 1 , in other possible embodiments, in the thickness direction c, the first protrusions 110 on one side of the polymer substrate layer 100 can also be arranged opposite to the first protrusions 110 on the other side of the polymer substrate layer 100.

[0062] As an example, in the first direction a, the distance between two adjacent first protrusions 110 is 250 to 2500 nm, such as but not limited to any one of the point values of 250 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, and 2500 nm or the range value between any two of them; in the second direction b, the distance between two adjacent first protrusions 110 is 500 to 5000 nm, such as but not limited to any one of the point values of 500 nm, 1000 nm, 2000 nm, 3000 nm, 4000 nm, and 5000 nm or the range value between any two of them.

[0063] In this embodiment, the distances between two adjacent first protrusions 110 in the first direction a and the second direction b are respectively limited to the above ranges, so that the recessed area has a more appropriate size. On this basis, a second protrusion group 120 is further provided in the recessed area, which can better relieve the stress concentration in the recessed area and better improve the tensile strength of the composite current collector 10.

[0064] It should be noted that the sizes of the first protrusion 110 and the second protrusion 121, and the thicknesses of the transition layer 200 and the conductive layer 300 are not specifically limited, as long as the corresponding multiple relationships can be satisfied, and the specific values can be adjusted adaptively according to actual needs.

[0065] As an example, H1 is 600 to 3000 nm (such as but not limited to any one of the point values of 600 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm, and 3000 nm or the range value between any two of them), and L1 is 1000 to 10000 nm (such as but not limited to any one of the point values of 1000 nm, 2000 nm, 4000 nm, 6000 nm, 8000 nm, and 10000 nm or the range value between any two of them).

[0066] As an example, H2 is 60 to 500 nm (such as but not limited to any one of the point values of 60 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm or the range value between any two of them), and L2 is 100 to 2000 nm (such as but not limited to any one of the point values of 100 nm, 200 nm, 500 nm, 1000 nm, 1500 nm, and 2000 nm or the range value between any two of them).

[0067] As an example, D1 is 2 to 100 nm (for example but not limited to any one of the point values of 2 nm, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, and 100 nm or the range value between any two of them), and D2 is 1000 to 2000 nm (for example but not limited to any one of the point values of 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, and 2000 nm or the range value between any two of them).

[0068] In this embodiment, H1, L1, H2, L2, D1, and D2 are respectively limited within the above ranges so that each parameter can be better matched, so that the surface of the conductive layer 300 has large protrusions and small protrusions with appropriate sizes and numbers, thereby better alleviating the stress concentration in the concave area and better improving the tensile strength of the composite current collector 10.

[0069] As an example, L1 / H1 = AL2 / H2, where A is 0.6 to 1.0, for example but not limited to any one of the point values of 0.6, 0.7, 0.8, 0.9, and 1.0 or the range value between any two of them.

[0070] In this embodiment, L1 / H1 = AL2 / H2 is set, where A is 0.6 to 1.0, so that the surface of the conductive layer 300 has large protrusions and small protrusions with more reasonable size differences, thereby better alleviating the stress concentration in the concave area and better improving the tensile strength of the composite current collector 10.

[0071] As an example, the thickness of the polymer substrate layer 100 is D3, and D3:H1 = (5 to 10):1, for example but not limited to any one of the point values of 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1 or the range value between any two of them.

[0072] It should be noted that the thickness of the polymer substrate layer 100 refers to the thickness of the planar area without protrusions.

[0073] In this embodiment, D3:H1 = (5 to 10):1 is set to facilitate the formation of the first protrusion 110 and the second protrusion group 120 on the surface of the polymer substrate layer 100.

[0074] It should be noted that the structures in the composite current collector 10 that are not specifically described or limited can be set according to the conventional selection in the art.

[0075] In a second aspect, the present application provides a method for preparing a composite current collector as described in the first aspect embodiment, including the following steps: S1 Form a first protrusion and a second protrusion group on both sides in the thickness direction of the polymer substrate layer by using a hot embossing technique to obtain a composite current collector precursor.

[0076] S2 Form a transition layer and a conductive layer on both sides of the composite current collector precursor respectively and sequentially by using a magnetron sputtering coating technique to obtain a composite current collector.

[0077] In this application, a method combining a hot embossing technique and a magnetron sputtering technique is used to prepare a composite current collector, which has the advantages of simple and easy process and high quality of the prepared composite current collector.

[0078] It should be noted that the hot embossing technique is a micro-nano processing method based on the principle of thermoplastic deformation. Specifically, this technique heats the material to the softening point and then imprints the micro-nano structure on the mold onto the material surface under a certain pressure; as the temperature decreases, the structure features on the mold are retained after the material solidifies. This technique has the advantages of high precision, high efficiency and high repeatability.

[0079] It should be noted that a continuous production process is adopted in the hot embossing stage and the magnetron sputtering stage, that is, after the hot embossing is completed, it is directly transported to the magnetron sputtering equipment for the preparation of the transition layer and the conductive layer. This production method can keep the material at a high cleanliness during the preparation process.

[0080] As an example, the step of forming a first protrusion and a second protrusion group on both sides in the thickness direction of the polymer substrate layer by using a hot embossing technique includes: Form a first protrusion and a second protrusion group on one surface of the first polymer substrate by using a hot embossing technique; form a first protrusion and a second protrusion group on one surface of the second polymer substrate by using a hot embossing technique; compound the other surface of the first polymer substrate and the other surface of the second polymer substrate on the two surfaces of the third polymer substrate respectively to form a composite current collector precursor.

[0081] In this embodiment, the first protrusion and the second protrusion group are first formed separately on two polymer substrates, and then the two substrates with the first protrusion and the second protrusion group and the two surfaces of the additional substrate are compounded to prepare a polymer substrate layer with the first protrusion and the second protrusion group on both side surfaces, which has the advantages of low equipment requirements and simple and easy process.

[0082] It should be noted that the step of forming the first protrusion and the second protrusion group on the surface of the first polymer substrate and the step of forming the first protrusion and the second protrusion group on the surface of the third polymer substrate can be carried out successively or synchronously. In the embodiments of this application, the synchronous execution is taken as an example.

[0083] As an example, the steps of synchronously forming the first protrusions and the second set of protrusions on the surfaces of the first and third polymer substrates by using a hot embossing technique include: S1 Plasma clean the first polymer substrate and the third polymer substrate respectively to remove dirt on the substrate surface and activate the surface; wherein, the process gas is selected from at least one of oxygen, nitrogen, argon, hydrogen, and methane, preferably oxygen; the cleaning bias voltage is -600 to -700 V; the cleaning current is 0.4 to 0.5 A. Then, convey the cleaned and activated first polymer substrate and the third polymer substrate to the corresponding hot embossing workbenches respectively, and then perform single-sided hot embossing to form the first protrusions and the second set of protrusions; wherein, the hot embossing temperature is 80 to 200 °C, preferably 100 to 120 °C; the hot embossing pressure is 1 to 10 MPa, preferably 2 to 5 MPa.

[0084] S2 Convey the first and third polymer substrate layers and the second polymer substrate layer (which has also been plasma cleaned) after hot embossing to a gluing platform for spray gluing, so that the first polymer substrate and the second polymer substrate are respectively laminated on the two surfaces of the third polymer substrate; wherein, the spray gluing pressure is 0.1 to 0.5 MPa, preferably 0.2 to 0.3 MPa; the spray gluing thickness is 0.1 to 2 μm, preferably 0.5 to 1 μm; the roll pressing pressure is 0.1 to 5 MPa, preferably 0.2 to 0.5 MPa.

[0085] S3 Convey the glued composite material to a shaping machine for heating and drying and then cooling and shaping; wherein, the drying temperature is 40 to 100 °C, preferably 40 to 60 °C; the cooling temperature is -30 to 10 °C, preferably -10 to 0 °C, to obtain a composite current collector precursor.

[0086] It should be noted that the steps and parameters in the magnetron sputtering stage can be set according to the conventional selection in the art.

[0087] As an example, in the steps of sequentially forming a transition layer and a conductive layer on both sides of the composite current collector precursor by using a magnetron sputtering coating technique, the deposition current is 40 to 50 A; the deposition temperature is 20 to 30 °C; the deposition pressure is 0.3 to 0.35 Pa; the deposition bias voltage is -150 to -200 V; the process gas for plating is selected from at least one of oxygen, nitrogen, argon, hydrogen, and methane, preferably argon.

[0088] It should be noted that the steps in the preparation method of the composite current collector that are not specifically described or limited can be set according to the conventional selection in the art.

[0089] In a third aspect, an embodiment of the present application provides a secondary battery, including the composite current collector provided in the embodiment of the first aspect.

[0090] In this application, the secondary battery includes the composite current collector provided in the embodiments of the first aspect. Since the composite current collector can effectively relieve the concentration of stress in the conductive layer and has excellent tensile strength, the prepared secondary battery has the advantages of good cycle performance and high safety.

[0091] The technical solutions of this application will be described in detail below with specific embodiments.

[0092] Example 1 The embodiment of this application provides a preparation method of a composite current collector, including the following steps: S1. Respectively convey the first polymer substrate (PET substrate with a thickness of 3000 nm), the third polymer substrate (PET substrate with a thickness of 3000 nm), and the second polymer substrate (PET substrate with a thickness of 2000 nm) to the corresponding cleaning chambers. Then, first evacuate the cleaning chambers to 5×10 -3 Pa, then introduce process gas (oxygen) until the air pressure in the cleaning chambers is 0.1 Pa, and then perform plasma cleaning; wherein, the cleaning bias voltage is -600 V; the cleaning current is 0.4 A. Then convey the first polymer substrate and the third polymer substrate after cleaning and activation to the corresponding hot embossing workbenches respectively, and then perform single-sided hot embossing to form a first protrusion and a second protrusion group; wherein, the hot embossing temperature is 100 °C and the hot embossing pressure is 2 MPa.

[0093] Specifically, referring to FIGS. 3 and Figure 4 , in the width direction and the length direction, between any two adjacent first protrusions on the same side of the second polymer substrate, a second protrusion group is provided, and between any two adjacent second protrusion groups, a first protrusion is provided; the second protrusion group has two second protrusions arranged at intervals in the length direction; in the thickness direction, the first protrusion on one side of the first polymer substrate is arranged opposite to the second protrusion group on one side of the third polymer substrate, and the second protrusion group on one side of the first polymer substrate is arranged opposite to the first protrusion on one side of the third polymer substrate; wherein, in the width direction, the distance between two adjacent first protrusions is 2000 nm; in the length direction, the distance between two adjacent first protrusions is 2000 nm; H1 of the first protrusion is 1500 nm, L1 is 4000 nm; H2 of the second protrusion is 110 nm, L2 is 420 nm, and A is 0.7.

[0094] S2 Convey the first, third polymer substrate layers and the second polymer substrate layer after hot embossing to a gluing platform for spray gluing, so that the first polymer substrate and the second polymer substrate are respectively laminated on the two surfaces of the third polymer substrate; wherein, the glue material is polyacrylic acid, the spray gluing pressure is 0.2 MPa, the spray gluing thickness is 0.5 μm, and the rolling pressure is 0.2 MPa.

[0095] S3 Convey the laminated composite material to a shaping machine for heating and drying and cooling and shaping; wherein, the drying temperature is 50 °C and the cooling temperature is 0 °C to obtain a composite current collector precursor.

[0096] S4 Convey the composite current collector precursor to a magnetron sputtering chamber, maintain the temperature in the chamber at 25 °C, introduce argon to maintain the chamber pressure at 0.31 Pa, and sequentially sputter to form a transition layer Cr and a conductive layer Cu (for the structure after forming the transition layer, refer to Figure 2 , and for the schematic diagram of the structure after forming the conductive layer, refer to Figure 3 ); wherein, the sputtering current of the Cr layer is 40 A, the deposition bias voltage is -150 V, and the thickness is 50 nm; the sputtering current of the Cu conductive layer is 50 A, the deposition bias voltage is -200 V, and the thickness is 1000 nm to obtain a composite current collector.

[0097] Example 2 The embodiment of the present application provides a method for preparing a composite current collector, which is only different from Example 1 in that: H1 of the first protrusion is 2000 nm and L1 is 3000 nm; H2 of the second protrusion is 100 nm and L2 is 500 nm, and A is 0.3.

[0098] Example 3 The embodiment of the present application provides a method for preparing a composite current collector, which is only different from Example 1 in that: H1 of the first protrusion is 2000 nm and L1 is 5000 nm; H2 of the second protrusion is 200 nm and L2 is 200 nm, and A is 2.5.

[0099] Example 4 The embodiment of the present application provides a method for preparing a composite current collector, which is only different from Example 1 in that: in step S1, the distribution of the formed protrusions is different, and the specific content is as follows: In the length direction, a second protrusion group is provided between any two adjacent first protrusions on the same side of the second polymer substrate, and a first protrusion is provided between any two adjacent second protrusion groups; the second protrusion group has two second protrusions arranged at intervals in the length direction; in the width direction, a plurality of first protrusions are provided, and there is no second protrusion group between any two adjacent first protrusions and the distance therebetween is 2000 nm; in the thickness direction, the first protrusions on one side of the first polymer substrate are arranged opposite to the second protrusion groups on one side of the third polymer substrate, and the second protrusion groups on one side of the first polymer substrate are arranged opposite to the first protrusions on one side of the third polymer substrate; wherein, in the length direction, the distance between two adjacent first protrusions is 2000 nm; the H1 of the first protrusion is 1500 nm, the L1 is 4000 nm; the H2 of the second protrusion is 110 nm, the L2 is 420 nm, and A is 0.7.

[0100] Example 5 The embodiment of the present application provides a method for preparing a composite current collector, which is only different from that of Example 4 in that: in step S1, in the thickness direction, the first protrusions on one side of the first polymer substrate are arranged opposite to the first protrusions on one side of the third polymer substrate, and the second protrusion groups on one side of the first polymer substrate are arranged opposite to the second protrusion groups on one side of the third polymer substrate.

[0101] Comparative Example 1 The comparative example of the present application provides a method for preparing a composite current collector, which is only different from that of Example 1 in that: in step S1, no hot embossing treatment is performed, that is, neither the first protrusions nor the second protrusion groups are provided on both sides of the polymer substrate layer.

[0102] Comparative Example 2 The comparative example of the present application provides a method for preparing a composite current collector, which is only different from that of Example 1 in that: in step S1, only the first protrusions are provided, and the second protrusion groups are not provided.

[0103] Comparative Example 3 The comparative example of the present application provides a method for preparing a composite current collector, which is only different from that of Example 1 in that: in step S4, no transition layer is formed, and the conductive layer is directly formed.

[0104] Test Example The composite current collectors prepared in Examples 1 to 5 and Comparative Examples 1 to 3 are respectively used as test samples, and then the tensile strength and the change rate of the tensile sheet resistance of each sample are tested, and the test results are statistically recorded in Table 1.

[0105] Specifically, the tensile strength test method is as follows: (1) Measure 10 specimens for each composite current collector sample, and take the minimum value as the test result; it is required that the length direction of the specimen is parallel to the axis of the fixture, and the sample is kept in a straight line.

[0106] (2) Tensile testing machine parameters: Tensile speed is 200 mm / min, gauge length is 50 mm, and width is 15 mm.

[0107] (3) If any of the following situations occur to the specimen, the test result is invalid: The sample breaks within the fixture jaws; improper operation; defects in the specimen itself; errors or other reasons causing data deviation.

[0108] Specifically, the test method for the change rate of sheet resistance during stretching is as follows: (1) Measure 10 specimens for each composite current collector sample, and take the minimum value as the test result; it is required that the length direction of the specimen is parallel to the axis of the fixture, and the sample is kept in a straight line.

[0109] (2) Tensile testing machine parameters: Tensile speed is 200 mm / min, gauge length is 50 mm, and width is 15 mm.

[0110] (3) Before stretching the sample, measure the sheet resistance using a four-point probe. R 0 ; When the elongation reaches 3%, measure the sheet resistance using a four-point probe R , and calculate the change rate of sheet resistance during stretching. The calculation formula is: (R - R 0 / R 0 ) × 100%.

[0111] (4) If any of the following situations occur to the specimen, the test result is invalid: The sample breaks within the fixture jaws; improper operation; defects in the specimen itself; errors or other reasons causing data deviation.

[0112] Table 1

[0113] Referring to Table 1, from the test results of Examples 1 - 5 and Comparative Examples 1 - 2, it can be seen that when both side surfaces of the polymer substrate layer have the first protrusions and the second protrusion groups, compared with those without the first protrusions and the second protrusion groups or only having the first protrusions, the corresponding composite current collector of the former has more excellent tensile strength and lower change rate of sheet resistance during stretching.

[0114] From the test results of Example 1 and Comparative Example 3, it can be seen that when a transition layer is provided between the conductive layer and the polymer substrate layer, compared with the case without a transition layer, the corresponding composite current collector of the former has more excellent tensile strength and lower change rate of sheet resistance during stretching.

[0115] From the test results of Examples 1 to 3, it can be seen that by setting L1 / H1 = AL2 / H2 and limiting A within the range of 0.6 to 1.0, compared with the case where A is not within the range, the corresponding composite current collector in the former case has more excellent tensile strength and lower change rate of tensile sheet resistance.

[0116] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A composite current collector, characterized in that: include: A polymer substrate layer, wherein both sides of the polymer substrate layer in the thickness direction have a plurality of first protrusions distributed at intervals and a plurality of second protrusion groups distributed at intervals, wherein the first protrusion has a height of H1 and a root outer diameter of L1, each second protrusion of the second protrusion group has a height of H2 and a root outer diameter of L2, H1>5H2 and L1>4L2, and the second protrusion group is provided between at least part of two adjacent first protrusions; A transition layer, wherein both sides of the polymer substrate layer have the transition layer in the thickness direction, each of the transition layers covers a plurality of the first protrusions and a plurality of the second protrusion groups on the same side, and the thickness of a single transition layer is D1; Conductive layer, the two transition layers have the conductive layer on one side away from the polymer substrate layer, the material of the conductive layer is different from the material of the transition layer and the density of the conductive layer is less than the density of the transition layer, the thickness of a single conductive layer is D2, and H2: (D1 + D2) = 1: (4~20).

2. The composite current collector according to claim 1, characterized in that: In the first direction and the second direction, a second protrusion group is arranged between any two adjacent first protrusions, and a first protrusion is arranged between any two adjacent second protrusion groups. The first direction is perpendicular to the second direction and both are perpendicular to the thickness direction.

3. The composite current collector according to claim 2, characterized in that: The first direction is a width direction, the second direction is a length direction, the second protrusion group includes a plurality of second protrusions, and the plurality of second protrusions in each second protrusion group are arranged at intervals along the second direction.

4. The composite current collector according to claim 3, characterized in that: In the thickness direction, the first protrusions on one side of the polymer substrate layer are arranged opposite to the second protrusions on the other side of the polymer substrate layer.

5. The composite current collector according to any one of claims 2 to 4, characterized in that: In the first direction, a distance between two adjacent first protrusions is 500-5000 nm; in the second direction, a distance between two adjacent first protrusions is 500-5000 nm.

6. The composite current collector according to claim 5, characterized in that H1 is 600~3000 nm, L1 is 1000~10000 nm, H2 is 60~500 nm, L2 is 100~2000 nm; Or / and, D1 is 2~100 nm, D2 is 1000~2000 nm.

7. The composite current collector according to claim 6, characterized in that: L1 / H1=AL2 / H2, wherein A is 0.6~1.0, or / and, the thickness of the polymer substrate layer is D3, D3:H1=(5~10):

1.

8. A method for preparing a composite current collector according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: forming the first protrusion and the second protrusion group on both sides of the polymer substrate layer in the thickness direction by using a hot stamping technique to obtain a composite current collector precursor; S2: using magnetron sputtering coating technology to respectively and sequentially form the transition layer and the conductive layer on both sides of the composite current collector precursor to obtain the composite current collector.

9. The method for preparing a composite current collector according to claim 8, characterized in that: The step of forming the first protrusion and the second protrusion group on both sides of the polymer substrate layer in the thickness direction by using the hot stamping technology comprises: Forming the first protrusion and the second protrusion group on a surface of a first polymer substrate by a hot embossing technique; Forming the first protrusion and the second protrusion group on a surface of a second polymer substrate by a hot embossing technique; The other surface of the first polymer substrate and the other surface of the second polymer substrate are respectively laminated on both surfaces of the third polymer substrate to form the polymer substrate layer.

10. A secondary battery, characterized in that: Comprising the composite current collector as described in any one of claims 1 to 7.

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