Composite current collector, preparation method thereof, and secondary battery

Abstract

The present application provides a composite current collector, a preparation method thereof, and a secondary battery, belonging to the field of composite current collector manufacturing technology. A polymer substrate layer has a plurality of first protrusions and a plurality of second protrusion groups spaced apart on both sides. The first protrusions have a height of H1 and a root outer diameter of L1, and the second protrusions have a height of H2 and a root outer diameter of L2, where H1 is greater than 5H2 and L1 is greater than 4L2. A second protrusion group is located between at least some adjacent first protrusions. The polymer substrate layer has a transition layer on both sides, with a thickness of D1 for each transition layer. Both transition layers have a conductive layer on the side facing away from the polymer substrate layer, with a thickness of D2 for each conductive layer, and H2:(D1+D2)=1:(4-20). 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 battery is installed, disassembled, or subjected to external collision and extrusion, the composite current collector generates additional mechanical stress, which may cause the conductive layer to rupture after long-term accumulation. In addition, during high-temperature charging, low-temperature discharge, or when the product is in an extreme temperature environment, the various layers of material in the composite current collector shrink to inconsistent degrees due to differences in thermal expansion coefficients, which can easily generate internal stress between the layers and cause the conductive layer to rupture. The rupture of the conductive layer will affect its effective contact with the active material, hindering charge transfer, thereby reducing the energy density of the battery and significantly reducing the endurance of the device. The rupture site is likely to form a local electrochemically unstable area during the battery charging and discharging process, accelerating the imbalance of the chemical reaction inside the battery, significantly shortening the battery's cycle life, and increasing the frequency of battery replacement.

[0003] At present, patents CN108155387A, CN117304541A and CN117304541A all combine the high flexibility of the polymer substrate layer with the corrugated structure of the conductive layer to improve the cracks caused by the mechanical deformation of the pole piece and the internal expansion of each layer of material. However, the stress concentration in the groove area between the folds is 6 to 8 times that of the fold area, and it is easy to break after being stretched, making it difficult to effectively improve the problem of easy cracking. In addition, patent CN118824606A reduces interfacial stress concentration and cracking by forming an elastomer layer on the surface of the base film with porous pits. However, its pit structure is still a stress concentration area, which is very easy to form cracks due to stress concentration, and the punching of the ultra-thin base film can easily lead to reduced 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 ever-increasing cycle performance and safety performance requirements 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, wherein the composite current collector can relieve stress concentration in a conductive layer and has excellent tensile strength.

[0006] The embodiment of the present application is implemented as follows:

[0007] In a first aspect, embodiments of the present application provide a composite current collector comprising a polymer substrate layer, a transition layer, and a conductive layer. The polymer substrate layer has a plurality of spaced-apart first protrusions and a plurality of spaced-apart second protrusion groups on both sides in the thickness direction, wherein each first protrusion has a height H1 and a root outer diameter L1, each second protrusion in the second protrusion group has a height H2 and a root outer diameter L2, H1 > 5H2 and L1 > 4L2, and a second protrusion group is located between at least some adjacent first protrusions. In the thickness direction, transition layers are provided on both sides of the polymer substrate layer, each transition layer covering the plurality of first protrusions and the plurality of second protrusion groups on the same side, and the thickness of each transition layer is D1. Both transition layers have a conductive layer on the side facing away from the polymer substrate layer, the conductive layer being made of a different material than the transition layer and having a lower density than the transition layer. The thickness of each conductive layer is D2, and H2:(D1+D2)=1:(4-20).

[0008] In the prior art, in order to improve the tensile strength of the composite current collector and to alleviate the problem of stress concentration in the conductive layer, the surface of the conductive layer is usually provided with multiple protrusions of similar shape and size and spaced apart. However, the inventors have found that the depressions between these adjacent protrusions are still areas of severe stress concentration, with the stress in the depressions being approximately 6 to 8 times that of the non-depressions, and the improvement in the tensile strength of the composite current collector is also relatively limited. In the present application, a plurality of spaced apart first protrusions and a plurality of spaced apart second protrusion groups (including second protrusions) are provided on both sides of the surface of the polymer substrate layer, and a second protrusion group is provided between at least some of the adjacent first protrusions. Specifically, the height of the first protrusion is H1 and the outer diameter of the root is L1, and the height of each second protrusion of the second protrusion group is H2 and the outer diameter of the root is L2, where H1>5H2 and L1>4L2; at the same time, a transition layer is added between the polymer substrate layer and the conductive layer, wherein the material of the conductive layer is different from that of the transition layer and the density of the conductive layer is less than the density of the transition layer. The invention discloses a novel composite current collector having a plurality of large protrusions with large sizes and spaced apart distributions, and a plurality of small protrusions between at least some of the two adjacent large protrusions. By cooperating with each other, the stress concentration in the recessed area and the non-recessed area of ​​the conductive layer can be effectively relieved simultaneously and effectively, and the composite current collector can have excellent tensile strength.

[0009] In some optional embodiments, in the first direction and the 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, and the first direction is perpendicular to the second direction and both are perpendicular to the thickness direction.

[0010] In the above technical solution, a second protrusion group is provided between any two adjacent first protrusions in the mutually perpendicular first and second directions, and a first protrusion is provided between any two adjacent second protrusion groups. This allows the multiple first protrusions and multiple second protrusion groups on the same side of the polymer substrate layer to be staggered in both the first and second directions. This provides more stress points, thereby better alleviating stress concentration in the recessed areas and also improving the tensile strength of the composite current collector. Furthermore, this layout gives the composite current collector a relatively regular overall structure and facilitates manufacturing.

[0011] In some optional 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.

[0012] 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 to be distributed at intervals along the length direction, which has the advantage of a more reasonable layout.

[0013] In some optional embodiments, 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.

[0014] In the above technical solution, the first protrusion on the first side of the polymer substrate layer is set to correspond 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 protrusion on the opposite second side, which can further increase the number of force points to better relieve the stress concentration in the recessed area. At the same time, it can further improve the tensile strength of the composite current collector.

[0015] In some optional 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.

[0016] In the above technical solution, the distance between the two adjacent first protrusions in the first direction and the second direction is limited to the above range respectively, so that the recessed area has a more appropriate size. On this basis, a second protrusion group is further added in the recessed area, which can better alleviate the stress concentration in the recessed area and better improve the tensile strength of the composite current collector.

[0017] In some optional embodiments, 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.

[0018] In the above technical solution, H1, L1, H2, L2, D1 and D2 are respectively limited to the above ranges so that the various parameters can be better matched, so that the surface of the conductive layer has large protrusions and small protrusions with more appropriate size and quantity and more reasonable arrangement, thereby better alleviating the stress concentration in the recessed area and better improving the tensile strength of the composite current collector.

[0019] In some optional embodiments, 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.

[0020] In the above technical solution, L1 / H1=AL2 / H2 is set, where A is 0.6~1.0, so that the surface of the conductive layer has large protrusions and small protrusions with more reasonable size differences, thereby better alleviating stress concentration in the recessed area and better improving the tensile strength of the composite current collector; in addition, D3:H1=(5~10):1 is set to facilitate the formation of the first protrusion and the second protrusion group on the surface of the polymer substrate layer.

[0021] In a second aspect, the present application provides a method for preparing the composite current collector according to the embodiment of the first aspect, comprising the following steps:

[0022] S1 uses a hot embossing technique to form a first protrusion group and a second protrusion group on both sides of the polymer substrate layer in the thickness direction to obtain a composite current collector precursor.

[0023] S2 uses magnetron sputtering coating technology to form a transition layer and a conductive layer on both sides of the composite current collector precursor respectively and in sequence to obtain a composite current collector.

[0024] In the above technical solution, the composite current collector is prepared by combining hot embossing technology with magnetron sputtering technology, which has the advantages of simple process and high quality of the prepared composite current collector.

[0025] In some optional embodiments, the step of forming the first protrusions and the second protrusion group on both sides of the polymer substrate layer in the thickness direction by using a hot embossing technique includes:

[0026] A first protrusion and a second protrusion group are formed on one surface of a first polymer substrate by hot embossing technology; a first protrusion and a second protrusion group are formed on one surface of a second polymer substrate by hot embossing technology; and 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.

[0027] In the above technical solution, the first protrusions and the second protrusion group are first formed separately on two polymer substrates, and then the two substrates with the first protrusion group and the second protrusion group and the two sides of the additional substrate are compounded to prepare a polymer substrate layer with the first protrusion and the second protrusion group on both sides. This preparation process has the advantages of low equipment requirements and simple and easy process.

[0028] In a third aspect, an embodiment of the present application provides a secondary battery, comprising the composite current collector provided in the embodiment of the first aspect.

[0029] In the above technical solution, the secondary battery includes the composite current collector provided in the first embodiment. Since the composite current collector can effectively relieve stress concentration in the conductive layer and has excellent tensile strength, the prepared secondary battery has the advantages of good cycle performance and high safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A schematic structural diagram of a polymer substrate layer provided in an embodiment of the present application;

[0032] Figure 2 This is a schematic structural diagram of a polymer substrate layer provided in an embodiment of the present application after a transition layer is provided;

[0033] Figure 3 A schematic diagram of a structure after a conductive layer is provided on a transition layer according to an embodiment of the present application;

[0034] Figure 4 This is a schematic structural diagram of another polymer substrate layer provided in an embodiment of the present application.

[0035] Icon: 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 DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0037] 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 for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without making any creative efforts shall fall within the scope of protection of the present application.

[0038] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0039] In the description of this application, it should be noted that the terms "upper," "lower," "horizontal," "inner," and "outer" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the product of this application is typically placed when in use. These terms are intended solely to facilitate the description of this application and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0040] Furthermore, terms such as "horizontal" and "overhanging" do not necessarily mean that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0041] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0042] In the prior art, in order to improve the tensile strength of the composite current collector and delay the problem of stress concentration in the conductive layer (which can easily cause the conductive layer to break when the composite current collector is subjected to a large external force impact or is used at extreme temperatures), the surface of the conductive layer is usually provided with multiple protrusions with similar shapes and sizes and spaced apart. However, the inventors have found that the recessed areas between these adjacent protrusions are still areas where stress concentration is more serious. The stress in the recessed areas is roughly 6 to 8 times that of the non-recessed areas, and the improvement in the tensile strength of the composite current collector is also relatively limited, so that the conductive layer is still prone to breakage when stress accumulates and plastic deformation occurs.

[0043] On this basis, the inventors further discovered that by adding smaller protrusions in the recessed area, the stress concentration in the recessed area can be effectively alleviated and the tensile strength of the composite current collector can be further improved, thereby improving the problem of the conductive layer of the composite current collector being easily broken during use (especially when subjected to large external force impact or used at extreme temperatures).

[0044] The following describes in detail a composite current collector, a preparation method thereof, and a secondary battery provided in this application.

[0045] See Figure 1 、 Figure 2 and Figure 3In a first aspect, an embodiment of the present application provides a composite current collector 10, comprising a polymer substrate layer 100, a transition layer 200, and a conductive layer 300. The polymer substrate layer 100 has a plurality of first protrusions 110 and a plurality of second protrusion groups 120 distributed at intervals on both sides in the thickness direction c, wherein the height of the first protrusion 110 is H1 and the outer diameter of the root is L1, and the height of each second protrusion 121 of the second protrusion group 120 is H2 and the outer diameter of the root is L2, H1>5H2 and L1>4L2, and there is a second protrusion group 120 between at least two adjacent first protrusions 110; in the thickness direction c, the polymer substrate layer 100 has a plurality of first protrusions 110 and a plurality of second protrusion groups 120 distributed at intervals on both sides in the thickness direction c. Both have a transition layer 200, each transition layer 200 covers the multiple first protrusions 110 and the multiple second protrusion groups 120 on the same side, and the thickness of a single transition layer 200 is D1; ​​the two transition layers 200 have a conductive layer 300 on the side away from the polymer substrate layer 100, the material of the conductive layer 300 is different from the material of the transition layer 200, and the density of the conductive layer 300 is less than the density of the transition layer 200, the thickness of a single conductive layer 300 is D2, and H2: (D1 + D2) = 1: (4~20).

[0046] In the present application, a plurality of first protrusions 110 and a plurality of second protrusion groups 120 (including second protrusions 121) are provided on both sides of the polymer substrate layer 100, and a second protrusion group 120 is provided between at least some of the adjacent first protrusions 110. Specifically, the height of the first protrusion 110 is H1 and the outer diameter of the root is L1. The height of each second protrusion 121 of the second protrusion group 120 is H2 and the outer diameter of the root 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, wherein the material of the conductive layer 300 is different from that of the transition layer 200 and the density of the conductive layer 300 is less than the density of the transition layer 200 (the addition of the transition layer 200). Layer 200 can effectively improve the problem that the conductive layer 300 and the polymer substrate layer 100 are easily detached during plastic deformation due to the mismatch between the expansion coefficient and the elastic modulus), and H2: (D1 + D2) = 1: (4~20) is also set, so that the surface of the conductive layer 300 of the composite current collector 10 also has multiple large-sized and spaced large protrusions, and also has small protrusions between at least some of the adjacent two large protrusions. Through the mutual cooperation of the large protrusions and the small protrusions, the stress concentration in the recessed area and the non-recessed area of ​​the conductive layer 300 can be simultaneously and effectively alleviated, and the composite current collector 10 can also have excellent tensile strength, thereby improving the problem that the conductive layer 300 is easily broken when the composite current collector 10 is subjected to a large external force impact or is used at extreme temperatures.

[0047] It should be noted that the material of each functional layer is not limited and can be set according to conventional selection in the art.

[0048] 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, wherein the material of the first protrusion 110 and the second protrusion 121 is the same as the material of the polymer substrate layer 100.

[0049] 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, aluminum oxide and copper oxide.

[0050] 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.

[0051] It should be noted that the outer contours 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. The embodiments of this application all take the conical shape as an example, where the root outer diameter refers to the maximum outer diameter.

[0052] It should be noted that in this application, H1>5H2 and L1>4L2 and H2:(D1+D2)=1:(4~20) are simultaneously limited because the inventors have found that controlling the relevant parameters within this range can effectively delay the concentration of stress in the recessed area of ​​the conductive layer 300 and effectively improve the tensile strength of the composite current collector 10.

[0053] As an example, 5H2

[0054] In this embodiment, controlling the relevant parameters within the above ranges can more effectively delay the concentration of stress in the recessed area of ​​the conductive layer 300 and more effectively improve the tensile strength of the composite current collector 10 .

[0055] It should be noted that the polymer substrate layer 100 may be a one-piece structure or a multi-layer composite structure, and may be adaptively adjusted according to the actual preparation process.

[0056] See 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 the first polymer substrate 100a and the third polymer substrate 100c have a first protrusion 110 and a second protrusion group 120 on the sides facing away from each other.

[0057] 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.

[0058] See 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. The first direction a is perpendicular to the second direction b and both are perpendicular to the thickness direction c.

[0059] 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. This allows the multiple first protrusions 110 and multiple second protrusion groups 120 on the same side of the polymer substrate layer 100 to be staggered in the first direction a and the second direction b. This provides more stress points, thereby better relieving stress concentration in the recessed area and, at the same time, giving the composite current collector 10 better tensile strength. Furthermore, this layout gives the composite current collector 10 the advantage of a relatively regular overall structure and ease of manufacture.

[0060] In other possible embodiments, the multiple first protrusions 110 and the multiple second protrusion groups 120 on the same side of the polymer substrate layer 100 may satisfy the following conditions in the first direction a and the second direction b: a second protrusion group 120 is provided between two partially adjacent first protrusions 110, and a first protrusion 110 is provided between two partially adjacent second protrusion groups 120, that is, the first protrusions 110 and the second protrusion group 120 are spaced apart only in a single direction.

[0061] In other possible embodiments, the multiple first protrusions 110 and the multiple second protrusion groups 120 on the same side of the polymer substrate layer 100 may satisfy only in the first direction a or 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, that is, the first protrusions 110 and the second protrusion group 120 are spaced apart only in a single direction.

[0062] See Figure 3 As an example, the first direction a is the width direction, the second direction b is the length direction, the second protrusion group 120 includes a plurality of second protrusions 121, and the plurality of second protrusions 121 of each second protrusion group 120 are arranged at intervals along the second direction b.

[0063] In this embodiment, the second protrusion group 120 includes a plurality of second protrusions 121 distributed at intervals, and the plurality of second protrusions 121 are arranged to be distributed at intervals along the length direction, which has the advantage of a more reasonable layout.

[0064] 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.

[0065] See Figure 4 As an example, in the thickness direction c, the first protrusions 110 on one side of the polymer base layer 100 are arranged opposite to the second protrusion group 120 on the other side of the polymer base layer 100 .

[0066] In this embodiment, the first protrusion 110 on the first side of the polymer substrate layer 100 is set to correspond 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 correspond to the first protrusion 110 on the opposite second side, which can further increase the number of stress points to better relieve the stress concentration in the recessed area. At the same time, it can further improve the tensile strength of the composite current collector 10.

[0067] See Figure 1 In other possible implementations, in the thickness direction c, the first protrusions 110 on one side of the polymer substrate layer 100 may also be arranged opposite to the first protrusions 110 on the other side of the polymer substrate layer 100 .

[0068] As an example, in the first direction a, the distance between two adjacent first protrusions 110 is 250~2500 nm, for example, but not limited to, a distance of any point value of 250 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm and 2500 nm, or a range value between any two of them; in the second direction b, the distance between two adjacent first protrusions 110 is 500~5000 nm, for example, but not limited to, a distance of any point value of 500 nm, 1000 nm, 2000 nm, 3000 nm, 4000 nm and 5000 nm, or a range value between any two of them.

[0069] In this embodiment, the distance between the two adjacent first protrusions 110 in the first direction a and the second direction b is limited to the above-mentioned range, so that the recessed area has a more appropriate size. On this basis, a second protrusion group 120 is further added in the recessed area, which can better alleviate the stress concentration in the recessed area and better improve the tensile strength of the composite current collector 10.

[0070] 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 they can meet the corresponding multiple relationships, the specific values ​​can be adaptively adjusted according to actual needs.

[0071] As an example, H1 is 600~3000 nm (for example, but not limited to, H1 is any point value of 600 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm and 3000 nm, or a range of values ​​between any two of them), and L1 is 1000~10000 nm (for example, but not limited to, L1 is any point value of 1000 nm, 2000 nm, 4000 nm, 6000 nm, 8000 nm and 10000 nm, or a range of values ​​between any two of them).

[0072] As an example, H2 is 60~500 nm (for example, but not limited to, H2 is any point value among 60 nm, 100 nm, 200 nm, 300 nm, 400 nm and 500 nm, or a range value between any two of them), and L2 is 100~2000 nm (for example, but not limited to, L2 is any point value among 100 nm, 200 nm, 500 nm, 1000 nm, 1500 nm and 2000 nm, or a range value between any two of them).

[0073] As an example, D1 is 2~100 nm (for example, but not limited to, D1 is any point value among 2 nm, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm and 100 nm, or a range of values ​​between any two of them), and D2 is 1000~2000 nm (for example, but not limited to, D2 is any point value among 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm and 2000 nm, or a range of values ​​between any two of them).

[0074] In this embodiment, H1, L1, H2, L2, D1 and D2 are respectively limited to the above ranges so that the various parameters can be better matched, so that the surface of the conductive layer 300 has large protrusions and small protrusions of relatively suitable size and number, thereby better alleviating the stress concentration in the recessed area and better improving the tensile strength of the composite current collector 10.

[0075] As an example, L1 / H1=AL2 / H2, where A is 0.6~1.0, for example but not limited to, A is any one of 0.6, 0.7, 0.8, 0.9 and 1.0 or a range between any two of them.

[0076] In this embodiment, L1 / H1=AL2 / H2 is set, where A is 0.6~1.0, so that the surface of the conductive layer 300 has large protrusions and small protrusions with more reasonable size differences, thereby better alleviating stress concentration in the recessed area and better improving the tensile strength of the composite current collector 10.

[0077] As an example, the thickness of the polymer substrate layer 100 is D3, and D3:H1=(5-10):1, for example but not limited to, D3:H1 is any one of 5:1, 6:1, 7:1, 8:1, 9:1 and 10:1, or a range between any two thereof.

[0078] It should be noted that the thickness of the polymer base material layer 100 refers to the thickness of the planar region excluding the protrusions.

[0079] In this embodiment, setting D3:H1=(5-10):1 facilitates forming the first protrusions 110 and the second protrusion group 120 on the surface of the polymer substrate layer 100 .

[0080] It should be noted that any structure not specifically described or limited in the composite current collector 10 may be configured according to conventional selections in the art.

[0081] In a second aspect, the present application provides a method for preparing the composite current collector according to the embodiment of the first aspect, comprising the following steps:

[0082] S1 uses a hot embossing technique to form a first protrusion group and a second protrusion group on both sides of the polymer substrate layer in the thickness direction to obtain a composite current collector precursor.

[0083] S2 uses magnetron sputtering coating technology to form a transition layer and a conductive layer on both sides of the composite current collector precursor respectively and in sequence to obtain a composite current collector.

[0084] In the present application, a composite current collector is prepared by combining hot embossing technology with magnetron sputtering technology, which has the advantages of a simple process and high quality of the prepared composite current collector.

[0085] It's important to note that hot embossing is a micro-nanofabrication method based on the principle of thermoplastic deformation. Specifically, the material is heated to its softening point, and then the micro-nanostructures from the mold are imprinted onto the surface under a certain pressure. As the temperature decreases, the material solidifies, retaining the structural features from the mold. This technique offers the advantages of high precision, high efficiency, and high repeatability.

[0086] It should be noted that the hot embossing stage and the magnetron sputtering stage adopt a continuous production process, 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 ensure that the material always maintains a high degree of cleanliness during the preparation process.

[0087] As an example, 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 embossing technology includes:

[0088] A first protrusion and a second protrusion group are formed on one surface of a first polymer substrate by hot embossing technology; a first protrusion and a second protrusion group are formed on one surface of a second polymer substrate by hot embossing technology; the other surface of the first polymer substrate and the other surface of the second polymer substrate are respectively composited on the two surfaces of a third polymer substrate to form a composite current collector precursor.

[0089] In this embodiment, the first protrusions and the second protrusion group are first formed separately on two polymer substrates, and then the two substrates with the first protrusion group and the second protrusion group and the two sides of the additional substrate are compounded to prepare a polymer substrate layer with the first protrusion and the second protrusion group on both sides of the surface, which has the advantages of low equipment requirements and simple and easy process.

[0090] It should be noted that the steps of forming the first protrusion and the second protrusion group on the surface of the first polymer substrate and the steps of forming the first protrusion and the second protrusion group on the surface of the third polymer substrate can be performed sequentially or simultaneously. In the embodiment of the present application, simultaneous performance is taken as an example.

[0091] As an example, the step of simultaneously forming the first protrusions and the second protrusion group on the surfaces of the first and third polymer substrates using a hot embossing technique includes:

[0092] S1: Plasma cleaning is performed on the first and third polymer substrates to remove surface dirt and activate the surfaces. The process gas is selected from at least one of oxygen, nitrogen, argon, hydrogen, and methane, preferably oxygen. The cleaning bias is -600 to -700 V, and the cleaning current is 0.4 to 0.5 A. The cleaned and activated first and third polymer substrates are then transferred to corresponding hot stamping stations and subjected to single-sided hot stamping to form first and second protrusion groups. The hot stamping temperature is 80 to 200°C, preferably 100 to 120°C, and the hot stamping pressure is 1 to 10 MPa, preferably 2 to 5 MPa.

[0093] S2: The first and third polymer substrate layers and the second polymer substrate layer (which have also been plasma cleaned) after hot stamping are transported to a gluing platform for spray gluing, so that the first polymer substrate and the second polymer substrate are respectively compounded on the two surfaces of the third polymer substrate; wherein the spraying pressure is 0.1~0.5 MPa, preferably 0.2~0.3 MPa; the spraying thickness is 0.1~2 μm, preferably 0.5~1 μm; the rolling pressure is 0.1~5 MPa, preferably 0.2~0.5 MPa.

[0094] S3: The composite material after bonding is transported to a shaping machine for heating, drying, and cooling for shaping; wherein the drying temperature is 40-100°C, preferably 40-60°C; the cooling temperature is -30-10°C, preferably -10-0°C, to obtain a composite current collector precursor.

[0095] It should be noted that the steps and parameters of the magnetron sputtering stage can be set according to conventional selections in the art.

[0096] As an example, in the step of forming a transition layer and a conductive layer respectively and sequentially on both sides of a composite current collector precursor using magnetron sputtering coating technology, the deposition current is 40~50 A; the deposition temperature is 20~30°C; the deposition pressure is 0.3~0.35 Pa; the deposition bias is -150~-200 V; and the coating process gas is selected from at least one of oxygen, nitrogen, argon, hydrogen and methane, preferably argon.

[0097] It should be noted that any steps not specifically described or limited in the method for preparing the composite current collector may be arranged according to conventional selections in the art.

[0098] In a third aspect, an embodiment of the present application provides a secondary battery, comprising the composite current collector provided in the embodiment of the first aspect.

[0099] In the present application, the secondary battery includes the composite current collector provided in the first embodiment. Since the composite current collector can effectively relieve stress concentration in the conductive layer and has excellent tensile strength, the prepared secondary battery has the advantages of good cycle performance and high safety.

[0100] The technical solution of the present application is described in detail below with reference to specific embodiments.

[0101] Example 1

[0102] The present invention provides a method for preparing a composite current collector, comprising the following steps:

[0103] S1: 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) are transported to the corresponding cleaning chambers, and then the cleaning chambers are vacuumed to 5×10 -3 Pa, then process gas (oxygen) is introduced into the cleaning chamber to a pressure of 0.1 Pa, followed by plasma cleaning. The cleaning bias is -600 V, and the cleaning current is 0.4 A. The cleaned and activated first and third polymer substrates are then transported to corresponding hot embossing stations and subjected to single-sided hot embossing to form the first and second protrusion groups. The hot embossing temperature is 100°C, and the hot embossing pressure is 2 MPa.

[0104] For details, see 3 and Figure 4 In the width direction and the length direction, a second protrusion group is provided between any two adjacent first protrusions located 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 along the length direction; in the thickness direction, the first protrusions on one side of the first polymer substrate are arranged opposite to the second protrusion group on the 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 the 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, and L1 is 4000 nm; H2 of the second protrusion is 110 nm, and L2 is 420 nm, and A is 0.7.

[0105] S2 transports the first and third polymer substrate layers and the second polymer substrate layer after hot stamping to a gluing platform for spray gluing, so that the first polymer substrate and the second polymer substrate are respectively compounded on the two surfaces of the third polymer substrate; wherein the glue material is polyacrylic acid, the spraying pressure is 0.2 MPa, the spraying thickness is 0.5 μm, and the roller pressure is 0.2 MPa.

[0106] S3: The composite material after bonding is transported to a shaping machine for heating, drying, and cooling for shaping; wherein the drying temperature is 50° C. and the cooling temperature is 0° C., to obtain a composite current collector precursor.

[0107] S4: The composite current collector precursor is transported to the magnetron sputtering chamber, the chamber temperature is maintained at 25 ° C, argon is introduced to maintain the chamber pressure at 0.31 Pa, and the transition layer Cr and the conductive layer Cu are sputtered in sequence (the structure after the transition layer is formed can be referred to Figure 2 , the structural diagram after the conductive layer is formed can be found in Figure 3 ); wherein, the sputtering current of the Cr layer is 40A, the deposition bias is -150V, and the thickness is 50 nm; the sputtering current of the Cu conductive layer is 50A, the deposition bias is -200V, and the thickness is 1000 nm, to obtain a composite current collector.

[0108] Example 2

[0109] The embodiment of the present application provides a method for preparing a composite current collector, which differs from Example 1 only 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.

[0110] Example 3

[0111] The embodiment of the present application provides a method for preparing a composite current collector, which differs from Example 1 only 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.

[0112] Example 4

[0113] This embodiment of the present application provides a method for preparing a composite current collector. The only difference between this method and Example 1 is that, in step S1, the distribution of the protrusions is different. The specific contents are as follows:

[0114] In the length direction, a second protrusion group is provided between any two adjacent first protrusions located 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 along the length direction; in the width direction, a plurality of first protrusions are provided, no second protrusion group is provided between any two adjacent first protrusions, and the spacing 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 group on the 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 the side of the third polymer substrate; wherein, 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.

[0115] Example 5

[0116] The embodiment of the present application provides a method for preparing a composite current collector, which differs from Example 4 only in that: in step S1, in the thickness direction, the first protrusion on one side of the first polymer substrate is arranged opposite to the first protrusion on the side of the third polymer substrate, and the second protrusion group on one side of the first polymer substrate is arranged opposite to the second protrusion group on the side of the third polymer substrate.

[0117] Comparative Example 1

[0118] The comparative example of the present application provides a method for preparing a composite current collector, which differs from Example 1 only in that: in step S1, no hot stamping treatment is performed, that is, there is no first protrusion and second protrusion group on both sides of the polymer substrate layer.

[0119] Comparative Example 2

[0120] The comparative example of the present application provides a method for preparing a composite current collector, which differs from Example 1 only in that, in step S1 , only the first protrusions are provided, and no second protrusion group is provided.

[0121] Comparative Example 3

[0122] The comparative example of the present application provides a method for preparing a composite current collector, which differs from Example 1 only in that in step S4, no transition layer is formed and a conductive layer is directly formed.

[0123] Test example

[0124] The composite current collectors prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were used as test samples, respectively. The tensile strength and tensile resistivity change rate of each sample were tested, and the test results were statistically summarized in Table 1.

[0125] Specifically, the tensile strength test method is as follows:

[0126] (1) For each composite current collector sample, 10 samples were measured and the minimum value was taken as the test result. The length direction of the sample was required to be parallel to the axis of the fixture and the sample was kept in a straight line.

[0127] (2) Tensile testing machine parameters: tensile speed is 200 mm / min, gauge length is 50 mm, and width is 15 mm.

[0128] (3) If any of the following conditions occur in the sample, the test result will be invalid: the sample is broken in the jaws of the fixture; improper operation; defects in the sample itself; errors or other reasons that cause data deviation.

[0129] Specifically, the test method for the change rate of tensile resistance is as follows:

[0130] (1) For each composite current collector sample, 10 samples were measured and the minimum value was taken as the test result. The length direction of the sample was required to be parallel to the axis of the fixture and the sample was kept in a straight line.

[0131] (2) Tensile testing machine parameters: tensile speed is 200 mm / min, gauge length is 50 mm, and width is 15 mm.

[0132] (3) Before stretching the sample, use a four-point probe to test the square resistance R 0; When stretched to 3% elongation, use a four-point probe to test the square resistance R , the change rate of tensile resistance is calculated, and the calculation formula is: (R-R0 / R0)×100%.

[0133] (4) If any of the following conditions occur in the specimen, the test result will be invalid: the specimen is broken in the jaws of the fixture; improper operation; defects in the specimen itself; errors or other reasons that cause data deviation.

[0134] Table 1

[0135]

[0136] Referring to Table 1, the test results of Examples 1 to 5 and Comparative Examples 1 to 2 show that when both sides of the polymer substrate layer have a first protrusion and a second protrusion group, the composite current collector corresponding to the former has better tensile strength and lower tensile resistance change rate than the composite current collector without the first protrusion and the second protrusion group or with only the first protrusion.

[0137] It can be seen from the test results of Example 1 and Comparative Example 3 that when a transition layer is provided between the conductive layer and the polymer substrate layer, the composite current collector corresponding to the former has better tensile strength and lower tensile resistance change rate than when no transition layer is provided.

[0138] From the test results of Examples 1 to 3, it can be seen that setting L1 / H1=AL2 / H2 and limiting A to the range of 0.6 to 1.0, compared with when A is not within the range, the composite current collector corresponding to the former has better tensile strength and lower tensile resistance change rate.

[0139] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A composite current collector, characterized in that: include: A polymer substrate layer having a plurality of first protrusions and a plurality of second protrusion groups on both sides of the polymer substrate layer in a thickness direction, wherein the first protrusion has a height H1 and a root outer diameter L1, and each second protrusion in the second protrusion group has a height H2 and a root outer diameter L2, where H1>5H2 and L1>4L2; A transition layer, wherein both sides of the polymer substrate layer have the transition layer in the thickness direction, each transition layer covers the plurality of first protrusions and the plurality of second protrusion groups on the same side, and the thickness of a single transition layer is D1; A conductive layer, wherein the two transition layers have a conductive layer on a side facing away from the polymer substrate layer, the conductive layer is made of a different material from the transition layer, and the density of the conductive layer is less than the density of the transition layer. The thickness of each conductive layer is D2, and H2: (D1 + D2) = 1: (4-20); In the first direction and the 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. 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.

2. The composite current collector according to claim 1, characterized in that In the thickness direction, the first protrusions on one side of the polymer base layer are arranged opposite to the second protrusions on the other side of the polymer base layer.

3. The composite current collector according to claim 1 or 2, wherein: 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.

4. The composite current collector according to claim 3, wherein 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, and D2 is 1000~2000 nm.

5. The composite current collector according to claim 4, 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.

6. A method for preparing a composite current collector according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: forming the first protrusions 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 form the transition layer and the conductive layer on both sides of the composite current collector precursor respectively and in sequence to obtain the composite current collector.

7. The method for preparing a composite current collector according to claim 6, wherein: The step of forming the first protrusions 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 protrusions and the second protrusion group on a surface of a first polymer substrate by a hot embossing technique; forming the first protrusions 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.

8. A secondary battery, characterized in that: The method comprises the composite current collector according to any one of claims 1 to 5.

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