A composite current collector and lithium-ion battery

Abstract

A composite current collector and lithium-ion battery are disclosed, comprising a metal conductive layer, within which elastomers are spaced apart, creating raised and recessed portions on the surface of the metal conductive layer. The outer surface of the elastomers also has an alloy coating layer. This design avoids repeated excessive stretching and breakage of the current collector during battery cycling, resulting in a composite current collector that balances high strength, high toughness, and low cost. This further improves the battery's energy density, enhances battery safety, and reduces battery costs.

Description

Technical Field

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

[0002] Lithium-ion batteries, due to their advantages such as small size, high energy density, good rate performance, and flexible design, have been widely used in portable electronic products, electric vehicles, and energy storage. In particular, with the increasing development and popularization of electric vehicles and lithium-ion battery electrochemical energy storage, the energy storage capacity and safety requirements of individual cells have placed increasingly stringent demands on the energy density and safety of lithium-ion batteries. Silicon and silicon-carbon anodes are prone to significant volume deformation when lithium ions are inserted, resulting in large lateral and longitudinal extension of the current collector. Furthermore, traditional polymer-based film tabs are difficult to weld and susceptible to electrolyte corrosion. Traditional lithium-ion battery current collectors are mostly single-metal layer current collectors or layered composite structures, which have many shortcomings. They cannot effectively suppress the longitudinal extension of the electrode sheet, and are prone to breakage due to excessive stretching of the current collector caused by lithium ion insertion and extraction. Polymer-based film tabs are difficult to weld and affect electron transport efficiency, are susceptible to electrolyte corrosion, and cannot effectively improve battery energy density by reducing the current collector thickness. It is difficult to simultaneously meet the requirements of high strength, high toughness, high energy density, and low cost.

[0003] Therefore, it is necessary to develop a new type of composite current collector as the negative electrode of lithium-ion batteries to improve battery energy density, enhance battery safety, and reduce battery costs. Utility Model Content

[0004] This invention addresses the problems existing in the prior art by proposing a new solution. By setting an elastomer with metal conductive layers wrapped on both sides of the elastomer, a composite current collector with raised and recessed parts on the surface is obtained. This solves the problem that when silicon and silicon-carbon, which are negative electrode active materials with high expansion rates, insert and extract lithium ions, the current collector undergoes large volume deformation, repeated excessive stretching, and large lateral and longitudinal extension, even fatigue damage and fracture. This further improves the energy density of lithium-ion batteries, enhances battery safety, and reduces battery production costs.

[0005] This utility model is achieved through the following technical solution: A composite current collector includes a metal conductive layer, in which an elastomer is disposed at intervals, forming protrusions and depressions on the surface of the metal conductive layer, and the outer surface of the elastomer also has an alloy coating layer.

[0006] The metal conductive layer described in this invention is not specifically limited, and those skilled in the art can select any one or more metal layers based on common knowledge in the field and actual needs; As an example, the metal conductive layer includes, but is not limited to, any one or more of conductive copper layers and conductive aluminum layers.

[0007] As a further preferred example, the conductive metal layer is a conductive copper layer; As one approach, adjacent elastomers are spaced at equal intervals, with the distance d between the edges of two adjacent elastomers being 1~20 mm.

[0008] As one embodiment, the longest distance 'a' of the elastomer on the large surface of the composite current collector is 1~20 mm, and the maximum thickness 'b' of the elastomer in the thickness direction of the composite current collector is 1~10 μm.

[0009] As one approach, the thickness c of the metal conductive layer in the composite current collector is 2~8 μm.

[0010] As a preferred embodiment, the ratio of the maximum thickness b of the elastomer in the thickness direction of the composite current collector to the thickness c of the metal conductive layer in the composite current collector is (1~1.3):1.

[0011] As a further preferred embodiment, adjacent elastomers are spaced at equal intervals, and the distance d between the edges of two adjacent elastomers is 3~7 mm.

[0012] As a further preferred embodiment, the longest distance 'a' of the elastomer on the large surface of the composite current collector is 5~15mm, and the maximum thickness 'b' of the elastomer in the thickness direction of the composite current collector is 1~6μm.

[0013] As a further preferred embodiment, the thickness c of the metal conductive layer in the composite current collector is 2~6 μm.

[0014] As a further preferred embodiment, the ratio of the maximum thickness b of the elastomer in the thickness direction of the composite current collector to the thickness c of the metal conductive layer in the composite current collector is 1:1.

[0015] As one embodiment, the shape of the elastomer is mirror-symmetrical about the metal conductive layer as the plane of symmetry, and has a circumferential axis of symmetry perpendicular to the plane of symmetry. The mirror-symmetrical structure surface of the elastomer has a circular arc transition.

[0016] As specific examples, one or more of the mirror cone and mirror frustum are shown.

[0017] As a further embodiment, the elastomer is shaped as a mirrored cone with a flattened double cone, mirror-symmetric with the metal conductive layer as the plane of symmetry, and has a circumferential axis of symmetry perpendicular to the plane of symmetry.

[0018] As a further embodiment, the elastomer is an elastomer with a Young's modulus of 1 to 100 MPa.

[0019] As a further embodiment, the elastomer is exemplary selected from one or more of the following: thermoplastic polyester elastomer (TPEE), silicone rubber (SR), nitrile rubber (NBR), thermoplastic polyurethane, ethylene vinyl acetate, polyether block polyamide, styrene-ethylene-butene-styrene block copolymer, ethylene octene copolymer, ethylene propylene diene monomer (EPDM) rubber, and natural rubber.

[0020] As a further embodiment, the alloy cladding layer includes one or more of the following: nickel-chromium alloy cladding layer, nickel-molybdenum alloy cladding layer, nickel-tungsten alloy cladding layer, titanium-tantalum alloy cladding layer, and titanium-zirconium alloy cladding layer. As a further option, the thickness of the alloy coating layer is 10~30 nm.

[0021] As a further improvement, a 10-20 mm wide unfilled area is reserved on each side of the composite current collector in the width direction.

[0022] As a further improvement, the spacing tolerance between the elastomers is ≤ ±0.2 mm.

[0023] This invention also provides a lithium-ion battery including the aforementioned composite current collector.

[0024] The features and beneficial effects of this utility model are as follows: By sandwiching a lattice-distributed elastomer within a metal conductive layer, a surface protrusion-recession topology is formed. This provides a buffer space for the volume expansion of the silicon-based anode while ensuring high conductivity through direct contact between the metal conductive layer and the recessed areas. Compared to traditional homogeneous metal conductive layers or full-layer polymer films, this design achieves synergistic optimization of stress and conductivity.

[0025] The elastomer employs a gradually curved surface structure such as a double cone. Its inclined surface decomposes the shear stress generated by volume expansion into normal components, improving stress buffering efficiency and avoiding localized stress concentration caused by right-angle structures. The composite current collector structure design endows it with high strength and high toughness, making it possible to significantly reduce the thickness of the metal conductive layer. Compared with traditional composite foils with a single polymer base film, this invention greatly reduces the amount of elastomer used, further reducing weight. Thinning the metal conductive layer and reducing the amount of elastomer directly reduces the weight of the current collector, thereby effectively improving the battery's mass energy density, enhancing battery safety, and reducing battery costs. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the internal structure of the composite current collector; Figure 2 This is a schematic diagram of the composite current collector surface.

[0028] Explanation of the reference numerals in the figure: Among them, 1. elastomer; 2. alloy coating layer; 3. metal conductive layer; 4. raised portion; 5. recessed portion; a) The longest distance between the elastomers on the large surface of the composite current collector; b) The maximum thickness of the elastomers in the thickness direction of the composite current collector; c) The thickness of the metal conductive layer in the composite current collector; d) The distance between the edges of two adjacent elastomers. Detailed Implementation

[0029] To facilitate understanding of this utility model, a more comprehensive description of this utility model will be provided below, along with embodiments of this utility model, but this does not limit the scope of this utility model.

[0030] This invention addresses the problems existing in the prior art by proposing a new solution. By setting an elastomer 1 and wrapping both sides of the elastomer 1 with a metal conductive layer 3, a composite current collector with surface protrusions 4 and depressions 5 is obtained. This solves the problem that when negative electrode active materials such as silicon and silicon-carbon with high expansion rates insert and extract lithium ions, the composite current collector undergoes large volume deformation, repeated excessive stretching and reduction, resulting in large lateral expansion and longitudinal extension of the negative electrode current collector, and even fatigue damage and fracture. This further improves the energy density of lithium-ion batteries, enhances battery safety, and reduces battery production costs.

[0031] This utility model is achieved through the following technical solution: A composite current collector includes a metal conductive layer 3, an elastomer 1 is disposed at intervals in the metal conductive layer 3, and protrusions 4 and depressions 5 are formed on the surface of the metal conductive layer 3. The outer surface of the elastomer 1 also has an alloy coating layer 2.

[0032] This invention relates to a composite current collector. By setting a metal conductive layer 3 and an elastomer 1 within the metal conductive layer 3, a composite current collector with surface protrusions 4 and recesses 5 is developed. Through the surface protrusion and recess structure features of the composite current collector and the elastic buffering and stress release effect of the elastomer 1, the problem of large volume deformation, microcracks on the surface of the composite current collector, large lateral and longitudinal stretching, and even fracture that occur when high expansion rate negative electrode active materials such as silicon and silicon-carbon insert and extract lithium ions is solved. This improves battery energy density, enhances battery safety, and reduces battery cost.

[0033] On the one hand, elastomer 1 is used, which has high elasticity and good tensile strength. It can buffer and reduce the longitudinal and transverse elongation of the composite current collector to a certain extent. Its elastic design allows the composite current collector to expand and contract appropriately with the insertion and extraction of lithium ions. This avoids the problem that when the negative electrode active material expands in volume, all the stress is absorbed by the surface metal conductive layer 3, resulting in surface microcracks, or even the composite current collector breaking due to repeated excessive stretching caused by the severe volume expansion of the negative electrode active material. It significantly reduces the net accumulated plastic strain in each cycle, greatly delays the process of the composite current collector becoming longer and thinner due to repeated stretching until it breaks, and significantly extends the fatigue life of the composite current collector.

[0034] On the other hand, the protruding and recessed design of the surface creates physical space for the expansion of the composite current collector during battery cycling. The expansion force of the negative electrode active material acts on the elastic body 1 of the protruding part 4, and part of the expansion energy is contained by this space, which significantly disperses and absorbs the expansion force that would originally act directly on the plane of the metal conductive layer 3, preventing the composite current collector from breaking due to excessive stretching caused by the expansion of the negative electrode active material. At the same time, the metal conductive layer 3 of the recessed part 5 forms a tight, low-resistance physical contact through pressing or other means during the manufacturing process, which improves the overall conductivity of the composite current collector. In addition, the compression of the protruding part 4 during battery cycling causes the metal conductive layer 3 on the surface of the elastic body 1 to deform. At this time, the protruding part 4 and the recessed part 5 on the surface provide deformation and extension space for the deformation of the metal conductive layer 3, avoiding the stretching and extension of the metal conductive layer 3, thereby extending the service life of the composite current collector.

[0035] Furthermore, the alloy coating layer 2 set between the elastomer 1 and the metal conductive layer 3 can further play the role of elastic buffering and corrosion resistance. The structural design of encapsulating the elastomer 1 inside the foil also solves the problem of electrolyte corrosion of the elastomer 1. The composite foil adopts the structural design of embedding the elastomer 1, which makes the composite current collector have high strength and high toughness. Therefore, the thickness of the metal conductive layer 3 can be appropriately reduced, thereby reducing costs. At the same time, compared with the traditional composite foil using a whole layer of base film as a buffer structure, this composite foil structure also reduces the amount of elastomer 1 used, further reducing costs.

[0036] In summary, this invention utilizes the excellent elasticity and resilience of the elastomer 1 combined with a three-dimensional protrusion-recession structure design to solve the problem that increasing the thickness of the metal conductive layer 3 improves strength but sacrifices conductivity, and that thinning the metal conductive layer 3 to increase flexibility easily leads to the breakage of the composite current collector. This design achieves a unique combination of a protruding portion 4 with the flexible buffering effect of the elastomer 1 and a recessed portion 5 with a high-strength, high-conductivity contact area, simultaneously improving excellent local flexibility and overall high conductivity and structural stability. It effectively suppresses the breakage of the composite current collector caused by the expansion of the negative electrode active material, avoiding safety hazards such as internal short circuits. This makes the use of silicon-based negative electrode active materials with high expansion rate and high capacity a more feasible option, which is one of the key ways to improve the energy density of lithium-ion batteries. The above solution effectively suppresses the longitudinal and lateral extension of the electrode sheet, reducing the risk of breakage due to excessive stretching of the composite current collector caused by lithium-ion insertion and extraction. Furthermore, by reducing the thickness of the composite current collector, it effectively improves the battery energy density at a lower cost, balancing the requirements of high strength, high toughness, high energy density, high safety, and low cost.

[0037] The metal conductive layer described in this invention is not specifically limited, and those skilled in the art can select any one or more metal layers based on common knowledge in the field and actual needs; As an example, the metal conductive layer 3 includes, but is not limited to, any one or more of a conductive copper layer and a conductive aluminum layer.

[0038] As a further preferred example, the metal conductive layer 3 is a conductive copper layer; This invention preferentially utilizes a conductive copper layer that meets the basic requirement of high conductivity while also achieving better material ductility and flexibility. This characteristic allows the conductive copper layer, when working in conjunction with the elastomer 1, to better adapt to the complex stress field generated by the repeated volume expansion and contraction of the negative electrode active material (such as silicon-based material) during battery cycling, significantly reducing the risk of microcracks or fractures in the metal conductive layer itself due to repeated stretching / compression. A tightly bonded, low-interface-resistance, and stable composite interface can be formed between the conductive copper layer and the alloy coating layer 2 disposed on the outer surface of the elastomer 1. This excellent interfacial bonding not only ensures excellent electrical connectivity within the composite current collector and guarantees overall conductivity but also significantly enhances the mechanical stability of the composite structure. Therefore, using a conductive copper layer can better achieve the goal of a high-strength, high-toughness, and long-life composite current collector.

[0039] As an example, adjacent elastic bodies 1 are spaced at equal intervals, and the distance d between the edges of two adjacent elastic bodies 1 is 1~20 mm.

[0040] As an example, the longest distance a of the elastomer 1 on the large surface of the composite current collector is 1~20 mm, and the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector is 1~10 μm.

[0041] As an example, the thickness c of the metal conductive layer 3 in the composite current collector is 2~8 μm.

[0042] As a further example, the ratio of the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector to the thickness c of the metal conductive layer 3 in the composite current collector is (1~1.3):1.

[0043] Based on the above features, this invention can further optimize the dimensions of the elastomer 1 individually or simultaneously. Specifically, it optimizes the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector, the longest distance a of the elastomer 1 on the large surface of the composite current collector, the distribution density and arrangement of the elastomer 1 in the composite current collector, and the ratio of the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector to the thickness c of the metal conductive layer 3 on both sides of the elastomer 1. This precise adjustment precisely regulates the unevenness of the protruding parts 4 and the recessed parts 5 of the composite current collector. This fine control further improves the overall extensibility and stress release distribution characteristics of the composite current collector, ensuring that the composite current collector has a reasonable and controllable expansion space and stress buffering path during charge-discharge cycles. Its core advantage lies in enabling the stress generated by the volume expansion of the negative electrode active material to be released and buffered more uniformly and effectively, thereby avoiding stress concentration caused by excessively high local protrusions or uneven distribution of the elastomer 1 in the composite current collector, as well as insufficient expansion space of the metal conductive layer 3 due to insufficient protrusion and recess degrees. On the one hand, by adjusting the size of the elastomer 1 itself, and by adjusting the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector and its longest distance a on the large surface of the composite current collector, the unevenness of the recessed portions 5 and the raised portions 4 formed on the surface of the composite current collector exhibits different states. The stress release paths from the expansion of the negative electrode active material are also different, and the area of ​​the metal conductive layer 3 covering the surface of the elastomer 1 is also different. At this time, the deformation space provided by the raised portions 4 to the composite current collector is also different. At the same time, optimizing the thickness of the metal conductive layer 3 can further adjust the unevenness of the composite current collector. In addition, it further improves the distribution of the elastomer 1 on the entire composite current collector, improves the buffering effect of the elastomer 1, and also avoids the problem of reduced conductivity caused by the excessive density of the elastomer 1 in the composite current collector, resulting in too little area of ​​the metal conductive layer 3 in the recessed portions 5 without the elastomer 1. Through the above-mentioned optimized design, the advantages of this composite current collector structure can be maximized. Under the premise of ensuring excellent conductivity and mechanical support, a composite foil with high tensile strength, high elongation at break, low sheet resistance, and high adhesion can be obtained, which significantly improves the long cycle life and safety reliability of the battery.

[0044] As a further preferred example, adjacent elastic bodies 1 are spaced at equal intervals, and the distance d between the edges of two adjacent elastic bodies 1 is 3~7 mm.

[0045] As a further preferred example, the longest distance a of the elastomer 1 on the large surface of the composite current collector is 5~15mm, and the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector is 1~6μm.

[0046] As a further preferred example, the thickness c of the metal conductive layer 3 in the composite current collector is 2~6 μm.

[0047] As a further preferred example, the ratio of the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector to the thickness c of the metal conductive layer 3 in the composite current collector is 1:1.

[0048] As an example, the shape of the elastomer 1 is mirror-symmetrical about the metal conductive layer 3 and has a circumferential axis of symmetry perpendicular to the plane of symmetry. The surface of the mirror-symmetrical structure of the elastomer 1 has a circular arc transition.

[0049] As some specific examples, the elastomer 1 is one or more of a mirror cone, a mirror frustum.

[0050] The elastomer 1, with the aforementioned design, allows the stress generated by the expansion of the negative electrode active material to be buffered and smoothly released by the rounded transition side structures of the mirrored cone and frustum of the elastomer 1. This stress buffering mechanism, inherent in the geometry itself, effectively avoids the stress concentration phenomenon that easily occurs in localized areas when using right-angled or abrupt edge structures, such as simple cubes, cylinders, frustums, and prisms. Stress concentration is a key factor inducing the initiation and propagation of localized microcracks in the current collector, which may lead to structural failure. By adopting this optimized geometric design, the expansion stress can be more evenly distributed and absorbed, significantly reducing the risk of localized microcracks in the current collector due to repeated stretching and contraction, thereby further improving the cyclic stability and reliability of the composite current collector.

[0051] As a further example, the shape of the elastomer 1 is a mirror cone, which is mirror symmetrical with the metal conductive layer 3 as the plane of symmetry, and has a circumferential axis of symmetry perpendicular to the plane of symmetry.

[0052] Specifically, the shape of the elastomer 1 can be complete or incomplete with its bottom surface in contact, such as a mirrored cone with a flattened double cone. The contact bottom surface of the double cone, i.e., the circumferential symmetry plane, is perpendicular to the large surface of the metal conductive layer 3. The progressive stress buffer formed by the side of the cone can gently buffer the stress caused by the volume expansion and contraction of the negative electrode active material. The shear stress generated by the volume expansion of the active material is decomposed by the inclined area on both sides formed by the two cones, avoiding the stress concentration problem caused by using other shapes of elastomer 1.

[0053] As a further example, the elastomer 1 is an elastomer with a Young's modulus of 1~100 MPa. As a further example, the elastomer 1 is selected from at least one of the following: thermoplastic polyester elastomer (TPEE), silicone rubber (SR), nitrile rubber (NBR), thermoplastic polyurethane, ethylene vinyl acetate, polyether block polyamide, styrene-ethylene-butene-styrene block copolymer, ethylene octene copolymer, EPDM rubber, and natural rubber, with a Young's modulus of 1 to 100 MPa.

[0054] As a further example, the alloy cladding layer 2 includes one or more of the following: nickel-chromium alloy layer, nickel-molybdenum alloy layer, nickel-tungsten alloy layer, titanium-tantalum alloy layer, and titanium-zirconium alloy layer.

[0055] As a further preferred example, the alloy coating layer 2 is a nickel-chromium alloy layer.

[0056] As a further example, the thickness of the alloy coating layer 2 is 10~30nm.

[0057] Since the alloy coating layer 2 set between the elastomer 1 and the metal conductive layer 3 plays a buffering role, on the one hand, the reasonable design of the thickness of the alloy coating layer 2 overcomes the problem that if the thickness of the alloy coating layer 2 is too high, the rigidity of the alloy coating layer 2 will not be able to resist the expansion and compression of the negative electrode active material, and the elasticity of the elastomer 1 will be lost, thus failing to buffer the expansion pressure of the negative electrode active material. On the other hand, it also overcomes the problem that if the thickness of the alloy coating layer 2 is too low, it will not be able to effectively play a buffering role.

[0058] As a further example, the composite current collector has an unfilled area of ​​10-20 mm on each side in the width direction.

[0059] This design simplifies the welding of polymer-based film tabs and makes them less susceptible to electrolyte corrosion.

[0060] As a further example, the spacing tolerance between the elastomers 1 is ≤ ±0.2 mm.

[0061] This invention also provides a lithium-ion battery including the aforementioned composite current collector.

[0062] As a specific example of the implementation of this utility model, detailed examples are provided below: Example 1:

[0063] (1) Material preparation: Polybutylene terephthalate (PBT) and polytetrahydrofuran ether diol (PTMG) raw materials with a mass ratio of 1:2, and epoxy chain extender ADR-4368 with a dosage of 0.5% of the total mass of polyethylene terephthalate and polybutylene succinate; (2) Preparation of elastomer 1: A high-precision mold with a double cone with a flattened upper and lower cone is used. The injection pressure is 80MPa, the temperature is 250℃, and the holding time is 20s. The raw materials in (1) are mixed evenly and then injection molded to obtain an elastomer 1 with a flattened upper and lower cone. The maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector is 3μm, and the longest distance a on the large surface of the composite current collector is 10mm. After molding, the surface of the elastomer 1 is cleaned to remove surface oil, impurities, etc., in order to enhance the adhesion of the subsequent coating. (3) Preparation of alloy coating layer 2: Turn on the radio frequency magnetron sputtering equipment, set the sputtering power to 200 W, the argon flow rate to 20 sccm, and the working pressure to 0.3 Pa. Select a nickel-chromium alloy target with a purity of 99.9% or higher, and perform magnetron sputtering on the surface of the elastomer 1. The sputtering time is 30 min, so that the nickel-chromium alloy is uniformly deposited on the surface of the elastomer 1 to form an alloy coating layer 2 with a thickness of 20 nm. (4) Preparation of the conductive metal layer 3: The elastomer 1 after the nickel-chromium alloy layer 2 is plated is placed in a specific electroplating mold with a conical grinding cone. The mold makes the spacing d between adjacent elastomers 1 (i.e., the distance between the edges of two adjacent elastomers) 5 mm, and ensures that the upper surface of the elastomer 1 is completely exposed. The current density is set to 3 A / dm. 2 At a temperature of 30 ℃ and a pH value of 2.0, a conductive copper layer with a thickness of 1.5 μm is deposited on the upper surface of elastomer 1. The above structure is then taken out, flipped 180 degrees and placed into a mold, and electroplating is performed again to deposit a conductive copper layer of the same thickness on the other side of elastomer 1. The upper and lower conductive copper layers form a metal conductive layer with a thickness of 3 μm, thus completing the preparation of the composite current collector.

[0064] Example 2: Unlike Example 1, the longest distance a of the elastomer 1 on the large surface of the composite current collector is 5mm, otherwise it is the same as Example 1.

[0065] Example 3: Unlike Example 1, the longest distance a of the elastomer 1 on the large surface of the composite current collector is 15mm, otherwise it is the same as Example 1.

[0066] Example 4: Unlike Example 1, the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector is 5 μm, otherwise it is the same as Example 1.

[0067] Example 5: Unlike Example 1, the interval d between adjacent elastomers 1 (i.e., the distance between the edges of two adjacent elastomers) is 2 mm, otherwise it is the same as Example 1.

[0068] Example 6: Unlike Example 1, the interval d between adjacent elastomers 1 (i.e., the distance between the edges of two adjacent elastomers) is 10 mm, otherwise it is the same as Example 1.

[0069] Example 7: Unlike Example 1, the sputtering time in S3 is 20 min and the thickness of the nickel-chromium alloy layer 2 is 10 nm. Everything else is the same as in Example 1.

[0070] Example 8: Unlike Example 1, the sputtering time in S3 is 40 min and the thickness of the nickel-chromium alloy layer 2 is 30 nm. Otherwise, it is the same as Example 1.

[0071] Example 9: Unlike Example 1, a conductive copper layer with a thickness of 3 μm is deposited on each side of the upper surface of the elastomer 1, and the thickness of the metal conductive layer is 6 μm. Everything else is the same as in Example 1.

[0072] Example 10: The elastomer 1 in the composite current collector has a cylindrical structure. The maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector is 3 μm, and the longest distance a on the large surface of the composite current collector is 10 mm. Other aspects are the same as in Example 1.

[0073] Example 11: Unlike Example 1, the interval d of the elastomer 1 (i.e., the distance between the edges of two adjacent elastomers) is 20 mm, otherwise it is the same as Example 1.

[0074] Example 12: The difference from Example 1 is that the thickness of the nickel-chromium alloy layer is 100 nm, otherwise it is the same as Example 1.

[0075] Comparative Example 1: The composite current collector has a layered sandwich structure. The composite current collector consists of two copper foil layers of uniform thickness on both sides and a base film layer of uniform thickness, with a total thickness of 6.5 μm. The base film layer is made of PET and has a thickness of 4.5 μm, while the copper foil layers on both sides each have a thickness of 1 μm.

[0076] Comparative Example 2: Unlike Example 1, after copper plating, the surface of the composite current collector is flat and does not have any protruding or recessed structures. Its overall thickness is 8 μm.

[0077] Test method: Tensile strength test: Refer to GB / T 5230-2020 and conduct the test using a vertical tensile testing machine.

[0078] Elongation at break test: The test was conducted according to GB / T 5230-2020 using a vertical tensile testing machine.

[0079] Sheet resistance test: Performed in accordance with GB / T 17473.3-2008, using a four-probe sheet resistance meter.

[0080] Adhesion test: The prepared composite current collector was adhered to the surface using 3M tape, and the peel force data was obtained by testing with a vertical tensile tester.

[0081]

[0082] This invention optimizes the structure of the composite foil to obtain a composite foil with high tensile strength, high elongation at break, low sheet resistance, and high adhesion.

[0083] Based on Examples 1-12 and Comparative Examples 1-2, compared to layered composite foils and composite current collectors with flat surfaces lacking protrusions and depressions, the composite current collector prepared by this invention exhibits moderate elasticity, appropriate protrusions and depressions, and the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector and the thickness c of the metal conductive layer 3 are within a reasonable range. This effectively improves tensile strength, elongation at break, and adhesion, while simultaneously reducing sheet resistance and enhancing the conductivity of the current collector. At this point, the tensile strength MD ≥ 200 MPa, tensile strength TD ≥ 150 MPa, elongation at break MD ≥ 50%, elongation at break TD ≥ 24%, sheet resistance ≤ 18 mΩ, and adhesion ≥ 3.3 N.

[0084] Both excessively thick and excessively thin alloy coating 2 are detrimental to obtaining composite current collectors with good ductility. A comparison of Examples 1 and 7, 8, and 12 shows that an excessively thick nickel-chromium alloy layer 2 makes the coating more brittle and hard, negatively impacting tensile strength, elongation at break, and adhesion. In this case, although tensile strength increases, elongation at break initially increases, then decreases due to increased brittleness. The elastomer 1 is constrained by the alloy coating layer 2, resulting in low elasticity and a relatively high likelihood of fracture. Furthermore, due to the excessive thickness of the alloy layer 2, sheet resistance initially decreases and then increases with increasing alloy coating thickness, while adhesion initially increases and then decreases.

[0085] Compared with Examples 1 and Examples 2-6, 9, and 11, this utility model improves tensile strength, elongation at break, and adhesion by simultaneously optimizing the shape and size of the elastomer 1, specifically the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector, the longest distance a of the elastomer 1 on the large surface of the composite current collector, the distribution density and arrangement of the elastomer 1 in the composite current collector, and the thickness c of the metal conductive layer 3. At the same time, it reduces sheet resistance and improves the conductivity of the current collector.

[0086] Specifically, comparing Examples 1, 2, 3, 4, and 9 with Examples 5, 6, and 11, when the following conditions are met simultaneously: the elastomers are evenly distributed at equal intervals in the composite current collector; the distance d between the edges of two adjacent elastomers 1 is 3~7 mm; the longest distance a of the elastomers 1 on the large surface of the composite current collector is 5~15 mm; the maximum thickness b of the elastomers 1 in the thickness direction of the composite current collector is 1~6 mm; and the thickness c of the conductive metal layer 3 in the composite current collector is 2~6 mm, then the following conditions can be met simultaneously: tensile strength MD≥219MPa, tensile strength TD≥175 MPa, elongation at break MD≥51%, elongation at break TD≥27%, sheet resistance ≤15.5 mΩ, and adhesion ≥4.9 N.

[0087] As can be seen from Examples 2-4 and Example 1, by optimizing the longest distance a of the elastomer 1 on the large surface of the composite current collector and the maximum thickness b in the thickness direction of the composite current collector within a certain range, the degree of protrusion and depression of the composite current collector and the distribution area of ​​the elastomer 1 in the composite current collector can be improved. A composite current collector with high tensile strength, high elongation at break and high adhesion can be obtained, which can better resist the volume expansion of the negative electrode active material.

[0088] As can be seen from Examples 1 and 5-6, 11, a longer spacing between the elastomers 1 increases tensile strength and reduces elongation at break and sheet resistance. When the spacing reaches 20 mm, it has a significant impact on tensile strength, elongation at break, and sheet resistance. Therefore, balancing the spacing between the elastomers 1 can further obtain a composite current collector with higher tensile strength, higher elongation at break, and lower sheet resistance.

[0089] As can be seen from Examples 1, 9, and Comparative Example 2, further optimization of the thickness of the metal conductive layer 3 can further obtain a composite current collector with better ductility. This improves the relationship between the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector and the thickness of the metal conductive layer 3 in the composite current collector. By adjusting the overall protrusion / recession degree of the composite current collector, the ductility of the metal conductive layer 3 is affected. Furthermore, the thickness difference also affects the elastic buffering effect of the elastomer. This avoids the problem of low protrusion / recession degree, reduced ductility, and decreased elasticity when the maximum thickness b of the elastomer 1 in the thickness direction of the composite current collector is small and the thickness c of the metal conductive layer 3 in the composite current collector is large. It also avoids the problem of excessively thick metal conductive layer 3, excessively high strength, insensitivity to volumetric deformation of battery active materials, poor buffering effect of the elastomer, and poor battery cycle performance. A certain matching relationship between the two (b and c) allows for better utilization of the elastic effect of the elastomer 1. Even when a composite current collector with an elastomer, as in Comparative Example 2, has a smooth surface without protrusion / recession structures, the technical effects of this invention cannot be achieved.

[0090] A comparison of Examples 1 and 10 shows that when the shape of the elastomer 1 is a double cone with its bottom surface in contact, and the contact bottom surface of the double cone, i.e. the circumferential symmetry plane, is perpendicular to the large surface of the metal conductive layer 3, compared to a cylinder, the progressive stress buffer formed by the side surface of the cone can gently buffer the stress caused by the volume expansion and contraction of the negative electrode active material. The shear stress generated by the volume expansion of the active material is decomposed by the inclined surface area on both sides formed by the two cones, avoiding the stress concentration problem caused by using other shaped elastomers 1. At this time, the tensile strength is high, the elongation at break is high, and the sheet resistance is low.

[0091] Examples 1-12 and Comparative Examples 1-2 were prepared as lithium-rich manganese-based positive electrode-silicon-carbon negative electrode pouch cells. Charge-discharge cycle tests were conducted at 25°C and 0.33C. The results are shown in Table 2.

[0092] Table 2

[0093] As shown in Table 2, this composite current collector has a higher capacity retention rate compared to layered composite foil. The thickness of the nickel-chromium alloy, the longest distance 'a' of the elastomer 1 on the large surface of the composite current collector, the maximum thickness 'b' of the composite current collector in the thickness direction, and the spacing between the elastomers 1 all have a significant impact on the cell's cycle performance due to factors such as the strength of the elastomer 1 and the degree of protrusion and indentation of the composite current collector.

[0094] In summary, this utility model addresses the problems existing in the prior art by proposing a new solution. By setting an elastomer 1 and metal conductive layers 3 on both sides of the elastomer 1, a composite current collector with surface protrusions 4 and depressions 5 is obtained. This solves the problem that when high-expansion-rate negative electrode active materials such as silicon and silicon-carbon intercalate and deintercalate lithium ions, the composite current collector undergoes large volume deformation, repeated excessive stretching and reduction, leading to large lateral and longitudinal extension of the negative electrode current collector, and even fatigue damage and fracture. This further improves the energy density of lithium-ion batteries, enhances battery safety, and reduces battery production costs, which is of great significance for the application of lithium-ion batteries.

[0095] It should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A composite current collector, characterized in that, It includes a metal conductive layer (3), an elastomer (1) is provided in the metal conductive layer (3) at intervals, so that the surface of the metal conductive layer (3) forms a protrusion (4) and a depression (5), and the outer surface of the elastomer (1) also has an alloy coating layer (2).

2. The composite current collector according to claim 1, characterized in that, The adjacent elastic bodies (1) are spaced at equal intervals, and the distance d between the edges of two adjacent elastic bodies (1) is 1~20 mm.

3. The composite current collector according to claim 1, characterized in that, The longest distance a of the elastomer (1) on the large surface of the composite current collector is 1~20 mm, and the maximum thickness b of the elastomer (1) in the thickness direction of the composite current collector is 1~10 μm.

4. The composite current collector according to claim 1, characterized in that, The thickness c of the metallic conductive layer in the composite current collector is 2~8 μm.

5. The composite current collector according to claim 1, characterized in that, The ratio of the maximum thickness b of the elastomer (1) in the thickness direction of the composite current collector to the thickness c of the metal conductive layer (3) in the composite current collector is (1~1.3):

1.

6. The composite current collector according to claim 1, characterized in that, The adjacent elastic bodies (1) are spaced at equal intervals, and the distance d between the edges of two adjacent elastic bodies (1) is 3~7 mm.

7. The composite current collector according to claim 1, characterized in that, The longest distance a of the elastomer (1) on the large surface of the composite current collector is 5~15 mm, and the maximum thickness b of the elastomer (1) in the thickness direction of the composite current collector is 1~6 μm.

8. The composite current collector according to claim 1, characterized in that, The thickness c of the metal conductive layer (3) in the composite current collector is 2~6 μm.

9. The composite current collector according to claim 1, characterized in that, The ratio of the maximum thickness b of the elastomer (1) in the thickness direction of the composite current collector to the thickness c of the metal conductive layer (3) in the composite current collector is 1:

1.

10. The composite current collector according to claim 1, characterized in that, The conductive metal layer (3) is selected from either a conductive copper layer or a conductive aluminum layer.

11. The composite current collector according to claim 1, characterized in that, The shape of the elastomer (1) is mirror-symmetrical with the metal conductive layer (3) as the plane of symmetry, and has a circumferential axis of symmetry perpendicular to the plane of symmetry. The surface of the mirror-symmetrical structure of the elastomer (1) has a circular arc transition.

12. The composite current collector according to claim 1, characterized in that, The elastic body (1) is one of a mirror cone or a mirror frustum.

13. The composite current collector according to claim 1, characterized in that, The shape of the elastomer (1) is a mirror cone with a flattened double cone, which is mirror symmetrical with the metal conductive layer (3) as the symmetry plane and has a circumferential symmetry axis perpendicular to the symmetry plane.

14. The composite current collector according to claim 1, characterized in that, The elastomer (1) is an elastomer (1) with a Young's modulus of 1~100 MPa.

15. The composite current collector according to claim 1, characterized in that, The elastomer is selected from one of the following: thermoplastic polyester elastomer (TPEE), silicone rubber (SR), nitrile rubber (NBR), thermoplastic polyurethane, ethylene vinyl acetate, polyether block polyamide, styrene-ethylene-butene-styrene block copolymer, ethylene octene copolymer, EPDM rubber, and natural rubber, with a Young's modulus of 1~100 MPa.

16. The composite current collector according to claim 1, characterized in that, The alloy cladding layer (2) includes one of the following: nickel-chromium alloy cladding layer, nickel-molybdenum alloy cladding layer, nickel-tungsten alloy cladding layer, titanium-tantalum alloy cladding layer, and titanium-zirconium alloy cladding layer.

17. The composite current collector according to claim 1, characterized in that, The alloy coating layer (2) is a nickel-chromium alloy layer.

18. The composite current collector according to claim 1, characterized in that, The thickness of the alloy coating layer (2) is 10~30 nm.

19. A lithium-ion battery comprising the composite current collector according to any one of claims 1 to 18.

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