Composite current collector and manufacturing method therefor, electrode sheet and secondary battery

Abstract

A composite current collector and a manufacturing method therefor, an electrode sheet and a secondary battery. The composite current collector comprises: a base film; at least one transition layer provided on the surface of at least one side of the base film, the transition layer being made of any one or a combination of at least two of metal niobium, metal tantalum, niobium alloy, tantalum alloy, a niobium-based compound or a tantalum-based compound; and a conductive layer provided on the surface of the side of the at least one transition layer relatively away from the base film. The transition layer having good compactness, stability and corrosion resistance is arranged between the base film and the conductive layer, on one hand, the charging and discharging cycle performance of batteries based on the composite current collector can be improved, and on the other hand, the safety performance of the composite current collector is effectively improved, thus improving the safety performance of batteries.

Description

Composite current collector and preparation method thereof, electrode sheet and secondary battery Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a composite current collector and a preparation method thereof, an electrode sheet and a secondary battery. Background Art

[0002] At present, composite current collectors based on polymer films have received widespread attention and application in the new energy industry. The preparation of this composite current collector usually adopts the method of physical vapor deposition (PVD) to deposit a layer of metal on a polymer film (such as polyester, polyolefin, etc.), thereby preparing a composite current collector with good conductivity. Compared with traditional current collectors, composite current collectors based on polymer films have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when used in the battery.

[0003] The current composite current collectors have the following main problems: ① The adhesion between the polymer base film and the metal layer in the composite current collector is low, which is easy to separate during the battery charge and discharge cycle, resulting in poor battery cycle performance; ② The composite current collector mainly relies on the insulation and flame retardant properties of the intermediate layer, namely the polymer film layer, to improve the safety of the battery. However, although this improves the battery safety performance, the improvement is limited.

[0004] Therefore, in order to further improve the charge-discharge cycle and safety performance of composite current collector-based batteries, it is necessary to develop a new composite current collector to promote the application and promotion of composite current collectors in secondary batteries.

[0005] Public content

[0006] In view of the shortcomings of the existing technology, the purpose of this application is to provide a composite current collector and its preparation method, electrode sheet and secondary battery. This application adds a transition layer with good density, stability and corrosion resistance between the base film and the conductive layer, which can effectively bridge the base film and the conductive layer, improve the adhesion between the two, reduce the formation of holes in the conductive layer, resist the erosion of the electrolyte and high temperature environment, and through Li +The electrochemical cycle causes the structure of the transition layer to transform from amorphous to crystalline, maintaining its cubic framework and nanostructure of the grains during the entire lithiation / delithiation process, thereby having excellent reversible capacity and cycle stability. The improvement in adhesion, the reduction in pore defects, and the improvement in corrosion resistance jointly improve the charge-discharge cycle performance of the battery prepared based on the composite current collector. On the other hand, the provision of the transition layer avoids the formation of a closed loop by the conduction of the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery. The present application can also regulate the crack growth and deformation range of the composite current collector by setting the transition layer material and structure, thereby further improving the safety performance of the composite current collector.

[0007] To achieve this goal, this application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a composite current collector, comprising:

[0009] basement membrane;

[0010] At least one transition layer provided on at least one side of the base film, wherein the material of the transition layer is any one of metallic niobium, metallic tantalum, niobium alloy, tantalum alloy, niobium-based compound or tantalum-based compound, or a combination of at least two thereof;

[0011] A conductive layer is provided on a surface of the at least one transition layer on a side relatively far away from the base film.

[0012] The transition layer described in the present application may be a single-layer or multi-layer structure; the crack growth deformation interval r(%) of the composite current collector is (b, e), wherein 0<b-2≤10, preferably, 0<b-2≤2, eb>15, preferably, eb>24, wherein b is the percentage value of the strain corresponding to the deformation starting point of crack nucleation of the composite current collector, and e is the percentage value of the strain corresponding to the deformation end point of complete fracture of the composite current collector; the crack growth deformation interval refers to the range of values ​​of the strain r(%) within the interval from the deformation starting point of crack nucleation of the composite current collector to the deformation end point of complete fracture of the composite current collector in the stress-strain curve.

[0013] In the present application, the crack growth deformation range of the composite current collector refers to the strain range including the three stages of crack nucleation zone, crack propagation zone, and complete fracture zone.

[0014] The present invention adds a transition layer with good density, stability and corrosion resistance between the base film and the conductive layer, which can effectively bridge the base film and the conductive layer and improve the adhesion between the two. The transition layer has dielectric properties, which can reduce the formation of holes in the process of preparing the conductive layer. The transition layer can also resist the erosion of the electrolyte and high temperature environment, and through Li +The electrochemical cycle causes its structure to transform from amorphous to crystalline, and maintains its cubic framework and its nanostructure during the entire lithiation / delithiation process, thus having excellent reversible capacity and cycle stability. The improvement of adhesion, the reduction of pore defects and the improvement of corrosion resistance jointly improve the charge and discharge cycle performance of the battery prepared based on the composite current collector; on the other hand, in the needle penetration test of battery safety testing, the steel needle applies a force in the Z direction to the composite current collector, causing microcracks in the transition layer, which quickly spreads and causes large-scale fractures. Due to the strong adhesion between the transition layer and the conductive layer, the conductive layer will undergo similar fractures along with the transition layer, thereby separating the conductive layer from the steel needle, avoiding the formation of a closed circuit by the positive and negative current collectors and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery. The transition layer described in the present application may be a single-layer or multi-layer structure. By adding the transition layer, the layers of the composite current collector have ductile heterogeneous properties. Under the action of external mechanical force, the transition layer first produces cracks and diffuses to the surrounding areas to produce more microcracks, forming multi-layer transition layers that diffuse microcracks and / or cracks that diffuse from the cracks between the transition layers to the metal layer, thereby regulating the crack growth and deformation range of the composite current collector, thereby cutting off the path between electrons, effectively improving the safety performance of the composite current collector, and promoting the promotion and application of the composite current collector.

[0015] Preferably, the transition layer is a single-layer or multi-layer structure, and the material of the transition layer is selected from at least one of metal niobium, metal tantalum, metal niobium alloy, metal tantalum alloy, metal niobium compound and metal tantalum compound.

[0016] Preferably, the material of the transition layer is at least one selected from the group consisting of metallic niobium, metallic tantalum, metallic niobium alloys, metallic tantalum alloys, metallic niobium compounds, and metallic tantalum compounds.

[0017] Preferably, the number of the transition layer is 1.

[0018] Preferably, the materials of the adjacent transition layers are the same or different. When the materials of the adjacent transition layers are the same, the adjacent transition layers can be regarded as one layer.

[0019] Preferably, the number of layers of the transition layer is 2 or more, preferably 3 to 5 layers.

[0020] As a preferred technical solution of the composite current collector described in this application, the transition layer meets at least one of the following conditions:

[0021] (1) The hardness of the multiple transition layers is the same;

[0022] (2) The hardness of at least one transition layer among the multiple transition layers is different from that of the other transition layers.

[0023] The test method of the hardness is not limited in this application, but a consistent method should be adopted for the hardness measurement of the multi-layer transition layer.

[0024] Preferably, among the transition layers, the transition layer with the highest hardness is transition layer A, and the transition layer with the lowest hardness is transition layer B, the transition layer B is in contact with the conductive layer, and / or the transition layer A is in contact with the polymer base film, and / or the transition layer A is closer to the polymer base film than the transition layer B.

[0025] In this preferred technical solution, the transition layer A with the highest hardness is in contact with the polymer film and / or is closer to the polymer base film than the transition layer B. In the needle penetration test of the battery safety test, the steel needle applies a force in the Z direction to the composite current collector. The transition layer A in the transition layer is hard and brittle, so cracks can be generated quickly. Since the transition layer B with the lowest hardness is in contact with the conductive layer, the transition layer B will slowly break along with the brittle layer, thereby increasing the length of the yield period, separating the conductive layer from the steel needle, avoiding the brittle fracture of the conductive layer, and the positive and negative current collectors are connected to form a closed circuit and the resulting thermal runaway of the battery, thereby improving the safety performance of the battery.

[0026] Preferably, the total thickness of the transition layer does not exceed 65% of the thickness of the conductive layer, preferably 20%-65%.

[0027] Preferably, the thickness ratio of at least one group of adjacent transition layers is (0.0001-10000):1.

[0028] As a preferred technical solution of the present application, the material of the base film is a polymer, and the polymer is any one or a combination of at least two of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS) or polyimide (PI).

[0029] Preferably, the base film has a thickness of 1 μm-10 μm, for example, 1 μm, 3 μm, 5 μm, 7 μm or 9 μm.

[0030] In this application, taking into account the application requirements of the composite current collector and the difficulty and cost of the preparation process, the thickness of the base film is limited to 1μm-10μm, which can meet the above requirements at the same time.

[0031] As a preferred technical solution of the present application, the niobium alloy is any one of niobium-germanium alloy, niobium-tin alloy, niobium-zirconium alloy, niobium-hafnium alloy, niobium-nickel alloy, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy or lithium niobate alloy, or a combination of at least two thereof.

[0032] Preferably, the tantalum alloy is any one of tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy or cobalt-tantalum-zirconium alloy, or a combination of at least two thereof.

[0033] Preferably, the niobium-based compound and the tantalum-based compound are independently any one of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides or tellurides, or a combination of at least two thereof.

[0034] Preferably, the oxide is any one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide or tantalum pentoxide, or a combination of at least two thereof.

[0035] Preferably, the nitride is niobium nitride and / or tantalum nitride.

[0036] Preferably, the carbide is niobium carbide and / or tantalum carbide.

[0037] Preferably, the sulfide is niobium disulfide and / or tantalum disulfide

[0038] Preferably, the fluoride is niobium pentafluoride and / or tantalum pentafluoride

[0039] Preferably, the silicide is niobium disilicide and / or tantalum disilicide.

[0040] Preferably, the phosphide is niobium phosphide and / or tantalum phosphide.

[0041] Preferably, the selenide is niobium diselenide and / or tantalum diselenide.

[0042] Preferably, the telluride is niobium ditelluride and / or tantalum ditelluride.

[0043] Preferably, the material of the transition layer is any one of metallic niobium, metallic tantalum, niobium pentoxide, tantalum pentoxide, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy, lithium niobate alloy, tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy, cobalt-tantalum-zirconium alloy, niobium nitride, tantalum nitride, niobium carbide or tantalum carbide, or a combination of at least two of them.

[0044] Preferably, transition layers are provided on both surfaces of the base film.

[0045] Preferably, the thickness of the transition layer on one side is greater than or equal to 5 nm, for example, it can be 5 nm, 10 nm, 30 nm, 50 nm, 70 nm, 90 nm, 120 nm, 150 nm or 200 nm, and is preferably 10 nm-100 nm.

[0046] Preferably, the thickness of the transition layer on one side is less than or equal to 65% of the thickness of the conductive layer.

[0047] Preferably, the thickness of the transition layer on one side is 10 nm-1300 nm.

[0048] Preferably, the composite current collector described in the present application comprises a transition layer on one side. Preferably, the thickness of the transition layer on one side is 10 nm-100 nm.

[0049] Preferably, the composite current collector described in the present application comprises multiple transition layers on one side, and the thickness of the transition layers on one side is 100 nm-1300 nm.

[0050] In the present application, if the thickness of the single-sided transition layer is too small, the improvement in battery safety performance will not be obvious; if the thickness of the single-sided transition layer is too large, the cycle and safety performance of the battery will not be further improved.

[0051] As a preferred technical solution of the present application, the material of the conductive layer is metal, and the metal includes any one of elemental aluminum, elemental copper, elemental gold, elemental silver, elemental nickel, elemental zinc, aluminum alloy, copper alloy, gold alloy, silver alloy, nickel alloy or zinc alloy, or a combination of at least two of them.

[0052] Preferably, the thickness of the conductive layer on one side is 500 nm-2000 nm, for example, 500 nm, 1000 nm, 1500 nm or 2000 nm, etc., preferably 600 nm-1200 nm, preferably 800 nm-1200 nm, preferably 600 nm-1000 nm.

[0053] In this application, if the thickness of the single-sided conductive layer is too small, the conductivity is poor, and if the thickness of the single-sided conductive layer is too large, it is not conducive to improving the energy density of the battery. A thickness of 600nm-1200nm can improve both conductivity and energy density.

[0054] As a preferred technical solution of the present application, a protective layer is provided on the surface of the conductive layer on a side relatively far away from the base film.

[0055] In the present application, the protective layer is provided to prevent the conductive layer from being chemically corroded or physically damaged.

[0056] Preferably, the material of the protective layer includes any one of metallic nickel, metallic chromium, nickel-chromium alloy, nickel alloy, copper alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, graphene or graphene oxide, or a combination of at least two thereof.

[0057] It should be noted that the materials of the protective layers on both sides of the current collector may be the same or different.

[0058] Preferably, the thickness of the protective layer on one side is 10 nm-100 nm, for example, 10 nm, 30 nm, 50 nm, 70 nm or 90 nm, etc., preferably 20 nm-80 nm.

[0059] It should be noted that the thickness of the protective layers on both sides of the current collector may be the same or different.

[0060] Preferably, the thickness of the protective layer on one side is less than one tenth of the thickness of the conductive layer on one side.

[0061] In the present application, if the thickness of the protective layer is too small, it is difficult to prevent the conductive layer from being chemically corroded or physically damaged. If the thickness of the protective layer is too large, there will be no further improvement and the overall thickness of the film will increase.

[0062] In a second aspect, the present application provides a method for preparing the composite current collector as described in the first aspect, the preparation method comprising the following steps:

[0063] At least one transition layer is formed on at least one surface of the base film, and then a conductive layer is formed on a surface of the at least one transition layer relatively away from the base film to obtain the composite current collector. Taking into account the application requirements of the composite current collector, while taking into account the difficulty and cost of the preparation process, the preferred thickness of the polymer base film is 1 μm to 10 μm, for example, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 9 μm or 10 μm.

[0064] It should be noted that the present application does not limit the preparation method of the base film. For example, a melt-extrusion-biaxial stretching method can be used.

[0065] As a preferred technical solution of the present application, the method for preparing the transition layer includes magnetron sputtering.

[0066] Preferably, the method for preparing the conductive layer includes any one of evaporation, magnetron sputtering, chemical plating, electroplating or chemical vapor deposition (CVD), or a combination of at least two thereof.

[0067] Preferably, after depositing the conductive layer, a protective layer is prepared on the surface of the conductive layer that is relatively far away from the base film.

[0068] Preferably, the protective layer is prepared by any one of physical vapor deposition, chemical vapor deposition, in-situ forming or coating, or a combination of at least two of them.

[0069] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0070] (1) preparing a polymer base film with a thickness of 1 μm-10 μm;

[0071] (2) a transition layer with a thickness of 10 nm to 100 nm is deposited on both sides of the polymer base film to obtain a composite film with a transition layer on the surface. The specific process conditions are: power of 5 kW to 20 kW (for example, 5 kW, 10 kW, 15 kW or 20 kW, etc.), argon flow rate of 50 mL / min to 60 mL / min (for example, 50 mL / min, 52 mL / min, 54 mL / min, 56 mL / min, 58 mL / min or 60 mL / min, etc.), vacuum degree of coating of 0.08 Pa to 0.1 Pa (for example, 0.08 Pa, 0.09 Pa or 0.1 Pa, etc.), coating time of 1 s to 20 s (1 s, 5 s, 10 s, 15 s or 20 s, etc.), cooling temperature of main roller during coating of 0 ° C to 20 ° C (0 ° C, 5 ° C, 10 ° C, 15 ° C or 20 ° C, etc.);

[0072] (3) depositing a conductive layer with a thickness of 500 nm to 2000 nm on each side of the composite film to obtain a composite film containing a transition layer and a conductive layer;

[0073] (4) Preparing a protective layer: placing the composite film containing the transition layer and the conductive layer in a raw material solution of the protective layer for immersion treatment, and then washing and drying to obtain the composite current collector.

[0074] In a third aspect, the present application provides an electrode sheet, comprising the composite current collector as described in the first aspect.

[0075] In a fourth aspect, the present application provides a secondary battery, comprising the electrode sheet as described in the third aspect.

[0076] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0077] Compared with the prior art, this application has the following beneficial effects:

[0078] The present invention adds a transition layer with good density, stability and corrosion resistance between the base film and the conductive layer, which can effectively bridge the base film and the conductive layer and improve the adhesion between the two. The transition layer has dielectric properties, which can reduce the formation of holes in the process of preparing the conductive layer. The transition layer can also resist the erosion of the electrolyte and high temperature environment, and through Li+ The electrochemical cycle causes its structure to transform from amorphous to crystalline, and maintains its cubic framework and its nanostructure during the entire lithiation / delithiation process, thus having excellent reversible capacity and cycle stability. The improvement of adhesion, reduction of pore defects and improvement of corrosion resistance jointly improve the charge and discharge cycle performance of the battery prepared based on the composite current collector; on the other hand, in the needle penetration test of battery safety testing, the steel needle applies a force in the Z direction to the composite current collector, causing microcracks in the transition layer, which quickly spreads and causes large-scale fractures. Due to the strong adhesion between the transition layer and the conductive layer, the conductive layer will undergo similar fractures along with the transition layer, thereby separating the conductive layer from the steel needle, avoiding the formation of a closed loop by the positive and negative current collectors and the resulting thermal runaway of the battery, improving the safety performance of the battery, and promoting the promotion and application of the composite current collector. The present invention provides a transition layer and a conductive layer on the surface of a polymer-based film. The addition of the transition layer imparts ductile heterogeneity between the layers of the composite current collector. Under the action of an external mechanical force, cracks first form in the transition layer and then spread to the surrounding area, forming multilayer cracks between the transition layer and the transition layer and / or the transition layer and the conductive layer. This regulates the crack growth and deformation range of the composite current collector, thereby cutting off the electron path, effectively improving the safety performance of the composite current collector, and promoting the promotion and application of the composite current collector. The composite current collector of the present invention has excellent battery safety. In the safety inspection needle penetration test, the needle penetration pass rate is, for example, above 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 is a schematic structural diagram of a composite current collector provided in one embodiment of the present application, wherein 1-first protective layer, 2-first metal layer, 3-first transition layer, 4-polymer base film, 5-second transition layer, 6-second metal layer, 7-second protective layer.

[0080] Figure 2 is a typical stress-strain curve diagram, where segments ab represent the elastic deformation stage; bc represents the yield stage, i.e., the crack nucleation zone; cd represents the strengthening stage; and de represents the local deformation stage. Finally, the specimen fractures when the stress reaches point e. Stages cd and de represent the crack propagation zones described in this disclosure. Point e represents the complete fracture point described in this application. DETAILED DESCRIPTION

[0081] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0082] In one embodiment, the present application provides a composite current collector, which includes a base film and at least one transition layer arranged on the surface of at least one side of the base film, the material of the transition layer is selected from any one or a combination of at least two of metallic niobium, metallic tantalum, niobium alloy, tantalum alloy, niobium-based compounds and tantalum-based compounds, and a conductive layer is arranged on the surface of the at least one transition layer on the side relatively away from the base film.

[0083] In one embodiment, the present application provides a composite current collector, comprising a polymer base film, wherein a transition layer and a conductive layer are sequentially provided on at least one surface of the polymer base film; and the value of the crack growth deformation interval r (%) of the composite current collector satisfies the following conditions:

[0084] The crack growth deformation interval refers to the deformation starting point of the composite current collector crack nucleation to the deformation end point of the composite current collector complete fracture in the stress-strain curve;

[0085] (1) The crack growth deformation interval r (%) is (b, e), where b is the percentage value of the strain corresponding to the deformation starting point of the composite current collector crack nucleation, and e is the percentage value of the strain corresponding to the deformation end point of the composite current collector complete rupture;

[0086] (2) 0<b-2≤10, preferably, 0<b-2≤2;

[0087] (3) eb>15, preferably, eb>24.

[0088] In the embodiment of the present application, 0<b-2≤10. For example, b-2 can be 0.5, 1, 2, 3, 3.5, 4, 5, 6, 6.5, 7, 8, 8.5, 9 or 10, etc.

[0089] In the embodiment of the present application, eb>15. For example, ba can be 15.5, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 or 28, etc.

[0090] As shown in the schematic diagram of the stress-strain curve in Figure 2, segment ab represents the elastic deformation stage, where stress is proportional to the specimen's strain. When stress is removed, deformation disappears. segment bc represents the yield stage, or crack nucleation zone, where the linear relationship between stress and strain is broken. Strain increases significantly, while stress initially decreases and then fluctuates slightly, resulting in a small jagged segment approaching the horizontal line on the curve. If unloaded, the specimen's deformation can only partially recover, retaining some residual deformation. segment cd represents the strengthening stage, where the specimen undergoes significant and uniform plastic deformation. Increasing the specimen's strain requires increasing stress. This phenomenon of increasing resistance to plastic deformation as plastic deformation increases is known as work hardening or deformation strengthening. segment de represents the localized deformation stage, where the specimen begins to undergo uneven plastic deformation and necking, resulting in a decrease in stress. Finally, the specimen fractures when stress reaches point e. Stages cd and de represent the crack propagation zones described herein. Point e represents the complete fracture point described herein.

[0091] In one embodiment of the present application, a transition layer and a conductive layer are arranged on the surface of a polymer base film. The addition of at least one transition layer enables the layers of the composite current collector to have ductile heterogeneity. Under the action of external mechanical force, cracks first appear in the transition layer and spread to the surrounding area to form multi-layer cracks, thereby regulating the crack growth and deformation range of the composite current collector, thereby cutting off the path between electrons, effectively improving the safety performance of the composite current collector, and promoting the promotion and application of the composite current collector.

[0092] In one embodiment, the transition layer is composed of at least one transition layer, and the material of the transition layer is selected from any one or at least two of metal niobium, metal tantalum, a compound of metal niobium, and a compound of metal tantalum.

[0093] In one embodiment, the material of the transition layer is selected from any one of metal niobium, metal tantalum, a metal niobium alloy, a metal tantalum alloy, a metal niobium compound, and a metal tantalum compound.

[0094] In the embodiment of the present application, the transition layer may be a multi-layer structure, and the materials of adjacent transition layers may be the same or different, and preferably, the materials of adjacent transition layers are different.

[0095] In one embodiment, the number of the transition layer is 1.

[0096] In one embodiment, the number of layers of the transition layer is 2 or more, for example, it can be 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 8 layers or 10 layers.

[0097] In one embodiment, a transition layer made of the same material is deposited in steps. In this case, the transition layer has a single-layer structure.

[0098] In one embodiment, two transition layers of the same or different materials are deposited in steps. At this time, the number of transition layers is 2. When the materials of these two layers are the same, it can be considered that the composite current collector includes one transition layer.

[0099] In one embodiment, the number of transition layers is 3 to 5, for example, 3, 4, or 5. If the number of transition layers is too small, the mechanical properties of the composite current collector cannot be effectively improved, and the improvement in battery safety performance is not significant. If the number of transition layers is too large, the total thickness of the transition layers is too thick, which will not further improve the conductivity and safety performance of the battery.

[0100] In one embodiment, the compound of metallic niobium and the compound of metallic tantalum are each selected from at least one of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides or tellurides containing the corresponding elements niobium and / or tantalum.

[0101] In one embodiment, the alloy of metallic niobium and the alloy of metallic tantalum include at least one of niobium-germanium alloy, niobium-tin alloy, niobium-zirconium alloy, niobium-hafnium alloy, niobium-nickel alloy, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy, lithium niobate alloy, tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy or cobalt-tantalum-zirconium alloy.

[0102] In one embodiment, the oxide comprises at least one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, or tantalum pentoxide. The niobium alloy is selected from at least one of niobium-germanium alloy, niobium-tin alloy, niobium-zirconium alloy, niobium-hafnium alloy, niobium-nickel alloy, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy, and lithium niobate alloy.

[0103] In one embodiment, the tantalum alloy is selected from at least one of tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy and cobalt-tantalum-zirconium alloy;

[0104] In one embodiment, the niobium-based compound and the tantalum-based compound are independently selected from at least one of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides, and tellurides;

[0105] In one embodiment, the oxide is selected from at least one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide and tantalum pentoxide;

[0106] In one embodiment, the nitride is selected from at least one of niobium nitride and tantalum nitride;

[0107] In one embodiment, the carbide is selected from at least one of niobium carbide and tantalum carbide;

[0108] In one embodiment, the sulfide is selected from at least one of niobium disulfide and tantalum disulfide;

[0109] In one embodiment, the fluoride is selected from at least one of niobium pentafluoride and tantalum pentafluoride;

[0110] In one embodiment, the silicide is selected from at least one of niobium disilicide and tantalum disilicide;

[0111] In one embodiment, the phosphide is selected from at least one of niobium phosphide and tantalum phosphide;

[0112] In one embodiment, the selenide is selected from at least one of niobium diselenide and tantalum diselenide;

[0113] In one embodiment, the telluride is selected from at least one of niobium ditelluride and tantalum ditelluride;

[0114] In one embodiment, the composite current collector comprises multiple transition layers, and the transition layers satisfy any one or more of the following conditions:

[0115] (1) The hardness of the multiple transition layers is the same;

[0116] (2) The hardness of at least one of the multiple transition layers is different from the hardness of the other transition layers. The test method of the hardness is not limited in this application, but a consistent method should be adopted for the hardness measurement of multiple transition layers.

[0117] In one embodiment, among the transition layers, the transition layer with the highest hardness is transition layer A, and the transition layer with the lowest hardness is transition layer B. The transition layer B is in contact with the conductive layer, and / or the transition layer A is in contact with the polymer base film, and / or the transition layer A is closer to the polymer base film than the transition layer B.

[0118] In this preferred technical solution, the transition layer A with the highest hardness is in contact with the polymer film and / or is closer to the polymer base film than the transition layer B. In the needle penetration test of the battery safety test, the steel needle applies a force in the Z direction to the composite current collector. The transition layer A in the transition layer is hard and brittle, so cracks can be generated quickly. Since the transition layer B with the lowest hardness is in contact with the conductive layer, the transition layer B will slowly break along with the brittle layer, thereby increasing the length of the yield period, separating the conductive layer from the steel needle, avoiding the brittle fracture of the conductive layer, and the positive and negative current collectors are connected to form a closed circuit and the resulting battery thermal runaway, thereby improving the safety performance of the battery.

[0119] In one embodiment, the total thickness of the transition layer does not exceed 65% of the thickness of the conductive layer, for example, it can be 65%, 63%, 62%, 60%, 58%, 55%, 52%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10% or 5%, etc., preferably 20%-65%.

[0120] In one embodiment, the ratio of the thickness of adjacent transition layers is (0.0001-10000):1, for example, 0.0001:1, 0.0005:1, 0.001:1, 0.005:1, 0.01:1, 0.05:1, 0.1:1, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, 30:1, 50:1, 100:1 , 500:1, 1000:1, 1500:1, 2000:1, 3000:1, 3500:1, 3700:1, 4000:1, 4500:1, 5000:1, 5500:1, 6000:1, 6500:1, 7000:1, 7500:1, 8000:1, 8500:1, 9000:1, 9500:1, or 10000:1, etc.

[0121] In one embodiment, the material of the polymer base film is selected from at least one of polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS) and polyimide (PI).

[0122] In one embodiment, the polymer base film has a thickness of 1 μm-10 μm, for example, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 9 μm or 10 μm, etc.

[0123] As a preferred technical solution of the composite current collector described in this application, the conductive layer is a metal layer.

[0124] In one embodiment, the material of the metal layer is selected from at least one of aluminum, copper, gold, silver, nickel, zinc, and alloys thereof, but is not limited to the aforementioned materials. Other materials that can provide conductivity to the composite current collector are also suitable for this application.

[0125] In one embodiment, the thickness of the metal layer is 500 nm to 2000 nm, for example, 500 nm, 600 nm, 700 nm, 750 nm, 800 nm, 900 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, or 2000 nm. If the metal layer is too thin, the conductivity is poor; if the metal layer is too thick, the prepared composite current collector is too thick and heavy, which is not conducive to improving the energy density of the battery. Considering both conductivity and energy density improvement, the above range is preferably selected, preferably 600 nm to 1000 nm.

[0126] In one embodiment, a protective layer is further provided on the surface of the conductive layer to prevent the conductive layer (e.g., metal layer) from chemical corrosion, physical damage, or oxidation. In one embodiment, the material of the protective layer is selected from at least one of nickel, chromium, nickel-chromium alloy, nickel-based alloy, copper-based alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, graphene, and graphene oxide.

[0127] In the embodiment of the present application, whether to set a protective layer can be decided according to the needs during actual use. Generally, when the material of the metal layer is copper, a protective layer needs to be set in the composite current collector; when the material of the metal layer is aluminum, a protective layer may not be set.

[0128] In one embodiment, the thickness of the protective layer is 10 nm to 100 nm, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., preferably 20 nm to 80 nm;

[0129] In one embodiment, the thickness of the protective layer does not exceed 1 / 10 of the thickness of the conductive layer, for example, 1 / 10, 1 / 12, 1 / 15, 1 / 17 or 1 / 20.

[0130] The composite current collector of the present application may have a protective layer on only one surface or on both surfaces. When both surfaces have protective layers, the materials of the protective layers on both surfaces may be the same or different, and the thickness may be the same or different, and those skilled in the art can select them as needed. In one embodiment, the composite current collector is composed of seven layers, from top to bottom: a protective layer, a metal layer, a transition layer, a polymer base film, a transition layer, a metal layer, and a protective layer.

[0131] In one embodiment, the present application provides a method for preparing the composite current collector as described above, the preparation method comprising the following steps:

[0132] forming a transition layer on at least one side of the polymer-based film;

[0133] A conductive layer is formed on the surface of the transition layer to obtain a composite current collector.

[0134] This application does not limit the preparation method of the polymer base film, and for example, it can be a melt-extrusion-biaxial stretching method. Taking into account the application requirements of the composite current collector, while taking into account the difficulty and cost of the preparation process, the preferred thickness of the polymer base film is 1 μm-10 μm, for example, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 9 μm or 10 μm, etc.

[0135] In one embodiment, the transition layer is prepared by magnetron sputtering.

[0136] In one embodiment, the conductive layer is prepared by any one of evaporation, magnetron sputtering, chemical plating, electroplating and chemical vapor deposition (CVD).

[0137] In one embodiment, the present application provides a battery, comprising the composite current collector described above or the composite current collector prepared by the above preparation method.

[0138] Example 1

[0139] This embodiment provides a composite current collector, comprising:

[0140] A base film, wherein the base film is a PP film with a thickness of 6 μm;

[0141] The transition layers provided on both sides of the base film include a first transition layer and a second transition layer, wherein the first transition layer and the second transition layer are both metal niobium layers with a thickness of 50 nm;

[0142] The conductive layers provided on the two sides of the at least one transition layer relatively away from the base film include a first conductive layer and a second conductive layer, wherein the first conductive layer and the second conductive layer are both single copper layers with a thickness of 900 nm;

[0143] The protective layers arranged on both sides of the conductive layer relatively away from the base film include a first protective layer and a second protective layer, and both the first protective layer and the second protective layer are made of chromium oxide with a thickness of 20 nm.

[0144] This embodiment also provides a method for preparing the composite current collector, which comprises the following steps:

[0145] (1) A 6 μm thick PP film was prepared by melt-extrusion-biaxial stretching method;

[0146] (2) The PP film was placed in a magnetron sputtering machine, and a 50 nm thick layer of metal niobium was deposited on both sides of the PP film to obtain a composite film with a metal niobium layer on both surfaces. The specific process conditions were as follows: a niobium target (purity: 99.99%) was used as the target material, the power was 10.8 kW, the flow rate of argon gas was 60 mL / min, the vacuum degree of the coating was 0.1 Pa, the coating time was 5 s, and the cooling temperature of the main roller during the coating process was 0°C;

[0147] (3) placing the composite film containing the metal niobium layer on both sides of the surface in a magnetron sputtering machine, and depositing a layer of elemental copper with a thickness of 900 nm on both sides of the composite film to obtain a composite film containing the metal niobium layer and the elemental copper layer on both sides of the surface, wherein the specific process conditions are: a copper target (purity: 99.99%) as the target material, a power of 12 kW, an argon flow rate of 70 mL / min, a coating vacuum of 0.1 Pa, a coating time of 100 s, and a cooling temperature of -5°C for the main roller during the coating process;

[0148] (4) Preparing a protective layer on the conductive layer: The composite film containing a metal niobium layer and a single copper layer on both surfaces is immersed in a 0.5 g / L chromic anhydride aqueous solution (25° C.) for 20 seconds, and then washed with a pure water tank. After washing, the composite current collector is dried in an oven at 60° C. to obtain the composite current collector.

[0149] Example 2

[0150] The difference between this embodiment and Example 1 is that the transition layer is a lithium niobate alloy layer, and the specific process conditions are: a lithium niobate target (purity: 99.99%) is used as the target material, the power is 11.7 kW, the flow rate of argon is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0151] The rest of the preparation methods and parameters remained the same as in Example 1.

[0152] Example 3

[0153] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium pentoxide layer, and the specific process conditions are: a niobium pentoxide target (purity: 99.99%) is used as the target material, the power is 18.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0154] The rest of the preparation methods and parameters remained the same as in Example 1.

[0155] Example 4

[0156] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium nitride layer, and the specific process conditions are: a niobium nitride target (purity: 99.99%) is used as the target material, the power is 11.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0157] The rest of the preparation methods and parameters remained the same as in Example 1.

[0158] Example 5

[0159] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium carbide layer, and the specific process conditions are: a niobium carbide target (purity: 99.99%) is used as the target material, the power is 11.6 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0160] The rest of the preparation methods and parameters remained the same as in Example 1.

[0161] Example 6

[0162] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium disulfide layer, and the specific process conditions are: a niobium disulfide target (purity: 99.99%) is used as the target material, the power is 12.3 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 0°C.

[0163] The rest of the preparation methods and parameters remained the same as in Example 1.

[0164] Example 7

[0165] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium pentafluoride layer, and the specific process conditions are: a niobium pentafluoride target (purity: 99.99%) is used as the target material, the power is 14.4 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0166] The rest of the preparation methods and parameters remained the same as in Example 1.

[0167] Example 8

[0168] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium disilicide layer, and the specific process conditions are: a niobium disilicide target (purity: 99.99%) is used as the target material, the power is 11.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0169] The rest of the preparation methods and parameters remained the same as in Example 1.

[0170] Example 9

[0171] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium phosphide layer, and the specific process conditions are: a niobium phosphide target (purity: 99.99%) is used as the target material, the power is 12.1 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0172] The rest of the preparation methods and parameters remained the same as in Example 1.

[0173] Example 10

[0174] The difference between this embodiment and embodiment 1 is that the transition layer is a niobium diselenide layer, and the specific process conditions are: a niobium diselenide target (purity: 99.99%) is used as the target material, the power is 18.8 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0175] The rest of the preparation methods and parameters remained the same as in Example 1.

[0176] Example 11

[0177] The difference between this embodiment and Example 1 is that the transition layer is a metal tantalum layer, and the specific process conditions are: tantalum target (purity: 99.99%) is used as the target material, the power is 15.5kW, the flow rate of argon gas is 50mL / min, the vacuum degree of the coating is 0.08Pa, the coating time is 5s, and the temperature of the main roller during the coating process is 10°C.

[0178] The rest of the preparation methods and parameters remained the same as in Example 1.

[0179] Example 12

[0180] The difference between this embodiment and Example 1 is that the transition layer is a tantalum-niobium alloy layer, and the specific process conditions are: a tantalum-niobium target (purity: 99.99%) is used as the target material, the power is 12.3 kW, the flow rate of argon gas is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 10°C.

[0181] The rest of the preparation methods and parameters remained the same as in Example 1.

[0182] Example 13

[0183] The difference between this embodiment and Example 1 is that the transition layer is a tantalum pentoxide layer, and the specific process conditions are: a tantalum pentoxide target (purity: 99.99%) is used as the target material, the power is 19.5 kW, the flow rate of argon gas is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 10°C.

[0184] The rest of the preparation methods and parameters remained the same as in Example 1.

[0185] Example 14

[0186] The difference between this embodiment and Example 1 is that the material of the transition layer is a mixture of niobium pentoxide and tantalum pentoxide, and the specific process conditions are: a mixture of niobium pentoxide and tantalum pentoxide (mass ratio of 1:1) (purity: 99.99%) is used as the target material, the power is 19.3 kW, the flow rate of argon gas is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0187] The rest of the preparation methods and parameters remained the same as in Example 1.

[0188] Example 15

[0189] The difference between this embodiment and Example 1 is that the material of the transition layer is a mixture of niobium pentoxide and lithium niobate alloy, and the specific process conditions are: using a mixture of niobium pentoxide and lithium niobate alloy (mass ratio of 1:1) (purity: 99.99%) as the target material, the power is 15.3 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0190] The rest of the preparation methods and parameters remained the same as in Example 1.

[0191] Example 16

[0192] The difference between this embodiment and Example 1 is that the material of the transition layer is a mixture of niobium carbide and niobium nitride. The specific process conditions are: a mixture of niobium carbide and niobium nitride (mass ratio of 1:1) (purity: 99.99%) is used as the target material, the power is 12.9 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0193] The rest of the preparation methods and parameters remained the same as in Example 1.

[0194] Example 17

[0195] The difference between this embodiment and Example 1 is that the material of the transition layer is a mixture of niobium carbide, niobium nitride and niobium pentoxide. The specific process conditions are: using a mixture of niobium carbide, niobium nitride and niobium pentoxide (mass ratio of 1:1:1) (purity: 99.99%) as the target material, the power is 12.5 kW, the argon flow rate is 50 mL / min, the vacuum degree of the coating is 0.1 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 20°C.

[0196] The rest of the preparation methods and parameters remained the same as in Example 1.

[0197] Example 18

[0198] The difference between this embodiment and embodiment 3 is that the thickness of the single-sided transition layer is 100 nm, that is, the specific process conditions for adjusting the transition layer are: the coating time is 10 s, and the temperature of the main roller during the coating process is 20°C.

[0199] The rest of the preparation methods and parameters remained the same as in Example 3.

[0200] Example 19

[0201] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided transition layer is 5 nm, that is, the specific process conditions for adjusting the transition layer are: power is 7.8 kW, argon flow rate is 50 mL / min, coating time is 1 s, and the temperature of the main roller during the coating process is 0°C.

[0202] The rest of the preparation methods and parameters remained the same as in Example 1.

[0203] Example 20

[0204] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided transition layer is 2 nm, that is, the specific process conditions for adjusting the transition layer are: power is 6 kW, argon flow rate is 50 mL / min, coating time is 1 s, and the temperature of the main roller during the coating process is 0°C.

[0205] The rest of the preparation methods and parameters remained the same as in Example 1.

[0206] Example 21

[0207] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided conductive layer is 500 nm, that is, the specific process parameters of the conductive layer are adjusted as follows: the coating time is 45 s.

[0208] The rest of the preparation methods and parameters remained the same as in Example 1.

[0209] Example 22

[0210] The difference between this embodiment and embodiment 1 is that the thickness of the single-sided conductive layer is 1200 nm, that is, the specific process parameters of the conductive layer are adjusted as follows: the coating time is 120 s.

[0211] The rest of the preparation methods and parameters remained the same as in Example 1.

[0212] Example 23

[0213] This embodiment provides a composite current collector, the structure of which is shown in FIG1 , comprising a first protective layer 1, a first metal layer 2, a first transition layer 3, a polymer base film 4, a second transition layer 5, a second metal layer 6, and a second protective layer 7 stacked in sequence;

[0214] The polymer base film 4 is made of polypropylene (PP) and has a thickness of 6 μm. The first transition layer 3 and the second transition layer 5 are both double-layer structures, each 150 nm thick, and are made of niobium carbide. The first metal layer 2 and the second metal layer 6 are both made of copper and have a thickness of 700 nm.

[0215] The preparation method of the composite current collector provided in this embodiment includes the following steps:

[0216] (1) Preparation of transition layer

[0217] A 6 μm thick PP film (prepared by biaxial stretching) was placed in a magnetron sputtering machine with a niobium carbide target (purity: 99.99%) as the target material. The power was 12.3 kW, the argon flow rate was 50 mL / min, the coating vacuum was 0.1 Pa, the coating time was 12 s, and the process was repeated twice. The temperature of the main roller during the coating process was 0°C.

[0218] (2) Preparation of metal layer:

[0219] The PP composite film containing a transition layer on the surface prepared above was placed in a magnetron sputtering machine, and a copper layer with a thickness of 700 nm was deposited on both sides of the composite film. The preparation conditions were: a copper target (purity: 99.99%) was used as the target material, the power was 12.0 kW, the argon flow rate was 70 mL / min, the coating vacuum was 0.1 Pa, the coating time was 70 s, and the cooling temperature of the main roller during the coating process was -5°C, thereby preparing a PP composite film containing a transition layer and a metal layer.

[0220] (3) Preparation of protective layer:

[0221] The PP composite film containing the transition layer and the conductive layer prepared above was immersed in a 0.5 g / L chromic anhydride aqueous solution (25°C) for 20 seconds, and then washed with a pure water tank. After washing, it was placed in a 60°C oven for drying to prepare a composite current collector.

[0222] Example 24

[0223] This embodiment provides a composite current collector, which is basically the same as Example 23, except that: the transition layer is a niobium pentoxide layer (with a thickness of 150 nm) and a tantalum pentoxide layer (with a thickness of 150 nm) stacked in sequence along the direction away from the polymer base film. The specific process conditions are: niobium pentoxide and tantalum pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 18.9 kW and 19.8 kW respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and the coating sequence are: first coating for 12 seconds to prepare the niobium pentoxide layer, and then coating for 12 seconds to prepare the tantalum pentoxide layer. The temperature of the main roller during the coating process is 10°C, and a PP composite film with a transition layer on the surface is prepared.

[0224] Example 25

[0225] This embodiment provides a composite current collector, which is basically the same as Example 24, except that: the transition layer is a niobium nitride layer (with a thickness of 150 nm) and a niobium carbide layer (with a thickness of 150 nm) stacked sequentially along the direction away from the polymer base film. The preparation conditions are as follows: niobium nitride and niobium carbide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.5 kW and 12.3 kW respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and the coating order are: first coating for 12 s to prepare the niobium nitride layer, and then coating for 12 s to prepare the niobium carbide layer, and the temperature of the main roller during the coating process is 10°C.

[0226] Example 26

[0227] This embodiment provides a composite current collector, which is basically the same as Example 24, except that: the transition layer is niobium carbide (with a thickness of 150 nm) and niobium pentoxide (with a thickness of 150 nm) stacked in sequence along the direction away from the polymer base film, along the direction away from the polymer base film, and the preparation conditions are as follows: niobium carbide and niobium pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.3 kW and 18.9 kW, respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and the coating order are: first coating for 12 s to prepare the niobium carbide layer, and then coating for 12 s to prepare the niobium pentoxide layer, and the temperature of the main roller during the coating process is 10°C.

[0228] Example 27

[0229] This embodiment provides a composite current collector, which is basically the same as Example 24, except that: the transition layer is niobium carbide (thickness of 150 nm) and tantalum pentoxide (thickness of 150 nm) stacked in sequence along the direction away from the polymer base film, and its preparation conditions are: niobium carbide and tantalum pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.3 kW and 19.8 kW respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and coating order are: first coating for 12 seconds to prepare the niobium carbide layer, and then coating for 12 seconds to prepare the tantalum pentoxide layer, and the temperature of the main roller during the coating process is 10°C.

[0230] Example 28

[0231] This embodiment provides a composite current collector, which is basically the same as Example 24, except that: the transition layer is niobium nitride (thickness of 150 nm) and niobium pentoxide (thickness of 150 nm) stacked in sequence along the direction away from the polymer base film. The preparation conditions are: niobium nitride and niobium pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.5 kW and 18.9 kW, respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and coating order are: first coating for 12 seconds to prepare the niobium nitride layer, and then coating for 12 seconds to prepare the niobium pentoxide layer, and the temperature of the main roller during the coating process is 10°C.

[0232] Example 29

[0233] Basically the same as Example 27, except that PET film is used.

[0234] Example 30

[0235] Basically the same as Example 27, except that PI film is used.

[0236] Example 31

[0237] This embodiment provides a composite current collector, which is substantially the same as that of Example 26, except that the transition layer is made of a mixture of niobium carbide and niobium pentoxide. Specifically, the transition layer comprises two layers made of the same material. Preparation conditions are as follows: niobium carbide and niobium pentoxide targets (purity: 99.99%), a power of 15.4 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, a coating time of 12 seconds, repeated twice, and a main roller temperature of 20°C during the coating process.

[0238] Example 32

[0239] This embodiment provides a composite current collector, which is basically the same as Example 26, except that the transition layer is niobium carbide (thickness of 100 nm) and tantalum pentoxide (thickness of 100 nm) stacked in sequence along the direction away from the polymer base film. The preparation conditions are as follows: niobium carbide and tantalum pentoxide targets (purity: 99.99%) are used as target materials, respectively, with powers of 12.3 kW and 19.8 kW, respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, a coating time and a coating order of: first coating for 10 s to prepare a niobium carbide layer, and then coating for 10 s to prepare a tantalum pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0240] Example 33

[0241] This embodiment provides a composite current collector, which is basically the same as Example 27, except that: the thickness of the transition layer, specifically, the transition layer is niobium carbide (thickness of 200 nm) and tantalum pentoxide (thickness of 200 nm) stacked in sequence along the direction away from the polymer base film, and its preparation conditions are: niobium carbide and tantalum pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.3 kW and 19.8 kW respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and the coating order are: first coating for 18 s to prepare the niobium carbide layer, and then coating for 18 s to prepare the tantalum pentoxide layer, and the temperature of the main roller during the coating process is 10°C.

[0242] Example 34

[0243] This embodiment provides a composite current collector, which is substantially the same as that of Embodiment 27, except that the transition layer has a three-layer structure, comprising a niobium carbide layer (100 nm thick), a niobium nitride layer (100 nm thick), and a niobium pentoxide layer (100 nm thick), stacked sequentially in a direction away from the polymer base film. The preparation conditions are as follows: niobium carbide, niobium nitride, and niobium pentoxide targets (purity: 99.99%) are used as target materials, with power of 12.3 kW, 12.5 kW, and 18.9 kW, respectively; an argon flow rate of 50 mL / min; a coating vacuum of 0.1 Pa; and a coating time and sequence of 10 s for the niobium carbide layer, 10 s for the niobium nitride layer, and finally 10 s for the niobium pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0244] Example 35

[0245] This embodiment provides a composite current collector, which is basically the same as Example 27, except that: the number of layers of the transition layer is a three-layer structure, and the transition layer is niobium carbide (thickness of 100 nm), niobium pentoxide (thickness of 100 nm) and tantalum pentoxide (thickness of 100 nm) stacked in sequence along the direction away from the polymer base film. The preparation conditions are: niobium carbide, niobium pentoxide and tantalum pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.3 kW, 18.9 kW and 19.8 kW, respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and the coating order are: first coating for 10 s to prepare a tantalum carbide layer, then coating for 10 s to prepare a niobium pentoxide layer, and finally coating for 10 s to prepare a tantalum pentoxide layer, and the temperature of the main roller during the coating process is 10°C.

[0246] Example 36

[0247] This embodiment provides a composite current collector, which is substantially the same as that of Embodiment 27, except that the transition layer has a three-layer structure, comprising a niobium pentoxide layer (100 nm thick), a niobium carbide layer (100 nm thick), and a tantalum pentoxide layer (100 nm thick), stacked sequentially in a direction away from the polymer base film. The preparation conditions are as follows: niobium pentoxide, niobium carbide, and tantalum pentoxide targets (purity: 99.99%) are used as target materials, with power of 18.9 kW, 12.3 kW, and 19.8 kW, respectively; an argon flow rate of 50 mL / min; a coating vacuum of 0.1 Pa; and a coating time and sequence of 10 s for the niobium pentoxide layer, 10 s for the niobium carbide layer, and finally 10 s for the tantalum pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0248] Example 37

[0249] This embodiment provides a composite current collector, which is basically the same as Example 35, except that: the transition layer has a three-layer structure, and the transition layer is niobium carbide (thickness of 70 nm), niobium pentoxide (thickness of 70 nm) and tantalum pentoxide (thickness of 70 nm) stacked in sequence along the direction away from the polymer base film. The preparation conditions are: niobium carbide, niobium pentoxide and tantalum pentoxide targets (purity: 99.99%) are used as target materials, respectively, the power is 12.3 kW, 18.9 kW and 19.8 kW, respectively, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time and coating order are: first coating for 6 seconds to prepare a niobium carbide layer, then coating for 6 seconds to prepare a niobium pentoxide layer, and finally coating for 6 seconds to prepare a tantalum pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0250] Example 38

[0251] This embodiment provides a composite current collector that is substantially the same as that of Embodiment 35, except that the transition layer has a three-layer structure, comprising a niobium carbide layer (150 nm thick), a niobium pentoxide layer (150 nm thick), and a tantalum pentoxide layer (150 nm thick), stacked sequentially in a direction away from the polymer base film. The preparation conditions are as follows: niobium carbide, niobium pentoxide, and tantalum pentoxide targets (purity: 99.99%) are used as target materials, with power of 12.3 kW, 18.9 kW, and 19.8 kW, respectively; an argon flow rate of 50 mL / min; a coating vacuum of 0.1 Pa; and a coating time and sequence of 12 s for the niobium carbide layer, 12 s for the niobium pentoxide layer, and finally 12 s for the tantalum pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0252] Example 39

[0253] This embodiment provides a composite current collector, which is basically the same as that of Example 26, except that: the transition layer has a four-layer structure, and the transition layer is a niobium carbide layer (with a thickness of 75 nm), niobium pentoxide (with a thickness of 75 nm), niobium carbide (with a thickness of 75 nm), and niobium pentoxide (with a thickness of 75 nm) stacked in sequence along the direction away from the polymer base film. The preparation conditions are as follows: niobium carbide and niobium pentoxide targets (purity: 99.99%) are used as target materials, respectively, with powers of 12.3 kW and 18.9 kW, respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, a coating time and a coating sequence of 7 seconds to prepare a niobium carbide layer, then 7 seconds to prepare a niobium pentoxide layer, then 7 seconds to prepare a niobium carbide layer, and finally 7 seconds to prepare a niobium pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0254] Example 40

[0255] This embodiment provides a composite current collector, which is basically the same as that of embodiment 26, except that: the transition layer has a five-layer structure, each layer has a thickness of 60nm, and the transition layer is a niobium carbide layer (thickness of 60nm), a niobium pentoxide layer (thickness of 60nm), a niobium carbide layer (thickness of 60nm), a niobium nitride layer (thickness of 60nm), and a tantalum pentoxide layer (thickness of 60nm) stacked in sequence along the direction away from the polymer base film. The preparation conditions are as follows: a first niobium carbide target, a niobium pentoxide target, a second tantalum carbide target, and a tantalum pentoxide target are used respectively. The targets used were niobium, niobium nitride, and tantalum pentoxide (99.99% purity) targets, with power outputs of 12.3 kW, 18.9 kW, 12.3 kW, 12.5 kW, and 19.8 kW, respectively. The argon flow rate was 50 mL / min, and the coating vacuum was 0.1 Pa. The coating time and sequence were as follows: first, 5 seconds for the niobium carbide layer, then 5 seconds for the niobium pentoxide layer, then 5 seconds for the niobium carbide layer, then 5 seconds for the niobium nitride layer, and finally 5 seconds for the tantalum pentoxide layer. The main roller temperature during the coating process was 10°C.

[0256] Comparative Example 1

[0257] The difference between this comparative example and Example 1 is that no transition layer is provided, that is, step (2) is not performed.

[0258] The rest of the preparation methods and parameters remained the same as in Example 1.

[0259] Comparative Example 2

[0260] The difference between this comparative example and Example 1 is that the transition layer is a nickel-chromium alloy layer, that is, the specific process conditions of step (2) are adjusted as follows: a nickel-chromium target (purity: 99.99%) is used as the target material, the power is 4 kW, the argon flow rate is 50 mL / min, the coating vacuum is 0.1 Pa, the coating time is 10 s, and the temperature of the main roller during the coating process is 20°C.

[0261] The rest of the preparation methods and parameters remained the same as in Example 1.

[0262] Comparative Example 3

[0263] This comparative example provides a composite current collector, which is basically the same as Example 24, except that it does not contain a transition layer.

[0264] Comparative Example 4

[0265] This comparative example provides a composite current collector, which is basically the same as Example 24, except that: the transition layer is a single-layer structure, and its preparation conditions are: using a niobium target (purity: 99.99%) as the target material, the power is 5.0kW, the argon flow rate is 50mL / min, the coating vacuum is 0.1Pa, the coating time is 1s, and the temperature of the main roller during the coating process is 20°C.

[0266] Comparative Example 5

[0267] This comparative example provides a composite current collector, which is basically the same as Example 24, except that the transition layer is traditional nickel-chromium, and its preparation conditions are: nickel-chromium target (purity: 99.99%) is used as the target material, the power is 4.1kW, the argon flow rate is 50mL / min, the coating vacuum is 0.1Pa, the coating time is 1s, and the temperature of the main roller during the coating process is 20°C.

[0268] Performance Testing

[0269] The adhesive force of the composite current collectors prepared in the above examples and comparative examples and the safety performance and cycle performance of the batteries assembled therefrom were tested. The specific testing methods are as follows:

[0270] (1) Adhesion test

[0271] The prepared flat composite current collector sample was cut into a specimen with a width of 24 mm and a length of 300 mm. One end of the cut specimen was folded with the adhesive surface to form a folded layer about 12 mm long. The other end of the specimen was attached to one end of a steel plate and rolled twice with an adhesive tape roller at a speed of 600 mm / min. The specimen was placed in an electronic peel tester with a test speed of 300 mm / min and a specimen width of 24 mm. The equipment automatically recorded the force value during the peeling process and reported the peel strength of the specimen accordingly.

[0272] (2) Safety performance test

[0273] ①Battery assembly:

[0274] For the positive electrode, the positive electrode current collector is made of aluminum foil (thickness is 13μm), and the positive electrode material is LiNi 0.6 Mn 0.2 Co 0.2 O2(NCM622);

[0275] For the negative electrode: the negative electrode current collector adopts the composite current collector prepared in the above embodiment and comparative example, and the negative electrode material adopts artificial graphite;

[0276] For the diaphragm, alumina ceramic-coated polyethylene diaphragm (thickness 25 μm) was used;

[0277] For the electrolyte, 1 mol·L -1LiPF6 carbonate solution, the solvent is a mixture of propylene carbonate, ethylene carbonate and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1;

[0278] The above materials are used to assemble a lithium-ion battery.

[0279] ②Acupuncture pass rate:

[0280] i. Use a needle penetration test to verify the safety performance of the battery, measure 100 samples, and record the pass rate.

[0281] ⅱ. Experimental procedures: The battery prepared above was placed in a needle puncture test apparatus, wherein the needle diameter was 3 mm, the puncture speed was 10 mm / s, the sampling interval was 100 ms, and the sampling time was 15 min. The battery was qualified if it did not explode, catch fire, or emit smoke. The puncture pass rate was recorded, i.e., the number of samples that passed × 100%.

[0282] (3) Cyclic performance test

[0283] The test steps include: 1) discharging the battery cell at I1 (1-hour discharge current) to the discharge termination voltage at 25°C and allowing it to stand for 30 minutes; 2) charging the battery cell at a constant current of I1 to the charge termination voltage, then switching to constant voltage charging, and stopping charging when the charge termination current drops to 0.05 times of I1, and allowing it to stand for 30 minutes after charging; 3) discharging the battery cell at I1 to the discharge termination voltage; 4) cycling continuously for 1000 times according to steps 1)-3), recording the battery capacity at the first cycle and the 1000th cycle, and calculating the battery capacity retention rate, which is the battery capacity at the 1000th cycle / the battery capacity at the first cycle × 100%.

[0284] (IV) Crack growth and deformation range:

[0285] The tensile test was carried out according to GB / T 1040.3-2006, and the stress-strain curve of the sample was plotted (see Figure 2). The starting point b of crack nucleation and the deformation end point e of complete fracture were recorded.

[0286] The starting point b and the deformation end point e are points b and e in the stress-strain curve diagram.

[0287] The test results are shown in Tables 1 and 2.

[0288] Table 1

[0289] analyze:

[0290] As can be seen from Table 1 above, the present application adds a transition layer between the base film and the conductive layer. On the one hand, it can effectively bridge the base film and the conductive layer, thereby improving the adhesion between the two. On the other hand, it effectively improves the charge and discharge cycle performance and safety performance of the battery based on the composite current collector, thereby promoting the promotion and application of the composite current collector.

[0291] From the data results of Examples 1-17, it can be seen that the use of transition layers of different materials affects the adhesion and conductivity of the composite current collector, thereby causing differences in the charge and discharge performance and safety performance of batteries based on the composite current collector.

[0292] It can be seen from the data results of Example 1, Example 3, Example 18 and Example 19 that an appropriate transition layer thickness is beneficial to improving the safety performance and cycle performance of the battery.

[0293] It can be seen from the data results of Example 1 and Example 20 that if the thickness of the transition layer is too small, it will be detrimental to bridging the base film and the conductive layer, and the charge and discharge cycle performance and safety performance of the battery will be greatly reduced.

[0294] It can be seen from the data results of Examples 1 and 21-22 that if the thickness of the conductive layer is too small, the conductivity is poor, and the battery cycle performance cannot be improved; if the thickness of the conductive layer is too large, it is not conducive to improving the energy density of the battery, and its cycle performance and safety performance are not significantly improved.

[0295] It can be seen from the data results of Example 1 and Comparative Example 1 that if a transition layer is not provided, the adhesion between the base film and the conductive layer will be too poor, copper removal will easily occur, and the safety performance of the battery based on this composite current collector will be extremely poor.

[0296] It can be seen from the data results of Example 1, Example 3, Example 13, Example 14, Example 17 and Comparative Example 2 that compared with using a traditional nickel-chromium alloy layer as a transition layer, a transition layer of any one of metallic niobium, metallic tantalum, niobium alloy, tantalum alloy, niobium-based compound or tantalum-based compound or a combination of at least two thereof can significantly improve the battery cycle performance and safety performance.

[0297] Table 2

[0298] As shown in Table 2, the present invention provides multiple transition layers and conductive layers on the surface of the polymer base film. The addition of the transition layers allows the layers of the composite current collector to have ductile heterogeneity. Under the action of mechanical external force, cracks first appear in the transition layer and spread to the surrounding area, forming interlayer cracks. The crack growth deformation interval r (%) of the composite current collector is regulated to meet the following conditions:

[0299] The crack growth deformation interval refers to the range of strain r (%) within the stress-strain curve, from the deformation starting point of the composite current collector crack nucleation to the deformation end point of the composite current collector complete rupture;

[0300] (1) b<r<e, wherein b is the percentage value of the strain corresponding to the deformation starting point of the composite current collector crack nucleation, and e is the percentage value of the strain corresponding to the deformation end point of the composite current collector complete rupture;

[0301] (2) 0<b-2≤10;

[0302] (3)eb>15.

[0303] Thus, the paths between electrons can be cut off, effectively improving the safety performance of the composite current collector. The puncture pass rate of the battery assembled with the composite current collector of the present application is above 80%.

[0304] Compared with not setting a transition layer (Comparative Example 3), the present application can effectively improve the safety performance of the battery by setting a transition layer on the surface of the polymer base film.

[0305] The applicant declares that while the above-mentioned embodiments are used to illustrate the technical solutions of this application, this application is not limited to these embodiments, and does not imply that this application must rely on these embodiments in order to be implemented. Persons skilled in the art should understand that any improvements to this application, equivalent replacements for the raw materials of the products of this application, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of this application.

Claims

1. A composite current collector, characterized in that: The composite current collector comprises: Basement membrane; At least one transition layer is disposed on at least one side of the base film, wherein the material of the transition layer is any one of metal niobium, metal tantalum, niobium alloy, tantalum alloy, niobium-based compound or tantalum-based compound or a combination of at least two thereof; A conductive layer is arranged on a surface of the at least one transition layer on a side relatively far from the base film.

2. The composite current collector according to claim 1, characterized in that: The base film is made of a polymer, and the polymer is selected from at least one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene and polyimide; Preferably, the base film has a thickness of 1 μm-10 μm.

3. The composite current collector according to claim 1 or 2, characterized in that: The value of the crack growth deformation interval r (%) of the composite current collector satisfies the following conditions: The crack growth deformation interval refers to the deformation starting point of the composite current collector crack nucleation to the deformation end point of the composite current collector complete fracture in the stress-strain curve; (1) The crack growth deformation interval r (%) is (b, e), wherein b is the percentage value of the strain corresponding to the deformation starting point of the composite current collector crack nucleation, and e is the percentage value of the strain corresponding to the deformation end point of the composite current collector complete rupture; (2) 0<b-2≤10, preferably, 0<b-2≤2; (3) eb>15, preferably, eb>24.

4. The composite current collector according to any one of claims 1 to 3, characterized in that: The niobium alloy is selected from at least one of niobium-germanium alloy, niobium-tin alloy, niobium-zirconium alloy, niobium-hafnium alloy, niobium-nickel alloy, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy and lithium niobate alloy; Preferably, the tantalum alloy is selected from at least one of tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy and cobalt-tantalum-zirconium alloy; Preferably, the niobium-based compound and the tantalum-based compound are independently selected from at least one of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides and tellurides; Preferably, the oxide is selected from at least one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide and tantalum pentoxide; Preferably, the nitride is selected from at least one of niobium nitride and tantalum nitride; Preferably, the carbide is selected from at least one of niobium carbide and tantalum carbide; Preferably, the sulfide is selected from at least one of niobium disulfide and tantalum disulfide; Preferably, the fluoride is selected from at least one of niobium pentafluoride and tantalum pentafluoride; Preferably, the silicide is selected from at least one of niobium disilicide and tantalum disilicide; Preferably, the phosphide is selected from at least one of niobium phosphide and tantalum phosphide; Preferably, the selenide is selected from at least one of niobium diselenide and tantalum diselenide; Preferably, the telluride is selected from at least one of niobium ditelluride and tantalum ditelluride; More preferably, the material of the transition layer is selected from at least one of metallic niobium, metallic tantalum, niobium pentoxide, tantalum pentoxide, niobium-titanium alloy, molybdenum-niobium alloy, aluminum-niobium alloy, lithium niobate alloy, tantalum-niobium alloy, tantalum-tungsten alloy, tantalum-tungsten-hafnium alloy, cobalt-tantalum-zirconium alloy, niobium nitride, tantalum nitride, niobium carbide and tantalum carbide; Preferably, transition layers are provided on both surfaces of the base film.

5. The composite current collector according to any one of claims 1 to 4, characterized in that: The thickness of the transition layer on one side is greater than or equal to 5 nm, preferably 10 nm-1300 nm, and / or the thickness of the transition layer on one side is less than or equal to 65% of the thickness of the conductive layer.

6. The composite current collector according to any one of claims 1 to 5, characterized in that: The composite current collector comprises a transition layer.

7. The composite current collector according to any one of claims 1 to 5, characterized in that: The composite current collector comprises multiple transition layers.

8. The composite current collector according to claim 6, characterized in that: The thickness of the transition layer on one side is 10nm-100nm.

9. The composite current collector according to claim 7, characterized in that: The thickness of the transition layer on one side is 100nm-1300nm.

10. The composite current collector according to claim 7, characterized in that: The transition layer satisfies at least one of the following conditions: (1) The hardness of the multiple transition layers is the same; (2) The hardness of at least one transition layer among the multiple transition layers is different from the hardness of the other transition layers.

11. The composite current collector according to claim 7, characterized in that: Among the transition layers, the transition layer with the highest hardness is transition layer A, and the transition layer with the lowest hardness is transition layer B. The transition layer B is in contact with the conductive layer, and / or the transition layer A is in contact with the polymer base film, and / or the transition layer A is closer to the polymer base film than the transition layer B.

12. The composite current collector according to any one of claims 1 to 11, characterized in that: The conductive layer is made of metal, and the metal is selected from at least one of elemental aluminum, elemental copper, elemental gold, elemental silver, elemental nickel, elemental zinc, aluminum alloy, copper alloy, gold alloy, silver alloy, nickel alloy and zinc alloy; Preferably, the thickness of the conductive layer on one side is 500nm-2000nm, preferably 600nm-1200nm.

13. The composite current collector according to any one of claims 1 to 12, characterized in that: A protective layer is provided on the surface of the conductive layer on a side relatively far from the base film; Preferably, the material of the protective layer is selected from at least one of metal nickel, metal chromium, nickel-chromium alloy, nickel alloy, copper alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper-chromium oxide, graphite, carbon black, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers, graphene and graphene oxide; Preferably, the thickness of the protective layer on one side is 10nm-100nm, preferably 20nm-80nm; Preferably, the thickness of the protective layer on one side is less than one tenth of the thickness of the conductive layer on one side.

14. A method for preparing a composite current collector according to any one of claims 1 to 13, characterized in that: The preparation method comprises the following steps: A transition layer is prepared on at least one side of the base film, and then a conductive layer is prepared on the surface of the at least one transition layer on a side relatively far from the base film to obtain the composite current collector.

15. The preparation method according to claim 14, characterized in that: The method for preparing the transition layer includes a magnetron sputtering method; Preferably, the method for preparing the conductive layer is selected from at least one of evaporation, magnetron sputtering, chemical plating, electroplating and chemical vapor deposition (CVD); Preferably, after depositing the conductive layer, a protective layer is prepared on the surface of the conductive layer on a side relatively far from the base film; Preferably, the protective layer is prepared by at least one method selected from physical vapor deposition, chemical vapor deposition, in-situ forming and coating.

16. The preparation method according to claim 14 or 15, characterized in that: The preparation method comprises the following steps: (1) preparing a polymer base film with a thickness of 1 μm-10 μm; (2) depositing at least one transition layer with a thickness of 10 nm to 100 nm on both sides of the polymer base film to obtain a composite film with a transition layer on the surface, wherein the specific process conditions are: power of 5 kW to 20 kW, argon flow rate of 50 mL / min to 60 mL / min, vacuum degree of coating of 0.08 Pa to 0.1 Pa, coating time of 1 s to 20 s, and cooling temperature of the main roller during coating of 0°C to 20°C; (3) depositing a conductive layer with a thickness of 500 nm to 2000 nm on both sides of the composite film to obtain a composite film containing a transition layer and a conductive layer; (4) Preparing a protective layer: placing the composite film containing the transition layer and the conductive layer in a raw material solution of the protective layer for immersion treatment, and then washing and drying to obtain the composite current collector.

17. An electrode sheet, characterized in that: The electrode sheet comprises the composite current collector according to any one of claims 1 to 13.

18. A secondary battery, characterized in that: The secondary battery includes the electrode sheet as claimed in claim 17.

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