A composite current collector, a preparation method thereof, and a battery

Abstract

The present invention discloses a composite current collector, a preparation method thereof, and a battery. The composite current collector includes a polymer film, and a transition layer and a conductive layer are sequentially disposed on at least one surface of the polymer film; the transition layer is a multi-layer structure; the crack growth interval r(%) of the composite current collector satisfies the following conditions: b < r < e, 0 < b - 2 ≤ 10, e - b > 15, where b is the starting point of crack nucleation of the composite current collector, and e is the deformation end point of complete fracture of the composite current collector. By adding a transition layer with a multi-layer structure to the composite current collector, the present invention enables the layers of the composite current collector to have a ductile isomeric property. Under the action of mechanical external force, cracks are first generated in the transition layer and spread around, forming inter-layer cracks, regulating the crack growth interval of the composite current collector, thereby cutting off the electron path, effectively improving the safety performance of the composite current collector, and promoting the popularization and application of the composite current collector.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and relates to a composite current collector, a preparation method thereof, and a battery. Background Art

[0002] At present, composite current collectors based on polymer films have received extensive attention and applications in the new energy industry. The preparation of such composite current collectors usually involves depositing a layer of metal on a polymer film (such as polyester, polyolefin, etc.) by physical vapor deposition (PVD) to prepare 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 applied in the battery.

[0003] However, the current composite current collectors still have the following problems: The composite current collector mainly relies on the insulation and flame retardant properties of the intermediate layer, i.e., the polymer film layer, to improve the safety performance of the battery. However, although this improves the safety performance to some extent, the improvement is limited. Therefore, in order to further improve the safety performance of batteries based on composite current collectors, it is necessary to develop a new composite current collector to promote the application and popularization of composite current collectors in batteries. Summary of the Invention

[0004] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide a composite current collector, a preparation method thereof, and a battery. By setting a transition layer and a conductive layer on the surface of the polymer film, and using the multi-layer structure of the transition layer to regulate the crack growth interval of the composite current collector, the safety performance of the composite current collector is effectively improved, and the popularization and application of the composite current collector are promoted.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a composite current collector, which includes a polymer film, and a transition layer and a conductive layer are sequentially disposed on at least one surface of the polymer film; the transition layer is a multi-layer structure; the crack growth interval r(%) of the composite current collector satisfies the following conditions:

[0007] (1) b < r < e, where b is the starting point of crack nucleation of the composite current collector, and e is the deformation end point of complete fracture of the composite current collector;

[0008] (2) 0 < b - 2 ≤ 10, preferably, 0 < b - 2 ≤ 2;

[0009] (3) e - b > 15, preferably, e - b > 24.

[0010] In the present invention, the crack growth interval of the composite current collector refers to the strain interval range including three stages: the crack nucleation region, the crack propagation region, and the complete fracture region.

[0011] In the present invention, a transition layer and a conductive layer with a multi-layer structure are provided on the surface of the polymer film. By adding the transition layer with a multi-layer structure, the layers of the composite current collector have the property of extended isomerism. Under the action of mechanical external force, cracks first occur in the transition layer and spread to the surrounding, forming cracks between multiple layers, regulating the crack growth interval of the composite current collector, thereby cutting off the electron path, effectively improving the safety performance of the composite current collector, and promoting the popularization and application of the composite current collector.

[0012] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved.

[0013] Preferably, the transition layer is composed of multiple functional layers, and the material of the functional layer is selected from any one or at least two of niobium metal, tantalum metal, niobium metal alloys, tantalum metal alloys, niobium metal compounds, and tantalum metal compounds.

[0014] Preferably, the material of the functional layer is selected from any one of niobium metal, tantalum metal, niobium metal alloys, tantalum metal alloys, niobium metal compounds, and tantalum metal compounds.

[0015] Preferably, the materials of adjacent functional layers are different.

[0016] Preferably, the number of functional layers is more than 2 layers, preferably 3 to 5 layers.

[0017] Preferably, the niobium metal compound and the tantalum metal compound are respectively selected from at least one of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides, or tellurides containing the corresponding elements niobium and / or tantalum.

[0018] Preferably, the niobium metal alloys and tantalum metal alloys 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.

[0019] Preferably, the oxides include at least one of niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, or tantalum pentoxide.

[0020] Preferably, the nitrides include at least one of niobium nitride or tantalum nitride;

[0021] Preferably, the carbide includes at least one of niobium carbide or tantalum carbide.

[0022] Preferably, the sulfide includes at least one of niobium disulfide or tantalum disulfide.

[0023] Preferably, the fluoride includes at least one of niobium pentafluoride or tantalum pentafluoride.

[0024] Preferably, the silicide includes at least one of niobium disilicide or tantalum disilicide.

[0025] Preferably, the phosphide includes at least one of niobium phosphide or tantalum phosphide.

[0026] Preferably, the selenide includes at least one of niobium diselenide or tantalum diselenide.

[0027] Preferably, the telluride includes at least one of niobium ditelluride or tantalum ditelluride.

[0028] As a preferred technical solution of the composite current collector of the present invention, the functional layer satisfies any one or more of the following conditions:

[0029] (1) The hardness of multiple layers of the functional layer is the same;

[0030] (2) The hardness of at least one functional layer in multiple layers of the functional layer is different from the hardness of other functional layers.

[0031] Preferably, in the transition layer, the functional layer with the highest hardness is functional layer A, and the functional layer with the lowest hardness is functional layer B. The functional layer B is in contact with the conductive layer, and / or the functional layer A is in contact with the polymer film, and / or the functional layer A is closer to the polymer film than the functional layer B.

[0032] In this preferred technical solution, the functional layer A with the highest hardness is in contact with the polymer film and / or is closer to the polymer film than the functional layer B. In the needle-punch test for battery safety detection, a steel needle exerts a force in the Z direction on the composite current collector. The functional layer A in the transition layer is hard and brittle, so cracks can be generated quickly. Since the functional layer B with the lowest hardness is in contact with the conductive layer, the functional layer B will break slowly along with the brittle layer, increasing the length during yielding, separating the conductive layer from the steel needle, avoiding brittle fracture of the conductive layer, forming a closed circuit for the positive and negative current collectors to conduct electricity, and thus preventing battery thermal runaway, improving the safety performance of the battery.

[0033] Preferably, the total thickness of the transition layer does not exceed 65% of the thickness of the conductive layer, preferably 20%-65%.

[0034] Preferably, the thickness ratio of at least one group of adjacent functional layers is (0.0001-10000):1.

[0035] Preferably, the material of the polymer film includes 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), or polyimide (PI).

[0036] Preferably, the thickness of the polymer film is 1 μm to 10 μm.

[0037] As a preferred technical solution of the composite current collector of the present invention, the conductive layer is a metal layer.

[0038] Preferably, the material of the metal layer is at least one of aluminum, copper, gold, silver, nickel, and zinc and their alloys.

[0039] Preferably, the thickness of the metal layer is 500 nm to 2000 nm, preferably 600 nm to 1000 nm.

[0040] In a third aspect, the present invention provides a method for preparing the composite current collector as described in the first aspect or the second aspect. The preparation method includes the following steps:

[0041] Form a transition layer on at least one side of the polymer film;

[0042] Form a conductive layer on the surface of the transition layer to obtain a composite current collector.

[0043] The present invention does not limit the preparation method of the polymer film. For example, it can be a melt-extrusion-biaxial stretching method. Considering the application requirements of the composite current collector, and taking into account the difficulty and cost of the preparation process, the preferred thickness of the polymer film is 1 μm to 10 μm. For example, it can be 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.

[0044] As a preferred technical solution of the method for preparing the composite current collector of the present invention, the preparation method of the transition layer is magnetron sputtering.

[0045] Preferably, the preparation method of the conductive layer is any one of evaporation plating, magnetron sputtering, electroless plating, electroplating, or chemical vapor deposition (CVD).

[0046] In a fourth aspect, the present invention provides a battery, which includes the composite current collector described in the first aspect or the second aspect or the composite current collector prepared by the preparation method described in the third aspect.

[0047] The numerical ranges described in the present invention include not only the above-listed point values, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the described range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) By providing a transition layer and a conductive layer with a multi-layer structure on the surface of the polymer film, the addition of the multi-layer structure transition layer enables the composite current collector to have a ductile heterogeneous property between layers. Under the action of mechanical external force, cracks first occur in the transition layer and spread to the surrounding area, forming inter-layer cracks, regulating the crack growth range of the composite current collector, thereby cutting off the electron path and effectively improving the safety performance of the composite current collector, promoting the popularization and application of the composite current collector.

[0050] (2) The composite current collector of the present invention has good battery safety, and in the needle-punch test of safety detection, the needle-punch passing rate is more than 80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a schematic structural diagram of a composite current collector provided by an embodiment of the present invention, wherein, 1 - first protective layer, 2 - first metal layer, 3 - first transition layer, 4 - polymer film, 5 - second transition layer, 6 - second metal layer, 7 - second protective layer.

[0052] Figure 2 is the stress-strain curve of the sample in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] The technical solution of the present invention will be further described below in conjunction with the drawings and through specific embodiments.

[0054] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0055] In one embodiment, the present invention provides a composite current collector, the composite current collector includes a polymer film, and a transition layer and a conductive layer are sequentially provided on at least one surface of the polymer film; the transition layer is a multi-layer structure; the crack growth range r(%) of the composite current collector satisfies the following conditions:

[0056] (1) b < r < e, where b is the starting point of crack nucleation and e is the deformation end point of complete fracture;

[0057] (2) 0 < b - 2 ≤ 10, preferably, 0 < b - 2 ≤ 2;

[0058] (3) e - b > 15, preferably, e - b > 24.

[0059] In the embodiments of the present invention, 0 < b - 2 ≤ 10. Exemplarily, b - 2 can be, for example, 0.5, 1, 2, 3, 3.5, 4, 5, 6, 6.5, 7, 8, 8.5, 9 or 10, etc.

[0060] In the embodiments of the present invention, e - b > 15. Exemplarily, b - a can be, for example, 15.5, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 or 28, etc.

[0061] In an embodiment of the present invention, a transition layer and a conductive layer with a multi - layer structure are provided on the surface of the polymer film. The addition of the multi - layer transition layer endows the layers of the composite current collector with extensional isomerism characteristics. Under the action of mechanical external force, cracks are first generated in the transition layer and spread around, forming inter - layer cracks, regulating the crack growth range of the composite current collector, thereby cutting off the electron path and effectively improving the safety performance of the composite current collector, promoting the popularization and application of the composite current collector.

[0062] In one embodiment, the transition layer is composed of multiple functional layers, and the material of the functional layer is selected from any one or at least two of niobium metal, tantalum metal, niobium metal compounds, and tantalum metal compounds.

[0063] In one embodiment, the material of the functional layer is selected from any one of niobium metal, tantalum metal, niobium metal alloys, tantalum metal alloys, niobium metal compounds, and tantalum metal compounds.

[0064] In the embodiments of the present invention, the materials of adjacent functional layers can be the same or different, and preferably the materials of adjacent functional layers are different.

[0065] In one embodiment, the number of functional layers is more than 2 layers, and can be, for example, 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 8 layers or 10 layers, etc.

[0066] In one embodiment, two functional layers with the same material are deposited step by step. At this time, the number of functional layers is a two - layer structure, and the materials of these two layers are the same.

[0067] In one embodiment, the number of functional layers is 3 - 5 layers, and can be, for example, 3 layers, 4 layers or 5 layers. If the number of layers of the transition layer is too small, the mechanical properties of the composite current collector cannot be improved well, and the improvement of the battery safety performance is not obvious; if the number of layers of the transition layer is too large, resulting in too thick total thickness of the transition layer, the conductivity and safety performance of the battery will not be further improved.

[0068] In one embodiment, the niobium compound and the tantalum compound are each independently selected from at least one of oxides, nitrides, carbides, sulfides, fluorides, silicides, phosphides, selenides, or tellurides containing the corresponding elements niobium and / or tantalum.

[0069] In one embodiment, the niobium alloy and the tantalum alloy 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.

[0070] In one embodiment, the oxide includes at least one of niobium monoxide, niobium dioxide, niobium sesquioxide, niobium pentoxide, or tantalum pentoxide.

[0071] In one embodiment, the nitride includes at least one of niobium nitride or tantalum nitride.

[0072] In one embodiment, the carbide includes at least one of niobium carbide or tantalum carbide.

[0073] In one embodiment, the sulfide includes at least one of niobium disulfide or tantalum disulfide.

[0074] In one embodiment, the fluoride includes at least one of niobium pentafluoride or tantalum pentafluoride.

[0075] In one embodiment, the silicide includes at least one of niobium disilicide or tantalum disilicide.

[0076] In one embodiment, the phosphide includes at least one of niobium phosphide or tantalum phosphide.

[0077] In one embodiment, the selenide includes at least one of niobium diselenide or tantalum diselenide.

[0078] In one embodiment, the telluride includes at least one of niobium ditelluride or tantalum ditelluride.

[0079] In one embodiment, the functional layer satisfies any one or more of the following conditions:

[0080] (1) The hardness of multiple layers of the functional layer is the same;

[0081] (2) The hardness of at least one layer of the functional layer among multiple layers of the functional layer is different from the hardness of other functional layers.

[0082] In one embodiment, in the transition layer, the functional layer with the highest hardness is functional layer A, and the functional layer with the lowest hardness is functional layer B. Functional layer B contacts the conductive layer, and / or functional layer A contacts the polymer film, and / or functional layer A is closer to the polymer film than functional layer B.

[0083] In this preferred technical solution, the functional layer A with the highest hardness contacts the polymer film and / or is closer to the polymer film than functional layer B. In the needle puncture test for battery safety detection, a steel needle applies a force in the Z direction to the composite current collector. The functional layer A in the transition layer is hard and brittle, so it can quickly generate cracks. Since the functional layer B with the lowest hardness contacts the conductive layer, functional layer B will slowly break along with the brittle layer, increasing the length during yielding. The conductive layer separates from the steel needle, preventing the brittle fracture of the conductive layer, the conduction of the positive and negative current collectors to form a closed circuit, and the resulting thermal runaway of the battery, thus improving the safety performance of the battery.

[0084] 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, it is 20% - 65%.

[0085] In one embodiment, the thickness ratio of adjacent functional layers is (0.0001 - 10000):1. For example, it can be 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.

[0086] In one embodiment, the material of the polymer film includes 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), or polyimide (PI).

[0087] In one embodiment, the thickness of the polymer film is 1 μm to 10 μm, and for example, it can be 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.

[0088] As a preferred technical solution of the composite current collector of the present invention, the conductive layer is a metal layer.

[0089] In one embodiment, the material of the metal layer is at least one of aluminum, copper, gold, silver, nickel, zinc and their alloys. However, it is not limited to the above-listed types, and other materials that can provide conductivity for the composite current collector are also applicable to the present invention.

[0090] In one embodiment, the thickness of the metal layer is 500 nm to 2000 nm, and for example, it can be 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, etc. If the thickness of the metal layer is too thin, the conductivity is poor; if the thickness of the metal layer is too thick, the prepared composite current collector is too heavy, which is not conducive to improving the energy density of the battery. Considering the conductivity and taking into account the improvement of the energy density, the above range is preferred, and 600 nm to 1000 nm is preferred.

[0091] In one embodiment, a protective layer is further provided on the surface of the conductive layer. The function of the protective layer is to prevent the conductive layer (such as the metal layer) from being chemically corroded, physically damaged or oxidized. In one embodiment, the material of the protective layer is 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.

[0092] In the embodiments of the present invention, whether to provide a protective layer can be determined according to the actual use requirements. Generally, when the material of the metal layer is copper, a protective layer needs to be provided in the composite current collector; while when the material of the metal layer is aluminum, a protective layer can be not provided.

[0093] In one embodiment, the thickness of the protective layer is 10 nm to 100 nm, and for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm or 100 nm, etc., and 20 nm to 80 nm is preferred;

[0094] In one embodiment, the thickness of the protective layer does not exceed 1 / 10 of the thickness of the conductive layer, such as 1 / 10, 1 / 12, 1 / 15, 1 / 17, or 1 / 20, etc.

[0095] In the composite current collector of the present invention, a protective layer may be provided only on one side surface, or protective layers may be provided on both side surfaces. When protective layers are provided on both side surfaces, the materials of the protective layers on both side surfaces may be the same or different, and the thicknesses may be the same or different, which can be selected by those skilled in the art according to needs. In one embodiment, the composite current collector is composed of 7 layers, from top to bottom in sequence: a protective layer, a metal layer, a transition layer, a polymer film, a transition layer, a metal layer, and a protective layer.

[0096] In one embodiment of the present invention, a method for preparing the composite current collector as described above is provided, and the preparation method includes the following steps:

[0097] Form a transition layer on at least one side of the polymer film;

[0098] Form a conductive layer on the surface of the transition layer to obtain a composite current collector.

[0099] The present invention does not limit the preparation method of the polymer film. For example, it can be a melt-extrusion-biaxial stretching method. Considering the application requirements of the composite current collector, and taking into account the difficulty and cost of the preparation process, the preferred thickness of the polymer film is 1 μm to 10 μm, such as 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.

[0100] In one embodiment, the preparation method of the transition layer is magnetron sputtering.

[0101] In one embodiment, the preparation method of the conductive layer is any one of evaporation coating, magnetron sputtering, electroless plating, electroplating, or chemical vapor deposition (CVD).

[0102] In one embodiment of the present invention, a battery is provided, and the battery includes the above composite current collector or the composite current collector prepared by the above preparation method.

[0103] Based on the above embodiments, several specific implementation cases are described here, as follows:

[0104] Example 1

[0105] This example provides a composite current collector, and its structural schematic diagram is shown in Figure 1, including a first protective layer 1, a first metal layer 2, a first transition layer 3, a polymer film 4, a second transition layer 5, a second metal layer 6, and a second protective layer 7 that are stacked in sequence;

[0106] Among them, the material of the polymer film 4 is polypropylene (PP), and the thickness of the polymer film 4 is 6 μm; both the first transition layer 3 and the second transition layer 5 are bilayer structures. The transition layer is a bilayer structure, with each layer having a thickness of 150 nm and the material being niobium carbide. The materials of the first metal layer 2 and the second metal layer 6 are both copper, and the thicknesses of the first metal layer 2 and the second metal layer 6 are both 700 nm.

[0107] The preparation method of the composite current collector provided in this embodiment includes the following steps:

[0108] (1) Prepare the transition layer

[0109] Place a 6-μm-thick PP film (prepared by the biaxial stretching method) in a magnetron sputtering machine. Use a niobium carbide target (purity: 99.99%) as the target material, with a power of 12.3 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, and a coating time of 12 s. Repeat twice, and the temperature of the main roller during the coating process is 0 °C.

[0110] (2) Prepare the metal layer:

[0111] Place the above-prepared PP composite film with a transition layer on its surface in a magnetron sputtering machine, and deposit a 700-nm-thick copper layer on each side of the composite film. The preparation conditions are: use a copper target (purity: 99.99%) as the target material, with a power of 12.0 kW, an argon flow rate of 70 mL / min, a coating vacuum of 0.1 Pa, and a coating time of 70 s. The cooling temperature of the main roller during the coating process is -5 °C, that is, a PP composite film containing a transition layer and a metal layer is prepared.

[0112] (3) Prepare the protective layer:

[0113] Place the above-prepared PP composite film containing a transition layer and a conductive layer in a 0.5 g / L chromic anhydride aqueous solution (25 °C) and soak it for 20 s. After the treatment is completed, wash it through a pure water tank. After the washing is completed, place it in an oven at 60 °C for drying, that is, a composite current collector is prepared.

[0114] Example 2

[0115] This embodiment provides a composite current collector, which is basically the same as Embodiment 1, except that: the transition layer is a niobium pentoxide layer (with a thickness of 150 nm) and tantalum pentoxide (with a thickness of 150 nm) stacked in sequence along the direction away from the polymer film. The specific process conditions are as follows: using niobium pentoxide and tantalum pentoxide targets (purity: 99.99%) as the target materials respectively, with powers of 18.9 KW and 19.8 KW respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, the coating time and coating sequence are: first coat for 12 s to prepare the niobium pentoxide layer, and then coat for 12 s to prepare the tantalum pentoxide layer. During the coating process, the temperature of the main roller is 10 °C, that is, a PP composite film with a transition layer on the surface is prepared.

[0116] Embodiment 3

[0117] This embodiment provides a composite current collector, which is basically the same as Embodiment 2, 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 in sequence along the direction away from the polymer film. Its preparation conditions are as follows: using niobium nitride and niobium carbide targets (purity: 99.99%) as the target materials respectively, with powers of 12.5 kW and 12.3 kW respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, the coating time and coating sequence are: first coat for 12 s to prepare the niobium nitride layer, and then coat for 12 s to prepare the niobium carbide layer. During the coating process, the temperature of the main roller is 10 °C.

[0118] Embodiment 4

[0119] This embodiment provides a composite current collector, which is basically the same as Embodiment 2, except that: the transition layer is a niobium carbide (with a thickness of 150 nm) and a niobium pentoxide (with a thickness of 150 nm) stacked in sequence along the direction away from the polymer film. Its preparation conditions are as follows: using niobium carbide and niobium pentoxide targets (purity: 99.99%) as the 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, the coating time and coating sequence are: first coat for 12 s to prepare the niobium carbide layer, and then coat for 12 s to prepare the niobium pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0120] Embodiment 5

[0121] This embodiment provides a composite current collector, which is basically the same as Embodiment 2, except that: the transition layer is a stack of niobium carbide (with a thickness of 150 nm) and tantalum pentoxide (with a thickness of 150 nm) in sequence along the direction away from the polymer film. Its preparation conditions are: using niobium carbide and tantalum pentoxide targets (purity: 99.99%) as the targets 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, and the coating time and coating sequence are: first coat for 12 s to prepare the niobium carbide layer, then coat for 12 s to prepare the tantalum pentoxide layer, and the temperature of the main roller during the coating process is 10 °C.

[0122] Example 6

[0123] This embodiment provides a composite current collector, which is basically the same as Embodiment 2, except that: the transition layer is a stack of niobium nitride (with a thickness of 150 nm) and niobium pentoxide (with a thickness of 150 nm) in sequence along the direction away from the polymer film. Its preparation conditions are: using niobium nitride and niobium pentoxide targets (purity: 99.99%) as the targets respectively, with powers of 12.5 kW and 18.9 kW respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, and the coating time and coating sequence are: first coat for 12 s to prepare the niobium nitride layer, then coat for 12 s to prepare the niobium pentoxide layer, and the temperature of the main roller during the coating process is 10 °C.

[0124] Example 7

[0125] It is basically the same as Embodiment 5, except that a PET film is used.

[0126] Example 8

[0127] It is basically the same as Embodiment 5, except that a PI film is used.

[0128] Example 9

[0129] This embodiment provides a composite current collector, which is basically the same as Embodiment 4, except that: the material of the transition layer is a mixture of niobium carbide and niobium pentoxide. Specifically, the transition layer has a two-layer structure, and the materials of these two layers are the same. Its preparation conditions are: using niobium carbide and niobium pentoxide targets (purity: 99.99%) as the targets, with 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 s, repeated twice, and the temperature of the main roller during the coating process is 20 °C.

[0130] Example 10

[0131] This embodiment provides a composite current collector, which is basically the same as Embodiment 4. The difference is that the transition layer is a niobium carbide (with a thickness of 100 nm) and tantalum pentoxide (with a thickness of 100 nm) laminated in sequence along the direction away from the polymer film. The preparation conditions are as follows: Using niobium carbide and tantalum pentoxide targets (purity: 99.99%) as the 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, the coating time and coating sequence are: first coat for 10 s to prepare the niobium carbide layer, and then coat for 10 s to prepare the tantalum pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0132] Example 11

[0133] This embodiment provides a composite current collector, which is basically the same as Embodiment 5. The difference is that: the thickness of the transition layer. Specifically, the transition layer is a niobium carbide (with a thickness of 200 nm) and tantalum pentoxide (with a thickness of 200 nm) laminated in sequence along the direction away from the polymer film. The preparation conditions are as follows: Using niobium carbide and tantalum pentoxide targets (purity: 99.99%) as the 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, the coating time and coating sequence are: first coat for 18 s to prepare the niobium carbide layer, and then coat for 18 s to prepare the tantalum pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0134] Example 12

[0135] This embodiment provides a composite current collector, which is basically the same as Embodiment 5. The difference is that: the transition layer is a three-layer structure, and the transition layer is a niobium carbide layer (with a thickness of 100 nm), a niobium nitride layer (with a thickness of 100 nm), and a niobium pentoxide layer (with a thickness of 100 nm) laminated in sequence along the direction away from the polymer film. The preparation conditions are as follows: Using niobium carbide, niobium nitride, and niobium pentoxide targets (purity: 99.99%) as the target materials respectively, with powers 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, the coating time and coating sequence are: first coat for 10 s to prepare the niobium carbide layer, then coat for 10 s to prepare the niobium nitride layer, and finally coat for 10 s to prepare the niobium pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0136] Example 13

[0137] This embodiment provides a composite current collector, which is basically the same as Embodiment 5, except that: the transition layer has a three-layer structure, and the transition layer is a niobium carbide (with a thickness of 100 nm), niobium pentoxide (with a thickness of 100 nm), and tantalum pentoxide (with a thickness of 100 nm) stacked in sequence along the direction away from the polymer film. Its preparation conditions are: using niobium carbide, niobium pentoxide, and tantalum pentoxide targets (purity: 99.99%) as the target materials respectively, with powers 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 the coating time and coating sequence are: first coat for 10 s to prepare the tantalum carbide layer, then coat for 10 s to prepare the niobium pentoxide layer, and finally coat for 10 s to prepare the tantalum pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0138] Example 14

[0139] This embodiment provides a composite current collector, which is basically the same as Embodiment 5, except that: the transition layer has a three-layer structure, and the transition layer is a niobium pentoxide layer (with a thickness of 100 nm), niobium carbide (with a thickness of 100 nm), and tantalum pentoxide (with a thickness of 100 nm) stacked in sequence along the direction away from the polymer film. Its preparation conditions are: using niobium pentoxide, niobium carbide, and tantalum pentoxide targets (purity: 99.99%) as the target materials respectively, with powers of 18.9 W, 12.3 kW, and 19.8 kW respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, and the coating time and coating sequence are: first coat for 10 s to prepare the niobium pentoxide layer, then coat for 10 s to prepare the niobium carbide layer, and finally coat for 10 s to prepare the tantalum pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0140] Example 15

[0141] This embodiment provides a composite current collector, which is basically the same as Embodiment 13, except that: the transition layer has a three-layer structure, and the transition layer is a niobium carbide (with a thickness of 70 nm), niobium pentoxide (with a thickness of 70 nm), and tantalum pentoxide (with a thickness of 70 nm) stacked in sequence along the direction away from the polymer film. Its preparation conditions are: using niobium carbide, niobium pentoxide, and tantalum pentoxide targets (purity: 99.99%) as the target materials respectively, with powers 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 the coating time and coating sequence are: first coat for 6 s to prepare the niobium carbide layer, then coat for 6 s to prepare the niobium pentoxide layer, and finally coat for 6 s to prepare the tantalum pentoxide layer. During the coating process, the temperature of the main roller is 10 °C.

[0142] Example 16

[0143] This embodiment provides a composite current collector, which is basically the same as Embodiment 13, except that: the transition layer has a three-layer structure, and the transition layer is a niobium carbide layer (with a thickness of 150 nm), 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 film. Its preparation conditions are as follows: Using niobium carbide, niobium pentoxide, and tantalum pentoxide targets (purity: 99.99%) as the target materials respectively, with powers 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 the coating time and coating sequence are: first coat for 12 s to prepare the niobium carbide layer, then coat for 12 s to prepare the niobium pentoxide layer, and finally coat for 12 s to prepare the tantalum pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0144] Example 17

[0145] This embodiment provides a composite current collector, which is basically the same as Embodiment 4, 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 film. Its preparation conditions are as follows: Using niobium carbide and niobium pentoxide targets (purity: 99.99%) as the 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, and the coating time and coating sequence are: first coat for 7 s to prepare the niobium carbide layer, then coat for 7 s to prepare the niobium pentoxide layer, then coat for 7 s to prepare the niobium carbide layer, and finally coat for 7 s to prepare the niobium pentoxide layer. The temperature of the main roller during the coating process is 10°C.

[0146] Example 18

[0147] This embodiment provides a composite current collector, which is basically the same as that in Embodiment 4, except that: the transition layer has a five-layer structure, with each layer having a thickness of 60 nm. The transition layer is a niobium carbide layer (with a thickness of 60 nm), a niobium pentoxide layer (with a thickness of 60 nm), a niobium carbide layer (with a thickness of 60 nm), a niobium nitride layer (with a thickness of 60 nm), and a tantalum pentoxide layer (with a thickness of 60 nm) that are sequentially stacked in a direction away from the polymer film. Its preparation conditions are as follows: using a first niobium carbide target, a niobium pentoxide target, a second niobium carbide target, a niobium nitride target, and a tantalum pentoxide target (purity: 99.99%) as the targets, with powers of 12.3 kW, 18.9 W, 12.3 kW, 12.5 kW, and 19.8 kW respectively, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, and the coating time and coating sequence are: first coat for 5 s to prepare the niobium carbide layer, then coat for 5 s to prepare the niobium pentoxide layer, then coat for 5 s to prepare the niobium carbide layer, then coat for 5 s to prepare the niobium nitride layer, and finally coat for 5 s to prepare the tantalum pentoxide layer. The temperature of the main roller during the coating process is 10 °C.

[0148] Comparative Example 1

[0149] This comparative example provides a composite current collector, which is basically the same as that in Embodiment 2, except that: it does not contain a transition layer.

[0150] Comparative Example 2

[0151] This comparative example provides a composite current collector, which is basically the same as that in Embodiment 2, except that: the transition layer has a single-layer structure, and its preparation conditions are as follows: using a niobium target (purity: 99.99%) as the target, with a power of 5.0 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, a coating time of 1 s, and the temperature of the main roller during the coating process is 20 °C.

[0152] Comparative Example 3

[0153] This comparative example provides a composite current collector, which is basically the same as that in Comparative Example 3, except that: the transition layer is traditional nickel-chromium, and its preparation conditions are as follows: using a nickel-chromium target (purity: 99.99%) as the target, with a power of 4.1 kW, an argon flow rate of 50 mL / min, a coating vacuum of 0.1 Pa, a coating time of 1 s, and the temperature of the main roller during the coating process is 20 °C.

[0154] Test and evaluation:

[0155] The mechanical properties of the prepared composite current collector and the safety performance of the assembled battery were tested here. The specific test methods are as follows:

[0156] 1. Crack growth range:

[0157] The tensile test was carried out in accordance with GB / T 1040.3-2006, and the stress-strain curve of the sample was plotted (see Figure 2 ), record the starting point b of crack nucleation and the deformation end point e of complete fracture.

[0158] The starting point b and the deformation end point e are the b point and the e point in the stress-strain curve diagram.

[0159] 2. Safety performance:

[0160] ① Battery assembly:

[0161] For the positive electrode, the positive current collector is made of aluminum foil (thickness 13 μm), and the positive electrode material is LiNi0.6Mn0.2Co0.2O2 (NCM622);

[0162] For the negative electrode: the negative current collector is the composite current collector prepared in the above-mentioned examples and comparative examples, and the negative electrode material is artificial graphite;

[0163] For the separator, an alumina ceramic-coated polyethylene separator (thickness 25 μm) is used;

[0164] For the electrolyte, a carbonate solution of 1 mol·L-1 LiPF6 is used, and 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;

[0165] Using the above materials, a lithium-ion battery was assembled.

[0166] ② Needle penetration rate:

[0167] ⅰ. The needle penetration experiment was used to verify the safety performance of the battery, 100 samples were measured, and the passing rate was recorded.

[0168] ⅱ. Experimental procedure: Place the battery prepared above in a needle penetration experimental device, where the diameter of the needle is 3 mm, the needle penetration speed is 10 mm / s, the sampling interval is 100 ms, the sampling time is 15 min, and the battery is qualified if it does not explode, catch fire or emit smoke. Record the needle penetration passing rate, that is, the number of passing samples × 100%.

[0169] The test results are shown in Table 1.

[0170] Table 1

[0171]

[0172]

[0173] As can be seen from Table 1, in the present invention, a transition layer and a conductive layer with a multi-layer structure are provided on the surface of the polymer film. By adding the transition layer with a multi-layer structure, the composite current collector has a ductile isomeric property between layers. Under the action of mechanical external force, cracks are first generated in the transition layer and spread to the surrounding area, forming inter-layer cracks, and regulating the crack growth range of the composite current collector to satisfy:

[0174] (1) b < r < e, where b is the starting point of crack nucleation and e is the deformation end point of complete fracture;

[0175] (2) 0 < b - 2 ≤ 10;

[0176] (3) e - b > 15.

[0177] Thereby, the electron path can be cut off, effectively improving the safety performance of the composite current collector. The needle penetration rate of the battery assembled with the composite current collector of the present invention is above 80%.

[0178] Compared with the case without a transition layer (Comparative Example 1), by providing a transition layer with a multi-layer structure on the surface of the polymer film, the present invention can effectively improve the safety performance of the battery.

[0179] The applicant declares that the present invention uses the above embodiments to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0180] The applicant declares that the present invention uses the above embodiments to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A composite current collector, characterized in that, The composite current collector includes a polymer film, and a transition layer and a conductive layer are sequentially disposed on at least one surface of the polymer film; The transition layer is composed of multiple functional layers; The multiple functional layers are niobium carbide, niobium pentoxide, and tantalum pentoxide sequentially stacked in a direction away from the polymer film; The conductive layer is a metal layer, and the thickness of the metal layer is 600 nm to 1000 nm; The total thickness of the transition layer is 20% - 65% of the thickness of the conductive layer; The crack growth interval r (%) of the composite current collector satisfies the following conditions: (1) b < r < e, where b is the starting point of crack nucleation of the composite current collector, and e is the deformation end point of complete fracture of the composite current collector; （2）0＜b-2≤2； (3) e - b > 24.

2. The composite current collector according to claim 1, wherein At least one group of adjacent functional layers in the transition layer has a thickness ratio of (0.0001 - 10000):

1.

3. The composite current collector according to claim 1, wherein The material of the polymer film includes at least one of polyethylene terephthalate, polypropylene, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene ether, polystyrene, or polyimide.

4. The composite current collector according to claim 1, wherein The thickness of the polymer film is 1 μm to 10 μm.

5. The composite current collector according to claim 1, wherein The material of the metal layer is at least one of aluminum, copper, gold, silver, nickel, and zinc and their alloys.

6. A method for preparing a composite current collector according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: Form a transition layer on at least one side of the polymer film; Form a conductive layer on the surface of the transition layer to obtain a composite current collector.

7. The preparation method of the composite current collector according to claim 6, wherein The preparation method of the transition layer is magnetron sputtering.

8. The preparation method of the composite current collector according to claim 6, wherein The preparation method of the conductive layer is any one of evaporation plating, magnetron sputtering, electroless plating, electroplating, or chemical vapor deposition.

9. A battery, characterized in that, The battery includes the composite current collector according to any one of claims 1 - 5 or the composite current collector prepared by the preparation method according to any one of claims 6 - 8.

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