A composite current collector, a preparation method thereof, and a lithium-ion battery

Abstract

The present disclosure provides a composite current collector, a preparation method thereof, and a lithium-ion battery. The composite current collector includes a polymer-based film and a composite conductive layer disposed on at least one surface of the polymer-based film; the composite conductive layer includes a transition layer and a metal layer that are alternately stacked, the transition layer includes a fluorocarbon material, and the fluorocarbon material is a fluorocarbon polymer. The present disclosure proposes a new composite current collector. By constructing a unique conductive layer structure with an alternately stacked transition layer and metal layer, the cycle charge and discharge performance and safety performance of a lithium-ion battery based on the composite current collector can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a composite current collector, a preparation method thereof, and a lithium-ion 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 generally 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 electrical 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] For composite current collectors, there are mainly two problems: ① Since the metal layer of the composite current collector is relatively thin and is continuously eroded by the electrolyte during the charge and discharge cycles of the battery, its performance decays significantly, resulting in poor charge and discharge cycle performance of the battery; ② Currently, the safety of the battery is mainly improved by relying on the insulation and flame retardant properties of the intermediate layer, that is, the polymer film layer. However, although this improves the safety performance of the battery to a certain extent, the improvement is limited.

[0004] Therefore, in order to further improve the charge and discharge cycle and 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

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a composite current collector, a preparation method thereof, and a lithium-ion battery. The present invention proposes a new composite current collector, and constructs a unique conductive layer structure by alternately laminating a transition layer and a metal layer, which can improve the charge and discharge cycle performance and safety performance of lithium-ion batteries based on this composite current collector.

[0006] To achieve this disclosure purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a composite current collector, which includes a polymer-based film and a composite conductive layer provided on at least one surface of the polymer-based film;

[0008] The composite conductive layer includes a transition layer and a metal layer alternately laminated, and the transition layer includes a fluorocarbon material, and the fluorocarbon material is a fluorocarbon polymer.

[0009] The present invention proposes a new composite current collector. By constructing a unique conductive layer structure through alternately stacked transition layers and metal layers, the cyclic charge-discharge performance and safety performance of lithium-ion batteries based on this composite current collector can be improved.

[0010] In the present invention, the transition layers and metal layers are alternately stacked, which helps to achieve layer-by-layer protection of the metal layers and adjust the grain structure of the metal layers, thereby promoting the improvement of the cyclic charge-discharge performance and safety performance of the batteries based on this composite current collector.

[0011] In the present invention, the transition layer contains fluorocarbon materials, and the transition layer has the following functions: ① Good barrier and tolerance to the electrolyte, which can achieve layer-by-layer protection of the metal layer, thereby promoting the improvement of the cyclic charge-discharge performance of the battery based on this composite copper current collector; ② It can block the penetration of adjacent metal layer grains, promote the re-nucleation and growth of grains, thereby generating non-penetrating and smaller-sized grains. The metal layer composed of non-penetrating and small-sized grains will generate microcracks after a certain deformation during the battery pinprick process and quickly spread to the surrounding area, resulting in large-area fracture and fragmentation of the metal layer, thereby realizing the separation of the metal layer from the steel needle, avoiding the conduction of the positive and negative current collectors to form a closed circuit and the resulting battery thermal runaway, thus improving the safety performance of the battery; ③ It can strengthen the strain hardening of the composite current collector and reduce local stress concentration, thereby promoting the propagation of cracks generated by the deformation of the metal layer of the composite current collector to the surrounding area during the battery pinprick process, continuously promoting large-area fracture and fragmentation of the metal layer, avoiding the conduction of the positive and negative current collectors to form a closed circuit and the resulting battery thermal runaway, and improving the safety performance of the battery. ④ Compared with carbon materials, carbon materials are more brittle, which means that the transition layer formed by carbon materials is more likely to break when stressed or loaded. Therefore, in the production process, the requirements for making the carbon layer are higher, and the materials and processes required for preparing the carbon layer are more complex and delicate. The production process requires more strict control and monitoring to ensure that the quality and performance of the carbon layer meet the requirements.

[0012] As a preferred technical solution of the present invention, the transition layer contains fluorocarbon materials.

[0013] In some embodiments, the fluorocarbon material is a fluorocarbon polymer.

[0014] In some embodiments, the fluorocarbon polymer is a polymer material containing fluorine elements and carbon elements.

[0015] In some embodiments, the fluorocarbon polymer is a polymer material composed of fluorine elements and carbon elements.

[0016] In some embodiments, the chemical composition of the fluorocarbon polymer is C x F y, wherein, 0.6 ≤ x / y ≤ 10, for example, it can be 0.6, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0017] In the present invention, if x / y is too low, that is, the carbon content is too low, resulting in poor conductivity of the transition layer, thus leading to poor conductivity of the prepared composite current collector and poor cycle performance of the battery; if x / y is too high, that is, the carbon content is too high, the flexibility of the transition layer becomes poor, and defects are easily generated, resulting in poor cycle performance of the battery.

[0018] In some embodiments, the weight-average molecular weight of the fluorocarbon polymer is 10 - 100 kDa, for example, it can be 10 kDa, 30 kDa, 50 kDa, 70 kDa, 90 kDa, 100 kDa, etc., and preferably 10 - 60 kDa.

[0019] In some embodiments, the crystallinity range of the fluorocarbon polymer is 20% - 80%, for example, it can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, etc.

[0020] In the present invention, increasing the crystallinity can improve the tolerance of the fluorocarbon layer to the electrolyte and promote its protective effect on the metal layer, thereby promoting the improvement of the battery cycle performance. However, the crystallinity should not be too high, as too high crystallinity will increase the brittleness of the fluorocarbon layer, resulting in defects easily generated during the production of battery electrodes and causing poor cycle performance of the battery.

[0021] As a preferred technical solution of the present invention, the number of layers of the transition layer > 2 layers, for example, it can be 3 layers, 4 layers, 6 layers, 8 layers, 10 layers, 12 layers, 14 layers, 16 layers, 18 layers, etc., and preferably 5 - 15 layers.

[0022] In the present invention, considering the disclosure effect and preparation efficiency, the number of layers of the transition layer is preferably 5 - 15 layers. If it is too small, the improvement effect of the prepared composite current collector on the battery safety will become poor; if it is too large, the efficiency of preparing the composite current collector is too low, and the performance of the composite current collector cannot be further significantly improved.

[0023] In some embodiments, the surface density of the fluorocarbon layer on the side close to the electrolyte is greater than the surface density of the fluorocarbon layer on the side close to the polymer base film.

[0024] In some embodiments, it is defined that the surface density of the fluorocarbon layer on the side close to the electrolyte is greater than the surface density of the fluorocarbon layer on the side close to the polymer base film, which is beneficial to improving the tolerance to the electrolyte.

[0025] In some embodiments, the single-layer thickness of the transition layer is 2 - 50 nm, for example, it can be 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc., and preferably 5 - 20 nm.

[0026] In the present invention, if the single layer thickness of the transition layer is too thin, the performance improvement is not obvious; if the single layer thickness of the transition layer is too thick, the safety performance of the composite current collector cannot be further improved, and it will lead to higher costs, poorer conductivity of the composite current collector, and ultimately worse cycle performance of the battery.

[0027] As a preferred technical solution of the present invention, the material of the metal layer includes metal element and / or metal alloy.

[0028] In the present invention, the function of the metal layer is to conduct electricity.

[0029] In some embodiments, the metal element includes any one of aluminum, copper, gold, silver, nickel or zinc.

[0030] In some embodiments, the metal alloy includes a combination of at least two of aluminum, copper, gold, silver, nickel, or zinc.

[0031] In some embodiments, the number of the metal layers is greater than 2 layers, for example, 3 layers, 4 layers, 6 layers, 8 layers, 10 layers, 12 layers, 14 layers, 16 layers or 18 layers, etc., preferably 5-15 layers.

[0032] In the present invention, considering the technical effect and preparation efficiency, the preferred number of metal layers is 5-15 layers. If it is too small, the effect of improving the safety of the battery by the prepared composite current collector will be poor. If it is too large, the efficiency of preparing the composite current collector will be too low and the performance of the composite current collector cannot be further significantly improved.

[0033] In some embodiments, the single layer thickness of the metal layer is 0-200 nm, excluding 0, for example, it can be 5 nm, 10 nm, 50 nm, 100 nm, 150 nm or 200 nm, etc., preferably 50-150 nm.

[0034] In the present invention, the single layer thickness of the metal layer should not be too thick, as too thick is not conducive to improving the safety performance of the battery. If the metal layer is too thin, it will affect the preparation efficiency and increase the cost.

[0035] As a preferred technical solution of the present invention, the thickness of the composite conductive layer is 500-2000 nm, for example, it can be 500 nm, 1000 nm, 1500 nm or 2000 nm, etc., preferably 800-1200 nm.

[0036] In the present invention, if the composite conductive layer is too thin, the conductivity is poor; if the composite conductive layer is too thick, the prepared composite current collector is not conducive to improving the energy density of the battery. Considering the conductivity and the improvement of energy density, the more preferred thickness is 800-1200nm.

[0037] In some embodiments, the thickness of the polymer-based film is ≥1 μm, preferably 1-10 μm, and can be, for example, 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 10 μm, etc.

[0038] In the present invention, considering the application requirements of the composite current collector and taking into account the difficulty and cost of the preparation process, the thickness of the polymer film is preferably 1-10 μm.

[0039] Preferably, the material of the polymer-based film includes 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).

[0040] As a preferred technical solution of the present invention, the composite current collector further includes a protective layer;

[0041] When the composite conductive layer is disposed on one surface of the polymer-based film, the protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film and the other surface of the polymer-based film; or,

[0042] When the composite conductive layer is disposed on one surface of the polymer-based film, the protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film; or,

[0043] When the composite conductive layer is disposed on both surfaces of the polymer-based film, the protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film.

[0044] In the present invention, the function of the protective layer is to prevent the composite conductive layer from being chemically corroded or physically damaged.

[0045] Preferably, the single-sided thickness of the protective layer is 5-100 nm, and can be, for example, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, etc., and is preferably 10-80 nm.

[0046] Preferably, the material of the protective layer includes any one or a combination of at least two of nickel, chromium, nickel-based alloy, copper-based alloy, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, copper chromate, cuprous chromite, carbon nano quantum dots, carbon nanotubes, carbon nanofibers, or graphene.

[0047] Second aspect, the present invention provides a method for preparing a composite current collector as described in the first aspect, and the preparation method includes the following steps:

[0048] Alternately deposit a transition layer and a metal layer on at least one surface of the polymer-based film to obtain the composite current collector.

[0049] The present invention does not limit the preparation method of the polymer-based film. Exemplarily, for example, it can be a melt-extrusion-biaxial stretching method.

[0050] As a preferred technical solution of the present invention, the preparation method of the transition layer includes magnetron sputtering or chemical vapor deposition, preferably magnetron sputtering.

[0051] Preferably, the specific process parameters of the magnetron sputtering method include:

[0052] The target is a mixture target of carbon material-fluorine-containing material, the target power is 1-10 kW, for example, it can be 1 kW, 3 kW, 5 kW, 7 kW, 9 kW or 10 kW, etc., the vacuum degree ≤ 0.1 Pa, for example, it can be 0.1 Pa, 0.08 Pa, 0.05 Pa or 0.03 Pa, etc., the gas flow rate is 20-500 mL / min, for example, it can be 20 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min or 500 mL / min, etc., and the coating time of a single-layer transition layer is 0.1-60 s, for example, it can be 0.1 s, 0.5 s, 1 s, 5 s, 10 s, 20 s, 30 s, 40 s, 50 s or 60 s, etc.

[0053] Preferably, the type of the gas includes argon.

[0054] Preferably, the carbon material includes graphite.

[0055] Preferably, the fluorine material includes polytetrafluoroethylene.

[0056] Preferably, the preparation method of the metal layer includes any one or a combination of at least two of physical vapor deposition, electroplating or electroless plating.

[0057] Preferably, after depositing the transition layer and the metal layer, a protective layer is also deposited, and the preparation method of the protective layer includes any one or a combination of at least two of physical vapor deposition, chemical vapor deposition, in-situ forming or coating.

[0058] Preferably, the physical vapor deposition includes vacuum evaporation or magnetron sputtering.

[0059] Preferably, the chemical vapor deposition includes atmospheric pressure chemical vapor deposition or plasma enhanced chemical vapor deposition.

[0060] Preferably, the specific steps of the in-situ forming method include: in-situ forming a metal oxide passivation layer on the surface of the metal layer.

[0061] Preferably, the coating method includes die coating, knife coating or extrusion coating method.

[0062] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0063] (1) Alternately depositing a transition layer and a metal layer on both surfaces of the polymer-based film to form a composite conductive layer;

[0064] The preparation method of the transition layer is magnetron sputtering method, and the specific process parameters include: the target is a mixture target of carbon material - fluorine-containing material, the target power is 1 - 10 kW, the vacuum degree ≤ 0.1 Pa, the gas flow rate is 20 - 500 mL / min, and the coating time of a single-layer transition layer is 0.1 - 60 s;

[0065] The preparation method of the metal layer is physical vapor deposition method, and the specific process parameters include:

[0066] The target is any one of a copper target, an aluminum target or a copper-aluminum alloy target, the target power is 10 - 14 kW (for example, it can be 10 kW, 11 kW, 12 kW, 13 kW or 14 kW, etc.), the gas flow rate is 20 - 500 mL / min (for example, it can be 20 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min or 60 mL / min, etc.), the vacuum degree ≤ 0.1 Pa (for example, it can be 0.1 Pa, 0.08 Pa, 0.05 Pa or 0.03 Pa, etc.), and the coating time of a single-layer metal layer is 5 - 20 s (for example, it can be 5 s, 10 s, 15 s or 20 s, etc.).

[0067] (2) Using the coating method to deposit a protective layer on the surface of the composite conductive layer away from the polymer-based film, and the specific process steps include:

[0068] Coating the coating liquid of the protective layer on the surface of the composite conductive layer, and drying to obtain the protective layer.

[0069] In the third aspect, the present invention provides a lithium-ion battery, and the lithium-ion battery includes an electrode pole piece, and the electrode pole piece includes the composite current collector as described in the first aspect.

[0070] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges 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 range.

[0071] Compared with the prior art, the present invention has the following beneficial effects:

[0072] (1) The present invention proposes a new composite current collector, and constructs a unique conductive layer structure through alternately stacked transition layers and metal layers, which can improve the cycle charge and discharge performance and safety performance of lithium-ion batteries based on the composite current collector.

[0073] (2) The preparation method provided by the present invention is simple and easy to implement, and is easy to scale up production. Specific Embodiments

[0074] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0075] Example 1

[0076] This example provides a composite current collector, which includes a polymer-based film and composite conductive layers disposed on both surface sides of the polymer-based film;

[0077] The composite conductive layer includes alternately stacked transition layers and metal layers. The transition layer includes a fluorocarbon material, and the fluorocarbon material is a fluorocarbon polymer;

[0078] The chemical composition of the fluorocarbon polymer is C x F y , where x / y = 5, and the weight average molecular weight of the fluorocarbon polymer is 32000 Da;

[0079] The number of layers of the transition layer is 10 layers, the single-layer thickness of the transition layer is 5 nm, the number of layers of the metal layer is 10 layers, the material of the metal layer is copper, and the single-layer thickness of the metal layer is 50 nm;

[0080] The thickness of the composite conductive layer disposed on one surface side of the polymer-based film is 550 nm;

[0081] The thickness of the polymer-based film is 4.5 μm, and the material is PET;

[0082] A protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film, and the single-sided thickness of the protective layer is 5 nm, and the material is graphene;

[0083] The thickness of the composite current collector is 5.61 μm.

[0084] This example also provides a preparation method for the above composite current collector, and the preparation method includes the following steps:

[0085] (1) Place the PET film prepared by the melt-extrusion-biaxial stretching method in a magnetron sputtering machine, and alternately deposit a transition layer and a copper layer on both surfaces of the PET film. The number of layers of the transition layer is 10, and the number of layers of the copper layer is 10, to obtain a PET composite film containing a composite conductive layer;

[0086] Among them, the single-layer preparation process parameters of the transition layer include: using a graphite-polytetrafluoroethylene mixture target (the mass ratio of graphite to polytetrafluoroethylene is 2.16:1) as the target, the target power is 3 kW, the flow rate of argon is 50 mL / min, the coating vacuum degree is 0.08 Pa, the coating time is 1 s, and the temperature of the main roller during the coating process is 0 °C;

[0087] Among them, the single-layer preparation process parameters of the copper layer include: using a copper target (purity 99.99%) as the target, the target power is 12 kW, the flow rate of argon is 50 mL / min, the coating vacuum degree is 0.08 Pa, the coating time is 5 s, and the temperature of the main roller during the coating process is 2 °C;

[0088] (2) Place the above-prepared PET composite film in a coating device, use a graphene solution with a solid content of 0.1 wt.% (the solvent is N-methylpyrrolidone) as the coating liquid, and then evenly coat the coating liquid on both surfaces of the PET composite film through the die coating process, and finally dry it at 70 °C to obtain a protective layer with a single-sided thickness of 5 nm, and finally obtain the composite current collector.

[0089] Example 2

[0090] The difference between this example and Example 1 is that the single-layer thickness of the metal layer in the composite conductive layer is 100 nm, and at the same time, the coating time in the single-layer preparation process parameters is adjusted to 10 s.

[0091] The remaining preparation methods and parameters are the same as those in Example 1.

[0092] Example 3

[0093] The difference between this example and Example 1 is that the single-layer thickness of the metal layer in the composite conductive layer is 150 nm, and at the same time, the coating time in the single-layer preparation process parameters is adjusted to 15 s.

[0094] The remaining preparation methods and parameters are the same as those in Example 1.

[0095] Example 4

[0096] The difference between this example and Example 1 is that the single-layer thickness of the metal layer in the composite conductive layer is 200 nm, and at the same time, the coating time in the single-layer preparation process parameters is adjusted to 20 s.

[0097] The remaining preparation methods and parameters are the same as those in Example 1.

[0098] Example 5

[0099] The difference between this example and Example 2 is that the single-layer thickness of the transition layer in the composite conductive layer is 2 nm, and at the same time, the coating time in the preparation process parameters of a single layer is adjusted to 0.4 s.

[0100] The remaining preparation methods and parameters are the same as those in Example 2.

[0101] Example 6

[0102] The difference between this example and Example 2 is that the single-layer thickness of the transition layer in the composite conductive layer is 20 nm, and at the same time, the coating time in the preparation process parameters of a single layer is adjusted to 4 s.

[0103] The remaining preparation methods and parameters are the same as those in Example 2.

[0104] Example 7

[0105] The difference between this example and Example 2 is that the single-layer thickness of the transition layer in the composite conductive layer is 50 nm, and at the same time, the coating time in the preparation process parameters of a single layer is adjusted to 10 s.

[0106] The remaining preparation methods and parameters are the same as those in Example 2.

[0107] Example 8

[0108] The difference between this example and Example 2 is that both the transition layer and the metal layer have 3 layers, and the single-layer thickness of the metal layer is 200 nm. At the same time, the coating time in the preparation process parameters of a single layer is adjusted to 20 s.

[0109] The remaining preparation methods and parameters are the same as those in Example 2.

[0110] Example 9

[0111] The difference between this example and Example 2 is that both the transition layer and the metal layer have 5 layers.

[0112] The remaining preparation methods and parameters are the same as those in Example 2.

[0113] Example 10

[0114] The difference between this example and Example 2 is that both the transition layer and the metal layer have 15 layers.

[0115] The remaining preparation methods and parameters are the same as those in Example 2.

[0116] Example 11

[0117] The difference between this embodiment and Embodiment 1 is that the material of the metal layer is aluminum. Meanwhile, in the preparation process parameters of the single layer, the target is adjusted to an aluminum target with a purity of 99.99%, the target power is adjusted to 10 kW, the coating vacuum degree is adjusted to 0.07 Pa, and the temperature of the main roller during the coating process is adjusted to 0 °C.

[0118] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0119] Embodiment 12

[0120] The difference between this embodiment and Embodiment 1 is that the material of the polymer-based film is adjusted to PP.

[0121] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0122] Embodiment 13

[0123] The difference between this embodiment and Embodiment 1 is that the chemical composition of the fluorocarbon polymer in the transition layer is C x F y , where x / y = 0.6. Meanwhile, in the preparation process parameters of the single layer, the mass ratio of graphite to polytetrafluoroethylene in the target is adjusted to 0.048:1, and the target power is adjusted to 5 kW.

[0124] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0125] Embodiment 14

[0126] The difference between this embodiment and Embodiment 1 is that the chemical composition of the fluorocarbon polymer in the transition layer is C x F y , where x / y = 10. Meanwhile, in the preparation process parameters of the single layer, the mass ratio of graphite to polytetrafluoroethylene in the target is adjusted to 4.56:1, and the target power is adjusted to 5 kW.

[0127] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0128] Embodiment 15

[0129] The difference between this embodiment and Embodiment 1 is that the single layer thickness of the metal layer in the composite conductive layer is 220 nm. Meanwhile, in the preparation process parameters of the single layer, the coating time is adjusted to 22 s.

[0130] The remaining preparation methods and parameters are the same as those in Embodiment 1.

[0131] Embodiment 16

[0132] The difference between this embodiment and Embodiment 2 is that the single layer thickness of the transition layer in the composite conductive layer is 55 nm. Meanwhile, in the preparation process parameters of the single layer, the coating time is adjusted to 11 s.

[0133] The remaining preparation methods and parameters are the same as those in Example 2.

[0134] Example 17

[0135] The difference between this example and Example 2 is that the single-layer thickness of the transition layer in the composite conductive layer is 1 nm, and at the same time, the coating time in the preparation process parameters of the single layer is adjusted to 0.2 s.

[0136] The remaining preparation methods and parameters are the same as those in Example 2.

[0137] Example 18

[0138] The difference between this example and Example 2 is that the number of layers of both the transition layer and the metal layer is 16.

[0139] The remaining preparation methods and parameters are the same as those in Example 2.

[0140] Example 19

[0141] The difference between this example and Example 8 is that the number of layers of both the transition layer and the metal layer is 2.

[0142] The remaining preparation methods and parameters are the same as those in Example 8.

[0143] Example 20

[0144] The difference between this example and Example 1 is that the chemical composition of the fluorocarbon polymer in the transition layer is C x F y , where x / y = 0.55. At the same time, in the preparation process parameters of the single layer, the mass ratio of graphite to polytetrafluoroethylene in the target is adjusted to 0.024:1, and the target power is adjusted to 6 kW.

[0145] The remaining preparation methods and parameters are the same as those in Example 1.

[0146] Example 21

[0147] The difference between this example and Example 1 is that the chemical composition of the fluorocarbon polymer in the transition layer is C x F y , where x / y = 11. At the same time, in the preparation process parameters of the single layer, the mass ratio of graphite to polytetrafluoroethylene in the target is adjusted to 5.04:1, and the target power is adjusted to 6 kW.

[0148] The remaining preparation methods and parameters are the same as those in Example 1.

[0149] Comparative Example 1

[0150] The difference between this comparative example and Example 1 is that the composite conductive layer does not contain a transition layer, that is, it only contains a metal layer with a single-sided thickness of 500 nm, and at the same time, the coating time in the preparation process parameters is adjusted to 50 s.

[0151] The remaining preparation methods and parameters are the same as those in Example 1.

[0152] Comparative Example 2

[0153] The difference between this comparative example and Example 1 is that the transition layer is replaced by a carbon layer, and at the same time, the target in the preparation process parameters of a single layer is adjusted to a graphite target.

[0154] The remaining preparation methods and parameters are the same as those in Example 1.

[0155] Performance Test

[0156] The composite current collectors prepared above are made into batteries. The specific steps include:

[0157] The positive current collector uses a traditional aluminum current collector (with a thickness of 13 μm), and the positive electrode material uses LiNi 0.6 Mn 0.2 Co 0.2 O2; the negative current collector uses the composite current collectors provided in Examples 1-10, Examples 12-21, and Comparative Examples 1-2, and the negative electrode material uses artificial graphite; for the separator, a polyethylene separator coated with aluminum oxide ceramic (with a thickness of 25 μm) is used; for the electrolyte, a 1 mol·L -1 LiPF6 carbonate solution, where the solvents include propylene carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1; using the above materials, a lithium-ion battery is assembled according to the relevant process; or,

[0158] The positive current collector uses the composite current collector provided in Example 11, and the positive electrode material uses LiNi 0.6 Mn 0.2 Co 0.2 O2; the negative current collector uses a traditional copper current collector (with a thickness of 6 μm), and the negative electrode material uses artificial graphite; for the separator, a polyethylene separator coated with aluminum oxide ceramic (with a thickness of 25 μm) is used; for the electrolyte, a 1 mol·L -1 LiPF6 carbonate solution, where the solvents include propylene carbonate, ethylene carbonate, and ethyl methyl carbonate, and the mass ratio of the three is 1:1:1; using the above materials, a lithium-ion battery is assembled according to the relevant process.

[0159] The lithium-ion batteries prepared above are tested for charge-discharge cycle performance and safety performance.

[0160] Charge and discharge cycle performance test: With a charge and discharge rate of 1C, the battery was cycled for 2000 times, and the battery capacity retention rate after 2000 cycles of charge and discharge was recorded, that is, the battery capacity after 2000 cycles of charge and discharge / the initial capacity of the battery × 100%.

[0161] Safety performance test: The safety performance of the battery was verified by a needle penetration experiment, which is as follows: 100 batteries prepared above were placed in a needle penetration experiment device. The diameter of the steel needle was 3mm, and the needle penetration speed was 10mm / s. If the battery did not explode, catch fire, or emit smoke during the needle penetration process, it passed; otherwise, it failed. Record the number of batteries that passed and failed, and the needle penetration pass rate of the battery can be obtained, that is, the number of passing batteries / the total number of batteries × 100%.

[0162] The test results are shown in Table 1.

[0163] Table 1

[0164]

[0165]

[0166] In addition, the elongation at break of Example 1 and Comparative Example 2 was also tested. The test method for the elongation at break was as follows: Samples were taken longitudinally along the prepared composite current collector, and then the elongation at break was tested with reference to GB / T 1040.3-2006 of the national standard.

[0167] The test results are shown in Table 2.

[0168] Table 2

[0169]

[0170] Analysis:

[0171] As can be seen from Tables 1 and 2 above, compared with traditional composite current collectors, due to the introduction of the transition layer, the prepared composite current collector can improve the battery capacity retention rate and needle penetration pass rate, that is, improve the charge and discharge cycle performance and safety performance of the battery.

[0172] From Examples 1-4 and Example 15, it can be seen that increasing the thickness of the metal layer, the charge and discharge cycle performance and safety performance of the battery based on the composite copper current collector both show a trend of first increasing and then decreasing. This may be because the change in the metal layer thickness will affect the grain size of the metal layer along the thickness direction, thereby affecting the fracture behavior of the metal layer during the needle penetration process, resulting in changes in safety performance. At the same time, the change in the grain size along the thickness direction will also affect the conduction resistance of electrons during the charge and discharge process of the battery, thereby affecting the charge and discharge cycle performance of the battery.

[0173] As can be seen from Example 2, Examples 5-7, and Examples 16-17, increasing the thickness of the transition layer shows a trend of improving the cyclic charge-discharge performance of the battery based on the composite copper current collector. However, when the thickness exceeds a certain value, the cyclic charge-discharge performance deteriorates. This may be because increasing the thickness of the transition layer can improve the barrier and tolerance of the transition layer to the electrolyte, thereby promoting the improvement of the cyclic charge-discharge performance of the battery based on this composite copper current collector. However, if the transition layer is too thick, it will affect the conductivity of the conductive layer, resulting in deterioration of the cyclic charge-discharge performance of the battery based on this composite copper current collector. Increasing the thickness of the transition layer also shows a trend of first increasing and then remaining unchanged in the safety performance of the battery based on the composite copper current collector. This may be because increasing the thickness of the transition layer can promote large-area fission of the conductive layer during the acupuncture process, causing the conductive layer to be more easily disconnected from the steel needle, thereby promoting the improvement of the safety performance of the battery based on this composite copper current collector. However, when the thickness exceeds a certain value, this effect will not be further promoted, resulting in the safety performance remaining unchanged.

[0174] As can be seen from Example 2, Examples 8-10, Examples 18-19, and Comparative Example 1, increasing the number of layers of the metal layer and the transition layer shows a trend of improving both the cyclic charge-discharge performance and the safety performance of the battery based on the composite copper current collector. This may be because increasing the number of layers can, on the one hand, enhance the multi-layer alternating structure of the transition layer and the metal layer, promoting the layer-by-layer protection of the metal layer, thereby promoting the improvement of the cyclic charge-discharge performance of the battery; on the other hand, increasing the number of layers can promote more easily large-area fission of the conductive layer during the acupuncture process, causing the conductive layer to be more easily disconnected from the steel needle, thereby promoting the improvement of the safety performance of the battery based on this composite copper current collector. However, when the number of layers exceeds 15, the performance improvement is not obvious. Considering the preparation efficiency of the composite current collector, the preferred number of layers is 5-15.

[0175] As can be seen from Example 1, Examples 13-14, and Examples 20-21, the chemical composition of the fluorocarbon polymer in the transition layer is C x F y . If x / y is too low, the carbon content is too low, resulting in poor conductivity of the transition layer, thereby causing poor conductivity of the prepared composite current collector and poor cyclic performance of the battery; if x / y is too high, the carbon content is too high, the flexibility of the transition layer becomes poor, and defects are easily generated, resulting in poor cyclic performance of the battery.

[0176] As can be seen from Example 1 and Comparative Example 2, if the fluorocarbon layer is replaced with a carbon layer, compared with the fluorocarbon layer, although the overall performance of the traditional composite current collector can be improved by setting a carbon layer, for example, the corrosion resistance is increased. However, the addition of the carbon layer also reduces the elongation at break of the material, making it more likely to break during the preparation of the electrode sheet, resulting in a lower yield rate of the prepared battery electrode sheet. This is because the carbon layer is more brittle than the fluorocarbon polymer, and its presence increases the brittleness of the overall material.

[0177] The applicant declares that the process method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for 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-based film and a composite conductive layer disposed on at least one surface of the polymer-based film; The composite conductive layer includes a transition layer and a metal layer that are alternately stacked. The transition layer includes a fluorocarbon material, and the fluorocarbon material is a fluorocarbon polymer; the chemical composition of the fluorocarbon polymer is C x F y , where 0.6 ≤ x / y ≤ 10; The number of layers of the transition layer is 5 - 15 layers; the single-layer thickness of the transition layer is 2 - 50 nm; The number of layers of the metal layer is 5 - 15 layers; The single-layer thickness of the metal layer is 0 - 200 nm, and 0 is not included.

2. The composite current collector according to claim 1, wherein The single-layer thickness of the transition layer is 5 - 20 nm.

3. The composite current collector according to claim 1, wherein, The material of the metal layer includes metallic elements and / or metal alloys.

4. The composite current collector according to claim 3, wherein The metallic element includes any one of aluminum, copper, gold, silver, nickel, or zinc; the metal alloy includes a combination of at least two of aluminum, copper, gold, silver, nickel, or zinc.

5. The composite current collector according to claim 1, wherein The single-layer thickness of the metal layer is 50 - 150 nm.

6. The composite current collector according to claim 1, wherein, The thickness of the composite conductive layer disposed on one surface of the polymer-based film is 500 - 2000 nm.

7. The composite current collector according to claim 6, wherein The thickness of the composite conductive layer disposed on one surface of the polymer-based film is 800 - 1200 nm.

8. The composite current collector according to claim 1, wherein The thickness of the polymer-based film ≥ 1 μm.

9. The composite current collector according to claim 8, wherein The thickness of the polymer-based film is 1 - 10 μm.

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

11. The composite current collector according to claim 1, wherein, The composite current collector further includes a protective layer; When the composite conductive layer is disposed on one surface of the polymer-based film, the protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film and the other surface of the polymer-based film; or, When the composite conductive layer is disposed on one surface of the polymer-based film, the protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film; or, When the composite conductive layer is disposed on both surfaces of the polymer-based film, the protective layer is disposed on the surface of the composite conductive layer away from the polymer-based film.

12. The composite current collector according to claim 11, wherein The single-sided thickness of the protective layer is 5 - 100 nm.

13. The composite current collector according to claim 12, wherein The single-sided thickness of the protective layer is 10 - 80 nm.

14. The composite current collector according to claim 11, wherein The material of the protective layer includes any one or a combination of at least two of nickel, chromium, nickel-based alloys, copper-based alloys, copper oxide, aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, graphite, carbon black, copper chromate, cuprous chromite, carbon nano quantum dots, carbon nanotubes, carbon nanofibers, or graphene.

15. A method for preparing a composite current collector according to any one of claims 1-14, characterized in that, The preparation method includes the following steps: Alternately deposit a transition layer and a metal layer on at least one surface of the polymer-based film to obtain the composite current collector.

16. The preparation method according to claim 15, characterized in that, The preparation method of the transition layer includes magnetron sputtering or chemical vapor deposition.

17. The preparation method according to claim 16, wherein, The preparation method of the transition layer is magnetron sputtering.

18. The preparation method according to claim 17, wherein The specific process parameters of the magnetron sputtering method include: The target is a mixture target of carbon material - fluorine-containing material, the target power is 1 - 10 kW, the vacuum degree ≤ 0.1 Pa, the gas flow rate is 20 - 500 mL / min, and the coating time of a single-layer transition layer is 0.1 - 60 s.

19. The preparation method according to claim 15, characterized in that, The preparation method of the metal layer includes any one or a combination of at least two of physical vapor deposition, electroplating, or electroless plating.

20. The preparation method according to claim 15, wherein After depositing the deposition transition layer and the metal layer, a protective layer is further deposited. The preparation method of the protective layer includes any one or a combination of at least two of physical vapor deposition method, chemical vapor deposition method, in-situ forming method or coating method.

21. The preparation method according to claim 15, characterized in that, The preparation method includes the following steps: (1) Alternately deposit a transition layer and a metal layer on both side surfaces of the polymer-based film to form a composite conductive layer; The preparation method of the transition layer is magnetron sputtering method. The specific process parameters include: the target is a mixture target of carbon material - fluorine-containing material, the target power is 1 - 10 kW, the vacuum degree is ≤ 0.1 Pa, the gas flow rate is 20 - 500 mL / min, and the coating time of a single-layer transition layer is 0.1 - 60 s; The preparation method of the metal layer is physical vapor deposition method. The specific process parameters include: The target is any one of a copper target, an aluminum target or a copper-aluminum alloy target, the target power is 10 - 14 kW, the gas flow rate is 20 - 500 mL / min, the vacuum degree is ≤ 0.1 Pa, and the coating time of a single-layer metal layer is 5 - 20 s; (2) Deposit a protective layer on the surface of the composite conductive layer away from the polymer-based film by coating method. The specific process steps include: Coat the coating solution of the protective layer on the surface of the composite conductive layer, and obtain the protective layer after drying.

22. A lithium-ion battery, characterized in that, The lithium-ion battery includes an electrode pole piece, and the electrode pole piece includes the composite current collector as described in any one of claims 1 - 14 or the composite current collector prepared by the preparation method as described in any one of claims 15 - 21.

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