3D composite current collector, preparation method thereof and electrode sheet

Abstract

The application provides a 3D composite current collector, a preparation method and an electrode sheet, and the 3D composite current collector comprises a fiber layer and a first metal layer and a second metal layer arranged below and above the fiber layer respectively, wherein the fiber layer comprises first high molecular fibers, second high molecular fibers and carbon nanotubes, the molecular weight of the first high molecular fibers is 50-100 g / mol, the molecular weight of the second high molecular fibers is 200-500 g / mol, the outer tube diameter of the carbon nanotubes is 1-2 nm, the inner tube diameter is 0.5-1.5 nm, and the thickness of the fiber layer is 8-20 mu m. The 3D composite current collector provided by the application can provide sufficient voids for infiltrating electrolyte and more lithium ion transmission channels by limiting the composition of the fiber layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of current collector materials, in particular to a 3D composite current collector and a preparation method thereof and an electrode sheet. BACKGROUND

[0002] Lithium ion batteries have been widely used in various fields such as mobile phones, notebook computers, electric vehicles and the like due to their high energy density, long cycle life and low self-discharge. As an important component of lithium ion batteries, the current collector has an important influence on the performance of lithium ion batteries.

[0003] The composite current collector is a new type of functional material, which is usually composed of a polymer layer and a surface metal plating layer. The composite current collector can greatly reduce the weight of the metal current collector. However, the lithium battery electrode is a porous electrode, and the internal voids are impregnated with electrolyte to provide lithium ion transmission channels. However, both the conventional metal current collector and the composite current collector are dense structures, which cannot provide lithium ion transmission channels inside, thereby affecting the impregnation of electrolyte and lithium ion transmission. SUMMARY

[0004] The present application provides a 3D composite current collector, which can provide sufficient voids for impregnating electrolyte and providing more lithium ion transmission channels by limiting the composition of the fiber layer.

[0005] The present application also provides a preparation method of the above-mentioned 3D composite current collector, which can prepare the above-mentioned 3D composite current collector.

[0006] The present application also provides an electrode sheet. Since the negative electrode sheet comprises the above-mentioned 3D composite current collector, the stability and conductivity of the battery can be improved.

[0007] In one aspect, the present application provides a 3D composite current collector, comprising: a fiber layer and a first metal layer and a second metal layer located above and below the fiber layer respectively, wherein the fiber layer comprises first high molecular fibers, second high molecular fibers and carbon nanotubes, the molecular weight of the first high molecular fibers is 58.69 g / mmol, the molecular weight of the second high molecular fibers is 249.68 g / mmol, the outer tube diameter of the carbon nanotubes is 1-2 nm, the inner tube diameter is 0.5-1.5 nm, and the thickness of the fiber layer is 8-20 µm; the first high molecular fibers and the second high molecular fibers are polyethylene terephthalate; the fiber layer is prepared by a method comprising the following steps:

[0008] S1: granulating the first high molecular fibers to form a first slice, adding the first slice into a screw extruder, and performing melt extrusion treatment at 226-228℃ to obtain a first slurry;

[0009] S2: melt the second high molecular fiber, then add carbon nanotubes into the melted second high molecular fiber, mix and granulate to form a second chip, add the second chip into a screw extruder, and perform melt extrusion treatment at 272-273°C to obtain a second slurry;

[0010] S3: the first slurry and the second slurry are fed into a spinning assembly to obtain a nascent fiber through spinning treatment, and the nascent fiber is cooled and solidified to obtain a fiber layer through webbing and hot rolling.

[0011] Optionally, the carbon nanotubes account for 0.5wt%-1wt% of the mass of the fiber layer.

[0012] Optionally, in the fiber layer, the mass ratio of the first high molecular fiber and the second high molecular fiber is 6-10:2-5.

[0013] And / or, the fiber diameter of the first high molecular fiber and the second high molecular fiber is independently 5-30µm.

[0014] Optionally, the thickness of the first metal layer and the second metal layer is independently 1-1.5µm.

[0015] Optionally, the first metal layer comprises a first nickel layer close to the fiber layer and a first copper layer away from the fiber layer, and the second metal layer comprises a second nickel layer close to the fiber layer and a second copper layer away from the fiber layer.

[0016] Optionally, the thickness of the first nickel layer is 8-10nm, the thickness of the second nickel layer is 8-10nm, the thickness of the first copper layer is 1-1.5µm, and the thickness of the second copper layer is 1-1.5µm.

[0017] Optionally, the porosity of the 3D composite current collector is 15%-40%.

[0018] In another aspect, the present application provides a preparation method of the 3D composite current collector as described above, comprising the following steps:

[0019] S1: granulate the first high molecular fiber to form a first chip, add the first chip into a screw extruder, and perform melt extrusion treatment at 226-228°C to obtain a first slurry;

[0020] S2: melt the second high molecular fiber, then add carbon nanotubes into the melted second high molecular fiber, mix and granulate to form a second chip, add the second chip into a screw extruder, and perform melt extrusion treatment at 272-273°C to obtain a second slurry;

[0021] S3: the first slurry and the second slurry are fed into a spinning assembly according to a mass ratio of 6-10:2-5, and after spinning treatment, a nascent fiber is obtained, and after cooling and solidification of the nascent fiber, webbing, hot roller pressing are performed to obtain a fiber layer;

[0022] S4: nickel is placed into a magnetron sputtering machine, a first nickel layer and a second nickel layer are deposited on the upper and lower surfaces of the fiber web, and then copper is placed into the magnetron sputtering machine, a first copper layer and a second copper layer are deposited on the surfaces of the first nickel layer and the second nickel layer, to obtain the 3D composite current collector.

[0023] In another aspect, the application provides an electrode sheet, comprising the above-mentioned 3D composite current collector and an active layer located on at least one functional surface of the 3D composite current collector.

[0024] The 3D composite current collector provided by the application can keep the thickness of the fiber layer within the range of 8-20µm, provide more lithium ion transmission channels for the 3D composite current collector, and facilitate the infiltration of electrolyte and the transmission of lithium ions, and on the other hand, the fiber layer contains carbon nanotubes with specific parameters, which can also ensure that the 3D composite current collector has excellent electrical conductivity. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the application and, together with the specification, serve to explain the principles of the application.

[0026] Figure 1 SEM picture of the fiber filament of Example 1 of the application. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to better understand the scheme of the application, the application will be further described in detail below. The following specific embodiments are only used to describe the principles and characteristics of the application, and the examples are only used to explain the application, and do not limit the scope of the application. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the application.

[0028] In this application, the terms "first", "second" are only used for descriptive purposes, to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the embodiments of the application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features.

[0029] The polymer layer of the common composite current collector is mostly polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polyimide and the like. These materials have good flexibility and more pore structures compared with metal, but due to the flexibility, wrinkles easily occur on the surface, affecting the thickness and flatness of the metal plating layer. In order to avoid wrinkles, the polymer layer can only be thinned, which will result in a dense composite current collector structure, which is not conducive to the infiltration of electrolyte and the transmission of lithium ions.

[0030] Through research, the present application finds that the problems of wrinkles easily occurring on the polymer layer and the dense composite current collector structure can be solved by regulating the molecular weight and composition of the polymer fiber layer. In detail:

[0031] In one aspect, the present application provides a 3D composite current collector, comprising: a fiber layer and first and second metal layers located above and below the fiber layer respectively, wherein the fiber layer comprises first and second polymer fibers and carbon nanotubes, the molecular weight of the first polymer fiber is 58.69 g / mmol, the molecular weight of the second polymer fiber is 249.68 g / mmol, the outer tube diameter of the carbon nanotube is 1-2 nm, the inner tube diameter is 0.5-1.5 nm, and the thickness of the fiber layer is 8-20 µm; the first and second polymer fibers are polyethylene terephthalate; and the fiber layer is prepared by a method comprising the following steps:

[0032] S1: granulating the first polymer fiber to form a first slice, adding the first slice into a screw extruder, and performing melt extrusion treatment at 226-228℃ to obtain a first slurry;

[0033] S2: melting the second polymer fiber, then adding carbon nanotubes into the melted second polymer fiber, mixing and granulating to form a second slice, adding the second slice into a screw extruder, and performing melt extrusion treatment at 272-273℃ to obtain a second slurry;

[0034] S3: the first slurry and the second slurry are sent into a spinning assembly, and after spinning treatment, a nascent fiber is obtained, and after cooling and solidification of the nascent fiber, webbing and hot rolling are performed to obtain a fiber layer.

[0035] In the present application, the fiber layer can not only improve the thickness of the fiber layer to provide more channels for lithium ion transmission, but also ensure that the 3D composite current collector has excellent electrical conductivity, because the fiber layer includes the first high molecular fiber, the second high molecular fiber and the specific carbon nanotube. The main reasons include: the fiber layer is composed of high molecular fibers with different molecular weights to form a skeleton, which can have rigidity and flexibility compared to a single molecular weight skeleton, which to some extent avoids the folding of the fiber layer. Subsequently, by introducing carbon nanotubes, the carbon nanotubes provide more channels inside the fiber layer for lithium ion transmission, and the carbon nanotubes form a three-dimensional conductive path in the fiber layer, thereby helping to collect electrons in the electrode material and conduct them to the external circuit, providing a low-resistance path for ions, so that the current can efficiently flow out or flow into the battery. The inner and outer diameters of the nanotube are within the above range, which can make the fiber layer have good conductive path while increasing its mechanical strength, thereby further avoiding the folding problem of the fiber layer.

[0036] The 3D composite current collector of the present application has the above advantages, can better adapt to the severe expansion and contraction of the new type of silicon-doped negative electrode during the charging and discharging process, ensure the integrity of the electrode structure, and improve the cycle life of the battery.

[0037] It can be understood that the outer diameter of the carbon nanotube should be greater than its inner diameter.

[0038] Exemplarily, the thickness of the fiber layer is any one value or a range composed of any two values selected from the group consisting of 8 µm, 9 µm, 10 µm, 11 µm, 12 µm, 13 µm, 14 µm, 15 µm, 16 µm, 17 µm, 18 µm, 19 µm, 20 µm, etc.

[0039] In a specific embodiment, the carbon nanotubes account for 0.5wt%-1wt% of the mass of the fiber layer.

[0040] The carbon nanotubes as described above can further improve the electrical conductivity of the 3D composite current collector and the thickness of the fiber layer of the 3D composite current collector.

[0041] Exemplarily, the carbon nanotubes account for 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt% or any range composed of any two values thereof of the mass of the fiber layer.

[0042] In a specific embodiment, the mass ratio of the first high molecular fiber to the second high molecular fiber in the fiber layer is 6-10:2-5.

[0043] The high molecular fibers as described above can further improve the thickness and uniformity of the fiber layer of the 3D composite current collector.

[0044] In an embodiment, the first and second high molecular fibers each independently have a fiber diameter of 5-30 µm.

[0045] Exemplarily, the first and second high molecular fibers each independently have a fiber diameter of any one of 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, 10 µm, 11 µm, 12 µm, 13 µm, 14 µm, 15 µm, 16 µm, 17 µm, 18 µm, 19 µm, 20 µm, 21 µm, 22 µm, 23 µm, 24 µm, 25 µm, 26 µm, 27 µm, 28 µm, 29 µm, 30 µm, or a range consisting of any two thereof.

[0046] In an embodiment, the first and second metal layers each independently have a thickness of 1-1.5 µm.

[0047] The first and second metal layers having the above-mentioned thickness are more conducive to reducing the contact impedance of the 3D composite current collector and the active material.

[0048] Exemplarily, the first and second metal layers each independently have a thickness of any one of 1 µm, 1.1 µm, 1.2 µm, 1.3 µm, 1.4 µm, 1.5 µm, or a range consisting of any two thereof.

[0049] In an embodiment, the first metal layer includes a first nickel layer close to the fiber layer and a first copper layer away from the fiber layer, and the second metal layer includes a second nickel layer close to the fiber layer and a second copper layer away from the fiber layer.

[0050] The first and second metal layers as mentioned above are conducive to further reducing the contact impedance of the 3D composite current collector and the active material.

[0051] In an embodiment, the first nickel layer has a thickness of 8-10 nm, the second nickel layer has a thickness of 8-10 nm, the first copper layer has a thickness of 1-1.5 µm, and the second copper layer has a thickness of 1-1.5 µm.

[0052] In some embodiments, the fiber layer of the present application can further contain additives such as dispersants, wetting agents, and defoaming agents; a dispersant is added to the coating liquid used to form the fiber layer for the purpose of improving dispersibility, coatability, or storage stability; a wetting agent or defoaming agent is added to the coating liquid used to form the fiber layer, for example, for the purpose of good affinity with the porous substrate, or the purpose of inhibiting air intake into the coating liquid.

[0053] The present application does not make special limitation to the dispersant, and exemplarily, the dispersant can be at least one of polyacrylate copolymer sodium salt, polyacrylate copolymer ammonium salt, and acid group-containing alkanol ammonium salt.

[0054] The present application does not make special limitation to the thickening agent, and exemplarily, the thickening agent can be at least one of carboxymethyl cellulose sodium, fumed silica, modified urea polymer, organic modified silicate, organic modified montmorillonite, and organic bentonite.

[0055] The present application does not make special limitation to the wetting agent, and exemplarily, the wetting agent can be at least one of polyether siloxane copolymer, organosilicon double structure copolymer, polyacrylate copolymer, polyether modified silicone oil copolymer, and polyoxyethylene alkylamine copolymer.

[0056] The present application does not make special limitation to the mass percentage content of the binder, dispersant, thickening agent, and wetting agent, and the additive content can be freely selected according to the purpose.

[0057] In a specific embodiment, the 3D composite current collector has a porous structure with a porosity of 15% to 40%; it has air permeability characteristics, and the air permeability range is 20 to 1000 s / 100mL, preferably 150 to 300 s / 100mL.

[0058] In some embodiments, the porosity test method of the 3D composite current collector is as follows:

[0059] The porosity is directly observed by scanning electron microscopy (SEM) or transmission electron microscopy (TEM), and quantitatively calculated by combining with image processing software (such as ImageJ).

[0060] In some embodiments, the first copper layer and the second copper layer comprise Cu, Zn, Ni, and Cr, and the weight percentage of the first metal layer and the second metal is 100%, wherein Cu≥99.0%, Zn≤0.5%, Ni≤0.5%, and Cr≤0.5%.

[0061] The first copper layer and the second copper layer composed of the above components are conducive to further reducing the contact resistance between the 3D composite current collector and the active material.

[0062] In another aspect, the present application provides a preparation method of the 3D composite current collector as described above, comprising the following steps:

[0063] S1: granulating the first polymer fiber to form a first slice, adding the first slice into a screw extruder, and performing melt extrusion treatment at 226-228℃ to obtain a first slurry;

[0064] S2: melt the second polymer fiber, then add carbon nanotubes into the melted second polymer fiber, mix and granulate to form a second chip, add the second chip into a screw extruder, and perform melt extrusion treatment at 272-273 DEG C to obtain a second slurry;

[0065] S3: the first slurry and the second slurry are fed into a spinning assembly according to a mass ratio of 6-10:2-5, and a nascent fiber is obtained through spinning treatment, and the nascent fiber is cooled and solidified, and then laid and hot-rolled to obtain a fiber layer;

[0066] S4: nickel is placed into a magnetron sputtering machine, a first nickel layer and a second nickel layer are deposited on the upper and lower surfaces of the fiber web, then copper is placed into the magnetron sputtering machine, a first copper layer and a second copper layer are deposited on the surfaces of the first nickel layer and the second nickel layer, and the 3D composite current collector is obtained.

[0067] In another aspect, the application provides an electrode sheet comprising the 3D composite current collector and an active layer on at least one functional surface of the 3D composite current collector.

[0068] In some embodiments, the active layer is attached to both surfaces of the 3D composite copper current collector, the surface density of the active layer is 1-100 mg / cm 2 , preferably 8-20 mg / cm 2 , the compacted density of the electrode sheet is 0.5-2 g / cm 3 , preferably 1.3-1.65 g / cm 3 .

[0069] In some embodiments, the electrode sheet is a negative electrode sheet, the active layer is composed of a negative electrode active material, a conductive agent and a binder, the negative electrode active material includes but is not limited to graphite, hard carbon, lithium titanate, silicon monoxide, silicon-carbon composite material, etc., the conductive agent includes but is not limited to conductive carbon, single-walled carbon nanotube, multi-walled carbon nanotube, etc., and the binder includes but is not limited to lithium carboxymethyl cellulose CMC-Li, sodium carboxymethyl cellulose CMC-Na, butylphenyl rubber emulsion SBR, acrylic polymer PAA, etc.

[0070] In some embodiments, the electrode sheet is a positive electrode sheet, the active layer comprises a positive electrode active material, a conductive agent and a binder, the positive electrode active material comprises at least one of lithium cobaltate, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum, lithium manganese phosphate, lithium iron phosphate, lithium manganese iron phosphate; the conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, metal powder, graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, sodium polyacrylate.

[0071] For a further understanding of the present application, the technical solutions of the present application will be described in detail below with reference to specific embodiments. It is obvious that the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0072] Unless otherwise specified, the reagents involved in the embodiments of the present application are all commercially available and can be purchased through commercial channels.

[0073] Embodiment 1

[0074] This example provides a 3D composite current collector with a porosity of 40%, which comprises a first copper layer 1 μm, a first nickel layer 8 nm, a fiber layer 20 μm, a second nickel layer 8 nm, and a second copper layer 1 μm stacked in sequence, the fiber layer comprises first PET fibers and second PET fibers with a mass ratio of 7:3, the first PET fibers have a molecular weight of 58.69 g / mmol and a diameter of 5-6 μm, and the second PET fibers have a molecular weight of 249.68 g / mmol and a diameter of 5-6 μm. The fiber layer further comprises 1 wt% of carbon nanotubes, the outer diameter of the carbon nanotubes is 1.8-2 nm, and the inner diameter is 1-1.5 nm.

[0075] The preparation method comprises the following steps:

[0076] S1: selecting first and second high molecular fiber base films, respectively, cleaning the surfaces to remove impurities such as oil stains and dust, and then drying to obtain pretreated first and second high molecular fiber base films;

[0077] S2: granulating the first high molecular fiber base film to form a first slice, adding the first slice to a screw extruder, and performing melt extrusion treatment at 226-228°C (the rotation speed of the 200cc metering pump in the screw extruder is 3-8 rev / min) to obtain a first slurry;

[0078] S3: melting the second high molecular fiber base film, then adding carbon nanotubes into the melted second high molecular fiber, mixing and granulating to form a second chip, and adding the second chip into a screw extruder to perform a melt extrusion treatment at 272-273°C (the rotation speed of a 200cc metering pump in the screw extruder is 10-15 rev / min) to obtain a second slurry;

[0079] S4: the first slurry and the second slurry are fed into a spinning assembly according to a mass ratio of 7:3 to perform a spinning treatment to obtain a nascent fiber, and the nascent fiber is cooled and solidified to obtain a fiber yarn with a longitudinal strength of 35N-38N, a transverse strength of 22-26N, and an orientation degree within 7%, and the fiber yarn is laid and hot-rolled (the hot-rolling temperature is 215-220°C) to obtain a fiber layer;

[0080] S5: a nickel target is placed into a magnetron sputtering machine, the fiber layer is placed into a vacuum cavity of the magnetron sputtering machine, an appropriate amount of argon gas is introduced as a protective gas, and then an electric field is applied to make the nickel target sputter, and the sputtered nickel metal particles are deposited on the upper and lower surfaces of the fiber layer to form a first nickel layer and a second nickel layer, a copper target is placed into the magnetron sputtering machine, an electric field is applied to make the nickel target sputter, and the sputtered copper metal particles are deposited on the surfaces of the first nickel layer and the second nickel layer to form a first copper layer and a second copper layer, thereby obtaining the 3D composite current collector.

[0081] Example 2

[0082] This example provides a 3D composite current collector, which is different from example 1 in that the porosity of the 3D composite current collector is 37%, the thickness of the fiber layer is 10μm, the fiber layer comprises first PET fibers and second PET fibers with a mass ratio of 8:2 and a diameter of 8-10μm, and the fiber layer further comprises 0.8wt% of carbon nanotubes with an outer tube diameter of 1.5-1.8nm and an inner tube diameter of 1-1.2nm.

[0083] The preparation method thereof is referred to example 1.

[0084] Example 3

[0085] This example provides a 3D composite current collector, which is different from example 1 in that it comprises a first copper layer 1.2μm, a first nickel layer 10nm, a fiber layer 10μm, a second nickel layer 10nm, and a second copper layer 1.2μm which are sequentially stacked.

[0086] The preparation method thereof is referred to example 1.

[0087] Comparative Example 1

[0088] A copper foil with a thickness of 6.5μm is used as the current collector.

[0089] Comparative Example 2

[0090] The example provides a composite current collector, which comprises a first copper layer 1 μm, a first nickel layer 8 nm, a PET fiber layer 10 μm, a second nickel layer 8 nm, and a second copper layer 1 μm which are sequentially stacked, the PET fiber layer only comprises the second PET fiber with a molecular weight of 249.68 g / mmol and the carbon nanotube of the embodiment 2, and does not contain the first PET fiber.

[0091] S1: melt the PET base film, then add the carbon nanotube into the melted PET, mix and granulate to form a second chip, add the second chip into a screw extruder, and perform a melt extrusion treatment at 272-273°C (the rotation speed of the 200cc metering pump in the screw extruder is 5-15 rev / min) to obtain a slurry;

[0092] S2: the slurry is sent into a spinning assembly, and is subjected to a spinning treatment to obtain a nascent fiber, the nascent fiber is cooled and solidified to obtain a fiber yarn, and the fiber yarn is subjected to webbing and hot roller pressing (the hot roller pressing temperature is 215-220°C) to obtain a fiber layer;

[0093] S3: a nickel target material is placed into a magnetron sputtering machine, the fiber layer is placed into a vacuum cavity of the magnetron sputtering machine, an appropriate amount of argon gas is introduced as a protective gas, and then an electric field is applied to make the nickel target material sputter, the sputtered nickel metal particles are deposited on the upper and lower surfaces of the fiber layer to form a first nickel layer and a second nickel layer, a copper target material is placed into the magnetron sputtering machine, an electric field is applied to make the nickel target material sputter, and the sputtered copper metal particles are deposited on the surfaces of the first nickel layer and the second nickel layer to form a first copper layer and a second copper layer, thereby obtaining the 3D composite current collector.

[0094] Comparative Example 3

[0095] The example provides a composite current collector, which comprises a first copper layer 1 μm, a first nickel layer 8 nm, a fiber layer 10 μm, a second nickel layer 8 nm, and a second copper layer 1 μm which are sequentially stacked, the fiber layer only comprises the second PET fiber with a molecular weight of 249.68 g / mmol of the embodiment 2, and does not contain the first PET fiber and the carbon nanotube.

[0096] The preparation method comprises the following steps:

[0097] S1: melt the PET base film, perform granulation to form a chip, add the chip into a screw extruder, and perform a melt extrusion treatment at 272-273°C (the rotation speed of the 200cc metering pump in the screw extruder is 5-15 rev / min) to obtain a slurry;

[0098] S2: the slurry is fed into a spinning assembly, and subjected to spinning treatment to obtain a nascent fiber, and the nascent fiber is cooled and solidified to obtain a fiber yarn, and the fiber yarn is subjected to webbing and hot roller pressing (hot roller pressing temperature: 215-220°C) to obtain a fiber layer;

[0099] S3: the nickel target material is placed into a magnetron sputtering machine, the fiber layer is placed into a vacuum cavity of the magnetron sputtering machine, an appropriate amount of argon gas is introduced as a protective gas, and then an electric field is applied to cause the nickel target material to sputter, and the sputtered nickel metal particles are deposited on the upper and lower surfaces of the fiber layer to form a first nickel layer and a second nickel layer, the copper target material is placed into the magnetron sputtering machine, and an electric field is applied to cause the nickel target material to sputter, and the sputtered copper metal particles are deposited on the surfaces of the first nickel layer and the second nickel layer to form a first copper layer and a second copper layer, thereby obtaining the 3D composite current collector.

[0100] Test Example

[0101] The negative electrode sheet is prepared by using the current collector of each of the above examples and comparative examples, including the following steps:

[0102] The thickening agent CMC-Na is dissolved in deionized water to form a 1.2 wt % thickening agent solution, and the raw materials are weighed according to the mass ratio of graphite: conductive agent Super-P: thickening agent: binder SBR 95:1.0:1.2:2.8, and then the thickening agent solution and each raw material are mixed uniformly to prepare a negative electrode slurry, which is coated on both sides of the current collector (single-layer coating surface density: 12 mg / cm 2 ). 3 3 3 3 The thickening agent CMC-Na is dissolved in deionized water to form a 1.2 wt % thickening agent solution, and the raw materials are weighed according to the mass ratio of graphite: conductive agent Super-P: thickening agent: binder SBR 95:1.0:1.2:2.8, and then the thickening agent solution and each raw material are mixed uniformly to prepare a negative electrode slurry, which is coated on both sides of the current collector (single-layer coating surface density: 12 mg / cm

[0103] Test Example 1

[0104] Comparison of air permeability of the current collector: sample the current collector of each example and comparative example, and the sample size is 100 100 mm, and there are 3 samples in each group. The samples are placed in the test head of the air permeability tester for air permeability test. The time required for 100 mL of air to pass through 1 square inch of sample under a pressure of 1.22 kPa is recorded as the test result Gurley value in Table 1.

[0105] Table 1

[0106]

[0107] ​​​From Table 1, the 3D composite copper current collector of the embodiment has more excellent air permeability.

[0108] Test Example 2

[0109] Negative plate impedance test: take the negative plate of the test example with the compaction degree of 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.62 g / cm 3 , respectively. The sample to be tested is taken at different three positions of each plate, and resistance test is performed. The resistance test adopts two-probe method, and the current transmission path is in turn through the test probe (upper) → the active material layer on the upper surface of the plate → the current collector → the active material layer on the lower surface of the plate → the test probe (lower). The results are shown in Table 2.

[0110] Table 2:

[0111]

[0112] From Table 2, compared with the negative plate using the conventional metal copper current collector of Comparative Example 1, the composite current collector of Comparative Example 3 has a very obvious increase in the impedance of the negative plate due to the non-conductivity of the fiber layer, and the composite current collectors of Comparative Examples 2-3 have poor uniformity due to the fact that the fiber layer thereof has only one kind of PET fiber, while the resistance of the negative plate of the 3D composite current collector of the embodiment does not change obviously, which shows that the 3D composite current collector of the embodiment can ensure the uniformity of the current collector while increasing the thickness of the fiber layer, so that it has good conductivity.

[0113] Test Example 3

[0114] Negative plate wettability comparison: take the negative plate of the test example with the compaction density of 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.62 g / cm 3 , respectively, die cut, the die cut size is 84 174 mm, then each sample is stacked in the mode of negative plate / separator (CN206849946 U, thickness 12 μm) / negative plate / separator in 21 layers to form a single electrode group, the outermost layer is wrapped with a separator, placed in an aluminum plastic film bag and injected with electrolyte, after standing for 1 hour, the excess electrolyte is poured out, and after continuing to stand for 12 hours, the electrode group is taken out and opened, the 11th negative plate in the middle position is weighed, and the mass increase ratio of the plate before and after absorbing electrolyte is calculated. The results are shown in Table 3.

[0115] Table 3:

[0116]

[0117] As can be seen from Table 3, compared with the conventional PET composite current collector using the conventional PET of Comparative Example 1 and Comparative Example 3, the liquid absorption speed of the negative electrode sheet using the 3D composite current collector of the application is significantly improved, indicating that the 3D composite current collector has a porous structure inside, which can significantly improve the electrolyte infiltration speed and improve the electrolyte infiltration effect, and can provide more electrolyte diffusion channels.

[0118] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, but not to limit it; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A 3D composite current collector, characterized by, Comprising: a fiber layer and a first metal layer and a second metal layer respectively located above and below the fiber layer, wherein the fiber layer comprises a first high molecular fiber, a second high molecular fiber and a carbon nanotube, the molecular weight of the first high molecular fiber is 58.69 g / mmol, the molecular weight of the second high molecular fiber is 249.68 g / mmol; the outer tube diameter of the carbon nanotube is 1-2 nm, and the inner tube diameter is 0.5-1.5 nm; the thickness of the fiber layer is 8-20 µm; the first high molecular fiber and the second high molecular fiber are polyethylene terephthalate; the fiber layer is prepared by a method comprising the following steps: S1: granulating the first high molecular fiber to form a first chip, adding the first chip into a screw extruder, and performing melt extrusion treatment at 226-228°C to obtain a first slurry; S2: melting the second high molecular fiber, then adding carbon nanotubes into the melted second high molecular fiber, and mixing and granulating to form a second chip, adding the second chip into a screw extruder, and performing melt extrusion treatment at 272-273°C to obtain a second slurry; S3: the first slurry and the second slurry are sent into a spinning assembly, and after spinning treatment, a nascent fiber is obtained, and after cooling and solidification, the nascent fiber is laid and hot rolled to obtain a fiber layer.

2. The 3D composite current collector of claim 1, wherein, The carbon nanotube accounts for 0.5wt%-1wt% of the mass of the fiber layer.

3. The 3D composite current collector of claim 1, wherein, In the fiber layer, the mass ratio of the first high molecular fiber and the second high molecular fiber is 6-10:2-5; And / or, the fiber diameter of the first high molecular fiber and the second high molecular fiber is independently 5-30 µm.

4. The 3D composite current collector of any of claims 1-3, wherein, The thickness of the first metal layer and the second metal is independently 1-1.5 µm.

5. The 3D composite current collector of claim 4, wherein, The first metal layer comprises a first nickel layer close to the fiber layer and a first copper layer away from the fiber layer, and the second metal layer comprises a second nickel layer close to the fiber layer and a second copper layer away from the fiber layer.

6. The 3D composite current collector of claim 5, wherein, The thickness of the first nickel layer is 8-10 nm, the thickness of the second nickel layer is 8-10 nm; the thickness of the first copper layer is 1-1.5 µm; the thickness of the second copper layer is 1-1.5 µm.

7. The 3D composite current collector of any of claims 1-3, wherein, The porosity of the 3D composite current collector is 15%-40%.

8. A method of making a 3D composite current collector according to any one of claims 1-7, wherein, Comprising the following steps: S1: granulating the first high molecular fiber to form a first chip, adding the first chip into a screw extruder, and performing melt extrusion treatment at 226-228°C to obtain a first slurry; S2: melting the second high molecular fiber, then adding carbon nanotubes into the melted second high molecular fiber, and mixing and granulating to form a second chip, adding the second chip into a screw extruder, and performing melt extrusion treatment at 272-273°C to obtain a second slurry; S3: the first slurry and the second slurry are sent into a spinning assembly, and after spinning treatment, a nascent fiber is obtained, and after cooling and solidification, the nascent fiber is laid and hot rolled to obtain a fiber layer; S4: nickel is placed into a magnetron sputtering machine to deposit a first nickel layer and a second nickel layer on the upper and lower surfaces of the fiber web, and then copper is placed into the magnetron sputtering machine to deposit a first copper layer and a second copper layer on the surfaces of the first nickel layer and the second nickel layer, to obtain the 3D composite current collector.

9. An electrode sheet characterized by The 3D composite current collector according to any one of claims 1-7, and an active layer located on at least one functional surface of the 3D composite current collector.

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