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

Abstract

The invention provides a 3D composite current collector, a preparation method and an electrode slice, the 3D composite current collector comprises a fiber layer, a first metal layer and a second metal layer, the first metal layer and the second metal layer are respectively arranged on the upper surface and the lower surface of the fiber layer, the fiber layer comprises a first polymer fiber, a second polymer fiber and a carbon nanotube, the molecular weight of the first polymer fibers is 50-100 g / mol, the molecular weight of the second polymer fibers is 200-500 g / mol, the outer diameter of the carbon nanotubes is 1-2 nm, the inner diameter of the carbon nanotubes is 0.5-1.5 nm, and the thickness of the fiber layer is 8-20 m. According to the 3D composite current collector provided by the invention, by limiting the composition of the fiber layer, enough gaps can be provided, so that electrolyte infiltration is facilitated, and more lithium ion transmission channels are provided.

Description

Technical Field

[0001] The present invention relates to the field of current collector materials, and particularly to a 3D composite current collector, a preparation method thereof, and an electrode sheet. Background Art

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

[0003] The composite current collector is a new type of functional material, usually composed of a polymer layer and a surface metal coating. The composite current collector can significantly reduce the weight of the metal current collector. However, the lithium battery electrode belongs to a porous electrode, and the internal voids are infiltrated with an electrolyte to provide a lithium-ion transmission channel. However, both the conventional metal current collector and the composite current collector are dense structures, and their interiors cannot provide a lithium-ion transmission channel, thus affecting the infiltration of the electrolyte and the lithium-ion transmission. Summary of the Invention

[0004] The present invention provides a 3D composite current collector, which can provide enough voids for infiltrating the electrolyte and provide more lithium-ion transmission channels by defining the composition of the fiber layer.

[0005] The present invention also provides a preparation method of the above 3D composite current collector, and the preparation method can prepare the above 3D composite current collector.

[0006] The present invention also provides an electrode sheet. Since the negative electrode sheet includes the above 3D composite current collector, it can improve the stability and conductivity of the battery when used in the battery.

[0007] On the one hand, the present invention provides a 3D composite current collector, including: a fiber layer, and a first metal layer and a second metal layer respectively located on the upper and lower surfaces of the fiber layer, wherein the fiber layer includes a first polymer fiber, a second polymer fiber, and carbon nanotubes, the molecular weight of the first polymer fiber is 50-100 g / mol, the molecular weight of the second polymer fiber is 200-500 g / mol, the outer diameter of the carbon nanotubes is 1-2 nm, the inner diameter is 0.5-1.5 nm, and the thickness of the fiber layer is 8-20 µm.

[0008] Optionally, the carbon nanotubes account for 0.5 wt%-1 wt% of the mass of the fiber layer.

[0009] Optionally, in the fiber layer, the mass ratio of the first polymer fiber to the second polymer fiber is 6-10:2-5;

[0010] And / or, the fiber diameters of the first polymer fiber and the second polymer fiber are each independently 5 to 30 µm.

[0011] Optionally, the thicknesses of the first metal layer and the second metal are each independently 1 - 1.5 µm;

[0012] Optionally, the first metal layer includes: a first nickel layer close to the fiber layer and a first copper layer far from the fiber layer, and the second metal layer includes: a second nickel layer close to the fiber layer and a second copper layer far from the fiber layer.

[0013] Optionally, the thickness of the first nickel layer is 8 - 10 nm, and 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.

[0014] Optionally, the porosity of the 3D composite current collector is 15% - 40%.

[0015] Optionally, the first polymer fiber and the second polymer fiber are each independently selected from one or more of: polyethylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, and polyimide.

[0016] On the other hand, the present invention provides a method for preparing a 3D composite current collector as described above, comprising the following steps:

[0017] S1: Granulate the first polymer fiber to form a first slice, add the first slice into a screw extruder, and perform a melt extrusion treatment at 226 - 228 °C to obtain a first slurry;

[0018] S2: Melt the second polymer fiber, then add carbon nanotubes to the molten second polymer fiber for mixing granulation to form a second slice, add the second slice into a screw extruder, and perform a melt extrusion treatment at 272 - 273 °C to obtain a second slurry;

[0019] S3: Feed the first slurry and the second slurry into a spinning assembly according to a mass ratio of 6 - 10:2 - 5, and after spinning treatment, obtain nascent fibers. After the nascent fibers are cooled and solidified, they are laid and hot roll-pressed to obtain a fiber layer;

[0020] S4: Place nickel in 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 place copper in 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.

[0021] In another aspect, the present invention 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.

[0022] For the 3D composite current collector provided by the present invention, by defining the molecular weights of the first polymer fiber and the second polymer fiber of the fiber layer and the composition of the carbon nanotubes, on the one hand, the thickness of the fiber layer can be maintained within the range of 8-20 µm, providing more lithium-ion transmission channels for the 3D composite current collector, facilitating the infiltration of the electrolyte and the transmission of lithium ions. On the other hand, since the fiber layer contains carbon nanotubes with specific parameters, the 3D composite current collector can also ensure excellent electrical conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments in accordance with the present invention, and are used together with the specification to explain the principles of the present invention.

[0024] Figure 1 SEM image of the fiber filaments of Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The specific embodiments listed below only describe the principles and features of the present invention, and the examples given are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0026] In the present application, the terms "first" and "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 quantity of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX may also be referred to as the second XX, and similarly, the second XX may also be referred to as the first XX. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0027] The polymer layers of ordinary composite current collectors are mostly made of materials such as polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, and polyimide. These materials have good flexibility and more pore structures compared to metals. However, due to their flexibility, wrinkles are likely to appear on the surface, affecting the thickness and flatness of the metal coating. To avoid wrinkles, the polymer layer can only be thinned, but this will result in a dense structure of the composite current collector, which is not conducive to the infiltration of the electrolyte and the transmission of lithium ions.

[0028] Through research, the present invention discovers that by regulating the molecular weight and composition of the polymer fiber layer, the problems of easy wrinkling of the polymer layer and densification of the composite current collector can be solved. Specifically:

[0029] On the one hand, the present invention provides a 3D composite current collector, including: a fiber layer, and a first metal layer and a second metal layer respectively located on the upper and lower surfaces of the fiber layer. Among them, the fiber layer includes a first polymer fiber, a second polymer fiber, and carbon nanotubes. The molecular weight of the first polymer fiber is 50-100 g / mol, the molecular weight of the second polymer fiber is 200-500 g / mol, the outer diameter of the carbon nanotubes is 1-2 nm, the inner diameter is 0.5-1.5 nm, and the thickness of the fiber layer is 8-20 µm.

[0030] In the present invention, since the fiber layer includes the first polymer fiber, the second polymer fiber, and specific carbon nanotubes, it can not only increase the thickness of the fiber layer, thereby providing more channels for lithium ion transmission, but also ensure that the 3D composite current collector has excellent electrical conductivity. The main reasons include: the fiber layer is composed of polymer fibers with different molecular weights to form a framework, which can have both rigidity and flexibility compared with a framework of a single molecular weight, which to a certain extent avoids the wrinkling of the fiber layer. Subsequently, by introducing carbon nanotubes, the carbon nanotubes provide more pores inside the fiber layer for facilitating 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, enabling the current to flow in or out of the battery efficiently. When the inner and outer diameters of the nanotubes are within the above ranges, the fiber layer can have a good conductive path while also increasing its mechanical strength, thereby further avoiding the wrinkling problem of the fiber layer.

[0031] Due to the above advantages, the 3D composite current collector of the present invention can better adapt to the severe expansion and contraction during the charge and discharge process of the new silicon-doped negative electrode, ensure the integrity of the electrode structure, and improve the cycle life of the battery.

[0032] It can be understood that the outer diameter of the carbon nanotubes should be greater than their inner diameter.

[0033] Exemplarily, the thickness of the fiber layer is any value among 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. or the range composed of any two of them.

[0034] Exemplarily, the molecular weight of the first polymer fiber is any value among 50 g / mol, 60 g / mol, 70 g / mol, 80 g / mol, 90 g / mol, 100 g / mol, etc. or the range composed of any two of them, and the molecular weight of the second polymer fiber is any value among 200 g / mol, 250 g / mol, 300 g / mol, 350 g / mol, 400 g / mol, 450 g / mol, 500 g / mol, etc. or the range composed of any two of them.

[0035] In a specific embodiment, the carbon nanotubes account for 0.5 wt% - 1 wt% of the mass of the fiber layer.

[0036] The carbon nanotubes as described above can further improve the conductivity of the 3D composite current collector and the thickness of the fiber layer of the 3D composite current collector.

[0037] Exemplarily, the carbon nanotubes account for any value among 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, etc. or the range composed of any two of them of the mass of the fiber layer.

[0038] In a specific embodiment, in the fiber layer, the mass ratio of the first polymer fiber to the second polymer fiber is 6 - 10:2 - 5.

[0039] The polymer fibers as described above can further improve the thickness and uniformity of the fiber layer of the 3D composite current collector.

[0040] In a specific embodiment, the fiber diameters of the first polymer fiber and the second polymer fiber are each independently 5 - 30 µm.

[0041] Exemplarily, the fiber diameters of the first polymer fiber and the second polymer fiber are each independently any value among 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, etc. or the range composed of any two of them.

[0042] In a specific embodiment, the thicknesses of the first metal layer and the second metal are each independently 1 - 1.5 µm.

[0043] The first metal layer and the second metal layer with the thicknesses as described above are more conducive to reducing the contact impedance between the 3D composite current collector and the active material.

[0044] Exemplarily, the thicknesses of the first metal layer and the second metal are each independently any value among 1 µm, 1.1 µm, 1.2 µm, 1.3 µm, 1.4 µm, 1.5 µm, etc. or the range formed by any two of them.

[0045] In a specific embodiment, the first metal layer includes: a first nickel layer close to the fiber layer and a first copper layer far from the fiber layer, and the second metal layer includes: a second nickel layer close to the fiber layer and a second copper layer far from the fiber layer.

[0046] The first metal layer and the second metal layer as described above are beneficial to further reducing the contact impedance between the 3D composite current collector and the active material.

[0047] In a specific embodiment, 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.

[0048] In some embodiments, in the fiber layer of the present invention, additives such as a dispersant, a wetting agent, and an antifoaming agent may also be included; in the coating liquid for forming the fiber layer, a dispersant is added for the purpose of improving dispersibility, coatability, or storage stability; in the coating liquid for forming the fiber layer, a wetting agent and an antifoaming agent are added, for example, for the purpose of making the affinity with the porous substrate good and suppressing air intake into the coating liquid.

[0049] The present invention does not particularly limit the dispersant. Exemplarily, the dispersant may be at least one of sodium polyacrylate copolymer salts, ammonium polyacrylate copolymer salts, and alkanol ammonium salts containing acidic groups.

[0050] The present invention does not particularly limit the thickener. Exemplarily, the thickener may be at least one of sodium carboxymethyl cellulose, fumed silica, modified urea polymers, organically modified silicate salts, organically modified montmorillonite, and organobentonite.

[0051] The present invention does not particularly limit the wetting agent. Exemplarily, the wetting agent may be at least one of polyether siloxane copolymers, organosilicon gemini copolymers, polyacrylate copolymers, polyether modified silicone copolymers, and polyoxyethylene alkylamine copolymers.

[0052] The present invention also does not particularly limit the mass percentage contents of the binder, dispersant, thickener, and wetting agent, and the addition contents corresponding to the purpose can be freely selected.

[0053] In a specific embodiment, the 3D composite current collector has a porous structure with a porosity of 15% - 40%; it has air permeability characteristics, and the air permeability ranges from 20 to 1000 s / 100mL, preferably 150 - 300 s / 100mL.

[0054] In some embodiments, the method for testing the porosity of the 3D composite current collector is as follows:

[0055] The pore morphology is directly observed by scanning electron microscopy (SEM) or transmission electron microscopy (TEM), and the porosity is quantitatively calculated in combination with image processing software (such as ImageJ).

[0056] In some embodiments, the first copper layer and the second copper layer include Cu, Zn, Ni, and Cr. Calculated by weight percentage of the first metal layer and the second metal, wherein Cu ≥ 99.0%, Zn ≤ 0.5%, Ni ≤ 0.5%, and Cr ≤ 0.5%.

[0057] Among them, the first copper layer and the second copper layer with the above composition are beneficial to further reduce the contact impedance between the 3D composite current collector and the active material.

[0058] In a specific embodiment, the first polymer fiber and the second polymer fiber are independently selected from one or more of polyethylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, and polyimide.

[0059] On the other hand, the present invention provides a method for preparing the 3D composite current collector as described above, including the following steps:

[0060] S1: Granulate the first polymer fiber to form the first slice, add the first slice into a screw extruder, and perform melt extrusion treatment at 226 - 228°C to obtain the first slurry;

[0061] S2: Melt the second polymer fiber, then add carbon nanotubes to the molten second polymer fiber for mixing granulation to form the second slice, add the second slice into a screw extruder, and perform melt extrusion treatment at 272 - 273°C to obtain the second slurry;

[0062] S3: Feed the first slurry and the second slurry into a spinning assembly according to a mass ratio of 6 - 10:2 - 5, perform spinning treatment to obtain nascent fibers, and after cooling and solidifying the nascent fibers, perform web laying and hot roll pressing to obtain a fiber layer;

[0063] S4: Place nickel in a magnetron sputtering machine to deposit the first nickel layer and the second nickel layer on the upper and lower surfaces of the fiber web, and then place copper in the magnetron sputtering machine to deposit the first copper layer and the second copper layer on the surfaces of the first nickel layer and the second nickel layer to obtain the 3D composite current collector.

[0064] In another aspect, the present invention provides an electrode sheet, which includes the above-mentioned 3D composite current collector and an active layer located on at least one functional surface of the 3D composite current collector.

[0065] In some embodiments, the active layer adheres to both sides of the 3D composite copper current collector, and the areal density of the active layer is 1-100 mg / cm 2 , preferably 8-20 mg / cm 2 ; the tap density of the electrode sheet is 0.5-2 g / cm 3 , preferably 1.3-1.65 g / cm 3 .

[0066] In some embodiments, the electrode sheet is a negative electrode sheet, and the active layer is composed of a negative electrode active material, a conductive agent, and a binder. The negative electrode material includes, but is not limited to, graphite, hard carbon, lithium titanate, silicon monoxide, silicon-carbon composite materials, etc. The conductive agent includes, but is not limited to, conductive carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, etc. The binder includes, but is not limited to, lithium carboxymethyl cellulose CMC-Li, sodium carboxymethyl cellulose CMC-Na, styrene-butadiene rubber latex SBR, acrylic polymers PAA, etc.

[0067] In some embodiments, the electrode sheet is a positive electrode sheet, and the active layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium nickel manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganese phosphate, lithium iron phosphate, and 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, and graphene; the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyvinyl alcohol, and sodium polyacrylate.

[0068] To further understand the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0069] Unless otherwise specified, the reagents involved in the embodiments of the present invention are all commercially available products and can be obtained through commercial channels.

[0070] Example 1

[0071] This example provides a 3D composite current collector with a porosity of 40%, which includes a first copper layer of 1 μm, a first nickel layer of 8 nm, a fiber layer of 20 μm, a second nickel layer of 8 nm, and a second copper layer of 1 μm stacked in sequence. The fiber layer includes first PET fibers and second PET fibers with a mass ratio of 7:3. The molecular weight of the first PET fiber is 58.69 g / mol, and the diameter is 5 - 6 μm. The molecular weight of the second PET fiber is 249.68 g / mol, and the diameter is 5 - 6 μm. The fiber layer also includes 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.

[0072] Its preparation method includes the following steps:

[0073] S1: Select the first and second polymer fiber base films, clean them respectively to remove impurities such as oil stains and dust on the surface, and then dry them to obtain the pretreated first and second polymer fiber base films;

[0074] S2: Granulate the first polymer fiber base film to form first slices, add the first slices into a screw extruder, and perform melt extrusion treatment at 226 - 228 °C (the rotational speed of the 200 cc metering pump in the screw extruder is 3 - 8 rev / min) to obtain the first slurry;

[0075] S3: Melt the second polymer fiber base film, then add carbon nanotubes into the molten second polymer fiber, perform mixing granulation to form second slices, add the second slices into a screw extruder, and perform melt extrusion treatment at 272 - 273 °C (the rotational speed of the 200 cc metering pump in the screw extruder is 10 - 15 rev / min) to obtain the second slurry;

[0076] S4: Feed the first slurry and the second slurry into a spinning assembly according to a mass ratio of 7:3, perform spinning treatment to obtain nascent fibers. After the nascent fibers are cooled and solidified, fiber filaments with a longitudinal strength of 35 N - 38 N, a transverse strength of 22 - 26 N, and an orientation degree within 7% are obtained. After laying the fiber filaments and hot roll pressing (the hot roll pressing temperature is 215 - 220 °C), a fiber layer is obtained;

[0077] S5: Place a nickel target in a magnetron sputtering machine, put the fiber layer into the vacuum chamber of the magnetron sputtering machine, introduce an appropriate amount of argon as a protective gas, then apply an electric field to cause the nickel target to sputter. The sputtered nickel metal particles are deposited on the upper and lower surfaces of the fiber layer to deposit the first nickel layer and the second nickel layer. Place a copper target in the magnetron sputtering machine, apply an electric field to cause the nickel target to sputter, and the sputtered copper metal particles are deposited on the surfaces of the first nickel layer and the second nickel layer to deposit the first copper layer and the second copper layer, obtaining the 3D composite current collector.

[0078] Example 2

[0079] 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 10 μm, the fiber layer includes a first PET fiber and a second PET fiber with a mass ratio of 8:2, both with a diameter of 8 - 10 μm, the fiber layer further includes 0.8 wt% of carbon nanotubes, the outer diameter of the carbon nanotubes is 1.5 - 1.8 nm, and the inner diameter is 1 - 1.2 nm.

[0080] Its preparation method refers to Example 1.

[0081] Example 3

[0082] This example provides a 3D composite current collector, which is different from Example 1 in that: it includes a first copper layer of 1.2 μm, a first nickel layer of 10 nm, a fiber layer of 10 μm, a second nickel layer of 10 nm, and a second copper layer of 1.2 μm stacked in sequence.

[0083] Its preparation method refers to Example 1.

[0084] Comparative Example 1

[0085] A copper foil with a thickness of 6.5 μm is used as the current collector.

[0086] Comparative Example 2

[0087] This example provides a composite current collector, which includes a first copper layer of 1 μm, a first nickel layer of 8 nm, a PET fiber layer of 10 μm, a second nickel layer of 8 nm, and a second copper layer of 1 μm stacked in sequence. The PET fiber layer only includes the second PET fiber with a molecular weight of 249.68 g / mol as in Example 2 and the carbon nanotubes as in Example 2, and does not contain the first PET fiber.

[0088] S1: Melt the PET base film, then add carbon nanotubes to the molten PET, mix and granulate to form a second slice. Add the second slice into a screw extruder and perform a melt extrusion treatment at 272 - 273 °C (the rotational speed of the 200 cc metering pump in the screw extruder is 5 - 15 rev / min) to obtain a slurry;

[0089] S2: Feed the slurry into a spinning assembly, perform spinning treatment to obtain primary fibers. After the primary fibers are cooled and solidified, fiber filaments are obtained. The fiber filaments are laid and hot roll pressed (the hot roll pressing temperature is 215 - 220 °C) to obtain a fiber layer;

[0090] S3: Place the nickel target in the magnetron sputtering machine, put the fiber layer into the vacuum chamber of the magnetron sputtering machine, introduce an appropriate amount of argon as the protective gas, and then apply an electric field to cause the nickel target to sputter. The sputtered nickel metal particles are deposited on the upper and lower surfaces of the fiber layer to deposit the first nickel layer and the second nickel layer. Place the copper target in the magnetron sputtering machine, apply an electric field to cause the nickel target to sputter, and the sputtered copper metal particles are deposited on the surfaces of the first nickel layer and the second nickel layer to deposit the first copper layer and the second copper layer, obtaining the 3D composite current collector.

[0091] Comparative Example 3

[0092] This example provides a composite current collector and a 3D composite current collector, including a first copper layer of 1 μm, a first nickel layer of 8 nm, a fiber layer of 10 μm, a second nickel layer of 8 nm, and a second copper layer of 1 μm stacked in sequence. The fiber layer only includes the second PET fiber with a molecular weight of 249.68 g / mol in Example 2, and does not contain the first PET fiber and carbon nanotubes.

[0093] Its preparation method includes the following steps:

[0094] S1: Melt the PET base film, granulate it to form slices, add the slices into a screw extruder, and perform a melt extrusion treatment at 272 - 273 °C (the metering pump speed of 200 cc in the screw extruder is 5 - 15 rev / min) to obtain a slurry;

[0095] S2: Feed the slurry into a spinning assembly, perform spinning treatment to obtain nascent fibers. After the nascent fibers are cooled and solidified, fiber filaments are obtained. After laying the fiber filaments and hot roll pressing (the hot roll pressing temperature is 215 - 220 °C), a fiber layer is obtained;

[0096] S3: Place the nickel target in the magnetron sputtering machine, put the fiber layer into the vacuum chamber of the magnetron sputtering machine, introduce an appropriate amount of argon as the protective gas, and then apply an electric field to cause the nickel target to sputter. The sputtered nickel metal particles are deposited on the upper and lower surfaces of the fiber layer to deposit the first nickel layer and the second nickel layer. Place the copper target in the magnetron sputtering machine, apply an electric field to cause the nickel target to sputter, and the sputtered copper metal particles are deposited on the surfaces of the first nickel layer and the second nickel layer to deposit the first copper layer and the second copper layer, obtaining the 3D composite current collector.

[0097] Test Example

[0098] Use the current collectors of the above examples and comparative examples to prepare negative electrode sheets, including the following steps:

[0099] The thickener CMC-Na was dissolved in deionized water to form a 1.2 wt % thickener solution. The raw materials were weighed according to the mass ratio of graphite, conductive agent Super-P, thickener, and binder SBR of 95:1.0:1.2:2.8. The thickener solution and the raw materials were then mixed to form a negative electrode slurry, which was coated on the current collector (single layer coating surface density was 12 mg / cm 2 ) on both sides, dried in an oven, then rolled at high temperature, and then cut and die-cut to prepare a single negative electrode sheet, and then baked at 110°C under vacuum conditions, and then compacted by a roller press, with the compaction degree set to 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.62 g / cm 3 , 5 samples were prepared for each compaction degree of the electrode to obtain a series of negative electrode sheets.

[0100] Test Example 1

[0101] Comparison of air permeability of current collector: Samples were taken from the current collector of each embodiment and comparative example, with a sample size of 100*100 mm, and 3 samples in each group. The samples were placed in the test head of the permeability meter for air permeability test. The time required for 100 mL of air to pass through 1 square inch of the sample was tested under a pressure of 1.22 kPa. The test results, Gurley values, were recorded in Table 1.

[0102] Table 1

[0103]

[0104] It can be seen from Table 1 that the 3D composite copper current collector of the embodiment has better air permeability.

[0105] Test Example 2

[0106] Negative electrode impedance test: compaction degree is 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.62 g / cm 3 For the negative electrode sheets of the test examples, samples to be tested were cut at three different positions of the electrode sheets for each degree of compaction, and resistance tests were performed. The resistance test adopted a two-probe method, and the current transmission path passed through the test probe (upper) → the surface active material layer on the electrode sheet → the current collector → the surface active material layer under the electrode sheet → the test probe (lower) in sequence. The results are shown in Table 2.

[0107] Table 2:

[0108]

[0109] As can be seen from Table 2, compared with the negative electrode sheet using the conventional metal copper current collector of Comparative Example 1, for the composite current collector of Comparative Example 3, due to the non-conductive fiber layer, the impedance of the negative electrode sheet increases significantly. Moreover, for the composite current collectors of Comparative Examples 2-3, since their fiber layers only have one kind of PET fiber, their uniformity is poor. However, the resistance change of the negative electrode sheet of the 3D composite current collector of the Examples is not obvious. This indicates that the 3D composite current collector of the present invention can ensure the uniformity of the current collector while increasing the thickness of the fiber layer, making it have good electrical conductivity.

[0110] Test Example 3

[0111] Comparison of the wettability of the negative electrode sheet: Take the negative electrode sheets of the test examples with tap densities of 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.62 g / cm 3 . Perform die-cutting on them, and the die-cut size is 84*174 mm. Subsequently, stack 21 layers of each sample in the manner of negative electrode sheet / separator (CN206849946 U, thickness 12 μm) / negative electrode sheet / separator to form a single-electrode electrode group. Wrap the outermost layer with a separator, place it in an aluminum-plastic film bag and inject electrolyte. After standing for 1 hour, pour out the excess electrolyte. After continuing to stand for 12 hours, take out the electrode group and disassemble it. Weigh the 11th negative electrode sheet at the middle position, and calculate the mass increase ratio of the electrode sheet before and after absorbing the electrolyte. The results are shown in Table 3.

[0112] Table 3:

[0113]

[0114] As can be seen from Table 3, compared with the conventional PET composite current collectors 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 present invention is significantly improved, indicating that the 3D composite current collector has a porous structure inside, which can significantly improve the electrolyte infiltration speed and the electrolyte infiltration effect, and can provide more electrolyte diffusion channels.

[0115] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some 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 present invention.

Claims

1. A 3D composite current collector, characterized in that: include: 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 polymer fiber, a second polymer fiber and carbon nanotubes, the molecular weight of the first polymer fiber is 50-100g / mol, the molecular weight of the second polymer fiber is 200-500g / mol; the outer diameter of the carbon nanotube is 1-2nm, and the inner diameter is 0.5-1.5nm; the thickness of the fiber layer is 8-20µm.

2. The 3D composite current collector according to claim 1, characterized in that: The carbon nanotubes account for 0.5wt%-1wt% of the fiber layer.

3. The 3D composite current collector according to claim 1, characterized in that: In the fiber layer, the mass ratio of the first polymer fiber to the second polymer fiber is 6-10:2-5; And / or, the fiber diameters of the first polymer fiber and the second polymer fiber are independently 5-30 μm.

4. The 3D composite current collector according to any one of claims 1 to 3, characterized in that: The thickness of the first metal layer and the second metal layer are independently 1-1.5 μm.

5. The 3D composite current collector according to claim 4, characterized in that: The first metal layer includes: a first nickel layer close to the fiber layer and a first copper layer far away from the fiber layer; the second metal layer includes: a second nickel layer close to the fiber layer and a second copper layer far away from the fiber layer.

6. The 3D composite current collector according to claim 5, characterized in that: The thickness of the first nickel layer is 8-10nm, and 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.

7. The 3D composite current collector according to any one of claims 1 to 3, characterized in that: The porosity of the 3D composite current collector is 15%-40%.

8. The 3D composite current collector according to any one of claims 1 to 3, characterized in that: The first polymer fiber and the second polymer fiber are independently selected from one or more of polyethylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, and polyimide.

9. A method for preparing a 3D composite current collector according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: granulating the first polymer fiber to form a first slice, adding the first slice into a screw extruder, and performing a melt extrusion process at 226-228° C. to obtain a first slurry; S2: melting the second polymer fiber, then adding carbon nanotubes to the molten second polymer fiber, mixing and granulating to form a second slice, adding the second slice to 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 fed into a spinning assembly in a mass ratio of 6-10:2-5, and spun to obtain primary fibers. The primary fibers are cooled and solidified, and then laid and hot rolled to obtain a fiber layer; S4: Nickel is placed in a magnetron sputtering machine to deposit a first nickel layer and a second nickel layer on the upper and lower surfaces of the fiber mesh, and then copper is placed in a magnetron sputtering machine to deposit a first copper layer and a second copper layer on the surface of the first nickel layer and the second nickel layer to obtain the 3D composite current collector.

10. An electrode sheet, characterized in that: It comprises the 3D composite current collector according to any one of claims 1 to 8 and an active layer located on at least one functional surface of the 3D composite current collector.

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