Highly anisotropic three-dimensional current collectors with optimized and tailored electron curvature towards the tab direction

Abstract

Disclosed embodiments relate to a current collector including a porous, free-standing three-dimensional structure and at least one current collector tab, the at least one tab being connected to the three-dimensional structure, the three-dimensional structure comprising at least one layer formed of one-dimensional (1D) nanomaterials, two-dimensional (2D) nanomaterials, or a mixture thereof, the nanomaterials in the layer being aligned toward the at least one tab.

Description

[Technical Field]

[0001] The present invention relates to an advanced three-dimensional (3D) current collector comprising a low-torque artificial electron percolation network present within a 3D body that exhibits non-uniform electrical conductivity toward the direction and / or placement of the current collector tabs, a method for fabricating such a current collector, and a device comprising the same. More specifically, the present invention relates to a current collector comprising a porous, free-standing 3D structure that includes one or more layers of nanomaterials aligned toward at least one current collector tab connected to the 3D structure. [Background technology]

[0002] In the past decade, research into electrical energy storage devices, such as lithium-based batteries, has been intensively pursued due to their important role in energy transition and their many applications, such as mobile phones, laptops, and electric vehicles. In particular, there is an ever-increasing demand for storage devices with improved power performance, higher energy density, longer lifespan, and safety. Such storage devices generally include a positive electrode, a negative electrode, a separator, and a redox-active material.

[0003] Current collectors are typically made of copper, nickel, or aluminum, which have isotropic electrical conductivity, and are attached to electrodes to extract current from the storage device. Current collector foils also provide mechanical support for the electrodes during subsequent cell manufacturing processes, using state-of-the-art slurry-based electrodes, thereby defining the current collector foil as a process substrate. However, for many applications, there is room for improvement in electrical properties, particularly electrical conductivity, as well as in physicochemical and thermal properties.

[0004] State-of-the-art alkali-ion batteries use transition metal (TM)-based positive electrodes, which typically exhibit a ~5% volumetric change during cycling. This means that a 30% average positive electrode porosity allows NCA, LCO, or other insertion or intercalation active materials to safely accommodate their volumetric changes within the electrode pores. However, next-generation positive and negative electrode active materials, including sulfur, lithium metal, silicon, germanium, and tin, with typical 30% porosity, lack sufficient volume to accommodate the long-term cyclic structural volume changes of such batteries. For example, sulfur theoretically expands by approximately 79% upon full lithiation and 157% upon sodiation, while lithium metal expands or contracts by 100% upon deposition or exfoliation (or dissolution). Furthermore, after the initial Li stripping / discharge, the lithium metal foil never achieves the same surface morphology as it had in the pristine state, with approximately 30% remaining as an irreversible defragmentation (or fragmentation) loss, which gradually increases with further cycles. To transport electrons within the electrode, typical slurry-based batteries must involve countless individual particles, forming electron percolation networks or pathways according to the particle-aggregate-cluster (PAC) principle.

[0005] In the case of sulfur, the volume change during cycling is ~79%, and the porosity of the state-of-the-art (SOA) cathode is ~45%. Therefore, it is clear that the available space cannot fully compensate for the volume change, which also affects the electrolyte seeping into or penetrating the cathode pores. Generally, this process is called "cathode breathing," and the cathode pores are constantly shrinking and expanding, and the electrolyte occupying the pores is expelled and re-entered during cycling. For "post-lithium" batteries, active materials must incorporate mechanisms to address the "expansion / contraction behavior (or breathing aspect)" of the electrode. Another important influencing factor is the current distribution non-uniformity (CDNU) factor, which is amplified by the periodic structural rearrangement of the cathode based on the PAC principle. The electrons (e) present in the SOA electrode are - The routing must be flexible enough to allow for extended cycling and minimize degradation of large area electrodes. The electrode size, active material loading per unit area, type of current collector, tab size, and tab placement all affect CDNU and are often the determining factor for cell failure during scale-up. While this is not the case for a coin-sized electrode to a 120 cm diameter electrode, which is typical for commercial batteries, the CDNU is still relatively small. 2 Good results are obtained with electrodes exceeding this.

[0006] Therefore, the object of the present invention is to provide a current collector that can selectively distribute electrons within an artificially created electron percolation network present within the current collector. The main effect of such a current collector is to improve and homogenize the CDNU within the electrode, resulting in the shortest migration path (less flexibility), reduced internal resistance due to improved electron transport, and non-uniform distribution of redox reactions between the electrodes.

[0007] Due to these exceptional properties, nanomaterials have been proposed for a variety of applications, including zero-dimensional (0D) materials such as quantum dots and nanoparticles, one-dimensional (1D) materials such as nanotubes, nanorods, nanofibers, and nanowires, and two-dimensional (2D) materials such as nanoplates and nanoflakes. If a material does not have dimensions small enough to be considered nanosized, it is not a nanomaterial. It is known that these nanomaterials can be used to prepare macroscale objects, such as free-standing three-dimensional (3D) networks, that do not require support. For example, carbon nanotubes (CNTs) can be formed into 3D networks or sheet / paper-like structures, commonly referred to as "buckypaper," consisting of entangled aggregates of randomly distributed CNTs. Buckypaper is typically fabricated by vacuum filtration of CNT and / or graphene dispersions and / or by sequentially lifting and stacking CNT / graphene layers using filter membranes. Recently, electrodes based on self-supporting buckypaper have attracted considerable attention and have been shown to exhibit excellent performance.

[0008] Methods for aligning CNTs have also been reported, including (i) mechanical stretching of cross-linked CNT mats as described in U.S. Pat. No. 8,246,886 (B2); and (ii) vertically aligned carbon nanotubes (VACNTs) as described in Wang et al. (Nanotechnology, 2008; 19(7), 75609; DOI: 10.1088 / 0957-4484 / 19 / 7 / 075609). (iii) application of large magnetic fields as disclosed in U.S. Patent Application No. 2002 / 0185770 and U.S. Patent No. 7,803,262 (B2); and (iv) application of electric fields as reported, for example, by Zhu et al. (J. Appl. Phys. 105, 054319 (2009); https: / / doi.org / 10.1063 / 1.3080243) and Zhang et al. (J. Nanosci. Nanotechnol. 9, 2887-2893, 2009; doi:10.1166 / jnn.2009.014).

[0009] Therefore, an object of the present invention is to provide a current collector that can be produced in an environmentally friendly manner without compromising the physical state and chemical properties of 1D / 2D nanomaterials, and that has excellent physicochemical, thermal, and electrical properties for various applications. Further objects will become apparent based on the following description and claims. Summary of the Invention

[0010] In one aspect, the present invention relates to a current collector comprising: a porous, free-standing three-dimensional structure; and at least one current collector tab, wherein the at least one tab and the three-dimensional structure are connected, and the three-dimensional structure comprises at least one layer formed from one-dimensional (1D) nanomaterials, two-dimensional (2D) nanomaterials, or a combination (or mixture) thereof, and wherein the nanomaterials in the layer are aligned toward the at least one tab.

[0011] One-dimensional and two-dimensional nanomaterials can be composed of pure carbonaceous materials, such as carbon nanotubes (CNTs) or graphene; doped carbonaceous materials, such as carbon doped with nitrogen, oxygen, or fluorine; non-carbonaceous materials, such as metals or metal oxides; or mixtures of any of the foregoing. 1D nanomaterials can be nanotubes, nanorods, nanofibers, or nanowires composed of any of the above materials, including, for example, carbon nanotubes or boron nitride carbon nanotubes. 2D nanomaterials can be nanosheets, nanoplates, or nanoflakes composed of the above materials, including, for example, graphene, graphene oxide, reduced graphene oxide, Mxenes, graphitic carbon nitride, hexagonal boron nitride, silicene, germanene, hexagonal boron nitride nanosheets, or transition metal dichalcogenide nanosheets.

[0012] In a further aspect, the present invention relates to a device comprising the current collector, such as an electrode, a primary or secondary energy storage device, or an electrochemical cell. The device may be, for example, a battery, which may be a battery comprising an alkali / alkaline earth metal / ion (e.g., Li, Na, K, Ca, Mg, Al, Zn, etc.) such as a lithium-ion battery, a sodium-ion battery, an aluminum-ion battery, a zinc-ion battery, a potassium-ion battery, a calcium-ion battery, or a magnesium-ion battery; or a battery comprising an alkali / alkaline earth metal chalcogenide such as a lithium-sulfur battery, a lithium-selenium battery, a lithium-sulfur-selenium battery, a sodium-sulfur battery, a sodium-selenium battery, an aluminum-sulfur battery, a potassium-sulfur battery, a calcium-sulfur battery, or a magnesium-sulfur battery; or a battery comprising an alkali / alkaline earth metal air such as a lithium-air battery, a sodium-air battery, an aluminum-air battery, or a zinc-air battery.

[0013] In another aspect, the invention relates to methods for fabricating current collectors, such as methods based on dielectrophoretic alignment of nanomaterials, layer-by-layer (LbL) assembly of layers of aligned nanomaterials, and connecting the assembled layers to current collector tabs by welding, stamping, or crimping.

[0014] For clarity, here are provided definitions of some terms used throughout this specification and claims, which should be used to determine the meaning of each expression unless the context requires a different meaning.

[0015] The terms "a" or "an" do not preclude a plurality. That is, the singular forms "a," "an," and "the" should be understood to include plural references unless the context clearly indicates or requires otherwise. In other words, unless expressly stated otherwise or the referenced context clearly suggests otherwise, all references to singular features or limitations in this disclosure shall include the corresponding plural features or limitations, and vice versa. Thus, the terms "a," "an," and "the" have the same meaning as "at least one" or "one or more," unless otherwise defined. For example, the expression "a material" includes a mixture of nanomaterials, etc.

[0016] The words "comprise", "comprises" and "comprising" and similar expressions (including or comprising) are to be interpreted in an open and inclusive sense as "including but not limited to".

[0017] Terms such as "essentially," "about," "approximately," "substantially," and the like in connection with a property or value include not only the exact property or exact value, but also any property or value that is normally considered to be within a normal range or variability accepted in the art.

[0018] The terms "binder-free" and "surfactant-free" mean that no binder or surfactant is intentionally included in the material, but do not exclude the presence of residual amounts. That is, the term "free" means that the material contains less than a functional amount of each component, typically less than 1% by weight, preferably less than 0.1% by weight, or more preferably less than 0.01% by weight, and 0% by weight of each component. [Brief explanation of the drawings]

[0019] [Figure 1] Figure 1 shows a schematic diagram of a porous, free-standing, three-dimensional structured layer of 1D nanomaterials aligned toward a single current collector tab.

[0020] [Figure 2] Figure 2 is a schematic illustration of a porous, free-standing, three-dimensional structured layer with 1D nanomaterials aligned toward two current collecting tabs.

[0021] [Figure 3] Figure 3 is a schematic illustration of a porous, free-standing, three-dimensionally structured layer with 1D nanomaterials aligned toward three current collecting tabs.

[0022] [Figure 4A] FIG. 4A is a photograph showing an example of a current collector fabrication process (500) that produces a layer of aligned 1D nanomaterials with a desired distance between the aligned nanomaterials (502).

[0023] [Figure 4B] Figure 4B is a cross-sectional photograph of a layer of aligned 1D nanomaterials.

[0024] [Figure 5] FIG. 5 is a flowchart showing a method for manufacturing a current collector.

[0025] [Figure 6]FIG. 6 shows the correlation between discharge energy and current distribution nonuniformity for various tab configurations with different tab numbers and / or tab placements. Modes for carrying out the invention

[0026] In a first aspect, the present invention provides a current collector comprising a porous, free-standing three-dimensional (3D) structure and at least one current collector tab; the at least one tab and the three-dimensional structure are connected, and the three-dimensional structure comprises at least one layer formed from a one-dimensional (1D) nanomaterial, a two-dimensional (2D) nanomaterial, or a mixture thereof, wherein the nanomaterials in the layer are aligned toward the at least one tab.

[0027] The inventors believe that the claimed current collectors provide a charge carrier (e -We found that this structure is effective in promoting the transport of electrons. In particular, we found that the 3D structure functions as an artificial electron percolation network, exhibiting anisotropic electrical conductivity with respect to the orientation of one or more current collecting tabs. This implanted artificial electronic percolation network possesses anisotropic planar electrical conductivity, with maximum electrical conductivity and minimum electron tortuosity optimized or enhanced toward the orientation and orientation of the current collecting tabs, and the difference in electrical conductivity between the region furthest from the electrode and the region closest to it is 8% to 120%. Generally, conductivity in the porous, free-standing 3D structures improves towards the direction / location of one or more current collector tabs, thereby reducing impedance while maintaining maximum uniformity of current to or from the electrodes, thereby ensuring reliable, optimized, and safe performance of devices comprising the current collectors in electrochemical cells containing alkali and / or alkaline earth (e.g., Li, Na, K, Ca, Mg, Al, Zn, etc.) metals / ions, or alkali / alkaline earth metal chalcogenides, or alkali / alkaline earth oxygen, or alkali / alkaline earth air, or primary or secondary rechargeable batteries, such as high-energy Li-ion batteries, Li-sulfur batteries, Li-oxygen batteries, etc.

[0028] Furthermore, the enhanced conductivity toward the current collector tabs was confirmed to be due to the presence of an artificial electron percolation network, which exhibits a significant anisotropy in electrical conductivity governed by the presence of highly enhanced, less tortuous electron paths (i.e., the aligned nanomaterials provide the shortest possible electron percolation trajectories (electronic flexibility) from the electrode to the tab). In contrast, conventional current collectors have a network of randomly distributed and interlocked materials, resulting in less uniform current distribution and significantly longer electron bending path lengths.

[0029] It was also found that the nanomaterials were distributed in a non-clustered manner, with directly adjacent nanomaterials (e.g., CNTs) arranged in a planar orientation with partial overlap along their length, thereby forming chains or nanocables. The nanocables thus formed were separated from each other by controlled spacing and essentially aligned parallel to each other, further improving the transport of charge carriers through the percolation network.

[0030] The current collector disclosed herein may be a current collector foil or a current collector substrate. In a generally preferred embodiment of the current collector, the three-dimensional structure is binder-free and / or surfactant-free. In this context, binder-free and / or surfactant-free may be understood to mean that the three-dimensional structure is essentially formed solely by nanomaterials.

[0031] Typically, the three-dimensional structure of the current collector disclosed herein can comprise two or more stacked layers, each of which can be independently formed of a 1D nanomaterial, a 2D nanomaterial, or a mixture thereof. For example, a first layer can be formed of a 1D nanomaterial such as CNTs, and a second layer stacked on the first layer can be formed of a 2D nanomaterial such as graphene, or a mixture (or combination) of 2D nanomaterials such as molybdenum disulfide / graphene nanosheets (MoS2 / GNSs).

[0032] According to a preferred embodiment generally applicable in the context of the present disclosure, the stacked layers in the three-dimensional structure are bonded by interlayer van der Waals bonds. The stacking of layers may be, for example, vertical, which allows for the combination of layers whose composition changes in the vertical direction. In one embodiment, layers made of 1D nanomaterials may be preferred. An exemplary embodiment of a 1D nanomaterial is, for example, CNT.

[0033] According to a further preferred embodiment, the current collector disclosed herein comprises a three-dimensional structure comprising a total of 2 to 5,000 stacked layers, 3 to 2,000 stacked layers, 4 to 1,000 stacked layers, 5 to 500 stacked layers, 6 to 200 stacked layers, 7 to 100 stacked layers, 8 to 50 stacked layers, 9 to 20 stacked layers, or 10 stacked layers. Typically, the three-dimensional structure has a total thickness of 0.1 to 50 μm, 0.25 to 40 μm, 0.5 to 30 μm, 0.75 to 20 μm, or 1 to 10 μm. In a currently preferred embodiment, the layers are stacked one on top of the other along the z-axis or the x-axis.

[0034] According to a preferred embodiment generally applicable within the context of the present disclosure, the stacked layers of the porous, free-standing 3D structure comprise a combination of: (i) more than one layer formed from 1D nanomaterials; and (ii) at least one layer formed from 2D nanomaterials, which has been found to increase the active surface area and improve electrical conductivity.

[0035] In the context of the present disclosure, the individual layers of 1D nanomaterials may be rotated relative to each other, for example, the individual layers of a porous freestanding 3D structure may be rotated 90° relative to each other if they are square shaped, or 120° relative to each other if they are hexagonal shaped.

[0036] In a further preferred embodiment, the porosity of the three-dimensional structure is at least 3% V / V, for example, 10% V / V or more, preferably 50% V / V or more, 80% V / V or more, or 90% V / V or more, more preferably 95% V / V or more, based on the total volume of the three-dimensional structure. Porosity can be measured using a helium pycnometer, in which a sample is sealed in a sealed container of a fixed volume at a fixed pressure. By this method, porosity is defined as the volume difference between the empty container and the container containing the sample. The morphology of the porous network can be determined, for example, by physical gas adsorption or computerized microtomography.

[0037] The alignment resulted in a three-dimensional structure with regular porosity, which also contributed to anisotropic electrical conductivity optimized towards the current collector tab / tabs.

[0038] According to the present invention, the 1D nanomaterial capable of forming the layer of the three-dimensional structure contained in the current collector may be a nanotube, a nanorod, a nanofiber, or a nanowire. In the context of the present disclosure, a carbon nanotube may be a single-walled (SWCNT), a double-walled (DWCNT), or a multi-walled (MWCNT). Typically, the 1D nanomaterial comprises or consists of a carbonaceous material, a non-carbonaceous material, or a mixture thereof. In this context, the size, shape, porosity, and chemical composition of the 1D nanomaterial are not particularly limited. For example, 1D nanomaterials can comprise or consist of carbon, including materials such as graphite and porous carbon; metals such as aluminum (Al), bismuth (Bi), boron (B), copper (Cu), gallium (Ga), germanium (Ge), indium (In), iron (Fe), gold (Au), molybdenum (Mo), platinum (Pt), ruthenium (Ru), silicon (Si), silver (Ag), selenium (Se), tin (Sn), titanium (Ti), tellurium (Te), tungsten (W), vanadium (V), zinc (Zn), their metal oxides such as CuO, ZnO, TiO2, MoO2, and WO2, and alloys of these metals; and transition metal dichalcogenides such as MoS2, WS2, VS2, VS4, TiS2, and TiS4, or complex mixtures of any of the foregoing. 1D nanomaterials can be doped and / or functionalized with one or more functional groups. Examples of doped 1D nanomaterials include 1D nanomaterials doped with heteroatoms such as fluorine, nitrogen, oxygen, or combinations thereof, such as nitrogen-doped carbon materials. Examples of functional groups include -O, -OH, -COOH, -F, -COO, -NO3, -NO2, -R, -Cl, and -NH. In the context of the present disclosure, 1D nanomaterials can be, for example, carbon nanotubes or boron-carbon-nitride nanotubes. The electrical conductivity of a layer formed from aligned 1D nanomaterials can be, for example, 10 along the alignment direction (or orientation direction). 2 S / cm~10 6S / cm. Within one currently preferred embodiment, the 1D nanomaterial is a carbon nanotube.

[0039] According to the present invention, the 2D nanomaterials capable of forming the layers of the three-dimensional structure contained in the current collector can be nanosheets, nanoflakes, or nanoplatelets. Typically, the 2D nanomaterials comprise or consist of carbonaceous materials, non-carbonaceous materials, or mixtures thereof. In this context, the size, shape, porosity, and chemical composition of the 2D nanomaterials are not particularly limited. For example, 2D nanomaterials include carbon, including materials such as graphite, porous carbon, graphene, and fullerenes; metals such as aluminum (Al), bismuth (Bi), boron (B), copper (Cu), gallium (Ga), germanium (Ge), indium (In), iron (Fe), gold (Au), molybdenum (Mo), platinum (Pt), ruthenium (Ru), silicon (Si), silver (Ag), selenium (Se), tin (Sn), titanium (Ti), tellurium (Te), tungsten (W), vanadium (V), and zinc (Zn); and their derivatives such as CuO, ZnO, TiO, MoO, and WO. The 2D nanomaterials may comprise or consist of metal oxides and alloys thereof; transition metal dichalcogenides such as MoS2, WS2, VS2, VS4, TiS2, and TiS4; transition metal carbides (MXenes) such as TiC, VC, Mo2C, TiAlC2, and Mo2TiC2; transition metal nitrides / carbonitrides such as graphitic carbon nitride (g-CN4), hexagonal boron nitride (h-BN), silicene, phosphorene, germanene, boron-carbon-nitride (BCN), aluminum nitride, molybdenum nitride, titanium nitride, and alloys thereof; or complex mixtures of any of the foregoing. The 2D nanomaterials can be doped and / or functionalized with one or more functional groups. Examples of doped 2D nanomaterials include 2D nanomaterials doped with heteroatoms such as fluorine, nitrogen, oxygen, or combinations thereof, such as nitrogen-doped carbon materials. Examples of functional groups include -O, -OH, -COOH, -F, -COO, -NO3, -NO2, -R, -Cl, and -NH. Examples of generally preferred 2D nanomaterials include, for example, nanosheets of graphene, graphene oxide, reduced graphene oxide, MXene, g-CN4, h-BN, silicene, phosphorene, germanene, BCN, transition metal dichalcogenides, or mixtures of the foregoing.The electrical conductivity of a layer formed from aligned 2D nanomaterials is, for example, 10 in the plane direction of the layer. 2 S / cm to 10 4 Within one embodiment, the 2D nanomaterial is a nanosheet of graphene, graphene / graphene oxide, or MoS2.

[0040] Included within the scope of the present disclosure are current collectors comprising two or more, three or more, four or more, five or more, six or more, or 2 to 10 current collector tabs. As shown in Figure 6, current distribution nonuniformity significantly impacts energy density. Figure 6 also demonstrates that the number and location of tabs are important factors affecting performance. In general, increasing the number of tabs improves overall performance, and we have found that tab configuration and overall performance are directly related. By providing highly anisotropic electrical conductivity with tailored electron curvature optimized toward the direction of one or more tabs, the tab configurations disclosed herein ensure a low current distribution nonuniformity coefficient and reduce Joule heating and associated adverse effects, such as irreversible electrochemical side reactions and reduced energy density. In other words, the tab configurations provided herein improve current distribution uniformity and overall performance, including improved energy output, cycling behavior, and safety.

[0041] The subject matter of the present disclosure also includes electrodes comprising the current collectors described herein. According to a further aspect, the present invention provides primary or secondary energy storage devices or electrochemical cells comprising the current collectors and / or electrodes disclosed herein. The device may be, for example, a battery, as described above. In one generally preferred embodiment, the storage device is a lithium-ion battery or a lithium-sulfur battery, particularly a lithium-sulfur battery, comprising at least one current collector according to the present invention. Devices according to the present invention have the advantages described above for the current collecting device. In particular, devices such as energy storage devices or electrochemical cells according to the present invention exhibit improved electrical and thermal properties, excellent cycling behavior, and enhanced safety, particularly due to the presence of an artificial percolation network toward the current collector tab.

[0042] In a further aspect, the present invention provides a method for producing a current collector, particularly the current collector described above, comprising the steps of: (a) providing a porous, free-standing three-dimensional structure comprising at least one layer formed from one-dimensional (1D) nanomaterials, two-dimensional (2D) nanomaterials, or a mixture (or combination) thereof, wherein the nanomaterials are aligned and have their longitudinal axes perpendicular to a substrate surface; and (b) connecting the three-dimensional structure of step (a) to at least one current collecting tab such that the nanomaterials contained in the three-dimensional structure are aligned toward the at least one tab.

[0043] The formation of 1D nanomaterials, 2D nanomaterials, or mixtures thereof in the form of nanotubes, nanorods, nanofibers, nanowires, nanosheets, nanoplates, or nanoflakes is generally known in the art. As noted above, 1D and 2D nanomaterials may include or be made of carbonaceous materials, non-carbonaceous materials, or mixtures thereof, and such materials are generally known in the art.

[0044] An example of a method for fabricating a current collector according to the principles described herein is shown as a flow chart in Figure 5. According to the method (500) for fabricating a current collector, forming a porous, free-standing layer of aligned nanomaterials can include providing a dispersion / suspension of nanomaterials (501 A1 and A2 or 501 B1 and B2), applying an external field to align the dispersed / suspended nanomaterials to form a layer (502), and recovering the layer (503).

[0045] In one generally preferred embodiment of the method, a dispersion / suspension of nanomaterials is prepared by adding the nanomaterials to a liquid medium followed by chemical and / or mechanical treatment (501 A1 and A2). In an alternative preferred embodiment of the method, a dispersion / suspension of nanomaterials is prepared by directly disposing the nanomaterials on the surface of a liquid medium, optionally followed by mechanical treatment (501 B1 and B2). In this context, dispersion or suspension means that the nanomaterials, e.g., CNTs and / or graphene, are individually dispersed or suspended in the liquid medium. In some embodiments, the dispersion / suspension is prepared at room temperature. In some embodiments, the dispersed / suspended nanomaterials float on the surface of the liquid medium. Suitable liquid media include water, ethanol, methanol, acetone, isopropanol (IPA), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO), or mixtures thereof. In some embodiments, the liquid medium can be water, a mixture of water and ethanol, or acetone. In some embodiments, the liquid medium can include one or more surfactants.

[0046] Chemical treatments can include, for example, functionalization and / or treatment with strong acids and / or surfactants. Suitable strong acids include, for example, nitric acid (HNO), sulfuric acid (HSO), and mixtures thereof. Examples of functionalization include the introduction of one or more functional groups selected from -O, -OH, -COOH, -F, -COO, -NO, -NO, -R, -Cl, and -NH.

[0047] Suitable surfactants include, for example, sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), polyoxyethylene octylphenyl ether (Triton X-100), and mixtures thereof. Surfactants are useful for preventing or avoiding the formation of aggregates. Suitable mechanical treatments include, for example, sonication, probe sonication, centrifugation, calendaring, ball milling, and combinations thereof. In some embodiments, the nanomaterials are subjected to sonication (501 A2) to ensure a uniform dispersion / suspension. In some embodiments, the nanomaterials are subjected to electrostatic dispersion (501 B2) under the application of direct current (DC). In some embodiments, the DC can be high voltage (HV) DC to ensure a uniform dispersion / suspension.

[0048] In a currently preferred embodiment of the method, an external force is applied to the dispersed / suspended nanomaterials, causing the nanomaterials to align (or orient) and form a layer. When the nanomaterials are aligned, their longitudinal axis is perpendicular to the substrate surface. The substrate surface may be, for example, the bottom surface of a container containing the dispersion / suspension or the surface of a filter membrane.

[0049] Suitable external forces include, for example, an electrostatic field, an electric field, a magnetic field, an electromagnetic field, or any combination of the foregoing. In one embodiment, an electrostatic field is applied to the dispersion. In another embodiment, the dispersion is subjected to an electric field (502). In a further embodiment, a magnetic field is applied to the dispersion. In yet another embodiment, an electromagnetic field is applied to the dispersion. In a currently preferred embodiment, an alternating current (AC) electric field is applied to the liquid dispersion / suspension to align the nanomaterials and form a layer. For example, the AC may be an HVAC (high voltage AC) power source, such as an HVAC operating at a power of 1 kV to 300 kV and a frequency in the range of 3 kHz to 1.2 MHz. The application of the external force causes the nanomaterials to align along the direction of the applied force, thereby forming a layer.

[0050] Additionally, external forces, such as electric-field-induced magnetic fields (the right-hand rule) generated by charges flowing through aligned / chained lines and external magnetic fields, preferably generated by Helmholtz coils, can generate internal forces in situ in nanomaterials. These internal forces can be used to control and / or adjust the spacing between aligned nanomaterials, as well as the porosity within the layer structure. In some embodiments, aligned 1D nanomaterials can form nanocables, as shown in Figures 1-4. For example, the spacing between lines formed by aligned nanomaterials (e.g., CNTs) can be adjusted by the amount of current flowing through the lines due to the in situ generated magnetic field, which in this case has a repulsive effect on adjacent lines formed by aligned nanomaterials (nanocables). A stronger current results in a stronger magnetic field, resulting in greater distances between individual nanocables; or conversely, a weaker current results in a weaker repulsive effect, resulting in more densely packed nanocables. Naturally, the same applies to porosity: the more densely packed the nanocables, the lower the porosity within the resulting layer.

[0051] In the present context, it is generally preferred to apply an electric field (AC and / or DC) for the alignment of nanomaterials in aqueous liquid dispersions / suspensions.

[0052] In a currently preferred embodiment of the method, the layer of aligned nanomaterials formed from the liquid dispersion of nanomaterials can be recovered by vacuum filtration using a filter membrane 503. It has been found that vacuum-assisted filtration through a suitable membrane can yield an aligned layer of nanomaterials without disturbing or altering the alignment, i.e., the direction of the nanocables formed and the distance between the nanocables.

[0053] The filter membrane may have nanopores, nanochannels, micropores, microchannels, macropores, macrochannels, or a combination thereof. In addition, the filter membrane may be hydrophilic or have a hydrophilic coating. In some embodiments, the filter membrane may be porous with various pore sizes ranging from 20 nm to 50 μm.

[0054] In a generally preferred embodiment, vacuum filtration can be performed at a slow rate, and in particular, the filtration rate can be as slow as possible. Slow filtration rates have been found to be particularly useful for maintaining alignment, allowing the layer of aligned nanomaterials to float on the surface of the liquid medium, allowing the layer of aligned nanomaterials to be easily collected / lifted from the liquid medium without disrupting the alignment. Filtration rates can range, for example, from 10 ml / min to 100 ml / min.

[0055] After filtration, the layer of aligned nanomaterials can be separated from the filter membrane, cured, washed, and / or dried. In a generally preferred embodiment, residual solvent and / or surfactant can be removed by washing with deionized water, isopropyl alcohol, methanol, or mixtures thereof; baking; or a combination of any of the foregoing. Generally, the presence of solvent or surfactant adversely affects the physical and / or electrical properties of the layer of aligned nanomaterials.

[0056] The thickness of the layer of aligned nanomaterials can be controlled by the filtered volume and / or concentration of the nanomaterials in the liquid dispersion, and can range, for example, from about 50 to 1000, 100 to 750, 200 to 600, 250 to 500, or 300 to 350 nm.

[0057] In some preferred embodiments, the layer of aligned nanomaterials can have at least one electrically conductive and / or electrochemically active planar surface, with a surface area of ​​several mm 2 ~several meters 2 , for example 10cm 2 ~100cm 2 The range can be as follows.

[0058] In a generally preferred embodiment of the method, porous, free-standing three-dimensional structures can be provided by layer-by-layer (LbL) assembly (504A), in which individual layers of aligned nanomaterials resulting from the dispersion and vacuum filtration steps described above are stacked one on top of the other. In some embodiments, the layers are stacked vertically on top of each other. In other words, the process of providing a porous, free-standing three-dimensional structure is performed by preparing one or more individual layers of aligned nanomaterials as described above and assembling them along the z-axis to stack the required number and type of individual layers (i.e., the nanomaterial components used to form the layers) on top of each other. In the context of the present disclosure, individual layers of 1D nanomaterials can be rotated relative to each other when performing the layer-by-layer (LbL) assembly (504B). For example, the individual layers of the porous, free-standing 3D structure can be rotated 90° relative to each other if the layers are square, or 120° relative to each other if the layers are hexagonal.

[0059] In preferred embodiments, layer-by-layer (LbL) assembly is performed to build up a total of 2-5,000, 3-2,000, 4-1,000, 5-500, 6-200, 7-100, 8-50, 9-20, or 10 or more layers of aligned nanomaterials. Typically, the three-dimensional structures obtained by LbL assembly of individual layers of aligned nanomaterials can have a total thickness of 0.1-50 μm, 0.25-40 μm, 0.5-30 μm, 0.75-20 μm, or 1-10 μm.

[0060] According to preferred embodiments generally applicable within the context of the present disclosure, the stacked layers of the three-dimensional structure comprise a combination of (i) and (ii): (i) more than one layer formed from 1D nanomaterials; and (ii) at least one layer formed from 2D nanomaterials. In some embodiments, a porous, free-standing 3D structure may be formed solely by assembling aligned nanomaterial layers composed of 1D nanomaterials.

[0061] The method further comprises connecting or incorporating at least one current collector tab into a porous, free-standing 3D structure comprising at least one layer of aligned nanomaterials such that the nanomaterials contained in the 3D structure are aligned toward the at least one tab. In a generally preferred embodiment of the method, a current collector tab can be connected or incorporated into the porous, free-standing 3D structure obtained by the LbL process described above to form a current collector foil or current collector substrate (506) as disclosed herein. In this context, it is essential that the aligned nanomaterials are aligned toward the current collecting tab upon connection. The alignment (or orientation) of the nanomaterials described herein with the current collecting tab is crucial for achieving anisotropic electrical conductivity and a highly enhanced, low-torture electron path from the electrode to the tab through the artificial electron percolation network formed by the porous, free-standing three-dimensional structure. In some embodiments, the current collector tabs may be connected to the porous, free-standing 3D structure by ultrasonic welding, resistance welding, laser welding, stamping, or crimping, such that the nanomaterials contained in the 3D structure align toward the tabs.

[0062] It should be noted that the specification and drawings are merely illustrative in nature and are not intended to limit the scope of the invention as defined by the appended claims.

Claims

1. A current collector comprising: a porous, free-standing three-dimensional structure; and At least one current collector tab and A current collector, wherein at least one tab is connected to a three-dimensional structure, the three-dimensional structure comprising at least one layer formed from a one-dimensional (1D) nanomaterial, a two-dimensional (2D) nanomaterial, or a mixture thereof, and the nanomaterial in the layer is aligned toward the at least one tab.

2. The current collector of claim 1 , wherein the three-dimensional structure is binder-free and / or surfactant-free.

3. 3. The current collector of claim 1 or 2, wherein the three-dimensional structure comprises two or more stacked layers, each layer independently formed from a one-dimensional nanomaterial, a two-dimensional nanomaterial, or a mixture thereof.

4. 4. The current collector of claim 3, wherein the stacked layers are bonded together by interlayer van der Waals bonds.

5. 5. The current collector according to claim 3 or 4, wherein the three-dimensional structure comprises 2 to 5000 stacked layers, 3 to 2000 stacked layers, 4 to 1000 stacked layers, 5 to 500 stacked layers, 6 to 200 stacked layers, 7 to 100 stacked layers, 8 to 50 stacked layers, 9 to 20 stacked layers, or 10 stacked layers.

6. The current collector of any one of claims 1 to 5, wherein the three-dimensional structure has an overall thickness of 0.1 to 50 μm, 0.25 to 40 μm, 0.5 to 30 μm, 0.75 to 20 μm, or 1 to 10 μm.

7. The current collector according to any one of claims 1 to 6, wherein the porosity of the three-dimensional structure is at least 3% V / V, preferably 50% V / V or more, 80% V / V or more, or 90% V / V or more, and more preferably 95% V / V or more, based on the total volume of the three-dimensional structure.

8. The current collector according to any one of claims 1 to 7, wherein the one-dimensional nanomaterial is a nanotube, a nanorod, a nanofiber, or a nanowire.

9. The current collector according to any one of claims 1 to 7, wherein the two-dimensional nanomaterial is a nanosheet, a nanoflake, or a nanoplatelet.

10. The current collector according to any one of claims 1 to 9, wherein the one-dimensional or two-dimensional nanomaterial comprises a carbonaceous material, a non-carbonaceous material, or a mixture thereof.

11. 11. The current collector of any one of claims 1 to 10, wherein the current collector comprises two or more, three or more, four or more, five or more, six or more, or two to ten current collector tabs.

12. An electrode comprising the current collector according to any one of claims 1 to 11.

13. A primary or secondary energy storage device or electrochemical cell comprising a current collector according to any one of claims 1 to 11 and / or an electrode according to claim 12.

14. 14. The storage device of claim 13, wherein the storage device is a lithium ion battery or a lithium sulfur battery.

15. A method for manufacturing a current collector, comprising: (a) providing a porous, free-standing, three-dimensional structure having at least one layer formed from one-dimensional (1D) nanomaterials, two-dimensional (2D) nanomaterials, or a mixture thereof, wherein the nanomaterials are aligned and have their longitudinal axes perpendicular to the substrate surface; and (b) connecting the three-dimensional structure of step (a) to at least one current collector tab such that the nanomaterial contained in the three-dimensional structure aligns toward the at least one tab; A method for producing a current collector, comprising:

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