Advanced anisotropic 3d current collector with customized electronic curvature optimized towards tab direction

Abstract

The disclosed embodiments relate to a current collector comprising a porous, separate three-dimensional structure, and at least one current collector tab. The at least one tab is connected to the three-dimensional structure. The three-dimensional structure comprises at least one layer formed of a one-dimensional (1D) nanomaterial, a two-dimensional (2D) nanomaterial or a mixture thereof, and wherein the nanomaterial in the layer is 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-tortuosity artificial electron percolation network present within a 3D body, the low-tortuosity artificial electron percolation network exhibiting non-uniform electrical conductivity in a direction and / or placement toward a current collector tab, a method of making such a current collector, and an apparatus comprising the current collector. More specifically, the present invention relates to a current collector comprising a porous, freestanding 3D structure comprising one or more nanomaterial layers aligned toward at least one current collector tab connected to the 3D structure. Background Art

[0002] Over the past decade, extensive research has been conducted on storage devices for electrical energy, such as lithium-based batteries, as they play a key role in energy conversion and in many applications, such as mobile phones, laptops, and electric vehicles. In particular, there is a growing demand for storage devices with improved power performance, higher energy density, longer lifespan, and safety. Such storage devices typically consist of a positive electrode, a negative electrode, a separator, and a redox-active material.

[0003] The current collector is typically made of copper, nickel, or aluminum, which has isotropic electrical conductivity, and is attached to the electrode to extract current from the storage device. In cutting-edge slurry-based electrodes, the current collector foil also provides mechanical support for the electrode as it moves through the subsequent battery cell manufacturing process, defining the current collector foil as a process substrate. However, for many applications, there is still potential to improve electrical properties, particularly electrical conductivity, as well as physicochemical and thermal properties.

[0004] State-of-the-art alkali-ion batteries using transition metal (TM)-based cathodes typically exhibit a volume fluctuation of approximately 5% over cycling. This means that, with an average cathode porosity of approximately 30%, NCA, LCO, or other intercalation or intercalation active materials can safely accommodate volume fluctuations within the electrode voids. However, next-generation cathode and anode active materials (including sulfur, lithium metal, silicon, germanium, tin, etc.), which typically have a porosity of 30%, do not provide sufficient volume to accommodate the structural volume changes of such batteries over time. For example, sulfur theoretically expands by approximately 79% upon full lithiation and approximately 157% upon sodiation, while lithium metal expands or contracts by 100% upon plating or stripping. Furthermore, after the first lithium stripping / discharge, lithium metal foil can no longer achieve a surface morphology similar to that in its original state, leaving an irreversible fragmentation loss of approximately 30%, which gradually increases with further cycling. Typical slurry-based batteries follow the particle-aggregate-cluster (PAC) principle to form electron percolation networks or pathways, and countless individual particles must participate in order to transport electrons within the electrode.

[0005] In the case of sulfur, the volume fluctuation during cycling is about 79%, and the porosity of state-of-the-art (SOA) cathodes is about 45%. Therefore, it is clear that the available space cannot fully compensate for the volume fluctuations, which also affects the electrolyte that is immersed in or penetrates the cathode voids. Generally, this process is called "cathode breathing", where the cathode voids are constantly shrinking and expanding, and the electrolyte occupying these voids is expelled and swept in and out during cycling. For "post-lithium" batteries, the active material must have built-in mechanisms to deal with the "breathing aspect" of the electrode. Another key factor that has an impact is the current distribution non-uniformity (CDNU) factor, which is amplified by the cyclic structural rearrangement of the cathode according to the PAC principle. The electron (e-) paths present within the SOA electrode must be flexible enough to allow extended cycling and allow large area electrodes with minimal degradation. Electrode size, areal active mass loading, type of current collector foil, tab size, tab placement, etc. all affect CDNU, and in most cases, they are key factors in battery cell failure during expansion, and from coin-sized to areas exceeding 120 cm 2 Good results were obtained with electrodes of 100 nm (which are typical for commercial batteries).

[0006] Therefore, the present invention aims to provide a current collector capable of selectively distributing electrons within an artificial electron percolation network present within the current collector. The primary function of such a current collector is to enhance and equalize the CDNU within the electrodes, thereby resulting in improved electron transport due to the shortest possible travel path (low tortuosity), reduced internal resistance, and a non-uniform distribution of redox reactions between the electrodes.

[0007] Due to their excellent properties, nanomaterials have been proposed for a wide range of applications, including zero-dimensional (0-D) 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 nanosheets. If a material does not have any dimensions that make it small enough to be considered nanosized, it is not a nanomaterial. It is well known that these nanomaterials can be used to prepare macroscopic objects, such as independent, self-supporting three-dimensional (3D) networks. For example, carbon nanotubes (CNTs) can be formed into 3D networks or sheet-like / paper-like structures, commonly referred to as "buckypaper", which consists of entangled assemblies of randomly distributed CNTs. Buckypaper is generally manufactured by vacuum filtering CNT and / or graphene dispersions and / or by sequentially lifting CNT / graphene layers through filtration membranes. Electrodes based on self-supporting buckypaper have recently gained significant attention and have been found to have excellent performance.

[0008] Methods for aligning CNTs have also been reported, including (i) mechanical stretching of a cross-linked CNT mat as described in U.S. Patent No. 8,246,886 B2, (ii) pushing or “domino pushing” or pulling of vertically aligned carbon nanotubes (VACNTs) as described by Wang et al. (Nanotechnology, 2008; 19(7), 75609; DOI: 10.1088 / 0957-4484 / 19 / 7 / 075609), (iii) applying a large magnetic field as described in U.S. Patent Application No. 2002 / 0 185770 and U.S. Patent No. 7,803,262 B2, and (iv) applying an electric field, such as reported 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, the object of the present invention is to provide a current collector with excellent physicochemical, thermal and electrical properties for various applications, which can be produced in an environmentally friendly manner without compromising the physical state and chemical properties of 1D / 2D nanomaterials. Further objects will become apparent from the following description and patent 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 connected to the three-dimensional structure, wherein the three-dimensional structure comprises at least one layer formed of one-dimensional (1D) nanomaterial, two-dimensional (2D) nanomaterial, or a mixture thereof, and wherein the nanomaterial in the layer is aligned toward at least one tab.

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

[0012] In another aspect, the present invention relates to a device comprising a current collector, such as an electrode, a primary or secondary energy storage device, or an electrochemical cell. The device can be, for example, 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, a magnesium ion battery; or 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, a magnesium sulfur battery; or an alkali / alkaline earth metal air battery, such as a lithium air battery, a sodium air battery, an aluminum air battery, a zinc air battery.

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

[0014] For the sake of clarity, some definitions of terms used throughout the specification and claims are given. Unless the context requires a different meaning, the definitions should be used to determine the meaning of the corresponding expression.

[0015] The terms "a" or "an" do not exclude plurality, i.e., the singular forms "a", "an" and "the" are to be understood as including plural referents, unless the context clearly indicates or requires otherwise. In other words, all references to singular features or limitations of the present disclosure shall include the corresponding plural features or limitations, and vice versa, unless expressly provided otherwise or the context of the reference clearly implies the contrary. Therefore, unless otherwise defined, the terms "a", "an" and "the" have the same meaning as "at least one" or "one or more". For example, reference to a "nanomaterial" includes a mixture of nanomaterials, etc.

[0016] The terms "comprise," "comprises," and "comprising" and similar expressions are to be interpreted in an open and inclusive sense to mean "including, but not limited to."

[0017] The terms "substantially," "about," "approximately," "substantially," and the like, with respect to an attribute or value, include the exact attribute or precise value, as well as any attribute or value that is typically considered to be within the normal range or variation accepted in the relevant technical field.

[0018] The terms "binder-free" and "surfactant-free" mean that no binder or surfactant is intentionally included in the material, but the presence of residual amounts is not excluded. In other words, the term "free" means that the material contains less than the functional amount of the corresponding ingredient, typically less than 1% by weight, preferably less than 0.1% or even less than 0.01%, and includes zero weight percentage of the corresponding ingredient. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0020] Figure 2 Schematic diagram of a porous, free-standing, three-dimensional structured layer with aligned 1D nanomaterials facing two current collector tabs.

[0021] Figure 3 Schematic diagram of a porous, free-standing, three-dimensional structured layer with aligned 1D nanomaterials facing three current collector tabs.

[0022] Figure 4A is a photograph showing an example of generating a layer of aligned 1D nanomaterials in a current collector fabrication process (500), wherein the aligned nanomaterials (502) have a desired distance between them. Figure 4B A photograph of a portion of an aligned 1D nanomaterial layer.

[0023] Figure 5 A flow chart illustrating a method of manufacturing a current collector is shown.

[0024] Figure 6 The dependence of the discharge energy on the current distribution inhomogeneity is shown for different tab configurations having different numbers of tabs and / or tab positions. DETAILED DESCRIPTION

[0025] In a first aspect, the present invention provides a current collector comprising: a porous, freestanding three-dimensional (3D) structure; and

[0026] At least one current collector tab is connected to the three-dimensional structure, wherein the three-dimensional structure includes at least one layer formed of one-dimensional (1D) nanomaterial, two-dimensional (2D) nanomaterial, or a mixture thereof, and wherein the nanomaterial in the layer is aligned toward the at least one tab.

[0027] The inventors discovered that the claimed current collector can effectively facilitate the transport of charge carriers (e-) between the current collector / battery electrode and an external source. In particular, the 3D structure was found to act as an artificial electron percolation network that exhibits anisotropic electrical conductivity toward the placement of one or more current collector tabs. In this implanted artificial electron percolation network with anisotropic regional electrical conductivity, where the maximum electrical conductivity and lowest electronic curvature are optimized or enhanced toward the orientation and placement of the current collector tabs, the difference in e-conductivity between the regions farthest from the electrode and the regions closest to the electrode ranged from 8% to 120%. Generally, the conductivity in the porous, free-standing 3D structure is enhanced toward the direction / placement of one or more current collector tabs, resulting in reduced impedance while maintaining maximum uniformity of current flow to or from the electrodes, thereby ensuring reliable, optimized and safer performance of devices including the current collectors (such as electrochemical cells or primary or secondary rechargeable batteries 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), including, for example, high-energy lithium-ion batteries, lithium-sulfur batteries, or lithium-oxygen batteries.

[0028] It was also observed that the enhanced conductivity toward one or more current collector tabs was due to the presence of an artificial electron percolation network that exhibited significant electrical conductivity anisotropy controlled by highly advanced low-tortuosity electron paths, i.e., aligned nanomaterials provided the shortest possible electron percolation trajectory (electron tortuosity) from the electrode to the tab. In contrast, conventional current collectors have a randomly distributed and assembled material network, resulting in a less uniform current distribution and a significantly increased path length for electron tortuosity.

[0029] It was also found that the nanomaterials were distributed in a non-aggregated manner and arranged so that directly adjacent nanomaterials (e.g., CNTs) partially overlapped along their length in the planar direction, thereby forming chains or nanocables. Thus, the formed nanocables were separated from each other by tailored spacing and aligned substantially parallel to each other, further improving the transport of charge carriers through the percolation network.

[0030] The current collector disclosed herein can 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 can be understood as the three-dimensional structure being essentially formed only of nanomaterials.

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

[0032] According to the preferred mode generally applicable in the context of the present disclosure, the superimposed layers in the three-dimensional structure are combined by interlayer van der Waals bonds. For example, the superposition of layers can be carried out in the vertical direction, which allows the combination of layers with variable vertical composition. In one embodiment, the layer made of 1D nanomaterial can be preferred. An exemplary embodiment of 1D nanomaterial is, for example, CNT.

[0033] According to another preferred embodiment, the current collector disclosed herein comprises a three-dimensional structure comprising a total of 2 to 5000 superimposed layers, 3 to 2000 superimposed layers, 4 to 1000 superimposed layers, 5 to 500 superimposed layers, 6 to 200 superimposed layers, 7 to 100 superimposed layers, 8 to 50 superimposed layers, 9 to 20 superimposed layers, or 10 superimposed layers. Typically, the three-dimensional structure has a total thickness of 0.1 μm to 50 μm, 0.25 μm to 40 μm, 0.5 μm to 30 μm, 0.75 μm to 20 μm, or 1 μm to 10 μm. In a generally preferred embodiment, the layers are stacked one on top of another along the z axis or the x axis.

[0034] According to a preferred approach generally applicable in the context of the present disclosure, the stacked layers of the porous, free-standing 3D structure include a combination of (i) more than one layer formed of a 1D nanomaterial; and (ii) at least one layer formed of a 2D nanomaterial. This combination has been found to provide increased active surface area, thereby improving electrical conductivity.

[0035] In the context of the present disclosure, the individual layers of 1D nanomaterials can be rotated relative to each other. For example, if the individual layers of the porous, free-standing 3D structure are square, they can be rotated 90° relative to each other; if they are hexagonal, they can be rotated 120° relative to each other.

[0036] In one of the other preferred embodiments, the porosity of the three-dimensional structure is at least 3% V / V based on the total volume of the 3D structure, such as 10% V / V or more, preferably, the porosity of the three-dimensional structure is 50% V / V or more, 80% V / V or more, or 90% V / V or more, based on the total volume of the 3D structure, more preferably, the porosity of the three-dimensional structure is 95% V / V or more based on the total volume of the 3D structure. Porosity can be measured using a helium pycnometer, in which the sample is enclosed in a closed container of fixed volume at a fixed pressure. With this technique, porosity is defined as the volume displacement 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 computer microtomography.

[0037] It is found that the three-dimensional structure has ordered porosity due to the alignment, which also helps to optimize the anisotropic electrical conductivity toward the current collector tab.

[0038] According to the present invention, the 1D nanomaterial of the layer of the three-dimensional structure contained in the current collector can be a nanotube, nanorod, nanofiber or nanowire. In the context of the present disclosure, the carbon nanotube can be a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT) or a multi-walled carbon nanotube (MWCNT). Typically, the 1D nanomaterial includes a carbonaceous material, a non-carbonaceous material or a mixture thereof, or is made 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 include carbon or can be made 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 oxides such as CuO, ZnO, TiO2, MoO2 and WO2; their alloys; and transition metal dichalcogenides such as MoS2, WS2, VS2, VS4, TiS2 and TiS4, or a composite mixture of any of the above elements. 1D nanomaterials can be doped and / or functionalized with one or more functional groups. Examples of doped 1D nanomaterials can be 1D nanomaterials doped with heteroatoms such as fluorine, nitrogen, oxygen or a combination thereof, for example, including nitrogen-doped carbon materials. Examples of functional groups include -O, -OH, -COOH, -F, -COO, -NO3, -NO2, -R, -Cl, -NH. In the context of the present disclosure, the 1D nanomaterial may be, for example, a carbon nanotube or a boron carbonitride nanotube. The electrical conductivity of a layer formed of aligned 1D nanomaterials may be, for example, 10 2 S / cm to 10 6 Within the scope of a generally preferred embodiment, the 1D nanomaterial is a carbon nanotube.

[0039] According to the present invention, the 2D nanomaterial of the layer of the three-dimensional structure contained in the current collector can be a nanosheet, a nanosheet or a nanosheet. Typically, the 2D nanomaterial includes a carbonaceous material, a non-carbonaceous material or a mixture thereof, or is made of a carbonaceous material, a non-carbonaceous material or a mixture thereof. In this context, the size, shape, porosity and chemical composition of the 2D nanomaterial are not particularly limited. For example, the 2D nanomaterial includes carbon or can be made of carbon, including the following materials such as graphite, porous carbon, graphene and fullerene; 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); their oxides such as CuO, ZnO, TiO2, MoO2 and WO2; their alloys; transition metal dichalcogenides such as MoS2, WS2, VS2, VS4, TiS2 and TiS4; transition metal carbides (MXenes) such as Ti2C, V2C, Mo2C, Ti3AlC2 and Mo2TiC2; transition metal nitrides / carbonitrides such as graphitic carbonitride (g-C3N4), hexagonal boron nitride (h-BN), silicene, phosphorene, germanene, boron carbonitride (BCN), aluminum nitride, molybdenum nitride, titanium nitride and alloys thereof; or a composite mixture of any of the above. The 2D nanomaterial can be doped with and / or functionalized with one or more functional groups. Examples of doped 2D nanomaterials can be 2D nanomaterials doped with heteroatoms such as fluorine, nitrogen, oxygen or a combination thereof, for example, including nitrogen-doped carbon materials. Examples of functional groups include -O, -OH, -COOH, -F, -COO, -NO3, -NO2, -R, -Cl, and -NH. Preferred examples of 2D nanomaterials include, for example, graphene nanosheets, graphene oxide, reduced graphene oxide, MXene, g-C3N4, h-BN, silicene, phosphorene, germanene, BCN, transition metal dichalcogenides, or mixtures thereof. The electrical conductivity of a layer formed of aligned 2D nanomaterials can be, for example, 10 2 S / cm to 10 4 Within the scope of one embodiment, the 2D nanomaterial is a nanosheet of graphene, graphene / graphene oxide or MoS2.

[0040] Within the scope of the present disclosure are current collectors that include two or more, three or more, four or more, five or more, six or more, or 2 to 10 current collector tabs. Figure 6 As shown, the current distribution non-uniformity has a significant impact on the energy density. Figure 6It was also shown that the number of tabs and their location are key factors affecting performance. In general, it was found that increasing the number of tabs can improve overall performance, and the tab configuration and overall performance are directly correlated. Due to the advanced anisotropic electrical conductivity with customized electronic curvature optimized towards the direction of one or more tabs, the tab configuration disclosed herein ensures low current distribution non-uniformity factors and reduces Joule heating and its associated adverse effects, such as irreversible electrochemical side reactions and reduced energy density. In other words, the tab configuration provided herein improves the uniformity of current distribution and overall performance, including, for example, improved energy output, cycling behavior, and safety.

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

[0042] In another aspect, the present invention provides a method for manufacturing a current collector, in particular a method for manufacturing a current collector as described above. The method for manufacturing a current collector comprises:

[0043] (a) providing a porous, free-standing three-dimensional structure comprising at least one layer formed of one-dimensional (1D) nanomaterial, two-dimensional (2D) nanomaterial, or a mixture thereof, wherein the nanomaterial is aligned and its longitudinal axis is perpendicular to the substrate surface; and

[0044] (b) connecting the three-dimensional structure of step (a) to at least one current collector tab such that the nanomaterial included in the three-dimensional structure is aligned toward the at least one tab.

[0045] The preparation 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 described above, 1D nanomaterials and 2D nanomaterials include carbonaceous materials, non-carbonaceous materials or mixtures thereof, or are made of carbonaceous materials, non-carbonaceous materials or mixtures thereof, and such materials are generally known in the art.

[0046] Figure 5An example of a method for manufacturing a current collector according to the principles described herein is shown in the form of a flow chart. According to the method (500) for manufacturing a current collector, the step of forming a porous independent layer made of aligned nanomaterials may include the following steps (501A1 and 501A2 or 501B1 and 501B2): providing a dispersion / suspension of nanomaterials, (502) applying an external field to align the dispersed / floating nanomaterials and form a layer, and (503) recovering the layer.

[0047] In a generally preferred embodiment of the method, nanomaterials are added to a liquid medium by (501A1 and 501A2), and then chemically and / or mechanically treated to prepare a dispersion / suspension of nanomaterials. In an alternative preferred embodiment of the method, nanomaterials are directly laid on the surface of a liquid medium by (501B1 and 501B2), optionally followed by mechanical treatment to prepare a dispersion / suspension of nanomaterials. In this context, dispersion or suspension means that nanomaterials (such as CNTs and / or graphene) are dispersed or suspended in a liquid medium in a separate form. In some embodiments, dispersion / suspension is prepared at room temperature. In some embodiments, dispersed / suspended nanomaterials float on the surface of a liquid medium. Suitable liquid media include water, ethanol, methanol, acetone, isopropyl alcohol (IPA), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO), or a mixture thereof. In some embodiments, the liquid medium can be water, a mixture of water and ethanol, or acetone. In some embodiments, the liquid medium may contain one or more surfactants.

[0048] Chemical treatment can include, for example, functionalization and / or treatment with a strong acid and / or a surfactant. Suitable strong acids include, for example, nitric acid (HNO3) and sulfuric acid (H2SO4) and mixtures thereof. Examples of functionalization include the introduction of one or more functional groups selected from -O, -OH, -COOH, -F, -COO, -NO3, -NO2, -R, -Cl, -NH2.

[0049] Suitable surfactants include, for example, sodium lauryl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), polyoxyethylene octylphenyl ether (TritonX-100) and mixtures thereof. Surfactants help prevent or avoid the formation of aggregates. Suitable mechanical treatments include, for example, ultrasonic treatment, probe-based ultrasonic treatment, centrifugation, calendering, ball milling and combinations thereof. In some embodiments, nanomaterial (501A2) is ultrasonically treated to ensure uniform dispersion / suspension. In some embodiments, nanomaterial (501B2) is subjected to an electrostatic dispersion process under applied direct current (DC). In some embodiments, DC can be high voltage (HV) DC to ensure uniform dispersion / suspension.

[0050] In a generally preferred embodiment of this method, the nanomaterials can be aligned and formed into a layer by applying an external force to the dispersed / suspended nanomaterials. When the nanomaterials are aligned, their longitudinal axes are perpendicular to the substrate surface. The substrate surface can be, for example, the bottom of a container containing the dispersion / suspension or the surface of a filter membrane.

[0051] Suitable external forces include, for example, electrostatic fields, electric fields, magnetic fields, electromagnetic fields, or any combination thereof. In one embodiment, the dispersion is subjected to an electrostatic field. In another embodiment, the dispersion is subjected to an electric field (502). In another embodiment, the dispersion is subjected to a magnetic field. In yet another embodiment, the dispersion is subjected to an electromagnetic field. In a generally preferred embodiment, an alternating current (AC) electric field can be applied to the liquid dispersion / suspension to align the nanomaterials and form a layer. For example, the AC can be an HVAC, 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. Due to the application of the external force, the nanomaterials align in the direction of the applied external force, thereby forming a layer.

[0052] Additionally, external forces can generate internal forces in situ in the nanomaterials, such as the electric field induced magnetic field (right-hand rule) generated by the charge flowing through the alignment / chain wire and the external magnetic field preferably generated by the Helmholtz coil. Such internal forces can be used to control and / or customize the inter-distance between the aligned nanomaterials and the porosity within the layer structure. In some embodiments, the aligned 1D nanomaterials can be formed into nanocables, such as Figure 1As shown in Figure 4. For example, the spacing between wires formed of aligned nanomaterials such as CNTs can be adjusted by the amount of current flowing through them due to an in-situ generated magnetic field, which has a repulsive effect on adjacent wires (nanocables) formed of aligned nanomaterials such as CNTs. The stronger the current, the stronger the magnetic field, and thus the spacing between individual nanocables increases; or vice versa, the weaker the current, the lower the repulsive effect, resulting in a more densely packed nanocables. Naturally, the same applies to porosity: the denser the nanocables are packed, the lower the porosity within the resulting layer.

[0053] In this context, it is generally preferred to apply an electric field (AC and / or DC) to align the nanomaterials in the water-based liquid dispersion / suspension.

[0054] In a generally preferred embodiment of the method, a layer of aligned nanomaterial formed from a liquid dispersion of nanomaterial can be recovered by vacuum filtration using a filter membrane (503). It was found that vacuum-assisted filtration through a suitable membrane allows obtaining a layer of aligned nanomaterial without disturbing or changing the alignment, i.e., the orientation of the formed nanocables and the distance between the nanocables.

[0055] The filter membrane can have nanopores, nanochannels, micropores, microchannels, macropores, macrochannels or a combination thereof. Additionally, the filter membrane can be hydrophilic or have a hydrophilic coating. In some embodiments, the filter membrane can be porous, having a variable pore size in the range of 20 nm to 50 microns.

[0056] In a generally preferred embodiment, vacuum filtration can be performed at a low speed, and in particular, the filtration speed can be as slow as possible. Slower filtration speeds have been found to be particularly helpful in maintaining alignment and causing the aligned nanomaterial layer to float on the surface of the liquid medium, making it easy to pick up / lift the aligned nanomaterial layer from the liquid medium without disturbing the alignment. The filtration speed can, for example, be in the range of 10 ml / min to 100 ml / min.

[0057] After filtration, the layer of aligned nanomaterial can be separated from the filter membrane, solidified, washed, and / or dried. In generally preferred embodiments, residual solvent and / or surfactant can be removed by washing with deionized water, isopropyl alcohol, methanol, or mixtures thereof, by calcination, or any combination thereof. Typically, the presence of solvents or surfactants can negatively impact the physical and / or electrical properties of the layer of aligned nanomaterial.

[0058] The thickness of the layer of aligned nanomaterial can be controlled by the amount of nanomaterial filtered and / or the concentration contained in the liquid dispersion. The thickness of the layer of aligned nanomaterial can be, for example, in the range of about 50 nm to 1000 nm, 100 nm to 750 nm, 200 nm to 600 nm, 250 nm to 500 nm, or 300 nm to 350 nm.

[0059] In some preferred embodiments, the aligned nanomaterial layer may have at least one conductive and / or electrochemically active planar surface. The surface area of ​​the planar surface may be several mm 2 to several meters 2 within the range, for example, within 10cm 2 Up to 100cm 2 within the range.

[0060] In a generally preferred embodiment of the method, a porous, independent three-dimensional structure can be provided by a (504A) layer-by-layer (LbL) assembly method, wherein the individual layers of aligned nanomaterials obtained from the above-mentioned dispersion and vacuum filtration steps are stacked one on top of another. In some embodiments, these layers are stacked one on top of another vertically. In other words, the step of providing a porous, independent three-dimensional structure is performed by preparing one or more separate layers of aligned nanomaterials as described above and assembling them by stacking the individual layers of the desired number and type (i.e., the nanomaterial components used to form the layers) one on top of another along the z-axis. In the context of the present disclosure, when performing the (504B) layer-by-layer (LbL) assembly method, the individual layers consisting of 1D nanomaterials can be rotated against each other. For example, if the individual layers of the porous, independent 3D structure are square, they can be rotated 90° against each other, and if they are hexagonal, they can be rotated 120° against each other.

[0061] According to a preferred embodiment, a total of 2 to 5000, 3 to 2000, 4 to 1000, 5 to 500, 6 to 200, 7 to 100, 8 to 50, 9 to 20, or 10 or more layers of aligned nanomaterials are stacked together by performing a layer-by-layer (LbL) assembly method. Typically, the three-dimensional structure obtained by LbL assembly of the individual layers of aligned nanomaterials can have a total thickness of 0.1 μm to 50 μm, 0.25 μm to 40 μm, 0.5 μm to 30 μm, 0.75 μm to 20 μm, or 1 μm to 10 μm.

[0062] According to a preferred approach generally applicable in the context of the present disclosure, the stacked layers of the three-dimensional structure include a combination of (i) and (ii): (i) more than one layer formed of 1D nanomaterial; and (ii) at least one layer formed of 2D nanomaterial. In some embodiments, a porous, free-standing 3D structure can be formed solely by assembling layers of aligned nanomaterials made of 1D nanomaterials.

[0063] The method further comprises the step of connecting or interweaving at least one current collector tab to a porous, freestanding 3D structure comprising at least one layer of aligned nanomaterials such that the nanomaterials contained in the 3D structure are aligned towards at least one tab. In a generally preferred embodiment of the method, the current collector tabs may be (506) connected or interwoven with the porous, freestanding 3D structure obtained by the above-described LbL process to form a current collector foil or current collector substrate as disclosed herein. In this context, it is crucial that the connection causes the aligned nanomaterials to align towards the current collector tabs. The alignment of the nanomaterials and the current collector tabs described herein is crucial for obtaining anisotropic electrical conductivity and highly advanced low-tortuosity electron paths from the electrodes to the tabs through the artificial electron percolation network formed by the porous, freestanding 3D structure. In some embodiments, the current collector tabs may be connected to the porous, freestanding 3D structure by ultrasonic welding, resistance welding, laser welding, stamping or crimping such that the nanomaterials contained in the 3D structure are aligned towards the tabs.

[0064] It should be noted that the description and drawings are of illustrative nature only and are not intended to limit the scope of the invention, which is defined by the appended claims.

Claims

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

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

3. The current collector according to claim 1 or 2, wherein: The three-dimensional structure includes two or more stacked layers, each of which is independently formed of a 1D nanomaterial, a 2D nanomaterial or a mixture thereof.

4. The current collector according to claim 3, wherein The stacked layers are bonded via interlayer van der Waals bonds.

5. The current collector according to claim 3 or 4, wherein: The three-dimensional structure includes a total of 2 to 5000 superimposed layers, 3 to 2000 superimposed layers, 4 to 1000 superimposed layers, 5 to 500 superimposed layers, 6 to 200 superimposed layers, 7 to 100 superimposed layers, 8 to 50 superimposed layers, 9 to 20 superimposed layers, or 10 superimposed layers.

6. The current collector according to any one of claims 1 to 5, wherein The three-dimensional structure has a total thickness of 0.1 μm to 50 μm, 0.25 μm to 40 μm, 0.5 μm to 30 μm, 0.75 μm to 20 μm, or 1 μm 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 based on the total volume of the three-dimensional structure. Preferably, the porosity of the three-dimensional structure is 50% V / V or more, 80% V / V or more, or 90% V / V or more based on the total volume of the three-dimensional structure. More preferably, the porosity of the three-dimensional structure is 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 1D nanomaterial is a nanotube, nanorod, nanofiber or nanowire.

9. The current collector according to any one of claims 1 to 7, wherein The 2D nanomaterial is a nanosheet, a nanoflake or a nanoplate.

10. The current collector according to any one of claims 1 to 9, wherein The 1D nanomaterial or the 2D nanomaterial is composed of a carbonaceous material, a non-carbonaceous material or a mixture thereof.

11. The current collector according to any one of claims 1 to 10, wherein The current collector includes two or more, three or more, four or more, five or more, six or more, or 2 to 10 current collector tabs.

12. An electrode comprising a 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. The storage device according to claim 13 , wherein: The storage device is a lithium-ion battery or a lithium-sulfur battery.

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

Images