Conductive coating, manufacturing method therefor, and electrode structure

Abstract

A conductive coating, a manufacturing method therefor, and an electrode structure. The electrode structure comprises a metal foil substrate, a conductive coating, and an electrode active substance layer. The conductive coating is applied on the surface of the metal foil substrate, and the thickness of the conductive coating on a single surface is 0.5 micrometers or less. The electrode active substance layer is coated on the conductive coating.

Description

Conductive coating, its manufacturing method and electrode structure Technical Field

[0001] This application relates to a conductive coating for an electrochemical device, a method for manufacturing the conductive coating, and an electrode structure, particularly to a conductive coating for a secondary battery, a method for manufacturing the conductive coating, and an electrode structure. Background Technology

[0002] Carbon nanotubes (CNTs) have been widely used in battery electrodes, conductive coatings, and advanced electronic materials due to their excellent conductivity, high specific surface area, and good mechanical strength. In lithium-ion battery applications, coating carbon nanotubes onto the surface of the current collector to form a conductive coating can reduce the contact resistance between the current collector and the active material layer, thereby improving the battery's charge and discharge performance.

[0003] However, when carbon nanotube coatings are applied to metal foil substrates such as aluminum or copper foil, it is often difficult to achieve extremely thin and uniform coatings, especially in the thickness range of 0.5 micrometers (μm) or even smaller. In existing technologies, carbon nanotube slurries are often coated using methods such as blade coating, spin coating, or spray coating, but challenges remain in terms of uniformity and thickness control.

[0004] Furthermore, existing technologies do not describe in detail the changes in optical properties exhibited by carbon nanotube coatings at extremely thin thicknesses. When the coating thickness is extremely thin, light produces unique optical effects on the coating surface, causing the coating to exhibit thickness-related changes in color and gloss. The application value of this optical property, such as its role as a basis for non-destructive thickness monitoring or quality control, is also not disclosed in existing technologies.

[0005] Therefore, it is necessary to provide an ultrathin conductive coating and its manufacturing method, which can not only improve the conductivity of the electrode, but also have measurable optical properties as a basis for judging the coating thickness and quality control. Summary of the Invention

[0006] One of the main objectives of this application is to provide a conductive coating, a method for manufacturing the conductive coating, and an electrode structure that can solve the problems mentioned in the prior art.

[0007] This application provides a conductive coating. The conductive coating is applied to the surface of a metal foil substrate, and the thickness of the conductive coating on one side is less than 0.5 micrometers. The optical properties of the conductive coating are related to its thickness.

[0008] This application provides a method for manufacturing a conductive coating, comprising: preparing a conductive slurry containing conductive carbon material, dispersant, solvent and binder; applying the conductive slurry to the surface of a metal foil substrate, such that the single-sided thickness of the coating is less than 0.5 micrometers; and removing the solvent by drying.

[0009] This application provides an electrode structure comprising a metal foil substrate, a conductive coating, and an electrode active material layer. The conductive coating is applied to the surface of the metal foil substrate, and the thickness of the conductive coating on one side is less than 0.5 micrometers. The electrode active material layer is applied on the conductive coating. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0011] Figure 1 is a schematic diagram of the secondary battery configuration according to an embodiment of this application;

[0012] Figure 2 is a schematic diagram of a microgravure printing device according to an embodiment of this application;

[0013] Figure 3 is a schematic diagram of an extrusion coating apparatus according to an embodiment of this application;

[0014] Figure 4 is a comparison of the capacity of carbon-coated aluminum foil and plain foil batteries under different C-rates according to embodiments of this application.

[0015] Figure 5 is a comparison of the average voltage of carbon-coated aluminum foil and plain foil batteries under different C-rates according to embodiments of this application.

[0016] Figure 6 is a comparison of the 3C discharge curves of carbon-coated aluminum foil and plain foil batteries according to embodiments of this application;

[0017] Figure 7 is a comparison of the capacity of carbon-coated aluminum foil batteries of different thicknesses under different C-rates according to embodiments of this application;

[0018] Figure 8 is a comparison of the average voltage of carbon-coated aluminum foil batteries of different thicknesses under different C-rates according to embodiments of this application;

[0019] Figure 9 is a comparison of the 3C discharge curves of carbon-coated aluminum foil batteries of different thicknesses according to embodiments of this application;

[0020] Figure 10 is a flowchart of the ultrathin conductive coating manufacturing method according to an embodiment of this application; and

[0021] Figure 11 is a schematic diagram of the electrode structure according to an embodiment of this application.

[0022] Symbol Explanation: 11: Cathode electrode; 12: Diaphragm; 13: Anode electrode; 100: Secondary battery; 110: Cathode material layer; 111: Cathode current collector; 130: Anode material layer; 131: Anode current collector; 200: Microgravure printing equipment; 210: Gravure cylinder; 220: Doctor blade; 230: Impression cylinder; 240: Ink supply system; 250: Drying system; 300: Extrusion coating equipment; 310: Slit die; 320: Coating roller; 330: Extruder; 340: Ink supply system; 350: Drying system; 360: Screw pump; 410, 420, 510, 520, 710, 720, 810, 820: Curves; 1100: Single-sided coated electrode; 1110: Metal foil substrate; 1120: Conductive coating; 1130: Electrode active material layer; S100: Slurry preparation step; S110: Coating step; S120: Drying step. Detailed Implementation

[0023] To make the features and advantages of the embodiments of this application more apparent and understandable, specific embodiments of this application are described in detail below with reference to the accompanying drawings. The following description contains specific information related to exemplary embodiments in the embodiments of this application. The accompanying drawings and detailed descriptions in the embodiments of this application are merely exemplary embodiments. However, the embodiments of this application are not limited to these exemplary embodiments. Other variations and embodiments of the embodiments of this application will be apparent to those skilled in the art. Unless otherwise stated, the same or corresponding elements in the drawings may be indicated by the same or corresponding reference numerals. Furthermore, the drawings and illustrations in the embodiments of this application are generally not drawn to scale and are not intended to correspond to actual relative dimensions.

[0024] For the purposes of consistency and ease of understanding, the same features are indicated by reference numerals in the exemplary drawings (although not in some examples). However, features in different embodiments may differ in other respects, and therefore should not be narrowly limited to the features shown in the drawings.

[0025] The terms "first," "second," and "third," etc., in the specification and accompanying drawings of the embodiments of this application are used to distinguish different objects, areas, levels, or steps, and are not used to describe a specific order (unless expressly required by the claims). Furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion.

[0026] The terms "connection" or "coupling" used in the embodiments of this application do not imply that there can be no space between the objects. That is, the connection or coupling between two objects can mean that the two objects are directly connected / coupled to each other, or that they are connected / coupled to each other through other objects.

[0027] In all descriptions related to specific numerical values ​​in the embodiments of this application, although not directly described, they all contain the meaning of "approximately," that is, these specific numerical values ​​will cover the possible numerical error range, thereby representing possible unintended effects and deviations in process or material selection. The numerical error range may include numerical changes that do not significantly change the material structure, properties, or effects, such as a range of 0% to 10% deviation, which is clear to those skilled in the art.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] The purpose of this application is to provide an ultrathin conductive coating with gloss variation characteristics, the thickness of which is less than a predetermined thickness (e.g., less than 0.5 micrometers), which can reduce the contact resistance between the current collector and the active material layer, while having measurable optical properties (e.g., gloss variation characteristics) to facilitate quality control.

[0030] Another objective of this application is to provide a method for manufacturing an ultrathin conductive coating, which allows for precise control of the coating thickness and judgment of coating quality through optical inspection (e.g., color and gloss detection). The optical properties of the ultrathin conductive coating are measured to serve as a basis for judging the thickness of the conductive coating. The ultrathin conductive coating has measurable optical properties, which are correlated with the thickness of the conductive coating.

[0031] Another objective of this application is to provide an electrode structure with an ultrathin conductive coating, which can be applied to a positive electrode (e.g., an aluminum foil substrate) or a negative electrode (e.g., a copper foil substrate) to improve the performance of electrochemical devices (e.g., secondary batteries or supercapacitors).

[0032] Example 1: Structure of the electrochemical device and application location of the ultrathin conductive coating

[0033] Please refer to Figure 1, which is a schematic diagram of the secondary battery configuration according to an embodiment of this application. This embodiment uses a secondary battery as an example to illustrate the application of the ultrathin conductive coating of this application, but it is not limited thereto and can also be applied to other electrochemical devices, such as supercapacitors, hybrid capacitors, etc.

[0034] As shown in Figure 1, the secondary battery 100 includes a cathode electrode 11, a separator 12, and an anode electrode 13. The cathode electrode 11 includes a cathode material layer 110 and a cathode current collector 111; the anode electrode 13 includes an anode material layer 130 and an anode current collector 131. The cathode electrode 11 and the anode electrode 13 are disposed on opposite sides of the separator 12.

[0035] More specifically, the cathode material layer 110 is disposed between the cathode current collector 111 and the separator 12, and the anode material layer 130 is disposed between the anode current collector 131 and the separator 12. When the secondary battery 100 is charged, cations (e.g., lithium ions, sodium ions, potassium ions, or magnesium ions) are deintercalated from the cathode material layer 110, pass through the electrolyte through the separator 12, and intercalate into the anode material layer 130. Conversely, when the secondary battery 100 is discharged, cations are deintercalated from the anode material layer 130, pass through the electrolyte through the separator 12, and intercalate into the cathode material layer 110, at which time electrons are output from the anode current collector 131 to the external circuit.

[0036] In a secondary battery structure, the cathode current collector 111 is typically a positive electrode, such as aluminum foil, aluminum alloy foil, or other metal foil suitable for the positive electrode potential range, with a thickness of approximately 4 to 30 micrometers. The anode current collector 131 is typically a negative electrode, such as copper foil, copper alloy foil, nickel-plated copper foil, or other metal foil suitable for the negative electrode potential range, with a thickness of approximately 4 to 20 micrometers.

[0037] The cathode material layer 110 may contain a positive electrode active material. The positive electrode active material may be selected from one or a combination of the following materials: olivine structure materials, such as lithium iron phosphate (LiFePO4, LFP), lithium manganese phosphate (LiMnPO4, LMP), lithium iron manganese phosphate (LiFexMn(1-x)PO4, LFMP); layered structure materials, such as lithium cobalt oxide (LiCoO2, LCO), lithium nickel cobalt manganese oxide (Li(NixCoyMnz)O2, NCM, of which NCM111, NCM523, NCM622, NCM811 are common compositions), lithium nickel cobalt aluminum oxide (Li(NixCoyAlz)O2, NCA), lithium-rich manganese-based materials (Li-rich Mn-based, LMR); spinel structure materials, such as lithium manganese oxide (LiMn2O4, LMO), lithium nickel manganese oxide (LiNi(0.5)Mn(1.5)O4, LNMO); or other suitable positive electrode active materials.

[0038] The anode material layer 130 may contain a negative electrode active material. The negative electrode active material may be selected from one or a combination of the following materials: carbon-based materials, such as natural graphite, artificial graphite, hard carbon, soft carbon, and mesophase carbon microspheres (MCMB); silicon-based materials, such as silicon powder, silicon oxide (SiOx), silicon-carbon composites (Si / C), and silicon nanowires; lithium titanate (Li4Ti5O4).12 ,LTO); metal oxides, such as tin oxide (SnO2) and iron oxide (Fe2O3); alloy materials, such as tin-based alloys and germanium-based alloys; or other suitable negative electrode active materials.

[0039] In this embodiment, an ultrathin conductive coating is disposed between the current collector and the active material layer. Specifically, for the cathode electrode 11, the ultrathin conductive coating of this embodiment is disposed between the cathode current collector 111 (e.g., aluminum foil) and the cathode material layer 110; for the anode electrode 13, the ultrathin conductive coating of this embodiment is disposed between the anode current collector 131 (e.g., copper foil) and the anode material layer 130.

[0040] The thickness of the ultrathin conductive coating in this embodiment is less than a predetermined thickness, for example, less than 0.5 micrometers, and more specifically, 0.1 to 0.3 micrometers. Compared to the thickness of the active material layer (typically 50 to 100 micrometers), the coating thickness ratio in this embodiment is approximately 1:100 to 1:500. Therefore, this ultrathin coating is difficult to clearly indicate in the battery cell hierarchy diagram shown in Figure 1. Figure 11 will enlarge to show the location and structural features of the ultrathin conductive coating in this embodiment.

[0041] The ultrathin conductive coating of this application embodiment has the following technical effects: First, it reduces the contact resistance between the current collector and the active material layer, and improves the conductivity of the electrode; Second, it enhances the adhesion between the active material layer and the current collector, and reduces the shedding of active material during charge and discharge cycles; Third, the coating has measurable optical properties (such as gloss change characteristics), which can be used as a basis for quality control and thickness judgment.

[0042] Example 2: Coating and Testing Methods for Conductive Paste

[0043] This embodiment illustrates the material composition, coating method, and testing method of the ultrathin conductive coating. Regarding the composition of the conductive paste, the conductive paste used in this embodiment contains the following components: The conductive material is a conductive carbon material. The conductive carbon material can be selected from one or a combination of the following materials: carbon nanotubes, including single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), multi-walled carbon nanotubes (MWCNTs), or mixtures thereof; graphene, including monolayer graphene, multilayer graphene, graphene oxide (GO), and reduced graphene oxide (rGO); carbon black, including conductive carbon black (e.g., Super P, Ketjen Black, acetylene black), furnace black, and channel black; carbon fibers, including vapor-grown carbon fibers (VGCF) and carbon nanotubes; fullerenes; or other suitable conductive carbon materials. In this embodiment, the conductive material contains carbon nanotubes (e.g., SWCNTs or MWCNTs) as the main conductive component, and graphene or conductive carbon black may be selectively added as auxiliary conductive components.

[0044] This application uses a dispersant to promote the uniform dispersion of the conductive material in a solvent. The dispersant may be selected from one or a combination of the following materials: polymeric dispersants, such as polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polyvinyl alcohol (PVA); cellulose derivatives, such as carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose (HPMC), and methylcellulose (MC); surfactants, such as sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), and Triton X-100; or other suitable dispersants. In this embodiment, the dispersant is polyvinylpyrrolidone (PVP).

[0045] This application uses solvents to form a coatable slurry. The solvent may be selected from one or a combination of the following materials: organic polar solvents, such as N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc); alcohol solvents, such as ethanol, isopropanol, ethylene glycol; aqueous solvents, such as deionized water or purified water; or other suitable solvents. In the embodiments, the solvent is N-methylpyrrolidone (NMP) or deionized water.

[0046] This application uses an adhesive to provide adhesion between the coating and the substrate. The adhesive may be selected from one or a combination of the following materials: fluorinated polymers, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and PVDF-HFP copolymer; water-based adhesives, such as styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (Na-PAA), lithium polyacrylate (Li-PAA), polyimide (PI), and polyacrylonitrile (PAN); cellulose-based adhesives, such as sodium carboxymethyl cellulose (Na-CMC); conductive polymers, such as polyaniline (PANI), polypyrrole (PPy), and PEDOT:PSS; or other suitable adhesives. In this embodiment, the adhesive is polyvinylidene fluoride (PVDF). When using an aqueous solvent, the adhesive may be a combination of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (Na-CMC), or a polyacrylic acid (PAA) based adhesive.

[0047] The solid content of the conductive paste is controlled within a predetermined solid content range, for example, 0.1% to 2%, and more preferably 0.3% to 1%. The viscosity of the conductive paste is controlled within a predetermined viscosity range, for example, 10 to 500 cps, and more preferably 50 to 200 cps.

[0048] Regarding the metal foil substrate, various metal foils suitable for electrochemical devices can be used as substrates in the embodiments of this application. For the positive electrode current collector, the metal foil substrate can be aluminum foil or aluminum alloy foil, with a thickness of 4 micrometers to 30 micrometers, and more specifically 10 to 15 micrometers. For the negative electrode current collector, the metal foil substrate can be copper foil, copper alloy foil, or nickel-plated copper foil, with a thickness of 4 micrometers to 20 micrometers, and more specifically 6 to 10 micrometers. The surface of the metal foil can be surface-treated to enhance the adhesion of the coating. Surface treatment methods include, but are not limited to: anodizing, roughening treatment (e.g., electrolytic etching, chemical etching), corona treatment, plasma treatment, or applying a primer layer.

[0049] Regarding the coating method, please refer to Figures 2 and 3. Figure 2 is a schematic diagram of a microgravure printing device according to an embodiment of this application, and Figure 3 is a schematic diagram of an extrusion coating device according to an embodiment of this application. The coating method of this application embodiment is not limited to these two methods, and other applicable continuous coating methods or batch coating methods may also be used, such as slot coating, doctor blade coating, roller coating, spraying, dip coating, spin coating, or screen printing.

[0050] As shown in Figure 2, the microgravure printing equipment 200 includes a gravure cylinder 210, a doctor blade 220, an impression cylinder 230, an inking system 240, and a drying system 250. The surface of the gravure cylinder 210 (also known as a gravure cylinder) is engraved with fine grooves to hold the conductive paste. The inking system 240 includes an ink reservoir and a pump to supply the conductive paste to the gravure cylinder 210. During operation, after the gravure cylinder 210 is coated with paste, the doctor blade 220 scrapes off excess paste from the surface of the gravure cylinder 210, leaving the paste only in the grooves. The metal foil substrate passes through the gap between the impression cylinder 230 and the gravure cylinder 210, and the paste is transferred to the surface of the metal foil, forming an ultra-thin conductive coating. The coating thickness target can be achieved by controlling the rotational speed, surface aperture ratio, and transfer rate of the gravure cylinder 210. The coated metal foil is dried by a drying system 250 to remove the solvent, forming a cured conductive coating.

[0051] As shown in Figure 3, the extrusion coating equipment 300 includes a coating roller 320, an extruder 330, an ink supply system 340, and a drying system 350. The extruder 330, through a screw pump 360, provides stable pressure to deliver the conductive paste from the ink supply system 340 to a slot die 310. The slot die 310 has a precise, narrow opening to control the amount and uniformity of the paste coating; its design determines the shape and thickness of the coating layer. During operation, the paste is extruded through the slot die 310 and coated onto the surface of the metal foil substrate. The coating roller 320 supports the metal foil substrate and controls the coating gap, ensuring uniform coating of the paste onto the substrate. The substrate transport system moves the metal foil substrate through the coating area at a constant speed. After coating, the metal foil passes through the drying system 350 to remove solvent, forming a cured conductive coating.

[0052] Regardless of the coating method used, the coating thickness on one side in the embodiments of this application is controlled within a predetermined thickness range, for example, less than 0.5 micrometers, and further, from 0.1 micrometers to 0.3 micrometers.

[0053] Regarding drying conditions, the coated metal foil needs to be dried to remove the solvent. Drying can be performed using hot air drying, infrared drying, vacuum drying, or a combination thereof. The drying temperature is set within a predetermined range, for example, 30°C to 200°C, and further, 80°C to 130°C. The drying time is 30 seconds to 30 minutes. For copper foil substrates, the drying temperature can be 60°C to 100°C to avoid copper foil oxidation. When using aqueous solvents, the drying temperature can be set to 60°C to 100°C to save energy and prevent substrate deformation.

[0054] Regarding optical detection methods, the ultrathin conductive coating of this application embodiment has unique optical properties. Due to the extremely thin coating thickness (e.g., less than 0.5 micrometers), light produces optical effects on the coating surface, such as Mie scattering, thin film interference, or surface plasma resonance, causing the coating to exhibit a recognizable color (e.g., dark blue, purple, gray, or brown), rather than the pure black of traditional thicker carbon coatings.

[0055] This application embodiment uses optical inspection equipment to inspect coating quality. The optical inspection equipment can be a color gloss meter, spectrophotometer, gloss meter, or a combination thereof. Measurement conditions can be set as needed. In this embodiment, the measurement conditions are set as follows: the geometric conditions adopt a predetermined geometric configuration, such as 45°:0° (i.e., the light source illuminates in a 45-degree circle, and the sensor receives the light perpendicularly), or other standard geometric configurations such as 45°a:0°, d / 8°, etc.; the gloss sensor adopts a predetermined angle, such as a 60-degree angle, or other angles such as 20 degrees, 85 degrees, etc.; the light source adopts a standard light source, such as a D65 standard light source, or other standard light sources such as D50, A, C, F2, F11, etc.

[0056] This application uses a color space to define the coating color. The color space can be L*a*b* color space (CIE 1976), L*C*h color space, XYZ color space, RGB color space, or other applicable color spaces. In this embodiment, the L*a*b* color space is used, where L* values ​​represent lightness, ranging from 0 to 100, where 0 is pure black and 100 is pure white; a* values ​​represent the red-green axis, with positive values ​​leaning towards red and negative values ​​towards green; b* values ​​represent the yellow-blue axis, with positive values ​​leaning towards yellow and negative values ​​towards blue. The color characteristic range of the ultrathin conductive coating in this application embodiment is: L* values ​​ranging from 0 to 40, further from 5 to 20; a* values ​​ranging from -30 to 30, further from -10 to 10; and b* values ​​ranging from -30 to 30, further from -15 to 5.

[0057] The ultrathin conductive coating of this application has a gloss unit (GU) range of 0 to 300. When the coating exhibits a deep blue appearance and the gloss unit (GU) falls within a predetermined gloss range (e.g., 60 to 100), it indicates that the coating thickness is within a target range (e.g., 0.3 micrometers to 0.5 micrometers). This optical characteristic can serve as a basis for non-destructive quality control in the production line.

[0058] Example 3: Electrode Preparation and Testing Methods

[0059] This embodiment illustrates a method for preparing electrodes using current collectors with ultrathin conductive coatings and a battery testing method.

[0060] Preparation of Carbon Coated Aluminum Foil (CCAF): Following the method described in Example 2, an ultra-thin conductive coating was applied to an aluminum foil substrate to form carbon-coated aluminum foil. The aluminum foil substrate thickness was 12.5 micrometers, and the coating thickness on one side was controlled to be less than 0.5 micrometers.

[0061] Preparation of the positive electrode: A positive electrode active material slurry is coated onto a carbon-coated aluminum foil, and after drying and rolling, the positive electrode is formed. The composition of the positive electrode active material slurry can be adjusted according to the selected positive electrode active material. Taking lithium iron phosphate (LFP) as an example, the composition of the positive electrode active material slurry may include: 90 to 98 wt% LFP (e.g., 96 wt%), 1 to 5 wt% binder (e.g., 2 wt%), and 1 to 5 wt% conductive additives (e.g., 2 wt%, such as a combination of 1 wt% conductive carbon black and 1 wt% carbon nanotubes). Taking high-nickel materials (e.g., NCM811) as an example, the composition of the positive electrode active material slurry may include: 90 to 96 wt% NCM811, 2 to 5 wt% binder, and 2 to 5 wt% conductive additives.

[0062] Battery Assembly and Testing: The positive electrode, negative electrode (e.g., lithium metal, graphite, or silicon-carbon composite negative electrode), and separator (e.g., polyethylene, polypropylene, or ceramic-coated separator) are assembled into a battery. After injecting electrolyte, charge-discharge tests are performed. Charge-discharge tests are conducted at different C-rates, where C-rate is defined as the current rate required for the battery to complete a full charge or discharge within one hour. For example, 1C indicates completion of charge-discharge within one hour, 3C indicates completion within 20 minutes, and 0.1C indicates completion within 10 hours. Taking a 1000mAh battery as an example, the 1C charging current is 1000mA, the 2C charging current is 2000mA, the 0.5C charging current is 500mA, and so on.

[0063] Experiment Example 1: Comparison of Battery Performance Between Carbon-Coated Aluminum Foil and Plain Aluminum Foil

[0064] This experiment compares the battery performance differences when using carbon-coated aluminum foil (CCAF) versus plain foil (non-CCAF, i.e., bare aluminum foil) as the positive electrode current collector.

[0065] Experimental conditions: The aluminum foil substrate thickness was 12.5 micrometers. The conductive coating thickness of the carbon-coated aluminum foil was 0.4 to 0.5 micrometers, exhibiting a deep blue appearance. The conductive material of the conductive coating was carbon nanotubes (MWCNTs), the dispersant was PVP, the binder was PVDF, and the solvent was NMP. The composition of the positive electrode active material was: LFP 96 wt%, binder (PVDF) 2 wt%, conductive carbon black (Super P) 1 wt%, and carbon nanotubes (MWCNTs) 1 wt%. The electrode coating amount was 12.04 mg / cm². 2 The coating density is 2.0 g / cm³. 3 Table 1 shows the measurement results of color and gloss of carbon-coated aluminum foil and plain foil.

[0066] Table 1

[0067] As shown in Table 1, the L* value of the dark blue carbon-coated aluminum foil is 11.35, far lower than the 57.11 of the plain foil, indicating that the carbon-coated aluminum foil has lower brightness (darker). The b* value of the carbon-coated aluminum foil is -2.30, exhibiting a slightly bluish hue. The gloss (GU) of the carbon-coated aluminum foil is 78.34, falling within the target range of 60 to 100, indicating that the coating thickness meets specifications. The plain foil, due to its specular surface, cannot have its gloss measured using conventional methods.

[0068] Please refer to Figures 4, 5, and 6. Figure 4 is a comparison of the capacity of carbon-coated aluminum foil and plain foil batteries under different C-rates according to an embodiment of this application. Figure 5 is a comparison of the average voltage of carbon-coated aluminum foil and plain foil batteries under different C-rates according to an embodiment of this application. Figure 6 is a comparison of the 3C discharge curves of carbon-coated aluminum foil and plain foil batteries according to an embodiment of this application.

[0069] As shown in Figure 4, there is almost no difference in capacity retention between carbon-coated aluminum foil (CCAF) and non-CCAF during high-rate discharge; their curves 410 and 420 nearly overlap. However, as shown in Figure 5, the carbon-coated aluminum foil (curve 510) exhibits a higher average operating voltage (Avg. Voltage) compared to the non-CCAF (curve 520), and this difference becomes more pronounced with increasing discharge rate. A higher average operating voltage means that the battery experiences a smaller voltage drop during high-rate discharge, indicating that the carbon-coated aluminum foil (CCAF) can reduce the impedance of the positive electrode current collector, resulting in better discharge performance.

[0070] As shown in Figure 6, the solid line represents carbon-coated aluminum foil (CCAF), and the dashed line represents non-CCAF. Experimental results show that although there is almost no difference in rate capacity retention between CCAF and non-CCAF batteries, when calculating the average voltage from the integrated area under the discharge curve, CCAF becomes more advantageous at higher discharge rates. Under 3C high-rate discharge conditions, the discharge plateau voltage of the CCAF battery is significantly higher than that of the non-CCAF battery.

[0071] As can be seen from Experiment Example 1, using the ultra-thin conductive coating (carbon-coated aluminum foil) of the present application embodiment as the positive electrode current collector can significantly improve the average operating voltage during high-rate discharge without sacrificing battery capacity, reduce the contact resistance between the current collector and the active material layer, and has better discharge performance.

[0072] Experiment Example 2: Comparison of Battery Performance with Carbon-Coated Aluminum Foil of Different Thicknesses

[0073] This experiment compares the effects of conductive coatings of different thicknesses on battery performance to verify the advantages of ultrathin coatings.

[0074] Experimental conditions: The aluminum foil substrate thickness was 12.5 μm. Two types of carbon-coated aluminum foil with different thicknesses were prepared: deep blue carbon-coated aluminum foil (Deep blue CCAF, coating thickness 0.4-0.5 μm) and black carbon-coated aluminum foil (Black CCAF, coating thickness 0.8-1.0 μm). The positive electrode active material composition was: LFP 96 wt%, binder (PVDF) 2 wt%, conductive carbon black (Super P) 1 wt%, and carbon nanotubes (MWCNT) 1 wt%. The electrode coating amount was 10.0 mg / cm². 2 The coating density is 1.85 g / cm³. 3 Table 2 shows the measurement results of color and gloss of carbon-coated aluminum foil of two different thicknesses.

[0075] Table 2

[0076] Table 2 shows that the L* values ​​of dark blue CCAF and black CCAF are similar (11.35 and 11.33 respectively), but their gloss (GU) differs significantly. The gloss of dark blue CCAF is 78.34, falling within the target range of 60 to 100; the gloss of black CCAF is 58.83, slightly below the target range. This result indicates that gloss can be used as an effective indicator of coating thickness: higher gloss (e.g., 60-100) indicates a thinner coating (e.g., 0.3-0.5 micrometers), and lower gloss (e.g., less than 60) indicates a thicker coating (e.g., greater than 0.5 micrometers).

[0077] Please refer to Figures 7, 8, and 9. Figure 7 is a comparison chart of the capacity of carbon-coated aluminum foil batteries of different thicknesses under different C-rates according to embodiments of this application; Figure 8 is a comparison chart of the average voltage of carbon-coated aluminum foil batteries of different thicknesses under different C-rates according to embodiments of this application; and Figure 9 is a comparison chart of the 3C discharge curves of carbon-coated aluminum foil batteries of different thicknesses according to embodiments of this application.

[0078] As shown in Figure 7, the dark blue carbon-coated aluminum foil (curve 710) and the black carbon-coated aluminum foil (curve 720) show almost no difference in capacitance retention during rate discharge. However, as shown in Figure 8, the dark blue carbon-coated aluminum foil (curve 810) has a higher average operating voltage (Avg. Voltage) compared to the black carbon-coated aluminum foil (curve 820).

[0079] As shown in Figure 9, the solid line represents dark blue carbon-coated aluminum foil, and the dashed line represents black carbon-coated aluminum foil. Experimental results show that although there is almost no difference in rate capacitance maintenance between the dark blue and black carbon-coated aluminum foils, when calculating the average voltage from the integrated area under the discharge curve, the dark blue carbon-coated aluminum foil becomes more advantageous at higher discharge rates. Considering that the coating thickness of dark blue CCAF is only half that of black CCAF, the material cost is lower, while performance is improved, demonstrating the advantages of ultra-thin coatings.

[0080] As demonstrated in Experimental Example 2, the ultra-thin conductive coating (thickness less than 0.5 micrometers) of this application embodiment, compared to a thicker coating (0.8-1.0 micrometers), can reduce material usage and cost while maintaining or even slightly improving battery performance. Furthermore, the difference in coating gloss (dark blue vs. black) can serve as a basis for non-destructive thickness monitoring.

[0081] As demonstrated in Experimental Examples 1 and 2, the ultrathin conductive coating of this application has several proven technical advantages. First, compared to bare metal foil, the ultrathin conductive coating of this application can effectively increase the average operating voltage during high-rate discharge, reduce the contact resistance between the current collector and the active material layer, and does not sacrifice battery capacity. Second, compared to thicker conductive coatings, the ultrathin conductive coating of this application (thickness less than a predetermined thickness, e.g., 0.5 micrometers) can reduce material usage and cost while maintaining or slightly improving battery performance. Furthermore, the ultrathin conductive coating of this application has measurable optical properties (e.g., gloss variation characteristics). When the gloss level (GU) falls within a predetermined range (e.g., 60 to 100), it indicates that the coating thickness meets specifications. This characteristic can serve as a basis for non-destructive quality control in production lines.

[0082] Example 4: Method for manufacturing an ultrathin conductive coating

[0083] Please refer to Figure 10, which is a flowchart of the ultrathin conductive coating manufacturing method according to an embodiment of this application. As shown in Figure 10, the manufacturing method of this embodiment includes a slurry preparation step S100, a coating step S110, and a drying step S120.

[0084] Regarding the slurry preparation step S100, a slurry containing carbon nanotubes, graphene or conductive carbon black, a dispersant, a solvent, and a binder is prepared. First, a predetermined amount of conductive material, such as carbon nanotubes (SWCNT or MWCNT) or other conductive carbon materials, is weighed. Next, a predetermined amount of conductive additive (e.g., graphene or conductive carbon black) is weighed; this is an optional step. Then, the dispersant (e.g., PVP or CMC) is dissolved in a solvent (e.g., NMP or deionized water) to form a dispersant solution. Next, the conductive material and conductive additive are added to the dispersant solution and dispersed (e.g., ultrasonic dispersion, high-speed stirring, or homogenization) to ensure the conductive material is uniformly dispersed in the solution. Finally, a binder (e.g., PVDF, SBR, or PAA) is added, and the mixture is stirred until homogeneous to form a conductive slurry. The solid content of the slurry is controlled within a predetermined range (e.g., 0.1% to 2%), and the viscosity is controlled within a predetermined range (e.g., 10 to 500 cps).

[0085] Regarding the coating step S110, the paste is applied to the surface of the metal foil substrate, resulting in a coating thickness of less than 0.5 micrometers on one side. The conductive paste can be applied to the metal foil substrate using a continuous coating method (e.g., microgravure printing or extrusion coating) or a batch coating method. When using microgravure printing, a gravure roller with a fine groove pattern is used to hold the paste, the paste amount is controlled by a doctor blade, and then the paste is transferred to the metal foil surface by an impression roller. When using extrusion coating, an extrusion coating head with a precision slit is used to control the paste output, and the gap between the coating head and the substrate is adjusted to control the coating thickness, ensuring the paste is uniformly applied to the metal foil surface. Regardless of the method used, the coating thickness on one side is controlled within a predetermined range (e.g., less than 0.5 micrometers, further less than 0.1 to 0.3 micrometers).

[0086] Regarding drying step S120, the solvent is removed through drying. The coated metal foil is fed into a drying apparatus and dried within a predetermined temperature range (e.g., 30°C to 200°C, or further, 80°C to 130°C). The drying time is 30 seconds to 30 minutes. During the drying process, the solvent evaporates, and the conductive material and conductive additives are cured on the surface of the metal foil, forming an ultra-thin conductive coating.

[0087] In another embodiment, the manufacturing method of this application may further include a testing step. In the testing step, an optical testing device (e.g., a color gloss meter) is used to test the dried coating. First, measurement parameters are set: geometric conditions (e.g., 45°C:0°), gloss sensor angle (e.g., 60-degree angle), and light source (e.g., a D65 standard light source). Next, the coating surface is measured, and color space values ​​(e.g., L*a*b* values) and gloss (GU) values ​​are recorded. Finally, the coating quality is judged: if all values ​​fall within a predetermined range (e.g., L* value 0 to 40, a* value -30 to 30, b* value -30 to 30, GU value 60 to 100), the coating quality is deemed acceptable.

[0088] The above manufacturing method can produce an ultrathin conductive coating with a thickness less than a predetermined thickness (e.g., less than 0.5 micrometers, or further from 0.1 to 0.3 micrometers), which has measurable optical properties and facilitates quality control.

[0089] Example 5: Electrode Structure

[0090] Please refer to Figure 11. Figure 11 is a schematic diagram of the electrode structure according to an embodiment of this application, corresponding to the enlarged structure of the cathode electrode 11 or anode electrode 13 shown in Figure 1. It should be noted that the thickness ratio of each layer in Figure 11 has been adjusted and enlarged to clearly show the electrode structure of the embodiment of this application, and does not represent the actual thickness ratio relationship.

[0091] As shown in Figure 11, the single-sided coated electrode 1100 includes a metal foil substrate 1110, a conductive coating 1120, and an electrode active material layer 1130. The metal foil substrate 1110 serves as a current collector for collecting and conducting current. In positive electrode applications, the metal foil substrate 1110 is aluminum foil or aluminum alloy foil with a thickness of 4 micrometers to 30 micrometers, and more preferably 10 to 15 micrometers, for example, 12.5 micrometers. In negative electrode applications, the metal foil substrate 1110 is copper foil, copper alloy foil, or nickel-plated copper foil with a thickness of 4 micrometers to 20 micrometers, and more preferably 6 to 10 micrometers.

[0092] A conductive coating 1120 is applied to the surface of the metal foil substrate 1110, and its thickness is less than a predetermined thickness, for example, less than 0.5 micrometers, and more preferably 0.3 to 0.5 micrometers. The conductive coating 1120 may exhibit a recognizable color, such as dark blue, purple, or gray, and its gloss (GU) falls within a predetermined range, for example, 60 to 100, and more preferably 70 to 90. The conductive coating 1120 comprises a conductive material, such as carbon nanotubes (SWCNT or MWCNT), graphene, or conductive carbon black, and a binder, such as PVDF, SBR, or PAA. The conductive coating 1120 reduces the contact resistance between the metal foil substrate 1110 and the electrode active material layer 1130.

[0093] An electrode active material layer 1130 is coated on a conductive coating 1120. In positive electrode applications, the electrode active material layer 1130 comprises a positive electrode active material, a binder, and a conductive additive. The positive electrode active material can be selected from olivine structure materials (e.g., LFP, LMP, LFMP), layered structure materials (e.g., LCO, NCM, NCA, LMR), spinel structure materials (e.g., LMO, LNMO), or combinations thereof. In one embodiment, the positive electrode active material is lithium iron phosphate (LFP), with a content of 90 to 98% by weight, for example, 96% by weight; the binder (e.g., PVDF) content is 1 to 5% by weight, for example, 2% by weight; and the conductive additive (e.g., conductive carbon black and / or carbon nanotubes) content is 1 to 5% by weight, for example, 2% by weight. In another embodiment, the positive electrode active material is a high-nickel material (e.g., NCM811 or NCA), with a content of 90 to 96% by weight; the binder content is 2 to 5% by weight; and the conductive additive content is 2 to 5% by weight. The coating amount of electrode active material layer 1130 is 8.0 to 15.0 mg / cm². 2 For example, 10.0 to 12.04 mg / cm³ 2 The coating density is 1.5 to 2.5 g / cm³. 3 For example, 1.85 to 2.0 g / cm³ 3 .

[0094] In negative electrode applications, the electrode active material layer 1130 comprises a negative electrode active material, a binder, and a conductive additive. The negative electrode active material can be selected from carbon-based materials (e.g., natural graphite, artificial graphite, hard carbon, soft carbon, MCMB), silicon-based materials (e.g., silicon powder, silicon oxide, silicon-carbon composites, silicon nanowires), lithium titanate (LTO), metal oxides (e.g., tin oxide, iron oxide), alloy materials (e.g., tin-based alloys, germanium-based alloys), or combinations thereof. In one embodiment, the negative electrode active material is graphite, with a content of 90 to 98% by weight, for example, 94 to 96% by weight; the binder (e.g., a combination of SBR and CMC, or PAA) has a content of 2 to 6% by weight; and the conductive additive has a content of 0 to 4% by weight. In another embodiment, the negative electrode active material is a silicon-carbon composite material, with a content of 80 to 95% by weight; the binder (e.g., PAA or Li-PAA) has a content of 3 to 10% by weight; and the conductive additive has a content of 2 to 5% by weight.

[0095] As shown in Experiment Example 1, the battery using electrode 1100 of this application exhibits a significantly higher average operating voltage during high-rate discharge compared to the battery using plain foil, with a smaller voltage drop. Experiment Example 2 shows that the thinner conductive coating (0.4-0.5 μm, dark blue CCAF) has a slightly higher average operating voltage during high-rate discharge compared to the thicker coating (0.8-1.0 μm, black CCAF), while also requiring half the material and incurring lower costs, demonstrating the advantages of ultra-thin coatings. Furthermore, coatings of different thicknesses exhibit different gloss levels, which can serve as a basis for non-destructive thickness monitoring.

[0096] The electrode structure in this application embodiment can also be a double-sided coating structure, that is, both opposite surfaces of the metal foil substrate are coated with a conductive coating and an electrode active material layer. This double-sided coating structure is suitable for the production of practical electrochemical devices (such as lithium-ion batteries, sodium-ion batteries, or supercapacitors) and can provide higher energy density.

[0097] When the electrode structure of this embodiment is applied to the positive electrode current collector, it can effectively reduce the contact resistance between the metal foil substrate and the positive electrode active material layer, improve the conductivity of the positive electrode, and enhance the adhesion between the positive electrode active material layer and the metal foil substrate, reducing the shedding of active material during charge-discharge cycles. Furthermore, the coating has measurable optical properties, which can serve as a basis for quality control and thickness determination.

[0098] In summary, the conductive coating, the method for manufacturing the conductive coating, and the electrode structure of the embodiments of this application have been fully and clearly described. It should be noted that this application is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

[0099] It should also be noted that any numerical values ​​mentioned in this application are not intended to limit the application to only the specified numerical values. Those skilled in the art will understand that there are permissible errors in each numerical value / composition ratio. As long as they do not significantly affect the results / functions to be achieved by each embodiment, any value that is similar to the disclosed numerical range is considered to be within the scope disclosed in this application.

Claims

1. A conductive coating, wherein: The conductive coating is applied to the surface of a metal foil substrate. The thickness of the conductive coating on one side is less than 0.5 micrometers, and the optical properties of the conductive coating are related to its thickness.

2. The conductive coating of claim 1, wherein the conductive coating comprises a conductive carbon material selected from one or a combination of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphene, or conductive carbon black.

3. The conductive coating as claimed in claim 1, wherein the thickness of one side of the conductive coating is 0.1 micrometer to 0.3 micrometer.

4. The conductive coating of claim 1, wherein the conductive coating has a deep blue appearance and a gloss (GU) in the range of 60 to 100.

5. The conductive coating as claimed in claim 1, wherein the metal foil substrate is aluminum foil or aluminum alloy foil, and the thickness is 4 micrometers to 30 micrometers.

6. The conductive coating as claimed in claim 1, wherein the color characteristics of the conductive coating are L* value 0 to 40, a* value -30 to 30, and b* value -30 to 30.

7. The conductive coating of claim 1, wherein the gloss (GU) of the conductive coating is in the range of 0 to 300.

8. A method for manufacturing a conductive coating, comprising: Prepare a conductive paste containing conductive carbon material, dispersant, solvent and binder; The conductive paste is coated onto the surface of a metal foil substrate, such that the coating thickness on one side is less than 0.5 micrometers; and The solvent is removed by drying.

9. The method for manufacturing the conductive coating as claimed in claim 8, wherein the conductive slurry has a solid content of 0.1% to 2% and a viscosity of 10 to 500 cps.

10. The method for manufacturing the conductive coating as claimed in claim 8, wherein the temperature of the step of removing the solvent by drying is from 30°C to 200°C, and the time is from 30 seconds to 30 minutes.

11. The method for manufacturing the conductive coating as claimed in claim 8, wherein the conductive carbon material is selected from one or a combination of single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, or conductive carbon black.

12. The method for manufacturing the conductive coating as claimed in claim 8, wherein the dispersant is selected from one or a combination of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and carboxymethyl cellulose (CMC).

13. The method for manufacturing the conductive coating as claimed in claim 8, wherein the solvent is selected from N-methylpyrrolidone (NMP), deionized water or other polar solvents.

14. The method for manufacturing the conductive coating as claimed in claim 8, wherein the adhesive is selected from one or a combination of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), or polyacrylic acid (PAA).

15. The method for manufacturing the conductive coating as claimed in claim 8, wherein the coating step is performed using a microgravure printing method or an extrusion coating method.

16. The method for manufacturing the conductive coating as claimed in claim 15, wherein the microgravure printing method comprises the following steps: The conductive paste is applied using a gravure roller. Excess paste on the surface of the gravure roller is removed by scraping with a scraper, leaving the paste in the groove; The paste is transferred onto the surface of the metal foil substrate through the gap between the impression cylinder and the gravure cylinder. as well as The solvent is removed by a drying system.

17. The method for manufacturing the conductive coating as claimed in claim 15, wherein the extrusion coating method comprises the following steps: The conductive slurry is fed into a slit die using an extruder. The slurry is extruded through the slit die and coated onto the surface of the metal foil substrate, wherein the coating roller supports the metal foil substrate and controls the coating gap; and The solvent is removed by a drying system.

18. The method for manufacturing the conductive coating as described in claim 8, further comprising: The L*a*b* color space was measured and the gloss (GU) was measured using optical inspection equipment.

19. An electrode structure, wherein the electrode structure comprises: Metal foil substrate; A conductive coating is applied to the surface of the metal foil substrate, and the thickness of the conductive coating on one side is less than 0.5 micrometers. as well as An electrode active material layer is coated onto the conductive coating.

20. The electrode structure of claim 19, wherein the conductive coating has a deep blue appearance and a gloss (GU) in the range of 60 to 100.

21. The electrode structure of claim 19, wherein the electrode active material layer comprises a positive electrode active material selected from one or a combination of lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), or lithium nickel cobalt aluminum oxide (NCA).

22. The electrode structure of claim 19, wherein the battery using the electrode structure has a higher average operating voltage at high discharge rates compared to a battery using plain foil.

23. The electrode structure of claim 19, wherein the thickness of the conductive coating is 0.3 micrometers to 0.5 micrometers, which, compared to a conductive coating with a thickness of 0.8 micrometers to 1.0 micrometers, has a higher average operating voltage at high-rate discharge.

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