METHOD FOR MANUFACTURING A SURFACE-MODIFIED SUBSTRATE USING LIQUID METAL AND A SURFACE-MODIFIED SUBSTRATE MANUFACTURED BY THE METHOD FOR MANUFACTURING THE SAME

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No. 10-2024-0189656, filed on Dec. 18, 2024, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a method for manufacturing a surface-modified substrate using a liquid metal and a surface-modified substrate manufactured by the method. More specifically, the present disclosure relates to a method for manufacturing a surface-modified substrate using a liquid metal capable of forming a homogeneous liquid metal alloy layer on the surface of the substrate, and a surface-modified substrate manufactured by the method.

Description of the Related Art

Recently, many techniques for modifying the surface of a metal film to form an alloy layer have been reported. For example, an alloy layer can be formed on the surface using a liquid metal. The surface-modified metal film is attracting attention as a material technology for anode-free batteries, which can reduce the weight and improve the energy storage density of secondary batteries.

Since a strategy to reduce the volume and weight of the anode itself is essential to improve the energy density of a secondary battery, there is an increasing industrial demand for the development of technologies that do not form an anode on the copper current collector, which has traditionally been used as an anode current collector.

Furthermore, the liquid metal used for the surface modification of the metal film is gaining attention as a material that maintains a liquid state even at low temperatures and possesses excellent electrical and thermal conductivity. However, if an oxide layer is formed on the surface of the liquid metal, the electrical and thermal conductivity deteriorate, and it changes the surface tension of the liquid metal surface, leading to the formation of a non-homogeneous coating layer.

Accordingly, the present disclosure provides a method for manufacturing a surface-modified substrate using a liquid metal, and a surface-modified substrate manufactured thereby.

SUMMARY OF THE DISCLOSURE

One object of the present disclosure is to provide a method for manufacturing a surface-modified substrate using a liquid metal, and a surface-modified substrate manufactured by the method, which can prevent the formation of a non-homogeneous coating layer during the formation of a liquid metal alloy layer by adding a surface treatment solution to the liquid metal to remove the oxide film on the surface of the liquid metal.

Another object of the present disclosure is to provide a method for manufacturing a surface-modified substrate using a liquid metal and a surface-modified substrate manufactured by the method, which can form fine liquid metal droplets through ultrasonic treatment, and wherein the formed fine droplets and the substrate react to provide a homogeneous liquid metal alloy layer.

In accordance with an aspect of the present disclosure, a method for manufacturing a surface-modified substrate using a liquid metal comprises the steps of: preparing a mixed solution by adding a surface treatment solution to a liquid metal; subjecting the mixed solution to ultrasonic treatment to form liquid metal droplets from which an oxide film has been removed; and immersing a substrate into the mixed solution in which the liquid metal droplets are formed to form a liquid metal alloy layer on the surface of the substrate, the liquid metal alloy layer is formed by the reaction between the fine liquid metal droplets formed by the ultrasonic treatment and the substrate.

According to an embodiment, the surface treatment solution may be an acidic solution or a basic solution.

According to an embodiment, the liquid metal may be an alloy composition of at least one selected from the group consisting of Gallium (Ga), Indium (In), Tin (Sn), Zinc (Zn), Cesium (Cs), Potassium (K), and Sodium (Na).

According to an embodiment, the weight ratio of the liquid metal to the surface treatment solution may be 1:2 to 1:50.

According to an embodiment, the substrate may comprise at least one selected from the group consisting of Pt (Platinum), Au (Gold), Ag (Silver), Cu (Copper), Al (Aluminum), Ni (Nickel), Sn (Tin), and Zn (Zinc).

According to an embodiment, the frequency of the ultrasonic treatment may be 5 kHz to 100 kHz.

According to an embodiment, the time for the ultrasonic treatment may be 10 seconds to 10 minutes.

According to an embodiment, the temperature of the ultrasonic treatment may be 10° C. to 50° C.

According to an embodiment, the step of immersing the substrate into the mixed solution in which the liquid metal droplets are formed to form a liquid metal alloy layer on the surface of the substrate may form a liquid metal alloy layer having a first thickness of 0.3 μm to 6 μm.

According to an embodiment, the step of immersing the substrate into the mixed solution in which the liquid metal droplets are formed to form a liquid metal alloy layer on the surface of the substrate may further comprise the step of forming a liquid metal molded layer by uniaxial pressing the liquid metal alloy layer.

According to an embodiment, the liquid metal molded layer is formed by uniaxial pressing the liquid metal alloy layer, and the second thickness of the liquid metal molded layer may be 0.1 μm to 4 μm.

According to an embodiment, the liquid metal molded layer is formed by uniaxial pressing the liquid metal alloy layer, and the surface coverage of the liquid metal molded layer may be 70% to 95%.

According to an embodiment, the uniaxial pressing may be performed 1 time to 5 times.

According to an embodiment, the pressure of the uniaxial pressing may be 10 MPa to 800 MPa.

A surface-modified substrate using a liquid metal according to an embodiment of the present disclosure is manufactured according to the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure.

According to an embodiment of the present disclosure, provided is a method for manufacturing a surface-modified substrate using a liquid metal, and a surface-modified substrate manufactured by the method, which can prevent the formation of a non-homogeneous coating layer during the formation of a liquid metal alloy layer by adding a surface treatment solution to the liquid metal to remove the oxide film on the surface of the liquid metal.

According to an embodiment of the present disclosure, provided is a method for manufacturing a surface-modified substrate using a liquid metal, and a surface-modified substrate manufactured by the method, which can form fine liquid metal droplets through ultrasonic treatment, and wherein the formed fine droplets and the substrate react to provide a homogeneous liquid metal alloy layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flow chart illustrating a method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure.

FIG. 2 is a graph of X-ray Diffraction (XRD) analysis for Comparative Example 1.

FIG. 3 is a graph of X-ray Diffraction (XRD) analysis for Example 3.

FIG. 4 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Comparative Example 1.

FIG. 5 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Comparative Example 2.

FIG. 6 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 1.

FIG. 7 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 2.

FIG. 8 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 3.

FIG. 9 is a cross-sectional image of Scanning Electron Microscope (SEM) for Example 3.

FIG. 10 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 4.

FIG. 11 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 5.

FIG. 12 is an image of the Tape Test result for Example 1 before additional external ultrasonic treatment after the alloying reaction.

FIG. 13 is an image of the Tape Test result for Example 3.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure will now be described more fully with reference to the accompanying drawings and contents disclosed in the drawings. However, the present disclosure should not be construed as limited to the exemplary embodiments described herein.

The terms used in the present specification are used to explain a specific exemplary embodiment and not to limit the present inventive concept. Thus, the expression of singularity in the present specification includes the expression of plurality unless clearly specified otherwise in context. It will be further understood that the terms “comprise” and/or “comprising”, when used in this specification, specify the presence of stated components, steps, operations, and/or elements, but do not preclude the presence or addition of one or more other components, steps, operations, and/or elements thereof.

It should not be understood that arbitrary aspects or designs disclosed in “embodiments”, “examples”, “aspects”, etc. used in the specification are more satisfactory or advantageous than other aspects or designs.

In addition, the expression “or” means “inclusive or” rather than “exclusive or”. That is, unless otherwise mentioned or clearly inferred from context, the expression “x uses a or b” means any one of natural inclusive permutations.

The terminology used in the following description was selected as generally and universally accepted in the relevant technical fields. However, other terms may be used depending on the development and/or changes in technology, conventions, or the preference of the skilled person. Therefore, the terms used in the following description should not be understood as limiting the technical idea, but should be understood as exemplary terms for describing the embodiments.

Furthermore, in specific cases, there are terms arbitrarily selected by the applicant, and in such cases, the detailed meaning thereof will be described in the corresponding part of the description. Accordingly, the terms used in the following description should be understood based on their inherent meaning and the entire contents of the specification, rather than merely the names of the terms.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with a meaning commonly understood by one of ordinary skill in the art to which this invention belongs. Furthermore, generally used dictionary terms are not interpreted ideally or excessively unless explicitly defined otherwise.

Meanwhile, in the description of the present invention, when it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, the terminology used herein is used to appropriately express the embodiments of the present invention, and this may vary depending on the intention of the user, the operator, or the custom of the field to which the present invention belongs. Therefore, the definitions of these terms should be determined based on the entire contents of this specification.

FIG. 1 is a flow chart illustrating a method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure.

The method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure includes: preparing a mixed solution by adding a surface treatment solution to a liquid metal (S110); forming liquid metal droplets from which an oxide film has been removed by subjecting the mixed solution to ultrasonic treatment (S120); and forming a liquid metal alloy layer on the surface of the substrate by immersing the substrate into the mixed solution in which the liquid metal droplets are formed (S130).

Accordingly, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure can provide the effect of modifying the surface of a substrate using an alloyable liquid metal and inducing stable charge/discharge reactions and suppressing dendrite formation on the substrate surface in a secondary battery to which it is applied.

First, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure proceeds with preparing a mixed solution by adding a surface treatment solution to the liquid metal (S110).

In the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure, the mixed solution can chemically modify or decompose the oxide on the surface of the liquid metal by adding the surface treatment solution to the liquid metal, thereby removing the surface oxide film. At this time, the surface treatment solution may be an acidic solution or a basic solution.

Generally, liquid metals maintain a liquid state even at low temperatures and are used as materials with excellent electrical and thermal conductivity. However, if an oxide film is formed on the surface, the electrical and thermal conductivity deteriorate, and the surface tension of the liquid metal surface is changed, which can lead to the formation of a non-homogeneous coating layer when the coating layer is formed.

The surface oxide film (surface oxide layer) of the liquid metal refers to a thin, rigid layer formed by the reaction of the metal with oxygen in the air, and the surface oxide film of the liquid metal can be removed by adding an acidic solution or a basic solution to the liquid metal.

Therefore, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure can remove the oxide film on the surface of the liquid metal by adding the surface treatment solution to the liquid metal, thereby preventing the formation of a non-homogeneous coating layer when the liquid metal coating layer is formed.

The acidic solution includes, but is not limited to, at least one selected from the group consisting of hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), hydrofluoric acid (HF), acetic acid (CH₃COOH), and citric acid (C₆H₈O₇), and any acidic solution capable of removing the oxide film may be used.

The basic solution includes, but is not limited to, at least one selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonium hydroxide (NH₄OH), and any basic solution capable of removing the oxide film may be used.

For example, when using a basic solution such as sodium hydroxide (NaOH) as the surface treatment solution for the liquid metal, the strong basic solution (NaOH) has high reactivity only with specific oxides, which allows for effective removal of the oxide film and surface activation of the liquid metal while minimizing physical damage to the metal.

For example, when applying liquid metal Gallium (Ga) to a Copper (Cu) substrate to form an alloy layer, due to the nature of liquid metal Gallium (Ga), oxidation occurs readily, which hinders smooth alloy formation, the reactivity of the liquid metal can be increased contributing to smooth alloy layer formation by adding a basic solution such as sodium hydroxide (NaOH) as the surface treatment solution.

The liquid metal may be, but is not limited to, an alloy composition of at least one selected from the group consisting of Gallium (Ga), Indium (In), Tin (Sn), Zinc (Zn), Cesium (Cs), Potassium (K), and Sodium (Na), and any alloyable liquid metal composition may be used.

For example, the liquid metal may include an alloy selected from the group consisting of Ga (Gallium), Ga—In (Gallium-Indium alloy), Ga—In—Sn (Gallium-Indium-Tin alloy), Ga—Sn (Gallium-Tin alloy), Ga—Zn (Gallium-Zinc alloy), Ga—Sn—Zn (Gallium-Tin-Zinc alloy), Ga—In—Sn—Zn (Gallium-Indium-Tin-Zinc alloy), Cs (Cesium), CsK (Cesium-Potassium alloy), CsNa (Cesium-Sodium alloy), NaK (Sodium-Potassium alloy), and NaKCs (Sodium-Potassium-Cesium alloy).

The weight ratio of the liquid metal to the surface treatment solution may be 1:2 to 1:50. If the weight ratio is less than 1:2, the oxide film on the liquid metal surface may not be sufficiently removed. If it exceeds 1:50, the substrate may be chemically damaged.

The mixing time of the liquid metal and the surface treatment solution may be 10 seconds or more. If the mixing time is less than 10 seconds, the oxide film on the liquid metal surface may not be sufficiently removed.

The mixing temperature of the liquid metal and the surface treatment solution may be 10° C. to 50° C. If the mixing temperature is below 10° C., the liquid metal may solidify. If it exceeds 50° C., the oxide film formation reaction on the liquid metal surface may be promoted.

Subsequently, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure proceeds with subjecting the mixed solution to ultrasonic treatment to form liquid metal droplets from which the oxide film has been removed (S120).

Generally, due to the inherent high surface tension of the liquid metal and the removal of the oxide film by the surface treatment solution, the liquid metal tends to form large droplets. However, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure can disperse the large droplets of the liquid metal into fine droplets by subjecting the mixed solution to ultrasonic treatment.

The frequency of the ultrasonic treatment may be 5 kHz to 100 kHz. If the frequency is less than 5 kHz, fine droplets may not be formed, preventing the induction of a homogeneous alloying reaction. If it exceeds 100 kHz, the size of the droplets becomes too small, resulting in increased surface energy and destabilization of the droplet shape.

The time for the ultrasonic treatment may be 10 seconds to 10 minutes. If the time is less than 10 seconds, the large liquid metal droplets may not be atomized into fine droplets. If it exceeds 10 minutes, the temperature of the solution may rise, promoting the oxide film formation reaction on the liquid metal surface.

The temperature of the ultrasonic treatment may be 10° C. to 50° C. The temperature of the ultrasonic treatment may be the same as the mixing temperature, which is 10° C. to 50° C.: if the temperature is below 10° C., the liquid metal may solidify; if it exceeds 50° C., the oxide film formation reaction on the liquid metal surface may be promoted.

Furthermore, generally, when a coating layer is formed directly on a metal substrate by adding a surface treatment solution to the liquid metal, the problem of large droplets of the liquid metal being formed, resulting in a non-homogeneous liquid metal alloy layer arises.

This is caused by the inherent high surface tension of the liquid metal and the removal of the oxide film by the surface treatment solution, leading to the phenomenon where the fine droplets of the liquid metal revert to large droplets. This results in the formation of a non-homogeneous coating layer corresponding to the shape of the large liquid metal droplets.

Specifically, as the oxide film of the liquid metal is removed, the liquid metal restores its inherent high surface tension. The high surface tension prevents the liquid metal from maintaining a state of separation into fine droplets, causing adjacent fine droplets to coalesce and form large droplets, which results in the limitation of a non-homogeneous coating layer being formed corresponding to the shape of the large liquid metal droplets.

Therefore, to solve the problems occurring in the conventional method of forming a coating layer on a metal substrate by adding a surface treatment solution to the liquid metal, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present invention performs the ultrasonic treatment of the mixed solution to form liquid metal droplets from which the oxide film has been removed, followed by immersing the substrate into the mixed solution in which the liquid metal droplets are formed to form a liquid metal alloy layer on the surface of the substrate (S130).

Finally, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present invention proceeds with immersing a substrate into the mixed solution in which the liquid metal droplets are formed to form a liquid metal alloy layer on the surface of the substrate (S130).

The substrate (110) may be a metal substrate, and may include, but is not limited to, at least one selected from the group consisting of Pt (Platinum), Au (Gold), Ag (Silver), Cu (Copper), Al (Aluminum), Ni (Nickel), Sn (Tin), and Zn (Zinc).

In the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure, the liquid metal alloy layer (120) can be formed through an alloying reaction by the direct reaction between the fine liquid metal droplets formed by the ultrasonic treatment and the substrate (e.g., metal substrate) (110).

Specifically, in the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present invention, the alloying reaction is initiated by the reaction between the fine droplets formed by the ultrasonic treatment and the substrate (110), and the thickness of the liquid metal alloy layer (120) formed by the alloying reaction can decrease due to the change in surface tension and wettability.

The first thickness (T₁) of the liquid metal alloy layer (120) may be 0.3 μm to 6 μm. If the first thickness (T₁) is less than 0.3 μm, the uniformity of the surface alloy layer may be reduced. If it exceeds 6 μm, the diffusion distance required for the liquid metal fine droplets to react with the substrate increases, which may inhibit the alloying reaction rate. (Here, the first thickness (T₁) refers to the height of the liquid metal alloy layer (120).)

The liquid metal alloy layer (120) may be formed on the substrate (110), and the first-first thickness (T_1-1) of the substrate (110) on which the liquid metal alloy layer (120) is formed may be 1 μm or more. If the first-first thickness (T_1-1) is less than 1 μm, there may be problems due to chemical damage in the acidic and basic solutions. (Here, the first-first thickness (T_1-1) refers to the height of the substrate (110) on which the liquid metal alloy layer (120) is formed.)

According to an embodiment, the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present invention may further include the step of forming a liquid metal molded layer (130) by subjecting the liquid metal alloy layer (120) to uniaxial pressing.

Uniaxial pressing is a method of shaping a metal by applying pressure in a single direction. The method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present invention can improve the density and degree of bonding and form a liquid metal molded layer (130) with a uniform thickness by subjecting the liquid metal alloy layer (120) to uniaxial pressing.

In the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present disclosure, by uniaxial pressing, the liquid metal alloy layer (120) is mainly composed of ductile metal elements. For example, the surface of the non-homogeneously deposited liquid metal alloy layer (120) is deformed in the horizontal direction by the pressure applied in the vertical direction, forming the surface of the liquid metal molded layer (130) with improved packing density.

Furthermore, the thickness of the substrate (110) on which the liquid metal molded layer (130) is formed may also decrease because the high pressure generated during uniaxial pressing removes or reduces micro-defects or voids inside the substrate (110), inducing recrystallization.

The second thickness (T₂) of the liquid metal molded layer (130) may be 0.1 μm to 4 μm. If the second thickness (T₂) is less than 0.1 μm, the uniformity of the alloy layer formed on the substrate surface may be reduced. If it exceeds 4 μm, the roughness of the surface alloy layer may increase. (Here, the second thickness (T₂) refers to the height of the liquid metal molded layer (130).)

The liquid metal molded layer (130) may be formed on the substrate (110), and the second-first thickness (T_2-1) of the substrate (110) on which the liquid metal molded layer (130) is formed may be 1 μm or more. If the second-first thickness (T_2-1) is less than 1 μm, there may be problems due to chemical damage in the acidic and basic solutions. (Here, the second-first thickness (T_2-1) refers to the height of the substrate (110) on which the liquid metal molded layer (130) is formed.)

The surface coverage of the liquid metal molded layer (130) may be 70% to 95%.

The uniaxial pressing may be performed 1 time to 5 times. If the uniaxial pressing is performed less than 1 time, the surface coverage may be reduced. If it is performed more than 5 times, the flatness of the substrate may be reduced.

The pressure of the uniaxial pressing may be 10 MPa to 800 MPa. If the pressure is less than 10 MPa, the surface coverage may be reduced. If it exceeds 800 MPa, the flatness of the substrate may be reduced.

Therefore, according to an embodiment of the present invention, provided is a method for manufacturing a surface-modified substrate using a liquid metal, and a surface-modified substrate manufactured by the method, which can form fine liquid metal droplets through ultrasonic treatment, and form a liquid metal alloy layer (120) by the reaction between the formed fine liquid metal droplets and the substrate (110) to provide a homogeneous liquid metal alloy layer (120).

The surface-modified substrate using a liquid metal according to an embodiment of the present disclosure is manufactured by the method for manufacturing a surface-modified substrate using a liquid metal according to an embodiment of the present invention, and includes the same components, so the description of the identical components will be omitted.

The surface-modified substrate using a liquid metal according to an embodiment of the present invention includes a substrate (110) and a liquid metal alloy layer (120) formed on the substrate (110), and the liquid metal alloy layer (120) is characterized by being formed by the reaction between the fine liquid metal droplets formed by the ultrasonic treatment and the substrate (110).

For example, when the surface-modified substrate using a liquid metal according to an embodiment of the present invention is used as a current collector for a secondary battery, it can be utilized as a material technology for an anode-free secondary battery.

An anode-free secondary battery (Non-Electrode Secondary Battery) is a concept different from traditional secondary batteries, referring to a system that performs electrochemical energy storage and release without an electrode, and is receiving attention for its potential to dramatically improve the energy density of a secondary battery.

Accordingly, when the surface-modified substrate using a liquid metal according to an embodiment of the present invention is applied to a secondary battery, the liquid metal alloy layer (120) formed by the bonding between the substrate (110) and the liquid metal suppresses the formation of lithium dendrites and other phenomena, thereby solving the problems of charge/discharge efficiency and long-term cycle stability.

Generally, the liquid metal alloy layer can secure long-term stability by controlling the oxidation/reduction of lithium ions and the lithium growth reaction, enabling the manufacture of anode-free secondary batteries that can store and release energy without an electrode.

Therefore, the surface-modified substrate using a liquid metal according to an embodiment of the present invention can replace the role of the current collector in a secondary battery, and due to the characteristics of liquid metal maintaining stability at high temperatures, it can operate efficiently in battery systems operating in high-temperature environments.

Furthermore, the surface-modified substrate using a liquid metal according to an embodiment of the present invention replaces the role of the current collector in a secondary battery, suppressing the formation of Dendrites that form on conventional anode-free current collectors, solving problems such as battery efficiency degradation and reduced durability during charge/discharge caused by dendrite formation, and can induce stable charge/discharge reactions in a secondary battery based on this.

Therefore, the surface-modified substrate using a liquid metal according to an embodiment of the present invention can be applied as a material technology for an anode-free secondary battery that reduces the weight and improves the energy storage density of the secondary battery by replacing the role of the current collector.

Hereinafter, the present disclosure will be described in more detail through examples. These examples are for more specific explanation of the present invention, and the scope of the present disclosure is not limited by these examples.

Comparative Example 1

Substrate Using Liquid Metal and Sodium Hydroxide (NaOH)

2 g of liquid metal Eutectic Gallium-Indium (EGaIn) and 40 g of sodium hydroxide (NaOH) solution were added to a vial, and a copper foil was immersed in the solution to induce wetting on the surface. After uniformly coating the surface of the current collector (substrate) to form a liquid metal alloy layer, the excess liquid metal EGaIn was removed using the wire bar coating method.

Comparative Example 2

Substrate Using Liquid Metal, Sodium Hydroxide (NaOH) and Ultrasonic Treatment

2 g of liquid metal Eutectic Gallium-Indium (EGaIn) and 40 g of sodium hydroxide (NaOH) solution were added to a vial, and external ultrasonic treatment was performed for about 5 minutes to induce the dispersion of liquid metal droplets. A copper foil was immersed in the solution containing the dispersed liquid metal droplets, and the liquid metal settled over time to form an alloy on the copper current collector. After inducing a chemical alloying reaction for 5 minutes, the recovered sample was washed with deionized water (DI water) and isopropyl alcohol (IPA), and dried at 80° C. for 5 minutes.

Comparative Example 3

Substrate Using Liquid Metal and Isopropyl Alcohol (IPA)

2 g of liquid metal Gallium (Ga) and 40 g of Isopropyl Alcohol (IPA) were added to a vial, and external ultrasonic treatment was performed for about 5 minutes to induce the dispersion of liquid metal droplets with a surface oxide film formed. A copper foil was immersed in the solution containing the dispersed liquid metal droplets and held for 5 minutes.

Example 1

Surface-Modified Substrate with 1 Time Alloying Reaction

2 g of liquid metal Gallium (Ga) and 40 g of sodium hydroxide (NaOH) solution were added to a vial, and external ultrasonic treatment was performed for about 5 minutes at over 30° C. to induce the dispersion of liquid metal droplets. A copper foil was immersed in the solution containing the dispersed liquid metal droplets, and the liquid metal settled over time to form an alloy on the copper foil. After inducing a chemical alloying reaction for 5 minutes, the recovered sample was washed with deionized water (DI water) and isopropyl alcohol (IPA) and dried at 80° C. for 5 minutes. Additionally, the finished surface-modified substrate using the liquid metal was immersed in the NaOH solution and subjected to external ultrasonic treatment for 5 minutes, recovered again, washed with DI water and IPA, and dried at 80° C. for 5 minutes.

Example 2

Surface-Modified Substrate with 2 Times Alloying Reactions

The surface-modified substrate manufactured according to Example 1 was subjected to a chemical alloying reaction for another 5 minutes. The recovered sample was then washed with DI water and IPA and dried at 80° C. for 5 minutes. Furthermore, the finished surface-modified substrate using the liquid metal was immersed in the NaOH solution one more time and subjected to external ultrasonic treatment for 5 minutes. It was recovered again, washed with DI water and IPA, and dried at 80° C. for 5 minutes.

Example 3

Surface-Modified Substrate with 3 Times Alloying Reactions

The surface-modified substrate manufactured according to Example 2 was subjected to a chemical alloying reaction for another 5 minutes. The recovered sample was then washed with DI water and IPA and dried at 80° C. for 5 minutes. Furthermore, the finished surface-modified substrate using the liquid metal was immersed in the NaOH solution one more time and subjected to external ultrasonic treatment for 5 minutes. It was recovered again, washed with DI water and IPA, and dried at 80° C. for 5 minutes.

Example 4

Surface-Modified Substrate Pressed at 10 Mpa

The surface-modified substrate manufactured according to Example 3 was subjected to pressing at a pressure of 10 MPa using a uniaxial press.

Example 5

Surface-Modified Substrate Pressed at 30 Mpa

The surface-modified substrate manufactured according to Example 3 was subjected to pressing at a pressure of 30 MPa using a uniaxial press.

Experimental Example 1

X-Ray Diffraction (XRD) Analysis

FIG. 2 is a graph of X-ray Diffraction (XRD) analysis for Comparative Example 1, and FIG. 3 is a graph of X-ray Diffraction (XRD) analysis for Example 3.

Referring to FIG. 2 and FIG. 3, it can be confirmed that a liquid metal alloy layer of Galliumide (CuGa₂) of Copper (Cu) and Gallium (Ga) was formed on the substrates of Comparative Example 1 and Example 3.

However, referring to FIG. 2, it can be confirmed that the liquid metal alloy layer of Galliumide (CuGa₂) formed on the substrate of Comparative Example 1 was formed as a non-homogeneous alloy layer due to the aggregation phenomenon of unreacted Indium (In), which will be described in detail in Experimental Example 2.

Experimental Example 2

Scanning Electron Microscope Sem) Image and Energy Dispersive Spectroscopy (EDS) Analysis

FIG. 4 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Comparative Example 1, and FIG. 5 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Comparative Example 2.

Referring to FIG. 4, it can be confirmed that although a liquid metal alloy layer of Galliumide (CuGa₂) was formed on the substrate of Comparative Example 1, it was formed as a non-homogeneous liquid metal alloy layer due to the aggregation phenomenon of unreacted Indium (In).

Also, referring to FIG. 5, it can be confirmed that although a liquid metal alloy layer of Galliumide (CuGa₂) was formed on the substrate of Comparative Example 2, an inhomogeneous alloy layer was formed as Indium (In) was locally distributed in the form of islands.

In particular, in the case of Comparative Example 3, the liquid metal alloy layer itself was not formed on the substrate, so it could not be confirmed by SEM image and EDS analysis.

However, FIG. 6 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 1, and FIG. 7 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 2.

Referring to the first image of FIG. 6, Example 1 formed a liquid metal alloy layer on the substrate by performing ultrasonic treatment using liquid metal Gallium (Ga) and sodium hydroxide (NaOH), immersing the substrate to induce an alloying reaction, washing, and drying. However, it can be confirmed that excessive Gallium (Ga) still exists.

Accordingly, referring to the second image of FIG. 6, Example 1 formed a liquid metal alloy layer on the substrate, followed by immersion in the NaOH solution to perform external ultrasonic treatment, and recovered again, washed, and dried, confirming that the excessive Gallium (Ga) was removed.

Therefore, Example 1, where the alloying reaction was performed once to remove excessive Gallium (Ga) and uniformly form a liquid metal alloy layer, can be confirmed by SEM image and EDS analysis.

Referring to FIG. 7, Example 2 formed a liquid metal alloy layer by performing the alloying reaction 2 times, confirming an improvement in area density compared to Example 1 where the alloying reaction was performed 1 time.

FIG. 8 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 3, and FIG. 9 is a cross-sectional Scanning Electron Microscope (SEM) image for Example 3.

Referring to FIG. 8, Example 3 formed a liquid metal alloy layer by performing the alloying reaction 3 times, confirming an improvement in area density compared to Example 1 (1 time alloying reaction) and Example 2 (2 times alloying reaction).

Referring to FIG. 9, the cross-section of Example 3 was analyzed using SEM, confirming that the liquid metal alloy layer was formed with a thickness of 4 μm.

FIG. 10 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 4, and FIG. 11 is an image of Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analysis for Example 5.

Referring to FIG. 10, Example 4 pressurized the liquid metal alloy layer of Example 3 at a pressure of 10 MPa using a uniaxial press, which allowed for the fabrication of a surface-modified film (substrate) containing a liquid metal molded layer with a homogeneous distribution of Copper (Cu) and Gallium (Ga) formed by the pressing.

Referring to FIG. 11, Example 5 pressurized the liquid metal alloy layer of Example 3 at a pressure of 30 MPa using a uniaxial press, which allowed for the fabrication of a surface-modified film (substrate) containing a liquid metal molded layer with a homogeneous distribution of Copper (Cu) and Gallium (Ga) formed by the pressing.

Experimental Example 3

Tape Test Analysis

FIG. 12 is an image of the Tape Test result for Example 1 before additional external ultrasonic treatment after the alloying reaction, and FIG. 13 is an image of the Tape Test result for Example 3.

Referring to FIG. 12, Example 1 formed a liquid metal alloy layer by performing the alloying reaction once, and excessive liquid metal residue was observed on the tape as shown in FIG. 12 during the formation process. However, to additionally control the leakage phenomenon during the formation process, external ultrasonic treatment can be performed by immersing it in NaOH solution, followed by recovery, washing, and drying to remove the excessive liquid metal.

Referring to FIG. 13, Example 3 formed a liquid metal alloy layer by performing the alloying reaction 3 times, and it was confirmed that all excessive liquid metal was removed.

Although the present disclosure has been described through limited examples and drawings, the present disclosure is not intended to be limited to the examples. Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure. Therefore, the scope of the present disclosure should not be limited to the described examples but should be defined not only by the claims described below but also by equivalents of these claims.