KR102188648B1 - Secondary battery comprising sparked graphene oxide sheet and Preparation method thereof - Google Patents

Abstract

The present invention relates to a secondary battery comprising a sparked reduced graphene oxide sheet and to a production method thereof. The secondary battery includes sparked reduced graphene oxide (sGO), thereby improving the wettability of beta alumina to a liquid metal so that the charge/discharge capacity and efficiency are excellent, and having excellent durability because it is stable even after repeated cycling.

Description

Secondary battery comprising sparked reduced graphene oxide sheet and method for manufacturing the same

The present invention relates to a secondary battery including a sparked reduced graphene oxide sheet and a method of manufacturing the same.

Various micro/nanostructured reservoirs for liquid metals with unique surfaces, pores and connection structures have been proposed in the field of energy storage systems research. Among them, carbon-based materials are ideal candidates for reservoirs. This is because carbon is the lightest material among the materials available as a reservoir structure. In addition, emerging carbon materials such as carbon nanotubes, graphene, and mesoporous carbon have the advantage of having excellent mechanical strength with a large surface area. Moreover, carbon materials are generally stable in the redox environment of Li and Na batteries. In particular, since graphene-based functional sheets having a large surface area have a 2D layered structure and connecting microstructures, many studies have been conducted as a structure material for battery electrodes and a channel guided reservoir. For example, a metal (e.g., Na, Li)/C composite electrode was fabricated through a melt infusion technique of a liquid metal on a graphene-based sheet. The metal/C composite electrode showed excellent performance by solving the main problems of the inherent bare metal anode such as dendritic formation and volume expansion. Despite the superior performance demonstrated in the experiments and the emergence of promising applications, understanding of the permeation of liquid metals for graphene-base sheets is still lacking. This is mainly because the microstructure of the graphene-base material and the distribution of chemical functional groups on the surface are complex. In electronic and electrochemical device applications, it is important that the metal layer maintains a solid adhesion to the surface of the graphene-base sheets, so a sufficient understanding of the chemical and physical properties of the metal/graphene-base sheets interface is required.

Electrochimica Acta 55 (2010) 3909-3914

An object of the present invention is to provide a secondary battery having excellent performance and a method of manufacturing the same by improving the wetting of a solid electrolyte beta alumina with respect to a liquid metal.

The present invention, sparked reduced graphene oxide (sparked reduced graphene oxide, sGO) and a solid electrolyte containing beta alumina (β″-Al ₂ O ₃ ); And

It provides a secondary battery including a negative electrode (anode) containing a liquid metal.

In addition, the present invention comprises the steps of preparing a sparked reduced graphene oxide sheet by contacting a graphene oxide sheet with a liquid metal; Laminating the prepared sparked reduced graphene oxide sheet on one side of beta alumina to prepare a solid electrolyte; And it provides a method for manufacturing a secondary battery comprising the step of forming a negative electrode containing a liquid metal through a charging reaction on the surface on which the sparked reduced graphene oxide sheet of the solid electrolyte is formed.

The secondary battery of the present invention includes sparked reduced graphene oxide (sGO), thereby improving the wettability of beta alumina to the liquid metal, which has excellent charging/discharging capacity and efficiency, and is stable even after repeated cycling and has excellent durability. There is this.

1 is an image showing a structure (a) of a secondary battery according to the present invention and a method (b) of manufacturing a sparked reduced graphene oxide sheet.
2 is an image photographed by a digital camera and a field emission scanning electron microscope of a graphene oxide sheet according to an embodiment.
3 is a graph showing the BET specific surface area measurement result of graphene oxide sheet according to an embodiment.
4 is an X-ray diffraction (XRD) result graph of a graphene oxide sheet according to an embodiment.
5 is a graph showing a result of Fourier transform infrared spectroscopy of a graphene oxide sheet according to an embodiment.
6 is an X-ray photoelectron spectral spectrum result graph of a graphene oxide sheet according to an embodiment.
7 is a graph showing a result of Raman spectroscopy analysis of a graphene oxide sheet according to an embodiment.
8 is a graph showing results of absorption experiments of liquid sodium and graphene oxide sheets by conducting molecular dynamics (MD) simulation.
9 is an image photographing a liquid sodium absorption process of a graphene oxide sheet according to an embodiment: (a) is sGO, (b) is a pGO sheet.
10 is an image photographing a result of a liquid metal absorption experiment of a graphene oxide sheet according to an embodiment: (a) is liquid potassium, and (b) is liquid lithium.
11 is a graph and an image showing a contact angle with respect to liquid sodium according to a temperature of beta alumina formed on one surface of a graphene oxide sheet according to an embodiment.
12 is a graph showing the charging/discharging result of the secondary battery according to an embodiment: (a) is a graph showing the initial cycle voltage characteristics of the secondary battery, and (b) is a plurality of charging/discharging of the secondary battery of Example 1. It is a voltage-capacity change graph according to a cycle, (c) is a voltage-capacity graph of a sodium beta-alumina battery containing pure beta alumina, and (d) is a graph according to the number of charge/discharge cycles of the secondary battery of Example 1. It is a graph showing the change in capacity and coulomb efficiency.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description.

However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention is a solid electrolyte containing sparked reduced graphene oxide (sGO) and beta alumina (β″-Al ₂ O ₃ ); And

It provides a secondary battery including a negative electrode (anode) containing a liquid metal.

A schematic diagram of a secondary battery according to the present invention is shown in FIG. 1. Referring to Figure 1, the secondary battery according to the present invention is a positive electrode (cathode); A solid electrolyte including beta alumina and sparked reduced graphene oxide sheet; And cathodes are sequentially stacked. Specifically, the anode; Beta alumina; It is a structure in which a sparked reduced graphene oxide sheet and a negative electrode are sequentially stacked, and the negative electrode is composed of a liquid metal, and a part of the liquid metal may permeate the sparked reduced graphene oxide sheet and be filled between the graphene layers. .

As an example, the sparked reduced graphene oxide according to the present invention is in the form of a sheet, and may serve as a wet sheet. Specifically, the sparked reduced graphene oxide has a graphene interlayer spacing of 3 nm to 4.5 nm, and may include a liquid metal between the graphene layers. More specifically, the sparked reduced graphene oxide has a graphene interlayer spacing of 3nm to 4.25nm 3nm to 4nm, 3nm to 3.8nm, 3nm to 3.5nm, 3.25nm to 4.5nm, 3.25nm to 4.25nm, 3.25nm to 4nm , 3.25nm to 3.8nm, 3.25nm to 3.5nm, 3.5nm to 4.5nm, 3.5nm to 4.25nm, 3.5nm to 4nm, 3.5nm to 3.8nm, 3.75nm to 4.5nm, 3.75nm to 4.25nm, 3.75nm To 4nm, or 4nm to 4.5nm. For example, the liquid metal included between the graphene layers may be at least one selected from the group consisting of sodium (Na), lithium (Li), and potassium (K), or sodium, lithium, or potassium.

In addition, the carbon/oxygen (C/O) atomic ratio of the sparked reduced graphene oxide may be 5 or more. Specifically, the carbon/oxygen (C/O) atomic ratio of the sparked reduced graphene oxide is 5 or more, 6 or more, 7 or more, 5 to 10, 6 to 10, 7 to 10, 5 to 8, 6 to 8 or It may be 7 to 8.

In addition, the BET specific surface area of the sparked reduced graphene oxide may be 200 to 400 m ² /g. Specifically, the BET specific surface area of the sparked reduced graphene oxide is 200 to 400 m ² /g, 200 to 350 m ² /g, 250 to 400 m ² /g, 250 to 350 m ² /g, 280 to 400 m ² /g, 280 to 350 m ² /g or 280 to 320 m ² /g. The sparked reduced graphene oxide according to the present invention has a porous structure and exhibits a high specific surface area, thereby providing an improved active area to the negative electrode.

In addition, the thickness of the sparked reduced graphene oxide may be 100 μm to 400 μm. Specifically, the thickness of the sparked reduced graphene oxide may be 100 μm to 150 μm, 150 μm to 200 μm, 200 μm to 250 μm, or 250 μm to 400 μm. By having the above thickness, it is possible to improve the secondary battery performance.

For example, the sparked reduced graphene oxide may be formed between beta alumina and a cathode.

The secondary battery according to the present invention includes the sparked reduced graphene oxide as described above on one side of the beta alumina, thereby improving the wettability of the liquid metal to improve the liquid metal wetting behavior for the solid electrolyte beta alumina. It is possible to improve the charging/discharging capacity and durability of the secondary battery.

As an example, the liquid metal constituting the negative electrode may be at least one selected from the group consisting of sodium (Na), lithium (Li), and potassium (K). Specifically, the liquid metal may be sodium (Na), lithium (Li), or potassium (K).

By having the configuration as described above, the secondary battery according to the present invention may have a charging/discharging capacity of 50mAh or more under a condition of 1.8 to 2.8 V cutoff voltage and 10 mA constant current at a temperature of 175°C. Specifically, the secondary battery according to the present invention may have a charge/discharge capacity of 60 mAh or more, 80 mAh or more, 90 mAh or more, 60 mAh to 100 mAh, or 100 mAh to 120 mAh under conditions of 1.8 to 2.8 V cutoff voltage and 10 mA constant current at a temperature of 175°C. .

As an example, the secondary battery according to the present invention includes a cathode; A solid electrolyte including beta alumina and sparked reduced graphene oxide sheet; And a structure in which anodes are sequentially stacked. Specifically, the anode is configured in a form in which the anode is supported in an anolyte containing sodium salt and NaAlCl ₄ . The positive electrode may be in a form containing a transition metal chloride. More specifically, the positive electrode may be in a form in which a positive electrode including small granules made of NaCl and nickel (Ni) is supported in a molten anolyte containing NaAlCl ₄ .

In addition, the present invention comprises the steps of preparing a sparked reduced graphene oxide sheet by contacting a graphene oxide sheet with a liquid metal;

Laminating the prepared sparked reduced graphene oxide sheet on one side of beta alumina to prepare a solid electrolyte; And

It provides a method of manufacturing a secondary battery comprising the step of forming a negative electrode including a liquid metal through a charging reaction on the surface on which the sparked reduced graphene oxide sheet of the solid electrolyte is formed.

The step of preparing the sparked reduced graphene oxide sheet of the present invention is shown schematically in FIG. 1. Specifically, the step of preparing the sparked reduced graphene oxide sheet may be performed by contacting the graphene oxide sheet with the molten liquid metal at a temperature of 200°C to 400°C. More specifically, the step of preparing a sparked reduced graphene oxide sheet is graphene oxide in a liquid metal melted at a temperature of 200°C to 350°C, 200°C to 300°C, 250°C to 400°C, or 250°C to 350°C. This can be done by touching the ends of the sheet. When the graphene oxide sheet is brought into contact with the molten liquid metal as described above, a spark reaction occurs, reducing the graphene oxide, reducing the oxygen functional group, and increasing the gap between the graphene layers. Accordingly, the specific surface area of the graphene oxide sheet may increase. For example, the liquid metal used for the spark reaction may be at least one selected from the group consisting of sodium (Na), lithium (Li) and potassium (K), or sodium, lithium, or potassium.

As an example, in the step of preparing a sparked reduced graphene oxide sheet, the sparked reduced graphene oxide sheet may be formed to a thickness of 100 μm to 400 μm. Specifically, the sparked reduced graphene oxide sheet may be formed to a thickness of 100 μm to 150 μm, 150 μm to 200 μm, 200 μm to 250 μm, or 250 μm to 400 μm.

In addition, the prepared sparked reduced graphene oxide sheet may have a graphene interlayer spacing of 3 nm to 4.5 nm. Specifically, the sparked reduced graphene oxide sheet has a graphene interlayer spacing of 3nm to 4.25nm 3nm to 4nm, 3nm to 3.8nm, 3nm to 3.5nm, 3.25nm to 4.5nm, 3.25nm to 4.25nm, 3.25nm to 4nm , 3.25nm to 3.8nm, 3.25nm to 3.5nm, 3.5nm to 4.5nm, 3.5nm to 4.25nm, 3.5nm to 4nm, 3.5nm to 3.8nm, 3.75nm to 4.5nm, 3.75nm to 4.25nm, 3.75nm To 4nm, or 4nm to 4.5nm.

In addition, the sparked reduced graphene oxide sheet prepared in the step of preparing the sparked reduced graphene oxide sheet may have a carbon/oxygen (C/O) atomic ratio of 5 or more. Specifically, the carbon/oxygen (C/O) atomic ratio of the sparked reduced graphene oxide is 5 or more, 6 or more, 7 or more, 5 to 10, 6 to 10, 7 to 10, 5 to 8, 6 to 8 or It may be 7 to 8.

The step of preparing the solid electrolyte according to the present invention may be formed using a method of laminating a sparked reduced graphene oxide sheet on one surface of beta alumina, but is not limited thereto. Specifically, a sparked reduced graphene oxide sheet may be stacked on one side of the beta alumina by physically pressing and fixing it with a current collector.

The step of forming the negative electrode according to the present invention is to assemble a battery in a form in which a sparked reduced graphene oxide sheet is placed on one side of a solid electrolyte coated with a small amount of metal, and a liquid metal is formed on the negative electrode through a charging reaction to form a negative electrode. Can be manufactured. Specifically, in the forming of the negative electrode, a liquid metal may fill the negative electrode portion through a charging reaction, and the liquid metal may be filled in the sparked reduced graphene oxide sheet. More specifically, in the step of forming the negative electrode, a solid metal of 5 mg or less is placed on the surface of the sparked reduced graphene oxide (sGO) of the solid electrolyte, and the liquid metal forms the negative electrode through a charging reaction at a temperature of 175°C or higher. Liquid metal may be filled inside the reduced graphene oxide sheet. The liquid metal may be reduced by moving metal ions from the positive electrode to the negative electrode through a beta alumina electrolyte and receiving electrons from the sparked reduced graphene oxide surface. At this time, the charging reaction can be charged until reaching the cut-off voltage of 2.8 V under conditions of 0.5 to 10 mA, 0.5 to 5 mA, or 0.5 to 2 mA, and the time is 2 to 17 hours, 2 to 10 hours. Alternatively, it may take 2 to 5 hours. Specifically, it can be charged with 0.6 mA (2 hours), 1 mA (10 hours), 2 mA (17 hours) or 4 mA (4 hours), and 10 mA until it reaches the cut-off voltage of 2.8 V. have.

As an example, in the step of forming the negative electrode, the liquid metal may be at least one selected from the group consisting of sodium (Na), lithium (Li), and potassium (K). Specifically, the liquid metal may be sodium (Na), lithium (Li), or potassium (K).

For example, in the step of forming the negative electrode, the liquid metal may be applied in an amount of 1 g/cm ³ to 4 g/cm ³ per unit volume. Specifically, in the step of forming the negative electrode, the liquid metal per unit volume of 0.85 g/cm ³ to 1.37 g/cm ³ , 1.37 g/cm ³ to 2.29 g/cm ³ or 2.29 g/cm ³ to 3.43 g/cm ³ Sheep can be applied.

As an example, an anode may be formed on the opposite side where the cathode is formed in the solid electrolyte. Specifically, the positive electrode may be prepared in a form in which the positive electrode is supported in an anolyte containing sodium salt and NaAlCl ₄ . The positive electrode can be prepared in a form containing a transition metal chloride. More specifically, the positive electrode may be prepared by supporting a positive electrode including NaCl and nickel (Ni) small particles in a molten anolyte containing NaAlCl ₄ .

Hereinafter, the present invention will be described in more detail through examples according to the present invention, but the scope of the present invention is not limited by the examples presented below.

Manufacturing Example 1

Graphene oxide (GO) solution was applied on a copper foil by drop casting, and then peeled from the copper foil to prepare a graphene oxide sheet. When the tip of the prepared graphene oxide sheet was brought into contact with molten sodium (Na) at 300°C, a spark reaction occurred immediately and a sheet of sparked reduced graphene oxide (sGO) was prepared. .

Manufacturing Example 2

The wet sheet (sGO sheet) prepared in Preparation Example 1 was brought into contact with liquid sodium to prepare a sparked reduced graphene oxide (Na-sGO) sheet in the form of impregnating liquid sodium into the sGO sheet through capillary phenomenon.

Comparative Production Example 1

Graphene oxide (GO) solution was applied on a copper foil by drop casting, and then peeled from the copper foil to prepare a graphene oxide sheet.

Comparative Production Example 2

The graphene oxide sheet prepared in Comparative Example 1 was heated at 130° C. for 1 hour in an argon (Ar) atmosphere to prepare a preheated graphene oxide (pGO) sheet.

Example 1

The sodium secondary battery (Na-NiCl ₂ battery) was manufactured in the form of a planar cell, and the negative and positive battery cases, alpha alumina (α-Al ₂ O ₃ ) fixture, and beta alumina (solid electrolyte) It is composed of β"-Al ₂ O ₃ ) disks (3cm ² active area). Beta alumina disks are glass-sealed to an alpha alumina fixture between the positive and negative electrodes to separate the cathode and the anode. The Na-NiCl ₂ battery is assembled in a discharged state, and a trace amount of solid sodium (< 5mg) is coated on the surface of beta alumina (β″-Al ₂ O ₃ ). Thereafter, a sheet of sparked reduced graphene oxide (sGO) prepared in Preparation Example 1 was stacked on one side, and a solid electrolyte layer was prepared by raising the temperature to 175° C. A trace amount of sodium is β″-Al ₂ O ₃ The prepared solid electrolyte layer was prepared so that the side on which sodium was formed was positioned on the negative electrode, and the positive electrode was composed of Ni, NaCl (Ni/NaCl molar ratio = 1.82) and ~1 g of the positive electrode additive. It consists of anodic granules and a molten anolyte containing NaAlCl ₄ .

Comparative Example 1

The same method as in Example 1 except that beta alumina (β"-Al ₂ O ₃ ), which is an untreated solid electrolyte, was used instead of using the sparked reduced graphene oxide (sGO) sheet prepared in Preparation Example 1 A sodium secondary battery was prepared.

Comparative Example 2

A sodium secondary battery was manufactured in the same manner as in Example 1, except that the preheated graphene oxide (pGO) prepared in Comparative Preparation Example 2 was used instead of the sparked reduced graphene oxide (sGO) sheet prepared in Preparation Example 1. .

Experimental Example 1

To confirm the shape of the sparked reduced graphene oxide (sGO) sheet according to the present invention, a digital camera targeting the graphene oxide sheets prepared in Preparation Example 1, Preparation Example 2, Comparative Preparation Example 1 and Comparative Preparation Example 2 And a field emission scanning electron microscope (FE-SEM), and the results are shown in FIG. 2. In addition, the specific surface area of the graphene oxide sheet prepared in Preparation Example 1 was measured, and the results are shown in FIG. 3.

2(a) is an image photographed with a digital camera of graphene oxide sheets prepared in Preparation Example 1, Preparation Example 2, Comparative Preparation Example 1, and Comparative Preparation Example 2. FIG. 2 (b) to (e) are images of graphene oxide sheets prepared in Preparation Example 1, Preparation Example 2, Comparative Preparation Example 1 and Comparative Preparation Example 2 taken with a field emission scanning electron microscope, The second line is a cross-sectional area shot, and the third line is an in-plane shot. 2, the graphene oxide sheet of Comparative Preparation Example 1 is typically a densely stacked structure, and the graphene oxide sheet of Comparative Preparation 1 and the preheated graphene oxide (pGO) sheet of Comparative Preparation 2 are interlayered. Because the interlayer gap size is very small, it is difficult to observe the difference between the two materials. On the other hand, looking at FIG. 2(d), it can be seen that the sparked reduced graphene oxide of Preparation Example 1 has a nanogap of several tens of sizes between the graphene oxide sheets. Specifically, when looking at the inserted image in the second row of FIG. 2(d), a uniform pore structure of several tens of nanometers and several layers of reduced graphene oxide sheets are formed, so that a nanogap of several hundred nanometers can be confirmed. . In addition, when looking at the planar image of FIG. 2(d), it can be seen that the sheet surface is porous after the spark reaction. In addition, the sheet prepared in Preparation Example 2 of FIG. 2(e) is prepared by injecting liquid sodium into Preparation Example 1, and while maintaining a uniform graphene layer structure, liquid sodium is uniformly filled in the nanogap, and the sGO sheet surface is It can be seen that it is covered with sodium.

3 is a graph measuring the specific surface area of the sparked reduced graphene oxide prepared in Preparation Example 1. Referring to FIG. 3, the BET specific surface area of the sparked reduced graphene oxide sheet according to the present invention is 292.83 m ^2. /g, and that the BET specific surface area of the graphene oxide sheet increases by more than 30 times to 8.0 m ^2. /g. Able to know. Accordingly, by using the sparked reduced graphene oxide sheet, wettability for a liquid metal (eg, liquid sodium) in the pore structure may be improved.

Experimental Example 2

In order to confirm the chemical properties of the wet sheet according to the present invention, X-ray diffraction analysis (X-ray diffraction, XRD) and Fourier analysis of the graphene oxide prepared in Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2 Fourier transform infrared (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Raman spectroscopy analysis experiments were performed, and the results are shown in FIGS. 4 to 7 .

4 is an X-ray diffraction (XRD) result graph of graphene oxide sheets prepared in Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2. FIG. 4, it can be seen that the diffraction pattern of the graphene oxide sheet of Comparative Preparation Example 1 has a (002) peak at a 2θ value of 10.52° and an interlayer spacing of 0.84 nm. In addition, when the 2θ value is 26.18°, a graphitic peak can be observed, and it can be seen that the interlayer spacing is 0.34 nm. Through this, it can be seen that the graphene oxide sheet includes the sp ³ domain of the oxidized region and the sp ² domain of the graphite region, and the sp ³ region is wider. In addition, the preheated graphene oxide sheet of Comparative Preparation Example 2 can confirm the (002) diffraction peak at 12.2°, which is a 2θ value slightly shifted to the elevation side than Comparative Preparation Example 1, and the interlayer spacing is about 0.72 nm. I can. It seems that the interlayer spacing is reduced than that of graphene oxide because pre-absorbed moisture between the graphene sheets is removed. In the sparked reduced graphene oxide (sGO) sheet of Preparation Example 1, the peak at a 2θ value of 10.52° disappeared, and it can be seen that oxygen functional groups were effectively removed.

5 is a graph showing the results of Fourier transform infrared spectroscopy of graphene oxide prepared in Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2. FIG. Referring to Figure 5, Comparative Preparation Example 1 can determine the hydroxyl group (-OH) with a broad peak with a peak of 1390cm ^-1 of 3000cm ^-1, 1249cm ^-1 and 1052cm ^-1-carbonyl group and a peak of 1716cm ^-1 peak The epoxy group of can be confirmed. On the other hand, in Preparation Example 1, almost no hydroxyl peak was detected after the spark reaction. In addition, in Comparative Preparation Example 2, residual moisture in graphene was removed several times as a result of the heat treatment, so that the hydroxyl group peak was significantly reduced, and although there was a slight peak shift, a more stable epoxy group could be confirmed. Through this, it can be seen that in the wet sheet according to the present invention, most of the hydroxyl groups are removed by the spark reaction.

6 is an X-ray photoelectron spectral spectrum result graph of graphene oxide prepared in Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2. FIG. 6(a), Preparation Example 1 had a C/O atomic ratio of 7.34, Comparative Preparation Example 1 had a C/O atomic ratio of 2.47, and Comparative Preparation Example 3 had a C/O atomic ratio of 3.21. It can be seen that the sparked reduced graphene oxide (sGO) of Example 1 significantly reduces the oxygen ratio. Referring to FIG. 6(b), as a C 1s graph, it can be seen that in the case of Preparation Example 1, the peak (286.5 eV) corresponding to C-OH decreases by about 52% compared to Comparative Preparation Example 1 after the spark reaction.

7 is a graph of Raman spectral analysis results of graphene oxide prepared in Preparation Example 1, Comparative Preparation Example 1 and Comparative Preparation Example 2. FIG. 7 can confirm thermal oxidation. Referring to FIG. 7, the sparked reduced graphene oxide (sGO) of Preparation Example 1 has a G band of 1589 cm ^-1 , and the preheated graphene oxide (pGO) of Comparative Preparation 2 has a G band of 1603 cm ^-1 It can be seen that the graphene oxide (GO) of Comparative Preparation Example 1 is located at 1609 cm ^-1 in the G band. In addition, Preparation Example 1 has a ratio of D band and G band (I _D / I _G ) value of 0.93, Comparative Preparation Example 1 has an I _D / I _G value of 1.08, Comparative Preparation Example 2 is I _D / I _G You can see that the value is 1.02. Through this, it can be seen that the sp ² region of the graphene oxide of Preparation Example 1 and Comparative Preparation 2 is removed while the oxygen functional group is removed, and in particular, the sparked reduced graphene oxide (sGO) of Preparation Example 1 is Comparative Preparation Example 1 It can be seen that compared to and 2, it has a more graphical area.

Experimental Example 3

In order to confirm the affinity of the wet sheet according to the present invention with liquid sodium, liquid sodium was added dropwise for Preparation Example 1 and Comparative Preparation Example 2 to determine the time and rate at which liquid sodium was absorbed and the number of absorbed liquid sodium atoms. It was measured, and the results are shown in FIGS. 8 to 10.

In the experiment, molecular dynamics simulation (MD Simulation) was performed to observe liquid sodium transport in Preparation Example 1 and Comparative Preparation Example 2. The simulation setup is as shown in Fig. 8(a), and the capillaries of Preparation Example 1 and Comparative Preparation Example 2 are located between a feed reservoir and a permeate reservoir composed of graphene to separate the two reservoirs. . Initially, the capillary and permeate reservoir are empty, and a fixed number of 46216 Na atoms corresponding to a density of 0.927 g/cm ³ is filled in the feed reservoir. The movement of liquid Na moves from the supply reservoir to the permeation reservoir through the capillary, and molecular dynamics simulations were performed for channels with 10 different interlayer gaps of 0.49 nm to 3.92 nm, which is graphene (0.34 nm). , Similar to the interlayer spacing of preheated graphene oxide (0.34nm-1.35nm) and sparked reduced graphene oxide (~4.2nm). In the simulation, the structures of pGO and sGO consist only of hydroxyl groups and epoxy groups on the carbon plane. Detailed composition information (eg oxygen concentration, functional group ratio) for the two materials is shown in Table 1 below. The carboxyl and carbonyl groups present mainly at the edges of graphene oxide (GO) were ignored in molecular dynamics simulations to focus on the graphene oxide surface-liquid Na surface interaction.

Sample Gr pGO Sparked-rGO Oxygen concentration 0 % 26.96% 12.84% Epoxy: Hydroxyl - 2.45: 1 4.19: 1 Interaction energy - -157.226(kcal/mole) -191.563
(kcal/mole)

Looking at (b) and (c) of Figure 8, in all simulations, sodium (Na) atoms enter the preheated graphene (pGO) and sparked reduced graphene oxide (sGO) capillaries, and through the capillary, the permeation reservoir from the supply reservoir. There was a tendency to go. With the interlayer spacing of graphene (Gr, d = 0.49 nm), preheated graphene oxide (pGO, d = 0.74 nm), and sparked reduced graphene oxide (sGO, d = 3.92 nm), it is transmitted through a capillary to the storage reservoir. The number of introduced sodium atoms was monitored as a function of time as shown in FIG. 8 (b). Referring to (d) and (e) of FIG. 8, the capillary tube completely reached the saturated state with liquid sodium within 50 ps for all cases. In FIG. 8(b), in the case of graphene and preheated graphene oxide (pGO), significant permeation of sodium atoms was not observed. However, in the range of d> 0.5 nm, the flow velocity gradually increases with the width of the capillary tube as shown in (c) of FIG. 8. This indicates that given the atomic radius of Na (0.23 nm), an interlayer spacing of d> 0.5 nm is required for the flow of liquid Na. However, in the case of a large-sized capillary tube, the Na atom concentration in the supply reservoir rapidly decreases due to the rapid permeation process, leading to a small pressure difference between the two reservoirs at 400 ps, thus slowing the penetration between the reservoirs. This is why the curve of the number of Na atoms penetrating into the capillary tube at 400 ps has a flat area in the capillary gap size area of 3 to 4 nm (Fig. 8(c)). As a result, it can be seen that the permeation amount of Na atoms through rGO capillaries (Fig. 8(b)) (13,193 atoms) for 400 ps is much greater than that of Gr (0 atoms) and GO capillaries (109 atoms).

Looking at (c) of FIG. 8, in order to check the increased transmittance of the sGO capillary according to the size of the interlayer gap compared to pGO (d = 0.74 nm), sGO (P _{sGO, d=0.4~4.0} ) and The ratio of the permeation rate of pGO (P _{GO, d=0.74} ) was calculated. It was confirmed that in the range of the general sGO interlayer spacing (d=3.0 ~ 4.0nm), the transmission rate of liquid Na through the sGO channel was 20 times faster than that of the pGO channel (d=0.74nm). Through this, it can be seen that sGO can be used as a better Na reservoir than GO. Through the molecular dynamics simulation, it can be seen that the sparked reduced graphene oxide (sGO) sheet having a wider interlayer spacing and an appropriate concentration of oxygen functional groups has structural and chemical advantages in the penetration behavior of liquid Na. have.

Figure 8 (d) and (e) artificially examined the behavior of liquid sodium for each interlayer interval in the simulation. In an actual experiment, not a simulation, it was confirmed that the preheated graphene oxide (pGO) had an interlayer spacing of 0.74 nm and the sparked reduced graphene oxide (sGO) had an interlayer spacing of ~4 nm. Specifically, FIGS. 8D and 8E illustrate the flow behavior of liquid sodium while changing the interlayer spacing of pGO of Comparative Example 1 and sGO of Example 1 from 0.49 nm to 3.92 nm. In order to compare with the actual experiment, it is meaningful to compare pGO (0.74 nm) and sGO (3.92 nm) similar to the interlayer spacing shown in the experiment in the simulation as shown in FIG. 8(b). Specifically, Figure 8 (d) and (e) are seen while changing the interlayer spacing of pGO and sGO equally, and seeing that the amount of absorbed sodium is similar under the same interlayer spacing, the flow of liquid sodium (Na) is C It can be seen that the interlayer spacing is more affected than the /O ratio.

9 is an image photographing a liquid sodium absorption process of graphene oxide of Preparation Example 1 and Comparative Preparation Example 2, (a) is an image of Preparation 1, and (b) is an image of Comparative Preparation 2. Referring to (a) of FIG. 9, it can be seen that the sparked reduced graphene oxide (sGO) of Preparation Example 1 is injected with liquid sodium very quickly, so that the liquid sodium spreads over the entire sGO sheet within a short time of less than 1 second. On the other hand, referring to (b) of FIG. 9, it can be seen that the injection rate of liquid sodium is very slow in the sheet of Comparative Preparation Example 2 due to the small interlayer gap size. Further, in addition to liquid sodium, liquid lithium and liquid potassium were also tested and the results are shown in FIG. 10, it can be seen that the sheet of Preparation Example 1 also rapidly absorbs liquid lithium and liquid potassium.

Experimental Example 4

In order to confirm the surface properties of the beta alumina containing the wet sheet according to the present invention, the sheets of Preparation Example 1 and Comparative Preparation Example 2 were formed on one side of the beta alumina and pure beta alumina (bare β″-Al ₂ O ₃ ) As a subject, a contact angle experiment for liquid sodium according to temperature (150°C to 300°C) was performed, and the results are shown in FIG. 11.

Referring to FIG. 11, the wettability of liquid sodium in beta alumina is significantly lowered at low temperatures. Specifically, in the case of pure beta alumina, it can be seen that the contact angle of liquid sodium is 112° at a temperature of 150° C., and when the temperature is lowered from 300° C. to 80°, the contact angle rapidly decreases. In the case of the beta alumina formed in Comparative Preparation Example 2 on one side, the contact angle of liquid sodium was 76° at a temperature of 150° C., and 58° at 300° C., so the contact angle was smaller than that of pure beta alumina, but still wetting for liquid sodium was Seems to be low. On the other hand, it can be seen that the beta alumina formed on one side of the sheet of Preparation Example 1 exhibits a contact angle of 0° at the total temperature, and thus has excellent wettability to liquid sodium. Through this, it can be seen that the wet sheet according to the present invention increases the contact area between the beta alumina and the liquid sodium, thereby improving the performance of the sodium beta-alumina battery.

Experimental Example 5

In order to evaluate the battery characteristics of the sodium beta-alumina battery comprising the wet sheet according to the present invention, charging/discharging experiments were conducted on the batteries of Example 1, Comparative Example 1 and Comparative Example 2 according to the present invention, The results are shown in FIG. 12.

12 is a charge/discharge experiment result of the batteries prepared in Example 1, Comparative Example 1 and Comparative Example 2, (a) is a graph showing the initial cycle voltage characteristics of the battery, (b) is prepared in Example 1 Voltage-capacity change graph according to several charge/discharge cycles of one battery, (c) is a voltage-capacity graph of sodium beta-alumina battery containing pure beta alumina of Comparative Example 1, and (d) is Example It is a graph showing the change in Ttareung capacity and Coulomb efficiency according to the number of charge/discharge cycles of the battery prepared in 1. Referring to FIG. 12(a), in the initial cycle, the battery of Example 1 was charged with 74 mAh, but the battery of Comparative Example 2 had a relatively low charging capacity of 30 mAh. Compared with the battery of Example 1, it can be seen that the voltage rise of the battery of Comparative Example 2 starts from a much lower charging capacity and reaches a cut-off voltage (2.8 eV) first. This is because the pGO sheet of Comparative Example 2 has a small surface area, a high oxygen content, and a small interlayer spacing, as can be seen in the molecular dynamics experiment and the liquid metal wettability experiment, so that the inflow of liquid sodium from the pGO sheet is difficult compared to the sGO sheet. . The secondary battery containing pure beta alumina (Bare β″-Al ₂ O ₃ ) of Comparative Example 2 was barely charged up to 20mAh, and due to the inefficient use of the anode material due to low sodium wetting properties. It showed very high overvoltage.

During the cycling test with a constant current of 10mA (3.4mA/cm ² ) and a cut-off voltage between 1.8 and 2.8V, looking at (b) of FIG. 12, the secondary battery of Example 1 is pure beta alumina (bare β″ It can be seen that unlike secondary batteries containing -Al ₂ O ₃ ), it shows very low overpotential and stable cycle performance. In addition, the charging capacity of the secondary battery (sGO-cell) of Example 1 was 70mAh in the first cycle and increased to 120mAh in the 11th cycle. This increase in capacity is due to the increased active area (Na/β"-Al ₂ O ₃ interface) through infusion and spreading of liquid sodium into the sparked reduced graphene oxide (sGO) sheet. Looking at (d) of Figure 8, it is shown that the coulomb efficiency is maintained at almost 100% during the 11 cycles of the secondary battery of Example 1. Through these results, sparked reduced graphene oxide (sGO) according to the present invention It can be seen that the sheet provides a stable channel of liquid sodium flow during the charging and discharging process, whereas the initial cycle achieved a low coulombic efficiency of 85% due to the liquid sodium remaining in the reduced graphene oxide (sGO) sheet sparked after discharge. However, as shown in Fig. 12(c), the secondary battery containing pure beta alumina (bare β″-Al ₂ O ₃ ) showed limited capacity for 11 cycles, which is between Na and β″-Al ₂ O ₃ This is due to poor Na wetting of bare β″-Al ₂ O ₃ which induces a small contact area of.

Claims (13)

A solid electrolyte including sparked reduced graphene oxide (sGO) and beta alumina (β″-Al ₂ O ₃ ); And
Secondary battery comprising a negative electrode (anode) containing a liquid metal. The method of claim 1,
The sparked reduced graphene oxide has a graphene interlayer spacing of 3 nm to 4.5 nm,
A secondary battery comprising a liquid metal between the graphene layers. The method of claim 1,
The secondary battery, characterized in that the thickness of the sparked reduced graphene oxide is 100 μm to 400 μm. The method of claim 1,
The secondary battery, characterized in that the carbon / oxygen (C / O) atomic ratio of the sparked reduced graphene oxide is 5 or more. The method of claim 1,
The liquid metal is a secondary battery, characterized in that at least one selected from the group consisting of sodium (Na), lithium (Li) and potassium (K). The method of claim 1,
Sparked reduced graphene oxide is a secondary battery, characterized in that formed between the beta alumina and the negative electrode. Preparing a sparked reduced graphene oxide sheet by contacting the graphene oxide sheet with a liquid metal;
Laminating the prepared sparked reduced graphene oxide sheet on one side of beta alumina to prepare a solid electrolyte; And
A method of manufacturing a secondary battery comprising the step of forming a negative electrode including a liquid metal through a charging reaction on the surface on which the sparked reduced graphene oxide sheet of the solid electrolyte is formed. The method of claim 7,
The step of preparing the sparked reduced graphene oxide sheet is a method of manufacturing a secondary battery, characterized in that it is performed by contacting the graphene oxide sheet with a molten liquid metal at a temperature of 200°C to 400°C. The method of claim 7,
In the step of preparing a sparked reduced graphene oxide sheet, the sparked reduced graphene oxide sheet is formed to a thickness of 100 μm to 400 μm,
The prepared sparked reduced graphene oxide sheet is a method of manufacturing a secondary battery, characterized in that the interval between graphene layers is 3nm to 4.5nm. The method of claim 7,
The sparked reduced graphene oxide sheet prepared in the step of preparing a sparked reduced graphene oxide sheet has a carbon/oxygen (C/O) atomic ratio of 5 or more. The method of claim 7,
The manufacturing method of a secondary battery, characterized in that the step of preparing the solid electrolyte is formed by laminating a sparked reduced graphene oxide sheet on one side of the beta alumina. The method of claim 7,
Forming the negative electrode is a method of manufacturing a secondary battery, characterized in that the liquid metal fills the negative electrode through a charging reaction, and the liquid metal is filled in the sparked reduced graphene oxide sheet. The method of claim 12,
In the step of forming a negative electrode, the liquid metal is at least one selected from the group consisting of sodium (Na), lithium (Li), and potassium (K).

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