Negative electrode for zinc-ion hybrid supercapacitor, comprising carbon-based composite protective layer, manufacturing method therefor, and zinc-ion hybrid supercapacitor

Abstract

The present invention relates to a negative electrode for a zinc-ion hybrid supercapacitor, comprising a carbon-based composite protective layer, a manufacturing method thereof, and a zinc-ion hybrid supercapacitor, wherein the negative electrode comprises: a zinc substrate; and a carbon-based composite protective layer positioned on the zinc substrate and including a graphene protective layer containing graphene and a carbon nanotube protective layer containing carbon nanotubes.

Description

Anode for a zinc-ion hybrid supercapacitor comprising a carbon-based composite protective layer, a method for manufacturing the same, and a zinc-ion hybrid supercapacitor

[0001] The present invention relates to a negative electrode of a zinc-ion hybrid supercapacitor. In particular, the present invention relates to a negative electrode for a zinc-ion hybrid supercapacitor comprising a carbon-based composite protective layer, a method for manufacturing the same, and a zinc-ion hybrid supercapacitor.

[0002] This application claims priority to Korean Patent Application No. 10-2023-0130072, filed September 27, 2023, and Korean Patent Application No. 10-2023-0179188, filed December 12, 2023, the entire contents of which are disclosed in the specification and drawings of the above applications are incorporated herein by reference.

[0003] Meanwhile, the present invention was supported by the following national research and development project.

[0004] Assignment ID: 2710004376

[0005] Assignment Number: RS-2024-00342112

[0006] Ministry of Science and ICT

[0007] Project Management Agency Name: National Research Foundation of Korea

[0008] Research Project Name: Individual Basic Research (Ministry of Science and ICT)

[0009] Research Project Title: Implementation of a High-Energy-Density Fiber-Type Power Source and Investigation of the Correlation Between Faraday Reaction and Inductive Charge Separation for Self-Charging

[0010] Project implementation organization name: Gyeongsang National University

[0011] Research period: May 1, 2024 - April 30, 2025

[0012] Environmental concerns and energy issues surrounding the use of fossil fuels have fueled growing interest in generating electricity using renewable energy sources such as solar and wind. However, the output of solar and wind power is not always stable and consistent due to unexpectedly diverse environmental and geographical conditions. To efficiently utilize variable renewable and clean energy, an electrical energy storage (EES) system capable of achieving high energy / power density and excellent cycling stability is required.

[0013] As renewable energy sources are gaining recognition as new sustainable energy sources, the demand for energy storage devices capable of storing and utilizing energy is increasing. Advances in energy storage technology are crucial to supplying efficient energy systems that meet demand. Among various energy storage technologies, aqueous electrolyte-based zinc-ion hybrid supercapacitors (ZIHCs) are attracting attention as a next-generation energy storage technology due to their low manufacturing cost, excellent stability, and high power density. This is due to the natural abundance of zinc, the stability of the aqueous electrolyte, and the low cathode potential of zinc metal. However, they have drawbacks such as relatively low energy density, performance degradation due to side reactions and corrosion on the zinc surface, and electrical short circuits caused by uneven dendrite growth. Therefore, an ideal zinc anode must satisfy three critical conditions: suppression of surface dendrite growth, corrosion, and side reactions.

[0014] To overcome these issues, various methods are being introduced, and among them, the approach of introducing a protective layer onto the surface of the zinc anode is attracting significant attention. Currently, protective layers using carbon materials, metal oxides, and polymers are being used, but these are still insufficient to achieve superior energy storage performance. Research and development on carbon-based protective layers is particularly needed.

[0015] Graphene has recently been recognized as a carbon-based protective layer capable of enhancing energy storage performance. However, graphene's two-dimensional planar structure suffers from performance degradation at high current densities due to uneven zinc ion deposition, dendrite growth, and a lack of numerous nucleation sites.

[0016] The present invention was conceived to solve the above-described problem, and aims to provide a negative electrode for a zinc-ion hybrid supercapacitor including a carbon-based composite protective layer, a method for manufacturing the same, and a zinc-ion hybrid supercapacitor.

[0017] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0018] A negative electrode for a zinc-ion hybrid supercapacitor according to the present invention comprises a zinc substrate and a carbon-based composite protective layer positioned on the zinc substrate, the carbon-based composite protective layer comprising a graphene protective layer including graphene and a carbon nanotube protective layer including carbon nanotubes.

[0019] In addition, the present invention includes a method for manufacturing a negative electrode for a zinc-ion hybrid supercapacitor, including a step of first coating a first solution of a mixture of graphene and a solvent on the surface of a zinc substrate and then drying it to form a graphene protective layer, and a step of second coating a second solution of a mixture of carbon nanotubes and a solvent on the surface of the graphene protective layer and then drying it to form a carbon nanotube protective layer.

[0020] The present invention further includes a negative electrode for a zinc-ion hybrid supercapacitor manufactured by the above manufacturing method.

[0021] The present invention further includes a zinc-ion hybrid supercapacitor including the above-described negative electrode.

[0022] According to the present invention as described above, by applying a carbon-based composite protective layer including a graphene protective layer and a carbon nanotube protective layer to a zinc substrate, it is possible to increase nucleation sites, suppress dendrites due to uniform deposition, and improve performance at high current densities.

[0023] In particular, the graphene protective layer is primarily formed on the surface of the zinc substrate and directly protects the surface of the zinc substrate, thereby suppressing surface dissolution and formation of by-products.

[0024] And the carbon nanotube protective layer is formed on the surface of the graphene protective layer, i.e., the top layer of the zinc substrate, to provide a large specific surface area and a one-dimensional network structure, which effectively suppresses the increase of nucleation sites and dendrite growth. Furthermore, the carbon nanotube protective layer using carbon nanotubes (FNCNT) doped with non-metallic elements such as fluorine (F) and nitrogen (N) improves wettability with the electrolyte, thereby further enhancing ion diffusion capacity and electrical characteristics.

[0025] As a result, by applying a carbon-based composite protective layer consisting of a graphene protective layer and a carbon nanotube protective layer that can be doped with a non-metallic element to a zinc substrate, it has the effects of surface protection, reduction of interfacial resistance, provision of many nucleation sites, and improvement of wettability with electrolyte, and when used as a negative electrode of a zinc-ion hybrid supercapacitor, it can secure energy density and cycle stability and impart fast ion transport capability at high current density.

[0026] The effects of the present invention are not limited to those mentioned above, and also include other effects that are not explicitly mentioned, although they can be clearly understood by those skilled in the art from the description throughout the specification.

[0027] Figure 1 is a schematic diagram showing the manufacturing process of a zinc cathode according to one embodiment of the present invention.

[0028] Figure 2 shows the results of experiments conducted to compare the surface structure and state of zinc cathodes (related to Experimental Example 1).

[0029] Figure 3 shows the results of an experiment conducted to compare the wettability of zinc cathodes (related to Experimental Example 2).

[0030] Figure 4 shows the results of an experiment conducted to show that fluorine (F) and nitrogen (N) were doped into carbon nanotubes (related to Experimental Example 3).

[0031] Figure 5 shows the results of experiments conducted to compare the stability of zinc cathodes and the uniform growth of zinc (related to Experimental Example 4).

[0032] Figure 6 shows the results of an experiment to compare the ion transfer capabilities of zinc cathodes (related to Experimental Example 5).

[0033] Figure 7 shows the results of an experiment to compare the energy storage capacity of zinc cathodes (related to Experimental Example 6).

[0034] Figures 8 and 9 show the results of an experiment conducted to compare the dendrite suppression capabilities of zinc cathodes (related to Experimental Example 7).

[0035] Figures 10 and 11 show the results of an experiment to compare the cycling stability (life characteristics) of zinc cathodes (related to Experimental Example 8).

[0036] Figure 12 is a schematic diagram showing the role and effect of a carbon-based composite protective layer according to one embodiment of the present invention.

[0037] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention, and methods for achieving them, will become clear with reference to the embodiments described in detail below together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

[0038] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise.

[0039] The terms "comprises" and / or "comprising" as used in the specification do not exclude the presence or addition of one or more other components, steps, operations and / or elements.

[0040]

[0041] The present invention relates to a cathode for a zinc-ion hybrid supercapacitor, and the present invention will be described in detail below.

[0042] A negative electrode for a zinc-ion hybrid supercapacitor according to the present invention comprises a zinc substrate and a carbon-based composite protective layer positioned on the zinc substrate, the carbon-based composite protective layer including a graphene protective layer including graphene and a carbon nanotube protective layer including carbon nanotubes.

[0043] That is, the cathode according to the present invention includes a carbon-based protective layer, and by including both a protective layer made of graphene and a protective layer made of carbon nanotubes, it can exhibit superior cathode performance compared to cases with only a graphene protective layer or only a carbon nanotube protective layer. The effect of including both is described in detail in the experimental examples below.

[0044] As the zinc substrate, zinc foil, etc. may be used, and without particular limitation, any zinc substrate that contains zinc and can be used as a current collector or negative electrode active material may be used.

[0045] Meanwhile, the stacking order of the graphene protective layer and the carbon nanotube protective layer in the carbon-based composite protective layer is very important for the characteristics of the cathode, and according to one embodiment of the present invention, it is preferable to have a structure in which the graphene protective layer is first formed on the surface of the zinc substrate, and the carbon nanotube protective layer is secondarily formed on the surface of the graphene protective layer. That is, they are stacked in the order of zinc substrate - graphene protective layer - carbon nanotube protective layer. This is because 1) the carbon nanotube protective layer is preferably formed on the top layer that is in direct contact with the electrolyte because it has better wettability with the electrolyte than the graphene protective layer (see Experimental Example 2), 2) the carbon nanotube protective layer has more nucleation sites than the graphene protective layer and can suppress the growth of irregular dendrites so it is preferably formed on the top layer (see Experimental Example 7), and 3) the graphene protective layer is preferably formed on the surface of the zinc substrate because it suppresses surface dissolution of the zinc anode and formation of by-products more effectively than the carbon nanotube protective layer (see Experimental Example 8).

[0046] Meanwhile, it is preferable that the carbon nanotubes are doped with one or more non-metallic elements selected from the group consisting of fluorine (OF), nitrogen (N), oxygen (O), phosphorus (P), boron (B), and sulfur (S). More specifically, it is preferable that the carbon nanotubes (FNCNTs) are doped with fluorine (F) and nitrogen (N). Such carbon nanotubes doped with non-metallic elements improve wettability with electrolytes compared to existing carbon nanotubes, thereby further improving ion diffusion capability and electrical characteristics. In particular, doping with fluorine (F) can improve wettability, and doping with nitrogen (N) can improve electrical characteristics.

[0047] The anode for a zinc-ion hybrid supercapacitor according to the present invention preferably has a water contact angle of less than 80°. More preferably, it may be 10° to 70°, and even more preferably, it may be 10° to 65°. Here, the water contact angle specifically refers to the water contact angle with respect to the surface of the carbon nanotube protective layer located on the uppermost layer of the anode (if doped with a non-metallic element, it becomes a carbon nanotube protective layer doped with a non-metallic element). As such, it has the characteristic of excellent wettability with an aqueous electrolyte due to its low water contact angle.

[0048] Meanwhile, the graphene forming the graphene protective layer and the carbon nanotube forming the carbon nanotube protective layer have specific surface areas of 10 to 500 m2, respectively. 2 g -1 It is desirable. In particular, the specific surface area of ​​the carbon nanotubes located at the top layer is important, and more specifically, the specific surface area of ​​the carbon nanotubes is 50 to 150 m 2 g -1 It is desirable that it is 10 m 2 g -1 If it is smaller than 500 m, compatibility with the electrolyte may be reduced, which may result in poor performance. 2 g -1 This is because if it is larger, the stability or electrical conductivity of the carbon structure may decrease.

[0049] Meanwhile, the ratio of the thickness of the graphene protective layer to the thickness of the carbon nanotube protective layer may be 1:1 to 5:1, and preferably 2:1 to 3:1. That is, the thickness of the graphene protective layer may be thicker than the thickness of the carbon nanotube protective layer.

[0050] Meanwhile, a method for manufacturing a negative electrode for a zinc-ion hybrid supercapacitor according to an embodiment of the present invention includes a step of first coating a first solution of a mixture of graphene and a solvent on the surface of a zinc substrate and then drying the solution to form a graphene protective layer, and a step of second coating a second solution of a mixture of carbon nanotubes and a solvent on the surface of the graphene protective layer and then drying the solution to form a carbon nanotube protective layer.

[0051] The solvent mixed with the above graphene or carbon nanotube may be a polar solvent, and specifically may be one of N-methylformamide (NMF), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dipropylene glycol monomethyl ether (DPM), sulfolane, N-methyl-2-pyrrolidone (NMP), N-ethyl pyrrolidone (N-ethyl pyrrolidone), and dipropylene glycol monoethyl ether (DPE). Among these, N-methyl pyrrolidone (NMP) may be particularly preferable.

[0052] As described above, the carbon nanotube is preferably a carbon nanotube doped with one or more non-metallic elements selected from the group consisting of fluorine (F), nitrogen (N), oxygen (O), phosphorus (P), boron (B), and sulfur (S), and more specifically, it may be a carbon nanotube (FNCNT) doped with fluorine (F) and nitrogen (N) manufactured by mixing a powder-type carbon nanotube and an aqueous solution of ammonium fluoride (NH4F) and heat-treating the mixture at a temperature of 400 to 900°C in a nitrogen atmosphere for 30 minutes to 3 hours. More specifically, the heat treatment time may be 1 to 2 hours.

[0053] Here, the concentration of the ammonium fluoride (NH4F) aqueous solution may be 0.1 to 5 M, and more specifically, 0.5 to 2 M. This is because if it is less than 0.1 M, structural defects may occur due to a lack of fluorine (F) and nitrogen (N), i.e., doping elements, and if it is more than 5 M, the existing carbon may be burned due to an excess of doping elements.

[0054] Meanwhile, the ratio (weight ratio) of the coating amount of the first solution mixing graphene and a solvent to the coating amount of the second solution mixing carbon nanotubes and a solvent may be 1:1 to 5:1, and preferably 2:1 to 3:1.

[0055] The present invention further includes a negative electrode for a zinc-ion hybrid supercapacitor manufactured by the above-described manufacturing method. The present invention further includes a zinc-ion hybrid supercapacitor including the above-described negative electrode.

[0056]

[0057] Below, specific embodiments and experimental examples of the present invention are examined.

[0058]

[0059] Example 1: Zinc cathode comprising a graphene protective layer and a CNT protective layer

[0060] A 50 ㎛ thick zinc foil was prepared as a zinc substrate, and washed with ethanol to remove any oily residue or other contaminants that may exist on the surface. Then, 15 ㎕ of a first solution containing a mixture of graphene and NMP solvent was first coated on the surface of the washed zinc substrate, and then dried to form a graphene protective layer. Then, 3 ㎕ of a second solution containing a mixture of carbon nanotubes (CNTs) and NMP solvent was secondarily coated on the surface of the graphene protective layer, and then dried to form a carbon nanotube protective layer. The drying was performed in an oven at 80°C. The graphene used had a specific surface area of ​​22.8 m 2 g -1The specific surface area of ​​the carbon nanotube (CNT) used is 117.4 m 2 g -1 am.

[0061]

[0062] Example 2: Zinc cathode comprising a graphene protective layer and a FNCNT protective layer

[0063] A zinc anode was manufactured in the same manner as in Example 1, except that a carbon nanotube protective layer was formed using carbon nanotubes (FNCNT) doped with fluorine (F) and nitrogen (N) instead of carbon nanotubes (CNT). The carbon nanotubes (FNCNT) used were manufactured by mixing carbon nanotube (CNT) powder and a 1 M ammonium fluoride (NH4F) aqueous solution prepared by dissolving 0.37 g of ammonium fluoride (NH4F) in 10 ml of distilled water, and heat-treating the mixture at 500°C in a nitrogen atmosphere. The carbon nanotubes (FNCNT) manufactured in this way have a structure in which fluorine (F) and nitrogen (N) are doped in the carbon lattice. The doping is described in detail in Experimental Example 3.

[0064]

[0065] Comparative Example 1: Zinc cathode containing only a graphene protective layer

[0066] A zinc anode was manufactured in the same manner as in Example 1, but after forming the graphene protective layer, the carbon nanotube protective layer was not formed and the zinc anode was dried to finish the manufacturing process.

[0067]

[0068] Comparative Example 2: Zinc cathode containing only a CNT protective layer

[0069] A zinc anode was manufactured in the same manner as in Example 1, but only a carbon nanotube protective layer was formed without forming a graphene protective layer, and then dried to finish.

[0070]

[0071] The above examples and comparative examples are summarized in Table 1 below.

[0072] ClassificationBare ZnExample 1Example 2Comparative Example 1Comparative Example 2Graphene protection layer-OOOXCarbon nanotube protection layer-O(CNT)O(FNCNT)XO(CNT)

[0073] In the drawings below, the zinc anode in the zinc substrate state without a protective layer is indicated as Bare Zn, the zinc anode of Comparative Example 1 in which only a graphene protective layer is formed is indicated as G-Zn, the zinc anode of Comparative Example 2 in which only a carbon nanotube (CNT) protective layer is formed is indicated as CNT-Zn, the zinc anode of Example 1 in which a graphene protective layer and a carbon nanotube (CNT) protective layer are formed is indicated as CNT@G-Zn, and the zinc anode of Example 2 in which a graphene protective layer and a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N) are formed is indicated as FNCNT@G-Zn.

[0074]

[0075] FIG. 1 is a schematic diagram showing a process for manufacturing a zinc anode according to an embodiment of the present invention, and more specifically, a process for manufacturing a zinc anode according to Example 2. Step 1 of the upper drawing is a schematic diagram showing a method for manufacturing a carbon nanotube (FNCNT) doped with fluorine (F) and nitrogen (N), and Step 2 of the lower drawing is a schematic diagram showing a method for manufacturing a zinc anode having a carbon-based composite protective layer formed by first forming a graphene protective layer on a zinc substrate and secondly forming a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N).

[0076]

[0077] In the following experiments, experiments were conducted on a zinc anode in a zinc-based state without a protective layer, a zinc anode of Comparative Example 1 having only a graphene protective layer formed, a zinc anode of Comparative Example 2 having only a carbon nanotube (CNT) protective layer formed, a zinc anode of Example 1 having a graphene protective layer and a carbon nanotube (CNT) protective layer formed, and a zinc anode of Example 2 having a graphene protective layer and a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N) formed.

[0078]

[0079] Experimental Example 1: Surface Structure and Condition

[0080] Figures 2 (a) to (e) are schematic diagrams showing the surface and side surface of each zinc anode, (f) to (i) are images of the actual surface observed using a scanning electron microscope (SEM), and (k) is the result of measuring the surface of the zinc anode of Example 2 using energy dispersive X-ray spectroscopy (EDX).

[0081] The surface appearance as expected from the schematic diagram was observed. When there was no protective layer, a smooth surface was observed (f), and in the case of Comparative Example 1, a 2D structured graphene was coated, and a layered graphene-like shape was observed (g), and in the case of Comparative Example 2, a 1D structured carbon nanotube was coated, and a nano-sized wire shape was observed (h). In the cases of Examples 1 and 2, the top layer was also a carbon nanotube protective layer, and a nano-sized wire shape was observed (i is Example 1, j is Example 2). However, looking at (k), which is the result of confirming the element distribution through EDX analysis, it can be confirmed that fluorine (F) and nitrogen (N) are distributed on the surface in the case of Example 2. That is, Example 2 has a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N).

[0082]

[0083] Experimental Example 2: Wetting Evaluation

[0084] Figures 3 (a) to (e) are the results of measuring the water contact angle on the surface of each zinc cathode, and (f) is a schematic diagram showing that wettability is improved when carbon nanotubes are doped with fluorine (F) and nitrogen (N).

[0085] As can be seen, when there is no protective layer, it exhibited a water contact angle of 113° (a), and in the case of Comparative Example 1, it exhibited a water contact angle of 116° (b), showing relatively very low wettability characteristics. In the case of Comparative Example 2, it exhibited a water contact angle of 78°, showing relatively improved wettability characteristics. Furthermore, in the case of Example 1, it exhibited a water contact angle of 77°, showing further improved wettability characteristics (d), and in the case of Example 2, it exhibited a water contact angle of 65°, showing the highest wettability characteristics (e).

[0086] This shows that carbon nanotubes with a 1D structure have better wettability characteristics than graphene with a 2D structure, and therefore, it is desirable for the carbon nanotube protective layer to be located at the very top of the zinc anode in terms of improving wettability with the electrolyte. Furthermore, it can be seen that a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N) is the most desirable in terms of wettability with the electrolyte. This wettability indicates the interfacial compatibility between the surface of the zinc anode and the aqueous electrolyte, and the high wettability characteristics can have the effect of improving the cycle performance and enhancing the safety of aqueous electrolyte-based zinc-ion hybrid supercapacitors.

[0087]

[0088] Experimental Example 3: Doping with Fluorine (F) and Nitrogen (N)

[0089] Figure 4 (a) shows the results of thermogravimetric analysis (TGA) to confirm the chemical composition of graphene, carbon nanotubes (CNTs), and fluorine (F) and nitrogen (N) doped carbon nanotubes (FNCNTs), (b) shows the results of differential scanning calorimetry (DSC) of carbon nanotubes (CNTs) with ammonium fluoride (NH4F), and (c) and (d) show the results of X-ray photoelectron spectroscopy (XPS) of fluorine (F) and nitrogen (N) doped carbon nanotubes (FNCNTs). Specifically, (c) shows the F 1s spectrum, and (d) shows the N 1s spectrum.

[0090] As shown here, the process of doping ammonium fluoride (NH4F) into the carbon lattice of carbon nanotubes (CNT) and the results of DSC analysis to confirm the ionic reactivity show that NH4F dissolution and decomposition occur at approximately 94℃ and 180℃, respectively, leading to doping of fluorine (F) and nitrogen (N) into the carbon lattice. When C6 and NH4F are heat-treated in a nitrogen atmosphere, the carbon bonds are broken and CH4 bonds are formed, creating defects in the carbon lattice, and fluorine (F) and nitrogen (N) are doped into the defects. In addition, the XPS analysis results of carbon nanotubes (FNCNT) doped with fluorine (F) and nitrogen (N) show that peaks corresponding to CF bonds and various nitrogen species appear, confirming that co-doping of fluorine (F) and nitrogen (N) has been successfully achieved.

[0091]

[0092] Experimental Example 4: Stability and Uniform Growth of Zinc

[0093] Figure 5 shows the voltage profile of symmetric cells manufactured using each zinc cathode, with a voltage of 0.5 mAcm -2 and 2.0mAcm -2This is the result measured at the current density. The symmetric cell used a glass fiber separator as the separator and an aqueous electrolyte of 2M ZnSO4 as the electrolyte.

[0094] Specifically, (a) is the result of the voltage profile during the zinc plating / stripping process in a symmetric cell. During the first 100 hours, a low current (0.5 mAcm -2 ) and then performed measurements at high current (2.0 mAcm -2 ) was used to perform measurements.

[0095] As can be seen here, in the case without a protective layer, a very high overpotential fluctuation was observed after 22 hours. This demonstrates the importance of the protective layer. In the case of Comparative Example 1, it was confirmed that the overpotential fluctuation was large due to the low nucleation sites for zinc plating and low wettability with the electrolyte. In the case of Comparative Example 2, although the network structure provided nucleation sites for zinc plating, the overpotential fluctuation was relatively high due to the unstable zinc plating / stripping process due to insufficient surface protection. In the case of Example 1, it showed a more stable overpotential fluctuation than other electrodes during the zinc plating / stripping process thanks to the advantages of the graphene protective layer that played a role in protecting the surface of the zinc anode and the carbon nanotube (CNT) protective layer that provided many nucleation sites for zinc plating. Furthermore, in the case of Example 2, the wettability and electrical conductivity were further improved by applying a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N), and the most stable zinc plating / stripping process was observed.

[0096] Meanwhile, (b) is 0.5 mAcm -2As shown in the results showing each voltage range at the current density, examples 1 and 2 showed a low voltage range of 100 mV or less, and example 2 showed the lowest voltage range. These results indicate that examples 1 and 2 promote uniform growth of zinc on the zinc anode, and example 2 is most preferable.

[0097]

[0098] Experimental Example 5: Ion Transport Ability

[0099] A zinc-ion hybrid supercapacitor was assembled using each zinc cathode and anode, a glass fiber separator, and an aqueous electrolyte containing 2 M ZnSO4. Specifically, the cathode used activated carbon as an active material, Super P as a conductive material, and PVDF as a binder, and these were mixed in a weight ratio of 8:1:1 to prepare a slurry, and N-methyl-2-pyrrolidone (NMP) was used as a solvent. Specifically, the activated carbon had a particle size of 3–6 μm and a specific surface area of ​​2,081 m 2 g -1 , and one having an amorphous crystal structure was used. The slurry manufactured in this way was coated on a graphite collector and then dried to manufacture a cathode. At this time, the loading amount was 1.5 mg cm -2 It was.

[0100] The electrochemical performance of the zinc-ion hybrid supercapacitor assembled in this way was tested as follows. Electrochemical impedance spectroscopy (EIS) was 10 5 ~10 -2 It was performed at an AC signal of 5 mV in the frequency range of Hz.

[0101] Figure 6 shows the results of evaluating the ion transfer capability of each zinc cathode. (a) is the result of analyzing the Nyquist plot (EIS plot), and (b) and (c) are R ct value, Z real and W-1 / 2 The results show the correlation between the two, and (d) shows the diffusion coefficient of the zinc anode. Warburg impedance coefficient (σ w ) and Zn ion diffusion coefficient (D) are calculated using equations (1) and (2) below, respectively. Re represents the total electrode resistance, R represents the gas constant, T represents the temperature, A represents the electrode area, n represents the number of electrons per molecule, F represents the Farady constant, and C represents the molar concentration of zinc ions, and these various variables are introduced into the equations. Figures 6 (b), (c), and (d) are based on the data in (a).

[0102]

[0103]

[0104] As shown in (a), the cases of examples 1 and 2 are relatively R ct It was observed that the values ​​were small, which can be understood as the carbon-based composite protective layer including the graphene protective layer and the carbon nanotube (CNT) protective layer promoted efficient electron transfer. In particular, the case of Example 2 had the lowest R ct The values ​​were shown. Also, as shown in (b), the resistance values ​​at the interface between the zinc anode and the electrolyte also showed low values ​​in the cases of Examples 1 and 2. In particular, Example 2 showed the lowest value. Also, as shown in (c), the ion transfer ability at the interface between the zinc anode and the electrolyte is the result shown through slope calculation, and (d) is the result showing the ion transfer ability per area (ion diffusion coefficient). Through these results, it was found that Examples 1 and 2 had excellent ion transfer ability, and in particular, Example 2 had the best ion transfer ability.

[0105]

[0106] Experimental Example 6: Energy Storage Capacity

[0107] Figure 7 (a) is 10 mVs -1The results show the CV (cyclic voltammetry) curves of zinc-ion hybrid supercapacitors based on each zinc cathode, (b) is a graph for charge and discharge, and (c) is a graph for 0.5 to 20.0 A g -1 This is a graph showing the specific capacity in the current density range, and (d) shows a Ragone plot comparing the power and energy density in the case of Example 2. The zinc-ion hybrid supercapacitor was assembled in the same manner as that assembled in Experimental Example 5.

[0108] Specifically, (a) has a scan rate of 10 mVs -1 , and the results show the CV curves of samples with a potential range of 0.2 to 1.8 V. The redox peaks appearing in these CV curves indicate the plating / stripping reaction of zinc ions at the zinc cathode, and Zn↔2e - +Zn 2+ It can be expressed by the reaction formula. The CV profiles were similar. In the case of Examples 1 and 2, the CV curves showed a higher peak current response and a smaller polarization potential, confirming that they exhibited improved reaction activity. In particular, Example 2 showed more improved reaction activity. (b) is a charge / discharge curve of each zinc negative electrode, and it can be confirmed that there was no phase change during charge and discharge, and it could be confirmed that Examples 1 and 2 had high capacities. In particular, Example 2 showed more high capacity. (c) is 0.5 to 20.0 A g -1The results show the rate performance in the current density range, showing the interface performance between the zinc anode and the aqueous electrolyte. As can be seen, the case without a protective layer showed the lowest energy storage performance, and in the case of Comparative Examples 1 and 2, the energy storage performance was relatively high, but the low wettability of graphene limited the energy storage performance, and the carbon nanotubes had high interfacial resistance, which limited the performance. On the other hand, in the case of Examples 1 and 2, the capacity and capacity retention rate increased, and in particular, Example 2 showed the best storage performance (0.5 A g -1 159mAhg at -1 , 20.0Ag -1 88mAhg at -1 ) This can be seen as an improvement in wettability with the electrolyte through fluorine (F) doping and an improvement in electrical properties through nitrogen (N) doping. (d) is a graph of energy density and power density for Example 2, 800 to 32,000 Wkg -1 Power density range of 255~141Whkg -1 It showed superior performance compared to previously reported hybrid supercapacitors.

[0109]

[0110] Experimental Example 7: Inhibition of Dendrites

[0111] Figures 8(a),(c),(e),(g),(i) are 3-D surface confocal laser scanning microscopy (CLSM) images of each zinc anode, and (b),(d),(f),(h),(j) represent height plots of each zinc anode. More specifically, (a),(c),(e),(g),(i) are images obtained at a high current density of 20 Ag. -1 3-D surface confocal laser scanning microscopy images after charging.

[0112] As shown here, irregular dendrite growth with a thickness of about 20 μm was observed in the absence of a protective layer (a, b). It is very important to suppress irregular dendrite growth for stability because it can penetrate the separator and cause an electrical short circuit through contact with the anode. In the case of Comparative Example 1, irregular dendrite growth of about 16 μm was observed (c, d) due to low wettability and insufficient provision of sufficient nucleation sites for zinc deposition. In the case of Comparative Example 2, dendrite growth of about 12 μm was observed to be deposited on a uniform surface due to the numerous nucleation sites provided by carbon nanotubes (CNTs) (e, f). In the case of Example 1, dendrite growth of about 10 μm, which is lower than this, was observed (g, h). In the case of Example 2, the most stable zinc deposition was observed at a high current density, and dendrites of about 3 μm were uniformly deposited, resulting in the flattest surface (i, j). This can be interpreted as being due to the improved wettability and electrical properties through doping with fluorine (F) and nitrogen (N).

[0113] Figures 9 (a) to (j) show the high current density of each zinc cathode, 20 Ag. -1 (a) is a scanning electron microscope (SEM) image taken after charging, and (k) is a schematic diagram of the zinc stripping and plating process.

[0114] As can be seen here, vertical dendrite growth was observed in the images (a, f) of the case without a protective layer and (b, g) of Comparative Example 1, which can be interpreted as being due to the dendrite growth being concentrated in some areas due to a lack of nucleation sites for zinc deposition during the charging process. Horizontal dendrite growth was observed in the images (c, h) of Comparative Example 2, (d, i) of Example 1, and (e, j) of Example 2. This can be attributed to the numerous nucleation sites provided by the carbon nanotubes. In particular, in the case of Example 1, it could be seen that the size of the dendrite was deposited relatively small due to the relatively excellent electric field effect caused by the electrical properties of graphene. In particular, in the case of Example 2, it could be seen that the size of the dendrite was deposited the smallest due to the effect of nitrogen (N) doped into graphene and carbon nanotubes.

[0115]

[0116] Experimental Example 8: Cycling Stability (Life Characteristics)

[0117] Figure 10 shows the experimental results of the cycling stability (lifetime characteristics) of zinc-ion hybrid supercapacitors based on each zinc cathode, specifically (a) is 10.0Ag -1 (a) is the result of measuring the capacity retention (%) for up to 45,000 cycles at a current density of , and (b) is the result of the X-ray diffraction (XRD) pattern after the cycling test. The zinc-ion hybrid supercapacitor was assembled in the same manner as that assembled in Experimental Example 5.

[0118] As can be seen, the cell operation stopped due to electrical interruption after 10,094 cycles in the case without a protective layer, 12,500 cycles in the case of Comparative Example 1, and 11,004 cycles in the case of Comparative Example 2. On the other hand, Examples 1 and 2 showed long-term stability of more than 35,000 cycles. In particular, Example 2 showed excellent stability of 93% for 45,000 cycles, compared to Example 1, which stopped operating after 36,900 cycles. In addition, the XRD pattern analysis results showed that the by-product peak of ZHS appearing at 7.8° was not detected in Example 2. In other words, in the case of the zinc anode of Example 2, the growth of by-products was effectively suppressed, and it can be seen that the surface of the zinc anode was most efficiently protected.

[0119] Figure 11 shows scanning electron microscope (SEM) images after cycling tests, in which surface dissolution and formation of by-products of the zinc anode were observed in the absence of an actual protective layer (a, f). In Comparative Example 1, surface dissolution of the zinc anode was somewhat suppressed due to the role of the graphene protective layer with a 2D structure (b, g). In Comparative Example 2, some by-products were observed because the carbon nanotube protective layer had a 1D structure (c, h). In Example 1, some by-products were also observed (d, i). On the other hand, Example 2 was most similar to the initial state of the zinc anode, and excellent long-life characteristics could be confirmed because no surface dissolution of the zinc anode or formation of by-products was detected (e, j). In other words, it can be seen that the zinc anode formed with a carbon-based composite protective layer including both a graphene protective layer and a fluorine (F) and nitrogen (N)-doped carbon nanotube (FNCNT) protective layer has the best cycling stability (life characteristics).

[0120]

[0121] In conclusion, the present invention forms a carbon-based composite protective layer including a graphene protective layer containing graphene and a carbon nanotube protective layer containing carbon nanotubes on the surface of a zinc substrate, and particularly forms a carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N), thereby having the function of a protective layer protecting the surface of a zinc anode, and has the following excellent characteristics: 1) improving wettability with an aqueous electrolyte to improve cycle performance of a battery, 2) promoting uniform growth of zinc, 3) improving the transfer ability of zinc ions, and consequently improving the energy storage capacity of a supercapacitor, and 4) suppressing the growth of dendrites and suppressing the generation of byproducts to improve the stability, safety, and lifespan of a supercapacitor.

[0122] Figure 12 is a schematic diagram showing the effects described above. More specifically, it shows (Ⅰ) how the graphene protective layer formed directly on the surface of the zinc anode prevents corrosion of the zinc anode and dissolution of zinc and reduces interfacial resistance; (Ⅱ) how the carbon nanotube (FNCNT) protective layer doped with fluorine (F) and nitrogen (N) formed on the uppermost layer of the zinc anode effectively suppresses the growth of dendrites by providing a large number of nucleation sites for zinc plating; (Ⅲ) how the wettability (compatibility) between the zinc anode and the electrolyte is improved due to the effect of fluorine (F) doping in the carbon lattice; and (IV) how the electrical characteristics are improved due to the effect of nitrogen (N) doping in the carbon lattice.

[0123]

[0124] Although embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

Claims

1. Zinc base; and A carbon-based composite protective layer comprising a graphene protective layer comprising graphene and a carbon nanotube protective layer comprising carbon nanotubes, positioned on the zinc substrate. Cathode for zinc-ion hybrid supercapacitors.

2. In paragraph 1, The above graphene protective layer is formed on the surface of the zinc substrate, Characterized in that the carbon nanotube protective layer is formed on the surface of the graphene protective layer. Cathode for zinc-ion hybrid supercapacitors.

3. In paragraph 1, The above carbon nanotube is characterized in that it is doped with one or more non-metallic elements among fluorine (F), nitrogen (N), oxygen (O), phosphorus (P), boron (B), and sulfur (S). Cathode for zinc-ion hybrid supercapacitors.

4. In paragraph 3, The above carbon nanotube is characterized in that it is doped with fluorine (F) and nitrogen (N). Cathode for zinc-ion hybrid supercapacitors.

5. In paragraph 1, Characterized in that the water contact angle of the carbon-based composite protective layer is less than 80°. Cathode for zinc-ion hybrid supercapacitors.

6. In paragraph 1, The above graphene and carbon nanotubes have specific surface areas of 10 to 500 m2, respectively. 2 g -1 characterized by, Cathode for zinc-ion hybrid supercapacitors.

7. A step of first coating a first solution of graphene and a solvent on the surface of a zinc substrate and then drying it to form a graphene protective layer; and A step of forming a carbon nanotube protective layer by secondarily coating a second solution of a mixture of carbon nanotubes and a solvent on the surface of the graphene protective layer and then drying the second solution. Method for manufacturing a cathode for a zinc-ion hybrid supercapacitor.

8. In paragraph 7, The above carbon nanotube is characterized in that it is a carbon nanotube doped with one or more non-metallic elements among fluorine (F), nitrogen (N), oxygen (O), phosphorous (P), boron (B), and sulfur (S). Method for manufacturing a cathode for a zinc-ion hybrid supercapacitor.

9. In paragraph 8, The above carbon nanotube is characterized in that it is a carbon nanotube doped with fluorine (F) and nitrogen (N), which is manufactured by heat-treating a mixture of carbon nanotubes and ammonium fluoride (NH4F) aqueous solution at a temperature of 400 to 900°C in a nitrogen atmosphere. Method for manufacturing a cathode for a zinc-ion hybrid supercapacitor.

10. In paragraph 7, Characterized in that the ratio of the coating amount of the first solution to the coating amount of the second solution is 1:1 to 5:

1. Method for manufacturing a cathode for a zinc-ion hybrid supercapacitor.

11. A negative electrode for a zinc-ion hybrid supercapacitor manufactured by any one of the manufacturing methods of Article 7.

12. A zinc-ion hybrid supercapacitor comprising the negative electrode of claim 1 or claim 11.

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