KR102366927B1 - Manufacturing method for porous electrode, porous electrode thereby and super capacitor comprising the porous electrode - Google Patents

Abstract

The present invention relates to a method for manufacturing a porous electrode, a porous electrode manufactured by the method, and a supercapacitor including the porous electrode, wherein the method for manufacturing a porous electrode according to an embodiment of the present invention comprises a transition metal on a substrate A first electroplating step; and performing a second electroplating of the transition metal-plated substrate.

Description

A porous electrode manufacturing method, a porous electrode manufactured by the manufacturing method, and a supercapacitor comprising a porous electrode

The present invention relates to a method for manufacturing a porous electrode, a porous electrode manufactured by the method, and a supercapacitor including the porous electrode.

Since their first introduction to electrochemical energy storage, supercapacitors with oxide and sulfide electrode materials have been considered promising candidates for energy transfer systems. Alternatively, instead of using oxide and sulfide electrode materials, pure metal materials may have better electrochemical energy storage performance than previous electrode materials due to polyvalent cations and high electrical conductivity. Primary metal pure capacitors can induce multiple charge/discharge electrons based on the oxidation state of metal cations, which can lead to high energy densities. Metal electrodes have excellent cycling stability due to reversible redox-reactions (metal deposition and dissolution reactions between metal cations and metal electrodes). Finally, the high conductivity of the metal electrode can also increase the overall energy storage performance.

Among the various metal electrode candidates, Zinc (Zn) metal electrode-ion supercapacitors (ZICs) with Zn ²⁺ electrolyte ions consist of zinc anode, activated carbon anode, ZnSO ₄ electrolyte, and separator. do. In particular, zinc is a promising candidate for electrochemical capacitors as it is a very safe material and at the same time is low cost and environmentally friendly. In the energy storage mechanism of the zinc-ion capacitor, the deposition and desorption of zinc-ions from the cathode to the zinc electrode are performed, and the adsorption and desorption of ions from the surface of the activated carbon electrode at the anode are performed. Therefore, it is a device that stores energy using the redox reaction at the cathode and the electric double layer reaction at the anode. In particular, zinc ions have high theoretical capacity and excellent compatibility with electrolytes, so that high energy density and long lifespan of capacitors can be achieved.

Despite these attractive advantages, the flat surface of zinc electrodes results in low power and energy densities due to long zinc ion diffusion paths that are undesirable for electrochemical reactions during charge and discharge processes at high current densities.

The present invention is to solve the above problems, and an object of the present invention is to increase the electrochemical reaction area and reduce the diffusion path of zinc ions during the charge/discharge process, thereby making it suitable as an electrode for a zinc ion supercapacitor in two dimensions and It is to provide a method for manufacturing a porous nano-structured electrode step by step, a porous electrode manufactured by the method, and a supercapacitor including the porous electrode.

However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

A method of manufacturing a porous electrode according to an embodiment of the present invention comprises the steps of: performing first electroplating on a substrate with a transition metal; and performing a second electroplating of the transition metal-plated substrate.

In an embodiment, the substrate may include Ni-foam, a carbon-containing substrate, or both.

In one embodiment, the carbon-containing substrate, carbon fiber, activated carbon, carbon black, acetylene black, furnace black, ketchup black, super-P (Super-P), fine graphite powder, carbon nanotubes (CNT), It may include at least one selected from the group consisting of fibrous carbon whiskers, vapor-grown carbon fibers (VGCF), graphene, and graphite.

In one embodiment, in the first electroplating step, a voltage of 0.5 V to 2 V may be applied for 10 seconds to 60 seconds.

In one embodiment, the second electroplating step may be to apply a voltage of 0.5 V to 2 V for 300 seconds to 500 seconds.

In one embodiment, the first electroplating step may be to nucleate the seeds of the transition metal.

In an embodiment, the second electroplating step may be to crystallize the nucleated seed.

In one embodiment, the transition metal is zinc (Zn), platinum (Pt), copper (Cu), nickel (Ni), silver (Ag), chromium (Cr), aluminum (Al), iron (Fe) , may include at least one selected from the group consisting of cobalt (Co) and ruthenium (Ru).

A porous electrode according to another embodiment of the present invention is manufactured by the method for manufacturing a porous electrode according to an embodiment of the present invention.

In one embodiment, the porous electrode may include porous interconnected two-dimensional nanopores.

In one embodiment, the specific surface area of the porous electrode may be 50 m ² /g to 3000 m ² /g.

In one embodiment, the pore diameter of the porous electrode may be 10 nm to 500 nm.

In one embodiment, the porous electrode may be a flat type, a fiber type, or one including both.

A supercapacitor according to another embodiment of the present invention includes: a cathode including a porous electrode according to an embodiment of the present invention; anode; and an electrolyte filled between the cathode and the anode.

In one embodiment, the supercapacitor has a capacitance of 400 F g ^-1 to 500 F g ^-1 at a current density of 0.5 A g ^-1 and 100 F g ^-1 at a current density of 20.0 A g ^-1 to 200 F g ^-1 may have a capacitance.

In one embodiment, the supercapacitor may have a capacitance retention of 98% or more in 1 to 10,000 galvanostatic charge-discharge cycles.

In one embodiment, the supercapacitor may be a zinc ion supercapacitor.

In the method of manufacturing a porous electrode according to an embodiment of the present invention, a two-dimensional and stepwise nanostructured porous electrode can be formed using a stepwise electroplating method.

The porous electrode according to an embodiment of the present invention may include a two-dimensional structure having a porous structure and a network structure at the same time to increase the electrochemical reaction area.

The supercapacitor according to an embodiment of the present invention may exhibit excellent energy storage capacity and energy storage performance by including a two-dimensional structure including a porous structure and a network structure at the same time.

1 is (a) a schematic diagram of a flat ZIC and Ragone plots (b) a schematic diagram of a two-dimensional and stepwise nanostructured Zn (2D-Zn) metal electrode according to an embodiment of the present invention.
2 is a current curve of (a) 2D-Zn/1.0, (b) 2D-Zn/1.8 and (c) 2D-Zn/1.8/1.0, ( d) SEM images of 2D-Zn/1.0, (e) 2D-Zn/1.8 and (f) 2D-Zn/1.8/1.0, (g) XRD pattern of 2D-Zn, (h) Zn for 2D-Zn 2p and (i) XRD spectra of Ni 2P.
3 is (a) low-resolution and (b) high-resolution SEM images of a Zn electrode on a Ni foam surface by electroplating at 1.8 V for 30 seconds according to an embodiment of the present invention.
4 is a schematic diagram of (a) zinc growth by a step-by-step plating process according to an embodiment of the present invention, (b) Ni foam, (c) 2D-Zn/1.8/5sec, (d) 2D-Zn/1.8/10sec , SEM images of (e) 2D-Zn/1.8/30 sec and (f) 2D-Zn/1.8/1.0 V/360 sec.
5 shows (a) low-resolution and (b) high-resolution TEM images of 2D-Zn/1.8/1.0, (c) selected area electron diffraction of 2D-Zn/1.8/1.0 according to an embodiment of the present invention; ; SAED) pattern.
6 is an XRD pattern of (a) AC N ₂ adsorption/desorption isotherm, and (b) AC according to an embodiment of the present invention.
7 is (a) Nyquist plots of the frequency before the charge/discharge test according to an embodiment of the present invention, (b) a cyclic voltammetry (CV) at a scan rate of 10mV s ⁻¹ in a potential range of 0.2 V to 1.8 V; FIG. ) curve, (c) specific capacitance calculated at current densities ranging from 0.5 A g ^-1 to 20.0 A g ^-1 in the potential range from 0.2 V to 1.8 V, (d) 500 W kg ^-1 to 20,000 W kg ^-1 Ragone plots related to power density and energy, (e) are graphs showing cycle stability at a current density of 10.0 A g ⁻¹ over 10,000 cycles.
8 is a CV curve of 2D-Zn/1.8 and 2D-Zn/1.8/1.0 at a scan rate varying from 5 to 200 mV s ⁻¹ in a potential range of 0.2 to 1.8V according to an embodiment of the present invention.
9 shows (a) GCD curves of 2D-Zn/1.8 and 2D-Zn/1.8/1.0 at current densities of 0.5 A g ^-1 according to an embodiment of the present invention, at current densities in the range of 0.5-20 A g ^-1 GCD curves of (b) 2D-Zn/1.8 and (c) 2D-Zn/1.8/1.0.
10 is a graph of the calculated specific capacitance of 2D-Zn1.8 and 2D-Zn/1.8/30s according to an embodiment of the present invention.
11 is a GCD curve of 2D-Zn/1.8 and 2D-Zn/1.8/1.0 at a voltage of 0.2 V to 1.8 V according to an embodiment of the present invention.
12 shows electrochemical impedance spectra (EIS) of initial flat-type ZICs using 2D-Zn/1.8/1.0 and 5,000 and 10,000 cycle ZIC according to an embodiment of the present invention.
13 is an XRD pattern of a 2D-Zn/1.8/1.0 electrode at different voltages during cycling according to an embodiment of the present invention.
14 is a flat diagram including (a) 2D-Zn@CF as an anode, AC@CF as a cathode, cellulose paper as a separator, ZnSO ₄ -PVA gel as an electrolyte, and a heat-shrinkable tube as a cell case according to an embodiment of the present invention; Schematic diagram of type ZIC, (b) SEM image of 2D@ZnCF of 2D Zn nanostructure grown on carbon fiber by electroplating, (c) XRD pattern of 2D-Zn@CF, (d) 2D-Zn@CF XPS spectrum of Zn 2p.
15 is a photographic image of (a) a carbon fiber tow and (b) a carbon fiber filament according to an embodiment of the present invention.
16 is an SEM image of cellulose paper as a separator according to an embodiment of the present invention.
17 is an image of a ZnSO ₄ gel electrolyte according to an embodiment of the present invention.
18 is a (a) low-resolution and (b) high-resolution SEM image of a carbon fiber according to an embodiment of the present invention.
19 is (a) low-resolution and (b) high-resolution SEM images of 2D Zn nanostructures on carbon fibers without surface functionalization according to an embodiment of the present invention.
20 is a C 1s XPS spectrum of a carbon fiber before (a) and after (b) surface functionalization according to an embodiment of the present invention.
21 shows 2D Zn nanostructure-decorated carbon fibers by electroplating at applied voltages of (a and b) 0.7 V and (c and d) 1.5 V according to an embodiment of the present invention.
22 is a TGA curve of 2D-Zn@CF from 200 °C to 950 °C in air at a heating rate of 10 °C/min ^-1 according to an embodiment of the present invention.
23 is a CV curve of 2D-Zn@CF at a scan rate varying from 5 mV s ⁻¹ to 200 mV s ⁻¹ in a potential range of 0.2 V to 1 1.8 V according to an embodiment of the present invention (a) (b) ) GCD curves of 2D-Zn@CF at current densities ranging from 0.05 mA cm ^-2 to 3 mA cm ^-2 .
24 is a graph showing the calculated specific capacitance of Zn 2D Zn nanostructures and 2D Zn@CF electrodeposited on carbon fibers at applied voltages of 0.7 V and 1.5 V according to an embodiment of the present invention.
25 is an EIS curve of Zn 2D Zn nanostructure and 2D-Zn@CF electrodeposited on carbon sesame oil at applied voltages of 0.7 V and 1.5 V according to an embodiment of the present invention.
26 is (a) 50 μW cm ^-2 to 3,000 μW cm ^-2 Ragone plots related to power density and energy, (b) cycle stability of 1.0 mA cm ^-2 for 10,000 cycles, (c) ) capacitance retention in straight, folded and knotted states, (d) capacitance retention achieved in water for 15 h, (e) in water driven by series and parallel connected fiber ZICs in the knotted state. A diagram showing a light emitting diode.
27 is (a and b) low-resolution and (c and d) high-resolution SEM images of ZIC 2D-Zn/1.8/1.0 and 2D-Zn@CF after 10,000 cycles according to an embodiment of the present invention.
28 shows GCD curves of two fibrous ZICs with (a) series and (b) parallel connected 2D-Zn@CF, (c) total device capacitance and parallel-connected fiber-based in accordance with an embodiment of the present invention. It is a graph showing the relationship between the number of ZICs.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes may be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all modifications, equivalents and substitutes for the embodiments are included in the scope of the rights.

The terms used in the examples are used for the purpose of description only, and should not be construed as limiting. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "have" are intended to designate that a feature, number, step, operation, component, part, or a combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiment belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In addition, in the description with reference to the accompanying drawings, the same components are given the same reference numerals regardless of the reference numerals, and the overlapping description thereof will be omitted. In describing the embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only for distinguishing the elements from other elements, and the essence, order, or order of the elements are not limited by the terms.

Components included in one embodiment and components having a common function will be described using the same names in other embodiments. Unless otherwise stated, descriptions described in one embodiment may be applied to other embodiments as well, and detailed descriptions within the overlapping range will be omitted.

A method of manufacturing a porous electrode according to an embodiment of the present invention comprises the steps of: performing first electroplating on a substrate with a transition metal; and performing a second electroplating of the transition metal-plated substrate.

In the method of manufacturing a porous electrode according to an embodiment of the present invention, a two-dimensional and stepwise nanostructured porous electrode can be formed using a stepwise electroplating method.

In an embodiment, the substrate may include Ni-foam, a carbon-containing substrate, or both.

In one embodiment, the carbon-containing substrate, carbon fiber, activated carbon, carbon black, acetylene black, furnace black, ketchup black, super-P (Super-P), fine graphite powder, carbon nanotubes (CNT), It may include at least one selected from the group consisting of fibrous carbon whiskers, vapor-grown carbon fibers (VGCF), graphene, and graphite.

In one embodiment, the Ni foam may have a porosity of 50% to 95%.

In one embodiment, in the first electroplating step, a voltage of 0.5 V to 2 V may be applied for 10 seconds to 60 seconds. In the first electroplating step, when a voltage of less than 0.5 V is applied for less than 10 seconds, nucleation of the transition metal seed may not be induced, and when a voltage of more than 2 V is applied for more than 60 seconds, plating This may not be uniform.

In one embodiment, the first electroplating step may be to nucleate the seeds of the transition metal.

In one embodiment, the second electroplating step may be to apply a voltage of 0.5 V to 2 V for 300 seconds to 500 seconds. In the second electroplating step, when a voltage of less than 0.5 V is applied for less than 300 seconds, crystal growth may not be induced, and when a voltage of more than 2 V is applied for more than 500 seconds, the density of the two-dimensional structure is It may not have a porous structure.

In an embodiment, the second electroplating step may be to crystallize the nucleated seed.

In one embodiment, the two-dimensional electrode having a porous structure and a network structure at the same time can be manufactured in the electroplating method performed step by step in two steps.

In one embodiment, the transition metal is zinc (Zn), platinum (Pt), copper (Cu), nickel (Ni), silver (Ag), chromium (Cr), aluminum (Al), iron (Fe) , may include at least one selected from the group consisting of cobalt (Co) and ruthenium (Ru). Preferably, it may be zinc in order to use the porous electrode of the present invention as a cathode of a zinc ion supercapacitor.

A porous electrode according to another embodiment of the present invention is manufactured by the method for manufacturing a porous electrode according to an embodiment of the present invention.

The porous electrode according to an embodiment of the present invention may include a two-dimensional structure having a porous structure and a network structure at the same time to increase the electrochemical reaction area.

In one embodiment, the porous electrode may include porous interconnected two-dimensional nanopores. It may have a porous structure and a network structure at the same time. Stepwise interconnected network porous electrodes can be fabricated through instantaneous rapid nucleation followed by slow growth formation of transition metals such as zinc.

In one embodiment, the specific surface area of the porous electrode may be 50 m ² /g to 3000 m ² /g. Preferably, it may be 100 m ² /g to 2000 m ² /g.

In one embodiment, the pore diameter of the porous electrode may be 10 nm to 500 nm. Although it is difficult to measure the diameter of a single pore because the pores have a network structure, the pores may have a diameter within the above range.

In one embodiment, the porous electrode may be a flat type, a fiber type, or one including both. The flat porous electrode may be manufactured by a two-step electroplating method using Ni foam, activated carbon, and carbon black, and the fibrous porous electrode may be manufactured by a two-step electroplating method on carbon fibers.

In one embodiment, when the flat porous electrode is used as a cathode of a supercapacitor, a high energy density can be achieved at a high power density, and an excellent long-term cycle of 10,000 or more can be achieved. In addition, when the fibrous porous electrode is used as a cathode of a supercapacitor, it can have excellent energy density at high power density, excellent energy storage performance, excellent cycling stability, excellent mechanical flexibility, and excellent waterproof properties.

A supercapacitor according to another embodiment of the present invention includes: a cathode including a porous electrode according to an embodiment of the present invention; anode; and an electrolyte filled between the cathode and the anode.

The supercapacitor according to an embodiment of the present invention may exhibit excellent energy storage capacity and energy storage performance by including a two-dimensional structure including a porous structure and a network structure at the same time.

In one embodiment, the anode may include a carbon material. The anode, as a carbon material, may include at least one selected from the group consisting of activated carbon, acetylene black, furnace black, carbon black, ketchup black, super-P, graphene, and graphite.

In one embodiment, the electrolyte may include 0.5 M to 3 M zinc sulfate. This electrolyte has a room temperature conductivity of about 50 mS/cm, which is smaller than an alkaline electrolyte (>400 mS/cm), and has the advantage that the reversibility of the electrochemical oxidation/reduction reaction is very large. As the electrolyte, in addition to zinc sulfate, zinc chloride (ZnCl ₂ ), zinc bromide (ZnBr ₂ ), zinc acetate (Zn(O ₂ CCH ₃ ) ₂ ) and zinc nitrate (Zn(NO ₃ ) ₂ ) selected from the group consisting of it could be Preferably, zinc sulfate shows the best performance. It can be inferred from the fact that it contains sulfate anion, which is most preferred in the process of electrodeposition of zinc.

In one embodiment, the supercapacitor has a capacitance of 400 F g ^-1 to 500 F g ^-1 at a current density of 0.5 A g ^-1 and 100 F g ^-1 at a current density of 20.0 A g ^-1 to 200 F g ^-1 may have a capacitance. The charging-discharging test may be performed under current density conditions of 0.5 A g ^-1 to 20.0 A g ^-1 .

In one embodiment, the supercapacitor may have a capacitance retention of 98% or more in 1 to 10,000 galvanostatic charge-discharge cycles. Preferably, it may have a capacitance retention of 99% even after 10,000 cycling. The porous structure of the anode reduces the diffusion distance of zinc-ions in the electrolyte at high current density, thereby exhibiting excellent capacitance retention at high charge/discharge rates. The excellent life-holding properties are due to the excellent reversibility of zinc-ion capacitors.

In one embodiment, the supercapacitor may be a zinc ion supercapacitor.

The supercapacitor according to an embodiment of the present invention has a porous structure including a network structure in which pores are interconnected, and exhibits excellent capacitance retention by reducing the diffusion distance of zinc-ions in the electrolyte at a high current density at a fast current density. Characteristics and excellent capacitance retention at fast charge/discharge rates can be exhibited.

The porous electrode according to an embodiment of the present invention was prepared as a two-dimensionally and stepwise nano-structured Zn (2D-Zn) metal electrode of a zinc ion supercapacitor. 2D-Zn metal electrodes were carefully obtained by voltage-specific electroplating to optimize the 2D morphology and hierarchical density in micron porous current collectors. These unique 2D Zn nanostructures can provide a shorter diffusion path for Zn ions, which provides high power densities (500–20,000 W kg ⁻¹ ). In addition, the enlarged surface area and metal-like conductivity of 2D-Zn could indicate a long cycle life with good energy density (208 Wh kg ⁻¹ ) and excellent cycling stability (~99%). In particular, due to the low standard electrode potential (-0.76 V) of Zn, 2D-Zn metal can be easily deposited in any form factor for fibrous current collectors that can be used for next-generation energy storage applications. The fibrous 2D-Zn metal electrode made of flexible carbon fiber exhibits excellent flexibility and knittability to external and environmental conditions, and this unique deposition method and the resulting staged 2D-Zn nanostructures It shows promise for good and practical supercapacitors.

Hereinafter, the present invention will be described in detail with reference to the following Examples and Comparative Examples. However, the technical spirit of the present invention is not limited or limited thereto.

summary

Recently, supercapacitors show high power density with long cycle life as energy-powering applications. Supercapacitors based on single metal electrodes with multivalent cations, multiple charge/discharge kinetics and high electrical conductivity may be a promising energy-storage system to replace commonly used oxide and sulfide materials. In an embodiment of the present invention, a staged nanostructured two-dimensional (2D)-Zn metal electrode-ion supercapacitor (ZIC) with greatly improved ion diffusion capacity and overall energy storage performance is disclosed. These nanostructures can also be successfully plated on a variety of flat and fibrous current collectors by controlled electroplating methods. ZIC exhibits excellent pseudo-capacitive performance with a high energy density of 208 Wh kg ^-1 and a power density of 500 W kg ^-1 , which is significantly higher than previously reported supercapacitors with oxides and sulfides. . In addition, the fibrous ZIC exhibits high energy-storage performance, excellent mechanical flexibility and excellent waterproof performance without significant capacitance degradation during bending tests. These results highlight the promising potential of nanostructured 2D Zn metal electrodes as a controlled electroplating method for future energy storage applications.

material

Ni-foam, Zn foil, zinc sulfate (ZnSO ₄ ), polyvinylidene difluoride, poly(vinyl alcohol) (PVA), polyvinylidene fluoride (PVDF) and N-Methyl-2-pyrrolidone (N-Methyl-2-pyrrolidone; NMP) was purchased from Sigma-aldrich. Carbon fiber (CF) was purchased from Easycomposites. Activated carbon was purchased from Power Carbon Technology. All chemicals were used without further purification.

Synthesis of 2D and Stepwise Nanostructured Zn (2D-Zn) Metal Electrodes for Flat Single Zinc (Zn) Metal Electrodes-Ion Supercapacitors (ZICs)

2D nanostructured Zn (2D-Zn) electrodes for single zinc (Zn) metal electrode-ion supercapacitors (ZICs) were successfully synthesized by a current-tailored electroplating method. Ni foam was used as a current collector for the substrate and the anode and cathode. The two-electrode cell for synthesizing 2D-Zn was composed of Ni foam as anode, Zn foil as cathode, and 2.0 M ZnSO ₄ solution as electrolyte. Electroplating was performed at a two-step voltage of 1.0 V, 1.8 V and 1.8 V to 1.0 V for 6 minutes (2D-Zn/1.0, 2D-Zn/1.8 and 2D-Zn/1.8/1.0, respectively). Ni foam and Zn foil were separated at 2 cm intervals. After electroplating, the 2D-Zn electrode was removed from the electrolyte and immediately rinsed thoroughly with distilled water.

Activated carbon for flat ZICs ( activated carbon; AC) Preparation of the cathode

Activated carbon (AC), carbon black (Super P, Alfa Aesar) and polyvinylidene difluoride (PVDF, Alfa Aesar) were used in NMP in a ratio of 8:1:1 to prepare a slurry for a working electrode. . The prepared slurry was coated on Ni foam and dried in air at 80° C. for 1 hour.

Synthesis of 2D-Zn (2D-Zn@CF) anodes on carbon fiber for fibrous ZICs

2D-Zn (2D-Zn@CF) on carbon fiber as an anode was successfully synthesized by current-specific electroplating. Carbon fiber was used for the substrate and current collector. The two-electrode cell for synthesizing 2D-Zn@CF was composed of carbon fiber as anode, Zn foil as cathode and 2.0 M ZnSO ₄ solution as electrolyte. Electroplating was performed at 1.0 V for 10 minutes. After electroplating, 2D-Zn@CF was removed from the electrolyte and immediately rinsed thoroughly with distilled water.

Fabrication of Activated Carbon (AC@CF) Cathode on Carbon Fiber for Fibrous ZICs

Activated carbon-decorated carbon fibers (AC@CF) as cathodes for fibrous ZICs were prepared by mixing paste composed of activated carbon as an active material, PVDF as a binder, and Super P as a conductive material in NMP in a ratio of 8:1:1. . Activated carbon was drop-cast onto the surface of carbon fibers and dried at 80 °C for 5 h under atmospheric conditions.

Preparation of gel electrolyte for fibrous ZICs

1.0 M ZnSO ₄ and PVA were mixed in deionized water to prepare a gel electrolyte. First, PVA was dissolved in deionized water with stirring at 80 °C until the solution became clear. Then, ZnSO ₄ was added and stirred at 80 °C until transparent. Finally, after cooling to room temperature, a gel electrolyte was obtained.

Characteristic measurement

The morphology of the Zn electrode was investigated by scanning electron microscopy (SEM). The nanostructures of 2D-Zn/1.8/1.0 were investigated by high-resolution transmission electron microscope (HR-TEM) after the fabrication process as follows: (i) electrodes of 2D-Zn/1.8/1.0 was immersed in acetone solution to separate structured 2D-Zn from the Ni foam surface and (ii) an ultra-thin carbon-coated copper grid was coated with the collected 2D-Zn solution and carefully dried. The crystal structure and chemical bonding state of the Zn electrode were observed using X-ray diffraction with Cu K _α radiation and X-ray photoelectron spectroscopy with Al K _α X-ray source, respectively. The binding energy of each spectrum is normalized to the C 1s core level (284.5 eV). The specific surface area, total pore volume, average pore size and pore volume fraction of AC were characterized with a Brunauer-Emmett-Teller using N ₂ adsorption. The content of 2D-Zn@CF was investigated using thermogravimetric analysis from 200 °C to 950 °C at a heating rate of 10 °C min ^-1 in air. The content of zinc and nickel in the prepared electrode was measured by inductively coupled plasma-mass spectroscopy (ICP-MS) analysis. Operating conditions are 1.6 kW of RF power.

Measurement of electrochemical properties

The energy storage performance of flat and fibrous ZICs was evaluated using the whole cell system. To investigate the electrochemical kinetics, electrochemical impedance spectroscopy (EIS) measurements were performed using fresh cells in the frequency range of 10 ⁵ Hz to 10 ^-2 Hz at an AC signal of 5 mV. Cyclic voltammetry (CV) was performed using a potentiostat/galvanostat at a scan rate of 10 mV s ⁻¹ . Galvanostatic charge-discharge (GCD) curves were tested over a potential range of 0.2 V-1.8 V at various current densities (flat: 0.5 to 20.0 A g ^-1 and fiber: 0.05 to 3.0 mA cm ² ) became Long cycling stability of ZICs was performed at current densities of 10.0 A g ⁻¹ (flat) and 1.0 mA cm ² (fibrous) over 10,000 cycles.

The specific capacitance of ZICs can be calculated with the following [Equation 1].

[Equation 1]

C _sp (F g ^-1 or cm ^-2 )= I/(m or A △V/dt)

where I (A) is the charge/discharge current, m (g) is the total mass of active materials such as zinc and activated carbon in the electrode, A (cm ⁻² ) is the area of the fabricated ZIC composed of anode and cathode fibers, ΔV is the potential window, and dt (s) is the discharge time. In addition, to measure the Zn mass loading on Ni foam and carbon fiber, a digital weighing scale with a precision of 0.1 mg after the electroplating process was used.

Energy density (E, Wh kg ^-1 or Wh cm ^-2 ) and power density (P, W kg ^-1 or W cm ^-2 ) are calculated by the following [Equation 2] and [Equation 3]:

[Equation 2]

E (Wh kg ^-1 or Wh cm ^-2 ) = 0.5CV 2/3.6

[Equation 3]

P(W kg ^-1 or W cm ^-2 ) = E/dt 3600

Results and Discussion

1 is (a) a schematic diagram of a flat ZIC and Ragone plots (b) a schematic diagram of a two-dimensional and stepwise nanostructured Zn (2D-Zn) metal electrode according to an embodiment of the present invention.

As shown in Fig. 1(a), the whole cell 2D-Zn//AC (AC, activated carbon) asymmetric supercapacitor has an electric double-layer with Zn/Zn ²⁺ on the anode and electrolyte ions on the cathode (activated carbon). The charge can be stored by surface Faradaic redox reactions between the formation of (Zn ions and sulfate ions). For flat ZICs, Ni foam was used for the current collector due to its microstructure, good chemical/mechanical stability, and high electrical conductivity. As shown in Fig. 1(b), a novel 2D-Zn electrode was successfully fabricated by voltage-specific electroplating on Ni foam. Compared with other reported synthesis methods, electroplating is well known as a very simple and easy synthesis method for depositing single phase metal materials and other material composites by controlling the concentration and precursor of the solution. It can also be applied to any metal substrate, even on flat, curved and rough substrates. In particular, the driving force of Zn deposition on a Ni metal substrate was studied in an embodiment of the present invention.

Deriving stepwise interconnected metal nanostructures and optimized morphological designs with controlled synthetic parameters for material nucleation and crystal growth are generally challenging, which provide advantageous electrochemical energy storage performance. Therefore, to obtain stepwise interconnected nanostructured 2D-Zn, the optimized initial voltage and step-by-step additional voltage were carefully applied. Various nucleation growth can be well controlled by precise initial operating voltages, and additional voltages can change the driving force for subsequent crystal growth levels. If the operating voltage is too low, low-level metal nucleation points are induced on the substrate, limiting subsequent crystal growth. However, since the operating voltage is too high, an excess amount of metal nucleation sites will be deposited on the substrate, and a relatively large and bulky metal morphology will be obtained. To optimize the operating voltage, two different operating voltages (1.0 V (2D-Zn/1.0) and 1.8 V (2D-Zn/1.8)) were compared as initial deposition conditions.

2 is a current curve of (a) 2D-Zn/1.0, (b) 2D-Zn/1.8 and (c) 2D-Zn/1.8/1.0, ( d) SEM images of 2D-Zn/1.0, (e) 2D-Zn/1.8 and (f) 2D-Zn/1.8/1.0, (g) XRD pattern of 2D-Zn, (h) Zn for 2D-Zn 2p and (i) XRD spectra of Ni 2P.

2A to 2B show deposition current curves of 2D-Zn/1.0 and 2D-Zn/1.8 during an electroplating method according to an embodiment of the present invention.

The electroplating procedure occurs when the Zn ²⁺ ions are relaxed towards the target substrate and exceed the activation energy of the Zn deposition when the system is out of electrostatic equilibrium due to the electric field generated in the electrolyte. At an operating voltage of 1.0 V, the current curve increased for 20 s, then reached an equilibrium level, which was not high enough to induce spontaneous Zn relaxation and nucleation, resulting in poorly coated Zn electrodes (unstructured Zn). led to It proves that in the initial electrostatic plating process, a high overpotential may be required to grow to the critical size of the Zn nuclei, where a new phase is required. On the other hand, at an operating voltage of 1.8 V, the initial current decreased due to the formation of Zn nuclei as well as the introduction of an electrostatic double layer (at the interface between the electrode and the electrolyte).

This phenomenon of deposition current indicates that a uniform plating process has begun. Thereafter, the current reaches equilibrium and is well maintained, suggesting that the formation of Zn nuclei leads to the dissolution of the initial bilayer. In addition, the deposited nanostructures of 2D-Zn/1.0 (FIG. 2(d)) and 2D-Zn/1.8 (FIG. 2(e)) were investigated using scanning electron microscopy (SEM), respectively. Fig. 2(d) shows that the 2D-Zn/1.0 electrode does not have a uniform 2D structure. Conversely, at an operating voltage of 1.8 V, the current curve starts at the highest point and saturates after 30 s. A thick and bulky structure of 2D-Zn/1.8 was observed (Fig. 2(e)). Therefore, both operating voltages of 1.8 V for initial nucleation growth within a short reaction time (30 s) and 1.0 V for crystal growth of Zn within a long reaction time (300 s) were used (2D-Zn). /1.8/1.0). As shown in Fig. 2(c), Zn seeds were uniformly decorated on the surface of the Ni foam at 1.8 V for 30 s (Fig. 3), and the operating voltage of 1.0 V was maintained for almost 300 s. The oriented crystal growth of Zn was induced. SEM images of 2D-Zn/1.8/1.0 (Fig. 2(f)) show stepwise interconnected 2D Zn nanostructures with a thickness of 10 nm to 25 nm and a length of 6 μm to 11 μm.

3 is (a) low-resolution and (b) high-resolution SEM images of a Zn electrode on a Ni foam surface by electroplating at 1.8 V for 30 seconds according to an embodiment of the present invention.

The formation mechanism of the stepwise interconnected 2D-Zn structure can proceed for the following reasons. By controlling the step-by-step deposition voltage, the nucleation and growth of Zn on the target substrate can be efficiently adjusted. After applying a high voltage for a short time frame (nucleation phase), a relatively large number of Zn seeds can be electrically deposited on the substrate compared to the low voltage. As a result, lowering the plating voltage after nucleation (growth step) can change the formation rate of Zn in the deposited Zn seeds, resulting in the formation of uniform and stepwise structured 2D-Zn. Therefore, the step-by-step electroplating method can systematically change the structure, uniformity and density of the 2D-Zn structure on the substrate by tuning the atomic assembly behavior. Thus, stepwise interconnected 2D-Zn electrodes can be fabricated through instantaneous fast nucleation and subsequent slow growth of Zn. Finally, on the surface of 2D-Zn, a network structure is formed and randomly distributed on the surface.

4 is a schematic diagram of (a) zinc growth by a step-by-step plating process according to an embodiment of the present invention, (b) Ni foam, (c) 2D-Zn/1.8/5sec, (d) 2D-Zn/1.8/10sec , SEM images of (e) 2D-Zn/1.8/30 sec and (f) 2D-Zn/1.8/1.0 V/360 sec.

As shown in Fig. 4(a), the schematic diagram shows detailed nucleation and growth steps on the target substrate during the step-by-step plating process. 4(b) to 4(f) show SEM images in the nucleation and growth stages during plating. These SEM images confirm that different seed sites and nanostructured Zn electrodes can be well tuned from low to high operating voltages.

5 shows (a) low-resolution and (b) high-resolution TEM images of 2D-Zn/1.8/1.0, (c) selected area electron diffraction of 2D-Zn/1.8/1.0 according to an embodiment of the present invention; ; SAED) pattern.

In addition, the electrode of 2D-Zn/1.8/1.0 was further measured by a high-resolution transmission electron microscope (HR-TEM), as shown in Figs. 5 (a) and (b). . It can be easily observed that the distance of the parallel lattice fringes is 0.23 nm, which corresponds to the (010) plane of a pure Zn crystal with a hexagonal structure. In addition, the crystalline properties of 2D-Zn/1.8/1.0 were demonstrated by a selected area electron diffraction (SAED) pattern (Fig. 5(c)). Six-fold symmetrical diffraction spots correspond to the [100] domain axis, showing that the 2D-Zn/1.8/1.0 Zn nanosheets represent hexagonal crystals of pure Zn metal.

In addition, X-ray diffraction (XRD) was performed to investigate the crystal structure of the 2D-Zn electrode. 2( g ) shows the XRD patterns of 2D-Zn/1.0, 2D-Zn/1.8 and 2D-Zn/1.8/1.0. Two sharp diffraction peaks are observed at 44.5 º and 51.8 º, corresponding to the (111) and (200) planes of the face-centered metal Ni. The diffraction peaks of 2D-ZN/1.8/1.0 at 36.2°, 38.9° and 43.2° can be in good agreement with the (002), (100) and (101) planes of the hexagonal Zn phase. The (002), (100), (101) indices are the most intense planes of Zn, clearly showing the formation of 2D-Zn along the c-axis. The oriented growth of Zn leads to the formation of interconnected 2D nanostructures. However, in the case of 2D-Zn/1.0, the diffraction peak of the hexagonal Zn phase is not observed due to the small amount of Zn, indicating that the electroplating voltage of 1.0 V is not active enough to deposit a large amount of Zn. X-ray photoelectron spectroscopy (XPS) was performed to analyze the chemical state of the 2D-Zn electrode. The XPS results of all electrodes show that the metallic Zn phase was successfully deposited (Fig. 2(h)). Since there is no additional heat treatment, it is clearly demonstrated by XRD and XPS analysis that there is no multiphase zinc complex (ZnO or Zn(OH) ₂ ) in the 2D-Zn electrode, so that the method of the present invention does not It was confirmed that it is very advantageous for depositing pure Zn metal without lateral formation reaction. The electrical conductivity of 2D-Zn is close to that of a pure metal, which can guarantee electrochemical performance. A low level of oxidation state of Ni ²⁺ is detected in 2D-Zn/1.0, because the Zn nanostructure is not completely covered on the Ni current collector (Fig. 2(i)).

In order to confirm the quantitative content of 2D-Zn/1.0, 2D-Zn/1.8 and 2D-Zn/1.8/1.0, inductively coupled plasma-mass spectroscopy (ICP-MS) analysis was performed. The Zn/Ni atomic ratios of the prepared electrodes are summarized in Table 1 below.

Table 1 shows changes in the atomic ratio of Zn/Ni in 2D-Zn/1.0, 2D-Zn/1.8, and 2D-Zn/1.8/1.0 according to an embodiment of the present invention.

Material Zn (at.%) Ni (at.%) 2D-Zn/1.0 3 97 2D-Zn/1.8 30 70 2D-Zn/1.8/1.0 26 64

2D-Zn/1.0 contains a relatively low Zn content, indicating insufficiently deposited Zn on the nickel substrate. On the other hand, 2D-Zn/1.8 and 2D-Zn/1.8/1.0 showed atomic content of 30% and 26%, respectively. Structured metallic Zn was successfully deposited within a high voltage initial potential. A flat 2D-Zn//AC ZIC asymmetric supercapacitor was fabricated through the novel nanostructure of the Zn electrode. For whole cell fabrication, active carbon (AC) was used as the cathode material.

6 is an XRD pattern of (a) AC N ₂ adsorption/desorption isotherm, and (b) AC according to an embodiment of the present invention. To investigate the pore structure of AC, as shown in Fig. S3a, BET measurements were performed using an N ₂ adsorption/desorption isotherm. The AC isotherm shows Type I characteristics, indicating the presence of Zn micropores (<2 nm) at a relatively low pressure (P/P0 <0.1). It also has a high surface area of 2,201 m ² g ^-1 . The XRD pattern of activated carbon (Fig. S3b) shows two broad peaks at about 26° and 43°, which correspond to the (002) and (100) planes of amorphous carbon, respectively.

The prepared activated carbon exhibits an amorphous form and has a large surface area of 2,201 m ² g ^-1 (FIG. 6(a)). In addition, (b) of FIG. 6 shows the XRD data of AC.

7 is (a) Nyquist plots of the frequency before the charge/discharge test according to an embodiment of the present invention, (b) cyclic voltammetry (Cyclic ^voltammetry ; CV) curve, (c) specific capacitance calculated at current density ranging from 0.5 A g ^-1 to 20.0 A g ^-1 in the potential range from 0.2 V to 1.8 V, (d) 500 W kg ^-1 to 20,000 W kg ^{− 1} Power density and energy-related Ragone plots, (e) A graph showing cycle stability at a current density of 10.0 A g ^-1 over 10,000 cycles.

7A shows Nyquist plots by electrochemical impedance spectroscopy (EIS) analysis. It can be seen that the charge transfer resistance (Rct) of 2D-Zn/1.8 and 2D-Zn/1.8/1.0 in the high-frequency region (semicircle diameter) is lower than that of 2D-Zn/1.0, so that the stepwise interconnected It can be seen that the Zn structure improves the electrical contact and charge transfer capability. In addition, the linear slope of the plot curve in the low-frequency region implies the ion diffusion behavior at the surface between the electrode and the electrolyte (referred to as the Warburg impedance). The steepest inclined electrode of 2D-Zn/1.8/1.0 represents the lowest.

The Warburg impedance ensures the best ion diffusion kinetics through the electrode. 7 (b) shows a CV (Cyclic Voltammetry) curve having a voltage range of 0.2 V to 1.8 V. Redox humps on the CV curves of the 2D-Zn/1.8 and 2D-Zn/1.8/1.0 electrodes represent the Faraday redox reaction from the deposition/exfoliation of Zn ions (Zn ↔ Zn ²⁺ + 2e ⁻ ). As shown in FIG. 8 , the CV curves of the 2D-Zn/1.8 and 2D-Zn/1.8/1.0 electrodes with increased scan rates maintain the original profile to indicate the Zn ion redox reaction. Also, Fig. 9 shows the electric charge discharge curve of the prepared Zn electrode. The GCD curves have almost similar charge and discharge times, and show excellent coulombic efficiency performance. In contrast, the CV curve of 2D-Zn/1.0 showed no significant redox hump. This result may imply that the relatively small amount of Zn and low surface area from unstructured Zn on the substrate is insufficient to induce a noticeable electrochemical reaction. In addition, small amounts of Zn cannot maintain cell charge balance within the whole cell configuration with AC-based cathodes, resulting in no significant redox hump.

To directly compare the morphology and electrochemical performance of 2D-Zn, five electrodes with different morphologies (thin Zn foil (no structure), 2D-Zn/1.0 (no Zn on the substrate), 2D-Zn/1.8/30sec (basic framework structure), 2D-Zn/1.8/1.0 (hierarchical structure) and 2D-Zn/1.8/360sec (bulky structure) were electrochemically tested through a two-electrode cell system, as shown in Fig. 7(c). , the specific capacitance of the electrode was calculated by the GCD curve and the mass of the active material.

In terms of capacitance performance, the 2D-Zn/1.8/1.0 electrode can reach the highest specific capacitance of 468 F g ^-1 at a current density of 0.5 A g ^-1 . In addition, a specific capacitance of 2D-Zn/1.8/1.0 at a high current density of 20.0 A g ^-1 can be maintained up to 150 F g ^-1 . In contrast, the 2D-Zn/1.0 electrode does not contain a large amount of Zn plating on the Ni substrate without specific structures. As a result, it has negligible electrochemical reactivity with Zn ions. The specific capacitances of the 2D-Zn/1.8/30s and 2D-Zn/1.8 electrodes were 436 F g ^-1 and 406 F g -1 and 406 F g ^-1 at a current density of 0.5 A g ^-1 , respectively, higher than that of the 2D-Zn/1.8/1.0 electrode. low (Fig. 10). These results indicate that an additional secondary electroplating step with an operating voltage of 1.0 V leads to a much larger surface area after the initial electroplating at 1.8 V. The 2D-Zn/1.8 electrode exhibits lower capacitance than the 2D-Zn/1.8/30s electrode.

32 %)을 가지며, 주로 2D-Zn/1.8/30s(%) (13.7 %) 및 2D-Zn/1.8 (

12.2 %)의 값보다 훨씬 크다. 이는 2D-Zn/1.8/1.0의 단계적 구조가 충분한 전해질 이온 접촉을 제공하므로 이온 확산의 운동성을 향상시킬 수 있음을 의미한다. 결과적으로, 유도된 2D-나노구조는 전기화학적 캐패시턴스와 전하-전송 운동학을 개선할 수 있다. 따라서, 단계적으로 상호 연결된 Zn 구조를 구축하기 위해 전기 도금의 2단계 프로세스는 전체적인 에너지 저장 성능을 높이는데 매우 유리하다. 도 11에 도시된 바와 같이, 평평하고 얇은 Zn 포일은 최저 캐패시턴스 (전류 밀도 0.5 A g^-1에서 280 F g^-1), 속도 유지율 (0.5 A g^-1 내지 150 F g^-1까지의 전류 밀도로부터

1 %), 및 가장 평평한 EIS Warburg 임피던스를 보여주며, 전극의 구조의 중요성을 입증한다.This is because 2D-Zn/1.8 has a much thicker and bulky 2D structure that can reduce the total active sites on the electrode surface. According to the rate holding result, the calculated rate holding value of 2D-Zn/1.8/1.0 with a hierarchical structure was the largest (

32%), mainly 2D-Zn/1.8/30s(%) (13.7%) and 2D-Zn/1.8 (

12.2%). This means that the hierarchical structure of 2D-Zn/1.8/1.0 can improve the kinetics of ion diffusion as it provides sufficient electrolyte ion contact. Consequently, the derived 2D-nanostructure can improve the electrochemical capacitance and charge-transfer kinetics. Therefore, the two-step process of electroplating to build a stepwise interconnected Zn structure is very advantageous to increase the overall energy storage performance. 11, the flat and thin Zn foil has the lowest capacitance (current density 0.5 A g ^-1 to 280 F g ^-1 ), rate retention (current density from 0.5 A g ^-1 to 150 F g ^-1 ). from

1%), and the flattest EIS Warburg impedance, demonstrating the importance of the structure of the electrode.

As highlighted in the Ragone plot (Fig. 3(d)), the electrode of 2D-Zn/1.8/1.0 exhibited a maximum energy density of 208 W h kg ^-1 at a power density of 500 W kg ^-1 , and a maximum energy density of 20,000 W kg ⁻¹ can be obtained with a residual energy density of 66 W h kg ⁻¹ , which is much higher than previously reported supercapacitors. In addition, the cycling stability of 2D-Zn/1.8/1.0 was tested at a current density of 10.0 A g ⁻¹ over 10,000 cycles (Fig. 3(e)). The 2D-Zn/1.8/1.0 electrode shows excellent cycling stability with a capacitance retention of 99% even after 10,000 cycles. In addition, as shown in Fig. 12, it did not change even after 5,000 and 10,000 cycles of cycling tests by charge transfer resistance and Warburg impedance EIS measurements, demonstrating the excellent electrochemical kinetics and stability of 2D-Zn ZIC.

5.3으로 증가하면 Zn₄SO₄ (OH)₆·5H₂O와 같은 징크 설페이트 하이드록사이드 하이드레이트(zinc sulfate hydroxide hydrate)가 전극 표면 상에 형성되고, 사이클링 프로세스동안 pH가 감소하면 침전(precipitation)이 재용해 된다. 그러나 본 발명의 전기화학적 시스템에서는 전극 표면에서 징크 설페이트 하이드록사이드 하이드레이트의 침전/용해 반응이 관찰되지 않았다. 2D-Zn 전극을 상이한 차단 전압과 함께 순환시키고, 각 전극의 XRD 실험을 수행하여 (도 13), 징크 설페이트 하이드록사이드 하이드레이트의 형성이 없음을 나타낸다. Zn 이온을 갖는 비활성 Ni 집전체가 안정적인 백본 및 전자 경로로 작용하여 부반응없이 안정적인 전기화학적 프로세스를 유도할 수 있다고 가정할 수 있다. 중요한 것은, 이 증착 방법은 에너지 저장 응용을 위해 다양한 전도성 기판과 쉽게 호환될 수 있기 때문에, 이 프로세스는 다양한 플랫폼을 갖는 다른 플렉서블 전도성 기판에 적용될 수 있으며, 단계적으로 상호 연결된 2D Zn 나노 구조를 성공적으로 제조할 수 있다.In previous studies involving Zn foil-based ZICs, the pH of the electrolyte was

When increasing to 5.3, zinc sulfate hydroxide hydrate such as Zn ₄ SO ₄ (OH) ₆ ·5H ₂ O is formed on the electrode surface, and when the pH decreases during the cycling process, precipitation is is re-dissolved. However, in the electrochemical system of the present invention, no precipitation/dissolution reaction of zinc sulfate hydroxide hydrate was observed on the electrode surface. The 2D-Zn electrodes were cycled with different cut-off voltages, and XRD experiments of each electrode were performed ( FIG. 13 ), indicating no formation of zinc sulfate hydroxide hydrate. It can be hypothesized that an inert Ni current collector with Zn ions can act as a stable backbone and electron pathway to induce a stable electrochemical process without side reactions. Importantly, since this deposition method is easily compatible with a variety of conductive substrates for energy storage applications, this process can be applied to other flexible conductive substrates with various platforms and successfully fabricated stepwise interconnected 2D Zn nanostructures. can be manufactured.

Therefore, for the successful formation of 2D-Zn metal on the flexible fiber substrate, the voltage-matched electroplating method can be systematically applied. The fibrous 2D-Zn ZIC exhibits excellent energy storage performance due to its well-woven 2D nanostructure. As shown in Fig. 14(a) and Fig. 15, a 2D-Zn structure (2D-Zn@CF) on carbon fiber was successfully prepared as an anode. Activated carbon on carbon fiber (AC@CF) was also carried out by solution casting method as cathode. To fabricate the full-cell fibrous ZIC, the AC@CF electrode was wrapped with cellulose paper as a separator (FIG. 16), and then the AC@CF electrode was further woven by a 2D-Zn@CF anode. A gel electrolyte ( FIG. 17 ) was prepared by a homogeneous mixture of 1 M zinc sulfate (ZnSO ₄ ) and poly(vinylalcohol) (PVA) in deionized water. A ZnSO ₄ /PVA gel electrolyte was carefully coated on the Zn//AC cell. Finally, heat shrink tubing was covered to encapsulate the fibrous ZIC for chemical and physical protection.

18 is a (a) low-resolution and (b) high-resolution SEM image of a carbon fiber according to an embodiment of the present invention. Scanning electron microscopy (SEM) was used to measure the microstructure of carbon fibers. Individual carbon fibers have a flat surface and a diameter of 8 μm to 9 μm ( FIG. 16 ). Since carbon fibers have excellent flexibility, carbon components are suitable for wearable backbones, and (1) Zn nanostructures deposited on long carbon fibers can handle strain without degrading energy storage performance; (2) It is expected that multiple carbon fiber bundles can provide large electrochemically active areas that act as adsorption/desorption sites for electrolyte ions. Individual carbon fibers have a flat surface and a diameter of 8 μm to 9 μm.

19 is (a) low-resolution and (b) high-resolution SEM images of 2D Zn nanostructures on carbon fibers without surface functionalization according to an embodiment of the present invention.

The poor surface wettability of carbon fibers can prevent uniform nucleation and growth of the electroplated metallic material (FIG. 19). Therefore, the surface functionalization of carbon fibers was performed to control the surface energy and wettability by the surface chemical oxidation method.

20 is a C 1s XPS spectrum of a carbon fiber before (a) and after (b) surface functionalization according to an embodiment of the present invention. After surface functionalization, the percentage of oxygen-containing functional groups in the carbon fiber increased from 21.7% to 40.7%, suggesting a good surface condition of the carbon fiber (Fig. 20). 14 (b) shows an SEM image of a 2D-Zn@CF cell under different electroplating voltage conditions according to an embodiment of the present invention. At an operating voltage of 1.0 V, interconnected nanostructures of Zn were successfully plated with a thickness of 10 nm to 25 nm and a length of 1 μm to 3 μm.

21 shows 2D Zn nanostructure-decorated carbon fibers by electroplating at applied voltages of (a and b) 0.7 V and (c and d) 1.5 V according to an embodiment of the present invention.

In contrast, at a voltage of 0.7 V, the plating potential is not sufficient to form a stepped nanostructure and leads to a flat coverage of Zn (Fig. 21(a) and (b)). On the other hand, at a voltage of 1.5 V, the expected two-dimensional Zn nanostructure was not observed except for the bulk form of Zn (Fig. 21(c) and (d)). As shown in Fig. 14(c), the XRD peak of 2D-Zn@CF is well indexed to the crystal structure of hexagonal Zn. In addition, the chemical state of metal Zn in the 2D-Zn@CF sample is verified by XPS analysis (Fig. 14(d)).

22 is a TGA curve of 2D-Zn@CF from 200 °C to 950 °C in air at a heating rate of 10 °C/min ^-1 according to an embodiment of the present invention. Thermogravimetric analysis was also performed to investigate the content of Zn on the carbon fibers ( FIG. 22 ). TGA was also performed in air at 200 °C to 950 °C to confirm the Zn content. The weight of the carbon fiber is assigned to a 100% loss, meaning that there is only one phase of the carbon composite without impurities. On the other hand, the TGA curve of 2D Zn@CFs contains a weight loss of 52% indicating the presence of Zn atoms. In addition, the weight loss curves of 2D Zn@CFs slightly increase with increasing temperature due to the oxidized Zn metal (ZnO). 2D-Zn@C shows a weight loss of 52%, indicating the presence of Zn atoms.

23 is a CV curve of 2D-Zn@CF at a scan rate varying from 5 mV s ⁻¹ to 200 mV s ⁻¹ in a potential range of 0.2 V to 1 1.8 V according to an embodiment of the present invention (a) (b) ) GCD curves of 2D-Zn@CF at current densities ranging from 0.05 mA cm ^-2 to 3 mA cm ^-2 . The electrochemical behavior of the fibrous 2D-Zn ZIC was investigated by CV curve and GCD curve (Fig. 23), which is in good agreement with the flat ZIC result.

24 is a graph of the calculated specific capacitance of Zn 2D Zn nanostructures and 2D Zn@CF electrodeposited on carbon fibers at applied voltages of 0.7 V and 1.5 V according to an embodiment of the present invention. The fibrous 2D-Zn ZIC can achieve a high specific capacitance of 56-24 mF cm ^-2 at a current density of 0.05-3.0 mA cm ^-2 (FIG. 24).

25 is an EIS curve of Zn 2D Zn nanostructure and 2D-Zn@CF electrodeposited on carbon sesame oil at applied voltages of 0.7 V and 1.5 V according to an embodiment of the present invention. In addition, the EIS results also clearly confirm that the interconnected nanostructures of 2D-Zn provide advantageous ion diffusion capacity (Fig. 25).

26 is (a) 50 μW cm ^-2 to 3,000 μW cm ^-2 Ragone plots related to power density and energy, (b) cycle stability of 1.0 mA cm ^-2 for 10,000 cycles, (c) ) capacitance retention in straight, folded and knotted states, (d) capacitance retention obtained in water for 15 h, (e) in water driven by series and parallel connected fiber ZICs in the knotted state. A diagram showing a light emitting diode.

Energy and power densities were calculated as highlighted in the Ragone plot (Fig. 26(a)). Fiber-type ZICs have high energy densities of 25 to 12 μW cm ^-2 , and also exhibit high cycling stability over 10,000 cycles as well as excellent power densities ranging from 50 to 3,000 μW cm ^-2 , which is similar to that of other reported fiber-type capacitors. even better (Fig. 26(b)).

27 is (a and b) low-resolution and (c and d) high-resolution SEM images of ZIC 2D-Zn/1.8/1.0 and 2D-Zn@CF after 10,000 cycles according to an embodiment of the present invention.

After the cycling test, the structural resolution of both ZIC 2D-Zn/1.8/1.0 and 2D-Zn@CF was investigated using SEM (Fig. 27). The original morphology 2D-Zn remained well after 10,000 cycles, indicating that the corresponding dendrites may not form on the Zn surface. Therefore, Zn ion energy storage applications are the best candidates for stable and long-term operation. In addition, (c) of FIG. 26 shows that the fibrous ZIC can maintain its original energy storage performance even when folded and knotted, indicating high mechanical flexibility of the fibrous ZIC.

These results confirm that the voltage-specific electroplating method is a powerful engineering tool for fabricating flexible energy storage applications. In addition, the water resistance of the ZIC was also tested. The electrochemical performance of the fibrous ZIC was evaluated under precipitation as shown in Fig. 26(d). The capacitance of the ZIC is well maintained in water for long-term use.

28 shows GCD curves of two fiber-like ZICs with (a) series and (b) parallel connected 2D-Zn@CF, (c) total device capacitance and parallel-connected fiber-based in accordance with an embodiment of the present invention. It is a graph showing the relationship between the number of ZICs.

Two fibrous ZICs were connected in series or in parallel (Fig. 28(a) and (b)). When two devices are connected in series, the charge/discharge voltage range is doubled and the total GCD time is doubled in parallel. Multi-fiber type ZICs (up to 5 devices) were connected in parallel (Fig. 28(c)), and the total capacitance increased proportionally with the number of connected ZIC devices. Finally, we demonstrated that multi-fiber type ZICs can successfully power red light-emitting diodes (LEDs) despite being strongly knotted in water (Fig. 26(e)).

conclusion

In summary, in an embodiment of the present invention, stepwise interconnected 2D Zn nanostructures were fabricated by an electroplating method to improve the overall ion and electron transport performance of supercapacitors. The flat ZIC achieves a high energy density of 208 Wh kg ^-1 at a high power density of 500 W kg ^-1 as well as an outstanding long-term cycle of over 10,000 cycles. In addition, the fibrous ZIC exhibits excellent energy density at high power density of 50 μWh cm ^-2 , excellent energy storage performance of 25 μWh cm ^-2 , excellent cycling stability, excellent mechanical flexibility, and excellent waterproof properties. The excellent performance of the supercapacitors fabricated according to the embodiment of the present invention is due to the nano-architecture providing electrochemically large active sites, high energy storage performance, and enhanced ion transport in the stepwise interconnected 2D-Zn nanostructures. I think it induces. Therefore, the present invention shows that the voltage tailored electroplating method and the following 2D-Zn structures can provide new insights for future wearable energy storage applications and can be applied to other devices such as zinc-ion anode batteries.

As described above, although the embodiments have been described with reference to the limited drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques are performed in an order different from the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (17)

A first electroplating step with a transition metal on the substrate; and
second electroplating the transition metal-plated substrate with the transition metal;
including,
The transition metal is zinc (Zn),
The first electroplating step is to apply a voltage of 0.5 V to 2 V for 10 seconds to 60 seconds,
The second electroplating step is to apply a voltage of 0.5 V to 2 V for 300 seconds to 500 seconds,
The first electroplating step is to apply a higher voltage than the second electroplating step,
The first electroplating step and the second electroplating step are performed in a two-electrode cell,
A method for manufacturing a porous electrode.
According to claim 1,
Wherein the substrate comprises a Ni-foam, a carbon-containing substrate, or both,
A method for manufacturing a porous electrode.
3. The method of claim 2,
The carbon-containing substrate may include carbon fiber, activated carbon, carbon black, acetylene black, furnace black, ketchup black, super-P (Super-P), fine graphite powder, carbon nanotubes (CNT), fibrous carbon whiskers, Which comprises at least one selected from the group consisting of vapor-grown carbon fiber (VGCF), graphene and graphite,
A method for manufacturing a porous electrode.
delete delete According to claim 1,
The first electroplating step is to nucleate the seeds of the transition metal,
A method for manufacturing a porous electrode.
7. The method of claim 6,
In the second electroplating step, the nucleated seed is crystal-grown,
A method for manufacturing a porous electrode.
delete A porous electrode prepared by the method of claim 1 .
10. The method of claim 9,
The porous electrode will include a porous interconnected two-dimensional nanopores,
porous electrode.
10. The method of claim 9,
The specific surface area of the porous electrode will be 50 m ² /g to 3000 m ² /g,
porous electrode.
10. The method of claim 9,
The pore diameter of the porous electrode will be 10 nm to 500 nm,
porous electrode.
10. The method of claim 9,
The porous electrode will include a flat type, a fibrous type, or both,
porous electrode.
A cathode comprising the porous electrode of claim 9;
anode; and
an electrolyte filled between the cathode and the anode;
containing,
super capacitor.
15. The method of claim 14,
The supercapacitor is
At 0.5 A g ^-1 current density, having a capacitance of 400 F g ^-1 to 500 F g ^-1 ,
At a current density of 20.0 A g ^-1 , it has a capacitance of 100 F g ^-1 to 200 F g ^-1 ,
super capacitor.
15. The method of claim 14,
wherein the supercapacitor has a capacitance retention of 98% or more in galvanostatic charge-discharge cycles of 1 to 10,000,
super capacitor.
15. The method of claim 14,
The supercapacitor is a zinc ion supercapacitor,
super capacitor.

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