KR102559521B1 - Vanadium Carbide Nanowire and Preparing Method thereof - Google Patents

Abstract

A vanadium carbide nanowire formed on a carbon cloth is provided. Vanadium carbide nanowires can be synthesized by a facile hydrothermal synthesis method and can be annealed in a hydrogen atmosphere. Vanadium carbide nanowires can be used as positive electrode active materials in lithium ion batteries or sodium ion batteries, and can exhibit excellent capacity stability even during long-term use, and can exhibit high mitigation ability even when volume changes due to positive ions.

Description

Vanadium carbide nanowire and manufacturing method thereof

A vanadium carbide nanowire and a method for manufacturing the same are provided.

Transition metal carbides can be used as excellent materials in various industrial fields, such as electronic devices, electrochemical catalysts, and energy storage devices. Among transition metal carbides, vanadium carbide has excellent chemical stability and electrical conductivity, is abundant in nature, and has various stoichiometric properties such as VC, V ₂ C, V ₄ C ₃ , V ₆ C ₅ , and V ₈ C ₇ . Also, vanadium has a relatively smaller atomic weight than IVB, VB, and VIB metals. Due to these characteristics of vanadium, vanadium carbide, especially V ₈ C ₇ , has a stable structure, and thus is valuable in various engineering fields. In vanadium carbide, vanadium atoms having a structure of P4 ₃ 32 are located slightly away from the face centered cubic (FCC) structure, and the aligned carbon atoms are arranged in empty spaces similar to Fm3m. Recently, according to a study using density functional theory, the hybrid orbital between the d orbital of vanadium and the s and p orbitals of carbon expands the d band structure showing metallic characteristics.

Lithium-ion batteries are mainly used as a power source for electronic devices, electric vehicles, and wearable devices due to their high energy density and excellent stability. In a lithium ion battery, the electrical storage capacity and energy density depend on the cathode active material having a relatively low theoretical capacity compared to the anode. In addition, since the chemical reaction of the cathode active material occurs at 1V or more higher than that of the anode active material, the cathode active material requires high electrochemical stability. The theoretical capacities of the widely used cathode materials LiCoO ₂ (lithium cobalt oxide), LiNiO ₂ (lithium nickel oxide), LiFePO ₄ (lithium iron phosphate oxide), and LiMn ₂ O ₄ (lithium manganese oxide) are 274, 275, 170, and 148 mAh/g, respectively, and the actual capacities are 160, 170, 160, and 13 At 0 mAh/g, it is much lower than the capacity (372 mAh/g) of graphite, an anode active material.

Oxide-based cathode active materials have poor stability when used for a long time due to low electrical conductivity. Among the cathode active materials, lithium cobalt oxide and lithium nickel oxide, which are the most used, show high price, low thermal/chemical stability, and rapid capacity loss. Lithium manganese oxide shows a phenomenon in which manganese is dissolved in an electrolyte due to a Jahn-Teller distortion phenomenon. LiNi _x Co _y Mn _1-xy O ₂ (LNCMO) developed to overcome these disadvantages has a relatively low price and high capacity, but has a non-homogeneous structure of lithium and nickel due to the high nickel content, which reduces the capacity and deteriorates thermal stability.

Vanadium oxide has an oxidation number of 2 to 5, so it is a promising cathode active material that shows a theoretical capacity of about 298 mAh/g when reacting with two lithium ions and about 442 mAh/g when reacting with three lithium ions. However, vanadium oxide shows a serious capacity decrease when used for a long time due to its low electrical conductivity (V ₂ O ₃ : 2.5 S/cm, VO ₂ : 10 ² S/cm, V ₂ O ₅ : 10 ^-2 S/cm).

Sodium ion batteries are in the limelight as a next-generation battery due to their low price compared to lithium and standard electrode potential as low as lithium. However, it has not been commercialized due to the absence of an appropriate cathode active material that can withstand volume expansion due to the size of a large sodium atom. In addition, Na ₃ V ₂ (PO ₄ ) ₃ , which is an excellent ionic conductor of sodium, is an attractive material but lowers the mobility of sodium ions due to its low surface area.

An embodiment is intended to exhibit excellent electrochemical performance and excellent capacity stability even when used for a long time in a lithium ion battery or a sodium ion battery.

One embodiment is to show a high surface area and high mitigation ability even in a volume change by positive ions in a lithium ion battery or a sodium ion battery.

In addition to the above tasks, embodiments according to the present invention may be used to achieve other tasks not specifically mentioned.

Vanadium carbide nanowires according to an embodiment are formed on a carbon cloth.

The carbon fabric may have a cylindrical shape, the vanadium carbide nanowires may include a plurality of vanadium carbide nanowires, and the plurality of vanadium carbide nanowires may be radially grown from the carbon fabric.

The vanadium carbide nanowire may include V ₈ C ₇ having a space group of P4 ₃ 32 .

A cathode active material for a lithium ion battery according to an embodiment includes vanadium carbide nanowires. Here, the vanadium carbide nanowires may be formed on the carbon fabric.

A cathode active material for a sodium ion battery according to an embodiment includes vanadium carbide nanowires. Here, the vanadium carbide nanowires may be formed on the carbon fabric.

A method for preparing a vanadium carbide nanowire according to an embodiment includes preparing a carbon fabric, preparing a first solution by mixing a vanadium precursor material and a carboxyl-based compound in water, preparing a second solution by ultrasonicating the first solution, adding an amine compound to the second solution and inserting the carbon fabric, hydrothermal synthesis, and annealing in a hydrogen atmosphere.

Carbon fabrics can be oxygen plasma coated.

A method for manufacturing vanadium carbide nanowires according to an embodiment includes preparing a carbon fabric, preparing a first solution by mixing ammonium metavanadate (NH ₄ VO ₃ ) and oxalic acid (C ₂ H ₂ O ₄ ) in water, preparing a second solution by ultrasonicating the first solution, adding hexamethylenetetramine (C ₆ H ₁₂ N ₄ ) to the second solution and inserting the carbon fabric, It includes thermally synthesizing, and annealing in a hydrogen atmosphere.

A lithium ion battery according to an embodiment includes a cathode active material including vanadium carbide nanowires.

A sodium ion battery according to an embodiment includes vanadium carbide nanowires.

According to an embodiment, a vanadium carbide nanowire having excellent electrochemical performance may be provided, and excellent capacity stability may be exhibited even when used for a long time in a lithium ion battery or a sodium ion battery, and a vanadium carbide nanowire having a high surface area may be provided, and may exhibit high mitigation ability even in a volume change due to positive ions in a lithium ion battery or a sodium ion battery.

1A to 1C are SEM images of vanadium carbide nanowires according to an embodiment.
1d to 1f are TEM images of vanadium carbide nanowires according to an embodiment.
2A is an XRD pattern of a vanadium carbide nanowire according to an embodiment, and FIG. 2B is an XRD pattern of a vanadium carbide nanowire after charging and discharging for 10 cycles.
Figure 2c is a graph by Raman spectroscopy of vanadium carbide nanowires according to an embodiment.
Figure 2d is a graph by Fourier transform infrared spectroscopy of vanadium carbide nanowires according to an embodiment compared to vanadium oxide nanowires.
2e and 2f are graphs of V 2p and C 1s of a vanadium carbide nanowire according to an embodiment by X-ray photoelectron spectroscopy.
3A and 3B are graphs showing charge/discharge cycles at 0.1 C and charge/discharge cycles at 0.1 to 120 C for 100 cycles when the vanadium carbide nanowire according to an embodiment is applied to a lithium ion battery.
3C is a graph showing specific capacitance at 0.1 to 120 C when the vanadium carbide nanowire according to an embodiment is applied to a lithium ion battery.
3D is a graph showing capacity stability compared to vanadium oxide nanowires when the vanadium carbide nanowires according to an embodiment are applied to a lithium ion battery.
3E is a CV graph when the vanadium carbide nanowire according to an embodiment is applied to a lithium ion battery.
3F is a diagram showing a graph obtained by electrochemical impedance spectroscopy and a Randle circuit, which is an equivalent circuit, when the vanadium carbide nanowire according to an embodiment is applied to a lithium ion battery.
4A is a graph showing charge/discharge cycles at 0.1 C for 100 cycles when the vanadium carbide nanowire according to an embodiment is applied to a sodium ion battery.
4B is a graph showing specific capacitance at 0.05 to 60 C when the vanadium carbide nanowire according to an embodiment is applied to a sodium ion battery.
4C is a graph showing capacity stability for 100 cycles when the vanadium carbide nanowire according to an embodiment is applied to a sodium ion battery.
4D is a CV graph when the vanadium carbide nanowire according to an embodiment is applied to a sodium ion battery.
4E is a diagram showing a graph obtained by electrochemical impedance spectroscopy and a Randl circuit, which is an equivalent circuit, when vanadium carbide nanowires according to an embodiment are applied to a sodium ion battery.
4F is a graph comparing capacity stability of other candidate materials for lithium ion batteries and sodium ion batteries and vanadium carbide nanowires according to an embodiment.
5 is a diagram schematically illustrating a method of manufacturing a vanadium carbide nanowire according to an embodiment.

With reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. This invention may be embodied in many different forms and is not limited to the embodiments set forth herein. In order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are used for the same or similar components throughout the specification. In addition, in the case of widely known known technologies, detailed descriptions thereof will be omitted.

Throughout the specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Then, a vanadium carbide nanowire and a manufacturing method thereof according to an embodiment will be described in detail.

By growing vanadium carbide nanowires (V ₈ C ₇ NW) on carbon cloth by hydrothermal synthesis, they can be used as cathode active materials for lithium-ion batteries or sodium-ion batteries. Vanadium oxide nanowires (V ₂ O ₃ NW) are grown through a facile hydrothermal synthesis method, and vanadium carbide is synthesized by reducing oxygen in vanadium oxide in a hydrogen/argon atmosphere. In contrast to vanadium oxide (V ₂ O ₅ NW) annealed in an oxygen atmosphere, when applied to lithium ion batteries and sodium ion batteries, it shows excellent stability and electrochemical performance in 500 charge/discharge tests. For example, as a cathode active material for a lithium ion battery, it shows an electric storage capacity per weight of about 203.9 mAh/g, and after 500 charge/discharge cycles, a capacity retention of about 91.12% and a coulombic efficiency of about 99.84% at a C-rate of 0.1C. In the case of a sodium ion battery, it shows an electricity storage capacity per weight of about 176.34 mAh/g. Due to the reduced oxygen vacancies in vanadium oxide, the surface area of vanadium carbide nanowires is about 5 times higher than that of vanadium oxide (183.27 m ² /g). In addition, vanadium carbide nanowires have a unique structure and exhibit high mitigation ability even in volume changes caused by positive ions in a lithium ion battery or a sodium ion battery. Compared to commercially available cathode active materials, vanadium carbide nanowires show excellent stability and electrical conductivity, and the synergistic effect with the three-dimensional carbon fabric makes it possible to contact more positive ions in lithium-ion batteries or sodium-ion batteries.

According to one embodiment, a vanadium carbide nanowire (V ₈ C ₇ NW) grown directly on a carbon fabric through a facile hydrothermal synthesis method is provided. The carbon fabric used as the current collector has a unique three-dimensional structure, excellent electrical conductivity, and chemical stability. Compared to commercially available electrodes with a two-dimensional structure (aluminum or copper), one-dimensional vanadium carbide nanowires grown on three-dimensional carbon fibers increase the contact area for cations through a high surface area and provide excellent electron transfer pathways. In addition, volume expansion can be alleviated due to the insertion of positive ions in a lithium ion battery or a sodium ion battery. Vanadium carbide nanowires can improve the electrochemical performance of a cathode active material of a lithium ion battery or a sodium ion battery.

Referring to FIG. 5 , vanadium carbide nanowires are formed on a carbon fabric. The carbon fabric is formed by gathering a plurality of carbon fibers to have a three-dimensional shape as a whole. The carbon fabric may have a cylindrical shape. A plurality of vanadium carbide nanowires are radially grown from a carbon fabric.

A method for preparing a vanadium carbide nanowire according to an embodiment includes preparing a carbon fabric, preparing a first solution by mixing a vanadium precursor material and a carboxyl-based compound in water, preparing a second solution by ultrasonicating the first solution, adding an amine compound to the second solution and inserting the carbon fabric, hydrothermal synthesis, and annealing in a hydrogen atmosphere.

First, prepare a carbon fabric. Carbon fabrics can be oxygen plasma coated. Since the carbon fabric itself is hydrophobic, in the case of oxygen plasma treatment, the mixed solution permeates well into the carbon fabric, so that nanowires can grow uniformly. For example, the carbon fabric may be coated with oxygen plasma for about 3 to 10 minutes at a pressure of about 0.1 to 0.5 torr and an output of about 30 to 70 W, and when a higher pressure and higher power than this are applied to the carbon fabric, damage to the carbon fiber may be applied and the physical stiffness of the carbon fiber may decrease.

Next, a first solution is prepared by mixing a vanadium precursor material and a carboxylic compound with water.

The vanadium precursor material may include ammonium metavanadate (NH ₄ VO ₃ ). For example, when ammonium metavanadate is used, the yield can be increased because it is well diluted in water as an intermediate when vanadium is purified.

The carboxylic compound may include a dicarboxylic acid compound. For example, the dicarboxylic acid-based compound may include oxalic acid. When oxalic acid is used, oxalic acid is easily diluted in water and reacts with vanadium to easily produce vanadium oxide.

A first solution may be prepared by mixing about 1.3 to 1.7 parts by weight of a vanadium precursor material and about 2.8 to 3.2 parts by weight of a carboxyl-based compound with about 60 to 100 parts by weight of water. Here, when the contents of the vanadium precursor and oxalic acid are insufficient, vanadium nanooxide nanowires (V ₂ O ₃ ) may not be uniformly generated, and when the contents of the vanadium precursor and oxalic acid are excessive, they may be grown in the form of wide plates or rods instead of thin nanowires.

Next, a second solution is prepared by sonicating the first solution. For example, ultrasonic treatment may be performed for about 80 minutes or more. Here, when the sonication time is less than 80 minutes, vanadium metavanadate and oxalic acid may not be completely diluted in water.

Next, after adding an amine compound to the second solution and inserting the carbon fabric, hydrothermal synthesis is performed.

The amine compound may include hexamethylenetetramine (C ₆ H ₁₂ N ₄ ). For example, hexamethylenetetramine can be easily diluted in water and can efficiently remove ammonium from ammonium metavanadate.

The amine compound may be used in an amount of about 0.1 to 0.4 parts by weight.

Hydrothermal synthesis may be performed in an oven at about 140 to 160 degrees Celsius for about 60 minutes or more. Here, if the hydrothermal synthesis time is lower than 60 minutes, the nanowires may not grow uniformly, and if the time is longer than 60 minutes, the length of the nanowires may continue to increase.

Next, annealing is performed in a hydrogen atmosphere.

In an atmosphere of about 2:1 to 4:1 hydrogen and argon, the annealing time may be 5 hours and 30 minutes or more. If the annealing time is short, oxygen may not be completely reduced in vanadium oxide.

Hereinafter, the present invention will be described in more detail with examples, but the following examples are only examples of the present invention and the present invention is not limited to the following examples.

Example

Synthesis of vanadium carbide nanowires through hydrothermal synthesis and annealing in hydrogen atmosphere

The carbon fabric was coated with oxygen plasma for 5 minutes at a pressure of 0.3 torr and an output of 50 W. 1.5 g of ammonium metavanadate (NH ₄ VO ₃ ) and 2.9 g of oxalic acid (C ₂ H ₂ O ₄ ) were diluted in 50 mL of purified water and ultrasonically injected for 90 minutes. Then, 0.22 g of hexamethylenetetramine (C ₆ H ₁₂ N ₄ ) is added and transferred to a Teflon autoclave vessel. After immersing the oxygen plasma-coated carbon fabric, it is hydrothermally synthesized in an electric oven at 150 degrees Celsius for 1 hour, and then transferred to room temperature and cooled naturally. After cooling, it is washed with ethanol and dried. After drying, it is heat-treated for 5 hours in an atmosphere of hydrogen and argon (3:1) in an electric heating furnace at 360 degrees Celsius.

material analysis

XRD (X-ray diffraction) analysis is performed at a voltage of 40 kV and a current of 300 mA. X-ray photoelectron spectroscopy is performed to identify vanadium carbide. Raman spectroscopy and Fourier-transform infrared spectroscopy are measured in the spectral ranges of 100 to 3000 /cm and 400 to 4000 /cm, respectively. Electron paramagnetic resonance analysis is performed under conditions of room temperature and 1 mW microwave output at an X-band frequency of 9.623 GHz. The morphology of the sample is observed with a scanning electron microscope and transmission electron microscopy, and a specific surface area analysis is performed using a nitrogen adsorption method. Measure the sheet resistance of the sample using a 4-point probe, and convert/calculate it into electrical conductivity.

electrochemical analysis

Vanadium carbide nanowires and lithium and sodium were used as positive and negative electrodes in Li-ion/sodium-ion batteries, respectively. The diameter of the electrode is 15 mm, and the weight of the active material is 3 mg. CR2032 coin cells are fabricated in an argon-filled glovebox. Polypropylene is used as a separator, and 1 M LiPF6 (EC:DMC 1:1) and 1 M NaPF6 (EC:PC 1:1) are used as electrolytes, respectively. The charge/discharge test is conducted at various current densities in the voltage range of 2 to 4 V. Electrochemical Impedance Spectroscopy was performed in the range of 500,000 Hz to 0.1 Hz with 10 mV RMS.

result

The vanadium carbide nanowires grown on the carbon fabric were clearly observed by SEM as shown in FIGS. 1A to 1C. The vanadium carbide nanowire has a length of 2 μm and a diameter of 140 nm. After 10 charge/discharge cycles, morphological changes of the vanadium carbide nanowires are observed. The volume of vanadium carbide nanowires is changed by intercalation/deintercalation of lithium ions. TEM images of vanadium carbide nanowires are shown in FIGS. 1D-1F. An abundant defect space is also predicted from the ratio of the carbon D peak to the graphitic G peak by Raman spectroscopy, as shown in FIG. 2c. Carbon occupies the space vacated by oxygen atoms during annealing in a hydrogen/argon atmosphere. The lattice of the vanadium carbide nanowires shows high crystallinity, as shown in Fig. 1f. The specific surface area (187.23 m ² /g) of the vanadium carbide nanowires was measured by the Brunauer-Emmett-Teller N ₂ adsorption method. The XRD patterns of the vanadium carbide nanowires shown in FIGS. 2a and 2b follow the chemical reaction formula below in the hydrothermal synthesis process.

V ₂ O ₃ + (5-x)C → 2VC _1-x + 3CO

VC _1-x belongs to the randomly distributed Fm3m space group. During annealing, the position of carbon is changed from amorphous to crystalline, and the crystal structure of Fm3m is changed to P4 ₃ 32 as shown in the chemical reaction below.

8VC _1-x + (8x-1)C → V ₈ C ₇

The XRD patterns agree well with the JCPDS card (89-1096). The peaks at 37.2°, 39.8°, 43.3°, 47.2°, 59.8°, 63.2°, 75.2°, and 78.5° represent planes of (222), (320), (400), (200), (520), (440), (622), and (542). These peaks belong to the cubic structure of the P4 ₃ 32 space loop and indicate the stability of the structure.

The XRD patterns after 10 charge/discharge cycles confirm the lithium and sodium storage mechanisms of the vanadium carbide nanowires. Since the positions of the peaks do not change even after charge/discharge, it can be seen that the cation storage of the vanadium carbide nanowire is intercalation/desorption. In addition, the d-spacing of the dominant (400) plane of the vanadium carbide nanowire is calculated by the cubic formula (1/d ² = h ² + k ² + l ² /a ² ). The calculated d-spacing value is 4.49 Å. Electrical conductivity is measured using a 4-point probe. The sheet resistance and electrical resistance of the vanadium carbide nanowires are 1.036 Ω/sq and 21.78 mΩ/cm, and the electrical conductivity is improved by 10 ³ compared to vanadium oxide. Structural/chemical changes of the vanadium carbide nanowires were confirmed by Raman spectroscopy as shown in FIG. 2c. The D and G bands of carbon are located at 1359 and 1600 cm ^-1 , and the I _D / I _G ratio is about 1.26, and the carbon changes from C sp ² to C sp ³ in the vanadium carbide nanowire. The D and G bands of carbon are also observed in Fourier transform infrared spectroscopy. The G band seen at a wavelength of 1625 cm ^-1 means a strong carbon bond (C=C), and the D band seen at a wavelength of 1448 cm ^-1 means that there are many defect spaces in the material. Most of the carbon atoms are located at sp ³ and the synthesized material shows high chemical activity due to localization of surface charge by defect spaces. Defects in the carbon atoms holding the vanadium atoms in the vanadium carbide nanowires are identified through EPR analysis. In a typical EPR spectrum of carbon, a value between 2.0016 and 2.0032 indicates the presence of free electrons, and the vanadium carbide nanowire showed a strong paramagnetic signal of 2.00266 and a g-factor value of 2.00266.

V 2p and C 1s spectra are analyzed by XPS. As shown in FIG. 2e, peaks observed at 523.45, 515.83, 518.67, and 511.63 eV in the V 2p spectrum coincide with V 2p 1/2 and V 2p 3/2. In addition, peaks at 287, 285, and 284 eV in the C 1s spectrum indicate C-O bonds, V-C bonds, and C-C bonds. The V-C bond means that the vanadium carbide nanowire was successfully synthesized.

Many defect spaces in vanadium carbide nanowires improve electrochemical performance. By applying various current densities (0.03, 0.06, 0.09, 0.13, 0.25, 0.63, 0.88, 1.25, 1.88, 2.5, and 3.75 A/g) in the voltage range of 2 to 4 V, the electrochemical performance was measured, and cyclic voltammetry was performed at a scan rate of 0.1 mV/s. In the case of the charge/discharge test, the vanadium carbide nanowire shows a specific capacitance of 303.28 mAh/g in the first cycle of a current density (0.1C) of 33.3 mA/g. After an irreversible reaction to create a solid-electrolyte interphase (SEI) layer on the surface, a specific capacitance of 277.20 mAh/g is shown in the 5th cycle. Afterwards, the specific capacitance was measured for 500 cycles, and the capacity retention capacity was 91.12% compared to the initial capacity. Vanadium carbide nanowires show a relatively low initial capacity compared to vanadium oxide nanowires (V ₂ O ₅ NW, 440.76 mAh/g). However, vanadium oxide nanowires show a rapid capacity drop due to high irreversible reactions in the ω phase. The specific capacitance of the vanadium carbide nanowires at various current densities was measured from 0.1 C to 120 C, as shown in Figs. 3b and 3c. It shows excellent rate performance due to its high electrical conductivity and structural stability. Also, 292.75, 285.54, 230.34, 207.99, 179.3, 134.97, 114.48, 93.79, 68.55, 51.37 at 0.1, 0.3, 0.5, 1, 2, 4, 6, 12, 60, and 120 C, and It shows a specific capacitance of 32.27 mAh/g. Current densities are listed in the table of FIG. 3C. At current densities of 33.33 and 50 mA/g, the vanadium carbide nanowires show excellent capacity retention rates during 500 charge/discharge cycles.

CV measurements are performed at a scan rate of 0.1 mV/s. The two peaks observed at 2.26 and 2.6 V represent reduction and oxidation reactions, respectively. Peaks due to reduction and oxidation reactions in the initial cycle are observed at 2.21 and 2.56 V due to irreversible reactions that make the SEI layer. After the initial cycle, the CV curve stabilizes. EIS can analyze the surface resistance caused by the movement of cations and the electrochemical reaction between the vanadium carbide nanowire and the electrolyte. In the high frequency region, the surface resistance due to the movement of lithium ions is 4.776 Ω. In the mid-frequency region, a semicircle is observed due to the high charge transfer and the rough surface of the active material. In addition, it exhibits a low charge transfer resistance and a high diffusion rate of ions is observed in a diffusion-controlled regime with a Warburg impedance of 50°.

In the case of a cathode for a sodium ion battery, a specific capacitance of 220.90 mAh/g is shown under a current density of 0.1C (20 mA/g) in the first cycle. And after the formation of the SEI layer, the 5th cycle shows a capacity of 200.82 mAh/g. As shown in FIG. 4 , the vanadium carbide nanowires have excellent structural stability at various current densities (0.05 to 60 C) in the rate capability test results. The cycle stability test at a current density of 0.1C shows a capacity retention rate of 93.34% compared to the initial capacity for 300 charge/discharge cycles.

CV measurement is performed at the scan rate under the same conditions as a lithium ion battery. Similar to Li-ion batteries, peaks due to two pairs of reduction/oxidation reactions in the first cycle are seen at 2.35 and 2.74 V. After the irreversible reaction is over, peaks are observed at 2.43 and 2.86 V. The positions of the peaks between the lithium-ion battery and the sodium-ion battery differ by the existing electrode potential difference (E ⁰ _Li/Li + = -3.04 V, E ⁰ _Na/Na + = -2.71 V). The surface resistance at high frequencies is 7.023 Ω, and the low charge transfer resistance at low frequencies is about 40 degrees. The electric circuit model corresponds to the Randle circuit. Referring to FIG. 4f , compared to other candidate materials, the vanadium carbide nanowires show excellent electrochemical performance.

Vanadium carbide nanowires can be successfully synthesized on carbon fabrics and confirmed through structural and morphological analyses. As a cathode active material for lithium and sodium ion batteries, vanadium carbide nanowires exhibit excellent electrochemical performance, high specific capacitance (303.28 and 220.9 mAh/g), excellent rate performance at a current density of 0.05 to 120 C, and excellent capacity retention during 500 and 300 charge/discharge cycles, respectively. Such excellent performance is achieved by the light weight of vanadium and carbon, the formation of defect spaces by the removal of oxygen atoms in the annealing process, and the one-dimensional nanowire with high electrical conductivity. It has a high specific surface area due to defect cavities and mitigates volume changes during charge/discharge. In addition, the improved electrical conductivity of the vanadium carbide nanowires shows excellent cycle stability during 500 charge/discharge cycles. The synergistic effect with the three-dimensional carbon fabric current collector can provide a flexible three-dimensional substrate that withstands the volume change caused by the intercalation of lithium and sodium ions. Accordingly, the vanadium carbide nanowires can be used as cathode active materials for lithium and sodium ion batteries.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also within the scope of the present invention.

Claims (12)

delete delete delete delete delete delete delete Preparing a carbon fabric;
Preparing a first solution by mixing a vanadium precursor material and a carboxylic compound in water;
preparing a second solution by ultrasonicating the first solution;
hydrothermal synthesis after adding an amine compound to the second solution and inserting the carbon fabric; and
Annealing in a hydrogen atmosphere
A method for manufacturing a vanadium carbide nanowire comprising a.
In paragraph 8,
The carbon fabric is a method for producing a vanadium carbide nanowire that is coated with oxygen plasma.
Preparing a carbon fabric;
Preparing a first solution by mixing ammonium metavanadate (NH ₄ VO ₃ ) and oxalic acid (C ₂ H ₂ O ₄ ) in water;
preparing a second solution by ultrasonicating the first solution;
Adding hexamethylenetetramine (C ₆ H ₁₂ N ₄ ) to the second solution, inserting the carbon fabric, and hydrothermal synthesis; and
Annealing in a hydrogen atmosphere
A method for manufacturing a vanadium carbide nanowire comprising a.
Including a cathode active material containing a vanadium carbide nanowire,
The vanadium carbide nanowires are formed on a carbon cloth, the vanadium carbide nanowires include a plurality of vanadium carbide nanowires, and the plurality of vanadium carbide nanowires are radially grown from the carbon cloth,
A lithium-ion battery whose specific capacitance remains above 175 mAh/g at a C-rate of 0.1C after 500 charge and discharge cycles.
Including a cathode active material containing a vanadium carbide nanowire,
The vanadium carbide nanowires are formed on a carbon cloth, the vanadium carbide nanowires include a plurality of vanadium carbide nanowires, and the plurality of vanadium carbide nanowires are radially grown from the carbon cloth,
A sodium-ion battery that maintains a specific capacitance of 150 mAh/g or more at a C-rate of 0.1C after 300 charge and discharge cycles.