KR20230012314A - Manufacturing method of interconnected graphitic carbon nanocubes containing nickel and nitrogen and use thereof - Google Patents

Abstract

The present invention relates to a method for synthesizing interconnected one-dimensional graphite nanocubes containing nickel and nitrogen and to application thereof as a functional separator for a lithium-sulfur battery and an electromagnetic wave shielding material. The structure of interconnected one-dimensional graphite nanocubes containing nickel and nitrogen induces internal reflection of EM waves and provides meso- and macro-porous spaces that can confine the active materials of lithium-sulfur cells. Nickel nanoparticles partially embedded inside graphite nanocubes act as self-absorbers and electrocatalysts for EM and EC barriers, respectively. Nitrogen atoms doped into the highly crystalline graphite wall not only improve the electrical conductivity against the conduction loss of EM waves but also enhance the chemical interaction with the active materials. Various electromagnetic and electrochemical analyses show that graphite nanocubes have excellent performance as EM and EC barriers. As a result, the electromagnetic wave shielding material based on graphite nanocubes, which is an EM barrier, shows an optimal RL value of -62.1 dB at 12.1 GHz with a small amount of graphite nanocubes. Additionally, a resulting lithium-sulfur battery using a graphite nanocube-based functional separator as an EC barrier shows excellent rate performance and stable cycling performance at high rates. The interconnected graphite nanocubes containing nickel and nitrogen according to the present invention have the effect of providing a wide range of alternatives for designing new carbon nanomaterials with unique microstructures and diverse functions.

Description

Manufacturing method and application of interconnected graphite nanocubes containing nickel and nitrogen

The present invention relates to a method for manufacturing interconnected N-doped graphitic nanocube with Ni nanoparticles (Ni@N-IGN) containing nickel and nitrogen and to use the same as an electromagnetic wave shielding material and a functional separator of a lithium-sulfur battery. It relates to applications, and more particularly, to the synthesis of interconnected one-dimensional graphite nanocube structures through chemical reaction between metal precursors and nitrogen-rich organic precursors and low-temperature heat treatment, and electromagnetic wave shielding materials and lithium using graphite nanocubes using the synthesis method -It relates to functional separators for sulfur batteries.

In the field of materials research, the development of allotropes of carbon nanomaterials with various dimensions from zero to three is receiving much attention. Among them, carbon nanomaterials with various dimensions show great potential as core materials in electromagnetic (EM) and electrochemical (EC) applications due to their excellent physical-chemical properties derived from their structural features.

In the field of electromagnetic wave absorption, carbon materials are attracting attention as electromagnetic wave shielding materials because of their advantageous properties such as high electrical conductivity and light weight. However, since carbon materials have poor impedance matching and can only use reflectance without absorption, EM wavelength absorption performance is insufficient, which limits achieving high standards for practical implementation.

Meanwhile, as the demand for sustainable energy sources continues to increase, lithium-sulfur (Li-S) batteries are promising candidates for next-generation EC energy storage systems due to their high energy density and low sulfur cost. As an EC barrier to solve important problems caused by complex mechanisms, functional membranes are a new concept that plays an important role in preventing the passage of active materials and promoting slow EC reactions. Despite significant progress in carbon-based functional separators, chemical fixation and catalytic effects are required for more high-performance separators.

Taken together, exploring new kinds of carbon nanostructures with desired functions to overcome the limitations of existing carbon nanostructures is of great interest in both research fields.

Accordingly, the present invention proposes interconnected graphite nanocubes doped with nickel and nitrogen having desirable functions as electromagnetic and electrochemical barriers in order to solve the above problems.

One object of the present invention is to provide a new type of carbon nanostructure and a manufacturing method through carbonization and phase transition of a coordination compound between a nitrogen-rich organic precursor and a nickel metal salt.

Another object of the present invention is to apply the interconnected graphite nanocubes as an electromagnetic wave shielding material and a functional separator of a lithium-sulfur battery, thereby providing the interconnected graphite nanocubes as new materials in both research fields.

In order to achieve the above object, the present invention provides a method for synthesizing interconnected graphite nanocubes. A method for producing interconnected graphite nanocubes containing nickel and nitrogen, comprising the steps of: 1) preparing a mixture by dissolving melamine in distilled water; 2) obtaining a dispersion by adding and dispersing nickel nitrate hexahydrate and sodium hydroxide to the mixture; and 3) obtaining a metal-organic compound by centrifuging the dispersion; 4) aging the metal-organic compound; 5) obtaining a powder by heat-treating the aged metal-organic compound at a temperature of 90 to 110 °C; 6) heating the powder to a temperature of 300 to 1000 °C; 7) further heat-treating the heated powder at a temperature of 900 to 950 °C; and 8) etching the carbide structure obtained in step 7) using a hydrochloric acid solution; can include

Preferably, nickel nitrate hexahydrate and sodium hydroxide in step 2) may be 40 to 50 parts by weight of nickel nitrate hexahydrate and 20 to 40 parts by weight of sodium hydroxide, based on 100 parts by weight of melamine in step 1).

Preferably, in step 2), the dispersion may be performed with an ultrasonic disperser for 2 to 4 minutes.

Preferably, the centrifugation in step 3) may proceed for 8 to 12 minutes at 8500 to 9500 rpm.

Preferably, the aging in step 4) may be performed by putting the metal-organic compound prepared in step 3) in distilled water and aging at a temperature of 80 to 90 °C for 4 to 6 hours.

Preferably, the temperature in step 6) may be raised to a temperature of 300 to 1000 °C at a rate of 5 °C/min in a furnace filled with nitrogen gas (N ₂ ).

Preferably, the heat treatment in step 7) may be an additional heat treatment for 2 to 4 hours.

Preferably, in step 8), the carbide structure is etched with a 0.5 to 1.5 M hydrochloric acid solution at a temperature of 75 to 85 ° C for 2 to 4 hours to remove nickel metal particles present on the outside of the carbide structure.

Preferably, an electromagnetic wave shielding material prepared by mixing 900 to 100 parts by weight of paraffin with 5 parts by weight of the interconnected graphite nanocubes containing nickel and nitrogen may be provided.

Preferably, 100 parts by weight of the interconnected graphite nanocubes containing nickel and nitrogen prepared above, 10 to 15 parts by weight of carbon black as a conductive material and 10 to 15 parts by weight of polyvinylidene fluoride (PVDF) as a binder It is possible to provide a functional separator for a lithium-sulfur battery prepared by mixing parts.

According to the present invention as described above, by providing interconnected graphite nanocubes prepared through aging and heat treatment of metal-organic compounds, electromagnetic wave shielding materials prepared using these graphite nanocubes, and functional separators for lithium-sulfur batteries, In both research fields, it is effective in achieving excellent shielding performance as an electromagnetic wave shielding material and high capacity of lithium-sulfur batteries by overcoming the limitations of existing carbon nanostructures.

1 shows (a) XRD patterns, (b) Raman spectra and (c) XPS measurement results of Examples 1 and 2 of the present invention and melamine.
2 shows (a) XRD patterns and (b) Raman spectra of carbonized samples for each temperature according to embodiments of the present invention.
3 shows TEM images of carbonized samples for each temperature of one embodiment of the present invention.
Figure 4 shows (a) XRD patterns, (b) Raman spectra, (c) XPS analysis, and (d) nitrogen isothermal adsorption curve and pore size distribution of the sample prepared in Example 7 of the present invention.
5 shows a TEM image of a sample prepared in Example 7 of the present invention.
6 is a characteristic analysis result of the sample prepared in Example 8 of the present invention as an electromagnetic wave shielding material. (a) permittivity, (b) magnetic permeability and (c) magnetic loss in the frequency range from 0.5 to 18 GHz.
7 shows (a) a graph of magnetic loss according to thickness and frequency of a sample prepared in Comparative Example 1 of the present invention, and (b) a theoretical absorption frequency band for each thickness and magnetic loss for each sample.
8 is an analysis result conducted to confirm the interaction and catalytic activity of the Ni@N-IGN-based functional separation membrane prepared in Example 9 and Comparative Example 2 of the present invention with polysulfide. (a) UV spectroscopy, (b) TEM and EDX images, (c) XPS Li 1s, (d) XPS S 2p, and (e) polysulfide diffusion experiments of Ni@N-IGN-based functional separators.
9 is an electrochemical analysis result of a lithium-sulfur battery incorporating functional separators based on Ni@N-IGN, MWCNT, and SWCNT prepared in Example 10 and Comparative Example 3 of the present invention. (a) CV curves measured at a scan rate of 0.1 to 1 mVs ^-1 , (b) rate performance test measured at a rate rate of 0.2 to 5C and (c) charge / discharge voltage curves measured at a rate rate of 0.2 to 5C show
10 shows analysis results of cycle performance measured at rates of 1,3, and 5C of a lithium-sulfur battery incorporating a Ni@N-IGN-based functional separator prepared in Example 10 of the present invention.

The present invention relates to interconnected graphite nanocubes containing nickel and nitrogen that exhibit excellent performance as electromagnetic wave shielding materials and functional separators for lithium-sulfur batteries. Graphite nanocubes can be obtained through phase transition and carbonization of a nickel-melamine coordination compound. Through XRD, Raman spectrum, XPS, and TEM analysis, it was found that one-dimensionally interconnected graphite nanocubes were synthesized that had a graphite shell with a high degree of graphitization, contained some nickel nanoparticles in the hollow structure inside, and contained nitrogen inside the graphite structure. Confirmed.

The electromagnetic wave shielding material prepared using the interconnected graphite nanocubes can induce internal reflection of EM waves from the hollow nanocube structure, and effective self-absorption can be expected from nickel nanoparticles partially included in the graphite nanocubes. . In addition, nitrogen-doped highly crystalline graphite walls can act as stable electrical pathways and contribute to the conduction loss of effective EM waves.

On the other hand, the functional separator of the lithium-sulfur battery prepared using the interconnected graphite nanocubes can accommodate and trap lithium polysulfide from meso- and macro-sized porous spaces inside the graphite nanocubes, which are the basic units of the interconnected graphite nanocubes. Nickel nanoparticles inside graphite nanocubes can act as catalysts to accelerate the reaction of lithium-sulfur batteries. In addition, the nitrogen-functionalized graphite structure not only provides improved electrical conductivity but also effectively prevents the shuttle effect through chemical interaction with lithium polysulfide.

Electromagnetic shielding materials and separators for lithium-sulfur batteries prepared using these interconnected graphite nanocubes can exhibit performance of an optimal RL value of -62.1dB at 12.1GHz even with a small amount of interconnected graphite nanocubes as an EM barrier. In addition, as a result of using the graphite nanocube functional separator interconnected by the EC barrier, the lithium-sulfur battery can exhibit high capacity and stable cycling performance even at high rates of 998 and 785 mAh g-1 at 1 and 5 C, respectively.

Hereinafter, the present invention will be described in detail.

According to one aspect of the present invention, a method for synthesizing interconnected graphite nanocubes is provided.

The synthesis method of the interconnected graphite nanocubes is 1) preparing a mixture by dissolving melamine in distilled water, 2) adding and dispersing nickel hydrate and sodium hydroxide to the mixture to prepare a dispersion, 3) centrifuging the dispersion Separating to obtain a metal-organic compound, 4) adding the metal-organic compound to distilled water and applying a certain temperature to obtain an aged mixture, 5) drying the aged mixture to obtain a powder, 6) Step of heating the powder to a target temperature of 330 to 900 ° C., 7) obtaining a carbon structure by additionally heat-treating the powder raised to the target temperature at 900 ° C., and 8) etching the carbon structure obtained by the heat treatment with a strong acid. include

The ratio of melamine and distilled water in step 1) is 40 parts by weight of distilled water when melamine is 1.37 parts by weight.

Nickel nitrate hexahydrate in step 2) is 0.42 parts by weight, and sodium hydroxide is 0.3 parts by weight. The dispersion was dispersed for 5 minutes using an ultrasonic disperser. In step 2), nickel nitrate hexahydrate reacts with sodium hydroxide to form alpha-nickel hydroxide (α-Ni(OH) ₂ ), and forms a metal-organic compound through interaction with melamine.

The centrifugation in step 3) was carried out for 10 minutes, and after centrifugation, unreacted residual ions were removed to obtain metal-organic compounds as precipitates.

Put the precipitate of step 4) in 40 parts by weight of distilled water, put it in an 85 degree convection oven, and age it for 5 hours. In this process, nitrate ions (NO3 ^- ) escape from the alpha-nickel hydroxide (α-Ni(OH) ₂ ) structure to form beta-nickel hydroxide (β-Ni(OH) ₂ ), Nitrate ions released from melamine interact with melamine and remain in the melamine structure.

The mixture of step 5) is heat-treated at 100 degrees to obtain a green powder.

The target temperature of step 6) is 320 to 1000 ° C, and the temperature is raised by 5 or 10 ° C per minute, and the sample when the temperature is raised by 5 ° C is the best.

The additional heat treatment in step 7) was performed for 60, 120, or 180 minutes, and samples maintained for 180 minutes are best.

For the acid treatment in step 8), 1M hydrochloric acid (HCl) was used.

According to another aspect of the present invention, a method for manufacturing an electromagnetic wave shielding material using interconnected graphite nanocubes is provided.

The method of manufacturing the electromagnetic wave shielding material includes 1) synthesizing interconnected graphite nanocubes, 2) mixing the interconnected graphite nanocubes with paraffin, and 3) preparing the mixture in a toroidal form.

The interconnected graphite nanocubes of step 1) are synthesized using the above-mentioned interconnected graphite nanocube synthesis method.

The weight ratio of the interconnected graphite nanocubes and paraffin in step 2) is 95 parts by weight of paraffin when the graphite nanocubes are 5 parts by weight.

In step 3), the mixture of graphite nanocubes and paraffin is compressed into a toroidal shape and prepared. At this time, the ratio of the outer diameter to the inner diameter is 3.04 for the inner diameter when the outer diameter is 7. The thickness of the sample is 1 to 4.5 mm, but is preferably 2.45 mm.

According to another aspect of the present invention, a method for manufacturing a functional separator for a lithium-sulfur battery using interconnected graphite nanocubes is provided.

The method for manufacturing a functional separator of a lithium-sulfur battery includes 1) synthesizing interconnected graphite nanocubes, 2) preparing a slurry by mixing the interconnected graphite nanocubes, a conductive material and a binder, 3) preparing the slurry coating a polypropylene (PP) separator using a doctor blade; and 4) drying the coated separator under vacuum.

The interconnected graphite nanocubes of step 1) are synthesized using the above-mentioned interconnected graphite nanocube synthesis method.

In step 2), when the interconnected graphite nanocubes are 8 parts by weight, the conductive material is 1 part by weight and the binder is 1 part by weight. A slurry is prepared by adjusting the viscosity while dispersing the mixture in a N-Methyl-2-pyrrolidone (NMP) solution.

Using the doctor blade of step 3), the slurry is coated on a polypropylene (PP) separator to a thickness of 10 μm.

The coated separator in step 4) is dried in a vacuum oven at 60 degrees.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and it will be apparent to those skilled in the art that the scope of the present invention is not to be construed as being limited by these examples.

Example 1.

After dissolving 1.37 g of melamine in 40 ml of distilled water, 0.42 g of nickel nitrate hexahydrate and 0.3 g of sodium hydroxide are mixed. This mixture is dispersed for 3 minutes in an ultrasonic disperser to obtain a compound in which melamine and alpha-nickel hydroxide (α-Ni(OH) ₂ ) react. The mixture was separated in a centrifuge at 9000 rpm for 10 minutes to remove unreacted ions and to obtain a precipitate. At this time, the sample name is α-Ni(OH) ₂ -Mel.

Example 2.

The precipitate obtained in Example 1 was put into 40 ml of distilled water and aged for 5 hours in a convection oven at 85 degrees. The mixture is heat-treated at 100 degrees to obtain a green powder. At this time, the sample name is β-Ni(OH) ₂ -Mel.

Example 3.

The powder obtained in Example 2 was heated at a rate of 5°C per minute in a nitrogen atmosphere using a box furnace to reach a target temperature of 330°C. At this time, the sample name is Ni@N-IGN_330.

Example 4.

It is performed in the same manner as in Example 3, but the target temperature is 440° C., and the sample name is Ni@N-IGN_440.

Example 5.

It is performed in the same manner as in Example 4, but the target temperature is 600° C., and the sample name is Ni@N-IGN_600.

Example 6.

It is performed in the same manner as in Example 5, but the target temperature is 900° C., and the sample name is Ni@N-IGN_900.

Example 7.

After the same procedure as in Example 6, the sample reaching the target temperature was additionally heat-treated at 900° C. for 3 hours. In order to remove the nickel metal particles present on the outside of the carbide structure obtained by heat treatment, an etching process was performed at 80 ° C. for 3 hours with a 1M hydrochloric acid (HCl) solution, and the sample name was Ni@N-IGN.

Example 8.

5 wt% of Ni@N-IGN obtained in Example 7 and 95 wt% of paraffin were mixed. Using the mixture, a toroidal-shaped sample having an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a thickness of 2.45 mm was prepared using a compressor to prepare an electromagnetic wave shielding material.

Example 9.

N-methyl-2-pyrrolidone (N-Methyl- A slurry is prepared by adjusting the viscosity while dispersing in a 2-pyrrolidone, NMP) solution. After coating the prepared slurry on a polypropylene (PP) separator, put it in a vacuum oven at 60 degrees and hold it in a vacuum state for 12 hours to dry it. Through the above process, a functional separator for a lithium-sulfur battery is prepared.

Example 10.

After mixing Ketjen Black and sulfur at a ratio of 7:3 and heat-treating at 155℃ for 12 hours, the cathode active material, conductive material (Super P), and binder (carboxymethyl cellulose, CMC) were dispersed in distilled water at a weight ratio of 8:1:1. A slurry is prepared by adjusting the viscosity. After coating the prepared slurry on aluminum foil, it was dried in a vacuum atmosphere to prepare a positive electrode for a lithium-sulfur battery. A coin cell was manufactured using a positive electrode and lithium metal as a negative electrode prepared in a dry room, and the functional separator prepared in Example 9 was used.

Comparative Example 1.

It is carried out in the same manner as in Example 8, but the thickness is adjusted to 1 to 4.5 mm.

Comparative Example 2.

Performed in the same manner as in Example 9, but instead of the interconnected graphite nanocubes prepared in Example 7, single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (Multi-wall carbon nanotubes, MWCNT ) is used.

Comparative Example 3.

Performed in the same manner as in Example 10, but instead of the interconnected graphite nanocube functional separator prepared in Example 9, single-wall carbon nanotubes (SWCNTs) prepared in Comparative Example 2, multi-walled carbon It is performed using a multi-wall carbon nanotube (MWCNT) functional separator and a basic polypropylene (PP) separator.

Test Example 1.

X-ray diffraction analysis, Raman analysis, and XPS analysis were performed on melamine and the samples prepared in Examples 1 and 2.

The X-ray diffraction pattern of each sample was analyzed using an X-ray diffractometer (G.N.R. Europe 600) using Ni beta-filtered CuKa radiation (λ = 0.154 nm), and Raman spectroscopy was performed using a Raman microscope (Ramanforce, Nanophoton). proceeded using XPS (K-Alpha, Thermo Fisher) was performed to analyze the chemical composition of each sample.

The results are shown in Figure 1.

1 shows melamine, a nitrogen-rich organic precursor, and samples prepared in Examples 1 and 2, α-Ni(OH) ₂ -Mel and β-Ni(OH), to analyze the growth behavior of interconnected graphite nanocube precursors. ) ₂ -Mel is the result of X-ray diffraction analysis, Raman analysis and XPS analysis.

Referring to FIG. 1A, all three samples showed characteristic peaks of melamine, indicating that melamine maintained its original structure without changing during the preparation of the precursor. In the α-Ni(OH) ₂ -Mel sample of Example 1, characteristic peaks of α-Ni(OH) ₂ were observed at 33.8 ° and 60.3 °, which correspond to the (101) and (110) planes. This indicates that α-Ni(OH) ₂ was synthesized as a result of the reaction between nickel nitrate hexahydrate and NaOH. In addition, the β-Ni(OH) ₂ -Mel sample of Example 2 showed different characteristic peaks at 33.7 °, 38.8 °, 52.8 ° and 59.7 °, indicating that β-Ni(OH) ₂ (100), ( 101), (102) and (110) planes. Through this, it can be seen that α-Ni(OH) ₂ was aged to β-Ni(OH) ₂ in the 5-hour aging process of Example 2.

Referring to FIG. 1b, Raman analysis shows that α-Ni(OH) ₂ -Mel of Example 1 is dominated by surface ν(OH) in the range of 3500-3700 cm ^-1 , whereas β-Ni(OH) of Example 2 ₂ -Mel represents bulk ν(OH) only. From the changes in the Raman spectrum, it can be seen that a phase transition occurred as water molecules and anions were removed from the α-Ni(OH) ₂ structure in the aging step. In addition, the characteristic peak corresponding to NO ₃ ^- in the range of 1000-1100cm-1 in β-Ni(OH) ₂ -Mel of Example 2 does not disappear, so that NO ₃ ^- escaped from the structure is not removed and bound to melamine indicates that it is

Referring to FIG. 1c, as a result of XPS N1s analysis of melamine and β-Ni(OH) ₂ -Mel of Example 2, -NH observed in melamine in β-Ni(OH) ₂ -Mel of Example 2 In addition to peaks corresponding to ₂ and -N=, additional peaks of -N ⁺ H= and NO ₃ ^- are observed. From this result, it can be seen that the NO ₃ ^- ions released in the aging step reacted with the protonated melamine to form melamine-NO ₃ ^- crosslinks.

Test Example 2.

X-ray diffraction analysis, Raman analysis, and transmission electron microscopy (TEM) analysis were performed on the samples prepared according to Examples 3 to 6.

The X-ray diffraction pattern of each sample was analyzed using an X-ray diffractometer (G.N.R. Europe 600) using Ni beta-filtered CuKa radiation (λ = 0.154 nm), and Raman spectroscopy was performed using a Raman microscope (Ramanforce, Nanophoton). proceed using TEM (JEM-2100F, JEOL) is used to observe the microstructure of the sample.

Results are shown in FIGS. 2 and 3 .

2 shows the thermal decomposition at 330, 440, 600, and 900 ° C to examine the carbonization behavior of β-Ni (OH) ₂ -Mel by temperature, and then X-ray diffraction analysis and Raman analysis of these samples. is the result of running

Referring to FIG. 2a, as a result of the XRD diffraction pattern analysis of the sample at each temperature, in β-Ni(OH) ₂ -Mel_330 of Example 3, the diffraction peak of melamine decreased, whereas the peak corresponding to β-Ni(OH) ₂ was almost disappear The pattern of β-Ni(OH) ₂ -Mel_440 in Example 4 shows the formation of Melem and NiO. In the case of β-Ni(OH) ₂ -Mel_600 of Example 5, it can be seen that carbon nitride (gC ₃ N ₄ ) was formed by polymerization of melem and NiO was reduced to nickel carbide. As a result of the analysis of β-Ni(OH) ₂ -Mel_900 in Example 6, peaks at 44.5 ° and 52 ° corresponding to the (111) and (200) planes of nickel metal appeared, indicating that nickel carbide was reduced at high temperature to nickel It can be seen that metal is formed, and it can be seen from the diffraction peak appearing at 26.5 ° that a graphite structure having high crystallinity is formed.

Referring to FIG. 2b, as a result of Raman analysis of the sample at each temperature, β-Ni(OH) ₂ -Mel_330 of Example 3 showed triazine skeletal vibrations in the 1000 cm ^-1 range and CN in the 1170-1740 cm ^-1 range. /C=N stretching peak is observed, and condensed melamine peak is observed. In β-Ni(OH) ₂ -Mel_440 of Example 4, triazine skeletal vibrations and CN/C=N stretching became sharp, and the peak corresponding to melamine disappeared. Also, a peak corresponding to NiO is observed at 500 cm-1. In the case of β-Ni(OH) ₂ -Mel_600 of Example 5, CC, D-, and G-bands corresponding to 700, 1368, 1560 and 3000 cm ^-1 regions are observed. Sharp G and 2D peaks are also observed in β-Ni(OH) ₂ -Mel_900 of Example 6. From this, it can be seen that highly crystalline graphite was formed.

3 is a result of performing TEM analysis on these samples after thermal decomposition at 330, 440, 600, and 900 ° C units to examine the carbonization behavior of β-Ni(OH) ₂ -Mel by temperature.

Referring to FIG. 3a, β-Ni(OH) ₂ -Mel_330 of Example 3 shows a condensed melamine structure.

Referring to FIG. 3B, the β-Ni(OH) ₂ -Mel_440 of Example 4 was further condensed and an overlapping melem sheet structure was observed.

Referring to FIG. 3c, round black particles of β-Ni(OH) ₂ -Mel_600 of Example 5 are observed, which are nickel carbide nanoparticles. Also, carbon nitride (gC ₃ N ₄ ) begins to grow in a unique one-dimensional structure around the nickel carbide nanoparticles.

Referring to FIG. 3D, in β-Ni(OH) ₂ -Mel_900 of Example 6, all of the carbon nitride (gC ₃ N ₄ ) is decomposed to form a uniform one-dimensional graphite structure as a whole. The one-dimensional graphite structure shows a structure in which cubes are interconnected, and shows a highly crystalline graphite structure. Also, nickel nanoparticles formed by reduction from nickel carbide were observed inside the structure.

Test Example 3.

X-ray diffraction analysis, Raman analysis, XPS analysis, nitrogen isothermal adsorption analysis, and transmission electron microscopy (TEM) analysis were performed on the sample prepared in Example 7.

The X-ray diffraction pattern of each sample was analyzed using an X-ray diffractometer (G.N.R. Europe 600) using Ni beta-filtered CuKa radiation (λ = 0.154 nm), and Raman spectroscopy was performed using a Raman microscope (Ramanforce, Nanophoton). proceed using XPS analysis (K-Alpha, Thermo Fisher) is performed to confirm the chemical composition of the sample, and nitrogen isothermal adsorption analysis is performed to analyze the specific surface area and pore size of the sample. TEM (JEM-2100F, JEOL) analysis proceeds to observe the microstructure of the sample.

Results are shown in Figures 4 and 5.

Referring to FIGS. 4A and 4B, as a result of X-ray diffraction analysis of Example 7 (Ni@N-IGN), a sharp (002) pattern was observed, indicating that the structure did not collapse during the acid treatment step. Through the appearance of diffraction patterns corresponding to the (111) and (200) planes of nickel metal, it can be seen that nickel metal present outside the structure is removed during the acid treatment process, and nickel metal present inside the structure still remains. . In addition, as a result of Raman analysis, the G and 2D-bands were still observed, confirming that the highly crystalline graphite structure had not collapsed.

Referring to FIG. 4c, the XPS N1s analysis result of Example 7 (Ni@N-IGN) confirmed that the nitrogen content was 3.85 at%, and through XPS N1s deconvolution, Pyridinic, which has good catalytic performance among nitrogen species, was confirmed. It can be seen that N and Pyrrolic N form the main.

Referring to FIG. 4d, through the nitrogen isothermal adsorption curve and pore size analysis of Example 7 (Ni@N-IGN), the specific surface area was 278.32 m ² g ^-1 and most of the pore sizes were 3-4 nm. It was confirmed that it was made.

Referring to FIG. 5, it was confirmed through the TEM analysis result of Example 7 (Ni@N-IGN) that a uniformly formed one-dimensional interconnected graphite nanocube structure was formed. As a result of measuring the interplanar distance using a high-resolution TEM image, it can be seen that the dark part corresponds to the Ni (111) plane at 0.20 nm and the shell part that forms the structure corresponds to the C (002) plane at 0.34 nm.

Test Example 4.

Permittivity, magnetic permeability, and magnetic loss (Reflection loss, RL) of the electromagnetic wave shielding material having a thickness of 1 to 4.5 mm prepared according to Example 8 and Comparative Example 1 were measured. Since the electromagnetic wave shielding materials of Example 8 and Comparative Example 1 cannot directly measure the permittivity and magnetic permeability of the conductive material, the electromagnetic wave shielding materials were prepared by mixing insulating paraffin and Ni@N-IGN.

The analysis results are shown in FIGS. 6 and 7 .

Referring to FIG. 6A, the real permittivity and imaginary permittivity of the electromagnetic wave shielding material having a thickness of 2.45 mm of Example 8 show values in the ranges of 6 to 10 and 1 to 3, respectively, in the 0.5 to 18 GHz frequency range. This is a value suitable for an EM wave absorbing film. It is observed that the real permittivity decreases and the imaginary permittivity increases in the frequency domain around 12 GHz. This results from interfacial polarization due to charge accumulation at the interface between nickel nanoparticles and graphite nanocubes and multiple reflections induced from the multilayer structure.

Referring to FIG. 6B, the real permeability and imaginary permeability of the electromagnetic wave shielding material having a thickness of 2.45 mm of Example 8 show values of -1.07 and -0.05, respectively, in the X-band (8-12 GHz) region. This is due to the presence of nickel nanoparticles inside the structure.

Referring to FIG. 6C, the magnetic loss was calculated from the measured permittivity and magnetic permeability using the following formula.

The RL peak appears at 12 GHz from the decrease in real permittivity and high permeability in the 12 GHz region. When the thickness is 2.45 mm, the optimal RL value of -62.1 dB is shown at 12.1 GHz.

Referring to FIG. 7A, RL measurement values in the 0.5-18 GHz frequency range for the electromagnetic wave shielding materials having a thickness of 1 to 4.5 mm manufactured in Example 8 and Comparative Example 1 are shown.

Referring to FIG. 7B, electromagnetic wave absorption of the thickness of 1 to 4.5 mm prepared in Comparative Example 1 was evaluated by the following 1/4 wavelength matching model.

where t _m is the thickness of the EM wavelength absorbing film, c is the luminous flux, and f _m is the frequency corresponding to the optimal RL value in the thickness. From the graph shown in FIG. 7B, it can be seen that the thickness calculated by the 1/4 wavelength matching model and the optimal RL value are well matched.

Test Example 5.

UV-vis spectroscopy, TEM and EDX analysis measured after an adsorption test on a polysulfide solution to confirm the interaction and catalytic ability of the Ni@N-IGN-based functional separation membrane prepared in Example 9 with polysulfide , XPS and polysulfide diffusion experiments were conducted.

The above results are shown in FIG. 8 .

Referring to FIG. 8A, the results of the adsorption test on the polysulfide solution for the Ni@N-IGN, MWCNT, and SWCNT-based functional separation membranes prepared in Example 9 and Comparative Example 2 and the UV-vis spectroscopy of the solution after adsorption Results are shown. 8a, it was confirmed that the solution containing Ni@N-IGN became transparent after the adsorption test, and the solution containing MWCNTs and SWCNTs was brown, the same as polysulfide. As a result of UV-vis spectroscopic measurement of the solutions, the superior adsorption performance of the Ni@N-IGN-based functional separator was confirmed compared to MWCNT and SWCNT through comparison of absorbance in the 250 ~ 300 nm region.

Referring to FIG. 8B , TEM and EDX images of the membrane were measured after performing an adsorption test on the polysulfide solution for the Ni@N-IGN-based functional membrane prepared in Example 9. Through the elemental sulfur mapping results, it can be seen that polysulfide is well adsorbed on the surface and inside of Ni@N-IGN. This is because the surface chemical interaction with polysulfide is improved from the presence of nitrogen in Ni@N-IGN, and the porous pores are used as lithium polysulfide reservoirs.

Referring to FIGS. 8C and 8D , these are XPS Li 1s and S 2p graphs measured after an adsorption test was performed on the Ni@N-IGN-based functional separation membrane prepared in Example 9 in a polysulfide solution. In the Li 1s spectrum of FIG. 8c, two peaks are observed at 54.7 and 55.7 eV corresponding to Li-S and Li-N. It can be seen that the polysulphide is captured on the surface through chemical interaction with surface nitrogen. In the S 2p spectrum of FIG. 8d, peaks corresponding to polysulfide appeared at 163.58 and 164.9 eV, and peaks at 167.3, 168.1, 168.8, and 169.9 eV corresponding to thiosulfate and polythionate species other than the two peaks were observed, indicating that Ni@N - It can be seen that the surface oxidation-reduction reaction of polysulfide was promoted through the IGN-based functional separation membrane.

Referring to FIG. 8E, it is a photograph of a polysulfide diffusion experiment progressing with respect to the Ni@N-IGN-based functional separator prepared in Example 9. A diffusion experiment was conducted with a functional separator in the middle, a polysulfide solution on one side, and distilled water on one side. As a result of the experiment, the color of the distilled water did not change even after 12 h, indicating that the Ni@N-IGN-based functional separation membrane effectively inhibited polysulfide elution.

Test Example 6.

CV test, rate performance test, A charge/discharge voltage curve measurement and a cycle performance test were conducted.

The performance results are shown in FIGS. 9 and 10 .

Referring to FIG. 9A, in the CV curve of the lithium-sulfur battery incorporating the Ni@N-IGN-based functional separator, two clear reduction peaks in the cathode scan and two oxidation peaks in the cathode scan are observed. Peaks I and II indicate a stepwise reduction of S8 to LiPS (LiSx, 4 ≤ x ≤ 8) and LiS. Peaks III and IV seen in the anodic scan indicate stepwise oxidation proceeding. In addition, the stable electrochemical reversibility of the Ni@N-IGN-based functional membrane is shown through the appearance of clear redox peaks even at high scan rates.

Referring to FIG. 9B, for the evaluation of electrochemical performance of a lithium-sulfur battery incorporating a general PP separator, MWCNT and Ni@N-IGN-based functional separator, rate control at 0.2 to 5 C (1C = 1672 mAg ^-1 ) This is the result of the performance test. In the case of lithium-sulfur batteries using PP separators and MWCNT-based functional separators, they did not operate at high rates and showed low capacity characteristics, but in lithium-sulfur batteries using Ni@N-IGN-based functional separators It showed significantly improved specific capacity, rate performance and stable Coulombic efficiency. Ni@N-IGN separator cells showed the highest average specific capacities of 1323, 1069, 998, 914, 866, 826 and 785 mAh g-1 at 0.2, 0.5, 1, 2, 3, 4 and 5C.

Referring to FIG. 9c, it can be confirmed that the reaction proceeds stably as the reaction flat surface is maintained without disappearing even at a high rate in the voltage profile of the lithium-sulfur battery in which the Ni@N-IGN-based functional separator is introduced.

Referring to FIG. 10, the Ni@N-IGN separator cell exhibited initial discharge capacities of 1067, 850, and 814 mAh g ^-1 in tests of 300 cycles at rates of 1,3, and 5C, respectively, after each cycle. 874, 714, and 644 mAh g ⁻¹ were preserved after 300 cycles at 1, 3 and 5 C. Cycle tests show that the Ni@N-IGN separator cell runs stably even after high rates and long cycles.

Above, a specific part of the present invention has been described in detail, and for those skilled in the art, it is clear that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (10)

1) preparing a mixture by dissolving melamine in distilled water;
2) obtaining a dispersion by adding and dispersing nickel nitrate hexahydrate and sodium hydroxide to the mixture; and
3) obtaining a metal-organic compound by centrifuging the dispersion;
4) aging the metal-organic compound;
5) obtaining a powder by heat-treating the aged metal-organic compound at a temperature of 90 to 110 °C;
6) heating the powder to a temperature of 300 to 1000 °C;
7) further heat-treating the heated powder at a temperature of 900 to 950 °C; and
8) etching the carbide structure obtained in step 7) using a hydrochloric acid solution; Method for producing interconnected graphite nanocubes containing nickel and nitrogen. According to claim 1,
Nickel nitrate hexahydrate and sodium hydroxide in step 2) are 40 to 50 parts by weight of nickel nitrate hexahydrate and 20 to 40 parts by weight of sodium hydroxide when 100 parts by weight of melamine in step 1) Nickel and nitrogen, characterized in that Method for producing interconnected graphite nanocubes comprising a. According to claim 1,
The dispersion in step 2) is a method for producing interconnected graphite nanocubes containing nickel and nitrogen, characterized in that the dispersion for 2 to 4 minutes with an ultrasonic disperser. According to claim 1,
The centrifugation of step 3) is a method for producing interconnected graphite nanocubes containing nickel and nitrogen, characterized in that proceeding at 8500 to 9500 rpm for 8 to 12 minutes. According to claim 1,
Aging in step 4) is performed by putting the metal-organic compound prepared in step 3) in distilled water and aging it at a temperature of 80 to 90 ° C for 4 to 6 hours, characterized in that the interconnected graphite containing nickel and nitrogen. Manufacturing method of nanocubes. According to claim 1,
In step 6), the temperature is raised to a temperature of 300 to 1000 ° C at a rate of 5 ° C / min in a furnace filled with nitrogen gas (N ₂ ), characterized in that the interconnected graphite nanoparticles containing nickel and nitrogen How to make cubes. According to claim 1,
The heat treatment in step 7) is a method for producing interconnected graphite nanocubes containing nickel and nitrogen, characterized in that additional heat treatment for 2 to 4 hours. According to claim 1,
In the etching of step 8), the carbide structure is etched with a 0.5 to 1.5 M hydrochloric acid solution at a temperature of 75 to 85 ° C for 2 to 4 hours to remove nickel metal particles present on the outside of the carbide structure Nickel and A method for producing interconnected graphite nanocubes containing nitrogen. An electromagnetic wave shielding material prepared by mixing 900 to 100 parts by weight of paraffin with 5 parts by weight of interconnected graphite nanocubes containing nickel and nitrogen prepared according to claim 1. 100 parts by weight of interconnected graphite nanocubes containing nickel and nitrogen prepared according to claim 1, 10 to 15 parts by weight of carbon black as a conductive material and 10 to 15 parts by weight of polyvinylidene fluoride (PVDF) as a binder A functional separator of a lithium-sulfur battery prepared by mixing parts by weight.

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