KR20090108331A - Process for preparing nanocrystalline manganese oxide having supercapacitor electrode property - Google Patents

Abstract

PURPOSE: A process for preparing nanocrystalline manganese oxide is provided to allow potassium permanganate to react to 3~4.5M ethylene glycol to produce spheral manganese dioxide nanoparticles. CONSTITUTION: A process for preparing nanocrystalline manganese oxide comprises the following step of allowing potassium permanganate to react to 3~4.5M ethylene glycol. The manganese oxide nanoparticles contain 0-45% moisture. The manganese oxide nanoparticles have second hollows. The specific surface area of the manganese oxide nanoparticles is 230m^2/g±10%. The average particle size of the manganese oxide nanoparticles is 8~15nm.

Description

Manufacturing Method of Manganese Oxide Nanoparticles with Ultra-High Capacity Electrode Characteristics {PROCESS FOR PREPARING NANOCRYSTALLINE MANGANESE OXIDE HAVING SUPERCAPACITOR ELECTRODE PROPERTY}

The present invention relates to a method for producing manganese oxide nanoparticles having ultra-high electrode characteristics. More specifically, a method for producing spherical manganese oxide manganese dioxide nanoparticles having a large specific surface area (230 m 2 / g ± 10%) by reacting ethylene glycol at a molar ratio of at least 3, preferably 3.5 to 4.5, with respect to potassium permanganate. It is about.

As manganese oxide of nanoparticles is known to be excellent as a high-capacity electrode recently, experts in this field have been continuously researching to manufacture manganese oxide of nanoparticles. In particular, it is reported that it is advantageous to prepare potassium permanganate by reacting with manganese salt (Mn ^{+ 2} ) in order to prepare manganese dioxide of nanoparticles (Non-Patent Documents 1 to 5). Moreover, several patents regarding the manufacturing method of a manganese oxide and a carbon nanotube composite electrode are also shown (refer patent document 1-2).

However, the manganese oxide shown in the non-patent document has a decrease in capacity relative to the initial capacity after a certain number of cycles at a constant current density, and is not satisfactory as a manganese oxide having charge / discharge characteristics, and the invention described in the patent document Manganese oxides of nanoparticles are not described as having properties, and studies on them have not been described.

[Patent Document 1] Republic of Korea Patent Registration No. 10-0666778

[Patent Document 2] Republic of Korea Patent Registration No. 10-0622737

[Non-Patent Document 1] Journal of the Electrochemical Society, 149 (11) A1419-A1422 (2002)

[Non-Patent Document 2] Journal of Power Sources 124 (2003) 330-337

[Non-Patent Document 3] Journal of the Electrochemical Society, 154 (2) A80-A88 (2007)

[Non-Patent Document 4] Journal of the Electrochemical Society, 154 (10) A901-A909 (2007)

[Non-Patent Document 5] Journal of Solid State Chemistry 144, 220-223 (1999)

As described above, the possibility of manganese oxide as a manganese oxide having ultra-high capacity electrode characteristics is already known, but when the charge / discharge experiments are conducted using the same, the discharge capacity decreases after a certain charge / discharge cycle, which makes it difficult to use. I'm experiencing it. In particular, as shown in the non-patent literature and the like, in order to obtain manganese oxide of nanoparticles, potassium permanganate was reduced by using inorganic materials such as potassium hydrogen boride, sodium dithioate, sodium hypophosphite, to prepare manganese oxide of nanoparticles. The manganese oxide has a capacity of about 80 to 300 F / g, but after 1000 cycles of these nanoparticle manganese oxides, the capacity decrease is about 5 to 50% with respect to the initial capacity.

The present inventors earnestly studied to solve the above-mentioned conventional problems, and as a result of reducing potassium permanganate to an excess of ethylene glycol, the dispersion constant of the reactant to be reduced due to the viscosity of ethylene glycol can be adjusted, and As a reducing agent, almost all of potassium permanganate is reduced to manganese dioxide of nanoparticles, and ethylene glycol is removed by washing the obtained manganese dioxide of nanoparticles, and secondary pores existing between particles are formed, making it very suitable as an ultra high capacity electrode. The present invention was completed.

Manganese oxide of the nanoparticles (average) obtained by the present invention has a large specific surface area (230 m 2 / g ± 10%) and manganese oxide [K _x MnO ₂ · yH because of having secondary pupils having an average particle diameter of 10 to 13 nm. ₂ O] is a spherical form having a water content of y to 0 to 0.425, and the ultracapacity electrode characteristics were evaluated, and the initial capacity was preserved as it is even after 1,000 cycles at 0.5 mA / cm 2 current density. Therefore, the synthesis of manganese oxide nanoparticles through a simple mixing process using manganese ions and a reducing agent at room temperature using only a beaker is very useful for economically and in large quantities to produce ultra-high capacity electrode materials having excellent cycle capacity retention characteristics. Do.

Hereinafter, the present invention will be described in detail. In addition, the accompanying drawings showing the results measured for the confirmation of the manganese oxide of the nanoparticles obtained by the examples will also be described.

The present invention relates to a method for producing manganese oxide by reducing potassium permanganate with ethylene glycol. It is known that the redox reaction of most inorganic compounds, especially the ionic reaction, is stoichiometric, but the reaction of inorganic and organic compounds is not. In the present invention, when the reduction reaction of potassium permanganate with ethylene glycol which is an organic compound is not seen to proceed stoichiometrically, when reacting at room temperature and atmospheric pressure,

K _x MnO ₂ yH ₂ O

[Wherein, 0.176 to 0.293, y is 0 to 0.425]

The compound represented by the chemical formula of is obtained.

In the above, the y value is the amount of water stabilized in the manganese lattice layer. If x and y values are within ± 25% of the above optimum conditions, they should be regarded as within the scope of the present invention. In other words, the x and y values are determined by experimental calculations. The y value described above is the sum of the water in the sample surface and the water in the lattice. Water present in the lattice is about 6%. If you calculate this proportionally, you get the y value. And x value is the value measured by ICP element analyzer. This value should take into account the margin of error since the machine operation and the sample analyzer and K are not stabilized in the lattice but may also be present on the particle surface. These values are reasonable when compared to the values present in the existing manganese oxide lattice. The numerical values of x and y in these compounds are not referred to herein and are simply referred to as manganese oxides.

In the reduction reaction of potassium permanganate and ethylene glycol, the reduction reaction cannot be completed sufficiently. Therefore, the amount of potassium permanganate is about 3 mol or more, preferably, relative to an excess of ethylene glycol, for example, potassium permanganate, which is sufficient to oxidize potassium permanganate. Is preferably from 3.5 to 4.5 molar ratios. The reaction of potassium permanganate with ethylene glycol is terminated when the solution of potassium permanganate is gradually changed from purple to brown with stirring of aqueous solution of potassium permanganate at room temperature (15 ~ 25 ℃) for about 30 minutes, and the reaction mixture is replaced with water and lower alcohol. Spherical manganese oxide nanoparticles containing a large specific surface area and adequate moisture are prepared by drying the manganese oxide obtained by washing and filtration at a high temperature in an air atmosphere, for example, 100 ° C. or lower.

The remaining of ethylene glycol in the manganese oxide after washing can be confirmed using CHNS. As a result of this reaction, the color of the obtained manganese oxide is brown, which is K _x MnO ₄ · yH ₂ O in which manganese (Mn) is mixed with a trivalent and tetravalent compound (wherein x is 0.176 to 0.293 and y is 0 to 0). 0.425, and the y value is the amount of water stabilized in the manganese lattice layer.) This compound can be identified by XANES, Power XRD, ICP, TG-DTA, or the like.

That is, in the formula, the K value is due to ICP measurement and the H ₂ O value can be obtained proportionally with the value of TG data, and the amount of water (y value) is (K _0.234 MnO ₂ mass + mass 18x) / 100 This can be obtained by calculating the% of water obtained between 120 and 250 ° C. from the mass of water (18 ×) / TG data.

As a result of measuring the EDS diagram of the components of the product obtained in the example, it can be seen that there are no impurities other than potassium, manganese and oxygen, as shown in Figure 2, and also from the XANES graph, as shown in Figure 4 It can be seen that it has a spectrum similar to the δ-MnO ₂ structure.

In particular, in the present invention, since the use of viscous ethylene glycol as a reducing agent of potassium permanganate, it is possible to control the dispersion constant of the reactant to be reduced, since the ethylene glycol is reduced in the particles, and then removed in the washing process between the particles It is believed that secondary pupils are produced at.

As shown in FIGS. 1 and 6, the manganese oxide obtained by the example of the method for preparing the nanoparticles of the manganese oxide of the present invention has secondary pores having a particle diameter of 10 to 15 nm and has moisture. The content is about 14% of the total product weight (the sum of the particle surface and the water present in the lattice), as shown in the TG diagram of FIG. 5, and the specific surface area value is 230 m 2 / g ± Confirmed to be 10%. As shown in Figure 9, it can be seen that there is a hysteresis in the BET curve, which means that the pupil is present in the obtained manganese oxide. As a result of performing a pore size distribution analysis based on this hysteresis, it can be confirmed that a pupil mainly having a size of 14.5 nm exists. This result is in good agreement with the results of the SEM photograph of FIG. 1. However, the above moisture content is one embodiment, and is not limited to the above value.

Thus obtained material can be seen in Figures 7 to 8 to maintain the initial capacity after 1,200 cycles, unlike the capacity reduction that is clearly seen within a few hundred charge / discharge cycle in the conventionally developed manganese oxide nanostructures.

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited by this embodiment.

Example 1

3.16 g (0.02 mol) of potassium permanganate (KMnO ₄ : ACS reagent, manufactured by Sigma) is dissolved in 200 mL of distilled water, and 5 ml of ethylene glycol (0.09 mol) is mixed with this aqueous potassium permanganate solution, and slowly Stir for 30 minutes. When the color of the reaction product changed from purple to brown while stirring, the reaction was stopped, and the obtained precipitate was filtered and separated, and then the obtained product was washed several times with distilled water and ethanol, and dried at 60 ° C. for about 24 hours to obtain manganese oxide of nanoparticles. Got.

The following experiment was conducted to measure the physical properties of the manganese oxide obtained above.

Experimental Example 1

Hereinafter, the results of experiments of the manganese oxide obtained above by electron microscope, EDS diagram, X-ray diffractometer, XANES, thermogravimetric analyzer (TG) and the like.

(Electron micrograph)

The result of image | photographing the manganese acid compound obtained above with the electron microscope is shown in FIG.

As shown in Fig. 1, the shape of the manganese oxide is almost spherical, and the particle diameter is 80 to 15 nm.

(Measurement by TEMEDX)

An EDS diagram obtained by measuring the manganese acid compound obtained above with TEMEDX is shown in FIG. 2. From this diagram it was confirmed that the final product was free of any other substances other than potassium, manganese and oxygen. (In the meantime, Cu comes from the Cu grid as the substrate and is not related to the material of the present invention).

(Measurement by X-ray diffractometer)

The pattern when the manganese oxide sample itself of the present invention obtained in the Example was measured with an X-ray diffractometer and after 5 hours of treatment at 300 ° C. is shown in FIG. 3.

From this figure, the XRD pattern FIG. 3A is the manganese oxide of the present invention and is almost amorphous in XRD. The stability of the manganese oxide of the present invention was evaluated at a temperature above 250 ^° C. because the temperature in the electrode could go to around 250 ^° C. for a variety of reasons when the ultracapacitive electrode was operating. Figure 3b is the result of measuring the XRD after the heat treatment of the manganese oxide of the present invention at 300 ^° C for 5 hours, as shown in the diagram, there was little change in the XRD pattern before and after the heat treatment. This can be confirmed that the manganese oxide developed in the present invention is also very excellent in the thermal stability required during full cell experiments.

(Measurement by XANES spectrometer)

To examine the Mn K-absorbing means XANES spectrum to investigate the oxidation state and local structure around manganese ions, the manganese oxide sample of the present invention obtained in the above example (solid line), and the standard Mn ₂ O ₃ (dash) - dotted lines), is shown in δ-MnO ₂ (dashed line) and α-MnO ₂ 4 compares the spectrum of a (dashed line). As shown in FIG. 4, all samples showed peaks P and P ′ corresponding to the transition from the 1s orbital to the 3d orbital in the pre-edge region, all of which are small in intensity. It is well known that since the transition is a transition that is not permitted by the dipolar selection rule, the peak intensity is small unless there is a tetrahedron without inversion center where mixing between dp orbitals can occur. . Therefore, it can be seen that in all samples of FIG. 4, manganese ions are stabilized at octahedral sites having +3 oxidation state. In addition, when the manganese ion has an oxidation state of +3, one peak P is shown; when the oxidation state of average manganese is +3 or more, two peaks P and P 'are shown, and the content of +4 is manganese ion. It is known that as this increases, the intensity of the P 'peak increases. As observed in FIG. 4, two P and P ′ are observed in the sample obtained in the example, wherein the peak P ′ manganese +4 shows a small peak intensity compared to MnO ₂ , which is a standard of ions. This fact indicates that manganese ions in these manganese oxides have a state of + 3 / + 4 mixed atoms. These conclusions support that the location of the main absorption edge of manganese oxide in the sample lies between the standard Mn ₂ O ₃ and MnO ₂ .

In the mainedge region, the standard sample shows several peaks corresponding to the allowable transition from the 1s orbital to the empty 4p orbital. Among them, peak B is observed for all samples, and previous studies have reported that the peak shows a large and sharp shape in a structure in which MnO ₆ octahedron is composed only of edge sharing. As shown in FIG. 4, the sharp peak B is observed in the manganese oxide sample prepared in Example and the standard δ-MnO ₂ , whereas the intensity of the peak is slightly decreased in the α-MnO ₂ standard. This confirms that the compound has a layered structure consisting of corner covalent MnO ₆ octahedron, and the standard α-MnO ₂ has a structure in which MnO ₆ octahedrons are mixed with corner covalent and vertex covalent.

Indirect information on the local structure can also be seen from the shape of the overall spectrum. The manganese oxide prepared in Example showed a spectrum shape very similar to that of the layered δ-MnO ₂ structure. Although the crystal structure of the manganese oxide sample cannot be identified from the XRD analysis, it can be confirmed that the crystal is locally crystallized to the δ-MnO ₂ structure from the fact that it shows a spectrum similar to that of the δ-MnO ₂ sample.

(Experiment on Ultra High Capacity Electrode Characteristics)

Potentiostat / Galvonostat (model PGS201T) was used to measure the ultracapacitive electrode characteristics and the results are shown in Table 7.

That is, stainless steel (SS) foil was used as a current collector. SS was roughened to increase adhesion to the active material coated with emery paper, and then washed well with a detergent and secondary distilled water. The electrode was mixed with 75% by weight of MnO ₂ , 20% by weight of acetylene black (AB) and 5% by weight of polyvinylidene fluoride (PVDF) for 1 hour in mortar, followed by several drops of n- Methylpyrrolidone (NMP) is dropped into mortar to make a slurry. The slurry mixture is coated on the SS foil and then dried at 100 ° C. in a vacuum atmosphere for 12 hours. The electrochemical characterization of the electrodes thus synthesized was measured with a three-pole electrode cell type. In the three-pole cell, the manganese oxide sample obtained in the above example was a working electrode, a platinum foil as a counter electrode, and Hg / HgO as a reference electrode.

Electrochemical characterization was performed using a 0.1 M Na ₂ SO ₄ electrolyte to measure cyclovoltammogram at 0 mV / s at 10 mV / s in the window potential region, as shown in FIG. There was no capacity reduction compared to the initial capacity even after 1200 cycles at / cm 2 current density. In FIG. 8, voltages were alternately measured at 0 V to 1 V at a current density of 0.5 mA / cm 2. The capacity of the material thus measured was calculated by the following equation.

Specific Capacitance (SC) = [I (A) t (s)] / [m (g) E (1)],

[Wherein I is the current (amps), t is the time (seconds), m is the amount of active material (grams) actually used in the reaction, and E is the range of charge / discharge cycles (V).]

The photographs of the final product prepared in Example 1 by electron microscopy are shown in FIG. 3, which were prepared by performing powder X-ray diffraction and chemical analysis followed by structural analysis and component analysis. Manganese oxide K _0, which has a main pupil of about 14.5 nm and a specific surface area of 230 m 2 / g ± 10%, is almost amorphous to X-ray and has a δ-MnO ₂ structure between silver particles and particles. it was confirmed that the _.234 MnO _{2 ·} 0.340H ₂ O.

Spherical manganese oxide nanoparticles having an appropriate amount of water and a large specific surface area prepared according to Examples 1 and 2 may be used as an ultra high capacity electrode material and a redox catalyst.

Only one exemplary embodiment of the present invention described above has been exemplified. When a large number of manganese oxides were prepared and tested, compounds of the range described in the description of the present invention were obtained.

Also, the specific terms used herein are merely used for the purpose of describing the present invention in detail to those skilled in the art, but are not used to limit the scope of the present invention as defined in the claims or the claims.

1 is a photograph observing the crystal form of the manganese oxide prepared in Example 1 of the present invention with an electron microscope.

Figure 2 shows the EDS diagram of the manganese oxide prepared in Example 1 of the present invention measured by TEMEDX.

Figure 3 shows the XRD pattern of the manganese oxide prepared in Example 1 of the present invention by X-ray diffractometer.

Figure 4 is a graph showing the results of measuring the manganese oxide prepared in Example 1 of the present invention by XANES. The prepared manganese oxide is represented by a solid line, Mn ₂ O ₃ is a dashed-dotted line, Mn ^IV O ₂ is a dashed-dotted-dotted line, δ-MnO ₂ is a dashed line, and α-MnO ₂ is represented by a dashed line.

5 is a result of measuring the moisture content of the manganese oxide prepared in Example 1 of the present invention by a thermal analyzer (TGA). The TG grains and the DTA pattern are shown together.

6 is a diagram showing the specific surface area and the pupil size distribution of the manganese oxide prepared in Example 1 of the present invention through a nitrogen adsorption and desorption experiment (left: BET curve, right: pupil distribution).

7 is a graph showing the results of measuring the cyclo-voltammogram characteristics of the manganese oxide prepared in Example 1 of the present invention using Potentiostat / Galvonostat.

FIG. 8 is a diagram in which charge / discharge capacities seen as ultracapacitive electrodes are calculated from the result of FIG. 7.

Claims (3)

It has a water content of 0 to 45% and a secondary pupil with respect to the total sample weight, characterized by reacting at least about 3 molar ratios and 4.5 molar ratios of ethylene glycol with respect to potassium permanganate, and having 230 ㎡ / g ± 10% A method for producing manganese oxide nanoparticles having a specific surface area and an average particle diameter of 8 to 15 nm. The manganese oxide nanoparticles according to claim 1, wherein the composition of the obtained manganese oxide has a general formula of K _x MnO ₂ -yH ₂ O (wherein x is 0.01 to 0.38 and y is 0 to 0.425). Method of preparation. The method for producing manganese oxide nanoparticles according to claim 1 or 2, wherein the specific surface area is 230 cm ³ / g ± 10%) and the average particle diameter is 8 to -15 nm.

Images