KR20140067187A - Reforming method of activated carbon for electric double layer capacitor - Google Patents
Reforming method of activated carbon for electric double layer capacitor Download PDFInfo
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- KR20140067187A KR20140067187A KR1020120121765A KR20120121765A KR20140067187A KR 20140067187 A KR20140067187 A KR 20140067187A KR 1020120121765 A KR1020120121765 A KR 1020120121765A KR 20120121765 A KR20120121765 A KR 20120121765A KR 20140067187 A KR20140067187 A KR 20140067187A
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- activated carbon
- hydrogen peroxide
- double layer
- electric double
- layer capacitor
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
- H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
- H01G11/22—Electrodes
- H01G11/30—Electrodes characterised by their material
- H01G11/32—Carbon-based
- H01G11/34—Carbon-based characterised by carbonisation or activation of carbon
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/318—Preparation characterised by the starting materials
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/13—Energy storage using capacitors
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Carbon And Carbon Compounds (AREA)
- Electric Double-Layer Capacitors Or The Like (AREA)
- Chemical & Material Sciences (AREA)
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Abstract
The present invention relates to activated carbon modification method for an electric double layer capacitor, and more particularly, to activated carbon to hydrogen peroxide (H 2 O 2) aqueous solution and then activated carbon pre-treatment stage to stir for a period of time In a; activated carbon finished with, the activated carbon pre-treatment step Removing the hydrogen peroxide remaining in the activated carbon by repeating the process of filtering the water after the filtration under reduced pressure, drying the activated carbon after the hydrogen peroxide removal step, and removing the activated carbon after the drying step by continuously injecting nitrogen gas Treating the activated carbon for an electric double layer capacitor comprising: heat treating the activated carbon in an inert atmosphere.
Description
The activated carbon used as the electrode material for the electric double layer capacitor has a problem that the internal resistance of the electrode is increased by the surface functional group and the increase of the resistance again affects the capacitance. The present invention relates to an activated carbon reforming method for an electric double layer capacitor capable of improving the capacitance and reducing the resistance by removing only the functional groups on the surface without damaging the distribution of the internal pores of the activated carbon.
An electric double layer capacitor (hereinafter, referred to as "EDLC"), which is being developed and commercialized for the purpose of applying to portable electronic devices and electric vehicles, has a high output characteristic and excellent cycle performance, It is an energy storage device that can be applied as a power source.
The electrical energy storage mechanism of EDLC uses the absorption and desorption of ions in the electrolyte at the maximized specific surface area to accumulate the charge and exhibits high output characteristics due to such a mechanism. However, the current maximum EDLC voltage does not exceed 2.8V because it can not be connected in series to a single cell with the lithium ion secondary battery, which is the main power source in the circuit.
To solve this problem, many researchers have attempted to develop an EDLC or a hybrid capacitor of 3V or more, substituting a lithium ion secondary battery material or doping with lithium, but a reduction in output characteristics due to a redox reaction .
Also, in the development of 3V class EDLC, due to the high specific surface area, decomposition reaction of electrolytic solution proceeds at the same time causing gas generation, and continuous gas generation causes deterioration of cycle characteristics due to desorption of electrode material and increase of internal pressure in the cell do.
The present invention relates to an activated carbon modified for an electric double layer capacitor which can reduce the resistance and improve the electrostatic capacity by changing the electrochemical characteristics of the activated carbon by removing the activated carbon surface functional group, which is one of the causes of gas generation, It is an object of the present invention to provide a method.
In order to achieve the above object,
The present invention relates to a method for preparing activated carbon, which comprises: a pre-treatment step of adding activated carbon to an aqueous solution of hydrogen peroxide (H 2 O 2 ) and stirring for 1 to 2 hours;
Removing the hydrogen peroxide remaining in the activated carbon by repeating the process of filtering the activated carbon after the activated carbon is filtered under reduced pressure,
Drying the activated carbon after the hydrogen peroxide removal step,
And a step of heat-treating the activated carbon after completion of the drying step in an inert atmosphere in which nitrogen gas is continuously injected. The present invention also provides a method for modifying an activated carbon for an electric double layer capacitor.
The modified activated carbon for an electric double layer capacitor according to the present invention has the effect of enhancing the capacitance and the resistance reduction characteristic by removing only the functional groups on the surface without damaging the internal pore distribution.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing an impedance measurement result of a cell composed of half cells of an electrode manufactured using activated carbon according to the present invention. FIG.
FIG. 2 is a graph showing the resistance values shown in FIG. 1 as a function of the cell's equivalent resistance (ESR) value and the polarization resistance or charge transfer resistance (Rp) graph.
FIG. 3 is a graph showing the impedance measurement results of EDLC obtained by symmetrically assembling electrodes manufactured using the activated carbon according to the present invention.
FIG. 4 is a graph showing measured values by increasing the voltage every 5 cycles at a capacitance measured through constant current charge / discharge.
5 is a graph showing the results of thermal analysis of activated carbon according to the present invention.
Hereinafter, the technical contents of the above description will be described in detail.
As described above,
An activated carbon reforming method for an electric double layer capacitor according to the present invention comprises:
An activated carbon pre-treatment step in which activated carbon is added to an aqueous hydrogen peroxide (H 2 O 2 ) solution and stirred for 1 to 2 hours,
Removing the hydrogen peroxide remaining in the activated carbon by repeating the process of filtering the activated carbon after the activated carbon is filtered under reduced pressure,
Drying the activated carbon after the hydrogen peroxide removal step,
And a step of heat-treating the activated carbon after the drying step under an inert atmosphere in which nitrogen gas is continuously injected.
The technical structure of each step according to the activated carbon modification method will be described as follows.
[Activated carbon pretreatment step]
The pretreatment of the activated carbon is intended to maximize the effect of the heat treatment. If the activated carbon is not subjected to the pretreatment process, the temperature rise may occur during the heat treatment. The problem of temperature rise is a problem of pore collapse due to combustion with the surface oxygen functional group It is desirable to carry out a preprocessing process according to the process presented here.
The activated carbon has a specific surface area of 2,000 m < 2 > / g and an oxygen content of 9% with respect to the total carbon. The pre-activated carbon is obtained by adding activated carbon to an aqueous solution of hydrogen peroxide (H 2 O 2 ) In this case, the hydrogen peroxide (H 2 O 2 ) aqueous solution is adjusted to have a concentration of 5 to 15 wt%.
If the concentration of the aqueous solution of hydrogen peroxide (H 2 O 2 ) is less than 5 wt%, only surface moisture adsorption will occur rather than the functional group change of the activated carbon. If the concentration exceeds 15 wt%, the effect of the strong oxidizing action will deform the pores of the activated carbon (H 2 O 2 ) aqueous solution has a high concentration of hydrogen peroxide (H 2 O 2 ) because the high concentration of hydrogen peroxide may contact the activated carbon with a high oxidizing power to generate a large amount of hydrogen, thereby threatening stability and causing scattering of activated carbon. It is preferable to adjust the concentration to 5 to 15 wt%.
If the agitation time exceeds 2 hours, the pores of the activated carbon may be collapsed and the surface modification phase may be excessively deformed. Therefore, the agitation time is preferably within a range of 1 to 2 hours.
[Hydrogen Peroxide Removal Step]
In this step, the hydrogen peroxide contained in the activated carbon through the activated carbon pretreatment step is removed,
If the hydrogen peroxide is not properly removed at this stage, hydrogen is generated by the hydrogen peroxide that is not treated during the heat treatment and the stability is deteriorated. Since the combustion of the activated carbon during the heat treatment due to oxygen generation may cause the problem of internal pore collapse, It is preferable to repeatedly rinse and remove hydrogen peroxide from the activated carbon.
[Drying step]
Activated carbon with residual hydrogen peroxide removed through filtration under reduced pressure and washing is subjected to a drying process, wherein drying is carried out at a temperature of 50 to 100 ° C for 12 to 15 hours in a dryer.
If the drying temperature is less than 50 ° C, the effect of removing moisture of the activated carbon is insufficient and there is a problem that it must be dried for a long time. If the drying process is not sufficiently performed, the heat transfer effect inside the activated carbon is insufficient during the heat treatment, It is preferable to carry out a drying process at a temperature of 50 to 100 DEG C for 12 to 15 hours for the purpose of complete moisture drying.
[Heat treatment step]
The activated carbon subjected to the drying process undergoes a heat treatment process. An important part of the heat treatment process is that the pores of the activated carbon are not collapsed and the reforming should be performed in a region that does not exceed the thermal stability range.
In order to achieve the above object, it is important to select an appropriate temperature. In the present invention, the optimum temperature for removing only the functional groups on the surface is limited to within a range of 300 to 700 ° C. without damaging the distribution of the internal pores of the activated carbon, .
The heat treatment time within the heat treatment temperature range is preferably adjusted within a range of 1 hour to 5 hours so that efficient heat transfer can be achieved.
If the heat treatment temperature is lower than 300 ° C, there is a problem in efficiently removing the functional groups of the activated carbon. When the heat treatment temperature exceeds 700 ° C, there is a problem of pore collapse of the activated carbon. Therefore, the temperature of the heat treatment is limited within the range of 300 to 700 ° C .
If the heat treatment time is less than 1 hour, there is a problem that the surface functional group is not removed. If the heat treatment time exceeds 5 hours, there is a problem of pore collapse or burning of activated carbon due to excessive heat treatment. It is preferable to limit the time within the range of 1 to 5 hours.
Hereinafter, the technical contents of the present invention will be described in detail.
Modified activated carbon
As a pretreatment process of the porous activated carbon, an aqueous solution of hydrogen peroxide (H 2 O 2 , 30 wt%) is made into an aqueous solution of 6 wt%, activated carbon is put into this solution and stirred.
At this time, the stirring time is about 30 minutes, which is a time point at which all the bubbles generated in the solution disappear.
After stirring, the reaction solution is filtered under reduced pressure and washed with water to remove the hydrogen peroxide remaining in the activated carbon and dried in a circulating drier at 60 ° C for 12 hours to remove moisture.
After the drying process, the activated carbon is continuously injected with nitrogen gas to form an inert atmosphere, and the heat treatment process is performed at 100 ° C intervals within the range of 300 to 700 ° C. At this time, the temperature increase rate is 5 ° C per minute.
When reaching the target temperature (300 ° C, 400 ° C, 500 ° C, 600 ° C, 700 ° C) at an interval of 100 ° C, the same temperature is maintained for 1 hour at the temperature.
Here, it is only means for adjusting the temperature change width for adjusting the temperature change at intervals of 100 DEG C to compare the result values, and the reason why the duration time is adjusted to one hour is also the same.
Electrode Manufacturing
A slurry was prepared using the activated carbon as described above. Within a solid content ratio of 23 wt%
1.5 wt% of CMC (Carboxyl methyl cellurose) as a viscosity controlling agent was dissolved in distilled water, and then conductive material (Acetylene Black, Super-P) was dispersed in an amount of 9 wt% based on the solid content.
Next, 85 wt% of activated carbon was added, and 2.5 and 2 wt% of SBR (styrene butadiene rubber) and PTFE (polytetrafluoroethylene) were added, respectively, followed by stirring to prepare an electrode slurry.
The prepared electrode slurry was coated on an etching aluminum foil (CS201, Korea JCC) to a thickness of 100 mu m and dried at 60 DEG C. The dried electrode was pressed using a roll press, followed by secondary drying in a reduced pressure dryer at 120 캜.
Evaluation cell
The electrode thus prepared was cut using a punch having a diameter of 16 mm, the half cell was assembled on the basis of lithium metal, and the EDLC was fabricated as a symmetric electrode.
The cell was assembled using a 1M LiBF 4 / PC nonaqueous electrolyte solution for the half cell and a 1M TEABF 4 / PC electrolyte solution for the EDLC.
[ Test Example 1 ]
The electrochemical characteristics of the cells prepared in Example 1 were analyzed using an electrochemical measuring instrument (Solartron, 1400-Series). Impedance was measured at 3V (vs. Li / Li + ) and EDLC was measured at 0.1V after constant voltage charging at fixed voltage for 10 minutes at 100kHz to 10mHz. The electrostatic capacitance of EDLC was measured by using Galvanostatic method.
Test result
Fig. 1 shows the impedance measurement results of a cell composed of half cells of an electrode manufactured using the treated activated carbon.
FIG. 1 (a) shows that the polarization resistance (Rp) value of the activated carbon is increased by about 26? Due to the hydrogen peroxide treatment of the activated carbon as a result of the impedance of the activated carbon treated with hydrogen peroxide and activated carbon as the starting material.
FIG. 1 (b) shows the result of heat treatment of the hydrogen peroxide-treated activated carbon, and it can be confirmed that the polarization resistance value is decreased according to the heat treatment condition, and the decrease region is clearly observed at 300 ° C. and 400 ° C. heat treatment conditions However, there is no significant difference in moving at 500 ° C.
The results are shown in FIG. 1 (a). The increased resistance due to the increase of the surface functional group in FIG. 1 (a) can be removed through heat treatment, but it can be judged that the heat treatment condition at a certain temperature or more is difficult. It can also be indirectly confirmed that the condition is about 500 ° C.
FIG. 2 is a graph showing the resistance values shown in FIG. 1 as a function of the cell's equivalent resistance (ESR) value and the polarization resistance or charge transfer resistance (Rp) , The increase in resistance due to the hydrogen peroxide treatment and the increase in the resistance can be removed through a heat treatment process as described above, and the characteristics can be confirmed to be lower than the resistance value of the initial activated carbon.
FIG. 3 shows a result of measurement of the impedance of the EDLC obtained by symmetrically assembling electrodes manufactured using the treated activated carbon, and shows the same tendency as that of FIG. 2.
FIG. 3 is a graph comparing impedance results of an activated carbon treated with an untreated activated carbon and a surface functional group through a hydrogen peroxide treatment. It can be seen that the electron transfer resistance of the hydrogen peroxide treated electrode is about 3 Ω higher. It can be expected that the electrochemical reaction increases as a surface reaction, due to the influence of the functional groups of the activated carbon on the characteristics of the ions adsorbed on the electrode surface.
FIG. 3 (b) shows that the resistance value of activated carbon treated to 300 to 700 ° C. shows a lower electron transfer resistance than that of untreated activated carbon. These characteristics impair the adsorption characteristics of ions in the electrolyte due to the functional groups adsorbed or formed on the surface of the activated carbon, which can be confirmed to be removed to a certain extent through heat treatment. However, the decreasing resistance value increases again under the heat treatment condition of 700 ° C.
FIG. 4 shows measured values obtained by increasing the voltage every 5 cycles with the capacitance measured through the constant current charge / discharge.
The measured value from 2.6V to 3V shows no increase in the capacitance due to the increase of the voltage range as the capacitance increases, and the cycle performance does not show any significant difference.
However, the values of capacitance were higher than those of activated carbon, except for the decrease of capacity by hydrogen peroxide treatment and the decrease of capacity under heat treatment condition of 700 ℃ based on untreated activated carbon. This result is shown in FIG. 4 (b), and it can be confirmed that the characteristic shows the maximum capacitance in the region of 500 ° C. as described above.
FIG. 5 shows the result of thermal analysis of the starting activated carbon. As a result of the capacitance change and resistance change at around 500 ° C. described above, the thermal decomposition reaction of activated carbon starts at about 500 ° C., .
Fig. 5 is a result of measurement in an air atmosphere, which is different from the evaluation method of nitrogen atmosphere, which is an experimental method, but it is expected that the characteristics can be gauged.
That is, depending on the pyrolysis characteristics of the activated carbon, the heat treatment condition exceeding 600 ° C. causes the combustion action of the activated carbon, and consequently, the decrease of the internal pore distribution and the surface carbon characteristic can be expected.
As a result, the capacitance change and the resistance change of FIG. 3 and FIG. 4 are caused by the functional groups on the surface. However, considering that the deterioration of characteristics is caused by the excessive heat treatment conditions, The temperature condition of the temperature is also considered to be inappropriate.
The modified activated carbon for an electric double layer capacitor according to the present invention enhances the properties of capacitance and resistance by removing only the functional groups on the surface without damaging the internal pore distribution.
Claims (4)
A step of repeatedly performing filtration under reduced pressure and washing with water the activated carbon after the activated carbon pretreatment step to remove hydrogen peroxide remaining in activated carbon;
Drying the activated carbon after the hydrogen peroxide removal step,
And a step of heat-treating the activated carbon after the drying step under an inert atmosphere in which nitrogen gas is continuously injected.
Wherein the aqueous solution of hydrogen peroxide (H 2 O 2 ) has a concentration of 5 to 15 wt%.
Wherein the heat treatment is performed in a temperature range of 300 to 700 ° C.
Wherein the activated carbon has a specific surface area of 2,000 m 2 / g and an oxygen content of 9% of the total carbon.
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| DE102014223497A1 (en) | 2014-06-02 | 2015-12-03 | Hyundai Motor Company | A method of estimating a voltage of an input terminal of an inverter and an engine control method using the same |
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| JP2002338222A (en) | 2001-05-10 | 2002-11-27 | Futamura Chemical Industries Co Ltd | Method for preparing activated carbon having controlled quantity of surface oxide |
| KR100805206B1 (en) * | 2005-12-28 | 2008-02-21 | 한국전기연구원 | Active Material For An Electrode, Electrode Comprising The Same and Manufacturing Method thereof |
| KR100911891B1 (en) * | 2007-11-12 | 2009-08-11 | 한국전기연구원 | Manufacturing method of activated carbon for electric double layer capacitor and the electric double layer capacitor electrode and the capacitor |
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