JP2006279003A - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor with a high electrostatic capacity. <P>SOLUTION: After an electric double layer capacitor is manufactured by using an electrode comprising activated carbon as a polarizable electrode and an aqueous solution with dissolved salt comprising group 1 and group 17 elements of a periodic table of elements as an electrolyte, a voltage impression process in the range of voltage from 0.4 V to 1.0 V is performed between a positive electrode and a negative electrode in such a state that heating is performed in the temperature range of room temperatures or the room temperature to 80°C. By this voltage impression process, oxygen content on the surface of the electrode is increased, and hydrophilic property is increased. Also, the pore volume of the activated carbon is increased. Such an electric double layer capacitor shows high electrostatic capacity, compared with the capacitor that has not received the voltage impression process. Moreover, dissolving organic matter that is compatible with water such as ethylene glycol in the electrolyte prevents the electrolyte from freezing even at -30°C. The electric double layer capacitor provided with such an electrolyte can considerably suppress a reduction in the electrostatic capacity due to a temperature drop. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor formed at an interface between a polarizable electrode and an electrolytic solution.

  An electric double layer capacitor is a type of capacitor that consists of a polarizable electrode and an electrolyte, and accumulates charge in the electric double layer at the interface between the electrode and the electrolyte formed by the electrolyte present between the opposing positive and negative electrodes. It is.

  Although this electric double layer capacitor has been mainly used as a backup power source for electronic equipment, it has recently been used in a hybrid form with a secondary battery or a solar battery and has an advantage of a long cycle life. Demand is increasing.

  However, higher capacity, higher output, and higher energy density are required in order to apply to a wider range of applications.

  As an electrolytic solution interposed between the positive electrode and the negative electrode, tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, tetraethylphosphonium tetrafluoroborate, etc. are dissolved in an aprotic organic solvent such as propylene carbonate or γ-butyrolactone. A non-aqueous organic solution (Patent Document 1) or an aqueous solution of sulfuric acid, hydrochloric acid, neutral salt, base, or the like is used (Patent Documents 2 and 3).

  As the separator located in the electrolyte, a glass fiber nonwoven fabric, a polypropylene nonwoven fabric or the like is used.

  Conventionally, as a polarizable electrode using activated carbon used for the positive electrode and the negative electrode, for example, an electrode obtained by spraying a current collector on activated carbon fiber or adhering by an evaporation method, or a small amount of fluorocarbon resin on activated carbon powder. An electrode that is mixed and press-molded into a current collector, and a paste prepared by mixing a small amount of acetylene black, an adhesive, and a volatile solvent into activated carbon powder is pressed onto a conductive rubber electrode, and then heated and pressurized. A sheet-like electrode or the like is used.

  In order to increase the capacitance of the carbon electrode of the electric double layer capacitor in which the polarizable electrode is immersed in an organic electrolyte, the polarizable electrode is formed of non-porous carbon having microcrystalline carbon similar to graphite, There has been proposed an electric double layer capacitor that uses an electric capacity to form an electric double layer by intercalating electrolyte ions with a solvent between layers of microcrystalline carbon similar to graphite by applying a voltage ( Patent Document 4).

  In order to improve the energy density of the electric double layer capacitor, it contains microcrystalline carbon with a layer structure similar to graphite, and the interlayer distance of the microcrystalline carbon similar to graphite for electric double layer capacitor by activation treatment It has also been proposed to use an electrode composed of carbon having a structure of 0.343 nm or less, which is slightly longer than graphite (Patent Document 5).

Furthermore, in order to improve the performance of the capacitor, a negative electrode mainly composed of a composite porous material having a graphitic carbon material deposited on the surface of activated carbon, a positive electrode mainly composed of activated carbon, and a lithium salt electrolyte in a non-aqueous solvent. A power storage element using an electrolyte containing nonaqueous lithium ions using a dissolved nonaqueous electrolyte has also been proposed (Patent Document 6).
JP 2004-335875 A Japanese Patent Laid-Open No. 9-293649 JP 2002-289477 A JP 2002-025867 A JP 2003-051430 A JP 2004-079321 A

  An object of the present invention is to increase the electrostatic capacity per unit weight or unit volume of an electric double layer capacitor that has been conventionally demanded.

  It is another object of the present invention to provide an electric double layer capacitor having a high electric capacity that can be used at low temperatures in cold regions.

  It is another object of the present invention to provide an electric double layer capacitor that is inexpensive, highly economical, and safe.

  A first invention is an electric double layer capacitor comprising an activated carbon as a polarizable electrode and an aqueous solution in which a salt composed of elements of Groups 1 and 17 of the periodic table of elements is dissolved as an electrolytic solution. After the electric double layer capacitor is assembled, it is manufactured by performing a voltage application process at room temperature and a voltage of 0.4 V to 1.0 V. When the voltage is applied to an electric double layer capacitor having an electrolytic solution composed of an aqueous solution containing ions of group 17 elements of the periodic table of elements and an activated carbon electrode, the electrode surface is oxidized, and the oxygen component on the surface increases. Increases hydrophilicity. At the same time, the pore volume of activated carbon increases. Thus, the activated carbon electrode immersed in the electrolytic solution containing halide ions in the electrolytic solution, and the activated carbon electrode improved by applying a voltage, the adsorption / desorption amount of ions in the electrolytic solution Will increase. Moreover, water has a lower viscosity than organic solvents, and the rate of adsorption and desorption of ions is faster. In an electric double layer capacitor using such an electrolyte, the charge / discharge rate is increased. Therefore, an aqueous solution in which a salt composed of elements of Group 1 and Group 17 of the periodic table of elements is dissolved is used as an electrolytic solution, and an electric double layer capacitor having a polarizable electrode as an electrode is assembled, and then a voltage application process is performed. Thus, a capacitor having a large capacitance can be manufactured.

  The electric conductivity of a 3.5 mol / l sodium bromide aqueous solution, which is one of the electrolytic solutions according to the present invention, is 199 mS / cm at 25 ° C., but the organic electrolytic solution 0.65 mol / l triethylmethylammonium tetra The electric conductivity at 25 ° C. of propylene carbonate in which fluoroborate is dissolved is 11 mS / cm (literature: functional chemistry series of electrons and ions Vol.2, the forefront of large-capacity electric double layer capacitors, page 262, NT. S, 2002). Therefore, the electrolytic solution used in the present invention has a high electrical conductivity, and an electric double layer capacitor using such an electrolytic solution has a small IR loss and a high capacitance.

  The second invention is produced by applying the voltage of the first invention in a temperature range of room temperature to 80 ° C. The voltage application processing temperature after the electric double layer capacitor assembly of the first invention is performed in the temperature range of room temperature to 80 ° C., thereby improving the voltage application processing effect and processing speed, and increasing the capacitance of the capacitor. Enlarge.

  Although the effect of the voltage application process described above is recognized even if it is 1 hour, it is preferably 3 hours or more, and the capacitance of the electric double layer capacitor produced increases with the elapsed time. The effect of the voltage application treatment for 7 days or more on the increase in the capacitance is slight compared with the case of the treatment for 7 days.

  The applied voltage in the voltage application process needs to be 0.4 V or more, and is preferably in the range of 0.5 V to 1.0 V.

  According to a third invention, in the electric double layer capacitor according to the first invention or the second invention, an odor is included in the electrolytic solution in which a salt composed of an element of Group 1 and Group 17 of the periodic table of elements is dissolved. An aqueous solution in which sodium chloride, potassium bromide, sodium chloride, or a mixture thereof is dissolved is provided as an electrolytic solution.

  According to a fourth invention, in the electric double layer capacitor according to the first invention or the second invention, an organic substance soluble in water is dissolved in an aqueous solution containing sodium bromide, potassium bromide, or a mixture thereof. An aqueous electrolyte solution that is not frozen even at −30 ° C. is used.

  According to a fifth invention, in the electric double layer capacitor according to the first invention, the second invention or the fourth invention, ethylene glycol or a solution thereof is added to an aqueous solution containing sodium bromide, potassium bromide, or a mixture thereof. An electrolytic solution in which a homolog is dissolved is used.

  A sixth invention is the electric double layer capacitor according to the first or second invention, wherein sodium bromide is added to an aqueous solution containing sulfuric acid or other inorganic acid, or potassium hydroxide or other inorganic base. In addition, an electrolytic solution in which potassium bromide or a mixture thereof is dissolved is used.

  A seventh invention is the electric double layer capacitor according to the first invention or the second invention, wherein sodium bromide is added to an aqueous solution containing magnesium bromide, sodium perchlorate, other neutral salt or a mixture thereof. , Potassium bromide, or a mixture thereof, and an electrolytic solution obtained by dissolving ethylene glycol or a homologue thereof.

  The mixing ratio of each component in the electrolytic solution is such that when the entire electrolytic solution is 100 parts by mass, the ionic substance is in the range of 5 to 40 parts by mass, the organic material compatible with water is in the range of 20 to 80 parts by mass, The balance is preferably water.

  A polypropylene nonwoven fabric, a glass fiber nonwoven fabric, etc. can be used for the separator located in electrolyte solution.

  In the first invention, the increase in the pore volume on the surface of the activated carbon electrode and the adsorption / desorption of ions due to the increase in hydrophilicity cause the increase in charge accumulation. Therefore, the electrode has a charge accumulation mechanism different from that of an electrode with intercalation of ions having a structure similar to that of graphite, and the speed of adsorption / desorption of ions is high, and charging / discharging at a high current density is also possible.

  In the second invention, the voltage application processing temperature after the assembly of the electric double layer capacitor of the first invention is performed in the temperature range of room temperature to 80 ° C., so that the voltage application processing effect is enhanced. Capacitance can be increased.

  In the third invention, by using this type of electrolytic solution, the capacitance of the capacitor is remarkably improved by the voltage application process described above.

  In the fourth invention, in addition to the components of the electrolytic solution in the third invention, an electric double layer that can operate even at −30 ° C. by using an aqueous electrolytic solution prepared by dissolving an organic substance soluble in water A capacitor can be manufactured.

  In the fifth invention, an aqueous electrolyte prepared by dissolving ethylene glycol or a homologue thereof is used as the water-soluble organic substance used in preparing the electrolyte that does not freeze even at −30 ° C. of the fourth invention. Thus, a safe and inexpensive electric double layer capacitor that can operate even at −30 ° C. can be manufactured.

  In the sixth invention, sulfuric acid or other inorganic acid, or potassium hydroxide or other inorganic base is added to the components of the aqueous electrolyte solution in addition to the salt composed of the elements of Groups 1 and 17 of the periodic table of elements. By using the aqueous electrolyte prepared in this manner, an electric double layer capacitor having a low internal resistance can be produced using an aqueous electrolyte having a high electrical conductivity.

  In the seventh invention, sodium bromide, potassium bromide, or a mixture thereof, magnesium bromide or sodium perchlorate, or other neutral salt, and ethylene glycol or a homologue thereof are dissolved in an aqueous electrolyte. By using the prepared electrolytic solution, an electric double layer capacitor that is safe and inexpensive and can be used even at −30 ° C. can be produced.

  As described above, the electric double layer capacitor according to the first to seventh inventions is manufactured in a normal atmospheric environment and manufactured in comparison with an electric double layer capacitor manufactured in a dry environment. The price of the equipment is very low. Also, the aqueous solution is highly safe without being ignited or ignited.

  In addition to high output, which is an advantage of an electric double layer capacitor with an aqueous electrolyte, an electric double layer capacitor that has high capacitance per unit weight or unit volume and can be used even at low temperatures and has high safety. It can be provided at low cost.

  The electric double layer capacitor of the present invention includes activated carbon as a polarizable electrode, and uses an aqueous solution containing a salt composed of elements of Groups 1 and 17 of the periodic table of elements as an electrolyte. When it is necessary to make it usable even at a low temperature, an electrolytic solution in which an organic substance soluble in water such as ethylene glycol is dissolved in the aqueous solution is used. The electric double layer capacitor is increased in capacitance per unit weight or unit volume by being subjected to voltage application treatment after being assembled at room temperature or heated. Thereby, the manufacturing cost can be reduced by using the aqueous electrolyte, and at the same time, an electric double layer capacitor having high capacitance and high output and high safety that can be used even at low temperatures can be provided.

As an example of the best mode for carrying out the present invention, an activated carbon fiber is bonded to an insoluble metal current collector as a polarizable electrode with a carbon paste, and a separator is provided between the two electrodes. The electric double layer capacitor is assembled by sandwiching, impregnating with an electrolytic solution, and pressing using an end plate. A 3.5 mol / l sodium bromide aqueous solution is used as the electrolytic solution. After the electric double layer capacitor is assembled, it is charged at a current density of ^2.5 mA / cm ² to 0.7 V, and then a constant voltage of 0.7 V is applied for 72 hours to produce an electric double layer capacitor.

  An electric double layer capacitor operable at −30 ° C. can be produced by using a mixed solution of water and ethylene glycol (volume ratio 2: 1) as the solvent of the electrolytic solution of the electric double layer capacitor.

  Specific examples of the electric double layer capacitor of the present invention are shown in FIGS. 1 is a cross-sectional view, and FIG. 2 is a plan view seen from above. A separator 3 is located between the positive electrode 1 and the negative electrode 2. These electrodes and separator are impregnated with an electrolytic solution. The positive electrode 1 and the negative electrode 2 are in contact with and electrically connected to current collectors 4 and 5 made of insoluble metal foil, respectively. An insulating chamber frame gasket 6 is disposed to seal the electrolyte. All of these are pressed by the insulating end plate 7 using bolts 8 and nuts 9.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these.

As a polarizable electrode, a 1 cm diameter disc-shaped activated carbon fiber non-woven fabric (BW555E manufactured by Toyobo Co., Ltd.) was bonded to a circular plate-shaped insoluble metal current collector having a diameter of 1 cm with a carbon paste to produce an electrode. A glass fiber nonwoven separator (GB-100R manufactured by Advantech) was sandwiched between the two sheets, impregnated with an electrolytic solution and pressed with an insulating end plate, and an electric double layer capacitor having the structure shown in FIG. 1 was assembled. A 3.5 mol / l sodium bromide aqueous solution was used as the electrolytic solution. The weight of the activated carbon fiber cloth is 18 mg / cm ² , the specific surface area is 1350 m ² / g, the bulk density is 0.42 g / ml, the pore volume of pore diameter of 1 to 10 nm is 0.730 ml / g, and the amount of acidic groups is It was 1.68 mmol / g. After assembling the electric double layer capacitor, constant current charging was performed at 70 ° C. and ^2.5 mA / cm ² to 0.7 V, and then a constant voltage of 0.7 V was applied for 72 hours to produce an electric double layer capacitor. . The electrostatic capacity in the discharge process at the 1000th cycle when charging / discharging at a current density of 10 mA / cm ² in a voltage range of 0.4 V to 0.8 V at 25 ° C. was 1.33 F.

  Except that the temperature of the voltage application process at the time of manufacturing the electric double layer capacitor was 25 ° C., the experiment was performed under the same conditions as in Example 1. As a result, the capacitance of the electric double layer capacitor manufactured by the voltage application process was 1.02F. Met.

As a result of experimenting under the same conditions as in Example 1 except that the current density at the time of measuring the discharge capacity when charging / discharging the electric double layer capacitor was ^2.5 mA / cm ² , the electric double layer capacitor manufactured by applying voltage application The capacitance of was 1.40F.

As a result of experimenting under the same conditions as in Example 1 except that the current density at the time of measuring the discharge capacity when charging / discharging the electric double layer capacitor was 50 mA / cm ² , the electric double layer capacitor manufactured by applying voltage was processed. The capacitance was 1.04F.

  As a result of an experiment under the same conditions as in Example 1 except that the voltage application time during the voltage application process at the time of manufacturing the electric double layer capacitor was 1 hour, the capacitance of the electric double layer capacitor manufactured by the voltage application process was 0 .87F.

  As a result of an experiment under the same conditions as in Example 1 except that the voltage application time during the voltage application process during the manufacture of the electric double layer capacitor was 6 hours, the capacitance of the electric double layer capacitor manufactured through the voltage application process was 0 .91F.

  As a result of an experiment under the same conditions as in Example 1 except that the voltage application time during the voltage application process at the time of manufacturing the electric double layer capacitor was 24 hours, the capacitance of the electric double layer capacitor manufactured by the voltage application process was 0 .93F.

  As a result of experimenting under the same conditions as in Example 1 except that the solvent of the electrolytic solution of the electric double layer capacitor was a mixed solution of water and ethylene glycol (volume ratio 2: 1), the electric double layer capacitor produced by applying the voltage was processed. The capacitance was 0.68F.

  As a result of experimenting under the same conditions as in Example 6 except that charge / discharge of the electric double layer capacitor and measurement of the discharge capacity were performed at −30 ° C., the capacitance of the electric double layer capacitor manufactured by applying the voltage was 0.44F. Met.

  As a result of experimenting under the same conditions as in Example 1 except that the electrolytic solution of the electric double layer capacitor was changed to 3.5 mol / l sodium chloride aqueous solution and the charge / discharge voltage range was changed to 0 V to 0.9 V, the voltage was applied and manufactured. The capacitance of the electric double layer capacitor was 0.86F.

  As a result of an experiment under the same conditions as in Example 1 except that the electrolytic solution of the electric double layer capacitor was changed to a 3.5 mol / l potassium bromide aqueous solution, the capacitance of the electric double layer capacitor manufactured by applying the voltage was 0. 78F.

  As a result of experimenting under the same conditions as in Example 1 except that the electrolytic solution of the electric double layer capacitor was changed to (2.0 mol sodium bromide + 1.5 mol sodium chloride) / l, the electric double layer capacitor manufactured by applying the voltage was processed. The capacitance was 0.96F.

After mixing activated carbon particles having a diameter of 5 μm and a surface area of 1830 m ² / g, acetylene black and a fluororesin-based adhesive (weight ratio 85: 5: 10) into a polarizable electrode of an electric double layer capacitor, heating and pressure molding The thickness of the activated carbon sheet layer was 250 μm, and the same as Example 1 except that an electrode obtained by pressure bonding a sheet having a basis weight of 21 mg / cm ² (Excelcellor sheet electrode manufactured by Japan Gore-Tex) to an insoluble metal current collector was used. As a result of the experiment under the conditions, the electrostatic capacitance of the electric double layer capacitor manufactured by applying the voltage was 1.02F.

  As a result of experimenting under the same conditions as in Example 1 except that the voltage range of charging / discharging of the electric double layer capacitor was set to 0V to 0.9V, the capacitance of the electric double layer capacitor manufactured by applying the voltage was 1.10F. Met.

  An experiment was performed under the same conditions as in Example 1 except that (2 mol sulfuric acid + 1.65 mol sodium bromide) / l aqueous solution was used as the electrolytic solution for manufacturing the electric double layer capacitor, and the charge / discharge voltage range was changed from 0 V to 0.9 V. As a result, the capacitance of the electric double layer capacitor manufactured by applying the voltage was 0.97F.

  The same conditions as in Example 1 were used except that (4 mol potassium hydroxide + 1.65 mol sodium bromide) / l aqueous solution was used as the electrolytic solution during the production of the electric double layer capacitor, and the charge / discharge voltage range was changed from 0 V to 0.9 V. As a result of the experiment, the capacitance of the electric double layer capacitor manufactured by applying the voltage was 0.99F.

  As a result of experimenting under the same conditions as Example 1 except that the charge / discharge measurement of the electric double layer capacitor was performed at 80 ° C. and the potential range of the charge / discharge measurement was 0V to 0.9V, The capacitance of the multilayer capacitor was 0.83F.

[Comparative Example 1]
The electric double layer capacitor was manufactured under the same conditions as in Example 1 except that no voltage application treatment was performed at the time of manufacturing the electric double layer capacitor. As a result, the capacitance of the electric double layer capacitor was 0.82F.

[Comparative Example 2]
The electric double layer capacitor was manufactured under the same conditions as in Example 15 except that no voltage application treatment was performed when the electric double layer capacitor was manufactured. As a result, the capacitance of the electric double layer capacitor was 0.71F.

[Comparative Example 3]
The electric double layer capacitor was manufactured and measured under the same conditions as in Example 8 except that no voltage application treatment was performed when the electric double layer capacitor was manufactured. As a result, the electric double layer capacitor had a capacitance of 0.60F.

[Comparative Example 4]
The electric double layer capacitor was manufactured and measured under the same conditions as in Example 9 except that no voltage application treatment was performed at the time of manufacturing the electric double layer capacitor. As a result, the capacitance of the electric double layer capacitor was 0.40F.

[Comparative Example 5]
The electric double layer capacitor was manufactured and measured under the same conditions as in Example 10 except that no voltage application treatment was performed at the time of manufacturing the electric double layer capacitor. As a result, the electric double layer capacitor had a capacitance of 0.60F.

[Comparative Example 6]
The electric double layer capacitor was manufactured under the same conditions as in Example 11 except that no voltage application treatment was performed at the time of manufacturing the electric double layer capacitor. As a result, the capacitance of the electric double layer capacitor was 0.56F.

[Comparative Example 7]
The electric double layer capacitor was manufactured under the same conditions as in Example 14 except that no voltage application treatment was performed at the time of manufacturing the electric double layer capacitor. As a result, the capacitance of the electric double layer capacitor was 0.71F.

[Comparative Example 8]
The electric double layer capacitor was manufactured and measured under the same conditions as in Example 16 except that no voltage application treatment was performed at the time of manufacturing the electric double layer capacitor. As a result, the capacitance of the electric double layer capacitor was 0.59F.

[Comparative Example 9]
The electric double layer capacitor was manufactured under the same conditions as in Example 13 except that the voltage application treatment was not performed when the electric double layer capacitor was manufactured. As a result, the capacitance of the electric double layer capacitor was 0.71F.

  From the above, after assembling an electric double layer capacitor using an activated carbon electrode and an aqueous electrolyte, by applying voltage application treatment, it can be used at low temperature in addition to high capacitance, high output, and high safety, An electric double layer capacitor can be provided at a low manufacturing cost.

It is sectional drawing of the electric double layer capacitor to which this invention is applied. It is the top view seen from the upper part of the electric double layer capacitor to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Current collector 5 Current collector 6 Gasket 7 End plate 8 Tightening bolt 9 Nut

Claims (7)

  An electric double layer capacitor comprising an activated carbon as a polarizable electrode and an aqueous solution in which a salt composed of elements of groups 1 and 17 of the periodic table of elements is dissolved as an electrolytic solution. Thereafter, an electric double layer capacitor produced by performing a voltage application process at room temperature and a voltage of 0.4 V to 1.0 V.   An electric double layer capacitor produced by applying the voltage of claim 1 in a temperature range of room temperature to 80 ° C.   The electric double layer capacitor according to claim 1 or 2, wherein an aqueous solution containing sodium bromide, potassium bromide, sodium chloride, or a mixture thereof is used as an electrolytic solution.   2. An aqueous electrolyte solution which is prepared by dissolving an organic substance soluble in water in an aqueous solution containing sodium bromide, potassium bromide or a mixture thereof, and which does not freeze even at −30 ° C. Or the electric double layer capacitor of 2.   5. The electricity according to claim 1, 2 or 4, wherein an electrolytic solution in which ethylene glycol or a homologue thereof is dissolved in an aqueous solution containing sodium bromide, potassium bromide, or a mixture thereof is used. Double layer capacitor.   An electrolyte solution in which sodium bromide, potassium bromide, or a mixture thereof is dissolved in an aqueous solution containing sulfuric acid, other inorganic acid, potassium hydroxide, or other inorganic base is used. 3. The electric double layer capacitor according to 1 or 2.   By dissolving sodium bromide, potassium bromide, or a mixture thereof, and ethylene glycol or a homologue thereof in an aqueous solution containing magnesium bromide or sodium perchlorate, or other neutral salts or mixtures thereof. 3. The electric double layer capacitor according to claim 1, wherein the obtained electrolytic solution is used.

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