JP6903312B2 - Capacitor charging / discharging method. - Google Patents

Description

The present invention relates to a method of charging and discharging a capacitor.

In recent years, efforts to address environmental problems have become important, and there is a demand for an efficient power source that has a lighter burden on the environment. One technology that is expected to contribute to this demand is an electrochemical capacitor. An electrochemical capacitor is a device for accumulating and outputting electric charges by using an electrochemical action, and an electric double layer capacitor is a typical example, and a redox capacitor is a newly proposed one. is there.

An electric double-layer capacitor has a pair of electrodes and an electrolytic solution arranged between the pair of electrodes, and is formed by adsorption of ions (non-Faraday reaction) generated at the interface between the electrolytic solution and the electrodes. It is a capacitor that can store electric charges using multiple layers, and it is highly expected that the capacity can be increased by using a carbon material or the like having a very large specific surface area as an electrode.

On the other hand, the redox capacitor is a capacitor capable of accumulating electric charges by utilizing the pseudo capacitance developed by a plurality of continuous redox (oxidation-reduction) reactions of the active material, and is larger than the above electric double layer capacitor. It has the advantages of capacity and superior instantaneous charge / discharge characteristics to batteries, and is expected to be more promising.

By the way, regarding the possibility of the above-mentioned capacitor, the following Patent Document 1 has a technical proposal regarding a capacitor having a copper nanostructure.

Japanese Unexamined Patent Publication No. 2011-195865

However, according to the technique described in the above patent document, the capacitance is only about 14 mAh / g, and a capacitor having a larger capacitance is desired.

Therefore, in view of the above problems, the present invention provides a method for charging / discharging a capacitor having a higher capacity.

As a result of diligent studies by the present inventors on the above-mentioned problems, it was discovered that by including a negative potential range for the operating electrode, it is possible to utilize the above-mentioned capacitor in which the capacitance is dramatically increased. However, the present invention has been completed.

That is, in the method of charging / discharging a capacitor according to one aspect of the present invention, an operating electrode, a counter electrode arranged to face the operating electrode, and an electrolytic solution filled between the operating electrode and the counter electrode are used. In the method of charging the including capacitor, the operating electrode is provided with a copper nanostructure on the surface, and charges and discharges the operating electrode including a negative potential range.

As described above, the present invention makes it possible to provide a method for charging / discharging a capacitor having a higher capacity.

It is sectional drawing of the capacitor which concerns on embodiment. It is a figure which shows the result of cyclic voltammetry of the capacitor which concerns on Example. It is a figure which shows the charge / discharge characteristic (relationship between potential and time) of the capacitor which concerns on Example. It is a figure which shows the charge / discharge characteristic (relationship between potential and time) of the capacitor which concerns on Example. It is a figure which shows the charge / discharge characteristic (relationship between potential and time) of the capacitor which concerns on Example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be implemented in many different embodiments, and is not limited to the specific examples in the embodiments and examples shown below.

(Capacitor)
FIG. 1 is a schematic cross-sectional view of the structure of a capacitor (hereinafter referred to as “the present capacitor”) 1 according to the present embodiment. The present capacitor 1 is a so-called electrochemical capacitor, and is arranged between a pair of electrodes 2a and 2b arranged to face each other, a copper nanostructure 3 formed on the pair of electrodes, and the pair of electrodes. It has an electrolyte layer 4. One of the pair of electrodes 2a and 2b is an operating electrode, and the other is a counter electrode arranged so as to face the operating electrode.

The pair of electrodes 2a and 2b in the capacitor 1 have conductivity and have a function of holding an electrolytic solution, and the material is not limited, but a conductive plate or an insulating plate is used. An example in which a conductive film is arranged on the surface can be exemplified. Examples of the conductive plate include, for example, a metal plate and a carbon plate, and examples of the conductive plate having the conductive film arranged on the insulating plate include insulation of glass, polyester film, polycarbonate film, and the like. Conductive film such as ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine-doped tin oxide), ATO (aluminum-doped tin oxide), GTO (gallium-doped tin oxide), etc. Can be illustrated by arranging. From the viewpoint of productivity, mechanical strength, price, and light weight, a metal plate or ITO is preferable.

The distance between the pair of electrodes 2a and 2b is not limited as long as the charge / discharge reaction is possible, but is preferably 10 μm or more and 5 cm or less, and more preferably 100 μm or more and 1 cm or less. .. When the thickness is 10 μm or more, the electric double layer can be sufficiently grown to cause an electrochemical reaction of charge and discharge, and when the thickness is 5 cm or less, the weight and size can be reduced.

The copper nanostructure 3 in the present capacitor 1 is formed so that the actual electrode area can be expanded. The copper nanostructure is not limited as long as the electrode area can be expanded, but copper nanowires, copper nanodendrites, porous copper, copper nano / microbeads and the like can be exemplified, and a larger actual surface area can be exemplified. It is more preferable to use copper nanowires from the viewpoint of forming the above. The amount of the copper nanostructure formed is not limited as long as a sufficient actual surface area can be obtained ^{, and is preferably, for example, 10 μg / cm 2} or more and 1 g / cm ² or less, and more preferably 50 μg / cm ² or more. It is 500 mg / cm ² or less.

Further, the copper nanostructure in the present capacitor 1 may be formed on only one electrode, but may be formed on both electrodes.

The electrolytic solution in the present capacitor 1 is a medium through which a current flows due to ionic conduction, and is not limited, but is a liquid electrolyte, a gel electrolyte, or a solid electrolyte composed of at least a solvent and a supporting electrolyte.

The solvent in the electrolytic solution of the present capacitor 1 can retain the supporting electrolyte and dissociate into ions, and is not limited to this, but is, for example, water, an organic solvent, or a gel-like substance. , Solid electrolyte can be exemplified, and organic solvents such as acetonitrile, propylene carbonate, N-methylpyrrolidone, and γ-butyrolactone are more preferable from the viewpoint of expanding the operating voltage and therefore improving the energy density.

Further, the supporting electrolyte of the electrolytic solution in the present capacitor 1 is capable of dissociating into ions in a medium and exhibiting ionic conduction, and is not limited thereto, but for example, when water is used as the solvent, LiCl, LiBr, Li ₂ SO ₄ , LiOH, LiClO ₄ , NaCl, NaBr, Na ₂ SO ₄ , NaOH, NaClO ₄ , KCl, KBr, K ₂ SO ₄ , KOH, KClO ₄ , (C ₂ H ₅ ) ₄ NOH When an organic solvent is used as the solvent, (C ₂ H ₅ ) ₄ NaClO ₄ , (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NPF ₆ , (C ₄ H ₉₎ ) ₄ NClO ₄ , (C ₄ H ₉ ) ₄ NBF ₄ , (C ₄ H ₉ ) ₄ NPF ₆ , LiClO ₄ , NaClO ₄ , KClO ₄ , (C ₄ H ₉ ) ₄ NOH. When forming a capacitor in which a copper nanostructure and an aqueous solvent are combined, LiOH, NaOH, KOH, (C ₂ H ₅ ) ₄ NOH and (C ₄ H _{9) are used from the viewpoint of the chemical stability of the copper nanostructure.} ) ₄ NOH is preferable. The amount of the supporting electrolyte contained is not limited as long as it can perform the above functions, but is 0.0002 parts by weight or more and 300 parts by weight or less when the weight of the solvent is 100 parts by weight. It is preferably 0.002 parts by weight or more and 40 parts by weight or less. When the amount is 0.0002 parts by weight or more, the electric double layer can be sufficiently formed in the charge / discharge electrochemical reaction, and when the amount is 300 parts by weight or less, the viscosity of the electrolytic solution is not excessively increased. It is possible to smoothly move ions in the electrolytic solution, and it is possible to shorten the time required for charging and discharging.

In this capacitor 1, by arranging the copper nanostructure on the electrode, the actual surface area of the electrode is expanded, and the surface of the copper nanostructure is reversible electrochemical oxidation reaction (charge) and reduction reaction (discharge). Therefore, it becomes a higher energy and higher output electrochemical capacitor that exhibits more stable charge / discharge characteristics. The electrochemical capacitor according to the present embodiment is classified as a redox capacitor because it utilizes a reversible electrochemical redox reaction occurring on the surface of copper nanostructures.

(Charging / discharging method)
Next, a charging / discharging method (hereinafter referred to as “the method”) of the present capacitor will be described. This method is connected to an external drive device, and a voltage can be applied between a pair of electrodes to accumulate an electric charge, and a short circuit or a reverse voltage can be applied to release the accumulated electric charge. More specifically, when a reference electrode (for example, a saturated calomel electrode SCE) is used, the voltage to be applied is not limited as long as it can be charged and does not exceed the decomposition voltage of the material. , It is necessary to include applying a negative potential to the reference electrode SCE, preferably the potential is in the range of -2V or more and 1V or less, and more preferably -1.5V or more and 0.75V. The voltage is preferably in the following range.

More specifically, as will be clarified from the experimental examples described later, an electrode having a copper nanostructure is produced, and the potential measurement range is a range including a negative voltage range, more specifically -1.5. Cyclic voltammetry was performed with the value set to ~ 0.75. As a result, good redox repetition characteristics were obtained even in this range, and copper (I) oxide represented by the following formula was reduced to copper, and copper (II) oxide was further reduced. Is reduced to copper. That is, this two-step reduction can dramatically store more charge.

As described above, the present invention makes it possible to provide a method for charging / discharging a capacitor having a higher capacity.

Hereinafter, the electrochemical capacitor electrodes described in the above embodiments have been actually manufactured and their effects have been confirmed. This will be described below.

Copper ammine complex [Cu (NH ₃ ) ₄ ] SO ₄ was added to 3M aqueous ammonia so that the final concentration was 25 mM, and Li ₂ SO ₄ as a conductive salt was added so that the final concentration was 0.1 M, and copper was added. An aqueous solution of ammine complex was obtained. Using this solution, using ITO as the cathode, a platinum plate as the anode, and a saturated calomel electrode as the reference electrode, electrolysis was performed ^{at a solution temperature of 18 ° C., an electrolytic potential of -1.45 V, and an energization amount of 2.0 C / cm 2.} A copper nanowire was formed as a copper nanostructure on the cathode.

Next, repeated cyclic voltammetry in an aqueous solution of lithium hydroxide was performed using an electrochemical analyzer (ALS Japan Inc. Model 750A) to evaluate the capacitor characteristics. Specifically, a 3-electrode glass cell is used, and a copper nanowire electrode (tetraammine sulfate 25 mM, electrolytic potential −1.45 V, Li ₂ SO ₄ concentration 0.1 M, ammonia water concentration 3 M, and energizing electricity are used as operating electrodes. were prepared under optimal conditions amounts 2.0C / cm ^2), SCE as a reference electrode, and the counter electrode was a platinum plate. A lithium hydroxide aqueous solution (0.1 M) was used as the electrolytic solution. The sweep range was −1.5V to 0.75V. The result is shown in FIG.

Next, these redox waves were assigned based on the literature. For the sake of simplicity, the oxidation wave near −0.3V was designated as A, and the peak near 0.4V was designated as B. It is known from the literature that these two reactions are oxidation of copper to copper (I) oxide and copper (II) oxide, respectively. However, since there are various theories about the order of reduction to copper, the corresponding peaks were examined. The opposite reduction waves were designated as C and D.

As a result of examining various changes in the sweep range, it was found that the reduction of copper (I) oxide to copper was carried out in the reaction of C, and the reduction of copper (II) oxide to copper was carried out in the reaction of D. .. To be precise, it was confirmed that the electrochemical reaction formulas (1) and (2) shown in the above embodiment were occurring. That is, this reaction can be caused by including a negative voltage range in the charging / discharging potential range, which is a method of charging / discharging a capacitor capable of performing high charging / discharging.

Next, these oxidation reactions were charged, and these reduction reactions were regarded as discharges, and a charge / discharge test was performed. FIG. 3 shows the charge / discharge characteristics (relationship between potential and time) obtained when an electrode area of 1.0 × 1.0 cm ^{2 and a constant current of 5.6 V / g are applied.} Each time the charge / discharge test was repeated, the time required for charge / discharge decreased and the capacity decreased, but the shape of the discharge curve changed from 2 to 50 times and after 60 times. From the shape of the discharge curve, copper (II) oxide and copper (I) oxide were reduced to copper at the same time at -1V in the first 50 times, but in the charge / discharge after 60 times, the discharge process becomes two stages. It was. Here, FIG. 4 shows an enlarged view of the charge / discharge curve after 60 times. The fact that the waveform has two stages in this way indicates that the reduction proceeds in two stages from copper (II) oxide to copper (I) oxide and from copper (I) oxide to copper.

Further, the discharge capacity was obtained from the analysis of the discharge curve. It was confirmed that it exceeded 300 mAh / g in at least 40 times of charging and discharging, and greatly exceeded 100 to 200 mAh / g of a commercially available lithium ion battery.

The results when the current density during charging / discharging is changed to 6.25 A / g are shown in FIG. 5 and the table below. As a result, the discharge capacity showed a value exceeding 200 mAh / g at least 100 times, which also exceeded the discharge capacity of a commercially available lithium ion battery.

The effectiveness of the present invention has been confirmed above.

The present invention has industrial applicability as a method for charging and discharging a capacitor.

Claims (4)

A method for charging a capacitor including an operating electrode, a counter electrode arranged to face the operating electrode, and an electrolytic solution filled between the operating electrode and the counter electrode.
The operating electrode has a copper nanostructure on its surface, and has a copper nanostructure on its surface.
If you measure the potential of the working electrode using a saturated calomel reference electrode, the potential of the working electrode that pairs with the saturated calomel reference electrode, including a negative potential range where the reduction reaction takes place in the copper oxide in said working electrode A method of charging and discharging a capacitor that charges and discharges so as to be used. The method for charging / discharging a capacitor according to claim 1, wherein the copper nanostructure is a copper nanowire. The method for charging / discharging a capacitor according to claim 1, wherein the saturated calomel reference electrode is charged / discharged so that the potential of the operating electrode is in the range of -2 V or more and 1 V or less. The method for charging / discharging a capacitor according to claim 1, wherein the electrolytic solution contains hydroxide ions.

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