JP2008066681A - Electrochemical capacitor and method of manufacturing zinc electrode used in the electrochemical capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To utilize zinc used as an electrode material of a secondary battery and being abundant in resources and as a material having a light weight and excellent environmental friendliness in an electrochemical capacitor being a hybrid capacitor which is capable of having a capacitance value, an energy density, and an output density larger than those of an EDLC (Electric Double Layer Capacitor) because one side electrode of the hybrid capacitor has a large pseudo-capacitance that involves a charge-transfer process. <P>SOLUTION: This electrochemical capacitor being a hybrid capacitor comprises an activated carbon fabric electrode as a positive electrode, a zinc electrode as a negative electrode, and an alkali hydroxide aqueous solution containing zinc oxide as an electrolyte. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrochemical capacitor using a water-based electrolyte and a method for producing a zinc electrode thereof.

  Conventionally, an electric double layer capacitor (sometimes abbreviated as EDLC in the drawings and specification) is an electrochemical energy device that stores electric charges in an electric double layer formed at the interface between a polarizable electrode and an ionic conductor, It is characterized by no movement of electrons at the electrode / electrolyte interface. In addition, since it has excellent charge / discharge cycle characteristics over a wide temperature range and uses environmentally friendly materials, it has been widely used as a power source for semiconductor memory backup and actuator backup.

  There are two types of EDLC: those using aqueous electrolytes and those using organic electrolytes. As the aqueous electrolyte, an aqueous solution of sulfuric acid is used, and as the organic electrolyte, an electrolyte such as tetraethylammonium tetrafluoroborate is dissolved in a solvent such as propylene carbonate. The aqueous electrolyte basically has a high dielectric constant and a low viscosity, so that the ionic conductivity is higher than that of the organic electrolyte. Therefore, it can be said that it is an advantageous system for rapid charge / discharge.

  Therefore, in recent years, a hybrid capacitor in which an activated carbon fiber cloth, which is a carbon-type electrode, and an electrode with a fast faradic electron transfer process has been proposed as a new capacitor system, and has been actively researched. The hybrid capacitor can have a larger capacitance, energy density, and output density than EDLC because one of the electrodes has a large pseudo capacitance with a charge transfer process.

  For example, in an electric double layer capacitor comprising a current collector, a polarizable electrode having activated carbon, a separator, and an organic electrolyte, the activated carbon is +1.0 V with respect to the standard electrode Ag / AgCl in a sulfuric acid aqueous solution. Polarizing electrodes for electric double layer capacitors (see Patent Document 1) and carbon for electric double layer capacitors that have been oxidized at a voltage of +1.4 V or less and then reduced at a voltage of -0.3 V or more and -0.7 V or less. The material is a carbon material for electric double layer capacitors having graphite-like microcrystalline carbon produced by subjecting a carbon material to activation treatment, and the interlayer distance of the microcrystalline carbon is 0.365 nm to 0.385 nm. (Patent Document 2), a separator comprising a polymer compound that is soluble in water and gels with an acidic substance or a basic substance, a separator, and an aqueous electrolyte Electric double layer capacitor characterized by using a gel solid electrolyte composite (Patent Document 3) have been proposed.

Japanese Patent Laid-Open No. 2000-124078 JP 2005-294850 A JP-A-2005-39196

  In the present invention, since one electrode of an electrochemical capacitor, that is, a hybrid capacitor (sometimes abbreviated as HC in the figure and specification) has a large pseudocapacitance accompanied by a charge transfer process, the capacitance, energy, and energy of EDLC are larger. As a development, zinc used in secondary battery electrode materials is generally compatible with aqueous electrolytes, and the standard electrode potential is less than the standard hydrogen electrode. It is as low as 0.76 V, has a large hydrogen overvoltage, and has a high energy density. And because it is abundant in resources, it is inexpensive, lightweight, and has excellent environmental compatibility.

  The first solution of the present invention is to comprise an activated carbon cloth electrode as a positive electrode as an electrochemical capacitor, a zinc electrode as a negative electrode, and an alkali hydroxide aqueous solution containing zinc oxide as an electrolyte.

  The alkali hydroxide aqueous solution is contained and fixed in the polymer hydrogel electrolyte.

  The zinc electrode uses an electrode obtained by galvanizing a copper foil having a uniform surface treatment.

  The second solving means of the present invention is to provide an electrochemical capacitor whose discharge capacity is positive electrode regulation.

  The hybrid capacitor using the activated carbon electrode and the zinc electrode of the present invention has a capacitance approximately three times that of an ordinary electric double layer capacitor, and operates stably in a wide voltage range of + 0.4V to + 1.4V. There is a feature in doing. Thus, it can be expected as a new power storage device having a large energy density and output density.

  Focusing on the use of a zinc electrode, we experimented to see if it could be adapted as an electrode for a hybrid capacitor. FIG. 1 is a schematic diagram of an example flow relating to the production of the electrodes used in this example.

FIG. 1 (a) shows a method for producing an activated carbon electrode. An activated carbon fiber cloth 1 is impregnated with a 7.3M KOH / 0.7M ZnO aqueous solution 2, and a nickel foil 3 is welded to one piece of the cloth state by spot welding. Current collector. On the other hand, FIG. 1B shows a method for producing a zinc electrode, in which a copper (Cu) foil 4 is used as a substrate and a quadrilateral is used as an electrode, and the elongated state 4a is used as a Cu current collector. Next, the copper foil was used as a negative electrode, immersed in a 7.3 M KOH / 0.7 M ZnO aqueous solution 5, and NiOOH / Ni (OH) ₂ was used for the counter electrode (positive electrode) 6 at a current density of 30 mA cm ⁻² . Electrodeposition was performed for 10 minutes to deposit zinc on the copper foil. The two electrodes thus prepared are held relative to each other through a separator 7 impregnated with a 7.3 M KOH / 0.7 M ZnO aqueous solution and held by a support 8 to form a measurement cell (see FIG. 1 (c)), various tests were carried out.

FIG. 2 is a schematic view of a method for producing one embodiment of a zinc electrode according to the present invention. A quadrilateral carbon paper is used as a substrate, and one end of this upper side is sandwiched between rectangular nickel foils serving as lead terminals and spot-welded is prepared. As an electrodeposition bath, using a 7.3 M KOH / 0.7 M ZnO aqueous solution and a NiOOH / Ni (OH) ₂ electrode electrode as a counter electrode, 10 mA at 30 mA cm ⁻² for 1.5 minutes at a constant current. Zinc was electrodeposited in the range of 1.5 cm. After electrodeposition, use immediately after washing with pure water.

  The zinc electrode prepared above was immersed in 20 ml each of a 7.3 M KOH aqueous solution, a 7.3 M KOH / 0.7 M ZnO aqueous solution, and a 7.3 M KOH / 1.3 M ZnO aqueous solution, and the potential until dissolution was measured. . A charge / discharge unit (Hokuto Denko, HJ10018M8 type) controlled by a personal computer was used as the experimental apparatus.

  As a result of the experiment on the influence of the concentration of the electrolytic solution on the corrosion (dissolution) behavior of zinc, the corrosion behavior of zinc when the concentration of zinc oxide in the electrolytic solution is changed is shown in the zinc electrode corrosion behavior of FIG.

まず、亜鉛が式（１）および式（２）の固相反応により酸化され、中間生成物層を形成する。 When zinc is present, it shows about -1.37 V, and the potential increases with dissolution of zinc. The dissolution of zinc in the electrolyte proceeds in the following process.

First, zinc is oxidized by the solid phase reaction of formula (1) and formula (2) to form an intermediate product layer.

Next, the produced intermediate product becomes zinc complex ions and dissolves in the electrolytic solution (formulas (3) and (4)).

  There was a large difference in the time until the zinc was completely dissolved between the electrolyte containing no zinc oxide and the electrolyte containing it. This is thought to be because the dissolution of zinc slows because the concentration gradient becomes gentle due to the presence of zinc oxide in the electrolyte in advance. Moreover, there is not much difference in the time until dissolution between the 7.3M KOH / 0.7M ZnO aqueous solution and the 7.3M KOH / 1.3M ZnO aqueous solution. That is, it can be seen that the ZnO concentration in the 7.3M ant potassium hydroxide is approximately the same with a large difference between 0.7 and 1.3M.

  Next, regarding the immobilization of the electrolyte, considering the use of the polymer hydrogel electrolyte, in the case of FIG. 2, the electrodeposition bath was set to 7.3 M KOH / PAAK, 7.3 M KOH / 0.7 M ZnO / PAAK, Made with 7.3M KOH / 1.3M ZnO / PAAK, hydrogel electrolyte. PAAK is an abbreviation for cross-linked potassium polyacrylate. A zinc electrode produced by the procedure shown in FIG. 2 was immersed in each polymer hydrogel, vacuumed for 5 minutes to bring zinc and polymer hydrogel electrolyte into close contact, and then the potential until dissolution was measured.

  Regarding the corrosion behavior of zinc in the polymer hydrogel electrolyte, the dissolution of zinc in the polymer hydrogel electrolyte having different concentrations of zinc oxide is shown in FIG. 4 showing the corrosion behavior of the zinc electrode in the polymer hydrogel electrolyte. As in the case of the electrolytic solution, there is a large difference in the time until the zinc is completely dissolved between the case where zinc oxide is not contained and the case where zinc oxide is not contained. This is also considered to be because the concentration gradient becomes gentle due to the presence of zinc in the electrolyte as in the case of the electrolytic solution. Moreover, it turned out that the time until complete dissolution is the same for the electrolytic solution and the polymer hydrogel electrolyte as a whole.

(Example 2)
Carbon foil (TGP-H-060 manufactured by Toray), Ni foil (manufactured by Nilaco) and glassy carbon (manufactured by Nilaco) polished with alumina and sonicated for 3 minutes, and Cu foil (manufactured by Nilaco) etched with hydrochloric acid for 1 minute As shown in the schematic diagram of the preparation of a zinc electrode using Cu mesh (made by Nilaco) as a substrate and FIG. 5 with different substrates, an aqueous solution of 7.3 M KOH / 0.7 M ZnO was used as an electrodeposition bath, and 30 mA cm ^−2. For 10 minutes to deposit zinc.

  The zinc thus prepared was immersed in 20 ml of a 7.3 M KOH / 1.3 M ZnO aqueous solution or a 7.3 M KOH / 0.7 M ZnO / PAAK hydrogel electrolyte, and the potential until dissolution was measured. FIG. 6 shows the solubility of the zinc electrode prepared above in the electrolyte solution, and FIG. 7 shows the solubility in the polymer hydrogel electrolyte.

  In either electrolyte, it can be seen that the time until zinc is completely dissolved depends on the surface morphology of the substrate. That is, if zinc is deposited on a substrate having a large surface area such as carbon paper or Cu mesh and a non-flat surface, the dissolution rate increases. However, in the case of a flat surface such as Cu foil or Ni foil, the time until dissolution is long. This is considered to be because the flatter substrate surface allows zinc to be deposited more uniformly during the precipitation, and the surface area becomes smaller, resulting in a lower dissolution rate.

  Glassy carbon is considered to be a substrate that is relatively difficult to dissolve because its surface is flat, but since it peels off from the substrate before all the zinc is dissolved during dissolution, the dissolution time is short in the electrolyte. It has become. In Cu and Ni, although Ni has a smaller hydrogen overvoltage, the time until Ni dissolves is longer. This seems to be because an oxide film was formed on the Ni surface because the surface was polished with alumina and subjected to ultrasonic treatment.

  FIG. 8 shows an X-ray photoelectron spectrum (XPS) of Ni surface treated with emery paper or alumina polishing / ultrasonic. By processing with alumina polishing and ultrasonic waves, the Ni peak of the substrate itself becomes smaller than that when processing with emery paper, and the peak of Ni oxide appears (FIG. 8 (a)). Show). In FIG. 8B, a large oxygen peak appears. Therefore, it can be seen that an oxide film is formed on the Ni surface by ultrasonic waves.

  In addition, FIG. 9 shows the dissolution (corrosion) behavior of zinc when using Ni polished with emery paper and Ni subjected to ultrasonic treatment by polishing with alumina. When it is polished with emery paper, the time until all zinc is dissolved is shorter than that processed with ultrasonic waves. Therefore, in the case of nickel, the hydrogen overvoltage is larger than that of copper due to the oxide film generated by ultrasonic treatment, so it is considered that the time until dissolution of zinc is longer than that of copper.

(Example 3)
Regarding the production of the activated carbon electrode for the electric double layer capacitor, all the electrodes of the electric double layer capacitor using the aqueous electrolyte solution were produced according to the procedure shown in FIG. An activated carbon fiber cloth (manufactured by Kuraray Co., Ltd.) cut to a size of 1 cm × 1 cm was dried while evacuating at 120 ° C. for 12 hours to remove impurities. The dried activated carbon fiber cloth was placed in a 10M KOH aqueous solution and evacuated to impregnate the electrolyte in the pores of the activated carbon fiber cloth.

  Next, an activated carbon fiber cloth impregnated with an electrolytic solution is placed on a nickel current collector (1 cm × 1 cm: manufactured by Nilaco) coated with carbon paste, and is attached by heating at 60 ° C. for 1 hour. An activated carbon electrode was prepared.

Example 4
On the other hand, all the activated carbon electrodes using the polymer hydrogel electrolyte were produced according to the procedure of the activated carbon electrode production schematic diagram impregnated with the polymer hydrogel electrolyte in FIG. Similarly to the aqueous electrolyte, the activated carbon cloth cut to a size of 1 cm × 1 cm was dried while evacuating at 120 ° C. for 12 hours to remove impurities. The dried activated carbon fiber cloth was placed in a 10M KOH aqueous solution and evacuated to impregnate the electrolyte in the pores of the activated carbon fiber cloth.

  Next, the activated carbon fiber cloth impregnated with the electrolytic solution was placed in 50 ml of 10M KOH, and 5 g of cross-linked potassium polyacrylate (manufactured by PAAK: Aldrich Chemical Company Inc.) was added to the gel while stirring. Thereafter, vacuuming was performed for 5 minutes to remove bubbles in the gel, and aging was performed at 30 ° C. for 72 hours. Then, the activated carbon fiber cloth impregnated with the polymer hydrogel was placed on a nickel current collector coated with a carbon paste and attached by heating at 60 ° C. for 1 hour to produce an activated carbon electrode for an electric double layer capacitor.

(Example 5)
For the assembly of the electric double layer capacitor cell, a measurement cell as shown in FIG. 1 was constructed using a separator made of sulfonated polypropylene impregnated with a polymer hydrogel electrolyte or a KOH aqueous solution (dry thickness 120 μm) and an activated carbon electrode. When impregnating the separator with the polymer hydrogel electrolyte, the KOH aqueous solution was first impregnated by evacuation in the same manner as in the preparation of the electrode, and gelling was performed by adding cross-linked potassium polyacrylate, followed by aging. Bipolar and tripolar cells were used for the measurement. As shown in the measurement cell experimental apparatus of FIG. 12, the tripolar cell was provided with a Hg / HgO reference electrode through a separator with a KOH aqueous solution. Various electrochemical measurements were performed at 25 ° C.

  The activated carbon cloth electrode for the hybrid capacitor was produced according to the procedure of the activated carbon electrode production method schematic diagram of FIG. 13 and other examples. An activated carbon fiber cloth (manufactured by Kuraray Co., Ltd.) cut to a size of 1 cm × 1 cm was dried while vacuuming at 120 ° C. for 12 hours to remove impurities. The dried activated carbon fiber cloth was placed in a 7.3 M KOH / 0.7 M ZnO aqueous solution and evacuated to impregnate the electrolyte in the pores of the activated carbon fiber cloth. Next, an activated carbon fiber cloth impregnated with an electrolytic solution is placed on a nickel current collector (1 cm × 1 cm: manufactured by Nilaco) coated with a carbon paste, and is pasted by heating at 60 ° C. for 1 hour to activate the hybrid capacitor. A carbon electrode was prepared.

The zinc electrode for the hybrid capacitor was produced according to the procedure of the schematic diagram of the zinc electrode production method of FIG. 14 and other examples. Using copper foil (1 cm × 1 cm: manufactured by Nilaco) etched with hydrochloric acid for 1 minute as a substrate, zinc was electrodeposited at 30 mA cm ⁻² for 10 minutes using a 7.3 M KOH / 0.7 M ZnO aqueous solution as an electrodeposition bath. . Thereafter, the zinc surface was rinsed with ultrapure water and dried to use as a zinc electrode.

ここで、Ｃ_cell：セルの静電容量、Ｃ_n：負極の静電容量、Ｃ_p：正極の静電容量である。式（６）は正極と負極のどちらかの静電容量が大きくなる、すなわち放電曲線の傾きが緩やかになれば、セルの静電容量も大きくなることを示している。 (Characteristic test)
Regarding the hybrid capacitor using the activated carbon electrode and the zinc electrode, the relationship between the electrostatic capacitance of the positive electrode and the negative electrode of the electrochemical capacitor and the electrostatic capacitance of the cell is as shown in Equation (6).

Here, C _{cell is} the capacitance of the cell, C _{n is the} capacitance of the negative electrode, and C _p is the capacitance of the positive electrode. Equation (6) shows that the capacitance of either the positive electrode or the negative electrode increases, that is, if the slope of the discharge curve becomes gentle, the capacitance of the cell also increases.

  In order to determine the voltage range in which the hybrid capacitor according to the present invention combining zinc and activated carbon fiber cloth operates stably, a charge / discharge test was conducted. FIG. 15 shows a charge / discharge curve of the hybrid capacitor. From FIG. 15A, the hybrid capacitor has an upper limit voltage of +1.4 V, which is about 1.5 times that of EDLC (−0.9 V), and is stable in a voltage range of +0.4 V to +1.4 V. I found it to work. The operating voltage range of the EDLC is 0V to -0.9V and the voltage difference is 0.9V, whereas the voltage difference of the hybrid capacitor is 1.0V. It was found that the hybrid capacitor operates stably over a larger voltage range than the electric double layer capacitor. This is considered to be because the electrolysis of water hardly occurs even at a high voltage because the hydrogen overvoltage of zinc is large, and the capacitor operates stably. Further, the electrostatic capacity calculated from the discharge curve of FIG. 15 using Equation (6) is 1.9 F, which is about three times that of the electric double layer capacitor.

  Further, from FIG. 15B, it can be seen that when the behavior of the positive electrode and the negative electrode during charging / discharging is observed, there is almost no change in potential of the negative electrode, so that the positive electrode is almost regulated. Therefore, it can be seen that the capacitance of the activated carbon electrode largely dominates the capacitance of the hybrid capacitor.

The result of the high rate discharge test of the hybrid capacitor according to the present invention is shown in FIG.
In the case of EDLC, IR drop starts to occur when the current density is 40 mA cm ⁻² or more, and the IR drop increases as the current density increases, and becomes about +0.2 V at 100 mA cm ⁻² . In the case of a hybrid capacitor, when the current density is 40 mA cm ⁻² or more, IR drop starts to occur, but the size of IR drop does not change much even when the current density increases, and the size of IR drop also increases. It is smaller than the electric double layer capacitor.

The discharge capacity at each current density is shown in the capacitance curve diagram of FIG. 17 hybrid capacitor.
Hybrid capacitor according to the present invention (indicated by ●) decrease in capacitance of up to 100 mA cm ^-2 is relatively small, even at 100 mA cm ^-2 or more electrostatic capacitance starts to decrease, electric double layer capacitor (indicated by ○) It has a larger capacitance.

FIG. 18 shows the high rate discharge rate (HRD). The HRD of the hybrid capacitor (indicated by ●) is almost the same as that of the electric double layer capacitor (indicated by ○) up to 100 mA cm ⁻² .

この式で、Ｅ：エネルギー密度（Ｗｈｇ^-1）、Ｃ：キャパシタンス（Ｆｇ^-1）、
Ｖ：電圧差（Ｖ）、Ｐ：出力密度（Ｗｇ^-1）、Δｔ：放電時間（ｈ）である。 Regarding the energy density and the power density, the energy density and the power density of the hybrid capacitor are calculated from the discharge curve of FIG. 16 using the equations (7) and (8), and the Ragone plot is shown in FIG.

In this formula, E: energy density (Whg ⁻¹ ), C: capacitance (Fg ⁻¹ ),
V: voltage difference (V), P: power density (Wg ⁻¹ ), Δt: discharge time (h).

  In general, the Ragone plot is more excellent as it has a higher energy density and does not decrease much even when the energy density becomes a high output density. From the Ragone plot, the energy density of the hybrid capacitor is about five times as large as that of the electric double layer capacitor. This is because the operating voltage range, upper limit voltage and capacitance of the hybrid capacitor are larger than those of the electric double layer capacitor. In addition, since the high rate discharge characteristics are excellent, even when the output density is high, the decrease in energy density is small and the output characteristics are very excellent.

  FIG. 20 shows the results of measuring the change over time of the current that flows when the hybrid capacitor is held at the upper limit voltage.

  The overall leakage current of the hybrid capacitor is larger than that of the electric double layer capacitor (FIG. 20 (a) shows the initial state change (seconds) of leakage, and FIG. 20 (b) shows the time unit. Showing change). Further, at the initial stage of little elution, no vibration is observed in the leakage current, but the leakage current is oscillated 1-2 hours after elution proceeds. This is considered due to the elution of zinc in the negative electrode into the electrolyte.

  FIG. 21 shows changes in cell voltage over time when capacitors are formed using a KOH aqueous solution (shown by a solid line) and a polymer hydrogel electrolyte (shown by a dotted line), and each is charged and opened to open circuit. And self-discharge curve at ELDC electrode when using KOH aqueous solution.

  From this, it can be seen that the self-discharge is suppressed in the direction using the polymer hydrogel (solid line). 22 shows the potential change between the positive electrode and the negative electrode during measurement, FIG. 22 (a) shows the case of using the polymer hydrogel electrolyte, FIG. 22 (b) shows the case of the KOH aqueous solution, and the KOH aqueous solution is also high. In the molecular hydrogel electrolyte, the voltage of the positive electrode decreases at the initial stage and does not change much thereafter.

  On the other hand, the voltage of the zinc electrode used as the negative electrode rises at a relatively constant rate. From this, it is understood that hydroxide ions having negative charges are difficult to leave from the electrode surface, while those having positive charges such as potassium ions are easily separated. It is considered that the polymer hydrogel electrolyte is less likely to leave ions than the KOH aqueous solution.

  Next, in the hybrid capacitor according to the present invention, when compared with the zinc electrode KOH system, the time-dependent change of the cell voltage when the circuit is opened after charging is shown in FIG. a) is a change in cell voltage, and FIG. 23B shows a change in potential of each electrode). The time is significantly longer than that of a normal electric double layer capacitor.

  In the case of an ordinary electric double layer capacitor (FIGS. 21 and 22), the voltage has decreased at a substantially constant rate, whereas in the case of a hybrid capacitor, it has decreased for a while, but has remained constant for a while. Yes, after that it has dropped sharply. It is thought that the rapid voltage drop at the zinc electrode represents the dissolution of zinc. Therefore, it is considered that the dissolution of zinc greatly affects the voltage holding characteristics as well as the leakage current.

  The charge / discharge cycle was repeated to evaluate the cycle stability of the hybrid capacitor. The result is shown in FIG.

  The capacitance is relatively constant until the 100th cycle, but gradually decreases after the 100th cycle. This is presumably because zinc dissolves into the electrolyte solution over time and the amount of active material decreases. Therefore, cycle characteristics can be improved if elution of zinc can be suppressed.

  The resistance of the hybrid capacitor interface was evaluated by the AC impedance method. The Nyquist plot at that time is shown in FIG.

  The resistance value is larger than that of an ordinary electric double layer capacitor using a KOH aqueous solution. This is presumably because the hybrid capacitor uses one that includes a faradic charge accumulation process on one electrode.

The resistance value calculated from the IR drop in the high rate discharge curve is shown in FIG. In this result, the resistance value was 20 to 120 mA cm ⁻² and averaged about 1.3Ω, which almost coincided with the resistance value of a normal electric double layer capacitor using a KOH aqueous solution.

  From FIG. 15, it was found that the hybrid capacitor is subject to positive electrode regulation. Therefore, if the operating potential range of the activated carbon fiber cloth is widened, it is expected that the operating voltage range as a hybrid capacitor is further expanded. Therefore, we investigated the use of the activated carbon fiber cloth for hybrid capacitors with an expanded operating potential range.

  FIG. 27 shows a cyclic voltammogram of the activated carbon fiber cloth after performing cyclic voltammetry. After 400 cycles (indicated by a dotted line), the rising of the oxidation peak of the activated carbon fiber cloth near +0.2 V is shifted to the positive potential side. This is because the oxidation of the activated carbon fiber cloth is approaching the end by repeated cycles. Therefore, it seems that the operating voltage range of the activated carbon fiber cloth is slightly expanded.

  Next, FIG. 28 shows the results of the charge / discharge test of the hybrid capacitor using the activated carbon fiber cloth after 400 cycles (FIG. 28 (a) is the cell voltage, the dotted line is the discharge voltage curve, and the solid line is the charge voltage curve). 28 (b) shows individual electrode potentials.) The potential range is +0.3 V to +1.6 V, and the voltage difference is expanded by 0.3 V compared to the previous case. However, it takes time from around +1.5 V in the charging process, which is slightly different from a typical ordinary capacitor charge / discharge curve which is symmetrical.

この式で、ｑ：クーロン効率（％）、Ｑ_d：放電電気量（ｍＡ ｓ ｃｍ^-2）、
Ｑｃ：充電電気量（ｍＡ ｓ ｃｍ^-2）である。 Moreover, the Coulomb efficiency calculated | required from Formula (9) is about 80%, and it turns out that it is based on an irreversible reaction, and it is thought that the oxidation of activated carbon fiber cloth is not complete | finished completely. .

In this equation, q: Coulomb efficiency (%), Q _d : discharge electric energy (mA s cm ⁻² ),
Qc: Charged electricity (mA s cm ⁻² ).

  Next, the aqueous electrolyte solution was replaced with KOH used in the above examples, and was used with NaOH.

(Example 6)
An activated carbon fiber cloth was impregnated with a 7.3M NaOH / 0.7M ZnO aqueous solution to produce an activated carbon electrode. Next, electrodeposition was performed using a 7.3 M NaOH / 0.7 M ZnO aqueous solution as an electrodeposition bath (current of 30 mA cm ⁻² for 10 minutes), and zinc was deposited on a copper substrate to prepare a zinc electrode. Various characteristics tests were performed using the hybrid capacitor (HC) manufactured in this way. The comparative electrode was treated with the KOH aqueous solution used in the above example, and the other conditions were the same.

(I) Measurement of impedance of zinc electrode The impedance was measured by applying an applied voltage of ± 5 mV in a frequency range of 0.01 to 20 kHz in a bipolar cell and measuring the response impedance at that time. As shown in FIG. 29, the results show that the use of an aqueous NaOH solution (indicated by ●) has a smaller resistance than that of KOH (indicated by ○).

(B) Leakage current When the current flowing when the voltage is held at +1.4 V in the HC capacitor is measured, the case of KOH shown in FIG. 30A and the case of NaOH shown in FIG. Although the leak current does not change, it can be seen that there is less vibration in the case of NaOH.

(C) Energy Density Ragone plot As shown in FIG. 31, there is almost no change in the energy density between NaOH (indicated by ●) and KOH (indicated by ○), and the decrease in NaOH is slightly slower.

(D) Voltage holding characteristics As shown in FIG. 32, the result of measuring the voltage change with time when the battery is charged to +1.4 V and opened is approximately twice as long as NaOH (solid line display) than KOH (dotted line display). The above voltage characteristics were shown.

(E) Charge / Discharge Test A charge / discharge characteristic test was conducted at 1 mA cm ⁻² . The operating voltage range was + 0.4V to + 1.4V. As shown in FIG. 33, in the case of NaOH (displayed with a solid line), the capacitance was 1.3 F, which was smaller than that in the case of KOH (displayed with a dotted line). There wasn't.

(F) High rate discharge test After charging 1 mA cm ^-2 , the discharge current density was changed, and the capacitance was shown in Fig. 34 (a) and the discharge efficiency in Fig. 34 (b) as a comparison with KOH. Overall, the capacitance is smaller than KOH (indicated by ●), but NaOH (indicated by ○) has a large characteristic that there is no decrease in capacitance even at a large current, and the high rate discharge capacity is almost the same as that of KOH. The same.

(G) Cycle characteristic test When charging / discharging at 5 mA cm- ² and evaluating the cycle characteristic, as shown in FIG. 35, NaOH (circled) is approximately three times the cycle characteristic compared to KOH (circled). was there.

  Such a characteristic is considered to be an effect by suppressing the dissolution of zinc in the zinc electrode in the electrode preparation using NaOH. However, even when KOH is used, it can be sufficiently used as a hybrid capacitor.

  Next, a test was conducted focusing on the current density when the zinc electrode was produced by the electrodeposition method. The result is described next.

The test hybrid capacitor was prepared by the same method as in Example 6, ie, using a 7.3 M NaOH / 0.7 M ZnO aqueous solution, and a current density of 30 mA cm ⁻² , 10 minutes electrodeposition (test A comparison was made between the electrode A) and the case of 15 mA cm- ² , 20 minute electrodeposition (test electrode B). We also focused on the state of zinc deposition.

(A) Impedance characteristic test The result implemented by the applied voltage of +/- 5mV at 0.01-20kHz like the above is shown in FIG. The test electrode A (indicated by a circle) has a smaller resistance, and the test electrode B (indicated by a black circle) has a larger resistance.

(B) Voltage holding characteristic test A test electrode was used as a hybrid capacitor, charged at 1 mA cm ^-2 , charged to +1.4 V, paused, and a change in voltage with time was measured. The result is shown in FIG. In the voltage holding characteristic test, there is almost no difference between the test electrode A (solid line display) and the test electrode B (dotted line display), and the voltage holding characteristic is good.

(C) High-rate discharge test FIG. 38 shows the results of the test electrode, which was charged at a charge current of 1 mA cm ⁻² as a hybrid capacitor and then subjected to each discharge current. The capacitance at 1 mA cm ^-2 is almost the same for the test electrode A (● indication) and the test electrode B (○ indication), but at a large current, the test electrode B is static. The capacity is low. As for the high rate discharge performance, as shown in FIG. 39, the high rate discharge performance is lowered for the test electrode B (◯), but not so much for the test electrode A (●).

(D) Cycle characteristic test The results of repeated charge and discharge at 5 mA cm ^-2 are shown in FIG. The test electrode A (indicated by ●) has a relatively stable capacitance. It shows that the test electrode B (indicated by a circle) is gradually decreasing.

  Regarding the above test, when the behavior of the zinc electrode and the surface state of the electrode are observed, it can be seen that the test electrode A is irregular and dendrite is formed, and is generally rough and has a large surface area. . In contrast, the test electrode B is expected to have a uniform and dense crystal structure on the surface and a small surface area. This is supported by the former having a smaller impedance (interface resistance) than the latter (FIG. 36) and excellent high-rate discharge characteristics (FIG. 38.39). Therefore, it can be seen that the capacitor characteristics are better when the time is taken with a relatively small current density.

(Example 7)
Next, the characteristic test of the hydrogel containing NaOH aqueous solution is performed.
10 g of cross-linked sodium polyacrylate (PAANA) was added to 100 ml of 7.3 M NaOH / 0.7 M ZnO aqueous solution, stirred and aged at 30 ° C. for 3 days to prepare a PAANA gel. Next, electrodeposition was performed in a 7.3M NaOH / 0.7M ZnO aqueous solution using copper previously treated with hydrochloric acid as a substrate and nickel hydroxide as the counter electrode (current density 15 mA cm ⁻² , 10 minutes). Precipitated. Then, the precipitated zinc was immersed in PAANA Na gel (at a distance of 5 mm from the surface and the bottom), and the time until the zinc was dissolved was measured.

  As shown in FIG. 41, the results indicate that dissolution is suppressed for 40 hours or more in the PAANA Na gel (dotted line display), but about 25 hours in the aqueous solution (solid line display). This test shows that dissolution of zinc can be further suppressed by using a hydrogel electrolyte that has absorbed an aqueous NaOH solution.

(Example 8)
Using the cell, the conductivity of 7.3M NaOH / 0.7M ZnO aqueous solution and PAANA Na gel was measured. The measurement was performed by applying an applied voltage of ± 5 mV in the frequency range of 10 Hz to 10 kHz, and the conductivity was calculated by measuring the response impedance.
The cell constant was calculated from equation (10) using the specific electrical conductivity (0.012856 S / cm) of 0.1 M KCl.

κ = R ⁻¹ (l / A) (10)
However, l / A = 1.23

From the obtained cell constant, the conductivity of the 7.3M NaOH / 0.7M ZnO aqueous solution and the PAANA gel was determined using the formula (10).
(A) 7.3 M NaOH / 0.7 M ZnO aqueous solution: 0.27 S / cm
(B) PAANA Na gel: 0.19 S / cm
It was found that the conductivity of the 7.3M NaOH / 0.7M ZnO aqueous solution was considerably smaller than that of the 7.3M KOH / 0.7M ZnO aqueous solution. Similarly, the PAANA Na gel was found to have a lower conductivity than the PAAK gel.

  In this way, the hybrid capacitor can have a large pseudo capacitance with one of the electrodes accompanied by a charge transfer process, and can have a larger capacitance, energy density, and output density than EDLC, and can be used as a computer backup power source or other It can also contribute greatly to industry.

It is the schematic of the electrode preparation methods by this invention. It is a manufacturing method schematic of the zinc electrode by this invention. This is the corrosion behavior of the zinc electrode. It is a corrosion behavior of a zinc electrode in a polymer hydrogel electrolyte. It is preparation schematic of the zinc electrode which made the board | substrate different. It is a solubility curve figure with respect to the electrolyte solution of the zinc electrode which made the board | substrate different. It is a solubility curve figure with respect to the polymer hydrogel electrolyte of the zinc electrode which made the board | substrate different. It is an XPS analysis figure of the nickel substrate surface. It is a dissolution behavior of a zinc electrode for nickel substrate processing. It is a schematic diagram of a manufacturing method of an activated carbon electrode. FIG. 3 is a schematic diagram for producing an activated carbon electrode impregnated with a polymer hydrogel electrolyte. It is a measurement cell experimental apparatus. It is the schematic of the manufacturing method of the activated carbon electrode of another Example. It is the schematic of the zinc electrode preparation method of another Example. It is a hybrid capacitor charging / discharging characteristic curve figure. It is a hybrid capacitor high rate discharge characteristic curve figure. It is an electrostatic capacity curve figure of a hybrid capacitor. It is a hybrid capacitor high rate discharge rate (HRD) curve figure. It is a comparative Ragone plot figure of EDLC and HC. It is a leak current aging figure of a hybrid capacitor. It is a self-discharge curve diagram of ELDC in the case of using a polymer hydrogel electrolyte and an aqueous solution. It is a self-discharge curve figure of an ELDC electrode in the case of using a polymer hydrogel electrolyte and an aqueous solution. It is a cell voltage time-dependent change figure in a charging / discharging open circuit. It is a charge-discharge cycle characteristic figure of a hybrid capacitor. Nyquist plots for the HC cell. It is IR drop calculation resistance value curve figure of the hybrid capacitor in a high rate discharge curve. FIG. 3 is a cyclic voltammogram before and after 400 cycles at an activated carbon electrode of ELDC. It is a charging / discharging curve figure after 400 cycles of the activated carbon electrode in a hybrid capacitor. An impedance measurement result is shown. It is a graph which shows a leakage current measurement result. It is a Ragone plot figure of energy density. It is a voltage holding characteristic diagram. It is a charging / discharging characteristic curve figure. It is a plot figure which shows a high rate discharge test result. It is a charging / discharging cycle characteristic curve figure. An impedance measurement result is shown. It is a voltage holding characteristic curve diagram. A high rate discharge test result is shown. The high rate discharge ability test result is shown. The cycle characteristic test results are shown. The dissolution behavior of a zinc electrode is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Activated carbon fiber cloth 2 7.3M KOH / 0.7MZnO aqueous solution 3 Nickel (Ni) current collector 4 Copper (Cu) substrate 4a Copper (Cu) current collector 5 7.3M KOH / 0.7M ZnO aqueous solution 6 NiOOH / Ni (OH) ₂ electrode 7 Separator 8 Support

Claims (11)

  An electrochemical capacitor comprising an activated carbon cloth electrode as a positive electrode, a zinc electrode as a negative electrode, and an alkali hydroxide aqueous solution containing zinc oxide as an electrolyte.   The electrochemical capacitor according to claim 1, wherein the aqueous alkali hydroxide solution is contained and fixed in a polymer hydrogel electrolyte.   3. The electrochemical capacitor according to claim 1, wherein the amount of zinc oxide in the alkali hydroxide aqueous solution 7.3 M is in the range of 0.7 to 1.3 M. 4.   The electrochemical capacitor according to claim 1, wherein the zinc electrode is an electrode obtained by galvanizing a copper foil having a uniform surface treatment.   The electrochemical capacitor according to claim 4, wherein the copper foil is a flat plate.   6. The electrochemical capacitor according to claim 5, wherein the copper foil is etched.   The electrochemical capacitor according to claim 1, wherein the alkali hydroxide is sodium hydroxide.   2. The electrochemical capacitor according to claim 1, wherein the discharge capacity is positive electrode regulation. A copper foil whose surface is etched uses a 7.3M NaOH / 0.7M ZnO aqueous solution as an electrodeposition bath, a NiOOH / Ni (OH) ₂ electrode as a counter electrode, and a constant current density of 15 to 30 mA cm ⁻² . A method for producing an electrochemical capacitor zinc electrode, characterized by depositing zinc with an electric current. A copper foil whose surface is etched uses a 7.3M KOH / 0.7M ZnO aqueous solution as an electrodeposition bath, a NiOOH / Ni (OH) ₂ electrode as a counter electrode, and a constant current density of 15 to 30 mA cm ⁻² . A method for producing an electrochemical capacitor zinc electrode, characterized by depositing zinc with an electric current.   The method for producing an electrochemical capacitor zinc electrode according to claim 9 or 10, wherein ZnO in the above description is in a range of 0.7 to 1.3M.

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