JP2023098109A - Redox capacitor and redox capacitor system - Google Patents

Abstract

To provide a redox capacitor and a redox capacitor system that have high safety against impact from the outside and can be put into practical use.SOLUTION: A positive electrode side conductive substrate 12 and a negative electrode side conductive substrate 15 are arranged so as to face each other at an interval. A positive electrode material 11 and a negative electrode material 14 are provided correspondingly to the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15, respectively, contain active materials, and are arranged mutually at an interval between the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 so as to be in contact with the corresponding positive electrode side conductive substrate 12 and negative electrode side conductive substrate 15, respectively. An acid electrolyte 19 is provided so as to be in contact with the positive electrode material 11 and the negative electrode material 14 between the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15. The positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 have corrosion resistance against the electrolyte 19.SELECTED DRAWING: Figure 1

Description

The present invention relates to redox capacitors and redox capacitor systems.

As a conventional redox capacitor, an electrochemical capacitor using a quinone-based compound as an electrode is known. is a sulfuric acid aqueous solution (0.5MH ₂ SO ₄ aq.), which is an acidic aqueous electrolyte (see, for example, Patent Document 1 or Non-Patent Document 1).

This full-cell redox supercapacitor has an electrode mass of 10 mg or less, an electrode diameter of 7 mm, and an electrode thickness of 100 µm or less. It has been confirmed that it exhibits excellent rate performance and that the capacity does not decrease even after 10,000 cycles.

International publication WO2014/156511

T. Tomai, S. Mitani, D. Komatsu, Y. Kawaguchi, I. Honma, “Metal-free aqueous redox capacitor via proton rocking-chair system in an organic-based couple”, Sci Rep 2014, 4, 3591.

The full-cell redox supercapacitor described in Patent Document 1 and Non-Patent Document 1 uses an acid-resistant glass beaker as a cell container, which is very dangerous because it is easily broken by an external impact. However, there is a problem that it is difficult to put it into practical use as it is.

The present invention has been made in view of such problems, and an object of the present invention is to provide a redox capacitor and a redox capacitor system that are highly safe against external shocks and that can be put into practical use.

In order to achieve the above object, a redox capacitor according to the present invention includes a pair of conductive substrates arranged to face each other with a space therebetween; a pair of inner electrode materials spaced from each other and disposed between each conductive substrate so as to contact each corresponding conductive substrate; and an acidic electrolyte.

In the redox capacitor according to the present invention, since each inner electrode material and electrolyte are arranged between a pair of conductive substrates, safety against external impact can be improved, and practical use is possible. . The redox capacitor according to the present invention preferably has a diaphragm made of an ion exchange membrane between each inner electrode material. Further, in the redox capacitor according to the present invention, one inner electrode material is made of a positive electrode material, the inner electrode material and the corresponding conductive substrate are the positive electrode body, and the other inner electrode material is made of a negative electrode material. Preferably, the inner electrode material and the corresponding conductive substrate are the negative electrode body.

In the redox capacitor according to the present invention, each conductive substrate may be made of a metal or other material as long as it has conductivity. For example, when the electrolyte contains sulfuric acid, austenitic stainless steel It may be made of a sheet of a conductive material derived from nature such as graphite, a conductive polymer, or the like.

The redox capacitor according to the present invention is provided corresponding to each conductive substrate and each inner electrode material, and each conductive capacitor is spaced apart from each other so as to sandwich the corresponding inner electrode material between the corresponding conductive substrate and the corresponding inner electrode material. It is preferred to have a pair of mesh current collectors positioned between the substrates. In this case, the current collector can hold each inner electrode material in contact with each conductive substrate. Also, by sandwiching each inner electrode material between each conductive substrate and each current collector, a relatively high capacity can be obtained. In addition, although the current collector is made of a gold mesh plate in Patent Document 1 and Non-Patent Document 1, it is not limited to gold and may be made of any material. Each current collector may be conductive, but may not be conductive. For example, when the electrolyte contains sulfuric acid, each current collector may be made of austenitic stainless steel, a sheet of a naturally occurring conductive material such as graphite, a conductive polymer, or the like. In this case, each current collector is cheaper than that of gold, and the material cost can be reduced.

A redox capacitor according to the present invention includes a pair of outer electrodes provided corresponding to each conductive substrate, containing an active material, and disposed outside each conductive substrate so as to be in contact with the corresponding conductive substrate. and a cover member provided to cover at least the outside of each outer electrode material. In this case, the cover member covering the outside of each outer electrode material can enhance the safety against impact from the outside. Each outer electrode member may be held in contact with each conductive substrate by a cover member. Alternatively, between a corresponding conductive substrate and a cover member to sandwich the corresponding outer electrode material between the corresponding conductive substrate to hold each outer electrode material in contact with each conductive substrate. It may have a pair of mesh-like outer current collectors positioned at the same height.

In the redox capacitor according to the present invention, the active material preferably contains quinone or hydroquinone. For example, the positive electrode contains chloranil or tetrachlorohydroquinone (TCHQ), and the negative electrode contains anthraquinone (AQ) or dichloroanthraquinone. (DCAQ). Moreover, it is preferable that each inner electrode material and each outer electrode material contain activated carbon supporting the active material. Activated carbon may be of any kind, such as commercially available ones produced by gas activation or alkali activation, and may be, for example, woody activated carbon. Each inner electrode material and each outer electrode material may contain, in addition to activated carbon, a thickener such as sodium CMC (carboxymethylcellulose), a binder such as polytetrafluoroethylene (PTFE), and the like.

In the redox capacitor according to the present invention, each inner electrode material preferably has a thickness of 0.5 mm or more. In this case, a relatively high specific discharge capacity can be obtained. In addition, each inner electrode material can be thickened, which is practical. The thickness of each outer electrode material is also preferably 0.5 mm or more.

A redox capacitor system according to the present invention has a plurality of redox capacitors according to the present invention, and each redox capacitor is connected in series.
The redox capacitor system according to the present invention has a plurality of redox capacitors according to the present invention, is highly safe against external shocks, and is highly practical. Also, depending on the number of redox capacitors, the voltage can be increased according to the application.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a redox capacitor and a redox capacitor system that are highly safe against external impact and can be put into practical use.

BRIEF DESCRIPTION OF THE DRAWINGS It is (a) sectional drawing which shows the redox capacitor of embodiment of this invention, (b) The perspective view which decomposed|disassembled the component. FIG. 10 is an exploded perspective view of constituent elements excluding a cover member, showing a modification of the redox capacitor of the embodiment of the present invention; BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective view which shows the redox capacitor system of embodiment of this invention. FIG. 4 is a graph showing the results of a discharge test at a 1 C rate of a half-cell battery using an electrode body having an electrode material supporting TCHQ of the redox capacitor of the embodiment of the invention. FIG. In the redox capacitor of the embodiment of the present invention, (a) a half-cell battery using an electrode body containing an electrode material supporting DCAQ and an electrode body whose current collector is a gold mesh , a graph showing charge-discharge test results at 1C rate, (b) a graph showing charge-discharge test results at 1C rate and C / 2 rate of a half-cell battery using an electrode body containing an electrode material supporting DCAQ. be. (a) TCHQ-supported electrode material and (b) DCAQ-supported electrode material of the redox capacitor of the embodiment of the present invention were mixed with electrolytic solutions (0.5MH ₂ SO ₄ aqueous solution) of pH = 0, 3, 4. It is a cyclic voltagram showing the measurement results of cyclic voltammetry when immersed in. A graph showing the results of a charge-discharge test using a full-cell battery of the redox capacitor of the embodiment of the present invention when the thickness of each electrode material is (a) 0.5 mm, (b) 1.0 mm, and (c) 1.5 mm. (d) Graph showing the rate performance at the thickness of each electrode material, (e) charge and discharge profile at the 2nd cycle and 100th cycle when the thickness of each electrode material is 1.0 mm and 1C rate, (f) each 4 is a graph showing the capacity retention rate from 1 to 100 cycles when the thickness of the electrode material is 1.0 mm and the rate is 1C. Graph showing changes in capacity retention with respect to the C rate, with reference to the capacity at the 1 C rate, when the thickness of each electrode material is 0.5 mm, 1.0 mm, and 1.5 mm in the redox capacitor of the embodiment of the present invention. is. For the redox capacitor system of the embodiment of the present invention, (a) a graph showing a charge/discharge test, and (inset) a graph showing changes in capacity retention with respect to the C rate, based on the capacity at the 1 C rate ( b) Charge/discharge profile at 2nd and 100th cycles at 1C rate, (c) Graph showing capacity retention from 1st to 100th cycles at 1C rate with a thickness of 1.0 mm for each electrode material , (d) is a graph showing changes in open-circuit voltage for 7 days after full charge.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described based on drawings, examples, and the like.
1 to 9 show redox capacitors and redox capacitor systems according to embodiments of the present invention.
As shown in FIG. 1, the redox capacitor 10 includes a positive electrode material 11, a positive conductive substrate 12, a positive current collector 13, a negative electrode material 14, a negative conductive substrate 15, a negative current collector 16, and a diaphragm 17. , gasket 18 and electrolyte 19 . The positive electrode material 11 , the positive conductive substrate 12 , and the positive current collector 13 constitute the positive electrode body 21 , and the negative electrode material 14 , the negative conductive substrate 15 , and the negative current collector 16 . constitutes the electrode body 22 on the negative electrode side.

The positive electrode material 11 is an electrode material, formed into a thin plate, and contains activated carbon carrying a positive electrode active material impregnated with quinone or hydroquinone. The positive electrode active material contained in the positive electrode material 11 consists of chloranil and tetrachlorohydroquinone (TCHQ), for example. The positive electrode-side conductive substrate 12 is conductive and has a plate shape, and is arranged so that one surface thereof is in contact with one surface of the positive electrode material 11 . The positive electrode-side current collector 13 has a mesh plate shape, and is arranged such that one surface is in contact with the other surface of the positive electrode material 11 so as to sandwich the positive electrode material 11 between itself and the positive electrode-side conductive substrate 12 . . The positive electrode-side current collector 13 is provided so as to cover the side surface of the positive electrode material 11 and contact the positive electrode-side conductive substrate 12 around the positive electrode material 11 .

The negative electrode material 14 is an electrode material, formed into a thin plate, and contains activated carbon carrying a negative electrode active material impregnated with quinone or hydroquinone. The negative electrode active material contained in the negative electrode material 14 consists of dichloroanthraquinone (DCAQ), for example. The negative electrode side conductive substrate 15 is conductive and has a plate shape, and is arranged so that one surface thereof is in contact with one surface of the negative electrode material 14 . The negative electrode-side current collector 16 has a mesh plate shape, and is arranged so that one surface thereof is in contact with the other surface of the negative electrode material 14 so as to sandwich the negative electrode material 14 between itself and the negative electrode-side conductive substrate 15 . . The negative electrode-side current collector 16 also covers the side surface of the negative electrode material 14 and is provided so as to be in contact with the negative electrode-side conductive substrate 15 around the negative electrode material 14 . In addition, the positive electrode material 11 and the negative electrode material 14 constitute inner electrode materials.

As shown in FIG. 1A, the redox capacitor 10 faces the positive electrode side current collector 13 and the negative electrode side current collector 16 with the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 facing outward. A space is provided between the positive electrode side current collector 13 and the negative electrode side current collector 16 in a combined state.

As shown in FIG. 1 , the diaphragm 17 is made of an ion-exchange membrane and arranged between the positive electrode current collector 13 and the negative electrode current collector 16 . The diaphragm 17 is made of, for example, ethylene resin, polypropylene, or Japanese paper. The gasket 18 surrounds the sides of the positive electrode material 11 , the negative electrode material 14 , the positive electrode current collector 13 , the negative electrode current collector 16 , and the diaphragm 17 so that the positive electrode conductive substrate 12 and the negative electrode conductive substrate 15 are separated. It is provided to block the gap between The gasket 18 is made of silicone rubber, for example.

As shown in FIG. 1(a), the redox capacitor 10 has a sealed storage chamber 20 inside the positive electrode side conductive substrate 12, the negative electrode side conductive substrate 15, and the gasket 18, and the storage chamber 20 is sealed. The positive electrode material 11, the negative electrode material 14, the positive electrode side current collector 13, the negative electrode side current collector 16, and the diaphragm 17 are accommodated in the chamber. The electrolyte 19 is an acidic liquid containing sulfuric acid, and is filled in the storage chamber 20 . Thereby, the electrolyte 19 is provided between the positive electrode material 11 and the negative electrode material 14 .

The positive electrode-side conductive substrate 12 , the positive electrode-side current collector 13 , the negative electrode-side conductive substrate 15 , and the negative electrode-side current collector 16 have corrosion resistance to the electrolyte 19 . The positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 may be made of any material as long as it has conductivity and corrosion resistance to the electrolyte 19 . Moreover, the positive electrode current collector 13 and the negative electrode current collector 16 may be made of any material as long as it has corrosion resistance to the electrolyte 19 . The positive electrode-side conductive substrate 12, the positive electrode-side current collector 13, the negative electrode-side conductive substrate 15, and the negative electrode-side current collector 16 are made of, for example, austenitic stainless steel, naturally-derived conductive material sheets such as graphite, or conductive polymers. etc.

Next, the action will be described.
In the redox capacitor 10, each of the electrode bodies 21 and 22 is provided with a positive electrode current collector 13 and a negative electrode current collector 16 facing each other. A positive electrode-side conductive substrate 12 and a negative electrode-side conductive substrate 15 are arranged outside so as to sandwich and cover the current collector 13 , the negative electrode-side current collector 16 , the diaphragm 17 , and the electrolyte 19 . Therefore, it is highly safe against impact from the outside and is practical. In addition, in the redox capacitor 10, the positive electrode material 11 and the negative electrode material 14 are separated between the positive electrode side conductive substrate 12 and the positive electrode side current collector 13 and between the negative electrode side conductive substrate 15 and the negative electrode side current collector 16, respectively. Since it is sandwiched between them, a relatively high capacity can be obtained.

In addition, as shown in FIG. 2, the redox capacitor 10 is arranged on the outer surface of the positive electrode side conductive substrate 12, that is, the surface opposite to the positive electrode material 11 so as to be in contact with the positive electrode side conductive substrate 12. an outer positive electrode material 11a, an outer negative electrode material 14a disposed on the outer surface of the negative conductive substrate 15, i.e., the surface opposite to the negative electrode material 14, in contact with the negative conductive substrate 15; A cover member (not shown) provided to cover the outside of the positive electrode material 11a and the outer negative electrode material 14a may be provided. In this case as well, the cover member provides high safety against impact from the outside and is practical. The outer positive electrode material 11 a is preferably made of the same electrode material as the positive electrode material 11 , and the outer negative electrode material 14 a is preferably made of the same electrode material as the negative electrode material 14 . Further, the outer positive electrode material 11a and the outer negative electrode material 14a constitute the outer electrode material.

[Production of redox capacitor 10]
A redox capacitor 10 shown in FIG. 1 was produced. Tetrachlorohydroquinone (TCHQ) was used as the positive electrode active material, dichloroanthraquinone (DCAQ: manufactured by Tokyo Chemical Industry Co., Ltd.) as the negative electrode active material, and Maxsorb (registered trademark: manufactured by Kansai Coke and Chemicals Co., Ltd.) as the activated carbon. Since chloranil is more stable in air and cheaper than TCHQ, chloranil (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was used as the positive electrode active material before making the full-cell battery. , converted chloranil to TCHQ.

First, 3 g of chloranil was dissolved in 3 L of acetone and sonicated for 1 hour. 7 g of activated charcoal was added to the solution after sonication, and sonication was further performed for 1 hour to disperse the activated charcoal in the solution. After that, the solution was kept at 80° C. and stirred to evaporate the acetone and impregnate the nanopores of the activated carbon with chloranil. The powder thus obtained and a polytetrafluoroethylene (PTFE) binder were mixed at a weight ratio of 9:1 and molded into pellets. At this time, no conductive additive was used. Thus, a pellet-shaped positive electrode material 11 supporting chloranil was produced. Similarly, 3 g of DCAQ was used instead of 3 g of chloranil to prepare pellet-like negative electrode material 14 supporting DCAQ.

Next, pellet-shaped positive electrode material 11 and negative electrode material 14 are applied to positive electrode side current collector 13 and negative electrode side current collector 16 made of SUS316 mesh (7 cm × 7 cm, 100 mesh, Φ0.05 mm). , respectively, were crimped. At this time, the positive electrode material 11 and the negative electrode material 14 each have a surface area of 15-20 cm ² , a thickness of 0.5-1.5 mm, and a weight of 1 g. After that, the positive electrode material 11 carrying chloranil was placed between the positive electrode current collector 13 and the positive electrode conductive substrate 12, and the negative electrode carrying DCAQ was placed between the negative electrode current collector 16 and the negative electrode conductive substrate 15. A positive electrode-side current collector 13 and a negative electrode-side current collector 13 are attached to a positive electrode-side conductive substrate 12 and a negative electrode-side conductive substrate 15 each made of a SUS316 plate (10 cm × 10 cm, thickness 0.1 mm) so as to sandwich the material 14 . The electric body 16 was spot-welded to produce an electrode body 21 on the positive electrode side and an electrode body 22 on the negative electrode side. Each of the electrode bodies 21 and 22 was immersed in an electrolytic solution (0.5 MH ₂ SO ₄ aqueous solution) and vacuumed for 1 hour to remove gas accumulated in the pores of the positive electrode material 11 and the negative electrode material 14 .

Next, the electrode body 21 having the positive electrode material 11 supporting chloranil was charged and discharged at a rate of 1.3 C in a half-cell battery to convert chloranil to TCHQ. At this time, Ag/AgCl (3M NaCl aq.) was used as the reference electrode, and an excessive amount of activated carbon electrode (activated carbon: Ketjenblack: PTFE = 7:2:1) was used as the counter electrode. , a potentiostat (manufactured by Solartron Analytical) and a power supply (“PWR801L” manufactured by Kikusui Electronics Co., Ltd.) were used. Thus, a positive electrode body 21 having the positive electrode material 11 supporting TCHQ and a negative electrode body 22 including the negative electrode material 14 supporting DCAQ were produced. The positive electrode body 21 and the negative electrode body 22 have the same weight.

A polypropylene separator having a thickness of 0.2 mm was used as the diaphragm 17 . The gasket 18 was made of silicon rubber having a thickness of 5 mm and was formed into a frame shape of 10 cm×10 cm on the outside and 8 cm×8 cm on the inside with a cutter. This gasket 18 was adhered to the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 made of SUS316 with liquid RTV silicon. A 0.5M H ₂ SO ₄ aqueous electrolytic solution (hereinafter, unless otherwise specified, pH=0) was used as the electrolyte 19 , and the storage chamber 20 was filled with the electrolyte 19 . Thus, the single-cell redox capacitor 10 shown in FIG. 1 was produced. The size of the single cell is 10 cm long, 10 cm wide, and 0.52 cm thick.

[Production of redox capacitor system 30]
Next, 12 single-cell redox capacitors 10 were prepared, and the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 of adjacent single cells were arranged along the thickness direction of each single cell so that they faced each other. lined up in a row. By electrically connecting the positive electrode side conductive substrate 12 and the negative electrode side conductive substrate 15 of adjacent single cells with a coated copper wire, a redox capacitor system 30 composed of a plurality of cells shown in FIG. 3 was produced. The fabricated redox capacitor system 30 uses positive electrode material 11 and negative electrode material 14 with a thickness of 1.0 mm.

[Electrochemical measurement using a half-cell battery]
First, using the positive electrode body 21 having a TCHQ with a thickness of 0.5 mm, a constant current discharge test was performed with a half-cell battery. A potentiostat (manufactured by Solartron Analytical) was used for the test. FIG. 4 shows the discharge test results at a 1C rate.

As shown in FIG. 4, the total capacity (Specific Capacity) is 181.3 mAh g ^-1 and the electric double layer (EDL) capacity is 20.4 mAh g ^-1 . The reduction capacity was confirmed to be 160.9 mAh g ⁻¹ . Further, since the theoretical oxidation-reduction capacity of chloranil is 217.9 mAh g ⁻¹ , the utilization rate of the electrode body 21 on the positive electrode side used in the test is 73.8%. Although the positive electrode body 21 used in the test has a mass load that is at least five times as large as that of the electrode at the basic research stage shown in Non-Patent Document 1, The utilization rate of the electrode was about the same as 75-86%.

Next, a charging/discharging test was performed with a half-cell battery using the negative electrode body 22 having DCAQ with a thickness of 0.5 mm. In addition, for comparison, a charging/discharging test was performed in the same manner on a case where the current collector of the electrode body 22 on the negative electrode side was made of a gold mesh. A potentiostat (manufactured by Solartron Analytical) was used for the test. Fig. 5(a) shows the charge/discharge test results at a 1C rate when the current collector is made of SUS316 and gold. FIG. 5(b) shows the charging/discharging test results (current collector made of SUS316) at 1C rate and C/2 rate.

As shown in FIG. 5(a), it was confirmed that the current collector made of SUS316 had almost the same charge/discharge curve as compared to the gold current collector, with no decrease in capacity. rice field. Also, in the detailed part, it was confirmed that the discharge curve made of SUS316 has a larger overvoltage in the plateau part by about 20 mV compared to the gold one, and the curve is slightly gentler in the slope part. This is probably due to the difference in electrical conductivity between gold and SUS316. In this way, since there is only a slight difference between SUS316 and gold, it is more cost effective to use a current collector made of SUS316 than to use an expensive gold current collector. It is considered to be advantageous in

[Cyclic voltammetry]
The positive electrode material 11 supporting TCHQ with a thickness of 0.5 mm and the negative electrode material 14 supporting DCAQ with a thickness of 0.5 mm were immersed in electrolyte solutions (0.5 MH ₂ SO ₄ aqueous solution) of pH = 0, 3, and 4, respectively. and cyclic voltammetry was performed. The scan rate in cyclic voltammetry was set to 10 mV/s. The cyclic voltagram of the positive electrode material 11 supporting TCHQ is shown in FIG. 6(a), and the cyclic voltagram of the negative electrode material 12 supporting DCAQ is shown in FIG. 6(b).

As shown in FIGS. 6( a ) and 6 ( b ), both positive electrode material 11 and negative electrode material 14 showed sharp peaks at pH=0, and no peaks were observed at pH=3 and 4. FIG. From this result, it can be said that the redox capacitor 10 operates only in a strong acid state.

[Electrochemical measurement by single-cell redox capacitor 10]
Using the single-cell redox capacitor 10 shown in FIG. 1, a charge-discharge test was performed with a full-cell battery. In the test, a potentiostat (manufactured by Solartron Analytical) was used, the voltage range was -0.2 V to 1.2 V, and the charge/discharge rate was 1C rate, 2C rate, 4C rate, and 8C rate. 7(a) to 7(c) show the charge/discharge test results when the thicknesses of the positive electrode material 11 supporting TCHQ and the negative electrode material 14 supporting DCAQ were set to 0.5 mm, 1.0 mm, and 1.5 mm, respectively. show. In addition, the rate performance at the thickness of each electrode material (positive electrode material 11 and negative electrode material 14) is shown in FIG. 7(d). FIG. 7(e) shows the charge/discharge profile of the electrode material, and FIG. 7(f) shows the capacity retention rate from 1 to 100 cycles when the thickness of each electrode material is 1.0 mm and the rate is 1C. Note that the C rate is calculated based on the theoretical capacity of the positive electrode material 11 supporting TCHQ.

As shown in FIGS. 7(a)-(c), the specific discharge capacity is 216 mAh g ⁻¹ at a 1 C rate for each electrode material with a thickness of 0.5 mm, whereas the 1.0 mm and 1.5 mm thickness electrodes For the material, they were 166 mAh g ^-1 and 140 mAh g ^-1 , respectively, and a decreasing trend was confirmed as the mass load increased. Also, the average discharge voltage was confirmed to be 0.387V. From the results of FIGS. 7A to 7C, the capacity retention ratios of the electrodes at 2C rate, 4C rate, and 8C rate were determined based on the capacity at 1C rate, and are shown in FIG.

As shown in FIG. 8, at the 2C rate, approximately 75% of the capacitance is retained for the 0.5 mm and 1.0 mm thick electrode materials, whereas 44% for the 1.5 mm thick electrode material. It was confirmed that only the Furthermore, when the charge/discharge rate is 4C, the capacities of 44%, 36%, and 14% are maintained for each electrode material of 0.5 mm, 1.0 mm, and 1.5 mm, respectively, and at 8C, 16% and 8.5%. , it was confirmed that the capacity of 4.3% was maintained. From this result, it can be said that the rate performance is lowered by increasing the thickness of each electrode material. This is probably because proton diffusion slows down in the thick electrode materials, and oxidation-reduction reaction with quinone does not proceed.

From this charge/discharge test result, when the energy density of a single cell with each electrode material having a thickness of 0.5 mm is obtained, it is 10.9 Wh kg ⁻¹ for all electrodes at a 1 C rate. The energy density at 12.5 Wh kg ⁻¹ was 87.2%. In this way, the energy density is sufficiently high, comparable to that of the basic research stage, so the practical redox capacitor 10 using thick electrodes shown in FIG. 1 can be sufficiently used even at a 1C rate. It can be said. The slight drop in energy density is considered to be mainly due to a drop in the utilization rate of the organic active material. In addition, TCHQ on the positive electrode side has a larger theoretical capacity than DCAQ on the negative electrode side, so if the weight of the electrodes is the same, the entire capacity cannot be used, which is also one of the causes of the decrease in energy density. It is believed that there is. The energy density is calculated based on the total mass of both electrodes.

Moreover, as shown in FIG. 7(e), it was confirmed that there was almost no difference between the charge/discharge profile at the 1C rate at the 2nd cycle and the charge/discharge profile at the 100th cycle. From this, it is considered that the capacity does not decrease even after 100 cycles. Moreover, as shown in FIG. 7(f), it was confirmed that 101.1% of the capacity was retained even after 100 cycles at the 1C rate. Considering that even the basic research stage shown in Non-Patent Document 1 does not show a decrease in capacity, it can be said that even the redox capacitor 10 scaled up to a practical size maintains excellent cycle performance. .

[Electrochemical measurement by multi-cell redox capacitor system 30]
A charge/discharge test was performed using a multi-cell redox capacitor system 30 (thickness of each electrode material: 1.0 mm) shown in FIG. In the test, a potentiostat (manufactured by Solartron Analytical) was used, the voltage range was -0.2 V to 12.0 V, and the charge/discharge rate was 1C rate, 2C rate, 4C rate, and 8C rate. The charge/discharge test results are shown in FIG. 9(a), the charge/discharge profiles at the 2nd cycle and the 100th cycle at the 1C rate are shown in FIG. 9(b), and the capacity from 1 to 100 cycles at the 1C rate Fig. 9(c) shows the retention rate, and Fig. 9(d) shows the transition of the open-circuit voltage for 7 days after full charge.

As shown in FIG. 9(a), the specific discharge capacity was 142 mAh g ⁻¹ at 1C rate, which was confirmed to be 86% of the single cell capacity shown in FIG. 7(b). Also, the average discharge voltage was 4.39 V, which was confirmed to be 12 times the average discharge voltage (0.387 V) of the single cell. From this result, the capacity retention rate of the electrode at 2C rate, 4C rate, and 8C rate was determined based on the capacity at 1C rate, and is shown in the insert of FIG. 9(a). This inset also shows the volume retention ratio of the single cell (1.0 mm thick electrode material) shown in FIG. As shown in the inset, the capacity retention rate was 62.6% for the 2C rate, 20.3% for the 4C rate, and 8.5% for the 8C rate, which were confirmed to be slightly lower than those of the single cell.

Also, from the charge/discharge test results, the energy density at a 1C rate was found to be 7.1 Wh kg ⁻¹ , which was confirmed to be lower than the energy density of a single cell. When single cells are connected in series, the overall capacity is determined by the single cell with the lowest capacity among all the connected single cells. Furthermore, if the voltage of each single cell is different, it will not be possible to charge and discharge all the single cells completely. Must. From these facts, the slightly lower capacity and inferior rate performance of the high-voltage cells compared to the single cells is due to the slightly different capacities and voltages of the 12 single cells connected in series. it is conceivable that.

As shown in FIG. 9(b), it was confirmed that the plateau capacity was lower in the charge/discharge profile at the 100th cycle than in the charge/discharge profile at the 1C rate at the 2nd cycle. Moreover, as shown in FIG. 9(c), it was confirmed that the capacity retention rate after 100 cycles was 85%. These results are different from the results of single cells with excellent cycle characteristics shown in FIGS. 7(e) and (f). The reason for this is considered as follows. That is, in the redox capacitor system 30 in which 12 single cells are connected in series, a slight voltage difference between the single cells causes overcharge or overdischarge of some of the single cells, causing the electrolyte 19 to become electrochemically Gas is generated in each of the electrode bodies 21 and 22 by decomposition. The portion of each electrode material that is in contact with the generated gas becomes electrochemically inactive, and the oxidation-reduction reaction of quinones cannot occur. Therefore, it is considered that the cycle characteristics are deteriorated.

As shown in FIG. 9(d), the open circuit voltage after 7 days was 6.6 V, which was confirmed to be higher than the discharge plateau voltage. This is probably because the voltage drop is caused only by the breakdown of the electric double layer (EDL), and most quinones are stable in the charged state and do not deteriorate even after 7 days.

A test was conducted in which the redox capacitor system 30 was used to charge a smartphone via a current regulator. In the test, when three light bulbs of red, green, and blue were connected in series with the smartphone, it was confirmed that the smartphone was charged and each light bulb lit up.

REFERENCE SIGNS LIST 10 redox capacitor 11 positive electrode material 12 positive electrode side conductive substrate 13 positive electrode side current collector 14 negative electrode material 15 negative electrode side conductive substrate 16 negative electrode side current collector 17 diaphragm 18 gasket 19 electrolyte 20 storage chamber 21 (positive electrode side) electrode body 22 Electrode body (on the negative electrode side)

11a Outer positive electrode material 14a Outer negative electrode material

30 redox capacitor system

Claims (8)

a pair of conductive substrates arranged to face each other with a space therebetween;
a pair of inner electrode materials corresponding to each conductive substrate and containing an active material and spaced between each conductive substrate so as to contact each corresponding conductive substrate;
and an acidic electrolyte provided between each conductive substrate and in contact with each inner electrode material. 1 provided corresponding to each conductive substrate and each inner electrode material, and disposed between each conductive substrate with a space therebetween so as to sandwich the corresponding inner electrode material between the corresponding conductive substrate and the conductive substrate; 2. The redox capacitor according to claim 1, comprising a pair of mesh-like current collectors. a pair of outer electrode materials corresponding to each conductive substrate and containing an active material and disposed outside each conductive substrate so as to be in contact with the respective conductive substrate;
a cover member provided to cover at least the outside of each outer electrode material,
3. The redox capacitor according to claim 1, comprising: 4. The redox capacitor according to any one of claims 1 to 3, further comprising a diaphragm made of an ion exchange membrane between each inner electrode material. the electrolyte comprises sulfuric acid;
The redox capacitor according to any one of claims 1 to 4, wherein the conductive substrate is made of austenitic stainless steel. the active material comprises quinone or hydroquinone;
The redox capacitor according to any one of claims 1 to 5, wherein each inner electrode material contains activated carbon supporting the active material. 7. The redox capacitor according to any one of claims 1 to 6, wherein each inner electrode material has a thickness of 0.5 mm or more. A redox capacitor system comprising a plurality of redox capacitors according to any one of claims 1 to 7, wherein each redox capacitor is connected in series.

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