Carbon-air secondary battery

Abstract

Provided is a carbon-air secondary battery that can secure a large amount of stored electricity, has high charge / discharge efficiency, and has excellent cycle characteristics. The secondary battery 1 has a reactor 20 in which an anode 21 is installed and which is separated from the outside by an electrolyte 23, and which stores carbon deposited during charging, and a structure 60 which surrounds the reactor 20 and suppresses heat loss due to radiative heat transfer from the reactor 20. During charging, carbon dioxide is electrolyzed on the surface of the anode 21, and carbon is deposited on the anode side, which is a closed system, and oxygen is generated at the cathode 22 from oxide ions which are generated at the anode 21 and which have permeated the electrolyte 23. During discharging, oxide ions are generated from oxygen at the cathode 22, and carbon and / or carbon monoxide are electrochemically oxidized on the surface of the anode 21 to generate carbon dioxide.

Description

[Technical field]

[0001] The present invention relates to a secondary battery, and more particularly to a secondary battery (carbon-air secondary battery) that utilizes a combination of electrochemical and thermochemical reactions of carbon. [Background technology]

[0002] Solid oxide fuel cells (SOFCs), which have a laminated structure in which an electrolyte layer (solid electrolyte layer) made of ion-conducting solid oxide (oxide ion conductor) is placed between a positive electrode (air electrode) and a negative electrode (fuel electrode), are expected to be the third-generation fuel cells, and their development is currently underway.

[0003] Solid oxide batteries use oxide ions (O 2- In this battery, an ionically conductive solid oxide having high permeability to electrolytes is used, and oxide ions generated at the positive electrode permeate the electrolyte and react with reducing agents such as hydrogen (H2), carbon monoxide (CO), and methane (CH4) at the negative electrode to generate electrical energy (for example, Patent Document 1).

[0004] In addition, a direct carbon fuel cell (DCFC) that uses solid carbon as a reducing agent (solid fuel) has been proposed. In particular, the present inventors have proposed a rechargeable direct carbon fuel cell (RDCFC) that utilizes thermal decomposition of hydrocarbons and the like to repeatedly supply solid carbon to the negative electrode of the DCFC (Patent Documents 2-3, Non-Patent Documents 1-3).

[0005] DCFCs and RDCFCs generate carbon dioxide (CO2) when carbon is oxidized at the negative electrode during discharge, but further improvements are required to realize a CO2 emission-free society.

[0006] The present inventors have proposed a carbon / air secondary battery (CASB) as a secondary battery (storage battery) that can repeatedly utilize carbon dioxide generated by discharge (Patent Document 4, Non-Patent Document 4).

[0007] A carbon-air secondary battery is a secondary battery that utilizes a combination of electrochemical and thermochemical reactions of carbon. In carbon-air secondary batteries, the negative electrode side is a closed system, and carbon dioxide can be stored inside the closed system. In carbon-air secondary batteries, when the battery is charged, carbon dioxide is converted into carbon through an electrochemical reaction at the negative electrode and a thermochemical reaction in the closed system, and carbon precipitates in the closed system. When the battery is discharged, this carbon is used as fuel, converted into carbon dioxide, and stored in the closed system. Therefore, carbon-air secondary batteries are CO2 emission-free.

[0008] In addition, the theoretical volumetric energy density of a carbon-air secondary battery is large, at 1625 Wh / L when storing carbon dioxide at 25°C and 6.4 MPa, and it is described that carbon-air secondary batteries can be used as stationary, large-capacity electricity storage systems.

[0009] For the practical application of carbon-air secondary batteries, it is necessary to secure as much stored electricity as possible in as compact a facility as possible. It is also important that there is no energy loss during charging and discharging (high charging and discharging efficiency). Furthermore, in terms of facility life and maintenance effort, a long cycle life is also important. From the above viewpoints and the like, further improvements are required in carbon-air secondary batteries. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 9-129256 [Patent Document 2] Patent No. 5226290 [Patent Document 3] Patent No. 5284596 [Patent Document 4] Patent No. 7182251 [Non-patent literature]

[0011] [Non-Patent Document 1] M. Ihara, K. Matsuda, H. Sato and C. Yokoyama, Solid State Ionics, 175, (2004), 51-54 [Non-Patent Document 2] M. Ihara and S. Hasegawa, J. Electrochem. Soc., 153 (8), (2006), A1544-A1546 [Non-Patent Document 3] S. Hasegawa and M. Ihara, J. Electrochem. Soc., 155 (1), (2008), B58-B63 [Non-Patent Document 4] K. Kameda, S. Manzhos and M. Ihara, J. Power Sources, 516, (2021), 230681 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above-mentioned background art, and an object of the present invention is to provide a carbon-air secondary battery that can secure a large amount of stored electricity, has high charge / discharge efficiency, and has good cycle characteristics. [Means for solving the problem]

[0013] As a result of intensive research to solve the above problems, the inventors have found that in order to efficiently use the carbon stored in the closed system (negative electrode side) of a carbon-air secondary battery, the temperature inside the cell must be raised during discharge, resulting in large energy loss, and that since the entropy loss (TΔS), which is theoretically a factor in reducing the charge / discharge efficiency, is almost zero in the charge / discharge reaction of a carbon-air secondary battery, the introduction of a highly insulating structure is likely to directly lead to an improvement in charge / discharge efficiency, and that even if the interval between charge / discharge is long, it is possible to suppress the efficiency decrease and to immediately discharge / charge. The inventors have found that by surrounding the cell of a carbon-air secondary battery with a specific structure, it is possible to reduce energy loss and obtain a secondary battery with high charge / discharge efficiency, and have completed the present invention.

[0014] That is, the present invention provides a cell including a negative electrode, a positive electrode, and an electrolyte made of a gas-impermeable and ion-conductive solid oxide disposed in contact with the negative electrode and the positive electrode, During charging, carbon dioxide is electrolyzed on the surface of the negative electrode, carbon is precipitated on the negative electrode side, which is a closed system, and oxygen is generated at the positive electrode from oxide ions that are generated at the negative electrode and permeate the electrolyte. a secondary battery in which, during discharge, oxide ions are generated from oxygen at the positive electrode, and carbon and / or carbon monoxide are electrochemically oxidized at a surface of the negative electrode to generate carbon dioxide, A reactor in which the negative electrode is installed and separated from the outside by the electrolyte, and in which carbon precipitated during charging is stored; and The present invention provides a secondary battery having a structure surrounding the reactor and suppressing heat loss due to radiative heat transfer from the reactor. Effect of the Invention

[0015] According to the present invention, it is possible to provide a carbon-air secondary battery that can secure a large amount of stored electricity, has high charge / discharge efficiency, and has good cycle characteristics. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing reactions in the secondary battery of the present invention (a) during charging and (b) during discharging. [Diagram 2] FIG. 1 is a conceptual diagram of a cell, a reactor, etc. in a secondary battery of the present invention. [Diagram 3] FIG. 2 is a conceptual diagram of a cell, a reactor, etc. in the secondary battery of the present invention (when the closed system has a tank). [Figure 4] FIG. 2 is a conceptual diagram of a cell, a reactor, etc. in a secondary battery of the present invention (when a closed system has a tank, and the reactor and the tank are connected via a reservoir 70). [Diagram 5] 1 is a graph showing the temperature and pressure dependences at equilibrium in the Boudouard reaction. [Figure 6] FIG. 2 is a conceptual diagram of a reactor in the secondary battery of the present invention, which is composed of an electrochemical reaction section and a thermochemical reaction section. [Figure 7] FIG. 2 is a conceptual diagram of a reactor etc. in a secondary battery of the present invention, in which gas is continuously circulated between an electrochemical reaction section and a thermochemical reaction section (during charging). [Figure 8] FIG. 2 is a conceptual diagram of a reactor etc. in a secondary battery of the present invention, in which gas is continuously circulated between an electrochemical reaction section and a thermochemical reaction section (during discharging). [Figure 9] FIG. 2 is a flow diagram in the secondary battery of the present invention (during charging), in which gas is continuously circulated between the electrochemical reaction section and the thermochemical reaction section and which is provided with a gas flow direction control means. [Figure 10] FIG. 2 is a flow diagram in the secondary battery of the present invention (during discharging) in which gas is continuously circulated between the electrochemical reaction section and the thermochemical reaction section and which is provided with a gas flow direction control means. [Figure 11] FIG. 2 is a flow diagram in the secondary battery of the present invention equipped with means for adjusting the temperature and pressure (during charging). [Figure 12] FIG. 1 is a flow diagram in a secondary battery of the present invention equipped with a means for adjusting temperature and pressure (when utilizing gas-liquid equilibrium in a tank during charging). [Figure 13] FIG. 2 is a flow diagram in the secondary battery of the present invention equipped with means for adjusting the temperature and pressure (during discharging). [Figure 14] FIG. 2 shows a flow diagram in a secondary battery of the present invention equipped with a combustor (during discharging). [Figure 15] FIG. 2 shows a flow diagram in a secondary battery of the present invention equipped with a gas ratio adjustment cell (during discharging). [Figure 16] FIG. 2 is a flow diagram of the secondary battery of the present invention, in which the reactor comprises an electrochemical reaction section and a thermochemical reaction section (when charging and without a reservoir). [Figure 17] FIG. 2 is a flow diagram of the secondary battery of the present invention, in which the reactor comprises an electrochemical reaction section and a thermochemical reaction section (when a reservoir is provided during charging). [Figure 18] FIG. 2 is a flow diagram of the secondary battery of the present invention, in which the reactor is composed of an electrochemical reaction section and a thermochemical reaction section (when gas-liquid equilibrium in the tank is utilized during charging). [Figure 19] FIG. 2 is a flow diagram of the secondary battery of the present invention, in which the reactor comprises an electrochemical reaction section and a thermochemical reaction section (during discharging). [Figure 20] FIG. 2 is a flow diagram in the secondary battery of the present invention, in which the reactor is composed of an electrochemical reaction section and a thermochemical reaction section and is equipped with a combustor (during discharging). [Figure 21] FIG. 2 is a conceptual diagram of a reactor in a secondary battery of the present invention in which the cell has multiple negative electrodes. [Figure 22] FIG. 1 is a conceptual diagram of a secondary battery of the present invention. [Diagram 23] FIG. 1 is a conceptual diagram of a secondary battery of the present invention (wherein the closed system has a tank, and the reactor and the tank are connected via a reservoir 70). [Figure 24] FIG. 1 is a perspective view of a cell, a reactor, etc., of a secondary battery according to embodiment 1 of the present invention. [Diagram 25] FIG. 1 is a cross-sectional view of a cell, a reactor, etc. of a secondary battery according to embodiment 1 of the present invention. [Figure 26] FIG. 2 is a cross-sectional view showing the position of a catalyst installation part in the secondary battery of the first embodiment of the present invention. [Figure 27] FIG. 4 is a perspective view of a cell, a reactor, etc. of a secondary battery according to embodiment 2 of the present invention. [Figure 28] FIG. 4 is a cross-sectional view of a cell, a reactor, etc. of a secondary battery according to embodiment 2 of the present invention. [Figure 29] FIG. 5 is a perspective view of a module, a gas flow path, etc. of a secondary battery according to embodiment 2 of the present invention. [Diagram 30] FIG. 5 is a cross-sectional view of a module, a gas flow path, etc. of a secondary battery according to a second embodiment of the present invention. [Diagram 31] FIG. 4 is a cross-sectional view of a cell, a reactor, etc. of a secondary battery according to embodiment 3 of the present invention. [Diagram 32] FIG. 5 is a cross-sectional view of a module, a gas flow path, etc. of a secondary battery according to a third embodiment of the present invention. [Diagram 33] FIG. 1 is a cross-sectional view of a cell, a reactor, etc. of a secondary battery according to embodiment 4 of the present invention. [Diagram 34] FIG. 1 is a cross-sectional view of a cell, a reactor, etc. of a secondary battery according to embodiment 4 of the present invention (when having a support material). [Diagram 35] 1 is a graph showing the results of charging and discharging in Verification Example 1. [Diagram 36] FIG. 1 is a schematic diagram of a reactor used in Verification Example 2, which is divided into an electrochemical reaction section and a thermochemical reaction section. [Figure 37] 13 is a graph showing the results of charging and discharging in Verification Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described below, but the present invention is not limited to the following embodiments and can be practiced in any modified form.

[0018] The secondary battery of the present invention is an improvement of a carbon / air secondary battery. The carbon / air secondary battery (CASB) was developed by the present inventors, and details thereof are described in Patent Document 4 and Non-Patent Document 4.

[0019] A schematic diagram of the vicinity of the electrodes of the secondary battery of the present invention is shown in Fig. 1. The secondary battery 1 of the present invention has a cell 10 composed of a negative electrode 21, a positive electrode 22, and an electrolyte 23 made of a gas-impermeable and ion-conductive solid oxide placed in contact with the negative electrode 21 and the positive electrode 22.

[0020] The negative electrode 21 side of the secondary battery 1 of the present invention forms a closed system 11 as described below, and carbon dioxide is stored within the closed system 11. The positive electrode 22 side of the secondary battery 1 of the present invention is usually an open system 12, and the positive electrode 22 is in contact with oxygen in the air. The oxygen on the positive electrode side is taken into the positive electrode 22 during discharge and participates in the reaction.

[0021] 1(a) is a schematic diagram showing the reaction during charging of the secondary battery 1 of the present invention. During charging, carbon dioxide is electrolyzed on the surface of the negative electrode 21, and carbon is precipitated on the negative electrode side, which is a closed system 11. The specific reaction that occurs in the negative electrode 21 during charging is presumed to be as follows.

[0022] CO2+2e - → CO+O 2- (R1) 2CO ←→ CO2+C (R2)

[0023] (R1) is a reduction reaction (electrochemical reduction reaction) on the surface of the negative electrode 21. (R2) is a thermochemical reaction between solid carbon and carbon dioxide with carbon monoxide, known as the Boudouard reaction. From (R1) and (R2), the total negative electrode reaction during charging is as follows:

[0024] CO2+4e - → C+2O 2- (R3)

[0025] In the case of charging, the overpotential is generally large, so it is thought to be difficult to electrochemically reduce carbon dioxide directly to carbon (directly causing (R3)). In addition, the production of carbon by reduction of carbon monoxide produced by (R1) (reaction formula (R4) below) is also considered difficult due to its large overvoltage. Therefore, the electrolysis of carbon dioxide is considered to have low energy efficiency.

[0026] CO+2e - → C+O 2- (R4)

[0027] Therefore, in the secondary battery 1 of the present invention, which is a carbon-air secondary battery, carbon monoxide is generated on the surface of the negative electrode 21 by a reduction reaction (R1), and the generated carbon monoxide is converted into carbon dioxide and carbon by a thermochemical reaction (R2), thereby depositing carbon on the side of the negative electrode 21.

[0028] The negative electrode 21 side is a closed system 11, and during charging, carbon (solid carbon) does not necessarily precipitate only on the surface of the negative electrode 21, but may also precipitate in places other than the surface of the negative electrode 21 (such as the wall surface in the closed system). If carbon (solid carbon) precipitates on the surface of the negative electrode 21, it may cause deterioration of the negative electrode 21. Therefore, as described below, it is desirable to make it easier for carbon to precipitate in places other than the surface of the negative electrode 21 by using a method such as a catalyst.

[0029] During charging, oxide ions (O 2- ) to produce oxygen (O2) (reaction (R5) below).

[0030] O 2- → 1 / 2O2+2e - (R5)

[0031] 1(b) is a schematic diagram showing the reaction during discharge of the secondary battery 1 of the present invention. During discharge, oxide ions are produced from oxygen at the positive electrode 22 (reaction (R6) below).

[0032] 1 / 2O2+2e - → O 2- (R6)

[0033] The side of the positive electrode 22 is usually an open system 12, and oxygen in the air can be used as the oxygen taken into the positive electrode 22 during discharge. The secondary battery 1 of the present invention may also have a gas flow path 51 in order to efficiently send oxygen to the positive electrode 22 during discharge. The gas flowing through the gas flow path 51 may be any gas that contains oxygen, and may be, for example, air or pure oxygen supplied from a gas cylinder or the like.

[0034] During discharge, carbon and / or carbon monoxide are electrochemically oxidized on the surface of the negative electrode 21 to produce carbon dioxide. The specific reaction that occurs in the negative electrode 21 during discharge is presumed to be as follows.

[0035] C+O 2- → CO+2e - (R7) C+2O 2- → CO2+4e - (R8) CO+O 2- → CO2+2e - (R9) 2CO ←→ CO2+C (R2)

[0036] (R7) to (R9) are oxidation reactions (electrochemical oxidation reactions) on the surface of the negative electrode 21. (R2) is a thermochemical reaction between the above-mentioned solid carbon and carbon dioxide, and carbon monoxide. The total negative electrode reaction during discharge is as follows:

[0037] C+2O 2- → CO2+4e - (R10)

[0038] During discharge, carbon attached to the surface of the negative electrode 21 is oxidized by oxide ions to produce carbon monoxide and carbon dioxide (reaction (R7) and reaction (R8)). In addition, carbon monoxide is oxidized by oxide ions on the surface of the negative electrode 2 to produce carbon dioxide (reaction (R9)). In addition, a thermochemical reaction (R2) occurs between solid carbon and carbon dioxide and carbon monoxide.

[0039] During charging, carbon (solid carbon) does not necessarily deposit only on the surface of the negative electrode 21, but may deposit in places other than the surface of the negative electrode 21. The carbon (solid carbon) deposited in places other than the surface of the negative electrode 21 is once converted to carbon monoxide by a thermochemical reaction (R2), and contributes to discharge by a reaction (R9). As described above, from the viewpoint of preventing deterioration of the negative electrode 21, it is desirable to facilitate deposition of carbon in places other than the surface of the negative electrode 21 during charging. In other words, it is desirable that the main reaction pathways in the negative electrode during discharging are (R2) and (R9), rather than (R7) and (R8).

[0040] 2 to 4 are conceptual diagrams of the cell 10, reactor 20, etc. in the secondary battery 1 of the present invention. Figs. 2 to 4 are conceptual diagrams and do not show specific shapes of the cell 10, reactor 20, etc. (Specific examples of the shapes of the cell 10, reactor 20, etc. will be described later). The secondary battery 1 of the present invention has a reactor 20 in which a negative electrode 21 is placed and which is separated from the outside by an electrolyte 23, and which stores carbon deposited during charging. Incidentally, "the reactor 20 is separated from the outside by the electrolyte 23" means that no exchange of gas occurs between the inside and outside of the reactor 20.

[0041] The electrolyte 23 is made of a gas-impermeable and ion-conductive solid oxide. The electrolyte 23 converts oxide ions (O 2- ) but does not allow the gases involved in the reaction (oxygen, carbon dioxide, carbon monoxide) to pass through.

[0042] In the secondary battery 1 of the present invention, the negative electrode 21 side is a closed system 11, so that the carbon monoxide partial pressure increases, and carbon can be easily precipitated. In addition, because the negative electrode 21 side is a closed system 11, carbon dioxide generated on the negative electrode 2 side by discharge is returned to carbon by charging, so the secondary battery 1 of the present invention does not emit CO2.

[0043] The reactor 20 constitutes a part of the closed system 11, and carbon (solid carbon) generated by charging is stored inside the reactor 20. The "inside of the reactor 20" where carbon is stored includes the surface of the negative electrode 21, the surface of the electrolyte 23, and parts of the wall surface of the reactor 20 that are not composed of the electrolyte 23, but the parts where it is desirable to store carbon (where carbon is deposited by charging) will be described later.

[0044] The carbon dioxide generated by the discharge is stored inside the closed system 11. The carbon dioxide may be stored in any state of gas, liquid, or solid inside the closed system 11. It is preferable to store the carbon dioxide in a liquid state because a large amount of carbon dioxide can be stored and excessive cooling is not required.

[0045] The closed system 11 in the secondary battery of the present invention may be composed of only the reactor 20 (FIG. 2). In the secondary battery of the present invention, it is preferable that the inside of the reactor 20 can be pressurized. In other words, it is preferable that the reactor 20 is made of a material or the like that can be pressurized. "Pressurizable" means that a pressure of 1 atmosphere or more can be applied.

[0046] Reaction (R2) is a reaction in which two molecules of carbon monoxide are produced from solid carbon and one molecule of carbon dioxide. As reaction (R2) proceeds to the left side, the inside of the reactor 20 is electrochemically pressurized. In addition, as described later, the inside of the reactor 20 may be pressurized by the pressurizing means 46.

[0047] The closed system 11 in the secondary battery of the present invention may have a pressurizable tank 40 connected to the reactor 20. That is, the closed system 11 may be composed of the reactor 20 and the tank 40 (FIGS. 3 and 4). In this case, since the carbon dioxide is stored in the tank 40, it is not necessary to make the inside of the reactor 20 pressurizable.

[0048] When the closed system 11 is composed of the reactor 20 and the tank 40, the reactor end 27 is connected to the tank 40 through the piping 41. When the closed system 11 is composed of only the reactor 20, the reactor end 27 is sealed. In the figures (FIGS. 24 to 34) showing specific cell structures described below, "27" is sealed or connected to tank 40 through piping 41 (piping 41 and tank 40 are omitted in FIGS. 24 to 34).

[0049] 3 and 4, when the closed system 11 is composed of the reactor 20 and the tank 40, the tank 40 is connected to the reactor 20 and can be pressurized. Carbon dioxide generated by discharge is stored in the tank 40 in a liquid state.

[0050] As shown in Figure 2, when the closed system 11 is composed of only the reactor 20, there are advantages such as a simple device configuration and a compact device. Due to these advantages, it is expected to be used as a portable power source. As shown in Figures 3 and 4, when the closed system 11 is composed of a reactor 20 and a tank 40, the storage capacity can be easily adjusted and improved by changing the capacity of the tank, and by changing the tank capacity according to the application, the system volume and storage capacity can be freely designed.

[0051] In the reactor 20 and the tank 40, the pressure at which carbon dioxide is stored is preferably 0.2 MPa or more, more preferably 1 MPa or more, even more preferably 3 MPa or more, and particularly preferably 6 MPa or more. Also, the pressure is preferably 100 MPa or less, more preferably 70 MPa or less, even more preferably 50 MPa or less, and particularly preferably 20 MPa or less. When the lower limit of the pressure is equal to or higher than the above range, it is easy to store a sufficient amount of carbon dioxide, and the liquefaction temperature can be increased, and the temperature suitable for storage can be brought closer to room temperature, thereby simplifying the cooling device. When the upper limit of the pressure is equal to or lower than the above range, the tank can be produced more inexpensively.

[0052] When the closed system 11 is composed of a reactor 20 and a tank 40, the reactor 20 and the tank 40 may be directly connected (Figure 3), or may be connected between the reactor 20 and the tank 40 via a reservoir 70 (Figure 4).

[0053] The secondary battery 1 of the present invention may have a control means for controlling the temperature and / or pressure during storage and / or supply of carbon dioxide between the reactor 20 and the tank 40, and the reservoir 70 is an example of such a control means. By maintaining the inside of reservoir 70 at a specific temperature and pressure, the temperature and pressure of the carbon dioxide stored and supplied to tank 40 can be automatically adjusted to intended values.

[0054] In addition to the reservoir 70, the control means in the secondary battery 1 of the present invention may be, for example, a pressure regulating valve.

[0055] As described above, it is desirable that the carbon dioxide generated by the discharge is stored in a liquid state inside the tank 40. For this reason, it is desirable that the control means performs control so as to efficiently carry out the carbon dioxide liquefaction process before the end of the discharge reaction. It is desirable to prevent the presence of carbon monoxide as much as possible inside the reactor 20 during the liquefaction process. Such control is for realizing such a state.

[0056] (R2) is a thermochemical reaction (Boudouard reaction). Figure 5 shows the temperature and pressure dependences of the Boudouard reaction at equilibrium. At the end of discharge, the thermochemical reaction (R2) is shifted to the right side (i.e., the partial pressure of carbon monoxide is reduced and the partial pressure of carbon dioxide is increased), thereby making it possible to efficiently carry out the carbon dioxide liquefaction process. In other words, the "control to efficiently carry out the carbon dioxide liquefaction process" performed by the control means is control to shift (R2) to the right-hand side. On the other hand, when the carbon monoxide partial pressure is low, the reaction overvoltage increases and the discharge efficiency decreases, so it is desirable for the control means to perform such control immediately before the end of the discharge reaction.

[0057] For example, by pressurizing the inside of the reactor 20 (increasing the total pressure inside the reactor 20), (R2) shifts to the right-hand side. An example of "control to efficiently carry out the carbon dioxide liquefaction process" performed by the control means is control to increase the total pressure in the reactor 20 at a constant temperature in the latter stage of the discharge reaction.

[0058] Also, by decreasing the temperature in the reactor 20, (R2) shifts to the right hand side. An example of "control to efficiently carry out the carbon dioxide liquefaction process" performed by the control means is control to lower the temperature inside the reactor 20 at a constant pressure in the latter stage of the discharge reaction.

[0059] During discharge, the carbon-air secondary battery consumes carbon (solid carbon) in the reactor 20. As described above, from the viewpoint of preventing deterioration of the negative electrode 21, it is desirable that the carbon (solid carbon) stored in the reactor 20 by charging is deposited (stored) at a location other than the surface of the negative electrode 21 in the reactor 20.

[0060] A catalyst that promotes carbon deposition is placed in locations other than the surface of the negative electrode 21 in the reactor 20, making it easier to deposit carbon in these locations, which makes it easier to prevent carbon deposition on the surface of the negative electrode 21. That is, in the secondary battery 1 of the present invention, it is preferable that a catalyst that promotes carbon deposition is provided in the negative electrode non-installed portion 24 and / or the electrolyte non-installed portion 25 inside the reactor 20. Here, the "negative electrode non-installed portion 24" refers to a portion on the electrolyte 23 inside the reactor 20 where the negative electrode 22 is not present. The "electrolyte non-installed portion 25" refers to a portion of the boundary (wall surface) separating the inside and outside of the reactor 20 that is not constituted by the electrolyte 23.

[0061] In order to more efficiently suppress deterioration of the negative electrode 21 due to deposition of carbon on the surface of the negative electrode 21, the electrochemical reaction field and the thermochemical reaction field may be separated on the negative electrode 21 side of the secondary battery 1, i.e., inside the reactor 20.

[0062] That is, in the secondary battery 1 of the present invention, the reactor 20 may comprise an electrochemical reaction section 20A in which the negative electrode 21 is installed, and a thermochemical reaction section 20B in which a catalyst that promotes carbon deposition is installed, and the electrochemical reaction section 20A and the thermochemical reaction section 20B may be connected by a pipe 41 which is a gas flow path.

[0063] FIG. 6 shows a conceptual diagram of a reactor 20 consisting of an electrochemical reaction section 20A and a thermochemical reaction section 20B. The electrochemical reaction section 20A is provided with a negative electrode 21. The thermochemical reaction section 20B has a catalyst installation section 26 in which a catalyst that promotes carbon deposition is installed.

[0064] On the surface of the negative electrode 21 of the electrochemical reaction portion 20A, a reaction (R1) occurs during charging, and a reaction (R9) occurs during discharging. Carbon monoxide produced by reaction (R1) during charging turns into carbon dioxide and carbon through a thermochemical reaction (R2). The electrochemical reaction section 20A and the thermochemical reaction section 20B are connected by a pipe 41, and gases involved in the reaction (carbon monoxide and carbon dioxide) move through the pipe 41 inside the reactor.

[0065] If carbon adheres to the negative electrode 21, it will cause the negative electrode 21 to deteriorate, so it is preferable to deposit carbon at a location other than the negative electrode 21. By dividing the reactor 20 into an electrochemical reaction section 20A and a thermochemical reaction section 20B and providing a catalyst installation section 26 in the thermochemical reaction section 20B, carbon deposition due to the thermochemical reaction (R2) becomes more likely to occur inside the thermochemical reaction section 20B, and carbon deposition on the negative electrode 21 can be suppressed. This makes it possible to prevent deterioration of the negative electrode 21, extend the life of the negative electrode 21, and reduce the labor required for maintenance.

[0066] By dividing the reactor 20 into an electrochemical reaction section 20A and a thermochemical reaction section 20B, the temperature and pressure of the electrochemical reaction field (electrochemical reaction section 20A) and the thermochemical reaction field (thermochemical reaction section 20B) can be controlled separately. That is, a temperature adjustment means (usually a heating means such as a heat exchanger or a heater) is provided around the electrochemical reaction section 20A and the thermochemical reaction section 20B, respectively, and the electrochemical reaction section 20A and the thermochemical reaction section 20B are equipped with a pressure adjustment means such as a pressure reducing valve or a pump. By dividing the reactor 20 into an electrochemical reaction section 20A and a thermochemical reaction section 20B, it is possible to cause the electrochemical reaction and the thermochemical reaction to occur under desired conditions, respectively, thereby improving the power generation efficiency.

[0067] In the secondary battery 1 of the present invention, gas may be continuously circulated between the electrochemical reaction section 20A and the thermochemical reaction section 20B. Figures 7 and 8 show conceptual diagrams of such a reactor. Furthermore, although not shown, even in the case where the reactor 20 of the secondary battery 1 of the present invention is not divided into the electrochemical reaction section 20A and the thermochemical reaction section 20B, the gas may be continuously circulated inside the closed system 11. In particular, when the secondary battery 1 of the present invention has a tank 40, the gas may be continuously circulated between the reactor 20 and the tank 40.

[0068] 7 and 8, the electrochemical reaction unit 20A and the thermochemical reaction unit 20B are connected by a pipe 41, and the thermochemical reaction unit 20B is further connected to a pipe 42 in the direction of a tank 40. In addition, a pipe 43 extends from the tank 40 in the direction of the electrochemical reaction unit 20A. With this configuration, gas is continuously circulated between the electrochemical reaction section 20A and the thermochemical reaction section 20B.

[0069] The reactor 20 as shown in FIGS. 7 and 8 desirably has a means for controlling the flow direction and flow rate of the gas circulating inside it. As a means for controlling the flow direction of the gas, for example, a three-way valve or a four-way valve can be used. As a means for controlling the flow rate of the gas, for example, a mass flow controller can be used.

[0070] The arrows in Fig. 7 indicate the direction of gas flow during charging. During charging, carbon dioxide stored in the tank 40 is actively supplied to the electrochemical reaction section 20A, reaction (R1) occurs efficiently at the negative electrode 21, and carbon monoxide generated by (R1) is transferred to the thermochemical reaction section 20B, where it is precipitated as carbon on the catalyst installation section 26 by thermochemical reaction (R2). Carbon dioxide generated by (R2) passes through pipes 42 and 43, and is supplied again to the electrochemical reaction section 20A, where it participates in reaction (R1).

[0071] The arrows in FIG. 8 indicate the direction of gas flow during discharge. During discharge, carbon stored in catalyst installation section 26 of thermochemical reaction section 20B and carbon dioxide in the closed system are reacted with carbon monoxide (R2) to generate carbon monoxide. The carbon monoxide moves to electrochemical reaction section 20A, causing discharge at negative electrode 21 through reaction (R9). By flowing gas in the direction of the arrows in FIG. 8, carbon monoxide can be efficiently sent to electrochemical reaction section 20A. Carbon dioxide generated by (R9) passes through pipes 43 and 42 and is supplied to thermochemical reaction section 20B again, where carbon monoxide is generated by reaction (R2).

[0072] The thermochemical reaction section 20B is provided with a catalyst installation section 26 in which a catalyst that promotes carbon deposition is installed. There is no particular limitation on how the catalyst installation section 26 is installed. For example, as shown in Figs. 6 to 8, the catalyst installation section 26 may be installed on the entire wall surface of the thermochemical reaction section 20B. Alternatively, a carrier such as glass wool may be installed in the thermochemical reaction section 20B, and the catalyst may be supported on the carrier to form the catalyst installation section 26 (not shown). Since the space inside the thermochemical reaction section 20B can be effectively utilized, it is preferable to form the catalyst installation section 26 by supporting the catalyst on a carrier.

[0073] In the thermochemical reaction section 20B, the Boudouard reaction (R2) occurs. As shown in Fig. 5, (R2) proceeds to the left side (carbon monoxide) at high temperature and low pressure, and proceeds to the right side at low temperature and high pressure. By changing the temperature and pressure of the thermochemical reaction section 20B during charging and discharging, charging and discharging can be performed under advantageous conditions. Specifically, during charging, it is desirable to set conditions that facilitate the accumulation of carbon in the catalyst installation section 26 of the thermochemical reaction section 20B, i.e., to set the thermochemical reaction section 20B at a low temperature and / or a high pressure. During discharging, it is desirable to set conditions that actively convert the carbon accumulated in the catalyst installation section 26 into carbon monoxide, i.e., to set the thermochemical reaction section 20B at a high temperature and / or a low pressure.

[0074] In the electrochemical reaction section 20A, in order to prevent deterioration of the negative electrode 21, it is desirable to prevent carbon from being deposited. As shown in FIG. 5, the Boudouard reaction (R2) tends to shift to the left side at high temperatures and low pressures (carbon monoxide tends to increase), and tends to shift to the right side at low temperatures and high pressures (carbon and carbon dioxide tend to increase).

[0075] Therefore, during charging (carbon deposition), it is desirable to make the temperature of the electrochemical reaction section 20A higher than the temperature of the thermochemical reaction section 20B. In this case, the temperature difference between the electrochemical reaction section 20A and the thermochemical reaction section 20B is preferably 100° C. or more, more preferably 150° C. or more, and particularly preferably 200° C. or more. During charging (carbon deposition), it is desirable to reduce the pressure in the electrochemical reaction section 20A.

[0076] By adjusting the temperature (or pressure) of the electrochemical reaction section 20A so that it is below the curve shown in FIG. 5, and by adjusting the temperature (or pressure) of the thermochemical reaction section 20B so that it is below the curve shown in FIG. 5, it is possible to prevent carbon deposition in the electrochemical reaction section 20A.

[0077] 9 and 10 show flow diagrams in the secondary battery of the present invention equipped with gas flow direction control means 44. The solid arrows in Fig. 9 show the gas flow direction during charging, and the dashed arrows in Fig. 10 show the gas flow direction during discharging. The gas flow control means 44 (for example, a three-way valve) makes it possible to easily change the gas flow direction during charging and discharging.

[0078] As shown in Verification Example 2 described below, by dividing the reactor 20 into an electrochemical reaction section 20A and a thermochemical reaction section 20B and making the temperature of the electrochemical reaction section 20A higher than the temperature of the thermochemical reaction section 20B, and by controlling the carbon monoxide partial pressure in the electrochemical reaction section 20A to be lower than the carbon monoxide partial pressure at equilibrium (FIG. 5), it is possible to prevent carbon deposition in the electrochemical reaction section 20A (particularly near the negative electrode 21), and the secondary battery 1 of the present invention can be stably charged and discharged without being affected by deterioration of the negative electrode 21 due to carbon deposition.

[0079] As described above, the secondary battery 1 of the present invention can be configured so that gas circulates inside the closed system 11. Furthermore, the secondary battery 1 of the present invention can be provided with a tank 40 that stores carbon dioxide produced by discharge in a liquid state. In such a case, in order to improve the energy efficiency of the entire system, it is desirable for the secondary battery 1 of the present invention to be equipped with a means (device) for adjusting the temperature and pressure.

[0080] The secondary battery 1 of the present invention desirably includes a heat exchange promotion means 45 (for example, a heat exchanger or a cooling fan). Moreover, the secondary battery 1 of the present invention desirably includes a pressurizing means 46 (for example, a pump or a compressor) and a depressurizing means 47 (for example, a pressure reducing valve).

[0081] In the secondary battery 1 of the present invention, which is equipped with means for adjusting temperature and pressure, such as heat exchange promotion means 45, pressurization means 46, and decompression means 47, flow diagrams during charging are shown in FIGS. 11 and 12, and a flow diagram during discharging is shown in FIG. 13.

[0082] The secondary battery 1 of the present invention preferably has heat exchange promotion means 45 for lowering the temperature of the gas (cooling the gas) in the flow path (piping) of the gas flowing from the reactor 20 (negative electrode 21) to the tank 40. In addition, the secondary battery 1 of the present invention preferably has pressurizing means 46 for pressurizing the gas in the flow path (piping). With this configuration, carbon dioxide generated at the negative electrode 21 during discharge can be easily liquefied and stored in the tank 40.

[0083] When the secondary battery 1 of the present invention has both the heat exchange promotion means 45 and the pressurizing means 46 in the flow path (piping) of the gas flowing from the reactor 20 (negative electrode 21) to the tank 40, it is preferable to place the heat exchange promotion means 45 on the reactor 20 side and the pressurizing means 46 on the tank 40 side (FIG. 13). In other words, it is preferable to pressurize the gas flowing out of the reactor 20 after lowering its temperature.

[0084] The secondary battery 1 of the present invention desirably has heat exchange promotion means 45 for increasing the temperature of the gas (heating the gas) in the flow path (piping) of the gas flowing from the tank 40 to the reactor 20 (negative electrode 21). With this configuration, the reaction (R2) tends to proceed to the left side, and carbon monoxide can be efficiently sent to the reactor 20 (negative electrode 21).

[0085] It is desirable that the secondary battery 1 of the present invention is configured so that the heat removed when lowering the temperature of the gas (cooling the gas) can be utilized when increasing the temperature of the gas (heating the gas). Moreover, it is preferable that the secondary battery 1 of the present invention is configured so that the work generated by the decompression by the decompression means 47 can be utilized when the pressurization by the pressurization means 46 is performed. This makes it possible to reduce energy loss in the entire system.

[0086] 12 (during charging) and 13 (during discharging), the gas flow inside the closed system 11 is the same. That is, whether carbon dioxide is absorbed into the tank 40 or released from the tank 40 is determined depending on whether the inside of the tank 40 is above or below the equilibrium composition. By changing the temperature and / or pressure of the tank 40, the absorption and release of carbon dioxide in the tank 40 can be controlled.

[0087] In a secondary battery in which gas circulates inside a closed system 11 and which is equipped with means (equipment) for adjusting the temperature and pressure, the circulating flow rate of carbon monoxide during discharge is important in determining the charge / discharge efficiency of the secondary battery 1. By controlling the circulating flow rate of carbon monoxide, it is possible to achieve high charge / discharge efficiency.

[0088] For this reason, it is desirable for the secondary battery 1 of the present invention to have, within the reactor 20, a means for measuring the ratio of carbon dioxide to carbon monoxide.

[0089] Moreover, it is more preferable that the secondary battery 1 of the present invention has a means for adjusting the ratio of carbon dioxide and carbon monoxide in the reactor 20 . By using such an adjustment means to adjust the ratio of carbon dioxide and carbon monoxide to a desired value, a desired circulation flow rate of carbon monoxide can be obtained, and the secondary battery 1 of the present invention can achieve high charge and discharge efficiency.

[0090] Examples of such conditioning means include a combustor to convert carbon monoxide to carbon dioxide, or a separate cell to adjust the ratio of carbon dioxide to carbon monoxide. In addition, it is also possible to adjust the ratio of carbon dioxide and carbon monoxide by shifting reaction (R2) to the left or right side by pressurizing or depressurizing, so pressurizing means or depressurizing means can also be such an adjustment means.

[0091] FIG. 14 shows a flow diagram during discharging in the secondary battery 1 of the present invention equipped with a combustor 48. The gas that has passed through the negative electrode 21 of the reactor 20 is sent to a combustor 48, where the carbon monoxide contained in the gas is converted into carbon dioxide by reaction with oxygen that is supplied separately.

[0092] 15 shows a flow diagram during discharging in the secondary battery 1 of the present invention including a gas ratio adjustment cell 80 (a cell separate from the cell 10 in the reactor 20). The gas ratio adjustment cell 80 is composed of a negative electrode 81, a positive electrode 82, and an electrolyte (not shown in FIG. 15). The gas that has passed through the negative electrode 21 of the reactor 20 is sent to the negative electrode 81 of the gas ratio adjustment cell 80, where the carbon monoxide contained in the gas is converted into carbon dioxide by reaction (R9).

[0093] As described above, the reactor 20 of the secondary battery 1 of the present invention may be divided into the electrochemical reaction section 20A and the thermochemical reaction section 20B. Flow diagrams for charging the secondary battery 1 are shown in Fig. 16 (when the reservoir 70 is not provided), Fig. 17 (when the reservoir 70 is provided), and Fig. 18 (when gas-liquid equilibrium in the tank is utilized). Flow diagrams for discharging the secondary battery 1 are shown in Fig. 19 and Fig. 20 (when a combustor is provided).

[0094] It should be noted that the flow diagrams shown in the figures of the present application are merely examples of flow diagrams for the secondary battery 1 of the present invention, and cases in which some of the components shown in the flow diagrams (e.g., gas flow direction control means 44, heat exchange promotion means 45, pressurization means 46, decompression means 47) are missing, cases in which components not shown in the flow diagrams are included, cases in which the order of some of the components is different, etc. are not outside the scope of the present invention.

[0095] In the secondary battery 1 of the present invention, deterioration of the negative electrode 21 due to carbon deposition is more likely to occur during charging, that is, when a carbon deposition reaction occurs. In the secondary battery 1 of the present invention, a method of using different negative electrodes 21 during charging and discharging can be considered as a means to avoid the drop in performance and the increase in frequency of maintenance that accompanies such deterioration.

[0096] That is, the cell 10 of the secondary battery 1 of the present invention may have a plurality of negative electrodes (a first negative electrode 21A and a second negative electrode 21B) (FIG. 21). The first negative electrode 21A and the second negative electrode 21B differ in how easily carbon deposits on their surfaces, and carbon deposits more easily on the surface of the second negative electrode 21B than on the surface of the first negative electrode 21A.

[0097] During charging, a voltage is applied between the first negative electrode 21A and the positive electrode 22. As a result, carbon dioxide is electrolyzed on the surface of the first negative electrode 21A to produce carbon monoxide (reaction (R1)). The carbon dioxide produced in reaction (R1) becomes carbon through a thermochemical reaction (R2). As described above, carbon is more likely to precipitate on the surface of the second negative electrode 21B, so during charging, carbon precipitates on the surface of the second negative electrode 21B.

[0098] During discharge, discharge is performed between the second negative electrode 21B and the positive electrode 22. Due to the discharge, carbon and / or carbon monoxide are electrochemically oxidized on the surface of the second negative electrode 21B to produce carbon dioxide (reactions (R7), (R8), and (R9)).

[0099] As shown in Verification Example 1 described later, by appropriately selecting the materials of the first negative electrode 21A and the second negative electrode 21B, it is possible to prevent carbon from being deposited on the surface of the first negative electrode 21A during charging. Therefore, by using different negative electrodes for charging and discharging, the negative electrode for charging, ie, the first negative electrode 21A, can be protected from deterioration caused by carbon deposition.

[0100] By selecting the materials for the first negative electrode 21A and the second negative electrode 21B taking into consideration the ease of carbon deposition, it is possible to make it easier for carbon to deposit on the surface of the second negative electrode 21B than on the surface of the first negative electrode 21A (specific materials will be described later). Furthermore, a catalyst that promotes carbon deposition may be provided only on the surface of the second negative electrode 21B, so that carbon is more likely to deposit on the surface of the second negative electrode 21B than on the surface of the first negative electrode 21A.

[0101] The area of ​​the first negative electrode 21A is desirably larger than the area of ​​the second negative electrode 21B. Moreover, the area of ​​the first negative electrode 21A is more desirably 1.5 times or more, and particularly desirably 3 times or more, the area of ​​the second negative electrode 21B. The area of ​​the first negative electrode 21A is larger than that of the second negative electrode 21B, and in particular, the ratio of the area of ​​the first negative electrode 21A to the area of ​​the second negative electrode 21B is equal to or larger than the above, so that a large amount of stored electricity can be secured. This makes it possible to sufficiently store fluctuating power such as that derived from a solar cell.

[0102] Carbon stored in areas other than the surface of the negative electrode 21 (solid carbon) is converted to carbon dioxide via the above-mentioned reactions (R2) and (R9) during discharge.

[0103] As can be seen from FIG. 5, the higher the temperature, the more likely the thermochemical reaction (R2) is to lean to the left side (the more likely CO is to be produced). Therefore, in a carbon-air secondary battery, in order to actively utilize the carbon (solid carbon) stored in areas other than the surface of the negative electrode 21 for discharge, it is necessary to make the temperature inside the reactor 20 high to facilitate the production of CO. Specifically, the temperature inside the reactor 20 during discharge needs to be about 400 to 1000°C. More preferably, it needs to be about 600 to 900°C.

[0104] The secondary battery 1 of the present invention has a structure 60 that surrounds the reactor 20 and suppresses heat loss from the reactor 20 due to radiative heat transfer.

[0105] As shown in FIGS. 22 and 23, a structure 60 surrounds the reactor 20 of the secondary battery 1 of the present invention. As described above, in a carbon-air secondary battery, in order to actively use the carbon (solid carbon) stored in areas other than the surface of the negative electrode 21 for discharging and to increase the discharge efficiency, it is necessary to heat the inside of the reactor 20 to a high temperature. In addition, in the charge / discharge reaction of a carbon-air secondary battery, the entropy loss (TΔS), which is theoretically a factor in reducing the charge / discharge efficiency, is almost zero, so the introduction of an advanced heat insulating structure is likely to directly lead to an improvement in the charge / discharge efficiency, and even if the interval between charge / discharge becomes long, it is possible to suppress the decrease in efficiency and to immediately charge / discharge. In the secondary battery 1 of the present invention, the structure 60 is provided to suppress heat loss due to radiation heat transfer, thereby preventing energy loss.

[0106] In the secondary battery 1 of the present invention, since solid carbon is not precipitated in the tank 40, there is no need to heat the inside of the tank. Therefore, as shown in Fig. 23, when the closed system 11 is composed of the reactor 20 and the tank 40, the structure 60 does not need to surround the tank 40 (it is preferable that it does not surround it).

[0107] Moreover, it is desirable for the structure 60 to cover as much of the reactor 20 as possible, but due to the need to provide piping 41 to the tank 40, a gas flow path, and the like, it is not necessary for the structure 60 to cover the entire reactor 20.

[0108] The surface of the structure 60 facing the reactor 20 preferably has a mirror structure. Since the surface on the reactor 20 side has a mirror structure, the amount of radiative heat transfer is suppressed, and heat loss during charging and discharging that would otherwise be caused by raising the reactor 20 to a high temperature can be efficiently suppressed. The mirror structure refers to a structure that reflects light ranging from infrared light to ultraviolet light, preferably from infrared light to visible light, and more preferably, infrared light.

[0109] Furthermore, it is desirable for the structure 60 to have a vacuum insulation layer, which can efficiently suppress heat loss regardless of the temperature range.

[0110] It is most desirable that the surface of the structure 60 facing the reactor 20 has a mirror structure and has a vacuum insulation layer. In this way, the charge / discharge efficiency can be improved, and the time required from a non-charged state to the start of charge / discharge can be shortened.

[0111] Specific examples of the shapes of the cells 10, reactor 20, etc. of the secondary battery 1 of the present invention will be described below.

[0112] (1) Aspect 1 In the secondary battery 1 of the first embodiment of the present invention, the reactor 20 is columnar and the bottom surface is composed of the electrolyte 23. Inside the reactor 20, the negative electrode 21 is disposed on the electrolyte 23, and outside the reactor 20, the positive electrode 22 is disposed at a position on the electrolyte 23 corresponding to the negative electrode 21 (FIG. 24 (oblique view), FIG. 25 (cross-sectional view)).

[0113] The reactor 20 has a columnar shape, for example, a circular cylinder (FIG. 24), a triangular prism, a square prism, or a hexagonal prism.

[0114] The bottom surface of the reactor 20 (one of the two bottom surfaces) is made of an electrolyte 23, and the other surfaces of the reactor 20 (the other bottom surface and the side surface) are electrolyte-free portions 25 where no electrolyte is provided. The electrolyte 23 and the electrolyte-free portions 25 form a partition wall that separates the inside and outside of the reactor 20.

[0115] In the reactor 20, the negative electrode 21 is placed on the electrolyte 23. The negative electrode 21 is preferably placed approximately in the center of the electrolyte 23, as shown in Figs. 24 and 25.

[0116] As shown in FIGS. 24 and 25, the outer edge of the electrolyte 23 may be a non-negative electrode portion 24 where the negative electrode 21 is not provided. In this case, the ratio of the area of ​​the portion where the negative electrode is not installed 24 to the surface area of ​​the electrolyte 23 inside the reactor 20 is preferably 0.1% or more, more preferably 0.5% or more, and particularly preferably 2% or more. Moreover, this ratio is preferably 80% or less, more preferably 50% or less, even more preferably 20% or less, and particularly preferably 3% or less. By setting the ratio within the above range, the cell output can be increased sufficiently, and a sufficient installation area for the catalyst installation section 26 can be secured.

[0117] Outside the reactor 20, a positive electrode 22 is placed on the electrolyte 23 at a position corresponding to the negative electrode 21. The shape and size of the part of the surface of the electrolyte 23 outside the reactor 20 that is occupied by the positive electrode 22 is preferably similar to the shape and size of the part of the surface of the electrolyte 23 inside the reactor 20 that is occupied by the negative electrode 21 .

[0118] The reactor end portion 27 may be present on the bottom surface of the reactor 20, which is the portion 25 where no electrolyte is installed (FIGS. 24 and 25), or may be present on the side surface of the reactor 20 (not shown).

[0119] A gas flow passage 51 for supplying oxygen to the positive electrode 22 may be provided outside the reactor 20. During discharge, an oxygen-containing gas, such as air or pure oxygen, is supplied to the gas flow passage 51. An outlet of the gas flow passage 51 is provided near the positive electrode 22, and the oxygen-containing gas can be efficiently supplied to the positive electrode 22 during discharge.

[0120] Furthermore, by providing gas flow channel 52 so as to surround the outside of gas flow channel 51, the flow of gas is improved, and the oxygen-containing gas can be more efficiently sent to positive electrode 22 during discharge. For example, as shown in FIGS. 24 and 25, a gas flow path 52 can be formed by forming a structure in which the side surface of the reactor 20 is continuous with the outside of the reactor 20 via the electrolyte 23.

[0121] By providing a catalyst inside the reactor 20 for facilitating the deposition of carbon, it is possible to make it easier to control the reaction inside the reactor 20 and improve cycle characteristics.

[0122] Within the reactor 20, the portion (catalyst installation portion 26) where a catalyst is installed to facilitate carbon deposition is preferably the non-negative electrode installation portion 24 on the electrolyte 23 or the portion on the electrolyte 23 side of the non-electrolyte installation portion 25 on the side of the reactor 20. In the example shown in FIG. 26, both the “negative electrode non-installed portion 24 on the electrolyte 23 ” and the “electrolyte 23 side portion of the electrolyte non-installed portion 25 on the side of the reactor 20 ” serve as the catalyst installation portion 26 .

[0123] Furthermore, the negative electrode 21 may be divided into a plurality of areas on the electrolyte 23, and the negative electrode non-installed portion 24, which is the interface between the areas, may be used as the catalyst installation portion . For example, by arranging a large number of negative electrodes 21 in a mesh-like manner on the electrolyte 23, the interfaces between the negative electrodes 21 become mesh-like negative electrode non-installed parts 24. By installing a catalyst in such mesh-like negative electrode non-installed parts 24, it is possible to form catalyst installed parts 26 (not shown).

[0124] In order to prevent deterioration of the negative electrode 21, it is desirable to avoid deposition of carbon on the negative electrode 21. On the other hand, from the viewpoint of reaction efficiency, it is desirable for carbon to be deposited in a portion of the reactor 20 as close as possible to the negative electrode 21. For this reason, the position of the catalyst installation section 26 as described above is optimal.

[0125] (2) Mode 2 In the secondary battery 1 of the second embodiment of the present invention, the reactor 20 is composed of a cylindrical electrolyte 23, a negative electrode 21 is provided on the inner surface of the cylinder, and a positive electrode 22 is provided on the outer surface of the cylinder (FIG. 27 (perspective view), FIG. 28 (cross-sectional view)).

[0126] In the secondary battery 1 of the second embodiment of the present invention, the cylindrical electrolyte 23 itself constitutes the reactor 20, and both ends of the electrolyte (cylinder) serve as the reactor end portions 27.

[0127] As described above, the reactor end 27 is sealed or connected to the tank 40 through the piping 41. In the secondary battery 1 of the embodiment 2, when the closed system 11 has the tank 40, one of the reactor end parts 27 may be connected to the tank 40 and the other reactor end part 27 may be sealed, or both of the two reactor end parts 27 may be connected to the tank 40. When both of the two reactor end parts 27 are connected to the tank 40, the two reactor end parts 27 may be connected to the same tank 40 or may be connected to different tanks 40.

[0128] When the reactor 20 (cylindrical electrolyte 23) is connected at its end 27 to the tank 40 through a pipe 41, the connection between the reactor end 27 and the pipe 41 can be made, for example, by using a fitting (e.g., Swagelok Ultra-Tor vacuum fitting) or by bonding with epoxy resin.

[0129] Since the cylindrical electrolyte 23 is easy to manufacture, it is desirable that the entire cylinder be made of the electrolyte 23, as shown in Figures 27 and 28. However, a case in which a part of the cylinder is made of something other than the electrolyte 23 (a part of the cylinder becomes an electrolyte-free part 25) does not fall outside the scope of embodiment 2 of the present invention. Furthermore, when the reactor end portion 27 is sealed, the sealing member may be formed of the electrolyte 23 or may be formed of a material other than the electrolyte 23 .

[0130] A negative electrode 21 is disposed on the inner surface of a cylinder made of electrolyte 23, and a positive electrode 22 is disposed on the outer surface of the cylinder. It is desirable that the shape and size of the portion of the outer surface of the cylinder occupied by the positive electrode 22 be similar to the shape and size of the portion of the inner surface of the cylinder occupied by the negative electrode 21.

[0131] When the reactor end 27 is connected to the tank 40, it is necessary to provide a space for connection to the pipe 41 near the reactor end 27 of the cylinder (electrolyte 23), and it is preferable not to place the negative electrode 21 and the positive electrode 22 therein. For this reason, it is desirable to place the negative electrode 21 and the positive electrode 22 near the center of the cylinder (electrolyte 23). In other words, it is desirable that both ends of the cylinder (electrolyte 23) be portions 24 where no negative electrode is placed.

[0132] When a catalyst for facilitating carbon deposition is installed inside the reactor 20, it is preferable to avoid installing the catalyst on the negative electrode 21. For this reason, a portion (negative electrode non-installed portion 24) where the negative electrode 21 is not installed, which is larger than the space required for connection with the pipe 41, may be provided on both end sides (reactor end portion 27 side) of the cylinder (electrolyte 23). When a catalyst is placed in the non-negative electrode portion 24 on both ends of the cylinder, it is desirable to arrange the catalyst placement portion 26 so that it is located near the electrolyte 23 in the non-negative electrode portion 24 .

[0133] As in the first embodiment, the negative electrode 21 may be divided into a plurality of areas on the electrolyte 23, and the interface between the areas, that is, the portion 24 where the negative electrode is not installed, may be used as the portion 26 where the catalyst is installed.

[0134] Although not shown, portions where the negative electrode 21 is not disposed may be provided in places near the center of the cylinder (electrolyte 23), and these portions may be used as catalyst installation portions 26. With this configuration, deterioration of the negative electrode 21 can be prevented, and the reaction efficiency can be improved.

[0135] The ratio of the area of ​​the portion where the negative electrode is not installed 24 to the surface area of ​​the inner surface of the cylindrical electrolyte 23 is preferably 1% or more, more preferably 2% or more, and particularly preferably 3% or more. Moreover, the ratio is preferably 50% or less, more preferably 30% or less, even more preferably 20% or less, and particularly preferably 5% or less. By setting the ratio within the above range, the cell output can be increased sufficiently, and a sufficient installation area for the catalyst installation section 26 can be secured.

[0136] A positive electrode 22 is placed on the outer surface of the cylinder (electrolyte 23), and during discharge, a reaction (R6) occurs as oxygen is taken into the positive electrode 22. The side of the positive electrode 22 is usually an open system and oxygen is supplied from the air, but by using a structure as shown in Figures 29 and 30, oxygen can be efficiently supplied to the positive electrode 22, improving discharge efficiency. That is, the secondary battery 1 of the second aspect of the present invention may have a module 50 in which a gas flow passage 51 is provided to cover the outside of a plurality of reactors 20 .

[0137] (3) Aspect 3 The secondary battery 1 of the third embodiment of the present invention has a reactor 20 disposed around a cylindrical electrolyte 23, a positive electrode 22 disposed on the inner surface of the cylinder (electrolyte 23), and a negative electrode 21 disposed on the outer surface of the cylinder (electrolyte 23) (Figure 31).

[0138] The secondary battery 1 of the third embodiment of the present invention is the same as the secondary battery 1 of the second embodiment in that the electrolyte 23 is composed of a cylindrical member, but the positional relationship between the negative electrode 21 and the positive electrode 22 on the surface of the electrolyte 23 is reversed from that of the secondary battery of the second embodiment. That is, in the secondary battery 1 of the third embodiment, the inside of the cylinder (electrolyte 23) serves as an oxygen flow path, and the periphery of the cylinder (electrolyte 23) serves as the reactor 20. The outer wall of the reactor 20 may be an electrolyte non-installed portion 25 (FIG. 31) or may be the electrolyte 23.

[0139] As in the secondary battery of embodiment 2, the reactor end 27 is sealed or connected to a tank 40 or the like through piping 41, and the reactor 20 wrapped around the cylinder (electrolyte 23) constitutes a closed system 11. The reactor end portion 27 can be connected to the tank 40 or the like, and the reactor end portion 27 can be sealed in the same manner as in the secondary battery of the second embodiment.

[0140] In the secondary battery 1 of the third aspect of the present invention, the shape, size, and arrangement method of the negative electrode 21 and the positive electrode 22 inside the reactor 20 can be the same as those of the secondary battery 1 of the second aspect, except that the positional relationship between the negative electrode 21 and the positive electrode 22 is reversed. Moreover, the arrangement of the catalyst installation portion inside the reactor 20 can be the same as that of the secondary battery 1 of the second embodiment.

[0141] The secondary battery 1 of the third embodiment of the present invention may have a module 50 in which a single common reactor 20 is disposed around a plurality of cylinders (electrolyte 23) (FIG. 32). The reactor 20 surrounds multiple cylinders (electrolyte 23), and the reactor end 27 is sealed or connected to a tank 40 or the like via piping 41, forming a closed system. The inside of each of the multiple cylinders (electrolyte 23) serves as an oxygen gas flow path 51.

[0142] (4) Aspect 4 In the secondary battery 1 of the fourth aspect of the present invention, the reactor 20 is cylindrical, and the inside and outside of the reactor 20 are separated by a plurality of alternately arranged annular electrolytes 23 and a plurality of annular interconnect materials 28. Outside the reactor 20, a plurality of positive electrodes 22 are arranged so as to be in contact with both the electrolyte 23 and the adjacent interconnect materials 28 and not to be in contact with each other. Inside the reactor 20, a plurality of negative electrodes 21 are arranged so as to be in contact with both the electrolyte 23 and the adjacent interconnect materials 28 and not to be in contact with each other. The positive electrodes 22 and the negative electrodes 21 in contact with any one of the electrolytes 23 are in contact with separate interconnect materials 28 on either side of any one of the electrolytes 23 (FIG. 33).

[0143] The interconnect material 28 is made of a conductive material, has a dense structure that is gas impermeable, and is resistant to oxide ions (O 2- ) is not allowed to pass through.

[0144] Both ends of the cylindrical reactor 20 are reactor ends 27 (sealed or connected to a tank 40), and an electrolyte 23 and an interconnect material 28, both of which are gas-impermeable, are disposed on the sides of the reactor 20, separating the inside of the reactor 20 from the outside.

[0145] A cathode 22 disposed outside the reactor 20 is in contact with both the electrolyte 23 and the adjacent interconnect material 28 , with an air gap 29 existing between the cathodes 22 .

[0146] The negative electrodes 21 disposed inside the reactor 20 are in contact with both the electrolyte 23 and the interconnect material 28 adjacent thereto, and the negative electrodes 21 are not in contact with each other. As shown in Fig. 33, the electrolyte 23 may be L-shaped and sandwiched between the negative electrodes 21, or a gap (not shown) may exist between the negative electrodes 21.

[0147] From the perspective of any electrolyte 23, the positive electrode 22 and the negative electrode 21 in contact with the any electrolyte 23 are each in contact with a separate interconnect material 28.

[0148] Since the secondary battery 1 of the fourth embodiment has the above-mentioned structure, it can be said that a large number of cells 10 each consisting of a negative electrode 21, a positive electrode 22 and an electrolyte 23 are connected in series by an interconnect material .

[0149] For example, in the case of the secondary battery 1 having a pair of electrodes (negative electrode 21, positive electrode 22) inside and outside a cylinder as in the embodiment 2, a gas concentration distribution occurs in the longitudinal direction of the cylinder, and the Nernst potential changes. As a result, a current flows in the longitudinal direction according to the potential difference, and at that time, a loss occurs due to Joule heat, and the electromotive force finally becomes the lowest voltage. The secondary battery 1 of the fourth embodiment has a large number of cells 10 connected in series, and therefore does not have such a problem and can achieve a high output density.

[0150] The secondary battery 1 of the fourth embodiment may further have a support material 30 on the inside of the negative electrode 21 disposed inside the reactor 20 (FIG. 34). The support material 30 has a certain degree of thickness and is porous.

[0151] The components of the secondary battery 1 of the embodiment 4, that is, the negative electrode 21, the positive electrode 22, the electrolyte 23, and the interconnect material 28, do not all require a thickness to perform their functions. Therefore, by providing the support material 30, the reactor 20 can be made strong even if these components are made thin.

[0152] Furthermore, by providing the support material 30, carbon is less likely to be deposited on the surface of the negative electrode during charging, making it easier to prevent deterioration of the negative electrode 21. A catalyst that promotes carbon deposition can be applied to the inner surface side of the support material 30 (a catalyst installation portion 26 can be provided), which makes it easier to prevent the negative electrode 21 from deteriorating.

[0153] Specific examples of materials used for each component of the secondary battery 1 of the present invention are described below. Unless otherwise specified, the specific examples of materials described below are applicable to any of the secondary battery 1 of the first embodiment, the secondary battery 1 of the second embodiment, the secondary battery 1 of the third embodiment, and the secondary battery 1 of the fourth embodiment.

[0154] The negative electrode 21 of the secondary battery 1 of the present invention includes a negative electrode material, a negative electrode current collector, and the like.

[0155] The negative electrode material is, for example, a composite metal oxide or a cermet. Here, "cermet" refers to a mixture of metal and metal oxide powders and sintered. The composite metal oxide and the cermet are preferably porous.

[0156] As the composite metal oxide, from the viewpoint of reliably obtaining sufficient output characteristics, durability, etc., during discharge, the following are particularly preferred: stabilized zirconia (Y2O3-ZrO2) containing yttria (hereinafter, may be referred to as "YSZ"); CeO2 doped with at least one selected from the group consisting of Gd, La, Y, Sm, Nd, Ca, Mg, Sr, Ba, Dy, and Yb (among which, in particular, CeO2 doped with Gd (hereinafter, may be referred to as "GDC") and CeO2 doped with Sm); Sc2O3-ZrO2 (hereinafter, may be referred to as "ScSZ"); Sm2O3-CeO2 (hereinafter, may be referred to as "SDC"); LaGaO3; and the like.

[0157] In order to obtain sufficient output characteristics during discharge, the composite metal oxide preferably has a conductivity of 0.01 to 10 S / cm at 1000°C.

[0158] The cermet is preferably a cermet of at least one metal selected from the group consisting of Ni, Pt, Au, Cu, Fe, W, and Ta and a composite metal oxide (particularly the above composite metal oxide). From the viewpoint of reliably obtaining sufficient output characteristics during discharge, a cermet of nickel and a composite metal oxide is preferred, and a cermet of nickel and the above composite metal oxide is particularly preferred.

[0159] Most preferred, in terms of output characteristics, are a cermet of nickel and YSZ (hereinafter sometimes referred to as "Ni / YSZ"), a cermet of nickel and GDC (hereinafter sometimes referred to as "Ni / GDC"), a cermet of nickel and ScSZ (hereinafter sometimes referred to as "Ni / ScSZ"), or a cermet of nickel and SDC (hereinafter sometimes referred to as "Ni / SDC").

[0160] When the cell 10 of the secondary battery 1 of the present invention has multiple negative electrodes, i.e., the first negative electrode 21A and the second negative electrode 21B, as described above, it is desirable to use a material that is prone to carbon deposition as the negative electrode material of the second negative electrode 21B. Examples of the material for the second negative electrode 21B include a cermet of Ni and the composite metal oxide, and a cermet of Fe and the composite metal oxide. As the material for the first negative electrode 21A to be used in combination with the material for the second negative electrode 21B, a negative electrode material which is less prone to carbon deposition than the above-mentioned material for the second negative electrode 21B can be appropriately used.

[0161] The shape and constituent materials of the current collector of the negative electrode 21 are not particularly limited as long as it has electronic conductivity and is chemically and physically stable in the operating temperature range of the secondary battery of the present invention, and the same ones as those used in known solid oxide batteries (SOFCs) can be used.

[0162] The positive electrode 22 of the secondary battery 1 of the present invention includes a positive electrode material, a positive electrode current collector, and the like.

[0163] There are no particular limitations on the composition or shape of the positive electrode material, and materials similar to those generally used in positive electrodes in known solid oxide fuel cells (SOFCs) can be used. For example, materials made of composite metal oxides such as (LaSr)MnO3 (hereinafter sometimes referred to as "LSM") and (LaSr)CoO3 (hereinafter sometimes referred to as "LSC") can be preferably used. Particularly preferred are materials such as La 0.85 Sr0.15 Examples include MnO3.

[0164] The configuration of the current collector of the positive electrode 22 is the same as that of the current collector of the negative electrode 21 described above, and the constituent material and shape are not particularly limited, and the same materials as those used in known solid oxide batteries (SOFCs) can be used.

[0165] The electrolyte 23 is an ionically conductive solid oxide. The electrolyte 23 is a solid oxide that conducts oxide ions (O 2- ) and at the same time functions as a partition to prevent direct contact between the reducing agent (the solid carbon mentioned above) and a gas containing oxygen (e.g., air), and has a dense structure that is gas impermeable. The material constituting this electrolyte 23 is not particularly limited, and any material used in known solid oxide batteries (SOFCs) can be used as appropriate, but it is preferable to compose it from a material that has high oxide ion conductivity, is chemically stable under conditions ranging from the oxidizing atmosphere on the side of the positive electrode 22 to the reducing atmosphere on the side of the negative electrode 21, and is resistant to thermal shock.

[0166] Preferred examples of materials that satisfy these requirements include stabilized zirconia such as yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ); lanthanum gallate; and ceria-based solid solutions.

[0167] In order to obtain sufficient output characteristics during power generation, the conductivity of the electrolyte 4 is preferably 0.01 to 10 S / cm at 1000°C.

[0168] The material forming the electrolyte-free portion 25 inside the reactor 20 is, for example, mullite, alumina, silicon carbide, quartz, or boron nitride. For example, it is desirable to form the electrolyte-free portion 25 from the above-mentioned materials because of the cost reduction and ease of processing.

[0169] The catalyst to be installed in the catalyst installation section 26 inside the reactor 20 may be, for example, a metal supported on glass wool. The metal is preferably a transition metal. Examples of the transition metal include Fe, Ni, Co, W, Ta, Pt, and Cu.

[0170] The material constituting the interconnect material 28 is, for example, La 1-x Sr x CrO3, La 1-x Ca x CrO3 (where x represents any number between 0 and 1).

[0171] The material constituting the support material 30 is, for example, a porous metal such as porous nickel, a porous electronically conductive oxide, or a porous metal / oxide mixed material.

[0172] The material constituting the structure 60 that surrounds the reactor 20 and suppresses heat loss due to radiative heat transfer from the reactor 20 is, for example, a laminated structural material of quartz and a metal such as Ni or Pt.

[0173] The secondary battery of the present invention is repeatedly charged and discharged by utilizing an oxidation-reduction reaction between carbon and carbon dioxide, and carbon (solid carbon) may be separately supplied into the reactor 20 at the beginning of the charge-discharge cycle.

[0174] There is no particular limitation on the method for separately supplying carbon (solid carbon) into the reactor 20, but an example of the method is to introduce an organic compound containing at least carbon and hydrogen as constituent elements into the reactor 20 and allow the thermal decomposition reaction of the organic compound to proceed. Examples of the organic compound include hydrocarbons such as methane, ethane, propane, and butane; and alcohols such as methanol, ethanol, propanol, and butanol. EXAMPLES

[0175] The present invention will be described in more detail below with reference to verification examples. The verification examples described herein are intended to show that the present invention is theoretically possible to implement and that the effects of the present invention described in this specification can be obtained, but do not necessarily show the manner in which the present invention is implemented.

[0176] Verification example 1 (study of negative electrode materials in secondary batteries with multiple negative electrodes) A carbon-air secondary battery (CASB) with multiple anodes was created. The electrolyte was YSZ, and the cathode was LSM / ScSZ. In the reactor, the first anode made of GDC and the second anode made of Ni / GDC were placed opposite the cathode on the electrolyte.

[0177] (Step 1) First, at a temperature of 800°C, the reactor on the negative side was filled with a mixed gas of CO and CO2 (volume ratio of CO:CO2 = 67.6:111), and the valve installed in the reactor was closed to make the reactor a closed system. 111 sccm of oxygen was flowed into the positive electrode (counter electrode) side of the cell to keep the oxygen partial pressure constant (to reduce the effect of voltage changes due to oxygen generation). From this state, a current of 10 mA was applied to the first negative electrode (GDC) and the counter electrode for 90 minutes to charge the battery.

[0178] (Step 2) In step 1, the first negative electrode (GDC) was used to discharge in order to check whether carbon was deposited on the first negative electrode (GDC). After step 1 was completed, the valve installed in the reactor was opened to open the reactor. Ar 189sccm was supplied to the reactor and the remaining CO and CO2 gases were exhausted. While supplying Ar, 0.1mA was applied to the first negative electrode (GDC) and the counter electrode, and discharged until the terminal voltage reached 0.1V. As described in Non-Patent Document 3 by the present inventors, when Ar is supplied at about 200 sccm, no discharge occurs due to gas such as CO.

[0179] (Step 3) In step 1, a second negative electrode (Ni / GDC) was used for discharge to check whether carbon was deposited on the second negative electrode (Ni / GDC). As in step 2, while supplying Ar to the reactor at the same flow rate, a current of 1.0 mA was applied to the second negative electrode (Ni / GDC) and the counter electrode, and the electrodes were discharged until the terminal voltage reached 0.1 V.

[0180] The results are shown in Figure 35. While no discharge occurred between the first negative electrode (GDC) and the counter electrode in step 2, discharge was confirmed between the second negative electrode (Ni / GDC) and the counter electrode in step 3.

[0181] In addition, when the state of the first anode (GDC) and the second anode (Ni / GDC) after charging in step 1 under similar experimental conditions was checked, the first anode (GDC) showed no visible change, whereas black carbon deposits were observed on the second anode (Ni / GDC).

[0182] As described above, it has been shown that by appropriately selecting the materials for the first and second negative electrodes, different negative electrodes can be used for charging and discharging, and carbon deposition on the negative electrode for charging (first negative electrode) can be prevented.

[0183] Verification example 2 (examination of the stability of charging and discharging in a reactor divided into an electrochemical reaction section and a thermochemical reaction section) A carbon-air secondary battery (CASB) was created in which the reactor was divided into an electrochemical reaction section 20A and a thermochemical reaction section 20B, as shown in Fig. 36. The periphery of the electrochemical reaction section 20A and the periphery of the thermochemical reaction section 20B were made to be able to be heated separately by heating means 20C and 20D, respectively.

[0184] (Charging steps) Gas was introduced from the side of the electrochemical reaction section 20A, and the gas that passed through the electrochemical reaction section 20A (negative electrode 21) was sent to the thermochemical reaction section 20B, and the gas that passed through the thermochemical reaction section 20B was exhausted to the outside. Charging was performed at 0.052 A with the temperature of the electrochemical reaction section 20A set to 900° C., the temperature of the thermochemical reaction section 20B set to 670° C., and a mixed gas of 40 sccm of carbon monoxide and 10 sccm of carbon dioxide being supplied to the electrochemical reaction section 20A. The direction of gas flow during the charging step is shown by the solid line in FIG.

[0185] (Discharge step) After the charging step was completed, gas was introduced from the side of the thermochemical reaction section 20B, and the direction of the gas flow was changed so that the gas that had passed through the thermochemical reaction section 20B (catalyst installation section 26) was sent to the electrochemical reaction section 20A, and the gas that had passed through the electrochemical reaction section 20A (negative electrode 21) was exhausted to the outside. The temperature of the electrochemical reaction section 20A was set to 900°C, the temperature of the thermochemical reaction section 20B was set to 670°C, 10 sccm of carbon dioxide was supplied to the thermochemical reaction section 20B, and oxygen was supplied to the positive electrode 22 to maintain a constant oxygen partial pressure. Discharge was performed at 0.052 A. The direction of gas flow during the discharge step is shown by the dashed line in FIG.

[0186] The above charging step, the above discharging step, and an interval step in which neither charging nor discharging was performed constituted one cycle, and this cycle was repeated twice.

[0187] The results are shown in Figure 37. Even after long-term charging and discharging, the voltage remained almost constant during both charging and discharging. In addition, the voltages during the charging and discharging steps were almost the same in the first and second cycles.

[0188] In other words, it was shown that if the inside of the reactor is divided into an electrochemical reaction section and a thermochemical reaction section, and conditions are set such that carbon deposition due to reaction (R2) is likely to occur in the thermochemical reaction section where a catalyst is installed, there is no fluctuation in voltage due to deterioration of the negative electrode. It is presumed that no carbon deposition occurs in the electrochemical reaction area (especially around the negative electrode).

[0189] In Verification Example 2, the purpose of the verification was to prevent deterioration of the negative electrode due to carbon deposition by separating the electrochemical reaction field and the thermochemical reaction field in the reactor 20, and the verification was performed with the reactor 20 as an open system. As described in this specification, by equipping the secondary battery 1 with a heat exchanger, pump, etc., it is possible to circulate a desired amount of gas (carbon monoxide, carbon dioxide) in a closed system in the closed system of the secondary battery 1, thereby creating a situation equivalent to that of Verification Example 2. [Industrial Applicability]

[0190] The secondary battery of the present invention is a carbon-air secondary battery which can secure a large storage capacity, has high charge / discharge efficiency, and has good cycle characteristics, and therefore can be widely used, for example, as a secondary battery for commercial use such as in factories and hospitals, for general households, and for transportation equipment such as automobiles, trains, and ships. [Explanation of symbols]

[0191] 1 Secondary battery 10 Cells 11 Closed system 12 Open system 20. Reactor 20A Electrochemical Reaction Section 20B Thermochemical reaction section 20C heating means 20D heating means 21 Negative electrode 21A first negative electrode 21B Second negative electrode 22 Positive electrode 23 Electrolytes 24 Negative electrode non-installation area 25 Non-electrolyte installation area 26 Catalyst installation part 27 Reactor End 28 Interconnect Materials 29 void 30 Support material 40 Tank 41 Piping 42 Piping 43 Piping 44 Gas flow direction control means 45 Heat exchange promotion means 46 Pressurizing means 47 Pressure reduction means 48 Combustor 50 Modules 51 Gas flow path 52 Gas flow path 60 structure 70 Reservoir 80 Gas ratio adjustment cell 81 Gas ratio adjustment cell negative electrode 82 Positive electrode of gas ratio adjustment cell

Claims

1. The battery has a cell including a negative electrode, a positive electrode, and an electrolyte made of a gas-impermeable and ion-conductive solid oxide disposed in contact with the negative electrode and the positive electrode, During charging, carbon dioxide is electrolyzed on the surface of the negative electrode, carbon is precipitated on the negative electrode side, which is a closed system, and oxygen is generated at the positive electrode from oxide ions that are generated at the negative electrode and permeate the electrolyte. a secondary battery in which, during discharge, oxide ions are generated from oxygen at the positive electrode, and carbon and / or carbon monoxide are electrochemically oxidized on the surface of the negative electrode to generate carbon dioxide, A reactor in which the negative electrode is installed and separated from the outside by the electrolyte, and in which carbon precipitated during charging is stored; and A secondary battery having a structure surrounding the reactor and suppressing heat loss due to radiative heat transfer from the reactor, A secondary battery, characterized in that the inside of the reactor can be pressurized, or the closed system has a pressurizable tank connected to the reactor.

2. A secondary battery as described in claim 1, wherein the closed system has a pressurizable tank connected to the reactor and has a control means for controlling the temperature and / or pressure during the storage and / or supply of carbon dioxide between the reactor and the tank.

3. 2. The secondary battery according to claim 1, wherein gas is continuously circulated within said closed system.

4. 4. The secondary battery according to claim 1, wherein the reactor comprises an electrochemical reaction section in which the negative electrode is disposed, and a thermochemical reaction section in which a catalyst for promoting carbon deposition is disposed, and the electrochemical reaction section and the thermochemical reaction section are connected by a pipe that is a gas flow path.

5. 5. The secondary battery according to claim 4, wherein the gas is continuously circulated between the electrochemical reaction section and the thermochemical reaction section.

6. The secondary battery according to claim 5 , further comprising a means for controlling a flow direction of the gas.

7. 4. The secondary battery according to claim 1, wherein the cell has a plurality of negative electrodes, and during charging, carbon dioxide is electrolyzed on a surface of a first negative electrode and carbon is precipitated on a surface of a second negative electrode, and during discharging, carbon and / or carbon monoxide are electrochemically oxidized on the surface of the second negative electrode to generate carbon dioxide.

8. The secondary battery according to claim 7 , wherein an area of ​​the first negative electrode is larger than an area of ​​the second negative electrode.

9. 4. The secondary battery according to claim 1, further comprising a means for measuring a ratio of carbon dioxide to carbon monoxide within said reactor.

10. 3. The secondary battery according to claim 2, further comprising a heat exchange promoting means for lowering a temperature of the gas and / or a pressurizing means for pressurizing the gas, the heat exchange promoting means being provided in a flow path of the gas flowing from the reactor to the tank.

11. 11. The secondary battery according to claim 2, further comprising a heat exchange promoting means for increasing a temperature of the gas in a flow path of the gas flowing from the tank to the reactor.

12. 4. The secondary battery according to claim 1, wherein a surface of the structure facing the reactor has a mirror structure.

13. 4. The secondary battery according to claim 1, wherein the structure has a vacuum insulation layer.

14. 4. The secondary battery according to claim 1, wherein a catalyst for promoting carbon deposition is provided in a portion of the reactor where no negative electrode is provided and / or a portion of the reactor where no electrolyte is provided.

15. 4. The secondary battery according to claim 1, wherein the reactor is cylindrical and has a bottom surface formed of the electrolyte, the negative electrode is disposed on the electrolyte inside the reactor, and the positive electrode is disposed on the electrolyte outside the reactor at a position corresponding to the negative electrode.

16. 16. The secondary battery according to claim 15, wherein a catalyst for promoting carbon deposition is provided inside the reactor in a portion of the electrolyte on which a negative electrode is not installed and / or in a portion of a side surface of the reactor on the electrolyte side in which an electrolyte is not installed.

17. 4. The secondary battery according to claim 1, wherein the reactor is made of a cylindrical electrolyte, the negative electrode is disposed on the inner surface of the cylinder, and the positive electrode is disposed on the outer surface of the cylinder.

18. 18. The secondary battery according to claim 17, comprising a module in which a gas flow path is provided outside a plurality of reactors.

19. 4. The secondary battery according to claim 1, wherein the reactor is disposed around the electrolyte which is a cylinder, the positive electrode is disposed on the inner surface of the cylinder, and the negative electrode is disposed on the outer surface of the cylinder.

20. 20. The secondary battery according to claim 19, further comprising a module in which a common reactor is disposed around a plurality of the cylinders.

21. 4. The secondary battery according to claim 1, wherein the reactor is cylindrical, the inside and outside of the reactor are separated by a plurality of alternately arranged annular electrolytes and a plurality of annular interconnect materials, the outside of the reactor is provided with a plurality of positive electrodes arranged in contact with both the electrolyte and the adjacent interconnect materials and such that the positive electrodes do not come into contact with each other, and the inside of the reactor is provided with a plurality of negative electrodes arranged in contact with both the electrolyte and the adjacent interconnect materials and such that the negative electrodes do not come into contact with each other, and the positive electrodes and negative electrodes in contact with any electrolyte are in contact with separate interconnect materials on either side of any electrolyte.

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