Secondary battery, negative electrode material for secondary battery, and method for producing same

Abstract

The present invention addresses the problem of providing a carbon-air secondary battery in which deterioration of a negative electrode (fuel electrode) is suppressed, and which has high charge / discharge efficiency and discharge capacity, has long lifespan, and requires less time and effort for maintenance.　A secondary battery 1 has a cell 20 comprising: a negative electrode 21; a positive electrode 22; and an electrolyte 23 which is composed of a gas-impermeable and ion-conductive solid oxide and installed in contact with the negative electrode 21 and the positive electrode 22. During charging, carbon dioxide is electrolyzed on the surface of the negative electrode 21, and carbon is deposited on the negative electrode 21, which is a closed system. A negative electrode material constituting the negative electrode 21 contains a mixed porous body of a metal and / or an oxide thereof and an ion-conductive oxide. The volume ratio of the metal in the mixed porous body is 30% or more, and the negative electrode material contains an oxygen non-stoichiometric oxide.

Description

Secondary battery, negative electrode material for the secondary battery, and method for producing the same

[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. The present invention also relates to a negative electrode material for such a secondary battery and a method for producing the same.

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

[0003] Solid oxide fuel cells use oxide ions (O ２－ The battery uses a solid oxide with high ion conductivity and high permeability to hydrogen (H ２ ), carbon monoxide (CO), methane (CH ４ ) or other reducing agents to generate electrical energy (see, for example, Patent Document 1).

[0004] Furthermore, a solid oxide electrolyzer cell (SOEC) is known as a water electrolysis device that utilizes the reverse reaction of a solid oxide fuel cell, and a device that can be used as both a solid oxide fuel cell (SOFC) and a solid oxide electrolyzer cell (SOEC) has also been proposed (for example, Patent Document 2).

[0005] To stably supply large amounts of electricity derived from renewable energy, a large-capacity electricity storage technology capable of adjusting the balance between electricity supply and demand is required. As such a technology, the inventors have proposed a carbon / air secondary battery (CASB) (Patent Document 3, Patent Document 4, Non-Patent Document 1). A carbon / air secondary battery is a secondary battery that utilizes a combination of electrochemical and thermochemical reactions of carbon.

[0006] The negative electrode side of a carbon-air secondary battery is a closed system, and carbon and carbon dioxide can be stored inside the closed system. In a carbon-air secondary battery, when charging, carbon dioxide is converted to carbon by an electrochemical reaction at the negative electrode and a thermochemical reaction in the closed system, and carbon is precipitated in the closed system. When discharging, this carbon is used as fuel, converted to carbon dioxide, and stored in the closed system. Therefore, a carbon-air secondary battery can store CO ２ It is emission-free.

[0007] Carbon-air secondary batteries are promising as a compact, large-capacity energy storage technology due to their high theoretical efficiency, theoretical volumetric energy density, and safety. Furthermore, unlike conventional batteries, carbon-air secondary batteries have the advantage that their storage capacity can be increased by increasing the amount of carbon and carbon dioxide stored. This feature makes carbon-air secondary batteries highly promising as a large-capacity energy storage technology.

[0008] The carbon-air secondary battery can be constructed using devices and materials similar to those used in solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). The anode (fuel electrode) is typically made of a mixture (cermet) of a metal such as nickel and an oxide-ion conductive oxide. Nickel acts as a catalyst for the Boudouard reaction (reaction (R2) described below) and also plays a role in conductor of electrons in the fuel electrode, which are necessary for the electrochemical reaction.

[0009] However, metal catalysts such as nickel can cause irreversible anode (fuel electrode) degradation due to carbonization and oxidation. While a higher amount of metal catalyst in the anode (fuel electrode) is preferable to increase the amount of carbon deposition on the anode (fuel electrode), the composition and structure of the metal catalyst and oxide-ion conductor must be controlled to reduce the overvoltage.

[0010] Carbon deposition during charging is inevitable in carbon-air secondary batteries. Therefore, in order to commercialize carbon-air secondary batteries, it is important to prevent the deterioration of durability due to carbon deposition and oxidation on the negative electrode (fuel electrode). There is a need to develop technology to solve this problem.

[0011] Japanese Patent Application Laid-Open No. 9-129256 Japanese Patent Application Laid-Open No. 2010-159458 Japanese Patent No. 7182251 International Publication No. 2024 / 190513

[0012] K. Kameda, S. Manzhos and M. Ihara, J. Power Sources, 516, (2021), 230681

[0013] 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 suppresses deterioration of the negative electrode (fuel electrode), has high charge-discharge efficiency and discharge capacity, has a long life, and requires little maintenance.

[0014] The present inventors have conducted extensive research to solve the above problems and have discovered the following facts, which have led to the completion of the present invention.

[0015] In other words, by controlling the composition and structure of the negative electrode (fuel electrode) of a carbon-air secondary battery to a specific value, deterioration of the negative electrode (fuel electrode) can be suppressed, and the charge-discharge efficiency and discharge capacity of the carbon-air secondary battery can be increased.

[0016] The present invention thus completed is as follows:

[0017] [1] A secondary battery comprising a cell including a negative electrode, a positive electrode, and an electrolyte made of a gas-impermeable and ion-conductive solid oxide placed in contact with the negative electrode and the positive electrode, wherein during charging, carbon dioxide is electrolyzed on the surface of the negative electrode, causing carbon to deposit on the negative electrode side, which forms a closed system, and oxygen is generated at the positive electrode from oxide ions generated at the negative electrode and which have permeated the electrolyte, and during discharging, 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, wherein the reactor in the closed system is a reactor in which the negative electrode is placed and which is separated from the outside by the electrolyte, and which stores carbon deposited during charging, and wherein the negative electrode material constituting the negative electrode contains a mixed porous body of an electronic conductor and an ion conductor, the volume ratio of the electronic conductor to the mixed porous body being 30% or more, and the negative electrode material contains an oxygen-non-stoichiometric oxide.

[0018] [2] The secondary battery according to [1], wherein the mixed porous body contains a metal.

[0019] [3] The secondary battery according to [2], wherein the metal is copper.

[0020] [4] The secondary battery according to [1], wherein the mixed porous body contains an electronically conductive oxide.

[0021] [5] The secondary battery according to [1], wherein a metal and / or an oxide is added to the negative electrode material.

[0022] [6] The secondary battery according to [1], wherein an oxide ion conductive oxide is added to the negative electrode material.

[0023] [7] The secondary battery according to [1], wherein a proton-conductive oxide is added to the negative electrode material.

[0024] [8] The secondary battery according to [7], wherein the proton-conducting oxide is a proton-conducting oxide having a perovskite structure or a perovskite-related structure.

[0025] [9] The secondary battery according to [1], wherein particulate metal and / or oxide is supported on the mixed porous body.

[0026]

[10] The secondary battery according to [9], wherein the oxide supported on the mixed porous body is an oxide ion conductive oxide.

[0027]

[11] The secondary battery according to [9], wherein the oxide supported on the mixed porous body is a proton-conducting oxide.

[0028]

[12] An anode material for a secondary battery according to any one of [1] to [4], comprising a mixed porous body of an electronic conductor and an ionic conductor, wherein the volume ratio of the electronic conductor in the mixed porous body is 30% or more, and the anode material contains an oxygen non-stoichiometric oxide.

[0029]

[13] The negative electrode material for a secondary battery according to any one of [5] to

[11] , characterized in that it contains a mixed porous body of an electronic conductor and an ionic conductor, the volume ratio of the electronic conductor in the mixed porous body being 30% or more, the negative electrode material contains an oxygen non-stoichiometric oxide, and further contains a metal and / or an oxide added to the negative electrode material.

[0030]

[14] A method for producing an anode material according to

[13] , characterized in that the metal and / or oxide is added to the anode material by dripping a precursor solution, inkjet printing, or using a powder slurry.

[0031] According to the present invention, it is possible to provide a carbon-air secondary battery that suppresses deterioration of the negative electrode (fuel electrode), has high charge-discharge efficiency and discharge capacity, has a long life, and requires little maintenance.

[0032] 1 is a schematic diagram showing a reaction in a secondary battery of the present invention. (a) During charging (b) During discharging A conceptual diagram of a cell, reactor, etc. in a secondary battery of the present invention (in the case of a single reactor). A conceptual diagram of a cell, reactor, etc. in a secondary battery of the present invention (in the case of a reactor having an electrochemical reaction section and a thermochemical reaction section). A schematic diagram of a reactor used in each evaluation example. A graph showing the measurement results of charge / discharge characteristics in Evaluation Example 1 (dependence on the volume occupied by Ni in the mixed porous body). A graph showing the measurement results of charge / discharge characteristics in Evaluation Example 1 (dependence on capacity). (a) Coulomb efficiency (b) Graph showing the measurement results of potential during discharge and subsequent charge in Charge / Discharge Efficiency Evaluation Example 2. (a) When the negative electrode (Ni / YSZ negative electrode) prepared in Production Example 2 was used (b) When the negative electrode (Ni / GDC negative electrode) prepared in Production Example 1 was used A graph showing the measurement results of potential during discharge and subsequent charge in Evaluation Example 3. 10A and 10B are graphs showing the results of measuring the charge-discharge characteristics (dependence on capacity) in Evaluation Example 4 (a) when the potential was discharged to 0 V, and (b) when the potential was limited to 0.75 V during discharge. 10B are graphs showing the relationship between the number of cycles and the charge-discharge efficiency in Evaluation Example 7 (a) Coulomb efficiency.

[0033] The present invention will be described below, but the present invention is not limited to the following embodiments and can be practiced with any modifications.

[0034] The secondary battery of the present invention is a carbon / air secondary battery (CASB). The carbon / air secondary battery was developed by the present inventors, and details thereof are described in Patent Document 3, Patent Document 4, and Non-Patent Document 1.

[0035] A schematic diagram of the vicinity of the electrodes of a secondary battery of the present invention is shown in Figure 1. The secondary battery 1 of the present invention has a cell 10 including a negative electrode 21, a positive electrode 22, and an electrolyte 23 made of a gas-impermeable, ion-conductive solid oxide disposed in contact with the negative electrode 21 and the positive electrode 22.

[0036] The negative electrode 21 side of the secondary battery 1 of the present invention is a closed system 11, and carbon and carbon dioxide are stored in 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 22 side is taken into the positive electrode 22 during discharge and participates in the reaction.

[0037] 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 deposited on the negative electrode side, which forms a closed system 11. The specific reaction at the negative electrode 21 during charging is presumed to be as follows.

[0038] CO ２ +2e － → CO+O ２－ (R1) 2CO ←→ CO ２ + C (R2)

[0039] (R1) is a reduction reaction (electrochemical reduction reaction) on the surface of the negative electrode 21. (R2) is a thermochemical reaction between solid carbon, carbon dioxide, and carbon monoxide, known as the Boudouard reaction. From (R1) and (R2), the total negative electrode reaction during charging is as follows:

[0040] CO ２ +4e － → C + 2O ２－ (R3)

[0041] In the case of charging, the overvoltage is generally large, so it is thought to be difficult to electrochemically reduce carbon dioxide directly to carbon (directly causing (R3)). In addition, the overvoltage is also large, so it is thought to be difficult to produce carbon by reducing carbon monoxide produced by (R1) (reaction formula (R4) below). Therefore, the energy efficiency of carbon dioxide electrolysis is low.

[0042] CO + 2e － → C+O ２－ (R4)

[0043] 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.

[0044] The negative electrode 21 side is a closed system 11, and during charging, carbon (solid carbon) does not necessarily deposit only on the surface of the negative electrode 21, but may also deposit in places other than the surface of the negative electrode 21 (such as the wall surface of the closed system). If carbon (solid carbon) deposits on the surface of the negative electrode 21, it may cause deterioration of the negative electrode 21. Therefore, it is desirable to make it easier for carbon to deposit in places other than the surface of the negative electrode 21 as much as possible. In the present invention, the negative electrode 21 side (closed system 11) is divided into an electrochemical reaction section 20A in which an electrode (negative electrode 21) is installed, and a thermochemical reaction section 20B in which a catalyst 26 that promotes carbon deposition and gasification is installed, and is configured to make it easier for carbon to deposit on the catalyst 26.

[0045] During charging, oxide ions (O ２－ ) to oxygen (O ２ ) is produced (reaction (R5) below).

[0046] O ２－ → 1 / 2O ２ +2e － (R5)

[0047] 1B 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).

[0048] 1 / 2O ２ +2e － → O ２－ (R6)

[0049] The side of the positive electrode 22 is usually an open system 12. The oxygen taken into the positive electrode 22 during discharge may be oxygen in the air or pure oxygen supplied from a gas cylinder or the like. From the viewpoint of cost, etc., it is desirable to use oxygen in the air.

[0050] During discharge, carbon dioxide is produced by electrochemically oxidizing carbon and / or carbon monoxide on the surface of the negative electrode 21. The specific reaction at the negative electrode 21 during discharge is presumed to be as follows.

[0051] C+O ２－ → CO + 2e － (R7) C + 2O ２－ → CO ２ +4e － (R8) CO+O ２－ → CO ２ +2e － (R9) 2CO ←→ CO ２ + C (R2)

[0052] (R7) to (R9) are oxidation reactions (electrochemical oxidation reactions) on the surface of the negative electrode 21. (R2) is the thermochemical reaction between the solid carbon and carbon dioxide and carbon monoxide. The total negative electrode reaction during discharge is as follows:

[0053] C + 2O ２－ → CO ２ +4e － (R10)

[0054] During discharge, carbon attached to the surface of the negative electrode 21 is oxidized by oxide ions to produce carbon monoxide and carbon dioxide (reactions (R7) and (R8)). In addition, carbon monoxide is oxidized by oxide ions on the surface of the negative electrode 21 to produce carbon dioxide (reaction (R9)). Furthermore, during discharge, a thermochemical reaction (R2) occurs between solid carbon and carbon dioxide and carbon monoxide.

[0055] During charging, carbon (solid carbon) does not necessarily deposit only on the surface of the negative electrode 21, but may also 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 first converted to carbon monoxide by thermochemical reaction (R2) and then contributes to discharge by reaction (R9). As described above, from the viewpoint of preventing deterioration of the negative electrode 21, it is desirable to facilitate carbon deposition in places other than the surface of the negative electrode 21 during charging. That is, it is desirable that the main reaction pathways at the negative electrode during discharge are (R2) and (R9), rather than (R7) or (R8).

[0056] 2 and 3 are conceptual diagrams showing the cell 10, reactor 20, etc. in the secondary battery 1 of the present invention. 2 and 3 are conceptual diagrams and do not show the specific shapes of the cell 10, reactor 20, etc.

[0057] Fig. 2 is a conceptual diagram of a secondary battery 1 of the present invention having a single reactor 20. Fig. 3 is a conceptual diagram of a secondary battery 1 of the present invention having a reactor 20 consisting of an electrochemical reaction section 20A in which a negative electrode 21 is installed and a thermochemical reaction section 20B in which a catalyst 26 that promotes carbon deposition is installed.

[0058] 3, an electrochemical reaction field where an electrochemical oxidation-reduction reaction occurs at the anode 21 and a thermochemical reaction field where carbon deposition and gasification (Boudouard reaction) occur are separated, and the temperature and pressure of the electrochemical reaction field (electrochemical reaction unit 20A) and the thermochemical reaction field (thermochemical reaction unit 20B) can be controlled separately. The electrochemical reaction unit 20A and the thermochemical reaction unit 20B are connected by a pipe 41, and gas flows between them.

[0059] The present invention is an invention in which the composition and structure of the negative electrode (fuel electrode) of the carbon-air secondary battery 1 are improved, and therefore the present invention is applicable to both the carbon-air secondary battery 1 having the reactor shown in FIG. 2 and the carbon-air secondary battery 1 having the reactor shown in FIG. 3.

[0060] Note that the reactor shown in FIG. 2 does not have a portion specialized for carbon deposition, and therefore carbon is more likely to deposit on the negative electrode, and negative electrode deterioration is more likely to occur, compared to the reactor shown in FIG. 3. That is, when evaluating negative electrode deterioration due to carbon deposition or the like, the reactor shown in FIG. 2 allows evaluation under more severe conditions. All of the examples (evaluation examples) in this specification were evaluated using the type of reactor shown in FIG. 2. The preferred negative electrode materials and configuration obtained by evaluation using the type of reactor shown in FIG. 2 can, of course, also be applied to carbon-air secondary batteries having a reactor of the type shown in FIG. 3.

[0061] The reactor 20 in the closed system 11 of the secondary battery 1 of the present invention has the negative electrode 21 installed inside and is separated from the outside by the electrolyte 23, and is configured to store carbon deposited during charging inside. Note that "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.

[0062] 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.

[0063] 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 by charging, and carbon is easily deposited. In addition, because the negative electrode 21 side is a closed system 11, carbon dioxide generated on the negative electrode 21 side by discharge is returned to carbon by charging. ２ No emissions.

[0064] The secondary battery 1 of the present invention is configured to store carbon generated by charging and carbon dioxide generated by discharging inside a closed system 11 including a reactor 20. The closed system 11 may have a tank for storing carbon dioxide generated by discharging in addition to the reactor 20. Details of such a tank are described in the specification of Patent Document 4.

[0065] The negative electrode material constituting the negative electrode 21 in the secondary battery 1 of the present invention contains a mixed porous body of an electronic conductor and an ionic conductor. Examples of the electronic conductor contained in the mixed porous body include metals and electronically conductive oxides. Examples of the ionic conductor contained in the mixed porous body include ionically conductive oxides. A mixed porous body containing a metal as the electronic conductor and an ionically conductive oxide as the ion conductor is produced, for example, by mixing and sintering powders of a metal and an ionically conductive oxide, and is also called a "cermet."

[0066] Specific examples of metals contained in the mixed porous body include nickel (Ni), platinum (Pt), gold (Au), copper (Cu), iron (Fe), tungsten (W), and tantalum (Ta). The mixed porous body may contain only one of the above metals, or may contain two or more metals.

[0067] An electronically conductive oxide is an oxide that exhibits electronic conductivity depending on the environment, such as the material composition, temperature, and atmosphere (e.g., oxygen partial pressure), and has metallic properties. Specific examples of the electronically conductive oxide contained in the mixed porous body include oxides represented by the following composition formula (A) and oxides represented by the following composition formula (B).

[0068]

[0069] In the composition (A), the meanings of the symbols are as follows:

[0070] A, A', and A'' are alkali metal elements, alkaline earth metal elements, or lanthanoid elements. Specific examples of alkali metal elements include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Specific examples of alkali metal elements include calcium (Ca), strontium (Sr), and barium (Ba). Specific examples of lanthanoid elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). It should be noted that A, A', and A'' are different from one another, and A' and A'' may not exist (that is, x1=0 and x2=0).

[0071] B, B', and B'' are magnesium (Mg), aluminum (Al), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), indium (In), tin (Sn), hafnium (Hf), tantalum (Ta), tungsten (W), platinum (Pt), or gold (Au). Note that B, B', and B'' are different from each other, and B' and B'' may not be present (i.e., y1 = 0 or y2 = 0).

[0072] x1, x2, y1, y2, and δ are numbers that satisfy the following conditions.

[0073] 0≦x1≦1 0≦x2≦1 0≦y1≦1 0≦y2≦1 0≦x1+x2≦1 0≦y1+y2≦1 0≦δ≦0.5

[0074] For example, in Evaluation Example 7 described later, in the composition formula (A), A is lanthanum, A' is strontium, B is chromium, B' is manganese, and A'' and B'' do not exist (x2 = 0, y2 = 0), that is, an oxide, La １－ｘ１ Sr ｘ１ Cr １－ｙ１ Mn ｙ１ O ３－δ (hereinafter, sometimes referred to as "LSCM") is contained in the negative electrode material at 50% (volume basis).

[0075]

[0076] In composition (B), the meanings of the symbols are as follows:

[0077] A, A', A'', B, B' and B'' are the same as those for composition (A).

[0078] n, x1, x2, y1, y2, and δ are numbers that satisfy the following conditions.

[0079] n=1, n=2, or n=3 0≦x1≦n+1 0≦x2≦n+1 0≦y1≦n 0≦y2≦n 0≦x1+x2≦n+1 0≦y1+y2≦n -0.3≦δ≦0.5

[0080] The mixed porous body may contain only one of the above-mentioned electronically conductive oxides, or may contain two or more of the above-mentioned electronically conductive oxides, or may contain both a metal and an electronically conductive oxide.

[0081] A specific example of the ion conductor (ion conductive oxide) contained in the mixed porous body is stabilized zirconia (Y ２ O ３ -ZrO ２ ) (hereinafter, sometimes referred to as "YSZ"), gadolinium (Gd)-doped CeO ２ (hereinafter, sometimes referred to as "GDC"), lanthanum (La)-doped CeO ２ , yttrium (Y) doped CeO ２ , samarium (Sm) doped CeO ２ , neodymium (Nd) doped CeO ２, calcium (Ca) doped CeO ２ , magnesium (Mg) doped CeO ２ , strontium (Sr) doped CeO ２ , barium (Ba) doped CeO ２ , dysprosium (Dy) doped CeO ２ , praseodymium (Pr) doped CeO ２ , europium (Eu) doped CeO ２ , erbium (Er) doped CeO ２ , holmium (Ho) doped CeO ２ , lutetium (Lu) doped CeO ２ , ytterbium (Yb) doped CeO ２ , Sc ２ O ３ -ZrO ２ (hereinafter sometimes referred to as "ScSZ"), Sm ２ O ３ -CeO ２ (hereinafter sometimes referred to as "SDC"), Sr and Mg doped LaGaO ３ , Pr ２ NiO ４ , Y-doped BaCeO ３ The mixed porous body may contain only one of the above ion conductors (ion conductive oxides), or may contain two or more of the above ion conductors (ion conductive oxides).

[0082] The mixed porous body, which is the negative electrode material of the secondary battery 1 of the present invention, is composed of an electronic conductor and an ionic conductor, and the volume ratio of the electronic conductor in the mixed porous body is 30% or more. Furthermore, this ratio is preferably 40% or more, more preferably 45% or more, and particularly preferably 50% or more. Furthermore, this ratio is preferably 90% or less, more preferably 80% or less, and particularly preferably 70% or less. Note that this ratio is expressed as a percentage by dividing the volume occupied by the electronic conductor by the volume of the mixed porous body. Here, the mixed porous body has a large number of pores, and in calculating the above ratio, the volume of the pores is not counted as the "volume of the mixed porous body."

[0083] In addition, some oxides may have both electronic and ionic conductivity (mixed conductors). In the present invention, a mixed conductor is classified as an electronic conductor when the electronic conductivity is higher than the ionic conductivity, and as an ionic conductor when the ionic conductivity is higher.

[0084] When the electron conductor occupies the above volume ratio in the mixed porous body, the secondary battery 1 is likely to have good Coulomb efficiency (the value obtained by dividing the discharged amount of electricity (Ah) by the charged amount of electricity (Ah), expressed as a percentage) and good charge / discharge efficiency (the value obtained by dividing the discharged power (W) by the charged power (W), expressed as a percentage). In particular, when the volume ratio of the electron conductor in the mixed porous body is 50% or more, the Coulomb efficiency and charge / discharge efficiency are unlikely to decrease even after repeated charge / discharge (the cycle characteristics of the secondary battery 1 are likely to be good).

[0085] In the secondary battery 1 of the present invention, in order to reduce overvoltage, it is necessary to maximize the length of the interface (triple-phase boundary, TPB) between the electronic conductor and the ionic conductor. The ratio of electronic conductors to ionic conductors that results in the longest triple-phase boundary is statistically determined by the particle shape (particularly size) and dispersion state of the electronic conductor and the ionic conductor. However, in the secondary battery 1 of the present invention, carbon is deposited on the negative electrode, and the larger the surface area of ​​the catalytic electronic conductor, the greater the amount of carbon deposition. For these reasons, the above-described effects can be achieved by setting the volume ratio of the electronic conductor in the mixed porous body within the above range.

[0086] The negative electrode material of the secondary battery 1 of the present invention contains an oxide with non-stoichiometric oxygen. The term "non-stoichiometric oxygen" refers to a characteristic in which a metal oxide contains metal ions with multiple valences, and the valence of the metal ions changes depending on the environment, such as oxygen partial pressure and temperature, causing the oxide ions in the metal oxide to increase or decrease so as to maintain electrical neutrality.

[0087] For example, cerium (Ce) is Ce ３＋ (trivalent) and Ce ４＋ Since cerium can be in the tetravalent state, GDC containing cerium is an oxide with non-stoichiometric oxygen. ３＋ (trivalent) state, and zirconium (Zr) is Zr ４＋ Since YSZ can only take on the (tetravalent) state, it is not an oxygen non-stoichiometric oxide.

[0088] Since the negative electrode material contains a non-stoichiometric oxide, the secondary battery 1 of the present invention can suppress oxidation of the negative electrode metal even when discharged at a potential at which the negative electrode metal thermodynamically oxidizes, thereby reducing overvoltage and improving robustness during subsequent charging. In contrast, if the negative electrode material does not contain a non-stoichiometric oxide, a large overvoltage will occur during the next charge if the battery is discharged at a potential at which the negative electrode metal oxidizes.

[0089] The negative electrode material of the secondary battery 1 of the present invention can achieve the above-mentioned effects as long as it contains an oxygen non-stoichiometric oxide in some form. For example, the ion conductor (ion conductive oxide) contained in the mixed porous body may be oxygen non-stoichiometric. Alternatively, the oxide added to the negative electrode material, which will be described later, may be oxygen non-stoichiometric. Furthermore, both the ion conductor (ion conductive oxide) contained in the mixed porous body and the oxide added to the negative electrode material may be oxygen non-stoichiometric.

[0090] As described above, the mixed porous body in the secondary battery 1 of the present invention may contain two or more types of ion conductors (ion conductive oxides). When the ion conductors (ion conductive oxides) contained in the mixed porous body have oxygen non-stoichiometry, at least one of the ion conductors (ion conductive oxides) may be an oxygen non-stoichiometric ion conductor (ion conductive oxide) (which can suppress oxidation of the metal of the negative electrode).

[0091] Examples of non-stoichiometric oxygen oxides contained in the negative electrode material of the secondary battery 1 of the present invention include GDC, SDC, Pr ２ NiO ４ , Y-doped BaCeO ３ The negative electrode material may contain only one of the above oxygen non-stoichiometric oxides, or may contain two or more of them.

[0092] Even if the negative electrode material does not contain non-stoichiometric oxygen oxides, the problem of large overvoltage occurring during the next charge can be prevented by adjusting the potential during discharge.

[0093] Specifically, in the secondary battery 1, overvoltage during subsequent charging can be reduced by discharging under conditions where the voltage difference between the reference electrode on the positive electrode 22 side and the negative electrode 21 is equal to or higher than the oxidation potential of the metal contained in the mixed porous body of the negative electrode 21, with the reference electrode (oxygen partial pressure) on the positive electrode 22 side as a reference. In addition, by doing so, deterioration of the negative electrode 21 due to repeated oxidation-reduction of the metal / metal oxide can be suppressed.

[0094] For example, when the metal contained in the mixed porous body of the negative electrode 21 is nickel, the oxidation potential is 0.71 V (relative to an oxygen partial pressure of 0.21 atm), and the above-described effect can be obtained by keeping the potential during discharge at 0.71 V or higher (relative to an oxygen partial pressure of 0.21 atm). This potential differs depending on the type of metal contained in the mixed porous body.

[0095] As described above, the problem of deterioration due to oxidation of the negative electrode 21 is a problem that can occur in all carbon-air secondary batteries. Therefore, it is presumed that the above-mentioned effects can be achieved in all carbon-air secondary batteries by limiting the potential during discharge as described above, regardless of the proportion of metal in the mixed porous body.

[0096] Specific examples of the metals contained in the mixed porous body in the secondary battery 1 of the present invention are given above, but among them, copper is particularly suitable. That is, it is desirable that the mixed porous body in the secondary battery 1 of the present invention contains copper.

[0097] When the mixed porous body in the secondary battery 1 of the present invention contains copper, the efficiency is less likely to decrease (the deterioration rate can be reduced) when the secondary battery 1 of the present invention is repeatedly charged and discharged.

[0098] It is desirable that a metal and / or an oxide be added to the negative electrode material in the secondary battery 1 of the present invention. In particular, it is desirable that an oxide-ion conductive oxide or a proton conductive oxide be added to the negative electrode material in the secondary battery 1 of the present invention.

[0099] As described above, the negative electrode material in the secondary battery 1 of the present invention contains a mixed porous body of a metal and / or its oxide and an ion-conductive oxide, and such a mixed porous body is produced by mixing powders of a metal and an ion-conductive oxide and sintering the mixture.

[0100] For example, a state in which particulate metal and / or oxide is supported on a mixed porous body can be said to be "a state in which a metal and / or oxide is further added to the negative electrode material." That is, the secondary battery 1 of the present invention may have particulate metal and / or oxide supported on the mixed porous body. The particulate oxide supported on the mixed porous body may be an oxide-ion conductive oxide or a proton conductive oxide.

[0101] The phrase "metal and / or oxide added to the negative electrode material" does not necessarily mean that the metal and / or oxide is present on the surface of the mixed porous body, as described above.

[0102] Examples of the proton-conductive oxide added to the negative electrode material include proton-conductive oxides having a perovskite structure or a perovskite-related structure.

[0103] "Perovskite structure" means ABO ３ A is, for example, La, Sr, Ca, Y, Ba, Pr, Ce, K, Na, Sm, Pb, Nd, Gd, Bi, Ag, Cs, Rb, Tl, Cd, Eu, Mg, Dy, Li, or Ho. B is, for example, Co, Cr, Mn, Ni, Ce, Gd, Al, Ti, Zr, Sc, Mg, Ga, Cu, Fe, Yb, Y, Nb, I, Ni, Sr, Bi, In, Ca, Sn, Ta, W, Th, U, Hf, Mo, Lu, Tm, Tb, Dy, Ho, Os, Rh, Ag, Tr, Sb, Zn, Pa, In, Re, or Er.

[0104] The term "perovskite-related structure" refers to a structure in which a perovskite structure or a part thereof (especially, BO) is present in the crystal structure. ６ As a perovskite-related structure, specifically, for example, the Ruddlesden-Popper structure (A ｎ＋１ B ｎ O ３ｎ＋１ ), Brownmillerite structure (A ２ B ２ O ５ ) are listed.

[0105] In the secondary battery 1 of the present invention, the metal and / or oxide added to the negative electrode material may be the same as or different from the metal and / or oxide contained in the mixed porous body produced by mixing and sintering.

[0106] Metals and their oxides are thought to have catalytic properties for adsorption / dissociation reactions, etc. By adding a metal and / or oxide to the negative electrode material of the secondary battery 1 of the present invention, the reaction area at the negative electrode can be increased, which is thought to reduce the overvoltage of the reaction at the negative electrode. Furthermore, the addition of a metal and / or oxide can change the coverage of chemical species adsorbed on the negative electrode surface, particularly on the surface near the three-phase interface, which may reduce the overvoltage.

[0107] The present invention also relates to a negative electrode material for a secondary battery, which contains a mixed porous body of an electronic conductor and an ionic conductor, wherein the volume ratio of the electronic conductor in the mixed porous body is 30% or more, and the negative electrode material contains a non-stoichiometric oxygen oxide (hereinafter, this may be referred to as "negative electrode material A").The present invention also relates to a negative electrode material for a secondary battery, which contains a mixed porous body of an electronic conductor and an ionic conductor, wherein the volume ratio of the electronic conductor in the mixed porous body is 30% or more, the negative electrode material contains a non-stoichiometric oxygen oxide, and further, a metal and / or an oxide is added to the negative electrode material (hereinafter, this may be referred to as "negative electrode material B").

[0108] Furthermore, the present invention also relates to a method for producing the above-mentioned negative electrode material (negative electrode material B), which is characterized in that a metal and / or an oxide is added to the negative electrode material by dropping a precursor solution, ink-jetting, or using a powder slurry.

[0109] These manufacturing methods use a fluid to add metal and / or oxide to the negative electrode material. The use of a fluid, particularly a precursor solution, allows the metal and / or oxide to be distributed throughout the mixed porous body, and by drying and then firing, the metal and / or oxide can be supported on the surface and even inside the negative electrode. In particular, the use of inkjet printing allows the metal and / or oxide to be added more uniformly.

[0110] The negative electrode 21 of the secondary battery 1 of the present invention includes a negative electrode current collector and the like in addition to the negative electrode material described above.

[0111] 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 provided in known solid oxide fuel cells (SOFCs) can be used.

[0112] 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.

[0113] The composition and shape of the cathode material are not particularly limited, and the same materials as those generally used in cathodes of known solid oxide fuel cells (SOFCs) can be used. For example, (LaSr)MnO ３ (hereinafter sometimes referred to as "LSM") system, (LaSr)CoO ３ (hereinafter, sometimes referred to as "LSC")-based composite metal oxide materials can be preferably used. ０．８５ Sr ０．１５ MnO ３ etc.

[0114] 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 provided in known solid oxide fuel cells (SOFCs) can be used.

[0115] The electrolyte 23 is an ion-conductive solid oxide. The electrolyte 23 contains oxide ions (O ２－) and also functions as a partition wall to prevent direct contact between the reducing agent (the aforementioned solid carbon and / or carbon monoxide) and the oxygen-containing gas (e.g., air), and has a gas-impermeable, dense structure. The constituent material of this electrolyte 23 is not particularly limited, and any known material used in solid oxide fuel cells (SOFCs) can be used as appropriate, but it is preferable to form the electrolyte from a material that has high oxide ion conductivity, is chemically stable, and is resistant to thermal shock under conditions ranging from the oxidizing atmosphere on the cathode 22 side to the reducing atmosphere on the anode 21 side.

[0116] 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.

[0117] Furthermore, from the viewpoint of obtaining sufficient output characteristics during power generation, the conductivity of the electrolyte 23 is preferably 0.01 to 10 S / cm at 1000°C.

[0118] The material forming the portion (reactor wall) inside the reactor 20 where the electrolyte 23 is not provided is, for example, mullite, alumina, silicon carbide, quartz, or boron nitride. For example, it is desirable to use the above-mentioned materials because of cost reduction and ease of processing.

[0119] As for more specific shapes of the reactor 20, the cells 10, etc. of the secondary battery 1 of the present invention, the shapes described in the specification of Patent Document 4 can be appropriately adopted.

[0120] The present invention will be explained in more detail below by way of evaluation examples. The evaluation examples described here are intended to demonstrate 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 represent modes for implementing the present invention.

[0121] In the evaluation examples shown in this specification, a carbon-air secondary battery (CASB) having a single reactor (the reactor is not separated into an electrochemical reaction section and a thermochemical reaction section) as shown in FIG. 4 was used.

[0122] <Preparation of a Cell for a Carbon-Air Secondary Battery> Preparation Example 1 (Preparation of a Cell Having a Ni / GDC Negative Electrode) A cell for a carbon-air secondary battery was prepared as follows.

[0123] (1) 8 mol% Y as an electrolyte ２ O ３ -ZrO ２ (8-YSZ; diameter 20 mm, thickness 0.25 mm; Tosoh Corporation) was used. (2) 1 part by mass of NiO powder (Kanto Chemical Co., Ltd.) and 0.4 parts by mass of GDC powder (AGC Seimi Chemical Co., Ltd.) were mixed and stirred overnight in a benchtop ball mill. (3) A solvent for the electrode paste was prepared consisting of α-terpineol (Kanto Chemical Co., Ltd.), dibutyl phthalate (Fujifilm Wako Pure Chemical Industries, Ltd.), Marialim (registered trademark; NOF Corporation) as a dispersant, and ethyl cellulose (Fujifilm Wako Pure Chemical Industries, Ltd.). (4) The dried NiO / GDC powder was mixed with the solvent to prepare a negative electrode (fuel electrode) paste. (5) The negative electrode (fuel electrode) paste was applied to one side of the electrolyte and sintered at 1300°C for 4 hours to form a negative electrode (fuel electrode). (6) The positive electrode (air electrode) paste was prepared by adding the above solvent to LSM powder (AGC Seimi Chemical Co., Ltd.). (7) The positive electrode (air electrode) paste was applied to the side of the electrolyte opposite to the surface on which the negative electrode (fuel electrode) was formed, and sintered at 1200°C for 4 hours. (8) To improve current collection, Pt paste (TR-7907; Tanaka Kikinzoku Kogyo Co., Ltd.) was applied to the positive electrode (air electrode). The negative electrode (fuel electrode) and positive electrode (air electrode) each had a working electrode and a reference electrode, each with an area of ​​approximately 0.52 cm. ２ , 0.16 cm ２ It was.

[0124] In the negative electrode of the cell prepared as described above, NiO in the negative electrode was reduced to Ni in a power generation experiment using hydrogen, which will be described later, and the volume ratio of Ni to GDC in the negative electrode became Ni:GDC = 50:50.

[0125] Production Example 1' (Preparation of Cell Having Ni / GDC Negative Electrode) A carbon-air secondary battery cell was prepared in the same manner as in Production Example 1, except that the amount of GDC powder relative to the NiO powder was changed in (2) of Production Example 1. The volume ratio of Ni to GDC in the negative electrode was in the range of Ni:GDC = 30:70 to 80:20.

[0126] Production Example 2 (Preparation of Cell Having Ni / YSZ Negative Electrode) A carbon-air secondary battery cell was prepared in the same manner as in Production Example 1, except that the powders used in (2) of Production Example 1 were changed to 1 part by mass of NiO powder (manufactured by Kanto Chemical Co., Inc.) and 0.4 parts by mass of YSZ powder (manufactured by Tosoh Corporation).

[0127] Production Example 3 (Preparation of a Cell with a Ni / YSZ Negative Electrode Containing SZY) A 1 mol / L SZY precursor solution was prepared by dissolving 1 mol of strontium nitrate powder (Kanto Chemical Co., Ltd.), 0.95 mol of zirconium chloride octahydrate powder (Kanto Chemical Co., Ltd.), and 0.05 mol of yttrium nitrate hexahydrate powder (Kanto Chemical Co., Ltd.) in ion-exchanged water. After carrying out the steps up to (5) of Production Example 2, the SZY precursor solution was added dropwise to the prepared Ni / YSZ negative electrode and sintered at 1300°C for 4 hours. Subsequently, steps (6) and beyond of Production Example 2 were carried out to prepare a carbon-air secondary battery cell. In the cell's negative electrode, the amount of NiO relative to SZY was SZY:NiO = 1:14 (mass ratio).

[0128] Production Example 4 (Preparation of Cell Having Cu / GDC Negative Electrode) A carbon-air secondary battery cell was prepared in the same manner as in Production Example 1, except that the powders used in (2) of Production Example 1 were changed to 1 part by mass of CuO powder (manufactured by Kanto Chemical Co., Ltd.) and 0.4 parts by mass of GDC powder (AGC Seimi Chemical Co., Ltd.).

[0129] Production Example 5 (Fabrication of Cell Having Ni-Added Cu / GDC Negative Electrode) A carbon-air secondary battery cell was fabricated in the same manner as in Production Example 4, except that after (4) in Production Example 4, a 0.5 mol / L aqueous solution of nickel nitrate was dropped onto the negative electrode and dried.

[0130] <Fabrication of Carbon-Air Secondary Battery and Operation Test> The fabricated cell was placed in an apparatus and an operation test was carried out as follows.

[0131] (1) Electrode materials and the like were placed in the device shown in Figure 3. A gold mesh (Sanwa Metal Co., Ltd.) was used as the current collector for the negative electrode (fuel electrode), and a platinum mesh (Sanwa Metal Co., Ltd.) was used as the current collector for the positive electrode (air electrode). (2) A platinum wire (0.3 mm diameter; Sanwa Metal Co., Ltd.) was used as the lead wire. Current control was performed using a power supply (Advantest Corporation), and potential measurements were performed using a digital multimeter (Advantest Corporation). (3) As an operational test to confirm the performance of the secondary battery (cell), a power generation experiment was conducted using 1% humidified hydrogen at 900°C. (4) 200 cm of hydrogen was applied to the negative electrode (fuel electrode). ３ / min and oxygen 1cm ３ / min, and the positive electrode (air electrode) was supplied with 100 cm of oxygen. ３ / min was supplied.

[0132] <Charge-Discharge Cycle of Carbon-Air Secondary Battery> A charge-discharge cycle was carried out by an oxidation-reduction reaction between carbon and carbon dioxide as follows.

[0133] (1) After hydrogen power generation, the temperature was lowered to 800°C in 1 hour, and the negative electrode (fuel electrode) side was purged with argon. (2) Next, 200 sccm of carbon dioxide was supplied for 5 minutes, and the negative electrode (fuel electrode) side was purged with carbon dioxide. (3) All the cocks on the negative electrode (fuel electrode) side were closed, and the space on the negative electrode (fuel electrode) side was made into a closed system. (4) 100 cm of oxygen was supplied to the positive electrode (air electrode). ３ / min. (5) This state was considered the initial state, and charge / discharge cycle operations were performed. (6) The charge / discharge cycle operations were performed at 800°C. (7) The current value was kept constant at 52 mA, the charging time was 60 minutes, and discharging was performed at a current value of 52 mA until the potential reached 0 V.

[0134] <Evaluation of Carbon-Air Secondary Batteries> Evaluation Example 1 (Volume Proportion of Ni in Ni / GDC Negative Electrode) The results of charge / discharge for carbon-air secondary batteries having the negative electrodes (Ni / GDC negative electrodes) prepared in Production Example 1 and Production Example 1′ are shown in FIGS. 5 and 6.

[0135] When the volume fraction of Ni in the Ni / GDC negative electrode was 50% or more, the decrease in efficiency (Coulombic efficiency and charge-discharge efficiency) after repeated charge-discharge cycles was effectively suppressed (Fig. 5). Furthermore, although the efficiency decreased as the capacity above 2 V increased, the highest Coulombic efficiency was observed when the volume fraction of Ni was 50% (Fig. 6(a)). When the volume fraction of Ni was 80%, the charge-discharge efficiency was high in the large capacity range where the voltage was above 2 V (Fig. 6(b)).

[0136] Evaluation Example 2 (Overvoltage when a negative electrode material having an oxygen non-stoichiometric oxide was used) In a carbon-air secondary battery having the negative electrode (Ni / GDC negative electrode) prepared in Production Example 1 and a carbon-air secondary battery having the negative electrode (Ni / YSZ negative electrode) prepared in Production Example 2, the change in potential when <1> discharging was performed and then <2> charging was performed is shown in Figure 7. The charge and discharge conditions were as follows: charging time was 30 minutes, and 100 cm3 of air was applied to the positive electrode. ３ 7A shows the results when the negative electrode (Ni / YSZ negative electrode) prepared in Production Example 2 was used, and FIG. 7B shows the results when the negative electrode (Ni / GDC negative electrode) prepared in Production Example 1 was used.

[0137] In the case of a carbon-air secondary battery with a Ni / YSZ negative electrode, a large overvoltage (the difference between the charging potential and the theoretical electromotive force) occurred at the beginning of charging, whereas in the case of a carbon-air secondary battery with a Ni / GDC negative electrode, the overvoltage could be suppressed to a low level. That is, the overvoltage could be suppressed to a low level by containing an oxygen non-stoichiometric oxide in the negative electrode material.

[0138] Evaluation Example 3 (Overvoltage when potential during discharge is suppressed) In Evaluation Example 2, a carbon-air secondary battery having the negative electrode (Ni / YSZ negative electrode) prepared in Production Example 2 was used, and the potential during <1> discharge was limited to 0.75 V (based on the reference electrode (oxygen partial pressure) on the positive electrode 22 side), followed by <2> charging, was measured. Figure 8(b) shows the change in potential during this period. Figure 8(a) shows the case where <1> discharge was performed to 0 V, and Figure 8(a) and Figure 7(a) are the same.

[0139] <1> When the potential during discharge was limited to 0.75 V (based on the reference electrode (oxygen partial pressure) on the positive electrode 22 side), the overvoltage during the initial stage of charge could be kept low. That is, even when the negative electrode material did not contain a non-stoichiometric oxygen oxide, by keeping the potential during discharge at or above the oxidation potential (0.71 V (relative to an oxygen partial pressure of 0.21 atm)) of the metal (nickel) contained in the mixed porous body of the negative electrode 21, the overvoltage during subsequent charge could be kept low, just as in the case when the negative electrode material contained a non-stoichiometric oxygen oxide.

[0140] Evaluation Example 4 (Charge-Discharge Characteristics When an Oxide is Added to the Negative Electrode Material) The results of charge-discharge for a carbon-air secondary battery having the negative electrode (Ni / YSZ negative electrode) prepared in Production Example 2 and a carbon-air secondary battery having the negative electrode (Ni / YSZ negative electrode with SZY added) prepared in Production Example 3 are shown in Figure 9. The charge-discharge conditions were a charging time of 30 minutes, and 100 cm3 of air was applied to the positive electrode. ３ The test was the same as in Evaluation Example 1 except that 1000 kJ / min was supplied.

[0141] It was confirmed that when SZY (oxide) was added to the negative electrode, the efficiency (Coulomb efficiency and charge / discharge efficiency) and the output density were improved compared to when SZY was not added.

[0142] Evaluation Example 5 (Charge / Discharge Characteristics When a Copper-Containing Negative Electrode is Used) Charging and discharging were performed using a carbon-air secondary battery having the negative electrode (Cu / GDC negative electrode) prepared in Production Example 4 and a carbon-air secondary battery having the negative electrode (Ni / GDC negative electrode) prepared in Production Example 1.

[0143] The values ​​of the Coulombic efficiency, charge / discharge efficiency, and power density at the 20th cycle were calculated as relative values ​​to those at the 1st cycle, and the results are shown in Table 1. This suggests that when the mixed porous body in the negative electrode contains copper, a decrease in efficiency is unlikely to occur even with repeated charge / discharge.

[0144]

[0145] Evaluation Example 6 (Charge-Discharge Characteristics When a Metal is Added to the Negative Electrode Material) Charging and discharging were performed using a carbon-air secondary battery having the negative electrode (Cu / GDC negative electrode) prepared in Production Example 4 and a carbon-air secondary battery having the negative electrode (Cu / GDC negative electrode with Ni added) prepared in Production Example 5.

[0146] The maximum values ​​of the coulombic efficiency, charge / discharge efficiency, and power density were calculated for each carbon-air secondary battery, and the results are shown in Table 2.

[0147]

[0148] Evaluation Example 7 (Charge / Discharge Characteristics When the Electronic Conductor is an Electronically Conductive Oxide (LSCM)) A carbon secondary battery having a single reactor as shown in FIG. 4 was fabricated, in which the anode (fuel electrode), cathode (air electrode), and electrolyte were made of the following materials.

[0149] ・Negative electrode (fuel electrode) La ０．７５ Sr ０．２５ Cr ０．５ Mn ０．５ O ３－δ and Ce ０．９ Gd ０．１ O ２－δ (Volume ratio 1:1) Positive electrode (air electrode) La ０．８ Sr ０．２ MnO ３－δ and (Sc ２ O ３ ) ０．１ (CeO ２ ) ０．０１ (ZrO2) ０．８９ (mass ratio 1:1) ・Electrolyte (Y ２ O ３ ) ０．０８ (ZrO ２ ) ０．９６ (Thickness 0.25 mm)

[0150] Using the above carbon secondary battery, a charge-discharge cycle was performed at 800° C. The current value during charging was constant at 52 mA, the charging time was 45 minutes, and the battery was discharged at a current value of 52 mA until the potential between the working electrodes reached 0 V. The results are shown in FIG.

[0151] The secondary battery of the present invention is used, for example, as a secondary battery for business use such as in factories and hospitals, for general households, and for transportation equipment such as automobiles, trains, and ships.

[0152] REFERENCE SIGNS LIST 1 secondary battery 10 cell 11 closed system 12 open system 20 reactor 20A electrochemical reaction section 20B thermochemical reaction section 21 negative electrode 22 positive electrode 23 electrolyte 26 catalyst 41 piping

Claims

1. A secondary battery comprising a cell comprising a negative electrode, a positive electrode, and an electrolyte made of a gas-impermeable, ion-conductive solid oxide placed in contact with the negative electrode and the positive electrode; during charging, carbon dioxide is electrolyzed on the surface of the negative electrode, depositing carbon on the negative electrode side, which forms a closed system, and oxygen is generated at the positive electrode from oxide ions generated at the negative electrode and which have permeated the electrolyte; during discharging, 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; the reactor in the closed system is a reactor in which the negative electrode is placed and separated from the outside by the electrolyte, and which stores carbon deposited during charging; the negative electrode material comprising the negative electrode contains a mixed porous body of an electronic conductor and an ion conductor, the volume ratio of the electronic conductor to the mixed porous body being 30% or more, and the negative electrode material contains an oxide with non-stoichiometric oxygen.

2. The secondary battery according to claim 1, wherein the mixed porous body contains a metal.

3. The secondary battery according to claim 2, wherein the metal is copper.

4. The secondary battery according to claim 1, wherein the mixed porous body contains an electronically conductive oxide.

5. The secondary battery according to claim 1, wherein a metal and / or an oxide is added to the negative electrode material.

6. The secondary battery according to claim 1, wherein an oxide ion conductive oxide is added to the negative electrode material.

7. The secondary battery according to claim 1, wherein a proton-conducting oxide is added to the negative electrode material.

8. The secondary battery according to claim 7, wherein the proton-conducting oxide is a proton-conducting oxide having a perovskite structure or a perovskite-related structure.

9. The secondary battery according to claim 1, wherein particulate metal and / or oxide is supported on the mixed porous body.

10. The secondary battery according to claim 9, wherein the oxide supported on the mixed porous body is an oxide-ion conductive oxide.

11. The secondary battery according to claim 9, wherein the oxide supported on the mixed porous material is a proton-conductive oxide.

12. A negative electrode material for a secondary battery according to any one of claims 1 to 4, comprising a mixed porous body of an electronic conductor and an ionic conductor, wherein the volume ratio of the electronic conductor in the mixed porous body is 30% or more, and the negative electrode material contains an oxygen non-stoichiometric oxide.

13. A negative electrode material for a secondary battery according to any one of claims 5 to 11, comprising a mixed porous body of an electronic conductor and an ionic conductor, the volume ratio of the electronic conductor in the mixed porous body being 30% or more, the negative electrode material containing an oxygen non-stoichiometric oxide, and further comprising a metal and / or an oxide added to the negative electrode material.

14. A method for producing an anode material according to claim 13, characterized in that the metal and / or oxide is added to the anode material by dripping a precursor solution, inkjet printing, or using a powder slurry.

Images