JP2018006057A - Iron-air battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an iron-air battery system capable of suppressing a decrease in discharge capacity.SOLUTION: An iron-air battery system includes an iron-air battery including a negative electrode including an iron element, an air electrode to which oxygen is supplied, an electrolyte layer disposed between the negative electrode and the air electrode, and a circulation path where the electrolyte circulates. The iron-air battery system also includes a potential control circuit temporally lowering the potential of the negative electrode to -1.2 V (vs. Hg/HgO) or less during discharge.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an iron-air battery system.

  An air battery using oxygen as an active material has many advantages such as high energy density. As an air battery, metal air batteries, such as an iron air battery and an aluminum air battery, are known, for example.

  One of the research subjects related to such a metal-air battery is to suppress a decrease in discharge capacity. In a metal-air battery, current flows as metal atoms in a metal negative electrode elute into the electrolyte as ions during discharge. Therefore, the concentration of metal ions in the electrolytic solution gradually increases with discharge. When the concentration of metal ions in the electrolytic solution becomes sufficiently high, metal oxide or metal hydroxide is deposited on the surface of the metal negative electrode, and the discharge capacity decreases.

In response to this problem, for example, Patent Document 1 discloses a metal-air battery that includes an electrolyte solution circulation structure, and the surface of the electrolyte solution tank includes a metal oxide or hydroxide that is an electrode active material. By having a material, a technique has been proposed in which precipitates are preferentially deposited on a substrate and the deposits are prevented from adhering to an electrode. Here, iron, zinc, and aluminum are disclosed as metal electrodes.

International Publication No. 2015/016101

  However, when iron is used as the negative electrode, iron ions have low solubility and are likely to be deposited on the electrode surface, so the electrode is passivated by the deposit, and the discharge capacity is reduced.

  The main object of the present invention is to provide an iron-air battery system capable of suppressing a decrease in discharge capacity.

  In order to achieve the above object, in the present invention, a negative electrode containing an iron element, an air electrode to which oxygen is supplied, an electrolytic solution layer disposed between the negative electrode and the air electrode, and the electrolytic solution In an iron-air battery system having an iron-air battery provided with a circulation path through which the gas circulates, a potential control circuit for temporarily setting the potential of the negative electrode to −1.2 V (vs. Hg / HgO) or less during discharge It is characterized by having.

  In the iron-air battery system of the present invention, by controlling the potential of the negative electrode to be −1.2 V (vs. Hg / HgO) or less temporarily during discharge, water in the electrolytic solution is decomposed to generate hydrogen. And the generated hydrogen removes the deposit on the negative electrode surface, and as a result, it is possible to suppress a decrease in discharge capacity. Therefore, according to this invention, the iron air battery system which can suppress the fall of discharge capacity can be provided.

It is the schematic which shows the structural example of the iron air battery system which has a circuit and the electric potential control circuit which concerns on embodiment of this invention. It is a flowchart explaining the control aspect which makes the electric potential of a negative electrode below -1.2V (vs.Hg / HgO). It is sectional drawing which shows the structural example of the iron air battery cell which concerns on embodiment of this invention.

  The present invention will be described below with reference to the drawings. In addition, the form shown below is an illustration of this invention and this invention is not limited to the form shown below.

  In the present invention, an iron-air battery is an electrolytic solution in which an iron oxidation reaction is performed in a negative electrode, a reduction reaction of oxygen, which is an active material, is performed in an air electrode, and is disposed between the negative electrode and the air electrode. Refers to a battery through which ions are conducted. The iron-air battery of the present invention may be a primary battery or a secondary battery.

FIG. 1 is a schematic diagram showing a configuration example of an iron-air battery system having a circulation path and a potential control circuit according to an embodiment of the present invention.
As shown in FIG. 1, the iron-air battery system 100 includes an iron-air battery 60, a potential control circuit 30 connected to the negative electrode 11, and a voltage sensor 40 that can detect a voltage. The iron-air battery cell 10 and a circulation path 21 through which the electrolyte solution 14 circulates are connected to the electrolyte layer 13, a tank 22 for containing the electrolyte solution 14 on the circulation path 21, and a circuit for circulating the electrolyte solution The iron-air battery cell 10 is connected to a device 50 that can use the electrical energy generated in the iron-air battery cell 10. The potential control circuit 30 includes a potential control unit 31 and a control command unit 32.

In the iron-air battery system 100, discharge starts in the iron-air battery cell 10 in response to a discharge request from the device 50, and a voltage is detected using the voltage sensor 40. The voltage detection result by the voltage sensor 40 is sent to the control command unit 32 as an output signal. The control command unit 32 is provided with a CPU 32a capable of executing the operation control of the potential control unit 31, and a storage device for the CPU 32a. The CPU 32a is configured by combining a microprocessor unit and various peripheral circuits necessary for its operation, and a storage device for the CPU 32a includes, for example, a ROM 32b for storing programs and various data necessary for operation control of the potential control unit 31, and the CPU 32a. The RAM 32c and the like functioning as a work area are combined. In addition to the configuration, the control command unit 32 in the iron-air battery system 100 functions by combining the CPU 32a with software stored in the ROM 32b. Information (output signal) related to the voltage detected by the voltage sensor 40 reaches the CPU 32a as an input signal via the input port 32d of the control command unit 32. The CPU 32a controls an operation command to the potential control unit 31 via the output port 32e based on the input signal and the program stored in the ROM 32b. That is, in the iron-air battery system 100, the control command unit 32 can function as a signal means, and the potential control unit 31 sets the potential of the negative electrode to −1.2 V (vs) according to the operation command given from the CPU 32a. .Hg / HgO) or less.

FIG. 2 is a flowchart illustrating a control mode in which the potential of the negative electrode is set to −1.2 V (vs. Hg / HgO) or less. The flowchart shown in FIG. 2 is executed by determining that the discharge has started based on the voltage detection result by the voltage sensor 40.
As shown in FIG. 2, it is determined whether or not there is a discharge request from the device 50 in step S1, and if a negative determination is made in step S1, the discharge is terminated. If an affirmative determination is made in step S1, the discharge is continued (step S2), and then it is determined in step S3 whether or not a predetermined discharge time T1 described later has elapsed. If a negative determination is made in step S3, the process returns to step S2. On the other hand, if an affirmative determination is made in step S3, the negative electrode potential is set to -1.2 V (vs. Hg / HgO) or less (step S4), and then the negative electrode potential is -1.2 V (vs. .Hg / HgO) It is determined whether or not a low potential time t2 that is equal to or lower than a predetermined low potential time T2 described later has elapsed. If a negative determination is made in step S5, the process returns to step S4. On the other hand, if a positive determination is made in step S5, the process returns to step S1.

The potential control unit 31 is characterized in that the potential of the negative electrode is set to −1.2 V (vs. Hg / HgO) or less. Specifically, it is connected to the negative electrode 11 and controlled so that the potential of the negative electrode becomes −1.2 V (vs. Hg / HgO) or less according to the operation command of the control command unit 32. Here, setting the potential of the negative electrode to −1.2 V (vs. Hg / HgO) or less is synonymous with setting the state of charge. The potential at the time of control may be equal to or lower than the potential at which water decomposes to generate hydrogen, for example, −1.2 V (vs. Hg / HgO) or lower. Moreover, the electric potential at the time of control should just be larger than -3.0V (vs.Hg / HgO), for example, and it shall be more than -2.0V (vs.Hg / HgO).
Here, the potential of −1.2 V (vs. Hg / HgO) indicates the potential of the negative electrode based on the potential of the Hg / HgO electrode.
The potential control unit 31 may be anything that can control the potential of the negative electrode 11, and examples thereof include a potential / current control device.

The control command unit 32 is characterized by giving an operation command to the potential control unit 31 to temporarily set the negative electrode potential to −1.2 V (vs. Hg / HgO) or less during discharge. Specifically, it is connected to the potential control unit 31 and gives an operation command for temporarily controlling the potential of the negative electrode during the discharge.
The timing for giving an operation command for temporarily setting the potential of the negative electrode to −1.2 V (vs. Hg / HgO) or lower during discharge may be performed before the negative electrode is completely passivated by precipitates. For example, it is preferably at least once every 3 hours, more preferably at least once every 2 hours, and even more preferably at least once every hour. Moreover, the timing which gives an operation command may be performed regularly for every fixed time interval, and may be performed at a different time interval. If the timing for controlling the potential is too small, the removal of the deposit on the negative electrode surface tends to be insufficient, and if it is too large, the discharge tends to be affected.
The average ratio of the time during which the potential of the negative electrode is temporarily reduced to −1.2 V (vs. Hg / HgO) or less during the discharge is determined by the precipitate on the negative electrode surface before the negative electrode is completely passivated by the precipitate. For example, it is preferably 1 to 300 seconds, more preferably 5 to 100 seconds, and further preferably 10 to 60 seconds with respect to 1 hour of discharge. If the average ratio of the time for controlling the potential is too short, the removal of the precipitate on the negative electrode surface tends to be insufficient, and if it is too long, the discharge tends to be affected.
The time when the potential of the negative electrode is set to −1.2 V (vs. Hg / HgO) or lower is sufficient as long as the precipitate on the negative electrode surface can be removed, and is preferably, for example, 1 to 300 seconds. It is more preferably 5 to 100 seconds, and further preferably 10 to 60 seconds. If the time for controlling the potential is too short, the deposit on the negative electrode surface tends to be insufficiently removed, and if it is too long, the discharge tends to be affected.
Therefore, the predetermined discharge time T1 described above is appropriately selected from, for example, 3 hours, 2 hours, or 1 hour. The predetermined low potential time T2 described above is appropriately selected from, for example, 1 to 300 seconds, 5 to 100 seconds, or 10 to 60 seconds. The predetermined discharge time T1 and the predetermined low potential time T2 are stored in advance in the ROM 32b.

The circulation path 21 is usually connected at two locations on the inflow side and the outflow side in the electrolyte layer 13 portion, and the electrolyte layer 13 and the electrolyte layer 13 so as to allow a one-way flow from the inflow side to the outflow side. Set the connection location of.
The circulation path 21 is also connected to the tank 22 at two locations on the inflow side and the outflow side.
During the discharge, the rotational speed of the pump is controlled so that the flow rate of the electrolyte is maintained at 0.1 to 3.0 L / min.
The material of the circulation path other than the electrolytic solution layer 13 and the tank is not particularly limited as long as it is stable to the electrolytic solution. Usually, polyethylene, polypropylene, polyethylene terephthalate, tetrafluoroethylene, Ni, SUS, Cu or the like is used.

The material of the tank 22 is not particularly limited as long as it is stable to the electrolytic solution, but usually polyethylene, polypropylene, polyethylene terephthalate, tetrafluoroethylene, Ni, SUS, Cu or the like is used.

FIG. 3 is a cross-sectional view showing a configuration example of the iron-air battery cell according to the embodiment of the present invention.
As shown in FIG. 3, the iron-air battery cell 10 includes a negative electrode 11, an air electrode 12 provided separately from the negative electrode 11, and an electrolyte layer 13 disposed between the negative electrode 11 and the air electrode 12. A negative electrode current collector 15 connected to the negative electrode 11, an air electrode current collector 16 connected to the air electrode 12, and an exterior body 17 that accommodates these, and a part of the exterior body 17 is water repellent. It is composed of a film 18. The iron-air battery 10 is configured so that the electrolytic solution 14 does not leak from the exterior body 17 using a water repellent film 18 or the like.

The negative electrode 11 contains at least a negative electrode active material.
Examples of the negative electrode active material include iron metal, iron alloy, and iron compound, and iron metal is preferable. Examples of the iron alloy include an alloy with a metal material selected from the group consisting of vanadium, silicon, aluminum, magnesium, zinc, and lithium. The metal other than iron constituting the iron alloy is one kind or two or more kinds. But you can. Examples of the iron compound include FeO, Fe ₃ O ₄ , Fe ₂ O ₃ , FeOOH, Fe (OH) ₂ , Fe (OH) ₃ , iron (III) nitrate, iron (III) chloride oxide, iron oxalate ( III), iron (III) bromide, iron (III) iodide and the like.
The purity of iron when the negative electrode is iron metal is not particularly limited. The lower limit of the elemental ratio of iron contained in the iron metal is preferably 50% or more, particularly 80% or more, more preferably 95% or more, and especially 99.5% or more. Further, the upper limit of the element ratio of iron contained in the iron metal may be 100% or less, 99.999% or less, 99.99% or less, 99 It may be 9% or less.
The iron alloy preferably has an iron content of 50% by mass or more when the mass of the entire alloy is 100% by mass.

The shape of the negative electrode 11 is not particularly limited, and examples thereof include plates, rods, particles, and mesh shapes. In addition, the particle diameter of the particles when the shape is particulate is preferably 1 nm or more, particularly 10 nm or more, more preferably 100 nm or more as the lower limit, and the upper limit is 100 mm or less, particularly 10 mm or less, and further 1 mm or less. Preferably there is.
The average particle diameter of the particles in the present invention is calculated by a conventional method. An example of a method for calculating the average particle size of the particles is as follows. First, a transmission electron microscope (hereinafter referred to as TEM) image or a scanning electron microscope (hereinafter referred to as SEM) image at an appropriate magnification (for example, 50,000 to 1,000,000 times). Then, for a certain particle, the particle diameter when the particle is regarded as spherical is calculated. Calculation of the particle size by such TEM observation or SEM observation is performed for 200 to 300 particles of the same type, and the average of these particles is taken as the average particle size.

The negative electrode 11 includes a negative electrode current collector 15 that collects current from the negative electrode as necessary. The material of the negative electrode current collector 15 is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, copper, and carbon. Examples of the shape of the negative electrode current collector 15 include a foil shape, a plate shape, and a mesh shape. An exterior body described later may have a function as the negative electrode current collector 15.
Further, the negative electrode current collector 15 may have a terminal serving as a connection portion with the outside.

The air electrode 12 contains at least a conductive material.
The conductive material is not particularly limited as long as it has conductivity, and examples thereof include a carbon material, a perovskite-type conductive material, a porous conductive polymer, and a metal body.
The carbon material may have a porous structure or may not have a porous structure, but preferably has a porous structure. This is because the specific surface area is large and many reaction fields can be provided. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon black, carbon nanotube, and carbon fiber.
A metal body can be comprised with the well-known metal stable with respect to electrolyte solution. Specifically, for example, the metal body has a metal layer (coating film) containing at least one metal selected from the group consisting of Ni, Cr, and Al formed on the surface, The whole may be composed of a metal material made of at least one metal selected from the group consisting of Ni, Cr, and Al. The form of the metal body can be a known form such as a metal mesh, a metal foil that has been punched, or a metal foam body.
As content of the electroconductive material in an air electrode, when the mass of the whole air electrode is 100 mass%, for example, it is preferable that it is 10-99 mass%, especially 50-95 mass%.

The air electrode 12 may contain a catalyst that promotes an electrode reaction, and the catalyst may be supported on the conductive material.
As the catalyst, a known catalyst having an oxygen reducing ability that can be used in an iron-air battery can be appropriately used. Examples of the catalyst include at least one metal selected from the group consisting of ruthenium, rhodium, palladium, and platinum; a perovskite oxide containing a transition metal such as Co, Mn, or Fe; a porphyrin skeleton or a phthalocyanine skeleton. Examples thereof include metal coordination organic compounds having inorganic ceramics such as manganese dioxide (MnO2) and cerium oxide (CeO2); and composite materials in which these materials are mixed.
For example, the content of the catalyst in the air electrode is preferably 0 to 90% by mass, and more preferably 1 to 90% by mass, when the mass of the entire air electrode is 100% by mass.

  Examples of a method for producing the air electrode 12 include a method in which the air electrode material such as a conductive material is mixed and rolled, and a method in which a slurry containing the air electrode material and a solvent is applied.

The air electrode 12 includes an air electrode current collector 16 that collects current as necessary. An example of the air electrode current collector 16 is nickel metal. An exterior body 17 to be described later may have a function as the air electrode current collector 16.
In addition, the air electrode current collector 16 may have a terminal serving as a connection portion with the outside.

The electrolyte solution layer 13 disposed between the negative electrode 11 and the air electrode 12 is filled with the electrolyte solution 14. The electrolytic solution layer 13 is connected to a circulation path of the electrolytic solution 14, and the electrolytic solution 14 flowing from the circulation path moves through the electrolytic solution layer 13 at a specific flow rate.

The electrolyte solution 14 is an aqueous solution containing at least a discharge reaction accelerator and an electrolyte compound.
The discharge reaction ^{accelerator, S 2-anion,} SCN ^- _anion, S ^{₂ O 3 2-} anions, _{and, (CH} 3) 2 NCSS ^- as long as it contains at least one anion selected from the group consisting of anionic is not particularly _limited, it preferably contains S ^{₂ O 3 2-} anions. Specific examples of the cation contained in the discharge reaction accelerator include Li ⁺ , K ⁺ , Na ⁺ , Rb ⁺ , Cs ⁺ , and Fr ⁺ , and K ⁺ and Na ⁺ are preferable. The cation contained in the discharge reaction accelerator is a cation of a metal that is electrochemically less basic than iron. Therefore, the cation hardly reacts with iron, which is a negative electrode metal, in the electrolytic solution. Therefore, if it is the said cation, it will be hard to inhibit the preferential adsorption | suction of the said anion to iron contained in a negative electrode metal for discharge reaction promotion.
Specific examples of the discharge reaction accelerator include Na ₂ S ₂ O ₃ , NaSCN, and (CH ₃ ) ₂ NCSSNa, and Na ₂ S ₂ O ₃ is preferable.
The content of the discharge reaction accelerator contained in the electrolytic solution is not particularly limited, but is 0.005 mol.
/ L or more and 0.1 mol / L or less is preferable.

The electrolyte compound is not particularly limited as long as it has solubility in water and expresses desired ionic conductivity, but the aqueous solution is preferably neutral or basic. From the viewpoint of improving reactivity, those that are basic are particularly preferred.
The electrolyte compound preferably contains at least one metal selected from the group consisting of Li, K, Na, Rb, Cs, Fr, Mg, Ca, Sr, Ba, and Ra. Specific examples of the electrolyte compound include LiCl, NaCl, KCl, MgCl ₂ , CaCl ₂ , LiOH, KOH, NaOH, RbOH, CsOH, Mg (OH) ₂ , Ca (OH) ₂ , and Sr (OH) _2. NaOH and KOH are preferable, and KOH is particularly preferable.
The concentration of the electrolyte compound is not particularly limited, but the lower limit is preferably 0.01 mol / L or more, particularly 0.1 mol / L or more, more preferably 1 mol / L or more, and the upper limit is preferably 20 mol / L or less. In particular, it is 10 mol / L or less, and further 8 mol / L or less.
When the concentration of the electrolyte compound is less than 0.01 mol / L, the solubility of the negative electrode metal may be reduced. On the other hand, when the concentration of the electrolyte compound exceeds 20 mol / L, the self-discharge of the iron-air battery is accelerated, and the battery characteristics may be deteriorated.
The pH of the electrolytic solution is preferably 7 or more, more preferably 10 or more, and particularly preferably 14 or more.

The iron-air battery has a separator for ensuring insulation between the air electrode 12 and the negative electrode 11 as necessary. It is preferable that a separator has a porous structure from a viewpoint of hold | maintaining electrolyte solution. The porous structure of the separator is not particularly limited as long as the electrolyte solution can be retained. For example, the separator has a mesh structure in which constituent fibers are regularly arranged, a nonwoven fabric structure in which constituent fibers are randomly arranged, independent holes, and connecting holes. Examples include a three-dimensional network structure. A conventionally well-known thing can be used for a separator. Specific examples include porous films such as polyethylene, polypropylene, polyethylene terephthalate, and cellulose, and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric.
The thickness of a separator is not specifically limited, For example, the range of 0.1-100 micrometers is preferable.
The porosity of the separator is preferably 30 to 90%, and more preferably 45 to 70%. If the porosity is too low, ion diffusion tends to be inhibited, and if it is too high, the strength tends to decrease.

The iron-air battery usually has an exterior body 17 that houses the air electrode 12, the negative electrode 11, the electrolyte layer 13, and the like.
Examples of the shape of the exterior body 17 include a coin type, a flat plate type, a cylindrical type, and a laminate type.
The material of the exterior body 17 is not particularly limited as long as it is stable to the electrolytic solution 14, but a metal body including at least one selected from the group consisting of Ni, Cr, and Al, and polypropylene, polyethylene, and A resin such as an acrylic resin may be used. When the exterior body 17 is a metal body, only the surface of the exterior body 17 may be composed of a metal body, or the entire exterior body 17 may be composed of a metal body.
The exterior body 17 is open to the atmosphere, has a hole for taking in oxygen from the outside, and has a structure in which at least the air electrode can sufficiently come into contact with the atmosphere. A water repellent film 18 or the like may be provided in the oxygen uptake hole.
The water repellent film 18 is not particularly limited as long as the electrolyte solution 14 does not leak and the air can reach the air electrode 12. Examples of the water repellent film 18 include porous fluororesin sheets (PTFE and the like), porous cellulose subjected to water repellent treatment, and the like.
As the oxygen-containing gas supplied to the air electrode 12, air is usually used.

  Examples will be described in more detail below.

<Example 1>
(Preparation of electrodes)
As a working electrode, 0.8 g of steel wool (Bonstar # 0000, a filling rate of approximately 0.8%, manufactured by Nippon Steel Wool Co., Ltd.) was prepared. And the said steel wool was immersed in acetone and ultrasonic cleaning was performed for 10 minutes. Then, a nickel mesh (100 mesh manufactured by Niraco Co., Ltd.) was processed into a box shape having a size of 25 mm × 25 mm × 5 mm, and the steel wool was placed therein.
As a counter electrode, a platinum foil (manufactured by Niraco Co., Ltd.) cut into a size of 30 mm × 30 mm × 0.1 mm was prepared. And the nickel ribbon (made by Nilaco Co., Ltd.) was welded to the said platinum foil, and the said nickel ribbon was used as current collection wiring.
As a reference electrode, an Hg / HgO electrode (manufactured by Interchem Corporation) was prepared.

(Preparation of electrolyte)
First, an 8 mol / L aqueous solution of KOH (manufactured by Wako Pure Chemical Industries, Ltd.) was prepared. And the said aqueous solution was hold | maintained for 8 hours at 25 degreeC in thermostat: LU-113 (made by ESPEC Corporation). Thereafter, Na ₂ S ₂ O ₃ (manufactured by Sigma-Aldrich) was added to the aqueous solution as a discharge reaction accelerator so as to be 0.01 mol / L. Next, the aqueous solution was stirred with an ultrasonic cleaner for 15 minutes. And the said aqueous solution was hold | maintained at 25 degreeC for 3 hours in the thermostat, and the electrolyte solution for iron-air batteries was obtained.

(Production of evaluation cell)
A cell container (volume 30 mL) was prepared, and the working electrode, the counter electrode, and the reference electrode were arranged in the cell container. Furthermore, a potential control unit was connected to the working electrode, and a control command unit was connected to the potential control unit.
Further, a circulation path was arranged so that the electrolyte solution circulated between the electrolyte layer and the tank, and a liquid pump was installed on the circulation path.
The electrolytic solution was put into a tank, a volatilization suppression lid was attached, and an evaluation cell was produced. The liquid pump flow rate was set so that the electrolyte flowed at a flow rate of 1.2 L / min in the electrolyte layer, and the measurement was performed after circulating the electrolyte.

<Comparative Example 1>
An evaluation cell was prepared in the same manner as in Example 1 except that the potential control unit was not connected to the working electrode.

<Comparative example 2>
(Preparation of electrodes)
As a counter electrode, a nickel mesh (100 mesh manufactured by Niraco Co., Ltd.) cut into a size of 25 mm × 25 mm × 5 mm was prepared. And the nickel ribbon (made by Nilaco Co., Ltd.) was welded to the said nickel mesh, and the said nickel ribbon was used as current collection wiring.
A working electrode and a reference electrode were prepared in the same manner as in Example 1.

(Production of evaluation cell)
As an electrolytic solution, 25 mL of the same electrolytic solution as in Example 1 was prepared.
A cell container (volume 30 mL) was prepared, and the working electrode, the counter electrode, and the reference electrode were arranged in the cell container. And 25 mL of each said electrolyte solution was thrown in into the cell container. Furthermore, a lid for suppressing volatilization was attached to each of the above cell containers to produce an evaluation cell.

(Measurement of discharge capacity)
The discharge capacity was measured using the evaluation cells of Example 1 and Comparative Examples 1-2.
First, the working electrode and the counter electrode of the evaluation cell were connected to a potential current controller (Biologic, VMP3). Then, in Example 1 and Comparative Example 1, the potential of the working electrode is maintained at −1.2 V (vs. Hg / HgO) for 90 minutes before discharging, and in Working Example 2, the potential of the working electrode is maintained for 10 minutes. -1.2 V (vs. Hg / HgO), and the oxide film on the iron surface of the working electrode was reduced and removed. Thereafter, in Comparative Example 2 having no circulation path, a decompression process was performed to remove hydrogen generated between the electrodes. In each of Example 1 and Comparative Examples 1 and 2, discharge was performed at a discharge current of 23 mA. Discharge was performed until the potential of the working electrode became 0 V (vs. Hg / HgO), and the discharge capacity was measured. In Example 1, after the discharge was performed for 1 hour, the potential of the working electrode was maintained at −1.2 V (vs. Hg / HgO) for 30 seconds, and then the discharge was continued.
Measurement result of discharge capacity per unit weight of negative electrode active material, Example 1 relative to discharge capacity per unit weight of Comparative Example 2 when the discharge capacity per unit weight of Comparative Example 2 was set to 0%, and Table 1 shows the rate of increase in discharge capacity per unit weight in Comparative Example 1.

  From the results shown in Table 1, it can be seen that the increase rate in Example 1 is significantly improved as compared with Comparative Examples 1 and 2, and the decrease in discharge capacity is suppressed. Further, in Example 1, the discharge capacity per unit weight is significantly larger than the charge capacity obtained by temporarily setting the potential of the negative electrode to −1.2 V (vs. Hg / HgO) or less during discharge. This is considered to be an effect obtained by suppressing the passivation of the electrode by removing the deposit on the negative electrode surface, not by the apparent improvement due to the charging of the treatment.

  As described above, in the iron-air battery system, by controlling the potential of the negative electrode to be −1.2 V (vs. Hg / HgO) or less temporarily during discharge, the reduction in discharge capacity is suppressed. I was able to. The effect is that during the discharge, the potential of the negative electrode is temporarily reduced to −1.2 V (vs. Hg / HgO) or less, whereby water in the electrolytic solution is decomposed and the generated hydrogen precipitates on the negative electrode surface. This is thought to be due to the removal of objects.

10 Iron-air battery cell 11 Negative electrode 12 Air electrode 13 Electrolyte 14 Separator 15 Negative electrode current collector 16 Air electrode current collector 17 Exterior body 18 Water repellent film 21 Circulation path 22 Tank 23 Liquid pump 30 Potential control circuit 31 Potential control section 32 Control command unit 32a CPU
32b ROM
32c RAM
32d Input port 32e Output port 40 Voltage sensor 50 Device 60 Iron-air battery 100 Iron-air battery system

Claims (1)

A negative electrode containing iron element;
An air electrode supplied with oxygen;
An electrolyte layer disposed between the negative electrode and the air electrode;
In an iron-air battery system having an iron-air battery provided with a circulation path through which the electrolyte circulates,
An iron-air battery system comprising a potential control circuit that temporarily lowers the potential of the negative electrode to -1.2 V (vs. Hg / HgO) or less during discharge.

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