Air battery system and method for charging and discharging air secondary battery

Abstract

To provide an air secondary battery system that prevents evaporation of an electrolytic solution, thereby having battery characteristics stable for a long period.SOLUTION: An air battery system 100 comprises: an air secondary battery 2 that accommodates an electrode group 8 including an air electrode 40 and a negative electrode 60 together with an alkaline electrolyte; a pump 3 that supplies air to the air secondary battery 2 when charging and discharging the air secondary battery; and adjustment means 4 that adjusts a dew point of the air. The air secondary battery includes: an air passage 22 through which an airflow passes and acts on the air electrode; an inlet 81A from which air is introduced toward the air passage; and an outlet 82A from which the airflow is exhausted. The adjustment means 4 measures a dew point of the introduced air as a primary-side dew point, measures a dew point of the exhausted airflow as a secondary-side dew point, and adjusts the primary-side dew point based on the secondary-side dew point.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an air battery system and a method for charging and discharging an air secondary battery. [Background technology]

[0002] Air batteries use oxygen from the air as the positive electrode active material and various metals such as Li, Zn, Al, and Mg as the negative electrode. Because they do not require a positive electrode active material inside the battery, they have attracted attention due to their high energy density and ease of miniaturization and lightweight design. Furthermore, air secondary batteries, which can be repeatedly charged and discharged, are expected to be used as driving power sources for electric vehicles and for storing renewable energy. In particular, air secondary batteries, which use hydrogen storage alloys or metallic zinc as the negative electrode and alkaline aqueous solution as the electrolyte, are expected to combine high energy density with safety. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-204300 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional air secondary batteries have been unable to perform stable charge / discharge reactions over long periods due to oxidation and deterioration of the air electrode during charging, capacity loss due to dissolution and precipitation of the negative electrode metal, and carbonic acid deterioration of the electrolyte. Furthermore, the structure and system for supplying the oxygen (air) required for discharge into the battery have not been optimized.

[0005] Furthermore, in air secondary batteries, if the humidity of the supplied air is too low, the electrolyte dries out and the concentration of the alkaline aqueous solution increases, which can lead to increased battery resistance and material degradation due to corrosion reactions. On the other hand, if the humidity of the supplied air is too high, the electrolyte becomes wet and the concentration of the alkaline aqueous solution decreases, which can lead to a decrease in the battery's electrical capacity and electrolyte leakage. The optimal air humidity that does not change the concentration of the electrolyte varies depending on the battery's ambient temperature environment, charging state, deterioration state, and operating conditions of the module in which the battery is incorporated. Therefore, it has been difficult to ensure stable operation over the long term by simply determining the humidity control conditions based on the battery's charge and discharge conditions.

[0006] In view of the above problems, an object of the present invention is to provide an air secondary battery system in which battery characteristics are stable over a long period of time, and a method for charging and discharging an air secondary battery. [Means for solving the problem]

[0007] In order to achieve the above object, the air battery system of the present invention is an air battery system comprising: an air secondary battery that houses an electrode group including an air electrode and a negative electrode together with an alkaline electrolyte; a supply means that supplies air to the inside of the air secondary battery when the air secondary battery is charged or discharged; and an adjustment means that adjusts the dew point of the air, wherein the air secondary battery comprises an air flow path configured so that an air flow passes through and interacts with the air electrode, a supply port through which air is introduced toward the air flow path, and an exhaust port through which the air flow is discharged, and the adjustment means measures the dew point of the introduced air as a primary side dew point, measures the dew point of the discharged air flow as a secondary side dew point, and adjusts the primary side dew point based on the secondary side dew point. [Effects of the Invention]

[0008] According to the air battery system of the present invention, stable battery characteristics can be maintained for a long period of time. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a block diagram showing an air battery system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the air secondary battery shown in FIG. [Figure 3] 1 is a flowchart showing control of the air battery system during charging and discharging of the air secondary battery. [Figure 4] The graph shows the change in cell voltage with respect to the number of charge / discharge cycles. [Figure 5] 10 is a flowchart showing control of the air battery system for an air secondary battery in a dormant state. DETAILED DESCRIPTION OF THE INVENTION

[0010] This embodiment will be described below with reference to the drawings.

[0011] An outline of an air battery system 100 according to the present embodiment is shown in Fig. 1. As shown in Fig. 1, the air battery system 100 includes an air secondary battery 2, a pump 3 that supplies air (oxygen) to the air secondary battery 2, and an adjustment unit 4 that adjusts the temperature and humidity of the air sent to the air secondary battery 2.

[0012] As shown in Fig. 2, an air secondary battery 2 is formed by stacking, for example, three air secondary battery cells (hereinafter referred to as battery cells) 1, connecting them in series, and housing them in a battery case 5. Each battery cell 1 includes, in order from the positive electrode side to the negative electrode side, a flow path plate 20, a water-repellent film 30, an air electrode (positive electrode) 40, a separator 50, a negative electrode 60, and a negative electrode current collector plate 70. The air electrode (positive electrode) 40 faces the negative electrode 60 with the separator 50 interposed therebetween.

[0013] The flow path plate 20 is made of a rectangular stainless steel plate. An air flow path 22 is formed on the surface of the flow path plate 20 facing the air electrode 40 by photoetching. Air that reacts with the air electrode 40 flows in the in-plane direction through the air flow path 22. Furthermore, the flow path plate 20 is plated with nickel to make it conductive. The air flow path 22 is a serpentine-shaped groove in a plan view. The flow path plate 20 also has a supply path 23 that introduces air into the air flow path 22 and a discharge path 24 through which air that has flowed through the air flow path 22 is discharged to the outside. The supply path 23 and the discharge path 24 each penetrate the flow path plate 20 in the thickness direction. The flow path plate 20 is located on the positive electrode terminal plate 11 side of the battery case 5.

[0014] Furthermore, a water-repellent film 30 is fixed to the surface of the flow path plate 20 by a frame 32 together with a gas diffusion film 31. The water-repellent film 30 is a microporous resin film made of polytetrafluoroethylene (PTFE), and allows air flowing through the air flow path 22 to pass to the air electrode 40 while preventing leakage of the alkaline electrolyte on the air electrode 40 side into the air flow path 22. Specifically, the water-repellent film 30 is fixed to the flow path plate 20 without covering the supply path 23 and the discharge path 24, while blocking the openings formed as grooves on the surface of the air flow path 22.

[0015] The gas diffusion membrane 31 is made of a nonwoven fabric made of polyolefin fibers, and distributes the air that flows through the air flow passages 22 and is necessary for the charge / discharge reaction of the air electrode 40 throughout the entire air electrode 40 .

[0016] The frame 32 is made of a rectangular stainless steel plate, and is nickel-plated after photoetching. The frame surface facing the water-repellent film 30 is flat, and the frame 32 fixes the water-repellent film 30 and the gas diffusion film 31 to the flow path plate 20, and the air electrode 40 is enclosed inside the frame 32.

[0017] The air electrode 40 is composed of a conductive electrode plate substrate having numerous pores and an air electrode mixture (positive electrode mixture) held within the pores and on the surface of the electrode plate substrate. Examples of such electrode plate substrates include foamed nickel and nickel mesh. The air electrode mixture contains a redox catalyst, a conductive agent, and a fluororesin. The redox catalyst is not particularly limited as long as it has a dual redox function. A preferred redox catalyst is pyrochlore-type bismuth ruthenium oxide.

[0018] The separator 50 is disposed between the air electrode 40 and the anode 60 to electrically insulate them. The separator 50 is made of a nonwoven fabric made of polyamide fiber or polyolefin fiber that has been subjected to a hydrophilic treatment, and contains an alkaline electrolyte therein. The alkaline electrolyte is a 5 mol / L aqueous solution of potassium hydroxide.

[0019] The negative electrode 60 comprises a conductive negative electrode substrate having numerous pores and a negative electrode mixture held within the pores and on the surface of the negative electrode substrate. Foamed nickel, for example, is used as the negative electrode substrate. The negative electrode mixture contains a hydrogen storage alloy powder made of hydrogen storage alloy particles capable of absorbing and releasing hydrogen as the negative electrode active material, a conductive agent, and a binder. Examples of the conductive agent that can be used include graphite and carbon black. The hydrogen storage alloy that constitutes the hydrogen storage alloy particles include, for example, a rare earth-Mg-Ni based hydrogen storage alloy.

[0020] The negative electrode current collector plate 70 is made of a conductive material, one side of which is electrically connected to the negative electrode 60, and the other side of which is electrically connected to the positive electrode side of an adjacent battery cell 1 connected in series, or to the negative electrode terminal plate 12 of the battery case 5.

[0021] The air electrode 40, separator 50, and negative electrode 60 constitute an electrode group 8, which is fixed to the flow path plate 20 by a gasket 33 to form one battery cell 1. The gasket 33 is made by punching out a rectangular polypropylene sheet and layering an ethylene propylene diene rubber (EPDM) or silicone rubber sheet (not shown) on the edge.

[0022] Furthermore, the supply path 23 and the exhaust path 24 of the flow path plate 20 each extend linearly from the flow path plate 20 to the negative electrode current collector plate 70 within one battery cell 1, forming an air intake path 81 and an exhaust path 82, respectively, within the battery cell 1. In the air intake path 81, air flowing in through an inlet 81A by the pump 3 flows toward the air flow path 22. Meanwhile, in the exhaust path 82, the air flow that has flowed through the air flow path 22 is discharged to the outside from an outlet 82A.

[0023] Three battery cells 1 are connected in series to form an air secondary battery 2, which is housed in a battery case 5. A positive electrode terminal plate 11 is electrically connected to one end of the battery case 5, and a negative electrode terminal plate 12 is electrically connected to the other end. Furthermore, the air battery system 100 has a main control unit 90 that controls the charging and discharging of the air secondary battery 2. The main control unit 90 includes a switch (not shown) that selects charging, discharging, or resting of the air secondary battery 2. In this disclosure, the "resting state of the air secondary battery" refers to a state in which neither charging nor discharging is being performed on the air secondary battery 2.

[0024] The pump 3 serves as a supply means and communicates with the intake passage 81 of the air secondary battery 2 via the primary flow path 41. The pump 3 takes in outside air and discharges it as an air flow toward the air secondary battery 2. In this embodiment, the pump 3 is made up of a compressor that pressurizes and discharges the taken-in air. The pump 3 can discharge air to the air secondary battery 2 not only when the air secondary battery 2 is being charged or discharged, but also when the air secondary battery 2 is at rest.

[0025] The adjustment unit 4 includes, as adjustment means, a primary-side dew point meter 14, a secondary-side dew point meter 15, and a dew point control unit 13. The primary-side dew point meter 14 is disposed in the primary-side flow path 41 between the pump 3 and the inlet 81A of the intake path 81 of the air secondary battery 2. The primary-side dew point meter 14 is composed of an appropriate type of dew point meter, such as a capacitance type or a mirror cooling type, and may be one that calculates the dew point from temperature and relative humidity. The primary-side dew point meter 14 measures the dew point of the air immediately before it is drawn into the inlet 81A of the air secondary battery 2 and outputs the measured dew point to the dew point control unit 13 as the primary-side dew point. The secondary-side dew point meter 15 is composed of the same type of dew point meter as the primary-side dew point meter 14 and is disposed near the outlet 82A of the exhaust path 82 of the air secondary battery 2. The secondary-side dew point meter 15 measures the dew point of the air flow discharged to the outside from the air secondary battery 2, and outputs it as the secondary-side dew point to the dew point control unit 13. The air flow that passes through the secondary-side dew point meter 15 is released to the outside of the air battery system 100. The dew point refers to the surface temperature when an object cools in the air and dew begins to form on the surface (Physics and Chemistry Dictionary), and depends on the temperature of the air flow and the absolute amount of water contained in the air flow per unit volume.

[0026] The dew point control unit 13 is disposed between the pump 3 and the primary dew point meter 14 in the primary flow path 41. The dew point control unit 13 includes a heater, a cooler, a humidifier, and a dryer, and heats or cools, or humidifies or dries the air flow delivered from the pump 3 based on the measured primary dew point and secondary dew point, thereby adjusting the dew point of the air flow, i.e., the primary dew point, and supplies the air to the air secondary battery 2.

[0027] Next, the operation of the air battery system 100 when charging or discharging the air secondary battery 2 will be described with reference to FIG. 3. When the main control unit 9 starts charging or discharging the air secondary battery 2 (step S1), the pump 3 operates to supply an air flow to the air secondary battery 2 (step S2). The supplied air is compressed in a room temperature environment using a compressor, passed through soda lime to remove CO2, and the flow rate is controlled using a mass flow meter. The humidity is adjusted by bubbling the air through temperature-adjusted ion-exchanged water. The temperature of the ion-exchanged water is controlled using a chiller. The air flow with adjusted humidity is introduced into the air secondary battery 2, which is being charged or discharged and placed in a thermostatic chamber at 25°C.

[0028] The air flows through the air flow paths 22 of each battery cell 1, and is discharged from the air secondary battery 2 via the exhaust path 82 and the secondary-side dew-point meter 15. At this time, the following reaction occurs inside the air secondary battery 2. Positive electrode (air electrode): 1 / 2O2 + H2O + 2e - ⇔ 2OH - Negative electrode: 2MH + 2OH - ⇔ 2H2O + 2M + 2e - Total reaction: 2MH + 1 / 2O⇔ 2M + H⇔O In the above formula, M is a hydrogen storage alloy.

[0029] When the air secondary battery 2 is discharged, oxygen is reduced at the air electrode 40 to generate hydroxide ions, which react with protons released from the hydrogen storage alloy in the anode 60, increasing the amount of water contained in the alkaline electrolyte. On the other hand, when the air secondary battery 2 is charged, the opposite reaction to the above occurs. In other words, the concentration of the alkaline electrolyte changes as the air secondary battery 2 is charged and discharged.

[0030] The concentration of alkaline electrolyte also changes depending on the humidity of the airflow itself. In batteries that use an alkaline aqueous solution as the electrolyte, an aqueous solution with a concentration of approximately 10 mol / kg is typically used to increase electrical conductivity. In this case, the partial pressure of the alkaline aqueous solution is approximately 50% of that of pure water. For example, supplying air with a relative humidity of 80% to the battery 2 moistens the electrolyte, while supplying air with a relative humidity of 20% dries the electrolyte. This change in electrolyte concentration can be quantified by measuring the primary-side dew point and the secondary-side dew point (step S3). The primary-side dew point is measured from the airflow immediately before it enters the inlet 81A of the battery case 5. Meanwhile, the secondary-side dew point is measured from the airflow immediately after it is discharged from the outlet 82A of the battery case 5.

[0031] Here, the secondary dew point changes depending on the ambient temperature environment, charging state, degradation state, and the operating conditions of the module in which the battery is installed (for example, the current value during charging and discharging). That is, the closer the battery is to being fully charged, the higher the electrolyte concentration, so the secondary dew point decreases, and when the ambient temperature is high and the charging and discharging rate is fast, the secondary dew point increases as the battery temperature rises.

[0032] Next, the measured primary dew point T1 and secondary dew point T2 are compared (step S4). The difference between the primary dew point T1 and secondary dew point T2 indicates the transfer of water from the supplied air to the alkaline electrolyte, and therefore the state of the alkaline electrolyte can be determined.

[0033] If the secondary dew point T2 is higher than the primary dew point T1, the dew point control unit 13 raises the primary dew point T1 of the air flow so that it is the same as the secondary dew point T2, and supplies the air flow with a higher dew point to the air flow path 22 (step S5).

[0034] On the other hand, if the secondary dew point T2 is lower than the primary dew point T1, the dew point control unit 13 lowers the primary dew point T1 of the air flow so that it is the same as the secondary dew point T2, and supplies the air flow with a lower dew point to the air flow path 22 (step S6).

[0035] Furthermore, when the secondary dew point T2 is the same as the primary dew point T1, the air flow is supplied to the air flow path 22 without the dew point control unit 13 adjusting the primary dew point T1 of the air flow.

[0036] During charging and discharging of the air secondary battery 2, the primary side dew point T1 and the secondary side dew point T2 are measured continuously or at predetermined intervals, and the primary side dew point T1 is adjusted to be the same as the secondary side dew point T2. The operations from step S3 to step S4 onwards are continued until charging and discharging of the air secondary battery 2 is stopped.

[0037] As described above, by adjusting the air flow introduced into the battery cell 1 so that the primary-side dew point T1 is the same as the secondary-side dew point T2, changes in the concentration and absolute amount of the alkaline electrolyte are suppressed, and an increase in the internal resistance of the air secondary battery 2 is suppressed. In other words, by suppressing changes in the alkaline electrolyte concentration over a long period of time, it is possible to extend the battery life.

[0038] Example 1 The charge / discharge cycle was 1 It, which corresponds to 80% of the maximum capacity estimated from the weight of the hydrogen storage alloy contained in the negative electrode. A 0.1 It × 10-hour charge and a 0.2 It discharge (end voltage: 1.2 V) were performed to confirm the battery capacity. Then, 90 cycles of charge / discharge were performed at 0.3 It so that the SOC (State of Charge) of the air secondary battery 2 was in the range of 40% to 60%. At this time, the air flow rate was set to 500 mL / min to achieve an oxygen utilization rate of 20% during discharge. In this example, the average dew point of the air discharged from outlet 82A was 22°C, and the dew point of the air at inlet 81A was adjusted by adjustment unit 4 to 22°C.

[0039] <Comparative Example> The air secondary battery of the example was placed in an environment with an initial temperature of 20°C, and without measuring or adjusting either the primary-side dew point or the secondary-side dew point, it was subjected to 30 charge / discharge cycles, with one cycle consisting of 0.1 It × 10 hours of charging and 0.2 It of discharging, in the same manner as in the example.

[0040] <Result> In the battery 2 of the example, the storage characteristics of the battery 2, including the electrical capacity, remained stable even after 90 charge / discharge cycles. On the other hand, in the battery of the comparative example, the overvoltage increased as the number of charge / discharge cycles increased. Figure 4 shows the change in overvoltage over time for the battery of the example and the battery of the comparative example. In the battery of the example, the dew point of the air flow supplied to the battery was 22°C, which is the average dew point of the exhaust air. On the other hand, in the battery of the comparative example, the dew point of the supplied air was 20°C, but the average dew point at the time of exhaust rose to 22°C. In other words, in the battery of the comparative example, it is estimated that an amount of moisture equivalent to the difference in dew points is exhausted from the alkaline electrolyte. Specifically, the difference in absolute humidity between air with a dew point of 22°C and air with a dew point of 20°C is 2.13 g / m 3 Therefore, in the comparative example, when the air flow is 500 mL / min for 60 hours, 3.83 g of water evaporates from the alkaline electrolyte, which is equivalent to 10% of the weight of the alkaline electrolyte.

[0041] In the comparative example, the battery weight decreased after 30 charge / discharge cycles, and the AC resistance at 1 kHz increased.

[0042] In the comparative example battery without dew point adjustment at the air flow inlet, overvoltage increased after 30 charge / discharge cycles, and 10% by weight of the alkaline electrolyte evaporated. In contrast, the battery of this example exhibited stable storage characteristics even after 90 charge / discharge cycles. The dew point of the air flow was the same at the intake and exhaust passages 81 and 82, suppressing changes in alkaline electrolyte concentration. Thus, by measuring and adjusting the dew point of the air flow at the battery inlet and outlet, the battery characteristics of the air secondary battery can be stabilized over a long period of time. In this example, the dew point of the supplied air flow was adjusted to 22°C as the optimum value. However, the optimum dew point varies depending on the ambient temperature, charge / discharge rate, and SOC. Therefore, it is preferable to appropriately control the dew point of the supplied air flow depending on the charge / discharge conditions of the air secondary battery or the installation environment of the air secondary battery.

[0043] In the above embodiment, the dew point of the exhaust air flow is measured, and the dew point of the introduced air flow is feedback-controlled by the dew point control unit 13 so that the dew point of the introduced air flow is the same as the measured dew point.

[0044] In another embodiment, the air secondary battery can be charged and discharged using the average value of the secondary dew point T2 for a predetermined period, for example, one day, as the target value for the primary dew point T1 for the next predetermined period, for example, the next day.

[0045] Next, the operation of the air battery system 100 when the air secondary battery 2 is in a resting state will be described with reference to FIG.

[0046] Even when the main control unit 9 detects that the air secondary battery 2 is at rest (step S11), it operates the pump 3 to supply an air flow to the air secondary battery 2 (step S12). The supplied air has its dew point adjusted by the adjustment unit 4 and is introduced into the air secondary battery 2, just as when the air secondary battery 2 is charged or discharged.

[0047] Next, the secondary dew point T2 is measured (step S13). The secondary dew point T2 is measured from the airflow immediately after it is discharged from the outlet 82A of the battery case 5. Next, the measured secondary dew point T2 is compared with a predetermined value P (step S14).

[0048] The appropriate concentration of the alkaline electrolyte is set in accordance with the specifications of the air secondary battery 2. A dew point that allows the alkaline electrolyte concentration to be maintained at an appropriate value is set to a predetermined value P. For example, when high battery output is required or when deterioration of components is to be suppressed, the alkaline electrolyte concentration is designed to be low, and therefore the relative humidity of the air discharged from the idle air secondary battery 2 is preferably 60% to 80% RH. On the other hand, when importance is placed on storage characteristics and charge acceptance, the alkaline electrolyte concentration is designed to be high, and therefore the relative humidity of the discharged air is preferably 40% to 60% RH. A dew point that allows these relative humidities to be maintained is set to the predetermined value P.

[0049] If the secondary dew point T2 is greater than a predetermined value P (T2 > P), this indicates that the amount of water vapor contained in the exhaust air is large and the concentration of alkaline electrolyte is high. Therefore, control is performed to lower the secondary dew point T2 by supplying air with a dew point lower than the measured primary dew point T1, for example, dry air (step S15).

[0050] On the other hand, if the secondary dew point T2 is smaller than the predetermined value P (T2 < P), this indicates that the amount of water vapor in the exhausted air is small and the concentration of the alkaline electrolyte is low. Therefore, control is performed so that the secondary dew point T2 is raised by supplying air with a dew point higher than the measured primary dew point T1, for example, moist air (step S16).

[0051] If the secondary dew point T2 is the same as the predetermined value P (T2=P), the primary dew point T1 of the airflow introduced into the air flow path 22 is not adjusted (step S17).

[0052] As described above, by measuring and adjusting the dew point of the air flowing through the air secondary battery 2 in a resting state, the dew point of the air flowing through the air secondary battery 2 can be restored to the initial state before the air secondary battery 2 was first used.

[0053] From the above, when the air secondary battery 2 is in a charging, discharging or resting state, by measuring the dew points on the intake side and exhaust side of the air flow through the air flow path 22 and adjusting the dew point on the intake side, it is possible to prevent evaporation of the alkaline electrolyte contained in the air secondary battery 2 and maintain stable battery characteristics over a long period of time.

[0054] The present invention is applicable not only to the hydrogen-air secondary battery using the hydrogen storage alloy as the negative electrode as described in the above embodiment, but also to any type of air battery using an alkaline electrolyte. [Explanation of symbols]

[0055] 2. Air secondary battery 3 Supply means 4 Adjustment means 22 Air flow path 40 Air electrode 60 negative electrode Entrance 81A 82A Exit 100 Air Battery System

Claims

1. an air secondary battery containing an electrode group including an air electrode and a negative electrode together with an alkaline electrolyte; a supply means for supplying air into the air secondary battery when the air secondary battery is charged or discharged; an adjusting means for adjusting the dew point of the air; An air battery system comprising: the air secondary battery comprises an air flow path configured so that an air flow passes through and interacts with the air electrode, a supply port through which air is introduced toward the air flow path, and a discharge port through which the air flow is discharged; The adjustment means measures the dew point of the introduced air as a primary side dew point, measures the dew point of the discharged air flow as a secondary side dew point, and adjusts the primary side dew point based on the secondary side dew point.

2. 2. The air battery system of claim 1, wherein the adjustment means measures the secondary-side dew point at intervals or continuously over a first period to calculate an average value, and adjusts the primary-side dew point so that the primary-side dew point becomes the same as the average value during a second period after the first period.

3. The air battery system in accordance with claim 1 , wherein the adjusting means adjusts the primary-side dew point so that the primary-side dew point is the same as the secondary-side dew point.

4. 4. The air battery system according to claim 1, wherein the adjustment means, when the air secondary battery is in a resting state, lowers the primary dew point when the secondary dew point is higher than a predetermined value, or raises the primary dew point when the secondary dew point is lower than the predetermined value, thereby bringing the secondary dew point closer to the predetermined value.

5. 5. The air battery system in accordance with claim 4, wherein the predetermined value is a dew point of air at which the concentration of the alkaline electrolyte can be maintained at an appropriate value.

6. A method for charging and discharging an air secondary battery comprising: an electrode group including an air electrode and a negative electrode accommodated together with an alkaline electrolyte; an air flow path configured to allow an air flow to pass through and interact with the air electrode; a supply port through which air is introduced toward the air flow path; and a discharge port through which the air flow is discharged, a primary-side measurement step of measuring the dew point of the introduced air as a primary-side dew point; a secondary-side measurement step of measuring the dew point of the discharged air flow as a secondary-side dew point; and adjusting the primary-side dew point based on the secondary-side dew point.

7. the secondary-side measurement step includes a step of measuring the secondary-side dew point at intervals or continuously over a first period, calculating an average value over the first period, and updating the average value as the secondary-side dew point; The method of claim 6 , wherein the adjusting step further comprises adjusting the primary-side dew point so that the primary-side dew point is the same as the updated secondary-side dew point during a second period after the first period.

8. 7. The method according to claim 6, wherein the adjusting step includes: comparing the secondary-side dew point with a predetermined value when the air secondary battery is in a resting state; and adjusting the primary-side dew point based on a comparison result between the secondary-side dew point and the predetermined value until the secondary-side dew point reaches the predetermined value.

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