Charging system for flow-type metal-air batteries and flow-type metal-air batteries

Abstract

This invention provides a charging system for flow-type metal-air batteries and a flow-type metal-air battery that can detach negative electrode active material particles from the negative electrode without consuming a large amount of power and are less prone to degradation. [Solution] The charging system for a flow-type metal-air battery comprises: a first layer having a first flow path formed therein; a positive electrode facing the first flow path; a second layer having a second flow path formed therein; a negative electrode facing the second flow path; a separator separating the first flow path and the second flow path from each other; a positive electrode liquid flowing through the first flow path; a negative electrode liquid flowing through the second flow path; and a control device that controls at least one selected from the group consisting of the flow velocity of the negative electrode liquid and the current flowing between the positive electrode and the negative electrode, based on at least one selected from the group consisting of the voltage applied between the positive electrode and the negative electrode and the liquid supply pressure of the negative electrode liquid.

Description

[Technical Field]

[0001] This disclosure relates to a charging system for flow-type metal-air batteries and to flow-type metal-air batteries. [Background technology]

[0002] Patent Document 1 discloses a system for generating metal particles. In this system, metal particles are generated on the surface of a cathode by electrolysis of a solution containing molten metal. When the formed metal particles have reached a sufficient size, they are removed from the surface of the cathode by a scraper or other suitable means (paragraphs 0014 and 0057). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent No. 7470351 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the system disclosed in Patent Document 1, a scraper or other suitable means must be moved along the surface of the cathode in order to remove metal particles from the cathode surface. Therefore, problems arise such as the consumption of power required to move the scraper or other suitable means, and the deterioration of the system due to the movement of the scraper or other suitable means along the surface of the cathode. For example, problems include wear and deterioration of the scraper or other suitable means, wear and deterioration of the cathode, and deterioration of the system due to clogging by metal particles that could not be removed from the surface of the cathode.

[0005] One aspect of this disclosure has been made in view of this problem. One aspect of this disclosure aims to provide, for example, a charging system for a flow-type metal-air battery and a flow-type metal-air battery that can detach negative electrode active material particles from the negative electrode without consuming a large amount of power and that are less prone to degradation. [Means for solving the problem]

[0006] A charging system for a flow-type metal-air battery according to a first aspect of the present disclosure comprises: a first layer having a first flow channel formed therein; a positive electrode facing the first flow channel; a second layer having a second flow channel formed therein; a negative electrode facing the second flow channel; a separator separating the first flow channel and the second flow channel from each other; a positive electrode fluid flowing through the first flow channel; a negative electrode fluid flowing through the second flow channel; and a control device that controls at least one selected from the group consisting of the flow velocity of the negative electrode fluid and the current flowing between the positive electrode and the negative electrode, based on at least one selected from the group consisting of a voltage applied between the positive electrode and the negative electrode and the fluid supply pressure of the negative electrode fluid.

[0007] A flow-type metal-air battery according to a second aspect of the present disclosure comprises a charging system for a flow-type metal-air battery according to a first aspect of the present disclosure and a discharge unit for a flow-type metal-air battery, wherein the control device controls at least one selected from the group consisting of the flow velocity and the current based on the discharge depth of the discharge unit for the flow-type metal-air battery. [Brief explanation of the drawing]

[0008] [Figure 1] This figure schematically illustrates a flow-type metal-air battery according to the first embodiment. [Figure 2] This is an exploded perspective view schematically illustrating a rechargeable cell provided in the flow-type metal-air battery of the first embodiment. [Figure 3] This is a schematic cross-sectional view illustrating a rechargeable cell provided in the flow-type metal-air battery of the first embodiment. [Figure 4A] This graph shows examples of the time variation of the current flowing between the positive electrode and the negative electrode of a charging cell in the flow-type metal-air battery of the first and fourth embodiments. [Figure 4B] This graph shows an example of the time change in the flow velocity of the negative electrode fluid in the second flow channel of the second layer of the charging cell provided in the first and fourth embodiments of the flow-type metal-air battery. [Figure 5] It is a flowchart showing the flow of processing performed by a control unit provided in the flow-type metal-air battery of the first embodiment. [Figure 6A] It is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of the charging cell provided in the flow-type metal-air battery of the first modification of the first embodiment and the first modification of the fourth embodiment. [Figure 6B] It is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow path of the second layer of the charging cell provided in the flow-type metal-air battery of the first modification of the first embodiment and the first modification of the fourth embodiment. [Figure 7A] It is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of the charging cell provided in the flow-type metal-air battery of the second embodiment and the fifth embodiment. [Figure 7B] It is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow path of the second layer of the charging cell provided in the flow-type metal-air battery of the second embodiment and the fifth embodiment. [Figure 8] It is a flowchart showing the flow of processing performed by a control unit provided in the flow-type metal-air battery of the second embodiment. [Figure 9A] It is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of the charging cell provided in the flow-type metal-air battery of the third embodiment. [Figure 9B] It is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow path of the second layer of the charging cell provided in the flow-type metal-air battery of the third embodiment. [Figure 10] It is a flowchart showing the flow of processing performed by a control unit provided in the flow-type metal-air battery of the third embodiment. [Figure 11A] It is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of the charging cell provided in the flow-type metal-air battery of the first modification of the third embodiment and the first modification of the sixth embodiment. [Figure 11B]A graph showing an example of the temporal change in the flow velocity of the negative electrode liquid in the second flow path of the second layer of the charging cell provided in the flow-type metal-air battery of the first modification of the third embodiment and the first modification of the sixth embodiment. [Figure 12A] A graph showing an example of the temporal change in the current flowing between the positive electrode of the charging cell and the negative electrode of the charging cell provided in the flow-type metal-air battery of the second modification of the third embodiment and the second modification of the sixth embodiment. [Figure 12B] A graph showing an example of the temporal change in the flow velocity of the negative electrode liquid in the second flow path of the second layer of the charging cell provided in the flow-type metal-air battery of the second modification of the third embodiment and the second modification of the sixth embodiment. [Figure 13] A flowchart showing the flow of processing performed by the control unit provided in the flow-type metal-air battery of the second modification of the third embodiment. [Figure 14] A diagram schematically illustrating the flow-type metal-air battery of the fourth embodiment. [Figure 15] A flowchart showing the flow of processing performed by the control unit provided in the flow-type metal-air battery of the fourth embodiment. [Figure 16] A flowchart showing the flow of processing performed by the control unit provided in the flow-type metal-air battery of the fifth embodiment. [Figure 17] A flowchart showing the flow of processing performed by the control unit provided in the flow-type metal-air battery of the sixth embodiment. [Figure 18] A flowchart showing the flow of processing performed by the control unit provided in the flow-type metal-air battery of the second modification of the sixth embodiment. [Figure 19] A diagram showing the content of processing performed by the control unit provided in the flow-type metal-air battery of the seventh embodiment. [Figure 20] A diagram showing the content of processing performed by the control unit provided in the flow-type metal-air battery of the seventh embodiment. [Figure 21] A diagram showing the content of processing performed by the control unit provided in the flow-type metal-air battery of the seventh embodiment. [Figure 22] This figure shows the processing performed by the control unit provided in the flow-type metal-air battery of the seventh embodiment. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0010] 1. First Embodiment 1.1 Flow-type metal-air battery Figure 1 is a schematic diagram illustrating a flow-type metal-air battery according to the first embodiment.

[0011] The flow-type metal-air battery 1 of the first embodiment shown in Figure 1 absorbs oxygen gas 11 from the surrounding air when discharging. When the flow-type metal-air battery 1 is charged, it releases oxygen gas 12 into the surrounding air.

[0012] The flow-type metal-air battery 1 is a flow-type zinc-air battery. Therefore, the negative electrode active material in the flow-type metal-air battery 1 is zinc. However, the flow-type metal-air battery 1 may be a flow-type metal-air battery other than a flow-type zinc-air battery. Therefore, the negative electrode active material in the flow-type metal-air battery 1 may be a metal other than zinc. Examples of metals other than zinc include cadmium, lithium, sodium, magnesium, lead, tin, aluminum, or iron. The metal constituting the metal species may consist only of the main component metal, or it may consist of an alloy of the main component metal and minor components. The metal species can be either a metal or an oxide. Whether the metal species is a metal or an oxide is determined according to the progress of the discharge reaction or the charge reaction.

[0013] As shown in Figure 1, the flow-type metal-air battery 1 comprises a positive electrode liquid 21, a negative electrode liquid 22, a storage unit 23, a discharge unit 24, a charging unit 25, and a control device 26.

[0014] 1.2 Positive electrode solution As shown in Figure 1, the positive electrode solution 21 includes the first electrolyte solution 31.

[0015] The first electrolyte 31 is an aqueous potassium hydroxide solution. The first electrolyte 31 may be an aqueous solution other than an aqueous potassium hydroxide solution, or an electrolyte other than an aqueous solution.

[0016] The water contained in the first electrolyte 31 is a reactant of the charging reaction that occurs in the charging section 25.

[0017] 1.3 Negative electrode solution As shown in Figure 1, the negative electrode solution 22 includes reduced negative electrode active material particles 41a, oxidized negative electrode active material particles 41b, negative electrode active material ions 42, and a second electrolyte 43.

[0018] As described above, the flow-type metal-air battery 1 is a flow-type zinc-air battery. Therefore, the negative electrode active material particles 41a in the reduced state, the negative electrode active material particles 41b in the oxidized state, and the negative electrode active material ions 42 are all zinc species. The negative electrode active material particles 41a in the reduced state are metallic zinc (Zn) particles, and the negative electrode active material particles 41b in the oxidized state are zinc oxide particles (ZnO), and the negative electrode active material particles 41a in the reduced state and the negative electrode active material particles 41b in the oxidized state are dispersed in the second electrolyte 43. Therefore, the negative electrode liquid 22 has a slurry-like consistency. The negative electrode active material particles 41a in the reduced state have a particle size of, for example, several μm, and the negative electrode active material particles 41b in the oxidized state have a particle size of, for example, several tens to several hundreds of nm. The negative electrode active material ions 42 are zincate ions (Zn(OH)4) 2- ) is dissolved in the second electrolyte 43.

[0019] The second electrolyte 43 is an aqueous potassium hydroxide solution. The second electrolyte 43 may be an aqueous solution other than an aqueous potassium hydroxide solution, or an electrolyte other than an aqueous solution.

[0020] The negative electrode active material ions 42 are reactants of the charging reaction that occurs in the charging section 25. The reduced negative electrode active material particles 41a are products of the charging reaction that occurs in the charging section 25.

[0021] 1.4 Storage Section The storage section 23 stores the negative electrode liquid 22. The storage section 23 has outlets 23a, inlets 23b, outlets 23c and inlets 23d. Outlets 23a and 23c allow the negative electrode liquid 22 to flow out. Inlets 23b and 23d allow the negative electrode liquid 22 to flow in.

[0022] 1.5 Discharge section The discharge unit 24 absorbs oxygen gas 11 from the surrounding air. Negative electrode liquid 22 flows into the discharge unit 24 from the storage unit 23. The discharge unit 24 uses the absorbed oxygen gas 11 and the incoming negative electrode liquid 22 to participate in a discharge reaction that generates discharge power, and then discharges the negative electrode liquid 22 that has participated in the discharge reaction back into the storage unit 23. The discharge unit 24 uses the reduced negative electrode active material particles 41a contained in the oxygen gas 11 and negative electrode liquid 22 to participate in the discharge reaction, eliminating the reduced negative electrode active material particles 41a and generating negative electrode active material ions 42.

[0023] As shown in Figure 1, the discharge unit 24 includes piping 51, a pump 52, piping 53, a discharge cell 54, and piping 55.

[0024] The piping 51 guides the negative electrode liquid 22 from the outlet 23a of the storage unit 23 to the inlet 52a of the pump 52. In this way, the piping 51 allows the negative electrode liquid 22 that has flowed out from the outlet 23a to flow into the inlet 52a.

[0025] Pump 52 discharges the negative electrode fluid 22 that has flowed into its inlet 52a from its outlet 52b. In doing so, pump 52 generates a flow of negative electrode fluid 22. As a result, pump 52 sends the negative electrode fluid 22 from the storage unit 23 to the discharge cell 54.

[0026] The piping 53 guides the negative electrode fluid 22 from the outlet 52b of the pump 52 to the inlet 54a of the discharge cell 54. In this way, the piping 53 allows the negative electrode fluid 22 that has flowed out from the outlet 52b to flow into the inlet 54a.

[0027] The discharge cell 54 absorbs oxygen gas 11 from the surrounding air. The discharge cell 54 discharges the negative electrode liquid 22 that has flowed into the inlet 54a of the discharge cell 54 from the outlet 54b of the discharge cell 54. At the same time, the discharge cell 54 involves the absorbed oxygen gas 11 and the incoming negative electrode liquid 22 in the discharge reaction, and discharges the negative electrode liquid 22 that has been involved in the discharge reaction from the outlet 54b. The discharge cell 54 outputs discharge power generated by the discharge reaction.

[0028] The piping 55 guides the negative electrode fluid 22 from the outlet 54b of the discharge cell 54 to the inlet 23b of the storage unit 23. In this way, the piping 55 allows the negative electrode fluid 22 that has flowed out from the outlet 54b to flow into the inlet 23b.

[0029] 1.6 Discharge Cell As shown in Figure 1, the discharge cell 54 comprises a layer 61, a negative electrode liquid 62, a positive electrode 63, a separator 64, and a negative electrode 65.

[0030] A channel 61a is formed in layer 61. The channel 61a extends from the inlet 54a of the discharge cell 54 to the outlet 54b of the discharge cell 54. Therefore, the channel 61a allows the negative electrode liquid 22 that flows into the inlet 54a to pass through, and the negative electrode liquid 22 that has passed through to flow out from the outlet 54b.

[0031] The negative electrode fluid 62 flows through the channel 61a of layer 61. The negative electrode fluid 62 is part of the negative electrode fluid 22 provided in the flow-type metal-air battery 1.

[0032] The positive electrode 63 comes into contact with the air surrounding the discharge cell 54. As a result, the positive electrode 63 is supplied with oxygen gas 11 contained in the air surrounding the discharge cell 54. This causes an oxygen reduction reaction, represented by equation (1), to occur at the positive electrode 63.

[0033] O2 + 2H2O + 4e- →4OH - (1)

[0034] The positive electrode 63 faces the flow path 61a of the layer 61 through the separator 64. As a result, the positive electrode 63 transfers OH, which is a product of the oxygen reduction reaction represented by formula (1), to the negative electrode liquid 62 flowing through the flow path 61a via the separator 64. - for delivery.

[0035] The negative electrode 65 faces the flow path 61a of the layer 61. As a result, the negative electrode 65 comes into contact with the negative electrode liquid 62 flowing through the flow path 61a. Thereby, in the negative electrode 65, an oxidation reaction of metallic zinc represented by formula (2) and formula (3) occurs.

[0036] Zn + 4OH - →Zn(OH)4 2- + 2e - (2) Zn(OH)4 2- →ZnO + H2O + 2OH - (3)

[0037] Due to the oxygen reduction reaction in the positive electrode 63 and the oxidation reaction of metallic zinc in the negative electrode 65, the overall reaction represented by formula (4) occurs in the discharge cell 54.

[0038] 2Zn + O2 → 2ZnO (4)

[0039] Therefore, the discharge cell 54 discharges when metallic zinc changes to zinc oxide.

[0040] 1.7 Charging section In the charging section 25, the negative electrode liquid 22 flows in from the storage section 23. The charging section 25 causes the inflowing negative electrode liquid 22 to participate in a charging reaction for regenerating the negative electrode liquid 22, and discharges the negative electrode liquid 22 that has participated in the charging reaction to the storage section 23. The charging section 25 causes the negative electrode active material ions 42 contained in the negative electrode liquid 22 to participate in the charging reaction, eliminates the negative electrode active material ions 42, and generates reduced negative electrode active material particles 41a.

[0041] As shown in Figure 1, the charging unit 25 includes piping 71, pump 72, piping 73, piping 74, pump 75, piping 76, power supply 77, charging cell 78, piping 79, and piping 80.

[0042] The piping 71 guides the positive electrode 21 from a supply source (not shown) to the inlet 72a of the pump 72. In this way, the piping 71 allows the positive electrode 21 that has flowed out of the supply source to flow into the inlet 72a.

[0043] Pump 72 causes the positive electrode liquid 21 that has flowed into the inlet 72a of pump 72 to flow out through the outlet 72b of pump 72. In doing so, pump 72 generates a flow of positive electrode liquid 21. As a result, pump 72 delivers the positive electrode liquid 21 from its supply source to the charging cell 78.

[0044] The piping 73 guides the cathode liquid 21 from the outlet 72b of the pump 72 to the inlet 78a of the charging cell 78. In this way, the piping 73 allows the cathode liquid 21 that has flowed out from the outlet 72b to flow into the inlet 78a.

[0045] The piping 74 guides the negative electrode liquid 22 from the outlet 23c of the storage unit 23 to the inlet 75a of the pump 75. In this way, the piping 74 allows the negative electrode liquid 22 that has flowed out from the outlet 23c to flow into the inlet 75a.

[0046] Pump 75 causes the negative electrode fluid 22 that has flowed into its inlet 75a to flow out through its outlet 75b. In doing so, pump 75 generates a flow of negative electrode fluid 22. As a result, pump 75 sends the negative electrode fluid 22 from the storage unit 23 to the charging cell 78. The flow direction of pump 75 can also be reversed to cause reverse flow.

[0047] The piping 76 guides the negative electrode fluid 22 from the outlet 75b of the pump 75 to the inlet 78b of the charging cell 78. In this way, the piping 76 allows the negative electrode fluid 22 that has flowed out from the outlet 75b to flow into the inlet 78b.

[0048] Power supply 77 inputs charging power to the charging cell 78.

[0049] The charging cell 78 discharges the positive electrode liquid 21 that has flowed into the inlet 78a of the charging cell 78 from the outlet 78c of the charging cell 78, and discharges the negative electrode liquid 22 that has flowed into the inlet 78b of the charging cell 78 from the outlet 78d of the charging cell 78. At the same time, the charging cell 78 involves the incoming positive electrode liquid 21 and negative electrode liquid 22 in a charging reaction caused by the charging power, discharges the positive electrode liquid 21 that has participated in the charging reaction from the outlet 78c, discharges the negative electrode liquid 22 that has participated in the charging reaction from the outlet 78d, and releases the oxygen gas 12 generated by the charging reaction into the air surrounding the charging cell 78.

[0050] The piping 79 guides the cathode electrolyte 21 from the outlet 78c of the charging cell 78 to the source of the cathode electrolyte 21. In this way, the piping 79 allows the cathode electrolyte 21 that has flowed out from the outlet 78c to flow into the source of the cathode electrolyte 21.

[0051] The piping 80 guides the negative electrode fluid 22 from the outlet 78d of the charging cell 78 to the inlet 23d of the storage unit 23. In this way, the piping 80 allows the negative electrode fluid 22 that has flowed out from the outlet 78d to flow into the inlet 23d.

[0052] 1.8 rechargeable cells Figure 2 is an exploded perspective view schematically illustrating a rechargeable cell provided in the flow-type metal-air battery of the first embodiment. Figure 3 is a cross-sectional view schematically illustrating a rechargeable cell provided in the flow-type metal-air battery of the first embodiment.

[0053] As shown in Figures 2 and 3, the charging cell 78 comprises a first layer 91, positive electrode liquid 92, positive electrode 93, current-carrying plate 94, gasket 95, second layer 96, negative electrode liquid 97, negative electrode 98, current-carrying plate 99, gasket 100, separator 101, gasket 102, and gasket 103.

[0054] The first layer 91 has a rectangular frame shape. Therefore, the first layer 91 has an opening surface 91p, an opening surface 91q, an end surface 91a, and an end surface 91c. The opening surfaces 91p and 91q are on opposite sides. The end surfaces 91a and 91c are on opposite sides. The first layer 91 may have a frame shape other than a rectangular frame shape.

[0055] A first channel 91e is formed in the first layer 91.

[0056] The first flow channel 91e of the first layer 91 is exposed to the opening surface 91p and the opening surface 91q, and has openings 91pe and 91qe on the opening surface 91p and the opening surface 91q, respectively.

[0057] The first flow channel 91e of the first layer 91 is exposed to the end faces 91a and 91c, and has an inlet 78a and an outlet 78c at the end faces 91a and 91c, respectively. Therefore, the first flow channel 91e extends from the inlet 78a to the outlet 78c. Thus, the first flow channel 91e allows the positive electrode liquid 92 that flows into the inlet 78a to pass through, and the positive electrode liquid 21 that has passed through to flow out from the outlet 78c.

[0058] The inlet 78a and outlet 78c of the charging cell 78 are located on the lower and upper sides, respectively. Therefore, the first flow path 91e of the first layer 91 guides the positive electrode liquid 92 from below to above. The inlet 78a may be located at a position other than the lower side, and the outlet 78c may be located at a position other than the upper side.

[0059] The positive electrode fluid 92 flows through the first channel 91e of the first layer 91. The positive electrode fluid 92 is part of the positive electrode fluid 21. As described above, the inlet 78a and outlet 78c of the charging cell 78 are located on the lower and upper sides, respectively. Therefore, the flow direction of the positive electrode fluid 92 in the first channel 91e is from bottom to top.

[0060] If the flow direction of the positive electrode liquid 92 is from top to bottom, the positive electrode liquid 92 will flow out of the first channel 91e of the first layer 91 even before the first channel 91e is completely filled with the positive electrode liquid 92. Therefore, it may not be possible to completely fill the first channel 91e with the positive electrode liquid 92. On the other hand, if the flow direction of the positive electrode liquid 92 is from bottom to top, the positive electrode liquid 92 will overflow from the first channel 91e after the first channel 91e has been completely filled with the positive electrode liquid 92. Therefore, the first channel 91e can be completely filled with the positive electrode liquid 92.

[0061] The oxygen gas 12 generated at the positive electrode 93 moves not only from bottom to top due to buoyancy, but also from bottom to top along with the flow of the positive electrode liquid 92. This promotes the discharge of oxygen gas 12 from the charging cell 78.

[0062] The positive electrode 93 has a rectangular plate shape. The positive electrode 93 is placed on the opening surface 91p of the first layer 91. As a result, the positive electrode 93 closes the opening 91pe of the first layer 91 and faces the first flow channel 91e of the first layer 91. As a result, the positive electrode 93 comes into contact with the positive electrode liquid 92 flowing through the first flow channel 91e. As a result, the oxidation reaction of water represented by equation (5) occurs in the positive electrode 93.

[0063] 4OH - →O2+2H2O+4e - (5)

[0064] Therefore, the charging cell 78 generates oxygen gas 12 through the oxidation reaction of water at the positive electrode 93. The generated oxygen gas 12 is discharged from the charging cell 78.

[0065] The positive electrode 93 consists of a metal, a spinel-based conductive oxide, a perovskite-based conductive oxide, etc. The metal is foamed nickel, etc. The spinel-based conductive oxide includes nickel, cobalt, etc.

[0066] The conductive plate 94 has a rectangular plate shape. The conductive plate 94 is placed on the opening surface 91p of the first layer 91, superimposed on the positive electrode 93. As a result, the conductive plate 94 contacts the positive electrode 93 and forms a current supply path to the positive electrode 93.

[0067] The gasket 95 is sandwiched between the opening surface 91p of the first layer 91 and the positive electrode 93 and the conductive plate 94, and liquid-tightly seals the space between the opening surface 91p of the first layer 91 and the positive electrode 93 and the conductive plate 94.

[0068] The second layer 96 has a rectangular frame shape. Therefore, the second layer 96 has an opening surface 96p, an opening surface 96q, an end surface 96b, and an end surface 96d. The opening surfaces 96p and 96q are on opposite sides. The end surfaces 96b and 96d are on opposite sides.

[0069] A second channel 96e is formed in the second layer 96.

[0070] The second flow channel 96e of the second layer 96 is exposed to the opening surface 96p and the opening surface 96q, and has openings 96pe and 96qe on the opening surface 96p and the opening surface 96q, respectively.

[0071] The second channel 96e of the second layer 96 is exposed to end faces 96b and 96d, and has an inlet 78b and an outlet 78d at end faces 96b and 96d, respectively. Therefore, the second channel 96e extends from the inlet 78b to the outlet 78d. Thus, the second channel 96e allows the negative electrode liquid 97 that has flowed into the inlet 78b to pass through, and the negative electrode liquid 97 that has passed through to flow out from the outlet 78d.

[0072] The inlet 78b and outlet 78d of the charging cell 78 are located on the lower and upper sides, respectively. Therefore, the second flow path 96e of the second layer 96 guides the negative electrode liquid 97 from below to above.

[0073] The negative electrode fluid 97 flows through the second channel 96e of the second layer 96. The negative electrode fluid 97 is part of the negative electrode fluid 22. As described above, the inlet 78b and outlet 78d of the charging cell 78 are located on the lower and upper sides, respectively. Therefore, the flow direction of the negative electrode fluid 97 in the second channel 96e is from bottom to top.

[0074] If the flow direction of the negative electrode fluid 97 is from top to bottom, the negative electrode fluid 97 will flow out of the second channel 96e of the second layer 96 even before the second channel 96e is completely filled with the negative electrode fluid 97. Therefore, it may not be possible to completely fill the second channel 96e with the negative electrode fluid 97. On the other hand, if the flow direction of the negative electrode fluid 97 is from bottom to top, the negative electrode fluid 97 will overflow from the second channel 96e after the second channel 96e has been completely filled with the negative electrode fluid 97. Therefore, the second channel 96e can be completely filled with the negative electrode fluid 97.

[0075] The negative electrode 98 has a rectangular plate shape. The negative electrode 98 is placed on the opening surface 96p of the second layer 96. As a result, the negative electrode 98 closes the opening 96pe of the second layer 96 and faces the second channel 96e of the second layer 96. As a result, the negative electrode 98 comes into contact with the negative electrode liquid 97 in the second channel 96e. As a result, zincate ions Zn(OH)4, which are produced by the oxidation reaction of metallic zinc represented by formulas (2) and (3), are formed at the negative electrode 98. 2- A negative electrode solution containing and / or zinc oxide (ZnO) is supplied to the negative electrode 98. This causes a reduction reaction to metallic zinc, represented by equations (6) and (7), to occur at the negative electrode 98.

[0076] ZnO + H2O + 2OH - →Zn(OH)4 2- (6) Zn(OH)4 2- +2e - →Zn+4OH - (7)

[0077] Therefore, the charging cell 78 generates reduced negative electrode active material particles 41a through a reduction reaction with metallic zinc at the negative electrode 98. The generated reduced negative electrode active material particles 41a adhere to the negative electrode 98.

[0078] The negative electrode 98 is made of a conductive material. The conductive material consists of carbon material and resin.

[0079] The conductive plate 99 has a rectangular plate shape. The conductive plate 99 is placed on the opening surface 96p of the second layer 96, superimposed on the negative electrode 98. As a result, the conductive plate 99 contacts the negative electrode 98 and forms a current supply path to the negative electrode 98.

[0080] The gasket 100 is sandwiched between the opening surface 96p of the second layer 96 and the negative electrode 98 and the conductive plate 99, and liquid-tightly seals the space between the opening surface 96p of the second layer 96 and the negative electrode 98 and the conductive plate 99.

[0081] The separator 101 has a sheet-like shape. The separator 101 is flexible. The separator 101 is placed on the opening surface 91q of the first layer 91. In this way, the separator 101 closes the opening 91qe of the first layer 91 and faces the first flow path 91e of the first layer 91. The separator 101 is also placed on the opening surface 96q of the second layer 96. In this way, the separator 101 closes the opening 96qe of the second layer 96 and faces the second flow path 96e of the second layer 96.

[0082] The separator 101 is sandwiched between the first layer 91 and the second layer 96. This separates the first channel 91e of the first layer 91 and the second channel 96e of the second layer 96 from each other. The separator 101 prevents the reduced negative electrode active material particles 41a and the oxidized negative electrode active material particles 41b from passing through. As a result, the separator 101 suppresses the movement of the reduced negative electrode active material particles 41a and the oxidized negative electrode active material particles 41b from the negative electrode liquid 97 to the positive electrode liquid 92.

[0083] Separator 101 has high ionic conductivity. As a result, separator 101 has high ionic conductivity. - It allows the hydroxide ions OH to pass through. - This allows the liquid to move from the negative electrode liquid 97 to the positive electrode liquid 92.

[0084] In the reduction reaction to metallic zinc at the negative electrode 98, i.e., the electrodeposition reaction of metallic zinc, the non-uniformity of the current distribution may cause dendritic metallic zinc to grow from the negative electrode 98. The separator 101 has high dendritic resistance. Therefore, the separator 101 prevents the growth of dendritic metallic zinc beyond the separator 101. This prevents the positive electrode 93 and the negative electrode 98 from short-circuiting each other via dendritic metallic zinc.

[0085] The gasket 102 is sandwiched between the opening surface 91q of the first layer 91 and the separator 101, and seals the space between the opening surface 91q of the first layer 91 and the separator 101 in a liquid-tight manner.

[0086] The gasket 103 is sandwiched between the opening surface 96q of the second layer 96 and the separator 101, and liquid-tightly seals the space between the opening surface 96q of the second layer 96 and the separator 101.

[0087] 1.9 Theoretical Voltage of Flow-Type Metal-Air Battery In the charging cell 78, the oxidation reaction of water at the positive electrode 93 and the reduction reaction to metallic zinc at the negative electrode 98 cause all the reactions represented by equation (8) to occur.

[0088] 2ZnO → 2Zn + O2(8)

[0089] Therefore, the charging cell 78 changes zinc oxide to metallic zinc when it is charged.

[0090] During the discharge and charge reactions, the potentials of the positive and negative electrodes are -1.25V and 0.40V, respectively, relative to a standard hydrogen electrode. Therefore, the theoretical voltage of the flow-type metal-air battery 1 is 1.65V.

[0091] 1.10 Control device As shown in Figure 1, the control device 26 includes a voltage measurement unit 111 and a control unit 112. The charging unit 25 and the control device 26 constitute a charging system.

[0092] Power supply 77 conducts a current I between the positive terminal 93 and the negative terminal 98.

[0093] The voltage measuring unit 111 measures the voltage V between the positive electrode 93 and the negative electrode 98. When taking the measurement, it is not necessary to directly measure the voltage between the positive electrode 93 and the negative electrode 98; instead, a conductive plate or similar object that is approximately equipotential to each electrode may be measured.

[0094] The control unit 112 controls the pump 75 to control the flow rate VL of the negative electrode liquid 22 in the second flow path 96e of the second layer 96. The control unit 112 also controls the power supply 77 to control the current I flowing between the positive electrode 93 and the negative electrode 98.

[0095] The control unit 112 controls the flow rate VL based on the voltage V.

[0096] The control unit 112 comprises a microcontroller and peripheral circuits. The microcontroller comprises a processor and memory. The processor executes a program stored in memory to cause the microcontroller and peripheral circuits to operate as the control unit 112. All or part of the processing performed by the microcontroller may be performed by dedicated electronic circuits.

[0097] 1.11 Control of Current Value and Flow Rate Figure 4A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell in the flow-type metal-air battery of the first embodiment. Figure 4B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell in the flow-type metal-air battery of the first embodiment.

[0098] In Figure 4A, time T is plotted on the horizontal axis and current I on the vertical axis. In Figure 4B, time T is plotted on the horizontal axis and flow velocity VL on the vertical axis.

[0099] As shown in Figure 4A, the control unit 112 maintains the current I at a constant current I1. Therefore, the control unit 112 keeps the current I constant at a constant current I1 during the period T0 to T4.

[0100] Furthermore, as shown in Figure 4B, the control unit 112 switches the flow velocity VL between a first flow velocity LV1 and a second flow velocity VL2. Therefore, the control unit 112 sets the flow velocity VL to the first flow velocity VL1 during period T0 to T1, to the second flow velocity VL2 during period T1 to T2, to the first flow velocity VL1 during period T2 to T3, and to the second flow velocity VL2 during period T3 to T4. The second flow velocity VL2 is slower than the first flow velocity LV1.

[0101] The first flow rate VL1 is the flow rate at which the amount of negative electrode active material ions 42 supplied to the negative electrode 98 is sufficient, and the reduction reaction of the negative electrode active material ions 42 to the reduced state negative electrode active material particles 41a occurs at the negative electrode 98, but the hydrogen generation reaction that competes with the reduction reaction does not occur at the negative electrode 98. The second flow rate VL2 is the flow rate at which the amount of negative electrode active material ions 42 supplied to the negative electrode 98 is insufficient, and the reduction reaction does not occur at the negative electrode 98, but the hydrogen generation reaction does occur at the negative electrode 98.

[0102] The hydrogen gas generated by the hydrogen generation reaction adheres to the reduced negative electrode active material particles 41a. This increases the buoyancy acting on the reduced negative electrode active material particles 41a. As a result, the force acting on the reduced negative electrode active material particles 41a increases.

[0103] Furthermore, the hydrogen gas generated by the hydrogen evolution reaction increases the internal pressure of the second channel 96e in the second layer 96. This locally increases the flow velocity of the negative electrode liquid 97 in the second channel 96e. As a result, the force acting on the reduced negative electrode active material particles 41a increases.

[0104] These features make it easy to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78 when a hydrogen generation reaction occurs.

[0105] However, the electricity used for the hydrogen generation reaction is not used for the reduction reaction. Therefore, when the hydrogen generation reaction occurs, the charging efficiency, which is the ratio of the electricity consumed in the reduction reaction to the electricity consumed by the charging unit 25, becomes low. For this reason, the hydrogen generation reaction is suppressed to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78.

[0106] During periods T1-T2 and T3-T4, when the hydrogen evolution reaction occurs, the voltage V increases as the hydrogen evolution reaction progresses and as time passes.

[0107] The control unit 112 controls timings T2 and T4 for switching the flow rate VL from the second flow rate VL2 to the first flow rate VL1 based on the voltage V. This allows the control unit 112 to change the length of the hydrogen generation reaction periods T1-T2 and T3-T4 based on the voltage V. This suppresses the hydrogen generation reaction to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. This increases the charging efficiency.

[0108] The control unit 112 switches the flow velocity VL from the second flow velocity VL2 to the first flow velocity VL1 in response to the rate of increase ΔV of the voltage V becoming greater than the set rate of increase ΔVs.

[0109] During the hydrogen evolution reaction periods T1-T2 and T3-T4, the voltage V strongly depends on the current I, but the rate of increase ΔV of the voltage V does not strongly depend on the current I. Therefore, instead of switching the flow rate VL in response to the voltage V becoming greater than a set voltage, the flow rate VL is switched in response to the rate of increase ΔV of the voltage V becoming greater than a set rate of increase ΔVs. This allows the timings T2 and T4 for switching the flow rate VL to be appropriate regardless of the current I.

[0110] If the duration of the hydrogen generation reaction periods T1-T2 and T3-T4 is longer than the appropriate length, the amount of hydrogen gas generated by the hydrogen generation reaction will be greater than the appropriate amount. As a result, the generated hydrogen gas will accumulate in the second channel 96e of the second layer 96. This will cause dry-firing, where the voltage V becomes an abnormal voltage. If the duration of the hydrogen generation reaction periods T1-T2 and T3-T4 is shorter than the appropriate length, the amount of hydrogen gas generated by the hydrogen generation reaction will be less than the appropriate amount. As a result, it will be difficult to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and to discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. As a result, the second channel 96e may become blocked by the reduced negative electrode active material particles 41a. For this reason, the set time rise rate ΔVs, which is compared with the time rise rate ΔV of the voltage V, is set so that the duration of the hydrogen generation reaction periods T1-T2 and T3-T4 is appropriate, for example, set to 1.35 V / s.

[0111] In the first embodiment, the current I is maintained at a constant current I1 during the period T0 to T4. However, the current I may be varied within a range where it is greater than or equal to a specific current during the period T0 to T4. Also, in the first embodiment, the flow velocity VL is maintained at a constant first flow velocity VL1 during the periods T0 to T1 and T2 to T3, and the flow velocity VL is maintained at a constant second flow velocity VL2 during the periods T1 to T2 and T3 to T4. However, the flow velocity VL may be varied within a range where it is greater than or equal to the first flow velocity VL1 during the periods T0 to T1 and T2 to T3, and the flow velocity VL may be varied within a range where it is less than or equal to the second flow velocity VL2 during the periods T1 to T2 and T3 to T4.

[0112] In the first embodiment, the charging system comprises a single charging cell 78. However, the charging system may also comprise a stack comprising multiple charging cells 78 electrically connected in series. If the charging system comprises a stack, the voltage measurement unit 111 measures the total voltage V of the stack and returns a voltage V / n value obtained by dividing the measured voltage V by the number n of the multiple charging cells 78. Based on the voltage V / n value, the control unit 112 controls timings T2 and T4 for switching the flow velocity VL from a second flow velocity VL2 to a first flow velocity VL1.

[0113] 1.12 Processing Flow Figure 5 is a flowchart showing the processing flow performed by the control unit provided in the flow-type metal-air battery of the first embodiment.

[0114] The control unit 112 executes steps S101 to S104 shown in Figure 5.

[0115] In step S101, the control unit 112 sets the flow rate VL to the first flow rate VL1. This ensures that the amount of negative electrode active material ions 42 supplied to the negative electrode 98 is sufficient. As a result, a reduction reaction occurs at the negative electrode 98, where the negative electrode active material ions 42 are reduced to negative electrode active material particles 41a. Consequently, the reduced negative electrode active material particles 41a adhere to the negative electrode 98 and grow.

[0116] In the following step S102, the control unit 112 determines whether the time t that has elapsed since the flow velocity VL was set to the first flow velocity VL1 is longer than the set time ts. If the control unit 112 determines that time t is longer than the set time ts, it executes step S103. If the control unit 112 determines that time t is shorter than the set time ts, it executes step S101.

[0117] Steps S101 and S102 cause the flow velocity VL to remain at the first flow velocity VL1 until a set time ts has elapsed since VL was set to the first flow velocity VL1. Furthermore, the state in which the flow velocity VL remains at the first flow velocity VL1 ends in synchronization with the elapsed time ts since VL was set to the first flow velocity VL1.

[0118] In step S103, the control unit 112 sets the flow rate VL to the second flow rate VL2. This makes the amount of negative electrode active material ions 42 supplied to the negative electrode 98 insufficient. As a result, a hydrogen generation reaction occurs at the negative electrode 98. This causes the reduced negative electrode active material particles 41a attached to the negative electrode 98 to be detached.

[0119] In the following step S104, the control unit 112 determines whether the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs. If the control unit 112 determines that the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs, it executes step S101. If the control unit 112 determines that the rate of increase ΔV of the voltage V is less than the set rate of increase ΔVs, it executes step S103.

[0120] In steps S103 and S104, the flow velocity VL remains at the second flow velocity VL2 until the voltage V rise rate ΔV reaches the set rise rate ΔVs. Furthermore, the state in which the flow velocity VL is at the second flow velocity VL2 ends in synchronization with the voltage V rise rate ΔV reaching the set rise rate ΔVs.

[0121] Steps S101 to S104 switch the flow velocity VL between a first flow velocity VL1 and a second flow velocity VL2. The time during which the flow velocity VL is at the first flow velocity VL1 is a set time ts. The time during which the flow velocity VL is at the second flow velocity VL2 is a variable time and changes according to the progress of the hydrogen evolution reaction.

[0122] 1.13 Variations Figure 6A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell in a flow-type metal-air battery of a first modification of the first embodiment. Figure 6B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell in a flow-type metal-air battery of a first modification of the first embodiment.

[0123] In Figure 6A, time T is plotted on the horizontal axis and current I on the vertical axis. In Figure 6B, time T is plotted on the horizontal axis and flow velocity VL on the vertical axis.

[0124] In the first embodiment, as shown in Figure 4B, the second flow velocity VL2 is greater than 0. Therefore, the control unit 112 keeps the pump 75 ON even while the flow velocity VL is set to the second flow velocity VL2, causing the pump 75 to generate the flow of the negative electrode liquid 22.

[0125] In contrast, in the first modified example of the first embodiment, as shown in Figure 6B, the second flow velocity VL2 is 0. It is considered 0 if it remains within ±0.5 for 5.0 seconds. Therefore, while the flow velocity VL is set to the second flow velocity VL2, the control unit 112 turns off the pump 75, preventing the pump 75 from generating a flow of the negative electrode liquid 22. Accordingly, the control unit 112 switches the flow velocity VL between the first flow velocity VL1 and the second flow velocity VL2 by switching the state of the pump 75 between the on state and the off state. When the second flow velocity VL2 is 0, the length of the hydrogen generation reaction period T1-T2 and period T3-T4 can be shortened compared to when the second flow velocity VL2 is greater than 0, and the power consumed by the pump 75 and other auxiliary equipment can be reduced. The flow rate of pump 75 depends on the voltage input to pump 75, and the microcontroller controls VL1, VL2, and 0 (pump off) by issuing signals. Therefore, by monitoring the voltage on the INPUT side of pump 75, if the value of the INPUT voltage is 0V, the flow rate can be considered to be 0. Even if the threshold is exceeded, if it exceeds the threshold by even 0.01 for 0.01 seconds, it is considered that the threshold has been exceeded.

[0126] 2. Second Embodiment The following describes the differences between the second embodiment and the first embodiment. For aspects not described, the same configuration as that used in the first embodiment is used in the second embodiment.

[0127] In the second embodiment, the control unit 112 controls the current I based on the voltage V.

[0128] Figure 7A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell in the flow-type metal-air battery of the second embodiment. Figure 7B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell in the flow-type metal-air battery of the second embodiment.

[0129] In Figure 7A, time T is plotted on the horizontal axis and current I on the vertical axis. In Figure 7B, time T is plotted on the horizontal axis and flow velocity VL on the vertical axis.

[0130] In the second embodiment, as shown in Figure 7A, the control unit 112 switches the current I between a first current I1 and a second current I2. Therefore, the control unit 112 sets the current I to the first current I1 during the period T0 to T1, the current I to the second current I2 during the period T1 to T2, the current I to the first current I1 during the period T2 to T3, and the current I to the second current I2 during the period T3 to T4. The second current I2 is greater than the first current I1.

[0131] Furthermore, as shown in Figure 7B, the control unit 112 maintains the flow velocity VL at a constant flow velocity VL1. Therefore, the control unit 112 maintains the flow velocity VL at a constant flow velocity VL1 during the period T0 to T4.

[0132] The first current I1 is smaller than the current Ih at which the hydrogen evolution reaction begins. This current allows the reduction reaction of the negative electrode active material ions 42 to the reduced negative electrode active material particles 41a to occur at the negative electrode 98, but the hydrogen evolution reaction, which competes with the reduction reaction, does not occur at the negative electrode 98. The second flow velocity VL2 is larger than the current Ih. This current allows the reduction reaction not to occur at the negative electrode 98, but the hydrogen evolution reaction does occur at the negative electrode 98.

[0133] The control unit 112 controls timings T2 and T4 for switching the current I from the second current I2 to the first current I1 based on the voltage V. This allows the control unit 112 to change the length of the hydrogen generation reaction periods T1-T2 and T3-T4 based on the voltage V. This suppresses the hydrogen generation reaction to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. This increases the charging efficiency.

[0134] The control unit 112 switches the current I from the second current I2 to the first current I1 in response to the rate of increase ΔV of the voltage V becoming greater than a set rate of increase ΔVs.

[0135] Figure 8 is a flowchart showing the processing flow performed by the control unit provided in the flow-type metal-air battery of the second embodiment.

[0136] In the second embodiment, the control unit 112 executes steps S111 to S114 shown in Figure 8.

[0137] In step S111, the control unit 112 sets the current I to the first current I1. This causes a reduction reaction to occur at the negative electrode 98, where the negative electrode active material ions 42 are reduced to the reduced negative electrode active material particles 41a. As a result, the reduced negative electrode active material particles 41a adhere to the negative electrode 98 and grow.

[0138] In the following step S112, the control unit 112 determines whether the time t that has elapsed since the current I was set to the first current I1 is longer than the set time ts. If the control unit 112 determines that time t is longer than the set time ts, it executes step S113. If the control unit 112 determines that time t is shorter than the set time ts, it executes step S111.

[0139] In steps S111 and S112, the state in which current I is set to the first current I1 continues until a set time ts has elapsed since current I was set to the first current I1. Also, in synchronization with the elapsed time ts since current I was set to the first current I1, the state in which current I is set to the first current I1 ends.

[0140] In step S113, the control unit 112 changes the current I to the second current I2. This causes a hydrogen generation reaction to occur at the negative electrode 98. As a result, the reduced negative electrode active material particles 41a attached to the negative electrode 98 are detached.

[0141] In the following step S114, the control unit 112 determines whether the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs. If the control unit 112 determines that the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs, it executes step S111. If the control unit 112 determines that the rate of increase ΔV of the voltage V is less than the set rate of increase ΔVs, it executes step S113.

[0142] In steps S113 and S114, the state in which current I is the second current I2 continues until the rate of increase ΔV of voltage V reaches the set rate of increase ΔVs. Also, in synchronization with the rate of increase ΔV of voltage V reaching the set rate of increase ΔVs, the state in which current I is the second current I2 ends.

[0143] In steps S111 to S114, the current I is switched between a first current I1 and a second current I2. The time during which the current I is the first current I1 is a set time ts. The time during which the current I is the second current I2 is a variable time and changes according to the progress of the hydrogen evolution reaction.

[0144] 3. Third Embodiment The following describes the differences between the third embodiment and the first embodiment. For aspects not described, the same configuration as that used in the first embodiment is employed in the third embodiment.

[0145] In the third embodiment, the control unit 112 controls the current I and flow rate VL based on the voltage V.

[0146] Figure 9A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell in a flow-type metal-air battery of the third embodiment. Figure 9B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell in a flow-type metal-air battery of the third embodiment.

[0147] In Figure 9A, time T is plotted on the horizontal axis and current I on the vertical axis. In Figure 9B, time T is plotted on the horizontal axis and flow velocity VL on the vertical axis.

[0148] In the third embodiment, as shown in Figure 9A, the control unit 112 switches the current I between a first current I1 and a second current I2. Therefore, the control unit 112 sets the current I to the first current I1 during the period T0 to T1, the current I to the second current I2 during the period T1 to T2, the current I to the first current I1 during the period T2 to T3, and the current I to the second current I2 during the period T3 to T4. The second current I2 is greater than the first current I1.

[0149] Furthermore, as shown in Figure 9B, the control unit 112 switches the flow velocity VL between a first flow velocity LV1 and a second flow velocity VL2. Therefore, the control unit 112 sets the flow velocity VL to the first flow velocity VL1 during period T0 to T1, to the second flow velocity VL2 during period T1 to T2, to the first flow velocity VL1 during period T2 to T3, and to the second flow velocity VL2 during period T3 to T4. The second flow velocity VL2 is slower than the first flow velocity LV1.

[0150] The first current I1 is smaller than the current Ih at which the hydrogen evolution reaction begins. This current allows the reduction reaction of the negative electrode active material ions 42 to the reduced negative electrode active material particles 41a to occur at the negative electrode 98, but the hydrogen evolution reaction, which competes with the reduction reaction, does not occur at the negative electrode 98. The second current I2 is larger than current Ih. This current does not allow the reduction reaction to occur at the negative electrode 98, but does allow the hydrogen evolution reaction to occur at the negative electrode 98.

[0151] The first flow rate VL1 is the flow rate at which the amount of negative electrode active material ions 42 supplied to the negative electrode 98 is sufficient, and the reduction reaction of the negative electrode active material ions 42 to the reduced state of the negative electrode active material particles 41a occurs at the negative electrode 98, but the hydrogen generation reaction that competes with this reduction reaction does not occur at the negative electrode 98. The second flow rate VL2 is the flow rate at which the amount of negative electrode active material ions 42 supplied to the negative electrode 98 is insufficient, and the reduction reaction does not occur at the negative electrode 98, but the hydrogen generation reaction does occur at the negative electrode 98.

[0152] When current I is switched to a second current I2 and the flow velocity VL is switched to a second flow velocity VL2, a large amount of hydrogen is generated in a short time compared to when current I is switched to a second current I2 but the flow velocity VL is maintained at the first flow velocity VL1, and when current I is maintained at the first current I1 and the flow velocity VL is switched to a second flow velocity VL2. When a large amount of hydrogen is generated in a short time in this way, it becomes easier to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and to discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. Therefore, the charging efficiency can be further increased.

[0153] The control unit 112 controls timings T2 and T4 to switch the flow velocity VL and current I from a second flow velocity VL2 and second current I2 to a first flow velocity VL1 and first current I1 based on the voltage V. This allows the control unit 112 to change the length of periods T1-T2 and T3-T4 in which the hydrogen generation reaction occurs, based on the voltage V. This suppresses the hydrogen generation reaction to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. This increases the charging efficiency.

[0154] In response to the rate of increase ΔV of voltage V becoming greater than the set rate of increase ΔVs, the control unit 112 switches the flow velocity VL and current I from the second flow velocity VL2 and second current I2 to the first flow velocity VL1 and first current I1.

[0155] Figure 10 is a flowchart showing the processing flow performed by the control unit provided in the third embodiment of the flow-type metal-air battery.

[0156] In the third embodiment, the control unit 112 performs steps S121 to S124 shown in Figure 10.

[0157] In step S121, the control unit 112 sets the current I to the first current I1 and the flow velocity VL to the first flow velocity VL1. This causes a reduction reaction to occur at the negative electrode 98, where the negative electrode active material ions 42 are reduced to the negative electrode active material particles 41a. As a result, the reduced negative electrode active material particles 41a adhere to the negative electrode 98 and grow. During the period when the current I is the first current I1 and the flow velocity VL is the first flow velocity VL1, the power consumed by the charging unit 25 is at its lowest.

[0158] In the following step S122, the control unit 112 determines whether the time t that has elapsed since setting the current I to the first current I1 and the flow velocity VL to the first flow velocity VL1 is longer than the set time ts. If the control unit 112 determines that time t is longer than the set time ts, it executes step S123. If the control unit 112 determines that time t is shorter than the set time ts, it executes step S121.

[0159] In steps S121 and S122, the state in which the current I is set to the first current I1 and the flow velocity VL is set to the first flow velocity VL1 continues until a set time ts has elapsed since the current I was set to the first current I1 and the flow velocity VL is set to the first flow velocity VL1. Also, in synchronization with the elapsed time ts since the current I was set to the first current I1 and the flow velocity VL is set to the first flow velocity VL1, the state in which the current I is set to the first current I1 and the flow velocity VL is set to the first flow velocity VL1 ends.

[0160] In step S123, the control unit 112 sets the current I to the second current I2 and the flow velocity VL to the second flow velocity VL2. This causes a hydrogen generation reaction to occur at the negative electrode 98. As a result, the reduced negative electrode active material particles 41a attached to the negative electrode 98 are detached.

[0161] In the following step S124, the control unit 112 determines whether the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs. If the control unit 112 determines that the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs, it executes step S121. If the control unit 112 determines that the rate of increase ΔV of the voltage V is less than the set rate of increase ΔVs, it executes step S123.

[0162] In steps S123 and S124, the state in which the current I is set to the second current I2 and the flow velocity VL is set to the second flow velocity VL2 continues until the rate of increase ΔV of the voltage V reaches the set rate of increase ΔVs. Also, in synchronization with the rate of increase ΔV of the voltage V reaching the set rate of increase ΔVs, the state in which the current I is set to the second current I2 and the flow velocity VL is set to the second flow velocity VL2 ends.

[0163] In steps S121 to S124, the current I and flow rate VL are switched between a first current I1 and first flow rate VL1 and a second current I2 and second flow rate VL2. The time during which the current I and flow rate VL are set to the first current I1 and first flow rate VL1 is a set time ts. The time during which the current I and flow rate VL are set to the second current I2 and second flow rate VL2 is a variable time that changes according to the progress of the hydrogen evolution reaction.

[0164] Figure 11A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell in a flow-type metal-air battery of the first modification of the third embodiment. Figure 11B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell in a flow-type metal-air battery of the first modification of the third embodiment.

[0165] In Figure 11A, time T is plotted on the horizontal axis and current I on the vertical axis. In Figure 11B, time T is plotted on the horizontal axis and flow velocity VL on the vertical axis.

[0166] In the third embodiment, as shown in Figure 9B, the second flow velocity VL2 is greater than 0. Therefore, the control unit 112 keeps the pump 75 ON even while the flow velocity VL is set to the second flow velocity VL2, causing the pump 75 to generate the flow of the negative electrode liquid 22.

[0167] In contrast, in the first modified example of the third embodiment, as shown in Figure 11B, the second flow velocity VL2 is 0. Therefore, while the flow velocity VL is set to the second flow velocity VL2, the control unit 112 turns off the pump 75, preventing the pump 75 from generating a flow of the negative electrode liquid 22. Accordingly, the control unit 112 switches the flow velocity VL between the first flow velocity VL1 and the second flow velocity VL2 by switching the state of the pump 75 between the on state and the off state. When the second flow velocity VL2 is 0, the length of the hydrogen generation reaction period T1-T2 and period T3-T4 can be shortened compared to when the second flow velocity VL2 is greater than 0, and the power consumed by the pump 75 and other auxiliary equipment can be reduced.

[0168] Figure 12A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell in a flow-type metal-air battery of a second modification of the third embodiment. Figure 12B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell in a flow-type metal-air battery of a second modification of the third embodiment.

[0169] In Figure 12A, time T is plotted on the horizontal axis and current I on the vertical axis. In Figure 12B, time T is plotted on the horizontal axis and flow velocity VL on the vertical axis.

[0170] In the second modification of the third embodiment, if the rate of increase ΔV1 of voltage V during the current hydrogen generation reaction period T3-T4 is not lower than the rate of increase ΔV2 of voltage V during the previous hydrogen generation reaction period T1-T2, the control unit 112 continues to switch the current I and flow velocity VL between the first current I1 and first flow velocity VL1 and the second current I2 and second flow velocity even after timing T4.

[0171] However, if the rate of increase ΔV1 of voltage V during the current hydrogen evolution reaction period T3-T4 is lower than the rate of increase ΔV2 of voltage V during the previous hydrogen evolution reaction period T1-T2, the control unit 112 performs maintenance processing during the following period T4-T5. When the control unit 112 starts the maintenance processing, it maintains the current I at the second current I2, as shown in Figure 12A, and switches the flow velocity VL from the second flow velocity VL2 to the third flow velocity VL3, as shown in Figure 12B. The third flow velocity VL3 has the opposite sign to the second flow velocity VL2. The third flow velocity VL3 may have the same absolute value as the second flow velocity VL2, or it may have a different absolute value from the second flow velocity VL2.

[0172] When maintenance is performed, a hydrogen generation reaction occurs. This makes it easy to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78.

[0173] In addition, when maintenance is performed, the negative electrode fluid 97 flows backward through the second channel 96e of the second layer 96. As a result, a force acting on the reduced negative electrode active material particles 41a acts in the opposite direction to the force acting on the reduced negative electrode active material particles 41a before the maintenance was performed. This makes it even easier to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78.

[0174] The reduced negative electrode active material particles 41a grow along the direction in which the negative electrode liquid 97 flows. Therefore, if the direction in which the negative electrode liquid 97 flows is constant, the reduced negative electrode active material particles 41a will continue to grow along that direction. In contrast, if the direction in which the negative electrode liquid 97 flows is not constant, it is possible to suppress the continued growth of the reduced negative electrode active material particles 41a along that direction. This is why it becomes even easier to detach the reduced negative electrode active material particles 41a from the negative electrode 98 when a force acting in the opposite direction acts on the reduced negative electrode active material particles 41a.

[0175] Figure 13 is a flowchart showing the processing flow performed by the control unit provided in the second modified example of the third embodiment of the metal-air battery.

[0176] In the second modified example of the third embodiment, the control unit 112 performs steps S131 to S136 shown in Figure 13.

[0177] In steps S131 to S133, the same processes as those performed in steps S121 to S123 shown in Figure 10 are carried out.

[0178] In the following step S134, the control unit 112 determines whether the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs. If the control unit 112 determines that the rate of increase ΔV of the voltage V is greater than the set rate of increase ΔVs, it executes step S135. If the control unit 112 determines that the rate of increase ΔV of the voltage V is less than the set rate of increase ΔVs, it executes step S133.

[0179] In step S135, the control unit 112 determines whether the rate of increase ΔV1 of voltage V during the period when the current I and flow velocity VL were set to the second current I2 and the second flow velocity VL2 is lower than the rate of increase ΔV2 of voltage V during the previous period when the current I and flow velocity VL were set to the second current I2 and the second flow velocity VL2. If the control unit 112 determines that the rate of increase ΔV1 of voltage V is lower than the rate of increase ΔV2 of voltage V, it executes step S136 and then step S131. If the control unit 112 determines that the rate of increase ΔV1 of voltage V is not lower than the rate of increase ΔV2 of voltage V, it executes step S131 without executing step S136.

[0180] In step S136, the control unit 112 performs maintenance processing.

[0181] In steps S135 and S136, the control unit 112 continues the alternating switching of current I and flow velocity VL without performing maintenance processing if the rate of increase ΔV1 of voltage V is not lower than the rate of increase ΔV2 of voltage V. If the rate of increase ΔV1 of voltage V becomes lower than the rate of increase ΔV2 of voltage V, it performs maintenance processing and then resumes the alternating switching of current I and flow velocity VL. The control unit 112 may also perform maintenance processing if voltage V satisfies conditions other than the condition in which the rate of increase ΔV1 of voltage V is lower than the rate of increase ΔV2 of voltage V.

[0182] 4. Fourth Embodiment The following describes the differences between the fourth embodiment and the first embodiment. For aspects not described, the fourth embodiment employs the same configuration as that used in the first embodiment.

[0183] Figure 14 is a schematic diagram illustrating a flow-type metal-air battery according to the fourth embodiment.

[0184] In the fourth embodiment, as shown in Figure 14, the control device 26 includes a pressure gauge side section 113 and a control unit 112. The pressure gauge side section 113 and the control unit 112 constitute a charging system.

[0185] The pressure gauge side 113 is connected to the piping 76 and measures the supply pressure P of the negative electrode fluid 22 guided by the piping 76. The measured supply pressure P represents the pressure applied to the second flow path 96e of the second layer 96.

[0186] In the fourth embodiment, the control unit 112 controls the flow velocity VL based on the liquid delivery pressure P.

[0187] Figure 4A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell provided in the fourth embodiment of the flow-type metal-air battery. Figure 4B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell provided in the fourth embodiment of the flow-type metal-air battery.

[0188] In the fourth embodiment, as shown in Figure 4A, the control unit 112 maintains the current I at a constant current I1.

[0189] Furthermore, as shown in Figure 4B, the control unit 112 switches the flow velocity VL between a first flow velocity LV1 and a second flow velocity VL2. The second flow velocity VL2 is slower than the first flow velocity LV1.

[0190] The first flow rate VL1 is the flow rate at which the reduction reaction of the negative electrode active material ions 42 to the negative electrode active material particles 41a occurs at the negative electrode 98, but the hydrogen evolution reaction that competes with the reduction reaction does not occur at the negative electrode 98. The second flow rate VL2 is the flow rate at which the reduction reaction does not occur at the negative electrode 98, but the hydrogen evolution reaction does occur at the negative electrode 98.

[0191] During periods T1-T2 and T3-T4, when the hydrogen evolution reaction occurs, the liquid supply pressure P increases as the hydrogen evolution reaction progresses and as time passes.

[0192] In the fourth embodiment, the control unit 112 controls timings T2 and T4 for switching the flow velocity VL from the second flow velocity VL2 to the first flow velocity VL1 based on the liquid supply pressure P. This makes it possible to suppress the hydrogen generation reaction to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. This makes it possible to increase the charging efficiency.

[0193] The control unit 112 switches the flow velocity VL from the second flow velocity VL2 to the first flow velocity VL1 in response to the rate of increase ΔP of the fluid supply pressure P becoming greater than the set rate of increase ΔPs.

[0194] The set time-based rate of increase ΔPs, which is compared with the time-based rate of increase ΔP of the liquid delivery pressure P, is set so that the periods T1-T2 and T3-T4 during which the hydrogen evolution reaction occurs are of appropriate duration, for example, it is set to 10.4 kPa / s.

[0195] Figure 15 is a flowchart showing the processing flow performed by the control unit provided in the fourth embodiment of the flow-type metal-air battery.

[0196] The control unit 112 executes steps S141 to S144 shown in Figure 15.

[0197] In steps S141 to S143, the same processes as those performed in steps S101 to S103 shown in Figure 5 are carried out.

[0198] In the following step S144, the control unit 112 determines whether the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs, it executes step S141. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is less than the set rate of increase ΔPs, it executes step S143.

[0199] In steps S143 and S144, the flow velocity VL remains at the second flow velocity VL2 until the rate of increase ΔP of the fluid supply pressure P reaches the set rate of increase ΔPs. In synchronization with the rate of increase ΔP of the fluid supply pressure P reaching the set rate of increase ΔPs, the state in which the flow velocity VL is at the second flow velocity VL2 ends.

[0200] Figure 6A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell provided in the first modified flow-type metal-air battery of the fourth embodiment. Figure 6B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell provided in the first modified flow-type metal-air battery of the fourth embodiment.

[0201] In the first modified example of the fourth embodiment, as shown in Figure 6B, the second flow velocity VL2 is 0. When the second flow velocity VL2 is 0, the lengths of the hydrogen generation reaction periods T1-T2 and T3-T4 can be shortened compared to when the second flow velocity VL2 is greater than 0, and the power consumed by the pump 75 and other auxiliary equipment can be reduced.

[0202] 5. Fifth Embodiment The differences between the fifth embodiment and the fourth embodiment will be explained below. For aspects not explained, the same configuration as that used in the fourth embodiment will be used in the fifth embodiment.

[0203] In the fifth embodiment, the control unit 112 controls the current I based on the fluid supply pressure P.

[0204] Figure 7A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell provided in the fifth embodiment of the flow-type metal-air battery. Figure 7B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell provided in the fifth embodiment of the flow-type metal-air battery.

[0205] In the fifth embodiment, as shown in Figure 7A, the control unit 112 switches the current I between a first current I1 and a second current I2. The second current I2 is greater than the first current I1.

[0206] Furthermore, as shown in Figure 7B, the control unit 112 maintains the flow velocity VL at a constant flow velocity VL1.

[0207] The first flow rate VL1 is the flow rate at which the reduction reaction of the negative electrode active material ions 42 to the negative electrode active material particles 41a occurs at the negative electrode 98, but the hydrogen evolution reaction that competes with the reduction reaction does not occur at the negative electrode 98. The second flow rate VL2 is the flow rate at which the reduction reaction does not occur at the negative electrode 98, but the hydrogen evolution reaction does occur at the negative electrode 98.

[0208] In the fifth embodiment, the control unit 112 controls timings T2 and T4 for switching the current I from the second current I2 to the first current I1 based on the liquid supply pressure P. This makes it possible to suppress the hydrogen generation reaction to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. This makes it possible to increase the charging efficiency.

[0209] The control unit 112 switches the flow velocity VL from the second flow velocity VL2 to the first flow velocity VL1 in response to the rate of increase ΔP of the fluid supply pressure P becoming greater than the set rate of increase ΔPs.

[0210] Figure 16 is a flowchart showing the processing flow performed by the control unit provided in the fifth embodiment of the flow-type metal-air battery.

[0211] The control unit 112 executes steps S151 to S154 shown in Figure 16.

[0212] In steps S151 to S153, the same processes as those performed in steps S111 to S113 shown in Figure 8 are carried out.

[0213] In the following step S154, the control unit 112 determines whether the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs, it executes step S151. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is less than the set rate of increase ΔPs, it executes step S153.

[0214] In steps S153 and S154, the current I remains at the second current I2 until the rate of increase ΔP of the fluid supply pressure P reaches the set rate of increase ΔPs. Furthermore, the state in which the current I remains at the second current I2 ends in synchronization with the rate of increase ΔP of the fluid supply pressure P reaching the set rate of increase ΔPs.

[0215] 6. Sixth Embodiment The following describes the differences between the sixth embodiment and the fourth embodiment. For aspects not described, the sixth embodiment employs the same configuration as that used in the fourth embodiment.

[0216] In the sixth embodiment, the control unit 112 controls the flow velocity VL based on the liquid delivery pressure P.

[0217] Figure 9A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell provided in the sixth embodiment of the flow-type metal-air battery. Figure 9B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell provided in the sixth embodiment of the flow-type metal-air battery.

[0218] In the sixth embodiment, as shown in Figure 9A, the control unit 112 switches the current I between a first current I1 and a second current I2. The second current I2 is greater than the first current I1.

[0219] Furthermore, as shown in Figure 9B, the control unit 112 switches the flow velocity VL between a first flow velocity LV1 and a second flow velocity VL2. The second flow velocity VL2 is slower than the first flow velocity LV1.

[0220] The first current I1 is the current at which the reduction reaction of the negative electrode active material ions 42 to the negative electrode active material particles 41a occurs at the negative electrode 98, but the hydrogen evolution reaction that competes with the reduction reaction does not occur at the negative electrode 98. The second flow rate VL2 is the current at which the reduction reaction does not occur at the negative electrode 98, but the hydrogen evolution reaction that competes with the reduction reaction does occur at the negative electrode 98.

[0221] The first flow rate VL1 is the flow rate at which the reduction reaction of the negative electrode active material ions 42 to the negative electrode active material particles 41a occurs at the negative electrode 98, but the hydrogen evolution reaction that competes with the reduction reaction does not occur at the negative electrode 98. The second flow rate VL2 is the flow rate at which the reduction reaction does not occur at the negative electrode 98, but the hydrogen evolution reaction does occur at the negative electrode 98.

[0222] The control unit 112 controls timings T2 and T4 to switch the flow velocity VL and current I from a second flow velocity VL2 and second current I2 to a first flow velocity VL1 and first current I1 based on the liquid supply pressure P. This makes it possible to suppress the hydrogen generation reaction to the minimum extent necessary to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78. This makes it possible to increase the charging efficiency.

[0223] The control unit 112 switches the flow velocity VL and current I from the second flow velocity VL2 and second current I2 to the first flow velocity VL1 and first current I1 in response to the rate of increase ΔP of the fluid supply pressure P becoming greater than the set rate of increase ΔPs.

[0224] Figure 17 is a flowchart showing the processing flow performed by the control unit provided in the sixth embodiment of the flow-type metal-air battery.

[0225] In the sixth embodiment, the control unit 112 performs steps S161 to S164 shown in Figure 17.

[0226] In steps S161 to S163, the same processes as those performed in steps S121 to S123 shown in Figure 10 are carried out.

[0227] In the following step S164, the control unit 112 determines whether the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs, it executes step S161. If the control unit 112 determines that the rate of increase ΔV of the voltage V is less than the set rate of increase ΔVs, it executes step S163.

[0228] In steps S163 and S164, the state in which the current I is set to the second current I2 and the flow velocity VL is set to the second flow velocity VL2 continues until the rate of increase ΔP of the fluid supply pressure P reaches the set rate of increase ΔPs. Also, in synchronization with the rate of increase ΔP of the fluid supply pressure P reaching the set rate of increase ΔPs, the state in which the current I is set to the second current I2 and the flow velocity VL is set to the second flow velocity VL2 ends.

[0229] Figure 11A is a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell provided in the first modified flow-type metal-air battery of the sixth embodiment. Figure 11B is a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell provided in the first modified flow-type metal-air battery of the sixth embodiment.

[0230] In the first modified example of the sixth embodiment, as shown in Figure 11B, the second flow velocity VL2 is 0. When the second flow velocity VL2 is 0, the lengths of the hydrogen generation reaction periods T1-T2 and T3-T4 can be shortened compared to when the second flow velocity VL2 is greater than 0, and the power consumed by the pump 75 and other auxiliary equipment can be reduced.

[0231] Figure 12A is also a graph showing an example of the time change of the current flowing between the positive electrode and the negative electrode of a charging cell provided in a second modified flow-type metal-air battery of the sixth embodiment. Figure 12B is also a graph showing an example of the time change of the flow velocity of the negative electrode liquid in the second flow channel of the second layer of the charging cell provided in a second modified flow-type metal-air battery of the sixth embodiment.

[0232] In the second modification of the sixth embodiment, if the rate of increase ΔV1 of the voltage V during the current hydrogen generation reaction period T3 to T4 is not lower than the rate of increase ΔV2 of the voltage V during the previous hydrogen generation reaction period T1 to T2, the control unit 112 continues to switch the current I and flow velocity VL between the first current I1 and first flow velocity VL1 and the second current I2 and second flow velocity even after timing T4.

[0233] However, if the rate of increase ΔV1 of the voltage V during the current hydrogen evolution reaction period T3-T4 is lower than the rate of increase ΔV2 of the voltage V during the previous hydrogen evolution reaction period T1-T2, the control unit 112 performs maintenance processing during the following period T4-T5. When the control unit 112 starts the maintenance processing, it maintains the current I at the second current I2, as shown in Figure 12A, and switches the flow velocity VL from the second flow velocity VL2 to the third flow velocity VL3, as shown in Figure 12B. The third flow velocity VL3 has the opposite sign to the second flow velocity VL2. The third flow velocity VL3 may have the same absolute value as the second flow velocity VL2, or it may have a different absolute value from the second flow velocity VL2.

[0234] When maintenance is performed, a hydrogen generation reaction occurs. This makes it easy to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78.

[0235] In addition, when maintenance is performed, the negative electrode fluid 97 flows backward through the second channel 96e of the second layer 96. As a result, a force acting on the reduced negative electrode active material particles 41a acts in the opposite direction to the force acting on the reduced negative electrode active material particles 41a before the maintenance was performed. This makes it even easier to detach the reduced negative electrode active material particles 41a from the negative electrode 98 and discharge the detached reduced negative electrode active material particles 41a from the charging cell 78.

[0236] Figure 18 is a flowchart showing the processing flow performed by the control unit provided in the second modified example of the sixth embodiment of the metal-air battery.

[0237] In the second modified example of the sixth embodiment, the control unit 112 performs steps S171 to S176 shown in Figure 18.

[0238] In steps S171 to S173, the same processes as those performed in steps S131 to S133 shown in Figure 13 are carried out.

[0239] In the following step S174, the control unit 112 determines whether the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is greater than the set rate of increase ΔPs, it executes step S175. If the control unit 112 determines that the rate of increase ΔP of the fluid supply pressure P is less than the set rate of increase ΔPs, it executes step S173.

[0240] In step S175, the control unit 112 determines whether the rate of increase ΔP1 of the fluid supply pressure P during the period when the current I and flow velocity VL were set to the second current I2 and the second flow velocity VL2 is lower than the rate of increase ΔP2 of the fluid supply pressure P during the previous period when the current I and flow velocity VL were set to the second current I2 and the second flow velocity VL2. If the control unit 112 determines that the rate of increase ΔP1 of the fluid supply pressure P is lower than the rate of increase ΔP2 of the fluid supply pressure P, it executes step S176 and then step S171. If the control unit 112 determines that the rate of increase ΔP1 of the fluid supply pressure P is not lower than the rate of increase ΔP2 of the fluid supply pressure P, it executes step S171 without executing step S176.

[0241] 7. Seventh Embodiment The following describes the differences between the seventh embodiment and the first to sixth embodiments. For aspects not described, the seventh embodiment employs the same configuration as that used in the first to sixth embodiments.

[0242] Figures 19 to 22 show the processing performed by the control unit provided in the flow-type metal-air battery of the seventh embodiment.

[0243] In the first to sixth embodiments, the control unit 112 controls the length of the hydrogen generation reaction periods T1-T2 and T3-T4 by controlling the current I and / or flow rate VL in response to the rate of increase ΔV of the voltage V becoming higher than a set rate of increase ΔVs or the rate of increase ΔP of the liquid supply pressure P becoming higher than a set rate of increase ΔPs.

[0244] In contrast, in the seventh embodiment, as shown in Figure 19, the control unit 112 further controls the length of the hydrogen generation reaction period T1-T2 and period T3-T4 based on the discharge depth D of the discharge unit 24 by controlling the current I and / or flow velocity VL based on the discharge depth D of the discharge unit 24.

[0245] For example, if the flow velocity VL is switched between a first flow velocity VL1 and a second flow velocity VL2, as in the first embodiment, the control unit 112 controls the flow velocity VL based on the discharge depth D of the discharge unit 24. As shown in Figure 20, the shallower the discharge depth D of the discharge unit 24, the earlier the timings T2 and T4 for switching the flow velocity VL from the second flow velocity VL2 to the first flow velocity VL1 are made, thereby shortening the length of the hydrogen generation reaction period T1-T2 and T3-T4.

[0246] Alternatively, if the current I is switched between a first current I1 and a second current I2, as in the second embodiment, the control unit 112 controls the current I based on the discharge depth D of the discharge unit 24, and as shown in Figure 21, the shallower the discharge depth D of the discharge unit 24, the earlier the timing of switching the current I from the second current I2 to the first current I1, thereby shortening the length of the hydrogen generation reaction periods T1-T2 and T3-T4.

[0247] Alternatively, if the flow velocity VL and current I are switched between a first flow velocity VL1 and a first current I1 and a second flow velocity VL2 and a second current I2, as in the third embodiment, the control unit 112 controls the flow velocity VL and current I based on the discharge depth D of the discharge unit 24, as shown in Figure 22. The shallower the discharge depth D of the discharge unit 24, the earlier the timing of switching the flow velocity VL and current I from the second flow velocity VL2 and a second current I2 to the first flow velocity VL1 and a first current I1, thereby shortening the length of the hydrogen generation reaction periods T1-T2 and T3-T4.

[0248] When the discharge depth D of the discharge section 24 is shallow, the amount of negative electrode active material ions 42 contained in the negative electrode liquid 97 is small, so the hydrogen generation reaction proceeds easily. On the other hand, when the discharge depth D of the discharge section 24 is deep, the amount of negative electrode active material ions 42 contained in the negative electrode liquid 97 is large, so the hydrogen generation reaction does not proceed easily. For this reason, if the length of the periods T1-T2 and T3-T in which the hydrogen generation reaction occurs is shortened as the discharge depth D of the discharge section 24 becomes shallower, the progress of the hydrogen generation reaction can be made appropriate.

[0249] Discharge by the discharge unit 24 and charge by the charge unit 25 are performed alternately.

[0250] The control unit 112 can determine the discharge depth D of the discharge unit 24 from the product of the current discharged by the discharge unit 24 and the time during which the discharge was performed by the discharge unit 24. The determined discharge depth D of the discharge unit 24 is the discharge depth of the discharge unit 24 at the time when the most recent discharge by the discharge unit 24 ended. The current discharged by the discharge unit 24 is a constant current.

[0251] Discharge depth D refers to the value (quotient) obtained by dividing the product of the discharge current and discharge time (Ah) by the initial (pre-discharge) volume Ah of the negative electrode fluid 97 (if zinc Mg is included, the volume is M × 0.82). A deep discharge depth D means that the value obtained by dividing the product of the current discharged by the discharge unit 24 and the time during which discharge was performed by the discharge unit 24 by the volume of the negative electrode fluid 97 before discharge is greater than 0.1 (10% depth). A shallow discharge depth D means that the value obtained by dividing the product of the current discharged by the discharge unit 24 and the time during which discharge was performed by the discharge unit 24 by the volume of the negative electrode fluid 97 before discharge is less than 0.1 (10% depth).

[0252] This disclosure is not limited to the embodiments described above, and may be replaced with configurations that are substantially the same as those shown in the embodiments, configurations that produce the same effects, or configurations that can achieve the same purpose. [Explanation of Symbols]

[0253] 1. Flow-type metal-air battery 21 Positive electrode solution 22 Negative electrode solution 23 Storage section 23a Outlet 23b Inlet 23c Outlet 23d inlet 24 Discharge section 25 Live parts 26 Control device 31 First Electrolyte 41a Reduced state negative electrode active material particles 41b Anode active material particles in an acidified state 42 Anode active material ions 43 Second electrolyte 51 Pipe 52 Pump 52a Inlet 52b Outlet 53 Pipe 54 Discharge cell 54a Inlet 54b Outlet 55 Pipe 61 Layer 61a Flow path 62 Anode solution 63 Cathode 64 Separator 65 Anode 71 Pipe 72 Pump 72a Inlet 72b Outlet 73 Pipe 74 Pipe 75 Pump 75a Inlet 75b Outlet 76 Pipe 77 Power source 78 Charging cell 78a Inlet 78b Inlet 78c Outlet 78d Outlet 79 Pipe 80 Pipe 91 First layer 91p Opening surface 91q Opening surface 91a End face 91c End face 91e First flow path 91pe Opening 91qe Opening 92 Cathode solution 93 Cathode 94 Current-carrying plate 95 Gasket 96 Second layer 96b End face 96d End face 96e Second channel 96p opening surface 96q opening surface 96pe opening 96qe aperture 97 Negative electrode solution 98 negative electrode 99 Electrical plate 100 gaskets 101 Separator 102 Gasket 103 Gasket 111 Voltage Measurement Unit 112 Control Unit 113 Pressure gauge side

Claims

1. A first layer in which the first channel is formed, The positive electrode facing the first flow path, A second layer in which a second channel is formed, The negative electrode facing the second flow path, A separator that separates the first flow path and the second flow path from each other, The positive electrode liquid flowing through the first channel, The negative electrode liquid flowing through the second channel, A control device that controls at least one selected from the group consisting of the flow velocity of the negative electrode liquid and the current flowing between the positive electrode and the negative electrode, based on at least one selected from the group consisting of the voltage applied between the positive electrode and the negative electrode and the pressure of the negative electrode liquid supply, A charging system for flow-type metal-air batteries, equipped with the following features.

2. The control device controls the flow rate based on the voltage. A charging system for a flow-type metal-air battery according to claim 1.

3. The control device switches the flow velocity between a first flow velocity and a second flow velocity that is slower than the first flow velocity. Controlling the flow velocity based on the voltage includes controlling the timing of switching the flow velocity from the second flow velocity to the first flow velocity based on the voltage. A charging system for a flow-type metal-air battery according to claim 2.

4. Controlling the timing based on the voltage includes switching the flow velocity from the second flow velocity to the first flow velocity in response to the rate of increase of the voltage exceeding a set rate of increase. A charging system for a flow-type metal-air battery according to claim 3.

5. The first flow velocity is the flow velocity at which the hydrogen generation reaction does not occur at the negative electrode. The second flow velocity is the flow velocity at which the hydrogen generation reaction occurs at the negative electrode. A charging system for a flow-type metal-air battery according to claim 3 or 4.

6. The second flow velocity is 0. A charging system for a flow-type metal-air battery according to claim 3 or 4.

7. The control device controls the current based on the voltage. A charging system for a flow-type metal-air battery according to claim 1.

8. The control device switches the current between a first current and a second current that is greater than the first current. Controlling the current based on the voltage includes controlling the timing of switching the current from the second current to the first current based on the voltage. A charging system for a flow-type metal-air battery according to claim 7.

9. Controlling the timing based on the voltage involves switching the current from the second current to the first current in response to the rate of increase of the voltage exceeding a set rate of increase. A charging system for a flow-type metal-air battery according to claim 8.

10. The first current is a current in which no hydrogen generation reaction occurs at the negative electrode. The second current is the current at which the hydrogen generation reaction occurs at the negative electrode. A charging system for a flow-type metal-air battery according to claim 8 or 9.

11. The control device controls the flow rate and current based on the voltage. A charging system for a flow-type metal-air battery according to claim 1.

12. The control device switches the flow velocity and current between a first flow velocity and a first current and a second flow velocity slower than the first flow velocity and a second current greater than the first current. Controlling the flow velocity and current based on the voltage includes controlling the timing of switching the flow velocity and current from the second flow velocity and second current to the first flow velocity and first current based on the voltage. A charging system for a flow-type metal-air battery according to claim 11.

13. Controlling the timing based on the voltage includes switching the flow velocity and current from the second flow velocity and second current to the first flow velocity and first current in response to the rate of increase of the voltage exceeding a set rate of increase. A charging system for a flow-type metal-air battery according to claim 12.

14. The first flow velocity and the first current are the flow velocity and current at which no hydrogen generation reaction occurs at the negative electrode. The second flow velocity and the second current are the flow velocity and current at which the hydrogen generation reaction occurs at the negative electrode. A charging system for a flow-type metal-air battery according to claim 12 or 13.

15. The second flow velocity is 0. A charging system for a flow-type metal-air battery according to claim 12 or 13.

16. Controlling the flow velocity and current based on the voltage includes switching the flow velocity from the second flow velocity to a third flow velocity having the opposite sign to the second flow velocity based on the voltage. A charging system for a flow-type metal-air battery according to claim 12 or 13.

17. Switching the flow velocity from the second flow velocity to the third flow velocity based on the voltage includes switching the flow velocity from the second flow velocity to the third flow velocity when the rate of increase of the voltage while the flow velocity and current are set to the second flow velocity and the second current is lower than the rate of increase of the voltage while the flow velocity and current were previously set to the second flow velocity and the second current. A charging system for a flow-type metal-air battery according to claim 16.

18. The control device controls the flow rate based on the liquid delivery pressure. A charging system for a flow-type metal-air battery according to claim 1.

19. The control device switches the flow velocity between a first flow velocity and a second flow velocity that is slower than the first flow velocity. Controlling the flow velocity based on the liquid delivery pressure includes controlling the timing of switching the flow velocity from the second flow velocity to the first flow velocity based on the liquid delivery pressure. A charging system for a flow-type metal-air battery according to claim 18.

20. Controlling the timing based on the fluid delivery pressure includes switching the flow velocity from the second flow velocity to the first flow velocity in response to the rate of increase of the fluid delivery pressure exceeding a set rate of increase. A charging system for a flow-type metal-air battery according to claim 19.

21. The first flow velocity is the flow velocity at which the hydrogen generation reaction does not occur at the negative electrode. The second flow velocity is the flow velocity at which the hydrogen generation reaction occurs at the negative electrode. A charging system for a flow-type metal-air battery according to claim 19 or 20.

22. The second flow velocity is 0. A charging system for a flow-type metal-air battery according to claim 19 or 20.

23. The control device controls the current based on the liquid supply pressure. A charging system for a flow-type metal-air battery according to claim 1.

24. The control device switches the current between a first current and a second current that is greater than the first current. Controlling the current based on the fluid delivery pressure includes controlling the timing of switching the current from the second current to the first current based on the fluid delivery pressure. A charging system for a flow-type metal-air battery according to claim 23.

25. Controlling the timing based on the fluid delivery pressure includes switching the current from the second current to the first current in response to the rate of increase of the fluid delivery pressure exceeding a set rate of increase. A charging system for a flow-type metal-air battery according to claim 24.

26. The first current is a current in which no hydrogen generation reaction occurs at the negative electrode. The second current is the current at which the hydrogen generation reaction occurs at the negative electrode. A charging system for a flow-type metal-air battery according to claim 24 or 25.

27. The control device controls the flow rate and current based on the liquid supply pressure. A charging system for a flow-type metal-air battery according to claim 1.

28. The control device switches the flow velocity and current between a first flow velocity and a first current and a second flow velocity slower than the first flow velocity and a second current greater than the first current. Controlling the flow velocity and current based on the fluid delivery pressure includes controlling the timing of switching the flow velocity and current from the second flow velocity and second current to the first flow velocity and first current based on the fluid delivery pressure. A charging system for a flow-type metal-air battery according to claim 27.

29. Controlling the timing based on the fluid delivery pressure involves switching the flow velocity and current from the second flow velocity and second current to the first flow velocity and first current in response to the rate of increase of the fluid delivery pressure exceeding a set rate of increase. A charging system for a flow-type metal-air battery according to claim 28.

30. The first flow velocity and the first current are the flow velocity and current at which no hydrogen generation reaction occurs at the negative electrode. The second flow velocity and the second current are the flow velocity and current at which the hydrogen generation reaction occurs at the negative electrode. A charging system for a flow-type metal-air battery according to claim 28 or 29.

31. The second flow velocity is 0. A charging system for a flow-type metal-air battery according to claim 28 or 29.

32. Controlling the flow velocity and current based on the fluid delivery pressure includes switching the flow velocity from the second flow velocity to a third flow velocity having the opposite sign to the second flow velocity based on the fluid delivery pressure. A charging system for a flow-type metal-air battery according to claim 28 or 29.

33. Switching the flow velocity from the second flow velocity to the third flow velocity based on the aforementioned liquid delivery pressure includes switching the flow velocity from the second flow velocity to the third flow velocity when the rate of increase in the liquid delivery pressure while the flow velocity and current are set to the second flow velocity and the second current is lower than the rate of increase in the liquid delivery pressure while the flow velocity and current were previously set to the second flow velocity and the second current. A charging system for a flow-type metal-air battery according to claim 32.

34. A charging system for a flow-type metal-air battery according to claim 1, Discharge section for flow-type metal-air battery, Equipped with, The control device controls at least one selected from the group consisting of the flow velocity and the current based on the discharge depth of the discharge section for the flow-type metal-air battery. Flow-type metal-air battery.

35. The control device controls the flow velocity based on the discharge depth. The control device switches the flow velocity between a first flow velocity and a second flow velocity that is slower than the first flow velocity. Controlling the flow velocity based on the discharge depth includes making the timing of switching the flow velocity from the second flow velocity to the first flow velocity earlier as the discharge depth becomes shallower. The flow-type metal-air battery according to claim 34.

36. The control device controls the current based on the discharge depth, The control device switches the current between a first current and a second current that is greater than the first current. Controlling the current based on the discharge depth includes making the timing of switching the current from the second current to the first current earlier as the discharge depth becomes shallower. The flow-type metal-air battery according to claim 34.

37. The control device controls the flow velocity and current based on the discharge depth. The control device switches the flow velocity and current between a first flow velocity and a first current and a second flow velocity slower than the first flow velocity and a second current greater than the first current. Controlling the flow velocity and current based on the discharge depth includes speeding up the timing of switching the flow velocity and current from the second flow velocity and second current to the first flow velocity and first current. The flow-type metal-air battery according to claim 34.

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