JP2017228351A - Reversible fuel cell storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that a fuel cell is inferior in followability for load variation, and a secondary cell can store power but the capacity stored in a battery is limited.SOLUTION: A reversible fuel cell storage battery has a first electrode containing nickel hydroxide, a second electrode containing hydrogen-storing alloy, a third electrode containing manganese dioxide, and a separator interposed between the first, second, and third electrodes. Oxygen gas generated from the first electrode by oxidation-reduction between the first and third electrodes, and hydrogen gas generated from the second electrode by oxidation-reduction between the second and third electrodes are stored separately in oxygen gas holder and hydrogen gas holder, and power is generated by the oxygen gas and hydrogen gas from the oxygen gas holder and hydrogen gas holder.SELECTED DRAWING: Figure 5A

Description

  The present invention relates to a reversible fuel cell that can store electrical energy supplied at the time of charging as chemical energy, and convert the stored chemical energy into electrical energy for use.

  Secondary batteries and fuel cells are known as highly efficient and clean energy sources. In recent years, development of electric vehicles, fuel cell vehicles, and trains that use such secondary batteries and fuel cells as power sources has been progressing worldwide.

  Fuel cells are attracting attention as power sources with high energy conversion efficiency and low environmental impact. The fuel cell cannot store electricity. However, it is possible to construct a kind of electric power storage system by combining a fuel cell and a hydrogen production apparatus using water electrolysis. Such a power storage system is called a reversible fuel cell (see Patent Document 1 and Patent Document 2). In such a reversible fuel cell in which a fuel cell and a water electrolyzer are combined, electrolysis of water, which is a reverse reaction of power generation, is performed using natural energy or night power when power is not generated. Thus, the power generation system using the reversible fuel cell manufactures its own fuel.

  On the other hand, the secondary battery is used not only as an electronic device but also as a power source for electric facilities such as electric tools that require large current discharge. In particular, recently, nickel hydride secondary batteries and lithium ion secondary batteries have attracted attention as batteries for hybrid vehicles driven by engines and batteries.

  A normal secondary battery is charged by receiving supply of electric energy and can store electricity. Patent Document 3 discloses a secondary battery that can be charged using a gas. Patent Document 4 discloses a new type of fuel cell that combines a secondary battery and a fuel cell that uses manganese hydroxide as a positive electrode active material and a hydrogen storage alloy as a negative electrode active material.

JP 2002-348694 A JP 2005-65398 A JP 2010-15729 A JP 2010-15783 A

  The secondary battery can store electricity. In addition, the output characteristics are excellent and the load followability is good. However, the amount of the negative electrode and the positive electrode active material depends on the volume of the battery. For this reason, there is a limit to the electric capacity that can be stored in the battery. And it is difficult for a secondary battery to raise energy density significantly.

  On the other hand, the fuel cell generates power (discharges) using hydrogen gas or oxygen gas supplied from the outside. For this reason, the fuel cell does not have a problem related to the limit of energy density, as the secondary battery has. However, since the fuel cell is inferior to the load fluctuation at the time of discharge, it is difficult to apply to a use with a large load fluctuation, and it is usually used in combination with a power storage device such as a secondary battery or a capacitor. There are many. Further, the fuel cell has a structural feature that the reaction space is small and the reaction rate is low because the gas diffusion electrode, which is a line where gas, liquid and solid simultaneously contact, is used as the reaction space. In order to solve this problem, there is a problem that an expensive catalyst such as platinum is required.

  Further, a fuel gas such as hydrogen gas used in the fuel cell is taken out from a hydrogen production apparatus (for example, Patent Document 1), and the generated gas is a brown gas in which the ratio of hydrogen to oxygen is 2: 1. is there. Therefore, care must be taken to ensure safety.

  The present invention has been made in consideration of such points, and an object thereof is to provide a reversible fuel cell storage battery having high energy density and excellent load followability.

In order to achieve the above object, a reversible fuel cell storage battery according to the present invention includes a first electrode containing nickel hydroxide, a second electrode containing a hydrogen storage alloy, and a standard electrode having a standard electrode potential of the first electrode. A third electrode that is smaller than the potential and larger than the standard electrode potential of the second electrode, and a separator that passes ions but does not allow electrons to pass between the electrodes, the first electrode, the first electrode, The two electrodes and the third electrode have holes.
In this configuration, the third electrode is disposed between the first electrode and the second electrode. The reversible fuel cell storage battery refers to a fuel cell capable of storing electricity capable of reversibly converting fuel gas and electric energy.

The reversible fuel cell storage battery according to the present invention includes an oxygen gas holder that holds oxygen gas generated from the first electrode by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode; And a hydrogen gas holder for holding hydrogen gas generated from the second electrode by an oxidation reaction using the second electrode as a cathode and a reduction reaction using the third electrode as an anode.
In a reversible fuel cell battery, oxygen is generated from the first electrode by an oxidation reaction using the fully charged first electrode as an anode, and hydrogen is generated from the second electrode by an oxidation reaction using the fully charged second electrode as a cathode. To do. Convert electrical energy into chemical energy of oxygen and hydrogen.
In this configuration, the generated hydrogen gas and oxygen gas are individually stored in the hydrogen gas holder and the oxygen gas holder without being mixed, so that they do not contact each other to generate Brownian gas, ensuring safety. Has been made. Further, the chemical energy of the hydrogen gas and oxygen gas stored in the hydrogen gas holder and the oxygen gas holder can be reconverted to electric energy when the battery is discharged.

  In the reversible fuel cell storage battery according to the present invention, a gas impermeable separator is disposed between the second electrode and the third electrode. In the reversible fuel cell storage battery according to the present invention, the gas impermeable separator is sandwiched between the separators. Furthermore, in the reversible fuel cell storage battery according to the present invention, the gas impermeable separator has an opening diameter of 1 μm or less.

  In the reversible fuel cell storage battery according to the present invention, an oxygen gas packing is disposed between the first electrode and the hydrogen gas holder, and a hydrogen gas packing is disposed between the second electrode and the oxygen gas holder.

  The reversible fuel cell storage battery according to the present invention includes a first electrode current collector that is inscribed in the hole of the first electrode, a third electrode current collector that is inscribed in the hole of the three electrodes, and the second electrode current collector. A second electrode current collector is provided around the periphery of the electrode.

  In the reversible fuel cell storage battery according to the present invention, the first electrode, the second electrode, and the third electrode are all substantially disk-shaped, and a notch is formed on a part of the circumference of the second electrode. The hydrogen gas holder is formed between the second electrode and the second current collector, connected to the first electrode and the third electrode, and the hole of the first electrode and the third electrode It has a partition which bisects the inner space formed by the hole of the electrode, and one of the inner spaces is the oxygen gas holder, and the other is an electrolyte holder holding the electrolyte.

The reversible fuel cell storage battery according to the present invention generates power by supplying the hydrogen gas to the second electrode and supplying the oxygen gas to the third electrode.
In this configuration, the reversible fuel cell storage battery according to the present invention can generate power using the oxygen gas and hydrogen gas generated by the oxidation-reduction reaction described above, and can also generate power using oxygen gas and hydrogen gas supplied from the outside. can do.

In the reversible fuel cell storage battery according to the present invention, the third electrode contains manganese dioxide. In the reversible fuel cell storage battery according to the present invention, the third electrode further contains nickel hydroxide.
In this configuration, by using manganese dioxide as the third electrode, a reversible fuel cell storage battery can be configured at low cost. Further, by adding nickel hydroxide to the third electrode, an electrode excellent in output characteristics and life characteristics can be obtained.

  In the reversible fuel cell storage battery according to the present invention, the substrate of the first electrode and the substrate of the third electrode are nickel-plated steel plates, and the substrate of the second electrode is nickel foam.

  In the reversible fuel cell storage battery according to the present invention, the hydrogen storage alloy is not coated on the outer periphery of the second electrode. In the reversible fuel cell storage battery according to the present invention, the active material is not applied to the inner peripheral portions of the first electrode and the third electrode.

  In the reversible fuel cell storage battery according to the present invention, an AC power source is connected to the first electrode, the second electrode, and the third electrode. According to this configuration, there is little time margin for the concentration gradient to grow on the surfaces of the first electrode and the second electrode, and overvoltage due to the concentration gradient can be suppressed. Highly efficient water electrolysis can be realized.

In the reversible fuel cell storage battery according to the present invention, the third electrode is connected to one terminal of the AC power source, and current to the AC power source is blocked between the other terminal of the AC power source and the first electrode. A first diode is connected in the direction, and a second diode is connected between the other terminal of the AC power source and the second electrode in a direction to block current from the AC power source.
According to this configuration, the anode of the first diode and the other terminal of the AC power supply are connected, the cathode of the first diode and the first electrode are connected, and the cathode of the second diode and the other terminal of the AC power supply are connected. Thus, the anode of the second diode and the second electrode are connected.

  In the reversible fuel cell storage battery according to the present invention, the frequency of the AC power source is 0.01 to 60 Hz. In this configuration, the frequency of the AC power source is more preferably 0.01 to 2 Hz.

  As described above, according to the reversible fuel cell storage battery according to the present invention, a space for storing hydrogen gas and oxygen gas separately, that is, by providing a holder, the electric energy supplied at the time of charging is stored as a gas, and the electric energy is stored. It can be used after re-conversion. For this reason, in this reversible fuel cell storage battery, the electrical energy that can be taken out is stored as chemical energy in each holder, and does not depend on the amount of active material contained in the electrode material, so that high energy density is achieved. It becomes possible.

In addition, in the conventional sealed secondary battery, energy that has been discarded as heat at the time of overcharging can be reused as electric energy, so that energy utilization efficiency is improved.
Furthermore, since electric energy is input and output through the electrode reaction of the secondary battery, charging is possible and followability with respect to load fluctuations is greatly improved as compared with conventional fuel cells. Moreover, such a battery can be manufactured and supplied at low cost by adopting a simple structure that does not require an additional member or device for supplying gas.

  The reversible fuel cell storage battery provided with the third electrode of the present invention is characterized by high energy density and excellent load followability. In addition, by separating the reaction that generates oxygen and the reaction that generates hydrogen, hydrogen gas and oxygen gas are not mixed, and safety is high.

It is a side view of the reversible fuel cell storage battery of this invention. It is a front view of one lid member of a reversible fuel cell storage battery. It is a front view of the other lid member of a reversible fuel cell storage battery. It is sectional drawing which shows the structure of a reversible fuel cell storage battery typically, Comprising: It is drawing showing the AA cross section in FIG. It is a top view of the 1st electrode (positive electrode). It is a top view of the 3rd electrode (intermediate electrode). It is a top view of the 2nd electrode (negative electrode). It is sectional drawing which shows the structure of a reversible fuel cell storage battery typically, Comprising: It is drawing showing the BB cross section in FIG. It is sectional drawing which shows the structure of a reversible fuel cell storage battery typically, Comprising: It is drawing showing the CC cross section in FIG. It is a circuit connection diagram when an alternating current power supply is connected to a reversible fuel cell storage battery. It is a graph (the 1) which shows a test result when using AC power supply. It is a graph (the 2) which shows a test result when using AC power supply.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and various other modifications are possible.

  Before moving on to the detailed description of the reversible fuel cell storage battery, the basic components of the electrode and the battery, which are the main components, will be described, and then the reversible fuel cell storage battery will be described. For convenience of explanation, the first electrode will be referred to as the positive electrode, the second electrode will be referred to as the negative electrode, and the third electrode will be referred to as the intermediate electrode. To do.

<Positive electrode active material>
The positive electrode active material is preferably nickel hydroxide. Moreover, since it is easy to achieve high capacity | capacitance, a positive electrode active material has a large bulk density, for example, a spherical thing is preferable.

<Hydrogen storage alloy>
The hydrogen storage alloy contained in the negative electrode is not particularly limited as long as it can store and release hydrogen. For example, AB5 type that is a rare earth alloy, AB2 type that is a Laves phase alloy, AB type that is a titanium-zirconium alloy, and A2B type that is a magnesium alloy can be used.

  Among these, from the viewpoints of hydrogen storage capacity, charge / discharge characteristics, self-discharge characteristics, and cycle life characteristics, it is preferable to be an AB5 type rare earth-nickel alloy containing a MmNiCoMnAl misch metal.

<Active material for intermediate electrode>
The active material is preferably such that the standard electrode potential of the intermediate electrode is between the standard electrode potential of the positive electrode and the negative electrode. Since the standard electrode potential of nickel hydroxide as the positive electrode active material is 0.480 V and the standard electrode potential of the hydrogen storage alloy of the negative electrode is -0.828 V, the standard electrode potential of the intermediate electrode is -0.828 to 0.480 V. If it is in the range. Examples of the active material for the intermediate electrode include cadmium, zinc, lead, and manganese dioxide. Among these, manganese dioxide is the most appropriate considering the price and environmental burden. The standard electrode potential of the intermediate electrode using manganese dioxide as an active material is 0.15 V, which is within the above range. Manganese dioxide has abundant reserves and is 1/5 to 1/10 the price of nickel hydroxide. As will be described later, the amount of nickel hydroxide required for the reaction can be greatly reduced by introducing the intermediate electrode.

  The intermediate electrode may contain nickel hydroxide in addition to manganese dioxide. By adding nickel hydroxide to the intermediate electrode, an electrode excellent in output characteristics and life characteristics can be obtained.

<Binder>
Examples of the binder include polyacrylic acid soda, methyl cellulose, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene-vinyl alcohol, ethylene vinyl acetate copolymer (EVA), polyethylene ( PE), polypropylene (PP), and styrene-ethylene-butylene-styrene copolymer (SEBS). The binder does not need to be added, and may be added as necessary.
When the total of the electrode materials such as the active material, the binder and the conductive auxiliary agent is 100% by weight, the weight ratio of the binder mixed in each electrode is 0.1 to 10% by weight. It is preferable.

<Conductive aid>
The conductive auxiliary agent may be a conductive powder. The conductive aid may be a carbon powder such as graphite powder, acetylene black, and ketjen black. Nickel fiber may be used. Nickel fiber is durable and has a long life expectancy. Nickel fiber can be produced by applying nickel plating to carbon fiber or olefin fiber. It may be nickel oxyhydroxide. Nickel oxyhydroxide is resistant to overcharging but expensive. When the total of the electrode materials such as the active material, the binder and the conductive auxiliary agent is 100% by weight, the weight ratio of the conductive auxiliary agent mixed in each electrode is in the range of 0.1 to 10% by weight. It is preferable. The conductive auxiliary agent does not need to be added, and may be added as necessary.

<Board>
The positive and negative substrates are desirably metals that have electron permeability but no gas permeability. On the other hand, the substrate of the intermediate electrode preferably has electron permeability and gas permeability. Therefore, a nickel-plated steel plate was used for the positive electrode substrate, a nickel-plated steel plate was used for the negative electrode substrate, and nickel foam was used for the intermediate electrode substrate.

[Positive electrode]
Nickel hydroxide was used as the active material, nickel fiber was used as the conductive additive, and ethylene vinyl acetate copolymer (EVA) was used as the binder, and the blending ratio was 100: 5: 5 by weight. A powdered positive electrode material was mixed and kneaded into a paste, and the paste was applied or filled on both sides of the substrate. After drying, the substrate was rolled with a roller press to produce a positive electrode. Note that. Although a nickel-plated steel plate is used as the substrate, it may be nickel metal or nickel-plated foil, and the shape may be a three-dimensional shape or a plate shape, and the active material may be applied to both sides.

[Negative electrode]
A hydrogen storage alloy was used as the active material, nickel fiber was used as the conductive aid, and ethylene vinyl acetate copolymer (EVA) was used as the binder, and the blending ratio was 100: 15: 10 by weight. Powdered negative electrode materials were mixed and kneaded into a paste, and the paste was applied or filled on both sides of the substrate. After drying, the substrate was rolled with a roller press to produce a negative electrode. Note that. Although a nickel-plated steel plate is used as the substrate, it may be nickel metal or nickel-plated foil, and the shape may be a three-dimensional shape or a plate shape.

[Intermediate electrode]
Manganese dioxide was used as the active material, nickel fiber was used as the conductive aid, and ethylene vinyl acetate copolymer (EVA) was used as the binder, and the blending ratio was 100: 15: 10 by weight. Powdered intermediate electrode materials were mixed and kneaded into a paste, and this paste was applied to a nickel foam substrate and coated, and after drying, the substrate was rolled with a roller press to produce an intermediate electrode. Note that. Nickel fiber may be used as the substrate, and the shape may be foil or plate.

[Electrolytes]
The electrolytic solution used in the present invention is not particularly limited as long as it is an alkaline aqueous solution usually used in water electrolysis. For example, potassium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), etc. Those obtained by dissolving one alkali substance or two or more alkali substances in water are preferred. From the viewpoint of battery output characteristics, the electrolytic solution is preferably an aqueous potassium hydroxide solution. The concentration of the alkaline substance in these electrolytic solutions is preferably 1 to 10 mol / L, and more preferably 3 to 8 mol / L.

[Separator]
The separator transmits protons without passing electrons. Examples of the separator include microporous membranes, woven fabrics, non-woven fabrics, and green compacts. Among these, non-woven fabrics are preferable from the viewpoint of output characteristics and production cost. The material of the separator is not particularly limited, but is preferably a separator having alkali resistance, oxidation resistance, and reduction resistance. Examples thereof include materials such as polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aramid, polyethylene, and polypropylene.

  The thickness is preferably in the range of 10 to 500 μm, more preferably in the range of 20 to 100 μm. If the thickness is 10 μm or less, the possibility of rare short-circuiting increases, and if it is 500 μm or more, the electrical resistance increases and heat loss increases. In this embodiment, a polypropylene nonwoven fabric having a thickness of 150 μm was employed. The separator preferably has an opening diameter of 10 μm or more so that hydrogen gas generated at the negative electrode permeates.

  The gas impermeable separator does not allow hydrogen gas or oxygen gas, particularly hydrogen gas, to pass therethrough. Examples of the form include a microporous membrane, a nonwoven fabric, and a green compact. Among these, a nonwoven fabric is preferable from the viewpoint of output characteristics and production cost. The material of the separator is not particularly limited, but is preferably a separator having alkali resistance, oxidation resistance, and reduction resistance. Examples thereof include materials such as polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aramid, polyethylene, and polypropylene.

  The gas impermeable separator preferably has an aperture diameter of 1 μm or less. A nonwoven fabric having a fiber diameter of about 1 μm was compressed by a press to a thickness of 24 μm, but may be appropriately selected within a range of 21 to 27 μm. Since the nonwoven fabric with a small fiber diameter is compressed, the pore diameter is small and gas does not pass when wetted with the electrolyte. An ion exchange resin membrane may be used instead of the nonwoven fabric.

[Battery body]
A structure of a reversible fuel cell storage battery according to the present invention will be described with reference to the drawings. FIG. 1 is a side view of a reversible fuel cell storage battery. The reversible fuel cell storage battery 1 has a battery body stored inside a rectangular parallelepiped. That is, a cylindrical battery body is housed in a rectangular sheath made of synthetic resin and a space covered by the lid members 4 attached to both ends of the sheath 3. The lid members 4 a and 4 b are attached so as to close the openings at both ends of the exterior 3, and the left and right lid members 4 and the exterior 3 are integrally assembled by four bolts 5.

  Front views of the left and right lid members 4 are shown in FIGS. 2A and 2B, respectively. One lid member 4a is provided with connection ports 6a, 6b, 6c that communicate with an oxygen holder, a hydrogen holder, and an electrolyte solution holder, which will be described later. The other lid member 4 b is provided with terminals 7 a, b, and c that are electrically connected to the positive electrode, the negative electrode, and the intermediate electrode, and is connected to an external device through these terminals 7.

  The structure of the battery body 2 of the reversible fuel cell storage battery will be described with reference to FIGS. FIG. 3 is a cross-sectional view taken along the line AA in FIG. 1 and schematically showing a cross section perpendicular to the axial direction of the battery body 2. 5A and 5B are a cross-sectional view taken along the line BB and a line CC in FIG. 3, respectively, and schematically showing a cross-section in the axial direction of the battery body 2.

  As shown in FIG. 3, the battery body 2 includes a positive electrode 11, a negative electrode 12, an intermediate electrode 13, and a separator 14 interposed between these electrodes as main components inside a cylindrical negative electrode current collector 27. It is housed and configured.

  The positive electrode 11, the negative electrode 12, and the intermediate electrode 13 are stacked in the axial direction of the battery body 2 via the separator 14 and are accommodated in the inner space of the negative electrode current collector 27 (see FIG. 5). The separator 14 holds an electrolytic solution, insulates the electrodes and allows ions to pass therethrough. The intermediate electrode 12 is formed by filling a nickel foam substrate with a hydrogen storage alloy so that gas can pass therethrough. The negative electrode 12 has a substantially disk shape whose outer diameter is slightly larger than the inner diameter of the negative electrode current collector 27, and has a shape obtained by cutting off a part on the circumference separated by 180 degrees. The outer periphery of the negative electrode 12 is in contact with the inner surface of the negative electrode current collector 27 except for the cut portion, and the two are electrically connected. A hydrogen gas holder 24 is formed in a notch portion between the cut-out portion of the negative electrode 12 and the negative electrode current collector 12.

  Both the positive electrode 11 and the intermediate electrode 13 have a substantially disk shape with a hole in the center. A positive electrode current collector 26 is disposed on the periphery of the hole of the positive electrode 11 so as to be in contact with the positive electrode 11. Further, an intermediate electrode current collector 28 is disposed on the periphery of the hole of the intermediate electrode 13 so as to be in contact with the intermediate electrode 13. Both the positive electrode current collector 26 and the intermediate electrode current collector 28 are formed of a part of a cylinder smaller than a semicircle. Since the positive electrode current collector 26 and the intermediate electrode current collector 28 are attached so as not to interfere with each other in position, the positive electrode 11 and the intermediate electrode 13 do not come into contact with each other to cause an electrical short circuit.

  The positive electrode current collector 26 and the intermediate electrode current collector 28 attached at a position 180 degrees apart are mechanically connected to each other by an insulating partition wall 21. The partition wall 21 plays a role of holding both positions. An inner space formed by the hole of the positive electrode 11 and the hole of the intermediate electrode 13 is divided into two by the partition wall 21, and one space forms the oxygen gas holder 22 and the other space forms the electrolyte solution holder 23.

  A ring-shaped oxygen gas packing 17 is provided between the inside of the hydrogen gas holder 24 and the outside of the positive electrode 11 so that the hydrogen gas generated at the negative electrode 12 and the oxygen gas generated at the positive electrode 11 do not contact each other. Similarly, a ring-shaped hydrogen gas packing 17 is provided between the outside of the oxygen gas holder 22 and the negative electrode 12.

  In the prior art electrode, the active material is applied over the entire surface of both sides of the substrate. However, when the active material expands due to charge and discharge, the coated portion swells from the end surface of the substrate, and the coated portion with high electrical resistance There was a problem of becoming a current collecting surface. In order to solve this problem, the coating method was devised in this example.

  Plan views of the positive electrode 11, the intermediate electrode 13, and the negative electrode 12 are shown in FIGS. 4A, 4B, and 4C, respectively. Each of the positive electrode 11 and the intermediate electrode 13 has protrusions 11p and 13p in which a part of the hole extends inward of the hole. The protrusions 11p and 13p are smaller than a semicircle. The positive electrode 11 and the intermediate electrode 13 are coated with an active material except for the protruding portions 11p and 13p. That is, the positive electrode 11 and the intermediate electrode 13 have portions 11a and 13a coated with an active material and uncoated portions 11p and 13p in a substrate state.

  The protrusion 11p of the positive electrode 11 and the positive electrode current collector 26 are assembled so as to contact each other, and the protrusion 13p of the intermediate electrode 13 and the intermediate electrode current collector 28 are assembled so as to contact each other. Since the active material is not coated on the protruding portions 11b and 13b of the electrode, the coated portion does not move beyond the substrate even if the volume of the active material varies. Current collection of the positive electrode 11 and the intermediate electrode 13 is performed on a substrate having a small electric resistance.

  The negative electrode 12 has a portion 12a coated with a hydrogen storage alloy and an uncoated portion 12p in a substrate state. That is, since the outer periphery of the negative electrode 12 is uncoated, even if the volume of the hydrogen storage alloy fluctuates, the coated portion does not move beyond the cut surface of the substrate, and current collection is performed by cutting the substrate with low electrical resistance. Done on the surface.

  As shown in FIG. 5A, each electrode is laminated in the axial direction of the battery body 2 (up and down direction in FIG. 5A) in the order of the positive electrode 11, the intermediate electrode 13, the negative electrode 12, and the positive electrode 11. Each of the electrodes 11, 12, and 13 includes a substrate 11p, 12p, and 13p and an active material layer 11a, 12a, and 13a coated thereon. A separator 14 is disposed between the positive electrode 11 and the negative electrode 12, and between the positive electrode 11 and the intermediate electrode 13, and insulates these electrodes while allowing permeation of ions. A gas impermeable separator 15 is disposed between the negative electrode 12 and the intermediate electrode 13 so as to be sandwiched between two separators 14. The gas impermeable separator 15 prevents hydrogen gas generated at the negative electrode 12 from flowing to the intermediate electrode 13. This serves to prevent the oxygen gas generated from the intermediate electrode 13 due to the reaction between the positive electrode 11 and the intermediate electrode 13 and the hydrogen gas generated at the negative electrode 12 from being touched.

  The outer peripheral ends of the positive electrode 11 and the intermediate electrode 13 are covered with a ring-shaped oxygen gas packing 17. This prevents the oxygen gas generated at the intermediate electrode 13 from coming into direct contact with the hydrogen gas in the hydrogen gas holder 24, and the oxygen gas generated at the intermediate electrode 13 through the separator 14 between the intermediate electrode 13 and the positive electrode 11. Contact with the hydrogen gas in the hydrogen gas holder 24 is prevented.

  Further, the peripheral edge portion of the hole of the negative electrode 12 is covered with a ring-shaped hydrogen gas packing 18. This prevents hydrogen gas generated in the negative electrode 12 from coming into contact with oxygen in the oxygen gas holder 22. Such gas packings 17 and 18 were made of polypropylene. The material is not limited to polypropylene as long as it is an insulating material and has alkali resistance, oxidation resistance, and reduction resistance.

  Since the substrate 11p of the positive electrode 11 is a nickel-plated steel plate and does not transmit gas, it is not necessary to cover the outer peripheral edge of the substrate with the oxygen gas packing 17. Further, since the substrate 12p of the negative electrode 12 is a nickel-plated steel plate and does not transmit gas, it is not necessary to cover the peripheral portion of the hole in the substrate with the hydrogen gas packing 18.

  As described above, the inner space of the positive electrode 11 and the intermediate electrode 13 is divided by the partition wall 21, one being the oxygen gas holder 22 and the other being the electrolyte solution holder 23. 5A is a view of the positive electrode current collector 26 as viewed, and FIG. 5B is a view of the intermediate electrode current collector 28 as viewed.

  The operation of the reversible fuel cell storage battery configured as described above will be described separately for the water electrolysis mode, the fuel cell operation mode, and the secondary battery operation mode.

(Water electrolysis mode)
The water electrolysis mode is a mode in which hydrogen gas and oxygen gas are generated using water electrolysis and electrode reaction. In this mode, hydrogen gas is generated from the negative electrode 12 and oxygen gas is generated from the positive electrode 11, but these hydrogen gas and oxygen gas are stored separately in the oxygen gas holder 22 and the hydrogen gas holder 24 without contacting each other. Is done.
The water electrolysis mode will be described using a reaction formula, divided into an oxygen gas generation step and a hydrogen gas generation step.

(STEP1)
This step is an oxygen generation reaction step. The positive electrode 11 is connected to a positive pole (hereinafter simply referred to as positive pole) of a DC power source (not shown), and the negative electrode (hereinafter simply referred to as negative pole) of the DC power source is connected to the intermediate electrode 13 to charge the positive electrode 11. When the above is performed, the reaction formula of the positive electrode 11 becomes the formula (1).
Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1)
When the positive electrode 11 is fully charged, oxygen is generated from the positive electrode 11 according to the reaction formula (2).
2OH ⁻ → 2e ⁻ + H ₂ O + 1 / 2O ₂ (2)
On the other hand, the reaction formula of the intermediate electrode is the formula (3).
MnO ₂ + H ₂ O + e ⁻ → MnOOH + OH ⁻ (3)
And the total reaction formula before full charge of the positive electrode and the intermediate electrode is
From Equation (1) and Equation (3), Equation (4) is obtained.
MnO ₂ + Ni (OH) ₂ → MnOOH + NiOOH (4)
Here, as the discharge of the intermediate electrode 13 proceeds, an irreversible manganese trioxide (Mn ₃ O ₄ ) is generated, so that the reaction is stopped before the generation of trimanganese tetraoxide. This is a measure considering the life of the intermediate electrode 13.
The total reaction formula after full charge is expressed by formulas (2) and (3) to (5).
_{2MnO 2 + H 2 O → 2MnOOH} + 1 / 2O 2 (5)

(STEP2)
This step is a hydrogen generation reaction step. When the positive electrode is connected to the intermediate electrode 13 and the negative electrode 12 is connected to the negative electrode 12 to charge the negative electrode 12, the reaction formula of the negative electrode 12 is expressed by equation (6) when the hydrogen storage alloy is represented by M.
2M + 2H ₂ O + 2e ⁻ → 2MH + 2OH ⁻ (6)
When the negative electrode 12 is fully charged and the hydrogen storage alloy does not store hydrogen, hydrogen is generated from the negative electrode 12 according to the reaction formula (7).
2H ₂ O + 2e ⁻ → 2OH ⁻ + H ₂ (7)
On the other hand, the intermediate electrode 13 is charged by taking in the hydroxide ions, and the reaction equation becomes the equation (8).
2MnOOH + 2OH ⁻ → 2MnO ₂ + 2H ₂ O + 2e ⁻ (8)
When the intermediate electrode 13 is fully charged, the reaction is stopped.
At this time, the total reaction formula between the intermediate electrode 13 and the negative electrode 12 is the formula (9).
_{2MnOOH → 2MnO 2 + H 2 (} 9)
The total reaction of the positive electrode 11, the intermediate electrode 13, and the negative electrode 12 including STEP1 and STEP2 is represented by the equation (10).
H ₂ O → H ₂ + 1 / 2O ₂ (10)

Thereafter, by performing STEP 1, oxygen gas is generated from the positive electrode 11, and the generated oxygen gas is stored in the oxygen gas holder 22. Next, by performing STEP 2, hydrogen gas is generated from the negative electrode 12, and the generated hydrogen gas is stored in the hydrogen gas holder 24.
A feature of the hydrogen generation reaction is that hydrogen generated by electrolyzing water in the oxygen generation reaction is stored in a hydrogen storage alloy, and hydrogen is taken out using an oxidation-reduction reaction of the electrode.

  By repeating the reaction of STEP1 and STEP2, hydrogen gas and oxygen gas can be generated with a time difference. By providing a time difference, hydrogen and oxygen can be separated and collected easily and safely while maintaining high purity. It should be noted here that the generation amounts of oxygen and hydrogen are regulated by the amounts of nickel hydroxide and hydrogen storage alloy as shown in the equations (5) and (7), respectively. By repeating the above, oxygen and hydrogen can be continuously generated. That is, by introducing an inexpensive third electrode (intermediate electrode), it is possible to reduce the amount of positive electrode active material and negative electrode active material required for the reaction.

(Fuel cell operation mode)
The fuel cell operation mode is a mode in which power generation is performed using hydrogen gas and oxygen gas stored in the hydrogen gas holder 24 and the oxygen gas holder 22, respectively. Also included is a mode in which the negative electrode 12 and the positive electrode 11 are charged with the hydrogen gas and oxygen gas stored in each holder, respectively. As hydrogen gas and oxygen gas, hydrogen gas and oxygen gas stored in the fuel gas generation mode may be used, or fuel gas produced elsewhere may be used. Hereinafter, the fuel cell operation mode will be described using a reaction formula.

The negative electrode 12 can be charged with hydrogen gas stored in the hydrogen gas holder 24. The reaction formula is shown in Formula (11).
2M + H ₂ → 2MH (11)
The intermediate electrode 13 can be charged with oxygen gas stored in the oxygen gas holder 22. The reaction formula is shown in Formula (12).
4MnOOH + O ₂ → 4MnO ₂ + 2H ₂ O (12)
If the negative electrode 12 and the intermediate electrode 13 are in a charged state, the battery unit 20 can generate power as a fuel cell.
At this time, the reaction formulas of the negative electrode 12 and the intermediate electrode 13 are the formulas (13) and (14), respectively.
2MH + 2OH ⁻ → 2M + 2H ₂ O + 2e ⁻ (13)
_{2MnO 2 + 2H 2 O + 2e} - → 2MnOOH + 2OH - (14)
The oxygen reduction reaction rate is slower than the hydrogen oxidation reaction rate, and there is a difference in the reaction rate. However, in the reversible fuel cell storage battery described here, the electrode capacity of the intermediate electrode using manganese dioxide as the active material is adjusted to be larger than the electrode capacity of the negative electrode using hydrogen storage alloy as the active material. The speed is balanced at the negative and intermediate electrodes.

The negative electrode and the intermediate electrode are charged with hydrogen gas and oxygen gas, respectively. At the same time, the negative electrode and the intermediate electrode in a charged state are discharged, so that the fuel cell can generate power. That is, the charge reaction of the formula (11) occurs in the negative electrode, and the discharge reaction of the formula (13) occurs, so that the negative electrode as a whole has the reaction shown in the formula (15).
H ₂ + 2OH ⁻ → 2H ₂ O + 2e ⁻ (15)
At this time, the hydrogen storage alloy of the negative electrode functions as a catalyst.
In addition, the charging reaction of the formula (12) occurs in the intermediate electrode, and the discharging reaction of the formula (14) occurs, so that the reaction as shown in the formula (16) is performed as the whole intermediate electrode.
1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻ (16)
At this time, manganese dioxide of the intermediate electrode acts as a catalyst.

(Secondary battery operation mode)
The secondary battery operation mode is a mode for charging and discharging as a secondary battery. The battery can be charged by using an external power source such as natural energy power generation, and discharged when the amount of power generated by natural energy is reduced to be used for adjusting power supply and demand. Hereinafter, the secondary battery operation mode will be described using a reaction formula.
The positive electrode and the negative electrode can be charged by an external power source. The reaction formula of the positive electrode is shown in the formula (17), and the reaction formula of the negative electrode is shown in the formula (18).
Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (17)
2M + 2H ₂ O + 2e ⁻ → 2MH + 2OH ⁻ (18)
The positive and negative electrodes in the charged state can supply power to the external load by discharging. The reaction formula is the reverse reaction of the above formulas (17) and (18).

Furthermore, in the state where the reaction of STEP1 in the water electrolysis mode and the subsequent STEP2 is completed, both the positive electrode and the negative electrode are in a charged state, and power can be supplied to the external load by discharging. The reaction formula of the positive electrode at this time is shown in Formula (19), and the reaction formula of the negative electrode is shown in Formula (20).
NiOOH + H ₂ O + e ⁻ → Ni (OH) ₂ + OH ⁻ (19)
MH + OH ⁻ → M + H ₂ O + e ⁻ (20)

  The reversible fuel cell storage battery according to the present embodiment stores, in addition to the energy that can be stored in the electrode by charging with electricity as a secondary battery, the electrical energy supplied during overcharging is stored as a gas in each gas holder 23, 24, This can be reconverted into electrical energy and used. Therefore, unlike the conventional secondary battery, the electric capacity of the reversible fuel cell storage battery is not limited by the amount of the active material, so the energy density of the reversible fuel cell storage battery is compared with the conventional secondary battery, It becomes possible to improve significantly (for example, several tens of times). Moreover, since the oxygen gas generated at the positive electrode 11 and the hydrogen gas generated at the negative electrode 12 are directly stored in the gas holders 23 and 24 at the time of overcharging, there is no need to additionally provide a gas booster or a communication path. A simple structure can be obtained.

  Furthermore, as described above, when the reversible fuel cell storage battery is discharged, electric energy is output based on the cell reaction. For this reason, as compared with the conventional fuel cell, the followability to the load and the power are greatly improved. Thereby, the reversible fuel cell storage battery can also be used for an application with a large load fluctuation that requires instantaneous high output. In this case, the reversible fuel cell storage battery can be used alone without requiring an additional power storage device such as a secondary battery or a capacitor.

  The hydrogen gas stored in the hydrogen gas holder and the oxygen gas stored in the oxygen gas holder can be reconverted to electric energy and used when the battery is discharged. Since oxygen gas and hydrogen gas are separated by gas packing, the safety of handling fuel gas (oxygen gas, hydrogen gas) is improved.

  A case of charging / discharging using an AC power supply will be described. FIG. 7 is a circuit connection diagram when an AC power source is connected to the reversible fuel cell storage battery. Each of the positive electrode 11, the negative electrode 12, and the intermediate electrode 13 is supplied with an alternating current from an alternating current power supply 45. As shown on the right side of FIG. 7, the alternating current waveform has a rectangular shape in which the swing widths on the positive side and the negative side are equal.

  A first diode 16 is connected between one terminal of the AC power supply 15 and the positive electrode 11 so that the current from the positive electrode 11 to the AC power supply 15 is cut off. In addition, a second diode 17 is connected between one terminal of the AC power supply 15 and the negative electrode 12 so that the current from the AC power supply 15 to the negative electrode 12 is cut off. The other terminal of the AC power supply 15 is directly connected to the intermediate electrode 13.

  In the positive half cycle, the current from the AC power supply 15 flows to the positive electrode 12 via the first diode 16 and returns to the AC power supply 15 via the intermediate electrode 13. In the negative half cycle, the current from the AC power supply 15 flows to the intermediate electrode 13 and returns from the second diode 17 to the AC power supply 15 via the negative electrode 12. In a positive half cycle in which a positive current flows, an oxygen generation reaction (the above STEP 3) occurs, and in a negative half cycle in which a negative current flows, a hydrogen generation reaction (the above STEP 4) occurs.

In the present embodiment, the operation is a so-called batch operation in which operation is performed by switching the reaction steps alternately in steps 3 and 4 in terms of time. On the other hand, since an alternating current is used in the present embodiment, a continuous operation is possible because a current flows alternately to each electrode.
In the water electrolysis system, the reaction at the positive electrode and the negative electrode occurs by diffusion of OH ^- ions, and a concentration gradient layer is generated around the electrode. This concentration gradient layer becomes a resistance in the electrode reaction, and the voltage between the electrodes is increased by this resistance. In the conventional water electrolysis system, the direction of current flow is constant from the negative electrode to the positive electrode, so that the concentration gradient layer becomes thick as the reaction continues and the voltage between the electrodes becomes excessive.

  On the other hand, in the present embodiment, a reaction occurs at the positive electrode in a cycle in which a positive current flows, and the negative electrode is in a resting state during this period. In the cycle in which a negative current flows, the reverse state occurs. As a result, there is no time for the concentration gradient to grow on the surface of the electrode, so that the overvoltage due to the concentration gradient can be kept small.

FIG. 8 and FIG. 9 show voltage changes when a rectangular wave current flows in a pulse shape. The horizontal axis indicates time in seconds, and the vertical axis indicates potential in units of V (volts). The scale on the left is the potential between the intermediate electrode and the negative electrode, and the scale on the right is the potential between the positive electrode and the intermediate electrode. The solid line is a graph showing the voltage between the intermediate electrode and the negative electrode and is a hydrogen generation reaction process. On the other hand, the broken line is a graph showing the voltage between the positive electrode and the intermediate electrode, and is an oxygen generation reaction process.
FIG. 8 is a graph showing a change in voltage when a pulsed current of 5 mA is passed in a cycle of 600 seconds. In both the solid line and the broken line, when a current is passed, the voltage suddenly rises due to electric resistance (IR drop) (range indicated by A). Thereafter, the resistance due to ion diffusion rate control due to the concentration gradient in the electrolyte increases, and the voltage gradually increases (range indicated by B). As the energization time becomes longer, the resistance due to ion diffusion increases.

  FIG. 9 is a graph showing a change in voltage when a pulsed current of 5 mA is applied at a cycle of 2 seconds. Compared to FIG. 8, it was confirmed that the resistance due to ion diffusion can be reduced by shortening the period. Thereby, electrolysis efficiency improves.

  The AC power source used in the present invention is not limited to a rectangular shape of 0.5 Hz. A sine wave AC power supply may be used, and the waveform shape is not limited. The frequency of the AC power supply is preferably 0.01 to 60 Hz. When the frequency is lower than 0.01 Hz, a time margin for growing the concentration gradient layer is provided. When the frequency is higher than 60 Hz, the conductance between the electrodes becomes a problem. Since power of the system can be used at 50 Hz and 60 Hz, power supply preparation becomes simple.

  The reversible fuel cell storage battery of the present invention can be suitably used as an industrial and consumer fuel cell.

DESCRIPTION OF SYMBOLS 1 Reversible fuel cell storage battery 2 Battery main body 3 Exterior 4 Cover member 5 Bolt 6 Connection port 7 Terminal
11 Positive electrode 12 Negative electrode 13 Intermediate electrode 14 Separator 15 Gas impermeable separator 17 Oxygen gas packing 18 Hydrogen gas packing 21 Bulkhead 22 Oxygen gas holder 23 Electrolyte holder 24 Hydrogen gas holder 26 Positive electrode current collector 27 Negative electrode current collector 28 Intermediate electrode current collector 31 Positive electrode terminal 32 Negative electrode terminal 33 Intermediate electrode terminal 37 Oxygen gas connection port 38 Hydrogen gas connection port 39 Electrolyte connection port 40 Bolt 41 Nut 45 AC power supply 46 First diode 47 Second diode

The reversible fuel cell storage battery according to the present invention includes an oxygen gas holder that holds oxygen gas generated from the first electrode by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode; And a hydrogen gas holder for holding hydrogen gas generated from the second electrode by a reduction reaction using the second electrode as a cathode and an oxidation reaction using the third electrode as an anode.
In a reversible fuel cell battery, oxygen is generated from the first electrode by an oxidation reaction using the fully charged first electrode as an anode, and hydrogen is generated from the second electrode by an oxidation reaction using the fully charged second electrode as a cathode. To do. Convert electrical energy into chemical energy of oxygen and hydrogen.
In this configuration, the generated hydrogen gas and oxygen gas are individually stored in the hydrogen gas holder and the oxygen gas holder without being mixed, so that they do not contact each other to generate Brownian gas, ensuring safety. Has been made. Further, the chemical energy of the hydrogen gas and oxygen gas stored in the hydrogen gas holder and the oxygen gas holder can be reconverted to electric energy when the battery is discharged.

A case of charging / discharging using an AC power supply will be described. FIG. 6 is a circuit connection diagram when an AC power source is connected to the reversible fuel cell storage battery. Each of the positive electrode 11, the negative electrode 12, and the intermediate electrode 13 is supplied with an alternating current from an alternating current power supply 45. As shown on the right side of FIG. 6 , the waveform of the alternating current has a rectangular shape in which the swing widths on the positive side and the negative side are equal.

FIG. 7 and FIG. 8 show voltage changes when a rectangular wave current flows in a pulse shape. The horizontal axis indicates time in seconds, and the vertical axis indicates potential in units of V (volts). The scale on the left is the potential between the intermediate electrode and the negative electrode, and the scale on the right is the potential between the positive electrode and the intermediate electrode. The solid line is a graph showing the voltage between the intermediate electrode and the negative electrode and is a hydrogen generation reaction process. On the other hand, the broken line is a graph showing the voltage between the positive electrode and the intermediate electrode, and is an oxygen generation reaction process.
FIG. 7 is a graph showing a change in voltage when a pulsed current of 5 mA is passed in a cycle of 600 seconds. In both the solid line and the broken line, when a current is passed, the voltage suddenly rises due to electric resistance (IR drop) (range indicated by A). Thereafter, the resistance due to ion diffusion rate control due to the concentration gradient in the electrolyte increases, and the voltage gradually increases (range indicated by B). As the energization time becomes longer, the resistance due to ion diffusion increases.

FIG. 8 is a graph showing a change in voltage when a pulsed current of 5 mA is applied at a cycle of 2 seconds. Compared to FIG. 7 , it was confirmed that the resistance due to ion diffusion can be reduced by shortening the period. Thereby, electrolysis efficiency improves.

Claims (17)

A first electrode comprising nickel hydroxide;
A second electrode containing a hydrogen storage alloy;
A third electrode having a standard electrode potential smaller than the standard electrode potential of the first electrode and larger than the standard electrode potential of the second electrode;
A separator that allows ions interposed between the electrodes to pass but does not allow electrons to pass;
Reversible fuel cell storage battery in which the first electrode, the second electrode, and the third electrode have holes An oxygen gas holder for holding oxygen gas generated from the first electrode by an oxidation reaction using the first electrode as an anode and a reduction reaction using the third electrode as a cathode;
2. The reversible fuel cell according to claim 1, further comprising: a hydrogen gas holder that holds hydrogen gas generated from the second electrode by an oxidation reaction using the second electrode as a cathode and a reduction reaction using the third electrode as an anode. Storage battery   The reversible fuel cell storage battery according to claim 2, wherein a gas-impermeable separator is disposed between the second electrode and the third electrode.   The reversible fuel cell storage battery according to claim 3, wherein the gas-impermeable separator is sandwiched between the separators.   The reversible fuel cell storage battery according to claim 4, wherein the gas-impermeable separator has an opening diameter of 1 μm or less.   The reversible fuel cell storage battery according to claim 2, wherein an oxygen gas packing is disposed between the first electrode and the hydrogen gas holder, and a hydrogen gas packing is disposed between the second electrode and the oxygen gas holder.   A first electrode current collector that is inscribed in the hole of the first electrode; a third electrode current collector that is inscribed in the hole of the three electrode; and a second electrode that circumscribes the periphery of the second electrode. The reversible fuel cell storage battery according to claim 2, further comprising a current collector. The first electrode, the second electrode, and the third electrode are all substantially disk-shaped,
A notch is provided in a part on the circumference of the second electrode, and the hydrogen gas holder is formed between the second electrode and the second current collector,
A partition wall that is connected to the first electrode and the third electrode and bisects an inner space formed by the hole of the first electrode and the hole of the third electrode;
The reversible fuel cell storage battery according to any one of claims 2 to 7, wherein one of the inner spaces is the oxygen gas holder and the other is an electrolyte holder that holds an electrolyte.   The reversible fuel cell storage battery according to claim 2, wherein power generation is performed by supplying the hydrogen gas to the second electrode and supplying the oxygen gas to the third electrode.   The reversible fuel cell storage battery according to claim 2, wherein the third electrode contains manganese dioxide.   The reversible fuel cell storage battery according to claim 10, wherein the third electrode further contains nickel hydroxide.   The reversible fuel cell storage battery according to claim 2, wherein the substrate of the first electrode and the substrate of the third electrode are nickel-plated steel plates, and the substrate of the second electrode is nickel foam.   The reversible fuel cell storage battery according to claim 12, wherein the hydrogen storage alloy is not coated on an outer peripheral portion of the second electrode.   The reversible fuel cell storage battery according to claim 12, wherein an active material is not coated on inner peripheral portions of the first electrode and the third electrode.   The reversible fuel cell storage battery according to claim 2, wherein an AC power source is connected to the first electrode, the second electrode, and the third electrode.   The third electrode is connected to one terminal of the AC power source, and a first diode is connected between the other terminal of the AC power source and the first electrode in a direction to block current to the AC power source, The reversible fuel cell storage battery according to claim 15, wherein a second diode is connected between the other terminal of the AC power source and the second electrode in a direction to block current from the AC power source. The reversible fuel cell storage battery according to claim 16, wherein the frequency of the AC power source is 0.01 to 60 Hz.

Images