JP2017123222A - Aqueous solution-based storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact aqueous solution-based storage battery of a large output type, which is high in battery voltage and suitable for large storage of electric power originating from a recyclable energy.SOLUTION: An aqueous solution-based storage battery comprises a structure in which a positive electrode and a negative electrode are separated from each other by a diaphragm. In the aqueous solution-based storage battery, hydroxyl ions contribute to a redox reaction of each or one of a positive electrode active material and a negative electrode active material; the diaphragm is composed of an ion-selective cation exchange membrane; and a negative electrode electrolyte is higher than a positive electrode electrolyte in pH.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aqueous storage battery.

  In recent years, depletion of resources and destruction of the environment are regarded as major problems on the earth, and there is a demand for the construction of a zero-emission society using renewable energy. However, the problem is that renewable energy has an unstable output and cannot be supplied according to power demand. Therefore, a storage battery capable of storing electric power on a large scale has attracted attention.

  Regarding storage batteries for power storage, various types of storage batteries having different components and operation methods such as lead storage batteries, lithium ion secondary batteries, NAS batteries, and redox flow batteries have been developed.

  For example, NAS batteries have a large capacity and a long life, and a system has been proposed that can be installed in megawatt units in large-scale renewable energy power plants such as wind farms and mega solars, and used for leveling applications for system linkage. ing. Lithium-ion secondary batteries have excellent power storage capacity per weight, high charge / discharge efficiency, and high output capability.As a backup system for home use, various capacities of various capacities have been obtained from various companies, especially in the wake of the Great East Japan Earthquake. Equipment is commercially available. Lead storage batteries are highly reliable and have a low cost per storage capacity, so they have been proposed for a wide range of applications such as load leveling for households and offices and leveling for renewable energy power plants. Since the redox flow battery stores the active material in a tank as a liquid and can easily increase its capacity, it is suitable for use in load leveling for offices and leveling in renewable energy power plants.

  In the case where zinc (Zn) is used as the negative electrode active material of the redox flow battery, the use of halogen as the positive electrode active material has been studied.

  Patent Document 1 discloses a power storage device having a configuration of a redox flow battery using zinc as a negative electrode active material, bromine, iodine, or the like as a halogen as a positive electrode active material, and having storage tanks for negative electrode and positive electrode electrolytes. Is disclosed.

JP 2014-10999 A

  As described above, for the large-scale introduction of renewable energy power expected in the future, it is preferable to use a NAS battery or a redox flow battery suitable for large-scale power storage. However, an organic solvent redox flow battery using a NAS battery or a Li salt has a risk of combustion, and therefore it is necessary to completely block outside air.

  In addition, an aqueous redox flow battery using a conventional metal ion is excellent in safety, but has a low electric capacity per unit. For this reason, a vast installation area is required, and the ratio of construction costs required for assembling the battery system increases. In addition, the battery voltage is low, and a large number of cells are required to increase the output. These problems increase the cost of the apparatus and suppress the increase in capacity of power storage.

  On the other hand, wind power generation facilities and solar power generation facilities are becoming larger in scale, and there is a tendency to increase the rate of introduction of renewable energy-derived electricity worldwide, and there is a large amount of power storage facilities for adjusting the power supply-demand gap. The demand for capacity is expected to increase rapidly in the future.

  In this way, as a need for a power storage system that stores electricity derived from renewable energy on a large scale, it is a highly safe aqueous solution system, but has a high weight and volume energy density, high battery voltage, and easy large-capacity power storage. Is required.

  An object of the present invention is to provide a large-power aqueous solution storage battery that is compact and suitable for large-scale storage of electric power derived from renewable energy and has a high battery voltage.

  In order to solve the above problems, the gist of the present invention is as follows.

  An aqueous storage battery having a structure in which a positive electrode and a negative electrode are separated by a diaphragm, and hydroxide ions contribute to the oxidation-reduction reaction of one or both of the positive electrode active material and the negative electrode active material. It is a selective cation exchange membrane and is characterized in that the pH of the negative electrode electrolyte is higher than the pH of the positive electrode electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the large output type aqueous solution type | system | group storage battery suitable for the large-scale storage of the electric power derived from renewable energy and a high battery voltage can be provided.

An example of a structural model figure of a storage battery by a present Example. The operation principle image figure of the storage battery by this invention. An example of the characteristic evaluation result which made the negative electrode by a present Example Zn and the positive electrode made the iodide ion. 1 is an example of a configuration model diagram of a one-pack type flow battery according to the present embodiment.

  The present invention relates to an aqueous storage battery, which is an aqueous storage battery having a structure in which a positive electrode and a negative electrode are separated by a diaphragm, and is used for the oxidation-reduction reaction of either or both of the positive electrode active material and the negative electrode active material. Product ions contribute, the diaphragm is an ion-selective cation exchange membrane, and the pH of the negative electrode electrolyte is higher than that of the positive electrode electrolyte. An example of the basic configuration of the aqueous solution storage battery according to the present invention is shown in FIG. The aqueous solution storage battery 100 includes a negative electrode electrolyte storage unit 1, a positive electrode electrolyte storage unit 2, a partition wall 3, a negative electrode 4, and a positive electrode 5. The partition 3 is an ion exchange membrane. The positive electrode electrolyte and the negative electrode electrolyte are aqueous solutions. The aqueous storage battery 100 is supplied with electric power from the power source 6 and charged. Then, electric power is supplied to the external load 7 and discharged. Although not shown, the redox flow battery may have a configuration in which an electrolyte stored in an external tank is circulated in at least one of the negative electrode electrolyte storage unit 1 and the positive electrode electrolyte storage unit 2. In this case, the aqueous solution storage battery 100 has a control circuit that issues a pump on / off command for circulating the electrolyte under a predetermined condition.

  One feature of the present invention is that hydroxide ions contribute to the oxidation-reduction reaction of either or both of the positive electrode active material and the negative electrode active material, and aqueous electrolytes having different pH are used for the positive electrode and the negative electrode. There is in being. FIG. 2 shows the operating principle of the storage battery according to the present invention. Higher voltage is important because higher power and higher capacity can be achieved as the battery voltage increases. However, since a general aqueous battery is likely to generate gas due to electrolysis of water, the battery voltage is limited to about 1.2V. In response to this problem, the present invention achieves higher voltage by adopting a configuration in which hydroxide ions contribute to the oxidation-reduction reaction and the pH of the negative electrode electrolyte is higher than that of the positive electrode electrolyte. be able to. Here, examples of the reaction in which hydroxide ions contribute to the oxidation-reduction reaction include oxidation-reduction by a reaction between a metal and a metal hydroxide. The reason why high voltage can be realized by this configuration is as follows. When hydroxide ions are used in the oxidation-reduction reaction, the oxidation-reduction potential E varies as the pH varies as shown in the equation of chemical equilibrium and oxidation-reduction potential of Formula 1. Specifically, E shifts to the low potential side as the pH increases.

E = E ⁰ -RT / nF (pH) ・ ・ ・ Formula 1
Here, E ⁰ is a standard redox potential, R is a gas constant, T is an absolute temperature, n is the number of electrons involved in the reaction, and F is a Faraday constant.

  A diagram showing the relationship between pH and E in Equation 1 is shown in FIG. When hydroxide ions contribute to the oxidation-reduction reaction, E varies depending on pH. For example, by lowering the pH on the positive electrode side and increasing the pH on the negative electrode side, it becomes possible to increase the voltage compared to the case of the same pH.

  However, when electrolytes having different pHs, that is, electrolytes having different concentrations of protons and hydroxide ions, are mixed, protons and hydroxide ions react and neutralize to become water. By this neutralization reaction, the pH of the positive and negative electrode electrolytes becomes equal. Thus, since the voltage cannot be increased when the neutralization reaction occurs, it is necessary to prevent the positive and negative electrolytes from being mixed by the diaphragm.

  On the other hand, as the battery reaction proceeds, the ion balance of the positive and negative electrodes changes. Therefore, in order to maintain the positive and negative ion balance, ions need to move inside the diaphragm. At this time, if hydroxide ions move inside the diaphragm, the neutralization reaction proceeds as described above. Therefore, ions moving inside the diaphragm need to be other than hydroxide ions. In order to select an ion species that moves inside the diaphragm as an ion other than hydroxide, the diaphragm needs to be an ion exchange membrane having ion selectivity, and a cation exchange membrane is used. Examples of ions that move through the diaphragm and maintain the positive and negative ion balance include alkali metal ions and alkaline earth metal ions. It may be a metal ion involved in the reaction.

  The active material is not particularly limited as long as it can be handled in a highly safe aqueous solution. Materials desirable as the positive electrode active material include halide ions such as iodide ions, bromide ions, and chloride ions. Halide ions are superior as an active material because of their high solubility in aqueous solutions and high volume energy density. In particular, among the halide ions, iodide ions and bromide ions can be handled as a flow battery because both oxidized species and reduced species are water-soluble ions. When a use as large-scale power storage is assumed, a flow battery capable of increasing the capacity only by increasing the amount of the electrolyte is preferable.

  A desirable material for the negative electrode active material is zinc. Zinc and zinc oxide are also used in primary batteries. The standard oxidation-reduction potential of zinc is -0.72V, and the standard oxidation-reduction potential of zinc oxide is -1.22V. It belongs to a category. For this reason, zinc and zinc oxide are suitable as the negative electrode active material.

  Moreover, zinc of a negative electrode active material can be handled as a flow battery by using a slurry-like electrolyte solution. Moreover, since the theoretical energy density of zinc is the highest in an aqueous solution system, only a positive electrode active material is allowed to flow, and a one-component flow battery in which the negative electrode side is a solid electrolyte may be used. The one-component flow battery can reduce the tank volume by half and reduce auxiliary equipment such as tanks, pumps, and piping. Therefore, it is advantageous in terms of installation area and cost as compared with a two-component flow battery in which both the negative electrode electrolyte and the positive electrode electrolyte are circulated.

  When zinc is used as the negative electrode active material, the concentration of zinc ions is preferably as high as possible, and needs to be 2 M / L or more which does not become diffusion-controlled. However, since the conductivity of the electrolytic solution decreases as the concentration increases, the battery is preferably about 3 to 15 M / L. Further, when zinc oxide is used as the active material, the concentration of the hydroxide ion as the reactant is preferably as high as possible, and it is necessary that the concentration be 2 M / L or more which does not become diffusion-controlled.

  The positive electrode active material is also preferably highly soluble. Sodium iodide has a solubility in an aqueous solution of 12 M / L, and the standard oxidation-reduction potential of iodide ions is 0.57 V. Therefore, it is suitable as a positive electrode active material from the viewpoint of solubility and reaction potential. The concentration is preferably 2 to 12 M / L which does not become diffusion-limited. The bromine compound has a solubility of about 2 M / L, but may have a standard oxidation-reduction potential of about 1.1 V, so that it can be used as a positive electrode active material.

  As for the electrode base material, the battery reaction of zinc and zinc oxide should proceed smoothly on the negative electrode side. Zn is suitable as the metal, but Ti, Fe, Cu, etc. may be used. Further, a chemically stable carbon material may be used. The positive electrode side is preferably a chemically stable carbon material because corrosion due to iodide ions or bromide ions becomes a problem. In order to further increase the reaction rate, a platinum group may be supported.

  The shape of the electrode substrate may be plate-like, but is preferably any of a porous body, mesh, expanded metal, fiber, felt, and non-woven fabric having a high specific surface area in order to increase the current density. When zinc is used as the negative electrode active material, it is necessary to select the shape of mesh, expanded metal, nonwoven fabric, etc. in consideration of the balance between the uniformity of the precipitation and the increase in the specific surface area because it uses the dissolution and precipitation of Zn ions. Further, when zinc oxide is used as the negative electrode active material, a fine porous particle shape in which zinc or zinc oxide fine particles are bound to an electrode substrate using a binder is preferable.

  Similarly, the shape of the electrode substrate on the positive electrode side may be plate-like, but in order to increase the current density, it may be any of a porous body, mesh, expanded metal, fiber, felt, and non-woven fabric with a high specific surface area. preferable.

  The storage tank, housing, and piping materials only need to be durable against corrosion by halides, and have mechanical strength that can withstand the weight of the electrolyte and the pressure of the pump. It is preferable to form with resin.

[Example 1]
FIG. 1 shows an example of a configuration model diagram of a storage battery. A metal solid active material is applied to the negative electrode, and oxidation and reduction is performed by a reaction between the metal and the metal hydroxide. Active material ions are applied to the positive electrode, and oxidation and reduction are performed on the electrode surface. Since the positive electrode is a reaction through hydroxide ions, the electrolytic solution becomes alkaline. The diaphragm uses a cation exchange membrane that inhibits the permeation of hydroxide ions and permeates ions that maintain the ion balance of the positive and negative electrodes, and the movement of ions accompanying the battery reaction utilizes alkali cations such as sodium ions.

Specifically, a zinc plate was used for the positive electrode and a carbon plate was used for the negative electrode. A 3M sodium hydroxide aqueous solution was used for the negative electrode electrolyte, a 3M sodium iodide aqueous solution was used for the positive electrode electrolyte, and a cation exchange membrane was used for the diaphragm. The negative electrode reaction is an oxidation-reduction reaction (formula 2) between zinc (Zn) and zinc hydroxide (ZnOH), and the standard electrode potential is 1.21V. The positive electrode reaction is an oxidation-reduction reaction (formula 3) of iodide ion (I ⁻ ) and triiodide ion (I ₃ ⁻ ), and the standard electrode potential is 0.57V.

Zn + OH-⇔ZnOH ₂ + 2e E0 = -1.21V ・ ・ ・ Formula 2
3I ^- ⇔I _3- + 2e E0 = 0.56V ・ ・ ・ Equation 3
The pH is 14 for the negative electrode and 4 for the positive electrode, and the moving cations are sodium ions. The battery voltage is 1.78 V, and a reaction at a potential higher than the water decomposition voltage (1.23 V) is possible.

  FIG. 3 shows an example of a discharge curve of a battery system in which zinc is used for the negative electrode and iodine ions are used for the positive electrode in the present embodiment of FIG.

[Comparative Example 1]
As a comparative example, an example in which zinc dissolution dissolution (standard electrode potential -0.72 V) is used for the oxidation-reduction reaction (Formula 4) and the negative electrode electrolyte and the positive electrode electrolysis are set to the same pH is shown. In the comparative example, zinc was used for the negative electrode, and zinc chloride aqueous solution was used for the positive and negative electrode electrolytes. The positive electrode side is the same as in Example 1. FIG. 3 shows an example of a discharge curve in the configuration model of the comparative example.

Zn ⇔Zn ²⁺ ＋ 2e E0 = -0.72V ・ ・ ・ Formula 2
The open circuit potential of the storage battery of this example was 1.78 V, which was higher than the open circuit potential (1.25 V) of the storage battery of the comparative example. When discharging at the same current density, the discharge voltage after 60 minutes of this example was 1.7 V, and the comparative example was 1.1 V, confirming that a voltage difference of 1.6 times could be realized. Thus, it is possible to realize a high voltage by adopting a configuration in which hydroxide ions contribute to the oxidation-reduction reaction and a pH of the negative electrode electrolyte is higher than that of the positive electrode electrolyte. In particular, by using zinc as the negative electrode active material and alkaline as the negative electrode electrolyte, and using a neutral halide aqueous solution as the positive electrode, an aqueous solution storage battery with high energy density and high output can be realized.

[Example 2]
FIG. 4 is an example of a configuration model of a flow battery 400 of 1 tank 1 pump that does not require an external tank for the positive electrode. The configurations of the active material and the electrolytic solution are the same as those in FIG. A positive electrode electrolyte 11 in which the positive electrode active material 10 is dissolved is stored in the external tank 9, and the positive electrode electrolyte 11 is supplied to the positive electrode electrolyte storage unit 2 via the pump 8, and the external tank 9 and the positive electrode electrolyte storage are stored. The cathode electrolyte 11 is circulated between the parts 2. Since the theoretical energy density of zinc is the highest as an aqueous solution system, only a positive electrode active material is allowed to flow, and a one-component flow battery with a negative electrode as a solid electrolyte can be used to store compact and large-capacity electric power. It becomes a power storage device suitable for.

Claims (6)

  An aqueous storage battery having a structure in which a positive electrode and a negative electrode are separated by a diaphragm, and hydroxide ions contribute to the oxidation-reduction reaction of one or both of the positive electrode active material and the negative electrode active material. An aqueous storage battery, which is a selective cation exchange membrane, wherein the pH of the negative electrode electrolyte is higher than the pH of the positive electrode electrolyte.   2. The aqueous solution storage battery according to claim 1, wherein the main ions moving through the diaphragm in accordance with the storage battery reaction are alkali metal ions or alkaline earth metal ions.   The aqueous solution storage battery according to claim 2, wherein the negative electrode electrolyte is alkaline, the negative electrode active material is a metal, and the oxidation-reduction reaction is performed by a metal, a metal hydroxide, and a metal oxide. System storage battery.   4. The aqueous solution storage battery according to claim 3, wherein the positive electrode active material is halide ions, and the electrolytic solution exhibits a pH buffering effect.   5. The aqueous solution type storage battery according to claim 1, wherein charge / discharge is performed by circulating at least one of a positive electrode electrolyte or a negative electrode electrolyte. 6.   5. The aqueous storage battery according to claim 1, wherein the negative electrode active material is zinc or zinc oxide, and the positive electrode active material is iodide ion dissolved in the positive electrode electrolyte. A one-component flow-type aqueous storage battery that circulates and charges and discharges.

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