JP2018195571A - Electrolyte solution, secondary battery, secondary battery system, and power generation system - Google Patents

Abstract

To provide: an electrolyte solution which is superior in output characteristic when used for a secondary battery; a secondary battery superior in output characteristic, which uses the electrolyte solution; and a secondary battery system and a power generation system, each including the secondary battery.SOLUTION: An electrolyte solution comprises: at least one of halogen molecules and halogen ions; and a compound which can form a complex in combination with the at least one of halogen molecules and halogen ions. In the electrolyte solution, at least part of the compound dissolves in a liquid medium, and the liquid medium includes water. The halogen molecule is at least one selected from a group consisting of a chlorine molecule, a bromine molecule and an iodine molecule. The halogen ion is at least one selected from a group consisting of a chlorine ion, a bromine ion and an iodine ion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolytic solution, a secondary battery, a secondary battery system, and a power generation system.

  A flow battery, which is a type of secondary battery, is capable of large-scale power storage of MWh class and is said to have excellent cost performance, and is expected to be applied in the renewable energy field, smart city field, etc. Has been.

  Until now, many researches have been made on vanadium ion-based flow batteries (V-based flow batteries) as flow batteries (see, for example, Patent Document 1), and application to demonstration plants has already been attempted. However, since a V-type flow battery uses vanadium which is a rare metal, there are significant problems in terms of cost.

Against this background, several new flow batteries that are advantageous in terms of cost, energy density, and temperature operating range have been proposed.
For example, a Zn / I-based flow battery using iodine ions as a positive electrode active material and zinc ions and zinc metal as a negative electrode active material has been proposed (see, for example, Patent Document 2). In addition, a secondary battery using a halogen compound such as iodine, chlorine, or bromine as a positive electrode active material and zinc as a negative electrode active material has been proposed (see, for example, Patent Document 3).
Since these positive electrode active materials and negative electrode active materials are less expensive than vanadium, which is a rare metal, costs can be reduced when used for secondary batteries such as flow batteries.

  In addition, between a negative electrode containing zinc as an active material, a complex adduct of iodine and a polymer capable of forming a complex adduct with iodine, and a positive electrode using a composition in which a carbon material is dispersed therein as an active material. A zinc / iodine secondary battery having a separator is proposed (for example, see Patent Document 4).

JP 2011-233372 A US Patent Application Publication No. 2015/0147673 U.S. Pat.No. 4,910,065 JP 63-205067 A

However, in the flow battery described in Patent Document 2 and the secondary battery described in Patent Document 3, an iodine film is deposited on the electrode surface along with the oxidation reaction of iodide ion (I ⁻ ) in the positive electrode electrolyte solution. When the iodine film is thickened, the resistance is increased and the oxidation current is reduced, which may reduce the output of the secondary battery.

In the Zn / iodine secondary battery of Patent Document 4, after dissolving a polymer capable of forming a complex adduct with iodine in an organic solvent, the carbon material is dispersed therein, and the organic solvent is removed by a press machine. The finely divided resin carbon composite that is included is pressed under pressure to form a positive electrode. Therefore, in this Zn / iodine secondary battery, the aforementioned polymer is used in a solid state fixed to the positive electrode. In the Zn / iodine secondary battery of Patent Document 4, the iodide ion in the electrolytic solution is converted to iodine (I ₂ ) on the electrode surface by an oxidation reaction, and forms a complex with the polymer fixed to the positive electrode. The complex has low electrical conductivity, and the output characteristics may be deteriorated.

An object of one embodiment of the present invention is to provide an electrolytic solution having excellent output characteristics when used in a secondary battery.
Another object of one embodiment of the present invention is to provide a secondary battery excellent in output characteristics, and a secondary battery system and a power generation system including the secondary battery.

  Specific means for solving the above problems include the following embodiments.

<1> An electrolytic solution comprising at least one of a halogen molecule and a halogen ion, and a compound capable of forming a complex with at least one of the halogen molecule and the halogen ion.
<2> The electrolytic solution according to <1>, further comprising a liquid medium, wherein at least a part of the compound is dissolved in the liquid medium.
<3> The electrolytic solution according to <2>, wherein the liquid medium includes water.
<4> The halogen molecule is at least one selected from the group consisting of chlorine molecules, bromine molecules and iodine molecules, and the halogen ions are at least selected from the group consisting of chlorine ions, bromine ions and iodine ions. The electrolytic solution according to any one of <1> to <3>, which is one.
<5> The electrolytic solution according to any one of <1> to <4>, wherein the halogen molecule is iodine, and the halogen ion is iodine ion.
<6> The electrolytic solution according to any one of <1> to <5>, wherein the compound is a polymer compound.
<7> The electrolyte solution according to <6>, wherein the polymer compound has a number average molecular weight of 200 to 1,000,000.
<8> The electrolyte solution according to <6>, wherein the polymer compound has a number average molecular weight of 5,000 to 500,000.
<9> The polymer compound is nylon-6, polytetrahydrofuran, polyvinyl alcohol, polyacrylonitrile, polyvinyl pyridine, polyvinyl pyrrolidone, polymethyl (meth) acrylate, polytetramethylene ether glycol, polyacrylamide, polypropylene glycol, polyethylene glycol, polyethylene oxide. And at least one selected from the group consisting of polyacetylene, poly (phenylene vinylene), polypyrrole, polyaniline, poly (phenylene sulfide), polythiophene, chitosan, amylose, starch, amylopectin, cellulose, glycogen, dextrin and cyclodextrin < Electrolyte as described in any one of 6>-<8>.
<10> The polymer compound includes at least one selected from the group consisting of polyvinylpyrrolidone, polyvinylpyridine, amylose, starch, amylopectin, glycogen, dextrin, and cyclodextrin, and any one of <6> to <8> Electrolyte as described in.
<11> The electrolytic solution according to any one of <6> to <8>, wherein the polymer compound includes polyvinylpyrrolidone.
A secondary battery provided with a <12> positive electrode, a negative electrode, and the electrolyte solution as described in any one of <1>-<11>.

<13> The secondary battery according to <12>, wherein the electrolytic solution is a positive electrode electrolytic solution containing at least one of the halogen molecules and the halogen ions as a positive electrode active material, and further includes a negative electrode electrolytic solution containing a negative electrode active material.
<14> The secondary battery according to <13>, wherein the negative electrode active material includes at least one of zinc and zinc ions.
<15> A cathode electrolyte reservoir that stores the cathode electrolyte, a anode electrolyte reservoir that stores the anode electrolyte, and the cathode electrolyte circulated between the cathode and the cathode electrolyte reservoir. The secondary battery according to <13> or <14>, wherein the secondary battery further includes a liquid feeding unit that circulates the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte reservoir.

<16> A secondary battery system comprising: the secondary battery according to any one of <12> to <15>, and a control unit that controls charging and discharging of the secondary battery.

<17> A power generation system comprising a power generation device and the secondary battery system according to <16>.
<18> The power generation system according to <17>, wherein the power generation device generates power using renewable energy.

One embodiment of the present invention can provide an electrolytic solution having excellent output characteristics when used in a secondary battery.
One embodiment of the present invention can provide a secondary battery with excellent output characteristics, and a secondary battery system and a power generation system including the secondary battery.

It is a block diagram which shows an example of a flow battery system. 2 is a cyclic voltammogram using the electrolytic solution of Example 1. FIG. 2 is a convective voltammogram using the electrolytic solution of Example 1. 3 is a Leich plot created based on a convective voltammogram using the electrolyte solution of Example 1. FIG. 3 is a cyclic voltammogram using the electrolytic solution of Comparative Example 1. 2 is a convective voltammogram using the electrolytic solution of Comparative Example 1.

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.

In the present disclosure, the numerical ranges indicated using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical description. . Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present disclosure, the content of each component in the electrolytic solution is the total of the plurality of types of substances present in the electrolytic solution unless there is a specific indication when there are multiple types of substances corresponding to the respective components in the electrolytic solution. Mean content.
Further, in the present disclosure, “content ratio” represents mass% of each component when the total amount of each electrolytic solution is 100 mass% unless otherwise specified.
Moreover, it will be apparent to those skilled in the art that the present invention can be practiced without utilizing some or all of the specific details described in the present disclosure. In addition, in order to avoid obscuring aspects of the present invention, detailed descriptions or illustrations of known points may be omitted.
In the present disclosure, “halogen ion” refers to an ion containing a halogen element that is reversibly generated by a redox reaction by a charge / discharge reaction. For example, a halogen molecule is reversibly generated from a halogen ion and another halogen ion is reversibly generated from a halogen ion by an oxidation-reduction reaction by charging and discharging.
In the present disclosure, “a compound capable of forming a complex with at least one of a halogen molecule and a halogen ion” refers to a compound capable of forming a complex with at least one halogen molecule in an electrolytic solution, and at least one halogen ion in the electrolytic solution. It refers to a compound that can form a complex.

[Electrolyte]
An electrolytic solution according to an embodiment of the present invention includes at least one of a halogen molecule and a halogen ion, and a compound capable of forming a complex with at least one of the halogen molecule and the halogen ion.

Usually, due to the charging reaction of the secondary battery, halide ions such as iodide ion (I ⁻ ) contained in the electrolyte undergo an oxidation reaction, and a film such as an iodine film is deposited on the electrode surface. As a result, the resistance is increased and the oxidation current is reduced, and the output of the secondary battery may be reduced. On the other hand, since the electrolytic solution of the present disclosure contains a compound capable of forming a complex with at least one of halogen molecules and halogen ions, by using this electrolytic solution for a secondary battery, halogen molecules, A halogen ion or the like and a compound capable of forming the above complex form a complex. Then, in the secondary battery, halogen molecules, halogen ions, etc. undergo oxidation-reduction reaction while maintaining the complex state, or the film such as iodine film on which the compound capable of forming the complex is deposited on the electrode surface is peeled off. In addition, since it forms a complex with the detached halogen molecule, it is presumed that deposition of a film such as an iodine film on the electrode surface is suppressed. Therefore, it is possible to reduce the thickness of the film, suppress the decrease in the oxidation current due to the resistance of the film, and improve the oxidation current as compared with the case where the compound capable of forming the complex is not used. it can. As described above, the secondary battery using the electrolytic solution of the present disclosure tends to be excellent in output characteristics.

(Halogen molecule and halogen ion)
Examples of halogen molecules include iodine molecules, bromine molecules, and chlorine molecules. Examples of halogen ions include iodine ions, bromine ions, and chlorine ions. Specifically, examples of the halogen ion include iodide ion (I ⁻ ), bromide ion (Br ⁻ ), chloride ion (Cl ⁻ ), triiodide ion (I ₃ ⁻ ), pentaiodide ion (I ₅ ^- ) Polyiodide ions and the like.

  The electrolytic solution is preferably one in which at least one selected from halogen compounds that give halogen ions and halogen molecules is dissolved or dispersed in a liquid medium.

  The halogen molecule is preferably an iodine molecule, the halogen ion is preferably an iodine ion, and the halogen compound is preferably an iodine compound.

Further, the electrolyte may contain an iodine compound as a halogen compound, the iodine _{compound, CuI, ZnI 2, NaI,} KI, HI, LiI, NH 4 I, BaI 2, CaI 2, MgI 2, SrI ₂ , CI ₄ , AgI, NI ₃ , tetraalkylammonium iodide, pyridinium iodide, pyrrolidinium iodide, sulfonium iodide and the like.

Iodine ions are preferably dissolved in the electrolytic solution. When water is used as the liquid medium, the iodine compound is preferably at least one of NaI, KI, and NH ₄ I. Since NaI, KI, and NH ₄ I have high solubility in water, the energy density of the secondary battery can be further improved by using at least one of NaI, KI, and NH ₄ I.

For example, CuI generates Cu ⁺ as a counter ion of I ^{− in} the electrolytic solution. The standard redox potential of the Cu ⁺ / Cu ²⁺ redox system is lower than the standard redox potential of the I ⁻ / I ₂ and I ⁻ / I ₃ ⁻ systems. For this reason, when CuI is used as the iodine compound, it becomes a hybrid potential between the Cu ⁺ / Cu ²⁺ system and the I ⁻ / I ₂ and I ⁻ / I ₃ ⁻ systems, and the I ⁻ / I ₂ and I ⁻ / I ₃ ^- is preferably the system decrease in positive electrode potential is a condition that does not become apparent.

In the electrolytic solution, the total content of the halogen compound and the halogen molecule is preferably 1% by mass to 80% by mass, more preferably 3% by mass to 70% by mass, and 5% by mass to 50% by mass. More preferably. By setting the total content of the halogen compound and the halogen molecule to 1% by mass or more, a secondary battery suitable for practical use with a high capacity tends to be obtained. Moreover, it exists in the tendency for the solubility or dispersibility in a liquid medium to become favorable because the total content rate of a halogen compound and a halogen molecule shall be 80 mass% or less. In addition, the content rate of a halogen compound and a halogen molecule represents the total content rate of the ion derived from a halogen compound and a halogen molecule in electrolyte solution. For example, when the halogen compound is an iodine compound and the halogen molecule is an iodine molecule, the iodine compound and the content of the iodine molecule are the ions derived from the iodine compound (for example, I ⁻ , I ₃ ⁻ , I ₅ ⁻ and their counter ions) and the total content of iodine molecules (I ₂ ).

In addition, the content of iodine ions and iodine molecules (total of I ⁻ , I ₃ ⁻ , I ₅ ⁻ and I ₂ ) in the electrolyte is preferably 1% by mass to 80% by mass, and 3% by mass to More preferably, it is 70 mass%, and it is still more preferable that it is 5 mass%-50 mass%.

In the electrolytic solution, iodine ions and iodine molecules are preferably present in any state of I ⁻ , I ₃ ⁻ , and I ₂ . Also, I ₂ is I ^- a reaction to I ₃ ^- to form a, I ₂ and I in the electrolytic solution ^- the ratio of A may preferably be adjusted in advance.

Further, the electrolytic solution may contain a redox substance other than halogen molecules and halogen ions. The redox substance other than halogen molecule and a halogen ^ion, _I - / I ₂ and ^I - / _{I 3} ^- system to form a mixed potential of the ^I - / _{I 2} and ^I - / _{I 3} ^- system of positive electrode potential Those in which the decrease in the thickness does not manifest are preferable.

  Examples of redox substances other than halogen molecules and halogen ions include chromium, vanadium, zinc, quinone compounds, lithium cobaltate, sodium manganate, lithium nickelate, cobalt-nickel-lithium manganate, and lithium iron phosphate. .

  The electrolyte solution may be a positive electrode electrolyte solution containing halogen molecules, halogen ions, etc. as a positive electrode active material, and further, if necessary, a positive electrode containing the aforementioned redox materials other than halogen molecules and halogen ions as a positive electrode active material. It may be an electrolytic solution. Moreover, as electrolyte solution, the negative electrode active material may be included with the positive electrode active material. As a preferable negative electrode active material, the negative electrode active material contained in the negative electrode electrolyte solution mentioned later is mentioned.

(Complex-forming compound)
The electrolytic solution contains a compound (hereinafter also referred to as “complex-forming compound”) capable of forming a complex with at least one of halogen molecules and halogen ions (hereinafter also referred to as “halogen etc.”). The complex-forming compound is not limited as long as it is a compound capable of forming a complex with halogen or the like contained in the electrolytic solution. It is preferable that at least a part of the complex-forming compound is dissolved in the liquid medium from the viewpoint of the battery reaction rate, and it is more preferable that all of the complex-forming compound is dissolved in the liquid medium.
When the electrolytic solution contains a compound capable of forming a complex with halogen or the like, the precipitation of halogen molecules caused by the oxidation-reduction reaction of halogen ions tends to be suppressed.

  Further, the complex-forming compound may be provided with a functional group. For example, when a water-soluble functional group is added to the polymer compound described later, the polymer compound tends to be easily dissolved in the liquid medium.

The complex-forming compound may be a monomer compound or a polymer compound. When a polymer compound is used as a complex-forming compound, by forming a complex with a halogen or the like, the above-described electrolytic solution is used as a positive electrode electrolytic solution, and a membrane having pores such as a polyolefin porous membrane is used as a separator. Even if it exists, since the movement to the negative electrode electrolyte such as halogen via the separator is suppressed, the decrease in capacity retention rate when the charge / discharge reaction of the secondary battery is repeated is suppressed, and the cycle characteristics tend to be excellent. is there. Therefore, when a polymer compound is used as a complex-forming compound, in a secondary battery such as a flow battery, a high cation exchange membrane such as Nafion (DuPont) or an anion exchange membrane such as Selemion (Asahi Glass Co.) is used. Even if a membrane having pores such as an inexpensive polyolefin porous membrane is used instead of a cost separator, the deterioration of cycle characteristics tends to be suppressed. Therefore, in a secondary battery such as a flow battery, a polyolefin porous membrane or the like used in a lithium ion battery or the like can be used as a separator, and the cost can be reduced. In addition, compared to ion exchange membranes such as cation exchange membranes and anion exchange membranes, membranes with pores, such as polyolefin porous membranes, have higher ion conductivity in the electrolyte solution, which increases the output of secondary batteries. It tends to be able to plan.
Examples of the polyolefin porous film include a polyethylene porous film, a polypropylene porous film, and a multilayer film thereof.

  The number average molecular weight of the polymer compound is preferably 200 to 1,000,000, more preferably 5,000 to 500,000. The number average molecular weight of the polymer compound can be measured by gel permeation chromatography, static light scattering method, mass spectrometry method or the like. When the number average molecular weight is 200 or more, even when the above electrolyte is used as a positive electrode electrolyte and a membrane having a pore such as a polyolefin porous membrane is used as a separator, There exists a tendency for the movement to a negative electrode electrolyte solution to be suppressed suitably. When the number average molecular weight is 1,000,000 or less, thickening of the electrolytic solution tends to be suppressed. By suppressing the thickening of the electrolytic solution, a decrease in the reaction rate of the secondary battery is suppressed, and the secondary battery tends to be easily used at a large current density.

  Examples of the polymer compound include nylon-6, polytetrahydrofuran, polyvinyl alcohol, polyacrylonitrile, polyvinyl pyridine (preferably poly-4-vinyl pyridine), polyvinyl pyrrolidone, polymethyl (meth) acrylate, polytetramethylene ether glycol, polyacrylamide, Polypropylene glycol, polyethylene glycol, polyethylene oxide, polyacetylene, poly (phenylene vinylene), polypyrrole, polyaniline, poly (phenylene sulfide), polythiophene, chitosan, amylose, starch, amylopectin, cellulose, glycogen, dextrin, cyclodextrin, etc. Among them, polyvinylpyrrolidone, polyvinylpyridine, amylose, starch, amylope Chin, glycogen, dextrin and cyclodextrin are preferable, polyvinyl pyrrolidone and polyvinyl pyridine are more preferred, and polyvinylpyrrolidone are more preferred. As these polymer compounds, 1 type may be used independently and 2 or more types may be used together.

  In particular, polyvinylpyrrolidone and polyvinylpyridine tend to form stable complexes with iodine molecules and iodide ions, and tend to have particularly excellent cycle characteristics in secondary batteries. In addition, starch, amylose, amylopectin, glycogen, dextrin and the like have a spiral structure in a liquid medium such as water, and iodine molecules tend to be incorporated into the spiral structure to form a stable complex.

  As the cyclodextrin, β-cyclodextrin and γ-cyclodextrin are preferably used. Compared with α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin having a larger ring size tend to take in iodine molecules and form complexes more easily.

When the halogen compound is an iodine compound and the halogen molecule is an iodine molecule, polyvinyl pyrrolidone is preferable as the polymer compound from the viewpoint of cycle characteristics in the secondary battery. Polyvinylpyrrolidone can form a complex with all of I ⁻ , I ₂ , I ₃ ⁻ and I ₅ ⁻ (Non-patent literature: “The interaction between polyvinylpyrrolidone and I ₂ as probed by Raman spectroscopy”, J. Molecular Structure. , 479 (1999) 93-98).

  In the electrolytic solution, the content of the complex-forming compound, preferably the content of the polymer compound is preferably 0.01% by mass to 50% by mass, and more preferably 0.1% by mass to 30% by mass. More preferably, it is 1 mass%-20 mass%. By setting the content of the complex-forming compound to 0.01% by mass or more, precipitation of halogen molecules tends to be suppressed. Moreover, it exists in the tendency which can avoid the extreme thickening of electrolyte solution by making the content rate of a complex formation compound into 50 mass% or less.

  The electrolytic solution may contain a compound that does not form a complex with a halogen molecule and a halogen ion. For example, the monomer component of said polymer compound is mentioned.

(Liquid medium)
The electrolytic solution is preferably one in which at least one selected from halogen compounds that give halogen ions and halogen molecules is dissolved or dispersed in a liquid medium. A liquid medium means a medium in a liquid state at room temperature (25 ° C.). The liquid medium is not particularly limited as long as it is a medium that can disperse or dissolve halogen ions, halogen molecules, and the like.

  Liquid media include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl isopropyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, diethyl ketone, dipropyl ketone , Ketone solvents such as diisobutyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl-n-propyl ether, diisopropyl ether, Tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl n-propyl ether, diethylene glycol methyl n-butyl ether, diethylene glycol di-n-propyl ether, diethylene glycol di -N-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl n-butyl ether, triethylene glycol di-n-butyl ether, triethylene glycol Ethylene glycol Ru-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol methyl n-butyl ether, tetraethylene glycol di-n-butyl ether, tetraethylene glycol methyl n- Hexyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol di-n-butyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl ether, dipropylene glycol Methyl-n-butyl ether, dipropylene glycol Cold di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl ether, tripropylene glycol methyl-n -Butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetrapropylene glycol methyl ethyl ether, tetrapropylene glycol methyl-n-butyl ether, tetra Propylene glycol di-n-butyl ether, tetrapropylene Ether solvents such as ethylene glycol methyl-n-hexyl ether; carbonate solvents such as propylene carbonate, ethylene carbonate, diethyl carbonate; methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, Sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, acetic acid Cyclohexyl, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate Dipropylene glycol ethyl ether, glycol diacetate, methoxytriethylene glycol acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, lactic acid n-butyl, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene Ester solvents such as glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone; acetonitrile, N-methyl Aprotic polarities such as rupyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide Solvent: methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopentanol, 2-methylbutanol, sec-pentanol, t-pentanol , 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol, sec-oct Tanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2- Alcohol solvents such as propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, Diethylene glycol monoethyl ether, diethylene glycol mono-n-butyl ether Diethylene glycol mono-n-hexyl ether, triethylene glycol monoethyl ether, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, etc. And terpene solvents such as α-terpinene, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, oximene, and ferrandrene; water and the like. A liquid medium may be used individually by 1 type, and may use 2 or more types together.

  As the liquid medium, water is preferable. By using water as the liquid medium, the electrolyte solution tends to have a low viscosity, and the secondary battery tends to have a high output.

Moreover, it is preferable that electrolyte solution contains the good solvent with respect to a halogen molecule other than water, and when electrolyte solution contains an iodine compound, an iodine molecule, etc., it is preferable to contain the good solvent with respect to an iodine molecule other than water. When the electrolytic solution (preferably positive electrode electrolytic solution) contains a good solvent for halogen molecules, the film formed on the positive electrode during the charge reaction is thinned, and the inhibition of the charge / discharge reaction by the film tends to be suppressed. Good solvents for halogen molecules, preferably good solvents for iodine molecules, amides such as dimethylformamide, diethylformamide, acetamide, dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, ketones such as acetone and methylethylketone, methyl acetate And esters such as ethyl acetate and methyl nicotinate; sulfoxides such as dimethyl sulfoxide; alcohols such as ethanol and ethylene glycol; ethers such as diethyl ether; pyridine derivatives such as nicotinamide and cyanopyridine. As a good solvent for halogen molecules, one kind may be used alone, or two or more kinds may be used in combination.
The good solvent for the halogen molecule in the electrolytic solution can be identified by measuring the retention time corresponding to the good solvent for the halogen molecule and the molecular weight of the monitor ion, for example, by gas chromatography.

  The content of the good solvent with respect to the halogen molecules in the electrolytic solution is preferably 0.1% by mass to 80% by mass, more preferably 1% by mass to 50% by mass, and 1% by mass to 30% by mass. It is more preferable that it is 1 mass%-15 mass%. The content of the good solvent with respect to the halogen molecules in the electrolyte is, for example, by using gas chromatography. Can be quantified by creating data and calculating from the calibration curve.

(Supporting electrolyte)
The electrolytic solution may further contain a supporting electrolyte. The supporting electrolyte is an auxiliary agent for increasing the ionic conductivity of the electrolytic solution. When the electrolytic solution contains the supporting electrolyte, the ionic conductivity of the electrolytic solution increases, and the internal resistance of the secondary battery tends to decrease.

The supporting electrolyte is not particularly limited as long as it is a compound that dissociates in a liquid medium to form ions. Supporting electrolytes include HCl, HNO ₃ , H ₂ SO ₄ , HClO ₄ , NaCl, Na ₂ SO ₄ , NaClO ₄ , KCl, K ₂ SO ₄ , KClO ₄ , NaOH, LiOH, KOH, alkylammonium salt, alkylimidazo Examples thereof include a lithium salt, an alkyl piperidinium salt, and an alkyl pyrrolidinium salt. Moreover, the halogen compound may serve as both the active material and the supporting electrolyte. These supporting electrolytes may be used individually by 1 type, and may use 2 or more types together.

(PH buffer)
The electrolytic solution may further contain a pH buffer. Examples of the pH buffer include acetate buffer, phosphate buffer, citrate buffer, borate buffer, tartrate buffer, Tris buffer, and the like.

(Defoamer)
The electrolytic solution may further contain an antifoaming agent. When the electrolytic solution contains an antifoaming agent, foaming of the electrolytic solution can be suppressed, and clogging of the electrolytic solution and mixing of bubbles into the cells in the flow battery can be suppressed. There is no restriction | limiting in particular in the kind of antifoamer, Silicone, such as polydimethylsiloxane, is mentioned.

  In the electrolytic solution, the content of the antifoaming agent is not particularly limited, and is preferably 0.001% by mass to 10% by mass, and more preferably 0.01% by mass to 5% by mass. When the content of the antifoaming agent is 0.001% by mass or more, the antifoaming effect tends to be sufficiently obtained, and when the content of the antifoaming agent is 10% by mass or less, It tends to be able to suppress thickening and the accompanying deterioration in battery characteristics.

(Conductive material)
The electrolytic solution may further contain a conductive material. Examples of the conductive material include carbon materials, metal materials, and organic conductive materials. The carbon material and the metal material may be particulate or fibrous.
Carbon materials include activated carbon (steam activated or alkali activated); carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite such as natural graphite, artificial graphite, and expanded graphite; carbon Nanotubes, carbon nanohorns, carbon fibers, hard carbon, soft carbon and the like can be mentioned.
Examples of the metal material include particles or fibers such as copper, silver, nickel, and aluminum.
Examples of the organic conductive material include polyphenylene derivatives.

  These electrically conductive materials may be used individually by 1 type, and may use 2 or more types together. Among these, as the conductive material, carbon material particles are preferable, and activated carbon particles are more preferable. When the electrolytic solution contains activated carbon particles as a conductive material, energy storage and release by forming an electric double layer on the surface of the activated carbon particles is possible, and the energy density and output density of the secondary battery tend to be improved.

(Method for preparing electrolyte)
The electrolytic solution can be prepared by adding an iodine compound, iodine molecule, etc., a complex-forming compound, and other components as required to the liquid medium. When preparing the electrolytic solution, heating may be performed as necessary.

[Secondary battery]
The secondary battery according to the present disclosure includes a positive electrode, a negative electrode, and an electrolytic solution according to the present disclosure. The secondary battery may include a positive electrode electrolyte containing at least one of a halogen molecule and a halogen ion as a positive electrode active material as an electrolyte of the present disclosure, and further a negative electrode electrolyte containing a negative electrode active material. Alternatively, the secondary battery may include a negative electrode electrolyte solution containing at least one of a halogen molecule and a halogen ion as a positive electrode active material and including a negative electrode active material as the electrolyte solution of the present disclosure.

(Positive electrode and negative electrode)
As a positive electrode and a negative electrode, you may use the positive electrode and negative electrode which are used for a conventionally well-known secondary battery.

  As the positive electrode and the negative electrode, it is preferable to use an electrochemically stable material in the potential range to be used. The shape of the positive electrode and the negative electrode is not particularly limited, and examples thereof include a mesh, a porous body, a punching metal, and a flat plate. Examples of the positive electrode and the negative electrode include carbon electrodes such as carbon felt, graphite felt, and carbon paper; metal plates made of metal such as titanium, zinc, stainless steel, aluminum, nickel, and copper; metal electrodes such as metal mesh; .

The positive electrode is preferably an electrode having corrosion resistance against iodide ions (I ⁻ ). Examples of the electrode having corrosion resistance against iodide ions include an electrode made of a metal such as titanium, a carbon electrode, and the like, and a carbon electrode is preferable from the viewpoint of cost.

  For example, when the electrolyte contains zinc ions as the negative electrode active material, the negative electrode is preferably a zinc electrode, an electrode composed of a galvanized metal, a carbon electrode, or the like.

  From the viewpoint of increasing the output of the battery by increasing the surface area of the positive electrode and the negative electrode, the shape of at least one of the positive electrode and the negative electrode may be a porous body, felt, paper, or the like having a large specific surface area. In addition, carbon felt, graphite felt, or the like may be disposed on at least one surface of the positive electrode and the negative electrode, and at least one of the positive electrode and the negative electrode has a hole through which an electrolyte can permeate. Exchanges may be made.

  Carbon felt, carbon paper, and the like may improve wettability of the electrolytic solution of the present disclosure, the negative electrode electrolytic solution described later, and the like by heat treatment, etching treatment, and the like. For example, the heat treatment is preferably performed at 300 to 1000 ° C. in an atmosphere containing oxygen for 0.1 to 100 hours.

  When the secondary battery includes the electrolytic solution of the present disclosure as the positive electrode electrolyte and further includes the negative electrode electrolyte, the arrangement of the positive electrode and the negative electrode is not particularly limited.

  On the other hand, when the secondary battery includes at least one of a halogen molecule and a halogen ion as a positive electrode active material and includes an electrolyte solution containing the negative electrode active material as the electrolyte solution of the present disclosure, the positive electrode active material gathers on the positive electrode side, and It is preferable to dispose the positive electrode and the negative electrode so that the negative electrode active material gathers on the negative electrode side.

(Reference electrode)
The secondary battery may include a positive electrode reference electrode for measuring the positive electrode potential, or may include a negative electrode reference electrode for measuring the negative electrode potential. In the secondary battery, the positive electrode reference electrode and the negative electrode reference electrode are not indispensable components. If necessary, the positive electrode reference electrode and the negative electrode reference electrode are used, and the positive electrode potential and the negative electrode potential in the secondary battery are used. May be measured.

The positive electrode reference electrode and the negative electrode reference electrode may be any one that can be converted into a potential with respect to a standard hydrogen electrode potential and can exhibit a stable electrochemical potential. The reference electrode used as the electrochemical potential standard is indicated in textbooks and the like as the basics of electrochemistry (for example, “Allen J. Bard and Larry R. Faulkner,“ ELECTROCHEMICAL METHODS ”p. 3, (1980), John Wiley & Sons, Inc. "). Reference electrodes include Ag / AgCl reference electrodes, saturated calomel electrodes, and the like, with Ag / AgCl reference electrodes being preferred.
When an Ag / AgCl reference electrode is used as the reference electrode, for example, an RE-1CP saturated KCl silver-silver chloride reference electrode (manufactured by BAS Corporation) may be used.
Further, a reference electrode other than the Ag / AgCl reference electrode may be used as the positive electrode reference electrode and the negative electrode reference electrode, and the measured potential may be converted into the potential of the Ag / AgCl reference electrode.

(Partition wall)
The secondary battery may further include a partition as a separator between the positive electrode and the negative electrode, and the positive electrode electrolyte containing the positive electrode active material and the negative electrode electrolyte containing the negative electrode active material may be separated by the partition. The partition wall is not particularly limited as long as it can withstand the usage conditions of the secondary battery, and can transmit water molecules, ions, etc., and suppress self-discharge. Include a porous solid electrolyte membrane, a polyolefin porous membrane, and a cellulose porous membrane.

  The secondary battery preferably includes the electrolytic solution of the present disclosure as a positive electrode electrolytic solution, and further includes a negative electrode electrolytic solution containing a negative electrode active material. Since the preferable configuration of the positive electrode electrolyte is the same as the above-described electrolyte of the present disclosure, the description thereof will be omitted, and the preferable configuration of the negative electrode electrolyte will be described below.

(Negative electrolyte)
The secondary battery may further include a negative electrode electrolyte containing a negative electrode active material. The negative electrode active material may be any material as long as the standard redox potential of the reaction system is lower than the standard redox potential of the positive electrode. For example, when only iodine ions and iodine molecules are used as the positive electrode active material, the negative electrode active material may be a material whose standard redox potential of the reaction system is lower than 0.536 V, which is the standard redox potential of the positive electrode. Examples of the negative electrode active material include zinc, chromium, titanium, vanadium, iron, tin, lead, viologen compounds, quinone compounds, and sulfur compounds such as Na ₂ S ₂ . The negative electrode active material may be these ions, or may be a compound of these metals such as lithium titanate, sodium titanate, and titanium oxide. The negative electrode electrolyte is preferably one in which the negative electrode active material is dissolved or dispersed in a liquid medium.

  The negative electrode electrolyte preferably contains at least one of zinc and zinc ions as a negative electrode active material. For example, zinc chloride, which is a kind of a compound containing zinc, has a very high solubility in water of 30 mol / L, a standard redox potential of zinc dissolution and precipitation reaction is as low as −0.76 V, and zinc and zinc compounds are Zinc and zinc ions are suitable as the negative electrode active material because they are inexpensive. The compounds containing zinc include zinc iodide, zinc acetate, zinc nitrate, zinc terephthalate, zinc sulfate, zinc chloride, zinc bromide, zinc oxide, zinc peroxide, zinc selenide, zinc diphosphate, acrylic acid Examples thereof include zinc, zinc hydroxide carbonate, zinc stearate, zinc propionate, zinc fluoride, and zinc citrate.

When the negative electrode electrolyte contains at least one of zinc and zinc ions, the negative electrode electrolyte may contain a chelating agent capable of forming a complex with zinc ions (Zn ²⁺ ). Examples of chelating agents include acetylacetone, citric acid, ethylenediamine, bipyridine, ethylenediaminetetraacetic acid, phenanthroline, porphyrin, and crown ether.

  Moreover, you may use together zinc and the compound containing zinc, In that case, it is preferable to arrange | position zinc so that it may contact electrically on a negative electrode.

  When the negative electrode electrolyte contains zinc, zinc ions, or the like as the negative electrode active material, in order to suppress zinc dendrite in the negative electrode, Ni plate, Ni mesh, etc. (non-patent document: “Inhibition of Zn dendrite growth using NixZn (1-x) Oanodic material during redox cycling test in Zn / Ni battery ”, Solid State Ionics 295, 13-24 (2016)), and the negative electrode electrolyte is Ni salt additive, zinc trifluoromethanesulfonate ( Zinc trifluoromethylsulfonate) etc. (Non-patent literature: “Dendrite-free nanocrystalline zinc electrodeposition from an ionic liquid containing nickel triflate for rechargeable Zn-based batteries”, Angew. Chem. Int. Ed. 55, 2889-2893 (2016)).

  The viologen compound that can be contained in the negative electrode electrolyte is not particularly limited as long as it has a viologen skeleton (bipyridinium skeleton) and functions as a negative electrode active material. For example, the viologen compound preferably has a large molecular weight from the viewpoint of suppressing diffusion toward the positive electrode electrolyte. Specific examples of the viologen compound include compounds represented by the following general formula (I).

In general formula (1), R ¹ and R ² each independently represents an alkyl group, an aryl group, or an aralkyl group. R ¹ and R ² are each independently preferably an alkyl group having 1 to 100 carbon atoms, an aryl group having 6 to 100 carbon atoms, or an aralkyl group having 7 to 100 carbon atoms, and an alkyl group having 1 to 10 carbon atoms. More preferably, it is a group.
In general formula (1), X < ^- > each independently represents a counter ion. Counter ions include F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like. Can be mentioned.

At least one of R ¹ and R ² may have a substituent having at least one charge. As a result, the viologen compound in the two-electron reduced state also retains electric charge and tends to be easily dissolved in the negative electrode electrolyte.

The viologen compound may be a polymer having a viologen skeleton in the main chain or side chain from the viewpoint of suitably suppressing diffusion toward the positive electrode electrolyte. Specific examples of the polymer having a viologen skeleton in the main chain include polymers represented by the following general formulas (2) to (4) (for example, “An aqueous, polymer-based redox-flow battery using non-corrosive , safe, and low-cost materials. ”, Nature, 527, 79 (2015); doi: 10.1038 / nature15746). In such a case, R ³ may or may not have a substituent having a charge.

In general formulas (2) to (4), R ¹ represents an alkylene group, R ² has the same meaning as R ^{1 in} general formula (1), R ³ represents a hydrogen atom or a methyl group, and X ⁻ represents general It is synonymous with X < ^- > of Formula (1). The alkylene group represented by R ¹ preferably has 1 to 10 carbon atoms.

When the negative electrode electrolyte contains a viologen compound, a neutral separator is preferably used because the viologen compound tends to be stable in a neutral aqueous solution. For example, in Nafion which is a cation exchange membrane, —CF ₂ —SO ₃ H is superacid, and therefore, it is preferable to replace protons with alkali ions, alkaline earth ions, or the like. For example, Nafion having a —SO ₃ K group, a —SO ₃ Na group, etc. is obtained by immersing Nafion in a 1M potassium hydroxide aqueous solution or a sodium hydroxide aqueous solution and treating at room temperature to 100 ° C. for 0.5 hour to 100 hours. By making it, it can be set as a substantially neutral separator.

  The quinone compound that can be contained in the negative electrode electrolyte is not particularly limited as long as it has a quinone skeleton and functions as a negative electrode active material. For example, the quinone compound preferably has a large molecular weight from the viewpoint of suppressing diffusion toward the positive electrode electrolyte. Examples of the quinone skeleton include a benzoquinone skeleton, a naphthoquinone skeleton, and an anthraquinone skeleton.

  The quinone compound may be a polymer having a quinone skeleton in the main chain or side chain from the viewpoint of suitably suppressing diffusion toward the positive electrode electrolyte. The quinone compound may be, for example, a polymer having a benzoquinone skeleton, a naphthoquinone skeleton, an anthraquinone skeleton, or the like in the main chain or side chain. The polymer having a quinone skeleton in the side chain may further have a structural unit having no quinone skeleton.

  In the negative electrode electrolyte, the content of the negative electrode active material is preferably 1% by mass to 80% by mass, more preferably 3% by mass to 70% by mass, and 5% by mass to 50% by mass. Is more preferable. By setting the content of the negative electrode active material to 1% by mass or more, a secondary battery having a high capacity and suitable for practical use tends to be obtained. Moreover, it exists in the tendency for the solubility or dispersibility in a liquid medium to become favorable because the content rate of a negative electrode active material shall be 80 mass% or less.

  The negative electrode electrolyte solution may contain other components such as a liquid medium, a supporting electrolyte, a pH buffering agent, an antifoaming agent, and a conductive material, as in the above-described positive electrode electrolyte solution. Since the usable liquid medium, supporting electrolyte, pH buffering agent, antifoaming agent, and conductive material are the same as the above-described electrolytic solution of the present disclosure, the description thereof is omitted.

(Method for preparing negative electrode electrolyte)
The negative electrode electrolyte can be prepared by adding a negative electrode active material and other components as necessary to a liquid medium. When preparing a negative electrode electrolyte, you may heat as needed.

The secondary battery of the present disclosure may be a flow battery. More specifically, the secondary battery includes a positive electrode electrolyte reservoir that stores a positive electrode electrolyte that is an electrolyte of the present disclosure, a negative electrode electrolyte reservoir that stores a negative electrode electrolyte, and a positive electrode and a positive electrolyte reservoir. The flow battery may further include a liquid feeding part that circulates the positive electrode electrolyte between the negative electrode and the negative electrode electrolyte storage part, and circulates the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte storage part.
Hereinafter, each configuration of the flow battery will be described.

(Cathode electrolyte reservoir and anode electrolyte reservoir)
The flow battery includes a positive electrode electrolyte storage part that stores a positive electrode electrolyte and a negative electrode electrolyte storage part that stores a negative electrode electrolyte. As a positive electrode electrolyte storage part and a negative electrode electrolyte storage part, an electrolyte storage tank is mentioned, for example.

(Liquid feeding part)
The flow battery includes a liquid feeding unit that circulates the positive electrode electrolyte between the positive electrode and the positive electrode electrolyte reservoir, and circulates the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte reservoir. The positive electrode electrolyte stored in the positive electrode electrolyte storage part is supplied to the positive electrode chamber (positive electrode electrolyte reaction tank) in which the positive electrode is arranged through the liquid supply part, and the negative electrode electrolyte stored in the negative electrode electrolyte storage part is supplied. The negative electrode chamber (negative electrode electrolyte reaction tank) in which the negative electrode is disposed is supplied through the section.

  In the flow battery, for example, the liquid supply unit circulates the positive electrode electrolyte between the positive electrode chamber and the positive electrode electrolyte storage unit and circulates the negative electrode electrolyte between the negative electrode chamber and the negative electrode electrolyte storage unit. And a liquid feed pump.

  A gasket may be disposed at the joint of the circulation path from the viewpoint of liquid tightness. There is no restriction | limiting in particular as a raw material of a gasket, PTFE (polytetrafluoroethylene), ethylene propylene rubber, Hyperon (trademark), vinyl chloride, etc. are mentioned. The material of the circulation path is not particularly limited, and examples thereof include vinyl chloride, PFA (perfluoroalkoxy fluororesin), PTFE, rubber, and glass.

  The amount of the positive electrode electrolyte to be circulated between the positive electrode chamber and the positive electrode electrolyte reservoir and the amount of the negative electrode electrolyte to be circulated between the negative electrode chamber and the negative electrode electrolyte reservoir are appropriately adjusted using a liquid feed pump, respectively. What is necessary is just to set suitably according to a battery scale, for example.

(Sampling part)
The flow battery may further include a sampling unit that samples the positive electrode electrolyte. By sampling the positive electrode electrolyte in the sampling unit, it is possible to analyze the concentration of components contained in the positive electrode electrolyte such as halogen ions, halogen molecules, and additives such as good solvents for halogen molecules. The sampling part should just be arrange | positioned at a positive electrode electrolyte storage part, a circulation path, a positive electrode electrolyte reaction tank etc., for example.

(Density adjustment unit)
In addition, the flow battery analyzes the positive electrode electrolyte sampled by the sampling unit, and adjusts the concentration of the component contained in the positive electrode electrolyte circulating between the positive electrode and the positive electrode electrolyte storage unit based on the analysis result A density adjusting unit may be further provided. Thereby, when the concentration of the component contained in the positive electrode electrolyte is insufficient compared to the specified amount, the required amount, etc., the insufficient component is added to the positive electrode electrolyte, and the concentration of the component contained in the positive electrode electrolyte Can be adjusted. The concentration adjusting unit may be disposed in, for example, the positive electrode electrolyte storage unit, the circulation path, the positive electrode electrolyte reaction tank, and the like.

(Concentration measurement unit)
The flow battery may have a concentration measuring unit that measures the concentration of halogen ions and halogen molecules in the positive electrode electrolyte. Examples of the concentration measuring unit include a potential measuring unit that measures a potential based on the concentrations of halogen ions and halogen molecules in the positive electrode electrolyte. The potential measuring unit has, for example, a current collecting electrode for measuring a potential based on the concentration of halogen ions and halogen molecules, and a reference electrode serving as a reference for the electrochemical potential, and measures the electrochemical potential of the reference electrode To do. By using the Nernst equation relating to the electrochemical potential, the concentrations of halogen ions and halogen molecules can be obtained from the measured electrochemical potential of the reference electrode standard. Examples of the collecting electrode include a platinum electrode and a graphite electrode, and examples of the reference electrode include an Ag / AgCl electrode. The concentration measurement unit may be disposed in, for example, the positive electrode electrolyte storage unit, the circulation path, the positive electrode electrolyte reaction tank, and the like.

In addition, the flow battery may include a configuration for estimating a state of charge (SOC) based on the concentration measured by the concentration measuring unit, preferably the potential measured by the potential measuring unit. For example, when only I ⁻ , I ₃ ⁻ , and I ₂ are considered as redox substances, the SOC is 0%. Basically, I ₃ ⁻ and I ₂ are not included in the positive electrode electrolyte, and only I ⁻ is included. It shows the state. The SOC of 100% basically indicates a state in which I ⁻ is not contained in the positive electrode electrolyte, and only I ₃ ⁻ and I ₂ are present.

[Secondary battery system]
The secondary battery system of the present disclosure includes the above-described secondary battery of the present disclosure and a control unit that controls charging / discharging of the secondary battery. The secondary battery system of the present disclosure may be a flow battery system in which the secondary battery is a flow battery, and the control unit controls charging / discharging of the flow battery and, if necessary, a sampling unit, a concentration adjustment unit, It may be configured to control the concentration measuring unit or the like.

(Control part)
The secondary battery system includes a control unit that controls charging and discharging of the secondary battery. For example, the control unit may be configured to control the charging voltage in the secondary battery system, the charging potential of the positive electrode and the negative electrode, and the like.
The charging voltage indicates a potential difference between the negative electrode and the positive electrode, and the charging potential indicates a potential difference with respect to a reference electrode (reference electrode) having a constant reference potential.

(Configuration example of flow battery system)
Next, a configuration example of a flow battery system which is a kind of the secondary battery system of the present disclosure will be described with reference to FIG. The flow battery system is not limited to the configuration shown in FIG. Further, the size of the members in FIG. 1 is conceptual, and the relative relationship between the sizes of the members is not limited to this. In addition, about each structure in the flow battery system 100, since it is the same as that of the structure mentioned above, the detailed description is abbreviate | omitted.

As shown in FIG. 1, the flow battery system 100 includes a positive electrode 11, a negative electrode 12, a positive electrode reference electrode 13, a negative electrode reference electrode 14, a partition wall 15, a positive electrode electrolyte 16, and a positive electrode electrolyte storage tank. 18, a negative electrode electrolyte 17, a negative electrode electrolyte storage tank 19, circulation paths 20 and 21 as a liquid supply part, a positive electrode electrolyte liquid feed pump 22 and a negative electrode electrolyte liquid feed pump 23, and a control unit (not shown). And). In the flow battery system 100, a configuration in which I ⁻ and I ₃ ⁻ which are iodine ions as halogen ions and iodine molecules as halogen molecules in the positive electrode electrolyte and zinc ions as the negative electrode active material will be described. In addition, p in FIG. 1 indicates a polymer compound that is a complex-forming compound. Although not shown in FIG. 1, at least a part of the polymer compound forms a complex with at least a part of iodine ions and iodine molecules. doing.

  As shown in FIG. 1, the flow battery system 100 includes a cell stack 30 including a plurality of single cells each including a positive electrode 11, a negative electrode 12, and a partition wall 15. FIG. 1 shows a cell stack 30 having five single cells. The number of single cells is not particularly limited. Moreover, in the flow battery system 100 shown in FIG. 1, the positive electrode reference electrode 13 and the negative electrode reference electrode 14 are arranged on the positive electrode 11 and the negative electrode 12 in the cell stack configuration, and potential measurement using the reference electrode is possible. It has become. Charging / discharging of the flow battery system 100 is controlled by a control unit (not shown).

  The flow battery system 100 circulates the positive electrode electrolyte 16 between the positive electrode electrolyte reaction tank in which the positive electrode 11 is arranged and the positive electrode electrolyte storage tank 18 as a liquid feeding unit, and the negative electrode electrolysis in which the negative electrode 12 is arranged. Circulation paths 20 and 21 for circulating the negative electrode electrolyte 17 between the liquid reaction tank and the negative electrode electrolyte storage tank 19, a positive electrode electrolyte liquid feed pump 22, and a negative electrode electrolyte liquid feed pump 23 are provided.

  Further, in the positive electrode electrolyte storage tank 18, a sampling unit 24 that samples the positive electrode electrolyte 16 and a potential measurement unit 25 that measures a potential based on the concentrations of iodine ions and iodine molecules in the positive electrode electrolyte 16 are arranged. ing.

[Power generation system]
A power generation system of the present disclosure includes a power generation device and the above-described secondary battery system of the present disclosure. The power generation system of the present disclosure can level and stabilize power fluctuations or stabilize power supply and demand by combining a secondary battery system and a power generation device.

  The power generation system includes a power generation device. The power generation device is not particularly limited, and examples thereof include a power generation device that generates power using renewable energy, a hydroelectric power generation device, a thermal power generation device, and a nuclear power generation device. Among them, a power generation device that generates power using renewable energy is preferable. .

  The amount of power generated by power generators using renewable energy varies greatly depending on weather conditions, etc., but when combined with a secondary battery system, the generated power can be leveled and supplied to the power system. it can.

  Examples of the renewable energy include wind power, sunlight, wave power, tidal power, running water, tide, geothermal heat, etc., preferably wind power or sunlight.

  In some cases, generated power generated using renewable energy such as wind power and sunlight is supplied to a high-voltage power system. In general, wind power generation and solar power generation are affected by weather such as wind direction, wind power, and weather, and thus generated power is not constant and tends to fluctuate greatly. If the generated power that is not constant is supplied to the high-voltage power system as it is, it is not preferable because it promotes instability of the power system. For example, the power generation system of the present embodiment can level the generated power waveform to the target power fluctuation level by superimposing the charge / discharge waveform of the secondary battery system on the generated power waveform.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, the technical scope of this invention is not limited to this.

[Example 1]
10 mM sodium iodide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., positive electrode active material), 1 M sodium perchlorate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., supporting electrolyte) and 10% by mass polyvinylpyrrolidone “PVP K30” ( 100 mL of a positive electrode electrolyte solution containing a polymer compound (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., number average molecular weight: 40,000) was prepared by dissolving each component in water. Using this prepared positive electrode electrolyte, “HR2-RD1-Pt8 / Au5 (gold diameter 5 mm electrode)” as the working electrode, platinum coil as the counter electrode, and Ag / AgCl (in saturated KCl aqueous solution) as the reference electrode, cyclic voltammetry Went. HR-301 (made by Hokuto Denko) was used for the electrode device, and HZ-5000 (made by Hokuto Denko) was used for the potentiostat. The results are shown in FIG. The potential difference (referred to as peak separation) between the oxidation peak and the reduction peak was 97 mV at 10 mV · s ⁻¹ . The number of reaction electrons in the redox reaction of I ⁻ / I ₃ ⁻ is 2/3, and the theoretical value of peak separation in the reversible redox reaction at that time is 85.5 mV. The experimental value (97 mV) is close to this theoretical value, and the electrolyte solution of Example 1 can be easily classified as a reversible oxidation-reduction reaction. Moreover, the electrode was rotated at 200 rpm (rotations / minute) to 3000 rpm, and convective voltammetry was measured (sweep speed: 10 mV · s ⁻¹ ). The results are shown in FIG. FIG. 4 is a diagram in which a Levic plot is created based on FIG. About 0.6V vs. Although a decrease in the current value is observed at Ag / AgCl or higher, the linearity of the Levic plot is relatively good, indicating that the current value is mainly governed by the diffusion of iodine ions that can be controlled by the rotation of the electrode. .

  20 mL of a positive electrode electrolyte solution containing 1 M sodium iodide (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and 10% by mass polyvinylpyrrolidone “PVP K30” (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., number average molecular weight: 40,000) Each component was prepared by dissolving in water. Moreover, 20 mL of 1M zinc sulfate (made by Fuji Film Wako Pure Chemical Industries, Ltd.) aqueous solution was used for the negative electrode electrolyte.

A cell for a flow battery was prepared and evaluated as a flow type secondary battery. Gasket made of ethylene propylene rubber, carbon felt as positive electrode and negative electrode (Toyobo Co., Ltd., XF30A, area: 5 cm ² , thickness: 4.3 mm) and polypropylene porous membrane cell guard 2400 as separator (Aldrich, average pore size: 26 nm) Was used. The positive electrode electrolyte and the negative electrode electrolyte were circulated at about 7 mL · m ⁻¹ . Biological-BCS-815 (manufactured by Biological) was used as the charge / discharge test apparatus. The charge / discharge cycle test was conducted 100 cycles at a current value of 0.1 A (20 mA · cm ⁻² ) at 0 V to 1.6 V. The capacity retention rate after 100 cycles was 94%.

[Example 2]
The battery characteristics were evaluated in the same manner as in Example 1 except that the content of polyvinylpyrrolidone in the positive electrode electrolyte was 20% by mass. The capacity retention rate after 100 cycles was 92%.

[Example 3]
The battery characteristics were evaluated in the same manner as in Example 1 except that the content of polyvinylpyrrolidone in the positive electrode electrolyte was 5% by mass. The capacity retention rate after 100 cycles was 95%.

[Example 4]
The battery characteristics were evaluated in the same manner as in Example 1 except that polyvinylpyrrolidone “PVP K15” (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) having a number average molecular weight of 20,000 was used as the positive electrode electrolyte. The capacity retention rate after 100 cycles was 95%.

[Example 5]
The battery characteristics were evaluated in the same manner as in Example 1 except that polyvinylpyrrolidone “PVP K60” (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) having a number average molecular weight of 80,000 was used as the positive electrode electrolyte. The capacity retention rate after 100 cycles was 93%.

[Example 6]
The same amount of starch (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., soluble) was used instead of polyvinylpyrrolidone as the positive electrode electrolyte, and the starch was dissolved in the positive electrode electrolyte at 60 ° C. as in Example 1. Battery characteristics were evaluated. The positive electrode electrolyte was used after cooling to room temperature. The capacity retention rate after 100 cycles was 91%.

[Example 7]
The battery characteristics were evaluated in the same manner as in Example 1 except that Nafion 212 (manufactured by Aldrich) was used as the separator instead of the polypropylene porous membrane cell guard. The capacity retention rate after 100 cycles was 91%.

[Example 8]
The battery characteristics were evaluated in the same manner as in Example 1 except that a positive electrode electrolyte containing 0.5% by mass of polydimethylsiloxane as an antifoaming agent was prepared. The capacity retention rate after 100 cycles was 95%.

[Example 9]
Battery characteristics were evaluated in the same manner except that ethanol was further added to the positive electrode electrolyte so as to be 5% by volume. The capacity retention rate after 100 cycles was 99%.

[Comparative Example 1]
100 mL of a positive electrode electrolyte solution containing 10 mM sodium iodide (Fuji Film Wako Pure Chemical Industries, Ltd., positive electrode active material) and 1 M sodium perchlorate (Fuji Film Wako Pure Chemical Industries, Ltd., supporting electrolyte) Prepared by dissolving in water. Voltammetry was performed in the same manner as in Example 1 except that this positive electrode electrolyte was used. The results are shown in FIGS. In FIG. 5, the oxidation of iodine ion I ⁻ includes the reaction process of precipitation of iodine molecule I ₂ , and the reduction of I ₃ ⁻ as the final oxidation product is the reaction of I ₃ ⁻ → I ₂ + I ⁻ . Therefore, it is presumed that an asymmetric cyclic voltammogram was observed due to passing through I ₂ . Further, in FIG. 6, at an electrode rotation speed of 500 rpm and 1000 rpm, about 0.6 V to 0.8 V vs. A sudden drop in current was observed at the Ag / AgCl potential. This indicates that a decrease in current was observed due to precipitation of iodine molecules on the electrode surface, and iodine molecule I ₂ precipitation inhibited diffusion of iodine ions I ^{− to} the electrode surface caused by rotation of the electrode. It shows that. Moreover, it is estimated by comparison with the result of FIG. 3 that when polyvinyl pyrrolidone is contained in the electrolytic solution, iodine molecule I ₂ precipitation is suppressed and output characteristics in the secondary battery are suppressed.
The battery characteristics were evaluated in the same manner as in Example 1 except that the positive electrode electrolyte prepared in Comparative Example 1 was used. The capacity retention rate after 100 cycles was 11%. This is because the iodine compound diffused to the negative electrode side and self-discharged.

  All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference, Incorporated herein by reference.

DESCRIPTION OF SYMBOLS 11 Positive electrode 12 Negative electrode 15 Partition 13 Positive electrode reference electrode 14 Negative electrode reference electrode 16 Positive electrode electrolyte 17 Negative electrode electrolyte 18 Positive electrode electrolyte storage tank (positive electrode electrolyte storage part)
19 Anode electrolyte storage tank (Anode electrolyte storage part)
20, 21 Circulation route (liquid feeding part)
22, 23 Liquid feed pump (liquid feed part)
24 Sampling unit 25 Potential measurement unit (concentration measurement unit)
30 cell stack 100 flow battery system

Claims (18)

  An electrolytic solution comprising at least one of a halogen molecule and a halogen ion, and a compound capable of forming a complex with at least one of the halogen molecule and the halogen ion.   The electrolytic solution according to claim 1, further comprising a liquid medium, wherein at least a part of the compound is dissolved in the liquid medium.   The electrolytic solution according to claim 2, wherein the liquid medium contains water.   The halogen molecule is at least one selected from the group consisting of chlorine molecule, bromine molecule and iodine molecule, and the halogen ion is at least one selected from the group consisting of chlorine ion, bromine ion and iodine ion. The electrolyte solution according to any one of claims 1 to 3.   The electrolytic solution according to claim 1, wherein the halogen molecule is iodine, and the halogen ion is iodine ion.   The said compound is a polymer compound, The electrolyte solution of any one of Claims 1-5.   The electrolyte solution according to claim 6, wherein the polymer compound has a number average molecular weight of 200 to 1,000,000.   The electrolyte solution according to claim 6, wherein the polymer compound has a number average molecular weight of 5,000 to 500,000.   The polymer compound is nylon-6, polytetrahydrofuran, polyvinyl alcohol, polyacrylonitrile, polyvinyl pyridine, polyvinyl pyrrolidone, polymethyl (meth) acrylate, polytetramethylene ether glycol, polyacrylamide, polypropylene glycol, polyethylene glycol, polyethylene oxide, polyacetylene, 6. It contains at least one selected from the group consisting of poly (phenylene vinylene), polypyrrole, polyaniline, poly (phenylene sulfide), polythiophene, chitosan, amylose, starch, amylopectin, cellulose, glycogen, dextrin and cyclodextrin. The electrolyte solution according to claim 8.   9. The polymer compound according to claim 6, wherein the polymer compound includes at least one selected from the group consisting of polyvinylpyrrolidone, polyvinylpyridine, amylose, starch, amylopectin, glycogen, dextrin, and cyclodextrin. Electrolytic solution.   The electrolyte solution according to any one of claims 6 to 8, wherein the polymer compound contains polyvinylpyrrolidone. A positive electrode;
A negative electrode,
A secondary battery comprising: the electrolyte solution according to any one of claims 1 to 11. The electrolytic solution is a positive electrode electrolytic solution containing at least one of the halogen molecule and the halogen ion as a positive electrode active material,
The secondary battery according to claim 12, further comprising a negative electrode electrolyte containing a negative electrode active material.   The secondary battery according to claim 13, wherein the negative electrode active material contains at least one of zinc and zinc ions. A positive electrode electrolyte reservoir for storing the positive electrode electrolyte;
A negative electrode electrolyte reservoir for storing the negative electrode electrolyte;
A liquid feeding part for circulating the positive electrode electrolyte between the positive electrode and the positive electrode electrolyte reservoir, and circulating the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte reservoir;
The secondary battery according to claim 13, which is a flow battery further comprising: The secondary battery according to any one of claims 12 to 15,
A control unit for controlling charge and discharge of the secondary battery;
A secondary battery system comprising: A power generator,
A power generation system comprising: the secondary battery system according to claim 16.   The power generation system according to claim 17, wherein the power generation device generates power using renewable energy.