WO2018016593A1

WO2018016593A1 - Secondary battery, secondary battery system, positive electrode electrolyte solution, and power generation system

Info

Publication number: WO2018016593A1
Application number: PCT/JP2017/026309
Authority: WO
Inventors: 祐一利光; 渉太伊藤; 杉政　昌俊; 酒井　政則; 北川　雅規; 明博織田; 修一郎足立
Original assignee: 日立化成株式会社
Priority date: 2016-07-21
Filing date: 2017-07-20
Publication date: 2018-01-25
Also published as: WO2018016592A1; WO2018016591A1; WO2018016590A1; WO2018016594A1; WO2018016595A1

Abstract

A secondary battery is provided with: a positive electrode; a negative electrode; a positive electrode electrolyte solution that contains a compound having a sulfinyl group and at least one of iodine ions and iodine molecules as a positive electrode active material; and a negative electrode electrolyte solution containing a negative electrode active material.

Description

Secondary battery, secondary battery system, positive electrode electrolyte and power generation system

The present invention relates to a secondary battery, a secondary battery system, a positive electrode electrolyte, 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.

Among the flow batteries, vanadium ion-type flow batteries (V-type flow batteries) are operated at the demonstration plant level. However, since the V-type flow battery uses vanadium which is a rare metal, it is considered to be a big problem in terms of cost.

On the other hand, a new flow battery that is said to be advantageous in terms of cost, energy density, temperature operating range, and the like has been proposed. Specifically, an electrolytic solution containing zinc metal and zinc ions as a negative electrode active material is used for the negative electrode electrolytic solution, and an electrolytic solution containing iodine ions (I ⁻ ) as a positive electrode active material is used for the positive electrode electrolytic solution, A flow battery (Zn / I-based flow battery) using a reaction of iodine ions is disclosed (for example, see Patent Document 1).

Since the positive electrode active material and the negative electrode active material of the Zn / I-based flow battery are less expensive than the rare metal vanadium, the flow battery using the positive electrode active material and the negative electrode active material is lower in cost than the V-based flow battery. Can be achieved.

US Patent Application Publication No. 2015/0147673

However, with the oxidation reaction of iodide ion (I ⁻ ) in the positive electrode electrolyte, an iodine film is deposited on the surface of the electrode, and thickening the iodine film increases the resistance and decreases the oxidation current. The output of the secondary battery may be reduced.

One embodiment of the present invention provides a high-power secondary battery and a secondary battery system, a positive electrode electrolyte that can be used in the secondary battery and the secondary battery system, and a power generation system including the secondary battery system. For the purpose.

Specific means for solving the above problems include the following embodiments.
<1> A positive electrode, a negative electrode, a positive electrode electrolyte containing a compound having at least one of iodine ions and iodine molecules and a sulfinyl group as a positive electrode active material, and a negative electrode electrolyte containing a negative electrode active material Next battery.
<2> The secondary battery according to <1>, wherein the negative electrode electrolyte contains at least one of zinc and zinc ions as the negative electrode active material.
<3> The secondary battery according to <1> or <2>, wherein the positive electrode electrolyte further contains a good solvent for iodine molecules other than the compound having the sulfinyl group.
<4> The positive electrode electrolyte reservoir that stores the positive electrode electrolyte, the negative electrolyte reservoir that stores the negative electrolyte, and the positive electrolyte circulates between the positive electrode and the positive electrolyte reservoir. <1> to <3>, wherein the flow battery further includes a liquid feeding part that circulates the negative electrode electrolyte between the negative electrode and the negative electrode electrolyte reservoir. Secondary battery.
<5> The secondary battery according to any one of <1> to <4>, further comprising a sampling unit that samples the positive electrode electrolyte.
<6> The electrolyte according to <5>, further comprising a concentration adjusting unit that analyzes the positive electrode electrolyte sampled by the sampling unit and adjusts the concentration of a component contained in the positive electrode electrolyte based on the analysis result. Next battery.
<7> The secondary battery according to any one of <1> to <6>, further including a concentration measuring unit that measures the concentration of iodine ions and iodine molecules in the positive electrode electrolyte.
<8> The concentration measuring unit is a potential measuring unit that measures a potential based on the concentration of iodine ions and iodine molecules in the positive electrode electrolyte, and the state of charge is estimated based on the potential measured by the potential measuring unit. <7> The secondary battery as described in.
<9> The secondary battery according to any one of <1> to <8>, further comprising a positive electrode reference electrode for measuring a potential of the positive electrode.
<10> charge and discharge are controlled, the charging potential of the positive electrode is Ag / AgCl reference electrode ^- is set below 1.05V relative to the potential of (Cl concentration saturation), one of <1> to <9> The secondary battery as described in one.
<11> charge and discharge are controlled, the charging potential of the positive electrode is Ag / AgCl reference electrode ^- is controlled to 1.5V or less relative to the potential of (Cl concentration saturation), one of <1> to <10> The secondary battery as described in one.

<12> The secondary battery according to any one of <1> to <9>, and the charge potential of the positive electrode by controlling charge / discharge to be based on the potential of the Ag / AgCl reference electrode (Cl ⁻ concentration saturation) As a secondary battery system.
<13> The secondary battery according to any one of <1> to <9> and a charge potential of the positive electrode with reference to a potential of an Ag / AgCl reference electrode (Cl ⁻ concentration saturation) by controlling charge / discharge As a secondary battery system.
<14> the control unit, the positive electrode charging potential Ag / AgCl reference electrode ^- is controlled to 1.5V below the potential as a measure of (Cl concentration saturation), the secondary battery system according to <12>.

<15> A positive electrode electrolyte solution containing at least one of iodine ions and iodine molecules and a compound having a sulfinyl group.

<16> A power generation system comprising: a power generation device; and the secondary battery system according to any one of <12> to <14>.
<17> The power generation system according to <16>, wherein the power generation device generates power using renewable energy.

According to one aspect of the present invention, a secondary battery and a secondary battery system having high output, a positive electrode electrolyte that can be used in the secondary battery and the secondary battery system, and a power generation system including the secondary battery system are provided. Can be provided.

It is a block diagram of the secondary battery system of one Embodiment. It is a block diagram of the flow battery system of one Embodiment. It is a lineblock diagram showing an example of a power generation system of one embodiment. It is a figure which shows an example of the power generation electric power short time waveform of wind power generation. 3 is a graph showing a potential waveform of normal pulse voltammetry performed in Example 1. It is a normal pulse voltammogram (current potential curve) in Example 1 (pulse width 50 ms). 2 is a graph showing a potential waveform of reverse pulse voltammetry performed in Example 1. FIG. It is a reverse pulse voltammogram (current potential curve) in Example 1 (initial potential 0.50V, 0.55V, and pulse width 50ms). It is a reverse pulse voltammogram (current potential curve) in Example 1, and is a graph showing the effect of dimethyl sulfoxide contained in the electrolytic solution (initial potential 0.60 V and pulse width 50 ms). 3 is a reverse pulse voltammogram in Example 1 (initial potential 0.90 V to 1.10 V and pulse width 50 ms). It is a reverse pulse voltammogram (current potential curve) in Example 1 (initial potential 1.40V, 1.50V, and pulse width 50ms). It is a normal pulse voltammogram (current-potential curve) in Example 2 (pulse width 50, 500, and 5000 ms). It is a normal pulse voltammogram (current potential curve) in Example 2, and is a graph showing the effect of dimethyl sulfoxide contained in the electrolytic solution (pulse width 5000 ms). It is a schematic diagram which shows the electrode reaction of the flow battery system of one Embodiment. It is the electric current electric potential curve of the positive electrode and negative electrode of a flow battery which were implemented in Example 3.

Hereinafter, embodiments for carrying out the present invention will be described in detail. 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 specification, numerical values indicated by 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 this specification, 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 range. Good. Further, in the numerical ranges described in this specification, 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 specification, the content of each component in the composition is the sum of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. It means the content rate of.
In the present specification, “content ratio” represents mass% of each component when the total amount of each electrolytic solution is 100 mass% unless otherwise specified.
Further, in this specification, “vol%” represents the volume% of each component when the total amount of each electrolytic solution is 100% by volume unless otherwise specified.
In addition, 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 and detailed contents described in this specification. 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 specification, “iodine ion” means at least one of I ⁻ and I ₃ ⁻ .

[Secondary battery]
A secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a positive electrode electrolyte containing at least one of iodine ions and iodine molecules and a compound having a sulfinyl group as a positive electrode active material, and a negative electrode active material Negative electrode electrolyte.

In the secondary battery of this embodiment, the positive electrode electrolyte contains a compound having a sulfinyl group. Therefore, the I ₂ film (iodine film) deposited on the electrode surface due to the oxidation reaction of I ⁻ is easily peeled off, and the I ₂ film can be made thin. Thus, reduction in the oxidation current caused by I ₂ film becomes resistance is suppressed, thereby improving the oxidation current as compared with the case of not using the compound having a sulfinyl group. Therefore, it is possible to increase the output of the secondary battery.

Furthermore, secondary batteries, charging and discharging are controlled, the charging potential of the positive electrode Ag / AgCl reference electrode ^- is preferably configured to be set below 1.05V relative to the potential of (Cl concentration saturation). Thereby, like the secondary battery system of the first embodiment described later, the generation of IO ₃ ⁻ can be suppressed, and the total concentration of iodine ions and iodine molecules when reversibly charged and discharged is maintained, and the positive electrode discharge capacity and The decrease in the positive electrode charge capacity is suppressed, and the cycle durability can be improved. Therefore, it exists in the tendency which can provide the secondary battery which satisfy | fills the charging conditions which are excellent in practicality.

Further, secondary batteries, charging and discharging are controlled, the charging potential of the positive electrode Ag / AgCl reference electrode ^- is preferably configured to be controlled below 1.5V relative to the potential of (Cl concentration saturation). Thereby, like the secondary battery system of 2nd Embodiment mentioned later, deterioration of a positive electrode (especially carbon electrode) can be suppressed, and positive electrode electrolyte solution contains ethanol which is a good solvent with respect to an iodine molecule. In some cases, decomposition of ethanol can be suppressed.

Specific examples of the components of the secondary battery of the present embodiment are the same as those of the secondary battery system described later, and thus description thereof is omitted.

<First Embodiment>
[Secondary battery system]
A secondary battery system according to a first embodiment of the present invention includes a positive electrode, a negative electrode, a positive electrode electrolyte containing at least one of iodine ions and iodine molecules and a compound having a sulfinyl group as a positive electrode active material, and a negative electrode active material and a control unit that sets below 1.05V potential as a measure of ^- (concentration saturated Cl), a and a negative electrode electrolyte containing, charge and discharge control to the charging potential of the positive electrode Ag / AgCl reference electrode. That is, the secondary battery system, the charge potential of the positive electrode, Ag / AgCl reference electrode in a secondary battery ^- a system comprising a control unit that sets below 1.05V relative to the potential of (Cl concentration saturation).
The secondary battery system may further include a positive electrode reference electrode for measuring the positive electrode potential.

Hereinafter, in the secondary battery system, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- describes problem when more than 1.05V relative to the potential of (Cl concentration saturation).

First, in the secondary battery system, the positive electrode electrolyte contains at least one of iodine ions and iodine molecules as a positive electrode active material. For this reason, iodide ions (I ⁻ ) are oxidized at the positive electrode by the charging reaction shown in the following formulas (1) and (2) to normally generate I ₃ ⁻ and I ₂ , and the generated I ₃ ⁻ And I ₂ are reduced to I ⁻ by the discharge reaction shown in the formulas (1) and (2) at the positive electrode.

3I ⁻ ⇔I ₃ ⁻ + 2e ⁻ (1)
2I ⁻ ⇔I ₂ + 2e ⁻ (2)

In the secondary battery system, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- if it exceeds 1.05V relative to the potential of (Cl concentration saturation), below, along with the charging reaction shown by the formula (1) and (2) It is presumed that the production reaction of IO ₃ ⁻ represented by the formula (3) occurs.

I ⁻ + 3H ₂ O → IO ₃ ⁻ + 6H ⁺ + 6e ⁻ (3)

The reaction represented by the above formula (3) is reported to be an irreversible reaction, and the reaction rate of the reverse reaction is extremely slow (Reference 1: P. Beran, and S. Bruchenstein, Voltammetry of Iodine (I) Cholride, Iodine and Iodate at Rotated Platinum Disk and Ring-Disk Electrodes, Analytical chemistry, 40, 1044 (1968).).

Further, I ₂ is generated from IO ₃ ⁻ generated by the above formula (3) by the Dushman reaction represented by the following formula (4).

IO ₃ ⁻ + 5I ⁻ + 6H ⁺ → 3I ₂ + 3H ₂ O (4)

Furthermore, the following formula (5) is obtained as the total reaction (formula (3) + formula (4)) of the above formula (3) and formula (4).

I ₂ + 6H ₂ O → 2IO ₃ ⁻ + 12H ⁺ + 10e ⁻ (5)

According to the document 1, the chemical reaction rate of the above formula (4) is faster than the electrochemical reaction of the above formula (3), and the rate limiting rate of the formula (5) using the formula (3) and the formula (4) as a constituent reaction. The process is an electrochemical reaction of formula (3). Therefore, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- presumably exceed the 1.05V reference to the potential of (Cl concentration saturation), the above reaction formula (3) to (5) has occurred Is done.

Therefore, Ag / AgCl reference electrode ^- when the charging at the positive electrode charging potential is repeated more than 1.05V relative to the potential of (Cl concentration saturation), IO based on the equation (3) by charging reaction of the positive electrode ₃ ^- is Generated. IO ₃ ⁻ has a slow reaction rate of the discharge reaction, which is the reverse reaction of the formula (3), and hardly returns to I ⁻ .

Furthermore, IO ₃ generated based on equation (3) ^- by reaction of formula (4), I in the electrolyte ^- reacted with, in the electrolytic solution without electron transfer at the positive electrode I ^- Is consumed.

Further, by the reaction shown in Equation (5) is the total reaction of the formula (3) and (4), IO ₃ by the reaction I ₂ ^- but is produced, in the same manner as in the reaction shown in equation (3) The reaction shown in Formula (5) is also an irreversible reaction. For this reason, it is presumed that the generated IO ₃ ⁻ has a slow reaction rate of the discharge reaction, which is the reverse reaction of the formula (5), and is very difficult to return to I ₂ .

Therefore, when charging is repeated at a positive electrode charging potential exceeding 1.05 V, the proportion of IO ₃ ⁻ that does not contribute to the discharge reaction increases, and the total concentration of I ⁻ and I ₂ decreases, which gradually increases. The secondary battery system has a problem that the positive electrode discharge capacity and the positive electrode charge capacity decrease.

On the other hand, the secondary battery system of this embodiment, the charge potential of Ag / AgCl reference electrode of the positive electrode to control the charge and discharge ^- a control unit that sets to 1.05V below the potential as a measure of (Cl concentration saturation) ing. Thus, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- can set the potential of the (Cl concentration saturation) below 1.05V as the reference, IO ₃ during charging of the secondary battery system ^- can inhibit the production reaction of. IO ₃ ^- By suppressing the generation of reversibly lowering of the positive electrode discharge capacity and the positive electrode charge capacity to maintain the total concentration of iodide ion and iodine molecule during charging and discharging is suppressed, thereby improving the cycle durability be able to. Therefore, in this embodiment, the secondary battery system which satisfy | fills the charging conditions excellent in practicality can be provided.

Furthermore, in the secondary battery system of the present embodiment, the positive electrode electrolyte contains a compound having a sulfinyl group. Therefore, the I ₂ film (iodine film) deposited on the electrode surface due to the oxidation reaction of I ⁻ is easily peeled off, and the I ₂ film can be made thin. Thus, reduction in the oxidation current caused by I ₂ film becomes resistance is suppressed, thereby improving the oxidation current as compared with the case of not using the compound having a sulfinyl group. Therefore, the output of the secondary battery system can be increased.

Note that the charging potential of the positive electrode in the secondary battery system is different from the charging voltage. The charging potential indicates a potential difference with respect to a reference electrode (reference electrode) having a constant reference potential. On the other hand, the charging voltage indicates a potential difference between the negative electrode and the positive electrode. Since the charging potential is based on a constant potential as a reference, when the potential is constant, it can be regarded as a constant value with respect to the potential of the reference electrode (reference electrode). However, the charging voltage, which is the potential difference between the negative electrode and the positive electrode, is apparently constant when the potential fluctuates in the same way between the negative electrode and the positive electrode. Therefore, since the potential of the positive electrode is not determined by the charging voltage, it is necessary to measure the potential of the reference electrode (reference electrode).

(Configuration of cathode electrolyte)
The secondary battery system includes a positive electrode electrolyte solution containing at least one of iodine ions and iodine molecules as a positive electrode active material. The positive electrode electrolyte is preferably one in which at least one selected from iodine compounds that give iodine ions (hereinafter also referred to as “iodine compounds”) and iodine molecules is dissolved or dispersed in a liquid medium.

The positive electrode electrolyte included in the secondary battery system contains at least one of iodine ions and iodine molecules as a positive electrode active material. That is, the positive electrode electrolyte may contain at least one of I ⁻ , I ₃ ⁻ and I ₂ .

The iodine ions and iodine molecules may be dissolved in the positive electrode electrolyte solution or in a solid dispersed state, and are preferably in a dissolved state. I ₂ is I ^- to form a, _{I 2} and I ^- ^- _{I 3} reacts with it is preferable to precondition the ratio of.

Further, positive electrode electrolyte may also contain an iodine 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 positive electrode electrolyte. 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, or NH ₄ I has 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 positive electrode electrolyte. 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, so that I ⁻ / I ₂ and I ⁻ / I ₃ ^- is preferably the system decrease in positive electrode potential is a condition that does not become apparent.

Further, the positive electrode electrolyte may contain a redox substance other than iodine ions and iodine molecules (I ⁻ , I ₃ ⁻ and I ₂ ). The redox substance other than iodine ion and iodine ^molecule, _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 iodine ions and iodine molecules include chromium, vanadium, zinc, quinone compounds, lithium cobaltate, sodium manganate, lithium nickelate, cobalt-nickel-lithium manganate, and lithium iron phosphate. .

(Compound having a sulfinyl group)
The secondary battery system includes a positive electrode electrolyte containing a compound having a sulfinyl group. Thereby, high output of a secondary battery system can be achieved.

Examples of the compound having a sulfinyl group include compounds in which at least one of an alkyl group and an aryl group is bonded to the sulfinyl group. Specific examples include dimethyl sulfoxide, diethyl sulfoxide, diphenyl sulfoxide, and methylphenyl sulfoxide. Of these, dimethyl sulfoxide is preferable.
The compound which has a sulfinyl group may be used individually by 1 type, and may use 2 or more types together.

(Liquid medium)
The positive electrode electrolyte is preferably one in which at least one selected from iodine compounds that give iodine ions and iodine 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 can disperse or dissolve the positive electrode active material.

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 -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 Cyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, tetraethylene glycol methyl n-butyl ether, tetraethylene glycol methyl n-hexyl ether, tetraethylene glycol di-n -Butyl 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 Recall 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 methyl n-hexyl ether, Tet Ether solvents such as propylene glycol di-n-butyl 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, acetic acid sec-butyl, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, cyclohexyl acetate , Methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, acetic acid diethylene glycol methyl ether, acetic acid diethylene glycol monoethyl ether, acetic acid dipropylene glycol methyl ether , Dipropylene glycol ethyl ether, Diacetate glycol, Diethyl acetate, Methoxytriglycol 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-methylpi Lidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide (hereinafter also referred to as “dimethylformamide”), N, N-dimethylacetamide (Hereinafter also referred to as “dimethylacetamide”) and the like; methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol, n-pentanol, isopent Tanol, 2-methylbutanol, sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol , N-octanol, 2-ethylhexanol, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, cyclohexanol, methylcyclo Alcohol solvents such as hexanol, benzyl alcohol, ethylene glycol, 1,2-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 mono Chill 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 , Glycol monoether solvents such as tripropylene glycol monomethyl ether; terpene solvents such as α-terpinene, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, ocimene, and ferrandrene; water, etc. Is mentioned. A liquid medium may be used individually by 1 type, and may use 2 or more types together.

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

(Good solvent for iodine molecules)
The positive electrode electrolyte may further contain a good solvent for iodine molecules other than the compound having a sulfinyl group. Although the I ₂ film is formed on the positive electrode by the charge reaction, the charge / discharge reaction may be inhibited if the I ₂ film becomes too thick. Thus, by that it contains a good solvent for molecular iodine in the positive electrode electrolyte with a compound having a contributing sulfinyl group thinning of I ₂ film, I ₂ film formed on the positive electrode is made thinner, I Inhibition of the charge / discharge reaction by the _two films tends to be more suitably suppressed.

Examples of good solvents for iodine molecules include nitriles, amides, ketones, esters, alcohols, ethers, pyridine derivatives, etc. Among them, nitriles, amides, ketones, esters and ethers are preferable from the viewpoint of further improving the oxidation current. Moreover, as a good solvent with respect to an iodine molecule, 1 type may be used independently and 2 or more types may be used together.

Good solvents for iodine molecules include nitriles such as acetonitrile and propionitrile, dimethylformamide, diethylformamide, acetamide, dimethylacetamide, amides such as N-methylpyrrolidone and N-ethylpyrrolidone, ketones such as acetone and methylethylketone, and methyl acetate And esters such as ethyl acetate and methyl nicotinate, alcohols such as ethanol and ethylene glycol, ethers such as diethyl ether, pyridine derivatives such as nicotinamide and cyanopyridine, and the like.

The good solvent for iodine molecules is preferably at least one selected from the group consisting of acetonitrile, dimethylformamide, N-methylpyrrolidone, methyl ethyl ketone, and ethyl acetate from the viewpoint of further improving the oxidation current.

Further, when the good solvent for iodine molecules is nitrile, the nitrile may be any of mononitrile, dinitrile, and polynitrile having three or more nitrile groups.

Examples of mononitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, hexanenitrile, heptanenitrile, octanenitrile, cyclobutanecarbonitrile, cyclohexanecarbonitrile, benzonitrile, naphthonitrile, phenylacetonitrile, and their derivatives. . Examples of mononitrile derivatives include halogenated mononitriles and alkylated mononitriles.

Dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimeonitrile, suberonitrile, azeronitrile, sebacononitrile, cyclobutanedicarbonitrile, cyclohexanedicarbonitrile, phthalonitrile, isophthalonitrile, terephthalonitrile, naphthalene dicarbonitrile, Examples thereof include 3,3′-oxydipropionitrile, 3,3 ′-(ethylenedioxy) dipropionitrile, 4,4′-oxydibenzonitrile, and derivatives thereof. Examples of dinitrile derivatives include halogenated dinitriles, alkylated dinitriles, and the like.

Polynitriles include 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,3,5-benzenetricarbonitrile, 1, Examples thereof include 2,3-tris (2-cyanoethoxy) propane, tris (2-cyanoethyl) amine, 1,2,2,3-propanetetracarbonitrile, and derivatives thereof. Examples of polynitrile derivatives include halogenated polynitriles and alkylated polynitriles.

Examples of good solvents for iodine molecules include alkyls such as isohexane and isooctane, alkyl halides such as chloroform and trichloroethylene, cycloalkyls such as methylcyclohexane and ethylcyclohexane, aryls such as toluene, o-xylene and m-xylene, methyl Examples also include ethers such as ethyl ether and dioxane, carbonates such as dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate and propylene carbonate, sulfones such as sulfolane, γ-butyrolactone, pyridine, tetrahydrofuran and dioxolane.
The good solvent for iodine molecules in the positive electrode electrolyte can be identified, for example, by measuring the retention time corresponding to the good solvent for iodine molecules and the molecular weight of monitor ions by gas chromatography.

The content of the good solvent with respect to iodine molecules in the positive electrode electrolyte is 0.1 vol% for a liquid at room temperature and normal pressure from the viewpoint of more suitably increasing the output of the secondary battery system by reducing the thickness of the I ₂ film. It is preferably ˜50 vol%, more preferably 1 vol% to 50 vol%, still more preferably 1 vol% to 30 vol%, still more preferably 2 vol% to 25 vol%, and 5 vol% to 15 vol. % Is particularly preferred. In addition, the content of the good solvent with respect to the iodine molecules described above is 0.01 mol / L for a solid at room temperature and normal pressure from the viewpoint of more suitably increasing the output of the secondary battery system by thinning the I ₂ film. It is preferably ˜5 mol / L, more preferably 0.1 mol / L to 2 mol / L.

The content rate of the good solvent with respect to iodine molecules in the positive electrode electrolyte is, for example, using gas chromatography, and using the concentration of the good solvent with respect to iodine molecules and the detected amount at the retention time corresponding to the good solvent with respect to iodine molecules as a calibration curve. It can be quantified by creating data and calculating from the calibration curve.

(polymer)
The positive electrode electrolyte may contain a polymer that forms a complex with iodine ions. When the positive electrode electrolyte contains a polymer that forms a complex with iodine ions, precipitation of iodine molecules that may occur during the redox reaction of iodine ions tends to be suppressed. Polymers that form complexes with iodine ions include nylon 6, polytetrahydrofuran, polyvinyl alcohol, polyacrylonitrile, poly-4-vinylpyridine, polyvinylpyrrolidone, polymethyl (meth) acrylate, polytetramethylene ether glycol, polyacrylamide, polypropylene glycol , Polyethylene glycol, polyethylene oxide and the like. These polymers may be used individually by 1 type, and may use 2 or more types together.

(Supporting electrolyte)
The positive electrode electrolyte may further contain a supporting electrolyte. The supporting electrolyte is an auxiliary agent for increasing the ionic conductivity of the electrolytic solution. When the positive electrode electrolyte contains the supporting electrolyte, the ionic conductivity of the positive electrode electrolyte 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. The supporting electrolyte may be used alone or in combination of two or more. Moreover, the salt containing iodine can serve as both the positive electrode active material and the supporting electrolyte.

(PH buffer)
The positive electrode electrolyte 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.

(Conductive material)
The positive electrode electrolyte 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 conductive materials may be used alone or in combination of two or more. Among these, as the conductive material, carbon material particles are preferable, and activated carbon particles are more preferable. When the positive electrode electrolyte contains activated carbon particles as a conductive material, it is possible to store and release energy by forming an electric double layer on the surface of the activated carbon particles, and the energy density and output density of the secondary battery tend to be improved.

(Method for preparing positive electrode electrolyte)
The positive electrode electrolyte can be prepared by adding a positive electrode active material and other components as necessary to a liquid medium. When preparing the positive electrode electrolyte, heating may be performed as necessary.

(Composition of positive electrode electrolyte)
In the positive electrode electrolyte, the content of iodine compound and iodine 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 it is. By setting the content of the iodine compound and iodine molecules to 1% by mass or more, a secondary battery system 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 an iodine compound and an iodine molecule shall be 80 mass% or less. The content of iodine compound and iodine molecule is the total content of ions derived from iodine compound (for example, counter ions of I ⁻ , I ₃ ⁻ and I ⁻ ) and iodine molecules (I ₂ ) in the positive electrode electrolyte. Represents a rate.

The content of iodine ions and iodine molecules (total of I ⁻ , I ₃ ⁻ and I ₂ ) in the positive electrode electrolyte is preferably 1% by mass to 80% by mass, and 3% by mass to 70% by mass. More preferably, the content is 5% by mass to 50% by mass.

In the positive electrode electrolyte, the content of the compound having a sulfinyl group is not particularly limited. From the viewpoint of more suitably increasing the output of the secondary battery system by reducing the thickness of the I ₂ film, 0.1 vol% to 50 vol% It is preferably 1 vol% to 50 vol%, more preferably 1 vol% to 30 vol%, still more preferably 2 vol% to 25 vol%, and even more preferably 5 vol% to 15 vol%. It is particularly preferred.

The content of the compound having a sulfinyl group in the positive electrode electrolyte can be obtained, for example, by gas chromatography using a calibration curve with the concentration of the compound having a sulfinyl group and the detected amount at the retention time corresponding to the compound having a sulfinyl group. It can be quantified by creating and calculating from a calibration curve.

(Configuration of negative electrode electrolyte)
The secondary battery system includes 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 thereof 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 ions. 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 low standard oxidation-reduction potential of −0.76 V in the dissolution and precipitation reaction of zinc, and zinc and zinc compounds Zinc and zinc ions are suitable as the negative electrode active material because they are inexpensive. Examples of the compound containing zinc include zinc chloride, zinc iodide, zinc bromide, zinc fluoride, zinc nitrate, zinc sulfate, and zinc acetate.

The negative electrode electrolyte solution may contain a liquid medium, a supporting electrolyte, a pH buffering agent, a conductive material, and the like, similar to the above-described positive electrode electrolyte solution. Since the usable liquid medium, supporting electrolyte, pH buffering agent, and conductive material are the same as those of the positive electrode electrolytic solution, description thereof is omitted.

In addition, about the positive electrode electrolyte and the negative electrode electrolyte, the liquid medium, the supporting electrolyte, the pH buffering agent, and the conductive material that are contained may be the same or different.

(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.

(Composition of negative electrode electrolyte)
In the negative electrode electrolyte, the content of the negative electrode active material (preferably the total of zinc and a compound containing zinc) is preferably 1% by mass to 80% by mass, and more preferably 3% by mass to 70% by mass. Preferably, the content is 5% by mass to 50% by mass. By setting the content of the negative electrode active material to 1% by mass or more, a secondary battery system 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 content rate of a negative electrode active material shall be 80 mass% or less.

There is no particular limitation on the ratio (Ec / Ea) between the energy capacity (Ec) that can be stored in the positive electrode electrolyte and the energy capacity (Ea) that can be stored in the negative electrode electrolyte. From the viewpoint of increasing the energy density of the secondary battery system, the ratio of Ec to Ea (Ec / Ea) is preferably 0.3 to 2.5, and more preferably 0.5 to 2.0. Preferably, it is 0.8 to 1.3.

(Positive electrode and negative electrode)
The secondary battery system includes a positive electrode and a negative electrode, and a positive electrode and a negative electrode used in a conventionally known secondary battery system may be used as the positive electrode and the negative electrode.

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 and graphite felt; metal plates made of metals such as titanium, zinc, stainless steel, aluminum, and copper; and metal electrodes such as metal mesh. Further, a conductive material such as InSnO ₂ , SnO ₂ , In ₂ O ₃ , or ZnO, fluorine-doped tin oxide (SnO ₂ : F), Sb-doped tin oxide (SnO ₂ : Sb), at least 1 containing a conductive material doped with impurities such as Sn-doped indium oxide (In ₂ O ₃ : Sn), Al-doped zinc oxide (ZnO: Al), and Ga-doped zinc oxide (ZnO: Ga). A laminate in which two layers are formed can also be used as an electrode.

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 negative electrode electrolyte contains zinc ions, 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.

(Reference electrode)
The secondary battery system may include a positive electrode reference electrode for measuring the positive electrode potential. In the secondary battery system, the positive electrode reference electrode is not an essential component, and the positive electrode potential in the secondary battery system may be measured using the positive electrode reference electrode as necessary.

The reference electrode for the positive electrode can be converted into a potential with respect to a standard hydrogen electrode potential (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 other materials as basic electrochemistry (for example, “Allen“ J.Bard and Larry R.Faulkner, “ELECTROCHEMICAL METHODS” p.3, (1980), John Wiley & Sons, " Inc. ")) Examples of the reference electrode include an Ag / AgCl reference electrode, a saturated calomel electrode, and an Ag / AgCl reference electrode is preferred.

When an Ag / AgCl reference electrode is used as the reference electrode, for example, a RE-1CP saturated KCl silver-silver chloride reference electrode (manufactured by BAS Corporation) may be used.

The positive electrode for the reference electrode, the potential of the measured cathode Ag / AgCl reference electrode ^- as long as it can be converted to the potential of (Cl concentration sat) is not limited to Ag / AgCl reference electrode, the other reference electrode It may be used.

The secondary battery system may further include a negative electrode reference electrode for measuring the negative electrode potential. The reference electrode may be provided at one location on the positive electrode, preferably at one location on each of the positive and negative electrodes, and more preferably at a plurality of locations on each of the positive and negative electrodes.

(Partition wall)
The secondary battery system of this embodiment further includes a partition as a separator film between the positive electrode and the negative electrode. The partition is not particularly limited as long as it can withstand the use conditions of the secondary battery system, and examples thereof include an ion conductive polymer film, an ion conductive solid electrolyte film, a polyolefin porous film, and a cellulose porous film. .

Examples of the ion conductive polymer membrane include a cation exchange membrane and an anion exchange membrane. Examples of commercially available cation exchange membranes include trade name Nafion (Aldrich), and examples of commercially available anion exchange membranes include trade name Selemion (Asahi Glass Co., Ltd.) and trade name Neocepta (Astom Co., Ltd.). It is done.

(Control part)
The secondary battery system, the charge potential Ag / AgCl reference electrode of the positive electrode to control the charge and discharge ^- a control unit that sets to 1.05V below the potential as a measure of (Cl concentration saturation). Thus, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- can set the potential of the (Cl concentration saturation) below 1.05V as the reference, IO ₃ during charging of the secondary battery system ^- can inhibit the production reaction of. By suppressing the production of IO ₃ ⁻ , the total concentration of iodine ions and iodine molecules (I ⁻ , I ₃ ⁻ and I ₂ ) during reversible charge / discharge is maintained, and the positive electrode discharge capacity and the positive electrode charge capacity are increased. The decrease is suppressed, and the cycle durability can be improved.

In addition, “the charging potential of the positive electrode is set to 1.05 V or less with respect to the potential of the Ag / AgCl reference electrode (Cl ⁻ concentration saturation)” in principle means that the charging potential of the positive electrode is 1.05 V or less. This means that the secondary battery is charged, and the charge potential of the positive electrode is allowed to exceed 1.05V. For example, when it is unavoidable that the charge potential of the positive electrode exceeds 1.05 V due to the influence of ripple noise or the like described later, the charge potential of the positive electrode may exceed 1.05 V.

For example, the control unit performs constant current charging until reaching the set voltage under the condition that the charging potential of the positive electrode does not exceed 1.05 V (vs. Ag / AgCl), and performs constant voltage charging after reaching the set voltage. The secondary battery is controlled as follows.

The control unit, the charging potential of the positive electrode, Ag / AgCl reference electrode ^- it is preferable to control the potential of the (Cl concentration saturation) to 1.5V below as a reference. By controlling the charging potential of the positive electrode to 1.5 V (vs. Ag / AgCl) or less, deterioration of the positive electrode (particularly, carbon electrode) tends to be suppressed. Further, when the positive electrode electrolyte contains ethanol as a good solvent for iodine molecules, the decomposition of ethanol is further suppressed by controlling the positive electrode charging potential to 1.5 V (vs. Ag / AgCl) or lower. There is a tendency.
Incidentally, "the charge potential of the positive electrode, Ag / AgCl reference electrode ^- control below 1.5V relative to the potential of (Cl concentration sat)" refers to a secondary battery charging potential of the positive electrode as follows 1.5V This means that charging is performed, and the charging potential of the positive electrode is not allowed to exceed 1.5V.

For example, when the charge potential of the positive electrode exceeds 1.5 V (vs. Ag / AgCl) due to the influence of ripple noise or the like described later, the control unit recharges the secondary battery so as to cut the excess by a high frequency filter or the like. To control. If the charge potential of the positive electrode falls within the range of 1.05 V to 1.5 V (vs. Ag / AgCl) even if ripple noise described later is superimposed, the control unit does not have to perform special control. This is because the generation reaction of IO ₃ ⁻ represented by the above-described equation (3) is considered difficult to follow a high-frequency signal such as ripple noise.

Further, in the secondary battery system, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- is preferable to set the potential of the (Cl concentration saturation) below 1.05V as the reference, it is set to 1.0V or less More preferably, it is more preferably set to 0.95 V or less.

(Configuration example of secondary battery system)
A configuration example of the secondary battery system of the present embodiment will be described with reference to FIG. The secondary 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. The positive electrode 3, the negative electrode 4, the partition wall 5, the positive electrode reference electrode 6, the negative electrode reference electrode 7, and the control unit are the above-described positive electrode, negative electrode, partition wall, positive electrode reference electrode, negative electrode reference electrode, and control unit. Since it is good, the description is omitted.

As shown in FIG. 1, the secondary battery system 50 includes a positive electrode electrolyte reaction tank 1, a negative electrode electrolyte reaction tank 2, a positive electrode 3, a negative electrode 4, a partition wall 5, a positive electrode reference electrode 6, and a negative electrode Reference electrode 7 and a control unit (not shown).

The positive electrode electrolyte reaction tank 1 is a tank for storing the positive electrode electrolyte, and the negative electrode electrolyte reaction tank 2 is a tank for storing the negative electrode electrolyte. For example, the charging reaction shown by dotted arrows in FIG. 1, I the positive electrode electrolyte in a reaction vessel 1 ^- is oxidized I ₃ ^- and I ₂ are generated, X ²⁺ negative electrode electrolyte in a reaction vessel 2 (X ^< ²⁺ ^> , X ^<+> represents a negative electrode active material) is reduced to generate X ^<+> . At this time, as shown in FIG. 1, electrons flow from the positive electrode 3 side to the negative electrode 4 side.
During the discharge reaction, I ₃ ⁻ and I ₂ in the positive electrode electrolyte reaction tank 1 are reduced to generate I ⁻ , and X ⁺ in the negative electrode electrolyte reaction tank 2 is oxidized to generate X ^2+. . At this time, electrons flow from the negative electrode 4 side to the positive electrode 3 side.

Here, the control unit, the charging potential of the positive electrode, Ag / AgCl reference electrode ^- reference to the potential of (Cl concentration saturation) for setting the 1.05V or less, IO ₃ during charging of the secondary battery system 50 ^- the The production reaction can be suppressed. IO ₃ ^- By suppressing the generation of reversibly lowering of the positive electrode discharge capacity and the positive electrode charge capacity to maintain the total concentration of iodide ion and iodine molecule during charging and discharging is suppressed, thereby improving the cycle durability be able to. Therefore, it is possible to provide the secondary battery system 50 that satisfies the charging condition with excellent practicality.

Further, the control unit, the influence of ripple noise, the like when the charging potential of the positive electrode can not be avoided that more than 1.05V, the charging potential of the positive electrode, Ag / AgCl reference electrode (Cl ^- concentration saturation) It is preferable to control it to 1.5 V or less with reference to the potential. By controlling the charging potential of the positive electrode to 1.5 V (vs. Ag / AgCl) or less, the deterioration of the positive electrode (particularly the carbon electrode) tends to be suppressed, and the positive electrode electrolyte is a good solvent for iodine molecules. When ethanol is contained, decomposition of ethanol tends to be further suppressed.

[Flow battery system]
The secondary battery system of the present embodiment includes a positive electrode electrolyte reservoir that stores a positive electrode electrolyte, a negative electrode electrolyte reservoir that stores a negative electrode electrolyte, and a positive electrode electrolyte between the positive electrode and the positive electrode electrolyte reservoir. The flow battery system may further include a liquid feeding part that circulates the negative electrode electrolyte solution between the negative electrode and the negative electrode electrolyte storage part.

(Cathode electrolyte reservoir and anode electrolyte reservoir)
The flow battery system includes a positive electrode electrolyte storage unit that stores a positive electrode electrolyte solution and a negative electrode electrolyte storage unit that stores a negative electrode electrolyte solution. 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 system 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 system, 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. A route and a liquid feed pump may be provided.

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.

In the flow cell system, similar to the above secondary battery system, the charge potential of the positive electrode, Ag / AgCl reference electrode ^- is preferably set to less than 1.05V relative to the potential of (Cl concentration saturation), 1.0 V More preferably, it is set to 0.95 V or less.

When the flow battery system is temporarily operated under a condition where the positive electrode charging potential exceeds 1.05 V, the sampling unit may periodically sample the positive electrode electrolyte during the operation period, and the concentration adjusting unit may be the flow battery. The concentration of the components contained in the positive electrode electrolyte is adjusted by adding positive electrode electrolyte or adding additives such as iodine ions, iodine molecules, sulfinyl group-containing compounds, and good solvents for iodine molecules. May be.

(Sampling part)
The flow battery system may further include a sampling unit that samples the positive electrode electrolyte. By sampling the positive electrode electrolyte in the sampling section, it is possible to analyze the concentration of components contained in the positive electrode electrolyte such as iodine ions, iodine molecules, compounds having sulfinyl groups, additives such as good solvents for iodine molecules, etc. For example, it is possible to analyze whether the concentration of the component contained in the positive electrode electrolyte is insufficient compared to the specified amount, the required amount, or the like.

The sampling unit may be disposed, for example, in the positive electrode electrolyte storage unit, or may be disposed in the circulation path. Moreover, the structure which samples a positive electrode electrolyte solution for every predetermined time may be sufficient as a sampling part. Note that the secondary battery system other than the flow battery system may further include a sampling unit that samples the positive electrode electrolyte, and for example, the sampling unit may be disposed in the positive electrode electrolyte reaction tank.

(Density adjustment unit)
In addition, the flow battery system analyzes the positive electrode electrolyte sampled by the sampling unit, and based on the analysis result, determines the concentration of the component contained in the positive electrode electrolyte circulating between the positive electrode and the positive electrode electrolyte storage unit. You may further provide the density adjustment part to adjust. The flow battery system includes a concentration adjustment unit, so that the positive electrode electrolyte sampled in the sampling unit can be used as a positive electrode electrolyte such as iodine ions, iodine molecules, compounds having a sulfinyl group, and additives such as good solvents for iodine molecules. When the concentration of the contained component 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.

For example, the concentration adjusting unit may be configured to add each component to the positive electrode electrolyte stored in the positive electrode electrolyte storing unit, or may be configured to add each component to the positive electrode electrolyte flowing through the circulation path. May be. Moreover, the addition of the additive to the positive electrode electrolyte may be performed during the operation of the flow battery or may be performed while the battery is stopped. The secondary battery system other than the flow battery system also has a concentration adjusting unit that analyzes the positive electrode electrolyte sampled by the sampling unit and adjusts the concentration of the component contained in the positive electrode electrolyte based on the analysis result. You may have. In the secondary battery system, for example, a concentration adjusting unit may be disposed in the positive electrode electrolyte reaction tank.

(Concentration measurement unit)
The flow battery system may have a concentration measuring unit that measures the concentration of iodine ions and iodine 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 iodine ions and iodine molecules in the positive electrode electrolyte. The potential measuring unit has, for example, a collecting electrode for measuring a potential based on the concentrations of iodine ions and iodine molecules, and a reference electrode serving as a reference for the electrochemical potential, and measures the electrochemical potential based on the reference electrode To do. By using the Nernst equation relating to the electrochemical potential, the concentration of iodine ions and iodine molecules can be determined 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.

Further, the control unit may estimate 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 of 0% basically means that I ₃ ⁻ and I ₂ are not included in the positive electrode electrolyte, and only I ^−. It shows the state. An SOC of 100% basically indicates a state in which I ⁻ is not contained in the positive electrode electrolyte, but only I ₃ ⁻ and I ₂ .

The concentration measuring unit may be disposed in the positive electrode electrolyte storage unit, or may be disposed in a circulation path through which the positive electrode electrolyte circulates. The secondary battery system other than the flow battery system may further include a concentration measuring unit that measures the concentration of iodine ions and iodine molecules in the positive electrode electrolyte. For example, the concentration measuring unit is provided in the positive electrode electrolyte reaction tank. May be arranged.

(Configuration example of flow battery system)
Next, a configuration example of a flow battery system, which is a kind of secondary battery system of the present embodiment, will be described with reference to FIG. The flow battery system is not limited to the configuration shown in FIG. Moreover, the magnitude | size of the member in FIG. 2 is notional, The relative relationship of the magnitude | size between 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. 2, 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, iodine ions and iodine molecules are contained in the cathode electrolyte, and the compound having a sulfinyl group is also contained in the cathode electrolyte, and zinc ions are contained in the anode electrolyte. It is a configuration.

As shown in FIG. 2, 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. 2 shows a cell stack 30 in which the number of single cells is five. The number of single cells is not particularly limited. In the flow battery system 100 shown in FIG. 2, 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). Similar to the above-described secondary battery system 50, the control unit sets the charging potential of the positive electrode 11 to 1.05 V (vs. Ag / AgCl) or less. Moreover, it is preferable that a control part controls the charging potential of the positive electrode 11 to 1.5V (vs. Ag / AgCl) or less. Furthermore, the flow cell system 100, the positive electrode 11 is the channel (e.g., the circulation path 20) is narrowed by being covered with the I ₂ film, a situation where the flow itself of positive electrode electrolyte 16 is inhibited undesirable. Therefore, from the viewpoint of thinning the I ₂ film at the positive electrode 11, the charging potential of the positive electrode 11 is preferably controlled to 1.4 V (vs. Ag / AgCl) or less.

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.

Furthermore, the positive electrode electrolyte storage tank 18 includes 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. ing.

Second Embodiment
[Secondary battery system]
A secondary battery system according to a second embodiment of the present invention includes a positive electrode, a negative electrode, a positive electrode electrolyte containing a compound having at least one of iodine ions and iodine molecules and a sulfinyl group as a positive electrode active material, and a negative electrode active material and a control unit for controlling the following 1.5V relative to the potential of the ^- (concentration saturated Cl), a and a negative electrode electrolyte containing, charge and discharge control to the positive electrode of the charging potential Ag / AgCl reference electrode. Note that the description of the configuration common to the first embodiment is omitted.

As described above, when the charge potential of the positive electrode exceeds 1.5 V, there are problems such as deterioration of the positive electrode (particularly the carbon electrode) and decomposition of ethanol as an additive. For this reason, by controlling the charging potential of the positive electrode to 1.5 V or less, the deterioration of the positive electrode (particularly, the carbon electrode) can be suppressed, and the positive electrode electrolyte is ethanol, which is a good solvent for iodine molecules. When it contains, decomposition | disassembly of ethanol can be suppressed.

When the charging potential of the positive electrode to charge under the condition of more than 1.05V, IO ₃ which does not contribute to the discharge reaction, as described above ^- that and the total concentration of I ₂ is reduced ^- the rate of increase, and I The secondary battery system tends to have a decrease in positive electrode discharge capacity and positive electrode charge capacity. Therefore, in the secondary battery system, the positive electrode discharge capacity and the positive electrode charge capacity in the secondary battery system are suppressed from decreasing, and the positive electrode electrolyte is sampled every predetermined time in the sampling unit, and the concentration is adjusted as necessary. The adjusting unit preferably adds iodine ions to the positive electrode electrolyte.

When the secondary battery system is operated under the condition that the charging potential of the positive electrode exceeds 1.05V, the sampling unit may sample the positive electrode electrolyte periodically during the operation period, and the concentration adjusting unit may be the secondary battery system. In addition, the addition of a positive electrode electrolyte, or an additive such as a good solvent for iodine molecules such as iodine ions, iodine molecules, sulfinyl groups, ethanol, etc. The density may be adjusted.

[Power generation system]
The power generation system of the present embodiment includes a power generation device and the above-described secondary battery system. The power generation system of the present embodiment 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.

Renewable energy includes wind power, sunlight, wave power, tidal power, running water, tide, geothermal heat, etc., preferably wind power or sunlight.

The generated power generated using renewable energy such as wind power and sunlight may be 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.

In addition, when applying the secondary battery system of this embodiment mentioned above to such a renewable energy field | area, in order to supply electric power to a high voltage | pressure system, it is 1.05V (vs. Ag) per unit cell of a secondary battery system. / AgCl) may be required for charging potentials. When the charging potential of the positive electrode of the single cell is 1.05 V (vs. Ag / AgCl), the entire charging voltage of the single cell, that is, the potential difference between the positive electrode and the negative electrode exceeds 3 V. Assuming that the entire charging voltage of a single cell is 3V, the charging voltage of each cell stack is 60V when 20 cell stacks of the secondary battery system are connected in series. Furthermore, when 10 cell stacks are connected in series, the charging voltage is 600V. The secondary battery system is charged by converting AC power generated by wind power generation or the like into DC power using an inverter. For this reason, the voltage range of the charge control voltage is determined in the relationship between the cell stack of the secondary battery system and the output of the inverter.

When the charging voltage of the inverter is constant, if the number of single cells in the cell stack is small, the charging voltage applied to each single cell increases. Conversely, when the number of single cell series in the cell stack is large, the charging voltage applied to each single cell becomes small. Therefore, when installing a secondary battery system in a power generation system using renewable energy, the charging voltage applied per single cell of the secondary battery system is the basic parameter of the inverter output and the number of single cells in the cell stack in series. Determined as

An example of the power generation system of this embodiment is shown in FIG. FIG. 3 is a configuration diagram in which a secondary battery system is applied to the wind power generation field. In FIG. 3, SB (SecondarySecondBattery) indicates a secondary battery, and PCS (Power Conditioning System) indicates an inverter control system for AC / DC conversion. SB and PCS in FIG. 3 correspond to the secondary battery system of the present embodiment described above. The secondary battery system in the power generation system of the present embodiment is preferably a flow battery system because it is advantageous for large-scale power storage.

The generated power waveform shown in FIG. 3 is an example of a power waveform generated by the wind power generator. In the case of wind power generation, the generated power varies greatly depending on the strength of the wind and the wind direction. When the power that fluctuates in this way is superimposed on a power system such as a transmission line, it affects the stabilization of the power system. Therefore, when supplying electric power from wind power generation to the power system, it is necessary to suppress fluctuations in the power of the power system.

In order to suppress this fluctuation, a charge / discharge waveform that reduces fluctuations in the generated power waveform is output from the secondary battery system and superimposed on the generated power waveform. The secondary battery system plays a role of leveling generated power obtained by wind power generation and supplying it as stabilized power.

Here, FIG. 4 shows a power waveform when the power waveform of the wind power generation in FIG. 3 is viewed on a shorter time scale. While the power waveform in the relatively long time region shown in the regions (a) and (b) of FIG. 4 is seen, the time waveform is shorter than the region (a), and the regions (a) and (b) In the meantime, in the three time regions on the longer side than the region (b), a pulse-like power generation waveform in the order of microseconds to milliseconds is seen. At this time, the secondary battery system uses a target output of wind power generated for a certain time width as a central value, and if the generated power is lower than that, the power is supplemented by discharging, and if it exceeds the target output, the generated power is used. Charging and discharging may be controlled so as to approach the target output.

The inverter is a converter for exchanging power between the charge / discharge signal of the secondary battery, which is DC information, and the generated power. Charging of the secondary battery is performed by converting AC power from the wind power generator into DC power. Inverters tend to generate pulsed high-frequency signals called ripple noise. Generally, these high-frequency signals can be removed by installing a capacitor that can support each frequency band in the PCS. However, in PCS in which these measures are not taken, a high-frequency ripple signal is applied to the secondary battery.

It is ideal if the response speed of the secondary battery can follow all the output fluctuations of the wind power PCS, but it is actually difficult. Due to the presence of the time constant (CR) defined by the electric double layer capacity at the electrode interface of the secondary battery and the resistance of the secondary battery, the battery has a power fluctuation signal in the order of microseconds to several tens of milliseconds. The reaction cannot follow. In FIG. 4, it is difficult to completely equalize power fluctuations in the time domain where signals in the microsecond order to millisecond order area gather and high frequency signals with superimposed ripple noise gather are charged and discharged by the secondary battery. In particular, in the case of a large-sized secondary battery, this behavior becomes apparent when the electric double layer capacity is increased by increasing the surface area of the electrode and the time constant is increased.

When the secondary battery system is applied to wind power generation, solar power generation, etc., during power generation, frequent charge / discharge is repeated via an inverter in order to level the generated power. The power signal supplied to the secondary battery including the ripple noise generated from the inverter includes a high-frequency power signal that exceeds the follow-up capability of the secondary battery. When a high-frequency power signal that cannot be followed by a secondary battery is applied to the secondary battery, the power is basically converted into heat. This heat tends to concentrate on the electrode terminals of the secondary battery, and tends to adversely affect the constituent materials of the secondary battery.

As described above, the charging voltage applied per unit cell of the secondary battery system is determined based on the inverter output and the number of single cells in series in the cell stack as basic parameters. There is also a relationship. Therefore, it is preferable to design the secondary battery system so that the charging potential of the positive electrode is 1.05 V (vs. Ag / AgCl) or less in consideration of the number of single cells connected in series, the number of cells stacked in series, and the charging voltage. Even if the design must accept that the voltage exceeds 1.05 V, the charging potential of the positive electrode should be controlled to 1.5 V (vs. Ag / AgCl) or lower in order to ensure the life of the secondary battery system. Is preferred.

When the secondary battery system is operated under the condition that the charge potential of the positive electrode exceeds 1.05 V (vs. Ag / AgCl) due to the design of the secondary battery system, the positive electrode electrolyte is used for the secondary battery during the operation period. It is preferable to add a negative electrode electrolyte and an iodine compound, a compound having a sulfinyl group, a good solvent for iodine molecules such as ethanol, and the like. However, a good solvent for iodine molecules that is volatile, such as ethanol, is preferably analyzed periodically even in an operating environment where the charge potential of the positive electrode does not exceed 1.05 V, and is added if necessary. .

Even when the secondary battery system is operated under the condition that the charging potential of the positive electrode does not exceed 1.05 V (vs. Ag / AgCl), the charging potential of the positive electrode exceeds 1.05 V with respect to the ripple noise of the inverter. It seems reasonable to think that the signal is included. Since the ripple noise of the inverter promotes the deterioration of the secondary battery system, it is preferable to install a capacitor having a bandwidth capable of absorbing the ripple noise in the PCS.

Further, the power generation system may be a system that controls charging / discharging of the secondary battery system in accordance with the supply and demand of the generated power generated by the power generation device. For example, when the supply amount of the generated power generated by the power generation device exceeds the demand amount in the power system, the secondary battery system performs charging, and the supply amount of the generated power generated by the power generation device is in the power system. The power generation system may be controlled such that the secondary battery system discharges when the demand is lower.

The power generation system combines a power generation device that uses renewable energy and a secondary battery system, so that the secondary battery system functions as a low-cost, high-energy density power storage system, and further reduces carbon dioxide emissions. And help solve the global problem of suppressing global warming.

Hereinafter, the present invention will be specifically described with reference to examples, but the scope of the present invention is not limited to these examples.

[Example 1]
First, the oxidation reaction was investigated by normal pulse voltammetry, and the electrode reaction of the positive electrode was verified.
FIG. 5 is a graph showing a potential waveform of normal pulse voltammetry performed in Example 1. In FIG. 5, Ei represents an initial potential, ΔEs represents a pulse increment, tp represents a pulse width, and τ represents a pulse period. The potential waveform shown in FIG. 5 was input to an electrochemical cell using a potentiostat as an electrochemical measuring device, and current values corresponding to each pulse potential and pulse time were measured.

The potentiostat is a general device in electrochemical measurement, and is controlled based on the electrochemical reaction that proceeds at the working electrode by controlling the pulse potential shown in FIG. 5 with respect to the reference electrode potential that is a reference for the potential. It is a device that detects current. In addition, a counter electrode is provided so that a current flows through the counter electrode. The input resistance of the reference electrode is very large and is a direct current resistance, usually at a level of 10 ¹⁴ ohms, and the current of the electrochemical reaction proceeding at the working electrode is in a circuit configuration that flows to the counter electrode.

The potentiostat includes a reference electrode serving as a potential reference, a working electrode subject to potential control, and a counter electrode. Recently, with the development of microcomputers, the normal pulse voltammetry waveform shown in FIG. 5 is generally designed to be integrated with the potentiostat function.

FIG. 6 is a normal pulse voltammogram in Example 1 (pulse width 50 ms). A voltammogram is a current-potential curve in which the current observed based on an electrochemical reaction is plotted against the potential. The electrolyte solution includes a solution containing 20 mM aqueous sodium iodide solution (95 vol%) containing 1 M sodium perchlorate (NaClO ₄ ) as a supporting electrolyte and dimethyl sulfoxide (5 vol%), which is a compound having a sulfinyl group. Used, glassy carbon (diameter 1.6 mm) was used for the electrode, and ΔEs = 0.05 V and τ = 20 s. In FIG. 6, the horizontal axis represents potential (V vs. Ag / AgCl), and the vertical axis represents current density (mA / cm ² ). The current density is a value obtained by dividing the current value 50 ms after the step to the oxidation potential by the electrode area (the same applies hereinafter). The measurement was performed in an environment with a liquid temperature of 25 ° C.

Next, reverse electrode voltammetry was used to investigate the reduction reaction that was the reverse of normal pulse voltammetry, and the positive electrode reaction was verified.

FIG. 7 is a graph showing a potential waveform of reverse pulse voltammetry performed in Example 1. Reverse pulse voltammetry can be performed using a programmed potentiostat similar to normal pulse voltammetry. Ei is an initial potential, Ec is a potential at which a reaction of interest does not proceed (conditioning potential), ΔEs is a reverse pulse potential increment, tc is a time for holding in Ec, td is a time for holding in Ei, and tp is a reverse pulse width. Ec = immersion potential, ΔEs = 0.05 V, tc = 10 s, td = 2 s.

Reverse pulse voltammetry has a function that allows more detailed examination of the behavior of the oxidation reaction of I ⁻ obtained by normal pulse voltammetry. That is, it can be verified what electrochemical behavior the product generated at the initial potential shows. When what is generated at the initial potential is an oxidation reaction product, when the reverse pulse potential reaches a certain potential region, the behavior of the reduction reaction of the oxidation reaction product can be captured.

The pulse potential of the reverse pulse is repeatedly incremented by the reverse pulse potential, and is stepped in the base direction with the initial potential Ei as the starting potential. When one potential step is completed, the oxidation potential reduction reaction is held at the conditioning potential Ec that is least likely to proceed. The time (tc) during which the boundary condition of the working electrode recovers to the same level as before the reaction is held at the conditioning potential Ec. After the time tc, the potential is stepped to the initial potential Ei, and an oxidation reaction (generally an oxidation or reduction reaction) proceeds on the working electrode during td. After controlling the initial potential for td time, a reverse pulse is applied. By repeating this, reverse pulse voltammetry is performed, and based on the relationship between the obtained reverse pulse current and potential, the reaction itself, the reaction mechanism, and the like can be examined closely.

In both normal pulse voltammetry and reverse pulse voltammetry, the boundary conditions of the working electrode are common between each pulse, so the concentration of the reactant reacting at the initial potential can be considered constant in the relationship between the reaction product and the potential. It is a great merit that it can be simplified in examining the relationship between current and potential. Since it returns to the conditioning potential after the end of one pulse, the information of any pulse potential does not accompany the history of reactants and the like generated at the pulse potential before the pulse. It can be said that the strength of normal pulse voltammetry and reverse pulse voltammetry is that the electrochemical information to be observed can be simply extracted as described above.

FIG. 8 is a reverse pulse voltammogram in Example 1 (initial potential 0.50 V or 0.55 V and pulse width 50 ms). 8 is a graph showing the relationship between the step potential and the current value after being held at the initial potential (0.50 V or 0.55 V for 2 seconds. The electrolyte contains 1 M sodium perchlorate as the supporting electrolyte. A solution containing 20 mM aqueous sodium iodide solution (95 vol%) and dimethyl sulfoxide (5 vol%) containing glassy carbon (diameter 1.6 mm) is used for the electrode, and the pulse width of the reverse pulse is 50 ms.

As shown in FIG. 8, when the initial potential was set to 0.50 V or 0.55 V, a clear limit current related to the reduction reaction was observed. Therefore, the product at the initial potential of 0.50V or 0.55V is an ion, and in this condition is I ₃ ⁻ . That, I ^- I ₃ is an oxidation reaction product ^- was confirmed behavior is reduced.

FIG. 9 is a reverse pulse voltammogram in Example 1, showing the effect of dimethyl sulfoxide contained in the electrolyte (initial potential 0.60 V and pulse width 50 ms). The electrolyte includes a solution containing 20 mM sodium iodide aqueous solution (95 vol%) and dimethyl sulfoxide (5 vol%) containing 1 M sodium perchlorate as a supporting electrolyte, and 1 M sodium perchlorate as a supporting electrolyte. A 20 mM aqueous solution of sodium iodide containing
When dimethyl sulfoxide was not contained in the electrolyte, it was observed that the reduction current value increased as the potential stepped. This behavior is a behavior observed in a solid-phase electrochemical reaction (for example, a dissolution reaction from a metal plating surface). Since the diffusion overvoltage accompanying diffusion from the solution is unnecessary, it was confirmed that as the pulse potential of the reverse pulse increases, the current of the reduction reaction increases without showing a limiting current. In the case of containing dimethyl sulfoxide, the reduction current was greatly observed in the region of 0.30 V to 0.60 V compared to the case of no addition, and the reduction current was decreased in the region of 0.25 V or less. This behavior is thought to be due to dissolution of reducing the I ₂ coating I ₂ film is facilitated by the inclusion of dimethylsulfoxide in the solution.

FIG. 10 is a reverse pulse voltammogram in Example 1 (initial potential 0.90 V to 1.10 V and pulse width 50 ms), and the initial potential is set higher than the initial potential in FIG. 9 (similarly held for 2 seconds) )is doing. The pulse widths of the electrolyte solution, the electrodes, and the reverse pulse are the same as those when the initial potential is 0.50V to 0.60V.

The reduction current values observed in Fig. 10 are roughly divided into two groups. One group is the case where the initial potential is 0.9 V, 0.95 V, and 1.00 V, and it was observed that the reduction current value greatly increased as the reverse pulse potential was stepped to the base. On the other hand, the other group is the case where the initial potential is set to 1.05V and 1.10V, and the reduction current value of the reverse pulse is compared with the case where the initial potential is set to 0.9V, 0.95V and 1.00V. It was a low value. In reverse pulse voltammetry, the difference in the reduction reaction rate of the chemical species generated at the initial potential is observed, so the difference in the reverse pulse voltammogram between these groups is the product difference due to the difference in the initial potential. It is the simplest to think about.

I ^- by the reaction shown in the following equation (6) and (7), _{I 3} ^- and to generate the _{I 2} are known.

2I ⁻ → I ₂ + 2e ⁻ (6)
3I ⁻ → I ₃ ⁻ + 2e ⁻ (7)

The standard oxidation-reduction potentials of Equation (6) and Equation (7) are approximately equal at 0.536 V (standard hydrogen electrode potential), respectively. Accordingly, the oxidation reaction products of I ⁻ produced at the initial potential of reverse pulse voltammetry are I ₂ and I ₃ ⁻ . The change of the standard electrode potential of the formula (7) with respect to the temperature is −0.148 mV per 1 ° C. (Yuta Tamamushi, “Electrochemistry (2nd edition)” p.300, (1991), Tokyo Chemical Dojin). That is, in an environment of −25 ° C. in which 50 ° C. is lowered from 25 ° C., the standard electrode potential of the formula (7) changes only from 0.536 (standard hydrogen electrode potential) to only 7.4 mV. Although the electrochemical potential basically depends on the temperature, it is considered that the relationship between the battery reaction and the potential does not have a large fluctuation of the 100 mV level at the practical living environment temperature as described above.

Here, when the initial potential exceeds 1.05 V, it is presumed that IO ₃ ⁻ is generated by the reaction represented by the following formula (3).

I ⁻ + 3H ₂ O → IO ₃ ⁻ + 6H ⁺ + 6e ⁻ (3)

As described above, the above-mentioned document 1 reports that the formula (3) is an irreversible reaction. Since Equation (3) is a irreversible reaction, is reached to the reverse pulse potential reduction reaction area, IO ₃ which generated ^- very slow rate of reaction, the resulting IO ₃ ^- is I by reduction ^- easily return to Guess that there is not.

IO ₃ ⁻ + 5I ⁻ + 6H ⁺ → 3I ₂ + 3H ₂ O (4)

I ₂ + 6H ₂ O → 2IO ₃ ⁻ + 12H ⁺ + 10e ⁻ (5)

The reaction shown in Equation (5) is the total reaction of the formula (3) and (4), by the reaction I ₂ IO ₃ ^- but is generated in the same manner as in the reaction shown in equation (3), wherein The reaction shown in (5) is also an irreversible reaction. For this reason, it is presumed that the generated IO ₃ ⁻ has a slow discharge reaction rate and is difficult to return to I ₂ .

For this reason, it is considered that when the initial potential exceeds 1.05 V, IO ₃ ⁻ is generated, and the reverse pulse voltammogram has a low reduction reaction rate.

Therefore, when dimethyl sulfoxide is contained in the positive electrode electrolyte, it is considered that IO ₃ ⁻ is generated by an irreversible reaction under a charge potential condition in which the charge potential of the positive electrode exceeds 1.05 V. Therefore, the charge potential of the positive electrode is 1 It is not preferable to operate in a state exceeding .05V.

FIG. 11 is a reverse pulse voltammogram in Example 1 (initial potential 1.40 V, 1.50 V and pulse width 50 ms), and the initial potential is set higher than the initial potential in FIG. 10 (similarly held for 2 seconds). )is doing. The pulse widths of the electrolytic solution, the electrode, and the reverse pulse are the same as those when the initial potential is 0.90V to 1.10V.

As shown in FIG. 11, it was found that the reduction current value observed with the reverse pulse was lower when the initial potential was 1.50 V or more than when the initial potential was 1.40 V. Further, it was found that the reduction current value tends to decrease as the initial potential is increased. From this, it was estimated that the electrode was inactivated by maintaining the initial potential at a noble potential of 1.50 V or higher.

[Example 2]
FIG. 12 is a normal pulse voltammogram in Example 2 (pulse widths 50, 500, and 5000 ms). As the electrolytic solution, a solution containing a 3M sodium iodide aqueous solution (95 vol%) and dimethyl sulfoxide (5 vol%) was used. The aqueous solution concentration on the order of 3M corresponds to the reaction active material concentration level in the actual secondary battery. In FIG. 12, the horizontal axis represents potential (Vvs. Ag / AgCl), and the vertical axis represents current density (A / cm ² ). FIG. 12 shows the current density when the pulse width is 50 ms, 500 ms, and 5000 ms. Other conditions are the same as in the first embodiment.

At tp = 50 ms, the current density increased monotonously with increasing potential. It was found that on the time scale with a pulse width of 50 ms, the amount of I ₂ film produced was small, ^and the electrode reaction of I ⁻ was not greatly inhibited by the film.

At tp = 500 ms, the current density decreased from around 1.5V. It was found that on the time scale with a pulse width of 500 ms, the I ₂ film thickened from around 1.5 V, and the I ⁻ electrode reaction was inhibited.

At tp = 5000 ms, the current values were almost equal from about 1.0 V to about 1.8 V. In the time scale with a pulse width of 5000 ms, it was confirmed that the thickness of the I ₂ film reached an equilibrium in a potential region near 1.0 V to 1.8 V.

FIG. 13 shows the effect of dimethyl sulfoxide contained in the electrolyte when tp = 5000 ms. As the electrolytic solution, a solution containing 3M sodium iodide aqueous solution (95 vol%) and dimethyl sulfoxide (5 vol%) and 3M sodium iodide aqueous solution were used.
When the electrolytic solution contained dimethyl sulfoxide, a current of about 1.0 V to about 1.8 V was greatly observed as compared with the case where the electrolytic solution did not contain dimethyl sulfoxide. This is probably because the addition of dimethyl sulfoxide to the electrolytic solution made the I ₂ film thinner and increased the amount of I ⁻ that reacted on the electrode.

The electrochemical measurement in which the supporting electrolyte concentration (sodium perchlorate in Example 1) is equivalent to the concentration of the reactive species of interest (I ^{− in} Example 1) is equivalent to the concentration of the reaction species (Example 1 is sodium chloride). Except for this, it is possible to observe the electrochemical reaction while keeping the electric double layer structure as the electrochemical reaction field constant. For this reason, there is an advantage that the existing electrochemical theory can be used simply in the study of the electrochemical reaction mechanism based on the absolute reaction kinetics. Therefore, in Example 1, the study on the electrochemical reaction was performed in a system containing a reactive species in the order of mM and a supporting electrolyte. In this example, the electrochemical reaction was examined under the condition of sodium iodide electrolyte solution in the concentration range of the actual secondary battery not including the supporting electrolyte, but basically it corresponds to the examination result in Example 1. I understand. That is, the charge potential control in the potential region exceeding 1.05 V is performed by the above formula (3) (I ⁻ + 3H ₂ O → IO ₃ ⁻ + 6H ⁺ + 6e ⁻ ) and formula (5) (I ₂ + 6H ₂ O → 2IO ₃ ⁻ As shown in + 12H ⁺ + 10e ⁻ ), IO ³⁻ is generated, which is not desirable.

Therefore, in the secondary battery containing dimethyl sulfoxide in the positive electrode electrolyte, it is preferable that the charge potential of the positive electrode does not exceed 1.05 V (Vvs. Ag / AgCl) that IO ₃ ⁻ can be generated by charging.

In the case of an actual flow battery, a situation where the flow path of the flow battery is narrowed by covering the positive electrode with a thick I ₂ film and the flow of the electrolyte itself is not desirable is undesirable. In this respect, it is desirable that the charging potential does not exceed 1.4V. In order to stably manage the reaction active materials involved in the charge / discharge reaction, particularly iodine ions and iodine molecules, the charge potential of 1.05 V (Vvs. Ag / AgCl) or less shown in Example 1 and Example 2 is used. Charge control with potential is preferred.

From FIG. 11, it is presumed that the electrode is inactivated by setting the potential to be nobler than 1.5 V. Therefore, in addition to suppressing the decomposition of ethanol, the deterioration of the positive electrode is suppressed. It is preferable to control charging at a potential of 1.5 V or less in the secondary battery.

[Example 3]
Next, regarding the flow battery system shown in FIG. 2, the current potential of the positive electrode and the negative electrode when the charge / discharge reaction was performed was examined. In this example, a solution containing 1 M sodium iodide (NaI) aqueous solution (95 vol%) and dimethyl sulfoxide (5 vol%) was used as the positive electrode electrolyte, and 0.5 M zinc chloride (ZnCl ₂ ) was used as the negative electrode electrolyte. The contained 1M ammonium chloride (NH ₄ Cl) aqueous solution was used, a carbon electrode was used as the positive electrode, and a zinc electrode (zinc coated mesh electrode) was used as the negative electrode.

In this example, the electrochemical reaction of the positive and negative electrodes and the standard electrode potentials are as follows, and the open circuit voltage of the flow battery is about 1.3 V in the standard state. Moreover, the schematic diagram of the electrode reaction of the flow battery system in Example 3 is shown in FIG.

Negative electrode Zn⇔Zn ²⁺ + 2e ^-- 0.76V

The positive electrode ^{_{^{^{3I - ⇔I 3 - + 2e -}}}} 0.53V
2I ⁻ ⇔I ₂ + 2e ⁻ 0.53V

FIG. 15 is a current-potential curve of the positive electrode and the negative electrode of the flow battery implemented in Example 3. The current-potential curve is obtained under the conditions of the flow battery system shown in FIG. 2 under the condition that the flow flow rate is 100 cm ³ / min and the battery is charged and discharged at a constant current.

The corresponding potential under various constant current controlled conditions is a value obtained by measuring the steady potential of each of the positive electrode and the negative electrode. The potential of each of the positive electrode and the negative electrode is a potential with respect to the Ag / AgCl reference electrode. In the flow battery environment of this example, the current density at which the potential of the positive electrode becomes 1.05 V (Vvs. Ag / AgCl) is about 400 mA / cm ² .

Therefore, in the flow battery of this embodiment, it is preferable that the charge control condition of the flow battery is such that the charge current density does not exceed 400 mA / cm ² . This suppresses the positive electrode potential from reaching a potential region nobler than 1.05 V, and the flow battery can be operated while suppressing the generation of IO ₃ ⁻ .

Japanese patent application 2016-143741 filed on July 21, 2016, PCT / JP2016 / 071917 filed on July 26, 2016, and US patent application 62/505519 filed on May 12, 2017. Is hereby incorporated by reference in its entirety.
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 1 Positive electrode electrolyte reaction tank 2 Negative electrode

electrolyte reaction tank

3, 11 Positive electrode 4, 12

Negative electrode

5, 15

Partition

6, 13 Reference electrode for

positive electrodes

7, 14 Reference electrode for negative electrodes 16 Positive electrode electrolyte 17 Negative electrode electrolyte 18 Positive electrode electrolyte Storage tank (cathode 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 50 Secondary battery system 100 Flow battery system

Claims

A positive electrode;
A negative electrode,
A positive electrode electrolyte containing at least one of iodine ions and iodine molecules and a compound having a sulfinyl group as a positive electrode active material;
A negative electrode electrolyte containing a negative electrode active material;
A secondary battery comprising:
The secondary battery according to claim 1, wherein the negative electrode electrolyte contains at least one of zinc and zinc ions as the negative electrode active material.
The secondary battery according to claim 1, wherein the positive electrode electrolyte further contains a good solvent for iodine molecules other than the compound having the sulfinyl group.
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 any one of claims 1 to 3, which is a flow battery system further comprising:
The secondary battery according to any one of claims 1 to 4, further comprising a sampling unit that samples the positive electrode electrolyte.
The secondary battery according to claim 5, further comprising a concentration adjusting unit that analyzes the positive electrode electrolyte sampled by the sampling unit and adjusts the concentration of a component contained in the positive electrode electrolyte based on the analysis result.
The secondary battery according to any one of claims 1 to 6, further comprising a concentration measuring unit that measures the concentration of iodine ions and iodine molecules in the positive electrode electrolyte.
The concentration measuring unit is a potential measuring unit that measures a potential based on the concentration of iodine ions and iodine molecules in the positive electrode electrolyte solution,
The secondary battery according to claim 7, wherein the state of charge is estimated based on the potential measured by the potential measurement unit.
The secondary battery according to any one of claims 1 to 8, further comprising a positive electrode reference electrode for measuring a potential of the positive electrode.
Charge and discharge are controlled, the charging potential of the positive electrode is Ag / AgCl reference electrode - is set below 1.05V relative to the potential of (Cl concentration saturation), to any one of claims 1 to 9 The secondary battery as described.
Charge and discharge are controlled, the charging potential of the positive electrode is Ag / AgCl reference electrode - is controlled below 1.5V relative to the potential of (Cl concentration saturation), to any one of claims 1 to 10 The secondary battery as described.
A secondary battery according to any one of claims 1 to 9,
And a control unit that sets to 1.05V or less relative to the potential of the - (Concentration saturated Cl), wherein by controlling the charging and discharging the positive electrode charging potential Ag / AgCl reference electrode
A secondary battery system comprising:
A secondary battery according to any one of claims 1 to 9,
A control unit for controlling the 1.5V below the potential as a measure of - (Concentration saturated Cl), charge and discharge control to the positive electrode of the charging potential Ag / AgCl reference electrode
A secondary battery system comprising:
Wherein, the positive electrode charging potential Ag / AgCl reference electrode - is controlled to 1.5V below the potential as a measure of (Cl concentration saturation), the secondary battery system according to claim 12.
A positive electrode electrolyte solution containing at least one of iodine ions and iodine molecules and a compound having a sulfinyl group.
A power generation system comprising: a power generation device; and the secondary battery system according to any one of claims 12 to 14.
The power generation system according to claim 16, wherein the power generation device generates power using renewable energy.