JP2003157882A - Operating Redox Flow Battery - Google Patents

Abstract

(57) [Problem] To provide a method for operating a redox battery in which vanadium is unlikely to be precipitated when used as a battery system, and a decrease in battery capacity and battery efficiency can be suppressed. SOLUTION: This is a method for operating a redox flow battery using a positive electrode electrolyte which changes from tetravalent vanadium ions to pentavalent vanadium ions during charging and reverses the reaction during discharging. The amount of change in the vanadium ion concentration and the sulfuric acid concentration in the positive electrode electrolyte from the initially adjusted concentration is measured to specify that the concentration is in a constant concentration equilibrium state. Then, the vanadium ion concentration and the sulfuric acid concentration in the positive electrode electrolyte in a concentration equilibrium state are adjusted to be in the following ranges. Vanadium ion concentration: 0.6 mol / l to 2.6 mol / l sulfuric acid concentration: 0.6 mol / l to 4.6 mol / l

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for operating a redox flow battery. In particular, the present invention relates to a method for operating a redox flow battery that can suppress the deposition of vanadium and prevent a decrease in battery capacity and battery efficiency.

[0002]

2. Description of the Related Art It has been proposed to use a redox flow battery for load leveling applications, voltage sag / blackout countermeasures, and the like.

Particularly, the vanadium redox flow battery has a high electromotive force, a large energy density, and since the electrolytic solution is a single element system, it can be regenerated by charging even if the positive electrode solution and the negative electrode solution are mixed. It has many of the advantages mentioned.

However, in such a vanadium redox battery, vanadium is deposited depending on the vanadium concentration, the sulfuric acid concentration, and the operating temperature, which causes problems such as a decrease in battery capacity and a decrease in voltage efficiency.

As a countermeasure against vanadium precipitation, the technique described in Japanese Patent Application Laid-Open No. 8-138716 is known. This publication discloses that the vanadium concentration is 2.5 mol / l or less and the sulfuric acid concentration is 3 mo.
As l / l, a method of operating the temperature of the electrolytic solution below 50 ° C. is disclosed.

[0006]

However, in the technique disclosed in the above publication, whether or not vanadium is dissolved is tested by the electrolytic solution itself, and it is not evaluated when it is operated as a battery system. When operated as a battery system, when charge and discharge are repeated, various ions and solvents in the electrolytic solution move through the diaphragm, and liquid transfer occurs in which the amount of the electrolytic solution in the positive electrode and the negative electrode increases and decreases. In consideration of such liquid transfer, it was unclear how the vanadium ion concentration and the sulfuric acid concentration were changed in each of the positive electrode and the negative electrode, and there was a difference in the deposition characteristics.

Further, even with respect to a high-concentration electrolytic solution having a vanadium concentration of more than 2.5 mol / l, no sufficient study has been made as to what behavior will occur.

Therefore, a main object of the present invention is to provide a method of operating a redox battery in which vanadium is less likely to be deposited when operated as a battery system and a decrease in battery capacity and battery efficiency can be suppressed.

[0009]

The present invention achieves the above object by specifying the range of vanadium ion concentration and sulfuric acid concentration of each electrolytic solution in each of the positive electrode and the negative electrode.

The present invention is a method for operating a redox flow battery using a positive electrode electrolyte in which the positive electrode changes from tetravalent vanadium ions to pentavalent vanadium ions during charging and reverse reaction occurs during discharging. The vanadium ion concentration in the positive electrode electrolyte and the amount of change from the initial adjusted concentration of the sulfuric acid concentration were measured to identify that the concentration was in a constant concentration equilibrium state, and the vanadium ion concentration in the positive electrode electrolyte solution in the concentration equilibrium state and Adjust the sulfuric acid concentration so that it falls within one of the following ranges. Vanadium ion concentration: 0.6 mol / l or more and 2.6 mol / l or less Sulfuric acid concentration: 0.6 mol / l or more and 4.6 mol / l or less Vanadium ion concentration: over 2.6 mol / l 3.1 mol / l or less Sulfuric acid concentration: 1.6 mol / l or more 4.6 mol / l or less and the temperature of the positive electrode electrolyte during battery operation is 10 ° C or more and 45 ° C
It is characterized by the following.

In addition, the present invention provides a negative electrode, when charging,
This is a method of operating a redox flow battery that uses a negative electrode electrolyte that changes from trivalent vanadium ions to divalent vanadium ions and causes the reverse reaction during discharge. The vanadium ion concentration in this negative electrode electrolyte and the amount of change from the initial adjusted concentration of sulfuric acid concentration were measured to identify that it was in a constant concentration equilibrium state, and the vanadium ion concentration in the negative electrode electrolyte solution in the concentration equilibrium state and Adjust the sulfuric acid concentration so that it falls within one of the following ranges. Vanadium ion concentration: 0.4 mol / l or more and 0.9 mol / l or less Sulfuric acid concentration: 1.4 mol / l or more and 4.9 mol / l or less Vanadium ion concentration: over 0.9 mol / l 1.9 mol / l or less Sulfuric acid concentration: 1.4 mol / l or more 4.4 mol / l or less Vanadium ion concentration: more than 1.9 mol / l 2.9 mol / l or less Sulfuric acid concentration: 1.4 mol / l or more and 3.4 mol / l or less And the temperature of the positive electrode electrolyte during battery operation is 10 ° C or more and 45 ° C
It is characterized by the following.

By adjusting the vanadium ion concentration and the sulfuric acid concentration of each of the positive electrode electrolyte and the negative electrode electrolyte to the above-mentioned vanadium ion concentration and sulfuric acid concentration, vanadium is less likely to be deposited even in consideration of the liquid transfer that occurs during actual operation, and the operation is excellent in battery efficiency. Can be realized.

The control of the concentration of the electrolytic solution is preferably performed by providing an electrolytic solution monitor in the redox flow battery system and measuring with this monitor. As the electrolytic solution monitor, a known one such as ICP emission spectroscopic analyzer: SPS4000 manufactured by Seiko Instruments Inc. can be used.

Usually, a redox flow battery comprises a cell in which a positive electrode cell and a negative electrode cell are separated by a membrane through which ions can pass. Each of the positive electrode cell and the negative electrode cell contains a positive electrode and a negative electrode. A positive electrode tank for supplying and discharging a positive electrode electrolytic solution is connected to the positive electrode cell via a conduit. Similarly, a negative electrode tank for supplying and discharging a negative electrode electrolytic solution is connected to the negative electrode cell via a conduit. Each electrolyte is circulated by a pump. The electrolytic solution monitor may be provided in a conduit or the like that connects the positive and negative electrode cells and the positive and negative electrode tanks.

In order to adjust the electrolytic solution to a predetermined concentration, the concentration may be adjusted by directly adding the electrolytic solution, or the positive electrode electrolytic solution and the negative electrode electrolytic solution may be communicated with each other to adjust the amount of electrolytic solution. It may be performed by increasing the frequency of the work for adjusting the nonuniformity. The frequency of adjustment is preferably once / day or more.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. (Test Example 1) First, when the vanadium redox flow battery was operated, it was examined how the vanadium ion concentration and the sulfuric acid concentration of the electrolytic solution changed. The redox flow battery used had the same structure as the above-mentioned conventional redox flow battery. The test conditions are as follows.

Battery reaction area: 1000 cm²× 5 cells Charge / discharge time: 1 hour / cycle each Open voltage at the end of charging: 1.55V / cell, approximately 90% full charge
Power state Current density during discharge: 0.07A / cm² Liquid volume equalization frequency: 1 time / day (for positive electrode electrolyte and negative electrode electrolyte
To adjust the non-uniformity of the amount of electrolyte due to liquid transfer.
) Liquid concentration measurement: Measured after the end of one cycle after equalizing the liquid volume System temperature: 25 ℃ Initial electrolyte component concentration: vanadium ion concentration 2 mol / l,
Sulfuric acid concentration 2mol / l (sulfate ion concentration: 4mol / l) The sulfuric acid concentration here is the free sulfuric acid concentration.
Not on concentration. Sulfate ion concentration is vanadium sulfate
And those that exist as sulfuric acid.
It Vanadium exists as vanadium sulfate in the electrolyte
To do.

Charging and discharging were carried out for one week under the above conditions, and the relationship between the elapsed time and the vanadium concentration and sulfuric acid concentration was investigated. The results are shown in Table 1 and the graph of FIG.

[0019]

[Table 1]

As is clear from Table 1 and FIG. 1, both the positive electrode electrolytic solution and the negative electrode electrolytic solution deviate from the initial component concentrations and reach a substantially constant concentration equilibrium state after a certain period of time.

(Test Example 2) Next, when the vanadium ion concentration and the sulfuric acid concentration were different, the initial voltage efficiency was compared with the voltage efficiency after a one-week charge / discharge test. Here, the cell is decomposed after being charged and discharged for one week, and divided into a positive electrode and a negative electrode. First, voltage efficiency was measured using a progress cell in which a positive electrode after charging and discharging for one week and a new negative electrode were incorporated, and the positive electrode was evaluated. Then, the voltage efficiency was measured using another progress cell in which the negative electrode after charging and discharging for one week and the new positive electrode were incorporated, and the negative electrode was evaluated. Test example, except that the system temperature was set to 10 ℃ and 45 ℃
The liquid concentration was measured in the same manner as in 1. The voltage efficiency is represented by discharge voltage / charge voltage. Then, the voltage efficiency of the cell in the initial stage is compared with the voltage efficiency of the elapsed cell after one week, and the decrease in efficiency is "○" when less than 1%, "△" when more than 1% and 3% or less is "△" when more than 3%. It was shown by "X". The test results are shown in Table 2.
The unit of vanadium ion concentration and sulfuric acid concentration is "mol /
l ”.

[0022]

[Table 2]

As is clear from Table 2, it was found that the decrease in voltage efficiency was small when the component concentration of the positive electrode electrolyte was as follows. Vanadium ion concentration: 0.6 mol / l or more and 2.6 mol / l or less Sulfuric acid concentration: 0.6 mol / l or more and 4.6 mol / l or less Vanadium ion concentration: over 2.6 mol / l 3.1 mol / l or less Sulfuric acid concentration: 1.6 mol / l or more 4.6 mol / l or less

Further, it was found that the voltage efficiency was less decreased when the component concentration of the negative electrode electrolyte was as follows. Vanadium ion concentration: 0.4 mol / l or more and 0.9 mol / l or less Sulfuric acid concentration is 1.4 mol / l or more and 4.9 mol / l or less Vanadium ion concentration: More than 0.9 mol / l and 1.9 mol / l or less Sulfuric acid concentration: 1.4 mol / l or more 4.4 mol / l or less Vanadium ion concentration: more than 1.9 mol / l 2.9 mol / l or less Sulfuric acid concentration: 1.4 mol / l or more and 3.4 mol / l or less

From the above, after operating the battery system,
It can be seen that efficient operation can be achieved by adjusting the concentration of the electrolyte so that the above-mentioned concentration condition is satisfied when the electrolyte is in a constant concentration equilibrium state.

[0026]

As described above, according to the operating method of the present invention, by prescribing the vanadium ion concentration, the sulfuric acid concentration and the operating temperature, the precipitation of the electrolytic solution can be suppressed and the efficient operation can be realized. You can

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the number of days that electricity has passed and the concentration of positive and negative electrode electrolyte components.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyuki Tokuda             3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture             Kansai Electric Power Co., Inc. F-term (reference) 5H026 AA10 EE01 EE11 HH05 HH08                       RR01

Claims (5)

[Claims] 1. A method for operating a redox flow battery using a positive electrode electrolytic solution, which changes from a tetravalent vanadium ion to a pentavalent vanadium ion during charging in a positive electrode and causes a reverse reaction thereof during discharging. It was determined that the vanadium ion concentration and sulfuric acid concentration in the solution from the initial adjusted concentration were measured to determine that the concentration was in a constant concentration equilibrium state, and the vanadium ion concentration in the positive electrode electrolyte solution in the concentration equilibrium state was 0.6 mol / min. l or more 2.6 mol /
A method of operating a redox flow battery in which the sulfuric acid concentration is adjusted to 0.6 mol / l or more and 4.6 mol / l or less and the temperature of the positive electrode electrolyte during battery operation is 10 ° C. or more and 45 ° C. or less. 2. A method for operating a redox flow battery using a positive electrode electrolyte, which changes from a tetravalent vanadium ion to a pentavalent vanadium ion at the time of charging in a positive electrode and causes a reverse reaction at the time of discharging. It was determined that the concentration of vanadium ion and sulfuric acid in the solution from the initial adjusted concentration was constant and that the concentration was in a constant concentration equilibrium state. more than 3.1 mol / l
Below is a method for operating a redox flow battery in which the concentration of sulfuric acid is adjusted to 1.6 mol / l or more and 4.6 mol / l or less, and the temperature of the positive electrode electrolyte during battery operation is 10 ° C or more and 45 ° C or less. 3. A method for operating a redox flow battery using a negative electrode electrolytic solution, which changes from a trivalent vanadium ion to a divalent vanadium ion during charging in the negative electrode and causes a reverse reaction thereof during discharging. The amount of change in vanadium ion concentration and sulfuric acid concentration from the initial adjusted concentration was measured to identify a constant concentration equilibrium state, and the vanadium ion concentration in the negative electrode electrolyte solution at that concentration equilibrium state was 0.4 mol / l or more 0.9 mol /
A method for operating a redox flow battery in which the sulfuric acid concentration is adjusted to 1.4 mol / l or more and 4.9 mol / l or less and the temperature of the negative electrode electrolyte during battery operation is 10 ° C. or more and 45 ° C. or less. 4. A method for operating a redox flow battery using a negative electrode electrolyte, which changes from a trivalent vanadium ion to a divalent vanadium ion during charging in a negative electrode and causes a reverse reaction thereof during discharging. The amount of change in vanadium ion concentration and sulfuric acid concentration from the initial adjusted concentration was measured to identify a constant concentration equilibrium state, and the vanadium ion concentration in the negative electrode electrolyte solution in the concentration equilibrium state was 0.9 mol / over 1.9mol / l
The following is a method for operating a redox flow battery in which the concentration of sulfuric acid is adjusted to 1.4 mol / l or more and 4.4 mol / l or less, and the temperature of the negative electrode electrolyte during battery operation is 10 ° C or more and 45 ° C or less. 5. A method for operating a redox flow battery using a negative electrode electrolytic solution, which changes from a trivalent vanadium ion to a divalent vanadium ion during charging in the negative electrode and causes a reverse reaction during discharging, wherein the negative electrode electrolysis is performed. It was determined that the vanadium ion concentration and the sulfuric acid concentration in the solution from the initial adjusted concentration were measured to determine that the concentration was in a constant concentration equilibrium state, and the vanadium ion concentration in the negative electrode electrolyte solution in the concentration equilibrium state was 1.9 mol / over 2.9mol / l
Below is a method for operating a redox flow battery in which the sulfuric acid concentration is adjusted to 1.4 mol / l or more and 3.4 mol / l or less, and the temperature of the negative electrode electrolyte during battery operation is 10 ° C or more and 45 ° C or less.