JP2000012064A - Vanadium redox battery electrolyte and vanadium redox battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vanadium redox battery containing a positive electrode electrolyte and a negative electrode electrolyte, which is improved so that precipitation of vanadium can be prevented, even if the vanadium concentration is increased. SOLUTION: A positive electrode liquid tank 4 stores a positive electrode electrolyte containing tetravalent and/or pentavalent vanadium ions. A negative electrode liquid tank 3 stores a negative electrode electrolyte containing 2-valent and/or trivalent vanadium ions. A first ion selected from the group consisting of potassium ion, rubidium ion, and ammonium ion is added to the negative electrode electrolyte, and a second ion selected from the group consisting of lithium ion and sodium ion is added to the positive electrode electrolyte. The first ion and the second ion are regulated to equal concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a vanadium redox battery electrolyte, and more particularly, to an improved vanadium redox battery capable of preventing precipitation even at a high concentration. It relates to an electrolytic solution. The present invention also relates to a vanadium redox battery using such a redox battery electrolyte.

[0002]

2. Description of the Related Art Japan's power demand has been increasing year by year. However, fluctuations in power demand tend to be remarkable year after year, reflecting the sophistication of the industrial structure and the improvement of the standard of living of the people. It is in. For example, assuming that the power demand in the daytime in summer is 100, that at dawn is 30 or less. On the other hand, when viewed from a power supply source, the ratio of nuclear power generation or large-scale thermal power generation, which does not desirably fluctuate in output, also tends to increase.

[0003] At present, power storage is performed by pumped storage power generation, but due to its limited location, it is said that new power storage technologies, especially technically and economically, are highly feasible. Secondary batteries for power storage have been actively studied. Among them, a redox flow battery has been particularly noted.

FIG. 1 is a schematic view of an all-vanadium redox battery disclosed in Japanese Patent Publication No. 2724817.

Referring to FIG. 1, an all-vanadium redox battery 1 includes a battery cell 2, a negative electrode solution tank 3 and a positive electrode solution tank 4. The inside of the battery reaction cell 2 is partitioned by a diaphragm 5 made of, for example, an ion exchange membrane or the like.
One side constitutes the negative electrode cell 2a and the other side constitutes the positive electrode cell 2b.

[0006] In the positive electrode cell 2b, a positive electrode 6 is provided as an electrode.
And the negative electrode 7 is stored in the negative electrode cell 2a. The positive electrode cell 2b and the positive electrode solution tank 4 are connected by a positive electrode solution circulation line 6, and the negative electrode cell 2a and the negative electrode solution tank 3 are connected.
Are connected by a negative electrode solution circulation line 9.

[0007] A pump 10 is provided in the positive electrode liquid circulation line 6, and a pump 11 is provided in the negative electrode liquid circulation line 9. A positive electrode electrolyte containing V ⁵⁺ / V ⁴⁺ is stored in the positive electrode liquid tank 4.
A negative electrode electrolyte containing V ²⁺ / V ³⁺ is stored therein. These ions are respectively dissolved in the aqueous sulfuric acid solution.

In an all-vanadium redox battery, at the time of charging, the V ²⁺ / V ³⁺
The sulfuric acid aqueous solution containing
And the electrons are received by the negative electrode 7, V ³⁺ is reduced to V ²⁺ and collected in the negative electrode liquid tank 3. On the other hand, an aqueous sulfuric acid solution containing V ⁵⁺ / V ⁴⁺ in the cathode solution tank 4 by the pump 10, sent to the positive cell 2b, and releasing electrons to an external circuit at the positive electrode 6, V ⁴⁺ is V ^{5 It} is oxidized to ⁺ and collected in the positive electrode solution tank 4.

During discharging, the negative electrode solution tank 3
A sulfuric acid aqueous solution containing V ²⁺ / V ³⁺ stored in the pump 1
The electrons are sent to the negative electrode cell 2a by 1 and emitted to the external circuit at the negative electrode 7, so that V ²⁺ is oxidized to V ³⁺ and collected in the negative electrode liquid tank 3. On the other hand, the sulfuric acid aqueous solution containing V ⁵⁺ / V ⁴⁺ ions stored in the positive electrode solution tank 4 is sent to the positive electrode cell 2 b by the pump 10, receives electrons from the external circuit at the positive electrode 6, and converts V ⁵⁺ to V ^{4 +. It} is reduced to ⁺ and collected in the positive electrode solution tank 4. In such an all-vanadium redox battery, the charge and discharge reactions in the positive electrode 6 and the negative electrode 7 are as shown in FIG.

[0010]

In a conventional all-vanadium redox battery, the above-mentioned positive electrode electrolyte and negative electrode electrolyte are prepared, for example, by the following method.

[0011] That is, prepare the VOSO ₄ of 0.1M~2M, dissolved in H ₂ SO ₄ of 0.1M～5M 4
Forming a trivalent vanadium ion and electrochemically reducing a part of the tetravalent vanadium ion to form an anolyte comprising a mixture of trivalent / divalent vanadium ions or a solution of divalent vanadium ions. Further, a part of the above-mentioned tetravalent vanadium ion is oxidized to form a catholyte comprising a solution of pentavalent vanadium ion. This type of battery is called a one-pack all-vanadium redox battery.

However, in such a one-part system, the vanadium ion concentration remains at about 2 mol / l at room temperature.

Therefore, when an aqueous solution of H ₂ SO ₄ is used as the electrolyte, V ^3+, which is the discharge state of the electrolyte of the negative electrode, is used.
There is a problem in that the upper limit of the concentration is low, and when the concentration is increased, precipitation tends to occur during charging and discharging. As a result, the upper limit of the solubility of vanadium ions in the negative electrode electrolyte remains at about 2 mol / l. In addition, there is a problem that the vanadium ion concentration is further reduced in order to increase the operating temperature of the battery.

Further, the above-mentioned prior art discloses that sodium salts and potassium salts are added to the electrolyte, but does not clearly disclose how to add them.

[0015] For example, Na ⁺ ions are mixed into the negative electrode, decreases the upper limit of the concentration of V ³⁺ are present inventors that precipitation of V ³⁺ is likely to occur is found. Also,
The present inventors have also found that when K ⁺ ions are mixed into the positive electrode, V ⁵⁺ precipitation is likely to occur. When such deposition of V ³⁺ and V ⁵⁺ occurs, the redox flow battery does not operate well and has a problem that a sufficient output cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to provide a vanadium redox battery electrolyte improved so that precipitation can be prevented even when the concentration of the electrolyte is increased.

Another object of the present invention is to provide a vanadium redox battery using such a vanadium redox battery electrolyte.

[0018]

The vanadium redox battery electrolyte according to claim 1 relates to a negative electrode electrolyte, which contains at least 1 mol / l of divalent and / or trivalent vanadium ions, and An ion selected from the group consisting of potassium ion, rubidium ion and ammonium ion is added at a maximum of 2 mol / l.

The present invention is effective when the above-mentioned vanadium ion concentration exceeds 1 mol. When the concentration of vanadium ions is 1 mol or less, vanadium ions are stable, and thus the above-mentioned addition of potassium ions or the like is unnecessary.

As a result of examining various additives, the present inventors have found that ions selected from the group consisting of the above-mentioned potassium ion, rubidium ion and ammonium ion improve the solubility of vanadium ions. Additives such as the potassium ions are trace amounts to 2 mol /
l. The reason why the maximum is 2 mol / l is that the upper limit of the solubility of these ions is taken into consideration.

[0021] In the vanadium redox battery electrolyte according to the second aspect, the potassium ion, rubidium ion or ammonium ion is added as a sulfate, phosphate or oxalate. By adding in the form of such a salt, a change in pH of the electrolytic solution can be suppressed. In addition, it does not cause double reaction with vanadium ions.

The electrolyte solution of the vanadium redox battery according to claim 3 relates to a positive electrode electrolyte solution, and is 1 mol / l.
An ion containing the above-mentioned tetravalent and / or pentavalent vanadium ions and selected from the group consisting of lithium ions and sodium ions at a maximum of 4 mol / l is added.

The present invention is particularly effective when the concentration of vanadium ions exceeds 1 mol. When the concentration of vanadium ions is 1 mol or less, vanadium ions are stable, so that additives such as lithium ions are unnecessary.

As a result of studying various additives, the present inventor has found that lithium ions or sodium ions improve the solubility of vanadium ions in the positive electrode electrolyte. The reason why the addition amount is set to a maximum of 4 mol / l is in consideration of the upper limit of the solubility of ions to be added.

In the vanadium redox battery electrolyte according to the fourth aspect, the lithium ions and sodium ions are added as sulfate, phosphate or oxalate. By adding in the form of a salt, the p
H change can be suppressed, and no double reaction occurs with the vanadium salt.

A vanadium redox battery according to claim 5, wherein a negative electrode solution tank for storing a negative electrode solution containing divalent and / or trivalent vanadium ions, and a positive electrode solution containing tetravalent and / or pentavalent vanadium ions And a positive electrode solution tank for storing the A first ion selected from the group consisting of potassium ions, rubidium ions and ammonium ions and a second ion selected from the group consisting of lithium ions and sodium ions are added to the above-mentioned electrolyte solution of both electrodes. I have. The first ion and the second ion are added to both electrodes at an equal concentration.

The positive electrode electrolyte and the negative electrode electrolyte in which the first ions and the second ions have the same concentration can be produced from one solution.

In a vanadium redox battery, unless it is a one-component configuration that allows the mixing of the positive electrode electrolyte and the negative electrode electrolyte, the requirement for the ion-exchange membrane to sequester substances becomes so severe that it cannot be put to practical use. The present invention avoids that.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a vanadium redox flow battery according to the present invention is basically the same as the conventional vanadium redox flow battery shown in FIG. The configuration of the positive electrode electrolyte and the configuration of the negative electrode electrolyte are basically the same as those of the conventional vanadium redox battery.

In the embodiment of the present invention, the negative electrode electrolyte contains
Add potassium, rubidium and ammonium ions. These ion concentrations are from 0 to 2 mol / l. The upper limit of the solubility of these ions is considered.

This addition can prevent precipitation even if the vanadium ion concentration of the negative electrode is increased to 2 mol or more. That is, the concentration of V ³⁺ can be increased. Specifically, the concentration of V ³⁺ is 2 mol / l at room temperature.
５5 mol / l.

The above potassium ion, rubidium ion,
Ammonium ions are preferably added as sulfates, phosphates or oxalates. When added in the form of a salt in this manner, a change in pH of the electrolytic solution can be kept small, and vanadium ions are not oxidized or reduced. Also,
Prevents the deposition of vanadium ions.

Lithium ions and sodium ions are added to the positive electrode electrolyte. The concentration of the ions to be added is a very small amount to 4 mol / l. The reason why the solubility is set to 4 mol at the maximum is that the solubility of vanadium ions will be reduced if dissolved further. By adding lithium ions and sodium ions at a maximum of 4 mol / l, V
⁵⁺ precipitation can be prevented.

Since lithium ions and sodium ions are added as sulfates, phosphates, and oxalates, the change in the pH of the electrolyte can be kept small, and the lithium ions and sodium ions can be added in the form of such salts. Thus, vanadium ions are not oxidized and reduced, and precipitation is reduced.

[0035]

EXAMPLES were prepared tetravalent vanadium VOSO ₄ · 3H ₂ O in aqueous sulfuric acid. Using this, by electrolysis,
Reduction was performed to ^prepare a negative electrode electrolyte composed of trivalent V ³⁺ . On the other hand, the sulfuric acid aqueous solution is oxidized by electrolysis,
A ^{V5 +} positive electrode electrolyte was prepared. VOSO ₄ concentration
The above experiment was repeated with various changes. Table 1 shows the results.

[0036]

[Table 1]

Next, under the same conditions, 1 mol of Na ₂ SO ₄ was added, and the same experiment as above was performed.

The results are shown in Table 2. In Table 2, "2 days",
“3 days”, “7 days”, and “overnight” indicate the times when the electrolyte was stable.

[0039]

[Table 2]

Next, Table 3 shows the results when 0.5 mol of K ₂ SO ₄ was added.

[0041]

[Table 3]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an all-vanadium redox battery.

FIG. 2 is a diagram showing chemical formulas for explaining the operation principle of an all-vanadium redox flow battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vanadium redox battery 2 Battery cell 3 Catholyte tank 4 Catholyte tank 5 Diaphragm 6 Positive electrode 7 Cathode 2a Negative electrode cell 2b Positive cell

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Nobuyuki Tokuda 3-3-22 Nakanoshima, Kita-ku, Osaka-shi, Osaka Kansai Electric Power Company F-term (reference) 5H026 AA10 CX10 EE11 EE15 HH05

Claims (5)

[Claims] (1) at least 1 mol / l of divalent and / or 3
Ion containing vanadium ions of a valence, and ions selected from the group consisting of potassium ions, rubidium ions and ammonium ions at a maximum of 2 mol / mol
1. Vanadium redox battery electrolyte added. 2. The vanadium redox battery electrolyte according to claim 1, wherein said potassium ion, rubidium ion and ammonium ion are added as sulfate, phosphate or oxalate. 3. Tetravalent and / or 5 or more 1 mol / l
1. A vanadium redox battery electrolyte comprising a vanadium ion having a valence and adding at most 4 mol / l of an ion selected from the group consisting of lithium ion and sodium ion. 4. The vanadium redox battery electrolyte according to claim 3, wherein said lithium ions and sodium ions are added as sulfate, phosphate or oxalate. 5. A negative electrode tank for storing a negative electrode electrolyte containing divalent and / or trivalent vanadium ions, and a positive electrode tank for storing a positive electrode electrolyte containing tetravalent and / or pentavalent vanadium ions. A first electrode selected from the group consisting of potassium ions, rubidium ions and ammonium ions in the electrolytes of both electrodes;
And a second ion selected from the group consisting of lithium ions and sodium ions are added to both electrodes at equal concentrations.