JP2003142142A - Operating method for vanadium redox flow battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operating method for a vanadium redox flow battery having a large rate of solution utilization and giving a high output. SOLUTION: The operating method is for the vanadium redox flow battery of high output operated in such a manner that an electrolytic solution is fed in circulation to an electrode and the discharge current density per unit area of electrode is made between 0.20 and 0.55 A/cm<2> , wherein the solution feeding amount per unit area of electrode of the electrolytic solution immediately before attaining the predetermined discharge ending voltage is made over 0.3 cc/ min×cm<2> .

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 has a high liquid utilization rate and high output.

[0002]

2. Description of the Related Art As a conventional method for operating a redox flow battery, a technique described in Japanese Patent Laid-Open No. 4-12464 is known. This publication discloses a redox flow provided with a current detection means for detecting a current flowing in a battery and a control means for controlling the pumping amount of the electrolyte solution based on a detection signal of the detection means to control the amount of the electrolytic solution delivered. A battery is disclosed. Then, it proposes an operation method in which unnecessary pump power is reduced by changing the flow rate of the electrolytic solution, and an optimum electrolytic solution flow rate can always be obtained with respect to the charge / discharge current value which changes every moment.

[0003]

However, in the conventional battery for load leveling, the total efficiency needs to be about 70%, and the output cannot be increased. The total efficiency is the ratio of output energy to input energy, which also takes into consideration the power of the pump used for electrolyte circulation and the efficiency of the inverter and battery. Generally, when the output is increased, the battery efficiency is decreased, and the overall efficiency is decreased.
The liquid utilization rate also decreases. To prevent this decrease in battery efficiency, it is effective to reduce the cell resistance, but if the cell thickness is reduced to reduce the cell resistance, the pump power for permeating the electrolytic solution into the cell must be increased. However, the overall efficiency will also decrease.

On the other hand, in the application of instantaneous voltage drop / power failure, there is a need to increase the output and reduce the cost per unit output even if the overall efficiency is sacrificed to some extent. However, no evaluation was made on the case where the current density was increased to a high output, particularly the current density and the liquid utilization rate, and there was no clear guideline for the operation with a high liquid utilization rate at a high output.

Therefore, a main object of the present invention is to provide a method for operating a redox flow battery, which has a high liquid utilization rate and a high output.

[0006]

According to the present invention, an electrolytic solution is circulated and supplied to an electrode so that a discharge current density per unit area of the electrode is 0.20.
A A / cm ² or more 0.55 A / cm ² higher output vanadium redox flow battery operating method of operating as follows. It is characterized in that the electrolyte is operated at a rate of 0.3 cc / min · cm ² or more per unit area of the electrode immediately before reaching a predetermined discharge cutoff voltage.

Conventionally, it has been suggested in Japanese Patent Laid-Open No. 12464/1992 that the output is increased by increasing the liquid sending amount. By the way, as shown in a test example described later, when the current density is increased, the liquid utilization rate is significantly reduced. The liquid utilization rate is a value obtained by subtracting the charge depth after discharging from the charge depth before starting discharging. In the case of a vanadium redox flow battery, the charge depth is the concentration of pentavalent vanadium ions in the positive electrode active material (Equation 1) for the positive electrode and the concentration of divalent vanadium ions in the negative electrode active material (Equation 2) for the negative electrode. Say V (5 values) / {V (5 values) + V (4 values)} V: Concentration (mol / l) ... Formula 1 V (2 values) / {V (3 values) + V (2 values)} V: Concentration (mol / l)… Equation 2

The amount of electrolyte required determines the amount of electrolyte used, and the amount of electrolyte determines the size of the system such as the tank capacity. That is, if the liquid utilization rate can be increased, the cost can be reduced.

According to the present invention, by controlling the amount of the electrolytic solution sent immediately before the discharge cutoff voltage is reached, the liquid utilization rate can be increased even with an output of high current density, and more efficient operation can be performed. it can.

Here, the discharge cutoff voltage is a voltage at the end of discharge. This cut-off voltage is generally 0.9 to 1.05 V / cell, though it depends on the usage conditions.

It is preferable that the time immediately before the cutoff voltage is reached is a time width before the time when the cutoff voltage is reached by the time required to replace the electrolytic solution in the cell. As a result, it is possible to perform a high output operation with a high liquid utilization rate. In actual operation, for example, how long the time T ₁ required for replacing the electrolytic solution in the cell is measured in advance. Next, discharge is performed once, the discharge voltage with respect to the discharge time is recorded, and the discharge voltage V ₁ before time T ₁ before the time when the discharge cutoff voltage is reached is confirmed. Then, when discharging again, the liquid transfer amount may be changed at the time when the discharge voltage reaches V ₁ at the latest.

In particular, the amount of liquid fed per unit area of the electrode in the operation before the time immediately before the discharge cutoff voltage is reached is 0.3 cc /
It is preferable to operate at less than min · cm ² . As a result, the power of the pump can be reduced and more efficient operation can be performed.

Furthermore, the present invention is, when driving the discharge current density per unit electrode area as follows 0.55 A / cm ² ultra 0.58A / cm ^2, the electrode unit of the electrolytic solution immediately before reaching the predetermined discharge censored voltage The feature is that the operation is performed with the liquid supply amount per area being 0.4 cc / min · cm ² or more.

Even when operating at such a high output, it is possible to realize an operation with a high liquid utilization rate by controlling the liquid supply amount as described above. Even in this case, it is preferable that the amount of liquid fed per unit area of the electrode is 0.4 cc / min · cm ^{2 or} less in the operation before immediately before the discharge cutoff voltage is reached.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. A vanadium redox flow battery was used to perform discharge by changing the amount of electrolyte fed and the current density, and the relationship between the current density and the liquid utilization rate at the end of discharge was investigated. The battery specifications and measurement methods used in the test are as follows.

<Battery specifications> Electrode area: 1570 cm ² × 25 cells Electrolyte solution: V; 1.7 (mol / l), sulfuric acid; 2.6 (mol / l) electrolyte solution 0.15 m ³ each for positive and negative electrodes

<Measurement / Evaluation Method> The depth of charge before the start of discharge was set to 75%, and the amount of liquid sent per unit area of the electrode was 0.2 to 0.8.
Discharge was performed at 0 cc / min · cm ² and a current density of 0.07 to 0.6 A / cm ² , and the liquid utilization rate under each condition was measured. Specifically, the discharge is performed once, and the discharge voltage with respect to the discharge time is recorded at that time. Next, the discharge voltage (V ₁ ) about 1 minute before reaching the discharge cutoff voltage is confirmed (for example, V ₁ : 1.05V). When the discharge voltage reaches V ₁ , the liquid transfer rate is changed. The discharge cutoff voltage was 1.0 V / cell. The conventional standard discharge conditions are a liquid transfer rate of 0.2 cc / min · cm ² and a current density of about 0.07 A / cm ² . Therefore, the evaluation was made on the basis of how much the liquid utilization rate increased compared to the liquid utilization rate in the case of the liquid transfer rate of 0.2 cc / min · cm ² . The test results are shown in Table 1 and the graph in FIG.

[0018]

[Table 1]

The following can be seen from Table 1 and FIG.

Conventional standard liquid transfer rate (0.2cc / min ・ c
Under the m ² ) condition, the liquid utilization rate decreases rapidly when the current density is increased.

[0021] The liquid supply rate by a 0.3cc / min · cm ² or more, even 0.08A / cm ² or more 0.55 A / cm ² or less of a high output,
The liquid utilization rate can be improved by about 5% or more. Especially 0.2
In the range of up to 0.5 A / cm ^2, the degree of improvement in the liquid utilization rate is extremely remarkable.

[0022] The liquid supply rate by a 0.4cc / min · cm ² or more, even 0.55 A / cm ² ultra 0.58A / cm ² or less of a high output, the liquid utilization of about 5% or more Can be improved.

Since increasing the liquid supply amount means increasing the pump power, increasing the liquid supply amount to 0.3 cc / min · cm ² or more only immediately before the discharge cutoff voltage makes the overall efficiency more efficient. You can perform various driving.

[0024]

As described above, according to the operating method of the present invention, the redox flow battery having a high output and a high liquid utilization rate is operated by defining the liquid feed amount immediately before the discharge cutoff voltage is reached. be able to.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between current density and liquid utilization rate.

   ─────────────────────────────────────────────────── ─── 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 HH00 HH06                 5H027 AA10 KK21 KK56 MM02

Claims (4)

[Claims] 1. A method for operating a vanadium redox flow battery, comprising supplying an electrolytic solution to an electrode in a circulating manner and operating at a discharge current density per electrode unit area of 0.20 A / cm ² or more and 0.55 A / cm ² or less, which comprises: A method for operating a vanadium redox flow battery, which is characterized in that the electrolyte solution is operated at a rate of 0.3 cc / min · cm ² or more per unit area of the electrode immediately before reaching a predetermined discharge cutoff voltage. 2. The amount of liquid sent per unit area of electrode in the operation before the discharge cutoff voltage is reached is 0.3 cc / min.
The vanadium redox flow battery operating method according to claim 1, wherein the vanadium redox flow battery is operated at a pressure of less than cm ² . 3. A circulating supplying an electrolytic solution to the electrode, a method of operating a vanadium redox flow battery to operate the discharge current density per unit electrode area as follows 0.55 A / cm ² ultra 0.58A / cm ^2, pre A method for operating a vanadium redox flow battery, which is characterized in that the electrolyte is operated at a rate of 0.4 cc / min · cm ² or more per unit area of the electrode immediately before reaching a predetermined discharge cutoff voltage. 4. The amount of liquid fed per unit area of electrode in the operation before the time immediately before the discharge cutoff voltage is reached is 0.4 cc / min.
4. The vanadium redox flow battery operating method according to claim 3, wherein the vanadium redox flow battery is operated at a pressure of less than cm ² .