JPS622464A - Electrolyte for redox flow battery - Google Patents

Abstract

PURPOSE:To prevent the effective quantity of each active material from decreasing due to the repetition of charging and discharge, by providing a dividing film between a positive and a negative electrodes to separate them from each other, and supplying the positive and the negative electrodes with a positive and a negative electrode liquids, and causing an electrolyte to contain both a positive and a negative electrode active materials. CONSTITUTION:Since an electrolyte containing both a positive and a negative electrode active materials is used as a positive and a negative electrode liquids, an electrode active material concentration gradient is hardly caused between a positive and a negative electrode chambers separated from each other by a dividing film, so that the electrode active materials are scarcely transferred through the dividing film. As a result, the effective quantity of the active material in each of the chambers hardly decreases even if charging and discharge are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in the composition of an electrolytic solution used as a positive electrode solution and a negative electrode solution in a redox flow battery.

[Prior Art] As a secondary battery for power storage, a redox flow battery is disclosed in Japanese Patent Laid-Open No. 60-25163.

FIG. 5 is a schematic configuration diagram for explaining an example of this conventional redox flow battery.

The redox flow battery 1 includes a cell 2, a positive electrode liquid tank 3, and a negative electrode liquid tank 4, and uses two tanks 3.4, so it is called a two-tank type. Inside the cell 2, there is a partition 1 made of, for example, an ion exchange membrane! It is partitioned by I5, and one side is the positive electrode cell 2.
a and the other side constitutes the negative electrode cell 2b, respectively. A positive electrode 6 and a negative electrode 7 are arranged as electrodes in the positive electrode cell 2a and the negative electrode cell 2b, respectively.

In the redox flow battery 1, an aqueous solution of ions whose electron valence changes, such as iron ions and chromium ions, is
The liquid is stored in a tank 3.4 and sent to the flow-through electrolytic cell 2 by pumps P, , P2, where it is charged and discharged by an oxidation-reduction reaction. For example, as a catholyte, 11: e S +
/ Fe 2 with Fe 2+ ions as the positive electrode active material
+/F e 2+ hydrochloric acid solution, Cr 2 as negative electrode liquid
Cr with + / Cr 3+ ions as negative electrode active material
When a 2+/Cr*+ hydrochloric acid solution is used, the electrochemical reactions at both electrodes 6.7 of each redox system are as follows: [Problems to be Solved by the Invention] As mentioned above, in the redox flow battery 1, As the electrolyte, a positive electrode solution and a negative electrode solution having different compositions were used. Therefore, while the charging and discharging operations are repeated, the positive electrode active material contained in the positive electrode liquid and the negative electrode active material contained in the negative electrode liquid move to the opposite electrode side via the diaphragm 5. As a result, the amount of effective active material in each electrolytic solution decreases, resulting in a problem that the battery capacity decreases.

However, conventionally, a highly selective ion exchange membrane is often used as the diaphragm 5 in order to prevent each electrode active material from migrating to the counter electrode. However, when an ion exchange membrane is used, the internal resistance of the battery cannot be reduced, and therefore high charge/discharge efficiency cannot be achieved.

Therefore, an object of the present invention is to provide an electrolytic solution for a redox flow battery that hardly causes a decrease in effective active substance *ffi even after repeated charging and discharging operations.

[Means for Solving the Problems] The present invention provides an electrolytic battery used in a redox flow battery that separates a positive electrode and a negative electrode by a diaphragm, supplies a positive electrode liquid to the positive electrode, and a negative electrode liquid to the negative electrode, and performs charging and discharging. The liquid is characterized by containing both a positive electrode active material and a negative electrode active material.

In this invention, since the electrolytic solution contains both the positive electrode active material and the negative electrode active material, when the electrolytic solution is used as the positive electrode liquid and the negative electrode liquid, the electrolytic solution can be used between both sides of the diaphragm in the cell, that is, between the positive electrode cell and the negative electrode cell. Almost no concentration gradient of the electrode active material occurs in the diaphragm, and therefore almost no mass transfer of the electrode active material occurs through the diaphragm. As a result, even if charging and discharging operations are repeated, the amount of effective active material in each cell hardly decreases.

When the electrolyte of this invention is used as a positive and negative electrode, the electrochemical reaction at the positive and negative electrodes is l”ec
When using a ms solution in which jL2 and CrC1a are dissolved, the following results are obtained.

Positive electrode: Negative electrode: Therefore, both electrode active materials Fe3”/F
Even if mixing of e'+ and Cr 8 + / Cr 2+ occurs, since the compositions of the positive and negative electrode solutions are almost the same, the composition of each electrolyte does not substantially change, and therefore the effective amount of active material There is almost no decrease in

Preferably, the positive electrode active material and the negative electrode active material are contained in approximately equimolar amounts. Thereby, the electrochemical reaction at the positive electrode and the negative electrode can be carried out without waste, and therefore charging and discharging operations can be carried out more efficiently.

In addition, in the above explanation, FeCQ, 2
Although the case where cr Cl13 and cr Cl13 were used was explained,
It goes without saying that the present invention is not limited to this, and that the various electrode active materials shown in the table below can be used.

[Effects of the Invention] As described above, in this invention, since both a positive electrode active material and a negative electrode active material are included, the positive electrode liquid and the negative electrode liquid can be composed of one type of electrolyte, and therefore, charging and discharging operations can be repeated. Even if the ffi electrode active material moves through the diaphragm, the compositions of the positive and negative electrode fluids can be kept approximately constant. Therefore, it is possible to reliably prevent the battery capacity from decreasing as the charging/discharging operation progresses.

In addition, since the diaphragm is not required to have a strict two-liquid separation function, it is possible to use not only ion exchange membranes but also porous membranes and
l1lfI! The diaphragm can be formed by discipline, etc., and as a result, the redox flow battery can be operated at high temperatures;
Alternatively, it is also possible to increase the output.

[Example] Using a flow-type electrolytic cell with an electrode area of 9 cn+', using a conventional two-component electrolyte and a one-component electrolyte according to the present invention,
A charge/discharge experiment was conducted. The electrodes were made of graphite plates and carbon mei cloth, and the diaphragms were made of ion exchange membranes.

, and the composition of the electrolyte is as follows.

(Example of the present invention: 1-liquid type) FeCjlz and C
rCl1. A solution containing equimolar amounts of a was used as a positive electrode solution and a negative electrode solution.

(Comparative example: 2-component type) A positive electrode solution was prepared by dissolving Feciz in an HCi solution of 10% by weight or less, and a negative electrode solution was prepared by dissolving CrclL3 in the same ICQ solution.

As a result, when the electrolytic solution of the present invention was used, there was almost no decrease in battery capacity, but when a two-component type, that is, a conventional electrolytic solution was used, there was a gradual decrease in battery capacity as the charging/discharging operation progressed. A decrease in battery capacity (charging/discharging time) was observed.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram for explaining an example of a conventionally known redox flow battery.

Claims (3)

[Claims] (1) An electrolytic solution used in a redox flow battery in which a positive electrode and a negative electrode are separated by a diaphragm, a positive electrode is supplied to the positive electrode, and a negative electrode is supplied to the negative electrode for charging and discharging, which comprises a positive electrode active material and a negative electrode active material. An electrolyte for a redox flow battery, characterized in that it contains both substances. (2) The electrolytic solution for a redox flow battery according to claim 1, which contains approximately equal moles of the positive electrode active material and the negative electrode active material. (3) The positive electrode active material is Fe^2^+/Fe^3^+
ions, and the negative electrode active material is Cr^2^+/Cr^
Claim 1 or 2, which is a 3^+ ion
Electrolyte for redox flow batteries as described in Section.