JPH0357172A - Zinc-halogen battery - Google Patents

Abstract

PURPOSE:To prevent deterioration in performance caused by increase in pH of an electrolyte by installing a pair of valves in pipelines for circulating an electrolyte between a negative electrolyte storage tank and a negative electrode reaction tank and closing the valves to keep the reaction tank in a sealed state when a battery is stood in a charged state. CONSTITUTION:Valves 50, 52 are installed in pipelines 40, 42 which are used to circulate an electrolyte between a negative electrode reaction tank 16 and a negative electrolyte storage tank 24. When a battery is stood in a charged state, by closing the valves 50, 52, the negative electrode reaction tank 16 is kept in a sealed state. As a result, hydrogen gas in the tank 16 can not escape from a reaction system, and additional hydrogen evolution and increase in pH of the electrolyte caused by the hydrogen gas evolution can be avoided.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a liquid circulating zinc-halogen battery, particularly a zinc-halogen battery that can cope with an increase in the pH of the electrolyte caused by hydrogen gas generated in the negative electrode side reaction tank. Regarding.

[Prior art] Zinc-halogen batteries have been developed in which bromine, which has high solubility in electrolytes and excellent electrode reaction characteristics, is used as the positive electrode active material and zinc is used as the negative electrode active material. Due to its many advantages such as energy density, it is attracting attention as a driving source for electric vehicles, for example.

FIG. 5 shows the principle structure of a general zinc-halogen battery, particularly a zinc monobromine battery, disclosed in Japanese Patent Application Laid-Open No. 57-199167.

Zinc is used as the metal on the negative electrode side in the illustrated example,
An electrochemical reaction expressed by the following formula is performed via an electrolytic solution 18 between a positive electrode side reaction tank 14 and a negative electrode side reaction tank 16 in which the positive electrode 10 and the negative electrode 12 are disposed, respectively.

(Positive electrode) 2Br- = Br2 +2e (Negative electrode) Zn
"+2 e- = Zn -・- (1) (Total) Zn" +2Br- = Zn+Br2 (12 charging action, 12 discharging action, respectively) In such a zinc-monobromine battery, bromide is used as the electrolyte 18. A zinc ZnBr2 aqueous solution is used, and a conductivity improver, a bromine complexing agent, a dendrite inhibitor, etc. are added as necessary.

During charging, the charging reaction shown in equation 1 is carried out in the reaction tank 14.16, and bromine Br= is generated on the positive electrode 10 side and dissolved in the electrolytic solution 18, while zinc Zn is precipitated on the negative electrode 12 side. A deposited layer of zinc is formed on the negative electrode 12.

In addition, on the discharge side, a reaction opposite to that during charging is performed, which is indicated by -, and on the positive electrode 10 side, bromine Br. is reduced, and the bromine ions B become one and dissolve in the electrolytic solution 18, and on the negative electrode 12 side, the deposited layer of zinc is oxidized to become substituent ions Zn''+, which are dissolved in the electrolytic solution 18.

The interiors of the reaction vessels 14 and 16 where such electrical reactions occur are separated by a separator film 20 to prevent self-discharge caused by bromine Br2 generated during charging.

This separator membrane 20 allows various ions in the electrolytic solution 18 to pass through in order to prevent self-discharge, but blocks the penetration of bromine B r 2 dissolved in this and the bromine complex formed by reacting with bromine Br 2 . It is something.

An ion exchange membrane or a porous membrane is generally used as the separator M2.0, but a porous membrane is preferable from the viewpoint of reducing the internal resistance of the electric ground.

The electrolyte circulation type battery includes a positive electrolyte storage tank 22 and a negative electrolyte storage tank 24 for storing energy obtained through a chemical reaction during charging.

An electrolyte circulation path is formed between the positive electrode side electrolyte storage tank 22 and the positive electrode side reaction tank 14 via piping 26, 28, and the positive electrode side reaction WI is carried out by a pump 30 provided in the circulation path.
The positive electrode side electrolyte 18a reacted in the storage tank 2
2, and the electrolytic solution 18a in the storage tank 22 is sent to the reaction tank 1.
4.

Here, when a bromine complexing agent is added to the electrolytic solution 18, bromine Br2 generated during charging is complexed and precipitated as a complex compound 32 insoluble in the electrolytic solution 18, and the complex compound 32 connects the bottom of the storage tank 22 to the complex storage section 3
4, it is sequentially precipitated and stored.

Further, a valve 3 is connected between the complex storage section 34 and the pipe 28.
A complex feed tube 38 having 6. This valve 36 is normally open, and the complex compound 32 precipitated in the complex storage section 34 is sent out for discharge toward the positive electrode side reaction tank 14 via the pipe 28.

Further, the negative electrode side electrolyte storage tank 24 similarly forms an electrolyte circulation path with the negative electrode side reaction tank 16 via piping 40.42, and a bomb 44 provided in the hook ring path Negative electrode side electrolyte 18 reacted in the negative electrode side reaction tank 16 used
b is directed to the storage tank 24, and new electrolytic solution 18b is supplied from the storage tank 24 to the reaction tank 16.

Thus, this zinc-monobromine battery has a storage tank of 22.24.
A sufficient amount of electrolytic WR18 is stored in the storage area 18, and when charging using the stored electrolytic solution 18, the charging reaction shown in the first equation is carried out, a complex compound of bromine is stored in the complex storage part 34, and zinc is deposited on the negative electrode 12. Layers can be formed to store power.

Further, during discharge, the bromine complex compound 32 stored in the complex storage section 34 is sent out toward the positive electrode side reaction tank 14,
Using the complex compound 32 and the zinc deposited layer formed on the negative electrode 12, the discharge reaction shown in the first equation can be performed and the charging power can be released.

[Problem to be Solved by the Invention 8] However, in the conventional zinc-bromine battery configured as described above, the pH of the electrolyte solution slowly but unnecessarily increases mainly due to the generation of hydrogen gas when left in a charged state. The problem was that it would rise.

When the pH in the electrolytic solution exceeds a predetermined value (usually 3), insoluble zinc oxide begins to form, which covers the electrode surface and causes a significant drop in battery performance.

For this reason, in the past, attempts have been made to suppress the pH increase by periodically adding an acid such as HBr. However, when an acid is added, the concentration of free bromine in the electrolytic branch increases as a result of an increase in Br- ions, resulting in a significant drop in energy efficiency, which cannot be avoided. .

In addition, when such a battery is installed in an electric vehicle or the like, the trouble of frequently replenishing the battery with acid is a heavy burden on the user.

In order to deal with the above-mentioned inconveniences, the present applicant proposed a method in previously filed Japanese Patent Application No. 1-011492 to prevent the generation of hydrogen gas by circulating the electrolyte on the negative electrode side when the battery is left in a charged state. He proposed a structure to suppress it.

Although gas generation itself could be prevented by this, there was a problem in that the total energy efficiency of the battery decreased due to power consumption for driving the pump while the battery was left unused.

In addition, if the battery is left unused for a long period of time, it is impossible to keep the pump running during that period, so the troublesome process of having to completely discharge the battery is required. Ta.

The present invention has been made in view of the above-mentioned conventional problems,
The purpose is to provide a zinc-halogen battery that has a simple structure and can effectively suppress the pH increase of the electrolyte during the battery charging period.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a pair of opening/closing devices in the middle of the piping for supplying/discharging and circulating the electrolyte between the negative electrode side electrolyte storage tank and the negative electrode side reaction tank. The present invention is characterized in that a valve is provided, and when the battery is left in a charged state, the on-off valve is closed to maintain the negative electrode side reaction tank in a sealed state.

[Function] According to the configuration of the present invention, the on-off valve is closed while the battery is left charged, and the inside of the negative electrode side reaction tank is kept in a sealed state, so that the generated hydrogen gas escapes from the system. Therefore, the generation of new hydrogen gas is effectively suppressed.

[Example] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

Components in the drawing that are equivalent to those of the conventional device shown in FIG.

FIG. 1 shows a diagram of the principle structure of a zinc-halogen battery according to the present invention. In the illustrated example, both electrolyte storage tanks 22 and 24 are connected by a transfer tube 41, and the difference in liquid amount between them is maintained within a certain range. Further, a gas venting pipe 53 in which a gas venting pressure valve 51 is interposed is connected to the upper part of the negative electrode side electrolyte storage tank 24.
It is constructed so that the internal pressure does not rise above a certain value.

As already explained, in the zinc-halogen battery as shown in FIG. 5, both the positive electrode electrolyte and the negative electrode electrolyte are placed in a circulating state during charging.

Therefore, zinc ions Zn2° and bromine ions B', which are reactants, are easily generated at the negative electrode or the positive electrode, and the reaction shown in the above equation (1) takes place.

There is also a problem in that the pH of the electrolytic solution increases beyond the allowable range due to hydrogen gas generation when the battery is left in a charged state, resulting in a significant deterioration in battery performance.

A feature of the present invention is that when the battery is left in a charged state, by sealing the inside of the reaction tank on the negative electrode side, zinc deposited on the negative electrode is suppressed from reacting with the electrolyte and generating hydrogen. It is in.

In the illustrated example, on-off valves 50 and 52 are provided in the middle of the pipes 40 and 42, respectively, which connect the negative electrode side reaction tank 16 and the negative electrode side electrolyte storage tank 24 to circulate the electrolyte between them.
is interposed.

Therefore, when the on-off valves 50 and 52 are closed when the battery is left in a charged state, that is, with the battery capacity remaining, the negative electrode side reaction tank 16 is placed in a sealed state.

As a result, the hydrogen gas remains in this sealed chamber and does not go out of the reaction system, so that new generation of hydrogen gas and an increase in the pH of the electrolytic solution 18 due to this can be reliably avoided.

Basically, it is sufficient to provide an on-off valve only on the negative electrode side piping 40 and 42 side, but hydrogen ions in the positive electrode side circulation system may diffuse into the negative electrode side reaction tank 16 through the separator membrane 20. The area of the reaction system becomes larger and hydrogen gas may be more likely to be generated.

For this reason, as shown in the illustrated example, on-off valves 54 and 56 are also provided on the positive electrode side pipes 26 and 28, and these on-off valves 50, 52, 54, and 56 are simultaneously closed when the battery is left in a charged state. , it is possible to more effectively stop the hydrogen gas generation reaction in the reaction tank.

Additionally, in order to reduce the differential pressure between the positive electrode side reaction tank and the negative electrode side reaction tank on both sides of the separator membrane 20 and reduce mechanical stress, it is better to provide an on-off valve in the positive electrode side piping. .

With the above configuration, it is possible to avoid the pH increase due to hydrogen gas generation, but for some reason self-discharge occurs inside the reaction vessels 14 and 16 while the battery is left unused, and the temperature of the reaction vessels rises abnormally. If such a situation occurs, the internal pressure of the reaction tank may rise excessively because the electrolytic solution 18 thermally expands or the gas generation reaction is accelerated.

In order to prevent such inconvenience, in the illustrated example, pressure valves 58 and 60 are provided in the middle of one of the pipes 42 and 28 on each pole side, and the branch recovery pipe 62, 64 corresponds to the electric angle (I liquid storage 24, 22
and piping 42, 28, and when the internal pressure of the reaction tanks 14, 16, which are placed in a sealed state, becomes abnormally high pressure, the electrolyte inside the reaction tank is released toward the electrolyte storage tanks 24, 22. It is configured as follows.

These pressure valves 58 and 60 automatically open and close according to changes in the internal pressure of the pipes 42 and 28 to which they are attached, but are set at a level that will not open when the electrolyte is circulated. Just leave it there.

Of course, during charging and discharging, the on-off valves 50, 52, 54
, 56 are all opened, and a predetermined charging/discharging reaction similar to the conventional one is performed.

FIG. 2 shows a second embodiment of the invention.

In the first embodiment, four on-off valves 50 to 56 were used to seal the reaction tank corresponding to each pole side, but in this embodiment, two valves common to both pole sides were used at the electrolyte inlet and outlet of the reaction chamber. 4-way valves 66 and 68 are used.

These 4-way valves 66 and 68 are set as shown in Figure 3 during charging and discharging, so that normal reactions occur, and on the other hand, when the battery is left in a charged state, they are set as shown in Figure 4. The entire reaction tank is then disconnected from communication with the electrolyte storage tank via piping and placed in a sealed state.

This embodiment also provides the same effects as the first embodiment.

[Effects of the Invention] As explained above, according to the present invention, an on-off valve is provided in the middle of the electrolyte supply/discharge pipe to the negative electrode side reaction tank, and the on-off valve is closed when the battery is left unattended. Since the inside of the negative electrode side reaction tank is kept in a sealed state, the generation of hydrogen gas due to the reaction between zinc and the electrolyte in the negative electrode side reaction tank during the battery storage period is effectively suppressed, and the pH of the electrolyte is It is possible to reliably prevent the deterioration of battery performance due to the increase in battery performance.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the present invention; Figs. 2, 3, and 4 are explanatory diagrams of the principle and operation of a second embodiment of the present invention; Fig. 5 is a diagram of the principle of the rice following device; . 14.16... Reaction tank 18... Electrolyte solution 50, 52. 54, 56 58.60... Pressure valve on/off valve

Claims (1)

[Scope of Claims] In a zinc-halogen battery in which a predetermined charging/discharging reaction is carried out by circulating positive and negative electrolytes in the positive and negative reaction tanks through piping, respectively, A zinc-halogen battery characterized in that on-off valves are interposed in each of the supply and discharge piping, and when the battery is left in a charged state, the on-off valves are closed to maintain the negative electrode side reaction tank in a sealed state. .