JPH0439873A - Zinc-bromine battery - Google Patents

Abstract

PURPOSE:To restrain self discharge of zinc to improve a battery efficiency by composing an electrolyte retainer of a nonwoven cloth impregnated with electrolyte, and a positive electrode is integrated with a negative electrode hermetically while the positive electrode is arranged at the upper side of the negative electrode. CONSTITUTION:In a packing 7 an electrolyte retainer 5 composed of a nonwoven cloth impregnated with electrolyte, and on which a negative electrode 2 made of carbon plastic electrode and retaining plates 8, 9 are mounted. The plates 8, 9 are fastened by screws 14 at eight positions around the plates 8, 9 to be fixed hermetically. By using the nonwoven cloth electrolyte can be set in each cell even between narrow electrodes. Bromine generated in a positive electrode 1 sinks downwards and thus the same efficiency as the case where deposits are extracted by an electrolyte circulation type battery is obtained. It is thus possible to restrain self discharge of zinc to improve a battery efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a zinc-bromine battery of a static electrolyte type in which the cell is placed horizontally.

B0 Summary of the Invention The electrolyte stationary zinc-bromine battery of claim (1) comprises a positive electrode and a negative electrode made of carbon plastic electrodes made by kneading and molding polyethylene, carbon black, and graphite under heat and pressure; It consists of a microporous membrane separator provided between the negative electrode and an electrolyte holder placed between the separator and the positive and negative electrodes, and the surface of the carbon plastic electrode of the positive electrode has a sheet-like shape. A positive electrode active layer made of activated carbon fibers is formed, and the electrolyte holder is made of a nonwoven fabric impregnated with an electrolyte, and the positive electrode is placed on the lower side and the negative electrode is placed on the upper side in an airtight manner. It is constructed in one piece.

Further, the electrolyte static type zinc-bromine battery according to claim (2),
A positive electrode and a negative electrode made of carbon plastic electrodes made by kneading and molding polyethylene, carbon black, and graphite under heat and pressure; a microporous membrane separator provided between the positive electrode and the negative electrode; and the separator and the positive and negative electrodes. and an electrolyte holder disposed between the positive electrode and the separator, and the electrolyte holder disposed between the positive electrode and the separator is made by impregnating a nonwoven fabric with a solution obtained by adding carbon black to the electrode solution. The negative electrode is arranged on the lower side and the negative electrode is arranged on the upper side, and is integrally constructed in an airtight manner.

C9 Prior Art Currently, large capacity zinc-bromine batteries are being developed for power storage. (Japanese Patent Publication No. 1-31665) This battery reaction is shown below. The electromotive force is 1.
It is 8V.

(Positive electrode) 2Br-, = Br2+2Br (Negative electrode) Zn
”+2e 4-Zn (-charging, ←-discharging) As the electrode material, for example, polyethylene was used as a binder, and carbon black and graphite were mixed in a weight ratio of approximately 6:3:1 to provide conductivity. A carbon plastic electrode is used.The surface of the positive electrode 25 is a sheet made of activated carbon fiber bonded by thermocompression in order to reduce the reaction overvoltage of bromine.

The electrolyte is charged in a tank separate from the battery body.

Circulate with a pump during discharge. Through this circulation, the bromine generated at the positive electrode reacts with the bromine complexing agent (quaternary amine) added to the electrolyte, becomes an oily precipitate, and is returned to a separate tank. During discharge, it is pumped into the cell. will be returned.

The components of the electrolytic solution include ZnBr2 with salts such as NH4Cl added to lower the resistance of the solution, Pb to prevent dendrites of negative electrode zinc, and promote uniform electrodeposition.
Sn.

These are a dendrite inhibitor consisting of quaternary ammonium salts 2, etc., and a bromine complexing agent. A separator made of ion exchange resin is used between the positive electrode and the negative electrode to prevent bromine generated at the positive electrode from diffusing to the negative electrode and self-discharge of zinc.

This zinc-bromine battery has been developed as an electrolyte circulation type. Considering a large-capacity stationary type for load leveling, etc., this is more advantageous, and the pump loss used for circulation is smaller than that of the entire battery.

If the electrolyte tank is placed separately and the liquid is circulated, the distance between the poles of the cell body can be reduced, and the concentration polarization of the electrochemical reaction can be reduced, making it possible to produce a highly efficient battery.

On the other hand, when using batteries as an emergency power source, high reliability and safety are required. Therefore, when conventional zinc-bromine batteries are used as an emergency power source, rotating parts such as pumps have poor reliability, and the piping required for circulation is also disadvantageous. Furthermore, the manifold used to share the electrolyte solution for each cell has the problem of shunt current. This is disadvantageous, for example, when charging is performed constantly, such as in floating charging. When shunt current occurs, there is a problem in that dendrites occur and short circuits occur. For the above reasons, an electrolyte stationary type is advantageous as an emergency power source.

D1 Problems to be Solved by the Invention However, in this case, a step of placing a nonwoven fabric impregnated with an electrolytic solution on an electrode is required, which poses a problem in workability and is not suitable for mass production. Furthermore, since dendrites grow with almost the same probability as with normal liquids, the problem of dendrite generation remains.

In addition, zinc-bromine batteries normally use sheet-shaped activated carbon fibers bonded under heat to have a large surface area, be stable against flow, and prevent falling off. In this case, the cost of the positive electrode active layer increases.

Furthermore, in the case of a stationary battery, a sealed structure is required for reasons such as reliability and maintainability. In this case, hydrogen gas (H2) may be generated from the negative electrode during charging.

If gas remains in the cell, problems such as a reduction in the effective area of the electrode, generation of dendrites due to current concentration, etc., and liquid leakage due to increased internal pressure occur.

To provide an electrolyte stationary zinc-bromine battery which is easy to form, can keep bromine generated at the positive electrode near the electrode, and can store an inexpensive positive electrode active layer and generated hydrogen.

80 Means for Solving the Problems In order to achieve the above objects, the electrolyte stationary zinc-bromine battery of the present invention is comprised of a carbon plastic electrode made by kneading and molding polyethylene, carbon black, and graphite under heat and pressure. It consists of a positive electrode and a negative electrode, a separator of a microporous membrane provided between the positive electrode and the negative electrode, and an electrolyte holder placed between the separator and the positive electrode and the negative electrode, and the carbon of the positive electrode A positive electrode active layer made of sheet-like activated carbon fiber is formed on the surface of the plastic electrode, and the electrolytic solution holder is made of a nonwoven fabric impregnated with an electrolytic solution, with the positive electrode on the lower side and the negative electrode on the upper side. It is placed on the side and is integrally constructed in an airtight manner.

In addition, instead of forming a positive electrode active layer made of activated carbon fibers on the positive electrode electrolytic surface, the electrolyte holder between the positive electrode and the separator is made by impregnating a nonwoven fabric with a liquid containing carbon black in the electrolyte to activate the positive electrode. It can also be used as a layer.

Since the F2 acting positive electrode is disposed at the bottom and the negative electrode at the top, bromine generated at the positive electrode sinks downward and does not diffuse from the positive electrode to the negative electrode. Therefore, self-discharge of zinc is suppressed, and battery efficiency is improved.

Since the electrolytic solution soaks into the nonwoven fabric and is retained, it is easy to evenly fill each cell with the electrolytic solution even in a narrow gap between electrodes. This also reduces leakage of the electrolyte to the outside.

When carbon black is added to the positive electrode side electrolyte, the carbon black comes into contact with the surface of the positive electrode and acts as a positive electrode active layer. Since this positive electrode active layer does not fall off from the surface of the positive electrode, it is possible to extend the life at low cost.

G. Example Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a cell showing a first embodiment of a static electrolyte type zinc-bromine battery, in which 1 is a positive electrode installed horizontally, 2 is a negative electrode installed horizontally on top of the positive electrode 1, and 3 is a negative electrode installed horizontally on top of the positive electrode 1. Separators 4 and 5 are provided between the positive and negative electrodes; 6.7 is an electrolyte holder in which an electrolyte is soaked in a nonwoven fabric provided between the positive electrode 1 and the separator 3; and between the negative electrode 2 and the separator 3; Frame-shaped packing provided on the outside of the edge of the nonwoven fabric, 8.9 is positive.

FRP holding plate in contact with the lower and upper sides of the negative electrode, 1
2.13 are positive and negative terminals pulled out from holes 10 drilled in the holding plates 8 and 9; 14 are tightening screws inserted into holes 11 drilled around the holding plates 8 and 9; .

Electrode material is polyethylene=6. Carbon black = 3.
A carbon plastic electrode (5 cm x 5 cm) containing graphite in a proportion of 1 was used.

The nonwoven fabric used was Chisso Co., Ltd. with a crevice weight of 170 g/m2 (trade name NP-170).

Also, the electrolyte is 3molZ n B r 2+ 2moA
'NH4C1+ l mo/bromine complexing agent + dendrite inhibitor was used.

Next, the method for making the battery will be explained.

■ Place a non-woven fabric (5X 5 = 25cm2) in the electrolyte solution in advance.
) and separators (thickness 0.6-1, 0 m
m.

(made of polyethylene with a porosity of 40-60%) is soaked for about 1 hour.

■ Place the positive electrode 1 with the positive electrode active layer a (carbon cloth) thermocompressed onto the carbon plastic electrode on the holding plate 8, place the frame-shaped polyethylene packing 6 on top of the positive electrode 1, and place the electrolytic material in the above A nonwoven fabric impregnated with a liquid, that is, an electrolyte holder 4 is placed.

■ On top of that, separator 3 soaked with the electrolyte from ■ above.
(5.5 Cm x 5.5 Cm), and then a frame-shaped packing 7 is placed on top of it.

(2) Place the electrolyte holder 5, which is a non-woven fabric impregnated with electrolyte, into the gasket 7, and insert the negative electrode 2, which is made of a carbon plastic electrode. Place the holding plate 9 on it.

■Finally, tighten the screws 14 at 8 places around the holding plate 8.9 to fix it.

According to this embodiment, since a nonwoven fabric impregnated with an electrolyte is used, the electrolyte can be evenly filled into each cell even in a narrow space between electrodes. Furthermore, since the bromine generated at the positive electrode sinks downward, the same effect as that of removing precipitates in an electrolyte circulation type battery can be obtained.

The test results of this battery are shown in FIGS. 2 to 4.

Figure 2 shows the voltage characteristics when charging at a charging current density of 20 mA/am2 for 1 hour and discharging at a discharging current density of 20 mA/cm2.This battery has a lower voltage efficiency than an electrolyte circulation type battery. Energy efficiency is 65%, although slightly lower.
was gotten.

Figure 3 shows the discharge end voltage 1. This shows the change in energy efficiency when a cycle charge/discharge test was performed as an OV/cell.
There was almost no change in energy efficiency even after 0 cycles.

FIG. 4 shows the decrease in efficiency when the battery was left for one month after being charged at 2QmA/cm2 for one hour, and the change after one week was small and was about 10%.

FIG. 5 is a sectional view of a cell showing a second embodiment of a static liquid zinc-bromine battery. Components that are the same as those shown in FIG. 1 are given the same reference numerals, and redundant explanation thereof will be omitted.

In FIG. 5, 1' is a positive electrode made of a carbon plastic electrode without a positive electrode active layer, and 4' is a nonwoven fabric impregnated with a positive electrode electrolyte containing carbon black.

In order to prevent bromine from diffusing into the negative electrode and to increase the concentration on the surface of the positive electrode, the positive electrode 1' was placed below and the negative electrode 2 was placed above. In this example, the electrode area was 5 cm x 5 cm.

The method for creating cells will be described below.

■ Prepare two containers containing electrolyte. Add 10 g of carbon black (Ketchen Black EC manufactured by Lion Akzo) to the electrolyte in one container, stir well, add the nonwoven fabric, and let it sink. The nonwoven fabric and separator were placed in the other container and left for 1 hour.

■ A positive electrode 1' made of an untreated carbon plastic electrode is placed on the holding plate 8, and an electrolyte holder 4 made of non-woven fabric soaked in an electrolyte containing carbon black is placed on top of the positive electrode 1'.
' is placed thereon to form a positive electrode layer.

■ Place the frame-shaped packing 6 made of polyethylene, and then place the separator 3.

(2) Place the packing 7 again, and place therein the electrolyte holder 5, which is a non-woven fabric impregnated with an electrolyte to which no carbon black is added, to form a negative electrode layer.

(2) Place the negative electrode 2 and the holding plate 9 made of carbon plastic on top of it.

■Finally, tighten the screws 14 at eight places around the circumference.

The same materials as in the first example were used for the electrodes, nonwoven fabric, electrolyte, and the like.

According to this embodiment, a certain amount of carbon black can be fixed as the positive electrode active layer, which is advantageous compared to a structure in which carbon cloth or the like is bonded by thermocompression.

The test results of this battery are shown in FIGS. 6 and 7.

Figure 6 shows the charging and discharging voltage characteristics when charging was performed for 1 hour at a charging current density of 20 mA 7cm2 and discharging was performed at a discharging current density of 20 mA 7cm2. There was no significant difference in the voltage change curve from the case of thermally fusion bonding.

In addition, a nonwoven fabric impregnated with an electrolytic solution to which 20 g 1500 m7 of carbon black was added had higher performance than carbon cloth heat-sealable carbon plastic (using electrodes).

Further, FIG. 7 shows the discharge end voltage 1. This shows the change in energy efficiency when a cycle charge/discharge test was conducted as an OV/cell, and the efficiency did not decrease until the 50th cycle was completed. After the 5th cycle of charging, the battery was disassembled and zinc electrodeposition was confirmed, but no significant dendrite formation was observed.

H0 Effects of the Invention Since the present invention is configured as described above, it produces the following effects.

■ Since the positive electrode is placed on the lower side, bromine generated at the positive electrode diffuses downward toward the positive electrode, suppressing self-discharge and improving battery efficiency.

■ Since the electrolyte is impregnated into a non-woven fabric, it is easier to pour the electrolyte, and there is less leakage of the electrolyte to the outside, improving reliability.

In the battery of claim (2), (1) Carbon black is added to the electrolyte on the positive electrode side, and this carbon black is used as the positive electrode active layer. A battery having a positive electrode active layer can be obtained at a comparatively low cost.

■ Since the electrolyte is used stationary without being circulated, carbon black does not fall off the positive electrode, resulting in a longer lifespan.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a horizontal cell showing the first embodiment of the present invention, FIG. 2 is a charge/discharge voltage characteristic curve diagram of the same cell, FIG. 3 is a charge/discharge cycle characteristic curve diagram of the same cell, and FIG. The figure is a self-discharge rate characteristic curve diagram, Figure 5 is a sectional view of a horizontal cell showing the second embodiment, Figure 6 is a charge/discharge voltage characteristic curve diagram of the same cell, and Figure 7 is a charge/discharge cycle of the same cell. It is a characteristic curve diagram. 1.1'... Positive electrode, 2... Negative electrode, 3... Separator, 4.4', 5... Electrolyte holder, 6.7...
Patsukin, 8.9...pressing board. Fig. 2 Fig. 1 Fig. 1 Example Fig. 3 Time (minutes) Charging cycle 1 person Fig. 4 Idle period (W) Fig. 2 Example Fig. 6 Fig. 7 Number of charging/discharging cycles

Claims (2)

[Claims] (1) A positive electrode and a negative electrode made of carbon plastic electrodes made by kneading and molding polyethylene, carbon black, and graphite under heat and pressure; a microporous membrane separator provided between the positive electrode and the negative electrode; and the separator. an electrolytic solution holder disposed between the positive electrode and the negative electrode, and a positive electrode active layer made of sheet-like activated carbon fiber is formed on the surface of the positive carbon plastic electrode, and the electrolytic solution The holder is made of a non-woven fabric impregnated with an electrolyte, and the positive electrode is placed on the lower side and the negative electrode is placed on the upper side, and the electrolyte stationary zinc-bromine battery is constructed in an airtight manner. (2) A positive electrode and a negative electrode made of carbon plastic electrodes made by kneading and molding polyethylene, carbon black, and graphite under heat and pressure, a separator made of a microporous membrane provided between the positive electrode and the negative electrode, and the separator. and an electrolytic solution holder placed between the positive electrode and the negative electrode, respectively, and the electrolytic solution holder placed between the positive electrode and the separator is made by impregnating a nonwoven fabric with a solution obtained by adding carbon black to the electrode solution. An electrolyte stationary zinc-bromine battery comprising: the positive electrode disposed on the lower side and the negative electrode disposed on the upper side, and integrally configured in an airtight manner.