JP3275336B2 - Method for manufacturing positive electrode of zinc bromine battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a positive electrode of a zinc bromine battery.

[0002]

2. Description of the Related Art A zinc bromine battery is a secondary battery using bromine as a positive electrode active material and zinc as a negative electrode active material. It is a peak-cut battery that stores excess power during the night to release the imbalance between power demand during the day and night, and discharges the power during the daytime when demand is high. At present, large capacity batteries are being developed for power storage. The chemical reaction of this battery is as follows: during charging: positive electrode: 2Br ⁻ → Br ₂ + 2e ⁻ , negative electrode: Zn
⁺⁺ + 2e ⁻ → Zn Discharge… Positive electrode: 2Br ⁻ ← Br ₂ + 2e ⁻ , Negative electrode: Zn
⁺⁺ + 2e ⁻ ← Zn.

[0003] As a material for the electrode, carbon black is used to impart conductivity using polyethylene as a binder.
A carbon plastic electrode in which graphite is mixed at about 6: 3: 1 is used. The surface of the positive electrode is formed by heat-sealing carbon cloth to reduce the reaction overvoltage of bromine. The electrolyte is placed separately from the battery body and circulated by a pump during charging and discharging. Bromine generated at the positive electrode reacts with a bromine complexing agent (quaternary amine) added to the electrolytic solution to form an oily precipitate, which is returned to the tank. At the time of discharging, the bromine is pumped into the cell and reduced. The component of the electrolyte is ZnBr
Add a salt such as NH ₄ Cl to reduce the resistance of the solution to ₂ ,
Pb, Sn, quaternary ammonium salts, and a bromine complexing agent for preventing dendrite of the negative electrode zinc and promoting uniform electrodeposition (3 mol / l ZnBr ₂ +2 mol)
_{NH 4 Cl + 1mol / l Br} ). A separator is used between the positive electrode and the negative electrode to prevent bromine generated in the positive electrode from diffusing into the negative electrode and causing self-discharge of zinc.

[0004]

In the positive electrode of the present battery, oxidation and reduction reactions of bromine are carried out. However, the reaction overvoltage is very large and the voltage loss of the battery is large. For this purpose, a carbon cloth (for example, a phenol-based carbon fiber sheet) is thermally fused to the electrode surface. However, this carbon cloth is very expensive, and is difficult to use when considering commercialization. Therefore, polyvinyl alcohol (PVA)
A method has been devised in which carbon fibers are impregnated with the use of a carbon fiber and fused to an electrode. However, the non-woven fabric and the carbon fiber do not have good affinity and are hardly impregnated. Therefore, the contact resistance with the electrode is high, and the characteristics at high current density are particularly poor. Therefore, it is necessary to newly improve the contact property and improve the battery characteristics.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for manufacturing a positive electrode of a zinc bromine battery, which aims at reducing the cost of manufacturing the electrode and improving the battery performance.

[0006]

According to the present invention, there is provided (1) a method in which 20 to 30 g / l of carbon fiber is added to an aqueous dispersion of conductive carbon black, the mixture is stirred at room temperature, and a polyethylene net is added to the liquid. After impregnating for 10 to 20 seconds and drying at a temperature of 80 to 100 ° C. for 10 to 20 minutes, the polyethylene net is fused to the surface of the carbon plastic electrode by heat press or lamination. The mixing ratio of the ink containing the ink is determined by adding 50 to 70 g / l of carbon fiber to a liquid obtained by mixing the ink and the aqueous dispersion of the conductive carbon black at a volume ratio of 2: 1 or less and stirring the mixture. After impregnating in the liquid, it is dried at a temperature of 100 ° C. for 5 minutes, and the polyethylene net is carbohydrated by heat press or lamination. It is characterized by fusing the surface of the plastic electrode.

[0007]

The aqueous dispersion of conductive carbon black is an aqueous dispersion in which carbon black having excellent conductivity, for example, Ketjen Black EC (Lion Corporation) is uniformly dispersed. Carbon black dispersed in water is anionic,
Either a cationic type or a nonionic type can be used.

The use of the aqueous dispersion of carbon black is for increasing the viscosity of the liquid and improving the dispersibility of the carbon fiber. The viscosity of the aqueous dispersion of carbon black is
Therefore, those having 900 to 300 cp are preferable.

The carbon fiber to be added to the aqueous dispersion of carbon black is preferably one that can pass through the eyes of the net in order to make the adhesion to the net to be used uniform, and is one-half the size of the eyes of the net. Those having a length of 4 to 1/6 are preferred, and generally commercially available ones having a length of 0.1 to 0.7 mm can be used. If the thickness is less than 0.1 mm, the adhesion to the net will be poor, and if it is more than 0.7 mm, the dispersibility in the aqueous dispersion will be poor.

For the same reason, the addition amount is 20 to 30 g /
l. With such an aqueous dispersion, 10
0 to 150 g / m ² of carbon fiber can be attached.

The aqueous dispersion of conductive carbon black can be used by mixing commercially available ink. By mixing the ink, it is possible to prevent carbon from falling off the electrode after lamination on carbon plastic due to the action of glue in the ink. The mixing ratio of the ink is 2: 1 or less in volume ratio between the ink and the conductive carbon black aqueous dispersion. This is because when the mixing ratio of the ink becomes 2: 1 or more, the overvoltage of the electrode increases.

When an aqueous dispersion of conductive carbon black and ink are mixed and used, carbon fiber can be added in an amount of from 30 g / l to 50 to 70 g / l.

[0013]

【Example】

Embodiment 1 Hereinafter, an embodiment of the invention described in claim 1 will be described with reference to the drawings. In the present invention, a method of attaching a carbon fiber to both sides of the net using a polyethylene net having a large eye gap instead of the nonwoven fabric was studied.
The net used was Takiron N-3. In order to improve the dispersibility of the carbon fiber, it is necessary to increase the viscosity of the liquid. Those that increase the viscosity also need conductivity. Therefore, the viscosity was increased by adding carbon fiber to carbon black.

The aqueous carbon black dispersion used was W-310A, W-311N, or W-37 manufactured by Lion Corporation.
0C. Carbon fiber (Donacarbo S-242, manufactured by Dainippon Ink) was changed to 0 to 30 g and added to the aqueous solution of carbon black. The average fiber system of the carbon fibers is 13 μm.

Then, a polyethylene net is impregnated therein, and the liquid is slightly agitated and taken out after 10 to 20 seconds.
Placed in a 00 ° C. oven for 20 minutes. This net was heat-pressed to obtain an electrode.

The length of the carbon fiber is set to 0.1, 0.
Although it was changed to 3,0.7 m / m, the dispersibility was poor at 0.7 m / m, and the adhesion to the net was poor at 0.1 m / m.
For this reason, 0.3 m / m is optimal.

The amount of carbon fiber added is 30 g / l
Above this, the carbon fiber aggregates and 2
If it is less than 0 g, the net mesh cannot be filled. Therefore, it is preferably between 20 and 30 g / l.

FIG. 1 shows an active net prepared by using the above-mentioned aqueous dispersion of carbon fiber and carbon black.
FIG. 1 (a) shows the case where the adhesion is small, and FIG. 1 (b) shows the case where the adhesion is good. The amount of carbon fiber attached is 100 to 150 g / m ² .

FIG. 2 shows that 3 mol / l ZnBr ₂ +0.
The results of cyclic voltammetry (polarization characteristics by a voltage-current method) performed on a 1 molBr ₂ solution at a scanning speed of 10 mA / sec are shown. In FIG. 2, curve A is the polarization characteristic of the electrode manufactured using the conventional carbon cloth, curve B is the polarization characteristic of the electrode manufactured using the polyethylene net, carbon fiber and carbon black according to the present invention, and curve C is the non-woven fabric. The polarization characteristics of the electrodes manufactured using carbon fibers are shown. FIG.
From this, it can be seen that the polarization characteristic B shows almost the same characteristic as the polarization characteristic A. For this reason, according to the present invention, even if a carbon cloth is not used unlike the related art, the same good battery performance as when the carbon cloth is used can be obtained and the cost can be reduced.

In the present invention, the battery performance and cost can be controlled by adjusting the amounts of carbon fiber and carbon black.

The characteristics of the aqueous carbon black dispersion, carbon fiber and polyethylene net used in the present invention are shown below. (1) Lion paste W series manufactured by Lion Corporation as shown in Table 1 is used as the water-dispersible carbon black.

[0022]

[Table 1]

(2) Donnacarbo S-240 series (powder-like carbon fiber obtained by finely cutting (milling) carbon fiber) as shown in Table 2 is used as the carbon fiber.

[0024]

[Table 2]

(3) As a polyethylene net, Takiron's registered trademark "trical net" N-3 is used.

Embodiment 2 Next, a second embodiment of the present invention will be described. Claim 1
As an alternative to the method using expensive carbon cloth, a polyethylene net was attached to a mixture of an aqueous dispersion of carbon black and carbon fiber to produce a positive electrode active layer. However, according to this method, the amount of carbon black is excessive, and the amount of carbon falling after lamination on the electrode is very large. If the dropout is large, it flows when the electrolyte is circulating in the battery, and the pattern is clogged, and the flow of the liquid is disturbed. This causes a reduction in efficiency and life. Therefore, it is necessary to reduce the amount of carbon black. However, when the amount is reduced, the viscosity of the solution decreases, and the dispersion of the carbon fiber becomes poor.

The adhesive force to the net is an effect of both the entanglement of the carbon fiber with the net and the large surface area of the carbon black producing the adhesive force to the net.
Carbon black increases the viscosity of the solution and improves the dispersibility of the carbon fiber. Therefore, when the amount of carbon black is reduced, the adhesive force to the net and the viscosity of the liquid are reduced. Then, the improvement of the adhesive strength of the carbon to the net was examined.

[0028] Donna carb S-2 in 100ml of commercially available ink
41 (Carbon fiber of Table 2 above, cut length 0.1
3m / m) up to 10-70g and after stirring well
Polyethylene trical net N-3 (polyethylene made by Takiron)
Ethylene net). After that, 100
C. and dried for 5 minutes. The amount of S241 is 10 g, 3
0 g, 50 g, and 70 g were performed at four points. Car in ink
Although the amount of bon is small, the net
Could be made to put a film on the eyes. Carbon fiber
Is a part that is evenly attached to 30 to 50 g,
It was thick. This is the glue paste in the ink
It is presumed to be playing a role. The amount of addition is about 2%
Seem. Polarization characteristics of 50g of carbon fiber
The characteristics were as shown by the broken line in FIG. Carbon black
In comparison with the characteristics (the characteristics of the solid line) of those using the water dispersion
About a two-fold reduction in characteristics was observed. However, using ink
In the case, carbon is almost completely removed from the electrode after lamination.
Was not.

[0029] The question of carbon dropout by using ink
Title was reduced, so to improve the properties,
Bonblack aqueous dispersion in a ratio of 2: 1, 1: 1, 1: 2
About carbon fiber S241
50 g was added and prepared. What was added in each of the above ratios
And laminate them to electrodes and evaluate their polarization characteristics
The results are shown in FIG.

In FIG. 5, A, B, C, and D indicate that the mixing ratio of the aqueous dispersion of carbon black to black ink is 1: 0, 1: 1, respectively.
The polarization characteristics in the case of 1: 2, 0: 1 are shown. According to FIG. 5, the characteristics of a mixture having a mixing ratio of 1: 1 (shown in B) are almost the same as those of only the aqueous dispersion of carbon black (shown in A). Therefore, it is understood that good characteristics can be obtained by using the mixed liquid having the mixing ratio of 1: 1.

Black ink prepared above and aqueous dispersion of carbon black (mixing ratio 1: 1) + carbon fiber S241
(50 g) of the solution was prepared in an amount of 50 liters, the polyethylene trical net was cut out to 40 cm × 40 cm, an active net was formed, and laminated on an electrode to form an 800 cm ² electrode. A 10-cell battery was stacked using these electrodes, and a battery operation test was performed. The test conditions were 10A (12.5m
(A / cm ² ) Charging for 8 hours, discharging at 10 A, and liquid temperature of 30 ° C. As a result, the voltage efficiency, Coulomb efficiency, and energy efficiency were as shown in Table 3.

[0032]

[Table 3]

From Table 3, it can be seen that the battery manufactured according to the present invention exhibits the same performance as a battery using a conventional carbon cloth or a commercially available carbon paper (for example, Toyobo).

[0034]

As described above, according to the first aspect of the present invention,
Carbon fiber was added to the aqueous dispersion of conductive carbon black, and a polyethylene net was impregnated in the dispersion and then dried and welded to the electrode, so that a positive electrode with good performance without using a carbon cloth And cost can be reduced. The conventional carbon cloth is very expensive in terms of cost since one fiber has micropores and one fiber is present. However, the performance of the bromine oxidation-reduction reaction can be sufficiently improved even in the absence of the micropores and the use of some carbon black and carbon fibers without pores. By adjusting the amounts of carbon fiber and carbon black, it is possible to control the performance and cost.

According to the second aspect of the present invention, carbon fiber is added to a mixture of an aqueous dispersion of black ink and conductive carbon black, and a polyethylene net is impregnated in the mixture, followed by drying. , The following excellent effects can be obtained.

(1) By using a commercially available black ink for carbon black, which is one of the conductive materials of the positive electrode active layer, it has become possible to sufficiently prevent the carbon from dropping off after the electrode is formed and to reduce the cost. .

(2) Carbon black has physical adhesion to the net due to its large surface area. This adhesive force and the yarn length of the carbon fiber interact to improve the adhesion to the net. The reason why the adhesion to the net is improved despite the small amount of carbon black added in the ink is due to the glue in the ink. This serves as a kind of glue, and its effect is greater than conventionally used polyvinyl alcohol.

(3) As described above with reference to FIG. 4 , since ink and carbon fiber alone are somewhat low in characteristics, carbon black is prepared by preparing a solution having a mixing ratio of ink and carbon black in an aqueous dispersion of 2: 1 or less. Dropout can be reduced and characteristics can be improved.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the invention according to claim 1,
(A) is an explanatory view showing the case where the adhesion of the carbon fiber and the aqueous dispersion of carbon black to the active net is small, and (b) is the case where the adhesion of the carbon fiber and the aqueous dispersion of carbon black to the active net is normal. FIG.

FIG. 2 is a polarization characteristic diagram showing the polarization characteristics of an electrode manufactured according to the embodiment of the present invention.

FIG. 3 is an explanatory view showing an embodiment of the invention as set forth in claim 2 and showing a situation in which carbon black and black ink adhere to an active net.

FIG. 4 is a polarization characteristic diagram showing the polarization characteristics of the electrode manufactured according to the invention of claim 1 and the polarization characteristics of the electrode manufactured by the method of the reference example .

FIG. 5 is a polarization characteristic diagram showing the polarization characteristics of the electrode manufactured according to the invention of claim 2 when the mixing ratio of black ink and the aqueous solution of carbon black is changed.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/96 H01M 4/88 H01M 12/08

Claims (2)

(57) [Claims] 1. An aqueous dispersion of conductive carbon black is added with 20 to 30 g / l of carbon fiber and stirred at room temperature, and a polyethylene net is added to the aqueous dispersion of 10 to 2 g.
A positive electrode of a zinc bromine battery, wherein the positive electrode is impregnated for 0 second, dried at a temperature of 80 to 100 ° C. for 10 to 20 minutes, and the polyethylene net is fused to the surface of the carbon plastic electrode by heat press or lamination. Manufacturing method. The mixing ratio of 2. A India ink containing glue, said Indian ink and conductive carbon black aqueous dispersion in a volume ratio of 2: 50 to 70 g of carbon fibers mixed submerged in 1 below
/ L and stirred, impregnated with a polyethylene net in the liquid, dried at a temperature of 100 ° C. for 5 minutes, and the polyethylene net is fused to the surface of the carbon plastic electrode by heat press or lamination. A method for producing a positive electrode of a zinc bromine battery.