JPH0750608B2 - Method for manufacturing hydrogen storage electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a hydrogen storage electrode used as a negative electrode of an alkaline secondary battery using hydrogen as a negative electrode active material,
For example, the present invention relates to a method for manufacturing a hydrogen storage electrode, which facilitates the manufacture of a large electrode and improves its discharge characteristics.

[Prior Art] Conventionally, as one of the alkaline secondary batteries, there is a metal oxide / hydrogen battery using a metal oxide as a positive electrode active material and hydrogen as a negative electrode active material. ,
There is a negative electrode that uses a hydrogen storage electrode containing a hydrogen storage alloy that stores and releases hydrogen reversibly. This hydrogen storage electrode is required to have good hydrogen storage / release and low resistance. For example, it is formed by mixing hydrogen storage alloy powder with a binder.

As an example of the already known use of the above-mentioned binder, Japanese Patent Laid-Open No. 61-16
Japanese Patent No. 470 discloses polytetrafluoroethylene (PTFE) powder.

JP-A-61-101957 discloses that the surface of a hydrogen-absorbing alloy powder is coated with copper to form microcapsules, and the microcapsules and fluororesin powder (binder) are kneaded and pressed against a current collector. Disclosed is a hydrogen storage electrode.

[Problems to be Solved by the Invention] However, the conventional hydrogen storage electrodes disclosed in the above-mentioned respective prior arts are inferior in shape stability because the hydrogen storage alloy powder is deformed by charging and discharging, and rapid (high rate). ) There was a problem in that the capacity was greatly reduced during discharge. In particular, when increasing the size of the electrode, even if the volume change rate and the deformation rate are the same, the large electrode has a larger absolute volume change amount or deformation amount than the small electrode.
As a result, the alloy powder is apt to fall off or break from the hydrogen storage electrode, and the shape stability is further deteriorated. It is possible to improve the bond strength, that is, the shape stability, by increasing the amount of the binder.However, if this is done, the amount of alloy powder is reduced, the permeability of the electrolyte and hydrogen ions inside the electrode is obstructed, and the electrical resistance is increased. Occurs, and the capacity during high rate discharge is significantly reduced.

Therefore, there has been a demand for a hydrogen storage electrode that is excellent in shape retention and discharge characteristics without increasing the amount of the binder as much as possible, especially in increasing the size thereof.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a hydrogen storage electrode having excellent discharge characteristics and shape retention.

[Means for Solving the Problems] A method for manufacturing a hydrogen storage electrode of the present invention is a method for producing a hydrogen storage alloy powder and an uncrosslinked silicone rubber, a resin powder, a metal powder,
The method is characterized in that after kneading with a gap powder made of at least one kind of ceramic powder, the mixture is supported by a current collector and pressure-molded, and at the same time, the silicone rubber is crosslinked.

In this way, when a gap powder having a different elastic modulus or coefficient of thermal expansion is mixed into the silicone rubber, a fine gap is generated between the silicone rubber and the gap powder, and the flowability of the electrolytic solution and hydrogen ions inside the electrode is improved. improves. As a result, the discharge characteristics are improved without impairing the shape stability of the silicone rubber.

As the hydrogen storage alloy powder, titanium-nickel alloy, lanthanum-nickel alloy, zirconium-nickel alloy or the like can be adopted, and the average particle diameter is preferably about 10 to 100 μm. It is possible to coat the hydrogen storage alloy powder with copper or nickel, and these coatings are preferably about 5 to 30 wt% of the weight of the microcapsules (hydrogen storage alloy powder coated with copper or nickel).

As the silicone rubber, dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl silicone rubber, phenyl vinyl silicone rubber, fluorinated silicone rubber and the like can be adopted.

As the uncrosslinked silicone rubber, for example, one-component type room temperature-curing type and two-component type heat-curing type may be mentioned. As a one-component room temperature curing type, for example SE9155 made by Toray KK, as a two-component heat curing type, for example CY52-made by Toray KK
There are 237 etc.

The molding pressure is preferably 50 to 300 kg / cm ² , and particularly preferably 100 to 250 kg / cm ² . If it is less than 50 kg / cm ² , the mechanical strength of the electrode is lowered and a sufficient binding force cannot be obtained, and the microcapsules are likely to drop off. Further, although the reason is unknown, the capacity at the time of high rate discharge is reduced. 300kg / cm ²
If it exceeds, the microcapsules become too close to each other, the porous structure is lost, the electrochemical hydrogen absorption and desorption is not smoothly performed, and the internal resistance increases and the capacity at the time of high rate discharge decreases. .

As the gap forming powder, at least one of resin powder, metal powder and ceramic powder can be adopted. Especially as resin powder, PTFE (polytetrafluoroethylene)
Powders and PTFE disversions (dispersions) are suitable.
Since PTFE forms a three-dimensional network structure by cross-linking and has a binding property even by itself, the amount of silicone rubber can be reduced and the total electrode weight can be reduced.

[Example] (First Embodiment) Alloy composition MmNi _3.5 CO _0.7 Al _0.8: Using (Mm misch metal) as a hydrogen storage alloy for the negative electrode. This alloy mechanically
Electroless copper plating was performed using a commercially available plating solution with a powder of 100 mesh or less. The plating amount at this time was set to 20% by weight with respect to the plated alloy.

To 4.5 g of this copper-plated alloy powder, 0.35 g of uncrosslinked silicone rubber and 0.15 g of gap powder were added and kneaded, and after preforming into a sheet, both sides of the nickel mesh (that is, the current collector in the present invention). 200 kg / cm ² at room temperature
A hydrogen storage electrode was manufactured by press molding at a pressure of.

One-part room temperature curable SE738 for uncrosslinked silicone rubber
(Manufactured by Toray KK) was used. In addition, SE9155, SE9158, SE737, SE738 (manufactured by Toray KK), KE45, KE42, KE3492, KE3493 (Shin-Etsu Chemical K
K) can also be used, and a two-component thermosetting silicone rubber, for example, CY52-237, SE1700 (manufactured by Toray KK) may be used. In order to sufficiently crosslink these uncrosslinked silicone rubbers, they were held at 150 ° C. for 30 minutes in a pressure-molded state.

PTFE, FEP (tetrafluoroethylene-
Hexafluoroethylene copolymer), carbon black, alumina, nickel, copper, polyvinylidene fluoride, sodium acrylate, Raney-nickel, CMC (carboxymethyl cellulose sodium), polyvinyl alcohol, polyamide, polyethylene, polypropylene, zirconia, stainless steel, Powder such as cobalt or dispersion was used alone.

The size of the electrode was 4 × 3 cm ² and the thickness was about 1 mm. This electrode was immersed in a 6N aqueous solution of potassium hydroxide with the nickel electrode as the counter electrode, repeated charging and discharging, and completely activated to serve as a negative electrode for a battery. The initial capacity of this hydrogen storage electrode was about 900 mAh.

On the other hand, a sintered nickel oxide plate with a capacity of 350 mAh was prepared as the positive electrode, these positive and negative electrodes were placed opposite to each other via a nylon nonwoven fabric separator, and lithium hydroxide was dissolved in a 5N potassium hydroxide aqueous solution at a rate of 1 mol / l. Dipped in the electrolyte
A positive electrode regulated battery with a nominal capacity of 350 mAh was constructed.

Therefore, the weight ratio of the copper-plated alloy powder, the uncrosslinked silicone rubber, and the gap powder is 90: 7: 3.

Charge these batteries created at 20 ℃, 0.5C current for 3 hours, and cut off voltage at each discharge current of 0.5C, 1C, 2C, 3C, 4C, 5C.
After discharging to 0.8 V, the dependence of battery capacity on discharge current was examined.
The results are shown in FIG. As a first comparative example, an electrode prepared by adding 0.35 g of uncrosslinked silicone rubber to 4.5 g of copper-plated alloy powder was used. As a second comparative example, PTFE powder was added to the alloy powder and heated at 300 ° C. and 300 kg / cm ² . A pressure-molded product is also shown. In this case, the PTFE powder is the same as the copper-plated alloy powder.
It was set to 5% by weight with respect to the sum of the PTFE powder.

The discharge capacity characteristics at each discharge rate of the battery equipped with the hydrogen storage electrode of this example, which was obtained by adding the silicone rubber and the void powder, were included in the shaded area in FIG. As is clear from this result, when the silicone rubber and the void powder are used, the capacity decrease at a high rate discharge is significantly smaller than that when only PTFE is used or when only silicone rubber is used.

Second Example Next, the total weight of the silicone rubber and the gap powder was fixed at 0.5 g, and the weight ratio of the silicone rubber and the gap powder was changed under the same conditions as in the first example. A negative electrode was molded, and a battery was prepared using this negative electrode under the same conditions as in the first embodiment.

Fig. 2 shows the relationship between the gap powder and the capacity retention rate at 5C discharge (the capacity at 0.5C discharge is 100%).

According to the results of this implementation, as shown in FIG. 2, the proportion of the gap powder is 5 to 80 wt%, especially 20 to 60 wt% with respect to the total weight of the silicone rubber and the gap powder. I found it good.

(Third Example) Next, the weight ratio of silicone rubber and gap powder was fixed at 7: 3, and silicone rubber was added to the total weight (total weight of copper-plated alloy powder, silicon rubber and gap powder). A negative electrode was molded under the same conditions as those of the first embodiment by changing the ratio of the total weight of the gap forming powder, and a battery was prepared using this negative electrode under the same conditions as the first embodiment.

As a first comparative example, a case where only silicone rubber was added and a case where only PTFE powder was added were molded under the same conditions as those of the comparative example of the first example.

According to the result of this experiment, as shown in FIG. 3, when PTFE powder was used as the gap powder, the above ratio was 1 to 15 wt%.
%, Particularly 2 to 10 wt%, and when other void powders are used, the above ratio is 3 to 25 wt%, especially 5 to 20 wt%.
It turned out that it is better to set wt%.

Fourth Example Next, using the same electrodes as those tested in the first example, the relationship between the number of charge / discharge cycles for activation and the increase in capacity was examined. As a comparative example, the characteristics of the case where only the silicone rubber was used as the binder without adding the void powder were also examined.

The charging / discharging condition was 300 mA for 4.5 hours, and 200 mA was discharged to 0.8 V for one charging / discharging cycle.

As shown in FIG. 4, it can be seen that the number of charge / discharge cycles can be significantly reduced by adding the gap powder to the silicone rubber.

[Effects of the Invention] As described above, in the method for producing a hydrogen storage electrode of the present invention, the hydrogen storage alloy powder is kneaded with the uncrosslinked silicone rubber and the void powder, and at the same time when the electrode is molded, the uncrosslinked silicone rubber is crosslinked. Since the hydrogen storage electrode is formed by completing the above, it was found that it is possible to improve the capacity lowering characteristic at the time of high rate discharge, as can be seen from the experimental results.

Furthermore, it has been found that the number of charge / discharge cycles for activation can be reduced.

Perhaps, although silicone rubber has excellent elastic deformability and excellent binding property corresponding to the deformation of alloy powder, and absorbs the deformation of alloy powder due to high rate discharge to reduce the internal electric resistance loss, etc. Since the binding property (that is, the adhesion property or the wettability) is too good, the surface of the alloy powder is coated and the permeability of the electrolytic solution or hydrogen ion into the electrode is lowered.

It is speculated that the mixing of the gap forming powder may improve the above-mentioned permeability through a minute gap in the environmental portion between the silicone rubber and the gap forming powder. Further, since PTFE has a binding property and porosity (resin network structure), the amount of silicone rubber can be reduced without deteriorating the discharge characteristics.

Therefore, according to the method for producing a hydrogen storage electrode of the present invention, it is possible to obtain high shape stability by silicone rubber, and it is possible to suppress the capacity decrease at the time of high-rate discharge, and to increase the size of the electrode. It is extremely effective.

From the viewpoint of the shape stability of the electrode, even a conventional PTFE or fluororesin binder will be slightly elastically deformed following the deformation of the microcapsules. However, the elastic deformation limit of such a binder is low, and when the deformation amount of the microcapsule increases, the bond between the binder and the microcapsule is microscopically broken (the microcapsule holding force of the binder is It is conceivable that the shape stability of the large electrode is impaired and the internal electrical resistance of the large electrode is increased, resulting in a significant decrease in capacity at high rate discharge.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a capacity lowering characteristic at a high rate discharge of a battery using the hydrogen storage electrode manufactured by the manufacturing method of the present invention, and FIG. 2 is a capacity powder weight and a capacity at 5C discharging. Fig. 3 is a characteristic diagram showing the relationship with the retention rate. Fig. 3 is a characteristic diagram showing the relationship between the total weight of the void powder and silicon rubber weight and the capacity retention rate at 5C discharge. It is a characteristic view which shows the effect of reducing the number of charge / discharge cycles for activation.

Claims (1)

[Claims] 1. A hydrogen storage alloy powder and an uncrosslinked silicone rubber are kneaded together with a gap powder made of at least one of resin powder, metal powder and ceramic powder, and the mixture is supported by a current collector and pressed. A method for producing a hydrogen storage electrode, characterized in that the silicone rubber is crosslinked simultaneously with molding.