JP2918559B2 - Manufacturing method of hydrogen storage electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hydrogen storage electrode in a storage battery using a metal oxide as a positive electrode and a negative electrode as a hydrogen storage electrode that repeatedly stores and discharges hydrogen.

[Conventional technology]

The conventional method of manufacturing a hydrogen storage electrode is mainly composed of a hydrogen storage alloy powder, a PTFE (polytetrafluoroethylene) as a fibrous binder and a conductive agent added thereto, and the mixture is sufficiently kneaded with a viscous liquid. A paste formed by sufficiently fibrous PTFE is filled in a foamed nickel substrate, dried, and then the filled plate is pressed and fired to produce the paste.

[Problems to be solved by the invention]

The conventional method for producing a hydrogen storage electrode described above is to prevent the hydrogen storage alloy powder from falling off and to improve the service life. All of the PTFE is fiberized to form a three-dimensional network, and the hydrogen storage alloy powder is bound and held in the mesh to achieve the above object.
Due to the fiberization of PTFE, the viscosity of the paste becomes extremely high,
The filling property of the paste into the foamed metal substrate is inferior, so that it is difficult to fill a sufficient amount of the hydrogen-absorbing alloy powder, resulting in a disadvantage that a large-capacity hydrogen-absorbing electrode cannot be obtained.

[Means for solving the problem]

The present invention eliminates the disadvantages of the conventional method for manufacturing a hydrogen storage electrode, and provides a method for manufacturing a hydrogen storage electrode in which the filling amount of paste, that is, the hydrogen storage alloy powder is increased and the falling-off prevention of the powder is ensured. In preparing a paste by kneading a mixture of a hydrogen storage alloy powder as a main component and a fibrous binder and a viscous agent liquid, the kneading is performed to such an extent that the binder hardly becomes fibrous. The method is characterized in that the paste is filled in a porous metal substrate, dried, and then the filled substrate is rolled to sufficiently convert the binder into fibers.

(Operation)

According to the present invention, the kneading of the compound is reduced to such an extent that the kneading hardly causes fiberization of the binder, so that the viscosity of the paste can be kept low. Since the porous metal substrate is filled with the low-viscosity paste, the paste can be easily and sufficiently filled up to the center of the substrate. That is, a large amount of the hydrogen-absorbing alloy powder and the unfibrillated binder can be uniformly contained throughout the entire substrate. Next, when the filled and dried substrate is rolled, the binder particles uniformly dispersed in the substrate are subjected to a shearing stress by rolling to form a uniform fiber, and the three-dimensional network is formed in the entire substrate. Formed. Thus, the hydrogen-absorbing alloy powder is bound and held in the network stretched over the entire network, so that an electrode having good life characteristics without falling off is obtained, and the filling amount of the hydrogen-absorbing alloy powder in the electrode is reduced. Because of the increase, an electrode having a large capacity can be obtained.

〔Example〕

 Next, examples of the present invention will be described.

Commonly used hydrogen storage alloy powders are metals with positive heat of hydride generation (Fe, Ni, Cu, Cr, Co, etc.) and negative metals (Ti, Zr, La, Ce, V, etc.) Are mixed in a melting furnace with an appropriate atomic ratio to obtain an alloy, which is pulverized immediately or through hydrogen embrittlement to obtain a powder. It is appropriately selected and used from such various kinds of hydrogen storage alloy powder. For example, LaNi _4.7 Al _0.3
100 parts by weight of hydrogen storage alloy powder such as N
Add 20 parts by weight of powder, 5 parts by weight of PTFE powder as a fibrous binder, and 80 parts by weight of a 3% aqueous solution of methylcellulose as a viscous liquid, and knead the mixture for about 10 minutes to obtain a low-viscosity paste. Was adjusted. In this short-time kneading, most of the PTFE particles in the paste are not fiberized, so that the paste has a low viscosity. The low-viscosity paste was filled in a porous metal substrate, for example, a foamed nickel substrate, and then dried at 80 ° C. for 1 hour. As described above, since the paste has a low viscosity, it can be easily filled up to the inner center of the substrate, and therefore, the paste can be uniformly and abundantly filled as a whole. Next, the filled and dried substrate was rolled in a rolling mill. The thickness of the substrate before rolling was about 1.6 mm, which was then rolled into a rolled plate of about 0.35 mm. Such rolling is generally and preferably performed a plurality of times. For example, a 1.6 mm substrate is reduced to 0.8 mm in the first rolling, and then 0.35 mm in the second rolling. By this rolling, the binder particles uniformly dispersed in the substrate are subjected to a shearing force, and all of them are fiberized to form the three-dimensional network in the rolled plate, and are uniformly formed in the mesh. The hydrogen storage alloy powder could be held and fixed.

Next, it is fired in the same manner as in the conventional method. For example,
By baking at 300 ° C. for 1 hour, the three-dimensional network of fibrous PTFE is fixed, whereby the filled hydrogen-absorbing alloy powder is bound and retained in the network network, thereby providing good prevention of falling off.

Thus, the production of the hydrogen storage electrode of the present invention was completed, but the electrode plate contained about 2 g / cm ² of the hydrogen storage alloy powder.

As a comparison, the kneading time of the above compound was set to 90 according to the conventional method.
Performed enough, the shear stress due to the kneading was applied to the binder particles to prepare a high-viscosity paste in which all of the content was fibrillated, and then this was filled in a foamed nickel substrate, but the filling property was poor. According to a conventional method, the hydrogen-absorbing electrode obtained through the drying, pressing, and firing steps contained only about 1 g / cm ^{2 of the} hydrogen-absorbing alloy powder. Also, almost no paste was filled in the deep center of the substrate. As is clear from this, according to the present method, the filling amount of the hydrogen storage alloy powder can be easily increased as compared with the conventional method.

Further, as a control example, a low-viscosity paste was filled in a substrate and dried according to the above-described production process of the present invention, and the filled and dried substrate was pressed according to a conventional method instead of rolling to produce a hydrogen storage electrode.

Thus, in comparison with the hydrogen storage electrode according to the present invention, the hydrogen storage electrode according to the conventional method described above and the hydrogen storage electrode according to the additional control example described above are each used as a negative electrode, and the capacity is sufficiently larger than these electrode plates. A battery A of the present invention, a conventional battery B, and a control battery C were each fabricated by combining a known Ni electrode plate as a positive electrode, and a charge / discharge cycle test was performed on these batteries. At this time, the charging was performed at 0.2 C at 130%, and the discharging was performed at 0.5 C up to −0.75 V vs Hg / HgO at the hydrogen electrode. The result is shown in FIG. In the drawings, A is a charge / discharge cycle characteristic area obtained by measuring a plurality of batteries incorporating the electrode of the present invention, B is a similar charge / discharge cycle characteristic area of a battery incorporating the conventional electrode,
C shows the same charge / discharge cycle characteristic region of the battery incorporating the comparative example electrode.

As is clear from this, the fact that the characteristic area A when the electrode of the present invention is used is not different from the charge / discharge cycle characteristic area B when the conventional electrode is used is due to the rolling process employed in the present method. It was confirmed that formation of a fibrous three-dimensional network can be achieved in the same manner as formation of a fibrous three-dimensional network of a binder by conventional kneading. or,
As shown by the charge / discharge cycle characteristic region C, in some pressing processes, a sufficient fibrous three-dimensional network of the binder is not formed, so that the binding and holding of the hydrogen storage alloy powder in the electrode cannot be obtained. This means that in the charge / discharge cycle process, the peeling and falling off of the hydrogen-absorbing alloy powder increases accordingly, in other words, it means that sufficient shear stress is not applied to the binder by the press, and the rolling is completed. It means that it is extremely effective for fiberizing the adhesive.

Thus, according to the present invention, as described above, the filling amount of the low-viscosity paste in the substrate can be doubled as compared with the filling of the high-viscosity paste according to the conventional method. It is particularly advantageous in that an electrode can be obtained as compared with the conventional method.

〔The invention's effect〕

Thus, when according to the present invention, based on the hydrogen storage alloy powder, kneading of a paste containing a fibrous binder,
Filling the porous metal substrate in a state where the viscosity of the paste is low while the binder is hardly fibrillated, so that the conventional fibrous binder is sufficiently kneaded into fibers to form a high-viscosity binder. As compared with filling the paste into the porous metal substrate, the paste can be filled in a much larger amount and up to the inside. Then, the filled dry substrate is subjected to a rolling treatment. And a three-dimensional network can be formed. Thus, it is possible to manufacture an excellent hydrogen-absorbing electrode having a remarkably large capacity as compared with an electrode according to a conventional method, and having a long life and preventing the hydrogen-absorbing alloy powder from falling off. Has an effect.

[Brief description of the drawings]

FIG. 1 shows a battery incorporating one example of the electrode obtained by the production method of the present invention, a battery incorporating one example of the electrode obtained by the conventional method, and one example of the electrode obtained by the control example. FIG. 4 is a comparison diagram of charge / discharge cycle characteristics of each battery.

Claims (2)

(57) [Claims] A kneaded mixture of a hydrogen storage alloy powder, a fibrous binder and a viscous agent liquid, and the kneading of the binder, the binder is almost completely fibrous. A method for producing a hydrogen-absorbing electrode, characterized in that the paste is filled in a porous metal substrate, dried, and then the filled substrate is rolled to sufficiently convert the binder into fibers. 2. The method according to claim 1, wherein said rolling is performed in a plurality of stages.