JPH0834099B2 - Manufacturing method of hydrogen storage alloy electrode - Google Patents

Description

The present invention relates to a method for producing a hydrogen storage alloy electrode. In particular, it is used in the production of alkaline secondary batteries.

(B) Conventional technology Hydrogen storage alloys have been studied for application to the negative electrode material of alkaline secondary batteries by utilizing the property of electrochemically reversibly storing and releasing hydrogen. Conventionally, the technology for forming hydrogen-absorbing alloy powder on electrodes is to use a thermoplastic resin powder such as polytetrafluoroethylene or polyethylene as a binder, mix it with hydrogen-absorbing alloy powder, and paste it with a solvent to heat it. Had formed. This electrode is generally used by incorporating it into a cell and electrochemically activating it with an electrolytic solution.

Also, in order to maximize the capacity of the hydrogen storage alloy that is an electrode active material and to fully exhibit the function as a secondary battery from the beginning, activate the hydrogen storage alloy and put the electrolyte in the electrode. It is necessary to fully soak into.
For this reason, it is necessary to increase the surface area of the electrode to make it easier for the electrolytic solution to permeate, and to perform the initial activation of the electrode after the electrode is manufactured. In order to increase the utilization rate of the electrode active material kneaded with the above-mentioned binder, the electrode surface is mechanically attached as shown in JP-A-61-193947 and JP-A-61-190858 from the viewpoint of increasing the electrode surface area. Methods have been proposed for making pores and making grooves with roller blades.

(C) The problem to be solved by the invention In the method for manufacturing a hydrogen storage alloy electrode described above, the discharge capacity of the battery is insufficient when the battery is configured so that the surface area of the electrode is not sufficiently large and the electrolyte does not easily penetrate, Further, there is a problem that an initial activation process of the electrodes is required at the time of manufacturing the battery and the battery manufacturing process becomes complicated.

The present invention has been made in order to solve the above-mentioned problems, and the surface area of the electrode is sufficiently large so that the electrolytic solution can easily permeate the hydrogen storage layer, and the initial activation step of the electrode can be omitted when manufacturing the battery. It is intended to provide a method for manufacturing an alloy electrode.

(D) Means for Solving the Problems According to the present invention, the hydrogen-storing alloy powder and the silicone-based resin are mixed under the condition that the silicone-based resin can flow, and the mixture is formed into a predetermined shape. It is made to flow and solidifies into a molded product, and then this molded product is placed in a pressurized hydrogen gas atmosphere of 40 to 60 atm to store hydrogen in this molded product and generate many fine cracks to absorb hydrogen. There is provided a method for producing a hydrogen storage alloy electrode, which comprises producing an alloy electrode.

In the present invention, the hydrogen-absorbing alloy powder and the silicone resin are mixed under the condition that the silicone resin can flow. The above-mentioned hydrogen storage alloy is for forming a negative electrode of a battery, and it is suitable that it can be used as a negative electrode active material, and an alloy having an appropriate equilibrium dissociation pressure of hydrogen in the operating temperature range of the battery. , For example, LaNi ₅ , MmNi ₅ or alloys thereof with other elements (Al, Co, Mn, etc.) added, rare earth alloys, TiNi, Ti ₂ Ni, TiNi ₂ , TiMn, etc. titanium alloys, ZrNi ₂
A zirconium-based alloy or the like can be used.

The above-mentioned polymer binder, which is a silicone-based resin, is for constituting a negative electrode of a battery, and is capable of forming a predetermined shape by binding hydrogen-absorbing alloy powder and forming fine cracks in the formed product. It is likely to occur, has alkali resistance, and is preferably in paste form. The above-mentioned mixing can be usually carried out at room temperature without a diluent when the silicone resin used is a paste at room temperature, and when the silicone resin used is highly viscous or solid at room temperature, it may be mixed with a diluent. It can be carried out by forming a paste having an appropriate viscosity or by heating until the paste has an appropriate viscosity. The mixing ratio of hydrogen storage alloy / silicone resin is preferably 100/5 to 100/30 in weight ratio.

In the present invention, this mixture is fluidized so as to have a predetermined shape and solidified to form a molded product. The above mixture is
Depending on the type of battery intended to be manufactured, it is usually applied by flowing it onto a current collector such as a metal net or metal foil, or by flowing it into a mold so as to form the shape of an electrode or sheet. You can

In the present invention, thereafter, the molded product is placed in a pressurized hydrogen gas atmosphere so that the molded product absorbs hydrogen and many fine cracks are generated. The above-mentioned pressurized hydrogen gas atmosphere is for causing hydrogen to be absorbed in this molded product and for generating many fine cracks, and a deaerator capable of making a vacuum and supplying hydrogen to a pressurized state. Using a reaction chamber having a hydrogen supply device capable of performing the above, the above-mentioned molded product is placed in this reaction chamber, and it is usually degassed to 10 ^-3 Torr or less, and then it changes depending on the temperature, but usually at 25 ° C, it is 40 ~ 60
It can be formed by supplying hydrogen gas at atmospheric pressure. Placement of the molded article in the pressurized hydrogen gas atmosphere,
The process is repeated until the pressure of the hydrogen gas introduced into the reaction chamber decreases due to the absorption of hydrogen in the molded product and then equilibrium is reached. By the treatment in this pressurized hydrogen gas atmosphere, the above-mentioned molded product occludes hydrogen, and accompanying this, volume expansion occurs in the hydrogen-absorbing alloy constituting the molded product, and the stress causes a large number of fine cracks (microcracks). ) Occurs. The obtained molded product can form the negative electrode of an alkaline secondary battery, for example.

(E) Action The arrangement of the molded product in the pressurized hydrogen gas atmosphere causes the molded product to occlude hydrogen gas, which causes a volume expansion of the hydrogen-storing alloy constituting the molded product, which causes a large number of stresses. Generates fine cracks. In addition, a coating film made of silicone resin is formed on the non-poisoned portion of the electrode caused by the generation of cracks, and the poisoning of the electrode is suppressed.

(F) Example 1 An example of the present invention will be described with reference to FIG. 10 parts by weight of LaNi _4.5 Al _0.5 powder (particle size 44 μm or less) as a hydrogen storage alloy and 2.8 parts by weight of one-component RTV silicone polymer (KE-45 manufactured by Shin-Etsu Silicone Co., Ltd.) as a polymer binder were mixed and kneaded to prepare an electrode mixture. Use as a paste. A nickel wire mesh (50 mesh) 2 as a current collector is placed on an aluminum foil (thickness 15 μm) 1 and 2.9 g of an electrode mixture paste 3 is applied per 10 cm ² . After the applied electrode mixture paste was cured, it was immersed in a 0.1 M KOH aqueous solution to remove the aluminum foil and washed with water to obtain a hydrogen storage alloy electrode sheet having a thickness of 1080 μm. This electrode sheet is punched and formed with a diameter of 15 mm. Next, this molded product is put into a reaction tube of a Sibelts apparatus having an internal volume of 20 cm ³ , vacuum degassed to 10 ⁻³ Torr, and then hydrogen gas is introduced into the reaction tube. Immediately after the introduction, the hydrogen gas pressure is 60 atm.
It becomes atmospheric pressure. After degassing again to 10 ^-3 Torr in vacuum, hydrogen is introduced. The pressure immediately after the introduction is 60 atm, and the pressure when the equilibrium is reached after 2 hours is 56 atm. Final degassing was performed up to 10 ^-3 Torr, air was leaked, and the hydrogen storage alloy electrode was manufactured by taking out from the reaction tube. A SEM photograph of this hydrogen storage alloy electrode is shown in FIG. It is observed that the electrode surface has microcracks. FIG. 4 shows the relationship between the time required to reach equilibrium and the pressure in the system when hydrogen is stored in the molded product in the Sibelts apparatus. FIG. 4A shows the first hydrogen storage, FIG. 4B shows the second hydrogen storage, and FIG. 4C.
Is a hydrogen storage alloy LaNi _4.5 Al _0.5 powder (particle size 44μ or less) 0.
It is the relationship between the hydrogen pressurization time of the 1st time and the 2nd time of 4 g, and the system internal pressure. A sheet electrode formed by supporting a hydrogen storage alloy with a silicon polymer reaches equilibrium faster during the second hydrogen storage than during the first hydrogen storage. The equilibrium arrival time of the hydrogen-absorbing alloy powder of FIG.
Considering that the same curve is traced both at the first time and the second time, the fact that the equilibrium arrival time at the time of hydrogen storage is faster in the case of the sheet electrode is not only the activation of the hydrogen storage alloy but also that of FIG. This is because fine cracks were formed on the electrode surface as shown in the SEM photograph. Coin type using the negative electrode of this hydrogen storage alloy electrode with minute cracks, the nickel electrode (diameter 15 mm, thickness 1080 μm) as the positive electrode, nylon nonwoven fabric (thickness 200 μm) as the separator, and 7.2 M KOH aqueous solution as the electrolyte. The nickel-hydrogen secondary battery of was produced. The negative electrode capacity was twice the positive electrode capacity. The discharge electrode in the first cycle of this battery is shown in D of FIG. Charge is i = 15
The discharge was performed at mA for 8 hours, and the discharge was performed at i = 2.5 mA (1.0 Vcut). The measurement temperature is 25 ° C.

Comparative Example 1 In Example 1, a hydrogen storage alloy electrode was produced in the same manner as in Example 1, except that hydrogen was not stored instead of storing hydrogen in the gas phase using a Sibelts apparatus.
A coin-type battery was manufactured in the same manner by using this hydrogen storage alloy electrode. A SEM photograph of the negative electrode is shown in FIG. Since hydrogen was not stored in the gas phase, fine cracks were not observed. The first cycle of the discharge curve of the battery is shown as E ₁ in FIG. 5, and the second cycle is shown as E ₂ in FIG. Charge and discharge conditions,
The measurement temperature is the same as in the example.

In this way, the electrode formed by carrying the hydrogen-absorbing alloy powder with the polymer binder, and the electrode that has absorbed hydrogen in the gas phase, can sufficiently bring out the discharge capacity from the first cycle after the battery is assembled. It was possible, and the battery characteristics were improved. In the present example, hydrogen was occluded twice, but even once it is effective.

(G) Effect of the Invention As described above, according to the present invention, the hydrogen storage alloy that is an active material can be activated, and the initial activation step by charging / discharging after battery assembly can be omitted. It is possible to provide a method for producing a hydrogen storage alloy electrode in which the electrode surface area can be increased by the fine cracks that can be formed, the electrolyte solution can be easily penetrated, and the discharge capacity can be sufficiently derived from the first cycle. Moreover, since a coating film is formed on the unpoisoned portion of the electrode caused by the crack by the silicone resin, poisoning of the electrode can be suppressed and the initial active state can be maintained for a long time. Becomes Therefore, a secondary battery having a high discharge capacity can be manufactured in a simplified process, which is of great industrial value.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing process of a hydrogen storage alloy electrode manufactured in an embodiment of the present invention, and FIG. 2 is a view of a hydrogen storage alloy electrode manufactured in an embodiment of the present invention, in which fine cracks are An enlarged view of a large number of surfaces, FIG. 3 is a view of a conventional hydrogen storage alloy electrode, and an enlarged view of a surface on which almost no fine cracks are present, and FIG. 4 are prepared in the embodiment of the present invention. FIG. 5 is a hydrogen pressure time-in-system pressure curve diagram when the hydrogen storage alloy sheet is hydrogen-pressurized in a Sibelts apparatus, and FIG. 5 is a discharge curve of the batteries produced in Examples and Comparative Examples of the present invention. 1 ... Aluminum foil, 2 ... Current collector, 3 ... Electrode mixture, A ... Hydrogen pressurization time of sheet electrode in the Sibelts device-system pressure curve (first time), B ... Sibelts device Pressurization time of the sheet electrode in the chamber-system pressure curve (second time), C ... Hydrogen storage alloy LaNi _4.5 Al _0.5 powder (particle size 44μ or less)
Between 0.4g hydrogen pressurization - system pressure curve (1, 2 th), D ...... discharge curve (first cycle) of the cell fabricated in Example, discharge curves of batteries fabricated in E ₁ ...... Comparative Example (1st cycle), E ₂ ... Discharge curve (2nd cycle) of the battery manufactured in the comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hirohisa Uchida 2-28-4 Tomigaya, Shibuya-ku, Tokyo Tokai University (72) Yoshito Matsumura 2-28-4 Tomigaya, Shibuya-ku, Tokyo Tokai University (56) Reference JP-A-63-264869 (JP, A)

Claims (1)

[Claims] 1. A hydrogen-absorbing alloy powder and a silicone-based resin are mixed under conditions that allow the silicone-based resin to flow, and the mixture is fluidized and solidified into a predetermined shape to form a molded product, after which By placing this molded product in a pressurized hydrogen gas atmosphere of 40 to 60 atm to store hydrogen in this molded product and generate a number of fine cracks to produce a hydrogen storage alloy electrode. Manufacturing method of storage alloy electrode.