JPH04167363A - Nickel electrode and metal hydride electrode and manufacture of battery using them - Google Patents

Abstract

PURPOSE:To obtain a pollution-free storage battery of high energy density by combining a hydrogen storage alloy electrode excellent in charge and discharge performance and an Ni electrode of high density that does not contain Cd. CONSTITUTION:Powder of an MmNi5 alloy the Ni of which is partially substituted by Al and one or two kinds of elements selected among Mn, Fe, Co and Cu is mixed with CO powder of 3 to 20wt.% and the mixture is packed in an alkali-resistant porous base to form a hydrogen storage alloy electrode. Powder of Co monoxide is mixed by 5 to 15wt.% in an active material obtained by dissolution of Zn by 2 to 8wt.% in spherical Ni monoxide powder of internal porous capacity 0.14ml/cc or less and the mixture is converted into a paste by addition of water and then packed in the alkali-resistant metal porous base and dry pressed to form an Ni electrode. Both of the electrodes are wound via a separator and a KOH water solution is injected therein and the electrodes are sealed and left for more than five hours and then initial charging is performed. By this constitution a high-capacity, pollution-free, totally Cd-free storage battery is obtained.

Description

Detailed Description of the Invention (Field of Application in Industry-1-) The present invention provides an electrode for a nickel hydride storage battery using a hydrogen storage alloy electrode as a negative electrode and a nickel hydroxide electrode as a positive electrode, and a method for manufacturing the battery. It is related to.

(Prior Art) As portable electronic devices progress, storage batteries that serve as their power sources are required to have even higher capacity and higher energy density. Recently, as a storage battery that meets these demands, a nickel metal hydride storage battery (nickel-metal hydride battery), which uses a hydrogen storage alloy electrode for the negative electrode and a nickel electrode for the positive electrode, has appeared, and its practical use is expected. .

To realize a high-capacity nickel-metal hydride battery, it is necessary to increase the energy density of the nickel hydroxide electrode. Conventionally, the mainstream of nickel electrodes has been sintered plates, whose energy density has been limited to 400 mA h/cc, and it has been difficult to achieve higher elongation. recent years,
A paste-type nickel electrode, in which a highly porous metal substrate is filled with nickel hydroxide powder as an active material, has been developed, and its energy density has been improved to around 500 mAh/cc.

However, in conventional paste-type nickel electrodes, it is essential to add a small amount of cadmium to the nickel hydroxide powder, which is the active material, in order to prevent electrode swelling that causes short circuits and shortened battery life. Due to environmental concerns, there is a desire to develop nickel-metal hydride batteries that do not contain any cadmium. Further, conventional nickel hydroxide powder is a porous material with many pores inside the particle, and has a problem that must be improved from the standpoint of packing it more densely.

Regarding hydrogen storage alloy electrodes, negative electrodes using MIoNis-based hydrogen storage alloys (which do not contain cadmium) have been put into practical use. The charging/discharging reaction of this electrode in an alkaline electrolytic solution is generally thought to have a reaction mechanism as shown in equation (1), although there are still some unknown points.

Charge M+H20+e: MH+OH-(1)' Discharge (M: M+aNis alloy) In other words, during charging, protons are reduced to hydrogen atoms on the alloy surface by receiving electrons from the outside, and are occluded in the hydrogen storage alloy. Ru. During discharge, occluded hydrogen atoms are ionized on the alloy surface and protons are released. Thus, in the charging and discharging reactions of hydrogen storage alloy electrodes, the alloy surface, where the ionization reaction (or reverse reaction) of hydrogen atoms occurs, plays an important role.

However, when MfflNis-based hydrogen storage alloys are repeatedly charged and discharged in an alkaline electrolyte, surface corrosion of the alloy progresses, resulting in the hydrogen atom ionization reaction described in 1-1.
This causes problems such as increased resistance between alloy particles (decreased electronic conductivity), etc., and the capacity gradually deteriorates until the end of its life.

Conventionally, in order to prevent the deterioration of these hydrogen storage alloys due to corrosion, methods have been developed to improve the corrosion resistance of the alloy itself by replacing part of the Ni in the MmNi5 alloy with other elements, and to improve the corrosion resistance of the alloy itself by replacing part of the Ni in the MmNi5 alloy with other elements. Methods such as etching and nickel lithography, or so-called microencapsulation, in which the surface of the alloy is coated with nickel or copper, are used. All of these are coated with corrosion-resistant nickel or copper on the alloy surface to prevent corrosion.

However, these methods cannot prevent alloy deterioration.
Although it is somewhat effective, it requires complicated processes such as alkaline etching or electroless plating, which increases manufacturing costs.

(Problems to be Solved by the Invention) As mentioned above, a nickel-metal hydride battery using a conventional paste-type nickel electrode (containing cadmium) and a hydrogen storage alloy electrode cannot be made into a completely state-free battery that does not contain cadmium. However, as long as nickel hydroxide powder with many internal pores is used as the positive electrode active material, the manufacturing method is complicated, resulting in an expensive battery.
The problem is that the battery capacity is only about 25% higher than that of conventional sintered batteries.

The present invention solves the various problems described above, and provides a hydrogen storage alloy electrode with a simple manufacturing process and excellent charge/discharge performance, and a high energy density nickel electrode that does not contain cadmium or hydrogen. This combination provides a completely pollution-free, high-energy-density nickel-metal hydride storage battery (nickel-metal hydride battery).

(Means for Solving the Problems) The present invention provides a method for replacing a part of Ni in an M+nNl5 alloy with Al and On.
.

A hydrogen storage alloy electrode is prepared by filling an alkali-resistant metal porous substrate with a mixture of hydrogen storage alloy powder substituted with one or more of Fe, Co, and Cu and 3 to 20% by weight of metallic cobalt powder; 5 to 15 weight percent of cobalt monoxide powder is mixed with an active material in which 2 to 8 weight percent of zinc is dissolved in spherical nickel hydroxide powder crystals with a pore volume of 0.14 mI/cc or less. Then, add water to make a paste, fill it into an alkali-resistant porous metal substrate, dry press it, then wrap it with the created nickel electrode through a separator, and after injecting an aqueous potassium hydroxide solution, seal it. This is a nickel/metal hydride storage battery characterized by being left alone for 5 hours or more and then being charged for the first time.

(Function) Deterioration of the hydrogen storage alloy negative electrode is caused by corrosion products deposited on the alloy surface, such as non-conductive substances such as La(OH)3, which make electron transfer between alloy particles impossible. However, as the metal cobalt powder maintains the electronic conductivity between the hydrogen storage alloy particles and between the alloy and the current collector through repeated charging and discharging, capacity reduction is suppressed, and the Since the effect of reducing the reaction overvoltage in equation 1) is also H, it is possible to provide a hydrogen storage alloy electrode with excellent charging and discharging performance and long life.

In addition, as the positive electrode active material, we use spherical high-density nickel hydroxide powder, which suppresses the development of internal volume compared to conventional powders, to increase the active material's 1f4 density, and by mixing cobalt monoxide powder, the active material By setting the utilization rate to 95% or more, it is possible to easily manufacture a nickel electrode with a high energy density of 550-600 mAh/cc. In addition, zinc dissolved in the crystals of nickel hydroxide powder has the same effect as conventional cadmium to prevent swelling of nickel electrodes, and its effect is more durable than cadmium. ing.

By using these electrodes for the negative and positive electrodes, it is possible to obtain a completely pollution-free nickel metal hydride storage battery that has a higher capacity than conventional batteries and does not contain any cadmium.

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

[Example 1] The hydrogen storage alloy and its electrode were created by the following method.

Mitshu Metal M+a, which is a mixture of rare earth elements (main components Ce: 50mff1%, La: 28% by weight, N
d: 16Im 96 ) and each component element of AI, Fe, and Cu are melted in a high frequency melting furnace to obtain MmNjs;s Al
A hydrogen storage alloy with a composition ratio of G, 5 Feo7Cuo, + was created. After heat treating this alloy in an argon atmosphere,
The powder was pulverized to 200 mesh or less to obtain a hydrogen storage alloy powder.

After adding and mixing 10 parts by weight of metallic cobalt powder (average particle size 1 to 15 μm) to 100 parts by weight of this hydrogen storage alloy powder, the mixture was made into a paste with a 3vt9o aqueous solution of polyvinyl alcohol. This paste was then mixed with a porosity of 9
The material was filled into a 5% nickel fiber porous material, vacuum dried, and then pressurized to improve the charge/discharge performance of the electrode device made by the conventional microencapsulation method. - By way of example, an embodiment of the invention (A) and a microencapsulated alloy electrode (B) coated with 20 wt. 96 nickel.

FIG. 1 shows a comparison of the capacity cycle characteristics of an alloy electrode (C) containing 20% by weight of nickel powder as a conductive aid and an electrode (D) containing no additive.

As is clear from FIG. 1, in this example (A) in which cobalt powder is added, the capacity increases at the beginning of the charge/discharge cycle, and the capacity decrease that accompanies subsequent cycles is prevented. . Moreover, as shown in FIG. 2, the average discharge potential shifted to the marked direction with respect to the cycle, and it was observed that the overvoltage during the discharge reaction decreased. On the other hand, in the conventional microencapsulated comparative example (B), although the capacity did not decrease with cycling, the initial capacity increase effect was not observed as in the present example (A), and the comparative example (C, D
) caused a gradual decrease in capacity.

The unique behavior of this cobalt powder alone is estimated as follows.

For example, since the metallic cobalt powder added in Example (A) can undergo the electrochemical dissolution precipitation reaction of equation (2) during the charging and discharging process of the hydrogen storage alloy electrode, ■ Co + 2 e -Co (Ig>complex ion -C
o (Oft) 2 (2) By repeating charging and discharging, cobalt is gradually dispersed and a conductive network of cobalt is formed, improving electronic conductivity between alloy particles.

On the other hand, cobalt having a 3d orbital is known as a hydrogen ionization catalyst in a hydrogen electrode.

The addition of cobalt powder in the present invention has the effect of increasing the electrode capacity in addition to the cycle life, but this suggests that the rate-determining rate of the discharge reaction is the hydrogen ionization process, and that cobalt is acting as a catalyst. Conceivable. On the other hand, the negative electrodes of Comparative Examples (C, D) after the capacity decrease also contained a large amount of hydrogen, so the electronic conductivity decreased as the surface corrosion of the alloy progressed. Is it a discharge reaction?
It is thought that the i11 was damaged and the capacity decreased.

Thus, it can be seen that the present Example (A) is a hydrogen storage alloy electrode that can be manufactured easily and has excellent cycle performance.

The effect of this cobalt powder is AB CY (here, A-Mi, Y, Ti, Hr, Zr, Ca, T
h, La5B = Ni, Co, Cu, Fe, Mn, C
= Al. Cr, Si) based alloys, T1Ni based alloys, Laves phase alloys (MgNi based, ZrLa based, Zr
Other hydrogen storage alloys such as Ni-based alloys also have stud effects.

On the other hand, nickel hydroxide powder, which is the active material of the positive electrode, The terminal and its electrodes were prepared as follows.

After adding ammonia to an aqueous solution of 3 to 8% by weight of zinc sulfate dissolved in nickel sulfate to form a nickel/ammine complex ion, an aqueous sodium hydroxide solution was added dropwise with vigorous stirring to form water in which zinc was dissolved as a solid solution. Nickel oxide powder was synthesized.

The nickel hydroxide powder obtained in this way is a conventional powder (
0,15 ml/g) of approximately 115 internal pore volumes (0,0 ml/g)
It is a spherical high-density particle with a particle size of 5ml/g), and its tapping density (bulk density) is lower than that of conventional powder (1,
6g/m+) and 2.0g/ml.

As a result, it is possible to increase the filling amount by about 2096 points compared to the conventional case.

In addition, zinc dissolved in crystals of nickel hydroxide powder is
In a range of 2% by weight or more, it was effective in preventing the formation of γ-Ni00H, which causes electrode swelling (increase in electrode thickness), and the durability of the effect was superior to that of cadmium. Increasing the amount of zinc lowers the proportion of nickel hydroxide;
From a practical standpoint, 2 to 8% by weight is appropriate.

After mixing cohardt monoxide powder with this high-density nickel hydroxide powder, CMC (carboxymethyl cellulose)
The paste was made into a paste with an aqueous solution of and filled into a Ninkel fiber porous substrate with a porosity of 9596, dried and then pressurized to prepare an electrode.

Here, the cobalt monoxide powder undergoes the chemical dissolution precipitation reaction of equation (3) in the electrolytic solution, spreads over 1 m of the surface of the nickel hydroxide particles, and changes to conductive Co0011 during the first charge. By forming a conductive network between the nickel hydroxide particles and the current collector, it has the effect of improving the usage rate of the active material to 95 to 100%. What is important here is to uniformly disperse cobalt throughout the electrode by the reaction of equation (3). For this purpose, it is necessary to leave it in the electrolytic solution for at least 5 hours or more.

Leaving it in the electrolyte Leaving it in the electrolyte CoO-”
Co (II) complex ion - first charge Co (Oll) 2- Co OOH (3) Capacity of the thus obtained nickel electrode (E) and a comparative example (F) using conventional nickel hydroxide powder is shown in Figure 3. This figure shows that the appropriate range for the amount of cobalt monoxide added is 2 to 15% by weight, and that the capacity of this example (E) is 600mAh/1.2 times that of the conventional electrode (F).
I can see that CC is improving. In addition, nickel electrode (E
), it can be seen that when the amount of cobalt monoxide added exceeds 15% by weight, the active material utilization rate increases, but the energy density decreases.

Next, the hydrogen storage alloy electrode and nickel electrode of the above example were wrapped together with a nylon nonwoven fabric separator interposed therebetween, and the specific gravity was 1.
．． A cylindrical sealed cylindrical chive metal hydride storage battery of AA size was prepared by diluting the potassium hydroxide aqueous solution of No. 24. The first charge of the battery was carried out after the liquid was injected and the battery was sealed, and the battery was left to stand for 5 hours or more for the above-mentioned reason.

The discharge characteristics of the battery thus prepared are shown in FIG. 4, and the cycle capacity characteristics are shown in FIG. It can be seen that the battery of the present invention (G) has a capacity about 1.2 times that of the conventional comparative example (H) and has excellent cycle characteristics.

In addition, in the above example, an example using a nickel fiber porous substrate was shown, but the invention is not limited to this, and expanded metal,
Metal mesh, nickel-plated punching metal, or the like may be used as the substrate.

Further, in the present invention, the same effect can be obtained by using metallic cobalt powder or cobalt monoxide powder, or by adding other cobalt compounds or cobalt-containing alloys that can be dissolved in an alkaline electrolyte.

(Effects of the Invention) As described above, by combining the hydrogen storage alloy electrode of the present invention and the nickel electrode, it is possible to create a nickel metal that has a higher energy density than the conventional one, does not contain cadmium, is pollution-free, and has a simple manufacturing process. Since it can provide a hydride storage battery, its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 shows the cycle capacity characteristics of the hydrogen storage alloy electrode of the present invention, Figure 2 shows the change in average discharge potential of the hydrogen storage alloy electrode of the invention, and Figure 3 shows the nickel electrode of the invention. Figure 4 is a diagram showing the capacity of a conventional nickel electrode. Figure 4 is a diagram showing the discharge characteristics of the nickel metal hydride storage battery of the present invention and a conventional battery. Figure 5 is a diagram showing the discharge characteristics of the nickel metal hydride storage battery of the invention and a conventional battery. FIG. 3 is a diagram showing cycle characteristics. Applicant Yuasa Battery Co., Ltd. Figure 2 1 2 3 4 5 6 7 B 9 10 Number of charge/discharge cycles (times) Figure 3 Coo addition Figure 4 Discharge capacity (mAh)

Claims (3)

[Claims] (1) As a hydrogen storage alloy, a part of Ni of MmNi_5 (Mm: misch metal) alloy is mixed with Al, Mn, Fe, and C.
A metal hydrogen characterized by using an alloy powder substituted with one or more types of Cu, mixed with metal cobalt powder in a range of 3 to 20% by weight, and filling this into an alkali-resistant metal porous body. Compound electrode. (2) Zinc is in a solid solution state in the range of 2 to 8% by weight in the crystals of nickel hydroxide powder exhibiting a spherical shape with an internal pore volume of 0.14 ml/g or less, preferably 0.05 ml/g or less. 1. A nickel electrode, characterized in that cobalt monoxide powder is mixed in an amount of 5 to 15% by weight with active material powder for a nickel electrode, and this mixture is filled into an alkali-resistant porous metal substrate. (3) Nickel/metal hydride, characterized in that the metal hydride electrode and the nickel electrode are wound together with a separator interposed therebetween, and after injecting an aqueous potassium hydroxide solution and sealing, the nickel/metal hydride electrode is left to stand for 5 hours or more for initial charging. Method for manufacturing compound batteries.