JPH04188561A - Alkaline storage battery - Google Patents

Abstract

PURPOSE:To make an alkaline storage battery equipped with excellent discharge characteristic by including metal oxide and/or metal ion in the battery, which uses powder of hydrogen absorption alloy exhibiting unevenness in the surface configuration. CONSTITUTION:Unevenness is provided on the surface of a powder 1 of hydrogen absorption alloy, and one or more of oxides and/or ions derived from Al, Zn, Ga, Ge, Sn, Si, Cr, Ti, and alkali earth metal are included in an alkali electrolyte 5. That is. unevenness exists on the surface of the hydrogen absorption alloy 1 at the neg. electrode, an appropriate space 4 is generated between a metal oxide 3 excellent in liquid affinity and the surface of the hydrogen absorption alloy 1, where the electrolyte 5 is retained, and the electrolyte will easily permeate to the alloy surface inside of the electrode. Thereby it is no more needed to attach oxides to the alloy surface by means of a heat treatment, and an excellent discharge characteristic is obtained only through subjecting the powder of hydrogen absorption alloy to an alkali treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in an alkaline storage battery using a hydrogen storage alloy as an active material, which is capable of electrochemically absorbing and releasing hydrogen, as a negative electrode.

BACKGROUND ART Hydrogen storage alloys that absorb and release large amounts of hydrogen have attracted attention as electrode materials with high energy density, and are being applied to alkaline storage batteries aiming for high capacity. but,
Hydrogen storage alloy electrodes have significantly lower activity in the initial electrochemical reaction than cadmium electrodes, so their discharge capacity is small for several cycles after battery construction, and it is difficult to achieve sufficient discharge capacity after a dozen or more cycles of charging and discharging. It becomes possible to obtain. This tendency is particularly remarkable when high rate discharge is performed at a low temperature (0° C.). This is due to the fact that the initial discharge overvoltage of the hydrogen storage alloy electrode is particularly high in this original product. Therefore, conventional methods for this type of electrode have been to increase the activation of the hydrogen storage alloy electrode by chemically absorbing and releasing hydrogen in a high-pressure hydrogen atmosphere, or by charging and discharging in an electrolytic solution. A method of increasing the effective reaction surface area by attaching a hydrophilic metal oxide to the surface of a storage alloy (Japanese Unexamined Patent Publication No. 2-51
No. 860) has been proposed.

Problems to be Solved by the Invention However, the methods for activating the electrodes include chemical absorption and release of hydrogen in a high-pressure hydrogen atmosphere, and washing and drying the charged and discharged electrodes in an electrolytic solution. This requires a complicated process.

In addition, the proposal shown in JP-A-2-51860 does not produce any effect by simply mixing a hydrogen storage alloy and an oxide, and requires coating the oxide rather than adhering it to the metal. After mixing the materials, complicated steps such as heat treatment in an oxidizing atmosphere or an inert atmosphere are required.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an alkaline storage battery with a simple configuration and excellent discharge characteristics from the beginning.

Means for Solving the Problem In order to solve this problem, the present invention constructs an alkaline storage battery by making metal oxides and/or metal ions exist in a battery using a hydrogen storage alloy powder having an uneven surface shape. It is something.

Potash HayabusaBy adding metal oxides and/or metal ions to a battery using hydrogen storage alloy powder with an uneven surface as the negative electrode, the overvoltage during discharge is reduced, improving the discharge characteristics of the battery. or improve.

In other words, at the negative electrode, due to the presence of irregularities on the surface of the hydrogen storage alloy, an appropriate space is created between the highly lyophilic metal oxide and the hydrogen storage alloy surface, and the electrolyte is retained there. This is because it easily penetrates into the surface of the hydrogen storage alloy inside the electrode. Therefore, it is not necessary to attach oxides to the surface of the hydrogen storage alloy by heat treatment, and excellent discharge characteristics can be obtained simply by alkali treatment of the hydrogen storage alloy powder. In addition, metal ions in the electrolyte and metal ions generated when oxides added to the positive and negative electrodes are dissolved in the alkaline electrolyte move to the surface of the negative electrode and precipitate as oxides, increasing the hydrophilicity of the negative electrode. For example, zincate ion ([Z'n (OH)
3]-), and because the exchange current density is high, the ability to supply OH- ions is high, and these OH- ions are required for the discharge reaction (the following equation (■)) on the hydrogen storage alloy electrode. It is thought that by being supplied as OH- ions, overvoltage is reduced and discharge characteristics are improved.

MHx+OH4MH! -1+H20+ e--"-■In addition, metal oxides added to the positive electrode and metal ions transferred to the positive electrode also increase the lyophilicity of the positive electrode active material and improve the discharge characteristics of the positive electrode. Nickel hydroxide In the case of a positive electrode that is used as a living substance, expansion of the positive electrode as the charge/discharge cycle progresses is suppressed, and a decrease in battery life can be suppressed.

EXAMPLES The details of the present invention will be described below with reference to FIGS. 1 and 2.

<Example 1> A hydrogen storage alloy that electrochemically absorbs and releases hydrogen, which is an active material, and its electrode were created by the following method.

Cerium approx. 40wt%, lanthanum approx. 30w
t%, Mitsushi metal (hereinafter referred to as Mm) mainly composed of about 13 wt% neodymium, nickel, cobalt, aluminum and manganese in an atomic ratio of 1+3.
55:0.75:0.3・0. Weigh it so that it becomes 4. This was melted in a high frequency melting furnace to obtain a composition of MmNi 3.55Mn0.4A, which has a CaCu5 type crystal structure.
Hydrogen storage alloy 1 of I□, 3 Co□, 75 was prepared.

Next, this alloy was heat-treated at a temperature of 1050°C in an Ar gas atmosphere and then mechanically crushed to obtain an average particle size of 20°C.
An alloy powder of μm was obtained. This powder has a specific gravity of 1.30 and is 80
It was immersed in a KOH aqueous solution heated to 0.degree. C. to perform surface etching, so that the uneven surface 2 had a composition containing more Ni than the internal alloy composition. After washing and drying this, a metal oxide (A1203.ZnO.

Mg0) powder 3 in various proportions (Fig. 1A)
.

Add l wt % aqueous solution of carboxymethyl cellulose to this to make a paste, with a thickness of 0.9 mm and a porosity of approximately 9.
It was filled into a sponge-like porous nickel material which was a 5% support. As shown in the enlarged view of FIG. 1B, a space 4 is formed between the powders in a paste state, and an electrolytic solution 5 is held between 1 and 3. This was dried at 100° C. and then pressed to form an electrode plate with an average thickness of 0.5 mm.

Next, this was cut into a width of 39m+n and a length of 80m+n,
Hydrogen storage alloy type electrodes having a charge/discharge capacity of 1600 mAh and containing various metal oxides were obtained.

The hydrogen storage alloy electrode obtained in this way was used as a negative electrode,
An electrode group is made up of a known foamed metal type nickel positive electrode with a capacity of 100,100 O and a separator made of a sulfonated polypropylene nonwoven fabric obtained by sulfonating a polypropylene nonwoven fabric, inserted into a metal case, and then KO according to 7.1 standard.
After injecting 2.2 d of H aqueous solution, seal it and AA (R6)
We made a prototype battery of the same size. Table 1 shows the type and amount of metal oxide added to the hydrogen storage alloy electrode (the amount added in terms of metal element), and the number of the battery using each hydrogen storage alloy electrode.

As a comparative example, a battery using an additive-free hydrogen storage alloy negative electrode is designated as A-1.

Five of each of these batteries were placed in an atmosphere of 20°C.
After initial charging at 100mA for 15 hours, 20'Om
1 with A. After discharging to Ov, the battery was left at 45° C. for 5 days.

Thereafter, these batteries were charged under the same conditions as above, left in an atmosphere at 0° C. for 2 hours, and discharged at a constant current of 3000 mA in this temperature atmosphere.

FIG. 2 shows the respective average discharge curves when a constant current discharge of 3000 mA was performed.

As a result, A-3 to 5. B-3~5. Batteries C-3 to C-5 added metal oxide to the hydrogen storage alloy electrode, so
Even when discharging with a large current of 3000 mA in an atmosphere at 0°C, the overvoltage of the negative electrode does not increase, and the terminal voltage remains at 1. The discharge capacity up to OV was 700 mAh or more, indicating excellent discharge characteristics.

On the other hand, Comparative Example A-1 and A-2 with a small amount of oxide added,
Batteries B-2 and C-2 have a discharge capacity of about ioomah until the terminal voltage drops to 1.0. The reason for this is that when a large current discharge of 3000 mA is performed in an atmosphere at 0° C., the supply of hydroxide ions on the surface of the negative electrode alloy powder becomes rate-determining, and the overvoltage during discharge increases.

In addition, Examples A-6 and B- in which metal oxide was added in excess
``6.C-6 battery has a discharge capacity of about 170mAh until the terminal voltage drops to 1.OV.

This is believed to be because when an excessive amount of metal oxide is added, the conductivity of the negative electrode is reduced by the metal oxide, which is an insulating substance. From the above, it is practically appropriate for the amount of metal oxide added to be 0.04 to 5 wt% in terms of metal element.

Note that in this example, Al2O3゜Zn was used as the metal oxide.
Although O and MgO were used, Ga, Ge, Sn, and Si were also used.

Similar results were obtained when oxides of alkaline earth metals such as Cr and Ti were used, or when two or more of them were used as a mixture.

In addition, although it was not shown in this example, initial discharge performed after battery construction or leaving the battery in an atmosphere above room temperature accelerates the reaction in which the added oxide becomes a hydrate. The discharge characteristics are further improved.

Further, the present invention relates to an alkaline storage battery using a negative electrode mainly composed of hydrogen storage alloy powder, but Ni-
Similar results can be obtained in Cd batteries by including metal oxides in the negative electrode.

<Example 2> The metal oxide-free hydrogen storage alloy electrode in Example 1 was used as a negative electrode, and 7.1 standard KO was used as an alkaline electrolyte.
Batteries were prepared in the same manner as in Example 1 using H aqueous solutions in which metal ions were dissolved in various proportions. Table 2 shows the concentration of metal ions in the alkaline electrolyte and the numbers of the prototype batteries.

Table 2 The average discharge curves of five of these batteries were examined under the same charging and discharging conditions as the pattern shown in Example 1.
As shown in the figure.

As a result, D-3 to D-5. E-3~5. In batteries F-3 to F-5, metal ions were added to the electrolyte, so the hydrated ions that penetrated the negative electrode surface and the inside of the negative electrode moved in the same way as the metal oxides added inside the negative electrode, and the hydrated ions penetrated into the negative electrode surface and inside the negative electrode. 3000m
Even when discharging with a large current of A, the overvoltage of the negative electrode does not increase,
The discharge capacity until the terminal voltage drops to 1.0V is 700
mAh or more, showing excellent discharge characteristics.

On the other hand, Comparative Example D-1 and D with a small amount of added metal ions
-1, E-2, and F-2 batteries have a discharge capacity of about 100 mAh until the terminal voltage drops to 1.0 . The reason for this is that when a large current discharge of 3030-0O is performed in an atmosphere at 0° C., the supply of hydroxide ions on the surface of the negative electrode alloy powder becomes rate-determining, and the overvoltage during discharge increases. In addition, Example D in which metal ions were added excessively
-6, E-6, and F-6 batteries have a discharge capacity of about 170 mAh when the terminal voltage reaches 1° Ov.

This is considered to be because the added metal ions were in a saturated state, so that some of the metal ions precipitated as metal oxides in an atmosphere of 0° C., which hindered the discharge reaction. From the above, the amount of metal ions added is 0.04 to 1 mol in terms of metal.
/l is suitable for practical use.

In this example, Al, Zn, and Mg were used as ions added to the alkaline electrolyte, but Ga.

Similar results were obtained when ions of the group of alkaline earth metals such as Ge, Sn, Si, Cr, Ti, etc. were used, or when two or more of them were used as a mixture.

Further, in this example, a case has been described in which metal ions are added only to the electrolytic solution, but similar effects can be obtained when the metal ions are added in combination with the addition of an oxide to the negative electrode.

Effects of the Invention As described above, according to the present invention, a metal oxide and/or metal ion is present in a battery using a hydrogen-absorbing alloy powder having an uneven surface shape to form an alkaline storage battery. This has the effect of providing an alkaline storage battery that has excellent discharge characteristics even when discharging at a large current in a temperature atmosphere.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing a state in which an electrolyte is held between a hydrogen storage alloy powder with an uneven surface and a metal oxide, and Figure 2 is an average discharge when a metal oxide is added to the negative electrode. FIG. 3 is a diagram showing an average discharge curve when metal ions are dissolved in an electrolytic solution. 1...Hydrogen storage alloy, 2...Ni-rich uneven surface, 3...Metal oxide powder, 5...
...An electrolytic solution held between the alloy surface and metal oxide powder. Name of agent: Patent attorney Haruaki Koebi and 2 others No. 1
Figure 1 - To the East, Banhonrei included Shu? ---M's ~ ○ concave surface bacteria 3 --- 1 is also l"i 1991 January 77 E

Claims (6)

[Claims] (1) A positive electrode mainly composed of a metal oxide, a negative electrode mainly composed of a hydrogen storage alloy powder that can electrochemically absorb and release hydrogen as an active material, a separator, and an alkaline electrolyte. In the alkaline storage battery, the hydrogen storage alloy powder has an uneven surface shape, and the power generation element contains Al, Zn, Ga, Ge.
, Sn, Si, Cr, Ti, and alkaline earth metals. (2) A claim characterized in that one of the elements constituting the hydrogen storage alloy is Ni, and the countless unevenness provided on the surface of the alloy has a higher proportion of Ni than the inner alloy. The alkaline storage battery according to item 1. (3) Al, Zn, Ga, Ge, Sn, Si,
2. The alkaline storage battery according to claim 1, wherein at least one of oxides from the group of Cr, Ti, and alkaline earth metals is added. (4) Al, Zn, Ga, Ge, Sn, Si, Cr, T
i. The alkaline storage battery according to claim 3, wherein the amount of the alkaline earth metal oxide added is 0.04 to 6 wt% in terms of metal element based on the hydrogen storage alloy. (5) Al, Zn, Ga, Ge, S in alkaline electrolyte
The alkaline storage battery according to claim 1, characterized in that the alkaline storage battery contains one or more of n, Si, Cr, Ti, and alkaline earth metal ions. (6) The alkaline storage battery according to claim 5, wherein the concentration of ions dissolved in the alkaline electrolyte is 0.04 to 1 mol/l in terms of metal.