JP3118832B2 - Alkaline storage battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an alkaline storage battery using, as a negative electrode, a hydrogen storage alloy capable of electrochemically absorbing and releasing hydrogen as an active material.

2. Description of the Related Art A hydrogen storage alloy that absorbs and releases a large amount of hydrogen attracts attention as an electrode material having a high energy density, and is being applied to an alkaline storage battery aiming at a high capacity. However, the hydrogen storage alloy electrode has a significantly lower activity in the initial electrochemical reaction than the cadmium electrode.Therefore, after the battery is constructed, the discharge capacity is small for several cycles, and the discharge is sufficient after repeated charging and discharging for more than ten cycles. It is possible to obtain capacity. This tendency is remarkable when high-rate discharge is performed at a low temperature (0 ° C.). This is because the initial discharge overvoltage of the hydrogen storage alloy electrode is particularly large. Therefore, conventionally, in this type of electrode, a method of increasing the activation of a hydrogen storage alloy electrode by chemically absorbing and releasing hydrogen under a high-pressure hydrogen atmosphere, or by charging and discharging in an electrolyte, A method of increasing the effective reaction surface area by attaching a hydrophilic metal oxide to the surface of an occlusion alloy
No. 51860).

Problems to be Solved by the Invention However, the method of activating the electrode is a method of chemically absorbing and releasing hydrogen under a high-pressure hydrogen atmosphere, and washing and drying the electrode after charging and discharging in an electrolytic solution. Such a complicated process is required.

Further, the proposal disclosed in Japanese Patent Application Laid-Open No. Hei 2-51860 cannot obtain the effect only by simply mixing the hydrogen storage alloy and the oxide, and it is necessary to coat the oxide rather than adhere it. After mixing the components, complicated steps such as heat treatment in an oxidizing atmosphere or an inert atmosphere are required.

An object of the present invention is to solve the above-mentioned problems and to provide an alkaline storage battery having excellent discharge characteristics from the beginning with a simple configuration.

Means for Solving the Problems In order to solve the problems, the present invention provides an alkaline storage battery in which a metal oxide and / or a metal ion is present in a battery using a hydrogen storage alloy powder having an uneven surface. Things.

Function The presence of ions of a metal oxide and / or a metal in a battery using a hydrogen storage alloy powder having an uneven surface as described above as a negative electrode reduces the overvoltage at the time of discharge, and the discharge characteristics of the battery. Is improved.

That is, in the negative electrode, an uneven space is present on the surface of the hydrogen storage alloy, so that an appropriate space is created between the metal oxide having excellent lyophilicity and the surface of the hydrogen storage alloy, and the electrolyte is held there. Is more likely to penetrate into the hydrogen storage alloy surface inside the electrode. Therefore, there is no need to attach an oxide to the surface of the hydrogen storage alloy by heat treatment,
Excellent discharge characteristics can be obtained by simply treating the hydrogen storage alloy powder with alkali. In addition, metal ions in the electrolytic solution and metal ions generated by dissolving the oxide added to the positive and negative electrodes in the alkaline electrolytic solution move to the surface of the negative electrode and precipitate as an oxide to increase the hydrophilicity of the negative electrode, For example, hydrated ions such as zincate ions ([Zn (OH) ₄ ] ²⁻ , [Zn (OH) ₃ ] ⁻ ), which have a high exchange current density,
^- high supply capacity of the ion, the OH ^- ions OH required for the discharge reaction (equation) on the hydrogen storage alloy electrode ^- overvoltage is reduced by supplying the ions is believed that discharge characteristics are improved.

^{_{MH x + OH - → MH x}} -1 + H 2 O + e - ...... The or metal oxide added to the positive electrode, metal ions transferred to the positive electrode also increases the lyophilic of the positive electrode active material, excellent discharge characteristics of the positive electrode To In the case of a positive electrode containing nickel hydroxide as a main active material, expansion of the positive electrode as the charge / discharge cycle progresses is suppressed, and a decrease in battery life can be suppressed.

Embodiment Hereinafter, details of the present invention will be described with reference to FIGS. 1 and 2. FIG.

<Example 1> A hydrogen storage alloy that electrochemically absorbs and releases hydrogen as an active material and electrodes thereof were prepared by the following method.

About 40wt% cerium, about 30wt% lanthanum, about neodymium
Mich metal (hereinafter, referred to as Mm) containing 13wt% as a main component, nickel, cobalt, aluminum and manganese are weighed so that their atomic ratios are respectively 1: 3.55: 0.75: 0.3: 0.4. This was melted in a high-frequency melting furnace to prepare a hydrogen storage alloy 1 having a CaCu ₅ type crystal structure and a composition of MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 . Next, this alloy was heat-treated in an Ar gas atmosphere at a temperature of 1050 ° C. and then mechanically pulverized to obtain an alloy powder having an average particle diameter of 20 μm. This powder was immersed in a KOH aqueous solution heated to 80 ° C. at a specific gravity of 1.30, and subjected to surface etching, and the uneven surface 2 was made to have a composition with more Ni than the internal alloy composition. After washing with water and drying,
It was mixed with powder 3 of a metal oxide (Al ₂ O ₃ , ZnO, MgO) at various ratios (FIG. 1A).

A 1 wt% aqueous solution of carboxymethylcellulose was added to this to form a paste, which was filled into a sponge-like porous nickel body as a support having a thickness of 0.9 mm and a porosity of about 95%. As shown in the enlarged view of FIG. 1B, a space 4 is formed between the powders in the paste state, and an electrolytic solution 5 is held between 1 and 3. This is dried at 100 ° C and then pressurized.
A 0.5 mm electrode plate was used.

Next, this was cut into a width of 39 mm and a length of 80 mm to obtain a hydrogen storage alloy electrode having a chargeable / dischargeable capacity of 1600 mAh and an addition amount of various metal oxides.

The hydrogen storage alloy electrode thus obtained was used as a negative electrode, and a known foamed metal nickel positive electrode having a capacity of 1000 mAh and a sulfonated polypropylene nonwoven fabric separator formed by sulfonating a polypropylene nonwoven fabric to form an electrode group, and a metal case was formed. And then 7.1 KOH aqueous solution
After injecting 2.2 cm ^3, it was sealed and a prototype of AA (R6) size battery was produced. Table 1 shows the type of metal oxide added to the hydrogen storage alloy electrode, the amount added (the amount added in terms of metal element), and the number of the battery using the respective hydrogen storage alloy electrode.
Shown in

As a comparative example, a battery using the hydrogen-absorbing alloy negative electrode to which no additive is added is designated as A-1.

Five of each of these batteries were placed in a 20 ° C atmosphere.
After the initial charge was performed at 100 mA for 15 hours, the battery was discharged at 200 mA to 1.0 V, and the battery was left at 45 ° C. for 5 days.

Thereafter, these batteries were charged under the same conditions as described above, discharged for 2 hours in an atmosphere of 0 ° C., 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 is performed.

As a result, batteries A-3 to 5, B-3 to 5, and C-3 to 5
0 ° C because metal oxide was added to the hydrogen storage alloy electrode
Even when discharging with a large current of 3000 mA in an atmosphere of, the overvoltage of the negative electrode does not increase, and the discharge capacity up to a terminal voltage of 1.0 V is 700 m
Ah or more, and showed excellent discharge characteristics.

On the other hand, Comparative Example A-1 and A-2, in which the added amount of oxide was small,
The batteries B-2 and C-2 have a discharge capacity of about 100 mAh until the terminal voltage drops to 1.0 V. This is because, when a large current discharge of 3000 mA is performed in an atmosphere of 0 ° C., the supply of hydroxide ions on the surface of the negative electrode alloy powder is rate-limiting, and the overvoltage at the time of discharge increases.

Examples A-6 and B-
The batteries of C-6 and C-6 have a discharge capacity of about 170 mAh until the terminal voltage drops to 1.0 V.

It is considered that when the metal oxide is excessively 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 to add 0.04 to 6 wt% of the metal oxide in terms of the metal element.

In this embodiment, Al ₂ O ₃ , ZnO, MgO
However, similar results were obtained when using oxides of the group of alkaline earth metals such as Ga, Ge, Sn, Si, Cr, Ti, and when using a mixture of two or more of them. Was done.

In addition, although the initial charge and discharge performed after the battery configuration and not shown in this example, the reaction of the added oxide to a hydrate is promoted by leaving the battery in an atmosphere at room temperature or higher, The discharge characteristics are further improved.

Further, the present invention relates to an alkaline storage battery using a negative electrode containing hydrogen storage alloy powder as a main constituent material.
Similar results can be obtained in a Cd battery by the presence of a metal oxide in the negative electrode.

<Example 2> An example in which the hydrogen-absorbing alloy electrode containing no metal oxide in Example 1 was used as a negative electrode, and an alkaline electrolyte solution obtained by dissolving metal ions at various ratios in a 7.1 N aqueous KOH solution was used. A battery was prepared in the same manner as in Example 1. Table 2 shows the concentrations of the metal ions in the alkaline electrolyte and the numbers of the prototype batteries.

FIG. 3 shows the results of examining the average discharge curve of each of these five batteries under the same charge / discharge conditions as the pattern shown in Example 1.

As a result, the batteries of D-3 to 5, E-3 to 5, and F-3 to 5 are:
Since metal ions were added to the electrolyte, the hydrated ions that permeated the negative electrode surface and inside the negative electrode moved in the same way as the metal oxide added inside the negative electrode, and discharged at a large current of 3000 mA in an atmosphere at 0 ° C. However, the overvoltage of the negative electrode does not increase
The discharge capacity before dropping to 1.0 V was 700 mAh or more, showing excellent discharge characteristics.

On the other hand, in the batteries of Comparative Example D-1 and D-2, E-2, and F-2 in which the amount of metal ions added is small, the discharge capacity until the terminal voltage decreases to 1.0 V is about 100 mAh. This is caused by 0 ° C
When a large current discharge of 3000 mA is performed in the atmosphere described above, the supply of hydroxide ions on the surface of the negative electrode alloy powder is rate-limiting, and the overvoltage at the time of discharge increases. The batteries of Examples D-6, E-6, and F-6 to which metal ions were excessively added had a discharge capacity of about 170 mAh when the terminal voltage was up to 1.0 V. It is considered that because the added metal ions were in a saturated state, in an atmosphere at 0 ° C., some of the metal ions were precipitated as metal oxides, which prevented the discharge reaction. From the following, the amount of metal ion added is 0.040 to 0.64 wt% in metal conversion.
% Is practically appropriate.

In this example, Al, Zn, and Mg were used as ions to be added to the alkaline electrolyte, but Ga, Ge, Sn, Si, Cr, Ti, and other ions of the group of alkaline earth metals were used. Similar results were obtained when two or more of them were used in combination.

Further, in the present embodiment, the case where the metal ions are added only to the electrolytic solution has been described. However, the same effect can be obtained when combined with the addition of the oxide to the negative electrode.

Effects of the Invention As described above, according to the present invention, a metal oxide and / or a metal oxide and / or a battery using a hydrogen-absorbing alloy powder having an uneven surface are provided.
Alternatively, by configuring an alkaline storage battery in the presence of metal ions, there is an effect that an alkaline storage battery having excellent discharge characteristics can be provided even when a large current discharge is performed in a low temperature atmosphere.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state in which an electrolytic solution is held between a hydrogen storage alloy powder and a metal oxide whose surface shapes are uneven, and FIG. 2 is an average discharge when a metal oxide is added to a negative electrode. FIG. 3 is a diagram showing a curve, and FIG. 3 is a diagram showing an average discharge curve when metal ions are dissolved in an electrolytic solution. 1 ... Hydrogen storage alloy, 2 ... Uneven surface with a lot of Ni, 3 ... Metal oxide powder, 5 ... Electrolyte held between alloy surface and metal oxide powder.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Matsumoto 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-130467 (JP, A) JP-A-2- 256161 (JP, A) JP-A-2-51860 (JP, A) JP-A-4-34849 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10 / 24-10 / 30 H01M 4/24-4/26 H01M 4/38

Claims (4)

(57) [Claims] 1. A positive electrode mainly composed of a metal oxide, a negative electrode mainly composed of a hydrogen storage alloy powder capable of electrochemically absorbing and releasing hydrogen as an active material, a separator, and an alkali. In an alkaline storage battery provided with a power generation element composed of an electrolyte, the hydrogen storage alloy powder has an uneven surface shape, and Al, Ga, Ge, Sn, Si, C
One or more ions and oxides selected from the group consisting of r, Ti, and alkaline earth metals form 0.04
Alkaline storage battery characterized by being present in an amount of up to 6% by weight. 2. One of the elements constituting the hydrogen storage alloy is Ni, and the countless irregularities provided on the surface of the alloy have a higher proportion of Ni than the internal alloy. 3. The alkaline storage battery according to claim 1, wherein 3. A patent characterized in that at least one of oxides of the group consisting of Al, Ga, Ge, Sn, Si, Cr, Ti and alkaline earth metals is added to the negative electrode. The alkaline storage battery according to claim 1. 4. A positive electrode mainly composed of a metal oxide; a negative electrode mainly composed of a hydrogen storage alloy powder capable of electrochemically absorbing and releasing hydrogen as an active material; a separator; In an alkaline storage battery provided with a power generating element composed of an electrolytic solution, the hydrogen storage alloy powder has an uneven surface shape, and Al, Ga, Ge, Sn, Si, C is contained in the alkaline electrolytic solution.
An alkaline storage battery characterized in that at least one ion selected from the group consisting of r, Ti, and alkaline earth metals is present as an element in an amount of 0.040 to 0.64% by weight.