JPH10125313A - Negative electrode for alkaline storage battery and alkaline storage battery equipped with negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a drop in the discharge characteristic of high efficiency, and provide a high charging and discharging cycle life by laying a porous gas- absorbing layer of nonwoven fabric, formed out of carbon fiber among a plurality of negative electrode plates. SOLUTION: Slurry is prepared by kneading, for example, 99wt.% of the powder of a hydrogen storage alloy for an electrode, with 1wt.% of polyethylene oxide powder as a binding agent and distilled water, and applied to both sides of a current collector. Also, the current collector is dried and rolled. A hydrogen storage plate 3 is thereby formed. Thereafter, nonwoven fabric made, for example, of carbon fiber having a 18μm diameter is laid between electrode plates 3 so formed and inserted in a bag type separator, that is forms a nickel- hydrogen battery negative electrode 5 filled with a gas-absorbing layer made of carbon fiber. In this case, the negative electrode 5 has a three-layer structure with a gas-absorbing layer positioned between two hydrogen storage alloy plates. As a result of fitting the gas-absorbing layer so formed, energy density per battery weight is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure suitable for use in a large battery such as a battery for an electric vehicle which requires rapid charging and high-rate discharging.

[0002]

2. Description of the Related Art Anode plates for alkaline storage batteries are roughly classified into two types, namely, a sintered type and a non-sintered type. The former is excellent in quick charge and high rate discharge characteristics although its energy density is relatively low. In the latter case, although the energy density was high, it was inferior to rapid charge and high rate discharge.

[0003] In a hydrogen storage alloy electrode currently in practical use, a non-sintered manufacturing method is generally used. As an example of the structure of such a non-sintered electrode plate, there can be mentioned a structure in which an active material layer made of a hydrogen storage alloy is applied to both surfaces of a punching metal serving as a core for collecting current, An increase in gas pressure inside the battery at the time of overcharging during rapid charging has been a problem.

Therefore, US Pat. No. 5,477,806 discloses a two-layered circuit for the purpose of solving such a problem.
A negative electrode for an alkaline storage battery having a three-layer structure in which one porous gas absorbing layer is interposed between two negative plates has been proposed. It discloses that a porous metal such as foamed nickel, plastic, or the like is used as the gas absorbing layer.

When the gas absorbing layer is made of a porous metal such as foamed nickel, if the gas absorbing layer is electrically connected to a current collector, it acts as a current collector for the negative electrode plate. High rate discharge characteristics are also improved. However, when a porous metal such as foamed nickel is used as the gas absorbing layer, there is a problem that the weight of the battery becomes heavy, which is disadvantageous in terms of weight energy density.

[0006] In addition, due to constant contact with oxygen at the time of overcharging to absorb oxygen gas, an oxide film is formed on the metal surface, and the conductivity with the active material is diminished in the long term. There was a problem that the discharge characteristics deteriorated.

[0007] On the other hand, plastic is lighter than the above-mentioned metals, but has a problem that it is inferior in high-rate discharge characteristics because of its insulating property.

Further, the nickel hydroxide positive electrode swells when charge / discharge cycles are repeated, and the swelling causes the electrolyte in the separator to be squeezed out. As a result, the electrolyte becomes insufficient. There has been a problem of being shorter.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made by forming a gas absorbing layer interposed between negative electrode plates by a carbon fiber nonwoven fabric.
It is an object of the present invention to improve the weight energy density of the battery while preventing the deterioration of the high rate discharge characteristics over a long period of time while maintaining excellent gas absorption performance, and to provide a battery excellent in charge / discharge cycle life. Make it an issue.

[0010]

A negative electrode for an alkaline storage battery having a porous gas absorbing layer interposed between a plurality of negative electrode plates, wherein the porous gas absorbing layer is made of carbon fiber nonwoven fabric. I do.

[0011]

[Function] Since a carbon fiber non-woven fabric is used as a porous gas absorbing layer interposed between a plurality of negative electrode plates, the weight can be reduced as compared with the use of a metal such as foamed nickel, and the weight energy density is improved. Can be done. In addition, since a carbon material such as a nonwoven fabric of carbon fiber does not form an oxide film on the surface unlike metal, electric contact between an active material such as a hydrogen storage alloy and a gas absorbing layer is maintained for a long time. Therefore, it is possible to prevent the high-rate discharge characteristics of the battery from being deteriorated for a long period of time. In addition, since the carbon fiber nonwoven fabric is softer and more elastic than the porous metal body, it applies sufficient structural pressure to the battery configuration from the initial stage of assembly, and when the positive electrode expands due to charge and discharge, the elasticity is high. In order to absorb the swelling and reduce the pressure applied to the separator, dryout of the separator can be prevented. Therefore, it is possible to obtain a battery having excellent charge / discharge cycle life.

[0012]

【Example】

(Example 1) First, a hydrogen storage alloy powder for an electrode was produced as follows.

Using commercially available misch metal Mm (mixture of rare earth elements), Ni, Co, Al, and Mn, each metal element of Mm: Ni: Co: Mn: Al is represented by 1:
Commercially available metal elements were weighed and mixed in a ratio of 3.4: 0.8: 0.6: 0.2. Then dissolving the mixture at a high frequency melting furnace under argon atmosphere and subjected to cooling to produce a hydrogen-absorbing alloy ingot represented by a composition formula _{MmNi 3.4 Co 0.8 Mn 0.6 Al 0.2} . Next, the hydrogen-absorbing alloy mass is annealed at 1000 ° C. for 8 hours in an inert gas, and the alloy mass is pulverized under an inert gas atmosphere so as to have an average particle size of 150 μm. An alloy powder was produced.

Further, the hydrogen-absorbing alloy powder is adjusted to pH = 1.
Was immersed in a hydrochloric acid solution for 20 minutes, washed sufficiently with ion-exchanged water, and dried to prepare a hydrogen storage alloy powder for an electrode.

A slurry was prepared by kneading 99% by weight of the hydrogen storage alloy powder for an electrode thus prepared, 1% by weight of a polyethylene oxide powder as a binder, and pure water.

The slurry is applied to both sides of a current collector made of punching metal, dried at 70 ° C. for 1 hour, and rolled to produce a 0.45 mm-thick hydrogen-absorbing alloy electrode. It was cut to a size of 62 × 65 mm.

A carbon fiber nonwoven fabric of carbon fiber having a fiber diameter of 18 μm and having a thickness of 0.6 mm and a size of 62 × 65 mm was interposed between the two hydrogen storage alloy electrode plates. Further, two hydrogen storage alloy electrode plates with the carbon fiber non-woven fabric interposed therebetween were inserted into a bag-like separator made of a nylon non-woven fabric to obtain a negative electrode for a nickel-metal hydride battery having a gas absorption layer made of a carbon fiber non-woven fabric.

The above-mentioned eleven negative electrodes for nickel-metal hydride batteries and ten sintered nickel positive electrodes of 62 × 65 mm in size manufactured by a known method are alternately laminated, and a current collector is welded to each of the positive electrode and the negative electrode. A plate group was prepared. FIG. 1 shows an electrode laminated structure of this electrode plate group.

In FIG. 1, reference numeral 1 denotes a separator for separating a positive electrode and a negative electrode, and 2 denotes a hydrogen storage alloy electrode plate 3
Is a gas absorption layer made of a nonwoven fabric of carbon fibers interposed between the carbon fibers.

Reference numeral 3 denotes a hydrogen storage alloy electrode plate, and reference numeral 4 denotes a sintered nickel positive electrode.

Reference numeral 5 denotes a negative electrode having a three-layer structure including a gas absorbing layer interposed between two hydrogen storage alloy electrode plates. The electrode group was inserted into a square case, and 23.8 g of a 31% by weight aqueous potassium hydroxide solution was injected as an electrolytic solution.
The sealed nickel-metal hydride battery A having a battery capacity of 10.1 Ah was fabricated by sealing the battery.

(Comparative Example 1) Instead of a porous gas-absorbing layer made of a nonwoven fabric of carbon fiber between two hydrogen-absorbing alloy electrode plates, a porous nickel metal porous material having a basis weight of 475 g / cm ² and a thickness of 0.5 mm was used. A sealed nickel-metal hydride battery X1 having a battery capacity of 10.1 Ah was produced in the same manner as in Example 1 except that an inert gas absorbing layer was interposed.

(Comparative Example 2) A sealed nickel-metal hydride battery having a battery capacity of 10.1 Ah in the same manner as in Example 1 except that no gas absorbing layer was interposed between the two hydrogen absorbing alloy electrode plates. X2 was produced.

A comparison of the weights of these batteries shows that a comparative battery X1 using a nickel metal porous body as a gas absorbing layer was manufactured.
The battery A of the present invention, which is composed of a carbon fiber nonwoven fabric as the gas absorbing layer, has a weight increase of 17.6 g as compared with the comparative battery X2 having no gas absorbing layer.
It was confirmed that the weight was reduced only by 2.1 g in comparison with.

The battery A of the present invention and the comparative batteries X1 and X2 were charged at 0.9 A for 16 hours at room temperature, and after a 1-hour pause, discharged at 4.5 A until the battery voltage reached 0.8 V. The battery was activated by repeating a cycle of pausing for 1 hour for 10 cycles.

Charge / Discharge Characteristics Test The batteries A, X1, and X2 that have completed the activation process are charged at 0.9 A for 16 hours in an environment with a battery temperature of 20 ° C., and after a 5-minute pause, the battery voltage is reduced at 18 A. A charge / discharge characteristic test of discharging to 0.8 V was performed, and the results are shown in FIGS. 2 and 3.

FIG. 2 shows a battery A of the present invention and a comparative battery X1,
FIG. 4 is a graph showing the charging characteristics of X2. As shown in the figure, the battery A of the present invention using a nonwoven fabric made of carbon fiber as a gas absorbing layer and the comparative battery X1 using a nickel metal porous body as a gas absorbing layer were gas It can be seen that the increase in battery internal pressure is significantly suppressed as compared with the comparative battery X2 without the absorption layer. This is presumably because the reaction area of the negative electrode that consumes oxygen gas generated from the positive electrode was improved by interposing a carbon fiber nonwoven fabric or a nickel metal porous body between the hydrogen storage alloy electrodes.

FIG. 3 shows the battery A of the present invention and the comparative battery X1,
FIG. 4 is a graph showing the discharge characteristics of X2. As shown in FIG. 4, the battery A of the present invention using a non-woven fabric made of carbon fiber as a gas absorbing layer and the comparative battery X1 using a nickel metal porous body as a gas absorbing layer were gaseous. It can be seen that the operating voltage and the discharge capacity are higher than those of the comparative battery X2 in which no absorption layer is interposed, and that excellent discharge characteristics are obtained. This is considered to be due to the fact that the non-woven fabric of carbon fiber and the porous nickel metal body have good conductivity, and the operating voltage at the time of high-rate discharge has been improved compared to a battery in which nothing is interposed between the hydrogen storage alloy electrode plates. .

Cycle Characteristics Test FIG. 4 shows 200 cells of the battery A of the present invention and the comparative batteries X1 and X2.
It is a figure showing the high rate discharge characteristic after a cycle.

The test conditions at this time are as follows:
The battery was charged at 0.9 A for 16 hours in an environment of 0 ° C., and the battery was discharged at a discharge current of 9 A for 24 minutes.

A charge / discharge cycle test was performed in which the battery was charged at 9 A for 27 minutes, paused for 2 minutes, discharged at 9 A for 24 minutes, and paused for 2 minutes as one cycle.

Then, the battery is discharged until the battery voltage becomes 0.8 V every 100 cycles of this process.
Charge for 16 hours, pause for 2 minutes, and 0.8V at 4.5A
The operation of discharging the battery and measuring the capacity was performed up to 600 cycles. On the way, at the end of 200 cycles, a high-rate discharge characteristic test was performed under the same conditions as the charge-discharge characteristic test described above.

Here, FIG. 4 shows a high-rate discharge characteristic test after 200 cycles, and FIG. 5 shows a cycle characteristic test up to 600 cycles.

As shown in FIG. 4, the battery A of the present invention using the nonwoven fabric made of carbon fiber as the gas absorbing layer has a lower operating voltage and discharge capacity than the comparative battery X1 using the nickel metal porous body as the gas absorbing layer. It can be seen that high discharge characteristics were obtained. The reason for this is that the comparative battery X1 using the nickel metal porous body with the progress of the charge / discharge cycle has an oxide film formed on the surface and the separator due to the decrease in the conductivity between the hydrogen storage alloy and the gas absorption layer and the expansion of the positive electrode. In contrast to the progress of dry-out, carbon fiber non-woven fabric does not form an oxide film on its surface, so it suppresses the decrease in conductivity between the hydrogen storage alloy and the gas absorption layer, and has a higher conductivity than the nickel metal porous body. It is also considered that, because of its high elasticity, it absorbs the swelling of the positive electrode, alleviates the pressure applied to the separator, and suppresses the dry-out of the separator.

As shown in FIG. 5, the battery A of the present invention using the carbon fiber non-woven fabric as the gas absorbing layer has the comparative battery X1 using the nickel metal porous body as the gas absorbing layer and the gas absorbing layer. It can be seen that the cycle characteristics are superior to the comparative battery X2 which is not provided. This is considered to be because the carbon fiber nonwoven fabric is rich in elasticity, so that the expansion of the positive electrode accompanying the charge / discharge cycle was absorbed and the dry-out of the separator was suppressed.

In this embodiment, 1 is provided between the two negative plates.
The example of the negative electrode for an alkaline storage battery having a three-layer structure in which three porous gas absorbing layers are interposed has been described.
The same effect can be obtained even with a negative electrode or the like having a five-layer structure in which two porous gas absorbing layers are interposed between two negative electrode plates. Similar effects can be obtained by using cadmium, zinc, or the like in addition to the hydrogen storage alloy as the negative electrode active material.

[0037]

As is apparent from the above, according to the present invention, a gas absorbing layer made of a nonwoven fabric of carbon fiber is interposed between a plurality of anode plates, so that excellent gas absorbing performance can be maintained while maintaining excellent gas absorbing performance. While improving the weight energy density,
A battery excellent in charge / discharge cycle life can be obtained by preventing a decrease in high-rate discharge characteristics over a long period of time, and its industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an electrode laminated structure of the present invention.

FIG. 2 is a view showing charging characteristics of a battery A of the present invention and comparative batteries X1 and X2.

FIG. 3 is a view showing high-rate discharge characteristics of a battery A of the present invention and comparative batteries X1 and X2.

FIG. 4 shows 200 of the battery A of the present invention and the comparative batteries X1 and X2.
It is a figure showing the high rate discharge characteristic after a cycle.

FIG. 5 is a view showing cycle characteristics of the battery A of the present invention and comparative batteries X1 and X2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Gas absorption layer 3 Hydrogen storage electrode plate 4 Nickel positive electrode 5 Negative electrode A Battery of the present invention X1, X2 Comparative battery

Claims (3)

[Claims] 1. A negative electrode for an alkaline storage battery, comprising a porous gas absorbing layer interposed between a plurality of negative electrode plates, wherein the porous gas absorbing layer is made of a non-woven fabric of carbon fiber. Negative electrode. 2. The negative electrode for an alkaline storage battery according to claim 1, wherein said negative electrode plate comprises a hydrogen storage alloy. 3. An alkaline storage battery comprising the negative electrode according to claim 1.