JPH0785873A - Negative electrode material for nickel-hydroxide secondary battery - Google Patents

Abstract

PURPOSE:To obtain stabilized negative electrode material for a secondary battery which has a large discharge capacity, large quick charging/discharging performance and a large discharge capacity from the initial time of a cycle, by using nickel-hydroxide as the negative electrode material for the secondary battery. CONSTITUTION:An alloy is used which is composed of 0.5-20% rhodium by atomic % density and the residual % palladium or which is composed of 0.5-20% rhodium, 0.5-15% nickel and the residual % palladium by atomic % density. Surface of this alloy is desirably coated with two layers of palladium black and platinum black in this order in a range of 1-2mg/cm<2>.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a negative electrode material used in a nickel-hydride secondary battery.

[0002]

2. Description of the Related Art Nickel oxyhydroxide (NiOO) is used for the positive electrode.
The alkaline secondary battery (storage battery) that uses H / Ni (OH) ₂ ) and a metal hydride for the negative electrode has a large discharge capacity and a long cycle life compared to the conventional nickel-cadmium secondary battery. In recent years, it has received particular attention. In such a battery, the negative electrode material used is a hydrogen storage alloy such as an intermetallic compound based on AB ₅ type misch metal or an AB ₂ type alloy based on Zr (Ti).

[0003]

However, these negative electrode alloys have problems in corrosion resistance to alkaline electrolytes, hydroxides formed during charge / discharge cycles, and rapid charge / discharge performance. On the other hand, although palladium and palladium alloys are expensive, they have excellent corrosion resistance to alkaline electrolytes and resistance to charge and discharge deterioration, and are also excellent in rapid charge and discharge.

[0004]

The present invention has solved the above problems and has a large discharge capacity when used as a negative electrode material for nickel-hydride secondary batteries, stable initial discharge characteristics, and rapid charging. It is an object of the present invention to provide a negative electrode material for a nickel-hydride secondary battery that can obtain discharge performance.

[0005]

The negative electrode material for a nickel-hydride secondary battery according to the present invention contains rhodium of 0.5% at an atomic% concentration.
Alloy containing 0.5 to 20% of the balance palladium, or an alloy of 0.5 to 20% rhodium, 0.5 to 15% nickel and the balance palladium. Furthermore, the present invention is a negative electrode material for a secondary battery, wherein the above alloy is coated with a superposition coating of palladium black and platinum black.

[0006]

When palladium is used as the negative electrode material for a nickel-hydride secondary battery, factors affecting the electrochemical characteristics are the size of the (α + β) two-phase hydride coexisting phase of palladium and its α and The magnitude of the diffusion coefficient of hydrogen in the β phase can be considered. When a nickel hydride secondary battery using palladium as a negative electrode is charged and discharged, a rapid change in electrode potential generally occurs during charging and the initial stage of discharging, and thereafter, a slow change in potential is continuously observed. This abrupt change is due to charge transfer at the interface between the hydride on the electrode surface and the electrolyte, and the gradual change is due to the diffusion process of hydrogen from the hydride. In order to improve the discharge characteristics, especially the discharge rate, it is necessary to increase the diffusion rate of hydrogen from the hydride electrode, and for that reason, the hydride of the negative electrode is unstable and the hydrogen diffusion coefficient is large. Is needed.

When rhodium or nickel is added to palladium, the hydride becomes unstable with the increase of the addition amount and hydrogen is easily desorbed, but on the other hand, the addition amount of the palladium-rhodium alloy or palladium increases. -The diffusion coefficient of hydrogen in the nickel alloy is reduced. for that reason,
Addition of rhodium and nickel in an amount that exactly balances the instability of hydride and the hydrogen diffusion coefficient makes an electrode with excellent charge and discharge characteristics. This is the reason why the amounts of rhodium and nickel added are limited, and the discharge characteristics deteriorate when the amount is less than the above range or exceeds the above range.

Further, in order to accelerate the charge transfer at the interface between the hydride on the electrode surface and the electrolytic solution, black of noble metal is applied to the electrode surface to reduce the overvoltage during the charge transfer. Palladium is used as the noble metal, and more preferably, palladium black is further coated with platinum black to exhibit extremely excellent catalytic activity. This is because when platinum black is used, the activation overvoltage due to charge transfer is further reduced as compared with palladium black, and therefore the electrode on which palladium black-platinum black is stacked has its electrochemical activity greatly improved. .

[0009]

EXAMPLE An electrode having a structure as shown in Table 1 was prepared as an example and a conventional example.

[0010]

[Table 1]

The electrode was prepared by melting each alloy into a rolled plate, and then using a foil having a thickness of 60 μm, an area of 1.5 cm × 1.5 cm, and a weight of 136 to 180 mg. Thereafter, each sample was annealed in vacuum at 850 ° C. for 2 hours. Subsequently, each sample was subjected to palladium black plating using a palladium plating bath having the following composition for activation, and then platinum black plating was performed on the palladium black using a platinum plating bath having the following composition.

(Palladium plating bath) Palladium chloride (PdCl ₂ ) 2% by weight Lead acetate (Pb (CH ₃ COO) ₂ ) 0.01% by weight 0.1 M hydrochloric acid Residual current density 150 mA / cm ² Temperature Room temperature (platinum plating bath) Platinum chloride Acid (H ₂ PtCl ₆ · 6H ₂ O) 3% by weight Lead acetate (Pb (CH ₃ COO) ₂ ) 0.02% by weight Water residual current density 10 mA / cm ² Temperature room temperature In addition, in any of the above plating A platinum plate was used.

In the charge / discharge test, an open H-type cell was used as an electrolytic cell, a 6M potassium hydroxide solution was used as an electrolytic solution, a Hg / HgO electrode was used as a reference electrode, and a NiOOH-cell having a size of 4 cm × 9 cm was used as a positive electrode (counter electrode). It was performed using a Ni (OH) ₂ electrode. Using a battery charging / discharging device at a temperature of 30 ± 0.3 ℃,
First, it was charged to 140% of the theoretical capacity of Pd _1-x X _x H _0.7 (X is Rh or Ni) at a constant current of 20 mA, and after a 10-minute rest, it was discharged to a predetermined discharge current within the range of 5 to 80 mA. And discharged to a final voltage of 0.8V. Then, after resting for 10 minutes, the above charge / discharge test was repeated up to 10 times again to examine charge / discharge characteristics.

As examples, Nos. 1, 2, 3, 4 and 5
Using the Pd alloy electrode of No. 10 and the pure Pd electrode of No. 10 as a conventional example, changes in discharge capacity when charging and discharging were repeated were examined. The result is shown in FIG. The discharge current was 10 mA. Compared to the electrode containing only palladium, the electrode containing rhodium had a higher discharge capacity and maintained a constant value even after repeated charging and discharging.

Using the No. 2, 3, 4 and 5 electrodes as an example and the No. 10 electrode as a conventional example, the change in discharge capacity when the discharge current was changed was examined.
Shown in. As shown in FIG. 2, as compared with the electrode containing only palladium, the electrode containing rhodium showed a smaller reduction rate when the discharge current was increased.

The electrodes of Nos. 6, 7 and 8 were used as examples, the electrode of No. 3 was used as a comparative example, and the electrode of No. 10 was used as a conventional example, and the discharge capacity when the discharge current was changed. What investigated the change is shown in FIG. Thus, the electrode obtained by further applying platinum black on palladium black had an excellent discharge capacity at a high discharge current.

The electrodes of Nos. 7, 8 and 9 were used as examples, the electrode of No. 3 was used as a comparative example, and No. 1 was used as a conventional example.
FIG. 4 shows the result of examining the polarization characteristics using the 0 electrode.
As seen here, in the electrode activated only with palladium black, the electrode with rhodium added had a lower overvoltage than the electrode with only palladium, and the electrode with platinum black overlaid on palladium black was The overvoltage dropped further.

[0018]

As described above, the negative electrode material for a secondary battery of the present invention is superior to the conventionally used palladium or the like in
It excels in its discharge capacity, rapid discharge (discharge capacity at high discharge current), and initial discharge characteristics. When nickel-hydride secondary batteries are produced, stable discharge characteristics are obtained, and it can be used for various purposes. It will be possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in discharge capacity when charging and discharging are repeated using an electrode material of the present invention and a conventional electrode material.

FIG. 2 is a diagram showing a change in discharge capacity when a discharge current is changed in the electrode material of the present invention and the conventional electrode material.

FIG. 3 shows changes in discharge capacity when the discharge current is changed in the electrode material of the present invention that is activated only by palladium black, that activated by palladium black and platinum black, and the conventional electrode material. Fig.

FIG. 4 shows polarization curves of the electrode material of the present invention and the conventional electrode material.

Claims (2)

[Claims] 1. An alloy consisting of 0.5 to 20% rhodium at the atomic concentration and the balance palladium, or 0.5 to 20 rhodium.
%, Nickel 0.5 to 15%, the balance being palladium, a negative electrode material for nickel-hydride secondary batteries. 2. The nickel-hydride 2 according to claim 1, wherein the surface of said alloy is coated with palladium black in an amount of 1 to 2 mg / cm ² , and platinum black is further coated thereon in an amount of 1 to ² mg / cm 2. Negative electrode material for secondary battery.