JPH0799691B2 - Method for manufacturing hydrogen storage electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a hydrogen storage electrode.

[Conventional technology]

As the composition of the hydrogen storage alloy powder that constitutes the hydrogen storage electrode, it has been common that Mm (Misch metal), Ni, and Co contain other trace components. For example, Japanese Patent Laid-Open No. 60-250558 discloses MmNixCoyMz as a hydrogen storage alloy.
(M: Al, Sn, Mg, etc.) is used, and Japanese Patent Application Laid-Open No. 63-164161 discloses MmNi5-x-y-zCoxMnyMz (M:
Al, Cr, Fe, etc.) are used.

These hydrogen storage alloy powders are generally molded together with a binder, a current collector, etc. to produce a hydrogen storage electrode.

JP-A-60-176063, 61-233966, 61-233967, 61
-285658, 62-15760, 62-31947, 63-141258,
63-146353, 63-146354, 63-175339, 63-17
5340, 63-175341, 63-175342, JP-A-1-132048
The gazette discloses that by immersing the hydrogen storage alloy powder or the hydrogen storage electrode in an alkaline aqueous solution, it is effective in improving the cycle life and the self-discharge characteristics.

[Problems to be Solved by the Invention]

The above-mentioned conventional hydrogen storage alloy powder has an oxide layer or a hydroxide layer formed on the surface by natural oxidation or the like, and the amount thereof is generally about 5 to 10%.

The present inventors have noticed that such an oxide layer or a hydroxide layer interferes with hydrogen absorption / desorption and conductivity, and that removal of this would improve the discharge capacity.

However, it was not possible to sufficiently remove the oxide layer and the hydroxide layer by the above immersion in the alkaline aqueous solution.

The present inventors conducted various tests from such a viewpoint and found a suitable method for removing the above-mentioned oxide layer and hydroxide layer, and by removing them, the activation cycle of the electrode was significantly shortened. It was found that the electrode utilization rate (that is, the ratio of the developed discharge capacity to the theoretical discharge capacity) and the cycle life were improved.

Therefore, the problem to be solved by the present invention is to provide a method for manufacturing a hydrogen storage electrode, which improves discharge capacity and cycle life.

[Means for Solving the Problems]

The method for producing a hydrogen storage electrode of the present invention comprises immersing the hydrogen storage alloy powder in an acidic aqueous solution in a predetermined concentration range for a predetermined time to remove the surface of the hydrogen storage alloy powder by 1 to 15 wt% by etching, and then rinsing with water to form an electrode. Is manufactured.

The acidic aqueous solution may be, for example, an aqueous solution of an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid or hydrofluoric acid, or an organic acid.

According to experiments, it was preferable to remove the oxide layer or the hydroxide layer on the surface of the hydrogen storage alloy powder by 1 to 10% by weight, preferably 3 to 8% by weight based on the weight of the hydrogen storage alloy. That is, the best effect was obtained in the state where these oxide layers and hydroxide layers were somewhat present. Such partial removal of the oxide layer can be accomplished by controlling the concentration and amount of aqueous acid solution and / or by controlling the pickling time.

Although natural oxidation starts again after pickling, it is naturally possible to determine the remaining amount of the oxide layer in consideration of the amount of natural oxidation between pickling and assembling the battery.

〔Example〕

Using (first embodiment) MmNi _3.5 Co _0.7 Al _0.8 as a hydrogen storage alloy for the negative electrode. This alloy is mechanically made into powder of 100 mesh or less,
To 100 g of this powder, 0.05N HCl aqueous solution was mixed at a ratio of 1, and the mixture was stirred for about 5 minutes, washed with water and dried.

To 4.2 g of this acid-treated powder, 0.5 g of nickel powder (average particle size 5 μm) and 0.25 g of PTFE dispersion (Daikin Industries D-1) were added and kneaded, and after preforming, both sides of the nickel expanded metal 300kg / at room temperature
A negative electrode was formed by molding at a pressure of cm ² . Electrode size is 4 × 3 cm ²
And the thickness is about 1 mm.

This electrode was combined with a sintered nickel electrode having a much larger capacity than the negative electrode via a polyamide non-woven fabric and immersed in a 6N aqueous potassium hydroxide solution to form a negative electrode regulated battery.

In addition, as a comparative example, a battery was constructed in the same manner as in the above example except that the acid treatment was not carried out.

Charge these two batteries at 20 ° C with a current of 500mA for 3 hours.
The utilization factor (the ratio of the actual capacity to the theoretical capacity (%)) of the negative electrode was examined by discharging to a final voltage of 0.8 V at 00 mA. The results are shown in FIG.

As is clear from the results, the electrode of this example has a shorter activation cycle and a significantly higher utilization rate than the comparative example. This is because the present invention removes most of the oxide layer on the surface of the alloy powder by acid treatment, whereas the comparative example covers the surface of the alloy with the oxide layer, and the electrochemical reaction does not occur smoothly. It is also considered that the internal electric resistance loss is large.

(Second Example) Next, a battery was manufactured in the same manner as in the first example except that the concentration of the HCl aqueous solution was variously changed, and the relationship between the negative electrode utilization rate and the cycle life was examined. The results are shown in Table 1. The cycle life was set to the point where the initial capacity reached 50%.

From the results, it is desirable that the HCl concentration when one HCl aqueous solution is mixed with 100 g of the alloy is 0.005 N or more and 0.1 N or less. More preferably, it is 0.01 N or more and 0.05 N or less. Depending on the alloy, the surface oxidation rate cannot be generally stated, but the etching removal rate (the ratio of the weight after etching to the original weight after etching) on the surface of the hydrogen storage alloy powder is preferably about 1 to 15 wt%. If this is less than 0.005N Since the acid concentration is low, the oxide layer cannot be removed sufficiently and the cycle life is long, but the negative electrode utilization rate is low. It is considered that when the content is more than 0.1 N, the oxide layer is entirely removed, the alloy deteriorates repetitively due to repeated charging and discharging, and the cycle life becomes short. In addition, the amount of alloy eluted into the acid during pickling also increases, resulting in poor yield.

Therefore, the acid concentration (or the amount of acid ions) within the above range
If so, the oxide layer can be removed and the utilization factor can be improved to the extent that the cycle life is not impaired.

(Third Example) Alloy powder subjected to the same acid treatment as that shown in the first example
90 parts by weight of Ni powder was mixed with 10 parts by weight of Ni powder, and PTFE dispersion was added and kneaded so that the solid content of PTFE was 3% by weight (based on the total of the mixed powder and the solid content of PTFE), and kneaded into a sheet. The obtained product was crimped to both sides of nickel expanded metal.

As a comparative example, instead of acid treatment, KOH solution (concentration 30 w
An electrode was prepared in the same manner as in the above-mentioned example except that the sample was subjected to alkali treatment for 5 hours at t% and a liquid temperature of 60 ° C.) or not treated at all.

Each of these electrode sheets was cut into a width of 33 mm and a length of 220 mm to obtain a negative electrode. The thickness is about 0.6 mm. This negative electrode was combined with a known sintered nickel positive electrode through a polypropylene non-woven fabric as a separator and formed into a spiral shape to form a sub-C size sealed battery.

The prepared battery was charged and discharged under the conditions of charging: 0.1 C × 15 hr, discharging: 0.2 C, 1 V, and the pressure sensor attached to the upper part of the battery was used to examine the internal pressure of the battery and the cycle life at the end of charging. The results are shown in FIGS. 2 and 3.

As is clear from the results, the battery using the electrode of this example has a lower battery internal pressure at the end of charging and a smaller increase in internal pressure due to repeated charge / discharge cycles, as compared with the battery using the alkali-treated and untreated electrodes. . Therefore, as for the cycle life, the battery using the electrode of the present invention shows a better result than the comparative example.

This is because the oxide layer is effectively removed and the electrochemical reaction on the alloy surface proceeds smoothly to the extent that cycle life characteristics are not deteriorated by acid-treating the alloy surface, so charging efficiency is improved. This is because generation of hydrogen gas is suppressed and the recombination reaction of oxygen gas is improved.

Compared with the untreated one, the alkaline treatment is effective in improving the cycle life and suppressing the rise in the internal pressure of the battery, but only the heterogeneous portion is removed, and the hydroxide layer and oxide layer are not removed. Therefore, it is considered that the battery performance is inferior to that of the acid treatment.

In addition, the hydrochloric acid aqueous solution was used this time, but other acidic aqueous solutions such as sulfuric acid, nitric acid, and hydrofluoric acid have the same effect.

〔The invention's effect〕

As described above, the surface is etched and removed by an acidic aqueous solution in an amount of 1 to 15 wt%, whereby the hydrogen storage alloy powder in which the oxide layer on the surface of the hydrogen storage alloy powder is partially removed is molded. It is possible to provide a battery having an improved utilization rate, a small increase in battery internal pressure due to repeated charging and discharging, and excellent cycle life characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a discharge capacity utilization rate of a battery using a hydrogen storage electrode of one embodiment of the present invention, and FIG. 2 is a line showing a change in internal pressure of a battery using a hydrogen storage electrode of one embodiment of the present invention. Figure,
FIG. 3 is a diagram showing the cycle life of a battery using the hydrogen storage electrode of one embodiment of the present invention.

Front Page Continuation (72) Inventor Mitsuharu Muta 2-chome Toyota-cho, Kariya City, Aichi Prefecture Masanori Suzuki, Inspector, Toyota Industries Corporation

Claims (1)

[Claims] 1. An electrode is prepared by immersing a hydrogen storage alloy powder in an acidic aqueous solution having a predetermined concentration range for a predetermined time to remove the surface of the hydrogen storage alloy powder by 1 to 15 wt% and then rinsing with water. And a method for manufacturing a hydrogen storage electrode.