JPH04179055A - Manufacture of hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To provide a battery having excellent cyclic lifetime characteristic by immersing a powder oif hydrogen storage alloy in an acid aqueous solution in the specific range of concentration for a certain specified period of time, followed by rinsing, and thus fabricating an electrode as object of invention. CONSTITUTION:Powder of hydrogen storage alloy is immersed in an acid aqueous solution in a specific range of concentration for a certain period, followed by rinsing, and thereby an electrode is fabricated. The rinse is made by immersing in aqueous solution of an inorganic acid-for example, chloric acid, sulfuric acid, and fluoric acid-and it is preferable to remove oxide layer or hydroxide layer in amount 1-10wt.% of the hydrogen storage alloy from the surfaces of the alloy powder, and a condition is generated, in which the oxide layer or hydroxide layer remains to a certain degree. This ensures that electrochemical reactions are made smoothly, and the discharge capacity and cyclic lifetime can be improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a hydrogen storage electrode.

[Conventional technology]

The composition of the hydrogen storage alloy powder constituting the hydrogen storage electrode is Mm (Mitshu Metal), Ni, and C.

In addition, those containing other trace ingredients are conventionally - boat fishing. For example, Japanese Patent Application Laid-open No. 60-250558 discloses MmNixCoyMz (M: Al1, S
JP-A-63-164161 uses MmNi 5-x-y-zC as a hydrogen storage alloy.
oxMnyMz (M: AI, Cr, Fe, et c
, ).

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

JP 61-176068, JP 61-288966, JP 61-283967, JP 61-285658, JP 62-
15760, 62-81947, 63-14125
8, 63-146358, 63-146354, 6B-175339, 63-175340, 63-
175341, 63-175842, JP-A-1-13
Publication No. 2048 discloses that immersing a hydrogen storage alloy powder or a hydrogen storage electrode in an alkaline aqueous solution is effective in improving cycle life and self-discharge characteristics.

[Problem to be solved by the invention]

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

The inventors of the present invention have realized that such oxide layers and hydroxide layers become obstacles to hydrogen absorption and release and conduction, and that removing them may improve discharge capacity.

However, the oxide layer and hydroxide layer could not be sufficiently removed by immersion in the alkali aqueous solution described above.

The present inventors conducted various tests from this viewpoint and found a suitable method for removing the above-mentioned oxide layer and hydroxide layer, and also found that their removal significantly shortened the electrode activation cycle. It has been found that the electrode utilization rate (that is, the ratio of the developed discharge capacity to the theoretical discharge capacity) and the cycle life are improved.

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

[Means to solve the problem]

The method for manufacturing a hydrogen storage electrode of the present invention includes immersing hydrogen storage alloy powder in an acidic aqueous solution having a predetermined concentration range for a predetermined time, and then
The feature is that the electrodes are prepared by washing with water.

Examples of the acidic aqueous solution include aqueous solutions of inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid, as well as organic acids.

According to experiments, it was preferable to remove the oxide layer or 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 a state where some of these oxide layers and hydroxide layers were present. Such partial removal of the oxide layer can be achieved by controlling the concentration and amount of the aqueous acid solution and/or by controlling the pickling time.

Note that natural oxidation starts again after pickling, but it is naturally possible to determine the remaining amount of the oxide layer by considering the amount of natural oxidation between pickling and assembling the battery.

〔Example〕

(First Example) MmNim, s COo, t Alo, * was used as a hydrogen storage alloy for the negative electrode. This alloy is mechanically
The powder should be less than mesh, and per 100g of this powder, 0
．． 05N HCI! The aqueous solutions were mixed in a ratio of 11 parts and stirred for about 5 minutes, then washed with water and dried.

To 4.5 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 powder were mixed. It was sandwiched between nickel expanded band metals and molded at room temperature under a pressure of 300 kg/al to form a negative electrode. The electrode size is 4×8 dl 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 nonwoven fabric, and immersed in a 6N caustic potassium aqueous solution to construct a negative electrode regulated battery.

Further, as a comparative example, a battery was constructed in the same manner as in the above example except that acid treatment was not performed.

These two batteries were charged at 20° C. for 8 hours with a current of 500 mA, and then discharged at 500 mA to a final voltage of 0.8 V to examine the utilization rate of the negative electrode. The results are shown in FIG.

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

(Second Example) Next, batteries were produced in the same manner as in the first example except for varying the concentration of the HC1 aqueous solution, and the relationship between the negative electrode utilization rate and the cycle life was investigated. The results are shown in Table 1. Note that the cycle life was defined as the point at which the initial capacity reached 50%.

From the results, HCI for 100g of alloy! When mixing 11 aqueous solutions, the HCf concentration is 0.005N or more. It is desirable that it be below IN. More preferably 0. It is desirable that it is not less than OIN and not more than 0.05N. Although the surface oxidation rate cannot be determined unconditionally depending on the alloy, it is desirable that the surface etching rate is about 1 to 15%. If this is less than 0.005N, the oxide layer cannot be removed sufficiently as shown in Table 1. Although the life is long, the negative electrode utilization rate is low.

If the amount exceeds 061N, the entire oxide layer will be removed, resulting in severe alloy deterioration due to repeated charging and discharging, and the cycle life will be shortened (this is thought to be the case).Also, the amount of alloy eluted into the acid during pickling increases, resulting in lower yield. Deteriorate.

Therefore, the acid concentration (or acid ion amount) falls within the above range.
If there is, the oxide layer can be removed to the extent that the cycle life is not impaired, and the utilization rate can also be improved.

(Third Example) 10 parts by weight of Ni powder was mixed with 90 parts by weight of alloy powder which had been subjected to the same acid treatment as that shown in the first example, and PTFE
PTFE dispersion was added and kneaded so that the solid content of the mixture was 3% by weight (based on the sum of the mixed powder and PTFE solid content), and the sheet was pressed onto both sides of nickel expanded band metal.

In addition, as a comparative example, electrodes were treated in the same manner as in the above example except that instead of acid treatment, electrodes were treated with alkali for 5 hours using KOH solution (concentration 30 wt%, liquid temperature 60°C) and electrodes were not treated at all. was created.

Each of these electrode sheets has a width of 33 mm and a length of 220 mm.
It was cut into pieces and used as a negative electrode. The thickness is approximately 0.6 mm. This negative electrode is passed through a polypropylene nonwoven fabric as a separator,
Combined with a known sintered nickel positive electrode to create a spiral shape,
A sub-C size sealed battery was constructed.

Charging the manufactured battery: 0. ICXI 5hr, discharge:
The battery was charged and discharged under the conditions of 0.2C and IV, and the internal battery pressure and cycle life at the end of charging were examined using a pressure sensor attached to the top of the battery. The results are shown in FIGS. 2 and 3.

As is clear from the results, the battery using the electrode of this example had a lower internal pressure at the end of charging (and was also less prone to internal pressure increase due to repeated charge/discharge cycles) than batteries using alkali-treated and untreated electrodes. Therefore, the battery using the electrode of the present invention shows better results in terms of cycle life than the comparative example.

This is because the oxide layer is effectively removed by acid treatment of the alloy surface to the extent that cycle life characteristics do not deteriorate, and the electrochemical reaction on the alloy surface progresses smoothly, resulting in improved charging efficiency. This is because hydrogen gas generation is suppressed and the recombination reaction of oxygen gas is improved.

Compared to untreated cells, alkaline treatment is effective in improving cycle life and suppressing increases in battery internal pressure, but it only removes inhomogeneous parts and does not remove the hydroxide or oxide layers. Therefore, it is thought that the battery performance is inferior to acid treatment.

Also, although a hydrochloric acid aqueous solution was used this time, other acidic aqueous solutions such as sulfuric acid, nitric acid, and hydrofluoric acid can have the same effect.

〔Effect of the invention〕

As described above, by using the acid-treated electrode of the present invention, the utilization rate of the electrode is improved, and it is possible to provide a battery with excellent cycle life characteristics with less increase in battery internal pressure due to repeated charging and discharging.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the discharge capacity utilization rate of a battery using a hydrogen storage electrode according to an embodiment of the present invention, and FIG. 2 is a diagram showing internal pressure changes of a battery using a hydrogen storage electrode according to an embodiment of the present invention. figure,
FIG. 3 is a diagram showing the cycle life of a battery using a hydrogen storage electrode according to an embodiment of the present invention.

Claims (1)

[Claims] 1. A method for producing a hydrogen storage electrode, which comprises immersing a hydrogen storage alloy powder in an acidic aqueous solution having a predetermined concentration range for a predetermined time, and then washing the powder with water to produce an electrode.