JPS5931180B2 - Chikudenchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a storage battery that extracts energy generated by an electrochemical reaction between oxygen and hydrogen stored in a cathode as electrical energy.

Although lead/lead oxide, nickel/cadmium, and other storage batteries are conventionally known, these storage batteries have relatively low discharge capacity densities in terms of weight and volume because they have oxide electrodes. In order to improve the discharge capacity density of alkaline storage batteries, it has been proposed to use an electrode that stores hydrogen as a cathode, but the discharge capacity density has not yet been sufficient. The present invention focuses on magnesium as an inexpensive material with a large hydrogen storage capacity, and adds nickel to it to improve the discharge capacity density.

Magnesium has a large hydrogen storage capacity per gram, but because it does not electrochemically absorb hydrogen, almost no hydrogen oxidation reaction is observed even when used as a metal hydride cathode, and the discharge capacity density is low. is equal to zero, but by adding nickel to magnesium, hydrogen can be easily absorbed and released electrochemically, and the electrochemical oxidation of hydrogen can be promoted in the alkaline electrolyte during discharge. The function of making water occurs.

Generally known simple magnesium and magnesium alloys absorb gaseous hydrogen to form the following metal hydride compounds.

Mg+H2=MgH｜・・・・・・・・・・・・・・・
(1) Mg2Ni+ 2H｜=Mg｜NiH4...
...(2) In formula (1), the hydrogen storage capacity per unit weight is approximately 1000cc/V (in formula 2, it is 45Occ).
/y, and on the other hand, the MgNi2 alloy has a very small amount of absorbed hydrogen.

Magnesium alone absorbs a large amount of gaseous hydrogen, but in an alkaline electrolyte, it forms a passivation film on the magnesium surface and becomes electrochemically inert.
In the case of nickel alloys, it is difficult to form a passivation film, which makes it easy to absorb and release hydrogen electrochemically. An embodiment of the present invention will be described in detail below.

- Commercially available high-purity magnesium and nickel were placed in a high-frequency melting furnace and melted in an inert gas stream consisting of argon, and then ground in a dry box in an argon stream and placed in a pressure-resistant reaction vessel. The gas inside is removed by suction, and then high-purity gas is introduced into the reaction vessel using a hydrogen cylinder, maintained at a constant pressure of 5 to 30 kg/Cd, and heated to 300 to 350°C to form a magnesium-nickel alloy. Hydrogen activation was performed.

After removing hydrogen from this hydrogenated powder alloy,
It is sieved into powder particles of ~10-odd microns, then compression molded with a few percent of thermally decomposable substances such as sodium sulfate, sodium phosphate, and polyvinyl alcohol, and sintered in a vacuum at 600 to 700°C for several hours. to make a porous alloy body.

The obtained alloy body was used as an electrode and immersed in an alkaline electrolyte, and charging and discharging was performed using a nickel counter electrode.The results shown in the figure were obtained. When nickel is added to magnesium, the discharge capacity density increases, reaching a maximum of 500% when the nickel content is around 55% by weight (alloy composition Mg2Ni).
It can be seen that it shows AVkg.

As the nickel content increases, it becomes MgNi, and up to alloys with the composition Mg, Nil:. A coexisting mixture of MgNi2,
Hydrogen storage capacity is mostly determined by Mg2Ni, and MgNi,
It can be seen that the discharge capacity density gradually decreases with Mg2Ni as the boundary because it absorbs almost no hydrogen.

For practical purposes, the discharge capacity density of a cathode for an alkaline storage battery must be at least 0.15 Ah/t or higher, otherwise it will have no characteristics compared to conventional ones, so the nickel content should be 20~
70% by weight is effective.

In addition, the discharge capacity density of general storage batteries is 100 to 150 Ah.
A! It can be seen that the present example exhibits a high reversible capacity and is effective in practice. Incidentally, in order to produce the alloy body, the magnesium-nickel alloy may be mechanically pulverized and sieved into a size of several microns to several tens of microns, without hydrogenating the magnesium-nickel alloy and turning it into powder. However, in this case, the alloy powder is mixed with a binder, compression molded, vacuum sintered, and then, when cooled, hydrogen is absorbed in a hydrogen atmosphere to form a porous alloy body.

If the strength is weak, grind it again and add a binder.
It can also be molded and sintered to form a porous body. As described above, the present invention is extremely inexpensive compared to titanium-nickel alloys and the like.

A storage battery with good discharge capacity density is provided by using a magnesium alloy containing nickel as a cathode and electrochemically absorbing hydrogen.

[Brief explanation of drawings]

The drawing is a relationship diagram between magnesium nickel alloy composition and energy storage capacity.

Claims (1)

[Claims] 1. A storage battery characterized in that a magnesium alloy containing nickel is used as a cathode, and hydrogen is electrochemically occluded in the cathode.