JPH0582024B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a so-called metal oxide/hydrogen battery in which a metal oxide is used as a positive electrode active material and hydrogen is used as a negative electrode active material. The present invention relates to a metal oxide/hydrogen battery with an improved hydrogen negative electrode whose main component is a hydrogen-absorbing metal.

[Technical background of the invention and its problems] Metal oxide hydrogen batteries that use hydrogen storage metal as the main component of the hydrogen electrode are attracting attention. By making this battery system, which originally has a high energy density, more advantageous in terms of volumetric efficiency and operating it more safely, it is possible to obtain a battery with excellent characteristics and reliability. This is to become.

Conventionally, LaNi ₅ has been tried most often as a hydrogen storage metal, and quite good results have been obtained. However, the pressure inside the sealed battery container is less than 50Kg/cm ² when hydrogen storage metal is not used.
Although the pressure has become smaller compared to 2000, it still shows a value of 2 to 5 Kg/cm ² at room temperature, which can be said to be a high pressure compared to, for example, a nickel cadmium battery (0 to 1 Kg/cm ² ). The fact that the pressure inside the battery is higher than atmospheric pressure has two drawbacks, in addition to the need to make the structure of the battery container somewhat strong. One is that the hydrogen gas molecules in the battery have a small molecular diameter, which makes it easy for them to gradually leak from the closed container into the atmosphere, which is undesirable from a safety standpoint. The stored hydrogen will be released,
The problem is that the capacity decreases, leading to self-discharge.

[Object of the invention] The present invention solves the above-mentioned drawbacks, and maintains the internal pressure of metal oxide/hydrogen batteries to ensure battery safety without leaking H ₂ and prevent self-discharge. The purpose is to provide a metal oxide/hydrogen battery with excellent battery characteristics.

[Summary of the Invention] The present invention provides a metal oxide/hydrogen battery having a hydrogen electrode whose main component is a hydrogen storage metal.
The hydrogen storage metal is a LaNi ₅ -group alloy in which a part of nickel is replaced with Mn, and
It is characterized in that the equilibrium plateau pressure at 20°C is 1 atm or less. The hydrogen storage alloy used may be any LaNi _5- based alloy in which part of the nickel is replaced with Mn, but the equilibrium plateau pressure at 20°C is 1 atm.
It is acceptable as long as it shows the following.

Specifically, examples include ANi _5-x Mn _x where A is at least one of La, Mm (Mitshu Metal), and Ca, and x is 0.2 or more.

In addition, Al, Si, Ge,
At least one metal selected from Fe, B, Ga, Cu, In, and Co may be added.

In addition, in the above composition, it is preferable that x≧0.6 or more. Specifically, MmNi _4.2 Mn _0.8 is preferable.

These metals are used as hydrogen electrodes using an appropriate method, while as metal oxide electrodes, for example, oxides (AgO or Ag ₂ O) or nickel oxyoxides (NiOOH) are used, and these are closely bonded through a separator. The metal oxide/hydrogen battery according to the present invention can be obtained by storing the battery in a container, adding an alkaline aqueous solution thereto, and then sealing the container.

[Examples of the Invention] Next, the present invention will be explained with reference to Examples. MmNi _4.2 Mn _0.8 is used as the hydrogen storage metal.

First, in MmNi _4.2 Mn _0.8 , the amounts of the metal elements shown in this elemental composition are ground into powder, mixed, and melted in a vacuum arc melting furnace to obtain a uniform solid solution. Next, crush this to a diameter of about 5 mm,
Next, by performing a so-called activation process,
The state is such that hydrogen can be easily absorbed and released.
At this time, the metal becomes a powder with a size of about 50 to 100 μm.

The activated metal, which has become a powder of approximately 100 μm in size, and a dispersion of polytetrafluoroelethene (PTFE) are mixed and thoroughly kneaded to form a sheet material with a thickness of 0.5 mm. The mixing ratio at this time was metal:PTFE=90:10 as a value in a dry state. These two sheets were pressed together from both sides of the nickel net to form an electrode body for a hydrogen electrode with a thickness of 0.8 mm.

On the other hand, as a positive electrode, a NiOOH electrode made of a nickel sintered body impregnated with an active material was used. A polyamide nonwoven fabric with a thickness of 0.3 mm was used as the separator, and an 8Mo/KOH solution was used as the electrolyte.

FIG. 1 shows the above components assembled into a battery. 1 is a negative electrode, 2 is a separator, and 3 is a positive electrode. 4 and 5 are negative and positive electrode terminals, respectively, and are electrically independent from the stainless steel container 6. Note that the container 6 is sealed by welding after the battery components are assembled therein. Further, 7 is a pipe for measuring internal pressure, and 8 is a pressure measuring device. The positive electrode 3 was wrapped in a U-shape with a separator 2, and the negative electrode 1 according to the present invention was placed in contact with both sides of the positive electrode 3, and was brought into close contact with an acrylic holder 9. 10 is an electrolytic solution. The capacity of the positive electrode is 1.0Ah, and the capacity of the negative electrode is 1.0Ah.
MmNi _4.2 Mn _0.8 is filled with an amount that absorbs H ₂ for 2.0Ah.

This battery was first brought to a state of 1 atm (0 Kg/cm ² ), then charged at 200 mAh for 5 hours, and then charged at 200 mAh.
Discharge to 1.0V (this is considered 1 cycle)
Figure 2A shows the pressure change when charging was repeated for 4 cycles in this manner and stopped after 5 cycles.
Figure 3B shows the pressure change and discharge curve when the 5th cycle of discharge is performed after 24 hours.
and shown in D. For comparison, LaNi ₅ and Ti ₂ Ni were used as hydrogen storage metals, and the battery fabrication method was exactly the same as in this example, and the measurement method was also the same. The results are shown in Figures 2a and b, and Figure 3, respectively. c, d, e,
Shown in f. In Figure 2, b is the pressure change of Ti ₂ Ni, c,
e is the pressure change of LaNi ₅ and Ti ₂ Ni, d, f
show the discharge curves of LaNi ₅ and Ti ₂ Ni, respectively. The temperature in both cases was 25°C. Furthermore, MmNi _4.2
The equilibrium plateau pressure at 20℃ for Mn _0.8 is 0.2atm
(0.4 atm at 25°C).

Note that a, c, and d in the figure indicate the internal pressure during charging/discharging cycles of LaNi ₅ , internal pressure when left unused, and battery voltage data, respectively.As can be seen from Figure 2, LaNi ₅ 's internal pressure increases each time it is charged While the pressure increases towards its equilibrium plateau pressure,
There is almost no increase in MmNi _4.2 Mn _0.8 . Furthermore, as shown in Figure 3, if left for 24 hours, LaNi ₅
In the battery using MmNi 4.2 Mn 0.8, the internal pressure increases and the discharge time becomes shorter, clearly self-discharging, whereas the battery using MmNi _4.2 Mn _0.8 has almost no pressure increase or self-discharge. . Also
The equilibrium plateau pressure of LaNi ₅ at 20°C is approximately 2 atm
(approximately 3 atm at 25°C).

In addition, b, e, and f in the figure indicate the internal pressure due to charging/discharging cycles of Ti ₂ Ni, internal pressure due to standing, and battery voltage data, respectively.As is clear from Figures 2 and 3, Ti ₂ Ni Since the plateau pressure is relatively small, the internal pressure does not increase and the same effect as MmNi _4.2 Mn _0.8 can be obtained, but as shown in f, the battery voltage fluctuates so much that it cannot be used practically as a battery.

[Effects of the Invention] As is clear from the above description, according to the present invention, it is possible to obtain a metal oxide/hydrogen battery that is safe, has extremely little self-discharge, and has excellent battery characteristics with small fluctuations in battery voltage. be able to.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of the metal oxide/hydrogen battery according to the present invention, Figure 2 is a curve diagram showing changes in battery internal pressure up to 5-cycle charging, and Figure 3 is when left for 24 hours after 5-cycle charging. Fig. 2 is a diagram showing changes in battery internal pressure and subsequent discharge curves. 1...Hydrogen negative electrode, 2...Separator, 3...Metal oxide positive electrode, 4, 5...Terminal, 6...Battery container, 7...Pipe for pressure measurement, 8...Pressure gauge, 1
0... Electrolyte.

Claims (1)

[Claims] 1 Metal oxide/hydrogen consisting of a positive electrode with a metal oxide as an active material, a negative electrode with a hydrogen storage alloy as a main component and hydrogen as an active material, an alkaline electrolyte, and a separator that separates the positive electrode and the negative electrode. In the battery, the hydrogen storage alloy is made of a LaNi ₅ alloy in which part of the nickel is replaced with Mn, and
A metal oxide/hydrogen battery characterized by using a battery having an equilibrium plateau pressure of 1 atm or less at °C.