JPS5840828B2 - Manufacturing method of hydrogen storage electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in hydrogen storage electrodes used, for example, as cathodes of alkaline storage batteries.

A hydrogen storage electrode uses a hydrogen storage material as an active material, and uses it as a current collector or electrode support, such as a nickel net, a nickel-plated iron net, or a metal porous material such as nickel that has a three-dimensional network structure, so-called A structure is used in which the metal foam is used to hold it.

Electrodes using a metal net as a current collector are generally manufactured by a method in which hydrogen storage material powder is bonded to both sides of the net by sintering, with the net in the center.

However, the bonding force is not as strong as that of a sintered body of a single metal.

In particular, the volume of the hydrogen storage material changes due to the storage and release of hydrogen during charging and discharging, and if this happens repeatedly, the bond between the electrode constituent materials weakens, the active material peels off or falls off, and the electrode capacity decreases. be.

On the other hand, electrodes using foamed metal have a structure in which the active material exists in a three-dimensional network, and the foamed metal is filled with hydrogen-absorbing material powder or a mixed powder of single metals that form a hydrogen-absorbing alloy and then pressurized. It is manufactured by molding and heat treatment at sintering or alloying temperatures.

In this case, since the active material is incorporated into the support, the characteristics and life of the electrode are further improved compared to the former.

However, the highly porous metal foam used here has a thin wire diameter of about 40 to 60 μm, and when heat treated, it may react with the hydrogen storage alloy or a part of the single metal, causing the foam metal to become alloyed. be.

As a result, the foam metal loses its original strength and becomes brittle.
This can cause cracks in the electrode and reduce the strength of the electrode itself.

Furthermore, some of the alloys formed by foamed metals form metal hydrides.

In such a case, the electrode strength is further reduced.

Therefore, if charging and discharging are repeated under severe conditions such as complete discharge at a low current density, the active material may not be able to withstand the stress caused by the change in volume, and a portion of the electrode may fall off.

For example, when using a titanium-nickel alloy as the active material, if the material of the foam metal is nickel, Ti2N
i, T1Ni, etc. to form metal hydride-forming alloys.

If you cut the electrode and observe its cross section, you can clearly see that the original shape of the foamed metal has partially disappeared.

An object of the present invention is to provide a hydrogen storage electrode that can be charged and discharged under severe conditions for a long period of time without causing any active material to fall off.

In the present invention, an electrolytic resistant metal net is pressurized and integrated on the surface of a foamed metal containing powder of a hydrogen absorbing material, particularly on both sides of a plate-like body, and heat treated at a temperature below the melting point of the electrode constituent material. It connects metal nets together.

Here, nickel, stainless steel, or the like is used for the metal net, and the wire diameter thereof is at least larger than the wire diameter of the foam metal skeleton, and is not very thick, and the mesh spacing is appropriate.

If the wire diameter of the net is small, it will become alloyed like foamed metal during heat treatment, and the reinforcing effect of the net will not be obtained.

On the other hand, if the electrode is thick, the ratio of the net to the weight and volume of the electrode increases, reducing the output capacity per unit weight and unit volume of the electrode.

Furthermore, if the mesh spacing is small, the net will not penetrate into the foamed metal sufficiently, resulting in peeling of the net.

If the mesh spacing is large, the active material is likely to peel off or fall off from the electrode surface, making it impossible to obtain the reinforcing effect of the net.

The present invention will be explained below with reference to Examples.

Example 1 Commercially available titanium with a purity of 99.5% or more and nickel are mixed at an atomic ratio of 2:1.

This sample was synthesized into an alloy in an arc melting furnace in an argon atmosphere, and then pulverized to obtain an alloy powder of 46 μm or less.

The obtained alloy powder mainly consists of T I 2 N i phase, and also T1Ni phase, TtNt3 phase, and T
Consists of an i-phase and a Ni-phase single metal.

Next, 10 g of this alloy powder was filled into a foamed metal made of nickel with a size of 50 x 50 mm, and both sides were filled with a wire diameter of 0.1.
A nickel net of the same size as the foamed metal was placed with a mesh spacing of 5 mm and a mesh spacing of 1, and after molding at a pressure of 1 ton/d to integrate the two, it was heated in a vacuum (10 = ~10-”Torr).
, ) at a temperature of 950℃ for 30 minutes to obtain a thickness of 1.
．． A 4 mm electrode was obtained.

This electrode is referred to as A, and for comparison, an electrode obtained by molding and heat-treating under the same conditions as above without bonding the nickel net is B1.Also, nickel net is used as an electrode support, and 1 ton of alloy powder is applied to both sides of the electrode. C is an electrode obtained by molding at a pressure of - and heat-treating under the same conditions as above.

An alkaline storage battery was constructed using these electrodes as a cathode and a known nickel electrode as an anode, and the drawing shows the change in discharge capacity when charging and discharging were repeated at a current of 100 mA per gram of active material of the cathode.

The discharge is at a cathode potential of 750 with respect to a standard mercury oxide electrode.
mV, and the lifetime was defined as the time when the capacity decreased to 1 or less of the initial 1 to 5 cycle capacity.

The discharge capacity was expressed as a value per unit weight of the cathode active material.

As is clear from the figure, although the initial capacity of the electrode of the present invention is not as large as that of the comparative example, it has excellent life characteristics, which is more than 4 times better than C and 1.5 times better than B.

In other words, in C, the active material is held on the electrode support only by bonding through sintering of the alloy particles, and with repeated charging and discharging, the bonding force gradually weakens, and as the charge and discharge cycles are repeated, the nickel net of the support is removed. , the active material often peels off and falls off, causing a decrease in capacity and shortening the life of the electrode.

In addition, in B, the foamed metal of the support formed an alloy with the alloy of the active material, resulting in a decrease in strength and cracking in some parts, and falling off from those parts was observed after repeated charging and discharging.

In contrast, in the electrode A of the present invention, both sides of the foamed metal are reinforced with nickel nets, so there is no loss of original shape due to cracks in the electrode plates or alloying of the reinforcing nets.

Therefore, even after repeated charging and discharging cycles of 300 cycles or more, there is hardly any dropout of the active material, and there is almost no decrease in capacity, showing good characteristics.

Example 2 Commercially available titanium and nickel powders with a purity of 9965% or higher were mixed at an atomic ratio of 2:1, and this mixed powder 1
0 g was filled into a foamed metal made of nickel with a size of 50 x 50 mm, nickel net was placed on both sides, and the mixture was press-formed at a pressure of 1 ton/d to integrate it.
5 at a temperature of 850℃ at 0-4~1.0-5Torr,)
A sintered electrode was obtained by heat treatment for a period of time.

In this case, the nickel net has a wire diameter of 0.05 mm to 0.05 mm.
6 mw and mesh spacing of 0.1 to 8 mm were used.

The electrode thus produced was used as a cathode, and a charge/discharge test was conducted in the same manner as in Example 1.

The results are shown in the table below.

In the table, the discharge capacity (Ah/g) is the capacity per 1 g of electrode, and shows the average value for 1 to 10 cycles.

In the eight types of electrodes shown in the table, the net wire diameter is small and alloys with the active material, most of the nickel wires have lost their original shape, and part of the net has peeled off after 80 charging and discharging cycles. However, as charge and discharge cycles were repeated, the peeled area gradually expanded and more active material fell off.

In cases 1 and 2, the active material fell out from between the meshes of the net, and as the charge/discharge cycles were repeated, the amount of increase in case 3 decreased, but the amount of increase in case 1 increased.

From these results, it can be seen that (1) and (2), Chinette hardly achieves the effect of reinforcing the electrode plate.

On the other hand, the electrodes C, 2, and E showed almost no change after 300 cycles, indicating that the net used for these electrodes was effective.

From the above results, the wire diameter of the metal net attached to both sides of the foamed metal is larger than the wire diameter of the foamed metal skeleton by about 40 to 60μ, and is 0.5 mm or less, and the mesh spacing of the net is 0.2 to 5. It can be seen that the above range is appropriate from both the reinforcement effect and output capacity density.

In the examples, a titanium-nickel alloy was used as the hydrogen storage alloy, but other hydrogen storage alloys that form an alloy with the foam metal, such as La Ni5, may be used.

MmNi, TiFe, Mg2Ni can also be applied.

In addition, the material of the metal net is conductive, nickel-plated iron with alkaline electrolyte, nickel-plated copper,
Alternatively, it can be applied to silver, stainless steel, etc.

As described above, according to the present invention, a hydrogen storage electrode having good characteristics over a long period of time can be obtained.

[Brief explanation of the drawing]

The drawings show changes in discharge capacity during charging and discharging of alkaline storage batteries using various hydrogen storage electrodes.

Claims (1)

[Claims] 1. A metal net is integrated with the surface of a metal porous body having a three-dimensional network structure containing powder of a hydrogen storage material by applying pressure, and is heated at a temperature at which the powder is sintered to form the metal net. A method for manufacturing a hydrogen storage electrode characterized by being integrally bonded.