JP3082341B2 - Hydrogen storage electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to a hydrogen absorbing electrode using a hydrogen storage alloy, particularly having a AB ₅ type hydrogen storage alloy phase, a nickel - relates to a hydrogen absorbing electrode which constitutes the hydrogen rechargeable battery Things.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery using a hydrogen storage alloy has a high energy density and a low pollution property without containing cadmium or the like. There is.

[0003]

Problems to be Solved by the Invention When used as a power source for portable equipment, the environment in which the battery is used (inside the equipment) becomes high with the recent multifunctionalization of the equipment, an increase in current consumption, and miniaturization. In many cases, improvement in high-temperature characteristics is indispensable for improving the performance of nickel-hydrogen batteries.

[0004] Among the high-temperature characteristics of nickel-hydrogen batteries,
Reduction of discharge capacity at high temperatures is one of the biggest problems.In the case of nickel-hydrogen secondary batteries using a hydrogen storage alloy, the characteristics of the hydrogen storage electrode, which is the negative electrode, are such as the discharge capacity at high temperatures. The effect on the battery performance is significant, and the development of a hydrogen storage alloy having excellent high-temperature characteristics has been desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to provide a hydrogen storage electrode which has excellent high-temperature characteristics and can constitute a long-life nickel-hydrogen battery. .

[0006]

Hydrogen storage electrodes of the invention In order to achieve the object] That this application is characterized by having at least a portion of the hydrogen storage alloy phase expressed by _{LmNi x Al y Co z Fe u} .

[0007]

[0008]

[0009]

[0010]

Here, Lm is a mixture of rare earth elements,
La in the mixture of rare earth elements is preferably set to 40 wt% or more. If La is less than 40 wt%, the discharge capacity of the obtained hydrogen storage electrode at high temperatures becomes insufficient, and La becomes
If the content is 40 wt% or more, there is no decrease in discharge capacity at high temperatures.

Further, in the hydrogen storage electrode of the invention of the present application, 3.5 ≦ x ≦ 4.5, 0.05 ≦ y ≦ 0.9, 0.1 ≦ z +
It is preferable that u ≦ 1.5 and 4.5 ≦ x + y + z + u ≦ 5.5.
If x is less than 3.5, the discharge voltage decreases, and if it exceeds 4.5, the ratio of y + z decreases, so that the effect of adding Al and Co cannot be obtained.

When y is less than 0.05, the lattice spacing in the crystal structure of the obtained hydrogen storage alloy becomes small, and the hydrogen storage rate decreases and the charging rate decreases. Conversely, if it exceeds 0.9, the lattice spacing of the crystal structure is excessively enlarged, the equilibrium dissociation pressure is reduced, and the hydrogen storage amount is reduced.

If z + u is less than 0.1, C contained in the alloy composition
Insufficient amount of o, increase of La amount and substitution of Al
The life of the obtained hydrogen storage alloy is reduced. Conversely z
When + u exceeds 1.5, the contents of Co and Fe in the obtained alloy become excessive, and the contents of other components, particularly Ni and Al, are relatively suppressed, resulting in an adverse effect such as a decrease in discharge capacity. Not preferred. Outside the range of 4.5 ≦ x + y + z ≦ 5.5, the stoichiometric ratio of the intermetallic compound having the AB ₅ structure is not preferable.

[0015]

The hydrogen storage electrode has a characteristic that the discharge capacity decreases at high temperatures. This phenomenon is related to the crystal structure of the hydrogen storage alloy, and the hydrogen storage alloy having a large lattice spacing in the crystal structure tends to have a high charging efficiency due to a high storage rate. Also, since the equilibrium dissociation pressure of the hydrogen storage alloy tends to decrease as the lattice spacing in the crystal structure increases, this equilibrium dissociation pressure can be used as an index for the degree of discharge capacity reduction.

It is generally known that the addition of Al is effective for increasing the crystal lattice spacing of an alloy. However, the addition of Al increases the lattice spacing and lowers the equilibrium dissociation pressure. Conversely, a decrease in the amount of hydrogen absorbed is seen. Therefore, the amount of Al substitution is limited, and 0.05 ≦ y ≦ 0.9.
Is appropriate. On the other hand, increasing the amount of La in Mm (misch metal) which corresponds to the A of the AB ₅ form hydrogen storage alloy, the absolute amount of total hydrogen Kanetsu Mm (△ H) for decreases, the overall hydrogen storage alloy The average dissociation pressure drops. Also, L
When the amount a is increased, the occlusion amount is also increased. Therefore,
Increasing the amount of La in Mm of MmNi _5, a part of Ni by appropriate amount replaced by Al, it is possible to lower the equilibrium dissociation pressure without decreasing the storage amount.

However, since both elements, Al and La, have an equilibrium potential lower than the hydrogen potential in the alkaline electrolyte, they also have the effect of promoting the corrosion of the alloy. Therefore, Al is added as described above. When the amount of La is increased, the obtained hydrogen storage alloy tends to corrode. When such an alloy having low corrosion resistance is used as an electrode, there is a problem that the life of the electrode is shortened due to the progress of corrosion in the use process.

However, the present inventors have found that C in the hydrogen storage alloy.
It was found that when o was included, the deterioration of the electrode characteristics due to the progress of corrosion was suppressed, and the effect of Co, which suppresses the deterioration of the electrode characteristics, was also clarified. It is known that the deterioration of the characteristics of the hydrogen-absorbing alloy electrode accompanying the progress of corrosion is due to corrosion products being interposed between the particles and lowering the conductivity of the alloy powder. On the other hand, the oxidation-reduction potential of Co and the charge / discharge potential region of the hydrogen storage electrode overlap, and the Co (II) complex ion generated by the corrosion of the alloy is reduced to Co metal at the charge potential of the hydrogen storage electrode. Form a conductive network. Therefore, in the alloy containing Co, it is confirmed that the conductivity between the alloy particles is compensated by the formation of such a conductive network as shown in FIG.

The corrosion mode of the alloy containing Co is Co
There is a large difference from the alloy containing no. Since this difference is observed even when Co powder is mixed with the alloy powder and added, it is considered that this difference in the corrosion form is caused by the precipitated Co or the Co complex ion eluted during the discharge.

Further, when the amount of hydrogen occluded in the electrode after charging and after discharging was measured, it was found that deep discharge was possible with an alloy containing Co as shown in FIG.
It is known that Co has excellent catalytic activity for hydrogen ionization reaction, and such a depth of discharge is considered to be a phenomenon caused by the catalytic action of the Co layer deposited on the alloy surface. .

As described above, by including Co in the alloy composition, the life is not shortened even when the amount of La is increased or Al is replaced, and the electrode can be maintained as a high-performance electrode. Further, when a part of Co other than Co is replaced by an appropriate amount of Fe element, the initial activation of the electrode is prompt, the flatness of the plateau is improved, and the corrosion resistance is improved. You can do it.

That is, an alloy containing Co generally forms a dense oxide film on the surface in air. Therefore, when an alloy material on which such a passive oxide film is formed is used for an electrode, it is necessary to repeat several cycles of charging and discharging to activate the electrode before use, or to perform alloying before manufacturing the electrode. It is necessary to take measures such as an operation of removing the surface film by etching the powder with an acid or an alkali or an inert atmosphere in all the electrode manufacturing steps.

In order to solve such problems caused by the addition of Co, changes in the initial capacity of the electrode due to various alloy compositions were examined. As shown in FIG.
It was found that when e was included, stable electrode characteristics could be obtained from the beginning, and the above-described various operations and countermeasures were not required at all. This is thought to be because Fe, which has an equilibrium potential slightly lower than the reversible hydrogen potential, elutes at the electrode in the open or discharging state, so that the above-mentioned passive oxide film may be easily destroyed. Further, the Fe complex ions eluted from the alloy in this way are reduced to metal at the time of charging similarly to Co, forming a conductive network.
e, the depth of discharge of the electrode also obtained by the conductive network forming action becomes deep, so that a part of Co
Even if it is replaced by e or the like, there is no adverse effect on the improvement of the properties of the hydrogen storage alloy by the addition of Co.

[0024]

Embodiments of the present invention will be described below. Example 1 A component element weighed to a target composition was put into a crucible, melted using a high-frequency melting furnace, cooled, and mechanically pulverized to obtain a hydrogen storage alloy powder sample. PVA is added to this powder
An aqueous solution of (polyvinyl alcohol) was added to form a paste, filled in a nickel fiber substrate, dried and pressed to form a hydrogen storage electrode. This hydrogen storage electrode was used as a negative electrode, and a pasted nickel electrode using a known high-density cadmium-less nickel hydroxide active material was used as a positive electrode to constitute an AA-size sealed nickel-hydrogen battery with a nominal capacity of 1100 mAH.

The battery capacity of this nickel-hydrogen battery,
Various characteristics such as battery life and discharge voltage were evaluated. Table 2
This shows the battery capacity at 45 ° C. assuming that the battery capacity at 0 ° C. is 100%. The compositions A to D of the examples of the present invention containing 60 wt% of La in Lm show little decrease in capacity even at 45 ° C., whereas La in Mm
It can be seen that in the comparative example in which the content is 29 wt%, the capacity is reduced by nearly 50%.

[0026]

[Table 1] Charge: 0.3C, 150% Discharge: 0.2C Final voltage 1.0V Lm: La = 60wt% in Lm Mm: La = 29wt% in Mm

FIG. 4 shows the result of examining how the battery capacity at 45 ° C. changes depending on the amount of La in Lm. It can be seen that when the La content is 30 wt% or more, the capacity reduction at 45 ° C. is suppressed, and when the La content is 40 wt% or more, the capacity reduction is almost prevented.

Table 2 shows the results of examining how the life of the battery changes depending on the alloy composition. Although the sample A and the sample B of the example containing Co have almost no change in the battery capacity, even if the alloy composition using Lm excellent in the high-temperature characteristics, the comparative example 2 of the composition not containing Co, In the sample of Comparative Example 3 using Mm and containing no Co, the battery capacity was extremely reduced, and it was found that the battery life was shortened due to the progress of alloy corrosion.

[0029]

[Table 2] Charge: 0.5 C, 150% Discharge: 1.0 C Final voltage 1.0 V C ₄₀₀ / C ₁₀ : Ratio of 400th cycle capacity to 10th cycle capacity Lm: La ≧ 40 wt% in Lm Mm: La = 29 wt% in Mm

When the battery of the comparative example after the above-mentioned characteristic test was disassembled and examined, a large amount of a hydroxide of a rare earth element constituting Mm was formed on the surface of the negative electrode, and the conductivity of the alloy powder also decreased. Was. On the other hand, in the battery using the hydrogen storage electrode according to the example of the present invention, there was no significant change from the initial state, and it was confirmed that the battery could endure a long cycle.

Example 2 A component element weighed to a desired composition was put into a crucible, melted using a high-frequency melting furnace, cooled, and then mechanically pulverized to obtain LmNi as a composition A in an example of the present invention.
_3.7 Al _0.3 Co _0.7 Fe _0.3 , MmNi _3.9 Al _0.3 Co _0.8 as Comparative Example B, and LmNi _3.6 Al _0.9 Mn _0.2 as Comparative Example C. An alloy powder sample was obtained. The La content in Lm was 60 wt%, and the La content in Mm was 29 wt%. An aqueous solution of PVA (polyvinyl alcohol) was added to the powder to form a paste. The paste was filled in a nickel fiber substrate, dried and pressed to form a hydrogen storage electrode.

The hydrogen storage electrode was used as a negative electrode, the paste type nickel electrode using a known high-density cadmium-less nickel hydroxide active material was used as a positive electrode, and an AA having a nominal capacity of 1100 mAH was used.
A sealed nickel-hydrogen battery was constructed. Various characteristics such as battery capacity, battery life, and discharge voltage of this nickel-hydrogen battery were evaluated.

FIG. 5 shows that the battery capacity at 20 ° C. is 100%.
The battery capacity at 45 ° C. is shown. It can be seen that the capacity of the battery of Example A using the composition of the invention of this application hardly decreased even at 45 ° C. Table 3
The results of examining the change in battery capacity with respect to the charge-discharge cycle are shown in FIG. In the battery using Comparative Example C, even if the alloy composition used Lm, which has excellent high-temperature characteristics, the battery life was reduced because the composition did not contain Co and Fe.

[0034]

[Table 3] Charging: 0.5 C, 0.99% discharge: 1.0 C end voltage 1.0V C ₄₀₀ / C _{10: 400} cycle capacity and 10th cycle ratio of capacity

When the battery of Comparative Example C was disassembled and examined, a large amount of the hydroxide of the rare earth element constituting Lm was formed on the surface of the negative electrode, and the conductivity of the alloy powder was also reduced. On the other hand, in the battery using the hydrogen storage electrode of Example A in which the invention of the present application was implemented, no significant change was observed from the initial state, and it was confirmed that the battery could withstand a long-term cycle.

FIG. 6 shows the results of examining the discharge voltages of the batteries of Example A, Comparative Example B, and Comparative Example C. As shown in the figure, it can be seen that the battery A of the example of the present invention has a high discharge voltage. Inspection by a current interrupter revealed that the electrode A of this example had smaller polarizations than the resistance overvoltage such as the activation overvoltage as compared with the comparative examples B and C. For this reason, in the electrode A of the embodiment, Co
It can be seen that the discharge reaction was smoothly performed by including Fe and Fe in the alloy composition.

In each of the above embodiments, a paste-type nickel electrode using high-density cadmium-less nickel hydroxide powder was used for the positive electrode. However, the present invention is not limited to this. A paste-type nickel electrode using nickel oxide powder may be used. Further, although a nickel fiber substrate was used as the substrate for the hydrogen storage electrode and the positive electrode, the invention is not limited to this, and expanded metal, foamed nickel, nickel-plated punching metal, or the like may be used.

[0038]

Represented by LmNi _x Al _y Co _z Fe _u According to the hydrogen absorbing electrode of the invention of this application as described above, according to the present invention
Having at least a portion of a hydrogen storage alloy phase, represented by Lm
La in the mixture of rare earth elements is 40 wt% or more, and
In order to contain Al in the range of 0.05 ≦ y ≦ 0.9 in component ratio
And the elements of Co and Fe in a component ratio of 0.1 ≦ z + u
≤ 1.5, this water
Batteries composed of elemental occlusion electrodes have a low cycle life, etc.
High temperature properties without lowering
In addition, complicated operations and measures must be taken to activate the battery.
It is activated immediately without taking any action, and the discharge voltage is high.
There is an effect that it can be a pond.

[0039]

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in conductivity of an alloy powder due to Co addition. FIG. 2 is a diagram showing the depth of discharge of an electrode. FIG. 3 is a diagram showing the relationship between various alloy compositions and discharge capacity. FIG. 4 is a diagram showing the relationship between the amount of La in Lm and the discharge capacity. FIG. 5 is a diagram showing the relationship between temperature and discharge capacity. 6 is a diagram showing the discharge voltage of the batteries of Examples and Comparative Examples.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masahiko Oshitani 6-6 Josai-cho, Takatsuki-shi, Osaka Yuasa Battery Co., Ltd. (56) References JP-A-60-250558 (JP, A) JP-A-62- 264557 (JP, A) JP-A-4-293746 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/38

Claims (1)

(57) [Claims] 1. A LmNi _x Al _y Co _z Fe hydrogen storage electrode, characterized in that it comprises at least a portion of the hydrogen storage alloy phase expressed by _u (Lm: a mixture of rare earth elements,
Of these, La ≧ 40 wt%, 3.5 ≦ x ≦ 4.5, 0.05 ≦ y ≦ 0.9, 0.
1 ≦ z + u ≦ 1.5, 4.5 ≦ x + y + z + u ≦ 5.5).