JPH0642368B2 - Alkaline storage battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alkaline storage battery using a hydrogen storage alloy that electrochemically stores and releases hydrogen as a negative electrode.

(Prior Art) Lead storage batteries and nickel-cadmium storage batteries are the most widely known as secondary batteries. However, since these storage batteries contain a solid active material in the negative electrode, the weight or capacity per unit Relatively low energy storage capacity. In order to improve this energy storage capacity, a storage battery has been proposed in which a hydrogen storage alloy is used as the negative electrode and nickel oxide is used as the positive electrode (USP 3,874,928). Here, the battery using LaNi ₅ alloy as the negative electrode has a short charge / discharge cycle life. In addition, since La (lanthanum) which is a constituent metal of the alloy is expensive, the cost of the electrode itself is naturally high.

An electrode composition obtained by improving this LaNi ₅ alloy negative electrode has also been proposed (JP-A-51-13934). LnNi ₅ and LnCo ₅ system in which a part of La is replaced with a rare earth metal is used for cost reduction, but the discharge capacity when an alkaline storage battery is constructed is small and the cycle life is short, so it is a practical battery. I can't say. On the other hand, a hydrogen storage material (Japanese Patent Application Laid-Open No. 57-19347).
No.) as an alloy consisting of four kinds of metals of MmNi _5-X A _XY B _Y (however, A and B are each one of Al, Cu, Mn, Co and Si, X = 0.1 ~
2, Y = 0.01 to 1.99) has been proposed. Here, Mm (Misch metal) is a material that is generally commercially available at a low price,
Its composition is La (lanthanum) 25-35 wt%, Ce (cerium) 40-50 wt%, Pr (praseodymium) 1-1.
5% by weight, Nd (neodymium) 4 to 15% by weight, other rare earths 1 to 7% by weight, Fe (iron) 0.1 to 5% by weight, other Si
(Silicon), Mg (Magnesium), Al (Aluminum) 0.
1 to 5% by weight) is a general term for a rare earth mixture composed of such as. And it is considered as a kind of metal for the following reasons. This is a natural ratio of C in monazite.
It refers to the metal obtained by reducing the crude chloride of a mixture of e, La, Nd, and other light rare earths by the usual electrolytic method. Therefore, a composition having a certain degree can be manufactured at low cost. However, when the alloy consisting of these four metals is used as a negative electrode for alkaline storage batteries, the discharge capacity per unit weight is not always large, unlike when handled in a gaseous state. is necessary.

(Problems to be Solved by the Invention) When the above alloy system is used for an electrode of an alkaline storage battery, LaNi ₅ is expensive and has a short cycle life. Although MmNi ₅ is inexpensive, it has a high hydrogen dissociation pressure (20 ° C., about 15 atm), and it is difficult to occlude hydrogen electrochemically. MmCo _{5, which} has been made easier to absorb hydrogen by lowering the hydrogen dissociation pressure, has a discharge capacity per unit weight reduced to 50% or less and is not practical. Therefore, as mentioned above, a hydrogen storage material composed of MmNi _5-X A _XY B _Y has been proposed, but even if the alloy composed of these four metals is used for the negative electrode of an alkaline storage battery, Unlike the case of handling in a gaseous state capable of storing, when the amount of Ni is large, hydrogen is not stored at the time of charging, and when the amount of metals A and B is large, the hydrogen storage amount becomes small. Not necessarily applicable to battery electrodes. This alloy of four kinds of metals is made into an alloy of five kinds of metals, and M ₁ and M ₂
The optimum metal was selected, and many experiments were repeated to determine the optimum composition for the battery electrode.

In view of the above problems, the present invention is to provide an alkaline storage battery having a large discharge capacity and a long cycle life by forming a negative electrode using a relatively inexpensive alloy material.

That is, in the present invention, particularly paying attention to Ni that increases the discharge capacity, not reducing the discharge capacity, also paying attention to metal La that lowers the hydrogen dissociation pressure so that hydrogen is easily stored in the negative electrode by charging, and a synergistic effect of both And M ₁ (Fe, Cu, Cr) and M ₂ (Si, A
The problem is solved by l).

(Means for Solving Problems) The present invention relates to an alkaline storage battery having a negative electrode, a positive electrode, a separator and an alkaline electrolyte, wherein the negative electrode has the formula Mm _1-X La _X Ni.
_Y (M ₁ · M ₂ ) _Z (However, the total amount of La represented by La / Mm + La is 35
% By weight, 0.08 <X <0.5, 3.5 <Y ≦ 4.3, 0.7 ≦ Z ≦ 1.
7,4.5 <Y + Z <5.5, M ₁ is 1 type from Fe, Cu, Cr, M ₂ is Si, A
Select one type from l, 0.1 ≤ Al ≤ 0.5, 0.1 for various metals
≦ Si ≦ 0.5, 0.2 ≦ Fe ≦ 0.8, 0.2 ≦ Cu ≦ 1.0, 0.2 ≦ Cr ≦ 0.8)
It is characterized in that it is made of a hydrogen storage alloy or hydride composed of five kinds of metals represented by

The composition of Mm (Misch metal) regarded as one metal here is roughly La: 25 to 35% by weight, Ce: 40 to 50% by weight, Nd: 5 to 15% by weight, Pr: 2 to 10% by weight, and others. Rare earth metals: 1-5% by weight, other metals (Fe, Mg, Si, A
l, etc.) 0.1 to 10% by weight.

(Function) Since La (lanthanum) is expensive, it is possible to use Mm, which is commercially available at low cost, as a main component to reduce the cost of the alloy material. However, when Mm is used, hydrogen dissociation is achieved compared to La. The pressure rises significantly. Therefore, even if MmNi ₅ is used for the battery negative electrode, it is difficult to store hydrogen during charging. After all, since it cannot be charged, its discharge capacity is also small. Therefore, in the present invention, the amount of Ni stored is improved by adjusting the amount of Ni, and M ₁ (Fe, Cu, C
r) The amount of hydrogen improves the charging efficiency of hydrogen, and M ₂ (Al, Si) has the function of significantly lowering the hydrogen dissociation pressure. When used in a sealed alkaline storage battery, it suppresses the rise in battery internal pressure. Moreover, by substituting 1 part La for Mm alone, the increase in hydrogen dissociation pressure can be further suppressed, the discharge capacity can be improved, and the cycle life can be extended.

(Example) Various samples made of five kinds of commercially available Mm, La, Ni, M ₁ (Fe, Cu, Cr) and M ₂ (Al, Si) were weighed and mixed so as to have a predetermined composition. Then, it was heated and melted using a high-frequency melting furnace by induction heating.

The Mm mentioned here is a mixture of commercially available inexpensive rare earth metals having a generally constant composition, and the composition is La:
25-35 wt%, Ce: 40-50 wt%, Nd: 5-1
5% by weight, Pr: 2-10% by weight, other rare earth metals 1-
5% by weight and 0.1-10% by weight of other metals.

After roughly crushing these various alloys, 38μ with a ball mill etc.
After being made into a fine powder of m or less, it is well mixed with a PVA (polyvinyl alcohol) resin solution (about 1% by weight), and the paste-like alloy is filled in a foamed nickel porous body and then pressurized. Then, it was made to dry and the lead was attached and it was set as the electrode. Although an alloy is used here, it may be used as a hydride. To investigate the capacity (Ah / g) of these electrodes, the following batteries were made.

The size of the electrode was 30 mm × 40 mm and the thickness was 1.2 mm. The hydrogen storage alloys used were 6 g each, and a negative electrode regulation battery was constructed so that the negative electrode capacity could be measured. The positive electrode is about 1.2A
Two publicly known sintered nickel electrode plates corresponding to h were used with the negative electrode sandwiched through a separator. 36 of these batteries
The battery was charged at 0 mA for 6 hours or more and discharged at 300 mA.
The measurement temperature was 45 ° C., and the discharge capacity per unit weight and the cycle life were compared. The results are shown in the figure. However, the capacity per unit weight is the result of measurement at 10 cycles, and the cycle life is the number of cycles when the capacity is reduced by about 20% from the initial capacity.

As shown in the figure, when the value of X becomes large, the capacity becomes high, but when the value of X becomes larger than 0.3, the capacity remains almost unchanged. Since the capacity is 45 ° C., it is about 30% lower than the capacity at 20 ° C. When there is no La, it is as low as about 0.12 Ah / g, and when the value of X reaches 0.08, the capacity rapidly increases, reaching at least a practical value of 0.2 Ah / g. Therefore, a value of X of 0.08 or more is excellent. Although it is the characteristic in the case of Cu as M ₁ , Cu, Fe, Cr, and Al as M ₂ , Cu, Fe, and Cu show almost the same tendency although there are some differences in capacitance. Especially, when the difference is made, the capacity is higher in the order of Cu>Fe> Cr.

On the other hand, when the value of X becomes large, the cycle life becomes long, but when the value of X becomes larger than 0.5, the cycle life becomes short conversely. Since the cycle life is 45 ° C., it is considered that the electrode having a large amount of La has a large expansion / contraction ratio, which leads to an increase in the resistance of the electrode itself and a decrease in the capacity due to a part of the alloy powder falling off. This tendency is the same as that of various metals.
Therefore, the value of X may be large from the viewpoint of the discharge capacity, but considering the cost of the electrode, the cycle life, etc.,
The optimum range is 0.08 <X <0.5. Even if the composition ratio of M ₁ and M ₂ is changed, this tendency is the same, but the value of Y is
When it is 3.5 or less, the discharge capacity is reduced due to the decrease in hydrogen storage amount, and when it is 4.31 or more, the hydrogen dissociation pressure becomes high, and electrochemical hydrogen storage (charging) becomes difficult.

The value of Z is also related to the composition of M ₁ and M ₂ , but if it is 0.69 or less, the effect of the added metal is not exerted, and the value of Y becomes large and the cycle life becomes short. Conversely, at 1.71 and above,
The value of Y becomes too small and the discharge capacity becomes small. Therefore, 0.7 ≦ Z ≦ 1.7 is said to be the optimum range.
On the other hand, in the metals of M ₁ and M ₂ , Fe, Cu and Cr are also related to the value of Z, and when 0.19 or less, when Z = 0.7, the addition effect is small and the cycle life is short, 0.81,1,1 Z =
At 1.7, the amount of added metal becomes too large, the discharge capacity decreases due to the decrease of Ni amount, and Y + Z becomes 5.5 or more, so that a homogeneous intermetallic compound is not formed and flatness during hydrogen storage is also obtained. Since it becomes worse, the discharge potential is lowered. Therefore, 0.2 ≦ Fe ≦ 0.8, 0.2 ≦ Cu ≦ 1.0, 0.2 ≦ Cr ≦ 0.8
The range of is desirable.

Al and Si are added to lower the hydrogen dissociation pressure to facilitate charging even at high temperature, but at 0.09 or less, the effect is hardly recognized. On the other hand, when it is 0.51 or more, when the Z value is 1.7, the addition amount becomes too large, and homogeneous dissolution becomes difficult,
Significantly reduce hydrogen storage. A decrease in the hydrogen storage amount causes a decrease in the electrochemical storage amount of hydrogen, which causes a reduction in the discharge capacity. Therefore, 0.1 ≦ Al ≦ 0.5 and 0.1 ≦ Si ≦ 0.5 are desirable ranges.

In this embodiment, a commercially available inexpensive Mm (La: containing 25 to 35 wt%)
In order to obtain a practically excellent alkaline storage battery, a suitable amount of La is added as a substitute in order to improve the battery characteristics, and the optimum range is determined by the synergistic effect of the Ni content and the M ₁ and M ₂ contents. You can

Here, the characteristics are compared from the viewpoint of the discharge capacity and the cycle life by using the open type alkaline storage battery, but the same can be said for the sealed type alkaline storage battery. For example LaNi ₅ ,
If a sealed alkaline storage battery in which the alloy used in this example is used as a negative electrode is configured as an improvement of MmNi _5, the cycle life is long, the rise in battery internal pressure is suppressed, and a highly safe battery can be obtained. However, it is desirable that the value of La / Mm + La is 35% by weight or more as the total amount of La. When the amount of La is small, the hydrogen dissociation pressure is high, and it becomes a region where charging is difficult, which is not preferable. At least 35% by weight of the total La amount is required.

(Effects of the Invention) As described above, according to the present invention, an alkaline storage battery having a large discharge capacity, a long cycle life, and a relatively low price can be obtained.

[Brief description of drawings]

As an example, the figure shows the relationship between the value of X and the capacity / cycle life when the negative electrode is Mm _1-X La _X Ni _3.8 (M ₁ · M ₂ ) _1.2 alloy.

Claims (2)

[Claims] 1. The formula Mm _1-X La _X Ni _Y (M ₁ .M ₂ ).
_Z (however, the total La amount represented by La / Mm + La is 35
% By weight, 0.08 <X <0.5, 3.5 <Y ≦ 4.3, 0.7 ≦ Z ≦ 1.
7,4.5 <Y + Z <5.5, M ₁ is ₁ from Fe, Cu, Cr
Species, M ₂ is selected from Si and Al, and various metals are 0.1 ≦ Al ≦ 0.5, 0.1 ≦ Si ≦ 0.5, 0.2 ≦ Fe ≦ 0.8, 0.2
It is within the range of ≤ Cu ≤ 1.0 and 0.2 ≤ Cr ≤ 0.8. ) An alkaline storage battery having a negative electrode, a positive electrode, a separator, and an alkaline electrolyte, which are made of a hydrogen storage alloy or hydride made of five metals represented by the formula (1). 2. In the above formula, Mm (Misch metal)
The composition of La: 25 to 35 wt%, Ce: 40 to 50 wt%, Nd: 5 to 15 wt%, Pr: 2 to 10 wt%, other rare earth metal 1 to 5 wt%, other metal 0.1 to 10 wt% % Hydrogen storage alloy as negative electrode. Claim (1)
The alkaline storage battery according to the item.