JPH0562429B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a sealed alkaline storage battery using a hydrogen storage alloy that electrochemically absorbs and releases hydrogen or a hydride thereof as a negative electrode. BACKGROUND OF THE INVENTION There are various types of secondary batteries, among which lead-acid batteries and nickel-cadmium batteries are the most widely known. However, since these batteries contain a solid active material in the negative electrode, their energy storage capacity per unit of weight or capacity is relatively low. In order to improve this energy storage capacity, storage batteries have been proposed that use a hydrogen storage alloy as the negative electrode and, for example, nickel oxide as the positive electrode (U.S. Patent No.
3874928 specification). This battery system has a higher capacity than nickel-cadmium storage batteries, and is expected to be a low-pollution storage battery. Problems to be Solved by the Invention Among the above-mentioned conventional technologies, batteries using LaNi ₅ alloy as a negative electrode have a problem of short cycle life. Furthermore, since La, which is a constituent metal of the alloy, is expensive, the cost of the electrode itself is inevitably high. Further, an electrode composition improved from this LaNi ₅ alloy has also been proposed (for example, in Japanese Patent Application Laid-Open No. 13934/1983). That is, a part of La was replaced with a rare earth metal.
LnNi ₅ and LnCo ₅ series are used to reduce costs, but sealed batteries have problems such as low capacity, especially high-temperature capacity, and shortened high-temperature cycle life, making them difficult to use as practical batteries. do not have. The present invention solves the above problems.
Provides a sealed alkaline storage battery whose negative electrode is constructed using relatively inexpensive materials, has a large discharge capacity, has a long charge/discharge cycle life at high temperatures of around 45°C, and has little increase in internal pressure due to gas generated during overcharging. The purpose is to Means for Solving the Problems As a result of various studies, the present invention has been developed based on the general formula Mm _1-x A _x
Niα _-y Coy−zMz (However, Mm is Mitsushi Metal,
A is Nb, Ta, which is an element with negative heat of hydride formation.
At least one member selected from the group consisting of V, Rb and Ba, and M is Mn, Mo, Cr, Sn, Si, Tl,
At least one selected from the group consisting of Sb, Bi, Al, Zn, Cu, Fe, In and Ga, and 0<x<
0.4, 4.5 < α < 5.5, 0 < y < 3, 0 < z < 1), a negative electrode made of a hydrogen storage alloy or its hydride, a positive electrode, a separator, and an alkaline electrolyte held therein. It is characterized by being configured as a sealed alkaline storage battery. Effect There is _a deep relationship between the heat of hydride formation (heat of hydrogen dissolution) of the hydrogen storage alloy itself and the hydrogen equilibrium dissociation pressure. The dissociation pressure decreases, and if it decreases too much as in the case of single metals, the alloy and hydrogen will form a very stable hydride, making it impossible to obtain excellent electrode performance. Therefore, in order to create the optimal intermetallic compound, we have developed a single metal with positive heat of hydride formation (endothermic melting type metal) and a negative metal with negative heat of hydride formation (exothermic melting type metal).
By alloying in combination with these, a hydrogen storage alloy with excellent performance can be obtained. For example, positive metals include Cr, Mo, Fe,
There are Mn, Pd, Pt, Ni, Ag, Cu, etc., and negative metals include V, Ta, Nb, Zr, Tl, La, Ce,
There are Sr, Ba, Rb, etc. Here, if we focus on a mixture of La, Ce, Nd, etc. (Mitsushi Metal), which is a particularly inexpensive material, and construct a battery using a well-known method, the high-temperature capacity will be small and the cycle life will be short. This is because rare earth elements themselves are chemically unstable. Therefore, when the same heat of hydride formation as these elements dissolves an element with negative properties, the two often replace each other, creating a stable compound, and at the same time, it also dissolves well with metals whose heat of hydride formation is positive. In this way, the metals dissolve into each other homogeneously, and moreover, the corrosion resistance is stronger than that of rare earth alone, and the ability to lower the hydrogen equilibrium dissociation pressure and absorb and release hydrogen is also improved. Therefore, when this is used as a negative electrode in a battery, it is possible to particularly increase high-temperature capacity and cycle life. Examples Commercially available La (purity 99% or more), Mm (Mitsushi Metal: La content 30% by weight, Ce content 50% by weight, Nd
(Content: 15% by weight, Pr and other contents: 5% by weight)
At least one metal selected from the group consisting of lanthanoid group metals such as Ca (purity of 95% or more), and Zr, Hf, Th, Nb, Ta, etc. of purity of 99% or more.
At least one metal selected from the group consisting of V, Rb, and Ba, Ni, Co, and Mn, Mo, Cr, Sn,
Si, Tl, Sb, Bi, Al, Zn, Cu, Fe, In and Ga
Select at least one selected from the group consisting of;
Each sample was weighed to a certain composition ratio and heated and melted in a high frequency melting furnace. Then, in order to homogenize the sample, high-temperature heat treatment was performed to obtain an alloy sample. In addition, hydrogenated alloy powder was also used if necessary. For comparison, LaNi ₅ , LaCo ₅ , MmNi ₅ ,
MmCo ₅ , LaNi _4.8 Al _0.2 , MmNi _4.8 Al _0.2 alloys, etc. were also prepared. After coarsely grinding these alloys, use a ball mill etc.
After making it into a fine powder of 38 μm or less, it was mixed with a polyvinyl alcohol resin solution having a concentration of 1% by weight. This paste-like alloy was applied to punching metal, and after drying, the leads were attached to serve as electrodes. The alloy composition of the electrodes used in the examples is shown in the table. Approximately 15 g of each alloy or its hydride was used as a negative electrode, and a known sintered nickel electrode was used as a positive electrode.
A hydrogen storage battery (nominal capacity 1.8Ah) was constructed. In addition, the negative electrode capacity of the battery was made larger than the positive electrode capacity so that the positive electrode rule was met. These batteries were charged at 0.2C for 7 hours and discharged at 0.2C repeatedly to examine cycle life and leakage from the batteries. The test temperature was 45°C in all cases. The results are shown in the table below. Electrodes No. 1 to 19 are comparative examples, and electrodes No. 20 to 43 are
shows an example of the present invention.

【table】

【table】

[Table] *In the table, samples are made into alloy hydrides.As is clear from the table, LaNi ₅ , LaCo ₅ , MmNi ₅ ,
A battery using MmCo ₅ electrodes 1, 2, 3, and 4 is
The capacity at the beginning of the charge/discharge cycle is small. The capacity of a battery using electrode 1 increases as the number of cycles increases, but after 20 to 30 cycles, the discharge capacity decreases significantly, reaching about 1/3 of the initial capacity, and at the same time, oxygen gas is intensely generated in an overcharged state. However, the internal pressure of the battery also rises to over 10 kg/cm ² . Furthermore, the battery using electrode 3 had a degraded performance after 20 cycles without being able to reach the rated capacity of 1.8Ah. This is thought to be because the hydrogen equilibrium dissociation pressure of the alloy is as high as 20 kg/cm ² or more at 45°C, making charging difficult. Further, the hydrogen storage capacity of electrodes 2 and 3 is less than half that of electrode 1, and therefore the discharge capacity is also small. As an improved version, electrodes 5 and 6 in which part of Ni is replaced with Al are
Although the battery life has improved to 50 to 60 cycles, the battery capacity has decreased due to leakage due to the increase in battery internal pressure. Electrode 7 in which part of Mm is replaced with La also has poor effects. Therefore, some of the Ni was replaced with other metals such as Co.
As a result of trying to replace it with , since it has the effect of lowering the equilibrium pressure, the improvement was improved to 60 to 70 cycles as shown in electrodes 8 and 9, but there was no significant improvement. Next, a Lnl-xAxNiα-yCoy alloy in which Zr, Hf, Ta, Nb, V, Th, etc. are added as A to a part of the lanthanide group metal mixture Ln, and an alloy in which some other metals are added to Co. Electrode 10 using
17 was prepared, but the cycle life could only be improved up to a maximum of 80 cycles. Among these, the electrode 10,
In No. 11, the value of α is larger than 5.5, the hydrogen equilibrium dissociation pressure is large, and it is considered that the performance deteriorates due to an increase in the internal pressure of the battery. The electrodes 13, 16, and 17 have a y value of 3 or more, have a small capacity due to a decrease in hydrogen storage capacity, and are subject to the negative electrode rule. Moreover, the gas pressure inside the battery increases during overcharging, preventing electrolyte leakage. This is thought to have caused the capacity to drop. The electrodes 14 and 15 have an x value of 0.4 or more, and when this value becomes 0.4 or more, the hydrogen storage capacity decreases significantly, and gas absorption during overcharging becomes difficult, causing the gas pressure inside the battery to increase. , electrolyte leaks and capacity decreases.
In this way, even if A is added to Ln, the value of α is
When it is less than 4.5, more than 5.5, or when the value of y is more than 3, and when the value of x is more than 0.4, it is due to a decrease in hydrogen storage capacity, high hydrogen equilibrium dissociation pressure, and gas absorption during overcharging. It is difficult to design an optimal battery system because various conditions such as an increase in gas pressure inside the battery cannot be balanced. Compared to these electrodes, some batteries equipped with electrodes 18 to 37 have lower initial characteristics, but
Even after 160 cycles, all have a nominal capacity of 1.8Ah. Furthermore, although the internal pressure of the battery was not measured, almost no electrolyte leakage from the battery was observed. If the amount of substitution of Ln with A is in the range 0<x<0.4, Ln
While ensuring the catalytic function and hydrogen storage capacity important for gas absorption, Zr, Hf, and
By adding any of Th, Nb, Ta, V, Rb, and Ba, it was possible to extend the cycle life. Among these, the range of substitution amount of 0.01<x≦0.2 is particularly excellent. When A is made larger than 0.4 and added to Ln,
This leads to loss of Ln function and capacity reduction. Also, if you do not include A at all, the effect will not appear. Therefore A
The effect becomes large when is replaced in the range of 0.01 to 0.4. An increase in the value of α related to the amount of Ni increases the hydrogen equilibrium dissociation pressure and deteriorates the flatness, resulting in a decrease in the hydrogen storage capacity, so the range of 4.5<α<5.5 is optimal. Therefore, the amount of substitution y is largely related to the remaining amount of Ni, and if the amount of Ni is small, the hydrogen absorption and release reaction rate on the electrode surface decreases, the electrode reaction does not occur smoothly, and the discharge voltage becomes low. From this, 0<y
A range of <3 is excellent. In particular, the range of 0.2<y≦2 exhibits the best battery performance. It can be seen that the electrodes marked with * in the table are examples using alloy hydrides, and have excellent cycle life. On the other hand, electrodes 32, 33, 34 with a z value of 0
It was also found that the cycle life was long due to the effect of A substitution for Ln and the optimal range conditions for Ni and Co. In batteries using such electrodes, the internal pressure of the battery increases because the oxygen gas generated from the positive electrode during overcharging electrochemically reacts with the hydrogen contained in the negative electrode on the surface of the negative electrode and is converted into water. increase is small.
Moreover, the structure is such that only hydrogen and oxygen act preferentially on the surface of the negative electrode. Furthermore, since the alloy negative electrode is durable and is not corroded by oxygen, it is possible to manufacture a battery with a long cycle life especially at high temperatures. In addition, in the examples, lanthanum (La) in Ln has a great influence on battery characteristics, but if the amount of La is too large, the battery performance and cost will increase due to a decrease in corrosion resistance. On the other hand, if the amount of La is too small, corrosion resistance is excellent, but there is a problem of increased pressure inside the battery. Therefore, from the viewpoint of cost performance, the amount of La contained in Ln is 30 to 70.
% by weight is optimal. Further, the equilibrium dissociation pressure in the examples is in the range of 0.1 to 5 atm at a temperature of 45°C, which is excellent in terms of high temperature capacity and high temperature cycle life. If this pressure is high, there will be a problem of charging efficiency and battery internal pressure will increase, and if it is low, there will be a problem of low discharge voltage, so the above range can be said to be optimal. Effects of the Invention As described above, the present invention provides a sealed alkaline storage battery that has a relatively large high-temperature capacity, has an excellent charge-discharge cycle life at high temperatures, and suppresses increases in internal gas pressure due to overcharging. can get.

Claims (1)

[Claims] 1 A sealed alkaline storage battery having a positive electrode, a negative electrode, a separator, and an alkaline electrolyte held therein, wherein the negative electrode has the general formula Mm _1-x A _x
Ni〓 _-g Co _yz M _z (However, Mm is at least La, Ce,
A is a mixture of metals containing Nd and three or more metals selected from the group consisting of Ca, and A is Zr, Hf, Nb,
At least one selected from the group consisting of Ta, V, Rb, Ba, Ti and Th, and M is Mn, Mo, Cr,
At least one selected from the group consisting of Sn, Si, Tl, Sb, Bi, Al, Zn, Cu and Fe, and 0<X
<0.4, 4.5<α<5.5, 0<y<3),
The amount of La contained in Mm is 40 to 70% by weight,
Hydrogen storage dissociation pressure is 0.1~ at 45℃ temperature
A sealed alkaline storage battery made of a hydrogen storage alloy or its hydride in the range of 5 atm.