JPH0459375B2 - - 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 as a negative electrode, and particularly relates to an improvement of the negative electrode. Conventional technology Lead-acid batteries and nickel-cadmium storage batteries are the most widely known secondary batteries of this type, but because these batteries contain a solid active material in the negative electrode, their weight or volume is small. The energy storage capacity per unit of is relatively low. In order to improve this energy storage capacity, a storage battery using a hydrogen storage alloy as a negative electrode and, for example, nickel oxide as a positive electrode has been proposed (US Pat. No. 3,874,928). This battery system has higher capacity than nickel-cadmium storage batteries and is expected to be a low-pollution storage battery. However, as a typical example of such a hydrogen storage alloy,
Batteries using LaNi ₅ alloy as a negative electrode have a problem of short cycle life. Furthermore, since lanthanum (La), the main constituent metal of the alloy, is expensive, the cost of the electrode itself is naturally high. Therefore, an electrode composition has been proposed that improves this LaNi ₅ alloy negative electrode and lowers the cost (Japanese Patent Laid-Open Publication No. 13934/1983). That is, La _1-x Mm _x Ni ₅ , La _1-x MmCo ₅ where part or all of La is replaced with Mitsushi metal (Mm)
This is a battery using a (O<x≦1) system. but,
These batteries have a problem in that their high rate discharge characteristics are poor, and in particular, their high rate discharge voltage is low due to low temperatures. Problems to be Solved by the Invention In a sealed storage battery using a La _1-x Mm _x Ni ₅ (O<x≦1) alloy as the negative electrode, an increase in battery internal pressure is observed with overcharging cycles. , the cycle life is shortened as well as the discharge capacity is reduced. Also La _1-x Mm _x
Ni ₅ (O<x≦1) alloys have problems such as a low high rate discharge voltage, and cannot be said to be a practical battery. There are still many technical issues, particularly in terms of discharge capacity at high temperatures and high rate discharge characteristics at low temperatures. In view of the above-mentioned problems, the present invention has been developed by constructing the negative electrode using a relatively inexpensive material.
℃), the discharge capacity is large at low temperatures (0℃)
The purpose of the present invention is to obtain a sealed alkaline storage battery that has excellent high-rate discharge characteristics and has a long charge/discharge cycle life. Means for solving the problem In order to solve this problem, the present invention uses the formula LnNi _x
(Cu _a・Mn _b・Al _c ) _Y [However, Ln is Mm alone or a mixture of Mm and La, the amount of La in Ln is 25 to 60% by weight, 3.5<x<4.3, Y=1.0, 0.2 ＜a＜1.2,
5 expressed as 0.15<b<0.85, 0.05<c<0.5]
A sealed alkaline storage battery is constructed from a negative electrode made of a hydrogen storage alloy or hydride, a positive electrode, a separator, and an alkaline electrolyte. Effect In such a configuration, since La is expensive, it is possible to reduce the cost of the alloy material by using Mm, which is commercially available at a low price. However, when using Mm, the hydrogen dissociation pressure is lower than that of La. increases significantly.
For example, the hydrogen dissociation pressure at 20℃ _is approximately
1.5 atm, MmNi ₅ is about 15 atm. Therefore, using LaNi ₅ for battery negative electrodes is expensive;
If cheap MmNi ₅ is used, the hydrogen dissociation pressure is too high, making charging difficult and increasing the internal pressure of the battery. On the other hand, when Co is used instead of Ni, the amount of hydrogen storage is reduced by about 50%, so the discharge capacity is also significantly reduced. Therefore, by adding optimal amounts of copper (Cu), manganese (Mn), and aluminum (Al) as substituents to this Ni part, we created a homogeneous intermetallic compound to fully demonstrate the functions of each added metal. , electrochemically absorbs and absorbs hydrogen better than rare earth binary or ternary alloys.
The release rate can be accelerated. In particular, the addition of Cu has the function of increasing high-rate discharge capacity, making it possible to extend high-temperature capacity, cycle life, and improve high-rate discharge characteristics. The details of the present invention will be described below with reference to Examples. Example Various commercially available samples made of Mm, Ni, Cu, Mn, and Al were weighed and mixed to a certain composition ratio, and heated and melted using an arc melting method. The Mm mentioned here is a mixture of rare earth metals that is generally commercially available, and its composition is 25 to 25% La.
35wt%, Ce (cerium) 40-50wt%, Nd (neodymium) 5-15wt%, Pr (praseodymium)
is 2 to 10 wt%, and other rare earth metals and other metals are 1 to 5 wt%. In addition to Mm alone, we also prototyped an alloy with some La added. As an example for comparison, MmNi ₅ ,
_{Mm0.5La0.5Ni5 , MmCo5 , Mm0.5La0.5Co5 were selected . _ _ _} After coarsely pulverizing these various alloys, they are further made into fine powders of 38 μm or less using a ball mill, etc., and thoroughly kneaded with an appropriate amount of polyvinyl alcohol resin solution (approximately 1 wt%). After applying the material homogeneously to the surface, applying pressure and drying, a lead was attached to form an electrode. Further, if necessary, the alloy can be used in the form of a hydride. This electrode was used as a negative electrode, and a positive electrode manufactured by a known method was combined therewith with a separator interposed therebetween.
A sealed type alkaline storage battery (capacity 1800mAh) was made and cycle life and high rate discharge tests were conducted.The alloy used was 12g larger than the positive electrode capacity.
(0.25Ah/g conversion), and this capacity corresponds to approximately 3Ah. The configuration of the sealed alkaline storage battery used in the test is shown in the figure. In the figure, a negative electrode plate 1 made of a hydrogen storage alloy and a nickel positive electrode 2 are spirally wound with a separator 3 in between, and inserted into a case 4 which forms a negative electrode terminal. Insulating plates 5 and 6 are applied above and below the electrode plate group, and the opening of the case 4 is sealed with a sealing plate 8 having a safety valve 7. Reference numeral 9 denotes a cap-shaped positive electrode terminal connected to the positive electrode lead 10 via the sealing plate 8. In addition, the battery charge/discharge condition is 0.2C.
(360mA) for 7 hours and discharged at 0.2C (360mA). Cycle life and high rate discharge were investigated as battery characteristics. The results are shown in Table 1. In the cycle life test, the life is defined as when the capacity drops to 20% of the initial capacity, and the number of cycles up to that point is indicated, and high rate discharge is 0.2C.
(360mA) 3C (5400mA) for capacity during discharge
The ratio of capacity during discharge is also displayed. The measurement temperature was 45°C for the former and 0°C for the latter.

[Table] Examples of conventional batteries are shown in No. 1, No. 2, No. 3, and No. 4, and representative examples of batteries of the present invention are shown in No. 5, No. 8, and No. 4.
Shown in 9. For comparison, batteries No. 6, No. 7, No. 10, and No.
Shown in No.11 and No.12. The hydrogen dissociation pressure for No. 1 battery is so high that it can hardly be charged at normal pressure. The battery No. 2 is made by adding La to Mm, which lowers the hydrogen dissociation pressure, so it is 50%
Although the battery can be charged and discharged several times, leakage phenomenon is observed due to the rise in battery internal pressure. Therefore, although the initial discharge capacity ratio appears to be relatively large, in battery No. 3, which has a small absolute value of discharge capacity, Co is eluted into the electrolyte, the cycle life is short, and the discharge capacity decreases. It's also small. Therefore, the high rate discharge capacity also showed an apparent value of about 30%. Battery No. 4 shows almost the same tendency as No. 3, and no major improvement is seen. In contrast, batteries No. 5, No. 8, and No. 9 of the present invention have a cycle life of more than 200 times, and moreover, while ensuring the specified discharge capacity (1800mAh), the discharge capacity ratio is 75~
It shows an improvement of about 3 times compared to conventional batteries. On the other hand, battery No. 6 is a case where the amount of Ni is large, and when the atomic ratio is 4.3 or more, the hydrogen dissociation pressure becomes high.
This increases the internal pressure of the battery, shortening its cycle life. Due to this influence, the discharge capacity ratio is also lower than that of the battery of the present invention. Battery No. 7 has a large amount of Cu, and when the atomic ratio exceeds 1.2, Cu dissolves in the electrolyte and deposits in the separator, resulting in a decrease in capacity due to micro short circuits. Therefore, the high rate discharge characteristics are also poor. In addition, batteries No. 10 and No. 11 are cases where the amount of Mn and the amount of Al are increased, but when the atomic ratio exceeds 0.85 and 0.5, respectively, homogeneous dissolution is not possible and the hydrogen storage capacity decreases significantly. This shortens the cycle life.
In addition, since homogeneous dissolution is not possible, the polarization of the electrode itself is large, resulting in a large voltage drop when high rate discharge is performed. Battery No. 12 is a case where the amount of Ni is reduced,
When the Cu, Mn, and Al components become too large, the discharge capacity is low, and the battery itself changes from the positive electrode to the negative electrode, which causes hydrogen gas to be generated from the negative electrode during overcharging, shortening the cycle life. However, the discharge capacity ratio is approximately 60% in the initial stage. In addition, when La in Ln is less than 25wt%, hydrogen storage alloys such as MmNi ₅ have a very high hydrogen dissociation pressure, which significantly increases the battery internal pressure during charging and has poor charging acceptability. It is almost impossible to charge at normal pressure. On the other hand, when La is 60wt% or more, the amount of La contained in Ln becomes too large,
Along with charge/discharge cycles, the alloy undergoes deterioration.
In addition to shortening the cycle life, La is expensive, which increases the price of the battery and makes it impractical. Also, since the amounts of La and Ce contained in Mm show almost constant values, if the cheapest Mm is used, La is 25 to 35 wt% and Ce is 40 to 50 wt%.
The optimum range is a mixture of the two.
Even if the amount is more or less than this range, La and Ce must be added separately for adjustment, which leads to an increase in cost and at the same time, the quality of the alloy lacks stability. Therefore, the mixture of La and Ce is 65-85wt%
By setting , it is possible to absorb variations in Mm and obtain stable characteristics. From the above results, Ln is either Mm alone or together with Mm.
It is a mixture with La, and La in Ln is 25 to 60 wt%
The value of x is preferably within the range of 3.5<x<4.3, Y
The value of is 1, the value of a is 0.2<a<1.2, the value of b is 0.15
The value of <b<0.85 and c in the range of 0.05<c<0.5 is most suitable for the alloy negative electrode of a practical battery. Sideways
It can be seen that Mm, Ni, Cu, Mn, and Al are important elements in forming a sealed battery. here,
Mm is a mixture of rare earth elements that are generally easy to purchase.
It refers to a metal obtained by reducing the crude chloride of a mixture of La, Nd, and other light rare earth elements using ordinary electrolytic methods. Therefore, using Mm, which can be purchased at a low price, provides a large cost advantage. So La and Ce in Mm
A metal containing about 65 to 85 wt% of is desirable. Effects of the Invention As described above, according to the present invention, it is possible to obtain a sealed alkaline storage battery which has a relatively large discharge capacity, is excellent in high rate discharge characteristics at low temperatures such as 0°C, and has a long cycle life at high temperatures such as 45°C. can.

[Brief explanation of the drawing]

The figure is a diagram showing the structure of a sealed alkaline storage battery used in an example of the present invention. 1... Negative electrode plate (hydrogen storage electrode), 2... Positive electrode plate,
3...Separator, 4...Case, 9...Positive terminal.

Claims (1)

[Claims] 1. A negative electrode made of a hydrogen storage alloy or hydride;
A sealed alkaline storage battery consisting of a positive electrode, a separator and an alkaline electrolyte, the negative electrode having the formula
LnNi _x (Cu _a・Mn _b・Al _c ) _Y [However, Ln is Mitsushi Metal alone or a mixture of Mitsushi Metal and La, and the amount of La in Ln is 25 to 60% by weight, 3.5<x
<4.3, Y=1.0, 0.2<a<1.2, 0.15<b<0.85,
A sealed alkaline storage battery comprising a five-element system expressed by 0.05<c<0.5. 2. The sealed alkaline storage battery according to claim 1, wherein the Mitsushi metal is composed of at least three kinds of rare earth metals, and the amount of La and Ce is within the range of 65 to 85% by weight.