JP2745501B2 - Sealed alkaline storage battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed alkaline storage battery using a hydrogen storage alloy which electrochemically stores and releases hydrogen as a negative electrode, and more particularly to an improvement of the negative electrode. is there. 2. Description of the Related Art Conventional secondary batteries of this type include lead-acid batteries and nickel batteries.
Cadmium batteries are the most widely known, but these batteries have a relatively low energy storage capacity per unit of weight or capacity due to the inclusion of a solid active material in the negative electrode. In order to improve the energy storage capacity, a storage battery using a hydrogen storage alloy as a negative electrode and a positive electrode using, for example, nickel oxide has been proposed (US Pat. No. 3,874,928). A battery using the LaNi ₅ alloy according to this proposal for the negative electrode has a short charge / discharge cycle life. Moreover, since lanthanum (La), which is a constituent metal of the alloy, is expensive, the cost of the electrode itself naturally increases. An electrode composition improved from this LaNi ₅ alloy negative electrode has also been proposed (JP-A-51-13934). In other words, LnNi ₅ and LnCo ₅ (Ln is a rare earth metal mixture) in which a part of La is replaced by misch metal (Mm) is used to reduce the cost. It is small and has a short cycle life, making it a practical storage battery.
The MmNi Meanwhile as a hydrogen storage material _5-x Al _xy Co _y (where x
= 0.1 to 2, y = 0.01 to 1.99) has been proposed (JP-A-57-19347).
Here, Mm is a generally available inexpensive material,
The composition is La25 ~ 35wt%, Ce (cerium) 40 ~ 50wt%, Pr
(Praseodymium) 2-10wt%, Nd (Neodymium) 5-15w
t%, 1-5wt% of other rare earths, Si as other metal
(Silicon), Mg (magnesium) Al (aluminum) 0.1 ~
This is a general term for rare earth mixtures composed of 10 wt% and the like.
These are considered a kind of metal name for the following reasons: In other words, C which exists in monazite at a natural ratio
The crude chloride of e, La, Nd and other light rare earth mixtures can be obtained usually by reduction by electrolysis, and commercially available Mm is called as one metal because its composition is determined to some extent. Many. However, when an alloy consisting of the four metals of Mm, Ni, Al, and Co is used for the negative electrode of a sealed alkaline storage battery, it is stored at a high temperature unlike the behavior in the gas state because it is handled in the electrolyte. The internal pressure of the battery tends to increase with the number of charge / discharge cycles, due to a small capacity retention rate when the battery is charged, a large increase in the internal pressure of the battery due to the gas generated at the time of overcharge, and an accumulation of residual hydrogen after discharge. is there. For this reason, it is not a practical sealed alkaline storage battery from the viewpoint of safety as well as shortening of cycle life. Problems to be Solved by the Invention The above alloys, that is, Mm, Ni, Al, Co 4 mainly composed of misch metal-nickel described in Japanese Patent Application Laid-Open No. 57-19347.
Investigation of charge / discharge characteristics using an alloy composed of various metals for the negative electrode of a sealed alkaline storage battery shows that, unlike the behavior of absorbing and releasing hydrogen in gaseous form, hydrogen is absorbed during charging when the amount of Ni is large. When the amount of Co is large, the hydrogen storage amount is small, and the high-temperature cycle life is short. On the other hand, Mm
When used alone, the hydrogen dissociation pressure is high, the pressure inside the battery is high due to the gas generated from the electrode at the time of overcharging, and a liquid leakage phenomenon occurs, especially when the temperature is high. Therefore,
Unlike the case of storing hydrogen in gaseous form, the negative electrode alloy used for sealed alkaline storage batteries replaces a part of Mm with La, Ni, A
It has been found through repeated experiments that a practical storage battery cannot be obtained unless l and Co contents are selected in the optimal range. Therefore, it was necessary to find out the optimum range by conducting a test of the sealed alkaline storage battery using more alloy compositions for the negative electrode. In the present invention, particularly, Ni, which increases the discharge capacity,
Focusing on metals La and Al, which lower the hydrogen dissociation pressure so that hydrogen can be easily absorbed into the negative electrode by charging, without lowering the discharge capacity, the La and Al both have a surplus effect and the function of oxygen gas absorption capacity of Co It is another object of the present invention to solve the above problems. Means the present invention for solving the problem, the formula _{Mm 1-x La x (Ni} a · Co b · Al c) [ here, x
Indicates the amount of La to be substituted for Mm, and regulates the amount of La so that the total amount of La expressed by La / Mm + La is in the range of 35 to 70 wt%.
5 <a + b + c <5.5, 3.5 <a <4.3, 0.5 <b <1.5, 0.1 <
The sealed alkaline storage battery comprises a negative electrode made of a hydrogen storage alloy or hydride composed of five metals represented by c <0.5], a positive electrode, a separator and an alkaline electrolyte. Here, the composition of Mm is generally La: 25 to 35 w
t%, Ce: 40 to 50 wt%, Nd: 5 to 15 wt%, Pr: 2 to 10 wt%, other rare earth metals: 1 to 5 wt%, other metals (Fe, Si, Al, Mg
Etc.): 0.1 to 10% by weight. Action 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 cost as a main component. The dissociation pressure increases significantly. Therefore, it is difficult to occlude hydrogen during charging even if an MmNi ₅ alloy is used for the negative electrode of the sealed alkaline storage battery. Eventually, the amount of electricity charged to the negative electrode is very small, and the discharge capacity is also small. On the other hand, MmNi _5-x Co _x (0.
Even if a hydrogen storage alloy material such as 1 <x <4.9) was used for the negative electrode, no significant improvement could be made. Therefore, by adjusting the amount of Ni, the amount of hydrogen occlusion is improved, the amount of Co is used to promote the charge acceptability of hydrogen, and by replacing a part of Mm with La and adding Al, the hydrogen dissociation pressure is reduced. The increase is suppressed, and the capacity retention and discharge capacity can be improved and the cycle life can be extended. Hereinafter, a detailed example of the present invention will be described. Example Commercially available samples composed of five kinds of metals of Mm, La, Ni, Co, and Al were weighed and mixed so as to have various compositions, and were heated and melted using a high-frequency melting furnace by induction heating. Here, Mm is a commercially available inexpensive mixture of rare earth metals, and has a composition of La: 25-35 wt%, Ce: 40
-50 wt%, Nd: 5-15 wt%, Pr: 2-10 wt%, other rare earth metals 1-5 wt%, other metals 0.1-10 wt%. In this embodiment, Mm having a La content of 30 wt% was used. After coarsely pulverizing these various alloys, they are further pulverized to a fine powder of 38 μm or less by a ball mill, etc., and kneaded well with an appropriate amount of a polyvinyl alcohol resin solution (about 1 wt%). After filling the body, pressing and drying, a lead was attached to form an electrode. If necessary, the alloy may be used as a hydride. This electrode was used as a negative electrode, and a positive electrode manufactured by a known method was combined with the positive electrode via a separator to form a sealed alkaline storage battery (capacity: 1800 mAh). A cycle life and a storage capacity test were performed. The alloy used was 12 g (0.25 Ah / g conversion) so as to be larger than the positive electrode capacity, and this capacity was equivalent to about 3 Ah. The figure shows the configuration of the sealed alkaline storage battery used in the test. In the figure, a negative electrode plate 1 made of a hydrogen storage alloy and a nickel positive electrode 2 are spirally wound via a separator 3 and inserted into a case 4 also serving as a negative electrode terminal. Insulating plates 5 and 6 are applied to the upper and lower sides of the electrode plate group, and the opening of the case 4 is sealed by a sealing plate 8 having a safety valve 7. 9 is a positive electrode lead 10 via a sealing plate 8.
This is a cap-shaped positive electrode terminal connected to. The battery was charged and discharged at 0.2 C (360 mA) for 7 hours and discharged at 0.2 C (360 mA). All measurement temperatures were 45 ° C. The cycle life test is 20 times the initial capacity.
% Is defined as the life, and the capacity retention is shown in the following table as the remaining capacity ratio by comparing the capacity after one week of discharge at a temperature of 45 ° C. after complete charge with the capacity before standing. Nos. 1 to 4 are shown as an example of a conventional battery, Nos. 5 to 7 are shown as an example of a battery of the present embodiment, and Nos. 5 to 7 are shown for comparison.
8,9 was shown. Battery No. 1 uses a high alloy negative electrode with a hydrogen dissociation pressure of 20 atm or more at room temperature, so it cannot be charged from the beginning,
Therefore, the discharge capacity is very small. Battery No.2,3,4 is 1
Although it is a crude metal that is regarded as a kind of metal, it is the No. 1 MmNi
Charge / discharge is possible because the hydrogen dissociation pressure is lower than _5, but it has a hydrogen dissociation pressure of several atmospheres to about 10 atm at room temperature, and the pressure inside the battery rises with repeated charge / discharge, and the electrolyte Leakage and the like, and the resistance in the battery increases and the capacity decreases. In particular, the internal pressure of the No. 4 battery rises significantly, and the leakage of the electrolyte is also great. On the other hand, the battery of No. 3 has a small negative electrode capacity, and the capacity of the negative electrode is reduced faster than other batteries. In any case, a commercially available battery using Mm alone has a pressure in the battery of 10 kg / cm ² or more due to an increase in internal pressure of the battery, which is a problem from the viewpoint of safety. In addition, naturally, since the hydrogen dissociation pressure is high, the degree of spontaneous release of hydrogen from the negative electrode is large, and the capacity retention shows a small value of 20 to 30%. This tendency becomes more pronounced at higher temperatures. Battery Nos. 5, 6, and 7 show no capacity decrease and no liquid leakage phenomenon even after 200 cycles, and the capacity retention rate is more than twice as high as that of the conventional battery. Battery No. 8 shows a case where La is used more than Mm, but the capacity retention ratio shows a relatively high value. However, when the amount of La increases, the La-based alloy deteriorates (hydroxide) together with the charge / discharge cycle. And
It is considered that the alloy composition changes and the capacity decreases. From this, the cycle life is completed at 180 times, and N
o.It is shorter than 5, 6, and 7. On the other hand, if La is increased, it is not practical because the price of the alloy material is increased. The battery of No. 9 has a small amount of Ni and a large amount of Co, which reduces the discharge capacity, dissolves Co in the electrolyte, and precipitates the dissolved Co in the separator, causing a micro short circuit. To shorten the cycle life. Due to this phenomenon, the capacity retention naturally decreases. As shown in this embodiment, the total amount of La expressed by La / Mm + La is preferably 35 to 70 wt% than that of Mm alone. When the total amount of La is larger than this range, the cycle life is shortened and the cost is reduced due to deterioration of La. It is not practical because it leads to up. Conversely, when the pressure decreases, the hydrogen dissociation pressure increases, and the charging efficiency becomes extremely poor at normal pressure. Therefore, the value of x is desirably in the range of 0.1 <x <0.6 in order to regulate the amount of La to be replaced with Mm and to set the total amount of La to 35 to 70 wt% as described above. On the other hand, if the value of a is 3.5
When <a <4.3, the hydrogen dissociation pressure is high,
Poor charge acceptance. Conversely, when it is small, there is a decrease in the discharge capacity which causes a decrease in the hydrogen storage amount. Also, when the value of b is 0.5 <b
When the value is larger than the range of <1.5, the capacity of the negative electrode is reduced and Co is easily dissolved in the electrolytic solution, and the dissolved Co is deposited in the separator, causing a micro short circuit. When the value of b is smaller than this range, the hydrogen dissociation pressure is high, and it becomes difficult to absorb oxygen gas generated from the positive electrode during overcharge,
This leads to an increase in battery internal pressure. Further, when the value of c is larger than the range of 0.1 <c <0.5, it is difficult to form a uniform composition of the alloy, and the discharge capacity becomes small due to the heterogeneity of the negative electrode alloy phase. Conversely, when this value is small, Al
Effect is small, and the cycle life due to an increase in battery internal pressure is shortened. The value of the sum of a, b and c is preferably in the range of 4.5 <a + b + c <5.5 in order to keep the alloy phase homogeneous. If it is smaller than this range, the hydrogen storage amount is small and the discharge capacity is also small. On the other hand, if it is large, a homogeneous alloy phase cannot be formed, and the internal pressure of the battery increases, so that the capacity retention rate also decreases.
By adding a specific metal in this way, the hydrogen dissociation pressure is lowered to slightly increase the bonding force between the metal (element) and hydrogen, and the release of hydrogen under no-load conditions is reduced to improve the capacity retention rate. I'm trying. In particular, the effect of the effect of adding La is great. In the present embodiment, Mm in which the La content in Mm is 30 wt% was used. However, the same effect can be obtained by using Mm having a La content of 25 wt% and 35 wt%, and the La content represented by La / Mm + La is 35-70w whole
t% is desirable. It is important to determine the substitution amount of La so as to fall within this range to make a practical battery. Regulating the amount of La, on the other hand, defines the content of other metals such as Ce. To produce a homogeneous alloy, Ni, Co, Al are first converted to a, b,
After mixing and dissolving with the composition of c, Mm and La are added again and redissolved. Further, when these alloys are heat-treated at a temperature of 800 to 1100 ° C. in an inert atmosphere or in a vacuum, and used as a negative electrode,
Discharge performance with excellent flatness is obtained. At 800 ° C. or lower, the effect of the heat treatment is insufficient, and a part of the heterogeneous phase is observed. On the other hand, if the temperature is set to 1100 ° C. or higher, Al is evaporated and the composition changes, which is not preferable. The same effect can be expected when an alloy is used for this kind of negative electrode or when it is used in a partially hydride state. Effect of the Invention As described above, according to the present invention, the capacity retention ratio is large,
In addition, a sealed alkaline storage battery having a long cycle life, low cost, excellent quality stability, and high practicability can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the structure of a sealed alkaline storage battery used in an embodiment of the present invention. 1 ... Negative electrode plate, 2 ... Positive electrode plate, 3 ... Separator, 4 ...
... case, 9 ... positive electrode terminal.

Claims (1)

(57) [Claims] A sealed alkaline storage battery comprising a negative electrode made of a hydrogen storage alloy or hydride, a positive electrode, a separator and an alkaline electrolyte, wherein the negative electrode has the formula Mm _1-x La _x (Ni _a · Co _b
・ Al _c ) [where Mm is misch metal, X indicates the amount of La to be substituted for Mm, and La of the whole negative electrode can be expressed by La / Mm + La.
The amount of La is regulated so that the amount is in the range of 35 to 70 wt%, and 4.5 <
a + b + c <5.5, 3.5 <a <4.3, 0.5 <b <1.5, 0.1 <c
A sealed alkaline storage battery comprising five kinds of metals represented by <0.5>. 2. In the formula Mm _1-x La _x (Ni _a Co _b Al _c ), the La content is regulated so that the total La content represented by La / Mm + La is in the range of 35 to 70 wt%, and x = 0.2 to 0.5, a = 3.7-3.9, b = 0.8-1.0, c
2. The sealed alkaline storage battery according to claim 1, wherein 0.2 to 0.3. 3. The composition of Mm (Misch metal) is La: 25 ~ 35wt%, Ce: 4
2. The sealed alkaline storage battery according to claim 1, comprising 0 to 50% by weight, Nd: 5 to 15% by weight, Pr: 2 to 10% by weight, 1 to 5% by weight of other rare earth metals, and 0.1 to 10% by weight of other metals.