JPH05290835A - Rectangular nickel-hydrogen storage battery - Google Patents

Abstract

PURPOSE:To realize high-energy densification with the utilization factor of a positive electrode improved, by lessen the area of a positive electrode plate compared with that of a negative electrode plate. CONSTITUTION:Positive electrodes 3 and negative electrodes 2 are composed so that the area of one of nickel hydroxide positive electrodes 3 is made 0.9 time or less that of one of hydrogen storage alloy negative electrodes 2 oppositely provided via separators 1. By thus lessening the area of the positive electrode 3 compared with that of the negative electrode 2, the electrode 3 can be retained in a platelike state not in a wavelike state even they are expanded after a charge/discharge cycle, allowing to receive sufficient dynamical press force from the faced negative electrodes 2. Consequently the energy density per battery weight can be increased with the discharge utilization factor of the positive electrodes 3 improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prismatic nickel-hydrogen storage battery, and more particularly to a prismatic nickel-hydrogen storage battery in which energy per weight is increased by improving the utilization rate of the positive electrode of a battery assembled under positive electrode capacity regulation.

[0002]

2. Description of the Related Art In recent years, a sealed nickel-metal hydride storage battery using nickel hydroxide for a positive electrode, a hydrogen storage alloy for a negative electrode, and an alkaline aqueous solution for an electrolyte has been attracting attention because it can achieve high energy density. The charging mechanism with this battery proceeds as follows. The discharge reaction is the opposite. Formula (1) for the positive electrode
In the negative electrode, the reaction of formula (2) occurs to the right of the reaction formula. e ⁻ is an electron, M is a hydrogen storage alloy, MH
Is a hydrogen storage alloy that has stored hydrogen.

Ni (OH) ₂ + OH ⁻ = NiOOH + H ₂ O + e ⁻ (1) M + H ₂ O + e ⁻ = MH + OH ⁻ (2) Therefore, the charging reaction of the entire battery can be expressed by the equation (3).

Ni (OH) ₂ + M = NiOOH + MH (3) In a nickel-metal hydride storage battery, when the potential of the negative electrode is large during discharge and the charge / discharge cycle life is shortened when polarized to a noble potential, the positive electrode capacity regulation is used. It is common.

However, during charging, not only the above reaction but also a side reaction occurs. Formula (4) occurs in the positive electrode as a side reaction.

4OH ⁻ = 2H ₂ O + O ₂ + 4e ⁻ (4) When this side reaction occurs, oxygen gas is generated, so that charging efficiency, that is, electric quantity efficiency is deteriorated.

The ratio of the side reactions of the formulas (1) and (4) at the positive electrode varies greatly depending on how the battery is made. Generally, in a cylindrical battery, the higher the battery binding rate, that is, the stronger the positive electrode and the negative electrode are pressed against each other in the battery case, the better the charging efficiency of the positive electrode and the easier the reaction of the formula (1) occurs. .. In a cylindrical nickel-metal hydride storage battery, the positive electrode and the negative electrode are made up of spirally wound electrode plates with almost the same area, and the binding ratio of the battery, that is, the inside of the battery case where the positive electrode, the negative electrode, and the separator are present. Positive electrode, considering the cross-sectional area of
It is said that when the area ratio of the negative electrode and the separator is 90% or more, the discharge utilization rate of the positive electrode after charging becomes 100%.

[0008]

However, in the prismatic battery, even if the binding rate is 95%, the discharge utilization rate of the positive electrode is 8%.
It was as small as 0%. Therefore, the energy density per weight of the battery was small.

An object of the present invention is to solve the above problems and to provide a prismatic nickel-hydrogen storage battery in which the energy density per weight of the battery is improved by improving the utilization rate of the positive electrode.

[0010]

According to the present invention, in a prismatic nickel-hydrogen storage battery using nickel hydroxide for the positive electrode, a hydrogen storage alloy for the negative electrode, and an alkaline aqueous solution for the electrolyte, the area of one positive electrode is equal to the area of one negative electrode. It is 0.9 times or less.

[0011]

In the prismatic nickel-hydrogen storage battery, the utilization rate of the positive electrode in the first cycle is high. However, it tended to decrease with charge / discharge cycles. When the battery was disassembled after 10 cycles, the positive electrode plate had a wavy shape between the negative electrode plates. It is considered that this is because the expansion of the positive electrode plate is more remarkable than that of the negative electrode plate, the positive electrode plate is less likely to expand in the thickness direction, and there is no escape area for the positive electrode which is about to expand. This tendency of the positive electrode plate to have a wavy shape is rarely seen in the cylindrical battery.

In the expanded positive electrode plate, a mechanical force for pressing is applied to the convex and concave portions which are in contact with the negative electrode plate through the separator, but the other parts are less likely to receive the mechanical force.
It was thought that this resulted in a drop in utilization. The high utilization rate of the positive electrode in the first cycle is probably because the positive electrode plate has not expanded yet. It has been considered that a battery with a high binding rate, which has been said to be a cylindrical battery until now, is good because the force to hold down the positive electrode plate becomes larger. When the cylindrical battery is disassembled, the positive electrode plate does not expand much in the vertical and horizontal directions. This indicates that in the cylindrical battery, the positive electrode plate is pressed strongly. It can be said that a prismatic battery is a weak construction method from the viewpoint of pressing the positive electrode plate.

Therefore, in the prismatic battery, the area of the positive electrode plate is made smaller than that of the negative electrode plate so that the positive electrode does not have a wavy shape even when expanded. As a result, it was considered that the positive electrode would expand in the vertical and horizontal directions even if it expanded, and that the pressing force from the negative electrode would not change. The reason why the high utilization rate in the first cycle is that it means that the force applied when the battery is constructed is sufficient as long as the positive electrode plate is not wavy.

Also in the cylindrical battery, the length of the positive electrode plate may be shorter than that of the negative electrode plate, and the positive electrode plate may be wound in a spiral shape. This is because it is wound in a spiral shape, so that it is necessary to lengthen the electrodes on the outer periphery in order to align the facing electrode surfaces of the positive and negative electrodes. In a cylindrical battery, the case serves as the negative electrode, so the negative electrode is brought to the outer circumference, and the positive electrode plate is often shorter. This is to make the electrode surfaces uniform, and does not consider expansion of the positive electrode. When assembling the battery,
It is clear from the fact that the positive electrode and the negative electrode are facing each other.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A prismatic nickel metal hydride storage battery according to an embodiment of the present invention will be described below with reference to the drawings.

Mm using misch metal (Mm), which is a hydrogen storage alloy and has a lanthanum content of 10%, as the negative electrode active material
Using Ni _3.55 Mn _0.4 Al _0.3 Co _0.75 , this alloy 1
Water was added to 9.4 g to make a paste. Width 60mm length 81
This paste was filled in nickel foam having a weight of 3.1 g and dried, and then compressed to a thickness of 1.20 mm to obtain a negative electrode plate. A nickel plate as a lead was spot-welded to the corner of the negative electrode plate. At this time, the theoretical capacity of one negative electrode plate is 5.63 Ah. Six negative plates were used for the test battery.

Next, nickel hydroxide, metallic cobalt, and cobalt hydroxide were weighed at a weight ratio of 100: 7: 5 as a positive electrode, and the powders were well mixed, and then 20 g of the mixed powder was added with water to form a paste. This paste was filled in nickel foam having a width of 60 mm, a length of 81 mm, and a weight of 3.1 g, dried, and then compressed to a thickness of 1.74 mm to obtain a positive electrode plate. A nickel plate as a lead was spot-welded to the corner of the positive electrode plate. At this time, the theoretical capacity of one positive electrode plate is 5.16 Ah. The area of the positive electrode plate is the same as that of the negative electrode.

The positive electrode plate thus prepared was cut out to prepare a positive electrode plate having an area smaller than that of the negative electrode. The vertical and horizontal dimensional ratios of the positive electrode plate were the same. For example, the area of the negative electrode plate is 80
% Positive electrode, the square root of 0.8 in the vertical and horizontal dimensions is 0.
By multiplying by 894, the width is 53.7 mm and the height is 72.4 mm. In the same way, positive electrode plates with various area ratios to the negative electrode were made. Five positive electrode plates of the same size thus produced were used for the test battery. That is, the area ratio is 1,0.95,0.90,0.
85, 0.80, 0.75, 0.70, 0.65, 0.
Five positive electrode plates of 60 were prepared and used for the test.

As shown in FIG. 1, the negative electrode 2 and the positive electrode 3 were arranged in this order so that the negative electrode 2 came to the outside through the sulfonation-treated polypropylene separator 1. This figure shows the case where the area ratio of the positive electrode 3 is 0.8. The lead of the negative electrode 2 was spot-welded to the nickel negative electrode terminal 4, and the positive electrode lead was spot-welded to the nickel positive electrode terminal (not shown). These electrode plates were placed in a case 5 of 3 mm thick, made of acrylonitrile-styrene resin, which had a length of 108 mm, a width of 69 mm, and a width of 18 mm. An aqueous solution of potassium hydroxide having a specific gravity of 1.3 was added as an electrolytic solution in an amount of 54 cc and 70.1 g.

A sealing plate 7 made of allylonitrile-styrene resin having a safety valve 6 operating at 2 atmospheres was adhered to the case 5 with an epoxy resin. After that, the positive electrode terminal and the negative electrode terminal 4 were pressed and fixed to the sealing plate 7 via an O-ring to form a sealed battery.

These batteries were tested at 20 ° C. for 15 hours at a rate of 15 hours.
The charging / discharging cycle of charging for 5 hours and discharging until the terminal voltage became 1 V at a rate of 5 hours was repeated. Table 1 shows the discharge capacity at the 50th cycle of these batteries and the utilization rate of the positive electrode active material.

From this, it can be seen that by making the area of the positive electrode plate smaller than that of the negative electrode, the utilization factor is improved especially when the area ratio is 0.9 or less.

The table also shows the energy density based on the total weight of the positive electrode plate, the negative electrode plate, and the electrolytic solution, which are the power generating elements. The average discharge voltage of each battery is the same as 1.25 V, and this energy density is divided by 1.25 to obtain the electricity quantity density per weight. Also from the viewpoint of this energy density, the area ratio is preferably 0.9 or less and 0.7 or more.

[0024]

[Table 1]

[0025]

As is apparent from the above description of the embodiments, according to the prismatic nickel-metal hydride storage battery of the present invention, the area of the positive electrode plate is made smaller than the area of the negative electrode plate to increase the utilization rate of the positive electrode. The energy density can also be improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a prismatic nickel metal hydride storage battery according to an embodiment of the present invention.

[Explanation of symbols]

 1 Separator 2 Negative electrode 3 Positive electrode

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsunori Komori 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yoshinori Toyokuchi 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A nickel hydroxide positive electrode provided facing each other via a separator, a hydrogen storage alloy negative electrode, and an alkaline electrolyte as main components, and the area of one positive electrode is less than the area of one negative electrode. A prismatic nickel-metal hydride storage battery comprising the positive electrode and the negative electrode that are 9 times or less.