JPH0547366A - Rectangular metal hydride storage battery - Google Patents

Abstract

PURPOSE:To suppress the dropping of the hydrogen storage alloy of a negative electrode and prevent the reduction of the current collecting property of the negative electrode during storage for a long period by inserting a metal sheet electrically connected to the negative electrode between the negative electrode faced to a metal outer can and the outer can. CONSTITUTION:The slurry of a hydrogen storage alloy is coated on a conducting carrier, then it is dried, pressurized, and cut, and two negative electrodes 1 are connected with the exposure section 2 of a conducting carrier to form a hydrogen storage alloy negative electrode. A nonporous nickel sheet 3 is welded to the negative electrode 1 including the exposure section 2 to form a negative structure. Three positive electrodes 4 and two sets of the negative structures are combined, an electrode body inserted with separator 5 between the positive and negative electrodes 4, 1 is inserted in an outer can 6, and the negative electrode 1 and the can 6 are electrically connected via the sheet 3. The hydrogen storage alloy is suppressed from being dropped from the negative electrode 1 when the electrode body is inserted into the outer can 6, even if part of the alloy is eluted to form an insulating film, the electric connection between the metal sheet 3 and the outer can 6 can be kept satisfactory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current collecting structure between a negative electrode and a metal outer can for a negative electrode terminal in a prismatic metal hydride storage battery having a negative electrode made of a hydrogen storage alloy.

[0002]

2. Description of the Related Art In recent years, as the weight and thickness of cordless devices have been reduced, it has been required to increase the capacity and size of batteries used as power sources for these devices. Regarding high capacity, it is lighter than lead acid batteries and nickel-cadmium batteries and can have higher capacities.In particular, it is equipped with a hydrogen storage alloy that can store and release hydrogen, which is the negative electrode active material, at normal pressure. A metal hydride storage battery using such an electrode as a negative electrode is drawing attention. On the other hand, regarding miniaturization,
Attention has been paid to a prismatic battery which has a good volume efficiency when formed into an assembled battery as compared with a conventional cylindrical battery and can be made thin.

As a conventional electrode current collecting method in a prismatic battery, there is one disclosed in Japanese Patent Application Laid-Open No. 1-200552. This current collecting method includes positioning the negative electrode on the outer surface of the electrode body in which the positive and negative electrodes and the separator are laminated, and placing the negative electrode located between the pair of positive electrodes inside the electrode body and the negative electrode located on the outer surface of the electrode body. , The negative support is connected through the exposed portion of the conductive support, and the exposed portion of the conductive support located on the lower surface of the electrode body is pressed against the inner bottom surface of the rectangular metal outer can that also serves as the negative electrode terminal. The negative electrode located on the outer surface of the electrode body is pressed against the inner surface of the metal outer can to electrically connect the negative electrode and the metal outer can.

Further, if the thickness of the electrode body is increased in order to press the negative electrode on the outer surface of the electrode body against the inner surface of the metal outer can, the outer surface of the electrode body is inserted when the electrode body is inserted into the metal outer can. The positioned negative electrode may come into contact with the opening edge of the metal outer can to cause the active material to fall off, and this drop does not occur.Therefore, in the rectangular nickel-cadmium battery, the sintered substrate is impregnated with the active material as the negative electrode. A sintered negative electrode having a high electrode plate strength produced by the above method was used.

However, in a metal hydride storage battery, the negative electrode has a hydrogen storage alloy as a main constituent substance, and this hydrogen storage alloy sinters the negative electrode active material as a salt solution of the active material like cadmium in a nickel-cadmium battery. It is impossible to take the means of impregnating the substrate in the form of liquid,
The hydrogen storage alloy is mixed in a powder state with a binder, and the mixture is held by an active material holder such as punching metal or nickel foam to form a non-sintered negative electrode.
However, the non-sintered negative electrode has a lower electrode plate strength than the sintered negative electrode, and when the electrode body is inserted into the metal outer can, it comes into contact with the metal outer can and the hydrogen storage alloy drops off from the negative electrode. However, the hydrogen storage alloy that has fallen off may cause a short circuit inside the battery.

Further, in a metal hydride storage battery, when the hydrogen storage alloy electrode of the negative electrode is brought into direct contact with a metal outer can to collect current, when the battery is left for a long period of time,
A part of the hydrogen storage alloy of the negative electrode may be dissolved and accumulated between the negative electrode and the metal outer can, which may form an insulating film and reduce the current collecting property.

[0007]

DISCLOSURE OF THE INVENTION The present invention is directed to a prismatic metal hydride storage battery which can prevent the hydrogen storage alloy powder from falling out of the negative electrode and can prevent the negative electrode from being deteriorated in current collecting property after being left for a long time. Is to provide.

[0008]

The prismatic metal hydride storage battery of the present invention comprises a negative electrode having a hydrogen absorbing alloy held on a conductive support, a positive electrode, and a separator positioned between the two electrodes. The electrode body is housed in a metal outer can that also serves as a negative electrode terminal, and the negative electrode is arranged on the surface of the electrode body that faces the metal outer can, and the extension of the conductive support or the conductive support is provided. The metal sheet electrically connected to the negative electrode and the metal outer can, which is interposed between the negative electrode and the metal outer can that face the metal outer can, and the negative electrode and the metal can via the extension of the conductive support or the metal sheet. It is characterized in that it is electrically connected to the outer can.

Further, the extension of the conductive support or the metal sheet interposed between the negative electrode and the metal outer can is made of a metal perforated plate to further enhance the effect.

[0010]

When a metal sheet is provided on the surface of the negative electrode located on the outer surface of the electrode body and facing the metal outer can, the metal sheet is exposed on the surface of the negative electrode when the electrode body is inserted into the metal outer can. Therefore, the hydrogen storage alloy, which is the main constituent material of the negative electrode, does not directly contact the inner surface of the metal outer can, and the hydrogen storage alloy can be prevented from falling off from the negative electrode.

When the battery is left for a long time, the hydrogen storage alloy of the negative electrode is partially eluted to form an insulating film. This film cannot be reduced to a conductive metal during charging, but When a metal sheet electrically connected to the negative electrode is interposed between the negative electrode located on the outer surface and the metal outer can, the insulating film is formed on the surface of the metal sheet facing the negative electrode. The electrical connection between the metal outer can and the metal outer can can be maintained, and the electrical connection between the metal outer can that also serves as the negative electrode and the negative electrode terminal can be favorably maintained. Although an insulating film is formed between the metal sheet and the negative electrode, since the metal sheet is electrically connected to the negative electrode in advance, the electric connection between the metal sheet and the negative electrode is not damaged.

Further, when the negative electrode and the metal outer can are directly contacted to collect current, the shape of the negative electrode changes due to charging and discharging to form irregularities on the surface of the negative electrode, and the adhesion between the negative electrode and the metal outer can is improved. Although it may be damaged, when the metal sheet is brought into contact with the metal outer can to collect current, the metal sheet does not change in shape like this, so it is possible to maintain contact between the surfaces and There is no increase in resistance.

As described above, by interposing the metal sheet electrically connected to the negative electrode between the negative electrode on the outer surface of the electrode body and the metal outer can to collect the current, the operating voltage and the discharge at the high rate discharge can be obtained. The capacity is improved and the cycle characteristics are also improved.

By the way, a metal hydride storage battery is generally configured to consume oxygen gas generated from a positive electrode at the time of overcharging at a negative electrode, and when a nonporous metal sheet is used as the metal sheet, Oxygen gas generated from the positive electrode reaches the negative electrode that is the counter electrode through the separator and is consumed, or after being discharged into the space in the battery,
It penetrates through a small gap between the negative electrode located on the outer surface of the electrode body and the metal sheet, reaches the negative electrode located on the outer surface of the electrode body, and is consumed. However, these alone cannot be said to have a sufficiently satisfactory oxygen gas consumption capacity.

Here, as the metal sheet interposed between the negative electrode on the outer surface of the electrode body and the metal outer can,
When a porous plate, particularly a metal porous plate having a three-dimensional structure, is used, oxygen gas released into the internal space of the battery can easily reach the negative electrode on the outer surface of the electrode body, and the oxygen gas consumption capacity of the negative electrode is improved.
This is because, in a metal porous plate having a three-dimensional structure such as foamed nickel, a sintered porous body of metal fibers or an expanded metal, the pore space in this porous plate serves as a flow path for oxygen gas, and oxygen gas flows in this space. This is because it is easy to pass through and reach the negative electrode on the outer surface of the electrode body. Further, although the oxygen gas consumption capacity is inferior to that of the three-dimensional metal porous plate, it is also effective when a two-dimensional metal porous plate such as punching metal is used. The reason is that when the metal sheet is non-porous, the negative electrode on the outer surface of the electrode body can consume oxygen gas only when oxygen gas passes through a slight gap between the metal sheet and the negative electrode. When a metal porous plate having a two-dimensional structure is used, in addition to this, oxygen gas that has entered through a slight gap between the metal porous plate and the outer can also passes through the holes provided in the metal porous plate to the negative electrode. Because it can reach.

[0016]

EXAMPLES Examples of the present invention will be described below. [Example 1] Commercially available misch metal (Mm, mixture of rare earth elements) as a raw material of a hydrogen storage alloy used for a negative electrode
After nickel, cobalt, aluminum and manganese are weighed in an element ratio of 1.0: 3.2: 1.0: 0.2: 0.6, they are melted and cast in a high frequency induction furnace. This makes M
A hydrogen storage alloy having a composition of mNi _3.2 CoAl _0.2 Mn _0.6 is obtained.

This alloy was mechanically pulverized and mixed with 1.0% by weight of polyethylene oxide based on the weight of the alloy and water as a dispersion medium to form a slurry. This slurry was applied to a conductive support made of punched metal plated with nickel and dried, and then pressed and cut to a predetermined thickness, and two negative electrodes were connected by exposed portions of the conductive support of the negative electrode. A storage alloy negative electrode was produced.

FIG. 1 is a perspective view of a negative electrode structure obtained by welding a non-porous nickel sheet 3 to an exposed portion 2 of a conductive support that connects the negative electrodes 1 and 1. FIG. FIG. 3 is a cross-sectional view of a battery A of the present invention manufactured using a structure.

In the figure, reference numeral 4 denotes a plate-shaped positive electrode having nickel hydroxide as an active material, and three positive electrodes and the negative electrode structure 2
A combination (four negative electrodes) is combined, and a separator 5 is interposed between the positive and negative electrodes 4 and 1 to form an electrode assembly. Reference numeral 6 denotes a square outer can made of nickel plated with iron, which also serves as a negative electrode terminal. Then, the electrode body is inserted into the outer can 6, and the nickel sheet 3 is arranged between the negative electrode 1 and the inner surface of the outer can 6 in a pressure contact state. [Example 2] In Example 1, a nickel wire mesh was used in place of the non-porous nickel sheet 3, and a battery was constructed in the same manner as in Example 1 except for the above. And Comparative Example In the above-described Example 1, the nickel sheet 3 was not connected to the exposed portion 2 of the conductive support of the negative electrode, and the negative electrode located on the outer surface of the electrode body was directly pressure-contacted with the metal outer can to make the battery. And this battery is referred to as comparative battery C.

The battery A of the present invention and the comparative battery C were respectively
After being charged with a current of 00 mA for 15 hours, it was discharged with a current of 2 A, and its discharge capacity and discharge voltage were measured. FIG. 5 is a drawing showing this result, and the discharge capacity is shown assuming that the discharge capacity of the battery A of the present invention is 100%.

It can be seen from FIG. 5 that the battery A of the present invention has a higher discharge capacity and a higher operating voltage than the comparative battery C. The battery of the present invention collects the negative electrode by contacting the nickel sheet electrically connected to the negative electrode and the inner surface of the metal outer can that also serves as the negative electrode terminal,
Since the nickel sheet, which has good conductivity, and the metal outer can are in face-to-face contact, the contact resistance between them is small, whereas the comparative battery is made of the insulating polyethylene oxide. Current is collected by contacting the surface of the negative electrode, which is bound with a hydrogen storage alloy with a sticker, and the metal outer can.The negative electrode surface has lower conductivity than the nickel sheet, and the contact resistance in the current collecting part is large. It is thought to be because

Also, the batteries A and B of the present invention and the comparative battery C were charged at a current of 100 mA for 15 hours, respectively, and then 2 A.
FIG. 6 shows the cycle characteristics when the charge / discharge cycle is repeated under the condition that the battery is discharged with the current and the discharge is stopped when the battery voltage becomes 1.0V. In the figure, the discharge capacity is shown assuming that the discharge capacity of the battery A of the present invention at the beginning of the cycle is 100%.

As is apparent from FIG. 6, the batteries A and B of the present invention have a longer cycle life than the comparative battery C. It is considered that this is due to the shape deformation of the negative electrode due to charge and discharge and the formation of the insulating film by the rare earth element eluted from the hydrogen storage alloy.

In the comparative battery C, current is collected by directly contacting the negative electrode and the metal outer can, and therefore the current collecting property is deteriorated due to the shape deformation of the negative electrode surface. However, in the batteries A and B of the present invention, the nickel sheet is used. Since the current is collected by bringing the nickel wire mesh and the metal outer can into contact with each other, the current collecting effect between the nickel sheet or the nickel wire mesh and the metal outer can is not deteriorated even when the shape of the negative electrode is deformed.

Further, as the charge / discharge cycle elapses, rare earth elements such as La constituting the hydrogen storage alloy of the negative electrode are eluted into the electrolytic solution to form an insulating compound and form a film. In Battery C, since this insulating film is formed between the negative electrode and the metal outer can, the current collection performance is reduced, whereas in the batteries A and B of the present invention, the nickel sheet or the nickel wire mesh and the metal outer can are used. Since an insulating film is not formed between and, good current collection between them can be maintained.

Next, FIG. 7 shows the results of examining changes in the internal resistance of the battery due to long-term storage of the battery. The test method is as follows. The battery A of the present invention and the comparative battery C were charged at a current of 100 mA for 15 hours, then discharged at a current of 2 A until the battery voltage became 1.0 V, and the batteries were left in an atmosphere of 40 ° C. Then, the internal resistance of the battery is measured.

From FIG. 7, it can be seen that the comparative battery C has a large increase in the internal resistance of the battery starting from about one month, whereas the battery A of the present invention shows almost no increase in the internal resistance of the battery even after being left for 3 months. .. It is considered that this point is also due to the formation of the insulating film by the rare earth element eluted from the hydrogen storage alloy as described above. [Example 3] In Example 1, a battery was constructed in the same manner as in Example 1 except that a metal porous plate made of foamed nickel was used in place of the non-porous nickel sheet 3, and this battery was used. Is referred to as Battery D of the invention.

Inventive batteries A, B and D and comparative battery C
The internal pressures of the batteries were measured when they were charged with a current of 2 A, and the results are shown in FIG. Further, the internal pressure of the battery when the batteries A and B of the present invention were charged with a current of 100 mA was measured, and the result is shown in FIG.

From FIG. 8, batteries B and D of the present invention in which a porous metal plate was interposed between the negative electrode on the outer surface of the electrode body and the outer can were
It can be seen that the internal pressure of the battery can be kept low. On the other hand, the battery A of the present invention and the comparative battery C using the non-porous metal sheet had a charging time of 2
When the time exceeds 0 minutes, the battery internal pressure rapidly increases.

This is because in the batteries B and D of the present invention, the oxygen gas generated from the positive electrode during overcharge passes through the inside of the metal porous plate interposed between the outer surface of the electrode body and the outer can, and It is considered that since the negative electrode on the outer surface was easily reached and consumed, the oxygen gas consumption capacity was increased and the internal pressure of the battery was kept low. On the other hand, in the battery A of the present invention and the comparative battery C, the negative electrode located on the outer surface of the electrode body was used unless oxygen gas passed through the slight gap between the electrode body and the non-porous metal sheet or the outer can. It is considered that the internal pressure of the battery increased sharply during overcharging because the oxygen gas could not be consumed and the sufficient oxygen gas consumption reaction was not performed.

From FIG. 9, when the charging current is relatively small, the battery A of the present invention using the non-porous metal sheet does not show a sharp increase in the battery pressure. This is because the oxygen gas generation rate in the battery is not as fast as that in the case of charging with the current of 2A shown in FIG. Even if a porous metal sheet is used, it can be sufficiently used. [Example 4] As a negative electrode, as shown in Fig. 3, the extension 7 of the conductive support of the negative electrode was made of a non-porous metal sheet, and this metal sheet was extended so as to cover one side surface of the negative electrode 1. As shown in FIG. 4, a battery E of the present invention was produced in the same manner as in Example 1 except that the negative electrode 1 and the positive electrode 4 were used one by one and combined. The same components as in Example 1 were assigned the same numbers.

It has been confirmed that the battery E of the present invention exhibits excellent characteristics in terms of discharge voltage, cycle characteristics and internal resistance of the battery after being left, like the other batteries of the present invention.

[0033]

According to the prismatic metal hydride storage battery of the present invention, a metal sheet electrically connected to an extension of the conductive support of the negative electrode or to the conductive support is provided with the negative electrode facing the metal outer can and the metal sheet. Since it is inserted between the outer can and the electrically conductive support is extended and the metal sheet is electrically connected to the metal outer can, the extension when inserting the electrode body into the metal outer can. The metal or metal sheet is exposed on the surface of the negative electrode, and the hydrogen storage alloy, which is the main constituent of the negative electrode, does not come into direct contact with the metal outer can, and the hydrogen storage alloy can be prevented from falling off from the negative electrode. Even if the hydrogen storage alloy of the negative electrode is partially eluted to form an insulating film, this film is formed on the surface of the extension portion or the metal sheet facing the negative electrode, and the extension portion or the metal sheet and the metal outer casing are formed. Since it does not hinder the electrical connection with the can, it is possible to maintain good current collecting performance of the negative electrode.

By using a porous metal plate as an extension of the conductive support or a metal sheet inserted between the negative electrode and the metal outer can, oxygen gas consumption capacity is improved and rapid charging is possible. Becomes

[Brief description of drawings]

FIG. 1 is a perspective view of a negative electrode structure used in a battery according to an embodiment of the present invention.

FIG. 2 is a sectional view of a battery according to an embodiment of the present invention.

FIG. 3 is a perspective view of a negative electrode structure used in a battery of another example of the present invention.

FIG. 4 is a cross-sectional view of a battery according to another embodiment of the present invention.

FIG. 5 is a discharge characteristic diagram of a battery.

FIG. 6 is a cycle characteristic diagram of a battery.

FIG. 7 is a diagram showing internal resistance of a battery after being left unattended.

FIG. 8 is a diagram showing the internal pressure of a battery when charged with a current of 2A.

FIG. 9 is a drawing showing the internal pressure of a battery when charged with a current of 100 mA.

[Explanation of symbols]

 1 Negative Electrode 2 Exposed Part of Conductive Support 3 Nickel Sheet (Metal Sheet) 4 Positive Electrode 5 Separator 6 Metallic Outer Can 7 Extended Part of Conductive Support

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsukasa Ito 2-18 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. An electrode body comprising a negative electrode having a hydrogen-absorbing alloy held on a conductive support, a positive electrode, and a separator interposed between the both electrodes, and a metal outer can that also serves as a negative electrode terminal. A metal sheet that is housed and has a negative electrode arranged on the surface of the electrode body that faces the metal outer can, and the metal sheet electrically connected to the extension of the conductive support or the conductive support is placed in the metal outer can. A prismatic metal hydride storage battery in which the negative electrode and the metal outer can are electrically connected to each other via an extension of the conductive support or a metal sheet while being inserted between the opposing negative electrode and the metal outer can. .. 2. The prismatic metal hydride according to claim 1, wherein the extension of the conductive support or the metal sheet interposed between the negative electrode and the metal outer can is a metal porous plate. Storage battery.