JPH1186897A - Sealed nickel hydrogen battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealed nickel hydrogen battery with which the cycle service life can be remarkably improved more than usual without the use of a complicated process and a material. SOLUTION: In a sealed nickel hydrogen battery, a safety valve 4 is provided in an upper end part of a case 1, and an electrolyte-holding porous body 2 is arranged on a gas storage space side in the case 1. An injection quantity of an electrolyte is also filled by increasing the quantity by 5 to 40% more than normal, so as to become higher than an upper end surface of a plate. When the electrolyte is filled above the upper end surface of the plate in this way, the cycle service life of the sealed nickel hydrogen battery can be markedly prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sealed nickel-metal hydride battery.

[0002]

2. Description of the Related Art A conventional sealed nickel-metal hydride battery in which an electrode assembly in which a nickel positive electrode plate and a hydrogen storage alloy negative electrode plate are formed in a spiral or laminated shape with a separator interposed therebetween is sealed in a case together with an electrolyte, A safety valve is provided on the top plate of the case to prevent the case from being ruptured due to an increase in battery internal pressure.

In a sealed nickel-metal hydride battery having such a safety valve, in order to prevent the electrolyte from leaking out of the safety valve when the safety valve is operated, an excessive amount of the electrolyte is used to prevent the electrolyte from leaking from the upper edge of the electrode plate in use. So that it does not stay in the gas storage space above it. That is, if the case is tilted, falls, or receives an external impact for some reason during the operation of the safety valve, the excessive electrolyte remaining in the gas reservoir space leaks or blows out from the opened safety valve. To do that. Such a situation also occurs when the safety valve malfunctions.

[0004] Since the electrolytic solution is for realizing ionic conduction between the positive and negative electrode plates, it is theoretically injected to the upper edge of the lower one of the two electrode plates. The amount of the injected electrolyte is generally limited to an amount that can be filled in the pores inside the porous electrode plate or the separator, since a capillary phenomenon actually exists. Therefore, conventionally, it does not contribute to the battery reaction, reduces the effective gas accumulation capacity of the gas storage space, and causes a danger of liquid leakage when the safety valve is activated. The injection amount is controlled so as not to excessively stay in the air core portion of the electrode assembly of the cylindrical battery or the gas reservoir space above the upper edge of the electrode plate.

[0005] The larger the volume of the gas reservoir space is, the larger the amount of gas generated can be. The effect of suppressing the increase in the internal pressure of the battery is reduced. The pressure resistance of the case (for example, 5 to 10 atmospheres) is reduced as much as possible within the allowable gas generation amount. In spite of the above description, it is normal for the manufactured battery to carry out several initial charge / discharge cycles (initial activation treatment) for activation of the electrode plate. A certain amount of electrolyte may increase the volume below the upper edge of the electrode plate, or the gas remaining there may be replaced by the electrolyte.
Therefore, in preparation for an increase in the amount of electrolyte that can be absorbed by the electrode plate and the separator due to the initial activation process, a certain amount of spare electrolyte is temporarily held in the gas reservoir space above the upper edge of the electrode plate. It is possible.

[0006] When the battery is shipped after the initial activation process, the spare electrolyte is completely absorbed by the electrode plate and does not stay at the upper edge of the electrode plate. Never.

[0007]

The most important issues in battery development are improvement of capacity per unit weight and deterioration of the battery over time, that is, extension of cycle life. Often, high capacity batteries have a short cycle life and long life batteries have a small capacity. The present invention has been made in view of the above problems, without using complicated steps and materials,
An object of the present invention is to provide a sealed nickel-metal hydride battery capable of significantly improving the cycle life as compared with the related art.

[0008]

According to the first aspect of the present invention, liquid leakage from the safety valve can be effectively prevented. According to the second aspect of the present invention, in the sealed nickel-metal hydride battery according to the first aspect, the electrolyte further includes an amount of the electrolytic solution in addition to the amount of the basic solution filled in the case within a range not reaching the upper edge of the electrode plate. The excess liquid amount is further added. This excess liquid amount is 5 to 40% of the basic liquid amount and 30% of the gas storage space volume.
It is set to ~ 70%. Thereby, the cycle life can be improved. When the amount of the liquid is less than the above range, the effect of extending the cycle life is not sufficient, and when the amount of the liquid exceeds the above range, the capacity per battery volume is remarkably reduced.

SUMMARY OF THE INVENTION The inventors of the present invention have found that a complicated process can be performed by accumulating an electrolytic solution in a part of a gas storage space in which there is no electrode plate located above the opposing portions of the positive and negative electrode plates which seem to be useless. It has been found that the cycle life of a sealed nickel-metal hydride battery can be improved to an unpredictable level without using any material. Although the reason has not been elucidated yet, the present inventors speculate as follows.

One reason is that in a sealed nickel-metal hydride battery, as the charge / discharge cycle is repeated, the electrode assembly expands and the case spreads mainly horizontally. While repeating this process several tens of times or more, the case is plastically deformed, so that the space below the upper edge of the electrode plate is increased, and the required amount of electrolyte may be increased. Another reason is that the hydrogen storage alloy powder constituting the negative electrode of the hydrogen storage alloy is pulverized by repetition of charge / discharge cycles many times, and the absorbable electrolyte amount (porosity) of the negative electrode of the hydrogen storage alloy increases accordingly. Thus, it is conceivable that the required amount of electrolyte solution increases.

In addition, since the electrolyte is contaminated during the charge / discharge cycle or the activity is reduced due to ion substitution or oxidation, it is conceivable that the larger the amount of the electrolyte, the smaller the effect of this problem. It is unknown at this time which reason is appropriate, but the cycle life of the sealed nickel-metal hydride battery is significantly improved by injecting the electrolyte until it stays in the gas storage space even after the initial activation treatment. Can be extended to

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a battery, a stacked battery can be employed in addition to a cylindrical sealed battery. Rare earth alloys, titanium alloys, zirconium alloys, etc. can be used as the hydrogen storage alloy powder.Methyl cellulose, carboxymethyl cellulose, etc. can be used as the thickener, and as the binder Can be made of polytetrafluoroethylene (PTFE), styrene-butadiene copolymer, or the like. As the electrolyte for a battery using a hydrogen storage alloy electrode, a KOH aqueous solution, KO
H, LiOH mixed aqueous solution, KOH, LiOH, NaOH
A mixed aqueous solution or the like can be used, and as the current collector, foamed nickel, punching metal, or the like can be used.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A sealed cylindrical nickel hydride battery to which the present invention is applied will be described below. FIG. 1 shows an axial partial cross-sectional view of a half portion on the positive electrode side of a cylindrical sealed nickel hydride battery of this embodiment. Reference numeral 1 denotes a cylindrical case whose one end opening is closed by a disc-shaped cover plate 3 via a resin ring 2 for electrical insulation. An opening 3a is formed in the cover plate 3, and a safety valve 4 for releasing pressure when the battery internal pressure rises is provided. The safety valve 4 is urged toward the opening 3a of the cover plate 3 by a spring 8a inside a cap-shaped + terminal 8 fixed to the upper surface of the cover plate 3.

Reference numeral 5 denotes an electrode assembly, which is formed in a cylindrical shape by stacking a positive electrode plate 6 and a negative electrode plate 7 via a separator (not shown) and spirally winding them. However, in FIG. 1, the electrode assembly 5 is schematically illustrated. 6
Reference numeral 1 denotes the upper edge of the positive electrode plate 6, and 71 denotes the lower edge of the negative electrode plate 7. The + terminal 8 is electrically connected to the disk-shaped current collector plate 9 which is resistance-welded to the upper edge 61 of the positive electrode plate 6 of the electrode assembly 5 via the lid plate 3 and the leads 9a. ing.

Similarly, the upper end surface of the current collector 10 is resistance-welded to the lower edge 71 of the negative electrode plate 7. More specifically, radial projections are provided on the lower end surface of the current collector plate 9 and the upper end surface of the current collector plate 10, and the projections are resistance-welded to the electrode plates 6 and 7. Reference numeral 12 denotes a porous body for holding an electrolyte, which is fixed to the gas storage space 14 side by a support member 15 so as to cover the opening 3a of the cover plate 3. Support member 15
Has an opening 15a for venting gas. Opening 1
The position of 5a and the shape of the support member 15 may be different from those shown. The electrolyte holding porous body 12 is made of an alkali-resistant porous material (for example, a polypropylene nonwoven fabric).
It has a function of holding the electrolyte when the battery is placed sideways or when venting gas.

A method for assembling this battery will be described below. First, the electrode assembly 5 is formed, and the current collector 10 is resistance-welded to the lower edge of the negative electrode plate 7, accommodated in the case 1, and welded to the bottom of the case 1. Next, the current collector plate 9 integral with the + terminal 8 is resistance-welded to the upper edge portion 61 of the positive electrode plate 6. Next, the current collecting plate 9 and the cover plate 3 are connected by a lead 9a.

The semi-finished battery formed in this way has 5
The electrolyte is injected into the space evacuated to 50 mHg. Thereafter, the cover plate 3 is caulked at one end of the case 1 via the resin ring 2 and the cover plate 3 is fixed. According to the above-described embodiment, since the opening inside the case 1 of the safety valve 4 is covered with the porous body 12 for holding the electrolytic solution, the internal pressure of the case increases and the safety valve 4 for venting gas is used. Even when it is opened, the electrolyte is held by the electrolyte holding porous body 12, so that liquid leakage from the safety valve 4 can be prevented. As described above, since the structure is such that liquid leakage from the safety valve 4 can be prevented, a large amount of excess liquid exceeds the amount (basic liquid amount) of the electrolytic solution absorbed and held by the electrode plate or the like. And the cycle life can be significantly improved as compared with the prior art. (Experiment) The composition was MmNi _3.6 Co _0.7 Al _0.4 Mn _0.3 (L
a / Mm = 0.6) mechanically pulverized hydrogen storage alloy powder having a mesh size of 100 mesh or less, nickel powder was mixed with the hydrogen storage alloy powder in an amount of 5 wt%, and MC (methyl cellulose) was used as a binder. A 2 wt% aqueous solution was added to the hydrogen storage alloy powder at 20 wt% and stirred to form a paste.

Next, this paste was applied on a punching metal having a thickness of 70 μm to produce a hydrogen storage alloy negative electrode 7. The dimensions of the hydrogen storage alloy negative electrode 7 are 246 mm in total length and 3 in width.
4 mm, thickness 0.46 mm. The positive electrode plate 6 has a total length of 186 mm, a width of 34 mm, and a thickness of 0.71 mm.
It is a Zn-based nickel hydroxide plate. The separator used was a polypropylene membrane having a weight of 70 g per square meter.

The electrolyte is 6.8N KOH and 0.8N L
4.36 g for sample 1, 4.82 g for sample 2, 5.23 g for sample 3, and 5.6 for sample 4.
0 g, and for Sample 5, 6.12 g. The negative electrode is 1.
It was designed to be seven times the capacity. The capacity of these batteries is 0.2
After the initial activation process of performing C charge / discharge 32 cycles,
Charging is 1C (2.4A) and rated capacity is 2.4Ah 110
%, And after a 30-minute pause, the operation was performed at 1 C (2.4 A) until the open terminal voltage reached 0.85 V, and a charge / discharge cycle of a 30-minute pause was performed 200 to 1500 times. In addition,
Ten samples of each of the samples 1 to 5 were prepared, and after the initial activation treatment, the sample was opened and the liquid level of the electrolyte was examined. In samples 4 and 5, the electrolytic solution exceeded the upper edge 61 of the positive electrode plate 6.

FIG. 2 shows the results. From FIG. 2, when the electrolyte solution did not exceed the upper edge 61 of the positive electrode plate 6 after the initial activation treatment, the cycle life was 600 times on average, but the sample 4 exceeded 800 times on average and the sample 5 Average 1300
Practically, a very effective result was obtained. (Modification) In the above embodiment, the porous body 12 for holding the electrolytic solution was used.
Although a synthetic resin nonwoven fabric mat was used, other liquid holding materials other than the above can be used.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a battery according to an example.

FIG. 2 is a characteristic diagram showing the results of a charge / discharge repetition test when the amount of injected electrolyte is variously changed in the batteries of Examples.

[Explanation of symbols]

 1 is a case, 3 is a cover plate (upper part of the case), 5 is an electrode assembly, 6 is a positive electrode plate, 7 is a negative electrode plate, 8 is a + terminal, 9 is a current collecting plate, and 10 is a current collecting plate. 12, a porous body for holding an electrolytic solution; 61, an upper edge portion of the positive electrode plate 6;

Claims (2)

[Claims] 1. A case having a safety valve at an upper end, a pair of positive and negative electrode plates wound or laminated with a separator interposed therebetween and housed in the case, and reaching an upper edge of the electrode plate. A sealed nickel-metal hydride battery having an electrolytic solution filled in the case within a range not to be deviated, wherein a gas reservoir space is formed between an upper end surface of the electrode plate and a lower surface of a top plate portion of the case. 3. The sealed nickel-metal hydride battery according to claim 1, further comprising a porous body for retaining an electrolyte, which is disposed in a gas storage space of the case so as to cover a valve port of the safety valve. 2. The sealed nickel-metal hydride battery according to claim 1, wherein the amount of the electrolytic solution is such that the liquid level does not exceed the upper edge of the electrode plate. The amount of the base solution is an amount of the base solution and the amount of the excess solution exceeding the base solution amount. The excess solution amount is 5 to 40% of the base solution amount of the electrolytic solution.
Characterized in that the volume is set to 30 to 70% of the volume of the gas reservoir space.