JPH0541205A - Alkaline secondary battery - Google Patents

Abstract

PURPOSE:To secure safety sufficiently even if a battery is improperly used by forming at least a part of a current path connecting a nickel positive electrode and a battery positive electrode terminal by a fusible alloy having a melting point of 100-200 deg.C. CONSTITUTION:At least a part of a current path connecting a nickel positive electrode and a battery positive electrode terminal 1 is formed by a fusible alloy 2 having a melting point of 100-200 deg.C in an alkaline secondary battery containing a group of plates having a nickel positive electrode. First a paste type nickel positive electrode is made, and to its end portion one end of a tab is welded so as to form a terminal for welding 1, whose both end portions are made of Ni or Ni plated Fe. The center portion of the tab is formed by a fusible metal 2 having a melting point of 120 deg.C. The alloy 2 is covered by a heat contraction tube made of fluororesin, so that the alloy 2 is isolated from electrolyte and so as to prevent the fused alloy 2 from causing an internal short circuit. Thereby it is possible to secure safety sufficiently even if the battery itself is used improperly.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alkaline secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices are becoming more portable and cordless due to higher integration of electronic components and advances in packaging technology. Along with this, there is an increasing demand for higher capacity of alkaline secondary batteries for driving the electronic devices.

In order to meet the demand for higher capacity, the nickel-cadmium secondary battery is improved in battery structure, the utilization rate of the nickel electrode as the capacity regulating electrode is improved, or the sintered type electrode is changed to the paste type electrode. By using electrodes, the battery capacity is improved by about 40%. Furthermore, as a nickel-hydrogen secondary battery using a hydrogen storage alloy for the negative electrode, one having a battery capacity increased to about twice that of the nickel-cadmium secondary battery has been developed.

However, the alkaline secondary battery has a risk of causing an accident when it is used improperly. For example, when an AA size nickel cadmium secondary battery in a fully charged state is short-circuited, an extremely large current of about 30 to 50 A flows at the beginning of the short circuit and the battery temperature rises sharply. There is a risk that the electrolyte will blow out from the safety valve that is installed, and that part of the battery can will glow red. Further, even when the alkaline secondary battery is continuously overcharged with a large current due to a failure of the quick charging device or the like, there is a risk as described above. The risk of inappropriate use of such an alkaline secondary battery increases as the capacity of the alkaline secondary battery increases.

In the battery pack containing a plurality of alkaline secondary batteries inside the case, a thermal fuse or a bimetal type overtemperature protector is provided inside the case in order to avoid an accident when the battery is improperly used. Safety devices such as the above are incorporated. However, no safety measures could be taken when using the battery alone.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the problems of the prior art, and provides an alkaline secondary battery having sufficient safety even when it is used improperly. It is the one we are trying to provide.

[0007]

The present invention relates to an alkaline secondary battery containing an electrode group having a nickel positive electrode,
The alkaline secondary battery is characterized in that at least a part of a conductive member that connects the nickel positive electrode and a battery positive electrode terminal is formed of fusible alloy having a melting point of 100 to 200 ° C.

Examples of the negative electrode which constitutes the electrode group together with the nickel positive electrode include a hydrogen storage alloy negative electrode and a cadmium negative electrode. For example, in the case of an electrode group in which a separator is interposed between a non-sintered nickel positive electrode and a hydrogen storage alloy negative electrode, the configuration will be described below.

As the non-sintered nickel positive electrode, a mixture of nickel hydroxide as an active material and a binder and, if necessary, cobalt oxide is added to a conductive core body as a current collector. What was formed is mentioned.

Examples of the binder to be mixed in the positive electrode mixture include polyacrylic acid salts such as sodium polyacrylate and potassium polyacrylate, and carboxymethyl cellulose (CMC). The compounding ratio of such a binder is preferably in the range of 0.1 to 2 parts by weight with respect to 100 parts by weight of nickel hydroxide.

The conductive core of the positive electrode has, for example, a two-dimensional structure such as punched metal, expanded metal, or wire mesh, three-dimensional structure such as foam metal, a sintered substrate of metal fibers, or a felt-like metal porous body. And the like.

The non-sintered nickel positive electrode is prepared by, for example, kneading the nickel hydroxide, the binder, and cobalt oxide in the presence of water to prepare a paste, and applying the paste to the conductive core. It is manufactured by performing roller pressing after drying. Examples of the hydrogen storage alloy negative electrode include a mixture of a hydrogen storage alloy powder, a conductive material powder, and a binder, which is formed on a conductive core body which is a current collector.

The hydrogen storage alloy blended in the mixture of the negative electrode is not particularly limited, and can store hydrogen electrochemically generated in the electrolytic solution and can absorb the stored hydrogen during discharge. Any substance that can be easily released may be used. For example, the general formula XY _5-a Z _a (where X is a rare earth element containing La, Y is Ni, Z is Co, Mn, Al, Fe, T
At least one element selected from i, Cu, Zn, Zr, Cr, V and B, and a represented by 0 ≦ a <2.0) is used. Specifically, LaNi ₅ , Mm
Ni ₅ , LmNi ₅ (Lm; lanthanum-enriched misch metal), and a part of these Nis as Co, Mn, A
Examples thereof include multi-element type elements substituted with elements such as 1, Fe, Ti, Cu, Zn, Zr, Cr, V, and B.

Examples of the conductive material powder blended in the mixture for the negative electrode include carbon black, graphite and acetylene black. The mixing ratio of the conductive material powder is preferably in the range of 0.1 to 4 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder. A more preferable mixing ratio of the conductive powder is 10% hydrogen storage alloy powder.
It is in the range of 0.1 to 2 parts by weight with respect to 0 parts by weight.

Examples of the binder to be blended in the negative electrode mixture include polyacrylic acid salts such as sodium polyacrylate and potassium polyacrylate, fluororesins such as polytetrafluoroethylene (PTFE), and Carboxymethyl cellulose (CMC) etc. can be mentioned. The blending ratio of the binder is 10% hydrogen storage alloy powder.
It is desirable that the amount be in the range of 0.1 to 5 parts by weight relative to 0 parts by weight.

The conductive core of the negative electrode has, for example, a two-dimensional structure such as punched metal, expanded metal, or wire mesh, three-dimensional structure such as foam metal, a sintered substrate of metal fibers, or a felt-like metal porous body. And the like.

The hydrogen storage alloy negative electrode is prepared by, for example, kneading the hydrogen storage alloy powder, the conductive material powder, and the binder in the presence of water to prepare a paste, and applying the paste to the conductive core. It is manufactured by performing roller pressing after drying.

Examples of the separator interposed between the non-sintered nickel positive electrode and the hydrogen storage alloy negative electrode include synthetic resin nonwoven fabrics such as nylon and polypropylene.

Examples of the fusible alloy having a melting point of 100 to 200 ° C. that forms at least a part of the current path include bismuth-based alloys such as Marott alloys and Newton alloys. The reason for limiting the melting point of such an alloy is that if the melting point is set to less than 100 ° C., even if the battery is used properly and is in a sufficiently safe state without boiling of the electrolytic solution, it cannot be used due to melting of the current path. Become. on the other hand,
If the melting point exceeds 200 ° C., even if the battery is used improperly and is in a dangerous state, the current path is not melted and the safety of the battery cannot be sufficiently ensured.

[0020]

According to the present invention, at least a part of the current path connecting the nickel positive electrode and the battery positive electrode terminal has a melting point of 100.
By forming the fusible alloy at ˜200 ° C., it is possible to obtain an alkaline secondary battery in which safety is sufficiently ensured even when improper use is made.

That is, the entire energizing current flows in the current path connecting the nickel positive electrode and the battery positive electrode terminal without distinction between charging and discharging. Therefore, when an improper use such as a short circuit is made and an excessive current flows in the current path, the fusible alloy having the melting point is melted and the current path is disconnected. Therefore, in the case of improper use such as a short circuit, accidents such as electrolyte squirting due to a sudden rise in battery temperature when an excessive current flows inside the battery can be prevented, and the secondary alkaline Sufficient battery safety can be ensured.

At the end of the life of the alkaline secondary battery,
Although the battery temperature rises rapidly even when the current value flowing inside the battery is small, when the battery temperature rises near the melting point of the molten alloy, the alloy melts and the current path is cut. Therefore, the safety of the alkaline secondary battery can be sufficiently ensured even when it is used at the end of its life.

[0023]

Embodiments of the present invention will now be described in detail with reference to the drawings. Example 1

First, 90 parts by weight of nickel hydroxide, 10 parts by weight of cobalt oxide as an additive, 0.3 parts by weight of CMC as a binder and 0.3 parts by weight of sodium polyacrylate were mixed and stirred. While adding water until a paste form was obtained, a positive electrode active material paste was prepared. Continuing,
This positive electrode active material paste was filled in a felt-like metal porous body, dried, and pressed to produce a paste-type nickel positive electrode. Subsequently, one end of a tab as shown in FIG. 1 was welded to the end of the obtained nickel positive electrode by a spot welder. That is, both ends of the tab are the welding terminals 1 made of Ni or Fe plated with Ni, and the central portion of the tab has a melting point of 120 ° C. which is also used for a commercially available claw thermal fuse or the like. Easy Fusion (Bi: Pb: Sn = 46.
1: 19.7: 34.2) 2. The fusible alloy 2 is coated with a heat-shrinkable tube made of fluororesin (not shown) in order to isolate the alloy 2 from the electrolytic solution and to prevent the molten alloy 2 from causing an internal short circuit. ..

On the other hand, lanthanum enriched misch metal (L
m), nickel, cobalt, manganese, and aluminum were weighed and mixed so that the composition was LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3, and then melted and cooled in a high-frequency induction furnace to prepare a hydrogen storage alloy ingot. Subsequently, this ingot was heat-treated in an electric furnace and then pulverized to obtain a hydrogen storage alloy powder. After mixing 1% by weight of carbon black, 0.5% by weight of CMC, and 0.5% by weight of sodium polyacrylate with the obtained hydrogen storage alloy powder, water was added with stirring until a paste was formed, and the negative electrode activity was A material paste was prepared. The negative electrode active material paste was applied to a punched metal, dried, and pressed to prepare a hydrogen storage alloy negative electrode.

Next, the nickel positive electrode and the hydrogen storage alloy negative electrode were wound around a nylon separator having a melting temperature of about 220 to 250 ° C., and these were housed in a battery can. Next, after pouring an alkaline electrolyte into the battery can and sealing it, an initial charge is performed to perform AA as shown in FIG.
A size nickel-hydrogen secondary battery was manufactured.

That is, the nickel positive electrode 3 is spirally wound with the separator 5 interposed between the nickel positive electrode 3 and the hydrogen storage alloy negative electrode 4, and is housed in the bottomed cylindrical battery can 6. The alkaline electrolyte is contained in the battery can 6. A circular metal plate 7 having a hole in the center is arranged in the upper opening of the battery can 6. Ring-shaped insulating gasket 8
Is disposed between the peripheral edge of the metal plate 7 and the upper opening of the battery can 6, and the battery can 6 and the metal plate 7 are hermetically sealed by caulking to reduce the diameter of the upper opening inward. It is fixed. The tab 9 has one end welded to the upper end of the positive electrode 3 and the other end welded to the lower surface of the metal plate 7.
The hat-shaped battery positive electrode terminal 10 is arranged on the metal plate 7 so as to cover the hole of the metal plate 7. The rubber safety valve 11 is arranged so as to close the hole of the metal plate 7 in the space surrounded by the metal plate 7 and the positive electrode terminal 10. The circular sealing plate 12 having a hole with a large opening in the center is arranged so as to pass the projection of the positive electrode terminal 10 through this hole, and the flange of the positive electrode terminal 10 is clamped together with the metal plate 7. The positive electrode terminal 10 is fixed. Exterior tube 1 with upper and lower openings bent inward
3 fixes the sealing plate 12 by covering the outer peripheral surface of the battery can 6 and sandwiching the peripheral edge of the sealing plate 12 with the inwardly bent opening end of the battery can 6. ing. A current path connecting the nickel positive electrode 3 and the positive electrode terminal 10 is constituted by the metal plate 7 and the tab 9. Example 2 and Comparative Examples 1 to 3 A nickel-hydrogen secondary battery similar to that of Example 1 was manufactured except that a tab having a central portion made of a material having a melting point shown in Table 1 below was used.

Regarding the batteries of Examples 1 and 2 and Comparative Examples 1 to 3 thus obtained, charging and discharging were performed assuming that the batteries were properly used while measuring the battery temperature by attaching a thermocouple to the side surface of each battery. Using the apparatus, a test was performed in which charging / discharging was performed in which the battery was charged to 200% at 1 CmA and discharged to 0.8 V at 1 A for 10 cycles. Battery characteristics were stable in this test 10
The discharge capacity of each battery after the end of charging in the second cycle, and
The maximum temperature reached on the side surface of each battery during the 0th cycle charging was examined. Further, each battery after this test was disassembled to examine whether or not the tab was melted. The results are also shown in Table 1 below.
In addition, in the battery of Comparative Example 3, the discharge capacity could not be measured because the tab melted down during 200% charging at 1 CmA.
Further, FIG. 3 shows changes in the battery temperature with respect to the amount of charged electricity when the battery of Example 1 was charged to 200% at 1 CmA.

Further, the batteries of Examples 1 and 2 and Comparative Examples 1 to 3 were subjected to a test of continuously charging at 5 A until the batteries could not be charged, assuming that the rapid charging device failed while measuring the battery temperature. It was In this test, the maximum temperature reached for each battery was examined. Further, each battery after this test was disassembled to examine whether or not the tab was melted. These results are shown in Table 1 below.
Also described in.

For the batteries of Examples 1 and 2 and Comparative Examples 1 to 3, while measuring the temperature on the side surface of the battery, 1 at 1/3 CmA was applied.
After charging 50%, a short circuit test was performed. In this test, the maximum temperature reached on the side surface of each battery was examined. Furthermore,
After the test, each battery was disassembled to check whether the tab was blown. The results are also shown in Table 1 below.

[0031]

[Table 1]

As is apparent from Table 1, the batteries of Examples 1 and 2 were blown out by the tabs and the battery temperature was 20 when the batteries were improperly used such as continuous charging at 5 A or short circuit.
It can be seen that the temperature is suppressed to 0 ° C or lower, and the safety is sufficiently secured. This is because the melting point of the fusible alloy forming the central portion of the tab is 100 to 200 ° C., so that the fusible alloy is melted due to an increase in battery temperature due to improper use.

On the other hand, in the battery of Comparative Example 1, the tab is not blown out even if the battery is improperly used such as continuous charging at 5 A or short circuit, and the battery temperature greatly exceeds 200 ° C., which is dangerous. Inviting the state. In fact, it was found that by disassembling the battery after the test, the nylon separator melted and caused an internal short circuit.

The battery of Comparative Example 2 had a battery temperature of 200 ° C. like the battery of Comparative Example 1, although the tab was blown out after improper use such as continuous charging at 5 A or short circuit. It greatly exceeds and leads to a dangerous condition.
This is because the melting point of the fusible alloy forming the central portion of the tab exceeds 200 ° C., so that the nylon separator melts before the tab melts and causes an internal short circuit.
This is because an extremely large current flows inside the battery and the battery temperature rises sharply. The battery of Comparative Example 3 is 1
It can be seen that even when the proper use of charging 200% with CmA is made, the tab is fused and becomes unusable.

Further, as is apparent from FIG. 3, in the battery of Example 1, at 200% charge at 1 CmA, the battery temperature greatly rises when the amount of charged electricity exceeds 100%, that is, in the overcharge region. But then the battery temperature is 9
When the temperature rises to around 0 ° C, the amount of heat generated by charging and the amount of heat radiated to the outside air reach equilibrium, and the rise in battery temperature stops.
Therefore, it can be seen that the safety can be sufficiently maintained when used properly. In addition, although the AA size battery has been described in the above-described embodiment, a similar effect can be obtained with a larger size A size battery or the like. Although the nickel-hydrogen secondary battery has been described in the above embodiment, the same effect can be obtained also in the nickel-cadmium secondary battery.

[0036]

As described in detail above, according to the present invention, it is possible to provide an alkaline secondary battery which is sufficiently secured in safety even when the battery is used improperly. A remarkable effect is achieved in the capacity-equipped alkaline secondary battery.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a tab used in a nickel-hydrogen secondary battery of Example 1.

FIG. 2 is a partially cutaway perspective view showing a nickel-hydrogen secondary battery of Example 1.

FIG. 3 is a characteristic diagram showing changes in battery temperature with respect to the amount of charged electricity when the nickel-hydrogen secondary battery of Example 1 was charged to 200% at 1 CmA.

[Explanation of symbols]

2 ... Easy fusion metal, 3 ... Nickel positive electrode, 4 ... Hydrogen storage alloy negative electrode, 5 ... Separator, 6 ... Battery can, 7 ... Metal plate, 9 ... Tab, 10 ... Battery positive electrode terminal.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Kaita Takeno 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Within Toshiba Battery Co., Ltd. (72) Yuuji Sato 1 Komukai-Toshiba-cho, Kawasaki-shi, Kanagawa Address Company Toshiba Corporation Research Institute

Claims (1)

[Claims] 1. In an alkaline secondary battery containing an electrode group having a nickel positive electrode, at least a part of a current path connecting the nickel positive electrode and a battery positive electrode has a melting point of 1.
An alkaline secondary battery, which is formed of easy fusion metal at a temperature of 0 to 200 ° C.