JPH09237619A - Safety valve device for sealed type battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably maintain a valve operating pressure over a long period, ensure reliability, with following capable even to changing of an internal pressure according to a rapid temperature rise of a battery, and eliminate bursting or the like due to a rise of internal pressure of the battery, in the case of using in a various portable equipments. SOLUTION: As an elastic valve unit 7 of a safety valve device for a sealed type battery, after a component consisting of a mixture of olefin system resin and ethylene propylene rubber is mixed with ethylene propylene rubber material (EPDM), by using this EPDM crosslinkaged, relating to a rise of internal pressure according to a rapid temperature rise of the battery, a valve operating pressure is decreased, so as to obtain high safety by making exhaust ability follow up. The elastic valve unit itself displays an oxidation suppressing effect of EPDM, high reliability is obtained over a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety valve device for improving the safety of a sealed battery, and more particularly to improvement of its gas exhaust capability at high temperatures.

[0002]

2. Description of the Related Art In recent years, with the spread of various portable devices, batteries,
In particular, rechargeable secondary batteries are widely used. Conventionally, lead storage batteries and nickel-cadmium storage batteries have been used as batteries used in these devices, but nickel-hydrogen storage batteries and lithium secondary batteries have been newly added.

Among these rechargeable batteries, in batteries using an aqueous electrolyte such as a lead storage battery, a nickel-cadmium storage battery and a nickel-hydrogen storage battery, the gas generated inside the battery is produced by the so-called Neumann method. By consuming on the opposite electrode, the battery can be sealed.

On the other hand, in a battery using a non-aqueous electrolytic solution such as a lithium secondary battery, gas cannot be lost inside the battery, and therefore, overcharging and overdischarging have been avoided to achieve hermetic sealing.

However, failure of the charger, misuse of the battery,
When an abnormal situation such as an external short circuit occurs, the internal pressure of the battery rises, which may lead to rupture. In order to prevent the battery from bursting, the secondary battery is usually equipped with a safety valve device to release the gas generated inside the battery to the outside when the internal pressure of the battery exceeds a preset value. .

Hereinafter, a sealed battery having a safety valve device will be described. FIG. 3 is an upper vertical sectional view showing a typical safety valve device for a sealed battery. In FIG. 3, a metal case 1, which is a battery container, is made of metal and has a gas vent hole 2a formed in the center through a gasket 3 which plays a role of maintaining insulation and airtightness in the upper part of the case 1. The sealing plate 2,
It is attached and fixed by caulking. Although not shown in detail in the inside of the case 1, there is provided a power generation element 4 including a positive electrode plate and a negative electrode plate which are superposed with a separator interposed therebetween, and a spirally wound electrode plate group and an alkaline electrolyte. It is stored. Further, the sealing plate 2 is provided with a cap-shaped positive electrode terminal 5 which is also used to form a safety valve device. The positive electrode terminal 5 has a cap shape,
A gas exhaust port 5a and a hole are formed in a part thereof. A valve chamber 6 is formed in a space surrounded by the positive electrode terminal 5 and the sealing plate 2, and an elastic valve body 7 is housed in the valve chamber 6 in a compressed state. As a mechanism of the elastic valve body 7, a mechanism utilizing the elasticity of a metal spring or rubber is generally used.

In the sealed battery having the above-mentioned structure, if the internal pressure of the battery rises due to excessive inflow of charging current due to failure of the charger or over-discharging accompanied by reversal of polarity, The gas in this state pushes up the elastic valve body and is discharged from the gas exhaust port 5a of the positive electrode terminal 5.

The above-mentioned safety valve device which is usually used is
The gas is set to be released to the outside when the internal pressure of the battery reaches 10 kg / cm ² or more. Therefore,
When overcharge is performed to the extent that gas generation does not occur rapidly, the internal pressure increases as the gas absorption capacity of the negative electrode decreases. At this time, even if the gas inside the battery is released to the outside, there is no problem, and if the charging is stopped and the internal pressure of the battery drops, the safety valve device returns to its original shape and is ready to be used again. Further, the rated allowable pressure of the safety valve may be increased to about 20 kg / cm ² in order to enable rapid charging.

[0009]

To solve this problem, the deformation rate of the elastic body is reduced by increasing the hardness of the elastic body forming the valve body or increasing the compression rate of the valve body, thereby reducing the internal pressure. Although the allowable value is increased, if a current above the set value flows into the battery and an abnormal gas occurs,
In the safety valve device using such an elastic body, the discharge rate from the gas exhaust port cannot keep up with the gas generation rate inside the battery. Therefore, the internal pressure of the battery rapidly rises and the battery bursts. Also, due to the temperature rise inside the battery, the elastic rubber valve body expands thermally to fill the valve chamber, and the original valve function (exhaust function)
Can no longer be maintained, and the internal pressure of the battery rises in the same manner as above, leading to rupture.

Therefore, in Japanese Unexamined Patent Publication No. 5-41204,
It is described that at least one of the packing material and the safety valve body has a melting point of 270 ° C. or lower in order to ensure safety when the battery is thrown into a fire. However, with this configuration, when an excessive current flows into the battery and the battery temperature rapidly reaches about 100 ° C., especially in the nickel-hydrogen storage battery, hydrogen stored in the negative electrode starts to be released, and the internal pressure of the battery becomes It suddenly rises and leads to a rupture. That is, the structure described in the above publication leaves room for improvement in order to cope with the rupture of the battery due to such an excessive current flow. Further, the publication also discloses that an olefin-based thermoplastic elastomer is used for the elastic valve body. However, in that structure, when the battery temperature rises, the softening or melting of the thermoplastic elastomer causes the valve operating pressure to drop too much, and the gas vent holes are substantially opened. As a result, outside air flows into the battery and accelerates the oxidation reaction of the hydrogen storage alloy of the negative electrode, and therefore it should be avoided.

As the elastic valve material, natural rubber, SBR rubber, ethylene propylene rubber, etc. have been proposed. Of these, ethylene-propylene rubber is the most excellent, but it gradually loses rubber elasticity mainly due to oxidation. Due to the deterioration of rubber elasticity over time, the valve operating pressure of the safety valve device is lowered, so that it is difficult to set the valve operating pressure for ensuring long-term reliability such as prevention of electrolyte leakage.

The present invention improves ethylene propylene rubber to maintain the valve operating pressure stable for a long period of time to ensure reliability, and to follow the change of the internal pressure due to the rapid temperature rise of the battery. It is an object of the present invention to provide a safety valve device for a sealed battery, which can eliminate the risk of rupture caused by an increase in internal pressure of the battery.

[0013]

In order to achieve the above object, a safety valve device for a sealed battery according to the present invention comprises, as its elastic valve element, a mixture of an olefin resin and ethylene propylene rubber (hereinafter referred to as R-EPDM). The following components were mixed with an ethylene propylene rubber raw material (hereinafter referred to as EPDM), and then the ethylene propylene rubber raw material was cross-linked.

Therefore, this elastic valve body basically has a structure in which EPDM mixed later is incorporated with R-EPDM therein. In this case, polypropylene or polyethylene is preferable as the olefin resin, and R-
The mixing amount in EPDM is 40 to 60% by weight, and EPDM is further mixed in this, so that the olefin resin is finally mixed with 5 parts by weight of the whole ethylene propylene rubber.
-30% by weight is optimal.

It is preferable that the valve working pressure of the safety valve device at 100 to 120.degree.
It was set so as to decrease to 60 to 20% of that at room temperature.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The R-EPDM forming the elastic valve body of the present invention described in claim 1 is characterized by a hard phase (resin phase) imparting thermoplasticity and a soft phase imparting elasticity. (Rubber phase). When a large current of a set value or more flows in the battery, which causes the battery temperature to rise and gas abnormalities to occur, the hard phase softens, causing the operating pressure of the elastic valve element to drop, and Therefore, the gas discharge rate from the gas exhaust port can be increased. By allowing the gas discharge rate to follow the internal gas generation rate, it is possible to prevent the battery internal pressure from rising and prevent the battery from bursting due to an abnormal internal pressure.

EPDM is mixed with R-EPDM,
Since it crosslinks itself, the crosslinked structure of EPDM is maintained even if R-EPDM softens at high temperature.
The PDM works to prevent the valve operating pressure from being excessively lowered, and after the valve is operated, the gas exhaust port is closed again and the outside air does not flow into the battery. As a result, in a battery, particularly a nickel-hydrogen storage battery or a lithium battery, it is possible to prevent the occurrence of an abnormal situation caused by the inflow of air or oxygen from the outside into the battery.

Further, the elastic valve body is composed of R-EPDM and EPD.
Since it is formed of a mixture with M, oxygen molecules are less likely to permeate from the surface of the elastic valve body to the inside, and EP accompanying oxidative deterioration
The destruction of the DM cross-linking structure is suppressed, the valve operating pressure is kept stable for a long time, and the reliability can be secured.

Regarding the mixing ratio of the olefin resin to the total ethylene propylene rubber, if the mixing ratio is 5% by weight or more, after mixing, EPDM is crosslinked to form an elastic valve body, and when a safety valve device is constructed, the battery is used as a battery. When a large current exceeding the set value flows, the battery temperature rises, and gas abnormalities occur, the hard phase (resin phase) softens, and the operating pressure of the elastic valve element decreases, As a result, the gas discharge rate from the gas exhaust port increases. Since the gas discharge rate follows the internal gas generation rate, it is possible to prevent the battery internal pressure from rising and prevent the battery from bursting. Furthermore, due to the effect of suppressing the oxidation of ethylene propylene rubber by the olefin resin in R-EPDM, it is possible to prevent the valve operating pressure from decreasing or fluctuating in the normal operating temperature range. On the other hand, when it is 30% by weight or more, after mixing, EPDM is cross-linked to form an elastic valve element, and when a safety valve device is configured, a large current of a set value or more flows in the battery, and when the battery temperature rises, the hard valve becomes hard. Since there are many phases (resin phases), when softened by heating, the valve operating pressure drops excessively and the gas exhaust port becomes open after valve operation. Especially, for nickel-hydrogen storage batteries and lithium batteries, air and oxygen from the outside It cannot be prevented from flowing into the battery and should be avoided. Therefore, the olefin resin is preferably 5 to 30% by weight based on the total ethylene propylene rubber.

[0020]

Embodiments of the present invention will be described below with reference to FIG. Note that FIG. 3 shows a safety valve device using a rubber elastic valve body, and the structure is such that the sealing plate 2 is provided with a positive electrode terminal 5 which is also used for constituting the safety valve device. The positive electrode terminal 5 has a cap shape, and a gas exhaust port 5a and a hole are formed in a part thereof. A valve chamber 6 is formed in a space surrounded by the positive electrode terminal 5 and the sealing plate 2, and an elastic valve body 7 mainly made of rubber is housed in the valve chamber 6 in a compressed state.

(Example 1) The safety valve device shown in FIG. 3 was constructed, and the mixing ratio of the olefin resin forming the elastic valve body 7 and the total ethylene propylene rubber was examined.

The olefinic resin in R-EPDM is
30% by weight, based on the total ethylene propylene rubber, of EPDM which is mixed with EPDM which has been previously heat treated at a temperature of 200 ° C. in EPDM and crosslinked, and then heat treated at a temperature of about 180 ° C. for 6 minutes. By mixing at a ratio of 5% by weight and 5% by weight, elastic valve bodies obtained by crosslinking the EPDM portion were prepared, and safety valve devices A, B and C of the present invention were constructed using these valve bodies.

As a comparative example, a safety valve device D using an elastic valve body in which an olefin resin is mixed at a ratio of 50% by weight with respect to all ethylene propylene rubber and a EPDM portion is subjected to a crosslinking treatment, and as a conventional example, only a safety valve device D is used. Each safety valve device E using the elastic valve body prepared from the above was constructed.

Using the above safety valve devices A to C of the present invention, an A-size sealed nickel alloy having a nominal capacity of 1600 mAh
A hydrogen storage battery was produced and used as batteries a, b and c, respectively. Further, the same safety valve device D of the comparative example and the safety valve device E of the conventional example were used to fabricate sealed nickel-metal hydride storage batteries similar to the above, and these batteries were designated as d and e.

Fifty types of batteries of the above-mentioned a to e were produced for each 50 cells, and a burst test was carried out assuming a control failure of the charger.
The results of continuous overcharging at a current of A (corresponding to 5C) are shown in (Table 1).

[0026]

[Table 1]

From Table 1, no rupture or ignition was observed in the batteries a, b and c according to the present invention. On the other hand, in the battery d of the comparative example, 8 cells out of 50 cells ignited. This is because the resin phase in the valve body softens due to the temperature rise of the battery in the overcharged state, so the valve operating pressure drops excessively, the gas exhaust port opens after the valve operates, and the outside air flows into the battery. It is thought that it depends. In the battery e of the conventional example, 17 cells out of 50 cells burst. This is because the EPDM in the safety valve device thermally expanded against the rise of the battery temperature and the battery internal pressure in the overcharged state, blocking the valve chamber to prevent the gas discharge, and the exhaust pressure function of the battery internal pressure was lowered, causing the explosion. Conceivable. In order to confirm the above results, the maintenance rate of valve operating pressure (when the initial value is 100) accompanying the temperature rise of the safety valve devices A to E of the batteries a to e was measured next. The result is shown in FIG.

From FIG. 1, safety valve devices A and B according to the present invention are shown.
The valve operating pressure in C and C begins to decrease in proportion to the amount of resin mixed in the valve body from around 100 ° C. due to the softening of the resin phase in the valve body due to the temperature rise. The temperature decreases to 60 to 20%, and at a temperature higher than that, the closing function of the elastic valve body is maintained by the crosslinked EPDM, and the valve operating pressure is kept almost constant. Therefore, since the maintenance rate of the valve operating pressure due to the temperature rise is reduced,
The valve body is plastically deformed and the exhaust pressure function is improved. As shown in the results (Table 1), the battery is highly safe.

Further, in the safety valve device D of the comparative example, the valve operating pressure is excessively lowered due to the softening of the resin phase in the valve body due to the temperature rise, and the function of closing the elastic valve body is not shown. It supports the result. Further, in the safety valve device E of the conventional example, the EPDM thermally expands due to the temperature rise, and the exhaust pressure function decreases, which shows the increase of the valve operating pressure.
The results for the batteries in Table 1 are supported.

(Embodiment 2) A to A shown in the above Embodiment 1
Using 5 kinds of safety valve devices of E, the heat deterioration resistance of the elastic valve body was examined. The valve operating pressure was measured after storing for a certain period in an environment of an ambient temperature of 65 ° C.
The relationship between the storage period and the valve operating pressure maintenance rate is shown in FIG.
As an index of the long-term reliability of the valve operating pressure of the safety valve device, the target was to maintain the valve operating pressure at a maintenance rate of 85% or more. From this FIG. 2, compared to the conventional safety valve device E using only EPDM, R-EPDM and EPDM are mixed,
Safety valve device A using an elastic valve body obtained by bridging EPDM,
The degree of deterioration of B, C and D due to heat is small. At the same time, it is also found that the heat resistance is improved for a long period of time by increasing the mixing ratio of the olefin resin to the total ethylene propylene rubber. Therefore, if the mixing ratio of the olefin resin of the present invention to the total ethylene propylene rubber is 5% by weight or more, it is clear that the reduction of the valve operating pressure can be prevented by the oxidation inhibiting effect of EPDM, and the safety valve having high long-term reliability A device can be provided.

[0031]

As described above, according to the safety valve device of the present invention, the valve operating pressure can be stably maintained for a long period of time to ensure reliability. Further, exhaust can be dealt with even when the internal pressure of the battery rises due to a rapid temperature rise such as when the battery is abnormally used, and a sealed battery for high safety can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing experimental results for confirming the effects in Example 1 of the present invention.

FIG. 2 is a graph showing a long-term reliability evaluation result of the valve operating pressure of the safety valve device according to the second embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view showing an example of a safety valve device for a sealed battery.

[Explanation of symbols]

 1 case 2 sealing plate 2a gas vent hole 3 gasket 5 positive electrode terminal 5a gas exhaust port 6 valve chamber 7 elastic valve body

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Suzuki, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Toshihisa Hiroshima, 1006, Kadoma, Kadoma City, Osaka Matsushita Electric Industrial

Claims (7)

[Claims] 1. A safety valve device for sealing an opening of a battery container accommodating a power generating element, wherein the safety valve device has a dish-shaped sealing plate having a gas vent hole in a central portion, and the safety valve device is disposed on the sealing plate. The elastic valve body is configured by an elastic valve body that closes the gas vent hole and a cap-shaped terminal that locates the valve body in a space that forms a valve chamber, and the elastic valve body is ethylene propylene cross-linked with an olefin resin. A safety valve device for a sealed battery, which is obtained by mixing an ethylene propylene rubber raw material with a component composed of a rubber mixture and then crosslinking the mixture. 2. The safety valve for a sealed battery according to claim 1, wherein the elastic valve body has a crosslinked ethylene propylene rubber raw material in which a mixture of an olefin resin having a lower softening point and ethylene propylene rubber is incorporated. apparatus. 3. The safety valve device for a sealed battery according to claim 1, wherein the olefin resin in the mixture of the olefin resin and ethylene propylene rubber is polypropylene or polyethylene. 4. A mixed amount of an olefin resin in a mixture of a component composed of a mixture of an olefin resin and ethylene propylene rubber and an ethylene propylene rubber raw material,
5-30% by weight based on the total ethylene propylene rubber
The safety valve device for a sealed battery according to claim 1 or 2. 5. A safety valve device for sealing an opening of a battery container accommodating a power generating element, the safety valve device having a plate-like sealing plate having a gas vent hole in a central portion thereof, and being disposed on the sealing plate. It is composed of an elastic valve body that closes the gas vent hole and a cap-shaped terminal that locates this valve body in the space that forms the valve chamber, and the elastic valve body is composed of a mixture of an olefin resin and ethylene propylene rubber. It is composed of a mixture of a component and an ethylene propylene rubber raw material, the ethylene propylene rubber raw material is a crosslinked one, and a mixture of an olefin resin and an ethylene propylene rubber is incorporated therein, and the olefin resin and the ethylene are mixed. A mixture of propylene rubber that plastically deforms by heating and substantially lowers the valve operating pressure when the battery becomes hot. Safety valve device. 6. A safety valve device for sealing an opening of a battery container accommodating a power generating element, the safety valve device having a dish-shaped sealing plate having a gas vent hole in a central portion thereof, the safety valve device being disposed on the sealing plate. It is composed of an elastic valve body that closes the gas vent hole and a cap-shaped terminal that locates the valve body in the space that forms the valve chamber. The valve operating pressure of the safety valve device is 100 to 100.
At 120 ° C., the valve operating pressure at room temperature is 60 to 20
Safety valve device for sealed batteries, characterized in that 7. The elastic valve body comprises a mixture of a component composed of a mixture of an olefin resin and ethylene propylene rubber, and a mixture of an ethylene propylene rubber raw material, wherein the ethylene propylene rubber raw material is crosslinked to form an olefin resin. The safety valve device for a sealed battery according to claim 6, wherein a mixture of ethylene propylene rubber is incorporated therein.