GB2094055A

GB2094055A - Hermetically sealed battery with a safety mechanism to prevent explosion.

Info

Publication number: GB2094055A
Application number: GB8205319A
Authority: GB
Original assignee: Hellesens AS
Current assignee: Hellesens AS
Priority date: 1981-03-03
Filing date: 1982-02-23
Publication date: 1982-09-08
Also published as: FR2501416A1; IL65084A0; DE3206607C2; JPS57176664A; GB2094055B; DE3206607A1; FR2501416B1; IL65084A; DK95481A

Abstract

A hermetically sealed battery with a safety mechanism to prevent explosion and consisting of a pointed member (9) mounted on the external of the battery, said member puncturing the battery, when it expands because of the internal pressure. <IMAGE>

Description

SPECIFICATION Hermetically sealed battery with a safety mechanism to prevent explosion This invention concerns a hermetically sealed bat terycomprisi#g a closed metal container which contains the current producing ingredients of the battery and which is provided with a safety mechanism to prevent explosion of the metal container.

Hermeticalysealed batteries of this kind are typically the so-called lithium batteries which contain metallic lithium as the anode material and e.g.

thionyi chloride as the electrolyte. The term "hermetically sealed" as used in the present specification should therefore be understood in the sense that not only is the container completely tight but the battery is of the type which is destroyed if the contents come into contact with the environment and which cannot be restored to function again even if the container after having been opened is sealed again. The container for such batteries is most often welded from a relatively thick plate of various steel alloys and designed to resist a considerable internal pressure, e.g. up to 10 atmospheres. However, such batteries may explode when a too high inner pressure is built up caused by a heating which may be e.g. an external heating due to fire or an internal heating due to short circuit seeing that batteries of this type have a high short circuit current.They must therefore be provided with a safety mechanism to prevent explosion.

The prior art safety mechanisms have been in the form of safety valves built into the container wall, e.g. a stopper-like insertion of glass or other corrosion resistant material which is pushed out at a certain temperature or a certain pressure, or a weakening of the container wall itself. However, these known solutions to the problem have substantial drawbacks, in part of production nature seeing that they are expensive and complicated, and in part functionally because they are not reliable.

The problem of reliability here contemplated is mainly that the valves should not open prematurely with the risk that people and equipment become destroyed by the discharged very corrosive and poisonous content but only in situations of catastrophe where an explosion would otherwise result.

Reliability in this respect is difficult to obtain because hermetically sealed batteries are designed to last for a very long period of time, e.g. 10-20 years, and during this long period corrosion can take place from inside so that a valve is shot out or a weakening in the container wall bursts at a pressure lower than intended.

Other drawbacks of the prior art safety mechanisms are that they are difficult to produce in such a way that they function at a very specific predetermined pressure and that they do not scatter the harmful contents of the container too much. For the fact is that they give a sudden opening of the entire valve opening with a resulting scattering of the contents of the container so that one might say that the only drawback of an explosion which they relieve is damage caused by shell fragments.

The battery according to the invention relieves the drawbacks of the prior art batteries by the characterising feature that externally on the metal container a pointed member is mounted at a short distance from and with the tip pointing at a surface of the container which will bulge out when the internal pressure in the container rises and which punctures the container at this bulging out.

This safety mechanism operates by puncturing the metal container when as a consequence of internal pressure the latter has expanded so much that the pointed member has penetrated the container wall.

Hereby complications of the container production is avoided, the mechanism can be adjusted to function at a definite pressure through regulation of the distance of the tip from the container wall, and the discharge of the contents of the container which takes place when the tip penetrates the container wall will not be so much like an explosion as when a valve is opened because the pointed member remains in the created opening and increases this opening very gradually.

The surface of the conainer wall in front of which the pointed member is to be placed depends on the shape of the container. When the metal container has the same thickness of plate everywhere it will in a flat battery be the side walls which bulge out when the internal pressure rises, and in a cylindrical battery it will be the end walls that bulge out. The pointed member should preferably be mounted in such manner that it is exclusively the distance of travel of the bulging surface when the battery expands which determines the distance between the surface and the pointed member. Therefore, the pointed member is preferably secured to the container at points of the latter which do not move when the container is expanding, e.g. on edges which are transition points between bulging and non-bulging surfaces.

According to the invention the pointed member is suitably mounted on a bridge which is attached to two points of the metal container, one in either end of the bridge, and which extends over the entire surface which bulges out when the internal pressure of the container rises. This provides a very secure attachment of the pointed member in the desired position, and at the same time the bridge acts as a shield which, when puncture of the container takes place, prevents the discharged liquid from scattering in the surrounding room.

Another embodiment of the battery is characterised in that the pointed member is mounted on a bracket which is attached at the border of the surface which bulges out when the internal pressure of the container rises, the bracket extending across the bulging surface so that the pointed member is situated in front of a portion of this surface which has a large distance of travel in the case of bulging.

This embodiment is advantageous from a production point of view because the mechanism can easily be attached to the container before the latter is sealed so that it is unnecessary to carry out any weldings of the sealed full container.

According to the invention the pointed member is suitably a pointed screw which passes through a nut.

In this embodiment the distance of the tip from the bulging surface of the container can easily be adjusted.

The invention is further illustrated in the drawing where Figures 1, 2, and 3 show the same embodiment of a cylindrical battery seen in two vertical sections at right angles to each other and in plan view, respectively, and Figure 4 a vertical section of an alternative embodiment of the top of a battery.

In Figures 1,2, and 3 1 is a metal cup and 2 a cover which by a welding seam 3 is secured to the cup so that the two parts together constitute a hermetically sealed metal container. In the cover 2 is a current collector 5 which is insulated from the cover by a insulating material 6, e.g. a glass bead. On two diametrically opposite edges on top of the container is attached a bridge 7 in which a nut 8 is inserted.

Through the nut passes a pointed screw 9 in the tip of which can be adjusted to a desired distance from the cover 2. When as a consequence of internal pressure in the battery the cover 2 bulges out, i.e.

upward, it will hit the tip of the screw 9 and at further bulging out the tip of the screw will penetrate the cover and puncture the container so that its contents are forced out. The bridge 7 which extends across the entire end surface of the battery constitutes a shield which prevents a too violent scattering of the contents.

In the illustated embodiment there is placed at the outer end of the screw 9 a second nut 10, which can be used to attach a wire 11 so that the safety mechanism can be used as the second current collector of the battery.

Figure 4 shows an alternative embodiment of the top of a battery. Here the current collector 5 is taken through a special portion 12 of the cover which by means of a welding seam is secured to the remaining part of the cover. Such embodiment may in certain cases be suitable because it may be hard to find an insulation material 6 which is compatible with the most commonly used container material, stainless steel. The special portion 12 may then be a different alloy which provides greater security of a durable attachment to the insulation material 6. In this embodiment the pointed member, here the screw 9, is mounted in such a way that it penetrates this special portion when the cover bulges out.This is advantageous because then a more expensive material than stainless steel can be selected for the special portion without the battery thereby becoming far more expensive, and consequently also a material which is more easily penetrated by the pointed member. The special portion 12 could also be of a smaller thickness than the rest of the cover.

In this embodiment the safety mechanism can also suitably be a pointed member which is mounted in a bracket attached to a single point at the edge of the cover 2 and extending over the middle of the cover so that the pointed member is situated above the special portion 12. This portion has the greatest distance of travel in the case of bulging whereas the edge of the cover does not travel far. Hereby the safety mechanism can be attached to the cover 2 before the latter is inserted in the container and the conainer is filled, the filling taking place through the opening in the current collector 5.

Claims

1. A hermetically sealed battery comprising a closed metal container which contains the current producing ingredients of the battery and which is provided with a safety mechanism to prevent explosion of the metal container, characterised in that externally on the metal container a pointed member is mounted at a short distance from and with the tip pointing at a surface of the container which will bulge out when the internal pressure in the container rises and which punctures the container at this bulging out.

2. A hermetically sealed battery as claimed in claim 1, characterised in that the pointed member is mounted on a bridge which is attached to two points of the metal container, one in either end of the bridge, and which extends across the entire surface which bulges out when the internal pressure in the container rises.

3. A hermetically sealed battery as claimed in claim 1, characterised in that the pointed member is mounted on a bracket which is attached atthe border of the surface which bulges out when the internal pressure in the container rises, which bracket extends over the bulging surface so that the pointed member is situated in front of a portion of this surface which has a large distance of travel in the case of bulging.

4. A hermetically sealed battery as claimed in claims 1-3, characterised in that the pointed member is a pointed screw passing through a nut.

5. A hermetically sealed battery as described above with reference to the accompanying drawings.

6. The features as herein described, or their equivalents, in any novel selection.