Galvanic element for high stresses

The present invention relates to a galvanic element, in particular an element of the button cell type, which has a long service life even when there are high mechanical or thermal loads. The element has a cathode, an anode, an electrolyte, a separator arranged between the anode and cathode, and a housing, which comprises a housing cup, a housing cover and a sealing element, the sealing element insulating the housing cup against the housing cover. According to the invention, the sealing element is rigidly connected to the separator.

This application claims priority from European Patent Application No. 09150875.4, filed Jan. 19, 2009, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a galvanic element, in particular of the button cell type, with a cathode, an anode, an electrolyte, a separator arranged between the anode and cathode and a housing. The housing comprises a housing cup, a housing cover and a sealing element, the latter insulating the housing cup against the housing cover.

BACKGROUND OF THE INVENTION

Galvanic elements, in particular of the type in button cell form, generally have a housing of this type. Galvanic elements of this type may contain a wide variety of electrochemical systems, for example zinc/MnO2, primary lithium systems or else secondary systems such as nickel/cadmium, nickel/metal hydride or secondary lithium systems.

The liquid-tight closure of such cells generally takes place by means of flanging the cup edge over the edge of the housing cover in connection with a plastics material ring, which is arranged between the housing cup and housing cover, and is simultaneously used as a sealing element and for the electrical insulation of the housing cup from the housing cover. Button cells of this type are known, for example, from DE 31 13 309.

In the known galvanic elements of this type, the separator is generally located in a sandwich-like manner between the anode and cathode, these three components being arranged concentrically with respect to one another. In this case, a narrow peripheral gap remains on the outside between the separator and the sealing element. In addition, the separator can slip, in particular in the case of high mechanical stressing of the galvanic element, in relation to the cathode and anode, whereby the existing gap is enlarged. Therefore, in the case of severe stressing of the galvanic element, for example by high temperatures or severe temperature fluctuations or if the element is subject to high accelerations or pressure differences, it may occur that particles of the cathode are released and move around the separator on the outside. This may lead to a short-circuit in the cell, which brings about a rapid and an uncontrolled self-discharge of the battery.

SUMMARY OF THE INVENTION

The present invention is based on the object of providing a galvanic cell of the type mentioned at the outset, in which this phenomenon is reliably avoided.

This object is achieved according to the invention in that the sealing element is rigidly connected to the separator. Thus, a peripheral gap no longer exists between the separator and the sealing element, through which particles from the cathode (or else the anode) move around the separator. It is also no longer possible for the separator to slip. Thus, a galvanic element is obtained which has a long service life even with high loads, for example in the case of high accelerations or high temperatures.

According to a preferred embodiment of the invention, the sealing element is substantially annular and is rigidly connected to the separator along its entire periphery. The galvanic element is divided into two chambers separated from one another by the continuous connection along the entire periphery, the anode being located in one of the chambers, and the cathode in the other chamber. The movement of individual particles around the separator is therefore ruled out.

The separator may be welded to the sealing element. Alternatively, the separator may also be glued to the sealing element. Other types of fastening are also conceivable, it being decisive that a permanent connection is obtained.

A sealing element is preferably used which has a substantially U-shaped cross-section in the radial direction. Sealing elements of this type are adequately known from the prior art and are generally used for galvanic cells according to the preamble of claim1. According to a preferred embodiment of the invention, the separator projects radially outwardly at least over the inner side in the radial direction of the U of the sealing element, i.e. over the inner sealing lip. In this case, the separator is preferably rigidly connected to this inner sealing lip of the sealing element so, together with the inner sealing lip of the sealing element, it forms a cup-like unit which can receive an electrode, for example the cathode.

The part of the separator projecting radially outwardly over the inner sealing lip of the sealing element preferably bends substantially perpendicularly in relation to the plane, in which the central region of the separator is located, and then extends in the U of the sealing element along the inner sealing lip. In this case, the part of the separator projecting radially outwardly over the inner sealing lip is preferably clamped in between the housing cover and the inner sealing lip of the sealing element. The separator is thus not only held in place by the, for example, glued or welded connection to the sealing element, but the separator slipping and therefore the production of a gap is also prevented by the separator being clamped in between the housing cover and seal. An additional securing is thus achieved.

According to a preferred embodiment of the invention, the galvanic element furthermore comprises at least one electrically conductive spring element, which is supported on the housing cup or the housing cover and, by means of an electrically conductive intermediate element, presses the cathode or the anode in the direction of the separator. In this case, the cathode or the anode is then in electrical contact by means of the intermediate element and the spring element with the housing cup or the housing cover. If only one spring element is used, this is preferably located on the cathode side, i.e. it is supported on the housing cup and presses the cathode by means of an electrically conductive intermediate element, which is located between the spring and the cathode, in the direction of the separator. A solution is particularly preferred in which a spring element is used both on the anode side and on the cathode side, in each case.

The spring element is used to increase the reliability of the electrical contact between the electro-active material of the cathode or the anode, on the one hand, and the housing, on the other hand. The contact resistance between the cathode or anode material and the housing may be increased by the action of temperature or by high mechanical stressing, so the contact is impaired. This applies, in particular, if a part of the electro-active material is already consumed. The spring element is in electrical contact with the housing on one side and, on the other side, presses an electrically conductive intermediate element onto the cathode or the anode, so an electrically conductive connection is always produced between the cathode or anode and the housing. A reliable electrical contacting is therefore ensured.

The spring element is preferably rigidly connected to the housing cup or the housing cover, for example welded. This rigid connection of the spring element to the housing cup or the housing cover may be produced before the actual assembly of the galvanic element. The spring element can thus already be centered in advance in relation to the housing cup or the housing cover and can no longer slip during subsequent assembly.

According to a particularly preferred embodiment of the invention, the spring element has at least three spring arms arranged symmetrically with respect to its centre. In this case, each of the spring arms has a contact face, which rests on the electrically conductive intermediate element. The pressing force of the spring is uniformly distributed over the electrically conductive intermediate element owing to these arms arranged in a star shape, so the intermediate element is pressed perpendicularly to the plane of the separator in the direction of the anode or cathode. The intermediate element is in turn used to distribute the pressing force of the three arms over a larger contact face, so the arms of the spring element cannot drill into the electro-active material of the electrode.

The electrically conductive intermediate element may, for example, comprise a circular disc with a central recess, the diameter of the circular disc substantially corresponding to the diameter of the cathode and the anode. Owing to the recess, space is obtained for the active material. In principle, a narrow annular disc is sufficient as the electrically conductive intermediate element, on which the spring arms are supported.

The button cell has a housing, which comprises a housing cup14and a housing cover12, as known from the prior art.

An annular sealing element20with a U-shaped cross-section is used to seal the housing. This sealing element is simultaneously used to electrically insulate the housing cup14and the housing cover12from one another. The use of sealing rings of this type with a U-shaped cross-section is known from the prior art, so a more precise description of the sealing element and its position between the cup14and the cover12when the cell is completely assembled (cf.FIG. 3) is not to be given here.

Seated in the housing cup14is a spring element24, which is produced precisely like the housing cup from a conductive material, for example a thin metal sheet. It may, for example, be punched out of a suitable metal sheet and then bent into shape. As can be seen inFIGS. 1 and 2, the spring element24has a substantially annular centre part26, from which three arms28extended to an identical length. The three arms28have a rectangular basic face, and issue from the annular centre part26in a star shape. An angle of 120 is in each case located between two adjacent arms28. The three arms28are angled away outwardly from the housing cup14. Before the cell is assembled, the spring element24is welded to the housing cup14.FIG. 2shows, at the top, the housing cup14with the spring element24welded thereon, and it can be seen that the annular centre part26of the spring element24is seated centrally in the housing cup14and rests flat on the base of the housing cup14, while the three angled arms28stand away from the base of the cup14and ensure the desired spring force, as will be described more precisely below.

An anode16, for example a lithium tablet, is located, as usual, on the side of the housing cover12. Located on the side of the housing cup14is a cathode18which may, for example, be a pressed manganese dioxide (MnO2) tablet.

A support ring30, which is shown separately inFIG. 1and is used as an electrically conductive intermediate element between the spring element24and the cathode18, is located between the cup14with the spring element24and the cathode18. This support ring30substantially has the shape of a cup with a circular base, which has a concentric circular recess32, and has a cylindrical wall which is perpendicular with respect to the base. The support ring30is, in this case, just large enough to receive the cathode18. Before assembly of the button cell, the cathode18is inserted into the support ring30, as shown inFIG. 2. If a spring element is used on the anode side, a simple metallic circular disc may also be used as the electrically conductive intermediate element instead of a support ring of this type, as at least in the example selected here with a metallic lithium tablet as the anode, no support is necessary at the edge.

The anode16and cathode18are separated from one another, as conventional, by a circular disc-shaped separator22. In the button cells known from the prior art, the separator22has substantially the same diameter, however, as the anode16and the cathode18, while here, as can be seen in particular inFIG. 1, the separator22has a larger diameter than the cathode18and the anode16.

Already before assembly of the button cell, the separator22and the sealing element20are connected to one another in a fastening region21. In order to connect the sealing element20to the separator22, the inner sealing lip for example, i.e. the inner side of the U of the sealing element20, may be coated at the top with an adhesive. The separator22is then placed in a centered manner on the sealing element20and pressed on, so an annular glued connection is obtained in the fastening region21. Alternatively, the separator may, however, also be welded to the sealing element20or fastened thereto in a different manner.

FIG. 2shows the spring element24connected to the sealing element20, and it is seen that the separator22still extends substantially in a plane. In this case, it rests on the inner sealing lip of the U-shaped sealing element20and projects radially outwardly beyond said sealing lip, so its outer edge rests loosely over the opening of the U-shaped sealing element.

During assembly of the button cell shown inFIG. 3, the procedure is as follows:

Firstly, the spring element24is welded to the cup14, as described above. The cathode18is inserted in the support ring30. Furthermore, the separator22, also as already described above, is connected to the sealing element20. The lithium tablet16, which forms the anode, is pressed into the housing cover12(compareFIG. 2). After carrying out these intermediate steps, the arrangement shown inFIG. 2is obtained.

The cover12with the anode16seated therein is then urged into the seal22already connected to the separator22. The edge of the housing cover12in the process folds the radially outer region of the separator22, which projects outwardly over the inner sealing lip of the sealing element20, and presses it into the position shown inFIG. 3. The separator22is now clamped in at its outer periphery between the housing cover12and the sealing element20and is therefore doubly secured against slipping. A division is thereby obtained of the interior of the cell into two chambers separated from one another by the separator22. Even if particles should detach from the cathode (or the anode), these cannot move around the separator22and thus cause a short-circuit.

In a next step, the cathode18saturated beforehand with an electrolyte and inserted in the support ring30is placed in the sealing element20and on the separator22.

Finally, the housing cup14is urged with the spring element24welded thereto onto the housing cover12, and the button cells are closed with a press.

As is seen inFIG. 3, the circular disc-shaped base of the support ring30is used as a contact face for the arms28of the spring element24. The arms28of the spring element angled in the direction of the support ring30and the cathode18press the support ring30away from the housing cup14onto the cathode18. An electrical contact is therefore produced between the cup14and the cathode18by means of the spring element24and the support ring30. Even if the cathode material is consumed, and even if the battery is subject to high mechanical stresses, high temperatures or high pressures, thanks to the construction with the spring element24and the support ring30, a reliable contact is ensured.

LIST OF REFERENCE NUMERALS

12housing cover14housing cup16anode18cathode20sealing element21fastening region22separator24spring element26central region of the spring element28arm of the spring element30support ring32recess in the support ring