CA2314626A1

CA2314626A1 - Secondary electrochemical cell

Info

Publication number: CA2314626A1
Application number: CA002314626A
Authority: CA
Inventors: Hans Leysieffer; Dirk A. Fiedler; Dieter Muller
Original assignee: Implex AG Hearing Technology
Current assignee: Cochlear Ltd
Priority date: 1999-07-30
Filing date: 2000-07-28
Publication date: 2001-01-30
Also published as: US7232625B2; DE19936063A1; US20070259255A1; US20020098410A1; EP1073132A1; AU4888900A; AU746488B2; DE19936063B4; US7713651B2

Abstract

A secondary electrochemical cell with at least one positive electrode and at least one negative electrode, said electrodes each comprising an active material are being directly received by a hermetically tight housing which includes or is in operative connection with at least one detector element. The detector element is designed or can be set to sense a predetermined unallowable operating state of the secondary electrochemical cell, and in an unallowable operating state of the secondary electrochemical cell, to actuate at least one switching element which prevents recharging and/or discharging of the secondary electrochemical cell. By making the housing as a hermetically tight protective housing, which is part of an implantable medical device, contamination of surrounding tissue with toxic substances and hazard to the implant wearer by a malfunction of the secondary electrochemical cell can be precluded under all operating conditions. Simultaneously all dimensions involved may be greatly reduced.

Description

f i ' -1- 39 CA
SECONDARY ELECTROCHEMICAL CELL
Background of the Invention Field of the Invention The invention relate:. to a secondary electrochemical cell with at least one positive electrode which comprises an active material and at least one negative electrode which comprises an active material, which electrodes are held directly in a housing which has at least one detector element or which is oper<~tively connected to one such detector element. The latter is designed or can be set to sense a predetermined unallowable operating state of the secondary electrochemical cell and, when there is an unallowable operating state of the secondary electrochemical cell, to actuate at least one switching element which prevents recharging and/or discharging of the secondary electrochemical cell.
Description of the Related Art In secondary electrochemical cells a pressure rise in the interior of the housing of the secondary electrochemical call can occur, for example, upon excess charging or discharging with an unallowably high current and such pressure rise can lead to deformation of the housing which can become so large that chemicals, especially in gaseous or liquid form, emerge from the housing in large amounts. Various protective mechanisms have been proposed to increase the operating safety of secondary elecl:rochemical cells.
Thus, publication EP-A-0 470 726 discloses a secondary electrochemical cell which has a cylindrical housing with a ~aressure membrane as the detector element. The housing directly accommodates the electrodes of the secondary electrochemical cell, the pressure membrane as part of the housing being integrated on the face side in the housing and bulging when the pressure rises in the interior of the housing, so that, as soon as the pressure within the housing reaches a predetermined value, a plate-shaped switching element which is centrally connected to the pressure membrane reversibly or irreversibly interrupts the electrical contact between an electrode and a terminal contact which is provided on the outside of the housing.

' -2- 39 CA
EP-A-0 322 112, EP-A-0 360 395 and EP-A-0 370 634 disclose providing electrochemical cells with a switching element which, when a certain still tolerable limiting deformation of the housing is exceeded, preferably irreversibly separates an electrical terminal contact from an associated electrochemically active electrode in order to prevent further deformation of the housing. The housing directly accommodates the electrodes and comprises an electrically conductive cylindrical housing section which is closed on the face side and which makes contact with an electrode, on the end face the plate-shaped switching element being attached centrally from the outside by means of an electrically insulating cement. The switching element which li~:ewise is electrically conductive, in its base position, forms an electrical connection via its outside edge between the housing section and the electrical terminal contact which projects to the outside and which is located in the center of the switching element. When the pressure :rises within the housing the face side of the housing section acting as the detector element bulges to the outside, whereby the contact between the housing section and the outside edge of the switching element and, thus, between the one electrode and the terminal contact is interrupted. Standard D-type cells are said to be a typical application of these switching elements. The bulging of the face side, starting from which the switching element interrupts electrical contact, in this case is 0.76 mm to 1.8 mm. For bulging of more than 1.8 mm emergence of chemicals from within the housing ordinarily has to be expected.
EP-A-0 674 351 discloses a secondary electrochemical cell with a housing which comprises a cutting device which can be actuated by a pressure membrane and which, when a limiting pressure is exceeded within the housing, irreversibly severs an electrical conductor which connects a terminal contact of the secondary electrochemical cell to an electrochemically active electrode.
Also, when using a switching element which interrupts the electrical connection between a terminal contact and the associated electrochemically active electrode when a certain pressure within the housing is exceeded, it is possible for the pressure to continue to rise and ultimately for chemicals to emerge from the housing of the electrochemical cell or for the latter even to explode. For this reason, for example in EP-A-0 364 995, EP-A-0 573 998 or EP-A-0 739 047 it is proposed that a pressure membrane which actuates the switching element and which is integrated into the housing be provided with a bursting area via which after activation of the switching element and a further pressure rise chemicals can emerge from the interior of the housing.

Summary of the Invention The mechanisms cited in the aforementioned prior art for increasing the operating safety of secondary electrochemical cells are not suited for those cells which are used as part of implantable medical devices, since (;specially high demands must be met for this purpose, especially with regard to saff;ty and reliability, with a simultaneously very extensive reduction of all dimensions. Thus, for example, contamination of surrounding tissue with toxic substances and hazard to the implant wearer by a malfunction of the secondary electrochemical cell must be precluded under all operating conditions. In electrochemical cells with a structure according to the described prior art this cannot be done since it turned out that especially toxic gases emerge in intolerably large amounts from the housing of the electrochemical cells even during proper, normal operation of the; electrochemical cell.
In commonly owned Canadian Patent Application No. 2,270,635, a protective device for a repeatedly rechargeable; electrochemical battery with a battery housing is disclosed, the protective device having at least one switching element which can be actuated by a detector element and which is designed or can be set to prevent recharging and/or discharging of the battery in a predetermined unallowable operating state thereof. Here the protective device comprises a hermetically tight protective housing which accommodates the battery housing, impresses on the detector element a change of shape in an unallowable operating state of the battery, and is part of an implantable device. Especially in a predetermined unallowably large expansion in the volume of the battery housing or emergence of gas from the interior of the battery housing which leads to an unallowably large pressure rise in the interior of the protective housing, a change of shape is impressed on the detector element by the protective housing, which change actuates the switching element. The latter can be made as a make contact which electrically short circuila a recharging circuit which can be supplied by means of a charging device.
An object of the invention is to provide a secondary electrochemical cell which meets the specific requirements for parts of implantable medical devices, and at the same time the construction effort is to be minimized.
The invention is a secondary electrochemical cell with the housing being made as a hermetically tight protective housing which is part of an implantable medical device.

All chemical substances of the secondary electrochemical cell are securely retained in the protective housing by the housing which directly accommodates at least one positive and at least one negative electrode of the secondary electrochemical cell being made as a hermetically tight protective housing.
Here hermetic tightncas is preferably defined as hermetic gas tightness as per Mil-Std 883 D. This ensures that when using the secondary electrochemical cell in an electronic implant which in turn is accommodated in a hermetically tight and furthermore biocompatible housing, not only liquid toxic; substances but also gases are prevented from emerging from the protective housing of the secondary electrochemical cell. The hermetic gas tightness of the protective housing reliably prevents risk of damage to the surrounding electronics. This means that the electronic circuits, especially integrated circuits, can remain unprotected since contamination even by extremely small amounts of emerging gases is not possible. If the secondary electrochemical cell is not accommodated in a housing of an electronic implant, but is implanted directly in its protective housing, the hermetic gas tightness as per Mil-Std 883 D
precludes corresponding contamination of the surrounding tissue. In this case, at least an outer side of the protective housing as a whole is furthermore made biocompatible.
The concept of direct accommodation of at least one positive electrode which comprises an active material and at least one negative electrode which comprises an active material in the housing of the secondary electrochemical cell which has been made as a protective housing is defined here in that between t:he hermetically tight protective housing and the electrodes there is no further housing which holds the electrodes, especially no housing which is used essentially to accommodate mechanical loads such as for example to accommodate compressive forces by gas evolution or the like of the secondary electrochemical cell and/or which has an electrically conductive housing section with an inside which makes contact with an electrode. This does not preclude electrical insulation or t:he like between at least one electrode and the protective housing, or electrical insulation and/or flexibly soft jacketing surrounding the electrodes.
Furthermore, in the protective housing there can be mechanical internals and/or it can be divided into several interior volumes, and wherein one interior volume can directly accommodate only one of the electrodes.
It goes without saying that the protective housing, in addition to the electrodes, accommodates other components of the secondary electrochemical cell which are necessary for the sequence of electrochemical reactions on the electrodes. This applies especially to an ' -5- 39 CA
electrolyte and optionally to a separator (diaphragm), which latter can be omitted when its function as an electrical insulator which allows ion migration is provided for by the electrolyte, as is the case for example in polymer electrolytes.
This invention is not limited to certain electrode/electrolyte systems, but rather fundamentally any common systems can be used. Examples include the following:
nickel-cadmium systems (sinter electrodes; bulk electrodes; liquid, pasty or solid electrolyte systems;
separator); nickel-metal hydride systems (sinter electrodes, bulk electrodes;
liquid, pasty or solid electrolyte systems; separator); lithium-based systems ((a) lithium metal or alloy anode, inorganic or organic dispersion or redox or other cathode; liquid, gel, pasty or solid electrolyte system; optionally separator; or (b) lithium intercalation anode, inorganic or organic dispersion or redox or other cathode; liquid, gel, pasty or solid electrolyte system;
optionally separator);
nickel-iron systems; nickel-.zinc systems; zinc-silver oxide systems; cadmium-silver oxide systems; zinc-manganese dioxide systems; redox systems such as, for example, quinone/hydroquinone systems; or zinc-mercury oxide systems and silver-metal hydride systems.
Within the framework of this invention, more than only one positive and one negative electrode can also be used, the electrodes being accommodated directly by the protective housing and in the conventional manner they can be series-connected or arranged in bipolar configuration for voltage multiplication or can be connected in parallel for capacity multiplication. A combination of these; types of connection is likewise possible.
The implantable medical device among others can be an active electronic hearing implant, a cardiac pacemaker., a drug dispenser, a neurostimulator or the like.
Recharging of the secondary electrochemical cell is preferably prevented by making at least one switching element as a break contact which is designed or which can be set to electrically interrupt, in an unallowable operating state of the secondary electrochemical cell, a recharging circuit which can be supplied by means of a charging device.
At least one switching element can furthermore be made as a break contact which is designed or which can be set; to electrically interrupt, in an unallowable operating state of the secondary electrochemical cell, a consumer circuit which is connected to the secondary electrochemical cell. Thus, it is possible, for example, to prevent in case of a short circuit in the consumer circuit an overly high electrical power from being withdrawn from the secondary ' -6- 39 CA
electrochemical cell. This, likewise, can cause an unallowable operating state of the secondary electrochemical cell, for example, in the form of exceeding a stipulated limit temperature or limit pressure within the hermetically tight protective housing. It is also conceivable for the break contact to be arranged such that it simultaneously interrupts both the recharging circuit and the consumer circuit.
In another preferred embodiment of the invention at least one switching element is made as a make contact which is designed or which can be set to electrically short circuit, in an unallowable operating state of the secondary electrochemical cell, a recharging circuit which can be supplied by means of a charging device, by which further energy supply to the secondary electrochemical cell is interrupted.
Furthermore, there ca.n be at least one switching element which is made as a make contact which is designed or which can be set to electrically short circuit the secondary electrochemical cell in an unallowable operating state thereof. Such make contact is especially feasible in serial coupling to an overcurrent protection unit which can irreversibly interrupt a current in a recharging circuit and/or consumer circuit of the secondary electrochemical cell.
The overcurrent protection unit can be made as a fuse which, in case of a short circuit, is burned through by the residual energy stored in the secondary electrochemical cell.
If the energy is not sufficient to do this, the secondary electrochemical cell can be completely discharged. It is likewise possible for at least one overcurrent protection unit to merely limit the current in the recharging circuit and/or consumer circuit, advantageously the overcurrent protection unit being made as a PTC resistor, the rf;sistance of which increases as the temperature increases.
Basically, the switching elements can reversibly or irreversibly interrupt a circuit into which they have been incorporated. Reversibly operating switching elements offer the advantage that their operation can be tested nondestructively, for example in the assembled state in interaction with other components of the secondary electrochemical cell or the implantable medical device.
If the stipulated unallowable operating state of the secondary electrochemical cell consists in exceeding a limit temperature, i.e. a stipulated .just still allowable temperature at a defined position of the secondary electrochemical cell, at least one detector element is designed or can be set to sense the temperature of the secondary electrochemical cell, especially within the protective housing, and when an unallowable temperature is reached to actuate at least one switching element.
Evolution of gas and/or swelling of the electrodes and/or a temperature rise during operation of the secondary electrochemical cell can lead to an increase of the pressure within the protective housing. If exceeding a limit pressure, i.e. a stipulated still allowable pressure within the protective housing, is chosen as the criterion for the stipulated unallowable operating state of the secondary electrochemical cell, at least one detector element is designed or can be set to sense the pressure in the interior of the protective housing which houses at least one electrode and when an unallowable pressure is reached to actuate at least one switching element. If the protective housing, which is hermetically tight to the outside, is interiorly divided into several sections, which are sealed relative to one another without, however, the need to ensure hermetic tightness among one another, the pressure can preferably be sensed in one of the sections. Swelling of the electrodes, which lead to expansion of their volume and the resulting pressure rise within the protective housing, can be sensed via a detector element, also by direct interaction of the; detector element with at least one electrode by, preferably, positioning the detector elerr~ent such that at least one electrode, in an unallowable operating state of the secondary electrochemical cell, contacts the detector element, possibly with the interposition of electrical insulation, and impresses on the detector element a change in shape which actuates at least one sv~ritching element.
At least one detector element is preferably designed or can be set such that, in an unallowable operating state of the secondary electrochemical cell, a change in shape is impressed on the element, which change in shape actuates at least one switching element. In such a case, the detector element can be arranged and/or made such that an elastic and/or plastic shape change is impressed on it, depending on the internal pressure and/or the temperature in the protective housing and/or swelling of the electrodes. Feasibly the shape change which is impressed on the detector element in an unallowable operating state of the secondary electrochemical cell mechanically actuates at least one switching element.
Direct mechanical actuation of the switching element by the change in shape of the detector element is especially reliable since it works necessarily v~~ithout being dependent on nonmechanical transmission elements.
This does not preclude, especially when two or more switching elements are redundantly present, at least one switching element from being actuated by means of evaluation electronics which sense the change in shape of the detector element.
Advantageously, an electrical extensometer is used which senses the change in shape of the detector element and responds with a change in an electrical quantity which is monitored by the evaluation electronics. If the electrical extensometer is a passive system, it can convert the change in shape of the detector elemE;nt into a change in its electrical resistance (strain gauge), its inductance or its capacitance. Alternatively, an active electrical extensometer can be used which, for example like a pic;zoeleme,nt, reacts with a change in charge to the change in shape which is applied to the extensometer t>y the detector element.
In another embodimf:nt of the invention at least one detector element is part of the protective housing and is made especially as a bulging membrane which preferably forms an outside or separating wall of the hermetically tight protective housing. At least one detector element can be accommodated within the protective housing. This allows space-saving construction and an easily predictable change in shape of the detector element when the pressure in the protective housing rises.
In particular, the thickness of the protective housing, which is especially critical for an implantable medical device, can be minimized when at least one membrane is integrated into a side wall of the hermetically tight protective housing, the direction of bulging of the membrane running essentially perpendicular to tlhe smallest extension of the protective housing. A cover or bottom of the protective housing which is provided in the direction of the smallest extent of the protective housing above or below the latter then preferably remains free of detector elements and switching elements so l:hat the thickness of the protective housing exceeds only slightly that of the electrode%electrolyte arrangement. Furthermore, it is possible to arrange at least one detector element outside the section of the protective housing which houses the electrodes and to bring it into fluid connection with the interior of the protective housing such that there is greater freedom in adaptation to the circumstances of the implantation site.
Redundant protection against: an unallowable operating state of the secondary electrochemical cell arises when, for example., there are two membranes, one of which is made as part of a make contact, and by means of which membrane, in an unallowable operating state of the secondary electrochemical cell, a contact pair of the make contact can be electrically short circuited. The second membrane can be made as part of a break contact and, by means of this second membrane, in an unallowable operating state of the secondary electrochemical cell, a contact pair of the break contact can be electrically disengaged.

The protective housing under all operating conditions must form a hermetically tight barrier with respect to the space located outside the protec.-tive housing. In particular, neither energy supply nor energy removal, nor the energy stored in the secondary electrochemical cell and the chemical processes ~,vhich take place during operation may lead to destruction of the hermetic tightness. Factors which should be considered, in particular, in the design of the protective housing and the choice of materials are: chemical effects of the electrolyte and electrodes on the protective housing at the storage and operating temperatures; electrochemical processes within the protective housing as a result of all conceivably possible charging and discharging processes; mechanical loads of the protective housing as a result of chemical, electrochemical or physical (especially thermal) processes such as gas evolution within the protective housing; swelling of the electrodes; changes in the ambient pressure; heating by energy supply or energy removal; and a change of the storage temperature.
A suitable protective housing can be attained especially as a hermetically tight material interconnection between at least one electrically conductive metallic housing section and at least one electrically insulating inorganic-nonmetallic housing section. The housing sections are preferably welded to one another, but can also be joined to one another hermetically tight by means of a soldering or brazing process.
Materials which are especially chemically inert to the electrode/electrolyte systems ordinarily used and which are resistant to the electrochemical processes which take place include metals and precious metals which form a passivation layer against chemical decomposition. They include among others: platinum, chromium nickel steel, nickel alloys, titanium, tantalum and niobium. Preferably, ceramics which can be materially interconnected in a hermetically tight manner to at least one metallic housing section are used as the inorganic-nonmetallic insulator materials.
In at least one electrically insulating inorganic-nonmetallic housing section an at least unipolar electrically conductive feed-through can be accommodated hermetically tight and electrically insulated. In such an embodiment, the insulator material can be used for electrical insulation of the poles of the feed-through both among one another and also with regard to adjoining electrically conductive metallic housing sections.
Preferably, at least one pole of the hermetically tight feed-through has a metallic contact pin which penetrates, hermetically tightly, the electrically insulating inorganic-nonmetallic housing section. The contact pins axe; preferably held in the insulating material, for example in a ceramic substrate, with the: insulating material in turn being hermetically tightly received in the outside wall of the protective housing by means of a material connection, preferably a solder or brazing connection, especially a gold brazing connection. Especially suitable materials for the contact pin c;an be platinum-iridium alloys.
It can be advantageous for the contact pins to be hermetically tightly received by means of a material connection in the electrically insulating inorganic-nonmetallic housing section, with the latter being hermetically tightly received by means of a material connection in a metallic receiver, the metallic; receiver likewise being materially connected to an outside wall of the protective housing. For connecting the metallic receiver to the outside wall of the protective housing a weld joint can be used.
In principal, the feed-through ~can be monopolar or multipolar.
Advantageously, at least one pole of the hermetically tight feed-through is in contact with the electrode of the secondary electrochemical cell. The hermetically tight feed-through enables not only transmission of energy but also, in principle, transmission of signals through a wall of the protective housing.
For example, the potential of a potential probe can be routed through the wall of the protective housing by means of a pole o~f the feed-through. Preferably, the potential probe is located in the electrolyte between a positive; and a negative electrode of the secondary electrochemical cell, as is described in commonly ov~ned Canadian Patent Application No. 2,270,689, which is hereby incorporated by reference in its entirety.
The dimensions of thf; electrically insulating section, which is provided in the protective housing and which is formed preferably by a ceramic material, can be minimized and limited to the section which accommodates the feed-through when the number of poles of the feed-through corresponds to the number of energy and signal taps, via which the secondary electrochemical cell is connected to other components of the implantable medical device. In this case, the remaining wall of the protective housing can be made from a metallic material the inside of which is electrically insulated with reference to the electrodes.
At least one electrically conductive metallic housing section can make contact with an energy or signal tap which is accommodated within the protective housing. In particular, at least one electrically conductive metallic housing section makes electrical contact with an electrode of the secondary electrochemical cell. An especially simple structure of the protective housing is attained when the positive and the negative electrodes of the secondary electrochemical cell are each. connected to an electrically conductive metallic housing section, the two metallic housing se<;tions being electrically insulated against one another, wherein a feed-through can be omitted.
In a manner known per se, the electrodes preferably have an electrical tap which in turn makes contact either with one pole of the hermetically tight feed-through or an electrically conductive metallic housing section from the inside of the protective housing.
Contact of the taps on the electrically conductive housing section or on the pole of the feed-through can be accomplished preferably directly via. weld, solder or brazing connections, or indirectly via electron-conductive intermediate elements which adjoin by force-fit, such as for example springs, pins, metal foams or the like.
In another embodiment of the invention, to increase the operating safety and to create redundancy, the protective housing is dimensioned such that its hermetic tightness is preserved even if in an unallowable operating state of the secondary electrochemical cell the cell can still be recharged or discharged. This means that even in case of a malfunction for example of the detector element and/or the switching element the protective housing up to certain upper limits withstands the physical loads which occur when the supply or removal of energy is not interrupted even if the secondary electrochemical cell enters an unallowable state.
If the outside of the protective housing as a whole is made biocompatible, the housing can be directly implanted and connected to a consumer via electrical lines which are permanently connected or which are detachable. Thus, the implantation site is irrelevant, as is described also in EP-A-0 982 784 and in the corresponding commonly owned Canadian Patent Application No. 2,270,683 which is hereby incorporated by reference in its entirety. Materials for the biocompatible protective housing can be preferably titanium, titanium alloys, niobium, tantalum, implantable steels or a composite of them or of other implantable metallic materials with ceramic materials such as aluminum oxide ceramics, and preferably jacketing of the entire protective housing with a biocompatible polymer, for example silicone, polytetrafluoroethylene (PTFE), polyurethane, parylene or the like.
These and further objects, features and advantages of the present invention will become apparent from the following; description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.
Brief L)escription of the Drawings Fig. 1 is a schematic circuit diagram with a secondary electrochemical cell which is incorporated into a consumer circuit and a recharging circuit;
Fig. 2 is a cross-sectional view of a first embodiment of a secondary electrochemical cell with a hermetically tight protective housing and a reversibly operating switching element;
Fig. 3 is a perspective; view of the embodiment of Fig. 2;
Fig. 4 is a partial viev~ of the embodiment of Fig. 2 in larger scale;
Fig. 5 is a cross-sectional view of a second embodiment of another secondary electrochemical cell;
Fig. 6 is a cross-sectional view of a third embodiment of a secondary electrochemical cell with a switching element in the closed state;
Fig. 7 is a cross-sectional view of the embodiment of Fig. 6 with a switching element in the opened state;
Fig. 8 is a cross-sectional view of another embodiment of a secondary electrochemical cell with a switching element in the closed state;
Fig. 9 is a cross-sectional view of the embodiment of Fig. 8 with a switching element in the opened state;
Fig. 10 is a cross-sectional view of another embodiment of a secondary electrochemical cell with an irreversibly operating switching element;
Fig. 11 is a cross-sectional view of another modified embodiment of a secondary electrochemical cell;
Fig. 12 is a cross-sectional view of a secondary electrochemical cell with a hermetically tight unipolar feed-through through the outside wall of a protective housing to form a current path to or from an electrode of the secondary electrochemical cell;
Fig. 13 is a perspective view of another embodiment of a secondary electrochemical cell with a short circuit switch and a burst strip as an irreversible break-contact;

Fig. 14 is a cross-sectional view of the embodiment of Fig. 13;
Fig. 15 is a perspective view of another embodiment of a secondary electrochemical cell;
Fig. 16 is a cross-sectional view of a secondary electrochemical cell with a hermetically tight bipolar feed-through as a current path to or from one positive and one negative electrode of the secondary electrochemical cell; and Fig. 17 is a cross-sectional view of a secondary electrochemical cell with a bipolar feed-through, the feed-through and two switching and detector elements being integrated in a side wall of the protective housing.
Detailed Description of the Invention According to Fig. 1, the secondary electrochemical cell as part of an implantable medical device has a protective housing 14 which hermetically tightly accommodates a positive electrode 2, a negative electrode 4, an electrolyte 12 and a separator 6 which is used to prevent an electrical short circuit between the electrodes 2, 4. The separator 6 which is positioned between the two electrodes 2 and 4 is used as an electrical insulator which, however, allows ion migration between the electrodes 2 and 4. The positive electrode 2 and the negative electrode 4 each have an electron-conductive tap 8 and 10, respectively, the tap 8 making contact with an electrically conductive housing section 13 and the tap 10 making contact with an electrically conductive housing section 11 of the protective housing 14. The two housing sections 11 and 13 are electrically insulated against one another by means of an inorganic-nonmetallic housing section 15 which is preferably made of ceramic material. Another electrically insulating inorganic-nonmetallic housing section 19 receives an electrically conductive feed-through which is used to pass a signal from a detector element 21 which is made as a temperature sensor and which senses the temperature of the secondary electrochemical cell at a stipulated site within the protective housing 14 and senses an unallowable operating state of the secondary electrochemical cell in the form of an unduly high temperature.
The housing sections 11 and 13 on their outsides each have a terminal 18 and 16, respectively, via which the negative electrode 4 and the positive electrode 2, respectively, are connected to a recharging circuit 22 and a consumer circuit 24. The protective housing 14 is operatively connected to another detector element 20 such that, in an unallowable operating state of the secondary electrochemical. cell in the form of an unduly high internal pressure within the protective housing 14, a change in shape is impressed on the detector element 20. In such a case, gas evolution and/or swelling of the electrodes 2, 4 and/or a temperature rise during operation of the secondary electrochemical cell can cause a pressure rise within the protective housing 14.
The secondary electrochemical cell in the consumer circuit 24 supplies, via a break contact 50, a consumer 26 of the implantable medical device which can be, for example, an implantable active hearing aid. The recharging circuit 22 has a receiver coil 28 which, together with a capacitor 30, forms a series-resonant circuit which is excited by a second series-resonant circuit (not shown) of an external transmission unit having the same resonance characteristics as is detailed in commonly owned U.S. Patent No. 5,279,292 which is hereby incorporated by reference in its entirety. Depending on the phase, the recharging circuit 22 is completed via diodes 32, 38 and 34, 36, respectively., a break contact 48, an overcurrent protection unit 42 and the electrodes 2, 4 which are accommodated in the protective housing 14. A
Zener diode 40 protects the secondary electrochemical cell from overly high voltage of the recharging circuit.
Parallel to the receiving coil :'8 and the capacitor 30 there is a make contact 44. Another make contact 46 is connected in paa-allel to the secondary electrochemical cell and the overcurrent protection unit 42.
As shown by the dot-dash line in Fig. 1, the detector elements 20 and 21 actuate the switching elements 44, 46, 48 and 50 which are part of the implantable medical device. For the detector element 20 this can be achieved either directly, for example by mechanical coupling of the detector element 20 and one or more switching elements, or indirectly via optional evaluation electronics 52 which senses the change in shape of the detector element 20 and electrically or electromechanically actuates one or more switching elements.
The evaluation electronics 52 furthermore is used to sense the signal of the detector element 21 which is made as a temperature sensor and to actuate one or more of the switching elements 44, 46, 48, and 50.
It goes without saying that not all switching elements 44, 46, 48, and 50 need be present and that the selection, which of the switching elements are actuated directly or via the optional evaluation electronics 52, can. be varied depending on the application and the desired redundancy. It can furthermore be provided that one switching element or several switching elements be actuated only wren both detector elements 20 and 21 signal an unallowable operating state of the secondary electrochemical cell.
The position of the switching elements 44, 46, 48 and 50 which is shown in Fig. 1 corresponds to a base position in normal operation. In the case of an unallowable operating state of the secondary electrochemical cell at least one of these switching elements is actuated.
A first embodiment of the secondary electrochemical cell is shown in Figs. 2 to 4 and includes a hermetically tight protective housing 54 with a cup-shaped cover 56 and a likewise cup-shaped bottom 58. A hollow cylindrical side wall 60 of the cover 56 is welded to a cover plate 62, which, as a bulging membrane, forms the detector element of the secondary electrochemical cell. The bottom 58 is formed by a hollow cylindrical side wall 64 and a bottom plate 66 which is welded thereto. The electrodes 2 and 4 of the secondary electrochemical cell are acco~mmodate;d within the protective housing 54, the positive electrode 2 having a tap which is a contact clip 68 and which makes contact with the inside of the side wall 60. The negative electrode 4 of the secondary electrochemical cell, by means of a contact clip 70 as a tap, is brought into electrically conductive contact with the inside of the side wall 64, a recess 74 in the edge area of the bottom plate 66 facilitating the installation of the contact clip 70. The contact clips 68 and 70 each are soldered, brazed or welded electrically conductively to the side wall 60 and 64, respectively, and both can be provided with an insulating layer 73 which surrounds them, for example in the form of an insulating hose which has been slipped thereon. It goes without saying that instead of the solder, brazing or weld connection the contact clips 68 and/or 70 contact the corresponding housing parts merely in a spring-biased condition, for which purpose either contact pressure elements such as metal foams or springs can be used or the contact clips 68, 70 themselves can provide for the necessary contact pressure. In principle, instead of the contact clip 69 and/or 70 any other form of electrical contact-making c;an also be used, for example a metal foam which has been inserted with bias between the bottom of the cover plate 62 and an end face of the electrode 2 facing it, advantageously another metal foam being interposed between the top of the bottom plate 66 and an end face of the electrode 4 facing it.
The interior of the protective housing 54 is filled with an electrolyte 12, the positive and the negative electrodes 2 and 4 being ;>eparated from one another by a separator 6 which is illustrated schematically and 'which prevents direct electrical contact between the electrodes 2 and 4, but allows ion migration. The cover 56 and the bottom 58 each have an electrical terminal 76 and 78, respectively, whit:h correspond to the terminals 16 and 18, respectively, as shown in Fig. 1, and both are made of an electrically conductive metallic material (for example, titanium) which is chemically inert to the electrolyte 12 and the electrodes 2, 4 and is resistant to the electrochemical processes which take place.
The side walls 60 and. 64 are vvelded, soldered or brazed hermetically tight to one another via their end faces, with the interposition of an insulating ring 80, the insulating ring 80 having a smaller inner diameter than the side walls 60 and 64. For example, oxide ceramic can be used as the material for the insulating ring 80.
On the cover plate 62 a switching element labeled 86 is attached; it corresponds to the make contact 44 of Fig. 1. As an important component the make contact 86 has a flexible contact carrier 92, for example of polyimide, which has the shape of a roughly rectangular thin-walled plate, one short side of which has a U-shaped notch so that two spring arms 1 O2, 104 are formed. Along the two longer sides on the top of the contact carrier 92 metal coatings 94 are attached which extend into the spring arms 102 and 104, where on each of the metal coatings 94 a section of a platinum wire is brazed as a contact 106 and 108, respectively, via a brazing connection 109. In the vicinity of the second short side of the contact carrier 94 contact plates 96 and 98, respectively, are connected. by means of a solder or brazing layer 100 to one or the other, respectively, of the two metal coatings 94. The contact plates 96 and 98 each carry a terminal 112 and 114, respectively, so that the terminal 112 is electrically connected to the contact 106 whereas terminal 114 is electrically connected to the contact 108.
At a short distance above the contacts 1 ~06 and 108 there is a contact bridge 110 with which the contacts 106, 108 can be brought into contact in order to electrically short circuit them. The flexible contact carrier 92 is connected via a multilayer structure to the cover plate 62 such that the contacts 106, 108 are located in the centrally above the cover plate 62 and when seen in top view extend along an axis of symmetry of the round cover plate 62. As is shown in Fig. 4, the multilayer structure between the contact Garner 92 and the cover plate 62 includes, starting from the bottom side of contact carrier 92 facing the cover plate 62, an adhesive layer 88, a spacer plate 90 and a second .adhesive layer 88. The multilayer structure extends roughly from the short side of the contact Garner 92., which has the contact plates 96, 98, up to the base of the U-shaped notch which separates the two spring arms 102, 104 so that the latter are positioned at an exactly stipulated distance above the cover plate 62.

The contact clip 68 can be a fizse which interrupts the electrical connection between the positive electrode 2 and terminal 76 when the current flowing through them exceeds a stipulated limit value. In this case, an insulation is to be provided between an end face of the positive electrode 2 facing the cover plate 62 and the cover plate 62 itself.
Similarly the contact clip 70 can also be designed as a fuse, and between the negative electrode 4 on the one side and the side wall 64 and/or the bottom plate 66 on the other side an insulation is to be provided which, even when this fuse fixses, prevents electrical contact by the negative electrode 4 directly contacting the housing parts 64 and/or 66.
If during operation of the secondary electrochemical cell the internal pressure within the protective housing S4 rises due to swelling (increase of volume) of the electrodes 2, 4 and/or by gas evolution and/or by a temperature increase, a bulge is specifically impressed on the detector element (cover plate 62) which is designed as a membrane because the other outside walls of the protective housing S4 are designed to be stiffer than the cover plate 62 and deform only little. When the electrodes 2, 4 swell they can also touch the inner surfaces of the cover plate 1 S 62 and the bottom plate 66 directly or indirectly via insulating layers and/or the electrolyte 12 which can be a solid electrolyte, and in this way may cause a change in shape of the cover plate 62.
The bulging of the cover plate 62 causes the contacts 106 and 108 of the contact bridge 110 to approach one another :in order t:o touch the contact bridge 110 and to electrically short circuit the terminals 112 and 114 and via the latter the recharging circuit 22 when a limit value of the internal pressure in the protective housing S4 is exceeded which signals a just still allowable operating state of the secondary electrochemical cell, whereby further power supply to the electrodes 2, 4 of the secondary electrochemical cell is suppressed.
The flexible configuration of the spring arms 102, 104 prevents them from being damaged when the 2S switching element 86 closes s,o that the break contact 86 in principle works reversibly. As the internal pressure in the protective housing 54 decreases, the switching element 86 again assumes its base position which is shown in Fig. 2.
The bulging of the cover plate 62 which leads to actuation of the switching element 86 is generally less than 300 microns, the protective housing S4 having, for example, an outside diameter of roughly 18 mm a:nd a height of less than S.S mm, measured from the bottom plate 66 to the cover plate 62.

Fig. 5 shows a second embodiment of a secondary electrochemical cell which has a protective housing 116 with a cup-shaped, one-part bottom 118 of electrically conductive material. The protective housing 116 is closed by a likewise electrically conductive cover 120, wherein an insulating ring 122 of oxide ceramic is soldered or brazed between the cover 120 and the bottom 118. The insulating ring 122 which has an inside diameter which is less than that of the side wall of the bottom 118 carries on its bottom a membrane 138 and on its top a contact membrane 134 which are electrically insulated against one another.
Both membranes 134 and 138 are made of electrically conductive material, the contact membrane 134 with its top being electrically insulated against the adjacent cover 120 by means of an insulating layer 148, and being electrically conductively connected to the bottom 118 via a metal coating 132, through hole plating 130 and a solder or brazing layer 128. The electrodes 2 and 4, the separator 6 and the electrolyte 12 are hermetically tightly surrounded by the bottom 118, the lower side of the insulating ring 122 and the membrane 138. The positive electrode 2 is centered in the protective housing 116 by an electrically insulating annular receiver 124 which is positioned between the side wall of the bottom 118 and the positive electrode 2 in the area between the separator 6 and the lower side; of the insulating ring 122 such that electrical contact between the side wall of the bottom 118 and the positive electrode 2 is prevented. A
recess 140 in the receiver 124 facilitates installation of the contact clip 68 by means of which the positive electrode 2 makes electrical contact with the bottom of the membrane 138. A
metal coating 142 on the lower side of the insulating ring 122, a through hole plating 144 through the insulating ring 122, and a solder or brazing layer 146 complete the electrical connection between the membrane 138 and the cover 120, with which an electrical terminal 152 is contacted. An electrical terminal 150 on the outer side wall of the bottom 118 is electrically connected to the negative electrode 4 via the bottom 118 and the contact clip 70 which is connected to the inner side wall of the bottom 118.
While, therefore, the membrane 138 is connected to the positive electrode 2, the contact membrane 134, which is located at a distance from the membrane 138 which corresponds to the thickness of the insulating ring 122, makes contact with the negative electrode 4. This distance is such that in an unallowable operating state of the secondary electrochemical cell a bulge is impressed on the membrane 138 which acts as the detector element, which bulge is sufficient for the membrane 138 to estalblish electrically conductive contact with the contact membrane 134 so that the secondary electrochemical cell is electrically short circuited. Furthermore, a section of the solder or brazing connection 146 can be dimensioned to form a fuse which irreversibly burns through if a recharging or a discharging current exceeds a stipulated limit value. Further energy supply and removal via the terminals 150, 152 thus is prevented.
In the embodiment of the secondary electrochemical cell which is shown in Fig.
5, the combination of the membrane 138 and the contact membrane 134 is used as a reversibly operating switching element which is a make contact and which is mechanically actuated by the detector element 138. Since the two terminals 150, 152 are surrounded by a biocompatible insulating jacket 149, and a biocompatible polymer 153, such as silicone, jackets the protective housing 116 and the housing-side ends of the terminals 150, 152, the protective housing 116 can be directly implanted. The entire unit which is shown in Fig. 5 can be used as an energy supply module with terminals 150, 152 which are electrically connected to other components of the implantable device, preferably detachably via a coupling element, as is described in commonly owned EP-A-0 982 784 and the corresponding Canadian Patent Application No.
2,270,683 which is hereby incorporated by reference in its entirety.
According to Figs. 6 and 7, a third embodiment of a secondary electrochemical cell has a protective housing 154 with an electrically conductive bottom which has a side wall 156 in the form of a tube section which is sealed on the face side thereof by a bottom plate 158. A
peripherally extending continuous weld 160 joins the bottom plate 158 to the side wall 156. A
ceramic insulating ring 162 is, fixed to the second face side of the side wall 156 by a solder or brazing layer 164, the insulating ring :162 having a round opening with an inside diameter which is smaller than the inside diameter of the side wall 156. A membrane 166 made of electrically conductive material and which spanning the opening is attached to the bottom of the insulating ring 162 facing the bottom plate 158, whereby a hermetically tight internal space is formed. This internal space holds the positive electrode via the receiver 124 such that electrical contact between the positive Electrode 2 and the side wall 156 is precluded and the electrode 2 simultaneously is centered in the protective housing 154. While the positive electrode 2 makes electrical contact with the membrane 166 from underneath by means of the contact clip 68, the contact clip 70 forms an electrical contact between the negative electrode 4 and the side wall 156. An electrically conductive contact membrane 168 with a central downwardly projecting contact point 170 is connected to the top of the insulating ring 162 and spans the opening of the latter. The contact membrane; 168 is formed such that it elastically bulges inwardly towards the membrane 166 and it is in electrical contact with the membrane 166 by means of the contact point 170. In this position of the contact membrane 168 energy can be supplied and removed to and from the secondary electrochemical cell via a terminal 174 which is electrically connected to the contact membrane 168 and a terminal 172 in contact with the outside of the side wall 156. If an unallowable operating state; of the secondary electrochemical cell occurs, the membrane 166 and with it thc; contact membrane 168 are caused to bulge outwardly to such an extent that the contact membrane 168 springs to the outside beyond an unstable equilibrium position, and the electrical contact between the two membranes 166, 168 remains interrupted even if the membrane 166 should again return to its original position as shown in Fig. 6.
A fourth embodiment of the secondary electrochemical cell which is illustrated in Figs.
8 and 9 has a protective housiing which differs from the protective housing 154 essentially only by the configuration of the membranes 166, 168 and their electrical contact-making. A
membrane 176 which corresponds to the membrane 166 centrally carries on its top a contact spring 180 comprising a pin 1. 82 and a spring plate 184. One end of the cylindrical pin 182 is fixed to the membrane 176 such that the longitudinal axis of the pin 182 is substantially normal to the membrane 176, and the: second end of the pin 182 is connected to the spring plate 184.
The pin 182 extends through an opening in a contact membrane 178 which corresponds to the contact membrane 168 of the protective housing 154, the spring plate 184, in the base position shown in Fig. 8, being in electrically conductive contact with the contact membrane 178 via a contact surface 185 which faces the top of the contact membrane 178 and which is located in the vicinity of the outside edge of the apring plate 184. In the base position the membranes 176, 178 extend substantially parallel to each other, and the contact surface 185 is spring-biased into contact with the contact membrane 178. In an unallowable operating state of the secondary electrochemical cell a outward bulge towards the contact membrane 178 is impressed on the membrane 176, whilst the contact membrane 178 essentially does not deform and retains its position. The bulging of the membrane 176 is sufficient to lift the contact surface 185 from the contact membrane 178 and to reversibly interrupt the electrical contact, but is not so large that the top of the membrane 176 comes into contact with the lower surface of the contact membrane 178. To prevent such a contact, even when the membrane 176 bulges more dramatically, the lower side of the contact membrane 178 is provided with an insulating layer 186.
A fifth embodiment of a secondary electrochemical cell is shown in Fig. 10 and includes a protective housing 190 with a one-piece, cup-shaped bottom 192, a likewise cup-shaped cover 194 and a membrane 196 which is connected by a weld 198 to the end sides of the bottom 192 and the cover 194 which are facing each other, the bottom 192, the cover 194 and the membrane 196 preferably being of the same electrically conductive material. The membrane 196 divides the protective housing 190 horizontally into a top cover area and a bottom, hermetically tight space which holds the positive and the negative electrodes 2 and 4, the separator 6 and the electrolyte 12. The negative electrode 4 makes contact by means of the contact clip 70 with the bottom 192, tile side wall of which receives a single-pole feed-through 214 via a ceramic substrate 212 in a hermetically tight manner and electrically insulated with respect to the side wall of the bottom 192. The contact clip 68 establishes electrical contact between the positive electrode 2 and one end of the feed-through 214 which projects into the hermetically tight space of the protective housing 190. The other end of the feed-through 214 projects outwardly beyond the side wall of the bottom 192 and is electrically connected to a terminal 216.
On the lower side of the membrane 196 facing the positive electrode 2 and on the inner 1 S surface of the side wall of the: bottom 192 adjacent to this electrode, a.n insulating layer 218 is applied to prevent electrical contact between the membrane 196 and the side wall of the bottom 192 and the positive electrode 2, respectively. A plunger 222 is disposed centrally on the top of the membrane 196 and projects into an opening in the cover 194. A burst element 204 spanning the opening is provided a short distance above the upper edge of the plunger 222. This element 204 includes, on its side facing the top of the cover 194, a substrate 206 with a conductive layer 208. The substrate 206 can be ceramic, for example, oxide ceramic, glass or the like. The conductive layer 208 on one side of the opening in the cover 194 makes contact with the latter via a contact clip 202 and on the opposite side of the opening is provided with a terminal 210 which in this way is electrically connected to the negative electrode 4 In an unallowable operating state of the secondary electrochemical cell a bulge is impressed on the membrane 196, whether by an increase in the volume of the electrodes 2, 4 and/or a temperature rise and/ or gas evolution in the operation of the secondary electrochemical cell, this bulge being sufficient for the plunger 222 to destroy the burst element 204 so that the conductive layer 208 between the contact clip 202 and the terminal 210 is irreversibly interrupted.
As is shown in Fig. 1 a, a sixth embodiment of a secondary electrochemical cell has a protective housing 224 with a, flat, electrically conductive, shell-shaped bottom 226 which is connected to a side wall 228 via its upwardly facing end face with the interposition of a ceramic insulating ring 229, said side wall 228 having the shape of a tube section.
The side wall 228 is hermetically tightly sealed at its upper face side by an electrically conductive membrane 230.
An insulating layer 232 is applied on the upwardly facing outside of the membrane 230, and an electrically conductive, brittle:-fracture: burst layer 234 is applied on the insulating layer 232.
The burst layer 234 in the area of the side wall 228 is connected electrically conductively to the membrane 230 at a first site via contact-making 236 and at a second diametrically opposite site to a terminal 238, wherein the burst 1<~yer 234 extends between these two sites in a strip-like manner. The positive electrode 2 is tapped via the terminal 238 from outside of the protective housing 224, for which purpose the positive electrode 2 is contacted by a contact clip 242 which forms via a weld connection 244 an electrical contact with the inside of the side wall 228. The negative electrode ~4 is connected via the contact clip 70 to the inside of the bottom 226 and can be tapped from outside the protective housing 224 by means of a terminal 240. It goes without saying that alternatively to the weld connection 244 there can also be, for example, a solder or brazing connection. In an unallowable operating state of the secondary electrochemical cell a bulge is impressed on the membrane 230 and irreversibly destroys the burst layer 234 and, thus, interrupts the electrical connection between the positive electrode 2 and the terminal 23 8.
A seventh embodiment of a secondary electrochemical cell is shown in Fig. 12 and includes a protective housing 252 which differs from the protective housing 224 essentially only by the configuration of the bottom 226 and of the current path to and from the positive electrode 2. The protective housing 2:52 has a bottom 254, the side walls of which extend up to the membrane 230 and are wc;lded thereto in a hermetically tight and electrically conductive manner, so that the insulating ring 22S~ of the protective housing 224 is eliminated. The positive electrode 2 is held in a cup-shaped, electrically insulating receiver 256 which electrically insulates the positive electrode 2 with reference to the side wall of the bottom 254 and the membrane 230 and keeps it in a predetermined position. The contact clip 68 is placed in the area of a recess 258 of the receiver 256 and is used for contact-making of the positive electrode 2 to a first end of a single-pole feed-through 260 which is held hermetically tight and electrically insulated in the side wall of the bottom 254. The second end of the feed-through 260 projects beyond the outside of the side wall of the bottom 254 and is brought via a contact clip 262 into electrical connection with the electrically conductive burst layer 234 which is completely insulated by an insulating layer 255 relative to the membrane 230 and the bottom 254.
According to Figs. 13 and 14, an eighth embodiment of a secondary electrochemical cell uses a modified protective housing 264 which corresponds for the most part to the protective housing 54 of Figs. 2 to 4, but does not use switching element 86 of the latter and in which the current path from amd to the; positive electrode 2 is accomplished in a modified form.
A rectangular burst strip 266 is coupled at about the outer thirds of its longer side via adhesive connections 268 and 270 to the cover plate 62 of the protective housing 264 at a stipulated distance from the outer edge ~of the cover plate 52 so that a bridging zone 272 is formed between the adhesive connections 268 and 270. A line of symmetry in the direction of the longer side of the burst strip 266 extends essentially parallel to a center line of the round cover plate 62, and the center of the; bridging zone 272 is located above the center of the cover plate 62. A conductive layer 276 is applied on the top of the burst strip 266 and extends over almost the entire top of the burst strip 266. The conductive layer 276 makes contact with the cover plate 62 in the area of one of the short sides of the burst strip by a contact clip 284 and makes contact in the area of the other short side of the burst strip with a terminal 286. Thus, an electrical connection is established bel:ween the terminal 286 and the positive electrode 2.
A predetermined breaking point in form of a perforation 274 is provided in the area of the bridging zone 272 which is free of the adhesive layer, near the center of the longer side of the burst strip 266. The predE;termined breaking point can of course also be produced in some other suitable way, for example by notching, scratching or narrowing the burst strip 266.
Adjacent to the perforation 2',~4 a wire section defining a short circuit contact 278 is fixed by a solder or brazing connection :Z80, and an counter contact 282 is positioned at a predetermined distance above the short circuit contact 278. The counter contact 282 is in electrical contact, via a contact clip 288, with the side wall 64, i.e. with the negative electrode 4.
In an unallowable operating state of the secondary electrochemical cell, a bulge is impressed on the cover plate 62 which defined a bulging membrane, and this bulge is transmitted via the adhesive connections 268, 270 to the burst strip 26fi which breaks along the perforation 274 as shown in Fig. 14. The short circuit contact 278 is pressed against the counter contact 282, and the short circuit current between the positive and the negative electrodes 2 and 4 is sufficient to burn through a possibly remaining fragment 290 of the conductive layer which at least partially spans the fracture site.

In this way, the current path between the positive electrode 2 and the terminal 286 is irreversibly interrupted.
Since it is necessary to predict the bulging which is required to break the burst strip 266 in the range of a few hundred microns, preferably in the range of less than 200 microns, the predetermined geometry of the burst strip 266 must be maintained very precisely. The material for the burst strip 266 can be, for example, glass or ceramic, and it can be advantageous to impress mechanical pretension on the burst strip 266 which increases the distance of the fracture sides after bursting of the predetermined breaking point. To achieve this, the burst strip 266 can be made as a composite element of at least a glass ar ceramic material and at least a metal which are cemented, scddered or brazed to one another. Pretensioning of the burst strip 266 ca.n likewise be induced by using a metal with shape memory (memory effect).
It is furthermore possible to produce the burst strip 266 from a piezoelectric material or at least provide it with such a layer. In deformations of the burst strip 266 which do not lead to its rupture, and which therefore do not: signal an unallowable operating state of the secondary electrochemical cell, electrical information delivered by the piezoelectric converter can be picked up in the form of char;;e changes by the optional evaluation electronics 52 in order for example to actuate a switching element which corresponds to the break contact 48 or 50 of Fig.
1 and to interrupt recharging ~or discharging of the electrodes 2, 4 of the secondary electrochemical cell before th.e secondary electrochemical cell reaches an unallowable operating state.
In the embodiment as shown in Figs 13 and 14, it is conceivable that the position of the perforation 274 and the short circuit contact 278 could be exchanged for one another with reference to the center of the longer side of the burst strip 266 so that the short circuit contact 278 comes to rest on the side of the rupture edge which is the right one in Fig. 14. In this case a short circuit current cannot burn through a possibly remaining fragment 290 of the conductive layer, but can cause a desired complete discharge of the secondary electrochemical cell, in which case the contact clips 68 and/or 70 would not have to be designed as fuses, as this is principally possible (compare: the corresponding statements relating to the protective housing 54 of Figs 2 to 4). If a multiple redundant protection is not necessary, it is furthermore conceivable to completely abandon the short circuit contact 278 and the counter contact 282, to use only the irreversible break contact function of the burst strip 266 and to design the latter such that in any case it is ensured that when the burst strip 266 ruptures a fragment 290 of the conductive layer does not remain.
A ninth embodiment of the secondary electrochemical cell is shown in Fig. 15 and differs from the embodiment of Figs. :Z to 4 essentially only in that, to increase the redundancy, a strain gauge 292 is applied in a meander configuration on the top of the cover plate 62. When the cover plate 62 bulges, the strain gauge 292 experiences a change in shape which leads to a change of its electrical resistance which is sensed via the terminals 292 and 296 by the evaluation electronics 52 and is used for example to actuate other switching elements, for example, an electrically actuated make contact which can be placed remote from the protective housing and functionally corresponds to the make contact 46 or the break contact SO of Fig. 1.
The evaluation electronics 52 can furthermore activate a warning means which is not shown and which notifies a user about the malfunction of the secondary electrochemical cell.
A protective housing 298 which is shown in Fig. 16 encompasses the switching element 86 which has already been described in conjunction with the protective housing 54 of Figs. 2 to 4 and differs from the protective housing 54 essentially only by the following configuration features: A metallic, preferably titanium bottom is made cup-shaped, and a hollow cylindrical side wall 300 is closed at its lower face side by a bottom plate 302 which is integrally connected to the side wall 300. A cover plate 301, which is a bulgable membrane, is welded in a hermetically tight manner to l:he top face side of the side wall 300 and preferably likewise is made of titanium. A cup-shaped receiver 306 is held within the protective housing 298 such that its cylindrical side wall has an oulaide diameter which corresponds to the inside diameter of the side wall 300 and its bottom plate rests on the bottom plate 302. The inside contour of the receiver 306 is matched to thc; outside contour of the positive electrode 2, the latter being fixed and centered in the radial direction within the protective housing 298. The receiver 306, like the already described receivers 124 (Figs. 5 to 9) and 256 (Fig. 12), is formed of an electrically insulating material, preferably of a plastic material such as polytetrafluoroethylene (PTFE), and insulates the positive electrode 2 with reference to the metallic outside walls of the protective housing 298. The receiver 306 is provided on the outside of its side wall with a recess 308 and is inserted into the protective housing 298 such that the recess 308 is facing an opening 310 which is made in the side wall 300 in radial direction.
The cylindrical opening 310 in the side wall 300 is surrounded on the outside of the side wall 300 by a flat cylindrical surface 312 into which an outwardly pointing shoulder 314 of a sleeve-shaped, metallic, preferably titanium receiver 316 is fitted and welded in a hermetically tight manner. In the receiver 316 an electrically insulating, inorganic-nonmetallic housing section of the protective housing 298 i:n the form of a ceramic substrate 318, for example, of A12O3, is held such that the substrate 318 with its outside diameter is matched to the inside diameter of the receiver 316 and is inserted into the latter up to a collar which is provided on the inside wall of the receiver 316 and is located in the axial direction on the side of the receiver 316 which faces the shoulder 314. On the opposite side the substrate 318 projects beyond the receiver 316 and is connecteal to it in a hermetically tight manner via a gold brazing connection 320. The substrate 318 in turn accommodates a bipolar feed-through 315 which includes two metallic contact pins 322 and 324, which preferably are made of a platinum-iridium compound and form one pole each of the; bipolar feed-through 315. The contact pins 322 and 324 which are shown in Fig. 16 in a position which has been turned by 90° around the axis of the receiver 316 penetrate the substrate 3 l 8 in the axial direction and are fixed hermetically tight in it in the same manner by a gold brazing connection 326. They have a length which is sufficient to axially project beyond the face side of the shoulder 314 and that of the substrate 318, the contact pins 322 and 324 projecting into the recess 308 on the side facing the interior of the protective housing 298. The pin 322 makes contact, via a contact clip 332, with the positive electrode 2, and a contact clip 330 forms a current path between the negative electrode 4 and the contact pin 324. The two contact clips 330 and 332 each are surrounded by an insulating hose 334. In order to definitely bring the metallic housing sections (i.e. the side wall 300, the bottom plate 302, the cover plate 304 .and the receiver 316) of the protective housing 298 to the potential of the negative electrode 4, t:he feed-through 31 S has a solder or brazing bridge 328 which extends between the contact pin 324 and the receiver 316. Outside of the protective housing 298 the positive electrode 2 and the negative electrode 4 are each tapped via a terminal 338 and 336, respectively.
The protective housing 298, when compared with the protective housing 54, can be produced with lower cost since the bottom of the protective housing 298 is made in one piece and no ceramic insulating ring 80 is used. The especially critical metal ceramic transition is minimized and limited to a part which is to be produced and tested separately and which includes the components 316.. 318, 322 and 324. This considerably contributes to increased compressive strength of the protective housing 298.

As follows from Fig. 17, the protective housing 340, viewed in the direction of its smallest extension, instead of a cylindrical cross section, can also have a different, for example roughly droplet-shaped cross section. In the embodiment of the protective housing 340 as shown in Fig. 17, the side wall is formed by a segment 342 in the form of a three quarters circle and two linear segments 344 and 346 which tangentially join both sides of the three quarters circle, the linear segments adyoining one another via a rounded area which lies between them.
The side wall is metallic, prei:erably of titanium, and together with a one-piece bottom plate forms a cup-shaped bottom. A cover plate, which is not shown and which likewise is preferably made of titanium, is welded in hermetically tight manner to the upper face of the side wall. For the sake of clarity the wall thickness of the segments 342, 344 and 346 is shown enlarged. The electrodes 2 and 4 are foxed within the protective housing 340 by a centering arrangement which is not shown, at least one of the electrodes 2 and 4 being electrically insulated, preferably by the centering arrangement, with reference to the cup-shaped bottom and the cover plate. The centering; arrangement can be a cup-shaped receiver similar to receiver 256 1 S (compare Fig. 12) or receiver 306 (Fig. 16) which in addition to the centering function also provides for electrical insulation. Furthermore, the inside of the cup-shaped bottom which faces the electrodes 2, 4 and/or the cover plate can be provided with an insulating layer.
A feed-through 348 is. bipolar, wherein, different form the embodiment shown in Fig.
16, the receiver 316 is omitted, so that a ceramic substrate 350 is soldered or brazed, not in the receiver, but directly into the side wall of the protective housing 340 in hermetically tight manner, for which preferably gold brazing filler metal is used. The ceramic substrate 350 is soldered or brazed into the linear segment 344, but it is also possible to house the former in the circular segment 342. Metallic contact pins 354 and 356 which each form one pole of the bipolar feed-through 348 are soldered or brazed in hermetically tight manner into the ceramic substrate 352 and are used for separate routing of the current path from or to the two electrodes 2 and 4 through the wall of the segment 344. With respect to the preferred selection of materials for the contact pins 354, 356. and the substrate 350 reference is made to the statements made with respect to the feed-through 315. In the feed-through 348 there can also be an electrical connection which is. similar to the solder or brazing bridge 328 (see Fig. 16) between the contact pin 354 or 356 and the segment 344 in order to definitely bring the housing to a negative or positive potential. Advantageously, the housing is connected electrically conductively to the negative c;lectrode 4, and the positive electrode 2 is insulated with respect to the housing.
A cylindrical opening in the segment 346, by means of a solder or brazing connection, accommodates a ceramic substrate 358 which is penetrated by two contact pins 360 and 362 S which are held in the substrate 358 via a solder or brazing connection and axially project beyond the substrate 358 at both sides thereof . The opening in the segment 346 is sealed in hermetically tight manner at the outside by a metallic membrane 364, the membrane 364, in the base state, i.e. at a not unduly elevated pressure within the protective housing 340, with its inside which faces the interior of the protective housing 340, contacting the contact pins 360 and 362 with a defined prestr~ess and electrically connecting them. The membrane 364 which acts as the detector element is, located outside of a section of the protective housing 340 which accommodates the electrodes 2 and 4, wherein an opening 366 in the substrate 358, which opening extends essentially in the direction of the longitudinal axis of the contact pins 360, 362, ensures a fluid connection bel:ween thc; membrane 364 and the section of the protective housing 340 which accommodates the electrodes 2 and 4.
A contact clip 372 directly connects a tap 384, provided on the positive electrode 2, with the contact pin 356 of the feed-through 348, and the second contact pin 354 of the feed-through 348 contacts a tap 382 of the negative electrode 4 vi.a a break contact. The break contact includes the membrane 364 anal a contact pair which is formed by the contact pins 360, 362. A contact clip 368 is provided between the tap 382 and the contact pin 360 and a contact clip 370 is provided between the contact pin 362 and the contact pin 354.
The membrane 364 does not allow detection of swelling of the electrodes 2, 4 by the electrodes 2, 4 directly or indirectly adjoining the membrane 364, but swelling of the electrodes 2 and 4 leads, in the same waxy as gas evolution and/or a temperature rise during operation of the secondary electrochemical cell, to an increase in the internal pressure in the protective housing 340. If within the hermetically tight protective housing 340 a predetermined pressure limit value which signals a just still allowable operating state of the secondary electrochemical cell is exceeded, a bulge is impressed on the membrane 364 which is in fluid communication with the interior of the protective housing 340 via the opening 366, and this bulge is sufficient to lift the membrane 364 offthe contact pins 360 and 362. The electrical connection between the two contact pins 360, 362 and thus between the negative electrode 4 and the contact pin 354 of the feed-through 348 is then reversibly interrupted.

The protective housing 340 has another switching element which is integrated in the circular segment 342 and is made as a reversible make contact. This switching element can be present additionally to or instead of the above described break contact. A
membrane 380 simultaneously is the detector element and part of the make contact. It is provided on the inside of the segment 342 which faces the electrodes 2, 4 and it closes an opening in the segment 342.
In the cylindrical opening a ceramic substrate 374 is soldered or brazed such that two contact pins 376 and 378, which axially penetrate the substrate 374 in the base position of the membrane 380, are at a predetermined distance to the outside of the membrane 380. The membrane 380 is made electrically conductive at least in its outside area adjacent to the contact pins 376, 378. Preferably, however, the entire membrane 380 is made electrically conductive, and preferably is made of a material corresponding to the material of the metallic bottom and the cover plate of the protective housing 340, and the membrane 380 preferably is welded into the segment 342. In this case the membrane 380 as a whole is at the electrical potential of the metallic housing parts.
The membrane 380 nf;eds not necessarily seal the opening in the segment 342 in a hermetically tight manner. It is sufficient if it is tight enough to experience a bulge at an unallowably high pressure rise within the protective housing 340 (in Fig. 17 shown by a broken line) which brings at least its conductive area into electrical contact with the contact pins 376 and 378 and electrically short circuits them. In such a case the hermetic tightness must be ensured by the substrate 374 which would have to be soldered or brazed in hermetically tight manner to the segment 342 and likewise to the contact pins 376, 378.
Furthermore, a compression space formed between the substrate 374 and the membrane 380 would have to be considered in the design of the membrane 380. Conversely, if the membrane 380 seals the opening in the segment 374 in hermetically tight manner, which is preferred, a hermetically tight configuration of the substrate 374 and the corresponding solder or brazing connections between the substrate 374 and the contact pins 376, 378 and the segment 342 is not absolutely necessary, but under certain circumstances is to be preferred.
It goes without saying; that the protective housing 340 can be designed such that swelling or expansion of the volume of the electrodes 2 and/or 4 in the direction of the bulging of the membrane 380, i.e. essentially perpendicular to the smallest extension of the protective housing 340, actuates the membrane 380 by the electrodes 2 and/or 4 contacting the membrane 380 directly or indirectly for example via an insulating layer. Preferred materials for the contact pins 360, 362, 376, 3',l8 and the substrates 358 and 374 of the break contact or the make contact, respectively, correspond to those of the contact pins 354 and 356 of the feed-through 348 and the substrate 350, respectively.
The make contact of the protective housing 340, which includes the membrane 380 and a contact pair which is formed by the contact pins 376, 378, can be used for example in a manner similar to the make contact 44 (see Fig. 1 ) in order to directly short circuit the recharging circuit 22. It is likewise possible to monitor the make contact by means of the evaluation electronics SZ which in turn actuates other switching elements or the already mentioned warning device.
One major advantage of the protective housing 340 is that it has a very flat design because all detector and switching elements as well as the feed-through are integrated into the side wall of the protective housing 34C1, and that it, in the direction of its smallest extension, has a thickness which exceeds than that of the electrode/electrolyte system substantially merely by the wall thicknesses of the bottom and the cover plate.
While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art.
Therefore, this invention is not limited toe the details shown and described herein, and includes all such changes and modifications.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A secondary electrochemical cell for an implantable medical device, said cell comprising:
a hermetically sealed housing;
a positive electrode in said housing;
a negative electrode in said housing;
said positive electrode and said negative electrode each comprising an active material;
a detector at least operatively connected to said housing, wherein said detector is adapted to sense a predetermined operating state of said cell; and a switch that is responsive to said detector sensing said predetermined operating state to switch from a first state to a second state, wherein said switch in said second state prevents at least one of a recharging operation and a discharging operation.

2. The cell of claim 1, wherein said first state of said switch is a closed circuit and said second state is an open circuit and wherein said second state interrupts a connection of said cell with a charging device.

3. The cell of claim 1, wherein said first state of said switch is a closed circuit and said second state is an open circuit and wherein said second state interrupts a connection of said cell with a consumer circuit.

4. The cell of claim 1, wherein said first state of said switch is an open circuit and said second state is a closed circuit and wherein said second state short circuits a recharging circuit connected to said cell.

5. The cell of claim 1, wherein said first state of said switch is an open circuit and said second state is a closed circuit and wherein said second state short circuits said cell.

6. The cell of claim 1, wherein said second state of said switch is irreversible.

7. The cell of claim 1, wherein said second state of said switch is reversible.

8. The cell of claim 1, further comprising at least one overcurrent protection unit that is adapted to limit current in at least one of a recharging circuit and a consumer circuit that is connected to said cell.

9. The cell of claim 8, wherein said protection unit is one of a reversible and an irreversible overcurrent protection unit.

10. The cell of claim 1, wherein said detector is a temperature detector and wherein said predetermined state is a predetermined temperature.

11. The cell of claim 1, wherein said detector is a pressure detector and wherein said predetermined state is a predetermined pressure.

12. The cell of claim 1, wherein said predetermined state is a predetermined shape of said detector.

13. The cell of claim 1, wherein said predetermined state is a predetermined shape of said housing.

14. The cell of claim 1, further comprising evaluation electronics that are responsive to said detector sensing said predetermined operating state to cause said switch to switch into said second state.

15. The cell of claim 1, wherein said detector is an extensometer.

16. The cell of claim 15, wherein said extensometer is a strain gauge.

17. The cell of claim 15, wherein said extensometer is a piezoelectric element.

18. The cell of claim 1, wherein said detector forms a portion of said housing.

19. The cell of claim 1, wherein said detector is enclosed within said housing.

20. The cell of claim 1, wherein said detector is positioned outside of a section of said housing receiving said electrodes and is in fluid communication with the interior of said housing.

21. The cell of claim 1, wherein said detector is a membrane.

22. The cell of claim 21, wherein said membrane forms a portion of one of an outside wall and a separating wall of said housing.

23. The cell of claim 21, wherein said membrane forms a portion of a side wall of said housing and wherein said membrane is adapted to bulge in a direction that is substantially perpendicular to the smallest dimension of said housing.

24. The cell of claim 21, wherein said membrane forms a portion of said switch and wherein said first state of said switch is an open circuit and said second state is a closed circuit.

25. The cell of claim 21, wherein said membrane forms a portion of said switch and wherein said first state of said switch i s a closed circuit and said second state is an open circuit.

26. The cell of claim 1, wherein said housing comprises at least one electrically conductive metallic housing section and at least one electrically insulating inorganic-nonmetallic housing section.

27. The cell of claim 26, wherein said electrically insulating inorganic-nonmetallic housing section comprises ceramic material.

28. The cell of claim 26, wherein said electrically insulating inorganic-nonmetallic housing section includes at least one monopolar electrically conductive feed-through that is hermetically sealed and electrically insulated.

29. The cell of claim 28, wherein said feed-through includes at least one pole with a metallic contact pin.

30. The cell of claim 29, wherein said contact pin is connected to said inorganic-nonmetallic housing section by means of a material connection and wherein said inorganic-nonmetallic housing section is connected to an outside wall of said housing by means of a material connection.

31. The cell of claim 29, wherein said contact pin is held hermetically sealed by means of a material connection in the inorganic-nonmetallic housing section, wherein said inorganic-nonmetallic housing section is held hermetically sealed by means of a material connection in a metallic receiver and wherein said metallic receiver is materially connected to an outside wall of said housing.

32. The cell of claim 28, wherein said feed-through includes at least one pole which is in contact with one of said :positive electrode and said negative electrode.

33. The cell of claim 26, wherein said electrically insulating inorganic-nonmetallic housing section is electrically connected to one of said positive electrode and said negative electrode.

34. The cell of claim 1, wherein said housing comprises a biocompatible material.