MXPA00001809A - Current interrupter for electrochemical cells - Google Patents

Abstract

A current interrupter assembly (220) for electrochemical cells (215) may be self-contained, sealed unit which may be separately inserted into the cell during cell construction. The current interrupter assembly (220) has particular utility for thin rechargeable cells and when inserted in the cell forms a portion of the electrical pathway between a cell electrode (211) and corresponding terminal (245). The current interrupt mechanism comprises a thin thermally responsive member preferably comprising a disk (250) of a shape memory metal alloy having a curvedsurface. When cell temperature exceeds a predetermined value the disk deflects to cause a break in the electrical pathway within the assembly.

Description

CURRENT SWITCH FOR ELECTROCHEMICAL CELLS DESCRIPTION OF THE INVENTION This invention relates to a current switch capable of responding thermally to an electrochemical cell, which safely prevents the flow of current through the cell in the presence of an excessive increase in the temperature thereof. The invention also relates to a current switch capable of responding to pressure, with a cell, which safely inactivates the cell in the presence of an excessive accumulation of gas pressure therein. Electrochemical cells, especially high energy density cells such as those in which lithium or lithium ion is an active material, are subject to leaks to ruptures which, in turn, can cause damage to the device which is activated by the cell or the surrounding environment. In the case of rechargeable cells, the increase in the internal temperature of the cell can result in an overload. An undesirable increase in temperature is often accompanied by a corresponding increase in the internal pressure of the gas. This probably happens in the case of an external short circuit condition. In addition, the internal gas pressure can be increased REF: 32848 in the case where the cell is over-discharged. It is desirable that safety devices accompany the cell without unduly increasing costs, size or mass of the cell. Such cells, particularly rechargeable cells using lithium or lithium ion as an active material, are subjected to leakage or rupture caused by an increase in the internal temperature of the cell which is often accompanied by a corresponding increase in pressure. It is likely that this is caused by conditions of abuse, such as overloading or a short circuit condition, which may occur during over-discharging. It is also important that these cells are hermetically sealed to avoid the escape of electrolyte solvent and the entry of moisture from the outside environment. As stated above, if such a cell is charged, self-heating occurs. A load too fast at an overloaded speed can lead to an increase in temperature. When the temperature exceeds a certain point, which varies from the chemistry and structure of the cell, an uncontrollable thermal and undesirable process condition begins. In addition, due to overheating, internal pressure builds up and the electrolyte can be suddenly expelled from the cell. It is preferable to start a controlled ventilation before this happens.

Some rechargeable cells are very thin, for example, thin prismatic cells or small-sized cylindrical cells for cell phones. It has been difficult to incorporate cori fi ed breaker safety devices within such cells due to their small size. But the need for such security devices is always greater due to the proximity of the cell to the consumer during the normal operation of a cellular phone. Conventional cell designs use an end cap which is placed which is inserted into an open-ended cylindrical casing after the anode and active cathode material and an appropriate separating material have been inserted into the cylindrical casing. the electrolyte The end cap is in electrical contact with one of the anode or cathode materials and the exposed portion of the end cap forms one of the terminals of the cell. A portion of the cell cover forms the other terminal. The present invention has one or several current-interrupter assemblies integrated within a single cell and advantageously applied to primary or secondary (rechargeable) cells. The end cap assembly of the invention has particular application for rechargeable cells, for example, rechargeable lithium ion cells, nickel metal hydride, nickel cadmium or other rechargeable cells, to eliminate the danger of overheating of the cell and buildup of pressure in the cell during exposure to high temperatures, charged or overcharged or inadequate, or a short of the cell. In one aspect, the invention is directed to a current interruption mechanism for thin prismatic cells or small diameter cylindrical cells. A small, thermally responsive, current-carrying switch assembly is located within the cell. The current switch assembly is preferably a self-contained, sealed device which has the advantage that it can be manufactured separately and inserted into the cell as a separate unit during the construction of the cell. The thermally-responsive current-interrupting mechanism within the self-contained assembly activates the interruption and prevents current from flowing through the cell when the cell interior is overheated or exceeds a predetermined temperature. The current-interrupting mechanism comprises a member capable of thermally responding, desirably a flexible disk preferably constituted of a metal alloy with shape recovery having a curved surface. In normal operation of the cell, the shape recovery allows the disk to preferably conform a portion of the electrical path between one of the electrodes of the cell and a terminal to which the electrode is connected. When the temperature inside the cell reaches a predetermined value, the disk with shape recovery is bent to interrupt the electrical path between the electrode and the terminal in this way inactivating the cell. In another aspect of the invention, the current switch assembly is a self-contained unit comprising both a current-interrupting mechanism capable of thermally responsive as well as a pressure-operated current-interrupting mechanism. The current switch assembly has an opposite end cap plate which functions as a cell terminal. When the assembly is placed in a cell and the cell is in normal operation, the end cap plate is in electrical communication with the electrode of the cell (anode or cathode). The current interruption mechanism comprises a flexible member capable of thermally responding, consisting of a metal alloy with shape recovery or a bimetal, desirably in the form of a curved disk, which may be in physical communication with an electrically conductive member flexible. The physical communication between the thermally responsive member and the flexible conductor member can be obtained by an electrically non-conductive movable rod placed between these two elements. In normal operation of the cell, the flexible conductor member forms a portion of the electrical path between one of the cell electrodes and the end cap (terminal). When the temperature inside the cell reaches a predetermined value, the thermally responsive member bends causing the non-conducting movable rod to push against the flexible conductor member which in turn causes it to bend and interrupt the electrical path between the electrode and the terminal. The assembly desirably also includes a pressure-operated current-interrupting mechanism which preferably includes a metal diaphragm driven by pressure. The diaphragm preferably forms a portion of the housing of the current switch assembly and bends when the pressure within the cell yields a predetermined level. Deflection of the diaphragm causes an interruption in the electrical path between the cell electrode and the corresponding terminal, thus inactivating the cell. In another aspect, the cell may contain the two previous types of self-contained current interruption assemblies, specifically one containing only one current-interrupting mechanism capable of thermally responding and the other containing both a current-interrupting mechanism capable of thermally responding and a pressure-operated current-interrupting mechanism.

This provides the cell with multiple and independent safety interrupter features. Such a design can be advantageously used if the cell is of sufficient diameter to accommodate both current-interrupter assemblies, for example a cell having a diameter or a total thickness between about 5 and 20 mm. In such an embodiment, the current switch assembly contains only the thermally responsive current-switching mechanism and can advantageously be placed completely within the interior of the cell so that it is closest to the hottest part of the cell. Figure 1 is an exploded perspective view of one embodiment of the current switch assembly of the invention placed completely inside a prismatic cell. Figure 2 is a cross-sectional view of the cell and the current switch assembly in Figure 1. Figure 3 is an exploded perspective view of the components of the power switch assembly shown in Figures 1 and 2. The Figure 4 is a perspective view of the prismatic cell with another embodiment of the current switch assembly shown projecting from one end of the cell.

Fig. 5 is a perspective view of a cylindrical cell with the same embodiment of the current switch assembly shown in Fig. 4. Fig. 6 is a cross-sectional view of the current switch assembly shown in Figs. and 5. Figure 7 is an exploded perspective view of the current switch assembly shown in Figures 4, 5 and 6. Figure 8 is a vertical cross-sectional view of a cylindrical cell containing the modes of the switch assembly of current shown in Figs. 2 and 6. In a preferred embodiment, the thermally capable current-carrying assembly 220 of the invention can be placed internally in its entirety within cell 215, as shown in Figs. Figure 1. Cell 215 may be a prismatic cell having a parallelepiped-like cover 225, as shown in Figure 1, but alternatively it may be a cylindrical cell. rich in small diameter. If cell 215 is a prismatic cell, it typically has a small total thickness of between about 3 and 10 mm, typically the prismatic cell is very thin and has a total thickness between about 3 and 6 mm. If cell 215 is a cylindrical cell of small diameter, the diameter will typically be between about 3 and 10 mm in diameter. The current assembly 220, as described herein, may be integrated into larger cells, for example, prismatic cells having a thickness between about 3 and 15 mm or a cylindrical cell having a diameter between about 3 and 15. mm, but assembly 220 has particular utility for small thickness prismatic cells or small diameter cylindrical cells. The cell 215 can be a primary or rechargeable cell such as a lithium ion cell, a nickel metal hydride cell, or a nickel cadmium cell, but advantageously it is a rechargeable cell such as a lithium ion cell. A rechargeable lithium ion cell is characterized by the transfer of lithium ions from the negative electrode to the positive electrode when the cell is discharged from the positive electrode to the negative electrode when charging the cell. Typically it can have a positive electrode of lithium oxide and cobalt (LixCoC02) or of lithium oxide and manganese of spinel crystal structure (LixMn204) and a negative carbon electrode. The negative electrode constitutes the anode of the cell during discharge and the cathode during charging, and the positive electrode constitutes the cathode of the cell during discharge and the anode during charging. The electrolyte for such cells can be constituted as a lithium salt dissolved in a mixture of non-aqueous solvents. The salt can be LiPFg and the solvents can advantageously be dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC) and mixtures thereof. In the specific embodiment shown in Figure 1, cell 215 is a prismatic lithium ion cell having a shell 225 formed of faces 205 (a) and 205 (b) of opposite flat bodies, faces 208 (a) and 208 ( b) flat sides, and flat faces 209 (a) and 209 (b). The positive terminal 245 and the negative terminal 246 are exposed from the same side face 208 (a) and are accessible for connection to a device to be activated. An electrode stack 235 is shown comprising a sheet of positive electrode material 211, a sheet of negative electrode material 213 with a conventional porous spacer material 212 therebetween. The stack 235 can be rolled in a conventional jelly roll manner and the rolled material then flattened so that it is placed compactly within the cell. A thermally capable current-capable assembly 220 of the invention can be integrated into a prismatic lithium-ion cell 215, as shown in Figure 1. In such an embodiment, the current-switch assembly is placed completely inside the interior of the cell and electrically connected to one end of the positive electrode 211 and the other end to the positive terminal 245. Thus, under normal operation, there is an electrical path between the positive electrode 211 and the positive terminal 245. In Figure 2 a preferred embodiment of the 220 current switch assembly is shown. An assembly 220 is a sealed and self-contained unit comprising a metal cover 280, a metal end cap 230, a current switch disk 250, preferably formed of an alloy with shape recovery, and a metal contact plate 295 which makes contact with the inner surface of the lid 230. The end cap 230 is concave so that its surface protrudes outwards, as shown in Figure 2. The cover 280 is in the form of a circular cup-shaped structure having a open end and a slightly protruding body, as shown in figure 3. Assembly 220 has an insulating ring 290 'between the peripheral edge of disc 250 and peripheral edge 230 (a) of end cap 230. The preferred structure for each of the mounting components 220 is shown in Figure 3. The current switch disk 250 has a thickness which is small compared to its diameter or its average width, and preferably is circular or cylindrical, but also it may have other shapes, for example it may be oval or elliptical or in the form of a thin parallelepiped or a thin elongated plate or plate, with one or more pairs of opposite edges which may not be parallel. Such structures preferably have a thickness which is less than about 30% of their length and also less than about 30% of their average width. Therefore, the term "disc" as used herein and specifically in relation to thermally responsive members 250, 350 and 352, is intended to be considered included for all other forms. In the case of an oval or elliptical shaped disc, the term average width will refer to the smallest diameter of its main face. The thickness of the disc 250 desirably is less than 1 mm, preferably between approximately 0.05 and 0.5 mm. In Figure 3 a preferred embodiment of the current switch disk 250 is shown, where it has an outer edge 258 and a hollow central portion 257. A resilient and flexible portion 255 protrudes inwardly in the portion 257 from the peripheral edge 258. The flexible portion 255 is advantageously made with a curvature 255 (a) slightly upward on its surface, as shown in Figure 3, so that its end 255 (b) in a first position against the contact plate 295 to complete the electrical path between positive electrode 211 and positive terminal 245. During normal operation, the current passes from the positive electrode 211 to the connector tab 287 (a), to the cover 280 towards the current switch disk 250 and the flexible portion 255, to make contact with the pin 295 for assembling the end cap 230 the connector tongue 287 (b) and then to the positive terminal 245. As can be seen from figure 1, the disc 250 'current switch is oriented inside the assembly so that the current passes through the thickness of the disc 250 and therefore the thicknesses of the flexible portions 255, to minimize the resistance . When the temperature inside the cell 215 exceeds a predetermined value, the end 255 (b) is bent inward, to a second position to interrupt contact with the contact plate 295 and thus interrupts the electrical path between the electrode 211 and terminal 245 to inactivate the cell. With reference to Figure 3, the power switch assembly 220 is designed to be easily constructed by inserting the current switch disk 250 into the open end cover 280 so that it rests on the bottom surface of the cover. An insulating ring 290 is then inserted over the disc 250 and the metal contact pin 295, which is in the form of a solid disc-shaped pin, is inserted through the opening 290 (a) in the insulating ring until it rests on the protruding resilient member 255, preferably composed of an alloy with shape recovery. The insulating inner ring 275 is inserted onto the end cap 230 and these two parts are then placed on the metal contact pin 295 so that the inner surface of the end cap 230 makes contact with the upper surface of the pin 295 of Contact. The peripheral edge of the cover 280 and the peripheral edge of the insulating inner ring 275 are then tightened on the peripheral edge 230 (a) of the end cap 230. Radial pressure is applied during tightening so that the peripheral edge 230 (a) of the end cap 230 bites the inner surface of the peripheral edge 275 (a) of insulating inner ring 275 to form a seal between the end cap 230 and cover 280. Figures 6 and 7 show another embodiment of the thermal current switch assembly, specifically assembly 320. This mode of the current switch is designed to protrude from one end of the prismatic cell, as shown in Figure 4. or from one end of a cylindrical cell, as shown in Figure 5. In such an embodiment, the total thickness of the prismatic cell is advantageously at least about 6 mm, typically between about 6 and 20 mm, which is a thickness large enough to accommodate assembly 320. If the cell is cylindrical, as shown in Figure 5, it is desirable that it have a diameter at least as large as the cells. elds of size AAA, in order to accommodate the assembly 320. Therefore, the assembly 320 can conveniently be applied to protrude from the end of cylindrical cells sizes AAA, A, C, or D, or, for example, cells that have a diameter between approximately 5 and 20 mm. When used in this manner, the protruding portion of the assembly 320, specifically the end cap 325, can conveniently form one of the cell terminals. The current switch assembly 320 may have an end cap 325 desirably in the form of an inverted cup which forms the upper portion of the assembly 320 and a cup-shaped body 370 which forms the lower portion of the assembly as shown in figure 6. End cap 325 and body 370 are formed of electrically conductive material. The base 372 of the cup-shaped body 370 preferably forms a pressure-driven diaphragm which is designed to be bent upward (towards the end cap 325) when the pressure within the cell exceeds a predetermined value. A member 350 or 352 that responds to heat, flexible, advantageously composed of an alloy with shape recovery or a bimetal, is located within the lower portion of the cup 370 and in proximity to the pressure diaphragm 372. The member capable of responding to heat desirably may be in the form of a disk, such as disk 350 or 352, and has a curved surface, as shown in Figure 7. Any structure may be used when an alloy is used With shape recovery or a bimetal, however, an elongated splint or parallelepiped structure 352 is preferred when the shape recovery alloy is used and circular disk structure 350 is preferred when the bimetal composition is used. Desirably, the disk 350 (or disk 352) is positioned within the assembly 320 so that it is substantially in a plane parallel to the surface of the end cap 325. An electrically insulating rod or plug 340 can be supported on the upper surface of the member 350 capable of responding by heat, flexible. The assembly 320 desirably includes a metal support ring 360 which can conveniently be located on the edge 374 of the body 370. The assembly 320 desirably includes a flexible and electrically conductive metal disk 330 which comprises a resilient member 334 and flexible that extends within the hollow portion 333 and the disk 330 from the peripheral edge 332 thereof. An insulating ring 335 is placed between the peripheral edge 332 of the disk 330 and the edge 362 of the metal support ring 360. The flexible conductor disk 330 is interposed between the peripheral edge 327 and the end cap 325 and the insulating ring 335. An insulating inner ring 375 surrounds the peripheral edge 327 of the end cap 325 and the peripheral edge 377 of the cup-shaped lower body 370, and an inner ring 375 also surrounds the disk 330 and the insulating ring 335. In turn, a cover 380 surrounds the insulating lower ring 375. With reference to Figure 7, the power switch assembly 320 can be constructed by first inserting the insulating inner ring 375 into the cover 380 so that the outer surface of the inner ring makes contact with the inner wall of the cover 380. a sub-assembly is constructed by inserting a member 350 or 352 capable of thermally responding within the cup-shaped body 370, and then by inserting a metal support ring 360 onto the flange 374 of the cup-shaped body 370. The plastic movable rod 340 is inserted through the central opening 363 of the support ring 360 so that it is supported on the member 350. The insulating ring 335 is placed on the support ring 360 in contact with its peripheral edge 362. The disk 330 is then placed on the insulating ring 335 so that the peripheral edge 332 of the disk 330 rests on the insulating ring 335. The end cap 325 is placed on the disk 330 so that the peripheral edge 327 of the end cap 325 abuts the peripheral edge 332 of the disk 330. The sub-assembly is then inserted into the cover 380 with the inner ring 375 insulator contained in it. The end 380 (a) of the cover 380 and the end 375 (a) of the inner ring 375 are then squeezed onto the peripheral edge 327 of the end cap 325 so that the sub-assembly and its components are kept hermetically and permanently in place. place and are sealed by the inner ring 375 of the surrounding cover 380. The assembly 320 can be inserted into a rechargeable cylindrical cell 400, for example a cylindrical lithium ion cell, as shown in Figure 8. The end cap 325 of the assembly 320 protrudes from one end of the cell and forms one of the terminals of the cell, typically the positive terminal. Similarly, assembly 320 can be inserted into the rechargeable prismatic cell, for example a prismatic lithium ion cell 500, shown in Figure 4. In such an application, the end cap 325 protrudes from one end of the cell and forms one of the terminals of the cell, typically the positive terminal. In either case, whether a cylindrical or prismatic cell is used, the cell optionally may also include an additional current switch assembly, specifically the 220 current switch assembly described above. By having two self-contained and separately housed circuit-breaker assemblies, the cell is provided with two thermally-capable current-interrupting switch systems which are activated independently of one another. A cell 400 with both mounts 220 and 320 current switches included in it, is shown in Fig. '8. Both mounts 220 and 320 current switches shown in Fig. 8 are in the "on" position, that is, in the position that allows current to flow normally from the electrode 211 to the terminal end cover 325. When the cell 400 is in such an operation mode, there is an electrical path between one of the electrodes of the cell, for example the electrode 211 and the cell terminal 325. In normal operation, current flows from the electrode 211 to the connecting tab 287 (a), to the cover 280 of the assembly 220, to the contact pin 295, to the end cap 230 and then to the tab 287 (b). ) connector. The current flows from the connector tab 287 (b) to the lower body 370 of the assembly 320. The current then flows from the body 370 to the support ring 360, to the resilient arm 334 of the disc 330 and then from the disc 330 to the lid 325 of terminal end. If the internal temperature of the cell will reach a predetermined value, the resilient member 215 capable of responding thermally bends downward thereby interrupting the electrical connection between the member 215 and the contact pin 295. This has the effect of cutting the electrical path between the electrode 211 and the end cap 325 to inactivate the cell. Further, if the internal temperature of the cell reaches another predetermined value, the member 350 (or 352) capable of thermally responding to the assembly 320 is bent upward to the position shown in Figure 6. This upward movement of the member 350 causes the plastic rod 340 to move up against the flexible resilient arm 334 of the disc 330. This causes the resilient arm 334 to interrupt contact with the support ring 360 thereby severing the electrical path between the electrode 211 and the electrode 211. 325 terminal end cap. If the internal temperature of the cell increases very rapidly, both members 215 capable of responding by heat from assembly 220 and member 350 (or 352) capable of responding by heat from assembly 320 will be activated simultaneously, causing the electrical path between the electrode 211 and the terminal end cap 325 spontaneously is interrupted in two places. This ensures an immediate inactivation of the cell and provides additional security that the cells will be deactivated in the event that one of the two members capable of responding for heat does not work. Alternatively, if the gas pressure within the cell accumulates and exceeds a predetermined value, the diaphragm 372 of the assembly 320 will be bent upwards which causes the plastic rod 340 to move up against the resilient arm 334 which causes the resilient arm 334 interrupts contact with the support ring 360. This in turn has the effect of suppressing the electrical path between the electrode 211 and the terminal end cap 325, thereby inactivating the cell. The diaphragm 372 only responds to the internal pressure of the cell and, as such, acts independently of the internal temperature of the cell. Thus, the pressure-activated diaphragm 372 ensures that the cell is inactivated if the gas pressure within the cell reaches a predetermined value regardless of the cell temperature. In the current switch mounting mode shown in FIGS. 2 and 3, the disk 250 capable of thermally responding with a resilient member 255 extending inwardly or a disk 350 or a disk 352 shown in FIGS. 6 and 7, is desirably composed of an alloy with shape recovery. The shape-recovery alloy can be selected from groups of known recovery alloys, for example, nickel-titanium (Ni-Ti), copper-zinc-aluminum (Cu-Zn-Al) and copper-aluminum-nickel (Cu-). Al-Ni). However, it has been determined that the most desirable alloy for the shape-saving alloy disc 250 or discs 350 or 352 is from a nickel-titanium alloy. A preferred memory alloy of titanium and nickel is available under the trade designation NITINOL alloy from Special Metals Corporation. Resilient member 255 or disc 250 or discs 350 or 352 can be a retrievable recovery alloy, this one that deforms when heated but returns to its original shape when cooled to room temperature without application of external force. However, it is desirable that the shape-recovery alloy member can not be re-established at room temperature, that is, that it deforms irreversibly when heated to its activation temperature. This ensures that the cell will not become operational once the conditions inside the cell have caused excessive internal heating. Therefore, disks 250, 350 and 352 are preferably manufactured using a NITINOL alloy that is not re-energized once it has been activated. The preferred memory disk 250 can conveniently be manufactured as a single piece of NITINOL alloy having a circular peripheral edge 258 from which a flexible member 255 protrudes inwardly. The flexible member 255 may conveniently be in a rectangular form fired with an outer leg 255 (d) bent upwardly separated from the inner leg 255 (c) by the folding lines 255 (a) (figures 2 and 3). The resilient member 255 may desirably be between about 2 and 5 mm wide and 3 and 8 mm long and of a thickness between about 0.05 and 0.5 mm. Leg 255 (d) is bent down along fold line 255 (a) when the temperature between about 60 ° C and 120 ° C causes an interruption in contact between member 255 and pin 295 of Contact. The disc 250 desirably can have a diameter between about 5 and 15 mm. In order to obtain such an activation effect, it has been determined that the thickness of the memory disk 250 and the resilient member 255 can advantageously be in a range between about 0.05 and 0.5 mm with a surface area such that the resistance of the member be less than approximately 15 milliohms. The form described above for the disk 250, specifically a hollow disk having a circular peripheral edge "from which a flexible portion 255 protrudes inwards is desirable, since it allows a reduced thickness and a good contact area to reduce the total resistance of the disc 250 as the current passes through its thickness during normal operation of the cell The shape recovery member 255 desirably does not have a strain of greater than about 8 percent The bend angle desirably it is between about 10 and 30 °, that is, the end 25 (b) is bent upwards at an angle of between about 10 and 30 ° with respect to the plane of the disk.This allows the memory member 255 to bend away from the disk. contact pin 295 and flatten when the activation temperature is reached.The application to lithium ion cells of the preferred design described above for the disk The shape recovery can result in a total resistance that is less than 5 milliohms which in turn allows a drainage of up to 5 amps under continuous cell operation. In the current mounting mode shown in Figures 6 and 7, the member capable of thermally responding in the form of a curved circular disc 350 or the disk in the form of a curved and thin elongate plate or parallelepiped 352 may advantageously be composed of a shape-recovery alloy as described above, preferably an alloy of NITINOL. (If disk 352 is in the form of a thin elongated tablet, it may be oval or have one or more pairs of opposite edges which are not parallel). Disc 350 or 352 is preferably manufactured to irreversibly deform when exposed to a predetermined temperature, desirably between about 60 ° C and 120 ° C. If the internal temperature of the cell exceeds a predetermined value, the disk or the curvature of the tablet is inverted or flattened causing the plastic rod 340 to push against the resilient arm 334 of the disk 330. This in turn causes an interruption in the electrical contact between the disk 330 and the metal support ring 360 as described above, to interrupt the flow of current. The alternatively thermally responsive disc 350 or 352 may be of a bimetallic construction, that is, it comprises two layers of different metals having a different coefficient of thermal expansion. If the bimetallic construction is used, the top layer of the bimetallic disk 350 or the board 352 (the layer closest to the end cap 325) can be composed of a metal of high thermal expansion, preferably a nickel-chromium alloy and the The underlying or lower layer may be composed of a low thermal expansion metal, preferably a nickel-iron alloy. Another suitable bimetallic composition is nickel and titanium. In such an embodiment, disk 350 (or disk 352) will be activated when the cell temperature is increased to at least 60 ° C and typically can be activated at a cell temperature between about 60 ° C and 120 ° C. It is also possible to choose metallic layers with high and low thermal expansion so that the discs 350 or 352 are not set except at a temperature below -20 ° C, which in most applications makes the device a device thermostatic single action.

With reference to the power switch assembly 220 (Figures 2 and 3), the cover can be formed of aluminum, stainless steel or titanium for added strength and corrosion resistance. The cover 280 desirably has a wall thickness of between about 0.1 mm and 0.5 mm. The cover 280 and therefore the assembly 220 is preferably between about 3 and 15 mm in diameter, typically between about 3 and 8 mm in diameter, and has a depth between about 1 and 10 mm, typically between about 1 and 3 mm . A mount 220 with such total dimensions can be inserted into very thin prismatic cells having a total thickness between about 3 and 6 mm without drastically reducing the capacity of the cell or damaging the functionality of the current breaker. The internally insulating ring 290 is desirably composed of a corrosion resistant thermoplastic material having a relatively high compressive strength and temperature stability. A preferred material for the insulating ring 290 is a liquid crystal polymer available under the tradename VECTRA polymer from Celanese Co. or a polyester available under the trade name VALOX polymer from the General Electric Plastics Company. The contact pin 295 is desirably formed of cold rolled steel or stainless steel so that it can be easily welded to the lower surface of the end cap 230. The contact pin 295 can be reversed with a precious metal such as Silver to decrease its resistance to contact. The end cap 230 is desirably formed of stainless steel, aluminum or titanium to provide the required combination of robustness and corrosion resistance and has a total diameter of between about 3 and 15 mm, preferably between about 4 and 8. mm, and a total bottom depth of about 1 mm, typically between about 0.1 and 1 mm. The insulative inner ring 275 may desirably have a thickness of between about 0.1 and 0.5 mm and a total diameter of between about 3 and 15 mm, preferably between about 4 and 8 mm. The inner ring 275 can be formed of a durable and corrosion-resistant thermoplastic material - although resilient, for example a high density polypropylene, which is inert to electrolyte and has sufficient resilience to provide a good seal between the cover 280 and the internal components of the assembly 220. With reference to the mounting 320 current switch (figures 6 and 7), the cover 380 can be formed of stainless steel or cold-rolled steel coated with nickel for robustness and corrosion resistance. The cover 380 desirably has a wall thickness of between about 0.1 mm and 0.5 mm. The cover 380 and therefore the assembly 320 is preferably between about 4 and 15 mm in total width diameter, preferably between about 4 and 8 mm, and has a depth between about 1 and 10 mm, typically between about 3 and 6 mm. An assembly 320 with such total dimensions can be inserted into the prismatic cells having a total thickness between about 6 and 20 mm, or cylindrical cells having a diameter between about 5 and 20 mm, without appreciably reducing the capacity of the cell or damage the functionality of the power switch. The end cap 325 typically has a total diameter between about 4 and 15 mm and a total depth between about 0.1 and 1 mm. The end cap 325 can be formed of stainless steel or cold rolled steel coated with nickel to provide robustness and adequate corrosion resistance. The flexible conductive disk 330 desirably has a diameter between about 4 and 15 mm and a thickness between about 0.1 and 0.5 mm. It is desirably composed of a resilient metallic material having good electrical conductivity and robustness such as a beryllium-copper alloy or a spring steel which can be coated with a precious metal such as gold or silver to decrease its contact resistance . The resilient arm 334 of the disc 330 desirably can be of a rectangular shape having a width of approximately 2 and 5 mm, a length between approximately 3 and 8 mm, and a thickness between approximately 0.1 and 0.5 mm. The insulating ring 335 desirably is composed of a corrosion resistant thermoplastic material having a relatively high compressive strength and temperature stability. A preferred material for the insulating ring 335 is a liquid crystal polymer available under the trade designation VECTRA polymer from Celanese Co. or a polyester available under the designation polymer VALOX from General Electric Plastics Company. The movable rod 340 can have a diameter or width between about 1 and 3 mm and a length between about 1 and 5 mm. The rod 340 is essentially non-electrically conductive (formed of material which has high resistivity) and can be thermally stable even when exposed to high temperatures, for example 120 ° C and above. A preferred material for rod 340 is a liquid crystal polymer available under the trade designation VECTRA from Celanese Co. The metal support ring 360 desirably has a diameter between about 4 and 15 mm, preferably between about 4 and 8 mm and a thickness between about 0.1 and 1 mm. The support ring 360 can be easily formed of stainless steel or cold rolled steel to provide adequate strength, material which can be coated with a precious metal such as gold or silver to decrease contact resistance. The depth of the body 370 in cup shape desirably can be between about 1 and 3 mm. The pressure-driven diaphragm 372 which desirably forms the base of the cup-shaped body 370 can have a diameter between about 4 and 15 mm and a wall thickness between about 0.1 and 0.5 mm. The cup-shaped body 360 and the diaphragm 372 can be easily formed from aluminum which deforms easily and permanently when exposed to a high pressure differential. The insulating inner ring 375 may desirably have a thickness of between about 0.1 and 0.5 mm and a total diameter of between about 4 and 15 mm. The inner ring 375 can be formed of a corrosion resistant thermoplastic material and durable, yet durable, for example, a high density polypropylene, which is inert to electrolytes and has sufficient resilience to provide a good seal between the cover 380 and the assembly 320 of the internal components. Although the invention has been described with reference to the preferred embodiments, it should be understood that modifications of the described embodiments are possible without departing from the concept of the invention. Therefore, it is not intended that the invention be limited to the specific embodiments but rather that it be defined by the claims and equivalents thereof. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (28)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. An electrochemical cell having a positive and a negative terminal, and a pair of positive and negative internal electrodes, the cell comprises a current switch assembly, the assembly comprises a housing, a chamber within the housing and a sealed end cap of the housing , the assembly has an electrically conductive path therethrough between the housing and the end cap, wherein the assembly comprises a means capable of thermally responding within the chamber to prevent current from flowing through the electrical path inside the chamber. assembly, the thermally responsive medium comprises a thermally responsive disk having a thickness less than its average diameter or width, wherein the disk is oriented within the assembly so that the current passes through the thickness of the disk during the normal operation of the cell, where at least a portion of the disk bends when the temperature within the assembly it reaches a predetermined level causing an interruption in the electrical path through the assembly, which causes the cell to stop working.

2. The combination according to claim 1, characterized in that the disk capable of thermally responding comprises an alloy with shape recovery.

3. The combination according to claim 1, characterized in that the thermally responsive disk is bimetallic.

4. The combination according to claim 1, characterized in that the disk capable of thermally responding has a thickness between 0.05 and 0.5 mm.

5. The combination according to claim 1, characterized in that the assembly is a self-contained unit located completely within the internal volume of the cell and wherein the cell is a rechargeable cell having a total thickness between about 3 and 10 mm.

6. The combination according to claim 1, characterized in that the assembly is a self-contained unit located completely within the internal volume of the cell and wherein the cell is a rechargeable prismatic cell having a total thickness between about 3 and 10 mm.

7. The electrochemical cell according to claim 1, characterized in that the assembly is a self-contained unit that is located completely within the internal volume of the cell and where the thermally capable disk has an opening therethrough and the disk has a outer edge with a flexible portion projecting into the opening from a portion of the outer edge, wherein the outer edge abuts a surface of an insulating member within the end cap assembly, wherein the flexible portion has a surface that it can be folded in a first position, where, when the temperature inside the cell reaches a predetermined level, the surface that can be bent moves to a second position causing an interruption in the electrical path.

8. The electrochemical cell, according to claim 1, characterized in that the assembly forms a portion of the electrical path between one of the electrodes and the corresponding cell terminal and wherein one of the housing in the end stage of the assembly is electrically connected to the electrode. one of the cell electrodes and the other is electrically connected to a corresponding cell terminal.

9. The electrochemical cell, according to claim 7, characterized in that the flexible portion has a thickness between approximately 0.05 and 0.5 mm.

10. An improved electrochemical cell of the type formed by a current interrupter assembly inserted into an open-end cylindrical housing for the cell, the cell also has a positive terminal and a negative terminal, and a pair of positive and negative internal 'electrodes', wherein the assembly has a housing, a chamber within the housing and an exposed end cap plate, the end cap plate is functional as the terminal of the cell, the improvement is characterized in that the end cap plate is electrically connected to one of the electrodes through an electrically conductive path within the end cap assembly, wherein the end cap assembly comprises therein an electrically conductive member, Flexible that forms a portion of the electrical path within the assembly, the end cap assembly further comprises a means capable of thermally responding to cause the current to stop flowing through the cell when a predetermined temperature level is reached, in that the thermally capable medium comprises a member of an alloy with shape recovery having a curved surface a, wherein the assembly further comprises a physical means for causing the movement of the flexible conductor member in response to the change in the curvature of the member surface with shape recovery, wherein, when the temperature of the cell reaches a predetermined temperature, the shape recovery member is bent by altering the curvature in at least a portion of its surface which causes movement of the flexible conductor member to interrupt the electrical path between the end cap plate and the electrode so that the current flows through the cell.

11. The electrochemical cell, according to claim 10, characterized in that the metal member with shape recovery comprises an alloy disk with shape recovery, wherein the disk has a curved surface which bends in the direction of its thickness when a predetermined temperature is reached.

12. The electrochemical cell, according to claim 11, characterized in that the disk has a thickness between approximately 0.05 and 0.5 mm.

13. The electrochemical cell according to claim 10, characterized in that the means for causing movement in the flexible conductor member in response to a change in the surface of curvature of the metal member with shape recovery is an electrically non-conductive member that is locates within the chamber and in physical communication with the shape-recovering member so that when the shape-recovering member is bent, the non-conducting member moves against the flexible conductor member to interrupt the electrical path between the cover plate of end and the electrode.

14. The electrochemical cell, according to claim 13, characterized in that the current switch assembly further comprises a pressure operated diaphragm having a surface exposed to the interior of the cell and a means for causing movement of the flexible conductor member in response to the Deflection of the diaphragm, in which, when the gas pressure inside the cell exceeds a predetermined value, the diaphragm is bent towards the inside of the assembly causing the means to cause movement to move the flexible conductor member so that the trajectory is interrupted between the end cap plate and the electrode to prevent current from flowing through the cell.

15. The electrochemical cell, according to claim 14, characterized in that the means for causing movement of the flexible member in response to deflection of the diaphragm is an electrically non-conductive member in physical communication with the diaphragm so that when the diaphragm is bent inwardly , towards the interior of the assembly, the non-conducting member pushes against the flexible conductor member to interrupt the electrical path between the end cap plate and the electrode.

16. The electrochemical cell, according to claim 15, characterized in that the means for causing movement of the flexible conductor member in response to a change in the surface curvature in the shape-recovering member and the means for causing movement of the flexible conductive member in Response to the deflection of the pressure-driven diaphragm is the same electrically non-conductive member.

17. The electrochemical cell, according to claim 13, characterized in that the electrically non-conductive member is an elongated plastic member.

18. The electrochemical cell according to claim 10, characterized in that the assembly further comprises a metal support ring within the chamber and connected to the housing in which a portion of the flexible conductor member makes contact with the support ring to complete the electrical path within the assembly and wherein the contact between the flexible conductor member and the support ring is interrupted when the temperature or gas pressure within the cell exceeds a predetermined value.

19. The electrochemical cell, according to claim 10, characterized in that the flexible conductor member comprises a disk having an opening therein, the disk having an outer edge with a flexible portion projecting into the opening from a portion of the outer edge , wherein the outer edge rests on a surface of an insulating member within the end cap assembly and the flexible portion can move in response to the deflection of the shape recovery member to cause an interruption in the electrical path.

20. The electrochemical cell, according to claim 10, characterized in that the cell further comprises a second current switch assembly, the assembly comprises a housing, a chamber within the housing and a sealed end cap of the housing, the second assembly has a path electrically conductive therethrough between the housing and the second end cap of the assembly, wherein the second assembly comprises a means capable of thermally responding within the chamber to prevent current from flowing through the electrical path within the assembly, the thermally capable medium comprises an alloy member with activable recovery when the temperature within the assembly reaches a predetermined level causing an interruption in the electrically conductive path through the second assembly thereby causing the cell to stop functioning.

21. The electrochemical cell, according to claim 10, characterized in that the cell is a rechargeable cell.

22. A current switch assembly for an electrochemical cell, the assembly is a self-contained sealed unit comprising a housing, a chamber within the housing and an end cap sealed from the housing, the assembly has an electrically conductive path therethrough between the housing and the housing. housing and the end cap wherein the assembly comprises a means capable of thermally responding to prevent current from flowing through the electrical path within the assembly, the thermally responsive means comprising a disk or an alloy with shape recovery having a curved surface, wherein the disk is oriented within the assembly to allow current to pass through the thickness of the disk, wherein the disk is activatable and the curvature of its surface is altered when the temperature within the assembly reaches a predetermined level causing an interruption in the electrical path through the assembly.

23. The current switch assembly, according to claim 22, characterized in that the thickness is between 0.05 and 0.5 mm.

24. The current switch assembly, according to claim 22, characterized in that the assembly is insertable inside a rechargeable prismatic cell having a thickness between approximately 3 and 6 mm, wherein the assembly forms a portion of the electrical path between one of the cell terminals and the corresponding cell terminal.

25. A current switch assembly for an electrochemical cell, the assembly is a sealed and self-contained unit comprising a housing, a chamber within the housing and an end cap sealed from the housing, the assembly having an electrically conductive path through the housing. same between the housing and the end cap, wherein the assembly is insertable into a cell to form a portion of the electrical path between one of the electrodes of the cell and the corresponding cell terminal, wherein the assembly comprises a member flexible conductor which forms a portion of the electrical path and a medium capable of thermally responding to prevent current from flowing through the electrical path when the temperature within the assembly exceeds a predetermined level, the thermally capable medium comprises a disk able to respond thermally from an alloy with recovery so that it has an curved surface, wherein the assembly further comprises a physical means for causing movement of the flexible conductor member in response to a change in the surface curvature of the disk capable of thermally responding where, when the temperature of the cell reaches a predetermined temperature, the disc is bent activating a physical medium so it moves the flexible conductor member to interrupt the electrical path inside the assembly.

26. The current switch assembly, according to claim 25, characterized in that the physical means for causing movement in the flexible conductor member is an electrically non-conductive member that is located within the chamber and in physical communication with the disk capable of responding thermally so that when the disk is bent, the non-conductor member pushes against the flexible conductor member to interrupt the electrical path within the assembly.

27. The current switch assembly, according to claim 25, characterized in that the thickness of the disc capable of thermally responding is between 0.05 and 0.5 mm.

28. The current switch assembly, according to claim 26, characterized in that the current switch assembly further comprises a pressure operated diaphragm forming a portion of the mounting housing and having a surface exposed to the environment outside the assembly to cause movement of the flexible conductor member in response to deflection of the diaphragm, wherein, when the gas pressure on the opposite side of the diaphragm exceeds a predetermined value, the diaphragm is bent into the interior of the assembly causing the non-conductor member to push the flexible conductor member so it interrupts the electrical path inside the assembly.