MXPA98008383A - Current switch for electroquimi cells - Google Patents

Abstract

The present invention relates to a current-interrupting mechanism for electrochemical cells. A thermally activated current switch mechanism (38) is integrated in an end cap assembly (10) for an electrochemical cell. The thermally responsive mechanism preferably includes a free floating bimetallic disk (40) or a mass of meltable material (Fig. 4, 175) for breaking an electrical path within the end cap assembly. The end cap assembly may also include a mechanism (48) integrated in it that interrupts the current that responds to the pressure. The mechanism responsive to the pressure is activated to divide or cut an electrical path within the cap assembly (10) to prevent current from passing through the cell, and includes a diaphragm (70) which breaks when there is a excessive pressure build-up of g

Description

CURRENT SWITCH FOR cprmf? ^ .v ^ nttf¡ ^ £? S DESCRIPTION OF THE TJWENTION This invention relates to a thermally-responsive current interrupter for an electrochemical cell, which safely prevents the flow of current through the cell in the presence of an excessive increase in the temperature of the cell. The invention also relates to a current switch that responds to the pressure for a cell, which safely interrupts the cell in the presence of excessive accumulation of gas pressure therein. Electrochemical cells, especially cells with high energy density such as those in which the active material is lithium, are subjected to leaks or 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 from overcharging. An undesirable increase in temperature is often accompanied by a corresponding increase in the internal gas pressure. This is likely to occur in the case of an external short circuit condition. It is desirable that there are REF devices. 28561 that accompany the cell without unduly increasing the cost, size or mass of the cell. Such cells, particularly rechargeable cells using lithium as the active material are subject 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 abusive conditions, such as overloaded or by a short circuit condition. It is also important that these cells are hermetically sealed to avoid the leakage of electrolyte solvent and the entry of moisture from the outside environment. As stated in the above, if such a cell is charged, self-heating occurs. A charge at too fast or an overloaded speed can lead to an increase in temperature. When the temperature exceeds a certain point, which varies based on the chemistry and structure of the cell, an uncontrollable thermal runaway 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 initiate controlled ventilation before this takes place.

Conventional cell designs use an end cap fitting which is inserted into an open-ended cylindrical vessel after the anode and cathode of the cell of active material and the appropriate separating material and electrolyte have been inserted into the cell. cylindrical vessel. The end cap is an electrical contact with one of the anode and cathode material 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 prior art describes means that respond to overpressure conditions which have been integrated into the fitting of the end cap of the cell. The present invention has one or more current interruption mechanisms integrated within a single end cap assembly which can be advantageously applied to primary or secondary (rechargeable) cells for example by inserting the end cap assembly at the open end of a cover for the cell. The end cap assembly of the invention has particular application to rechargeable cells, for example lithium ion, metal and nickel hydride, nickel cadmium or other rechargeable cells, to solve the danger of cell overheating and pressure buildup in the cell during exposure to high temperatures, excessive or inadequate charging, or short circuit of the cell. In one aspect, the invention is directed to an end cap assembly for an electrochemical cell in which the end cap assembly has a thermally-responsive current-interrupting mechanism integrated therein which is activated to interrupt and prevent current from flowing through the cell when the interior of the cell is overheats to exceed a predetermined temperature. The end cap assembly has an exposed end cap plate which functions as a terminal of the cell. When the assembly is applied to a cell and the cell is in normal operation, the end cap plate is in electrical communication with a cell electrode (anode or cathode). The thermally activated current-interrupting mechanism, integrated within the end cap assembly may comprise a bimetallic member that bends when exposed to a temperature above a predetermined value. The deflection of the bimetallic member pushes against a movable metal member to sever the electrical connection between an electrode of the cell and the end cap terminal plate and thus prevents current from flowing through the cell. Alternatively, in another aspect of the invention, a thermally responsive pellet may be used in place of the bimetallic member. If the temperature of the cell exceeds a predetermined value, the tablet melts causing the metal member supported thereon to bend sufficiently to interrupt the electrical path between an electrode of the cell and the end cap terminal plate. A breakable plate or membrane can be integrated into the end cap assembly together with the thermally responsive current-interrupting mechanism. When the pressure inside the cell accumulates to exceed a predetermined value, the plate or membrane is broken allowing the gas inside the cell to escape to the external environment. In another aspect, the invention is directed to an end cap assembly for cells, particularly rechargeable cells, where the end cap has two current interruption mechanisms integrated in it, one responds thermally and the other responds to the pressure . The thermally responsive current-interrupting mechanism may preferably utilize a bimetallic member or a thermally responsive meltable pellet which is activated to interrupt and prevent the flow of current through the cell when the cell interior is overheated to exceed a default temperature. The current-interrupting mechanism that responds to pressure is activated to interrupt the flow of current between the gas pressure in the cell when it accumulates and exceeds a predetermined value. In such a case, the pressure interrupting mechanism may cause a metal diaphragm inside the end cap assembly to bend, thereby interrupting the electrical connection between the end cap plate of the cell and a cell electrode. , so it prevents the current from flowing through the cell. In the case of an excessive accumulation of gas pressure, the metal diaphragm also breaks allowing the gas to be channeled to the inner chambers within the end cap assembly and outward to the external environment through a series of holes of ventilation. Another aspect of the invention is directed to a sealing mechanism for the end cap assembly of the invention. The sealing mechanism prevents leakage of electrolyte, liquid or gas from the inside of the end cap to the external environment and prevents the entry of moisture into the cell. The features of the invention will be better appreciated with reference to the drawings in which: Figures 1, 2 and 3 are vertical cross-sectional views taken through the observation lines 1-1 of the end cap assembly of the figure 6Figure 1 shows the thermally activated current-interrupting mechanism and the pressure-interrupting current-interrupting mechanism in circuit-connected mode. Figure 2 shows the thermally activated current interruption mechanism in interrupted circuit mode. Figure 3 shows the mechanism of interruption of current activated by pressure in interrupted circuit mode, activated by pressure. Figure 4 is a vertical cross-sectional view of another embodiment of an end cap assembly having a pressure-activated current-interrupting mechanism and a thermally activated current-interrupting mechanism therein, in which the member Heat sensitive is softened to release a flexible member to open the circuit. Figure 5 is an exploded perspective view of the end cap assembly components of the invention shown in the embodiment of Figure 1. Figure 6 is a perspective view of the bottom of the end cap assembly showing the plate resistant to pressure and ventilation openings through them.

Figure 7 is a perspective view showing the end cap assembly of the invention that is inserted into the open end of a cylindrical cover of a cell. Fig. 8 is a perspective view showing a cell completed with the end cap assembly of the invention inserted in the open end of a cylindrical cover of a cell with the end cap plate of the assembly forming a terminal of the cell . The assembly 10 of the end cap (Figure 1) of the invention can be applied to the primary or secondary (rechargeable) cells. In a preferred embodiment, the end cap assembly 10 can be inserted into the open end 95 of a cover typically cylindrical for the cell (Figure 7). The cells contain a positive electrode (cathode in discharge), a negative electrode (discharge anode), a separator and an electrolyte, and positive and negative external terminals in electrical communication with the positive and negative electrodes, respectively. Now with reference to Figure 1 of the drawings, the end cap assembly 10 designed for insertion into the open end of a cell cover comprises a sub-assembly 38 of thermally activatable current-interrupter and a sub-assembly 48 of pressure relief integrated in the same. Sub-assemblies 38 and 48 are separated by a common support plate 60. The sub-assemblies 38 and 48 are retained within a cover 30 which defines the outer wall of the end cap assembly 10. The switch sub-assembly 38 is defined at its upper end by a cup-shaped end cap plate 20 and its lower end by a contact plate 15 which is welded to the support plate 60. The cup-shaped end cap plate 20 forms one of the external terminals of the cell. The support plate 60 separates the chamber 68 within the sub-assembly 38 of the chamber 78 within the pressure release subassembly 48. The contact plate 15 is electrically connected to the support plate 60 which in turn is electrically connected to an electrode 88 (anode or cathode) of the cell when the end cap assembly 10 is applied to a cell. A thermally responsive circuit breaker mechanism (40, 50) is provided to complete the circuit between the contact plate 15 and the end cap 20. If the temperature within the cell exceeds a predetermined threshold value, the switch mechanism activates an interrupting electrical contact between the end cap 20 and the contact plate 15 thereby preventing current from flowing through the cell. The pressure release sub-assembly 48 comprises a thin metallic diaphragm 70 connected to a pressure-resistant plate 80 which in turn is electrically connected to a cell electrode 88 through a conductive tongue 87 which is soldered to the plate 80. (The pressure resistant plate is electrically conductive and is of sufficient thickness so as not to deform substantially at elevated pressures of at least about 4.14 x 106 pascal (600 psi)). If the gas pressure inside the cell accumulates to exceed a predetermined threshold value, the diaphragm 70 opens outward to interrupt the electrical contact with the pressure resistant plate 80 so that current is prevented from flowing to or from the cell. The pressure resistant plate 80 and the support plate 60 preferably have perforations 73 and 63, respectively therein which help to vent the gas and relieve pressure build-up within the cell. In the preferred embodiment shown in Figure 1, the end cap assembly 10 can be used in a rechargeable cell, for example, a rechargeable lithium ion cell. (A lithium ion rechargeable cell is characterized by the transfer of lithium ions from the negative electrode to the positive electrode before the discharge of the cell and from the positive electrode to the negative electrode when the cell is charged. cobalt and lithium (LixCo02) or lithium manganese oxide 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 may be constituted by a lithium salt dissolved in a mixture of non-aqueous solvents The salt may be LiPF6 and the solvents may advantageously include dimethyl (DMC), ethylene carbonate (EC), propylene carbonate (PC) and mixtures thereof The present invention is applicable t also to other rechargeable cells, for example, metal and nickel hydride cells and nickel cadmium cells. Each cap assembly 10 comprises an end cap terminal 20 which is typically the positive terminal of the rechargeable cell, a metal support plate 60 which forms the support base under the cover plate 20, and a disc 35 insulation between the end cap 20 and the support plate 60. The lid assembly 10 is advantageously also provided with a pressure release diaphragm 70 below the support plate 60, as shown in Figure 1. The diaphragm 70 can be welded to an underlying pressure resistant plate 80. This can be conveniently accomplished by welding the base 72 of the diaphragm 70 to an embossed portion 82 of the underlying pressure resistant plate 80. The diaphragm 70 may be of a material that is electrically conductive and of minimum thickness between about 0.1 and 0.5 millimeters, based on the pressure at which the diaphragm is intended to act. The diaphragm 70 can desirably be aluminum. The diaphragm 70 is advantageously wedged so that it breaks at a predetermined pressure. That is, the surface of the diaphragm may be stamped or scored so that one portion of the surface is of a thickness smaller than the rest. A preferred diaphragm 70 for use in the present invention is coined to impose a groove 70a in a semicircular or "C" shape on its surface. Advantageously, the shape of the groove is equal to or similar to the shape of a main portion of the peripheral edge of the diaphragm 70 and is advantageously positioned in proximity to the peripheral edge. The particular pressure at which the ventilation takes place is controllable by varying parameters such as the depth, placement or shape of the groove as well as the hardness of the material. When the pressure becomes excessive, the diaphragm will break along the grooved line. The end cap 20 and the support plate 60 define a chamber 68 therebetween which are suitable for thermally activating the sub-assembly 38 current switch. The insulating disk 35 is formed from a peripheral base portion 35a and a downwardly inclined arm 35b extending therefrom. The arm 35b extends into the chamber 68. The diaphragm 70 is designed to break when the accumulation of gas within the cell reaches a predetermined threshold level. The region between the support plate 60 and the diaphragm 70 form a chamber 78 within which the gas accumulation within the cell can be ventilated by rupture of the diaphragm 70. The sub-assembly 38 current switch comprises a bimetallic disk 40 which it responds thermally, a metal contact plate 15 in electrical contact with a member 50 similar to resilient spring. As shown in Figures 1 and 5, the resilient member 50 can be formed of a single flexible member having an outer circular peripheral portion 50a from which a disc retention tab portion 50c extends radially inwardly to maintain generally the bimetallic disc 40 freely in place during any orientation of the cell and at the same time without restricting its click action movement. This member can be welded at a point of the portion 50a exterior to the plate 20 of the end cap with a central contact portion 50b in contact with the plate 15. Additionally, the contact portion 50b can be designed with an area at reduced cross section so that it can act as a disintegrable fusion bond to protect against energy discharge conditions. The bimetallic disc 40 is positioned to freely engage the inclined arms 35b of the insulating disc 35, arms which act as the disc housing for the disc 40. The bimetal disc 40 preferably includes a central opening for receiving an enhanced contact portion of the disc. 15 metal contact plate. The contact plate 15 is preferably welded to the support plate 60 and provides a surface for the resilient support member 50, as shown in Figure 1. There is an electrically insulating inner ring 25 which extends over the peripheral edge of the support member 50. the end cap 20 and along the lower peripheral edge of the diaphragm 70. The inner ring 25 also makes contact with the outer edge of the subassembly 38, as shown in Figure 1. There may be a metal ring 55 which is folded on the upper edge of the inner ring 25 and pressed against the diaphragm 70 to seal the inner components of the end cap assembly. The inner ring 25 serves to electrically insulate the end cap 20 of the folded ring 55 and also to form a seal between the support plate 60 and the fold 55. The cover 30 of the end cap assembly 10 can be formed from a truncated cylindrical member that is best shown in Figure 5. In a completed cell assembly (Figure 8) the outer surface of the cover 30 will come into contact with the interior surface of the cell cover 90. The support plate 60 provides a base for the components of the sub-assembly 38 to be supported and preferably is curved to maintain the active radial compression force against the inner surface of the inner ring 25. The support plate 60 can be provided with perforations 63 on its surface for venting gas to the upper chamber 68 when the diaphragm 70 is broken. The gas which passes to the upper chamber 68 will vent to the external environment through the primary vent holes 67 in the end cap 20. The cover 30 of the end cap assembly is in contact with the cover 90 of the cell which is in electrical contact with the opposite terminal, typically at the negative terminal on the cover of a rechargeable lithium ion cell. Therefore, the inner ring 25 provides electrical insulation between the end cap 20 and the outer wall 30, that is, between the two terminals of the cell so it avoids shorting the cell. There may be an additional insulating ring, specifically an insulating spacer ring 42 between the upper portion of the outer wall 30 and the pressure plate 80, as illustrated in FIG. 1, in addition, to ensure that there are no short between the positive terminals and negative of the cell. Preferably, the diaphragm 70 is in the form of a cup constituted of aluminum having a thickness advantageously of between about 76 and 254 μm (3-10 mils). At such thicknesses, the solder between the base 72 of diaphragm and the support plate 80 breaks and the base 72 of the diaphragm comes off and separates from the support plate 80 (figure 3) when the internal gas pressure inside the cell is increased to a threshold value of at least between approximately 6,894 x 105 and 13.89 x 105 pascal (100-200 psi). (Such pressure buildup occurs for example if the cell was charged at a higher voltage than the recommended or if the cell was shorted or used in the wrong way). Nevertheless, if desired, can be conveniently adjusted to the thickness of the diaphragm base 72 to be congested at other pressure levels. The separation of the diaphragm base 72 from the plate 80 interrupts all electrical contact between the diaphragm 70 and the plate 80. This separation also interrupts the electrical path between the end cap 20 and the cell electrode 88 in contact with the plate 80. so that the current can no longer flow to or from the cell, and carrying out an interruption in the cell. Even after the current path is broken, if the pressure within the cell continues to increase for other reasons, for example, heating in a furnace, the vent diaphragm 70 will also preferably break at a threshold pressure of at least about 17.2. x 105 and 27.6 x 105 pascals (250-400 psi) to avoid explosion of the cell. In such extreme circumstances, the rupture of the ventilation diaphragm 70 allows the gas inside the cell to be ventilated through the ventilation holes 73 (FIGS. 1 and 6) in the pressure resistant plate 80 so that the gas enters the lower chamber 78 (figure 1), then the gas will pass from the lower chamber 78 to the upper chamber 68 through the ventilation holes 63 in the support plate 60 (figure 1) and if desired to the holes of necessary ventilation (not shown) in the insulating disc 35. The gas collected in the upper chamber 68 will be vented to the external environment through the primary vent holes 67 in the end cap plate 20. The current-interrupting feature of the invention can be described with reference to Figures 1-3. It should be noted that in the specific embodiment shown therein, one of the cell electrodes is brought into contact with the plate 80 through the tongue 87 when the end cap assembly 10 is applied to a cell. During the normal operation of the cell, the plate 80 in turn is electrically connected to the end cap plate 20. In a lithium ion cell, the electrode 88 is in contact with the plate 80, it can conveniently be the positive electrode. This electrode will be isolated from the cell cover 90. The negative electrode (not shown) will be connected to the cover 90 of the cell. The embodiment of Figure 1 shows the configuration of the end cap assembly before the current is interrupted either by activation of the bimetallic disk 40 thermal current switch or activation of the pressure release diaphragm 70. In the specific embodiment illustrated in Figure 1, the plate 80 is in electrical contact with the diaphragm 70 and the diaphragm 70 is in electrical contact with the support plate 60. The support plate 60 is in electrical contact with the contact plate 15 which is in electrical contact with the resilient member 50 which in turn is in electrical contact with the end cap 20. In the integrated end cap design of the invention shown in Figure 1, the electrical contact between the electrode 88, in contact with the pressure plate 80, and the end cap 20 can be interrupted in two ways. As described above, if pressure builds up in the cell at a predetermined threshold, the contact between the diaphragm 70 and the pressure plate 80 is interrupted as the base 72 of the diaphragm becomes bent away from the pressure plate 80. This interruption in the circuit prevents current from flowing to or from the cell. Alternatively, if the cell overheats, the bimetallic disk 40 of the thermal break sub-assembly 38 is activated and thus pushes up from the bushing 35b whereby it causes the resilient member 50 to lose contact with the contact plate 15. This in turn interrupts the electrical path between the electrode tab 87 and the end cap 20, thereby preventing current from flowing to or from the cell. It is an advantage of the invention to incorporate these two interruption mechanisms within a single end stage assembly 10., which is insertable into the open end of a cell container as a single unit. The bimetal disk 40 is preferably not physically attached to the underlying insulating disk 35, but rather is free to move and that is, it rests in free floating condition on the disk arm 35b, as shown in Fig. 1. In such a case. design the current does not pass through the bimetallic disk 40 at any time regardless of whether the cell is charging or discharging. This is because the disk 40, when inactivated, does not make electrical contact with the contact plate 15. However, if the cell is overheated beyond a predetermined threshold temperature, the bimetallic disk 40 is designed in the proper calibration so that it fractures or deforms (Figure 2) causing it to urge the resilient member 50 away from the plate 15 of contact, thereby preventing current from flowing between the cell terminals. The bimetallic disk 40 is calibrated so that it has a predetermined concave shape which allows the disk to act when a given threshold temperature is reached. The free floating design of the bimetallic disc 40 on the insulating disc arm 35b as described above does not allow current to pass through it at any time regardless of whether the cell is being charged or discharged. This makes the calibration of the disk 40 easier and more accurate, since there is no heating effect caused by current flow through the bimetal disk 40 (I2R heating). The bimetallic disk 40 can conveniently comprise two different metal layers having different coefficient of thermal expansion. The top layer of the bimetallic disk 40 (the layer closest to the end layer 20) can be composed of a high thermal expansion metal preferably a nickel-chromium-iron alloy, and the underlying layer or bottom layer can be composed of a metal of low thermal expansion, preferably a nickel-iron alloy. In such an embodiment the disk 40 can be activated when the temperature increases by at least between about 60 and 75 ° C, causing the disk 40 to deform sufficiently to push the resilient member 50 away from contact with the contact plate 15. It is also possible to choose high and low thermal expansion metal layers so that the disc 40 does not reset except at a temperature below -20 ° C which, in most applications, returns a thermostatic device to the device. unique action The preferred materials for the components described above are described as follows: the end cap 20 is preferably made of stainless steel or nickel-coated steel of between about 0.2 and 0.375 mm (8 to 15 mils) thick to provide adequate support, strength and corrosion resistance. The outer wall 30 of the end cap assembly 10 is preferably also made of stainless steel or nickel-coated steel having a thickness between about 0.2 and 0.375 mm (8 and 15 mils). The pressure plate 80 preferably is aluminum having a thickness between about 0.25 and 0.5 mm (10 and 20 mils) which can be reduced in the center to between about 0.05 and 0.125 mm (2-5 mils) and the contact point welded with the base 72 of the diaphragm. The insulating separation ring 42 may be composed of a high temperature thermoplastic material such as a high temperature polyester for strength and durability available under the trade designation VALOX from General Electric Plastics Company. The crimped ring 55 is preferably made of stainless steel or nickel-coated steel having a thickness between about 0.2 and 0.375 mm (8-15 mils) for strength and corrosion resistance. The diaphragm 70 is preferably made of aluminum having a thickness of between about 0.075 and 0.25 mm (3-10 mils). At such thicknesses, the diaphragm will break away from its weld to the pressure plate 80 when the internal gas pressure exceeds the threshold pressure of between about 6.89 x 105 and 17.2 x 105 pascal (100-250 psi). If the internal gas pressure exceeds a pressure between approximately 17.2 x 10 s and 27.6 x 105 pascal (250 and 400 psi), the diaphragm 70 will break to provide additional release of gas pressure buildup. The insulating disc 35 on which the bimetallic disk 40 rests is preferably made of a material of high compressive strength to increase thermal stability and low mold shrinkage. A suitable material for the disc 35 is a liquid crystal polymer or the like of thickness between about 0.25 and 0.75 mm (10-30 mils) available under the trade designation VECTRA from Celanese Co. The support plate 60 is preferably made of steel stainless steel or nickel-coated steel to provide adequate strength and corrosion resistance at a thickness between about 0.25 and 0.75 mm (10-30 mils). The flexible member 50 is advantageously formed of beryllium-copper, nickel-copper alloy, stainless steel or the like which has a good spring action and excellent electrical conductivity. A suitable thickness for the resilient member 50 when formed from a beryl-copper or nickel-copper alloy is between about 0.075 and 0.2 mm (3-8 mils) to provide sufficient strength and current carrying capacity. This material may be coated or coated with silver or gold in the contact region to provide less electrical resistance in this area. The contact plate 15 is advantageously formed of cold rolled steel coated with a precious metal such as gold or silver to decrease contact resistance and improve reliability. It can also be formed from a nickel-copper, stainless steel or nickel-coated steel alloy. The inner ring 25 is typically made of polymeric material such as nylon or polypropylene. The seal around the components of the end cap assembly must be watertight in order to prevent the electrolyte, either in the form of liquid or vapor, from entering the end cap chambers or leaving the cell. After the end layer assembly 10 is completed, it can be inserted into the open end 95 of a cylindrical cell cover 90 shown in Fig. 7. The circumferential edge of the cell cover 90 at the open end thereof. it is welded to the outer wall of the cover 30 of the end layer assembly 10 to provide a tight and watertight seal between the end cap assembly 10 and the cell cover 90. The radial pressure of the circumferential wall of the ring 55 folded against the inner ring 25 and the diaphragm 70 produces a hermetic seal around the inner components of the end layer assembly 10. An alternative embodiment of the end cap design that has a pressure relief mechanism and a thermally activated current-interrupting mechanism, integrated therein, is shown in the end cap assembly 110 in Figure 4. The embodiment of Figure 4 is similar to that described above with respect to Figures 1-3 except that the bimetallic disc is not used for activate the spring-like mechanism. Instead, a thermal pellet 175 is provided to retain a resilient spring-like member 150 in electrical contact with the contact plate 115. The contact plate 115 in turn is in electrical contact with the end cap plate 20. The resilient member 150 may be constituted by an elongated metallic arm 150a which is welded at one end to support the plate 60. The support plate 60 is in electrical contact with the diaphragm 70 which in turn is welded to the portion 82 pre-lifted plate 80 resistant to the underlying pressure. An electrode tab 87 is in electrical contact with the plate 80. The resilient member 150 preferably ends at its opposite end in a cup-shaped or convex portion 150b which contacts the contact plate 115. There is an electrical insulating disk 120 on the peripheral edge 60a of a support plate 60 to prevent direct contact between the support plate 60 and the contact plate 115. Therefore, there will be electrical contact between the support plate 60 and the end cap 20 to the extent that the resilient member 150 is retained against the contact plate 115. The support plate 60 in turn is in electrical contact with the aluminum diaphragm 70 which is in contact with the plate 80 and a cell electrode 88 through the tongue 87 when the end cap assembly 110 is applied to the plate. one cell (The end cap assembly 110 can be applied to a cell by inserting it into the open end of a cylindrical cover 90 in the same manner as described above with reference to the embodiment shown in Figure 1). Therefore, a resilient member 150 pressed against the contact plate 115 is retained by the thermal chip 175, there is an electrical contact between a cell electrode 88 (through the tongue 87) and the end cap plate 20 allows normal operation of the cell. If the cell overheats beyond a predetermined threshold temperature, the pellet 175 melts so that it removes the support for the resilient member 150. The melt of the chip 175 causes the resilient member 150 to break down with a click and interrupt the electrical contact with the contact plate 115. This in effect interrupts the electrical path between the electrode tab 87 and the end cap 20 thereby preventing the current from flowing to or from the cell. If the internal gas pressure within the cell exceeds a predetermined value, the diaphragm 70 will break so it will interrupt the electrical contact between the plate 80 and the diaphragm 70 and also allow the gas to escape to the external environment through the holes 63 and 67 of ventilation in the support plate 60 and the end cap 20, respectively. The preferred materials for the end stage 20, the support plate 60, the contact plate 115 and the aluminum diaphragm 70 mentioned in the embodiment shown in figure 4 can be the same as those described for the corresponding elements having the same reference numbers shown in figures 1-3. The contact plate 115 is preferably formed of stainless steel or cold rolled steel coated with nickel, which in turn is coated with silver or gold to decrease its contact resistance. The insulating disk 120 shown in Figure 4 is preferably made of a high temperature thermoplastic material having excellent dielectric properties. A preferred material for disk 120 may be a polyimide available under the trade designation KAPTON of E.I. DuPont Co. or a high temperature polyester available under the trade designation VALOX from General Electric Plastics Co. The resilient member 150 can advantageously be formed from a beryl-copper alloy of thickness between about 0.125 and 0.25 mm (5-10 mils of inch) to provide good conductivity when in contact with the plate 115 and a reliable spring action when the pressure of the pad 105 against it is removed. Additionally, the flexible arm 150 can be coated with silver or gold to increase its conductivity. The thermal chip 175 is advantageously formed of a polymer having a relatively low melting point, for example, between about 65 ° C and 100 ° C, but still excellent compression strength to keep the flexible arm 150 in place during the operation normal of the cell. A suitable material for thermal pellet 175 having such properties is a polyethylene wax available under the trade designation POLI AX from Petrolyte Co. A thermal pellet 175 of such polyethylene wax melts within a desirable temperature range between about 75 ° C. and 80 ° C. An exploded view of the end cap assembly 10 of Figure 1 is shown in Figure 5. The end cap assembly 10 can be manufactured by assembling the components shown in Figure 5 in the following order: A pre-assembly is formed which comprises the components 20, 50, 40, 35, 15, 60, 70, 25 and 55. This is conveniently carried out by first inserting the inner plastic ring 25 into the folded ring 55, then inserting the vent diaphragm 70 into the inner ring 25 and then insert the support plate 60 with the contact plate 15 welded thereto into the vent diaphragm 70. After this, the insulating disk 35 is placed around the contact plate 15 and the bimetal disk 40 is placed to rest on an arm 35b inclined downwardly of the insulating disk 35. The bimetal disk 40 does not join the insulating disk 35 but rests on it in a free floating condition, with the insulating disk which helps to act as a positioning means for the bimetallic disk. The upper surface of the upper end of the resilient spring-like member 50 is welded to the circumferential edge of the end cap 20. The end cap 20 with the resilient member 50 welded thereto is then placed on the insulating disc 35 so that the raised central portion of the contact plate 15 contacts the inner end of the resilient member 50 and the lower surface of the resilient member 50. The outer end of the resilient member 50 contacts the circumferential edge of the insulating disk 35. Therefore, the outer end of the resilient member 50 is wedged between the end cap 20 and the insulating disk 35 and the opposite or inner end of the member 50 is in contact with the contact plate 15. Thereafter, the ring 55 is mechanically folded over the upper edge of the inner ring 25 to retain the upper end of the inner ring 25 pressed firmly against the circumferential edge of the end cap 20. This folding is carried out by applying mechanical force along the centroidal (vertical) axis of the ring 55. Then, in a second folding step, mechanical pressure is applied radially to the walls of the folded ring 55, so that it is completed the assembly of the pre-assembly. Radial folding serves to keep the internal components of the preassembly firmly and hermetically sealed within the ring 55. The pre-assembly is then inserted into the metal cover 30 so that the lower surface of the folded ring 55 bears against the lower inner edge of the cover 30. After which, the lower surface of the folded ring 55 is welded to the lower inner surface of the cover 30. The pressure plate 80 is then closed with a blow on the lower part of the insulating separation ring 42 and the ring 42 with the pressure plate 80 attached thereto and then placed against the outer bottom surface of the cover 30 so that the raised center portion of the pressure plate 80 contacts the vent diaphragm 70. This point of contact between the pressure plate 80 and the diaphragm 70 is then welded at points whereby the construction of the end cap assembly 10 is completed. The end cap assembly 10 can be applied to a cell, for example, by inserting it into the open end of the cylindrical cover 90 of a cell, as shown in FIG. 7 and welding the outer surface of the cover 30 to the inner surface of the cylindrical cover 90 at the open end 95 of FIG. the same. This results in cell 100 shown in Figure 8 with an end cap assembly 10 that is firmly sealed within the cylindrical cover 90 and the end cap plate 20 forming a terminal of the cell. Although this invention has been described in terms of certain preferred embodiments, the invention is not limited to the specific embodiments but rather is defined by the claims and equivalents thereof. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (28)

1. An end cap assembly for application to an electrochemical cell having positive and negative terminals, and a pair of internal electrodes (anode and cathode), the end cap assembly comprises a housing and an exposed end cap plate, the plate is functional as a cell terminal, the end cap assembly has an electrically conductive path therethrough which allows the end cap plate to be electrically connected to a cell electrode when the end cap assembly is applied to a cell, the end cap assembly further comprises: a) a thermally responsive means to prevent current from flowing through the electrical path, wherein the thermally responsive medium is activatable when the temperature within the End cap reaches a predetermined level causing a break in the electrical path.

2. The end cap assembly according to claim 1, characterized in that it further comprises: b) a pressure-responsive means comprising a rupturable member located at the end of the end cap assembly opposite the plate end cap, the ruptureable member is broken when the gas pressure on the side thereof beyond the end cap plate reaches a predetermined level producing a break in the member that allows the gas to pass through. the same.

3. The end cap assembly according to claim 1, characterized in that the cell has a cylindrical cover and the end cap assembly is applied to the cell by inserting it into the open end of the cylindrical cover and welding the cap assembly end to the deck.

4. The end cap assembly according to claim 1, characterized in that the thermally responsive means comprises a chamber within the end cap assembly and further comprises a bimetallic member and an electrically conductive resilient member, the resilient member forms a portion of the electrical path, wherein the temperature of the cell within the assembly reaches a predetermined level and the bimetallic member is deformed so that it pushes against the resilient metal member causing a break in the electrical path.

5. The end cap assembly according to claim 4, characterized in that the bimetallic member rests freely on a surface of an electrically insulating member within the end cap assembly.

6. The end cap assembly according to claim 5, characterized in that a portion of the resilient metal member is interposed between a portion of the end cap plate and a portion of the electrically insulating member and wherein the end cap assembly comprises a contact plate which forms part of the electrical path, wherein the resilient member is in electrical contact with the contact plate.

7. The end cap assembly according to claim 2, characterized in that it comprises a separation member positioned across the inner width of the end cap assembly and between the end cap plate and the breakable member, the separation member separates the thermally responsive medium from the responding medium by pressure.

8. The end cap assembly according to claim 7, characterized in that the separation member comprises a metal plate having at least one opening therein so that when the ruptureable member is broken, the gas passes to through the opening into the chamber inside the end cap assembly.

9. The end cap assembly according to claim 8, characterized in that the end cap plate has at least one opening therethrough so that when the breakable member is broken, the gas collected from the camera passes through the end cap opening and to the external environment.

10. The end cap assembly according to claim 7, characterized in that the breakable member comprises a rupturable diaphragm.

11. The end cap assembly according to claim 6, characterized in that when the bimetallic member reaches a predetermined temperature, it is deformed causing the resilient conductive member to interrupt its critical connection with the contact plate, thereby causing a break in the electric path

12. The end cap assembly according to claim 10, characterized in that it further comprises an electrically insulating inner ring in contact with the peripheral edge of the end cap plate and the peripheral edge of the diaphragm, the end cap assembly further comprises a metal member (folded member) that is mechanically folded around the inner ring to retain the diaphragm plate and the end cap plate under mechanical compression.

13. The end cap assembly according to claim 12, characterized in that it further comprises a metal cover around the folding member.

14. The end cap assembly according to claim 13, characterized in that the end cap assembly is applied to a cell when inserting into the open end of a cylindrical cover for the cell and welding the outer surface of the cover to the surface Inside the cover, whereby the end cap assembly is hermetically sealed inside the cylindrical cover with the end cap plate comprising a terminal of the cell that is exposed to the external environment.

15. The end cap assembly according to claim 1, characterized in that the thermally responsive means comprises a resilient conductive member in electrical contact with the end cap plate, and a meltable mass of material that retains the resilient conductive member in connection with the end cap plate. electrical between the end cap plate and another conductive portion of the end cap assembly, the other conductor portion is adapted to be electrically connected to the cell electrode when the end cap assembly is applied to a cell thereby providing a electrical connection between the end cap plate and the electrode during the operation of the cell, when the temperature of the cell reaches a predetermined level, the mass of material is melted thereby causing movement in the resilient metal member to cut the connection electrical between the end cap plate and the cell electrode so the operation is avoided e the cell.

16. An electrochemical cell of the type formed by an end cap assembly inserted into a cylindrical cover with an open end for the cell, the cell also has a positive and negative terminal and pair of internal electrodes (anode and cathode) where the assembly of end cap has a housing and a cover plate of opposite end, the end cap plate is functional as a cell terminal, the improved cell is characterized in that it comprises an end cap plate which is electrically connected to one of the electrodes through an electrically conductive path within the end cap assembly, wherein the end cap assembly comprises: a) a thermally responsive means to prevent current from flowing through the cell, wherein the medium which responds thermally is activatable when the temperature inside the cell reaches a predetermined level that causes a break in the electrical path ca between the end plate and the electrode so that current is prevented from flowing through the cell, and b) means that respond to the pressure that allow the gas from inside the cell to pass into the interior of the cap assembly of end when the internal gas pressure inside the cell reaches a predetermined level.

17. The electrochemical cell according to claim 16, characterized in that the thermally responsive means for preventing current from flowing through the cell comprises a chamber within the end layer assembly and further comprises a bimetallic member and an electrically conductive resilient member, the resilient member is in electrical contact with the end cap plate and a cell electrode, whereby an electrical path is provided therebetween, wherein, when the temperature of the cell reaches a predetermined level, the bimetallic member is deforms and pushes against the resilient member causing the resilient member to interrupt the electrical path between the end cap plate and the cell electrode thereby preventing operation of the cell.

18. The electrochemical cell according to claim 17, characterized in that the bimetallic member rests freely on the surface of an electrically insulating member within the end cap assembly.

19. The electrochemical cell according to claim 18, characterized in that a portion of the resilient member is interposed between a portion of the end cap plate and a portion of the electrically insulating member.

20. The electrochemical cell according to claim 16, characterized in that the pressure-responsive means comprises a rupturable diaphragm located at the end of the end cap assembly opposite the end cap plate, the diaphragm plate being It breaks when the gas pressure on the side of the same beyond the end cap plate reaches a predetermined level which produces a break in the diaphragm that allows the gas to pass through it.

21. The electrochemical cell according to claim 20, characterized in that it further comprises a separation member positioned across the inner width of the end cap assembly between the end cap plate and the breakable member, the separation member it separates the thermally responding medium from the medium that responds by pressure.

22. The electrochemical cell according to claim 20, characterized in that the end cap plate has at least one opening therethrough so that the gas which passes into the upper chamber can pass through the opening from end cap to external environment.

23. The electrochemical cell according to claim 20, characterized in that the end cap assembly comprises a contact plate thereon which forms part of the electrical path, wherein the resilient member is in electrical contact with the contact plate.

24. The electrochemical cell according to claim 20, characterized in that, when the temperature of the cell reaches a predetermined temperature, the bimetallic member is deformed causing the resilient metal member to interrupt its electrical connection with the contact plate.

25. The electrochemical cell according to claim 20, characterized in that it further comprises an electrically insulating inner ring in contact with the peripheral edge of the end cap plate and the peripheral edge of the diaphragm plate, the end cap assembly further comprises a metallic member (folded member) which is mechanically folded around the inner ring to retain the diaphragm plate and the end cap plate under mechanical compression.

26. The electrochemical cell according to claim 25, characterized in that it further comprises a metal cover around the folded member.

27. The electrochemical cell according to claim 26, characterized in that the end cap assembly is applied to a cell by inserting it into the open end of a cylindrical cover for the cell and welding the outer surface of the cover to the inner surface of the cell. cover, whereby the end cap assembly is hermetically sealed within the cylindrical cover and the end cap plate comprises a terminal of the cell and is exposed to the external environment.

28. The electrochemical cell according to claim 16, characterized in that the thermally responsive means comprises an electrically conductive resilient member, in electrical contact with the end cap plate and a meltable mass of material which retains the resilient member in position to provide a electrical connection between the end cap plate and a cell electrode, where, when the temperature of the cell reaches a predetermined level, the mass of material melts causing movement in the resilient member to interrupt the electrical connection between the end cap plate and the cell electrode so the operation of the cell is avoided.