MXPA99009232A - Current interrupter for electrochemical cells - Google Patents

Abstract

A current interrupt mechanism for electrochemical cells is disclosed. A thermally activated current interrupt mechanism (38) is integrated into an end cap assembly (10) for an electromechanical cell. The thermally responsive mechanism (38) preferably includes a free floating bimetallic disk (40) or shape memory alloy member which deforms when exposed to elevated temperature causing a break in an electrical pathway within the end cap assembly. This prevents current from flowing through the cell and effectively shuts down an operating cell. The end cap assembly may include a pressure responsive mechanism (48) which ruptures when there is extreme gas pressure build-up. Gas is allowed to escape from the cell interior to the external environment through a series of vent apertures (63, 67) within the end cap assembly.

Description

CURRENT SWITCH FOR ELECTROCHEMICAL CELLS DESCRIPTION OF THE INVENTION This invention relates to a thermally sensitive current switch, for a battery or electrochemical cell, which safely prevents the flow of current through the cell after an excessive increase in the temperature of the same. The invention also relates to a pressure sensitive current switch, for a cell, which safely shuts off the cell after excessive gas pressure is formed therein. Electrochemical cells, especially high energy density cells such as those in which lithium is an active material, are subject to leakage or rupture which, in turn, can cause damage to the device that is energized by the cell or to the surrounding environment. In the case of rechargeable cells, the rise in the internal temperature of the cell can result from overload. Undesirable increases in temperature are often accompanied by a corresponding increase in the internal pressure of the REF .: 31496 gas. This is likely to occur in the case of an external short-circuit condition. It is desirable that security devices accompany the cell without unduly increasing the cost, size or mass of the cell. Such cells, particularly rechargeable cells that use lithium as an active material, are subject to leakage or rupture caused by an elevation in the internal temperature of the cell, which is often accompanied by a corresponding 1-increase in pressure. This is likely to be caused by abusive conditions, such as overloading or a short circuit condition. It is also important that these cells are hermetically sealed to allow the discharge of the electrolytic solvent and the entry of moisture from the outside environment. As stated above, if such a cell is overloaded, self-heating occurs. Charging at too fast a speed or rapid overload can lead to an increase in temperature. When the temperature exceeds a certain point, which varies depending on the chemistry and the structure of the cell, an undesirable and uncontrollable thermal unbalance condition begins.

In addition, due to overheating, an internal pressure is constituted, and the electrolyte can be suddenly expelled from the cell. It is preferable to start controlled ventilation before this takes place. Conventional cell designs employ an end cap accessory which is inserted into an open-ended cylindrical housing after the anode and cathode active material of the cell and the appropriate spacer material and electrolyte have been inserted into the housing cylindrical. The end cap is in electrical contact with one of the anode or cathode material and the exposed portion of the end cap forms one of the terminals of the cell. A portion of the cell housing forms the other terminal. The present invention has one or more current interruption mechanisms integrated within a simple end cap assembly which can be advantageously applied to the primary or secondary (rechargeable) cells, for example, by inserting the end cap assembly into the open end of a housing for the cell. The end cap assembly of the invention has particular application to rechargeable cells, for example, to cells of lithium ions, nickel metal hydride, cadmium-nickel cells or other rechargeable cells, to overcome the danger of overheating of the cell , and constitution of the cell during exposure to high temperatures, excessive or inadequate load, or short circuit of the cell. In one aspect, the invention is directed to an end cap assembly for an electrochemical cell wherein the end cap assembly has a thermally sensitive current interruption mechanism integrated therein., which is activated to interrupt and prevent current from flowing through the cell when the inside of the cell 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 flexes when exposed to the temperature above a predetermined value. The deflection of the bimetallic member pushes against a movable metal member to divide the electrical connection between an electrode of the cell and the end plate of the end cap, thereby preventing the current from flowing through the cell. Alternatively, in yet another aspect of the invention, a thermally sensitive pellet may be used, instead of the bimetallic member. If the temperature of the cell exceeds a predetermined value, the thermal pellet melts causing a metal member supported on it to deviate or flex sufficiently to divide the electrical path between an electrode of the cell and the end plate of the end cap. In still another aspect of the invention, the thermally sensitive current interrupting mechanism may include a shape memory alloy member, integrated within the end cap assembly. During normal operation of the cell, the shape memory member provides a portion of the path or electrical path between the end cap plate and one of the electrodes of the cell, to allow current to pass through the cell. When the temperature of the cell reaches a predetermined value, the shape memory member is flexed whereby the electrical path is broken and immediately the flow of current through the cell is interrupted. A rupturable plate or membrane can be integrated into the end cap assembly, together with the thermally sensitive current interrupting mechanism. When a pressure within the cell exceeding a predetermined value is constituted, the plate or membrane ruptures, allowing the gas inside the cell to escape into the external environment. In still another aspect, the invention is directed to an end cap assembly for cells, particularly rechargeable cells, wherein the end cap has two current interruption mechanisms integrated in it, one that is thermally sensitive and the other that is sensitive to the pressure. The thermally sensitive current-interrupting mechanism may preferably employ a bimetallic member, a shape memory member or a thermally sensitive meltable pellet, which is activated to interrupt and prevent the flow of current through the cell, when the interior of the cell the cell overheats to exceed a predetermined temperature. The pressure sensitive current interrupting mechanism is activated to interrupt the current flow, when the gas pressure in the cell is constituted to exceed a predetermined value. In such a case, the pressure sensitive switch mechanism can cause a metal diaphragm within the end cap assembly to flex or deflect, thereby dividing the electrical connection between the end cap end plate of the cell and an electrode of the end cap. cell, which prevents the current from flowing through the cell. In the case of excessive constitution of gas pressure, the metal diaphragm also breaks allowing the gas to be channeled to the inner chambers inside the extreme cap assembly, and outward to the external environment, through a series of ventilation holes . Yet 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 the electrolyte, liquid or gas inside the extreme lid towards 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 transverse views taken through the visual angles 1-1 of the end cap assembly of Figure 6.

Figure 1 shows the thermally activated current-switching mechanism, and the pressure-activated current-interrupting mechanism, in circuit-connected mode.

Figure 2 shows the thermally activated current-switching mechanism in interrupted circuit mode.

Figure 3 shows the pressure-activated current-interrupting mechanism, in the pressure activated mode, of interrupted circuit.

Figure 4 is a vertical cross-sectional view of yet another embodiment of an end cap assembly, having the pressure-activated current-switching mechanism and the thermally-activated current-interrupting mechanism, integrated therein, in which a heat-sensitive member it softens to release an elastic member to open the circuit.

Figure 5 is an exploded perspective view of the components of the end cap assembly of the invention, shown in the embodiment of Figure 1 or Figure 9.

Figure 6 is a perspective view of the bottom of the end cap assembly showing the pressure resistant plate and the ventilation openings therethrough.

Figure 7 is a perspective view showing the end cap assembly of the invention, which is inserted into the open end of a cylindrical housing of a cell.

Figure 8 is a perspective view showing a completed cell, with the end cap assembly of the invention inserted into the open end of a cylindrical housing of a cell with end cover plate of the assembly, forming a terminal of the cell .

Figure 9 is a vertical cross-sectional view showing the thermally activated current-switching mechanism using a shape memory member and the pressure-activated current-switching mechanism in the connected circuit mode. «Figure 10 is a vertical cross-sectional view showing the thermally activated current-interrupting mechanism used by the shape memory member in the interrupted circuit mode.

The end cap assembly 10 (Figure 1) of the invention can be applied to the primary or secondary (rechargeable) cells. In a preferred embodiment, the end cap assembly 10 is insertable within the open end 95 of a housing typically cylindrical for the cells (Figure 7). The cells contain a positive electrode (cathode in the discharge), a negative electrode (anode in the discharge), the separator and the electrolyte and the positive and negative external terminals in electrical communication with the positive and negative electrodes, respectively. Referring now to Figure 1 of the drawings, an end cap assembly 10 designed for insertion into the open end of a cell housing, comprises a sub-assembly 38, thermally activatable current interrupter, and a sub-assembly 48 for pressure relief. integrated in this one. The sub-assemblies 38 and 48 are separated by a common support plate 60. The sub-assemblies 38 and 48 are maintained within a cover 30 which defines the outer wall of the end cap assembly 10. The sub-assembly switch 38 is defined at its upper end by an end cap plate 20, cup-shaped and at its bottom 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 terminals extreme of the cell. The support plate 60 separates the chamber 68 within the thermal sub-assembly 38 of the chamber 78, within the sub-assembly 48 of pressure relief. 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 sensitive 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 the contact electrical rupture between the end cap 20 and the contact plate 15, thereby preventing the current from flowing through the cell. The pressure relief sub-assembly 48 comprises a thin metal diaphragm 70 connected to a pressure-resistant plate 80 which in turn is electrically connected to a cell electrode 88 through the conductive tab 87, which is welded to plate 80. (The pressure resistant plate is electrically conductive and of sufficient thickness so that it does not deform substantially at elevated pressures to at least about 4.14 x 106 pascals (600 psi). The cell 70 is formed to exceed a predetermined threshold value, the diaphragm 70 bulges outward to break the electrical contact with the pressure resistant plate 80, thereby preventing current from flowing to or from the cell. pressure resistant and support plate 60 also preferably have perforations, 73 and 63, respectively, in these, which helps to vent the gas and to relieve the constitution No pressure inside the cell. In the preferred embodiment shown in Figure 1, the end cap assembly 10 can be used on a rechargeable cell, for example, a rechargeable lithium ion cell. (A rechargeable lithium ion cell is characterized by the transfer of lithium ions from the negative electrode to the positive electrode, after discharge from the cell and from the positive electrode to the negative electrode after cell charging. typically have a positive electrode of lithium oxide and cobalt (LixCo02) or lithium manganese oxide of the spinel crystal structure (LixMn20) 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 comprise a lithium salt dissolved in a mixture of non-aqueous solvents.The salt may be LiPF6 and the solvents may advantageously include dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC) and mixtures thereof. The present invention is also applicable to other rechargeable cells, for example, nickel metal hydride cells and nickel and cadmium cells. The end 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 a support base under the cover plate 20, and an insulating disk 35. between the end cap 20 and the support plate 60. The cap assembly 10 is also advantageously provided with a pressure relief 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 elevated portion 82 of the underlying pressure-resistant plate 80. The diaphragm 70 should be made of material that is electrically conductive and of a minimum thickness of between about 0.1 and 0.5 millimeters, depending on the pressure at which the diaphragm is intended to act. The diaphragm 70 can be desirably aluminum. The diaphragm 70 is advantageously coined so that it breaks at a predetermined pressure. That is, the surface of the diaphragm can be stamped or etched with acid so that a portion of the surface is thicker than the rest. A preferred diaphragm 70 for use in the present invention is coined to impose a semicircular notch or in the form of * C "70a on its surface.The shape of the notch is advantageously the same or similar to the shape of a larger portion of the edge. peripheral of the diaphragm 70 and advantageously placed in proximity to the peripheral edge.The particular pressure at which ventilation takes place, it is controllable by varying the parameters such as the depth, placement or shape of the notch as well as the hardness of the material. When the pressure becomes excessive, the diaphragm will break along the line of the notch. The end cap 20 and the support plate 60 define a chamber 68 therebetween, in which a sub-assembly 38, thermally activated current switch is located. The insulating disc 35 is formed of a peripheral base portion 35a and a downward sloping arm 35b extending therefrom. The arm 35b extends into the chamber 68. The diaphragm 70 is designed to break when the constitution of the gas within the cell reaches a predetermined threshold level. The region between the support plate 60 and the diaphragm 70 forms a chamber 78 within which the constitution of the gas within the cell can be vented after the rupture of the diaphragm 70. The sub-assembly 38 current switch comprises a thermally bimetallic disc 40 sensitive, a metal contact plate 15 in electrical contact with a resilient member 50 in the form of a spring. As shown in Figures 1 and 5, the elastic member 50 can be formed of a simple flexible member having an outer circular peripheral portion 50a from which a portion of the disc retaining tab 50c extends radially inwardly to generally holding the bimetallic disk 40 freely in place during any orientation of the cell, while not restricting its action movement under pressure. This member can be welded at a point of the outer portion 50a to the end cap plate 20, with a central contact portion 50b in contact with the plate 15. Furthermore, the contact portion 50b can be designed with a reduced cross-sectional area , so that it can act as a disintegrable fusion bond or union to protect against conditions of rapid energy variation. The bimetallic disk 40 is positioned to freely engage the inclined arms 35b of the insulating disk 35, whose arms act as the disk seat for the disk 40. The bimetallic disk 40 also preferably includes a central opening for receiving a high contact portion of the disk. the metal contact plate 15. The contact plate 15 is preferably welded to the support plate 60 and provides a surface for the elastic member 50, for rest as shown in Figure 1. There is an electrically insulating washer 25 which is extends over the peripheral edge of the end cap 20 and along the peripheral edge of the bottom of the diaphragm 70. The washer 25 also borders the outer edge of the sub-assembly 38, as shown in Figure 1. There may be a metal ring 55 which is wound on the upper edge of the washer 25 and pressed against the diaphragm 70 to seal the interior components of the tap assembly to extreme. The washer 25 serves to electrically insulate the end cap 20 of the rigid ring 55, and also to form a seal between the support plate 60 and the rigid ring 55. The cover 30 of the end cap assembly 10 can be formed from the member cylindrical truncated shown best in Figure 5. In a completed cell assembly (Figure 8) the outer surface of the cover 30 will come into contact with the inner surface of the housing 90 of the cell. The support plate 60 provides a base for the components of the subassembly 38 to rest, and is preferably in the form of an arc to maintain the active radial compressive force against the internal surface of the washer 25. The support plate 60 may be provided with perforations 63 in its surface for venting the gas to the upper chamber 68 when the diaphragm 70 breaks. The gas passing into the upper chamber 68 will be vented 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 housing 90 of the cell, which is in electrical contact with the opposite terminal, typically the negative terminal in the case of the rechargeable lithium ion cell. In this way, the washer 25 provides electrical insulation between the end cap 20 and the outer wall 30, that is, between the two terminals of the cell, whereby shorting of the cell is prevented. There may be an additional insulating ring, namely the support ring 42 between the upper portion of the outer wall 30 and the pressure plate 80 as illustrated in Figure 1, also to ensure that there is no short between the positive and negative terminals. of the cell. The diaphragm 70 is preferably in the form of a cup comprised of aluminum having a thickness advantageously of between about 76.2 and 254 microns (3 and 10 mils). At such a thickness, the weld between the base 72 of the diaphragm and the support plate 80 breaks and the base 72 of the diaphragm bulges and separates from the support plate 80 (Figure 3) when the internal pressure of the gas within the cell is raised to a threshold value of at least between about 6,894 x 105 and 13.89 x 105 passages (100 psi and 200 psi). (Such pressure constitution could occur for example if the cell was being charged at a higher voltage than recommended, or if the cell was shorting or was misused). However, if desired, the thickness of the base 72 of the diaphragm may conveniently be adjusted to bulge at other pressure levels. The separation of the diaphragm base 72 from the plate 80 breaks all electrical contact between the diaphragm 70 and the plate 80. This separation also breaks the electrical path between the end cap 20 and the electrode 8,8 of the cell, in contact with the plate 80, so that the current can no longer flow to or from the cell, effectively turning off the cell. Even after the path or current path is broken and the pressure inside the cell continues to rise for other reasons, for example, heating in a furnace, the vent diaphragm 70 will also preferably break at a threshold pressure of at least between approximately 17.2 x 105 and 27.6 x 105 pascals (250 and 400 psi) to prevent the explosion of the cell. In such extreme circumstances, the rupture of the ventilation diaphragm 70 allows the gas coming from the interior of the cell to be vented through the ventilation holes 73 (Figures 1 and 6) in the pressure resistant plate 80, after the which gas enters the lower chamber 78 (Figure 1). The gas will then pass from the lower chamber 78 towards the upper chamber 68 through the ventilation holes 63 in the support plate 60 (Figure 1) and if necessary the ventilation holes (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 characteristics of the invention can be described with reference to Figures 1-3. It should be noted that in the specific embodiment shown herein, one of the cell electrodes comes 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 in contact with the plate 80 may conveniently be the positive electrode. This electrode will be isolated from the case or housing 90 of the cell. The negative electrode (not shown) will be connected to the case or housing 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 current, thermal switch, or activation of the pressure relief diaphragm 70. In the specific mode shown 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 layer 15 which is in electrical contact with the elastic 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 plate pressure 80 and the end cap 20, can be interrupted in two ways. As described above, if the pressure is constituted in the cell at a predetermined threshold, the contact between the diaphragm 70 and the pressure plate 80 is broken as the base 72 of the diaphragm bulges 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 sub-assembly 38 thermal switch is activated and in doing so the bimetallic disk pushes up from the insulator 35b thereby causing the elastic member 50 to disengage from the contact plate 15. This in effect separates the electrical path between the tab 87 of the electrode and the end cap 20, thereby preventing the current from flowing to or from the cell. It is an advantage of the invention to incorporate these two switch mechanisms within a simple end cap assembly 10 which is insertable within the open end of a housing or cell housing as a single unit. The bimetallic disk 40 is preferably not physically coupled to the underlying insulating disk, but rather is free to move, ie it rests in free floating condition on the disk arm 35b as shown in Figure 1. In such design, the current does not pass through the bimetallic disk 40 at any time, regardless of whether the cell is in charge or discharge. This is because the disk 40, when inactivated, is not in electrical contact with the contact plate 15. However, if the cell overheats beyond a predetermined threshold temperature, the bimetallic disk 40 is designed for calibration appropriate, such that it pressurizes or deforms (Figure 2) causing it to push the elastic member 50 away from the contact plate 15, thereby preventing the current from flowing between the terminals of the cell. The bimetallic disc 40 is calibrated so that it has a predetermined plate shape which allows the disc to be driven when a given threshold temperature is reached. The free floating design of the bimetallic disc 40 on the arm 35b of the insulating disc as described above, does not allow the current to pass through it at any time, regardless of whether the cell is in charge or discharge. This makes the calibration of the disk 40 easier and more accurate, since there is no heating effect caused by the current flow through the bimetal disk 40 (I3R heating). The bimetallic disk 40 may conveniently comprise two dissimilar metal layers having different coefficients of thermal expansion. The top layer of the bimetallic disk 40 (the layer closest to the end cap 20) can be composed of a high thermal expansion metal, preferably a nickel-chromium-iron alloy and the underlying or lower layer can be composed of a metal Low thermal expansion, preferably nickel-iron alloy. In such an embodiment the disc 40 can be activated when the temperature rises at least between about 60 to 75 ° C, causing the disc 40 to deform sufficiently to push the elastic member 50 away from contact with the contact plate 15. It is also possible choose metallic layers of high and low thermal expansion, such that disc 40 will not be readjusted except at a temperature below -20 ° C, which in most applications makes the device a simple-acting thermostatic device. The preferred materials for the above-described components are described as follows: the end cap 20 is preferably made of stainless steel or nickel-plated steel with a thickness between about 0.2 and 0.375 mm (8 to 15 mils) to provide adequate support, rigidity and resistance to corrosion. The outer wall 30 of the end cap assembly 10 is also preferably made of stainless steel or nickel plated steel having a thickness between about 0.2 and 0.375 mm (8 and 15 mils). The pressure plate 80 is preferably aluminum having a thickness between about 0.25 and 0.5 mm (10 and 20 mils) which may be reduced in the center to between about 0.05 and 0.125 mm (2 and 5 mils) ) at the welded contact point with the base 72 of the diaphragm. The insulating support ring 42 may be composed of a high temperature thermoplastic material such as high temperature polyester for strength and durability, available under the trade designation VALOX from General Electric Plastics Company. The rigid or crimped ring 55 is preferably made of stainless steel or nickel-plated steel, having a thickness between about 0.2 and 0.375 mm (8 and 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 and 10 mils). At such thicknesses the diaphragm will break away from its weld to the pressure plate 80, when the internal gas pressure exceeds a threshold pressure between approximately 6.89 x 105 and 17.2 x 105 pascal (100 and 250 psi). If the internal pressure of the gas exceeds a pressure between about 17.2 x 105 and 27.6 x 105 pascal (250 and 400 psi) the diaphragm 70 will break to provide additional relief to the gas pressure buildup. The insulating disc 35 on which the bimetal disk 40 rests is preferably of a material of high compressive strength and high thermal stability and low mold shrinkage. A suitable material for disk 35 is a liquid crystalline polymer or the like, of thickness between about 0.25 and 0.75 mm (10 and 30 mils) available under the trade designation VECTRA from Celanese Company. The support plate 60 is preferably made of stainless steel or nickel-plated steel to provide adequate strength and corrosion resistance at a thickness of between about 0.25 and 0.75 mm. (10 and 30 thousandths of an inch). The elastic member 50 is advantageously formed of beryllium-copper alloy, nickel-copper, stainless steel or the like, which has good spring action and excellent electrical conductivity. A suitable thickness for the elastic member 50, when formed of beryllium-copper alloy, or copper-copper alloy, is between about 0.075 and 0.2 mm (3 and 8 mils) to give sufficient strength and carrying capacity. This material can be plated or embedded with plate 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, plated with a precious metal such as gold or silver to decrease the contact resistance and improve the reliability. This may also be formed of an alloy of nickel-copper plate, stainless steel, or nickel-plated steel. The washer 25 is typically made of polyhedral material such as nylon or polypropylene. The seal around the components of the end cap assembly must be watertight in order that the electrolyte, both in the form of liquid and vapor, is prevented from entering the chambers of the end cap or leaving the cell. After the end cap assembly 10 is completed it can be inserted into the open end 95 of a cylindrical cell case or housing 90 shown in Figure 7. The circumferential edge of the cell case 90 at the open end thereof, it is welded to the outer wall of the cover 30 of the end cap assembly 10, to provide a hermetically tight seal between the end cap assembly 10 and the case 90 of the cell. The radial pressure of the circumferential wall of the rigid ring 55 against the washer 25 and the diaphragm 70, produces a hermetically tight seal around the inner components of the end cap assembly 10. An alternative embodiment of the end cap design having a pressure relief mechanism and the thermally activated current-interrupting mechanism, integrated therein, is shown as an 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 a bimetallic disc is not used to activate the spring-like mechanism. Rather, a thermal pellet 175 is provided to retain a resilient member 150 in the form of a spring, 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 elastic member 150 may comprise an elongated metal arm 150a, which is welded at one end to the support plate 60. The support plate 60 is in electrical contact with the diaphragm 70, which in turn is welded to a portion. elevated 82 of plate 80 resistant to pressure, underlying. An electrode tab 87 is in electrical contact with the plate 80. The elastic member 150 preferably ends at its opposite end in a cup-shaped or convex portion 150b which contacts the contact plate 115. There is a electrical insulating disk 120 on the peripheral edge 60a of the support plate 60 to prevent direct contact between the support plate 60 and the contact plate 115. In this way, there will be electrical contact between the support plate 60 and the end cap 20, as long as the elastic member 150 is held pressed 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 an electrode 88. of cell through the tab 87, when the end cap assembly 110 is applied to a cell. (The end cap assembly 110 can be applied to a cell by inserting it into the open end of a cylindrical case 90, in the same manner as described above with reference to the embodiment shown in Figure 1). ThusAs the elastic member 150 is held pressed against the contact plate 115 by the thermal pellet 175, there is electrical contact between a cell electrode 88 (through the tongue 87) and the end cap plate 20 which allows normal operation of cell. If the cell overheats beyond a predetermined threshold temperature, the pellet 175 melts, whereby the support for the elastic member 150 is removed. The melting of the pellet 175 causes the elastic member 150 to press fit with downward direction and break the electrical contact with the contact plate 115. This in effect divides the electrical path between the tab 87 of the electrode and the end cap 20, thus preventing the current from flowing to or from the cell. If the internal pressure of the gas within the cell exceeds a predetermined value, the diaphragm 70 will break, whereby the electrical contact between the plate 80 and the diaphragm 70 is divided and also allows the gas to escape into the external environment. through the ventilation holes 63 and 67 in the support plate 60 and the end cap 20, respectively. The preferred materials for the end cap 20, the support plate 60, the contact plate 115 and the aluminum diaphragm 70 referenced in the embodiment shown in Figure 4, may be the same as those described for the elements corresponding ones having the same reference numbers shown in Figures 1-3. The contact plate 115 is preferably formed of stainless steel or cold-rolled steel plated with nickel, plated with silver or gold to decrease its electrical 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 high temperature polyester available under the trade designation VALOX from General Electric Plastics Company. The elastic member 150 can be advantageously formed of beryllium-copper alloy of thickness between about 0.125 and 0.25 mm (5 and 10 mils) to provide good conductivity when in contact with the plate 115 and reliable spring action when the pressure of the pellet 175 against it is removed. In addition, the elastic arm 150 can be plated with silver or gold to increase its conductivity. The thermal pellet 175 is advantageously formed of a polymer having a relatively low melting point, for example, between about 65 ° C and 100 ° C but still has excellent compressive strength to keep the elastic arm 150 in place during the normal operation of the cell. A suitable material for the thermal pellet 175 having such properties is a polyethylene wax available under the trade designation POLY AX from Petrolyte Company. A thermal pellet 175 of such polyethylene wax melts within a desirable temperature range of between about 75 ° C and 80 ° C. Another alternative embodiment is shown in Figures 9 and 10. This embodiment is essentially the same as the embodiment described in Figures 1-2 and for the same application except that the thermally sensitive current-interrupting mechanism comprises an alloy member 45 shape memory instead of bimetallic disk 40 and spring 50. A shape memory alloy is an alloy by which a plastically deformed metal is restored to its original shape by a phase change of solid state, caused by heating . The shape memory response is caused by the strong crystallographic relationship between the low temperature stable phase known as martensite and the high temperature stable phase known as austenite. The shape to be remembered is formed in the austenite phase when the alloy is held in place and heated, and when the alloy is cooled the material develops the martensitic structure. In use, when the shape memory alloy is heated it returns to its remembered form in the austenite phase. Shape memory alloys for the application described herein are commercially available, for example, from Special Metals Corp. of New Hartford, N.Y. The shape memory alloy member 45 (Figure 9) is electrically conductive and may advantageously have the same shape as the spring 50.

(Figure 1) . Thus, it can be desirably formed of a simple partially hollow disk, for example, a disk 45 having a discontinuous surface, namely a surface with an opening 45f (FIG. 5) therethrough. The disc 45 has an outer edge 45a (Figure 5) and a flexible portion 45b projecting inwardly, within the hollow portion, for example in the opening, from the peripheral edge 45a. The flexible portion 45b is advantageously preformed with a slight flexion 45e on its surface, as shown in Figure 9, so that its terminal end 45c rests flat against the contact plate 15 to complete the electrical path between the positive electrode 87 and the end cap 20. The thickness of the flexible portion 45b is smaller than its length. The thickness of the flexible portion 45b is desirably less than 1 mm, preferably between 0.2 and 0.5 mm. The flexible member 45b is oriented horizontally within the end cap assembly 10, as shown in Figure 9, so that the path or current path through the member 45b will be at least substantially in the direction of its thickness and preferably and Essentially the entire path or current path through the number 45b can be in the direction of its thickness. If the internal temperature of the cell becomes too high for any reason, for example, the occurrence of an uncontrolled exothermic reaction, the metal memory member 45 will be flexed and flattened, thereby breaking the electrical contact with the plate. contact 15. In the application to rechargeable batteries, particularly lithium ion cells, the metallic memory alloy 45 can be preformed by manufacture to be desirably flexed at a temperature between 60 ° C and 120 ° C. When such a temperature is reached, the metallic memory member 45 will immediately flex to interrupt the flow of current and shut down the cell, thereby preventing the exothermic reaction that could lead to a thermal runaway situation. A desirable shape memory alloy for activation at such temperatures can be selected from the known groups of memory 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 memory alloy member 45 is a nickel-titanium alloy for application as the current switch described above, for electrochemical cells. A preferred nickel-titanium memory alloy is available under the trade designation NITINOL alloy from Special Metals Corporation. The shape memory member 45 may be of a resettable or re-hardening alloy, that is, one that deforms when heated but returns to its original shape after cooling, without the application of external force. However, the shape memory metal 45 for the present application does not need to be resettable or reedable, that is, it can irreversibly deform when heated to its activation temperature. The memory element 45 of the NITINOL alloy of preferred alloy material is usually manufactured such that it is not resettable or reenergized once it is activated. The preferred memory element 45 of the NITINOL alloy can conveniently be manufactured as a single piece having a circular peripheral edge (Figure 5) from which a flexible portion projects inwardly. The flexible portion 45b may conveniently be rectangular in shape and comprises an outer portion 45d and an inner portion 45c separated by the flexure 45e. The memory element 45 flexes along the flexure 45e when a predetermined activation temperature is reached, preferably a temperature between about 60 ° C and 120 ° C, the element 45b deviates away from contact with the contact plate 15 as shown in Figure 10, thus interrupting the flow of current inside the cell. In order to achieve such an activation effect it has been determined that the thickness of the NITINOL alloy member 45 can advantageously be in a range between about 0.2 and 0.5 mm, with a surface area such that the strength of said member is less than about 5 milliohms. The above-described shape for the memory member 45, namely a hollow disk having a circular outer edge 45a from which a flexible portion 45b projects inwardly, is desirable, since this allows the reduced thickness and the area of good contact reduce the complete strength of the member 45. The shape memory member 45 desirably does not have a strain of not more than about 8 percent. Also, the angle between the portion 45c and 45d is desirably between about 10 and 30 degrees. This allows the memory member 45b to flex or deflect away from the contact plate 15 and flatten when the activation temperature is reached. In the application to lithium ion cells, the preferred design described above for the memory member 45, can result in its complete strength being less than 5 milliohms. which in turn allows a draining or depletion of current of up to 5 amps under continuous operation of the cell. Although a rectangular shape for the flexible portion 45b is desirable, other shapes may also be used, for example, the member 45 of the flexible portion may be somewhat tapered so that the average width of the member 45b is smaller than the average width of the member 45b. the 45d portion. In the preferred design, the lower surface of the memory element 45 can be smooth, ie without leg or projections emanating therefrom. The memory metal 45 has the advantage of requiring fewer components since the spring 50 used in connection with the bimetallic disk mode can be eliminated. In this way, the memory element 45 has been constituted into a simple element with dual properties of heat-sensitive activation and bending similar to the spring after such activation. Also the spring-like force per unit mass of the memory element 45 is greater than that of the bimetallic disk 40. This property makes the memory element 45 particularly suitable for application to small cells, for example cells of AAA size or cells rechargeable prismatic, thin. In this case, the cells having a diameter or width smaller than the width of the cells or cells size AAA, width less than about 10.0 mm, the pressure diaphragm 70, fracturable, can be eliminated due to the small space available within the 10 extreme cover assembly. In such an application, the memory member 45 and the preferred structural design described above for the end cap assembly 10 could be employed except that the support plate 60 and the diaphragm 70 could be fused into a single member having the shape and orientation of the plate 60 shown in Figure 9. In such a design, the lower chamber 78 and the ventilation holes 63 could be eliminated. The contact plate 15 can also be optional, since the shape memory member 45b can be in direct electrical contact with the plate 60, which could thus function as the contact plate. A preferred embodiment of an end cap assembly incorporating a metal memory element 45 also has a pressure sensitive diaphragm 70, which is activated to expand in the manner illustrated in Figure 3, to break the electrical path between the electrode positive 87 and the end cap plate 20, when the pressure inside the cell reaches a predetermined level. Also as previously described with reference to the embodiments shown in Figures 1-3, the pressure sensitive diaphragm 70 (Figures 9 and 10) may also have notches 63 that are designed to break., to allow the gas to pass through them when the pressure inside the cell exceeds a predetermined level. If the build-up of pressure within the cell is drastic, the central portion 45 of the diaphragm 70 will also break, thereby allowing a wider area for the escape of gas from the interior of the cell. An enlarged view of the end cap assembly 10 of Figures 1 and 9 is shown in Figure 5. The end cap assembly 10 can be made by assembling or assembling the components shown in Figure 5, in the following order: With reference to the construction of the embodiment shown in Figure 1, a pre-assembly is formed comprising the components 20, 50, 40, 35, 15, 60, 70, 25 and 55. With reference to the construction of the embodiment shown in FIG. Figure 9, the pre-assembly is formed comprising the components 20, 45, 35, 15, 60, 70, 25 and 55. The pre-assembly of the embodiment shown in Figure 1 is conveniently achieved firstly by inserting the plastic washer 25 inside of the rigid ring 55, then inserting the vent diaphragm 70 into the washer 25 and then inserting the support plate 60 with the contact plate 15 welded thereto, into the vent diaphragm 70. After this the insulating disk 35 is cabbage ocado around the contact plate 15 and the bimetallic disk 40 is placed to rest on the arm 35b with slope outwardly of the insulating disk 35. The bimetallic disk 40 is not attached to the insulating disk 35, but rests on it in a condition of free floatation, with the insulating disc that helps to act as a placement medium for the bimetallic disc. The upper surface of the outer end of the spring-like elastic member 50 is welded to the circumferential edge of the end cap 20. The end cap 20 with the elastic member 50 welded thereto is then placed on the insulating disk 35, so that the raised central portion of the contact plate 15 contacts the inner end of the bed of the elastic member 50 and the bottom surface of the outer end of the elastic member 50 makes contact with the circumferential edge of the insulating disk 35. In this way, the outer end of the elastic member 50 is welded between the end cap 20 and the insulating disc 35, and the opposite or inner end of the member 50 is in contact with the contact plate 15. The pre-assembly of the embodiment shown in Figure 9 is constructed in a similar manner, except that the bimetallic disk 40 is removed and the shape memory member 45 is employed in place of the spring 50. In this way, the pre-assembly of the embodiment shown in Figure 9 is conveniently achieved first by inserting the plastic washer 25 into the rigid ring 55, then inserting the vent diaphragm 70 into the washer 25 and then inserting the support plate 60 with the plate contact 15 welded to it, inside the ventilation diaphragm 70. The memory member 45 is then welded to the circumferential edge of the end cap 20. The end cap 20 with the memory member 45 welded thereto is then placed on the insulating disk 35, so that the raised central portion of the contact plate 15 contacts the inner end of the memory member 45, and the bottom or bottom surface of the outer end of the memory member 45 makes contact with the circumferential edge of the disk insulator 35. In this way, the outer end of the memory member 45 is wedged between the end cap 20 and the insulating disk 35, and the opposite or inner end of the member 45 is in contact with the contact plate 15.

With reference to the construction either to the embodiment of Figure 1 or 9, the ring 55 is then mechanically wrapped or crimped onto the upper edge of the washer 25 to hold the upper end of the washer 25 pressed tightly against the circumferential edge of the seal. the end cap 20. This wrapping is achieved by the application of mechanical force along the centroidal (vertical) axis of the ring 55. Subsequently in a second wrapping or crimping step, mechanical pressure is applied radially to the walls of the rigid ring 45. , which completes the pre-assembly assembly. The radial wrapping serves to keep the internal components of the pre-assembly tight, and hermetically sealed within the ring 55. The pre-assembly is then inserted into the metal cover 30, so that the bottom or bottom surface of the rigid ring 55 rests against the edge internal bottom of the cover 30. After this, the bottom or bottom surface of the rigid ring 55 is welded to the lower inner surface of the cover 30. The pressure plate 80 is then press fit into the bottom of the ring Support 42, insulator and support ring 42 with the pressure plate 80 coupled to it is then placed against the outer bottom surface of the cover 30, so that the raised central portion of the pressure plate 80 makes contact with the diaphragm of ventilation 70. This point of contact between the pressure plate 80 and the diaphragm 70 is then spot welded, thereby completing the construction of the lid assembly 10 extreme The end cap assembly 10 can be applied to a cell, for example, by insertion of it into the open end of the cylindrical housing or housing 90 of a cell, as shown in Figure 7, and by welding the outer surface of the cover 30 to the inner surface of the cylindrical housing 90 at the open end 95 thereof. This results in the cell 100 shown in Figure 8 with the mounting 10 of the end cap being hermetically sealed inside the cylindrical housing 90, and the end cap plate 20 forming a terminal of the cell. While 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 to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (28)

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

1. An end cap assembly for application to an electrochemical cell, having a positive terminal and a negative terminal and a pair of internal electrodes (anode and cathode), the end cap assembly comprises a housing, a chamber within the housing, and an exposed end cap plate, said plate is functional as a cell terminal, the end cap assembly has an electrically conductive path or path therethrough which allows the end cap plate to be electrically connected to a cell electrode In addition, when the end cap assembly is applied to a cell, the end cap assembly is characterized in that it further comprises: a) the thermally sensitive means for preventing current from flowing through the electrical path, wherein the thermally sensitive medium comprises a shape memory alloy member, activatable when the temperature inside the end cap assembly reaches a predetermined level, pro voiding a break in the electrical way, and b) a pressure sensitive means comprising a breakable member located at the end of the end cap assembly, opposite to the end cap plate, the breakable member is broken when the gas pressure on the side thereof further away from the end cap plate reaches a predetermined level, producing a break in the member, allowing the gas to pass through it.

2. The end cap assembly according to claim 1, characterized in that the shape memory alloy comprises a nickel-titanium alloy.

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

4. The end cap assembly according to claim 1, characterized in that the thermally sensitive medium comprises a chamber within the end cap assembly, the shape memory alloy member, forming a portion of the electrical path, wherein, when the The temperature of the cell within said assembly reaches a predetermined level, the shape memory alloy member is deformed, thereby causing a break in the electrical way.

5. The end cap assembly according to claim 4, characterized in that the shape memory element comprises a flexible member of the single piece construction having a flexure surface, wherein, when the temperature of the cell within the assembly reaches a predetermined level, the surface of said shape memory member is deformed causing a break in the electrical way.

6. The end cap assembly according to claim 4, characterized in that the shape memory member comprises a disk having an opening therethrough, 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, where the flexible portion has a flexural surface, wherein, when the temperature of the cell within the assembly reaches a At the predetermined level, the bending surface is deformed causing a break in the electric way.

7. The end cap assembly according to claim 6, characterized in that the outer edge of the shape memory member is sandwiched between a portion of the end cap plate and a portion of the electrically insulating member, and wherein the end cap assembly it comprises a contact plate forming part of an electrical path, wherein the shape memory member is in electrical contact with the contact plate.

8. The end cap assembly according to claim 1, characterized in that it further 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 sensitive medium of the medium that is sensitive to pressure.

9. The end cap assembly according to claim 8, characterized in that the separation member comprises a metal plate having at least one opening therein, so that when the breakable member is broken, the gas passes through said opening and towards the camera inside the end cap assembly.

10. 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 chamber passes through the cap. extreme lid opening and towards the external environment.

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

12. The end cap assembly according to claim 11, characterized in that it further comprises an electrically insulating washer 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 ( curling member) mechanically wound around the washer, to hold the diaphragm 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 crimping member.

14. The end cap assembly according to claim 13, characterized in that the end cap assembly is applied to a cell by inserting it into the open end of a housing or cylindrical case for the cell, and welding the outer surface of said housing. cover to the internal surface of the housing, after which the end cap assembly is tightly sealed inside the cylindrical case with the end cap plate comprising a terminal of the cell that is placed towards the external environment.

15. The end cap assembly according to claim 1, characterized in that the shape memory alloy member comprises a disk having an opening through the thickness thereof, the shape memory member having a peripheral edge with a flexible portion. which projects inwardly toward the opening from a portion of the peripheral edge, wherein the edge rests on a surface of an insulating member within the end cap assembly, wherein, when the temperature of the cell within the cell assembly reaches a predetermined level, the flexible portion deforms causing a break in the electric way.

16. An improvement in an electrochemical cell of the type formed by an end cap assembly inserted into an open-ended cylindrical housing or housing for the cell, the cell also having a positive terminal and a negative terminal and a pair of internal electrodes (anode and cathode), wherein the end cap assembly has a housing and an exposed end cap plate, the end cap plate is functional as a cell terminal, the enhancement is characterized in that it comprises the end cap plate that 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) the thermally sensitive medium comprising an electrically conductive shape memory alloy member to prevent current flows through the cell, wherein the shape memory member comprises a flexible member having a A flex surface and a thickness smaller than its length, the flexible member is oriented within the end cap assembly, so that the current passes substantially in one direction through the thickness of the flexible member, wherein when the temperature inside the cell reaches a predetermined temperature V, the memory member it flexes along the flexure surface causing a break in the electrical path between the end cap plate and the electrode, thereby preventing current from flowing through the cell.

17. The electrochemical cell according to claim 16, characterized in that the shape memory member comprises a disk having an opening through the thickness thereof, the disk having a peripheral outer edge with the flexible member projecting in an inward direction in the opening, from a portion of the peripheral edge, the flexible member has a flexural surface that deviates or flexes when the temperature of the cell reaches a predetermined level.

18. The electrochemical cell according to claim 16, characterized in that the shape memory member comprises a nickel-titanium alloy.

19. The electrochemical cell according to claim 16, characterized in that it further comprises b) the pressure sensitive medium that allows gas from the interior of the cell to pass into the interior of the end cap assembly when the internal pressure of the gas within the the cell reaches a predetermined level.

20. The electrochemical cell according to claim 19, characterized in that the pressure-sensitive means comprises a frangible diaphragm plate located at the end of the end cap assembly, opposite the end cap plate, the diaphragm plate is broken when the pressure of the gas on the side thereof farthest from the end cap plate reaches a predetermined level producing a break in the diaphragm, allowing the gas to pass therethrough.

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 and between the end cap plate and the rupturable diaphragm, and the separation member separates the medium thermally sensitive of the medium sensitive to pressure.

22. The electrochemical cell according to claim 21, characterized in that the end cap plate has at least one opening therethrough so that the gas produced in the cell can pass through the opening of the end cap towards the 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 shape memory member is in electrical contact with the plate. Contact.

24. The electrochemical cell according to claim 18, characterized in that when the temperature of the cell reaches a value between about 60 ° C and 120 ° C, the shape memory member is deformed causing the shape memory member to separate its connection electrical with the contact plate.

25. The electrochemical cell according to claim 20, characterized in that it further comprises an electrically insulating washer 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 metal member (curling member) mechanically wound around the washer, to hold 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 metallic cover around the crimping 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 housing or housing for the cell, and welding the outer surface of the cover to the inner surface of the housing, after which the end cap assembly is tightly sealed within the cylindrical housing or housing with the end cap plate, comprising a terminal of the cell that is exposed to the external environment.

28. An extreme cap assembly for application to an electrochemical cell that has a positive terminal and a negative terminal, 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 through it, which allows the end cap plate to be electrically connected to a cell electrode, when the end cap assembly is connected to a cell, the end cap assembly further comprises a) the thermally sensitive medium to prevent that the current flows through the electric way, where the thermally sensitive medium is activatable when the temperature inside the end cap assembly reaches a predetermined level, causing a break in the electric way, where the thermally sensitive medium comprises a chamber within the end cap assembly, and further comprises a shape memory alloy member, the shape memory alloy member, forms a p Orifice of the electrical way, wherein a portion of the alloy member of the shape member comprises a disk having an opening through the thickness thereof, the disk having an outer edge with a flexible portion projecting inwardly in direction. 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, wherein, when the temperature of the cell within the assembly reaches a predetermined level the flexible portion is deformed causing a break in the electric way.