Electrochemical cells and current collectors therefor

Abstract: Current collector assemblies (10) and electrochemical cells made with them are disclosed. The current collector has a stiff, rigid washer (20), repositioned closerly to adjacent to a bottom plate (24) at its central region and the washer maintains the traditional function of controlling the positioning of a seal body (14) of the current collector assembly (10). Increasing stiffness, rigidity, and the repositioning of the washer is accomplished by structurally sculpturing the cross-section of the washer, hardening the temper of the washer, and providing a plateau (88) adjacent the center of the bottom plate (24). Washer vent holes in the bottom plate (24) are located away from the central region, which is the most vulnerable part of the bottom plate. The washer (20) provides both support to the seal body (14) against outwardly-directed internal pressures within the cell and support to the bottom plate (24) against inwardly directed impact forces from outside the cell. The current collector assembly (10) permits safe, effective venting of pressure in the cell; reduces early activation of venting structures in the current collector assembly; contains fewer piece parts than known structurally-robust current collectors; is easy to make and assemble, and provides superior tolerance to outside impact forces.

Description: This invention relates to primary and rechargeable electrochemical cells, such as cylindrical alkaline manganese dioxide cells, and methods of making and using such cells. Current collector assemblies for electrochemical cells have been used for many years. Current collectors for alkaline manganese dioxide electrochemical cells are well known. Numerous disclosures of such current collector assemblies have been made, including the following patents: Country Patent No Inventor Issue Date U.S.A. 3,042,734 Carmichael et al. 1960 U.S.A. 3,314,824 Spanur 1967 U.S.A. 3,617,386 Bosben et al. 1971 U.S.A. 3,663,301 Ralston et al. 1972 U.S.A. 3,740,271 Jammet et al. 1973 U.S.A. 3,764,392 Kuwazaki et al. 1969 U.S.A. 3,954,505 Anderson 1976 U.S.A. 4,075,398 Levy 1978 U.S.A. 4,191,806 Levy 1980 U.S.A. 4,227,701 Tsuchida et al. 1980 U.S.A. 4,476,200 Markin et al. 1984 U.S.A. 4,537,841 Wiacek et al 1985 U.S.A. 4,670,362 Wiacek et al. 1987 U.S.A. 5,008,161 Johnston 1991 U.S.A. 5,015,542 Chaney et al. 1991 U.S.A. 5,051,323 Murphy et al. 1991 U.S.A. 5,227,261 Georgopoulos 1993 U.S.A. 5,248,568 Getz 1993 U.S.A. 5,422,201 Georgopoulos 1995 U.S. Patent Application No. 08/407,391, filed 20 March 1995 and entitled "Battery Sealing Cap," is also of interest. This is now US-A-5 672 443. The disclosure herein discusses the invention within the context of a cylindrical alkaline manganese dioxide cell. However, the invention is not limited to alkaline manganese dioxide cells. Rather, the invention can be practiced with a wide variety of cell structures, and incorporating a wide variety of combinations of electrochemical reactants well known in the art. Thus, the invention can be applied to carbon-zinc electrochemical cells, alkaline manganese dioxide cells, and lithium cells, as well as primary and rechargeable cells. Cylindrical alkaline manganese dioxide electrochemical cells typically comprise a centrally disposed zinc anode surrounded by a plurality of ring shaped manganese dioxide cathode members. The anode and cathode are disposed within a metal container or can having an open top end. Electrical connection to the anode is generally effected by placing an elongated metal member, commonly referred to as a current collector or nail, within the zinc anode. The nail may be forcibly driven through a resilient and electrically nonconductive seal body or gasket that forms a closure over the zinc anode material and manganese dioxide cathode material. Thus, the seal body effectively closes off the open top surfaces of the active electrochemical materials from the outside environment. The top end of the current collector protrudes above the seal body for physical and electrical connection to an electrically conductive metal bottom plate. A primary length of the elongated shank of the current collector is inserted into the zinc anode material. A small portion of the exterior surface of the shank of the current collector resides within the seal body, in sealing engagement therewith. Prior to manufacturing a cylindrical alkaline manganese dioxide electrochemical cell, the current collector and seal body are usually preassembled to form a current collector subassembly. The outer peripheral edge of the seal body, and the portion of the seal body surrounding the centrally located opening, are usually reinforced by thickening the seal body material at those locations. At least one portion of the seal body between the reinforced areas may be made thinner in cross-section to permit the seal body to rupture when internal pressure within the cell exceeds a predetermined limit. The reinforced portion of the seal body that surrounds and defines the centrally located opening is commonly referred to as the "hub." When the current collector is inserted through the opening, there is preferably an interference fit, between the sidewalls defining the central opening of the hub, and the current collector because the diameter of the central opening is less than the diameter of the nail. An interference fit between the nail and the opening is required so that caustic electrolyte or other liquid chemicals in the cell cannot escape from the cell interior by creeping along the surface of the nail and through the central opening. Depending on the particular design used in a given cell, and in addition to the two components of the current collector subassembly described above, the complete current collector assembly may additionally include a washer, a bottom plate, a gasket puncture plate, a vent pressure control plate, a rivet, or any combination of the foregoing components. Heretofore, the primary focus in designing improved current collector assemblies has been directed toward minimizing the tendency for the cells to leak electrolyte. This design goal has been addressed in numerous ways. Materials from which the seal body is fabricated have been strengthened. The current collector nails have been lubricated prior to insertion through the central opening. Tightness of the fit between the nail and the central opening, or between the outer peripheral edge of the seal body and the inner surface of the can, has been increased. It is common for reactions taking place within an electrochemical cell to generate gases as products of such reactions. The generation of such gases causes well known increase in pressure within the cell, generally referred to as "internal pressure." Internal pressure within a cell using the current collector assembly 10 of FIGURE 1(a) causes seal body 14 to deflect upwardly. The higher the pressure, the greater the deflection in the seal body. While it is preferable to maintain all materials, including gases, sealed within the cell, in some environments, and in some individual cells, it is necessary to provide for release of internal cell pressure in preference to allowing the pressure to build up to the point where the crimp is opened up, dismembering the cell, or worse, the cell may explode or otherwise burst. Thus, in cell types which carry significant potential for bursting, the design typically provides for release of gases from the cell at a predetermined internal pressure. On the other hand, if the cell is generally open to the atmosphere, electrolyte can evaporate from the cell, causing the cell to dry out and become useless. Thus, while venting of the cell should be provided for, the cell should generally be closed to gaseous escape except when the predetermined internal pressure is reached. In addition, the cell must be sufficiently rugged that it tolerates external impacts, especially impacts on its anode and cathode ends without deleterious effect on the integrity of the cell, or its operation. Specifically, the cell must withstand being dropped on either end without excessive denting of the cell body. In a test of particular interest, a flashlight having 2 or more cells therein is dropped on its tail end, causing the protruding cathode nubbin of the trailing cell to impact against the center of the bottom plate of the anode assembly of the cell at the lens-end of the flashlight. Desirably, the cell is sufficiently robust, structurally, that the bottom plate of the anode end is not appreciably damaged in such test. In addition, the cell should be able to withstand being dropped on the anode assembly without significant damage to the anode end, or otherwise to the cell. The combined requirements that the cell not leak electrolyte, that the cell properly vent excess pressure within the cell, and that the cell be sufficiently robust to withstand significant external impacts, tend to compete with each other. The leaktightness and robust structural requirements demand a strong cell structure. The requirement for venting gas demands that at least some part of that robust structure develop a gaseous leak under certain conditions. As discussed hereinafter, cells known to the inventors tend to fall into one of two classes. In the first class, the cells are sufficiently robust that they withstand the above-described impact testing. They generally do not leak electrolyte, and they generally vent internal pressure as required. However, such cells have a relatively large number of piece parts and thus carry an undesirably high cost of production. In the second class, the cells generally do not leak electrolyte unless they are subjected to significant external impacts at the anode end. However, upon such external impacting, the central region of the bottom plate of the cell is significantly dented, with subsequent leakage of electrolyte being common. In addition, the external impact commonly activates the venting of the cell, independent of the internal pressure, within the cell. Thus, there remains a practical requirement for a cell having the desired combination of high strength at the anode end of the cell, tightness against leakage of electrolyte, a generally effective gaseous seal, along with proper venting, all at an economic cost, preferably using a minimum number of piece parts. It is an object of this invention to provide an improved structurally robust electrochemical cell wherein the bottom plate at the anode end of the cell has excellent tolerance for, and resistance against, impact forces directed against the outer surface of the bottom plate. It is another object to provide improved cells wherein the cell reliably vents at predetermined pressures. This invention can provide robust cells, cells which reliably vent, cells which use a desirably small number of piece parts in their anode current collector assemblies, which assemblies are easily assembled, and which enjoy corresponding cost advantages. The current collector assemblies of the invention solve certain problems, and the invention provides solutions to problems existing in the prior art. For example, the invention provides a current collector assembly which (a) permits safe and effective venting of pressure which can build up in the cell; (b) contains fewer piece parts than known structurally robust current collectors, and is therefore less expensive than prior art current collector assemblies; (c) prevents or minimizes early activation of venting structures built into the current collector assembly; (d) is easy to implement; and (e) provides superior tolerance to impact forces imposed on the outer surface of the bottom plate of the cell. In its most basic embodiment, the current collector of the invention provides a stiffer, more rigid washer, repositioned closer to the bottom plate at the central region of the bottom plate. Increasing stiffness, rigidity, and the repositioning of the washer is accomplished by a combination of structurally sculpturing the cross-section of the washer to achieve an I-beam affect, hardening the temper of the washer, and providing a sculptured plateau adjacent the center of the bottom plate. In addition, vent holes in the washer are moved outwardly, away from the central region where the bottom plate is most vulnerable to attack, thus providing maximum strengthening material in the region where it is most needed for structural support. The current collector assembly of the present invention has three preferred features: (a) a seal body having a central hub, an outer member extending outwardly away from the hub, and a vent panel between the hub and the outer member; (b) an electrically conductive current collector extending through an aperture in the hub, and electrically and physically mounted to a bottom plate which closes the cell; and (c) an improved, structurally robust, stiff, rigid washer which provides both (i) support to the seal body against outwardly-directed internal pressures within the cell and (ii) support to the bottom plate against inwardly directed impact forces from outside the cell. The invention will now be explained in more detail by way of example in the following description, with reference to the accompanying drawings, in which: FIGURE 1(a) shows a pictorial exploded view of a first prior art current collector assembly. FIGURE 1(b) shows a cross-sectional view of the current collector assembly of FIGURE 1(a) disposed within a cylindrical alkaline manganese dioxide electrochemical cell. FIGURE 2(a) shows a pictorial exploded view of a second prior art current collector assembly. FIGURE 2(b) shows a cross-sectional view of the current collector assembly of FIGURE 2(a) disposed within a cylindrical alkaline manganese dioxide electrochemical cell. FIGURE 2(c) shows a cross-sectional view as in FIGURE 2(b), after the bottom of the cell has received a significant external impact force. FIGURE 3(a) shows a pictorial exploded view of a current collector assembly of the invention. FIGURE 3(b) shows a cross-sectional view of the current collector assembly of FIGURE 3(a) disposed within a cylindrical alkaline manganese dioxide electrochemical cell. FIGURE 3(c) shows a cross-sectional view as in FIGURE 3(b), after the bottom of the cell has received a significant external impact force. FIGURES 4(a) and 4(b) shows second and third embodiments of the washer of the invention in cathode assemblies. FIGURE 5(a) shows a plan view of an improved washer of the invention. FIGURE 5(b) shows a cross-section of the washer of FIGURE 5(a), taken at 5(b)-5(b) of FIGURE 5(a). FIGURE 6 shows an exemplary electrochemical cell using an improved washer, and anode assembly, of the invention. FIGURE 7 shows a representative side elevation of a test stand used to test anode assemblies of the invention for impact tolerance. FIGURE 8 is a graph showing comparative results of drop tests performed on anode assemblies of the invention, and prior art anode assemblies. FIGURE 9 is a graph showing comparative amounts of deflection for given amounts of force applied to the washer. FIGURE 10 is a graph showing vent ruptures from comparative drop tests. FIGURE 11 is a bar chart showing comparative pressures at which seal bodies ruptured in anode assemblies. The invention is defined in the appended claims and is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of being embodied, practiced or carried out in various ways. Also, it is to be understood that the terminology and phraseology employed herein is for purpose of description and illustration only. Throughout the drawings, like numbers refer to like parts. The terms "cell," "electrochemical cell," and "battery" are used interchangeably, and may refer to a dry cell, an electrochemical cell, a battery, or a plurality of electrochemical cells, dry cells, or batteries, or the like. As used herein, directional terms such as "up," "down," "upper," "lower," "upwardly," "downwardly," "top," and "bottom" relate to the orientations shown on the drawings being discussed. Once a direction has been discussed with respect to a given element, that same orientation is held consistent for that element, even in e.g. FIGURE 6 where the orientation is reversed, unless otherwise specifically changed in a specific discussion. FIGURE 1(a) shows a pictorial exploded view of a prior art current collector assembly 10 used in a primary cylindrical alkaline manganese dioxide electrochemical cell manufactured by EVEREADY® Battery Company, Saint Louis, Missouri. Current collector assembly 10 comprises current collector 12, gasket or seal body 14, vent rupture control plate 16, gasket puncture plate 18, washer 20, rivet 22, and bottom plate 24. Current collector 12 is secured to the bottom side of seal body 14 by rivet 22, which is inserted through central opening 26 of seal body 14. Rivet 22 is in electrical contact with bottom plate 24. FIGURE 1(b) shows a cross-sectional view of the prior art current collector assembly of FIGURE 1(a) when assembled and disposed inside a cell, with the bottom (anode end) of the cell at the top of the FIGURE. Inner sidewalls 28 of cup-shaped cathode can 30 engage outer upstanding wall 34 of seal body 14. The open end edges of can 30 are crimped inwardly at 32 so that the distal edge 36, and proximate portions, of upstanding wall 34 is crimped between can 30 and the outer peripheral edge 38 of bottom plate 24, thereby forming a desirably tight bottom seal for the cell. Referring again to FIGURES 1(a) and 1(b), as the internal pressure becomes great enough, upstanding radial portions of the seal body, shown adjacent teeth 40 in FIGURE 1(b), engage teeth 40 of gasket puncture plate 18. As the internal pressure of the cell increases further, continued upward movement of seal body 14 pushes the thickness of seal body 14 past the ends of teeth 40. The generally immobile teeth 40 thus puncture seal body 14, making holes in the seal body. Once punctured, seal body 14 permits egress of gas through the holes, thereby relieving the pressure inside the cell. FIGURE 2(a) shows a pictorial exploded view of prior art current collector assembly 10 used in a primary cylindrical alkaline manganese dioxide electrochemical cell manufactured by RAYOVAC® Corporation of Madison, Wisconsin. As seen in FIGURE 2(a), current collector assembly 10 comprises current collector 12, gasket or seal body 14, washer 20, and bottom plate 24. When the internal pressure of a cell containing current collector assembly 10 of FIGURE 2(a) reaches a certain predetermined level, seal body 14 ruptures at thin-walled vent panel 46, permitting egress of gas from the cell, and thereby relieving pressure inside the cell. FIGURE 2(b) shows a cross-sectional view of the prior art current collector assembly 10 shown in FIGURE 2(a) when assembled and disposed inside a cell, with the bottom (anode end) of the cell at the top of the FIGURE. Inner sidewalls 28 of can 30 engage outer peripheral edges 34 of seal body 14. The open end edges of can 30 are crimped inwardly at 32 so that the distal edge 36, and proximate portions, of upstanding wall 34 is crimped between can 30 and the outer peripheral edge 38 of bottom plate 24, thereby forming a desirably tight bottom seal for the cell. An external impact force may be delivered to the outer surface of bottom plate 24 when a cell, or a flashlight containing one or more cells, is dropped to the ground or onto any hard surface. A cell containing a current collector assembly 10 of the embodiment of FIGURES 1(a) and 1(b) displays generally good resistance to impact forces delivered to the outer surface of bottom plate 24. Under normal impact force conditions, the integrity of seal body 14 is normally preserved, and the cell does not rupture or leak electrolyte as a result of such impact forces. Contrary to the embodiment of FIGURES 1(a) and 1(b), a cell containing a current collector assembly 10 of the embodiment shown in FIGURES 2(a) and 2(b) does not consistently display good resistance to impact forces delivered to the outer surface of bottom plate 24. FIGURE 2(c) shows the cell of FIGURE 2(b) after a downwardly directed impact force of relatively significant magnitude has been delivered to the outer surface of bottom plate 24. In FIGURE 2(c), the impact force has dented the central region 78 of the main body 66 of bottom plate 24 inwardly, pushing current collector 12 and central hub 44 inwardly of the cell, and thus detaching central hub 44 from the remainder of seal body 14 at vent panel 46. With the seal body 14 thus ruptured, electrolyte may leak from the cell of FIGURE 2(c) through ruptured vent panel 46. The seal body 14 of the cell of FIGURE 1(b) often does not rupture when impact forces act on bottom plate 24. However, the cathode assembly of the cell of FIGURE 1(b) contains 7 major components, namely current collector 12, seal body 14, vent rupture control plate 16, gasket puncture plate 18, washer 20, rivet 22, and bottom plate 24. The seal body 14 of the cell of FIGURE 2(b) does often rupture when impact forces act on bottom plate 24. However, the cathode assembly of the cell of FIGURE 2(b) contains only four major components, namely current collector 12, seal body 14, washer 20 and bottom plate 24. Thus, while the current collector assembly shown in FIGURES 1(a) and 1(b) exhibits robust performance respecting external impact forces, it is complex in design and has a relatively large number (7) of piece parts. By comparison, the current collector assembly shown in FIGURES 2(a) and 2(b) contains 42% fewer piece parts, thereby reducing inventory costs, parts costs, labor and manufacturing costs, and the like; but does not exhibit satisfactory tolerance for external impact forces. The foregoing description shows that known current collector assemblies which provide good resistance to external impact forces contain a relatively larger number of piece parts, are expensive to manufacture, and bear related higher unit costs. Known current collector assemblies which contain a relatively smaller number of piece parts, and which therefore are not unduly expensive to manufacture, do not provide acceptable resistance to external impact forces. What is needed is a current collector assembly which provides good resistance to external impact forces, but which also contains a relatively smaller number of piece parts. Referring now to FIGURES 3(a), 3(b), and 3(c), there is shown a current collector assembly 10 of this invention. The current collector assembly 10 includes seal body 14, current collector 12, washer 20, and bottom plate 24. Overall, seal body 14 is generally shaped like a disk, and is made from electrically nonconductive material. Seal body 14 generally comprises central hub 44, outer member 52, upstanding outer wall 34 depending from an outer edge of outer member 52, and vent panel 46 between central hub 44 and outer member 52. In seal body 14, central hub 44 has an upper surface 48, a lower surface 50, and central aperture 26. Aperture 26 extends between the upper and lower surfaces 48, 50, along a central axis 60 of the seal body, and respectively of the aperture 26. Aperture 26 has a length extending along the axis 60, and includes inwardly facing sidewall 64 extending along that length. Aperture 26 has upper and lower ends, corresponding with upper and lower ends of sidewall 64, adjacent upper and lower surfaces 48, 50 respectively. Outer upstanding wall 34 depends from the outer edge of outer member 52 and thus defines the outer perimeter of the seal body. Central hub 44 has a seat 62 generally below and adjacent upper surface 48 Outer member 52 has a top surface 54 and a bottom surface 56, and is generally disposed in an imaginary plane 58. Outer member 52 extends in a generally outward direction from central hub 44. Vent panel 46 can be disposed anywhere between hub 44 and the outer perimeter of seal body 14, and is here shown between hub 44 and an inner edge of the outer member. Vent panel 46 has a thickness "T1" less than a respective thickness "T2" between top and bottom surfaces 52, 54 of the outer member, and less than a respective thickness between the upper and lower surfaces of central hub 44. Thus, vent panel 46 has the smallest thickness of the major elements of the seal body. Accordingly, when pressure builds up inside a cell using the seal body of FIGURES 3(a)-(c), rupture of the seal body to relieve the pressure is effected by the seal body 14 being ruptured at vent panel 46. Suitable materials from which the seal body may be manufactured include plastics, such as, for example nylon, polypropylene, and filled polypropylene. Preferred material is nylon, especially injection molded nylon 6,6. Electrically conductive bottom plate 24 has a main body 66 generally lying in a second imaginary plane 68 which is aligned with outer member 52 of seal member 14, and respectively with first imaginary plane 58. An outer ring 70 depends downwardly from main body 66, and generally extends outwardly parallel to main body 66. A plurality of holes 72 extend through bottom plate inwardly of the outer edge of outer ring 70, and adjacent the outer edge of main body 66. A preferred material for use as the bottom plate in alkaline manganese dioxide primary cells is nickel plated low carbon cold rolled strip steel, number 2 finish, number 4 temper. Current collector 12 is an elongated electrical conductor, and generally resembles a nail. The current collector thus has a head 74, and an elongated shank 76 extending away from head 74. Preferably, the current collector 12, and especially the shank 76, is symmetrically shaped. Most preferably, shank 76 is shaped like a rod. The outer surface of shank 76 is preferably free of imperfections such as burrs, nicks, and scratches. Non-symmetrical current collectors may be used provided accommodating modifications are made in cooperating ones of the other elements of the current collector assembly 10. Current collector 12 can be made from a wide variety of conductive materials such as brass, zinc, zinc alloys, nickel plated steel, and tin plated steel. The material preferred for a given cell will depend on the other structural and chemical elements to be used in the cell. A preferred current collector for use in alkaline manganese dioxide primary cells is a nail made from 0.057" (1.4mm) Ø nickel brass wire which is electroless tin plated to a tin thickness of 0.08 µm after the current collector is shaped as shown in FIGURES 3(a)-3(c). Shank 76 has a cross-section slightly larger than the cross-section of aperture 26 in seal body 14. Shank 76 can be pushed through aperture 26, but only with a frictional engagement between sidewall 64 of aperture 26 and the outer wall of the shank. Head 74, at its top, is welded or otherwise secured physically and for electrical conduction, to a central region 78 of main body 66 of bottom plate 24. Washer 20 is generally disk-shaped, but has specific shape, material, and positioning requirements which provide it with physical properties critical to the invention. Preferred material for washer 20 is a metal disk stamped from 0.031" (0.8mm) thick hot-dip zinc coated, number 3 temper, galvanized cold rolled carbon steel. The resulting stamped washer has a generally uniform thickness, allowing for slight deformities from the stamp-forming process. Other materials, including other metal alloys, are contemplated as being suitable so long as then provide structural support to the bottom plate, and to seal body 14, as described herein. The washer of the prior art structure shown in FIGURES 2(a)-(c) is made from similar material but having the softer temper number 4. Washer 20 is generally aligned with outer member 52 of seal body 14, and thus is generally aligned with first and second imaginary planes 58, 68, and can be described as generally following its own imaginary plane 80, though with significant deviations on both sides of plane 80. The washer 20 is also aligned with the seal member across central axis 60. Outer ring 82 of washer 20 is generally parallel with plane 80, generally corresponds with and underlies outer ring 70 of the bottom plate (FIGURES 3(a)-(c)), and extends circumferentially about the washer. Central aperture 84 extends through the washer 20, centered on axis 60, and has an inwardly facing edge 86. As shown, the distance between aperture 84 and central region 78 of main body 66 is preferably less than the distance between outer ring 82 and the central region 78. Imaginary plane 80 generally passes through inwardly facing edge 86 of aperture 84. Circular plateau 88 extends upwardly between aperture 84 and outer ring 82, preferably closer to aperture 84 than to outer ring 82. Thus, upper surface 90 of the washer has a convex contour at plateau 88, and the lower surface 92 has a corresponding concave contour. In preferred embodiments, the inner and outer edges of plateau 88 define generally upstanding segments 94 of the washer extending circumferentially about significant portions of the circumference of the washer (referring to orientations shown in FIGURES 3(a)-3(c). In general, upstanding segments 94 intersect plane 80 at angles of at least about 30 degrees, preferably 45 degrees to 60 degrees. Angles up to 90 degrees are acceptable so long as the material can be formed without undue stress and cracking of the metal. Circumferentially inclined upstanding segments 94 reinforce the washer structurally against downward deflection when subjected to downwardly-directed forces. Thus, the upstanding segments 94 provide an I-beam type reinforcement to an otherwise rather flat washer. The overall effect of the upstanding segments is to increase resistance of the washer to bending at and adjacent the plateau 88. With plateau 88 positioned radially close to aperture 84, plateau 88 is in a good position to absorb impact forces focused toward the central region of main body 66. Preferred angles are around 45 to 60 degrees. These intermediate angles can be formed in a variety of suitable materials without excess stress and cracking, and provide the desirable I-beam rigidified effect. Preferred inner radius "R" on opposing sides of the upstanding segments 94 is 0.025 to 0.060" (0.63-1.5mm), with most preferred inner radius about 0.04" (1mm). In a preferred embodiment, plateau 88 is displaced from plane 80, and thus from aperture 84, by 0.06 to 0.08" (1.5-2mm) upwardly; while outer ring 82 is displaced from plane 80, and thus from aperture 84, by 0.025 to 0.045" (0.6-1.1mm). In all embodiments, plateau 88 is positioned radially sufficiently close to aperture 84 to provide physical structural support to bottom plate 24 in the central region thereof. The support should be effective to reinforce bottom plate 24 against impact forces against the outer surface of the bottom plate. In washer 20 of the invention, disclosed in FIGURES 3(a)-(c), pressure relief holes 96 are spaced outwardly from plateau 88 in order that the holes 96 not weaken the structural supporting effect of plateau 88. The function of washer 20 in conventional current collector assemblies as discussed above is to position and retain the seal body 14 at the desired location along central axis 60. In general, prior art current collector assemblies were directed at preventing deflection of the seal body, especially outwardly-directed deflection, toward bottom plate 24. Excessive such movement is known to result in leakage of electrolyte. Washers 20 of the invention maintain this traditional function while, in addition, providing primary structural support to bottom plate 24 against inwardly-directed impact forces imposed against the outer surface of bottom plate 24. Thus, in the prior art structures discussed above, the washer 20 is spaced too far from bottom plate 24 to provide structural support to bottom plate 24 in absorbing outside impact forces on the bottom plate until after the vent panel has been ruptured. In the invention, the washer is close enough to the bottom plate that the bottom plate moves a much shorter distance (e.g. 0.010"(0.25mm)) before contacting the washer. Further, the washer is stiffer, and more rigid than prior art washers. Thus, when a force is imposed against the bottom plate, the force is transferred to the washer more quickly (after a shorter distance of travel of the bottom plate), and the bottom plate is more effective in absorbing the force and distributing and dissipating the force within the battery structure without imposing such force on hub 44 to such an extent that the vent panel 46 ruptures. Further, as shown by the deflection tests represented in FIGURE 9, the washer of the invention is effective to resist gradually increased force essentially devoid of the impact feature. Thus, the force being resisted by washer 20 need not be an impact force, and can be a gradually applied force. In the prior art structure of FIGURES 1(a) and 1(b), the washer is spaced from bottom plate 24 by about 0.024" (0.6mm). In the prior art structure of FIGURES 2(a) and 2(b), the washer is spaced from bottom plate 24 by about 0.050" (1.3mm), and has a temper number 4, which is too soft to provide adequate support to base plate 24. In the invention herein, the washer 20 is structurally reinforced, as compared to conventional washers used in anode current collector assemblies, by means of the curvilinear cross-sectional shape, giving it its plateau contour, and by its harder temper. In addition, the plateau 88 is positioned sufficiently close to bottom plate 24 to provide primary structural support in absorbing an outside impact force against the outer surface of bottom plate 24. Further, the distance between axis 60 and plateau 88 is held sufficiently small that impact forces imposed generally on bottom plate adjacent axis 60 will be transferred to washer 20 without damaging movement of bottom plate against current collector 12. Thus, the inner radius of the plateau, adjacent bottom plate is desirably no more than 0.15 inch to 0.25" (3.8-6.3mm). In order that impact forces can be readily transferred from the bottom plate to washer 20, the top surface of plateau 88 is generally positioned within a distance "D" of 0.018" (0.46mm) from the inner surface of bottom plate 24. Preferred spacing between plateau 88 and bottom plate 24 is 0.003 to 0.015" (0.07-0.38mm). Spacings of between 0.006 and 0.012" (0.15-0.3mm) are most preferred. The most preferred spacings provide a good balance between (i) providing some assured spacing between washer 20 and bottom plate 24 and (ii) placing the washer sufficiently close to the bottom plate that the washer provides effective structural support to the bottom plate at impact. Comparative "D" is shown in Prior Art FIGURES 1(b) and 3(b) to illustrate areas of the cross-sections which can be compared. In the conventionally available product of the Prior Art shown in FIGURE 1A, 1B, "D" is about 0.024" (0.6mm). In the conventionally available product of the Prior Art, shown in FIGURE 2A, B, C, "D" is about 0.050" (1.3mm). Especially the 0.050" (1.3mm) spacing is inadequate to protect vent panel 46 from premature rupture. However, spacing greater than 0.018" (0.46mm) can protect vent panel 46 where the washer is sufficiently rigid as in the novel washers 20 disclosed herein. Thus, spacings up to about 0.030" (0.8mm) are contemplated, although the spacing is generally no more than about 0.024" (0.6mm). It is critical that the washer 20 be sufficiently hard and stiff in order to satisfactorily support bottom plate against impact forces. The hardness of the unsatisfactory control washer of FIGURE 2A, B, C is shown in Table 1, in comparison with the hardness of satisfactory washers as described for the invention. Washer Type Vickers Rockwell B Control 125 69 Invention 159 81 A preferred embodiment of the current collector assembly 10 of FIGURES 3(a)-(c) is assembled as follows. Head 74 of current collector 12 is welded to the inside surface of bottom plate 24, at the center of the bottom plate. The shaft 76 of the current collector is then inserted through aperture 84 of washer 20, and is driven through aperture 26 of the hub, accompanied by frictional engagement between the shank and the sidewall 64 of the aperture. A sealant is placed on the portion of the shank which will be under the head and protruding into the hub. Seal body 14 is coated with a synthetic rubber coating to protect the seal body from chemical action of the electrochemical reactants to be contained in the electrochemical cell. The current collector assembly is then complete, and ready for use in an electrochemical cell. Referring to FIGURE 3(b) wherein the current collector assembly has been assembled into an electrochemical cell, a central portion of washer 20 adjacent aperture 84, and including edge 86, is seated on seat 62 of hub 44, controlling the position of the hub 44, and thus of seal body 14. Washer 20 especially positions and retains the seal body against outwardly-directed pressures built up in the cell by e.g. chemical reactions taking place within the cell. In the embodiment of FIGURES 3(a)-(c), the edge 86 extends somewhat under the head 74 of current collector 12, providing direct support to the head 74 against forces directed inwardly against the bottom plate. However, in general, the washer need not extend under head 74 in order to provide the desired level of support for bottom plate 24 because the small radius of plateau 88 positions the plateau close enough to head 74 to provide adequate protection for the head in most situations. FIGURE 4(a) illustrates a second embodiment of washer structure wherein the aperture 84 has an opening sufficiently large to receive head 74 therethrough. Accordingly, in the embodiment of FIGURE 4(a) of the invention, washer 20 provides no direct support of the current collector itself. Rather, washer 20 protects the current collector by supporting bottom plate 24 adjacent head 74. FIGURES 3(a)-(c) and 4(a) illustrate washers wherein the structure from plateau 88 inwardly generally describes a stretched-out "S" shape. FIGURE 4(b) shows yet another embodiment of the washer wherein plateau 88 extends generally to the outer edge of head 74 and the inner upstanding segment 94 of the washer touches and directly supports head 74 at its outer radius. In this embodiment, the structure from plateau 88 inwardly generally describes a downwardly-opening "C" shape, wherein the final inwardly disposed horizontal portion of the washer adjacent edge 86 has been omitted. Accordingly, in FIGURE 4(b), edge 86 faces downwardly, rather than inwardly. FIGURE 5(a) shows detail of washer 20 from the top. FIGURE 5(b) shows an enlarged cross-section of the washer, especially illustrating plateau 88, and the height of plateau 88 above aperture 84. The current collector assembly as described above is incorporated into e.g. an alkaline manganese dioxide electrochemical cell as follows. An appropriate number of rings 98 of manganese dioxide cathode material are stacked in a cathode can 30. A separator 100 is then inserted inside the manganese dioxide rings. An appropriate amount of zinc anode material 102 is then placed inside the separator, the combination of anode material, cathode material, and separator then generally filling the cathode can. The anode current collector assembly 10 is then placed in the can, driving the shank 76 of the current collector 12 into the anode material 102. This brings the shank into electrical contact with the zinc anode material, and brings the coated bottom surface 56 of outer member 52 of seal body 14 into sealing contact with the manganese dioxide cathode material, separator 100, and the zinc anode material. The outer edges of upstanding wall 34 engage inner sidewalls 28 of the can. The can 30 is then crimped at groove 104 adjacent seal body 14; and the distal ends of the cathode can are crimped inwardly at 32. The distal edge 36 and proximate portions, of sidewall 34 is then crimped inwardly. This urges the ends of the can material, and the distal edge 36 and sidewall portions of outer upstanding wall 34 against the outer circumferential edge of bottom plate 24, and indirectly against the outer circumferential edge of washer 20. This crimping completes the closure of the cell, including the incorporation of the anode current collector assembly 10 into the cell, thereby forming a desirably tight bottom seal for the cell. The cathode plate 106, including the contact nubbin, is secured to the closed bottom of the cathode can as appropriate. FIGURE 6 illustrates the finished cell just described. As seen therein central axis 60 of the current collector assembly 10 also serves as the central axis of the cell. Plateau 88 has been described and illustrated as circular, encompassing aperture 84. Plateau 88 comprehends a variety of configurations, only one of which is illustrated. The critical parameters respecting plateau 88 are its location, the stiffening properties provided by the upstanding segments 94, and the hardness of the tempered washer. Plateau 88 need not be circular. It does not need to completely enclose aperture 84. It does not need to be circumferential in nature. It can be discontinuous. It does need to be close enough to aperture 84 that it supports the bottom plate adjacent head 74 and axis 60. TESTING All testing on cells as described below was conducted using "D-size" cells. The control cells used washers as described with respect to the FIGURE 2(a)-(c). Temper of the control washers was temper number 4. Current collector assemblies as described above with respect to FIGURES 3(a)-(c) were made and drop tested using test apparatus illustrated in FIGURE 7. The standard test for evaluating the bottom current collector assembly is one 3' (0.91 m) drop of the cells in a 3-cell flashlight. The dropped flashlight is left "on" to discharge the cells, thus enhancing the possibility of leakage. A laboratory drop test apparatus was built to simulate drop testing in a flashlight. While the instrument provided a controlled test method, it did not completely duplicate the effect of one cell impacting upon another in a flashlight. When a flashlight is dropped, part of the force of impact against the bottom plate is absorbed by the deformation of the impacting cell's cathode nubbin and can bottom. The laboratory drop test used a solid steel nubbin 240 on a steel slide 220 (same weight as a standard "D-size" cell) mounted on a track 230 using wheels 225. The cell being tested was supported from the bottom by support block 210. In the drop tests, the slide 220 was dropped onto the bottom plate 24 of the cell from heights of 1 to 4' (0.3-1.2m). FIGURE 7 shows the cell in terms of the position of current collector assembly 10. Cells having current collector assemblies of the invention as described above with respect to the FIGURE 3 series, and prior art current collector assemblies described with respect to the FIGURE 2 series, were tested. After the drop, the amount of denting in the bottom plate was measured. The cells were then opened and the vent panels 46 checked for rupture. For the control cells of the FIGURE 2 series, the effect of a 3' (0.91m) drop using the laboratory tester correlated well with the same drop of a 3-cell flashlight. In both cases, the bottom plate was dented about 0.07" (1.8mm), and the vent panel 46 was ruptured. For cells with the washer 20 of the invention, the laboratory drop test caused greater damage than did the flashlight drop test. The magnitude of denting with the laboratory test was double the denting with the flashlight drop test, and some vents were ruptured. However, the denting was less severe, and rupturing was less frequent, using the washers of the invention. FIGURE 8 shows graphically the results of the testing. As seen therein, the cells using the washers of the invention had significantly less denting than cells using the control washer. At 2' (0.61m) drop height, the cells of the invention had vent panels intact after the drop, while the vent panels in cells using the control washer had ruptured. Another test was conducted to illustrate differences between the washer 20 of the invention and washers used in prior art current collector assemblies. In this test, increasing force was gradually applied to the center of the washer over an area equivalent to the size of the positive nubbin on a standard "D-size" cell. The washers were supported on their bottom surfaces at their outer edges. The deflection of the washer was recorded as a function of the force applied. FIGURE 9 shows the results graphically. As seen therein, control washers of the prior art (FIGURE 2 series) began to yield significantly at less than 50 pounds of force, while the washers of the invention did not exhibit any significant yield until about 200lbf (91kgƒ) was applied. Cells of the invention were also subjected to comparative flashlight drop testing. A 3-cell flashlight was dropped from a predetermined height with the flashlight left "on." The standard test was modified by opening the cells after completing the specified number of drops, and inspecting the cells to determine vent damage. Only the cell at the lens end of the flashlight was examined. The results show that repeated drops do proportionately less damage than the initial drop, perhaps because the nubbin of the impacting cell is also partially crushed by the impact of the first drop. Table 2 following illustrates the relative difference between the depth of crush in cells of the invention and in control cells. Corresponding results are shown graphically in FIGURE 10. Bottom Plate Type Test Washer No. Cells Depth of Crush No. Ruptured Vent Panels One 3-Foot Drop Control 3 0.070 inch 3 One 3-Foot Drop Invention 3 0.011 inch 0 Three 3-Foot Drops Control 3 0.081 inch 3 Three 3-Foot Drops Invention 3 0.017 inch 0 3-foot = 0.91m; 0.070" = 1.8mm; 0.011" = 0.28mm; 0.081" = 2mm 0.017" = 0.43mm; FIGURE 3(c) shows the cross-section of the embodiment of FIGURES 3(a) and 3(b) after the bottom plate has received an impact force such as described herein with respect to testing. As seen therein, the washer, including the central portion of the washer at aperture 84, is in substantially the same place as before the impact force was applied. This can be seen by comparing the position of the washer in FIGURE 3(c) with that depicted in FIGURE 3(b). Referring to FIGURE 3(c), hub 44 has been moved slightly downwardly on shank 76. The amount of downward movement has been exaggerated in FIGURE 3(c) in order that the difference be readily noticeable. This downward movement of the hub results in outer member 52 extending from upstanding wall 34 toward the hub at a downward angle, seen in FIGURE 3(c). However, vent panel 46 remains intact, preventing electrolyte leakage while being available to vent internal cell pressure if necessary. FIGURE 11 further illustrates the unexpected benefits obtained using washers of the invention. As mentioned above, it is critical that vent panels 46 rupture when the pressure in the cell reaches a predetermined value. Speaking generally to standard "D-size" cells, the vent panels should rupture at pressures of 280 to 440 psig (19.3-30 bar). Cells of the invention (FIGURE 3(a)-(c) were subjected to pressure testing, along with control cells which used washers of the FIGURE 2 (a)-(c). Twenty five cells each were tested for the control structure and the invention structure. Except for the washer design, and the minor differences in the design of hub 44, comparing e.g. FIGURES 2(b) and 3(b), the cells were identical. Table 3 shows the number of cells rupturing at each pressure level tested. FIGURE 11 shows the same results as a bar chart. Table 3 follows immediately hereafter. Burst Pressure, psig Number of Washers Having Ruptured Vent Panels (bar) Control Invention 360 (24.8) 1 380 (26.2) 1 8 400 (27.6) 1 12 420 (28.9) 1 4 440 (30.3) 1 460 (31.7) 1 480 (33.1) 500 (34.5) 520 (35.8) 540 (37.2) 560 (38.6) 580 (40.0) >600 (41.3) 20 Total No. of Cells Tested 25 25 As shown in Table 3 and FIGURE 11, the vent panels in the cells of the invention all ruptured within the desired range whereas the vent panels in only 5 of the control cells ruptured in the desired range. The remainder of the cells did not rupture at pressures up to 600 psig (41.3 bar). For the control cells, only 20% of the vent panels functioned properly. It is entirely unexpected that modifying the washer 20 as done in the invention would improve proper activating of the vent panels 46. The particular embodiments of the present anode current collector assemblies have robust resistance to external impact forces in combination with few piece parts and corresponding economical assembly. Such current collector assemblies can be used for a wide variety of primary and rechargeable electrochemical cells, and may be used in any dry cell characterized by having any known electrochemical system. Although only a few exemplary embodiments of this invention have been described in detail above, many modifications are possible in the exemplary embodiments without materially departing from the teachings herein. It is noted herein that shank 76 of current collector 12 can be somewhat smaller in cross-section than the aperture 26 in hub 44. In such embodiments, glue or other bonding or adhesive material can be used to secure the shank to sidewall 28. Accordingly, in such embodiments, the outer wall of shank 76 may not directly engage the sidewall 28 of the aperture. Further, while the shank 76 has been illustrated as rod-shaped, the shank can accommodate a variety of shapes at its outer surface, including for example serpentine shape, screw threads, and flat sided cross-sections. Hub 44 has been illustrated as having a seat 62 receiving the inner edge of washer 20 adjacent- aperture 84. In other embodiments, hub 44 can have a groove in a side wall of the hub, as illustrated under the head of rivet 22 in prior art FIGURE 1(b), receiving edge 86 of aperture 84. The inner edge and aperture 84 are, of course, sized accordingly to fit into such groove. As seen above, prior art current collector assemblies relied on the bottom plate to absorb inwardly-directed impact forces. By contrast, current collectors of the invention rely primarily on the washer 20 to absorb such forces. The improved washer is more rigid, harder, and more sculptured than prior art washers. Because of the design features of washer 20 of the invention and close proximity of the plateau to bottom plate 24, the washer 20 gives support to the bottom plate after less deflection of the bottom plate, and provides a stiffer and less deflectable resistance than the softer and less rigid washers of the prior art. As used herein and in the claims following, phrases referring to the washer "supporting the bottom plate" against inwardly-directed force include the washer being in contact with the bottom plate, and all spacings of the washer from the bottom plate wherein the washer provides primary support against inwardly imposed impact forces. Typically, such primary support is sufficient that the vent panel is not ruptured by a single 3' (0.91m) drop test of a 3-cell flashlight, and premature leakage of electrolyte by failure of a vent panel or other element of the seal body, is avoided or attenuated.

Claims: A current collector assembly (10) for closing and sealing a cup-shaped container (30) having electrochemically active materials therein, for thereby forming an electrochemical cell, and for collecting current from the electrochemically active materials contained therein, said current collector assembly comprising: (a) a resilient and electrically non-conductive seal body (14) having an opening (26) extending therethrough; (b) a current collector subassembly including (i) a current collector (12) inserted through the opening (26) in the seal body (14) and for insertion into one of the electrochemically active materials, and (ii) a bottom plate (24) for closing the cell at the cup-shaped container (30) and for providing a portion of the outer surface of the cell, said current collector providing electrical continuity between the electrochemically active material and an outer surface of the cell at said bottom plate; and (c) a structurally reinforcing washer (20) between said seal body (14) and said bottom plate (24), said washer comprising a rigid disk having a structurally reinforcing shape providing sufficient strength to protect said bottom plate against inwardly-directed force imposed on said bottom plate. A current collector assembly as in Claim 1 wherein said washer (20) provides primary structural support protecting said current collector assembly (10) against inwardly-directed impact forces. A current collector assembly as in Claim 1 or Claim 2 wherein said washer (20) is spaced no more than about 0.018 inch (0.46mm), preferably no more than about 0.015 inch (0.38mm) and more preferably between about 0.003 inch (0.08mm) and about 0.012 inch (0.30mm), for example between about 0.006 inch (0.15mm) and about 0.012 inch (0.30mm) from said bottom plate (24). A current collector assembly as in Claim 1, 2, or 3, said current collector assembly (10) positioning and retaining said seal body (14) against outwardly directed force disposed inside the cell. A current collector assembly as in any of Claims 1 to 4, wherein said washer (20) has upstanding arcuate segments (94) thereof providing structural reinforcement and bending resistance to said washer. A current collector assembly as in any of Claims 1 to 4, wherein said washer (20) has a central aperture (84), the structurally reinforcing shape comprising a plateau (88) extending effectively about the aperture in a curvilinear pattern, and having upstanding, radially arcuate segments (94) thereof disposed adjacent said aperture, said upstanding arcuate segments providing structural reinforcement and bending resistance to said washer (20). A current collector assembly as in any preceding Claim, said washer (20) facilitates proper venting of a vent panel (46) in said seal body (14). A current collector assembly as in any preceding Claim, wherein said washer (20) protects a vent panel (46) in said seal body (14) against being prematurely activated by inwardly-directed impact force applied at said bottom plate. A current collector assembly (10) for an electrochemical cell, said current collector assembly comprising an electrically insulating seal body (14), an elongate electrically conductive current collector (12) secured on one end thereof to an electrically conductive bottom plate (24), and a generally disk-shaped washer (20), said seal body (14) having a central hub (44), a vent element (46), and an outer member (52) extending in an outward direction from said hub (44), said hub (44) having a first aperture (26) extending therethrough centrally disposed about and along a central axis (60) of said current collector assembly, the first aperture (26) having a length extending in the direction of the central axis, an inwardly facing sidewall (64) extending along the length, said hub (44) further comprising a surface (62) extending thereabout receiving said washer, at least a portion of said vent element (46) having a first thickness measured along the direction of the central axis, less than a respective second thickness through one of said hub and said outer member, said vent element (46) rupturing and thereby enabling egress of material therethrough when pressure exerted on the said seal body (14) at said vent exceeds a predetermined value, said current collector (12) having an elongate circumferential surface (76) extending through the first aperture (26) and frictionally engaging the inwardly facing sidewall (64) of the first aperture, said electrically conductive bottom plate (24) having a central region (66), and a second outer perimeter (70) contiguous with said central region, and being generally aligned with said seal body across the central axis, and said disk-shaped washer (20) being generally aligned with said seal body (14) across the central axis, said washer comprising a rigid disk having a structurally reinforcing shape, said washer having first and second upper and lower opposing surfaces (90, 92), and a third thickness therebetween, said washer having a first outer perimeter (82), and a second aperture (84) comprising an inwardly facing edge (86) thereof centered about the central axis and received and engaged by the receiving surface (62) of said hub (44), the first upper surface (90) of said washer (20) having a convex contour and the second lower surface (92) having a corresponding concave contour, between the second aperture (84) and the outer perimeter (82), said washer (20) providing primary support to said bottom plate (24) against inwardly-directed forces on said bottom plate (24), and thus protecting said vent element (46) against premature rupture. A current collector assembly (10) for an electrochemical cell, said current collector assembly comprising: (a) an electrically insulating seal body (14) having a first upper surface (48), a second lower surface (50), a central hub (44), a vent element (46), and an outer member (52) disposed substantially in a first imaginary plane and extending outwardly of said hub (44) to a first seal body outer perimeter, said hub (44) having a first aperture (26) extending therethrough centrally disposed about a central axis (60) of said seal body, said hub having one of a seat (62) and a groove on the first upper surface (48), the first aperture (26) having inwardly facing sidewalls (64), a first top end proximate the top surface (48), and second opposing bottom end proximate the bottom surface (50), and a length therebetween, said vent element (46) being disposed between said hub (44) and the outer perimeter, at least a portion of said vent element (46) having a first thickness measured along the direction of the central axis, less than a respective second thickness through one of said central hub (44) and said outer member (52), said vent panel (46) rupturing and thereby enabling egress of gas therethrough when said outer member (52) and said inner hub (44) are held substantially stationary and pressure exerted by a gas on the second lower surface exceeds a predetermined value; (b) an elongate electrically conductive current collector (12) having a third top end (74), an outer peripheral sidewall (76) extending through the first aperture (26) in alignment with the central axis to a fourth bottom end (24), the third top end (74) being proximate the first top end (25), said outer peripheral sidewall (76) of said current collector engaging the inwardly facing aperture sidewalls (64); (c) a substantially disc-shaped washer (20), disposed in general alignment with the first horizontal plane, the washer having an outer washer perimeter (82), a second aperture (84), comprising an inwardly facing edge (86) thereof centered about the central axis, and an upwardly disposed surface (88) between the second aperture (84) and the outer perimeter, and generally encompassing the second aperture (84), said inwardly facing edge (86) of said second aperture (84) being engaged by said one of said seat and said groove, said disk-shaped washer comprising a rigid disk and a structurally reinforcing shape, providing structural support to protect said bottom plate (24) against inwardly-directed force; and (d) an electrically conductive bottom plate (24) disposed in general alignment with the first horizontal plane, said bottom plate having a central region (66), a fifth upper surface, a sixth lower surface, and a thickness therebetween, and a second outer perimeter (70), the central region (66) extending outwardly from the central axis (60) toward the second outer perimeter (70), the second outer perimeter being contiguous with the central region (66). A current collector assembly (10) for closing and sealing a cup-shaped container (30) having electrochemically active materials (98, 102) therein, for thereby forming an electrochemical cell, and for collecting current from the electrochemically active materials contained therein, said current collector assembly comprising: (a) a resilient and electrically non-conductive seal body (14) having an upstanding wall (34) and an opening (26) therethrough; (b) a current collector subassembly including (i) a current collector (12) inserted through the opening (26) in the seal body (14) and for insertion into one of the electrochemically active materials (102), and (ii) a bottom plate (24) for closing the cell at the cup-shaped container (30) and for providing a portion of the outer surface of the cell, said current collector providing electrical continuity between the electrochemically active material (102) and an outer surface of the cell at said bottom plate (24); and (c) a washer (20) between said seal body (14) and said bottom plate (24), said washer having a central aperture (84), said washer (20) comprising a rigid disk and a structurally reinforcing shape comprising circumferentially inclined upstanding radially arcuate segments (94) providing structural strength to protect said bottom plate (24) against inwardly-directed force. A current collector assembly (10) for closing and sealing a cup-shaped container having electrochemically active materials (98, 102) therein, for thereby forming an electrochemical cell, and for collecting current from the electrochemically active materials contained therein, said current collector assembly comprising: (a) a resilient and electrically non-conductive seal body (14) having an opening (26) therethrough, and a closed and sealed vent panel (46) for venting gaseous pressure at a predetermined pressure level; (b) a current collector subassembly including (i) a current collector (12) inserted through the opening (26) in the seal body (14) and for insertion into one of the electrochemically active materials (102), and (ii) a bottom plate (24) for closing the cell at the cup-shaped container (30) and for providing a portion of the outer surface of the cell, said current collector (12) providing electrical continuity between the electrochemically active material (102) and an outer surface of the cell at said bottom plate (24); and (c) a washer (20) between said seal body (14) and said bottom plate (24), said washer comprising a rigid disk having a central aperture (26) and an outer perimeter (82), and a structurally reinforcing shape comprising an upstanding radially arcuate segment (94) extending upwardly about said washer (20) between the central aperture (26) and the outer perimeter (82), said segment providing structural support to protect said bottom plate (24) against inwardly-directed force, thereby protecting said vent panel (46) against premature rupture in response to inwardly directed force imposed against said bottom plate (24). A current collector assembly (10) for closing and sealing a cup-shaped container (30) having electrochemically active materials (98, 102) therein, for thereby forming an electrochemical cell, and for collecting current from the electrochemically active materials contained therein, said current collector assembly comprising: (a) a resilient and electrically non-conductive seal body (14) having an opening (26) extending therethrough; (b) a current collector subassembly including (i) a current collector (12) inserted through the opening (26) in the seal body (14) and for insertion into one of the electrochemically active materials (102), and (ii) a bottom plate (24) for closing the cell at the cup-shaped container (30) and for providing a portion of the outer surface of the cell, said current collector (12) providing electrical continuity between the electrochemically active material and an outer surface of the cell at said bottom plate (24); and (c) a washer (20) between said seal body (14) and said bottom plate (24), said washer (20) comprising a rigid disk having a central aperture (26) and an outer perimeter (82), and a structurally reinforcing shape comprising an upstanding radially arcuate segment (94) extending upwardly between said central aperture (26) and said outer perimeter (82), thereby positioning an upper portion of said washer (20) no more than about 0.03 inch (0.76mm) from said bottom plate (24), said upstanding radially arcuate segment (94) and said upper portion thereby supporting said bottom plate (24) against inwardly-directed force, and thus shielding said current collector (12) from the effect of such inwardly-directed force. An electrochemical cell made with a current collector assembly as in any of the preceding claims.

Inventors: DAVIDSON GREGORY J, KENYON KENNETH H, PASSANITI JOSEPH L, DAVIDSON, GREGORY J., KENYON, KENNETH H., PASSANITI, JOSEPH L.
Applicants: RAY O VAC CORP, RAYOVAC CORPORATION
Application year: 1996
Main classification: H01M2
IPC codes: H01M2