Method of making a galvanic cell having a resealable vent closure

#This invention relates to sealed galvanic dry cells, and more particularly to a low pressure resealable vent for releasing excessive gas pressure from inside the dry cell. The invention also relates to a method for making galvanic dry cells having resealable vent closures.

#Galvanic cells may generate large quantities of gas under certain conditions during use. Since these cells are required to be tightly sealed at all times in order to prevent loss of electrolyte by leakage, high internal gas pressures may develop. Such pressures may cause leakage, bulging or possible explosion of the cell if not properly vented. If a vent valve is employed, it must be resealable in order to avoid drying out of the electrolyte over the life of the cell and to prevent ingress of oxygen from the atmosphere which can cause wasteful corrosion of the anode.

#In the past, several different types of resealable pressure relief vent valves have been used for releasing high internal gas pressures from inside a sealed galvanic cell. One type of valve that has been commonly used consists basically of a valve member such as a flat rubber gasket which is biased into sealing position over a vent orifice by means of a resilient member such as a helical spring. The resilient member or spring is designed to yield at a certain predetermined internal gas pressure so as to momentarily break the seal and allow the gas to escape through the vent orifice.

#The present invention will become more apparent from the following description thereof when considered together with the accompanying drawings which are set forth as being exemplary of embodiments of the present invention and are not intended, in any way, to be limitative thereof and wherein:

#FIG. 1 is a sectional elevation taken through a partially assembled dry cell showing the cathode mix and the cathode collector rod within a container anode.

#FIG. 2 is a similar view of the partially assembled cell of FIG. 1 except that an elastomeric sponge gasket is shown slid over the cathode collector rod and resting on the edge of the container;

#Referring in detail to FIG. 1, there is shown a partially assembled typical galvanic dry cell including a cylindrical container 2 which is made of an electrochemically consumable metal such as zinc and which serves as the anode for the cell. The cell container 2 includes therein a cathode depolarizer mix cake 4 containing, for example, manganese dioxide, a conductive material such as carbon black and an electrolyte. The cathode depolarizer mix cake 4 could be molded around a central cathode collector rod 6 or the cathode depolarizer mix 4 could be fed into container 2 as a wet mix containing virtually all of the cell's electrolyte and then the cathode collector rod 6 forced down into the center of the depolarizer mix 4. The cathode collector rod 6 could be a carbon rod impregnated with a wax or an organic resin to render it both liquid and gas impermeable. Whether the depolarizer mix is molded into a bobbin type structure in a separate operation prior to cell assembly or fed directly into the container 2 and packed therein, the cathode collector rod 6 is inserted into the depolarizer mix 4 such that its end protrudes through the open end of the container 2. A separator 8 surrounds the cathode depolarizer mix 4 and separates it from the inner side wall of the container 2 while a bottom cup separator 10 separates the depolarizer mix 4 from the bottom inner surface of the container 2. The separator may be a thin film separator, e.g., a thin bibulous paper coated with a paste. The top of the separator 8 is shown folded down on the depolarizer mix 4 thereby leaving the usual air space 12 to accommodate any liquid spew that may be formed on discharge of the cell.

#FIG. 2 shows the same numbered components of FIG. 1 with the addition of an elastomeric sponge annular gasket 14 having an opening 16 at its center and being disposed on top of the container 2 with the collector rod 6 projected through said opening 16. Since annular gasket 14 is made of a resilient material, the diameter of opening 16 could be less than the diameter of the cathode collector rod 6 whereupon the gasket 14 could then be forced over and onto rod 6.

#FIG. 3 shows the same numbered components of FIG. 2 with the addition of a plastic closure or cover 18 molded with an electrode terminal cap 20 at its center. The cover 18 should be a rigid structure and would usually be made of plastic. As shown in FIG. 3, the cover side wall 22 is tapered slightly inwardly and has a circular recess or opening 24 defined by a portion of the inner wall 26 of cover 18 and the inner surface 27 of terminal cap 20. In assembling the cover-cap members 18-20 into the cell, the cover-cap members 18-20 are first aligned with the recess 24 over rod 6 and then the members 18-20 are forced downward on top of the elastomeric sponge gasket 14 thereby inserting the gasket 14 and members 18-20 into the container 2. During the insertion of members 18-20 into container 2, the gasket 14 is compressed between the cover side wall 22 and the inner upper wall 28 of container 2. Specifically, the peripheral segment 30 of gasket 14 is compressed between the inner upper wall 28 of container 2 and the cover side wall 22. Optionally, a thin film of a grease may be applied to the cover side wall 22, the top and/or bottom surface of the peripheral segment 30, and/or the inner wall 28 of container 2 prior to assembly to aid in the vent sealing of the cover-gasket interface and/or gasket-container wall interface.