Electrochemical cell safety vent

Abstract

A safety vent is provided for incorporation into sealed electrochemical cells. The vent is particularly applicable to cells experiencing transient conditions producing pressures above 250 psi (17.6 kg/cm.sup.2). By configuring a cover plate to plastically deform at elevated pressures, an increased venting area can be produced. The increased venting area allows for venting of solid matter which may be forced into vent holes during high temperatures and pressures. Effective plastic deformation is obtained by proper selection of a ductile material and cover plate thickness. By ensuring that vent clogging does not occur, pressures are limited and the integrity of the cell is maintained. By incorporating this vent into a cell, methods of successfully passing industry standard test procedures for secondary cells are provided. The vent also includes an elastomeric sealing element which is captured between the cover plate and a rigid upper plate. The upper plate has a skirt that covers the sealing element but is lifted out of the way of vented matter by the deforming cover plate. Testing of example nickel-metal hydride based Cs cells demonstrate successful survival of a 'hot plate' and 'continuous overcharge' test procedures. The invention includes cells having increased safety by incorporation of the novel vent structure.