Abstract: A formation procedure for a NiMH electrochemical cell is disclosed that significantly shortens the time required to fully form such a cell. The formation procedure includes a first step during which the cell is charged at a constant voltage of preferably 1.0 volt for approximately three hours. A second charging step is performed by applying either a constant charge current at a predetermined rate of C/3 for five hours or applying a constant voltage of 1.45 to 1.5 volts for five to nine hours. A third step may optionally be used whereby the cell is charged at a constant current of C/10 for about two hours. NiMH cells subjected to this formation procedure have a much greater percentage of the starting cobalt material in the positive electrode converted to CoOOH thereby improving the conductive matrix formed about the Ni(OH)2/NiOOH particles, which constitute the active material of the positive electrode.

Abstract: A cell grading test fixture includes an array of cell sockets electrically interconnected in series so that current through the entire array of cells flows through each of the cells once inserted into the fixture. Associated with each socket is an indicator which indicates to the operator when a cell voltage has fallen to a predetermined level. Each socket of the test fixture includes a spring-loaded switch contact such that upon removal of a cell which has dropped below a threshold voltage, the movable contact engages the contact of an adjacent socket, shorting out the cell location such that the series circuit of cells continues to provide a current path for the remaining cells.

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.