AN ACCOUNT OF THE DEVELOPMENT OF THE FIRST VALVE-REGULATED LEAD ACID CELL/

In 1967 work was begun on the research and development of small, cylin drical lead/acid cells containing spirally-wound electrodes. Four year s later the resulting products were offered for sale: a cell equivalen t in size to the conventional manganese dioxide D-cell, and another ha ving twice the capacity. These cells were the first to use a separator material consisting of microfiber glass paper, now generally termed ' absorbent glass mat'(AGM). The sulfuric acid electrolyte incompletely saturates this separator, permitting oxygen gas transport directly thr ough the separator to react with the sponge lead negative plate during overcharge of the cell. Thus, a recombination reaction is achieved wh ich is analogous to that used in the sealed nickel-cadmium cell. A num ber of technical developments were incorporated, including substantial compression of the plate-separator assembly. This greatly lengthened the service life of these first 'valve-regulated' cells. In the follow ing years, many sizes of rectangular batteries, using the principles d escribed, have been manufactured throughout the world.