No abstract

The capacity of seawater activated batteries containing magnesium anodes is often limited by clogging. During discharge the space between the electrodes of the cells nearest to the negative terminal gradually fill with an insoluble precipitate that replaces the seawater electrolyte and reduces battery capacity.The problem of clogging has been encountered in both high and low discharge rate batteries. In batteries designed for high rate (15 min) applications, the electrolyte is forced through each cell. In these applications, the flow of electrolyte is usually sufficient to flush the insoluble precipitate from the cells. However, Faletti and Nelson (1) found that the use of AZ61 magnesium anodes which had not been properly heat treated resulted in the formation of an adherent precipitate during high rate discharge. This precipitate could not be flushed from the affected cells and caused a reduction in battery capacity.Clogging is usually more severe in batteries designed for low rate applications. In these batteries the electrolyte is not forced through the cells and there is a greater tendency for the precipitate to build up and reduce capacity. This problem was encountered during the development of a low rate (6 hr, 150 mA constant current discharge) 10 cell, 15V, AgC1/Mg seawater battery at the Naval Ordnance Laboratory, White Oak, Maryland. When prototype batteries were discharged in seawater, a flocculent adherent precipitate formed that gradually filled the space between electrodes in those cells nearest to the negative terminal of the battery. The precipitate also formed outside these cells and blocked the bottom water-entry holes. This condition limited the capacity to less than half of that theoretically available. However, when similar batteries were discharged in aqueous sodium chloride of equal salinity, a granular nonclogging precipitate was formed. This fine precipitate together with hydrogen gas escaped through the top port hole of each negative cell. As a result, the capacity of these batteries was two to four times greater than those discharged in seawater.