Impedance of Silver Oxide‐Zinc Cells

Abstract

Over 100 sealed cells were subjected to prolonged periods of storage over a range of temperatures and storage modes including open circuit, trickle charge, and float charge. Impedances of these cells were monitored throughout and to the end of the storage period at which point their transient voltage characteristics were observed at the onset of discharge. Results revealed that the impedances of these cells tended to increase with time on stand and that the magnitude of the impedance rise was dependent primarily on temperature and to a lesser degree on storage mode. Typical values for 50 A‐hr cells were usually less than 100 mohm at time zero (immediately after activation) and from 1 to 30 ohm after 6–10 months of storage. Transient voltages of these cells were noted to drop sharply during the first msec of discharge and then to rise and reach a stabilized value during the following few seconds. Magnitude of the initial drop as well as the stabilized voltage values were found to be related to impedance but not in a linear manner. Magnitude and duration of the low transient voltages may be unacceptable in some applications of these cells. Cause for the impedance variations is attributed to changes that occur at the positive electrode. Results provide new and useful information for designers and users of power systems.