Zinc Electrode Morphology in Alkaline Solutions: II . Study of Alternating Charging Current Modulation on Pasted Zinc Battery Electrodes

Abstract

The dependence of the faradaic conductance and the morphology of pasted zinc electrodes on the charging method has been investigated. The charging methods included d.c. (3–125 mA‐cm2) and d.c. (3–125 mA‐cm2) with superimposed square waves of a.c. of various amplitudes and frequencies (0.1–5000 Hz). In the case of d‐c charging, the faradaic conductance goes through a maximum at ∼75 mA‐cm2. The decrease in the faradaic conductance at higher current densities (100 mA‐cm2) is related to the formation of dense zinc deposits on the electrode surface. At low d.c. (<30 mA‐cm2), superimposition of a.c. promotes growth of zinc close to the current collector and results in small amounts of dispersed hexagonal zinc deposits on the current collector. Except where dense deposits are formed at high current density, the remainder of the zinc deposit has a very fine structure. Pulsed charging at low current densities (<30 mA‐cm2) is beneficial in that it increases the electrode faradaic conductance and promotes growth of the zinc deposit close to the current collector. The relaxation time for the double layer in pasted zinc electrodes is ∼50 msec. This indicates that the optimum frequency for pulsed charging is between 1 and 10 Hz.