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Several approaches have been tried to reduce Al corrosion in primary and secondary alkaline batteries. The most successful to date has been the addition of ZnO to the electrolyte, which results in the spontaneous deposition of a protective metallic Zn film on the Al surface. However, there is a limited understanding in the literature of the structure of this Zn film and how that structure (i) influences the protection of Al, and (ii) is influenced by the electrolyte composition. This work aims to develop a fundamental understanding of the protection mechanism against Al corrosion when zincate is added to KOH electrolytes. This was accomplished through morphological studies of the resulting Zn film using SEM, XRD, N2 adsorption, and measurements of H2 gas evolution as well as electrochemical characterization during discharge. It was found that adding saturated ZnO to KOH electrolytes provides the most protective Zn film with good adherence and high density, which can lower the Al corrosion rate by 2 orders of magnitude. Moreover, configurations with a capacity near the Al theoretical capacity were achieved. [ABSTRACT FROM AUTHOR]