Development of silica based coatings on zinc particles for improved oxidation behavior in battery applications

ZnO and Zn(OH)2 layers formed on zinc metal upon contact with aqueous media, like 6 M KOH electrolyte used in zinc air batteries, do not provide sufficient protection against further zinc oxidation leading to hydrogen evolution as well as self-discharge of the battery itself. In this work, the syntheses of artificial coatings based on silica, SiO2, were investigated, which should improve zinc metal oxidation stability to reduce aqueous corrosion of battery grade zinc particles. For synthesis of silica coatings the precursor tetraethyl orthosilicate (TEOS) was used. Chemical vapor deposition (CVD) in synthetic air and chemical solution deposition (CSD) under argon in polyol media were used for synthesis of these coatings on zinc under different thermal conditions. Zinc silicate formation was observed upon CVD while silica was formed upon CSD. The capability of the silicate based coatings to enhance oxidation resistance of zinc was analyzed via volumetric measurement of hydrogen evolution upon wet corrosion in 6 M KOH. Thermodynamic calculations were used to analyze the composition of the synthesized coatings and their compositional changes in concentrated KOH. As a result, silicate based coatings are able to reduce zinc corrosion by almost 40% by formation of protective layers in 6 M KOH. These results were confirmed by hot air corrosion tests.