Investigation of the corrosion behavior of highly As-doped crystalline Si in alkaline Si-air batteries

High corrosion rate is one of the major obstacles that have to be overcome in order to establish practical application of primary alkaline Si-air batteries. At the current state of development the theoretical specific capacity of 3820 mAh/g is reduced to 120 mAh/g in long term operable alkaline Si-air batteries, with most of the capacity losses being due to corrosion reactions. In the present work the corrosion behavior of highly As-doped <100> oriented silicon wafers, that have proved stable performance as anode materials is summarized for a scope of conditions that may arise in battery operation. More specific, corrosion rates are presented and discussed with respect to (i) time dependence, (ii) influence of KOH electrolyte concentration, (iii) chemical vs. electrochemical corrosion, and (iv) corrosion under anodic potentials as present during the discharge of batteries. Corrosion rates were found to exhibit stable time profiles for immersion times longer than 8 h. With respect to concentration dependence, three ranges of KOH concentrations were identified. Within each range, the corrosion behavior is governed by similar mechanisms, but different limiting factors. Potentiodynamic measurements show that large part of the corrosion is chemical in nature. Under discharge conditions corrosion increases whereby the discharge potential, corrosion rates, and mass conversion efficiencies depend on KOH concentrations and discharge current densities.