A recent concept of metal-air batteries, Si-air, has a good potential to play a major role in the primary battery market due to possessing the second most abundant element in Earth’s crust as an anode. The main drawback of this system is the low practical discharge capacities both in aqueous alkaline and room temperature ionic liquids. In the previous studies, limitation of discharge is suggested to originate from a formation of an oxide layer on the Si surface, which prevents further oxidation of the active material.^1,2,3 Additionally, there is a high corrosion rate of Si in aqueous systems that results in low anodic mass utilization efficiencies.

The main objective of current work is to find an approach to overcome the discharge limitations in aqueous alkaline systems. Electrochemical characterizations of Si-air cells were carried out by galvanostatic discharge experiments with Si wafers under controlled ambient conditions. The complete consumption of the active Si in the cell was achieved when a suitable setup, i.e. sufficient electrolyte, was employed. Discharge behavior of the Si-air cells was also investigated along with variations of temperature and molarity of alkaline electrolyte.

Since large amounts of the Si mass were consumed in the corrosion reaction during the experiments, the current work focuses also on corrosion studies. From the data on Si anode mass and discharge capacities, the corrosion rate and anodic mass utilization efficiencies were calculated. To have a better insight into the corrosion mechanism, nuclear magnetic resonance experiments were performed on the Si dissolution in alkaline electrolyte. From these experiments, formation of different Si-O-H silicate species as products of the corrosion reaction was identified. Moreover, the effect of corrosion products on the discharge performance and corrosion rate was studied as well. Based on the experimental results, specific discharge capacities of Si-air batteries are discussed while taking the corrosion process into account.

In summary, in spite of the corrosion process, the main goal to overcome the discharge limitations was accomplished by complete consumption of the active Si during the discharge. The effect of corrosion products on the discharge performance was investigated and the results will be reported.

References
1. Cohn, G., Eichel, Rüdiger-A., Ein-Eli, Y. Phys. Chem. Chem. Phys. 15, 3256–63 (2013).
2. Zhong, X., Zhang, H., Liu, Y., Bai, J., Liao, L., Huang, Y., Duan, X. ChemSusChem 5, 177–80 (2012).
3. Park, DW., Kim, S., Ocon, JD., Abrenica, GHA., Lee, JK., Lee, J. ACS Applied Materials & Interfaces 7, 3126–3132 (2015).