Uncovering the Mechanisms behind the Limited Discharge Duration of Silicon-Air Batteries with Alkaline Electrolytes
Authors: Schalinski Richard , Schweizer Stefan L , Wehrspohn Ralf B 
Published: February 2024

The demand for electronic devices with high storage capacities and long-lasting batteries has motivated the development of new battery systems. Metal-air and semiconductor-air batteries are particularly interesting due to their high capacity densities due to the use of air for the cathode reaction. The Si-air battery was introduced as a battery system that operated with a room-temperature ionic liquid or KOH as the electrolyte.[1,2] However, the practical capacity density is reduced to a fraction of the theoretical value in liquid electrolytes, and the passivation of the silicon anode in aqueous electrolytes is a major challenge.[3,4] Increasing the surface area of the Si electrode can reduce the local reaction rate and enable the dissolution of the reaction products, but it also increases the overall corrosion rate. A threshold temperature and the addition of fresh electrolyte solution can also extend the discharge duration.[3,5]

Silicon-air batteries have the potential to become the next generation of batteries, as they are made from non-critical raw materials and have a high theoretical capacity. However, silicon-air batteries using alkaline electrolytes suffer from early passivation and termination of discharge. To understand this process, we investigated the correlation between dissolved silicon in the electrolyte and the discharge duration until passivation. Our findings revealed that silicate enrichment in the electrolyte reduces the flow of reaction products away from the silicon surface, leading to rapid oxidation and passivation of the surface.[6]

We utilized various techniques, including electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), to investigate this phenomenon further. Our results showed that the silicate concentration in the electrolyte plays a crucial role in determining the performance of silicon-air batteries. A lower concentration of silicates in the electrolyte leads to sustained discharge, while a higher concentration results in early passivation and termination of discharge.
In conclusion, our investigation highlights the critical role of silicates in the performance of silicon-air batteries utilizing alkaline solutions. Our findings suggest that controlling the concentration of silicates in the electrolyte is crucial to ensure the sustained discharge of these batteries. This study provides essential insights into the mechanisms governing the passivation of silicon surfaces in alkaline electrolytes, which will aid in the development of more efficient and sustainable energy storage solutions.
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