Remarkable impact of water on the discharge performance of a silicon-air battery

Here, we report on a Si-air/ionic liquid electrolyte battery whose performance improves with small amounts of water in the electrolyte. The shift of the generation zone of the SiO₂ discharge product from the air cathode surface into the bulk region of the liquid electrolyte, caused by water addition, is demonstrated through various means. Addition of 15vol% water leads to an increase of 40% in the discharge capacity as compared to the capacity obtained using a pure ionic liquid electrolyte. If the water content increases above 20vol%, the Si-air cell capacity dramatically decreases. The water-ionic liquid electrolyte mixture shows a maximum in the ionic conductivity with a water content of 10vol%. In-depth studies indicate a reduced amount of discharge product at the air electrode using 15vol% H₂O electrolyte. The morphology of the anode surface, as well as the developed surface film in the presence of water-containing ionic liquid, is reported. This study shows that exposing a Si-air battery to a humid environment does not result in capacity losses, but rather improves cell performance.