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Keywords:

  • batteries;
  • electrochemistry;
  • ionic liquids;
  • oxidation;
  • silicon

Abstract

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 15 vol % 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 20 vol %, 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 10 vol %. In-depth studies indicate a reduced amount of discharge product at the air electrode using 15 vol % 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.