Mohammad Asadi¹, Cong Liu², Patrick Phillips³, Peter Zapol², Robert F. Klie ³, Larry A. Curtiss², Amin Salehi-Khojin¹

¹Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA

²Materials Science Division, Argonne National Laboratory, Argonne, IL, 60439, USA

³Department of Physics, University of Illinois at Chicago, Chicago, IL, 60607, USA

   Lithium–oxygen (Li-O₂) batteries have been recognized as an emerging technology for energy storage systems owing to their high theoretical specific energy^1-4. In this study, we discovered a system based on molybdenum disulfide (MoS₂) nanoflakes and an ionic liquid (IL) that work together as an effective co-catalyst for discharge and charge in a Li-O₂ battery.  Cyclic voltammetry results show superior reaction rates for this co-catalyst at lower overpotentials for both oxygen reduction (15 mV) and evolution (20 mV) reactions compared to Au and Pt metal catalysts under identical experimental conditions. This MoS₂/IL co-catalyst also performs remarkably well in the Li-O₂battery system with 85% round-trip efficiency and reversibility up to 50 cycles.

   Deferential Electrochemical mass spectroscopy (DEMS), X-ray diffraction (XRD), Fourier transform spectroscopy (FT-IR) and Raman experiments were used to elucidate the cell performance.  The results show the fully formation and decomposition of Li₂O₂ and demonstrate the cell cyclability and stability by the absence of any side products after 50 cycles charge and discharge. Atomic scale characterizations (STEM and EELS experiments) and DFT calculations were used to elucidate the mechanism by which the MoS₂ nanoflakes and the ionic liquid electrolyte act together to promote the catalytic properties of the MoS₂. The MoS₂/IL co-catalyst discovered in this work provides new opportunities for exploiting the unique properties of ionic liquids such as their stability in Li-air batteries as well as activity of MoS₂as a cathode material.

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