Sulfone-Based Electrolytes for Nonaqueous Li–O2 Batteries

We investigated the use of sulfone-based electrolytes for the Li–O 2 battery. The study compared the behavior of three commercially available sulfones: ethyl vinyl sulfone (EVS), tetramethylene sulfone (TMS), also called sulfolane, and ethyl methyl sulfone (EMS). First, we carried out a preliminary investigation of the oxygen reduction reaction and oxygen evolution reaction (ORR/OER) as a function of solvent type and Li + concentration. Then, TMS and EMS were tested (LiTFSI salt) in Li–O 2 cells. The cells exhibited initial capacities around 1800 and 2000 mAh.g –1 carbon, respectively. The capacity retention on cycling was quite low. We analyzed the reaction products during discharge and charge by means of powder X-ray diffraction, infrared spectroscopy, 1 H-nuclear magnetic resonance, and mass spectrometry. Although EVS was at first sight the most attractive sulfone, since it is a liquid at room temperature, it was the least stable in the presence of oxygen; its vinyl group was attacked by reduced O 2 species. On the other hand, both TMS and EMS performed better during the first five cycles; Li 2 O 2 formation and decomposition was the main reaction, although some byproducts formed during cycling. After five cycles, there was still a considerable amount of Li 2 O 2 formed, but decomposition to form Li 2 CO 3 became significant, and it accumulated at the O 2 electrode. This was the likely reason for capacity fading.