A highly reversible Li-O-2 battery utilizing a mixed electrolyte and a cathode incorporating Co3O4

The present work mainly focuses on aprotic electrolytes in order to improve the performance of Li-O2 cells. The single-solvent electrolytes are based on tetraethylene glycol dimethyl ether (TEGDME), dimethyl sulfoxide (DMSO) and ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), respectively. Compared to TEGDME and EMITFSI electrolytes, the DMSO electrolyte leads to higher reversible Li-O2 cells, even though decomposition of DMSO is observed. In this work, novel blended TEGDME (20 wt%)-DMSO (80 wt%), EMITFSI (20 wt%)-TEGDME (80 wt%) and EMITFSI (20 wt%)-DMSO (80 wt%) based electrolytes are first proposed and investigated in the assembled Li-O2 cells. Incorporating with a Co3O4 catalysed cathode, the EMITFSI-DMSO electrolyte results in an optimized Li-O2 battery, showing a lower voltage gap and a higher reversibility. In such a system, 80% of the recharge occurs at a potential underneath 4.0 V vs. Li+/Li. The low recharge voltage can suppress the decomposition of DMSO and favour a longer cycle life. More than 65 consecutive cycles are achieved at a current density of 0.1 mA cm-2 with a cut-off capacity of 835 mA h gelectrode -1. The improved electrochemical performance is attributed to the enhanced ionic conductivity of the mixed electrolyte. In addition, the EMITFSI-DMSO electrolyte is considered more stable, since the ionic liquid could alleviate the decomposition of DMSO provoked by the intermediate superoxides