1,3-Dimethyl-2-imidazolidinone: an ideal electrolyte solvent for high-performance Li-O₂ battery with pretreated Li...

Electrolytes are widely considered as a key component in Li-O₂ batteries (LOBs) because they greatly affect the discharge-charge reaction kinetics and reversibility. Herein, we report that 1,3-dimethyl-2-imidazolidinone (DMI) is an excellent electrolyte solvent for LOBs. Comparing with conventional ether and sulfone based electrolytes, it has higher Li₂O₂ and Li₂CO₃ solubility, which on the one hand depresses cathode passivation during discharge, and on the other hand promotes the liquid-phase redox shuttling during charge, and consequently lowers the overpotential and improves the cyclability of the battery. However, despite the many advantages at the cathode side, DMI is not stable with bare Li anode. Thus, we have developed a pretreatment method to grow a protective artificial solid-state electrolyte interface (SEI) to prevent the unfavorable side-reactions on Li. The SEI film was formed via the reaction between fluorine-rich organic reagents and Li metal. It is composed of highly Li⁺-conducting Li_xBO_y, LiF, Li_xNO_y, Li₃N particles and some organic compounds, in which Li_xBO_y serves as a binder to enhance its mechanical strength. With the protective SEI, the coulombic efficiency of Li plating/stripping in DMI electrolyte increased from 20% to 98.5% and the fixed capacity cycle life of the assembled LOB was elongated to 205 rounds, which was almost fivefold of the cycle life in dimethyl sulfoxide (DMSO) or tetraglyme (TEGDME) based electrolytes. Our work demonstrates that molecular polarity and ionic solvation structure are the primary issues to be considered when designing high performance Li-O₂ battery electrolytes, and cross-linked artificial SEI is effective in improving the anodic stability.