The correlation of the properties of pyrrolidinium-based ionic liquid electrolytes with the discharge–charge performances of rechargeable Li–O2 batteries

Abstract Pyrrolidinium-based ionic liquids (ILs), such as PYR 13 TFSI, PYR 14 TFSI, and PYR 1(2O1) TFSI, exhibit high thermal and electrochemical stability with wide electrochemical windows as electrolytes for application to rechargeable Li–O 2 batteries. In this work, several fundamental properties of three ILs are measured: the ionic conductivity, oxygen solubility, and oxygen diffusion coefficient. The oxygen electro-reduction kinetics is characterized using cyclic voltammetry. The performances of Li–O 2 batteries with these IL electrolytes are also investigated using electrochemical impedance spectroscopy and galvanostatic discharge–charge tests. The results demonstrate that the PYR 1(2O1) TFSI electrolyte battery has a higher first-discharge voltage than the PYR 13 TFSI electrolyte and PYR 14 TFSI electrolyte batteries. Both PYR 13 TFSI- and PYR 1(2O1) TFSI-based batteries exhibit higher first-discharge capacities and better cycling stabilities than the PYR 14 TFSI-based battery for 30 cycles. A theoretical analysis of the experimental results shows that the diffusion coefficient and solubility of oxygen in the electrolyte remarkably affect the discharge capacity and cycling stability of the batteries. Particularly, the oxygen diffusion coefficient of the IL electrolyte can effectively facilitate the electrochemical oxygen electro-reduction reaction and oxygen concentration distribution in the catalyst layers of air electrodes. The oxygen diffusion coefficient and oxygen solubility improvements of IL electrolytes can enhance the discharge–charge performances of Li–O 2 batteries.