Electrochemical Characteristics of Lithium-Air Secondary Battery Using Amide-Based Ionic Liquids (Supporting Information)

We fabricated lithium-air secondary batteries (LABs) employing amide-based ionic liquids (ILs) as electrolytes and evaluated their electrochemical characteristics. Lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA) was employed as the lithium salt, N-methyl-N-propylpyrrolidinium-TFSA (Py₁₃ system) with a cyclic aliphatic cation in the ILs, and N, N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium-TFSA (DEME system) with an acyclic aliphatic cation. The constant-current discharge-charge tests with the capacity controlled at 200 mAh (g-carbon)⁻¹ showed that the overvoltage of the LABs using the Py₁₃ system was lower than those of LABs using the DEME system and the organic solvent-based system electrolyte. The cycling performance of the DEME system rapidly decreased at the 74th cycle, while the Py₁₃ system showed 200 mAh (g-carbon)⁻¹ up to the 100th cycle, indicating a high stability. Electrochemical impedance measurements showed that the LABs using the Py₁₃ system had the lowest interfacial resistance after the 1st charge. These results indicated that the use of the Py₁₃ system with a relatively high electrical conductivity and low viscosity as the electrolyte would stabilize the cycling performance of the LABs.