Electrochemical Characteristics of Lithium-Air Secondary Battery Using Amide-Based Ionic Liquids

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.