Evaluation and analysis of Li-air battery using ether-functionalized ionic liquid

Li-air battery using ionic liquids, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) amide (DEME-TFSA) and N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)amide (PP13-TFSA), as the solvents for electrolyte have been studied. A significant improvement of discharge capacity has been observed for DEME-TFSA (4315 mAh g−1-electrode at current density of 0.1 mA cm−2), compared with PP13-TFSA. As a discharged product, aggregates reaching 4 μm diameter in size are formed on the surface of cathode, almost 80% of the products are decomposed after charge. By using Raman spectroscopy, two typical peaks attributed to Li2O2 were detected from the discharged aggregates. From the cross sectional SEM images, vacancy occupation ratios of discharged and charged electrodes are estimated, and they are in good agreement with the theoretical calculations. The discharged products formed inside of the cathode are not decomposed completely by charge.