Ionic liquids (ILs) are comprised entirely of ions, and they possess unique physico-chemical properties such as non-volatility, non-flammability, high thermal stability, and high ionic conductivity, which make so distinct from conventional molecular liquids. Since ILs are essentially ionic conductors, their utilization as novel electrolytes for electrochemical devices, such as rechargeable lithium batteries, double-layer capacitors, dye-sensitized solar cells, and fuel cells, has also been the subject of intense study. The authors present our early trial to apply an IL as an electrolyte for a rechargeable lithium cell. We also review scientific progresses and problems for practical application in this field.