The research covers the synthesis of ionic liquids containing anions fluoroboric acid and quaternary ammonium cations with one ether group. The ionic conductivities of 1M solutions of the synthesized ionic liquids in acetonitrile were measured. They range from 27 to 36 mS/cm, which allows to use solutions as working electrolytes in electrochemical capacitors. It was found that the window of electrochemical stability of the investigated ionic liquids constitutes 3.6-6.1 V and depends on cation structure.