Electrochemical capacitors have been devised using hybrid electrolytes containing either lithium or magnesium salt and high-density graphite (HDG) electrodes. The cells exhibit single- electrode discharge capacitance of 355 muF/ cm(2) at 1 mA/ cm(2) discharge rate for magnesium-containing ormolytes at 80 degreesC. Typical response times have been calculated to be of the order of 0.28 s for magnesium ion and 0.73 s for lithium ion containing ormolytes. A typical coin-type cell exhibits excellent cyclability of more than 10(3) cycles at a discharge current density of 1 mA/cm(2). (C) 2003 The Electrochemical Society.