ELECTROCHEMICAL CAPACITOR BASED ON LITHIUM ION EXCHANGE IN AQUEOUS ELECTROLYTE
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-18
Electrochemical capacitors represent a new tech- nology providing higher specific capacitance than conventional electrolytic capacitors. These devices offer energy and power densities intermediate between conventional capacitors and conventional recharge- able batteries. One group of these capacitors-often referred to as "ultracapacitors:' "pseudocapacitors: or "redox" capacitors-is based on fast, Faradaic elec- trochemical reactions. Most of the prior work in this field involves metal oxide electrodes with highly corrosive electrolytes such as sulfuric acid or potas- sium hydroxide. The reader is referred to reference 1 for a review.' Devices are typically constructed using the same electrode material for the anode and cathode. This permits stacking cells in series where the anode of one cell acts as the cathode ofthe next cell in series. When using these "bipolar" electrodes, the useful voltage of the cell will be determined by the voltage range of the electrochemical reaction. However, many of the known electrochemical capacitor systems have relatively narrow voltage windows (5 1 V) over which the reaction occurs. Thus, the energy from a single cell is limited and a larger number of cells must be connected in series to meet the required operational voltage. This situation limits the energy density of the device and increases manufacturing complexity.