Browse Prior Art Database

ELECTROCHEMICAL CAPACITOR BASED ON LITHIUM ION EXCHANGE IN AQUEOUS ELECTROLYTE

IP.com Disclosure Number: IPCOM000007345D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-18
Document File: 3 page(s) / 130K

Publishing Venue

Motorola

Related People

Jason N. Howard: AUTHOR [+2]

Abstract

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.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 3

MO7VROLA Technical Developments Volume 24 March 1995

ELECTROCHEMICAL CAPACITOR BASED ON LITHIUM ION EXCHANGE IN AQUEOUS ELECTROLYTE

by Jason N. Howard and George Thomas

  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.

  While the mechanism of the reaction is gener- ally assumed to involve exchange of protons between the electrode and electrolyte, charge balance can also be achieved through the exchange ofother ions, notably Li+. Literature reports have demonstrated the effects of pH and the exchange of Li+ during the oxidation and reduction of box.* The present paper describes the construction and testing of an electrochemical capacitor based on IrOx and Li+ aqueous electrolytes at near neutral pH. This sys- tem has the distinct advantage of employing a non- corrosive electrolyte leading to an inherently safer

device. Furthermore, the electrochemical reaction occurs over a large potential window providing greater efficiency.

RESULTS

  IrOx electrodes were formed by electrochemically oxidizing iridium metal. Figures 1 compares cyclic voltammograms (CV) of IrOx in 1M LiCIOd (pH =
6) and 1M H2S04 electrolyte. In both cases, more anodic or cathodic voltages lead to the electrolytic decomposition of water. The redox reaction is completely reversible and kineticall...