Investigation into the use of quinone compounds-for battery cathodes

Abstract

As organic cathode materials investigated in the past are reduced irreversibly and, therefore, can only be used in primary cells, we investigated quinones/hydroquinones, which are known to act as completely reversible redox couples. Most of the quinones are, however, slightly soluble and partly unstable in electrolyte solution. In order to test their stability electrochemically we mixed the quinones with carbon. The open-circuit potentials of the solid quinone/hydroquinone systems measured in 2 N H 2SO 4 are very close to the values of the redox potentials measured in alcoholic solutions. Diphenoquinones, which have a potential of about 950 mV (nhe) do not have the required stability. Only tetrachloro- p-benzoquinone (chloranil) and tetramethyl- p-benzoquinone (duroquinone) have been found to be sufficiently insoluble and completely stable, the redox potentials being 668 and 478 mV, respectively. In the case of galvanostatic discharge the potential is almost constant. With chloranil the polarization is only 30 mV at a cd of 60 mA/cm 2. Even at a current drain of 600 mA/cm 2, 50 per cent of the active material is available for discharge at potentials exceeding 200 mV. In concentrated aqueous ammonium chloride solution the reduction takes place in two one-electron steps separated by approximately 70 mV. This does not happen in zinc chloride solution. The capacity (Ah/kg) of the quinones is in the same range as that of the inorganic depolarizers, but the hydroquinones can be reoxidized with oxygen using hydrophobic electrodes. Thus the quinone electrode is regenerated with air and its capacity is practically unlimited. Regeneration with hydrogen peroxide is also possible. Particular quinones are insoluble in organic solvents used for organic electrolyte solutions and are therefore superior to heavy metal salts as cathode materials in high-energy density secondary batteries.