Lithium-based batteries are the current power sources used in electronic fuses for medium caliber munitions. These batteries are most commonly constructed from metallic lithium as the anode, thionyl chloride as the electrolyte, and a transition metal oxide or chalcogenide as the cathode. All three components are environmentally unacceptable and alternatives currently being used, such as sulfuryl chloride electrolytes, are equally harmful. Alternative power sources are needed to meet the energy demands of the munitions without posing a health risk to the users or the environment.
The objective of this project was to develop supercapacitors constructed from environmentally benign organic polymers with high oxidation potentials as power supplies for medium caliber munitions.
The fabrication and study of the high-power polymer-based supercapacitors was undertaken in three phases of research. Organic polymers with significantly different reduction potentials spanning the necessary 4 V were first synthesized. Polymer/electrolyte combinations that provide ideal discharge properties capable of delivering the required current densities were identified. Supercapacitors constructed from the new hybrid polymer cathodes and polythiophene and poly(3-methylthiophene) were then measured in combination with chemically innocuous electrolytes.
Novel poly(anilinothiophenyl) and poly(anilinofuranyl) hybrid polymers were synthesized for supercapacitor applications. The parent monomers undergo electrochemical polymerization at 0.4-0.9 V depending on the substituents on the phenyl rings. Nitro derivatives are more difficult to oxidize by 0.13 V compared to benzoyl analogs. Redox activity of the resulting polymers is retained with acetonitrile electrolytes. The new polymers are reversibly oxidized at potentials of 0.4-1.2 V. The nitro derivative of the poly(anilinofuranyl) material exhibited the most positive oxidation potential. This material was further investigated as a cathode material in an all-organic polymer supercapacitor. Discharge currents of a polythiophene/0.8 M [Bu4N]BF4/poly(nitroanilinofuranyl) supercapacitor were 20% greater than those obtained for the best all polythiophene device under similar electrolytic conditions. These results indicate that the new polymer hybrid materials are promising candidates for developing improved all-organic supercapacitors.
The polymer-based supercapacitors investigated in this project have the potential to meet the energy demands of munitions without compromising the environment. Because of the low cost of the organic polymers, a cost-effective and environmentally benign alternative to lithium batteries would be provided with the construction of these new power supplies. (Project Completed – 2006)