Li|LiI|iodine primary galvanic cell and Zn|ZnI 2|iodine secondary galvanic cell using poly(2,5-thienylene), poly(2,5-pyrrolylene), and their analogues as positive electrodes

Abstract

Iodine adducts of chemically prepared poly(2,5- thienylene) show good electrical conductivity over a range of iodine content of 10–90 wt.%. The adducts serve as good active materials of positive electrodes of Li|LiI|iodine galvanic cells. Discharge curves of the galvanic cell at 500 kgω load show stable voltage (2.8–2.3 V) until about 85% of added iodine is consumed in the cell reaction. Poly(2,5-thienylene), poly(2,5-pyrrolylene), and their derivatives prepared both chemically and electrochemically are useful as materials for positive electrodes of Zn|ZnI 2|cation- exchange membrane|ZnI 2|iodine secondary cells. The cells using the polymers show about 100% current efficiency and 85% energy efficiency, and are rechargeable more than 200 times. Utilization of electric conducting π-conjugated polymers as electrodes of primary and secondary cells is a subject of recent interest [1–7]. Among the electric conducting polymers, those constituted of recurring 5-membered heterocycles have high stabilities against air and heat. They show good electric conductivity when doped with electron acceptor or donor ▪ and are suitable as electrodes of the cells. Two methods have been developed for the preparation of the polymers. Method 1: Transition metal catalyzed dehalogenation polycondensation of dihalo-compounds with magnesium or zinc [8–13]. e.g., ▪ Method 2: Anodic oxidation of thiophene, pyrrole, or their derivatives [14–21]. e.g., ▪ We now report utilization of the polymer as positive electrodes of Li|LiI|iodine primary and Zn|ZnI 2|- cation-exchange membrane|ZnI 2|iodine (abbreviated as Zn|ZnI 2|iodine) secondary cells.