Zn|ZnI2| iodine secondary galvanic cells using iodine adducts of nylon-6 and other polymers as positive electrodes

Zn|ZnI2| iodine galvanic cells using carbon plate electrodes coated with polymer + carbon powder mixtures are rechargeable with minor self-discharge when a positive ion exchanging film is used as the separator. Among the polymers tested (nylon-6, Poly(tetrahydrofuran), poly(acrylonitrile), poly(methly methacrylate), poly(vinly Alcohol), poly(N-vinylpyrrolidone), and poly(4-vinylpridine)), nylon-6 and poly(tetrahydrofuran) have the highest ability to absorb iodine and afford secondary galvanic cells showing the best rechargeability: the secondary galvanic cells are rechargeable more than 500 times with about 100% current efficiency and 81–83% energy efficiency when charged and discharged at 2 mA/cm2 at 25°C. The average charging and discharging voltages of the secondary cell using nylon-6 are 1.42 and 1.18 V, respectively. The cell prepared by using nylon-6 generates about 80 mA/cm2 of an initial short-circuit current and 0.3–80 mA/cm2 of a steady-state short-circuit current when the cell is dipped into a aqueous solution containing I−3. The steady-state short-circuit current increases with increasing I−3 concentration and a linear correlation holds between the logarithm of the steady-state short-circuit current and the logarithm of [I−3] in the range of [I−3] = 0.05–0.5 mol/1.