LITHIUM POLYMER SECONDARY CELL USING DISULFIDE-POLYANILINE COMPOSITE CATHODE AND GEL ELECTROLYTE

A lithium polymer secondary cell using an organodisulfide-polyaniline composite cathode and a polyacrylonitrile gel electrolyte has been developed. The composite cathode was prepared as a mixture of 2,5-dimercapto-1,3,4-thiadiazole (organodisulfide) powders, polyaniline powders, and the gel electrolyte. Organodisulfide and polyaniline were considered to form an adduct providing a characteristic discharge curve monotonously decreasing from 4.0 to 2.5 V. To examine the charge-discharge cycle capability of the cell, the polarizability of the metallic lithium and gel electrolyte interface was tested at first, and then the charge-discharge cycle performance of the cell using the composite cathode with different composition was tested. The gel electrolyte containing LiBF4 was found to afford a higher current output of over 1mA/cm(2) even after cycling the voltage of a Li/gel electrolyte/Li cell 50 times within +/- 0.5 V at 1 mV/s. As to the composition of the cathode, the mole ratio of disulfide to polyaniline was found to be quite decisive to obtain a higher charge-discharge cycle performance. Degradation in discharge capacity was markedly reduced as the mole ratio of disulfide to polyaniline decreases below 1. The cell with a composite cathode having an optimized composition provided a higher capacity of 80 mAh/g-cathode even after 30 charge-discharge cycles.