Comparison of lithium//polyaniline secondary batteries with different dopants of HCl and lithium ionic salts

Polyanilines doped either with a protonic acid (HCl) or an electrolytic solution containing a lithium ionic salt (LiPF₆ or LiBF₄) are prepared and their electrochemical characteristics for use as polymer electrodes of lithium secondary batteries are investigated. An emeraldine base (EB) film doped with HCl has the highest d.c. conductivity (approximately 10 S/cm). An EB-LiPF₆ film has higher conductivity (approximately 0.52 S/cm) than an EB-LiBF₄ (approximately 0.082 S/cm) film. X-ray photoelectron spectroscopic analysis of the films shows that some of the quinoid rings in EB are transformed into benzeniod rings through a doping process to generate polarons. The charge-discharge characteristics of lithium secondary batteries using the polyaniline films as positive electrodes are determined. The cell using the EB-LiPF₆ film and an electrolytic solution containing LiPF₆ exhibits the highest specific discharge capacity (approximately 50 mA h/g), whereas the cell using EB-HCl and LiPF₆ solution has superior performance in the rapid saturation of discharge capacity and in stability.