Effect of PF₆^-Anion on the Properties of Lithium-Polypyrrole Battery during Polypyrrole Film Formation

A high charging-discharging efficiency was obtained for Li/LiClO₄-PC (propylene carbonate)/PPy (polypyrrole) battery, when a PPy film formed in LiPF₆/PC by electropolymerization was used in a LiClO₄ electrolyte after PF₆^- anion undoping. The anion doping-undoping process for the PPy film electrodes was examined with the usual electrochemical techniques. A Li/LiClO₄/PPy cell was also tested with a constant current charging-discharging performance. The relationship between sweep rate and anodic peak current shown in the cyclic voltammograms obtained for the PPy film formed in the LiClO₄ electrolyte indicates a typical diffusion-controlled process, while a reaction-controlled process was found to be involved in the PPy film electrode formed in the LiPF₆ electrolyte. The relationship between undoping level and elapsed time indicated that the diffusion rate of the ClO₄^- doped in the PPy film formed in LiPF« has a higher value than that of the ClO₄^- doped in the PPy film formed in LiClO₄. SEM observations showed that the PPy films formed in LiPF₆ were rougher than those formed in LiClO₄. Infrared (IR) spectral measurements confirmed that there are no essential differences in the manner of bonding of the PPy films formed in LiPF₆ (PPy+PF₆^-) and LiClO₄ (PPy+ClO₄^-). Consequently, a morphology of the PPy films was suggested to be a very important factor in determining the kinetics of the anion doping-undoping process and, therefore, charging-discharging properties of Li/LiClO₄-PC/PPy battery.