Influence of electropolymerized current density on polypyrrole electrode of lithium ion cells

In this research, different polypyrrole (PPy) film samples with same thickness were electro-polymerized on Pt micro-disk electrode by method of chronopotentiometry at current densities, ranging from 0.05 mA· cm^-2 to 10 mA· cm^-2. The electrochemical behaviors of obtained PPy samples were investigated in lithium perchlorate-proylene carbonate electrolyte by electrochemical methods: cyclic voltammetry (CV), chronopotentionmetry and electrochemical impedance spectroscopy (EIS). The results indicated that the polyprrole samples fabricated at suitable current density, that was, 1-5 mA· cm^-2, could exhibit better electrochemical behavior, such as, higher degree of electrochemical redox reversibility, more positive redox potential, and larger capacity. It was found that each of the potential response signals was considerably stable and there was a clear linear relationship between corresponding potential response signal and used electro-polymerization current density in the process of electro-polymerization reaction. At the condition of suitable current density, corresponding potential signal was changed from 3.9 V to 4.1 V (vs Li/Li⁺) with the increasing of used electro-polymerization current density. Moreover, each outstanding properties, for example, the most doping degree, 30% or so, lower membrane impedance and charge transfer impedance at oxidated state, could be achieved on the PPy samples fabricated at abovementioned suitable current density. It was also found that each kind of obtained polypyrrole sample exhibited excellent columbic efficiency and electrochemical reversibility during galvanostatic charge/discharge process in the electrolytes of Li-ion battery. Those polypyrrole samples obtained at abovementioned suitable electro-polymerization condition should be promising candidate for the fabrication of the positive electrode of secondary lithium/LiClO₄ /polypyrrole battery.