Synthesis of a novel ferrocene-contained polypyrrole derivative and its performance as a cathode material for Li-ion batteries

A novel ferrocene-contained pyrrole, 4-(1H-pyrrol-1-yl) phenyl ferrocenecarboxylate (FcPy) was synthesized by esterification of 4-(1H-pyrrol-1-yl) phenol (PLPY) and ferrocenecarboxylic acid. Then the homopolymer of FcPy (PFcPy), copolymer of FcPy and pyrrole (P(FcPy-co-Py)), polypyrrole (PPy) were prepared by chemical oxidative polymerization. And the structure, morphology, electrochemical properties of prepared polymers were characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), cyclic voltammograms (CV) and electrochemical impedance spectra (EIS), respectively. Also, the charge/discharge properties of the prepared polymers were studied by galvanostatic charge-discharge testing. The results demonstrated that the introduction of ferrocene to polypyrrole obviously improved the specific capacity of PPy cathode and gave a well-defined plateau at the potential rang of about 3.5 V. Under our experimental conditions, the discharge capacity of undoped PPy-based electrodes only presented 16.5 mAh g−1 at 20 mA g−1 between 2.5 and 4.2 V, while PFcPy-based electrodes exhibited an initial discharge capacity of up to 43.2 mAh g−1. Specially, the P(FcPy-co-Py)-based electrodes even showed a discharge capacity of 68.1 mAh g−1 and the improved discharge platform, which were ascribed to the resonance doping effect of pendant group, the advanced electrochemical nature of ferrocene moiety and the loose morphology of copolymer.