Self-assembly LiFePO4/polyaniline composite cathode materials with inorganic acids as dopants for lithium-ion batteries

Carbon-coated LiFePO4 (C-LFP) composites incorporated with electrochemically-active conducting polymer polyaniline (PANI) are fabricated via a self-assembly process. Inorganic acids HCl, H2SO4 and H3PO4 are used as dopants for PANI. The C-LFP/PANI composites are characterized by thermogravimetric analysis, scanning electron microscopy, electrochemical impedance spectroscopy, Raman spectra and four-probe resistivity measurements. Our results show that a remarkable improvement in capacity and rate capability can be achieved in the C-LFP/PANI composite cathodes doped with HCl and H3PO4. The C-LFP/PANI-HCl composite exhibits the best electrochemical performance, which gives a ca. 15% capacity enhancement at 0.2 C and 40% enhancement at 5 C compared to the parent C-LFP. The mechanism for the enhancement has been discussed.