Insight into the improvement of rate capability and cyclability in LiFePO4/polyaniline composite cathode

Abstract

A simple and efficient strategy was employed to enhance high-rate performance for carbon-coated LiFePO₄ (C-LFP) by incorporating with conducting polymer polyaniline (PANI). C-LFP was synthesized via a solid state reaction whereas PANI was formed in situ by chemical oxidative polymerization of aniline with ammonium persulfate as an oxidizer to achieve the C-LFP/PANI composites. Specific capacities as high as 165 mAh g⁻¹ at 0.2 C, 133 mAh g⁻¹ at 7 C and 123 mAh g⁻¹ at 10 C were obtained in C-LFP/7 wt.% PANI composite. Moreover, the composite exhibits remarkably improved cyclability as compared with the parent C-LFP. The mechanism has been carefully investigated for the improvement in the electrochemical performance. Experimental results show that the charge transfer impedance decreases significantly and the cathode surface becomes much smooth over cycling with modification of conductive PANI. The incorporated PANI can work not only as an additional host for Li⁺-ion insertion/extraction, but also as a binder to modify the electrode surface and a container for electrolyte to penetrate into C-LFP particles.