Preparation and Performances on C-LiFePO4/Polytriphenylamine Composite as Cathode Material for Lithium-Ion Batteries

An olivine LiFePO4/carbon (C-LiFePO4) nanocrystallinematerial was prepared using a low-temperature solvothermalmethod, followed by a high-temperature post-annealing process. Then polytriphenylamine (PTPAn)-modified C-LiFePO4 (C-LiFePO4/PTPAn) was prepared, as a composite for novel cathodes for lithium-ion batteries, by solution blending of the C-LiFePO4 nanocrystallinematerial and the electroactive conducting polymer PTPAn. The effects of PTPAn coating of the C-LiFePO4/PTPAn samples were investigated using X-ray diffraction (XRD), scanning electronmicroscopy (SEM), transmission electronmicroscopy (TEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge testing. The results indicated that the solution blending method produced a compact PTPAn coating on the C-LiFePO4, providing an effective electronic/ionic conducting pathway and enhancing the electrochemical activities of C-LiFePO4-based composites. The C-LiFePO4/10%(w) PTPAn electrode displayed an improved initial discharge capacity of 154.5mAh·g-1 at 0.1C, a superior high-rate performance discharge capacity of 114.2 mAh·g-1 at 10C, and excellent cycling stability.With further increases in the PTPAn content of the coating on the C-LiFePO4/PTPAn composite, the electrochemical properties of the composite decreased. Electrochemical impedance measurements also demonstrated that the PTPAn coating significantly decreased the charge-transfer resistance of the C-LiFePO4 electrode.