High Rate Performance of Nano-Structured LiFePO4/C Cathode Material Prepared by a Polymer-Assisted Method from Inexpensive Iron(III) Raw Material

A spherical carbon coated nano-structured LiFePO 4 composite is synthesized by a polymer-assisted method from inexpensive iron(III) raw material. The synthesis process includes two steps: (1) nano-FePO 4 /polyaniline composites with core–shell structure are synthesized through the in-situ polymerization of aniline; (2) LiFePO 4 /C composites are prepared through carbothermal reduction with the nano-FePO 4 /polyaniline and sucrose as raw materials. The structure, surface morphology of the materials and the properties of the coated carbon are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The obtained nano-structured LiFePO 4 /carbon composite has a spherical morphology compose of ordered olivine structure, which is coated with 2 nm thick amorphous layer of carbon. At the same time, the materials are linked together by amorphous carbon from sucrose decomposition. The aniline plays an important role during the synthesis process. The electrochemical properties of the materials are tested by charge–discharge measurements. The obtained nano-structured LiFePO 4 /carbon composite shows excellent electrochemical properties, especially its high rate performance. It exhibits initial discharge capacities of 138, 136, 118, 103, and 92 mA h g –1 at 0.2, 1, 10, 20, and 30 C rate between 3.65 and 2.0 V, respectively. That makes it a promising cathode material for advanced power Li-ion batteries. The excellent electrochemical properties of the materials can be ascribed to the two different amorphous carbons. The carbon coated on the surface of LiFePO 4 effectively reduces inter-particle agglomeration of the LiFePO 4 particles. The carbon interlinked between the composite improve the electronic conductivity. Those shorten the lithium ions diffusion length and improve the electric contact between LiFePO 4 particles.