Controlled Preparation and Surface Structure Characterization of Carbon-Coated Lithium Iron Phosphate and Electrochemical Studies as Cathode Materials for Lithium Ion Battery

Amorphous carbon-coated lithium iron phosphate (C-LiFePO4) particles have been mass synthesized at the commercial scale by a controlled solid-state reaction method. Particles morphologies, olivine-type phase structures and the carbon coating features were investigated in details by various techniques as X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) imaging, and transmission electron microscopy (TEM, HRTEM) imaging, selected-area electron diffraction (SAED), X-ray energy dispersive spectroscopy microanalysis (XEDS), and X-ray photoelectron spectroscopy (XPS). Single-crystal nature of the olivine type LiFePO4 structures was revealed by XRD and SAED analyses. TEM imaging showed rough nanoparticles spherical features with average size range of 50-200 nm. Homogenous coating features of carbon layers on the particles surface and olivine-LiFePO4 phase are clearly observed in HR-TEM imaging and confirmed by the corresponding SAED pattern. Elemental binding energy from XPS analysis also confirmed that an amorphous sp2 carbon coating layer and olivine type LiFePO4 structures. It is indicated that the characteristics of sp2 type conducting-coating layer on the particles surfaces gave rise to improved electrical conductivity by reducing the diffusion path of the electron and lithium ions, as directly evidenced from our charge-discharge cycling testing as the cathode in the Lithium ion battery cell.