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.