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

Abstract

Amo rphous carbon-coated lithiu m iron phosphate (C-LiFePO4) particles have been mass synthesized at the commercial scale by a controlled solid-state reaction method. Particles morphologies , o livine-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 ) imag ing, selected-area electron diffraction (SAED), X-ray energy dispersive spectroscopy microanalysis (XED S), and X-ray photoelectron spectroscopy (XPS). Single-crystal nature of the olivine type LiFePO4 structures was revealed by XRD and SA ED analyses. TEM imaging showed rough nanoparticles spherical features with average size range of 50-200 n m. Ho mogenous 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 b inding energy fro m XPS analysis also confirmed that an amo rphous 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 lithiu m ions, as directly evidenced fro m our charge-discharge cycling testing as the cathode in the Lithiu m ion battery cell.