Ultrathin and uniform carbon-layer-coated hierarchically porous LiFePO4 microspheres and their electrochemical performance

Abstract

Uniform and complete coverage of ultrathin carbon layer coatings on the surface of nano-sized LiFePO4 (LFP) particles prepared using a supercritical alcohol route was investigated. In the presence of oleylamine, nanosized oleylamine-modified LFP particles were synthesized in supercritical ethanol because particle growth was inhibited. When the oleylamine-modified LFP was calcined, uniform coverage of carbon layers with thicknesses of 1.5-2.0 nm on individual LFP particles was achieved. The carbon-coated LFP (C-LFP) exhibited hierarchical porous nano/micro sphere morphology with a porosity of 45.6%. In comparison with bare LFP synthesized in the absence of oleylamine, C-LFP exhibited excellent Li ion uptake performance; C-LFP delivered a reversible discharge capacity of 158.4 mAh g(-1) after 100 cycles at 0.1 C and a rate performance of 84.0 mAh g(-1) at 20 C. In addition, after 700 continuous cycles at 10 C, the C-LiFePO4 electrode exhibited a reversible discharge capacity of 84.0 mAh g(-1) with small capacity loss. Electrochemical impedance tests revealed that the uniform and ultrathin carbon coating improved charge transfer kinetics and lithium diffusion into the active material. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.