Effects of carbon content on the electrochemical performance of LiFePO4/C core/shell nanocomposites fabricated using FePO4/polyaniline as an iron source

Nanosized LiFePO4/C core/shell nanocomposites with different carbon shell thicknesses have been synthesized by a simple two-step procedure. The effects of carbon shell thickness on the electrochemical performance of these LiFePO4/C core/shell nanocomposites have been investigated. It shows that the LiFePO4/C core/shell nanocomposites with low carbon shell thicknesses exhibit poor electrochemical performance when used in lithium ion batteries, presumably due to presence of structural disorders and defects in the particle surface layers. An increase of carbon shell thickness can remove the structural disorders and defects. The LiFePO4/C core/shell nanocomposites with higher carbon shell thicknesses therefore exhibit significantly improved electrochemical performance. However, further increase of carbon shell thickness would lead to a decrease in the charge/discharge capacity of the LiFePO4/C core/shell nanocomposites, although these LiFePO4/C core/shell nanocomposites still exhibit high cycling stability. That is because excess carbon shell coating would hinder the penetration of the electrolyte solution into the carbon layers and the inward/outward diffusion of Li+ ions through the carbon layers, which decreases the charge/discharge capacity of the LiFePO4/C core/shell nanocomposites. (C) 2012 Elsevier B.V. All rights reserved.