Carbon surface layers on a high-rate LiFePO4

Transmission electron microscopy (TEM) was used to image particles of a high-rate LiFePO4 sample containing a small amount of in situ carbon. The particle morphology is highly irregular, with a wide size distribution. Nevertheless, coatings, varying from about 5 to 10 nm in thickness, could readily be detected on surfaces of particles as well as on edges of agglomerates. Elemental mapping using energy-filtered TEM indicates that these very thin surface layers are composed of carbon. These observations have important implications for the design of high-rate LiFePO4 materials in which, ideally, a minimal amount of carbon coating is used. (c) 2006 The Electrochemical Society.