Structural and surface modifications of LiFePO4 olivine particles and their electrochemical properties

LiFePO4-based olivine compounds were prepared by the usual ceramic method, where some modifications were carried out in order to improve the electrical conductivity of the cathode compound. Considering that the cathode is made up of electrochemical active particles and a nonactive polymer binder, two different methods were applied. The first one is related to the improvement of the interparticle conduction, and the other is the enhancement of the conductivity in the active particle itself. The former was attained with thermal decomposition of an organic additive (pyrene) during the sample preparation process, and the precipitated carbon was investigated with Raman spectroscopy. The bulk conductivity of the olivine was improved with a partial substitution of Fe2+ with Mn2+, where the holes were incorporated into the valence band. These modifications significantly altered the electrochemical properties of the olivine cathode: large specific capacity (>140 mAh/g) and small capacity fading. Although the importance of carbon deposition was confirmed as reported elsewhere, the structural modification effect was also more important than the surface one. The result will contribute to reduce carbon content of LiFePO4-based positive electrodes, which is important for their practical use. (C) 2006 The Electrochemical Society.