Nanostructured LiMPO₄ (M = Fe, Mn, Co, Ni) – carbon composites as cathode materials for Li-ion battery

¹ Technische Universitaet Darmstadt, Materials Science Department, Petersenstrasse 23, D-64287, Darmstadt, Germany
² Center of Smart Interfaces, Darmstadt University of Technology, Petersenstrasse 32, D-64287, Darmstadt, Germany

^a email: ldimesso@surface.tu-darmstadt.de

Abstract

Nanostructured materials are considered to be strong candidates for fundamental advances in efficient storage and/or conversion. In nanostructured materials transport kinetics and surface processes play determining roles. This work describes recent developments in the synthesis and characterization of composites which consist of lithium metal phosphates (LiMPO₄, M = Fe, Mn, Co, Ni) coated on nanostructured carbon supports (unordered nanofibers, foams). The composites have been prepared by coating the carbon structures in aqueous (or polyols) solutions containing lithium, metal ions and phosphates. After drying out, the composites have been thermally treated at different temperatures (between 600-780°C) for 5-12 hours under nitrogen. The formation of the olivine structured phase was confirmed by the X-ray diffraction analysis on powders prepared under very similar conditions. The surface investigation revealed the formation of an homogeneous coating of the olivine phase on the carbon structures. The electrochemical performance on the composites showed a dramatic improvement of the discharge specific capacity (measured at a discharge rate of C/25 and room temperature) compared to the prepared powders. The delivered values were 105 mAhg^-1 for M = Fe, 100 mAhg^-1 for M = Co, 70 mAhg^-1 for M = Mn and 30 mAhg^-1 for M = Ni respectively.