Steve Bewlay

Synthesis and characterization of LiFePO4 and LiTi0.01Fe0.99PO4 cathode materials

Nanocrystalline LiFePO 4 and doped LiTi 0 . 0 1 Fe 0 . 9 9 PO 4 powders were synthesized via a sol-gel preparation route. High-resolution tunneling electron microscopy observation and energy dispersive spectroscopy, mappingshow the homogeneous distribution of dopant Ti cations in the crystals. Fe and O K-edge X-ray absorption near-edge structure (XANES) measurements show that Ti 4 + doping induces an increased unoccupied d-state in LiFePO 4 , resulting in an enhanced p-type semiconductivity. In situ Fe K-edge XANES measurements of Ti-doped and undoped LiFePO 4 electrodes have been performed to determine the change of Fe valence during the lithium intercalation and de-intercalation processes. Both LiFePO 4 and doped LiTi 0 . 0 1 Fe 0 . 9 9 PO 4 cathodes demonstrate good electrochemical performance.

Tungsten Disulfide Nanotubes for Lithium Storage

WS 2 nanotubes were synthesized by sintering amorphous WS 3 at high temperature under flowing hydrogen. High-resolution transmission electron microscopy observation revealed that the as-prepared WS 2 nanotubes have an open end with an inner hollow core of about 4.6 nm. We studied the lithium intercalation behavior of WS 2 nanotubes. The WS 2 nanotubes demonstrated a stable cyclability in a wide voltage range (0.1-3.1 V vs. Li/Li + ). The nanotubes could provide a new class of electrode materials for lithium-ion batteries.