Synthesis and Electrochemistry of Li- and Na-Fulleride Doped Mesoporous Ta Oxides

A mesoporous tantalum oxide lithium fulleride composite was synthesized by solution intercalation of C60 into a prefabricated Li-TaTMS material and characterized by elemental analysis, X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorptiondesorption, X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID) magnetometry, and solid-state 13C and 7Li NMR. The room conductivity measurements of Li fulleride material showed that this material was insulating, as opposed to previously synthesized K and Na based mesoporous Ta oxide fulleride composites with similar composition, which were semiconducting or metallic. Solid-state 7Li NMR of this lithium composite exhibited a single Li environment. XPS measurements indicated an oxidation of the tantalum oxide walls had occurred upon intercalation of the fullerene 13C NMR, and Raman measurements were consistent with one fulleride species in the pores. Electrochemical measurements revealed largely irreversible behavior upon intercalation/deintercalation of Li+ into this material. This was attributed to the insulating nature of this composite impeding charge transport through the channels. In contrast, the corresponding Na fulleride intercalate showed reversible Li insertion, possibly due to enhanced charge transport through the semiconducting structure.