Raman investigation of the structural changes in anatase LixTiO2 upon electrochemical lithium insertion

Micro-Raman spectrometry and x-ray diffraction (XRD) experiments were performed on the anatase LixTiO2 system (0 less than or equal to x less than or equal to 0.6) produced from the electrochemical discharge of a TiO2 composite cathode in propylene carbonate -LiClO4 solution at room temperature. Raman spectrum modifications indicate local structural and chemical changes as lithium enters the anatase host lattice. The existence of a tetragonal to orthorhombic phase transition is clearly demonstrated by the Raman and XRD measurements. Moreover, lithium extraction is only partially quantitative for Li uptake less than or equal to0.5, as shown both from structural and electrochemical data in the 3-1.5 V potential range. For the first time, the Raman fingerprint of the lithium titanate (LT) Li0.5TiO2 orthorhombic phase is clearly evidenced. A theoretical analysis of the lattice dynamics suggested a complete interpretation of the experimental Raman spectra in the Li,TiO2 system, which provided valuable information on the Li atom positions and coordination in LT. Taking into account the possibility of rather short Li-O distances, the complex band structure in the high-wavenumber region is assigned to the Li-O vibrations. Furthermore, spectra simulation offers an explanation for the new shape of the TiO2 lattice modes observed in the low-wavenumber region. Copyright (C) 2004 John Wiley Sons, Ltd.