Raman investigation of the structural changes in anatase Li_<i>x</i>TiO₂ upon electrochemical lithium insertion

<jats:title>Abstract</jats:title><jats:p>Micro‐Raman spectrometry and x‐ray diffraction (XRD) experiments were performed on the anatase Li<jats:sub><jats:italic>x</jats:italic></jats:sub>TiO<jats:sub>2</jats:sub> system (0 ≤ <jats:italic>x</jats:italic> ≤ 0.6) produced from the electrochemical discharge of a TiO<jats:sub>2</jats:sub> composite cathode in propylene carbonate LiClO<jats:sub>4</jats:sub> 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 ≤0.5, 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) Li<jats:sub>0.5</jats:sub>TiO<jats:sub>2</jats:sub> orthorhombic phase is clearly evidenced. A theoretical analysis of the lattice dynamics suggested a complete interpretation of the experimental Raman spectra in the Li<jats:sub><jats:italic>x</jats:italic></jats:sub>TiO<jats:sub>2</jats:sub> 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 TiO<jats:sub>2</jats:sub> lattice modes observed in the low‐wavenumber region. Copyright © 2004 John Wiley & Sons, Ltd.</jats:p>