Raman characterization of Li(Al1-xCox)O2

Abstract
For the first time, we measured Raman spectra from Li(Al1-xCox)O2 (x = 0.5 to 0.9), a new cathode material for lithium batteries. Whereas LiCoO2 sintered at 400 °C develops a spinel structure, Li(Al1-xCox)O2 sintered at 380 °C is amorphous, as shown by its single broad Raman band. Li(Al1-xCox)O2 sintered at 700 or 900 °C shows Raman peaks independent of x that coincide with those from LiCoO2, indicating that Li(Al1-xCox)O2 has the α–NaFeO2 structure (space group R3m). Traces of the impurity phase Co3O4 appear in samples treated at 900 °C but not at 700 °C. The Raman peak widths exceed those in LiCoO2, suggesting that replacement of Co by Al increases disorder among the Li ions.