Raman spectroscopic determination of phase evolutions in LiAl_xCo_1−xO₂ battery materials

Superior battery materials LiAlxCo_1−xO₂ (x = 0.0, 0.1, 0.3, 0.5, and 0.7) were synthesized using a solution-based route at various sintering temperatures (450–800 °C). In this communication, we report on the use of Raman spectroscopy to study effect of composition and sintering temperature on the resulting material. The phase evolutions in LiAlxCo_1−xO₂ compositions were studied using micro-Raman spectroscopy and a phase diagram is proposed based on the observations. For less Al content, the low-temperature phases of LiAlxCo_1−xO₂ showed Raman spectra corresponding to a monoclinic (space group C2/m) structure, while a low-temperature spinel (space group Fd3m) phase was observed for 50% or more Al in these compounds. All these compositions exhibited a layered hexagonal (space group R3m) structure when sintered above 700 °C. Raman spectra also revealed residual Co₃O₄ in the low-temperature forms of LiCoO₂ and LiA1_0.01Co_0.9O₂.