Study of the Local Order in LiNi1-yCOyO2 Oxides Synthesized by Soft Chemistry

Lattice dynamics of LiNi1-yCoyO2 solid solution are investigated using Raman and FTIR measurements. Evolution of the vibrational spectra, i.e., frequency shift and band broadening of the stretching modes of either (Ni1-yCoyO2)O-6 or LiO6 octahedra, are studied as a function of the calcination temperature of the LiNi1-yCoyO2 solid solution. Results show that the solid solution exhibits a one-mode behavior with an increase of the (Ni1-yCoyO2)(n) sheet covalency upon substitution of cobalt for nickel. The change in the covalency corresponds to an increase of the Madelung constant with decreasing the c/a value. The broadening of the vibrational bands for Ni-rich compounds is the result of the cation mixing in the crystal layers. The partially disordered cation distribution appearing in lithium nickelate materials can also explain the observed broadening of the Raman spectra.