X-ray Diffraction, EPR, and 6Li and 27Al MAS NMR Study of LiAlO2−LiCoO2 Solid Solutions

The preparation of solid solutions of the LiAlO 2 −LiCoO 2 system in the complete composition range is described. Powder X-ray diffraction gives direct information about the partial substitution of Co by Al atoms, together with a fractional occupancy of tetracoordinated sites by aluminum atoms. EPR of impurity Ni 3+ ions and 6 Li and 27 Al MAS NMR spectroscopies are used to assess for cation distribution. 6 Li NMR spectra show a single resonance of lithium ions in octahedral sites. 27 Al NMR spectra show that the distribution of Al atoms in tetrahedral and octahedral sites changes with composition. EPR spectra evidence that Ni 3+ impurity ions in the Al y Co 1 - y O 2 layers prefer mainly Al 3+ ions as first neighbors. The potential applicability of these materials as intercalation electrodes is also evaluated in lithium anode cells. A poor lithium ion diffusivity, resulting from the presence of aluminum in both tetrahedral and octahedral sites, may limit the applicability of LiAl y Co 1 - y O 2 cathodes. The partial substitution of Co by Ni leads to an improvement of the electrochemical performance.