Lithium-nickel cobalt oxides with spinel structure prepared at low temperature. XRD, XPS, and EIS measurements

Li, Co and Ni mixed oxides of composition LiNixCo2−xO4 (x=0.25, 0.5, 0.75 and 1) were prepared at 280°C by the Pechini sol–gel method. The Rietveld refinement of the X-ray diffraction data indicated that all the obtained compounds crystallize in the Fd3m space group characteristic of cubic spinel-related oxides. XPS studies on these oxides reveal the presence of Ni2+, Ni3+, Co3+ and Co4+ ions at the surface. The diffusion coefficients of the Li+ ion in the oxide lattice, determined by EIS measurements, are larger (10−13cm2s−1≤D≤10−10cm2s−1) than that shown by the non-substituted cobalt-lithium oxide, LiCo2O4 (D=10−16cm2s−1) and present similar values to those of layered oxides of related composition. ► LiNixCo2−xO4 spinel oxides are prepared by a sol-gel method. ► XPS measurements show Ni2+, Ni3+, Co3+ and Co4+ ions. ► Co4+ ions content in the B-spinel sites determinate high charge transference impedance values. ► Low Li+ ion diffusion coefficients on the oxides were observed.