On the LixNi0.70Fe0.15Co0.15O2 system:: An X-ray diffraction and Mossbauer study

The structural modifications and redox processes occurring during lithium deintercalation from the quasi-stoichiometric Li-0.97(Ni0.70Fe0.15Co0.15)(1.03)O-2 phase were studied by X-ray diffraction and Mossbauer spectroscopy. A solid solution is observed in the whole deintercalation domain (0.08 less than or equal to x less than or equal to 0.97); Rietveld refinement of the XRD pattern shows a strong decrease of the M-O bond distance upon lithium deintercalation. The Mossbauer study shows that nickel and iron ions are simultaneously oxidized, a large number of the iron ions being stabilized in the high-spin tetravalent state. Comparison with the data obtained in the Li-x(Ni,Ee)O-2 system emphasizes the effect of the small cobalt ions on the facility to oxidize iron ions. (C) 2001 Academic Press