Structural and electrochemical characterization of the LiNi1-yTiyO2 electrode materials obtained by direct solid-state reactions
Résumé
LiNi1-yTiyO2 (y ≤ 0.15) layered oxides were synthesized at high temperature by solid-state reactions. Rietveld refinements of their X-ray and neutron diffraction patterns showed that these phases were characterized by an α-NaFeO2-type structure with the following cationic distribution: (Li1-zNi2+z)3b(Ti4+tNi2+t+zNi3+1-z-2t)3aO2 [t = y(1 + z)]. The amount of Ni2+ ions in the lithium site increases with y. A magnetic study confirmed the presence of paramagnetic ions in the interslab space and, therefore, the cationic distribution. These materials used as positive electrode in lithium batteries show reversible behavior. A large decrease of the capacity is observed with increasing y, because of the presence of extra nickel ions in the lithium sites. For the "LixNi0.95Ti0.05O2" composition, 144 mA h/g are obtained in discharge at the 14th cycle at the C/20 rate. The "LixNi1-yTiyO2" phases were characterized for y = 0.05 and 0.10: the simultaneous presence of titanium ions in the slab and of a significant amount of extra nickel ions in the lithium sites prevents phase transitions upon cycling.