Structural and Electrochemical Characterization of the LiNi₁₋yTiyO₂ Electrode Materials Obtained by Direct Solid-State Reactions

LiNi 1 - y Ti y O 2 ( 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-NaFeO 2 -type structure with the following cationic distribution: (Li 1 - z Ni 2+ z ) 3b (Ti 4+ t Ni 2+ t + z Ni 3+ 1 - z - 2 t ) 3a O 2 [ t = y (1 + z )]. The amount of Ni 2+ 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 “Li x Ni 0.95 Ti 0.05 O 2 ” composition, 144 mA h/g are obtained in discharge at the 14th cycle at the C /20 rate. The “Li x Ni 1 - y Ti y O 2 ” 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.