Lithium/nickel mixing in the transition metal layers of lithium nickelate: high-pressure synthesis of layered Li[LixNi1−x]O2 oxides as cathode materials for lithium-ion batteries

Novel compositions Li[LixNi1−x]O2, 0<x<0.2, with a layered structure, have been prepared under high-pressure in an oxygen-rich atmosphere using a piston-cylinder type apparatus. A new structural feature of these compositions as compared to well-known Li[Ni]O2 is the development of mixed [LixNi1−x]O2-layers in addition to nearly pure Li-layers. The replacement of Ni3+ by Li+ in nickel-rich layers is compensated for by the appearance of Ni4+ ions. The use of Li[LixNi1−x]O2 as a cathode material in a lithium ion cell shows a different electrochemical behavior as compared to Li[Ni]O2. Below 4.6 V the cell capacity is always below 115 mA g−1. On increasing the voltage upper limit, an irreversible transformation into a solid with a stoichiometry to LixNiO2 takes place. On further cycling Li[LixNi1−x]O2 displays a reversible lithium insertion, reaching a capacity of about 190 mA h g−1 between 5.0 and 2.7 V after several cycles.