Exploration of a Metastable Normal Spinel Phase Diagram for the Quaternary Li–Ni–Mn–Co–O System

In an attempt to enlarge the normal spinel phase diagram for the quaternary Li–Ni–Mn–Co–O system, the transformation at moderate temperatures (150–210 °C) of layered Li 0.5 (Ni 1– y – z Mn y Co z )O 2 ( R 3̅ m ), which were obtained by an ambient-temperature extraction of lithium from Li 0.5 (Ni 1– y – z Mn y Co z )O 2, into normal spinel-like ( Fd 3̅ m ) Li(Ni 1– y – z Mn y Co z ) 2 O 4 has been investigated. The phase-conversion mechanism has been studied by joint time-of-flight (TOF) neutron and X-ray diffractions, thermogravimetric analysis, and bond valence sum map. The ionic diffusion of lithium (3a, 6c) and nickel (3a, 3b) ions has been quantified as a function of temperature. The investigated spinel phases are metastable, and they are subject to change into rock-salt phases at higher temperatures. The phases have been characterized as cathodes in lithium-ion cells. The study may serve as a strategic model to access other metastable phases by low-temperature synthesis approaches.