Investigation of Formation Mechanism of Meta-Stable Ni-rich Spinels from Layered Compounds through in-situ Neutron Diffraction

Speaker: Jack Kan, China Spallation Neutron Source

Program Description
In an attempt to enlarge the normal spinel phase diagram for the quaternary Li–Ni–Mn–Co oxide system, the transformation at moderate temperatures (150–210 °C) of layered Li0.5(Ni1–y–zMnyCoz)O2 (R3̅m), which were obtained by an ambient-temperature extraction of lithium from Li0.5(Ni1–y–zMnyCoz)O2, into normal spinel-like (Fd3̅m) Li(Ni1–y–zMnyCoz)2O4 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. A bond valence sum map has been performed to understand the ionic diffusion of lithium ions in the Ni-rich layered, spinel, and rock-salt structures. The study can aid the understanding of the possible phases that could be formed during the cycling of Ni-rich layered oxide cathodes.