Low-Temperature Synthesis, Structural Characterization, and Electrochemistry of Ni-Rich Spinel-like LiNi2–yMnyO4 (0.4 ≤ y ≤ 1)

The thermal conversion of chemically delithiated layered Li0.5Ni1–yMnyO2 (0.2 ≤ y ≤ 0.5) into spinel-like LiNi2–yMnyO4 (0.4 ≤ y ≤ 1) has been systematically investigated in this paper. The formed spinel-like phases are metastable and cannot be accessed by a conventional high-temperature solid-state method. The layered-to-spinel transformation mechanism has been studied by the Rietveld refinement of in situ neutron diffraction as a function of temperature (25–300 °C). In particular, the ionic diffusion of Li and M ions is quantified at different temperatures. Electrochemistry of the metastable spinel-like phases obtained has been studied 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. Finally, the study can aid the understanding of the possible phases that could be formed during the cycling of Ni-rich layered oxide cathodes.