Low-Temperature Synthesis, Structural Characterization, and Electrochemistry of Ni-Rich Spinel-like LiNi_2–<i>y</i>Mn_<i>y</i>O₄ (0.4 ≤ <i>y</i> ≤ 1)

Abstract

The thermal conversion of chemically delithiated layered Li_0.5Ni_1–<i>y</i>Mn_<i>y</i>O₂ (0.2 ≤ <i>y</i> ≤ 0.5) into spinel-like LiNi_2–<i>y</i>Mn_<i>y</i>O₄ (0.4 ≤ <i>y</i> ≤ 1) has been systematically investigated. 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 <i>in situ</i> 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. The study can aid the understanding of the possible phases that could be formed during the cycling of Ni-rich layered oxide cathodes