(De)lithiation-Induced Phase Transitions of LiMTiO₄ Spinels

Abstract

Nanocrystalline LiMn 3+ TiO 4 (~10 nm, annealed in air at 500°C) and LiFe 3+ TiO 4 (3~5 nm, annealed in argon at 600°C) were synthesized by a sol-gel route, and their structural changes upon Li + extraction and reinsertion were investigated. To determine accurately the phase compositions of the nanosized materials, we used combined techniques of X-ray diffraction (XRD) Rietveld refinement and synchrotron pair distribution function (PDF) analysis. Partial lithium from LiMTiO 4 (M = Mn, Fe) can be extracted on charging to 4.8 V, leading to Li-deficient Li 1-x MTiO 4 with a phase splitting into two spinel phases. Over subsequent cycling between 1.5 and 4.8 V, more than one Li + can be reversibly reinserted into the framework, resulting in a Li-rich Li x+y MTiO 4 . Upon lithiation, Li 1+y MnTiO 4 undergoes a reversible spinel/rock-salt phase transition together with the formation of certain amounts of tetragonal phase, whereas LiFeTiO 4 maintains a spinel structure.

Nanoscale spinel LiFeTiO4for intercalation pseudocapacitive Li+storage

“…41,42 Furthermore, we confirmed that the crystal structure of the electrochemically generated Li 1.93 FeTiO 4 is different from that of chemically prepared Li 2 FeTiO 4 (Fm% 3m). 43,44 In addition, the lithiation voltage for the spinel LiFeTiO 4 is about 0.2 V higher than that for the chemically synthesized rock-salt Li 2 FeTiO 4 (B2.4 V). 43 These results indicate a small effect of Li + insertion/extraction on the spinel host framework and thus a single-phase and quasi zero-strain lithiation/delithiation behaviour.…”