A mechanism study of synthesis of Li₄Ti₅O ₁₂ from TiO₂ anatase

The formation mechanism of a spinel-type lithium titanate Li ₄Ti₅O₁₂ with TiO₂ anatase as raw material, in both a conventional solid-state reaction (SSR) and a cellulose-assisted glycine-nitrate combustion (cellulose-GN) process are comparatively studied. XRD characterization demonstrates high-purity Li ₄Ti₅O₁₂ forms at 750 °C by the cellulose-GN synthesis, which occurs at a temperature at least 100 °C lower than that via SSR. The solid-phase reaction between TiO₂ and lithium compounds to form Li-Ti-O spinel and the phase transition of TiO₂ from anatase to "inert" rutile phase occur competitively during both synthesis processes. SEM results suggest that the solid precursor from the cellulose-GN process has a smaller particle size and a more homogenous mixing of the reactants than that in the SSR. Temperature-programmed oxidation experiments demonstrate that cellulose thermal pyrolysis creates a reducing atmosphere, which may facilitate the oxygen-ion diffusion. Both factors facilitate the formation of Li-Ti-O spinel, while the TiO₂ anatase transforms to TiO₂ rutile during the SSR, which has slow lithium-insertion kinetics. As a result, a high calcination temperature is necessary to obtain a phase-pure Li₄Ti₅O₁₂. Charge-discharge and EIS tests demonstrate the Li₄Ti₅O₁₂ obtained by the cellulose-GN process shows much better low-temperature electrochemical performance than that obtained by standard SSR. This improvement attributes to the reduced particle size due to the lower synthesis temperature.