A mechanism study of synthesis of Li4Ti5O12 from TiO2 anatase

The formation mechanism of a spinel-type lithium titanate Li4Ti5O12 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 Li4Ti5O12 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.