Reaction mechanisms of Li0.30La0.57TiO3 powder with ambient air: H+/Li+ exchange with water and Li2CO3 formation

The proton/lithium exchange property of the lithium lanthanum titanate Li0.30La0.57TiO3 ( named LLTO) is shown to occur at room temperature under ambient air. The H-1 and Li-7 MAS NMR, TGA analysis and IR spectroscopy techniques are used to probe reaction mechanisms. XRPD analysis gives evidence of the topotactic character of this exchange reaction. As for exchange in aqueous solution, it is shown that Li0.30La0.57TiO3 is able to dissociate water on the grain surface and then to exchange H+ for Li+ into the perovskite structure. Lithium hydroxide is then formed on the grain surface and afterwards reacts with CO2 contained in air to form Li2CO3. It is shown that this mechanism is reversible. When the aged sample ( aging in air for 5 months at room temperature) is annealed at 400 degrees C for two hours, the initial LLTO sample is totally recovered, a mass loss is observed and the carbonate signal in IR spectra disappears, demonstrating the reversibility of the carbonation reaction process.