Structural evolution during the reaction of Li with nano-sized rutile type TiO2 at room temperature

Rutile type TiO2 nanoparticles (10 nm × 200 nm in size) were prepared using a precipitation method in aqueous solution. Their lithium reactivities were followed using both classical galvanostatic insertion and in situ XRD measurements, and compared to that of a bulk and commercial nano-sized (50 nm) rutile TiO2 sample so as to stress the interlink between Li insertion electrochemical capacity and crystallite size. For the highly divided material, we obtained a reversible capacity of 0.5 Li ion per formula unit after a first reduction step during which, the material is irreversibly transformed. Such a reduction step is shown to enlist two solid solution domains followed by the formation of a rocksalt type phase LiTiO2. Such a specific reactivity of nano-sized rutile TiO2 is explained in terms of better lattice strains accommodation during the insertion of lithium.