Although numerous efforts have been devoted to the spinal Li 4 Ti 5 O 12 anode material of lithium-ion batteries (LIBs), controllable synthesis of high-purity Li 4 Ti 5 O 12 nanoparticles under hydrothermal conditions has not yet been achieved. The current work systematically investigates the relationship between phase compositions of the Li−Ti−O system with the corresponding critical conditions. By determining the phase composition using the Rietveld refinement of XRD patterns, the relationship between key hydrothermal parameters and the resultant purity of Li 4 Ti 5 O 12 is revealed, and the formation mechanism of Li 4 Ti 5 O 12 using crystalline TiO 2 nanoparticles (Evonik Aeroxide P25, Hombikat 8602, and rutile TiO 2 ) and amorphous hydrous TiO 2 spheres (AHTS) as TiO 2 precursors in an aqueous LiOH solution is demonstrated accordingly. The hydrothermal process cannot generate Li 4 Ti 5 O 12 directly, while lithium titanium oxide intermediates (LTOIs), e.g., Li 2 TiO 3 and Li 2−x H x Ti 2 O 4 (OH) 2 , are obtained upon partial lithiation of crystalline or amorphous TiO 2 in the LiOH solution, respectively. Nanostructured TiO 2 @LTOIs can be formed since the underlying phase transition follows the classic in situ crystallization mechanism, as evidenced by the successful self-template synthesis using AHTS. Li 4 Ti 5 O 12 is formed by the solid-state reaction between the TiO 2 core and the LTOI shell at elevated temperatures (∼700 °C). At optimal conditions, the molar ratio of Li/Ti in all TiO 2 @LTOIs should be greater than a stoichiometric ratio of 4:5 since the solid-state reaction is found to promote the evaporation of lithium species. The comparative studies for the lithium storage properties of our assembled half-and full-cell LIBs demonstrate that the high phase purity of Li 4 Ti 5 O 12 enhances the electrochemical performances and that the spherical morphology delivers better cyclic stability.

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