Designing Hierarchical Assembly of Carbon-Coated TiO2 Nanocrystals and Unraveling the Role of TiO2/Carbon Interface in Lithium-Ion Storage in TiO2

Despite the many benefits of hierarchical nanostructures of oxide-based electrode materials for lithium-ion batteries, it remains a challenging task to fully exploit the advantages of such materials partly because of their intrinsically poor electrical conductivities. The resulting limited electron supply to primary particles inside secondary microparticles gives rise to significant variation in the lithium-ion (Li+) storage capability within the nanostructured particles. To address this, facile annealing, where in situ generated carbon-coated primary particles were assembled into porous microagglomerates, is demonstrated to prepare nanostructured titanium dioxide (TiO2). A systematic study on the effect of the carbon coating reveals that it is exclusively governed by the characteristics of the TiO2/carbon interface rather than by the nature of the carbon coating. Depending on their number, oxygen vacancies created by carbothermal reduction on the TiO2 surface are detrimental to Li+ diffusion in the TiO2 lattice, and structural distortion at the interface profoundly influences the Li+ (de)­intercalation mechanism. This new insight serves as a stepping stone toward understanding an important yet often overlooked effect of the oxide/carbon interface on Li+ storage kinetics, thereby demanding more investigations to establish a new design principle for carbon-coated oxide electrode materials.