Interfacial Nanosized and Oxygen Vacancy Engineered Homojunction Anatase/Rutile-TiO2 Core-Shell Microspheres for Synchronous High-Capacity and Ultrafast Lithium Storage

The slow diffusion rate of lithium ions limits commercial TiO 2 from being used at scale in LiBs. This paper presents the strategy used to synthesize a homojunction anatase/rutile-TiO 2 core-shell microsphere enriched with oxygen vacancies. Oxygen vacancies and interfacial shared storage accelerate electron mobility and improve lithium-ion diffusion kinetics. Electrochemical AC impedance measurements show that the Li + diffusion coefficient of A/R-TiO 2 -V o 2 samples with oxygen vacancies is (1.14 × 10 -12 cm 2 /s), which is higher than the diffusion coefficient of A/R-TiO 2 samples without oxygen vacancies (9.28 × 10 -14 cm 2 /s). The study of the effect of oxygen vacancy content on crystal structure and lithium-ion storage capabilities was quantitatively modulated. The specific capacity of an A/R-TiO 2 -V o 2 anode containing a moderate number of oxygen vacancies was 405 mAh/g after 450 cycles at 0.5 C, which is 121% of the theoretical maximum. This high-capacity behavior can be mainly attributed to the synergistic effect of core-shell hollow structures, interfacial shared storage, and oxygen vacancies generating additional active sites located at grain boundaries that are available for lithium storage. This strategy of oxygen defect engineering combined with heterojunctions can be extended to other materials with similar dilemmas.