Double-shelled Co^sub 3^O^sub 4^@TiO^sub 2^@C yolk-shell spheres as anode material for enhanced cycling stability of lithium ion batteries

In this paper, double-shelled Co3O4@TiO2@C yolk-shell spheres have been successfully synthesized for enhanced the cycling stability of lithium ion batteries (LIBs). The inter-layer SiO2 as a sacrificial layer is removed by LiOH ethylene glycol/water solution at hydrothermal treatment, while the Co3O4 spheres are grown into the Co3O4 flowers due to the Ostwald ripening process. The morphologies, element contents, structure, element distribution and compositions of the samples are characterized by SEM, TEM, EDS, XRD and XPS. When evaluated as anode material, the double-shelled TiO2@C layer and void space can not only prevent the aggregation of Co3O4 and electrode polarization, but also improve the charge transfer and lithium ions diffusion. Remarkably, the double-shelled Co3O4@TiO2@C yolk-shell spheres can still deliver stable and reversible capacities of approximately 400 mAh g-1 at the current density of 200 mA g-1 during 100 cycles, far higher than those of Co3O4 spheres (about 100 mAh g-1). Cyclic voltammetry curves also show that the Co3O4@TiO2@C yolk-shell spheres possess superior reversible reactions for lithium ions insertion-extraction. As such, our work demonstrates a rational way to improve the electrochemical performance of metal oxides for LIBs.