Cr2O3@TiO2 yolk/shell octahedrons derived from a metal–organic framework for high-performance lithium-ion batteries

• Novel porous Cr2O3@TiO2 yolk/shell structure constructed from MIL-101(Cr).
• Multiple-core structure with small core size and moderate BET surface area.
• Exhibiting improved lithium storage performance compared with bare Cr2O3 due to the yolk/shell structure.

To make use of a metal–organic framework MIL-101(Cr3+) as template and core generator, we report synthesis of a novel nanoscale yolk/shell octahedron of Cr2O3@TiO2 and its high performance as the anode material for lithium ion battery. Nanoscale MIL-101(Cr3+) was coated with amorphous TiO2 shell and calcinated under Ar and then in air atmospheres to form nanoscale Cr2O3@TiO2. After heat treatment, the amorphous TiO2 coated MIL-101(Cr) was transformed into nanosized Cr2O3 crystals with crystalline TiO2 cover, forming multicore yolk/shell octahedrons, as demonstrated from their SEM and TEM morphologies. The resulting Cr2O3@TiO2 has moderate porosity with the BET surface area of 146 m2 g−1, and the diameter of its Cr2O3 cores is 10–40 nm. It has demonstrated a reversible capacity of 510 mA h g−1 after 500 cycles at 0.5 C charge/discharge rate, which is much better than the bare nano Cr2O3 without TiO2 shell, and is one of the best-performed Cr2O3 anode materials. The improved electrochemical performance of Cr2O3@TiO2 is attributed to its small particle size with moderate porosity for the infiltration of electrolyte and the fast diffusion of Li+ ions, its void space within yolk/shell structure to buffer volumetric variation of Cr2O3 and its TiO2 shell to restrain pulverized inner particles.

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