Construction of CoO three-dimensional mesoporous framework structures from zeolitic imidazolate framework-67 with enhanced lithium storage properties.

High-porosity mesoporous framework structures are attractive for electrochemical energy storage and other applications. Herein we demonstrate a novel synthesis strategy to make zeolitic imidazolate framework-67 oxidize to a CoO three-dimensional mesoporous framework structure. This strategy relies on the oxygen-limitation effect of the closed nanocage and the affinity effect of polyvinylpyrrolidone towards zeolitic imidazolate framework-67. Several TiO nanospheres, as the unique structure junctions, are uniformly embedded within the CoO framework to enhance the framework strength. The TiO/hydrous titania polyhedron nanocage, as the protecting shell, further encapsulates the CoO framework, forming a perfect capsule-type hybrid. As anode materials for lithium-ion batteries, TiO@CoO framework capsules show superior lithium storage performance with high reversible capacity, stable cycling life and good rate capability. A reversible capacity of 1042 mAh g can be delivered after 200 cycles at a current density of 300 mA g. The average discharge capacity over 200 cycles reaches 926 mAh g. This demonstrates the superiority of this material structure and its great potential as an anode for high-performance lithium-ion batteries. This work indicates a new strategy to take advantage of metal-organic frameworks to synthesize their mesoporous framework derivatives.