Embedding Co3O4 nanoparticles in three-dimensionally ordered macro-/mesoporous TiO2 for Li-ion hybrid capacitor.

Lithium-ion hybrid capacitors (LICs) have gained increasing focus owing to their high energy/power densities. The development of anodes with superior rate capability is an effective way to surmount the kinetic mismatch between anodes and cathodes, and thus, enhancing the energy/power densities. Herein, Co3O4 nanoparticles embedded in three-dimensionally (3D) ordered macro-/mesoporous TiO2 (Co3O4@TiO2) are synthesized through an in situ method from dual templates. Differing from the composite prepared by loading active nanoparticles on support, Co3O4 nanoparticles are embedded in TiO2 framework, which can improve the stability of the electrode. Furthermore, the hierarchically porous structure of TiO2 is in favor of the rapid diffusion of ions and electrolyte. As a result, The Co3O4@TiO2-2 composite with an optimized Co3O4 content (~25 wt%) delivers a high capacity of 944.1 mAh g-1 after 100 cycles at 0.1 A g-1 and high-rate capability (405.7 mAh g-1 after 1000 cycles at 5 A g-1). The LIC assembled with Co3O4@TiO2-2 anode and activated carbon (AC) cathode delivers high energy/power densities (maximum, 87.9 Wh kg-1/10208.9 W kg-1) and great cycle stability (88.1%, 6000 cycles, 0.5 A g-1).