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, Co 3 O 4 nanoparticles embedded in three-dimensionally (3D) ordered macro-/mesoporous TiO 2 (Co 3 O 4 @TiO 2 ) are synthesized through an in situ method from dual templates. Differing from the composite prepared by loading active nanoparticles on support, Co 3 O 4 nanoparticles are embedded in TiO 2 framework, which can improve the stability of the electrode. Furthermore, the hierarchically porous structure of TiO 2 is in favor of the rapid diffusion of ions and electrolyte. As a result, The Co 3 O 4 @TiO 2 -2 composite with an optimized Co 3 O 4 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 Co 3 O 4 @TiO 2 -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 ).