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).