3D ordered amorphous and porous TiO 2 framework anode with low insertion barrier and fast kinetics for K-ion hybrid capacitors.

TiO is considered as a low cost, long-term stable, and safe anode for high power K-ion hybrid capacitors (KICs) due to its abundant reserve, small volume expansion rate, and sloping voltage plateau that avoids K-ion plating at high voltage polarization. However, the enhancement of its low capacity and sluggish kinetics caused by poor electroconductivity and high insertion barrier is still challenging to further develop high-performance KICs. Herein, the reduced graphene oxide (rGO) is embedded in the walls of 3D ordered macro-/mesoporous TiO (termed as TiO@rGO framework) to create intimate TiO/rGO interfaces, ensuring the effectively electron transportation during potassiation/depotassiation of TiO while maintaining rapid ions/electrolyte diffusion. Furthermore, the controlled amorphous TiO framework can further lower the lattice insertion energies, contributing to a fast accommodation of K-ion. As expected, the amorphous TiO@rGO framework (TiO@rGO-1) exhibits a superior rate capability (148.8 mAh g at 5 A g) and cycling stability (171.2 mAh g at 1 A g after 800 cycles). The assembled KICs can reach a high energy/power density of 125.2 Wh kg/4267.4 W kg as well as a long-term lifespan. This tactic provides a reliable and general way to design a TiO-based anode with fast kinetics toward high-performance KICs.