Three-dimensionally ordered porous TiNb₂O₇ nanotubes: A superior anode material for next generation hybrid supercapacitors

Hybrid supercapacitors are a very appealing power source with high energy density and power density because they employ both the merits of lithium ion batteries and supercapacitors. To balance such hybrid systems, the rate of the redox component must be substantially comparative to the levels of the double layer process. As far as the insertion-host material TiNb₂O₇ is concerned, we have used facile step electrode design consisting of the physically assisted template infusion of Ti-Nb sol into the pores of AAO followed by in situ conversion into porous TiNb₂O₇ nanotubes within the AAO walls under calcination, and finally making those templates dissolve away. Using such an electrode as the battery type anode and a graphene grass electrode as the capacitor type cathode, we successfully constructed a novel hybrid supercapacitor. Within a voltage range of 0-3 V, a high energy density of ∼74 W h kg^-1 is achieved and it could remain as much as ∼34.5 W h kg^-1 at a power of 7500 W kg^-1. The present research sheds new light on the development of energy storage devices with both high energy density and high power density.