Fast-Charging High-Energy Battery-Supercapacitor Hybrid: Anodic Reduced Graphene Oxide-Vanadium(IV) Oxide Sheet-on-Sheet Heterostructure.

The battery-supercapacitor hybrid (BSH) device has potential applications in energy storage and can be a remedy for low-power batteries and low-energy supercapacitors. Although several studies have investigated electrode materials (particularly for a battery-type anode material) and design for BSHs, the energy density and power density are insufficient (far from the levels required for practical applications). Herein, a hierarchical vanadium(IV) oxide on reduced graphene oxide (rGO@VO2) heterostructure as an anode and activated carbon on carbon cloth (AC@CC) as a cathode are proposed for fabricating an advanced BSH. The mixed valency of V ions inside the as-prepared VO2 matrix (V3+ and V4+) facilitates redox reactions at a low potential, giving rise to rGO@VO2 as a typical anode with a working potential of 0.01-3 V (vs Li/Li+). The sheet-on-sheet heterostructured rGO@VO2 yields a high specific capacity of 1214 mAh g-1 at 0.1 A g-1 after 120 cycles, with a high rate capability and stability. The rGO@VO2//AC@CC BSH device exhibits a maximum gravimetric energy density of 126.7 Wh kg-1 and a maximum gravimetric power density of ∼10 000 W kg-1 within a working voltage range of 1-4 V. Moreover, it exhibits fast charging times of 5 and 834 s with energy densities of 15.6 and 82 Wh kg -1, respectively.