Free-standing graphene/vanadium oxide composite as binder-free electrode for asymmetrical supercapacitor.

Preparation of free-standing electrode materials with three-dimensional network architecture has emerged as an effective strategy for acquiring advanced portable and wearable power sources. Herein, graphene/vanadium oxide (GR/VO) free-standing monolith composite has been prepared via a simple hydrothermal process. Flexible GR sheets acted as binder to connect the belt-like VO for assembling three-dimensional network architecture. The obtained GR/VO composite can be reshaped into GR/VO flexible film which exhibits more compact structure by ultrasonication and vacuum filtration. A high specific capacitance of 358Fg for GR/VO monolith compared with that of GR/VO flexible film (272Fg) has been achieved in 0.5molLKSO solution when used as binder free electrodes in three-electrode system. An asymmetrical supercapacitor has been assembled using GR/VO monolith as positive electrode and GR monolith as negative electrode, and it can be reversibly charged-discharged at a cell voltage of 1.7V in 0.5molL KSO electrolyte. The asymmetrical capacitor can deliver an energy density of 26.22Whkg at a power density of 425Wkg, much higher than that of the symmetrical supercapacitor based on GR/VO monolith electrode. Moreover, the asymmetrical supercapacitor preserves 90% of its initial capacitance over 1000 cycles at a current density of 5Ag.