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/V₂O₅) free-standing monolith composite has been prepared via a simple hydrothermal process. Flexible GR sheets acted as binder to connect the belt-like V₂O₅ for assembling three-dimensional network architecture. The obtained GR/V₂O₅ composite can be reshaped into GR/V₂O₅ flexible film which exhibits more compact structure by ultrasonication and vacuum filtration. A high specific capacitance of 358Fg^-1 for GR/V₂O₅ monolith compared with that of GR/V₂O₅ flexible film (272Fg^-1) has been achieved in 0.5molL^-1K₂SO₄ solution when used as binder free electrodes in three-electrode system. An asymmetrical supercapacitor has been assembled using GR/V₂O₅ 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^-1 K₂SO₄ electrolyte. The asymmetrical capacitor can deliver an energy density of 26.22Whkg^-1 at a power density of 425Wkg^-1, much higher than that of the symmetrical supercapacitor based on GR/V₂O₅ monolith electrode. Moreover, the asymmetrical supercapacitor preserves 90% of its initial capacitance over 1000 cycles at a current density of 5Ag^-1.