High Density of Free-Standing Holey Graphene/PPy Films for Superior Volumetric Capacitance of Supercapacitors

The volumetric performance is a vitally important metric for portable electronic and wearable devices with limited space. However, it is contradictory for the most supercapacitors in the connection between the volumetric and gravimetric capacitances. Herein, we report a simple strategy to prepare a free-standing and binder-free holey graphene/PPy film that possesses a dense microstructure but still high gravimetric capacitances. The holey graphene/PPy film own high-efficiency ion transport channels and big ion-accessible surface area to achieve high-powered supercapacitor electrodes, which have a superior volumetric capacitance (416 F cm^-3) and high gravimetric capacitance (438 F g^-1) at 1.0 A g^-1 in 6 M KOH electrolyte. Meanwhile, it possesses high rate capability and good cycling performance (82.4% capacitance retention even after 2000 cycles). Furthermore, the volumetric energy density of assembled holey graphene/PPy film symmetric supercapacitor can show high as 22.3 Wh L^-1. Such densely packed free-standing holey graphene/PPy film is a very significant electrode material for compact and miniaturized energy storage equipment in the further.