Controlled swelling of graphene films towards hierarchical structures for supercapacitor electrodes

Graphene films are promising electrode materials for flexible energy-storage device because of their excellent electrochemical stability, flexible and lightweight, etc. However, due to strong van der Waals (vdWs) interaction, graphene film based devices exhibit inadequate material utilization and low ion transport speed. Here we demonstrate a novel strategy of graphene oxide (GO) film swelling to prepare free-standing graphene hydrogel (GH) films with controlled structure for high-performance electrode. The regulation of GO film swelling is achieved by changing acting force (e.g., vdWs, hydrogen bonding and electrostatic repulsion) between GO nanosheets. After reaction, the resulting GH films with highly orientational hierarchical porous structure exhibit excellent electrochemical performance with impressive gravimetric capacitance of 237.6 F g−1 at 1 A g−1 and high areal capacitance of 608 mF cm−2 at 1 mA cm−2. Besides, assembled GH film based Zinc-ion hybrid supercapacitors (ZHSs) show a large capacity of 99.3 mAh g−1 and a very high specific energy of 76.2 Wh kg−1. Moreover, the ZHSs display excellent capacity retention rate of ~90% after 10,000 charge/discharge cycles. These results indicate that constructing unique structure GH films by utilizing swelling behavior of GO films is an innovative, simple and practical technology for preparation of electrode materials.