Graphene-based electrochemical capacitors with integrated high-performance

The rapid development of portable electronics and hybrid vehicles requires electrochemical capacitors (ECs) with excellent integrated performances. Herein, we report such an EC based on the dense graphene hydrogel films (packing density = 1.18 ± 0.01 g cm⁻³) prepared by hydrothermal reduction of highly oxidized graphene oxide (HGO) sheets with lateral dimensions of 1–2 μm, followed by mechanical compression. This EC exhibited high areal (366 ± 6 mF cm⁻²), gravimetric (232 ± 3 F g⁻¹) and volumetric (273 ± 1 F cm⁻³) specific capacitances at 1 A g⁻¹, ultrahigh rate-capability (80% capacitance retention at 100 A g⁻¹), and good electrochemical stability. The effects of the structural defects and lateral sizes of graphene sheets on their electrochemical performances are studied, offering a guidance of rational designing graphene materials for their applications in ECs.