A regular, compact but microporous packing structure: High-density graphene assemblies for high-volumetric-performance supercapacitors

Conventional graphene powder materials exhibit ultralow density characteristics, severely restricting their practical application. For addressing this issue, we propose a facile but efficient strategy for optimization of the graphene packing structure. Through the electrostatic orientation effect of K⁺ ions, a highly regular and compact graphene assembly with a high density is fabricated, at the same time, interlayer micropores are preserved due to the separation effect of K⁺ ions intercalated between graphene layers, optimizing the delicate balance between the dense and porous characteristics of graphene. Besides, good wettability to electrolytes and Faradaic pseudo-capacitance further improve the capacitive performances. Accordingly, a volumetric capacitance as high as 508 F cm^-3 is achieved for the produced graphene film, which is the highest value for carbon-based electrode materials in aqueous electrolytes to date. Furthermore, the unique packing structure is retained for the graphene assembly in a powder form, and the symmetric two-electrode supercapacitors based on the produced graphene powder material with a mass loading density of 6-8 mg cm^-2, close to the value of commercial supercapacitors, exhibit a good high-rate capability and a volumetric energy density as high as 30.2 W h L^-1.