Carbon-carbon dense network composite with hierarchical structure for additive-free and high volumetric performance supercapacitor

High density carbon composite (AC3/G) with hierarchical porous structure is prepared by packing biomass-based carbon (ACs) into graphene network (rGO), via microwave-assisted hydrothermal treatment followed by capillary evaporation-induced drying. Graphene oxide is reduced during the treating process and acts as frame network to embed the ACs. ACs are packed into the network with a density up to 1.23 g/cm3 for AC3/G. ACs can prevent the agglomeration of rGO, and channels formed between rGO sheets and ACs facilitate the hierarchical porous structure. When AC3/G is used as a binder and conductive additive-free electrode in the three-electrode system, a high volumetric capacitance of 775 F/cm3 at 0.5 A/g is achieved with excellent cycling stability of 97.05%. When assembled into a flexible solid-state supercapacitor device with lignin hydrogel electrolytes, the high-density electrode delivers high volumetric and gravimetric energy densities of 9.7 W h/L and 7.9 W h/kg, with volumetric capacitance of 326 F/cm3 at 0.5 A/g. Remarkably, the study paves a new idea for preparation of energy devices with high volumetric performance using biomass resources.