Stress-assisted design of stiffened graphene electrode structure toward compact energy storage

Abstract

The low spatial charge-storage density of porous carbons greatly limits volumetric performance in electrochemical capacitors. An increase of charge-storage density requires structural refinements to balance the trade-offs between the porosity and density of materials, but the limited mechanical properties of carbons usually fail to withstand effective densifying processes and obtain an ideal pore structure. Herein, we design the stiffened graphene of superior bending rigidity, enabling the fine adjustments of pore structure to maximize the volumetric capacitance for the graphene-based electrodes. The in-plane crumples on graphene sheets are found to contribute largely to the bending rigidity, which is useful to control the structural evolution and maintain sufficient ion-accessible surface area during the assembling process. This makes the capacitance of stiffening activated graphene keep 98% when the electrode density increases by 769% to reach 1.13 g cm−3 after mechanical pressure, an excellent volumetric energy density of 98.7 Wh L-1 in an ionic-liquid electrolyte is achieved. Our results demonstrate the role of intrinsic material properties on the performance of carbon-based electrodes for capacitive energy storage.