Dense yet highly ion permeable graphene electrodes obtained by capillary-drying of a holey graphene oxide assembly

The density and ion channel abundancy of an electrode material must be elaborately balanced to achieve a high volumetric energy density for any energy storage devices. As a typical example, graphene shows great potential in different energy storage devices but its low density and ion diffusion barrier effect limit its practical uses. In the present work, H₂O₂ etching was introduced into the hydrothermal assembly of graphene oxide (GO) to decrease the lateral size of GO and create in-plane holes, and after a capillary drying process, a high-density holey graphene monolith (HHGM) with numerous and interconnected ion transporting channels was obtained. The smaller sheet size leads to a more densified assembly while in-plane holes are beneficial to ion transportation in the HHGM, which well balance the high density and fast ion diffusion in the electrode. As a result, the HHGM shows an impressive rate performance, coupled with a high volumetric capacitance.