Electrode thickness design toward bulk energy storage devices with high areal/volumetric energy density

The practical application of energy storage device requires high areal/volumetric energy density. One of the strategies is to design bulk electrode with hierarchical porous structure for the application of supercapacitor. Significantly, the energy storage electrochemical performance of the bulk electrode is highly influenced by the pore structure regulation and electrolyte infiltration. Therefore, it is necessary to design thick electrodes with proper pore structures and investigate the effect of thickness on the supercapacitance performance. In this work, bass wood is selected as the carbon source of electrode because of its hierarchical porous structure and easy processing into different thicknesses. The wood-derived carbon thick electrode with a thickness of 1.532 mm (CWT1.532) presents the best supercapacitance performance. Such electrode possesses a high active material loading of 54.75 mg cm−2. The symmetrical supercapacitor from CWT1.532 electrode displays remarkable specific capacitance of 65 F g−1 and areal/volumetric capacitance of 0.846 F cm−2 and 2.67 F cm−3 at 1.0 mA cm−2, respectively. It also exhibits mass/areal/volumetric power densities of 38.47 W kg−1, 500 mW cm2 and 1580 mW cm−3 as well as the corresponding energy densities of 9.04 Wh kg−1, 117.5 mWh cm−2 and 0.374 mWh cm−3, respectively. Moreover, the symmetrical supercapacitor shows an attractive cycling stability with a supercapacitance retention of 81.48% at 20 mA cm−2 even after 15 000 long-term cycles. This work provides an essential understanding about the effect of different thicknesses on the thick electrode-assembled supercapacitance and inspires future practical application in other energy storage areas.