Wood‐Derived, Conductivity and Hierarchical Pore Integrated Thick Electrode Enabling High Areal/Volumetric Energy Density for Hybrid Capacitors

For the proliferation of the supercapacitor technology, it is essential to attain superior areal and volumetric performance. Nevertheless, maintaining stable areal/volumetric capacitance and rate capability, especially for thick electrodes, remains a fundamental challenge. Here, for the first time, a rationally designed porous monolithic electrode is reported with high thickness of 800 µm (46.74 mg cm^-2 , with high areal mass loading of NiCo₂ S₄ 6.9 mg cm^-2 ) in which redox-active Ag nanoparticles and NiCo₂ S₄ nanosheets are sequentially decorated on highly conductive wood-derived carbon (WC) substrates. The hierarchically assembled WC@Ag@NiCo₂ S₄ electrode exhibits outstanding areal capacitance of 6.09 F cm^-2 and long-term stability of 84.5% up to 10 000 cycles, as well as exceptional rate capability at 50 mA cm^-2 . The asymmetric cell with an anode of WC@Ag and a cathode of WC@Ag@NiCo₂ S₄ delivers areal/volumetric energy density of 0.59 mWh cm^-2 /3.93 mWh cm^-3 , which is much-improved performance compared to those of most reported thick electrodes at the same scale. Theoretical calculations verify that the enhanced performance could be attributed to the decreased adsorption energy of OH^- and the down-shifted d-band of Ag atoms, which can accelerate the electron transport and ion transfer.