Vertical-array channel engineering of wood-structured thick electrode to assemble high-performance supercapacitors

Abstract

Thick electrodes can reduce the ratio of inactive constituents (e.g., conductive and binder agents) in the overall cell to boost energy and power densities, yet suffering from longer ion diffusion paths has overlooked. Tailoring sustainable wood-structured ultrathick electrode with low-tortuosity hierarchical structure is a promising alternative to achieve energy-dense and stable supercapacitors (SCs). Herein, the present work reports a facile vertical-hole engineering that perforates artificial small orifices (∼0.5 mm diameter) across the bulk wood in the perpendicular direction to connect the parallel channels, constructing the well-aligned freeway of self-standing wood monolithic electrode with a thickness of 1.3 − 4.2 mm. Ions and electrons thereby acquire less time travelling to abundant active spots throughout the holistic wood thick electrode, which results in low cell resistance, high rate capability and energy density. Benefitting from the holey structure, the optimum wood thick electrode (with a thickness of 2.5 mm) exhibits a remarkable areal capacitance of 27.2F cm⁻² at 1 mA cm⁻² and long-term cycling stability, allowing its aqueous symmetric SCs with a maximum areal energy density of 3.16 mWh cm⁻² at 1280 mW cm⁻². The assembled quasi-solid-state device delivers a high areal capacitance (2.9F cm⁻² at 1 mA cm⁻²) and energy density (1.1 mWh cm⁻²), also indicating the excellent lifespan and structural integrity. The fluidic simulation confirms that the drilled holes enhance the mass transfer of electrolyte, thereby enabling ion exchange and reducing the concentration polarization in the cell. The superior structure of wood-structured ultrathick electrode not only exploits the feasibility in SCs, but also illumines a bright direction to develop renewable electrodes via pore engineering of earth-abundant biomass.