Wood-Like Low-Tortuosity Thick Electrode for Micro-Redoxcapacitor with Ultrahigh Areal Energy Density and Steady Power Output

Conventional MXene-based thick electrodes with stacked and tortuous microstructures suffer from sluggish charge transport and low-utilization of active substances, thus a limited boost in areal energy density of the assembled micro-supercapacitors (MSCs). Herein, the duplication of wood-like microstructure is realized in MXene/Ag-nanowires (AgNWs) hybrid aerogel electrode (WL-M/A-AE) via directional freeze-drying technique. Benefitting from the uniform 3D vertically-aligned microchannels as the highways for ions transport throughout the matrix, the WL-M/A-AE with a thickness of up to 2000 µm can achieve a 50-times higher of Cl⁻ diffusion coefficient relative to closely restacked film electrode with the same mass loading of MXene. Furthermore, the evenly interspersed AgNWs serving as percolation network within the electrode matrix can facilitate horizontal electrons transmission between vertically-aligned loose MXene flakes, while reversibly capture/release Cl⁻ ions via phase conversion (Ag⇔AgCl) to raise the charge storage capacity of the WL-M/A-AE. Thus, when coupling with Zn anode, the assembled micro-redoxcapacitor adopting polyacrylamide/ZnCl₂+NH₄Cl hydrogel electrolyte can deliver an areal energy density up to 292.5 µWh cm⁻² in a more stable way (a smooth discharge plateau contributing 40.9% of the energy). The demonstrated hybrid thick electrode with wood-like low-tortuosity microstructure promises an effective avenue for tackling the performance bottlenecks facing traditional MSCs. © 2023 Wiley-VCH GmbH.