3D Printed Ordered Hierarchically‐Porous Electrodes for Developing High‐Performance Quasi‐Solid‐State Aqueous Nickel‐Iron Batteries

Abstract Structural engineering offers a viable and broadly applicable approach for further enhancing the energy density of aqueous nickel‐iron (Ni‐Fe) batteries without changing the fundamental battery chemistries. Herein, the synthesis of 3D printed low‐tortuosity and ultra‐thick ordered hierarchically porous reduced graphene oxide (rGO)‐based microlattice electrodes for high‐performance aqueous Ni‐Fe batteries through direct writing (DIW) 3D printing technology is presented. Significantly, the areal specific capacitance of the 3D printed electrodes scales positively with electrode thickness, whereas the gravimetric capacitance remains relatively constant, indicating that the capacitive performance is not constrained by ion diffusion and exhibits rapid kinetic behavior, even at elevated mass‐loading levels and in the context of ultra‐thick electrodes. Based on a 3 m KOH aqueous electrolyte, the 3D printed aqueous Ni‐Fe cell (thickness: ≈2 mm) exhibits high areal specific capacity (≈0.353 mAh cm⁻²), high volumetric energy/power density (≈1.15 mWh cm⁻² at 48.00 mW cm⁻²), and excellent long‐term cycling performance (≈81.25% capacitance retained after 5000 cycles). As a micro‐battery device, 3D printed quasi‐solid‐state Ni‐Fe battery (3DP QSS Ni‐Fe) device with 4 mm thickness still exhibits a high areal capacity of 0.525 mAh cm⁻², and excellent cycle stability with ≈81.1% capacity retention after 10000 cycles. The promising 3D printed strategy provides a novel avenue for the controllable assembly of higher‐dimensional architectures, thereby paving the way for the advancement of next‐generation materials and devices.