A Bilayer Electrode Architecture Enabling SnO ₂ ‐Induced Spatial‐Controllable Zinc Deposition for Ultra‐High‐Areal‐Capacity Zinc‐Based Flow Batteries

Aqueous zinc-based flow batteries (ZFBs) show great promise for large-scale energy storage. However, the practical deployment of ZFBs is hindered by a limited areal capacity, due to uncontrolled zinc deposition and low utilization of electrode volume. Herein, we propose a spatially controllable deposition strategy enabled by a bilayer electrode architecture, featuring a SnO₂-functionalized carbon felt (CF) as the bottom layer and a pristine CF as the top layer. This architecture introduces a steep gradient in nucleation overpotential and zincate affinity that counteracts the ionic migration trend, reversing the deposition behavior from surface-clogging mode to internal-to-external filling. This unique mechanism enables an ultrahigh areal capacity of 330 mAh cm^-2 and an ultrahigh volumetric capacity of 1100 mAh cm^-3, representing a 65% improvement over conventional electrodes. Even under a harsh condition of 100% state of charge and 100% depth of discharge at 240 mAh cm^-2, the battery demonstrates exceptional durability over 175 cycles. This work significantly expands volume utilization for zinc deposition via a bilayer electrode design, providing a robust strategy for regulating spatial deposition behavior and paving the way for practical high-areal-capacity ZFBs.