Stepwise Activation‐Guided Zn Deposition for Ultra‐High Capacity in Flowless Zn–Br Batteries

ABSTRACT Flowless Zn–bromine batteries (FL–ZBBs) are attracting attention as a route to overcome the inherent system‐level limitations of conventional flow batteries. However, the difficulty of achieving high ZnBr ₂ utilization and ultra‐high areal capacity jeopardize practical feasibility: Under practically relevant conditions, Zn‐hosting electrodes suffer from top‐plating issues and dendrite‐triggered “dead” Zn accumulation, which deteriorates reversible Zn plating/stripping. This work presents a stepwise activation (SWA) electrode that guides top‐plating‐free, bottom‐to‐top sequential Zn deposition. The SWA architecture is designed by introducing insulating porous membranes physically separating stacked CF layers while electrically linking through controlled partial Zn penetration. Benefiting from SWA‐guided Zn deposition, FL‐ZBBs can stably retain higher Coulombic and energy efficiencies even at a high current cycling (20 mA cm ⁻² ) over 10 000 cycles. For the first time, we demonstrate a stable ultra‐high capacity cycling (100 mAh cm ⁻² ) of FL‐ZBB with SWA electrode by maximizing the ZnBr ₂ utilization (∼33%). This simple, scalable SWA design offers broad applicability, enabling high‐capacity operation in flowless batteries and extending to other metal‐deposition‐limited redox systems.