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 ZnBr2 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 ZnBr2 utilization (similar to 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.