Extending the life-time of Zn-Br₂ batteries by targeted local confinement of bromine complexes

Flowless zinc–bromine batteries (FL-ZBBs) are promising for grid-scale energy storage due to their high theoretical energy density and inherent safety. Yet, their practical implementation is hindered by rapid self-discharge, parasitic oxygen evolution, and limited solubility of bromine-complexing agents (BCAs) in aqueous media. Here, we present a Targeted Local Presence (TLP) strategy, in which hydrophobic BCAs are immobilized within porous activated carbon cloth (ACC) electrodes, forming confined water-repelling domains that stabilize bromine species and suppress side reactions. By systematically varying the alkyl-chain length of pyridinium based BCAs, we demonstrate control over the size of molecular aggregates and their interactions with polybromide ions, establishing a tunable framework linking molecular design to macroscopic electrochemical stability. Nuclear magnetic resonance (NMR) spectroscopy combined with electrochemical analysis confirms that this tunable confinement enhances bromine retention and reversibility. The optimized TLP cathodes deliver 200 mAh/g at 1 A g⁻¹ with > 98% Coulombic efficiency over 1000 cycles and enable operation up to 2.7 V in 0.1 M ZnBr₂ aqueous solutions. This work provides a scalable strategy that unites molecular-level design, electrodes’ architecture, and interfacial chemistry to advance durable, high-performance flowless Zn–Br₂ batteries.