Reconstructing a Gd3+-enriched inner Helmholtz plane with a dynamic electrostatic shielding effect for highly reversible Zn–bromine flow batteries

Abstract

Zinc–bromine flow batteries (ZBFBs) are promising candidates for large-scale energy storage, with their cycling lifetime determined by the reversibility of the Zn anode. However, dynamic fluctuations in ion concentration within the Inner Helmholtz Plane (IHP) at the Zn anode–electrolyte interface inevitably induce Zn²⁺ ion concentration polarization and tip effects, resulting in dendrite growth and the hydrogen evolution reaction (HER), thus ultimately shortening the battery cycling lifetime. In this work, a Gd³⁺-enriched IHP is reconstructed by dynamically adsorbing Gd³⁺ cations to maintain a uniform Zn²⁺ ion concentration and stabilize the electric field distribution within the IHP. Specifically, the selective adsorption of Gd³⁺ ions promotes preferential growth of the Zn (101) crystal facet and repels protons, thereby simultaneously suppressing Zn dendrite growth and the HER. Benefiting from the highly stable IHP of the reversible Zn anode, the Zn‖Zn symmetric flow battery demonstrates over 10 000 cycles (more than 2000 hours) with an ultra-high cumulative areal capacity of 53 A h cm⁻². Meanwhile, the ZBFB with Gd³⁺-electrolyte achieves over 3300 hours of charge–discharge cycling, showing a 22-fold increase in cycling lifetime compared to the control electrolyte. This study provides new insights into designing highly reversible Zn anodes for flow battery systems with commercial grade cycling life.