Reducing Dead Species by Electrochemically‐Densified Cathode‐Interface‐Reaction Layer towards High‐Rate‐Endurable Zn||I‐Br Batteries

Interhalogen‐involved aqueous Zn||halogen batteries (AZHBs) are latent high‐energy systems for grid‐level energy storage, yet usually suffer from poor high‐rate endurability caused by the formation of “dead species”. Herein, via an electrochemically‐densified cathode‐interface‐reaction layer (CIRL), Zn||I−Br batteries involving interhalogen reactions between the I2 cathode and Br− from the electrolytes are initially achieved with excellent high‐rate endurability. Different from that in diluted electrolytes, the CIRL formed in Br−‐concentrated electrolyte is denser and water‐lean, which enables halogen species conversion with a more rapid charge transfer and lower activation energy. More importantly, the CIRL robustly affords a decent I2 conservation by accelerated conversion kinetics and limited species diffusion, thereby endowing the Zn||I−Br batteries with an ultralong high‐rate lifespan. The electrochemical mechanism is sufficiently verified by multiple spectral characterizations. Consequently, Zn||I−Br batteries in Br−‐concentrated (20 m) electrolytes exhibit an overwhelming rate capability and lifespan to those in Br−‐diluted (2 m) electrolytes. Typically, when cycled at a large current density of 10 A g−1, an ultralong lifespan of over 25,000 cycles is achieved with a high retention of 98.3 %. This study provides new insight into the CIRL‐dictated active species conservation for high‐rate endurable AZHBs, which could apply to other high‐energy interhalogen batteries. A densified cathode‐interface‐reaction layer (CIRL) is electrochemically formed in Br−‐concentrated electrolytes, which remarkably reduces the “dead species” phenomena usually present in diluted electrolytes, enabling Zn||I−Br batteries involving interhalogen conversion with excellent high‐rate endurability.