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.