Tetravalent organic cation-enabled dual interfacial regulation for durable aqueous zinc–iodine batteries

Interfacial instability from polyiodide shuttling and zinc electrode degradation critically limits the reversibility of aqueous zinc–iodine batteries. Existing mono-valent organic cation strategies offer insufficient charge density and pose challenges in maintaining interfacial protection under dynamic electric field conditions. Here, we present an electrolyte design incorporating a high-valent organic cation (HVOC) —a tetravalent cation derived from 1,1,4,4,7,7,10,10-octaallyltetraazacyclodecane trifluoromethanesulfonate—that enables electrostatically engineered bipolar interfaces. The HVOC establishes a durable cationic positive electrode–electrolyte interphase on the iodine electrode that not only effectively immobilizes polyiodide species through strong electrostatic interactions under dynamic field reversals, but also facilitates iodine redox kinetics. Simultaneously, the HVOC drives the formation of a hybrid organic–inorganic solid electrolyte interphase on the zinc electrode that homogenizes zinc deposition and mitigates side reactions. This bipolar interfacial regulation enables zinc–iodine batteries with an N/P ratio of 2.43 to achieve 40.7% of zinc utilization and 95.4% of iodine utilization, with minimal capacity decay of 0.016% per cycle over 1,000 cycles at 0.4 A g–1, and stable performance across a wide temperature range from –40 to 60 oC. This work presents a viable electrolyte design paradigm using HVOC chemistry for advanced aqueous battery systems. Interfacial instability limits aqueous zinc–iodine batteries. Here, the authors introduce a high-valent organic cation electrolyte that electrostatically engineers bipolar interfaces to suppress polyiodide shuttling and regulate Zn deposition, resulting in markedly improved cycling stability.