A Dilute Electrolyte Additive Enables Synergistic Thermodynamic and Kinetic Modulation for Durable Four-Electron Zn-I2 Batteries

Abstract

Aqueous zinc-iodine batteries (ZIBs) based on four-electron I -/I 0 /I + redox chemistry hold great promise for high-energy-density energy storage. However, their practical deployment faces critical challenges, mainly including the polyiodide shuttle effect, hydrolysis of I⁺, sluggish iodine conversion kinetics and poor reversibility of Zn anodes. Herein, we propose a low-concentration electrolyte strategy by employing choline chloride (ChCl) as a dual-functional additive to achieve highly efficient four-electron ZIBs. It has been demonstrated that Ch + not only suppresses the polyiodide shuttle by forming strong complexation but also stabilizes the ICl intermediate and regulates the I-Cl bonding strength to facilitate the subsequent conversion to I 2 for the iodine cathode, thereby overcoming the key kinetic bottleneck of the I 0 /I⁺ redox process. Simultaneously, Ch⁺ facilitates the Zn 2+ transfer kinetics and inhibits the water activity, effectively promoting the uniform Zn plating with suppressed side reactions. Benefitting from these advantages, the ZIBs assembled with dilute ChCl deliver a high specific capacity of 445 mAh g -1 at 1 A g -1 and achieve a 75% capacity retention after 50,000 cycles at a high current density of 10 A g -1 . This work provides a facile strategy to simultaneously address the thermodynamic and kinetic issues to enable highperformance four-electron ZIBs.