A dilute electrolyte additive enables the synergistic thermodynamic and kinetic modulation for durable four-electron Zn–I₂ batteries

Aqueous zinc–iodine batteries (ZIBs) based on four-electron I⁻/I⁰/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 is demonstrated that Ch⁺ not only suppresses polyiodide shuttle by strong complexation but also stabilizes the ICl intermediate and regulates the I–Cl bonding strength to facilitate the subsequent conversion to I₂ at the iodine cathode, thereby overcoming the key kinetic bottleneck of the I⁰/I⁺ redox process. Simultaneously, Ch⁺ facilitates Zn²⁺ transfer kinetics and inhibits water activity, effectively promoting uniform Zn plating with suppressed side reactions. Benefitting from these advantages, the ZIBs assembled with dilute ChCl deliver a high specific capacity of 445 mA h g⁻¹ at 1 A g⁻¹ and achieve 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 high-performance four-electron ZIBs.