A Self-Phase-Separated Deep Eutectic Solvent-Based Biphasic Electrolyte for Durable Four-Electron Zn-I₂ Batteries...

Aqueous four-electron zinc-iodine batteries (4eZIBs) hold great promise for long-term energy storage, but their practical application is severely hindered by the multiple drawbacks, including Zn dendrite growth, polyiodide shuttle, and I⁺ hydrolysis. Such limitations can be effectively mitigated by employing biphasic electrolytes featuring a liquid-liquid interface, which enables efficient immobilization of the dissolved reaction intermediates. However, such systems frequently employ toxic organic solvents, which not only pose flammability risks but also struggle to adapt to extreme temperature conditions. Herein, we design a novel self-stratified biphasic electrolyte via liquid-liquid phase separation of choline chloride (ChCl)-trifluoroacetamide (TFA) deep eutectic solvent (DES) and ZnSO₄/H₂O/ ethylene glycol solution. The upper DES phase effectively confines polyiodide anions, suppresses shuttle effect and stabilizes I⁺ species, while the bottom aqueous phase regulates Zn²⁺ solvation structure and inhibits dendrite formation and side reactions. Benefiting from the synergistic functional separation, the Zn-I₂ battery realizes highly reversible four-electron conversion, effectively suppresses battery self-discharge, and delivers superior cycling stability over 21000 cycles as well as wide temperature tolerance ranging from -30°C to 50°C. This work offers novel insights into the design of safe and eco-friendly biphasic electrolytes and provides an effective strategy for the construction of high-performance 4eZIBs.