Dual-Additive Synergistic Complementation Electrolyte Engineering with “Job-Sharing” Modulation Mechanism for Long-Lifespan Zn-Iodine Batteries

The large-scale practical application of Zn-iodine batteries (ZIBs) with environmental benignity and cost-effectiveness is hindered by the challenges of poor reversibility of Zn anode and serious polyiodide shuttling. Herein, a dual-additive synergistic complementation electrolyte engineering method is proposed to promote Zn2+ transport, enhance Zn deposition reversibility, and improve iodine conversion kinetics by introducing lactulose and caffeine into 1 M ZnSO4. It is revealed that lactulose can reduce the desolvation barrier by substituting the coordinated water of Zn2+ ions and increase the Zn2+ transference number by hydrogen bond-assisted SO42–/H2O-locking. As a bilateral interfacial stabilizer, high polar caffeine is preferentially adsorbed on the Zn anode owing to its p-π conjugated structure and a "push–pull electron" effect, which renders (002)-textured Zn plating. Furthermore, the conjugated polar system of caffeine can firmly immobilize I3–, further stabilizing the I2/I– redox behavior. Consequently, the Zn//Zn cells deliver dendrite-free Zn stripping/plating cycling for 3500 h at 1 mA cm–2/1 mAh cm–2, and survive over 1300 h even at a high depth of discharge of 71.0%. This "job-sharing" modulation mechanism offers a practical strategy for the development of long-lifespan ZIBs.