Establishing Ultralow Self-Discharge Zn-I₂ Battery by Optimizing ZnSO₄ Electrolyte Concentration

As one of promising candidates for large-scale energy-storage systems, Zn-I₂ aqueous battery exhibits multifaceted advantages including low cost, high energy/powder density, and intrinsic operational safety, but also suffers from fast self-discharge and short cycle/shelf lifespan associating with I₃ ^- shuttle, Zn dendrite growth, and corrosion. In this paper, the battery's self-discharge rate is successfully suppressed down to an unprecedent level of 17.1% after an ultralong shelf-time of 1 000 h (i.e., 82.9% capacity retention after 41 days open-circuit storage), by means of manipulating solvation structures of traditional ZnSO₄ electrolyte via simply adjusting electrolyte concentration. Better yet, the optimized 2.7 m ZnSO₄ electrolyte further prolongs the cycle lifespan of the battery up to >10 000 and 43 000 cycles at current density of 1 and 5 A g^-1, respectively, thanks to the synthetic benefits from reduced free water content, modified solvation structure and lowered I₂ dissolution in the electrolyte. With both long lifespan and ultralow self-discharge, this reliable and affordable Zn-I₂ battery may provide a feasible alternative to the centuries-old lead-acid battery.