Enhancing the Cycle Life of Zinc-Iodine Batteries in Ionic Liquid-Based Electrolytes.

ABSTRACT

Aqueous zinc-iodine (Zn-I2) batteries are gaining significant attention due to their low-cost, high safety and high theoretical capacity. Nevertheless, their long cycle and durability have been hampered due to the use of aqueous media that, over time, lead to Zn dendrite formation, hydrogen evolution reaction, and polyiodide dissolution. Xiao et al. recently reported the addition of an imidazolium-based ionic liquid (IL) to an aqueous electrolyte and found that the IL plays a key role in modifying the solvation of Zn2+ ions in the bulk electrolyte and the inner Helmholtz plane, repelling H2O molecules away from the Zn anode surface. UV/Vis and NMR spectroscopy also indicates a strong interaction between imidazolium cation [EMIM]+ and I3 -, thereby reducing polyiodide shuttling and enhancing the cycle life of the battery. Overall, a capacity decay rate of only 0.01 % per cycle after over 18,000 cycles at 4 A g-1, is observed, making the use of IL additives in aqueous electrolytes highly promising candidates for Zn-I2 batteries.