Imidazolium-based ionic liquids as proton reservoir for stable polyaniline cathode in zinc-iodine batteries

Aqueous zinc (Zn)-iodine (I 2 ) batteries (ZIBs) are promising large-scale energy storage systems with high safety and low cost. However, the practical application of ZIBs is hindered by the dissolution of I 3 - ions, which leads to the shuttle effect and the loss of active iodine. Herein, we adopt an electrolyte modification strategy using two imidazolium-based ionic liquids (1-butyl-3-methylimidazolium iodide ([BMIM]I) and 1-ethyl-3-methylimidazolium iodide ([EMIM]I)) as electrolyte additives to restrain the dissolution of I 3 - ions and enhance the performance of ZIBs. To be specific, the imidazole rings in [BMIM] + and [EMIM] + can be used as the proton sources, promoting the conversion of imine to protonated amines –NH + = in the polyaniline and subsequent adsorption of I 3 - ions. Therefore, the dissolution of I 3 - ions and shuttle effect are prevented, facilitating the reaction kinetics of cathode. As a proof of concept, the ZIB using [BMIM]I and [EMIM]I as electrolyte additives demonstrates remarkable cycling performance (72.2 % capacity retention after 1000 cycles) at a high current density of 20 mA cm −2 .