A Zinc–Bromine Battery with Deep Eutectic Electrolytes

Abstract A deep eutectic solvent (DES) is an ionic liquid‐analog electrolyte, newly emerging due to its low cost, easy preparation, and tunable properties. Herein, a zinc–bromine battery (ZBB) with a Zn‐halide‐based DES electrolyte prepared by mixing ZnBr 2 , ZnCl 2 , and a bromine‐capturing agent is reported. The water‐free DES electrolyte allows a closed‐cell configuration for the ZBB owing to the prevention of Br 2 evaporation and H 2 evolution. It is found that the Cl − anion changes the structure of the zinc‐halide complex anions and demonstrated that it improves the ion mobility and electrode reaction kinetics. The DES electrolyte with the optimized ZnCl 2 composition shows much higher rate capability and a cycle life 90 times longer than that of a ZnCl 2 ‐free DES electrolyte. A pouch‐type flexible ZBB battery based on the DES electrolyte exhibits swelling‐free operation for more than 120 cycles and stable operation under a folding test, suggesting its potential in consumer applications such as wearable electronics.