A Zinc-Bromine Battery with Deep Eutectic Electrolytes

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 ZnBr2, ZnCl2, 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 ZnCl2 composition shows much higher rate capability and a cycle life 90 times longer than that of a ZnCl2-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.

Automated summary

This study reports a newly emerging ionic liquid-analog electrolyte called deep eutectic solvent (DES), which is characterized by its low cost, easy preparation, and tunable properties. A zinc-bromine battery (ZBB) with a DES electrolyte based on zinc halides, prepared by mixing ZnBr2, ZnCl2, and a bromine-capturing agent, is introduced. The optimized DES electrolyte shows improved rate capability and longer cycle life compared to the DES electrolyte without ZnCl2. A pouch-type flexible ZBB battery based on the DES electrolyte exhibits swelling-free operation and stable performance under a folding test, indicating its potential in consumer applications such as wearable electronics.