A four-electron Zn-I2 aqueous battery enabled by reversible I-/I2/I+ conversion

Electrochemically reversible redox couples that embrace more electron transfer at a higher potential are the eternal target for energy storage batteries. Here, we report a four-electron aqueous zinc-iodine battery by activating the highly reversible I-2/I+ couple (1.83V vs. Zn/Zn2+) in addition to the typical I-/I-2 couple (1.29V). This is achieved by intensive solvation of the aqueous electrolyte to yield ICl inter-halogens and to suspend its hydrolysis. Experimental characterization and modelling reveal that limited water activity and sufficient free chloride ions in the electrolyte are crucial for the four-electron process. The merits of the electrolyte also afford to stabilize Zn anode, leading to a reliable Zn-I-2 aqueous battery of 6000 cycles. Owing to high operational voltage and capacity, energy density up to 750Whkg(-1) based on iodine mass was achieved (15-20wt% iodine in electrode). It pushes the Zn-I-2 battery to a superior level among these available aqueous batteries. Electrochemically reversible redox couples that embrace more electron transfer at a higher potential are desired for high energy density batteries. Here, the authors report a four-electron aqueous zinc-iodine battery by boosting the iodine electrochemistry in deliberately designed electrolytes.

Automated summary

In this study, a four-electron aqueous zinc-iodine battery was developed by enhancing the iodine electrochemistry using a specially designed electrolyte. Experimental characterization and modeling showed that limited water activity and sufficient free chloride ions in the electrolyte are crucial for the four-electron process. The advantages of the electrolyte also help stabilize the zinc anode, leading to a high energy density and reliable cycling performance for the Zn-I-2 aqueous battery.