Highly soluble iodide/triiodide (I-/I3-) couples are one of the most promising redox-active species for high-energy-density electrochemical energy storage applications. However, to ensure high reversibility, only two-thirds of the iodide capacity is accessed and one-third of the iodide ions act as a complexing agent to stabilize the iodine (I2), forming I3- (I2I-). Here, we exploit bromide ions (Br-) as a complexing agent to stabilize the iodine, forming iodine–bromide ions (I2Br-), which frees up iodide ions and increases the capacity. Applying this strategy, we demonstrate a novel zinc/iodine–bromide battery to achieve an energy density of 101 W h Lposolyte+negolyte-1 (or 202 W h Lposolyte-1), which is the highest energy density achieved for aqueous flow batteries to date. This strategy can be further generalized to nonaqueous iodide-based batteries (i.e. lithium/polyiodide battery), offering new opportunities to improve high-energy iodide-based energy storage technologies.
Energy Environ. Sci., 2017, Advance Article
DOI: 10.1039/C6EE03554J
http://pubs.rsc.org/en/content/articlelanding/2017/ee/c6ee03554j#!divAbstract
