Review of the I−/I3− redox chemistry in Zn-iodine redox flow batteries

Zn-iodine redox flow batteries have emerged as one of the most promising next-generation energy storage systems, due to their high energy density, low cost and superior safety. However, the low I2 utilization and shuttle effect of iodine species greatly inhibit their practical use. Numerous approaches have been attempted to address these issues and push the energy density and cycling stability toward the practicable level. In this review, we summarize the recently-developed functional strategies including electrode design and electrolyte optimization to improve the adsorption capability and utilization efficiency of the iodine species. Finally, we provide some discussion on the remaining challenges and future perspectives of the Zn-iodine redox flow batteries.