Insights on Polyidide Shuttling of Zn-I2 Batteries by I3−/I− Electrolytes Based on the Dual-Ion Battery System

The rechargeable zinc-iodine (Zn-I₂) battery is a promising energy storage system due to its high theoretical capacity, low cost, and safety. So far, most researchers agree that the poor electrical conductivity of iodine and the shuttling of polyiodide lead to a rapid decrease in capacity and low coulombic efficiency (CE) during cycling, which seriously hinders their further development and application. Herein, to understand the polyidide shuttling effects in Zn-I₂ battery, we utilize I₃^-/I^- electrolytes as the active capacity source coupled with carbon cloth, devoid-of-iodine (I₂) loading cathode, to simulate the behavior of the shuttling of polyidide in the Zn-I₂ battery, based on the concept of a dual-ion battery system. Experiments show that these batteries exhibit a specific capacity of 0.24 mAh·cm^-2 at 1.0 A·cm^-2 and 0.2 mAh·cm^-2 at 20 A·cm^-2, corresponding to 1.0~1.3 mg active mass of I₂, based on the 2I^-/I₂ redox couple (221 mAh·g^-1). It is noteworthy that the inclusion of polyiodide enhances the electrochemical and redox activity, which is advantageous for electrochemical performance; however, it is limited to the polyiodine reduction on the Zn surface (Zn + I₃^- → 3I^- + Zn²⁺).