Trace cesium iodide for uniform zinc deposition and enhanced cathode kinetics in aqueous Zn-I2 batteries

Aqueous zinc-iodine batteries (AZIBs) are considered a very promising way to store energy. However, inherent issues such as cathodic slow I₂/I⁻ redox kinetics and anodic zinc (Zn) dendrite growth, limit the practical application of AZIBs. Here, we used just a trace amount of the electrolyte additive cesium iodide (CsI) for homogeneous deposition of Zn 2+ and enhanced cathode kinetics in AZIBs. The introduction of Cs + produces electrostatic shielding layers that regulate the homogenization of Zn 2+ deposition. Besides, I - promotes cathodic kinetics to achieve the effect of increasing the battery capacity. Electrochemical tests show that by adding 5 mM trace CsI to the Zn-Zn symmetric cell, the cycling time was increased to 650 h, and the Zn-Cu half-cell's cycling time was increased to 3000 cycles under conditions of 5 mA cm −2 . More importantly, Zn-I 2 cells can stably cycle for 10000 cycles at 1 A g −1 and 10 A g −1 . The average capacity increased to 97.54 mAh g −1 after 100 cycles at 1 A g −1 and 74.57 mAh g −1 after 100 cycles at 10 A g −1 . After 100 cycles, the Zn-I 2 full cell's capacity retention rose from 2.41 % to 57.47 % under the conditions of 1 A g −1 and a 5.6 N/P ratio.