A Dual Plating Battery with the Iodine/[ZnIx(OH₂)4−x]2−x Cathode

Plating battery electrodes typically deliver higher specific capacity values than insertion or conversion electrodes because the ion charge carriers represent the sole electrode active mass, and a host electrode is unnecessary. However, reversible plating electrodes are rare for electronically insulating nonmetals. Now, a highly reversible iodine plating cathode is presented that operates on the redox couples of I 2 /[ZnI x (OH 2 ) 4− x ] 2− x in a water‐in‐salt electrolyte. The iodine plating cathode with the theoretical capacity of 211 mAh g −1 plates on carbon fiber paper as the current collector, delivering a large areal capacity of 4 mAh cm −2 . Tunable femtosecond stimulated Raman spectroscopy coupled with DFT calculations elucidate a series of [ZnI x (OH 2 ) 4− x ] 2− x superhalide ions serving as iodide vehicles in the electrolyte, which eliminates most free iodide ions, thus preventing the consequent dissolution of the cathode‐plated iodine as triiodides.