Dual Plating Battery via 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/[ZnIx(OH2)(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 [ZnIx(OH2)(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.