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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 I2/[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. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable batteries are promising solutions for large-scale energy storage. Such batteries have the merit of low cost, innate safety, and environmental friendliness. To date, most known aqueous ion batteries employ metal cation charge carriers. Here, we report the first 'rocking-chair' NH4-ion battery of the full-cell configuration by employing an ammonium Prussian white analogue, (NH4)1.47Ni[Fe(CN)6]0.88, as the cathode, an organic solid, 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), as the anode, and 1.0 m aqueous (NH4)2SO4 as the electrolyte. This novel aqueous ammonium-ion battery demonstrates encouraging electrochemical performance: an average operation voltage of ca. 1.0 V, an attractive energy density of ca. 43 Wh kg−1 based on both electrodes' active mass, and excellent cycle life over 1000 cycles with 67 % capacity retention. Importantly, the topochemistry results of NH4+ in these electrodes point to a new paradigm of NH4+-based energy storage. [ABSTRACT FROM AUTHOR]