A Dual Plating Battery with the Iodine/[ZnI_x(OH₂)_4−x]^2−x Cathode

Abstract

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.

Self‐Assembled Solid‐State Gel Catholyte Combating Iodide Diffusion and Self‐Discharge for a Stable Flexible Aqueous Zn–I2 Battery

“…This might be due to the side reactions that occur at the electrolyte/electrode interface and believed to be more competitive at relatively high rates. [ 39,40 ] However, for a nonmetal to serve as an electrode in the present case, the iodine redox chemistry is associated with a continuous “plating/stripping” process between anionic (I − ) and neutral (I 2 ) phases, [ 18 ] whose kinetics are much lower than those of common battery redox couples. Moreover, the iodine phase in the charged state has a low conductivity, which requires a suitable conductive matrix to support the reliable electron transfer at the cathode side.…”

“…ARZIBs are also integrated with a double plating mechanism having iodine/[ZnI x (OH 2 ) 4− x ] 2− x cathode, achieving excellent reversibility. [ 18 ] Wang et al. introduced a unique way of pH‐dependent self‐protection ARZIB to overcome overcharge difficulties.…”

Enhanced Redox Kinetics and Duration of Aqueous I2/I− Conversion Chemistry by MXene Confinement

“…However, the carbon materials currently confine I 2 solely by physical means including adsorption and impregnation, resulting in uneven loading and sluggish interactions, especially considering its electrical neutrality and large radius. [ 12,13 ] Another noticeable issue concerns the generation of polyiodides and the associated shuttle effect, which can lead to undesirable self‐discharge problems. [ 4 ]…”

“…The recorded polarization voltage rose from 0.04 V at 1 A g −1 to 0.15 V at 18 A g −1 (Figure S10, Supporting Information), far superior to any other reported I 2 -metal counterparts, as summarized in Figure 2i and Table S1 (Supporting Information). [2,13,24,40,50,51] The prolonged cycle stability has always been a concern plaguing I 2 redox systems, whose capacity fades due to the loss of I 2 or reaction products (I − or I 3 − ) by parasitic shuttling. [52][53][54] Interestingly, using an eIM cathode, the trapping effect triggered by nanosized galleries efficiently resolves this issue.…”

Rechargeable Aqueous Zinc‐Ion Batteries with Mild Electrolytes: A Comprehensive Review

“…However, the solubility of ZnSO 4 in aqueous electrolyte is limited, preventing the development of ZnSO 4 ‐based “water‐in‐salt” electrolyte. On the other hand, other cheap yet high solubility Zn salts, such as ZnCl 2 , and ZnI 2 etc., have also been proposed to prepare “water‐in‐salts” electrolytes for long‐life ZIBs. One should be aware that the effects of these “water‐in‐salt” electrolytes are double sides: the lack of free‐water slows down detrimental corrosion reaction and dendrite growth speed, but may also eliminate the beneficial influence of free‐water on electrochemical reactions on cathodes …”