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  1. Abstract

    Iron ion batteries using Fe2+as a charge carrier have yet to be widely explored, and they lack high‐performing Fe2+hosting cathode materials to couple with the iron metal anode. Here, it is demonstrated that VOPO4∙2H2O can reversibly host Fe2+with a high specific capacity of 100 mAh g−1and stable cycling performance, where 68% of the initial capacity is retained over 800 cycles. In sharp contrast, VOPO4∙2H2O's capacity of hosting Zn2+fades precipitously over tens of cycles. VOPO4∙2H2O stores Fe2+with a unique mechanism, where upon contacting the electrolyte by the VOPO4∙2H2O electrode, Fe2+ions from the electrolyte get oxidized to Fe3+ions that are inserted and trapped in the VOPO4∙2H2O structure in an electroless redox reaction. The trapped Fe3+ions, thus, bolt the layered structure of VOPO4∙2H2O, which prevents it from dissolution into the electrolyte during (de)insertion of Fe2+. The findings offer a new strategy to use a redox‐active ion charge carrier to stabilize the layered electrode materials.

     
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  2. 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−xin a water‐in‐salt electrolyte. The iodine plating cathode with the theoretical capacity of 211 mAh g−1plates 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−xsuperhalide 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.

     
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  3. 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−xin a water‐in‐salt electrolyte. The iodine plating cathode with the theoretical capacity of 211 mAh g−1plates 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−xsuperhalide 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.

     
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  4. Abstract

    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 maqueous (NH4)2SO4as 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−1based 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.

     
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  5. Abstract

    The sluggish ion diffusion and electrolyte freezing with volumetric changes limit the low‐temperature performance of rechargeable batteries. Herein, a high‐rate aqueous proton battery (APB) operated at and below −78 °C via a 62 wt% (9.5 m) H3PO4electrolyte is reported. The APB is a rocking‐chair battery that operates with protons commuting between a Prussian blue cathode and an MoO3anode. At −78 °C, the APB full cells exhibit stable cycle life for 450 cycles, high round‐trip efficiency of 85%, and appreciable power performance. The APB delivers 30% of its room‐temperature capacity even at −88 °C. The proton storage mechanism is investigated by ex situ synchrotron XRD, XAS, and XPS. The APB pouch cells demonstrate no capacity fading at −78 °C, and thus offers a safe and reliable candidate for high‐latitude applications.

     
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  6. Abstract

    We report reversible electrochemical insertion of NO3into manganese(II, III) oxide (Mn3O4) as a cathode for aqueous dual‐ion batteries. Characterization by TGA, FTIR, EDX, XANES, EXAFS, and EQCM collectively provides unequivocal evidence that reversible oxidative NO3insertion takes place inside Mn3O4. Ex situ HRTEM and corresponding EDX mapping results suggest that NO3insertion de‐crystallizes the structure of Mn3O4. Kinetic studies reveal fast migration of NO3in the Mn3O4structure. This finding may open a new direction for novel low‐cost aqueous dual‐ion batteries.

     
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  7. Abstract

    We report reversible electrochemical insertion of NO3into manganese(II, III) oxide (Mn3O4) as a cathode for aqueous dual‐ion batteries. Characterization by TGA, FTIR, EDX, XANES, EXAFS, and EQCM collectively provides unequivocal evidence that reversible oxidative NO3insertion takes place inside Mn3O4. Ex situ HRTEM and corresponding EDX mapping results suggest that NO3insertion de‐crystallizes the structure of Mn3O4. Kinetic studies reveal fast migration of NO3in the Mn3O4structure. This finding may open a new direction for novel low‐cost aqueous dual‐ion batteries.

     
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