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Highlights: The porous structure and interconnected conductive pathways accommodate a large amount of iodine, entrap polyiodides and guarantee its efficient utilization. While the Fe single atom catalyst efficiently catalyzes the iodine/polyiodide conversion. With "confinement-catalysis" host, the ZnǀǀI2 battery delivers a high capacity of 188.2 mAh g−1 at 0.3 A g−1, excellent rate capability with a capacity of 139.6 mAh g−1 at 15 A g−1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Rechargeable aqueous zinc iodine (ZnǀǀI2) batteries have been promising energy storage technologies due to low-cost position and constitutional safety of zinc anode, iodine cathode and aqueous electrolytes. Whereas, on one hand, the low-fraction utilization of electrochemically inert host causes severe shuttle of soluble polyiodides, deficient iodine utilization and sluggish reaction kinetics. On the other hand, the usage of high mass polar electrocatalysts occupies mass and volume of electrode materials and sacrifices device-level energy density. Here, we propose a "confinement-catalysis" host composed of Fe single atom catalyst embedding inside ordered mesoporous carbon host, which can effectively confine and catalytically convert I2/I− couple and polyiodide intermediates. Consequently, the cathode enables the high capacity of 188.2 mAh g−1 at 0.3 A g−1, excellent rate capability with a capacity of 139.6 mAh g−1 delivered at high current density of 15 A g−1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Furthermore, the electrocatalytic host can also accelerate the I + ↔ I 2 conversion. The greatly improved electrochemical performance originates from the modulation of physicochemical confinement and the decrease of energy barrier for reversible I−/I2 and I2/I+ couples, and polyiodide intermediates conversions. [ABSTRACT FROM AUTHOR]

Though massive efforts have been devoted to exploring Br‐based batteries, the highly soluble Br2/Br3− species causing rigorous "shuttle effect", leads to severe self‐discharge and low Coulombic efficiency. Conventionally, quaternary ammonium salts such as methyl ethyl morpholinium bromide (MEMBr) and tetrapropylammonium bromide (TPABr) are used to fix Br2 and Br3−, but they occupy the mass and volume of battery without capacity contribution. Here, we report an all‐active solid interhalogen compound, IBr, as a cathode to address the above challenges, in which the oxidized Br0 is fixed by iodine (I), thoroughly eliminating cross‐diffusing Br2/Br3− species during the whole charging and discharging process. The Zn||IBr battery delivers remarkably high energy density of 385.8 Wh kg−1, which is higher than those of I2, MEMBr3, and TPABr3 cathodes. Our work provides new approaches to achieve active solid interhalogen chemistry for high‐energy electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

Proposed are Prussian blue analogue hosts with ordered and continuous channels, and electrocatalytic functionality with open Co and Fe species, which facilitate maximum I2 utilization efficiency and direct I2 to I− conversion kinetics of the I2 reduction reaction, and free up 1/3 I− from I3−. Co[Co1/4Fe3/4(CN)6] exhibits a low energy barrier (0.47 kJ mol−1) and low Tafel slope (76.74 mV dec−1). Accordingly, the Co[Co1/4Fe3/4(CN)6]/I2//Zn battery delivers a capacity of 236.8 mAh g−1 at 0.1 A g−1 and a rate performance with 151.4 mAh g−1 achieved even at 20 A g−1. The battery delivers both high energy density and high‐power density of 305.5 Wh kg−1 and 109.1 kW kg−1, higher than I2//Zn batteries reported to date. Furthermore, solid‐state flexible batteries were constructed. A 100 mAh high capacity solid‐state I2//Zn battery is demonstrated with excellent cycling performance of 81.2 % capacity retained after 400 cycles. [ABSTRACT FROM AUTHOR]