Bidirectional Confined Redox Catalysis Manipulated Quasi‐Solid Iodine Conversion for Shuttle‐Free Solid‐State Zn‐I2 Battery

Abstract

AbstractElectrochemically reversible conversion of I2/I− redox couple in a controllable iodine speciation manner is the eternal target for practical metal‐iodine batteries. This contribution demonstrates an advanced polyiodide‐free Zn‐I2 battery achieved by the bidirectional confined redox catalysis‐directed quasi‐solid iodine conversion. A core‐shell structured iodine cathode is fabricated by integrating multiporous Prussian blue nanocubes as a catalytic mediator, and the polypyrrole sheath afforded a confinement environment that favored the iodine redox. The zincate Znx+1FeIII/II[Fe(CN)6]y has substantially faster zinc‐ion intercalation kinetics and overlapping kinetic voltage profiles compared with the I2/ZnI2 redox, and behave as a redox mediator that catalyze reduction of polyiodides via chemical redox reactions during battery discharging and an exemplary reaction is Zn(I3)2+2Znx+1FeII[Fe(CN)6]y=3ZnI2+2ZnxFeIII[Fe(CN)6]y,ΔG=−19.3 kJ mol−1). During the following recharging process, the electrodeposited ZnI2 can be facially activated by iron redox hotspots, and the ZnxFe[FeIII/II(CN)6]y served as a cation‐transfer mediator and spontaneously catalyze polyiodides oxidation (Zn(I3)2+2ZnxFe[FeIII(CN)6]y=3I2+2Znx+1Fe[FeII(CN)6]y,ΔG = −7.72 kJ mol−1), manipulating the reversible one‐step conversion of ZnI2 back to I2. Accordingly, a flexible solid‐state battery employing the designed cathode can deliver an energy density of 215 Wh kgiodine−1.