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

Abstract Electrochemically reversible conversion of I 2 /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‐I 2 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 Zn x+1 Fe III/II [Fe(CN) 6 ] y has substantially faster zinc‐ion intercalation kinetics and overlapping kinetic voltage profiles compared with the I 2 /ZnI 2 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(I 3 ) 2 +2Zn x+1 Fe II [Fe(CN) 6 ] y =3ZnI 2 +2Zn x Fe III [Fe(CN) 6 ] y , ΔG =−19.3 kJ mol −1 ). During the following recharging process, the electrodeposited ZnI 2 can be facially activated by iron redox hotspots, and the Zn x Fe[Fe III/II (CN) 6 ] y served as a cation‐transfer mediator and spontaneously catalyze polyiodides oxidation (Zn(I 3 ) 2 +2Zn x Fe[Fe III (CN) 6 ] y =3I 2 +2Zn x+1 Fe[Fe II (CN) 6 ] y , ΔG = −7.72 kJ mol −1 ), manipulating the reversible one‐step conversion of ZnI 2 back to I 2 . Accordingly, a flexible solid‐state battery employing the designed cathode can deliver an energy density of 215 Wh kg iodine −1 .