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

Abstract

Electrochemically 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=-19.3kJmol-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=-7.72kJmol-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 215Wh kgiodine -1.