Self‐Assembled Solid‐State Gel Catholyte Combating Iodide Diffusion and Self‐Discharge for a Stable Flexible Aqueous Zn–I2 Battery

Abstract Aqueous rechargeable zinc–iodine batteries (ARZIBs) represent a promising form of sustainable energy storage, having highly abundant and environmentally workable elements. The low utilization of solid iodine and self‐discharge due to the diffusive properties of the soluble polyiodides in aqueous media hamper the stability and device design. The concept of building a solid‐state ARZIB with self‐discharge control by limiting iodide diffusion employing solid–gel reactions with water‐based gel‐embedded I 3 − /I − in block copolymer bearing highly active iodine components is demonstrated. The catholyte gel has an amphiphilic property that provides high solubility for iodine and better ionic conductivity from the cubic microcrystalline self‐assembled structures. This gel prevents long range iodide ion diffusion in multilayer self‐assemblies of the catholyte followed by the gel electrolyte layer due to self‐trapped polyiodides at the core–shell interface and inside the hydrophobic core of micelles. By contrast, positive zinc ions easily diffuse through the hydrophilic poly(ethylene oxide)‐water‐rich channels. This solid matrix results in a discharge capacity of 210 mAh g −1 (at 1 C rate) and stability with a retaining capacity of 94.3% after 500 cycles, including self‐discharge protection. The flexible module device shows excellent flexibility during deformations and the ability to power gadgets with stable performance.