An integrated design for high-energy, durable zinc–iodine batteries with ultra-high recycling efficiency†

Zinc–iodine batteries (ZIBs) have long struggled with the uncontrolled spread of polyiodide in aqueous electrolytes, despite their environmentally friendly, inherently safe, and cost-effective nature. Here, we present an integral redesign of ZIBs that encompasses both the electrolyte and cell structure. The developed self-sieving polyiodide-capable liquid–liquid biphasic electrolyte can achieve an impressive polyiodide extraction efficiency of 99.98%, harnessing a meticulously iodine-containing hydrophobic solvated shell in conjunction with the salt-out effect. This advancement facilitates a membrane-free design with a Coulombic efficiency of ∼100% at 0.1C, alongside an ultra-low self-discharge rate of ∼3.4% per month and capacity retention of 83.1% after 1300 cycles (iodine areal loading: 22.2 mg cm⁻²). Furthermore, the integrated cell structure, paired with the low-cost electrolyte ($4.6 L⁻¹), enables rapid assembly into A h-level batteries within hours (1.18 A h after 100 cycles with a capacity retention of 86.7%), supports electrolyte regeneration with ∼100% recycling efficiency, and extends to ZIBs with a two-electron iodine conversion reaction. This endeavor establishes a novel paradigm for the development of practical zinc–iodine batteries.