Hydrophobic ionic liquid enabled polyiodide confined transport in a cathode, realizing high areal capacity, stable zinc–iodine batteries

Aqueous zinc–iodine batteries are promising energy storage candidates due to their high safety and moderate cost. A high areal-capacity iodine cathode is the key to achieving practical batteries towards commercialization. However, high iodine loading exacerbates polyiodide shuttling and reduces the electrical conductivity of the electrodes. The traditional solution to these problems using a porous carbon matrix has a limited effect towards shuttling and leads to low volumetric energy density. In this study, we proposed a hydrophobic liquid ionic conductive agent to mediate confined iodine transport in a thick electrode, realizing a highly stable zinc–iodine battery with ultra-high iodine mass loading. A zinc–iodine battery with an ionic liquid conductive agent demonstrates an increase to 130% of the volumetric capacity compared with traditional porous carbon cathodes, reaching a 7-fold increase in cycle life (3500 cycles) at 10 mg cm⁻² iodine loading and a 40-fold increase (2000 cycles) at 40 mg cm⁻², with an initial areal capacity of 6.30 mAh cm⁻² and a capacity decay of 0.00495% per cycle. An ultra-high loading of 60 mg cm⁻² with an areal capacity of 11.55 mAh cm⁻² (193 mAh g⁻¹) can also be achieved. Consequently, the Ah-level Zn–I₂ pouch cell assembled with a highly loaded thick electrode demonstrates excellent cycling stability, substantiating its potential for practical application.