Restraining the shuttle effect of polyiodides and modulating the deposition of zinc ions to enhance the cycle lifespan of aqueous Zn–I2 batteries

The boom of aqueous Zn-based energy storage devices, such as zinc–iodine (Zn–I2) batteries, is quite suitable for safe and sustainable energy storage technologies. However, in rechargeable aqueous Zn–I2 batteries, the shuttle phenomenon of polyiodide ions usually leads to irreversible capacity loss resulting from both the iodine cathode and the zinc anode, and thus impinges on the cycle lifespan of the battery. Herein, a nontoxic, biocompatible, and economical polymer of polyvinyl alcohol (PVA) is exploited as an electrolyte additive. Based on comprehensive analysis and computational results, it is evident that the PVA additive, owing to its specific interaction with polyiodide ions and lower binding energy, can effectively suppress the migration of polyiodide ions towards the zinc anode surface, thereby mitigating adverse reactions between polyiodide ions and zinc. Simultaneously, the hydrogen bond network of water molecules is disrupted due to the abundant hydroxyl groups within the PVA additive, leading to a decrease in water activity and mitigating zinc corrosion. Further, because of the preferential adsorption of PVA on the zinc anode surface, the deposition environment for zinc ions is adjusted and its nucleation overpotential increases, which is favorable for the dense and uniform deposition of zinc ions, thus ensuring the improvement of the performance of the Zn–I2 battery. This investigation has inspired the development of a user-friendly and high-performance Zn–I2 battery.