Iodine encapsulation using anionic polyelectrolytes for rechargeable zinc-iodine batteries

Abstract

Rechargeable zinc-iodine batteries are attractive as promising candidates for electrical energy storage due to their abundant resources, low cost, and high safety. However, these batteries still have some problems, such as poor cycling stability and high self-discharge due to the leakage of iodine species from the positive electrode. Anionic polyelectrolytes can be applied as supportive binders to alleviate this issue because these polyelectrolytes can encapsulate iodine species and facilitate the transfer of other active species. In this study, different types of anionic polyelectrolytes, including sodium carboxymethyl cellulose (Na-CMC), sodium alginate (Na-Alg), and sodium polystyrene sulfonate (Na-PSS), were investigated. The batteries were fabricated in CR2025 cells to investigate the electrochemical performance. The results showed that the positive electrodes processed with these anionic polyelectrolytes as supportive binders could show remarkable high-rate capability and improve specific capacity reach to 127.37 mAh g-1, which used PVA-NaCMC binder while it only 104.06 mAh g-1 when using a PVA binder. Additionally, these anion polyelectrolytes can encapsulate iodine species in positive electrodes better than a PVA binder leading to a low self-discharge rate. Therefore, positive electrodes with these anionic polyelectrolytes as supportive binders are promising binders for the positive electrode in the rechargeable zinc-iodine batteries.