Effective Iodine Encapsulation for Rechargeable Zinc-Iodine Enclosed Battery

The increasing demand for electricity and the intense degree of electrification require greener, safer, and more cost-effective rechargeable battery technologies. Among these available technologies, lithium-ion batteries (LIBs) are the most feasible option for various applications. Nonetheless, LIBs show several drawbacks such as safety problems, recycling, and most specifically the cost and material abundance. One possible approach to address this issue is to replace lithium (Li) with a high volumetric capacity metal such as zinc (Zn). Zn has a higher specific volumetric capacity of 5,855 mAh cm -1 compared to that of Li (2,066 mAh cm -1 ). Besides, Zn has a lower cost. Even more, it is environmentally friendly, safe, and non-toxic. The redox capacity of Zn is -0.763 V vs. standard hydrogen potential (SHE). Thus, it is better for an aqueous electrolyte with the application of near-neutral electrolytes. Among various zinc-based redox chemistries, the I - /I 2 redox couple shows the most promising and excellent electrochemical performances. Iodine has low cost and high abundance. The initial work of a zinc-iodine battery was demonstrated as a flow battery by the PNNL National Laboratory at Northwestern University. The battery shows excellent performance with high energy efficiency. However, a flow battery is not appropriate for portable application and requires periodic maintenance. Fabrication of zinc-iodine battery in an enclosed cell form factor is thus challenging. In this work, a zinc-iodine enclosed battery is demonstrated by encapsulating iodine (active material) and iodide species (discharge product) on the positive electrode material with activated carbon and anionic polyelectrolyte. Activated carbon adsorbs on iodine its surface and trapped in its pores, while anionic polyelectrolyte prevents iodide species from escaping the electrode surface. Though zinc-iodine cell is a conversion-type as the electrochemical reactions taking place during charging and discharging of the battery result in new chemical compounds, the behavior of the battery proposed is similar to an insertion-type battery. The charge storage and charge-transfer characteristics of the battery are examined. The results show that the battery exhibits an ultrafast charging rate of 6C-10C. The battery displays very high round-trip efficiency above 90%, even charging/discharging at 6C. Also, the cell shows excellent stability with low capacity fading (less than 5% after 2,000 cycles). Consequently, the battery exhibited excellent electrochemical performance, good cyclability with the maximum specific capacity of 145 mAh/g I at 1.5C. Overall, the proposed zinc-iodine enclosed cell is very promising for high rate applications. Figure 1