Commonalities and Characteristics Analysis of Fluorine and Iodine used in Lithium-Based Batteries

Among optimization strategies for solving the poor ion transport ability and electrolyte/electrode interface compatibility problems of lithium (Li)-based batteries, halogen elements, such as fluorine (F) and iodine (I), have gradually occupied an important position because of their superb electronegativity, oxidizability, ionic radius, and other properties. The study commences by outlining the shared mechanism by which F and I enhance solid-state lithium metal batteries' electrochemical performance. In particular, F and I can considerably improve ion transport capacity through chemical means such as intermolecular interactions and halogenation reactions. Furthermore, the utilization of F and I significantly enhances the stability of the electrolyte/electrode interface via physical strategies, encompassing doping techniques, the application of surface coatings, and the fabrication of synthetic intermediate layers. Subsequently, the characteristics of F and I used in Li-based batteries are elaborated in detail, focusing on the fact that F can provide additional energy density as an anode material but by different mechanisms. Additionally, I can considerably activate dead lithium at the negative electrode, and F can act as a new carrier. Finally, a rational concept of the synergistic effect of F and I is proposed and the feasibility of F–I bihalide solid electrolytes is explored.