High‐Capacity, Long‐Life All‐Solid‐State Lithium–Selenium Batteries Enabled by Lithium Iodide Active Additive

Abstract Selenium (Se) shows promise as a cathode candidate for all‐solid‐state lithium (Li) batteries due to its impressive theoretical volumetric energy density, much higher electronic conductivity, and improved safety in comparison to those for sulfur (S). An active cathode additive, lithium iodide (LiI) is demonstrated, to address the major challenge for all‐solid‐state Li–Se batteries, namely the sluggish redox kinetics resulting from the huge solid‐state conversion barrier. The LiI additive enhances Li + transport and provides catalytic sites for Se cathode, thus endowing the batteries with accelerated reaction kinetics and extra capacity. DFT calculation and experimental analysis clearly reveal that LiI additive efficiently accelerates the conversion between polyselenide intermediates and Li 2 Se. With the above advantages, the battery with LiI using Li 6 PS 5 Br electrolyte gives an outstanding capacity of 862 mAh g Se −1 beyond the theoretical specific capacity of Se and a superlong life over 1800 cycles at 1C under room temperature. This work offers a simple strategy to facilitate the kinetics of all‐solid‐state Se cathodes and paves the way for the practicality of high‐capacity and long‐life all‐solid‐state Li–Se batteries.