Reclaiming Inactive Lithium with a Triiodide/Iodide Redox Couple for Practical Lithium Metal Batteries

High-energy-density lithium (Li) metal batteries suffer from a short lifespan owing to apparently ceaseless inactive Li accumulation, which is accompanied by the consumption of electrolyte and active Li reservoir, seriously deteriorating the cyclability of batteries. Herein, a triiodide/iodide (I₃⁻/I⁻) redox couple initiated by stannic iodide (SnI₄) is demonstrated to reclaim inactive Li. The reduction of I₃⁻ converts inactive Li into soluble LiI, which then diffuses to the cathode side. The oxidation of LiI by the delithiated cathode transforms cathode into the lithiation state and regenerates I₃⁻, reclaiming Li ion from inactive Li. The regenerated I₃⁻ engages the further redox reactions. Furthermore, the formation of Sn mitigates the corrosion of I₃⁻ on active Li reservoir sacrificially. In working Li | LiNi_0.5Co_0.2Mn_0.3O₂ batteries, the accumulated inactive Li is significantly reclaimed by the reversible I₃⁻/I⁻ redox couple, improving the lifespan of batteries by twice. This work initiates a creative solution to reclaim inactive Li for prolonging the lifespan of practical Li metal batteries.