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 | LiNi0.5 Co0.2 Mn0.3 O2 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.