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 | LiNi0.5Co0.2Mn0.3O2 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. A triiodide/iodide (I3−/I−) redox couple is introduced with a SnI4 initiator to reclaim inactive Li. The reduction of I3− converts inactive Li into soluble LiI, and the oxidation of LiI by a delithiated cathode realizes the restoration of Li ion in cathode from inactive Li. The regenerated I3− by oxidation engages the further redox reactions.