Challenges and prospects of dead Li⁰ reactivation in lithium metal batteries

High-energy-density lithium (Li) metal batteries (LMBs) are promising next-generation energy storage technologies. However, the continuous and irreversible inactive metallic Li (dead Li⁰) generation severely limits battery lifespans. Notably, reactivating dead Li⁰ in addition to reducing its formation is also crucial for achieving long-life LMBs. Though prototype strategies (e.g., electrochemical protocols, redox chemistry) have achieved partial reactivation of dead Li⁰, their feasibility in practical cells remains limited by the large proportion of dead Li⁰ that persists. Directly reconnecting exposed dead Li⁰ with electrodes by introducing external electronically conductive materials is a promising solution, yet it fails to achieve the expected reactivation. To achieve efficient reactivation of dead Li⁰, key procedures including Li-stripping-related issues (e.g., mass transport, ion/electron transfer), solid electrolyte interphase (SEI) evolution, and effective dead Li⁰ exposure should be concurrently considered. The answer may be obtained through in-depth mechanistic studies using advanced characterization techniques. Additionally, insights into dead Li⁰ reactivation can be gained from existing methods (e.g., high cutoff voltage, lower current density) and from detecting environmental changes around the reactivated dead Li⁰ to identify favorable conditions. Such recognition of dead Li⁰ reactivation promises LMBs with prolonged lifespan, which can further be extended to other battery systems.