Unlocking cycle life of lithium metal batteries.

Lithium-ion Coulombic efficiency (Li CE) is widely used to evaluate interfacial stability and predict cycle life in lithium-ion batteries but fails in lithium-metal batteries (LMBs), in which higher Li CE does not reliably lead to longer cycle life. Here, we reveal that electrolyte depletion caused by unstable solid electrolyte interphases (SEIs) leads to electrolyte dry-out and induces lithium compensation through anode-to-cathode cross-talk, whereby soluble anionic species formed at the anode migrate to the cathode and release Li+ from electrolyte salts upon oxidation. We establish quantitative relationships among SEI quality, electrolyte consumption, and lithium compensation, enabling accurate cycle life prediction. The SEI quality-based framework derives quantitative guidelines for electrolyte design to extend electrolyte lifetime and sustain long cycle life in high-energy LMBs under ultra-lean electrolyte conditions.