Designing Metal Phosphide Solid-Electrolyte Interphase for Stable Lithium Metal Batteries Through Electrified Interface Optimization and Synergistic Conversion

• Strategic heterostructure design creates electrified interfaces that induce a fully ionized depletion region and built-in electric field, enhancing Li affinity and promoting uniform current distribution for stable Li deposition. • The SnP0.94/CoP heterostructure enables in situ conversion to a mixed ionic/electronic conductor (MEIC) during cycling, ensuring long-term stability of the modulation layer. • SCP@Li symmetric cells achieve low overpotential for 750 cycles at 5 mA cm−2, demonstrating excellent cycling stability. • LiFePO4//SCP@Li full cells show imperceptible capacity decay of 0.03% per cycle over 800 cycles at 0.5 C, highlighting practical applicability.