In Situ Evolution of Artificial Interphase Enabling Stable, High‐Performance Lithium Metal Batteries

The instability of the solid‐electrolyte interphase (SEI) remains a critical bottleneck for the deployment of lithium (Li) metal batteries (LMBs). Addressing the limitations of static protective coatings, this study investigates the dynamic evolution of a Mg 3 N 2 ‐based artificial layer on Li metal anodes. We identify a spontaneous conversion reaction that generates a hybrid interphase composed of Li 3 N and Mg‐Li alloy. Note that this reaction is not static; it intensifies during repeated plating/stripping cycles, continuously reinforcing the interface. The resulting Li 3 N component facilitates rapid ionic transport, while the lithiophilic Mg‐Li alloy lowers the nucleation overpotential and suppresses dendritic growth. This synergetic mechanism results in superior electrochemical performance, including 91.5% capacity retention in full cells paired with high‐loading LiFePO 4 after 600 cycles at 1C (2 mA cm −2 ). These findings provide insight into designing adaptive interphases that chemically evolve to sustain long‐term protection in aggressive electrochemical environments.