Lithium metal batteries (LMBs) are obtaining increasing attention in view of their advantage of theoretical energy density up to 500 Wh kg −1 or higher. However, their performance exploitation is still retarded by anode dendrite growth, dead Li buildup, and electric contact loss at the interface. In order to overcome these challenges, herein, we proposed a defect engineering of a C−N polymer to construct a N-deficient ultrathin film (27 nm) with an unusually narrow bandgap (0.63 eV) as an artificial solid electrolyte interphase (SEI) by reactive thermal evaporation. This defective C−N film enables a nanostructured modulation of Li plating without severe dendrite extrusion and electric disconnection. Its high lithiophilicity is expected to trigger a desired space charge effect in the SEI with enhanced charge-transfer ability, which leads to significant reduction of both the nucleation (17.5 mV at 1 mA cm −2 ) and plateau overpotentials (70 mV at 3 mA cm −2 ) during Li plating and stripping. This interposition of a defect structure also endows Li/ Cu cells with extended cycling reversibility over 400 cycles and a highly stable Coulombic efficiency of 99% at 3 mA cm −2 . The interconnection preservation of the Li plating network modulated by the C−N interphase guarantees a high capacity retention of LiFePO 4 -based LMBs. The advantage of N-extraction from C 3 N 4 is comprehensively discussed in combination with the results based on g-C 3 N 4 decoration.

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