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 LiFePO4-based LMBs. The advantage of N-extraction from C3N4 is comprehensively discussed in combination with the results based on g-C3N4 decoration.
Keywords: Li metal batteries; N-deficient C−N network; anode interface modification; artificial SEI film; dendrite suppression.