Ultrathin Defective C–N Coating to Enable Nanostructured Li Plating for Li Metal Batteries

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.