Electric‐Field‐Driven Bilayer Interphase from Oxygenated Nanodiamond‐Carbon Nanoparticles for Dendrite‐Free Lithium Metal Batteries

ABSTRACT Lithium metal batteries (LMBs) offer exceptional energy density but are severely limited by dendrite formation and unstable interphases. Here, this work presents an electric field–driven in situ strategy to construct a vertically graded interphase using an oxygen‐rich nanodiamond/carbon (O‐ND/C) composite. During Li plating, conductive carbon migrates toward the current collector, forming a C‐enriched conductive sublayer beneath a lithiophilic O‐ND‐rich insulating layer. This bilayer architecture homogenizes Li‐ion flux, lowers the nucleation barrier, and simultaneously ensures mechanical robustness and electronic insulation, thereby enabling dendrite‐free Li deposition. The optimized O‐ND with 10 wt% of C interphase demonstrates outstanding electrochemical stability, maintaining an ultralow overpotential of 9.5 mV for 5800 h in symmetric cells and an average Coulombic efficiency (CE) of 98.8% to 700 cycles. In full‐cell configurations with LiFePO 4 cathodes, stable operation is sustained for up to 1500 cycles, areal capacity of 12.1 mAh cm −2 retained 9.9 mAh cm −2 after 50 cycles even under industrially relevant high cathode loading (93.8 mg LFP cm −2 ). Complementary density functional theory calculations confirm that O‐ND surfaces enhance Li adsorption and diffusion, corroborating the experimental results. This work provides mechanistic insight into field‐driven interphase engineering and offers a practical pathway toward safe, high‐energy density LMBs.