Thickness-Dependence of 2D g-C₃N₄ Artificial Interface Layers on Lithium Metal Deposition

Constructing artificial interfacial layers using 2D materials with tunable physicochemical properties is a promising strategy to fabricate high-performance lithium (Li) metal anodes. However, their structural evolution during solid-electrolyte interphase (SEI) formation and the thickness effects on charge transport remain elusive. Herein, 2D g-C₃N₄ layers with varied thicknesses are developed on the surface of copper foil to evaluate the thickness effects of artificial SEI on Li metal deposition. It is demonstrated that a thin g-C₃N₄ layer (≈2 nm) is rapidly decomposed and fractured under the impact of Li-ion flux, while a thick g-C₃N₄ layer (≈50 nm) impedes the transport of lithium ions and electrons simultaneously, hindering the Li metal deposition underneath. Notably, a g-C₃N₄ layer with moderate thickness (≈10 nm) dominates in-situ generation of stable g-C₃N₄/Li₃N hybrid artificial SEI and enables fast Li-ion transport, which induces uniform Li deposition. The lithium electrode protected by the moderate-thickness g-C₃N₄ layer exhibits outstanding cycling stability with a high average Coulombic efficiency of ≈98.92% for over 380 cycles and enables stable cycling of full cell with 50% Li excess and lean electrolyte. This proof-of-concept study provides essential guidance for the application of 2D materials in constructing artificial SEI for Li metal anodes.