Ultra-High Fluorine Enhanced Homogeneous Nucleation of Lithium Metal on Stepped Carbon Nanosheets with Abundant Edge Sites

Disordered nucleation sites and a fragile solid electrolyte interphase on the reactive interface tend to cause uncontrolled growth of lithium dendrites, which induce severe safety concerns and prevent lithium metal batteries from finding practical applications. Herein, novel stepped carbon nanosheets with abundant step edges and ultra-high fluorine content (37.44 at%) are fabricated by combining an improved molten salt synthesis method with C4F8 vacuum plasma treatment. The solvent-induced spatial confinement effect, i.e., orientation carbonization of pitch macromolecules, leads to the formation of step-edge-enriched nanoarrays. Meanwhile, the adequate exposure of edge sites on the basal plane of carbon nanosheets is conducive to achieve the ultra-efficient doping of elemental fluorine in only 10 min. Further experiments and theoretical calculations demonstrate that the coupling effect of sufficient edge sites and active semi-ionic C-F/covalent CF2 groups on the carbon surface can not only form 2D fluorinated lithium chain and a robust Li-F network, but also effectively facilitate Li ion redox kinetics and morphological stability, presenting a step-edge-guided plating process. As such, the developed anodes deliver an ultra-low nucleation overpotential (approximate to 10.5 mV), high Coulombic efficiency (>98% over 385 cycles), ultra-long cycling duration for up to 3000 h under approximate to 10 mV, and excellent full battery performance.

Automated summary

In this study, stepped carbon nanosheets with abundant step edges and ultra-high fluorine content were fabricated and found to effectively control the growth of lithium dendrites, improving the safety and practicality of lithium metal batteries.