Fluorine–Nitrogen Codoped Carbon Host for Horizontal Lithium Growth with Lithium Fluoride-Rich Solid Electrolyte Interphase in Lean-Lithium Batteries

Lithium (Li) metal is considered as a highly promising anode material for next-generation rechargeable batteries due to its ultrahigh theoretical capacity (3860 mAh g^-1) and the lowest redox potential (-3.04 V vs standard hydrogen electrode (SHE)). Nevertheless, its practical application is significantly impeded by uncontrolled dendrite formation, unstable solid electrolyte interphase (SEI), and low Coulombic efficiency, which collectively compromise cycling stability and safety. In this work, we present a fluorine and nitrogen codoped porous carbon (FNC) framework as an engineered host for regulating lithium nucleation and interfacial chemistry. Nitrogen doping enhances surface lithiophilicity and reduces nucleation overpotential, while fluorine incorporation facilitates the in situ formation of a LiF-rich SEI layer with superior mechanical robustness and chemical stability. The FNC host promotes planar lithium deposition and mitigates electrolyte decomposition and volume fluctuations. Compared with nitrogen-doped carbon (NC) and bare copper substrates, the FNC@Cu electrode exhibits markedly lower overpotential and dendrite-free horizontal lithium growth, leading to suppressed dead Li accumulation and enhanced reversibility. It achieves a Coulombic efficiency (CE) of 94% over 100 cycles at 2 mA cm^-2 and retains 97% over 300 cycles under lean-lithium conditions. Full cell tests with LiFePO₄ cathodes reveal a stable cycling performance with 95.1% capacity retention after 250 cycles (N/P ratio = 1.5), highlighting the practical viability of the FNC framework. These results underscore the efficacy of heteroatom codoping and interfacial design for realizing high-performance, lean-lithium metal batteries.