A synergistic PAN/LiF hybrid layer enabling highly stable lithium metal anodes via in situ interface engineering

Abstract

Lithium metal anodes (LMAs) offer exceptional promise for cutting-edge energy storage applications owing to their unparalleled theoretical specific capacity and extremely low electrode potential. However, the practical implementation of LMAs remains impeded by intrinsic material challenges, primarily chemically incompatible interfaces with electrolytes and uncontrolled Li dendrite growth. To address these challenges, an organic/inorganic hybrid protective layer is constructed for LMAs, consisting of polyacrylonitrile (PAN) and LiF, where LiF is generated through in situ conversion of ammonium hydrogen fluoride (NH₄HF₂) with Li. As expected, the PAN/LiF hybrid layer integrates the mechanical rigidity and electronic insulation of LiF with the flexibility of the PAN matrix, enabling continuous protection of the anode against interfacial side reactions and suppressing Li dendrite growth during cycling. In addition, density functional theory (DFT) calculations further confirm the good affinity of the PAN/LiF layer toward Li⁺, thus facilitating fast Li⁺ diffusion kinetics and lowering Li nucleation barriers. Consequently, the PAN/LiF layer-protected anodes achieve ultra-stable plating/stripping for 1200 h with ultralow voltage hysteresis. When integrated with LiFePO₄ (LFP) cathodes, the PAN/LiF–Li‖LFP full cells demonstrate exceptional cycling stability for more than 500 cycles at both 1C and 3C rates, retaining 83.6% capacity with minimal capacity loss (3.8% after 500 cycles). The PAN/LiF–Li anodes also demonstrate excellent performance with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes and pouch cells, further highlighting the practical viability of this artificial interface strategy for developing long-term cycling and high-performance Li metal batteries.