Multifunctional Interlayer Including Metal Fluoride–Modified PAN/PSF–Based Superfine and Porous Carbon Nanofibers for Stable Lithium Metal Cells

In this study, yttrium fluoride–modified PAN/PSF–based superfine and porous carbon nanofibers (YF3–PAN/PSF-CNFs) based on the “Tug-of-War” refinement mechanism of heterogeneous viscous fluid are designed and prepared through electro-blow spinning and subsequent carbonization processes. The prepared YF3–PAN/PSF-CNFs are applied as an important component of the functional interlayer to study its effect on the electrochemical performance and safety of lithium metal cells. The interconnected framework of YF3–PAN/PSF-CNFs, with high conductivity and a large specific surface area, can provide facilitated lithium ion and electron transmission channels and lower local current density. The lithiophilic YF3 also can provide enough active sites to produce an alloying reaction with lithium ions to uniformly guide lithium deposition. For the assembled Li||LiFePO4 battery, after 650 cycles at 0.5 C, it still maintained a high specific discharge capacity of 154.9 mAh g–1. The assembled Li||Li symmetric battery, based on the prepared functional interlayer, further presented that the functional YF3–PAN/PSF-CNFs interlayer can significantly suppress the growth of lithium dendrites and greatly improve cycle stability, with the batteries having relatively stable low overpotential within a 1000-h cycle time, and the voltage amplitude is basically stable within ±0.1 V. At the same time, the assembled lithium–sulfur (Li||S) cell equipped with the interlayer based on the YF3–PAN/PSF-CNFs also presents outstanding cycle stability. The main reasons for this result are ascribed to the synergistic effect of physical confinement and chemical adsorption of the YF3–PAN/PSF-CNFs effectively reducing the “shuttle effect” of lithium polysulfide. All the results illustrate that the application of the YF3–PAN/PSF-CNFs interlayer can provide insights into enhancing electrochemical performances and protecting the lithium anode of the lithium metal cell.