Regulating li kinetics at the lif/li2o sei constructed by single-source synchronous strategy to enhance li anodes stability in lithium-sulfur batteries

Abstract

During charge and discharge, enhancing the Li+ transport capability of the solid electrolyte interphase (SEI) while simultaneously blocking electronic conduction is an effective strategy for suppressing lithium dendrite growth and mitigating volume expansion at the Li-metal anode interface. In this study, density functional theory (DFT) calculations of Gibbs free energies were used to identify 2-fluoro-3-nitropyridine (FNP), a fluorine- and oxygen-containing additive, which facilitates the formation of a LiF/Li2O-rich SEI. Upon reacting with metallic lithium, FNP facilitates the formation of an SEI layer composed of interlaced LiF crystallites, which provide high ionic conductivity, and Li2O crystallites, which offer superior electronic insulation. This architecture enables the fabrication of a highly stable Li-metal anode, denoted as LiF/Li2O-Li. The formation mechanism was verified via in situ Raman spectroscopy, while in situ scanning electron microscopy (SEM) revealed significantly suppressed volume expansion. After 500 cycles, the LiF/Li2O-Li anode thickness increased from 55 μm to 105 μm (an expansion factor of 1.9), whereas the pristine Li anode expanded from 89 μm to 198 μm (a factor of 2.2). Symmetric Li||Li cells utilizing this anode exhibited stable cycling for 600 h at a current density of 1 mA cm−2 and areal capacity of 1 mA h cm−2 respectively. Furthermore, lithium-sulfur cells employing the LiF/Li2O-Li anode demonstrated excellent stability with a capacity decay rate of only 0.201% per cycle over 120 cycles at 0.2C, maintaining superior performance even under high sulfur loading and lean electrolyte conditions.