Construction of a robust and high ion-conductivity SEI using a multifunctional additive to achieve high-rate and large-capacity lithium metal anodes

Abstract

Despite the ultrahigh theoretical capacity (3860 mAh g⁻¹) and low redox potential (−3.04 V vs. SHE), Li metal anodes suffer from low coulombic efficiency and dendrite growth, especially in carbonate electrolytes due to their high polarity and reactivity. Herein, triethyl 2-fluoro-2-phosphonoacetate (TFPA) is proposed as an effective additive to construct a robust LiF/Li₃PO₄-rich solid electrolyte interphase (SEI), as confirmed by density functional theory (DFT) and and X-ray photoelectron spectroscopy (XPS). The LiF provides high interfacial energy while Li₃PO₄ ensures high ionic conductivity, enabling stable Li deposition. With 0.5 wt% TFPA, Li‖Li symmetric cells stably cycle for 600 h at 5.0 mA cm⁻² and 5.0 mAh cm⁻². Full cells using high-loading LiNi_0.8Co_0.1Mn_0.1O₂ or LiCoO₂ cathodes and thin Li (50 µm, N/P = 3.0) also show markedly enhanced cycling and rate performance.