Construction of robust and high ion-conductivity SEI by 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), the practical use of Li metal anode has been still plagued by the low Coulombic efficiency (CE) and uncontrollable dendrite growth, which could be more serious in carbonate electrolytes due to their higher polarity and chemical reactivity. Herein, triethyl 2-fluoro-2-phosphonoacetate (TFPA) has been proposed as a novel film-forming additive to achieve high-rate and large-capacity Li metal batteries in carbonate electrolyte. Both density functional theory calculations (DFT) and X-ray photoelectron spectroscopy (XPS) depth profiling reveal that TFPA additive can preferentially adsorb on Li metal and in-situ construct a robust solid electrolyte interphase (SEI) rich in LiF and Li₃PO₄, which possess high interfacial energy and high ionic conductivity, respectively. Owing to the synergistic effect of LiF and Li₃PO₄, the Li||Li symmetric cells with 0.5 wt% TFPA deliver an impressive long-term cycle performance for 600 h at high current density of 5.0 mA cm⁻² and high areal capacity of 5.0 mAh cm-2 in carbonate electrolyte. Moreover, the full cells assembled by high-loading LiNi0.8Co0.1Mn0.1O2 or LiCoO2 cathode and thin Li metal anode (50 µm) with N/P ratio of 3.0 also demonstrate greatly improved cycling stability and rate capability.