Synergistic dual electrolyte additives for fluoride rich solid-electrolyte interface on Li metal anode surface: Mechanistic understanding of electrolyte decomposition

Abstract

Improving the quality of the solid-electrolyte interphase (SEI) layer is highly imperative to stabilize the Li-metal anodes for the practical application of high-energy–density batteries. However, controllably managing the formation of robust SEI layers on the anode is challenging in state-of-the-art electrolytes. Herein, we discuss the role of dual additives fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2, LiPF) within the commercial electrolyte mixture (LiPF6/EC/DEC) considering their reactivity with Li metal anodes using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Synergistic effects of dual additives on SEI formation mechanisms are explored systematically by invoking different electrolyte mixtures including pure electrolyte (LP47), mono-additive (LP47/FEC and LP47/LiPF), and dual additives (LP47/FEC/LiPF). The present work suggests that the addition of dual additives accelerates the reduction of salt and additives while increasing the formation of a LiF-rich SEI layer. In addition, calculated atomic charges are applied to predict the representative F1s X-ray photoelectron (XPS) signal, and our results agree well with the experimentally identified SEI components. The nature of carbon and oxygen-containing groups resulting from the electrolyte decompositions at the anode surface is also analyzed. We find that the presence of dual additives inhibits undesirable solvent degradation in the respective mixtures, which effectively restricts the hazardous side products at the electrolyte-anode interface and improves SEI layer quality.