Revealing the synergistic effect of LiF and Li3N in solid electrolyte interphases for stable lithium metal batteries using in situ electrochemical atomic force microscopy

Abstract

Inorganic components in the solid electrolyte interphases (SEIs) on lithium (Li) metal play a critical role in Li metal batteries (LMBs) since the presence of numerous inorganic constituents may promote ion diffusion and mechanical strength. However, manipulating inorganic components and acquiring an in-depth understanding of their roles in LMBs remain challenging. Herein, we deliberately introduce different kinds of inorganic components (e.g., LiF, Li₃N, and their complexes) into SEIs on Li metal in LMBs by electrolyte engineering. Through in situ atomic force microscopy and electrochemical experiments, the roles of the specific inorganic component in SEIs played in the process of Li nucleation and evolution are revealed, and the detailed synergistic effect of LiF and Li₃N is clarified. We demonstrate that the simultaneous presence of LiF and Li₃N in SEIs enables homogeneous and dense lithium metal nucleation and growth, improving both the chemical stability and mechanical strength of SEIs for highly stable LMBs. In contrast, individual LiF and Li₃N in SEIs induce needle morphology of Li metal and discrete Li deposition, respectively. These findings can provide rational guidelines for optimizing SEIs through electrolyte engineering for stable LMBs.