Redefining LiF as a Nanostructured Building Block for Interphase Engineering in Lithium Metal Batteries

Lithium metal batteries (LMBs) are regarded as promising next-generation energy storage systems due to their high theoretical capacity and low reduction potential. However, their practical application is fundamentally limited by the instability of the solid electrolyte interphase (SEI) formed at the lithium metal-electrolyte interface. LiF-rich SEIs have been widely proposed as an effective solution, as LiF provides strong electronic insulation that suppresses continuous electrolyte decomposition. Importantly, the performance of LiF-rich SEIs is governed not simply by LiF content, but by the nanoscale structure, spatial distribution of LiF, and its heterogeneous interfaces with other SEI components. This review summarizes LiF-rich SEI formation strategies based on electrolyte-driven in situ processes and ex situ artificial coatings, and compares the structural and dynamic characteristics of the resulting interphases. Emphasis is placed on fluorinated electrolyte design using salts, additives, and solvents, which enables simultaneous electronic insulation and lithium-ion transport through LiF nano structuring and interface engineering. Furthermore, LiF-rich SEIs are redefined as assemblies of controllable nanoscale building blocks, highlighting the role of grain boundaries and heterogeneous interfaces. Computational approaches, including density functional theory, molecular dynamics, and machine-learning-based methods, are discussed as key tools for SEI engineering and predictive design.