Probing Interfacial Electrolyte Chemistry and SEI Failure Mechanisms on Lithium-Metal Anodes via Establishing a...

The formation and failure of the solid electrolyte interphase (SEI) govern the reversibility, stability, and safety of Li metal anodes. However, the dynamic construction process of the SEI and the associated multiphase product evolution originating from interfacial electrolyte decomposition remain insufficiently understood. Herein, we establish a multichannel interfacial product analysis paradigm that enables the tracking of distinct products during electrolyte decomposition and SEI evolution across gaseous, volatile, solid, dead Li, and thermal-response pathways. Using traditional and fluorinated carbonate electrolytes as model systems, we demonstrate that the traditional electrolyte undergoes continuous carbonate fragmentation, forming an SEI enriched in organic and carbonate species with limited passivation capability, thereby inducing interfacial reconstruction, dead Li accumulation, and pronounced gas evolution under thermal stress. In contrast, fluorinated electrolytes follow a more convergent decomposition pathway to form a LiF-rich composite SEI, which reduces dead Li formation, stabilizes Li plating/stripping, and markedly suppresses the release of interfacial gases during thermal decomposition. More broadly, this integrated multitechnique characterization system provides a powerful analytical tool to precisely resolve SEI formation and failure processes, thereby offering scientific insights and practical engineering strategies for developing safer and highly reversible Li-metal batteries.