25:T520,Lithium metal batteries (LMB) have high energy densities and are crucial for clean energy solutions. The characterization of the lithium metal interphase is fundamentally and practically important but technically challenging. Taking advantage of synchrotron X-ray, which has the unique capability of analyzing crystalline/amorphous phases quantitatively with statistical significance, we study the composition and dynamics of the LMB interphase for a newly developed important LMB electrolyte that is based on fluorinated ether. Pair distribution function analysis revealed the sequential roles of the anion and solvent in interphase formation during cycling. The relative ratio between Li₂O and LiF first increases and then decreases during cycling, suggesting suppressed Li₂O formation in both initial and long extended cycles. Theoretical studies revealed that in initial cycles, this is due to the energy barriers in many-electron transfer. In long extended cycles, the anion decomposition product Li₂O encourages solvent decomposition by facilitating solvent adsorption on Li₂O which is followed by concurrent depletion of both. This work highlights the important role of Li₂O in transitioning from an anion-derived interphase to a solvent-derived one.26:T45b,Solid electrolyte interphase (SEI) engineering is an efficient approach to enhancing the cycling performance of lithium metal batteries. Lithium hexafluorophosphate (LiPF₆) is a popular electrolyte salt. Mechanistic insights into its degradation pathways near the lithium metal anode are critical in modifying the battery electrolyte and SEI. In this work, we elucidate plausible reaction pathways in multiple representative electrolyte systems. Through ab initio molecular dynamics simulations, lithiation and electron transfer are identified as the triggering factors for LiPF₆ degradation. Meanwhile, we find that lithium morphology and charge distribution substantially impact the interfacial dissociation pathways. Thermodynamic evaluation of the solvation effects shows that higher electrolyte dielectric constant and lithiation extent profoundly assist the LiPF₆ decomposition. These findings offer quantitative thermodynamic and electronic structure information, which promotes rational SEI engineering and electrolyte tuning for lithium metal anode performance enhancement.

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