Evolution and Interplay of Lithium Metal Interphase Components Revealed by Experimental and Theoretical Studies.

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 LiO and LiF first increases and then decreases during cycling, suggesting suppressed LiO 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 LiO encourages solvent decomposition by facilitating solvent adsorption on LiO which is followed by concurrent depletion of both. This work highlights the important role of LiO in transitioning from an anion-derived interphase to a solvent-derived one.