Composition‐Dependent Solvation in Low‐Concentration Multi‐Salt DME Electrolytes: Correlations With Lithium Deposition and Interfacial Evolution

Lithium metal battery behavior is strongly influenced by the electrolyte environment from which the solid–electrolyte interphase develops, yet the effects of combining anions in dilute multi‐salt formulations remain incompletely understood. Combinations of LiFSI, LiTFSI, and LiNO ₃ in DME, at a total Li ⁺ concentration of 1 mol kg ⁻¹ , were investigated using complementary spectroscopy, electrochemistry, and microscopy. Raman and ¹ H/ ⁷ Li NMR spectroscopy reveal composition‐dependent changes in imide‐anion association, DME coordination‐sensitive spectral features, and the average Li ⁺ environment. These changes are accompanied by interfacial impedance responses and lithium deposit morphologies. Most notably, all nitrate‐containing formulations show improved preservation of a lithium reservoir formed on Cu, sustaining 80–86 reversible cycles with average Coulombic efficiencies close to 99%, while displaying limited impedance evolution and more continuous deposits. Within this nitrate‐containing series, FSI and TFSI produce distinct spectroscopic and interfacial responses, even though a ranking in reservoir reversibility cannot be established. TFSI is shifted predominantly toward noncontact environments upon nitrate addition, whereas FSI retains a substantial contribution from contact‐associated configurations. The combined results demonstrate that multi‐salt electrolytes cannot be described as simple superpositions of their single‐salt components and support a working interpretation in which the anion composition modulates the prereduction Li ⁺ solvation ensemble and subsequent interfacial evolution.