Conductometric Analysis of Ion Equilibrium in Li⁺/F⁻ and Mg²⁺/F⁻ Hybrid Electrolyte Solutions (Supporting Information)

Fluoride shuttle batteries are expected to be innovative with high energy density superior to lithium-ion ones as on-board power-source for electric vehicles. However, the low solubility of fluoride ion in organic solvents makes it difficult to choose electrolytes. Kawasaki et al. have reported that no precipitation appears in γ-butyrolactone solution of CsF at high concentrations in the presence of excess amounts of Li⁺ or Mg²⁺ cation.¹ Such solutions are called hybrid electrolyte ones. In this study, we performed conductometric titration of Li⁺- or Mg²⁺-containing solutions with CsF solutions to elucidate the ion equilibrium. The titration curves were analyzed on models including precipitation of LiF or MgF₂ and formation of Li₂F⁺ and LiF₂⁻ triple ion or MgF⁺ associated one to evaluate the corresponding equilibrium constants. The results indicate that no precipitation appears in certain ranges of the F⁻/Li⁺ or F⁻/Mg²⁺ molar ratio by the triple/associated ion formation. Details of the conductometric analysis are discussed together with some problems involved in the proposed method.