Structural modification by adding Li cations into Mg/Cs-TFSA molten salt facilitating Mg electrodeposition

Abstract

Liquid structures of Li/Mg/Cs-TFSA (TFSA: bis(trifluoromethylsulfonyl)amide, N(SO 2 CF 3 ) 2 -) molten-salt systems have been investigated by Raman spectroscopy and high-energy X-ray diffraction. The Raman spectroscopic measurements indicate that the cis-conformer of the TFSA anion is more favorable than the trans-conformer in the molten salts containing Li + and/or Mg 2+ , whereas the latter is dominant for a pure Cs[TFSA] molten salt. The present reverse Monte Carlo (RMC) structural modelling suggests that the coordination number of the anion around Mg, N Mg-anion , decreased in Li 0.1 Mg 0.1 Cs 0.8 [TFSA] 1.1 molten salt compared to that in Mg 0.1 Cs 0.9 [TFSA] 1.1 . The Mg-anion distance under the coexistence of Li + is found to be about 10-15 % longer than that without Li + at around N Mg-anion ~ 1.5, which means the increase of free volume around Mg cations in the Li-contained molten salt. Thus, the electrodeposition of Mg in alkali-TFSA molten salts would be facilitated under the coexistence of Li cations.

Structure Design of Long‐Life Spinel‐Oxide Cathode Materials for Magnesium Rechargeable Batteries

“…[17,18] When the oxygen vacancy increases, the following tendencies would appear: i) decrease in the valence of Mn, and ii) increase in the 16d site vacancies, leading to the increase of single-phase reaction capacity. Figure 2d shows the first discharge (Mg insertion) and the subsequent charge (Mg extraction) behavior of ZnMnO 3 obtained by using an ionic liquid electrolyte of (Mg10/Cs90) TFSA, [21] where the operating temperature was set at 150 °C for facilitating Mg 2+ diffusion. Since Mg metal is well known to be readily passivated by TFSA anion, [22][23][24] to measure the exact electrode potentials, we used a Li-metal reference in a separated glass tube with a ceramic filter; see Supporting Information for details of the Mg-metal reference and its comparison to the Li-metal reference.…”