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.