New inorganic ionic liquids possessing low melting temperatures and wide electrochemical windows: Ternary mixtures of alkali bis(fluorosulfonyl)amides

Four kinds of ternary phase diagrams of alkali bis(fluorosulfonyl)amides, LiFSA–NaFSA–KFSA, LiFSA–NaFSA–CsFSA, LiFSA–KFSA–CsFSA and NaFSA–KFSA–CsFSA, have been constructed. All the ternary systems possess the only one eutectic point around equimolar composition with the temperature of 309–318 K. The electrochemical window of the eutectic LiFSA–KFSA–CsFSA ((xLi, xK, xCs) = (0.30, 0.35, 0.35)) is as wide as 5.4 V at 323 K with the cathode limit being lithium metal deposition. The electrochemical window of the eutectic NaFSA–KFSA–CsFSA ((xNa, xK, xCs) = (0.40, 0.25, 0.35)) is 4.9 V at 323 K with sodium metal deposition as the cathode limit reaction.

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► Four ternary phase diagrams of alkali bis(fluorosulfonyl)amides were constructed.
► These ternary systems possess eutectic temperature at as low as 309–318 K.
► Electrochemical window of LiFSA–KFSA–CsFSA is as wide as 5.4 V at 323 K.
► Electrochemical window of NaFSA–KFSA–CsFSA is 4.9 V at 323 K.
► These inorganic ILs are promising as electrolytes for Li and Na batteries.