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 ((x(Li), X-K, x(Cs))= (0.30, 0.35, 0.35)) is as wide as 5.4V at 323 K with the cathode limit being lithium metal deposition. The electrochemical window of the eutectic NaFSA-KFSA-CsFSA ((x(Na), X-K, x(Cs))= (0.40, 0.25, 0.35)) is 4.9V at 323 K with sodium metal deposition as the cathode limit reaction. (C) 2012 Elsevier Ltd. All rights reserved.