A binary molten salt electrolyte based on lithium bis(perfluoromethanesulfonyl)imide [LiN(SO2CF3)(2), LiTFSI] and CF3SO3K has been prepared and characterized by thermogravimetry/differential thermal analysis (TG/DTA), electrochemical impedance spectroscopy, and cyclic voltammetry. TG/DTA shows that the thermal stability of the electrolyte is good. The eutectic temperature of the LiTFSI/CF3SO3K is 160 degrees C at a molar ratio of 1:1. The conduction behavior of low LiTFSI concentration mixtures is consistent with the Arrhenius equation, while others do not conform. The ionic conductivities of all measured electrolytes exceeded 10(-2) S/cm above 250 degrees C. The electrochemical window was 4.5 V at 240 degrees C.