A number of iodide-based electrolytes (LiCI-LiI, LiI-KI, LiCl-LiBr-LiI, LiCl-LiI-KI and LiF-LiCI-LiI) were considered to be used in thermal batteries. Ionic conductivity of multi-cation and all-lithium electrolytes were evaluated. They were compared to the classical electrolytes (LiCl-KCl, LiF-LiBr-KBr and LiF-LiCI-LiBr) used in thermal battery applications. Measurements were realised by electrochemical impedance spectroscopy (E.I.S.). It was shown that some all-lithium iodide-based electrolytes exhibit interesting ionic conductivities and are suitable as electrolytes in thermal batteries. It was pointed out that activation energy E-a was close to 11 kJ mol(-1) for multi-cation electrolytes, whereas it was equal to 7 kJ mol(-1) for all-lithium electrolytes. (c) 2006 Elsevier B.V. All rights reserved.