Lithium ion conducting gel polymer electrolytes composed of insoluble lithium tetrakis(pentafluorobenzenethiolato) borate (LiTPSB), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-BFP) and ethylene carbonate-propylene carbonate mixed solvent (EC-PC) were prepared and their ionic conductivities and electrochemical stabilities were investigated. Ionic conductivity was largely dependent on the contents of EC-PC and LiTPSB. Gel polymer electrolyte containing optimized content of 50 (LiTPSB)-50 (PVDF-RFP/EC-PC (13:87 wt.%)) exhibited ionic conductivity of 4 x 10(-4) S cm(-1) at 30 degrees C, lithium ion transference number of 0.33 and anodic oxidation potential of 4.2 V. (c) 2005 Elsevier B.V. All rights reserved.