The effect of tris(pentafluorophenyl) borane (TPFPB) as an anion receptor on the ionic conductivities of the liquid electrolyte, EC/DMC (1/2.5, v/v)/1 M LiClO4, was investigated. It is found that the dissociation degree of lithium salts, the viscosity of the conducting medium, and the mobility of anions were changed by introducing TPFPB into the liquid electrolyte. The transference number of the liquid electrolyte was enhanced with increasing the TPFPB content, but the total ionic conductivity was decreased due to the decreasing anionic conductivity as a result of the anion trapping effect of TPFPB. The ionic conductivities of the separators soaked in the liquid electrolyte were much lower than those of the liquid electrolytes. The electrolyte retention of the separator can be improved by the interaction between TPFPB and DMC. The electrochemical stability of the liquid electrolyte was also enhanced by addition of TPFPB. © 2004 Elsevier Ltd. All rights reserved.