An interpenetrating network (IPN), comb-type, siloxane-based solid polymer electrolyte solid polymer electrolyte was prepared and its electrochemical properties were evaluated. The cross-linking reaction conditions were established from accelerated rate calorimetry studies. An IPN solid ploymer electrolyte with 60 wt % of the comb-shaped siloxane showed an ionic conductivity of greater than 5 x 10(24) S/cm at 37degreesC, with a wide electrochemical stability window of up to 4.5 V vs. lithium. A Li metal/solid polymer electrolyte/LiNi0.8Co0.2O2 cell showed promising discharge capacities above 130 mAh/g and good cycling performance. (C) 2002 The Electrochemical Society.