Gel electrolytes were prepared by swelling a self-assembling ABA triblock copolymer with different amounts of a solution of I M lithium bis(trifluoromethylsulfonyl)imide salt in gamma-butyrolactone. The triblock copolymer had endblocks of polyethylene (PE) and midblocks of poly(ethylene oxide-co-propylene oxide) (PEOPO), where the former blocks constituted 10 wt% of the copolymer. Thus, the electrolyte solution was contained in physical networks consisting of PEOPO chains interconnected by crystalline PE phase domains. The gels showed a stepwise increase in the ionic conductivity as a consequence of the melting of the PE domains at approximately 100 degreesC. Also, the conductivity at room temperature increased significantly after annealing above this temperature. Block copolymer gels containing 70 wt% of electrolyte solution reached conductivities of 1 mS/cm at 20 degreesC.