A new class of lithium salt with single-ionic characteristics, lithium sulfonated styrene oligomer (LiSSO) [(CH2CHC6H5)(7)-(CH2CHC6H4SO3-Li+)(2)], was synthesized and its complex with poly(ethylene oxide) (PEO) was prepared. The maximum ionic conductivity of the PEO/LiSSO complex at 65 degreesC was 2.1 x 10(-4) S/cm at a salt concentration of [Li+]/[EO] = 0.20. The lithium cationic transference number (t(+)) of the PEO/LiSSO complex was found to be 0.95, and the polymer electrolyte was electrochemically stable up to 6.2V.