New hectorite and organo-hectorite clays have been prepared using different silica sol sources, in order to examine the importance of sol particle size, pH, and surface chemistry on the final matrix. Polymer–clay nanocomposites (PCN) are prepared by intercalating polyethylene oxide in the clay layers of lithium hectorites. The resulting films are physically and electrochemically evaluated. Conductivity values, activation energies, and lithium transference numbers indicate that the PCNs are single ion conductors with transference numbers close to unity. The activation energies are in the range of 0.02V, two orders of magnitude lower than the conventional polymer electrolytes.