A series of polymer-clay nanocomposites have been synthesized, characterized, and electrochemically tested as possible candidates for polymer electrolytes in lithium ion cells. Only cations are mobile in these materials, rather than both cations and anions, leading to a higher conductivity. The nanocomposites are based on synthetic lithium hectorite (SLH) and different mass ratios of polyethylene oxide (PEO). Transparent films with excellent mechanical strength are obtained with conductivity that is comparable to more traditional polymer electrolytes made with added lithium salts.