In the present work, temperature dependent lithium transference number T-Li(+) of poly (ethylene oxide)/LiClO4 composite solid polymer electrolytes containing mesoporous silica SBA-15 was studied. T-Li(+) reaches a low value around the melting point (T-m) of the polymer electrolyte and increases as temperature deviates from T-m, which is due to the different mechanisms of lithium conduction and anion conduction. While the anion transport mainly involves hopping between free volumes large enough to accommodate the ions, lithium ions are transferred by making and breaking of bonds with motion between coordinating sites. In comparison with the polymer electrolyte without SBA-15, the composite polymer electrolytes containing SBA-15 exhibit higher values of T-Li(+) and lithium conductivity. (c) 2008 Elsevier B.V All rights reserved.