A novel PEO-based nanocomposite polymer electrolyte is prepared by using solid super acid sulphated-zirconia (SO42- ZrO2, SZ) as the filler. Polarized optical microscopy (POM) and differential scanning calorimeter (DSC) results show that part of SZ particles may act as the nucleus of PEO spherulites and thus increase the amount of PEO spherulites. On the other hand, other SZ particles, which do not act as the nucleus, can restrain the recrystallization tendency of PEO chains through Lewis acid-base interaction and hence decrease the growth speed of PEO spherulites. As a result, the PEO component in PEO-LiCIO4-SZ can maintain a high amorphous state for a long time. The room temperature ionic conductivity of PEO-LiCIO4-SZ is relative high and stable compared with pristine PEO-LiCIO4, indicating that it is promising for all solid-state rechargeable lithium ion batteries. (c) 2005 Elsevier Ltd. All rights reserved.