Electrospun polymer nanofibrous mats loaded with ionic liquids (ILs) and lithium salts are promising non-volatile electrolytes owing to their high ionic conductivities. However, the large cations of ILs are difficult to diffuse into solid electrodes, whereas the lithium ions in ILs tend to form anionic complexes with the IL anions, reducing the number of free lithium ions. To address these issues, octa(3-hydroxy-3-methylbutyldimethylsiloxy) polyhedral oligomeric silsesquioxane (POSS-OH), which has large specific surface area and functionality number, is incorporated into electrospun poly(vinylidene fluoride-cohexafluoropropylene) (PVDF-co-HFP) nanofibrous mats, and the mats are used to host LiClO4/1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4). It is found that PUSS-OH can significantly increase both ionic conductivity and lithium transference number of the electrolytes owing to the Lewis acid-base interactions of PUSS-OH with ClO4 and BF4. The electrochromic device using the hybrid mat (with 5 wt % PUSS-OH) loaded with LiClO4/BMIWBF4 as the electrolyte shows significantly improved transmittance contrast and switching time, as a result of increased number of free lithium ions. (C) 2014 Elsevier Ltd. All rights reserved.