Chemically cross-linked ultrathin electrospun poly(vinylidene fluoride-co-hexafluoropropylene) nanofibrous mats as ionic liquid host in electrochromic devices

In this work, ultrathin free-standing electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) nanofibrous mats are realized through the use of 1,3-diaminopropane as the chemical cross-linking agent. The cross-linking reaction occurs within the nanofibers as well as between the nanofibers that are in touch, forming relatively strong inter-fiber junctions and hence resulting in remarkable improvement in structural integrity of the electrospun mats with very small thickness. The chemically cross-linked electrospun mats are used as the host for 1-butyl-3-methylimidazolium tetrafluoroborate to prepare ionic liquid (IL)-based polymer electrolytes, and the effects of cross-linking on swelling and crystallization behaviors of the mats are studied. The results show that with a low degree of cross-linking, a high ionic conductivity of 2.6 mS/cm can be achieved, which is mainly due to the presence of a significant amount of free ILs in the interpenetrating pores of the mats. An electrochromic device is fabricated using this electrolyte to demonstrate the potential of the mat as IL host, especially its capability to greatly reduce IL consumption.