Polyvinylidene fluoride-co-chlorotrifluoroethylene and polyvinylidene fluoride-co-hexafluoropropylene nanofiber-coated polypropylene microporous battery separator membranes

Nanofiber‐coated polypropylene (PP) separator membranes were prepared by coating a Celgard® microporous PP membrane with electrospun polyvinylidene fluoride‐co‐chlorotrifluoroethylene (PVDF‐co‐CTFE) and PVDF‐co‐CTFE/polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐co‐HFP) nanofibers. Three PVDF polymer solutions of varying compositions were used in the preparation of the nanofiber coatings. Two of the polymer solutions were PVDF‐co‐CTFE blends made using different types of PVDF‐co‐HFP copolymers. The PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP blend nanofiber coatings have been found to have comparable adhesion to the PP microporous membrane substrate. The electrolyte uptakes and separator–electrode adhesion properties of nanofiber‐coated membranes were evaluated. Both the electrolyte uptake and the separator–electrode adhesion were improved by the nanofiber coatings. The improvement in electrolyte update capacity is not only related to the gelation capability of the PVDF copolymer nanofibers, but also attributed to the increased porosity and capillary effect on nanofibrous structure of the electrospun nanofiber coatings. Enhancement of the separator–electrode adhesion was owing to the adhesion properties of the copolymer nanofiber coatings. Compared with the PVDF‐co‐CTFE/PVDF‐co‐HFP blend nanofiber coatings studied, the PVDF‐co‐CTFE coating was more effective in improving the electrolyte uptake and separator–electrode adhesion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 A new type of battery separator membrane is developed by coating a traditional microporous membrane separator with electrospun polyvinylidene fluoride copolymer nanofibers. The electrospun nanofibers have diameters between 100 and 200 nm and form an interconnected network on the microporous membrane substrate but do not interfere with the microporous structure of membrane substrate. The addition of the polymer nanofibers to the separator membrane improves the electrolyte uptake capacities and separator‐electrode adhesion properties for use in batteries.