A poly(ethylene terephthalate) nonwoven sandwiched electrospun polysulfonamide (PSA) fibrous separator was developed for application in lithium-ion batteries (LIBs). The poly(ethylene terephthalate) nonwoven served as a mechanical support and the PSA layers provided the separators with nanoporous structures. This novel composite separator possessed better thermal stability and electrolyte wettability than commercial polypropylene separator and the sandwiched nonwoven endowed the separator with an improved mechanical strength (17.7 MPa) compared to the pure electrospun PSA separator. The cells assembled with this composite separator displayed excellent discharge capacity (122.0 mAh g(-1) after 100 cycles) and discharge C-rate capacity. (C) 2017 Wiley Periodicals, Inc.