A cross-linked fibrous composite separator was prepared by thermal cross-linking between reactive silica nanoparticles and tri(ethylene glycol) diacrylate on a fibrous polyacrylonitrile (PAN) membrane. The cross linked fibrous composite separator exhibited a three-dimensional and fully interconnected network structure in which the silica particles were firmly attached onto the PAN nanofibers through the chemical cross-linking. The separator showed good electrolyte wettability and excellent thermal stability at elevated temperatures. A lithium-ion cell composed of a graphite negative electrode, the cross-linked fibrous composite separator soaked with liquid electrolyte and a LiNi0.6Co0.6Mn0.2O2 positive electrode exhibited cycling performance and thermal safety superior to those of a cell prepared with a conventional polypropylene separator.