A composite core@sheath nanofibrous separator for lithium ion batteries is fabricated via coaxial electrospinning, using thermosetting PI as the core material and PVDF-HFP as the sheath material. It is demonstrated that the PI@PVDF-HFP nonwovens display remarkably improved tensile strength up to 53MPa and high thermal stability up to 300 degrees C. The electrochemical characterization shows that cells using core@sheath nonwovens as separators display better rate capability and better cycling capacity retention. Considerable mechanical strength, higher thermal stability and preferable rate capability might make this kind of core@sheath nonwovens promising separators for higher-power application.