Nanofibrous membranes of polyacrylonitrile (PAN) prepared by electrospinning technique were converted to partially oxidized PAN (oxy-PAN) at 230 degrees C and at different time periods. The physical properties and electrochemical characteristics of oxy-PAN membranes were investigated for use as separator membrane in lithium ion battery (LIB). The optimized oxy-PAN membrane showed high tensile strength and thermal stability along with high electrolyte uptake and high ionic conductivity at room temperature. Impedance spectroscopic studies of oxy-PAN membranes revealed good stability and compatibility with lithium electrode and liquid electrolyte which are favorable attributes for long-term storage of lithium ion batteries. The Li/oxy-PAN/LiFePO4 cell delivered stable and excellent cycle performance. (C) 2015 Elsevier Ltd. All rights reserved.