The electrospun fibrous membranes used as lithium-ion battery separators have been widely studied due to the advantages of high porosity, large specific surface area and adjustable structural characteristics. In order to obtain thermal stable and high-strength electrospun fibrous membranes for lithium-ion battery separators, the oriented poly(phthalazinone ether sulfone ketone) (PPESK) fibrous membranes were fabricated and then hot pressed with two pieces of membranes overlaid perpendicularly. The prepared hot-pressed composite oriented PPESK membranes show high tensile strength of 22.8 MPa at both horizontal and vertical directions. The hot-pressed oriented PPESK membranes are thermally dimensional stable even at the high temperature of 200 degrees C. In addition, the novel PPESK fibrous membranes exhibit high porosity (70%), superior electrolyte uptake (525%), low interfacial resistance (268 ohm) with electrodes and excellent ionic conductivity (1.39 mS cm(-1)). The simulated cells using the new separators show high discharge capacity and excellent rate capability, which demonstrates the novel membranes have potential to be used as separators for power lithium-ion batteries.