Composite polymer gelled membranes have been prepared an electrospinning technique. Electrospinning of polymer fibers or electrospraying of particles is typically accomplished by applying a strong electric field (ca. 1-25 kV cm(-1)) to a polymer solution or slurry of solids in an appropriate solvent. The fibers are collected as a mat (membrane) on a grounded target such as Al, Cu, Ni, etc. Typical membranes (mats) consist of nanometer size fibers and have porosities of 65-85%. In the present paper, we describe the fabrication of electrospun membranes for use as gelled electrolytes in Li and Li-ion batteries. The electrospun polymer membranes used in this work are based on the polyintides (PIs) Matrimid and Ultem 1000. Pure PI membranes have been prepared, and blends of Matrimid and Ultem with PVdF-HFP and PAN have been studied in 250 mAh and 7 Ah Li-ion cells. Fully imidized polyimides such as Matrimid and Ultem 1000 do not form gels, and are used as a host matrix of high mechanical strength to immobilize the gelling constituents PVdF or PAN. (c) 2007 Elsevier B.V. All rights reserved.