An approach was developed to fabricate functionalized separators capable of providing long-term overcharge protection for secondary lithium batteries. Free-standing non-woven fiber membranes consisting of an electroactive polymer and a supporting polymer were prepared by an inexpensive and scalable electrospinning technique. The membranes sustained large shunt current densities despite the presence of an inert polymer component that dilutes the electroactive polymer. A bilayer fiber separator prepared by this method provided a reversible voltage-regulated current shunt for a Li1.05Mn1.95O4/Li cell for more than 1000 135% overcharge cycles at a 2/3 C rate, which is the most stable overcharge protection yet reported. This approach enables better distribution of the electroactive polymer which should reduce the cost of overcharge protection separators. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.