A battery separator for a lithium-ion battery includes a nonwoven fiber mat that is composed of entangled microfibers having an average fiber diameter of less than 6 microns. The nonwoven fiber mat also includes a binder that binds the microfibers together and a polymer component that is dispersed homogeneously through or within the entangled microfibers so that the polymer component is uniformly distributed throughout the nonwoven fiber mat and so that the entangled microfibers, the binder, and the polymer component form a single layer component or product. The polymer component is configured to melt within the nonwoven fiber mat when exposed to a sufficiently high heat in order to effectively interrupt an electro-chemical process of the lithium-ion battery and thereby prevent overheating of the lithium-ion battery. The nonwoven fiber mat is typically between 0.1 and 20 mils thick.