NOVELTY - The method involves providing a collector substrate with a collection face. A first non-woven polymer fiber mat (22) is electrospun onto the collection face of the collector substrate. Ceramic particles are applied over a top surface (34) of the first non-woven polymer fiber mat. A second non-woven polymer fiber mat (24) is electrospun over the first non-woven polymer fiber mat and the ceramic particles, where the second non-woven polymer fiber mat comprises a fibrous web (30) of polymer fibers (28) that are different from polymer fibers in the first non-woven polymer fiber mat.    USE - Method for making a composite separator i.e. thin and electrically insulative mechanical barrier composite separator, disposition between a negative electrode and a positive electrode in an electrochemical battery cell of a lithium ion battery connected to an electrical device e.g. electrical load such as electric motor for a hybrid-electric vehicle (HEV), an extended range electric vehicle (EREV) and a power-generating device such as AC wall outlet, internal combustion engine and vehicle alternator.    ADVANTAGE - The method enables a composite separator for physically separating confronting electrodes to prevent short-circuits in an electrochemical battery cell. The method enables an intermediate ceramic particle layer to structurally reinforce the composite separator to improve thermal and compressive strength of the composite separator if the ceramic particles chosen have better thermal and mechanical properties, so that an intermediate ceramic particle layer can render manufacture of the composite separator to be quicker and more efficient due to quick fabrication of the intermediate ceramic particle layer, the non-woven polymer fiber mats are not required to be thick by including the ceramic particle layer in the composite separator, and less time is required for electrospinning process.    DETAILED DESCRIPTION - The ceramic particles are made of barium titanate or strontium-doped barium titanate. An INDEPENDENT CLAIM is also included for a composite separator for use in an electrochemical battery cell of a lithium ion battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a composite separator.    Non-woven polymer fiber mats (22, 24)    Polymer fibers (28)    Fibrous web (30)    Top surface of non-woven polymer fiber mats (34)    Bottom surface of non-woven polymer fiber mats (36)