NOVELTY - A separator structure is in the form of flat, foldable or rollable porous layer having thickness of 50 mu m or less, and comprises micro-fibrillated nanofibers randomly-oriented in flat porous layer, and intermixed and spaced-apart with ceramic particles. Nanofibers have diameter of 0.01-2 mu m. The composition of micro-fibrillated nanofibers is chosen from cellulose, poly(acrylonitrile), polyamides, and polyethylene terephthalate. The separator structure has pore volume of 20-90% of the total volume of the structure.    USE - Separator structure is used for lithium-ion electrochemical cell (claimed) for lithium ion battery. Uses include but are not limited to vehicle traction motors, alternating current wall outlet, internal combustion engine, vehicle alternator, hybrid vehicles and electric vehicles.    ADVANTAGE - The separator structure has excellent shrinkage resistance, mechanical property, durability, strength, operational reliability, dimensional stability and temperature resistance, and is economical. The lithium-ion electrochemical cell using separator structure has excellent electrochemical performance.    DETAILED DESCRIPTION - A separator structure is in the form of flat, foldable or rollable porous layer having thickness of 50 mu m or less, and comprises micro-fibrillated nanofibers randomly-oriented in flat porous layer, and intermixed and spaced-apart with ceramic particles. Nanofibers have diameter of 0.01-2 mu m. The flat layer separator structure is porous for infiltration with liquid electrolyte. The separator structure is resistant to shrinkage when heated to 150 degrees C. The composition of micro-fibrillated nanofibers is chosen from cellulose, poly(acrylonitrile), polyamides, and polyethylene terephthalate. The separator structure has pore volume of 20-90% of the total volume of the structure. INDEPENDENT CLAIMS are included for the following:    (1) lithium-ion electrochemical cell (12); and    (2) manufacture of Separator (18).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of lithium-ion electrochemical cell.    Lithium ion battery (10)    Lithium-ion electrochemical cell (12)    Negative electrode (14)    Positive electrode (16)    Separator (18)