NOVELTY - A separator (50) has an insulating ceramic layer (300) provided on surface of a porous resin base material (200). The base material has a surface modification layer (221) in an interface portion with ceramic layer. The ratio of light-absorbing intensity ( alpha ) by stretching vibration of carbon-carbon bonding with respect to light-absorbing intensity ( beta ) by symmetrical deformation vibration of carbon-hydrogen bonding in methyl group is 0.015-0.055, according to reflective measurement of surface of porous resin base material having surface-modification layer.    USE - Separator is used for lithium ion secondary battery for vehicles (both claimed) e.g. motor vehicles (e.g. car), hybrid vehicles and electric vehicles.    ADVANTAGE - The separator prevents short circuit and shutdown of lithium ion secondary battery. The battery comprising the separator is excellent in safety and reliability.    DETAILED DESCRIPTION - A separator is interposed between positive electrode and negative electrode. The separator has an insulating ceramic layer provided on surface of a porous resin base material. The porous resin base material has a porous polyethylene layer (210) as internal layer and porous polypropylene layers (220,230) as external layers. The ceramic layer contains inorganic filler and binder. The porous resin base material has a surface modification layer in an interface portion with ceramic layer. The ratio of light-absorbing intensity ( alpha ) by stretching vibration of carbon-carbon (C=C) bonding with respect to light-absorbing intensity ( beta ) by symmetrical deformation vibration of carbon-hydrogen bonding in methyl group is 0.015-0.055, according to reflective measurement of surface of porous resin base material having surface-modification layer by infrared spectroscopy. An INDEPENDENT CLAIM is included for manufacture of separator.    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of separator.    Separator (50)    Resin base material (200)    Polyethylene layer (210)    Polypropylene layers (220,230)    Surface-modification layer (221)    Ceramic layer (300)