SEPARATOR WITH HEAT RESISTANT INSULATING LAYER

A separator with a heat resistant insulation layer (1) includes a porous substrate layer (3), and a heat resistant insulation layer (5a, 5b) formed on one surface or both surfaces of the porous substrate layer (3) and containing inorganic particles and a binder. R represented by the mathematical formula 1 is in a range from 0.3 to 20, and a ratio of an unit mass of the heat resistant insulation layer to an unit mass of the porous substrate layer (an unit mass of the heat resistant insulation layer / an unit mass of the porous substrate layer) is in a range from 0.5 to 2.5, Accordingly, the separator with a heat resistant insulation layer can have improved resistance to an internal short circuit (short-circuit resistance). R = Tensile Strength in MD Direction × Fracture Strain in MD Direction Tensile Strength in TD Direction × Fracture Strain in TD Direction