A lithium ion secondary battery, the separator, and a method for their preparation

A separator (24) is provided with heat-resistant layer containing inorganic oxide particles and a binder (241) on at least one side, the component of the inorganic oxide particles, aluminum oxide in the range of 5 to 200 ppm by weight those which contains gallium. Lithium ion secondary battery is one having an electrode body formed by laminating while sandwiching the separator (24) between the positive electrode plate and the negative electrode plate, and impregnating the electrode member nonaqueous electrolyte. Thus, while using a separator (24) having a heat-resistant layer (241), it is the resistance increases unlikely lithium ion secondary battery is used in high-rate conditions, the separator, and methods for their preparation are provided.