LITHIUM ION SECONDARY BATTERY

Provided is a lithium ion secondary battery including, as components accommodated in a container, a positive electrode that intercalates and deintercalates lithium, a negative electrode that intercalates and deintercalates lithium, a nonaqueous electrolytic solution that contains a lithium salt, and a separator that is interposed between the positive electrode and the negative electrode. The separator includes a porous resin layer containing polyolefin as a main component. In a full charge state, when observing a cross-section of the lithium ion secondary battery after performing a nail penetration test in which a metal nail having a diameter of 3 mm penetrates through a central portion of the lithium ion secondary battery at 80 mm/sec for short-circuiting of the lithium ion secondary battery, an average thickness of the porous resin layer in a range of 1 mm to 3 mm in an in-plane direction from a peripheral edge of a nail hole is equal to or greater than 10% of an average thickness of the porous resin layer before the nail penetration test, and the porous resin layer remains at a position within 1 mm in the in-plane direction from the peripheral edge of the nail hole.