Lithium ion secondary battery

A lithium ion secondary battery comprising:

• a positive electrode mixture layer provided on a main plane of a positive electrode current collector and including a positive electrode active material intercalating or deintercalating lithium ions;
• a negative electrode mixture layer provided on a main plane of a negative electrode current collector and including a negative electrode active material intercalating or deintercalating lithium ions;
• an electrolyte layer provided between the positive electrode mixture layer and the negative electrode mixture layer;
• and
• an insulator covering a region ranging from a part of the main plane of the positive electrode current collector, the part being not provided with the positive electrode mixture layer, to a part of a surface of a sloped portion included in the positive electrode mixture layer, wherein
• the sloped portion has thickness sloped toward a terminal of the positive electrode mixture layer,
• the surface of the sloped portion comprises at least two slopes which are not parallel or perpendicular to the main plain of the positive electrode current collector and a tangent line that is in contact with the surface in at least two contact points, and the at least two slopes comprise a depressed part between two adjacent contact points on the tangent line, and
• an end of the insulator is positioned between the contact point that is closest to the terminal of the positive electrode mixture layer and the contact point farthest from the terminal of the positive electrode mixture layer along the tangent line.