SECONDARY BATTERY AND BATTERY SYSTEM

A secondary battery in accordance with the present invention includes a square battery can (1) at which a positive electrode terminal and a negative electrode terminal are installed, an electrode assembly disposed in the square battery can and is formed by a lamination of a sheet-shaped positive electrode (2) electrically connected to the positive electrode terminal and a sheet-shaped negative electrode (3) electrically connected to the negative electrode terminal with a separator interposed therebetween, a fixing tape (9), and first and second auxiliary insulating sheets (8) each having a first part having a width substantially the same as a width of the electrode assembly in a length direction of a surface of the square battery can on which the positive electrode terminal and the negative electrode terminal are formed, and a second part having a center positioned on substantially a same line perpendicular to the surface as a center of the first part in the length direction and a width larger than the width of the electrode assembly in the length direction. The first and second auxiliary insulating sheets (8) are disposed at opposite positions to sandwich the electrode assembly therebetween from sides of the surface along the length direction and connected to each other by the fixing tape in the first part in the state of pressing the electrode assembly.