Abstract: Each prismatic cell is provided with a rolled electrode assembly, and the rolled electrode assembly has a flat section with a flat outer peripheral surface and two curved sections with a curved outer peripheral surface. Each spacer has a substrate and multiple ribs protruding on at least one side of the substrate, and the ribs are formed so as to face the flat section of the rolled electrode assembly and extend in a direction substantially perpendicular to the rolling axis of the rolled electrode assembly. The ribs have a length of 60 to 100 when the height of the flat section of the rolled electrode assembly is represented by 100, and the relationship 2?B/A?10 is satisfied where A is the width of the ribs and B is the distance between adjoining ribs.

Abstract: In a cross section parallel to a thickness direction of a negative electrode active material layer, an average tortuosity ratio is 1.5 to 2.5. The average tortuosity ratio is calculated by the following formula: “R=B/A”. In the formula, “R” represents the average tortuosity ratio. “B” represents an average value of lengths of shortest routes each extending from a contact point between a negative electrode substrate and a negative electrode active material particle to a surface of the negative electrode active material layer along contour lines of a plurality of negative electrode active material particles. “A” represents an average value of a thicknesses of the negative electrode active material layer.