Secondary battery

A secondary battery, comprising an electrode assembly including a belt-like positive electrode, a belt-like negative electrode, and a belt-like separator,

• wherein the positive electrode and the negative electrode are laminated via the separator in a thickness direction,
• the positive electrode includes a positive electrode core elongated in a longitudinal direction orthogonal to the thickness direction and to a width direction, and a positive electrode active material layer formed on a surface of the positive electrode core,
• the negative electrode includes a negative electrode core elongated in a longitudinal direction orthogonal to the thickness direction and to a width direction, and a negative electrode active material layer formed on a surface of the negative electrode core, and
• the negative electrode core exhibits varying tensile elongation percentages depending on locations in the width direction, measured on specimens each encompassing an entire dimension of the negative electrode core in the thickness direction, such that a first tensile elongation percentage at a center portion of the negative electrode core in the width direction is higher than a second tensile elongation percentage at both end portions of the negative electrode core in the width direction.