COPPER ALLOY FOIL, NEGATIVE ELECTRODE FOR LITHIUM ION SECONDARY BATTERY, LITHIUM ION SECONDARY BATTERY, AND METHOD FOR MANUFACTURING COPPER ALLOY FOIL

PROBLEM TO BE SOLVED: To make possible to keep a sufficient binding performance with a binder resin and a sufficient tensile strength even after having gone through a thermal treatment in a manufacturing process of a negative electrode for lithium ion secondary battery.SOLUTION: A copper alloy foil comprises 0.20-0.40 mass% of Cr, a total of 0.01-0.40 mass% of at least one element of Ag, Sn, In, Ti and Zr with the balance including Cu. The ratio I/Iof {220} plane diffraction peak intensity Ito {200} plane diffraction peak intensity Iobtained from X-ray diffraction measurement by the 2 / method on a principal surface is larger than 2. A 1%-proof strength measured by Total elongation or Extension-Under-Load-Method is 85% or larger of the tensile strength.