NOVELTY - A copper foil comprises a surface-treated layer which has azole compound and carbonyl group on at least one portion of its surface. The carbonyl detection strength of outermost layer is 0.1 or more, measured by X-ray photoelectron spectroscopy (XPS). The nitrogen, carbon and oxygen are detected by the depth direction analysis by XPS. The average value (D0) of depth range with nitrogen and carbon detected amount which is more than background level is 2 nm or more. The average value (D1) of a depth range with oxygen detected amount which is more than background level is 6 nm or less.    USE - Copper foil is used for electrical power collector for forming negative electrode for lithium ion secondary battery (all claimed). Uses include but are not limited to mobile telephones, electric vehicle, notebook-type personal computer, digital camera, and video camera.    ADVANTAGE - The copper foil has high adhesiveness and corrosion resistance.    DETAILED DESCRIPTION - A copper foil comprises a surface-treated layer which has azole compound and carbonyl group in at least one portion of its surface. The carbonyl detection strength of the outermost layer is 0.1 or more, measured by X-ray photoelectron spectroscopy (XPS). The nitrogen, carbon and oxygen are detected by the depth direction analysis by XPS. The average value (D0) of a depth range with nitrogen and carbon detected amount which is more than background level is 2 nm or more. The average value (D1) of a depth range with oxygen detected amount which is more than background level is 6 nm or less. The peak of azole compound is detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS). INDEPENDENT CLAIMS are included for the following:    (1) lithium ion secondary battery negative electrode electrical power collector;    (2) negative electrode electrical power collector;    (3) negative electrode material for lithium ion secondary batteries; and    (4) lithium ion secondary battery.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic structure of lithium ion battery.    Positive electrode (1)    Separator (2)    Negative electrode (3)    Positive electrode power collector (4)    Positive electrode active material (5)