To provide an electrolytic copper foil capable of suppressing recrystallization (crystal growth) in thermal history in a manufacturing process of a wiring board and a battery, preventing excessive deterioration in tensile strength and proof stress, and keeping rigidity and folding resistance required in a manufacturing process of the wiring board and the battery.
In the electrolytic copper foil, the number of crystal grains whose grain size is 2 μm or less is 20,000 pieces or more in the range of 300 μm square, and the number of crystal grains whose grain size is 10 μm or more is less than 10 pieces, and the tensile strength in the normal state is 300 MPa or more and less than 400 MPa. The electrolytic copper foil is suitable for the wiring board and the battery.
