A lithium-ion battery, including a battery cell, an electrolytic solution, and a packaging film. The battery cell is formed by winding a positive electrode plate and a negative electrode plate that are separated by a separator. The lithium-ion battery is half-charged to obtain a half-charged full battery. The half-charged full battery is stripped of the packaging film to obtain a half-charged cell. When a width of the half-charged full battery is w1, a width of the half-charged cell is w2, and g=w2/w1, the following conditional expression (1) is satisfied: 0.4