A method for regenerating a cell having an electrode assembly, in which electrodes and a separator are alternately combined with each other, an electrolyte, and a battery case accommodating the electrode assembly and the electrolyte according to the present invention includes performing a negative pressure processing process in which a negative pressure is applied to the cell to allow a gas disposed between the electrodes to move outside the electrode assembly and performing an ultrasonic wave processing process in which the cell is stimulated by ultrasonic waves to allow the electrolyte disposed outside the electrode assembly to move between the electrodes.