The spring piece is mainly used to support the battery. If there is no spring piece, the battery will be pressed very flat during the process of pressing the battery, and the internal components may be crushed. The spring piece is only added to the negative electrode side. If the spring piece is added to both the positive and negative electrodes, the buckle cannot be closed during the battery pressing step, causing the electrolyte to come into contact with the air, and the experiment fails.