The “actuation” mentioned in this application means that the pressure relief mechanism 6 performs an action or is activated to be in a specific state, so that the internal pressure of the battery cell 400 can be released. The actions performed by the pressure relief mechanism 6 may include but are not limited to: cracking, breaking, tearing, or opening at least part of the pressure relief mechanism 6. When the pressure relief mechanism 6 is actuated, high-temperature and high-pressure substances inside the battery cell 400 are discharged from the actuated part as emissions. In this way, the pressure of the battery cell 400 can be released under the condition that the pressure or temperature is controllable, to avoid more serious potential accidents. The emissions from the battery cell 400 mentioned in this application include but are not limited to electrolyte, fragments of positive and negative electrode plates and separator because of dissolution or breaking, high-temperature and high-pressure gas and flames generated by reactions, and the like. The high-temperature and high-pressure emissions are discharged toward the direction in which the pressure relief mechanism 6 is provided on the battery cell 400, and more specifically, can be discharged in the direction toward the area in which the pressure relief mechanism 6 is actuated. The force and destructive power of such emissions may be enormous, or even great enough to break through one or more structures such as a cover in that direction.