Top cover assembly, battery cell, battery and electrical apparatus

A top cover assembly, comprising:

• a top cover configured to be connected to a case of a battery cell and provided with a through hole;
• a connecting element arranged on the top cover and provided with an installation hole communicating with the through hole and a first channel extending to an outside from a hole wall of the installation hole, wherein an opening, communicating with the outside, of the first channel is provided with a first gas permeable membrane;
• and
• a pressure relief valve arranged in the installation hole, configured to slide in the installation hole under a pressure, and provided with a second channel, wherein one end of the second channel communicates with a side, away from the connecting element, of the top cover, and another end of the second channel is configured to be switched between:
• a seal state, in which the other end of the second channel and an opening, in the hole wall of the installation hole, of the first channel are staggered;
• and
• a pressure relief state, in which the other end of the second channel communicates with the opening, in the hole wall of the installation hole, of the first channel so as to release pressure to the outside.