Top cover assembly, battery cell, battery and electrical apparatus

A top cover assembly includes a top cover, a connecting element, and a pressure relief valve. The top cover is configured to be connected to a case of the battery cell and provided with a through hole. The connecting element is arranged on the top cover and provided with an installation hole communicating with the through hole and a first channel extending to the outside from a hole wall of the installation hole. An opening, communicating with the outside, of the first channel is provided with a first gas permeable membrane. The pressure relief valve is arranged in the installation hole, is configured to slide in the installation hole under a pressure, and is provided with a second channel.