The embodiments of the application provide a battery cell and a manufacturing method and system therefor, a battery and an electric device. An end cover assembly includes: a battery box including a first wall and a pressure relief mechanism; and a protective member positioned on an outer side of the first wall and including a body portion, a shielding portion and a weak portion. The shielding portion can block emissions released from other battery cells, so as to reduce risk of melt-through of the pressure relief mechanism caused by the emissions. When thermal runaway occurs in the battery cell, the weak portion is broken under the action of a high-temperature and high-pressure substance, such that the high-temperature and high-pressure substance are discharged in time.