An end cover assembly for a secondary battery, comprising an end cover, provided with a through hole for injecting electrolyte therethrough and comprising a connecting portion; a sealing assembly, configured to seal the through hole; a locking-fixing member, configured to be movable relative to the connecting portion in a radial direction of the through hole, so as to realize switching between a locked state and an unlocked state of the locking-fixing member and the connecting portion, wherein in the locked state, the locking-fixing member presses against the sealing assembly to restrict the end cover from being separated from the sealing assembly; in the unlocked state, the end cover and the sealing assembly are separable to allow the electrolyte to be injected from the through hole; wherein the locking-fixing member is snap-fitted with the connecting portion, so that the locking-fixing member and the connecting portion are in the locked state; the sealing assembly comprises a position-limiting member and a sealing member, the sealing member seals the through hole, and the sealing member is arranged between the position-limiting member and the end cover; the position-limiting member comprises a pressing-against portion and a position-limiting portion, the pressing-against portion is connected to the position-limiting portion and covers at least a part of the sealing member, and the locking-fixing member presses against the position-limiting portion to restrict the end cover from being separated from the sealing assembly; the end cover further comprises a body portion, and the connecting portion is a boss protruding from a surface of the body portion; the through hole is located outside the connecting portion and penetrates the body portion in its own axial direction; each of the position-limiting member and the sealing member has an annular structure and is sleeved and connected to the connecting portion. an end cover, provided with a through hole for injecting electrolyte therethrough and comprising a connecting portion; a sealing assembly, configured to seal the through hole; a locking-fixing member, configured to be movable relative to the connecting portion in a radial direction of the through hole, so as to realize switching between a locked state and an unlocked state of the locking-fixing member and the connecting portion, wherein in the locked state, the locking-fixing member presses against the sealing assembly to restrict the end cover from being separated from the sealing assembly; in the unlocked state, the end cover and the sealing assembly are separable to allow the electrolyte to be injected from the through hole; wherein the locking-fixing member is snap-fitted with the connecting portion, so that the locking-fixing member and the connecting portion are in the locked state; the sealing assembly comprises a position-limiting member and a sealing member, the sealing member seals the through hole, and the sealing member is arranged between the position-limiting member and the end cover; the position-limiting member comprises a pressing-against portion and a position-limiting portion, the pressing-against portion is connected to the position-limiting portion and covers at least a part of the sealing member, and the locking-fixing member presses against the position-limiting portion to restrict the end cover from being separated from the sealing assembly; the end cover further comprises a body portion, and the connecting portion is a boss protruding from a surface of the body portion; the through hole is located outside the connecting portion and penetrates the body portion in its own axial direction; each of the position-limiting member and the sealing member has an annular structure and is sleeved and connected to the connecting portion.