Battery cell, method and system for manufacturing same, battery, and electrical device

A battery cell, comprising:

• a housing having an opening;
• an electrode assembly, accommodated in the housing;
• and
• an end cap, comprising a cap body and a protruding structure, wherein at least a part of the cap body is disposed around the protruding structure and laser-welded to the housing so that the end cap fits and covers the opening, wherein
• in a thickness direction of the end cap, the protruding structure protrudes from an inner surface of the cap body toward the electrode assembly, and blocks a laser beam during welding between the cap body and the housing;
• and
• a first recess is formed on the end cap at a position corresponding to the protruding structure, the first recess is recessed from an outer surface of the cap body toward the electrode assembly, and the first recess is configured to release a stress during welding between the cap body and the housing.