Patent ID: 7273678

Claim:
A secondary cell having an electrode unit ( 4 ) comprising in superposed layers a positive electrode ( 41 ) in the form of a strip, a negative electrode ( 43 ) in the form of a strip and a separator ( 42 ) interposed therebetween, the electrode unit ( 4 ) being housed in a cell can ( 1 ) comprising a bottomed cylinder ( 15 ) and a lid ( 11 ) closing an opening portion of the cylinder, a current collector in the form of a strip forming the positive electrode ( 41 ) or the negative electrode ( 43 ) and having a projecting edge ( 48 ) at at least one of opposite ends of the electrode unit ( 4 ) which one end is opposed to a bottom wall of the cylinder ( 15 ), a current collector plate ( 50 ) covering the edge ( 48 ) and comprising a plate having a plurality of protrusions ( 52 ) extending radially outward from the center of the plate and protruding toward the current collector edge ( 48 ), the protrusions ( 52 ) biting into the current collector edge ( 48 ) and being welded to the current collector edge ( 48 ), the current collector plate ( 50 ) being welded to the bottom wall of the cylinder ( 15 ), the secondary cell being characterized in that a surface of the current collector plate ( 50 ) to be joined to the cylinder ( 15 ) has a flat region R extending on a predetermined closed-loop track on the surface intermediate the center and outer edge of the current collector plate and intersecting the plurality of radially extending protrusions, portions of the current collector plate ( 50 ) and the cylinder ( 15 ) to be joined being subjected along the flat region R to laser welding from outside the cylinder ( 15 ).