US Patent 7273678 Secondary cell

A secondary cell comprises an electrode unit housed in a cell can comprising a cylinder having a bottom and a closed opening, and a current collector plate 50 is provided at one end of the electrode unit. The current collector plate 50 has a plurality of protrusions 52 extending radially thereof and joined to an edge of the electrode unit. The surface of the current collector plate 50 to be joined to the bottom wall of the cylinder has a flat region R extending on a predetermined closed-loop track on the surface, and the portions of the current collector plate 50 and the cylinder to be joined are subjected along the flat region R to laser welding from outside the cylinder.