Cell safety valve and method for manufacturing the same

A cell safety valve which has a thin valve plate formed on a sheet-shaped sealing plate for sealing the cell such that if the inner pressure of the cell exceeds a predetermined value, the valve plate breaks to release a gas in the cell to the outside, in which the valve plate has a dome-shaped dome portion formed thereon and, at its middle or near it, a break groove formed for facilitating the breaking of the valve. By this construction, it is possible to prevent the electrolyte from leaking while reducing the cell-to-cell difference in the operating pressure of the safety valve and ensuring a sufficient open area at the time of the operations of the safety valve.