Patent ID: 7195839

Claim:
An electrochemical battery cell comprising: a positive electrode, a negative electrode and an electrolyte; a container comprising a side wall, an open end and a closed end, the closed end comprising a first metal plate that is an integral part of the container, wherein the positive electrode is formed in the shape of a cylinder located adjacent to the side wall of the container and the negative electrode is disposed in a cavity within the positive electrode; a closing element, comprising at least one member selected from the group consisting of a second metal plate and a seal, disposed in and closing the open end of the container; and a pressure relief vent, comprising at least one interrupted annular reduced thickness groove, formed in a vent-containing metal plate; wherein: the reduced thickness groove is formed in the shape of an interrupted circle interrupted in at least two places, each by an unthinned section of the vent-containing metal plate, to form at least two reduced thickness arcs, wherein each of the arcs has a single radius of curvature and the arcs are located such that all of their radii of curvature have a common locus, and wherein the interrupted annular reduced thickness groove is centered in the vent-containing metal plate and the reduced thickness groove is formed closer to a center than a periphery of the vent-containing metal plate; the vent is capable of opening at the groove, when an internal cell pressure exceeds a predetermined difference above an external pressure, such that an area of the vent-containing plate radially inside the groove remains attached to an area of the vent-containing plate radially outside the groove by one or more of the unthinned sections interrupting the groove; and the vent-containing metal plate is the first metal plate, and wherein there are no reduced thickness grooves inside the at least one interrupted annular reduced thickness groove.