Battery cell with improved pressure relief vent

An electrochemical battery cell comprising a positive electrode, a negative electrode and an electrolyte;

• a container comprising a side wall, an open end and an integral closed end;
• a closing element, comprising at least one member selected from the group consisting of a metal plate and a seal, disposed in and closing the open end of the container;
• and a pressure relief vent, wherein:
• the positive electrode is adjacent to the container side wall, and the negative electrode is disposed within a cylindrical cavity in the positive electrode;
• the pressure relief vent comprises an interrupted, reduced thickness groove formed in the closed end of the container;
• the interrupted, reduced thickness groove is interrupted in at least two places, each by an unthinned section of the closed end of the container, to form at least two reduced thickness arcs disposed in a single annular ring;
• the closed end of the container is free of intersecting reduced thickness grooves;
• and
• 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 closed end of the container radially inside the groove remains attached to an area of the closed end of the container radially outside the groove by one or more of the unthinned sections interrupting the groove, wherein the pressure relief vent comprises first and second interrupted, reduced thickness grooves, each interrupted by unthinned sections of the closed end of the container to form at least two reduced thickness arcs disposed in a single annular ring and configured such that the difference between the internal pressure and external pressure at which the pressure relief vent is capable of opening is different at the first and second grooves.