Overcharge protection battery vent

DETAILED DESCRIPTION The present invention provides improved cell pressure control systems having a two stage control mechanism.
In the first stage, increased cell pressure causes a conductive deflection member to deflect to a position where it opens an electrical contact and places the cell in open circuit.
This prevents current from flowing through the cell and thereby possibly slowing or preventing further increases in cell pressure.
An important advantage of this invention is that the electrical connection is through a pressure contact.
That is, the contact relies only upon the compressive pressure of two conductive members pushing against one another (as opposed to the fluid pressure discussed elsewhere herein).
Unlike the above-described mechanism, it does not rely on a weld which can be difficult to form with the precise strength required to function as a pressure sensitive contact.
If the cell's internal pressure continues to increase even after the pressure contact is opened, the second stage of the pressure control mechanism is activated.
Specifically, a pressure rupturable region in the above-mentioned deflection member will rupture and relieve the cell's internal pressure.
Typically, the pressure rupturable region will be a region of reduced material thickness in the conductive deflection member.
More preferably, the pressure rupturable region will be a scored region, and most preferably it will be a circularly scored region.
In a first aspect, the present invention provides a cell cap subassembly for controlling pressure build-up in a cell.
The cell cap subassembly can be characterized as including the following features: (1) a terminal contact for making electrical contact with an external circuit; (2) a conductive deflection member in electrical contact with the terminal contact; and (3) a conductive pathway making a pressure contact with the conductive deflection member.
The conductive pathway provides at least a portion of a pathway for electrons flowing between the pressure contact and an electrode