Patent ID: 7294429

Claim:
A primary alkaline cell comprising a negative and a positive terminal, and an outer housing having a pair of opposing flat sides running along a portion of the length of said housing; said housing having a closed end and opposing open end and said housing not having any integral cylindrical sections; said cell further comprising an anode comprising zinc and a cathode comprising MnO 2 within said housing, a separator between said anode and cathode, and an end cap assembly sealing the open end of said housing; wherein the cathode comprises at least one cathode slab having an opening defined therethrough devoid of cathode material, with at least a portion of the outer surface of said cathode contacting the inside surface of said housing, said end cap assembly sealing the open end of said housing thereby forming a boundary surface around the cell interior; wherein the cathode comprises a plurality of rectangular shaped cathode slabs; wherein each of said slabs has a central opening devoid of cathode material; wherein said cathode slabs are stacked within the housing along the cell's central longitudinal axis so that said openings devoid of cathode material form a central core along said longitudinal axis, with the outer surface of said cathode contacting the inside surface of said housing; wherein said cell comprises a vent mechanism located on said boundary surface, wherein said vent mechanism activates to release gas pressure from within the cell as said gas pressure rises, said vent mechanism comprising a first rupture zone comprising a groove on said boundary surface, said groove defining an underlying material region thinner than the average thickness of said boundary; and a second rupture zone forms a weld on said boundary surface, wherein the first zone ruptures when gas pressure within the cell rises to a first pressure level and said second zone ruptures when gas pressure within the cell rises to a second pressure level being higher than said first pressure level allowing gas from within the cell to escape from the cell interior through said ruptures; wherein the cell is balanced so that the cathode is in excess such that the ratio of theoretical capacity of the MnO 2 based on a theoretical specific value of 370 mAmp-hr per gram MnO 2 , divided by the mAmp-hr capacity of zinc based on a theoretical specific value of 820 mAmp-hr per gram zinc, is between about 1.2 and 2.0.