Zero mercury air cell

Abstract

An improved button air cell is provided that contains zero mercury, is free of indium on the sealing surface of the anode cup and has an active material comprising zinc alloyed with lead. Also provided is a method of forming a button electrochemical cell free of mercury and having no indium on the inner surface of the anode cup.

The invention claimed is:  
     
         1 . A button electrochemical cell comprising: 
 an anode mixture comprising a zinc composition;    an aqueous alkaline electrolyte;    a seal; and    an anode cup having a sealing surface for contact with the seal and an anode contacting surface for contact with the anode mixture;    wherein the cell is free of added mercury and the anode cup sealing surface has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper.    
     
     
         2 . The cell defined in  claim 1 , wherein the anode cup anode contacting surface has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper.  
     
     
         3 . The cell defined in  claim 1 , wherein the anode contacting surface comprises a layer of copper.  
     
     
         4 . The cell defined in  claim 1 , wherein the zinc composition, when tested for 24 hours at 71° C. in an aqueous solution of 45 weight percent KOH, produces 0.5 cubic centimeters or less gas per 5 grams of the zinc composition.  
     
     
         5 . The cell defined in  claim 4 , wherein the zinc composition, when tested for 24 hours at 71° C. in an aqueous solution of 45 weight percent KOH, produces 0.15 cubic centimeters or less gas per 5 grams of the zinc composition.  
     
     
         6 . The cell defined in  claim 4 , wherein the zinc composition comprises an alloy of zinc and lead.  
     
     
         7 . The cell defined in  claim 6 , wherein the zinc composition comprises 400-550 parts per million of lead relative to the weight of the zinc composition.  
     
     
         8 . The cell defined in  claim 1 , wherein the anode mixture comprises indium hydroxide.  
     
     
         9 . The cell defined in  claim 1 , wherein the electrolyte comprises zinc oxide.  
     
     
         10 . The cell defined in  claim 1 , wherein the anode mixture comprises a polyethylene glycol composition.  
     
     
         11 . The cell defined in  claim 1 , wherein the polyethylene glycol composition is present in an amount of 10 to 500 parts per million relative to the weight of the zinc composition.  
     
     
         12 . The cell defined in  claim 1 , wherein the anode cup is straight-walled.  
     
     
         13 . A button electrochemical cell comprising: 
 an air electrode;    an anode mixture comprising a zinc composition;    an aqueous alkaline electrolyte;    a seal; and    an anode cup having a sealing surface for contact with the seal and an anode contacting surface for contact with the anode mixture;    wherein the cell is free of added mercury and the anode cup sealing surface has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper.    
     
     
         14 . A button electrochemical cell comprising: 
 an air electrode;    an anode mixture comprising a zinc composition;    an aqueous alkaline electrolyte;    a seal; and    an anode cup having a sealing surface for contact with the seal and an anode contacting surface for contact with the anode mixture;    wherein the cell is free of added mercury, the anode cup sealing surface has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper, and the anode cup anode contacting surface has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper.    
     
     
         15 . The cell defined in  claim 14 , wherein the anode contacting surface comprises a layer of copper.  
     
     
         16 . The cell defined in  claim 15 , wherein the zinc composition, when tested for 24 hours at 71° C. in an aqueous solution of 45 weight percent KOH, produces 0.5 cubic centimeters or less gas per 5 grams of the zinc composition.  
     
     
         17 . The cell defined in  claim 16 , wherein the anode mixture comprises indium hydroxide.  
     
     
         18 . The cell defined in  claim 17 , wherein the electrolyte comprises zinc oxide.  
     
     
         19 . The cell defined in  claim 18 , wherein the anode mixture comprises a polyethylene glycol composition.  
     
     
         20 . A button electrochemical cell comprising: 
 an air electrode;    an anode mixture comprising a zinc composition;    an aqueous alkaline electrolyte;    a seal; and    an anode cup having a sealing surface for contact with the seal and an anode contacting surface for contact with the anode mixture; wherein:    the cell is free of added mercury;    the zinc composition, when tested for 24 hours at 71° C. in an aqueous solution of 45 weight percent KOH, produces 0.15 cubic centimeters or less gas per 5 grams of the zinc composition;    the anode cup sealing surface has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper; and    the anode cup anode contacting surface comprises a layer of copper and has thereon no non-in situ-deposited metal with a hydrogen overvoltage higher than that of copper.    
     
     
         21 . The cell defined in  claim 20 , wherein: 
 the anode mixture comprises indium hydroxide;    the electrolyte comprises zinc oxide; and    the anode mixture comprises a polyethylene glycol composition, the polyethylene glycol composition present in an amount of 10 to 500 parts per million relative to the weight of the zinc composition.