Alkaline cells having low toxicity rechargeable zinc electrodes

Abstract

A nickel zinc alkaline cell has a zinc oxide negative electrode supported on a conductive substrate, an alkaline electrolyte, and a positive electrode having nickel hydroxide paste supported on a conductive substrate. The negative zinc oxide electrode comprises 85% to 95% zinc oxide powder, 1% to 10% bismuth oxide, 1% to 2% of a binder, and 0.05% to 5% by weight of a fluoride salt chosen from the group consisting of: sodium, potassium, rubidium, caesium, lithium, and mixtures thereof. Typically, the fluoride salt is potassium fluoride, in the amount of 0.5% by weight of the zinc oxide.

1 - 10 . (canceled)  
     
     
         11 . A nickel zinc alkaline cell comprising: 
 a negative electrode supported on a conductive substrate wherein said negative zinc oxide electrode comprises zinc oxide, bismuth oxide, and a fluoride salt;    an alkaline electrolyte comprising (a) a salt of boric acid present in a concentration of a concentration of 0.6 to 1.3 moles per liter, and (b) a stoichiometric excess of alkali hydroxide of between 2.5 moles and 5 moles per liter; and    a positive electrode comprising nickel hydroxide supported on a second conductive substrate.    
     
     
         12 . The nickel zinc alkaline cell of  claim 11 , wherein said fluoride salt is a salt of a metal selected from the group consisting of sodium, potassium, rubidium, caesium, lithium, and mixtures thereof.  
     
     
         13 . The nickel zinc alkaline cell of  claim 11 , wherein said fluoride salt is potassium fluoride in the amount of 0.05% to 4.5% by weight of said zinc oxide.  
     
     
         14 . The nickel zinc alkaline cell of  claim 11 , wherein said fluoride salt is potassium fluoride in the amount of 0.5% by weight of said zinc oxide.  
     
     
         15 . The nickel zinc alkaline cell of  claim 13 , wherein said bismuth oxide is present in the amount of 3% to 9% by weight of said zinc oxide.  
     
     
         16 . The nickel zinc alkaline cell of  claim 11 , wherein said positive electrode further comprises a conductivity enhancement additive selected from the group consisting of 2% to 3% by weight of nickel metal powder, 2% to 3% by weight of cobalt metal powder, and mixtures thereof.  
     
     
         17 . The nickel zinc alkaline cell of  claim 13 , wherein said positive electrode further comprises a conductivity enhancement additive selected from the group consisting of 2% to 3% by weight of nickel metal powder, 2% to 3% by weight of cobalt metal powder, and mixtures thereof.  
     
     
         18 . The nickel zinc alkaline cell of  claim 11 , wherein the alkali hydroxide comprises sodium hydroxide.  
     
     
         19 . The nickel zinc alkaline cell of  claim 11 , wherein the alkali hydroxide comprises potassium hydroxide.  
     
     
         20 . The nickel zinc alkaline cell of  claim 18  or  19 , wherein alkali hydroxide further comprises lithium hydroxide.  
     
     
         21 . The nickel zinc alkaline cell of  claim 20 , wherein the lithium hydroxide is present in a concentration of 0.05 to 3 moles per liter.  
     
     
         22 . The nickel zinc alkaline cell of  claim 11 , wherein nickel hydroxide is provided in the form of a paste.  
     
     
         23 . The nickel zinc alkaline cell of  claim 11 , wherein the negative electrode comprises zinc oxide in amount of between 85% and 95% by weight and bismuth oxide in an amount of between 1 and 10% by weight.  
     
     
         24 . The nickel zinc alkaline cell of  claim 11 , wherein the conductive substrate of the negative electrode comprises copper.  
     
     
         25 . The nickel zinc alkaline cell of  claim 11 , wherein the second conductive substrate comprises a nickel foam.