Alkaline Electrochemical Cell with Reduced Gassing

Abstract

Electrochemical cells including a casing or cup for direct electrical contact with a negative electrode or counter electrode and serving as the current collector for the electrode. The casing includes a substrate having a plated coating of an alloy including copper, tin and zinc, the coating having a composition gradient between the substrate and the external surface of the coating wherein the copper content is greater adjacent the substrate than at the external surface of the coating and the tin content is greater at the external surface of the coating than adjacent the substrate. Methods for forming a coated casing and an electrochemical cell including a coated casing are disclosed, preferably including providing an electrode casing with a coating utilizing variable current density plating that reduces discoloration of a surface exposed to the ambient atmosphere.

1 . An electrochemical cell, comprising:
 a first and a second electrode;   a separator disposed between the first electrode and the second electrode;   an aqueous alkaline electrolyte; and   a cell housing comprising a first electrode housing and a second electrode housing and an electrically insulating seal member disposed between the first electrode housing and second electrode housing, the cell housing containing the first electrode, second electrode, separator and electrolyte, wherein   the first electrode housing is in contact with the first electrode and has an interior surface and an exterior surface and comprises a substrate plated with an alloy layer, wherein the alloy layer comprises copper, tin and zinc, and wherein the substrate is a copper-stainless steel-copper triclad substrate.   
   
   
       2 . The electrochemical cell according to  claim 1 , wherein a surface portion of the plated alloy layer has a lower copper content than a portion of the plated alloy layer contacting the substrate. 
   
   
       3 . The electrochemical cell according to  claim 1 , wherein the first electrode is a negative electrode comprising zinc and the second electrode is a positive electrode comprising at least one of manganese dioxide, a silver oxide and a catalytic material for reducing oxygen or for generating hydrogen or oxygen. 
   
   
       4 . The electrochemical cell according to  claim 2 , wherein the cell is a button cell. 
   
   
       5 . The electrochemical cell according to  claim 4 , wherein the first electrode is free of added mercury. 
   
   
       6 . The electrochemical cell according to  claim 1 , wherein the interior surface and the exterior surface of the first electrode housing substrate are post-plated with the plated alloy layer. 
   
   
       7 . The electrochemical cell according to  claim 3 , wherein the first electrode is a gelled electrode comprising a gelling agent and zinc, and the second electrode is a catalytic electrode comprising carbon, a binder, and manganese oxide. 
   
   
       8 . The electrochemical cell according to  claim 3 , wherein the second electrode comprises a silver oxide. 
   
   
       9 . The electrochemical cell according to  claim 1 , wherein the cell is a hydrogen generating cell and the second electrode casing includes at least one aperture, and wherein the second electrode is a catalytic electrode that includes at least one layer for excluding oxygen from the cell located between the aperture and the catalytic electrode. 
   
   
       10 . The electrochemical cell according to  claim 2 , wherein the portion of the plated alloy layer contacting the substrate has a thickness greater than a thickness of the surface portion of the plated alloy layer. 
   
   
       11 . The electrochemical cell according to  claim 10 , wherein the portion of the plated alloy layer contacting the substrate has a ratio of copper from 50 to 70 weight percent, tin from 26 to 42 weight percent, and zinc from 3 to 9 weight percent measured at a central portion of the exterior surface of the first electrode casing by SEM/EDS, and wherein the surface portion of the plated alloy layer has a ratio of copper from 36 to 46 weight percent, tin from 42 to 57 weight percent and zinc from 6.5 to 9.5 weight percent measured at a central portion of the exterior surface of the first electrode casing by SEM/EDS. 
   
   
       12 . An electrochemical cell, comprising:
 a first and a second electrode;   a separator disposed between the first electrode and the second electrode;   an aqueous alkaline electrolyte; and   a cell housing comprising a first electrode housing and a second electrode housing and an electrically insulating seal member disposed between the first electrode housing and second electrode housing, the cell housing containing the first electrode, second electrode, separator and electrolyte, wherein   the first electrode housing is in contact with the first electrode and has an interior surface and an exterior surface and comprises a substrate plated with an alloy layer, wherein the alloy layer comprises copper, tin and zinc, and wherein the substrate is a clad material including a copper layer clad to each side of a layer of metal.   
   
   
       13 . The electrochemical cell according to  claim 12 , wherein the layer of metal of the first electrode housing comprises steel. 
   
   
       14 . The electrochemical cell according to  claim 13 , wherein the first electrode housing substrate is a copper-stainless steel-copper triclad substrate. 
   
   
       15 . The electrochemical cell according to  claim 12 , wherein a surface portion of the plated alloy layer has a lower copper content than a portion of the plated alloy layer contacting the substrate. 
   
   
       16 . The electrochemical cell according to  claim 12 , wherein the first electrode is a negative electrode comprising zinc and the second electrode is a positive electrode comprising at least one of manganese dioxide, a silver oxide and a catalytic material for reducing oxygen or for generating hydrogen or oxygen. 
   
   
       17 . The electrochemical cell according to  claim 13 , wherein the cell is a button cell. 
   
   
       18 . The electrochemical cell according to  claim 17 , wherein the first electrode is free of added mercury. 
   
   
       19 . The electrochemical cell according to  claim 12 , wherein the interior surface and the exterior surface of the first electrode housing substrate are post-plated with the plated alloy layer. 
   
   
       20 . The electrochemical cell according to  claim 12 , wherein the first electrode is a gelled electrode comprising a gelling agent and zinc, and the second electrode is a catalytic electrode comprising carbon, a binder, and manganese oxide. 
   
   
       21 . The electrochemical cell according to  claim 16 , wherein the second electrode comprises a silver oxide. 
   
   
       22 . The electrochemical cell according to  claim 12 , wherein the cell is a hydrogen generating cell and the second electrode casing includes at least one aperture, and wherein the second electrode is a catalytic electrode that includes at least one layer for excluding oxygen from the cell located between the aperture and the catalytic electrode. 
   
   
       23 . The electrochemical cell according to  claim 15 , wherein the portion of the plated alloy layer contacting the substrate has a thickness greater than a thickness of the surface portion of the plated alloy layer. 
   
   
       24 . The electrochemical cell according to  claim 23 , wherein the portion of the plated alloy layer contacting the substrate has a ratio of copper from 50 to 70 weight percent, tin from 26 to 42 weight percent, and zinc from 3 to 9 weight percent measured at a central portion of the exterior surface of the first electrode casing by SEM/EDS, and wherein the surface portion of the plated alloy layer has a ratio of copper from 36 to 46 weight percent, tin from 42 to 57 weight percent and zinc from 6.5 to 9.5 weight percent measured at a central portion of the exterior surface of the first electrode casing by SEM/EDS. 
   
   
       25 . A method for forming a plated housing for an electrochemical cell, comprising the steps of:
 providing an electrode housing comprising a metal substrate having a copper interior surface layer and a copper exterior surface layer with a metal layer disposed between the interior surface layer and the exterior surface layer; and   plating a metal alloy layer on the substrate with a plating solution comprising copper, tin and zinc with a combination of two different current densities.   
   
   
       26 . The method according to  claim 25 , wherein the housing is formed having a lower copper content on a surface portion of the plated alloy layer compared to a bulk of the plated alloy layer plated at a higher current density. 
   
   
       27 . The method according to  claim 25 , further including lowering the current density at an end of the alloy plating step. 
   
   
       28 . The method according to  claim 27 , wherein the housing metal layer disposed between the interior surface layer and the exterior surface layer comprises steel. 
   
   
       29 . The method according to  claim 28 , wherein the electrode housing substrate is a copper-stainless steel-copper triclad substrate. 
   
   
       30 . The method according to  claim 26 , wherein a first current density of the plating ranges from 10 to 1.076 amps per square meter, and wherein a second current density of the plating ranges from 1.0 to 27.0 amps per square meter with the proviso that the second current density is lower than the first current density. 
   
   
       31 . The method according to  claim 26 , wherein the surface portion of the plated alloy layer has a higher weight percentage of tin and a lower weight percentage of copper compared to the bulk of the plated alloy layer. 
   
   
       32 . The method according to  claim 30 , wherein the first current density of the plating is at least 26.9 amps per square meter and at most 107.6 amps per square meter, and wherein the second current density of the plating is at least 4.3 amps per square meter and at most 16.2 amps per square meter. 
   
   
       33 . The method according to  claim 32 , wherein the bulk of the plated alloy layer has a ratio of copper from 50 to 70 weight percent, tin from 26 to 42 weight percent, and zinc from 3 to 9 weight percent measured at a central portion of the exterior surface of the electrode casing, and wherein the surface portion of the plated alloy layer has a ratio of copper from 36 to 46 weight percent, tin from 42 to 57 weight percent and zinc from 6.5 to 9.5 weight percent, measured at a central portion of the exterior surface of the electrode casing by SEM/EDS.