Zinc plate shape change inhibition

Claim 2

IN A SECONDARY ELECTROCHEMICAL CELL COMPRISING A ZINC ELECTRODE HAVING A FACE WITH CENTRAL AND EDGE PORTIONS, A COUNTERELECTRODE SUBSTANTIALLY UNIFORMLY SPACED FROM SAID ZINC ELECTRODE FACE AND AN ION PERMEABLE, TREE-SUPPRESSING MEMBRANE BETWEEN THE ELECTRODE AND COUNTERELECTRODE, SAID EDGE PORTIONS BEING SUBJECTED TO HIGHER CHARGING CURRENT DENSITIES THAN SAID CENTRAL PORTION, THE IMPROVENENT COMPRISING A PLATING EFFICIENCY DEPRESSANT SELECTIVELY LOCATED IN THE HIGH CURRENT DENSITY PATH BETWEEN SAID EDGE PORTION AND THE COUNTERELECTRODE AND ADJACENT THE HIGH-CURRENT-DENSITYSUBJECTED EDGE PORTION BUT NOT THE LOWER-CURRENT-DENSITYSUBJECTED CENTER PORTION OF SAID ZINC ELECTRODE FOR SUBSTANTIALLY EQUALIZING THE PLATING RATES AT THE EDGE AND CENTER PORTIONS REGARDLESS OF CURRENT DISTRIBUTION ACROSS SAID FACE, AND MEANS FOR SPACING SAID DEPRESSANT FROM SAID EDGE PORTION, SAID DEPRESSANT HAVING A LOWER HYDROGEN OVERVOLTAGE THAN ZINC TO REDUCE THE PLATING EFFICIENCY OF ZINC AT THE EDGE PORTION BELOW ITS PLATING EFFICIENCY AT THE CENTRAL PORTION AND TO THEREBY FORESTALL ZINC ELECTRODE SHAPE CHANGES DURING CYCLING.

Claim 3

In a secondary electrochemical cell comprising a zinc electrode having a face with central and edge portions, a counterelectrode substantially uniformly spaced from said zinc electrode face and an ion permeable, tree-suppressing membrane between the electrode and counterelectrode, said edge portions being subjected to higher charging current densities than said central portion, the improvement comprising a plating efficiency depressant selectively located in the high current density path between said edge portion and the counterelectrode and adjacent the high-current-density-subjected edge portion but not the lower-current-density-subjected center portion of said zinc electrode face for substantially equalizing the plating rates at the edge and center portions regardless of the current distribution across said face, and means for spacing said depressant from said edge portion, said depressant having a lower hydrogen overvoltage than zinc and a potential at least as noble as iron to reduce the plating efficiency of zinc at the edge portion below its plating efficiency at the central portion and to thereby forestall zinc electrode shape changes during cycling and to reduce the

Claim 4

In a secondary electrochemical cell comprising a zinc electrode having a face with central and edge portions, a counterelectrode substantially uniformly spaced from said zinc electrode face and an ion permeable, tree-suppressing membrane between the electrode and counterelectrode, said edge portions being subjected to higher charging current densities than said central portion, the improvement comprising a plating efficiency depressant selectively located in the high current density path between said edge portion and the counterelectrode and adjacent the high-current-density-subjected edge portion but not the lower-current-density-subjected center portion of said zinc electrode face for substantially equalizing the plating rates at the edge and center portions regardless of the current distribution across said face, and means for spacing said depressant from said edge portion, said depressant having a lower hydrogen overvoltage than zinc and a potential at least as noble as iron to reduce the plating efficiency of zinc at the edge portion below its plating efficiency at the central portion and to thereby forestall zinc electrode shape changes during cycling and to reduce the

Claim 5

In a secondary electrochemical cell comprising a zinc electrode having a face with central and edge portions, a counterelectrode substantially uniformly spaced from said zinc electrode face and an ion permeable, tree-suppressing membrane between the electrode and counterelectrode, said edge portions being subjected to higher charging current densities than said central portion, the improvement comprising a frame-like absorbent first mat selectively located in the high current density path between said edge portion and the counterelectrode and adjacent the high-current-density-subjected edge portion but not the lower-current-density-subjected center of said face and an electrolyte-saturated second mat spacing said first mat from said edge portion, said first mat being impregnated with a zinc-reducible compound of a plating efficiency depressant having a lower-hydrogen overvoltage than zinc and which upon contact with zinc forms said depressant in said second mat to reduce the plating efficiency of zinc at the edge portion below its plating efficiency at the central portion to thereby forestall zinc electrode shape changes during cycling by substantially equalizing the plating rates at the edge and center portions regardless of the

Claim 6

In a secondary electrochemical cell comprising a zinc electrode having a face with central and edge portions, a counterelectrode substantially uniformly spaced from said zinc electrode face and an ion permeable, tree-suppressing membrane between the electrode and counterelectrode, said edge portions being subjected to higher charging current densities than said central portion, the improvement comprising a frame-like absorbent first mat selectively located in the high current density path between said edge portion and the counterelectrode and adjacent the high-current-density-subjected edge portion but not the lower-current-density-subjected center of said face and an electrolyte-saturated second mat spacing said first mat from said edge portion, said first mat being impregnated with a zinc-reducible compound of a plating efficiency depressant having a lower-hydrogen overvoltage than zinc and which upon contact with zinc forms said depressant in said second mat to reduce the plating efficiency of zinc at the edge portion below its plating efficiency at the central portion to thereby forestall zinc electrode shape changes during cycling by substantially equalizing the plating rates at the edge and center portions regardless of the

Claim 7

In a secondary electrochemical cell comprising a zinc electrode having a face with central and edge portions, a counterelectrode substantially uniformly spaced from said zinc electrode face and an ion permeable, tree-suppressing membrane between the said electrode and counterelectrode, said edge portions being subjected to higher charging current densities than said central portion, the improvement comprising a frame-like absorbent first mat selectively located in the high current density path between the edge portion and the counter-electrode and adjacent near the high-currentdensity-subjected edge portion but not the lower-current-density-subjected center portion of said face and an electrolyte-saturated second mat spacing the first mat from said edge portion, said first mat being impregnated with ferrous hydroxide.

Claim 8

In a secondary electrochemical cell comprising a zinc electrode having a face with central and edge portions, a counterelectrode substantially uniformly spaced from said zinc electrode face and an ion permeable, tree-suppressing membrane between the said electrode and counterelectrode, said edge portions being subjected to higher charging current densities than said central portion, the improvement comprising a frame-like absorbent first mat selectively located in the high current density path between the edge portion and the counter-electrode and adjacent near the high-currentdensity-subjected edge portion but not the lower-current-density-subjected center portion of said face and an electrolyte-saturated second mat spacing the first mat from said edge portion, said first mat being impregnated with ferrous hydroxide.