A rechargeable cell or battery is provided in which shape change of the zinc anode is combatted by profiling the ionic conductivity of the paths between the electrodes. The ion flow is greatest at the edges of the electrodes and least at the centers, thereby reducing migration of the zinc ions from edges to the center of the anode. A number of embodiments are disclosed in which the strength and/or amount of electrolyte, and/or the number and/or size of the paths provided by the separator between the electrodes, are varied to provide the desired ionic conductivity profile

Cohn, E. M.

English

NASA Technical Reports Server

United States Patent [191 1 1 I 3,972,727 
Cohn [451 Aug. 3, 1976 
[ 541 RECHARGEABLE BATTERY WHICH 
COMBATS SHAPE CHANGE OF THE ZINC 
ANODE 
[75] Inventor: Ernest M. Cohn, Washington, D.C. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[22] Filed: Aug. 13, 1975 
[21] Appl. No.: 604,374 
[52] 
[ 5 1 ] 
[58] 
U.S. CI .................................... 136/30; 136/143 
Int. CLZ ........................................... HOlM 4/38 
Field of Search ............... 136/30, 31, 125, 142, 
136/143 
~ 5 6 1  References Cited 
UNITED STATES PATENTS 
3,226,260 12/1965 Drengler ............................... 136/30 
3,505,l 15 4/1970 McBreen .............................. 136/30 
3,672,998 6/1972 Dailand, Jr. .......................... 136/30 
3,876,470 4/1975 McBreen ........................ 
Primary Examiner-John H. Mack 
Assistant Examiner-C. F. LeFevour 
Attorney, Agent, or Firm-Nina M. Lawrence; John R. 
Manning; Gary F. Grafel 
is71 ABSTRACT 
A rechargeable cell or battery is provided in which 
shape change of the zinc anode is combatted by profil- 
ing the ionic conductivity of the paths between the 
electrodes so that ion flow is greatest at the edges of 
the electrodes and least at the centers thereof, thereby 
reducing migration of the zinc ions from edges to the 
center of the anode. A number of embodiments are 
disclosed, wherein the strength and/or amount of elec- 
trolyte, and/or the number and/or size of the paths 
provided by the separator between the electrodes, are 
varied to provide the desired ionic conductivity 
profile. 
8 Claims, 5 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19760022611 2020-03-20T02:22:23+00:00Z
U.S. Patent Aug. 3, 1976 
FIG: / 
0' 
FIG. 3 
FIG 4 
-30" 
3,972,727 
10 
3 
(18 /I6 FIG 2 
3,972,727 
2 
According to a first embodiment of the invention, the 
RECHARGEABLE BATTERY WHICH COMBATS amount or thickness of the separator material is pro- 
SHAPE CHANGE OF THE ZINC ANODE filed so that the density or thickness of the separator is 
greatest at the center of the electrodes and least at the 
ORIGIN OF THE INVENTION 5 edges, so that the flow path for the ions in the electro- 
The invention described herein was made by an em- lyte is easier and more direct at the edges of the elec- 
ployee of the United States Government and may be trodes. In a second embodiment, a porous separator is 
manufactured and used by or for the Government of used which is constructed so that the pores therein are 
the United States of America for governmental pur- concentrated at the edges and that there are relatively 
poses without the payment of any royalties thereon or 10 few pores at the center. A similar effect is produced in 
therefor. a third embodiment by the use of a porous separator 
constructed so as to include relatively large pores at the 
edges and relatively small pores at the center. In an- 
other embodiment, a separator arrangement is pro- 
chargeable cells or batteries and concerns an improved 15 vided which defi-nes a series of chambers containing 
technique for combatting electrode shape change. electrolytes of different strengths, the strengths of the 
electrolytes being greatest at the edges and becoming 
progressively weaker towards the center, so that the 
A serious problem associated with zinc electrodes ionic conductivity of the paths to the edges of the elec- 
used in rechargeable batteries is the tendency of the 20 trodes is substantially greater than that of the paths to 
active material of the electrode, viz., the zinc, to mi- the central regions of the electrodes. 
grate from the periphery of the electrode to the center. Other features and advantages of the invention will 
This redistribution of the zinc, which is often termed be set forth in, or apparent from, the detailed descrip- 
“shape change”, not only renders the edges of the zinc tion of the preferred embodiments of the invention 
electrodes inactive (so-called “edee corrosion”) but 25 found hereinbelow. 
1 
FIELD OF THE INVENTION 
The present invention is related to secondary or re- 
BACKGROUND OF THE INVENTION 
BRIEF DESCRIPTION OF THE DRAWINGS also reduces activity’at the center ‘;f the electrode by causing densification of the zinc at the center. 
A good discussion of the problem of “shape change” FIG. 1 is a perspective view of a plate-pack of secon- 
and various techniques for combatting this problem is dary storage battery with the cover and separators 
found in U.S. Pat. No. 3,493,434 (Goodkin). Afurther 30 removed; 
patent which deals with this problem in U.S. Pat. No. FIG. 2 is a diagrammatic representation, in side ele- 
3,669,746 (Devitt et al). . vation, of a portion of a plate-pack illustrating a first 
The Goodkin patent is of particular interest because 
of the concern therein with transporting the zinc from FIG. 3 is a front view of a separator constructed in 
the outer edge of the electrode to the center thereof so 35 accordance with a second embodiment of the inven- 
that, in accordance with a first embodiment, the zinc is tion; 
deposited in a concave depression in the center which FIG. 4 is a front view, similar to FIG. 3, of a separator 
is specifically designed to receive replated zinc. In a constructed in accordance with a third embodiment of 
second embodiment, the concentration or density of the invention; and 
the zinc is increased in a region near the periphery of 40 FIG. 5 is a front view of an electrolyte-containing 
the electrode and is reduced towards the center, so as separator arrangement for positioning between elec- 
to lessen the effect of the zinc which migrates from the trodes, wherein each annulus, in sequence, contains an 
edge to the center and reduce densification at the cen- electrolyte of decreasing strength, beginning with the 
ter. strongest electrolyte in the outer annulus. 
embodiment of the invention; 
AT .& 
SUMMARY OF THE INVENTION DESCRIPTION OF THE PREFERRED 
EMBODIMENTS The present invention is concerned kith combatting 
shape change in the zinc electrodes of a rechargeable Referring to FIG. 1, the plate-pack of a conventional 
battery by profiling the conductivity of the path be- secondary battery is shown with the casing and separa- 
tween the electrodes so that it is easier for ions to travel 50 tors removed. The plate-pack, which is generally de- 
at and near the edges of the electrodes and more diffi- noted 10, includes battery terminals 12 and 14, which 
cult for the ions to travel in and near the center of the are individually connected through bus bars 16 and 18 
electrodes. Thus, rather than accepting substantial to a plurality of‘ positive plates 20 and a plurality of 
migration of the zinc from the edges to the center of the negative plates 22, respectively. The connections be- 
electrodes and compensating for this migration by in- 55 tween bus bar 16 and positive plates 20, and between 
creasing the amount or the density of the zinc at the bus bar 18 and negative plates 22, are made through 
edges, as is done in the Goodkin patent discussed suitable leads 24 and 26, respectively. 
above, the present invention is concerned with prevent- Before proceeding further, the basic make-up or 
ing or reducing this migration of zinc ions toward the construction of an electrochemical cell will be consid- 
center by controlling the ionic conductivity of the path 60 ered. Such a cell comprises electodes, viz., at least one 
between electrodes. It is noted that in the embodiment cathode corresponding to positive plates 20, and at 
disclosed in the Goodkin patent wherein a central cav- least one anode corresponding to negative plates 22, 
ity or recession is provided, the ion flow could be and an electrolyte (not shown), all contained within a 
greater in the center where the cavity was filled with a housing or casing. To make the cell more portable, the 
strong electrolyte. In contrast, in accordance with the 65 electrolyte, which is usually a liquid, is soaked up in a 
invention, current is deliberately encouraged to flow to separator (not shown in FIG. 1) which thus acts simi- 
edges of the electrodes, rather than to the center, so as larly to a wet sponge. The electrodes (anodes and cath- 
to minimize shape change. odes) comprise at least two parts, viz., the electroni- 
3,972,727 
3 
cally conductive current conductor or plaque, and the 
“active material” deposited on or within the conduc- 
tor. In secondary or rechargeable cells or batteries, 
such as are being considered here, the active material is 
used to give off (discharge) or take up (charge) energy 
repeatedly. The plaque facilitates charge and discharge 
by providing an easy (highly conductive) path between 
the active material and the external leads, ‘Zorrespond- 
ing to leads 24 and 26. The electrical circuit is com- 
pleted within the cell between electrodes by the elec- 
trolyte, which is ionically conductive, in contrast to the 
electrodes, which are electrically conductive. 
Referring to FIG. 2, a first embodiment of the inven- 
tion is illustrated. In accordance with this embodiment, 
separators 30 are disposed between the zinc anodes 22 
and the cathodes 20, which separators are density pro- 
filed so as to control the ionic conductivity of the paths 
between the electrodes. The separators 30 are each 
formed by plates or discs of varying sizes, with the 
larger sized discs 30a being located adjacent to the 
respective electrodes and the intermediate sized discs 
30b positioned between discs 30a and a center disc 30c. 
It is important to note that the discs 30a, 306 and 30c 
are normally compressed together. It might also be 
noted at this point that in FIG. 2, bus bars 16 and 18 are 
off-set in height for purposes of clarity. In any event, it 
will be appreciated that with the separators 30 formed 
as shown in FIG. 2, and the spaces between the separa- 
tor discs filled with electrolyte, the ionic conductivity 
of the path between the electrodes is greater at the 
edges of the electrode and less at the center, because of 
the relatively greater amount of separator material at 
the center and relatively greater amount of electrolyte 
near the edges. Thus, current will be encouraged to 
flow to the edges of the electrodes, thereby combatting 
edge corrosion and shape change. It will, of course, be 
understood that the particular shape and arrangement 
of the separator disc should not be taken as limiting, 
and other shapes and arrangements can be used to 
produce the same end. 
Referring to FIG. 3, a portion of a separator con- 
structed in accordance with a further embodiment of 
the invention is shown. In this embodiment, a separa- 
tor, denoted 30’, is provided which is of the porous 
type and includes a plurality of pores 32. As illustrated, 
the separator is constructed so as to be highly porous at 
the edge and less porous at the center so that, again, the 
ionic conductivity of the path between the electrodes is 
greater at the edge that at the center. 
FIG. 4 illustrates a further embodiment which is simi- 
lar to that of FIG. 3, but wherein pore sizes of a portion 
of a separator, denoted 30”, decrease toward the cen- 
ter. Thus, the size of the pores 34 at the edge of separa- 
tor 30’’ is larger than of the pores 36 adjacent thereto; 
and the latter pores are, in turn, larger than the pores 
38, located at the center. Again, the effect is to provide 
a relatively high conductivity path to the edges of the 
electrodes, between which the separator is positioned 
and a relatively low conductivity path to the electrode 
centers. 
A further embodiment of the invention is illustrated 
schematically in FIG. 5. In this embodiment, the sepa- 
rator arrangement includes a plurality of spacer rings 
40,42,44, and 46, which form annular electrolyte 
chambers 50, 52,54 and central chamber 56. The 
strengths of the electrolytes in annular chambers 50, 
52,54 and central chamber 56 are made to be progres- 
sively weaker, proceeding from the outside toward the 
4 
center, so that the electrolyte in outer chamber 50 is 
the strongest and that in central chamber 56 is the 
weakest. As before, the effect is to increase the ionic 
conductivity of the path between the edges of adjacent 
electrodes as compared with that of the path between 
the central portions of those electrodes. 
It will be appreciated that the embodiments de- 
scribed above can be combined, and that characteris- 
tics, such as the size, quality and/or number of the ion 
I o  paths and/or the strength and/or amount of electrolyte, 
can be used separately or in combination to provide the 
desired ionic conductivity profile. 
Although the invention has been described relative to 
preferred embodiments thereof, it will be understood 
by those skilled in the art that modifications and varia- 
tions can be effected in these embodiments without 
departing from the scope and spirit of the invention. 
I claim: 
1. In a secondary power source, comprising at least 
2o one rechargeable electrochemical cell, comprising a 
housing, at least one cathode electrode located within 
the housing, at least one zinc anode electrode located 
within the housing, a separator between the electrodes, 
25 and an electrolyte for enabling ion transfer between 
said electrodes, the improvement wherein said separa- 
tor profiles the ionic conductivity between the elec- 
trodes so that ion flow is greatest at the edges of the 
electrodes and least at the center of the electrodes, so 
3o as to combat migration of the zinc ions of the anode 
electrode from the edge thereof to the center thereof. 
2. A secondary power source as claimed in claim 1, 
wherein said separator is disposed between the elec- 
trodes and provides increased electrolyte in the region 
3. A secondary power source as claimed in claim 1, 
wherein said separator comprises a spacer arrangement 
disposed between the electrodes and defining a plural- 
ity of chambers containing electrolytes of different 
4. A secondary power source as claimed in claim 1, 
wherein said separator comprises a porous separator. 
5. A secondary power source as claimed in claim 2, 
wherein said separator comprises a plurality of separa- 
45 tor discs of different sizes, said separator discs being 
compressed together and being arranged to provide a 
thicker portion at the center of the electrodes, and a 
thinner portion at the edges of the electrodes. 
6. A secondary power source as claimed in claim 3, 
50 wherein said spacer arrangement comprises a plurality 
of concentric rings defining annular chambers therebe- 
tween, the ionic conductivity of the electrolytes in the 
annular chambers increasing progressively beginning at 
the center so that the electrolyte in the innermost annu- 
55 lar chamber has the relatively lowest ionic conductivity 
and the outermost chamber has the highest ionic con- 
ductivity. 
7. A secondary power source as claimed in claim 4, 
wherein the pores of said porous separator are of sub- 
60 stantially the same size and said separator includes a 
substantially greater concentration of pores at the 
edges thereof than the center thereof. 
8. A secondary power source as claimed in claim 4, 
wherein the pores of said separator are of different 
65 sizes and the larger pores are concentrated in the re- 
gion of the separator which lies adjacent to the edges of 
the electrodes. 
35 of the edges of the electrodes. 
40 ionic conductivity. 
* * * * *  
d 
UNITED STATES PATENT AND TRADEMARK OFFICE 
CERTIFICATE OF CORRECTION 
PATENT NO. : 5,972,727 
DATED : 8/3/76 
INV,ENTOR(S) :Ernst M. C o b  
are hereby corrected as shown below: 
I t  i s  certified that error appears in the above-identified patent and that said Letters Patent 
In the heading of the printed specification, correct the 
Inventorls first name by deleting llErnestll and inserting 
--Ernst-- 
S g n e d  and 5ealed this 
Eighteenth Day O f  October 1977 
[SEAL] 
Attest: 
RUTH C. MASON 
Attesting ODcer 
LUTRELLE F. PARKER 
Acting Commissioner of Patents and Trademarks 


Rechargeable battery which combats shape change of the zinc anode

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