CA1195103A

CA1195103A - Nico.sub.3 electrode material and electrode

Info

Publication number: CA1195103A
Application number: CA000422484A
Authority: CA
Inventors: John F. Jackovitz; Joseph Seidel; Earl A. Pantier
Original assignee: Westinghouse Electric Corp
Current assignee: Westinghouse Electric Corp
Priority date: 1982-03-03
Filing date: 1983-02-28
Publication date: 1985-10-15
Also published as: US4443526A; DE3361883D1; JPS58163163A; BR8300982A; EP0092656A1; ZA831418B; ES520245A0; JPH0439186B2; EP0092656B1; ES8407112A1

Abstract

ABSTRACT OF THE DISCLOSURE
A battery plate is made by loading a supporting porous metallic plaque with an electrode paste comprising (1) NiCO3, (2) cobalt additive, (3) sufficient water to form a paste, and optionally (4) a deflocculant.

Description

1~5~

1 ~0,0~5 NiC03 ELECTRODE MAT~RIAL AMD ELECTRODE

BACKGROUND OF THE INVENTION
In present iron-nickel batteries, the nickel electrode can contain an electrode paste prepared from an aqueous slurry of: (1) NiC3-2Ni(H)2~4~2 or 2NiCO303Ni(OH)2~4H20, i.e., hydrat~d mixtures of nickelous carbonate-nickelous hydroxide, and (2) CoC03 and/or Co~OH)2. This slurry must be oxidized with hypochlorite ion, hxpobromite ion, or the like, prior to drying and application to the plaque, as taught by Jackovitz et al., in U.S. Pate~t 3,928,068. Such plaques require from 5 to lS charge-discharge "formation" cycles to achieve maximum electrochemical output.
While the output o this paste approaches about 0.24 amp-hr/gram, close to the theoretical output of about lS 0.26 amp-hr~'gram, it would be highly advantageous if outputs even closer to theoretical could be reali~ed. In addition, the required oxidation of the hydrated, hydroxy containing nickel material adds to the cost of the final .~ electrode plate. Finally, the hydrated, hydroxy containing nickel material is itself~ expensive~ and difficult to obtain commercially, and is subject to significant expan~
sion after hundreds of cycles. There has been a long felt need then, for a less expensive nickel electrode paste of hi~her output, requiring less "formation" pre conditioning, which would also show little expansion during its useful lifetime.

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2 50,04S
SUMMARY OF THE INVENTION
The above need was filled by utilizing an aqueous paste comprising: (1) anhydrous nickel carbonate (NiC03), and (2) a cobalt compound preferably selected ~rom CoC03, Co(OH)2, hydrates thereof, and mixtures thereof. The preferred content of cobalt additive is from a~out 1 wt.%
to about 7 wt.%, based on NiC03 weight. The ~JiC03 is blended with water, the cobalt additive, and preferably, a deflocculant, to provide a spreadable paste. Optionally, nickel hydroxide can also be added, in an amount up to about 50 wt.% based on NiC03 weight. The paste is rolled or otherwise applied into a porous support, preferably of a iber metal constrution, and then sized to a desired thickness, using a press, or the like, to provide a nicXel electrode.
The nickel electrode of this invention requires only one charge-discharge "formation" cycle to achieve maximum electrochemical output. The paste of this inven-tion shows outstanding dimensional stability, loaded electrodes showing little significant thickness increase after hundreds of continuous cycles. Output after 30 cycles approaches 0.26 amp-hr/gram, and the NiC03 is both relatively inexpensive and readily obtainable commercially.
Unexpectedly, it was found that the NiC03 is oxidized sufficiently or electrode operation during the initial charging step, producing NiO2-H20 and C02, with a large portion of the C02 being absor~ed by the alkali hydroxide electrolyte.
BRIEF DESCRIP~ION OF THE DRAWINGS
For a bett~r understanding of the invention, reference may be made to the preferred embodiments exem-plary of the invention, shown in the accompanying drawings, in which:
Eig. 1 shows a preferred electrode plate loaded with the material of this invention; and Fig. 2 is a graph showing the performance of electrode plates prepared in the Examples, in terms of 5~'~3~

3 50,045 output capacity vs. cycle number, in relation to the theoretical capacity value.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of a battery, utilizing the S active material and electrode plate of this invention, would generally comprise a plurality of alternate positive nickel plates and negative plates such as, for example, loaded iron active material plates. This stack~up would contain plate separators between the positi.ve and negative plates, all contacted by alkaline electrolyte, such as KOH
alone or with a minor amount of LiOH additive, and housed in a case having a cover, a vent, and positive and n~gative terminals.
Preferred loaded electrode plates, shown in Fig.
1, are made from metal fibers, preferably nickel, or metal protectlve coated fibers, such as nickel coated steel or iron. A very suitable material is nickel coated steel wool. The plaque 10, is a flexible, expansible, compacted sheet of relatively smooth, generally contacting, inter-mingled, metal fibers as shown at 11 in the body of theplaque. The plaque has, in the embodiment shown, top edge 12 coined to a high density.
The coined area provides a base to which lead tab 13, which is attached to the battery terminals, is ZS spot welded. The plague is generally between about 85%
and g5% porous. This range is preferable in providing improved conductivity and electrolyte permeability, while maintaininy enou~h body for good plaque loading. Active nickel electrode material is loaded into the interstices of the body of this fibrous plaque to provide an electrode plate. This invention, however, is not restricted to the preferred plaque structure described herein, and the active material can be used with other supporting, porous metallic plaque structures.
The metal fibers are preferably diffusion bonded in a protective atmosphere at temperatures up 'c~ the sintering point of the fibers used. In diffusion bonding, S.~

4 50,045 the fibers must not be melted, or protuberances will be formed reducing active material loading (volume) within the plague. There should only be a metallurgical bond and interdiffusion of atoms across the fiber interface at fiber contact points 14 along the fiber lengths. Diffusion bonding provides a flexible, expansible electrode structure having a larg~ pore volume into which acti~e material can be pasted or otherwise impregnated. Diffusion bonding also lowers the electrode plate resistance appreciably and th~s the internal cell resistance in a finished cell.
The electrode paste composition of this invention is prepared by admixing: (1) anhydrous nickel carbonate, (2) a minor amount of a cobalt compound preferably selected from the group consisting of CoC03, Co(OH)2, hydrates thereof, and mixtures thereof, (3) at least sufficient water to form a fluid paste, (4) 0 to about 50 wt.%, based on nickel carbonate weight, of nickel hydroxide (Ni(0~)2), and preferably (5) an amount of a deflocculant effective to modify the zeta potential of the admixture, i.e., distribute the residual charge of the solid particles, so ~-~ that a high solids, aqueous, fluid paste is provided~using a minimal amount of water. Useful deflocculants include, for example, anionic surfactant material~such as sodium salts of carboxylated polyelectrolytes, or alkali salts of naphthalene sulf-onic acid derivatives, and the liXe, as are well known in the art.
The cobalt additive content ranges from about 1 wt.% to about 7 wt.% based on NiC03 weight. The cobalt material is useful to get maximum electrochemical output from the plate. No oxidant is required for the active material composition, its use being specifically excluded, and prior chemical oxidation is not required. The term "anhydrous" is used herein to mean a compound that does not contain water combined as water of crystalli~ation, and specifically excludes hydroxyl ( 0~) groups.
The electrode paste is applied to the interstices of a porous plaque, to form a positive electrode plate.

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50,045 Application can be accomplished by rolling or pressing the paste into the plaque. The plaque is dried and pressed~ or pressed while moist~ to compact the active material The plate is then coupled with a negative plate and charge-disch~rga cycled once in electrolyte comprising aqueousKOH. The charge current density must bo effective to form hydrated NiO2 and evolve C02. Charging is initially at a current density of about 10 to about 50 mA. /5q. inch for about 48 hours, followed by a booster charge of about 140 to abou~ 180 mA./sq.inch for about 4 hours. Charging initially at over about 50 mA./sq.inch could evolve C02 to such an extent that the electrode structure could be damaged.
The charging reaction proceeds as follows:
3 1/202 ~ H20 ~ NiO2-H20 ~ C02 ~1) 2KOH + C02 ~ K2C03 + H20 (2) If the concentration of K2C03 becomes too high, an electro-lyte change may be considered. The charged active material has a density of about 2.4 grams/cu.cm. After dozens of cycles, the active material achieves a true density of about 2.4 ~o 2.6 ~rams/cu.cm. depending on the strength and type of electrolyte, and this range is comparable to the initial NiC03 density. Thus, no substantial increase in active material volume occurs over the electrode cycle life and thus minima~ electrode swelling occurs. This may be compared to electrodes prepared solely from Ni(OH)2 and Co(OH)2, which unde~go significant density decrease (and volume increase) during cycling, and which can expand as much as 30% after hundreds of cycles. This expansion is always followed by a performance decline. The inclusion of up to about 50 wt.% of Ni(OH)2 in the NiC03 based composition causes a maximum six percent swell.ing on continued cycling, principally in the intarior OI the electrode, and is somewhat compensated for by the non-expansion of the carbonate portion. Over about 50 wt.%,swelling will advance beyond ten percent on continued cycling, and will not ~e controlled by the carbonate portion.

6 50,045 A paste was prepared by admixing in a ball mill:
95 grams of anhydrous nickel carbonate (sold commerciall~
by Sheperd Chemical Co.), 5 grams of CoC03, 85 grarn~ of water and 9 grams of a 25% solids aqeuous solution of a sodium salt of a carboxylated polyelectrolyte deflocculant (sold co~nercially by R. T. Vanderbilt Co. under the trade name Darvan 7). The paste was rolled into a 90% porou~, 1 sq.in. nickel-plated fiber metal plaque and dried. Dry loading was ~.0 grams/sq.in., and the initial thickness was 0.096 inch.
The NiC03 pasted, positive electrode was set opposite an iron electrode in electrolyte comprising 25%
K0~ solution, to form an electrochemical cell. Charging of the positive electrode was initially at 20 mA./sq.in.
for 48 houxs, followed by a booster charge of 160 mA./
sq.in. for 4 hour~. Discharge was at the rate of 160 mA./sq.in. The performance was measured and is shown as electrode (A) curve in Fig. 2 of the drawings. After 50 cycles the positive electrode had a thickness of 0.097 inc~, showing an insignificant increase over its initial thickness.
In a similar manner, a paste was prepared by admixing: 95 grams of ar~ydrous nickel carbonate, 4 grams of Co(OH)2, 85 grams of water and 9 grams of Darvan 7.
The paste was rolled into a grid similar to that described heretofore Qnd dried. Dry loading waC 1.9 grams/sq.in., and the initial thickness was 0.096 inch. The NiC03 pasted electrode was cycled as described heretofore, and the performance measured and shown as electrode (Bj curve in Fig. 2. ~fter 50 cycles the electrode had a thickness of 0.097 inch, showing an insignificant increas~ over its initial thickness.

A paste was prepared by admixing in a ball mill:
100 grams of anhydrous nickel carbonate, 85 grams of water and 9 grams of Darvan 7. No cobalt additive was used.

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7 50,045 The paste was incorporated into a fiber metal grid and tested electrochemically as in Example 1. Performance is shown as electrode (C) curve in Fig. 2.
As can be seen from Fig. 2, the cobalt containing electrode paste of this invention provides pasted elec-trodes which retain theoretical output of about 0.26 ampere-hours/gram for between 25 to 38 cycles, curves ~A) and (B). Without cobalt additive, output drops to below 0.20 ampere-hours/gram of NiC03. Thus, a cobalt compound is an important additive to the paste. Theoretical output is shown as line (X).

Claims

We claim:

1. A composition comprising:
(A) NiCO3, and (B) a cobalt compound.

2. An electrode paste comprising: the admixture of (A) anhydrous nickel carbonate, (B) a cobalt compound selected from the group consisting of CoCO3, Co(OH)2, hydrates thereof and mixtures thereof, and (C) sufficient water to form a paste.

3. The electrode material of claim 2, also containing an effective amount of deflocculant.

4. The electrode material of claim 3, where the deflocculant is a polyelectrolyte material and is present in the range of about 1 wt.% to about 15 wt.% based on anhydrous nickel carbonate weight.

5. The electrode material of claim 2, where the cobalt additive is present in the range of about 1 wt.% to about 7 wt.% based on anhydrous nickel carbonate weight, and the electrode material also contains up to about 50 wt.% of nickel hydroxide, based on anhydrous nickel car-bonate weight.

6. An electrode comprising a porous supporting metallic plaque containing the electrode material of claim 2.

7. An electrode according to claim 6, where said metallic plaque comprises flexible, bonded fibers selected from the group consisting of nickel and nickel coated metal.

8. An electrode according to claim 6, where said electrode is charged once in alkali electrolyte at a current density effective to form hydrated NiO2 and evolve CO2.

9. A method of preparing a charged electrode containing active electrode material comprising the steps of:
(A) applying an electrode paste to a porous plaque, said electrode paste comprising anhydrous nickel carbonate, (B) charging the plaque containing the paste once, in an alkali electrolyte, at a current density effective to form hydrated NiO2 and evolve CO2.

10. The method of claim 9, where the charge current density is initially up to about 50 mA./sq.in., and the electrode paste also contains a cobalt compound present in the range of about 1 wt.% to about 7 wt.% based on anhydrous nickel carbonate weight, an effective amount of deflocculant, and up to about 50 wt.% of nickel hydroxide based on anhydrous nickel carbonate weight.

11. The method of claim 10, where the initial charge is followed by an additional charge at a current density of up to about 180 mA./sq.in., and the cobalt compound is selected from the group consisting of CoCO3, Co(OH)2, hydrates thereof and mixtures thereof.

12. An electrode prepared by the method of claim 9.

13. An electrode paste consisting essentially of the admixture of:
(A) anhydrous nickel carbonate, (B) up to about 50 wt.% of nickel hydroxide, based on anhydrous nickel carbonate weight, (C) a cobalt additive compound, and (D) sufficient water to form a paste.

14. An electrode comprising a porous supporting metallic plaque containing an electrode material consisting essentially of the admixture of:

(A) anhydrous nickel carbonate, (B) up to about 50 wt.% of nickel hydroxide, based on anhydrous nickel carbonate weight, and (C) a cobalt additive compound.

15. The electrode of claim 14 as positive plates in a battery comprising a plurality of alternating positive nickel plates and negative plates.

16. The electrode of claim 15, where the negative plates are iron active material plates.

17. The electrode paste of claim 13, where the cobalt compound is added in an amount of from about 1 wt.% to about 7 wt.%, based on anhydrous nickel carbonate weight, and is selected from the group consisting of CoCO3, Co(OH)2, hydrates thereof, and mixtures thereof.

18. The electrode paste of claim 13, also contain-ing an effective amount of deflocculant.

19. The electrode material of claim 18, where the deflocculant is a polyelectrolyte material and is present in the range of about 1 wt.% to about 15 wt.% based on anhydrous nickel carbonate weight.

20. The electrode of claim 14, where the cobalt com-pound is added in an amount of from about 1 wt.% to about 7 wt.%, based on anhydrous nickel carbonate weight, and is selected from the group consisting of CoCO3, Co(OH)2, hydrates thereof, and mixtures thereof, and the admixture also contains an effective amount of deflocculant.