CA1050237A - Method for preparing a stable tetravalent nickel oxyhydroxide having the formula ni2ox.h2o wherein x is greater than 3.0 and less than 4.0 - Google Patents

Abstract

METHOD OF PREPARING STABLE NiOOH

ABSTRACT OF THE DISCLOSURE
Stable NiOOH is prepared by mixing an alkali metal hydroxide with nickel hydrate and ozonating the resultant mixture.

Description

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~0~0237 METHOD OF PREPAR ING STABLE NiOOH
BACKGROUND OF THE INVENT ION
1. Field of the Invention - This invention relates to a method for preparing stable NiOOH by mixing an alkali metal hydroxide with a nickel hydrate and ozonating the resultant mix-ture. More particularly, the nickel hydrate is mixed with po-tassium hydroxide, sodium hydroxide, lithium hydro~ide, rubidium hydroxide or cesium hydroxide and the resultant mixture is then dry ozonated. The resultant stable NiOOH is a useful cathodic material in both primary and secondary batteries.

2. Description of the Prior Art - The nickel zinc couple has been the subject of extensive investigation and experi-mentation in the last several years. Recent work has indicated possible recharging of the system, and the proven long life capabilities of the nickel electrode combined with the high rate and energy density of the zinc electrode result in a practical high energy secondary battery. There has been, however, little commercial success in the area of primary nickel-zinc cells and the principal reason for this lack of success has been the in-stability of the nickel oxyhydroxide utilized as a cathodic material in such cells~ The form of nickel oxide ~enerally uti-lized in these primary cells has been trivalent nickel oxyhy-droxide which is commonly produced by such methods as the electro-chemical oxidation of nickel hydroxide and alkaline electrolyte based on KOH as the major component or the ozonation of nickel-II
hydroxide at a temperature of from 20 to 110C. Such tri~alent ......
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nickel oxyhydroxide will, however, when contacted with alkaline solutions, give off oxygen according to the following equation:
4 NiOOH + 2H20 = 4Ni(OH)2 + 2 This evolved oxygen has a detrimental effect on cell capacity and capacity maintenance and additionally may cause the cells in which it is used to bulge or even explode.
It has recently become known that high-valency amor-phous nickel oxides could be stabilized at their high-valent state and could be successfully exploited faradàically thus per- ¦
mitting their use as a cathodic material in primary cells. Tetra~
valent nickel oxyhydroxide is now recognized as satisfying the requirements for use as a cathodic material in primary cells.
It has heretofore been disclosed that a stable tetra-valent nickel oxyhydroxide can be prepared electxochemically; see for example Tuomi, Journal of the Electrochemical Society, January 1965, pages 1 to 12. Tuomi in this article discloses the preparation of "tetravalent nickel" by charging crystalline Ni(OH)2 at 125 milliamps for 17 days in a suitable electrolyte.
A novel method has now been discovered for the prepara tion of stable tetravalent nickel oxyhydroxide which tetravalent nickel oxyhydroxide is useful as a cathodic material in both primary and secondary batteries.
~' ~ SUMMARY O~ THE INVENTION
., This invention is directed to a method for preparing stable tetravalent nickel oxyhydroxide by mixing an alkali metal hydroxide with nickel hydrate and dry ozonating the resultant mixture.

DESCRIPTION OF-THE DRAWINGS
1. Figure 1 is a graphic representation of the gassing rate of the stable nickel oxyhydroxide depolarizer prepared according to the method of this invention plotted against the time in days.
2. Figure 2 is a graphic representation of the gassing rate of nickel oxyhydroxide depolarizer to which the metal hydroxide has been added subsequent to the ozonation of the nickel hydrate plotted against the time in days.

DESCRIPTION OF THE INVENTION
A novel method has now been discovered for the preparation of stable tetravalent nickel oxyhydroxide which is an effective and efficient cathodic material for use in both primary and secondary batteries. If x in the formula -Ni20XH2O- (nickel oxyhydroxide) is 3.0, the product is trivalent.
If x in the formula is more than 3.0 then the product is at least partially converted to the tetravalent state. Ideally, a product wherein the value of x is 4.0, i.e., the entire compound is in the tetravalent state. This is, however, the "ideal" state and for the purposes of this invention the term tetravalent shall mean nickel oxyhydroxide wherein the value of x is more than 3Ø
In the process of this invention, a dry alkali metal hydroxide is mixed with the dry nickel hydrate, i.e., Ni(OH)2, and the resultant mixture is dry ozonated to produce stable tetravalent nickel oxyhydroxide.

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, ' , ~: : ' , ~ ' ;2 37 The dry nickel hydrate is readily available ccmmercially. By the term dry aIkali metal hydroxide as used herein is meant a dry hydroxide of potassium, sodium, lithium, cesium, rubidium and mixtures thereof, potassium hydroxide being the preferred material. These metal hydroxides often contain bound water and for the purpose of this patent will be used as supplied by the manufacturers in a solid form. The amount of metal hydroxide mixed with the nickel hydrate is from about 5 to about 40 wt.
percent based on the weight of the dry nickel hydrate. Depending upon the ; particular alkali metal hydroxide utilized in the preparation of the stable nickel oxyhydroxide, the useful concentration range for each of the metal hydroxides listed above are as follows:
Potassium hydroxide about 5 to about 40 wt percent Sodium hydroxide about 5 to about 30 wt percent Cesium hydroxide about 5 to about 40 ~t percent Rubidium hydroxlde about 5 to about 40 wt percent Lithlum hydroxide about 5 to about 20 wt percent.
Thus this invention seeks to provide a method for preparing a stable tetravalent nickel oxyhydroxide having the formula N120X.H20 wherein x is greater than 3.0 and less than 4.0 which comprises mixing nickel hydrate with an alkali metal hydroxide and dry ozonating the mixture, wherein the constitution of, and quantity based on the weight of the nickel hydrate of alkali metal hydroxide is chosen from one of from 5% to 40% potassium hydroxide; from 5% to 40% of cesium hydroxide; from 5% to 40% of rubidium hydroxide; from 5% to 30% of sodium hydroxide and ~rom 5% to 20% of lithium hydroxide.

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The nickel hydrate and alkall metal hydroxide may be mixed by -any method kncwn in the art. For example, the dry nickel hydrate may be placed in a ceramic ball-mill and pellets of the selected alkali metal hydroxide may be ground into fine powder, e.g., in a mortar and pestle, and the ground metal hydroxide powder may be added to the nickel hydrate in the ball-mill. The mixture could then be ball-milled for about 30 mlnutes or until a fine pc~der is produced. The resultant fine - 4a -' ~ B

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powder may then be passed through a screen, e.g., 50 mesh, to I eliminate large particles prior to ozonation.
- 1~ The mixture obtained above would then be dry ozonated by an appropriate method, for example, the mixture could be transferred from the ball-mill to an Erlenmeyer flask and the flask could be rotated by a small motor while ozone is passed over the mixture in the rotating flask. The ozone oxidizes the nickel hydrate-metal hydroxide mixture into nickelic oxyhydroxide "nickelic oxide" as evidenced by the immediate change of the green Ni(OH)2 into black NiOOH "Ni203 . H20" according to this reaction: 03 + 2 Ni(OH)2 2 NiOOH + H20 + 2 Continued ozonation leads to the formation of black and gray tri and tetravalent mixture of the nickelic oxide. At the end of ! I the ozonation process, most of the nickel hydrate is converted ¦ into gray tetravalent nickelic oxide Ni(OH)4 "NiO2 2 H20"
accordiDg to this reaction: ¦
., ~ 03 + 2 NiOOH + 3 H20 2 NiO2 2 H20 + 2 The preæence of the metal hydroxide is beneficial for this reaction to proceed as shown in Table 1.

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~050237 Table I: E~fect of KOH Addition and Time of Ozonation on the ~ Formation o~ Tri and Tetravalent Nickeli~ Oxide I Valency of Nickel (x) in Ni20X
End Product Ni(OH)l 2 NI(OH) -KOH2 Starting Starti~g Material Material Time o~ Ni20X where Color Ni20X where Color Ozonation of End of End ~Hrs) x = Product x t Product

3 2.2326 Black 2.1070 Black 6 2.4680 Black 2.2480 Black 12 2.7462 Black 2.7504 Black 24 2.9482 Black 3.0942 Black-Gray 36 2.9500 Black 3.2022 Gray 48 2.9004 Black 3.5202 Gray , 72 2,9801 Black 3.5700 Gray lThree hundred grams o~ Ni(OH)2 are ball-milled in a ceramic ball-mill and passed through 50 mesh screen before ozonation.
Ni~ety grams oi' KOH (85% KOH, 15% H20) are mlxed with 300 grams , o~ Ni(OH)2 in a ceramic ball-mill and passed through 50 mesh screen before ozonation.
The ozonation is continued until the mixture becomes ¦ gray in color indicatlng the attainment o~ a tetravalent state wherein the mean valency o~ the oxide exceeds 3.00. Ozonation ¦ may be conducted at room temperature, however, i~ it is desired ¦ to ozonate at cool temperature, the rotating ~lask may be immersed ¦ in a cold bath of running water. The resultant product is ¦stable tetravalent nickel oxyhydroxide, which may be used ef~ec-¦ tively in cathode prepa~ation for both primary and secondary ¦ batteries.
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~L~S~)23~7 Size 725 and 825 primary cells could be prepared for example by incorporating into a typical cell of the appropriate dimensions, the cathode utilizing the stable nickel oxyhydroxide prepared according to the method of this invention. Such a cell has a two-part container comprising an upper section or cap which houses the negative electrode or anode and the lower section or cup which houses the positive electrode or cathode.
Useful anode material include cadmium, indium, zinc, magnesium, aluminum, titanium and manganese, cadmium, indium and zinc being preferred and gelled or semi-gelled zinc being st preferred. The bottom cup may be made of any suitable material such as nickel-plated steel, and the cap may likewise be made of any suitable material known in the art such as tin-plated steel.
The cap is insulated from the cup by means of an insulating and sealing collar which may be made of any suitable electrolyte resistant material, such as high-density polyethylene or neoprene and it may be integrally molded around the edges of the cap for insulating the cap from the can and also to constitute an airtight enclosure. The negative electrode is separated from the positive electrode by means of an electrolyte absorbent layer and a separator. The electrolyte absorbent layer may be made of electrolyte resistant highly absorbent substances such as matted cotton fibre. Such material is available commercially for example under the trademark "Webril"*. The separator layer may be any suitable semi-permeable material such as "Viskon"* or "Dexter"* regenerated cellulosic material.

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' . ' ' ' ' ' , ' ' . ' - ' ',. '" '' ' ','.' ~ , .' ', ,'" ,', ', ' ' " ' ' ' '~', ' ' ~ " ' "' ", ' ' ' - '' ` ' ' ' . ' 3~7 A suitable cathode may be selected utilizing a stable nickel oxyhydroxide prepared according to the method of this invention. The particular cathode prepared will be dependent upon the type of cell being made and the use to which it is to be put. For example, in a typical 725 or 825 cell five parts of stable nickel oxyhydroxide may be dry mixed with one part of a carbon material, e.g., graphite for increasing the mixed conductivity. To that dry mix may be added 1% "Teflon"* (Whitcon-8"*) to serve as a binder and a lubricant and 7.5% electrolyte prewet of 50%
potassium hydroxide. These components could be mixed well in for example a Patterson-Kelly* blender or Abbe* mixer or any other mixing apparatus.
After the mix becomes homogeneous, the cathode mix can be pelletized on appropriate apparatus. A pellet thus prepared could then be inserted into the lower section or cup of the cell where it would function as a positive electrode or cathode.
EXAMPLBS
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The following 0xamples are intended to be merely illustrative of the invention and not in limitation thereof. Unless otherwise indicated, , all quantities are by weight.
Example 1:
Samples of nickel hydrate tNi(OH)2) (total 50 grams) con-taining 1% Co(OH)2 were prepared. Potassium hydroxide pellets were ground into fine powder and added to each nickel hydrate sample in the amount of ` 1, 5, 10, 15, 20, 25 and 30% by weight. The material was then ball-milled ; for 15 minutes and then ozonated for three hours at cool temperatures, i.e., about 15 C in a Welsbach ozonator Model T-408*.

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-5023'~ 1 Additional nickel hydrates samples were prepared and "
ozonated as above hut without the addition of the potassium hydroxide. After ozonation, potassium hydroxide was added to the NiOOH as above in the amount of 1, 5, 10, 15, ~0, 25 and 30% by weight.
The ozonated mixtures prepared above were tested for gassing by placing one gram of each sample in a separate 12cc centriiuge tube and filling the rest of the tube with 50% KOH.
The tubes were placed in a glycol bath maintained at a constant temperature of 145. Triplicate tests were made on each sample.
Gassing was observed by measuring the height of KOH solution and a pipette stoppered over the centrifuge tube. Gassing rates were expressed in terms of cc of gas for one gram of material per day on test. Moisture determinations were done by a Cenco moisture balance.
Data in Table ~ below indicate that the KOH addition in amounts of 10% or greater before ozonation produced an ex- ~
tremely stable nickel oxyhydroxide with greatly reduced gassing.¦
The total gas collected for the untreated gram control was 3.06 cc/gm of nickel oxyhydroxide after one week on test.
When the KOH was added to nickel oxyhydroxide after ozonation, some reduction in gassing of the nickel oxyhydroxide was obtained. For example, the total gas in a week was 1.97, 1.45 and 1.10~ cc/gm for 10, 15 and 20% KOH additives, respectiveL
~y. Figures 1 and 2 show these effects.
Surprisingly, however, concentrations of 10 to 30%
KO~d added eiore o~onation ~cc~rding to the ~ethod oi' the prcsent _ g_ ., ~~ ' '1 ; , ~ , ~i)5~23'~
invention were unexpectedly effective in reducing gassing of the nickel o:gyhydroxide. For example~ the total gas evolved in a week was ,45, .20 and .15 ~c/gm for 10, 15 and 20% KOH additives~
respectively. See Figures 1 and 2 for graphic representations of these effects.
Table 2: Gassing Rates of NiOOH Treated with Various Amounts of KOH before and after Ozonation i Total Gas ¦ KOH Time of KOH Evolved at %
% Addition 145F (cc/gm/wk) Moisture 1 Before Ozonation 2.36 1.8 Before Ozonation 1.10 4.8 ¦ 10 Be~ore Ozonation .45 7.2 ¦ 15 Before Ozonation .20 9.4 1 20 BeIore Ozonation ,15 11.0 ¦ 25 Before Ozonation .23 11.2 Before Ozonation .17 12.0 1 After Ozonation 2.61 1.7 AIter Ozonation 1.97 4.2 , 10 After Ozonation 1.45 6.2 ¦ 15 After Ozonation 1.10 8.0 ¦ 20 After Ozonation 1.45 9.2 j 25 After Ozonation 1.35 10.4 After Ozonation 1.23 11.4 0 Control 3.06 1.4 ~.
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31.050~:37 Example 2:
Cells size 725 were constructed and tested. Each cell has an outside diameter of .736 - .738 inches, a height of .210 -.230 inches and a volume of .095 cubic inches. The cell has a two part container comprising an upper section or cap which houses the neg~tive electrode or anode and a lower section or cup which houses positive electrode or cathode. The bottom cup is made of nickel plated steel and the cap is made of tin plated steel. The cap is insulated from the cup by means of an insula-ting and sealing collar of polyethylene and is integrally molded around the edges of the cap for insulating the cap from the cap and also to constitute airtight enclosure. The negative electrod of the cell comprises a gelled or semi-gelled zinc. The zlnc ~ e~ectrode is separated ~rom the positive electrode by means of ¦ an electrolyte absorbent layer and a separator. The electrolyte ¦ absorbent layer is made of electrolyte resistant, highly absor-bent matted cotton fibres. The separator layer ls Viskon. The depolarizer was inserted into the cell in pellet form, one pellet per cell.
The dry cathode mix consisted of:

¦ 5 parts nickel oxyhydroxide (NiOOH) 1 part graphite and to that dry mix the following were added:

1% "Teflon" (Wh~tcon-8") to serve as a binder and a lubricant 7.5% ~weight %~ of a 50% ~OH - 50% H2O solution The above components were mixed well in a Patterson-Kelley blender and after the mix became homogeneous, pellets were made of the cathode mix on suitable pelletizing apparatus. Each pellet weighed 1.69 + or - .01 gram. See Table 3 below for test results.

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:` lOS02~7 As can be seen from the data above, primary cells utilizing tetravalent NiOOH depolarizer prepared according to the method of the inventi on (2, 3, 4 and 5) display unexpectedly reduced cell expansion. Potassium and sodium hydroxides are pre-;
ferred metal hydroxides because of the high Ilash amperage and reduced impedance resulting in cells. Using hydroxides as in 6 I and 7 resulted in trivalent NiOOH that showed severe expansion of cells at elevated temperature (145F/l wk.).
Example 3:
¦I Cells size 825 were constructed in the same manner as the 725 size cells of Example 2 except the f ollowing dimen-sions were different:

I Outside Cell Diameter: .900 - .905 inches (22.86-22.99 mm~
Cell Height: .218 - .228 inche8 (5.54-5.79 mm) ¦ Volume: .116 cubic inches (1.90 cubic cm) ¦~ Weight: 3 ounces (8.50 grams) Each depolarizer pellet weighed 1.79 + or - .Ol gram.
See Table 4 below for test results.
, I Table 4: 825 Size Cells In all instances Ni(OH)2 was ozonated to NiOOH in preparation of the cell depolarizer, but cells tested varied in that the follow-iDg various additional depolaris;er preparation steps were ta;ken:

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~S~237 Control 15% 15% 15% 15%
No NaOH KOH Be(OH)2 Ca(OH)2 Addition Added Added Added Added Initial cell capacity 1~2 216 229165 182 to O.90V cut-off voltage : I Percent capacity re- 80.0 87.5 91.0 -- --: I tention at 4 wks j at 113-50%
Il Percent capacity re- 55.0 67.5 75.5 -- -- j i¦ tention at 12 wks l~ at 113-50%
: ll Percent capacity re- 81.5 92.0 93.0 67.0 70.0 tention at 2 yrs at RT (70F) Cell ht. increase at .0080 .0005 .0030 -- --J 4 wks at 113 50%
(inches) Cell ht. increase at ,0150 .0005 .0035.018 .0170 12 wks at 113-50%
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A Cell ht. incr0ase at .0100 .0005 .0020.0120 .0130!
2 yrs. at RT (70F) , (inches) .~ (1) 113-50% - at 113F and 50% relative humidity s (2) Cells discharged at 300 ohms 16 H/D
As can be seen from the data above, primary cells uti-lizing a NiOOH depolarizer prepared according to the method of this invention, i.e., 15% NaOH or 15% KOH added before ozonation, ~ display unexpectedl~ low degrees of cell bulging and good capacit : retention as a result of the unexpected NiOOH stability in the , cell.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing a stable tetravalent nickel oxyhydroxide having the formula Ni2OX.H2O wherein x is greater than 3.0 and less than 4.0 which comprises mixing nickel hydrate with an alkali metal hydroxide and dry ozonating the mixture, wherein the constitution of, and quantity based on the weight of the nickel hydrate of alkali metal hydroxide is chosen from one of from 5% to 40% potassium hydroxide; from 5% to 40% of cesium hydroxide; from 5% to 40% of rubidium hydroxide; from 5% to 30% of sodium hydroxide and from 5% to 20% of lithium hydroxide.

2. A method according to claim 1 wherein the alkali metal hydroxide is potassium hydroxide.

3. A method according to claim 1 wherein the alkali metal hydroxide is sodium hydroxide.

4. A method according to claim 1 wherein the alkali metal hydroxide is lithium hydroxide.

5. A method according to claim 1 wherein the dry ozonation is carried out at room temperature.

6. A method according to claim 1 wherein the ozonation is carried out at about 15°C.