Note: Descriptions are shown in the official language in which they were submitted.
:
~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.
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37
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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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
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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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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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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
.~
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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Additional nickel hydrates samples were prepared and
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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
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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.
~ - 11-
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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%
~ (inches~ I
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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