U.S. patent number RE34,752 [Application Number 08/005,157] was granted by the patent office on 1994-10-04 for alkaline battery with a nickel electrode.
This patent grant is currently assigned to Yuasa Corporation. Invention is credited to Heiichi Hasegawa, Masahiko Oshitani, Hiroshi Yufu.
United States Patent |
RE34,752 |
Oshitani , et al. |
October 4, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Alkaline battery with a nickel electrode
Abstract
A nickel electrode for an alkaline battery comprises a porous
alkaline-proof metal fiber substrate used as a current collector,
and active material for the electrode. The active material includes
nickel hydroxide powder active material, to which zinc or magnesium
is added at a rate in a range of .[.3.]..Iadd.1.Iaddend.-10 wt % or
1-3 wt %, respectively. The zinc and magnesium is in a solid
solution in crystal of the nickel hydroxide, and the active
material forms principle compound of paste, which is loaded in the
electrode.
Inventors: |
Oshitani; Masahiko (Takatsuki,
JP), Hasegawa; Heiichi (Takatsuki, JP),
Yufu; Hiroshi (Takatsuki, JP) |
Assignee: |
Yuasa Corporation (Takatsuki,
JP)
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Family
ID: |
26499707 |
Appl.
No.: |
08/005,157 |
Filed: |
January 15, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
358118 |
May 30, 1989 |
04985318 |
Jan 15, 1991 |
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Foreign Application Priority Data
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Jul 19, 1988 [JP] |
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63-180047 |
Oct 18, 1988 [JP] |
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63-262047 |
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Current U.S.
Class: |
429/223;
252/182.1 |
Current CPC
Class: |
H01M
4/52 (20130101); H01M 4/32 (20130101); Y02E
60/10 (20130101) |
Current International
Class: |
H01M
4/32 (20060101); H01M 4/52 (20060101); H01M
004/32 () |
Field of
Search: |
;429/223 ;252/182.1 |
References Cited
[Referenced By]
U.S. Patent Documents
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4016091 |
April 1977 |
Jackovitz et al. |
4399005 |
August 1983 |
Fritts et al. |
4628593 |
February 1986 |
Fritts et al. |
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Other References
Oshitani et al, Masahiko, "A study on the swelling of a sintered
nickel hydroxide electrode" Journal of Applied Electrochemistry, 16
(1986) pp. 403-412 (Month unavailable)..
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Primary Examiner: Kalafut; Stephen
Attorney, Agent or Firm: Armstrong, Westerman, Hattori,
McLeland & Naughton
Claims
What is claimed is:
1. Active material for a nickel electrode comprising:
nickel hydroxide powder active material; and
zinc or magnesium which is added to said active material at a rate
in a range of .Badd..[.3.]..Baddend..Iadd.1.Iaddend.-10 wt% or 1-3
wt%, respectively, said zinc and magnesium being in a solid
solution in crystal of said nickel hydroxide, and in distribution
of pore radii calculated from .[.the.]. a desorption side at
nitrogen adsorption isotherm of said powder, development of pore
having a radius of 30 .ANG. or more being prevented, and an entire
pore volume rate being controlled at 0.05 ml/g or less.
2. Active material as claimed in claim 1 wherein said active
material powder, which includes nickel hydroxide and .[.a small
amount of.]. said zinc or magnesium, is produced by deposition of
sulfate solution thereof as starting material in aqueous solution
having pH 11-13 controlled by caustic soda or caustic potash
together with ammonium sulfate.
3. A nickel electrode comprising;
a porous alkaline-proof metal fiber substrate used as a current
collector; and
active material for the electrode;
said active material including;
nickel hydroxide powder active material, to which zinc or magnesium
is added at a rate in a range of
.Badd..[.3.]..Baddend..Iadd.1.Iaddend.-10 wt% or 1-3 wt%,
respectively, said zinc and magnesium being in a solid solution in
crystal of said nickel hydroxide; and
said active material forming principle compound of paste, which is
loaded in said electrode. .[.4. A nickel electrode as claimed in
claim 3 wherein a small amount of cobalt in a solid solution exists
in addition to said
zinc or magnesium..]. 5. A nickel electrode as claimed in claim 3
wherein divalent cobalt compound, which forms cobalt complex ion
when .[.dissolven.]..Iadd.dissolved .Iaddend.in alkaline aqueous
solution, is
added to said active material powder at a rate in a range of 5-15
wt%. 6. A nickel electrode as claimed in claim .[.3.]. .Iadd.5
.Iaddend.wherein conductive additives are not included, and
.[.the.]. conductivity between said .[.nickel.]. .Iadd.metal
.Iaddend.fiber .Iadd.substrate .Iaddend.and particles of said
active material is substantially maintained only by
virtue of said cobalt compound additive. 7. An alkaline battery
assembled with a nickel electrode as recited in claim .[.2.].
.Iadd.3 .Iaddend.without formation, maintained under standing
condition one or more days after supplying electrolyte therein, and
initially charged after cobalt compound additive is completely
dissolved and deposited.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an alkaline battery with a nickel
electrode, and particularly to the alkaline battery and the nickel
electrode as well as active material for the nickel electrode.
(2) Description of the Prior Art
Alkaline batteries commonly used are called as sintered batteries,
and have structures in which nickel hydroxide is loaded in a
micro-porous substrate formed of a perforated steel sheet to which
nickel powder is sintered. The electrode of this type requires
repetition of active material loading processes for several times,
resulting in complicated and thus expensive manufacturing process.
Further, since the porosity of the substrate is restricted, loading
density of the active material, is low, and thus an energy density
of the electrode can be approximately 400 mAh/cc at most.
In attempt to improve this, electrodes other than that of the
sintered type have been broadly developed. In an example of them,
graphite powder of about 20-30 wt% (weight percentage) is mixed as
conductive additive with nickel hydroxide powder coated with cobalt
hydroxide, and then, this mixture is formed into a sheet-like shape
and is fixedly pressed to a nickel plate to form the electrode.
Since the above conductive additive itself does not contribute to
capacity of the electrode, it reduces capacity density, and causes
generation of a large amount of carbonate due to decomposition of
the graphite. Therefore, this electrode can not be used in
batteries having small amount of electrolyte, such as sealed nickel
cadmium batteries. In order to overcome the above disadvantages,
manufacturers start to provide pasted nickel electrodes for
practical use, in which a metal fiber substrate having a high
porosity of about 95% is used. In these electrodes, CoO powder,
which forms conductive network for the active material, is added to
the nickel hydroxide powder active material which is produced from
nickel sulfate aqueous solution and sodium hydroxide aqueous
solution, and viscous aqueous solution of carboxymethyl-cellulose
is further added thereto to form paste, which is loaded in the
fiber substrate. This conductive network forms current paths which
are more effective than those by graphite, does not decompose, and
thus does not produce carbonate. This electrode is less expensive
than the sintered electrode, and has high energy density of about
500 mAh/cc.
However, as weights of portable electronics equipment have recently
been reduced, the high energy density of about 600 mAh/oc is
required in the market. In order to comply with this requirement,
the density of the nickel hydroxide power itself must be increased,
because the porosity of the substrate is limited. The nickel
hydroxide powder of the high density has been used as a part of
material for parkerizing steel plates. In the manufacturing
thereof, nickel nitrate or nickel sulfate is dissolved in weak
basic ammonia acqueous solution and is stabilized as tetra-amine
nickel (II) complex ion, and the nickel hydroxide is deposited
while adding sodium hydroxide aqueous solution to it. This
deposition is slowly performed so as to prevent development of
voids in particles.
Since this method does not perform random deposition, as is done in
the conventional method it can produce the nickel hydroxide having
good crystallinity with less grain boundary, i.e., less pore
volume, and thus a high density.
However, due to the unique characteristics, this powder causes some
problem when used as the active material for the battery as it
is.
For example, the charge-discharge reaction of the nickel hydroxide
electrode is performed by free movement of proton in the crystal of
the nickel hydroxide. However, due to the high density of the
nickel hydroxide and thus to the high compactness of the crystal,
the free movement of the proton in the crystal is restricted.
Further, since the current density increases in accordance with the
reduction of the specific surface area, a large amount of higher
oxide .gamma.-NiOOH may be produced, which may cause fatal
phenomena such as stepped discharge characteristics and/or
swelling. The swelling due to the production of .gamma.-NiOOH in
the nickel electrode is caused by the large change of the density
from high density .beta.-NiOOH to low density .gamma.-NiOOH. The
inventors have already found that the production of .gamma.-NiOOH
can effectively be prevented by addition of a small amount of
cadmium in a solid solution into the nickel hydroxide. However, it
is desired to achieve the substantially same or more excellent
effect by utilizing additive other than the cadmium from the
viewpoint of the environmental pollution.
Accordingly, it is an object of the invention to provide active
material for nickel electrode, in which the density of the nickel
hydroxide is increased, and the production of .gamma.-NiOOH, which
may be caused due to the increased density, can be prevented by
less poisonous additive, so that the useful life may be extended
and the utilization factor of the active material may be improved.
It is also an object of the invention to provide a nickel electrode
utilizing said active material and an alkaline battery utilizing
it.
SUMMARY OF THE INVENTION
According to the invention, active material for a nickel electrode
comprises nickel hydroxide powder active material, and zinc or
magnesium which is added to said active material at a rate in a
range of .[.3.]..Iadd.1.Iaddend.-10 wt % or 1-3 wt%, respectively,
said zinc and magnesium being in a solid solution in crystal of
said nickel hydroxide, and in distribution of pore radii calculated
from the a desorption side at nitrogen adsorption isotherm of said
powder, development of pre having a radius of 30 .ANG. or more
being prevented, and an entire pore volume rate being controlled at
0.05 ml/g or less.
Further, according to the invention, a nickel electrode comprises a
porous alkaline-proof metal fiber substrate used as a current
collector; and active material for the electrode; said active
material including; nickel hydroxide powder active material, to
which zinc or magnesium is added at a rate in a range of
.[.3.]..Iadd.1.Iaddend.-10 wt% or 1-3 wt%, respectively, said zinc
and magnesium being in a solid solution in crystal of said nickel
hydroxide; and said active material forming principle compound of
paste, which is loaded in said electrode.
The nickel hydroxide having a high density, i.e., having a minimum
inner pore volume, causes the production of a large amount of the
higher oxide .gamma.-NiOOH. However, the inventors have found that
metal ion of different sorts, particularly zinc ion or magnesium
ion located in the crystal of the nickel hydroxide can suppress
production of .gamma.-NiOOH.
At the outside of the nickel hydroxide, in order to improve the
conductivity between the active material particles and the current
collector, the cobalt compound powder may be mixed therewith and
dissolved in the battery electrolyte, and then maybe deposited
between the current collector and the active material particles by
virtue of the reaction of (HCoO.sub.2
--.fwdarw..beta.-CO(OH).sub.2) prior to charging. When charged, by
virtue of electrochemical oxidation by a reaction of
(.beta.-CO(OH).sub.2 .fwdarw.CoOOH), it changes into highly
conductive cobalt oxyhydroxide, whereby the flow of the electron
can flow smoothly between the nickel fiber of the current collector
and the particles of the nickel hydroxide, resulting in increase of
the utilization factor. This reaction is illustrated in a modelled
form in FIG. 1. As shown therein, the important feature of this is
that it is kept standing after the electrolyte is supplied, and the
cobalt compound powder electrode is dissolved so as to interconnect
the current collector nickel fiber and the active material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating dissolving of cobalt
compound in modelled form;
FIG. 2 is a diagram illustrating a relationship between pH of
deposition solution, particle pore volume and ratio of
.gamma.-NiOOH:
FIG. 3 is a diagram illustrating a relationship between specific
surface area and pore volume of nickel hydroxide;
FIG. 4 is a diagram illustrating curves of prore size distribution
of the conventional nickel hydroxide powder and that according to
the invention,
FIG. 5 is a diagram illustrating a relationship between standing
conditions and an active material utilization factor;
FIG. 6 is a diagram illustrating a relationship between various
conditions of nickel hydroxides and an active material
utilization;
FIG. 7 is a diagram illustrating a relationship between an addition
ratio of CoO, an active material utilization factor and a energy
density per volume of a plate;
FIG. 8 is a diagram illustrating a relationship between an addition
ratio of zinc and a ratio of NiOOH;
FIG. 9 is a diagram illustrating a ratio of .gamma.-NiOOH at the
end of discharge of various conditions of nickel hydroxides;
FIG. 10 is a diagram for comparing discharge voltage
characteristics of the electrode including a large amount of
.gamma.-NiOOH and that according to the invention;
FIG. 11 is a diagram illustrating a relationship between the active
material, charge/discharge temperature and active material
utilization;
FIG. 12 is a diagram illustrating a relationship between various
conditions of cobalt compound additive and the active material
utilization;
FIG. 13 is a diagram illustrating pore size distribution of the
conventional nickel hydroxide powder and that according to the
invention;
FIG. 14 is a diagram illustrating X-ray diffraction patterns at the
end of the charge of various conditions of magnesium-added high
density powder;
FIG. 15 is a diagram illustrating a relationship between the
addition ratio of magnesium and the ratio of .gamma.-NiOOH;
FIG. 16 is a diagram illustrating the ratio of .gamma.-NiOOH at the
end of discharge of the various conditions of nickel hydroxide;
FIG. 17 is a diagram illustrating a relationship between the ratio
of .gamma.-NiOOH and thickness of the electrode when the active
material including various conditions of additives are used in the
electrodes and they are overcharged;
FIG. 18 is a diagram illustrating charge potential characteristics
of the electrodes including various amount of magnesium
additives;
FIG. 19 is a diagram illustrating a relationship between the
magnesium addition ratio and the active material utilization;
and
FIG. 20 is a diagram illustrating discharge potential
characteristics of the electrodes including various amount of
magnesium additives.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the invention will be detailed
hereinafter.
Ammonium sulfate is added to aqueous solution of nickel sulfate to
which a small amount of zinc sulfate was added to stabilize ion of
nickel and zinc as ammine complex ion.
This solution is dropped into sodium hydroxide aqueous solution,
while rapidly stirring it, to gradually decompose the complex ion
and thus deposit and grow nickel hydroxide particles including the
zinc in a solid solution state. This deposition is gradually
performed in the weak alkaline solution of about pH 11-13 and the
temperature in a range of about 40.degree.-50.degree. C. Depending
on the pH of the deposition solution, the nickel hydroxide
particles having various characteristics can be obtained.
In FIG. 2, there is shown a relationship between pore volume of
powder consisting of only nickel hydroxide and ratio of
.gamma.-NiOOH.
As the pH is lower, the pore volume becomes smaller, and thus the
powder has the high density. On the other hand, there is tendency
that as the powder is produced at lower pH, more .gamma.-NiOOH is
produced. A region satisfying the above two factors is a hatched
region between the respective inflection points, which is in a
range of about pH 11-13.
FIG. 3 illustrates a relationship between the pore volume and
specific surface area. As the pH of the deposition solution is
changed, the pre volume of the nickel hydroxide changes, and at the
same time, the specific surface area changes. Specimens A-E
consists of only the nickel hydroxide, a specimen F contains
additive of zinc in the solid solution, and a specimen G consists
of only the nickel hydroxide produced by the conventional
method.
In the above conventional method, the nickel hydroxide particles
are deposited in alkaline aqueous solution of high concentration of
pH 14 or more, without adding ammonium sulfate.
Each specimen shows the random particle deposition and the tendency
that the pore volume in the particle increases in accordance with
the increase of the specific surface area. Thus, there is
correlation between the specific surface area and the pore volume,
and independently of compound, the material having less pore volume
and thus high density has less specific surface area.
FIG. 4 illustrates dispersion of pore radii of the nickel hydroxide
according to the conventional method and the high density nickel
hydroxide according to the invention, which is obtained from a
desorption side at nitrogen absorption isotherm.
The nickel hydroxide GI according to the conventional method, is
deposited by dropping the nickel sulfate solution into the sodium
hydroxide aqueous solution having a high concentration, of which pH
is 14.5 and the temperature is about 50.degree. C.
Pore exists at a large amount in a wide range of the pore radius
from 15-100 .ANG. at the specific surface area of about 65 m.sup.2
/g therein. The particle has the pore volume of 0.15 ml/g, which is
as much as 30%-40% of the particle volume (0.41 ml/g), and thus has
a large void rate. In contrast to this, the nickel hydroxide F
according to the invention has the small pore volume of 0.03 ml/g,
which is only a quarter of that of said particle GI. This indicates
that the particle F(Zn) the density higher by 20%-30% than the
particle GI. This indicates that the specific area and the void
volume should must be as small as possible to obtain the active
material of the high density. The nickel hydroxide is mixed with a
small amount of powder of cobalt compound such as CoO,
.alpha.-Co(OH).sub.2, .beta.-Co(OH).sub.2, or cobalt acetate, which
produces Co(II) complex ion when dissolved in alkaline electrolyte.
Then, aqueous solution including carboxymethyl-cellulose of 1% is
added at the ratio of 30 wt% thereto to produce flowable paste
liquid. A predetermined amount of this paste liquid is loaded into
alkaline-proof metal fiber substrate, e.g., nickel fiber substrate,
having porosity of 95%, and a nickel electrode is formed by drying
the substrate after the loading.
In order to recognize the active material utilization factor as
well as the ratio of .gamma.-NiOOH by charge and discharge, a
battery is assembled, in which this nickel electrode and a cadmium
electrode are used with none-woven cloth polypropylene separator
therebetween, and potassium aqueous electrolyte having a specific
gravity of 1.27 is added thereto. After the adding of the
electrolyte, the battery is kept standing without supplying the
electric current at the corrosion potential of the mixed cobalt
compound, and interconnection is established in the nickel
hydroxide powder by .gamma.-Co(OH).sub.2. FIG. 5 illustrates a
relationship between the standing conditions of the nickel
electrode and the active material utilization in the battery which
includes the nickel hydroxide having the specific surface area of
65 m.sup.2 /g and CoO as the additive. With respect to the
condition for the standing, which is process for the formation of
the important conductive network, it can be seen that the high
utilization can be obtained in a shorter period as the
concentration of the electrolyte and the temperature increase. It
can also be seen that the amount of the dissolved CoO also
effectively functions. This is caused by the uniform dispersability
of CoO by the complete dissolution deposition of the additive,
i.e., by the formation of the more uniform network.
In FIG. 6, there is shown the relationship between the various
conditions of nickel hydroxides and the utilization of the active
material under the appropriate standing condition. The active
material consisting of only the nickel hydroxide represents a
proportional relationship between the specific surface area and the
active material utilization. This fact shows that the high or large
specific surface area is required for the high active material
utilization. This means that the low density active material having
the large pore volume is preferable in view of the aforementioned
result, and thus it is impossible to increase the energy density of
the electrode. However, the specimen F(Zn) including a small amount
of zinc added into the crystal of the nickel hydroxide shows the
high utilization which is substantially same as that of the
conventional powder GI, in spite of the fact that it has the small
specific surface area. The energy density per unit volume of the
plate is 504 mAh/cc in the conventional powder GI, and 620 mAh/cc
in the high density powder F(Zn), which is higher by 20% than the
conventional powder GI. This indicates the fact that a large amount
of the high density powder can be loaded in the substrate having
the same volume, as compared with the conventional powder. Since
the active material utilization factor is close to the theoretical
value, the pore volume of the high density active material powder
at the time of paste loading, which is required for satisfying the
energy density of 600 mAh/cc, must be 0.05 ml/g or less. This
effect by the addition of the zinc can be inferred to be caused by
the form of the crystal of the nickel oxyhydroxide, because a large
amount of .gamma.-NiOOH having low reversibility is produced when
it has a low utilization and a small amount of .gamma.-NiOOH is
produced when the zinc is added. For the reaction of the active
material, it is necessary to permit smooth movement of the electron
from the current collector to the surfaces of the active material
particles, and it is essential to form the network of the
conductive CoOOH particles in the isolated condition, in which they
exist on the particle surfaces without being solid-solved in the
nickel hydroxide, as described before. With respect to the CoO
additive forming this network, if the amount thereof is increased,
the active material utilization rate increases. Thus, although the
more additive can establish the more perfect network, there is a
tendency that the energy density of the plate decreases from the
value of about 15%, because the additive itself contributes only to
the conductivity, and neither practically charge nor discharge.
Correlation between the composition of the nickel hydroxide powder
and the ratio of .gamma.-NiOOH is inspected by a X-ray analysis of
the plate at the end of the charge, which has been performed at
high current density of 1C.
From FIG. 8, it can be seen that when the zinc (or magnesium) in
the solid solution is added to the crystal of the nickel hydroxide,
the ratio of .gamma.-NiOOH decreases in proportion to the increase
of the addition rate.
Although .gamma.-NiOOH can be more effectively suppressed when the
addition ratio is increased, excessively large ratio causes
isolation, resulting in reduction of the utilization factor.
The isolated zinc hydroxide exists, and mixture of the dissolved
zinc complex ion and cobalt complex ion is deposited in the course
of the dissolving and re-depositing of the cobalt oxide additive,
which deteriorates the conductivity, and thus the utilization. If
the zinc is added at the ratio of 10 wt% or more, it is not
solid-solved.
High density powder A without the zinc in FIG. 10 has a discharge
voltage different from that of the high density powder F(Zn), due
to production of a large amount of .gamma.-NiOOH, and represents
stepped discharge characteristics as shown in FIG. 10. As shown in
FIG. 8, the effect for preventing the production of .gamma.-NiOOH
is achieved by the addition of zinc of 3% or more, and
.gamma.-NiOOH completely extinguishes at the addition of 10%.
This effect of the zinc can be maintained even if different
element, e.g., cobalt, coexists in the solid solution. FIG. 11
illustrates a relationship between the active material,
charge-discharge temperature and active material utilization.
Further, in the material H, to which both the zinc and cobalt are
added in the solid solution, there is another advantage that the
charge performance is improved in a high temperature of about
45.degree. C., as compared with the material F(Zn) including only
the zinc. FIG. 12 illustrates a relationship of the active material
utilization with respect to the additives for forming the network
of CoOOH.
The reason that the order of the active material utilization is
CoO>.alpha.-Co(OH).sub.2 >.beta.-Co(OH.sub.2 is considered to
be based on the solubility in the electrolyte. That is;
.beta.-Co(OH).sub.2 is prone to be oxidized by the oxygen dissolved
in the supplied electrolyte into brown Co(OH).sub.3 having low
solubility. On the other hand, with respect to .alpha.-Co(OH).sub.2
it changes through .beta.-Co(OH).sub.2, i.e., .alpha.-Co(OH).sub.2
.fwdarw..beta.-Co(OH).sub.2), so that Co(HO).sub.3 is less prone to
be produced. With respect to CoO, Co(OH).sub.3 (this can be
represented by CoOH.sub.2) is not produced at all, and thus is
considered to be the most superior additive. Specifically, in view
of the solution speed, it is desirable to form the additive having
low crystallinity, which is heated and formed in hot inert
atmosphere at a temperature between 200.degree. C. and 800.degree.
C., using .beta.-Co(OH).sub.2 as starting material.
The electrode having loaded paste, which is formed by immersing the
nickel hydroxide powder in HCoO.sub.2 --ion and forming the cobalt
hydroxide layer on the surfaces of the particles, has the
utilization which is less than that of the electrode including CoO
powder mixed therein and is nearly same as that of the electrode
including .beta.-Co(OH).sub.2 powder mixed therein. Further, the
utilization is also investigated in another electrode. This
electrode includes powder which forms conductive CoOOH layer on the
surface of the oxyhydroxide powder, which is specifically formed by
removing nickel fiber, i.e., current collector, from electrode
including the CoO powder mixed therein after charging and
discharging it. This powder is re-loaded in a form of paste
thereon. This electrode is found to have the low utilization. This
indicates a very important matter. Thus, it is essential that the
conductive network (CoOOH) between the active material and the
current collector is formed in the manufactured electrode. If CoOOH
layer is pre-formed on the surfaces of the active material
particles, the perfect network can not be established. Therefore,
it is essential to provide a standing step for performing the
dissolving and re-deposition of CoO powder after the assembly of
the electrode in the battery, invention, using the CoO additive,
the utilization can be increased to a high value close to the
theoretical value by the dissolving and re-deposition process,
without using additional conductive material, so that the
conductive additive is unnecessary, and thus the formation of the
carbonate, which may be caused due to oxidation decomposition, can
be prevented, and it can be used in the electrode for the sealed
nickel cadmium battery.
Then, a second embodiment of the invention will be detailed
hereinafter.
Ammonium sulfate is added to aqueous solution of nickel sulfate to
which a small amount of magnesium sulfate was added to produce
ammine complex ion of nickel and magnesium.
This solution is dropped into sodium hydroxide aqueous solution,
while rapidly stirring it, to gradually decompose the complex ion
and thus deposit and grow nickel hydroxide particles including the
magnesium in a solid solution state. This deposition is gradually
performed in the weak alkaline solution of about pH II-13 and the
temperature in a range of about 40.degree.-50.degree. C. Depending
on the pH of the deposition solution, the nickel hydroxide
particles having various characteristics can be obtained.
The characteristics of this nickel hydroxide are same or similar to
those, which are previously described with reference to FIGS. 2 and
3.
FIG. 13 illustrates dispersion of pore radii of the nickel
hydroxide according to the conventional method and the high density
active material, i.e., the nickel hydroxide, including the
magnesium added thereto according to the invention for the
comparison of them.
The nickel hydroxide GII according to the conventional method, is
deposited by dropping the nickel sulfate solution into the alkaline
solution having a high concentration, of which pH is 14.5 and the
temperature is about 50.degree. C.
This exists at a large amount in a wide range of the pore radius
from 15-100 .ANG. at the specific surface area of about 66 m.sup.2
/g. The particle has the pore volume of 0.136 ml/g, which is as
much as 30%-40% of the particle volume (0.4 ml/g), and thus has a
large void rate. In contrast to this, the nickel hydroxide F(Mg)
according to the invention has the small pore volume of 0.028 ml/g,
which is only a quarter of that of said particle GII. The nickel
hydroxide is mixed with a small amount of powder of cobalt compound
such as CoO, .alpha.-Co(OH).sub.2, .beta.-Co(OH).sub.2, or cobalt
acetate as is done in the embodiment previously described, which
produces Co(II) complex ion when dissolved in alkaline electrolyte.
Then, aqueous solution including carboxymethyl-cellulose of 1% is
added thereto to produce flowable paste liquid. A predetermined
amount of this paste liquid is loaded into alkaline-proof metal
fiber substrate, e.g., a nickel fiber substrate, having porosity of
95%, and nickel electrode is formed by drying the substrate after
the loading.
In order to recognize the active material utilization as well as
the ratio of .gamma.-NiOOH by charge and discharge, a battery is
assembled, in which this nickel electrode is used as a counter
electrode to cadmium electrode with none-woven cloth polypropylene
separator therebetween. The utilization of this battery has been
investigated under the conditions, which are same as those
previously described with reference to FIGS. 5 and 6, and the
results same as those shown in FIGS. 5 and 6 are obtained.
Correlation between the various conditions of nickel hydroxides and
the ratio of .gamma.-NiOOH is inspected by the X-ray analysis of
the plate at the end of the charge, which has been performed at a
high current density of 1C. Peak of the X-ray analysis is
illustrated in FIG. 14.
As shown in FIG. 15, when the magnesium at the solid solution is
added to the crystal of the nickel hydroxide, the ratio of
.gamma.-NiOOH decreases as the amount of the additive
increases.
In FIG. 17, there is shown a relationship between the ratio of
.gamma.-NiOOH in the overcharged condition and the thickness of the
electrode. As the ratio of .gamma.-NiOOH increases, the thickness
of the electrode increases. Thus, in order to obtain the electrode
having long useful life, it is necessary to suppress the formation
of .gamma.-NiOOH. The addition of the magnesium can also be
effective to this suppression.
A feature of the solid solution addition of the magnesium is that
the discharge potential is increased to a large extent as shown in
FIG. 20. There is a tendency the the potential increases as the
addition ratio increases. On the other hand, as shown in the FIG.
8, the charge potential causes a competitive reaction of oxidation
of the active material and the evolution of the oxygen, resulting
in reduction of the capacity, as shown in FIG. 20, so that
excessive addition will cause disadvantage which can be prevented
in a range of 1-3 wt%. It is considered that the addition of the
magnesium causes distorsion in the nickel hydroxide crystal, by
which the smooth diffusion of the proton in the solid phase can be
achieved.
This effect of the magnesium can be maintained even if different
element, e.g., cobalt, coexists in the solid solution, as is
previously described with reference to FIG. 11.
Also in this second embodiment, although the metal fiber sintered
material is used as the substrate, other various materials may also
be used. Said effect obtained by the addition of the magnesium can
also be obtained in the nickel hydroxide having the high
crystallinity which is formed by various methods.
As described hereinabove, according to the invention, the density
of the nickel hydroxide is increased, and the formation of
.gamma.-NiOOH, which may be caused by the increase of the density,
is prevented by the additive having low toxicity. Therefore, the
present invention provides the active material for the nickel
electrode as well as the nickel electrode using it, which have the
long useful life and the high utilization of the active material,
and can also provide the alkaline battery employing them, and thus
the invention has high industrial value.
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