U.S. patent application number 10/067472 was filed with the patent office on 2002-09-19 for nickel electrode active material for alkaline storage batteries and nickel positive electrode using the same.
Invention is credited to Hayashi, Kiyoshi, Ikoma, Munehisa, Morishita, Nobuyasu.
Application Number | 20020132166 10/067472 |
Document ID | / |
Family ID | 12587972 |
Filed Date | 2002-09-19 |
United States Patent
Application |
20020132166 |
Kind Code |
A1 |
Hayashi, Kiyoshi ; et
al. |
September 19, 2002 |
Nickel electrode active material for alkaline storage batteries and
nickel positive electrode using the same
Abstract
Disclosed is an active material for constituting a nickel
electrode for alkaline storage batteries which has a high
utilization at high ambient temperatures and therefore realizes a
battery of higher energy density and a longer cycle life. The
nickel electrode active material comprises a nickel hydroxide
powder prepared from nickel sulfate and contains SO.sub.4.sup.2- at
0.4 wt % or less in the crystal of the powder. The nickel hydroxide
is preferably solid solution nickel hydroxide incorporating therein
at least one element selected from the group consisting of cobalt,
cadmium, zinc and magnesium.
Inventors: |
Hayashi, Kiyoshi;
(Toyohashi-shi, JP) ; Morishita, Nobuyasu;
(Toyohashi-shi, JP) ; Ikoma, Munehisa; (Shiki-gun,
JP) |
Correspondence
Address: |
AKIN, GUMP, STRAUSS, HAUER & FELD, L.L.P.
ONE COMMERCE SQUARE
2005 MARKET STREET, SUITE 2200
PHILADELPHIA
PA
19103
US
|
Family ID: |
12587972 |
Appl. No.: |
10/067472 |
Filed: |
February 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10067472 |
Feb 5, 2002 |
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09255583 |
Feb 22, 1999 |
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6358648 |
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Current U.S.
Class: |
429/223 ;
252/182.1; 429/222; 429/229; 429/231.6 |
Current CPC
Class: |
Y10T 29/49108 20150115;
C01P 2006/80 20130101; Y02E 60/10 20130101; C01P 2006/40 20130101;
C01G 53/04 20130101; C01P 2002/74 20130101; H01M 4/32 20130101;
H01M 4/52 20130101; Y02E 60/124 20130101; H01M 10/345 20130101 |
Class at
Publication: |
429/223 ;
252/182.1; 429/222; 429/229; 429/231.6 |
International
Class: |
H01M 004/32; H01M
004/52 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 1998 |
JP |
10-040704 |
Claims
1. A nickel electrode active material for alkaline storage
batteries comprising a nickel hydroxide having a content of sulfate
ions in a crystal of nickel hydroxide of 0.4 wt % or less, wherein
the sulfate ions have been removed from the crystal of nickel
hydroxide with an alkaline solution having a pH of 13.0 to
14.0.
2. The nickel electrode active material according to claim 1,
wherein the nickel hydroxide is a solid solution nickel hydroxide
and incorporates at least one element selected from the group
consisting of cobalt, cadmium, zinc and magnesium.
3. A pasted nickel positive electrode for alkaline storage
batteries comprising a nickel hydroxide having a content of sulfate
ions in a crystal of nickel hydroxide of 0.4 wt % or less, wherein
the sulfate ions have been removed from the crystal of nickel
hydroxide with an alkaline solution having a pH of 13.0 to
14.0.
4. The pasted nickel positive electrode according to claim 3,
wherein the nickel hydroxide is a solid solution nickel hydroxide
and incorporates at least one element selected from the group
consisting of cobalt, cadmium, zinc and magnesium.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application claims the benefit of U.S. patent
application No.09/255,583, filed on Feb. 22, 1999, the disclosure
of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an active material for
constituting a nickel electrode for use in an alkaline storage
battery such as nickel-metal hydride storage battery,
nickel-cadmium storage battery and so on, and a nickel positive
electrode using the same.
[0003] With the current rapid and wide spread of information
equipment such as portable phone, PHS, notebook-type type personal
computer, etc., there is a serious demand for a secondary battery
that has a high energy density and exhibits excellent performance
as a battery even at high ambient temperatures. There has been a
demand for the development of a novel secondary battery with a high
energy density as a power source for electric vehicles, as well as
a battery which is suited for use in a wide range of ambient
temperatures. In order to answer such demand, a provision of a high
capacity to the nickel-cadmium storage battery using a conventional
sintered nickel positive electrode has been realized in the field
of nickel-cadmium storage battery, density including a foamed metal
nickel positive electrode which has a 30 to 60% higher capacity
than the former electrode has been developed. Furthermore, a
nickel-metal hydride battery having a higher capacity than the
nickel-cadmium storage battery which includes a hydrogen storage
alloy as the negative electrode has also been developed. This
nickel-metal hydride storage battery has a 2-fold or higher
capacity than the nickel-cadmium storage battery using the sintered
nickel positive electrode.
[0004] The above-noted various high capacity alkaline storage
batteries include a sintered porous nickel substrate, a
three-dimensional foamed porous nickel substrate of high porosity
(90% or more) or a porous nickel fiber substrate being filled with
a nickel hydroxide powder as an active material at a high density.
The use of such porous substrates of high porosity has led to
improvements of the energy density: Compared to 400 to 500
mAh/cm.sup.3 of the conventional sintered nickel positive
electrode, the recent sintered nickel positive electrode affords
450 to 500 mAh/cm.sup.3 and the foamed metal nickel positive
electrode affords 550 to 650 mAh/cm.sup.3.
[0005] However, the above-mentioned nickel positive electrodes have
a common drawback: the energy density is high around room
temperature but low at high ambient temperatures. This may be
because when charged at high ambient temperature, these electrodes
are liable to evolve oxygen upon charge of nickel hydroxide to
nickel oxyhydroxide. In other words, oxygen evolution at the
positive electrode inhibits sufficient charge of nickel hydroxide
to nickel oxyhydroxide during charge, leading to poor utilization
of the active material nickel hydroxide.
[0006] The following are proposed methods for solving the
above-mentioned problem.
[0007] (1) Add a cadmium oxide powder or a cadmium hydroxide powder
to the positive electrode;
[0008] (2) Incorporate a cadmium oxide in a nickel hydroxide powder
(see Japanese Laid-Open Patent Publication No. Sho 61-104565);
and
[0009] (3) Incorporate a compound of yttrium, indium, antimony,
barium or beryllium in the positive electrode (see Japanese
Laid-Open Patent Publication No. Hei 4-248973).
[0010] The methods (1) and (2) are intended to improve the
utilization of nickel hydroxide active material at high ambient
temperature by the presence of a cadmium oxide inside or in close
contact with a nickel hydroxide powder. These methods can best
utilize 80% or so of the nickel hydroxide active material at high
ambient temperature. In order to further increase the utilization
of nickel hydroxide at high ambient temperature, there is a need to
increase the content of cadmium oxide in the nickel hydroxide or in
the nickel positive electrode. However, there is a problem that
increased content of cadmium oxide improves the utilization of
nickel hydroxide at high ambient temperature to as high as 90% or
so, but adversely reduces its utilization around room
temperature.
[0011] From the aspect of current issue of environmental pollution,
nickel-metal hydride storage battery which is free of heavy metal
cadmium has been noted recently. Therefore, the use of nickel
positive electrode containing a cadmium oxide is not suited for
nickel-metal hydride storage battery.
[0012] The last method (3) adsorbs a compound of yttrium, indium,
antimony, etc. on the surface of nickel oxide active material,
expecting the following effects: (i) an elevation in oxygen
evolution overvoltage as a competitive reaction in response to
charge at high ambient temperatures, (ii) an increase in charge
efficiency, that is, oxidation of nickel hydroxide to nickel
oxyhydroxide, and (iii) an improvement of utilization at high
ambient temperatures. However, simple application of this method
only does not offer those expected effects due to non-homogeneous
distribution of the additive in the active material paste or
others. In order to have prominent effects, the use of additive in
a large amount becomes mandatory, but this hinders realization of a
high capacity battery.
BRIEF SUMMARY OF THE INVENTION
[0013] The object of the present invention is to provide a nickel
hydroxide active material for use in nickel positive electrode that
can solve the above-mentioned problems and offer an alkaline
storage battery having a higher capacity and a longer cycle
life.
[0014] The present invention is based on the discovery from an
experiment focusing on the fact that the amount of impurities
contained in a nickel hydroxide active material powder,
particularly the impurity of sulfate ion (SO.sub.4.sup.2-) present
in the nickel hydroxide powder obtained from nickel sulfate plays a
significant role in determining electrode characteristics that
regulation of the amount of sulfate ion as an impurity can improve
the charge efficiency of nickel hydroxide active material at high
temperatures and is effective for elongating the cycle life of the
resultant battery.
[0015] The present invention provides an active material for
constituting a nickel electrode comprising a nickel hydroxide
powder formed-from nickel sulfate wherein the content of impurity
SO.sub.4.sup.2- in the crystal of nickel hydroxide is 0.4 wt % or
less (hereinafter wt% is represented by % simply).
[0016] The nickel hydroxide used here is preferably solid solution
nickel hydroxide incorporating therein at least one element
selected from the group consisting of cobalt, cadmium, zinc and
magnesium.
[0017] The present invention can improve the utilization of
positive electrode active material at high ambient temperatures and
increase the filling amount of the nickel hydroxide by reducing the
conventional amount of additive. The present invention therefore
can provide a high performance alkaline storage battery operable in
a wide range of ambient temperature.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0018] FIG. 1 is a graph illustrating the correlation between the
content of SO.sub.4.sup.2- in the nickel hydroxide and diffraction
intensity at (001).
[0019] FIG. 2 is a sketch illustrating a model crystal structure of
nickel hydroxide.
[0020] FIG. 3 is an exploded oblique cut view illustrating the
essential parts of a nickel-metal hydride storage battery in one
example of the present invention.
[0021] FIG. 4 is a graph illustrating the correlation between the
content of SO.sub.4.sup.2- in the nickel hydroxide and utilization
of nickel positive electrode at various temperatures.
[0022] FIG. 5 is a graph illustrating changes in discharge capacity
by charge/discharge cycles at an ambient temperature of 25.degree.
C. observed in batteries including various nickel positive
electrodes in accordance with one example of the present
invention.
[0023] FIG. 6 is a graph illustrating changes in discharge capacity
by charge/discharge cycles at an ambient temperature of 45.degree.
C. observed in batteries including various nickel positive
electrodes in accordance with one example of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Nickel hydroxide used in the present invention can be
synthesized by reacting an aqueous nickel sulfate solution with an
alkali such as sodium hydroxide. Preliminary preparation of an
aqueous nickel sulfate solution containing ammonium as a complex
forming agent is desirable. In preparation of solid solution nickel
hydroxide incorporating therein an element such as cobalt, the
usual method adds a salt of incorporating element, such as cobalt
sulfate, to the aqueous nickel sulfate solution. Removal of the
sulfate ion in the nickel hydroxide synthesized from the starting
material nickel sulfate is successfully achieved by treating the
resultant nickel hydroxide with an aqueous alkaline solution such
as sodium hydroxide. The degree or extent of removal of the sulfate
ion can be controlled by adjusting pH of the aqueous alkaline
solution used, and duration and times of alkali treatment.
[0025] If the nickel hydroxide powder thus obtained is reduced in
amount of SO.sub.4.sup.2- in the crystal, it can also be reduced in
disorder of the crystal and can have uniform crystals, which leads
to homogeneous electrochemical reaction of the nickel hydroxide in
response to charge and discharge. Uniform crystal growth is
considered to reduce the number of defective or disordered crystal,
contributing to improvement of conductivity of nickel
hydroxide.
[0026] FIG. 1 shows the correlation between the content of
SO.sub.4.sup.2- in the crystals and diffraction intensity at (001)
in X-ray diffraction. As clearly seen from FIG. 1, nickel hydroxide
powders having low contents of SO.sub.4 .sup.2- are increased in
diffraction intensity at (001) and are decreased in disordered
crystals along the (001) plane. FIG. 2 shows a sketch of a model
crystal structure of nickel hydroxide. The SO.sub.4 .sup.2- is
considered to essentially exist inside the nickel hydroxide
crystals as shown in FIG. 2, and nickel hydroxide with reduced
amounts of So.sub.4 .sup.2- shows better crystal growth and more
homogeneous crystal along the (001) plane than the conventional
nickel hydroxide. As a result, number of disordered crystals
decreases which improves the conductivity between the crystals of
nickel hydroxide.
[0027] Furthermore, the reduction in number of disordered crystal
suggests uniform progress of charge reaction of nickel hydroxide to
nickel oxyhydroxide. Improved conductivity of nickel hydroxide and
uniform charge reaction are particularly effective for suppressing
the competitive reaction of oxygen evolution represented by the
formula (2), which affects the charge efficiency of the active
material at high ambient temperatures, against the charge reaction
of nickel hydroxide to nickel oxyhydroxide represented by the
formula (1). This in turn improves the charge efficiency. Uniform
charge/discharge reaction is also effective for suppressing the
production of undesirable .gamma.-nickel oxyhydroxide upon
overcharge of the active material and the expansion of the active
material, which leads to elongation of cycle life of the resultant
battery.
Ni(OH).sub.2+OH.sup.-NiOOH+H.sub.2O+e.sup.- (1)
2OH.sup.-1/2.multidot.O.sub.2+H.sub.2O+2e.sup.- (2)
[0028] When nickel hydroxide is solid solution nickel hydroxide
incorporating therein at least one element selected from the group
consisting of cobalt, cadmium, zinc and magnesium, that nickel
hydroxide can produce an elevated oxygen evolution overpotential by
the intrinsic or synergistic effect of the incorporated element(s)
thereby reducing oxygen evolution. As a result, the charge
efficiency of nickel hydroxide at high ambient temperatures can be
improved greatly. The use of such solid solution nickel hydroxide
powder in accordance with the present invention realizes a long
life alkaline storage battery that can be operated even in a wider
range of ambient temperature.
[0029] In the following, the present invention will be described by
way of concrete examples.
EXAMPLE 1
[0030] Nickel hydroxide used in this example was produced by mixing
and stirring an aqueous nickel sulfate solution and an aqueous
sodium hydroxide solution thereby depositing nickel hydroxide. In
order to stabilize any metal ion such as nickel ion, the aqueous
nickel sulfate solution contains ammonia as a complex forming
agent.
[0031] Various nickel hydroxide materials produced under the same
condition were subjected to alkali treatment with one of aqueous
sodium hydroxide solutions having different pH values (alkali
treatment) to remove anions such as sulfate ion in each nickel
hydroxide material, washed with water and dried, and used in the
experiment. pH values of the aqueous sodium hydroxide solution
ranged from 13.0 to 14.0. At that time, the content of
SO.sub.4.sup.2- in the nickel hydroxide produced can be controlled
by adjusting pH value of the alkaline solution, duration and times
of alkali treatment. Nickel hydroxide with no alkali treatment
contained 1.0 to 1.2% SO.sub.4.sup.2-. The nickel hydroxide powder
thus produced was a sphere having a mean particle size of about 10
.mu.m.
[0032] Table 1 lists the content of SO.sub.4.sup.2- in each nickel
hydroxide powder used in the experiment. The content of
SO.sub.4.sup.2- was determined by indirect measurement of sulfur
(S) by ICP spectrometry and direct quantitation by ion
chromatography. There was no discrepancy between the values based
on ICP those by ion chromatography.
1 TABLE 1 No. SO.sub.4.sup.2- content (%) 1 0.05 2 0.2 3 0.3 4 0.4
5 0.5 6 0.8 7 1.0
[0033] The nickel positive electrode used here was produced as
follows: Each of the nickel hydroxide powders as produced was mixed
with a cobalt powder, a cobalt hydroxide powder and a zinc oxide
powder in a weight ratio of 100:7:5:3. Water was added to the
mixture and kneaded to make a paste, which was filled into a foamed
porous nickel substrate having a porosity of 95% and a surface
density of 450 g/cm.sup.2, dried, pressed, and cut to a
predetermined size (thickness 0.5 mm, width 35 mm, length 110 mm),
and the nickel positive electrode thus produced had a theoretical
capacity of 1,000 mAh.
[0034] The positive electrode thus produced was used to produce a
sealed nickel-metal hydride storage battery of AA size with a
regulated capacity by the positive electrode (theoretical capacity:
1,000 mAh). The structure of this battery is shown in FIG. 3. In
the figure, numeral 10 designates an electrode group. The electrode
group is a spiral combination of a nickel positive electrode 12
produced in the above-mentioned manner and a negative electrode 11
of a hydrogen storage alloy represented by the formula
MmNi.sub.3.6Co.sub.0.7Mn.sub.0.4Al.sub.0- .3 where Mm is an
abbreviation of Misch metal with a sulfonated polypropylene
separator being interposed therebetween, and is accommodated in a
case 14 as a negative terminal. After pouring an alkaline
electrolyte (2.0 cm.sup.3) prepared by dissolving lithium hydroxide
at 20 g/l in an aqueous potassium hydroxide solution having a
specific gravity of 1.3 over the electrode group, the case 14 was
sealed with a sealing plate 16 mounted with a safety vent 18 and a
terminal 19. Numeral 15 designates an insulating plate for
insulating the case 14 from the electrode group, numeral 17
designates a gasket, and numeral 20 designates a positive current
collector for electrically connecting the positive electrode 12 and
the sealing plate 16.
[0035] Batteries having one of the various positive electrodes
produced in the above-mentioned manner were evaluated for their
utilization of the positive electrode active material. Each battery
was tested by consecutive charge and discharge cycles under the
conditions of charge with a current of 0.1 C. at ambient
temperatures of 25, 35, 45 and 55.degree. C. for 15 hours, followed
by a 3-hour rest at an ambient temperature of 25.degree. C. and
subsequent discharge with a current of 0.2.degree. C. at the same
ambient temperature of 25.degree. C. until the voltage drops to 1.0
V. The discharge capacity at each testing temperature was
determined in each battery at the second cycle of the
above-mentioned charge/rest/discharge cycle. Based on the discharge
capacity at the second cycle, the correlation between the content
of SO.sub.4.sup.2- in the nickel hydroxide powder of the positive
electrode and utilization of the positive electrode was analyzed,
and the results are shown in FIG. 4. The utilization of the
positive electrode was calculated using the following equation:
Positive electrode utilization (%) =(Discharge capacity
(Ah))/(Theoretical capacity of positive electrode (Ah))
[0036] As shown in FIG. 4, the utilization of nickel positive
electrode at high ambient temperatures increases by reducing the
content of SO.sub.4.sup.2-. The unitization at 35, 45 and
55.degree. C. becomes stabilized particularly at an SO.sub.4.sup.2-
content of 0.4% or less. When the content of SO.sub.4.sup.2- is
decreased to as low as 0.2% or less, the utilization is stabilized
at a value around a constant value. Therefore, the effect of the
present invention can be achieved when the content of
SO.sub.4.sup.2- is 0.4% or less, and an SO.sub.4.sup.2- content as
low as 0.2% or less is particularly effective.
[0037] Then, batteries No. 1, 4, 5 and 7 containing SO.sub.4.sup.2-
at the contents shown in Table 1 were tested by consecutive charge
and discharge cycles under the conditions of charge at ambient
temperatures of 25 and 45.degree. C. with a current of 1 C. for 1.3
hours and discharge with a current of 1 C. until the voltage shows
1.0 V. Changes in discharge capacity with the cycles are shown in
FIG. 5 and FIG. 6.
[0038] As evident from FIG. 5 and FIG. 6, batteries No. 1 and 4
retained a high capacity even after 500 cycles at ambient
temperatures of 25 and 45.degree. C. These batteries underwent
further cycles and retained a discharge capacity of 50% or more of
their initial discharge capacity until 800 to 900 cycles. Batteries
No. 5 and 7, on the other hand, were decreased in capacity
gradually; the capacity decreased down to 50% or less of their
initial discharge capacity after 200 to 400 cycles. These results
may indicate that reductions of the impurity SO.sub.4.sup.2- in the
nickel hydroxide active material to 0.4% or less have led to
decreases in the number of disordered crystals of the nickel
hydroxide and uniform progress of oxidation and reduction of the
nickel hydroxide by charge and discharge, thereby elongating the
cycle life of the resultant batteries. As such, reduced content of
SO.sub.4.sup.2- to as low as 0.4% or less improves the charge
efficiency at high ambient temperatures, realizing a long cycle
life of the battery. In order to improve the positive electrode
utilization, lesser contents of SO.sub.4.sup.2- are more
preferable; contents of 0.3% or less increases the positive
electrode utilization to as high as 95% or more.
EXAMPLE 2
[0039] Spherical powders of solid solution nickel hydroxide
incorporating therein one or two elements selected from the group
consisting of cobalt, cadmium, zinc and magnesium were produced.
Solid solution nickel hydroxide powders were produced in the same
manner as in Example 1, except that a sulfate of one or two
elements to be incorporated is dissolved in a similar aqueous
nickel sulfate solution to that used in Example 1. The percentage
of incorporated element(s) and the percentage of SO.sub.4.sup.2- in
the respective solid solution nickel hydroxide powders are shown in
Table 2.
2 TABLE 2 Incorporated element(s) and impurity(%) No. Co Zn Cd Mg
SO.sub.4.sup.2- 11 0 0 0 0 0.30 12 1 0 0 0 0.27 13 0 1 0 0 0.32 14
0 0 1 0 0.31 15 0 0 0 1 0.30 16 0 0 0 0 0.28 17 1 1 0 0 0.25 18 1 0
1 0 0.32 19 1 0 0 1 0.30
[0040] These nickel hydroxide powders were mixed with a cobalt
powder, a cobalt hydroxide powder and a zinc oxide power in a
weight ratio of 100:7:5:3, and using those mixtures thus produced,
various positive electrodes were produced and fabricated into
batteries for experiments in a manner similar to that in Example
1.
[0041] Those batteries were tested by consecutive charge discharge
cycles under the conditions of charge at ambient temperatures of
25, 35, 45 and 55.degree. C. with a current of 1 C. for ours and
discharge at 1 C. until the voltage shows 1.0 V. the discharge
capacity decreased by 50% of the initial capacity, then that
battery was taken as ending its life as a battery. The cycle life
in each battery thus examined is in Table 3.
3 TABLE 3 Cycle life (cycles) No. 25.degree. C. 35.degree. C.
45.degree. C. 55.degree. C. 11 900 760 650 455 12 980 850 720 550
13 975 840 715 530 14 990 860 725 555 15 950 855 730 550 16 955 860
720 540 17 960 835 710 530 18 975 845 705 520 19 980 860 720
520
[0042] Table 3 clearly shows that batteries having positive
electrodes of solid solution nickel hydroxide incorporating therein
one or more elements of cobalt, cadmium, zinc and magnesium are
improved in cycle life at high ambient temperatures compared to
those having positive electrodes of nickel hydroxide incorporating
none of those elements.
[0043] By improvement of nickel hydroxide active material by
incorporating therein certain elements, it is possible to produce a
long life battery which can afford a stable capacity in a wide
range of ambient temperature.
[0044] In the foregoing examples, although one or two of cobalt,
cadmium, zinc and magnesium are incorporated in the solid solution
nickel hydroxide powder of the present invention, solid solution
nickel hydroxide incorporating therein three or more of these
elements can also ensure an identical effect.
[0045] As discussed above, the present invention can provide a
nickel positive electrode for use in alkaline storage battery which
ensures a high capacity in a wide range of ambient temperature and
a long cycle life for the battery.
[0046] Although the present invention has been described in terms
of the presently preferred embodiments, it is to be understood that
such disclosure is not to be interpreted as limiting. Various
alterations and modifications will no doubt become apparent to
those skilled in the art to which the present invention pertains,
after having read the above disclosure. Accordingly, it is intended
that the appended claims be interpreted as covering all alterations
and modifications as fall within the true spirit and scope of the
invention.
* * * * *