U.S. patent application number 15/425816 was filed with the patent office on 2017-08-17 for positive electrode active material for alkaline secondary battery and alkaline secondary battery including the positive electrode active material.
The applicant listed for this patent is FDK CORPORATION, FUJITSU LIMITED. Invention is credited to Shuuichi Doi, Yuzo Imoto, Takeshi Ito, Yuji Kataoka, Masaru Kihara, Takashi Yamazaki, Takayuki Yano, Shigekazu Yasuoka.
Application Number | 20170237065 15/425816 |
Document ID | / |
Family ID | 58009741 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170237065 |
Kind Code |
A1 |
Ito; Takeshi ; et
al. |
August 17, 2017 |
POSITIVE ELECTRODE ACTIVE MATERIAL FOR ALKALINE SECONDARY BATTERY
AND ALKALINE SECONDARY BATTERY INCLUDING THE POSITIVE ELECTRODE
ACTIVE MATERIAL
Abstract
A nickel-hydrogen secondary battery includes an electrode group
comprising a separator, a positive electrode, and a negative
electrode, and the positive electrode contains a positive electrode
active material including a base particle comprising a nickel
hydroxide particle containing Mn in solid solution and a conductive
layer comprising a Co compound and covering the surface of the base
particle, wherein the X-ray absorption edge energy of Mn detected
within 6500 to 6600 eV by measurement with an XAFS method is 6548
eV or higher.
Inventors: |
Ito; Takeshi; (Tokyo,
JP) ; Imoto; Yuzo; (Tokyo, JP) ; Kihara;
Masaru; (Tokyo, JP) ; Yano; Takayuki; (Tokyo,
JP) ; Yasuoka; Shigekazu; (Tokyo, JP) ; Doi;
Shuuichi; (Isehara, JP) ; Yamazaki; Takashi;
(Kawasaki, JP) ; Kataoka; Yuji; (Yokohama,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FDK CORPORATION
FUJITSU LIMITED |
Tokyo
Kanagawa |
|
JP
JP |
|
|
Family ID: |
58009741 |
Appl. No.: |
15/425816 |
Filed: |
February 6, 2017 |
Current U.S.
Class: |
429/206 |
Current CPC
Class: |
H01M 4/50 20130101; H01M
4/52 20130101; H01M 10/30 20130101; Y02E 60/10 20130101; C01P
2002/52 20130101; H01M 4/366 20130101; H01M 4/32 20130101; H01M
2300/0014 20130101; H01M 2004/028 20130101; C01P 2002/50 20130101;
H01M 10/345 20130101; C01G 53/04 20130101; C01P 2004/80 20130101;
C01G 51/04 20130101 |
International
Class: |
H01M 4/36 20060101
H01M004/36; H01M 4/50 20060101 H01M004/50; H01M 10/34 20060101
H01M010/34; H01M 4/52 20060101 H01M004/52 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2016 |
JP |
2016-024991 |
Claims
1. A positive electrode active material for an alkaline secondary
battery, comprising: a base particle comprising a nickel hydroxide
particle containing Mn in solid solution and a conductive layer
comprising a Co compound and covering a surface of the base
particle, wherein: an X-ray absorption edge energy of the Mn
detected within 6500 to 6600 eV by measurement with an XAFS (X-ray
Absorption Fine Structure) method is 6548 eV or high.
2. The positive electrode active material for an alkaline secondary
battery according to claim 1, wherein: a content of the Mn is 0.1%
by mass or more and 2.0% by mass or less based on a quantity of the
nickel hydroxide.
3. The positive electrode active material for an alkaline secondary
battery according to claim 1, wherein: the conductive layer
contains an alkali metal.
4. The positive electrode active material for an alkaline secondary
battery according to claim 3, wherein: the alkali metal is Na.
5. The positive electrode active material for an alkaline secondary
battery according to claim 3, wherein: the alkali metal is Na and
Li.
6. The positive electrode active material for an alkaline secondary
battery according to claim 1, wherein: the measurement with an XAFS
method is XAFS measurement with a fluorescence yield method.
7. An alkaline secondary battery comprising a container and an
electrode group contained together with an alkaline electrolytic
solution in the container, wherein: the electrode group comprises a
positive electrode and a negative electrode laminated with a
separator sandwiched therebetween, and the positive electrode
contains the positive electrode active material for an alkaline
secondary battery according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates to a positive electrode active
material for an alkaline secondary battery and an alkaline
secondary battery including the positive electrode active
material.
[0003] Description of the Related Art
[0004] Nickel-hydrogen secondary batteries are known as one of
alkaline secondary batteries. Known examples of positive electrodes
for such nickel-hydrogen secondary batteries include unsintered
positive electrodes. Such unsintered positive electrodes are
produced in the following manner, for example.
[0005] First, a nickel hydroxide particle as a positive electrode
active material, a binder, and water are kneaded together to
prepare a positive electrode admixture slurry, and a positive
electrode base material comprising a nickel foam sheet having a
porous structure is filled with the positive electrode admixture
slurry. Then, an intermediate product of a positive electrode is
formed through a drying process for the slurry and a rolling
process to densify the positive electrode admixture. Thereafter,
the intermediate product is cut in predetermined dimensions and
thus an unsintered positive electrode is produced. Such unsintered
positive electrodes have an advantage of allowing for filling with
a positive electrode active material in a higher density than in
the case of sintered positive electrodes.
[0006] Nickel hydroxide in a single substance has a low
conductivity, and it is thus difficult for unsintered positive
electrodes to enhance the utilization efficiency of a positive
electrode active material. In view of this, a nickel hydroxide
particle is typically subjected to a treatment to enhance the
conductivity, and the nickel hydroxide particle with an enhanced
conductivity is used. Known examples of such nickel hydroxide
particles with an enhanced conductivity include a nickel hydroxide
particle disclosed in Japanese Patent Laid-Open No. 10-154508.
Specifically, cobalt hydroxide is precipitated on the surface of a
nickel hydroxide particle and then heat-treated to convert the
cobalt hydroxide on the surface of the nickel hydroxide particle
into cobalt oxyhydroxide. Since cobalt oxyhydroxide is excellent in
conductivity, cobalt oxyhydroxide on the surface of the nickel
hydroxide particle comes into interparticle contact to form a
conductive network. As a result, the conductivity of a positive
electrode is enhanced, which leads to enhancement of the
utilization efficiency of a positive electrode active material.
[0007] As alkaline secondary batteries are increasingly used for a
wide variety of applications, the desire for improvement of the
cycle life characteristics has been growing. In such circumstances,
containing Mn in solid solution in a nickel hydroxide particle is
known as one example of techniques to improve the cycle life
characteristics of an alkaline secondary battery (e.g., see
Japanese Patent Laid-Open No. 09-115543).
[0008] In order to achieve further improvement of the performance
of an alkaline secondary battery, development of a battery having
an enhanced utilization efficiency of a positive electrode active
material and improved cycle life characteristics in combination has
been desired in recent years. From such a viewpoint, attempts have
been made to impart excellent cycle life characteristics to a
battery having an enhanced utilization efficiency of a positive
electrode active material through development of an alkaline
secondary battery with a particle obtained by forming a cobalt
compound layer, which is excellent in conductivity, on the surface
of a nickel hydroxide particle containing Mn in solid solution as a
positive electrode active material particle.
[0009] If a battery connected to a circuit is left to stand for a
long period, the battery discharges to a voltage lower than a
predetermined cut-off voltage, which is what is called
deeply-discharged state.
[0010] If a battery having an enhanced utilization efficiency of a
positive electrode active material and improved cycle life
characteristics in combination as described above, that is, a
battery with a particle obtained by forming a cobalt compound
layer, which is excellent in conductivity, on the surface of a
nickel hydroxide particle containing Mn in solid solution as a
positive electrode active material particle comes into a
deeply-discharged state, the following failures are caused.
[0011] First, the potential of the positive electrode becomes equal
to or lower than the reduction potential of cobalt oxyhydroxide due
to the deep discharge, and as a result the cobalt oxyhydroxide
forming the conductive network on the surface of the positive
electrode active material is reduced. As the cobalt oxyhydroxide is
reduced, the cobalt oxyhydroxide layer on the surface of the nickel
hydroxide particle is partly lost and the conductive network is
destroyed. As a result, the chargeability of the battery is
degraded and a capacity comparable to the initial capacity cannot
be obtained any more even if the battery is charged again. In other
words, the capacity recovery rate of the battery is lowered.
[0012] In addition, the Mn contained in solid solution in the
nickel hydroxide particle involves in accelerating reduction of
cobalt oxyhydroxide when the battery comes into a deeply-discharged
state, and thus the presence of Mn promotes destruction of the
conductive network. Moreover, the Mn itself is reduced and eluted
in a deeply-discharged state, and as a result the bulk portion of
nickel hydroxide becomes brittle and deteriorated. As the bulk
portion of nickel hydroxide is deteriorated, the capacity of the
battery is further lowered. It follows that a battery with nickel
hydroxide containing Mn in solid solution is excellent in cycle
life characteristics but the capacity recovery rate is largely
lowered when the battery comes into a deeply-discharged state.
[0013] A battery whose capacity recovery rate has been lowered as
described above cannot provide a required capacity even if the
battery is charged again, which makes it difficult to normally
operate electric devices or the like.
SUMMARY OF THE INVENTION
[0014] A positive electrode active material for an alkaline
secondary battery is provided, including a base particle comprising
a nickel hydroxide particle containing Mn in solid solution and a
conductive layer comprising a Co compound and covering the surface
of the base particle, wherein the X-ray absorption edge energy of
the Mn detected within 6500 to 6600 eV by measurement with an XAFS
(X-ray Absorption Fine Structure) method is 6548 eV or higher.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will become more fully understood from
the detailed description given hereinafter and the accompanying
drawings which are given by way of illustration only, and thus, are
not limitative of the present invention, and wherein:
[0016] FIG. 1 is a perspective view illustrating a nickel-hydrogen
secondary battery according to one embodiment of the present
invention by partial cutting; and
[0017] FIG. 2 is a graph showing an XAFS spectrum of a sample of a
positive electrode active material in Example 1 acquired by using a
fluorescence yield method.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Hereinafter, a nickel-hydrogen secondary battery 2 according
to an embodiment of the present invention (hereinafter, referred to
as battery) will be described with reference to the accompanying
drawings.
[0019] Although the battery 2 to be used for the present invention
is not limited, an AA cylindrical battery 2 shown in FIG. 1 used
for the present invention will be described as an example.
[0020] As illustrated in FIG. 1, the battery 2 includes an outer
can 10 having a bottomed cylindrical shape with an open top. The
outer can 10 has conductivity, and its bottom wall 35 functions as
a negative electrode terminal. To the opening of the outer can 10,
a sealing element 11 is fixed. The sealing element 11, which
includes a lid plate 14 and a positive electrode terminal 20, seals
the outer can 10 and provides the positive electrode terminal 20.
The lid plate 14 is a circular member having conductivity. In the
opening of the outer can 10, the lid plate 14 and a ring-shaped
insulation packing 12 surrounding the lid plate 14 are disposed,
and the insulation packing 12 is fixed to an opening periphery 37
of the outer can 10 through caulking of the opening periphery 37 of
the outer can 10. It follows that the lid plate 14 and the
insulation packing 12 cooperate to airtightly block the opening of
the outer can 10.
[0021] The lid plate 14 has a central through-hole 16 at its
center, and a valving element 18 made of rubber to plug the central
through-hole 16 is disposed on the outer surface of the lid plate
14. Onto the outer surface of the lid plate 14, the positive
electrode terminal 20 having a cylindrical shape with a flange and
made of metal is electrically connected in such a way as to cover
the valving element 18. The positive electrode terminal 20 pushes
the valving element 18 toward the lid plate 14. A degassing hole,
which is not illustrated, is opened in the positive electrode
terminal 20.
[0022] In normal conditions, the central through-hole 16 is
airtightly closed with the valving element 18. If a gas is
generated in the outer can 10 and the inner pressure increases, on
the other hand, the valving element 18 is compressed due to the
inner pressure to open the central through-hole 16, and as a result
the gas is discharged from the outer can 10 to the outside through
the central through-hole 16 and the degassing hole (not
illustrated) of the positive electrode terminal 20. It follows that
the central through-hole 16, the valving element 18, and the
positive electrode terminal 20 serve as a safety valve for the
battery.
[0023] An electrode group 22 is contained in the outer can 10. The
electrode group 22 includes a positive electrode 24, a negative
electrode 26, and a separator 28 each of which is band-shaped, and
they are spirally wound with the separator 28 sandwiched between
the positive electrode 24 and the negative electrode 26. In other
words, the positive electrode 24 and the negative electrode 26 are
laminated together with the separator 28 sandwiched therebetween.
The outermost periphery of the electrode group 22 is formed by a
part (outermost peripheral portion) of the negative electrode 26
and contacts the inner peripheral wall of the outer can 10. It
follows that the negative electrode 26 and the outer can 10 are
electrically connected together.
[0024] In the outer can 10, a positive electrode lead 30 is
disposed between one end of the electrode group 22 and the lid
plate 14. More specifically, one end of the positive electrode lead
30 is connected to the positive electrode 24 and the other end is
connected to the lid plate 14. Thus, the positive electrode
terminal 20 and the positive electrode 24 are electrically
connected together via the positive electrode lead 30 and the lid
plate 14. A circular upper insulating member 32 is disposed between
the lid plate 14 and the electrode group 22, and the positive
electrode lead 30 extends through a slit 39 provided in the upper
insulating member 32. Similarly, a circular lower insulating member
34 is disposed between the electrode group 22 and the bottom of the
outer can 10.
[0025] The outer can 10 further contains a predetermined quantity
of an alkaline electrolytic solution (not illustrated) injected
therein. The electrode group 22 is impregnated with the alkaline
electrolytic solution, and the alkaline electrolytic solution
allows chemical reaction between the positive electrode 24 and the
negative electrode 26 in charging/discharging (charge/discharge
reaction) to proceed. The alkaline electrolytic solution to be used
is preferably an alkaline electrolytic solution containing at least
one of KOH, NaOH, and LiOH as a solute.
[0026] For the material of the separator 28, for example, a
polyamide nonwoven fabric or a polyolefin nonwoven fabric such as a
polyethylene nonwoven fabric and a polypropylene nonwoven fabric
may be used. It is preferred to impart a hydrophilic functional
group to such a polyamide nonwoven fabric or polyolefin nonwoven
fabric.
[0027] The positive electrode 24 includes a conductive positive
electrode base material having a porous structure and a positive
electrode admixture held in voids in the positive electrode base
material.
[0028] For the positive electrode base material, for example, a
nickel foam sheet may be used.
[0029] The positive electrode admixture contains a positive
electrode active material particle 36 and a binder 42, as
schematically illustrated in the circle S in FIG. 1. The binder 42
functions to bind the positive electrode active material particles
36 together, and simultaneously bind the positive electrode active
material particles to the positive electrode base material. For the
binder 42, for example, carboxymethyl cellulose, methyl cellulose,
a PTFE (polytetrafluoroethylene) dispersion, or an HPC
(hydroxypropyl cellulose) dispersion may be used.
[0030] The positive electrode active material particle 36 includes
a base particle 38 and a conductive layer 40 covering the surface
of the base particle 38.
[0031] The base particle 38 comprises a nickel hydroxide particle
containing Mn in solid solution.
[0032] The content of Mn in solid solution in nickel hydroxide is
over 0% by mass, and preferably 0.1% by mass or more and 2.0% by
mass or less based on the quantity of nickel hydroxide.
[0033] The Mn contained in solid solution in the nickel hydroxide
particle has been subjected to oxidation treatment to provide a
higher valence. When the X-ray fluorescence from Mn is measured to
acquire the spectrum by using an XAFS (X-ray Absorption Fine
Structure) method, the X-ray absorption edge energy of Mn is
detected within 6500 to 6600 eV. In embodiments of the present
invention, Mn having an X-ray absorption edge energy of 6548 eV or
higher as measured by using the XAFS method is used.
[0034] Now, the XAFS method will be described.
[0035] In general, an element has a property of strongly absorbing
an X-ray with energy corresponding to its core electron binding
energy. A part at which the X-ray absorption coefficient of a
substance largely increases is called an absorption edge, and the
energy of an X-ray corresponding to the absorption edge is called
X-ray absorption edge energy. Different elements have different
core electron binding energy. If an element is irradiated with an
X-ray with energy higher than the core electron binding energy of
the element, the core electron is released and transitions to an
unoccupied states, and as a result the X-ray absorption coefficient
increases. Accordingly, observation of the X-ray absorption
spectrum including the absorption edge for an element provides
information on the X-ray absorption fine structure (XAFS
oscillation) reflecting the local structure around an element of
interest, and thus the local structure around an element of
interest can be understood through analysis of the XAFS
oscillation. In addition, the position of an absorption edge is
known to shift due to the change of electronic state of an element,
and thus the valence of an element of interest can be understood
through comparison of the absorption edge. Example of measurement
methods to acquire an average X-ray absorption spectrum of a sample
as described above by using the XAFS method include a transmission
method in which a sample is irradiated with an X-ray and the X-ray
intensities before and after passing through the sample are
measured to directly determine the X-ray absorption, and a
fluorescence yield method in which a sample is irradiated with an
X-ray and X-ray fluorescence emitted from an atom excited due to
absorption of the X-ray is measured. Both methods can provide
similar results through analysis of the local structure or valence
of an element of interest. In embodiments of the present invention,
the content of Mn in solid solution in nickel hydroxide is over 0%
by mass, and preferably 0.1% by mass or more and 2.0% by mass or
less, and the quantity of Mn is significantly smaller than that of
nickel. Accordingly, it is desirable to use the fluorescence yield
method.
[0036] In embodiments of the present invention, the intensity of
X-ray fluorescence emitted when a sample is irradiated with a
synchrotron X-ray is measured by using the fluorescence yield
method to acquire an XAFS spectrum (hereinafter, referred to as
fluorescence XAFS spectrum). Then, the absorption edge of Mn in the
fluorescence XAFS spectrum acquired is determined to analyze the
valence of Mn. Specifically, a sample is irradiated with an X-ray
and the intensity of X-ray fluorescence emitted from the sample is
measured by using the fluorescence yield method while the energy of
the X-ray radiation is continuously changed, and thus a
fluorescence XAFS spectrum as illustrated in FIG. 2 is acquired. In
the graph of the fluorescence XAFS spectrum in FIG. 2, the vertical
axis represents absorption coefficients obtained by removing
contributions of atoms other than the Mn atom as the background
from the XAFS spectrum acquired in the measurement and then
normalizing the resultant so that the average value of absorption
coefficients from an absorption edge to a high energy region (6800
to 7200 eV), in which the XAFS oscillation reflecting the atomic
arrangement around the Mn atom attenuates to be unrecognizable, is
1.0, and the horizontal axis represents the range of X-ray energy
from 6540 eV to 6560 eV. In embodiments of the present invention, a
part at which the absorption coefficient reaches 0.3 in FIG. 2 is
defined as the absorption edge of Mn, and the X-ray energy
corresponding to the absorption edge is defined as the X-ray
absorption edge energy of Mn.
[0037] A larger X-ray absorption edge energy of Mn measured
indicates a higher degree of oxidation, in other words, a higher
valence. It follows that Mn provided with a higher valency such
that the X-ray absorption edge energy is 6548 eV or high is used in
embodiments of the present invention. In the case of Mn, valences
corresponding to X-ray absorption edge energy of 6548 eV or high
are valences of 3.5 or higher.
[0038] Preferably, at least one of cobalt and zinc is further
contained in solid solution in the above-described nickel
hydroxide. Cobalt contributes to enhancement of the interparticle
conductivity of a positive electrode active material particle, and
zinc reduces the swelling of a positive electrode associated with
progression of charge/discharge cycles and contributes to
improvement of the cycle life characteristics of a battery.
[0039] The content of the above element in solid solution in the
nickel hydroxide particle based on the quantity of nickel hydroxide
is preferably 0.5 to 5.0% by mass for cobalt, and preferably 3.0 to
5.0% by mass for zinc.
[0040] The average particle size of the base particle 38 is
preferably set within 8 .mu.m to 20 .mu.m. Specifically, the
electrode reaction area of an unsintered positive electrode can be
increased to provide a battery with a higher power through
increasing the surface area of a positive electrode active
material, and thus the average particle size of the base particle
38, as a base of the positive electrode active material, is
preferably as small as 20 .mu.m or smaller. However, the proportion
of the conductive layer 40 to the whole increases as the particle
size of the base particle 38 decreases with the thickness of the
conductive layer 40 to be precipitated on the surface of the base
particle set to a constant value, and as a result the quantity of
an Ni compound becomes relatively small, which disadvantageously
causes reduction of unit capacity. In view of the production yield
of the base particle 38, the particle size is preferably 8 .mu.m or
larger. More preferred range is 10 .mu.m to 16 .mu.m.
[0041] A Co compound is employed for the conductive layer 40 to
cover the surface of the base particle 38. Although the thickness
of the conductive layer 40 is not limited, the thickness is
preferably 0.1 .mu.m, for example. In order to form a Co compound
layer having a thickness of 0.1 .mu.m, metal Co in a quantity of
approximately 2.0% by mass to 5.0% by mass based on the total mass
of the base particle is required.
[0042] It is preferred to employ a high-valent cobalt compound such
as cobalt oxyhydroxide (CoOOH) for the Co compound for the
conductive layer 40. In addition, the high-valent cobalt compound
preferably contains an alkali metal. More preferably, Na is
employed for the alkali metal. Hereinafter, a cobalt compound
containing Na is referred to as sodium-containing cobalt compound.
More specifically, the sodium-containing cobalt compound is a
compound in which Na is incorporated in a crystal of cobalt
oxyhydroxide (CoOOH). It is preferred to allow a cobalt compound to
contain Na as mentioned above because the homogeneity of the
thickness of a conductive layer to be obtained increases.
[0043] Here, the homogeneity of the thickness of the conductive
layer refers to the degree of thickness difference between thick
portions and thin portions in the conductive layer. The smaller the
thickness difference between thick portions and thin portions is,
the higher the homogeneity is, and the larger the thickness
difference between thick portions and thin portions is, the lower
the homogeneity is.
[0044] If the homogeneity of the thickness of the conductive layer
40 is low, rupture or break of the conductive layer 40 starts at a
thin portion of the conductive layer 40 in deep discharge, and the
conductive network is partly destroyed. As a result, the capacity
recovery rate of a battery to be obtained is lowered. If the
homogeneity of the thickness of the conductive layer 40 is high and
the thickness is almost homogeneous, on the other hand, rupture or
break of the conductive layer is less likely to occur in deep
discharge, and the conductive network is maintained in a proper
state. As a result, lowering of the capacity recovery rate of a
battery to be obtained is reduced.
[0045] It is more preferred to allow the cobalt compound layer as
the conductive layer 40 to further contain Li because the
conductivity of the conductive layer 40 becomes enhanced.
[0046] The above base particle 38 can be produced, for example, in
the following manner.
[0047] First, nickel sulfate and manganese sulfate are weighed so
as to achieve a predetermined composition, and these nickel sulfate
and manganese sulfate are charged into, for example, a 1 N sodium
hydroxide aqueous solution containing ammonium ions, and the
resultant is stirred to prepare a mixed aqueous solution. To the
mixed aqueous solution, for example, a 10 N sodium hydroxide
aqueous solution is gradually added to react, and thus the base
particle 38 containing nickel hydroxide as a main component
containing Mn in solid solution can be precipitated. In the case
that not only Mn but also Zn and Co are allowed to be contained in
solid solution in a nickel hydroxide particle, nickel sulfate,
manganese sulfate, zinc sulfate, and cobalt sulfate are weighed so
as to achieve a predetermined composition, and they are charged
into a 1 N sodium hydroxide aqueous solution containing ammonium
ions, and the resultant is stirred to prepare a mixed aqueous
solution. While the resultant mixed aqueous solution is stirred, a
10 N sodium hydroxide aqueous solution is gradually added to the
mixed aqueous solution to react, and thus the base particle 38
containing nickel hydroxide as a main component containing Mn, Zn,
and Co in solid solution can be precipitated.
[0048] Then, the conductive layer 40 is formed in the following
procedure.
[0049] The base particle 38 obtained as described above is charged
into an ammonia aqueous solution, and to this aqueous solution, a
cobalt sulfate aqueous solution is added. Thereby, cobalt hydroxide
precipitates on the surface of a core of the base particle 38, and
thus a composite particle including the conductive layer 40
comprising cobalt hydroxide is formed. The composite particle
obtained is subjected to heat treatment in convection of air in a
high temperature environment at a predetermined heating temperature
for a predetermined heating duration. In the heat treatment, a
temperature of 80.degree. C. to 100.degree. C. is preferably
retained for 30 minutes to 2 hours. This heat treatment converts
the cobalt hydroxide on the surface of the above composite particle
into a highly-conductive cobalt compound (e.g., cobalt
oxyhydroxide).
[0050] In the case that the conductive layer 40 is allowed to
contain Na, which is a preferred mode, a sodium hydroxide aqueous
solution is sprayed onto the above composite particle being
subjected to heat treatment in convection of air in a high
temperature environment. This treatment converts the cobalt
hydroxide on the surface of the above composite particle to a
highly-conductive cobalt compound (e.g., cobalt oxyhydroxide) and
allows the cobalt hydroxide to incorporate Na therein. Thereby, an
intermediate product particle covered with the conductive layer 40
comprising a cobalt compound containing Na can be obtained.
[0051] It is more preferred to allow the cobalt compound as the
conductive layer 40 to further contain Li because the conductivity
of the conductive layer 40 becomes enhanced. In order to allow the
cobalt compound to contain Na and Li, heat treatment is performed
through spraying a lithium hydroxide aqueous solution together with
a sodium hydroxide aqueous solution onto the above composite
particle being placed in convection of air in a high temperature
environment. Thereby, an intermediate product particle covered with
the conductive layer 40 comprising a cobalt compound containing Na
and Li can be obtained. A cobalt compound in which Li is
incorporated in a crystal of cobalt oxyhydroxide (CoOOH) has an
extremely high conductivity, and thus a proper conductive network
capable of enhancing the utilization efficiency of an active
material in a positive electrode can be formed.
[0052] The above intermediate product particle is washed with pure
water and then subjected to drying.
[0053] Subsequently, a sodium chlorite aqueous solution containing
sodium chlorite as a solute is prepared in a predetermined
quantity. The content of sodium chlorite contained in the sodium
chlorite aqueous solution is preferably set to 5.0% by mass to
20.0% by mass. The sodium chlorite aqueous solution prepared is
then heated. The heating temperature is preferably set to
50.degree. C. to 80.degree. C. The above intermediate product
particle is then charged into the sodium chlorite aqueous solution
retained at the heating temperature set, and the resultant is
stirred for a predetermined duration for oxidation treatment of Mn.
The predetermined duration for stirring is preferably set to 30
minutes to 120 minutes.
[0054] The intermediate product particle after the completion of
the oxidation treatment is washed with pure water and then dried
with hot air at approximately 60.degree. C. Thereby a positive
electrode active material particle can be obtained including a base
particle comprising a nickel hydroxide particle containing Mn
provided with a higher valence in solid solution and a conductive
layer comprising cobalt oxyhydroxide containing Na or Li and
provided on the surface of the base particle.
[0055] Since the positive electrode active material according to
embodiments of the present invention contains Mn in solid solution,
a battery including the positive electrode active material
according to embodiments of the present invention is basically
excellent in charge/discharge cycle characteristics. The Mn
contained in solid solution in nickel hydroxide, which has been
subjected to the above-described oxidation treatment, has been
provided with a higher valence such that the X-ray absorption edge
energy is 6548 eV or high. If Mn has been provided with a higher
valence in this way, Mn itself is prevented from being reduced and
eluted into an alkaline electrolytic solution even when a battery
comes into a deeply-discharged state, and in addition reduction of
Co in the conductive layer by Mn is also prevented from
accelerating. Since reduction and elution of Mn itself is thus
prevented, deterioration of the bulk portion of nickel hydroxide is
prevented, and thereby lowering of the capacity is prevented.
Accordingly, the positive electrode active material according to
embodiments of the present invention contributes to reduction of
lowering of the capacity recovery rate of a battery. Since
reduction of Co in the conductive layer by Mn is also prevented
from accelerating, destruction of the conductive network is also
reduced. Also owing to this, the positive electrode active material
according to embodiments of the present invention contributes to
reduction of lowering of the capacity recovery rate of a
battery.
[0056] Subsequently, the positive electrode 24 is produced, for
example, in the following manner.
[0057] First, a positive electrode admixture slurry containing the
positive electrode active material particle 36 obtained as
described above, water, and the binder 42 is prepared. For example,
a nickel foam sheet is filled with the positive electrode admixture
slurry, and dried. After being dried, the nickel foam sheet filled
with a nickel hydroxide particle, etc., is rolled and cut, and thus
the positive electrode 24 is fabricated.
[0058] In the positive electrode 24 thus obtained, the positive
electrode active material particles 36 comprising the base particle
38 the surface of which is covered with the conductive layer 40
comes into interparticle contact as illustrated in the circle S in
FIG. 1, and the conductive layer 40 forms a conductive network.
[0059] It is preferred to further add at least one selected from
the group comprising a Y compound, Nb compound, W compound, and Co
compound, as an additive, to the positive electrode 24. The
additive prevents Co from being eluted from the conductive layer 40
when deep discharge is repeated, and destruction of the conductive
network is reduced. Accordingly, the additive contributes to
improvement of the durability against repeated deep discharge. It
is preferred to use, for example, yttrium oxide for the Y compound,
to use, for example, niobium oxide for the Nb compound, to use, for
example, tungsten oxide for the W compound, and to use, for
example, cobalt hydroxide for the Co compound.
[0060] The additive is added into the positive electrode admixture,
and the content is preferably set in the range of 0.2 to 2.0 parts
by mass based on 100 parts by mass of the positive electrode active
material particle. This is because an additive content of less than
0.2 parts by mass does not provide an effect of preventing Co from
being eluted from the conductive layer, and an additive content of
more than 2.0 parts by mass causes saturation of the effect and
leads to relative reduction of the quantity of the positive
electrode active material, which results in lowering of
capacity.
[0061] Next, the negative electrode 26 will be described.
[0062] The negative electrode 26 includes a band-shaped, conductive
negative electrode base, and a negative electrode admixture is held
on the negative electrode base.
[0063] The negative electrode base comprises a sheet of a metal
material with through-holes distributed therein, and for example, a
punched metal sheet may be used. The negative electrode admixture
fills not only the through-holes of the negative electrode base,
but also is held as a layer on both surfaces of the negative
electrode base.
[0064] The negative electrode admixture contains a hydrogen storage
alloy particle capable of occluding/releasing hydrogen as a
negative electrode active material, a conductive agent, and a
binder. The binder functions to bind the hydrogen storage alloy
particle and the conductive agent together, and simultaneously bind
the hydrogen storage alloy particle and the conductive agent to the
negative electrode base. A hydrophilic or hydrophobic polymer may
be used for the binder, and carbon black or graphite may be used
for the conductive agent.
[0065] The hydrogen storage alloy in the hydrogen storage alloy
particle is not limited, and a hydrogen storage alloy commonly used
for nickel-hydrogen secondary batteries may be employed.
[0066] The negative electrode 26 can be produced, for example, in
the following manner.
[0067] First, a hydrogen storage alloy powder comprising a hydrogen
storage alloy particle, a conductive agent, a binder, and water are
kneaded together to prepare a negative electrode admixture paste.
The negative electrode admixture paste obtained is applied onto a
negative electrode base and dried. After being dried, the negative
electrode base with the attached hydrogen storage alloy particle,
etc., is rolled and cut, and thus the negative electrode 26 is
fabricated.
[0068] The positive electrode 24 and the negative electrode 26 each
fabricated as described above are spirally wound with the separator
28 sandwiched therebetween, and thus the electrode group 22 is
formed.
[0069] The electrode group 22 thus obtained is contained in the
outer can 10. Subsequently, a predetermined quantity of an alkaline
electrolytic solution is injected into the outer can 10.
Thereafter, the outer can 10 containing the electrode group 22 and
the alkaline electrolytic solution is sealed with the sealing
element 11 provided with the positive electrode terminal 20, and
thus the battery 2 according to embodiments of the present
invention can be obtained. The battery 2 obtained is subjected to
initial activation treatment to make the battery ready for use.
EXAMPLES
1. Production of Battery
Example 1
(1) Fabrication of Positive Electrode
[0070] Nickel sulfate, zinc sulfate, cobalt sulfate, and manganese
sulfate were weighed so as to achieve a Zn content of 4.0% by mass,
a Co content of 1.0% by mass, and a Mn content of 0.1% by mass each
based on the quantity of Ni, and they were added to a 1 N sodium
hydroxide aqueous solution containing ammonium ions to prepare a
mixed aqueous solution. While the mixed aqueous solution obtained
was stirred, a 10 N sodium hydroxide aqueous solution was gradually
added to the mixed aqueous solution to react, and then the pH
during the reaction was stabilized within 13 to 14 to produce a
base particle 38 comprising a nickel hydroxide particle containing
nickel hydroxide as a main component containing Zn, Co, and Mn in
solid solution.
[0071] The base particle 38 obtained was washed three times with
pure water in a quantity 10 times as much as that of the base
particle 38, and then dehydrated and dried. The particle size of
the base particle 38 obtained was measured with a laser
diffraction/scattering particle size distribution analyzer, and the
mean volume diameter (MV) of the base particle 38 was found to be
11 .mu.m.
[0072] Subsequently, the base particle 38 obtained was charged into
an ammonia aqueous solution, and a cobalt sulfate aqueous solution
was added thereto while the pH during the reaction was maintained
within 9 to 10. Thereby, a composite particle including a core of
the base particle 38 and a cobalt hydroxide layer having a
thickness of approximately 0.1 .mu.m resulting from precipitation
of cobalt hydroxide on the surface of the core was obtained.
[0073] Then, the composite particle was subjected to heat treatment
in convection of oxygen-containing air in an environment of
80.degree. C. for 45 minutes while a 12 N sodium hydroxide aqueous
solution was sprayed, by which the cobalt hydroxide on the surface
of the composite particle is converted into highly-conductive
cobalt oxyhydroxide, and Na is incorporated in the cobalt
oxyhydroxide layer, and as a result a conductive layer 40
comprising cobalt oxyhydroxide containing Na is formed. Thereafter,
the composite particle including the cobalt oxyhydroxide layer was
collected through filtration, and washed with pure water. The
washed composite particle was then charged into a sodium chlorite
aqueous solution in a quantity 10 times as much as that of the
composite particle. Here, the sodium chlorite aqueous solution,
being an aqueous solution containing 10% by mass of sodium
chlorite, had been heated and was retained at 60.degree. C. And
then, the sodium chlorite aqueous solution at 60.degree. C. into
which the composite particle had been charged was stirred for 60
minutes for oxidation treatment of Mn contained in solid solution
in the base particle. The composite particle after the completion
of the oxidation treatment was washed with pure water and dried
with hot air at approximately 60.degree. C. Thereby was obtained a
positive electrode active material particle 36 including a base
particle 38 comprising a nickel hydroxide particle containing Mn
provided with a higher valence in solid solution and a conductive
layer 40 comprising cobalt oxyhydroxide containing Na and provided
on the surface of the base particle 38.
[0074] Subsequently, 0.3 parts by mass of a yttrium oxide powder,
0.2 parts by mass of HPC (hydroxypropyl cellulose), 0.2 parts by
mass of a PTFE dispersion, and 50 parts by mass of ion-exchanged
water were mixed with 100 parts by mass of a positive electrode
active material powder comprising the positive electrode active
material particle 36 fabricated as described above to prepare a
positive electrode admixture slurry, and a sheet of nickel foam as
a positive electrode base material was filled with the positive
electrode admixture slurry. The nickel foam filled with the
positive electrode admixture slurry was subjected to drying, and
the nickel foam filled with the positive electrode admixture was
then rolled. Thereafter, the nickel foam filled with the positive
electrode admixture was cut in a predetermined shape to obtain a
positive electrode 24 for the size AA.
(2) Fabrication of Negative Electrode
[0075] First, a hydrogen storage alloy powder comprising an
LaNi.sub.5 particle, as an AB.sub.5 type hydrogen storage alloy,
was prepared. The particle size of the LaNi.sub.5 particle was
measured with a laser diffraction/scattering particle size
distribution analyzer, and the mean volume diameter (MV) of the
LaNi.sub.5 particle was found to be 60 .mu.m.
[0076] Subsequently, 0.4 parts by mass of a sodium polyacrylate
powder, 1.0 part by mass of a carbon black powder, and 30 parts by
mass of ion-exchanged water were added to 100 parts by mass of the
hydrogen storage alloy powder, and the resultant was kneaded to
prepare a negative electrode admixture paste.
[0077] The negative electrode admixture paste was homogeneously
applied onto both surfaces of a punched metal sheet as a negative
electrode base so as to achieve a constant thickness. The punched
metal sheet was a thin iron sheet having a thickness of 60 .mu.m
and the surface had been nickel-plated.
[0078] After the paste was dried, the punched metal sheet holding
the negative electrode admixture was rolled, and then cut in
predetermined dimensions to obtain a negative electrode 26 for the
size AA.
(3) Assembly of Nickel-Hydrogen Secondary Battery
[0079] The positive electrode 24 and negative electrode 26 obtained
were spirally wound with a separator 28 sandwiched therebetween to
fabricate an electrode group 22. The separator 28 used for
fabrication of the electrode group 22 comprised a sulfonated
polypropylene nonwoven fabric, and the thickness was 0.1 mm (basis
weight: 53 g/m.sup.2).
[0080] Separately, an alkaline electrolytic solution comprising an
aqueous solution containing NaOH and LiOH was prepared. The
alkaline electrolytic solution had an NaOH concentration of 7.0 N
and an LiOH concentration of 1.0 N.
[0081] Then, the electrode group 22 was contained in an outer can
10 having a bottomed cylindrical shape, and a predetermined
quantity of the alkaline electrolytic solution prepared was
injected thereinto. Thereafter, the opening of the outer can 10 was
sealed with a sealing element 11, and assembled an AA
nickel-hydrogen secondary battery 2 with a nominal capacity of 2000
mAh.
(4) Initial Activation Treatment
[0082] The battery 2 obtained was left to stand in an environment
of 25.degree. C. for 12 hours, and then three cycles of
charging/discharging operation were performed for the battery 2, in
each of which the battery 2 was charged at a charging current of
0.1 It for 16 hours and thereafter discharged at a discharging
current of 0.2 It to a battery voltage of 1.0 V. By such initial
activation treatment, the battery 2 was made ready for use.
Example 2
[0083] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 1 except that the base particle 38 was
produced so as to achieve a Mn content of 1.0% by mass.
Example 3
[0084] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 1 except that the base particle 38 was
produced so as to achieve a Mn content of 2.0% by mass.
Example 4
[0085] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 1 except that the base particle 38 was
produced so as to achieve a Mn content of 2.5% by mass.
Comparative Example 1
[0086] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 1 except that oxidation treatment for Mn
contained in solid solution in the base particle was not
performed.
Comparative Example 2
[0087] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 2 except that oxidation treatment for Mn
contained in solid solution in the base particle was not
performed.
Comparative Example 3
[0088] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 3 except that oxidation treatment for Mn
contained in solid solution in the base particle was not
performed.
Comparative Example 4
[0089] A nickel-hydrogen secondary battery was fabricated in the
same manner as in Example 4 except that oxidation treatment for Mn
contained in solid solution in the base particle was not
performed.
2. Evaluation of Positive Electrode Active Material and
Nickel-Hydrogen Secondary Battery
(1) Analysis by Using Fluorescence XAFS Method
[0090] In each of Examples 1 to 4 and Comparative Examples 1 to 4,
a part of the positive electrode active material powder had been
taken in advance as a sample for analysis by using the fluorescence
XAFS method.
[0091] The samples for analysis by using the fluorescence XAFS
method were subjected to XAFS analysis by using the fluorescence
yield method with a synchrotron X-ray from a large-scaled
synchrotron radiation facility (e.g., Super Photon ring-8:
SPring-8). The specific procedure is as follows.
[0092] First, a sample in an appropriate quantity was applied onto
a carbon tape. The carbon tape holding the sample was set on a
sample stage in a 19-element Ge semiconductor detector
(manufactured by CANBERRA Industries Inc.). For the detector, the
ROI (region of interest) was set to the Mn K.alpha. line at an
energy of approximately 5900 eV.
[0093] And then, the sample was irradiated with an synchrotron
X-ray. The intensity of the Mn K.alpha. line was measured while the
energy of the synchrotron X-ray irradiation was scanned through
changing the angle of the Si (111) crystal monochromator, and thus
the fluorescence XAFS spectrum of Mn was acquired by using the
fluorescence yield method. By using this procedure, the
fluorescence XAFS spectrum data of Mn was acquired for each of the
samples in Examples 1 to 4 and Comparative Examples 1 to 4.
[0094] The energy of a synchrotron X-ray was calibrated through
setting the angle of the Si (111) crystal monochromator to
12.7184.degree. when a pre-edge peak near 8980.3 eV was observed in
an XAFS spectrum of a copper foil.
[0095] Here, the graph of the fluorescence XAFS spectrum obtained
for the sample in Example 1 is shown in FIG. 2. From FIG. 2, the
X-ray energy corresponding to an absorption edge, at which the
absorption coefficient reached 0.3, was defined and determined as
the X-ray absorption edge energy of Mn. An XAFS spectrum was
acquired for each of Examples 2 to 4 and Comparative Examples 1 to
4 in the same manner, and the X-ray absorption edge energy of Mn at
an absorption edge (a position at which the absorption coefficient
reached 0.3) was determined from the graph. The results are shown
as "X-ray absorption edge energy of Mn" in Table 1.
[0096] A higher value of the X-ray absorption edge energy of Mn
indicates that the valence of Mn is higher, i.e., the Mn has been
provided with a higher valence.
(2) Measurement of Capacity Recovery Rate after Deep Discharge
[0097] The battery after the initial activation treatment in each
of Examples 1 to 4 and Comparative Examples 1 to 4 was charged in
an environment of 25.degree. C. under what is called -.DELTA.V
control, specifically, charged at 1.0 It until the battery voltage
after having reached the maximum value was lowered by 10 mV, and
then discharged at 0.2 It in the same environment until the battery
voltage reached 1.0 V, and the initial capacity was determined.
[0098] Thereafter, each battery was left to stand with a resistor
of 2.OMEGA. connected to the battery in an environment of
60.degree. C. for 14 days to bring the battery into a
deeply-discharged state.
[0099] Each of the batteries after being brought into a
deeply-discharged state was subjected to three charge/discharge
cycles in each of which charging was performed at 1.0 It in an
environment of 25.degree. C. under -.DELTA.V control and
discharging was then performed at 0.2 It in the same environment
until the battery voltage reached 1.0 V. And then, the capacity
after the third cycle (capacity after deep discharge) was
measured.
[0100] The capacity recovery rate after deep discharge was
determined by using the following equation (I), and the results are
shown in Table 1.
Capacity recovery rate after deep discharge [%]=(capacity after
deep discharge/initial capacity).times.100 (I)
[0101] A higher value of the capacity recovery rate after deep
discharge indicates a higher resistance to deep discharge and that
destruction of the conductive network is reduced.
TABLE-US-00001 TABLE 1 Content of X-ray Capacity Mn in solid
absorption recovery rate solution in base Oxidation edge energy
after deep particle [% treatment of Mn discharge by mass] of Mn
[eV] [%] Example 1 0.1 performed 6548 100 Example 2 1.0 performed
6548 100 Example 3 2.0 performed 6548 99 Example 4 2.5 performed
6548 95 Comparative 0.1 not 6547 95 Example 1 performed Comparative
1.0 not 6547 92 Example 2 performed Comparative 2.0 not 6547 89
Example 3 performed Comparative 2.5 not 6547 84 Example 4
performed
(3) Discussion
[0102] For the batteries in Examples 1 to 4, the capacity recovery
rates after deep discharge are in the range of 95% to 100%. For the
batteries in Comparative Examples 1 to 4, on the other hand, the
capacity recovery rates after deep discharge are in the range of
84% to 95%. From the results, it can be seen that the capacity
recovery rates of the batteries in Examples 1 to 4 are better than
those of the batteries in Comparative Examples 1 to 4, and the
batteries in Examples 1 to 4 each have an improved resistance to
deep discharge in comparison with the batteries in Comparative
Examples 1 to 4.
[0103] In the batteries in Examples 1 to 4, Mn contained in solid
solution in the nickel hydroxide particle in the positive electrode
was subject to oxidation treatment and was provided with a higher
valence such that the absorption edge energy reached 6548 eV.
Accordingly, we infer that reduction of Co in the conductive layer
by the Mn is prevented from accelerating even in a
deeply-discharged state and deterioration of the bulk portion of
the nickel hydroxide particle due to elution of the Mn itself is
also prevented; and as a result the conductive network is
maintained in a proper state after deep discharge and nickel
hydroxide as a positive electrode active material is maintained in
a proper state, and thus the batteries in Examples 1 to 4 each have
an excellent capacity recovery rate after deep discharge.
[0104] In the batteries in Comparative Examples 1 to 4, on the
other hand, Mn contained in solid solution in the nickel hydroxide
particle in the positive electrode was not subject to oxidation
treatment and was not provided with a higher valence. Accordingly,
we infer that reduction of Co in the conductive layer by the Mn is
accelerated in a deeply-discharged state, and the Mn itself is
eluted and the bulk portion of the nickel hydroxide particle
becomes brittle and deteriorated; as a result a thin portion of the
Co compound layer is reduced and deteriorated in deep discharge and
the conductive network is partly destroyed, and thus the batteries
in Comparative Examples 1 to 4 each have a lowered capacity
recovery rate after deep discharge; and in addition proper battery
reaction cannot proceed due to the deterioration of the bulk
portion of the nickel hydroxide particle, which also causes the
lowering of the capacity recovery rate after deep discharge.
[0105] The capacity recovery rate after deep discharge in
Comparative Example 1 is 95%. On the other hand, the capacity
recovery rate after deep discharge in Example 1 is 100%, a value
improved by 5% in comparison with that in Comparative Example 1. In
comparison with Example 1 and Comparative Example 1, the content of
Mn in solid solution in the nickel hydroxide particle is an
identical value of 0.1% by mass and in contrast Example 1 and
Comparative Example 1 are different in terms of whether oxidation
treatment was performed. Due to this, the X-ray absorption edge
energy of Mn is different between Example 1 and Comparative Example
1, the former being 6548 eV and the latter being 6547 eV.
[0106] The capacity recovery rate after deep discharge in
Comparative Example 2 is 92%. On the other hand, the capacity
recovery rate after deep discharge in Example 2 is 100%, a value
improved by 8% in comparison with that in Comparative Example 2. In
comparison with Example 2 and Comparative Example 2, the content of
Mn in solid solution in the nickel hydroxide particle is an
identical value of 1.0% by mass and in contrast Example 2 and
Comparative Example 2 are different in terms of whether oxidation
treatment was performed. Due to this, the X-ray absorption edge
energy of Mn is different between Example 2 and Comparative Example
2, the former being 6548 eV and the latter being 6547 eV.
[0107] The capacity recovery rate after deep discharge in
Comparative Example 3 is 89%. On the other hand, the capacity
recovery rate after deep discharge in Example 3 is 99%, a value
improved by 10% in comparison with that in Comparative Example 3.
In comparison with Example 3 and Comparative Example 3, the content
of Mn in solid solution in the nickel hydroxide particle is an
identical value of 2.0% by mass and in contrast Example 3 and
Comparative Example 3 are different in terms of whether oxidation
treatment was performed. Due to this, the X-ray absorption edge
energy of Mn is different between Example 3 and Comparative Example
3, the former being 6548 eV and the latter being 6547 eV.
[0108] The capacity recovery rate after deep discharge in
Comparative Example 4 is 84%. On the other hand, the capacity
recovery rate after deep discharge in Example 4 is 95%, a value
improved by 11% in comparison with that in Comparative Example 4.
In comparison with Example 4 and Comparative Example 4, the content
of Mn in solid solution in the nickel hydroxide particle is an
identical value of 2.5% by mass and in contrast Example 4 and
Comparative Example 4 are different in terms of whether oxidation
treatment was performed. Due to this, the X-ray absorption edge
energy of Mn is different between Example 4 and Comparative Example
4, the former being 6548 eV and the latter being 6547 eV.
[0109] The above comparison between Examples and Comparative
Examples suggests that oxidation treatment of Mn to make the
absorption edge energy of Mn 6548 eV or high is effective for
improvement of the capacity recovery rate after deep discharge even
in the case that the content of Mn in solid solution in the nickel
hydroxide particle is unchanged.
[0110] In order to achieve a capacity recovery rate of 95% or
higher, which is the highest capacity recovery rate achieved in
Comparative Examples, it is considered effective to set the content
of Mn in solid solution in the nickel hydroxide particle to 0.1% by
mass to 2.0% by mass and perform oxidation treatment of Mn so that
the absorption edge energy of Mn reaches 6548 eV or high.
[0111] These results demonstrate that setting the X-ray absorption
edge energy of Mn in a nickel hydroxide particle containing Mn in
solid solution to 6548 eV as measured by using the fluorescence
XAFS method allows for providing a battery which takes advantage of
excellent cycle life characteristics derived from Mn contained in
solid solution and is less affected by deep discharge and in which
lowering of the capacity recovery rate is reduced.
[0112] The present invention is never limited to the
above-described embodiments and Examples, and may be variously
modified. A battery to be used for the present invention is only
required to be an alkaline secondary battery, and examples thereof
include, in addition to nickel-hydrogen secondary batteries,
nickel-cadmium secondary batteries and nickel-zinc secondary
batteries. The mechanical structure of a battery is not limited,
and not only a circular battery but also a square battery may be
used.
[0113] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be obvious to one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *