U.S. patent application number 10/923386 was filed with the patent office on 2005-01-27 for non-sintered type thin electrode for battery, battery using same and process for same.
Invention is credited to Matsumoto, Isao.
Application Number | 20050019664 10/923386 |
Document ID | / |
Family ID | 26598851 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050019664 |
Kind Code |
A1 |
Matsumoto, Isao |
January 27, 2005 |
Non-sintered type thin electrode for battery, battery using same
and process for same
Abstract
An electrode substrate is formed by mechanically processing a
nickel foil so as to be made three dimensional through the creation
of concave and convex parts, and then, this substrate is filled
with active material or the like so that an electrode is
manufactured, wherein the above described concave and convex parts
are rolling pressed so as to incline in one direction. Furthermore,
an electrode for secondary battery is formed by using the above
described method.
Inventors: |
Matsumoto, Isao; (Osaka-Shi,
JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Family ID: |
26598851 |
Appl. No.: |
10/923386 |
Filed: |
August 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10923386 |
Aug 20, 2004 |
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09870257 |
May 30, 2001 |
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6800399 |
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Current U.S.
Class: |
429/235 ;
205/271; 29/2; 429/245 |
Current CPC
Class: |
H01M 2004/021 20130101;
H01M 4/622 20130101; H01M 4/661 20130101; H01M 4/667 20130101; Y02E
60/10 20130101; H01M 4/0409 20130101; H01M 4/663 20130101; H01M
4/242 20130101; H01M 10/052 20130101; H01M 4/0404 20130101; H01M
4/32 20130101; H01M 6/10 20130101; H01M 4/745 20130101; H01M 4/74
20130101; Y10T 29/49115 20150115; H01M 10/345 20130101; Y10T 29/10
20150115 |
Class at
Publication: |
429/235 ;
429/245; 029/002; 205/271 |
International
Class: |
H01M 004/80; H01M
004/66; C25D 003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2000 |
JP |
2000-261780 |
Oct 18, 2000 |
JP |
2000-318407 |
Claims
1-10. (cancelled)
11. Process for producing a non-sintered thin electrode for
batteries, which comprises the steps of: filling into or coating on
conductive electrode substrate in a wide belt-like form with the
paste of powders that contain mainly active material or
pseudo-materials; pressing the filled or coated conductive
electrode substrate between a pair of rollers; and cutting into a
desirable size; wherein (a) the conductive electrode substrate has
an unevenness produced on the conductive electrode substrate by
unevenness processing except for a part which remains even with a
desirable width at least on both sides along the longitudinal
direction, (b) the conductive electrode substrate has innumerable
hollow concave and convex parts formed by the unevenness
processing, (c) the thickness of the conductive electrode substrate
which made a thin electrolyte-proof metal plate into a three
dimensional form with said concave and convex parts is 0.5 to 2.0
times as large as the thickness of the final electrode, and (d) the
number of concave parts is not less than half the number of concave
and convex parts, wherein the said concave parts are adjacent and
closest to a convex part, the number of groups of concave parts is
not less than half the number of groups of concave and convex
parts, wherein the said groups of concave parts are adjacent and
closest groups of convex parts, the number of convex parts is not
less than half the number of concave and convex parts wherein the
said concave and convex parts are adjacent and closest to a concave
part, and the number of groups of convex parts is not less than
half the number of groups of concave and convex parts, wherein the
said concave and convex groups parts are adjacent and closest to
groups of concave parts.
12. Process for producing a non-sintered thin electrode for
batteries according to claim 11, wherein said conductive electrode
substrate: is processed to produce said unevenness by means of
pressing between dies in which the upper and the lower dies are
formed to have the same unevenness so as to engage with each other,
pressing between rollers in which the upper and the lower rollers
are formed to have the same unevenness so as to engage with each
other, or depositing nickel with the electrolytic nickel deposition
method; and is provided with alternating columns of numerous
concave parts or concave part groups and columns of numerous convex
parts or convex part groups which are substantially in parallel and
spaced at a constant interval while making an angle in a range of
about 30 to 60 degrees with respect to longitudinal direction of
the substrate.
13. Process for producing a non-sintered thin electrode for
batteries according to claim 12, wherein said conductive electrode
substrate employed to form the non-sintered thin electrode is roll
pressed and contoured in one direction in the vicinity of both
surfaces of the said conductive electrode substrate.
14. Process for producing a non-sintered thin electrode for
batteries according to claim 11, wherein the formation process
applies a rolling press operation at least twice, wherein a first
rolling press operates at a relatively high speed and with low
pressure in an opposite rolling direction to the direction in which
the electrode proceeds while a second press operates between
rollers with larger diameters than those of the first rolling press
at a lower speed than the first rolling press and with higher
pressure than the first rolling press in the same direction that
the electrode proceeds.
15. Process for producing a non-sintered thin electrode for
batteries according to claim 11, wherein the process comprises the
step of; pressing slightly by rubbing the surfaces of the
conductive electrode between a slit with a brush, while being
filled in or coated on with active material or pseudo-active
material, before pressing the filled or coated conductive electrode
substrate between a pair of rollers.
16. Process for producing a non-sintered thin electrode for
batteries according to claim 11, wherein after being cut into a
desirable size, the said electrode is immersed in a liquid wherein
a fine powder of synthetic resin is dispersed or the same liquid is
sprayed onto the surfaces of said electrode so that said electrode
is thinly coated with the fine powder of said synthetic resin.
17. Process for producing a non-sintered thin electrode for
batteries according to claim 16, wherein said synthetic resin is
any of fluoride resin, polyolefin, polyvinyl-type and polysulfone
resin powders or copolymers of which the main material is the above
resins.
18. A secondary battery wherein electrodes, at least one thin
electrode obtained by filling or coating a power of which a main
component is active material powders or pseudo-active material
powders to the conductive electrode substrate which has a three
dimensional structures and an opposite electrode with separator are
sealed in a battery case, wherein: (a) the conductive electrode
substrate has an innumerable number of hollow concave and convex
parts; (b) a thickness of the conductive electrode substrate, made
of a metal foil with electrolyte-proof resistance properties in a
three dimensional form with said concave and convex parts, is
nearly the same as the thickness of the final electrode; (c) the
number of concave parts is not less than half the number of concave
and convex parts wherein the said concave and convex parts are
adjacent and closest to a convex part, the number of groups of
concave parts is not less than half the number of concave and
convex parts, wherein the said concave and convex parts are
adjacent and closest to a convex part, the number of convex parts
is not less than half the number of concave and convex parts,
wherein the said concave and convex parts are adjacent and closest
to a concave part, and the number of groups of convex parts is not
less than half the number of groups of concave and convex parts,
wherein the said concave and convex parts are adjacent and closest
to groups of concave parts; and (d) the walls of said concave and
convex parts bend in the direction of the thickness of said
conductive electrode substrate so as to incline to a greater extent
in one direction in relation to proximity to the edges of the
concave and convex parts.
19. The secondary battery according to claim 18, wherein said
battery case has a bottom whose thickness (t.sub.2) can withstand
welding and a ratio (t.sub.1/t.sub.2) of the thickness (t.sub.2) of
the bottom to a thickness (t.sub.1) of the side walls is 1.5 or
more.
20. The secondary battery according claim 19, wherein a thicker
part is provided inside of the battery case along the border
between the wall surface and the bottom in said battery case.
21. The secondary battery according to claim 19, wherein a positive
terminal of an adjoining secondary battery is welded directly, or
via a metal connector, to the bottom of said battery case.
Description
FIELD OF INVENTION
[0001] The present invention relates to a paste type thin electrode
for a battery, in which the cost is reduced and the high rate
discharge characteristics and the cycle life are improved, and to a
secondary battery using this electrode.
BACKGROUND OF THE INVENTION
[0002] At present electrodes for batteries, used commercially for
secondary batteries, are broadly categorized as sintered type
electrodes and non-sintered type electrodes. In the sintered type
electrodes, active material is filled into a highly porous three
dimensional substrate where metal powder is sintered to have a
large porosity on both sides of a two dimensional metal substrate.
In the non-sintered type electrodes, the active material powder
with a binder is coated on a two dimensional metal substrate or
grid, or filled into a three dimensional substrate, such as foamed
nickel, metal bag or tube, without employing a sintered
substrate.
[0003] In general, the former exhibits excellent characteristics in
electronic conductivity (high-rate charge and discharge
characteristics) due to a large amount of metal used in the
sintered plaque and has a long cycle-life with excellent mechanical
strength and stability in the shedding of active material, while it
has the defect that the electrode is heavy and has a small
volumetric energy density due to a small amount of active material
impregnated therein because of a large volume of the electrode
substrate.
[0004] On the contrary, a representative and simple non-sintered
type electrode is inexpensive and light weight, and has a large
volumetric energy density because of using an inexpensive substrate
of a small volumetric amount in the electrode, which is easy to
manufacture, through the coating or direct filling process of
active material powder, while it entails the problem that the
entire electrode is inferior in current collection ability as a
whole, in the mechanical strength and in the holding of the active
material. These are significant problems in secondary batteries
where charging and discharging is repeated and, therefore, a
variety of ideas are incorporated into respective battery
systems.
[0005] As a result, non-sintered types have a variety of substrates
to improve the above problems, as represented by a paste type or an
application type, wherein active material powder is mixed with
conductive material or a binder which is then mixed together with a
solution and the obtained paste or slurry is coated on a two
dimensional substrate of a variety of shapes, or in some cases the
active material powders are filled in a pocket type or a tube type
substrate which has innumerable small pores for electrochemical
reactions.
[0006] As examples of non-sintered type electrodes, which are of
the former type, a cadmium negative electrode, a metal hydride
negative electrode for alkaline storage batteries, the positive and
negative electrodes for lithium ion batteries and the positive and
negative electrodes for lead acid batteries are cited. Non-sintered
type batteries which are of the latter type are, for example,
employed in part of the nickel positive electrode for large scale
alkaline storage batteries or for certain types of lead acid
batteries. As a substrate of the electrodes described herein,
punching metal, a metal screen, foamed metal, a metal grid or the
like are individually utilized according to the battery systems or
the purpose.
[0007] However, recently, new types of electrodes in which a paste
of active materials is filled into a foamed nickel porous substrate
or into a nickel fiber substrate, which have a three dimensional
structure, in the high density (hereinafter abbreviated as 3DM
type), have started being employed as proposed in U.S. Pat. No.
4,251,603, which belongs to another non-sintered type in
classification. However, though these types of electrodes have a
high capacity and a high reliability and are easily made to have
higher capacity and to be lighter weight compared with the sintered
type, due to a small amount of metal employed in the substrate,
they have the technical problems that the mechanical strength is
low and the electronic conduction of the entire electrode is
inferior due to a large pore diameter within the substrate and, in
addition, have the technical problem that the cost of the substrate
is high.
[0008] Since the present invention of paste type electrode relates
to an improvement of the three dimensional substrate used in the
above described 3DM system, in particular for alkaline storage
battery system currently, for the convenience of the detail
technological description of prior art, a nickel positive electrode
for a small sealed cylindrical Ni/MH batteries is focused on
thereafter.
[0009] As for the nickel positive electrode for alkaline storage
batteries, the sintered type electrode, which was developed in
Germany during the Second World War, has a high performance and is
durable, which replaced the previous non-sintered type electrode,
that is to say, the pocket type electrode, and, therefore, a
sintered type electrode started to be used for rectangular Ni/Cd
batteries requiring high performance and high reliability. As for
the negative electrode, a similar conversion to the sintered type
has occurred. As for the electrodes of sealed cylindrical Ni/Cd
batteries developed afterwards, sintered type positive and negative
electrodes have become the most popular because they are easily
processed into thin electrodes. The small sealed cylindrical
batteries represented by this nickel-cadmium battery (Ni/Cd
battery) have achieved a dramatic growth as a power supply for
portable compact electronic equipments, such as camcorders or CD
players, which have achieved a remarkable growth in Japan starting
in the 1980's. However, in the 1990's, a new type of nickel-metal
hydride storage battery (Ni/MH battery) and a lithium ion battery
successively have been put into practical use so as to begin
expansion into the market of nickel-cadmium batteries.
[0010] And, as for a new market, applications for power supplies as
power tools, applications for mobile power supplies, that is to
say, for electrical vehicles (EVs), hybrid electrical vehicles
(HEVs), electric power assisted bicycles or the like have newly
started growing in recent years, and for those power supplies
mainly Ni/MH batteries have started being used. A nickel positive
electrode is employed for the positive electrodes of the above
described Ni/Cd batteries and Ni/MH batteries for which the growth
recently has been remarkable and the sintered types and 3DM types
are used respectively, according to the applications under the
present circumstances.
[0011] As for the structure of this nickel positive electrode for a
mass-production level, the non-sintered type was limited only to
the pocket type, due to the electrode mechanical stability. The
pocket type electrode has a structure wherein active material
powder is filled into a electrolyte proof metal bag with
innumerable small pores to prevent the shedding of active metal
powders as described above. The sintered type adopts a structure
wherein a solution of active material salt is impregnated into the
space of a three dimensional sintered plaque, followed by the
process of conversion to the active material with alkaline
solution. Naturally, the active material in this case is not in a
powder condition.
[0012] Another non-sintered 3DM type, which is different from the
pocket type, is reported as a nickel positive electrode employing
foamed nickel in the ECS Fall Meeting (Detroit) Abstract No. 10 in
1981. This electrode has a structure using a foamed nickel porous
body as a substrate, into which active material powder is
filled.
[0013] Though a light weight nickel positive electrode with a high
capacity is realized by using this foamed nickel as a substrate, it
has the problems that the high power drain of the entire active
material is not sufficient due to the large diameter of the
internal spherical space, which is approximately 450 .mu.m in the
case of even the smallest diameter, and it is expensive. Therefore,
batteries using a sintered type nickel positive electrode which
exhibit excellent characteristics in high-rate discharge are still
the most popular for applications requiring high power drain.
[0014] However, the following shortcomings of the sintered type
electrodes for those applications have been increasing, as problems
in practical use, while applications are expanding, and, therefore,
the introduction of the paste type electrodes are desirable. The
shortcomings are: small energy density; heavy weight; large
self-discharge due to the well-known shuttle reaction between
nitride and nitrate ions, which is not present in the non sintered
type. Since those applications require a high-rate discharge, thin
electrodes are, in general, employed to increase the electrode
surface area in order to have a large active area, which also
increases the area of the substrates of the electrodes.
Accordingly, a two dimensional substrate or a three dimensional
substrate of low cost are particularly required and also light
weight is a prerequisite for these high-power uses.
[0015] Therefore, new structures of three dimensional substrates to
replace expensive foamed nickel such as in the 3DM type, which is a
kind of the paste type of light weight, are proposed as
follows:
[0016] (1) One sheet of electrode is formed by overlapping a
plurality of extremely thin electrodes wherein active material
powder is coated on the porous substrate, such as thin punched
metal and foamed metal.
[0017] (2) Innumerable pieces of metal in the form of bristle or
whisker are attached to a porous substrate, such as metal foil and
punched metal (U.S. Pat. No. 5,840,444).
[0018] (3) Burrs are provided on a metal plate in the direction of
the thickness of the plate (U.S. Pat. No. 5,543,250).
[0019] (4) A metal plate is processed to have a three dimensional
corrugated form. Holes with burrs are provided on the crests of the
corrugated form so as to increase the three dimensional shape (U.S.
Pat. No. 5,824,435).
[0020] The structures or the substrates in the above described (1)
to (4), however, have not solved all of the problems. In (1), there
still remains the problem of the active mass shedding of each thin
electrode due to the swelling of the active material during charge
and discharge cycles, which essentially cannot be prevented. In
(2), the thickness of the paste layer lacks uniformity due to the
low binding strength between the metal fiber in bristle or whisker,
or due to the non-uniformity of the holes of the substrate itself
with respect to its characteristics and, additionally, it costs
more than the conventional substrates. In (3), the structure is
basically not three dimensional and, therefore, it has problems in
the shedding of the active material powders following a decay in
charge and discharge characteristics. In (4), though the above
described problems have been improved to some extent and low cost
can be expected, there still remains the problem that a desired
three dimensional substrate shape is difficult to maintain.
Because, the substrate of the corrugated form is easily expanded in
the direction of the wave form during the electrode press work,
which leads to the problem that the active material is easily
peeled off from the substrate when it is wound into an electrode of
a spiral form or when charging and discharging are repeated.
[0021] In addition, power supplies for electric power tools are
desired, derived from how power tools are used, to have high-rate
discharge characteristics, and the batteries for power-use, such as
electric vehicles (EVs), hybrid electric vehicles (HEVs) and
electric power assisted bicycles are desired to have improved
high-rate discharge characteristics, particularly desired to be
smaller and to be lighter in order to secure space within the
vehicles and in order to improve fuel efficiency respectively, that
is to say, to increase volume energy density (Wh/l) and gravimetric
energy density (Wh/kg).
SUMMARY OF THE INVENTION
[0022] The present inventor solved the above described problems by
forming an electrode for alkaline storage batteries as an
application example as follows:
[0023] (a) Forming a conductive electrode substrate from a metal
foil which is provided with innumerable concave and convex hollow
parts or forming the same shape metal substrate by the metal
deposition through an electrolytic method;
[0024] (b) Adjusting the thickness of the above described electrode
substrate to substantially the same thickness as that of the
electrode;
[0025] (c) For limiting the above described substrate to become two
dimensional, partially or as a whole, by the electrode press work
after filling the paste of active material powders as the main
material, arranging the position of said concave and convex parts
of the conductive electrode substrate to maintain the current
collection ability of the whole electrode; and
[0026] (d) Preventing the peeling of the active material powders
layer from the substrate through the spirally winding process of
the electrode and also the shedding of active material powders that
formed the electrode through the repetitive charging and
discharging afterwards, by bending the walls of the concave and
convex hollow parts into one direction specifically in the vicinity
of the edge, just as to wrap the space between the concave and the
next concave or the convex and the next convex in order to prevent
the shedding of the active material powders.
[0027] In addition, by maintaining all the active material powder,
within 150 .mu.m in the distance from the nearest conductive
electrode substrate, the charging and discharging reaction,
particularly the high rate discharge reaction, of the active
material powder is enhanced and by using a cylindrical battery case
wherein a ratio (t.sub.2/t.sub.1) of the thickness (t.sub.2) of the
bottom to the thickness (t.sub.1) of the side walls is 1.5 or more,
that is to say, by using a case of which the side walls have become
thinner, the secondary battery is further made lighter and made
larger in capacity
[0028] Though the present invention is not particularly limited to
a nickel positive electrode, in the case of application for a
nickel positive electrode, in particular, a thinner nickel positive
electrode is provided in which the thickness is 500 .mu.m or less
for alkaline storage batteries, and the electrode uses an
inexpensive, light weight and conductive metal substrate that can
be formed only through mechanical operations on a metal foil or
only through electrolytic metal deposition on the same pattern,
without sintering or plating, resulting in excellent
characteristics in charge and discharge characteristics,
restraining the shedding of active material powder and light
weight. Therefore, an inexpensive, light weight sealed cylindrical
or prismatic nickel-metal hydride battery (Ni/MH battery) that
shows excellent characteristics of high-rate charge/discharge and
long cycle-life is achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic cross section view of a nickel
positive electrode according to one mode of the present
invention;
[0030] FIG. 2 shows a nickel positive electrode according to one
embodiment of the present invention. The cross section view along
A-A is shown in FIG. 1;
[0031] FIG. 3 shows a sealed cylindrical Ni/MH battery (AA size)
construction according to one mode of the present invention;
[0032] FIG. 4 shows an electrode substrate in a wide belt-like form
utilized for the nickel positive electrode according to one mode of
the present invention;
[0033] FIGS. 5(a) and 5(b) show two examples of patterns for
unevenness processing;
[0034] FIG. 6 shows a pressing process for the nickel positive
electrode according to one mode of the present invention;
[0035] FIG. 7 is a cross section view of the electrode after
filling the paste of active material powder into the substrate;
[0036] FIG. 8 shows high-rate discharge characteristics of a sealed
cylindrical Ni/MH battery (AA size) using a nickel positive
electrode according to one embodiment of the present invention;
[0037] FIG. 9 shows cycle-life characteristics of a sealed
cylindrical Ni/MH battery (AA size) using a nickel positive
electrode according to one mode of the present invention.
[0038] FIG. 10 shows a stroking and squeezing step;
[0039] FIG. 11 is an enlarged cross section view of a battery case
manufactured through the stroking and squeezing step;
[0040] FIG. 12 shows high-rate discharge characteristics of the
nickel positive electrode according to one mode of the present
invention (half cell); and
[0041] FIG. 13 shows high-rate discharge characteristics of the
nickel positive electrode according to one mode of the present
invention (half cell).
DESCRIPTION OF PREFERRED EMBODIMENTS
[0042] In the following, in reference to the drawings, a sealed
cylindrical nickel-metal hydride battery is described as an example
wherein an electrode obtained by winding a nickel positive plate 1,
whose main material is nickel hydroxide powder and whose electrode
thickness is 500 .mu.m or less, and an alloy negative plate 2,
whose main material is hydrogen absorption alloy powders and of
which electrode thickness is much thinner than that of the positive
electrode, together with a separator 3 made of non-woven sheet of
polyolefin-type synthetic resin fiber, is inserted into a
cylindrical metal case and then an alkaline electrolyte solution is
poured in the case, which is then sealed.
[0043] Here, an electrode obtained by filling the paste 10, that
has been obtained by mixing the main material and the like, into a
conductive electrode substrate 9 which is made three dimensional
through a press work applied to a nickel foil of a thickness of 20
to 50 .mu.m between the upper and the lower plate dies, wherein an
innumerable number of concavities and convexities are mutually
provided so as to engage each other and, then, by pressing after
drying, is used as the positive electrode. From the viewpoint of
cost-effectiveness and ease for producing the same type of a
substrate, particularly in the case where the thickness close to 20
.mu.m, the method of electrolytic nickel deposition is available as
well. In this case, the nickel deposition of about 20 .mu.m is
carried out on the cathode, the surface of which has innumerable
hollow concavities and convexities of a desired pattern, in the
conventional electrolysis bath of pH 2.0 containing mainly nickel
sulfate. And, this method can also can provide a long strip of
substrate with innumerable hollow concavities and convexities by
employing a rotary drum as the cathode. After the said substrate is
annealed at approximately 850.degree. C. to have much more
mechanical strength, it can be used for the electrode
substrate.
[0044] Long cycle-life electrodes with excellent charge/discharge
characteristics can be obtained through the three dimensional
structure of the substrate, which is made as a Shree dimensional
model to almost the same thickness as the electrode, particularly,
through a structure wherein the shapes of the hollow concavities
and convexities bend, in one direction, to a greater extent in
relation to proximity to the edges so as to wrap the space of the
substrate. The resultant structure is excellent in current
collection and wraps the active mass tightly in a manner not
inferior to that in the sintered type or 3DM type.
[0045] Long cycle-life electrodes with excellent charge/discharge
characteristics can be obtained because the above described
conductive electrode substrate has a structure which is excellent
in current collection performance and the wrapping of the active
material powder is not inferior to that of sintered type or 3DM
type, since it is made to be a three dimensional structure of
approximately the same thickness as the final electrode,
particularly, to be a structure wherein the closer to the edges of
the hollow unevenness the stronger they become and the more bent
they are in one direction so as to enclose(?) the space areas in
the substrate. In addition, since this substrate can be
manufactured only by passing between dies which engage with each
other through the unevenness, it becomes inexpensive because of the
simple process and when it is wound to an electrode of a spiral
wound form, the electrode is not broken apart. As a result, Ni/MH
batteries are obtained that are easy to process and which are
inexpensive with high performance and high reliability.
[0046] Since the alloy negative electrode is improved in the
electric current collection performance due to the thickness which
is approximately 1/2 of the positive electrode, it can withstand a
high-rate discharge of approximately 20C discharge at room
temperature. However, in the case that a much higher rate discharge
is necessary, it is preferable to adopt a three dimensional nickel
electrode substrate according to the present invention for the
alloy negative electrode.
[0047] Here, though, Ni/MH batteries are described for the
convenience of the description above, the present invention can be
applied in the same way to electrodes for Ni/Cd batteries or Li
secondary batteries which need a high-rate discharge.
[0048] FIG. 1 shows a cross section view taken along line A-A in
FIG. 2 of the nickel positive electrode 1 according to the present
invention. In FIG. 1, a nickel metal part forming a three
dimensional nickel substrate is denoted as 9, and mixed powder
mainly containing nickel hydroxide powder filled into this
substrate is denoted as 10 and a hollow area is denoted as 11. The
walls of the convex part B or B' and of the concave part C or C' in
the three dimensional substrate processed from a nickel foil have a
contour while tilting to one side and the edge D or D' of nickel
part is less thick and further more tilting to the side. This
contour and the tilt of the edges limit the shedding of the
fillings such as the active material powder from the substrate. The
tilt of the edges do not cause microscopic short circuit with the
opposite electrode by becoming an electrode whisker and, therefore,
this also has the effect of making the shortest distance from the
nickel substrate to the active material powder grain (in the
vicinity of M in the figure) which is farthest away to be shorter
than in the case of not bending (in the vicinity of M'), that is to
say, the effect of enhancing the current collection ability of the
entire electrode is provided. In the case of a nickel positive
electrode, when the commercially available active material powder
is used and the distance from the conductive electrode substrate
becomes more than 150 .mu.m, the deterioration of voltage at
high-rate discharge occurs and the rate of utilization of the
active material is lowered. Therefore, it is preferable to use a
metallic plate wherein the conductive electrode substrate of a thin
electrolyte-proof metal foil has a three dimensional structure by
forming innumerable concave and convex parts and the shortest
distance between a majority of said powders and the said conductive
electrode substrate is maintained within 150 .mu.m. In addition,
unlike the electrode substrate which has electric conductivity, the
active material has very little electric conductivity since it is
mainly composed of Ni(OH).sub.2. Therefore, it is preferable to add
about 5 wt % of a powder with electric conductivity and cobalt
oxide in the active material powder paste in order to enhance
current collection characteristics. Further, in the case where
further improvement of high-rate discharge characteristics is
desired with the requirement of higher power as a battery, it is
preferable to use the active materials in the active material layer
on a substrate having a three dimensional structure by forming
concave and convex parts with the shortest distance between a
majority of said powders and the said conductive electrode
substrate being-maintained within 150 .mu.m. This because when the
amount of a powder with electric conductivity and cobalt oxide
added in the active material powder in order to enhance current
collection characteristics is increased, the amount of the active
materials contained is decreased. When the specific explanation is
made using the Figure, it is preferable to decide the size of the
concavities and convexities as well as the pitch so that the
distance between the m' in FIG. 1 and the closest conductive
electrode substrate is maintained within 150 .mu.m.
[0049] FIG. 2 shows an overall view of a nickel positive electrode
1 which has a structure as shown in FIG. 1, which is a thin nickel
positive electrode whose the thickness is 500 .mu.m or less.
[0050] FIG. 3 is a schematic diagram of a sealed cylindrical Ni/MH
battery construction of AA size which is obtained by the
combination of a thin nickel positive electrode in FIG. 2 and a
thin alloy negative electrode wherein MmNi5 type hydrogen absorbing
alloy powder is coated on punched(?) metal in the same way as in a
prior art. With respect to each of the components other than
electrodes of the battery, basically they are the same as those in
a conventional battery structure.
[0051] The conductive electrode substrate according to the present
invention may be any material as long as it has a conductivity and
the process for providing the unevenness and for contour and tilts
of the walls is possible after the filling of the active material
powder and is not limited particularly. However, the material of
the conductive electrode substrate is properly used at least on the
surface of the conductive electrode substrate by selecting one kind
or more from a group consisting of nickel, copper, aluminum, lead
and alloys whose main components are those metals, which are
employed in a variety of electrodes for batteries at present.
Particularly, it is preferable for materials used as a nickel
electrode for an alkaline storage battery to be selected at least
one from a group consisting of cobalt, calcium, titanium, silver,
yttrium, lanthanide, carbon and/or their oxides, which are arranged
on the major part of the surface, from the view point of easiness
of processing. The thickness of the conductive electrode substrate
which is made three dimensional with the hollow concave and convex
parts of the conductive electrode substrate according to the
present invention is the thickness which is approximately the same
as the final electrode which is pressed after the powder mainly
containing the active material powder or pseudo-active material
powder is filled in or coated on the electrode and, more
concretely, it is preferable for the above described thickness of
the conductive electrode substrate to be 0.5 to 2.0 times as large
as the thickness of the final electrode.
[0052] In the case that the thickness of the above described
conductive electrode substrate is 0.5 or less times as large as the
thickness of the final electrode, the high rate discharge
characteristics are slightly lowered, and the contact area between
the active material powders or pseudo-active material powders and
conductive electrode substrate is decreased, which is not
preferable because the active material powder becomes to be
shedded. In the case that the thickness of the above described
conductive electrode substrate is 2.0 or more times as large as the
thickness of the final electrode, it becomes difficult to form a
metal foil with concave and convex parts and to form the same by an
electrolytic deposition method as well, and therefore it is not
preferable. Particularly, in the case that the present invention is
used for a nickel positive electrode, it is preferable that the
thickness of the conductive electrode substrate is 1.0 to 2.0 times
as large as the thickness of the final electrode. Here, the final
electrode refers to an electrode obtained by press work after the
paste that mainly contains active material powders is filled in or
is coated on.
[0053] The innumerable concave and convex parts which are hollow in
the conductive electrode substrate according to the present
invention represent concave and convex parts in a shape of having
the inner wall surfaces while the concave and the convex forms are
not filled in with the material forming the conductive electrode
substrate.
[0054] The pseudo-active material in the present invention is the
material that absorbs and desorbs active material such as Li
(lithium), H (hydrogen), or the like. The active material may be
occluded in the pseudo-active material or may be occluded in a form
of a compound with other materials as long as it is released as a
active material.
[0055] The method of filling in or coating of the paste of which
the main material is the active material powders or the
pseudo-active material powders according to the present invention
is not particularly limited, and a well known method for filling in
or coating can be applied.
[0056] The shapes of the concave parts and convex parts in the
conductive electrode substrate according to the present invention
are not particularly limited and, therefore, they may be a hollow
cone form, or a hollow polygonal pyramid form such as a triangular
pyramid form, quadrangular pyramid form or a hexagonal pyramid
form. Though the respective edges of the concave parts and convex
parts may have open holes or may be closed, it is preferable to
have open holes since the strength against mechanical (physical)
peeling of the active material layer and uniformity of the
electrode reaction on active material layers on both sides of the
substrate are easily obtained.
[0057] The above described conductive electrode substrate in the
present invention is a substrate having innumerable microscopic
concavities and convexities on the major part of the surface, which
is preferable for increasing the cycle life and the high-rate
charge / discharge characteristics since is further increases the
electric conductivity between the substrate and the active material
or pseudo-active material.
[0058] As for the arrangement pattern of most concave and convex
parts in the above described substrate according to the present
invention, it is preferable for columns of many concave parts or
concave part groups, as well as columns of many convex parts or
convex part groups to be mutually provided approximately in
parallel to each other to form an angle in the range of 30 degrees
to 60 degrees with the direction of electrode length. By providing
the above described columns of many concave parts or concave part
groups, as well as columns of many convex parts or convex part
groups, alternately approximately parallel to each other, the
distance between respective convex parts (concave parts) is easily
maintained at a constant value and stability is provided, which
lead to good wrapping ability of the active material powders in the
substrate and good conductivity over the entire electrode.
[0059] The conductive electrode substrate in the present invention
has the following concave and convex parts or groups thereof. That
is, the number of the concave parts is not less than half the
number of concave and convex parts, wherein the said concave and
convex parts are adjacent and closest to the convex part, the
number of groups of concave parts is not less than half the number
of groups of concave and convex parts, wherein the said groups of
concave and convex parts are adjacent and closest to the groups of
convex parts, the number of convex parts is not less than half the
number of concave and convex parts, wherein the said concave and
convex parts are adjacent and closest to the concave part, and the
number of groups of convex parts is not less than half the number
of groups of concave and convex parts, wherein the said concave and
convex parts are adjacent and closest to the groups of concave
parts.
[0060] Together with this, as described in the above, by providing
columns of many concave parts or concave part groups and many
convex parts or convex part groups at an angle within the range of
30 degrees to 60 degrees with the direction of electrode length, an
excessive expansion and an uneven expansion of the substrate can be
restrained at the time of press work of the electrode to maintain a
uniform three dimensional substrate within the electrode.
[0061] The contour and the tilts of the walls of the convex and the
concave parts in the conductive electrode substrate according to
the present invention can be formed through press work with a
rolling press machine comprising pre-press work through a pair of
rollers with small diameters and real press work for forming the
final electrode through a pair of rollers with large diameters.
Since this press work processing is applied to the conductive
electrode substrate wherein the active material or the
pseudo-active material is filled in or coated on, the walls of the
concave and convex parts are made to have contours in the direction
of the thickness of the conductive electrode substrate so as to be
more tilted in one direction at areas closer to the edges of the
concave and convex parts. If the thickness of the substrate before
filling in the active material powder is large enough, when the
active material powder is filled in the substrate having a thick
thickness as shown in the partially enlarged view of FIG. 7, both
surfaces of the substrate may be bent slightly in advance so as to
be bent in one direction. In addition, in the above described roll
press work, pre-pressuring may be carried out by passing the
processed material through a slit with a doctor knife or a rubber
spatula or by brushing with a rotary rush. And, in the case that
the conductive electrode substrate is made three dimensional to a
greater degree as described above, inclination of the concave and
convex parts in one direction, particularly a greater inclination
of the edge parts as shown in Part D of FIG. 1 can be effectuated,
by means of press work with a rolling machine only using a large
diameter roll, and omitting a pre-press process.
[0062] It is preferable that the final electrode is coated with
fine powders of fluororesin. This is in order to prevent the edges
of the concave and convex parts of the conductive electrode
substrate from sticking out of the electrode like whiskers or from
sticking out of the separator, which can cause short circuits, in
addition to preventing the active material powder from shedding.
Accordingly, as for the kinds of synthetic resins used for the
coating of the electrode, in addition to the fluororesin, resins
having electrolyte-proof and binding characteristics such as resins
containing polyolefine, polyvinyl-type and polysulfone powders or
their copolymers as the main material can be applied.
[0063] In the case that the paste-type thin electrode for batteries
according to the present invention is processed into a spiral
electrode, the edges of the concave and convex parts of the
conductive electrode substrate are, preferably, tilted in the
direction perpendicular to the winding direction so as to prevent
them from forming whiskers through the electrode swelling due to
the repetition of charging and discharging.
[0064] In addition, a secondary battery according to the present
invention is a battery wherein the above described electrodes are
inserted into a battery case and the positive electrode lead is
connected to a lid by means of spot welding, or the like, and then
the lid is caulked to the aperture part of the battery case.
[0065] A secondary battery according to the present invention can
be obtained by inserting the above described electrodes according
to the present invention into a container of a battery case of the
desired external diameter size such as D, C, AA, AAA and AAAA.
[0066] As for a battery case in a secondary battery according to
the present invention, in the case that the secondary battery of
the present invention is used in the application where the capacity
is enlarged and weight reduced in, for example, a battery for an
HEV, it is preferable to use a light weight battery case wherein
the ratio (t.sub.2/t.sub.1) of the thickness (t.sub.2) of the
bottom to the thickness (t.sub.1) of the side wall is 1.5 or more
and, moreover, it is more preferable for the ratio
(t.sub.2/t.sub.1) of the thickness (t.sub.2) of the bottom to the
thickness (t.sub.1) of the side wall to be approximately 2.0, from
the view point of extra strength against internal cell pressure of
the side walls of the container and a secure crack prevention which
might occur from the spot welding to the bottom. In the case that a
secondary battery according to the present invention shows superior
characteristic in connecting cells in series by spot welding which
is important for HEVs, or the like, the battery has a, thick bottom
case in the conventional, preventing from making a blow-hole in a
battery during the welding process. In further explanation, making
the ratio (t.sub.2/t.sub.1) of the thickness (t.sub.2) of the
bottom to the thickness (t.sub.1) of the side wall 1.5 or more, the
thickness that can withstand the spot welding is secured for the
thickness of the bottom compared to an ordinary battery case where
the thickness of the side walls and the thickness of the bottom of
a battery case are approximately the same. In addition, by making
the side walls thinner it becomes possible to reduce the weight of
the battery case by approximately 30% without changing the material
so that the inside volume simultaneously increases, which allows
the capacity of the secondary battery to be larger. Here, the above
described welding is carried out according to a well known welding
method and is carried out within the range of 1000.degree. C. to
3000.degree. C. of the welding temperature at the spot welding
part.
[0067] In a secondary battery according to the present invention,
in the case of a battery case of AAAA size wherein the ratio
(t.sub.2/t.sub.1) of the thickness (t.sub.2) of the bottom to the
thickness (t.sub.1) of the side wall is 1.5 or more, when a battery
case in which the thickness of the bottom is approximately 0.2 mm
and the thickness of the side walls is 0.11 mm
(t.sub.2/t.sub.1=1.82), a capacity increase of approximately 5% is
achieved compared to the case where a battery case of the same
material is used in which the thickness of the bottom is
approximately 0.2 mm and of which the thickness of the side walls
is 0.2 mmm (t.sub.2/t.sub.1=1).
[0068] Though the material of the battery case in a secondary
battery of the present invention is not particularly limited, it is
preferable to use iron with an applied nickel plating for an
alkaline storage battery from the viewpoint of electrolyte-proof
properties and it is preferable to use aluminum, or aluminum alloy,
in addition to iron for a lithium secondary battery from the
viewpoint of weight reduction.
[0069] Though the above described battery case can be manufactured
by a well known method, including several times of ironing
processes, it is preferable to manufacture by drawing and ironing
processing at the same time in order to attain a thinner side wall
and a ratio (t.sub.2/t.sub.1) of the thickness (t.sub.2) of the
bottom to the thickness (t.sub.1) of the side wall of 1.5 or more.
In case that the battery case is manufactured by ironing process
using many processing steps to move closer to the desired battery
case structure, generally the thickness of the bottom and of the
side walls become approximately equal. However, since ironing with
drawing process is a method for forming a cylindrical container 14
with a bottom from a metal plate through extrusion by one
revolution of the spindle 13 as shown in FIG. 10, a battery case
having a desired thickness of the side walls easily can be formed
to gain the above described battery case by adjusting the gap
between the spindle and the mold 15.
[0070] In the battery case of a secondary battery according to the
present invention, it is preferable that thicker parts are provided
along the border between the side walls 16 and the bottom 17 within
the battery case in order to secure the mechanical strength. The
above described thicker parts are the parts indicated by R in FIG.
11 and by processing the external periphery of the edge part of the
spindle used at the time of battery case formation so as to be
rounded, the thicker parts of the corresponding battery case can be
provided easily. Effects can be recognized even when a spindle to
which a slight rounding processing is applied is used and rounding
of 1 mm of diameter is appropriate for a battery case of AA size
without lowering the battery capacity.
[0071] Though a secondary battery according to the present
invention can be made lighter in battery weight by employing the
above described electrodes, a further lighter secondary battery can
be provided by using a battery case in which the side walls are
further thinner and in which the ratio (t.sub.2/t.sub.1) of the
thickness (t.sub.2) of the bottom to the thickness (t.sub.1) of the
side wall is 1.5 or more.
EMBODIMENTS
[0072] Next, a concrete embodiment of the present invention is
described.
PRODUCTION EXAMPLE
[0073] As shown in FIG. 10, a nickel plated steel plate (plating
thickness of 1 .mu.m) having a thickness of 0.3 mm,which is punched
out into a circle, is submitted to one cycle of ironing with
drawing by spindle 13 in the manner known in the art so as to form
a cylindrical container 14 with a bottom. More concretely, as for
the dimensions the outer diameter is 14 mm, the thickness of the
side walls is 0.16 mm and the thickness of the bottom is 0.25 mm.
Here, it is preferable to provide thicker parts R at the border
part of the inside of the case between the side walls and the
bottom, in order to prevent the physical strength of the border
from being weakened.
Embodiment 1
[0074] Nickel foil in a wide belt-like form, having a thickness of
30 .mu.m, is pressed between a pair of dies (or between rollers)
wherein innumerable microscopic conical concavities and convexities
are formed on the surface of the both dies so that a three
dimensional conductive electrode substrate having innumerable
microscopic hollow chimney shapes in the nickel electrode substrate
9 of FIG. 4 is manufactured. Two examples of the possible kinds of
patterns of the concave and convex parts of the nickel substrate 9
in FIG. 4 are shown in FIGS. 5(a) and 5(b) which are the partially
enlarged figures of the nickel electrode substrate, wherein parts B
and C in FIG. 5 indicate the convex parts and the concave parts,
respectively. The closest parts to the convex parts (concave parts)
in FIG. 5(a) are all concave parts (convex parts) and in FIG. 5(b)
the closest parts to the convex parts (concave parts) are concave
parts (convex parts) in a ration of four out of six. In the present
embodiment the pattern of FIG. 5(a) is adopted. The closest parts
to the convex parts (concave parts) in FIG. 5(a) are all concave
parts (convex parts) wherein the diameter of the hollow
substantially conical structure is about 60 to 80 .mu.m at the base
and 35 to 45 .mu.m in the edges. They are completely formed by a
press work between a pair of the upper and lower dies to which
unevenness of the same pattern as in FIG. 5(a) is provided so that
if the thickness of the foil is thin, the majority of the edges of
concavities and convexities have openings. The thickness of the
substrate, which is formed three dimensional Offh concave and
convex parts, is 500 .mu.m, which is thicker than the thickness of
the final electrode by approximately 100 .mu.m. The pitch between
the convex parts column and the closest convex parts (or the pitch
between concave parts and the closest concave parts column) is 150
to 250 .mu.m in the wide belt-like form. The angle (m) formed by
the columns of the convex parts (concave parts) with the
longitudinal direction of the electrode substrate is approximately
45 degrees. A part to where this type of uneven processing is not
applied is denoted as 12, a part of which is utilized as an
electrode lead. A slight corrugated form processing may be applied
to the part 12 in the longitudinal direction of the electrode
substrate for the purpose of alleviating the distortion with the
parts where the active material exists due to the electrode
swelling at the time of press work.
[0075] The paste of the active material powders with fluororesin
powders is filled into the nickel electrode substrate 9 to which
innumerable microscopic hollow chimney form concave and convex
parts are provided-in accordance with the pattern of FIG. 5(a). As
for the active material powders, the main component is nickel
hydroxide and, here, active material powder of spherical form whose
grain diameter is approximately 10 .mu.m, formed of approximately 1
wt. % of cobalt and approximately 3 wt. % of zinc dissolved into
nickel hydroxide so as to form a solid solution, is employed. This
active material powders (approximately 75 wt %) is kneaded with a
water solution (approximately 25 wt %) wherein approximately 1 wt.
% carboxymethyl cellulose, approximately lwt. % of polyvinyl
alcohol are dissolved. Then, cobalt oxide (CoO) and zinc oxide
(ZnO) in a ratio of approximately 3 wt % and approximately 2 wt. %
of the said active material powders are added respectively to gain
the final paste. This paste of mixed powder including the active
material is filled into the nickel electrode substrate 9 and, then,
is partially dried, of which the condition is shown in the
partially enlarged figure of FIG. 5.
[0076] Next, the nickel electrode substrate obtained by filling in
the paste of mixed powder including the active material and then by
drying it is passed between a pair of rollers with diameters of
approximately 30 mm rotating at a relatively high speed represented
by S and S' in FIG. 6 so that the surfaces are rubbed and lightly
compressed with the revolution number of 10 rpm/sec. It then is
pressed between the rollers with diameters of Approximately 450 mm
represented by N and N' so as to be strongly pressed into the
tickness of 400 .mu.m. This nickel positive electrode has become an
electrode even lighter than the lightest 3DM type electrode
according to a prior art since the nickel body only occupies 3 vol.
%, which makes the amount of metal approximately half of 6 to 9
vol. % of the conventional 3DM tppe.
[0077] This electrode is cut into a width of 40 mm and a length of
150 mm and, after that, is immerged in a suspension of microscopic
powders of fluororesin of a concentration of approximately 3 wt %
and, then, is dried to gain a nickel positive electrode. This is
combined with a negative electrode of the conventional MmNi.sub.5
type hydrogen absorbing alloy wherein the thickness is 220 .mu.m,
the width is 40 mm and the length is 210 mm so as to be inserted
into an AA size battery case of, which is obtained as a production
example. In addition, by sealing with the lid 6, which also works
as a positive terminal and is known in the art, and a gasket 5 as
in FIG. 3, a sealed cylindrical Ni/MH battery of AA size is
manufactured, of which the theoretical capacity of the positive
electrode is 1550 mAh. And, as for the separator an unwoven cloth
of sulfonated poly-olefin resin fiber of the thickness of 120 .mu.m
is adopted while a KOH solution of approximately 30 wt. % is used
for the electrolyte.
[0078] Here, for the purpose of evaluating the characteristics of
the nickel positive electrode in particular, that is to say, in
order to avoid the effect of the characteristics of the negative
electrode on the cell performances as much as possible, the
standard battery is made to have a theoretic capacity of the
negative electrode as much as 1.8 times as large as that of the
positive electrode by adjusting the normally designed capacity
balance of the positive and negative electrodes. For reference,
commercially used batteries have the negative electrodes which are
1.3 to 1.6 times as large.
[0079] FIG. 8 shows a mean value of high-rate discharge
characteristics for ten cells of this battery indicated as q. The
discharge voltage indicated along the vertical axis shows the
voltage at the time of 50% of DOD (Depth of Discharge) of the
theoretical capacity.
Comparative Examples 1 to 3
[0080] As Comparative Example 1, a battery is manufactured in the
same way as in Embodiment 1 except for the usage of the electrode
substrate which is pressed between conventional plates, that is to
say, the processing is the same except for that no operations for
bending the edges of the concave and convex parts in one direction
are applied to the conductive electrode substrate and, then, the
discharge characteristics are examined, of which the result is
indicated as p in FIG. 8.
[0081] As Comparative Example 2, a battery is manufactured in the
same way as in Embodiment 1 except for the use of 3DM type nickel
positive electrode which is an electrode manufactured in the same
way as in Embodiment 1 except that a conventional foam nickel
porous body (trade name: Cellmet made by Sumitomo Denko) is used
for the conductive electrode substrate, and the examination result
of this case is indicated as o in FIG. 8.
[0082] As Comparative Example 3, a battery is manufactured in the
same way as in Embodiment 1 except for the use of a conductive
electrode substrate for which the pitch between convex column and
next convex column is 400 .mu.m (approximately twice as in
Embodiment 1), and the result of this case is indicated as n in
FIG. 8.
[0083] As a result of Embodiment 1 and Comparative Examples 1 to 3,
the case of the present embodiment exhibits the most excellent
characteristics and has a voltage close to 1V even at the time of
10C-rate discharge. Particularly, the effects obtained by making
the distance between the convex parts column and the neighboring
convex parts column to be 200 .mu.m are large. That is to say, in
this case, the distance to the farthest distant active material
powders represented by M' in FIG. 1 is in the range of 70 to 100
.mu.m. Though the battery of p indicated an excellent high drain
characteristic, it exhibits a large capacity deterioration after
the completion of 500 cycles as opposed to a battery according to
the present invention, which exhibits little decay in capacity even
after the completion of 700 cycles in a cycle-life test which
repeats IC-rate discharging and IC-rate charging (110% charge of
the discharge capacity) at a temperature of 20.degree. C. as shown
in FIG. 9. In this case both batteries in Embodiment 1 and
Comparative Example 1 are tested for ten cells, however, in FIG. 9
two cells each which exhibit the upper and the lower
characteristics among them are eliminated so as to use a mean value
of six cells which exhibit the remaining intermediate
characteristics. Here, as for a battery in p, two cells out of the
ten cause a short circuit before and after the one hundredth cycle.
The effect due to the contour of the concave and convex edges is
extremely large with respect to causing a short circuit.
[0084] That is to say, in the case that a structure of the
conductive electrode substrate according to the present invention
is adopted, excellent in high-rate discharge characteristics are
obtained, and the wrapping of the powders containing the active
material is improved so as to gain a battery whose cycle life is
excellent and wherein a microscopic short circuit rarely occurs
(the reliability is high).
[0085] The substrate of the alloy negative electrode according to
the present embodiment is improved slightly in the characteristics
of q in FIGS. 8 and 9 when the nickel electrode substrate according
to the present invention is adopted. That is to say, it is
understood that a similar effect is obtained in a thin alloy
negative electrode. In addition, a similar effect can be expected
for a Li secondary battery, which requires a high-rate discharge,
maintainability of excellent active material powders, and excellent
cycle life because of a similar principle.
Embodiment 2
[0086] A sealed cylindrical NuMH battery is manufactured in the
same way as in Embodiment 1 except for the use of the conductive
electrode substrate to which the pattern of the partially enlarged
FIG. 5(b) is applied as a pattern for unevenness in the processing
of the nickel foil. High-rate discharge characteristics and cycle
life were also examined with this battery as well. In this case
also, the pitch between the adjacent convex and convex parts across
the concave parts or between the adjacent concave and concave parts
across the convex parts is 200 .mu.m. The angle m' made between
columns of the convex parts or columns of the concave parts and the
direction of the length of the electrode is 30 degrees.
[0087] In the case of the present embodiment also, the same
characteristics as in Embodiment 1 are obtained, showing excellent
high-rate discharging and cycle-life characteristics.
[0088] Here, in a nickel electrode using the substrate obtained by
corrugated form processing a nickel foil in the longitudinal
direction of the electrode substrate or in the perpendicular
direction to that longitudinal direction (in such cases the angle
corresponding to m' is 90 degrees or 0 degrees), the active
material powder sheds at the time of spirally winding processing
and, therefore, utilization of the active material has been
significantly lowered from the initial point for most cells.
[0089] Judging from the present embodiment, it is considered that
the current collection characteristics become excellent in the case
that the angle between the columns of the convex parts or the
concave parts and the longitudinal direction is in a range of about
30 to 60 degrees, so as to be able to prevent the nickel electrode
substrate from being changed partially or completely to a two
dimensional form at the time of rolling press work and to retain
the nickel substrate deposited on the entire electrode.
Embodiment 3
[0090] A sealed cylindrical Ni/MH battery is manufactured in the
same way as in Embodiment 1 except for the use, as the conductive
electrode substrate, of a conductive electrode substrate obtained
by forming a nickel foil with a rolling mill while attaching cobalt
foils or cobalt powders on both sides of a nickel plate which is
originally thick when nickel is processed. High-rate discharge
characteristics and cycle life were examined with this battery as
well. Here, the amount of cobalt is 0.5 wt. % of the nickel. In
this case since the cobalt oxide generated on the substrate surface
is superior to that of nickel in electronic conductivity, the
high-rate discharging characteristics are only slightly improved
compared with the case of Embodiment 1.
Embodiments 4 to 9
[0091] A sealed cylindrical Ni/MH battery is manufactured in the
same way as in Embodiment 3 except that in Embodiment 4 calcium is
attached to the surface of the nickel foil instead of cobalt foil
attached thereto. In addition, titanium, silver, yttrium,,
lanthanide, or carbon is used instead of the cobalt foil in
Embodiment 3 to obtain Embodiments 5 to 9, respectively. The
cycle-life and discharging characteristics of the sealed
cylindrical Ni/MH battery in each embodiment are examined and
recognized to have a little effect in the improvement of the
cycle-life and high-rate discharging characteristics. Here, with a
little more boron content on the surface of the substrate, in any
cases, some effect was recognized in the improvement of
distribution in the cycle-life.
Embodiment 10
[0092] A sealed cylindrical Ni/MH battery is manufactured in the
same way as in Embodiment 1 except for making the surface of the
nickel foil in Embodiment 1 a rough surface having innumerable
microscopic concave and convex parts by mechanical forming or fine
nickel powder coating. The cycle-life and discharging
characteristics of the sealed cylindrical NuMH battery according to
the present embodiment are examined and recognized to be improved
in the cycle-life and high-rate discharging characteristics,
approximating Embodiment 3.
Embodiment 11
[0093] Nickel foil in a wide belt-like form of the thickness of 30
.mu.m is pressed between a pair of dies (or between rollers)
wherein innumerable microscopic cone concavities and convexities
are formed on the surface of the both dies so that a three
dimensional conductive electrode substrate provided in the pattern
of FIG. 5(a) is manufactured.
[0094] The thickness of a three-dimensional conductive electrode
substrate due to concavities and convexities was 140 .mu.m, and the
pitch between the concavity and the closest convexities was 140
.mu.m both in the longitudinal direction and in the perpendicular
direction.
[0095] Here, active material powder of spherical particles, whose
diameter is approximately 10 .mu.m, formed by approximately 1 wt. %
of cobalt and approximately 3 wt. % of zinc dissolved into nickel
hydroxide so as to form a solid solution, are employed. The active
material powders are kneaded with a solution wherein approximately
1 wt. % carboxymethyl cellulose and approximately 1 wt. %
of-polyvinyl alcohol are dissolved and, in addition, cobalt oxide
(CoO) and zinc oxide (ZnO) are added in a ratio of approximately 3
wt % and approximately 2 wt. % of nickel hydroxide, respectively,
to obtain the paste. This paste is filled into the electrode ,
thereby obtaining the thin electrode, the final electrode whose
thickness is the same as that of the conductive electrode
substrate. Here, in this final electrode, the pattern of
concavities and convexities was so arranged that the distance from
the active material that is farthest from the conductive electrode
substrate to the conductive electrode substrate is 100 .mu.m.
Embodiment 12
[0096] The final electrode was obtained by the same method as in
Embodiment 11 except that the thickness of a three-dimensional
conductive electrode substrate due to concavities and convexities
was 210 .mu.m, and the pitch between the concavity and the closest
convexities was 210 .mu.m both in the longitudinal direction and in
the perpendicular direction. Here, in this final electrode, the
pattern of concavities and convexities was so arranged that the
distance from the active material that is farthest from the
conductive electrode substrate to the conductive electrode
substrate is 150 .mu.m.
Comparative Example 4
[0097] A thin electrode that is the final electrode was obtained by
the same method as in Embodiment 11 except that the thickness of a
three-dimensional conductive electrode substrate due to concavities
and convexities was 280 .mu.m, and the pitch between the concavity
and the closest convexities was 280 .mu.m both in the longitudinal
direction and in the perpendicular direction. Here, in this final
electrode, the pattern of concavities and convexities was so
arranged that the distance from the active material that is
farthest from the conductive electrode substrate to the conductive
electrode substrate is 200 .mu.m.
Comparative Example 5
[0098] A thin electrode that is the final electrode was obtained by
the same method as in Embodiment 11 except that the thickness of a
three-dimensional conductive electrode substrate due to concavities
and convexities was 420 .mu.m, and the pitch between the concavity
and the closest convexities was 420 .mu.m both in the longitudinal
direction and in the perpendicular direction. Here, in this final
electrode, the pattern of concavities and convexities was so
arranged that the distance from the active material that is
farthest from the conductive electrode substrate to the conductive
electrode substrate is 300 .mu.m.
Evaluation of Embodiments 11 and 12; and Comparative Examples 4 and
5
[0099] As for the thin electrode obtained by Embodiments 11 and 12
as well as Comparative Examples 4 and 5, a secondary battery was
prepared by the same method as in Embodiment 1 and the high-rate
discharge was examined. The results of 0.5C-rate discharging and
5C-rate discharging are shown in FIGS. 12 and 13, respectively. The
result of Embodiment 11 is shown as e and i, the result of
Embodiment 12 is shown as f and j , the result of Comparative
Example 4 is shown as g and k, and the result of is Comparative
Example 5 is shown as h and l. The high-rate discharge
characteristics of the secondary battery using the thin electrode
obtained by Embodiments 11 and 12 were good without any large
voltage or capacity deterioration both with 0.5C-rate discharging
and 5C-rate discharging. On the other hand, the high-rates
characteristics of the secondary battery using the thin electrode
obtained by Comparative Examples 4 and 5 was good at 0.5C-rate
discharging, showing the large voltage and capacity deterioration,
but the high-rate discharge characteristics at 5C-rate discharging
was not good. As for Embodiments 11 and 12, by maintaining the
distance from the active material that is farthest from the
conductive electrode substrate to the conductive electrode
substrate within 150 .mu.m , excellency in high-rate discharge
characteristics were obtained.
[0100] The present application claims priority of Japanese
application No.2000-261780 and No.2000-318407, the disclosures of
which are incorporated herein by reference. While a detailed
description of the invention has been provided above, the present
invention is not limited thereto and various modifications will be
apparent to those of skill in the art. The invention is defined by
the claims that follow.
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