Note: Descriptions are shown in the official language in which they were submitted.
CA 02236421 1998-OS-O1
A GROUND PLATE FOR THE SUBSTRATE OF A SECONDARY BATTERY
ELECTRODE, A SUBSTRATE OF A SECONDARY BATTERY ELECTRODE, A
PRODUCTION METHOD THEREOF, AND AN ELECTRODE AND A BATTERY
PRODUCED THEREOF
FIELD OF THE INVENTION
The present invention relates to a ground plate for a substrate of a secondary
battery electrode and a substrate of a secondary battery electrode produced
thereof, and
a secondary battery electrode and a secondary battery produced thereof.
THE BACKGROUND ART
In a nickel- cadmium secondary battery served as a high output battery, an
electrode comprising a substrate having a layer of sintered porous metal with
a large
surface area is used so as to generate a large current. The substrate having a
layer of
sintered porous metal is produced by pressing nickel powder onto a perforated
steel
sheet, that is, a ground plate, which is plated by nickel with a thickness of
60 to 80 a m,
or by applying slurry of nickel powder to it and thereafter sintering the same
at a
temperature of 900 to 1100 ~ C in an anti- oxidizing atmosphere. In the
above- mentioned temperature range, there is generated necking caused by the
solid
phase diffusion at the contacting portions of nickel powders with each other,
and nickel
powders are sintered. At the same time bonding is caused at the contacting
portions
between the perforated steel sheet with a nickel- plated layer and the nickel
powders
due to the solid phase diffusion of nickel. Thus, the substrate of a secondary
battery
electrode is produced by bonding the sintered porous nickel layer, which is
composed of
the nickel powders bonded to each other at the necking portions to form a
network
themselves and have about 80% of porosity, to the steel sheet or the ground
plate.
However, the substrate of a secondary battery electrode of such structure,
that the sintered porous metal is bonded to the ground metal plate only by the
solid
phase diffusion, has not enough bonding strength, so that the sintered porous
metal
often peels off from the ground metal plate when the substrate is rolled up
and fixed into
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a cylindrical battery container. This peeling- off occurs particularly in the
center portion
of the rolled-up substrate where the roll-up radius is too small, which causes
problems
as shown in Fig.l (a) such that an active material falls off due to the
peeling- off of the
sintered porous metal from the ground metal plate, or the fallen active
material and
sintered porous metal crash through the separator, to cause a short circuit.
So far, several measures have been taken to increase the bonding strength of
the sintered porous metal to the ground metal plate which constitute a
substrate of a
secondary battery electrode and to improve the strength of the sintered porous
metal.
Those are as follows:
1) A layer containing metal fiber is formed near the ground metal plate as a
core material in order to increase the strength of the sintered metal (Laid
Open
Japanese Patent No. Sho 64- 24364) .
2) A layer added by cobalt or the like is formed near the ground metal plate
as a core material in order to enhance the solid phase sintering and increase
the
strength of the sintered metal (Laid Open Japanese Patent No. Hei 5-174831) .
3) A surface of the ground metal plate is roughened by etching in order to
increase the contacting area thereof with the sintered metal (Laid Open
Japanese Patent
No. Hei 4-162360) .
4) TD nickel plate is used as the ground metal plate in order to increase the
anti-peeling strength of it with yttoria particle contacting nickel particle
(Laid Open
Japanese Patent No. Sho 61-130405) .
However, these improvement shills remain within a solid phase sintering
technology, and they cannot drastically increase the bonding strength of the
sintered
porous metal to the ground metal plate constituting a substrate of a secondary
battery
electrode.
The object of the present invention is to provide a ground plate for a
substrate
of a secondary battery electrode and a substrate, and a secondary battery
electrode and a
secondary battery using the same, having sufficient bonding strength so as not
to cause
peeling- off of the sintered porous metal from the ground metal plate when the
electrode is rolled up and fixed into a cylindrical battery container.
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DISCLOSURE OF THE INVENTION
According to the present invention, a substrate having
sufficient bonding strength so as not to cause the peeling-off of a
sintered porous metal from a ground metal, can be produced by means
of generating a small quantity of a liquid phase when the sintered
porous metal is heat-bonded to the ground metal plate.
In the electrode current collector or ground plate for a substrate
of a secondary battery electrode of the present invention, a metal layer
having a melting point lower than that of a steel sheet is formed on at
least one side of the steel sheet.
Also, a nickel layer is formed on at least one side of a steel
sheet, and further a layer (if metal having a melting temperature lower
than that of the nickel layer is formed on the nickel layer.
A nickel-phosphorus layer is preferable as a layer of the metal
having a low melting point, and it is also preferable that a boronized
layer is formed on at least one side of a steel sheet.
Also, the ground plate of the present invention has a nickel
layer, formed on at least one side of a steel sheet, and further a
boronized layer is formed on the nickel layer.
It is also preferable that such a ground plate has a large
number of pores having small diameters.
A producing method of a ground plate for a substrate of a
secondary battery electrode of the present invention is characterized in
that a metal layer having a melting point lower than that of a steel sheet
is formed at least on one side of the steel sheet having a large number of
pores with small diameters.
In one aspect of the invention there is an electrode current
collector of a secondary battery electrode comprising a steel sheet, a
boronized layer formed on at least on one side of said steel sheet, and a
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porous nickel layer adhered to said steel sheet through said
boronized layer of metal.
In another aspect of the invention there is an electrode current
collector of a secondary battery electrode comprising a steel sheet, a first
nickel layer formed at least on one side of said steel sheet, a fused layer
of metal having a melting point lower than that of said nickel layer
formed on said nickel layer, and a porous nickel layer adhered to said
first nickel layer through said fused layer of metal, wherein said fused
metal layer is a boronized layer.
In a further aspect of the invention there is an electrode current
collector of a secondary battery electrode comprising a steel sheet, a first
nickel-layer formed at least on one side of said steel sheet, a fused layer
of metal having a meeting point lower than that of said nickel layer
formed on said nickel layer, and a porous nickel layer adhered to said
first nickel layer through said fused layer of metal, in the form of a coil.
In yet another aspect of the invention there is A secondary battery
electrode substrate comprising:
a steel sheet;
optionally a first nickel layer formed on at least one side of said
steel sheet;
a boronized layer formed over said steel sheet on at least one side
thereof or over said optional first nickel layer when present; and
a porous sintered nickel layer adhered to said steel sheet or
said optional nickel layer when present, through said boronized layer.
In yet a further aspect of the invention there is an electrode
current collector of a secondary battery electrode comprising a steel
sheet, a first nickel layer formed at least on one side of said steel sheet, a
fused layer of metal having a melting point lower than that of said nickel
layer formed on said nickel layer, and a porous nickel layer adhered to
said first nickel layer through said fused layer of metal, wherein said
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fused metal is a layer of nickel-phosphorous, and wherein said
steel sheet has a plurality of holes having diameters of 1-3 mm.
In one embodiment of the invention there is a secondary battery
electrode substrate comprising:
a steel sheet;
a first nickel layer formed at least on one side of said steel sheet;
a fused layer of metal formed over said first nickel layer, said fused
layer of metal having a melting point lower than that of said steel sheet
and said nickel layer; and
a porous sintered nickel layer adhered to said nickel layer through
said fused layer of metal,
wherein said fused metal layer is a boronized layer.
In another embodiment of the invention there is an electrode
substrate comprising:
a steel sheet;
a first nickel layer formed at least on one side of said steel sheet;
a fused layer of metal formed over said first nickel layer, said fused
layer of metal having a melting point lower than teat of said steel sheet
and said nickel layer; and
a porous sintered nickel layer adhered to said nickel layer through
said fused layer of metal,
said substrate being in the form of a coil.
In a further embodiment of the invention there is in a secondary
battery comprising a secondary battery electrode, said secondary battery
electrode comprising a substrate impregnated with an active material,
the improvement wherein said substrate is a secondary battery electrode
substrate comprising:
a steel sheet;
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a first nickel layer formed at least on one side of said steel sheet;
a fused layer of metal formed over said first nickel layer, said fused
layer of metal having a melting point lower than that of said steel sheet
and said nickel layer; and
a porous sintered nickel layer adhered to said nickel layer
through said fused layer of metal.
In yet another embodiment of the invention there is in a secondary
battery comprising a secondary battery electrode, said secondary battery
electrode comprising a substrate impregnated with an active material,
the improvement wherein said substrate is a secondary battery electrode
substrate comprising:
a steel sheet;
a first nickel layer formed at least on one side of said steel sheet;
a fused layer of metal formed over said first nickel layer, said fused
layer of metal having a melting point lower than that of said steel sheet
and said nickel layer; and
a porous sintered nickel layer adhered to said nickel layer through
said fused layer of metal,
wherein said fused metal layer is a layer of nickel phosphorous.
In yet a further embodiment there is an electrode current
collector of a secondary battery electrode comprising a steel sheet having
a plurality of holes having diameters of 1-3 mm, a first nickel layer
formed at least on one side of said steel sheet, a fused layer of metal
having a melting point lower than that of said nickel layer formed on
said nickel layer, and a porous nickel layer adhered to said first nickel
layer through said fused layer of metal.
Also, it is characterized in that a nickel layer is formed at least
on one side of a steel sheet having a large number of pores with small
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diameters, and further a metal layer whose melting temperature is lower
than that of nickel is formed on the nickel layer.
Further also, it is possible to form a nickel layer on a steel
sheet having a large number of pores with small diameters, and further
to be boronized after that.
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It is preferable in the above-mentioned producing methods that the metal
layer having a low melting temperature is composed of nickel-phosphorus alloy.
Further, a porous layer is formed on a ground plate for a substrate of a
secondary battery electrode of the present invention.
It is preferable in the above- mentioned substrate of a secondary battery
electrode that the porous layer is prepared by sintering nickel powder.
A producing method of a substrate of a secondary battery electrode of the
present invention is characterized in that a porous layer is formed on a
ground plate by
forming a layer of metal powder having a melting point higher than that of a
metal layer
having a low melting point, heating it at a temperature between not less than
the
melting temperature of the metal layer having a low melting point and less
than that of a
steel sheet or the metal powder, and sintering the metal powder, and the
porous layer is
bonded to the ground plate at the same time.
Also, it is characterized in that a porous layer is formed on a ground plate
by
forming a layer of powdered metal that can be eutectically alloyed with boron,
heating it
at a temperature between not less than the melting temperature of the
eutectically
alloyed metal and less than that of a steel sheet or the metal powder, and
sintering the
metal powder, and the porous layer is bonded to the ground plate at the same
time.
A secondary battery electrode of the present invention is characterized in
that
the above-mentioned substrate of an electrode has an active material
impregnated
therein, and a secondary battery of the present invention comprises the
above- mentioned secondary battery electrode .
BRIEF DESCRIPTION OF THE DRAWII\1GS
Figure 1 (a) is a schematic view showing a conventional substrate of a
secondary battery electrode, and Figure I (b) is another schematic view
showing a
substrate of a secondary battery electrode of the present invention.
Figure 2 is a graphic view showing charging and dischaging characteristics
obtained in case where a battery is charged and discharged using the secondary
battery
electrode, to which a substrate of a secondary battery electrode of the
present invention
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is applied, as a positive electrode.
MOST PREFERRED EMBODIMENT OF THE INVENTION
A substrate of an electrode of the present invention is prepared by forming a
layer of metal having a melting point lower than that of a ground plate, for
example a
layer of nickel-phosphorus eutectic alloy, at least on one side of the ground
plate,
forming a metal powder layer on the above-mentioned metal layer, and sintering
the
metal powder at a temperature between not less than the melting point of the
metal
layer and not more than that of the metal powder to thereby form a porous
layer and at
the same time to bond the porous layer to the substrate.
Also, a porous layer is formed by forming a layer of powdered metal that can
be eutectically alloyed with phosphorus at least on one side of a boronized
ground plate,
and sintering the powdered metal at a temperature between not less than the
melting
point of the formed eutectic alloy and not more than that of the powdered
metal,
whereby the porous layer is bonded to the ground plate at the same time. Thus,
it is
possible to produce a substrate of a secondary battery electrode having such
excellent
bonding strength of the porous layer to the ground plate that the porous layer
does not
peel off or fall off from the ground plate when the substrate is rolled up and
fixed into a
cylindrical battery container.
Since the substrate of an electrode of the present invention essentially has a
surface area as large as possible so as to flow a large current, a steel sheet
or a
nickel-plated steel sheet having a thickness of 25 to I00 ,c~ m is used as a
metal plate
to be the ground plate for a sintered porous metal.
The metal plate to be a ground plate may be one with a large number of holes
having small diameters of 1 to 3mm formed by punching or the like, one
perforated
using a chemical etching process or an electro- chemical etching process, or
another one
having a surface mechanically roughened using a sand- blasting or using an
embossed
roll.
In a practical mode of the substrate of an electrode of t1e present invention,
a
layer of metal having a melting point lower than that of a ground metal plate
is formed
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on the above-mentioned ground metal plate.
In this case, a metal layer is formed on a ground metal plate and then a
porous
layer is formed on it by forming a layer of powdered metal having a melting
point higher
than that of the metal layer and sintering the powdered metal, while the
porous layer is
bonded to the metal plate to thereby a melt part of metal layer and generate a
liquid
phase, which promotes the diffusion between the ground metal plate and the
powdered
metal consisting the porous layer. Thus, the metal layer essentialy has a
melting point
lower than those of the ground metal plate and the powdered metal consisting
the
porous layer so as to obtain excellent bonding strength.
For example, in a case where a sintered layer composed of nickel powder as a
porous layer is bonded to a ground metal plate such as a steel sheet, or a
nickel-plated
steel sheet, or those perforated sheets as mentioned above, nickel-phosphorus
eutectic
alloy and the like, prepared by a plating method are preferable as the metal
layer.
These eutectic alloys have melting points lower than that of pure nickel.
Therefore,
when the nickel powder layer formed on the eutecticalloy layer is heated and
sintered at
a temperature between not less than the melting point of the eutectic alloy
and not more
than that of pure nickel, the eutectic alloy melts to generate a liquid phase,
which promotes the diffusion between the nickel powder and the steel sheet as
the
ground metal plate and /or the nickel plating layer on it, thereby also
promoting the
strong bonding between them.
In view of productivity, electrolytical plating is preferably selected as a
nickel
plating method for the formation of the aforementioned nickel- plated steel
sheet, and
gloss plating, semi- gloss plating or mat plating using a known watt bath or a
sulfamic
acid bath are available. The plating thickness is preferably 0.5 to 10 ,u m.
Electroless plating as well as the electrolytical plating is available for the
formation of the aforementioned eutectic alloy layer. However, the latter is
more
preferable because a required plating thickness is obtainable in a shorter
period of time.
As an industrial plating bath for the electrolytical nickel-phosphorus
plating, a bath
mainly containing nicl~el sulfate or nickel chloride, or a bath containing
nickl sulfamide
and phosphorous such as supplied from phosphorous acid, phosphoric acid, or
hypo
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phosphorous acid, and /or phosphite, phosphate or hypophosphite is preferably
used.
The nickel-phosphorus plating layer has a thickness of preferably 0.5 to IO ,u
m. A
suffcient liquid phase is not generated in the plating layer having a
thickness less than
0.5 ~t m and the strong bonding cannot be obtained, while more than enough
liquid
phase is caused in the plating layer having a thickness more than 10 ,ct m and
the liquid
metal penetrates into vacant spaces of the sintered metal, which causes
unfavorable
decrease of porosity. The content ratio of phosphorus in the plating is
preferably 5 to
13 weight percent in order to generate the liquid phase.
In another practical mode of the substrate of an electrode of the present
invention, a ground plate is produced by boronizing the above-mentioned steel
plate or
nickel-plated steel sheet, and a porous layer is formed on it by layering a
powdered
metal which is eutectically alloyed with the boronized layer and sintering the
powdered
metal at a temperature between not less than the melting point of the eutectic
alloy and
not more than that of the surface layer of the ground plate or that of the
powdered metal.
According to this producing method when the porous layer is bonded to the
surface of
the ground plate, a part of the metal layer melts to thereby generate a liquid
phase,
which promotes the diffusion between the surface of the ground plate and the
powdered
metal consisting the porous layer and the bonding between them is also
promoted.
The detail of this case is explained below.
After a steel sheet or a nickel- plated steel sheet is boronized to be a
ground
plate, a porous layer composed of powdered metal is provided by forming a
Iayer of the
powdered metal which is eutectically alloyed with boron on the ground plate
and
sintering the powdered metal at a temperature between not less than the
melting point
of the eutectic alloy and not more than those of the surface layer of the
ground plate or
the powdered metal. The eutectic alloy melts to generate a liquid phase, which
promotes the diffusion between the ground plate and the powdered metal
consisting the
porous layer, whereby the bonding between them is more strengthened.
For example, in a case where a steel plate is used as a ground plate and a
sintering layer composed of nickel powder is bonded on the ground plate as a
porous
layer, the steel sheet is boronized. A layer of nickel powder is formed on the
boronized
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layer, the nickel powder is sintered at a temperature between not less than
the melting
point of nickel- boron eutectic alloy and not more than that of nickel, and at
the same
time, a liquid phase of the nickel-boron eutectic alloy is generated on the
interface
between the steel sheet and the nickel powder, which promotes the diffusion
between
the steel sheet and the nickel powder, resulting in strong bonding. The
boronized layer
has a thickness of preferably 0.5 to 10 ,u m. The boronized layer with a
thickness of
less than 0.5 ~c m, is insufficient for producing enough eutectic alloy during
the
sintering period, with the result that a liquid phase is not enough generated,
whereby
the diffusion bonding is not enough either. On the other hand, it takes too
many hours
to produce a boronized layer having a thickness of more than 10 ,u m, which is
not
practical.
After forming a metal layer on the ground plate as mentioned above, a layer of
metal powder is formed on it and then the metal powder is sinteted to produce
a
sintered porous layer. Since the metal powder must be sintered at the
temperature
where the aforementioned metal layer melts, the metal powder essentially has a
melting
temperature higher than that of the metal layer. After impregnated with an
active
material, the sintered porous metal comes to contact alkaline electrolyte so
that it
should have excellent durability to alkali. From the view points as mentioned
above,
nickel powder or powder of alloy mainly composed of nickel is preferable as
the metal
powder. A particle diameter of the metal powder is suitably selected
considering the
porosity and the strength of the sintered layer. The coarse powder having a
large
particle diameter is preferable for increasing the porosity, while it has not
enough
strength because the contacting points of each particle per unit volume are
decreased.
On the other hand, a sintered porous Iayer composed of a fine powder having a
small
particle diameter has increased strength, but decreased porosity. A preferable
particle
diameter of the metal powder is 2 to 10 a m.
After a slurry is prepared by dispersing the metal powder into water or
organic solvent with a viscous agent composed of water soluble resin or one
soluble in a
specified organic solvent, the slurry is applied to the metal layer formed on
the
aforementioned ground plate. Viscosity of the slurry is controlled by
regulating the
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quantities of the dispersing agent, and water or the organic solvent to be
added to the
metal powder so as to form a uniform coat layer with a desired thickness.
After applying the slurry in which the metal powder is dispersed, into the
metal layer, water or the organic solvent is dried off. After that, the ground
metal plate
having a layer composed of the metal powder and the dispersing agent dried off
from the
slurry is sintered in a reductive atmosphere. Vacuum or a mixed gas such as
hydrogen
and nitrogen produced by decomposing ammonia can be used as the reductive
atmosphere. The sintering temperature is preferably not less than the melting
temperatur a of the metal layer and lower than that of the metal powder by 300
to 600
° C. In a case where the metal powder is pure nickel, it is preferably
900 to 1100
C.
Thus, a substrate of a secondary battery electrode to which a porous layer
prepared by sintering a ground metal plate and metal powder is bonded can be
manufactured.
A nickel hydroxide electrode is produced by impregnating nickel nitrate as an
active material into the thus manufactured substrate of an electrode followed
by dipping
into sodium hydroxide aqueous solution, so as to use it as an electrode for a
secondary
battery.
EXAMPLES
The present invention is explained more in detail below in accordance with
the examples.
Example 1)
A ground plate was produced by plating on a steel sheet having a thickness of
80 I-~ m with nickel- phosphorus alloy using a nickel- phosphorus bath having
a
composition as mentioned below at the current density of 10 A/dm 2. It was
confirmed
by a wet analysis method that about 10 weight % of phosphorus was contained in
the
thus produced nickel-phosphorus film and the melting temperature of the
nickel-phosphorus alloy having this composition was about 880 ~ C.
CNickel-phosphorus plating bath]
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nickel sulfate 240 g/1
nickel chloride 45 g/1
boric acid ~ 30 g/1
phosphorous acid20 g/1
bath temperature60 C
PH 1 to 1.5
Porous sintered nickel layers were formed on both sides of the ground plate in
the following manner. At first, carboxymethyl cellulose as a viscous agent was
dissolved into water and 4% solution was prepared. A slurry was prepared by
dispersing nickel powder having a particle size of 2 to 3 ,u m in the viscous
solution.
The slurry was applied to both sides of the aforementioned nickel- phosphorus
plated
steel sheet with a coating machine, and then the moisture component was dried
off in
the electric oven. The nickel- phosphorus plated steel sheet coated with the
slurry was
heated for 15 minutes at 1000 ° C in the mixed gas consisting of 25% of
hydrogen and
75% of nitrogen, and then cooled off. Thus, a substrate having a porous layer
of
sintered nickel on one side of it was produced. The bonding strength of the
porous
layer of sintered nickel to the steel sheet was evaluated as follows:
The substrate having the thus produced porous layer of sintered nickel was
bended at 180 ° angle in the bending diameter of lmm, 2mm and 4mm
respectively, and
the degree of the peeling- off of the porous layer of sintered nickel from the
steel sheet
was evaluated with the naked eye based on the following standards. The results
are
shown in Table 2.
[Standards for evaluation
Oo : Cracks were caused in the sintered nickel layer
but no peeling- off was observed.
0 : Cracks were caused in the sintered nickel layer
and a little peeling- off was observed in the
center portion of the bending.
D : Cracks were caused in the sintered nickel layer
and peeling- off was observed in considerable
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portion of the bending.
Cracks were caused in the sintered nickel layer and
peeling- off was observed in the whole portion of
the bending.
(Examples 2 to 4)
A nickel plating layer of 2 a m was formed on a steel sheet having a
thickness of 80 ,u m using a Watt bath having a composition as mentioned below
at the
current density of 10 A/dm 2.
Further, a nickel- phosphorus plating layer having the thickness as shown in
Table 2 was formed on the nickel plating layer in the same manner as that of
Example 1.
Thus, a ground plate was manufactured.
Watt bath
nickel sulfate 300g/I
nickel chloride 45gJ1
boric acid 30g/1
bath temperature 50 ' C
pH 4 to 4.5
The same porous sintered
nickel layers as that
of Example 1 were formed
on
both sides of the ground plate in the same manner as that of Example 1. With
regard to
the substrate in this case having the porous layer of sintered nickel thus
prepared, the
degree of the peeling- off of the sintered nickel layer from the nickel-
plated steel sheet
having a large number of holes as a ground plate was evaluated by the
observation with
the naked eye based in the same manner as that of Example 1, to thereby
evaluate the
bonding strength of the sintered nickel layer to the nickel plated steel
sheet. The
results are shown in Table 2.
(Examples 5 to 7)
A nickel plating layer of 4 a m was formed on a steel sheet having a
thickness of 80 a m using a sulfamic acid bath having a composition as
mentioned
below at the current density of 10 A/dm ~ .
Further, a nickel- phosphorus plating layer was formed on the nickel plating
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layer using the same nickel- phosphorus plating bath in the same manner as
that of
Example 1. Thus, a ground plate was manufactured.
CSulfamic acid bath
nickel sulfamide 400g/1
nickel chloride 20g/1
boric acid 30g/1
Sodium lauryl sulfate 0.5g/1
bath temperature 50 ' C
PH 4
The same porous sintered
nickel layers as that of
Example 1 were formed on
both sides of the ground plate in the same manner as that of Example 1. With
regard to
the substrate in this case having the porous layer of sintered nickel thus
prepared, the
degree of the peeling-off of the sintered nickel layer from the nickel-plated
steel sheet
having a large number of holes as a ground plate was evaluated by the
observation with
the naked eye based in the same manner as that of Example 1, to thereby
evaluate the
bonding strength of the sintered nickel layer to the nickel plated steel
sheet. The
results are shown in Table 2.
(Example 8)
A nickel plating layer and a nickel- phosphorus plating layer were formed on
either sides of a steel sheet in the same manner as that of Example 5, and
then a large
number of holes having small diameters were punched in the above mentioned
plating
layers using a punching press (punching steel sheet) . Further, porous layers
of
sintered nickel were formed on both sides of the steel sheet in the same
manner as that
of Example 1 to thereby prepare a substrate.
With regard to the substrate in this case having the porous layer of sintered
nickel thus prepared, the degree of the peeling- off of the sintered nickel
layer from the
ground plate was evaluated by the observation by the naked eye in the same
manner as
that of Example l, to thereby evaluate the bonding strength of the sintered
nickel layer
to the nickel plated steel sheet. The results are shown in Table 2.
(Example 9)
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A nickel plating layer of 4 a m was formed on a steel sheet as the same as
that of Example 1 having a thickness of 80 a m using a sulfamic acid bath. A
boronized layer was formed on the surface of the nickel plated steel sheet by
burying
the same in a pot filled with boron powder, and then heating the same for I
hour at the
temperature of 950 ' C. in the mixed gas consisting of 25% of hydrogen and 75%
of
nitrogen. Thus, a ground plate was obtained. It was confirmed by the cross-
section
observation that the thickness of the boronized layer was about 2 a m. The
same
slurry as that of Example 1 was applied in the same manner as that of Example
1 to one
side of the boronized steel sheet, and the moisture component was dried off.
The
boronized steel sheet coated with the slurry was heated for 30 minutes at the
temperature of 1150 ' C, in the mixed gas of 25% of hydrogen and 75% of
nitrogen, and
thereafter cooled off. Thus, a substrate having a porous layer of sintered
nickel formed
on one side thereof was obtained. With regard to the substrate thus produced,
the
degree of the peeling- off of the sintered nickel layer from the steel sheet
as a ground
plate was evaluated by the naked eye observation in the same manner as that of
Example 1, thereby evaluating the bonding strength of the sintered nickel
layer to the
steel sheet. The results are shown in Table 2.
(Examples 10 to 14)
A nickel plating layer having the thickness as shown in Table 1 was formed on
a steel sheet having thickness of 60 a m in which a large number of tiny holes
were
formed (perforated steel sheet) using a sulfamic acid bath having a
composition
mentioned below at the current density of 10 A/dm z .
~Sulfamic acid bath]
nickel sulfamide 400g/I
nickel chloride 20g/1
boric acid 30g/1
Sodium lauryl 0.5g/1
sulfate
bath temperature 50 ' C
pH 4
A nickel- phosphorus plating layer was formed on the steel sheet using the
- 13-
CA 02236421 1998-OS-O1
same nickel- phosphorus plating bath as that of Example 1. Thus, the ground
plates
having thicknesses as shown in Table 1 were obtained. And then, a nickel
slurry was
applied to it in the same manner as that of Example 1 and the moisture
conponent was
dried off. The ground plate coated with the slurry was sintered in the same
manner as
that of Example l, thereby producing a substrate having a porous layer of
sintered nickel.
With regard to the substrate thus produced, the degree of the peeling- off of
the
sintered nickel layer from the steel sheet as a ground plate was evaluated by
the naked
eye observation in the same manner as that of Example 1, thereby evaluating
the
bonding strength of the sintered nickel layer to the steel sheet. The results
are shown
in Table 2.
CComparative Examples 1, 2)
Nicl~el plating layers having a thickness as shown in Table 1 were formed on
both sides of the steel sheet in the same manner as that of Example 1 using a
sulfamic
acid bath as shown in Examples 5 to 7. But a nickel-phosphorus plating such as
earned out in the cases of Examples I to 8 was not formed. And then, a porous
layer of
sintered nickel was formed in the same manner as that of Example 1. With
regard to
the thus produced steel sheet having the porous layer of sintered nickel, the
degree of
the peeling- off of the sintered nickel layer from the steel sheet was
evaluated by the
naked eye observation based on the same standards as shown in the above
Examples to
thereby evaluate the bonding strength of the sintered nickel layer to the
steel sheet.
The results are shown in Table 2.
Comparative Examples 3, 4)
Nickel plating layers having thicknesses as shown in Table 1 were formed on
both sides of the same perforated steel sheet as that of Examples 10 to 14
using the
same sulfamic acid bath as the aforementioned. But a nickel- phosphorus
plating such
as carried out in Examples was not formed. And then, a porous layer of
sintered nickel
was formed in the same manner as that of the Examples. With regard to the thus
produced steel sheet having the porous layer of sintered nickel, the degree of
the
peeling- off of the sintered nickel layer from the steel sheet was evaluated
by the naked
eye observation based on the same standards as shown in the above Examples, to
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CA 02236421 1998-OS-O1
thereby evaluate the bonding strength of the sintered nickel layer to the
steel sheet.
The results are shown in Table 1. And all these results are shown in Table 2.
As shown in Figure I, since the substrate having 'the ground plate of the
present invention has excellent bonding strength of the sintered porous layer
to the
ground plate; peeling- off or falling- off of the sintered porous layer is
scarecely caused
when the substrate is subjected to a bending work.
(The evaluation of the electrode performance)
The substrate of Example 3 was dipped into an aqueous solution of nickel
nitrate under reduced pressure so that nickel nitrate is impregnated into the
porous
layer of the sintered nickel. After that, the aforementioned porous layer of
the sintered
nickel was treated in an aqueous solution of 25 weight °!o of sodium
hydroxide so that
the nickel nitrate is made into nickel hydroxide. Thus, an electrode was
obtained. An
electrode of the substrate according to Comparative Example I was obtained in
the same
manner.
The charging and dischaging characteristics obtained in a case, where the
secondary battery electrode of the present invention was used as a positive
electrode in
an aqueous solution of 6 normal of potassium hydroxide, was measured under a
constant
current (discharging ratio:3C) using a nickel mesh as a counter electrode and
a silver
chloride electrode as a reference electrode.
The measurement results obtained from one case where the electrode
comprising the substrate of Example 3 (the present invention) was used and
from the
other case where the electrode comprising the substrate of Comparative Example
I
(conventional) was used are shown in Figure 2. As shown in Figure 2, the
battery
using the electrode comprising the ground plate and the substrate of the
present
invention was little polarized and showed an excellent charging and
discharging
characteristics.
This is because the substrate of a secondary battery electrode of the present
invention has a porous layer having excellent bonding strength to a ground
plate.
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CA 02236421 1998-OS-O1
POSSIBILITY OF USE IN INDUSTRY
In the substrate of a secondary battery electrode of the present invention,
since a sintered porous metal has excellent bonding strength to a ground metal
plate,
the sintered porous layer does not peel off even when the substrate is
subjected to a
severe work such as bending.
Also, since the ground plate of the present invention has a porous layer
formed on it by forming a metal powder layer on its plating layer and
sintering the same,
whereby the sintered porous layer has excellent bonding strength to the ground
plate,
the sintered porous layer does not peel off even when the ground plate is
severely
formed such as in bending.
Further, since the ground plate of the present invention is a sheet having a
large number of holes produced by punching a steel sheet having a plating
layer, the
sintered porous layer has excellent bonding strength to the ground plate after
forming a
metal powder layer on the plating layer and sintering them and the sintered
porous layer
does not peel off even when it is severely formed such as in bending.
Still further, since the ground plate of the present invention has a
boronizing
layer, and a metal powder layer is formed on the boronizing layer and is
sintered, the
sintered porous layer has excellent bonding strength to the ground plate even
when it is
formed and the sintered porous layer does not peel off even when it is
severely formed
such as in bending, similarly to the case where a nickel-phosphorus plating
layer is
formed on the ground plate.
Since the ground metal plate is a punched steel sheet and is characterized in
that at least one side of the punched steel sheet is boronized, a layer of
powdered metal
which is eutectically alloyed with boron is formed on it, a porous layer is
formed by
sintering at a temperature not less than the melting temperature of the
eutectic alloy
and not more than those of the ground metal sheet and the powdered metal, and
the
porous layer is bonded to the ground metal plate at the same time, the porous
layer
formed by sintering the layer of powdered metal to the ground metal plate has
excellent
bonding strength to the ground metal plate and the sintered porous layer does
not peel
off even when it is severely formed such as in bending.
- is -
CA 02236421 1998-OS-O1
Still further, since the porous layer is produced by sintering nickel powder
and
the diffusion between the porous layer and the ground plate is promoted by the
melting
of a layer of metal with a low melting temperature at the time of sintering,
the porous
layer has excellent bonding strength to the ground plate and the sintered
porous layer
does not peel off even when it is severely formed such as in bending. Also,
since nickel
has excellent durability to alkali, the substrate of a secondary battery
electrode of the
present invention has excellent corrosion resistance when it contacts alkaline
electrolyte.
Sill further, the electrode of the present invention is produced by
impregnating an active material into any of the aforementioned substrates for
an
electrode, and the secondary battery using the electrode of this invention
shows
excellent charging and discharging characteristics.
- m-
CA 02236421 2005-11-09
Table I
Sample Sheet Ni Ni-P Remarks
plating plating
thickness thickness
Example 80 a m steel sheet - 2 a
1 m
Example 80 um steel sheet2 um 1 um
2
Example 80 um steel sheet2 um 2 um
3
Example 80 um steel sheet2 um 4 um
4
Example 80 um steel sheet4 um 2 um
Example 80 um steel sheet4 um 4 um
6
Example 80 um steel sheet4 um 6 um
7
Example 80 a m steel sheet4 a 2 a punched after
8 m m being plated
Example 80 a m steel sheet4 a - boronized
9 m
Example 60 a punched steel 2 a 1 a
m sheet m m
Example 60 a Punched steel 2 a 2 a
I1. m sheet m m
Example 60 a punched steel 4 a 2 a
12 m sheet m m
Example 60 a punched steel 4 a 4 a
i3 m sheet m m
Example 60 a punched steel 4 a 6 a
14 m sheet m m
Comparative 80 a m steel sheet2 a -
Example m
1
Comparative 80 a m steel sheet4 a -
Example m
2
Comparative60 a Punched steel 2 a -
Example m sheet m
3
Comparative60 a punched steel 4 a
Example m sheet m -
4
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CA 02236421 2005-11-09
Table 2
Evaluation of bonding strength of sintered nickel layer to ground plate
Sample Evaluation of
the bonding strength
after bending
at 180 angle
Bending diameter Bending diameter Bending diameter
1 mm Z mm 2 mm
Example O O O
1
Example O O
Z
Example O O
3
Example O O O
4
Example O O O
Example ~ ~ O
6
Example O ~ O
7
Example O
8
Example d O
9
Example O O O
Exanmple O O O
11
Example O O
12
Example O ~ O O
13
Example O ~ O
14
Comparativex D O
Example
1
Comparativex D O
Example
2
ComparativeD O O
Example
3
ComparativeD O O
Example
4
-17b-
