U.S. patent application number 09/903482 was filed with the patent office on 2002-02-14 for connecting part for connecting internal components of lead acid battery.
This patent application is currently assigned to JAPAN STORAGE BATTERY CO., LTD.. Invention is credited to Ishiguro, Hiroyuki, Omae, Takao.
Application Number | 20020018931 09/903482 |
Document ID | / |
Family ID | 26595860 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018931 |
Kind Code |
A1 |
Omae, Takao ; et
al. |
February 14, 2002 |
Connecting part for connecting internal components of lead acid
battery
Abstract
The use of the Pb--Sn alloy containing Ag and Se of the present
invention as a connecting part for connecting internal components
makes it possible to improve the resistance of straps, poles and
cell connectors to general corrosion and grain boundary corrosion,
inhibit the occurrence of the stress corrosion cracking and enhance
the alloy strength, thus providing a lead acid battery having an
excellent reliability.
Inventors: |
Omae, Takao; (Kyoto, JP)
; Ishiguro, Hiroyuki; (Kyoto, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Assignee: |
JAPAN STORAGE BATTERY CO.,
LTD.
|
Family ID: |
26595860 |
Appl. No.: |
09/903482 |
Filed: |
July 12, 2001 |
Current U.S.
Class: |
429/160 ;
429/161; 429/178; 429/211 |
Current CPC
Class: |
C22C 11/06 20130101;
H01M 10/06 20130101; H01M 4/685 20130101; Y02E 60/10 20130101; H01M
50/571 20210101; H01M 50/541 20210101; H01M 50/543 20210101; H01M
50/534 20210101 |
Class at
Publication: |
429/160 ;
429/161; 429/178; 429/211 |
International
Class: |
H01M 002/24; H01M
002/28; H01M 002/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2000 |
JP |
P. 2000-210904 |
Mar 30, 2001 |
JP |
P. 2001-098047 |
Claims
What is claimed is:
1. A connecting part for connecting internal components of a lead
acid battery, which comprises a Pb--Sn alloy comprising Ag and
Se.
2. The connecting part for connecting internal components of a lead
acid battery according to claim 1, wherein the content of Ag is
from 0.01 to 1.0% by weight based on the weight of Pb, the content
of Se is from 0.001 to 0.05% by weight based on the weight of Pb
and the content of Sn is from 0.5 to 5.0% by weight based on the
weight of Pb.
3. The connecting part for connecting internal components of a lead
acid battery according to claim 1, which is a strap.
4. The connecting part for connecting internal components of a lead
acid battery according to claim 2, which is a strap.
5. The connecting part for connecting internal components of a lead
acid battery according to claim 1, which is a pole.
6. The connecting part for connecting internal components of a lead
acid battery according to claim 2, which is a pole.
7. The connecting part for connecting internal components of a lead
acid battery according to claim 1, which is a cell connector.
8. The connecting part for connecting internal components of a lead
acid battery according to claim 2, which is a cell connector.
9. A lead acid battery comprising a connecting part for connecting
internal components according to any one of claims 1 to 8.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to improvement in the
corrosion resistance of a connecting part for connecting internal
components of a lead acid battery.
BACKGROUND ART
[0002] As the connecting parts for connecting internal components
of lead acid batteries such as the strap and the pole, a Pb--Sb
alloy containing Sb in an amount of from 2.0 to 4.0% by weight or a
Pb--Sn alloy containing Sn in an amount of from 1.0 to 5.0% by
weight has been used hitherto. Among these alloys, the Pb--Sn alloy
has been mainly used as the connecting part for valve regulated
lead acid batteries having a limited amount of electrolyte. This is
because Sb causes an adverse effect when it enters into the
battery.
[0003] The Pb--Sn alloy is a typical eutectic alloy. A Pb--Sn alloy
containing Sn in an amount of about 3.0% by weight is formed by
lead-rich primary crystals and a crystal structure comprising
Sn-rich phase deposited at the grain boundary between the primary
crystals. Thus, the Pb--Sn alloy having the foregoing composition
can have their primary crystals to grow to a large size. Since the
Sn-rich phase deposited at the crystal boundary has a low strength,
a cavity (crack) could be produced in the grain boundary at the
solidification step.
[0004] In the valve regulated lead acid battery, the connecting
part for connecting internal components could be corroded. This is
attributed to the following oxygen reduction reaction involving the
reduction of oxygen gas produced at the positive electrode on a
lead part:
Pb+1/2O.sub.2+H.sub.2SO.sub.4.fwdarw.PbSO.sub.4+H.sub.2O (1)
[0005] Since such a lead part is exposed to the exterior of the
electrolytic solution, it does not undergo charge-discharge
reaction as occurring in the part soaked in the electrolytic
solution. Thus, once converted to lead sulfate (PbSO.sub.4), this
lead part cannot be converted back to lead (Pb). Therefore, the
oxygen reduction reaction represented by the foregoing equation (1)
causes general corrosion which is uniform corrosion of the surface
of the lead part.
[0006] In the Pb--Sn alloy, Sn-rich phase deposited at the grain
boundary can be easily corroded, causing corrosion to proceed along
the grain boundary (grain boundary corrosion). Further, the Pb--Sn
alloy is subject to stress developed by the volumetric change of
corrosion products that causes the grain boundary to be cracked
(stress corrosion cracking). In the worst case, the connecting part
would be broken.
[0007] As an approach for overcoming the problem that grain
boundary corrosion can easily occur due to the growing of crystals
of Pb--Sn alloy, there is proposed a method of adding Se, Te, etc.
to a Pb--Sn alloy in an unexamined published Japanese patent
application No. 9-167611. This method is to add a nucleant such as
Se to a Pb--Sn alloy in order to make grains fine and hence solve
the problem of grain boundary corrosion and stress corrosion
cracking.
[0008] However, it was found that even the Pb--Sn alloy comprising
the nucleant such as Se has the following problems. That is to say,
the alloy comprising finely divided crystal particles is little
subject to the progress of grain boundary corrosion but cannot be
prevented from general corrosion due to the oxygen reduction
reaction. Thus, such a lead part gradually causes reducing in
thickness during use in a valve regulated lead acid battery.
[0009] Further, a cell connector made of a Pb--Sn alloy comprising
large crystals undergoes grain boundary corrosion along the area at
which the cell connector is connected, sometimes causing the
connecting part to break due to vibration or impact during use.
This fracture occurs along the connecting area (final
solidification interface). Therefore, this fracture is presumably
attributed to the facts that the final solidification interface can
easily have an Sn-rich phase thereon and thus can be easily
corroded, this Sn-rich phase has a low strength and thus is
brittle, and the cell connector is subject to tensile or shearing
stress on the connecting area due to vibration, impact or the like.
This problem can also occur with a Pb--Sn alloy comprising fine
grains including Se or the like incorporated therein. Thus, by this
alloy, the strength of final solidification interface has not
sufficiently improved.
[0010] Accordingly, it has therefore been a great requirement that
the Pb--Sn alloy to be used in the connecting part for connecting
internal components of a lead acid battery be prevented from grain
boundary corrosion, be less subject to general corrosion and have
an enhanced strength in itself and a connecting area.
SUMMARY OF THE INVENTION
[0011] The present invention has the following embodiments.
[0012] (1) A connecting part for connecting internal components of
a lead acid battery, which comprises a Pb--Sn alloy containing Ag
and Se.
[0013] (2) The connecting part for connecting internal components
of a lead acid battery according to (1) above, wherein the content
of Ag is from 0.01 to 1.0% by weight based on the weight of Pb.
[0014] (3) The connecting part for connecting internal components
of a lead acid battery according to (1) or (2) above, wherein the
content of Se is from 0.001 to 0.05% by weight based on the weight
of Pb.
[0015] (4) The connecting part for connecting internal components
of a lead acid battery according to any one of (1) to (3) above,
wherein the content of Sn is from 0.5 to 5.0% by weight based on
the weight of Pb.
[0016] (5) The connecting part for connecting internal components
of a lead acid battery according to any one of (1) to (4) above,
which is a strap.
[0017] (6) The connecting part for connecting internal components
of a lead acid battery according to any one of (1) to (4) above,
which is a pole.
[0018] (7) The connecting part for connecting internal components
of a lead acid battery according to any one of (1) to (4) above,
which is a cell connector.
[0019] (8) A lead acid battery comprising a connecting part for
connecting internal components according to any one of (1) to (7)
above.
[0020] The first embodiment of implication of the present invention
is characterized in that a lead acid battery has a connecting part
for connecting internal components comprising a Pb--Sn alloy
containing Ag and Se.
[0021] In accordance with the present invention, the connecting
part for connecting internal components has an enhanced resistance
to general corrosion (resistance to conversion to lead sulfate). At
the same time, the crystal particles of the lead alloy can be
finely divided to disperse Sn-rich phase deposited at the grain
boundary, making it possible to improve the resistance to grain
boundary corrosion. Further, the enhancement of resistance to grain
boundary corrosion can be accompanied by the prevention of the
stress corrosion cracking. Moreover, the strength of the alloy can
be enhanced, and the castability and weldability of the alloy can
be improved.
[0022] The present invention is also characterized in that a Pb--Sn
alloy to be used in connecting parts for connecting internal
components contains Ag and Se in an amount of from 0.01 to 1.0% by
weight, and from 0.001 to 0.05% by weight, and Sn from 0.5 to 5.0%
by weight, respectively.
[0023] Further, the arrangement that the content of Ag, Se and Sn
in the Pb--Sn alloy containing Ag and Se fall within the above
defined range makes it possible to remarkably enhance both of
general corrosion resistance and grain boundary corrosion
resistance and hence obtain a high alloy strength. Moreover, in
order to exert a more sufficient effect of improving general
corrosion resistance, it is more preferred that the content of Ag
and Se be from 0.02 to 1.0% by weight and from 0.005 to 0.05% by
weight, respectively.
BRIEF DESCRIPTION OF THE INVENTION
[0024] FIG. 1 is a schematic diagram illustrating a section of a
corroded strap.
[0025] FIG. 2 is a diagram illustrating the relationship between
the content of Ag and the thickness of the generally corroded
layer.
[0026] FIG. 3 is a graph illustrating the relationship between the
content of Se and the depth of progress of grain boundary
corrosion.
[0027] FIG. 4 is a diagram illustrating the difference in shear
fracture force among different types of alloys.
DETAILED DESCRIPTION OF THE INVENTION
[0028] In the present invention, the connecting part for connecting
internal components is not specifically limited as long as it
exists partly or entirely in the lead acid battery and is a
component or member other than positive and negative electrodes to
be used in the assembly of the lead acid battery. Examples of the
connecting part for connecting internal components include strap,
strap-forming additive lead (burning rod), pole, and cell
connector. Examples of the cell connector include through the
partition type cell connector, and over the partition type cell
connector.
[0029] In the present invention, the process for the preparation of
the alloy to be used as a connecting part for connecting internal
components is not specifically limited. Any ordinary casting
process for the preparation of an alloy may be utilized to prepare
the alloy. The process for forming the alloy into a connecting part
for connecting internal components is not specifically limited as
long as the alloy thus prepared can be formed into a connecting
part for connecting internal components having a predetermined
shape.
[0030] The process for the preparation of a lead acid battery from
the connecting part for connecting internal components of the
invention is not specifically limited. Any ordinary preparation
process for use in the preparation of a lead acid battery may be
utilized to prepare the lead acid battery of the invention.
[0031] Embodiment of the present invention will be further
described with reference to a lead acid battery comprising Pb--Sn
alloys having different Ag contents and Se contents as connecting
parts for connecting internal components as examples. The term "%
by weight" as used herein is synonymous with "% by mass".
EXAMPLE 1
[0032] Alloys comprising Pb-1.0 wt % Sn alloy as a base and
containing Ag and Se in various amounts of from 0 to 2.0% by weight
and from 0 to 0.05% by weight, respectively, were prepared as the
connecting part for connecting internal components of a lead acid
battery.
[0033] Since the solubility of Se in a lead alloy depends on the
temperature, Se can be added only up to a certain concentration in
a commonly used alloy preparation temperature range. Accordingly,
the upper limit of the added amount of Se was made to be 0.05% by
weight.
[0034] These alloys were each used to prepare a strap, a pole and a
cell connector, which were then assembled to a 12V 20 Ah absorptive
grass mat-type valve regulated lead acid battery. As a battery
element there was used a battery element having an ordinary
structure obtained by stacking positive and negative electrodes
having a Pb--Ca alloy grids pasted with active materials with fine
glass fiber separators interposed therebetween.
[0035] The sample alloys were each used to prepare a cell
connector. While the sample alloy having the same composition as
that used for pole and cell connector was being melted by a gas
burner and supplied, the electrode tabs and the cell connectors
were melted and solidified to form a strap. The thickness of the
strap was 5 mm. Subsequently, the elements were inserted into a
polypropylene battery case. The cell connectors were then connected
by electrical resistance welding. Then, an absorptive grass
mat-type valve regulated lead acid battery was assembled.
[0036] In order to evaluate the connecting part for connecting
internal components, these batteries were respectively subjected to
the floating charge test. This test was carried out at a
temperature of 60.degree. C. and a floating charge voltage of 13.65
V for 10 months. The batteries thus tested were each disassembled.
The components were then withdrawn for the examination of
corrosion.
[0037] In batteries which showed much corrosion, the strap, pole
and cell connector were all found corroded. As a representative
portion to be examined, a cross section of the strap was observed
for corrosion to compare the corrosion resistance of alloys. A
typical cross section of the strap is shown in FIG. 1. There are
observed a general corrosion layer 2 which has grown relatively
uniformly and a grain boundary corrosion 3 which proceeds deeply
along the crystal grain boundaries. In the Figure, the reference
numeral 1 indicates a strap, and the reference numeral 4 indicates
an electrode tab. The evaluation of sample alloy was carried out by
the measurement of the thickness of the general corrosion layer 2
and the depth of progress of corrosion in the grain boundary
corrosion 3.
[0038] FIG. 2 shows the results of measurement of the thickness of
the general corrosion layer. The results are plotted with the
content of Ag as the abscissa and the ratio of the thickness of the
corrosion layer to the initial thickness of the strap as the
ordinate. In order to determine the thickness of the corrosion
layer, the measurements obtained at five points on the surface of
the strap were averaged.
[0039] When the content of Ag exceeds 0.005% by weight, the
thickness of the general corrosion layer tends to show a sudden
drop. However, when the content of Ag is not smaller than 0.05% by
weight, as the content of Ag increases, the thickness of the
corrosion layer decreases gradually but not so remarkably. FIG. 2
shows the results measured at the Ag content of 0.002% by weight or
more. The results obtained when no Ag was added were almost the
same with the results obtained when the amount of Ag was 0.002% by
weight.
[0040] The alloys having Se incorporated therein showed much less
general corrosion than those free of Se when the content of Ag is
not smaller than 0.01% by weight. This presumably means that the
effect of inhibiting general corrosion exerted by the incorporation
of Ag is synergistically accelerated by the incorporation of Se.
However, when the content of Se exceeds 0.01% by weight, the
resulting effect of inhibiting general corrosion tends to be
lessened.
[0041] From the standpoint of improvement of resistance to general
corrosion, the Pb--Sn alloy containing both Ag and Se is useful
when the content of Ag is from 0.01 to 1.0% by weight. Preferably,
the alloy contains Se in an amount of from 0.001 to 0.05% by
weight. More preferably, it is considered that the alloy contains
Ag and Se in an amount of from 0.02 to 1.0% by weight and from
0.005 to 0.05% by weight, respectively.
[0042] FIG. 3 illustrates the results of measurement of the depth
of progress of grain boundary corrosion. The results are plotted
with the content of Se as the abscissa and the ratio of the depth
of progress of grain boundary corrosion to the initial thickness of
the strap as the ordinate. The depth of progress of grain boundary
corrosion is represented by the linear distance between the surface
and the forward end of grain boundary corrosion which shows the
deepest progress toward the interior of the strap.
[0043] The depth of progress of grain boundary corrosion tends to
decrease with the rise of the content of Se. It was found that the
depth of progress of grain boundary corrosion decreases remarkably
when the content of Se is not smaller than 0.001% by weight and
decreases gradually until the content of Se reaches 0.05% by
weight.
[0044] It was further found that by merely adding Ag in an amount
of not smaller than 0.01% by weight, the depth of progress of grain
boundary corrosion shows a remarkable drop as compared with the
alloys free of Ag. This presumably means that the effect of
inhibiting grain boundary corrosion exerted by the incorporation of
Se is synergistically accelerated by the incorporation of Ag. The
more the content of Ag is, the less is the depth of progress of
grain boundary corrosion. However, when the content of Ag is not
smaller than 1%, the tendency for decrease of depth of progress of
grain boundary corrosion is lessened.
[0045] From the standpoint of improvement of resistance to grain
boundary corrosion, the Pb--Sn alloy containing both Ag and Se
preferably contains Se in an amount of from 0.001 to 0.05% by
weight as well as Ag in an amount of from 0.01 to 1.0% by
weight.
[0046] The reason why the incorporation of Ag causes the drop of
amount of general corrosion is unknown. However, the following
reason can be roughly proposed. As previously mentioned, the
corrosion of lead alloys in the valve regulated lead acid battery
presumably involves the reaction of oxygen produced on the positive
electrode with a lead alloy and sulfuric acid leading to the
production of lead sulfate and water, which is oxygen-reduction
reaction represented by the scheme (1). Ag acts as a catalyst in
the reduction of oxygen to cause a reaction represented by the
following scheme (2) by which oxygen is directly reduced to water
and thus is consumed. As a result, general corrosion due to the
oxygen-reduction reaction represented by the scheme (1) is
lessened.
1/2O.sub.2+H.sub.2.fwdarw.H.sub.2O (2)
[0047] It has heretofore been said that the effect of Se on the
improvement of resistance to grain boundary corrosion is attributed
to the fact that Se acts to make the crystal structure fine and
hence disperse Sn-rich phase deposited on the grain boundaries. As
can be seen in the results of test, the incorporation of Ag in
addition to Se exerts an unexpectedly great synergistic effect of
improving resistance to both grain boundary corrosion and general
corrosion. It can be thought that Ag exerts a catalytic oxygen
reduction effect to accelerate the effect of inhibiting grain
boundary corrosion exerted by the incorporation of Se and a good
synergistic effect on the inhibition of progress of general
corrosion accompanying the fine grains by the incorporation of
Se.
[0048] In addition to the strap, the pole and cell connector were
observed. The results were similar to that of the strap.
EXAMPLE 2
[0049] The effect of the content of Sn was examined. As the sample
metals there were prepared alloys comprising as a base a Pb--Sn
alloy containing Ag and Se in an amount of 0.1% by weight and 0.02%
by weight, respectively, and Sn in an amount of from 0 to 7.0% by
weight. These sample alloys were each used to prepare a connecting
part for connecting internal components. Using these connecting
parts, a battery was assembled in the same manner as in Example 1,
and subjected to the floating charge test in the same manner as in
Example 1.
[0050] When the content of Sn fell below 0.5% by weight, the size
of crystal increased, the effect of Se to make the crystal
structure fine was not found, and the strap thus tested showed
grain boundary corrosion deep therein. On the other hand, when the
content of Sn exceeded 5% by weight, the alloys exhibited
deteriorated general corrosion resistance that increased the
thickness of the corrosion layer. These results show that the
effect of the present invention can be well exerted when the range
of the content of Sn in the Pb--Sn alloy is from 0.5 to 5.0% by
weight.
EXAMPLE 3
[0051] The strength of alloys containing Ag and Se incorporated
therein was examined. For this test, a pair of cell connectors
prepared from the foregoing alloys was disposed on both sides of a
synthetic resin plate having a hole with a diameter of 8 mm formed
therein. The two cell connectors were then connected to each other
by the electrical resistance welding method. The shear fracture
force required to twist off the cell connectors at the connecting
portion when the connecting portion is under the application of a
rotational force (shearing stress) was measured.
[0052] FIG. 4 illustrates the results of the measurement of shear
fracture force versus the kind of the alloys tested (content of Ag
and Se in the alloys). The breaking torque ratio in the ordinate in
the Figure indicates the ratio of shear fracture force at the
connecting portion on the various alloys to that at the connecting
portion on the Pb--Sn alloy free of Ag and Se.
[0053] The Pb--Sn alloy containing 0.01% by weight of Se showed no
great improvement of ratio of breaking torque as compared with the
Pb--Sn alloy free of Ag and Se. However, the alloy containing 0.1%
by weight of Ag showed a breaking torque ratio rise of about 14%.
Further, the alloy containing both 0.1% by weight of Ag and 0.01%
by weight of Se showed a breaking torque ratio rise of about 27%.
It can thus been seen that while the single addition of Se does not
make much contribution to the enhancement of strength, the addition
of both Ag and Se makes it possible to drastically enhance the
strength at the connecting portion on the alloy.
[0054] The reason for this enhancement of strength is not well
known. However, it is thought that by adding Ag or Ag and Se in
combination, the brittleness of Sn-rich phase deposited at grain
boundaries can be overcome, making it possible to remarkably
enhance the strength at the connecting portion on the alloy.
[0055] The use of the Pb--Sn alloy containing Ag and Se of the
present invention as a connecting part for connecting internal
components makes it possible to improve the resistance of straps,
poles and cell connectors to general corrosion and grain boundary
corrosion, inhibit the occurrence of the stress corrosion cracking
and enhance the alloy strength, thus providing a lead acid battery
having an excellent reliability.
[0056] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
[0057] This application is based on Japanese patent applications
No. 2000-210904 filed on Jul. 12, 2000 and No. 2001-098047 filed on
Mar. 30, 2001, the entire contents thereof being hereby
incorporated by reference.
* * * * *