Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
` ``` ~04~ 4
RELATED APPLICATIONS
Millex, Serial No. 158,871, filed December 14, 1972,
for: "Battery Contalner Cover".
Mao and Rao, Serial No. 209,677, filed September 20,
1974, for: "Lead Basa Calcium-Tin ~lloy and Use Thereof".
Rao and Mao, Serial No. 209,678, filed September 20,
1974, ~or: "Lead Base Cadmium Tin Alloy Useful for Forming
Battery Components".
Mao ~nd Lannoye, Serial No. 214,431, filed November 22,
~0 1974, for: "Cadmium-Antimony-Lead-Alloy for Maintenance-free
Lead-Acid Battery".
Mao, Rao and Trenter, Serial No. 236,233, filed on
September 24, 1975, for: "Maintenance-free Battery".
This invention relates to lead-acid storage batteries
and, more particularly, to maintenance-free batteries having
improved current draw characteristics.
Lead base alloys have been used for storage battery
plate grids for many years. The electrochemical characteristics
of le~d as well as its low cost make it suitable as a primary
materiaI, ~ut alloying ingredients must be included because
of the ~nherent physical weakness of the lead. A large number
of di~erent alloying materials in variou~ peraentages and com-
binations ha~e been considered. Antimony-lead alloys containing
anywhere from about 4.5 to 12~ by weight antimony have been
used for the preparation of the grids for lead-acid batteries.
~he principal function of the antimony constituent is to impart
adequate grid strength as well as permitting easy castins of the
grid. Lithium and combinations of lithium and tin have likewise
29 been employed as shown in U. S. Patent No. 3,647,545. Still
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further, Canadian Patent ~20,393 describes a lead base alloy con-
taining cadmium and antimony for use in forming battery grids.
As shown in that patent, alloying about 2.5 to 3% cadmium with
2.5% antimony in a lead alloy imparts a tensile strength con-
siderably above that which would ordinarily be expected.
Recently, much interest has been placed upon providing
automotive type, wet cell, lead-acid storage batteries in configur-
ations which can be readily installed and which require,once in
service, no further maintenance throughout the expected life of the
battery. One aspect of this effort to provide such maintenance-free
batteries is to utilize internal components that make it unnecessary
to inspect and replenish electrolyte levels in the cells over the
normal battery life.
To achieve this maintenance-free objective, substantial
elimination of water losses must be achieved. This requires
that the grids employed in the maintenance-free battery draw
only a small current during constant voltage overcharge so that
only minimum gas generation occurs with the accompanying water
loss being concomitantly minimized. With conventional automotive
batteries using antimony-lead grids typically containing about
4.5% by weight antimony, the current draw at the completion of
charging is unacceptably high for maintenance-free battery
applications. In addition, it is known that self-discharge of
- a wet lead-acid battery employing an antimony alloy is caused
primarily by the dissolution of antimony from the grids and its
subsequent deposition on the negative plates, where it causes
electrochemical reactions that discharge the lead to lead sulfate.
For these reasons, the development of suitable materials for
grlds in maintenance-free batteries has primarily emphasized the
use of lead base alloys not containing antimony.
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The copending Mao and Rao application, identified here-
in, presents one type of alloy suitable for forming the grids of
maintenance-free batteries. Thus, a lead base alloy containing,
by weight, 0.06 to 0.10~ calcium and 0.10 to 0.40% tin is dis-
closed. A further approach is described in the previously identi-
fied Rao and Mao application. This discloses a cadmium-tin-lead
alloy which is useful in forming components of the battery elements,
including the battery grid in a maintenance-free battery.
A still further approach is described in the herein
identified Mao and ~annoye application in which a lead based
alloy containing, typically, from about 1.0 to 2.0~ antimony
and fro~ a~out 1.2 to about 2.2% cadmium is disclosed. Lead-
acid batter~ grids can be easily cast from such an alloy, and
the grids may be advantageously employed in the preparation of
~aintenance~free batteries to provide superior characteristics.
While SUCll alloys do provide suitable materials for
forming ~atter~ grids for use in maintenance-free battery
applications, it would be highly desirable to be able to provide
m~intenance-free batteries in which the current draw character-
istics of the grids may be further decreased.
It is accordin~l~ an ob]ect of the present inventionto provide a maintenance-free battery having exceptional current
draw characteristics~
Another object provides a method for decreasing the
current draw characteristics of alloys used in such applications.
A still further and more specific object of this inven-
tion lies in the provision of a maintenance-free battery employ-
ing calcium-lead or calcium-tin~lead alloy grids which possess
29 improved current draw characteristics.
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Yet anotner object is to provide a method of lessen-
ing the criticality of the impuritie~ typically observed for
tne alloys used to form the battery grids in maintenance-free
battery applications.
Other objects and advantages of the present invention
will be apparent as the following description proceeds.
While the invention is susceptible of various modifi-
cations and alternative forms, specific embodiments thereof
will hereinafter be described in detail. It should be under-
stood, however, that it is not intende~ to limit the invention
to the particular forms disclosed, but, on the contrary, the ;
intention is to cover all modifications, equivalents and alter-
natives falling wit~in the spirit and scope of the invention as
expressed in the appended claims.
In general, the present invention is predicated on :
the discovery that the addition of elemental cadmium (e.g.--
as a flne powder) or a cadmium compound to the electrolyte in
certain levels in a maintenance-free battery application signifi-
cantly diminishes the current draw, and thus the water consumption,
so as to improve the performance of the battery.
The cadmium compound which is utilized in accordance
with this invention may comprise cadmium sulfate or any other
cadmium compound which is~ sufficiently soluble in aqueous
sulfuric acid solutions to provide the requisite amount of the ~ ;
cadmium, (2~ not substantially harmful to either the battery com-
ponents or to the performance of the battery in use and ~3) not
susceptible to producing a lead salt that would likely precipitate
in sufficient amounts which would significantly reduce the porosity
29 ~of the battery plates. For example, cadmium hydroxide could
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suitably be used.
The amount of the cadruium compound which is used
should be sufficient to decrease the current draw during constant
voltage ovPrcharge. Typically, the ~attery at this stage will
be in a fully charged condition. While the amount can vary so
long as the amount of cadmium provided is sufficient to decrease
the current draw to the extent required, it has been found suit-
able to utilize amounts in the range of from about 0.1~ (or
somewhat less) to about 0.3~, based upon the total weight of the
electrolyte, and even up to about 0.5~ by weight when the cadmium
compound employed is cadmium sulfate. All that is required is
for the cadmium compound to be added to the elec-trolyte, suitably
prior to the sealing of the cover to the battery container.
While it is certainly expeditious to add the cadmium affording
compound directly to the electrolyte, it should be appreciated
that the compound may be added to the battery in any manner so
long as the resultant cadmium in the electrolyte is in the desired
range. For example, the cadmium compound may be added to the
electrode paste. When compounds other than cadmium sulfate are
2Q employed, the amount can desirably, of course, be varied to
~rovide the same amount of cadmium that would be provided by the
amount of cadmium in the cadmium sulfate in the range set forth
herein.
With respect to the materials used to form the electrodes
or battery grids, any material can be used so long as the material
does not contain any impurities in an amount that would adversely
affect in a significant fa5hion the functioning of the cadmium.
For example, if an alloy containing antimony is used, the amount
22 of antimony present shouId be sufficiently low so as not to
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completely eliminate the benefits achieved by the addition of the
cadmium. Thus, it is preferred to utllize an alloy for the
negative electrodes wnich is essentially free of antimony.
Typically, it is believed suitable to use an alloy for the
positive electrodes where the antimony content is no more than
about 2 to 3~ by weight. It is preferred to utilize calcium-
lead alloys for the positive and negative grids, typically
containing calcium in an amount from about 0.01 to about 0.15%
by weight of the alloy, and preferably about 0.06 to 0.10%.
The calcium-lead alloy may, if desired, include other alloying
ingredients so long as the current draw characteristics are
not significantly adversely affected. It is particularly pre-
f~rred to employ a lead base alloy containing about 0.06~ to
about 0.10% calcium, preferably 0.07% - 0.09%, and a tin
~ content of about 0.1% to about 0.4%, preferably 0.20~ - 0.30~.
Alloys of this latter type have a remarkakly improved resistance
to drossing, thus permitting rapid casting and accurate calcium
CDntent control. Batteries prepared with grids fabricated from
this alloy also have unexpectedly improved capacity retention
2Q characteristics.
It should be appreciated that such alloys can contain
negligible amounts of impurities such as are typically found in
commercially available battery grade lead. While impurities
may be contained in the calcium and tin components, the relatively
small amounts of these components make the typical impurities
unimportant. Thus, as has been set forth herein, it should be
appreciated that the alloys of the present invention can include
other ingredients so long as they do not adversely affect the
29 desirable features attributable to the present invention.
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The particular configuration for the battery can
vary wlthin wide limits, and the specific construction is not
critical insofar as this invention is concerned. Suitable
embodiments are shown in the copending Miller and Mao and ~-
Lannoye applications identified herein.
It is theorized that the cadmium that is added to
the electrolyte preferentially migrates to the negative electrode
and is deposited thereon during charging.
The following examples are illustrative, but not in
limitation of tne present invention. Unless otherwise specified,
all percentages are by weight.
Example 1
A single 70 Ampere Elour capacity cell having 6 positive
and 7 negative electrodes formed of a lead based alloy having
0.08~ by weight calcium and about 0.25 - 0.30~ tin was exposed
to varying cell voltages at ambient condition and at elevated
temperatures. The current draw was compared for the cell having
no additive ~control cell~ to the same cell containing 0.5%
by weight cadmium in the electrolyte. An electrolyte compris-
2~ ing sulfuric acid having a specific gravity of 1.265 was u~ed.
The current draw charact~ristics at the various equili-
brium voltages ~i.e.--after the cell has been at the voltage
charge condition for about one week~ are set forth in Table
1 below:
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Example 2
Two Group 24 maintenance-free batteries having
capacities of 81 Ampere Hours were tested to show the effects
of the inclusion of a cadmium compound in accordance with the
present invention on the current draw characteristics of the
batteries. Two different charge voltages were used, and the
grids were formed of the lead base alloys described in Example
l. The gassing current draw was then measured after the
batteries had been on charge conditions overnight. The
10 results ~re shown in Table 2: ~
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Example 3
A number o~ tl~e Group 24 batteries described in the
previous example were subjected to tests at higher temperatures
with varying amounts of additives and were tested as described
in the previous example. The results are shown in Table 3.
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Thus, as has been seen, the present invention provides
a maintenance-free battery which is characterized by improved -
gassing current characteristics. As is also illustrated in
Example 1, the inclusion of suitable amounts of the cadmium
in accordance with the present invention results in a signifi-
cantly more electronegative electrodQ. It should also be noted
that the current draw values taken at equilibrium conditions
in Example 1 may be more representative of the improvement that
can be achieved pursuant to this invention rather than the
values taken prior to reaching equilibrium, as in Examples 2
and 3.
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