Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Ihis invention relates ~o hattery plates, and moro particularly
to an improvement in the method of producing said plates. In producing
battery plates, it is desirable to produce plates which are capable of
carrying high currents for rapid charging and output performance, while
at the same time reducing their weight and size. The present invention
teaches tlle production of battery plates which have a reduced internal
resistance over present lead-antimony plates and which are smaller in
; size and weight.
; It is an object of the present invention to provide an improved
battery plate of an aluminum core having a lead coating deposited thereon.
It is a further object of the present invention to provide a
method for forming battery plates of higher conductivity and superior
charging capability. ~
It is a further object of the present invention according to -
a second embodiment thereof to produce an aluminum core battery plate
; having a lead coating deposited thereon without the need for precoatings
of materials such as zinc and/or silver.
` The invention may be generally defined as a battery plate for
a lead-acid storage battery comprising a substantially oxide-free
aluminum core and a coating of substantially pure lead over the core.
A coating of zinc is provided over the substantially pure lead coating
and a coating of silver is provided over the zinc coating. Furthermore,
a second lead coating is provided over the silver coating.
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'I'he invention includcs a method for making this battery
comprising the steps of: (a) placing a substantlally oxide-free
aluminum core to be coated and a supply of pure lead in a chamber of
reduced atmospheric pressure; (b) heating the lead to its vaporizing
point; and (c) condensing lead on said core by maintaining said core
at a temperature below the vaporizing point of lead to form a lead film
thereon .
In accordance with this invention, in order to obtain as light
a battery as possible, the core of the plate of the battery is made of a
lightweight conductive metal, preferably aluminum. While other metals
such as copper or silver are considered, however, aluminum has the
highest conductivity per unit of weight, is most economical and has
adequate physical strength, and therefore is preferred.
The aluminum should preferably be of a commercially pure type.
The aluminum is formed into a shape suitable for a battery plate. The
plate is then cleaned in a well known manner in a solution of a
detergent in which a suitable wetting agent has been placed. It is
thereafter washed in water and is provided with a barrier layer to the
lead.
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In accordance with this invention, the barrier layer
is provided and the internal resistance of the battery cell is
minimized by removing the natural aluminum oxide which coats
the surface of the aluminum while simultaneously replacing it
with a protective conductive coatiny. A protective coating
may be applied using metals, such as zinc, nickel, or chrome,
but zinc is preferred because it is a better thermal conductor
and its thermal expansion and contraction characteristics are
more compatible with those of aluminum. The protective coating
is applied by dipping the core in a solution consisting of from
13 to 70 ounces of zinc oxide per gallon of sodium hydroxide at
room temperature. After the first dipping of from 2 to 5 sec-
onds, a second dipping for from 2 to 5 seconds is advis~d. To
improve the bonding of the coating additives~ they are added
to the solution into which the core is dipped. These may be a `~
solution of 1 to 5 ounces of either ferric chloride or rochelle
salts to a gallon of water. These additives insure that a
tightly bonded pure zinc filmg without cracks or blisters is
le~t on the aluminum surface.
The solution into which the aluminum plate is dipped
is at room temperature. A weight of about 0.02 mg. of zinc ~ -
per square inch is desirable. The other indicated metals
namely, nickelg or chrome, may be deposited using the same
method as described for zinc. The aluminum oxide is removed
while simultaneously depositing the zinc coating to prevent ~;
reformation of the aluminum oxide, which is an insulator~ and
makes poor contact with other materials.
If an inspection reveals~ after the first zinc dip-
ping that there are still impurities on the surface, the battery
3 plate is dipped into a solution of 50% nitric acid at room
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temperature ~or a few seconds. Thereafter, the ~atte~y plate
is rinsed in pure water and dipped in the original zinc oxide-
sodium hydroxide mixture again.
Thereafter, the aluminum plate which is now coated
-~ 5 with pure zinc has a second mechanical barrier layer o~ an
electrically conductive metal, such as silver, a ~ew angstroms
thick, deposited over the zinc coating. This is achieved by
placing the battery core for from 2 to 4 seconds in a regular
silver plating solution. By way of example, the silver plat-
ing solution can be a mixture of 1/2 to 3/4 ounce of silver
cyanide to a gallon of water. This solution is mixed with an
equal solution of 10 to 12 ounces of potassium cyanide to a gal-
- lon of water. Temperature of the solution is maintained be-
tween 70 to 85 degrees. The voltage which is applied to the
electrolytic solution is from 4 to 6 volts and the current den-
sity is from 15 to 25 amperes per square foot.
The two electrically conductive barrier layers which
are deposited on the aluminum core prevent any grain migration
between the aluminum and the lead and avoid any galvanic action
that otherwise acts to deteriorate the cell and tend to increase
its resistance.
The final lead coating which is deposited on the cell
can be applied by electroplating, spraying, sintering, or any
other well-known techniques. With a cell of this construction,
purer lead may be employed than otherwise. Antimony is usually
present in standard battery plates. It is added to the lead
or alloying constituents to increase hardness of the lead used
in the manufacture of the plates. Such plates release a large
proportion o~ the surface antimony which migrates toward the
3 negative plates~ thereby contaminating the electrolyte and
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adversely affecting battery performance, as by increasing the
positive plate corrosion, and increasing the sel~-discharye
rate. These problems may be avoided when pure lead is used.
With the battery plate made in accordance with the present in-
vention, there is no need for a hard lead plate and therefore,
pure lead can be used.
Lead normally has up to 0.5% of antimony, which has
little effect in cell operation. Antimony may be removed from
the lead which has been deposited on the battery plate by dip-
ping the lead covered battery plate into a solution made of a
mixture of 2 to 5 volumes of hydrogen peroxide with one volume
of sulfuric acid having a specific gravity of 1.2, ~or a time
on the order of one hour.
Description of the Second Embodiment
In order to o~tain a film of pure lead with good ad-
herence qualities directly on an aluminum core, it is necessary
to use one or more of the following vacuum techniques: thermal
evaporation~ plasma deposition (sputtering) or ion implantation
(thermal evaporation with ionization).
TheLmal evaporation of lead onto an aluminum core is
accomplished by heating pure lead in a vacuum chamber causing
i-t to vaporize and recondense onto the core, to form a lead
film thereon. The steps include placing pure lead into a fila-
ment boat which is connected to a high current low voltage
power supply. The heat from the filament is transferred to the
lead by conduction. When the temperature o~ the lead reaches
the evapoxation point, it begins to evaporate. The vaporized
molecules move from their source to the other solid surfaces
in the vacuum chamber such as the core and the chamber walls
3 condensing thereon due to the temperature differential. Con-
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densation produces the :Lead Eilm ~onnation on the alumin~n
core. No removal of the al~ninum oxide is obtained in khis pro-
cess. However~ such removal is a desirable objective in mak-
ing high performance battery plates, and thus where this tech-
nique is used the aluminum oxide is substantially removed bya sodium hydroxide bath or the like prior to placing the alumi-
num into the vacuum chamber.
E~AMPI,E I
A pure lead film was deposited on an aluminum core
having its oxide coating substantially removed, in a vacuum
chamber having a pressure of 2 x 10 5 torr. The rate of depo-
sition was 50 angstroms per minute.
EXAMPLE II
In a vacuum chamber having a pressure o~ 2 x 10-7 torr,
a film of pure lead was obtained on an aluminum core with a de-
position rate of 15l000 angstroms per minute.
In both examples a uniform film having good adhesion properties
was obtained.
A second vacuum deposition technique known as ion
2~ sputtering may be employed. In ion sputtering two electrodes
are immersed in an inert gas medium at reduced pressure. The
material to be coated, ~or example, an aluminum core, is utiliz-
ed as the cathode. The coating material to be deposited on the
aluminum, for example, lead, is utilized as the anode. A plasma
is maintained by either a D.C. or R.F. potential which continual-
ly ionizes the inert gas molecules. The electrodes are bom-
barded by the gaseous ions in the presence of a high electric
field. The kinetic energy of the gaseous ions (on the order of
150 to 600 electron volts) exceeds the bonding energy of the
3~ surface molecules of the electrodes causing them to be dislodged
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from the sur~ace. In the case of the aluminwn cathode, khis
produces a removal of the alumin~n oxide surface layer for ef-
fectively cleaning the aluminum plate. In the case of pure lead
this bombardment is effective for dislodging molecules from the
surface. The lead molecules are accelerated by the electric
field thereby to cause a lead film to condense and adhere to
the cleaned aluminum cathode.
EX~MPLE III
In a vacuum chamber of 1.0 to 15 x 10-3 torr and utiliz-
10ing 50 to 600 watts of R.F. power, a deposition rate of approxi-
mately 1,000 angstroms per minute of lead onto the cleaned alumi-
num core is obtained.
A third technique combines the first two techniques
and produces an increased deposition rate. The third technique
is known as ion~plating. As in the sputtering technique, elec-
trodes are immersed in an inert gas medium such as argon at re-
duced pressure. The alwminum substrate which is to receive the
film is connected as the cathode. A plasma is maintained either
by a D.C. or R.F. potential. An evaporation source is utilized
as the anode and may be a boat or filament together with the
evaporant lead. Positive ions in the plasma are accelerated
towards the cathode (the aluminum core) by the electrical field
gradient thereby bombarding and continuously cleaning the plate's
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core prior to the film deposition. ;~
2~ Whila the surface of the aluminum is cleaned by the
- plasma bombardment, the pure lead is evaporated by heat. The
evaporated lead becomes ionized on passing through the plasma.
The ionized lead atoms are accelarated towards the cathode (the
aluminum core) simultaneously with the sputtering action which
3 is cleaning the surface. In this manner the aluminum sur~ace
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is sputtered, removing the al~ninum oxide, both before and
during plating. This maintains a clean surface until the first
monolayer of the lead film is deposited on the surface, and
at the same time roughens the surface to insure strong adhesion
of the first monolayer. The higher the velocity with which
the lead particles are accelerated, the deeper the penetration
of the lead onto the surface of the aluminum.
The plasma bombarding of the core is essential for
it is effective to remove the naturally occurring aluminum
oxide from the surface of the core. Further, it cleans and
etches the surface to reduce surface defects~ The removal of
the aluminum oxide and the cleaning of the surface produce
greatly improved electrical characteristics. Removal of the
oxide also facilitates the proper deposition of lead onto the
aluminum, a result which has not heretofore been obtainable
without the utilization of intermediate depositions of metals
such as zinc between the lead and aluminum surfaces.
It is desirable to provide shutters between the cathode
- and anode to collect the removed aluminum oxide and other par-
ticles which are freed from the aluminum substrate by the sput-
tering process to thereby reduce contamination.
EXAMPLE IV
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Ion plating in a vacuum chamber having a pressure of
from 5 x 10~5 to 8 x 10-4 torr/ a film of 1,000 to 15,000 ang-
stroms per minuta of high purity lead was deposited on the
aluminum coreO The dielectric was kept at about 10 to 13 mm `
at 20 to 25 millitorr with a current density o~ approximately
0.3 to 0.8 m amps per cm2.
Film deposition rates are nearly linear functions of
3 the deposition period. By varying the process parameters of
pressure, power and electrode distance the film deposition rate
can be changed as desired. The lead may be vapori~ed by resis-
tance heating in a dielectric crucible heated by eddy currents
induced by an external R.F. diode coil. Use of this technique
permits deposition rates up to about 200,000 angstroms per
minute.
Although the foregoing description discloses a tech-
nique for forming battery plates wherein lead is directly coat-
ed onto aluminum as the aluminum oxide layer is removed, it is
also possible to utilize the present invention where a mechani- -
cal barrier coating is first placed over the aluminum. For ex-
ample, as disclosed in the first embodiment of the invention,
an aluminum core can have its oxide removed and replaced with
-~ pure zinc followed by a thin layer of silver and thereafter a
lead film. Additional lead is then deposited over the lead
film by the present method. A similar example is an oxide free
aluminum plate which has been silver plated and then has a lead
film formed thereon.
A third variation is to first deposit a lead film on
~ the aluminum by the present method and to then add a lead coat
ing by the electrochemical plating technique of the first em-
bodiment. A sufficiently porous coating formed in this manner
will eliminate the need for lead paste usually required for
ne~ative plates.
A final variation is to deposit directly by the vacu-
um techniques of the present embodiment lead oxide on the alumi-
num core.
Utilization of plates formed according to this inven-
tion will not be subject to the usual hydrogen embrittlement.
3 meir performance is superior in comparison to lead-antimony
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type plates. Further3 the use o~ such plates will produce a
battery cell having higher efficiency and discharge rate at low
temperatures. The plates are thinner than the standard plates
and thus a larger number of plates can be placed in a given
cell. A partial improvement in the performance of a battery
having plates according to the present invention is due to the
absence of the antimony usually present in lead. The present
process by use of pure lead eliminates the electrical couple
formed between lead and antimony which tends -to cause self-
1~ discharging and create internal resistance in the battery. Anadditional advantage is the improved circulation of electrolyte
between the thinner plates which carries away small bubbles
usually present in a standard cell further reducing internal re-
sistance.
: 15 While I have described embodiments of this invention
in some detail, it will be understood that this description and
illustrations are offer~d merely by way of example, and that
the invention is to be limited in scope only by the appended
: claims.
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