Note: Descriptions are shown in the official language in which they were submitted.
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BATTERY CELL COATING AP;PAR.ATQS AND METHDD
CROSS REFERENCES TO RELATED APPLICATIONS
This application claims the: benefit of U.S.
Provisional Patent Application No. 60/081,400 filed on
April 10, 1998.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
BACKGROUND OF TH:E INVENTION
The field of invention is Electrochemical batteries,
more particularly, a method and apparatus for applying an
electrochemically active materiaal onto an ultra-thin
metal film for use in electrochemical batteries.
Developments in the field of electrochemical
batteries have produced batteries having electrochemical
cells that have bath excellent charge and discharge,
characteristics. These cells require ultra-thin films of
a metal such as lead, nickel or metal alloys having a
thickness of 2-5 mils coated with extremely thin layers
of an electrochemically active material, having a
thickness of approximately 1-5 mils.
A typical electrochemical cell, as shown in Figs. 2
and 3, includes an ultra-thin strip 2 of lead alloy of
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approximately 2 inches in width and 2-5 mils thick. The
electrochemically active materia,Z 3 is a compound that
includes lead monoxide, sodium sulfate and other inactive
materials. The compound 3 is applied to the top and
bottom surfaces of the metal strip 2, coating the entire
width of the strip 2 except for an uncoated strip edge 4
approximately .2 inches wide on both surfaces of the
strip to provide an uncoated electrical connection
surf ace .
Methods have been developed to produce lead and
other suitable metals and alloys in the form of an ultra-
thin film that is suitable for use in these
electrochemical cells. The use of these ultra-thin
strips is disclosed in U.S. Pate.nt 5,677,078."
The electrochemically active material can be
applied to the metal strip in a fluid form and then dried
to produce a solid coating. Var3.ous means and methods to
coat the ultra-thin metal films have proved less than
satisfactory. One particular meahod sprays the aqueous
solution onto the sides of the metal films. Due to
environmental hazards that exist: with spraying a solution
containing metals such as lead, this method is
unacceptable for use.
Other methods coat a side of the thin film using a
roller apparatus that applies the fluid solution to a
film that is supported by a backing roller to prevent the
ultra-thin film from breaking. The use of a backing
roller only allows coating a single side of the film at a
time with an intermediate dryinc3 step, thus lengthening
the time necessary to manufacture the electrochemical
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cell. The use of a coating roller also does not typically
provide a clean edge that is suitable for an electrical
connection without masking the edge at the point of
application or a subsequent step of wiping.
A method used to coat both sides of a thin film
simultaneously is to dip the entire film in the aqueous
solution. This particular method does not provide an
uncoated edge without a subsequent step of wiping or
other method to remove some of the coated material.
Additionally, this particular method requires that the
same coating material is applied to both sides of the
film, which is unacceptable for certain applications,
such as in use with bi-polar batteries.
Providing a clean edge for an electrical connection
is important to ensure the performance of the assembled
battery. The steps described above such as wiping and
masking have proven unacceptable for various reasons.
wiping does not always completely remove the coated
material leaving a residue that affects'the battery
performance. Additionally, the thin film has a low
tensile strength that~is subject to tearing during the
wiping process.
Masking is a process of covering the area that is
not to be coated during the coating process. Typically,
a roller covers the edge as the remaining portion of the
strip is coated. This roller tends to become fouled,
that is coating material can be splattered on the masking
roller which is then transferred to the edge that should
be left clean, thus reducing the: battery performance.
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BRIEF SLtMMARY OF T'~iE INVENTION
In one of its aspects, the invention relates to a
method and apparatus for coating both sides of a thin ,
metal strip with electrochemically active material by the
use of coating rod mechanism acting on a single side of
the metal strip. The method is preferably carried out by
applying the coating to one facE: of the strip drawn from
the supply roll, reversing the direction of travel of the
strip coating the opposite side of the strip and drying
the coated sides. The dried anc~ coated strip may be
wound up on a take up reel.
In the preferred embodiment:, the strip from the feed
roll first passes a web guide which reverses the
direction of travel of the stri~> before the first side is
coated. The strip then passes around a second web guide
which again reverses the strip direction of travel before
the second side of the strip is coated and the coated
strip is dried., The web guides, supply reel, and take-up
reel controls the speed and ten.aion in the strip so that
back up rolls are not needed at the coating mechanisms.
The invention also resides in a coating mechanism
that includes a reservoir, a mixing rod relating through
fluid coating material in the reservoir, and a coating
rod receiving coating material i:rom the mixing rod and
applying the coating material to the strip. The mixing
rod is longitudinally grooved and the coating rod is
circumferentially grooved.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view of a ultra-thin strip
coating apparatus incorporating the present invention;
Fig. 2 is a plan view of a portion of a coated
ultra-thin strip that can be produced by the apparatus of
Fig. 1;
Fig. 3 is a cross sectional 'view of the strip in
Fig. 2;
Fig. 4 is a plan view of a coating mechanism of the
apparatus of Fig. 1;
Fig. 5 is a cross sectional view of the coating
mechanism of Fig. 4;
Fig. 6 is a front sectional view of the coating
mechanism of Fig. 4;
Fig. ? is an elevational view of a mixing rod of
Fig. 4;
Fig. 8 is an end view of the. mixing rod of Fig. 7;
Fig. 9 is an elevational view of a coating rod of
Fig. 4;
Fig. 10 is an end view of the coating rod of Fig.
9:
Fig. 11 is an exploded view of the coating rod drum
of Fig. 9; and
Fig. 12 is an alternative coating rod and doctor
blade configuration for the apparatus of Fig. 1.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODTMENTS
Referring to Fig. 1, an embodiment of the present
invention is a coating method and apparatus 10 that coats
both sides of a thin strip 12 of: lead foil with a thiw
layer of electrochemically active paste having a density
of approximately 3.5-4 grams/cm3 for use in batteries,
such as described in U.S. patent. nos. 5,047,300 and
5677,078 which are incorporated herein by reference. The
coating apparatus 10 includes a foil supply reel 24, a
first web guide assembly 16, a first coating mechanism
18, a second web guide assembly 20, a second coating
mechanism 22, a drying assembly 24 , and a take up reel
26. The entire apparatus is mounted on a side of a
vertical base (not shown).
As shown in Fig. 1, the supply reel 14 has a thin
lead foil strip 12 wound thereon and is rotably mounted
to the vertical base. The thin lead foil I2 unwinds from
the supply reel 14 and travels underneath an idler roller
28 that helps maintain a constant tension in the foil
strip 12 in cooperation with the: supply reel I4 and the
first web guide assembly 16.
The first web guide assemb7.y 16 is disposed along a
foil strip path 30 and changes t:he foil strip 12
orientation by reversing the fo~.1 strip direction of
travel, exposing a downwardly facing first side 32 of the
strip 12 to the first coating mechanism 18. The web
guide assembly 16, such as an Ac:cuGlide II Model 060802
narrow web guide assembly available from AccuWeb; Inc.,
Madison, Wisconsin, has a pair of cork-wrapped rollers 32
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and 33 rotably mounted between a pair of opposing
sidewalls 34 , one roller 33 being disposed above the
other 32. The sidewalls 34 are :rigidly mounted to a
bracket (not shown) which is mounted to the apparatus
base (not shown) by bolts or other methods known in the.
art.
The foil strip 22 having an upwardly facing first
side engages the web guide lower roller 32 and changes
direction upwardly 90 degrees to engage the upper roller
33 which changes the foil direction rearwardly 90
degrees, thus reversing the original travel direction of
the foil I2 and facing the foil :First side 32 downwardly.
The web guide dual roller assembly 16 prevents over
bending of the foil 12 causing breakage.
The first web guide assembly 16 also accurately
guides the foil strip I2 over the first coating assembly
18 using a microprocessor controlled web guide control
system (not shown), such as an AccuGuide III Micro 1000
microprocessor-pulsed compensated ultrasonic web guide
control system available from AccuWeb, Inc. of Madison,
Wisconsin. The control system receives inputs from an
ultrasonic edge detector (not shown) that is part of the
web guide control system and assembly as provided by
AccuWeb, Inc., to determine the foil edge and shifts the
rollers 32 and 33 using actuators in the desired
direction to properly align the foil 1.2 above the coating
mechanism 18, with respect to the detected edge. Other
methods known in the art may be used to guide the foil
without departing from the present invention.
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The first coating mechanism. 18 is disposed along the
foil path 30 following the first~web guide assembly 16
and coats the downwardly facing side 32 of the foil 12
with an electrochemically active; solution. The coating
mechanism 18 coats the foil strip 12 using a method and
apparatus not previously known i,n the art to provide a
consistent coating thickness having well defined coating
edges that terminate inward from the foil edges.
Although the coating mechanism 1.8 is novel as described
herein, any coating apparatus ox' method that can coat a
fdil strip 12, such as used to coat a single side of a
strip, may be used without deviating from the intent of
the present invention.
As shown in Figs. 4-6, the. coating mechanism 18 has
25 a base assembly 40, mixing rod X62, coating rod 44, and a
doctor blade 46. The base assembly 40 has a base 48 that
is a nonreactive material block with a front 50, a rear
52, a top 54, a bottom 56 and two sides 58. A cavity 60
formed in the block top 54 defines a bottom wall 63 of a
reservoir. Opposing nonreactive material sidewalk 62
mounted to each side 58 of the base 48 by bolting or
other means known in the art, define substantially
straight reservoir sidewalls 64. The reservoir holds the
electrochemically active coating material prior to
coating.
The bottom wall 63 of the :reservoir has a feed
portion 66 and a coating portion 68. The feed portion 66
slopes inwardly and downwardly :having a rounded bottom 70
to collect the coating for feeding into the rotating
mixing rod 42. The curved coating portion 68 is disposed
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above and rearward of the feed portion 66 and
accommodates the notably mounted-coating rod 44 that is
fed coating material by the mixing rod 42.
A countersunk bore 72 in th.e base front 50
communicates with the feed portion 66 of the reservoir..
The countersunk portion of the bore 72 is threaded to
receive a fitting (not shown) on, a coating material
supply line. The supply line supplies the reservoir with
coating material for use during the coating process.
Clean out holes, 74 and 75, in the base bottom 56
communicate with feed portion 66 and coating portion 68
of the reservoir, respectively, to facilitate cleaning
the reservoir. The holes, 74 and 7S, each have a
threaded countersunk portion for receiving thzeaded plugs
3.5 (not shown) to prevent the coating material from leaking
out during the coating process. Four threaded mounting
holes 76 in the base bottom 56 receive bolts to mount the
coating mechanism 18 to a brackea (not shown) rigidly
mounted to the apparatus base.
The mixing rod 42 is rotabl.y mounted to the coating
mechanism base sidewalls 62 and has a cylindrical drum 78
that feeds coating material to t:he coating rod 44 and is
supported by an axially extending shaft 80. The drum 78
extends substantially the entire: width of the reservoir
in close proximity to the rounded bottom 70 of the
reservoir feed portion 66.
As shown in Figs. 7-8, the: drum 78 outer surface
has twelve axial grooves 82 fornning scallops in the drum
surface that agitate the coating material in the
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reservoir and scoops up the coating material, feeding it
to the coating rod 44.
The mixing rod shaft 80 extends axially along a
central axis of the mixing rod 42. Each end of the shaft
80 extends into one of the base assembly sidewalls 66 and
is rotably mounted therein. Ones end 86 of the shaft 80
extends through the sidewall 66 and has a gear 88 mounted
thereon for engaging an adjacent. gear 90 mounted on a
coating rod shaft 92.
The coating rod 44, shown :in Figs. 9-12, is
disposed above and rearward of t:.he mixing rod 42 and
receives coating material fed by the mixing rod 42. The
coating material is upwardly applied by the rotating,
coating rod 44 to the downwardly facing side 32 of the
lead foil 12 traveling overhead. Preferably, the foil
direction of travel is opposing to the coating rod 44
rotation providing a smooth consistent coating thickness
on the foil 12.
The coating rod 44 has a drum 94 that extends
substantially the entire width of the reservoir and is
supported by an axially extending shaft 92. The coating
rod drum 94 applies the coating layer to the foil 12
substantially equal in width to the drum 94. The foil 12
is aligned by the web guide 16 with the respect to the
coating rod drum 44 in order to leave at least one edge
and a portion inward from the edge of the foil uncoated
for attachment to electrical connectors. If the foil 12
is wider than the drum 94 both edges and portions inward
from the edge of the foil can remain uncoated.
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Referring to Fig. 11, the coating rod drum 94 has a
plurality of circumferential grooves 96 on its outer
surface. The circumferential grooves 96 carry the
coating, fed by the mixing rod 42, to the downwardly
facing foil surface providing a substantially consistent
coating thickness. The grooves 96 are circumferential, as
opposed to helical as found in a wire wound coating .
apparatus, to provide a sharp clean coating edge on the
foil 12 that is inward of the foil edge.
Preferably, the grooves 96 are cut into the drum
surface and substantially equally spaced along the drum
length. The groove width, depth, and shape have an
effect on the coating thickness applied to the fail. For
example, equally spaced circumferential V-shaped grooves
96 cut into the drum surface approximately .040 inches
apart having a depth of approximately .040 inches provide
a coating thickness of approximately .005 for the coating
material having a viscosity of approximately 2000- 12000
cps. The v - shape of the grooves forms an angle A of 60
degrees.
The coating rod shaft 92 extends axially along a
central axis 98 of the coating rod 44. Each end, 100 and
102, of the shaft 92 extends into one of the base
assembly sidewalls 62 and is rot~ably mounted therein.
One shaft end 100 extends througlh the sidewall 62 has a
gear 90 mounted thereon for engaging the adjacent gear 88
mounted on the mixing rod shaft .80. The opposite coating
rod shaft end 102 extends through the opposite coating
mechanism base sidewall 62 and i;s adapted to mate with a
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drive motor (not shown) for rotably driving the coating
rod shaft 92 and counter rotating feed rod shaft 80.
As shown in Figs. 4-5, a doctor blade 46 adjustably
mounted to the coating mechanism base top 54 with an edge
108 adjacent to the coating rod ~44 prevents splattering.
and helps provide a consistent coating thickness. The
blade 46 is nonreactive material having a pair of
parallel slots 104 formed therein for slidable adjustable
movement. The blade 46 is mounted by bolts (not shown)
inserted through the slots 104. The bolts are received
by threaded holes 106 in the base top 54.
The doctor blade edge i08 should be adjusted as
close as possible toward the coating rod 44 without
causing the material to build up on the blade 46.
Preferably, the blade 46 is adjusted to define a gap of
.002 - .004 inches between the blade edge 108 and the
coating rod drum 44.
Referring back to Fig. 1, once the downwardly
facing first side 32 of the foil 12 has been coated, the
foil 12 travels along its path 30 toward the second web
guide assembly 20. The second web guide assembly 20 is
essentially identical to the first web guide assembly 16.
The second web guide assembly 16 changes the foil strip
12 orientation by reversing the strip 12 direction of
travel, thus the downwardly facing first foil side 32
having a freshly coated surface faces upwardly and the
second foil side 36 faces downwa.rdly, exposed to the
second coating mechanism 22.
The second web guide 20 guides the foil 12 over the
second coating mechanism 22 as described for the first
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web guide 16. The second coating mechanism 18 is
substantially identical to the first coating mechanism
18. Tension in the foil 12 maintained by the Web guides
16 and 20, idler rollers 28 and 38, and reels 14 and 26,
eliminates the need for a,backing roller at the first and
second coating mechanisms 18 and 22 as the coating is
applied.
The use of two independent coating mechanisms 18 and
22 advantageously allows application of the coating on
the second side 36 of the foil 22 while the coating on
the first side 32 is still wet, thus eliminating an
intermediate drying step. Additionally, using two
independent coating mechanisms 1.8 and 22, allows the user
to apply a coating on the first side 32 of the foil 12
that is different from the coating applied to the second
side 36 of the foil 12 for use i.n bi-polar batteries and
the like.
The foil 12 having a moist coating on both sides is
then passed through a drying apparatus 24 to reduce the
moisture content in the coating. to approximately '7-B%.
Preferably, the drying apparatus 24 consists of infra red
heating elements (not shown) di:aposed above and below the
foil path 30 that are directed at the coated foil l2.as
it travels along the foil path :30. The infra red heating
elements provide a consistent d~.~y heat.
The dried coated foil 12 then engages an idler
roller 38 prior to being wound up on the take up reel 26.
The idler roller 38 in cooperation with the second web
guide assembly 20 and take up reel 26 helps maintain the
tension in the coated foil.
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The coating apparatus components described above are
controlled by a microprocessor control system (not shown)
that coordinates the operation of: each component during
the coating process. Sensors (nc>t shown) such as laser
S micrometers and moisture sensing equipment provide inputs
to the microprocessor for processing to adjust foil
travel speed, coating rod rotatic>nal speed, heating
levels and the like, in order to meet set criteria.
Furthermore, stopping rotation of the coating rod,
effectively stops the application of the coating material
to the foil. Therefore, the control system allows the
user to stop rotation of a coating mechanism coating rod
in order to provide the entire width of a portion of the
traveling foil without coating material.
An alternative feed coating rod 44 and doctor blade
46 configuration shown in Fig. :L2, is a coating rod 44
With a drum 110 having circumfere:ntial grooves 112 formed
on a central portion 114 of the drum surface and two
nongrooved portions 116 axially ESxtending from the
central portion 114 to the drum Ends 118. The grooved
central portion 114 has an outsic3e drum diameter larger
than the nongrooved portions 116 creating a diameter
differential between the grooved and nongrooved portions,
114 and 116.
A doctor blade 46 has an ed~~e 108 with a notched
central portion 120 to receive tlhe grooved central
portion 114 of the coating rod drum 110. The notched
portion 120 length is slightly larger than the length of
the grooved portion 114 on the drum 110 and the depth is
slightly larger than the diameter differential of. the two
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drum portions 114 and 116, allowing the nonnotched
portion 122 of the doctor blade 46 to be set closer to
the nongrooved portion 116 of the coating drum 110 than
the grooved portion 116.
The notched doctor blade in combination with a
partially grooved coating rod drum allows precise
doctoring of the coating edge on the foil strip. The
portion of the doctor blade adjacent to the grooved
portion of the drum provides a smooth consistent
thickness coating as described in the first embodiment.
The nonnotched portion of the doctor blade cleanly
defines the coating edge at the edge of the grooved
section of the coating rod and prevents the deposition of
excess material on the foil edge that is to remain
uncoated.
While there has been shown and described what are at
present considered the preferred. embodiment of the
invention, it will be obvious to those skilled in the art
that various changes and modifications can be made
therein without departing from the scope of the
invention.
