Apparatus for fabricating pasted electrodes

A slurry loading apparatus for automatically loading a slurry into a substrate, the substrate having a front surface, a back surface opposite said front surface and an interior with voids between the front and back surfaces, the apparatus including a device for introducing the slurry onto the front surface and into the voids where excess slurry passes through the substrate and exits the back surface, and a device for repeatedly forcing the excess slurry back onto the back surface and into the voids.

FIELD OF THE INVENTION 
The present invention relates generally to the fabrication of pasted 
electrodes for an alkaline battery. More specifically, it relates to an 
automated apparatus and improved method for rapidly and uniformly pasting 
a solid particulate slurry into a continuous web of a porous substrate 
material. 
BACKGROUND OF THE INVENTION 
There are two basic types of rechargeable alkaline cells. These are nickel 
cadmium (NiCd) cells and nickel metal hydride (Ni-MH) cells. Both types of 
cells utilize positive and negative electrodes and the positive electrodes 
of both types of cells are composed of a nickel hydroxide material. At 
present, both sintered and pasted positive electrodes are used in NiCd and 
Ni-MH cells. 
Sintered positive electrodes are constructed by applying a slurry, 
comprising nickel powder, to a substrate. This is followed by high 
temperature sintering whereby the individual nickel particles weld at 
their points of contact, resulting in a porous material. The sintered 
material is then impregnated with active material. Sintered electrodes 
have the advantage of being able to withstand shock and vibration because 
the active material sticks very well to the substrate. However, sintered 
electrodes have the disadvantage of having a comparatively low energy 
density. In order to increase energy density the current trend has been 
away from sintered electrodes toward the pasted ones. 
Pasted electrodes using a nickel foam substrate exhibit satisfactory energy 
density as well as ruggedness. Such pasted positive electrodes are useful 
in both NiCd and Ni-MH rechargeable cells. The nickel foam substrate is 
manufactured by nickel plating polyurethane foam and then burning off the 
polyurethane. The resulting nickel foam is then loaded via a slurry with 
nickel hydroxide, the active ingredient of the positive electrode. 
Manual and automated methods of pasting foam are known in the art. Manual 
methods tend to be slow and tedious. The process begins by combining and 
mixing the ingredients, adjusting the viscosity of the slurry for maximum 
loading, pouring the slurry over the foam substrate, and then spreading it 
over the surface of the foam with a spatula. 
Certain properties of the foam affect loading. Variations in such factors 
as foam pore size, porosity, and depth affect how well the slurry can 
penetrate through the foam after it is poured onto one side of it. Such 
factors also determine the viscosity of the slurry that must be used in 
the loading process, as well as the amount of effort needed to force the 
slurry into the foam to achieve maximum loading. Very slow seepage may 
even require that the slurry be applied and pushed in from both sides of 
the foam, greatly increasing the time and effort needed to complete the 
loading process. 
Besides the inherent slowness of the manual loading process, it has other 
disadvantages. The time needed to complete the process gives the slurry 
suspension time to settle. Hence, the viscosity of the slurry may change 
during the course of the loading process, resulting in electrodes 
exhibiting nonuniform densities of active material. 
Hand loading, like all "by hand" operations is dependent on the individual 
performing the operation. If time and cost are not a factor, a skilled 
craftsman can produce positive electrode material of the highest quality. 
Automatic loading can speed the process of applying slurry to foam. Several 
types of automated loading methods are used in practice. The most common 
are those which rely on mechanically rubbing or forcefully spraying the 
slurry into the foam. 
Spraying methods automatically load the foam by spraying it from either one 
or both sides. One such method/apparatus is described in U.S. Pat. No. 
4,582,098 (to Matsumoto et al, issued Apr. 15, 1986). The major problem 
with spraying (and especially those processes that rely on nothing more 
than spraying the slurry onto the foam from a single side) is that it 
results in a nonuniform application of the active nickel hydroxide 
ingredient into the foam substrate. 
If a slurry, supplied at a certain flow rate, is simply sprayed from a 
single nozzle onto one of the surfaces of a porous foam substrate 
material, the liquid and solid components making up the slurry suspension 
separate because the liquid portion of the slurry penetrates more easily 
through the pores of the foam. This results in a nonuniform distribution 
of the nickel hydroxide active material. Slurry containing a higher 
concentration of solid will deposit near the surface that is closer to the 
nozzle, while slurry with a lower concentration of solid will penetrate 
deeper into the interior of the substrate material. Hence, spraying slurry 
with a single nozzle from just one side is unsatisfactory from the 
standpoint of a uniform concentration of active material through the 
entire volume of the foam. 
There are other problems associated with automated loading that rely solely 
upon a spraying process. The filling density of the foam is sensitive to 
factors directly related to the spraying system used. For example, the 
filling density is affected by such factors as the amount of air that 
enters the slurry, the flow rate of the slurry at the nozzle port, and the 
distance between the foam and the spray nozzle spout. 
Spraying the slurry onto both sides of the substrate, as disclosed in U.S. 
Pat. No. 4,582,098, fails to overcome all of these problems. Variations in 
filling density introduced into the process by the spray mechanisms are 
still present in such a two nozzle system. Furthermore, even when spraying 
from opposite sides some of the slurry that is sprayed at the surface 
rebounds and never penetrates the porous interior. 
Thus, a loading system is needed that will combine the speed and 
noninvasiveness of an automated spray method with the superiority of 
loading seen in "by hand" application. 
SUMMARY OF THE INVENTION 
One object of the present invention is an automated pasting apparatus that 
achieves high, uniform loading at a rapid rate. 
This and other objects are achieved by a slurry loading apparatus for 
automatically loading a slurry into a substrate, the substrate having a 
front surface, a back surface opposite the front surface and an interior 
with voids between the front and back surfaces. The apparatus comprises 
means for introducing the slurry onto the front surface and into the 
voids, with excess slurry passing through the substrate and exiting the 
back surface; and means for repeatedly forcing the excess slurry onto the 
back surface of the substrate and into the voids. 
Other objects are obtained by the apparatus described above that further 
comprises a forcing cylinder and an outer cylinder exterior to and 
concentric with the forcing cylinder about a slurry axis, where the means 
for introducing the slurry is positioned on the outer cylinder and the 
forcing cylinder functions as the means for forcing excess slurry onto the 
back surface and into the voids. 
Other objects are obtained by the apparatus described above where the means 
for introducing the slurry is a slurry inlet nozzle, and the means for 
forcing the excess slurry is a paddle wheel fan comprising a plurality of 
blades configured to push the excess slurry onto the back surface and into 
the voids. 
Other objects are achieved by a method for loading a slurry into a 
substrate, the substrate having a front surface, a back surface opposite 
to the front surface, and voids between the two. The method comprising the 
steps of: (a) introducing the slurry onto the front surface and into the 
voids such that excess slurry passes through the substrate; (b) forcing 
excess slurry onto the back surface and into the voids; (c) wiping excess 
slurry from the front and the back surface; (d) recirculating the excess 
slurry by reintroducing the excess slurry onto the front surface. 
Still other objects are attained by a nickel hydroxide slurry comprising 
nickel hydroxide, cobalt, cobalt monoxide, water, ethyl alcohol and 
polyvinyl alcohol.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is an apparatus for automatically loading a slurry 
into a substrate material. This apparatus can be adapated for use with any 
substrate material and is specifically intended for use with substrate 
having a front surface, a back surface and an interior containing voids 
capable of retaining the slurry. Such substrate material most commonly 
used is nickel foam. 
The present invention includes a means for introducing the slurry at the 
front surface of the substrate. The means for introducing the slurry is 
generally intended to be some type of nozzle. In operation, this nozzle is 
connected to a slurry reservoir and a pump. The slurry reservoir contains 
means for mixing and monitoring the slurry composition to assure that the 
slurry is maintained at the desired composition and consistancy. In 
general, slurry composition is varied to accomodate variations in the 
substrate so that loading is uniform. The pump delivers slurry from the 
reservoir at sufficient pressure through the nozzle to force the slurry 
onto the front surface of the substrate, and into the voids, and out the 
back surface of the substrate. 
Variations in the pore size and porosity of the substrate as well as 
variations in the viscosity of the slurry are factors which affect the 
ability of the slurry to adequately penetrate the substrate. Changing the 
flow rate and pressure of the slurry can compensate for such variations 
and thus help to ensure that the slurry will sufficiently wet and 
penetrate the entire width of the substrate. The nozzle for introducing 
the slurry at the front surface of the substrate is preferably configured 
to include means for varying the flow rate and pressure of the slurry. 
This may be an adjustable orifice that permits varying both the flow 
pressure and flow rate of the slurry delivered through the use of 
adjustable plates, a needle valve, a gate valve, or any other adjustment 
means known in the art. 
FIGS. 1 and 2 show the slurry inlet nozzle 30 as the means for introducing 
the slurry. The slurry inlet nozzle can be adjusted to change the flow 
rate and flow pressure of the slurry applied to the substrate. The slurry 
inlet nozzle 30 is shown in more detail in FIG. 2. The slurry inlet nozzle 
includes an entrance orifice 32 which is an opening of fixed dimension. It 
also includes an adjustable exit orifice 34 which is a slit of fixed width 
and adjustable height. The width of the slit is at least as wide as the 
width of the substrate. The height of the exit orifice 34 can be adjusted 
to change the flow rate and flow pressure of the slurry that exits the 
nozzle. The adjustable exit orifice comprises a fixed plate 35, an 
adjustable plate 37 which is parallel to the fixed plate, and at least two 
adjusting screws 39 that are threaded through the adjustable plate 37. The 
adjusting screws are threaded through the adjustable plate so that 
rotation of the adjusting screws 39 moves the adjustable plate 37 closer 
to or further away from the fixed plate 35, thereby narrowing or widening 
the height of the exit orifice. Adjusting the height of the exit orifice 
34 changes the area of the exit opening. This changes the flow rate and 
flow pressure of the slurry that exits from the nozzle. 
The slurry inlet nozzle 30 is positioned on the outer cylinder 2 as shown 
in FIG. 1. FIG. 1 can be specifically described as including a slurry 
chamber 8, the region of the slurry loading apparatus where the slurry is 
actually applied to unloaded substrate. The slurry chamber is defined by 
an inner cylinder 1 and an outer cylinder 2. Both the inner and outer 
cylinders are concentric about the slurry axis 3. The distance between the 
inner and outer cylinders can be any distance appropriate for adequate 
loading. Generally, this distance depends upon the type and thickness of 
the substrate being used. A nickel foam substrate of thickness of about 
0.06 inches is used in the embodiment of the present invention shown in 
FIG. 1. 
The outer cylinder 2 includes a substrate entry port 4 through which 
substrate enters the slurry chamber as well as a substrate exit port 5 
through which loaded substrate exits the slurry chamber. The outer 
cylinder 2 also includes a slurry entry port 6 through which the slurry 
enters the slurry chamber and a slurry exit port 7 through which slurry is 
removed from the slurry chamber. 
After the initial application of slurry from the slurry inlet nozzle 30 
onto the front surface of the substrate, slurry penetrates the porous 
interior of the substrate and partially fills the voids. Excess slurry 
passes through and exits at the back surface of the substrate. Despite the 
fact that slurry passes through and exits the back side of the substrate, 
the voids within the porous interior of the substrate are only partially 
filled. As a result, maximum loading is not achieved. 
The prior art, such as U.S. Pat. No. 4,582,098 (to Matsumoto et al, issued 
Apr. 15, 1986) attempts to maximize loading by using two nozzles 
positioned on opposite sides of the substrate. This technique suffers from 
problems dealing with variations in the filling density of the substrate 
that are introduced by the spray mechanisms. Moreover, the method also 
suffers from the fact that even when spraying from opposite sides, some 
slurry rebounds off the surface of the substrate and fails to penetrate 
the substrate interior. Hence, loading is still not maximized. 
The present invention overcomes the problems with the prior art by 
providing means for repeatedly forcing excess slurry into the back surface 
of the substrate. Such repeated action ensures that the slurry penetrates 
and fills the voids so as to maximize loading. 
Preferably, the means for forcing excess slurry is a forcing cylinder which 
is positioned between and concentric with the outer cylinder 2 and the 
inner cylinder 1. An embodiment of the forcing cylinder is the paddle 
wheel fan 42 shown in FIG. 3. The paddle wheel fan 42 has a plurality of 
blades 44 And two rims 46 and 47 that hold the blades firmly in place. The 
blades and rims are attached so as to form a cylindrical structure, with 
the rims forming the ends of the cylinder and the blades spaced 
equidistantly around the rims. In the present invention, the paddle wheel 
fan 42 is positioned between and concentric with the inner and outer 
cylinders 1 and 2. The distance between the paddle wheel fan 42 and outer 
cylinder 2 must be large enough to enable the substrate to move in between 
the two. However, this distance should also be small enough so that the 
movement of the substrate relative to the outer cylinder creates a 
turbulent motion in the slurry present within this region. This turbulence 
forces additional slurry through the front surface of the substrate. In an 
embodiment of the present invention, this distance is preferably between 
0.05 to 0.5 inches, more preferably between 0.15 and 0.3 inches, and most 
preferably about 0.22 inches. The distance between the inner cylinder 1 
and the paddle wheel fan 42 is chosen to minimize the amount of slurry 
used during the loading process. 
FIG. 3 shows the paddle wheel shaft 48. The paddle wheel shaft 48 is 
collinear with the slurry axis 3. The paddle wheel shaft 48 is 
mechanically coupled to the paddle wheel fan 42. In FIG. 3 this is via the 
paddle wheel backplate 49. Rotation of the paddle wheel shaft 48 rotates 
the paddle wheel fan 42. 
The substrate that is guided into the slurry chamber 8 fits between the 
paddle wheel fan 42 and the outer cylinder 2. The substrate moves in the 
direction from the substrate entry port 4 to the substrate exit port 5 
along the lower section of the slurry chamber that connects the two ports. 
As mentioned above, the slurry is introduced onto the front surface of the 
substrate by the slurry inlet nozzle 30. While some of the slurry remains 
within the porous interior of the substrate, excess slurry passes through 
the substrate and exits at the back surface. The rotation of the paddle 
wheel fan 42 causes the blades 44 to push the excess slurry back into the 
substrate through the back surface. The direction of paddle wheel fan 
rotation, speed of rotation, as well as blade angle and shape are all 
important factors in optimizing the amount of slurry loaded. 
In an embodiment of the present invention, the paddle wheel fan 42 rotates 
in the same direction as the movement of the substrate within the slurry 
chamber. The speed of the paddle wheel fan relative to that of the 
substrate is important not only in optimizing the loading of the substrate 
but also in ensuring that loading occurs without damage to the substrate. 
The paddle wheel fan must rotate fast enough so that the blades propel the 
slurry in the direction of the substrate with enough force to ensure that 
the slurry forms a viscous barrier between the substrate and the moving 
blades. Preferably, the paddle wheel fan rotates faster than the movement 
of the substrate. More preferably, the paddle wheel fan rotates up to four 
times faster than the movement of the substrate. Most preferably, the 
paddle wheel fan rotates approximately twice as fast as the movement of 
the substrate. 
The blades are positioned around the paddle wheel fan to optimize loading 
and to push the slurry onto the back surface of the substrate as the 
paddle wheel fan rotates. In the embodiment of the present invention 
illustrated in the Figures, the blades are flat rather than curved and are 
positioned to form a backward inclined system whereby the tip of each 
blade (i.e. the edge remote from the slurry axis) is inclined away from 
the direction of rotation. Other embodiments of the paddle wheel fan and 
blades are also feasible. The blades may be curved. As well, the blades 
may be forward inclined or even radially positioned. 
FIG. 4 shows that the angle of inclination for each blade is measured as 
the angle .theta. between the blade and the radius drawn to the tip of 
that blade. Generally, the angle .theta. is between 0 and 90 degress. 
Preferably, the angle .theta. of the blades is between 20 and 60 degrees. 
More preferably, the angle .theta. of the blades is between 30 to 40 
degrees. Most preferably, the angle .theta. of the blades is about 37 
degrees. 
In summary, excess slurry exiting at the back surface of the substrate is 
forced back through the substrate at the back surface in order to achieve 
greater loading. In the embodiment described, this is accomplished by the 
rotation of the paddle wheel fan 42, whereby the movement of the blades 44 
pushes the slurry into the substrate as the substrate moves along the 
lower half of the slurry chamber between the paddle wheel fan and outer 
cylinder. 
Other embodiments of means for forcing the slurry back into the substrate 
are also conceivable. Other possibilities include vibrational, 
accoustical, electrical, thermal or any other means known in the art to 
repeatedly push the slurry into the substrate. As well, the path of the 
substrate is not limited to the circular path outlined above. Other 
configurations may be more optimal depending upon the substrate and slurry 
used as well as the means for introducing slurry and means for forcing 
excess slurry chosen. 
After slurry has been applied to both the front and back surfaces of the 
substrate, the surfaces are wiped and smoothed. The present invention 
provides means for wiping and smoothing both surfaces of the substrate as 
it exits the slurry chamber. This includes a first plate and a second 
plate positioned to pinch the substrate. It also includes an adjusting 
mechanism for varying the pressure the wiping plates exert on the 
substrate during the wiping and smoothing process. 
FIG. 1 shows an embodiment of the present invention that incorporates two 
wiping plates, a fixed wiping plate 18 and an adjustable wiping plate 20. 
As the loaded substrate leaves the slurry chamber through the substrate 
exit port, it becomes sandwiched between the two plates. The plates are 
positioned to form a wedge that pinches the substrate so that contact is 
made on both the front and back surfaces. The pressure exerted by the 
plates on the front and back surfaces of the substrate wipes and smoothes 
the surfaces. 
The present invention provides an adjusting mechanism for varying the 
pressure exerted by the wiping plates. One embodiment of the adjusting 
mechanism is an adjustment bar 22 which can be rotated about a fixed axis. 
The bottom of the adjustable wiping plate 20 is attached to the adjustment 
bar 22. As the adjustment bar 22 is rotated, the pressure in which the 
substrate is pinched by the wiping plates changes. 
As the substrate moves within the slurry chamber (from the substrate entry 
port 4 to the substrate exit port 5), the paddle wheel fan repeatedly 
forces slurry onto the substrate's back surface. Only a portion of the 
slurry within the slurry chamber is actually loaded into the substrate. 
Slurry that is not loaded into the substrate remains in the chamber. This 
residual slurry follows the path of the substrate and paddle wheel fan. It 
moves toward and collects at the slurry exit port 7 of the outer cylinder. 
The present invention includes means for removing the excess slurry from 
the slurry exit port so that it can be recirculated and reintroduced via 
the slurry inlet nozzle. The recirculation of the unloaded slurry helps 
prevent wasted slurry, a expensive component of the final electrode. 
An embodiment of the present invention also includes an outer enclosure 
which encloses the slurry chamber. Shown in FIG. 1, the outer enclosure 12 
serves as a frame for attaching other parts of the apparatus. It also 
serves to prevent the escape of volatile components of the slurry. The 
outer enclosure 12 is designed so that one or more of its surfaces can 
easily be removed to allow access for maintenance and cleaning of the 
slurry loading apparatus. 
Substrate enters the outer enclosure 12 through the substrate entry 
aperture 10. The substrate exits the outer enclosure 12 through the 
substrate exit aperture 11 after loading has taken place. On the exterior 
of the outer enclosure 12, adjacent to the substrate entry aperture 10, is 
the outer substrate guide 9. The outer substrate guide 9 gently guides the 
substrate through the substrate entry aperture 10, helping to prevent any 
damage to the substrate. An inner substrate guide 15 is attached to the 
interior of the outer enclosure, adjacent to the substrate entry aperture 
10. Once inside the outer enclosure 12, the inner substrate guide 15 
guides the substrate through the substrate entry port 4 and into slurry 
chamber. 
Another aspect of the present invention is a method for loading a slurry 
into any substrate having a front surface, a back surface and voids 
between the two. While the present invention discusses nickel foam 
substrate particularly, it is likewise adaptable to any battery substrate 
material having void spaces defined between outer surfaces such as 
compacted nickel fibers, nickel coated graphite fibers, etc. The method of 
the invention comprises introducing the slurry onto the front surface and 
into the voids, such that excess slurry passes through the substrate; 
repeatedly forcing excess slurry onto the back surface and into the voids; 
wiping excess slurry from the front and the back surfaces of the 
substrate; and recirculating the excess slurry to avoid waste. 
The nickel hydroxide slurry used in the loading process of the invention is 
a unique mixture of solid and liquid ingredients which form a suspension 
when combined. The composition of ingredients used to make the slurry in 
accordance with the present invention is nickel hydroxide, cobalt, cobalt 
monoxide, ethyl alcohol, water and polyvinyl alcohol (PVA). Preferably, 
the percentages by weight of the ingredients are nickel hydroxide in the 
range of 40% to 80%, cobalt in the range of 1% to 10%, cobalt monoxide in 
the range of 1% to 10%, water in the range of 10% to 30%, ethyl alcohol in 
the range of 1% to 20%, and polyvinyl alcohol in the range of 0.10% to 2%. 
More preferably, the percentages by weight of the ingredients are nickel 
hyroxide in the range of 50% to 70%, cobalt in the range of 2% to 5%, 
cobalt monoxide in the range of 2% to 6%, water in the range of 15% to 
25%, ethyl alcohol in the range 5% to 15%, and polyvinyl alcohol in the 
range of 0.10% to 1%. Most prefereably, the percentages by weight of the 
ingredients is nickel hydroxide are about 62.4%, cobalt is about 3.4%, 
cobalt monoxide is about 4.3%, water is about 18.2%, ethyl alcohol is 
about 9.2%, and polyvinyl alcohol about 0.32%. 
EXAMPLE 
An embodiment of the slurry loading apparatus described in the present 
invention was built having the following specifications: Distance between 
outer cylinder and paddle wheel fan of about 0.22 inches, speed of paddle 
wheel fan about twice as fast as the speed of substrate, and blade angle 
of about 37 degrees. 
The slurry loading apparatus with the above specifications was run using a 
nickel foam substrate with a thickness of about 0.06 inches, and a slurry 
with the following mix of ingredients (percentages are by weight of 
ingredient): 
nickel hyroxide--about 62.4%, 
cobalt--about 3.4%, 
cobalt monoxide--about 4.3%, 
water--about 18.2%, 
ethyl--about 9.2%, and 
polyvinyl alcohol--about 0.32%. 
The loading results achieved were as follows: 
______________________________________ 
Loading Rate 
Loading Density 
______________________________________ 
Using Loading Apparatus 
5'/minute 1.43 gm/sq inch 
"By Hand" Application 
1'/minute 1.39 gm/sq inch 
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It is understood that the present invention can also be used in ways not 
specifically described above. For example, the described loading apparatus 
could also be used for fabricating pasted negative electrodes with 
alternative substrate materials. Further modifications and usages will be 
readily apparent to those skilled in the art without departing from the 
spirit and the scope of the present invention. Further, the above 
description is in no way intended to limit the scope of the following 
claims.